Degradation Effects on Comined Cycle Power Plant Performance

urbines tur-d Gaserfor-cycleessorr deg-roce-he pa-

on the

Downl

A. I. Zwebek

P. Pilidis

Department of Power Engineering andPropulsion,

School of Engineering,Cranfield University,

Bedford MK43 0AL, UK

Degradation Effects on CombinedCycle Power Plant Performance—Part III: Gas and Steam TurbineComponent Degradation EffectsThis paper presents an investigation of the degradation effects that gas and steam tcycles components have on combined cycle (CCGT) power plant performance. Gabine component degradation effects were assessed with TurboMatch, the CranfielTurbine simulation code. A new code was developed to assess bottoming cycle pmance deterioration. The two codes were then joined to simulate the combinedperformance deterioration as a whole unit. Areas examined were gas turbine comprand turbine degradation, HRSG degradation, steam turbine degradation, condenseradation, and increased gas turbine back pressure due to HRSG degradation. The pdure, assumptions made, and the results obtained are presented and discussed. Trameters that appear to have the greatest influence on degradation are the effectsgas generator.@DOI: 10.1115/1.1639007#

9

i

aah

n

s

-t

cot

a

s

t

o

ct onofe onam

onpathred

tur-

for-anyd.on

rine

nethat

a

I

IntroductionThe rapid improvement of gas turbine technology in the 19

drove combined cycle thermal efficiency to nearly 60% with naral gas as a fuel~Briesch and Bannister@1#!. It will probably goeven higher in the future. This high plant efficiency along wlow emissions and competitive capital and running costs madecombined cycle gas turbine~CCGT! plant a very popular primemover for electricity generation.

This interest increase in the CCGT plants led to the userssuch plants to become more concerned about the plant’s behafter running for long times. As a result, simulation codesdeveloped to predict the behavior of such power plants and tsubsystems on a thermo-fluid dynamic basis~Erbes and Gay@2#,Roy-Aikins @3#, and Thermoflow@4#!.

This is the third in a series of three technical papers lookingthe degradation effects that different components of combicycle have on the plant’s performance.

The first paper~Zwebek and Pilidis@5#! presented the effectthat gas turbine components degradation have on gas turbinehence on the overall CCGT plant, the second paper~Zwebek andPilidis @6#! discussed the steam~bottoming! cycle component degradation effects have on CCGT plant. The conclusion of thepapers mentioned above is summarized herein. In the first pa@5#, it was concluded that the GT turbine degradation hasutmost effect on gas turbine as well as on steam turbine cyperformances compared to GT compressor. Also, it was shthat the GT exhaust temperature has a predominant effecsteam cycle efficiency over the GT exhaust mass flow. Becathe CCGT plant is more dependent on the gas turbine, andwas expected, the CCGT plant performance was more sensitivchange in gas turbine cycle conditions than to the changesteam turbine cycle conditions.

The conclusion from the second paper,@6#, was that, within theHRSG unit, the evaporator degradation is the utmost effecfault on steam turbine cycle performance compared to superheand economizer. Also concluded that, the steam turbine isentr

Contributed by the International Gas Turbine Institute~IGTI! of THE AMERICANSOCIETY OF MECHANICAL ENGINEERSfor publication in the ASME JOURNAL OFENGINEERING FOR GAS TURBINES AND POWER. Paper presented at the Interntional Gas Turbine and Aeroengine Congress and Exhibition, Amsterdam, The Nerlands, June 3–6, 2002; Paper No. 2002-GT-30513. Manuscript received byDec. 2001, final revision, Mar. 2002. Associate Editor: E. Benvenuti.

306 Õ Vol. 126, APRIL 2004 Copyright © 2

oaded 11 Feb 2008 to 138.250.82.63. Redistribution subject to ASME li

0stu-

ththe

ofviorreeir

ated

and

woper,theleswnon

uses ite to

in

ingaterpic

efficiency as a performance parameter has the uppermost effesteam turbine cycle power and efficiency. Finally, the effectsHRSG and condenser degradations on steam cycle and hencCCGT plants performance is very low compared to the steturbine unit components degradation.

