Research On Combustion Of Low Calorific Value Fuel And Fuel Pretreatment And Pollution Control Technology In CFB Boiler

The circulating fluidized bed boiler has wide fuel adaptability and is suitable for the combustion of low-calorific value fuels.Coal slime,coal gangue,sludge,and gasification slag are fuels with low calorific value,and its use in circulating fluidized bed furnace combustion is one of its large-scale and efficient utilization methods.However,the high water content of sludge and gasification slag and the small particle size of gasification slag bring difficulties to their combustion and utilization.The unstable combustion of low-calorific value fuels and increased pollutant emissions after combustion will also increase the difficulty of their utilization.In the context of ultra-low emissions,in order to achieve stable combustion of low-calorific value fuels in circulating fluidized bed boilers,this article focus on the drying of low-calorific value fuels,as well as the combustion characteristics and pollutant emission characteristics in the process of fuel mixed combustion.And proposed a fuel mixed combustion program,in order to provide support for the combustion of low-calorific value fuel in the circulating fluidized bed boiler.In this paper,the dewatering and microwave drying characteristics of sludge and gasification residue were studied by using molding machine and microwave dryer.Through research,it is found that sludge is difficult to form and dehydrate.When the sludge and gasification residue are mixed at a ratio of 1:1,under a molding pressure of 5 MPa,the comprehensive dehydration rate is 61.22%,but its moisture content is still high;microwave drying found that the gasification slag enhanced the wave absorption performance of the sludge,and its small particle size would reduce the resistance along the way to water evaporation.In view of the synergy of the two fuels in the two dehydration methods,this chapter proposes a drying process that combines forming dehydration and microwave drying to reduce drying energy consumption.The combustion characteristic experiment of low calorific value fuel in air atmosphere is carried out by thermogravimetric analyzer.Through research,it is found that the whole combustion process of blended coal（the ratio of coal slime to coal gangue is 1:1）is stable and the comprehensive combustion characteristics are better.When sludge is added to the mixed coal,the high volatile content of the sludge reduces the ignition temperature of the mixed coal by 109.80℃.The addition of sludge improves the combustion performance of the mixed coal in the early stage,but the entire combustion process is unstable and comprehensive combustion performance Getting worse.When gasification slag is added to the mixed coal,its combustion process is relatively stable,but its combustion intensity decreases and its comprehensive combustion performance deteriorates.Therefore,when blending sludge and gasification slag,a small proportion of blending should be selected.In an air atmosphere,a tube furnace is used to conduct pollutant emission experiments on low-calorific value fuels at different temperatures,and a test-350 flue gas analyzer is used to analyze and test SO₂and NOx.The addition of sludge and gasification slag to the mixed coal is beneficial to the reduction of SO₂ emissions,and the gasification slag has a synergistic effect on inhibiting the release of SO₂.The two admixing methods have no synergistic effect on inhibiting the release of NOx,and have little effect on the total amount of NOx released.Based on the above research,a large proportion of burning coal sludge and a small proportion of mixed burning coal gangue,sludge and gasification slag are proposed in the circulating fluidized bed.Combining engineering practice,a process of mixing low calorific value fuel-extrusion molding dehydration-microwave drying dehydration-mixing into the furnace is proposed.This process can avoid the blockage of the feeding process and solve the problem that the particle size is too fine to meet the combustion of the circulating fluidized bed.