Coal Mines In China Research Articles

Efficient prevention of coal spontaneous combustion using cooling nitrogen injection in a longwall gob: An application case

Conventional nitrogen injection in longwall gobs often fails to achieve the expected fire protection effect due to the lack of cooling function. To address this issue, a technical solution of cooling nitrogen injection was proposed to prevent the coal spontaneous combustion (CSC) in gobs, and the corresponding deep-cooling equipment system was developed. This system was applied on-site in a coal mine in China and had achieved favorable cooling results. Furthermore, the multi-physics coupling model of CSC in gob was upgraded to be applicable to nitrogen injection conditions. The effects of nitrogen injection parameters were then quantitatively evaluated. The results show that (i) the cooling nitrogen entering the gob can significantly reduce the temperature of the high-temperature zone, about 5 °C, thus effectively reducing the risk of the CSC in gobs; (ii) the simulation results under nitrogen injection are in good agreement with the on-site data, which verifies the accuracy of the nitrogen injection model; (iii) there is an optimal location of the nitrogen injection point in gob, which can suppress the CSC to the maximum extent. This technology of cooling nitrogen injection can be further promoted and applied to other mines with severe spontaneous combustion.

Relieving Pressure and Improving Permeability of Soft Coal at Top and Bottom by Hydraulic Cavitation

For enhancing the effect of gas extraction, applying Wuyang Coal Mine in China as the engineering background, the technology of hydraulic cavitation at the top and bottom of soft coal (HCTBSC) with low permeability was put forward. FLAC3D was utilized to build the calculation model, and Tecplot was employed to process data of the results, revealing the characteristics of stress variation in coal seam for different cavitation radius and different distribution forms of cavitation. The field test scheme of HCTBSC was determined to verify the simulation results. Results show that the effectiveness of stress relief (ESR) is controlled by the cavitation radius and cavitation distribution forms. The dimension of pressure relief emanates via the cavitation elongating outward with the cavitation radius, and the stress changes in the coal are different due to different cavitation distribution forms. The field test proves that the technology of HCTBSC is more effective in relieving pressure, increasing the productiveness of gas extraction, and decreasing the scourge of coal and gas protrusion. The obtained conclusions in this study provide guidance for the hydraulic cavitation application in soft coal.

Structural Stability and Surrounding Rock Integrity Analysis for Goaf-Side Entry with Small Coal Pillars in Longwall Mining

Goaf-side entry with small coal pillars (GESCPs) has an intrinsic advantage of improving the coal recovery ratio by implementing drifts with a small pillar size next to previous goafs. This technology is increasingly gaining popularity in the longwall mining of underground coal mines in China. This study focuses on understanding the critical condition of the main roof failure above the solid coal side of the goaf-side entry and investigating the key parameters that affect the structural stability of the surrounding rocks for GESCP. Mechanical models of the main roof and multi-layer cracking structures of the side wall of GESCP were established and the limiting equilibrium equation for the structural stability of the surrounding rock was proposed. The characteristics affecting the main parameters of the structural stability of the surrounding rock were analyzed. The research findings suggest that the integrity of the coal side walls plays a major role in maintaining the structural stability of the surrounding rock for GESCP under the given cross-sectional dimensions. Other factors, including the uniform load of overburden, the width of the coal pillar, the length of the roof hanging along the goaf side, and the fracture length in the main roof of the entry side wall, are less important. The key to achieving structural stability of the surrounding rocks for GESCP is to enhance the strength of the supporting coal side walls and, especially, to ensure the integrity of the small coal pillars. These conclusions were verified by engineering practice at the 1252(1) haulage gateway in a Coal Mine in China.

