DESIGN AND OPERATION STRATEGIES OF A GT CHPP FOR DISTRICT HEATING PURPOSES

Transcription

1 U.P.B. Sci. Bull., Series C, Vol. 73, Iss. 2, 2011 ISSN x DESIGN AND OPERATION STRATEGIES OF A GT CHPP FOR DISTRICT HEATING PURPOSES Christin RĂDUCANU 1, Roxn PĂTRAŞCU 2 Lucrre prezintă concluziile rezultte în urm modelării funcţionării unei centrle de coenerre vând l bză ITG cre limenteză cu căldură sub formă de pă fierbinte un rup de consumtori urbni. Modelre funcţionării nsmblului ITG + CR pe prcursul unui n i în considerre modificre srcinii termice totle centrlei de coenerre concomitent cu modificre temperturii erului tmosferic. În privinţ modului de relre srcinii termice, reducere debitului de pă de reţe l srcini termice prţile re c efect reducere nesemnifictiv indicelui de coenerre. În privinţ numărului de unităţi ITG + CR cre trebuie instlte într-o centrlă de coenerre pentru limentre unei rupări de consumtori urbni, cest depinde de mărime rportului între srcin termică mximă (corespunzătore temperturii exteriore de -15 o C) şi srcin termică minimă (corespunzătore temperturii exteriore de 36 o C). The purpose of this pper is to recommend prt lod desin nd opertin strtey for Gs Turbine CHPP supplin district hetin consumers. A computer model of the entire het supply system (CHPP, therml network, therml substtions nd het consumers) is used to substntite the wy tht prt lod opertion influences CHPP performnces. For specific type of GT nd specific type of therml substtion, the computer model results showed tht there is no optiml wy to control the het lod durin winter time. The computer model results lso showed tht the rtio between mximum nd minimum bse het lod (HRWB het lod) should not be reter thn 2. For vlues reter tht 2, the cumultive sum of CHPP income will turn netive t hih ir tempertures, durin the whole summertime. This sitution chnes for the better if insted of one GT unit we instll two units hvin toether the sme rted power. The two GT units cn be desined to use only one het recovery unit (HRWB). Keywords: combined het nd power, s turbine, prt lod opertion, het lod control 1. Introduction The pper s purpose is to recommend desin nd opertion strteies for Gs Turbine CHPP (Combined Het nd Power Plnt) supplin district hetin 1 2 Assoc. Prof., Enery Genertion & Use Chir, Power Genertion Fculty, University POLITEHNICA of Buchrest, Romni Assoc. Prof., Enery Genertion & Use Chir, Power Genertion Fculty, University POLITEHNICA of Buchrest, Romni, e-mil: op3003@yhoo.com

2 306 Christin Răducnu, Roxn Pătrşcu consumers (community hetin). Residentil het consumers re usully supplied with hot wter t temperture tht cn rech derees Celsius. The wter is heted first in het recovery wter boiler (HRWB) usin exhust ses from the s turbine (GT) nd then, if necessry nd only durin wintertime, in pek lod wter boiler. The overll het demnd of roup of residentil Romnin consumers consists in spce hetin nd wrm wter supply, both components bein vrible in time (durin dy, durin seson, durin yer). Recent mesurements showed tht its minimum vlue (between 8 nd 16 %) is reched durin summer. In Romni, CHPP for district hetin purposes is considered het source, the electricity bein secondry product. Under those circumstnces, when the overll het lod decreses, the bse het lod decreses s well. Hot wter flow rte cn either be kept constnt or becomes vrible (incresin or decresin). The decrese of the bse het lod is ledin to GT prt lod opertion nd it is tkin plce simultneously with the increse of ir temperture. This prticulr spect influences the rtio between the electric power enerted by GT nd the mount of het recovered from the exhust ses flow rte correspondin to tht power output, known s coenertion index, nd consequently overll CHP plnt performnces. Both desin nd opertion of such CHPP must consider mesures to improve plnt performnces nd especilly plnt finncil benefits. 2. Computer model A computer model of the entire het supply system (CHPP, therml network, therml substtions nd het consumers) is used to substntite the wy tht vrition of hot wter prmeters (flow rte nd tempertures) nd ir temperture influence CHPP nnul performnces. P = 5,8 0,035 t P = Q D t mx = B P = 22,67 0,07464 t 0 ( 0,1625 t + 58,5) P + ( 1,655 t + 154,0) 2 t t P0 = 28,4 + 2,86 + 1, = 0,408 0,00011 t When the s turbine electric output decreses, exhust s temperture nd in some cses exhust s flow rte decreses s well. A specific s turbine (TGC435CT) prt lod behviour mde public by the mnufcturer (TUMA TURBOMACH SA) is used s prt of this computer model (see equtions (1)

