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The topic of waste combustion/co-combustion is critical, given the increasingly restrictive legal regulations regarding its environmental aspects. In this paper, the authors present the test results of selected fuels of different compositions: hard coal, coal sludge, coke waste, sewage sludge, paper waste, biomass waste and polymer waste. The authors conducted a proximate and ultimate analysis of the materials and mercury content in them and their ashes. An interesting element of the paper was the chemical analysis of the XRF of the fuels. The authors conducted the preliminary combustion research using a new research bench. The authors provide a comparative analysis of pollutant emissions—especially mercury emission—during the combustion of the material; this is an innovative element of this paper. The authors state that coke waste and sewage sludge are distinguished by their high mercury content. The value of Hg emission during the combustion depends on the initial mercury content in the waste. The results of the combustion tests showed the adequacy of mercury release compared to the emissions of other compounds considered. Small amounts of mercury were found in waste ashes. The addition of a polymer to 10% of coal fuels leads to a reduction in mercury emissions in exhaust gases. [ABSTRACT FROM AUTHOR]

Moisture content of rock/coal can change its mechanical properties and absorption capacities, which can directly affect gas diffusivity, change the stress distribution and hence cause significant impacts on the overall gas or coal extraction process. Observation of the water penetration process and water distribution in the coal matrix will be beneficial for the understanding of the fluid-solid coupling mechanism in hydraulic fracturing, aquifer cracking and coal seam infusion. However, the observation of water penetration process and the determination of water distribution mode were hard to be non-destructively achieved as coal is a non-uniform, inhomogeneous and un-transparent material. µ-CT imaging, which is based on variation of X-ray attenuation related to the density and atomic composition of the scanned objects, enables a four-dimensional (spatial-temporal) visualise of the heterogeneous and anisotropic coal samples. The primary aim of this paper is extending the application of µ-CT imaging to explore the moisture penetration and distribution within coal samples during water infusion process, which has been reported by very little literature. The working principle and procedures of CT imaging was firstly introduced. Then, the determination equation of moisture distribution based on density profile was established. The CT determined moisture content has been compared with weighting method for verification. The paper has demonstrated that µ-CT can be used for non-destructively imaging the moisture distribution within coal samples. [ABSTRACT FROM AUTHOR]

A high static load state significantly increases the risk of rock burst occurrences on the island working face, posing a significant threat to the safety of coal mine production. This paper focused on the engineering background of the 8204-2 working face at Tashan Coal Mine. Field research indicated that there were noticeable differences in the frequency of coal bursts in different regions and working face ranges, with the mine pressure being complex and severe. Through theory analysis, the stress concentration degree of the island working face was mainly affected by the buried depth, working face length, gob length, coal seam thickness, and coal pillar width. The stress distribution and plastic zone changes of the island working face, influenced by different factors, were studied by numerical simulation. The entity coal stress equation of the island working face was fitted and the mechanism of rock burst in the island working face was revealed. The research findings presented in this paper provide important theoretical support and technical guidance for the safe and efficient mining of island working faces. [ABSTRACT FROM AUTHOR]

This paper presents the results of the research on the structure and thermal properties of materials made from fly ash based on high-density polyethylene (HDPE). Composites based on a polyethylene matrix with 5, 10, and 15 wt% fly ash from hard coal combustion content were examined. Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) was used to identify characteristic functional groups present in the chemical structure of polyethylene and the composites based on its matrix. Structural analysis was performed using X-ray diffraction (XRD), a differential scanning calorimeter (DSC), and microscopic examinations. Mechanical properties were also examined. Analysis of the thermal effect values determined by the DSC technique, XRD, and FTIR-ATR allowed the evaluation of the crystallinity of the tested materials. Polyethylene is generally considered to be a two-phase system consisting of crystalline and amorphous regions and is a plastic characterized by a significant crystalline phase content. Based on the FTIR-ATR spectra, DSC curves, and XRD, the effect of the filler and the changes occurring in the materials studied resulted in a decrease in the degree of crystallinity and a change in the melting point and crystallization temperature of the polymer matrix were established. Microscopic examinations were carried out to analyze the microstructure of the composites to collect information on the distribution and shape of the filler particles, indicating their size and distribution in the polymer matrix. Furthermore, the use of scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS) allowed for the microanalysis of the chemical composition of the filler particles. [ABSTRACT FROM AUTHOR]

This article presents abstracts of papers presented at the 60th annual meeting of the Association of American Geographers held in Syracuse, New York, on March 29, 1964 to April 1, 1964. The intention of the paper "Changing Markets and Modes of Transportation for Coal: A Survey" is to acquaint geographers with changes in the coal industry and attempted changes in transporting coal to electric power plants. The paper "The Electricity Industry of British Columbia since 1950" constitutes a brief description of the production, transmission and consumption phases of the electricity industry of British Columbia. The paper "The Pennsylvania Anthracite Industry--A Status Report" attempts to update the image of the Pennsylvania anthracite-mining industry among members of the geographical profession.

The work presents a detailed analysis of the possibilities of the thermal processing of clay raw material granulates in a fluidized bed reactor powered by coal fuel. Potential customers of calcined granulates include the following: plants producing refractory materials for the steel industry, producers of refractory concrete, sanitaryware plants, tile plants, large-size tile plants, industry abrasives, chemicals, paints, paper, food and medical industries and others. The advantage of the presented fluid bed calcination technology is the possibility of the continuous operation of the reactor and the short time of the material in the bed, compared to the previously used methods of calcination in a shaft and rotary kiln, which lasts less than twenty minutes in the temperature range of 650–850 °C. During the experimental studies of calcination in the fluidized bed layer, the influence of the type of coal, its particle size and the mass share of coal in the feed mixture on the calcination process and the final product obtained was analysed. As a result of the conducted research, it was proven that solid fuels such as anthracite and steam coal type 31.2 (flaming) can be successfully used in the fluidized bed calcination process of clay materials. The key parameter determining the fluidized bed calcination process is the fuel particle distribution. [ABSTRACT FROM AUTHOR]

Shallow-buried, hard, and extra-thick coal seams are very common in Xinjiang, China, but there are relatively few studies on the mine pressure law and the development characteristics of water-flowing fracture zones (WFFZs) during the mining of such coal seams. In this paper, the mine pressure of the top coal caving face in a shallow, hard coal seam with a hard roof and full bedrock (SHCSHRFB) is analysed, the laws of the surrounding rock deformation and stress of the open-off cut and roadway in the large-mining-height top coal caving face are studied, the characteristics of roof-breaking and overburden fracture development are analysed using the physical similarity simulation method, supporting suggestions for roadways are put forward, and three development stages of the WFFZ are analysed. Field monitoring shows that the hydraulic support stress in SHCSHRFB is weak, but the coal wall and roadway stability are good, which is significantly different from the results in the typical shallow-buried thin bedrock working faces. The measured height of the WFFZ is close to the physical similarity simulation results, but quite different from those arising from use of the empirical formula. [ABSTRACT FROM AUTHOR]

