NUMERICAL EVALUATION OF PARTICLE STRUCTURE EVOLUTION AND FRAGMENTATION DURING COAL COMBUSTION AT DIFFERENT HEATING RATE

The modification in the particle size distribution of a coal feed occurring over combustion/gasification because of particle fragmentation can significantly affect process performances. Most literature models developed in the past account only for primary fragmentation. A mathematical model has been developed that calculates the evolution of temperature, pressure, porosity and concentration of the main chemical species within a coal particle during pyrolysis and beyond throughout char combustion. The model eventually calculates maps of internal stress and estimates the probability of particle's rupture. Tailored computational experiments was performed with reference to a medium rank coal. Heating rates ranging from the low one typical of fluidized bed reactors (102 K/s) up to the very high heating rate distinctive of pulverized fire (PF) and entrained flow gasifiers (105 K/s) have been considered.