GasÕSteam Turbine Performance Deterioration. Even un-der normal engine operating conditions, with good inlet filtratisystems, and using a clean fuel, the gas turbine engine flowcomponents will become fouled, eroded, corroded, and covewith rust scale,~Diakunchak @7#, Lakshminarasimha et al.@8#,Tabakoff@9#, and Tabakoff et al.@10#, and others!. The results willthen be an engine performance deterioration. Since the gasbine, in this case, is connected to another plant~steam cycle!which is entirely dependent on it, then the concern due to permance deterioration will increase. This is due to the fact thatfailure or malfunctioning within the gas turbine will be magnifieas it would be affecting the two~CCGT! plants at the same time

This paper explores different component degradation effectsa simple combined cycle~CCGT! plant of Fig. 1. The plant undeconsideration is composed of a single-shaft industrial gas turbcoupled with a single-pressure HRSG steam~bottoming! cycle.

The ~design point! specifications of both gas and steam turbiplants used with this unfired cycle were chosen in such a waythey represent an existing typical real cycle, as follows:

Gas Turbine Specificationsinlet mass flow5408.6 kg/seccompressor pressure ratio515.2turbine entry temperature51697.80 Kexhaust mass flow5419.4 kg/secexhaust temperature5871.24 Kpower5165.93 MWthermal efficiency535.57%

Steam Turbine Specificationslive steam pressure565.4 barlive steam temperature5537.8°Csteam mass flow567 kg/secsteam turbine isentropic effic.589.48%superheater surface area58424.8 m2

evaporator surface area529315.6 m2

economizer surface area538004.1 m2

condenser surface area53942.9 m2

-eth-GTI,

004 by ASME Transactions of the ASME

cense or copyright; see http://www.asme.org/terms/Terms_Use.cfm

e

n

t

oc

lo

h

ni

po-ple.let

effi-pre-tur-

so-

)

ap

effi-uch

fndthehe

ate GT

ntsultsnt.wast on5%

y to

wnfied,the

he

Downl

HRSG efficiency581.11%steam turbine plant power output576.4541 MWsteam turbine plant efficiency533.97%

The effects of the gas turbine degradation on steam cycle,hence on the CCGT plants performance as whole was invgated. The faults investigated were the following:

i. compressor isentropic effic. degradation,ii. turbine isentropic efficiency degradation,iii. compressor and turbine fouling,iv. compressor and turbine erosion,v. economizer degradation,vi. evaporator degradation,vii. superheater degradation,viii. steam turbine fouling,ix. steam turbine erosion,x. ST isentropic efficiency degradation,xi. condenser degradation,xii. combination of all faults mentioned above, andxiii. gas turbine back pressure increase due to heat excha

~HRSG! surfaces fouling.

The terms fouling and erosion are used in the context of owork, ~Diakunchak@7# and Lakshminarasimha et al.@8#!. In thecase of gas turbine unit, because the combustion system islikely to be a direct cause of gas turbine performance deteriora~Diakunchak@7#! it was assumed not to degrade for the followinreasons:

i. Combustion chamber faults that affect GT overall perfmance are rare in comparison to those faults that may oin the compressor and turbine.

ii. Any malfunctioning in the combustion chamber woumean increased emissions, which is not allowed by envirmental laws in many places.

Fault RepresentationIn order to investigate the effects of faults mentioned in pre

ous section on the Gas/steam turbine plants performancestanding alone units, and hence on CCGT plant as a whole, tfaults were fed into the program as a percent reduction oforiginal design point value~shown 0.0 in Table 1!. This is done asfollows:

Fouling: GT compressor, GT turbine, and ST turbine foulingrepresented by reduced flow capacity at the inlet of the compoplus a reduction in the component isentropic efficiency. By doso, it is assumed that there is a blockage in the inlet area of

Fig. 1 Schematic diagram of a single pressure CCGT powerplant

Journal of Engineering for Gas Turbines and Power


andsti-

ger

her

nottiong

r-cur

dn-

vi-as aese

the

isentngthe

component due to fouling along with a decrease in the comnent’s isentropic efficiency due to surface roughness, for exam

Erosion: Compressor erosion is represented by a lower inmass flow capacity and a reduction in compressor isentropicciency. On the other hand, GT and ST turbines erosion is resented by an increased flow capacity plus a reduction in thebine isentropic efficiency~Lakshminarasimha et al.@8#!.

These two phenomena are represented by changing thecalled nondimensional mass flow~Eq. ~1!! of the component maps~Table 1!.

