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

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.