Technology comparison of CFB versus pulverized fuel firing for utility power generation

Transcription

1 Technology compison of CFB vesus pulveized fuel fiing fo utility powe genetion by J. Utt* nd R. Giglio* J o u n l Synopsis Recent developments in ciculting fluidized bed (CFB) oncethough supeciticl technology (OTSC) hve enbled this technology to be offeed s utility-scle ltentive competing hed-to-hed with pulveized fuel (PF) OTSC offeings. One cle exmple is the CFB supeciticl unit t the Łgisz Powe Plnt in Polnd, owned by PoludniowyKoncenEnegetyczny SA (PKE). This unit hs now been in commecil opetion fo thee full yes, exhibiting vey good pefomnce, nd hs vlidted Foste Wheele s pefomnce model t this utility scle s well s fo units in the 600 MW e nd 800 MW e size nges offeing net efficiency of ~43 pe cent (LHV bsis). This opeting unit hs lso poven the use of the wold s fist FW/BENSON veticl-tube OTSC low mss flux technology. Since the Łgisz oiginl intentionl tende specified OTSC PF technology, it is impotnt to note tht the ltentive selection of CFB OTSC technology ove conventionl PF technology is of histoic significnce, not only fo the vlidtion of the CFB supeciticl pltfom s vible ltentive to conventionl PF technology, but it lso positions the CFB OTSC with fuel flexibility fo offeing of sizes up to nd including 800 MW e units. This ppe exploes the diffeences between CFB OTSC technology nd stndd PF OTSC in utility powe genetion. Selection citei, fuel buning nge in both technologies, nd othe selection dives e discussed. Economic nlysis of both technologies, bsed on existing cses, is lso povided. Also discussed e the technicl dvntges nd uses of ech technology. Foste Wheele hs ecently been wded contct fo fou units of CFB OTSC technology, which utilizes 2 on 1 configution of two 550 MW e CFB OTSC boiles on two single 1000 MW e tubines. Essentilly this povides fuel-flexible low-emissions ltentive to MW e solid fuel powe block. Keywods OTSC CFB technology, OTSC PF technology, comping PC nd CFB economics, pulveized fuel, low mss flux, supeciticl CFB, sub citicl CFB, supeciticl PF/PC, sub-citicl PF/PC, PC vesus CFB, high-efficiency stem cycle, fuel flexibility, powe plnt cse ssumptions, fuel bitge, wide nge of fuels, vitions in fuel qulity, low fuel qulity, low fuel costs, low emissions. In tody s globl utility powe genetion industy the most widely used technology fo lge-scle utility col-fied stem genetos hs been pulveized fuel fiing so-clled stem qulity col. These pulveized fuel (PF) boiles fie col in diffeing configutions including wll fiing, cone fiing, nd in some cses fo low-voltile fuels, ch fiing.the col fied in these boiles is genelly high- to medium-qulity bituminous col, which in mny cses is beneficited though some type of wshing. Foste Wheele hs designed nd supplied ove MW of the type of solid-fuel stem genetos discussed in this ppe. These units include () sub-citicl nd supeciticl pulveized fuel/col (PF/PC) wllfied stem genetos fiing high- to mediumqulity bituminous, sub-bituminous cols, (b) sub-citicl nd supeciticl ch-fied units fiing low-voltile nthcite, nd (c) subciticl nd supeciticl ciculting fluidized bed (CFB) stem genetos fiing wide y of solid fuels, including ll cols, petoleum coke, biomss, wste col, nd oil shle to nme few. Tble I Col in electicity genetion South Afic 93% Polnd 92% PR Chin 79% Austli 77% Kzkhstn 70% Indi 69% Isel 63% Czech Rep 60% Moocco 55% Geece 52% USA 49% Gemny 46% Souce: IEA 2010 P p e Intoduction Col-fied powe plnts ccount fo ove 40 pe cent of ll electicity genetion globlly. Some counties hve even highe pecentges of col-bsed electicity genetion, s shown in Tble I. * Foste Wheele Globl Powe Goup. The Southen Aficn Institute of Mining nd Metllugy, SA ISSN X/ This ppe ws fist pesented t the, Industil Fluidiztion South Afic Confeence, Novembe 2011, Cdle of Humnkind, South Afic. The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 112 JUNE

