K Handouts

Faculty Dr Parin Shah amp Prof Ronak Patel

Lecture No 1-2

Introduction of Boilers Indian Boilers Regulation (IBR) Boiler Systems Boiler

Types and Classifications Fire tube boilers Water tube boilers Packaged Boiler

Stoker Fired Boiler Chain-Grate or Travelling-Grate Stoker Boiler Spreader Stoker

Boiler Pulverized Fuel Boiler Fluidized Bed Boiler

A boiler is an enclosed vessel that provides a means for combustion heat to be

transferred into water until it becomes heated water or steam The hot water or steam

under pressure is then usable for transferring the heat to a process Water is a useful

and cheap medium for transferring heat to a process When water is boiled into steam

its volume increases about 1600 times producing a force that is almost as explosive

as gunpowder This causes the boiler to be extremely dangerous equipment that must

be treated with utmost care

The process of heating a liquid until it reaches its gaseous state is called evaporation

Heat is transferred from one body to another by means of (1) radiation which is the

transfer of heat from a hot body to a cold body without a conveying medium (2)

convection the transfer of heat by a conveying medium such as air or water and (3)

conduction transfer of heat by actual physical contact molecule to molecule

Indian Boiler Regulation

The Indian Boilers Act was enacted to consolidate and amend the law relating to

steam boilers Indian Boilers Regulation (IBR) was created in exercise of the powers

conferred by section 28 amp 29 of the Indian Boilers Act

IBR Steam Boilers means any closed vessel exceeding 2275 liters in capacity and

which is used expressively for generating steam under pressure and includes any

mounting or other fitting attached to such vessel which is wholly or partly under

pressure when the steam is shut off

The boiler system comprises of feed water system steam system and fuel system

The feed water system provides water to the boiler and regulates it automatically to

meet the steam demand Various valves provide access for maintenance and repair

The steam system collects and controls the steam produced in the boiler Steam is

directed through a piping system to the point of use Throughout the system steam

pressure is regulated using valves and checked with steam pressure gauges The fuel

system includes all equipment used to provide fuel to generate the necessary heat

The equipment required in the fuel system depends on the type of fuel used in the

system The boiler system comprises of feed water system steam system and fuel

system The feed water system provides water to the boiler and regulates it

automatically to meet the steam demand Various valves provide access for

maintenance and repair The steam system collects and controls the steam produced

in the boiler Steam is directed through a piping system to the point of use

Throughout the system steam pressure is regulated using valves and checked with

steam pressure gauges The fuel system includes all equipment used to provide fuel to

generate the necessary heat The equipment required in the fuel system depends on the

type of fuel used in the system

Lecture No 3-4 Performance Evaluation of Boilers

Boiler Efficiency Direct Method Indirect Method Examples related to these

methods

Boiler Efficiency Thermal efficiency of boiler is defined as the percentage of heat input that is effectively utilised to generate steam There are two methods of assessing boiler efficiency

1) The Direct Method Where the energy gain of the working fluid (water and steam) is compared with the energy content of the boiler fuel

2) The Indirect Method Where the efficiency is the difference between the losses and the energy input

Advantages of direct method

Plant people can evaluate quickly the efficiency of boilers

Requires few parameters for computation

Needs few instruments for monitoring

Disadvantages of direct method

Does not give clues to the operator as to why efficiency of system is lower

Does not calculate various losses accountable for various efficiency levels

Lecture No 5-6 Boiler Blowdown

Conductivity as Indicator of Boiler Water Quality Intermittent Blowdown

Continuous Blowdown Blowdown calculations Benefits of Blowdown

When water is boiled and steam is generated any dissolved solids contained in the water

remain in the boiler If more solids are put in with the feed water they will concentrate

and may eventually reach a level where their solubility in the water is exceeded and they

deposit from the solution Above a certain level of concentration these solids encourage

foaming and cause carryover of water into the steam The deposits also lead to scale

formation inside the boiler resulting in localized overheating and finally causing boiler

tube failure It is therefore necessary to control the level of concentration of the solids

and this is achieved by the process of blowing down where a certain volume of water is

blown off and is automatically replaced by feed water - thus maintaining the optimum

level of total dissolved solids (TDS) in the boiler water Blow down is necessary to

protect the surfaces of the heat exchanger in the boiler However blow down can be a

significant source of heat loss if improperly carried out

Conductivity as Indicator of Boiler Water Quality

Since it is tedious and time consuming to measure total dissolved solids (TDS) in boiler

water system conductivity measurement is used for monitoring the overall TDS present

in the boiler A rise in conductivity indicates a rise in the contamination of the boiler

water

Conventional methods for blowing down the boiler depend on two kinds of blowdown -

intermittent and continuous

Intermittent Blowdown

The intermittent blown down is given by manually operating a valve fitted to discharge

pipe at the lowest point of boiler shell to reduce parameters (TDS or conductivity pH

Silica and Phosphates concentration) within prescribed limits so that steam quality is not

likely to be affected In intermittent blowdown a large diameter line is opened for a short

period of time the time being based on a thumb rule such as ldquoonce in a shift for 2

minutesrdquo

Intermittent blowdown requires large short-term increases in the amount of feed water

put into the boiler and hence may necessitate larger feed water pumps than if continuous

blow down is used Also TDS level will be varying thereby causing fluctuations of the

water level in the boiler due to changes in steam bubble size and distribution which

accompany changes in concentration of solids Also substantial amount of heat energy is

lost with intermittent blowdown

Continuous Blowdown

There is a steady and constant dispatch of small stream of concentrated boiler water and

replacement by steady and constant inflow of feed water This ensures constant TDS and

steam purity at given steam load Once blow down valve is set for a given conditions

there is no need for regular operator intervention

Even though large quantities of heat are wasted opportunity exists for recovering this

heat by blowing into a flash tank and generating flash steam This flash steam can be used

for pre-heating boiler feed water or for any other purpose

Benefits of Blowdown

Good boiler blow down control can significantly reduce treatment and operational costs

that include

Lower pre-treatment costs

Less make-up water consumption

Reduced maintenance downtime

Increased boiler life

Lower consumption of treatment chemicals

Lecture No 7-8 Boiler Water Treatment Deposit Control Impurities causing deposits Silica Internal Water Treatment External Water Treatment Ion-exchange process (Softener Plant) De-aeration Mechanical de-aeration Chemical de-aeration Reverse Osmosis Recommended boiler and feed water quality

Boiler Water Treatment Producing quality steam on demand depends on properly

managed water treatment to control steam purity deposits and corrosion A boiler is the

sump of the boiler system It ultimately receives all of the pre-boiler contaminants Boiler

performance efficiency and service life are direct products of selecting and controlling

feed water used in the boiler

When feed water enters the boiler the elevated temperatures and pressures cause the

components of water to behave differently Most of the components in the feed water are

soluble However under heat and pressure most of the soluble components come out of

solution as particulate solids sometimes in crystallized forms and other times as

amorphous particles When solubility of a specific component in water is exceeded scale

or deposits develop The boiler water must be sufficiently free of deposit forming solids

to allow rapid and efficient heat transfer and it must not be corrosive to the boiler metal

Lecture No 9-10 Energy Conservation Opportunities

Stack Temperature Feed Water Preheating using Economiser Combustion Air

Preheat Incomplete Combustion Excess Air Control Radiation and Convection Heat

Loss Automatic Blowdown Control Reduction of Scaling and Soot

Losses Reduction of Boiler Steam Pressure Variable Speed Control for Fans

Blowers and Pumps Effect of Boiler Loading on Efficiency Proper Boiler

Scheduling Boiler Replacement

Stack Temperature

The stack temperature should be as low as possible However it should not be so low

that water vapor in the exhaust condenses on the stack walls This is important in fuels

containing signficant sulphur as low temperature can lead to sulphur dew point

corrosion Stack temperatures greater than 200degC indicates potential for recovery of

waste heat It also indicate the scaling of heat transferrecovery equipment and hence

the urgency of taking an early shut down for water flue side cleaning

Feed Water Preheating using Economiser Typically the flue gases leaving a

modern 3-pass shell boiler are at temperatures of 200 to 300 oC Thus there is a

potential to recover heat from these gases The flue gas exit temperature from a boiler

is usually maintained at a minimum of 200 oC so that the sulphur oxides in the flue

gas do not condense and cause corrosion in heat transfer surfaces When a clean fuel

such as natural gas LPG or gas oil is used the economy of heat recovery must be

worked out as the flue gas temperature may be well below 200oC The potential for

energy saving depends on the type of boiler installed and the fuel used For a typically

older model shell boiler with a flue gas exit temperature of 260oC an economizer

could be used to reduce it to 200oC increasing the feed water temperature by 15oC

Increase in overall thermal efficiency would be in the order of 3 For a modern 3-

pass shell boiler firing natural gas with a flue gas exit temperature of 140oC a

condensing economizer would reduce the exit temperature to 65oC increasing thermal

efficiency by 5

Combustion Air Preheat

Combustion air preheating is an alternative to feedwater heating In order to improve

thermal efficiency by 1 the combustion air temperature must be raised by 20 oC

Most gas and oil burners used in a boiler plant are not designed for high air preheat

temperatures Modern burners can withstand much higher combustion air preheat so

it is possible to consider such units as heat exchangers in the exit flue as an alternative

to an economizer when either space or a high feed water return temperature make it

viable

Incomplete Combustion

Incomplete combustion can arise from a shortage of air or surplus of fuel or poor

distribution of fuel It is usually obvious from the colour or smoke and must be

corrected immediately

In the case of oil and gas fired systems CO or smoke (for oil fired systems only) with

normal or high excess air indicates burner system problems A more frequent cause of

incomplete combustion is the poor mixing of fuel and air at the burner Poor oil fires

can result from improper viscosity worn tips carbonization on tips and deterioration

of diffusers or spinner plates

With coal firing unburned carbon can comprise a big loss It occurs as grit carry-over

or carbon-in-ash and may amount to more than 2 of the heat supplied to the boiler

Non uniform fuel size could be one of the reasons for incomplete combustion In

chain grate stokers large lumps will not burn out completely while small pieces and

fines may block the air passage thus causing poor air distribution In sprinkler

stokers stoker grate condition fuel distributors wind box air regulation and over-fire

systems can affect carbon loss Increase in the fines in pulverized coal also increases

carbon loss

Excess Air Control

Excess air is required in all practical cases to ensure complete combustion to allow

for the normal variations in combustion and to ensure satisfactory stack conditions for

some fuels The optimum excess air level for maximum boiler efficiency occurs when

the sum of the losses due to incomplete combustion and loss due to heat in flue gases

is minimum This level varies with furnace design type of burner fuel and process

variables It can be determined by conducting tests with different air fuel ratios

Radiation and Convection Heat Loss

The external surfaces of a shell boiler are hotter than the surroundings The surfaces

thus lose heat to the surroundings depending on the surface area and the difference in

temperature between the surface and the surroundings The heat loss from the boiler

shell is normally a fixed energy loss irrespective of the boiler output With modern

boiler designs this may represent only 15 on the gross calorific value at full rating

but will increase to around 6 if the boiler operates at only 25 percent output

Repairing or augmenting insulation can reduce heat loss through boiler walls and

piping

Automatic Blowdown Control

Uncontrolled continuous blowdown is very wasteful Automatic blowdown controls

can be installed that sense and respond to boiler water conductivity and pH A 10

blow down in a 15 kgcm2 boiler results in 3 efficiency loss

Reduction of Scaling and Soot Losses

In oil and coal-fired boilers soot buildup on tubes acts as an insulator against heat

transfer Any such deposits should be removed on a regular basis Elevated stack

temperatures may indicate excessive soot buildup Also same result will occur due to

scaling on the water side High exit gas temperatures at normal excess air indicate

poor heat transfer performance This condition can result from a gradual build-up of

gas-side or waterside deposits Waterside deposits require a review of water treatment

procedures and tube cleaning to remove deposits An estimated 1 efficiency loss

occurs with every 22oC increase in stack temperature

Reduction of Boiler Steam Pressure

This is an effective means of reducing fuel consumption if permissible by as much as

1 to 2 Lower steam pressure gives a lower saturated steam temperature and without

stack heat recovery a similar reduction in the temperature of the flue gas temperature

results

Steam is generated at pressures normally dictated by the highest pressure

temperature requirements for a particular process In some cases the process does not

operate all the time and there are periods when the boiler pressure could be reduced

The energy manager should consider pressure reduction carefully before

recommending it Adverse effects such as an increase in water carryover from the

boiler owing to pressure reduction may negate any potential saving Pressure should

be reduced in stages and no more than a 20 percent reduction should be considered

Variable Speed Control for Fans Blowers and Pumps

Variable speed control is an important means of achieving energy savings Generally

combustion air control is effected by throttling dampers fitted at forced and induced

draft fans Though dampers are simple means of control they lack accuracy giving

poor control characteristics at the top and bottom of the operating range In general if

the load characteristic of the boiler is variable the possibility of replacing the dampers

by a VSD should be evaluated

Effect of Boiler Loading on Efficiency

The maximum efficiency of the boiler does not occur at full load but at about two-

thirds of the full load If the load on the boiler decreases further efficiency also tends

to decrease At zero output the efficiency of the boiler is zero and any fuel fired is

used only to supply the losses The factors affecting boiler efficiency are

As the load falls so does the value of the mass flow rate of the flue gases through the

tubes This reduction in flow rate for the same heat transfer area reduced the exit flue

gas temperatures by a small extent reducing the sensible heat lossBelow half load

most combustion appliances need more excess air to burn the fuel completely This

increases the sensible heat loss In general efficiency of the boiler reduces

significantly below 25 of the rated load and as far as possible operation of boilers

below this level should be avoided

Proper Boiler Scheduling

Since the optimum efficiency of boilers occurs at 65-85 of full load it is usually

more efficient on the whole to operate a fewer number of boilers at higher loads

than to operate a large number at low loads

Boiler Replacement

The potential savings from replacing a boiler depend on the anticipated change in

overall efficiency A change in a boiler can be financially attractive if the existing

boiler is

Old and inefficient

Not capable of firing cheaper substitution fuel

Over or under-sized for present requirements

Not designed for ideal loading conditions

The feasibility study should examine all implications of long-term fuel availability

and company growth plans All financial and engineering factors should be

considered Since boiler plants traditionally have a useful life of well over 25 years

replacement must be carefully studied

Lecture No 11-12 Pumps and Pumping System

Pump Types Centrifugal Pumps Pump Performance Curve Hydraulic power pump

shaft power and electrical input power

Pump Types

Pumps come in a variety of sizes for a wide range of applications They can be

classified according to their basic operating principle as dynamic or displacement

pumps Dynamic pumps can be sub-classified as centrifugal and special effect pumps

Displacement pumps can be sub-classified as rotary or reciprocating pumps

In principle any liquid can be handled by any of the pump designs Where different

pump designs could be used the centrifugal pump is generally the most economical

followed by rotary and reciprocating pumps Although positive displacement pumps

are generally more efficient than centrifugal pumps the benefit of higher efficiency

tends to be offset by increased maintenance costs

Since worldwide centrifugal pumps account for the majority of electricity used by

pumps the focus of this chapter is on centrifugal pump

Centrifugal Pumps

A centrifugal pump is of a very simple design The two main parts of the pump are the

impeller and the diffuser Impeller which is the only moving part is attached to a

shaft and driven by a motor Impellers are generally made of bronze polycarbonate

cast iron stainless steel as well as other materials The diffuser (also called as volute)

houses the impeller and captures and directs the water off the impeller

Pump Performance Curve

The pump is a dynamic device it is convenient to consider the pressure in terms of

head ie meters of liquid column The pump generates the same head of liquid

whatever the density of the liquid being pumped The actual contours of the hydraulic

passages of the impeller and the casing are extremely important in order to attain the

highest efficiency possible The standard convention for centrifugal pump is to draw

the pump performance curves showing Flow on the horizontal axis and Head

generated on the vertical axis Efficiency Power amp NPSH Required (described later)

are also all conventionally shown on the vertical axis plotted against Flow as

illustrated in Figure

Lecture No 13-14 System Characteristics

Static Head vs Flow Friction Head vs Flow System with High Static Head System

with Low Static Head Pump Curves Head- Flow Curve Pump operating point

In a pumping system the objective in most cases is either to transfer a liquid from a

source to a required destination eg filling a high level reservoir or to circulate liquid

around a system eg as a means of heat transfer in heat exchanger

A pressure is needed to make the liquid flow at the required rate and this must

overcome head lsquolossesrsquo in the system Losses are of two types static and friction

head

Static head is simply the difference in height of the supply and destination reservoirs

as in Figure In this illustration flow velocity in the pipe is assumed to be very small

Another example of a system with only static head is pumping into a pressurised

vessel with short pipe runs Static head is independent of flow and graphically would

be shown as in Figure

Figure Static Head Figure Static Head vs Flow

Pump Curves

The performance of a pump can be expressed graphically as head against flow rate

The centrifugal pump has a curve where the head falls gradually with increasing flow

This is called the pump characteristic curve

Pump operating point

When a pump is installed in a system the effect can be illustrated graphically by

superimposing pump and system curves The operating point will always be where the

two curves intersect Fig

Lecture No 15-16 Factors Affecting Pump Performance

Matching Pump and System Head-flow Characteristics Effect of over sizing the

pump Energy loss in throttling

Matching Pump and System Head-flow Characteristics

Centrifugal pumps are characterized by the relationship between the flow rate (Q) they

produce and the pressure (H) at which the flow is delivered Pump efficiency varies with

flow and pressure and it is highest at one particular flow rate

The Figure below shows a typical vendor-supplied head-flow curve for a centrifugal

pump Pump head-flow curves are typically given for clear water The choice of pump for

a given application depends largely on how the pump head-flow characteristics match the

requirement of the system downstream of the pump

Effect of over sizing the pump

As mentioned earlier pressure losses to be overcome by the pumps are a function of flow

ndash the system characteristics ndash are also quantified in the form of head-flow curves The

system curve is basically a plot of system resistance ie head to be overcome by the pump

versus various flow rates The system curves change with the physical configuration of

the system for example the system curves depends upon height or elevation diameter

and length of piping number and type of fittings and pressure drops across various

equipment - say a heat exchanger

A pump is selected based on how well the pump curve and system head-flow curves

match The pump operating point is identified as the point where the system curve

crosses the pump curve when they are superimposed on each other

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

meet the steam demand Various valves provide access for maintenance and repair

The steam system collects and controls the steam produced in the boiler Steam is

directed through a piping system to the point of use Throughout the system steam

pressure is regulated using valves and checked with steam pressure gauges The fuel

system includes all equipment used to provide fuel to generate the necessary heat

The equipment required in the fuel system depends on the type of fuel used in the

system The boiler system comprises of feed water system steam system and fuel

system The feed water system provides water to the boiler and regulates it

automatically to meet the steam demand Various valves provide access for

maintenance and repair The steam system collects and controls the steam produced

in the boiler Steam is directed through a piping system to the point of use

Throughout the system steam pressure is regulated using valves and checked with

steam pressure gauges The fuel system includes all equipment used to provide fuel to

generate the necessary heat The equipment required in the fuel system depends on the

type of fuel used in the system

Lecture No 3-4 Performance Evaluation of Boilers

Boiler Efficiency Direct Method Indirect Method Examples related to these

methods

Boiler Efficiency Thermal efficiency of boiler is defined as the percentage of heat input that is effectively utilised to generate steam There are two methods of assessing boiler efficiency

1) The Direct Method Where the energy gain of the working fluid (water and steam) is compared with the energy content of the boiler fuel

2) The Indirect Method Where the efficiency is the difference between the losses and the energy input

Advantages of direct method

Plant people can evaluate quickly the efficiency of boilers

Requires few parameters for computation

Needs few instruments for monitoring

Disadvantages of direct method

Does not give clues to the operator as to why efficiency of system is lower

Does not calculate various losses accountable for various efficiency levels

Lecture No 5-6 Boiler Blowdown

Conductivity as Indicator of Boiler Water Quality Intermittent Blowdown

Continuous Blowdown Blowdown calculations Benefits of Blowdown

When water is boiled and steam is generated any dissolved solids contained in the water

remain in the boiler If more solids are put in with the feed water they will concentrate

and may eventually reach a level where their solubility in the water is exceeded and they

deposit from the solution Above a certain level of concentration these solids encourage

foaming and cause carryover of water into the steam The deposits also lead to scale

formation inside the boiler resulting in localized overheating and finally causing boiler

tube failure It is therefore necessary to control the level of concentration of the solids

and this is achieved by the process of blowing down where a certain volume of water is

blown off and is automatically replaced by feed water - thus maintaining the optimum

level of total dissolved solids (TDS) in the boiler water Blow down is necessary to

protect the surfaces of the heat exchanger in the boiler However blow down can be a

significant source of heat loss if improperly carried out

Conductivity as Indicator of Boiler Water Quality

Since it is tedious and time consuming to measure total dissolved solids (TDS) in boiler

water system conductivity measurement is used for monitoring the overall TDS present

in the boiler A rise in conductivity indicates a rise in the contamination of the boiler

water

Conventional methods for blowing down the boiler depend on two kinds of blowdown -

intermittent and continuous

Intermittent Blowdown

The intermittent blown down is given by manually operating a valve fitted to discharge

pipe at the lowest point of boiler shell to reduce parameters (TDS or conductivity pH

Silica and Phosphates concentration) within prescribed limits so that steam quality is not

likely to be affected In intermittent blowdown a large diameter line is opened for a short

period of time the time being based on a thumb rule such as ldquoonce in a shift for 2

minutesrdquo

Intermittent blowdown requires large short-term increases in the amount of feed water

put into the boiler and hence may necessitate larger feed water pumps than if continuous

blow down is used Also TDS level will be varying thereby causing fluctuations of the

water level in the boiler due to changes in steam bubble size and distribution which

accompany changes in concentration of solids Also substantial amount of heat energy is

lost with intermittent blowdown

Continuous Blowdown

There is a steady and constant dispatch of small stream of concentrated boiler water and

replacement by steady and constant inflow of feed water This ensures constant TDS and

steam purity at given steam load Once blow down valve is set for a given conditions

there is no need for regular operator intervention

Even though large quantities of heat are wasted opportunity exists for recovering this

heat by blowing into a flash tank and generating flash steam This flash steam can be used

for pre-heating boiler feed water or for any other purpose

Benefits of Blowdown

Good boiler blow down control can significantly reduce treatment and operational costs

that include

Lower pre-treatment costs

Less make-up water consumption

Reduced maintenance downtime

Increased boiler life

Lower consumption of treatment chemicals

Lecture No 7-8 Boiler Water Treatment Deposit Control Impurities causing deposits Silica Internal Water Treatment External Water Treatment Ion-exchange process (Softener Plant) De-aeration Mechanical de-aeration Chemical de-aeration Reverse Osmosis Recommended boiler and feed water quality

