The Research Boiler at Agglomeration of the bed material in - - PDF document

2010-11-16 1

Agglomeration of the bed material in fluidized bed reactors for thermal conversion of biomass - A threat for the development of the technology

Lars-Erik Åmand and Britt-Marie Steenari Chalmers University of Technology Göteborg, Sweden

The Research Boiler at Chalmers Univ. of Techn.

Chalmers Gasification Process

Heat, Electricity, Steam

Flue Gas

Gas

Chalmers 12 MW CFB boiler

Camera

Hot Bed Material Steam Fuel, e.g. Biomass Waste, Coal or Sludge Hot Bed Material Air Combustible Gas Fuel Steam

Combustion/Gasification of “Dirty” Biomass:

• Forest residues
• Straw
• Salix
• Residues from bio-ethanol plants?
• Residues from biodiesel plants
• Refuse derived waste (RDF)
• Solid recovered fuel (SLF)

Leads to:

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Deposits on tube panel in convection section

Leads to

contains reactive alkali (K and Na) and chlorides

Forest residues as fuel

and corrosion….

…and agglomerates in the particle seal of the boiler This presentation has the focus

• n agglomeration in fluidized

beds for thermal conversion: The Research Boiler at Chalmers Univ. of Techn.

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Inlet to the cyclone from the top of the riser section Further into the cyclone Inlet to cyclone Outlet from cyclone on the top on the gas side

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Centre of cyclone seen from above Cyclone leg seen from above. Plugg of agglomerate of sand particles at the bottom. Cyclone leg seen from the inside

• f the particle seel

Another picture from the inside of the particle seal after combustion of 100% of bark

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An agglomerate from the particle seal burning 100 % bark An agglomerate from the particle seal

Scanning electron microscope (SEM)

Electron Gun Condenser Lenses Objektive Lenses Image

• Acc. Voltage: 5-35 kV

Resolution: 10-20 nm Sample Objektive Lenses Scan Coils Aperture Detector

SEM on agglomerate

• f previous photos

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5 4 3 2 1

SEM-EDX on agglomerate. Spot analysis on surface of elements

9 8 7 6

Cross-section of agglomerate of quartz sand particles

Molten phase of potassium sodium calcium silicates (K-Na-Ca-Si-O)

Sludge ash particle No sludge ash components in molten phase (only traces) Municipal sewage sludge (MSS) and wood+ straw pellets

SEM-EDX of bed material

quartz sand coated with K+Ca+Mg+P Coarse sludge ash particles of Al+Si+K!+Fe+P

Line scan of outer layer of bed particle consisting of quartz burning bark pellets only

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Line scan of outer layer of bed particle consisting of quartz burning bark pellets only

Calcium in the outer layer. Potassium in the inner layer

SEM image

• f particles

taken from the bottom the bottom bed burning bark and waste SEM image

• f particles

taken from the bottom the bottom bed burning bark and waste Line scan of outer layer of bed particle consisting of quartz burning bark pellets only

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SEM image

• f bed

particle consisting of quartz burning bark, waste and sludge Line scan of outer layer of bed particle consisting of quartz burning bark, waste and sludge Fuel: Wood and Straw Layers of K, Si and Ca. Inner layer of K+Si,

400 μm

layer of K Si,

• uter layer rich

in Ca. Bottom bed sample 23% straw on dry basis

”Stone” of straw ash Dp=3 mm Quartz bed material Dp= 0.3 mm Char from wood pellets

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Conclusion: Theory of agglomeration of the bed material in FBC

Ash

A) Melt A) Melt between bed sand particles C) Ash + Ash Reaction Glass melt formation Alkali + SiO2- sand Sticky coating on bed particles Sticky coating on quartz bed particles D) Direct adhesion between ash particles Solid ash Particles B) Chemical Reaction

Acknowledgements

• Main funding from the Swedish Energy

administration

• Additional funding from VärmeForsk

Additional funding from VärmeForsk

• Additional funding from the utility

company Vattenfall