Experimental and mechanism study on NO formation characteristics and N chemical reaction mechanism in ammonia-coal co-firing

Carbon-free ammonia can significantly reduce CO2 emissions from coal-fired power generation. However, the high nitrogen content of ammonia can lead to high NOx emissions when it is co-fired with coal. Therefore, it is necessary to explore the formation mechanism of NOx in ammonia-coal co-firing to reduce the emission of nitrogen oxides. In this study, the high-temperature furnace experimental platform and CHEMKIN software were combined to investigate the NO formation characteristics and the pathway analyses of the ammonia-N/coal-N reactions during ammonia-coal co-firing under a broad temperature range and variable ammonia blending ratios. The experimental results showed that when the temperature was below 1200 ℃, the amount of NO formed increased with the increase in the ammonia blending ratio. At and above 1300 ℃, the amount of NO formed first increased and then decreased with the increase in the ammonia blending ratio. The blending of ammonia reduced the fuel-N to NO conversion rate. The CHEMKIN simulation results showed that when the temperature was below 1200 ℃, the growth rate of ROP for each elementary reaction of NO formation was higher than that for each elementary reaction of NO reduction. Above 1300 ℃, the growth rate of ROP for each elementary reaction of NO reduction increased significantly, exhibiting a decrease in the NO concentration during ammonia-coal co-firing. The simulation results were in good agreement with the experimental results. Through ROP analysis, sensitivity analysis, and reaction path analysis, it was concluded that HNO was the main intermediate product of NO formation, NH and NH2 free radicals were the main groups of NO reduction, and OH free radicals had a significant influence on NO formation.