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In this paper, the No. 30201 working face of a specific colliery was determined as the study area in the Yushen mining area, China. The objective of this paper is to determine the optimal position for pressure regulation measures during the final mining stage. A mechanical calculation model for stabilized coal pillar was developed. The analytical solution for the front abutment pressure function was obtained. Limit equilibrium theory and beam theory were employed to compute the critical width value of the stabilized coal pillar. The analysis focused on examining the spatiotemporal relationship between the rotational deformation of the main roof and the stability of the retracement channel. The study utilized numerical simulation to investigate the failure characteristics of the surrounding rock and the stress redistribution in the stabilized coal pillar within the working face. Through comprehensive analysis, a reasonable width of 15 m for the stabilized coal pillar was determined and successfully implemented in field practices. A method of using Artificial Neural Network (ANN) to select the stabilized coal pillar width was proposed. The input characteristics of ANN were determined through theoretical analysis. Four models of BP, WOA-BP, PSO-BP, and CPSO-BP were trained. The calculation accuracy of each model is evaluated by three quantitative metrics: MAE, MRE, and RMSE. The MAE value of the CPSOBP model is 0.9489, showing a reduction of 70.87% compared to the BP model, 55.84% compared to the WOA-BP model, and 51.26% compared to the PSOBP model. The MRE value is 0.0559, which is 71.51%, 56.29%, and 53.24% lower than the other models, respectively. The RMSE value is 1.0617, which is 68.92%, 56.13%, and 53.03% lower than other models, respectively. The four models were employed to compute the width of the stabilized coal pillar. The values for the BP, WOA-BP, PSO-BP, and CPSO-BP models were 12.7 m, 16.3 m, 14.1 m, and 15.2 m, respectively, indicating that the CPSO-BP model can effectively determine the width of the stabilized coal pillar. [ABSTRACT FROM AUTHOR]

Environmentally persistent free radicals (EPFRs) can pose exposure risks by inducing the generation of reactive oxygen species. As a new class of pollutants, EPFRs have been frequently detected in atmospheric particulate matters. In this study, the seasonal variations and sources of EPFRs in a severe cold region in Northeastern China were comprehensively investigated, especially for the high pollution events. The geomean concentration of EPFRs in the total suspended particle was 6.58 × 10 13 spins/m 3 and the mean level in winter was one order of magnitude higher than summer and autumn. The correlation network analysis showed that EPFRs had significantly positive correlation with carbon component, K + and PAHs, indicating that EPFRs were primarily emitted from combustion and pyrolysis process. The source appointment by the Positive Matrix Factorization (PMF) model indicated that the dominant sources in the heating season were coal combustion (48.4%), vehicle emission (23.1%) and biomass burning (19.4%), while the top three sources in the non-heating season were others (41.4%), coal combustion (23.7%) and vehicle emissions (21.2%). It was found that the high EPFRs in cold season can be ascribed to the extensive use of fossil fuel for heating demand; while the high EPFRs occurred in early spring were caused by the large-scale opening combustion of biomass. In summary, this study provided important basic information for better understanding the pollution characteristics of EPFRs, which suggested that the implementation of energy transformation and straw utilization was benefit for the control of EPFRs in severe cold region., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The effective production scheduling of dry bulk ports is a challenging task that demands meticulous planning, task allocation based on customer requirements, as well as strategic route and timing scheduling. Dry bulk ports dedicated to handling commodities like coal and iron ore frequently engage in blending operations as a strategic imperative to gain market competitiveness. The process of blending coal and ore entails the timely arrival of the requisite raw materials at predetermined locations. Simultaneously, it necessitates the coordination of the sequencing of goods entering and departing the port to align with the operational demands associated with material stockpiles. This paper describes and analyzes an operational scheduling problem encountered by one of the largest coal blending sea ports in China. Specifically, a rich constraint programming model is presented to define operation sequences integrating daily inbound and outbound services provided by the port, minimizing the overall operation time. In order to enhance the practicality of the method, a CP-based adaptive simulated annealing local search algorithm has been designed and developed for the optimization problem. The empirical validation of the proposed method is conducted using both real production data and generated experimental data adhering to specific rules. The results conclusively demonstrate the efficacy and feasibility of the proposed method. This also substantiates its practicality and effectiveness in real-world applications, facilitating efficient production and energy-saving operations for the coal port. [ABSTRACT FROM AUTHOR]

The current approach to life cycle carcinogenic impact assessment (LCCA) is hindered by its static and linear characteristics. This situation prevents the accurate prediction of the incidence, associated damage, and potential economic burden of cancer. This study explores a highly comprehensive pathway for LCCA assessment. It uses the impacts of Tracheal, bronchus, and lung (TBL) predicted by the LCCA of China's coal power industry through a screened statistical regression model as the research target. The latest global burden of disease estimates is utilized to quantify the health damage from TBL incidence, whereas an approach combining the actual cost of health and human capital is applied to further assess the economic burden of TBL. Findings indicate that the traditional and static LCCA method, which relies on animal toxicity data, can lead to underestimations in actual LCCA. The interaction among spatiotemporal meteorological factors, epidemiological cancer disease burden, and socioeconomic behaviors allows exhibits nonlinearity due to the changes in the combined toxicity of mixed key substances. Following the active implementation of ultralow emission and energy-saving transformations in China's coal power industry, the national percentage of TBL cancer incidence caused by pollutants from the coal power industry decreased from 25.2 % in 2004 to 11.5 % in 2020. Results indicate that the established dynamic LCCA model based on temporal and spatial climate, socioeconomic, and epidemiological cancer data can be feasibly employed for the accurate impact evaluation and mitigation of carcinogens in practical applications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

To improve the recovery for corner coal left over in mines, taking the Xin'an Mine in China as the research object, the gradual increase support mining method for recovering corner coal is proposed in this study and the evolution of the overlying strata pressure is investigated. The dynamic process of the overburden roof in the corner coal and the hydraulic support were simulated by using FLAC3D software. Results show that, under the gradual increase support mining, the abutment pressure over the mining working face is less than 21 MPa. The overlying rock over the coal seam roof forms a periodic breaking--collapse cycle with a periodic pressure step distance of 10 m and the hydraulic support load is 13-25 MPa. Based on that, the gradual increase support mining method including a scheme of three supports and three chutes adding for every 9 m is designed and the corner coal is fully recovered. The obtained conclusions provide a significant reference for predicting strata movement over the corner coal, which can help aid in designing such mining method in engineering applications. [ABSTRACT FROM AUTHOR]

China's growing demand for bulk chemicals and concerns regarding energy security are scaling up coal-to-olefins (CTO) production. Three generations of independent dimethyl ether/methanol-to-olefins technologies have been successively launched with greatly improved production efficiencies. However, to date, widespread concerns regarding the intensive environmental impacts and potential economic risks have not been addressed in the context of this industrialization. Here we show that, through the technological progress from the first to the third generation, life cycle energy consumption, water consumption, and carbon emissions can be reduced to 119.5 GJ/t, 27.6 t/t, and 9.1 t CO 2 -eq/t, respectively, and human health damage, ecosystem quality damage, and resource scarcity impacts can be decreased by 40.5 %, 50.1 %, and 16.4 %, respectively. This is accompanied by an excellent performance in terms of production cost, net present value, and internal return rate at 792.5 USD/t, 173.4 USD/t, and 19.4 %, respectively. Substantial environmental and economic benefits can be gained by coupling renewables in the form of using green hydrogen from solar and wind power to synthesize methanol. Particularly, life cycle carbon emissions and resource scarcity impacts are reduced by 23.4 % and 22.4 %, respectively, exceeding the reduction in technological progress. However, coupling renewables increases the life cycle energy consumption to 154.5 GJ/t, counteracting the benefits of technological progress. Our results highlight the importance of technological progress and coupled renewables for enhancing the sustainability of the CTO industry., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Economic policies affect companies' production decisions. And the energy consumption volume is an intuitive reflection of the enterprise's production decisions. In China, coal is the main source of carbon emissions and the most important energy source. Therefore, the coal market and the uncertainty of economic policies are both directly tied to the carbon market. This study explores both the direct impact of economic policy uncertainty and coal price on carbon prices as well as the indirect impact of economic policy uncertainty on carbon prices through coal prices by utilizing the DCC-GARCH model and the NARDL model. The findings indicate that the dynamic correlations between coal prices and the CEPU are always negative and that those between the price of carbon and the CEPU vary by area. Meanwhile, the dynamic correlations between coal and carbon prices are only positive in Shenzhen and Beijing. Both coal prices and economic policy uncertainty produce asymmetrical impacts on carbon prices. Some policy implications are provided for developing the carbon markets in light of the results drawn from the study., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Based on the panel data of 30 provinces (municipalities and autonomous regions) in China from 2005 to 2019, this paper uses Gini coefficient decomposition and kernel density estimation to investigate the regional differences and dynamic evolution trend of rural energy carbon emission intensity in China. Then, the convergence model is used to analyze the convergence characteristics and influencing factors of carbon emission intensity. The study found the following: (1) During the observation period, the carbon emissions of coal energy and oil energy were much higher than those of gas energy. The carbon emissions of rural energy consumption experienced three stages of development, and the carbon emission intensity showed a downward trend as a whole. The spatial distribution pattern of total carbon emissions present an "adder" distribution, and the spatial agglomeration phenomenon gradually strengthens with the passage of time. (2) The Gini coefficient of China's rural energy consumption carbon emission intensity shows a trend of "Inverted N-shaped." The Gini coefficient of carbon emission intensity in the eastern and northeastern regions shows an increasing trend, while the Gini coefficient of carbon emission intensity in the western and central regions shows a downward trend. The super variable density is the main source of carbon emission intensity difference. The peak value of the main peak of the nuclear density curve of the carbon emission intensity increased significantly, the bimodal form evolved into a single peak form, and the density center moved to the left. (3) The carbon emission intensity of rural energy consumption in the whole, central, and western regions of China has the characteristic of σ convergence, while the carbon emission intensity in the eastern and northeastern regions does not have the characteristic of σ convergence. There is a significant spatial positive correlation in the carbon emission intensity, there is also a significant β convergence characteristic, the speed of conditional β convergence is significantly higher than that of absolute β convergence, and the spatial interaction will further improve the convergence speed. Industrial structure, industrial agglomeration, and energy efficiency will increase the convergence speed. In terms of sub-regions, the conditional convergence rate of carbon emission intensity in the four regions shows a decreasing trend in the northeast, central, eastern, and western regions., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

