y-

S.Er Osmir, Tu

Keywords:Exergy analysisAdvanced exergetic analysisExergy destructionElectricity generation facility

erfoin T

namely endogenous, exogenous, avoidable and unavoidable exergy destruction rates. Through this anal-

essor,

generation facilities in industry. CHP facilities produce electricityand heat energy from one type of fuel, generally natural gas. Theefciency of such a facility can reach 7080% [1]. In addition tothe economic and efciency benets, their environmental impactis an important factor. Gas turbines have low greenhouse gas emis-sions compared to many other power generation systems.

and they do notnt affects one an-hrough ad

There are a few studies on advanced exergy-based analpower-generating systems in the open literature [315]. Tsnis [3] discussed the weaknesses of conventional exergyanalyses in developing improvement strategies and presented ad-vanced exergy, advanced exergoeconomic and exergoenvironmen-tal analyses as solutions to these weaknesses. Tsatsaronis andMoung-Ho [4] were the rst to develop the concepts of avoidableand unavoidable exergy destruction, which were used to deter-mine the potential of improving the thermodynamic performanceand cost effectiveness of a system. Cziesla et al. [5] investigated

Corresponding author. Tel.: +90 (228) 2160061; fax: +90 (228) 216 05 88.E-mail addresses: eacikkalp@gmail.com, emin.acikkalp@bilecik.edu.tr

(E. Akkalp).

Energy Conversion and Management 82 (2014) 146153

Contents lists availab

Energy Conversion

seUnfortunately, gas turbines also have disadvantages. Gas turbinemaintenance costs are high, they are sensitive to ambient condi-tions, and they are sensitive to electricity voltage change. Gas tur-bines are primarily used in combined heat and power (CHP)

improvement of the system or its components,provide any information about how one componeother. This lack of information can be addressed texergy-based methods [2,3].http://dx.doi.org/10.1016/j.enconman.2014.03.0060196-8904/ 2014 Elsevier Ltd. All rights reserved.vanced

yses ofatsaro--basedand a turbine while they have been widely used in the industryand transportation sectors. For example, they are used in energyproduction facilities, aircrafts, transport ships, and even cars andmotorcycles. Gas turbines have some particular advantages, suchas low annual cost, fast activation, exible operation, and fastand easy maintenance. In addition, the most important advantageof gas turbines is that their efciency is high (approximately 40%).

assessing the performance of energy conversion systems. Exergyis the maximum work that can be obtained from a system. Exer-gy-based analyses help determine the irreversibilities (entropygeneration) and how a source can be used effectively. However,exergy-based analyses lack some information, which will be dis-cussed in Section 3.2 in more detail. Basically, the results of anexergy-based analysis cannot be used to consider the potential1. Introduction

Gas turbines consist of a comprysis, the improvement potentials of both the components and the overall system along with the interac-tions between the components are deducted based on the actual operational data. The analysis indicatesthat the combustion chamber, the high pressure steam turbine and the condenser have high improve-ment potentials. The relations between the components are weak because of the ratio of the endogenousexergy rates of 70%. The improvement potential of the system is 38%. It may be concluded that one shouldfocus on the gas turbine and combustion chamber for improving the system, being the most importantcomponents of the system.

2014 Elsevier Ltd. All rights reserved.

a combustion chamber

All energy conversion systems must be analyzed in terms ofenergetic, economic, and environmental aspects for a proper man-agement. Exergy-based analyses are very convenient methods forAccepted 1 March 2014Available online 27 March 2014

system is determined to be 40.2% while the total exergy destruction rate of the system is calculated to be78.242 MW. The exergy destruction rate within the facilitys components is divided into four parts,Advanced exergy analysis of an electricitusing natural gas

