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Research Article
THERMODYNAMIC ANALYSIS OF GANDHINAGAR
THERMAL POWER STATIONaProf. Alpesh V. Mehta*,bMr.Manish Maisuria, cMr.Mahashi Patel
Address for Correspondence
aAsst.Prefessor, G.H.Patel College Of Engineering And Technology, V.V.Nagarb,c
Students, G.H.Patel College Of Engineering And Technology,
[email protected],[email protected]
ABSTRACT
Energy and environment both are core for human comfort and peripheral for global survival now-a-days.
Modern economic pressure demands re-examination of the existing power generating plants for various options
for their techno-economical and efficient operations. This paper presents a detailed energy study based on the
first law analysis of the coal fired thermal power station namely Gandhinagar Thermal Power Station (GTPS).In this paper, a detailed energy study is shown for 210MW, Unit-4 of coal fired thermal power plant atGandhinagar Thermal Power Station (GTPS) to evaluate the plant and subsystem{feed water heaters(high
pressure and low pressure),etc} efficiencies. The boiler efficiency is calculated using indirect method after
estimating the various heat losses in the boilers. It highlights the positive features of this power plant as well as
brings out areas where further detailing and corrective measures are required for efficient utilization of the
sources available in the plant. Energy analysis is used to evaluate the overall thermal efficiency of the plant bycomputing the individual efficiency of the boiler (86.84%), steam turbine (43.5%), and generator (98%). The
overall efficiency of the plant (Unit-4) appears to be 37.01%.
KEY WORDS: Power generating plant, boiler, steam turbine, first law analysis.
1. INTRODUCTION
Power consumption per capital indicates the
industrial and economical growth of the
country and thereby represents the living
standard of the people of the same. The whole
world is in grip of electrical energy crisis and
pollution due to the power plants. The overall
power scene in India shows heavy shortages in
almost all the states. The government of India
has advocated Energy for all by the year
2012. Even though the Indian power sector is
at the forth place of the power production in
the world. The significant role of thermal
power station in Indias power generation
scenario can be gauged from the truth that they
supply about 66% of the total installed
capacity. Some of the available options are to
evaluate overall and individual component
efficiencies and to identify and assess
thermodynamic losses, thereby improving the
energy efficiencies of the system. Energy like
many other commodities should be evaluated
and the conventional energy analysis, based on
the first law of thermodynamics, evaluates
energy mainly on the quality.
Very careful analysis of the problem and
proper planning and execution is necessary to
solve the power crisis in India. So in this
paper, a detailed energy study is shown for
210MW, Unit-4 of coal fired thermal power
plant at Gandhinagar Thermal Power Station
(GTPS) to evaluate the plant and
subsystem{feed water heaters(high pressure
and low pressure),etc} efficiencies. The first
law analysis is used to assess the overall plant
performance. In operation and maintenance of
a power plant, the feed water heaters are
practically neglected compared with other
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components. Efficient and reliable service
from feed water heaters requires more care in
both operations and maintenance than care that
has been taken for nay other components of
power plant.
1.1Literature Review
Power plant is an assembly of a system, where
electricity is being generated by using
different mechanical and electrical equipment
and different processes. The basic components
of the plants are steam generator {Steam
generator is a complex integration of boiler
along-with accessories (furnace, super heater,
re-heater, boiler, economizer & air pre-heater
etc.) and various auxiliaries such as pulverizer,
burners, fans, stokers, dust collector and
precipitators, ash-handling equipment &
chimney.}, steam turbine, steam condenser
and feed water pump.
1.2The Principle types of Power Plants
The Principle types of Power Plants are as
below:
1. Steam Plants using coal, oil or nuclear
fission.
2. Internal combustion engine Plant.
3. Gas turbine Plant.
4.