The issue of transport in underground hard coal mines is very rarely described in the literature. The financial aspects of this issue are even less often analyzed. Publications in this area focus on technical issues and the safety of mining crews. More attention is paid to transport in open-pit mines. The above premises and practical needs imply the need to conduct economic analyses of transport systems in underground hard coal mines. This paper is a scientific communication, which presents the concept of a multi-criteria cost analysis as a tool to support the selection of the optimal transportation option in an underground hard coal mine. Considerations in this area have not been carried out in the relevant literature, and the problem of selecting a transportation option is a complex and necessary issue in the practice of underground mines with extensive mine workings. The methodology presented includes five cost criteria (costs of carrying out the transportation task; route expansion costs; rolling stock maintenance costs; depreciation costs; and additional personnel costs). The simultaneous application of criteria relating to utility properties in addition to cost criteria makes it possible to adopt a specific technical and organizational model of the transportation system based on the indication of the optimal solution, resulting from the mathematical construction of functions of objectives relating to utility and cost. The optimal variant of the designed system and configuration of the material transportation system in underground workings takes into consideration the following: (1) seven utility criteria (KU1—transportation task completion time; KU2—compatibility of transportation systems; KU3—continuous connectivity; KU4—co-use with other transportation tasks; KU5—safety; KU6—inconvenience; KU7—operation under overplanning conditions) and (2) five cost criteria (KK1—costs of implementing the transportation task; KK2—costs of route expansion; KK3—rolling stock maintenance costs; KK4—depreciation costs; KK5—additional personnel costs). Based on the aforementioned criteria, two objective functions are built for each option: utility and cost. They present divergent goals; therefore, they are non-cooperative functions. Both utility and costs strive for the maximum. In the developed methodology, an ideal point is usually a fictitious solution representing a set of maximum values among all the achievable values in a set of solutions, but it is impossible to achieve this simultaneously based on all the criteria. This point illustrates the maximum utility and lowest cost among the alternatives considered, which is obviously impossible for any of the variants to meet at the same time, although it indicates the possibilities of the technique and the range of costs. For the developed method, a so-called "PND" nadir point is also determined, representing the least-preferred level of achievement of all goals simultaneously, determined from the set of optimal points in the Pareto sense. The originality of the conceptual considerations undertaken stems from: filling the gap in the economic methodology of complex transportation systems evaluation; embedding considerations in the trend concerning complex transportation systems of underground mines; and focusing considerations on the pre-investment phase, making it possible to optimize costs before expenditures are incurred. [ABSTRACT FROM AUTHOR]

The paper presents research on the influence of grain size of selected coals and their structural parameters on the diffusion coefficient and methane sorption isotherms. Two coals from Polish hard coal mines, differing in the coal rank, were tested. Sorption isotherms for methane were determined. An unconventional sequence of pressures 0→0.1→0→0.5→0→1.5 MPa was employed to assess the speed of achieving sorption equilibrium at different pressures. The studies of CH4 accumulation kinetics were performed on various grain classes of the tested coals. Both the sorption capacity of coal and the diffusion coefficient proved to be highly sensitive to the experimental methodology. Critical measurement parameters in terms of determining the diffusion coefficient concerning the assumptions of the Crank model were indicated. The influence of the equivalent radius of coal grain on the process kinetics was demonstrated. The stepwise pressure increase factor was examined in the context of minimising the impact of sorption isotherm non-linearity on the results. The importance of the width of the grain class of coals was determined to reduce their maceral inhomogeneities. These factors are the most common reason that makes it difficult to quantitatively compare diffusion coefficient values. [ABSTRACT FROM AUTHOR]

The paper presents the analysis of hard coal beneficiation in a jig with regard to the optimal useful fraction recovery in concentrate and non-useful fraction in tailings. The process was evaluated based on the industrial sampling of a jig for coal fines and granulometric and densimetric analyses of collected product samples under laboratory conditions. In separated size-density fractions of partition products, yields of products were calculated, and their ash contents were determined. The beneficiation curves were plotted on the basis of the results of granulometric, densimetric and chemical analyses of obtained size-density fractions, the balance of partition products and appropriate calculations. This made it possible to evaluate the process to optimise the device's operation to obtain higher recovery with the possibly highest concentrate quality. In the paper, the hard coal beneficiation results were evaluated with regard to the optimal organic fraction recovery in concentrate and mineral components in tailings with respect to the process control. The obtained characteristics of beneficiation were analysed to select the optimal technological coefficients for optimisation of the device's operation on the basis of the Fuerstenau curve, Halbich curve and selectivity curve. Multi-criteria elaboration of research material, on the basis of the qualitative approach of selectivity and Fuerstenau curves, indicated differentiation during the beneficiation of fine and coarse particles from the range of granulation being directed to the jigging process. This is a commonly known fact, but it is not necessarily used in industrial practice. [ABSTRACT FROM AUTHOR]

This paper discusses the impact of coal abrasive materials of varied petrographic composition and claystones containing admixtures of coal matter on the surface wear of wear-resistant martensitic steels. Wear tests were conducted at a test stand for three petrographic varieties of hard coal: vitrinite, clarinite, and durinite, and five samples of claystone. These tests revealed no significant effect of the type of coal abrasive used on the value of mass loss from the surface of the wear-resistant steel samples. The reason behind the foregoing is the observed tendency of coal abrasives, irrespective of their petrographic variety, to penetrate surface irregularities, especially those attributable to previous surface treatment of the samples and the impact of wear products. The dominant forms of surface damage were surface fatigue chipping and scratches caused by the particles which detached themselves from the surface of the steel samples, as observed for all the analysed coal variants. On the surfaces of the samples seasoned in the presence of claystones, highly varied forms of damage were observed: microcutting, scaly surface cracks, delamination, and deep cracks. In these cases, it was possible that the abrasive grains had been pressed into the steel surface irregularities, but no layered forms of the pressed-in abrasive material were observed to have developed. The paper also presents a model for the formation of coal films and discusses their possible effect on wear minimisation. [ABSTRACT FROM AUTHOR]

Ground movement is a critical concern for urban safety, and understanding its causes and consequences is essential. Mining of hard coal in the Ruhr area of Germany has caused long-term subsidence, leading to building damage and sinkholes in affected cities. The multi-temporal interferometric synthetic aperture radar (MTInSAR) technique has been widely adopted for estimating ground movement at millimetre-level accuracy using spaceborne SAR data. Although many European government institutes have implemented this technique for monitoring purposes, the European Ground Motion Service (EGMS) provides up-to-date ground movement products (until the end of 2020) across 31 countries. However, these products may not always meet the requirements for local use due to being untimely or missing important features. This paper demonstrates how we estimated ground movement in Ahlen, around the Ruhr area of Germany, using EGMS data as a priori and reference source. We implemented MTInSAR using Sentinel-1 data from 2018 to 2021 and compared our results with those of EGMS. Our results reveal the movement one year ahead, contain more measurement points, and cover natural areas such as cropland and bare soil. We interpreted several movement scenarios in detail, and our work highlights the benefits of EGMS as an open-source overview for local monitoring applications. We also explored the influence of soil conditions on ground movement. Our findings suggest that the overall uplift trend observed during the post-mining phase has been mitigated or even reversed, likely due to soil shrinkage resulting from drought conditions, particularly in areas with high organic soil content. [ABSTRACT FROM AUTHOR]

