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Cofiring in large scale CFB - Experience gained from

experiments with the worlds largest biofuel fired CFB ofAlholmens Kraft, Finland

Pasi Vainikka, VTT Processes, Finland

2nd World Conference and Technology Exhibition on Biomass for Energy, Industry and Climate Protection


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VTT TECHNICAL RESEARCH CENTRE OF FINLAND

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VTT PROCESSES

FP5 Project partnersMaximum biomass use and efficiency in large-scale co-firing (BIOMAX)

VTT Processes, Finland Alholmens Kraft, Finland Kvaerner Power, Finland

CIRCE Foundation, Spain Elsam Engineering, Denmark Abo AkademiUniversity, Finland


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Contents Alholmens Kraft CHP plant general features

The experiment matrix

Fuel properties Emissions of SO2 and SO2autoreductions achieved

Emissions of NO

Deposition measurements

Composition of deposits

Means to avoid chlorine deposition

Protective elements

Protective elements from fuel blending

Source:

Kvaerner Power Oy


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The boiler

Annual proportion of fuels:

Peat 50%

Wood fuels 25% (LR, Bark)

Coal 25%

2.5 years of successful

operation in open electricity

market

Operates with anything from

100% coal to 100% biofuel Combusts the fuels in any given

combination while staying within

the emission limits

Consumes a truck load of peat

in 7 minutes

30,000 truck deliveries annually

Furnace measures 8.5m by

24m and is 40m in height

550MWth194kg/s, 165bar, 545C


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The Process


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The experiment matrix

X--32501816

X--32501815

X--28254714

---26254913

-48-4210-12

-60-40--11

--90-10-10

--100---9

--37--638---39-617

---3324436

--2525-505

---4456-4

--24-50263

----5952

----43571

LimeWood

chips

Logging

residueBarkCoalPeat


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Fuel properties

9.68.1-10.29.222.510.9LHV

19.621.121.927.020.5HHV

HEATING VALUE (MJ/kg)

0.0040.0140.0100.0100.020Cl

0.0140.060.040.30.15S

34.441.040.28.233.3O

1.50.40.721.5N

5.86.05.64.55.2H

55.050.051.073.053.1C

ULTIMATE ANALYSIS OF DRY SOLIDS (wt-%)

3.32.52.5126.8Ash (wt-%, D.S.)

41.740-5248-521241.8Total moisture

WCLRBarkCoalPeatFUELS


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Sources of contributing elements

0

2

4

6

8

10

12

14

100%L

R

50%

LR+5

0%Bark

40%

LR+4

0%Bark

+20%Pe

at

20%

LR+4

0%Bark

+40%Pe

at

10%

LR+4

0%Bark

+50%Pe

at

15%LR

+25%

Bark

+45%

Peat

+15%Co

al

30%

LR+3

5%Pe

at+3

5%Coal

100%Co

al

wt-%

Ca*0.5 K Zn*10 P Na Al Si*0.5


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Sources of contributing elements

0.00

0.04

0.08

0.12

0.16

0.20

100%

LR

50%

LR+5

0%Bark

40%

LR+4

0%Bark

+20%P

eat

20%

LR+4

0%Bark

+40%P

eat

10%

LR+4

0%Bark

+50%P

eat

15%LR

+25%

Bark

+45%

Peat

+15%C

oal

30%

LR+3

5%Pe

at+3

5%Coal

wt-%

0

1

2

3

4

S/Clatomicratio

S Cl S/Cl atomic ratio


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0.0

0.2

0.4

0.6

0.8

1.0

lr100

lr90/c1

0

wc6

0/b4

0

wc4

8/b4

2/c10

p63/lr3

7

p54/b2

3/lr2

3

p61/b3

9

p43/b3

3/c2

3

c56/b4

4

p95/

c5

p49/b2

6/c25

p26/c5

0/lr2

4

p57/

c43c1

00

p

47/b28

/c25

+L

c

50/b32

/p18

+L

c50/b

32/p18

+L+FA

SO

2emission

0

0.1

0.2

0.3

Sulphu

rcontent(wt-%)

Sulphur content

SO2 emission


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0 10 20 30 40 50 60 70 80 90 100

Share of biomass in fuel blend (% )

SO2reduction

S02 reduction

SO2 reduction withlimestone feeding


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Sources of contributing elements:

TGA test

75

80

85

90

95

100

200 300 400 500 600 700 800 900

Temperature (C)

Weight-%(%)

~20% fall

Logging residue chips, ashed in 500 C

Courtesy of Markku Orjala


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Sources of contributing elements:

TGA test

75

80

85

90

95

100

200 300 400 500 600 700 800 900

Temperature (C)

Weight-%(%)

