THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 345 E. 47th St., New York, N.Y G I `60

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1 E S THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 345 E. 47th St., Ne York, N.Y G I `60 The Society shll not be responsible for sttements or opinions dvnced in ppers or discussion t meetings of the Society or of its Divisions or Secs, or printed in its publictions. Discussion is printed only it the pper is published in n ASME Journl. Authoriztion to photocopy for internl or personl use is grnted to librries nd other users registered ith the Copyright Clernce Center (CCC! provided $3/rticle or $4/pge is pid to CCC, 222 Roseood Dr., Dnvers, MA Requests for specil permission or bulk reproduction should be ddressed to the ASME Technicl Publishing Deprtment Copyright 1998 by ASME All Rights Reserved Printed in U.S.A. HUMID AIR TURBINE CYCLES WITH WATER RECOVERY: HOW TO DISPOSE HEAT IN AN EFFICIENT WAY Umberto Desideri nd Frncesco Di Mri Istituto di Energetic, University di Perugi Vi G. Durnti 1A/ Perugi, Itly Tel. +39/75/ Fx +39/75/ e-mil: udes@isten.ing.unipg.it, fdm@isten.ing.unipg.it, ABSTRACT Since the humid ir turbine (HAT) cycle s first presented by Ro nd Joiner (1990), severl modifictions ere proposed to the originl configurtion to fther improve its efficiency. In the lst yers, the ttention s focused in the ter recovery from flue gs nd in determining the most suitble systems to seprte ter from gs nd solving the problem of lo temperture t the stck. In ll the bove studies it s shon tht condensing ter from flue gs requires significnt flo rte of cooling medium (generlly ter) hich is needed to remove condenstion het hich must then be disposed in the environment. This orsens poer plnt performnce becuse lrge cooling toers re needed. On the other hnd, the reduced cost of ter tretment my compenste the dditionl costs of the condenstion equipment. In this pper, the introduction of n Orgnic Rnkine Cycle (ORC), hich trnsforms in mechnicl poer frction of the het recovered from the HAT cycle, both in the ter recovery system nd in other het exchngers, is presented. Results ere obtined by using three different fluids nd mximizing the ORC input exergy. The substnces hich ere used re the conventionl R502 refrigernt fluid, mmoni nd the ne AF134, hich is replcing phsed-out CFCs in refrigertion systems. NOMENCLATURE P pressure (P) T temperture (K) TIT turbine inlet temperture (K) (i pressure rtio 11 efficiency (%) Subscripts AC fter-cooler mb mbient c compressor cc combustion chmber cold cold side CON condenser dehumidifier crit criticl e electric genertor EV evportor GT gs turbine hot hot side IDF Induced Drft Fn m mechnicl OT ORC turbine p pol PUMP polytropic pp pinch point REC recupertor 1 LPC 2 HPC INTRODUCTION In the lst fifteen yers severl different energy conversion systems configurtions ere proposed to increse performnce of poer plnts. In prticulr, gs turbine bsed poer plnts seem to be the most interesting solutions for electricl poer productions for the next century. The highest efficiency vlues re ctully chieved by the combined cycles tht utilize the het rejected from gs turbine to generte stem hich is then used in stem turbine to produce dditionl poer. These, hoever, re economiclly interesting for medium- nd lrge-size poer plnts. Another solution, more suited for smll- nd medium-size poer plnts, is to increse gs turbine performnce. A good nd proven Presented t the Interntionl Gs Turbine & Aeroengine Congress & Exhibition Stockholm, Seden June 2 June 5,1998