WATi

PAis increased or reduced (1

Component Efficiency Degradation: This is modeled by re-ducing the component isentropic efficiency of the appropriate mand keeping all other parameters at their design point~DP! levels.In this case, it was assumed that the component isentropicciency might decrease from its DP value due to any reason, sas blade tip rubs or FOD.

Heat Exchanger Degradation: The degradation of either othe heat exchangers~economizer, evaporator, superheater, acondenser! was simulated by assuming a percent reduction inoriginal DP value of the overall heat transfer coefficient of theat exchanger in concern.

Gas Turbine Back Pressure: The increased back pressurethe gas turbine exhaust is represented as an increase in thexhaust outlet pressure.

The above-mentioned faults are applied to different componeof the plant in different values. Table 1 summarizes these faand their ranges at which they were applied to each compone

Therefore, throughout this study, it was assumed that thereno component washing or any type of maintenance carried outhe gas and steam turbine plants until the deterioration reachedfrom the original design point performance.

Combined Cycle Degradation SimulationBefore starting any degradation simulations it was necessar

establish a datum working line~design point performance! of bothplants. This base line performance point is represented by~0.0!value in Table 1 above and on all deterioration graphs shobelow. Once the design point performance has been identithen the magnitude of faults representing a physical fault ofcomponent in consideration,~see ‘‘faults representation’’!, to beimplanted on each component has to be established.

Unfortunately, although there is a lot of work published on tsubject of gas turbine performance deterioration~Tabakoff @9#,

Table 1 Representation of component degradation

Fault Represented By Range

Compressor fouling Drop inG 0.0–~25.0%!Drop in hC 0.0–~22.5%!

Compressor erosion Drop inG 0.0–~25.0%!Drop in hC 0.0–~22.5%!

Turbine fouling Drop inG 0.0–~25.0%!Drop in hT 0.0–~22.5%!

Turbine erosion Rise inG 0.0–~15.0%!Drop in hT 0.0–~22.5%!

FOD Drop inhC andhT 0.0–~25.0%!Gas turbine backpressure

GT Back pressurerise

0.0–~13.0%!

Economizer degradation Drop inU 0.0–~25.0%!Evaporator degradation Drop inU 0.0–~25.0%!Superheater degradation Drop inU 0.0–~25.0%!Condenser degradation Drop inU 0.0–~25.0%!Steam turbine fouling Drop inG 0.0–~25.0%!

Drop in hT 0.0–~22.5%!Steam turbine erosion Rise inG 0.0–~15.0%!

Drop in hT 0.0–~22.5%!FOD Drop inhT 0.0–~25.0%!

APRIL 2004, Vol. 126 Õ 307


l

n

-

nls

n

ra-ver

. 3gasac-

ure

e itor

wasto

umes

esssure

byost

gas, it

Downl

Tabakoff et al.@10#, Diakunchak@7#, and Lakshminarasimha et a@8#, and others!, the applied degradation magnitude to each coponent, when simulating gas turbines deterioration performain most cases is either arbitrary or based on some publishedperimental results. Therefore, in present study the values mtioned by Diakunchak@7# and Escher@11# were taken as a guidelines from which the implanted faults were estimated. Table~Zwebek and Pilidis@5#! shows a summary of how componeisentropic efficiency changes vary with degradation. These vawere applied in all calculations to the appropriate component

Based on what is mentioned above, in the case of steam turplant, it was also assumed that every 1.0% deterioration in mflow capacity~fouling or erosion! would result in a deteriorationof ~0.50%! in steam turbine isentropic efficiency.

Unfortunately, not much literature was found on the subjectCCGT plant degradation, or on modeling of this problem, incluing the effect of GT back pressure rise. Therefore to simulateeffect of back pressure on gas turbine performance, due to HRdegradation some assumptions have been made. An increaback pressure by'0.0025 atm results in a reduction in gas turbipower by '0.3%. Typical back pressure ranges from 0.0250.037 atm above the design value. Because of the inherent plems which accompanies the increase of back pressure, e.g.,

Table 2 Component isentropic efficiency variation with degra-dation

Physical Fault

NondimensionalMass FlowChange~A!

