Exergetic analysis and evaluation of coal-fired supercritical thermal power plant and natural gas-fired combined cycle power plant

ORIGINAL PAPER

Exergetic analysis and evaluation of coal-fired supercriticalthermal power plant and natural gas-fired combined cycle powerplant

V. Siva Reddy • S. C. Kaushik • S. K. Tyagi

Received: 6 April 2013 / Accepted: 4 June 2013

� Springer-Verlag Berlin Heidelberg 2013

Abstract The present work has been undertaken for

energetic and exergetic analysis of coal-fired supercritical

thermal power plant and natural gas-fired combined cycle

power plant. Comparative analysis has been conducted for

the two contestant technologies. The key drivers of ener-

getic and exergetic efficiencies have been studied for each

of the major sub-system of two contestant technologies.

Overall energetic and exergetic efficiency of coal-fired

supercritical thermal power plant are found to be 43.48 and

42.89 %, respectively. Overall energetic and exergetic

efficiency of natural gas-fired combined cycle power plant

are 54.47 and 53.93 %, respectively. The major energetic

power loss has been found in the condenser for coal-fired

supercritical thermal power plant. On the other hand, the

major energetic power loss has been found in both the

condenser and heat recovery steam generator for gas-fired

combined cycle thermal power plant. The exergetic anal-

ysis shows that boiler field is the main source of exergetic

power loss in coal-fired supercritical thermal power plant

and combustion chamber in the gas-fired combined cycle

thermal power plant. It is concluded that natural gas-fired

combined cycle power plant is better from energetic and

exergetic efficiency point of view. These results will be

useful to all involved in the improvement of the design of

the existing and future power plants.

Keywords Thermal power plant � Energetic efficiency �Exergetic efficiency � Supercritical �Heat recovery steam generator

Abbreviations

B Boiler

BFP Boiler feed water pump

C Air compressor

Con Condenser

Com Combustion

CC Combustion chamber

CEP Condensate extract pump

D Deaerator

EXP Expansion valve

f Fuel

FWH Feed water heater

GT Gas turbine

gen Generation

heat High temperature heat exchanger

HPH High pressure feed water heater

HPT High pressure turbine

HFP High pressure feed water pump

HRSG Heat recovery steam generator

IPT Intermediate pressure turbine

LPT Low pressure turbine

LPH Low pressure feed water heater

LFP Low pressure feed water pump

p Combustion products

V. Siva Reddy (&)

Sardar Patel Renewable Energy Research Institute, Vallabh

Vidhyanagar 388 120, Gujarat, India

e-mail: [email protected]

S. C. Kaushik

Centre for Energy Studies, Indian Institute of Technology Delhi,

Hauz Khas, New Delhi 110016, India

S. K. Tyagi

Sardar Swaran Singh National Institute of Renewable Energy,

Jalandhar-Kapurthala Road, Wadala Kalan, Kapurthala 144601,

Punjab, India

123

Clean Techn Environ Policy

DOI 10.1007/s10098-013-0647-x

Introduction

In this paper, a thermodynamic comparison of coal-fired

supercritical thermal power plant and natural gas-fired

combined cycle power plant is performed using energetic

and exergetic analyses. The comparisons are intended to

identify areas where the potential for performance

improvement is high. Currently, about 80 % of electricity

in the world is produced from fossil fuels (coal, petroleum,

fuel-oil, natural gas) fired thermal power plants (Hasan

et al. 2009). Supercritical coal-fired thermal power plants

that are cleaner, more efficient, and less costly than the

current coal-fired power plants. The efficiency of power

plants in developing countries is still around 32–35 %

lower heating value. Further improvement in efficiency can

be achieved by using supercritical steam conditions. Cur-

rent supercritical coal-fired power plants have efficiencies

around 45 %. Combined cycle power plants are currently

one of the most important options for the construction of

new generating capacity as well as for the replacement and

renovation of existing units. Current natural gas-fired

combined cycle power plant have efficiencies around 55 %

(Naterer et al. 2010).

