NO Formation Mechanism during Oxy-Fuel Combustion of Pyridine

To reveal the formation mechanism of NO during coal combustion under O₂/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 O₂/CO₂ compared to air combustion. Especially at ¿=0.8, it dropped by 50%.