Against the accelerating global transition toward low- and zero-carbon energy systems, ammonia (NH₃) has attracted considerable attention as a promising carbon-free fuel and hydrogen carrier because of its carbon-free nature, ease of storage and transportation, and well-established supply infrastructure. However, its high ignition temperature, low burning velocity, and narrow stable combustion range make stable and efficient combustion difficult. In addition, the formation of nitrogen oxides (NOₓ) and unburned NH₃ remains a major challenge to the large-scale clean utilization of ammonia. Bubbling fluidized bed (BFB) combustion, characterized by favorable gas–solid mixing, efficient heat transfer, and broad fuel flexibility, can provide a stable and relatively uniform high-temperature reaction environment, offering potential advantages for combustion stabilization and pollutant control. In this study, pure ammonia combustion experiments were conducted in a laboratory-scale BFB reactor to systematically investigate the effects of stoichiometric ratio, bed material conditions, reaction temperature, and fluidization velocity on combustion and emission characteristics. The results showed that increasing the stoichiometric ratio significantly increased NO emissions while markedly reducing unburned NH₃. Increasing the fluidization velocity shortened the effective residence time of the gaseous fuel in the reactor, thereby increasing unburned NH₃ emissions. Reaction temperature had a pronounced effect on N₂O formation: N₂O emissions decreased to nearly zero above 850 °C, whereas a substantial increase was observed at 750 °C. Bed material conditions also significantly influenced ammonia combustion and pollutant emissions, although relatively complex trends were observed. Overall, this study identifies the major effects of key operating parameters on pure ammonia combustion in BFB systems and provides an experimental basis for further investigations of coupled operating conditions, fluidized-bed operation optimization, and complex nitrogen conversion mechanisms relevant to ammonia combustion and co-firing systems. These findings provide useful guidance for the design and optimization of efficient, stable, and low-emission ammonia combustion systems in bubbling fluidized beds.

Ammonia,Bubbling fluidized bed,NOₓ,Zero-carbon energy