Emin Akkalp a,, Haydar Aras b, Arif Hepbasli caDepartment of Mechanical and Manufacturing Engineering, Engineering Faculty, BilecikbDepartment of Mechanical Engineering, Engineering and Architecture Faculty, EskisehicDepartment of Energy Systems Engineering, Engineering Faculty, Yasar University, Izm

a r t i c l e i n f o

Article history:Received 5 December 2013

a b s t r a c t

This paper deals with the pisehir Industry Estate Zone

journal homepage: www.elgenerating facility

. University, Bilecik, Turkeyangazi University, Eskisehir, Turkeyrkey

rmance assessment of an electricity generation facility located in the Esk-urkey using advanced exergy analysis method. The exergy efciency of the

le at ScienceDirect

and Management

vier .com/locate /enconman

(HRSG), a high pressure steam turbine (HPST), a low pressure

Subscripts

EN endogenousEX exogenous

u exergetic efciency (%)

n anall of an externally red combined power plants componentsaccording to both avoidable and unavoidable exergy destruction;the associated costs were dened, and the results of their studywere discussed. Kelly et al. [6] dened the exogenous and endoge-nous exergy destructions that determine the interactions betweencomponents, and they were the rst to submit the calculationmethod they presented. The calculations were expressed using asimple refrigeration cycle and a simple gas turbine cycle. Razmaraand Saray [7] investigated the destruction of exogenous andendogenous exergy by the engineering method for a simple gasturbine cycle operating using different fuels. The irreversibilitiesobserved in the components were described and compared forthese fuels. Morosuk and Tsatsaronis [8] applied advanced exergyanalysis to a simple gas turbine cycle to assess its performanceand discussed their calculation methods in detail. Tsatsaronis andMorosuk [9] performed advanced exergy analysis of a natural gasliquefaction plant using a three-stage refrigeration cycle. They de-ned the improvement potentials and interactions between thecomponents. Morosuk et al. [10] analyzed a natural gas degasica-

Nomenclature

_E exergy rate (MW)_m mass ow rate (kg/s)P pressure (kPa)T temperature (K)y exergy destruction ratio

AbbreviationsAC air compressorCC combustion chamberCOND condenserGT gas turbineHPST high pressure steam turbineHRSG heat recovery steam generatorLPST low pressure steam generator

E. Akkalp et al. / Energy Conversiotion plant that produced electricity using advanced exergy and ad-vanced exergoenvironmental methods. They concluded that theexpander II, the heat exchanger II and the pump deserved the mostattention in improving the thermodynamic efciency and reducingthe environmental impact of the plant. Wang et al. [11] analyzed apower plant operating under supercritical conditions using ad-vanced exergy analysis and proposed suitable optimization strate-gies. They recommend that the generator be improved rst,followed by the turbines. Petrakopoulou et al. [12] studied a com-bined power plant using advanced exergy and conventional analy-ses and demonstrated the superiority of the former. They reportedthat an advanced exergy analysis provided a wide range of optimi-zation strategies and potential improvements. Petrakopoulou et al.[13] applied advanced exergy and advanced exergoenvironmentalanalysis methods to a combined power plant. They determinedthat 68% of the environmental impact of the system was unavoid-able. In Refs. [14,15], an advanced exergoeconomic analysis wasapplied to a combined (CHP) system and oxy-fuel power plant withCO2 capture, and the methodology employed to conduct advancedexergoeconomic analysis was explained in a detailed manner.

In the present paper, an advanced exergy analysis method is ap-plied to an electricity-generating facility using natural gas. Thus,the actual potential improvements of the system and the relation-ships between the components are determined, and possible sug-gestions towards increasing the system efciency are provided.steam turbine (LPST) and a condenser (COND). Approximately37 MW of electricity is generated by the system, but the processsteam cannot be used because of the chemicals included in thesteam. A 45.07 air/fuel ratio combustion equation for natural gasis as follows [1619]:

0:9334CH4 0:00211C2H6 0:00029C3H8 0:00012C4H10 0:06408N2 26:51870:7748N2 0:2059O2 0:0003CO2 0:01H2O! 0:9469CO2 2:3800H2O 3:5831O2 20:8671N2 12. System description

The electricity-generating facility using natural gas is shown inFig. 1. This system is located in the Eskisehir Industry Estate Zone,Turkey. The system consists of a compressor (AC), a combustionchamber (CC), a gas turbine (GT), a heat recovery steam generatorUN unavoidable

Greek lettersg isentropic/energetic efciency (%)D destructionF fuelk kth componentL lossP producttot total

SuperscriptsAV availabled Management 82 (2014) 146153 147The specic heat of the combustion gas and the air can becalculated from Eqs. (2) and (3), respectively [1619]:

cP;gasT 0:935301 0:010577102

T 0:017218105

T2

0:072386109

T3 2

cP;airT 1:04841 0:000383719T 9:45378107

T2

5:490311010

T3 7:929811014

T4 3

The lower heating value of the natural gas, the gas constant ofthe combustion gas and the gas constant of air are 44661 kJ/kg,0.2947 kJ/kg K and 0.2870 kJ/kg K, respectively, and the specicexergy of natural gas (CaHb) is calculated as follows [20]:

ech;FLHV

kF 1:033 0:0169 ba0:0698

a4

where kF is 1.0308. The xed parameters of the system are listed inTable 1.

the investigated system.

