The paper presents the variability of hard coal output, methane content and methane emissions into coal workings and into the atmosphere from the two most methane-gassy coal mines in Poland. The Budryk mine is one of the youngest mines in Poland, but it is the most methane-gassy as well. In 2016, the total CH₄ emissions exceed 140 million of m³. This large increase in methane emissions to mine workings is primarily related to the increase in the depth of coal extraction (up to 1290 m) and, consequently, the rapid increase in the methane content in coal seams (up to 10–12 m³/Mg coal^daf). On the other hand, in the Pniówek mine, methane emission was the highest at the beginning of the study period (1986–1991). During the following years, emission decreased to the values of less than 140 million of m³, which were still one of the largest amounts of emitted methane in the entire Upper Silesian Coal Basin. The coexistence of natural factors, such as the geological structure and gas distribution, as well as mining-related factors, i.e. the depth of mining, the intensity of coal extraction determines the temporal variability of methane emissions in the studied mines.

Methane emissions into mine workings and the atmosphere are still a significant environmental and work safety problem. Since 2000, the Rydułtowy coal mine, located in the western part of the Upper Silesian Coal Basin, has been struggling with significant methane emissions compared to the previous period. The distribution of the methane content in coal seams was analysed, and the factors that influenced it were reviewed. Then, the annual variability in methane emissions in mining excavations was investigated, and the depth of coal extraction was linked to methane conditions and the time of mining works. It has been shown that the currently observed distribution of methane in coal seams is the result of, inter alia, the geological development of the western part of the basin, the lithological character of coal-bearing Carboniferous deposits and overburden, and fault tectonics. The sorption capacity of coal seams decreases with increasing temperature and the coal rank. The amount of methane emitted into mine workings depends mainly on the methane content in the coal seams in mining sites and on the sorption capacity of the coal seams. The depth of exploitation, increasing from year to year, leads to an increase in the methane content in coal seams and a simultaneous decrease in the sorption capacity of coal, which will result in higher methane emissions in the future.

The Upper Silesian Coal Basin (USCB) is the largest coal basin in Poland and one of the largest in Europe. It is the most industrialised region in the country. The main natural source of energy is hard coal, which was produced by 65 mines in the early nineties. The USCB geology is very diverse...

Between 1997 and 2016 we observed important changes in hard coal extraction and methane emission in the Upper Silesian Coal Basin. Hard coal extraction in the near future will be very dangerous because it will be necessary to reach deeper methane-rich coal seams. Permanent monitoring of the volume of emitted and captured methane is necessary to combat the methane hazard. The predictability of gaseous hazards are important in order to keep underground work safe. We gathered and analysed data from three coal companies: Katowice Coal Holding, the Coal Company, Jastrzębie Coal Company and in the whole of the Upper Silesian Coal Basin for the last twenty years and this allowed us to notice changes and CH ₄ trends in ventilation emission and demethanation. There is a decrease in the extraction of hard coal from year to year. At the same time there is an increase in the total methane emissions which forces actions aimed to effective contracting the methane hazard. Specifically, methane emission has been increasing for years, making hard coal extraction very dangerous. We observed increases in CH ₄ vent emission and volume of methane coming from underground drainage systems. Much more methane is released during hard coal extraction at deeper mine levels. Throughout the entire research period the methane hazard increased. Therefore, the development of modern technologies for methane capturing should contribute to improvement of hazardous conditions for coal mining in the basin.

The paper presents the variability of methane emissions in mining excavations in the Brzeszcze mine (Poland) against the background of hard coal output, geological and mining factors. The geological structure of the Upper Silesian Coal Basin (USCB) is very diverse. The Brzeszcze coal deposit is located close to the large and permeable Jawiszowice fault which increases the methane hazard during mining activities performed close to this fault. The overall decrease in hard coal output (1988–2018) has coincided with a rapid increase in methane emissions (1997–2018). Throughout the study period, hard coal output decreased threefold from 3.9 to 1.2 million Mg annually. Coal extraction in high methane content beds (e.g. 510, 405/1, 364, 352) increases the total methane (CH4) emission into mining excavations, aggravating the methane hazard due to the high explosiveness of the gas. To protect miners, coal workings need to be continuously ventilated, taking the harmful gas out of the mine (ventilation air methane emission) or methane needs to be captured by underground methane systems (degassing). Every year, over 34 million m3 of CH4 is captured by the drainage systems and over 70 million m3 CH4 (average) is discharged through ventilation shafts into the atmosphere. The presence of the large, permeable regional dislocation, the Jawiszowice fault zone, shaped the methane concentration in the fault vicinity, when the highest methane emissions during coal mining was studied.

The gravimetric method for determining coal gas sorption has many advantages and limitations. The article presents the influence of various factors on the results of methane sorption on coal. In mining practice, in addition to sorption properties of coal, knowledge of methane sorption capacity and effective diffusion coefficient determined when assuming a unipore sorption/desorption model are crucial for predicting sudden releases of methane from coal seams to a mine ventilation environment. In Poland, determining sorption capacities of coals for methane is mandatory when starting mining operations in new parts of coal deposits threatened by outbursts. Traditionally, gravimetric microbalances, such as intelligent gravimetric analysis (IGA), are used to determine adsorption capacity and desorption rate. Recently, newer microbalances XEMIS have been introduced to the market. Two gas laboratories, AGH in Krakow and CLP-B in Jastrzebie-Zdroj, respectively, compared experimental adsorption isotherms using XEMIS microbalances with mutually exchanged coal samples. Both sorption capacity at the pressure of 1 bar ($a_{1bar}$) and effective diffusion coefficient ($D_e$) were independently determined for the coal samples tested. The results obtained are comparable despite the use of different microbalance XEMIS models. The conducted studies and comparative evaluation of the results allowed for assessing procedures for determining sorption properties using XEMIS microbalances. The exchange of laboratory experiences also allowed for the identification of methodology factors crucial for the development of a uniform procedure for conducting similar studies with XEMIS microbalance. The proposed factors for testing the sorption behavior of methane in coal structures may be helpful in mining practice.