Thermo-environmental analysis of an open cycle gas turbine power plant with regression modeling and optimization

Journal of the Energy Institute 87 (2014) 81e88

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Journal of the Energy Institute journal homepage: http://www.journals.elsevier.com/journal-of-the-energyinstitute

Thermo-environmental analysis of an open cycle gas turbine power plant with regression modeling and optimization Abdul Ghafoor Memon a, *, Rizwan Ahmed Memon a, Khanji Harijan a, Muhammad Aslam Uqaili b a b

Department of Mechanical Engineering, Mehran University of Engineering and Technology, Jamshoro 76062, Pakistan Department of Electrical Engineering, Mehran University of Engineering and Technology, Jamshoro 76062, Pakistan

a r t i c l e i n f o

a b s t r a c t

Article history: Received 29 April 2013 Accepted 17 June 2013 Available online 29 March 2014

In this paper, a gas turbine cycle is modeled to investigate the effects of important operating parameters like compressor inlet temperature (CIT), turbine inlet temperature (TIT) and pressure ratio (PR) on the overall cycle performance and CO2 emissions. Such effects are also investigated on the exergy destruction and exergy efficiency of the cycle components. Furthermore, multiple polynomial regression models are developed to correlate the response variables (performance characteristics) and predictor variables (operating parameters). The operating parameters are then optimized. According to the results, operating parameters have a significant effect on the cycle performance and CO2 emissions. The largest exergy destruction is found in the combustion chamber with lowest exergy efficiency. The regression models have appeared to be a good estimator of the response variables. The optimal operating parameters for maximum performance have been determined as 288 K for CIT, 1600 K for TIT and 23.2 for PR. Ó 2014 Energy Institute. Published by Elsevier Ltd. All rights reserved.

Keywords: gas turbine exergy regression optimization

1. Introduction The gas turbine based power plants are receiving considerable attention due to their shorter lead time, operational flexibility and lower greenhouse gas emissions. To optimize such plants, it is important to find and quantify the operating/design parameters through some thermodynamic analysis that may ultimately improve thermodynamic performance and mitigate environmental impact. Many researchers have reported that the performance of gas turbine cycles is strongly influenced by compressor inlet temperature (CIT), turbine inlet temperature (TIT), pressure ratio (PR), air-to-fuel-ratio and isentropic efficiencies of air compressor and gas turbine [1e3]. In addition to energy analysis, exergy analysis has become an increasingly important thermodynamic tool for the design and analysis of energy systems and many researchers have suggested the use of exergy analysis in the evaluation of thermodynamic performance of any energy system for efficient utilization of energy resources and small environmental impact [4e7]. The primary goal of exergy analysis is to identify the irreversibilities occurred mainly because of chemical reactions, heat transfer and friction in the systems. The exergy analysis has been widely applied to many gas turbine based power plants [8e13]. According to the results, the plants’ exergy efficiency, exergy destruction, power-toheat ratio, and specific fuel consumption are greatly influenced by the operating parameters, and that the combustion chamber is a major contributor in the exergy destruction of the plants [8e13]. Global warming, especially due to CO2 emissions is one of the environmental challenge humanity faces today. Use of fossil fuels for power production is considered as a prime source of CO2 emissions; in fossil fuels the emissions from coal are the highest and that from natural gas the least. Therefore, researchers are keen to explore different environmental impact mitigation strategies while exploiting fossil fuels for power production [7,14]. In the current article, a greater focus has been placed on the gas turbine cycle. In this regard the thermodynamic and environmental analyses of an open cycle gas turbine power plant are carried out in order to investigate the impact of important operating parameters, CIT, PR and TIT on the performance characteristics like net power output, fuel consumption, energy and exergy efficiencies, and CO2 emissions. The impact of operating * Corresponding author. E-mail addresses: [email protected] (A.G. Memon), [email protected] (R.A. Memon), [email protected] (K. Harijan), [email protected] (M.A. Uqaili). http://dx.doi.org/10.1016/j.joei.2014.03.023 1743-9671/Ó 2014 Energy Institute. Published by Elsevier Ltd. All rights reserved.