In the process of coal mining, prevention and control of water hazard is essential. It is the precondition for water hazard control to detect and determine the distribution of underground water-conducting channels. In urban environments, traditional methods such as active source seismic exploration and transient electromagnetic exploration commonly used in the field are difficult to carry out effectively due to various factors. In this paper, the microtremor survey method (MSM) and the opposing coils transient electromagnetic method (OCTEM) are adapted to conduct the surface exploration of the coal mine water-conducting channels in the urban environment. Combined with the detection results of the low-velocity area and the low-resistivity area, the distribution of water-conducting channels is preliminarily analyzed and determined, which is basically consistent with the drilling and coring results. It verifies the feasibility and accuracy of the comprehensive exploration method used in this paper., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The magnitude of pretension force serves as an important indicator of the effectiveness of anchor bolt active support and is one of the significant factors influencing the stability of tunnel surrounding rock. Therefore, in practical engineering, it is crucial to establish the relationship between pretension torque and pretension force. However, current research in this field has some limitations. With a specific mine in western China as the engineering background, this paper first analyzed the influence factors of surrounding rock deformation and failure, established a mechanical model for pretension structure of anchor bolt support, and derived the quantitative relationship between pretension torque and pretension force based on hypothetical conditions. Finally, it proposed the loss effect of anchor bolt support and modified the pretightening loss coefficient for engineering application. The research results show that the actual pretightening force of anchor support is lower due to the influence of deep soft coal seam, which leads to failure of coal pillar under mining stress. The loss effect of surrounding rock on pretightening force was represented by a coefficient k, and the modified value of the coefficient was calculated as 0.19∼0.43. By applying the modified relationship between pretightening torque and pretightening force, it was found that the actual pretightening torque of 300 Nm applied to 11307 return air roadway effectively controlled surrounding rock deformation and failure, with coal pillar displacement less than 120 mm. [ABSTRACT FROM AUTHOR]

Coal mines' water inrush is one of the five major disasters that affect the safety of coal mine production. The assessment of coal mines' water inrush is a prerequisite for preventing and controlling coal mines' water inrush. To objectively and effectively evaluate the risk of water inrush in the coal seam roof and overcome the shortage of single assignment methods, two methods, the analytic hierarchy process and the entropy method, are used in this paper to determine each evaluation factor's subjective and objective consequences. Game theory is applied to obtain the combined weights of each influencing factor to make up for the lack of a single assignment method. Taking the roof of Coal Seam No. 7 in mining Areas I and II of Dananhu Coal Mine No. 7 as an example, six primary evaluation indexes are created to control water inrush in the coal seam roof. The comprehensive weights of each index is determined; a vulnerability index evaluation model is established; and the results of the water inrush risk zone in the coal seam roof of Dananhu Coal Mine No. 7 are obtained using the GIS spatial analysis function. The results show that the discriminatory effects of the zoning model have a high accuracy and can provide a reference basis for future coal seam mining control work in this mine. [ABSTRACT FROM AUTHOR]

Shenfu Dongsheng coal field is a cross-century energy base which is developed and constructed in China. In recent years, some mines have successively entered to the coal seam of the second layer. Due to the reasons of early mining, many coal pillars are left in the coal seam of the first layer, resulting in the phenomenon of strong ore pressure in the mining range before and after the coal pillar in the lower coal seam and even causing the buckling accident. In order to solve such safety problems, this paper takes the 22,307 working face in Bulianta coal mine as the research object, adopts physical similarity simulation experiment and theoretical analysis to systematically study the overlying rock characteristics and abnormal ore pressure manifestation mechanism of shallow and close coal seam in different working stages. The results show that the roof overburden of the key layer in the lower group bends and sinks when the coal pillar is mined, resulting in the activation and instability of the "masonry beam" structure formed by the roof of the upper coal seam. When the coal pillar is discharged, the residual concentrated coal pillar and the room type coal pillar are unstable under the action of high supporting stress, resulting in shear failure of the inter-layer rock in the upper part of 22,307 working face, causing the strong dynamic pressure of the working face to appear and then leading to the buckling accident. The working resistance of the support in each stage is obtained by establishing the structure diagram of the overlying rock under each stage and the corresponding mechanical structure model. Finally, the working resistance required by the support in the mining stage under the goaf is 16,692.6 kN, the working resistance required by the support in the coal pillar stage is 19,692.6 kN, the working resistance required by the support in the mining stage under the concentrated coal pillar is 13,150.6 kN, and the working resistance required by the support in the coal pillar stage is 19,215.6 kN. [ABSTRACT FROM AUTHOR]

Carbon capture, utilization, and storage (CCUS) technology is a vital technical path to realize the low-carbon transformation of the coal power industry as well as a key means to ensure the safe and stable operation of the future power system. However, the current development path of coupling coal power and CCUS technology is not clear, and there is room for the optimization of the corresponding policy mechanism. This paper quantitatively estimates the contribution of CCUS application in the coal power industry to China's low-carbon energy transition strategy, describes the future development path of coal power's CCUS industrialization from the spatio-temporal dimension, and further constructs a comprehensive supporting policy system framework. The results show that the development of coupling coal power and CCUS technology is technically and economically feasible, which can not only achieve deep decarbon-ization of the power system and bring significant output and employment dividends in the coal power industry, but also effectively control the average carbon price level of society. In terms of the temporal dimension, the development path of coal power's CCUS industrialization in the future should be divided into three stages: technology research, development, and demonstration (2021--2030), large-scale application (2030--2040), and commercial development (2040--2060). In terms of the spatial dimension, the technically and economically feasible regions for cluster development are the Ordos Basin, the Junggar Basin, the Bohai Bay Basin, etc. Constructing a comprehensive policy support system framework incorporating ' macro support, fiscal and tax finance, market mechanism, technology research, development, and demonstration, as well as management system' is conducive to realizing a large-scale CCUS application in the coal power industry. In the stage of technology research, development, and demonstration of coal power's CCUS application, more definitive incentive policies such as storage subsidies, compensation for power generation hours, and feed-in tariff subsidies should be implemented. When the project cost drops to a certain extent, there should be a gradual transition to market-based policy tools such as carbon trading and green electricity trading mechanisms, and green finance should also be promoted. Based on the relevant conclusions, some targeted policy suggestions are put forward to provide references for promoting the green and low-carbon transformation of China's coal power industry. [ABSTRACT FROM AUTHOR]

Liquid-solid fluidized bed (LSFB) sorting has been widely used in coarse coal slurry sorting in coal preparation plants in China. In this paper, the vertical distribution of high-ash fine sludge in the LSFB column was studied in depth, and the results showed that in the vertical direction of the column, the gradient of ash change of the + 0.25 mm particles was obviously larger than that of the −0.25 mm particles. For + 0.25 mm particles, the low-density fine coal particles accumulate in the middle and upper parts, while the high-density particles accumulate in the middle and lower parts, and the overflow −0.25 mm particles are basically uniformly distributed in each density class. In the overflow port and the upper part of the column, the ash content of −0.25 mm particle size is obviously higher than that of + 0.25 mm particle size, and the −0.125 mm high ash and fine sludge basically accumulate in the upper part of the LSFB, and eventually enter the overflow to seriously pollute the fine coal. This study is of great significance for the development and application of LSFB sorting machine and the optimization of coarse coal slurry sorting and recovery process. [ABSTRACT FROM AUTHOR]

