| A large number of facts have proved that gas outburst accidents mainly occurred in the tectonic coal development zone,and the outburst point occurred in the coal seam or coal layer formed by tectonic coal.Guhanshan mine is coal and gas outburst mine,There have been 10 coal and gas outburst accidents since 1990.Main mining 21 coal seam gas content is high and pressure is big.Under the action of tectonic compression and shear,a deep layer of soft layer is formed at the bottom.The existence of soft layers leads to the decrease of coal strength and permeability,and the difficulty of moving gas to the bottom plate increases,and it is easy to form high-energy gas accumulation zone.In order to effectively prevent the coal seam gas disaster of 21 coal seam in guhanshan mine.In this paper,the main research theme is“The Characteristics of Gas Adsorption/Desorption from 21 Coal and Its Influence in Gas Extraction in Guhanshan Coal Mine”By the ways of experimental study,theoretical analysis the pore structure characteristics and adsorption/desorption characteristics of soft coal and hard coal were studied.And the difference of adsorption and desorption of soft and hard coal was analyzed.The causes of the differences were analyzed from the perspective of pore structure.According to the difference of the adsorption and desorption of soft and hard coal,the influence of the gas extraction was analyzed.Main conclusions of this paper are as follows:?1?Analyze the pore structure characteristics of soft and hard coal by the liquid nitrogen adsorption experiment and mercury intrusion experiment.By using the pore-size-ranges measured by liquid nitrogen experiment and mercury intrusion experiment.When D>33nm,the results of mercury intrusion experiment can be employed and when D?33nm,the results of liquid nitrogen experiment can be adopted.We can combine the results together and analyze the pore structure characteristics of soft and hard coal.For soft coal sample,its volume and surface of micropore,minipore,mesopore and macropore are more than that of hard coal sample.By processing experimental data of mercury injection experiment and liquid nitrogen adsorption experiment Fractal dimension for soft and hard coal were respectively analyzed.The fractal dimension of hard coal sample obtained from liquid nitrogen adsorption experiment are less than that of soft coal sample and fractal dimension of hard coal sample obtained from mercury injection experiment are more than that of soft coal sample.Compared with hard coal,the surface roughness and irregularity of soft coal micropores and small holes are larger,while the surface roughness of mesoporous and macropore is smaller.?2?The gas adsorption characteristics and differences of soft and hard coal were investigated through isothermal adsorption experiment under different initial adsorption pressure.Under the same initial adsorption pressure,with the increase of adsorption time,the cumulative adsorption quantity of soft and hard coal gradually increased and eventually stabilized,and the adsorption rate decreased gradually.After reaching the adsorption equilibrium,the cumulative adsorption quantity and initial adsorption rate of soft coal were greater than that of hard coal,respectively 1.231.65times of hard coal and 1.811.91 times.With the increase of initial adsorption pressure,the cumulative adsorption quantity and initial adsorption rate of soft and hard coal increased.Compared with hard coal,the cumulative adsorption quantity and initial adsorption rate of soft coal increased rapidly with the increase of initial adsorption pressure.?3?The gas desorption characteristics and differences of soft and hard coal were studied by the desorption experiment under different adsorption equilibrium pressure.Under the same adsorption equilibrium pressure,the cumulative desorption of soft and hard coal increases with time,and the rate of desorption decreases with time.The first minute cumulative desorption,ultimate desorption and the first minute desorption rate of soft coal were larger than that of hard coal,which was 1.914.04 times of hard coal,1.251.65 times and 1.703.27 times,respectively.But the desorption rate of the 30min and the 120min was smaller than that of the hard coal.Under different adsorption equilibrium pressure,the cumulative desorption and desorption rate of soft coal and hard coal increased with the increase of pressure.The first minute cumulative desorption,ultimate desorption and the first minute desorption rate of soft coal increased at a greater speed with the increase of equilibrium pressure.Moreover,the desorption rate of the 30min and the 120min of hard coal increased at a greater speed with the increase of equilibrium pressure.?4?Based on the experimental study of the pore structure characteristics of soft and hard coal,the pore volume,BET specific surface area and fractal dimension of coal samples were selected as the characteristic parameters of pore structure of coal and its influence on adsorption and desorption characteristics was analyzed.Compared with hard coal,the BET specific surface area,micropore volume and fractal dimension of granular soft coal are larger.It provides more adsorption position for gas adsorption on coal surface,larger gas migration channel and stronger gas adsorption capacity.Therefore,in the same condition,the gas adsorption capacity of soft coal is greater.At the time of desorption,the initial concentration gradient of soft coal is higher,and the cumulative desorption capacity and initial desorption rate are greater.?5?After the coal seam is unloaded,it was found that because the desorption capacity of soft coal is larger and the desorption rate is faster,the extraction concentration and discharge flow are greater in the early stage of gas extraction.Compared with soft coal,desorption of hard coal is a gradual process.In the early stage of desorption,the desorption rate is smaller than that of soft coal.But the desorption rate of hard coal is higher than that of soft coal in the later stage.Therefore,the extraction effect is mainly affected by hard coal in the late stage of extraction.Due to the slow decay of desorption rate of hard coal and the long desorption time,it may cause the gas extraction cycle to be too long and affect the production replacement. |
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