Coal combustion fluid mechanics

The CaO from CaCOs decomposition, the other new specie involved in the combustion mechanisms at LCL runs, is a solid porous material, which behaves like a fluid at the fluidised bed. That means that its interactions with radicals from coal are not limited and the radicals could be adsorbed [9] into its porous structure, hindering their total oxidation and, in consequence, promoting their interaction. This fact is corroborated by the Coronene formation in LCL experiments. Coronene (Co) is the most stable of the PAH studied and the radicals trend in their stabilization will be towards Co formation. Besides, as result of the fluidisation movement and the high temperature, CaO can be fragmented into smaller particles, elutriation and attrition phenomena, the smaller particles formed undergoing entrainment by the airflow. 

A knowledge of mass transfer is essential for the understanding of the mechanism of combustion of coal in a turbulent fluidized bed. If the kinetic rate of combustion of the fuel is known, one can estimate the burning rate using the information on the mass transfer rate. The rate of transfer of oxygen from the bulk of the bed to the particle surface, k, is often expressed as the dimensionless Sherwood number, Sh = kgdp/Dg- For diffusion to a fixed single sphere in an extensive fluid, Sherwood number may be expressed as [28, 29]... 

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