Prediction of structure evolution and fragmentation phenomena during combustion of coal: Effects of heating rate

Literature models developed to predict evolution of coal particles over the very first instances of coal combustion/gasification processes only account for primary fragmentation, a phenomenon that can significantly modify the particle size distribution of a coal feed. In this paper, a model that goes beyond primary fragmentation and considers also the effects of combustion of both char and volatiles within the pores on the fragmentation propensity of particles is presented. The model is able to predict the evolution of temperature, pressure, porosity, and concentration of the main chemical species within the particle. Ultimately, the model calculates maps of internal stress and probability of rupture. A campaign of computational experiments is presented with reference to a medium rank coal undergoing different heating rates: when the heating rate is high, the effect of combustion is to augment the probability of fragmentation and to change the very mode of particle rupture; differently, at low and moderate heating rate, combustion plays a negligible effect on particle fragmentation phenomena.