2 Technology compison of CFB vesus pulveized fuel fiing fo utility powe genetion Thee hve been thee significnt milestones elted to utility stem genetos chieved by Foste Wheele in the lst few yes. The fist cme in 2009 with the successful completion nd commecil opetion of the wold s lgest nd fist supeciticl CFB, the Łgisz 460 MW e CFB OTSC BENSON veticl tube design in Polnd. The poject ws oiginlly specified s PF unit but the supeciticl CFB ws selected s n ltentive due to the CFB s bility to bun wide nge of fuels, which fvoubly impcted the life cycle economics. The second is the Longview 760 MW e supeciticl PF BENSON veticl ibbed tube (VRT) design, which hs ecently been put into successful commecil opetion in Mdisonville, Vigini in theusa. The thid is the ecent contct wded fo fou 550 MW e supeciticl CFB BENSON veticl units to be supplied to Koe Southen Powe Compny (Kospo) fo thei Smcheok Geen Powe poject in South Koe. This poject fetues 2 on 1 configution of two ech 550 MW CFB units on single 1000 MW tubine with two septe 1000 MW powe blocks. The significnce of the Smcheok Poject is tht it ws wded bsed upon the fvoble envionmentl fetues nd economics of the CFB units in stight-up competition with two single 1000 MW PC units on two single 1000 MW e tubines. ecovey es of the boiles e simil, with the exception of the ehet stem tempetue contol scheme, mjo diffeences cn be seen in the funce sections. One mjo diffeence is tht the CFB utilizes continuous hot solids etun system to the funce, which offes mny dvntges. The CFB hot solids ciculting system cts s theml flywheel which inceses solids etention time, esulting in good cbon bunout nd homogeneous het flux thoughout the funce nd etun system. A couple of key benefits of this theml flywheel effect e: ) Cpbility of buning wide nge of fuel b) Ability to tolete vitions in fuel qulity on el-time bsis. This lone fvoubly ffects the vible O&M economics. While the PC uses otting mills nd tnspot i to delive fuel to multiple levels of bunes to fie the pulveized fuel, the CFB boile uses sttup bunes fo initil wm up, then when eching solid fuel tempetue pemit the solid fuel is gvity-fed to the units with vitully no flme pesent. The combustion tempetue emins fily constnt between C. Tend to highe efficiency genetion In tody s expnding col genetion mkets, the tend is to instll lge 660 MW to 1000 MW single o multiple PF units with once though supeciticl (OTSC) technology with stem pessues ppoching 300 b nd tempetues ound 600 C. The dvntge of using incesingly highe efficiency stem cycles is to impove net plnt het te, which essentilly poduces the sme mount of electicity with educed fuel usge, educed emissions to the tmosphee (CO 2, SO x, NO x, Hg, nd dust), while lso educing opetion nd mintennce (O&M) cost. Figue 1 illusttes the impovement in net plnt het te s the stem tempetue nd pessue is incesed fom sub-citicl to supeciticl conditions. Technology compisons The diffeences between the PC nd the CFB e shown in Figue 2 fo supeciticl design. Although the het Souce: FW Intenl Modeling Figue 1 Impovement in net plnt het te with incesing stem tempetue nd pessue Figue 2 Compison of the fetues of the lgescle OTSC PC nd OTSCCFB 450 JUNE 2012 VOLUME 112 The Jounl of The Southen Aficn Institute of Mining nd Metllugy