The irregular shape of mineral particles directly affects the angle of repose, bulk density and flow-properties, and the interaction behaviour between the particles and a contact surface. This paper presents a dataset of spatial data and shape parameters collected from 37 gangue particles and 135 anthracite coal particles, which come from the Shangzhuang Coal Mine. The particle surface models were obtained by a Wiiboox white light raster 3D scanner and Reeyee software. To obtain the scanning surface, each particle was scanned 8 times in different axial rotation directions. The final scanning model was obtained by stacking two scanning surfaces, and the shape parameters, such as length ratio, flatness ratio, and Zingg index, were obtained. This dataset is particularly useful for researchers and engineers who want to investigate the shape of coal and gangue particles or who want to test or benchmark measurement methods concerning the three-dimensional morphology of particles. [ABSTRACT FROM AUTHOR]

This paper presents the jig operating properties of the selected final parameters of the hard coal concentrate. The quality parameters of the product, such as the yield and ash content, were evaluated in terms of the technical and hydrodynamic parameters of the jig's operation. The research program included a series of experiments in which the efficiency and the amount of hutch water were changed. The variables selected and analyzed were divided into two categories, i.e., one related to the characteristics of the concentrate produced, and the other to the characteristics of the jig operation. Models were built for narrowed particle size fractions based on concentrate yield and ash content in the concentrate. In addition, a multidimensional analysis was performed, considering variables such as machine throughput, which was determined by the flow rate of the material, the amount of hutch water, the quality of the concentrate, and the amount of concentrate, as well as the accuracy of the jig operation expressed by the imperfection. Two main parameters were taken into account for modeling the operation to examine their significance of influence on the final responses in terms of the possibility of adjusting the value of independent settings of the jig operation. The presented approach to modeling the operation of the jig can be extended by considering the impact of other parameters, taking into account the variability of the final effect, as long as it is allowed under the industrial conditions of machine operation and the assumed production requirements. The approach presented in this paper is a new technique, which was not found in the literature. [ABSTRACT FROM AUTHOR]

The torrefaction process represents a thermal conversion technique conducted at relatively low temperatures ranging between 200 to 300 °C. Its objective is to produce fuel with a higher energy density by decomposing the reactive portion of hemicellulose. In this study, the kinetics of mass loss during torrefaction were investigated for willow. The experiments were carried out under isothermal conditions using thermogravimetric analysis. Batch torrefaction reactor designs were conducted and explained in detail. Co-combustion of willow with hard coal (origin: Katowice mine) in different mass ratios (25% biomass + 75% coal, 50% biomass + 50% coal, and 75% biomass + 25% coal) was conducted in addition to raw biomass torrefaction. TG/MS analysis (a combination of thermogravimetric analysis with mass spectrometry analysis) was performed in the research. The optimal torrefaction conditions for willow were identified as an average temperature of 245 °C and a residence time of 14 min, resulting in the lowest mass loss (30.15%). However, it was noted that the composition of torgas, a by-product of torrefaction, presents challenges in providing a combustible gas with sufficient heat flux to meet the energy needs of the process. Prolonged residence times over 15 min and higher average temperatures above 250 °C lead to excessive energy losses from volatile torrefaction products, making them suboptimal for willow. On the other hand, the co-combustion of torrefied biomass with hard coal offers advantages in reduced sulfur emissions but can lead to increased NOx emissions when biomass with a higher nitrogen content is co-combusted in proportions exceeding 50% biomass. This paper summarizes findings related to optimizing torrefaction conditions, challenges in torgas composition, and the emissions implications of co-combustion. [ABSTRACT FROM AUTHOR]

Underground mining in coal mines causes strong disturbance to geological structures and releases a large amount of elastic strain energy. When the roof is a hard and thick rock layer, it is easy to cause dynamic disasters such as rock burst. To analyze the impact of a deep thick and hard roof fracture on the safe mining of thick coal seams, this paper studied the dynamic evolution process of the stress field, displacement field, energy field, and plastic zone of the coal seam and overlying strata during the mining process using FLAC3D numerical simulation. The results show that as the working face continues to be mined, the concentrated stress in the overlying strata first increases and then decreases, and the support pressure in front of the working face continues to increase. When it advances to 100 m, collapse occurs, and the stress increases sharply; the bottom plate undergoes plastic failure, resulting in floor heave. The overlying strata mass in the top plate exhibits downward vertical displacement, while the rock mass in the bottom plate exhibits upward vertical displacement, with a maximum subsidence of 4.51 m; energy concentration areas are generated around the working face roadway, forming an inverted "U" shape. When collapse occurs, the energy density decreases slightly; the direction of the plastic zone changes from "saddle shaped" to complete failure of the upper rock layer, and the overlying strata is mainly shear failure, which expands with the increase in mining distance. The research results have important practical significance for guiding the safe mining of deep thick and hard roof working faces. [ABSTRACT FROM AUTHOR]

This paper presents a test stand for the capture of CO2 from flue gases arising due to firing pulverised hard coal. The stand, financed from the 2014-2021 Norway Grants, is installed at a Polish power plant. The innovation of the proposed CO2 capture method, developed by the Norwegian partner in the project (SINTEF Industry), lies in the use of activated carbon in the process of temperature swing adsorption in a moving bed. The paper also presents preliminary results of numerical simulations performed using the General PROcess Modelling System (gPROMS) software. The simulations concerned the operation of a supercritical power unit combined with a system for capturing CO2 from flue gases. Transient operation of the system was analysed, assuming rapid changes in the power unit load. Special attention was paid to the CO2 capture process energy consumption at an increase in load by 5% of the power unit nominal capacity in 30 s. It is found that the proposed CO2 capture method "keeps up" with such rapid load changes at the method energy consumption smaller than 2 MJ/kg CO2. [ABSTRACT FROM AUTHOR]

Mining exploitation of hard coal is conducted in the Silesian region in Poland. As a result, the post-mining void is formed which leads to non-uniform lowering of the ground level. Consequently, thousands of buildings are vertically deflected. This type of deflection causes troublesome use of buildings, underestimates their value, and in extreme situations leads to exceeded limit states. Therefore, such buildings are rectified by non-uniform elevations by means of jacks. On the basis of the analysed rectification processes, the method of determining the deflection of a building and the height of elevating its corners were presented depending on the type of building. This paper is a review of methods of determining the deflection of buildings having different sizes: single-storey buildings, single-storey buildings with a usable attic, two-storey buildings, and 11-storey buildings. Moreover, specific situations were analysed, in which the elevation height was determined by a range of additional works performed during rectification. This review was used to develop guidelines for determining deflection values and specifying the height of non-uniform elevation of corners. [ABSTRACT FROM AUTHOR]

