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Abstract

Asimple model has been developed to predict the heterogeneous ignition temperature for single coal particles under conditions of negligible, natural and forced convections. These conditions cause different sizes Of volatile matter cloud that surround the coal particle. The model is based on the ignition Of a single coal particle heated by irradiation from spot heaters in a cold (ambient) surrounding. Energy from the particle surface oxidation, volatile matter combustion and physical heating from the spot heaters are all included in rhe particle energv balance. General ignüion criterion is used to determine the ignition point. The agreement between the experimental and predicted results is fairly good as far as the effects of particle size and volatile matier are concerned. The gas temperature emerged as the most effective model parameter influencing the ignition temperature. In the absence of volatiles in lhe particle vicinity, as for the forced convection case, the gas temperature remained almost constant and so did the ignition temperature. For the cases where volatiles surround rhe particle, lugh gas temperatures as well as ignition temperatures were obtained. This is mainly attributed to the combustion of the volatiles contributing to the gas temperature rise and possibly raising the particle temperalure.

Publisher Name

University of Dar es Salaam

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