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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "H: Geo-Energy".

Deadline for manuscript submissions: closed (15 June 2023) | Viewed by 18285

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Prof. Dr. Shengrong Xie

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Guest Editor

School of Energy and Mining Engineering, China University of Mining & Technology (Beijing), Beijing 100083, China
Interests: the theory and technology of resources exploitation; rock pressure and strata control; the mining disaster prevention and control
Special Issues, Collections and Topics in MDPI journals

Dr. Dongdong Chen

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Guest Editor

School of Energy and Mining Engineering, China University of Mining & Technology (Beijing), Beijing 100083, China
Interests: the theory of structural fracture of rock slab in quarry; control of roadway surrounding rock; coal mining and mine disaster prevention and control
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Green mining of coal resources aims to realize the best economic and environmental benefits in the process of coal resource development, which is relevant to the sustainable development of the earth. Green mining technologies include: water-preserved mining for water resource protection; filling mining for the protection of the earth and buildings; simultaneous extraction of coal and gas for realization of gas discharge; intelligent green mining to realize emission reduction; clean energy development in mining enterprises for the realization of resource transformation; and water and soil ecological restoration for the ecological protection of mining areas.

This Special Issue aims to introduce and disseminate the latest progress of regulations and methods in green coal mining, covering new paths of green mining, new breakthroughs in traditional mining technologies, and innovations in ecological protection of mining areas.

Topics of interest for publication include, but are not limited to, the following:

Improvement of coal resources in recovery rate and mining efficiency;
Innovation and application of water-preserved mining technology;
Intelligent green mining technology;
Clean and low-carbon utilization of coal;
Innovation and application of filling mining technology;
Ecological restoration of mining areas;
Disposal of abandoned mines;
Underground fluidized mining of coal;
Innovation and application of simultaneous extraction of coal and gas technology;
Utilization of associated resources in deep coal measures;
Development path of coal enterprises with the background of "double carbon";
Co-utilization of coal and biomass/waste.

Prof. Dr. Shengrong Xie
Dr. Dongdong Chen
Guest Editors

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Keywords

green mining
peak carbon dioxide emissions, carbon neutral
ecological restoration
abandoned mines
clean and low carbon
no-pillar mining method
filling mining
water-preserved mining
gas discharge
intelligent mining
fluidized mining
associated mineral resources of coal measures

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Published Papers (11 papers)

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Research

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19 pages, 12526 KiB

Open AccessArticle

Mechanism and Control of Asymmetric Floor Heave in the Gob-Side Coal Roadway under Mining Pressure in Extra-Thick Coal Seams

by Deqiu Wang, Yun Zheng, Fulian He, Jiayu Song, Jianlong Zhang, Yanhao Wu, Pengpeng Jia, Xiaohui Wang, Baoping Liu, Feifei Wang, Yajiang Zhang and Kai Tao

Energies 2023, 16(13), 4948; https://doi.org/10.3390/en16134948 - 26 Jun 2023

Cited by 2 | Viewed by 1076

Abstract

Due to their tense mining succession relationship, gob-side roadways may undergo significant deformation under multi-mining pressure. In this article, many methods, such as on-site research, a theoretical analysis, a numerical simulation and an industrial experiment, are used to research the mechanism of asymmetric floor heave in a gob-side coal roadway affected by mining pressure during the mining of extra-thick coal seams. Our main research is as follows: (1) By monitoring the floor deformation in the roadway on site, it is concluded that the roadway floor shows asymmetry, indicating that the floor displacement near the coal pillar side is relatively large. (2) Based on a lateral overburden structure model of the roadway, the calculation formulas of the horizontal vertical stress caused by the roadway excavation and the excavation of the upper working face are derived separately, and the vertical stress coupling curves on both sides of the roadway during the mining of the upper working face are obtained through a numerical simulation. It is concluded that the cause of the asymmetric floor heave in the roadway is an uneven distribution of vertical stress. (3) The numerical simulation shows a symmetrical distribution of the floor displacement curve during the roadway excavation with a max. displacement of 49.5 mm. The floor displacement curve during the mining of the upper working face is asymmetric with a max. displacement of 873 mm at a distance of 1 m from the central axis near the coal pillar side. The range of the plastic zone in the roadway gradually expands with the mining of the upper working face, and the maximum depth of floor failure is 5.5 m. (4) According to the cooperative control principle of “roof + two sides + floor”, an asymmetric floor heave joint control scheme of “floor leveling + anchor cable support + concrete hardening” is proposed. The floor deformation monitoring results indicate that the max. floor heave at the measurement point near the coal pillar in the roadway is 167 mm, and the floor heave is effectively controlled. Full article