Hydroelectric Plant.In steam power plant coal or oil is used as a
fuel for generation of high pressure and high
temperature steam. In the boilers / the steam
generators steam is produced and then utilised
to drive the steam turbines which are coupled
to generator to get electricity. The furnace may
employee grate burning of solid fuel,
pulverised fuel in burner or furnace oil in oil
burners. The Plant may content server with
saving devices such as super-heaters,
economiser, air preheater, reheaters, steam
traps etc. which effect on overall efficiency of
coal or oil fired thermal power plants. The
equipment for firing of fuel into furnace and
handling of fuel and ash are other important
aspects of plant study. One should also focus
on auxiliary equipments and need of
condensing exhausting steam, water treatment,
water cooling, dust removal, Draft control, etc.
In Nuclear stations heat is produce in a reactor
which replaces the convectional boiler.
1.3 Classification of steam generator or
boiler
Classification of steam generator or boilers
can be made in different ways. From the point
of view of application, they can be;
a) Utility steam generator ,b) Industrial steam
generator, c)Marine steam generator.
1.3.1 Utility steam generator
Utility steam generator is those used by
utilities for electric-power generating plants.
Depending on whether the pressure of steam is
below or above the critical pressure (221.2
bar), that can be either subcritical or
supercritical units. The subcritical steam
generators are water tube drum type and theyusually operate at between 130-180bar steam
pressure. The supercritical steam generators
are drum less once-through tube and operate at
240 bar pressure. Majority of the utility steam
generators are of the 170-180 bar water tube-
drum variety, which produce superheated at
about 540-5800C with one or two stages of
reheating.
1.3.2 Industrial steam generators
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Industrial steam generators are those used in
process industries like sugar, paper, and jute
and so on, and institution like hospital,
commercial and residential building
complexes. They are smaller in size. They
operate pressures ranging 5 to 105 bar with
steam capacities up to 125 kg/s.
1.3.3 Marine steam generators
Marine steam generators are used in many
marine ships and ocean liners driven by steam
turbines. They are usually oil-fire. They
produce superheated steam at about 60-65 bar
and 5400C.
1.3About power plant
The Rankine cycle is the basic cycle for
operation of steam power plant. Thermal
power station means a factory for conversion
of chemical energy of fuel into electrical
energy. Coal fired units produce electricity by
the burning coal in a boiler to heat water to
produce steam. The steam, at tremendous
pressure, flow into a turbine, which rotates
armature of generator to produce the
electricity. The steam is condensate and
converted back into water, and the returned to
the boiler to complete the closed cycle.
The basic requirements of thermal power plantare:
Raw material should be available
continuously, generated energy should be
utilized properly and qualified staff should be
available as per requirement and proper
provision of removal of ash and other by-
products during power generation.
Basic points to be considered during site
selection are as follows:
Type and cost of the land, availability of fuel,
transportation facility, service water facility,
availability of staff, near to the load centre, ash
disposal facility, away from residential area.
2. About Gandhinagar Power Plant
Gujarat State Electricity Corporation Limited
(GSECL) was incorporated in August 1993
and is registered under the Companies Act,
1956 with the objectives to initiate a process
of restructuring of Power Sector and to
mobilize resources from the market for adding
to the generating capacity of the State and
improving the quality and cost of existing
generation. The Company was promoted by
erstwhile Gujarat Electricity Board (GEB) as it
is wholly owned subsidiary in the context of
liberalization and as a part of efforts towards
restructuring of the Power Sector. The
operations of GSECL were limited to Power
Stations units Gandhinagar Thermal Power
Station, Wanakbori Thermal Power Station,
Utran GBPS & Dhuvaran Combined Cycle
Power Plant (CCPP) till the complete
unbundling of erstwhile GEB was undertaken
upto 31st March 2005. The Gandhinagar
Thermal Power Station is located at
Gandhinagar, the capital of Gujarat nearAhmedabad. It is a Coal Based Power
Station. It is on the bank of Sabarmati River.
There are two units of 120 MW each (Unit no.
1 & 2), three units of 210 MW each (Unit no.
