boiler expt 2

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BANGLADESH UNIVERSITY OF ENGINEERING & TECHNOLOGY Course No.: ME 404 Course Title: Power Plant Engineering Sessional Experiment No.: 2 Name of the Experiment: Study of a Boiler Date of Performance 18/09/2011 Name: Aashique Alam Rezwan Student No.: 06 10 012 Date of Submission 9/10/2011 Section: “A” Group: A 12 Dept: Mechanical Engineering

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Page 1: Boiler Expt 2

1

BANGLADESH UNIVERSITY OF ENGINEERING & TECHNOLOGY

Course No.: ME 404

Course Title: Power Plant Engineering Sessional

Experiment No.: 2

Name of the Experiment:

Study of a Boiler

Date of Performance

18/09/2011

Name: Aashique Alam Rezwan

Student No.: 06 10 012

Date of Submission

9/10/2011

Section: “A” Group: A12

Dept: Mechanical Engineering

Page 2: Boiler Expt 2

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Experiment No.: 2

Name of the Experiment:

Study of a Boiler

Objectives:

The objectives of this experiment are as follows –

o To study the different accessories & mountings of a boiler

o To study the operations of a boiler

o To study the boiler capacities

o To study the water treatment operations for boiler

Specifications

Brand Name Philipp Loos GmbH

Model 12 D-57629 Norken

Country of Make Germany

Capacity 1600 kg/hr

Maximum working pressure 16 bar

Type of Burner Dual Fuel Burner (Natural Gas/Diesel)

Fuel/fuels used Natural Gas

Boiler Mountings & Accessories

Boiler Mountings

1. Water Level Indicator / Water Gauge

2. Pressure Gauge

3. Safety Valve

4. Stop Valve

5. Feed Valve

6. Blow Down Valve

7. Fusible Plug

8. Steam Scrubber

9. Manhole and Handhole Covers

Boiler Accessories

1. Superheater

2. Attemperator

3. Economiser

4. Air Preheater

5. Feed Water Heater

6. Feed Pump

7. Injectors

8. Draught Production Equipment

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Fig. 1: Schematic Diagram of the Boiler

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Boiler Mountings

Pressure Gauge

Fig. 2: Pressure Gauge

A pressure gauge is used to measure the pressure of the steam inside the steam boiler. It is fixed in front of the

steam boiler. The pressure gauges generally used are of Bourden type.

A Bourden pressure gauge, in its simplest form, consists of an elliptical elastic tube bent into an arc of a circle.

This bent up tube is called Bourden’s tube.

One end of the tube gauge is fixed and connected to the steam space in the boiler. The other end is connected to

a sector through a link. The steam, under pressure, flows into the tube. As a result of this increased pressure, the

Bourden’s tube tends to straighten itself. Since the tube is encased in a circular curve, therefore it tends to

become a circular instead of straight. With the help of a simple pinion and sector arrangement, the elastic

deformation of the Bourden’s tube rotates the pointer. This pointer moves over a calibrated scale, which directly

gives the gauge pressure.

Pressure Governor & Water Level Regulator

Fig. 3: Pressure Governor & Water Level Regulator

Thermal energy is transported to the water inside the boiler body by means of heating. The water grows warm

and vaporizes, the steam pressure in the boiler rises. As soon as the working pressure is attained, the pressure

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governors cut of heating. There upon, when pressure drops for approx. 7% in consequences of the extraction of

steam, the pressure governor will connect up the furnace again.

Owing on the extraction of steam the water level in the boiler body drops. As soons as the water level has

dropped to approx. 4 cms above the low water level (NW), the water level regulator gives an electric pulse to

the switch gear. There upon the feed pump will start, it conveys water from the feed water tank into the boiler.

After a short time the water level in the boiler has risen again by this, there upon the water level regulator will

cut off the feed pump by means of an electric pulse.

Safety Valve

Fig. 4: Spring Loaded Safety Valve

These are the devices attached to the steam chest for preventing explosions due to excessive internal pressure of

steam. A steam boiler is, usually, provided with two safety valves. These are directly placed on the boiler. The

function of a safety valve is to blow off the steam when the pressure of steam inside the boiler exceeds the

working pressure.

A spring loaded safety valve is mainly used for locomotives and marine boilers. It is loaded with spring instead

of weights. The spring is made of round or square spring steal rod in helical form. The spring may be in tension

or compression, as the steam pressure acts along the axis of the spring. In actual practice, the spring is placed in

compression.

According to the original prescriptions the valve must be adjusted in such a manner that it begins to let the

steam out exactly when having reached the licensed pressure. Therefore the pressure governors are regulated so

that they cut off the furnace a short time before attaining the licensed pressure.