Boiler Water Treatment Producing quality steam on demand depends on properly

managed water treatment to control steam purity deposits and corrosion A boiler is the

sump of the boiler system It ultimately receives all of the pre-boiler contaminants Boiler

performance efficiency and service life are direct products of selecting and controlling

feed water used in the boiler

When feed water enters the boiler the elevated temperatures and pressures cause the

components of water to behave differently Most of the components in the feed water are

soluble However under heat and pressure most of the soluble components come out of

solution as particulate solids sometimes in crystallized forms and other times as

amorphous particles When solubility of a specific component in water is exceeded scale

or deposits develop The boiler water must be sufficiently free of deposit forming solids

to allow rapid and efficient heat transfer and it must not be corrosive to the boiler metal

Lecture No 9-10 Energy Conservation Opportunities

Stack Temperature Feed Water Preheating using Economiser Combustion Air

Preheat Incomplete Combustion Excess Air Control Radiation and Convection Heat

Loss Automatic Blowdown Control Reduction of Scaling and Soot

Losses Reduction of Boiler Steam Pressure Variable Speed Control for Fans

Blowers and Pumps Effect of Boiler Loading on Efficiency Proper Boiler

Scheduling Boiler Replacement

Stack Temperature

The stack temperature should be as low as possible However it should not be so low

that water vapor in the exhaust condenses on the stack walls This is important in fuels

containing signficant sulphur as low temperature can lead to sulphur dew point

corrosion Stack temperatures greater than 200degC indicates potential for recovery of

waste heat It also indicate the scaling of heat transferrecovery equipment and hence

the urgency of taking an early shut down for water flue side cleaning

Feed Water Preheating using Economiser Typically the flue gases leaving a

modern 3-pass shell boiler are at temperatures of 200 to 300 oC Thus there is a

potential to recover heat from these gases The flue gas exit temperature from a boiler

is usually maintained at a minimum of 200 oC so that the sulphur oxides in the flue

gas do not condense and cause corrosion in heat transfer surfaces When a clean fuel

such as natural gas LPG or gas oil is used the economy of heat recovery must be

worked out as the flue gas temperature may be well below 200oC The potential for

energy saving depends on the type of boiler installed and the fuel used For a typically

older model shell boiler with a flue gas exit temperature of 260oC an economizer

could be used to reduce it to 200oC increasing the feed water temperature by 15oC

Increase in overall thermal efficiency would be in the order of 3 For a modern 3-

pass shell boiler firing natural gas with a flue gas exit temperature of 140oC a

condensing economizer would reduce the exit temperature to 65oC increasing thermal

efficiency by 5

Combustion Air Preheat

Combustion air preheating is an alternative to feedwater heating In order to improve

thermal efficiency by 1 the combustion air temperature must be raised by 20 oC

Most gas and oil burners used in a boiler plant are not designed for high air preheat

temperatures Modern burners can withstand much higher combustion air preheat so

it is possible to consider such units as heat exchangers in the exit flue as an alternative

to an economizer when either space or a high feed water return temperature make it

viable

Incomplete Combustion

Incomplete combustion can arise from a shortage of air or surplus of fuel or poor

distribution of fuel It is usually obvious from the colour or smoke and must be

corrected immediately

In the case of oil and gas fired systems CO or smoke (for oil fired systems only) with

normal or high excess air indicates burner system problems A more frequent cause of

incomplete combustion is the poor mixing of fuel and air at the burner Poor oil fires

can result from improper viscosity worn tips carbonization on tips and deterioration

of diffusers or spinner plates

With coal firing unburned carbon can comprise a big loss It occurs as grit carry-over

or carbon-in-ash and may amount to more than 2 of the heat supplied to the boiler

Non uniform fuel size could be one of the reasons for incomplete combustion In

chain grate stokers large lumps will not burn out completely while small pieces and

fines may block the air passage thus causing poor air distribution In sprinkler

stokers stoker grate condition fuel distributors wind box air regulation and over-fire

systems can affect carbon loss Increase in the fines in pulverized coal also increases

carbon loss

Excess Air Control

Excess air is required in all practical cases to ensure complete combustion to allow

for the normal variations in combustion and to ensure satisfactory stack conditions for

some fuels The optimum excess air level for maximum boiler efficiency occurs when

the sum of the losses due to incomplete combustion and loss due to heat in flue gases

is minimum This level varies with furnace design type of burner fuel and process

variables It can be determined by conducting tests with different air fuel ratios

Radiation and Convection Heat Loss

The external surfaces of a shell boiler are hotter than the surroundings The surfaces

thus lose heat to the surroundings depending on the surface area and the difference in

temperature between the surface and the surroundings The heat loss from the boiler

shell is normally a fixed energy loss irrespective of the boiler output With modern

boiler designs this may represent only 15 on the gross calorific value at full rating

but will increase to around 6 if the boiler operates at only 25 percent output

Repairing or augmenting insulation can reduce heat loss through boiler walls and

piping

Automatic Blowdown Control

Uncontrolled continuous blowdown is very wasteful Automatic blowdown controls

can be installed that sense and respond to boiler water conductivity and pH A 10

blow down in a 15 kgcm2 boiler results in 3 efficiency loss

Reduction of Scaling and Soot Losses

In oil and coal-fired boilers soot buildup on tubes acts as an insulator against heat

transfer Any such deposits should be removed on a regular basis Elevated stack

temperatures may indicate excessive soot buildup Also same result will occur due to

scaling on the water side High exit gas temperatures at normal excess air indicate

poor heat transfer performance This condition can result from a gradual build-up of

gas-side or waterside deposits Waterside deposits require a review of water treatment

procedures and tube cleaning to remove deposits An estimated 1 efficiency loss

occurs with every 22oC increase in stack temperature

Reduction of Boiler Steam Pressure

This is an effective means of reducing fuel consumption if permissible by as much as

1 to 2 Lower steam pressure gives a lower saturated steam temperature and without

stack heat recovery a similar reduction in the temperature of the flue gas temperature

results

Steam is generated at pressures normally dictated by the highest pressure

temperature requirements for a particular process In some cases the process does not

operate all the time and there are periods when the boiler pressure could be reduced

The energy manager should consider pressure reduction carefully before

recommending it Adverse effects such as an increase in water carryover from the

boiler owing to pressure reduction may negate any potential saving Pressure should

be reduced in stages and no more than a 20 percent reduction should be considered

Variable Speed Control for Fans Blowers and Pumps

Variable speed control is an important means of achieving energy savings Generally

combustion air control is effected by throttling dampers fitted at forced and induced

draft fans Though dampers are simple means of control they lack accuracy giving

poor control characteristics at the top and bottom of the operating range In general if

the load characteristic of the boiler is variable the possibility of replacing the dampers

by a VSD should be evaluated

Effect of Boiler Loading on Efficiency

The maximum efficiency of the boiler does not occur at full load but at about two-

thirds of the full load If the load on the boiler decreases further efficiency also tends

to decrease At zero output the efficiency of the boiler is zero and any fuel fired is

used only to supply the losses The factors affecting boiler efficiency are

As the load falls so does the value of the mass flow rate of the flue gases through the

tubes This reduction in flow rate for the same heat transfer area reduced the exit flue

gas temperatures by a small extent reducing the sensible heat lossBelow half load

most combustion appliances need more excess air to burn the fuel completely This

increases the sensible heat loss In general efficiency of the boiler reduces

significantly below 25 of the rated load and as far as possible operation of boilers

below this level should be avoided

Proper Boiler Scheduling

Since the optimum efficiency of boilers occurs at 65-85 of full load it is usually

more efficient on the whole to operate a fewer number of boilers at higher loads

than to operate a large number at low loads

Boiler Replacement

The potential savings from replacing a boiler depend on the anticipated change in

overall efficiency A change in a boiler can be financially attractive if the existing

boiler is

Old and inefficient

Not capable of firing cheaper substitution fuel

Over or under-sized for present requirements

Not designed for ideal loading conditions

The feasibility study should examine all implications of long-term fuel availability

and company growth plans All financial and engineering factors should be

considered Since boiler plants traditionally have a useful life of well over 25 years

replacement must be carefully studied

Lecture No 11-12 Pumps and Pumping System

Pump Types Centrifugal Pumps Pump Performance Curve Hydraulic power pump

shaft power and electrical input power

Pump Types

Pumps come in a variety of sizes for a wide range of applications They can be

classified according to their basic operating principle as dynamic or displacement

pumps Dynamic pumps can be sub-classified as centrifugal and special effect pumps

Displacement pumps can be sub-classified as rotary or reciprocating pumps

In principle any liquid can be handled by any of the pump designs Where different

pump designs could be used the centrifugal pump is generally the most economical

followed by rotary and reciprocating pumps Although positive displacement pumps

are generally more efficient than centrifugal pumps the benefit of higher efficiency

tends to be offset by increased maintenance costs

Since worldwide centrifugal pumps account for the majority of electricity used by

pumps the focus of this chapter is on centrifugal pump

Centrifugal Pumps

A centrifugal pump is of a very simple design The two main parts of the pump are the

impeller and the diffuser Impeller which is the only moving part is attached to a

shaft and driven by a motor Impellers are generally made of bronze polycarbonate

cast iron stainless steel as well as other materials The diffuser (also called as volute)

houses the impeller and captures and directs the water off the impeller

Pump Performance Curve

The pump is a dynamic device it is convenient to consider the pressure in terms of

head ie meters of liquid column The pump generates the same head of liquid

whatever the density of the liquid being pumped The actual contours of the hydraulic

passages of the impeller and the casing are extremely important in order to attain the

highest efficiency possible The standard convention for centrifugal pump is to draw

the pump performance curves showing Flow on the horizontal axis and Head

generated on the vertical axis Efficiency Power amp NPSH Required (described later)

are also all conventionally shown on the vertical axis plotted against Flow as

illustrated in Figure

Lecture No 13-14 System Characteristics

Static Head vs Flow Friction Head vs Flow System with High Static Head System

with Low Static Head Pump Curves Head- Flow Curve Pump operating point

In a pumping system the objective in most cases is either to transfer a liquid from a

source to a required destination eg filling a high level reservoir or to circulate liquid

around a system eg as a means of heat transfer in heat exchanger

A pressure is needed to make the liquid flow at the required rate and this must

overcome head lsquolossesrsquo in the system Losses are of two types static and friction

head

Static head is simply the difference in height of the supply and destination reservoirs

as in Figure In this illustration flow velocity in the pipe is assumed to be very small

Another example of a system with only static head is pumping into a pressurised

vessel with short pipe runs Static head is independent of flow and graphically would

be shown as in Figure

Figure Static Head Figure Static Head vs Flow

Pump Curves

The performance of a pump can be expressed graphically as head against flow rate

The centrifugal pump has a curve where the head falls gradually with increasing flow

This is called the pump characteristic curve

Pump operating point

When a pump is installed in a system the effect can be illustrated graphically by

superimposing pump and system curves The operating point will always be where the

two curves intersect Fig

Lecture No 15-16 Factors Affecting Pump Performance

Matching Pump and System Head-flow Characteristics Effect of over sizing the

pump Energy loss in throttling

Matching Pump and System Head-flow Characteristics

Centrifugal pumps are characterized by the relationship between the flow rate (Q) they

produce and the pressure (H) at which the flow is delivered Pump efficiency varies with

flow and pressure and it is highest at one particular flow rate

The Figure below shows a typical vendor-supplied head-flow curve for a centrifugal

pump Pump head-flow curves are typically given for clear water The choice of pump for

a given application depends largely on how the pump head-flow characteristics match the

requirement of the system downstream of the pump

Effect of over sizing the pump

As mentioned earlier pressure losses to be overcome by the pumps are a function of flow

ndash the system characteristics ndash are also quantified in the form of head-flow curves The

system curve is basically a plot of system resistance ie head to be overcome by the pump

versus various flow rates The system curves change with the physical configuration of

the system for example the system curves depends upon height or elevation diameter

and length of piping number and type of fittings and pressure drops across various

equipment - say a heat exchanger

A pump is selected based on how well the pump curve and system head-flow curves

match The pump operating point is identified as the point where the system curve

crosses the pump curve when they are superimposed on each other

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 3-4 Performance Evaluation of Boilers

Boiler Efficiency Direct Method Indirect Method Examples related to these

methods

Boiler Efficiency Thermal efficiency of boiler is defined as the percentage of heat input that is effectively utilised to generate steam There are two methods of assessing boiler efficiency

1) The Direct Method Where the energy gain of the working fluid (water and steam) is compared with the energy content of the boiler fuel

2) The Indirect Method Where the efficiency is the difference between the losses and the energy input

Advantages of direct method

Plant people can evaluate quickly the efficiency of boilers

Requires few parameters for computation

Needs few instruments for monitoring

Disadvantages of direct method

Does not give clues to the operator as to why efficiency of system is lower

Does not calculate various losses accountable for various efficiency levels

Lecture No 5-6 Boiler Blowdown

Conductivity as Indicator of Boiler Water Quality Intermittent Blowdown

Continuous Blowdown Blowdown calculations Benefits of Blowdown

When water is boiled and steam is generated any dissolved solids contained in the water

remain in the boiler If more solids are put in with the feed water they will concentrate

and may eventually reach a level where their solubility in the water is exceeded and they

deposit from the solution Above a certain level of concentration these solids encourage

foaming and cause carryover of water into the steam The deposits also lead to scale

formation inside the boiler resulting in localized overheating and finally causing boiler

tube failure It is therefore necessary to control the level of concentration of the solids

and this is achieved by the process of blowing down where a certain volume of water is

blown off and is automatically replaced by feed water - thus maintaining the optimum

level of total dissolved solids (TDS) in the boiler water Blow down is necessary to

protect the surfaces of the heat exchanger in the boiler However blow down can be a

significant source of heat loss if improperly carried out

Conductivity as Indicator of Boiler Water Quality

Since it is tedious and time consuming to measure total dissolved solids (TDS) in boiler

water system conductivity measurement is used for monitoring the overall TDS present

in the boiler A rise in conductivity indicates a rise in the contamination of the boiler

water

Conventional methods for blowing down the boiler depend on two kinds of blowdown -

intermittent and continuous

Intermittent Blowdown

The intermittent blown down is given by manually operating a valve fitted to discharge

pipe at the lowest point of boiler shell to reduce parameters (TDS or conductivity pH

Silica and Phosphates concentration) within prescribed limits so that steam quality is not

likely to be affected In intermittent blowdown a large diameter line is opened for a short

period of time the time being based on a thumb rule such as ldquoonce in a shift for 2

minutesrdquo

Intermittent blowdown requires large short-term increases in the amount of feed water

put into the boiler and hence may necessitate larger feed water pumps than if continuous

blow down is used Also TDS level will be varying thereby causing fluctuations of the

water level in the boiler due to changes in steam bubble size and distribution which

accompany changes in concentration of solids Also substantial amount of heat energy is

lost with intermittent blowdown

Continuous Blowdown

There is a steady and constant dispatch of small stream of concentrated boiler water and

replacement by steady and constant inflow of feed water This ensures constant TDS and

steam purity at given steam load Once blow down valve is set for a given conditions

there is no need for regular operator intervention

Even though large quantities of heat are wasted opportunity exists for recovering this

heat by blowing into a flash tank and generating flash steam This flash steam can be used

for pre-heating boiler feed water or for any other purpose

Benefits of Blowdown

Good boiler blow down control can significantly reduce treatment and operational costs

that include

Lower pre-treatment costs

Less make-up water consumption

Reduced maintenance downtime

Increased boiler life

Lower consumption of treatment chemicals

Lecture No 7-8 Boiler Water Treatment Deposit Control Impurities causing deposits Silica Internal Water Treatment External Water Treatment Ion-exchange process (Softener Plant) De-aeration Mechanical de-aeration Chemical de-aeration Reverse Osmosis Recommended boiler and feed water quality

Boiler Water Treatment Producing quality steam on demand depends on properly

managed water treatment to control steam purity deposits and corrosion A boiler is the

sump of the boiler system It ultimately receives all of the pre-boiler contaminants Boiler

performance efficiency and service life are direct products of selecting and controlling

feed water used in the boiler

When feed water enters the boiler the elevated temperatures and pressures cause the

components of water to behave differently Most of the components in the feed water are

soluble However under heat and pressure most of the soluble components come out of

solution as particulate solids sometimes in crystallized forms and other times as

amorphous particles When solubility of a specific component in water is exceeded scale

or deposits develop The boiler water must be sufficiently free of deposit forming solids

to allow rapid and efficient heat transfer and it must not be corrosive to the boiler metal

Lecture No 9-10 Energy Conservation Opportunities

Stack Temperature Feed Water Preheating using Economiser Combustion Air

Preheat Incomplete Combustion Excess Air Control Radiation and Convection Heat

Loss Automatic Blowdown Control Reduction of Scaling and Soot

Losses Reduction of Boiler Steam Pressure Variable Speed Control for Fans

Blowers and Pumps Effect of Boiler Loading on Efficiency Proper Boiler

Scheduling Boiler Replacement

Stack Temperature

The stack temperature should be as low as possible However it should not be so low

that water vapor in the exhaust condenses on the stack walls This is important in fuels

containing signficant sulphur as low temperature can lead to sulphur dew point

corrosion Stack temperatures greater than 200degC indicates potential for recovery of

waste heat It also indicate the scaling of heat transferrecovery equipment and hence

the urgency of taking an early shut down for water flue side cleaning

Feed Water Preheating using Economiser Typically the flue gases leaving a

modern 3-pass shell boiler are at temperatures of 200 to 300 oC Thus there is a

potential to recover heat from these gases The flue gas exit temperature from a boiler

is usually maintained at a minimum of 200 oC so that the sulphur oxides in the flue

gas do not condense and cause corrosion in heat transfer surfaces When a clean fuel

such as natural gas LPG or gas oil is used the economy of heat recovery must be

worked out as the flue gas temperature may be well below 200oC The potential for

energy saving depends on the type of boiler installed and the fuel used For a typically

older model shell boiler with a flue gas exit temperature of 260oC an economizer

could be used to reduce it to 200oC increasing the feed water temperature by 15oC

Increase in overall thermal efficiency would be in the order of 3 For a modern 3-

pass shell boiler firing natural gas with a flue gas exit temperature of 140oC a

condensing economizer would reduce the exit temperature to 65oC increasing thermal

efficiency by 5

Combustion Air Preheat

Combustion air preheating is an alternative to feedwater heating In order to improve

thermal efficiency by 1 the combustion air temperature must be raised by 20 oC

Most gas and oil burners used in a boiler plant are not designed for high air preheat

temperatures Modern burners can withstand much higher combustion air preheat so

it is possible to consider such units as heat exchangers in the exit flue as an alternative

to an economizer when either space or a high feed water return temperature make it

viable

Incomplete Combustion

Incomplete combustion can arise from a shortage of air or surplus of fuel or poor

distribution of fuel It is usually obvious from the colour or smoke and must be

corrected immediately

In the case of oil and gas fired systems CO or smoke (for oil fired systems only) with

normal or high excess air indicates burner system problems A more frequent cause of

incomplete combustion is the poor mixing of fuel and air at the burner Poor oil fires

can result from improper viscosity worn tips carbonization on tips and deterioration

of diffusers or spinner plates

With coal firing unburned carbon can comprise a big loss It occurs as grit carry-over

or carbon-in-ash and may amount to more than 2 of the heat supplied to the boiler

Non uniform fuel size could be one of the reasons for incomplete combustion In

chain grate stokers large lumps will not burn out completely while small pieces and

fines may block the air passage thus causing poor air distribution In sprinkler

stokers stoker grate condition fuel distributors wind box air regulation and over-fire

systems can affect carbon loss Increase in the fines in pulverized coal also increases

carbon loss

Excess Air Control

Excess air is required in all practical cases to ensure complete combustion to allow

for the normal variations in combustion and to ensure satisfactory stack conditions for

some fuels The optimum excess air level for maximum boiler efficiency occurs when

the sum of the losses due to incomplete combustion and loss due to heat in flue gases

is minimum This level varies with furnace design type of burner fuel and process

variables It can be determined by conducting tests with different air fuel ratios

Radiation and Convection Heat Loss

The external surfaces of a shell boiler are hotter than the surroundings The surfaces

thus lose heat to the surroundings depending on the surface area and the difference in

temperature between the surface and the surroundings The heat loss from the boiler

shell is normally a fixed energy loss irrespective of the boiler output With modern

boiler designs this may represent only 15 on the gross calorific value at full rating

but will increase to around 6 if the boiler operates at only 25 percent output

Repairing or augmenting insulation can reduce heat loss through boiler walls and

piping

Automatic Blowdown Control

Uncontrolled continuous blowdown is very wasteful Automatic blowdown controls

can be installed that sense and respond to boiler water conductivity and pH A 10

blow down in a 15 kgcm2 boiler results in 3 efficiency loss

Reduction of Scaling and Soot Losses

In oil and coal-fired boilers soot buildup on tubes acts as an insulator against heat

transfer Any such deposits should be removed on a regular basis Elevated stack

temperatures may indicate excessive soot buildup Also same result will occur due to

scaling on the water side High exit gas temperatures at normal excess air indicate

poor heat transfer performance This condition can result from a gradual build-up of

gas-side or waterside deposits Waterside deposits require a review of water treatment

procedures and tube cleaning to remove deposits An estimated 1 efficiency loss

occurs with every 22oC increase in stack temperature

Reduction of Boiler Steam Pressure

This is an effective means of reducing fuel consumption if permissible by as much as

1 to 2 Lower steam pressure gives a lower saturated steam temperature and without

stack heat recovery a similar reduction in the temperature of the flue gas temperature

results

Steam is generated at pressures normally dictated by the highest pressure

temperature requirements for a particular process In some cases the process does not

operate all the time and there are periods when the boiler pressure could be reduced

The energy manager should consider pressure reduction carefully before

recommending it Adverse effects such as an increase in water carryover from the

boiler owing to pressure reduction may negate any potential saving Pressure should

be reduced in stages and no more than a 20 percent reduction should be considered