IsentropicEfficiencyChange

~B!RatioA:B

Compressor fouling Gc↓ hc↓ ;1:0.5Compressor erosion Gc↓ hc↓ ;1:0.5Compressor corrosion Gc↓ hc↓ ;1:0.5Turbine fouling GT↓ hT↓ ;1:0.5Turbine erosion GT↑ hT↓ ;1:0.5Turbine corrosion GT↓ hT↓ ;1:0.5Foreign object damage GC/T↓ hC/T↓ ;1:2.0Thermal distortion GT↑↓ hC/T↓ ;1:2.0Blade rubbing GC↓ & GT↑ hC/T↓ ;1:2.0

308 Õ Vol. 126, APRIL 2004


.m-ce,ex-en-

2tues.

bineass

ofd-theSG

se inetorob-high

torque on the shaft, coupling forces on thrust bearing, and vibtion, it was assumed that maximum it can go up to 0.03 atm othe DP value.

It is worth reminding the reader here that the values in Figand in the following successive figures are also including theturbine back pressure rise due to HRSG degradation. This iscomplished by implanting a value of GT exhaust back pressrise with a corresponding GT degradation~fouling/erosion! valueas shown in Table 3.

Gas Turbine Degradation Simulation ResultsDue to its working nature and depending on the place wher

is installed, it was assumed that the gas turbine might foulerode. Therefore, the simulation strategy of the gas turbinedivided into two different categories. The first strategy wasassume that the gas turbine will foul up~25.0%! from its originalDP performance. On the other hand, the second strategy assan erosion in gas turbine gas path components up to~15.0%!from their DP performance. In parallel with each of the casmentioned above, an amount increase in gas turbine back predue to degraded HRSG was assumed as shown in Table 3.

As Fig. 2 shows, a back pressure increase of~3.0%! resulted ina reduction in gas turbine thermal efficiency and power~22.0%! approximately. While the exhaust mass flow was almconstant, the exhaust temperature increased by about~0.75%!from its original DP value.

Figure 3 summarizes the main performance parameters ofturbine and how they vary with degradation. As it can be seen

Table 3 GT back pressure distribution along with other com-ponents degradation

GT Back Pressure GT Fouling GT Erosion

11.0% 21.0% 11.0%11.5% 22.0% 12.0%12.0% 23.0% 13.0%12.5% 24.0% 14.0%13.0% 25.0% 15.0%

Fig. 2 Back pressure effects on GT performance

Transactions of the ASME


Journal of Engineeri

Downloaded 11 Feb 2008 to 13

Fig. 3 GT performance parameters variation with gas turbine cycle componentdegradation

a

o

r

e

o.s

t

n

bye inithue

re

s ined

nss isl-

leassitless

cle. 5.werr ass in-aust

eamand,

ongnd

isthe

tharly

edrre-

seems that the effect of either fouling or erosion is tending to ha similar curvature trend, but the magnitude is different.

As this figure shows, the maximum degradation consequewas encountered with gas turbine power deterioration due tocomponent erosion. This was around~215.2%! from the originalDP value. The corresponding plant thermal efficiency drop wabout~211.5%!.

The combination of decreased compressor mass flow withincreased turbine flow capacity, due to erosion by 5%, led thigher ~about 2.5%! reduction in the plant’s overall efficiency incomparison to the case where both components are experienfouling. This is due to the fact that the decreased pressurethrough the turbine due to erosion resulted in a lower power oput of the turbine, and hence a reduced overall power outputhe engine which then reflected on the engine’s overall efficienThis shows that the erosion effect of gas turbine gas path comnents on the gas turbine performance is higher than the foueffect.

Steam Cycle Degradation Simulation ResultsAs it was explained above, since the trend of the GT degra

tion due to either fouling or erosion is the same, and they odiffer in the magnitude, and due to the limited space~page num-bers allowed for this paper! it was decided to discuss only thfault which gave the higher impact on GT performance whsimulating the bottoming cycle. Therefore, as already showsince the GT erosion effects were predominant over the effecfouling, it was decided to use its values when simulating stecycle performance degradation.

The most important steam turbine cycle performance deterition simulation results are represented graphically in Figsthrough 8. It is worth reminding the reader here that the valuethese figures are including also the gas turbine degradation~ero-sion! and GT exhaust back pressure rise effects due to HRdegradation as shown in Fig. 3.