This work investigates the decarbonization potential of large-scale implementation of BECCS (in the form of biomass co-firing and post-combustion amine-based CO2 capture) in over 150 existing coal-fired power plants in China, combining GIS-based geospatial analysis of biomass availability from agricultural residues and modelling of the techno-environmental performance of the retrofitted power plants. Using a 500-m resolution map of cropland in China, the availability of residual biomass at a radius of 25–100 km from each power plant is estimated. The biomass yield is then matched with the required input for a set of co-firing scenarios, identified by the optimal mix of different co-firing ratios (10%, 25%, and 40%) and increasing % of total plant's capacity to be retrofitted with the chosen BECCS system. Power generation performance and required biomass for the retrofitted plants are modelled in the Integrated Environmental Control Model (IECM). According to the results, the total decarbonization potential of the modelled large-scale implementation of BECCS ranges from 0.3 to 1.8 Gt CO2/yr (15–81% of BAU emissions), depending on the biomass collection radius. The Chinese provinces of Shandong, Jiangsu, Anhui, and Henan have the most potential for BECCS implementation, while coal-rich regions (e.g. Inner Mongolia) or highly developed coastal areas (Guangdong, Zhejiang) are constrained by local biomass availability. Overall, this work demonstrates the significant potential of the sustainable large-scale implementation of BECCS in China and provides suggestions to policymakers to include this technology in the portfolio of solutions towards carbon neutrality. [ABSTRACT FROM AUTHOR]

Driven by the goal of achieving sustainable development and carbon neutrality. Addressing environmental pollution and remediating land damage have become critical challenges in resource-based cities and regions with low land use efficiency. As a response, this study focuses on the 23 provinces where China's coal resource-based cities are situated. Utilizing data from 2014 to 2020, this research employs the SBM-Undesirable model, which considers undesirable outputs in efficiency calculations, and the Tobit regression test. It aims to explore the spatio-temporal variations in industrial transformation within resource-based cities and its impact on the efficiency of green space utilization. Furthermore, it analyzes the characteristics and the extent of the influence of factors such as industrial structure adjustments on urban land use efficiency, maximizing the output of land as a factor of production. The results show that: (1) Over the 7-year period studied, China consistently made nationwide adjustments to land area and land use structure to meet the needs of urban development (2) The regression test results show that the industrial transformation of resource-based cities can promote the improvement of green space utilization efficiency. The positive influence coefficient is 0.064 and is significant at a 1% level. (3) Environmental regulation, government expenditure, international trade, and green cover play a positive role in promoting green land use. The study provides valuable insights for policymakers and urban planners seeking to foster sustainable development in resource-based cities. [ABSTRACT FROM AUTHOR]

There are abundant low-rank coal resources in China. However, its higher AAEMs (alkali and alkaline earth metals) content and the release of AAEMs during combustion cause serious fouling and slagging problems. In this paper, a method of removing AAEMs and ash from low-rank coal to produce clean coal by organic acid leaching was proposed. The leaching effects of four organic acids were compared, the leaching mechanism of citric acid was analyzed, and the removal behavior of AAEMs and ash was investigated. The results show the effect of citric acid is better than others. During the leaching process, the citric acid ionizes H+, which reacts with inorganic minerals of AAEMs, completes ion exchange with AAEMs Organics. Under the relative optimized experimental conditions, the content of Na2O in coal ash is 0.9%, which is in line with the standard of power coal in China. The removal efficiency of alkaline earth metals Ca and Mg are significantly lower than those of alkali metals Na and K. The trend in the removal efficiency of Ca and ash are consistent. Citric acid leaching is an effective and promising method to produce clean coal from low-rank coal. [ABSTRACT FROM AUTHOR]

With the deterioration of underground coal quality, hundreds of millions of tons of coal slime in China need to be treated using flotation methods every year. However, the design and selection of coal slurry flotation collectors lack theoretical guidance. In this paper, the quantitative structure–activity relationship (QSAR) model between the molecular structure descriptors of collectors and the flotation recovery and selectivity index is established by using pure kaolinite/clean coal flotation experiments and molecular simulation techniques. Flotation results showed that the flotation recovery rate of kaolinite by collectors with larger head group size, such as DDMAC, DDP, and DTAC, is higher than that of the other collectors with smaller head group size. DDA, DDP, and DD have similar flotation capabilities for clean coal, and their selectivity was slightly better than others. The QSAR model between the molecular structure descriptor and the selectivity index was successfully constructed by combining flotation experiments and molecular simulation results. The reliability of this model has been proven through theoretical analysis and flotation experiments. The molecular simulation results indicate that all eight collectors can advertise on 001 (−) surface of kaolinite, but the final advertisement configuration is different. DDA has less coverage on the surface of kaolinite. When the collector is DDA, the concentration of water molecules near the 001 (−) surface of kaolinite is the highest, indicating that the collector DDA has the weakest effect on improving the hydrophobicity of the 001 (−) surface of kaolinite. DDMAC and DDBAC have the best facilitation to the surface hydrophobicity of kaolinite 001 (−). The research results have theoretical guidance significance for the selection and design of mineral flotation collectors. [ABSTRACT FROM AUTHOR]

Coal and gas outburst is a type of coal mine dynamic disaster with complex causes and serious consequences. In China, the number and scale of outburst disasters are among the highest in the world. It is an inevitable stage for outburst that the mechanical instability of the combination of intact coal and tectonic coal (CICTC) in strata. The dip angle of the interface has an important influence on the instability of CICTC-containing gas. To further understand the instability process of CICTC, the uncoordinated deformation of CICTC was defined. According to this, three strain conditions were delimited. The variations of stress under three strain conditions were analyzed, the expressions of additional interfacial stress were established. Then, based on the Mohr–Coulomb criterion, the strength characteristics and failure forms were analyzed. It was found that the dip angle deflects the principal stress in the interface, and the influences of additional stresses on the value of principal stress are opposite. These two reasons make the principal stress state and instability process of the combination complicated. Finally, combined with actual parameters, the instability processes of CICTC under different stress paths and buried depths were studied. It can be found that the failures of CICTC under different stress paths were concentrated appearing in the tectonic coal body, intact coal interface, and tectonic coal interface. With the increase of buried depth, the initial maximum principal stress increases and the reduction from additional stresses to the strength of intact coal interface enhances, which makes the combination damage easily and the failure form change. The research results in this paper can provide a theoretical basis to prevent and control the outburst of the combination containing gas considering the dip angle of the interface. Highlights: The uncoordinated deformation of combination considering the dip angle was first defined. The expressions of additional interfacial stress of combination considering the dip angle were established The influences of different stress paths and buried depths for the instability of combination were discussed quantificationally. [ABSTRACT FROM AUTHOR]

• Ecological restoration is not just an environmental issue and it is a societal problem. This paper analyzes ecological restoration and its impact on society in coal resource-based areas, focusing on the Ruhr region in Germany and Liulin County in China. Through the analysis and comparison, the study not only reveals the unique ecology-social system and explain the reasons for dependence on coal, but the finding shows that industrial transformation is a key factor in determining ecological restoration of coal resource-based regions. • The industries abandoned by the Ruhr area were taken over by China. Shanxi Province is very similar to the Ruhr area in terms of ecological destruction and social development at that time. The Ruhr region has become one of the most polluted areas in the world due to its coal and steel industry. After nearly 40 years of arduous practice, ecological governance and economic transformation in the Ruhr area achieved initial success. • Shanxi Province in China is a hub for energy and heavy chemical industries, and it ranks first in coal production nationally.. The Liulin county is located in the west of Shanxi Province, it is a typical coal mining subsidence and is scattered with numerous villages affected by subsidence due to coal mining. Shanxi Province and the Liulin county is undergoing difficult industrial transformation. • The author of this work visited the Duisburg-Essen University for a year, located in the Ruhr area of Germany, and learned about the ER and transformation in the Ruhr. When the author returned to China, she conducted field research for a two-month survey in Liulin County. Therefore, the author collected a large amount of literature ,data sources and gained practical experiences in these two areas. The coal resource-based areas rely on coal resources and primary processing as their pillar industries, such as the old industrial areas in China and Germany. Long-term, large-scale coal mining has significantly damaged the ecological environment of mining areas. Environmental restoration refers to repairing, rehabilitating, or revitalizing ecosystems that have been degraded, damaged, or destroyed by human activities or natural disasters. In fact, ecological restoration is not just an environmental issue and it is a societal problem. Ecological restoration is closely linked to natural resources, the environment, the economy, society, and politics. These factors form a social ecological system and it is the basis for local stability and sustainable development in the coal resource-based areas. In this process, the relationship between government, enterprise, and local people is constantly being reshaped and defined, then it causes changes in the local social ecology and political ecology. The paper researches the Ruhr area in Germany and the Liulin County in China, the former is a world-famous old industrial and the latter is a typical coal mining subsidence district. By analyzing and comparing the ecological restoration and significant social changes in the Ruhr area and the Liulin County at different periods, the findings show the unique ecology— social system of the coal resource-based area, then enhances the effective measures for ecological restoration and sustainable development of the coal resource-based areas. [ABSTRACT FROM AUTHOR]

