Vesna Bariši}1, Edgardo Coda Zabetta1,Arto Hotta1, Boguslaw Krzton2 1 Foster Wheeler Energia Oy, R&D Department, Varkaus, Finland2 Foster Wheeler Energia Polska, Global Sales & Marketing, Warszawa, Poland

Foster Wheeler Experience in Combustion ofLow-Grade High-Ash Fuels in CFBs

Orig i nal sci en tific paperUDC: 662.613-912

Fos ter Wheeler’s cir cu lat ing fluidized bed boiler tech nol ogy meets to day’smar ket de mand for util ity-size boil ers with ca pa bil ity to fire broad range offuel qual i ties from low-grade high-ash fu els, good qual ity bi tu mi nous andan thra cite coals to var i ous bio mass and waste fu els. The high ef fi ciency cir -cu lat ing fluidized bed boil ers are de signed for firm emis sion per for manceand high re li abil ity. The fo cus of this pa per will be on ex am ples of cir cu lat -ing fluidized bed boil ers uti lized both in re-pow er ing and new pro jects andus ing hard-to-burn fu els such as low-heat ing value, high-ash/mois ture/sul -fur coals and coal wastes, oil shale, and dif fi cult bio mass.

Key words: cir cu lat ing fluidized bed (CFB), coal, coal waste, oil shale,high-ash fuels

In tro duc tion

Fos ter Wheeler is a global en gi neer ing and con struc tion con trac tor and a sup -plier of power equip ment. Among other prod ucts, the com pany of fers state-of-the-artboil ers for heat and elec tric ity gen er a tion based on cir cu lat ing fluidized bed (CFB) tech -nol ogy. Boil ers are of fered for a va ri ety of fu els and mixes, in clud ing fos sil-de rived fu els(e. g. coal, waste coal, petcoke), peat, bio mass-de rived fu els (e. g. wood, ag ri cul tural res i -due, bio-sludge), and waste fu els (e. g. con tam i nated wood, SRF, TDF).

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Dur ing the past 30 years Fos ter Wheeler has booked nearly 350 CFB boil ers, ofwhich al most 240 are de signed for coal and wastes from the coal min ing in dus try with to -tal ther mal ca pac ity of 47000 MWt (fig. 1). All the boil ers share the same cir cu lat ingfluidization prin ci ple; how ever, de pend ing on the qual ity of fuel, the boil ers dif fer sig nif i -cantly in de sign and op er a tion.

Re spond ing to an ever-grow ing de mand for power gen er a tion, CFB boiler tech -nol ogy has de vel oped to meet util ity-scale re quire ments (fig. 2). To day, the larg est CFBunits based on nat u ral cir cu la tion are two 300 MWe CFB boil ers at Jack son ville En ergyAu thor ity in Jack son ville, Fla., USA. These boil ers burn ei ther 100% coal, or 100% pe -tro leum coke, or any com bi na tion of the two. The larg est units in terms of phys i cal di men -sions are three 262 MWe CFB boil ers at Turow power plant in Po land. The fuel for theseboil ers is lig nite with mois ture con tent of 45 wt.%, which in creases the flue gas flow con -sid er ably. The net ef fi ciency of con ven tional sub-crit i cal de signs is ap prox i mately38-40%, de pend ing on fuel and con denser con di tions.

Dur ing re cent years, once-through super criti cal CFB tech nol ogy has been de -vel oped, en abling the CFB de vel op ment to pro ceed to me dium-scale (<500 MWe) com -mer cial pro jects such as Lagisza, with net ef fi cien cies near 45%. How ever, scal ing up thetech nol ogy fur ther to util ity size of 600-800 MWe with net ef fi ciency of 45-50% is neededto ful fill the fu ture re quire ments of util ity op er a tors.

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Fig ure 1. Fos ter Wheeler's CFB ref er ences (as by Sep tem ber 2, 2008)

Scal ing-up of Fos ter Wheler’s CFB boiler tech nol ogy has been achieved through de vel op ment of a sec ond-gen er a tion de sign. This de sign fea tures in te gra tion of the sep a -ra tor for cir cu lat ing sol ids and the fur nace (fig. 3a). A wa ter/steam cooled rect an gu larsep a ra tor re placed the hot round cy clone with heavy re frac tory lin ing, which was dis tinc -tive for the first-gen er a tion de sign. This con cept of fers sev eral ad van tages, such as:– less re frac tory in the sys tem, thus re duc ing main te nance cost,– shorter start-up time due to less tem per a ture sen si tiv ity in the re frac tory,– no ex pan sion joints be tween the sep a ra tor and the com bus tion cham ber, and– smaller foot-print of the boiler, which can be very im por tant in re-pow er ing schemes

