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Research Papers: Energy From Biomass

Biomass Ash-Bed Material Interactions Leading to Agglomeration in FBC

[+] Author and Article Information
H. J. Visser

 Energy Research Centre of the Netherlands (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlandsh.visser@ecn.nl

S. C. van Lith

Department of Chemical Engineering, Technical University of Denmark, Lyngby DK-2800, Denmark

J. H. Kiel

 Energy Research Centre of the Netherlands (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlands

J. Energy Resour. Technol 130(1), 011801 (Jan 25, 2008) (6 pages) doi:10.1115/1.2824247 History: Received June 18, 2004; Revised October 16, 2006; Published January 25, 2008

In (bubbling) fluidized-bed combustion and gasification of biomass, several potential problems are associated with the inorganic components of the fuel. A major problem area is defluidization due to bed agglomeration. The most common found process leading to defluidization in commercial-scale installations is “coating-induced” agglomeration. During reactor operation, a coating is formed on the surface of bed material grains and at certain critical conditions (e.g., coating thickness or temperature) sintering of the coatings initiates the agglomeration. In an experimental approach, this work describes a fundamental study on the mechanisms of defluidization. For the studied process of bed defluidization due to sintering of grain-coating layers, it was found that the onset of the process depends on (a) a critical coating thickness, (b) on the fluidization velocity when it is below approximately four times the minimum fluidization velocity, and (c) on the viscosity (stickiness) of the outside of the grains (coating).

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Agglomeration of bed material after coating formation from the gas phase (1) or melt formation of ash components (2)

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Figure 2

Quartz bubbling-fluidized bed reactor

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Figure 3

Defluidization temperature versus fluidization velocity, expressed as number of times the theoretical minimum fluidization velocity (Umf), for coated bed material

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Figure 4

SEM image of straw-derived bed material grains prior to the fluidization experiments (white rims=coating)

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Figure 5

SEM image of a willow-derived bed material grain after a Step 2 fluidization experiment. Note the light colored coating and the division in an inner and an outer coating.

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Figure 6

Coating viscosity at defluidization temperature versus fluidization velocity. The dotted lines roughly indicate expected behavior.

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Figure 7

Coating viscosity at defluidization temperature versus fluidization velocity for willow-derived bed material

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Figure 8

Coating viscosity at defluidization temperature versus fluidization velocity for straw-derived bed material

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