Abstract: In order to study the combustion characteristics of the supercritical coal-fired boilers,the velocity,trajectory of pulverized coal particles,temperature and composition distribution characteristics and NO_x release features during coal combustion in the 600 MW counter-rotating swirling boiler were numerically studied using CFD( Computational Fluid Dynamics) numerical simulation software.The standard k-ε model and lagrangian random orbit model were explored to simulate gas-phase turbulent flow and gas-solid two-phase flow.The solid fuel was simulated by the discrete phase model,besisdes,the pulverized coal combusted in the furnace was simulated by the non-premixed combustion model.The convection term adopted the second order upwind to obtain a more accurate understanding of the matter.Considering the high temperature of the boiler furnace and the large amount of radiation heat transfer,the P1 radiation model was used to calculate the radiation heat transfer between the gas-gas and the gas-solid.The standard wall function method was used to calculated flow heat transfer,which could save the space and calculation time. The results show that the cross-section velocity of the staged combustion boiler is symmetric,the gas flow is full and the combustion is stable.Besides,the symmetrical reflux caused by swirling combustion in the furnace could enhance the disturbance between the gas flow in the furnace and the pulverized coal particles,and then strengthen the heat and mass transfer and increase the residence time of the pulverized coal particles in the furnace.The particle size of pulverized coal in the furnace could affect the combustion process.Specifically,the smaller the particle size the shorter the residence time of pulverized coal particles is in the furnace,which will influence the combustion and burnout of the fuel and the efficiency of the boiler.On the contrary,if the particle size is too large,the pulverized coal particles fall into the ash hopper slagging by their own gravity,and impacts the normal safe operation of the boiler.Therefore,the proper particle size is significantly important for the combustion process in the furnace.The average temperature of the flue gas in the furnace rises and then decreases along the height of the furnace and then reach to about 1 100 K in the cross section of the furnace exit.The temperature in the burnout zone is slightly reduced due to the supplemented over-fire-air.The distribution of various components in the furnace are X = 11.093 5 m section,along the height of the furnace,the volume fraction of O_2 first rises and then decreases,the volume fraction of CO_2 increases gradually,the volume fraction of CO first rises and then decreases,the staged combustion reduces the overall NO_x production,and the concentration of NO_x at the furnace outlet is about 385.14 mg/m~3.