calculation of lossess

7/28/2019 Calculation of Lossess

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Calculation of lossess

From the given cooling towerparameters,evaluate the following:

) Make up water requirement per day

) Evaporation loss

i) Blow down loss

Cooling water temperature : 37C

Outlet water temperature : 32 C

Drift losses : 0.1 %

No. of concentrating cycles : 3

Estimation of cooling tower losses:

a) Drift loss : 0.1%

b) Evaporation loss : Range (temp. difference, C) x 100/675

={(37-32)/675} x100=0.74%

c) Blow down loss : Evaporation loss/(No. of concentrating cycle-1)

={0.74/(3-1)}=0.37%

Total make up water requirement : 0.1 + 0.74 + 0.37 = 1.21%

Cooling water circulation rate : 1260 m3/h

Make up water requirement : 1260 x 0.0121 = 15.2 m3/h


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=364.8 m3/day

By using a ruggedized portable ultrasonic leak detector, Mr. Brian Thorp, PdM

Technician for Seminole Electric has been able to provide quick leak detection and

repair on an aging steam condenser, allowing the utility to provide maximum powerduring high demand periods.

In today's competitive electric power generation market attention must be given to

improving the condensers operating efficiency. Steam turbines cannot attain their

specified performance without an efficient condenser. Tube leaks that affect condenser

performance are critical. Most condenser tubes are designed to last at least 30 years

before replacement is required. Unfortunately, normal plant operation, changes in water

chemistry and other unforeseen circumstances often create a much shorter life for

tubes. Most condensers are overbuilt to allow for a certain percentage of tubes to be

plugged when a leak is detected.

When high sodium levels occur in the condensate, the water leaving the condenser

must be polished through resin exchange and a boiler blow down. When this happens,

cost is increased and the output of the power plant is reduced.

Ultrasonic Technology

Ultrasonic Leak detectors work like simple microphones that are sensitive to high

frequency sounds ranging from 20 kHz (a kHz or kilohertz is one thousand cycles per

second) to 100 kHz. To put that in perspective, most humans can hear up to 17-19 kHz.


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Using a sensitive piezoelectric crystal element as a sensor element, minute high

frequency sound waves excite or flex the crystal creating an electrical pulse that is

amplified and then heterodyned or translated into an audible frequency that the

technician can hear through a pair of noise reduction headphones.

As a leak passes from a high pressure to a low pressure, it creates turbulence. The

turbulence generates a high frequency sound component, which is detected by the

sensitive piezoelectric element, allowing the technician to quickly guide the instrument

to the loudest point in order to pinpoint the leak.

Several ultrasonic detectors use parabolic reflectors or elliptical reflectors to enhance

and concentrate the leak signal, which can be useful when detecting small leaks or

scanning at a great distance.

The effects of condenser tube leaks

The condenser is the largest heat exchanger in the condensate/feedwater network. It is

located under the steam turbine generator. When the steam exits the turbine, it is

passed over cool pipes that condense it back to liquid water. The purified water is

pumped back


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to the boiler to be heated to steam again. The same purified water is boiled and

condensed over and over.

Keeping the condenser tubes in the condenser from leaking river water used for cooling

into the steam or clean side of the condenser is a key to achieving optimum

performance of the plant. Fresh water leaking into the purified system can wreak havoc

by causing corrosion throughout the system and can significantly reduce operating life if

not rapidly addressed.

COAL DEMAND RATE FOR THERMAL POWER PLANT

The poorer the plants overall efficiency (n), the plant load factor (PLF) and the coal

quality being used, the higher will be the coal demand rate for Thermal Power

Generation.

The quality of coal is a function of its carbon content, which is appreciated to some

extent by volatile matter content (an inducing force) and depreciated by moisture

content and ash content (opposing forces) when analyzed on equilibrated basis (at 40degree C temperature and 60% Relative Humidity).


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The plant load factor (PLF) is the ratio of Average load and Maximum load on plant for a

particular period, say, an hour or a day or a month or a year. In many cases, the

maximum demand is less than the capacity of plant (designated as 50 MW or 110 MW

or 210 MW or 500MW unit).

The plants overall efficiency (n) is the ratio of theoretical heat rate (output 860 K.Cal.)

and actual heat rate(input- GCV in K.Cal.) required for generation of 1 unit of

power(Kwh). It depends on many variables and is usually around 27%. The theoretical

heat rate can be calculated as follows:

1 Kwh = 1000 x 1 x 60 x 60 Joule/Second

= 3.6 x 1,000,000 Joule

= 3.6 x 238.8 K.Cal (1 Mega Joule =238.8K.Cal)

= 860 K.Cal.