Marousek et al. (2012) verified the economic advantage

of the upgraded steam explosion technology linked to the

biogas station at a commercial scale for straw methano-

genesis. New engineering and process optimization

developed over 472 trials led to the choice of a setup that

doubled the net present value of the investment. Marousek

(2013) was investigated the removal of hardly fermentable

ballast from the maize silage to reduce the retention times,

volumes of fermentors, and associated heating require-

ments. The technology was designed to run on the waste

heat from the flue gases (490 �C) at the cogeneration unit

linked to the 1 MW biogas station.

Performing exergetic and energetic analyses together

can give complete magnitudes, location, and causes of

irreversibilities/losses in the plants. It also provides more

significant assessment of the efficiency of the individual

components of the plant (Kaushik et al. 2011). Kotas

(1984) carried out detailed mass, energy, exergy balances

for a reference steam power plant and investigated

the effect of the most important process parameters on the

exergetic efficiency. Ameri et al. (2009) have done the

analysis based on effects of the load variations and ambient

temperature upon the performance of the power plant. He

estimated the exergy destruction and exergy loss of each

component of the thermal power plant.

Sengupta et al. (2007) determined the effect of regen-

eration on exergy efficiency by successively removing the

high pressure regenerative heaters out of operation. Siamak

et al. (2008) presented a design method based on pinch

technology and exergy analysis to reduce heat transfer

irreversibility of the feedwater heaters network in steam

power plants. Srinivas (2009) concentrated on improving

the performance of a triple-pressure combined cycle with a

deaerator location. Singh and Kaushik (2012) conducted a

parametric study for the plant under various operating

conditions, including different operating pressures, tem-

peratures, and flow rates, in order to determine the

parameters that maximize plant performance. Khaliq and

Kaushik (2004) presented a second law analysis of the

reheat combined Brayton/Rankine power cycle. Ahmet

et al. (2006) performed energy and exergy analysis of a

combined cycle power plant for the identification of the

potential for improving efficiency of the system. Reddy and

Mohamed (2007) performed exergy analysis of a natural

gas-fired combined cycle power generation unit to inves-

tigate the effect of the gas turbine inlet temperature and

pressure ratio on exergetic efficiency for the plant and

exergy destruction/losses for the components. Xiaojun and

Defu (2007) have been performed parametric analyses for

the combined cycle to evaluate the effects of several fac-

tors, such as the gas turbine inlet temperature, the con-

denser pressure, on the performance of the combined cycle

power plant. Srinivas et al. (2007) presented an analysis of

the gas cycle which is a topping cycle. They have sepa-

rately compared the effect of inter-cooling and reheating on

the performance of the combined cycle plant. Woudstra

et al. (2010) determined the cogeneration process, levels of

steam generation to reduce the heat transfer losses in the

heat recovery steam generator (HRSG) and the exergy loss

due to the exhaust of flue gas to the stack.

The manuscript presents detailed energetic and exergetic

analysis of coal-fired supercritical thermal power plant, and

natural gas-fired combined cycle power plant. Comparative

performance evaluation and component wise energetic and

energetic power loss are also presented here.

Energetic and exergetic analysis of power plants

In an open flow system there are three types of energy

transfer across the control surface namely work transfer,

heat transfer, and energy associated with mass transfer and/

or flow. The first law of thermodynamics or energy balance

for the steady flow process of an open system is given by

X_Qk þ _m hi þ

Czi

2þ gZi

� �¼ _m ho þ

Czo

2þ gZo

� �þ _W ;

ð1Þ

where Qk heat transfer to system from source at tempera-

ture Tk, and W is the net work developed by the system.

The other notations C is the bulk velocity of the working

V. Siva Reddy et al.

123

fluid, Z is the altitude of the stream above the sea level, and

g is the specific gravitational force.

The energetic or first law efficiency (gI) of a system and/

or system component is defined as the ratio of energy

output to the energy input to system/component, i.e.,

gI ¼Desired output energy

Input energy supplied: ð2Þ

Exergy of steady flow stream of matter is the sum of kinetic,

potential, and physical exergy. The kinetic and potential

energy are almost equivalent to exergy. The physical specific

exergy exi and exo depends on initial state of matter and

environmental state. Exergetic analysis is a useful method; to

complement but not to replace energy analysis.

