Estimation of condensate mass flow rate during purging time in heat recovery steam generator of combined cycle power plant Ehyaei,M.

Transcription

1 Esman f cndensae mass flw rae durn purn me n hea recvery seam enerar f cmbned cycle pwer plan Ehyae,M. () () sssan Prfessr f Islamc zad Unversy, Pards Branch, P.O. Bx 6555/35, Pards New Cy, ehran,iran, el: E-mal: alehyaee@yah.cm bsrac: In hs paper he ransen mdeln f HRSG (Hea recvery seam enerar) n purn me was cnsdered. In purn me, cmpressed ar frm he as urbne was used pure a cmbusble as frm HRSG. Durn hs me; seam cndensae was frmed n he superheaer sae whch shuld be draned cmpleely avd sme prblems such as defrman f superheaers. Because f hs reasn, esman f dran frman s essenal avd hs prblem. In hs paper an enery mdel was prvded and hs mdel was slved by MLB sfware. verae mdel errr s abu 5%. Resuls shw ha, durn pure me, seam emperaure was decreased frm 502 ( C) (Superheaer 2), 392 ( C) (Superheaer) and 266 ( C) (Evaprars &2) 30 ( C), 30 ( C) and 220 ( C), respecvely and als seam pressure was decreased frm 52 (bar) 23(bar) durn pure me. end f pure me, cndensae frman was abu 220 (l) when nle as emperaure was equal 00 ( C) and pure as mass flw rae was equal (k/s). Keywrds: purn, cndensae, hea, recvery - Inrducn Hea recvery seam enerar r (HRSG) s an enery recvery hea exchaner ha recvers hea frm a h as sream. I prduces seam ha can be used n a prcess r used drve a seam urbne. cmmn applcan fr an HRSG s n a cmbned-cycle pwer san, where h exhaus frm a as urbne s fed a HRSG enerae seam whch n urn drves a seam urbne. hs cmbnan prduces elecrcy mre effcenly han eher he as urbne r seam urbne alne []. Hea recvery seam eneran has hree dfferen peran mdes, nrmal, sarup and shudwn ha n a cmbned-cycle, sarup prcedure s separaed n hree prmary phases, purn f HRSG; as urbne speed-up, synchrnzan, and ladn; and seam urbne speed-up, synchrnzan, and ladn [2]. In purn me, cmpressed ar frm he as urbne s used pure cmbusble ases frm HRSG, durn hs me; cndensae s frmed n he superheaer. Purn requred as a precndn sar he as urbne hruh he bler, s a cmmn requremen f all bler cdes ensure safey peran f he plan. hs rule s hsrcally evlved, snce n he bennn f bler peran severe accdens ccurred [3-4]. Durn purn me,

2 cndensae s frmed n he superheaer. If he cndensae s n cmpleely draned frm all superheaer ubes befre seam flw s esablshed durn he sar up, w adverse cnsequences are resul [5]: Frs, cndensae ha fen s sll sub-cled s ejeced n lare quany n he ule header and ppe manfld where quench-cls her maeral. On h sars afer rps, he ule header and manfld can be mre han 200 C abve sauran emperaure. Durn warm sars, he ule header wll be clse sauran emperaure bu he ule manfld emperaure wll sll be subsanally hher. Secnd, ubes have dfferen averae emperaures a dfferen mes because hey d n clear f cndensae smulaneusly. Sme ubes wll be clear f cndensae and herefre wll be cled by seam flw, whle hers wll have par f he ube flled wh cndensae a sauran r lwer emperaure. Sll her ubes wll be sanan and herefre a he pure ar r exhaus as emperaure. Desns ha have sff ube arranemens cnneced headers a each end develp. hus, he un wll develp lare sresses a ube-aachmen welds when her ubes n he same rw are a dfferen emperaure. elmnae bh f hese effecs, he cndensae needs be remved frm he lwer headers a he peak rae a whch frms. Bu ha s n easly accmplshed. Many researchers have been cnduced abu mdeln f HRSG [6-]. Dechamps descrbed a mehd used cmpue he ransen perfrmances f asssed crculan hea recvery seam enerars. In hs mahemacal mdeln bundle f ubes n each par f HRSG replaced wh equvalen lnear hea exchaner [6]. Valdes e.al prpsed a mehdly denfy he ms relevan desn parameers ha mpac n he hermal effcency and he ecnmc resuls f cmbned cycle as urbne pwer plans n full and par lads [7]. Mhaheh e.al develped a new mehd fr mdeln a seam cycle n advanced cmbned cycles by ranzn nn-lnear equans and her smulaneus sluns by use f he hybrd Newn mehds [8]. Gdy e.al prpsed Opmal desns f a CCG pwer plan characerzed by maxmum secnd law effcency values. hese hermdynamc pmal sluns were fund whn a feasble peran ren by means f a nn-lnear mahemacal prrammn (NLP) mdel, where decsn varables (.e. ransfer areas, pwer prducn, mass flw raes, emperaures and pressures) culd vary freely [9]. Wudsra e.al nvesaed nernal exery effcency fr cmbned cycles used he same as urbne bu have dfferen seam bmn cycles. Dfferences dd rnae frm he number f 2