To achieve carbon neutrality, China must grasp the intricate factors driving coal market, as it addresses coal consumption and reduces the carbon footprint. While previous studies have identified certain factors, they have largely overlooked the impact of the overall industry sector on the coal market. In this paper, a hybrid causal machine learning model was proposed that combine with least absolute shrinkage and selection operator (LASSO), multiple linear regression (MLR), peter and clark momentary conditional independence (PCMCI) and interpretable machine learning. The approach employed a complex network perspective to identify 10 key factors in China's coal market from three dimensions: industrial sector, foreign trade and energy market. The hierarchical pattern of these factors is classified into two levels: direct factors, primarily encompassing crude oil futures, exchange rates and architectural decoration, and intermediary factors, mainly including the chemical industry and building material. Interestingly, this paper reaffirms the roles of crude oil futures and exchange rates in the coal market, as identified in prior studies. Additionally, it uncovers new influential factors primarily driven by the chemical industry and architectural decoration, previously unexplored. Furthermore, this paper found a significant contemporaneous relationship between crude oil futures and coal price index (0.151) as well as coal consumption (0.102), and the strong relationship between coal consumption and the Indonesian Rupiah to Chinese Yuan exchange rate (0.063) was also confirmed. Among the emerging dominant factors, the coal price index and the chemical industry (0.145), along with coal consumption and building materials (0.250), also exhibit a strong contemporaneous relationship. These findings highlight the importance of considering the entire industry sector while analyzing the coal market and promoting a cleaner transformation of the industry in China, and the paradigm presented not only applicable to the coal market, but can be extended to other industries. [Display omitted] • Better grasping key factors in China's coal market critical to carbon neutrality. • A comprehensive study encompassing industrial sector, foreign trade and energy market. • A novel hybrid machine learning models and industry-wide features are introduced. • Identification and categorization of direct and intermediary factors. • Findings offer a new paradigm for decision-making, driving cleaner production reforms. [ABSTRACT FROM AUTHOR]

Using fracturing fluids to modify coal seams to boost their permeability is an essential way to address the technical challenges of the resourceful and efficient extraction of coalbed methane from coal reservoirs in China. However, some current fracturing fluids are toxic or corrosive and pollute groundwater resources, which becomes one of the obstacles to the development of fracturing and penetration technology. Five new types of composite clean fracturing fluids were developed in this paper with Yunnan anthracite coal in China as the research object. The changing rules of functional groups and pore structures, which have a vital influence on gas adsorption and permeability of the treated coal samples, were systematically explored through infrared spectroscopy and low-temperature nitrogen adsorption experiments, and the highly efficient, environmentally friendly, and safe fracturing fluids that are suitable for the experimental coal seams were preferred. The new fracturing fluid effectively reduces the structure of aliphatic hydrocarbon and the structure of oxygen-containing functional groups, improves aromaticity, and lowers the adsorption capacity of coal for methane. Meanwhile, it simplifies the pore structure of coal and improves the average pore diameter. The research results are essential to the clean production and efficient exploitation of coalbed methane resources and safe coal production. • Five new clean fracturing fluids was prepared. • Analyze the effect of different clean fracturing fluids on coal microstructure. • Explored the mechanism of action of clean fracking fluids on coal. • Determined the optimal ratio of clean fracturing fluid. [ABSTRACT FROM AUTHOR]

The development of coalbed methane (CBM) in China is susceptible to the influence of microstructure. Therefore, it is crucial to understand the extension laws of hydraulic fractures and engineering responses in coal reservoirs affected by microstructure development. Utilizing the Dahebian block in western Guizhou as the study area, this investigation examines the coal reservoir characteristics, fracturing, and drainage engineering analysis of the well DC1 group in the region. The aim is to discuss the spatial distribution characteristics of hydraulic fractures, geological controlling factors influenced by microstructure, and their corresponding engineering responses. The results indicate that, for coal reservoirs unaffected by microstructure, the extension laws of the fracture network in both longitudinal and planar directions are influenced by burial depth and the regional stress field. In the microstructural belt, tectonic stress dominates, causing changes in the ground stress field. Consequently, the hydraulic fracture network deviates from the direction of the maximum principal stress during the extension process. When a secondary fracture is nearby, the hydraulic fracture network extends towards the shortest path radial secondary fracture direction, leading to a rapid increase in fracture width per unit length until it intersects with the secondary fracture. Additionally, the presence of secondary joints near the microfault structure decreases fracturing pressure and results in a dense distribution of the fracture network. This promotes the formation of a complex fracture network, favorable for fracturing. The extension of the fracture network in complex structural development areas is influenced by the microfault structure between wells, which is reflected in the fracturing construction pressure and fluid output. This accounts for the significant variations in the early drainage performance of CBM wells. [ABSTRACT FROM AUTHOR]

In order to study the carbon emission of coal resources from mining to utilization and its influencing factors, the Life Cycle Assessment method was used to calculate the carbon emission of coal mining, transportation and consumption from 2001 to 2018, Then, Logarithmic Mean Divisia Index method is used to decompose the factors that affect the carbon emissions in each stage: (1) Mining stage: energy structure, energy intensity, per capita output, personnel scale; (2) Transportation stage: Diesel utilization efficiency, coal cargo turnover; (3) Consumption stage: economic scale, industrial structure, coal consumption intensity, respectively calculate the contribution value and contribution rate of each factor to carbon emission growth. The results show that the carbon emission in the whole life cycle of coal mainly comes from the stage of mining and consumption; Energy intensity, diesel utilization efficiency and coal consumption intensity have inhibitory effects on carbon emissions, and personnel scale and industrial structure have changed from promoting factors to restraining factors; Per capita output, coal cargo turnover and economic scale have a sustained role in promoting carbon emissions; The energy structure effect is unstable. Through in-depth analysis of the above carbon emission influencing factors, relevant conclusions and suggestions are put forward. [ABSTRACT FROM AUTHOR]

Coal is one of the most important fossil energy sources and is ensuring global energy security. Annual maximum NDVI (Normalized Difference Vegetation Index) data is an important indicator for the research in balancing coal mining and vegetation conservation. However, the existing annual maximum NDVI data displayed lower values with temporally inconsistent and a noticeable mosaic line. Here we propose an algorithm for automatically generating the annual maximum NDVI of China's coal bases in Google Earth Engine called: Auto-NDVIcb. The accuracy of the Auto-NDVIcb algorithm has been verified with an average RMSE of 0.087 for the 14 coal bases from 2013 to 2022. Based on the proposed Auto-NDVIcb algorithm, an annual maximum NDVI dataset for all 14 coal bases in China from 2013 to 2022 was publicly released. This dataset can be fast and automatically updated online. Hence, the public dataset will continuously serve to monitor the vegetation change induced by coal mining, exploring the mechanism of vegetation degradation, and providing scientific data for developing vegetation protection policies in coal mines. [ABSTRACT FROM AUTHOR]

This study focuses on coalbed methane (CBM) wells in high-ranking coal seam as the research subject. Considering the influence of effective stress and matrix shrinkage, a comprehensive permeability calculation model for CBM reservoirs is established. Based on this model, the variations in pressure and permeability during well production are quantified. By integrating static geological parameters, a finely classified classification of CBM wells is achieved using self-organizing map (SOM) neural network. Subsequently, an analysis of production dynamic characteristics and productivity differences among different types of CBM wells is performed, followed by providing drainage optimization suggestions. The results of SOM analysis show that 7,000 m3/d and 1,500 m3/d can be used as the production boundaries for the wells with different productivity in Block P. The daily gas production of exceptional well exceeds 7,000 m3/d, and the permeability remains relatively stable throughout the drainage process of this well. The daily gas production of the potential well ranges from 1,500 to 7,000 m3/d, and the permeability exhibits a significant decrease during the drainage process. The daily gas production of Inefficient well is consistently below 1,500 m3/d with moderate permeability variation. In addition to well location and structural geology, production variability is also influenced by the matching of reservoir conditions and drainage systems. This is primarily manifested in discontinuous drainage systems and rapid decline in bottom hole pressure (BHP) during early production. The analysis of drainage parameters indicates that in order to achieve optimal production from CBM wells, the BHP should exhibit an initial rapid decline followed by a slowly decrease during the early production period, with an average pressure drop ranging from 0.005 to 0.02 MPa/d. The research findings can offer technical guidance for the future advancement of CBM in the P Block. [ABSTRACT FROM AUTHOR]

