Continuous combustion of ammonia in a bubbling fluidized bed: Experimental and simulation study

Ammonia, as a carbon-free energy carrier, supports the large-scale use of renewable energy, and its combustion is a key utilization pathway. This study examines the continuous combustion of ammonia in a bubbling fluidized bed using experiments and numerical simulations. The effects of equivalence ratio, fluidization velocity, secondary air injection location, and secondary oxygen ratio were investigated. Measurements focused on temperature distribution, ammonia conversion, and NO emissions, while simulations based on a two-fluid model revealed key reaction pathways. Results show that combustion mainly occurs in the dense phase. Lower equivalence ratios increase NO emissions, while fuel-rich conditions reduce NO but lower ammonia conversion. Higher fluidization velocity shortens residence time, reducing both NO emissions and conversion. The dense phase shows a catalytic effect on ammonia decomposition, affecting reactor temperature. At 900 °C, equivalence ratio of 1, and 40 % diluted oxygen, the main pathway from NH₃ to NO is: NH₃ → NH₂ → H₂NO → HNO → NO Notably, staged combustion, though typically used for NO reduction, increases NO and N₂O emissions in fluidized beds due to higher freeboard temperatures and enhanced conversion of NH₂/NH to NO.