3 pressure levels a whch seam s eneraed n he HRSG (Hea Recvery Seam Generar). he evaluan ncludes respecvely a snle pressure, duble pressures and rple pressures HRSG. he seam pressures were pmzed wh reard verall plan effcency usn a mul-parameer pmzan prcedure. hey shwed ha nernal exery evaluan was useful mehd cycle perfrmance prmn [0]. Bahadr e.al prvded a smple mdel esman f he percen f blwdwn ha s flashed seam as a funcn f flash drum pressure and peran bler drum pressure fllwed by he calculan f he amun f hea recverable frm he cndensae []. Due leraure survey, n research has been cnduced he HRSG durn purn me. In hs paper, ransen mdeln f HRSG esmae f cndensae mass flw rae durn purn me was cnduced. Fr hs purpse, a ransen analycal mdeln f HRSG was prepared and he effec f cln as emperaure and mass flw rae n cndensae was nvesaed. In addn effec f pure me n cndensae was als cnsdered. In summary, he fllwns are he specfc cnrbun f hs sudy n he subjec maer area: ransen mdeln f hea recvery seam enerar (HRSG), especally durn pure me Cmparn he numercal upu f he mdel wh he acual measuremens a a real pwer plan, cmpuer prram cde was develped n he MLB whch culd be appled fr smulan f any ypes f HRSG, 2- Sysem descrpn he ypcal pwer and seam eneran plan, whch we cnsdered n hs research cnsss f he fllwns ems: Gas urbne and enerar: Fur 4 V94.2 as urbne enerar and auxlares, HRSG : w 2 Snle pressure level wase hea recvery seam enerars, Cmmn sysem: w 2 spray ray ype deaerars, Seven 7 bler feed waer pumps (sx 6 elecrc mr drven and ne seam urbne drven), w 2 recrculan pumps, Fur 4 Bser pumps, w 2 fuel l pump, blw dwn sysem, sampln sysem and dsn sysem Wase hea frm as urbne exhaus hea passes hruh he ndvdual HRSG wll enerae seam. Each HRSG eneraes HP seam HP seam cmmn header. ls LP seam s 3

4 prduced hruh le dwn san whch s surce s HP seam exraced frm HP cmmn header. Demne waer s suppled exernal deaerars hruh preheaer whch s emperaure shall be ncreased befre eners preheaer by recrculan pumps. Feed waer he HRSG and uxlary Bler ecnmzer shall be fed by a cmmn feed pumps, whch shall ake her sucn frm he feed waer srae ank. hs HRSG has he fllwn cndn: Each HRSG maxmum capacy : k/h (rss), Insallan: Oudr, ype : Fred, Naural crculan, Operan mde : Cnsan pressure, Duc & casn wll be nsulaed fr surface emperaure belw 60 C a amben emperaure 37 C, Gas pressure drp: mmh2o based n sac head, HRSG cnfuran: Lenh (Frm Dverer cener Oule Sack Cener): m nd Inle Duc nle: 5 De, Fure () shws he schemac daram f sysem. Fr mahemacal mdeln, hree cnrl vlumes are cnsdered. hese cnrl vlumes are w superheaers, 2 and evaprar, whch are shwn n Fure (). Durn purn me, nle HP seam drum and aemperar are clsed. Purn me s abu 300 (s), whch cndensae s frmed n superheaers, 2 and evaprar are draned hruh a dran whch s lcaed belw superheaers. Specfcan f HRSG hean surface s shwn n able (). Seam cndns n evaprar and superheaers and 2 are shwn n able (2). he pure as specfcan s shwn n able (3). 4