(This article belongs to the Special Issue Method and Technology of Green Coal Mining)

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19 pages, 4134 KiB

Open AccessArticle

Study on Source Identification of Mixed Gas Emission and Law of Gas Emission Based on Isotope Method

by Gang Xu, Yaping Hou, Hongwei Jin and Zhongwei Wang

Energies 2023, 16(3), 1225; https://doi.org/10.3390/en16031225 - 23 Jan 2023

Cited by 1 | Viewed by 1310

Abstract

It is of great significance to obtain the source of mixed gas emission from the working face and the law of gas emission from each coal seam for the targeted implementation of gas control measures. Based on the principle that the hydrocarbon isotope values of gas in different coal seams have significant variability, a hydrocarbon isotope method for identifying the source of gas emission is proposed. Taking Pingmei No. 6 Coal Mine as the study area, the distribution characteristics of each value were obtained by testing the values of carbon and hydrogen isotopes in the gas of mined coal seams and adjacent coal seams; by testing the hydrocarbon isotope value of CH₄ in the mixed gas of coal seam, the proportion of gas emission in each coal seam is determined and the law of gas emission in each coal seam is studied. The results show that the variation law of the proportion of gas emission in each coal seam can be divided into three stages: the dominant stage of gas emission in the mining layer (stage I), the stage of gas emission in the long-distance adjacent coal seam (stage II), and the dynamic equilibrium stage of gas emission in each coal seam (stage III). In the process of working face mining, the amount of gas emission in the mining layer remains in a small fluctuation state, and the proportion of gas emission decreases rapidly in stage I and stage II, and remains stable in stage III; the amount of gas emission and the proportion of gas emission in adjacent coal seams increase rapidly in stage I and stage II, and remain stable in stage III; the mixed gas emission of the working face increases rapidly in stage I and stage II, and remains stable in stage III. The calculation formula of the gas emission rate of the adjacent coal seam is established; during the development of the height of the mining fractured zone, the gas emission rate of the adjacent coal seam increases exponentially, and the gas emission ratio and gas emission amount of the adjacent coal seam increase; after the height of mining fracture zone tends to be stable, the gas emission rate, the proportion of gas emission, and the amount of gas emission remain of adjacent coal seams remain in a small fluctuation state. Full article

(This article belongs to the Special Issue Method and Technology of Green Coal Mining)

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26 pages, 20539 KiB

Open AccessArticle

New Technology of Pressure Relief Control in Soft Coal Roadways with Deep, Violent Mining and Large Deformation: A Key Study

by Shengrong Xie, Hui Li, Dongdong Chen, Shaohua Feng, Xiang Ma, Zaisheng Jiang and Junqi Cui

