NO Formation Mechanism during Oxy-Fuel Combustion of Pyridine

To reveal the formation mechanism of NO during coal combustion under O-2/CO2 atmosphere, pyridine, as a nitrogenous model compound of coal, was combusted in a horizontal furnace. The influences of oxygen excess coefficient, CO2 concentration and combustion atmosphere on the release of NO was studied. The concentration of CO, NH3 and HCN in flue gas were also measured and analyzed in detail. Under reducing atmosphere, the formation rate of NO increased gradually while HCN and NH3 decreased with increasing CO2 concentration, which resulted from the fact that H radicals were consumed by high concentration of CO2 and the diffusion resistance of H radicals were also enhanced. In oxidizing atmosphere, the formation of NO was inhibited by increasing CO2 concentration, because the increasing CO2 limited the availability of the atomic oxygen then favored the increment of OH radicals, which meant more amino-group and cyano-group could be preserved instead of being oxidized to NO. As oxygen excess coefficient increased, the formation rates of HCN and NH3 decreased gradually while NO had a progressive rise and NH3 exhibited a higher formation rate than HCN. The formation rate of NO revealed a significant drop in the atmosphere of O-2/CO2 compared to air combustion. Especially at alpha= 0.8, it dropped by 50%.