Underground Hydro-Pumped Energy Storage Using Coal Mine Goafs: System Performance Analysis and a Case Study for China

In response to the Paris climate agreement, the Chinese government has taken actions to improve the energy structure by reducing the share of coal-fired thermal power and increasing the use of clean energy. However, due to the extreme shortage of large-scale energy storage facilities, the utilization efficiency of wind and solar power remains low. This paper proposes to use abandoned coal mine goafs serving as large-scale pumped hydro storage (PHS) reservoir. In this paper, suitability of coal mine goafs as PHS underground reservoirs was analyzed with respects to the storage capacity, usable capacity, and ventilation between goaf and outside. The storage capacity is 1.97 × 106 m3 for a typical mining area with an extent of 3 × 5 km2 and a coal seam thickness of 6 m. A typical goaf-PHS system with the energy type αw=0.74 has a performance of 82.8% in the case of annual operation, able to regulate solar-wind energy with an average value of 275 kW. The performance of the proposed goaf-PHS system was analyzed based on the reservoir estimation and meteorological information from a typical region in China. It has been found that using abandoned coal mine goafs to develop PHS plants is technically feasible in wind and solar-rich northwestern and southwestern China.

Decision-Making on Reuse Modes of Abandoned Coal Mine Industrial Sites in Beijing Based on Environment-Economy-Society Matter-Element Models

Redevelopment of abandoned coal mine industrial sites (ACMISs) has been one of the critical research topics in recent years. The ecological system of ACMISs, which involves environmental, economic, and social characteristics, is an environment-economy-society (EES) composite system. Many factors with conflicting effects are involved in the sustainable development of this system. The matter-element analysis method presented in this paper can transform counteracting problems among influencing factors into compatible problems. This analytical approach leads to a reduction of the uncertainty of these influencing factors and provides a suitable research method to solve the complexity when selecting the most suitable reuse mode of the ACMIS. In this study, eight state-owned ACMISs in the suburbs of Beijing were investigated, and a suitability evaluation index system based on the EES conceptual framework was built. Targeting four reuse modes, including the residential area, the park, the scientific research and office campus, and the business district, we established a matter-element decision-making model to evaluate the priority of reuse mode selections scientifically. The results of our calculations show that the optimal reuse mode for the Qianjuntai, Muchengjian, and Huapogen ACMISs is the park; for the Da’anshan and Changgouyu ACMISs is the business district; for the Datai ACMIS is the scientific research and office campus; and for the Wangping ACMIS is the residential area. Since the suitability level of reusing the Anjiatan ACMIS in any of the four reuse modes is relatively low, it is recommended to reserve it for governmental strategically reserved open space. These real cases demonstrate that the research method is feasible and can be applied to reuse mode decisions for similar abandoned coal mines.

Case study of gas drainage well location optimization in abandoned coal mine based on reservoir simulation model

The development of abandoned coal mine gas has multiple advantages in terms of safety, economy, environment, and society. Due to previous excavations, the gas distribution is heterogeneous, thereby hindering well location optimization. In this study, considering the Shenbei abandoned coal mine as an example, the authors developed a workflow for well location optimization through simulation. The workflow includes: (1) the setup of an initial reservoir simulation model with the preliminary well location designed by experience; (2) the optimization of the well location based on the flowline distribution, and it is preferred that the well connect a large number of flowlines; (3) the simulation based on the optimized well location, and (4) repetition of the steps until the optimized well locations are determined. Moreover, the role of fracturing is also examined through simulation scenarios. The simulation results show that the locations of the two originally designed wells (1# and 4#) should be optimized due to the relatively low gas production without fracturing. The two wells are optimized according to the flow streamlines, demonstrating performance improvement. Moreover, the simulation results also show that there is no need to optimize the well 4# location if the fracturing technology is applied. An additional well is suggested based on the flow streamline analysis and gas production performance simulation. The main conclusions drawn from this study are as follows. (1) Five optimized well locations are determined for the Shenbei abandoned coal mine, and they should be located within the “O” ring, a high permeability region nearby the previous excavation zone; (2) Fracturing is an effective method for stimulating gas production; however, the extent of fracturing varies from well to well; (3) The workflow applied in this study is effective for the well location optimization in abandoned coal mines.

Analysis of Influencing Factors of Modification Potential of Abandoned Coal Mine Into Pumped Storage Power Station

By modifying underground spaces of abandoned coal mines into underground pumped storage power stations, it can realize the efficient and reasonable utilization of underground space and, at the same time, meet the increasing demand for energy storage facilities of the grid, bringing social, economic, and environmental benefits. Previous research in this area has been limited to the stage of conceptual discussion, and there is no scientific evaluation method for the modification and utilization potential of abandoned coal mine spaces. Establishing a scientific evaluation indicator system forms the basis for evaluating the underground space development and utilization capacity of abandoned mines. Based on the principle of pumped energy storage and the characteristics of coal mine roadway conditions, this paper utilized an analytical hierarchy process (AHP) to evaluate the main influencing factors, including elevation difference between the upper and lower reservoirs, reservoir capacity, roadway surrounding rock stability, and roadway permeability. It analyzed the modification potential of underground spaces and then verified the development potential of the underground spaces of abandoned mines by a statistic model. The study found that the elevation difference between the upper and lower reservoirs is the most influential indicator; second, the capacity of the upper and lower reservoirs is also an important evaluation indicator. The research methods and conclusions will provide useful tools and decision-making basis for analyzing the feasibility and techno-economic benefit of modifying the underground spaces of abandoned coal mines into pumped storage power stations.