Abstract: In the short term,the status quo of coal as the main energy in China will not change.Because coal combustion will release a lot of NO_xand cause serious environmental pollution,so the control of NO_xin coal combustion process is very important.Chain grate furnace as one of the most widely used coal-fired boilers in China must be paid more attention to the reduction of NO_xemission.Especially with the implementation of Boiler Air Pollutant Emission Standard(GB 13271—2014),the NO_xemission value of grate furnace in key areas should not be higher than 200 mg/m~3,the technology of low-nitrogen combustion and NO_xremoval in chain grate furnace has attracted wide attention.In order to reduce the NO_xemission of chain grate furnace,meet the requirements of national environmental protection,reduce the cost of operation and maintenance of enterprises and improve the economic benefits of enterprises,the technical improvement study of flue gas recirculation and SNCR denitrification system was performed in a 4×75 t/h chain grate furnace of a heating station at Gaoxin District in Xi'an to reduce the NO_xemission.The influence of the parameters of SNCR and flue gas recirculation coupled low nitrogen combustion system,such as flue gas recirculation ratio,the feed ratio of recirculation flue gas in primary and second air chamber,the ammonia nitrogen molar ratio and the change of boiler load on NO_xremoval efficiency and combustion characteristics were researched.The optimum operating parameters of flue gas recirculation coupled with SNCR technology were determined.The results show that the SNCR coupled flue gas recirculation low nitrogen combustion technology can effectively reduce the NO_xemission of chain grate furnace.When the flue gas recirculation rate is 16%-18%,the feed ratio of recirculation flue gas in primary air chamber is 82%,and the molar ratio of ammonia nitrogen is 0.78,the SNCR coupled flue gas can achieve the best denitrification efficiency in the circulating system.At this point,the denitration efficiency of SNCR coupling flue gas recycling is up to 56%and the denitrification efficiency of SNCR single operation is 40%and the actual NO_xemission is reduced from 250 mg/m~3to 110 mg/m~3,which is much higher than the national emission standard of NO_x.