The underground coal gasification (UCG) technology converts coal into product gas and provides the option of environmentally and economically attractive coal mining. Obtained syngas can be used for heating, electricity, or chemical production. Numerous laboratory coal gasification trials have been performed in the academic and industrial fields. Lab-scale tests can provide insight into the processes involved with UCG. Many tests with UCG have been performed on ex situ reactors, where different UCG techniques, the effect of gasification agents, their flow rates, pressures, and various control mechanisms to improve gasification efficiency and syngas production have been investigated. This paper provides an overview of recent research on UCG performed on a lab scale. The study focuses on UCG control variables and their optimization, the effect of gasification agents and operating pressure, and it discusses results from the gasification of various lignites and hard coals, the possibilities of steam gasification, hydrogen, and methane-oriented coal gasification, approaches in temperature modeling, changes in coal properties during gasification, and environmental risks of UCG. The review focuses on laboratory tests of UCG on ex situ reactors, results, and the possibility of knowledge transfer to in situ operation. [ABSTRACT FROM AUTHOR]

The current problems associated with the maintenance of hard coal longwall mining depend on the application or use of extraction technologies. In order to make the best use of these technologies, a new approach based on simulation studies is necessary. This paper aims to develop a mathematical model for the powered roof support's operation. The three groups of professionals involved in the testing of the roof support were involved in the work on changing the hydraulic system of the powered roof support stand. These professionals were powered roof support's designers, researchers and users. The research subject was the development of a mathematical model as a starting point for conducting simulations. The model is based on d'Alembert's principle and the equation of the balance of flow rates. Based on the developed model, it is possible to determine the pressure in the space under the piston of the hydraulic prop. The results obtained in the simulations are the basic assumptions for the development of a prototype that would solve the current problems in the hydraulic systems of powered roof supports. The adopted research methodology assumed the development of a mathematical model, simulation in the MATLAB environment and verification of the model on a test stand. The obtained results of simulation tests based on the developed mathematical model were confirmed in bench tests. Simulation and bench tests determined the correctness of the assumptions made for the development of the prototype model. Based on the analysis of the results, the nature of the work of the future prototype has been predetermined. The next stage will be the testing of the prototype, which is to be included in the hydraulic system of the prop of powered roof support in the future. The model mentioned before is the baseline model, and it will be modified depending on the application of the future design in real conditions. Simulation studies of powered roof support will allow the structure that is used currently to be optimised, so as to adapt it to increasingly difficult working conditions. [ABSTRACT FROM AUTHOR]

Background: The transition of the Ruhr region in Germany from a hard coal belt into a knowledge-based economy with a dynamic service sector and state of the art universities over the past 60–80 years has been widely touted as a successful example of how just and fair low carbon energy transitions can unfold. Methods: This paper leverages documentary analysis of data across a wide array of sources to test these claims and identify lessons by creating a novel just energy transition framework. Results: The study finds economic motivation, mindset and reorientation—not environmental concerns—to be the defining features for at least the first two decades of this shift. The lack of willingness to acknowledge environmental impacts and market realities has delayed the transition and led to wasteful allocation of resources towards supporting the hard coal mining industry. The prominence given to distributional justice cushions the victims of this transition financially, but does not allow a broad based coalition to advance the transition process. It is in the second phase (mid-1980s onwards that we see procedural aspects of justice come forth and support greater ownership and sustainability of the transition to emerge, while the evidence of recognition justice continues to be scant. Conclusions: There are many nuanced successes in the Ruhr's example, along with some failures worth highlighting. It is in the breakdown of this transition into two distinct phases and their nuances (particularly in the domain of justice) that fresh insights emerge and allow for a better understanding of what constitutes a suitable energy transition in a particular socio-economic and political context. As the international community embarks on ambitious greenhouse gas reduction targets, it can maximise the benefits and minimise the damages and costs by considering these realities on the ground. [ABSTRACT FROM AUTHOR]

In the paper are presented and discussed the results of a more complex research of technology portfolio's competitiveness in power systems with high penetration of intermittent renewable energy sources (i-RES). Possible technology portfolios compositions are analyzed. The portfolios comprise very high participation of i-RES, as well as a certain participation of energy storage technologies, but also and other energy technologies like nuclear and fossil fueled power plants. Within the research are developed new competitiveness indicators i.e., dispatchability indicator and the technology portfolio's assured capacity. The latter is defined on the basis of recently published Ulrich's and Schiffer's paper. Obtained results point out that inclusion of pumped-hydro storage plants improves portfolio's dispatchability. However, within the researched interval up to PHS installed capacities relative to i-RES capacities of 0.3. Numerical values of the dispatchability indicators are still below their values for the portfolio without i-RES. Increased participation of nuclear power plants contribute to the improvement of numerical values of the dispatchability indicators. The sensitivity analysis for the case of two times smaller cost of pumped hydro storage capacities is also performed. Hypothetical change of power system's technology structure in sense of substitution hard coal and lignite fired power plants with wind generators or with nuclear power plants is also analyzed. The analysis points out that the substitution with nuclear power plants enables much better results regarding power system's ability to change the power on demand than substitution with wind generators, particularly in the countries with high participation of hard coal and/or lignite in electricity generation. [ABSTRACT FROM AUTHOR]

This special issue compiles seventy-six original papers covering the following topics: mechanical properties and fracture behavior of deep rock, rock failure behavior under multifield coupling and multiscale systems, dynamic failure characteristics and constitutive properties of deep rock, mechanical behaviours of rock fractures during shearing, energy evolution characteristics during rock fracturing, experimental or numerical simulation of rockbursts, failure mechanism of spalling in deep tunnels, rock and structure response under blast and impulsive loading, and prevention and control of disasters in deep rock engineering. G. Deng et al. numerically simulate the evolution of mining-induced fracture network in a coal seam and its overburden under the top coal caving method. Q. Ma et al. give the dynamic behavior and energy evolution characteristic of deep roadway sandstone containing weakly filled joint at various angles. [Extracted from the article]

Mercury is ranked third on the Substance Priority List, an index of substances determined to pose the most significant potential threat to human health compiled by the Agency for Toxic Substances and Disease Registry. This element is activated with the extraction of hard coal and accumulated in the natural environment or re-emitted from the waste deposited on dumping grounds. So far, studies on mercury content have focused on the analysis of the dumps surface and the adjacent areas. In this paper, the detection of mercury content inside mining waste dumping grounds was analysed. The recognition of mercury content in the profile of the mining waste dump is important in terms of the dismantling of the facility. The dismantling may pose a risk of environmental pollution with mercury due to the possibility of increased fire risk, re-emission, and the transfer of xenobiotics to another place. In this paper, the study of mercury content in the mining waste dump profile was presented. The research demonstrated that there is no significant relationship between the mercury content and the sampling depth. The mercury content in the mining waste was determined based on the rank and origin of hard coal only. Therefore, intensive efforts should be undertaken to identify the environmental hazards arising from the dismantling of mining waste dumps and to adopt measures to prevent these hazards. [ABSTRACT FROM AUTHOR]