A Study on the Development and Evolution of Fractures in the Coal Pillar Dams of Underground Reservoirs in Coal Mines and Their Optimum Size

The western mining areas of China, which are rich in coal resources, lack water resources. Large-scale and high-intensity coal mining in China’s western mining areas has led to the loss of groundwater resources. Underground reservoirs in coal mines are an effective means of achieving the protection and utilization of water resources in these western mining areas. One of the important standards for the safety of an underground reservoir in a coal mine involves checking whether the development of cracks in the coal pillar dam body, under the dual stress conditions of overlying strata and lateral water pressure, passes through the coal pillar dam body or its top and bottom plates, forming a seepage channel for mine water. This article focuses on the safety issues associated with coal pillar dams in the underground reservoirs of coal mines. From the perspectives of overlying rock pressure and lateral water pressure on coal pillar dams, mechanical models, numerical calculations, and similar simulation methods were used to analyze macroscopic deformation, displacement, and crack development in coal pillar dams of different sizes under vertical and horizontal stress and to study the optimum width of coal pillar dams. Our research results indicated that the optimal width of the coal pillar dam body can be determined via numerical simulation based on the deformation and stress state in a given dam. When the horizontal stress increases, the smaller the coal pillar width is, the greater the increment of syy and sxx becomes, and the more likely the coal pillar is to be damaged. Similar simulations showed that the smaller the size of the coal pillar is, the easier it is to generate stress concentration, and the more likely this stress is to “eat away” the coal pillar dam body. There is a certain relationship between the size of the coal pillar dam and the range of crack development. The larger the coal pillar size is, the less obvious the stress concentration effect becomes, and the less likely the crack is to penetrate the internal and external parts of the reservoir. Taking the Shangwan mine as an example, it was determined that the maximum water head height that could be carried by the 15-m coal pillar dam body was 50 m. A comprehensive study of the development and evolution of cracks in the coal pillar dam of an underground reservoir in a coal mine, and the characteristics of sliding instability, was conducted to determine the optimal size and maximum water storage height of a coal pillar that does not penetrate the inner and outer parts of the reservoir. The development and evolution of cracks are important factors affecting the stability of coal pillar dams. This study can expand and improve the basic theory of underground reservoirs in coal mines, provide a scientific basis for determining the optimum size of a coal pillar dam, guarantee the long-term safe and stable operation of the coal pillar dams of underground reservoirs in coal mines, and continuously save mine water resources and increase the economic benefits of coal mines. These implications are of great significance for the long-term stable operation of underground reservoirs in coal mines under similar geological conditions.

Study on the Mechanism of Surrounding Rock Deformation and Its Control for Roof Cutting Retained Gob-Side Entry in Close-Distance Coal Seams Co-Mining

Sustainable development in coal mining requires a continuous and efficient method of coal extraction. Research shows that gob-side entries retained through roof cutting retained gob-side (RCGE) are vital for improving mining efficiency, enhancing coal recovery rates, and enabling continuous production. However, the mechanism of surrounding rock deformation during close-distance co-mining of coal seams with this technique is not yet clear. For the Jiaokou coal mine in China, due to an unreasonable stagger distance between upper and lower working faces, the gob-side entries retained at the 9102 tailgate and 10102 headgate experience severe rock pressure, leading to significant prop damage and a sharp reduction in the cross-section of the entry. This greatly hampers the reuse of these entries. To investigate this issue, we established a model to study the stress distribution of surrounding rocks at different stagger distances (20 m, 40 m, 60 m, 80 m, and 120 m) through numerical simulation and optimized the support parameters for the retained entries. Our research found that when the subsidence of the roof in the upper coal seam exceeds 0.74 m but is less than 1.33 m, there is sliding instability in the mining body. When the subsidence exceeds 1.33 m, the mining body will rotate and deform, causing significant mining pressure within the retained entry. A stagger distance of 40 m between the upper and lower working faces can reduce pressure on the face during the mining of the lower coal seam. Extensive field measurements of rock pressure revealed that the damage rate of the single column in the gob-side entries of the upper and lower coal seams does not exceed 5% and 1%, respectively. In summary, this study provides a practical method to reduce damage to entries during the mining process, thereby increasing the continuous production capability of the coal mine. This is critical for the sustainable development of coal mining.

