Advances in Coal and Water Co-Mining
1
State Key Laboratory of Coal Resources and Safe Mining (CUMT), China University of Mining & Technology, Xuzhou 221116, China
2
School of Mines, China University of Mining & Technology, Xuzhou 221116, China
*
Authors to whom correspondence should be addressed.
Energies 2023, 16(6), 2666; https://doi.org/10.3390/en16062666
Submission received: 14 December 2022
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Accepted: 8 March 2023
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Published: 13 March 2023
(This article belongs to the Special Issue Advances in Coal and Water Co-mining)
1. Introduction
According to data from the BP Statistical Review of World Energy 2020 [1], fossil energy still accounts for a major part of the world’s energy supply, with coal accounting for around 26% of global primary energy. Large-scale, high-intensity underground coal mining can cause damage to the overburdened structure of the coal seam roof, resulting in a shift in the aquifer’s water circulation pattern from the inter-bed runoff to vertical runoff, with most of the groundwater collapsing into overburdened fissures and mining areas [2]. This leads to environmental problems such as falling groundwater levels, surface rivers drying up and the desertification of vegetation [3].
The special nature of the coal production base’s geological environment dictates that the protection and scientific use of the limited water resources in the coal development process must be prioritized in order to maintain and improve the fragile mining ecology. Therefore, the “coal and water co-mining” Special Issue should attract attention and concern. The technical, economic and infrastructural barriers associated with this subject also need to be overcome. This can be achieved with the help of researchers. The following is a brief review of the development of the “coal and water co-mining” Special Issue.
Water-preserved coal mining: In 1992, Fan [4] first proposed the concept and method of water-preserving coal mining in response to environmental water problems arising in the northern part of the Ordos Basin in China. In 1995, after a study of hydrogeological and environmental problems in the Yushenfu mining area, the geological zoning of water-preserving coal mining conditions was established, and the term “water-preserving coal mining” was used for the first time [5]. In 2017, Fan [6] proposed a new coal-mining technology that sought an optimal balance between the amount of coal mined and the carrying capacity of the water resources. This technology controlled the movement of rock layers to maintain the structural stability of aquifers (rock formations) that had water supply significance and ecological value or demonstrated water level changes within a reasonable range. Following the introduction of this technology, a variety of relevant research subjects, scientific and engineering problems and methods of water-preserving coal mining were proposed [7,8]. A water-retention coal mining technology characterized by the “blocking method” was formed.
Coal mine underground reservoir: Using the Shendong mine as a production and experimental base, Gu has been exploring technologies for the conservation and use of mine water since 1995. Based on the concept of “guide-storage-use”, the “coal mine underground reservoir” academic concept and technical system was proposed in 2015 [9]. Namely, by connecting an artificial dam and a coal pillar dam (which was formerly a safe coal pillar) to form a closed space in the mining area for mine water storage, the mine water can be filtered and purified by in situ gangue and then used underground or on the surface for agriculture and industry. This coal mine underground reservoir technology was popularized and applied in the Shendong mine, providing more than 95% of the water for the mine. This effectively alleviated the contradiction between water conservation and safe and efficient coal mining. Coal mine underground reservoir technology is currently being applied as a new technology in many coal mines in western China. However, it still faces some challenges [10], including (1) evaluating the impact of coal mining on groundwater systems and the dynamic balance of regional water resources theory; (2) developing basic theoretical research and key technologies for underground water reservoirs in coal mines; and (3) developing theories and technologies for the ecological construction of mining areas based on the protection of water resources, etc.