3 Desin nd opertion strteies of GT CHPP for district hetin purposes 307 bove). Without supplementry firin, the mount of het recovered from the exhust ses depends upon exhust ses nd hot wter flow rtes nd inlet tempertures. Gses flow rte decrese is technicl chrcteristic of specific s turbine. Insted, hot wter flow rte decrese or increse cn be decided by the het supply system opertor, provided the wter pumps re properly controlled. The mount of het recovered from the exhust ses depends upon exhust ses flow rte nd temperture nd het exchner effectiveness s follows: Q = ε D c t t (2) CG RC ( ) w Hot wter flow rte cn be relted to the spce hetin enery demnd by mens of numeric coefficient [1]: r D i Q i r = = xi D i Q (3) mx 0 i Its vlue must be positive 0 r 1 nd constitutes distinct wy to ensure het lod control durin nnul system opertion. From technicl viewpoint r cn be reter thn 1 ( r 1), but its vlue is limited by the increse of hot wter temperture durin nnul opertion. We must emphsize tht numeric coefficient r influences only prt of the entire hot wter flow rte. This prt corresponds only to the spce hetin demnd nd vries with r only durin wintertime. The rest of the hot wter flow rte durin wintertime nd the whole hot wter flow rte durin summertime re not influenced by r. A therml substtion is het trnsformer consistin in two or three wterwter het exchners locted between the het source (CHPP) nd the het consumers. Its scheme is influencin wter tempertures nd flow rte within the system. In this cse there re two het exchners, one for spce hetin nd the other for wrm wter, supplied in prllel with hot wter comin from CHPP. Both het exchners re operted t different tempertures nd het lods thn the rted vlues (desin point) durin yer. The therml substtion model for such situtions is lso bsed on het exchners effectiveness [2]. Air temperture rne nd het lod profile correspond to n ri ner Buchrest. 3. Model results The computer model enerted ret mount of useful dt. Every vlue ws obtined s function of ir temperture nd CHPP correspondin het lod.

4 308 Christin Răducnu, Roxn Pătrşcu Considerin the durtion for ech ir temperture, vere nnul vlues of severl CHPP prmeters nd performnce indices could be clculted. CHPP prmeters clculted s functions of ir temperture re: ) Hot wter nd exhust ses flow rtes nd tempertures; b) Power output nd het recovered from exhust ses; c) Coenertion index nd CHPP overll efficiency; d) Cumultive sum of CHPP income. Dt displyed in tble 1 show how much nd when coenertion index is influenced by the numeric coefficient r. A comprison of the lst three columns of tble 1 illustrtes tht they re slihtly different only in wintertime, when the numeric coefficient r is influencin the mount of hot wter flow rte. Coenertion index Air temperture Reltive Numeric coefficient r (derees Celsius) CHPP het lod 0 0, ,000 0,674 0,674 0, ,937 0,661 0,660 0, ,859 0,647 0,645 0, ,780 0,633 0,631 0, ,693 0,620 0,617 0, ,606 0,607 0,604 0, ,511 0,593 0,592 0, ,407 0,580 0,580 0, ,288 0,570 0,570 0, ,136 0,492 0,492 0, ,130 0,467 0,467 0, ,125 0,446 0,446 0, ,120 0,420 0,420 0, ,115 0,392 0,392 0, ,110 0,366 0,366 0, ,105 0,333 0,333 0, ,100 0,296 0,296 0, ,095 0,247 0,247 0,247 Tble 1 Durin summertime, the three vlues of the coenertion index re identicl becuse hot wter flow rte nd ll other CHPP prmeters re the sme [3]. The first two columns of tble 1 lso show the reltion between ir temperture nd CHPP het lod for n ri ner Buchrest. The lst three columns of tble 1 correspond to mximum to minimum bse het lod rtio equl to 2.1. Annul coenertion index nd CHPP overll efficiency were lso clculted (tbles 2 nd 3). The results of these clcultions re extremely comprehensive.