3, 4 & 5) with a total installed capacity of 870
MW. All the above units are of BHEL make.
Commissioning dates of unit no. 1 to 5 are
13.03.1977, 10.04.1977, 20.03.1990,
20.07.1991 and 17.03.1998 respectively.
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Based on the data available in table 1, table 2
and table 3 for Gandhinagar Thermal Power
Station, we have done a) Energy analysis, b)
Boiler losses calculations, c) Turbine
efficiency, and d) Effectiveness of heaters.
Table 1: Boiler Specifications
Unit-3 &4 Unit-5
Actual value
Particular
Design
valueUnit-3 Unit-4
Design value Actual
value
Load(MW) 210 150 180 210 210
Type Radiant Reheat, Natural
Circulation,
Radiant Reheat, Natural
Circulation,
Capacity(T/hr) 690 480 520 690 662
Feed water temp(0C) 247 165 232 245.6 241
Steam at boiler outlet(Kg/cm2)
SH 155 135 153 155 147.3
RH 38.1 26 33 36.11 34.14
Steam temp at Boiler outlet(0C)
SH 540 540 540 540 541
RH 540 530 540 540 542
Fuel used coal coal
Efficiency (%) 85.77 82.91 81.79 85.77 81.83
Table 2: Turbine specification
Unit-3 &4 Unit-5
Actual value
Particular
Design
value Unit-3 Unit-4
Design
value
Actual value
Capacity(MW) 2x 210MW 1x 210MW
No. of stages of cylinder 690 480 520 690 662
HP turbine 25 25
IP turbine 20+20 20+20
LP turbine 8+8 8+8
Critical Speed 600 to 300
Exhaust temp(0C) 45-55 54 52 44-57 40.2
Efficiency 43.24 37.22 47.71 43.24 41.37
Table 3: Coal specification
Particular Unit-3 &4 Unit-5
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Actual valueDesign
value Unit-3 Unit-4
Design
value
Actual value
Type Bituminous Bituminous
Caloric value(Kcal/Kg) 3800 3000Ash content (%) 35 42
Volatile matter (%) 23 23
Sulphur content (%) 1 0.5
Quality required (MT/hr) 139.5 94.63 109.5 177 125.77
Storage capacity (MT) 300000 222003
3. Result analysis and discussion
Energy is conserved in every device or process
i.e. in balance; it can be neither produced nor
consumed. Energy entering with fuel,
electricity, flowing streams of matter, and so
on can be accounted for in the products and by
products. Energy cannot be destroyed. Energy
analysis is based on the first law of
thermodynamics and it is the measured of
quality only.
The data for boiler operation and turbine
operation of unit-4 of GTPS at full load were
observed and relevant parameters have been
estimated.
Using these data and compiled value, First law
analysis (energy analysis) is carried out for the
given thermal power plant.
The performance of a plant is evaluated by
calculating the overall efficiency of unit by
using the individual efficiencies of boiler,
turbine and generator.
The 210 MW units taken for analysis is to
consider being having the following system:
SYSTEM 1 : Boiler system.
SYSTEM 2 : Steam cycle.
SYSTEM 3 : Cooling water system.
SYSTEM 1 (Boiler system) consists of the
following components and is shown in
figure1; Combustor, Heat exchangers.
Figure 1 Folw of fluids on boiler
SYSTEM 2 (Steam cycle) consists of the
following components and is shown in
figure2; Turbine, Condenser(C), Feed Water
Heater (FWH), Pump (P)
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SYSTEM 3 (Cooling Water System) consists
of the following components; Circulating
water pumps, Fans.
The performance of a plant is evaluated bycalculating the individual efficiencies of the
boiler, turbine and generator. The efficiency of
the boiler is evaluated by indirect method. In
the indirect method the input is assumed to be
100% and the various losses encountered in
the boiler are calculated and subtracted from
100. The various losses in the boiler are;
Energy losses due to the exhaust gases ,
Energy losses due to unburn carbon ,Energy
losses due to incomplete combustion Energy
losses due to moisture in fuel ,Energy losses
due to hydrogen in fuel , Energy losses due to
moisture coming with air supplied ,Energylosses due to ash and slag, Energy losses due
to radiation loss.
