Experimental and numerical evaluation of coal-N conversion characteristic during preheating-combustion under O₂/CO₂ atmosphere

High-temperature preheating and O-2/CO2 combustion have been proven effective for de-NOx and CO2 capture. In this study, we combined these two methods to investigate the transformation characteristics of volatile-N and to validate whether the reduction of nitrogen in volatile-N is enhanced during preheating of pulverized coal (PC) under the O-2/CO2 atmosphere. The conversion of coal-N to NOx and its precursors during the preheating process under the O-2/CO2 atmosphere was examined through experimental and numerical approaches. The results indicate that the gasification of CO2 during the preheating stage increases the volatilization of coal-N. Subsequently, in a high-temperature, strongly reducing atmosphere, up to 52.21% of the coal-N is directly converted into N-2. Furthermore, the presence of CO2 also participates in gas-phase reactions, leading to changes in the relative proportions of free radicals such as O, H, and OH. Additionally, it increases the concentration of CO, thereby facilitating the reduction of NO during the combustion stage. The experimental findings indicate a synergistic effect between preheating and O-2/CO2 combustion in reducing NO formation. Furthermore, by implementing further air staging, the NO emissions can be reduced by an additional 49.60%, with NO emissions down to 109.70 mg.m(-3).