Effects of H2O on NO Emission during Oxy-coal Combustion with Wet Recycle

This study investigated the characteristics of NO emissions during oxy-coal combustion with wet-recycle, especially in the presence of high H2O concentrations. The oxy-combustion was carried out using two types of coal, namely Leiyang (LY) anthracite and Zhundong (ZD) bituminous coals, inside a 24 kW drop tube furnace under different O2/CO2/H2O atmospheres. The results showed that the NO conversion increased with decreasing CO2concentration from 70% to 30% and decreased with increasing H2O concentration from 10% to 40%. Under the experimental conditions employed in this study, the fuel-N conversion for both LY and ZD coals under the oxy-coal wet recycled combustion was lower than that under the oxy-coal dry recycled combustion. The results indicated that H2O and CO2showed a competitive effect on NO emissions, though both of them have positive effect on NO reduction. In order to investigate the effects of H2O/CO2on recycled NO, oxy-coal combustion experiments were also performed with the initial addition of NO concentrations of 900 ppmv. The results showed that NO reduction ratio in O2/CO2was lower than that in O2/CO2/H2O for both coals under our experimental conditions. It is believed that the results of this study can provide some fundamental information on the effect of H2O/CO2on the characteristics of NO emissions during oxy-coal combustion with wet-recycle.