The GT degradation effects on ST as well as on CCGT plawas plotted within the graphs showing those plants degradaFigure 4 shows the effects of degraded topping~GT! as well asbottoming ~ST! cycles on the steam flow through the bottomicycle. As this figure shows, the increase in steam mass flow~about

ng for Gas Turbines and Power

8.250.82.63. Redistribution subject to ASME li

ve

nceGT

as

ana

cingatiout-t ofcy.po-ling

da-nly

ened,t ofam

ra-4in

SG

ntsion.

g

8.3%! was at its highest value with superheater degradation5%. Although the expectation was to see the highest changmass flow variation with GT degradation, the results came up wdifferent values. In reality, this increase in mass flow was not dto degraded superheater. In fact as Zwebek and Pilidis@6# showed,the effect of degraded superheater alone on steam mass flow~without gas turbine degradation! is almost negligible~10.51%!.Therefore, as Eq.~1! shows, the inlet conditions at the ST inlet acontrolled by the so-called nondimensional mass flow~Eq. ~1!above!. Now by comparing the superheater degradation effectFigs. 4, 7, and 8 with GT degradation effects it will be observthat while steam live pressure is almost constant~Fig. 7!, therewas an increase in steam mass flow. Now to fulfil the conditioof Eq. ~1!, then the live steam temperature must increase. Thithe result obtained~as Fig. 8 shows!. The same discussion is amost applicable to all other conditions.

It is well known from the very basics of steam turbine cyctheory that the steam turbine power is a function of steam mflow and its enthalpy. Now by comparing Fig. 5 with Fig. 4would be observed that the steam turbine power is more orfollowing the mass flow behavior.

The effects of degraded topping as well as bottoming cycomponents on steam turbine power plant are illustrated in FigAs this figure shows, the largest displacement of ST turbine pofrom its original DP value was encountered with superheatewell as condenser degradations. Again as stated above, thicrease in ST power is merely due to increased gas turbine exhtemperature due to GT degradation which led to increase stmass flow and hence to increase the ST power. On the other hthe lowest effect on ST power resulted from GT degradation alwith ST turbine isentropic efficiency degradation; this was arou14.2%.

One of the very important results obtained from this studythat, unlike the case with GT or ST degradations alone whererelationship between performance parameter variation~ST power,ST Rankine, etc.! and deterioration is linear, in the case of boplants deteriorated the relationship obtained was also nelinear.

Cerri @12# stated that the maximal CCGT efficiency is reachwhen the GT exhaust temperature is higher than the one co

APRIL 2004, Vol. 126 Õ 309


310 Õ Vol. 126, APR


Fig. 4 ST steam mass flow variation with gas and steam cycles component deg-radation

td

fi-

the

e

sponding to the maximum GT efficiency; i.e., as GT exhaust teperature goes up, the CCGT efficiency goes up. Since gas turefficiency is already at its maximum, and still by increasing Gexhaust temperature~due to any reason! the CCGT will increase.This would then implicitly indicate that this increase is gainedincreased steam turbine plant’s power due to the increased sturbine inlet conditions as explained above. This exactly coinciwith the results obtained in the current study~see Fig. 5!.

The next important performance parameter to discuss herthe steam turbine plant~Rankine! efficiency variation with degra-

IL 2004


m-bineT

byeames

e is

dation, which is illustrated in Fig. 6. The thermal efficiency denition of steam turbine~bottoming! plant is given by

hR5WSC

QHRSG. (2)

This equation shows that the steam turbine~bottoming! cycleefficiency is a function of steam turbine net power output andheat transferred in the HRSG (QHRSG), which is representing theheat input to the steam cycle. Now by looking at Fig. 9 it will b

Fig. 5 Steam turbine power variation with gas and steam cycles component deg-radation



Journal of Engineeri


Fig. 6 Rankine efficiency variation with gas and steam cycles component degrada-tion

fi

oxi-

asns.

bek

eamspec-ue

seen that all types of degradations resulted into an increase inHRSG efficiency, i.e., increasedQHRSG. As Fig. 5 shows, al-though ST power increased with all types of degradation as wyet the increase in theQHRSG ~relative to DP value! in some caseswas higher than the increase in ST power. This led to theefficiency to fall with such cases. This can be clearly seen incase of ST turbine isentropic degradation. In this case, thecrease in ST power was around 4.2% with 5% degradation.though ~as Fig. 9 shows! there was an increase in HRSG efciency by about 4.2%~for the same magnitude of degradation! as

ng for Gas Turbines and Power


the

ell,

STthein-

Al--

well, nevertheless, the increase inQHRSG was predominant andhence resulted in decreasing the ST turbine efficiency by apprmately 3.3%.

