# Impact of biomass co- c ombustion
on SCR DeNOx operation

by:

H

a ns Je ns e n

- H o l m Joa k im

Reim er Thø gerse n Peter Lind en hoff

Haldor Top s ø e A/S

Presented at Powe r-G en E u rop e , Germ any, 2009 Best pape r a w ard within th e confe r en ce track ‘Coal, Nucl ea r & Biomass Gene ration’Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 2 of 2 3



### Abstract

With increa si ng req u ireme n ts for re du ctions of CO 2 e m issi on s fro m the powe r -gene rating in dustry, there is a considerable in terest in the utilisation of biom ass and munici pal and industrial

wa ste in po wer plant boil e rs. Com b ined with still tighter limits on e m issi on of NOx, the use o f bioma ss fuel rep r e s ent s a chall enge to t he de si gn ers of Selective Catalytic Red u ction (S CR) units si nce the useful life o f the SCR cat a lyst can b e significa ntly reduced.

The me cha n i s m s re spo n si ble for the cat a lyst dea ctivation are di scu s sed. Alkali -metal aerosol s formed d u rin g comb ustio n of biomateria l can at wo rst cau s e compl e te dea ctivation of the cata

lyst within a few thou sa nd hours of ope ration. Other compon ents a s e.g. pho sph o rou s can

cau s e severe fouling of the catalyst su rf ace.

The pap er d e s cribe s a nu mber of SCRs implem ente d to meet these ne w challe nge s and in

clud es exp e ri ence from a variety of plants firi ng bio m a ss in Eu rop e and the USA. Results from installatio n s i n units firing 100% biom ass as well a s installatio n s in units with co-comb u stio n o f bioma ss with coal a nd oil a r e presented.

These expe ri ences d e mon s trate that ch oosi ng the rig h t plant confi guratio n and prop er cataly st formulatio n, the neg ative effect can be li mited. Up to 20 wei ght per cent bioma s s ca n be cocomb uste d wi th the coal s without any noticea ble im pa ct on catalyst lifetime. The use of SCR on 100% biom ass-fired boil e rs may be done as a tail- en d installatio n to minimise the amount of poisoning sp ecie s ente r in g the SCR.

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 3 of 2 3



### Contents

Introduc t ion

............................................................................................................................... ..... 4
SCR de activa tion mech ani sm s

..................................................................................................... 6
Alkali and al kaline-ea rth metals

................................................................................................ 6 Phosp h o r ou s

........................................................................................................................... 10
Ars e nic

............................................................................................................................... ..... 11 Examples of experie nce from bioma s s-f i red boil e rs

................................................................... 11
DO NG Ene r g y , Avedøre Powe r Station, Denm ark

................................................................. 11
DO NG Ene r g y , Studstrup Powe r Station, Denma r k

............................................................... 13
Electra bel, La ngerl o Power Station, Belgium

......................................................................... 16 Vattenfall, Combined Heat and Power, Swed en

..................................................................... 17
Sierra Po we r, Californi a, USA

................................................................................................. 19 Vattenfall, Amage r Powe r Station, Denmark

.......................................................................... 20
Con c lu sion s

............................................................................................................................... .. 22

R e fe re nc es

............................................................................................................................... ... 23

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 4 of 2 3



### Introduction

An increa sed prod uctio n of electri c ity fro m rene wa ble energy sou r ces is b e ing p r omoted an d bioma ss co -firing with coal in existing co al-fir e d po wer plants re presents an o p tio n for com b ine d renewable and foss il energy utilisation to reduce CO 2 emission s. Biomass is con s ide r ed CO 2 neutral with resp ect to the gree nho use g a s bal an ce if the use of fossil fuel in harv e sting a nd transpo rting the bioma s s is not co n s ide r ed. Dire ct co -firing, i.e. firing the coal a n d bioma ss in the same b o il er, is the sim p lest an d mo st wi dely ap pl ied tech nolo g y for co-firi ng bioma ss.

Possi ble bio m ass source s co mpri se e. g.:

Wa stes a nd resid u e s

- Woo d and b a r k: fore st or tree trimming s, sawdu s t, demolition wo od , crate s

- A g ric u lt ural r e sid u e s : st ra w, oliv e resi d ue, co con u t c h ips

- Animal wa ste s : Poultry litter, meat bone meal

- MSW, se wag e slud ge, pap er wa ste Peat Agricultural e nergy cro p s: Switchg r a s s, miscanthu s, popla r and wi llow, bamb o o

Biomass an d coal h a ve fun damentally di fferent fuel propertie s . Bio m ass (a nd lo w-ran k coal s) contai ns la rg er rel a tive qu antities of alkali and al kalin e-ea rth elem ents (p otassi um, sodiu m , calcium, mag n e s ium ) , pho sp horo u s a nd chlorin e than coal. As all the con s tituents of the biomass enter the boil e r, seve ral te chni cal con c e r ns a r i s e. Hig her fuel chlo ri ne co ntents can lead to greate r hig h -t empe rature corrosi on in bo ilers. Accel e rated fouling a nd sla gging can occu r wh e n high potassium containi ng fuels are utilised.

Also for the o peratio n of SCR system s there a r e te ch nical challe ng es a s soci ated with co

comb ustio n o f biomass an d coal in b o ile rs de sig ned f o r co al. The constitue n ts of biomass hav e the potential to impair the SCR a s the SCR cataly st s are susce p tib l e to ‘poiso nin g ’ due to co nden sation of volatile inorg anic spe c ie s on the cata ly st su rface. Formation of sul phate- o r ph o s

phate-ba sed depo sits o n the cataly st su rface o r r eacti on with the catalyst’s a c tive spe c ie s can signifi cantly redu ce catalyst activity, resu lting in sho r te r lifetime. Biomass in the form of wa ste s may also con t ribute elem e n ts su ch a s a r se nic.

Table 1 sho w s example s o f ‘poison o u s ’ comp one nt s i n the ash of variou s fuel s a nd the relate d SCR catalyst dea ctivation rates. Figu re 1 sho w s the d eactivation trend for vari ou s fuel types a s

ac tivity relative to fres h-cataly st activity versu s op erating ti me. The activity curve s have be en cal c ulate d usi ng a dea ctiva t ion model de veloped by Haldor T o p s øe that consi ders ash dep osi

tion rate, pore pluggi ng de velopment an d chemi c al im pact on a c tive sites.