Energies 2022, 15(23), 9208; https://doi.org/10.3390/en15239208 - 5 Dec 2022

Cited by 8 | Viewed by 1436

Abstract

Previous studies have shown that the influence of deep dynamic pressure on the surrounding rock control of a coal roadway is one of the difficulties in mine roadway support. Based on the investigation of the headgate 11231 in a coal mine, this study analyzes the damage characteristics of coal roadway surrounding rock affected by deep dynamic pressure, expounds on the difficulties of controlling the roadway surrounding rock, and creatively proposes a cooperative control technology of external anchor–internal unloading for regulating large deformation of roadways. The vertical stress distribution and transfer law of surrounding rock with different hole-making depths, spacing, and lengths after roadway excavation were simulated and studied, and an appropriate parameter range of hole-making space in the stage without dynamic pressure influence was obtained. Considering the influence of mining dynamic pressure, the surrounding rock pressure relief effect of each optimized hole-making parameter was analyzed. In addition, the optimal hole-making parameters (the hole-making depth, spacing, and length were 8 m, 3.2 m, and 3 m, respectively) that can effectively reduce the high stress of roadway shallow surrounding rock in two stages (without and with dynamic pressure) and ensure integrity of the shallow surrounding rock were obtained. The actual field application shows that the new technology can reduce the higher rib deformation by approximately 850 mm and achieve a good surrounding rock control effect. The research and practice show that the pressure relief control for soft coal roadways with deep, violent mining and large deformation has achieved success, providing technical support for the maintenance of the same type of roadway. Full article

(This article belongs to the Special Issue Method and Technology of Green Coal Mining)

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22 pages, 18854 KiB

Open AccessArticle

Study on Stability and Control of Surrounding Rock in the Stopping Space with Fully Mechanized Top Coal Caving under Goaf

by Fulian He, Bingquan Liu, Deqiu Wang, Dongdong Chen, Yanhao Wu, Liming Song, Xiang Ma, Qiucheng Ye, Zaisheng Jiang, Fangfang Guo, Weiguang Wang and Yiyi Wu

Energies 2022, 15(22), 8498; https://doi.org/10.3390/en15228498 - 14 Nov 2022

Cited by 4 | Viewed by 1466

Abstract

Under the condition of fully mechanized top coal caving in close-distance coal seams, the surrounding rock of the stopping space easily loses stability during the withdrawal of mining equipment in the working face because the lower coal seam working face is located under the goaf and the overburden rock has a large range of complex interaction. Field investigation, theoretical analysis, laboratory experiment, similar simulation experiment, numerical simulation, and field industrial tests are used to carry out the research on the stability and control of the surrounding rock in the large section stopping space under the goaf in this paper. The research conclusions are as follows. (1) It is determined that the lower coal seam working face can only stop mining under the goaf, and the reasonable stopping position under the goaf should ensure that the key block fracture line of the main roof is behind the support. (2) The interaction law between the main roof’s key blocks of the upper and lower coal seams is analyzed, and the catastrophic conditions for sliding instability and rotary instability of the main roof’s key blocks of the upper and lower coal seams are obtained. (3) “Anchorage with push and pull equipment-Embedded anchorages and trays” integral anchoring technology is developed. The dimensions of the push and pull equipment are determined. (4) Through numerical simulation of the distribution characteristics of the anchor cable pre-stress field, the asymmetric control scheme of “Partition long and short anchor cables + Integral polyurethane mesh + Embedded anchorages and trays for roof protection” is determined. The rock pressure observation shows that the withdrawal of the working face equipment is implemented safely. Full article

(This article belongs to the Special Issue Method and Technology of Green Coal Mining)

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24 pages, 10767 KiB

Open AccessArticle

Study on the Influence and Control of Stress Direction Deflection and Partial-Stress Boosting of Main Roadways Surrounding Rock and under the Influence of Multi-Seam Mining

by Dongdong Chen, Fangfang Guo, Zijian Li, Xiang Ma, Shengrong Xie, Yiyi Wu and Zhiqiang Wang