Input = 1 (in million K.Cal/hr.)= a+bL+cL2+dL3)

Where L = Output or load in KWH and a, b, c and d are constants.

Heat Rate = I/L = a/L+b+cL+dL2

Plants overall = L/1.

efficiency (n)

Thus, there is a very complex calculation of exact heat input required and hence the

exact specific consumption of coal. However, a hypothetical estimate of coal demand

rate for Thermal Power can be arrived at for varying specific consumption of coal and

PLF on pro-rata basis as given in the table below.


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COAL DEMAND RATE in T/100 MW/DAY

SPECIFIC COAL CONSUMPTION IN KG/KWH

PLF %

Sp. Con. 0.6 0.65 0.70 0.75 0.80 0.85 0.90

50

55

60

720

792

864

780

858

936

840

924

1008

900

990

1080

960

1056

1152

1020

1122

1224

1080

1188

129665 936 1014 1092 1170 1248 1326 1404

70

75

1008

1080

1092

1170

1176

1260

1260

1350

1344

1440

1428

1530

1512

1620

80 1152 1248 1344 1440 1536 1632 1728

85

90

95

100

1224

1296

1368

1440

1326

1404

1482

1560

1428

1512

1596

1680

1530

1620

1710

1800

1632

1728

1824

1920

1734

1836

1938

2040

1836

1944

2052

2160

For Grade E Coal of

UHV=3361 K.Cal/Kg

GCV =4400 K.Cal/Kg

For Grade F Coal of

UHV=2401K.Cal/Kg

GCV=3800 K.Cal. /kg

For Grade G Coal of

UHV =1301 K.Cal. /Kg

32.6 30.1 27.9

32.3

26.1

30.2

24.4

28.3

23.0

26.6

33.7

21.7

25.1

31.8


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GCV=3000 K.Cal/Kg.

Required Overall efficiency (n) of Thermal Power Plant in

%

From the above table, it may be seen that the coal demand rate remains the same even

if the quality of coal goes down provided the plants overall efficiency is improvedcorrespondingly (say, by about 3% - 4% for switching over from Grade E to F and about

6% - 7% for F to G and Vice Versa.

However, for referable gnomon, it may be worthwhile to remember that while the day-to-

day demand of coal at 80% PLF may be around 1500T/day/100 MW the annual

demand at 62.5%PLF (National average of 1996-97 upto Dec.96) will be roughly 4

million T/1000MW for E Grade of coal at about 27% plant efficiency).

Utilisation of installed generating Capacity


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With the introduction of new design of generating units, certain difficulties arose in their

efficient operation and maintenance. The availability of coal in the country is such that

the higher grades of coal, which have higher calorific value, have been exhausted and

progressively lower grades of coal are being made available for electricity generation in

the power stations. This had resulted into operational problems with the boilers

designed for higher grades of coal and also put more pressure on coal handling plants

etc. As a result of these technical and managerial problems, the utilisation level of coal

based power stations in the country declined in the late 1970s and early 1980

Besides quantity, the quality of Indian coal has been a major problem and concern for

the power supply industry. With ash content of coals being in the range of 30-50%, the

beneficiation of coal assumes special significance. Establishment of washeries

therefore assumes a great importance and country has t o address this problem

seriously.

Energy extract ion from coal

The two fundamental processes for extraction of energy from coal are (i) Direct Solid

Combustion such as conventional Pulverised Coal (PC) Combustion or the emerging

Fluidised Bed Combustion (FBC) and (ii) Indirect combustion through Coal Gasification

followed by coal gas combustion. Fluidised Bed Combustor is a three-in-one

device characterised by highly desirable features of multi-fuel capability,

pollution (SO2 and Nox) control, and energy conservation. All the four members of

this family, namely Atmospheric Fluidised Bed Combustor (AFBC), Circulating Fluidised

Bed Combustor (CFBC), Pressurised Fluidised Bed Combustor (PFBC) andPressurised Circulating Fluidised Bed Combustor (PCFBC) have the potential for clean

power generation. Additionally, PFBC and PCFCB systems operating in a combined

cycle mode (Rankine and Brayton) have the potential for overall plant efficiencies of the

order of 40-45% compared to 33-37% efficiencies offered by power plants based on

Conventional PC firing, AFBC and CFBC operating on a single (Rankine) cycle.


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EFFICIENCY (STATION HEAT RATE) OF COAL/LIGNITE BASED

THERMAL POWER STATION

Station Heat Rate (SHR) is an important factor to assess the efficiency of a thermal

power station. Efficiency of TPS is a function of station heat rate and it is inversely

proportional to SHR. If SHR reduces, efficiency increase, resulting in fuel saving.

