Influence of Flue Gas Circulation Mode on the Formation of SO₃

The influence of flue gas circulation mode on the formation mechanism of SO₃ was analyzed by chemical reaction kinetics. Results show that more SO₃ would be produced in oxy-fuel combustion mode compared with traditional conditions, among which maximum concentration of SO₃ appears in the mode of wet flue gas circulation. The formation of SO₃ could be promoted by high concentrations of free radicals, such as O, OH and HOSO₂ generated in combustion process due to existence of high initial O₂, SO₂ and H₂O volume fractions. The generation rate of SO₃ increases with reducing initial SO₂ concentration, and with rising initial O₂ and H₂O concentration. The mode of oxy-fuel combustion may result in high flue gas acid dew point, and in wet flue gas circulation mode, the acid dew point is the highest. The acid dew point could be effectively reduced by flue gas desulfurization and dehydration.