Energies 2022, 15(21), 8257; https://doi.org/10.3390/en15218257 - 4 Nov 2022

Cited by 10 | Viewed by 1495

Abstract

A large coal pillar (usually more than 90 m) is generally left in place to ensure the stability of main roadway groups, due to its long service lifespan, which commonly also causes a significant loss of coal resources. The design of the width of the protective coal pillar and the control system of the surrounding rock are directly determined by the characteristics of the stress field and the damage mechanism under the influence of the mining activities. However, there are few studies on the effects of the partial-stress boosting and the direction deflection of the stress field on the failure evolution of the surrounding rock (especially in multi-seam mining). In this paper, theoretical analysis and numerical simulation are used to investigate the direction evolution of the maximum principal stress in front of the working face with malposition distances between the upper and lower working faces during the influence of double coal seams mining. Furthermore, a large-scale numerical model is used to study the deviatoric stress evolution of the surrounding rock and the propagation process of the plastic zone in the main roadway group with different widths of protective coal pillars. Then, an asymmetric cooperative anchoring classification method is proposed to strengthen the roadway support, depending on the critical area of the deviatoric stress in the roadway surrounding rock. The peak zone deflection of the deviatoric stress determines the evolution direction of the plastic area, and the peak value of the deviatoric stress presents a typical asymmetric stress boosting on both sides of the roadway. These findings are validated by the on-site ground pressure monitoring results and the practical failure modes of the surrounding rock. Full article

(This article belongs to the Special Issue Method and Technology of Green Coal Mining)

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11 pages, 4350 KiB

Open AccessArticle

Experimental Study on Damage Fracture Law of Coal from Solid-Propellant Blasting

by Huaibao Chu, Mengfei Yu, Bo Sun, Shaoyang Yan, Haixia Wei, Guangran Zhang, Donghui Wang and Jie Xu

Energies 2022, 15(21), 8104; https://doi.org/10.3390/en15218104 - 31 Oct 2022

Cited by 1 | Viewed by 1334

Abstract

The low permeability of coal seams has always been the main bottleneck restricting coalbed methane drainage. In this paper, a coal seam anti-reflection technology with solid-propellant blasting was proposed, and the composition and proportion of the solid propellants were determined based on the principle of oxygen balance. The authors designed a solid-propellant blasting damage fracture experiment of simulation coal, tested the impact pressure on a blast hole wall, measured the ultrasonic wave velocity, explosive strain and crack propagation velocity, and then revealed the blasting damage fracture process and mechanism of coal based on the experimental results and damage fracture mechanics theory. The history curve of impact pressure time can be divided into three processes including the slow pressurization process, dramatic increase process, and nonlinear pressure relief process. The pressure distribution along the whole blasting hole was uneven, and the peak pressure was relatively small, but the pressure action time was long. The damage and fracture process of coal solid-propellant blasting can be divided into two stages including the rapid damage fracture development stage and the stable slow damage fracture development stage. Firstly, the explosion stress wave produced and rapidly accelerated the radial cracks extension; secondly, the cracks slowly expanded over a large area by the combined effects of the high-pressure gases, the gas, and the original rock stress. Full article

(This article belongs to the Special Issue Method and Technology of Green Coal Mining)

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17 pages, 11752 KiB

Open AccessArticle

Experimental Study on Deformation Behavior and Permeability Evolution of Sandstone Responding to Mining Stress

by Yang Liu, Tong Zhang, Jun Wu, Zhengyang Song and Fei Wang

Energies 2022, 15(19), 7030; https://doi.org/10.3390/en15197030 - 25 Sep 2022

Viewed by 1333

Abstract

Mining-induced hydromechanical behavior of sandstone is critical to mining safety and disaster prevention. To investigate the evolution behavior of the mechanical and permeability properties of sandstone, mining-induced stress was imitated by increasing axial stress and decreasing confining stress, and a set of hydromechanical experiments were further performed, incorporating the effect of in situ stress, pore pressure, and mining stress. The results show the similar variation tendencies of the deformation and permeability of sandstone under different loading paths of in situ stress and pore pressure. Most sandstone samples maintain a compression state for the peak stress condition. The failure mode evolved from shear failure to shear–tension failure with the increase in in situ stress. The stress-relief effect significantly effects the permeability, since the permeability of sandstone increases exponentially with decreasing effective confining stress. The growth rate of permeability in Stage II is significantly greater than that in Stage I. One order of magnitude of permeability was presented at the peak stress situation. A fitting exponential model based on the alteration of effective confining stress was proposed to describe the permeability evolution dominated by the stress-relief effect, and the discovered permeability model can accurately describe the experimental results. The research results provide significant guidance for understanding the hydromechanical behavior and water hazard prevention for underground coal mines. Full article