Station heat rate improvement also helps in reducing pollution from TPS. On

monitoring, the data of station heat rate parameters had been received from, 54 Nos.

Thermal Power Stations during 2000-01. The data of operating station heat rate

parameters so received have been compiled & analysed for instituting an incentive

scheme on Improved Station Heat Rate (SHR) and have been compared with design

SHR of the above thermal power station, for the year 2000-01 . The analysis of station

heat rate so carried out has been highlighted in Annexures- I to V. The analysis of

Station Heat parameters as given below has been carried out broadly in two categories

of the stations with SHR variation between (a) 0-10% and (b) >10%. The stations under

0-10% categories have been considered as efficient and greater than 10% as poorly

operating. All the stations analysed have used coal as primary fuel to generate power

and oil as secondary fuel for starting purposes.. The analysis has been carried out on

the station basis. Stations may comprise of any size of units.

The following assumptions have been taken for the analysis of station heat rate

ASSUMPTIONS:-

1. Analysis of only those power stations has been carried out where data of at least 9

months operation was available.


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2. Design station heat rate has been evaluated based on design data of turbine heat

rate and boiler efficiency as submitted by TPS and compared with operating

station heat.

3. The data of various parameters of station heat rate such as fuels calorific value

generation, fuel consumption etc. have been taken from TPS authorities / SEBs

/utilities on monthly basis.

4. Actual oil consumption is converted into equivalent coal consumption and added to

actual coal consumption to make it as effective coal for calculating heat rate w.r.t.

coal GVC on monthly basis as oil consumption is less compared to coal.

Weighted average of coal GVC and oil GCV have been computed yearly for

calculating heat rate for the year.

5. Oil GCV has been assumed as 10,000 Kcal/1 in case any station has not submitted

the data of oil GVC.

6. All India figures are indicated on weighted average basis with respect to generation of

the year for available data for the year 2000-01.

3.0 SALIENT FEATURES OF THE GROSS STATION HEAT RATE DATA ANALYSIS:

3.1 The gross Station Heat Rate (SHR) deviation of operating SHR with respect

to design SHR for the year 2000-01 given at Annexture-I & II and main

highlights of outcomes for the years 2000-01 is given below.


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a) ALL INDIA STATION HEAT RATE

Year Capacity(M

W)

Design

SHR

(Kcal/kwh)

Operating

SHR

(Kcal/Kwh)

% deviation %

Improveme

nt over

2000-01

1999-00 - 2422.51 2914 20.28 -

2000-01 33060.5 2408.34 2763 14.71 -

Above table indicates that the estimated weighted average operation SHR at All India

basis are as 2914 Kcal/Kwh, and 2763 Kcal/Kwh for the year 1999-2000 and 2000-01

respectively. This analysis indicates that there is significant improvement in operating

station heat rate during 2000-01 with respect to 1999-00. Similar is the case with also

SHR variation for 1999-2000 and 2000-01 w.r.t. design heat rate which would be

evident from Chart- ALL INDIA STATION HEAT RATE;

(b) REGION WISE STATION HEAT RATE

Region Years Design SHR Operating

SHR

% Deviation %Improvem

ent w.r.t.

preceding

year

Northern 2000-2001 2483.18 2972.27 19.7 -

Southern 2000-2001 2434.38 2722.36 11.83 -

Western 2000-2001 2357.02 2612.17 10.83 -

Eastern 2000-2001 2381.75 3306.02 38.81 -

The above table indicates that the OPSHR level of Northern Region as 2972.27

K.Cal/Kwh the years 2000-2001. The OPSHR of Southern Region indicated as 2722.36


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Kcal/Kwh for the years 2000-01. Western Region and Eastern Region do not show any

improvement in OPSHR

c) The number of efficient power stations during the years 2000-01 whose SHR

deviation w.r.t. design heat rate in the range of two categories (0-5%, 5-10%) are given

in the following table.Details are given at Annexure-II.

Total station analysed 54

No. of stations in the range of SHR deviation (0-5%) 7

No. of stations in the range of SHR deviation (5-10%) 9

Total efficient stations SI. No.(2+3) in the range of (0-10%) 16

No. of stations with SHR deviation more than 10% 38

d) As per Annexure-I & II, it is observed that, Ib Valley (OPGC), Sikka (RPL),

Bhusawal (MSEB) have been assessed as best station for 2000-2001 with SHR

deviations 0.34%, 1.65% and 3.41% respectively.

e) Barauni, Nellore, Chandrapura (DVC), Paricha and Santaldih (WBSEB) have been

assessed as poorly performing TPS with SHR deviation more than 60% and up to

103%.

f) About 40 stations at an average of last three years are operating at very poor SHR

having variations in SHR greater than 10% and up to 100%. These stations need proper

monitoring and Energy Audit implementation.

g) Efficiency of all Stations is highlighted in Annexure-IV , it indicates that the efficiency

of Thermal Power Stations varies from 19% to 37% for the Year, 2000-2001. Dahanu

(BSES), Chandrapur (MSEB). Rayalseema & Ib valley are some of the stations which

have recorded their efficiency in the range of 35% to 37%.

