Small Coal Mines Research Articles

Analysing the application of a flexible formwork pre-cast wall driving roadway along goaf in a large mining height face

The technology of building a retaining roadway along goaf or a protecting roadway with a small coal pillar has been developed and applied for many years, and a satisfactory supporting effect has been obtained in medium–thick coal seam and thin coal seam mining. However, the gob-side roadway or small coal pillar mining in a thick coal seam is still subjected to technical problems occasioned by factors such as high roadway, high support pressure beside roadway, and waste of coal resources. To solve these problems, the author proposes an innovative technology of coal-free mining: the technology of driving roadway along goaf with a flexible formwork pre-cast wall. The article utilizes the 3503 and 3505 working faces of Wangzhuang Coal Industry Group as the research background, and comprehensively introduces the principle of the technology and the overburden rock movement law. Through theoretical calculations and numerical simulations, the support resistance and support parameters of flexible formwork pre-cast walls have been determined and successfully performed in industrial practice. The results indicate that the combination of the flexible mould pre-cast wall coal pillar-free mining technology and roof cutting process is more conducive to the maintenance of the roadway in the lower working face, and effectively reduces the stress and deformation of the surrounding rock. The roof and floor of the drivage roadway move, and the deformation of the two sides is small; furthermore, the overall roadway retention effect is satisfactory, which meets the requirements of mining in the lower working face. The coal pillar pertaining to the 20 m section of the 5 m high mining height face was recovered for Wangzhuang Coal Mine, and the recovery rate of the coal resources and the driving speed of the roadway were improved. The proposed method can be popularised and applied in this mine and even in the mining of 15# large-height coal seams in the two cities.

Simulation on Harmful Gas Control by Balanced Pressure Ventilation in the Fully Mechanized Caving Face under Sealed Fire Area of Small Coal Mine.

The harmful gas in the sealed fire area of a small coal mine rushes into the mining face of the lower coal seam, which restricts the efficient promotion of the working face. In this paper, based on the evolution law of caving coal rock dilatation coefficient, the characteristics of the heterogeneous distribution of permeability and voidage in goaf were obtained, and the mathematical model of gas migration in goaf is constructed. The numerical solution of gas migration in goaf under the sealed fire area of a small coal mine was realized by using the Free and Porous Media Flow module and the Transport of Dilute Matter in Porous Media module in COMSOL Multiphysics, and the corresponding measure was proposed. The results show that the fresh air flows into the goaf from both the inlet air roadway and the working face and then flows out from the upper corner. Driven by the air flow, the CO in the overlying sealed fire area of a small coal mine flows out from the upper corner of the working face, resulting in the CO overlimit. Due to the influence of air leakage and the CO overlimit in the working face, low oxygen occurs in the working face. According to the characteristics of gas emission, balanced pressure ventilation technology is proposed to control the low oxygen in the working face and the CO overlimit in the upper corner. It is found that the balanced pressure ventilation obviously increases the pressure of the working face, reduces the pressure difference between the two ends of the working face by 45.7-26.7%, and decreases the air leakage to the goaf in the upper corner of the inlet air roadway. The field application shows that the problems of low oxygen in the working face and a CO overlimit in the upper corner are effectively solved.

Source reduction and end treatment of acid mine drainage in closed coal mines of the Yudong River Basin.

After the closure of the Yudong coal mine, the pH value was approximately 3.0, and the Fe and Mn concentrations reached 380 and 69 mg/L, respectively, in the acid mine drainage (AMD), causing serious pollution to the water bodies in the nearby watershed. Combined with the formation conditions of AMD, the comprehensive treatment technology of source reduction-end treatment is adopted to treat the AMD. The treatment area of the goaf is 0.3 km3, the filling and grouting volume is about 6.7 m3, and the curtain grouting volume is 4,000 m3. Through the grouting and sealing treatment in the goaf, the water volume is reduced to less than 85% of the initial volume (100 m3/h). After the end treatment, the pH value of the effluent is around 7.0, the content of Fe and Mn is less than 0.1 mg/L, and the removal rate is above 99%. The project was subsequently operated at RMB 0.85 yuan/t. This project is aimed at the treatment of AMD from small coal mines in complex terrain conditions. It has the characteristics of low cost and high efficiency and can provide an effective treatment technology for AMD in southwestern China and areas with the same geological conditions.

