| Gas is the main gas in coal seams.Studying the rules of gas absorption and desorption in coal seams is beneficial to gas extraction and can effectively reduce the danger of coal and gas outburst.The relatively complex pore structure of the coal body can reflect the physical and chemical properties of a variety of coal samples with different coal formation processes and different environments.Therefore,it is necessary to study the adsorption and desorption rules of the coal with the pore structure.In this paper,Pingdingshan No.10 Mine has been taken as the research object.The multi-scale,multi-faceted,and systematic analysis of the pore structure of coal samples on its adsorption and desorption rules is made.Further,the correlation between the adsorption characteristics of coal samples and their desorption rules was analyzed by using the cuttings gas desorption index which applied in the production process.This article mainly draws the following conclusions:1)The 4 coal samples of Pingdingshan No.10 Coal Mine have low natural moisture content and ash content,with volatile content between 22.12%and 23.9%,and the maximum vitrinite reflectance between 1.23%and 1.32%,which are moderately metamorphic bituminous coals.The maximum firmness cofficient both are less than 0.5,the maximum initial velocity of Ji15 coal seam is 13.6 mmHg,and the maximum of Ji16 coal seam is 15.2 mmHg.Both coal seams have coal and gas outburst danger,and the outburst danger of Ji16 coal seam is greater.2)There are discontinuous pore structures inside the two coal seam coal samples.The pores of the Ji15 coal seam coal sample are not as open and connected as the Ji16coal seam coal sample,including a large number of semi-closed holes and columnar holes.The specific surface area of micropores of four groups of coal samples accounts for 99.59%99.85%of the total surface area,and the volume of micropores accounts for 85.4%95.0%of the total pore volume.Among the 4 groups of coal samples,the structure of 2#coal samples in coal seam Ji15 is the most complex.On the whole,the pore structure of coal sample in coal seam Ji16 is simpler than that in coal seam Ji15.3)In terms of adsorption characteristics,the a of the coal sample of the Ji15 coal seam is greater than that of the Ji16 coal seam,among them,the a of 2#coal sample is the largest,which is 21.49 m3/t.In terms of desorption characteristics,the desorption performance of Ji16 coal seam coal samples is higher than that of Ji15 coal seam,among them,the desorption capacity of 2#coal samples in 120min is the largest,which is8.41m3/t at 4 MPa.4)The pores below 2 nm are adsorption pores and 2100 nm are diffusion pores.The a of coal sample is mainly affected by the pore volume and specific surface area of the adsorption pore,which increase with their increase,and the fit degree is 0.937 and0.886 respectively.And the a has a positive correlation with the fractal dimension D1,which indicates that the rougher the coal surface,the more uneven the structure,and the stronger the adsorption capacity.The initial desorption Q30 and desorption rate of coal samples are mainly affected by the pore volume of the diffusion pores,which increase with the increase of the pore volume,and the fit degree is 0.987.There is a negative correlation with the fractal dimension D2,indicating that the simpler the pore structure,the larger the initial gas desorption amount and desorption rate.5)There is a well-fit linear relationship between K1 and?h2.The values of the cuttings gas desorption index K1 and?h2 are positively correlated with the equilibrium gas pressure,and there is a well-fitted power relationship.When the other conditions are unchanged,the values of K1 and?h2 are positively correlated with the adsorption constants a and b,and increase with the increase of a and b,and are in a linear relationship with the a.In the low gas content area,the values of K1 and?h2 increase with the increase of gas content,and they are linearly related. |
PDF Full Text Request