Study On Combustion And Fragmentation Process And Gas Release Law Of Single Coal Slime

Coal slime is a kind of poor-quality coal washed out.With the increasingly tight energy situation,how to make better use of coal slime and create value for society has become an urgent problem for people.It is an effective new way to burn slime in Circulating fluidized bed boiler.With the development of CFB boilers toward large-scale,this requires us to study the combustion mechanism of coal slime and provide theoretical support for the design of new fluidized beds.This paper first observes the physical phenomenon of coal slime combustion in a tube furnace through a high-speed camera.Research shows that the combustion process of coal slime is mainly divided into two cases.Among them,the combustion of large-diameter coal slime particles at high temperatures mainly undergoes four processes:heated evaporation drying process;high temperature fragmentation process;volatile homogeneous combustion process;char heterogeneous combustion process.The first process will cause the volume to shrink or expand slightly;the second process is fragmentation,resulting in a rapid decrease in volume;the third process produces a flame phenomenon,and floc on the surface of the slime ball;the fourth process flame disappears,the volume gradually decreases and has the longest duration.The small diameter slime ball does not break at low temperatures.According to whether coal slime combustion process is fragmentation,it can be divided into fragmentation areas and non-fragmentation areas.It can be seen that the fragmentation time of coal slime is affected by the diameter and temperature.As the diameter increases and the temperature increases,the fragmentation coal time of slime will be advanced.At high temperatures,the effect of diameter on its crushing time decreases.At the same time,the degree of fragmentation is also affected by these two factors.The larger the diameter,the higher the temperature,and the more severe the fragmentation.The ignition delay time increases with increasing diameter and decreases with increasing temperature.Burn-out time increases with increasing diameter and decreases with increasing temperature.The internal temperature change of coal slime is divided into three stages,the rapid rise stage,the maintenance of high temperature stage,and the rapid recovery of the furnace temperature stage.In the temperature rise stage,the larger the diameter,the smaller the slope.In this paper,thermogravimetric mass spectrometry experiments were conducted to investigate the mass change and gas release law of coal slime under rapid temperature rise.Compared with the ordinary heating,under the condition of rapid heating,the weight loss rate is accelerated,the gas precipitation is advanced,and the ignition phenomenon occurs.The weight loss interval during the combustion phase is gradually divided into two sections,namely the volatile ignition combustion phase and the char combustion phase;The larger the diameter of coal slime,the more obvious the weight loss interval in the later period,and the large diameter coal slime suddenly changes during the weightlessness due to fragmentation,and the gas release process suddenly increases;Under the condition of rapid temperature rise,the higher the final temperature of the slime,the more water and carbon dioxide gas are precipitated,the less volatiles are released,the more oxygen is consumed,and the less time it takes to complete the combustion.It means that the higher the final temperature,the more sufficient the combustion.According to the thermogravimetric mass spectrometry experiment of 6mm diameter coal slime at 1000?,the combustion phenomenon of coal slime in tube furnace can be verified.The coal slime combustion process also experienced four weightless stages.The air pressure generated by internal moisture and volatilization during combustion is the main cause of coal slime fragmentation.