Ammonia blend ratio impact on combustion characteristics and NOx emissions during co-firing with sludge and coal in a utility boiler

This study investigates the effects of the ammonia blend ratio and the number of nozzle layers on boiler combustion characteristics and NOx emissions by the computational fluid dynamics simulation method. The conclusions indicate that, as ammonia is injected from a single-layer of secondary air nozzles, with the ammonia blend ratio increases, the combustion temperature decreases, when the blend ratio is 60%, the combustion temperature decreases by about 300 K. When ammonia is injected into the furnace from multiple-layers of nozzles, and under the premise of the same ammonia blend ratio, the overall impact on the furnace temperature is smaller than that of ammonia entering from a single-layer of nozzles. When the blend ratio of the ammonia is 40%, the NOx emission of ammonia entering the furnace from two layers of secondary air nozzles is about 22.47% higher than when it is injected into the furnace from a single-layer of nozzles. After raising the ammonia mixing ratio, the NOx at the furnace outlet shows an inverted-parabola change, which first decreasing and then increasing.