Performance and application of new inorganic retarding sealing material suitable for multi-scale fractures

Gas extraction is an important way to solve coal mine gas in China. At present, the development of new and more efficient gas sealing materials is an urgent problem in China's coal mining industry. In order to improve the gas extraction efficiency and promote the development and utilization of coalbed methane, we developed a new inorganic slow setting material which used bentonite as main material. We added two kinds of organic modified materials and two kinds of inorganic modified materials to optimize the sealing performance, and analyzed the viscosity, sealing and particle size changes after modification. The rheological properties and diffusion properties of sealing materials was studied. Meanwhile, field experiments were carried out to verify that it has more efficient sealing performance than traditional cement materials and could improves the efficiency of gas drainage and reduces mine gas disaster accidents.

Isothermal adsorption characteristics of various phases of CO2 and CH4 in different rank coals

ABSTRACT Using the remaining coal seams of closed coal mines for CO2 geological storage can effectively slow down the greenhouse effect and realize the redevelopment and utilization of closed coal mines. The burial depth of coal seams in closed coal mines in China covers an extensive range, and CO2 and CH4 could exist in various phases in the coal. The existing experimental objects for CO2 adsorption in coal are mainly associated with the supercritical and gaseous phases, and a research gap comparison between the CO2 adsorption characteristics in the liquid phase and those of other phases is very obvious. Herein, the isotherm adsorption experiments of CO2 and CH4 in different phases on different rank coal samples are methodically conducted in the pressure range of 0-12MPa. The experimental results indicate that the excess adsorption capacity of gaseous CO2 and CH4 (gas pressure <4MPa) rapidly raises with the growth of the adsorption pressure; however, a significant difference for the case of the medium- and high-pressure stage (>4MPa) is detectable. With the growth of the adsorption pressure, the excess adsorption capacity of the supercritical CH4 gradually reaches the maximum value and then remains stable, where the maximum experimental value is 1.009 mmol/g. While the excess adsorption capacity of CO2 near the critical pressure of liquid and supercritical state rapidly reduces and then tends to be stable. The maximum adsorption capacity is capable of touching 2.096 mmol/g, which is stable around 0.5 mmol/g. The analysis indicates that the change in the excess adsorption amount of CO2 near the critical pressure corresponds to the change in its density. The absolute adsorption capacity of CO2 and CH4 monotonically grows in the pressure range of 0-12MPa, and the absolute adsorption capacity of the same coal sample follows the following order: liquid CO2 > supercritical CO2 > CH4. The maximum adsorption capacity values for these substances in order are 2.493, 2.345, and 1.296 mmol/g. With the growth of the coal rank, the Gibbs free energy, specific surface area, and adsorption capacity of the understudied coal samples exhibit a U-shape relationship as a function of their coal ranks.

Where risk, where capability? Building the emergency management capability structure of coal mining enterprises based on risk matching perspective

The emergency management capability of coal mine enterprises is a crucial element of coal mine safety management. Exploring the structure of the emergency management capability of coal mine enterprises under the perspective of risk matching is conducive to clarifying the core nodes of emergency management capability construction. A qualitative analysis of Chinese underground coal mine accident reports, related laws and regulations, and relevant academic papers was conducted using grounded theory. Currently, the risks in underground coal mines in China can be divided into source-generated risks, derivative risks, and residual risks. The elements of emergency management capabilities that match them are absorption capability, detection and control capability, and response capability. At the same time, some capability elements across different risks are summarized as internal enhancement and external enhancement, respectively. The study provides a reference for coal mining enterprises to improve emergency management capability and reduce risks.

