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Experience from waste co-combustionin Vattenfall fluidized bed boilersMatts Almark

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Co-combustion, waste & biofuels

• Waste fractions containing unwanted elements– Chloride, alkali, heavy metals

• Increased fouling & corrosion compared to “clean”biofuels

• Some experiences and observations with differentamounts of waste derived fuels in fuel mix

• Measurement of alkali chlorides in flue gas -monitoring fuel quality

• Additives and other solutions• Myllykoski, Idbäcken, Munksund

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Munksund

• CFB• 96 MWth

• Bark (> 80%)• Sawdust, woodchips• Cardboard reject (<6%)

SH2

SH1

Intrex

SH2

SH1

Intrex

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Myllykoski

• BFB• 88 MWth

• Bark, peat, forestresidues,sludge,recycled wood

• (Recycled EnergyFuels)

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Idbäcken

• BFB• 105 MWth

• Biomix +Recycledwood (50%)

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Fuel chemistry derived problems - characterization

• Measurement of gaseous alkali chlorides – IACM

• Deposit probes– Fouling rates– Deposit chemistry – corrosion rates

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IACM – In situ Alkali Chloride Monitor

• UV lamp and detector

KClNaClSO2

KClNaClSO2

KClNaClSO2

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IACM as fuel quality monitor

(Biofuel boiler)

Bränsleanalys vs IACM

0

5

10

15

20

25

30

35

0 0,01 0,02 0,03 0,04 0,05

Cl i bränsle [vikt % TS]

KC

l i rö

kgas

[ppm

vg]

KCl i rökgas [ppm]

Fuel Cl vs. IACM

Cl in fuel, % ds

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Reduction of alkali chlorides - ChlorOut

• (NH4)2SO4 → 2 NH3 + SO3 + H2O

• SO3 + H2O + 2KCl → 2HCl + K2SO4

• Also reduction of NOx and CO emissions

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Munksund

• No waste; waste addition; waste + ChlorOut• Measured levels of KCl and deposit chlorine content

0

5

10

15

20

25

30

35

40

KCl SO2

IACM

KC

l, SO

2, p

pm

No waste

6% waste

6% waste + ChlorOut

0

4

8

12

16

SEM - S SEM - Cl SEM - K

S, C

l, K

(wei

ght %

)

No waste

6% waste

6% waste+ ChlorOut

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Normal & with ChlorOut addition

Without ChlorOutChloride conc. 12%deposits 6 g/m2/h

With ChlorOutChloride conc. <0.2%deposits 2 g/m2/h

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Bio/recycled wood 50/50

Without ChlorOut

Chloride 25%

Fouling rate 21 g/m2/h

With ChlorOut;

Chloride <0.2%

Fouling rate 6 g/m2/h

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Myllykoski K7

• Operating on a wide mix of fuels• Peat, bark, forest residues, sludge• Recycled wood, recycled energy fuels• REF (~5%)

• High levels of S from peat and sludge

• S/Cl or S/alkali above what usually consideredcritical limits

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Myllykoski K7, IACM

• Removal of REF from fuel mix; week 50/2005 &2006

0

5

10

15

20

25

27 Nov 05 7 Dec 05 17 Dec 05 27 Dec 05 6 Jan 06 16 Jan 06

KC

l (pp

m)

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Flue gas temperature

400

450

500

550

600

650

700

27.6 16.8 5.10 24.11 13.1 4.3 23.4

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Flue gas temperature & pressure loss

400

450

500

550

600

650

700

27.6 16.8 5.10 24.11 13.1 4.3 23.4

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Idbäcken

• Removal of coal from fuel mix

• Increasing fouling and corrosion

• ChlorOut as S-additive

• SH replaced to E1250

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Idbäcken, fuel distribution over bed

• With increasing share of recycled wood problemswith deposit formation over fuel feed points

• Uneven temperature in bed – problems reachinghigh loads

• Mixing in freeboard

• Improved fuel feeding system - reduced depositformation– Reduced amounts of fines and rapidly volatilized

burning immediately above fuel feed points– More even heat release in bed

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Idbäcken, fuel distribution table

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CO concentrations (Johannes BFB)

0 0,5 1 1,5 2 2,5 3 3,5

CO - bark, bakvägg

CO- Bark + 20% PTP, bakvägg

CO- Bark, frontväggCO- Bark + 20% PTP, frontvägg

0

1000

2000

3000

4000

5000

6000

7000

CO [ppm tg]

Instick från höger sidovägg [m]

"Frontvägg"

"Höger sidovägg"

"Eld

stad

ens

cent

rum

"

Approx. pos för bränsleinmatning

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Idbäcken, remaining issues

• Deposit formation in furnace wall

• Furnace wall corrosion

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Bed fluidization issues –metal waste

• With recycled fuels in certain cases high amountsof incombustible matter, metal waste

• Nails in recycled wood• Will not fluidize in the bed, decreased mixing• Forming defluidized zones

• Difficulties removing metal waste with bed bottomsnot designed for the task

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Removal of metal waste (Myllykoski)

• Nails forming tangled lumps

• Manually removed

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“Rassausaukko”

• Bed bottom manually cleaned without need forshut-down

• Reduced load on natural gas

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Conclusions

• Waste fractions can be co-combusted with biofuels• Feed arrangement must be looked over• Spreading of fuel – especially in BFB:s

• Increased fouling & corrosion risk compared to“clean” fuels

• Increased amounts of chlorine, alkali, heavy metals

• Bed bottom capacity to deal with (metal) waste

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Conclusions (2)

• Fuel quality can be monitored with IACM

• SH fouling rates correlating with measured alkalichloride levels

• Additives (ChlorOut) – reduction of alkali chlorides,fouling rate and corrosion risk