Graphite can be artificially converted from anthracites under high temperatures; however, the exact mechanism through which inorganic minerals contribute to the graphitization process is still unknown. In light of this, several selected minerals in different amounts were added to demineralized anthracite coal. The anthracite–mineral mixtures were subjected to artificial graphitization experiments under temperatures ranging from 1700 to 2900 °C in the laboratory. The obtained series of coal-based graphites with various levels of graphitization were characterized by X-ray diffraction (XRD), and the derived structural parameters, such as d002 and FWHM (002), La, and Lc were used to compare the carbon structural evolution during the high temperature treatment and mineral catalytic graphitization. Moreover, the amorphous carbon of anthracite is eventually transformed into the highly ordered crystalline carbon of coal-based graphite. The five added minerals show interesting structural variation during the graphitization process, in which pyrite is decomposed into iron (Fe), illite, quartz, and kaolinite, which can react with disordered carbon in organic matter to form moissanite (SiC), while dolomite seems to react with sulfur to form oldhamite (CaS). At temperatures less than 2300 °C, the minerals could significantly enhance the catalytic effect. There is a clear difference in the catalytic effect of different minerals on graphitization. Kaolinite exhibits the strongest catalytic effect. The minerals dolomite, illite, and quartz only show a certain degree of catalysis. Pyrite, however, only has a limited effect on improving the degree of graphitization at a temperature of 1700 °C. However, once the temperature exceeds 2300 °C, the dominant factor controlling the graphitization of anthracite appears to be the temperature. According to the growth pattern at microcrystalline sizes (La and Lc), the minerals' catalytic effects can be classified into three groups. The first group includes minerals that preferentially promote La growth, such as pyrite, illite, and quartz. The second group includes minerals that preferentially promote Lc growth, such as dolomite. Finally, kaolinite is in a separate group that promotes microcrystal growth in both the lateral and vertical directions simultaneously. The mechanisms of the minerals' catalytic graphitization are discussed in this paper. The promotion role of minerals in the artificial graphitization process may help to optimize the graphitization process and reduce the process cost in the future. [ABSTRACT FROM AUTHOR]

Methane and coal dust explosions are among the most common causes of disasters in hard coal mining. Therefore, it is important for occupational safety in hard coal mines operating under methane and coal dust explosion hazards to identify possible ignition sources, whether due to natural or technical factors. One technical source of ignition can be mechanical sparks generated during operation of mechanical equipment and high surface temperatures of equipment components during operation. This paper presents the methodology and results of thermal imaging and strength testing of roadway support elements under dynamic loading. The goal of the tests was to identify the potential explosive atmosphere ignition sources during the operation of the support under the conditions of rock bursts. The scope of testing encompassed the temperature measurements by means of thermal camera of friction prop and yielding support frame sliding joint elements at yield under dynamic impact loading (simulating a burst). Significant joint element heating and mechanical sparking was observed during the testing of arching yielding support frame sliding joints and straight friction prop joints as a result of friction at yield. Some of the aspects defined in standard PN-EN ISO80079-36:2016 include the maximum temperature T max =150°C for a surface that can accumulate a layer of coal dust. Tests of the friction joints have shown that during impact loading, numerous mechanical sparks are produced at the friction joints of sections of the steel prop, with the surface temperature of the sections starting from 169.6°C and reaching up to 234.1°C. During tests it was also to determined emissivites of the tested sliding joints constructed from V29-V32 secrions depending on corrosion products which consist in range 0.842–0.873. Such a high temperature can initiate an explosive mixture consisting of methane, air and coal dust. [ABSTRACT FROM AUTHOR]

The shortage of investment areas may be at least partially satisfied by the development of reclaimed post-mining areas. These are often subsidence zones levelled with hard coal mine waste or reclaimed sub-level old dumps of this waste. From the geotechnical point of view, such grounds represent anthropogenic grounds containing mine waste, and they are considered as possessing unfavourable properties in terms of the foundation of building structures. The paper initially presents the analysis of the properties of waste from the hard coal mining industry, emphasising that they expose several beneficial properties enabling their safe use. The second part of the article is devoted to the determination of soil density using the DPSH probe. It has been found that the applicable standards lack complex relationships that would allow for a reliable interpretation of the measurement results in a wide range of soil types. The last part presents exemplary results of measurements made with the DPSH probe at a construction site. The obtained results allowed for the formulation of several conclusions regarding the possibility of building on a ground made of hard coal waste and the use of dynamic sounding to assess the geotechnical properties of such anthropogenic soil. [ABSTRACT FROM AUTHOR]

This paper investigates the removal efficiency of a honeycomb electrostatic precipitator (ESP) applied to control particulate matter (PM) emissions from a small-scale boiler with combustion lignite and hard coal. The specifics of the precipitation of emissions from small-scale boilers are discussed, and the design principles for relevant ESPs are presented and used. The ion-induced nucleation of sulfuric acid occurred, causing the drastic penetration of 19 nm particles through the ESP. Despite this, the overall collection efficiency was sufficient to meet the EU's Ecodesign Directive requirements. Back corona was not detected. The optimal ESP performance is defined with further parameters: a current density of 0.5 mA/m2 at an electric field strength of about 2.7 × 105 V/m; a minimal specific collecting area of ESP (SCA) of 60 m2/(m3/s); and Nt-product of 4.5 × 1014 s/m3. Such parameters of ESPs should ensure adequate PM emissions control for any type of boiler with similar emissions characteristics. The composition of collected fly ash particles was analysed, and a method for fly ash utilisation was proposed. This research may be helpful for designing ESPs to control PM emissions for small-scale units with fossil fuel combustion. [ABSTRACT FROM AUTHOR]

Although highly developed countries are trying to diversify away from coal-based energy, many economies rely on this resource. Its consumption results in the production of carbon dioxide, which promotes global warming, necessitating its sequestration. This paper presents the sorption–dilatometric relationships of hard coal samples differing in vitrinite and inertinite content. The studies were carried out under isothermal conditions (298 K) at a free pressure drop complemented by measurements under non-isothermal conditions (298 K to 323 K). The tests were performed on an original apparatus, based on the operation of an Arduino microcontroller. For the natural porosity to be preserved and for a better representation of the behaviour of the coal–gas system, samples in the form of cuboidal blocks were used, making this apparatus unique worldwide. Based on the study, it appears that the difference in petrographic composition affects the behaviour of the coal structure, influencing differences in the sorption–dilatometric properties. In the case of the sample with higher vitrinite content, the amount of adsorbed gases is higher. [ABSTRACT FROM AUTHOR]

As one of the main fossil fuels globally, coal can be enriched with a variety of critical metal elements in specific geological conditions. This paper investigates the mineral compositions and concentrations of major and minor element oxides and trace elements in the No. 9 coal from the Xinyuan mine of the northern Qinshui coalfield, China, and discusses the modes of occurrence and enrichment mechanisms of critical metal elements such as Li, Ga, Th and REY. The mineral compositions of the No. 9 coal are primarily represented by clay minerals and quartz, with a small amount of calcite, siderite, anatase, etc. The major element oxides in the No. 9 coal are dominated by SiO2 and Al2O3. Compared with world hard coal, the No. 9 coal of the Xinyuan mine is rich in Li (CC = 8.00) and Th, slightly enriched with Pb, Sc, Ga, Y, La, Ce, Tb, Dy, Er, Yb and Hg, and depleted in Mn, Co, Ni, Rb, Cs and Tl. The critical metal elements such as Li, Ga, Th and REY that enriched No. 9 coal mainly occur in aluminum silicates. The genetic type of the critical metal elements in the No. 9 coal from the Xinyuan mine is source rock-controlled type. The critical metal minerals and solutions from the source area were transported to the study area by the action of water. Due to the change of swamp water conditions, the critical metal elements were combined with clay minerals and enriched the coal. [ABSTRACT FROM AUTHOR]