The exergy flow for steady flow process of an open

system is given by

X1� Ta

Tk

� �_Qk þ

X

in

_m� exi ¼ _ExW þX

out

_m� exo þ _I

ð3Þ_Ex ¼ _m½ðh0 � h0

aÞ � Taðs� saÞ�

h0 ¼ hþ C2

2þ gZ

_I ¼ Ta_Sgen

_ExW is useful work done on/by system, _I is irreversibility

of process and h0 is the methalpy as summation of

enthalpy, kinetic energy, and potential energy, Ta is

ambient temperature.

The exergetic or second law efficiency (gII) is defined as

gII ¼Actual thermal efficiency

Maximum possible ðreversibleÞthermal efficiency

¼ Exergy output

Exergy input

ð4Þ

The key component of exergetic analysis of coal-fired

supercritical thermal power plant and natural gas-fired

combined cycle power plant has been explained in Siva

Reddy et al. (2012, 2013).

Results and discussion

A computational model was developed for carrying out the

energetic and exergetic analysis of the system using

Engineering Equation Solver (EES) software (Klein and

Alvarado 2011).

(A) The following parameters have been used during the

coal-fired supercritical thermal power plant analysis:

• Atmospheric condition is taken as the 299 K and

1.0 bar.

• Combustion excess air for complete combustion:

20 %.

353629

10

Coal

Air

5

C

LPH1

LPH2LPH3HPH3

HPH2

HPH1

32

1516

3020

22

28

24

6 11

8

3 7

14

1

4

34

25

9

21

23

19 18

CEP

BFP

26

27

39

13

31

3738

2

B

EXP1

EXP2

Ash

b

f

G

Deaerator17

12

HPH4LPH4

Turbo Pump

P1P2

a

LPTIPTHPT

33

40

Fig. 1 Schematic view of coal-fired supercritical thermal power plant

Exergetic analysis and evaluation

123

• The inlet condition for high pressure steam

turbine is taken as 300 bar and 863 K.

• The condenser pressure is assumed to be

0.05 bar.

• Isentropic efficiency of turbine is taken as 90 %.

• The energy rejection in the condenser is treated as

a loss.

• Generator efficiency is 100 %.

(B) The following parameters have been used during the

gas-fired combined cycle power plant analysis:

• Atmospheric condition is taken as the 299 K and

1.0 bar.

• Combustion excess air: 300 %.

• The condenser pressure is assumed to be

0.11 bar.

Table 1 Stream data for coal-

fired super critical thermal

power plant

Stream ID Fluid Mass flow

(kg/s)

Temperature

(K)

Pressure (bar) Sp. enthalpy

(kJ/kg)

Sp. entropy

(kJ/kg K)