Table 2Mass ow rates, pressures, temperatures, energy rates and exergy rates for theelectricity facility using natural gas.

Point Fluid _m (kg/s) T (K) P (kPa) _E (MW)

anFig. 1. Schematic of

Table 1Fixed parameters of the electricity facility using natural gas.

Parameter Unit Value

_WAC MW 51.082

148 E. Akkalp et al. / Energy Conversion3. Analyses done

3.1. Conventional exergy analysis

The main equations for the exergy analysis of the kth compo-nent and the overall system are the same [6,21], but there is onedifference associated with the treatment of the exergy losses: Itis assumed that the system boundaries used for all exergy balancesare at the temperature T0 of the reference environment, and there-fore, there are no exergy loses associated with the kth component[6,22]. Exergy losses appear only at the level of the overall system[6]. The exergy destruction rate can be calculated as follows [21]:

_ED _EF _EP 5The exergetic efciency is [21]:

/ _EF_EP

or / 1_ED_EF

6

The exergy destruction ratio is a ratio of the component exergydestruction rate to the total exergetic fuel rate [21]:

yk _ED;k_EF;tot

7

For the overall system [21]:

_EF;tot _EP Xk

_ED;k _EL 8

where _EL is the rate of exergy loss of the system or control volumeto the environment, which can no longer be used. The properties at

_WGT MW 85.183_WHPST MW 10.278_WLPST MW 4.394

gAC 0.790gGT 0.730gHPST 0.890gLPST 0.370d Management 82 (2014) 146153various locations and the results of the conventional exergy analysisof the system are described in Tables 2 and 3, respectively.

3.2. Advanced exergetic analysis

3.2.1. Unavoidable and avoidable exergy destructionsThe inefciencies of a thermal cycle are caused by exergy

destruction (entropy generation or irreversibilities). Part of theexergy destruction is avoidable, while part of it is not. The unavoid-able exergy destruction rate _EUND;k results from technological and

1 Air 138.00 284.15 101.32 0.0462 Air 138.00 621.15 1045.00 42.6483 Fuel 2.59 298.15 2292.00 121.3024 Combustion gas 140.59 1311.15 992.75 125.1425 Combustion gas 140.59 811.15 112.00 34.3006 Combustion gas 140.59 398.15 103.20 2.1627 Water 16.39 353.15 6850.00 0.4208 Water 3.82 351.15 560.00 0.0699 Water 16.39 772.15 6500.00 22.634

10 Water 3.82 468.15 510.00 2.87911 Water 16.39 438.15 395.00 11.46912 Water 20.21 443.15 420.00 14.36713 Water 20.21 315.65 8.50 2.75314 Water 20.21 309.15 8.20 0.01515 Water 722.23 298.15 300.00 0.13016 Water 722.23 309.15 285.00 1.206

Table 3Exergetic parameters of the electricity facility using natural gas.

Component _EF (MW) _EP (MW) _ED (MW) / y

AC 51.082 42.602 8.480 0.840 0.030GT 90.846 85.183 5.663 0.940 0.020CC 121.302 73.982 47.32 0.610 0.150HRSG 32.034 25.024 7.010 0.780 0.020HPST 11.165 10.278 0.887 0.920 0.003LPST 11.614 4.394 7.220 0.380 0.020COND 2.738 1.076 1.662 0.390 0.005

economic limitations and cannot be improved. The avoidable partof the exergy destruction rate _EAVD;k is the remaining part of theexergy destruction rate and represents the improvement potentialof the component.

For calculating the unavoidable exergy destruction, each com-ponent is considered in isolation and separated from the system.The ratio of the exergy destruction per unit of product exergy _ED_EP

UN

kis calculated assuming operation with high efciency and

low losses. Equations used for calculating avoidable and unavoid-able exergy destruction rates can be seen in Fig. 2. In addition,these equations can be listed as follows:

Unavoidable exergy destruction rate is:

_EUND;k _EP;k_ED;k_EP;k

!UN9

Avoidable exergy destruction rate is:

veals the effects of the system on the considered component

seen in Fig. 2.

