Study on the regulation of fuel staging on NO formation during ammonia-coal co-firing: Effects of co-firing ratio, fuel staging rate and air staging on NO formation

To address carbon emission reduction demands, ammonia application in coal-fired power plants has become increasingly critical. This study investigates the effects of ammonia co-firing ratios (30%, 40%), burner-axial ammonia injection ratios (2:1, 1:1, 1:2), and overfire air on NO emissions. Results show that rising axial ammonia injection reduces NO emissions at a declining rate but increases ammonia slip, while suppressing NO formation in the main combustion zone and enhancing axial reduction. Numerical simulations reveal that NO formation pathways differ significantly among ratios: NO is generated via N radicals and NH intermediates under 2:1 and 1:1 conditions, with an opposite trend under 1:2. Oxygen, ammonia concentration and temperature dominate nitrogen intermediate conversion. The 1:1 staging ratio presents the best overall performance in balancing combustion stability and pollutant control.