On Modelling the Burning of a High-Ash Coal in a Fluidized Bed

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Abstract
A general expression for the burnout time of high-ash coal particles in a fluidized bed is developed taking into account the formation of an ash layer of uniform external diameter on the basis of the shrinking core model of burning of coal particles. The model has been developed to take elutriation into account. The expression is validated against an experimental study carried out in an atmospheric fluidized bed combustor employing a Portuguese anthracite of high ash content. The results show that the combustion of the Portuguese anthracite particles is influenced by the particle size and this is adequately accounted for by the expression deduced in this paper. Particles below I mm in diameter are preferentially elutriated and their combustion is controlled by diffusion mechanisms through the ash layer, which does not include large pores. The combustion of larger particles is still influenced by diffusion mechanisms, but with increased importance of diffusion through the gas film layer.

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