5 Fure (): Schemac daram f sysem. able (): Specfcan f HRSG hean surface Gemery Daa Fn Daa Weh Cmpnen SL S SN SLN HS N Fnned N ube OD hck Lenh Fns s hk Heh ype ube Fn al (mm) (mm) (-) (-) (m^2) (-) (mm) (mm) (m) (/m) (mm) (mm) (-) (n) (n) (n) SH-HP SOLID SH-HP SOLID EV-HP SERRED EV-HP SERRED able (2): Seam cndns n evaprar and superheaers and 2 Cmpnen Pressure (bar) emperaure (C) Seam cndn SH-HP Superhea SH-HP Superhea EV-HP Saurae EV-HP Saurae 5

6 able (3): Pure as specfcan Gas cmpnen emperaure ( C) Pressure (Bar) m P (k/s) me (s) N 2 (76%) O 2 (2%) CO 2 (%) Ohers (%) 3- Mahemacal mdeln he hea balance fr each cnrl vlume can be wren as fllwn: m p C P d d P m f C f df d m s du d s m h m C ( ) () w f n u In whch, mp s a al ppe mass n each cnrl vlume (k), Cp s a specfc hea f ppe (kj/k C), p s a ppe emperaure ( C), s me (s), mf s a al fn mass n each cnrl vlume (k), Cf s a specfc hea f fn (kj/k C), al seam mass nsde ppes n each cnrl vlume (k), (kj/k), f s a fn emperaure ( C), Us ms s a s an nernal enery f seam m s a pure as mass flw rae (k/s), C s a cnsan pressure specfc hea f p pure as (kj/k C), n s an nle pure as emperaure ( C), u s a ule pure as emperaure ( C), m w p s a cndensae mass flw rae (k/s), Cw s a specfc hea f cndensae (kj/k C) and h f p s a cndensae enhalpy (kj/k). bve equan can be wren fr hree cnrl vlumes whch are shwn n fure (). In eneral, hs equan shws enery cnservan n cnrl vlumes. Frs furh erms n lef hand f abve equan, shw ppes, fns, seam, cndensan enery varan wh cl as flwn. Rh sde f abve equan shws enery varan f pure ar whch flws cnrl vlumes shwed n Fure. ls enery as reducn rae s equal hea ransfer beween as and HRSG cnrl vlume: U m C ( ) (2) ln n u In whch, U s an verall hea ransfer cnducvy (W/m 2 C), ransfer surface (m 2 ) and ln s a l-mean emperaure ( C). Fn emperaure can be calculaed by he fllwn equan [2]: s an verall hea 6

7 f U U s u (3) U U In whch U s an nsde ubes verall hea ransfer ceffcen (W/m 2 C) and nernal surface (m 2 ). Overall hea ransfer ceffcen can be calculaed by he fllwn equan [2]: U In whch, d s an ff ff ln ( ) (4) h 2k m d h ff, ff are fuln facrs nsde and usde f ubes (m 2 C/W), k m s a hermal cnducvy f ube wall (W/m C), d, d are ule and nle ppe dameers (m), h, h are ule and nle hea cnvecn ceffcen (W/m 2 C) and s a fn effecveness. Inle and ule verall hea ransfer ceffcens can be calculaed by he fllwn equans [2]: U U d ff ln ( ) (5) 2k d m ff (6) h Oule verall hea ransfer ceffcen can be calculaed by he fllwn equan [2]: h d 2h m 0.67 C C3 C5 ( )( )GCpm Pr (7) d f In whch, C,C3, C5 are cnsans, d s ule ppe dameer (m), h s a fn heh (m), m s an averae pure as emperaure ( C), G s a as mass velcy (k/m 2 s), Cp m s a mxure as hea capacy (kj/k C) and Pr s a prandl number. G as mass velcy can be calculaed by he fllwn equan: G N W L S m d 2nbh N w s a number f ppes wde, L s a effecveness lenh f ppe (m), S s a ransverse pch (m), n s a number f fns per meer (NO/m), b s a fn hckness (m) and h s a fn heh (m). C, C 2 and C 3 are baned frm able (4). In hs able S and S L are ransverse and lnudnal pches (m) and s s a fn clearance (m), whch can be calculaed by he fllwn equan: s b n (8) (9) 7

