Experimental Study On Deposition Law Of Coal And Rock Particles In Mining-induced Fracture

Pressure-relieved gas drainage using surface boreholes is an effective gas extraction method.This method has many advantages and has been widely used in China.However,in the process of surface drilling and extraction,there is often a phenomenon that the gas flow will suddenly or gradually decrease.One of the main reason for this phenomenon is that coal and rock particles in the extraction gas flow block the mining-induced fractures.At present,the research of coal and rock particles clogging fractures is mostly based on coal bed methane gas production channels,and there has not been many research on particle migration and deposition rules under the condition of mining-induced fracture diameter shrinkage.Here in,this article made an analysis on coal and rock particles collected from a mine extraction system,and a horizontal single-fracture gas-solid two-phase flow experimental system was constructed to influence the particle migration and deposition behavior in the fracture with a diameter shrinkage,the influence of the gas-solid two-phase flow parameters and the fracture geometric parameters on the particle deposition.Conducted experimental research.(1)Through the measurement of the particle size distribution,true density and stocking angle of the dust particles collected in the high extraction roadway extraction system of 22612 working face and 28620 working face,The results show that the diameter distribution of two groups of particle is relatively close,mainly distributed in the range of 100?m ~ 800?m.The most frequent particle size of the two groups of particles is 352?m,that is,the particle size with the largest number of particles is 352?m.When the particle size is less than this value,the proportion of particle size gradually increases When the particle size is larger than this value,the proportion of particle size gradually decreases;the true relative density values of two groups of particles are 2.04 and 1.84 respectively,which are higher than the density of ordinary bituminous coal;the average stocking angle of the two groups of particles is 30.33 °,which has good fluidity.(2)The typical movement behavior of the particles in the fracture is studied.It is found that with the decrease of air velocity,the particle motion state is: suspensionsubsiding-deposition-blocking.When the air velocity is higher,the particles move in the fracture is in the suspended state,which is not easy subsid,when the gas velocity decreased,there are some particles could not maintain the suspension state,and began to subside.The sedimentation reached a certain scale to form a deposit,and the deposition continued to develop to block the fracture.Based on this,there are two critical values: critical deposition air velocity and effective plugging air velocity.The critical deposition air velocity is the critical point at which particles subside to the deposit.The effective plugging gas velocity is the critical value at which particles deposit to form a blockage.Experiments using three particle size groups in the range of 200-300 ?m,300-550 ?m and 550-700 ?m,the critical deposition velocities are 1.39 m / s,1.56 m / s,and 1.79 m / s,and the effective clogging velocities are 1.16 m / s,1.42 m / s,and 1.68 m / s,respectively.(3)The typical law of particle deposition is revealed: the particle deposition is divided into three stages in time.The first stage is the horizontal development stage.The particle deposition forms three unconnected particle beds in the horizontal direction,and then gradually communicates.This stage lasts about 60 minutes.The particle deposition height develops slowly,and the deposition quality accounts for 53.78% ~ 61.89%,the local resistance is generally stable,with a small amount of fluctuation;the second stage is a vertical development stage,which lasted 100 minutes.The particle deposition height increased rapidly,and the deposition mass accounted for more than 80%.The local resistance increased rapidly,from the previous 9.4Pa to 12.9Pa;the third stage is the stable stage,the particle deposition height no longer increases,the deposition quality no longer increases,and the local resistance tends to stabilize.From the horizontal development stage,the particle deposition has developed to some extent,but the local resistance is generally stable.When the deposition height does not reach a certain level,the local resistance will not increase,but will be in a relatively stable state.(4)The effects of two-phase flow parameters and diameter shrinkage geometry parameters on particle deposition were studied.The factors such as the velocity of air,particle size,and solid-gas ratio affect the deposition by changing the two-phase flow motion energy,which is active Influencing factors,such as the increase of the conveying gas velocity,the distance between the particle deposition and the diameter reduction are 110 cm,106cm,84 cm and 51 cm,respectively,which leads to the difference in the development time,height,quality and local resistance of the particle deposition;diameter shrinkage ratio and diameter shrinkage angle is the passive influencing factors that affect the particle deposition through its own local resistance and collision.For example,when the diameter shrinkage ratio increases,its own local resistance increases from 6.6Pa to 27 Pa,which results in the energy loss of the twophase flow motion.As the diameter shrinkage ratio increases,the deposition height before diameter reduction also increases,which are 6.5mm,7.5mm,10.5mm and 12 mm,respectively.(5)The influence degree of the above factors is sorted,and the influence degree from high to low is: air velocity> particle size> solid-gas ratio> diameter reduction ratio> diameter reduction angle,taking the sensitivity coefficient of local resistance increment as an example,The sensitivity coefficient of the air velocity is 6.22,the particle size is 3.29,the solid-gas ratio is 2.78,the diameter reduction ratio is 0.7,and the diameter reduction angle is 0.5.It can be seen that the air velocity is the first factor that affects particle deposition.At the same time,the active influencing factors for particle deposition are greater than the passive influencing factors.The paper has 58 pictures,6 tables,and 63 references.