Variable Speed Control for Fans Blowers and Pumps

Variable speed control is an important means of achieving energy savings Generally

combustion air control is effected by throttling dampers fitted at forced and induced

draft fans Though dampers are simple means of control they lack accuracy giving

poor control characteristics at the top and bottom of the operating range In general if

the load characteristic of the boiler is variable the possibility of replacing the dampers

by a VSD should be evaluated

Effect of Boiler Loading on Efficiency

The maximum efficiency of the boiler does not occur at full load but at about two-

thirds of the full load If the load on the boiler decreases further efficiency also tends

to decrease At zero output the efficiency of the boiler is zero and any fuel fired is

used only to supply the losses The factors affecting boiler efficiency are

As the load falls so does the value of the mass flow rate of the flue gases through the

tubes This reduction in flow rate for the same heat transfer area reduced the exit flue

gas temperatures by a small extent reducing the sensible heat lossBelow half load

most combustion appliances need more excess air to burn the fuel completely This

increases the sensible heat loss In general efficiency of the boiler reduces

significantly below 25 of the rated load and as far as possible operation of boilers

below this level should be avoided

Proper Boiler Scheduling

Since the optimum efficiency of boilers occurs at 65-85 of full load it is usually

more efficient on the whole to operate a fewer number of boilers at higher loads

than to operate a large number at low loads

Boiler Replacement

The potential savings from replacing a boiler depend on the anticipated change in

overall efficiency A change in a boiler can be financially attractive if the existing

boiler is

Old and inefficient

Not capable of firing cheaper substitution fuel

Over or under-sized for present requirements

Not designed for ideal loading conditions

The feasibility study should examine all implications of long-term fuel availability

and company growth plans All financial and engineering factors should be

considered Since boiler plants traditionally have a useful life of well over 25 years

replacement must be carefully studied

Lecture No 11-12 Pumps and Pumping System

Pump Types Centrifugal Pumps Pump Performance Curve Hydraulic power pump

shaft power and electrical input power

Pump Types

Pumps come in a variety of sizes for a wide range of applications They can be

classified according to their basic operating principle as dynamic or displacement

pumps Dynamic pumps can be sub-classified as centrifugal and special effect pumps

Displacement pumps can be sub-classified as rotary or reciprocating pumps

In principle any liquid can be handled by any of the pump designs Where different

pump designs could be used the centrifugal pump is generally the most economical

followed by rotary and reciprocating pumps Although positive displacement pumps

are generally more efficient than centrifugal pumps the benefit of higher efficiency

tends to be offset by increased maintenance costs

Since worldwide centrifugal pumps account for the majority of electricity used by

pumps the focus of this chapter is on centrifugal pump

Centrifugal Pumps

A centrifugal pump is of a very simple design The two main parts of the pump are the

impeller and the diffuser Impeller which is the only moving part is attached to a

shaft and driven by a motor Impellers are generally made of bronze polycarbonate

cast iron stainless steel as well as other materials The diffuser (also called as volute)

houses the impeller and captures and directs the water off the impeller

Pump Performance Curve

The pump is a dynamic device it is convenient to consider the pressure in terms of

head ie meters of liquid column The pump generates the same head of liquid

whatever the density of the liquid being pumped The actual contours of the hydraulic

passages of the impeller and the casing are extremely important in order to attain the

highest efficiency possible The standard convention for centrifugal pump is to draw

the pump performance curves showing Flow on the horizontal axis and Head

generated on the vertical axis Efficiency Power amp NPSH Required (described later)

are also all conventionally shown on the vertical axis plotted against Flow as

illustrated in Figure

Lecture No 13-14 System Characteristics

Static Head vs Flow Friction Head vs Flow System with High Static Head System

with Low Static Head Pump Curves Head- Flow Curve Pump operating point

In a pumping system the objective in most cases is either to transfer a liquid from a

source to a required destination eg filling a high level reservoir or to circulate liquid

around a system eg as a means of heat transfer in heat exchanger

A pressure is needed to make the liquid flow at the required rate and this must

overcome head lsquolossesrsquo in the system Losses are of two types static and friction

head

Static head is simply the difference in height of the supply and destination reservoirs

as in Figure In this illustration flow velocity in the pipe is assumed to be very small

Another example of a system with only static head is pumping into a pressurised

vessel with short pipe runs Static head is independent of flow and graphically would

be shown as in Figure

Figure Static Head Figure Static Head vs Flow

Pump Curves

The performance of a pump can be expressed graphically as head against flow rate

The centrifugal pump has a curve where the head falls gradually with increasing flow

This is called the pump characteristic curve

Pump operating point

When a pump is installed in a system the effect can be illustrated graphically by

superimposing pump and system curves The operating point will always be where the

two curves intersect Fig

Lecture No 15-16 Factors Affecting Pump Performance

Matching Pump and System Head-flow Characteristics Effect of over sizing the

pump Energy loss in throttling

Matching Pump and System Head-flow Characteristics

Centrifugal pumps are characterized by the relationship between the flow rate (Q) they

produce and the pressure (H) at which the flow is delivered Pump efficiency varies with

flow and pressure and it is highest at one particular flow rate

The Figure below shows a typical vendor-supplied head-flow curve for a centrifugal

pump Pump head-flow curves are typically given for clear water The choice of pump for

a given application depends largely on how the pump head-flow characteristics match the

requirement of the system downstream of the pump

Effect of over sizing the pump

As mentioned earlier pressure losses to be overcome by the pumps are a function of flow

ndash the system characteristics ndash are also quantified in the form of head-flow curves The

system curve is basically a plot of system resistance ie head to be overcome by the pump

versus various flow rates The system curves change with the physical configuration of

the system for example the system curves depends upon height or elevation diameter

and length of piping number and type of fittings and pressure drops across various

equipment - say a heat exchanger

A pump is selected based on how well the pump curve and system head-flow curves

match The pump operating point is identified as the point where the system curve

crosses the pump curve when they are superimposed on each other

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 5-6 Boiler Blowdown

Conductivity as Indicator of Boiler Water Quality Intermittent Blowdown

Continuous Blowdown Blowdown calculations Benefits of Blowdown

When water is boiled and steam is generated any dissolved solids contained in the water

remain in the boiler If more solids are put in with the feed water they will concentrate

and may eventually reach a level where their solubility in the water is exceeded and they

deposit from the solution Above a certain level of concentration these solids encourage

foaming and cause carryover of water into the steam The deposits also lead to scale

formation inside the boiler resulting in localized overheating and finally causing boiler

tube failure It is therefore necessary to control the level of concentration of the solids

and this is achieved by the process of blowing down where a certain volume of water is

blown off and is automatically replaced by feed water - thus maintaining the optimum

level of total dissolved solids (TDS) in the boiler water Blow down is necessary to

protect the surfaces of the heat exchanger in the boiler However blow down can be a

significant source of heat loss if improperly carried out

Conductivity as Indicator of Boiler Water Quality

Since it is tedious and time consuming to measure total dissolved solids (TDS) in boiler

water system conductivity measurement is used for monitoring the overall TDS present

in the boiler A rise in conductivity indicates a rise in the contamination of the boiler

water

Conventional methods for blowing down the boiler depend on two kinds of blowdown -

intermittent and continuous

Intermittent Blowdown

The intermittent blown down is given by manually operating a valve fitted to discharge

pipe at the lowest point of boiler shell to reduce parameters (TDS or conductivity pH

Silica and Phosphates concentration) within prescribed limits so that steam quality is not

likely to be affected In intermittent blowdown a large diameter line is opened for a short

period of time the time being based on a thumb rule such as ldquoonce in a shift for 2

minutesrdquo

Intermittent blowdown requires large short-term increases in the amount of feed water

put into the boiler and hence may necessitate larger feed water pumps than if continuous

blow down is used Also TDS level will be varying thereby causing fluctuations of the

water level in the boiler due to changes in steam bubble size and distribution which

accompany changes in concentration of solids Also substantial amount of heat energy is

lost with intermittent blowdown

Continuous Blowdown

There is a steady and constant dispatch of small stream of concentrated boiler water and

replacement by steady and constant inflow of feed water This ensures constant TDS and

steam purity at given steam load Once blow down valve is set for a given conditions

there is no need for regular operator intervention

Even though large quantities of heat are wasted opportunity exists for recovering this

heat by blowing into a flash tank and generating flash steam This flash steam can be used

for pre-heating boiler feed water or for any other purpose

Benefits of Blowdown

Good boiler blow down control can significantly reduce treatment and operational costs

that include

Lower pre-treatment costs

Less make-up water consumption

Reduced maintenance downtime

Increased boiler life

Lower consumption of treatment chemicals

Lecture No 7-8 Boiler Water Treatment Deposit Control Impurities causing deposits Silica Internal Water Treatment External Water Treatment Ion-exchange process (Softener Plant) De-aeration Mechanical de-aeration Chemical de-aeration Reverse Osmosis Recommended boiler and feed water quality

Boiler Water Treatment Producing quality steam on demand depends on properly

managed water treatment to control steam purity deposits and corrosion A boiler is the

sump of the boiler system It ultimately receives all of the pre-boiler contaminants Boiler

performance efficiency and service life are direct products of selecting and controlling

feed water used in the boiler

When feed water enters the boiler the elevated temperatures and pressures cause the

components of water to behave differently Most of the components in the feed water are

soluble However under heat and pressure most of the soluble components come out of

solution as particulate solids sometimes in crystallized forms and other times as

amorphous particles When solubility of a specific component in water is exceeded scale

or deposits develop The boiler water must be sufficiently free of deposit forming solids

to allow rapid and efficient heat transfer and it must not be corrosive to the boiler metal

Lecture No 9-10 Energy Conservation Opportunities

Stack Temperature Feed Water Preheating using Economiser Combustion Air

Preheat Incomplete Combustion Excess Air Control Radiation and Convection Heat

Loss Automatic Blowdown Control Reduction of Scaling and Soot

Losses Reduction of Boiler Steam Pressure Variable Speed Control for Fans

Blowers and Pumps Effect of Boiler Loading on Efficiency Proper Boiler

Scheduling Boiler Replacement

Stack Temperature

The stack temperature should be as low as possible However it should not be so low

that water vapor in the exhaust condenses on the stack walls This is important in fuels

containing signficant sulphur as low temperature can lead to sulphur dew point

corrosion Stack temperatures greater than 200degC indicates potential for recovery of

waste heat It also indicate the scaling of heat transferrecovery equipment and hence

the urgency of taking an early shut down for water flue side cleaning

Feed Water Preheating using Economiser Typically the flue gases leaving a

modern 3-pass shell boiler are at temperatures of 200 to 300 oC Thus there is a

potential to recover heat from these gases The flue gas exit temperature from a boiler

is usually maintained at a minimum of 200 oC so that the sulphur oxides in the flue

gas do not condense and cause corrosion in heat transfer surfaces When a clean fuel

such as natural gas LPG or gas oil is used the economy of heat recovery must be

worked out as the flue gas temperature may be well below 200oC The potential for

energy saving depends on the type of boiler installed and the fuel used For a typically

older model shell boiler with a flue gas exit temperature of 260oC an economizer

could be used to reduce it to 200oC increasing the feed water temperature by 15oC

Increase in overall thermal efficiency would be in the order of 3 For a modern 3-

pass shell boiler firing natural gas with a flue gas exit temperature of 140oC a

condensing economizer would reduce the exit temperature to 65oC increasing thermal

efficiency by 5

Combustion Air Preheat

Combustion air preheating is an alternative to feedwater heating In order to improve

thermal efficiency by 1 the combustion air temperature must be raised by 20 oC

Most gas and oil burners used in a boiler plant are not designed for high air preheat

temperatures Modern burners can withstand much higher combustion air preheat so

it is possible to consider such units as heat exchangers in the exit flue as an alternative

to an economizer when either space or a high feed water return temperature make it

viable

Incomplete Combustion

Incomplete combustion can arise from a shortage of air or surplus of fuel or poor

distribution of fuel It is usually obvious from the colour or smoke and must be

corrected immediately

In the case of oil and gas fired systems CO or smoke (for oil fired systems only) with

normal or high excess air indicates burner system problems A more frequent cause of

incomplete combustion is the poor mixing of fuel and air at the burner Poor oil fires

can result from improper viscosity worn tips carbonization on tips and deterioration

of diffusers or spinner plates

With coal firing unburned carbon can comprise a big loss It occurs as grit carry-over

or carbon-in-ash and may amount to more than 2 of the heat supplied to the boiler

Non uniform fuel size could be one of the reasons for incomplete combustion In

chain grate stokers large lumps will not burn out completely while small pieces and

fines may block the air passage thus causing poor air distribution In sprinkler

stokers stoker grate condition fuel distributors wind box air regulation and over-fire

systems can affect carbon loss Increase in the fines in pulverized coal also increases

carbon loss

Excess Air Control

Excess air is required in all practical cases to ensure complete combustion to allow

for the normal variations in combustion and to ensure satisfactory stack conditions for

some fuels The optimum excess air level for maximum boiler efficiency occurs when

the sum of the losses due to incomplete combustion and loss due to heat in flue gases

is minimum This level varies with furnace design type of burner fuel and process

variables It can be determined by conducting tests with different air fuel ratios

Radiation and Convection Heat Loss

The external surfaces of a shell boiler are hotter than the surroundings The surfaces

thus lose heat to the surroundings depending on the surface area and the difference in

temperature between the surface and the surroundings The heat loss from the boiler

shell is normally a fixed energy loss irrespective of the boiler output With modern

boiler designs this may represent only 15 on the gross calorific value at full rating

but will increase to around 6 if the boiler operates at only 25 percent output

Repairing or augmenting insulation can reduce heat loss through boiler walls and

piping

Automatic Blowdown Control

Uncontrolled continuous blowdown is very wasteful Automatic blowdown controls

can be installed that sense and respond to boiler water conductivity and pH A 10

blow down in a 15 kgcm2 boiler results in 3 efficiency loss

Reduction of Scaling and Soot Losses

In oil and coal-fired boilers soot buildup on tubes acts as an insulator against heat

transfer Any such deposits should be removed on a regular basis Elevated stack

temperatures may indicate excessive soot buildup Also same result will occur due to

scaling on the water side High exit gas temperatures at normal excess air indicate

poor heat transfer performance This condition can result from a gradual build-up of

gas-side or waterside deposits Waterside deposits require a review of water treatment

procedures and tube cleaning to remove deposits An estimated 1 efficiency loss

occurs with every 22oC increase in stack temperature

Reduction of Boiler Steam Pressure

This is an effective means of reducing fuel consumption if permissible by as much as

1 to 2 Lower steam pressure gives a lower saturated steam temperature and without

stack heat recovery a similar reduction in the temperature of the flue gas temperature

results

Steam is generated at pressures normally dictated by the highest pressure

temperature requirements for a particular process In some cases the process does not

operate all the time and there are periods when the boiler pressure could be reduced

The energy manager should consider pressure reduction carefully before

recommending it Adverse effects such as an increase in water carryover from the

boiler owing to pressure reduction may negate any potential saving Pressure should

be reduced in stages and no more than a 20 percent reduction should be considered

Variable Speed Control for Fans Blowers and Pumps

Variable speed control is an important means of achieving energy savings Generally

combustion air control is effected by throttling dampers fitted at forced and induced

draft fans Though dampers are simple means of control they lack accuracy giving

poor control characteristics at the top and bottom of the operating range In general if

the load characteristic of the boiler is variable the possibility of replacing the dampers

by a VSD should be evaluated

Effect of Boiler Loading on Efficiency

The maximum efficiency of the boiler does not occur at full load but at about two-

thirds of the full load If the load on the boiler decreases further efficiency also tends

to decrease At zero output the efficiency of the boiler is zero and any fuel fired is

used only to supply the losses The factors affecting boiler efficiency are

As the load falls so does the value of the mass flow rate of the flue gases through the

tubes This reduction in flow rate for the same heat transfer area reduced the exit flue

gas temperatures by a small extent reducing the sensible heat lossBelow half load

most combustion appliances need more excess air to burn the fuel completely This

increases the sensible heat loss In general efficiency of the boiler reduces

significantly below 25 of the rated load and as far as possible operation of boilers

below this level should be avoided

Proper Boiler Scheduling

Since the optimum efficiency of boilers occurs at 65-85 of full load it is usually

more efficient on the whole to operate a fewer number of boilers at higher loads

than to operate a large number at low loads

Boiler Replacement

The potential savings from replacing a boiler depend on the anticipated change in

overall efficiency A change in a boiler can be financially attractive if the existing

boiler is

Old and inefficient

Not capable of firing cheaper substitution fuel

Over or under-sized for present requirements

Not designed for ideal loading conditions

The feasibility study should examine all implications of long-term fuel availability

and company growth plans All financial and engineering factors should be

considered Since boiler plants traditionally have a useful life of well over 25 years

replacement must be carefully studied

Lecture No 11-12 Pumps and Pumping System

Pump Types Centrifugal Pumps Pump Performance Curve Hydraulic power pump

shaft power and electrical input power

Pump Types

Pumps come in a variety of sizes for a wide range of applications They can be

classified according to their basic operating principle as dynamic or displacement

pumps Dynamic pumps can be sub-classified as centrifugal and special effect pumps

Displacement pumps can be sub-classified as rotary or reciprocating pumps

In principle any liquid can be handled by any of the pump designs Where different

pump designs could be used the centrifugal pump is generally the most economical

followed by rotary and reciprocating pumps Although positive displacement pumps

are generally more efficient than centrifugal pumps the benefit of higher efficiency

tends to be offset by increased maintenance costs

Since worldwide centrifugal pumps account for the majority of electricity used by

pumps the focus of this chapter is on centrifugal pump

Centrifugal Pumps

A centrifugal pump is of a very simple design The two main parts of the pump are the

impeller and the diffuser Impeller which is the only moving part is attached to a

shaft and driven by a motor Impellers are generally made of bronze polycarbonate

cast iron stainless steel as well as other materials The diffuser (also called as volute)

houses the impeller and captures and directs the water off the impeller

Pump Performance Curve

The pump is a dynamic device it is convenient to consider the pressure in terms of

head ie meters of liquid column The pump generates the same head of liquid

whatever the density of the liquid being pumped The actual contours of the hydraulic

passages of the impeller and the casing are extremely important in order to attain the

highest efficiency possible The standard convention for centrifugal pump is to draw

the pump performance curves showing Flow on the horizontal axis and Head

generated on the vertical axis Efficiency Power amp NPSH Required (described later)

are also all conventionally shown on the vertical axis plotted against Flow as

illustrated in Figure

Lecture No 13-14 System Characteristics

Static Head vs Flow Friction Head vs Flow System with High Static Head System

with Low Static Head Pump Curves Head- Flow Curve Pump operating point

In a pumping system the objective in most cases is either to transfer a liquid from a

source to a required destination eg filling a high level reservoir or to circulate liquid

around a system eg as a means of heat transfer in heat exchanger

A pressure is needed to make the liquid flow at the required rate and this must

overcome head lsquolossesrsquo in the system Losses are of two types static and friction

head

Static head is simply the difference in height of the supply and destination reservoirs

as in Figure In this illustration flow velocity in the pipe is assumed to be very small

Another example of a system with only static head is pumping into a pressurised

vessel with short pipe runs Static head is independent of flow and graphically would

be shown as in Figure

Figure Static Head Figure Static Head vs Flow

Pump Curves

The performance of a pump can be expressed graphically as head against flow rate

The centrifugal pump has a curve where the head falls gradually with increasing flow

This is called the pump characteristic curve

Pump operating point

When a pump is installed in a system the effect can be illustrated graphically by

superimposing pump and system curves The operating point will always be where the

two curves intersect Fig

Lecture No 15-16 Factors Affecting Pump Performance

Matching Pump and System Head-flow Characteristics Effect of over sizing the

pump Energy loss in throttling

Matching Pump and System Head-flow Characteristics

Centrifugal pumps are characterized by the relationship between the flow rate (Q) they

produce and the pressure (H) at which the flow is delivered Pump efficiency varies with

flow and pressure and it is highest at one particular flow rate

The Figure below shows a typical vendor-supplied head-flow curve for a centrifugal

pump Pump head-flow curves are typically given for clear water The choice of pump for

a given application depends largely on how the pump head-flow characteristics match the

requirement of the system downstream of the pump

Effect of over sizing the pump

As mentioned earlier pressure losses to be overcome by the pumps are a function of flow

ndash the system characteristics ndash are also quantified in the form of head-flow curves The

system curve is basically a plot of system resistance ie head to be overcome by the pump

versus various flow rates The system curves change with the physical configuration of

the system for example the system curves depends upon height or elevation diameter

and length of piping number and type of fittings and pressure drops across various

equipment - say a heat exchanger

A pump is selected based on how well the pump curve and system head-flow curves

match The pump operating point is identified as the point where the system curve

crosses the pump curve when they are superimposed on each other

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

water level in the boiler due to changes in steam bubble size and distribution which

accompany changes in concentration of solids Also substantial amount of heat energy is

lost with intermittent blowdown

Continuous Blowdown

There is a steady and constant dispatch of small stream of concentrated boiler water and

replacement by steady and constant inflow of feed water This ensures constant TDS and

steam purity at given steam load Once blow down valve is set for a given conditions

there is no need for regular operator intervention

Even though large quantities of heat are wasted opportunity exists for recovering this

heat by blowing into a flash tank and generating flash steam This flash steam can be used

for pre-heating boiler feed water or for any other purpose

Benefits of Blowdown

Good boiler blow down control can significantly reduce treatment and operational costs

that include

Lower pre-treatment costs

Less make-up water consumption

Reduced maintenance downtime

Increased boiler life

Lower consumption of treatment chemicals

Lecture No 7-8 Boiler Water Treatment Deposit Control Impurities causing deposits Silica Internal Water Treatment External Water Treatment Ion-exchange process (Softener Plant) De-aeration Mechanical de-aeration Chemical de-aeration Reverse Osmosis Recommended boiler and feed water quality

Boiler Water Treatment Producing quality steam on demand depends on properly

managed water treatment to control steam purity deposits and corrosion A boiler is the

sump of the boiler system It ultimately receives all of the pre-boiler contaminants Boiler

performance efficiency and service life are direct products of selecting and controlling

feed water used in the boiler

When feed water enters the boiler the elevated temperatures and pressures cause the

components of water to behave differently Most of the components in the feed water are

soluble However under heat and pressure most of the soluble components come out of

solution as particulate solids sometimes in crystallized forms and other times as

amorphous particles When solubility of a specific component in water is exceeded scale

or deposits develop The boiler water must be sufficiently free of deposit forming solids

to allow rapid and efficient heat transfer and it must not be corrosive to the boiler metal

