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  • Mechanism study on the enhanced $▫SO^3 and NO^2▫$ formation in pressurized oxy-combustion
    Wang, Xuebin ...
    Pressurized oxy-combustion (POC) is a promising technology that can significantly reduce the energy penalty associated with first-generation oxy-combustion for CO2 capture in coal-fired power plants. ... However, higher pressure enhances the production of strong acid gases, including SO3 and NO2, aggravating the threat of corrosion. The formation of NO2 and SO3 in the gas-phase and their interaction in the post-flame region have not been adequately addressed, particularly at elevated pressures. In this study, the synergistic promotion of SO3 and NO2 is kinetically evaluated under representative post-flame conditions for POC (1-15 atm, 700-1100 oC). We begin by validating the mechanism, which includes nitrogen and sulfur chemistry based on GRI 3.0, and 72 species and 428 reactions. The effects of temperature and pressure on this synergistic promotion are studied, and rate of production analysis is adopted to illustrate this interaction mechanism under POC conditions. Finally, SO3 and NO2 formation in a POC furnace is compared with that in a practical atmospheric air-combustion (AAC) furnace. The calculations show that the interaction of SOx and NOx indeed accelerates the conversion rates of NO to NO2 and SO2 to SO3, and the acceleration is much stronger at elevated pressures and lower temperatures. ROP (Rate of Production) analysis indicate that under POC conditions, due to the strong interaction between SOx and NOx, the formation pathways of SO3, through HOSO2+O2=HO2+SO3, and NO, through HO2+NO=NO2+OH, are dramatically promoted. These two reactions are linked by the reaction SO2+OH+M=HOSO2+M, resulting in a strong 0231-1 cycle, which can be represented by the global reaction NO+SO2+O2%NO2 +SO3. This cycle is the major route for the formation of both SO3 and NO2 at elevated pressures, while the reversible reaction SO2+NO2=SO3+NO can be treated as in equilibrium. The radical HOSO2 can be considered as a quasi-steady state intermediate. A comparison of SO3 and NO2 yields for a POC furnace and an AAC furnace shows that SO3 and NO2 formation in a POC furnace can be respectively approximately 50 and 10 times than those in an AAC furnace. The high concentrations of SO3 and NO2 in the flue gas of POC furnaces respectively increase the acid dew point by 105 and 75 oC, which suggests a greater threat of low-temperature corrosion if wet flue gas recirculation is used to control temperature. These results suggest that when boiler is pressurized, staged oxy-combustion with low recycle is preferred over un-staged pressurized oxy-combustion with recycle.
    Source: SDEWES 2019 [Elektronski vir] (Str. 1-12)
    Type of material - conference contribution ; adult, serious
    Publish date - 2019
    Language - english
    COBISS.SI-ID - 98145793

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