Study on High and Low Temperature Performance of Mineral Powder Modified Rubber Asphalt Mortar

With the increase of coal mining in China, a large amount of waste coal gangue is produced. How to reuse waste coal gangue is an important research direction. The research results showed that the improvement of base asphalt mortar by coal gangue powder could improve the performance of matrix asphalt, however, search of rubber asphalt mortar modified by coal gangue powder is rarely reported. High and low-temperature performance is the critical performance of asphalt mortar. So the limestone powder modified base asphalt mortar (LPMBAM), limestone powder modified rubber asphalt mortar (LPMRAM), and coal gangue powder modified rubber asphalt mortar (CGPMRAM) are prepared, the high and low-temperature performance of asphalt mortar are analyzed by cone penetration tests and bending beam rheological tests (BBR). The results show that the cone penetration of asphalt mortar decreases with the increase of the filler-asphalt ratio and the decrease of the temperature. The shear strength and the stiffness modulus increase with the rise in the filler-asphalt ratio and the decrease in temperature. At the same filler-asphalt ratio and temperature, the order of cone penetration is CGPMRAM &lt; LPMRAM &lt; LPMBAM, and the order of shear strength is CGPMRAM &gt; LPMRAM &gt; LPMBAM, so the high-temperature performance of CGPMRAM is better than that of LPMRAM, much better than LPMBAM, the order of stiffness modulus is LPMRAM &lt; CGPMRAM &lt; LPMBAM so the low-temperature performance of LPMRAM and CGPMRAM is better than that of LPMBAM. By the double linear model, the optimum filler-asphalt ratio is determined to be 0.44~0.46 for LPMRAM and 0.42~0.43 for CGPMRAM. Microscopic tests show that the surface of coal gangue powder is rougher than that of limestone powder. The content of active oxides such as SiO2 and Al2O3 in coal gangue is about 7.8 times that of limestone powder. These physical and chemical properties make coal gangue powder able to adsorb rubber asphalt better and improve the high-temperature performance of CGPMRAM while slightly worsening the low-temperature performance of CGPMRAM but still better than LPMBAM.

How do rotifer communities respond to floating photovoltaic systems in the subsidence wetlands created by underground coal mining in China?

Along with the increasing demand for energy and pressure to reduce carbon emissions, floating photovoltaic (FPV) systems are increasingly built on the surface of water bodies with the aim to produce clean energy. However, little is known about how FPV systems influence freshwater ecosystems, e.g., their zooplankton communities. We investigated how rotifer communities responded to FPV systems in subsidence wetlands created by underground coal mining in the North China Plain. Diversity metrics of the rotifer communities were compared between wetlands with and without FPV systems. The density of rotifers was higher in wetlands without FPV systems. In contrast, rotifer diversity as represented by Shannon-Weiner and Pielou evenness indices was higher in the FPV-covered wetlands, while there was no difference in species richness between the two types of wetlands. Furthermore, community structures differed between the two types of wetlands, in large part reflecting differences in the relative abundance of five dominant species found in both types of wetlands. These differences in rotifer assemblages were in large part explainable from environmental changes caused by the FPV panels, notably reduced light availability and water temperature, leading to reduced phytoplankton production. These findings show that FPV systems cause major changes to rotifer communities in these subsidence wetlands and likely in wetlands more generally, and monitoring of the longer-term effects is recommended given the fundamental role of zooplankton in freshwater ecosystems.

Isotope radon measurement method to identify spontaneous combustion regions in coal gangue hills: case study for a coal mine in China

ABSTRACT Long-term accumulation of coal gangue hill has a high risk of spontaneous combustion, and the toxic and harmful gases emitted by spontaneous combustion seriously pollute the atmosphere. The key to managing the spontaneous combustion fire of coal gangue hill lies in the accurate measurement of fire source location. However, measuring the fire source location of surface coal gangue hill lacks experimental and empirical research. In this paper, an oxidation warming experiment was conducted on the coal gangue samples, and the law of radon gas exhalation from coal gangue under different temperatures was analyzed. At the same time, surface thermometry and isotope radon measurement were applied to measure the high-temperature areas inside the gangue hill, and the measurement results were compared. The experimental results show that as the temperature of gangue increases, the amount of radon gas exhalation in gangue shows a changing trend of rising first and then decreasing. The radon exhalation from coal gangue can be divided into three stages. In the I stage (30 ~ 100°C), the evaporation of pore water in coal gangue leads to the exhalation of radon in water, causing the increase of radon concentration; in the II stage (100 ~ 350°C), the coal gangue is pyrolyzed at high temperature, and a large amount of radon is exhalated from the closed pores; in the III stage (350 ~ 450°C), after the first two stages of radon release, the number of radon atoms in this stage decreases, leading to a rapid decrease of radon concentration. The field measurement results show that compared with the surface thermometry method, the isotope radon measurement method is less disturbed by external conditions, and the circled fire area is more accurate, which has essential theoretical significance and practical application value for the accurate measurement of fire source location in coal gangue hill.