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 5 of 2 3

Bitum i n o u s coal PRB
coal Hea v y fuel oil Peat
P C boiler Wood CFB boiler
A s h m g / N m 3 1 5
, 0 0 0 6

, 0 0 0 1 0 0 6

, 0 0 0 1

, 5 0 0 Soluble potas sium w t % 0.15 0.5 - 0.3 5.2 Soluble sod i u m w t % 0.12 1.5 1.5 0.2 0.7
N i c k e l w t %

- - 2 0 0

. 0 1

- V a n a d i u m w t %

- - 2 0 0

. 0 1

- P h o s p h o r o u s w t % 0

. 1 0

. 8

- 1 1 5 C a l c i u m w t % 0

. 5 2 2 1

. 1 1 5 5 SCR cat a lyst deactivation % per 10,000 hours (model sim u l a ti on cf. F i gure 1) 1 2 2 0 5 6 0 4 6

Ta ble 1 F l y ash c haract e ristics of vario u s fuels

0% 20% 40% 60% 80% 100%

0 10, 000 20, 000 30, 000 40, 000 50, 000 60, 000 O p er a t i o n ho ur sRelativecatalystactivity,k/k0

W ood B i t u m i nous c oal H eav y f uel oil Light f uel oil

PRB c o a l

Figure 1 Exp e cted d eac tivation of SCR cata ly st for various fuel t y pes

For biom ass f i ring the SCR catalyst dea ctivation rate is sig n ifica n tly higher. Typi cal dea ctivation rates fo r insta llation in a hig h -du s t po sitio n are sho w n i n Table 2.

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 6 of 2 3

F u e l D e a c tiv a t i o n r a t e
100% straw 50% per 1,0 00 hou rs Woo d : - Pulverised -fuel boile r - CFB boiler - Grate-fired boiler 60% per 1 0 ,0 00 hou rs 45% per 1 0 ,0 00 hou rs 25% per 1 0 ,0 00 hou rs Peat-fired b o i l er 30% per 1 0 ,0 00 hou rs Coal -fire d boi ler 10% per 1 0 ,0 00 hou rs Heavy fuel oil fired boile r 5% per 10,0 00 hou rs Gas-fire d boil e r 2% per 10,0 00 hou rs

Ta ble 2 T y pic a l SCR c a tal y st deactiv a tion rates. Actual d eactiv a tio n rate dep en ds on sp ecific fuel com positi on



### SCR deactivation mechanisms

Alkali and alkaline-e a rth metals

Alkali-m e tal a e ro sol s forme d durin g co m bustio n of bio m aterial a r e well kno w n to be able to se

verely impa ct the performa n ce of SCR catalysts. The sub

- mi cro n p a rticle s ad he re to the surfa c e of the catalyst and are rea d ily transp o rt ed to the acti ve sites by su rface diffu sio n . Spectro s co pic studie s sugg est that the poiso ning me chani sm oc cu rs via chemi c a l bondin g of the alkali metal to the cru c ial –V-O H site s, the so-call ed Brøn st ed-aci d sites whi c h also a d sorb a nd “a ctivate” the ammoni a, forming –V-OM (M bei ng K or Na ) and thereby blo cking the cataly tic cycle (see Figure 2). Exposure to al kali-metal a e ro sol s ca n at wors t c a us e c o mplete loss of ac tivity of th e catalyst withi n a few t hou sand ho urs of operation.

V O V O O H

V O V O O M M

Ac i d

- base Redox

Figure 2 Basica ll y, the SCR reacti on i n volv es both a c id-b as e an d redo x cata l y t i c functio n s. T he reactio n is initiat ed b y the ads orpti on of ammoni a on Brø n sted acid sites (V 5+ -OH), follo w e d b y “ac t ivation” of ammon i a via re action w i t h red o x site s (V= O ). T h is “activated” form of ammonia th en reacts w i t h gas eous or w e akl y adsorb ed NO, prod ucin g N 2 and H 2 O w h il e rele asin g V 4+ -OH. T o complete the cata l y tic c y cl e, the V 4+ -OH speci e s is o x id is ed b y eith er N O or O 2 to regenerate the orig in al V= O species (from [ 1 ])

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 7 of 2 3

Cf. Table 2, e x posu r e to flue gas from straw comb u s tio n results in a very rapid cat a lyst dea ctivation. Studies have sho w n the flue gas to have a high mass co nce n tration (up to more tha n 2 g/Nm 3 , depen ding on type of stra w) of submicro n par t i cle s of 0.15-0.30 μm size (num ber g e o

metric m ean diamete r). Th e particl es, which a r e mo st ly compa c t agglome r ate s , con s i s t of almost pu re pot assium chlo ri de and sulp h a te wi th mino r amou nts of sodi um, pho sphorou s and cal c ium [ 2 ].

In a study by the CHE C group at the Te chni cal Unive r sity of Denm ark in colla bo ration with Ha ldor To psøe, full-len g th mo nolith cataly st sample s were exposed to aero s ol s of p u re pota s siu m chlo ride a nd -sulp hate in a ben ch-scale reacto r sh own in Figure 3 [ 3 ]. An aerosol of the salt wa s then gen erat ed by injectin g the solutio n of the sa lt into the flue gas close to the burn e r whe r e the temperature was 1 000 –115 0° C. Activities of the catalysts were measured in situ at 350° C typically 2–3 times pe r day. The cataly st activities a s a function of e x posu r e time to the flue gas are sho w n in Figure 4.

Figure 3 Exp e rim ental s e t-up for catal yst ex posure tes t s (from [ 3 ])

Figure 4 (left) sho w s that a fter exposu r e to KC l aero s o l s at 350° C fo r 715 ho urs, the cataly st relative activity was ab out 69%, which corres pon ds to a deactivatio n of about 1.0 % per day. There wa s al so a fast de crease of the adso r ption cap a city for NH 3 on the cataly st. Then the system wa s cleane d and without additio n of KCl t he catalyst wa s tested for a noth e r 235 h o u r s. Duri ng this p e riod the cata lyst activity rema ined at ab out 69% and the amount of chemi s o r be d ammoni a also levelled off. This confirm s that ca talyst deactivation stops when addition of KCl is

c e as ed

.