2 solution is stem injection in the turbine, s it demonstrted by the GE-STIG cycles (Bron nd Cohn, 1981; Tuzson, 1992; Rice, c) nd by the Cheng cycle (Sd nd Cheng, 1992). Stem injection complictes the plnt configurtion ith n increse in cpitl costs, but the dvntges in terms of efficiency nd poer output mkes this solution economiclly dvntgeous in mny different pplictions. Stem injection hs lso other dvntges such s the possibility of controlling poer output by reducing the injected stem flo rte, keeping the TIT quite constnt, nd reducing NOx emissions. Recently the humid ir turbine ptented by Fluor Dniel (Fig. 1) s dded to these type of cycles, together ith the CHAT cycle (Nkhmkin, et l., 1995). The HAT cycle consists of n intercooled nd regenerted gs turbine here stem is introduced in humidifiction process before the combustion chmber. The HAT cycle seems to be ble to rech very high efficiency (over 50 %) ith loer plnt costs thn for combined cycles. The HAT cycle, similrly to the other stem injected cycles, hs the gretest drbck in the high ter consumption tht represents lso n environmentl problem (Nguyen nd Den Otter, 1994). To different devices for recovering ter from the gs turbine exhust gsses hve been proposed: 1) direct contct dehumidifier (Bettgli nd Fcchini, 1994) nd 2) surfce het exchnger for reducing the temperture of the exhust gs belo the de point (Bombrd, 1995; Bidini, et l., 1996; Desideri nd Di Mri, 1997). Anyy, the reduction of the gs temperture requires dditionl het rejection devices, tht ill increse the plnt cpitl costs nd uxiliry poer consumption. Considering the stem condenstion process described by Bidini et. l. (1996) the mount of recoverble het is lrge frction of the injected one. Stecco et. l. (1993,b) studied the doption of n externl cooler (ExC) for cooling the inter-cooler (IC) nd the fter-cooler (AF) circultion ter, hich is beneficil to increse the cycle efficiency (Dy nd Ro, 1993). Hoever, this device increses the mount of het rejected to the environment. A possible solution to reduce the size of the het rejection devices nd increse the HAT cycle performnce is to utilize n orgnic Rnkine cycle (ORC) hich recovers prt of the het hich ould be rejected from the men nd lo temperture het sources nd produces dditionl poer. In this pper the insertion of three different ORCs ith mmoni, HFA134 nd R502, s studied. The ORC does not eliminte the need of cooling toers the reject het from the externl cooler nd the ter recovery system to the environment, but it mkes it possible to produce dditionl poer ith to het sources divided by very lo temperture difference. With het source not exceeding 120 C nd het sink t mbient temperture it ould not be possible to use stem bottoming cycle to recover het. The cooling system of the ORC my be the sme s tht used for the HAT cycle lone. Wet cooling toers ere considered in the present study, even though open loop cooling ter circultion or dry cooling cn be used. The difference due to the presence of the ORC is reduction in the het lod of the toers. After the introduction of n ORC, the HAT poer plnt prcticlly becomes combined cycle. Hoever, it must be noted tht the HAT cycle my ork in stnd lone mode ithout the ter recovery system nd the ORC ith very high efficiency. On the other hnd, combined cycle hs high efficiency only hen both the gs nd the stem cycles re operting together. If the stem cycle is sitched off, the gs turbine in simple cycle configurtion hs n efficiency hich ill be loer thn 40%. CYCLE COMPONENTS Figure 1 shos the HAT cycle configurtion studied in this pper. This is the one described