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List of symbols: AC Cp CC CIT E EnE ExE G GT h h LHV LHV M _ m N_ P PR Q_ R R2 s T TIT _ W

air compressor specific heat at constant pressure (kJ kg
1 K
1) combustion chamber compressor inlet temperature (K) emissions energy efficiency (%) exergy efficiency (%) generator gas turbine specific enthalpy (kJ kg
1) molar specific enthalpy (kJ kmol
1) lower heating value (kJ kg
1) molar lower heating value (kJ kmol
1) molar mass (kg kmol
1) mass flow rate (kg s
1) molar flow rate (kmol s
1) pressure (MPa) pressure ratio heat transfer rate (kW) gas constant (kJ kg
1 K
1) coefficient of determination (%) specific entropy (kJ kg
1 K
1) temperature (K) turbine inlet temperature (K) power (kW) specific exergy flow (kJ kg
1) exergy transfer rate (kW)

x X_

b g l h ε

mass fraction of chemical species specific heat ratio molar fuel-to-air ratio isentropic efficiency effectiveness of regenerator

Subscripts a air avg average c combustion D destruction F fuel f formation g combustion gas i ith component in influx out exflux p products Q heat r reactants W work X exergy j number of carbon k number of hydrogen o dead (environment or reference) state Superscript o standard reference state of 25  C and 1 atm.

Greek letters a mole fraction of chemical species

parameters on the exergy destruction rate and exergy efficiency of individual plant components is also investigated. Furthermore, multiple polynomial regression (MPR) models are developed to find the strength of correlation between response variables (performance characteristics) and predictor variables (operating parameters). Finally, optimization is performed to maximize the specific power, energy and exergy efficiencies considered as the objective functions. A program is developed in the Engineering Equation Solver (EES) [15] software to model the power plant. 2. Cycle description Fig. 1 exhibits the open cycle gas turbine power plant under investigation. The atmospheric air is drawn in to the air compressor and compressed to a pressure depending on the PR. Fuel is injected into the compressed air in the combustion chamber and the mixture is combusted, heating it to the temperature according to the TIT. The combustion products expand through a gas turbine, creating the turbine work output. The hot products finally dissipated to the atmosphere. The assumptions for analysis of the power plant are tabulated in Table 1. 3. Thermodynamic model equations The thermodynamic analysis of the power plant is carried out using the following equations: Continuity equation:

X

_ in
m

X

_ out ¼ 0 m

(1)

Energy equation:

_ þ Q_ eW

X

_ in hin
m

X

_ out hout ¼ 0 m

(2)

X_ out
X_ D ¼ 0

(3)

Exergy equation:

X_ Q eX_ W þ

X

X_ in e

X

The specific exergy is given by:

x ¼ ðheho ÞeTo ðs
so Þ The change in entropy for an ideal gas is given by:

(4)

A.G. Memon et al. / Journal of the Energy Institute 87 (2014) 81e88

83

Fig. 1. A simple open cycle gas turbine power plant under investigation.

s
so ¼ CP;avg ln

    T P eR ln To Po

(5)

The rate of exergy transfer to the power plant is given by:

_ F xF X_ F ¼ m

(6)

The specific chemical exergy of gaseous hydrocarbon fuels ðCj Hk Þ, is approximated as [12]:

xF ¼

  k 0:0698 ðLHVÞF 1:033 þ 0:0169 e j j

(7)

For the combustion process, Eq. (2) can be written as:

Q_ c ¼

X

  X   N_ r hof þ h
ho e N_ p hof þ h
ho r

(8) p

The rate of heat transfer from the combustion chamber during the combustion process is determined as:

  Q_ c ¼ 0:02N_ F LHV F

(9)

The net power output from the power plant is given by:

  _ _ net ¼ h W _ W GT
W AC G

(10)

where

_ _ a ðh2
h1 Þ W AC ¼ m

(11)

and

_ _ g ðh3
h4 Þ W GT ¼ m The air enthalpy in kJ kg

(12)
1

can be determined from the following relationship:

Table 1 Assumptions for thermodynamic evaluation of the power plant. 1. 2. 3. 4.

