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The weakening of hard coal–rock mass is the core common problem that is involved in the top coal weakening in hard and thick coal seams, the hard roof control during the initial mining stage in the longwall mining face, and the hanging roof control in the gob of non-coal mine. Based on the characteristics of pulse hydraulic fracturing and constant pumping rate hydraulic fracturing, a weakening method for hard coal–rock mass by combining pre-pulse and constant pumping rate hydraulic fracturing is proposed. A complete set of equipment for the combined pulse and constant pumping rate hydraulic fracturing construction in the underground coal mine is developed. The pulse and constant pumping rate hydraulic fracturing technology and equipment were applied in the top coal weakening of the shallow buried thick coal seam. Compared with no weakening measures for top coal, the average block size of the top coal caving was reduced by 42% after top coal hydraulic fracturing. The recovery rate of the top coal caving mining face reached 85%, and it increased by 18% after hydraulic fracturing.

The functioning and development of the extractive industry depends on many unusual conditions that are not found in other industries, such as the size of deposits, the level of natural and technical hazards, geographic location, or the method of mineral extraction (open pit or underground). Therefore, it is difficult to use universal development assessment methods for such specific production units. As a result, the research undertaken in this article aims to develop an indicator method for evaluating the development potential of underground hard coal mines. This method is based on a theoretical and practical analysis of the conditions of functioning of hard coal mines, expert research, and multiple case studies verifying the operation of the presented development indicator. The first part of the article is devoted to identifying and analyzing the criteria for assessing the functioning of underground hard coal mines. Next, the essence and methodology of creating and interpreting the proposed indicator was presented. The second part of the article is empirical, and contains the results of the assessment carried out using the developed indicators for five Polish hard coal mines for the years 2011–2015. The results of the research indicate that the most important factors in the development of hard coal mines relate to the geological and mining conditions, and those concerning natural hazard levels. However, during the functioning, the financial conditions and related production conditions, which ultimately determine the survival and development of underground mining plants, gain in significance.

This article presents a new, in-house developed method of selecting a variant of the transport system in the underground of a mine, using multi-variant decision support, taking into account the specificity of an underground mining plant. The implementation of the method should facilitate the selection of the most optimal transport system, ensuring continuity and the lowest operating costs. Seven functional criteria are proposed herein, which may be of a stimulant or destimulant nature. Each criterion was assigned a specific scoring weight reflecting the level of significance, with the sum of the weights being 100. The highest scores for the variants in the individual criteria go to those characterized by the following traits: the shortest transport time, the highest compatibility with the transport system already existing in the mine, transport routes with the greatest coverage communication, allow workers to be transported to the front of the excavation as quickly as possible, are most compatible with the existing transport systems in terms of the reinforcement and removal of longwalls, have a drive with the lowest operational hazard, have the least negative impact on the atmosphere of workings (exhaust gas emissions), and those that will ensure the best functioning of transport in emergency situations involving risk or uncertainty. For each criterion, a scoring formula based on specific parameters is provided. The method was used to select the optimal variant of the transport system in one of the mines, where four long walls were cut and four long galleries were drilled. Out of ten variants, the variant that should ensure the highest degree of reliable transport operation and continuity of operation has been determined using seven usability criteria.

The Polish power generation system is based mostly on coal-fired power plants. Therefore, the coal mining sector is strongly sensitive to changes in the energy sector, of which decarbonization is the crucial one. The EU Emission Trading System (EU ETS) requires power generating companies to purchase European Emission Allowances (EUAs), whose prices have recently soared. They have a direct impact on the cost efficiency of hard coal-fired power generation, hence influence the consumption of hard coal on the power sector. In this context, the objective of this paper is to estimate the hard coal consumption in various regions of Poland under selected forecasts of the EUA price. To investigate this question, two models are employed:  - the PolPower_LR model that simulates the Polish power generation system,  - the FSM _LR model that optimizes hard coal supplies. Three scenarios differentiated by the EUA price are designed for this study. In the first one, the average EUA price from 2014–2017 is assumed. In the second and third, the EUA prices are assumed accordingly to the NPS and the SDS scenario of the World Energy Outlook. In this study we consider only existing, modernized, under construction and announced coal-fired power generation units. The results of the study indicate that regardless of the scenario, a drop in hard coal consumption by power generation units is observed in the entire period of analysis. However, the dynamics of these changes differ. The results of this analysis prove that the volume of hard coal consumption may differ by even 136 million Mg (in total) depending on the EUA prices development scenario. The highest cumulated volume of hard coal consumption is observed in the Opolski, Radomski and Sosnowiecki region, regardless of the considered scenario.