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Coal was first used in China for ornaments starting about 6000 years ago. Its use as fuel for households and light industry began about 2000 years ago, but coal production and consumption remained low until the end of the nineteenth century due to weak industrialisation. Thereafter, a series of political events drove progressive industrialisation that required the increasing exploitation of the nation's vast coal resources. These events were the Treaty of Shimonoseki in 1895, the creation of the state of Manchuguo by Japan in 1932, the Communist accession to power in 1949 and the start of opening up in 1978. Advances in mining technology and expanding transport networks allowed coal to become a major source of primary commercial energy, which it remains today. Since 2012, the slowing rate of economic growth combined with the rapid expansion of renewable energy has steadily reduced the share of coal in the energy mix. Standards of safety, resource management and environmental protection were low throughout most of the long history of coal in China. Moreover, mine workers were marginalised and many local officials were directly involved in the mining. Only in this century has the government achieved some success in addressing these challenges. [ABSTRACT FROM AUTHOR]

Deep coalbed methane (DCBM) reservoirs hold exceptional potential for diversifying energy sources. The Ordos Basin has attracted much attention due to its enormous resource reserves of DCBM. This work focuses on the Jiaxian area of the Ordos basin, and the multi-factor quantitative evaluation method on the sealing of cap rocks is established. The abundant geologic and reservoir information is synthesized to explore variable factors affecting the gas content. Results indicate that the sealing capacity of the coal seam roof in the Jiaxian area, with a mean sealing index of 3.12, surpasses the floor's sealing capacity by 13.87%, which averages 2.74. The sealing of the coal seam roof has a more positive impact on the enrichment of coalbed methane (CBM). In addition, the conditions for preserving gas would be boosted as coal seam thickness increased, leading to enhanced gas content in coal seams. The CH4 content increases by an average of ~2.38 m3/t as coal seam thickness increases with the interval of 1 m. The increasing burial depth represents the incremental maturity of organic matter and the gas generation ability in coal seams, which contributes to improving the gas content in coal seams. There is a positive correlation between the degree of coal fragmentation and the gas content of the coal seam to a certain extent. These findings provide valuable insights for targeted drilling strategies and enhancing natural gas production capacity in the Jiaxian area of the Ordos Basin. [ABSTRACT FROM AUTHOR]

The porosity characteristics of coal seams serve as a pivotal factor in assessing the development potential of coalbed methane (CBM) resources, significantly influencing the adsorption and permeability capabilities of coal reservoirs, as well as the accumulation, entrapment, and preservation of CBM. In this study, we focused on the coal seams of the Xishanyao Formation in the western part of the southern Junggar Basin (NW China). By leveraging the complementarity of nuclear magnetic resonance (NMR), low-temperature liquid nitrogen experiments, and high-pressure mercury intrusion porosimetry (MIP) in spatial exploration range and precision, we conducted a comprehensive analysis to achieve a fine description of porosity characteristics. Furthermore, we explored the coal petrology factors controlling the pore characteristics of the Xishanyao Formation, aiming to provide geological evidence for the selection of favorable areas and the development potential evaluation of CBM in the study area. The results indicate the following: (1) The total pore volume of the coal samples is 6.318 × 10−3 cm3/g on average, and the micropore volume accounts for a relatively high proportion (averaging 44.17%), followed by the fine pores (averaging 39.41%). The average porosity is approximately 3.87%, indicating good gas storage and connectivity of the coal seams, albeit with some heterogeneity. The coal reservoir is dominated by micropores and fine pores with diameters less than 100 nm, and the pore structure is characterized by low pore volume and high pore area. (2) The pore structure is influenced by both the coalification degree and the coal maceral. Within the range of low coalification, porosity increases with the increase in coalification degree. Building upon this, an increase in the vitrinite content promotes the development of micropores and fine pores, while an increase in the inertinite content promotes the development of meso–macropores. The clay mineral content exhibits a negative correlation with the adsorption pore volume ratio and a positive correlation with the seepage pore volume ratio. [ABSTRACT FROM AUTHOR]

Substituting renewable energy for coal power under the carbon neutrality goal is an inevitable path for power system transformation, while the high share of renewable energy leads to a rapid rise in system flexibility demand. Currently, coal-fired power is still one of the most economical and reliable large-scale flexible resources in China. Therefore, the issue of how to mitigate the conflict between cleanliness and flexibility for coal-fired power is urgent to be solved. Accordingly, this paper established an optimization framework for the retirement and technology adoption of coal-fired power units with high spatial-temporal resolution, and the regional carbon emission budget is estimated from a top-down perspective. Secondly, a dynamic carbon quota allocation method considering technological innovation and adoption is proposed. The carbon trading cost of the units is evaluated from a bottom-up perspective, to realize the interaction between the obligatory policy constraints of the top-level target and the flexible incentives of the market mechanism. Finally, the empirical analysis was conducted in the Beijing-Tianjin-Hebei region of China. The optimal solution achieved by proposed method results in a substantial 27% reduction in total costs while keeping the increase in carbon emissions below 3%. By analyzing the dynamic evolution path of coal and the scale of diffusion of multi-type technologies, the differences in the roles coal power assuming at various stages of decarbonization are discussed. The robustness of the model and the validity of the proposed method were verified by comparing the dynamic/static carbon quota allocation. Overall, this study provides an effective optimization model for investigating the low-carbon technology adoption timing for coal power in Beijing-Tianjin-Hebei region, and offers valuable insights for other coal-dominated emerging economies seeking for power system transformation roadmap in the forthcoming net-zero carbon age. • A decision-making optimization model of CCPs low-carbon technology is proposed. • A dynamic CET system with upper-lower layer interaction is introduced. • The proposed dynamic CET system results in 27% reduction in total costs. • The high-resolution data of coal power in Beijing-Tianjin-Hebei region are used. • The strategy to solve the conflict between cleanliness and flexibility is given. [ABSTRACT FROM AUTHOR]

The pore-fracture structure of deep coal reservoirs is highly important for evaluating, exploring, and developing coalbed methane (CBM) resources. This study considers three coal samples from the DJ57 well in the Benxi Formation in the Daning–Jixian block on the eastern margin of the Ordos Basin as the research object. Based on the coal quality parameters of the coal samples, field emission scanning electron microscopy (FE-SEM), gas adsorption experiments, high-pressure mercury intrusion porosimetry (MIP), and microcomputed tomography (micro-CT) scanning were used to quantitatively characterize the nanoscale pores and microscale fractures in deep coal reservoirs and to evaluate the pore-fracture structure at different scales. The results reveal that the pore types in the Benxi Formation coal samples are diverse and include mainly organic matter (OM) pores, inorganic pores (intraparticle and interparticle pores), and microfractures. The organic pores are diverse in shape and mainly exhibit round, oval, and wedge shapes, while the microfractures exhibit slender stripes or serrated curves. The multiscale quantitative characterization of deep coal reservoir pores and fractures is based on a variety of pore characterization methods, and the pore and fracture volume distributions are mainly U-shaped, revealing the coexistence of micropores and microfractures. The volumes of micropores (0.3–2 nm), mesopores (2–50 nm), macropores (50 nm to 10 μm), and microfractures (>10 μm) account for 78.00%, 6.78%, 2.08%, and 13.14%, respectively, of the total pore volume (PV). Based on a full-scale pore-fracture splicing calculation, the total permeability of the Benxi Formation coal samples ranges from 5.77 to 28.22 mD. The observation results indicate that the microfractures are connected to each other, forming a network structure with strong connectivity. The microfractures are mainly associated with pore diameters > 100 μm, accounting for approximately 95% of the total permeability. Moreover, micropores in deep coal reservoirs provide a large space for CBM adsorption, and microfractures enhance the seepage capacity of CBM. [ABSTRACT FROM AUTHOR]