3 Technology compison of CFB vesus pulveized fuel fiing fo utility powe genetion The diffeence in combustion tempetue between the boiles is dmtic, s shown in Tbles II nd III. The lowe combustion tempetue in the CFB genetes much less theml NOx, while lso poducing moe even tempetue pofile in the funce comped to the PC unit. The compison of the ttibutes in Tbles II nd III shows why mny utitlities fvou the CFB s technology choice, especilly in tody s utility genetion climte given the concens fo cbon emissions blnced ginst the economics of powe mde vilble to meet egionl demnd. The diffeence in the het flux pofiles between the two technologies is shown in Figue 3. The het flux compison illusttes the diffeence in design equiements fo evpoto tube cooling of the CFB vesus the PC. Both units utilize Foste Wheele s BENSON low-mss flux evpotos, lthough thee is less tube to-tube diffeentil tempetue in the CFB, which educes het stesses to the boile tubes nd enhnces the long-tem elibility. The gphic shown below the het flux gphics plots the het flux input of the CFB comped to the pecentge of PC wll-fied nd PC ch unit het flux s function of funce height. The pek fluxes of the PC units e in the bune zones, while the CFB het flux is fily constnt thoughout the funce. Dives to conside PC - stem col edily vible A good exmple of dives tht would influence the selection of PC ove CFB would be high vilbilty of locl stemqulity low-sulphu col with eltively elxed emission Tble II PC ttibutes Combustion temp C In-funce soot blowes noml pctice Melting sh could cuse potentil slgging in funce Fst bun Open flme Achieving esonble NO x levels equie low NO x bunes with SCR No sulphu etention in the funce Gete possibility of het-elted tube dmge due to highe tempetue diffeentils between wte nd flme nd high het flux in the bune zone Sensitive to sudden chnges in fuel qulity Tble III CFB ttibutes Combustion tempetue C No funce slgging No funce soot blowing NO x fomtion educed due to stged combustion SNCR dd- on simple SO 2 etention simple by dding limestone into the funce SO x cptue Flue gs tempetue pofile homogenous thoughout the funce lowes stess due to educed diffeentil tempetue between gs nd wte side Insensitive to sudden chnges in fuel qulity Long esidence time fo good cbon bun out J o u n l P p e Souce: FW intenl modelling Figue 3 CFB vs. PC het flux compison The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 112 JUNE

4 Technology compison of CFB vesus pulveized fuel fiing fo utility powe genetion equiements (e.g. SO x limits bove 2000 mg/nm3 nd NO x limits bove 750 mg/nm3). In othe wods, no selective ctlytic edcution system (SCR) o flue gs desulphuiztion (FGD) system would be equied on the bck end of the PC unit in this exmple. In this exmple, thee my be t fist slight cost dvntge in selecting the PC ove the CFB. Howeve, if equied to tchet down emissions t some futue dte, thee e substntil etofit cpitl costs tht would hve to be ccounted fo in the nlysis of lifecycle costs of the plnt. With scubbe costs in the nge of US$125 $270 pe kilowtt fo new units, it could cost s much s US$500 pe kilowtt to etofit units. CFB - low emission equiements/lowe fuel qulity vilble On the othe hnd, if the emission equiements wee much lowe, e.g. below 200 mg/nm3, nd thee is esonble ccess to lowe qulity fuel with highe sulphu content nd lowe heting vlue o highe sh, this could esily fvou the CFB becuse of its bility to bun lowe qulity fuels while mintining low emissions without the ddition of the SCR o FGD systems tht would be necessy fo PC. Fo clee undestnding of the diffeences in fuel buning cpbility of ech technology, efe to Figue 4, which it compes the fuel buning nge in heting vlue vesus the buning difficulty of most of tody s fuels. Note the fuel nge of the PC in the blck cicle, s comped to the nge of the ed ectngle fo the