where the new boiler has to fit into an ex ist ing build ing or ex ist ing site.The sec ond-gen er a tion de sign was in tro duced in 1992, and in 1996 the de sign

was en hanced with in tro duc tion of INTREX™ - in te grated heat exchanger lo cated in thefur nace (fig. 3b). INTREXTM ex tract heat from the hot cir cu lat ing ma te rial that is re -turned from the sep a ra tor, or sol ids are taken di rectly from the lower part of the fur nace.Con tin u ous flow of dense sol ids en ables high heat-rate co ef fi cients within a small phys i -cal space, and pre vents for ma tion of de pos its on tube sur faces. No me chan i cal de vicesare needed and all re quired con trols are per formed by air fluidization. Super heat ers andre-heters of INTREXTM type are par tic u larly ef fec tive in de signs for fu els that can causecor ro sion on con ven tional heat sur faces, and for large-scale util ity boil ers.

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Fig ure 2. Scal ing-up of Fos ter Wheeler's CFB boilers

Due to its eco nomic ad van tage, abun dance and short age of al ter na tives, coal isex pected to re main the dom i nant fuel for the fore see able fu ture, ei ther for new powerplants, or to re place older or in ef fi cient units. A large num ber of coal-based plants willneed to be built in Eu rope and world wide in the next de cade. How ever, CO2 emis sionsfrom fos sil-fired power gen er a tion are a ma jor con trib u tor to cli mate change. As a re sult,mod ern power plants are ex pected to com ply with high ef fi ciency and firm en vi ron men tal per for mance. When con sid er ing ei ther new plant or repowering of old units, uti li za tionof proven high ef fi ciency CFB tech nol ogy is an ideal so lu tion. High ef fi ciency leads tolower fuel re quire ments, and lower lev els of ash and emis sions, in clud ing CO2. In ad di -tion, CFB tech nol ogy has proven ex cel lent in fuel flex i bil ity and co-fir ing of CO2-neu tralfu els with dif fer ent grades of coals, which can fur ther re duce CO2 emis sion. The ad van -tages of CFB tech nol ogy will be briefly de scribed in the fol low ing chap ter.

Ad van tages of CFB tech nol ogy with em pha sis onfuel flex i bil ity

CFB pro cess pro vides an ideal burn ing en vi ron ment for a wide va ri ety of fu els.The ad van tages of CFB tech nol ogy can be sum ma rized as fol lows:– fuel flex i bil ity and multi-fuel fir ing,– low SO2 emis sions due to ef fi cient sul fur cap ture with lime stone in the fur nace,– low NOx emis sion due to low com bus tion tem per a ture and air-stag ing,

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Fig ure 3. Fea tures of sec ond-gen er a tion Fos ter Wheeler’s CFB boiler de sign(a) wa ter/steam cooled in te grated sep a ra tor (1992-), (b) INTREXTM superheater (1996-)

– low CO and CxHy due to tur bu lent con di tions and good mix ing,– sec ond ary flue gas clean-up sys tems typ i cally not needed,– sta ble op er at ing con di tions and good turn-down ra tio,– sup port fir ing is not needed ex cept dur ing start-up pe ri ods,– in creased ca pac ity pos si ble within the same foot print as old boil ers, and– no need for fuel pul ver iz ing.

One of the im por tant ad van tages of CFB tech nol ogy is the pos si bil ity of burn inga di verse range of fu els al ter nately and/or si mul ta neously. Fuel flex i bil ity in cludes both awide range of heat ing val ues and the pos si bil ity of burn ing fu els with very dif fer ent phys i -cal and chem i cal prop er ties. The types of fu els used in CFB boil ers in clude coal of var i ous de grees of carbonification, waste coal, pe tro leum coke, peat, wood-de rived fu els, ag ri cul -tural and agro-in dus trial wastes, sludge, solid re cov ered fu els, tires, etc (see fig. 4). Fig ure5 com pares chem i cal prop er ties of few se lected fu els used in com mer cial boil ers.

CFB boil ers can ef fec tively deal with wide vari a tions in coal qual ity, which canex ist even within coals from a sin gle mine. In an at tempt to min i mize the op er a tionalcosts, util i ties seek pos si bil i ties to uti lize cheaper, lower-grade coals with high mois ture,ash and sul fur con tent (see also fig. 5). Low-grade coals that have been al ready used inpower pro duc tion, es pe cially in Po land, have been lo cal lig nite coals or lower-rank bi tu -mi nous coals, which do not have an ex port mar ket due to low qual ity. Uti li za tion of thesecoals in old pul ver ized coal and stoker fired boil ers – which usu ally were not equippedwith nei ther de sul phuri sa tion, nor proper dust re moval in stal la tions – have caused manyen vi ron men tal prob lems in the form of gas eous and dust emis sions. How ever, low-grade

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Fig ure 4. Type of fu els (co-)fired in Fos ter Wheeler’s CFB boil ers

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Fig ure 5. Fuel prop er ties (data from Fos ter Wheeler’s fuel da ta base)

coals have been used in en vi ron men tally sound way in a num ber of high ef fi ciency CFBboil ers; ex am ples of two power sta tions, Turow and Jaworzno, uti liz ing lo cal low-gradecoals will be given in the fol low ing sec tion.