As Figs. 5 and 6 show, the ST turbine isentropic efficiency ha predominant effect over all other types of ST cycle degradatioThis is in agreement with the conclusion established by Zweand Pilidis@6#.

The degradation effects of gas and steam plants on live stpressure and temperature are expressed on Figs. 7 and 8, retively. As Fig. 7 shows, the blockage of the steam turbine inlet d

Fig. 7 Live steam pressure variation with gas and steam cycles component deg-radation

APRIL 2004, Vol. 126 Õ 311


312 Õ Vol. 126, APR


Fig. 8 Live steam temperature variation with gas and steam cycles componentdegradation

p

f

rt

pera-ase

ress-GTts

to fouling by 5.0% resulted in about 11.6% increase in live stepressure at the ST turbine inlet. The combination of all other tyof degradation with steam turbine fouling reduced the inlet prsure to about 11.0%. On the other hand, the degradation ocomponents along with steam turbine erosion by 5.0% resulteonly 0.3%~approximately! reduction in live steam pressure.

In the case of live steam temperature, as Fig. 8 shows, the eof different components degradation on live steam temperatumostly controlled by increased gas turbine exhaust temperaAs already shown above~see Fig. 3! the effect of gas turbine

IL 2004


ames

es-all

d in

ffecte isure.

components degradation was to increase the GT exhaust temture. This, then by itself, led the live steam temperature to incre~see explanation above!.

Combined Cycle Degradation ResultsThe degradation results have been explained in part by add

ing the two cycles separately. Figure 10 shows the whole CCplant’s power and how it varies with GT and ST plandegradation.

Fig. 9 HRSG efficiency variation with gas Steam cycles component degradation



Journal of Engineerin


Fig. 10 CCGT power variation with gas and steam cycles component degradation

tT

te

eg-

ely

ntsly.gasbyndture

As this figure shows, although there was an increase inpower~see Fig. 5!, the decrease that was caused by GT power~seeFig. 3! was predominant. This actually is a straightforward ressince GT power counts for the two thirds of the total amountCCGT power. Figure 11 is a reproduction of Fig. 9 showingCCGT efficiency is actually following the behavior of CCGpower.

As the two previous figures showed, the GT turbine degradaalone was having the least effect on CCGT plant power andciency. On the other hand, when the ST component effects wincluded in the degradation, the outcome deterioration resstarted to increase. As these two figures show, the largest de

g for Gas Turbines and Power

.250.82.63. Redistribution subject to ASME li

ST

ultofhe

ionffi-ere

ultsgra-

dation effect was due to the ST turbine isentropic efficiency dradation along with GT degradation. This was about210.7% and24.3% deterioration in CCGT power and efficiency respectivwith 25.0% degradation.

Figures 9 and 12 illustrate the degradation effects of both plaon HRSG efficiency (hHRSG) and stack temperature, respectiveThe stack temperature is mainly a measure of the amount ofturbine exhaust heat utilization by the bottoming cycle. Also,definition, HRSG efficiency is a function of stack temperature aHRSG exhaust inlet temperature for a given ambient tempera~Eq. ~3!!

Fig. 11 CCGT efficiency variation with gas steam cycles component degradation

APRIL 2004, Vol. 126 Õ 313


314 Õ Vol. 126, APR


Fig. 12 Stack temperature variation with gas and steam cycles component deg-radation

a

a

o

it

toes

ignof

st.

cleation

cleada-

ur-

4,E

n,’’n-

hHRSG5TGin2TStack

TGin2Tamb. (3)

This equation shows that, for a given HRSG inlet exhaustambient temperatures, the HRSG efficiency increases withcreased stack temperature (TStack) and vice versa.

While, as Zwebek and Pilidis@5# showed, the effects of GTcomponent degradation resulted in decreasingTStack, the effectsof ST component degradation Zwebek and Pilidis@6# came up~somewhat! with opposite results. Now, as Fig. 12 shows,though in this case both plants were degraded, all types of dedation led to decreasingTStack and hence increasing thehHRSG~see Fig. 11!. This leads us to a conclusion that the effects of Gdegradation onhHRSG are predominant over the effect ST compnent degradation.

