Synergistic SOx/NOx 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 SOx and NOx 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 SOx and NOx 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 SOx and NOx 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.