Emission characteristics of coal combustion in different O 2/N 2, O 2/CO 2 and O 2/RFG atmosphere

Abstract

This study investigates the emission characteristics of CO 2, SO 2 and NOx in the flue gas of coal combustion by varying the compositions and concentrations of feed gas (O 2/CO 2/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 CO 2 in O 2/CO 2 combustion system is 95% as the feed gas is 30% O 2/70% CO 2. The average concentration of CO 2 in the flue gas of O 2/CO 2 coal combustion system is higher than 90% and much higher than that of O 2/N 2 coal combustion system. This high concentration of CO 2 is beneficial for the separation of CO 2 from the flue gas by adsorption or absorption technologies. The maximum concentration of CO 2 in O 2/N 2 combustion system is only 34% at the feed gas 50% O 2/50% N 2, the concentration of CO 2 is increased with the concentration of O 2 in feed gas. By O 2/CO 2 combustion technology, higher concentration of SO 2 is produced as the feed gas is 30% O 2/70% CO 2 or 40% O 2/60% CO 2, while higher concentration of NOx is produced as the feed gas is 20% O 2/80% CO 2 or 50% O 2/50% CO 2. The mass flow rates of CO 2, SO 2 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% CO 2. 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 2 combustion technology, higher concentrations of SO 2 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/CO 2 combustion system.