MODEL FOR THE SELF-HEATING REACTION OF COAL AND CHAR

A mathematical model of the self-heating reaction of coal or char in bulk has been developed. The model takes into account a local oxidation reaction which depends on temperature and the concentrations of unreacted and reacted oxygen. The transport processes of diffusion and convection take the mobile reactant, oxygen, from the boundary to the distributed reaction where heat energy is released, and then convey the latter back to the boundary. The equations of the model are evaluated numerically and results are in general agreement with those predicted by the Theory of Thermal Explosions appropriate to the assumptions of the model. Various situations arise in the heating regime, depending on whether the conversion reaction is controlled by thermal conduction, reactant diffusion, reactant convection, or thermal convection where no distinct separation exists between the various cases. Some guidelines emerge for evaluating safe storage conditions for coal or char where the criterion of safety has to be specified for different materials, probably as a maximum safe temperature and maximum time of storage. © 1979.