Peat, ashed in 500 C

Courtesy of Markku Orjala


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0.0

0.2

0.4

0.6

0.8

1.0

lr100

lr90/c10

wc4

8/b4

2/c1

0

wc6

0/b4

0

p54/b2

3/lr2

3

p63/lr3

7

c56/b4

4

p61/b3

9

p43/b3

3/c2

3

p26/c5

0/lr2

4

p47/b2

8/c25

+L

p47/b2

8/c25

c50/b3

2/p1

8+L

c50/b32

/p18

+L+FA

p95/

c5

p57/

c43c1

00

N

Oxemission

0.0

0.5

1.0

1.5

2.0

Nitrogencontent(w

t-%)

Nitrogen content

NOx emission


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MP2:flue gas 510-550C

probe 350C

MP1:flue gas 700-750C

probe 540C

Deposit probe locations


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Radial variation in composition and temperature

NOTE THE

TEMPERATURE

INCREASE ON THE

EDGE OF DEPOSIT

Courtesy of Pasi Makkonen

CourtesyofMarttiAho

0

4

8

12

16

20

24

28

Wind 50 angle Lee

wt-%

Na2O K2O Cl

Wt-%

N2O

ClK2O

Wind 50 Lee


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Boundary conditions: Temperature

10CrMo910

R2

= 0.79

X20CrMoV121

R 2 = 0.88

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

350 370 390 410 430 450 470 490 510 530 550

STEAM TEMPERATURE, C

ESTIMATEDLIFETIM

E,a

'

10C rMo910 X20CrMoV121 SS2338 Esshete 1250 AC 66 Predicted

CORROSION DET ECT ION LIMIT

Courtesy of Pasi Makkonen

Dr Salmenoja:~450C is a threshold temperaturefor chlorine induced corrosion

supports findings of Dr Makkonen

This corresponds to400-415C steam temperature

On average, ~415C is reached after 1st superheater in TLS>500C CFB/BFB


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Composition in 50

angle 350

C probe

0

5

10

15

20

Na2O Al2O3 SiO2 SO3 Cl K2O CaO

Wt-%ind

eposits

Biom ass Biom ass + 10% Coal Biom ass + 55% Coal


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Means to avoid chlorine corrosion: Sulphur

0

10

20

30

40

50

60

70

80

2.0 2.5 3.0 3.5 4.0 4.5

S/Cl atomic ratio

HCl-conversion,

%

100%load

45%load

100%loadwith limestonefeeding

0

10

20

30

40

50

60

70

80

0.0 0.5 1.0 1.5 2.0 2.5

S/Cl effectiveatomic ratio

HCl-conversion,

%

100%load

45%load

100%loadwithlimestonefeeding

Sulphation of alkali chlorides:

2KCl + SO2+ O2+ H2O K2SO4+ 2HCl Gas phaseeffect!


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Means to avoid chlorine deposition: Aluminosilicates

Kaolin, Al2O32SiO2,was fed to the bed (BFB) Dosing: 25, 50 and 80wt-% of the ash flow

Fuel 20% AGW + 80% Bark

0

15

30

45

60

75

No additive 0.25 x Ash flow 0.5 x Ash flow 0.8 x Ash flow

HCl-conversion, %

Cl in deposits x 10, wt-%


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Means to avoid chlorine corrosion: Coal minerals

Alumininosilicatescan also react with alkalis liberating HCl:

Al2Si2O72H2O Al2O32SiO2Al2O32SiO2+ 2KCl + H2O K2O Al2O3 2SiO2+ 2HCl

The most abundant mineral iskaolinite(above) andillite(or range of aluminosilicates)

The key issue is whether there is alkali metalbound alreadyin the aluminosilicate


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The objective

Fe K Cl

Fe K Cl

Fe Na K

O Al Si

S CaCl


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Heat transfersurface

Lack ofprotecting

compounds

Low ashcontent

RIS

KYCOMPOUND

SALKALICHLORIDES

Cl releasescorrosion

BARK/FOREST RESIDUE

CASE 1. BARK/FOREST RESIDUE

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CASE 2. PROTECTING POWER OF COAL

FOREST RESIDUE COAL

Co-combustion

PROTE

CTING REACTIO

NSALKALI

SILICATES,

SULPHATES

ALKALICHLORIDES

RISKY C

OMPOUNS

SULPHUR DIOXIDE,Al-SILICATES

PROTECTIVES

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Conclusions

In CFB conditions high SO2autoreduction can be achieved by cofiringbiomass with peat and/or coal due to high Ca content of wood fuels

In CFB conditions peat/wood/coal cofiring produces less NOx than pure

coal or wood fuel firing Chlorine bearing deposit formation can be avoided by appropriate fuel

blending. Protective elements can be supplied in the boiler in peatand/or coal ash

As a result of fuel blending, change in the composition of fuel ash can

dramatically change ash melting behaviour S/Cl atomic ratio in fuel is not an appropriate parameter in describing

corrosion propensity of fuel blends in biomass cofiring. Instead,estimation for this ratio in gas phase could be used as a guideline

With higher shares of peat and especially coal, the effect of aluminium

silicates should also be assessed The amount of nitrous oxide, N2O, increases steeply when coal is

blended to the biomass blend. This could be an issue if there will beemission limits for this compound in the future

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