Abstract: The material balance in a CFB boiler can affect the safe,stable,and efficient operation of a CFB boiler.Studying the material balance in a furnace can guide the actual boiler operation.Based on the ash formation and attrition experimental method proposed by Tsinghua University,this paper obtained the intrinsic ash formation characteristics data of three coal types used in a 660 MW ultrasupercritical CFB boiler.The structure of this 660 MW ultra supercritical CFB boiler was simplified to some extent.Only the furnace,separator and recycling valve were retained.Considering the conditions of particle attrition,size reduction,and particle segregation,the material balance of the boiler circuit was numerically simulated with the one dimensional chamber model.The experimental results showed that blending three kinds of coal samples with different properties had a good effect and could meet the requirements of CFB boiler material balance.When the bed pressure was in the range of 5 000-7 000 Pa,increasing the bed pressure drop can increase the residence time of bed material,and the effect was more obvious especially when the particles were in the intermediate particle size range (0.125-3.2 mm).Increasing the bed pressure drop had a limited effect on increasing the particle concentration in the dilute phase of the upper furnace.With a low bed pressure drop of 5 000 Pa,optimizing the particle size distribution of the coal sample had a small effect on the residence time of the particles in the furnace,but it had a significant effect on increasing the particle concentration in the upper part of the furnace.After optimizing the particle size distribution of the coal,the optimized bed pressure drop of the 660 MW ultra supercritical CFB boiler was 5 000 Pa.The CFB boiler also had a good operation at 5 000 Pa bed pressure,which could reduce the power consumption of fans in actual power plant and make power plant become more energy saving