calculation of lossess
TRANSCRIPT
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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.