As global consumption of fossil fuels continues to increase

the transition from fossil fuels to carbon-free alternative fuels is crucial for achieving the goals of carbon neutrality. As a carbon-free fuel

ammonia (NH3) has the advantages of high energy density

high hydrogen content

and safe storage and transportation

which has garnered significant attention. The utilization of ammonia co-firing has the potential to significantly reduce carbon emissions from coal-fired boilers. It also demonstrates excellent compatibility with existing coal-fired generation facilities

including pulverized coal and fluidized bed boilers. This review first introduces the fundamental research on ammonia combustion

emphasizing key challenges such as combustion instability and elevated nitrogen oxide (NOx) emissions. Moreover

the current status of ammonia co-combustion with solid fuels is comprehensively reviewed

and the reaction mechanisms of ammonia with volatiles and char are elucidated. Furthermore

recent research on ammonia co-firing in pulverized coal and fluidized bed boilers is outlined

and the effects of varying ammonia injection ratios and positions on NOx emissions are explored

with particular emphasis on the issue of nitrous oxide (N2O) emissions in fluidized bed boiler combustion. Finally

the key challenges and future works are also discussed

providing valuable insights to facilitate the development and application of ammonia co-firing technology in coal-fired boilers.