Realizing efficient and clean ammonia combustion in fluidized beds: A perspective based on experiment and simulation

Ammonia co-firing in circulating fluidized bed boilers as carbon-free alternative fuel is a promising pathway toward grid stability and decarbonation of existing units. However, NO emissions control remains a critical challenge. In this study, the combustion characteristics of ammonia in a bubbling fluidized bed combustor, and the effects of gas-solids flow on ammonia conversion and NO selectivity are comprehensively analyzed by combining computational particle fluid dynamics simulation. The experimental results showed that ammonia was completely burned under all conditions with the NH3 slip below 2 ppm, while NO concentration increased with increasing excess air ratio. Simulation results showed good agreement with the experiments and revealed that ammonia conversion predominantly occurred within the bed. Distinct differences in ammonia conversion and NO selectivity were observed between the bubble and emulsion phases. Near the bottom of the bed (Z = 0.002), a higher particle volume fraction resulted in a higher local temperature and consequently enhanced ammonia oxidation rates. Accordingly, NH3 exhibits a significantly higher conversion in the emulsion phase. At Z = 0.02, in the emulsion phase, the local reaction rate of NO reduction was higher than that of NO formation, while the reverse occurred in the bubble phase. As a result, the emulsion phase exhibited significantly lower NO emissions and NO selectivity compared with the bubble phase. Finally, a perspective for realizing efficient and clean ammonia combustion is proposed, providing valuable insights for the development of fluidized bed ammonia combustion technology.