This study investigates the emission characteristics of CO2, SO2 and NOx in the flue gas of coal combustion by varying the compositions and concentrations of feed gas (O-2/CO2/N-2) and the ratios of recycled flue gas. The differences between O-2/recycled flue gas (O-2/RFG) combustion and general air combustion are also discussed. Experimental results indicate that the maximum concentration Of CO2 in O-2/CO2 combustion system is 95% as the feed gas is 30% O-2/70% CO2. The average concentration of CO2 in the flue gas of O-2/CO2 coal combustion system is higher than 90% and much higher than that of O-2/N-2 coal combustion system. This high concentration of CO2 is beneficial for the separation of CO2 from the flue gas by adsorption or absorption technologies. The maximum concentration of CO2 in O-2/N-2 combustion system is only 34% at the feed gas 50% O-2/50% N-2, the concentration of CO2 is increased with the concentration of O-2 in feed gas. By O-2/CO2 combustion technology, higher concentration of SO, is produced as the feed gas is 30% O-2/70% CO2 or 40% O-2/60% CO2, while higher concentration of NOx is produced as the feed gas is 20% O-2/80% CO2 or 50% O-2/50% CO2. The mass flow rates of CO2, SO, and NOx in the flue gas are all increased with the ratio of recycled flue gas except for the feed gas 20% O-2/80% CO2. The enhanced mass flow rates of air pollutants in such O-2/RFG combustion system are also beneficial for improving the control efficiencies of air pollution control devices. By O-2/N, combustion technology, higher concentrations of SO2 and NOx are produced as the feed gas is 21% O-2/79% N-2. The results also indicate that the formation of NOx in general air combustion system is higher than that in O-2/RFG or O-2/CO2 combustion system. (c) 2006 Elsevier B.V. All rights reserved.