A kinetic evaluation on NO_2 formation in the post-flame region of pressurized oxy-combustion process

摘要

Pressurized oxy-combustion (POC) is a promising technology that can significantly reduce the energy penalty associated with first generation oxy-combustion for CO_2 capture in coal-fired power plants. However, higher pressure enhances the production of strong acid gases, including NO_2 and SO_3, which could aggravate the corrosion threat during flue gas recirculation. In this study, the conversion of NO to NO_2 has been kinetically evaluated in a plug flow reactor under representative post-flame conditions of pressurized oxy-combustion. The effects of residence time, temperature, pressure, O_2, H_2O, CO, and SO_2 on NO_2 formation are studied. The calculations show that when pressure is increased from 1 to 15 bar, NO_2 is increased from 1 to 60 ppm, and the acid dew point increases by over 80°C. Higher pressure and temperature greatly reduce the time required to reach equilibrium, e.g., at 15 bar and 1300°C, equilibrium is reached in 1 millisecond and the NO_2/NO is about 0.8%. -The formation and destruction of NO_2 is generally through the reversible reactions: NO+O+M=NO_2+M, HO_2+NO=NO_2+OH, and NO+O_2=NO_2+O. With increasing pressure and decreasing temperature, O plays a much more important role than HO_2 in the oxidation of NO. A higher water vapor content accelerates NO_2 formation in all cases by providing more O and HO_2 radicals. The addition of CO or SO_2 also promotes the formation of NO_2. Finally, NO_2 formation in a POC furnace is compared with that in a practical atmospheric air-combustion (AAC) furnace and the comparison shows that NO_2 formation in a POC furnace can be over 10 times that of an AAC furnace.