The pos si bil ity of us ing coal washery re jects in CFB boil ers has proved par tic u -larly valu able in Po land, for ex am ple in power sta tion Jaworzno. Mod ern CFB tech nol ogy pro vides an ef fi cient and prof it able way to pro duce power from these wastes which oth er -wise would need to be dis posed in a land fill, while also pro vid ing some profit from thewaste coal rather than pay ing fees for its dis posal.

At pres ent, most CFB in stal la tions are de signed for multi-fuel ca pa bil ity, i. e. forcom bus tion of more than one solid fuel [1]. Coal and peat are com mon fu els in multi-fuelCFB in stal la tions to gether with wood or wood-based fuel [2].

Uti li za tion of bio mass as a sus tain able en ergy source is al ready seen as one of the key op tions in the short and me dium term for mit i gat ing CO2 emis sions. How ever, thephys i cal and chem i cal char ac ter is tics of the di verse spec trum of bio mass fu els vary widely[3]. Uti li za tion of bio mass fu els in CFB boil ers may cause op er a tional prob lems, such asag glom er a tion, de posit for ma tion, and cor ro sion [4, 5]. How ever, such prob lems can belim ited with proper boiler de sign, suit able boiler op er a tion, al ter na tive bed ma te ri als orad di tives, and most ef fec tively by co-com bus tion with coal or peat that can cap ture prob -lem atic el e ments from bio mass/wastes. Coal co-com bus tion is ap plied for ex am ple inNPS util ity, Thai land, to fire high shares of lo cal bio mass rice husk and eu ca lyp tus bark.

The fol low ing sec tion will briefly pres ent ex am ples of uti li za tion of CFB tech -nol ogy in re-pow er ing, and in multi-fuel com bus tion op tion. De tails of dis cussed pro jectscan be found in pub li ca tions by [2, 6-12].

Re-pow er ing with high ef fi ciency CFB

Over 60% of ex ist ing coal-fired power plants through out Eu rope are more than20 years old (fig. 6), and many with mod est ef fi ciency [2]. Con se quently, this will re sults ina sub stan tial need for new ther mal power plants in the near fu ture.

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Fig ure 6. Age struc ture ofpower plants in Eu ro peancoun tries [2]

Turow Power Sta tion S. A., Bogatynia, Po land

One of the most re mark able repowering pro jects us ing fluidized bed tech nol ogyis the Turow power sta tion in the Silezsia re gion of south ern Po land. This sta tion orig i -nally com pris ing of 10 units, each of 200 MWe in ca pac ity, has un der gone an ex ten sivere-pow er ing pro cess: three of the units were re ha bil i tated with back end emis sion equip -ment, six units were re placed with CFB boil ers, and one unit is de com mis sioned. Thespace avail able for the new units was very lim ited, how ever, CFB boil ers could fit into theold boiler house sec tions.

CFB tech nol ogy was con sid ered ide ally suited for burn ing Pol ish lig nite coal, forwhich de sign val ues of LHV, mois ture con tent, ash con tent and sul fur con tent var ied inthe ranges 7.1-10.2 MJ/kg, 40-48 wt.%, 6.5-31.5 wt.%, and 0.4-0.8 wt.%, re spec tively. Forthe fuel prop er ties see also fig. 5.

The Turow power sta tion with six CFB units is cur rently the larg est in the worldbased on fluidized-bed tech nol ogy. The first three units are of first-gen er a tion CFB de -sign, and were de liv ered in 1998 – Units 1 and 2, and in 2000 – Unit 3. Sec ond-gen er a tionde sign was se lected for the last three units, which were de liv ered in 2002 – Unit 5, and in2004 – Units 4 and 6. Im ple ment ing the sec ond-gen er a tion de sign in creased the ca pac ityto 262 MWe in stead of 235 MWe, within the foot print of the old pul ver ized coal 200 MWe

units. Better steam val ues and better over all per for mance also lead to better over all ef fi -ciency: 40.4% com pared to 31.2% of orig i nal boil ers [2]. The com par i son of main boilerdata is shown in tab. 1. The cross-sec tion of Turow Power Sta tion S. A. units 4-6 is shownin fig. 7.