Coal gangue is a byproduct of coal mining and processing, and according to incomplete statistics, China has amassed a substantial coal gangue stockpile exceeding 2600 large mountains, which poses a serious threat to the ecological environment. Utilizing gangue as a coarse aggregate to produce gangue concrete (GC) presents a promising avenue for addressing the disposal of coal gangue; however, gangue concrete presents several challenges that need to be tackled, such as low strength and poor resistance to repeated loads. In this study, polypropylene fibers (PPFs) were incorporated into gangue concrete to enhance its utilization rate. Uniaxial compressive and repeated loading experiments were then conducted to investigate the uniaxial strength and fatigue properties of polypropylene fiber-reinforced gangue concrete (PGC) with varying gangue substitution rates (20%, 40%, and 60%) and different polypropylene fiber admixtures (0, 0.1%, 0.2%, and 0.3%). The findings indicate that incorporating gangue at a substitution rate of 40% could notably enhance the uniaxial compressive strength of PGC, resulting in a maximum increase of 19.4%. In the repeated loading experiments, the ductility of PGC was enhanced with the incorporation of PPFs, resulting in a reduction of 33.76% in the damage factor and 19.42% in residual strain for PGC-40-0.2 compared to PGC-40-0. A PPF content of 0.2% was found to be optimal for enhancing the fatigue performance of PGC. Scanning electron microscope (SEM) testing proved the improvement effect of polypropylene fiber on gangue concrete from a microscopic perspective. This study provides crucial experimental data and a theoretical foundation for the utilization of gangue concrete in complex stress environments. [ABSTRACT FROM AUTHOR]

The stress field of the roadway under multi-seam mining is complex due to multiple mining disturbances. The bolting control of the roadway under multi-seam mining has attracted wide concern. Moreover, conventional metal supporting materials in the coal rib are prone to sparks when shearer works, and new bolting materials are urgently needed. Taking a track roadway under multi-seam mining in China as the engineering case, the mining-induced stress field of the track roadway under multi-seam mining was investigated through numerical simulation and lab and field tests. The test evaluated the mechanical behaviour of FRP bolts and rebar bolts, as well as their anchorage performance under different conditions. Comparative analysis was conducted on the deformation and failure characteristics of the roadway under different bolting parameters to determine an optimised bolting scheme for the track roadway in the I011501 working face. The results show that the goafs and the remaining coal pillars in the overlying coal seams increase the stress in the track roadway in the I011501 working face, especially for the lower rib and roof. The tensile force of the 27 mm-diameter FRP bolt is 1.2 times that of the 22 mm-diameter rebar bolt. The shear strength of the full-length anchored FRP bolt is 70.8% higher than that of the endanchored bolt. The peak stress of the full-length-anchored bolt is in the shallow coal and rock mass. The optimised bolting scheme of the track roadway subject to multi-seam mining is determined, and the cost of the optimised bolting scheme is lower by about 25.2%, as compared with the primary bolting scheme. numerical simulation and field application results indicate that the optimised bolting scheme can significantly reduce the deformation and plastic failure of the track roadway in the I011501 working face, which is under multi-seam mining conditions. [ABSTRACT FROM AUTHOR]

Owing to the increasing challenges associated with coal mine exploration and development, extremely precise surveys with high-resolution images are required to support production. Conventional inversion methods cannot provide sufficiently precise images of the complex lithologies in coal measure strata. Accordingly, this study performed research in Qiyuan mining area, Shanxi Province, China, and predicted the complex lithology on the basis of facies control using waveform indication inversion and waveform indication simulation. Horizontal changes in seismic waveforms were used to reflect lithologic assemblage characteristics for facies-controlled constraints, and the vertical mapping the connection between seismic waveform and logging curves was shown. Moreover, high-resolution inversions of wave impedance and natural gamma parameters were conducted. Combined with lithologic shielding and accurate time–depth conversion, the inversions enabled the precise characterization of the lithological assemblage distribution in the study area. Our results showed that waveform indication inversion could distinguish between coal seams and limestone, whereas waveform indication simulation based on natural gamma could effectively distinguish between sandstone and mudstone. Furthermore, the horizontal resolution was improved and the vertical resolution extended to a thickness of 2–3 m. In addition, the inversion results were highly consistent with drilling results, with an error <0.1 m. Therefore, waveform indication inversion and simulation could be applied to coal mines for safe and efficient production. [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]

In the fields of coal dust control and coalbed methane (CBM) development, wettability is a crucial parameter of coal, often determined by the coal–water contact angle (CA). In order to construct an accurate CA prediction model, extensive data on industrial components, element content, and coal CAs were collected. Two sets of data were utilized: a large sample comprising 98 data groups gathered from various sources, and a small sample consisting of 16 data groups collected from a single source. These datasets were employed to develop models using three machine learning (ML) methods: K-nearest neighbor, support vector regression, and back-propagation neural network. The results revealed a significant underfitting phenomenon in all three ML methods when applied to the training and testing datasets of the large sample. This underfitting can be attributed primarily to the variations in coal sample handling by different scholars. Conversely, the three ML methods exhibited pronounced overfitting on the training dataset of the small sample, resulting in limited generalization ability on the testing dataset. This limitation arises from the small amount of data in the small sample. To address this, the synthetic minority oversampling technique was employed to generate augmented samples for the small sample. The correlation of determination of the augmented samples ranges from 0.82 to 0.92, indicating an excellent fit. Additionally, the fit superiority ratios of the training and testing datasets fell between 0.92 and 1. This approach effectively avoids the risk of underfitting in large-sample datasets and overfitting in small-sample training datasets. In the final stage, the developed model was used to predict the wettability of coal samples from three coal mines in the Qinshui Basin, China. The predicted CA values demonstrated a high level of agreement with the CA values measured in the laboratory. This comprehensive study thoroughly analyzed the underlying reasons behind the failure of ML models to effectively handle large- and small-sample data for CAs. It also provides a valuable solution to the above problems by data augmentation with small samples, which holds great significance in enabling quick and accurate prediction of CAs using limited coal parameter data. [ABSTRACT FROM AUTHOR]

As China's coal mines have transitioned to deep mining, the ground stress within the coal seams has progressively increased, resulting in reduced permeability and poor wetting ability of conventional wetting agents. Consequently, these agents have become inadequate in fulfilling the requirements for preventing washouts during deep mining operations. In response to the aforementioned challenges, a solution was proposed to address the issues by formulating a composite wetting agent. This composite wetting agent combines a conventional surfactant with a chelating agent called tetrasodium iminodisuccinate (IDS). By conducting a meticulous screening of surfactant monomer solutions, the ideal formulation for the composite wetting agent was determined by combining the monomer surfactant with IDS. Extensive testing, encompassing evaluations of the composite solution's apparent strain, contact angle measurements, and alterations in the oxygenated functional groups on the coal surface, led to the identification of the optimal composition. This composition consisted of IDS serving as the chelating agent and fatty alcohol polyoxyethylene ether (JFCS).Subsequent assessment of the physical and mechanical performance of the coal briquettes treated with the composite wetting agent revealed notable enhancements. These findings signify significant advancements in the field and hold promising implications. Following the application of the composite wetting agent, notable reductions were observed in the dry basis ash and dry basis full sulfur of coal. Additionally, the water content within the coal mass increased significantly, leading to a substantial enhancement in the wetting effect of the coal body. This enhanced wetting effect effectively mitigated the coal body's inclination towards impact, thereby offering technical support for optimizing water injection into coal seams and preventing as well as treating impact ground pressure. [ABSTRACT FROM AUTHOR]

The water yield of aquifers increases the risk of water inflow, threatens the safe production of coal mines, and even causes geological disasters and construction hazards. To predict water yield quickly and accurately, multiple composite factors are used to invert unit water inflow rates to judge water yield grade. Taking the typical representative of north China-type coal fields as an example, six factors are selected: aquifer thickness, the radius of influence, normalized drawdown, permeability coefficient, the core rate of drilling holes, and the proportion of clay thickness to the thickness of the lower group. The whale optimization algorithm (WOA)–convolutional neural network (CNN)–support vector machine (SVM) model is established with the unit water inflow rate as the forecast target, and different models are selected for comparison. The water yield zoning map is obtained by bringing the borehole data into the model for prediction. The findings indicate that the root mean square error and average absolute error of the composite predictive model models are 0.0318 and 0.0268, respectively, and the model outperforms alternative models. The predicted water yield zoning aligns well with the actual conditions, offering a novel paradigm for water yield assessment. [ABSTRACT FROM AUTHOR]