Lecture No 9-10 Energy Conservation Opportunities

Stack Temperature Feed Water Preheating using Economiser Combustion Air

Preheat Incomplete Combustion Excess Air Control Radiation and Convection Heat

Loss Automatic Blowdown Control Reduction of Scaling and Soot

Losses Reduction of Boiler Steam Pressure Variable Speed Control for Fans

Blowers and Pumps Effect of Boiler Loading on Efficiency Proper Boiler

Scheduling Boiler Replacement

Stack Temperature

The stack temperature should be as low as possible However it should not be so low

that water vapor in the exhaust condenses on the stack walls This is important in fuels

containing signficant sulphur as low temperature can lead to sulphur dew point

corrosion Stack temperatures greater than 200degC indicates potential for recovery of

waste heat It also indicate the scaling of heat transferrecovery equipment and hence

the urgency of taking an early shut down for water flue side cleaning

Feed Water Preheating using Economiser Typically the flue gases leaving a

modern 3-pass shell boiler are at temperatures of 200 to 300 oC Thus there is a

potential to recover heat from these gases The flue gas exit temperature from a boiler

is usually maintained at a minimum of 200 oC so that the sulphur oxides in the flue

gas do not condense and cause corrosion in heat transfer surfaces When a clean fuel

such as natural gas LPG or gas oil is used the economy of heat recovery must be

worked out as the flue gas temperature may be well below 200oC The potential for

energy saving depends on the type of boiler installed and the fuel used For a typically

older model shell boiler with a flue gas exit temperature of 260oC an economizer

could be used to reduce it to 200oC increasing the feed water temperature by 15oC

Increase in overall thermal efficiency would be in the order of 3 For a modern 3-

pass shell boiler firing natural gas with a flue gas exit temperature of 140oC a

condensing economizer would reduce the exit temperature to 65oC increasing thermal

efficiency by 5

Combustion Air Preheat

Combustion air preheating is an alternative to feedwater heating In order to improve

thermal efficiency by 1 the combustion air temperature must be raised by 20 oC

Most gas and oil burners used in a boiler plant are not designed for high air preheat

temperatures Modern burners can withstand much higher combustion air preheat so

it is possible to consider such units as heat exchangers in the exit flue as an alternative

to an economizer when either space or a high feed water return temperature make it

viable

Incomplete Combustion

Incomplete combustion can arise from a shortage of air or surplus of fuel or poor

distribution of fuel It is usually obvious from the colour or smoke and must be

corrected immediately

In the case of oil and gas fired systems CO or smoke (for oil fired systems only) with

normal or high excess air indicates burner system problems A more frequent cause of

incomplete combustion is the poor mixing of fuel and air at the burner Poor oil fires

can result from improper viscosity worn tips carbonization on tips and deterioration

of diffusers or spinner plates

With coal firing unburned carbon can comprise a big loss It occurs as grit carry-over

or carbon-in-ash and may amount to more than 2 of the heat supplied to the boiler

Non uniform fuel size could be one of the reasons for incomplete combustion In

chain grate stokers large lumps will not burn out completely while small pieces and

fines may block the air passage thus causing poor air distribution In sprinkler

stokers stoker grate condition fuel distributors wind box air regulation and over-fire

systems can affect carbon loss Increase in the fines in pulverized coal also increases

carbon loss

Excess Air Control

Excess air is required in all practical cases to ensure complete combustion to allow

for the normal variations in combustion and to ensure satisfactory stack conditions for

some fuels The optimum excess air level for maximum boiler efficiency occurs when

the sum of the losses due to incomplete combustion and loss due to heat in flue gases

is minimum This level varies with furnace design type of burner fuel and process

variables It can be determined by conducting tests with different air fuel ratios

Radiation and Convection Heat Loss

The external surfaces of a shell boiler are hotter than the surroundings The surfaces

thus lose heat to the surroundings depending on the surface area and the difference in

temperature between the surface and the surroundings The heat loss from the boiler

shell is normally a fixed energy loss irrespective of the boiler output With modern

boiler designs this may represent only 15 on the gross calorific value at full rating

but will increase to around 6 if the boiler operates at only 25 percent output

Repairing or augmenting insulation can reduce heat loss through boiler walls and

piping

Automatic Blowdown Control

Uncontrolled continuous blowdown is very wasteful Automatic blowdown controls

can be installed that sense and respond to boiler water conductivity and pH A 10

blow down in a 15 kgcm2 boiler results in 3 efficiency loss

Reduction of Scaling and Soot Losses

In oil and coal-fired boilers soot buildup on tubes acts as an insulator against heat

transfer Any such deposits should be removed on a regular basis Elevated stack

temperatures may indicate excessive soot buildup Also same result will occur due to

scaling on the water side High exit gas temperatures at normal excess air indicate

poor heat transfer performance This condition can result from a gradual build-up of

gas-side or waterside deposits Waterside deposits require a review of water treatment

procedures and tube cleaning to remove deposits An estimated 1 efficiency loss

occurs with every 22oC increase in stack temperature

Reduction of Boiler Steam Pressure

This is an effective means of reducing fuel consumption if permissible by as much as

1 to 2 Lower steam pressure gives a lower saturated steam temperature and without

stack heat recovery a similar reduction in the temperature of the flue gas temperature

results

Steam is generated at pressures normally dictated by the highest pressure

temperature requirements for a particular process In some cases the process does not

operate all the time and there are periods when the boiler pressure could be reduced

The energy manager should consider pressure reduction carefully before

recommending it Adverse effects such as an increase in water carryover from the

boiler owing to pressure reduction may negate any potential saving Pressure should

be reduced in stages and no more than a 20 percent reduction should be considered

Variable Speed Control for Fans Blowers and Pumps

Variable speed control is an important means of achieving energy savings Generally

combustion air control is effected by throttling dampers fitted at forced and induced

draft fans Though dampers are simple means of control they lack accuracy giving

poor control characteristics at the top and bottom of the operating range In general if

the load characteristic of the boiler is variable the possibility of replacing the dampers

by a VSD should be evaluated

Effect of Boiler Loading on Efficiency

The maximum efficiency of the boiler does not occur at full load but at about two-

thirds of the full load If the load on the boiler decreases further efficiency also tends

to decrease At zero output the efficiency of the boiler is zero and any fuel fired is

used only to supply the losses The factors affecting boiler efficiency are

As the load falls so does the value of the mass flow rate of the flue gases through the

tubes This reduction in flow rate for the same heat transfer area reduced the exit flue

gas temperatures by a small extent reducing the sensible heat lossBelow half load

most combustion appliances need more excess air to burn the fuel completely This

increases the sensible heat loss In general efficiency of the boiler reduces

significantly below 25 of the rated load and as far as possible operation of boilers

below this level should be avoided

Proper Boiler Scheduling

Since the optimum efficiency of boilers occurs at 65-85 of full load it is usually

more efficient on the whole to operate a fewer number of boilers at higher loads

than to operate a large number at low loads

Boiler Replacement

The potential savings from replacing a boiler depend on the anticipated change in

overall efficiency A change in a boiler can be financially attractive if the existing

boiler is

Old and inefficient

Not capable of firing cheaper substitution fuel

Over or under-sized for present requirements

Not designed for ideal loading conditions

The feasibility study should examine all implications of long-term fuel availability

and company growth plans All financial and engineering factors should be

considered Since boiler plants traditionally have a useful life of well over 25 years

replacement must be carefully studied

Lecture No 11-12 Pumps and Pumping System

Pump Types Centrifugal Pumps Pump Performance Curve Hydraulic power pump

shaft power and electrical input power

Pump Types

Pumps come in a variety of sizes for a wide range of applications They can be

classified according to their basic operating principle as dynamic or displacement

pumps Dynamic pumps can be sub-classified as centrifugal and special effect pumps

Displacement pumps can be sub-classified as rotary or reciprocating pumps

In principle any liquid can be handled by any of the pump designs Where different

pump designs could be used the centrifugal pump is generally the most economical

followed by rotary and reciprocating pumps Although positive displacement pumps

are generally more efficient than centrifugal pumps the benefit of higher efficiency

tends to be offset by increased maintenance costs

Since worldwide centrifugal pumps account for the majority of electricity used by

pumps the focus of this chapter is on centrifugal pump

Centrifugal Pumps

A centrifugal pump is of a very simple design The two main parts of the pump are the

impeller and the diffuser Impeller which is the only moving part is attached to a

shaft and driven by a motor Impellers are generally made of bronze polycarbonate

cast iron stainless steel as well as other materials The diffuser (also called as volute)

houses the impeller and captures and directs the water off the impeller

Pump Performance Curve

The pump is a dynamic device it is convenient to consider the pressure in terms of

head ie meters of liquid column The pump generates the same head of liquid

whatever the density of the liquid being pumped The actual contours of the hydraulic

passages of the impeller and the casing are extremely important in order to attain the

highest efficiency possible The standard convention for centrifugal pump is to draw

the pump performance curves showing Flow on the horizontal axis and Head

generated on the vertical axis Efficiency Power amp NPSH Required (described later)

are also all conventionally shown on the vertical axis plotted against Flow as

illustrated in Figure

Lecture No 13-14 System Characteristics

Static Head vs Flow Friction Head vs Flow System with High Static Head System

with Low Static Head Pump Curves Head- Flow Curve Pump operating point

In a pumping system the objective in most cases is either to transfer a liquid from a

source to a required destination eg filling a high level reservoir or to circulate liquid

around a system eg as a means of heat transfer in heat exchanger

A pressure is needed to make the liquid flow at the required rate and this must

overcome head lsquolossesrsquo in the system Losses are of two types static and friction

head

Static head is simply the difference in height of the supply and destination reservoirs

as in Figure In this illustration flow velocity in the pipe is assumed to be very small

Another example of a system with only static head is pumping into a pressurised

vessel with short pipe runs Static head is independent of flow and graphically would

be shown as in Figure

Figure Static Head Figure Static Head vs Flow

Pump Curves

The performance of a pump can be expressed graphically as head against flow rate

The centrifugal pump has a curve where the head falls gradually with increasing flow

This is called the pump characteristic curve

Pump operating point

When a pump is installed in a system the effect can be illustrated graphically by

superimposing pump and system curves The operating point will always be where the

two curves intersect Fig

Lecture No 15-16 Factors Affecting Pump Performance

Matching Pump and System Head-flow Characteristics Effect of over sizing the

pump Energy loss in throttling

Matching Pump and System Head-flow Characteristics

Centrifugal pumps are characterized by the relationship between the flow rate (Q) they

produce and the pressure (H) at which the flow is delivered Pump efficiency varies with

flow and pressure and it is highest at one particular flow rate

The Figure below shows a typical vendor-supplied head-flow curve for a centrifugal

pump Pump head-flow curves are typically given for clear water The choice of pump for

a given application depends largely on how the pump head-flow characteristics match the

requirement of the system downstream of the pump

Effect of over sizing the pump

As mentioned earlier pressure losses to be overcome by the pumps are a function of flow

ndash the system characteristics ndash are also quantified in the form of head-flow curves The

system curve is basically a plot of system resistance ie head to be overcome by the pump

versus various flow rates The system curves change with the physical configuration of

the system for example the system curves depends upon height or elevation diameter

and length of piping number and type of fittings and pressure drops across various

equipment - say a heat exchanger

A pump is selected based on how well the pump curve and system head-flow curves

match The pump operating point is identified as the point where the system curve

crosses the pump curve when they are superimposed on each other

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 7-8 Boiler Water Treatment Deposit Control Impurities causing deposits Silica Internal Water Treatment External Water Treatment Ion-exchange process (Softener Plant) De-aeration Mechanical de-aeration Chemical de-aeration Reverse Osmosis Recommended boiler and feed water quality

Boiler Water Treatment Producing quality steam on demand depends on properly

managed water treatment to control steam purity deposits and corrosion A boiler is the

sump of the boiler system It ultimately receives all of the pre-boiler contaminants Boiler

performance efficiency and service life are direct products of selecting and controlling

feed water used in the boiler

When feed water enters the boiler the elevated temperatures and pressures cause the

components of water to behave differently Most of the components in the feed water are

soluble However under heat and pressure most of the soluble components come out of

solution as particulate solids sometimes in crystallized forms and other times as

amorphous particles When solubility of a specific component in water is exceeded scale

or deposits develop The boiler water must be sufficiently free of deposit forming solids

to allow rapid and efficient heat transfer and it must not be corrosive to the boiler metal

Lecture No 9-10 Energy Conservation Opportunities

Stack Temperature Feed Water Preheating using Economiser Combustion Air

Preheat Incomplete Combustion Excess Air Control Radiation and Convection Heat

Loss Automatic Blowdown Control Reduction of Scaling and Soot

Losses Reduction of Boiler Steam Pressure Variable Speed Control for Fans

Blowers and Pumps Effect of Boiler Loading on Efficiency Proper Boiler

Scheduling Boiler Replacement

Stack Temperature

The stack temperature should be as low as possible However it should not be so low

that water vapor in the exhaust condenses on the stack walls This is important in fuels

containing signficant sulphur as low temperature can lead to sulphur dew point

corrosion Stack temperatures greater than 200degC indicates potential for recovery of

waste heat It also indicate the scaling of heat transferrecovery equipment and hence

the urgency of taking an early shut down for water flue side cleaning

Feed Water Preheating using Economiser Typically the flue gases leaving a

modern 3-pass shell boiler are at temperatures of 200 to 300 oC Thus there is a

potential to recover heat from these gases The flue gas exit temperature from a boiler

is usually maintained at a minimum of 200 oC so that the sulphur oxides in the flue

gas do not condense and cause corrosion in heat transfer surfaces When a clean fuel

such as natural gas LPG or gas oil is used the economy of heat recovery must be

worked out as the flue gas temperature may be well below 200oC The potential for

energy saving depends on the type of boiler installed and the fuel used For a typically

older model shell boiler with a flue gas exit temperature of 260oC an economizer

could be used to reduce it to 200oC increasing the feed water temperature by 15oC

Increase in overall thermal efficiency would be in the order of 3 For a modern 3-

pass shell boiler firing natural gas with a flue gas exit temperature of 140oC a

condensing economizer would reduce the exit temperature to 65oC increasing thermal

efficiency by 5

Combustion Air Preheat

Combustion air preheating is an alternative to feedwater heating In order to improve

thermal efficiency by 1 the combustion air temperature must be raised by 20 oC

Most gas and oil burners used in a boiler plant are not designed for high air preheat

temperatures Modern burners can withstand much higher combustion air preheat so

it is possible to consider such units as heat exchangers in the exit flue as an alternative

to an economizer when either space or a high feed water return temperature make it

viable

Incomplete Combustion

Incomplete combustion can arise from a shortage of air or surplus of fuel or poor

distribution of fuel It is usually obvious from the colour or smoke and must be

corrected immediately

In the case of oil and gas fired systems CO or smoke (for oil fired systems only) with

normal or high excess air indicates burner system problems A more frequent cause of

incomplete combustion is the poor mixing of fuel and air at the burner Poor oil fires

can result from improper viscosity worn tips carbonization on tips and deterioration

of diffusers or spinner plates

With coal firing unburned carbon can comprise a big loss It occurs as grit carry-over

or carbon-in-ash and may amount to more than 2 of the heat supplied to the boiler

Non uniform fuel size could be one of the reasons for incomplete combustion In

chain grate stokers large lumps will not burn out completely while small pieces and

fines may block the air passage thus causing poor air distribution In sprinkler

stokers stoker grate condition fuel distributors wind box air regulation and over-fire

systems can affect carbon loss Increase in the fines in pulverized coal also increases

carbon loss

Excess Air Control

Excess air is required in all practical cases to ensure complete combustion to allow

for the normal variations in combustion and to ensure satisfactory stack conditions for

some fuels The optimum excess air level for maximum boiler efficiency occurs when

the sum of the losses due to incomplete combustion and loss due to heat in flue gases

is minimum This level varies with furnace design type of burner fuel and process

variables It can be determined by conducting tests with different air fuel ratios

Radiation and Convection Heat Loss

The external surfaces of a shell boiler are hotter than the surroundings The surfaces

thus lose heat to the surroundings depending on the surface area and the difference in

temperature between the surface and the surroundings The heat loss from the boiler

shell is normally a fixed energy loss irrespective of the boiler output With modern

boiler designs this may represent only 15 on the gross calorific value at full rating

but will increase to around 6 if the boiler operates at only 25 percent output

Repairing or augmenting insulation can reduce heat loss through boiler walls and

piping

Automatic Blowdown Control

Uncontrolled continuous blowdown is very wasteful Automatic blowdown controls

can be installed that sense and respond to boiler water conductivity and pH A 10

blow down in a 15 kgcm2 boiler results in 3 efficiency loss

Reduction of Scaling and Soot Losses

In oil and coal-fired boilers soot buildup on tubes acts as an insulator against heat

transfer Any such deposits should be removed on a regular basis Elevated stack

temperatures may indicate excessive soot buildup Also same result will occur due to

scaling on the water side High exit gas temperatures at normal excess air indicate

poor heat transfer performance This condition can result from a gradual build-up of

gas-side or waterside deposits Waterside deposits require a review of water treatment

procedures and tube cleaning to remove deposits An estimated 1 efficiency loss

occurs with every 22oC increase in stack temperature

Reduction of Boiler Steam Pressure

This is an effective means of reducing fuel consumption if permissible by as much as

1 to 2 Lower steam pressure gives a lower saturated steam temperature and without

stack heat recovery a similar reduction in the temperature of the flue gas temperature

results

Steam is generated at pressures normally dictated by the highest pressure

temperature requirements for a particular process In some cases the process does not

operate all the time and there are periods when the boiler pressure could be reduced

The energy manager should consider pressure reduction carefully before

recommending it Adverse effects such as an increase in water carryover from the

boiler owing to pressure reduction may negate any potential saving Pressure should

be reduced in stages and no more than a 20 percent reduction should be considered

Variable Speed Control for Fans Blowers and Pumps

Variable speed control is an important means of achieving energy savings Generally

combustion air control is effected by throttling dampers fitted at forced and induced

draft fans Though dampers are simple means of control they lack accuracy giving

poor control characteristics at the top and bottom of the operating range In general if

the load characteristic of the boiler is variable the possibility of replacing the dampers

by a VSD should be evaluated

Effect of Boiler Loading on Efficiency

The maximum efficiency of the boiler does not occur at full load but at about two-

thirds of the full load If the load on the boiler decreases further efficiency also tends

to decrease At zero output the efficiency of the boiler is zero and any fuel fired is

used only to supply the losses The factors affecting boiler efficiency are

As the load falls so does the value of the mass flow rate of the flue gases through the

tubes This reduction in flow rate for the same heat transfer area reduced the exit flue

gas temperatures by a small extent reducing the sensible heat lossBelow half load

most combustion appliances need more excess air to burn the fuel completely This

increases the sensible heat loss In general efficiency of the boiler reduces

significantly below 25 of the rated load and as far as possible operation of boilers

below this level should be avoided

Proper Boiler Scheduling

Since the optimum efficiency of boilers occurs at 65-85 of full load it is usually

more efficient on the whole to operate a fewer number of boilers at higher loads

than to operate a large number at low loads

Boiler Replacement

The potential savings from replacing a boiler depend on the anticipated change in

overall efficiency A change in a boiler can be financially attractive if the existing

boiler is

Old and inefficient

Not capable of firing cheaper substitution fuel

Over or under-sized for present requirements

Not designed for ideal loading conditions

The feasibility study should examine all implications of long-term fuel availability

and company growth plans All financial and engineering factors should be

considered Since boiler plants traditionally have a useful life of well over 25 years

replacement must be carefully studied

Lecture No 11-12 Pumps and Pumping System

Pump Types Centrifugal Pumps Pump Performance Curve Hydraulic power pump

shaft power and electrical input power

Pump Types

Pumps come in a variety of sizes for a wide range of applications They can be

classified according to their basic operating principle as dynamic or displacement

pumps Dynamic pumps can be sub-classified as centrifugal and special effect pumps

Displacement pumps can be sub-classified as rotary or reciprocating pumps

In principle any liquid can be handled by any of the pump designs Where different

pump designs could be used the centrifugal pump is generally the most economical

followed by rotary and reciprocating pumps Although positive displacement pumps

are generally more efficient than centrifugal pumps the benefit of higher efficiency

tends to be offset by increased maintenance costs

Since worldwide centrifugal pumps account for the majority of electricity used by

pumps the focus of this chapter is on centrifugal pump

Centrifugal Pumps

A centrifugal pump is of a very simple design The two main parts of the pump are the

impeller and the diffuser Impeller which is the only moving part is attached to a

shaft and driven by a motor Impellers are generally made of bronze polycarbonate

cast iron stainless steel as well as other materials The diffuser (also called as volute)

houses the impeller and captures and directs the water off the impeller

Pump Performance Curve

The pump is a dynamic device it is convenient to consider the pressure in terms of

head ie meters of liquid column The pump generates the same head of liquid

whatever the density of the liquid being pumped The actual contours of the hydraulic

passages of the impeller and the casing are extremely important in order to attain the

highest efficiency possible The standard convention for centrifugal pump is to draw

the pump performance curves showing Flow on the horizontal axis and Head

generated on the vertical axis Efficiency Power amp NPSH Required (described later)

are also all conventionally shown on the vertical axis plotted against Flow as

illustrated in Figure

Lecture No 13-14 System Characteristics

Static Head vs Flow Friction Head vs Flow System with High Static Head System

with Low Static Head Pump Curves Head- Flow Curve Pump operating point

In a pumping system the objective in most cases is either to transfer a liquid from a

source to a required destination eg filling a high level reservoir or to circulate liquid

around a system eg as a means of heat transfer in heat exchanger

A pressure is needed to make the liquid flow at the required rate and this must

overcome head lsquolossesrsquo in the system Losses are of two types static and friction

head

Static head is simply the difference in height of the supply and destination reservoirs

as in Figure In this illustration flow velocity in the pipe is assumed to be very small

Another example of a system with only static head is pumping into a pressurised

vessel with short pipe runs Static head is independent of flow and graphically would

be shown as in Figure

Figure Static Head Figure Static Head vs Flow

Pump Curves

The performance of a pump can be expressed graphically as head against flow rate

The centrifugal pump has a curve where the head falls gradually with increasing flow

This is called the pump characteristic curve

Pump operating point

When a pump is installed in a system the effect can be illustrated graphically by

superimposing pump and system curves The operating point will always be where the

two curves intersect Fig

Lecture No 15-16 Factors Affecting Pump Performance

Matching Pump and System Head-flow Characteristics Effect of over sizing the

pump Energy loss in throttling

Matching Pump and System Head-flow Characteristics

Centrifugal pumps are characterized by the relationship between the flow rate (Q) they

produce and the pressure (H) at which the flow is delivered Pump efficiency varies with

flow and pressure and it is highest at one particular flow rate

The Figure below shows a typical vendor-supplied head-flow curve for a centrifugal

pump Pump head-flow curves are typically given for clear water The choice of pump for

a given application depends largely on how the pump head-flow characteristics match the

requirement of the system downstream of the pump

Effect of over sizing the pump

As mentioned earlier pressure losses to be overcome by the pumps are a function of flow

ndash the system characteristics ndash are also quantified in the form of head-flow curves The

system curve is basically a plot of system resistance ie head to be overcome by the pump

versus various flow rates The system curves change with the physical configuration of

the system for example the system curves depends upon height or elevation diameter

and length of piping number and type of fittings and pressure drops across various

equipment - say a heat exchanger

A pump is selected based on how well the pump curve and system head-flow curves

match The pump operating point is identified as the point where the system curve

crosses the pump curve when they are superimposed on each other

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 9-10 Energy Conservation Opportunities