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Ta ble 1. Main boiler data for Turow Power Sta tion S. A. units 1-6

Boilers

No. 1-3 No. 4-6

Capacity MWt 528.9 557

Main steam flow kgs-1 185.4 195.5

Main steam pressure bar 131 169

Main steam temperature °C 540 565

Reheated steam pressure bar 24 39

Reheated steam temperature °C 540 585

Guaranteed emissions, 6% O2 content, dry flue gas

NOx mgNm-3 371

SOx mgNm-3 347

CO mgNm-3 150

Dust mgNm-3 50

Guar an teed emis sions are shown in tab. 1. Good emis sion con trol in CFB boileris achieved by low com bus tion tem per a ture and even tem per a ture pro file through theheight of the fur nace, a staged com bus tion, good res i dence times, and mix ing con di tions.

The Turow power sta tion is now in suc cess ful op er a tion, and meet ing all guar an -ties. It is note wor thy that there has been a con sid er able emis sions re duc tion com pared tothe orig i nal sit u a tion: NOx has been re duced by 19%, SO2 by 92%, dust by 91%, and CO2

by 24%.

Elektrownia Jaworzno III S. A., Jaworzno, Po land

In the Jaworzno Pro ject three old pul ver ized coal fired boil ers were re placed with two70 MWe CFB boil ers fir ing lo cal high-ash andhigh-mois ture bi tu mi nous coal. In ad di tion,these boil ers can fire, up to 50% of en ergy in put,coal slurry that is de liv ered from the ad ja centcoal-mines (fig. 8). Fuel prop er ties are sum ma -rized in fig. 5.

The boil ers uti lize sec ond-gen er a tion of Fos -ter Wheeler CFB de sign with com pact sep a ra -tors and INTREXTM super heat ers (fig. 9).Steam and feed-wa ter data of one boiler at nom -i nal ca pac ity are: to tal heat out put 180 MWt,steam flow 72.2 kg/s, steam pres sure 137 bar,

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Fig ure 7. Cross-sec tion of Turow Power Sta tion S. A. units 4-6

Fig ure 8. Coal slurry

steam tem per a ture 540 °C, andfeedwater tem per a ture 220 °C.

The boil ers are in com mer -cial op er a tion since No vem ber1999.

AS Narva Elektrijaamad, Narva, Es to nia

Es to nia’s elec tric ity gen er -a tion is more than 90% basedon com bus tion of oil-shale. AS Narva Elektrijaamad ownsand op er ates two larg estoil-shale-burn ing power pla-nts in Es to nia (and world -wide), Eesti and Balti, lo catednear the town of Narva. A

com bined in stalled ca pac ity of two power plants is 2705 MW of elec tric ity and 589 MWof dis trict heat ing. Plants, orig i nally build with pul ver ized fuel (PF) tech nol ogy, werecom mis sioned dur ing the years 1959-1973. Due to their age and poor eco nomic and en -vi ron men tal per for mance re lated to PF fir ing of oil shale the util ity de cided to re-power two 200 MWe units with fluidized-bed tech nol ogy. Af ter pre lim i nary in ves ti ga tions andpi lot-scale com bus tion tests, CFB tech nol ogy was found to be the most suit able for oilshale fir ing in terms of pro cess be hav ior and gas eous emis sions. The en gi neer ing, pro -cure ment and con struc tion con tract for the de sign and sup ply of four new 100 MWe

CFB boil ers was signed be tween AS Narva Elektrijaamad and Fos ter Wheeler EnergiaOy in May 2001. The pro ject also in cluded the mod ern iza tion and up grad ing of two ex ist -ing 200 MWe steam tur bine-gen er a tors to 215 MWe. The first of the new blocks, Eestiblock 8, started com mer cial op er a tion in Feb ru ary 2004 and was fol lowed by Balti block11 later dur ing the same year. The units are de signed to pro duce 90 kg/s of super heatedsteam at 13.1 MPa pres sure and 540 °C tem per a ture, and re-heat steam at 2.7 MPa pres -sure. The load range 40-100% of MCR.

Es to nian oil shale is a very dif fi cult-to-burn fuel due to its unique prop er ties (seefig. 5). High al kali and chlo rine con tent in oil-shale ash has caused sig nif i cant cor ro sionand foul ing prob lems in PF units, re sult ing in de creased avail abil ity. Gas eous emis sions,es pe cially SO2 and par tic u late emis sion, have been high. In CFB com bus tion the SO2

emis sion is con sid er ably re duced due the in her ent lime stone con tent of oil-shale ash,which fa vors sul fur cap ture in CFB con di tions. SO2 and NOx emis sions have been re -duced by 90% and 30%, re spec tively, while par tic u late emis sion has de creased sig nif i -cantly com pared to the old PF units with less ef fi cient elec tro static pre cipi ta tors.Im proved ef fi ciency and de creased car bon ate de com po si tion in CFB has de creased theCO2 emis sion per pro duced power unit by nearly 24%.