LEVEL OF IMPROVEMENT


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Level of Improvement in Station Heat Rate for the year 1999-00 & 2000-

2001 with respect to preceding year is given at Annexure-III.

The outcomes are given below:

4.1 The Station Heat Rate is improving consistently form the year 2000-01

with respect to preceding year including efficient Station as well as poor

Station. The level of improvement varies form 0.03% to 20.5% over the

preceding year. The numbers of Stations showing improvement are given

in the following table:

Year No. of Stations No. of Improved Level of % of improved

Analysed Stations Improvement(%) Stations

2000-01 54 27 0.12% - 14.4% 50%

UNIT CAPACITY GROUPWISE ANALYSIS

Annexure-V indicates that

5.1 The operating heat rate of the 250 MW group stations is 2313

Kcal/kWh for the year 2000-2001

5.2 The operating station heat rate of the 200/210 MW group stations is as

2678 Kcal/kWh for the year 2001-01.

5.3 The operating station heat rate of67.5 MW group stations are as 3243

Kcal/kWh for the year 2000-01 .


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5.4 The operating station heat rate of 62.5 Mw group stations are as

3050.48 Kcal/kWh for the year 2000-01.

5.5 The operating stations heat rate of (30-140) MW combination group

stations are as 3562 Kcal/kWh for the year 2000-01 .

5.6 There is no significant improvement in operating station heat rate of

the group of 250MW, 120MW, 110MW, 60MW, 55MW, (30-500)

MW combination and 30 MW.


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MAJOR FACTORS AFFECTING HEAT RATE

IT SHOULD BE KNOWN

Under normal circumstances the system efficiency of a power plant may be improved

only by 0.5% to 1% through additional energy efficiency measure.

There are success stories and reports about power plants in India that reduced Gross

Heat Rate i.e. specific energy consumption per kWh generated, by 20% within 1 year.

It is true that under normal circumstances, the system efficiency of a power plant may

be improved only by 0.5 % to 1%, as the overall power plant efficiency calculations


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includes the losses in the condenser, which is maximum for a steam cycle (or combined

cycle) power plant, and mostly this system operates up to the expectation and nothing

much can be done, if already the power plant has a good maintenance management

system. The Turbine and Generator efficiency cannot be increased much. So the

efficiency gain comes from the different measures like reducing the boiler losses by

taking various actions in this regard.

Gross Unit Heat Rate=

Gross Turbin e Heat Rate

Boi lerEff ic iency

Heat Rate depends on a lot of factors, including the boiler efficiency. It not only

depends on the boiler efficiency but the other factors like Steam temperature, Flue

gas losses, Make up losses, Unburnt carbon losses, Fuel properties and overall

the ageing factor of the TURBINE.

If the conditions are already up to the maximum achievable limits, it may not be possible

to reduce the heat rate by as much as 20%. But if the plant is not being maintained up

to the mark and the operational parameters are not being maintained, it is certainly

possible to do by taking various measures.

First: Ageing of Turbine

The manufacturers guaranteed heat rate for equipment like Turbine also has a gradually

aging tendency. The ageing increases the heat rate. This heat rate deterioration is on

account of increase of clearances, disturbing of seals; deposits on turbine blade etc. To

arrest the deterioration and to bring back the heat rate to its design value the only

solution available is to take the turbine under Capital Overhaul.


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If flow path correction, re-adjustment of clearances between the stationary & moving

parts, refining if required will help in bringing back the heat rate to its original value. The

quality of work carried out during the overhaul, will play vital role in heat rate

improvement. The turbine heat rate is further affected by boiler efficiency to arrive at the

station heat rate. Similar exercise carried out at the boiler to improve efficiency will

resulting heat rate improvement in station. The equipment like turbine has a gradually

ageing tendency. The ageing increases the heat rate over a period of time.

As per BHEL, after the major overhauling, the turbine performance is considered

to be as good as new turbine and the ageing calculation again starts from the

commissioning of the turbine after the major overhaul.

Second:Parameters other than ageing of turbine, which affects

the Gross Heat Rate.