Stack Temperature Feed Water Preheating using Economiser Combustion Air

Preheat Incomplete Combustion Excess Air Control Radiation and Convection Heat

Loss Automatic Blowdown Control Reduction of Scaling and Soot

Losses Reduction of Boiler Steam Pressure Variable Speed Control for Fans

Blowers and Pumps Effect of Boiler Loading on Efficiency Proper Boiler

Scheduling Boiler Replacement

Stack Temperature

The stack temperature should be as low as possible However it should not be so low

that water vapor in the exhaust condenses on the stack walls This is important in fuels

containing signficant sulphur as low temperature can lead to sulphur dew point

corrosion Stack temperatures greater than 200degC indicates potential for recovery of

waste heat It also indicate the scaling of heat transferrecovery equipment and hence

the urgency of taking an early shut down for water flue side cleaning

Feed Water Preheating using Economiser Typically the flue gases leaving a

modern 3-pass shell boiler are at temperatures of 200 to 300 oC Thus there is a

potential to recover heat from these gases The flue gas exit temperature from a boiler

is usually maintained at a minimum of 200 oC so that the sulphur oxides in the flue

gas do not condense and cause corrosion in heat transfer surfaces When a clean fuel

such as natural gas LPG or gas oil is used the economy of heat recovery must be

worked out as the flue gas temperature may be well below 200oC The potential for

energy saving depends on the type of boiler installed and the fuel used For a typically

older model shell boiler with a flue gas exit temperature of 260oC an economizer

could be used to reduce it to 200oC increasing the feed water temperature by 15oC

Increase in overall thermal efficiency would be in the order of 3 For a modern 3-

pass shell boiler firing natural gas with a flue gas exit temperature of 140oC a

condensing economizer would reduce the exit temperature to 65oC increasing thermal

efficiency by 5

Combustion Air Preheat

Combustion air preheating is an alternative to feedwater heating In order to improve

thermal efficiency by 1 the combustion air temperature must be raised by 20 oC

Most gas and oil burners used in a boiler plant are not designed for high air preheat

temperatures Modern burners can withstand much higher combustion air preheat so

it is possible to consider such units as heat exchangers in the exit flue as an alternative

to an economizer when either space or a high feed water return temperature make it

viable

Incomplete Combustion

Incomplete combustion can arise from a shortage of air or surplus of fuel or poor

distribution of fuel It is usually obvious from the colour or smoke and must be

corrected immediately

In the case of oil and gas fired systems CO or smoke (for oil fired systems only) with

normal or high excess air indicates burner system problems A more frequent cause of

incomplete combustion is the poor mixing of fuel and air at the burner Poor oil fires

can result from improper viscosity worn tips carbonization on tips and deterioration

of diffusers or spinner plates

With coal firing unburned carbon can comprise a big loss It occurs as grit carry-over

or carbon-in-ash and may amount to more than 2 of the heat supplied to the boiler

Non uniform fuel size could be one of the reasons for incomplete combustion In

chain grate stokers large lumps will not burn out completely while small pieces and

fines may block the air passage thus causing poor air distribution In sprinkler

stokers stoker grate condition fuel distributors wind box air regulation and over-fire

systems can affect carbon loss Increase in the fines in pulverized coal also increases

carbon loss

Excess Air Control

Excess air is required in all practical cases to ensure complete combustion to allow

for the normal variations in combustion and to ensure satisfactory stack conditions for

some fuels The optimum excess air level for maximum boiler efficiency occurs when

the sum of the losses due to incomplete combustion and loss due to heat in flue gases

is minimum This level varies with furnace design type of burner fuel and process

variables It can be determined by conducting tests with different air fuel ratios

Radiation and Convection Heat Loss

The external surfaces of a shell boiler are hotter than the surroundings The surfaces

thus lose heat to the surroundings depending on the surface area and the difference in

temperature between the surface and the surroundings The heat loss from the boiler

shell is normally a fixed energy loss irrespective of the boiler output With modern

boiler designs this may represent only 15 on the gross calorific value at full rating

but will increase to around 6 if the boiler operates at only 25 percent output

Repairing or augmenting insulation can reduce heat loss through boiler walls and

piping

Automatic Blowdown Control

Uncontrolled continuous blowdown is very wasteful Automatic blowdown controls

can be installed that sense and respond to boiler water conductivity and pH A 10

blow down in a 15 kgcm2 boiler results in 3 efficiency loss

Reduction of Scaling and Soot Losses

In oil and coal-fired boilers soot buildup on tubes acts as an insulator against heat

transfer Any such deposits should be removed on a regular basis Elevated stack

temperatures may indicate excessive soot buildup Also same result will occur due to

scaling on the water side High exit gas temperatures at normal excess air indicate

poor heat transfer performance This condition can result from a gradual build-up of

gas-side or waterside deposits Waterside deposits require a review of water treatment

procedures and tube cleaning to remove deposits An estimated 1 efficiency loss

occurs with every 22oC increase in stack temperature

Reduction of Boiler Steam Pressure

This is an effective means of reducing fuel consumption if permissible by as much as

1 to 2 Lower steam pressure gives a lower saturated steam temperature and without

stack heat recovery a similar reduction in the temperature of the flue gas temperature

results

Steam is generated at pressures normally dictated by the highest pressure

temperature requirements for a particular process In some cases the process does not

operate all the time and there are periods when the boiler pressure could be reduced

The energy manager should consider pressure reduction carefully before

recommending it Adverse effects such as an increase in water carryover from the

boiler owing to pressure reduction may negate any potential saving Pressure should

be reduced in stages and no more than a 20 percent reduction should be considered

Variable Speed Control for Fans Blowers and Pumps

Variable speed control is an important means of achieving energy savings Generally

combustion air control is effected by throttling dampers fitted at forced and induced

draft fans Though dampers are simple means of control they lack accuracy giving

poor control characteristics at the top and bottom of the operating range In general if

the load characteristic of the boiler is variable the possibility of replacing the dampers

by a VSD should be evaluated

Effect of Boiler Loading on Efficiency

The maximum efficiency of the boiler does not occur at full load but at about two-

thirds of the full load If the load on the boiler decreases further efficiency also tends

to decrease At zero output the efficiency of the boiler is zero and any fuel fired is

used only to supply the losses The factors affecting boiler efficiency are

As the load falls so does the value of the mass flow rate of the flue gases through the

tubes This reduction in flow rate for the same heat transfer area reduced the exit flue

gas temperatures by a small extent reducing the sensible heat lossBelow half load

most combustion appliances need more excess air to burn the fuel completely This

increases the sensible heat loss In general efficiency of the boiler reduces

significantly below 25 of the rated load and as far as possible operation of boilers

below this level should be avoided

Proper Boiler Scheduling

Since the optimum efficiency of boilers occurs at 65-85 of full load it is usually

more efficient on the whole to operate a fewer number of boilers at higher loads

than to operate a large number at low loads

Boiler Replacement

The potential savings from replacing a boiler depend on the anticipated change in

overall efficiency A change in a boiler can be financially attractive if the existing

boiler is

Old and inefficient

Not capable of firing cheaper substitution fuel

Over or under-sized for present requirements

Not designed for ideal loading conditions

The feasibility study should examine all implications of long-term fuel availability

and company growth plans All financial and engineering factors should be

considered Since boiler plants traditionally have a useful life of well over 25 years

replacement must be carefully studied

Lecture No 11-12 Pumps and Pumping System

Pump Types Centrifugal Pumps Pump Performance Curve Hydraulic power pump

shaft power and electrical input power

Pump Types

Pumps come in a variety of sizes for a wide range of applications They can be

classified according to their basic operating principle as dynamic or displacement

pumps Dynamic pumps can be sub-classified as centrifugal and special effect pumps

Displacement pumps can be sub-classified as rotary or reciprocating pumps

In principle any liquid can be handled by any of the pump designs Where different

pump designs could be used the centrifugal pump is generally the most economical

followed by rotary and reciprocating pumps Although positive displacement pumps

are generally more efficient than centrifugal pumps the benefit of higher efficiency

tends to be offset by increased maintenance costs

Since worldwide centrifugal pumps account for the majority of electricity used by

pumps the focus of this chapter is on centrifugal pump

Centrifugal Pumps

A centrifugal pump is of a very simple design The two main parts of the pump are the

impeller and the diffuser Impeller which is the only moving part is attached to a

shaft and driven by a motor Impellers are generally made of bronze polycarbonate

cast iron stainless steel as well as other materials The diffuser (also called as volute)

houses the impeller and captures and directs the water off the impeller

Pump Performance Curve

The pump is a dynamic device it is convenient to consider the pressure in terms of

head ie meters of liquid column The pump generates the same head of liquid

whatever the density of the liquid being pumped The actual contours of the hydraulic

passages of the impeller and the casing are extremely important in order to attain the

highest efficiency possible The standard convention for centrifugal pump is to draw

the pump performance curves showing Flow on the horizontal axis and Head

generated on the vertical axis Efficiency Power amp NPSH Required (described later)

are also all conventionally shown on the vertical axis plotted against Flow as

illustrated in Figure

Lecture No 13-14 System Characteristics

Static Head vs Flow Friction Head vs Flow System with High Static Head System

with Low Static Head Pump Curves Head- Flow Curve Pump operating point

In a pumping system the objective in most cases is either to transfer a liquid from a

source to a required destination eg filling a high level reservoir or to circulate liquid

around a system eg as a means of heat transfer in heat exchanger

A pressure is needed to make the liquid flow at the required rate and this must

overcome head lsquolossesrsquo in the system Losses are of two types static and friction

head

Static head is simply the difference in height of the supply and destination reservoirs

as in Figure In this illustration flow velocity in the pipe is assumed to be very small

Another example of a system with only static head is pumping into a pressurised

vessel with short pipe runs Static head is independent of flow and graphically would

be shown as in Figure

Figure Static Head Figure Static Head vs Flow

Pump Curves

The performance of a pump can be expressed graphically as head against flow rate

The centrifugal pump has a curve where the head falls gradually with increasing flow

This is called the pump characteristic curve

Pump operating point

When a pump is installed in a system the effect can be illustrated graphically by

superimposing pump and system curves The operating point will always be where the

two curves intersect Fig

Lecture No 15-16 Factors Affecting Pump Performance

Matching Pump and System Head-flow Characteristics Effect of over sizing the

pump Energy loss in throttling

Matching Pump and System Head-flow Characteristics

Centrifugal pumps are characterized by the relationship between the flow rate (Q) they

produce and the pressure (H) at which the flow is delivered Pump efficiency varies with

flow and pressure and it is highest at one particular flow rate

The Figure below shows a typical vendor-supplied head-flow curve for a centrifugal

pump Pump head-flow curves are typically given for clear water The choice of pump for

a given application depends largely on how the pump head-flow characteristics match the

requirement of the system downstream of the pump

Effect of over sizing the pump

As mentioned earlier pressure losses to be overcome by the pumps are a function of flow

ndash the system characteristics ndash are also quantified in the form of head-flow curves The

system curve is basically a plot of system resistance ie head to be overcome by the pump

versus various flow rates The system curves change with the physical configuration of

the system for example the system curves depends upon height or elevation diameter

and length of piping number and type of fittings and pressure drops across various

equipment - say a heat exchanger

A pump is selected based on how well the pump curve and system head-flow curves

match The pump operating point is identified as the point where the system curve

crosses the pump curve when they are superimposed on each other

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

to an economizer when either space or a high feed water return temperature make it

viable

Incomplete Combustion

Incomplete combustion can arise from a shortage of air or surplus of fuel or poor

distribution of fuel It is usually obvious from the colour or smoke and must be

corrected immediately

In the case of oil and gas fired systems CO or smoke (for oil fired systems only) with

normal or high excess air indicates burner system problems A more frequent cause of

incomplete combustion is the poor mixing of fuel and air at the burner Poor oil fires

can result from improper viscosity worn tips carbonization on tips and deterioration

of diffusers or spinner plates

With coal firing unburned carbon can comprise a big loss It occurs as grit carry-over

or carbon-in-ash and may amount to more than 2 of the heat supplied to the boiler

Non uniform fuel size could be one of the reasons for incomplete combustion In

chain grate stokers large lumps will not burn out completely while small pieces and

fines may block the air passage thus causing poor air distribution In sprinkler

stokers stoker grate condition fuel distributors wind box air regulation and over-fire

systems can affect carbon loss Increase in the fines in pulverized coal also increases

carbon loss

Excess Air Control

Excess air is required in all practical cases to ensure complete combustion to allow

for the normal variations in combustion and to ensure satisfactory stack conditions for

some fuels The optimum excess air level for maximum boiler efficiency occurs when

the sum of the losses due to incomplete combustion and loss due to heat in flue gases

is minimum This level varies with furnace design type of burner fuel and process

variables It can be determined by conducting tests with different air fuel ratios

Radiation and Convection Heat Loss

The external surfaces of a shell boiler are hotter than the surroundings The surfaces

thus lose heat to the surroundings depending on the surface area and the difference in

temperature between the surface and the surroundings The heat loss from the boiler

shell is normally a fixed energy loss irrespective of the boiler output With modern

boiler designs this may represent only 15 on the gross calorific value at full rating

but will increase to around 6 if the boiler operates at only 25 percent output

Repairing or augmenting insulation can reduce heat loss through boiler walls and

piping

Automatic Blowdown Control

Uncontrolled continuous blowdown is very wasteful Automatic blowdown controls

can be installed that sense and respond to boiler water conductivity and pH A 10

blow down in a 15 kgcm2 boiler results in 3 efficiency loss

Reduction of Scaling and Soot Losses

In oil and coal-fired boilers soot buildup on tubes acts as an insulator against heat

transfer Any such deposits should be removed on a regular basis Elevated stack

temperatures may indicate excessive soot buildup Also same result will occur due to

scaling on the water side High exit gas temperatures at normal excess air indicate

poor heat transfer performance This condition can result from a gradual build-up of

gas-side or waterside deposits Waterside deposits require a review of water treatment

procedures and tube cleaning to remove deposits An estimated 1 efficiency loss

occurs with every 22oC increase in stack temperature

Reduction of Boiler Steam Pressure

This is an effective means of reducing fuel consumption if permissible by as much as

1 to 2 Lower steam pressure gives a lower saturated steam temperature and without

stack heat recovery a similar reduction in the temperature of the flue gas temperature

results

Steam is generated at pressures normally dictated by the highest pressure

temperature requirements for a particular process In some cases the process does not

operate all the time and there are periods when the boiler pressure could be reduced

The energy manager should consider pressure reduction carefully before

recommending it Adverse effects such as an increase in water carryover from the

boiler owing to pressure reduction may negate any potential saving Pressure should

be reduced in stages and no more than a 20 percent reduction should be considered

Variable Speed Control for Fans Blowers and Pumps

Variable speed control is an important means of achieving energy savings Generally

combustion air control is effected by throttling dampers fitted at forced and induced

draft fans Though dampers are simple means of control they lack accuracy giving

poor control characteristics at the top and bottom of the operating range In general if

the load characteristic of the boiler is variable the possibility of replacing the dampers

by a VSD should be evaluated

Effect of Boiler Loading on Efficiency

The maximum efficiency of the boiler does not occur at full load but at about two-

thirds of the full load If the load on the boiler decreases further efficiency also tends

to decrease At zero output the efficiency of the boiler is zero and any fuel fired is

used only to supply the losses The factors affecting boiler efficiency are

As the load falls so does the value of the mass flow rate of the flue gases through the

tubes This reduction in flow rate for the same heat transfer area reduced the exit flue

gas temperatures by a small extent reducing the sensible heat lossBelow half load

most combustion appliances need more excess air to burn the fuel completely This

increases the sensible heat loss In general efficiency of the boiler reduces

significantly below 25 of the rated load and as far as possible operation of boilers

below this level should be avoided

Proper Boiler Scheduling

Since the optimum efficiency of boilers occurs at 65-85 of full load it is usually

more efficient on the whole to operate a fewer number of boilers at higher loads

than to operate a large number at low loads

Boiler Replacement

The potential savings from replacing a boiler depend on the anticipated change in

overall efficiency A change in a boiler can be financially attractive if the existing

boiler is

Old and inefficient

Not capable of firing cheaper substitution fuel

Over or under-sized for present requirements

Not designed for ideal loading conditions

The feasibility study should examine all implications of long-term fuel availability

and company growth plans All financial and engineering factors should be

considered Since boiler plants traditionally have a useful life of well over 25 years

replacement must be carefully studied

Lecture No 11-12 Pumps and Pumping System

Pump Types Centrifugal Pumps Pump Performance Curve Hydraulic power pump

shaft power and electrical input power

Pump Types

Pumps come in a variety of sizes for a wide range of applications They can be

classified according to their basic operating principle as dynamic or displacement

pumps Dynamic pumps can be sub-classified as centrifugal and special effect pumps

Displacement pumps can be sub-classified as rotary or reciprocating pumps

In principle any liquid can be handled by any of the pump designs Where different

pump designs could be used the centrifugal pump is generally the most economical

followed by rotary and reciprocating pumps Although positive displacement pumps

are generally more efficient than centrifugal pumps the benefit of higher efficiency

tends to be offset by increased maintenance costs

Since worldwide centrifugal pumps account for the majority of electricity used by

pumps the focus of this chapter is on centrifugal pump

Centrifugal Pumps

A centrifugal pump is of a very simple design The two main parts of the pump are the

impeller and the diffuser Impeller which is the only moving part is attached to a

shaft and driven by a motor Impellers are generally made of bronze polycarbonate

cast iron stainless steel as well as other materials The diffuser (also called as volute)

houses the impeller and captures and directs the water off the impeller

Pump Performance Curve

The pump is a dynamic device it is convenient to consider the pressure in terms of

head ie meters of liquid column The pump generates the same head of liquid

whatever the density of the liquid being pumped The actual contours of the hydraulic

passages of the impeller and the casing are extremely important in order to attain the

highest efficiency possible The standard convention for centrifugal pump is to draw

the pump performance curves showing Flow on the horizontal axis and Head

generated on the vertical axis Efficiency Power amp NPSH Required (described later)

are also all conventionally shown on the vertical axis plotted against Flow as

illustrated in Figure

Lecture No 13-14 System Characteristics

Static Head vs Flow Friction Head vs Flow System with High Static Head System

with Low Static Head Pump Curves Head- Flow Curve Pump operating point

In a pumping system the objective in most cases is either to transfer a liquid from a

source to a required destination eg filling a high level reservoir or to circulate liquid

around a system eg as a means of heat transfer in heat exchanger

A pressure is needed to make the liquid flow at the required rate and this must

overcome head lsquolossesrsquo in the system Losses are of two types static and friction

head

Static head is simply the difference in height of the supply and destination reservoirs

as in Figure In this illustration flow velocity in the pipe is assumed to be very small

Another example of a system with only static head is pumping into a pressurised

vessel with short pipe runs Static head is independent of flow and graphically would

be shown as in Figure

Figure Static Head Figure Static Head vs Flow

Pump Curves

The performance of a pump can be expressed graphically as head against flow rate

The centrifugal pump has a curve where the head falls gradually with increasing flow

This is called the pump characteristic curve

Pump operating point

When a pump is installed in a system the effect can be illustrated graphically by

superimposing pump and system curves The operating point will always be where the

two curves intersect Fig

Lecture No 15-16 Factors Affecting Pump Performance

Matching Pump and System Head-flow Characteristics Effect of over sizing the

pump Energy loss in throttling

Matching Pump and System Head-flow Characteristics

Centrifugal pumps are characterized by the relationship between the flow rate (Q) they

produce and the pressure (H) at which the flow is delivered Pump efficiency varies with

flow and pressure and it is highest at one particular flow rate

The Figure below shows a typical vendor-supplied head-flow curve for a centrifugal

pump Pump head-flow curves are typically given for clear water The choice of pump for

a given application depends largely on how the pump head-flow characteristics match the

requirement of the system downstream of the pump

Effect of over sizing the pump

As mentioned earlier pressure losses to be overcome by the pumps are a function of flow

ndash the system characteristics ndash are also quantified in the form of head-flow curves The

system curve is basically a plot of system resistance ie head to be overcome by the pump

versus various flow rates The system curves change with the physical configuration of

the system for example the system curves depends upon height or elevation diameter

and length of piping number and type of fittings and pressure drops across various

equipment - say a heat exchanger

A pump is selected based on how well the pump curve and system head-flow curves

match The pump operating point is identified as the point where the system curve

crosses the pump curve when they are superimposed on each other

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Repairing or augmenting insulation can reduce heat loss through boiler walls and

piping

Automatic Blowdown Control

Uncontrolled continuous blowdown is very wasteful Automatic blowdown controls

can be installed that sense and respond to boiler water conductivity and pH A 10

blow down in a 15 kgcm2 boiler results in 3 efficiency loss

Reduction of Scaling and Soot Losses

In oil and coal-fired boilers soot buildup on tubes acts as an insulator against heat

transfer Any such deposits should be removed on a regular basis Elevated stack

temperatures may indicate excessive soot buildup Also same result will occur due to

scaling on the water side High exit gas temperatures at normal excess air indicate

poor heat transfer performance This condition can result from a gradual build-up of

gas-side or waterside deposits Waterside deposits require a review of water treatment

procedures and tube cleaning to remove deposits An estimated 1 efficiency loss

occurs with every 22oC increase in stack temperature

Reduction of Boiler Steam Pressure

This is an effective means of reducing fuel consumption if permissible by as much as

1 to 2 Lower steam pressure gives a lower saturated steam temperature and without

stack heat recovery a similar reduction in the temperature of the flue gas temperature

results

Steam is generated at pressures normally dictated by the highest pressure

temperature requirements for a particular process In some cases the process does not

operate all the time and there are periods when the boiler pressure could be reduced

The energy manager should consider pressure reduction carefully before

recommending it Adverse effects such as an increase in water carryover from the

boiler owing to pressure reduction may negate any potential saving Pressure should

be reduced in stages and no more than a 20 percent reduction should be considered