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Fig ure 9. Cross-sec tion of Elektrownia Jaworzno III S. A.CFB unit

In the CFB boil ers, foul ing and cor ro sion prob lems in the con vec tive super heat -ers have been pre vented by care ful choice of steam tem per a ture for each super heat ingstage and by us ing ef fec tive heat sur face clean ing meth ods. INTREXTM super heat ers areused as the last super-/reheat ing stage, and re frac tory-lined sep a ra tors as sec ond super -heat ing stage, al low ing lower steam tem per a ture to be used in con vec tive super-/re-heater sec tions where the risk of high-tem per a ture cor ro sion is high est. The new CFBboil ers use pneu matic fuel feed ing with many feed ing points, re sult ing in good fuel mix -ing and pro vid ing fa vor able con di tions for sul fur bind ing in the lower fur nace (fig. 10).

The care ful CFB boilerde sign has re solved the prob -lems re lated to oil shale com -bus tion: dur ing the first yearof com mer cial op er a tion nosigns of sig nif i cant foul ing orcor ro sion of heat exchangershas oc curred in the new boil -ers at the Narva Power Plants.Im proved avail abil ity, lowermain te nance costs and higheref fi ciency of the new unitshave sig nif i cantly im provedthe unit’s eco nom ics. Ac cord -ing to the per for mance tests,the net ef fi ciency of the CFBunits is 38-39%, whereas inthe PF units it is in the rangeof 29-30%. A big part of theef fi ciency im prove ment is de -riv ing from the lower car bon -ate de po si tion and higher sul fa tion rate in CFB combustion, the ef fect of which is about0.4 MJ/kg or 5% com par ing with PF [9].

Eesti and Balti power plants were granted a tran si tion pe riod con cern ing the EU Large Com bus tion Plant Di rec tive emis sion lim its un til the end of 2015, af ter which theold PF blocks must be out of ser vice. Due to pos i tive ex pe ri ences from two first unitsre-pow ered with CFB tech nol ogy, Narva Power Plants is plan ning to pro ceed by re-pow -er ing two to five ad di tional 200 MWe units with CFB tech nol ogy, the best avail able tech -nol ogy for oil shale fir ing.

Poludniowy Koncern Energetycny (PKE), Lagisza, Po land

CFB is not only suit able for hard-to-burn fu els, but the tech nol ogy is also ide allysuited for qual ity bi tu mi nous coal. Through a con tin u ous scale-up and de vel op ment pro -cess, CFB tech nol ogy has now reached me dium util ity scale with once-through super criti -cal boiler tech nol ogy.

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Fig ure 10. The ba sic de sign of the CFB boil ers at the A. S. Narva Eletkrijaamad power sta tions

Uti li za tion of Siemens’ BENSON low mass-flux ver ti cal tub ing tech nol ogy of -fers some clear ad van tages for CFB tech nol ogy in clud ing a lower pres sure drop over thefur nace tub ing, re sult ing in less power needed for feed wa ter pumps and lower aux il iarypower con sump tion. The com bus tion tem per a ture in a CFB is ho mog e nous both ver ti -cally and hor i zon tally, which means that the heat flux is rel a tively uni form, and the risk ofover heat ing is not pres ent as it is in con ven tional tech nol ogy with a heat flux that can beup to three times higher lo cally.

The first com pany to ben e fit from OTU CFB tech nol ogy with super criti calsteam pa ram e ters will be the Pol ish util ity, Poludniowy Koncern Energetyczny S.A.(PKE). The new 460 MWe (gross) unit will re place old power blocks of Lagisza PowerPlant. The ex ist ing blocks were erected in 1960’s and con sist of seven units (110-125 MWe

each). Two of them will be shut down af ter the new 460 MWe unit is com mis sioned. Thenew boiler will be built ad ja cent to the old boil ers and many of ex ist ing plant sys tems likecoal han dling and wa ter treat ment will be ren o vated and uti lized for the new CFB unit.

Main fuel for the boiler is bi tu mi nous coal. The source of fuel con sists of 10 lo cal coalmines with wide range ofcoal pa ram e ters, prov ingonce more the fuel flex i bil -ity of the CFB tech nol ogy.Ta ble 2 sum ma rizes pa ram -e ters of de sign fuel andover all fuel range. Boilerde sign is op ti mized with apos si bil ity for com bus tionof ad di tional fu els. Mainad di tional fuel is coal slurry that is avail able in large

amounts in lo cal coal mines. Due to CFB tech nol ogy char ac ter is tics, wet coal slurry canbe com- busted with 30% share by fuel heat in put. Coal wash ing re jects can also be

burned in form of dry coalslurry gran u lates with ashare up to 50% of heat in -put. Boiler is de signed alsoto uti lize bio mass fu els up to10% of fuel in put. The bio -mass feed ing equip ment isin cluded in the de liv ery as an op tion.