Development, effectiveness, and deficiency of China's Coal Mine Safety Supervision System

Coal mine safety is closely related to the stable development of China's economy. Coal mine safety supervision system provides a powerful guarantee of coal mine safety. A comprehensive review of the reform process of China's coal mine safety supervision system is important for exploring its impact on coal mine safety production. This study focuses on the reform process of China's coal mine safety supervision system from the establishment of the State Administration of Coal Mine Safety (SACMS, later renamed the National Mine Safety Administration (NMSA) in 2020) in 1999–2022. The safety status and safety supervision systems of the coal mining industry and the construction industry are compared to verify the importance of the establishment of the SACMS. It is found that the coal mine safety status has improved significantly, and the number of fatalities has decreased steadily, which is in sharp contrast with the accident trend in the construction industry. Finally, this study compared the coal mine safety status between the United States and China. Results show that there is still a gap between the two countries in coal mine safety levels. Coal mine geological conditions, coal mining technology, safety training, and coal mine safety supervision forces are the influencing factors of coal mine safety. Based on the advanced experience of the United States, this research puts forward suggestions for China's safety supervision. In addition, the law enforcement activities of the NMSA are also reflected in this study. The outcomes are significant for understanding the containment effect of coal mine safety supervision on coal mine accidents. Besides, the research also provides professional materials for coal mine enterprises and other production industries, which is conducive to promoting the safe production of various industries to a certain extent.

Sustainable Development of Underground Coal Resources in Shallow Groundwater Areas for Environment and Socio-Economic Considerations: A Case Study of Zhangji Coal Mine in China.

Coal resources in China are developed in several regions with shallow groundwater, and large mining-related surface subsidence can have negative impacts on agriculture, land and water resources as well as existing and future socio-economic resources. All these are important for sustainable resource development. Dynamic subsidence reclamation (DSR) planning concepts are evaluated here for another case study with analyses over a 11-year period. In DSR topsoil, subsoil, farming, and water resources management are dynamically synergized concurrent with mining ahead of and behind the projected dynamic subsidence trough. The study area involved mining five longwall faces (and post-mining reclamation) to assess if DSR could have improved both the environment and socio-economic conditions for post-mining land use as compared to using traditional reclamation (TR) and TR-modified (TR(MOD)) approaches. The results show that: (1) Upon final reclamation, farmland area and water resources in DSR and TR (MOD) will have increased by 5.6% and 30.2% as compared to TR. Removing soils ahead of mining before they submerge into water is important for farmland reclamation and long-term economic development. (2) Due to topsoil and subsoil separation and storage in the DSR plan, reclaimed farmland productivity should recover quickly and agriculture production should be larger than TR and TR(MOD) plans. (3) For a simplified economic model, the total revenue in the DSR plan should be 2.8 times more than in TR and 1.2 times larger than in TR (MOD) plan. (4) The total net revenue of the TR(MOD) plan should be increased by 8.1% as compared with the TR plan. The benefits will be much greater for analyses over longer periods. Overall, the DSR plan will allow for an improved socio-economic environment for new businesses to support disrupted workforces during and after mining.

How Do COVID-19 Risk, Life-Safety Risk, Job Insecurity, and Work-Family Conflict Affect Miner Performance? Health-Anxiety and Job-Anxiety Perspectives.