CFB. This clely shows the fuel flexibility of the CFB. When this flexibility is coupled with with the bility to bun o blend lowe-cost fuels, the economics clely fvou the CFB. Economic nlysis A ecent Foste Wheele study ws completed comping the economics of PC nd CFB technolgies. The esults of this study e summized in Tble IV. This nlysis compes the two stem geneto technologies fo plnt configued fo n output of 660 MW e. The bse technology is PC comped with CFB fo thee diffeent fuels, ll using supeciticl stem cycles. Figue 4 Fuel heting vlue. buning difficulty Tble IV Powe plnt cse ssumptions Cse Units Plnt type PC CFB CFB CFB Stem cycle technology Supeciticl OTU Supeciticl OTU Supeciticl OTU Supeciticl OTU Additionl economicl fuels plnt cn utilize All cols, petcoke, All cols, petcoke, All cols, petcoke, biomss biomss biomss Additionl pollution contol equied Dy FGD + SCR Dy FGD Plnt goss powe cpcity MW e Plnt net powe cpcity MW e Plnt utiliztion fcto % Plnt net efficiency % HHV Fuel 6000 kcl col 6000 kcl col 4900 kcl col Petcoke Fuel sulfu content % Fuel cost $/Mbtu Fuel cost $/tonne Electicity poduction cost $/MWh Svings in electicity poduction cost $/MWh Bse Annul svings in electicity poduction cost1 M$/ye Bse Plnt EPC cpitl cost $/KWe Additionl plnt EPC cost svings B$ Bse Note 1 - Assumes 595 MW e continuous output fo 90% of the time Souce: Foste wheele intenl study 452 JUNE 2012 VOLUME 112 The Jounl of The Southen Aficn Institute of Mining nd Metllugy

5 Technology compison of CFB vesus pulveized fuel fiing fo utility powe genetion The col used in the exmple fo the PC is typicl 6000 kcl/kg stem col. The supeciticl CFB compison in column 2 is bsed upon utilizing the sme col s the supeciticl PC. Note thee is few pe cent decese in electicity poduction costs, but n lmost US$150 pe kilowtt eduction in cpitl cost fo the CFB becuse of the FGD system equied fo the PC. The economics of buning lowe heting vlue col in CFB is shown column 3, nd typicl petoleum coke in column 4. The dt clely shows tht the CFB option cn offe incesed vlue fo powe poduction s comped to the PC, especilly when buning lowe gde fuel o petoleum coke. The CFB petcoke-fied unit s poduction cost is US$20 pe megwtt-hou less thn tht of the PC unit fiing the 6000 kcl col. When the dvntge of fuel bitge fo the CFB is dded, s shown in Tble V fo the 600 MW exmple, not only is the cpitl cost educed due to less equipment being equied (no FGD + Denox), but thee is potentil fo US$14.6 million pe ye fuel sving with 10 ye NPV of US$95 million. This sving cn be even gete when buning even lowe gde fuels o blends of wste fuels nd biomss, fo exmple. Conclusions Histoicl picing nd futue globl col pice pojections continue to put pessue on solid fuel plnt economics. Howeve, the tends lso suggest tht in the long tem, picing will dop fom the cuent pek of ound US$110 pe ton FOB nd settle in t ound $80 pe ton FOB in bout 5 yes. Afte tht, globl picing is pedicted to be stble fo the next 15 yes o so. Since fuel is the lgest contibuto to plnt s opeting costs, fuel supply geements will lwys ply significnt ole in the finncil success of given poject. A key selection dive to mke the cse fo eithe technology will be the fuel secuity issue. Fuel uncetinty tends to fvo CFB technology. The cse fo pulveized col The PC (PF) boile hs been the stndd fo lge col-fied utility plnt pplictions fo the pst sevel decdes. The units hve poven elibility, nd when coupled with the ight i-qulity contol systems (AQCS) cn chieve the lowe stndds of emissions equied in mny of the globl utility mkets tody. Additionlly, with the incesing demnd fo bette efficiency, PF units e edily vilbe with supeciticl stem pmetes. The success