1 Steam 450.00 863 300 3,414.8 6.2005

2 Steam 28.23 644.2 76.8 3,063.3 6.2668

3 Steam 33.37 607.2 58.37 3,002.5 6.2795

4 Steam 388.4 607.2 58.37 3,002.5 6.2795

5 Steam 388.4 883 57.2 3,684.4 7.2200

6 Steam 21.91 769.4 28.1 3,451.3 7.2577

7 Steam 47.87 639.1 11.04 3,190.5 7.3092

8 Steam 318.62 603.98 8.34 3,121.4 7.3253

9 Steam 17.71 529.9 4.42 2,977.3 7.3593

10 Steam 17.72 421.8 1.48 2,770.6 7.4215

11 Steam 11.11 352.4 0.46 2,642.1 7.6222

12 Steam 13.89 330.8 0.18 2,497.4 7.6186

13 Steam 258.19 305.9 0.05 2,349.8 7.7045

14 Water 296.48 305.4 0.05 135.77 0.4697

15 Water 296.48 306 22 140.26 0.4772

16 Water 296.48 331 22 244.65 0.8050

17 Water 325.31 353 22 336.73 1.0742

18 Water 325.31 383 22 462.91 1.4171

19 Water 343.02 413.5 22 592.49 1.7425

20 Water 450.00 456 10.82 776.33 2.1682

21 Water 450.00 462.5 344 821.8 2.1858

22 Water 450.00 489.05 344 937.27 2.4285

23 Water 450.00 524.92 344 1,098.1 2.7457

24 Water 450.00 550.54 344 1,217.7 2.9681

25 Water 450.00 554.85 344 1,238.3 3.0053

26 Water 21.91 576.8 28.1 3,009.7 6.5958

27 Water 28.23 531.8 75.26 1,128.6 2.8663

28 Water 28.23 531.8 58.37 1,128.8 2.8707

29 Water 61.59 495.5 57.2 956.02 2.5346

30 Water 61.59 495.66 28.1 956.02 2.5416

31 Water 83.50 475.1 27.54 862.19 2.3485

32 Steam 23.47 639.1 11.04 3,190.5 7.3092

33 Steam 24.40 639.1 11.04 3,190.5 7.3092

34 Water 24.40 309.16 0.06 2,336.1 7.5827

35 Water 13.89 330 0.18 238.63 0.7934

36 Water 28.82 351.6 0.46 329.14 1.0589

37 Water 28.82 352 22 332.08 1.0610

38 Water 17.71 412.8 4.42 588.36 1.7371

39 Water 17.71 413.14 22 590.95 1.7387

40 Water 17.72 381 1.46 452.96 1.3967


123

• The heat rejection in the condenser is treated as a

energy loss.

• Generator efficiency is taken as 100 %.

Exergetic analysis of coal-fired supercritical thermal

power plant

Detailed flow diagram of coal-fired supercritical thermal

power plant is shown in Fig. 1. The symbols identifying the

streams and state point properties are described in Table 1.

Process descriptions reported previously (Romeo et al. 2008;

Alobaid et al. 2009; Siva Reddy et al. 2013) for each is

summarized. Generally, in thermal power plant boiler con-

cept was a drum-type boiler, which was replaced by the once-

through type boiler in supercritical thermal power plant to

increase efficiency. The main advantage is that quick

response to load changes, shorter start up time and better

suited for sliding pressure operation. The boiler of the case-

study power plant produces 450 kg/s of live steam at 300 bar

and 863 K. There is a single reheat at 883 K.

Mass flow, enthalpy, entropy, energetic power, and

exergetic power of water/steam at each thermodynamic

state point are represented in Fig. 1 corresponding to

design conditions (as shown in Table 1) of coal-fired

supercritical thermal power plant.

Energetic and exergetic power inputs of different com-

ponents in the power plant are shown in Fig. 2. Exergetic

power input is less than the energetic power input for all

the components, except in the boiler (where exergetic

power input 1,428.50 MW is more than energetic power

input 1,408.93 MW), because chemical exergy of the fuel

is more than the energy of the fuel. Energetic and exergetic

power inputs to the drift pumps and condensate extract

pump is very low compared to the remaining components.

In regenerative heat exchangers exergetic power input is

less than the energetic power input, because steam has

higher entropy. Figure 3 shows energetic and exergetic

power outputs of different components in the power plant.

Exergetic power output is less than the energetic power

output for all the components. In the boiler, this difference

has been found more (i.e., energetic power output is

1,350.46 MW as compared to exergetic power output

731.39 MW) because of fuel has higher chemical exergy

and steam has higher entropy. In regenerative heat

exchangers (HPH, LPH), exergetic power output is less

than the energetic power output, as water temperature

increases entropy also increases.

Energetic and exergetic power losses of different com-

ponents in the power plant are shown in Fig. 4. Among all

the components major exergetic power loss 697.11 MW as

compared to energetic power loss is 58.47 MW has been

found in the boiler. In condenser, energetic power loss

(566.44 MW) is high as compared to the exergetic power

loss (128.32 MW). But in the turbines (HPT, IPT, LPT,

and TG) and pumps (CEP, BFP, P1, and P2) energetic and

exergetic power losses are negligible. In regenerative heat

exchangers (HPH1, HPH2, HPH3, HPH4, LPH1, LPH2,

LPH3, and LPH4) exergetic power loss is higher than the

energetic power loss. Figure 5 shows energetic and exer-

getic efficiency of coal-fired supercritical thermal power

plant. Exergetic efficiency is lower than the energetic

efficiency in all heat transfer components of the power

plant (i.e., Boiler, HPH1, HPH2, HPH3, HPH4, LPH1,

LPH2, LPH3, and LPH4). The electric power generating

(HPT, IPT, LPT, and TG) and consuming (CEP, BFP, P1,

and P2) units have higher exergetic efficiency. Overall

plant energetic and exergetic efficiencies have been found

43.48 and 42.89 %, respectively. These results show sim-

ilar trend as reported by Singh and Kaushik (2012).