Remembering Herbert Gutman's Work, Culture, and Society Fifty Years On

Remembering Herbert Gutman's <i>Work, Culture, and Society</i> Fifty Years On

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.

Research on comprehensive detection and visualize of hidden cavity goaf

At present, the research on goaf at home and abroad mainly focuses on four aspects: detection technology, stability evaluation technology, governance technology and quality control technology. The most important of the above four aspects is goaf detection technology. In order to ensure the accuracy and precision of exploration, many geophysical methods and high-density geological drilling are usually used for exploration. In case of complex terrain, this method will increase the workload rapidly, and can not achieve a good balance between exploration cost and exploration quality. Goaf exploration methods are still in the development stage, and each geophysical exploration method has its limitations. This study makes full use of the existing detection technology to detect the complex mined-out area of East Open-pit Mine, 9 inferred mined-out areas and 9 suspected mined-out areas were found by using 3D seismic exploration method, transient electromagnetic method is used to delineate 223 abnormal areas at different elevations within the exploration range. 58 drilling holes are arranged in the suspected mined-out area of East Open-pit Mine. Combined with geological software, 3D model map of mined-out area is drawn, and the causes of formation of mined-out area are classified and analyzed. Using 3D laser scanning technology to study the visualization of hidden mined-out areas, the hidden mined-out areas are divided into three types through visualization research, and its formation mechanism is analyzed. It can be applied to detection of open-pit mines which have small underground coal mines and many mined-out areas with complex geometric shapes and has great significance to the proposal of stability treatment scheme of mined-out area. The novelty of this study is prove the area, shape, roof thickness and height of the mined-out area by using joint detection method and the hidden mined-out area is visualized by 3D laser scanning technology.

A Study on the Propagation Trend of Underground Coal Fires Based on Night-Time Thermal Infrared Remote Sensing Technology

Underground coal fires in coal fields endanger the mine surface ecological environment, endanger coal resources, threaten mine safety and workers’ health, and cause geological disasters. The study of methods by which to monitor the laws that determine the way underground coal fires spread is helpful in the safe production of coal and the smooth execution of fire extinguishing projects. Based on night-time ASTER thermal infrared images of 2002, 2003, 2005 and 2007 in Huangbaici and Wuhushan mining areas in the Wuda coalfield, an adaptive-edge-threshold algorithm was used to extract time-series for underground coal fire areas. A method of time-series dynamic analysis for geometric centers of underground coal fire areas was proposed to study the propagation law and development trend of underground coal fires. The results indicate that, due to the effective prevention of the external influences of solar irradiance, topographic relief and land cover, the identification accuracy of coal fires via the use of a night-time ASTER thermal infrared image was higher by 7.70%, 13.19% and 14.51% than that of the daytime Landsat thermal infrared image in terms of producer accuracy, user accuracy and overall accuracy, respectively. The propagation direction of the geometric center of the time-series coal fire areas can be used to represent the propagation direction of underground coal fires. There exists a linear regression relationship between the migration distance of the geometric center of coal fire areas and the variable-area of coal fires in adjacent years, with the correlation coefficient reaching 0.705, which indicates that the migration distance of the geometric center of a coal fire area can be used to represent the intensity variation of underground coal fires. This method can be applied to the analysis of the trends of underground coal fires under both natural conditions and human intervention. The experimental results show that the Wuda underground coal fires spread to the southeast and that the area of the coal fires increased by 0.71 km2 during the period of 2002–2003. From 2003 to 2005, Wuda’s underground coal fires spread to the northwest under natural conditions, and the area of coal fires decreased by 0.30 km2 due to the closure of some small coal mines. From 2005 to 2007, due to increased mining activities, underground coal fires in Wuda spread to the east, south, west and north, and the area of coal fires increased dramatically by 1.76 km2.