The hydro-mining technology is considered as a promising method of bituminous coal excavation. The paper presents the results of the in-situ experimental campaign and modelling of hydro-cutting technology application. The proposed innovative technology was tested in terms of the effects of the distance between the outlet of water from the nozzle and a sidewall, pressure of the water jet, as well as the type of a nozzle on hydro-mining effectiveness. The hydro-cutting tests of coal seam performed in the Experimental Mine "Barbara" in Poland proved that the increase in water pressure in the range 20–40 MPa only slightly affects the coal face structure, while high pressure, of 80–100 MPa, has a significant impact on a coal face structure. The experimental results also showed the major effects of operating time as well as the distance of the water jet on the effectiveness of coal face mining. [ABSTRACT FROM AUTHOR]

Poland is a big user of fossil fuels for electricity and heat production. The most important fossil fuel is hard, brown coal and the Polish energy system is based on this source. However, the world has begun to decarbonize the climate and reduce the carbon dioxide and methane which are the main gasses impacting climate change. The main aim of this paper was to recognize changes in Polish coal sector. We focused our attention to the economic situation and employment in coal sector in Poland. The time rage included 1989–2020 and the prognosis 2021–2025. The Polish coal sector faced dramatic changes. The number of hard coal mines decreased from 70 in 1990 to 21 in 2020. In the same timeframe, the prices for hard coal increased from 12.37 PLN/dt to 313.27 PLN/dt. The employment decreased from more than 350 thousand to less than 100 thousand people in hard coal mines. The decrease changes are the effect of strict policies of the European Union. The economic situation of Polish hard coal mines is rather poor. Polish mines achieved negative economic results due to the effect of poor management. We used advanced statistics, including the Augmented Dickey–Fuller test (ADF), to measure the stationarity of analyzed time series. We also used Generalized AutoRegressive Conditional Heteroskedasticity (GARCH) models and conducted a prognosis. Our research proved that the time series describing the hard coal economic situation were not stationary. The Generalized AutoRegressive Conditional Heteroskedasticity (GARCH) models confirmed big changes in Polish coal sector economic results. The elaborated prognosis of variables proved that the price of hard coal will increase in 2021–2025. Moreover, the economic situation will be worse. Our analysis confirmed that global trends of the hard coal sector were influenced by the European Union (EU) energy policy and closing down the mines. The economic situation of Polish hard coal sector worsened. [ABSTRACT FROM AUTHOR]

In this paper, we report new records of rare diatoms that have recently been found in Southern Poland. Planothidium nanum was found only in the upper reaches of the Centuria River, which is not exposed to human influence, while Navicula flandriae was found in two rivers (the Bolina and the Mleczna) affected by salt mine water from hard coal mines. The impact of anthropogenic salinity on diatom communities is as yet poorly documented. Therefore, we conducted a survey on this phenomenon. We surveyed seven sampling sites for diatom assemblages and habitat characteristics, including three sampling sites impacted by mine water. Navicula flandriae was recorded at both sampling sites affected by salt mine water and in two other rivers (the Centuria and the Mitręga), indicating its wide preference for salinity. We confirmed the occurrence of P. nanum at the same site where this species was found and described in our previous paper. In addition, we recorded the occurrence of this species at two other sites in habitats with similar characteristics (lower reaches of the Centuria and Wiercica rivers). Our results indicate a more common occurrence of N. flandriae and P. nanum, which means that further monitoring of diatoms is necessary. [ABSTRACT FROM AUTHOR]

Backfilling technology is not always used by mining enterprises, which is conditioned by technological and economic factors, such as the need for high mining rates and costs for the technological processes of transporting backfill materials from the daylight surface to the mined-out space. This concerns the underground mining of hard coal, which is a strategic energy resource, in the mines of Ukraine. This paper aims to study the effect of leaving the waste bottom rocks in the mined-out space of the longwall face without their drawing to the earth's surface on the geomechanical state of the rocks surrounding the longwall face. The geomechanical assessment of the stress state of the rock mass surrounding the longwall face, when leaving the waste rocks from the seam bottom rocks in the mined-out space, is performed by the finite element method using the Ansys software package. A geomechanical model has been developed and substantiated, which adequately reflects the mining-geological conditions for seam mining within the extraction site, the actual structure and properties of the coal-bearing rock stratum, the parameters of the longwall face and the modified powered support for the processes of leaving the rocks in the mined-out space. The values and patterns have been determined of the decrease in the stress intensity concentrations in the coal-bearing roof mass in the frontal bearing pressure zone and destressing zone with an increase in the ratio of the rock pack thickness to the extracting seam thickness. The relative indicators of the load on the powered support section and the lowering of its roof have been determined by the ratio of the thickness of the rock pack formed in the mined-out space to the extracting seam thickness. The proposed mining method is of significant commercial and research interest for owners of coal mines developing thin coal seams because environmental costs for placing waste on the surface are reduced, and the energy potential of coal is increased due to the separation of waste rocks from coal in underground conditions. The need for a cycle of beneficiation of mined mass is eliminated and the geomechanical conditions of coal mining processes are improved. [ABSTRACT FROM AUTHOR]

Coal wall rib-spalling is regarded as a key technical problem influencing safe and efficient mining of fully mechanized working face with great mining height (FGH) while the coal wall stability is influenced by the strength of the coal body, of which the internal joint fissures have a crucial impact on the strength of the coal body. This research attempted to explore how the coal wall stability of FGH is influenced by the occurrence of joint fissures. This paper uses physical and numerical simulations to systematically analyze the instability characteristics and displacement law of FGH. Research results show that the form and scope of the instability of coal wall rib-spalling depend on the state of the coal seam joint fissures development area, and the development state of coal seam joint fissures is related to the combination of the coal seam joints; under the condition of hard coal, the coal wall stability is better at the inclination angle of 90°, and less stable at 45° and 135°; under the condition of medium-hard coal and joint surface inclination angle of 45° and 135°, the smaller the spacing of joint surface, the larger the area of the working face rib-spalling, and the less stable the coal wall. [ABSTRACT FROM AUTHOR]