Water Level Indicator

Fig. 5: Water Level Indicator

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It is an important fitting, which indicates the water level inside the boiler to an observer. It is a safety device,

uipon which the correct working of the boiler depends. This fitting may be seen in front of the oiler, and are

generally tow in number.

Feed Check Valve

Fig. 6: Feed Check Valve

It is a non-return valve, fitted to a screwed spindle to regulate the lift. Its function is to regulate the supply of

water, which is pumped into the boiler, by the feed pump. This valve must have its spindle lifted before the

pump is started. It is fitted to the shell slightly below the normal water level of the boiler.

Blow off Cock

Fig. 7: Blow off Cock

The principal functions of a blow off cock are:

1. To empty the boiler whenever required

2. To discharge the mud, scale or sediments which are accumulated at the bottom of the boiler

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Boiler Accessories

Feed Pump

Fig. 8: Boiler Feed Pump

The feed pump is one of the most important accessories for a boiler unit. Its function is to take the feed water

from the reservoir and to force it into the boiler against the steam pressure.

Superheater

Fig. 9: Superheater

A superheater is an important device of a steam generating unit. Its purpose is to increase the temperature of

saturated steam without raising its pressure. It is generally an integral part of a boiler, and is placed in the path

of hot flue gases from the furnace. The heat, given up by these flue gases, is used in superheating the steam.

Such superheaters, which are installed within the boiler, are known as integral superheaters.

Economizer

An economizer is a device used to heat feed water by utilizing the heat in the exhaust flue gases before leaving

through the chimney. As the name indicates, the economizer improves the economy of the steam boiler.

It is a surface heat exchanger where water flows through the cast iron pipes or steel tubes and flue gases pass

around them. There are two general types of economizer namely (i) independent type and (ii) integral type.

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Other Accessories & Mountings

Fig. 10: Flame Sight Hole

Fig. 11: Water Quality Indicator

Fig. 12: Burner

Fig. 13: Gas Pressure Gauge

Fig. 14: Control Panel, Controller Relay

Fig. 15: Water Softener / Water Treatment Plant

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Water Flow Circuit

Fuel Flow Circuit

Gas (Supply Line)

Pressure Gauge

Gas On/Off Valve (Ball

Valve) Gas Filter

Gas Regulator Push Type Pressure

Gauge

Gas Control Valve

(Solenoid) Throttle Valve

Cross Flow Mixing

Chamber Burner

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Boiler Capacity

Tonnage Rating

The Tonnage Rating is widely used as a datum by shell boiler manufacturers to give a boiler a rating which

shows the amount of steam in kg/h. It is the amount of water evaporated from feed water at 100° C and formed

into dry and saturated steam at 100° C at normal atmospheric pressure. Each kilogram of steam would then have

received 2 257 kJ of heat from the boiler.

Shell boilers are often operated with feed water temperatures lower than 100°C. Consequently the boiler is

required to supply enthalpy to bring the water up to boiling point.

kW Rating

Some manufacturers will give a boiler rating in kW. This is not an evaporation rate, and is subject to the same

Tonnage Rating.

To establish the actual evaporation by mass, it is first necessary to know the temperature of the feed water and

the pressure of the steam produced, in order to establish how much energy is added to each kg of water. The

following equation can then be used to calculate the steam output:

(

) ( )

( ⁄ )

Boiler hp Rating

This unit tends to be used only in the USA, Australia, and New Zealand. A boiler horsepower is not the

commonly accepted 550 ft lbf/s and the generally accepted conversion factor of 746 Watts = 1 horsepower does

not apply.

In New Zealand, boiler horsepower is a function of the heat transfer area in the boiler, and a boiler horsepower

relates to 17 ft² of heating surface, as depicted in Equation:

( )

In the USA and Australia the readily accepted definition of a boiler horsepower is the amount of energy required

to evaporate 34.5 lb of water at 212°F atmospheric conditions.

Operations of Air and Fuel Flow for Firing a Boiler

1. Blow out of the exhaust gas.

2. Checking the water level in the boiler and if level is below the safety level water is refilled.

3. Air is blown in by starting blower.

4. Natural Gas acts as fuel passes through pressure gauge, regulator and solenoid valve and finally enters

into the burner.

5. Air and gas mixes in proportional limit and produce spark in the electric spark rod.

6. Pilot flame is established then full combustion starts.

7. The fire or hot flue gasses from the burner is channeled through tubes that are surrounded by the fluid

to be heated.

