Effects of ammonia co-firing ratios and injection positions in the coal–ammonia co-firing process in a circulating fluidized bed combustion test rig

Ammonia (NH3) co-firing is a promising technology for reducing greenhouse gas emissions in coal-fired power plants. Prior to commercialization, an experimental study on coal–NH3 co-firing in a pilot-scale circulating fluidized bed (CFB) combustion test rig was conducted for technical verification. The comprehensive combustion characteristics, including pollutant emission, combustion efficiency, and ash properties, of NH3 co-firing with sub-bituminous coal in a CFB combustion test rig and the CO2 reduction according to NH3 co-firing ratios under two different injection positions (dense bed zone (DBZ) and wind box (WB) with primary air) were investigated. When NH3 was injected at the DBZ, NO emissions decreased as the NH3 co-firing ratio increased and CO emissions increased more rapidly than with only coal-fired combustion. Compared with only coal-fired combustion, a 25.4% NH3 co-firing ratio at the WB position simultaneously reduced NO and CO concentrations, achieving the highest combustion efficiency without ash-related problems. However, N2O emissions increased by > 1.5 times, indicating the formation of N intermediates during NH3 burning. Therefore, with minor retrofitting, coal–NH3 co-firing at the WB position is a feasible solution for simultaneously reducing CO2, NO, and CO emissions in commercial CFB combustion plants.