Steady-state operation of power plant components. Ideal gas behavior by air and combustion gas constituents. Complete combustion of fuel (modeled as methane, CH4). Change in kinetic energy (and exergy) and potential energy (and exergy) of fluid streams neglected. Only chemical exergy of the fuel is considered. 5. Lower heating value (LHV) of CH4 50,050 kJ kg
1 6. Dead-state condition 101.325 kPa and 298 K 7. Pressure of inlet air and exhaust combustion gas 101.325 kPa 8. Pressure drop in combustion chamber 5% 9. Isentropic efficiency of air compressor 85% 10. Isentropic efficiency of gas turbine 88% 11. Generator efficiency 97% 12. Heat transfer from combustion chamber 2% of LHV of fuel 13. Mass flow rate of air 1 kg/s 14. Average specific heat and specific heat ratio of air 1.015 kJ/kg K and1.4 15. Average specific heat and specific heat ratio of combustion gas 1.163 kJ/kg K and 1.35 16. Gas constant for air and combustion gas 0.29 and 0.293 kJ kg
1 K
1 17. Molar air composition [12] 77.48% N2, 20.59% O2, 0.03% CO2 and 1.90% H2O

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  ha ¼ 0:7748hN2 þ 0:2059hO2 þ 0:0003hCO2 þ 0:019hH2 O Ma

(13)


1

where enthalpy of each constituent hi is in kJ kmol . The temperature of air leaving air compressor and exhaust gas leaving gas turbine can be calculated respectively from the following relationship:

i. h T2 ¼ T1
T1
ðPRÞðga
1Þ=ga T1 hs;AC

(14)

h i T4 ¼ T3
hs;GT T3
T3 ðP4 =P3 Þðgg
1Þ=gg

(15)

The complete combustion of CH4 can be written as:







lCH4 þ ð0:7748N2 þ 0:2059O2 þ 0:0003CO2 þ 0:019H2 OÞ/ 1 þ l aN2 N2 þ aO2 O2 þ aCO2 CO2 þ aH2 O H2 O aN2 ¼

0:7748 1þl

; aO2 ¼

0:2059
2l 1þl

; aCO2 ¼

(16)

0:0003 þ l 0:019 þ 2l ; aH2 O ¼ 1þl 1þl

The mass fraction of ith constituent of the combustion gas is given by:

bi ¼

ai Mi Mg

a Mi ai Mi

¼ Pi

(17)

i

The combustion gas enthalpy, in kJ kg
1, is then given by:

hg ¼

X

bi hi

(18)

i

The fuel consumption is calculated from the following equation:

_F ¼ m

! MF l _a m Ma

(19)

The mass flow rate of combustion gas is then determined as:

_ F þm _a _g ¼ m m

(20)

The rate of heat transfer to the power plant is given by:

_ F ðLHVÞF Q_ in ¼ m

(21)

The energy and exergy efficiencies are respectively given by:

" EnE ¼

_ net W Q_

# (22)

in

" ExE ¼

_ net W X_ F

# (23)

Using Eq. (19), the amount of CO2 emissions (kg MWh
1) is determined as:

ECO2 ¼

_ CO2 m  1000 _ net W

(24)

The exergy destruction rate and the exergy efficiency of plant components are determined from the equations given in Table 2. Table 2 Expressions for exergy destruction/loss rate and exergy efficiency of power plant components/streams.

