Experimental Study Of Gas Desorption Diffusion And Adsorption Diffusion In Deformed Coal

Gas accident,especially the gas outburst,is often happened at the deformed coal,through the research on coal's all kinds of pore structure distribution and diffusion regularity,we can derive indicators what can be used for prevention of coal and gas outburst accident,it's of great significance to the safety production of coal mine.The writer collected the coal from No.8 mine of Pingdingshan,No.6 mine of Hebi and mine of Zouzhuang,also collected a variety of useful experimental data,by the means of pressured-mercury testing and low temperature liquid nitrogen adsorption experiments,the writer had comparative analysis of pore structure distribution of coals who have different metamorphic grade and different coal structure.By the effective means of volume adsorption/desorption experiments and gravimetric high-pressure isothermal adsorption/desorption experiments,gas diffusion rules of coals were carried out research and discussion,those coal samples have different particle size,different coal structure,different metamorphic grade and under different pressure.Several conclusions are drawn as follows:?1?The pore structure and pore size distribution of coal samples with different metamorphic degree are obvious.lignite have the most large porosity,and obvious is greater than all the other samples,the porosity of high metamorphic degree of coal?meager lean coal and anthracite?is smaller,long flame coal has the lowest porosity;Through the variation of porosity,low metamorphic degree of coal samples' porosity range larger,and to high degree of metamorphism stage(R_0,max=1.89⁴.37%),the change of porosity was not obvious;big hole and the transition pore of total pore volume accounted for the leading role,both in the low metamorphic degree and high metamorphic degree,big hole has the development,the middle hole has the highest proportion in the lignite which has the lowest development degree,the transition hole and the micro hole has the obvious advantage in the high rank coal.To coal samples with high metamorphic degree and low metamorphic degree,the contribution to surface area is dominated by the transition pore and micro pore;?2?The pore volume and specific surface area of each size range of the deformed coal is different from that of the undeformed coal.Compared to the undeformed coal form the same seam,it is found that deformed coal's total pore volume and specific surface area were significantly increased.In addition,mesopore's volume ratio and specific surface area ratio has decreased,on the whole,volume ratio,specific surface area ratio of the transition hole and micro hole have increased significantly.Fine diameter bottle pore of the deformed coal is developed,the main is open pore in the undeformed coal,and also little fine diameter bottle pore;?3?Conclusions were founded by the desorption experiment: Under the same conditions,the effect of pressure on desorption rate and initial effective diffusion coefficient is not significant;On the whole,desorption rate of the coal sample who have the particle size of 0.25⁰.5mm is greater than that of the coal sample who have the particle size of 0.5¹.0mm,initial effective diffusion coefficient of the coal sample who have the particle size of 0.5¹.0mm is greater than that of the coal sample who have the particle size of 0.25⁰.5mm;for the undeformed coal,overall,desorption rate of the meager lean coal from Hebi No.6 mine is more than that of the fat coal from Pingdingshan No.8 mine,initial effective diffusion coefficient has the same law,and for the deformed coal,desorption rate of the fat coal from Pingdingshan No.8 mine is more than that of the meager lean coal from Hebi No.6 mine,and initial effective diffusion coefficient has the same law,too;in most cases,the initial effective diffusion coefficient of the deformed coal is significantly greater than that of the undeformed coal,and the desorption rate of the deformed coal is greater than that of the undeformed coal;?4?In the gravimetric high pressure isothermal adsorption experiment,the change of the adsorption capacity of coal samples with the pressure was studied,it's found that the amount of adsorption increased rapidly with the increase of adsorption equilibrium pressure in the early stage;in the middle stage,the growth rate decreased and the amount of adsorption increased slowly,and the adsorption amount decreased at the later stage.In addition,the curve of adsorption and desorption don't overlap,there's a clear hysteresis loop,the adsorption and desorption of methane showed non reversibility;?5?In the early stage of gas adsorption,the adsorption capacity will have a short period of rapid growth,then enter the slow growth stage,and finally tend to be stable.Releationship between the time reached the adsorption equilibrium and the effective diffusion coefficient is that ‘the greater effective diffusion coefficient was,the shorter the time reached adsorption equilibrium'.Pressure in a certain range of threshold value will have two completely opposite effect on the diffusion coefficient,that is ‘positive promoting effect and negative blocking effect'.