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 NOx owing to the high nitrogen in ammonia. This study proposes a novel low-NOx swirl burner with a scalable dual-channel ammonia pipe for coal-ammonia co-firing, and evaluates the combustion and NOx 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 NOx 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 NOx 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 NOx reduction. Overall, the cases with lower ROC (0.1, 0.2) are suggested with low NOx (below 120 ppm) and carbon content in fly ash (below 3.50 %) for the low ammonia blending ratio in this study.