Air compressor

Power plant component/stream

Exergy destruction/loss rate _ X_ ¼ W þ X_
X_

Combustion chamber

X_ D;CC ¼ X_ 2 þ X_ F
X_ 3

ExECC ¼ 1


Gas turbine

_ X_ D;GT ¼ X_ 3
X_ 4
W GT

ExECC ¼ 1


Gas turbine mechanical shaft

_ _ _ X_ D;GTMS ¼ W GT
W AC
W net

ExEGTMS ¼ 1


Stack

X_ L;stack ¼ X_ 4

e

D;AC

AC

1

2

Exergy efficiency ExEAC ¼ 1


X_ D;AC _ AC þX_ 1 W _X D;CC X_ 2 þX_ F X_ D;GT X_ 3

X_ D;GTMS _ GT W

A.G. Memon et al. / Journal of the Energy Institute 87 (2014) 81e88

85

Fig. 2. Effect of CIT on exergy destruction rate and exergy efficiency of the power plant components for TIT ¼ 1200 K and PR ¼ 11.

Fig. 3. Effect of CIT on the power plant performance for TIT ¼ 1200 K and PR ¼ 11.

4. Results and discussion In this section, the results of the thermodynamic, environmental and regression analyses of the power plant are presented. In the first part of the discussion, results of energy, exergy and environmental analyses of the power plant components and the overall power plant are discussed, including assessments of the effects of varying operating parameters on the performance. Afterwards, MPR modeling results are presented along with optimization. 4.1. Thermodynamic and environmental analyses The results of parametric study to show the effects of operating parameters on the performance characteristics of the power plant are exhibited in Figs. 2e7. The operating parameters, CIT, TIT and PR change in the ranges of 288e328 K, 900e1600 K and 4e36, respectively. The ranges of PR and TIT values selected for analysis have been adopted from the design values of leading gas turbine manufacturers, like Siemens SGT and General Electric MS model series for power generation [16,17]. Figs. 2 and 3 show the effects of CIT on performance characteristics for TIT ¼ 1200 K and PR ¼ 11. As shown in Fig. 2, the combustion chamber incurs the most significant exergy destruction among the plant components, stem mainly from the irreversibilities associated with the combustion reaction; followed by the exergy loss due to stack. The air compressor, gas turbine and gas turbine mechanical shaft contribute only a small towards the total exergy destruction. The total exergy destruction rate of the power plant is maximum at CIT ¼ 288 K (i.e., 518 kW) and decreases as the CIT increases. The main source of exergy destruction in the combustion chamber is due to large temperature difference across it (i.e., T3
T2 ). This decreases with an increase in the CIT at given TIT, resulted in a decrease in the exergy destruction rate of the combustion chamber. The variation in the exergy destruction rate of the air compressor and gas turbine, and exergy loss due to stack with respect to CIT is not pronounced. The exergy efficiency of air compressor, gas turbine and gas turbine mechanical shaft remain nearly constant, while that of combustion chamber increases marginally with the CIT. The net power output, fuel consumption, energy and exergy efficiencies decrease while the CO2 emissions increases with an increase in CIT, as shown in Fig. 3. At relatively higher CIT values, the air density decreases which, with constant air mass flow rate, resulted in a higher

Fig. 4. Effect of TIT on exergy destruction rate and exergy efficiency of the power plant components for CIT ¼ 288 K and PR ¼ 11.

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A.G. Memon et al. / Journal of the Energy Institute 87 (2014) 81e88

Fig. 5. Effect of CIT on the power plant performance for CIT ¼ 288 K and PR ¼ 11.