For a designed 250 MW unit, the approximation of the parameters can be as

follows:

1. Main Steam and Reheat temperature:

For every 1drop in Main Steam/ R H temperature than the designed value of 537 C,

causes a heat loss ofapprox 0.67 KCal/KWh,

2. Main Steam Pressure

For every 1 KG/CM2 drop in Main Steam Pressure at Turbine Inlet than the design

value i.e 150 KG/CM2 causes a heat loss of approx. 1.31 KCal/KWh

3. Flue gas temperature


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Forevery 1C rise in Flue gas temperature at Air Preheater outlet than the design

value i.e 134 C causes a heat loss of approx. 1.13 KCal/KWh

The Inputs required for Calculation of Heat Rate are:

Load (MW)

MS flow (Feed water flow to Eco.) ton/h

MS temperature Deg C

MS pressure kg/sq.cm

Reheater Flow ton/h

CRH temperature Deg C

CRH pressure kg/sq cm

Reheater temperature Deg C

Reheater Pressure kg/sq cm

FW Temp. at Eco.inlet Deg C

FW pre. Eco.inlet kg/sq.cm

Condenser vacuum

Auxiliary Power Consumption %


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MS/CRH/HRH/FW Enthalpy kJ/kg K

By using these inputs actual heat rate is calculated. If a power plant is maintaining

these parameters up to the maximum possible conditions and there is no scope

for further improvement, it may not be possible to improve the heat rate any further by

a larger extent, although the conditions are not always ideal and there is always a scope

for improvement somewhere or the other. If the power plant is old or not being

maintained properly or even the operational parameters are not being monitored

properly, surely the heat rate will go up for that plant. Then by proper monitoring and

control and by following a stringent maintenance management system, the parameters

can be improved to have a moving trend towards achieving the design value and this

will lead to improvement (reduction) in the heat rate for that plant. So it is not such that

heat rate cannot be reduced by 20%. The only thing is that it totally depends on the

operating condition of the plant and a will to achieve that. There are instances where not

only heat rate but also several other parameters have been improved by a large extent

by NTPC in the cases where it has taken over the plants from SEBs.

Third: Loading of the plant

This factor also plays a very important role in the gross unit heat rate of the power

station.Generally a power plant operates consistently at full or rated capacity, as it feeds

to the grid or sell the power to a larger base of consumer like State Electricity Boards

and the load variation is much less, unless otherwise necessary. So maintaining the

various parameters required for obtaining a good heat rate is not a much problem,

assuming the other conditions in the plant being good.

But in the plant like ours, the generation has to be varied as per the demand of the

consumers, which have a general tendency to fall down during night hours and

again move up in the morning hours, especially in the winter season. So to match the

demand, the power station has to back down the generation below the rated


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capacity of the plant (say our load goes down to 420-450 MW, whereas the rated

capacity is 500 MW) during night hours and again move up in the day time.. During this

process of variation of load, while going down or going up, the parameters affecting

the HEAT RATE cannot be kept at the constant level, as the demand have to be

matched with the generation at every point of time. So a variation occurs in the

various parameters affecting the Heat Rate. In this condition it is very difficult to control

the heat rate and keep it down to the expected level. As we have seen above the affect

of variation of some parameters on the heat rate, it can be easily understood that the

variation in these parameters is going to deteriorate the heat rate rather than to lower it.

So this factor cannot be neglected.

Fourth: Average load of the plant.

Also if the plant is run at a lower load than its rated capacity, not only the other

parameters will be affected but also the auxiliary power consumption of the plant

will be higher than the somewhat designed aux power consumption, which will

affect (increase) the sent out heat rate, the calculation and projection of which is still not

prevalent in case of Indian power plant. In foreign countries, this factor is very well taken

into account for the calculation and benchmarking purposes. So overall it can be seen

that Whether the HEAT RATE CAN BE IMPROVED & TO WHAT EXTENT , depends

totally on several factors related to the calculation of Heat Rate and not a single factor.

But yes, it is true that that still a lot of plants are there in India, whose heat rate can be

improved, if so desired by taking various actions, as is clear from the above explanation.

Fifth: Tripping of the Unit

Last but not the least is the condition of unit tripping. If by proper monitoring,

maintenance and other preventive measures, the trippings are brought to the

minimum, the heat rate improvement can be achieved. After the tripping, when the unit

is lighted up again, a loss called Start up loss come into picture, which increases the

heat rate as the quantum of loss increases. So if avoidable Unit trippings are arrested,


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this loss will become less and the improvement in Heat Rate can be achieved. Thus we

can see that the various conditions, under which there is deterioration in the Heat Rate,

can be possibly controlled to improve this important aspect of a power plant.

calculation of lossess

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