Variable Speed Control for Fans Blowers and Pumps

Variable speed control is an important means of achieving energy savings Generally

combustion air control is effected by throttling dampers fitted at forced and induced

draft fans Though dampers are simple means of control they lack accuracy giving

poor control characteristics at the top and bottom of the operating range In general if

the load characteristic of the boiler is variable the possibility of replacing the dampers

by a VSD should be evaluated

Effect of Boiler Loading on Efficiency

The maximum efficiency of the boiler does not occur at full load but at about two-

thirds of the full load If the load on the boiler decreases further efficiency also tends

to decrease At zero output the efficiency of the boiler is zero and any fuel fired is

used only to supply the losses The factors affecting boiler efficiency are

As the load falls so does the value of the mass flow rate of the flue gases through the

tubes This reduction in flow rate for the same heat transfer area reduced the exit flue

gas temperatures by a small extent reducing the sensible heat lossBelow half load

most combustion appliances need more excess air to burn the fuel completely This

increases the sensible heat loss In general efficiency of the boiler reduces

significantly below 25 of the rated load and as far as possible operation of boilers

below this level should be avoided

Proper Boiler Scheduling

Since the optimum efficiency of boilers occurs at 65-85 of full load it is usually

more efficient on the whole to operate a fewer number of boilers at higher loads

than to operate a large number at low loads

Boiler Replacement

The potential savings from replacing a boiler depend on the anticipated change in

overall efficiency A change in a boiler can be financially attractive if the existing

boiler is

Old and inefficient

Not capable of firing cheaper substitution fuel

Over or under-sized for present requirements

Not designed for ideal loading conditions

The feasibility study should examine all implications of long-term fuel availability

and company growth plans All financial and engineering factors should be

considered Since boiler plants traditionally have a useful life of well over 25 years

replacement must be carefully studied

Lecture No 11-12 Pumps and Pumping System

Pump Types Centrifugal Pumps Pump Performance Curve Hydraulic power pump

shaft power and electrical input power

Pump Types

Pumps come in a variety of sizes for a wide range of applications They can be

classified according to their basic operating principle as dynamic or displacement

pumps Dynamic pumps can be sub-classified as centrifugal and special effect pumps

Displacement pumps can be sub-classified as rotary or reciprocating pumps

In principle any liquid can be handled by any of the pump designs Where different

pump designs could be used the centrifugal pump is generally the most economical

followed by rotary and reciprocating pumps Although positive displacement pumps

are generally more efficient than centrifugal pumps the benefit of higher efficiency

tends to be offset by increased maintenance costs

Since worldwide centrifugal pumps account for the majority of electricity used by

pumps the focus of this chapter is on centrifugal pump

Centrifugal Pumps

A centrifugal pump is of a very simple design The two main parts of the pump are the

impeller and the diffuser Impeller which is the only moving part is attached to a

shaft and driven by a motor Impellers are generally made of bronze polycarbonate

cast iron stainless steel as well as other materials The diffuser (also called as volute)

houses the impeller and captures and directs the water off the impeller

Pump Performance Curve

The pump is a dynamic device it is convenient to consider the pressure in terms of

head ie meters of liquid column The pump generates the same head of liquid

whatever the density of the liquid being pumped The actual contours of the hydraulic

passages of the impeller and the casing are extremely important in order to attain the

highest efficiency possible The standard convention for centrifugal pump is to draw

the pump performance curves showing Flow on the horizontal axis and Head

generated on the vertical axis Efficiency Power amp NPSH Required (described later)

are also all conventionally shown on the vertical axis plotted against Flow as

illustrated in Figure

Lecture No 13-14 System Characteristics

Static Head vs Flow Friction Head vs Flow System with High Static Head System

with Low Static Head Pump Curves Head- Flow Curve Pump operating point

In a pumping system the objective in most cases is either to transfer a liquid from a

source to a required destination eg filling a high level reservoir or to circulate liquid

around a system eg as a means of heat transfer in heat exchanger

A pressure is needed to make the liquid flow at the required rate and this must

overcome head lsquolossesrsquo in the system Losses are of two types static and friction

head

Static head is simply the difference in height of the supply and destination reservoirs

as in Figure In this illustration flow velocity in the pipe is assumed to be very small

Another example of a system with only static head is pumping into a pressurised

vessel with short pipe runs Static head is independent of flow and graphically would

be shown as in Figure

Figure Static Head Figure Static Head vs Flow

Pump Curves

The performance of a pump can be expressed graphically as head against flow rate

The centrifugal pump has a curve where the head falls gradually with increasing flow

This is called the pump characteristic curve

Pump operating point

When a pump is installed in a system the effect can be illustrated graphically by

superimposing pump and system curves The operating point will always be where the

two curves intersect Fig

Lecture No 15-16 Factors Affecting Pump Performance

Matching Pump and System Head-flow Characteristics Effect of over sizing the

pump Energy loss in throttling

Matching Pump and System Head-flow Characteristics

Centrifugal pumps are characterized by the relationship between the flow rate (Q) they

produce and the pressure (H) at which the flow is delivered Pump efficiency varies with

flow and pressure and it is highest at one particular flow rate

The Figure below shows a typical vendor-supplied head-flow curve for a centrifugal

pump Pump head-flow curves are typically given for clear water The choice of pump for

a given application depends largely on how the pump head-flow characteristics match the

requirement of the system downstream of the pump

Effect of over sizing the pump

As mentioned earlier pressure losses to be overcome by the pumps are a function of flow

ndash the system characteristics ndash are also quantified in the form of head-flow curves The

system curve is basically a plot of system resistance ie head to be overcome by the pump

versus various flow rates The system curves change with the physical configuration of

the system for example the system curves depends upon height or elevation diameter

and length of piping number and type of fittings and pressure drops across various

equipment - say a heat exchanger

A pump is selected based on how well the pump curve and system head-flow curves

match The pump operating point is identified as the point where the system curve

crosses the pump curve when they are superimposed on each other

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Effect of Boiler Loading on Efficiency

The maximum efficiency of the boiler does not occur at full load but at about two-

thirds of the full load If the load on the boiler decreases further efficiency also tends

to decrease At zero output the efficiency of the boiler is zero and any fuel fired is

used only to supply the losses The factors affecting boiler efficiency are

As the load falls so does the value of the mass flow rate of the flue gases through the

tubes This reduction in flow rate for the same heat transfer area reduced the exit flue

gas temperatures by a small extent reducing the sensible heat lossBelow half load

most combustion appliances need more excess air to burn the fuel completely This

increases the sensible heat loss In general efficiency of the boiler reduces

significantly below 25 of the rated load and as far as possible operation of boilers

below this level should be avoided

Proper Boiler Scheduling

Since the optimum efficiency of boilers occurs at 65-85 of full load it is usually

more efficient on the whole to operate a fewer number of boilers at higher loads

than to operate a large number at low loads

Boiler Replacement

The potential savings from replacing a boiler depend on the anticipated change in

overall efficiency A change in a boiler can be financially attractive if the existing

boiler is

Old and inefficient

Not capable of firing cheaper substitution fuel

Over or under-sized for present requirements

Not designed for ideal loading conditions

The feasibility study should examine all implications of long-term fuel availability

and company growth plans All financial and engineering factors should be

considered Since boiler plants traditionally have a useful life of well over 25 years

replacement must be carefully studied

Lecture No 11-12 Pumps and Pumping System

Pump Types Centrifugal Pumps Pump Performance Curve Hydraulic power pump

shaft power and electrical input power

Pump Types

Pumps come in a variety of sizes for a wide range of applications They can be

classified according to their basic operating principle as dynamic or displacement

pumps Dynamic pumps can be sub-classified as centrifugal and special effect pumps

Displacement pumps can be sub-classified as rotary or reciprocating pumps

In principle any liquid can be handled by any of the pump designs Where different

pump designs could be used the centrifugal pump is generally the most economical

followed by rotary and reciprocating pumps Although positive displacement pumps

are generally more efficient than centrifugal pumps the benefit of higher efficiency

tends to be offset by increased maintenance costs

Since worldwide centrifugal pumps account for the majority of electricity used by

pumps the focus of this chapter is on centrifugal pump

Centrifugal Pumps

A centrifugal pump is of a very simple design The two main parts of the pump are the

impeller and the diffuser Impeller which is the only moving part is attached to a

shaft and driven by a motor Impellers are generally made of bronze polycarbonate

cast iron stainless steel as well as other materials The diffuser (also called as volute)

houses the impeller and captures and directs the water off the impeller

Pump Performance Curve

The pump is a dynamic device it is convenient to consider the pressure in terms of

head ie meters of liquid column The pump generates the same head of liquid

whatever the density of the liquid being pumped The actual contours of the hydraulic

passages of the impeller and the casing are extremely important in order to attain the

highest efficiency possible The standard convention for centrifugal pump is to draw

the pump performance curves showing Flow on the horizontal axis and Head

generated on the vertical axis Efficiency Power amp NPSH Required (described later)

are also all conventionally shown on the vertical axis plotted against Flow as

illustrated in Figure

Lecture No 13-14 System Characteristics

Static Head vs Flow Friction Head vs Flow System with High Static Head System

with Low Static Head Pump Curves Head- Flow Curve Pump operating point

In a pumping system the objective in most cases is either to transfer a liquid from a

source to a required destination eg filling a high level reservoir or to circulate liquid

around a system eg as a means of heat transfer in heat exchanger

A pressure is needed to make the liquid flow at the required rate and this must

overcome head lsquolossesrsquo in the system Losses are of two types static and friction

head

Static head is simply the difference in height of the supply and destination reservoirs

as in Figure In this illustration flow velocity in the pipe is assumed to be very small

Another example of a system with only static head is pumping into a pressurised

vessel with short pipe runs Static head is independent of flow and graphically would

be shown as in Figure

Figure Static Head Figure Static Head vs Flow

Pump Curves

The performance of a pump can be expressed graphically as head against flow rate

The centrifugal pump has a curve where the head falls gradually with increasing flow

This is called the pump characteristic curve

Pump operating point

When a pump is installed in a system the effect can be illustrated graphically by

superimposing pump and system curves The operating point will always be where the

two curves intersect Fig

Lecture No 15-16 Factors Affecting Pump Performance

Matching Pump and System Head-flow Characteristics Effect of over sizing the

pump Energy loss in throttling

Matching Pump and System Head-flow Characteristics

Centrifugal pumps are characterized by the relationship between the flow rate (Q) they

produce and the pressure (H) at which the flow is delivered Pump efficiency varies with

flow and pressure and it is highest at one particular flow rate

The Figure below shows a typical vendor-supplied head-flow curve for a centrifugal

pump Pump head-flow curves are typically given for clear water The choice of pump for

a given application depends largely on how the pump head-flow characteristics match the

requirement of the system downstream of the pump

Effect of over sizing the pump

As mentioned earlier pressure losses to be overcome by the pumps are a function of flow

ndash the system characteristics ndash are also quantified in the form of head-flow curves The

system curve is basically a plot of system resistance ie head to be overcome by the pump

versus various flow rates The system curves change with the physical configuration of

the system for example the system curves depends upon height or elevation diameter

and length of piping number and type of fittings and pressure drops across various

equipment - say a heat exchanger

A pump is selected based on how well the pump curve and system head-flow curves

match The pump operating point is identified as the point where the system curve

crosses the pump curve when they are superimposed on each other

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 11-12 Pumps and Pumping System

Pump Types Centrifugal Pumps Pump Performance Curve Hydraulic power pump

shaft power and electrical input power

Pump Types

Pumps come in a variety of sizes for a wide range of applications They can be

classified according to their basic operating principle as dynamic or displacement

pumps Dynamic pumps can be sub-classified as centrifugal and special effect pumps

Displacement pumps can be sub-classified as rotary or reciprocating pumps

In principle any liquid can be handled by any of the pump designs Where different

pump designs could be used the centrifugal pump is generally the most economical

followed by rotary and reciprocating pumps Although positive displacement pumps

are generally more efficient than centrifugal pumps the benefit of higher efficiency

tends to be offset by increased maintenance costs

Since worldwide centrifugal pumps account for the majority of electricity used by

pumps the focus of this chapter is on centrifugal pump

Centrifugal Pumps

A centrifugal pump is of a very simple design The two main parts of the pump are the

impeller and the diffuser Impeller which is the only moving part is attached to a

shaft and driven by a motor Impellers are generally made of bronze polycarbonate

cast iron stainless steel as well as other materials The diffuser (also called as volute)

houses the impeller and captures and directs the water off the impeller

Pump Performance Curve

The pump is a dynamic device it is convenient to consider the pressure in terms of

head ie meters of liquid column The pump generates the same head of liquid

whatever the density of the liquid being pumped The actual contours of the hydraulic

passages of the impeller and the casing are extremely important in order to attain the

highest efficiency possible The standard convention for centrifugal pump is to draw

the pump performance curves showing Flow on the horizontal axis and Head

generated on the vertical axis Efficiency Power amp NPSH Required (described later)

are also all conventionally shown on the vertical axis plotted against Flow as

illustrated in Figure

Lecture No 13-14 System Characteristics

Static Head vs Flow Friction Head vs Flow System with High Static Head System

with Low Static Head Pump Curves Head- Flow Curve Pump operating point

In a pumping system the objective in most cases is either to transfer a liquid from a

source to a required destination eg filling a high level reservoir or to circulate liquid

around a system eg as a means of heat transfer in heat exchanger

A pressure is needed to make the liquid flow at the required rate and this must

overcome head lsquolossesrsquo in the system Losses are of two types static and friction

head

Static head is simply the difference in height of the supply and destination reservoirs

as in Figure In this illustration flow velocity in the pipe is assumed to be very small

Another example of a system with only static head is pumping into a pressurised

vessel with short pipe runs Static head is independent of flow and graphically would

be shown as in Figure

Figure Static Head Figure Static Head vs Flow

Pump Curves

The performance of a pump can be expressed graphically as head against flow rate

The centrifugal pump has a curve where the head falls gradually with increasing flow

This is called the pump characteristic curve

Pump operating point

When a pump is installed in a system the effect can be illustrated graphically by

superimposing pump and system curves The operating point will always be where the

two curves intersect Fig

Lecture No 15-16 Factors Affecting Pump Performance

Matching Pump and System Head-flow Characteristics Effect of over sizing the

pump Energy loss in throttling

Matching Pump and System Head-flow Characteristics

Centrifugal pumps are characterized by the relationship between the flow rate (Q) they

produce and the pressure (H) at which the flow is delivered Pump efficiency varies with

flow and pressure and it is highest at one particular flow rate

The Figure below shows a typical vendor-supplied head-flow curve for a centrifugal

pump Pump head-flow curves are typically given for clear water The choice of pump for

a given application depends largely on how the pump head-flow characteristics match the

requirement of the system downstream of the pump

Effect of over sizing the pump

As mentioned earlier pressure losses to be overcome by the pumps are a function of flow

ndash the system characteristics ndash are also quantified in the form of head-flow curves The

system curve is basically a plot of system resistance ie head to be overcome by the pump

versus various flow rates The system curves change with the physical configuration of

the system for example the system curves depends upon height or elevation diameter

and length of piping number and type of fittings and pressure drops across various

equipment - say a heat exchanger

A pump is selected based on how well the pump curve and system head-flow curves

match The pump operating point is identified as the point where the system curve

crosses the pump curve when they are superimposed on each other

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 13-14 System Characteristics

Static Head vs Flow Friction Head vs Flow System with High Static Head System

with Low Static Head Pump Curves Head- Flow Curve Pump operating point

In a pumping system the objective in most cases is either to transfer a liquid from a

source to a required destination eg filling a high level reservoir or to circulate liquid

around a system eg as a means of heat transfer in heat exchanger

A pressure is needed to make the liquid flow at the required rate and this must

overcome head lsquolossesrsquo in the system Losses are of two types static and friction

head

Static head is simply the difference in height of the supply and destination reservoirs

as in Figure In this illustration flow velocity in the pipe is assumed to be very small

Another example of a system with only static head is pumping into a pressurised

vessel with short pipe runs Static head is independent of flow and graphically would

be shown as in Figure

Figure Static Head Figure Static Head vs Flow

Pump Curves

The performance of a pump can be expressed graphically as head against flow rate

The centrifugal pump has a curve where the head falls gradually with increasing flow

This is called the pump characteristic curve

Pump operating point

When a pump is installed in a system the effect can be illustrated graphically by

superimposing pump and system curves The operating point will always be where the

two curves intersect Fig

Lecture No 15-16 Factors Affecting Pump Performance

Matching Pump and System Head-flow Characteristics Effect of over sizing the

pump Energy loss in throttling

Matching Pump and System Head-flow Characteristics

Centrifugal pumps are characterized by the relationship between the flow rate (Q) they

produce and the pressure (H) at which the flow is delivered Pump efficiency varies with

flow and pressure and it is highest at one particular flow rate

The Figure below shows a typical vendor-supplied head-flow curve for a centrifugal

pump Pump head-flow curves are typically given for clear water The choice of pump for

a given application depends largely on how the pump head-flow characteristics match the

requirement of the system downstream of the pump

Effect of over sizing the pump

As mentioned earlier pressure losses to be overcome by the pumps are a function of flow

ndash the system characteristics ndash are also quantified in the form of head-flow curves The

system curve is basically a plot of system resistance ie head to be overcome by the pump

versus various flow rates The system curves change with the physical configuration of

the system for example the system curves depends upon height or elevation diameter

and length of piping number and type of fittings and pressure drops across various

equipment - say a heat exchanger

A pump is selected based on how well the pump curve and system head-flow curves

match The pump operating point is identified as the point where the system curve

crosses the pump curve when they are superimposed on each other

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Pump operating point

When a pump is installed in a system the effect can be illustrated graphically by

superimposing pump and system curves The operating point will always be where the

two curves intersect Fig

Lecture No 15-16 Factors Affecting Pump Performance

Matching Pump and System Head-flow Characteristics Effect of over sizing the

pump Energy loss in throttling

Matching Pump and System Head-flow Characteristics

Centrifugal pumps are characterized by the relationship between the flow rate (Q) they

produce and the pressure (H) at which the flow is delivered Pump efficiency varies with

flow and pressure and it is highest at one particular flow rate

The Figure below shows a typical vendor-supplied head-flow curve for a centrifugal

pump Pump head-flow curves are typically given for clear water The choice of pump for

a given application depends largely on how the pump head-flow characteristics match the

requirement of the system downstream of the pump

Effect of over sizing the pump

As mentioned earlier pressure losses to be overcome by the pumps are a function of flow

ndash the system characteristics ndash are also quantified in the form of head-flow curves The

system curve is basically a plot of system resistance ie head to be overcome by the pump

versus various flow rates The system curves change with the physical configuration of

the system for example the system curves depends upon height or elevation diameter

and length of piping number and type of fittings and pressure drops across various

equipment - say a heat exchanger

A pump is selected based on how well the pump curve and system head-flow curves

match The pump operating point is identified as the point where the system curve

crosses the pump curve when they are superimposed on each other

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 15-16 Factors Affecting Pump Performance

Matching Pump and System Head-flow Characteristics Effect of over sizing the

pump Energy loss in throttling

Matching Pump and System Head-flow Characteristics

Centrifugal pumps are characterized by the relationship between the flow rate (Q) they

produce and the pressure (H) at which the flow is delivered Pump efficiency varies with

flow and pressure and it is highest at one particular flow rate

The Figure below shows a typical vendor-supplied head-flow curve for a centrifugal

pump Pump head-flow curves are typically given for clear water The choice of pump for

a given application depends largely on how the pump head-flow characteristics match the

requirement of the system downstream of the pump

Effect of over sizing the pump

As mentioned earlier pressure losses to be overcome by the pumps are a function of flow

ndash the system characteristics ndash are also quantified in the form of head-flow curves The

system curve is basically a plot of system resistance ie head to be overcome by the pump

versus various flow rates The system curves change with the physical configuration of

the system for example the system curves depends upon height or elevation diameter

and length of piping number and type of fittings and pressure drops across various

equipment - say a heat exchanger

A pump is selected based on how well the pump curve and system head-flow curves

match The pump operating point is identified as the point where the system curve

crosses the pump curve when they are superimposed on each other

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

A pump is selected based on how well the pump curve and system head-flow curves

match The pump operating point is identified as the point where the system curve

crosses the pump curve when they are superimposed on each other

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 17-18 Efficient Pumping System Operation

Effect of speed variation Effects of impeller diameter change Pump suction

performance (NPSH)

Effect of speed variation

As stated above a centrifugal pump is a dynamic device with the head generated from a

rotating impeller There is therefore a relationship between impeller peripheral velocity

and generated head Peripheral velocity is directly related to shaft rotational speed for a

fixed impeller diameter and so varying the rotational speed has a direct effect on the

performance of the pump All the parameters shown in fig 62 will change if the speed is

varied and it is important to have an appreciation of how these parameters vary in order to

safely control a pump at different speeds The equations relating rotodynamic pump

performance parameters of flow head and power absorbed to speed are known as the

Affinity Laws

Pump suction performance (NPSH)

Liquid entering the impeller eye turns and is split into separate streams by the leading

edges of the impeller vanes an action which locally drops the pressure below that in

the inlet pipe to the pump

If the incoming liquid is at a pressure with insufficient margin above its vapour

pressure then vapour cavities or bubbles appear along the impeller vanes just behind

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

the inlet edges This phenomenon is known as cavitation and has three undesirable

effects

1) The collapsing cavitation bubbles can erode the vane surface especially when

pumping water-based liquids

2) Noise and vibration are increased with possible shortened seal and bearing life

3) The cavity areas will initially partially choke the impeller passages and reduce the

pump performance In extreme cases total loss of pump developed head occurs

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 19-20 Flow Control Strategies

Pump control by varying speed Pumps in parallel Stopstart control Flow control

valve By-pass control Fixed Flow reduction Meeting variable flow reduction

Energy Conservation Opportunities in Pumping Systems

Pump control by varying speed

To understand how speed variation changes the duty point the pump and system curves

are over-laid Two systems are considered one with only friction loss and another where

static head is high in relation to friction head It will be seen that the benefits are different

Example for the Effect of Pump Speed Change with a System with High Static

Head

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Energy Conservation Opportunities in Pumping Systems

Ensure adequate NPSH at site of installation

Ensure availability of basic instruments at pumps like pressure gauges flow

meters

Operate pumps near best efficiency point

Modify pumping system and pumps losses to minimize throttling

Adapt to wide load variation with variable speed drives or sequenced control

of multiple units

Stop running multiple pumps - add an auto-start for an on-line spare or add a

booster pump in the problem area

Use booster pumps for small loads requiring higher pressures

Increase fluid temperature differentials to reduce pumping rates in case of heat

exchangers

Repair seals and packing to minimize water loss by dripping

Balance the system to minimize flows and reduce pump power requirements

Avoid pumping head with a free-fall return (gravity) Use siphon effect to

advantage

Conduct water balance to minimise water consumption

Avoid cooling water re-circulation in DG sets air compressors refrigeration

systems cooling towers feed water pumps condenser pumps and process

pumps

In multiple pump operations carefully combine the operation of pumps to

avoid throttling

Provide booster pump for few areas of higher head

Replace old pumps by energy efficient pumps

In the case of over designed pump provide variable speed drive or downsize

replace impeller or replace with correct sized pump for efficient operation

Optimise number of stages in multi-stage pump in case of head margins

Reduce system resistance by pressure drop assessment and pipe size

optimisation

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 21-22 Fans and Blowers

Difference between Fans Blowers and Compressors Types of Fans Characteristics

and Typical Applications

Fans and blowers provide air for ventilation and industrial process requirements Fans

generate a pressure to move air (or gases) against a resistance caused by ducts

dampers or other components in a fan system The fan rotor receives energy from a

rotating shaft and transmits it to the air

Difference between Fans Blowers and Compressors

Types of Fans Characteristics and Typical Applications

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 23-24 Fan Performance Evaluation and Efficient System Operation