Fig. 6. Effect of PR on exergy destruction rate and exergy efficiency of the power plant components for CIT ¼ 288 K and TIT ¼ 1200 K.

compressor work that in turn produces a lower net power. The diminution of fuel consumption with CIT is not as pronounced as net power output; this effect leads to a decrease in the efficiencies and an increase in the CO2 emissions to the environment. The efficiencies and CO2 emissions are inversely related as can be seen from the trend of variation in these quantities in Fig. 3. Figs. 4 and 5 depict the variation in performance characteristics with respect to TIT at CIT ¼ 288 K and PR ¼ 11. It is noted from Fig. 4 that the combustion chamber is the major site of exergy destruction; exergy loss due to stack is the next most prominent site. The air compressor, gas turbine and gas turbine mechanical shaft contribute a little towards the total exergy destruction of the power plant. Roughly equal contributions to the exergy destruction are made by the air compressor and gas turbine which remain constant as the TIT increases. The total exergy destruction rate increases as the TIT increases, primarily due to simultaneous increase in the combustion chamber exergy destruction rate and the stack exergy loss rate. The main reason of increase in the combustion chamber exergy destruction rate is the increase in temperature difference across it (i.e., T3
T2 ) since CIT remain constant. The temperature of exhaust gas also increases as the TIT increases, which causes higher exergy loss rate via stack for higher TIT values. As the TIT increases, the exergy efficiency of air compressor, combustion chamber and gas turbine mechanical shaft remain nearly constant while that of gas turbine increases only marginally. As shown in Fig. 5, the net power output, fuel consumption, energy and exergy efficiencies increase while the CO2 emissions decreases with an increase in the TIT. It is observed that the increase in net power output and fuel consumption is nearly linear; the former being steeper than the latter, and the efficiency curves are rather steep at low TIT but flattens out starting with a TIT value of about 1400 K. Therefore, increase in the efficiencies with an increase in the TIT is not as pronounced at a higher TIT value that is also limited due to the thermal durability of the turbine blades. The diminution curve of CO2 emissions is roughly a mirror image of the efficiency curves, as noted before in Fig. 3. Figs. 6 and 7 demonstrate the impact of PR on the performance characteristics for CIT ¼ 288 K and TIT ¼ 1200. According to Fig. 6, the combustion chamber continues to play a major role in the total exergy destruction rate of the power plant. The total exergy destruction rate decreases as the PR increases; contribution of air compressor and gas turbine steadily grows, while that of the combustion chamber and the exergy loss rate due to stack decreases. At higher PR, the temperature ratio of the air compressor and gas turbine increases causing an increase in the temperature difference across these components since CIT and TIT are fixed. This results in an increase in the exergy destruction rate of these components. Similarly with an increase in the PR, the temperature difference across the combustion chamber (i.e.,

Fig. 7. Effect of PR on the power plant performance for CIT ¼ 288 K and TIT ¼ 1200 K.