8 nd Reynlds number: Re Gd (0) able (4): Facrs C,C 3 and C 5 fr sld and serraed fns n n-lne and saered arranemens Sld fns: C 0.25 Re In-lne: exp( 0.25h /s) C 3, C5.(0.75.5exp( 0.7Nd)) exp( 2S Saered: exp( 0.25h /s) C 3 2 C5 0.7 ( exp( 0.7Nd ))exp( S L L /S /S ) ) Serraed fns: C 0.25 Re 0.35 In-lne: exp( 0.35h /s) C 3, C5.(0.75.5exp( 0.7Nd)) exp( 2S Saered: exp( 0.35h /s) C 3 2 C5 0.7 ( exp( 0.5Nd ))exp( S L L /S /S ) ) Fr averae nsde ppe hea ransfer ceffcen, we use he fllwn equan [3]: h k / 2 f f / 2 / Prf () f In whch k f s a hermal cnducvy f lqud phase nsde ppe (W/m C), phase densy nsde ppe (k/m 3 ), number f lqud phase and f s a lqud f s lqud phase vscsy (NS/m 2 ), Pr f s a prandl s an nerfacal shear sress (N/m 2 ). sress whch s calculaed by he fllwn equan [4]: s an nerfacal shear 2 G f (2) 2 In whch f s an nerfacal frcn facr evaluaed as fr snle-phase ppe flw a a mean vapr mass velcy G. Fr bh sld and serraed fns, effecveness s [3]: f ( E) (3) Fr sld fns [46]: 2 n 2h 2d h d b 2bh (4) f 8

9 d ( nb) (5) f E s fn effcency can be calculaed by he fllwn equan [3]: E (6) d 2h m h d m s a facr whch can be calculaed by he fllwn equan [4]: m 2h kb 0.5 (7) In whch k s a fn hermal cnducvy (W/m C). Fr serraed fns [3]: 2bh d n 0.5b h (8) f ws In whch, ws s a fn wdh (m). Facr m can be calculaed by he fllwn equan [4]: m 2h (b ws) kbws 0.5 (9) he calculan prcess s as fllwn: - Equan () whch shws enery balance beween cl as (pure ar) and cnrl vlumes s cupled wh equan (2) whch shws hea ransfer beween pure ar and HRSG. 2- Parameers ncluded n equans () and (2) are calculaed by equans (3) (9) 3- One secnd s cnsdered as sep calculan. 4- Resuls and dscussn Fr valdan he resuls, he cmparsn beween mdel and expermenal daa s appled. Fure (2) shws cmparsn f sysem pressure varan durn purn me beween mdel and measured daa. d areemen beween mdel and measured daa s bserved. 9

10 P(kPa) Mdel Measured daa me(sec) Fure (2): Cmparsn f sysem pressure varan durn purn me beween mdel and measured daa Fure (3) shws varan f ule pure as emperaure frm superheaers &2 and evaprar durn pure me. frs, pure as enered he frs cnrl vlume (supeheaer2), and s warmed n hs cnrl vlume, afer, pure as enered he secnd and hrd cnrl vlumes (superheaer and evaprar) and als s warmed n hese cnrl vlumes. I s bserved ha, ule pure as emperaure frm evaprar s hher han superheaer and als ule pure as emperaure frm superheaer s hher han superheaer 2 durn pure me. Fure (4) shws he seam emperaure varan n super heaers &2 and evaprar durn pure me. Snce, pure cl as has a mnmum emperaure n hs cnrl vlume, and has n been warmed ye, seam emperaure n superheaer 2 has he ms emperaure decrease rae durn pure me, s seam emperaure s decreased frm 502 ( C) 30 ( C). Mnmum decrease seam emperaure rae s ccurred n evaprar. I can be seen frm Fure (4), hs reducn s abu 47 ( C) durn pure me. hs varan has w reasns; Frs reasn s relaed pure as whch has been warmed n superheaers &2 befre enered evaprar, s he effec f pure as cln s reduced; Secnd reasn s relaed mass f seam, ppes and fns whch are mre han superheaers &2. Fure (5) shws he ppe emperaure varan n superheaers &2 and evaprar durn pure me. hs varan s smlar Fure (4). 0

