Ammonia cofiring in coal-fired boilers is one of the promising technical routes for decarbonization of existing coal-fired power plants. However

ammonia cofiring may potentially result in drastic increase of NO_x emissions due to its high nitrogen content. Effective control of NO_x emissions is thus one of the key factors that affect the technical feasibility of ammonia cofiring in coal-fired boilers. The formation of NO_x during ammonia-coal cofiring is affected by the ammonia combustion as well as its interaction with the coal combustion process. There are significant differences in volatile content of different coal types which may strongly affect the NO_x formation characteristics of ammonia cofiring. For this reason

the NO_x formation characteristics of ammonia cofiring with bituminous and lean coals that have distinct volatile contents are investigated by an experimental rig that allows for flexible control of the combustion environment of ammonia. The results show that

the NO_x emissions from bituminous and lean coals show different trends with the increase of ammonia cofiring ratio under different ammonia cofiring modes. Because of the significant differences in volatile matter content between bituminous and lean coals and the consequent differences in the amount of O_2 consumption

the distributions of O_2 concentration in the furnace are substantially different between the two coals. This results in different competition relationships between the NO formation and reduction reactions of ammonia in the furnace

which consequently leads to different NO_x formation and emission characteristics between the two coals.