Abstract: In order to further control pollutant emissions and achieve the goal of carbon neutrality,oxy-fuel combustion technology has received more and more attention as a clean combustion technology.Combined with oxy-fuel combustion technology and preheating combustion technology based on circulating fluidized bed,it is beneficial to further reduce NO_x emissions and improve fuel adaptability.For exploring the migration path of NO_x of different fuels with preheating oxy-fuel combustion technology and based on the O_2/CO_2 combustion technology of circulating fluidized bed preheating,Shenmu bituminous coal and semi-coke were used as contrast fuels,and the perfectly stirred reactor (PSR) in CHEMKIN software were used with preheated fuel as the input parameters.Moreover,the rate of production analysis (ROP) and sensitivity analysis (SA) were used to explore the migration path of NO_x in combustion. Comparing the simulation calculation results with the previous experimental results,the results show that the two-stage PSR model can perform a good calculation simulation of the gas-phase combustion in the down-fired combustor (DFC),and the adaptability of the model is good,and the method of the input parameter setting is feasible.In the O_2/CO_2 atmosphere,the combustion of CO_2 in the DFC is dominated by the formation reaction.Besides,the increase of CO_2 partial pressure promotes the generation of NO.The basic migration path of the gas-phase reaction of nitrogen-containing in the combustion process of bituminous coal and semi-coke is consistent.In the main combustion zone,the main path of NH_3 conversion is NH_3→NH_2→NH→HNO→NO,the reactions of NH→N→NO are occurred during the combustion of bituminous coal.In addition to the consumption reaction,HCN can also be generated by the reaction of hydrocarbon groups with NO.The increase in the concentration of hydrocarbon groups can promote the formation of NH_3 and HCN for semi-coke.