A.G. Memon et al. / Journal of the Energy Institute 87 (2014) 81e88

87

T3
T2 ) at constant TIT and the temperature of exhaust gas decrease; resulting in the decrease in the combustion chamber exergy destruction rate and stack exergy loss rate. The exergy efficiency of the air compressor and combustion chamber increases, while the exergy efficiency of gas turbine decreases and that of the gas turbine mechanical shaft remains nearly constant with an increase in the PR. According to Fig. 7, the net power output increases as the PR increases. As the PR increases, both the compressor and turbine works increase, but beyond certain PR values, increments in the compressor work are higher than that for turbine work; thereby the net power output starts to decrease, if other parameters remain same. The net power output in the simple cycle reaches maximum when PR is around 9 and decreases afterwards. The fuel consumption decreases with an increase in the PR. This is due to fact that the temperature of compressed air increases as the PR increases, which require less fuel to reach the desired TIT, for a fixed gas flow to the turbine. This diminution is more pronounced at lower PR values. It is also noted that the energy and exergy efficiencies increase with the PR, reaches maximum at about PR ¼ 16 and then starts to decrease. The reason is that as PR is increased beyond 16, the increase in compressor work overwhelms the decrease in the fuel consumption, which leads to a decrease in the efficiencies. Accordingly, CO2 emissions decrease with the increase in PR mainly due to decrease in the efficiencies, which reaches a minimum at PR around 16 and then starts to increase. 4.2. Regression modeling and optimization In this section, the development of multiple polynomial regression (MPR) models is discussed. These models are used to examine how multiple predictor variables (i.e., operating parameters) are related to the response variables (i.e., performance characteristics) of the power plant. The specific power (net power output to fuel consumption ratio), energy and exergy efficiencies are considered as the response variables; each one is regressed to three predictor variables, CIT, TIT and PR simultaneously by an MPR equation of order 3. The models are developed with the help of the parametric table constructed in EES, containing nearly 148 points, showing the values of each response variable with given values of predictor variables. These models are valid to estimate the response variable from the predictor variables in the range 288e328 K for CIT, 900e1600 K for TIT and 4e36 for PR. The coefficient of determination (R2) is calculated for each model which indicates how much better the function estimates the response variable. A high R2 value indicates that the predictor variables are a good estimator of the response variable. Furthermore, optimization is performed which is a process of minimization and/or maximization of objective functions by varying the single or multiple predictor variable(s). Here, every response variable is considered as the objective function with CIT, TIT and PR nominated as the predictor variables. Such multi-dimensional optimization is processed by using direct-search method (also known as derivative-free method). By this method, the objective functions are maximized by using a series of one-dimensional searches to locate the optimum value of each predictor variable. The regression models and optimum operating conditions are exhibited in Table 3.

Table 3 Multiple regression models and optimum operating conditions. Specific power (MJ kg
1) wsp ¼ 6:98372794 þ 06
4:03800982 þ 04*CIT þ 3:70247783 þ 01*CIT2 þ 6:21290070
02*CIT3
7:55901278 þ 03*PR
1:84833201 þ 02*PR2 þ 6:49506445
01*PR3
1:29302110E þ 04*TIT þ 4:61837884 þ 00 *TIT2 þ 6:06956997E
05*TIT3 þ 1:82745632 þ 01*CIT*PR þ 9:33072290
01*CIT*PR2 þ 8:62626523 þ 01*CIT*TIT
3:16739852
02*CIT*TIT2
2:91697447
02*CIT2 *PR
1:90119175
03*CIT2 *PR2
1:40533493
01*CIT2 *TIT þ 5:16595107
05*CIT2 *TIT2 þ n

8:61509629E þ 00*PR*TIT
3:00070182E
03*PR*TIT2 þ 1:57555918
02*PR2 *TIT
1:51265998
06*PR2 *TIT2 ;

R2 ¼ 98:43

o

Maximization of wsp (CIT, TIT, PR): 20.926 (288.1, 1600, 23.27) Energy efficiency (%) EnE ¼
4:33219710 þ 03 þ 3:12084149 þ 01*CIT
6:50714725E
02*CIT2 þ 2:33908709
05*CIT3
1:02940655 þ01*PR
5:79080353
01*PR2 þ 1:30530799
03*PR3 þ 5:88466554 þ 00*TIT
2:45908898
03*TIT2 þ 1:21982479
07*TIT3 þ6:40927592
03*CIT*PR þ 3:18601589
03*CIT*PR2
3:77072645
02*CIT*TIT þ 1:40996125
05*CIT*TIT2
8:20729832
06*CIT2 *PR
5:99187733
06*CIT2 *PR2 þ 6:62171858
05*CIT2 *TIT
2:46163985
08*CIT2 *TIT2 þ 1:67932881
02*PR*TIT
5:84278779
06*PR*TIT2 þ 4:71167084
05*PR2 *TIT
8:72602435
09*PR2 *TIT2 ;