A transition away from coal power always maintains a high level of complexity as there are several overlapping considerations such as technical feasibility, economic costs, and environmental and health impacts. Here, we explore the cost-effectiveness uncertainty brought by policy implementation disturbances of different coal power phaseout and new-built strategies (i.e., the disruption of phaseout priority) in China based on a developed unit-level uncertainty assessment framework. We reveal the opportunity and risk of coal transition decisions by employing preference analysis. We find that, the uncertainty of a policy implementation might lead to potential delays in yielding the initial positive annual net benefits. For example, a delay of six years might occur when implementing the prior phaseout practice. A certain level of risk remains in the implementation of the phaseout policy, as not all strategies can guarantee the cumulative positive net benefits from 2018–2060. Since the unit-level heterogeneities shape diverse orientation of the phaseout, the decision-making preferences would remarkably alter the selection of a coal power transition strategy. More strikingly, the cost-effectiveness uncertainty might lead to missed opportunities in identifying an optimal strategy. Our results highlight the importance of minimizing the policy implementation disturbance, which helps mitigate the risk of negative benefits and strengthen the practicality of phaseout decisions. China's use of coal is complex to establish a clean and low-carbon transition for the country. With an uncertainty assessment framework, this study displays the risks of missing opportunities in obtaining cumulative positive net benefits and identifying an optimal transition strategy. [ABSTRACT FROM AUTHOR]

The wettability of coal is an important factor influencing hydraulic stimulation. Field-trial data has proven that high-pressure N2 injection plays a positive role in increasing the coalbed methane (CBM) production rate. For the purpose of investigating the mechanism by which N2 promotes the gas rate, multiple experiments were conducted sequentially on the wettability of anthracite under different N2 pressures. Testing of the coal surface contact angle was conducted under 0.1–8 MPa nitrogen pressure using a newly built contact angle measuring device. The coal samples were collected from the Xinjing Coal Mine in the Qinshui Basin, China. The test results revealed that the contact angle increased with increasing N2 pressure. That is, the contact angle was 77.9° at an N2 pressure of 0.1 MPa and gradually increased to 101.4° at an infinite N2 pressure. In contrast, the capillary pressure decreased with an increasing N2 pressure, from 0.298 MPa to −0.281 MPa. The relationship between contact angle and N2 pressure indicated that the wettability was reversed at a N2 pressure of 5.26 MPa, with a contact angle of 90° and a capillary pressure of 0 MPa. The capillary pressure reversed to a negative value as the N2 pressure increased. At the microlevel, a high N2 pressure increases the surface roughness of coal, which improves the ability of the coal matrix to adsorb N2, forming the gas barrier that hinders the intrusion of water into the pores of the coal matrix. The results of this study provide laboratory evidence that high-pressure N2 injection can prevent water contamination and reduce the capillary pressure, thus benefiting coalbed methane production. [ABSTRACT FROM AUTHOR]

CO2 injection in coal seams, which is a significant initiative to mitigate environmental problems caused by greenhouse gases, often leads a sequence of changes in the physical properties of coal reservoirs. To look into how the pore structure changes in the process of CO2 sequestration, we selected fresh coal from Huoerxinhe coal mine in China as the object. Then, acid treatment and SC-CO2 extraction were used to dissolve Organic and inorganic components in coal. Thus, by using SEM, LTGA-N2 apparatus and XRD, the characteristics of pore parameter and fractal dimension variation were discussed. The research results show that, the APS of samples THF, HCL-HF and Y-C increase, while the total PV decreases and the pore connectivity deteriorates. The pore connectivity of Samples THF and HCL-HF is improved (THF-C, HCL-HF-C), but the total pore volume continuously reduces. In addition, solvents treatment and SC-CO2 extraction mainly act on the microporous fraction. After solvents pretreatment, the changes in the pore size distribution curves are mainly manifested in the reduction of number of micropores, especially in the micropores around 3–4 nm. There is a small increase in micropores for samples Y-C and HCL-HF-C, with the pore size mainly concentrated around 4 nm, while the pores of the sample THF-C mainly show an increase within the scope of 3–16 nm. Generally, solvent pretreatment and SC-CO2 extraction help to simplify pore structure. However, the sample HCL-HF-C shows opposite change characteristics. In a short period of time, the larger pore fractal dimension, the less beneficial it is to the flow of CO2, while pore fractal dimension becomes progressively less useful in assessing pore connectivity with increasing time. [ABSTRACT FROM AUTHOR]

The Permian Longtan Formation in the Songzao coalfield, Southwest China, has abundant coalbed methane (CBM) stored in high-rank coals. However, few studies have been performed on the mechanism underlying the differences in CBM gas content in high-rank coal. This study focuses on the characterization of coal geochemical, reservoir physical, and gas-bearing properties in the coal seams M6, M7, M8, and M12 based on the CBM wells and coal exploration boreholes, discusses the effects of depositional environment, tectono-thermal evolution, and regional geological structure associated with CBM, and identifies major geological constraints on the gas-bearing properties in high-rank coal. The results show that high-rank coals are characterized by high TOC contents (31.49~51.32 wt%), high Tmax and R0 values (averaging 539 °C and 2.17%), low HI values (averaging 15.21 mg of HC/g TOC), high porosity and low permeability, and high gas-bearing contents, indicating a post-thermal maturity and a good CBM production potential. Changes in the shallow bay–tidal flat–lagoon environment triggered coal formation and provided the material basis for CBM generation. Multistage tectono-thermal evolution caused by the Emeishan mantle plume activity guaranteed the temperature and time for overmaturation and thermal metamorphism and added massive pyrolytic CBM, which improved the gas production potential. Good geological structural conditions, like enclosed fold regions, were shown to directly control CBM accumulation. [ABSTRACT FROM AUTHOR]

Australia is a long-term key partner of China in coal trading, which is famous for high-quality coal and its price advantage. However, affected by the evolution of international political and economic situation, China has issued a coal ban on Australian coal since the end of 2020. The potential environmental consequences of this coal ban remain unclear. So, this paper quantifies the ban's impact on air pollution, human health and climate change by simulating the emission difference between the port scenario (simulating the emissions due to Australian coal import under business as usual) and the mine scenario (simulating the emissions due to domestic coal mining that converted from import share of Australian coal), and monetizes the losses into economic costs for direct comparison. The results illustrate the emission of SO 2 , VOCs and GHG in mine scenario grows up to 102, 12 and 6 times the amount of that in port scenario, mainly deriving from coal mining process in the North China Plain and Yunnan-Guizhou Plateau. It shows that the potential alternative of replacing import with mining leads to PM 2.5 pollution exacerbation and O 3 pollution abatement, which causes 148 (95 % CI: 101–183) non-communicable diseases and respiratory disease-related deaths in total. As for GHG, the emission of BC in transportation process and fugitive methane in coal mining process contribute to an impressive effect on warming potential with few quantities, which is worth noting in control process. In total, the environmental deterioration resulted in an economic loss of approximately 934 million yuan. The undiminished demand for high-quality industrial coal as well as growing carbon tax could make the economic value of the coal ban's environmental consequences more considerable in the near future. This research emphasizes the contradiction between economic development and environmental improvement caused by excessive dependence on coal and addresses a critical knowledge gap in assessing the ban's environmental impact by economic value. The result directly demonstrates the environmental consequences of the potential mining-replacing-import alternative and helps better understand environmental influences on the Chinese government's decision. [ABSTRACT FROM AUTHOR]

In the second of two companion papers, we quantify the potential ultimate benefits for public health and radiative forcing from the phase-out of coal use in China. With the baseline year of 2015, we estimate that the premature deaths and disability-adjusted life years (DALYs) in China will be reduced by 375,000 persons and 8.90 × 106 years (GEMM model), which is 41.7% and 54.5% of the total number of premature deaths and DALYs caused by PM 2.5 from anthropogenic sources, effectively improving the health of the population. The provinces with the most significant decreases in fatalities and disabilities are concentrated in large coal-consuming provinces. Regarding age distribution, the phase-out of coal use will effectively extend the life expectancy of the elderly, especially in the age group of 65–89 years. Health benefits' growth rate upsurges notably once more than half of coal is phased out. Based on the Parallel Offline Radiative Transfer (PORT) model, the global annual average radiative forcing due to changes in short-lived climate pollutants (SLCPs), including sulfate, black carbon, organic carbon, and O 3 associated with the phase-out of coal use, is 0.34 W m−2, -0.048 W m−2, 0.00064 W m−2, and 0.00055 W m−2, respectively. The complete phase-out of coal use in China also reduces the emission of long-lived climate pollutants (LLCPs) and causes negative radiative forcing. Among them, the global annual average radiative forcing of CO 2 , CH 4 , and N 2 O is −0.0073 W m−2, -5.48 × 10−5 W m−2, -1.60 × 10−5 W m−2. If the lifetimes of pollutants are considered, the total global reduction in heat uptake is −2.29 × 107 J m−2 over 100 years, dominated by the decrease of CO 2 , which will slow the rate of global warming and thus may reduce the probability of extreme weather events. This report will incentivize relevant policymakers to remove coal significantly to achieve carbon neutrality. [Display omitted] • Coal phase-out in China avoids half of premature deaths and DALYs attributed to PM 2.5 emission from anthropogenic sources. • The health benefits experiences an upsurge when coal removal exceeds 50%, non-linearly related to the coal removal. • Sulfate and CO 2 dominate positive and negative radiative forcing. Considering the lifetime, a cooling effect will occur. [ABSTRACT FROM AUTHOR]