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 8 of 2 3

The cat a lyst activity as a functio n of exposure time t o K 2 SO 4 is sh own in Fig u re 4 (right ). The relative activity decre ased to 86% duri n g t he first 300 hours, co rres pondi ng to a dea ctivation rate of 1.1% per day. Then the relative ac tivity kept decrea s ing at a rate of abo ut 0.4% per d a y; i.e. only 40% of the deactiv a tion rate ob served for cata lysts expo sed to KCl at a similar ae ro sol load. This diff eren ce i s ascribed to the di fference in ae rosol pa rticle size sin c e stu d ies with direct imp r eg na tion of catalyst with KCl and K 2 SO 4 sho w ed the s e to have equ al p o iso n ing effe ct. Similar to the KCl-a e ro sol e x posu r e tes t, the c a talys t capac i ty for NH 3 chemisorp t ion decrea s e d faster tha n the relative acti vity. The active site s within the catalyst st ructu r e, altho ugh not pa rticipating in th e SCR rea c tion, rea c t with potassium re sulting in a fa ster de crea se in the catalyst

c a pac i ty for NH 3 chemisorp t ion than the observed a c ti vity which is i m pede d by the mass tran sf e r re sist a n c e s.



### KCl aer os o l s K 2 

### SO 4 

### aero s o l s

K C l d ep os iti on s t o ppe d 

### KCl aer os o l s K 2 

### SO 4 

### aero s o l s

K C l d ep os iti on s t o ppe d 

### KCl aer os o l s K 2 

### SO 4 

### aero s o l s

K C l d ep os iti on s t o ppe d

Figure 4 Catal y st activit y a nd chem isor bed N H 3 on the catal y st as a functi on of ex posure time to potassi um chlo ride a nd p o tas s ium sul phate aeros ols (from [ 3 ])

SEM-EDX an alyse s sh owe d that potassi um par tly dep osited o n the catalyst oute r wall but mainly penet rated into the catalyst wall and the NH 3 chemi s o r ptio n measureme n ts reveal ed that the Brøn sted acid sites h a d reacte d with potassium a n d were re nde red ina c tive for NH 3 adsorption and sub s eque nt rea c tion with NO. The co ncl u si on was that che m ical poi so ni ng of active sites i s the do minating de a c tivation mechani sm but p h ysical blo cki ng of the su rface may al so contri bute to the loss of acti vity.

Figure 4 (ri gh t) sho w s for compa r ison th e dea ctiv ation trend of a catalyst exposed to the flue gas fro m a straw-fi red p o wer plant, Ma snedø, in De n m ark. The de activation rat e is app roximately 50% per 1,000 h o u r s, very similar to what wa s observed in t he KCl-aerosol exposure
tes t.

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 9 of 2 3

Figure 5 sh o w s results fro m activity test and analy s is of catalyst sa mples from a pilot installati on on a CFB wo od-fired boile r at Nässjö, Swed en. It is seen that at an uptake in ex ce ss of 0.2

- 0. 3 % by weight of (solu b le ) al kali metal s , the impact on catalyst activity is very signi ficant and at about 1% an almost compl e te loss of activity is obse r ved.

0% 20% 40% 60% 80% 100%

0. 0 0

. 2 0. 4 0

. 6 0. 8 1

. 0

W e i g h t pe r c e n t pot as si um e q ui v a l e nt s on ca t a l y s t

w

t %

K

+ 1. 7× w t %

N aRelative specificcatalystactivity

Figure 5 Deactiv a tion of T opsø e DN X ® SCR catal y st as function of uptake of sol ubl e alka limetals. Sodi u m and potass i u m are w e i ghte d accord ing to their mol a r w e i ght

The co ncl u si on is that ch e m ical poi so ni ng of ac tive si tes is the do minating de a c tivation mechanism, but foul ing of the surf ace a r ea m a y also cont rib u t e to the loss of activity in a practi cal ap

plication.

Ca S O 4 F O U L I N G L AYE R

Figure 6 High c onte n t of calcium i n fuel can cause dea ctivation of the catal y st in the SCR un it. T he scannin g electro n micros cop y pictur e sh o w s a t y pica l fouli ng l a yer o n the catal y st surfac e se en in SC R unit s firing hi gh-ca l c ium sub- bitum i no us coals.

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 1 0 of 23

Fouling i s a p h ysical blo c kage of the cat a lyst pore system by aero s ols or oth e r sub-mi cron a s h particl es. Fig u re 6 sho w s how a catalyst exposed to cal c ium

- cont aining fly ash from bu rning of sub

- bitumi no us Powde r Ri ver Basin (P RB) coal ha s develop ed a den se layer o f calcium sul

phate which prevent s the NOx in the flue gas to reach the active si tes in the inte rior of the catalys t.

Phosphoro u s Orga nically bound p h o s ph orou s in fuel i s rele ased a s gas-pha se p hospho rou s d u ring the com

bustio n pro c e ss. Th e pho sphorou s re act s in the ga s p hase to form polypho sph o ric-a c id a e rosol s whi c h d u r ing coolin g-o ff conden se s in the catalyst pore s . Rea c t i ons with e.g. cal c ium an d alkali metal s form sub-micron parti cle s o f pyro- or p o lypho sph a tes whi c h de po sit on the cataly st surfa c e, cau s ing pore blo c king a nd surf ace ma ski ng with an en sui ng loss of cat a lyst activity.

In some ca se s seve re de a c tivation ha s been repo rte d . Up to 50% dea ctivation has b een o b

serve d after 4

, 000 ope ratio n hours when 5% bone re si due or se wag e slud ge ha s been co-fi r ed with bitumino us coal [ 4 ]. These investig ations reveal that phospho r seem s to accumul a te in the
cat a ly st s u rf a c e.

Figure 7 sh o w s a c cumul a tion of pho sph o rou s in t he o u ter 50 -10 0 micron s of the wall of a cat a

lyst from a PRB-fire d boile r. In this ca se phos pho r pe netrate s dee p e r into the cat a lyst stru cture than the su b micron calci u m-oxide a e ro sol s , wh i c h d e mon s trate s that the pho sp horo u s com

poun ds h a ve a high mobilit y.



