Co-firing characteristics and fuel-N transformation of ammonia/pulverized coal binary fuel.

• Flue gas emission characteristics of NH 3 /pulverized coal co-firing process with a wide range of NH 3 blending ratios were studied in a drop tube furnace. • Effects of coal type, NH 3 injection mode, temperature, excess air ratio (α) and NH 3 co-firing ratio (E NH3) were compared to achieve efficient combustion and low pollutants emission. • Fuel-N transformation analysis was conducted to explore the nitrogen migration characteristics in high temperature NH 3 /coal co-firing process which have not yet been investigated before. • Through staged combustion strategy, E NH3 = 40 % is the optimal NH 3 co-firing ratio which not only can reduce half of CO 2 but also achieve the minimum NO x conversion rate and low residual NH 3 level. As a feasible way to decarbonize coal combustion under the background of carbon neutrality in recent years, ammonia co-firing with pulverized coal is receiving considerable critical attention from the academic and industrial communities. This paper investigates the effects of coal type, NH 3 injection mode, temperature, excess air ratio (α) and NH 3 co-firing ratio (E NH3) on combustion characteristics and fuel-N transformation of ammonia/pulverized coal in a 6 kW drop tube furnace. Emission of O 2, CO 2 , CO, NO, NO 2 and NH 3 at the furnace exit was monitored online. The unburned carbon (UBC) content and elementary composition in fly ash were also tested. Results show that NO x generation behaviors of premixed and staged modes are significantly different. Typically, NO x emission peaks at E NH3 = 20 % under high temperature and staged mode. As for NH 3 /coal cases at 1000 °C, NO x level is even lower than pure coal combustion, but NH 3 residue is higher. The water gas shift reaction (WGSR) under fuel-rich condition generates more CO, and the conversion ratio from fuel-N to NO x decreases when α diminishes. Ammonia co-firing can achieve lower CO emission with anthracitic coal from Gongyi (GY-coal) while lower NO x emission with bituminous coal from Inner Mongolia (IM-coal). Ammonia co-firing can considerably improve the transformation from fuel-N to N 2. From the perspective of emission control and decarbonization, E NH3 = 40 % is an optimal ammonia co-firing ratio which not only can reduce half of CO 2 but also brings the conversion ratio from fuel-N to NO x and residual NH 3 to the minimum level. The micromorphology of ash samples is greatly affected by coal/ammonia co-firing. In premixed mode, the surface of ash sample is porous and adhered to each other; while in staged mode, obvious fractures and cuts exist between the ash particles due to the sharp decrease of local gas temperature. [ABSTRACT FROM AUTHOR]