by Desideri nd Di Mri (1997) ith the ddition of the ORC. The mbient ir is compressed in to stge (LPC, HPC) inter (IC) nd fter (AC) cooled compressor. The cooled nd compressed ir enters the evportor-sturtor (EV), in hich mss flo rte is incresed by the ter evportion, then the recupertor (REC), in hich sturted ir is heted, nd then the combustion chmber (CC). After the blde-cooled turbine the gs exchnges het first in the recupertor ith the humid ir exiting the EV, nd then in the economizer (EC) ith the circultion ter frction from the EV. At the economizer outlet there is condenserdehumidifier (CON) to recover ter nd het. Problems t the stck, due to the lo flue gs temperture, re voided by the doption of n Induce Drft Fn (IDF). The cooling ter floing through the IC nd the AC is mixed ith the frction coming out of the EC nd injected t the top of the EV. At the EV outlet ter frction is circulted in to the EC nd the frction needed for the IC nd AC, ithout the evported one, is cooled in the externl cooler ExC nd circulted to the IC nd AC. At the ExC outlet the circulted ter is mde up of the evported ter hich is not recovered. Figure 1: HAT cycle ith ter recovery nd ORC. (CC: combustion chmber, CON: condenser - dehumidifier, EC: economizer, EV: evportor, GT: gs turbine, HPC: high pressure compressor, IDF: induced drught fn, LPC: lo pressure compressor, OT: ORC turbine, REC: recupertor) The ter evportion is mde in direct contct het exchnger (EV) in hich the cold compressed ir is heted nd humidified by the hot ter incresing both its temperture nd ter content. In this process the increse of ir temperture is due to mss nd het exchnge beteen ter nd ir. Furthermore the ter evportes t rising pressure: i.e. t ech step the ter sturtion pressure is t the mixture temperture, reducing the exergy loss during the het 2

3 exchnge (Gllo, et l., 1995). The ORC, tht utilizes the het rejected from the ExC nd from the CON for producing n dditionl poer frction, is ne component introduced in the HAT cycle. HEAT AND STEAM RECOVERY SYSTEM SIMULATION AND OPTIMIZATION First l efficiency of therml engines depends on the rtio of the het rejected to the environment over the het input. In previous HAT cycle configurtions the het vilble t the externl-cooler (ExC) outlet required cooling toers or het exchnger to be rejected. Furthermore the need to reduce the cycle environmentl impct, due to lrge ter consumption, suggest to dopt n exhust gsses dehumidifier (Bettgli nd Fcchini, 1994; Bombrds, 1994; Bidini et. l.,1996; Desideri nd Di Mri, 1997). This device lso requires cooling toers for het rejection. Since this het is rejected t reltively high tempertures, rnging from 350 to 400 K, it is possible to produce more poer output ith the doption of lo enthlpy drop cycles E cooling curves t the end of preheting, during the vporiztion process nd t the ter condenstion strting point, if there is enough het for superheting the fluid. The simultion code, dded to tht developed for the HAT cycle, mtches these operting conditions by djusting the vporiztion temperture nd the fluid flo rte. For ech HAT cycle configurtion nd CON outlet temperture, the simultion code stops hen the inlet exergy reches its mximum vlue. The inlet exergy is clculted s the product of the specific exergy nd of the mss flo rte nd it represents the mximum vilble poer entering the ORC. MAIN ASSUMPTIONS AND SIMULATION PARAMETERS Tble 1 shos the min properties of the fluids studied nd tble 2 the min prmeters used in the hole cycle simultion. Tble 1: Chrcteristics of lo enthlpy drop fluids Substnce Mole eight