_EAV ;END;k _EEND;k _EUN;END;k 15

_EAV ;EXD;k _EAVD;k _EAV ;END;k 16

4. Results and discussion

According to the conventional exergy analysis, thermodynami-cally, the most important component seems to be the combustionchamber because of exhibiting the maximum exergy destructionrate of the system components (47.32 MW). Exergy destruction ismeasure for the irrevesibilities in a system. As expected, that thehighest exergy destruction rate is at the CC because chemical reac-tions cause irreversibilities highly. Therefore, one should focus onthe improvement of the CC. Increasing the airfuel mass ratiocan cause decreasing the exergy destruction rates. The minimumexergy destruction rate is due to the HPST (0.887 MW). Similarly,

E. Akkalp et al. / Energy Conversion an[23]. Equations used for calculating endogenous and exogenousexergy destruction rates can be seen in Fig. 3._EAVD;k _ED;k _EUND;k 10

3.2.2. Destruction of endogenous and exogenous exergyThe destruction of endogenous _EEND and exogenous _EEXD exer-

gy are used to determine relationships between the components ofthe investigated system. Endogenous exergy destruction is theexergy destruction that occurs in the component itself. Exogenousexergy destruction is the exergy destruction caused by the othercomponents. The endogenous part of the exergy destruction isassociated only with the irreversibilities occurring within the kthcomponent when the following two conditions are simultaneouslyfullled:

All other components operate in an ideal manner. The component being considered operates with its current ef-ciency [2,3].

The exogenous part of the exergy destruction rate is calculatedby subtracting the endogenous exergy destruction rate from thereal exergy destruction rate. The exogenous exergy destruction ofa component can be divided as _EEX;nD;k , which represents the effectsof the nth component on the irreversibilities on the kth compo-nent. The difference between the sum of all the _EEX;nD;k terms andthe overall exogenous exergy destruction rate is described as mex-ogenous exergy destruction. Mexogenous exergy destruction re-Fig. 2. Dividing exergy destruction rate to avoidable and unavoidable parts [2].Unavoidable endogenous, unavoidable exogenous, avoidableendogenous and avoidable exogenous destruction rates, respec-tively, are:

_EUN;END;k _EENP;k_ED;k_EP;k

!UN13

_EUN;EXD;k _EUND;k _EUN;END;k 14Exogenous exergy destruction rate is:

_EEXD;k _ED;k _EEND;k 11Mexogenous exergy destruction rate is;

_EMEXD;k _EEXD;k Xj1r1rk

_EEX;nD;k 12

3.2.3. Splitting unavoidable and avoidable exergy destructionThe unavoidable endogenous exergy destruction rate _EUN;END;k ,

the unavoidable exogenous exergy destruction rate _EUN;EXD;k , theavoidable endogenous exergy destruction rate _EAV ;END;k and theavoidable exogenous exergy destruction rate _EAV ;EXD;k are can be

Fig. 3. Dividing exergy destruction rate into endogenous and exogenous parts [2].d Management 82 (2014) 146153 149the maximum exergy efciency is due to the GT (0.92), while theminimum efciency is obtained for the LPST (0.38). This meansthat the efciency of the GT is the closest to the efciency of Car-

not, while the LPST is far away from it. Exergy destruction ratio isanother parameter to evaluate the system performance. It repre-sents the ratio of the exergy destruction rate to the total fuel exer-gy ratio. The exergy destruction rates of the other components, theexergy efciencies and the exergy destruction ratios are listed inTable 3. In addition, the magnitudes of the exergy destructionrates, the exergy efciency, and the exergy destruction ratios ofthe system are shown in Figs. 46, respectively.

