Effect of CO2 gasification reaction on oxy-combustion of pulverized coal char

For oxy-combustion with flue gas recirculation, as is commonly employed, it is recognized that elevated CO2 levels affect radiant transport, the heat capacity of the gas, and other gas transport properties. A topic of widespread speculation has concerned the effect of the CO2 gasification reaction with coal char on the char burning rate. To give clarity to the likely impact of this reaction on the oxy-fuel combustion of pulverized coal char, the Surface Kinetics in Porous Particles (SKIPPY) code was employed for a range of potential CO2 reaction rates for a high-volatile bituminous coal char particle (130 μm diameter) reacting in several O2 concentration environments. The effects of boundary layer chemistry are also examined in this analysis. Under oxygen-enriched conditions, boundary layer reactions (converting CO to CO2, with concomitant heat release) are shown to increase the char particle temperature and burning rate, while decreasing the O2 concentration at the particle surface. The CO2 gasification reaction acts to reduce the char particle temperature (because of the reaction endothermicity) and thereby reduces the rate of char oxidation. Interestingly, the presence of the CO2 gasification reaction increases the char conversion rate for combustion at low O2 concentrations, but decreases char conversion for combustion at high O2 concentrations. These calculations give new insight into the complexity of the effects from the CO2 gasification reaction and should help improve the understanding of experimentally measured oxy-fuel char combustion and burnout trends in the literature.