Effect of Reaction Conditions on Nitrogen Conversion During Char-O₂/NO Combustion

Nitrogen conversion during char-O₂ combustion with a high initial-NO concentration (char-O₂/NO combustion) is an important issue for low-NOx technologies and oxy-fuel combustion technologies, such as air/fuel-staged and flue gas recycling combustion. This study employed both experimental and numerical methods to investigate the mechanisms of N conversion and formation during char-O₂/NO combustion. In the numerical model, the mass and heat transfer processes are governed by unsteady convection-diffusion partial differential equations. The numerical results agree well with the experimental findings, assuming NO is the sole primary N-containing product. Based on the numerical results, the effects of reaction conditions on N conversion were decoupled. As the O₂/fuel stoichiometric ratio increases, the char-N release rate substantially rises, and the shrinkage of pore surface area becomes significant, leading to poorer NO reduction performance. With an increase in initial-NO concentration, the apparent conversion of char-N to NO decreases, while the NO reduction efficiency remains almost unchanged. Due to the lower temperature sensitivity of mass transfer limitations in the char-NO reaction compared to the char-O₂ reaction, NO reduction performance is enhanced at higher reaction temperatures.