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Based on the greening and low interference disposal requirements of coal gangue in high-yield and high-efficiency mines in Inner Mongolia and Shaanxi, and by integrating the existing theories and technologies such as underground filling technology of coal gangue, mine yellow mud grouting technology, and the evolution law of mining overburden fractures, a technology of filling goaf with coal gangue slurry for green disposal of coal gangue is proposed. The principle and technical framework of the technology of filling goaf with coal gangue slurry are clarified. This paper expounds on the technological process of technology of filling goaf with coal gangue slurry, establishes three types of slurry filling systems, such as centralized ground layout, ground and underground coordinated layout, and centralized underground layout, and constructs three slurry filling methods, including low-level grouting, adjacent level grouting, and high-level grouting, forming seven kinds of technology models of filling goaf with coal gangue slurry, including ground centralized pulping + high-level grouting, ground centralized pulping + adjacent grouting, ground centralized pulping + low level grouting, ground and underground coordinated pulping + adjacent grouting, ground and underground coordinated pulping + low level grouting, underground centralized pulping + adjacent grouting, and underground centralized pulping + low level grouting, and gives the selection process of technology models of filling goaf with coal gangue slurry. Based on the different conditions and requirements of Haidaze Coal Mine and Huangling No. 2 Coal Mine, engineering tests were carried out on two different technology modes, namely, ground and underground coordinated pulping + low level grouting and ground and underground coordinated pulping + adjacent grouting, based on simulation tests of low level grouting and adjacent grouting. The tests prove the feasibility of filling goaf with coal gangue slurry and explore the way for the theoretical research of the technology of filling goaf with coal gangue slurry and greening and low interference disposal of coal gangue. [ABSTRACT FROM AUTHOR]

The Jurassic coalfield in northern Shaanxi, China is one of the seven largest coalfields in the world. It is located in an arid region of northwestern China, with poor water resources and fragile ecological environment. Due to coal mining, the rock layers on the coal seam will be slumped and fractured to produce fissures. The penetrated fissures will cause a mine water burst disaster and cause damage to groundwater and surface water. The strip filling method can control the expansion of the diversion fissure zone and protect the groundwater and surface water from the underground mining of coal. In this paper, the effects of different strip filling conditions on the diversion fissure zone are studied by discrete element numerical experiments. The study indicates that the upward-fissure and the downward-fissure penetrations are the direct causes of the instability of the water-blocking rock group. After the upward fissure extends to a certain extent, there will be a downward fissure. Under the condition of controlling the width of the filling strip and the compressive strength, the strip filling method can effectively prevent the upward and downward fissures of the water-blocking rock group from penetrating and can ensure that the surface water system is not affected by the underground coal mining activities. [ABSTRACT FROM AUTHOR]

Coal-rock interface identification technology was pivotal in automatically adjusting the shearer's cutting drum during coal mining. However, it also served as a technical bottleneck hindering the advancement of intelligent coal mining. This study aimed to address the poor accuracy of current coal-rock identification technology on comprehensive working faces, coupled with the limited availability of coal-rock datasets. The loss function of the SegFormer model was enhanced, the model's hyperparameters and learning rate were adjusted, and an automatic recognition method was proposed for coal-rock interfaces based on FL-SegFormer. Additionally, an experimental platform was constructed to simulate the dusty environment during coal-rock cutting by the shearer, enabling the collection of coal-rock test image datasets. The morphology-based algorithms were employed to expand the coal-rock image datasets through image rotation, color dithering, and Gaussian noise injection so as to augment the diversity and applicability of the datasets. As a result, a coal-rock image dataset comprising 8424 samples was generated. The findings demonstrated that the FL-SegFormer model achieved a Mean Intersection over Union (MIoU) and mean pixel accuracy (MPA) of 97.72% and 98.83%, respectively. The FL-SegFormer model outperformed other models in terms of recognition accuracy, as evidenced by an MIoU exceeding 95.70% of the original image. Furthermore, the FL-SegFormer model using original coal-rock images was validated from No. 15205 working face of the Yulin test mine in northern Shaanxi. The calculated average error was only 1.77%, and the model operated at a rate of 46.96 frames per second, meeting the practical application and deployment requirements in underground settings. These results provided a theoretical foundation for achieving automatic and efficient mining with coal mining machines and the intelligent development of coal mines. [ABSTRACT FROM AUTHOR]