The effect of the environment temperature values (273.15 K,283.15 K and 298.15 K) on the exergy efciency, the exergydestruction rates and the exergy destruction ratios is also investi-gated through a parametric study undertaken, as shown in Figs. 57. It is clear from Fig. 7 that the environment temperature has nobig effect on the components. Similar to the exergy destructionrate, the dead state temperature has no important effect on thecomponents exergy efciencies and exergy destruction ratios, asillustrated in Figs. 8 and 9.

tion of exogenous exergy _EEXD;k, _EAV ;EXD;k and _EUN;EXD;k revealed that theexergy destruction within each of these components could be de-creased by the increase in the exergy destruction within the othercomponents. Avoidable exergy destruction indicates the improve-ment potential for the components, while unavoidable exergy

AC

GT

CC

HRSG

0.0 0.2 0.4 0.6 0.8 1.0Exergy Efficiencies of Components

Syste

m C

ompo

nent

s

Fig. 5. Exergy efciencies of the components in the system.

AC

GT

CC

HRSG

HPST

LPST

COND

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16Exergy Destruction Ratios of Components

Syste

m C

ompo

nent

s

Fig. 6. Exergy destruction ratios of the components in the system.

AC GT CC HRSG HPST LPST COND

0

10

20

30

40

50

Exer

gy d

estru

ctio

n ra

te (M

W)

Components

298.15 K 283.15 K 273.15 K

Fig. 7. Variation of exergy destruction rates with environmental temperature.

150 E. Akkalp et al. / Energy Conversion anUncertainties in the measurement and total exergy values aregiven as follows:

Uncertainties for temperature, mass ow rate and pressure are0.5 C, 0.5% and 0.91%, respectively. Uncertainties associatedwith the total fuel exergy rate, the product exergy rate and theexergy efciency are calculated to be 4.537%, 3.171% and 4.254%,respectively.

The details of the advanced exergy analysis of the system inves-tigated are presented as follows while the assumptions for the ad-vanced exergy analysis are listed in Table 4. The results for theadvanced exergy analysis are also listed in Tables 5 and 6. Assump-tions for the advanced exergy analysis are divided into two parts.Theoretical conditions are dened for determining the endogenousand exogenous exergy destruction rates. For determining theavoidable and unavoidable exergy destruction rates, assumptionsmust represent limitations that cannot be reached at a decade.The following results are based on the parameters given in Table 5.

The endogenous exergy destruction rates are greater than thecorresponding exogenous exergy destruction rates for the GT, CC,HPST and LPST, i.e., the exergy destruction in each of these compo-nents resulted from the component itself. The maximum endoge-nous exergy destruction is in the CC, due to the great chemicalirreversibility caused by the combustion process in it. The exoge-nous exergy destruction rates were found to be greater thanendogenous exergy destruction rates for the AC, HRSG and COND,i.e., these components were affected at higher levels by other com-ponents, and the exergy destruction within each of these compo-nents could be reduced by increasing the exergy destructionwithin the other components. The negative values for the destruc-

AC

GT

CC

HRSG

HPST

LPST

COND

0 10 20 30 40 50

Syste

m C

ompo

nent

sExergy Destruction Rates of Components (MW)

Fig. 4. Exergy destruction rates of the components in the system.HPST

LPST

COND

d Management 82 (2014) 146153destruction indicated the constraints. The unavoidable exergydestruction was greater than the avoidable exergy destruction ofeach of the system components, except for the HPST and COND.

This observation led to that the system had a low potential forimprovement. However, the maximum potential for improvementwas in the CC (23.350 MW), which could be realized by enhancingthe combustion efciency. The largest fraction of the avoidableexergy destruction rate was endogenous (12.259 MW) and theremaining part (11.091 MW) was exogenous. In addition, investi-gating the mexogenous exergy destruction of each component,GT exhibited the maximum effect on the CCs exergy destruction,

AC GT CC HRSG HPST LPST COND0.0

0.2

0.4

0.6

0.8

1.0

Exer

gy e

ffici

ency

Component

298.15 K 283.15 K 273.15 K

Fig. 8. Variation of exergy efciencies with environmental temperature.

AC GT CC HRSG HPST LPST COND0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

Exer

gy d

estru

ctio

n ra

tio

Components

298.15 K 283.15 K 273.15 K

Fig. 9. Variation of exergy destruction ratios with environmental temperature.

Table 4Assumptions used in the advanced exergy analysis.

