SO3 Formation under Oxyfuel Combustion Conditions

The sulfur chemistry in oxyfuel combustion systems has received growing attention lately. The formation of SO3 is of special concern, because of the elevated SO2 concentrations found in oxyfuel, compared to air-fuel conditions. The present study focuses on the gas-phase chemistry and examines the impact of different combustion parameters and atmospheres on the formation of SO3 in oxyfuel and air-fuel flames, using a detailed gas-phase model. The work also includes a summary of the presently available SOx data from experiments in laboratory and pilot-scale combustors. The reviewed experimental data, as well as the modeling results, show significantly increased SO3 concentrations in oxyfuel, compared to air-fuel conditions. The modeling results reveal a complex behavior of the SO3 formation, which is influenced by direct and indirect effects of the SO2, O-2, NOx, and CO content in the flue gas. One of the main contributors to the increased SO3 concentration in oxyfuel, compared to air-fuel conditions, is the high concentration of SO2 in oxyfuel combustion. The modeling also shows that the stoichiometry, residence time, and flue-gas cooling rate are critical to the SO3 formation. Thus, in addition to the stoichiometry of the flame, the flue-gas recycling conditions are likely to influence the formation of SO3 in oxyfuel combustion.