Experimental study of influence of temperature on fuel-N conversion and recycle NO reduction in oxyfuel combustion

Coal combustion in O-2/CO2 environment was examined with a bituminous coal in which the gas-phase and char combustion stages were considered separately. The effects of temperature (1000-1300 degrees C) and the excess oxygen ratio lambda (0.6-1.4) on the conversion of volatile-N and char-N to NOx were studied. Also, the reduction of recycle NOx by fuel-N was investigated under various conditions. The results show that fuel-N conversion to NO in O-2/CO2 is lower than that in O-2/N-2. In O-2/CO2 atmosphere, the volatile-N conversion ratios vary from 1-7% to 15-24% under fuel-rich and fuel-lean conditions, respectively. The char-N conversion ratios are 11-28% and 30-50% under fuel-rich and fuel-lean conditions, respectively. The influences of temperature on the conversion of volatile-N to NO under fuel-rich and fuel-lean conditions are contrary. A significant difference for char-N conversion in fuel-rich and fuel-lean conditions is observed. The experimental data of recycle NO reduction indicate that the reduction of recycle NO by gas-phase reaction can be enhanced by volatile-N addition in fuel-lean condition at high temperature, while in fuel-rich condition, the volatile-N influence cancelled out and the overall impact is small. NO/char reaction competes with the conversion of fuel-N to NO at higher temperatures. (C) 2010 Published by Elsevier Inc. on behalf of The Combustion Institute.