Observed changes in China’s methane emissions linked to policy drivers

China is set to actively reduce its methane emissions in the coming decade. A comprehensive evaluation of the current situation can provide a reference point for tracking the country's future progress. Here, using satellite and surface observations, we quantify China's methane emissions during 2010-2017. Including newly available data from a surface network across China greatly improves our ability to constrain emissions at subnational and sectoral levels. Our results show that recent changes in China's methane emissions are linked to energy, agricultural, and environmental policies. We find contrasting methane emission trends in different regions attributed to coal mining, reflecting region-dependent responses to China's energy policy of closing small coal mines (decreases in Southwest) and consolidating large coal mines (increases in North). Coordinated production of coalbed methane and coal in southern Shanxi effectively decreases methane emissions, despite increased coal production there. We also detect unexpected increases from rice cultivation over East and Central China, which is contributed by enhanced rates of crop-residue application, a factor not accounted for in current inventories. Our work identifies policy drivers of recent changes in China's methane emissions, providing input to formulating methane policy toward its climate goal.

Pollution Characteristics and Risk Assessments of Mercury in Jiutai, a County Region Thriving on Coal Mining in Northeastern China

Among human activities, coal mining and the combustion of fossil fuels are important sources of mercury in the environment. Research on mercury pollution in coal mining areas and surrounding cities, especially in densely populated areas, has always been at the forefront of this research field. In order to study the characteristics of environmental mercury pollution in small and medium-sized coal mining areas and surrounding towns in China, this study selected the main urban area of Jiutai District, a typical mining town in the Changchun City circle industrial base in northeast China, as the research object. In this study, the geo-accumulation index (Igeo) was used to study the soil mercury pollution degree in Jiutai District, the potential ecological risk index (Er) was used to evaluate the potential ecological risk of soil mercury in the study area, and the human exposure risk assessment model was used to evaluate the non-carcinogenic risk of soil mercury to the human body. The results showed that 32% of the soil samples in the study area had a higher mercury content than the regional soil background value of Jilin Province (0.04 mg·kg−1). According to the Igeo, 19% of the sample sites in the study area were polluted (index &gt; 0). In general, the soil mercury pollution level in Jiutai District is low, and the polluted areas are mainly concentrated in the northeast of the study area. The Er of the soil mercury in the study area ranged from 7.2 to 522.0, with 32% of the sampling sites having a moderate or above potential ecological risk (Er &gt; 40), and the potential ecological risk level of the soil mercury was higher in the northeast of the study area. The non-carcinogenic risk index (HQ) and total non-carcinogenic risk value (HI) of the soil mercury were all far less than 1, indicating that soil mercury pollution in the study area did not harm the health of local adults. The oral ingestion of soil mercury is the main form of human exposure to mercury.

Reform and development of coal mine safety in China: An analysis from government supervision, technical equipment, and miner education

Coal mine safety management has been one of the most successful public governance cases in China in the last 20 years. This paper systematically analyzes the reform measures and experience effects of the Chinese government in coal mine safety governance. It does so from three aspects: government supervision, technical equipment, and miner training. The results show that the number of coal mine accidents in China has fluctuated greatly, which can be divided into five stages. Small and medium-sized coal mines, dominated by township and village coal mines, are the key targets of coal mine safety management in China. Two policies —"shutting down small coal mines” and “integrating resources"—have strengthened the government's safety management of small coal mines. Secondly, the establishment of the State Administration of Coal Mine Safety has solved the supervision conflict caused by the multiple identities of agents and represents a turning point in China's coal mine safety management. Third, coal mine mechanization has a significant negative correlation with the number of accidental deaths and is a crucial measure for improving the intrinsic safety of coal mines. Fourth, the improvement of miners' overall education level has an obvious effect on enhancing coal mine safety. Following long-term safety education and skills training, the number of unsafe actions caused by knowledge deficits and cognitive errors gradually fell. More accidents are caused by the coal mine management giving wrong orders and illegal commands. Finally, this paper discusses the potential deficiencies of coal mine safety management in China at present, and makes some policy suggestions.