5 Desin nd opertion strteies of GT CHPP for district hetin purposes 309 Annul coenertion index Mximum to minimum Numeric coefficient r = bse het lod rtio 0 0,25 0,5 0,75 1 1,05 0,572 0,572 0,571 0,571 0,570 1,57 0,551 0,551 0,550 0,550 0,549 2,10 0,523 0,523 0,523 0,522 0,521 2,62 0,502 0,502 0,501 0,501 0,500 3,14 0,483 0,482 0,482 0,481 0,480 Annul CHPP overll efficiency Mximum to minimum Numeric coefficient r = bse het lod rtio 0 0,25 0,5 0,75 1 1,05 0,849 0,849 0,849 0,849 0,850 1,57 0,843 0,843 0,843 0,843 0,844 2,10 0,831 0,832 0,832 0,832 0,833 2,62 0,821 0,821 0,821 0,822 0,822 3,14 0,810 0,811 0,811 0,811 0,812 Tble 2 Tble 3 It is obvious tht the vlue of the numeric coefficient r hs very smll influence on both nnul vere vlues. The computer model is ble to obtin specific optiml vlue or rne for the numeric coefficient r in order to insure mximum electricity supplied to the rid. Its tret is the difference between the nnul mount of electricity produced nd the nnul mount of electricity consumed to drive hot wter pumps. This specific optiml vlue or rne does exist nd it is influenced by the wy tht coenertion index decreses when hot wter flow rte decreses. This is the cse for coenertion stem turbines [2]. If the coenertion index does not decrese t ll or not enouh, the nnul mount of electricity supplied to the rid does not rech mximum vlue t specific vlue of the numeric coefficient r. By consequence, the numeric coefficient r hs not n optiml vlue or rne. This is the cse of s turbine operted in coenertion mode. It is lso obvious tht the nnul overll efficiency of the combined het nd power plnt is in the sme sitution versus the numeric coefficient r. The conclusion is tht from technicl viewpoint, het lod control cn be relised by ny r vlue in rne between 0 nd 1, nd even reter then 1, without influencin the nnul mount of electricity supplied to the rid by CHPP. There re, however, two conditions: ) Vrible speed drive for the electric motors drivin wter pumps; b) Effective control of hot wter distribution to ech therml substtion.

6 310 Christin Răducnu, Roxn Pătrşcu Cumultive sum of CHPP income MEUR Air temperture Mximum to minimum bse het lod rtio (derees Celsius) 1,05 1,57 2,10 2,62 3, ,042 0,030 0,024 0,021 0, ,121 0,087 0,070 0,060 0, ,229 0,165 0,134 0,115 0, ,422 0,307 0,250 0,216 0, ,676 0,496 0,407 0,353 0, ,965 0,716 0,592 0,517 0, ,230 0,924 0,771 0,679 0, ,452 1,106 0,933 0,830 0, ,587 1,230 1,052 0,945 0, ,607 1,259 1,043 0,913 0, ,623 1,275 1,029 0,881 0, ,637 1,286 1,012 0,846 0, ,650 1,289 0,992 0,811 0, ,660 1,288 0,970 0,778 0, ,668 1,282 0,949 0,746 0, ,674 1,276 0,931 0,721 0, ,677 1,269 0,917 0,703 0, ,678 1,264 0,909 0,694 0,539 Tble 4 The computer model results lso show tht the rtio between mximum nd minimum bse het lod (HRWB het lod) should not be reter thn 1.5. Dt displyed in tble 4 show tht if this rtio is reter tht 1.5, the cumultive sum of CHPP income decreses t hih ir tempertures, durin summer. The explntion is tht every income correspondin to ir tempertures reter thn 12 derees Celsius is netive. By consequence, nnul profit will be hiher if the GT unit is shut down nd the hot wter boiler is runnin durin summer [4]. This sitution chnes for the better if insted of one GT we instll two units. Those two GT units will hve toether the sme rted power thn the one. The dvnte of this solution consists in the possibility tht one of the two units will be operted only on winter. The other will be operted the whole yer, so tht ech unit nnul vere reltive het lod will be hiher. The two GT units cn be desined to use only one het recovery unit (HRWB). 4. Conclusions Air temperture rne nd het lod profile mch n ri ner Buchrest. For specific GT unit nd specific type of therml substtion, computer model ble to obtin specific optiml vlue or rne for the numeric coefficient r ws vilble. Its tret ws to insure mximum electricity supplied to the rid [5]. This specific optiml vlue or rne depends upon the wy tht