0

200000

400000

600000

800000

1000000

1200000

1400000

Boi

ler

(B)

HP

TIP

TL

PT

TR

CE

PB

FP P1

P2

HP

H1

HP

H2

HP

H3

HP

H4

LP

H1

LP

H2

LP

H3

LP

H4

Dea

erat

or

exergetic power input

energetic power input

Pow

er (

kW)

Coal fired supercritical thermal power plant components

Fig. 2 Energetic and exergetic inputs of coal-fired supercritical

thermal power plant components

0

200000

400000

600000

800000

1000000

1200000

1400000

exergetic power outputenergetic power output

Pow

er (

kW)


Fig. 3 Energetic and exergetic power output of coal-fired supercrit-

ical thermal power plant components


123

Exergetic analysis of gas-fired combined cycle

power plant

Detailed flow diagram of gas-fired combined cycle power

plant is shown in Fig. 6. The symbols identifying the streams

and state point properties are described in Table 2. Process

descriptions reported previously (Reddy and Mohamed

2007; Siva Reddy et al. 2012) for each is summarized.

Considering for analysis cumulative gas-fired combined

cycle with multi-pressure HRSG as shown in Fig. 6. Using

the balance energy and mass equations for each component

in the power plant, energy, exergy flows and at each node of

the plant can be calculated the numerically as well as ana-

lytically, for given set of operating conditions. The com-

bustion chamber of the case-study power plant produces

366 kg/s of live flue gas at 10 bar and 1,293 K. After

expanding in the turbine the flue gases enter to HRSG with a

temperature of 823 K.

Mass flow rate, enthalpy, entropy, energetic power, and

exergetic power of air/combustion products and water/

steam at each thermodynamic state point are represented in

Fig. 2 corresponding to design point of (as shown in

Table 2) gas-fired combined cycle power plant.

Energetic and exergetic power inputs of different compo-

nents in the power plant are shown in Fig. 7. Exergetic power

input is less than the energetic power input for all the com-

ponents. Combustion chamber (CC) and HRSG have major

difference compared to other components. Energetic and ex-

ergetic power input in CC are 1,095.20 and 770.73 MW,

respectively. Energetic and exergetic power input in HRSG

are 555.38 and 172.97 MW, respectively. Energetic and ex-

ergetic power inputs in pumps (CEP, HFP, LFP) are low

compared to other components in the power plant.

Figure 8 shows energetic and exergetic power outputs of

different components in the power plant. Exergetic power

output is less than the energetic power output for all the

components. Combustion chamber (CC) and HRSG have

more difference compared to other components. Energetic

and exergetic power output in CC are 1,068.98 and

624.97 MW, respectively. Energetic and exergetic power

output in HRSG are 344.35 and 138.46 MW, respectively.

Energetic and exergetic power losses of different com-

ponents in the power plant are shown in Fig. 9. Among the

0

100000

200000

300000

400000

500000

600000

700000

800000

Boi

ler

(B)

HP

TIP

TL

PT

TR

CE

PB

FP P1

P2

HP

H1

HP

H2

HP

H3

HP

H4

LP

H1

LP

H2

LP

H3

LP

H4

Dea

erat

or

Con

dens

er

energetic power loss

exergetic power loss


Pow

er (

kW)

Fig. 4 Energetic and exergetic power losses of coal-fired supercrit-

ical thermal power plant components

0

10

20

30

40

50

60

70

80

90

100energetic efficiency exergetic efficiency

Eff

icen

cy(

)η


Fig. 5 Energetic and exergetic

efficacies of coal-fired

supercritical thermal power

plant


123

all components combustion chamber (CC) have major ex-

ergetic power loss 145.76 MW and with compared to

energetic power loss 26.22 MW. HRSG has more energetic

power loss of 211.03 MW and with compared to exergetic

power loss 34.51 MW. In condenser, energetic power loss

is high 215.48 MW compared to the exergetic power loss

16.00 MW. But in the turbines (HPT, LPT, and GT) and

pumps (CEP, HFP, and LFP) energetic and exergetic power

losses are smaller quantities.

