Comprehensive effect of the coal rank and particle size on ammonia/coal stream ignition

Co-firing green ammonia and coal in power plants is expected as an attractive method to phase down coal power. During the co-firing process, the ignition and combustion of pulverized coal particles are comprehensively affected by coal rank and particle size. However, the influences of coal rank and particle size on ammonia/coal stream ignition are unknown. In this study, the coal ignition process of different coal ranks (lignite, sub-bituminous, bituminous, and anthracite) and particle sizes (ranging from 63 to 120 µm) were investigated using a novel two-stage flat flame burner at various co-firing ratios. Multi-optical methods, including CH and NH chemiluminescence and high-speed backlight videography, were used to characterize the ignition process. Co-firing ammonia in the hot gas environment has both positive and negative effects on subsequent pulverized coal combustion. The positive effect is the elevated ambience temperature, while the negative effect is the consumption of oxygen in the reaction zone due to the ammonia reaction. Due to the positive effect, co-firing with ammonia in hot gas environment can induce the transition of the ignition mode. For high rank coal (e.g., anthracite) and large coal particles, the ignition mode transitions from heterogeneous ignition dominance to hetero-homogeneous joint ignition dominance. In contrast, For low-rank coal and small coal particles, co-firing ammonia further enhances the homogenous ignition and combustion. These findings contributes to the further application of the ammonia-coal co-firing technology.