The rapid development of science and technology, and the restructuring of the mining extraction industry, bring about profound changes in the structure and complexity of technological equipment used in mining. In this paper, the Reliability Centered Maintenance (RCM) method has been applied to analyze the components of the KSW-460NE shearer machine, which fails quite frequently. The cutter drums do not match from a constructive point of view, and the concrete operation conditions, alongside the picks (being in direct contact with coal and hard inclusions) and guides are submitted to intense abrasion wear, showing a great number of failures. The data collected following the machine's exploitation allowed parameter determination characterizing the reliability of the components mentioned, the manner of failure, and the effects. Using calculation methods, it has been possible to facilitate the interpretation of the result in view of establishing measures required to improve maintenance of the dominant components of the machine, determining replacement intervals, in accordance with an imposed reliability and maintainability. The results of the study assist in the choice of suitable hardening materials for the reconditioning of cutter drums and guides that are necessary for practical trials, by which their operating times, and replacement intervals, respectively, might be additionally improved. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic with subsequent economic fluctuations during consecutive epidemics waves and preventive measures in the form of lockdowns, and Russia's invasion of Ukraine have had a meaningful impact on the European economy, including the energy market. These events have caused an increase in the prices of many products, including fossil fuels, and also a lack of their availability. The changes inspired the authors to conduct research on the current situation in Poland in the field of renewable energy and coal. The paper describes the research on the impact of the development of RES (mainly photovoltaic sources) on the change in the energy generation profile in the case of Poland. The article analyzes the impact of RES (renewable energy sources) on the reduction of CO2 emissions. The conducted analysis was based on the historical similarity of the replacement of conventional (carbon) sources by PV (photovoltaics) by determining in how many cases (%), a specific carbon source will be displaced. Based on the prepared forecast, it was determined that by the end of the year, the installed capacity in PV will reach the level of 11,213 MWp (in wind energy, it will be 7875 MWp). Replacement (reduction of consumption) of approximately 1.5 million Mg of hard coal and 2.87 million Mg of lignite was concluded to be possible (~4.4% and 6.3% of the hard-coal and lignite volume used for energy production). Limiting this volume of hard coal and lignite will also reduce CO2 emissions in the entire NPS by 5.24 million Mg (−5%) in 2022. [ABSTRACT FROM AUTHOR]

Currently, the Polish power industry is mainly based on solid fuels, such as hard coal and lignite, and there is a problem with the management of significant amounts of combustion waste. One of the directions of recovery of these types of waste is underground hard coal mining operations, where the general problem of their management is the variability of physical and chemical properties resulting from the combustion of fuels of different parameters in power boilers with different exhaust gas cleaning solutions, mainly desulphurization methods. One of the solutions for energy production currently in use is the combustion of coal in fluidized bed boilers, in which the so-called dry desulfurization method is adopted. As a result of this process, a fine-fraction waste with the European code 10 01 82 is created, which is characterized by pozzolanic features, enabling its use wherever specific strength parameters are expected from the material. One such technology is the liquidation of underground workings based on the pouring of a hydro-mixture into the fenced-off space of the workings using a gravity-fed pipeline. The space to be filled is fenced off by closing it on both sides with dams, usually made of brick walls, located at an appropriate distance. It should be taken into account that the hydro-mixture will tend to slow the sedimentation of solid particles on the spreading path, and working may have a variable slope. The paper presents the results of laboratory tests of the physical and mechanical properties of hydro-mixtures made on the basis of selected energy waste from a fluidized bed boiler, along with a practical example of its application for the liquidation of underground workings. [ABSTRACT FROM AUTHOR]

Limestone flour is used in a variety of industrial sectors such as power and heat generation, glass-making, paper-making, the construction industry and construction materials manufacturing, the production of agriculture, plastics and rubber goods, as well as coal mining, and environmental protection. This paper aims to characterize and interpret the limestone flour supply and demand trends in the main applications in Poland in the last decade. In order to track the changes of domestic consumption for this commodity, its major users have been surveyed along with analyses of data from the Statistics Poland (GUS). The results showed that during 2009–2018 the coal-fired power plants became the biggest customer of limestone flour utilized as a sorbent in the wet flue gas desulfurization method (FGD). This method has been implemented in the vast majority of Polish power plants. It is estimated that in the last decade the total annual production capacity of limestone flour at the milling plants in Poland increased by 1.5 million tons, to around 6.0 million tons. In the forthcoming years, this is expected to continue to increase despite EU restrictions on fossil fuel use (especially hard coal and lignite). Other promising areas of future growth are: for limestone flour of medium quality—the construction materials manufacturing and the construction industry itself, for limestone flour of the highest quality—the glass industry, while for fine-grained limestone flour of high-quality—the plastics and rubber industries. In terms of resource security, it is worth noting that Poland is a country rich in limestone deposits. However, only some of them, that is, limestone rock varieties of the Jurassic and Devonian ages from the Kielce vicinity in central Poland are suitable for the production of high-quality limestone flour for the needs of the mentioned industries. The paper analyses the potential of the limestone flour production from the available limestone rock deposits with respect to the current and future needs of the domestic market in Poland. [ABSTRACT FROM AUTHOR]

The paper presents a brief outline of the European Union Climate and Energy Package in early 2020, as well as the EU's plans in this respect until 2030 (Winter Package and Green Deal) and even further until 2050 (EU's climate neutral target). Also the current condition of power generation in Poland and challenges for Polish energy sector in the nearest future are discussed. The Energy Policy of Poland until 2040 (EPP 2040) is analysed in relation to possible risks and dangers. Some improvements are proposed in regard to the implementation of the document. In addition, the current volume and perspectives of hard coal and lignite mining in Poland until 2040 are discussed and compared with an expected demand for coal in Polish power plants and combined heat and power stations. On the basis of the prognosis of energy consumption in the period 2031-2040, there seems to appear a serious risk of energy shortage due to a possible delay in a nuclear power project and lack of lignite mining at the level defined in EPP 2040 policy. Therefore, some variants of providing the security of energy supplies are taken into account and thoroughly analysed in the paper. [ABSTRACT FROM AUTHOR]

The date assumed as the beginning of the pandemic in Poland is 4 March 2020, the date of the first confirmed case of the virus. This article presents the actions undertaken by the management of underground hard coal mining plants concerning the risk of epidemic related to SARS-CoV-2. This work shows a set of implemented recommendations, guidelines and decisions, which were established after the appearance of the first wave of cases in Poland. What is more, it discusses measures aiming at reducing the risk of spreading the coronavirus among the mineworkers. The suggestions for different variants of the decision-making process concerning the pandemic and which have an enormous impact on the operating expenses of the company are also made. The paper presents the results of the study on actions taken in individual mining companies and good work practices recommended to be applied. [ABSTRACT FROM AUTHOR]

Underground mining operations are subject to a number of natural hazards. Events resulting from these hazards are difficult to predict, and if they occur, they disrupt the entire mining process and pose a great danger to the crew. Some of the most dangerous include ventilation hazards involving methane explosions and fires caused by the spontaneous combustion of coal. The complex state of the underground environment means that these hazards oftentimes occur simultaneously, making mining conditions even worse. The following paper addresses this issue by developing the methodology for determining areas endangered by methane explosions and spontaneous coal combustion in goaves. The reference to goaves results from the fact that this particular area is most frequently affected by spontaneous coal combustion and the accumulation of dangerous amounts of methane. The developed methodology was based on model tests with the use of the CFD method and data necessary to develop a numerical model. The research encompassed a real longwall in one of the hard coal mines, ventilated with the Y system during its exploitation, which is beneficial in the case of the methane hazard but worsens the safety in terms of the self-ignition of coal. As a result of the conducted research, for the exploitation conditions, dangerous zones were specified due to the potential possibility of methane explosion and self-heating of coal. The basis for determining dangerous zones was the criteria of occurrence of the examined phenomena. In this study, the zones were identified for each of the investigated hazards separately and for their simultaneous occurrence. Thus, the aim of the study, which involved the determination of potentially hazardous zones by applying modern methods of modelling in the mining area, was achieved. The results are an immensely important source of information for activities aimed at improving safety in the studied area in relation to the studied threats. [ABSTRACT FROM AUTHOR]