P T;t (kg/kmole) (MP) (K) HFA AMMONIA R The simultions hve been done for three TIT vlues, rnging from 1173 to 1373 K, nd for gs turbine pressure rtios rnging from 8 to 30. The condenser-dehumidifier outlet temperture s studied in the rnge from 308 to K nd stopping clcultion if no ter ere condensed before reching K. During the clcultions ll the therml losses in the cycle components, except tht in the combustion chmber, hve been disregrded. The mixtures of stem nd ir, nd of stem nd combustion products, hve been considered s idel, except in the evportor nd condenser, here the to phses ere clculted seprtely. The combustion s ssumed complete. Specific recovered het [kj/kg] Figure 2: Het trnsfer curves in the externl cooler (ExC) nd in the condenser (CON) In the considered HAT cycle configurtion (Fig. 1) the het input to the ORC is the sum of the het rejected from the externl-cooler (ExC) nd from the condenser-dehumidifier (CON). Since the fluid tht is cooled in the ExC is ter nd the fluid cooled in the CON is gs ith high ter content, the mtching the hot nd cold curves in the het exchngers of the ORC is very importnt for high ORC efficiency. Figure 2 shos ho the typicl cooling curves of ter nd humid gs hve been mtched to conventionl heting nd vporiztion curve of lo enthlpy drop fluid. Due to its loer men temperture, the ExC ter cooling curve is utilized in the preheting zone, heres the exhust gsses re utilized in the vporiztion nd superhet zone. The het exchnge process s clculted by tking into ccount the rel orgnic fluid thermodynmic properties nd some opertionl constrints. In prticulr, these re represented by the minimum temperture differences (Fig. 2) tht re locted t the ExC inlet nd CON outlet nd in three more points long the het exchnge curve. In fct, depending on the ORC fluid therml cpcity, it is necessry to verify the bsence of intersection of the heting nd Tble 2: Min cycle prmeters Prmeter vlue unit Prmeter vlue unit Tmb 288 K LTAc.cod 10 K Pmb P IPI,AC 2 % +mb 60 % LPREC 2 % 2/(i l 0.8 OTEV,nOt 48 K rlp,l,e 88 % ATpp,EV 20 K llpol,gt 87 % ATREC,hot 10 K 11is,OT 80 % OTREC,cold 10 K rlp 85 % OTEC,hot 10 K Tim 98 % OTEC,tO1d 10 K fl 99 % OPCC 2 % lie 98 % PCON 1000 P ATIC,hot 10 K RIo OTIC,com 10 K tlpol,idf 92 % ATAC,hot 10 K fuel nt. gs MAIN RESULTS Due to the reltively lo temperture of the ORC het source, the best cycle performnce is chieved by the R502, tht is the fluid ith the loer criticl temperture. It is possible to note tht depending on the fluid utilized, there is dehumidifier outlet

4 temperture tht mximizes the cycle efficiency nd poer (Fig. 3). In ll the figures poer output nd efficiency increse re shon together becuse n increse in poer output oing to the presence of the ORC cuses the sme increse in efficiency: e 17 = 71HAT+ORC - 77HAT 7?HAT _ WHAT+ORC IQHAT -WHAT /QT _ WHAT+ORC - WHAT WHAT /QHAT WHAT This is prticulrly true for HF134 nd R502 becuse the curves for mmoni re prcticlly constnt. In ny cse the sensitivity to condenser outlet temperture is quite negligible. The loer is the fluid criticl temperture the higher is the outlet temperture for mximum efficiency. Its vlue is lso function of R nd T1T. This is due to the higher ltent het of the mmoni thn of the R502. A lo outlet temperture mens higher injected ter recovery nd so lrger mount of het vilble in the dehumidifier during the condenstion process, tht corresponds to the lo enthlpy fluid vporiztion. Generlly, t the end of the vporiztion, the exhust gs het content is high enough for superheting the ORC fluid. If the vporiztion ltent het is smller, lo