of the Longview 760 MW e supeciticl PF poject hs poven the BENSON VRT technology is vible solution fo tody s supeciticl PC ppliction. In most developed counties the emissions equiements dictte the inclusion of selective ctytic eduction (SCR) system s well s eithe dy fluegs desulphuiztion system (FGD) o wet FGD in dditon to bck-end pticulte collection systems, ll of which fom the full AQCS. It is likely tht the PC will continue to be stongly consideed when looking t tody s plnt equiements, nd will continue to be fvoued when stem-qulity col is edily vilble in long-tem contcts within the defined limits of heting vlues, sh content, moistue content, sulphu content, nd especilly sh fusion tempetues. Howeve, if the oginl design fuel is not consistently vilble then thee e exteme chllenges in PF fiing when fuel switching is diven by economic fctos. In othe wods, the PC becomes limited s to which fuels cn be fied without mking expensive modifictions to the boile to ccommodte the new fuels. The cse fo CFB The CFB, on the othe hnd, is not seveely limited by the qulity of fuel which cn be fied, bsed on the oiginl design. In othe wods, the fvouble economics of the CFB come into ply when n owne cn puchse diffeent qulity fuel thn oiginlly designed fo, s discussed elie in this ppe. The CFB boile hs long been viewed nd ccepted in the industy s vible technolgy in the MW e subciticl clss units. As shown in Figue 5, the Foste Wheele CFB hs stedily gown to lge sizes with supeciticl nd ult-supeciticl stem vlues. It should lso be noted tht while incementlly incesing stem output, the Foste Wheele CFB hs neve hd n issue elted to scle-up in its development histoy. The Łgisz CFB unit in Polnd hs successfully demonstted once-though supeciticl (OTCS) technology nd vlidted the Foste Wheele design plfom fo the lge 550, 660, nd 800 MW e units. While the Łgisz CFB unit competed diectly with PC unit in the intil intentionl bid tende nd won, it is lso significnt to note tht the Kospo Smcheok poject OTSC CFBs wee selected s the pefeed technology ove the PC due to the multiple fuel cpbility nd fvoble emission flexibility, s well s educed vible O&M costs. J o u n l P p e Tble V 600 MWe net CFB supeciticl plnt opeting t 90% cpcity fcto Plnt pmete Units 6000 kcl 4900 kcl Indonesin Annul fuel 10 ye NPV fuel South Aficn col sub-bituminous col bitge ($/ye) bitge ($) Plnt net powe MW e Fuel cost $/metic ton Fuel heting vlue kcl/kg Fuel heting vlue MJ/Kg Plnt cpcity fcto % 90% 90% Fuel consumption Metic ton/ye Fuel cost $/ye Diffeence in fuel pice $ $ Souce: Foste wheele model The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 112 JUNE

6 Technology compison of CFB vesus pulveized fuel fiing fo utility powe genetion Figue 5 Evolution of the Foste Wheele CFB Souce: Foste Wheele sles dtbse fo Foste Wheele-seved mkets MW e CFBs poweing MW e stem tubines Advnced ult supeciticl veticl tube stem technology 603/603 C stem tempetues Fiing wide nge of impot nd domestic cols Commecil opetion expected Units 1 nd 2: mid-2015 Units 3 nd 4: end of Poven dvnces in supeciticl/ult-supeciticl CFB technology now clely povide competition fo lge-scle utility PC offeings in the 500 MW to 1000 MW size nges. The competitive picing nd fuel flexibility offeed by the OTSC CFB cn bing cetinty to the invesment decision by utility plnt ownes, especilly given the uncetinty in pedicting futue globl fuel costs nd vilbility. The OTSC CFB cn cpitilize on fuel bitge nd oppotunity fuels Figue 6 The Kospo Smcheok Poject MWe SC CFBs while poviding highly competitive vlue nd educed emissions fo mny yes into the futue. 454 JUNE 2012 VOLUME 112 The Jounl of The Southen Aficn Institute of Mining nd Metllugy