The content of natural methane in hard coal seams, called methane-bearing capacity, is the basic parameter that enables the level of methane hazard to be determined in hard coal mines. This parameter is also used to determine the potential quantities of methane that can be collected and used for energy purposes and the amount of its harmful emission to the atmosphere. Direct methods are most often used to determine methane-bearing capacity. An important aspect that has a great influence on the final result of the research is the gas losses generated at the stage of sampling. Under the conditions of the Polish mining industry, the direct drill cuttings method is used to determine the methane-bearing capacity. Gas losses are compensated for in this method with the use of the coefficient 1.12, by which the obtained result is multiplied. In this paper, a multi-parameter analysis of gas loss in the determination of methane-bearing capacity in hard coal seams has been carried out. Several experiments were performed to identify the most important aspects to be taken into account to obtain a correct result. A methane-bearing capacity test was conducted using two direct methods: the direct drill cuttings method, otherwise known as the single-phase vacuum degassing method, and a method based on the United States Bureau of Mines standards. Sorption studies, such as methane sorption kinetics tests, were also conducted in which sorption properties, such as sorption capacity, effective diffusion coefficient, and half sorption time, were determined. Methane sorption isotherms were also determined, and pore structure was analysed. Based on the obtained test results, an analysis was carried out which made it possible to present appropriate conclusions concerning the gas losses during the methane-bearing capacity test, generated at the stage of sampling. The final result of the work was the proposal of a new gas loss coefficient for the direct drill cuttings method of methane-bearing capacity determination. [ABSTRACT FROM AUTHOR]

The Young's modulus and Poisson's ratio, parameters reflecting the elastic response of a rock to stress, are the key parameters used in many engineering activities, such as hard coal mining and natural gas extraction. The objective of this paper was to present the results of complex laboratory measurements of the static and dynamic Young's modulus and Poisson's ratio for Upper Carboniferous hard coals from the Upper Silesian Coal Basin. The coals differed in geologic age (Mudstone Series—younger coals; Upper Silesian Sandstone Series—older coals) and petrographic structure (vitrain, clarain, and durain lithotype). Elastic parameters of the coals were determined following compression tests under a complex state of stress, as well as using the ultrasonic method in reservoir conditions. On this basis, linear functional dependences between parameters such as UCS, differential stress, confining pressure, strain rate, P- and S-wave velocities, and the static and dynamic Young's modulus and Poisson's ratio were determined. These dependences turned out to be linear, with strong and very strong correlation, as indicated by the high coefficients of determination, R2. These new results significantly broaden the knowledge of elastic properties of Carboniferous hard coals, especially in the field of geoengineering, underground coal gasification, and reservoir stimulation for coal bed methane extraction. [ABSTRACT FROM AUTHOR]

The paper shows the results of researching the rollers used in belt conveyors working in a hard coal mine. Rollers should be characterized by low rotation resistance, which results in low power consumption of the propulsion unit. The tests conducted aimed to assess the technical condition of the new C-type rollers after several years of operation in a hard coal mine. The research was carried out from the new approach to the standard issues of roll testing and verification in a hard coal mine. Laboratory tests were combined with testing the entire belt conveyor in terms of power demand. The research was carried out for 3 years and it was monitored how the dynamic resistance of the working rollers changed and how this translates into the power demand consumed by the belt conveyor in a hard coal mine. The aim of the research was a new approach to the research of rollers used in conveyors operating in a mine. [ABSTRACT FROM AUTHOR]

This paper presents a test stand equipped, among others, with two boilers intended for the combustion of solid fuels. The first is a single-fuel boiler designed to burn wood pellets only. The second is a multi-fuel boiler intended for the combustion of mainly hard coal (basic fuel) with the grain size of 0.005-0.025 m. Wood pellets can also be fired in this boiler, which in such a case are treated as a substitute fuel. There is a developed and verified algorithm for the control of the multi-fuel boiler operation in a wide range of loads for the basic fuel. However, for the substitute fuel (wood pellets) there are no documented and confirmed results of such testing. The paper presents selected results of testing performed during the combustion of wood pellets in a multi-fuel automatically stoked boiler. Several measuring series were carried out, for which optimal operating conditions were indicated. These conditions may serve as the basis for the development of the boiler operation control algorithm. A detailed analysis was carried out of the flue gas temperatures obtained at the outlet of the boiler combustion chamber and of the contents of carbon monoxide and oxygen in the boiler flue gases. [ABSTRACT FROM AUTHOR]

The advanced deep hole blasting (ADHB) is commonly used to improve the fragmentation of thick hard top coal in longwall top coal caving (LTCC) mining. This paper presents an acoustic method to quantitatively evaluate the effectiveness of the ADHB. First, the variations of P‐wave velocity of hard coal samples under uniaxial and triaxial compression are obtained from the laboratory acoustic test. Then, an acoustic wave method based on seismic tomography is proposed to assess the effectiveness of the ADHB by introducing the P‐wave velocity attenuation model into the data processing. Finally, a field seismic tomography test is conducted to obtain the distribution of the P‐wave velocity of top coal before and after the ADHB implementation. And the P‐wave velocity attenuation is calculated to estimate the fragmentation effectiveness of ADHB. The results indicate that the P‐wave velocity attenuation model could well represent the broken degree of hard coal, suggesting that the proposed acoustic wave method could quantitatively evaluate the fragmentation effectiveness by exporting the nephogram of P‐wave velocity attenuation. The present study may provide technical support for improving the recovery ratio of thick hard top coal for LTCC mining. [ABSTRACT FROM AUTHOR]

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Coal permeability is a key parameter that affects the drainage of coal bed methane (CBM). Owing to the lower original permeability of coal seams in China, more attention was paid to the study of damage‐induced permeability laws. However, the theory of damage‐induced permeability still needs to be improved. In this paper, the permeability evolution experiments during the complete stress–strain process of coal were carried out firstly. The results are shown that with the increase in axial strain, the coal permeability decreases slowly at first, then increases rapidly, and finally increases slowly or even remains unchanged, and the peak stress point can be regarded as the extreme point of permeability. Then, the equivalent plastic strain was used to describe the damage of coal. Based on the above results, a new damage‐induced permeability model was developed, and the new model can match the experimental data of permeability very well. In addition, solid–gas coupling models of coal were developed based on the new permeability model, and the numerical results show that there is a region of sudden increase in permeability around the borehole where plastic failure occurs, which indicates that the damage‐induced permeability model is reasonable. Finally, the results of numerical simulation of gas predrainage in combination of soft coal and hard coal under different cases were used to optimize the borehole layout of gas predrainage in the field. [ABSTRACT FROM AUTHOR]