exhust gs outlet temperture does not llo n efficient superheting process due to the minimum temperture difference t the ter condenstion strting point (Fig. 2). =12 =12 p=12 C Eb 73 U 49 -O-TIT =1173K -O-TIT = 1273K -8-TIT = 1373 K p = 10 AMMONIA Y TIT =1173 K ITIT=1273K -A- TIT = 1373 K HFAI346 -O- TIT = 1173 K 49TIT=1273K R502 -b- TIT =1373 K S pmt NO WATER RECOVERY 9=8 NOWATER I = 8 N RECOVER' VER l l Condenser outlet temperture (K) Condenser outlet temperture (IQ Condenser outlet ter pereture (IQ 360 () (b) (c) Figure 3: Mximum cycle efficiency Vs condenser outlet temperture 46V Ul [ R502 EFFICIENCY = 5.8% x 340 FLOW RATE =1.04 kpmgs WORK = 8.92 kj)kge ENTROPY (kjmplk) ENTROPY (kjac9lg ENTROPY (kjiicglc () (b) (c) Figure 4: T-s digrms of the ORCs t best HAT cycle efficiency /] z.s =8 1=10 -O- TIT K 2.2 -O-TIT=1273K = TIT = 1313K AMMONIA = t R502 NO WATER RECOVERY P - H 1.-^-TIT=1173K 1.0 = 12.1 / 1.0 ti _TIT=1273K I TIT= 1373 K NO WATER RECOVERY NO WATER RECOVERY 0.6 ne =1 D Condenser outlet terrperture (IQ Condenser outlet temperture (K) Condenser outlet temperture (K) () (b) (c) Figure 5: Poer nd efficiency increse Vs condenser outlet temperture IL

5 1N 440 R D_ TIT 1173 K y 400 o-- TIT = 1273 K A TIT = 1373 K 'Y y p-8 p=12 NO WATER RECOVERY Condenser outlet temperture (K) Figure 6: ORC specific ork per unit mss dry ir Vs condenser outlet temperture For this reson the exhust outlet temperture for mximum efficiency rises chnging the fluid from mmoni to BF134 nd to R502. Figure 4 shos the mmoni, HFA134 nd R502 T-s cycle digrms. The mximum specific ork is chieved by the mmoni but, due to the high mount of het required during the vporiztion, the cycle poer output is kept lo by the smll flo rte. The R502 hs the loest specific ork but the highest flo rte giving the highest poer output. In the best efficiency operting conditions the expnsion end point of orgnic fluids is in the superheting region ith n increse in the het rejected t the condenser. This mount of het cn be utilized for preheting the fuel before the injection in the combustion chmber. Considering the different operting conditions studied in this pper, the best benefits in terms of poer nd efficiency re chieved for men TIT vlues (i. e K, Fig. 5) heres, t high TIT, the ORC positive effect is reduced due the high HAT cycle performnce. At lo TIT, the het vilble in the ExC nd CON is too lo ith negtive consequences on the ORC performnce. The cycle specific ork, referred to the compressor inlet unit ir flo rte, is represented in figure 6 s function of the dehumidifier outlet temperture for the best cycle operting conditions. Mximum poer output increse does not lys correspond to mximum ter recovery from the HAT cycle condenser (Fig. 7). The choice to privilege ter recovery ith respect to efficiency ill minly depend on the cost or vilbility of ter. Only mmoni llos to mximize performnce together ith ter recovery. In the HAT cycle, ter consumption is very importnt cpitl nd environmentl fctor nd so reduction in cycle performnces cn be ccepted hen it is needed to reduce the use of ter. Figure 7 shos the condensed ter recovery relted to the poer (nd efficiency) increse. It is possible to note tht for the BFA134 the mximum poer increse operting conditions t 1173 nd 1273 K re quite independent from the dehumidifier outlet temperture t I, U =10 =12 AMMONIA e =8 S -B- TIT 1173 K -TR=1273K = b-tit = 1373 K 40 - Trr = 1173 K -0-TIT= 1273K 20 O.-TIT = 1373 K t I 8 v U HFA134 B=8 100 t R502 -o-tr=1173k -o- T1T= 1273K -d- TIT = 1373 K 112 =10 B= , ,4 0,8 0,8 1,0 1, ,8 2,0 2, , 0, , , ,0 2,2 2,4 2,6 Poer/ Efficiency increse (%) Poer! Efficiency incese (%) Poer / Efficiency increse (%) () (b) (c) Figure 7: Recovered ter Vs cycle poer output increse 1,6 3,8 -o- TIT=1173K HFAI34 t -O-TIT = 1273K -0- TIT = 1173 K 3,2 t -A TIT = 1373K 1,2 AMMONIA -O-TIT = 1273 K -8--TIT = 1373 K S 2,8 O g o. 2,4 2,0 to W I I,6 }- t 3,2 3,6 2,8 2.4 R502 2,0 -- TIT K -0- TIT = 1273 K 1, =1373K u 4u Z Pressure rtio Premn rtio Pressure rtio () (b) (c) Figure 8: Poer nd efficiency increse Vs gs turbine pressure rtio 30 5

