ASSESSSMENT OF THE SORPTION EQUILIBRRIUM OF METHANE DURING ITS GENERATION IN A COAL SEAM
Authors:   N.S. Polyakov Institute of Geotechnical Mechanics under the National Academy of Sciences of Ukraine (IGTM, NASU), Minieiev Serhii , Prusova Alla ,   N.S. Polyakov Institute of Geotechnical Mechanics under the National Academy of Sciences of Ukraine (IGTM, NASU), Yanzhula Oleksii ,   Capital Construction and Investments of the Coal Directorate of JV LLC “Metinvest Holding”, Minieiev Oleksandr ,   National Technical University Dnipro Polytechnic
Published: January 2023

Purpose. Study the adsorption equilibrium of adsorbed during the generation of methane in coal massif to determine the conditions for its implementation at different depths of mining operations. Methods. The thermodynamic research methodology, numerical calculation methods, mathematical processing of research results using approximation methods. Results. The entropy change of the «adsorbed methane – coal» system shows that the initial state of adsorbed methane during its generation in a coal seams determined by the depth of the seam and the degree of filling of its pores with methane. The results of the calculation showed, that the sorption equilibrium of the “methane – coal” system in the mountain massif is energetically most probable at the degree of filling of the pores with methane, which is θ = 40%. When θ < 40 % an irreversible spontaneous process of adsorption of methane by coal occurs, but when θ > 40% – its desorption, the degree intensity of which can be estimated by the ratio obtained in the work. It has been established that at the depth of the coal seam there is only low-intensity process, and at Н > 500 m – the process is more intensive. Therefore, when methane is generated at depths of Н < 500 m, it is likely that due to weak desorption and high sorption bond energy, the pores tend to be filled with methane almost completely. When Н > 500 m they tend to sorption equilibrium, so they are filled with methane by only 40%. The rest of the volume of gas generated in the coal seam at depths greater than 500 m, as a result of an intensive desorption process, migrates into the intervening rock seam. Scientific novelty. As opposed to a priori accepting opinions about what the initial state of methane adsorbed in coal is always characterized by the complete filling of pores with gas, numerical calculations dedicated to this issue have been performed for the first time in the paper. Calculations are based on modern ideas about the generation of methane in coal with the help of the separation of methyl group and hydrogen atoms from aliphatic fringes, which combine to form methane molecules. At the same time, the dependence of the change in the entropy of the “adsorbed coal – methane” system on the depth of occurrence and the degree of filling of its pores with methane during the generation of methane in the coal seam has been established. Practical significance. The research results make it possible to obtain fundamentally new regularities of the processes of mass transfer and filtration of methane in the mountain massif at great depths. The use of new laws makes it possible to adjust the existing technologies of mine ventilation and methods of safe mining operations in emission-hazardous and highly gas-bearing coal seams, to develop fundamentally new technologies in this direction, as well as to make more accurate calculations of methane reserves in various rocks of the mountain massif.