### 0 1 2 3 4 5

0 200 400 600 800 Di st an ce ( μ m)Concentration,wt% 

### P h os p h or o u s S u lphur

Figure 7 Sub-surfac e ph osph orous l a ye r in the outer 5 0 -10 0 microns of the surface of a catal y st expose d to flue g a s from phosp horo u s-cont ain i ng fue l

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 1 1 of 23

Arse nic

Arse nic (A s) i s a co mpon e n t present in most of the world’ s co al an d co-co m bu st ion of e.g.

wa ste and se wag e slu dge can contri but e to fuel arse nic content. Whe n the co al is burned, arseni c is relea s ed in the furnace as a g a s eo us oxid e, As 2 O 3 . As 2 O 3 cond en se s in the poro u s catalyst st ru cture an d may then blo c k the access to the catalytically active sites. Arse nic in
gaseou s form can be a mai n contri buto r to dea ct ivation of catalysts in SCR DeNOx units on coal -fire d boil e rs.

The suscepti b ility of the catalyst to poisoning from exposure to arsenic depends strongly on the
pore stru cture of the catal y st. A highly poro u s cata ly st with a diverse po re st ru cture ha s a hig h resi stan ce to wards a r seni c poi soni ng a s the prese n ce of macro-p o re s en su re a c cess to activ e sites eve n wh en the micro-pore s hav e b e com e plug g ed by arseni c.



### Examples of experience from biomass-fired boilers

DO NG Energ y , A v edøre Po w e r Sta t ion , Denmark
DO NG Ene r g y ’s Avedøre Powe r Station Unit 2 is a combine d heat and po wer pl ant, located i n Cop enh agen, Denma r k. It wa s com m issioned in 2 001 and is on e of the world’ s most efficient power pla n ts with an en erg y efficiency u p to 94%.



## Stra w

Na tu r a l g a s Oi l

Na tu r a l g a s Electrici t y Distric t he a

S t e a mturbine Bio m a s s boi l e r

M a in

- b i o l e r : 

## Stra w

Na tu r a l g a s Oi l

Na tu r a l g a s Electrici t y Distric t he a

S t e a mturbine Bio m a s s boi l e r

M a in

- b i o l e r :

47 5 M W

2 x 5 5 M W 40 M W 

### G a s t urb i nes 45 M W

39 0 M W 

## W o o d p e l l ets Bi o m a s s bo ile r

10 0 MW th



### Ma in bo iler 80 0 MW th



### G as t u rb i n es St ea m T u rbi n e Fu e l o il

Coal f l y ash Nat u r a l gas W o od pel l e t s

Natur a l gas Stra w

El e c t r i c it y Di st r i ct Heati n g

Figure 8 DONG Energ y ’ s Avedø re Po w e r Station Un it 2, Denmark [ 5 ]

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 1 2 of 23

Avedøre Unit 2 use s a mult i-fuel co ncept devel ope d b y DONG En e r gy. The unit con s i s ts of an 800 M W th ma in boiler, a 10 0 MW th straw-fired b o iler a nd 2×135 M W th gas turbi nes (se e Figu re 8). The ultra-sup e rcriti cal boiler wa s ori g inally develo ped to burn n a tural ga s an d heavy fuel oil but wa s retrofitted in 2002 to fire up to 30 0,000 tonn es per yea r of pulverised woo d pellets a s a n addition al fue l . The furna c e is desi gne d for co al firing and ha s a tan gential firing system with sixteen lo w-NOx burne rs. The unit is eq u i pped with du st filter, SCR De NOx and d e sul phu risation units.

It was expe rienced [ 6 ] that co-firi ng of wood pell e ts a nd f uel oil re sulted in dep o s its in the con

vective part o f the boiler an d in the air-preheate r . The depo sits con s isted of alkali from bioma ss and sulph u r a nd vanadi um from the fuel oil. Such dep osits a r e corrosive an d cat a lyse s the formation of SO 3 . This resulte d in pluggin g of the air-p re heater, in corrosi on in the electrostati c pre c ipitato r a nd ga s pre h e a ter as well a s dea ctivation of the SCR.

An accele rate d dea ctivation wa s expe cted as t he wo od’s relatively high co ntent of potassium and chlori de partly vapori s es du ring co mbustio n , forming a fine a e ro sol of KCl and K 2 SO 4 particle s . A catalyst dea ctivation monitori ng prog ra m m e was initiated. Experien c e d u ring wo od-oil co-fi r ing sho w ed that the catalyst de act i va ted rathe r fast as sho w n in Figure 9.

0 50

. 0 0 0 100

. 0 0 0 150

. 0 0 0 200

. 0 0 0 250

. 0 0 0 300

. 0 0 0 350

. 0 0 0

2 001 20 02 200 3 2 004 20 05 200 6 2 007 Y earTonnes

0 50.00 0 100

. 0 00 150

. 0 00 200

. 0 00 250

. 0 00 300

. 0 00 350

. 0 001000 Nm3 Fu e l o i l
W ood p e l l et s Fl y

a s h
N a t u r a l gas

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 1 00%

0 5

. 000 10. 000 1 5

. 0 0 0 20. 000 2 5

. 0 0 0 30. 000 3 5

. 0 0 0 Oper at in g H oursRelativecatalystactivity,k/k0 F uel: Oil/ gas

F u el: Oil / gas / w ood pellet s

D eac t i v a t i on rat e : 25% / 10 000 hours

New l a yer

- 20 06
O l d l a y e r - 20 01 De a c ti v a ti o n r a te : 15% / 10 000 hours

Figure 9 F uel histor y a n d catal y st de ac tivation o n DO NG Energ y ’s A v edø re Po w e r Station Un it 2

It was de cide d to apply wa shin g of the catalyst. The wa shin g pro c ess wa s re qui red to be fa st as it would have to be done freque ntly due to the rapi d d eactivation. An in-situ wa sh ing pro c e s s usin g availabl e untreate d water wa s dev elope d to avoid time con s u m ing rem o val and re

inse rtion of the catalyst an d t he outage wa s red u ced to three days [ 7 ]. In the following years

wa shin g wa s applie d seve ral times pe r year. Ho weve r, after three years and con s umptio n of 600,00 0 tonn es of wo od p e llets, the acti vity of the catalyst had be e n redu ce d by more tha n 50%. It was concl ude d that the washe s had not be en able to effecti v ely counter dea ctivation of the catalyst a nd the cataly st wa s re plac ed in 200 6 after five years of operatio n.