Research on Application of Fully Mechanized Caving Mining Technology in Small Coal Mine with Three Soft and Unstable Seams

Research on Application of Fully Mechanized Caving Mining Technology in Small Coal Mine with Three Soft and Unstable Seams

Zoning Control Technology of Gob-Side Roadway Driving with Small Coal Pillar Facing Mining in a Special Isolated Island Working Face: A Case Study

The gob-side roadway in an isolated island working face is a typical representative of a strong mining roadway, which seriously restricts the efficient and safe production of underground coal mines. With the engineering background of the main transportation roadway 1513 (MTR 1513) of the Xinyi Coal Mine, this paper introduces the engineering case of gob-side roadway driving with small coal-pillar facing mining in an isolated island working face under the alternate mining of wide and narrow working faces. Through comprehensive research methods, we studied zoning disturbance deformation characteristics and stress evolution law of gob-side roadway driving under face mining. Based on the characteristics of zoning disturbance, MTR 1513 is divided into three zones, which are the heading face mining zone, the mining influenced zone, and the mining stability zone. A collaborative control technology using pressure relief and anchoring is proposed, and the differentiated control method is formed for the three zones. For the heading face mining zone, the control method of anchoring first and then pressure relief is adopted; for the mining influenced zone, the control idea of synchronous coordination of pressure relief and anchorage is adopted; for the mining stability zone, the control method of anchoring without pressure relief is adopted. Engineering practices show that the disturbance influence distance of working face 1511 on MTR 1513 changes from 110 m advanced to 175 m delay. At this time, the surrounding rock deformation is effectively controlled, which verified the rationality of the division and the feasibility of three zoning control technology. The research results can provide reference for gob-side roadway driving with small coal pillar facing mining in a special isolated island working face.

Research on Strong Ground Pressure of Multiple-Seam Caused by Remnant Room Pillars Undermining in Shallow Seams

Numerous room-and-pillar mining goaf are apparent in western China due to increasing small coal mining activities, which causes the collapse of the overlying coal pillars and the occurrence of strong ground pressure on the longwall face and surface subsidence. In this study, Yuanbao Bay Coal Mine, Shuozhou, Shanxi, was selected to study the collapse of the overlying coal pillars on the longwall face and reveal the mechanism of the pillar collapse and the disaster-causing mechanism caused by strong ground pressure. Results show that the dynamic collapse process of coal pillars is relatively complicated. First, the coal pillars on both sides of the goaf are destroyed and destabilized, followed by the adjacent coal pillars, which eventually cause a large-scale collapse of the coal pillars. This results in a large-scale cut-off movement of the overlying strata, and the large impact load that acts on the longwall face causes an unmovable longwall face support. Moreover, the roof weighting is severe when strong ground pressure occurs on the longwall face, causing local support jammed accidents. Furthermore, the data of each measurement point of the strata movement inside the ground borehole significantly increases, and the position of the borescope peeping error holes in the ground drill hole rise steeply. The range of movement of the overlying strata increases instantaneously, and the entire strata begin to move. Research on the mechanism of strong ground pressure can effectively prevent mine safety accidents and avoid huge economic losses.