Water resources affected by mining: Since 2011, Yao has focused on key scientific issues in the co-extraction of coal and water in ecologically fragile mining areas [11], carrying out systematic, basic, theoretical and applied technological research on water–rock (coal) interactions. Based on the entire life cycle of coal mining, in 2020, Yao et al. [12] proposed the concept of a “mining-affected water resource”. Due to the influence of the overlying rock fissures caused by coal mining, the surface water system, the quaternary aquifer water and aquifer water from the overlying rock pore fissure are transported along the hydraulic fissure channel. They then gather in the offset area, fissure area or mining area, where they form a mining-affected water resource. These types of extracted water resources are classified according to their state of motion and spatial location relationships. The technical principles of the extracted water resources’ development have also been described. In 2021, Yao et al. [13] proposed the theory that coal and water co-mining conflicts will accompany the entire life cycle of coal mining and the post-coal mining period. They accordingly put forward a series of recommendations, including the proposal that state agencies should actively participate in medium- and long-term planning for coal mining and should increase the investment in science and technology for regional coal development.
It is evident that via the efforts of researchers, the issue of “coal and water co-mining” has been developing and progressing since the 1990s. This has resulted in a series of relevant theories and advanced technologies that effectively relieved the pressure on environmental protection in coal mining areas and created substantial economic, social and environmental benefits. However, scientific and engineering difficulties still exist. In Section 2, a brief summary of the research is provided in chronological publication order. In Section 3, some brief conclusions are drawn, and further research directions are indicated.
2. A Short Review of the Paper in This Issue
The first paper [14] in this Special Issue is presented by Li et al., who proposed a fluidization gangue-grouting technology for filling the collapse area. Backfill mining is an important technical approach in coal and water co-mining that can effectively reduce the environmental impact of underground coal mining. The current research on underground filling mainly focuses on the paste filling, solid filling and grouting filling of the overburdened separation layer after scaffolding. The prediction method for residual space in the collapse area and the slurry diffusion law of gangue fluidization filling are two key aspects for successfully implementing this technology and for maximizing the use of goaf for gangue backfilling to reduce the overburden settlement. Based on existing studies, Li et al. used a transient electromagnetic method to detect the collapsed coal seam in a coal caving face. They investigated the distribution pattern of the measured anomalous zone in the collapsed mining area, which reflected the distribution pattern of the remaining space from the side. Additionally, the diffusion law of the fluidised coal gangue slurry in the caving goaf was simulated and analysed by the COMOSL simulation software, and a field-filling test was carried out. The paper identified that using high- and low-fluidised fillings in crumbling mining areas can safely and effectively handle gangue in mines. The results of the study provided theoretical support for the use of gangue fluidised filling technology in areas with a thick coal seam header.
3. Conclusions
The Special Issue “Advances in Coal and Water Co-mining” has collected two published papers describing relevant scientific developments in the methods and applications of coal and water co-mining.
It is essential to continuously advance research on this topic. Promising aspects that should be investigated in the near future include (but are not limited to) the following:
- Geological condition survey identification;
- The evaluation of hydrogeological conditions;
- Slope stability control technology;
- The relationship between vegetation and groundwater level;
- The structural protection of water-bearing (septic) seams during coal mining;
- Surface and groundwater reservoir technology;
- Coal and water co-mining technology;
- Mechanisms of water–coal (rock) interactions;
- The integrated use of mining water resources;
- Water damage control in coal mines;
- The detection and prediction of the height of the hydraulic fracture zone;
- Influence mechanisms of the ecological environment in mining areas;
- Mine land reclamation and ecological reconstruction technology.
Author Contributions
The authors, Q.Y. and L.Y. contributed equally to this work. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Acknowledgments
We would like to especially thank all authors who submitted their work to this Special Issue.
Conflicts of Interest
The authors declare no conflict of interest.
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Yao, Q.; Yu, L. Advances in Coal and Water Co-Mining. Energies 2023, 16, 2666. https://doi.org/10.3390/en16062666
AMA Style
Yao Q, Yu L. Advances in Coal and Water Co-Mining. Energies. 2023; 16(6):2666. https://doi.org/10.3390/en16062666
Chicago/Turabian StyleYao, Qiangling, and Liqiang Yu. 2023. "Advances in Coal and Water Co-Mining" Energies 16, no. 6: 2666. https://doi.org/10.3390/en16062666
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