7 Desin nd opertion strteies of GT CHPP for district hetin purposes 311 coenertion index decreses when hot wter flow rte decreses. In the cse of coenertion stem turbines this decrese is importnt [2] nd the optiml vlue for r is close to zero. In the cse of GT nd HRWB, the coenertion index does not decrese enouh to ensure n optiml vlue or rne for the numeric coefficient r. As consequence of this sitution, the supply system opertor is free to estblish ny r vlue. The computer model results lso show in wht wy the rtio between mximum nd minimum bse het lod influences CHPP nnul benefit. Dt displyed in tble 4 show tht for rtio reter tht 1.5, the cumultive sum of CHPP income decreses durin summertime. It is the result of GT prt lod opertion t hih ir tempertures tht hppens durin summertime. By consequence, nnul profit will be hiher if the GT unit is shut down nd the hot wter boiler is runnin durin summer. This sitution chnes for the better if insted of one GT we instll two units. Those two GT units will hve toether the sme rted power thn the first one. The dvnte of this solution consists in the possibility tht one of the two units will be operted only on winter. The other will be operted the whole yer, so tht ech unit nnul vere reltive het lod will be hiher. In order to reduce the investments costs, the two GT units cn use only one HRWB. This type of CHPP income nlysis should be included in ny fesibility study for s turbine bsed CHPP used for district hetin. There is however difficult problem concernin rel informtion nd dt on prt lod nd different ir temperture behviour of specific GT included in mnufcturer s offer prior to fesibility study. For different resons, offer informtion on the subject is often not complete or comprehensive. 5. Nomenclture (symbol list) P GT electric output, MW; P 0 GT electric idle consumption, MW; mx P GT mximum electric output for specific ir temperture, MW; Q B GT fuel consumption, MW; D GT exhust ses flow rte, k/s; Q CG het recovered from GT exhust ses, MW; t GT exhust ses temperture, o C; t ir temperture, o C; t w hot wter temperture, o C; D hot wter flow rte relted to spce hetin demnd, k/s; i D - hot wter flow rte relted to spce hetin demnd correspondin to i0

8 312 Christin Răducnu, Roxn Pătrşcu minimum ir temperture, k/s; c specific het for exhust ses, kj/kk; Q i spce hetin demnd, MW; Q spce hetin mximum demnd, MW; i0 ε RC HRWB effectiveness; - constnt dimensionless coefficient. R E F E R E N C E S [1] I.M. Zinher, Ghidrvliceskie I teploviie rejimi teplofictionih sistem (Hydrulic nd therml reimes of centrlized het supply systems ) Izdtelzvo Enerhi, Moskv 1976 [2] C. Rducnu, V. Athnsovici, I.S. Dumitrescu, Crestere eficientei sistemelor de termoficre din Romni prin plicre reljului mixt (Improvement of centrlized het supply systems efficiency by mens of mixed het lod control). Enery conservtion for buildins in Estern Europe, Buchrest, 1997, pp [3] C. Hewett, Policies for Micropower Future. Coenertion nd On-Site Power Production, November-December 2001 [4] V. Athnsovici, R. Ptrscu, C. Rducnu, Aspecte tehnice le coenerrii de mic putere CMP (Technicl spects of smll scle CHP), Revist Eneretic, iulie 2001, p [5] ***, Intellient Enery for Europe, Prormme , COM 2002.