The Lagisza CFB boileris dimensioned ac cord ing todata given in tab. 3. The gen -eral boiler lay-out was basedon the con ven tional in-linear range ment al ready ap -

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Ta ble 2. Fuel prop er ties for the Lagisza pro ject

Coal rangeCaol slurry range(max 30% input)

Lower heat value MJkg-1 18-23 7-17

Moisture content % 6-23 27-45

Total ash content % 10-25 28-65

Sulfur content % 0.6-1.4 0.6-1.6

Ta ble 3. Boiler data for the Lagisza 460 MWe CFB boiler

Maximum continuous flow kgs-1 359.8

Minimum continuous flow kgs-1 143.9

HP steam pressure at turbine inlet MPa 27.50

HP steam temperature at turbine inlet °C 560

Cold re-heated steam flow kgs-1 306.9

Cold re-heated steam pressure MPa 5.46

Cold re-heated steam temperature °C 314.3

RH steam temperature at IP turbine inlet °C 580

Feed water temperature °C 289.7

plied for Units 4-6 of the Turow power plant. Fig ure 11 shows sche mat ics of the boiler.De tailed de scrip tion of the once-through boiler de sign and re lated as pects can be foundin [8].

The emis sion re quire -ments for the Lagisza boilerare ac cord ing to Eu ro peanUn ion di rec tive for LargeCom bus tion Plants, and con -sid er able emis sion re duc tion is ex pected com pared to ex -ist ing PF unit. The emis sionsof sul fur di ox ide are con -trolled with lime stone feed -ing into the fur nace. With the de sign coal a sul fur re duc -tion of 94% is re quired, andthat shall be achieved in theCFB with a cal cium to sul furmo lar ra tio of 2.0-2.4. Theni tro gen ox ide emis sions arecon trolled with low com bus -tion tem per a ture and staged com bus tion. There are also pro vi sions made for a sim pleam mo nia in jec tion sys tem (SNCR), how ever that is not re quired on de sign coals. Com -pared to orig i nal plants, NOx is ex pected to be re duced by 71%, and CO2 by 28%. Par tic u -late emis sions are con trolled by elec tro static precipitator. The plant ef fi ciency isex pected to be im proved from 34.7% to nearly 44%.

Scal ing up once through super criti cal CFB boil ers to 800 MWe

Fur ther de vel op ment of CFB tech nol ogy to even larger sizes and higher plant ef -fi cien cies is an on go ing chal lenge. Fos ter Wheeler and Endesa, to gether with a group ofother in ter ested com pa nies from Ger many, Greece, Fin land, and Spain have ini ti ated astudy for an 800 MWe power plant with ul tra-super criti cal steam pa ram e ters based onCFB tech nol ogy. The group has been work ing on a con cep tual boiler de sign to better un -der stand the fea si bil ity of a large CFB de sign. The pre lim i nary re sults show that the ac -tual scale-up of crit i cal CFB com po nents such as the fur nace, sol ids sep a ra tors, andfluidized bed heat exchangers to 800 MWe is pos si ble. The ac tual re quired scale-up of thedi men sions and size of the plant com po nents is quite mod er ate due to the mod u lar ap -proach adopted for the boiler de sign [8]. Fos ter Wheeler will be ready to of fer 800 MWe

CFB units by the end of 2009.

Multi-fuel com bus tion in CFB boil ers

Fos ter Wheeler is con tin u ously work ing on im prov ing the co-com bus tion ca pa -bil ity of its CFB boil ers. From a tech ni cal stand point, co-fir ing of bio mass and waste ap -pears best in large coal-fired units, where all avail able bio mass and waste can amount to

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Fig ure 11. The 460 MWe once-through CFB at PKE, Lagisza

only a mi nor share of the ther mal in put. In re turn, the coal-fired unit ben e fits from moreeco nom i cal fu els and better CO2 per for mance. In ad di tion, co-com bus tion of bio massand waste fu els is an ef fec tive method to coun ter act ag glom er a tion, foul ing and cor ro -sion, dif fi cul ties which of ten arise dur ing com bus tion of these types of fuel. In co-fir ingcase, com pounds con tained in coal cap ture the prob lem atic el e ments from bio mass andwaste, with no ad di tional losses or costs [5].

