Oxy-coal combustion exhibits different characteristics of combustion, flow and heat transfer from those of air-coal combustion, due to the high concentration of CO2 and H2O in the product gases. Using computational modeling, this study investigated the combustion and wall heat flux (WHF) of a 100 MWe boiler under air- and oxy-coal combustion conditions. The boiler had 12 swirl burners installed on the front wall for thermal input of 284 MWth. Flame temperatures and corresponding WHF in oxy-coal combustion increased linearly as O-2 concentration increased from 24% to 30%. The case with 28% O-2 achieved the same level of WHF with that of air-coal combustion, which had a similar adiabatic flame temperature. Due to the lower heat capacity, the gas temperature above the burner region lowered more rapidly in air-coal combustion than in oxy-coal combustion. The proportion of char converted by CO2 and H2O increased from approximately 8% in air-coal combustion to 19-23% in oxy-coal combustion. The increased rates of endothermic gasification reactions by CO2 and H2O lowered the temperature in the internal recirculation zone during oxy-coal combustion. This retarded char oxidation upstream of the flames. (c) 2012 Elsevier Ltd. All rights reserved.