The combustion of coal and some other solid fuels

This paper outlines some of the key issues currently being debated regarding the combustion of coal and of some biomass materials. It attempts to summarize the present approaches toward the quantification of the fundamental processes of solid fuel combustion for use in computer models. Some aspects of the various chemical and physical processes are included, such as heating-up of particles, devolatilization, and subsequent char formation. Of particular interest is the prediction of char properties, such as composition, surface areas, and morphology, since these impact on char combustion. The available models for devolatilization, char formation, and heterogeneous oxidation are considered for application to both coal and biomass, and a description in terms of the fundamental molecular processes of a coal particle is explored. Char combustion models, including global intrinsic reaction rates, are outlined. The latter has clear advantages, but requires inputs of char physical properties which, at present, cannot be predicted a priori. Intimately linked with the processes of devolatilization and char combustion are NOx formation and carbon burnout,:and special attention is given to these important factors. Finally, the general methods for modeling coal reaction processes are outlined, and illustrative examples are given with regard to the current situation in the application of these submodels to computer modeling of pulverized and coal bed combustion.