An analytical model for the combustion of coal particles

A model for the combustion of coal particles is developed which accounts for the gasification and pyrolysis reactions throughout the particles, oxidation reactions at the particles' outer surface, distributed gas‐phase reactions around the particles, and transport of heat and mass throughout the reaction zones. The model shows that the combustion of large particles is dominated by gasification and gas‐phase reactions. As large particles burn and shrink, however, the mechanism changes to one dominated by surface oxidation. This change in mechanism can be gradual or very rapid (even discontinuous) depending on the combustion conditions. The particle size at which this transition takes place decreases as the bulk gas temperature or oxygen concentration increase. The proposed model is used to predict the conversion of pulverized coal as a function of time; the results agree with literature data for particles of 26‐32 μm radius.