System Characteristics Fan Characteristics System Characteristics and Fan Curves

Fan Laws

System Characteristics and Fan Curves

Fan Laws

The fans operate under a predictable set of laws concerning speed power and

pressure A change in speed (RPM) of any fan will predictably change the pressure

rise and power necessary to operate it at the new RPM

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 25 Fan Design and Selection Criteria

Fan Performance and Efficiency Safety margin Installation of Fan System

Resistance Change

Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size The air-flow required depends on the process

requirements normally determined from heat transfer rates or combustion air or flue

gas quantity to be handled System pressure requirement is usually more difficult to

compute or predict Detailed analysis should be carried out to determine pressure drop

across the length bends contractions and expansions in the ducting system pressure

drop across filters drop in branch lines etc These pressure drops should be added to

any fixed pressure required by the process (in the case of ventilation fans there is no

fixed pressure requirement) Frequently a very conservative approach is adopted

allocating large safety margins resulting in over-sized fans which operate at flow

rates much below their design values and consequently at very poor efficiency

Once the system flow and pressure requirements are determined the fan and impeller

type are then selected For best results values should be obtained from the

manufacturer for specific fans and impellers

The choice of fan type for a given application depends on the magnitudes of required

flow and static pressure For a given fan type the selection of the appropriate impeller

depends additionally on rotational speed Speed of operation varies with the

application High speed small units are generally more economical because of their

higher hydraulic efficiency and relatively low cost However at low pressure ratios

large low-speed units are preferable

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 26-27 Flow Control Strategies

Pulley change damper control inlet guide vane control variable speed drive and

series and parallel operation of fans

Flow Control Strategies

Typically once a fan system is designed and installed the fan operates at a constant speed

There may be occasions when a speed change is desirable ie when adding a new run of duct

that requires an increase in air flow (volume) through the fan There are also instances when

the fan is oversized and flow reductions are required

Pulley Change

When a fan volume change is required on a permanent basis and the existing fan can handle

the change in capacity the volume change can be achieved with a speed change The simplest

way to change the speed is with a pulley change For this the fan must be driven by a motor

through a v-belt system The fan speed can be increased or decreased with a change in the

drive pulley or the driven pulley or in some cases both pulleys As shown in the Figure a

higher sized fan operating with damper control was downsized by reducing the motor (drive)

Damper Controls

Some fans are designed with damper controls Dampers can be located at inlet or outlet

Dampers provide a means of changing air volume by adding or removing system

resistance This resistance forces the fan to move up or down along its characteristic

curve generating more or less air without changing fan speed However dampers provide

a limited amount of adjustment and they are not particularly energy efficient

Variable Speed Drives

Although variable speed drives are expensive they provide almost infinite variability in

speed control Variable speed operation involves reducing the speed of the fan to meet

reduced flow requirements Fan performance can be predicted at different speeds using

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

the fan laws Since power input to the fan changes as the cube of the flow this will

usually be the most efficient form of capacity control However variable speed control

may not be economical for systems which have infrequent flow variations When

considering variable speed drive the efficiency of the control system (fluid coupling

eddy-current VFD etc) should be accounted for in the analysis of power consumption

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 28-29 Fan Performance AssessmentStatic Total and Velocity Pressure Measurements and Calculations

The fans are tested for field performance by measurement of flow head temperature on the fan side and electrical motor kW input on the motor side

Air flow measurement

Static pressure

Static pressure is the potential energy put into the system by the fan It is given up to

friction in the ducts and at the duct inlet as it is converted to velocity pressure At the

inlet to the duct the static pressure produces an area of low pressure

Velocity pressure

Velocity pressure is the pressure along the line of the flow that results from the air

flowing through the duct The velocity pressure is used to calculate air velocity

Total pressure

Total pressure is the sum of the static and velocity pressure Velocity pressure and

static pressure can change as the air flows though different size ducts accelerating and

de-accelerating the velocity The total pressure stays constant changing only with friction

losses The illustration that follows shows how the total pressure changes in a system

The fan flow is measured using pitot tube manometer combination or a flow sensor

(differential pressure instrument) or an accurate anemometer Care needs to be taken

regarding number of traverse points straight length section (to avoid turbulent flow

regimes of measurement) up stream and downstream of measurement location The

measurements can be on the suction or discharge side of the fan and preferably both

where feasible

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Measurement by Pitot tube

The Figure shows how velocity pressure is measured using a pitot tube and a

manometer Total pressure is measured using the inner tube of pitot tube and static

pressure is measured using the outer tube of pitot tube When the inner and outer tube

ends are connected to a manometer we get the velocity pressure For measuring low

velocities it is preferable to use an inclined tube manometer instead of U tube

manometer

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 30 Energy Savings Opportunities in fan operation

Energy Savings Opportunities

Minimizing demand on the fan

1 Minimising excess air level in combustion systems to reduce FD fan and ID fan

load

2 Minimising air in-leaks in hot flue gas path to reduce ID fan load especially in

case of kilns boiler plants furnaces etc Cold air in-leaks increase ID fan load

tremendously due to density increase of flue gases and in-fact choke up the

capacity of fan resulting as a bottleneck for boiler furnace itself

3 In-leaks out-leaks in air conditioning systems also have a major impact on

energy efficiency and fan power consumption and need to be minimized

The findings of performance assessment trials will automatically indicate potential areas

for improvement which could be one or a more of the following

1 Change of impeller by a high efficiency impeller along with cone

2 Change of fan assembly as a whole by a higher efficiency fan

3 Impeller derating (by a smaller dia impeller)

4 Change of metallic Glass reinforced Plastic (GRP) impeller by the more energy

efficient hollow FRP impeller with aerofoil design in case of axial flow fans

where significant savings have been reported

5 Fan speed reduction by pulley dia modifications for derating

6 Option of two speed motors or variable speed drives for variable duty conditions

7 Option of energy efficient flat belts or cogged raw edged V belts in place of

conventional V belt systems for reducing transmission losses

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 31 HVAC and Refrigeration system

Introduction to Refrigeration System Types of Refrigeration System

The Heating Ventilation and Air Conditioning (HVAC) and refrigeration system

transfers the heat energy from or to the products or building environment Energy in

form of electricity or heat is used to power mechanical equipment designed to transfer

heat from a colder low-energy level to a warmer high-energy level

Refrigeration deals with the transfer of heat from a low temperature level at the heat

source to a high temperature level at the heat sink by using a low boiling refrigerant

There are several heat transfer loops in refrigeration system as described below

Thermal energy moves from left to right as it is extracted from the space and expelled

into the outdoors through five loops of heat transfer

Indoor air loop In the leftmost loop indoor air is driven by the supply air fan

through a cooling coil where it transfers its heat to chilled water The cool air

then cools the building space

Chilled water loop Driven by the chilled water pump water returns from the

cooling coil to the chillerrsquos evaporator to be re-cooled

Refrigerant loop Using a phase-change refrigerant the chillerrsquos compressor

pumps heat from the chilled water to the condenser water

Condenser water loop Water absorbs heat from the chillerrsquos condenser and the

condenser water pump sends it to the cooling tower

Cooling tower loop The cooling towerrsquos fan drives air across an open flow of the

hot condenser water transferring the heat to the outdoors

Figure Heat Transfer Loops In Refrigeration System

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 32-33 Vapour Compression Refrigeration Alternative Refrigerants for

Vapour Compression Systems

Types of Refrigeration System

Vapour Compression Refrigeration

Heat flows naturally from a hot to a colder body In refrigeration system the opposite

must occur ie heat flows from a cold to a hotter body This is achieved by using a

substance called a refrigerant which absorbs heat and hence boils or evaporates at a

low pressure to form a gas This gas is then compressed to a higher pressure such that

it transfers the heat it has gained to ambient air or water and turns back (condenses)

into a liquid In this way heat is absorbed or removed from a low temperature source

and transferred to a higher temperature source

The refrigeration cycle can be broken down into the following stages

1 - 2 Low pressure liquid refrigerant in the evaporator absorbs heat from its

surroundings usually air water or some other process liquid During this process it

changes its state from a liquid to a gas and at the evaporator exit is slightly

superheated

2 - 3 The superheated vapour enters the compressor where its pressure is raised There

will also be a big increase in temperature because a proportion of the energy input

into the compression process is transferred to the refrigerant

3 - 4 The high pressure superheated gas passes from the compressor into the

condenser The initial part of the cooling process (3 - 3a) desuperheats the gas before

it is then turned back into liquid (3a - 3b) The cooling for this process is usually

achieved by using air or water A further reduction in temperature happens in the pipe

work and liquid receiver (3b - 4) so that the refrigerant liquid is sub-cooled as it

enters the expansion device

4 - 1 The high-pressure sub-cooled liquid passes through the expansion device which

both reduces its pressure and controls the flow into the evaporator

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Figure Schematic of a Basic Vapor Compression Refrigeration System

It can be seen that the condenser has to be capable of rejecting the combined heat

inputs of the evaporator and the compressor ie (1 - 2) + (2 - 3) has to be the same as

(3 - 4) There is no heat loss or gain through the expansion device

Alternative Refrigerants for Vapour Compression Systems

The use of CFCs is now beginning to be phased out due to their damaging impact on

the protective tropospheric ozone layer around the earth The Montreal Protocol of

1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the

production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a

phased manner with an eventual stop to all production by the year 1996 In response

the refrigeration industry has developed two alternative refrigerants one based on

Hydrochloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon

(HFC) The HCFCs have a 2 to 10 ozone depleting potential as compared to CFCs

and also they have an atmospheric lifetime between 2 to 25 years as compared to 100

or more years for CFCs (Brandt 1992) However even HCFCs are mandated to be

phased out by 2005 and only the chlorine free (zero ozone depletion) HFCs would be

acceptable

Until now only one HFC based refrigerant HFC 134a has been developed HCFCs are

comparatively simpler to produce and the three refrigerants 22 123 and 124 have been

developed The use of HFCs and HCFCs results in slightly lower efficiencies as compared to

CFCs but this may change with increasing efforts being made to replace CFCs

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 34-35 Absorption Refrigeration Common Refrigerants and Properties

Selection of a Suitable Refrigeration System

Absorption Refrigeration

The absorption chiller is a machine which produces chilled water by using heat such as

steam hot water gas oil etc Chilled water is produced by the principle that liquid

(refrigerant) which evaporates at low temperature absorbs heat from surrounding when it

evaporates Pure water is used as refrigerant and lithium bromide solution is used as absorbent

Heat for the vapour absorption refrigeration system can be provided by waste heat extracted

from process diesel generator sets etc Absorption systems require electricity to run pumps

only Depending on the temperature required and the power cost it may even be economical

to generate heat steam to operate the absorption system

Common Refrigerants and Properties

A variety of refrigerants are used in vapor compression systems The choice of fluid

is determined largely by the cooling temperature required Commonly used

refrigerants are in the family of chlorinated fluorocarbons (CFCs also called Freons)

R-11 R-12 R-21 R-22 and R-502

Table Properties of Commonly used Refrigerants

RefrigerantBoiling Point

(oC)

Freezing Point (oC)

Vapor Pressure

(kPa)

Vapor Volume (m3 kg)

Enthalpy Liquid (kJ

kg)Vapor

(kJ kg)

R - 11 -2382 -1110 2573 061170 19140 38543

R - 12 -2979 -1580 21928 007702 19072 34796

R - 22 -4076 -1600 35474 006513 18855 40083

R - 502 -4540 --- 41430 004234 18887 34231

R - 7 (Ammonia)

-3330 -777 28993 041949 80871 48776

Table Performance of Commonly used Refrigerants

Refrigerant Evaporating Press (kPa)

Condensing Press (kPa)

Pressure Ratio

Vapor Enthalpy (kJ

kg)COP

carnot

R - 11 204 1255 615 1554 503

R - 12 1827 7446 408 1163 470

R - 22 2958 11921 403 1628 466

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

R - 502 3496 13086 374 1062 437

R - 717 2365 11665 493 1034 478

Selection of a Suitable Refrigeration System

A clear understanding of the cooling load to be met is the first and most important part of

designing selecting the components of a refrigeration system Important factors to be

considered in quantifying the load are the actual cooling need heat (cool) leaks and internal

heat sources (from all heat generating equipment) Consideration should also be given to

process changes and or changes in ambient conditions that might affect the load in the

future Reducing the load eg through better insulation maintaining as high a cooling

temperature as practical etc is the first step toward minimizing electrical power required to

meet refrigeration needs With a quantitative understanding of the required temperatures and

the maximum minimum and average expected cooling demands selection of appropriate

refrigeration system (single-stage multi-stage economized compression compound

cascade operation direct cooling secondary coolants) and equipment (type of refrigerant

compressor evaporator condenser etc) can be undertaken

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 36 Performance Assessment of Refrigeration Plants

The cooling effect produced is quantified as tons of refrigeration(TR)

1 TR of refrigeration = 3024 kCalhr heat rejected

The refrigeration TR is assessed as TR = Q xCp x (Ti ndash To) 3024

Where Q is mass flow rate of coolant in kghr

Cp is coolant specific heat in kCal kg deg C

Ti is inlet temperature of coolant to evaporator (chiller) in 0C

To is outlet temperature of coolant from evaporator (chiller) in 0C

The above TR is also called as chiller tonnage

The specific power consumption kWTR is a useful indicator of the performance

of refrigeration system By measuring refrigeration duty performed in TR and the

kiloWatt inputs kWTR is used as a reference energy performance indicator

In a centralized chilled water system apart from the compressor unit power is

also consumed by the chilled water (secondary) coolant pump as well condenser

water (for heat rejection to cooling tower) pump and cooling tower fan in the

cooling tower Effectively the overall energy consumption would be towards

Compressor kW

Chilled water pump kW

Condenser water pump kW

Cooling tower fan kW for induced forced draft towers

The specific power consumption for certain TR output would therefore have to

include

Compressor kWTR

Chilled water pump kWTR

Condenser water pump kWTR

Cooling tower fan kWTR

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 37 Factors Affecting Performance amp Energy Efficiency of Refrigeration

Plants Energy Saving Opportunities

a) Cold Insulation

Insulate all cold lines vessels using economic insulation thickness to minimize

heat gains and choose appropriate (correct) insulation

b) Building Envelope

Optimise air conditioning volumes by measures such as use of false ceiling and

segregation of critical areas for air conditioning by air curtains

c) Building Heat Loads Minimisation

Minimise the air conditioning loads by measures such as roof cooling roof

painting efficient lighting pre-cooling of fresh air by air- to-air heat exchangers

variable volume air system otpimal thermo-static setting of temperature of air

conditioned spaces sun film applications etc

e) Process Heat Loads Minimisation

Minimize process heat loads in terms of TR capacity as well as refrigeration level

ie temperature required by way of

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains loss of chilled water idle flows

iv) Frequent cleaning de-scaling of all heat exchangers

f) At the Refrigeration AC Plant Area

i) Ensure regular maintenance of all AC plant components as per

manufacturer guidelines

ii) Ensure adequate quantity of chilled water and cooling water

flows avoid bypass flows by closing valves of idle equipment

iii) Minimize part load operations by matching loads and plant

capacity on line adopt variable speed drives for varying process load

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

iv) Make efforts to continuously optimize condenser and

evaporator parameters for minimizing specific energy consumption and

maximizing capacity

v) Adopt VAR system where economics permit as a non-CFC

solution

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 38-39 Introduction to Cooling Water System Cooling Tower Types-

Natural draft and Mechanical draft Cooling Tower Performance

Cooling towers are a very important part of many chemical plants The primary task of a

cooling tower is to reject heat into the atmosphere They represent a relatively

inexpensive and dependable means of removing low-grade heat from cooling water The

make-up water source is used to replenish water lost to evaporation Hot water from heat

exchangers is sent to the cooling tower The water exits the cooling tower and is sent back

to the exchangers or to other units for further cooling Typical closed loop cooling tower

system is shown in Figure

Cooling Tower Types

Cooling towers fall into two main categories Natural draft and Mechanical draft

Natural draft towers use very large concrete chimneys to introduce air through the media

Due to the large size of these towers they are generally used for water flow rates above

45000 m3hr These types of towers are used only by utility power stations

Mechanical draft towers utilize large fans to force or suck air through circulated water

The water falls downward over fill surfaces which help increase the contact time between

the water and the air - this helps maximise heat transfer between the two Cooling rates of

Mechanical draft towers depend upon their fan diameter and speed of operation

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Cooling Tower Performance

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 40-41 Factors Affecting Cooling Tower Performance Efficient System

Operation Performance Assessment of Cooling Towers Energy Saving Opportunities

in Cooling Towers

Factors Affecting Cooling Tower Performance

Capacity

Heat dissipation (in kCalhour) and circulated flow rate (m3hr) are not sufficient to

understand cooling tower performance Other factors which we will see must be

stated along with flow rate m3hr For example a cooling tower sized to cool 4540

m3hr through a 139oC range might be larger than a cooling tower to cool 4540 m3hr

through 195oC range

Range

Range is determined not by the cooling tower but by the process it is serving The

range at the exchanger is determined entirely by the heat load and the water

circulation rate through the exchanger and on to the cooling water

Range oC = Heat Load in kcalshour Water Circulation Rate in LPH

Thus Range is a function of the heat load and the flow circulated through the system

Wet Bulb Temperature

Wet bulb temperature is an important factor in performance of evaporative water

cooling equipment It is a controlling factor from the aspect of minimum cold water

temperature to which water can be cooled by the evaporative method Thus the wet

bulb temperature of the air entering the cooling tower determines operating

temperature levels throughout the plant process or system Theoretically a cooling

tower will cool water to the entering wet bulb temperature when operating without a

heat load However a thermal potential is required to reject heat so it is not possible

to cool water to the entering air wet bulb temperature when a heat load is applied

The approach obtained is a function of thermal conditions and tower capability

Energy Saving Opportunities in Cooling Towers

Follow manufacturerrsquos recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust

Optimise cooling tower fan blade angle on a seasonal andor load basis

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Correct excessive andor uneven fan blade tip clearance and poor fan balance

On old counter-flow cooling towers replace old spray type nozzles with new

square spray ABS practically non-clogging nozzles

Replace splash bars with self-extinguishing PVC cellular film fill

Install new nozzles to obtain a more uniform water pattern

Periodically clean plugged cooling tower distribution nozzles

Balance flow to cooling tower hot water basins

Cover hot water basins to minimise algae growth that contributes to fouling

Optimise blow down flow rate as per COC limit

Replace slat type drift eliminators with low pressure drop self extinguishing

PVC cellular units

Restrict flows through large loads to design values

Segregate high heat loads like furnaces air compressors DG sets and isolate

cooling towers for sensitive applications like AC plants condensers of

captive power plant etc A 1oC cooling water temperature increase may

increase AC compressor kW by 27 A 1oC drop in cooling water

temperature can give a heat rate saving of 5 kCalkWh in a thermal power

plant

Monitor LG ratio CW flow rates wrt design as well as seasonal variations

It would help to increase water load during summer and times when approach

is high and increase air flow during monsoon times and when approach is

narrow

Monitor approach effectiveness and cooling capacity for continuous

optimisation efforts as per seasonal variations as well as load side variations

Consider COC improvement measures for water savings

Consider energy efficient FRP blade adoption for fan energy savings

Consider possible improvements on CW pumps wrt efficiency improvement

Control cooling tower fans based on leaving water temperatures especially in

case of small units

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 42-43 Introduction to Waste Heat Recovery Classification and

Application Benefits of Waste Heat Recovery

Waste heat is heat which is generated in a process by way of fuel combustion or

chemical reaction and then ldquodumpedrdquo into the environment even though it could still

be reused for some useful and economic purpose The essential quality of heat is not

the amount but rather its ldquovaluerdquo The strategy of how to recover this heat depends in

part on the temperature of the waste heat gases and the economics involved Large

quantity of hot flue gases is generated from Boilers Kilns Ovens and Furnaces If

some of this waste heat could be recovered a considerable amount of primary fuel

could be saved

Heat Losses ndashQuality

Depending upon the type of process waste heat can be rejected at virtually any

temperature from that of chilled cooling water to high temperature waste gases from

an industrial furnace or kiln Usually higher the temperature higher the quality and

more cost effective is the heat recovery In any study of waste heat recovery it is

absolutely necessary that there should be some use for the recovered heat Typical

examples of use would be preheating of combustion air space heating or pre-heating

boiler feed water or process water With high temperature heat recovery a cascade

system of waste heat recovery may be practiced to ensure that the maximum amount

of heat is recovered at the highest potential An example of this technique of waste

heat recovery would be where the high temperature stage was used for air pre-heating

and the low temperature stage used for process feed water heating or steam raising

Benefits of Waste Heat Recovery

Benefits of lsquowaste heat recoveryrsquo can be broadly classified in two categories

Direct Benefits

Recovery of waste heat has a direct effect on the efficiency of the process This is

reflected by reduction in the utility consumption amp costs and process cost

Indirect Benefits

a) Reduction in pollution A number of toxic combustible wastes such as carbon

monoxide gas sour gas carbon black off gases oil sludge Acrylonitrile and

other plastic chemicals etc releasing to atmosphere ifwhen burnt in the

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

incinerators serves dual purpose ie recovers heat and reduces the

environmental pollution levels

b) Reduction in equipment sizes Waste heat recovery reduces the fuel

consumption which leads to reduction in the flue gas produced This results in

reduction in equipment sizes of all flue gas handling equipments such as fans

stacks ducts burners etc

c) Reduction in auxiliary energy consumption Reduction in equipment sizes gives

additional benefits in the form of reduction in auxiliary energy consumption

like electricity for fans pumps etc

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No44 Development of a Waste Heat Recovery System Commercial Waste

Heat Recovery Devices

Understanding the process

Understanding the process is essential for development of Waste Heat Recovery

system This can be accomplished by reviewing the process flow sheets layout

diagrams piping isometrics electrical and instrumentation cable ducting etc

Detail review of these documents will help in identifying

a) Sources and uses of waste heat

b) Upset conditions occurring in the plant due to heat recovery

c) Availability of space

d) Any other constraint such as dew point occurring in an equipments etc

After identifying source of waste heat and the possible use of it the next step is to

select suitable heat recovery system and equipments to recover and utilise the same