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 1 3 of 23

To red u ce the impact of wood co-firi ng, injectio n of co al fly ash into the furna c e was initiated in 2006. The fly ash, aroun d six tonnes/ho u r , is inject e d throu gh the fo ur “ove r bu rn er air p o rts”, above the third burn e r level

. This solved the above-me ntioned p r obl ems with d e p o sits, an d the sulp huri c a c id aero s ol s in the sta ck were also redu ce d signifi cantly [ 5 ]. Furtherm o re, the coal fly ash to some degree captu r es woo d -ash compo nent s that poiso ns t he SCR catal y st such as alkali -metal a e ro sol s , cal c i u m and ph osphorou s and t h is ha s re du ced the cataly st dea ctivation
to aroun d 15 % per 10,00 0 hours co mpa r ed to on ave r age a p p r oxi m ately 25% per 10,00 0 ho urs before fly-a s h injection a s shown in Figu re 9.

DO NG Energ y , Studstrup Po w e r Sta t io n, Denmark
DO NG Ene r g y ’s Studstru p Powe r Station has tw o 35 0 MWe PC b o ilers – Unit s 3 and 4 – whi c h were put into operation in 1 984 an d 198 5

. The units ha ve since then been mod e rnise d reg u larl y and in 20 02 a conversio n to comm ercial operat io n wit h co-co m bu st ion of grou nd stra w wa s initiated. In each of the two units, four o u t of 24 burn e rs we re mod i fied into grou nd-stra w firin g by using the core air pi pe s of the coal-b urne rs for the air/s t raw suspens i on. Up to five tonnes/h our of st raw can b e fired throu gh e a ch b u rn er. With up to 10 % co-firin g of stra w, the fly ash from the units can be utilised in the concrete industry.

Pilot tes t s As dea ctivation of high-du st SCR ca taly st is one the critical issue s of straw co-fi r ing, slip -stre a m

rea c tors were installed o n Units 3 a nd 4

. An exposure time of 5,000 hours was achi eved in the perio d 200 2-2003. On Uni t 4 the averag e stra w share was 1 1 % on a weig ht basi s and 7% on energy basi s

. Unit 3 wa s 1 00% coal -fire d and the test reacto r on thi s unit wa s u s ed as a coal

referen c e for the dea ctivation tests.

0. 5 0. 6 0. 7 0. 8 0. 9 1. 0

0 1

, 000 2

, 000 3, 00 0 4

, 000 5, 000 6, 000
E x po sure t i m e , h oursRelativespecific catalystactivity,k/k0

C o al r e f e r e nc e 7% st r a w co- f i r i n g

Figure 1 0 Relativ e spec ifi c catal y st activit y as function of ex posure time

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 1 4 of 23

Thre e differe nt types of ca talysts we re i n vestigat e d . Figure 10 sho w s the relative spe c ific a c ti vity as a fun c tion of exposu r e time for a Top s øe catalyst. There is no di stingui sh able differen c e in the dea ctivation trend from exposu r e to flue ga s fr om coal -firin g an d from 7% straw co-firi ng. The ob se rved deactivation wa s found to be ca used by arse nic a nd formatio n of surface fouling layers.

Full scale In 2007 the two unit s we re retrofitted wit h SCR DeNO x units with T opsø e DNX ® c a talys t. Shortly after start

- up of the DeNOx plant on Unit 4, a rapid increa se in p r e s sure drop wa s ob serve d a nd insp ectio n of the rea c tor re vealed severe pluggi ng of the catalyst. Detaile d investigation of th e plugg ed catal y st sho w ed th at the semina l reason was l a rge a s h p a rti c le s, up to 10 mm in length, prim arily originating from the kn ots of the gro u n d stra w, cf. Figure 1 1

.

Figure 1 1 Severe p l u ggi n g of the SCR catal y st Studs trup Po w e r Station’s U n it 4 cau s ed b y lar ge stra w
- ash p a rti c les, seen as b l ack parti c l es i n the other w i se gre y c oal as h

The cat a lyst wa s unlo ade d for wa shin g on site . The clea ning was done by sub m ersion of th e

c a talys t modules into hot water, approximatel y 50°C, combin ed wit h aeratio n (a “hot bub ble bath”, see Fig u re 12 ). The wa shin g wa s by and la rg e su ccessful, h o weve r still le aving som e 1 5

- 20% of the ch annel s plug g ed. This coul d be ascri bed to the fact th at the fly ash had pa rtly hardened.

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 1 5 of 23

Figure 1 2 W a shin g of catal y st modu le s at Studstrup Po w e r Statio n

To avoid future incid ents, fine-m e shed scre en s we re built into the flue ga s du ct at the exit of the boiler to filter out large r a s h particle s , se e Fi gure 13. The co -firin g of stra w on Unit 3 had bee n

su spe nde d u n til sufficient experie nce h ad bee n coll e c ted on Unit 4. After five months of sat i sfactory pe rformance of Uni t 4 with no increa se in press u re drop ac ross the c a taly s t, it was decide d to equi p Unit 3 with simila r scre e n s.

Figure 1 3 Installati on of l a rge p a rticle a s h screens i n the flue g a s duc t on Studstrup Po w e r Station Un its 3 and 4 (a do pted from [ 8 ])

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 1 6 of 23

Electrab e l, Langerlo Po w e r Station, Belgium

Electra bel op erate s two id entical 2 50 M W e coal-f i r ed boilers at their Lang erl o Powe r Station at Gen k , Belgiu m. The two b o ilers we re o r iginally (in the mid 1970ie s ) con s tru c ted as oil-fi red b o ilers b u t we re conve r ted to coal firin g in 1985 -86. As part of the so -call ed La nge rlo 200 0 Environm ental Project the two units were ret r ofitt ed with flue-g a s d e sul phuri s atio n a nd SCR De NOx system s in th e late 1990i e s

.