China's need for energy resources is growing every day. Future energy demands will be partly met by low-temperature pyrolysis of oil-rich coal, which is a form of coal-to-oil technology. Under the existing fully-mechanized coal mining technology, oil-rich coal is mechanically broken into different particle sizes by a shearer and used in different industrial utilization directions. However, due to differences in particle size and material composition, the pyrolysis products of oil-rich coal with different natural particle sizes are different, which affect the pyrolysis efficiency of oil-rich coal with different particle sizes. In order to explore the differences and influencing factors of pyrolysis products of oil-rich coal with different particle sizes, and taking Jurassic oil-rich coal in northern Shaanxi as the research object, the differences and causes of pyrolysis production of oil and gas from nine kinds of oil-rich coal with different natural particle sizes under existing coal mining conditions are discussed according to particle size characteristics, pore structure, heat transfer velocity and molecular structure. The findings demonstrate that the pyrolysis characteristics of coal do not show a single trend with change in particle size. With decrease in particle size, the ash and sulfur contents were relatively high, and the tar yield increased first and then decreased. In contrast, the light fraction decreased overall, and the heavy fraction decreased. The tar yield of 0.125–0.25 mm was the highest, and the tar content was 1.996 g. For the gas components produced by pyrolysis, the contents of CH4, CO and H2 first increased and then decreased with decrease in particle size, while the contents of CO2 and CnHm showed the opposite trend. Larger particles (about 30 mm) affect the escape efficiency of pyrolysis products and the amount of carbon deposition due to the difference in porosity (interparticle resistance) of the inner surface and pyrolysis bed, resulting in secondary reactions of the products escaped from a primary reaction, thus affecting the differences in pyrolysis products. The heat transfer process of coal was affected by particle size, and the thermal conductivity increased gradually with decrease in particle size, which is consistent with the change of tar yield with particle size. The maceral components and molecular structure functional groups in coal with different particle sizes were also different, which resulted in the differences in tar yield. Studies have shown that smaller particle sizes have longer alkyl side chains, and pyrolysis accompanied by rising temperature causes different changes in the aliphatic hydrocarbon content in coal coke after pyrolysis. The aliphatic hydrocarbon content decreased the most when the particle size was 0.125 mm, which is more beneficial to the improvement of tar yield. In addition, vitrinite is a good carrier of tar yield, and the granular coal vitrinite after crushing is enriched to smaller particles. [ABSTRACT FROM AUTHOR]

Coal seams were buried extremely shallowly in the trench slope area, which is prone to inducing surface cracks, seriously threatening the surface environment and mine safety production. The development of surface mining cracks varies at different locations in the trench slope area. In this research, we aimed to study the dynamic characteristics and laws of surface crack widths at different mining locations in the trench slope area and reveal the evolution mechanism of surface crack widths. Taking the 125,203 working face in Anshan Coal Mine in Shaanxi Province, China, as the geological prototype, we analyzed the full-cycle dynamic change law and planar distribution law of the surface crack widths in the trench slope area by combining the unmanned aerial vehicle remote sensing technology and field actual measurements and revealed the dynamic evolution mechanism of surface mining cracks in the trench area. The research results showed that the dynamic changes of surface crack widths varied at different locations of the slope. The surface crack width in the downslope area increased first and then stabilized with the advance of the working surface; the crack width at the bottom of the trench shows the dynamic change characteristic of increasing–decreasing–slightly increasing–stabilizing with the continuous advance of the working surface. The surface crack width in the upslope area showed the dynamic change of increasing–decreasing–stabilizing with the continuous advance of the working surface. Influenced by the surface morphology, the development mechanisms of surface mining cracks were different. The research results can provide practical guidance for selecting the best treatment time for surface cracks in different areas. [ABSTRACT FROM AUTHOR]

