Study and operation analysis on blended combustion of coal water slurry gasification fine slag in CFB boiler

At present,the many years’ development of China’ s coal chemical industry has led to a rapid increase in the amount of fine slag treatment in the domestic coal gasification system. After being filtered by vacuum belt or plate frame filter,the moisture content of gasification fine slag generally reaches 40% - 60%,and the mass fraction of dry basis residual carbon is usually 18%-50%. The harmless treatment and resource utilization of coal gasification fine slag has become a pain point that needs to be solved urgently in the coal chemical industry at home and abroad. Based on the characteristics of coal water slurry gasification fine slag,the influence of coal water slurry gasification fine slag on mixing combustion was studied from the aspects of carbon residue(calorific value),moisture content,mixing proportion and mixing combustion characteristics of coal water slurry gasification fine slag. After deep dehydration and drying,the moisture content of the gasification fine slag of the coal water slurry gasifier of a group in Shaanxi Coal Group Weihua Company is reduced to about 28%. After blending with the raw coal,the blended fuel is easy to be transported and its fluidity will not cause raw coal blockage and interruption. After adjusting the moisture content and calorific value of the blended fuel to meet the requirements of the CFB boiler,it will have little impact on the heat exchange efficiency and operating life of the boiler. Based on the analysis of the operation of the CFB boiler blended with gasification fine slag, the boiler operation parameters such as bed temperature, flue gas oxygen content, flue gas temperature,bed differential pressure and so on have little change after blended combustion. The concentration of SO2 and NOx in flue gas does not change dramatically and will not affect the boiler desulfurization and denitrification system. The carbon content of boiler fly ash is reduced from 10%-20% to 5%-10% after blended combustion,which proves that the appropriate amount of blending can promote the combustion. After the blended combustion of gasification fine slag,the amount of fly ash entering the tail flue will increase because its ash content is higher than that of raw coal. When the mixing proportion is less than 15%,the design margin of bag filter can meet the mixing condition. Reducing the moisture content of gasification fine slag to about 28% at one time,and then burning it in the CFB boiler can save the disposal cost of fine slag,and burning the residual carbon in fine slag to produce steam can achieve the purpose of energy conservation,and the increased fly ash after burning can be used for building materials,so the economic and environmental benefits are very considerable. It is an energy-conserving,environment-friendly,and practical way for the resource utilization of solid waste. © 2023 China Coal Society. All rights reserved.