Since 20 03 bi omass ha s b een co-fired with the co al and the amo u n t now con s titutes 10 -20% on mass ba sis. On avera ge the fuel blen d is co m p o s ed of 86% coal, 3% olive resi due, 4% drie d

se wag e slu d g e and 7% wo od du st from hard boa rd p r odu ction. Two thirds of the coal fired i s low-alkali South African co al to limit the overa ll al kali conte n t of the fuel blend. Table 3 sho w s the fuel and a s h an alyse s . It is seen that the bi oma ss contri bute s si gnifica nt amo unt of phosphorou s and alkali metal s . Sewag e slu d ge co ntain s h i gh sul phu r le vels and h e a vy metals can be in high co nce n tration s . Sewag e slu d ge also ha s much hi ghe r ash conte n t than biom ass and to avoid probl ems with slag ging an d to maintain a s h quality, co-firing rate is generally limited.

Proxi m at e an al ysis S outh A f r i can US CO NS O L Sew a g e
s l ud ge Ol ive

res i d u e Wood Bl e nd

Moi s tur e % wet 8.45 6.61 8.18 15.9 5 5.45 7.90 Ash % dr y 14.8 3 8.18 45 .0 7 10.8 2 1.12 12.8 1 Vol a ti les % dr y 24.0 1 38 .3 5 47 .9 3 72.7 9 79.1 5 34.4 7 Lo w e r h e at in g val ue kJ / k g 25,0 45 29 ,1 09 10 ,7 27 15,9 1 0 17,3 6 8 24,9 51 Hardgro v e ind e x HG I 53 55 40

Ult i mate an al y s is Carbon, tot a l % dr y 71.4 9 77 .1 7 30 .5 8 46.7 6 47.7 4 69.3 6 H y dro gen % dr y 3.93 5.21 7.50 5.95 5.90 4.64 O x y gen % dr y 7.49 5.80 13 .9 8 34.6 6 37.2 0 10.1 0 Ni trog en % dr y 1.67 1.43 0.54 1.22 7.88 1.98 Sul p h u r % dr y 0.59 2.21 1.54 0.06 0.07 1.06 Chl o r i ne pp m dr y 30 93 0 11 00 10,0 0 0 160 646 F l uori ne pp m dr y 211 83 30 0 107 71 163

A s h anal ysi s SiO 2 % dr y 50.5 6 44 .8 0 41 .0 0 28.9 3 8.20 47.4 7 Al 2 O 3 % dr y 38.9 1 22 .7 0 13 .0 0 3.00 20.4 5 31.5 9 Ti O 2 % dr y 2.27 1.03 1.10 0.20 44.5 0 2.1 Fe 2 O 3 % dr y 3.42 19 .1 0 11 .0 0 3.94 8.02 7.4 CaO % dr y 1.20 4.35 13 .0 0 23.2 8 8.65 3.9 MgO % dr y 0.25 0.97 1.50 12.8 0 2.68 0.87 K 2 O % d r y 0.77 1.58 1.70 17.3 4 2.46 1.47 Na 2 O % d r y 0.07 0.98 1.50 4.54 1.06 0.54 P 2 O 5 % dr y 1.28 0.39 12 .0 3.4 16.6 2.6 As pp m dr y 35

Ta ble 3 T he fuel blen d fired at Electra be l’s Lan ger lo Po w e r Statio n, Belg ium

At the annual stops catalyst elements ha ve been take n for ch emica l analysi s and activity tests. Figure 14 sho w s the cataly st dea ctivation trend ove r a perio d of 55 ,000 ope ratin g hours.

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 1 7 of 23

It is remarka b l e that the activity has stabi lised at a leve l aroun d 75% but this is in good a c cordan ce with a dea ctivation model devel o ped at Ha l dor Topsø e . After an initial de activation pe

riod, the dea ctivation almost ceas es. Th e arse nic cont ent in the cat a lyst increa se d with ope rating time until a level of 0.25% by weight at wh ich n o furthe r upta k e occurred, correspon ding to establi s hm ent of equilibrium with the flue gas co ncentration of gaseous arseni c. This level of arseni c ha s o n ly a margin a l influence on the ac tivity of the high-p o rosity Top s øe catalyst.

0% 20 % 40 % 60 % 80 % 1 00%

0 1 0, 000 2 0, 000 30, 000 4 0

, 000 50, 0 00 6 0

, 0 00 O p erat i o n h o u r sRelative catalystactivity,k/k0

U n i t 1 el e m e n t s U n i t 2 el e m e n t s D e ac t i v a t i on m ode l

Figure 1 4 SCR catal y st d eactivati on at Electrab el’s L a nger lo Po w e r Station, Bel g iu m

Like wi se, ch e m ical an alyse s have sho w n only a very mode st uptake of alkali me tals, arou nd 0.2% by weig ht sodium pl u s pota ssi um, and le ss tha n 0.1% by weight pho sph o rous h a s b een found. After the initial accu mulation, the s e level s hav e been con s t ant and do n o t differ from what can be observed in catalyst on 10 0% coal -fired units. A slight fouling of the catalyst su rface with fly ash seem s to functio n as a ‘ passivating’ l a yer in whi c h the alkali met a ls have lo w mobility.

Vattenfall, Combined Heat and Po w e r, S w eden Upp s al a CHP is a 400 M W th /125 MW e combined h eat and po we r pl ant locate d in Upp s ala, Swede n. In 2005, the exist i ng SNCR wa s retr ofitted with an up-flo w high-d u st SCR unit equip ped wit h Topsoe DNX ® catalyst. The pulveri se d

- fuel boile r is 100% biom ass fired, bu rnin g

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 1 8 of 23

peat and u p to 30% woo d dust. The pla n t is operatin g 2-3,00 0 ho urs p e r yea r durin g winte r sea

son s when th ere is a d e ma nd for heat.

Catalyst sam p les were tested in 2007 a nd 200 8 after the first two sea s o n s. The measu r e d re

sidu al activity is sho w n in F i gure 1 5 . It is see n that duri ng 5,000 o p e r ating ho urs the cataly st has lost 37% of its activity, corresp ondi ng to an expon enti a l dea ctivation rate of 60% per 10,00 0 hours.

