Study on the Adsorption Mechanism of Gas of Deep Coal Seams Based on the Characteristics of the Coal Pore Fractal Medium

Although the porosity of coal possesses statistical fractal characteristics, the relationship between the characteristics of the coal pore fractal medium and its characteristics of adsorption thermodynamics and dynamics remains unclear. Therefore, in this study the lignite of the Beizao Mine, fiery coal of the Caiyuan Mine, coking coal of the Xiqu Mine, and anthracite of the Guhanshan Mine were selected as the research coal samples to carry out coal adsorption of CH₄ experiments under the conditions of high temperature high pressure and equilibrium water. The Fractal-Langmuir model of adsorption based on the characteristics of the coal pore fractal medium was established based on the experimental data. The characteristics of the coal pore fractal medium and its adsorption law on the CH₄ and adsorption regulatory mechanism were analyzed based on the above. The research results demonstrated that the established Fractal-Langmuir adsorption model had universal theoretical significance, and its precision was high. In addition, the fractal Langmuir volume (V_F-L ) of lignite decreased with the increase of temperature; the V_F-L of coking coal increased with the increase of temperature; and the V_F-L of fiery coal and anthracite first increased then decreased with the increase of temperature. The increment rate of change of adsorption capacity increased with the increase in the grade of coal, indicating that the adsorption capacities of the different metamorphic degrees of coal were different, and the required pressures for reaching saturation adsorption were also different. If the grade of the coal was high, then the required pressure for reaching saturation adsorption was high as well. Under the same pressure conditions, the effects of different grades of coal, temperature and moisture on the adsorption of coal were different. The effect of temperature on the adsorption of lignite was greater than that of moisture; the effect of temperature on the adsorption of coking coal was less than that of moisture; and the effects of temperature and moisture on the adsorption of fiery coal and anthracite were as follows: the effect of temperature was less than that of moisture when the temperature transitioned from 30°C to 40° C, while the effect of temperature was greater than that of moisture when the temperature transitioned from 40°C to 50°C.