Economic Evaluation of Waste Heat Recovery System

It is necessary to evaluate the selected waste heat recovery system on the basis of

financial analysis such as investment depreciation payback period rate of return etc

In addition the advice of experienced consultants and suppliers must be obtained for

rational decision

Next section gives a brief description of common heat recovery devices available

commercially and its typical industrial applications

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture No 45-46 Recuperators Heat Wheels Heat Pipe Economiser Plate heat

exchanger Waste Heat Boilers Heat Pumps Thermocompressor

Recuperators

In a recuperator heat exchange takes place between the flue gases and the air through

metallic or ceramic walls Duct or tubes carry the air for combustion to be pre-heated

the other side contains the waste heat stream A recuperator for recovering waste heat

from flue gases is shown in Figure

Heat Wheels

Heat wheel is finding increasing applications in low to medium temperature waste

heat recovery systems Figure is a sketch illustrating the application of a heat wheel

It is a sizable porous disk fabricated with material having a fairly high heat capacity

which rotates between two side-by-side ducts one a cold gas duct the other a hot gas

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

duct The axis of the disk is located parallel to and on the partition between the two

ducts As the disk slowly rotates sensible heat (moisture that contains latent heat) is

transferred to the disk by the hot air and as the disk rotates from the disk to the cold

air The overall efficiency of sensible heat transfer for this kind of regenerator can be

as high as 85 percent Heat wheels have been built as large as 21 metres in diameter

with air capacities up to 1130 m3 min

A variation of the Heat Wheel is the rotary regenerator where the matrix is in a

cylinder rotating across the waste gas and air streams The heat or energy recovery

wheel is a rotary gas heat regenerator which can transfer heat from exhaust to

incoming gases

Its main area of application is where heat exchange between large masses of air

having small temperature differences is required Heating and ventilation systems and

recovery of heat from dryer exhaust air are typical applications

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper the best

known conductor In other words heat pipe is a thermal energy absorbing and

transferring system and have no moving parts and hence require minimum

maintenance

The Heat Pipe comprises of three elements ndash a sealed container a capillary wick

structure and a working fluid The capillary wick structure is integrally fabricated into

the interior surface of the container tube and sealed under vacuum Thermal energy

applied to the external surface of the heat pipe is in equilibrium with its own vapour

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

as the container tube is sealed under vacuum Thermal energy applied to the external

surface of the heat pipe causes the working fluid near the surface to evaporate

instantaneously Vapour thus formed absorbs the latent heat of vapourisation and this

part of the heat pipe becomes an evaporator region The vapour then travels to the

other end the pipe where the thermal energy is removed causing the vapour to

condense into liquid again thereby giving up the latent heat of the condensation This

part of the heat pipe works as the condenser region The condensed liquid then flows

back to the evaporated region A figure of Heat pipe is shown in Figure

Heat Pumps

In the various commercial options previously discussed we find waste heat being

transferred from a hot fluid to a fluid at a lower temperature Heat must flow

spontaneously ldquodownhillrdquo that is from a system at high temperature to one at a lower

temperature When energy is repeatedly transferred or transformed it becomes less

and less available for use Eventually that energy has such low intensity (resides in a

medium at such low temperature) that it is no longer available at all to perform a

useful function

It has been taken as a general rule of thumb in industrial operations that fluids with

temperatures less than 120oC (or better 150oC to provide a safe margin) as limit for

waste heat recovery because of the risk of condensation of corrosive liquids

However as fuel costs continue to rise even such waste heat can be used

economically for space heating and other low temperature applications It is possible

to reverse the direction of spontaneous energy flow by the use of a thermodynamic

system known as a heat pump

The majority of heat pumps work on the principle of the vapour compression cycle In

this cycle the circulating substance is physically separated from the source (waste

heat with a temperature of Tin) and user (heat to be used in the process Tout) streams

and is re-used in a cyclical fashion therefore called closed cycle In the heat pump

the following processes take place

1 In the evaporator the heat is extracted from the heat source to boil the

circulating substance

2 The circulating substance is compressed by the compressor raising its pressure

and temperature The low temperature vapor is compressed by a compressor

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

which requires external work The work done on the vapor raises its pressure

and temperature to a level where its energy becomes available for use

3 The heat is delivered to the condenser

4 The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve where the cycle repeats

The heat pump was developed as a space heating system where low temperature

energy from the ambient air water or earth is raised to heating system temperatures

by doing compression work with an electric motor-driven compressor The

arrangement of a heat pump is shown in figure

Faculty Prof Ronak Patel

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture 1-2

Introduction Air compressors account for significant amount of electricity used in Indian

industries Air compressors are used in a variety of industries to supply process

requirements to operate pneumatic tools and equipment and to meet instrumentation

needs Only 10-30 of energy reaches the point of end-use and balance 70-90 of

energy of the power of the prime mover being converted to unusable heat energy and

to a lesser extent lost in form of friction misuse and noise

Compressor Types

Compressors are broadly classified as Positive displacement compressor and Dynamic

compressor

Positive displacement compressors increase the pressure of the gas by reducing the

volume Positive displacement compressors are further classified as reciprocating and

rotary compressors

Dynamic compressors increase the air velocity which is then converted to increased

pressure at the outlet Dynamic compressors are basically centrifugal compressors and are

further classified as radial and axial flow types Flow and pressure requirements of a

given application determine the suitability of a particulars type of compressor

Positive Displacement Compressors

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Reciprocating compressors are the most widely used type for air compression They

are characterized by a flow output that remains nearly constant over a range of

discharge pressures Also the compressor capacity is directly proportional to the

speed The output however is a pulsating one

Reciprocating compressors are available in many configurations the four most widely

used of which are horizontal vertical and horizontal balance-opposed and tandem

Vertical type reciprocating compressors are used in the capacity range of 50 ndash 150

cfm Horizontal balance opposed compressors are used in the capacity range of 200 ndash

5000 cfm in multi-stage design and up to 10000 cfm in single stage designs

Reciprocating compressors are also available in variety of types

1048707Lubricated and non-lubricated

1048707Single or multiple cylinder

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture 3-4

Compressor Performance

Capacity of a compressor is the full rated volume of flow of gas compressed and

delivered at conditions of total temperature total pressure and composition prevailing

at the compressor inlet It sometimes means actual flow rate rather than rated volume

of flow This also termed as Free Air Delivery (FAD) ie air at atmospheric

conditions at any specific location Because the altitude barometer and temperature

may vary at different localities and at different times it follows that this term does not

mean air under identical or standard conditions

Compressor Efficiency DefinitionsSeveral different measures of compressor efficiency are commonly used volumetric

efficiency adiabatic efficiency isothermal efficiency and mechanical efficiency

Adiabatic and isothermal efficiencies are computed as the isothermal or adiabatic power

divided by the actual power consumption The figure obtained indicates the overall

efficiency of compressor and drive motor

Isothermal Efficiency

Isothermal Efficiency=Actual measured input powerIsothermalPower

Isothermal power (kW) = P1 x Q1 x loger367

P1 = Absolute intake pressure kg cm2

Q1 = Free air delivered m3hr

r = Pressure ratio P2P1

Bureau of Energy Efficiency 533 Compressed Air System The calculation of isothermal

power does not include power needed to overcome friction and generally gives an

efficiency that is lower than adiabatic efficiency The reported value of efficiency is

normally the isothermal efficiency This is an important consideration when selecting

compressors based on reported values of efficiency

Volumetric Efficiency Compressor Displacement = Π x D2 x L x S x χ x n

Compressed Air System Components

Compressed air systems consist of following major components Intake air filters

inter-stage coolers after coolers air dryers moisture drain traps receivers piping

network filters regulators and lubricators

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Intake Air Filters Prevent dust from entering compressor Dust causes sticking

valves scoured cylinders excessive wear etc

Inter-stage Coolers Reduce the temperature of the air before it enters the next stage

to reduce the work of compression and increase efficiency They are normally water-

cooled

After Coolers The objective is to remove the moisture in the air by reducing the

temperature in a water-cooled heat exchanger

Air-dryers The remaining traces of moisture after after-cooler are removed using air

dryers as air for instrument and pneumatic equipment has to be relatively free of any

moisture The moisture is removed by using adsorbents like silica gel activated

carbon or refrigerant dryers or heat of compression dryers

Moisture Drain Traps Moisture drain traps are used for removal of moisture in the

compressed air These traps resemble steam traps Various types of traps used are

manual drain cocks timer based automatic drain valves etc

Bureau of Energy Efficiency 543 Compressed Air System

Receivers Air receivers are provided as storage and smoothening pulsating air

output - reducing pressure variations from the compressor

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture 5-6

Need for cogeneration Thermal power plants are a major source of electricity supply in India The conventional

method of power generation and supply to the customer is wasteful in the sense that only

about a third of the primary energy fed into the power plant is actually made available to

the user in the form of electricity In conventional power plant efficiency is only 35

and remaining 65 of energy is lost The major source of loss in the conversion process

is the heat rejected to the surrounding water or air due to the inherent constraints of the

different thermodynamic cycles employed in power generation Also further losses of

around 10-15 are associated with the transmission and distribution of electricity in the

electrical grid

Principle of Cogeneration

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation

of two different forms of useful energy from a single primary energy source typically

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

mechanical energy and thermal energy Mechanical energy may be used to drive an

alternator for producing electricity or rotating equipment such as motor compressor

pump or fan for delivering various services Thermal energy can be used either for direct

process applications or for indirectly producing steam hot water hot air for dryer or

chilled water for process cooling

Cogeneration provides a wide range of technologies for application in various domains of

economic activities The overall efficiency of energy use in cogeneration mode can be up

to 85 per cent and above in some cases

Classification of Cogeneration Systems

Cogeneration systems are normally classified according to the sequence of energy use and

the operating schemes adopted

A cogeneration system can be classified as either a topping or a bottoming cycle on the

basis of the sequence of energy use In a topping cycle the fuel supplied is used to first

produce power and then thermal energy which is the by-product of the cycle and is used

to satisfy process heat or other thermal requirements Topping cycle cogeneration is

widely used and is the most popular method of cogeneration

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture 7-8

Topping Cycle

A gas turbine or diesel engine producing electrical or mechanical power followed by a heat

recovery boiler to create steam to drive a secondary steam turbine This is called a combined-

cycle topping system

The second type of system burns fuel (any type) to produce high-pressure steam that then

passes through a steam turbine to produce power with the exhaust provides low-pressure

process steam This is a steam-turbine topping system

A third type employs heat recovery from an engine exhaust andor jacket cooling system

flowing to a heat recovery boiler where it is converted to process steam hot water for further

use

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific

and depends on several factors as described below

Base electrical load matching

Base thermal load matching Electrical load matching

Thermal load matching

Important Technical Parameters for Cogeneration

While selecting cogeneration systems one should consider some important technical

parameters that assist in defining the type and operating scheme of different

alternative cogeneration systems to be selected

Heat-to-power ratio

Heat-to-power ratio is one of the most important technical parameters influencing the

selection of the type of cogeneration system The heat-to-power ratio of a facility

should match with the characteristics of the cogeneration system to be installed It is

defined as the ratio of thermal energy to electricity required by the energy consuming

facility Though it can be expressed in different units such as BtukWh kcalkWh

lbhrkW etc here it is presented on the basis of the same energy unit (kW)

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture 9-10

Electrical system

Steam Turbine Steam turbines are the most commonly employed prime movers for cogeneration

applications In the steam turbine the incoming high pressure steam is expanded to a

lower pressure level converting the thermal energy of high pressure steam to kinetic

energy through nozzles and then to mechanical power through rotating blades

Extraction Condensing turbine In this type steam entering at High Medium Pressure

is extracted at an intermediate pressure in the turbine for process use while the remaining

steam continues to expand and condenses in a surface condenser and work is done till it

reaches the Condensing pressure(vacuum)

The overall thermal efficiency of an extraction condensing turbine cogeneration system is

lower than that of back pressure turbine system basically because the exhaust heat cannot

be utilized (it is normally lost in the cooling water circuit) However extraction

condensing cogeneration systems have higher electricity generation efficiencies

Gas Turbine

The fuel is burnt in a pressurized combustion chamber using combustion air supplied by a

compressor that is integral with the gas turbine In conventional Gas turbine gases enter

the turbine at a temperature range of 900 to 1000oC and leave at 400 to 500 oC The very

hot pressurized gases are used to turn a series of turbine blades and the shaft on which

they are mounted to produce mechanical energy Residual energy in the form of a high

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

flow of hot exhaust gases can be used to meet wholly or partly the thermal (steam)

demand of the site

Gas Turbine Efficiency Turbine Efficiency is the ratio of actual work output of the turbine to the net input energy

supplied in the form of fuel For stand alone Gas Turbines without any heat recovery

system the efficiency will be as low as 35 to 40 This is attributed to the blade

efficiency of the rotor leakage through clearance spaces friction irreversible turbulence

etc

Since Exhaust gas from the Gas Turbine is high it is possible to recover energy from the

hot gas by a Heat Recovery Steam Generator and use the steam for process

Net Turbine Efficiency

Above efficiency figures did not include the energy consumed by air compressors fuel

pump and other auxiliaries Air compressor alone consumes about 50 to 60 of energy

generated by the turbine Hence net turbine efficiency which is the actual energy output

available will be less than what has been calculated In most Gas Turbine plants air

compressor is an integral part of Turbine plant

Problems based on Economics of a Gas Turbine Based Co-generation

Calorific value ndash

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture11-12

Electric motors Types

Introduction Motors convert electrical energy into mechanical energy by the interaction between the

magnetic fields set up in the stator and rotor windings Industrial electric motors can be

broadly classified as induction motors direct current motors or synchronous motors All

motor types have the same four operating components stator (stationary windings) rotor

(rotating windings) bearings and frame (enclosure)

Motor Types Induction Motors

Induction motors are the most commonly used prime mover for various equipments in

industrial applications In induction motors the induced magnetic field of the stator

winding induces a current in the rotor This induced rotor current produces a second

magnetic field which tries to oppose the stator magnetic field and this causes the rotor to

rotate

The 3-phase squirrel cage motor is the workhorse of industry it is rugged and reliable

and is by far the most common motor type used in industry These motors drive pumps

blowers and fans compressors conveyers and production lines The 3-phase induction

motor has three windings each connected to a separate phase of the power supply

Direct-Current Motors

Direct-Current motors as the name implies use direct-unidirectional current Direct

current motors are used in special applications- where high torque starting or where

smooth acceleration over a broad speed range is required

Synchronous Motors

AC power is fed to the stator of the synchronous motor The rotor is fed by DC from a

separate source The rotor magnetic field locks onto the stator rotating magnetic field and

rotates at the same speed The speed of the rotor is a function of the supply frequency and

the number of magnetic poles in the stator

Motor Characteristics Motor Speed The speed of a motor is the number of revolutions in a given time frame typically

revolutions per minute (RPM) The speed of an AC motor depends on the frequency

of the input power and the number of poles for which the motor is wound

Power Factor

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

The power factor of the motor is given as kVAkW Cos Factor Power ==φ

As the load on the motor comes down the magnitude of the active current reduces

However there is no corresponding reduction in the magnetizing current which is

proportional to supply voltage with the result that the motor power factor reduces

with a reduction in applied load Induction motors especially those operating below

their rated capacity are the main reason for low power factor in electric systems

Motor Efficiency Two important attributes relating to efficiency of electricity use by AC Induction

motors are efficiency (η) defined as the ratio of the mechanical energy delivered at

the rotating shaft to the electrical energy input at its terminals and power factor (PF)

Motors like other inductive loads are characterized by power factors less than one

As a result the total current draw needed to deliver the same real power is higher than

for a load characterized by a higher PF

The efficiency of a motor is determined by intrinsic losses that can be reduced only by

changes in motor design Intrinsic losses are of two types fixed losses- independent of

motor load and variable losses - dependent on load

Fixed losses consist of magnetic core losses and friction and windage losses Magnetic

core losses (sometimes called iron losses) consist of eddy current and hysteretic losses in

the stator They vary with the core material and geometry and with input voltage

Friction and windage losses are caused by friction in the bearings of the motor and

aerodynamic losses associated with the ventilation fan and other rotating parts

Variable losses consist of resistance losses in the stator and in the rotor and

miscellaneous stray losses Resistance to current flow in the stator and rotor result in heat

generation that is proportional to the resistance of the material and the square of the

current (I2R) Stray losses arise from a variety of sources and are difficult to either

measure directly or to calculate but are generally proportional to the square of the rotor

current

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture13-14

Tests for Determining Efficiency

No Load Test The motor is run at rated voltage and frequency without any shaft load

Input power current frequency and voltage are noted The no load PF is quite low and

hence low PF watt meters are required From the input power stator I2R losses under no

load are subtracted to give the sum of Friction and Windage (FampW) and core losses

F amp W losses test is repeated at variable voltages It is useful to plot no-load input kW

versus Voltage the intercept is Friction amp Windage kW loss component

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

FampW and core losses = No load power (watts) ndash (No load current) 2 times Stator resistance

Stator and Rotor I2R Losses The stator winding resistance is directly measured by a

bridge or volt amp method The resistance must be corrected to the operating temperature

For modern motors the operating temperature is likely to be in the range of 1000C to

1200C and necessary correction should be made Correction to 750C may be inaccurate

The correction factor is given as follows

Rotor I2R losses = Slip times (Stator Input ndash Stator I2R Losses ndash Core Loss)

Accurate measurement of slip is possible by stroboscope or non-contact type tachometer

Slip also must be corrected to operating temperature

Factors Affecting Energy Efficiency amp Minimising Motor Losses in Operation Power Supply QualitySizing to Variable Load Industrial motors frequently operate under varying load conditions due to process

requirements A common practice in cases where such variable-loads are found is to

select a motor based on the highest anticipated load In many instances an alternative

approach is typically less costly more efficient and provides equally satisfactory

operation With this approach the optimum rating for the motor is selected on the

basis of the load duration curve for the particular application Thus rather than

selecting a motor of high rating that would operate at full capacity for only a short

period a motor would be selected with a rating slightly lower than the peak

anticipated load and would operate at overload for a short period of time

Power Factor Correction As noted earlier induction motors are characterized by power factors less than unity

leading to lower overall efficiency (and higher overall operating cost) associated with

a plantrsquos electrical system Capacitors connected in parallel (shunted) with the motor

are typically used to improve the power factor The impacts of PF correction include

reduced kVA demand (and hence reduced utility demand charges) reduced I2R losses

in cables upstream of the capacitor (and hence reduced energy charges) reduced

voltage drop in the cables (leading to improved voltage regulation) and an increase in

the overall efficiency of the plant electrical system

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

Lecture 15-16

A gas flare alternatively known as a flare stack is an elevated vertical conveyance

found accompanying the presence of oil wells gas wells rigs refineries chemical

plants natural gas plants and landfills They are used to eliminate waste gas which is

otherwise not feasible to use or transport They also act as safety systems for non-

waste gas and is released via pressure relief valve when needed to ease the strain on

equipment They protect gas processing equipments from being overpressured Also

in case of an emergency situation the flare system helps burn out the total reserve gas

Flare and vent systems exist in essentially all segments of the oil and gas industry and

are used for two basic types of waste gas disposal intermittent and continuous

Intermittent applications may include the disposal of waste volumes from emergency

pressure relief episodes operator initiated or instrumented depressurization events

(eg depressurization of process equipment for inspection or maintenance purposes

or depressurization of piping for tie-ins) plant or system upsets well servicing and

testing pigging events and routine blowdown of instruments drip pots and scrubbers

Continuous applications may include disposal of associated gas andor tank vapours at

oil production facilities where gas conservation is uneconomical or until such

economics can be evaluated casing gas at heavy oil wells process waste or byproduct

streams that either have little or no value or are uneconomical to recover

There are inconsistencies in what individual companies may include in their reported

vented and flared volumes and depending on the jurisdiction this information may

not be reported at all The vented and flared volumes reported in production accounting

statistics typically comprise where applicable casing gas venting waste associated gas

flows treater and stabilizer off-gas and gas volumes discharged during process upsets

and equipment depressurization events Storage and loadingunloading losses are

assumed to be generally excluded from reported vented volumes and therefore are

assessed separately

Miscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas compressor start gas purge gas and

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency

blanket gas that is discharged directly to the atmosphere dehydrator still column off-gas

purge gas and releases from inspection and maintenance activities

Where vented and flared volumes are reported all measured quantities are usually

captured however flow meters are normally only installed on larger continuous vent

or flare systems if at all Where there is no measurement data the volumes may still

be estimated The problems here are the lack of detailed estimation guidelines the

lack of any formal tracking of the activity data needed to make many of these

estimates (eg frequency and details of equipment or piping blowdown events

frequency of compressor engine starts etc) and differences in which sources

individual operators are even considering

At gas processing plants acid gas volumes are normally reported separately from

other venting or flaring volumes however the latter amounts are reported as a single

aggregated value Venting and flaring from gas gathering systems is also reported as a

single aggregate value

Some operators have tended to use vented and flared entries as balancing terms to

achieve reasonable metering differences when completing production accounting

reports

The problems with conserving or vented and flared volumes may include small

volumes involved at individual sites inconsistencies in flow poor access to gas

gathering systems concerns about putting any back-pressure on the casing in order to

use the gas and operational difficulties associated with using this gas (eg freeze-up

problems in the winter) in the absence of any costly onsite dehydration facilities

The actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas The amount of residual flow in intermittent

flare systems is the sum of the purge gas flow rate and leakage rates into the flare

system

• Boiler Efficiency
• Conductivity as Indicator of Boiler Water Quality
• • Intermittent Blowdown
  • Continuous Blowdown
  • Benefits of Blowdown
  • Incomplete Combustion
  • Excess Air Control
  • Proper Boiler Scheduling
  • • Pump Types
    • Matching Pump and System Head-flow Characteristics
    • • Fan Laws
      • Flow Control Strategies
      • Variable Speed Drives
      • Table Properties of Commonly used Refrigerants
      • • Range
        • Wet Bulb Temperature
        • Heat Losses ndashQuality
        • • Benefits of Waste Heat Recovery
          • Understanding the process
          • • A variation of the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams The heat or energy recovery wheel is a rotary gas heat regenerator which can transfer heat from exhaust to incoming gases
            • • Lecture 1-2
              • Introduction
              • Gas Turbine Efficiency
              • • Net Turbine Efficiency
                • • Induction Motors
                  • Direct-Current Motors
                  • Synchronous Motors
                  • • Tests for Determining Efficiency