Reduction of Recycled NOx by Simulated Coal Volatiles in Oxy-Fuel Combustion

The reduction of recycled NO by simulated coal volatiles (CH4 and NH3) during oxy-fuel combustion has been studied in a flow reactor. Special emphasis was given to the effects of different variables on the reduction of recycled NO, and to the comparison with results obtained in air-fired combustion. The experiments were conducted in a temperature range of 873–1273 K. The stoichiometries varied from fuel-rich to fuel-lean. The results showed higher temperature favored the reduction of recycled NO under fuel-rich conditions, and the recycled NO reduction obtained in CO2 was much lower than that obtained in N2. However, under stoichiometric and fuel-lean conditions, the recycled NO reduction decreased with increasing temperature, and a slightly higher recycled NO reduction was obtained in CO2 compared to that in N2. Higher recycled NO concentration accelerated its reduction. The recycled NO reduction decreased with increasing CO2 concentration under fuel-rich conditions, while it increased under fuel-lean conditions. Higher CO maximum concentration was obtained in the CO2 case due to the CO2 + H ⇔ CO + OH reaction. But a decrease in the CO concentration was observed when the CO2 concentration reached a certain level. This indicates there are other important reactions responsible for the effect of a high concentration of CO2 besides CO2 + H reaction.