Coal Mining Technology Research Articles

Mining Industry Impact on Environmental Sustainability, Economic Growth, Social Interaction, and Public Health: An Application of Semi-Quantitative Mathematical Approach

The mining industry plays a significant role in economic growth and development. Coal is a viable renewable energy source with 185.175 billion deposits in Thar, which has not been deeply explored. Although coal is an energy source and contributes to economic development, it puts pressure on environmental sustainability. The current study investigates Sindh Engro coal mining’s impact on environmental sustainability and human needs and interest. The Folchi and Phillips Environmental Sustainability Mathematics models are employed to measure environmental sustainability. The research findings demonstrated that Sindh Engro coal mining is potentially unsustainable for the environment. The toxic gases (methane, carbon dioxide, sulfur, etc.) are released during operational activities. The four significant environment spheres (atmosphere, hydrosphere, biosphere, and lithosphere) are negatively influenced by Thar coal mining. The second part of the analysis results shows that human needs and interests have a positive and significant relationship except for human health and safety with Sindh Engro coal mining. Environmental pollution can be controlled by utilizing environmentally friendly coal mining operations and technologies. Plantation and ecological normalization can protect the species, flora, and fauna of the Thar Desert. The government of Pakistan and the provincial government of Sind should strictly check the adaptation of environmental standards. Furthermore, the researchers should explore the environmental issues and solutions so that coal mining becomes a cost-efficient and environmental-friendly energy source in Pakistan.

Comparative study of model tests on automatically formed roadway and gob-side entry driving in deep coal mines

Automatically formed roadway (AFR) by roof cutting with bolt grouting (RCBG) is a new deep coal mining technology. By using this technology, the broken roadway roof is strengthened, and roof cutting is applied to cut off stress transfer between the roadway and gob to ensure the collapse of the overlying strata. The roadway is automatically formed owing to the broken expansion characteristics of the collapsed strata and mining pressure. Taking the Suncun Coal Mine as the engineering background, the control effect of this new technology on roadways was studied. To compare the law of stress evolution and the surrounding rock control mechanisms between AFR and traditional gob-side entry driving, a comparative study of geomechanical model tests on the above methods was carried out. The results showed that the new technology of AFR by RCBG effectively reduced the stress concentration of the roadway compared with gob-side entry driving. The side abutment pressure peak of the solid coal side was reduced by 24.3%, which showed an obvious pressure-releasing effect. Moreover, the position of the side abutment pressure peak was far from the solid coal side, making it more beneficial for roadway stability. The deformation of AFR surrounding rock was also smaller than the deformation of the gob-side entry driving by the overload test. The former was more beneficial for roadway stability than the latter under higher stress conditions. Field application tests showed that the new technology can effectively control roadway deformation. Moreover, the technology reduced roadway excavation and avoided resource waste caused by reserved coal pillars.

Inhibition of Gas Explosion by Nano-SiO2 Powder under the Condition of Obstacles

The existing methods of gas explosion suppression are mainly the use of flameproof water shed or rock powder shed. This passive explosion suppression device often does not adapt to the speed of flame movement due to the time of forming powder mist or water mist due to the action of shed frame, so it cannot play an effective role in actual use. Powder explosion suppression technology has been widely used in the field of combustible gas explosion suppression because of its excellent explosion suppression characteristics, convenient storage and use, nontoxic and pollution-free, low cost. In this paper, the inhibition of gas explosion by nano-SiO2 powder under the condition of obstacles is studied. It is found that the superfine powder with the main component of SiO2 has certain effect on explosion-proof and initial explosion inhibition. Among them, the effect of Nano-SiO2 is the most obvious. The concentration of 100 mg/L nano-SiO2 powder (the average particle size is 50 nm) in 20 L near spherical vessel can reduce the explosion limit range of methane to 6.95–13.75%, and the maximum overpressure of alkane air body with methane concentration of 7% can be reduced to 0.179 mpa. The research in this paper has an effective significance for the control of gas explosion by powder under the condition of obstacles, and provides suggestions for the improvement of coal mining technology in China.

