Experimental and numerical study on the effects of coal on ammonia-N conversion behavior during ammonia-coal co-firing

Co-firing ammonia with pulverized coal presents a promising strategy for reducing CO2 emissions in coal-fired power plants. However, there are concerns regarding the NOx formation behavior of ammonia. In this study, the effects of coal on ammonia-N (NH3-N) conversion behavior were explored by combustion experiments using a drop tube furnace, and the interactions between ammonia and coal were further analyzed using computational fluid dynamics (CFD) simulations. The results showed that co-firing ammonia and coal/char could increase NOx formation, and the conversion ratio of fuel-N into NOx was also increased. The comparison of ammonia-coal and ammonia-char co-firing demonstrated that coal had a stronger effect on NH3-N conversion than char, further inferring that both char and volatile significantly increased the conversion of NH3-N to NOx. The simulation results suggested that 23.82% of the total NO emissions originated from coal, and 76.18% from ammonia in ammonia-coal co-firing, indicating that NH3-N was the primary source of the increased NOx, and the interactions between ammonia and coal/char increased the conversion of NH3-N to NOx. The interaction between coal (both volatile and char) and ammonia contributed to an overall increase in the ammonia average reaction rate, with the ammonia's average oxidation reaction rate displaying a much more pronounced increase. This further led to the formation of NOx and the conversion of NH3-N to NOx in ammonia-coal co-firing conditions.