Methane is accompanied by most of the coal deposits. The methane hazard is excessive content of this gas in the mining excavations. This is a source of high risk security and continuity of the mine. The Piast–Ziemowit is the only non-methane mine in the Polish Mining Group. In 2015, 66,4% of the coal mined in Kompania Węglowa S.A. mines comes from methane coal seams. Methane drainage is the most effective but very costly method of combating methane hazard.The costs of prevention and eradication of methane hazard is charged to the costs of coal mining. Therefore, performance of methane drainage in the mines of the Polish Mining Group is adapted to the scale of the methane hazard. The article presents an analysis of the costs of prevention of methane hazard for mines with different absolute methane and its impact on the level of these costs.

Methane explosions are among the greatest hazards in the Polish coal mining industry and unfortunately continue to cause many catastrophes. The constant growth of the depth of coal exploitation in the conditions of the high concentration of mining causes the increase of absolute methane content and methane seam pressure from the mined seams. This situation directly affects the increase in the level of methane hazard in the underground work environment. It is therefore obvious to undertake intensive research that will allow for the development of appropriate solutions that help to exclude the risk of mining catastrophes resulting from the ignition and/or methane explosion. In addition to the development of methane hazard prevention methods, an indispensable element of this approach is a very accurate identification of the mechanisms of the combustion and explosion of this gas. The article presents the method of investigation and examples of results of methane explosions carried out in the 400 m experimental gallery of the Experimental Mine “Barbara” of the Central Mining Institute – the only large scale underground experimental facility in Europe. A n analysis has been performed of the influence of the methane release into mining workings on the distribution of the gas concentration and on the course of its explosion or combustion. The data collected characterizes thermodynamic phenomena that form the basis for determining the level of the explosion hazard. Large scale studies have also allowed to assess the risk of conditions that are sufficient for the development of a coal dust explosion initiated by methane explosions. The large scale of the experiments and the system of continuous recording of the course of the experiments allowed the specific characteristics of the methane explosion and burning in underground mining workings to be identified and isolated. For the first time, the course of experiments was recorded via a camera system deployed along the gallery.

This paper presents mathematical models enabling the calculation of the distribution and patterns of methane inflow to the air stream in a longwall seam being exploited and spoil on a longwall conveyor, taking into account the variability of shearer and conveyor operation and simulation results of the mining team using the Ventgraph-Plus software. In the research, an experiment was employed to observe changes in air parameters, in particular air velocity and methane concentration in the Cw-4 longwall area in seam 364/2 at KWK Budryk, during different phases of shearer operation in the area of the mining wall in methane hazard conditions. Presented is the method of data recording during the experiment which included records from the mine’s system for automatic gasometry, records from a wireless system of eight methane sensors installed in the end part of the longwall and additionally from nine methane anemometers located across the longwall on a grid. Synchronous data records obtained from these three independent sources were compared against the recording the operating condition of the shearer and haulage machines at the longwall in various phases of their operation (cleaning, cutting). The results of the multipoint system measurements made it possible to determine the volume of air and methane flow across the longwall working, and, consequently, to calculate the correction coefficients for determining the volume of air and methane from measurements of local air velocity and methane concentration. An attempt was made to determine the methane inflow from a unit of the longwall body area and the unit of spoil length on conveyors depending on the mining rate. The Cw-4 longwall ventilation was simulated using the data measured and calculated from measurements and the simulation results were discussed.

A mathematical model for the purposes of methane hazard assessment in mines was developed in the Central Mining Institute as part of the statutory activities conducted in 2017 and 2018. The model describes the course of kinetics of methane sorption on coal samples while taking into account the diffusion coefficient. The paper presents the formulas describing the mathematical model of methane emission from coal sidewall to longwall working, taking into account the sorption properties of coal – sorption capacity of coal (related to methane) and the effective diffusion coefficient of methane in coal. In the light of the conducted research, such a methodology for describing this phenomenon enables a more precise determination of the amount of methane released to the longwall from the exploited coal seam, which in turn makes it possible to select appropriate methane prevention measures.

In longwall absolute methane emission rate forecasting, the range of the destressing zone is determined empirically and is not considered to be dependent on the geomechanical parameters of the rock strata. This simplification regarding destressing zone determination may result in significant differences between the forecast and the actual methane emission rates. During the extraction of coal seams using a system involving longwalls with caving under the conditions of low rock mass geomechanical parameters, the absolute methane emission rate forecasts are typically underestimated in comparison to the actual methane emission rates.

In order to examine the influence of the destressing zones on the final forecasting result and to assess the influence of the rock mass geomechanical parameters on the increased accuracy of forecast values, destressing zones were determined for three longwalls with lengths ranging from 186 to 250 m, based on numerical modelling using the finite difference method (FDM). The modelling results confirmed the assumptions concerning the upper destressing zone range adopted for absolute methane emission rate forecasting. As for the remaining parameters, the destressing zones yielded great differences, particularly for floor strata. To inspect the accuracy of the FDM calculation result, an absolute methane emission rate forecasting algorithm was supplemented with the obtained zones. The prepared forecasts, both for longwall methane emission rates as well as the inflow of methane to the longwalls from strata within the destressing zone, were verified via underground methane emission tests. A comparative analysis found that including geomechanical parameters in methane emission rate forecasting can significantly reduce the errors in forecast values.

The methane hazard is one of the most dangerous phenomena in hard coal mining. In a certain range of concentrations, methane is flammable and explosive. Therefore, in order to maintain the continuity of the production process and the safety of work for the crew, various measures are taken to prevent these concentration levels from being exceeded. A significant role in this process is played by the forecasting of methane concentrations in mine headings. This very problem has been the focus of the present article. Based on discrete measurements of methane concentration in mine headings and ventilation parameters, the distribution of methane concentration levels in these headings was forecasted. This process was performed on the basis of model-based tests using the Computational Fluid Dynamics (CFD). The methodology adopted was used to develop a structural model of the region under analysis, for which boundary conditions were adopted on the basis of the measurements results in real-world conditions. The analyses conducted helped to specify the distributions of methane concentrations in the region at hand and determine the anticipated future values of these concentrations. The results obtained from model-based tests were compared with the results of the measurements in realworld conditions. The methodology using the CFD and the results of the tests offer extensive possibilities of their application for effective diagnosis and forecasting of the methane hazard in mine headings.