Component Operating Theoretical UnavoidableConditions Conditions Conditions

AC g 0:79 g 1 g 0:85CC DP 52 kPa DP 0 DP 0

k 2:91 k 2:91 k 3:5GT g 0:73 g 1 g 0:80HRSG DTmin 200 K DTmin 0 DTmin 150 K

DP %5 DP 0 DP 0HPST g 0:89 g 1 g 0:95LPST g 0:37 g 1 g 0:50COND DTmin 6:5 K DTmin 0 DTmin 5 K

DP %5 DP 0 DP 0

Table 5Advanced exergy parameters of the system.

Component _ED;k (MW) _EEND;k (MW)_EEXD;k (MW)

_EAVD;k (MW)_EUND;

AC 8.48 1.662 6.818 0.982 7.GT 5.663 10.283 4.620 1.489 4.CC 47.320 24.989 22.331 23.350 23.HRSG 7.010 1.052 5.958 0.376 6.HPST 0.887 0.538 0.349 0.496 0.LPST 7.220 15.703 8.483 1.481 5.COND 1.662 0.753 0.909 1.007 0.

E. Akkalp et al. / Energy Conversion and Management 82 (2014) 146153 151and the ACs exergy destruction must be increased to decreasethe CCs exergy destruction. The mexogenous exergy destructionof the COND had a negative value, i.e., the systems exergy destruc-tion must be increased to decrease CONDs exergy destruction.Using only the conventional exergy analysis, the AC and HRSGwere concluded to have high exergy destruction rates. However,when evaluating these components using advanced exergy analy-sis, 7580% of these components exergy destruction rates weredetermined to be associated with other components because theyhave high exogenous exergy destruction rates. Exogenous exergydestruction rates for AC and HRSG are (6.818 MW) and(5.958 MW) respectively.

The mexogenous exergy destruction rates of the AC and HRSGdetermined which components had signicant effects on them.According to Table 6, the results of analyzing the mexogenousexergy destruction indicated that CC and GT affected the ACequally and that the HRSG was affected primarily by the CC. To de-crease the exergy destruction of these components, both CC and GThad to be improved. For the GT and LPST, the results of the conven-tional exergy analysis were misleading. Although the GT and LPSThad higher exergy destruction rates, their potentials for improve-ment were low and associated with the exergy destruction ratesof the other components. The results of the advanced exergy anal-ysis of the HPST and COND concluded that one should focus onimprovements in each of the components themselves rather thanthe effects of other components.

Figs. 1013 indicated the breakdown of the advanced exergeticdestruction parameters for the entire system. According to Fig. 10,the endogenous exergy destruction apparently had the highest rate(70.3%). This high rate led to that the relationships between thesystem components were very weak for the system. A similar re-sult was apparent in the data shown in Fig. 11. The potentialimprovement of the exergy destruction cost rates of the entire sys-tem was only 37.3%. In addition, 76.5% of this improvement poten-tial was based on the components themselves (Fig. 12). It isapparent in Fig. 13, that the unavoidable parts of the exergydestruction rate were primarily endogenous.

The following results are acquired when the considered plant iscompared to some systems in the literature [412]: In Ref. [4], theauthors dened the avoidable and the unavoidable exergetic partsof a cogeneration system. They determined that avoidable part ofthe exergy destruction consisted of 41% of the total exergy destruc-tion. This means that the improvement potential of the system isrelatively low. In Ref. [5], a similar investigation was performedfor externally red combined-cycle power plant. The resultsshowed that the avoidable exergy destruction was equal to 33%.Thus, the system had a lower improvement potential. Compressor

k (MW) _EAV ;END;k (MW)

_EAV ;EXD;k (MW)_EUN;END;k (MW)

_EUN;EXD;k (MW)

498 0.530 1.512 2.192 5.306174 7.625 6.136 2.658 1.516970 12.259 11.091 12.730 11.240634 0.915 1.291 1.967 4.667391 0.308 0.188 0.230 0.161

739 2.945 1.464 12.758 7.019655 0.627 0.380 0.126 0.529

3 had the biggest improvement potential. In Ref. [6], refrigerationand simple gas turbine systems were investigated. Their exergydestructions were divided into endogenous and exogenous parts.In the refrigeration system, the endogenous part of the exergydestruction rate was 67.6%. So, the relations of the components atthe systemwere weak because of high endogenous exergy destruc-

ferent fuels. For both system, endogenous exergy destruction ratesof the system was bigger than exogenous exergy destruction rates.approximately 64% of total exergy destruction rate was endogenousin simple gas turbine cycle and similarly, about 78% of the totalexergy destruction rate was endogenous in the cogeneration sys-

Table 6Mexogenous exergy parameters of the system.