0% 20% 40% 60% 80% 1 00%

0 5
, 000 10, 000 15, 000 20, 000

O p e r a t i ng H our sRelative specific activity,k/k0

E l e m e n t a c ti v i ty te t s E x pon en t i al deact i v a t i on t r en d

Figure 1 5 SCR catal y st a c tivit y versus o perati ng h our s after 5,000 h o u r s in Vattenfall ’ s Uppsa l a CH P

The peat an d wood contai n 1-2 wt% pot assium an d a r oun d 1 wt% pho sph o ro us in the ash. Chemi c al a n a l ysis of cataly st sam p les sh owe d only a mode st uptake of solubl e a l kali metal s (aroun d 0.1 wt%) wherea s 0.5- 0.8 wt% iron and 0.2

- 0. 4 wt% magne sium was fou nd. The content of phosp horo u s h ad in cre a sed g r ad ually from 0.2 6 wt% after 2,000 ho urs to 0.66 wt% after 5,000 ho urs. The pho sp ho rou s wa s fou nd prim arily in the outer 2 00 micron s of the catalyst wall at a level up to 1 wt%, cf. Figure 1 6

.

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 1 9 of 23

0. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 0

0 5 0 0 1000 1500 2000
D i st a n ce ( μ m )Weight-% P h os p h or ou s P o t a ssi u m

Figure 1 6 Exam pl e of dis t ributio n of pho sphor ous a nd potassi um thro ugh the c a tal y s t w a l l of a catal y st sampl e from Vattenfall U pps a l a CHP, S w e d e n

. T he phos ph orous is pr edo mina ntl y fo un d at the surface.

Sierra Po w e r, California, USA

Sierra Po we r Corpo r ation i n Terra Bella, Calif orni a, USA operate s a small 9 M W grate-fi red boiler at a sa w mill, fuelled by wood an d demoliti on wood. The pla n t provides a d i spo s al site for local g r ee n waste lumb er manufa c turers and p a lle t manufa c turers. The plant started up in 1 986. In 2008 the pl ant wa s retrofitted with S CR De NOx lo cated do wn stream a cy clon e.

A catalyst ele m ent wa s tested after 3,00 0 operati ng h ours. The ele m ent wa s cov e red with fine ash a nd was mech ani cally clea ned with air befo r e test ing. The activ i ty showe d 93 % activity relative to the fresh catalyst, corre sp ondi ng to a dea ctivation rate of 22% per 1 0 ,0 00 hou rs. Thi s is far lower th an the dea cti v ation rate of 60% per 1 0 ,0 00 hou rs exp e rien ce d for the pulveri se d

fuel boiler at Upp s al a CHP describ ed ab ove.

Chemi c al a n a l ysis reve aled that the catalyst had accu mulated mo re than 1% by weig ht solu ble potassium a n d also min o r amount s of sodium (T abl e 4). It was therefore de cid e d to test wash

ing of the cat a lyst in hot water to po ssib l y remove the alkali-metal salts. The washing resulted in more tha n 60 % redu ction o f the alkali metal cont ent. Surpris i ngly, however, the c a talys t ac tivity drop ped from 93% for the air-cle aned catalyst to 79% for the water-wa sh ed ca talyst.

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 2 0 of 23

Serv ice hours 0 3,000 A i r cleane d Wa t e r w a s h e d Catalys t ac tivity % relative to f r esh 1 0 0 9 3 7 9

Potassi um, m g /kg 200 12,720 4,820 Sodium, mg/kg 500 1,760 500 Phosp h o r ou s, wt % 0.33 0.25

Ta ble 4 Catal y st activit y a nd chem ical anal ys is of catal y st from Sierra Po w e r, USA

It is concl ude d that grate-fi ring of biom a ss d o e s not e v aporate al ka li metals and relea s e the salts a s ae ro sol s to the sa me deg ree a s does p u lveri s ed -fuel o r CFB firing and thus that this boiler type ca use s le ss SCR cataly st de activation, cf. Table 2. Rath er, the alkali -metal salts a r e found a s larg er pa rticle s wi th other a s h constitu e n ts which may de p o sit on the ou ter su rface of the catalyst. This explai ns the rathe r mo dest de crea se in ac tivity fo r the Sierra Power c a taly s t in spite of accu mulation of m o re than 1 wt% potassi um

. Washing of the cataly st re sults in di ssol ution of the sal t s and tra n sp ort to the cata lyst interior (see Figu re 17 ) and bon ding to the vanadium active si tes. The re sid ual activity of 79% is in fair accordan ce with the pota ssi um level of

arou nd 0.5%, cf. Figure 5.

0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9

1

0 200 4 0 0 600 800 1 000 1200

D i s t an ce ( μ m )Weight-%

Figure 1 7 Potassium pr ofile thro ugh th e catal y st w a l l after w a t e r w a s h i ng

Vattenfall, Amager Po w e r Station, Denmark Vattenfall’s Amage r Powe r Station in Copenh agen, D enma r k h a s t h ree u n its tha t are all pro d u c

ing ele c tric p o we r to the grid and di strict heati ng. Unit s 1 and 2 were origin ally identical a nd taken into service in 197 0/1971. Unit 3 wa s take n into servi c e in 1 991. Since 2 0 04 Unit 1 ha s been o u t of service a nd th e turbine, the boiler a nd the environm ent al control syst ems a r e bei n g repla c e d . We t flue gas de sulphu risation and SCR syst em inclu d ing a rege ne rative gas-ga s he at

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 2 1 of 23

excha nge r ha s bee n su ppli ed by Alstom [ 9 ]. The upgraded Unit 1 will have a firing cap a city of 350 MJ/ s and be in servi c e again in 20 0 9

.

The unit ha s been d e si gne d to be very flexible reg a rdi ng fuel mix and ca n burn coal, pelletised
stra w, woo d pellets, or co al-bio ma ss in an arbitrar y mixture. Fuel oil can b e used as start-up or emergen cy fuel. The stra w has hi gh pota ssi um and lo w ash co nten ts with the po tential of a rapid d e a c tivation of the SCR catalyst, cf. Tabl e 2. Compa r ing the comp ositio n of ashe s from coal a nd from stra w it is se en that the po ta ssi um co ntent differ one orde r of mag n itude (T able 5), also o n an energy ba si s (Table 6 )

.

