Performance Evaluation of Cross-Flow Heat Exchanger in Coal-Fired Power Plant under Particulate Condition

Transcription

1 การประช มว ชาการเคร อข ายว ศวกรรมเคร องกลแห งประเทศไทย ต ลาคม 2547 จ งหว ด-ขอนแก น Perfrmnce Evlutn f Crss-Flw Het Exchnger n Cl-Fred Pwer Plnt under Prtculte Cndtn Ppt Jungjndee Me Mh Pwer Plnt Opertn Dvsn Electrcty Genertng Authrty f Thlnd Me Mh, Lmpng 52220, Thlnd Tel.: Fx.: E-ml: ppt.ju@egt.c.th Thwn Suchrtkul Deprtment f Mechncl Engneerng Chng M Unversty Chng M 50200, Thlnd Tel.: Fx: , E-ml: thwn@dme.eng.cmu.c.th Abstrct Ths reserch wrk s t study the perfrmnce f the crssflw het exchnger f 300 MW Me Mh cl-fre pwer plnt. Nrmlly, ths equpment exchnges het between the ht flue gs nd the nlet cmbustn r whch perted under hgh cntent f fly sh nd t brngs t get lwer het trnsfer perfrmnce. Unfrtuntely, frm the prevus wrk, there s n mre dt but the het trnsfer degrdtn f het exchnger due t the hgh prtculte cndtn. Frm ths study, t ws fund tht the flue gs sde het trnsfer ceffcent ws lwer thn tht f Zhukusks s mdel pprxmtely %. Therefre, the new emprcl crreltn fr predctng the het trnsfer ceffcent f ths crss-flw het exchnger ws ls develped n ths wrk nd t ws fund tht the develped mdels cn predct the expermentl dt qute well. 1. Intrductn A het exchnger s devce tht s used t trnsfer therml energy frm hgher temperture het surce t lwer temperture het snk. There re mny types f het exchnger pplcble t the recvery f wste het such s shell-nd-tube het exchnger, plte-type het exchnger, nd crss-flw het exchnger. The crss flw type s sutble fr recverng het frm hgh temperture flue gs. In Me Mh cl-fred pwer plnts, there re mny type f crss-flw het exchnger especlly the prmry r heter. Ths het exchnger s recvered het frm the hgh temperture flue gs t wrm up the cmbustn r. Fgure 1 shws the schemtc dgrm f the pwer plnt ncludng the prmry r heter. Nrmlly, ths heter s perted under the hgh prtculte cndtn whch re fly sh frm the cmbustn prcess nd trend t decresed ts perfrmnce. Unfrtuntely, there s lck f dt but the perfrmnce decresng due t ths cndtn. Therefre, the bjectve f ths reserch wrk s t nvestgte the perfrmnce f the crss-flw het exchnger knwn s prmry r heter f Me Mh pwer plnt under hgh prtculte cndtn. Mrever, the emprcl mdel s develped fr predctng the perfrmnce f ths equpment. 2. Perfrmnce Dt In ths wrk, the prmry r heter f 300 MW Me Mh cl-fred pwer plnt, unt 12 s selected fr nvestgtng. The test dt were recrded 12 tmes, every hur, durng genertn utput between MW, perted wth cl fuel. The cllected dt nd the dmensn f ths het exchnger s shwn n tble 1 nd 2 respectvely. The n-lne tube rrngement f prmry r heter s shwn n fgure 2.

2 Fgure 1 Schemtc dgrm f Me Mh pwer plnt Tble 1 Perfrmnce dt f the prmry r heter Tme (h) Ld (MW) cl flw (t/h) Ar flw (kg/s) T h T h T c T c Tble 2 Dmensn f prmry r heter Crss flw, 1 flue gs Type pss nd 3 cmbustn r pss Number f tubes 1,540 Number f tube rws 28 Tube rrngement Inlne Trnsverse tube ptch Lngtudnl tube ptch Tube dmeter m Tube length m/pss Fgure 2 In-lne tube rrngements f prmry r heter