The coronavirus pandemic (COVID-19) has created challenging working conditions in coal-production activities. In addition to the massive loss of resources for miners, it has had a devastating impact on these individuals' mental health. Based on the conservation of resources (COR) theory and a resource-loss perspective, this study examined the impact of COVID-19 risk, life-safety risk, perceived job insecurity, and work-family conflict on miners' job performance. Moreover, this study investigated the mediating role of job anxiety (JA) and health anxiety (HA). The study data were collected through online structured questionnaires disseminated to 629 employees working in a coal mine in China. The data analysis and hypothesis generation were conducted using the structural equation modeling (partial least squares) method. The results demonstrated that the perception of COVID-19 risk, life-safety risk, job insecurity, and work-family conflict negatively and significantly impacted miners' job performance. In addition, JA and HA negatively mediated the relationships between the perception of COVID-19 risk, life-safety risk, perceived job insecurity, work-family conflict, and job performance. The findings of this study can give coal-mining companies and their staff useful insights into how to minimize the pandemic's effects on their operations.

Characteristic Developments of the Water-Conducting Fracture Zones in Weakly Cemented Overlying Strata of Jurassic Coal Mines in Western China

The overlying weakly cemented, and poorly performing strata in Jurassic mines of western China have mechanical properties that are generally lower than those in the Carboniferous-Permian coal mines of central and east China. During coal mining, the overlying strata easily deform and fracture. These then formed water-conducting channels, triggering a series of eco-environmental issues, including ground fracturing, collapsed surfaces, declined underground water levels, deserted lands, and even severe water/sand burst accidents. To study the fracture characteristics of weakly cemented overlying strata and the evolution law of water-conducting fractures in Jurassic coal mines in western China, this study selected Tashidian Erjingtian Mine in Korla, Xinjiang, as the research object. Based on the simulation data obtained with physical analog model testing and field monitoring results, the authors investigated the development of water-conducting fractures in the weakly cemented overlying strata during the coal seam mining process. We simultaneously determined the location of key strata in the working face based on key stratum theory. According to the present research results, key strata controlled the development height of water-conducting fractures. When the primary key stratum or sub-key stratum was not fractured, the development of water-conducting fractures was stagnant; water-conducting fractures developed abruptly when the primary key stratum or sub-key stratum was cracked. The heights of water-conducting fractures in the weakly cemented overlying strata of western China exceeded that of similar stopes of central and east China. These research results provided theoretical and technical support for safety in production at Tashidian Coal Mine. In addition, they offered a reference for green and safe production in Jurassic coal mines of western China.

Crack Evolution Behaviors and Bursting Liability of Sandstone with Different Sizes: An Experimental Study.

The size ranges of ore pillars play important roles in preventing the occurrences of rock burst phenomena. Due to the lack of research on the relationship between crack evolution behaviors and bursting liability of rocks with different sizes, uniaxial compression tests on sandstone with different height-to-diameter ratios (H/D) were conducted. The results showed that the mechanical parameters of sandstone have obvious size effects, in which both the peak strength and peak strain decrease with increases in the H/D. Moreover, the brittle index modified value (BIM) decreased, but the impact energy index increased gradually, which indicated the increase of bursting liability. With the increases in the BIM, the overall crack strain parameters increased, thereby indicating a positive correlation. With the increase in the impact energy index, the crack strain decreased and the bursting liability became higher. Although the axial crack closure stress and axial crack damage stress increased with the increases in BIM (indicating a positive correlation), the bursting liability became increasingly smaller. The crack stress decreased with the increases in the impact energy index, and the bursting liability became stronger. The findings of this study will potentially provide experimental references for furthering the current understanding of the mechanism of rock bursts in underground coal mines in China.