6 This mens tht it is possible to mximize the condensed ter ithout significnt penlty in cycle performnce. On the other hnd, both the mmoni nd the R502 hve very limited outlet temperture rnge t hich the mximum cycle efficiency corresponds. The R502 llos cycle poer nd efficiency increse of bout the 2.2% ith 50% ter recovery, heres the mmoni llos to condense bout the 100% of the injected ter ith n increse in cycle performnce rnging from 1.4 to 1.6%. The HFA134 llos n increse in cycle performnce rnging from 1.8 to 2% ith condensed ter frction rnging from 70 to 80%. For lo TIT vlues, the het utilized for injected ter vporiztion, minly comes from the compressors (i.e. IC nd AC). When 0 rises, both the injected ter frction nd the T9 increse (Bidini, et l., 1996) incresing both the EC exhust gs temperture nd the het recovered in the CON. It is then possible to produce dditionl poer ith the ORC (Fig. 8). At high TIT vlues, the het recovered from the gs turbine exhust is n importnt frction of the het utilized in the EV. For this reson, t lo pressure rtios, n increse in 0 mens n increse in the ter flo rte in the EC nd reduction in the gs turbine exhust temperture. Then the CON inlet gs temperture is reduced nd so the het recovered in the EC, relted to tht recovered in the IC nd AC. Thus the T12 increses together ith the het, vilble for the ORC producing higher ORC poer output (Fig. 8). The ORC positive effect is higher t lo thn t high TIT due to the loer HAT cycle efficiency. As the TIT rises the ORC poer output rises but becomes smller frction of the gs turbine one. ECONOMICAL CONSIDERATIONS The doption of lo enthlpy drop cycle represent n dvntge from the thermodynmic point of vie. Economiclly, this dvntge is still true only if the instlled kw cost increse is less or equl to the poer increse. For this reson n economicl nlysis s done by ssuming n HAT cycle plnt cost bout 700$/kW nd ORC cycle cost rnging from 1000 to 2000 $/kw by step 250 $/kw. U) 3 C Cl ^o H FA ORC cycle plnt cost ($IkW) Figure 9: Plnt cost increse relted to bsic HAT cycle, for different ORC plnt cost. Figure 9 shos the influence of the cpitl cost of n ORC- HFA134 cycle on the hole poer plnt cost increse relted to bsic HAT cycle cost. The mximum poer increse due to the doption of the HFA134 fluid is bout 2%. For this reson the mximum ORC cycle cpitl cost for economicl convenience is loer thn $/kw. For higher ORC cost the thermodynmic dvntge still remin but the kwh cost ill increse. The cost of ter tretment does not chnge in the to cses. The presence of the ORC does not chnge the mount of ter recovered nd the mount of ter hich needs to be treted to be used in the evportor. CONCLUSIONS The use of the het rejected from the HAT cycle, in the injected ter recovery process nd in the externl-cooler, for feeding n ORC shos the possibility of incresing the cycle efficiency nd poer output from 1.6%, using mmoni, to 2% using HFA134 to 2.2% using R502. In terms of efficiency this mens n increse bout point, but the presence of the ORC reduces the size of externl cooling