n

R2 ¼ 99:25

o

Maximization of EnE (CIT, TIT, PR): 41.84 (288, 1600, 23.12) Exergy efficiency (%) ExE ¼
4:20793989 þ 03 þ 3:03210883 þ 01*CIT
6:32519949
02*CIT2 þ 2:27995566
05*CIT3
9:69880808 þ00*PR
5:69210497
01*PR2 þ 1:26659826
03*PR3 þ 5:70992955 þ 00*TIT
2:38616329
03*TIT2 þ 1:18335847
07*TIT3 þ 4:29338604
03*CIT*PR þ 3:14022086
03*CIT*PR2
3:65893170
02*CIT*TIT þ 1:36825770
05*CIT*TIT2
4:77449371
06*CIT2 *PR
5:89480924
06*CIT2 *PR2 þ 6:42550342
05*CIT2 *TIT
2:38886897
08*CIT2 *TIT2 þ 1:62945020
02*PR*TIT
5:66913801
06*PR*TIT2 þ 4:57180044
05*PR2 *TIT
8:47808094
09*PR2 *TIT2 ;

Maximization of ExE (CIT, TIT, PR): 40.59 (288, 1600, 23.11)

n

R2 ¼ 99:25

o

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A.G. Memon et al. / Journal of the Energy Institute 87 (2014) 81e88

It can be seen from Table 3 that the optimum values of CIT and TIT for maximum specific power and efficiencies are obtained as 288 and 1600 K, respectively. It is obvious that the CIT should be as low as possible while the TIT should be as high as possible for maximum performance, provided thermal and mechanical durability of the plant is ensured. The optimum PR value for maximum performance is obtained around 23.2. The power plant operation under these optimum operating parameters leads to a higher specific power output and efficiencies with lower CO2 emissions. 5. Conclusion In this paper, a comprehensive thermodynamic and regression modeling of an open cycle gas turbine power plant is dealt. The thermodynamic results have shown combustion chamber as a major contributor towards the exergy destruction rate mainly due to irreversibilities associated with the combustion reaction and large temperature difference across it. The exergy loss due to stack is the next most prominent site of irreversibilities, where the large work potential possessed in the hot exhaust gases is lost. Approximately equal contributions to the exergy destruction rate are made by the air compressor and gas turbine whereas the gas turbine mechanical shaft is an only marginally smaller contributor. Therefore, the combustion chamber has the lowest exergy efficiency among all power plant components. The significant effects of variation in CIT, TIT and PR on different thermodynamic quantities of the plant have been noted. According to the results, the exergy destruction rate of combustion chamber decreases as the CIT increases, while the variation in the exergy destruction rate of air compressor and gas turbine, and stack exergy loss rate is not pronounced with respect to CIT. The exergy destruction rate of combustion chamber and exergy loss rate due to stack increase as the TIT increases while that of air compressor and gas turbine remain constant. With an increase in PR, the exergy destruction rate of combustion chamber and exergy loss rate due to stack decrease and that of air compressor and gas turbine increase. The net power output, fuel consumption, energy efficiency and exergy efficiency of the plant decrease while CO2 emissions increases with an increase in the CIT and decrease in the TIT. The net power output and the efficiencies increase with the PR, reaches maximum at PR ¼ 8 and 16, respectively; decrease afterwards. The fuel consumption always decreases with the PR, while the CO2 emissions decrease with an increase in the PR, reaches minimum at PR ¼ 16 and subsequently increases. The CO2 emissions are therefore inversely related to the efficiency of the power plant. The MPR model equations have been developed to correlate the response variables with the predictor variables and found estimating each response variable with a great degree of accuracy since appended with high R2 values. The optimal operating parameters for maximum performance and minimum CO2 emissions have been determined as 288 K for CIT, 1600 K for TIT and 23.2 for PR. It is concluded that, for higher performance with lower CO2 emissions, the CIT should be chosen as low as possible and the TIT should be chosen as high as possible. However, the former is constrained by the additional energy use and costs in bringing down the inlet air temperature in the chillers, while the latter is restricted by the metallurgical limits. Acknowledgement The authors acknowledge the support provided by Mehran University of Engineering and Technology, Jamshoro, Pakistan. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]

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