Effect of CO 2 gasification reaction on oxy-combustion of pulverized coal char

Abstract

For oxy-combustion with flue gas recirculation, as is commonly employed, it is recognized that elevated CO 2 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 CO 2 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 CO 2 reaction rates for a high-volatile bituminous coal char particle (130 μm diameter) reacting in several O 2 concentration environments. The effects of boundary layer chemistry are also examined in this analysis. Under oxygen-enriched conditions, boundary layer reactions (converting CO to CO 2, with concomitant heat release) are shown to increase the char particle temperature and burning rate, while decreasing the O 2 concentration at the particle surface. The CO 2 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 CO 2 gasification reaction increases the char conversion rate for combustion at low O 2 concentrations, but decreases char conversion for combustion at high O 2 concentrations. These calculations give new insight into the complexity of the effects from the CO 2 gasification reaction and should help improve the understanding of experimentally measured oxy-fuel char combustion and burnout trends in the literature.