The characteristics of NO production mechanism on flue gas recirculation in oxy-firing condition

The characteristics of NO production mechanisms in counter-flow flames with gasified coal syngas have been computationally studied through detailed chemical reactions and transport properties. The combustion of gasified coal syngas with N2/O2 mixture causes a significant increase in nitric oxide emission due to the higher flame temperature and considerable amount of nitrogen in the oxidant. The nitric oxide emission can be reduced efficiently by using a CO2/O2 mixture instead of an N2/O2 mixture as the oxidant. The NO production mechanism was analyzed in detail through the overall chemical reaction pathways. The phenomenon of NO decomposition was observed for flue gas recirculation when the CO2/O2 mixture was used as the oxidizer and coal was gasified with O2/steam. The adoption of O2/steam gasification in the oxy-firing condition could considerably reduce the thermal NO and fuel NO due to the low nitrogen in the fuel and low flame temperature. However, reverse reactions of fuel NO as in NO→HNO and HNO→NH were observed when combustion flue gases were recirculated. Also, the fuel-N conversion rate of coal syngas combustion was investigated in the oxy-firing condition.