A novel low-NOx swirl burner with coal-ammonia co-firing: Effect of ammonia ratio in the dual channels on combustion and NOx formation

Coal-ammonia co-firing is a promising technology for reducing CO₂ emissions in coal-fired boilers. However, coal-ammonia co-firing may cause significant NO_x owing to the high nitrogen in ammonia. This study proposes a novel low-NO_x swirl burner with a scalable dual-channel ammonia pipe for coal-ammonia co-firing, and evaluates the combustion and NO_x formation under different ammonia ratios of the dual channels (i.e., inner and outer channels). The results show that the ammonia is injected into the low-oxygen and high-CO environment behind the internal recirculation zone, contributing to the ammonia pyrolysis and inhibiting the ammonia oxidation reaction. Low NO_x is successfully achieved with high combustion efficiency. In addition, it is observed that the effect of the ammonia ratio of the dual channels on the combustion and NO_x formation is slight for the high ammonia blending ratio (20 %), while it is prominent for the low ammonia blending ratio (10 %). Especially, for the low ammonia blending ratio, lower ammonia ratio in the outer channel can obtain high velocity of ammonia stream in the inner channel, contributing to NO_x reduction. Overall, the cases with lower R_OC (0.1, 0.2) are suggested with low NO_x (below 120 ppm) and carbon content in fly ash (below 3.50 %) for the low ammonia blending ratio in this study.