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Control of Water Level Indicator

By means of the water level indicator it is possible to control the water level in the boiler. Normally in automatic

mode of operation, this level is approx. 4 – 8 cms. above to low water mark. The water level must nit drop

below this mark, as otherwise the heating surfaces may be destroyed.

The water level indicator consists of the upper and the lower cock respectively sloping spindle valve, and the

glass pipe respectively reflection glass inset, inserted between the same.

For keeping the glass clean it is to be recommended to pen the cleansing tap placed at the lower end of the water

level indicator. The water that escapes under pressure, will rinse the glass.

In case a leakage should exist at the water level indicator, this may be removed by tightening the tension nuts

that caulk the glass, respectively the hand wheel.

In case of the sloping spindle valve water level indicator the tension nuts for the glass inset are to be found at the

back of the inset. Here it is recommendable to tighten crosswise from the middle.

When tightening, the connection valves of the water level indicator at the boiler must be blocked, because, at

improper handling, the glass may crack, and the escaping hot water or steam mixture may endanger persons.

To test a gauge glass, the following procedure should be followed:

Close the water cock and open the drain cock for approximately 5 seconds.

Close the drain cock and open the water cock. Water should return to its normal working level

relatively quickly. If this does not happen, then a blockage in the water cock could be the reason, and

remedial action should be taken as soon as possible.

Close the steam cock and open the drain cock for approximately 5 seconds.

Close the drain cock and open the steam cock. If the water does not return to its normal working level

relatively quickly, a blockage may exist in the steam cock. Remedial action should be taken as soon as

possible.

The authorized attendant should systematically test the water gauges at least once each day and should

be provided with suitable protection for the face and hands, as a safeguard against scalding in the event

of glass breakage.

Functions and Pressure Setting of Safety Valve

These are the devices attached to the steam chest for preventing explosions due to excessive internal pressure of

steam. A steam boiler is, usually, provided with two safety valves. These are directly placed on the boiler. The

function of a safety valve is to blow off the steam when the pressure of steam inside the boiler exceeds the

working pressure.

The safety valve installed is of a tested type and spring-loaded. By means of the spring

1. The surface of packing is pressed upon the packing ring

2. The power of the spring is arranged in such a manner that the contact surface is lifted only at an

adjusted pressure of 10 or 13 bar for example. Then the overpressure will escape and the spring brings

the packing surfaces back to the packing position.

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According to the official prescriptions the valve must be adjusted in such a manner that it begins to let the steam

out exactly when having reached the licensed pressure. Therefore the pressure governors are regulated so that

they cut off the furnace a short time before attaining the licensed pressure. Thereby it is prevented that the safety

valve is set in operation in case of each slight pressure rise.

Examination of readiness for function

It is recommendable to let the safety valve blow off from time to time by means of lifting the level in order to be

sure of the readiness for function of the valve and in order to prevent that boiler scale can deposit.

Relief in case of leakage

It may occur that, after blowing-off, dirt may deposit between the contact surfaces, in this case some steam will

continue to escape through the valve. Open again the safety valve by lifting the lever. The contact surface is

lifted from the packing seat; steam will escape and will eventually take off the substances. By releasing the

lever, the valve is closed again.

If this does not help one should, only under pressure, turn the cone on its seat to an for approx. ¼ turn by means

of square at the upper spindle end. Therefore the cover must be unscrewed and taken off. The cone on its seat

may only be turned if the safety valve is below the blowing-off pressure or a pressure being only slightly below

the blowing-off pressure. If this is not noted, one turn of the cone will destroy the contact surface. A tight

closing will not be guaranteed any more.

Fig. 16: Safety Valve

Hydraulic Test of a Boiler

The equipment should have been hydrostatically tested to a minimum of 1½ times the design pressure, in the

factory, and copies of the Manufacturer's Data report, signed by the Authorized Inspector witnessing and

evidencing the test forwarded to all jurisdictional bodies as well as to the Client. However, the complete system,

along with all interconnecting piping, should be hydrostatically tested before start-up to comply with code

requirements and to check for leaks that may have occurred during shipping and handling. This test should be

completed under the supervision of and witnessed by an Authorized Inspector who should represent the State or

municipality having jurisdiction or the insurance company covering the installation. At the option of this

inspector, the hydrostatic test may be at 1½ times the design pressure of the equipment, or at a pressure slightly

less than the setting of the lowest safety valve. The latter test will avoid the necessity of blanking or gagging of

safety valves, removing piping and plugging various pipe openings, removing controls and gage glasses, etc

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The boiler and process lines must be completely vented in order to fill them with water. The following is a

recommended procedure for hydraulic testing:

1. Open the steam drum vent valve and gag the safety valves in accordance with safety valve manufacturer's

recommendations. In lieu of gagging, the safety valves may be removed and replaced with test plugs or blind

flanges.

