Abstract: The effects of coal types on the NO_x formation characteristics of ammonia-coal co-firing are investigated by simulating the NO_x formation process of ammonia co-firing with bituminous and anthracite coals in a one-dimensional test furnace. The results show that the NO emissions tend to decrease and then increase with the increase of NH₃ co-firing ratio when co-firing with bituminous coal; while the NO emissions of ammonia-anthracite coal tend to decrease and then increase with the ammonia co-firing ratio, and these emissions are significantly higher than those from bituminous coal co-firing. Despite the significant differences in the NO formation characteristics of both coals, it can be found that they are governed by the same mechanism, i.e., the net NO formation of ammonia-coal co-firing is determined by the competition between the NO-formation and NO-reduction reaction pathways of NH₃ in different O₂ environments along the furnace. In the present study, NH₃ is injected into the furnace later than the coal stream such that the combustion of NH₃ is later than the coal volatile matter. This affects the NH₃ combustion environment in the main combustion zone, and consequently, the formation of NO. Because of the significant differences in volatile matter content between bituminous and anthracite coals and the resultant differences in the amount of O₂ consumption, the distribution of O₂ concentrations in the furnace is substantially different between the two types of coals. This results in different competition relationships between the NO-formation and NO-reduction reaction pathways of NH₃, causing different NO formation and emission characteristics between the bituminous and anthracite coals.