The boiler efficiency is calculated, using the
indirect method after estimating the various
heat losses in the boiler. Table 4 represent the
reading taken for the boiler and coal mill.
Based on the data available in table 4 , the
calculations are made for boiler losses and the
results are shown in table 5.
Figure 2: Steam cycle
Figure 3: Energy Balance of Steam Generator
Table 4: Data for boiler and coal mills
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Content Unit Value
Load MW 210.36
Coal flow rate T/hr 140.35
Steam flow rate T/hr 593.37FW inlet temp.
0C 232
Mills
Mill power KW 900
Total air flow T/hr 690.2
Relative humidity % 60.42
Absolute humidity (Kg water/kg dry air) Kg 0.0195
Dry bulb temp.0C 30
Wet bulb temp. 0C 27
FD fan discharge temp0C 37.9
APH inlet gas temp0C 299
APH outlet gas temp0C 157.9
Oxygen in APH inlet % 4
Oxygen in APH outlet % 4.3
CO2in APH inlet % 14.8
CO2in APH outlet % 14.5
Nitrogen in APH inlet % 14.5
Combustibles in bottom ash % 6.6
Combustibles in fly ash % 0.7
Table 5: Result obtained for boiler and coal mills
Types of losses KJ/kg %
Energy losses due to the exhaust gas(Q2) 2501.1 5.29
Energy losses due to unburn carbon(Q3) 250.98 0.52
Energy losses due to incomplete combustion. (Q4) 2209.2 4.64
Energy losses due to moisture in fuel. (Q5) 237.80 0.40
Energy losses due to hydrogen in fuel. (Q6) 143.0 0.29
Energy losses due to moisture coming with air supplied. (Q7) 601.48 1.21
Energy losses due to ash and slag. (Q8) 384.65 0.81
Total losses 6328.21 13.16
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Chart 1 Energy Balance of Steam Generator
From the chart1, it is clear that losses Energy
losses due to the exhaust gas are more
compared to all boiler losses. Which is
5.2%.the next highest is losses due to
incomplete combustion, which is 3.4%. The
lowest losses occur in boiler due to moisture in
air, which is 0.14%. Due to these energy losses
boiler efficiency is decrease 13.16%.
Table no 6 represent the data available for the turbine.
Content Parameter Unit Reading
Load L MW 210.36
Turbine inlet steam flow MS T/hr 593.37
Super heater steam pressure PSH Kg /cm2
149.36
Super heater steam temp. TSH0C 532.92
Hot Re-heater steam pressure PHRH Kg /cm2 35.09
Hot Re-heater steam temp THRH0C 534.81
Cold Re-heater steam pressure PCRH Kg /cm2 34.81
Cold Re-heater steam temp TCRH0C 335.45
Feed Water pressure before Economiser PFW Kg /cm2 174.66
Feed Water temp. before Economiser TFW0C 241.09
Enthalpy of super heater steam HS KJ/Kg 3549.97
Enthalpy of Hot Re-heater steam HHRH KJ/Kg 3561.4
Enthalpy of Cold Re-heater steam HCRH KJ/Kg 3104.1
Enthalpy of feed water HFW KJ/Kg 1009.4
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From the available data for the turbine,
following calculations are made to calculate
the turbine efficiency.
Turbine inlet steam flow = 593.37 T/hr =164.825 kg/s.