(This article belongs to the Special Issue Method and Technology of Green Coal Mining)

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22 pages, 66504 KiB

Open AccessArticle

Study on the Long-Distance Gas Pre-Drainage Technology in the Heading Face by Directional Long Borehole

by Yunbing Hou, Junqi Cui and Ruipeng Liu

Energies 2022, 15(17), 6304; https://doi.org/10.3390/en15176304 - 29 Aug 2022

Cited by 3 | Viewed by 1485

Abstract

Gas control in the heading face of a coal roadway is an important and difficult point in coal mining in China. On the basis of analyzing the disadvantages of high gas control cost and long drainage period in the existing mine heading face, a long-distance pre-drainage method of long-distance drilling is proposed to control the gas in the heading face so as to improve the tunneling speed. Applied to the engineering geological conditions of Changcun coal mine, the technology is studied in detail. First, a gas migration model considering permeability changing with time is established, and the model is put into the numerical simulation software to study the variation law of permeability and gas pressure under the conditions of single borehole and multi-borehole drainage. The results show that with the increase of drainage time, the permeability around the borehole increases gradually, the gas pressure decreases gradually, and the permeability at the borehole boundary increases the most, reaching 1.2 times the initial permeability. In the process of multi-borehole drainage, there will be mutual influence between boreholes, but with the increase of borehole spacing, the degree of this influence gradually decreases. Second, according to the results of numerical simulation, a reasonable gas drainage scheme is designed and applied in the field. The field application shows that the technology has a good gas drainage effect, the gas drainage concentration and flow are at a high level for a long time, the drilling cuttings quantity is always lower than the critical value, and the excavation length of roadway increases by more than 50 m per month. These results indicate that this technology is a promising method to realize the safe and rapid excavation of a mine coal roadway. Full article

(This article belongs to the Special Issue Method and Technology of Green Coal Mining)

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21 pages, 43906 KiB

Open AccessArticle

Control Techniques for Gob-Side Entry Driving in an Extra-Thick Coal Seam with the Influence of Upper Residual Coal Pillar: A Case Study

by Shengrong Xie, Fangfang Guo and Yiyi Wu

Energies 2022, 15(10), 3620; https://doi.org/10.3390/en15103620 - 15 May 2022

Cited by 6 | Viewed by 1919

Abstract

In multi-seam mining, the residual coal pillar (RCP) in the upper gob has an important influence on the layout of the roadway in the lower coal seam. At present, few papers have studied the characteristics of the surrounding rock of gob-side entry driving (GED) with different coal pillar widths under the influence of RCP. This research contributes to improving the recovery rate of the extra-thick coal seam under this condition. The main research contents were as follows: (1) The mechanical parameters of the rock and coal mass were obtained using laboratory experiments coupled with Roclab software. These parameters were substituted into the established main roof structure mechanics model to derive the breakage position of the main roof with the influence of RCP, and the rationality of the calculation results was verified by borehole-scoping. (2) Based on numerical simulation, the evolution laws of the lateral abutment stress in the lower working face at different relative distances to the RCP were studied. FLAC3D was used to study the whole space-time evolution law of deviatoric stress and plastic zone of GED during driving and retreating periods with various coal pillar widths under the influence of RCP. (3) The plasticization factor P was introduced to quantify the evolution of the plastic zone in different subdivisions of the roadway surrounding rock, so as to better evaluate the bearing performance of the surrounding rock, which enabled a more effective determination of the reasonable coal pillar width. The field application results showed that it was feasible to set up the gob-side entry with an 8 m coal pillar below the RCP. The targeted support techniques with an 8 m coal pillar could effectively control the surrounding rock deformation. Full article

(This article belongs to the Special Issue Method and Technology of Green Coal Mining)

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Review

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26 pages, 32645 KiB

Open AccessReview

Application of Gob-Side Entry Driving in Fully Mechanized Caving Mining: A Review of Theory and Technology

by Dongdong Chen, Jingkun Zhu, Qiucheng Ye, Xiang Ma, Shengrong Xie, Wenke Guo, Zijian Li, Zhiqiang Wang, Shaohua Feng and Xiangxiang Yan