Na tional Power Sup ply Co., Ltd. Power Plant, Tha Toom, Thai land

The Na tional Power Sup ply Co., Ltd. (NPS) Power Plant, lo cated in Tha Toom vil -lage of Prachinburi prov ince in Thai land, started com mer cial op er a tion in Feb ru ary 1999(fig. 12). The power plant is equipped with two iden ti cal units of 150 MWe or 370 MWt.Each unit is de signed to pro duce 134 kg/s of super heated steam at 162 bar pres sure and542 °C tem per a ture, and 122 kg/s of re-heat steam at 542 °C tem per a ture and pres sure of 16 to 38 bar de pend ing on boiler load.

The NPS Power Plant isfeed ing 60% of its power out putto the Elec tric ity Gen er at ingAu thor ity of Thai land (EGAT)un der Thai land’s small powerpro ducer pro gram. The pro cesssteam and the re main der of thepower are sold to lo cal cus tom -ers of the In dus trial Park 304and to the nearby Ad vance Agro pulp and pa per mill.

The main fu els used in bothboil ers are an thra cite and/or bi -tu mi nous coal, and ad di tion ally,up to 50 en-% the boil ers are de -signed to co-fire lo cal bio mass:rice husk and eu ca lyp tus bark.Rice husk is pur chased from thelo cal sup pli ers while eu ca lyp tusbark is a waste prod uct from thenearby Ad vance Agro pulp and

pa per mill.As it can be seen from fig. 5, chem i cal prop er ties of the bio mass fu els dif fer sig nif i -

cantly be tween each other, and from those of coals. Rice husk is a very spe cial bio mass fuelwith ash con tent of 15-20 wt.% in dry sol ids, which is higher com pared to many other bio massfu els. Rice husk ash con tains over 90% SiO2 in most cases, mak ing it very dif fer ent from thestraws of other ce re als and even the rice straw ash. It does not cause foul ing or slag ging, buthas slightly ero sive ef fect due to a large par ti cle size and sharp edged SiO2 par ti cles in ash.The erosivity of rice husk is high enough to “sand blast” to some ex tent the boiler whenco-fired with for ex am ple eucaliptus bark that have ash with foul ing pro pen sity [4].

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Fig ure 12. Two CFBs at the NPS power plant in Thai land

Eu ca lyp tus bark is an other ex cep tional bio mass that can con tain very high con -tents of chlo rine. Con cen tra tions up to 0.98 wt.% have been an a lyzed, al though nor mallythe val ues are 0.2-0.3 wt.% in dry sol ids [4]. Com bined with ash com posed mainly of cal -cium and po tas sium com pounds, such high chlo rine level is known to in crease boiler foul -ing, and superheater cor ro sion.

Fired in high ef fi ciency boil ers with high steam tem per a tures and pres sures, theneg a tive prop er ties of such bio mass fu els and their ashes are am pli fied. Nev er the less,thanks to proper un der stand ing of in ter ac tions among ashes of co-fired fu els, and re ac -tions of flue gas com po nents with the ash com po nents, both rice husk and eu ca lyp tus bark have been ef fi ciently uti lized in two NPS boil ers that fea ture the sec ond-gen er a tion CFBde sign with INTREXTM super heat ers. The boil ers have been in suc cess ful op er a tion fornearly ten years, with good availability.

Con clu sions

Cir cu lat ing fluidized bed boiler tech nol ogy has de vel oped to meet util ity-scalere quire ments. Own ing to high ef fi ciency, ex cel lent multi-fuel ca pa bil ity and low emis -sions of ma jor pol lut ants (SO2, NOx, CO, CO2, particulates, etc.) the tech nol ogy of fers re -li able so lu tion for both repowering of old power plants and build ing a new plant. CFBtech nol ogy has proved ex cel lent with low-grade fu els, such as lig nite and low-grade bi tu -mi nous coals, coal washery re jects, oil shale, and with good qual ity fu els. Co-com bus tionof var i ous types of bio mass and waste fu els in CFB boil ers has proven as ef fi cient and eco -nomic way to re duce CO2 emis sions, and to min i mize landfiling. CFB tech nol ogy is to daycom mer cial for sizes up to 500 MWe with once-through super criti cal tech nol ogy, and bythe end of 2009 Fos ter Wheeler will be ready to of fer 800 MWe CFB units.

Ref er ences

[1] Bariši}, V., Hupa, M., On Changes in Bed-Ma te rial Par ti cles from a 550 MWt CFB BoilerBurn ing Coal, Bark and Peat, Fuel, 86 (2007), 3, 464-468

[2] Jäntti, T., Eriksson, T., Hotta, A., Hyppänen, T., Nuortimo, K., Cir cu lat ing Fluidized-BedTech nol ogy - to ward Zero CO2 Emis sions, Power Gen er a tion Eu rope 2006, Pro ceed ings onCD, Co logne, Ger many, May 30 – June 1, 2007

[3] ***, Phyl lis, The Com po si tion of Bio mass and Waste, En ergy Re search Cen tre of Neth er -lands (ECN), Unit Bio mass: Petten, The Neth er lands (http://www.enc.nl.phyl lis)