Rockburst is a dynamic rock mass failure occurring during underground mining under unfavorable stress conditions. The rockburst phenomenon concerns openings in different rocks and is generally correlated with high stress in the rock mass. As a result of rockburst, underground excavations lose their functionality, the infrastructure is damaged, and the working conditions become unsafe. Assessing rockburst hazards in underground excavations becomes particularly important with the increasing mining depth and the mining-induced stresses. Nowadays, rockburst risk prediction is based mainly on various indicators. However, some attempts have been made to apply machine learning algorithms for this purpose. For this article, we employed an extensive range of machine learning algorithms, e.g., an artificial neural network, decision tree, random forest, and gradient boosting, to estimate the rockburst risk in galleries in one of the deep hard coal mines in the Upper Silesian Coal Basin, Poland. With the use of these algorithms, we proposed rockburst risk prediction models. Neural network and decision tree models were most effective in assessing whether a rockburst occurred in an analyzed case, taking into account the average value of the recall parameter. In three randomly selected datasets, the artificial neural network models were able to identify all of the rockbursts.

Poland is a country with the highest anthropogenic mercury emission in the European Union. According to the National Centre for Emissions Management (NCEM) estimation yearly emission exceeds 10 Mg. Within that approximately 56% is a result of energetic coal combustion. In 121 studied coal samples from 30 coal mines an average mercury content was 112.9 ppb with variation between 30 and 321 ppb. These coals have relatively large contents of chlorine and bromine. Such chemical composition is benefitial to formation of oxidized mercury Hg , which is easier to remove in Air Pollution Control Devices. The Hg (mercury content to net calorific value in working state) ratio varied between 1.187 and 13.758 g Hg · TJ , and arithmetic mean was 4.713 g Hg · TJ . Obtained results are close to the most recent NCEM mercury emission factor of 1.498 g Hg · TJ . Value obtained by us is more reliable that emission factor from 2011 (6.4 g Hg · TJ ), which caused overestimation of mercury emission from energetic coal combustion.

Underground coal storage bunkers serve as crucial infrastructural components in the coal mining industry, providing secure and accessible locations for the storage of mined coal. The interaction between stored coal and underground water in coal storage bunkers indeed poses significant challenges due to the unpredictable nature of the resulting coal-water mixture. This phenomenon is particularly prevalent in coal mines operating under water hazards, where groundwater infiltration into storage areas can lead to the formation of coal-water mixtures, altering the physical properties of the stored coal. The interaction between coal and water can result in the formation of coal-water mixtures (hydromixture), which exhibit complex rheological properties. These mixtures may vary in viscosity, density, and particle size distribution, making their behavior difficult to predict. Underground water may exert hydrostatic pressure on the stored coal, influencing its mechanical behavior and compaction properties. Changes in pressure can result in coal compaction or expansion, affecting bunker stability and the integrity of surrounding rock strata. The main goal of the paper was to determine the values of pressure field variations exerted by the flowing hydromixture within underground coal storage bunkers. This objective reflects a critical aspect of understanding the dynamic behavior of coal-water mixtures (hydromixture) under varying conditions, particularly in environments where water hazards pose significant challenges to storage and operational stability. The paper utilized computational fluid dynamics (CFD) methods to examine the changes in pressure within underground coal storage bunkers induced by the flow of coal-water mixtures. The examination of damage to an underground coal storage bunker due to stress distribution was conducted using the finite element method (FEM). This computational technique is widely utilized in engineering and structural analysis to model complex systems and predict the behavior of materials under various loading conditions The results of the CFD numerical simulation were compared with the mathematical models.