Figure 10 shows energetic and exergetic efficiency of

gas-fired combined cycle power plant. Among them feed

water heater (FWH) and deaerator have the high energetic

efficiencies are 91.26 and 88.90 %, respectively, and as

compared to exergetic efficiencies are 52.08 and 76.20 %,

respectively, because in mixing entropy generation is more.

The electric power generation (HPT, LPT and GT) and

consuming (CEP, HFP, and LFP) units have exergetic

efficiency is higher than the energetic efficiency. Overall

plant energetic and exergetic efficiencies have been found

54.47 and 53.93 %, respectively. These results show sim-

ilar trend as reported by Srinivas et al. (2007).

Comparative analysis of power losses in the components

of coal-fired supercritical thermal power plant

and natural gas-fired combined cycle power plant

The energetic power loss (in percentage of total loss) of

each components of the coal-fired supercritical thermal

power plant and the gas-fired combined cycle power plant

Air

FuelFuel

16

Air1

CC

Deaerator

G

CC

HP-Drum

LP-Drum

CEP

HFP

LFP

HRSG

23

41 l

2 l 3 l

4 l

5 6

7

8

9

10

11

15

Condenser

13 12

GT.1

14

Hp-Supp

Hp-Evap

Hp-Econ2

Hp-Econ1

CPH

Lp-Econ

Lp-Evap

Lp-Supp

FWH

b

a

c

d

GT.2C.2 C.1

LPTLPTHPT

Fig. 6 Schematic view of gas-fired combined cycle power plant


123

are shown in Figs. 11 and 12, respectively. The energetic

power loss in the condenser and boiler of the coal-fired

supercritical thermal power plant has been found 71.14 and

7.34 %, respectively. Remaining components has very less

percentage of energetic power losses. In the condenser and

HRSG of the gas-fired combined cycle power plant has

been found 40.03 and 39.21 %, respectively. Remaining

components has very less percentage of energetic power

losses in this case also. The corresponding exergetic power

loss (in percentage of total loss) of each components of the

coal-fired supercritical thermal power plant and the gas-

fired combined cycle power plant are shown in Figs. 13

and 14. The exergetic power loss in the boiler of coal-fired

supercritical thermal power plant has been found maxi-

mum, i.e., 85.45 %. Exergetic power loss in the combus-

tion chamber and HRSG of the gas-fired combined cycle

power plant is 60.90 and 14.41 %, respectively. Remaining

components has very less percentage of exergetic power

Table 2 Stream data for gas-

fired combined cycle power

plant

Stream

points

Fluid Mass flow

(kg/s)

Temperature

(K)

Pressure

(bar)

Sp. enthalpy

(kJ/kg)

Sp. entropy

(kJ/kg K)

1 Air 360 302 1.013 428.20 3.8916

10 Air 360 302 1.013 428.20 3.8916

2 Air 360 637 10.2 772.45 3.9918

20 Air 360 637 10.2 772.45 3.9918

3 Flue gas 366 1,345 9.6 1,484.7 7.6409

30 Flue gas 366 1,345 9.6 1,484.7 7.6409

4 Flue gas 366 824 1.10 872.96 7.6731

40 Flue gas 366 824 1.10 872.96 7.6731

5 Water 103.46 321.105 3.64 201.72 0.679

6 Water 159.14 345.24 3.64 302.72 0.9821

7 Water 159.14 409.42 3.64 573.85 1.702

8 Water 87.94 410.4 72.6 582.56 1.7052

9 Steam 87.95 791.23 55.25 3,471.5 6.9809

10 Steam 87.95 479.68 5.6 2,867.2 7.034

11 Water 20.68 409.7 21.3 576.2 1.7031

12 Steam 10.34 474.32 5.6 2,855.6 7.0097

13 Steam 103.47 474.32 5.6 2,855.6 7.0097

14 Steam 103.47 323 0.1235 2,283.6 7.1227

15 Water 103.47 321 0.1123 200.98 0.6778

16 Flue gas 732 383 1.013 318.11 6.6428

0

200000

400000

600000

800000

1000000

energetic power input

exergetic power input

Gas fired combined cycle power plant

Pow

er (

kW)

Fig. 7 Energetic and exergetic power inputs of gas-fired combined

cycle power plant components

0

200000

400000

600000

800000

1000000

1200000

energetic power output exergetic power output

Gas fired combined cycle power plant components

Pow

er (

kW)