Energies 2023, 16(6), 2691; https://doi.org/10.3390/en16062691 - 13 Mar 2023

Cited by 9 | Viewed by 1631

Abstract

China has abundant coal resources, and the distribution of coal seams is complex. Thick coal seams account for more than 45% of all coal seams. Fully mechanized top coal caving mining has the advantages of large production, high efficiency, and low cost. In fully mechanized caving mining, especially in fully mechanized caving mining of extra-thick coal seams, the mining space is ample, the mine pressure is severe, and the roadway maintenance is complex. As a result, it is necessary to summarize and discuss the gob-side entry driving of fully mechanized caving in theory and technology, which will help to promote the further development of fully mechanized caving gob-side entry driving technology. First, in recent years, the research hotspots of gob-side entry driving have focused on the deformation mechanism and the control method of the roadway surrounding rock. Secondly, this paper discusses the theoretical models of the “triangle-block” and “beam” for the activity law of the overlying strata in gob-side entry driving, including the lateral breaking “large structure” model, compound key triangle block structure model in the middle and low position, the high and low right angle key block stability mechanics model, elastic foundation beam model, low-level combined cantilever beam + high-level multilayer masonry beam structure model, and the vertical triangular slip zone structure model. It introduces the “internal and external stress field theory” and the “stress limit equilibrium zone model”. Thirdly, it summarizes several numerical simulation analysis methods in different conditions or research focuses and selects appropriate constitutive models and simulation software. Finally, it introduces surrounding rock control technology, including two ribs, the roof, and under challenging conditions. It provides a method reference for support in similar projects. Full article

(This article belongs to the Special Issue Method and Technology of Green Coal Mining)

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20 pages, 7727 KiB

Open AccessReview

Application of Pre-Splitting and Roof-Cutting Control Technology in Coal Mining: A Review of Technology

by Shengrong Xie, Yiyi Wu, Fangfang Guo, Hang Zou, Dongdong Chen, Xiao Zhang, Xiang Ma, Ruipeng Liu and Chaowen Wu

Energies 2022, 15(17), 6489; https://doi.org/10.3390/en15176489 - 5 Sep 2022

Cited by 14 | Viewed by 2384

Abstract

According to the development requirements of green mining of coal resources, it is imperative to improve the extraction rate of coal and the application of safe and efficient mining technology. Pre-splitting and roof cutting technology is widely used in reducing residual coal pillars and safe pressure relief mining, which has become the crucial technology for pillar-free mining methods. Therefore, it is essential to review and discuss the research hotspots, cutting-edge methods, principles of action, and application areas of the development of this technology. Above all, the research data on pre-splitting and roof-cutting development in the past ten years are summarized and outlined. The research’s hot spots are pressure relief technology and gob-side entry retaining technology. Then, the functional forms of pre-splitting and roof cutting technology are discussed and compared, including explosive blasting (directional energy gathering blasting, liquid explosive blasting, and composite blasting), hydraulic fracturing, liquid CO₂ gas fracturing, and mechanized roof cutting (chain arm saw machine and directional cutting roof rig). Through the analysis of field application cases, the application field is divided into three major areas: non-coal pillar mining (gob-side entry driving with narrow coal pillar, gob-side entry retaining with the filling body, completely gob-side entry retaining, and “N00” construction method), pressure relief at working face (thick and hard main roof cracking and end area hard roof cracking), and pressure relief at roadway (gob-side roadway pressure relief and blasting pressure relief technology for roadways). By detailing the process of each application technology one by one, the principle and mode of pre-splitting in each technology are expounded. Finally, the development prospects of pre-splitting and roof cutting in new technical methods, deep pressure relief mining, intelligent unmanned mining, and green and efficient mining are prospected, providing references for similar projects. Full article

(This article belongs to the Special Issue Method and Technology of Green Coal Mining)

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