Exogenous exergy destructionof each component (MW)

Effects of the other components on theexogenous exergy destruction (MW)

AC CC 2.7196.818 GT 2.689

MX 1.410

CC GT 24.37322.331 AC-4.732

MX 2.690

HRSG AC 0.0985.958 CC 2.174

GT 0.626MX 3.060

HPST AC 0.0250.349 CC 0.022

GT-0.013HRSG 0.035MX 0.280

COND AC 0.1330.909 CC-0.048

GT 1.850HRSG-0.140HPST 0.420LPST 3.178MX-4.484

152 E. Akkalp et al. / Energy Conversion antion rate. The endogenous exergy destruction part of the systemFig. 10. Breakdown of the endogenous and exogenous exergy destruction rates ofthe system.

Fig. 11. Breakdown of the available and unavoidable exergy destruction rates of thesystem.was 68.9%, and similar to the refrigeration cycle, the relations ofthe components were weak. In Ref. [7], one investigated a simplegas turbine cycle and cogeneration system that operated with dif-

Fig. 12. Breakdown of the avoidable destruction of rates the system.

Fig. 13. Breakdown of the unavoidable exergy destruction rates of the system.d Management 82 (2014) 146153tem. In Ref. [8], advanced exergy analysis for chemical reacting sys-tems was performed using a simple open gas turbine cycle. It wasfound that 77% of the exergy destruction rate was endogenousand only 29% of the system had improvement potential. A systemgenerating electricity and vaporizing liqueed natural gas wasinvestigated with advanced exergy analysis [9]. 88% of the exergydestruction rate was endogenous and its 57% was improvable. Asystem that included liquid natural gas regasication and an elec-tricity generation system was also analyzed using advanced exer-gy-based methods in Ref. [10]. One found that the system had57% improvement potential. In Ref. [11], endogenous exergy ratewas 85% for the system and its improvement potential was only8%. In Ref. [12],endogenous exergy rate consisted of 83% of the totalexergy destruction. In addition to that the improvement potentialof the systemwas 33%. When the considered systemwas comparedto others, endogenous exergy destruction rates of the systems werehigher, ranging from 65% to 85% generally as it was our consideredsystem. The improvement potentials of the other system also variedfrom 30% to 40% while our system had 37.3% improvement poten-tial. Based on the results listed above, our system represents a goodagreement with ones in the literature.

5. Conclusions

In this paper, we have assessed the performance of an electric-ity generation facility using natural gas through advanced exergyanalysis based on the actual operational data. We have concluded

that conventional exergy analysis could lead to misinterpretationsthat result in incorrect improvement strategies. In addition, onewas not able to provide any information about the relationshipsbetween the components of the system through the conventionalexergy analysis only while these shortcomings could be addressedusing an advanced exergy analysis.

We have listed some concluding remarks as follows:

(a) The relations between the components are week becausetotal endogenous exergy destruction rate is 70% of the totalexergy destruction.

(b) The improvement potential of the system is 38%, meaningthat systems improvement potential is low.

(c) An advanced exergy analysis of the system determined thatone should focus on the GT and CC for possible improvementof the system, which are the most important components ofthe system.

(d) This paper also clearly indicates that conventional exergyanalyses are not enough to evaluate an energy conversionsystem and it is recommended performing advanced based

[6] Kelly S, Tsatsaronis G, Morosuk T. Advanced exergetic analysis: approaches forsplitting the exergy destruction into endogenous parts. Energy2009;34:38491.

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Acknowledgement

The authors are very grateful to the reviewers for their valuableand constructive comments, which have been utilized to improvethe quality of the paper. They also would like to thank all the tech-nical staff of the investigated facility, located in the EskisehirIndustry Estate Zone in Turkey.

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Advanced exergy analysis of an electricity-generating facility using natural gas1 Introduction2 System description3 Analyses done3.1 Conventional exergy analysis3.2 Advanced exergetic analysis3.2.1 Unavoidable and avoidable exergy destructions3.2.2 Destruction of endogenous and exogenous exergy3.2.3 Splitting unavoidable and avoidable exergy destruction

4 Results and discussion5 ConclusionsAcknowledgementReferences