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The course and results of experimental studies of efficient methane separation from mining gases mixture, performed at a pilot plant, are presented in the paper. It was indicated and justified that appropriate modifications should be realized in the vacuum pressure swing adsorption (VPSA) method along with (PSA) method for improving of efficient technology of methane recovery from coal mine methane gas. Those studies were preceded by experiments at laboratory scale. The results of experiments at pilot scale created bases for preliminary assumptions for the planned project of industrial scale installation. The pilot plant was made in the Coal Mine "Pniówek" J.S.W. S.A., Silesian Basin, Poland, where in the raw gas from drainage methane gas from coal beds are: on average about 53 vol% CH 4 , as well as nitrogen, oxygen and carbon dioxide. On the basis of experimentally established optimum work conditions of the pilot plant the gas was enriched forming the methane-rich gas 96 vol% CH 4. Then the efficiency of methane separation reached 90-92% while the re-circulated methane to feed gas ratio changed within q=1.0-1.2. High-methane gas of such good quality, obtained at so high recovery efficiency, can be introduced to the high-methane gas network.

Methane sorption capacity is of significance in the issues of coalbed methane (CBM) and depends on various parameters, including mainly, on rank of coal and the maceral content in coals. However, in some of the World coals basins the influences of those parameters on methane sorption capacity is various and sometimes complicated. Usually the rank of coal is expressed by its vitrinite reflectance Ro. Moreover, in coals for which there is a high correlation between vitrinite reflectance and volatile matter Vdaf the rank of coal may also be represented by Vdaf. The influence of the rank of coal on methane sorption capacity for Polish coals is not well understood, hence the examination in the presented paper was undertaken. For the purpose of analysis there were chosen fourteen samples of hard coal originating from the Upper Silesian Basin and Lower Silesian Basin. The scope of the sorption capacity is: 15-42 cm3/g and the scope of vitrinite reflectance: 0,6-2,2%. Majority of those coals were of low rank, high volatile matter (HV), some were of middle rank, middle volatile matter (MV) and among them there was a small number of high rank, low volatile matter (LV) coals. The analysis was conducted on the basis of available from the literature results of research of petrographic composition and methane sorption isotherms. Some of those samples were in the form (shape) of grains and others - as cut out plates of coal. The high pressure isotherms previously obtained in the cited studies were analyzed here for the purpose of establishing their sorption capacity on the basis of Langmuire equation. As a result of this paper, it turned out that for low rank, HV coals the Langmuire volume VL slightly decreases with the increase of rank, reaching its minimum for the middle rank (MV) coal and then increases with the rise of the rank (LV). From the graphic illustrations presented with respect to this relation follows the similarity to the Indian coals and partially to the Australian coals.

The changes in the permeability of coal-bed reservoirs with methane, as associated with gas depletion, are the consequence of two opposing processes, namely geomechanical compaction that narrows down fractures, and matrix shrinkage, which, in turn, widens fractures. Many previous studies on the effects of these processes have emphasised, albeit not always, the circumstances and conditions that led to a greater coal permeability, with a natural decrease in the pore pressure of methane during its production, and, in consequence, to an increase in the cumulative volume of this gas. However, in some coal basins, there are beds where the methane production has failed to reach the appropriate level, whether in economic or engineering terms. This paper identifies some reasons for the failed attempts at well exploration of gas from such coal beds. Specifically, it describes seven parameters to be considered in relation to CBM, including geomechanical parameters such as Young's modulus, Poisson's ratio, and the initial porosity, which define coal cleat compressibility, a very important parameter, and parameters related to methane desorption, i.e., desorption-induced volumetric strain, the Langmuir pressure, and the initial pressure of gas within the bed. In addition to cleat compressibility, there are other, equally important parameters, such as the rebound pressure and recovery pressure, which are defined by the following parameters in order of importance: Young's modulus, desorption-induced volumetric strain, initial pressure of methane, the Langmuir pressure, and Poisson's ratio. To assess the impact of these parameters on changes in permeability, we used the Cui-Bastin model. The simulation results were analysed to allow us to present our findings.There are two important processes related to reservoir pressure depletion, which have opposing effects on in-situ coal permeability [5][6][7]. The first is a geomechanical phenomenon where cleats narrow down as a result of increased effective stress. The second, occurring mainly at a later stage of production, is the widening of the cleats due to coal matrix shrinkage caused by methane desorption. When this matrix shrinkage is greater than the compaction of coal, there is an increase in permeability, which, in turn, facilitates a constant deliverability of methane. The processes described above are mainly observed in the bituminous coals. In the case of coals with a vitrinite reflectance above 2%, the shrinkage/swelling effect is lost.The geomechanical properties of coal are represented by such parameters as Young's modulus E, Poisson's ratio v, and the associated cleat compressibility c f . The matrix shrinkage as a result of desorption is represented by the coal maximum strain at an infinite pressure ε l and the Langmuir pressure P L , which is found in an equation similar to the Langmuir equation. Other important parameters include the cleat porosity φ and the initial pressure of methane P o [1,3]. The values of these and other parameters are determined on the basis of la...