Referen ce c o al Stra w SiO 2 4 7 3 0

- 6 0 Al 2 O 3 3 1 0

. 4

- 1

. 7 Fe 2 O 3 6

. 3 0

. 3

- 1

. 0 C a O 4

. 2 7

- 1 4 M g O 1

. 7 1

. 7

- 2

. 3 TiO 2 1

. 1

- Na 2 O 0

. 9 0

. 4

- 1

. 2 K 2 O 2.0 14-2 9

Ta ble 5 Comp ositio n of coal and stra w as he s (% b y w e ig ht)

Referen ce c o al Stra w L H V M J / k g 22.8-2 6

. 2 1 5 Ash co ntent % by weight 6-18 4.5 K 2 O in ash % by weight 2.0 14-2 9 K 2 O per MJ g/MJ 0.046 – 0.13 7 0.42 – 0.87

Ta ble 6 Ash content of potassi um on bas is of fuel en erg y co ntent

To enabl e co al-st r a w co -firing in any de sire d ratio, th e SCR DeNO x system wa s cho s en a s a tail-end install a tion, located downstream the ESP and wet FGD to minimise the amount of harmful a s h constitue n ts re achi ng the SCR rea c tor (F igure 1 8 ).

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 2 2 of 23

Figure 1 8 Genera l la yo ut of Vattenfall A m ager Po w e r Station Un it 1 (from [ 9 ])



### Conclusio n s

Dire ct co -firin g of biomass with fossil fue l is a simple a nd wid e ly app lied tech nolo g y for combi n

ing ren e wabl e and fossil e nergy utilisation to redu ce CO 2 . Howeve r, the relea s e of alkali-meta l

aero s ol s form ed duri ng co mbustio n and phospho rou s ash can cau s e ra pid de activation of SCR catalyst s. Th e experie nce from a numb e r of installati ons of To psø e ’s DNX ® cat a ly st sho w s t hat :

− Co-fi r ing of u p to 20% biomass can be done wi thout cau s in g extra o rdin ary de activation of the c a talys t compared to 100% c oal firing.

− For 10 0% bio m ass firing th e dea ctivation rate can be as hig h as 6 0 % per 10,00 0 hours in a pulveri sed

- fu el fired boile r. In a grate-fired boile r the dea ctivation rate is lower, 22% per 10,000 h ours, presuma b ly becau se le ss al kali -metal a e ro sol s are re leased.

− It is not possi ble to remove alkali metal s bond ed to the catalyst’s a c t i ve sites by si mple wa

t e r wa shin g. On t he co nt ra ry , alkali-m e t a l salt s d epo sited in the outer su rfa c e of the cataly st may be tran sported to the i n terio r , cau s i ng additio nal dea ctivation.

− The form ation of large

- pa rticle ash (LP A ) dur in g co mbustio n of biomass mu st con s id ere d

, necessitating installatio n of LPA screen s.

− The use of SCR o n 100% bioma s s-fire d boilers may be don e as a tail-end in stall a tion to minimise the amount of poi soni ng spe c ie s enteri ng the SCR.

− Injection of coal fly ash in a woo d -fuel o il co-fired boil e r ca n re du ce proble m s with depo sits in the conve c tive part of the boiler a nd i n the air-pre h eater an d sig n ific ant ly red u ce cat a ly st dea ctivation rate by capturi ng poi so n o u s con s tituent o f the wood a s h.

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.Impa c t of bi o m a s s c o -c ombus tion o n SC R De NOx ope ra tion Page 2 3 of 23



### Ref e rence s

1. Topsøe, N.Y, Infrared Spe c tro s copi c In vestigatio ns of Environment al De NOx an d Hydrot reatin g Catalysts, Doctoral disse r tati on, Techni cal University of Denma r k (1998 )

2. Chri sten se n, K.A., The format ion of sub m icron pa rticl e s from the combu s tion of stra w, Ph.D. thesi s , Techn i cal University of Denmark (1995 )

3. Zheng, Y., A. D. Jen s e n , J. E. John s on, J. R. Thøgerse n, Dea c tivation of V 2 O 5 -W O 3 -TiO 2 SCR catalyst at biomass fired po wer pl a n ts, Appl. Cat a l. B, 83 (200 8), 186

4. Brand en stein

, Actual state of kno w led g e , Catdea ct project, E.ON. engin eeri ng GmbH (200 2)

5

. J e ns en , J

. P., H

. D

. Sø r e nse n , J

. H a ns en , S. L. Christensen, De acti vation of high dust deNOx cataly st whe n co -combu sting he a vy fuel oil and bioma ss, El ectri c Power Confe r en ce, Chi c ag o 200 7

6. Berg, M. and J.P. Jen s en, Biomass an d se con dary fu els in Denma r k, VGB Power Te ch (200 8)

7. Pederse n, L. S., A. D. Jens en, Selective catalytic re du ction of NO in a biomass-fired full scale PF boil e r, Dan s k Ke miingeni ørko nferen ce, Co penh agen, Ju ne 200 6

8. Bille, T., Bio m ass co-firin g, developme n t and ex peri ences with op eration, Expp erts Confe r

ence, Brussel s (20 0 8 )

9. Cre s pi, M., M. Porle, A.-C. Larsson, R. L a Civita, A. R. Nielsen, The influence of bioma ss burni ng in the desig n of an SCR in stallati on, Powe r-G en Euro pe (2 008)

Presented at Po w e r- G en Eu rope, G e rm an y , 2009 Best paper a w a r d w i thi n the con f erence track ‘ C o a l

, Nucl ear & Bi omass G enerati o n ’

Inf o r m ation c o n t ai ned her e i n is c onf id ent ial ; it m a y n o t be us e d f o r an y pur pos e other tha n f o r whic h it has b een is s ued, an d m a y not b e us e d b y
or dis c l os e d to thir d par t i es with out w r itte n ap pr o v al of Hald or T ops ø e A/ S.