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 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 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.