• Fatigue effect of the PHF is dependent on the time scale of pulsating loading. • Coal porosity increases with the increased pulsating pressure based on the LF-NMR. • A larger pulsating pressure leads to a lower cracking pressure. • The PHF creates more cracks and higher porosity than the HF according to CT images. Coalbed methane recovery can largely ease the crisis of annually increasing energy consumption of China. Low permeability and porosity of deep coal reservoirs mainly cause the low gas production rate. Pulsating hydraulic fracturing (PHF) is an alternative tool to improve the reservoir permeability and stimulate the gas productivity. However, little has been done to directly observe the fatigue damage in coal created by the pulsating loading. Because the fatigue damage is primarily governed by the time-length of PHF period. Therefore, the effect of long period pulsating loading of PHF on coal damage has been investigated in this work. Results show that long-period pulsating loading of PHF can cause significant damage in coal. The low-field NMR data indicates coal porosity increases with the increase of maximum pulsating pressure. Pulsating pressure also plays an important role in the cracking pressure. A larger pulsating pressure leads to a lower cracking pressure. Comparison of PHF and HF damaged coal investigated by the X-ray CT indicates the PHF creates more fractures and higher porosity than conventional hydraulic fracturing. The increase ratios of the coal porosity by HF and PHF are 40 %–60 % and 80 %–100 %, respectively. This paper provides a better understanding the mechanism of the coal damage by the PHF under long-period pulsating loading which is of great importance for optimizing PHF technique and generating connected fracture networks. [ABSTRACT FROM AUTHOR]

Coal structure is closely related to microscopic and macroscopic properties of coal, and its accurate identification is of great significance to coalbed methane (CBM) reservoir evaluation, hydraulic fracturing performance and production efficiency prediction. The identification of coal structure based on geophysical logging data has become a popular topic as well as a challenge. The emerging Machine Learning (ML) provides convenience for this issue. Under this background, in the case of the Shanxi Formation No. 3 coal seam and the Taiyuan Formation No. 15 coal seam in Mabidong Block, Qinshui Basin, China, this paper proposed a new coal structure identification method based on geophysical logging data using Wavelet Transform (WT) and Particle Swarm Optimization Support Vector Machine (PSO-SVM) algorithms. Our results showed that the vertical resolution of logging data can be effectively improved when sym5 wavelet basis and third level decomposition were selected in wavelet decomposition, and 4.5 was selected as the weighting coefficient in wavelet reconstruction. The coal structure prediction model based on the logging data processed by WT was established by PSO-SVM algorithm, where PSO was used for parameter optimization (optimal penalty factor C and width parameter σ) and SVM with Radial Basis Function (RBF) kernel was used for model establishment. The Hold-out Cross Validation (HO CV) method was used to test the generalization ability of the prediction model, and the accuracy (ACC) of coal structure prediction in the training set and testing set was 94.26% and 88.46%, respectively. The prediction model was applied to identify the coal structure of two coring wells and the predicted coal structure class was consistent with the true coal structure class, confirming the validity of the model. The coal structure prediction results in the whole study area showed that the tectonic conditions control the coal structure. This work provides new insights for coal structure identification. • A new coal structure identification method based on geophysical logging data was proposed. • The vertical resolution of logging data was improved based on Wavelet Transform (WT). • The coal structure prediction model was established based on Particle Swarm Optimization Support Vector Machine (PSO-SVM). [ABSTRACT FROM AUTHOR]

• 1 Stress distribution was recalculated by stress-softening and prominent dilatancy. • 2 Gas-bearing coal under impact loading was a compaction followed by ruin process. • 3 Measures principles were mainly aimed at fracture and stress-concentration areas. • 4 Preliminary goal-reaching parameter based on principles was proposed and applied. As the increasing demand for coal and the depletion of shallow coal resources, the tendency of coal mining in China is progressively shifting to deeper areas, which brings about a circumstance where the frequency and intensity of coal and gas outburst accidents have further deteriorated. Nowadays, there are many outburst prevention measures being applied on site, while this disaster still occurs from time to time. Therefore, to better improve the preventing outcome of them, this paper came forward with some principles, based on the mechanical theory of deep mining and damage evolution procedure concerning coal containing gas underneath the impact load. The primary conclusions were as follows: the stresses, strains, and associated widths in the three areas, namely fracture area, plastic area, and elastic area, in front of the working face were recalculated by considering stress-softening and dilatancy of coal mass. The damage evolution of gas-bearing coal mass under impact loading was displayed in the LS-DYNA numerical simulation as a process of compaction followed by destruction. The proposed principles could be split into two perspectives, one for the fracture area, specifically, to minimize the descending of the coal mass's strength in this area; another for the stress-concentration zone, namely, to abate the thrust due to extrusion and deformation, on the coal body which was located in the front area. According to those principles, a preliminary goal-reaching parameter was proposed and it was implemented for the evaluation of advanced drilling. The results will cooperate to rationalize the design and layout of local outburst prevention measures, thereby enhancing the efficiency of control and ameliorating the deteriorating scenario of outburst disasters. [ABSTRACT FROM AUTHOR]

Igneous intrusions into coal affect the safety, productivity, and economic viability of many coal mines. Also, the alterations in coal caused by igneous intrusions encompass a deterioration in coal quality, a decrease in permeability, an enhancement of coal rank, and geochemical and mineralogical compositions. Although there have been some studies related to the effects of igneous intrusions on the inorganic constituents in the coal, the mechanism of newly formed chemical and mineralogical associations caused by igneous intrusions has not been fully understood. This paper investigates the mineralogical and geochemical responses of coal to thermal alteration by igneous intrusion into an Early Permian coal seam in Hebei Province, North China. The Fengfeng coalfield is structurally complex, experiencing variable rates of burial and uplift, with abundant intrusions during the upper Jurassic and maximum burial in the Cretaceous resulting in an increase in rank to the north. In the search for critical minerals and elements, intrusions and hydrothermal alteration are often cited as the source for elevated concentrations. Towards the intrusion, the coal rank indicators increase from semi-anthracite to anthracite over a 500-cm distance, as does the mineral matter. The clay minerals present in coals include NH 4 -illite, kaolinite, paragonite, and chlorite (chamosite and cookeite), which were all resulted from igneous intrusions. The epigenetic minerals mainly include quartz, ankerite, calcite, pyrite, and apatite, which were derived from fluids permeating into the coal seam and chemically interacting with the original minerals or precipitating directly to form new minerals. Geochemical indicators in this coal indicate hydrothermal solutions derived from igneous intrusion. The enrichment of Li and Hg is linked to the igneous activity, potentially influencing the utilization of the coal adjacent to the intrusions. However, the concentrations of the remaining elements in the coal closest to the intrusion show no significant changes, thereby supporting the notion of a "non-universal effect" of igneous intrusions on the elemental composition and concentrations. • Towards the intrusion, the coal rank indicators increase, as does mineral matter. • Various clay minerals in coal are associated with hydrothermal fluids. • Epigenetic minerals show at least three stages of hydrothermal fluids. • Geochemical indicators are used to characterize hydrothermal fluids from intrusion. • The enrichment of Li and Hg in coal nearby intrusion is linked to igneous activity. [ABSTRACT FROM AUTHOR]

Aiming at the problem of the low reuse rate of mine water due to the high content of heavy metals in mine water, in this research, the microcharacterization means of EDX, XRD, BET, SEM, and FT-IR were used to characterize the nonstick coal in a mine in western China. The effects of solid–liquid ratio, solution pH, solution temperature, adsorption time, and initial concentration of the solution on the adsorption of Fe(II) by the nonstick coal were analyzed. The adsorption performance of nonstick coal on adsorbed Fe(II) was analyzed under different influencing factors. The results showed that the adsorption capacity and unit removal rate of the coal samples gradually decreased with the increase in the solid–liquid ratio; the adsorption amount increased with the increase in pH in an "S" shape, and the adsorption effect was better in the range of pH = 5~7; and the adsorption amount increased linearly with the temperature. The quasi-secondary kinetic model and Langmuir model could fit the adsorption kinetic curve and isothermal adsorption curve better, which indicated that the adsorption of Fe(II) by the nonstick coal was dominated by the chemical adsorption of the monomolecular layer. The quantitative analysis of the FT-IR results showed that the adsorption of Fe(II) was mainly by complexation with -OH detached from the coal samples to produce precipitation. [ABSTRACT FROM AUTHOR]