Validation of local coal supply effectiveness in the hard-to-reach Arctic zones in Yakutia

The article discusses shipment of coal to the Arctic regions of Yakutia. High transportation costs increase almost three times the price of one ton of the solid fuel. Coal fields in the Arctic have social rather than commercial value. The key target of local coal mining is enhancement of energy preparedness of population rather than money making. The review of modern methodological approaches to assessing the efficiency of using local coal resources in hard-to-reach areas reveals a wide range of such approaches, their ambiguity and neglect of the Arctic activities peculiarities. The paper presents a new approach for evaluation of small coal opencasts operating in remote Polar regions in Yakutia. The approach is based on the economic and mathematical model of substitution of local coal for imported coal. The technical and economic indicators of a small coal mine is calculated in terms of Krasnorechensky deposit of thermal coalm, and the effect of replacing imported coal by local coal in the Abyi district is evaluated. The results of the study show feasibility of in-house coal supply in the isolated and hard-to-reach areas of the Arctic by means of creation of small coal opencasts, which enhances the energy security and reduces the socio-economic tension.

Application of Magnetic Resonance Detection in Goaf Water in Wuhai

The mine water disaster in our country has always been the key factor restricting the development of coal production. Due to the unreasonable small coal mine development, mining in some mining area, the destruction of the waterproof coal pillar, lead to the formation of the mined-out area, and goaf water. Because the goaf water does great harm to coal field exploration and development, the prevention and control of goaf water disasters are very important. In this study, aiming at a large area of exploration space, the method of magnetic resonance can be used to detect groundwater, and two magnetic resonance instruments are used to work together. In order to ensure the accuracy and effectiveness of the data collected by the two instruments, improve the efficiency of exploration work and save field exploration time, the basic model of detecting groundwater with magnetic resonance sounding (MRS) method instrument is established, the influencing factors of MRS are analyzed, and the effective signal value of detecting groundwater with MRS instrument is calculated. Through numerical simulation, the optimal distance between the coils laid on the ground when the two MRS instruments are working at the same time is determined. Furthermore, the practicability of the method is verified via a field case performed in a mining area in Wuhai, China. This method can be used as a guide for large-scale field exploration in the future.

Research on heating technology of regenerative oxidation used low concentration CBM in small coal mine

Aiming at the problems such as low CBM utilization rate caused by low concentration CBM with methane content less than 8% extracted from a small coal mine in Hancheng mining area, Shaanxi Province, and serious environmental pollution caused by coal-fired hot blast stove for heating, the heat storage and oxidation heating technology of ultra-low concentration gas in small coal mine was studied by combining field investigation and heat balance calculation, and ultra-low concentration gas regenerative oxidation was obtained through thermal oxidation technology scheme. This technology replaces the coal-fired hot blast stove, realizes “coal and CBM mining and sharing” in the coal mine, and constructs a virtuous cycle development of “promoting drainage by using and promoting safety by drainage”. The research shows that: the scheme improves the utilization rate of CBM in the mining area, cancels the consumption of coal combustion, and can use 2.59 million Nm3 of pure CBM every year, generating 1.95 million yuan of economic benefits. And the emissions reduction of CO2 equivalent is 36000 tons. The benefits of safety, economy and environmental protection are remarkable. This technology is especially suitable for the utilization of ultra-low concentration CBM whose concentration is less than 8%, which has practical significance to improve the CBM utilization rate and promote the realization of the goal of “zero emission”.

Experimental study on performance of high purity nitrogen supply system in liquefaction unit of low concentration coalbed methane

Aiming at the problems such as low CBM utilization rate caused by low concentration CBM with methane content less than 8% extracted from a small coal mine in Hancheng mining area, Shaanxi Province, and serious environmental pollution caused by coal-fired hot blast stove for heating, the heat storage and oxidation heating technology of ultra-low concentration gas in small coal mine was studied by combining field investigation and heat balance calculation. This technology replaces the coal-fired hot blast stove, realizes “coal and CBM mining and sharing” in the coal mine, and constructs a virtuous cycle development of “promoting drainage by using and promoting safety by drainage”. The research shows that: the scheme improves the utilization rate of CBM in the mining area, cancels the consumption of coal combustion, and can use 2.59 million Nm3 of pure CBM every year, generating 1.95 million yuan of economic benefits. And the emissions reduction of CO2 equivalent is 36000 tons. The benefits of safety, economy and environmental protection are remarkable. This technology is especially suitable for the utilization of ultra-low concentration CBM whose concentration is less than 8%, which has practical significance to improve the CBM utilization rate and promote the realization of the goal of “zero emission”.

