Effects of air flow distribution and equivalence ratios for staged combustion in an ammonia burner

Ammonia is gaining research attention as an ecofriendly fuel because of the lack of CO2 emissions during combustion; however, their slow flame speeds, low flame temperatures, and high NOx emissions necessitate additional control measures. Therefore, an optimized combustor design is essential for commercial applications such as power plants and boilers. The ammonia combustion characteristics and NO and N2O formations are investigated in this study using a self-designed 100 kWth burner with varying oxidizer flow ratios and equivalence ratios. Experimental results indicate that, under conditions of a swirl number of 0.80 applied to the primary oxidizer, a primary-to-secondary oxidizer flow ratio of 2:8, a burner zone equivalence ratio of 0.85, and an over fire air (OFA) zone equivalence ratio of 0.15, the flue gas composition was NO at 80 ppm @ 6 % O2, N2O at 14 ppm, and ammonia at 30 ppm. These results were attributed to optimized equivalence ratios in the burner and OFA zones combined with an air-staged combustion and strong swirl intensity applied to the primary oxidizer, which creates an intense recirculation zone. In addition, the low injection velocity of ammonia and optimal oxidizer velocity effectively compensated for the inherently low combustion speed of ammonia. The results of this study can be applied to the design of ammonia-fueled burners that can achieve stable combustion while minimizing NO and N2O emissions.