Heat input to turbine
= {turbine inlet steam flow X (SH enthalpy-
FW enthalpy)} +{HRH steam flow X (HRH
enthalpy CRH enthalpy)
= {164.825 X (3549.97 1009.4)} + {140.1 X
(3561.4 3104.1)}
= 482817.18 KJ/Kg
Turbine efficiency = power generation/ heat
input to turbine= {210.36 X 103/ 482817.18}
= 43.5%
Superheater temperature 532.920C and
pressure 149.36 Kg/cm2. That means that
quality of steam is rich. Reheater temperature
534.810C it is nearly superheater temperature
532.920C so, we can say that reheater is good
condition. Feed water temperature is 241.090C
it is nearby 2500C that is desirable. Due to
turbine losses, we get turbine efficiency is
very low which is 43.5%.
Generator efficiency is taken as 98%
So the overall efficiency
= (boiler efficiency X turbine efficiency X
generator efficiency)= (0.8684 X 0.435 X 0.98)
= 37.01%
Due to the turbine efficiency and boiler
efficiency, we get overall efficiency is
37.01%. It is very low.
Overall heat rate = (1 / overall efficiency)
= 2.701 KJ/S
The efficiency of the turbine is determined
estimating the net heat input to turbine and
electrical power plant from the generator in
terms of heat values. Thus turbine efficiency
obtained is 43.5%.
The generator efficiency is taken as 98%.
Then the overall efficiency is estimated as
37.01%.
The above results are shown in the table no 7
shown below:
Table .7 Different efficiencies of power plant Chart 2 Compression of Energy Efficiencies
Component Efficiency (%)
Boiler 86.84%
Turbine 43.5%
Generator 98.0%
Overall efficiency 37.01%
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Table 8: Represents the observation taken for the high pressure feed water heater (HPH)
cascaded backward and effectiveness of heaters to be found.
Contents Unit
Load MW 210.36FW flow t/hr 593.87
HPH 5 shell pressure Kg/cm2
36
HPH 6 shell pressure Kg/cm2 16
FW temperature HPH 5 IN0C 163.7
FW temperature HPH 5 OUT0C 200.7
FW temperature HPH 6 OUT 0C 244
Enthalpy of drain water from HPH 5 KJ/Kg 2757
Enthalpy of drain water from HPH 5 KJ/Kg 2598.62
Figure 4 Flow diagram of HP Heater
Effectiveness of heater
= (FW Temp rise)/ (Tsat tempTFW temp)
Effectiveness of HPH6 = (243-200.7)/(244.2-
200.7) =0.97
Effectiveness of HPH5= (200.7 163.7) /
(201.1 163.7) =0.98
Net heat grain to feed water and actual heat
gained by feed water is respectively 3600
KJ/Kg and 4131.17 KJ/Kg. That shows that
system is perfect. Effectiveness of the heater
HPH6 and HPH5 is 0.97 and 0.98 that is
nearly 100%. In general, the total losses =
13.16% , Boiler efficiency = 100 13.26 =
86.84%, Turbine efficiency = 43.5% ,HP
heater effectiveness HPH5 and HPH6 are 0.98
and 0.97.
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CONCLUSION
From the energy analysis made for the unit-4,
210MW of the GTPS the following
conclusion are drawn:. It is seen that boiler efficiency is
highest, which is 86.84% and the heat
losses are only 13.16%.
Out of all the boiler losses, the highest
heat losses 5.29% occurs due to the
exhaust gas.
The turbine efficiency is very less and
is estimated as 43.5% Because of the
several turbine losses like ; Losses in
regulating valve, Nozzle friction
losses , Blade friction losses , Disc
friction losses , Partial admission
losses , Gland leakage losses, Cary
over losses.
From the thermodynamic analysis
using first law of thermodynamics, we
can conclude that, energy analysis
evaluates the plant quantitatively. The
power plant overall efficiency is
37.01%.
The effectiveness of HP heater
working in good condition should
have an effectiveness of 0.85. The
performance of HPH6 and HPH5 are
in good conditions as their
effectiveness 0.97 and 0.98.
6. ACKNOWLEDGMENTS
We are very much thankful to peoples of
Gandhinagar thermal power plant for
providing sufficient data for plant. We are also
thankful to those who help directly or
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