3 3. Dt Reductn In ths experment, ht gs flwng utsde the tube bnk trnsfers het t the nsde tube r nd the het trnsfer rte ( Q ) cn be clculted s Q = m& c T T ), (1) p ( Q = m& c ( T T ) g. (2) g pg g The het trnsfer rte cn be clculted n the frm f lg men temperture dfference methd s Q = UAF. (3) T lm The verll het trnsfer ceffcent re f the het exchnger cn be evluted n the term f therml resstnce s 1 1 = UA h A ( D / D ) ln + 2πk L t 1 +. (4) h A The tube sde het trnsfer ceffcent cn be estmted by Dttus-Belter equtn [1] n the term f Nusselt number s 0.8 n Nu = Re D Pr. (5) Nte tht Nusselt number, Reynlds number nd Prndtl number n ths wrk re defned s h D Nu =, (6) k Ths equtn s the functns f Reynlds number nd Prndtl number s k f h = 0.27 ReD, Pr. (9) D Nte tht the flue gs sde Reynlds number s defned s ρ f Vmx D ReD, =, µ f (10) where ST Vmx = S D V. (11) T 4. Results nd Dscussn Fgure 3 shws the pwer plnt ld whch vred between MW. Ld (MW), Cl flw (t/h), Ar flw (kg/s) Cl-fre pwer plnt, unt 12 Ld Cl Ar flw Tme (h) Fgure 3 Pwer plnt ld Crss-flw het exchnger 4m& Re D, =, (7) π D µ c p µ Pr =. (8) k Het trnsfer rte (W) Tme (h) Fr the flue gs sde, Zhukusks s equtn [2] s dpted fr evlutng the het trnsfer ceffcent ( h ). Fgure 4 Het trnsfer rte f prmry r heter

4 Fgure 4 shws the het trnsfer rte f prmry r heter. It ws fund tht the het trnsfer rte s prllel wth pwer plnt ld. Fgure 5 shws the het trnsfer ceffcent frm the experment, It ws fund tht the het trnsfer ceffcent ws nerly cnstnt nd lwer thn tht vlue clculted frm Zhukusks s equtn pprxmtely %. Ths result my be cme frm the effect f prtculte mtter (fly sh). Actully, Zhukusks s equtn ws selected fr clcultng the szng f het exchnger. Hwever, ths crreltn grees well wth the clen r cndtn. Therefre, the pplctn f ths equtn fr evlutng the szng f het exchnger perted under hgh prtculte cndtn, my hs sme errr. T vd the mstken, the new crreltn s develped fr evlutng the het trnsfer ceffcent f the prmry r heter. Equtn 12 shws the detl f ths crreltn whch wrks well f pplyng fr ths crss-flw het exchnger where 0.043< k <0.0451, < Re D < 36956, nd < Pr < h crreltn (W/m 2 K) h experment (W/m 2 K) Fgure 6 The cmprsn f the new mdel nd the expermentl dt Fgure 6 shws the cmprsn f the develped crreltn nd the expermentl dt. The lnes whch shwn n the fgure, ndcte the devtn frm the verge vlue +5% nd -5%. It ws fund tht the new crreltn cn predct the expermentl qute well. h (W/m 2 K) Crreltn Experment tme (h) 5. Cnclusn 1. The prtculte mtter hs n effect n the perfrmnce f the crss-flw het exchnger. 2. Zhukusks s equtn cn predcted pprxmtely % hgher thn tht f the expermentl vlue. 3. The new mdel cn predct the dt qute well. h = Fgure 5 Het trnsfer ceffcent f prmry r heter k D D ( Re ) Pr (12) 6. Acknwledgement The uthrs grtefully cknwledge the supprt prvded by the Electrcty Genertng Authrty f Thlnd. Reference [1] Hewtt, G.F., Shres, G.L. nd Btt, T.R. (1994), Prcess Het Trnsfer, Bc Rtn, CRC Press, [2[ Incrper, F.P. nd Dewtt, D.P. (2002), Intrductn t het trnsfer, 4 th edtn, Jhn Wley & Sns Inc., USA. [3] Shh, R.K., Sekulc, D.P. (2003), Fundmentls f het exchnger desgn, Jhn Wley & Sns Inc., CANADA.

5 Nmenclture A Are (m 2 ) c p Specfc het (J/kg K) D Dmeter (m) h Het trnsfer ceffcent (W/m 2 K) k Therml cnductvty (W/m K) L Length (m) m& Mss flw rte (kg/s) Nu Nusselt number P Pressure (N/m 2 ) Pr Prndtl number Q Het trnsfer rte (W) ReD Reynlds number Trnsverse tube ptch (m) St Sl T U V Lngtudnl tube ptch (m) Temperture Overll het trnsfer ceffcent (W/m 2 K) Velcty (m/s) Greek symbl µ Dynmc vscsty (Ps) ρ Densty (kg/m 3 ) Subscrpt Ar sde f Flue gs sde Inner (Ar sde) mx Mxmum Outer (Flue gs sde) t Tube