11 s (C) (C) Oule as emp SHI Oule as emp SHII Oule as emp EV me(sec) Fure (3): Varan f ule pure as emperaure frm superheaers &2 and evaprar durn pure me Seam emp SH.I Seam emp SH.2 Seam emp EV me(sec) Fure (4): Seam emperaure varan n superheaers &2 and evaprar durn pure me Fure (5): Ppe emperaure varan n superheaers &2 and evaprar durn pure me

12 Fure (6) shws cndensae mass frman durn pure me. I can be seen, cndensae frman sars afer 80 (s) f pure sar. end f pure me, cndensae frman s abu 238 (k) r 238 (l) whch shuld be draned frm superheaers. Fure (7) shws varan f cndensae mass frman hruh purn me wh pure as emperaure (Mdel and measured upu daa). verae mdel errr s abu 5%. Frm hs fure, can be cncluded ha, f pure as emperaure decreases frm 25( C) 25( C) wh same pure as mass flw rae ( (k/s)), cndensae mass frman ncreases frm 238(k) 258(k). Fure (6): Cndensae mass frman durn pure me Fure (7): Varan f cndensae mass frman hruh purn me wh pure as emperaure 2

13 5- Cnclusns Bler and cmbusn safey cdes requre ha HRSG s are pured prr sar-up ensure ha any remann cmbusble ases frm he as urbne are remved and d n presen a rsk f explsn. hs purn prcess requres he mvemen f lare vlumes f cld amben ar hruh he HRSG whch cls he seam whn he h ubes and resuls n cndensan. Lare vlumes f cl cndensae can be frmed whch hen fall n bm headers whch, because f her hck walls and mass, reman h. hs causes lcal quenchn and pssble crackn a sress cncenrans such as ube penerans. I s mpran ha he hh vlumes f cndensae whch may be eneraed durn he pure are draned prr re-sar. Oherwse, hs cndensae wuld reman a he lwer sauran emperaure (337 C a 40 bar) unl evapraed, cln areas f he superheaer and reheaer even huh adjacen secns may have reached he superheaer emperaure (560 C). an hs can ve rse lare hermal sresses and pssble permanen defrman f ubes knwn as ube bwn. ube bwn, nce has ccurred, can lead by-passn f h ases whch can hen mpne drecly n cler dwnsream cmpnens and resul n vbran ssues, causn furher faue falures.in hs paper nvesaed he mahemacal mdeln f ransen HRSG durn pure me n rder dran cndensae frman n superheaers. Fr hs purpse, a cmpuer prram cde was wren n MLB smulae HRSG durn pure me. Fr valdan he mdel, numercal upu f prram was cmpared wh measured daa n real pwer plan whch averae errr s abu 5%. Durn pure me, seam emperaure decreases frm 502 ( C), 392 ( C) and 266 ( C) 30 ( C), 30 ( C) and 220 ( C), respecvely and als seam pressure decreases frm 52 (bar) 23(bar) durn pure me. end f pure me, cndensae frman s abu 220 (l) when nle as emperaure s equal 00 ( C) and pure as mass flw rae s equal (k/s). Nmenclaure: al ppe mass n each cnrl vlume (k) mp Inernal surface (m 2 ) al seam mass nsde ppe n each cnrl vlume (k) ms Overall hea ransfer surface (m 2 ) mw Cndensae mass flw rae (k/s) p Fn hckness (m) b 3

