China is a country dominated by coal-fired power generation. In order to reduce the CO2 emissions of coal-fired power plants,it is important to develop low-carbon alternative fuels and corresponding combustion technologies. Compared with hydrogen,ammonia has considerably lower storage and transportation costs,and is safer and more reliable. Thus,it is considered as a better energy carrier and carbon-free fuel. It is a more practical and feasible technical route to reduce CO2 emission of coal-fired boilers at this stage by replacing part of pulverized coal with ammonia and cofiring coal with ammonia in the boiler. In order to examine the technical feasibility of ammonia cofiring in coal-fired boilers,the world′s largest 40 MWth ammonia-coal cofiring test facility equipped with a full-scale ammonia-coal cofiring burner and ammonia supply system was designed and fabricated, and the cofiring tests of 0-25% ammonia cofiring ratios (calorific value) were conducted on this facility.The results show that the boiler can establish stable ignition and combustion at all ammonia cofiring ratios,and the char burnout of ammonia cofiring cases is better than that of pure coal combustion cases. With air-staging combustion,the boiler NOx emission can be controlled lower than that of coal combustion case at high ammonia cofiring ratios. However,at overfire air rates higher than 20%,the further increase of overfire air rate has no significant effect on the NOx emission,but significantly increase the boiler CO emission and the unburned carbon content in fly ash,and hence,reduce the boiler efficiency. Therefore,there is an optimal overfire air rate at which both the NOx emission and char burnout can be kept at low level. The boiler excess O2 level also has significant impacts on boiler NOx and NH3 emissions. With the decrease of excess O2,the boiler NOx emission decreases significantly,while the NH3 emission increases rapidly. Thus,there is an optimal range of excess O2 within which the boiler NOx and NH3 emissions can be both kept at low level. The industrial scale test in this paper verifies the feasibility of ammonia-coal cofiring technology in coal-fired boilers,reveals the key parameters that affect boiler NOx emission and fuel burnout,and provides a promising technical advancement direction for the coal-fired power plants to achieve signification reduction of CO2 emissions.