ConclusionsThe results obtained showed that the erosion of gas turbine

path components has a predominant effect on its performancethe effect of fouling.

The results obtained are in agreement with those found inliterature. The combination of the two~upper and bottoming! cy-cle’s degradations leads to a nearly linear behavior of the deteration results.

The obtained degradation effects of GT plant on steam cyplant’s performance are in agreement with the published datathe authors found in open literature,@12#.

The combination of GT component degradation with ST turbisentropic efficiency degradations led to the highest deterioraof CCGT plant power and efficiency.

The combination of both plant component degradation leddecreasing the stack temperature (TStack). This shows that the ef-fects of GT degradation onTStack and hence onhHRSG are pre-dominant over the effect ST component degradation.

Nomenclature

atm 5 atmospheric pressureCCGT 5 combined cycle gas turbine plant

DP 5 design pointGT 5 gas turbine

IL 2004

.250.82.63. Redistribution subject to ASME li

ndde-

l-gra-

T-

gasover

the

rio-

clethat

neion

to

HRSG 5 heat recovery steam generatorQ 5 heat transfer

ST 5 steam turbineT 5 temperatureG 5 nondimensional mass flowh 5 efficiencyU 5 heat transfer coefficient

Subscripts

C 5 GT compressorCC 5 combined cycleGT 5 gas turbineST 5 steam turbine

i 5 inletGin 5 HRSG inletSC 5 steam cycle

T 5 turbineStack 5 HRSG exit

References@1# Briesch, M. S., and Bannister, R. L., 1995, ‘‘A Combined Cycle Designed

Achieve Greater Than 60 Percent Efficiency,’’ ASME J. Eng. Gas TurbinPower,117.

@2# Erbes, M. R., and Gay, R. R., 1989, ‘‘Gate/Cycle Predictions of the Off-DesPerformance of Combined-Cycle Power Plants,’’ Winter Annual Meetingthe ASME, San Francisco, CA.

@3# Roy-Aikins, J. E. A., 1995, ‘‘BRAKINE: A Programming Software for thePerformance Simulation of Brayton and Rankine Cycle Plants,’’ Proc. InMech. Engrs., Part A, J. Power Energy,209.

@4# Thermoflow, 1999,Thermoflex®, Fully Flexible Heat Balance Modelling-Users Manual.

@5# Zwebek, A. I., and Pilidis, P., 2001, ‘‘Degradation Effects on Combined CyPower Plant Performance, Part 1: Gas Turbine Cycle Component DegradEffects,’’ ASME Paper 2001-GT-388.

@6# Zwebek, A. I., and Pilidis, P., 2001, ‘‘Degradation Effects on Combined CyPower Plant Performance, Part II: Steam Turbine Cycle Component Degrtion Effects,’’ ASME Paper 2001-GT-389.

@7# Diakunchak, I. S., 1992, ‘‘Performance Deterioration in Industrial Gas Tbines,’’ ASME J. Eng. Gas Turbines Power,114.

@8# Lakshminarasimha, A. N., Boyce, M. P., and Meher-Homji, C. B., 199‘‘Modelling and Analysis of Gas Turbine Performance Deterioration,’’ ASMJ. Eng. Gas Turbines Power,116.

@9# Tabakoff, W., 1986, ‘‘Compressor Erosion and Performance DeterioratioAIAA/ASME 4th Joint Fluid Mechanics, Plasma Dynamics, and Laser Coference, Atlanta, GA, May 12–14.



G

u

gi-

s,’’

Downl

@10# Tabakoff, W., Lakshminarasimha, A. N., and Pasin, M., 1990, ‘‘SimulationCompressor Performance Deterioration due to Erosion,’’ ASME J. Eng.Turbines Power,112.

@11# Escher, P. C., 1995, ‘‘Pythia: An Object-Oriented Gas Path Analysis Comp

Journal of Engineering for Gas Turbines and Power


ofas

ter

Program for General Applications,’’ Ph.D. thesis, School of Mechanical Enneering, Cranfield University, UK.

@12# Cerri, G., 1987, ‘‘Parametric Analysis of Combined Gas-Steam CycleASME J. Eng. Gas Turbines Power,109.

APRIL 2004, Vol. 126 Õ 315


Degradation Effects on Comined Cycle Power Plant Performance

Documents

Transcript of Degradation Effects on Comined Cycle Power Plant Performance