Crack closure effect during the impact coal seam with high-pressure air blasting and the influence of gas drainage efficiency

The crack closure in impact coal seams induced by high-pressure air blasting greatly affects gas drainage efficiency. The length of the crack closure was calculated and analyzed based on energy and elastic theories. The closure region was then determined to be 3.8 m from the blasting hole. The results of a high-pressure air blasting experiment in the underground of one coal mine in China showed that the effect of crack closure on gas drainage efficiency manifested as a decreased amplitude of gas emission in the crack closure region. At 1.0–4.0 m from the blasting hole, the amplitude of gas emission in the observation holes first increased and then decreased with increasing distance from the blasting hole. At 1.8–2.5 m from the blasting hole, the amplitude of the gas emission was maximal. At 4.0 m from the blasting hole, the crack was nearly closed, and the gas emission in the observation holes was minimal. The theoretical calculation had good consistency with the field test results; thus, it can provide an important reference for an appropriate arrangement of gas drainage boreholes.

Instability prediction model of remaining coal pillars under remining disturbance

AbstractTo address the instability timing problem of residual coal pillars under mining disturbance, their stress migration law and instability mechanism were studied via numerical simulation, physical simulation, and engineering tests considering residual coal remining in the 3101 working face of the Shenghua Coal Industry. The results show that as the mining progresses, the stress concentrates on both sides of the remaining coal pillar and empty roadway. When the first coal pillar in front of the working face loses its bearing capacity, the stress is transmitted forward, resulting in the advanced collapse of the empty roadway roof and an excessive load on the second coal pillar in front of the working face. Additionally, the critical value prediction model of the coal pillar stability safety factor was constructed. If is less than the critical value during the repeated mining period, the remaining coal pillar must be reinforced. A hollow grouting crossed anchor is selected for coal pillar reinforcement; thus, realizing the safe mining of the remaining coal pillars. Our research results provide theoretical support for the safe secondary mining of coal in China and similar coal mines worldwide.

Facility-Level Emissions and Synergistic Control of Energy-Related Air Pollutants and Carbon Dioxide in China.

Boilers involve ∼60% of primary energy consumption in China and emit more air pollutants and CO2 than any other infrastructures. Here, we established a nationwide, facility-level emission data set considering over 185,000 active boilers in China by fusing multiple data sources and jointly using various technical means. The emission uncertainties and spatial allocations were significantly improved. We found that coal-fired power plant boilers were not the most emission-intensive boilers with regard to SO2, NOx, PM, and mercury but emitted the highest CO2. However, biomass- and municipal waste-fired combustion, regarded as zero-carbon technologies, emitted a large fraction of SO2, NOx, and PM. Future biomass or municipal waste mixing in coal-fired power plant boilers can make full use of the advantages of zero-carbon fuel and the pollution control devices of coal-fired power plants. We identified small-size boilers, medium-size boilers using circulating fluidized bed boilers, and large-size boilers located in China's coal mine bases as the main high emitters. Future focuses on high-emitter control can substantially mitigate the emissions of SO2 by 66%, NOx by 49%, PM by 90%, mercury by 51%, and CO2 by 46% at the most. Our study sheds light on other countries wishing to reduce their energy-related emissions and thus the related impacts on humans, ecosystems, and climates.

Development status of coal mining in China

Coal mining in China is facing the transition from output to quality. Based on the total mining capacity and average production, the current situation of coal mining at mine, city, and province levels is analysed, and data in support for the layout of sustainable mining development and the optimization of output provided. The results show that 87% of China's coal is mined by underground methods, with an average production capacity of 0.93 Mt/a per mine. Open pit mining accounts for 13%, with an average mine production capacity of 5.73 Mt/a. The average mining capacity of coal mines in China is 1.05 Mt/a, with 1181 coal mines with an average capacity less than 0.3 Mt/a, accounting for 35% of the total coal mines but contributing only 4.51% to output. They are distributed in about 48 cities in six provinces, seriously restricting the transition to green coal mining. The coal industry should speed up the closure of small coal mines in key provinces and cities, eliminate outdated production capacity in the central region, increase the speed and proportion of coal resources moving westward, and promote high-quality development of coal mining.