THERMAL SCIENCE

International Scientific Journal

Thermal Science - Online First

online first only

A kinetic evaluation on no2 formation in the post-flame region of pressurized oxy-combustion process

ABSTRACT
Pressurized oxy-combustion 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 NO2 and SO3, aggravating the corrosion threat during flue gas recirculation. In the flame region, high temperature NOx exists mainly as NO, while conversion from NO to NO2 happened in post-flame region. In this study, the conversion of NO → NO2 has been kinetically evaluated under representative post-flame conditions of pressurized oxy-combustion after validating the mechanism (80 species and 464 reactions), which includes nitrogen and sulfur chemistry based on GRI-Mech 3.0. The effects of residence time, temperature, pressure, major species (O2/H2O), and minor or trace species (CO/SOx) on NO2 formation are studied. The calculation results show that when pressure is increased from 1 to 15 bar, NO2 is increased from 1 to 60 ppm, and the acid dew point increases by over 80ºC. Higher pressure and temperature greatly reduce the time required to reach equilibrium, e.g., at 15 bar and 1300ºC, equilibrium is reached in 1 millisecond and the NO2/NO is about 0.8%. The formation and destruction of NO2 is generally through the reversible reactions: NO+O+M=NO2+M, HO2+NO=NO2+OH, and NO+O2=NO2+O. With increasing pressure and decreasing temperature, O plays a much more important role than HO2 in the oxidation of NO. A higher water vapor content accelerates NO2 formation in all cases by providing more O and HO2 radicals. The addition of CO or SO2 also promotes the formation of NO2. Finally, NO2 formation in a Pressurized oxy-combustion furnace is compared with that in a practical atmospheric air-combustion furnace and the comparison show that NO2 formation in a Pressurized oxy-combustion furnace can be over 10 times that of an atmospheric air-combustion furnace.
KEYWORDS
PAPER SUBMITTED: 2020-04-15
PAPER REVISED: 2020-07-31
PAPER ACCEPTED: 2020-08-02
PUBLISHED ONLINE: 2020-09-06
DOI REFERENCE: https://doi.org/10.2298/TSCI200415236W
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