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Analysis of the application of methane-bearing capacity test methods in the conditions of Polish mining

Karbownik Marcin

Journal of Sustainable Mining

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2022

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Vol. 21, iss. 4

309--318

EN

The methane hazard is one of the natural hazards occurring in hard coal mining. The content of natural methane in hard coal seams, the so-called methane-bearing capacity, is one of the key parameters that allow for proper assessment of the methane hazard and the state of the threat of gas and rock outbursts. For safety purposes, there is a constant need to improve the methods for the determination of this parameter. In the conditions of Polish mining, the method used for methane-bearing capacity determination is the direct drill cuttings method. This paper contains a comparative study presenting three different methods of methane-bearing capacity determination. Tests were conducted using two direct methods (the drill cuttings method and the United States Bureau of Mines (USBM) method), and the indirect method based on the desorption intensity index. On the basis of the obtained test results, it was found that the results obtained with the USBM method were slightly higher than those obtained with the direct drill cuttings method. Gas losses, an important element affecting the final value of the assay, were also analysed. This comparative study will evaluate the validity and applicability of the above methods under specific conditions in hard coal mining.

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The unipore and bidisperse diffusion models for methane in hard coal solid structures related to the conditions in the Upper Silesian Coal Basin

Karbownik Marcin, Krawczyk Jerzy, Schlieter Tomasz

Archives of Mining Sciences

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2020

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Vol. 65, no. 3

591--603

EN

The safety of mining operations in hard coal mines must be constantly developed and improved. There is ongoing multi-directional research focused at best recognition of the phenomenon associated with the properties of the coal-gas system and its connections with mining and geological conditions. This article presents the results of sorption experiments on coals from the Upper Silesian Coal Basin, which are characterized by varying degrees of coalification. One of the parameters that describes the kinetics of methane sorption, determining and providing valuable information about gas hazard and in particular the risk of gas and rock outbursts, is the effective diffusion coefficient De. It is derived from the solution of Fick’s second law using many simplifying assumptions. Among them is the assumption that the carbon matrix consists of only one type of pore-micropores. In fact, there are quite often at least two different mechanisms, which are connected to each other, related to the diffusion of methane from the microporous matrix and flows occurring in voids and macropores. This article presents both the unipore and bidisperse models and a set of comparisons which fit them to experimental curves for selected coals. For some samples the more complex bidisperse model gave much better results than the classic unipore one. The supremacy of the bidisperse model could be associated with the differences in the coal structure related to the coalification degree. Initial results justify further analyses on a wider set of coals using the methodology developed in this paper.

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Tests of methane desorption and emission from samples of hard coal in the context of mine closures through flooding

Krause Eugeniusz, Karbownik Marcin

Journal of Sustainable Mining

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2019

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Vol. 18, iss. 3

127--133

EN

Forecasts of methane emissions during and after flooding a closed gassy hard coal mine and the evaluation of possible methane migration to the surface in post-mining areas, after cutting off the vertical ventilation workings of hard coal mines from the surface, provide valuable information which can help to ensure public safety. This article presents research into the influence of changes in the hydrostatic pressure of a water column in a flooded mine on the volume of methane emission and migration from hard coal seams, during and after the flooding of a closed mine. The tests were conducted based on a modified research method developed by the French National Institute for Industrial Environment and Risks (INERIS), France, and the Central Mining Institute (GIG), Katowice, Poland. A test stand for gas desorption and autoclaves for emissions, under controlled pressure and temperature, were used. The tests were conducted and changes in pressure in the autoclaves over time were observed. The observations led to the conclusion that water inhibits methane desorption and emission from coal to varying extents, depending on the hydrostatic pressure exerted. Based on the conducted tests, developed a model of methane emission into flooded goafs was developed. A method of determining index k2 was also developed, which lowers the forecast volume of methane emission into goafs depending on the value of the hydrostatic pressure of the water column and the level of submersion. Results of the tests form the basis to calculate forecasts in the developed model of methane emission into the goafs of a mine during its closure, which, as a consequence, enables the identification of the level of methane hazard and the selection of preventive measures aimed at combating methane hazard during and after the closure of a gassy mine.