Aiming at the problem of difficult mining of coal resources under buildings, railroads and water bodies in northern Shaanxi, China, a narrow strip filling mining (NSFM) method is proposed. The four-wheel cyclic mining and filling technology is systematically introduced, the method of theoretical analysis, numerical simulation and physical similarity simulation experiment is adopted to carry out the research, and the pressure rule of filling body—coal pillar and the control effect of roof in the mining and filling process are clarified. The finite beam model of elastic foundation is established, the discriminative basis of roof instability is put forward, and the key parameters of filling mining are deduced. The numerical simulation results show that in the process of four-wheel cyclic mining and filling, the backfill filled in this stage starts to participate in the load bearing after the next stage of coal pillar is mined, and the backfill regularly shares the overburden load in stages. The overall subsidence pattern of the immediate roof is similar to that of the "square basin", and the final subsidence of the immediate roof is 0.08 m, which is at a relatively low level. The physical similarity simulation experiment verifies the above conclusion, no separation layer and cracks appear in the roof of coal seam, and the filling body and coal pillar maintain stable safe bearing state. This method can improve the recovery rate of coal resources, control the roof subsidence in a small range, and provide a feasible solution for sustainable mining of coal seam under buildings, railroads and water bodies. [ABSTRACT FROM AUTHOR]

Under the pressure of water shortages, coal mine water has been allocated as a national water resource in China. However, the existence of harmful trace elements (HTEs) in coal mine water causes environmental risks and health concerns over its reuse. Through a lixiviation experiment, the dominant factors affecting the dissolution of HTEs in coal were simulated and analyzed, and the environmental risks of HTEs in coal mine water in China were evaluated for the first time. The average dissolved content levels of HTEs from coal were Mn > Cu > Zn > Ni > Ba > Cr > Co > V > Mo > Se > U > Pb > Cd, and the average maximum dissolution rates were Ni > Co > Mo > Zn > Cu > Cd > Mn > Se > Ba > Cr > U > Pb > V. Oxidation–reduction potential (Eh) and pH are the dominant factors controlling HTE dissolution. Higher oxygen exposure levels induce Eh and pH development, resulting in more HTE dissolution. This study constructed the dissolution potential index (FC) of HTEs from coal. Based on the results of the FC model, the areas with the highest migration potential and environmental risk of HTEs from coal seams to mine water are located in southern China, especially in the southwest, followed by areas of eastern Inner Mongolia and Shanxi and Shaanxi provinces. The corresponding risks in other regions are relatively low; thus, mine water utilization remains an effective option. This study provides an effective reference for the analysis of HTE enrichment in coal mine water and an evaluation of its safe utilization. [ABSTRACT FROM AUTHOR]

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The Majiagou Bridge comprising four sub-bridges is adjacent to the Weiqiang coal mine, Yulin City, Shaanxi Province, China. The mining of the longwall panel No. 1307 may damage the Majiagou Bridge. In this study, we predicted the mining-induced bridge movements using the finite element method (FEM) to examine whether the progressive mining of the longwall panel will pose a negative impact on the Majiagou Bridge. We reconstructed detailed three-dimensional models of the four sub-bridges by considering the superstructures and substructures. The input mechanical properties of the strata are estimated by calibrating with available field monitoring data. Effect of traffic load on the bridge subsidence is also accounted. The numerical predictions are: (1) after the panel No. 1307 is mined, the maximum vertical and horizontal displacements of the four bridges are 61.2 mm and 84.8 mm respectively, which occur on the sub-bridge D that is closest to the longwall panel, (2) traffic load has much less pronounced effect on the Majiagou Bridge than that due to mining, and (3) the maximum tilt and horizontal strain of the sub-bridges are 3.42e−5 m/m and 2.19e−5 m/m, which occur on sub-bridge B and sub-bridge A, respectively. In terms of tilt, the Majiagou Bridge is safe whereas it is to be damaged in terms of horizontal movement that is more critical in causing structural damage. Therefore, we suggest that a reasonably wider protective coal pillar should be set if the panel No. 1307 is to be mined, to ensure the safety of the Majiagou Bridge. [ABSTRACT FROM AUTHOR]