Research on Operation and Construction of the Development Model of “Gas Extraction-Gas Power Generation-Sales” in Small Coal Mine

Aiming at the problem that a large number of small coal mines in Yunnan Province are not effectively utilized, with a small coal mine in the region as the background, a variety of methods are used to analyze and study its low-concentration gas power generation project, and it is obtained that the key to the success of a low-concentration gas power generation project in a small coal mine is the integrated technology system of gas source security under the leadership of the concept of “gas management first”. On the basis of the gas source guarantee, the low-concentration gas power generation project of this small coal mine has been running efficiently for 4 years, generating economic income of about 4032 million yuan per year, reducing the co2 of about 44.7 ten thousand tons to improve the level of coal mine safety production, and guarantee the coal mine production standards.

Position optimisation for a roadway under small coal mines in same coal seam: a case study

AbstractAccording to the failure law of the 1070 main roadway, this paper proposes a reasonable position for large section roadways under small coal mines and a design for seven roadway positions. RS2 software was used to establish a numerical model to select a reasonable position for the roadway. The influences of roadway positions on roof separation amount, roof subsidence, lateral displacement on the ribs, vertical stress on ribs and roadway failure areas were revealed. On the basis of influence laws, reasonable positions for the roadway could be determined. In this study, a center distance of 5 m was deemed a reasonable position. Finally, an industrial test was conducted at the original roadway. The experimental results indicate that the deformation of the roadway could be well controlled and the roadway position is reasonable.

Issues of providing solid fuel to the Arctic regions of Yakutia and their solutions based on the potential development of the local raw material base

Relevance. The interest of science and practice in the large-scale development of subarctic and arctic territories, in particular the Russian Far East and Siberia, has sharply increased in the world. Coal enterprises in remote and inaccessible areas of the region in the face of intense inter-fuel competition are faced with the need to comprehensively increase production efficiency. The successful solution of these problems is counteracted by a complex of unfavorable factors, which, compared with the regions of traditional subsoil use, significantly increase the cost of any activity and predetermine high specific energy consumption in conditions of increased risks of various nature. They are most pronounced in the northern regions of the Republic of Sakha (Yakutia) with their extreme natural and climatic conditions, where due to the simultaneous effect of the low level of infrastructure development; very complex logistics; seasonality and discrepancies in the delivery of goods by water and road; scattered across a huge area of a small number of settlements, etc. there is a sharp complication of the conditions for the normal provision of all types of resources used. The priorities here are normal functioning of the local population, improving energy and environmental safety with acceptable economic and social efficiency. Purpose of the work: to substantiate the need and the possibility of adjusting geotechnological solutions when mining coal deposits with open pits of small and ultra-low thickness when they operate as part of local fuel and energy complexes to increase the efficiency and safety of deliveries to remote areas and improve the quality of coal shipped. Method of research. Generalization and analysis of scientific and technical literature. Using the method of analogy the selection of criteria for creation of micro-sections for coal mining in the Arctic regions of Yakutia and the effectiveness of their implementation in the system of providing solid fuel to consumers in hard-to-reach areas were made. Research results. A solid fuel supply scheme is proposed that meets the coal needs of remote areas of Yakutia, which is based on the concept of creating new local small coal mines near consumers to replace the existing expensive, complex and unreliable scheme. A complex of geotechnical criteria and boundary conditions oriented to small coal openings is presented, on the basis of which it is possible to reveal resource-saving, technical and technological capabilities of the chain, economically acceptable and environmentally efficient development of coal deposits. Link optimization can result from the immediate horizontal and vertical integration of small open cuts in the coal supply chain to consumers. Conclusions. The development of local deposits is one of the ways to increase the stability of the solid fuel supply chain to consumers, as well as the energy security of the inaccessible northern regions of Yakutia and support their economic and social development.