14 Number f fns per meer (NO/m) n Cnsans C,C2,C3,C5 Number f ppes wde N w Specfc hea f fn (kj/k C) Cf Prandl number Pr Specfc hea f pure as (kj/k C) C Prandl number f lqud phase Pr f Specfc hea f ppe (kj/k C) Cp Reynlds number Re Specfc hea f seam (kj/k C) Cs Fn clearance (m) s Specfc hea f cndensae (kj/k C) Cw he mxure as hea capacy Lnudnal pch (m) S L (kj/k C) Cp m ransverse pch (m) S Inle ppe dameers (m) d me (s) Oule ppe dameers (m) d Fn emperaure ( C) f Fns effcency E Ppe emperaure ( C) p Inerfacal frcn facr f Fuln facrs nsde f ubes Seam emperaure ( C) s (m 2 C/W) ff Fuln facrs usde f ubes Inle pure as emperaure ( C) n (m 2 C/W) ff Oule pure as emperaure ( C) u Gas mass velcy (k/m 2 s) G verae pure as emperaure ( C) m mean vapr mass velcy G l-mean emperaure ( C) Ln Fn heh (m) h Overall hea ransfer cnducvy Inle hea cnvecn ceffcen (W/m 2 C) U (W/m 2 C) h Insde ubes verall hea ransfer Seam nernal enery (kj/k) U s Oule hea cnvecn ceffcen ceffcen (W/m 2 C) U (W/m 2 C) h Fn wdh (m). ws Cndensae enhalpy (kj/k) hf p Greek symbls Fn hermal cnducvy (W/m C) k Lqud phase densy nsde ppe hermal cnducvy f lqud phase (k/m 3 ) ρf nsde ppe (W/m C) k f hermal cnducvy f ube wall Fn effecveness ɳ (W/m C) km 4

15 Lqud phase vscsy (NS/m 2 ) f Lenh f ppe (m) L al fn mass n each cnrl vlume Inerfacal shear sress (N/m 2 ) τ (k) mf Pure as mass flw rae (k/s) m p References: [] J.H.Hrlck. "Cmbned pwer plans pas, presen, and fuure". SME Jurnal f Enneern fr Gas urbnes and Pwer 7 (995) [2] S.Sanaye,S. and M.Rezazadeh, " ransen hermal mdeln f hea recvery seam enerars n cmbned cycle pwer plans", Inernanal jurnal f enery research 22 (2006) [3] M.Pearsn. and R.W.ndersn " Relably and Durably frm Lare Hea Recvery Seam Generars". Prceedn Insue Mechancal Enneern 999: 23 Par. [4] R.Krwech, R.; L.Sanley; LLC Delak vd damae frm HRSG cycln; Pwer Maazne, March/prl 998 [5] "HRSG Users Handbk, "Desn Operan and Manenance", R.C.Swankekamp, HRSG Users Grup,2006 [6] P.J.Dechamps. "Mdeln he ransen behavr f hea recvery seam enerars". Jurnal f Pwer and Enery 209 (995) [7]: M. Valdes,. Rvra, M.D. Duran, Influence f he hea recvery seam enerar desn parameers n he hermecnmc perfrmances f cmbned cycle as urbne pwer plans, In, Jurnal f Enery Research 28 (2004) [8]: M. Mhaheh, J. Shayean, hermdynamc pmzan f desn varable and hea exchaners layu n HRSGs fr CCG usn enec alrhm, ppled hermal Enneern 29 (2009) [9]: E. Gdy, N.J. Scenna, S.J. Benz, Famles f pmal hermdynamc sluns fr cmbned cycle as urbne (CCG) pwer plans, ppled hermal Enneern 30 (200) [0]: N. Wudsra,. Wudsra,. Prne,. van der Sel, hermdynamc evaluan f cmbned cycle plans, Enery Cnversn and Manaemen 5 (200) []:. Bahadr*, H.B.Vuhaluru. mehd fr esman f recverable hea frm blw dwn sysems durn seam eneran. Enery 35 (200) [2]: ESCO Crp. ESCO Fnube Manual. ulsa, OK: ESCO, 979. [3]: Carpener, E.F. and Clburn,.P., 95." he effec f velcy n cndensan nsde ubes", Prc. Of General Dscussn n Hea ransfer,20-26, IMechE/SME. [4]: Cller, J.G., "Cnvecve bln and cndensan", Secnd edn, 98. 5