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3. Mixed Fuel Firing

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Chemical Aspects of Industrial Utilization of Biofuels

1. Introduction2. Fuel Burning Characteristics3. Combustion Equilibria4. Melting Equilibria and Ash Behavior5. High Temperature Corrosion6. Flue Gas Emission Chemistry7. Mixed Fuel Firing

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Challenges in Multi-Fuel Firing in FBC

Emission Limits Fouling of Heat Surfaces Superheater Corrosion Bed Sintering Ash Utilization

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Fuels in the Latest Major FBC Projects

Wood fuels 16/23Peat 10/23Coal 8/23Sludges 8/23Pet Coke 4/23

Multi-Fuel vs Single Fuel 20 vs 3

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Number of Publications on “Co-combustion" or “Co-firing" ScienceFinder, January 2003, after (Leckner 2003).

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Challenges in Multi-Fuel Firing in FBC

How Can Fundamental Research Contribute?

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Fuel Interaction in FBC

FoulingSintering

Emissions

Fuel A 50% Fuel B

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Fuel Interaction in FBC

FoulingSintering

Emissions linear

Fuel A 50% Fuel B

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Gaseous Emissions SO2 and NOx

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Chalmers CFBC Tests with Coal, Wood, Sludge

(Leckner, Åmand)

12 MW CFBC with external coolingConstant conditions (temp., air distribution)Results for fundamental analysis and modelling

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SO2 Emission with Wood-Coal (Leckner et al.)

Sulphurdioxide

ppm(6% O2)

Wood 50%(Energy)

Coal0

100

200

300

400

500

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SO2 Emission with Wood-Coal(Leckner et al.)

Sulphurdioxide

ppm(6% O2)

0

100

200

300

400

500

Wood 50%(Energy)

Coal

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NO Profiles in CFBC(Leckner et al.)

0 2 4 6 8 10 12

Reactor height, m

0

100

200

300

400

500Secondary air

Wood

Coal

NO

x pp

m

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Nitrogen Oxides with Coal and Wood(Leckner et al.)

Coal Wood

Volatile, % db 40 80N(fuel), % db 1.6 0.14

CFBC NO, ppm 50 60

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NO Emission with Wood-Coal(Leckner et al.)

Nitricoxideppm

(6% O2)

0

50

100

150

Wood 50%(Energy)

Coal

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NO Emission with Wood-Coal(Leckner et al.)

Nitricoxideppm

(6% O2)

0

50

100

150

Wood 50%(Energy)

Coal

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NO Emission with W&C (Leckner et al.)

Nitricoxideppm

(6% O2)

0

50

100

150

Wood 50%(Energy)

Coal

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Superheater Foulingin BFBC

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BFBC for Biomass Fuels

Rice huskEucalyptus bark

Fuel

Fly ash

Fouling

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Ash Forming Elements in Rice Husk and Eucalyptus BarkRICE HUSK

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

Si Al Fe Ti Mn Ca Mg P Na K S Cl

mg/

(kg

dry

solid

s)

Unreactive, calculatedReactiveTotal in

EUCALYPTUS BARK

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

Si Al Fe Ti Mn Ca Mg P Na K S Cl

mg/

(kg

dry

solid

s)

Unreactive, calculatedReactiveTotal in

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Rice Husk & Rice Husk Ash

Rice husk, untreated

Rice husk ash (laboratory ash)200 µm

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Rice Husk: Boiler Fly Ash vs. Laboratory Ash

2nd pass ash from the boiler Rice husk laboratory ash

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Eucalyptus Bark & Eucalyptus Bark Ash

Eucalyptus bark ash (laboratory ash)

Eucalyptus bark, untreated

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Fly Ash of Rice Husk and Eucalyptus Bark

Rice husk ash

Silica (SiO2)

Not Molten

Large Particles

Eucalyptus bark ash

Chlorides and Sulphates of K, Na, and Ca

Partially Molten > 700ºC

Vapours, Small Particles

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Fly Ash Particles Approaching Tube Surfaces

Rice husk ash Bark ash

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Fouling Test Facility (University of Toronto)

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100% Rice Husk

After 40 minutes

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100% Bark

After 40 minutes

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Fly Ash Particles Approaching Tube Surfaces

Rice husk ash Bark ash

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Probe Deposits: Rice Husk - Bark

Depositionrate

mg/m2-sec

Rice husk 50%(Dry Mass)

Bark0

5

10

15

20

25

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Fly Ash Particles Approaching Tube Surfaces

Rice husk ash

Rice husk & bark ash

Bark ash

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36% Bark - 64% Rice Husk

After 40 minutes

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Test Tube Surfaces after Exposure (40 min)

100% Rice husk, Deposit Mass = 10 mg

Rice/Eucalyptus 64/36 % Deposit Mass = 13 mg

100% Eucalyptus bark,Deposit Mass = 195 mg

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Rice husk 50% Bark

Probe Deposits: Rice Husk - Bark

Depositionrate

mg/m2-sec

0

5

10

15

20

25

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Rice husk 50% Bark

Probe Deposits: Rice Husk - Bark

Depositionrate

mg/m2-sec

0

5

10

15

20

25

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Rice husk 50% Bark

Probe Deposits: Rice Husk - Bark

Depositionrate

mg/m2-sec

0

5

10

15

20

25

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Probe Deposits: Peat - Straw

Mass ofelementsas oxides

(mg)

0

50

100

150

300

350

Peat 50% Straw

250

200

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Probe Deposits: Peat - Straw

Mass ofelementsas oxides

(mg)

0

50

100

150

300

350

Peat 50% Straw

250

200

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Mass of Element Oxides in Deposits

Mass ofelementsas oxides

(mg)

0

50

100

150

250

300

Peat 50% Bark

200

ClSO3K2ONa2OMgOCaOMnOCr2O3Fe2O3SiO2Al2O3

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Conclusions (i)

Mixed-Fuel Firing Great Potential for FBCMajor Challenge to Boiler Manufacturers & Operators:

Emission ControlBed Sintering and Fouling ControlCorrosion Control

Fuel Interaction May Cause Surprises (Non-Linear Relationships)

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Conclusions (ii)- How Can Fundamental Research Contribute?

- We Need Fundametal Studies on- Emission Chemistry Interactions- Ash Interactions- Fuel Characterization for Mixed-Fuel Firing- Modelling of Mixed Fuel Systems

...to Interprete Pilot and Full Scale Experiences