Effect of char gasification reaction order on bounding solutions for char combustion

Abstract

The rate of oxidation and surface temperature of a char particle during combustion is determined by the combined action of reactions of carbon with oxygen and CO 2 at the surface and carbon monoxide with O 2 in the gas phase. Limiting values for the rates and temperature were determined by Amundson et al. assuming that the CO 2 and CCO 2 reactions were first order with respect to the gas reactant concentration. Results are presented here for the cases in which the CO 2 reaction is zeroth order and the CCO 2 reaction is both first and zero order to bound the reaction orders found in practice. Allowance for zeroth order kinetics is found to have a profound effect on the shape of the bounding solutions for burning rates and temperatures, most notably by showing that diffusion-limited combustion can occur at much lower temperatur than would be predicted using first order kinetics.