Effect Of Load On Gas Adsorption Characteristics Of Coal Left In Abandoned Mines

With the continuous optimization of the production structure of China’s coal industry,the number of abandoned mines is increasing year by year.After abandoned coal mining,the load environment has its particularity and complexity,which has great influence on the characteristics of coal adsorbing gas.In order to probe into the effect of load change on the characteristics of waste coal adsorbing gas,and accurately construct the calculation model of waste coal adsorbing gas resource,the paper combines theoretical analysis,by means of numerical simulation and similar experiments,the remaining coal is divided into "pillar-type" and "Bulk-type" coal,the distribution of elastoplastic region and the evolution law of overburden stress of the coal pillar are simulated,on the basis of this,the characteristics of gas adsorption in the process of load bearing stress change of coal seam no.3 in Jincheng mining area were tested on "TCWS-4 gas seepage experimental system" and "test device for deformation and permeability of coal bearing rock in the process of adsorption/desorption".The main conclusions reached are as follows:The internal bearing stress state of coal pillar with wide and narrow size is different.After the long-time stress evolution,the residual coal body rebalances,and the wide coal pillar forms the low stress on both sides,the high stress in the middle,and reaches the peak value in the limit equilibrium zone However,the stress of the narrow coal pillar is low on both sides,then the stress rises and reaches the peak value in the middle of the coal pillar.Under other conditions,the load-bearing stress increases gradually with the decrease of coal pillar size.When the coal pillar size decreases from 50 m to 30 m,the load-bearing stress only increases by 3.43 MPa When the coal pillar size decreases from30 m to 15 m,the bearing stress increases by 13.65 MPa.In each loading stage,the two types of residual coal experienced the rapid adsorption stage,the adsorption transition stage and the adsorption stable stage.The experimental results show that the methane adsorption of coal samples increases at first and then decreases with the increase of axial load when the gas pressure is 1.21 MPa,the maximum difference of adsorption capacity between adjacent loading intervals was 1.05 m L/g,and the adsorption capacity of methane increased with the increase of axial load when the charging pressure was 1.95 MPa,at the same loading stage,the maximum difference of the adsorption capacity at high charging pressure was greater than that at low charging pressure,and the maximum difference was 2.2 m L/g.The experimental results show that the methane adsorption of coal samples increases first and then decreases with the increase of axial load when the gas pressure is 1.19 MPa,the maximum difference of adsorption capacity between adjacent loading intervals was 3.59 m L/g.Before and after the destruction of coal,the change trend of adsorption amount is different.Before the coal body is destroyed,the permeability of the coal body decreases with the loading,which is disadvantageous to the gas migration,and there are a lot of micro-pore structures,therefore,the amount of methane adsorbed by coal increases with the increase of axial load at this stage.After the coal body is destroyed,the permeability increases and the inner pore volume increases,which is favorable for gas migration,and the energy loss increases in the process of molecular movement,therefore,in this stage,the amount of methane absorbed by coal decreases with the increase of axial load.Therefore,the load factor should be taken into account in the calculation model of adsorbed gas resource of abandoned coal mine.