2. Open the vents on the interconnecting piping. Close steam outlet valve.

3. Isolate pressure switches, gauge glasses or control components that are not intended to be subjected to a

hydrostatic test.

4. Fill the system with treated water in accordance with recommendations from the Clients water treatment

consultant. The test water temperature range must be 70°F minimum to 120°F maximum (100°F to 120°F water

temperature is preferred). Care should be taken so that all air is vented while the equipment is being filled. Fill

the equipment until water overflows the vent, then close the vent.

5. Apply pressure slowly. The recommended rate of pressure increase is less than 50 psi per minute. Proper

control must be maintained so that pressure does not exceed the desired setting of the local steam boiler

inspecting agency. Do not subject any pressure part to more than 1½ times the design pressure rating of any

component.

6. When the proper test pressure is reached, inspection in accordance with the test objective can begin. Examine

the system for any leaks. If no leaks are visible, hold the system in a pressurized static condition for a period

long enough to satisfy the code requirement.

7. Upon completion of the test, release pressure slowly through a small drain valve. Then fully open vents and

drains when the pressure drops to 20 psig. Particular

Care must be given to make sure that parts not normally containing water during Operations are drained free of

water. The system should be drained fully after hydrostatic testing, to prevent freezing, if the unit is installed in

a cold weather area, and to minimize corrosion of the metal surfaces.

8. If temporary handhole or manway gaskets were used for the test, they should be replaced with regular service

gaskets before readying the unit for operation. Gaskets should never be reused. Replace gage glass if necessary

and make sure that the gauge cocks are open. Remove all blanks or gags from safety valves and install relief

valves, if removed.

9. Additional inspection at this time by the Authorized inspector will determine whether the installation

including piping arrangements, valve gauges and controls and other equipment on the unit meets Code and/or

other jurisdictional requirements.

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Discussion

In this experiment we have been studied in great details of a fire tube boiler. Boiler is one of the most important

appliances for any industry. It is also an essential part of a power generation plant. The boiler or steam boiler is

equipment used for producing steam. The American Society of Mechanical Engineers (ASME) gives the

following definition of the steam generating unit:

“A combination of apparatus for producing, furnishing or recovering heat together with the apparatus for

transferring the heat so made available to the fluid being heated and vaporized”

A steam boiler is a closed vessel in which steam is produced from water by the application of heat. Heat is

usually produced due to the combustion of fuel in a furnace. The hot gas generated in a furnace is called furnace

gas. It is also known as flue gas as it passes through a pipe called the flue.

The volume occupied by the water in the boiler drum is called the water space and the space above the water

surface is known as steam space. Heating surface is that part of the boiler which is exposed to hot gases on one

side and water or steam on the other.

The steam produced in a boiler is used for

► Power Generation: Mechanical work or electrical power may be generated by expanding steam in the

steam engine or steam turbine.

► Heating: The steam is utilized for heating the residential and industrial buildings in cold weather and

for producing hot waters for hot water supply.

► Utilization of steam for industrial processes such as for sizing and bleaching etc. in textile industries.

Steam is also used in many other industries like sugar mills and chemical industries.

The boiler we studied in our Boiler Laboratory is essentially of a fire tube type boiler. It can also be classified

by the number of passes present in the boiler. The boiler, we studied is a three pass boiler having five tube in

each pass.

Fig. 17: Three Pass Principle of Boiler

The characteristics of a water tube boiler are discussed below:

o The hot gases from the furnaces pass through the tubes which are surrounded by water

o For a given power, the floor area required for the generation of steam is more than a water tube boiler

o Overall efficiency with economizer is up to 75%

o The transportation and erection is difficult

o It can cope reasonably with sudden increase in load but for a shorter period

o The water does not circulate in a definite direction

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o The operating cost is less

o The bursting chances are less

o The bursting produces greater risk to the property

o It is not suitable for large plant

The boiler, steam boiler, is one of the most important and essential part of equipment for any industrial process.

So, the knowledge of a boiler, in many respects, is very important. In this experiment we have learnt

accessories, mountings and also the operating procedures of a steam boiler. These knowledge will certainly help

in our professional life.

References:

1. Operations Manual, Steam Boiler, Philipp Loos GmbH

2. Boiler’s Manual, Philipp Loos GmbH

3. Dampfkessel, Loos, Bosch Group

4. Khurmi, R., S., Gupta, J., K., “Thermal Engineering”, 2006

5. Roy, K., P., “Elements of Heat Engines”, 1988

6. Vasandani, V., P., Kumar, D., S., “Heat Engineering”, 1995