Fig. 8 Energitic and exergetic power outputs of gas-fired combined



123

losses in both types of power plants. The variation of ener-

getic and exergetic efficiencies of the coal-fired supercritical

thermal power plant and the gas-fired combined cycle power

plant with respect to condenser pressure are shown in

Figs. 15 and 16, respectively. The performance of the coal-

fired supercritical thermal power plant and the gas-fired

combined cycle power plant is evaluated for condenser

pressures from 0.07 to 0.16 bar. Energetic and exergetic

efficiencies are slight linearly increases with respect to

decreasing of condenser pressure at constant mass flow rate

of steam. In the coal-fired supercritical thermal power plant

for the condenser pressure range of 0.16–0.07 bar, energetic

efficiency is improved from 41.53 to 43.32 %, and exergetic

efficiency is increased from 40.96 to 42.72 %. In the gas-

fired combined cycle power plant for the condenser pressure

range of 0.16–0.07 bar, energetic efficiency is improved

from 53.89 to 55.75 %, and exergetic efficiency is increased

from 53.35 to 55.20 %. This is mainly because lowered

condenser pressure leads to higher output and efficiency of

the steam turbine. Condenser pressure has no effect on the

performance of gas turbine in gas-fired combined cycle

power plant.

0

40000

80000

120000

160000

200000

energetic power lossexergetic power loss


Pow

er (

kW)

Fig. 9 Energetic and exergetic power losses of gas-fired combined


0

10

20

30

40

50

60

70

80

90

100

energetic efficiency exergetic efficiency


Eff

icie

ncy

()η

Fig. 10 Energitic and exergetic efficiencies of gas-fired combined cycle power plant components

Fig. 11 Component wise energetic power loss, given as the percent-

age of total energetic power loss for coal-fired supercritical thermal

power plant


123

Conclusion

The major energetic power loss has been found in con-

denser for coal-fired supercritical thermal power plant, and

the major energetic power loss has been found in condenser

followed by HRSG for gas-fired combined cycle thermal

power plant. The exergetic analysis shows that boiler is the

Fig. 12 Component wise energetic power loss, given as the percent-

age of total energetic power loss for gas-fired combined cycle power

plant

Fig. 13 Component wise exergetic power loss, given as the percent-

age of total exergetic power loss for coal-fired supercritical thermal

power plant

Fig. 14 Component wise exergetic power loss, given as the percent-

age of total exergetic power loss for natural gas-fired combined cycle

power plant

40.5

41

41.5

42

42.5

43

43.5

0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0.16


Condenser pressure (bar)

Eff

icie

ncy(

)η

Fig. 15 Variation of energetic and exergetic efficiencies of coal-fired

supercritical thermal power plant with respect to condenser pressure

53

53.5

54

54.5

55

55.5

56

0.07 0.09 0.11 0.13 0.15


Condenser pressure (bar)

Eff

icie

ncy(

)η

Fig. 16 Variation of energetic and exergetic efficiencies of natural

gas-fired combined cycle power plant with respect to condenser

pressure


123

main source of exergetic power loss in coal-fired super-

critical thermal power plant and combustion chamber is the

main source of exergetic power loss in the gas-fired com-

bined cycle thermal power plant. The exergetic power loss

in condenser is small, due to low quality energy rejection.

Thus, the exergetic analysis provides a more accurate

measurement of the actual inefficiencies in the system and

the true location of these inefficiencies. The results of ex-

ergetic analysis of the power plants show that the boiler

and combustion chamber requires improvements. The

overall coal-fired supercritical thermal power plant’s

energetic and exergetic efficiency are 43.48 and 42.89 %,

respectively. The overall natural gas-fired combined cycle

power plant’s energetic and exergetic efficiency are 54.47

and 53.93 %, respectively. Final conclusion of the analysis

is that the natural gas-fired combined cycle power plant has

more efficiency than that of coal-fired supercritical thermal

power plant. In the factor of environmental degradation and

direct high grade energy savings natural gas-fired com-

bined cycle power plant is more viable than the supercrit-

ical plants due to its moderate efficiency.

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Documents

Exergetic analysis and evaluation of coal-fired supercritical thermal power plant and natural gas-fired combined cycle power plant