Synergistic SO_x/NO_x chemistry leading to enhanced SO₃ and NO₂ formation during pressurized oxy-combustion

Pressurized oxy-combustion is a promising technology that can significantly reduce the energy penalty for CO₂ capture in coal-fired power plants. However, higher pressure might enhance the production of strong acid gases, including SO₃ and NO₂, which will lead to higher rates of corrosion. In this study, we investigated a reduced but combined SO_x and NO_x mechanisms and the synergistic formation of SO₃ and NO₂ was kinetically evaluated under different pressures and temperatures up to 15 atm and 1100 °C. The calculation results show that the interaction of SO_x and NO_x significantly accelerates the conversion rates of SO₂ to SO₃ and NO to NO₂, and the acceleration is much stronger at elevated pressures and comparatively low temperatures. With a strong interaction between SO_x and NO_x due to elevated pressures, the formation pathways of SO₃ and NO₂ through HOSO₂ + O₂ = HO₂ + SO₃ and HO₂ + O = NO₂ + OH, respectively, are dramatically promoted. These two reactions are linked by the reaction SO₂ + OH + M = HOSO₂ + M, resulting in a ‘strong’ cycle, which can be represented by the global reaction NO + SO₂ + O₂ = NO₂ + SO₃. This cycle is the major route for the formation and destruction of both SO₃ and NO₂ at elevated pressures.