devices. The results sho tht t ech HAT cycle operting condition there is dehumidifier outlet temperture tht mximizes the cycle performnces. This temperture is higher for the R502 nd loer for the mmoni nd so the condensed ter in the dehumidifier is bout 50% of the injected ter for the R502 nd bout 100% for the mmoni. The best compromise beteen performnces increse nd ter recovery is represented by the HFAI34 tht t mximum cycle efficiency llos to condense bout 70-80% of the injected ter. An increse in HAT cycle pressure rtio hs positive effect but there is reduction in the hole cycle efficiency. ACKNOWLEDGEMENTS Funding of MURST nd CNR is grtefully cknoledged. REFERENCES Bettgli, N., Fcchini, B., 1994, "Wter recovery in stem injection cycles", in Energy for the 21" Century: Conversion, Utilistion nd Environmentl Qulity, Ed. E. Crnevle et l., SGE, Pdov, Itly, pp , Proceedings of Floers '94, 6-8 July, Florence, Itly. Bidini, G., Desideri, U., Di Mri, F., 1996, "Thermodynmic Anlysis of Injected Wter Recovery Systems for the HAT Cycle", Proceedings of the 1996 ASME Winter Annul Meeting, November, Atlnt, Georgi. Bidini, G., Desideri, U., Di Mri, F., Gllo, W.L.R., "Humid Air Turbine (HAT) Cycle: Stte of the Art nd Perspectives", Proceedings of the 3rd Ltin Americn Congress: Electricity Genertion nd Trnsmission, 9-13 November, Cmpos do Jordo, Brsil. Bombrd, P., "Recupero di clore e cqu d gs di scrico di turbin gs d lto contenuto di umidit: trttzione teoric del processo di deumidificzione e dimensionmento dello scmbitore", Proceedings, ATI - Atti dell'vii Convegno Nzionle, Tecnologi e Sistemi Energetici Complessi, SGE, Pdov, Itly, pp , (in Itlin). Bron, D.H., Cohn, A., 1981, "An Evlution of Stem Injected Combustion Turbine Systems", Journl of Engineering for 6

7 Gs Turbines nd Poer, Vol. 103, pp Dy, W.H., Ro, A.D., 1993, "FT4000 HAT ith Nturl Gs Fuel", Turbomchinery Interntionl, Jn/Feb, pp Desideri, U., Di Mri, F., 1997,"Wter recovery from the HAT cycle exhust gs: A possible solution to reduce stck temperture problems", Interntionl Journl ofenergy Reserch, Vol. 21, Gllo, W.L.R., Bidini, G., Bettgli, N., Fcchini, B. 1995, "The evportor process simultion nd the HAT cycle (Humid Air Turbine) performnce", ASME Pper 95-CTP-59 Nkhmkin, M., Sensen, E.C., Wilson, J.M., Gul, G., Polsky, M., 1995, "The Cscded Humidified Advnced Turbine (CHAT), ASME Pper 95-CTP-5. Nguyen, H.B. nd den Otter, A., 1994, "Development of Gs Turbine Stem Injection Wter Recovery (SIWR) System", ASME Journl of Engineering for Gs Turbines nd Poer, Vol. 116, pp Ro, D., nd Joiner, J.R., "A technicl nd economic evlution of the humid ir turbine cycle", Proceedings, Electric Poer Reserch Institute Contrctors Meeting, Plo Alto, Cliforni. Sd, M. A., Cheng, D.Y., 1992, "Cheng Cycle Il, recent dvncements in gs turbine stem injection", in Energy For The Trnsition Age, Ed. S.S. Stecco nd M.J. Morn, Nov Science, Ne York, pp Stecco, S.S., Desideri, U., Fcchini, B., Bettgli, N., 1993, "The Humid Air Cycle: Some Thermodynmic Considertion.", ASME Pper 93-GT-77. Stecco, S.S., Desideri, U., Bettgli, N., 1993b, "Humid Air Gs Turbine Cycle: Possible Optimiztion." ASME Pper 93-GT Rice, I.G., 1993, "Stem Injected Gs Turbine Anlysis: Prt I- Stem Rtes", ASD4E Pper 93-GT-132. Rice, I.G., 1993b, "Stem Injected Gs Turbine Anlysis: Prt 11-Stem Cycle Efficiency", ASME Pper 93-GT-420. Rice, I.G., 1993, "Stem Injected Gs Turbine Anlysis: Prt III-Stem Regenerted Het", ASME Pper 93-GT-421. Tuzson, J., 1992, "Sttus of Stem Injected Gs Turbines", Journl of Engineering for Gs Turbines nd Poer, Vol. 114, pp