[4] Hiltunen, M., Bariši}, V., Coda Zabetta, E., Com bus tion of Dif fer ent Types of Bio mass inCFB Boil ers, Pro ceed ings on CD, 16th Eu ro pean Bio mass Con fer ence, Va len cia, Spain, 2008

[5] Coda Zabetta, E., Bariši}, V., Peltola, K., Hotta, A., Fos ter Wheeler Ex pe ri ence with Bio massand Waste in CFBs, Pro ceed ings on CD, 33rd In ter na tional Tech ni cal Con fer ence on Coal Uti -li za tion & Fuel Sys tems, Clearwater, Fla., USA, 2008

[6] Hotta, A., Nuortimo, K., Eriksson, T., Palonen, J., Kokki, S., CFB Tech nol ogy Pro vides So lu -tions to Com bat Cli mate Change, Pro ceed ings on CD, 9th In ter na tional Con fer ence on Cir cu -lat ing Fluidized Beds, Ham burg, Ger many, 2008

[7] Psik, R., Jablonski, J., Wyszynski, J., Turów Re ha bil i ta tion Pro ject - The World’s Larg est CFB Repowering Pro ject, Pro ceed ings on CD, Power Gen er a tion Eu rope 2005, Mi lan, It aly, June28-30, 2005

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[8] Hotta, A., Venäläinen, I., De sign and Scale-up Phi los o phy of One-through CFB Boil ers withSuper criti cal Pa ram e ters, VGB PowerTech, 4 (2006), 4, 66-71

[9] Hotta, A., Uus, M., Parkkonen, R., En hanced Per for mance Us ing CFB Boil ers to Fire OilShale Com pared to PC Tech nol ogy, Pro ceed ings on CD, Power Gen er a tion Eu rope 2005, Mi -lan, It aly, June 28-30, 2005

[10] Venäläinen, I., Psik, R., 460 MWe Super criti cal CFB Boiler De sign for Lagisza Power Plant,Pro ceed ings on CD, Power Gen er a tion Eu rope 2004, Bar ce lona, Spain, May 25-27, 2004

[11] Navarrete Fernández, E., Pol ish Op er at ing Ex pe ri ence from Burn ing Coal, Pro ceed ings onCD, Coal Washery Re ject and Brown Coal in Cir cu lat ing Fluidized Bed Boil ers, Enerji 2003,Is tan bul, Tur key

[12] Pyykkönen, A., Hotta, A., Fos ter Wheeler’s 2 ́ 150 MWe CFB Boil ers Started up Suc cess fullyin NPS Power Plant in Thai land, Pro ceed ings on CD, Power Gen er a tion Asia 2000, Bang kok,Thai land

Apstrakt

Vesna BARI[I]1, Edgardo Koda ZABETA1,Arto HOTA1, Boguslav K[TON2

1 Foster Wheeler Energia Oy, R&D Department, Varkaus, Finska2 Foster Wheeler Energia Polska, Global Sales & Marketing, Warszawa, Poland

Iskustva kompanije „Fos ter Wheeler” u sagorevawugoriva sa visokim sadr`ajem pepela

Tehnologija Fos ter Wheeler-a bazirana na sagorevawu u cirkulacionom flu-

idizovanom sloju uspe{no zadovoqava potrebe savremenih sistema za proizvodwu

toplote i elektri~ne energije pru`aju}i mogu}nost za upotrebu {irokog spektra

goriva, kao {to su kvalitetni bituminozni ugqevi, antracit, nisko-kalori~nih

goriva sa visokim sadr`ajem pepela, razli~iti tipovi biomase i otpada. Pored

fleksibilnosti u izboru goriva, visoke efikasnosti i pouzdanosti, Fos ter Wheeler

kotlovi sa cirkulacionim fluidizovanim slojem koncipirani su tako da zadovoqe i

najstro`ije zahteve o emisiji zaga|iva~a. U ovom radu predstavqeno je nekoliko

projekata u kojima je iskori{}ena tehnologija sagorevawa u cirkulacionom flui-

dizovanom sloju bilo za rehabilitaciju starih ili za izgradwu novih kotlova, a

koriste}i goriva kao {to su ugqevi sa visokim sadr`ajem pepela/vlage/sumpora,

ugqeni otpad, ugqeni {kriqci, i specifi~na biomasa.

Kqu~ne re~i: kotlovi sa cirkulacionim fluidizovanim slojem, ugaq, ugqeniotpad, {kriqci, goriva sa visokim sadr`ajem pepela

Odgovorni autor / Cor re spond ing au thor (V. Bari{i})E-mail: vesna.barisic@fwfin.fwc.com

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