Due to the poor cavability of top coal, the connection between the high-level gas drainage lane and the gob is not sufficient during the initial mining stage in a extra-thick coal seam with hard roof and hard coal in longwall top coal caving. The gases gathering in the gob area will suddenly release and cause extrusion when the upper roof first collapses and falls, which will result in gas overrunning and affecting the safety production. Based on the propagation law of hydraulic fractures and the cause of gas overrunning, a new technology was put forward to solve the gas overrunning during the initial mining stage in longwall top coal caving operations. A method for designing the drilling hole parameters for hydraulic fracturing was formed. Hydraulic fracturing was carried out in the measure lane to weaken the top coal and roof and induce the mining pressure to break coal; through this the cavability of the top coal and roof could be improved. Simultaneously, the connection between the gob and the high-level gas drainage lane, and the permeability of the coal seam, could be improved; moreover, the gas drainage effect could be enhanced. The field test in the Tashan Coal Mine indicated that the high-level gas drainage lane was completely connected with the gob after hydraulic fracturing when the working face advanced 15 m, and the gas concentration at the upper corner of the working face was maintained at a level of 0.3% during the initial mining stage. Furthermore, the gas overrunning during the initial mining stages was avoided, and safety was guaranteed.

The European Union’s climate policy and the energy transition associated with it force individual countries, their economies and their industrial sectors to carry out thorough changes, often of a deep, high-cost and restructuring nature. The aim of the article is to provide a multidimensional assessment of the forms and effects of the restructuring of coal mining companies in Poland in light of the current energy transition process. The research problem is encapsulated within the following two interdependent questions: Has the restructuring process allowed the coal mining industry to achieve sufficient efficiency to sustainably compete in the open market, and to what extent, if at all, have the objectives of restructuring been achieved from the perspective of changes in the energy mix? The research covers all coal mining companies included in the official statistics. It adopts a long-term perspective (1990–2020), dating from the beginning of the systemic transformation in Poland. The research involved the use of multivariate financial analysis methods, including the logit model for predicting the degree of financial threat, as well as taxonomic methods for assessing the dissimilarity of structures and their concentration. The general conclusion of the research is that there has been a lack of consistency (follow-up) between the forms and effects of restructuring in coal mining companies in Poland on the one hand and changes in the composition of the country’s energy mix as a result of the energy transition on the other. In particular, this means that such restructuring, being neither effective nor efficient, has failed to accelerate change in the energy mix.

Coal seam drilling for pressure relief is one of the most widely adopted measures to mitigate rock bursts. However, conventional drilling methods exhibit limited effectiveness in hard coal seams and may compromise the integrity of roadway support structures. To optimize traditional pressure relief drilling parameters, this study investigated the influence of coal seam strength and borehole diameter on pressure relief efficiency based on elastoplastic mechanics theory. A novel mechanical reaming technology for pressure relief and rock burst prevention in hard coal seams was developed and subjected to field trials. Multiple monitoring techniques were employed to evaluate its performance in terms of both pressure relief and support stability. The conclusion was drawn that: (1) The higher the strength of the coal seam, the smaller the radius of the plastic zone of the borehole; therefore, the pressure relief effect of the borehole in the hard coal seam is poor. After increasing the diameter of the borehole, the radius of the plastic zone increases, but when the diameter of the borehole increases to 300 mm, the increasing trend of the radius of the plastic zone weakens. Thus, only increasing the diameter of the borehole cannot improve the pressure relief effect of the borehole without limit. (2) An innovative hard coal seam pressure relief and anti-impact technology, termed support, deep pressure relief, unloading-support coupling, the elastic energy accumulated in the coal body through a deep large borehole while utilizing a shallow small borehole to maintain the bearing capacity of the support structure, thereby achieving a balance between pressure relief and support. (3) In comparison to conventional drilling areas, the volume of coal seam drilling powder in the mechanical reaming area has increased by 3.1 times, and the number of per meter has risen by 70%, significantly enhancing the pressure relief effect. Additionally, the anchoring force of the roof anchor cable in the mechanical reaming area has decreased by up to 29%, the variation in tension of the anchor cable on the sides has been reduced by up to 51.8%, the convergence of the two sides of the roadway has diminished by up to 63%, the convergence between the roof and floor has decreased by up to 51%, and both the stress on the support structure and the deformation of the surrounding rock have been significantly reduced. These research findings provide a theoretical foundation and technical support for the prevention and control of rock bursts in similar hard coal seam mining roadways.