Изменение горного давления при отработке пласта угля длинным очистным забоем

Development of the geomechanical processes is of great importance for human activity in the underground conditions. Coal mining is accompanied by displacement of the enclosing rocks, which requires a special approach to study of the geomechanical processes. In particular, this is due to an increase in the productivity of the excavation sections. Increase in the volume of the second working, the length of the longwalls and the size of the extraction pillars will transform all the geomechanical processes occurring in the face. Modern coal mining technologies are associated with certain specific features of the displacement of enclosing rocks, which necessitate the development of new approaches to the study of the geomechanical processes. The intensification of work inevitably leads to a change in the geomechanical environment in the vicinity of the face. The article discusses the methods and means of studying the process of rocks displacement as a result of construction of the mine workings. For example, a site is selected at the mine named after S.M. Kirov, long-face No. 24-62. Depth to the developed seam is from 476 to 520 m from the installation chamber. Average thickness of the seam is 2.5 m, length of the face is 300 m, length of the pillar is 2500 m. The average rate of advance is 10 m / day. Based on the monitoring of the rock pressure indicators on the mechanized support section, the wave-like nature of the rock pressure distribution in a long-face during mining of the extraction pillar was determined. The surface of the pressure domes was rebuilt using the Surfer software product, which allowed to track the processes in the face part of the longwall. Data on the pressure in the roof supports were used. In the calculations, the average rock density was assumed to be 2.5 m3/t. Since the surface of the pressure vaults makes it possible to judge the processes in the bottomhole of the mined seam, the height of the random collapse zone is determined from the pressure readings in the support struts. It is the one which presses on the powered support. Repetitive areas of the increased rock pressure were noted approximately every 200–250 m. Profiles of the surface of pressure arches along the length and in the long-face building cross are given. Considering the processes of structuring the rock mass, an algorithm for finding the height of the pressure arch was developed, which ensures a satisfactory convergence with the actual data.

Investigation on the effect of superheated water vapor on gas production from pyrolysis of long-flame coal

A self-developed superheated water vapor pyrolysis system was used to conduct superheated water vapor pyrolysis experiments on Tashan and Madaotou long-flame coals at 350–534 °C. The gas phase products were analyzed by gas chromatography. The yield and composition of gas phase pyrolysis products from two different long-flame coals were determined, and the role of superheated water vapor in the pyrolysis process was elucidated. The optimal temperature of the long-flame coal injection superheated water vapor mining technology was obtained through heat value analysis. The results showed that when the temperature of the superheated water vapor exceeded 400 °C, the yield and combustible components of the gas phase products rapidly increased. As such, the release rate reached 10–15 times that observed below 400 °C, and the components of the combustible gases, such as hydrocarbon gas and hydrogen, exceeded 80%. Superheated water vapor not only is an excellent heat and mass transfer medium, but also provides a reactant for the re-formation reaction of hydrocarbon gas. The pyrolysis of long-flame coal under superheated water vapor at 500 °C yielded the best economic benefits. The low calorific value of gas phase products produced via pyrolysis per ton of coal per unit time could reach 715 MJ/(t·h).

Research on Optimization of Carbon Emission Reduction of Coal Supply Chain System in Iron and Steel Industry

The steel industry is an important basic industry for the development of the national economy and national defense construction, but it is also a major source of energy consumption and environmental pollution. In particular, the carbon emissions in the process of coal combustion and steelmaking are huge. This situation urgently needs to be improved and optimized. Therefore, based on the perspective of the coal supply chain in the steel industry, this paper constructs a multi-objective planning model to achieve a balanced optimization of total economic costs and carbon emission reduction, and verifies the effectiveness of the model through specific case data. This paper sets three different emission reduction scenarios, discusses and analyzes the changes of economic total cost and carbon emission under different emission reduction scenarios, and finds that suppliers with good coal mining technology and low carbon emission factor have more opportunities to be selected and can obtain more coal market orders. At the same time, steel plants with mature processing technology and low carbon emission factor can further gain market competitive advantage and undertake more steelmaking tasks. Finally, based on results, management suggestions for coal suppliers and steel plants are provided.

The Spatiotemporal Characteristics of Coupling Effect between Roof and Backfill Body in Dense Backfill Mining

Backfill mining has become an important part of coal mine green mining technology. In this paper, the spatiotemporal characteristics of coupling effect between the roof and dense backfill body were analyzed by theoretical analysis and similar simulation test, and Xingtai Mine in China was taken as an engineering case for verification. The results show that the larger subsidence of the roof is, the stronger the supporting capacity of the backfill body is, and the interaction between the two is more obvious, thus showing a coupling effect. This coupling effect presents a regular variation with the increase of backfill distance and time, that is, the coupling degree of roof and backfill body is high in the middle of goaf and low in the vicinity of the coal pillar in spatial distribution, and the coupling behavior of roof and backfill body continues to occur slowly with time. Through the monitoring of stress and displacement in the engineering site and the analysis of borehole observation results, the spatiotemporal coupling effect between roof subsidence and backfill support is fully verified. The research results are of great significance to the control of surrounding rock in backfill mining, the study of the mechanical aging characteristics of backfilling materials, and the optimization of backfill body support performance.

Discussion on the Development of Coal Mining Technology and Coal Mining Automation Technology

Discussion on the Development of Coal Mining Technology and Coal Mining Automation Technology

Constitutive Model of Solid Backfill Materials and Numerical Simulation of Overburden Movement and Deformation in Backfill Mining

Solid backfill mining is an efficient and environmental-friendly coal mining technology, which can effectively solve the problems of coal gangue pollution, water resource loss, and surface subsidence. Based on the mechanical behavior of backfill materials in the compaction process, volume strain was used to express the deformation modulus, and a constitutive model of backfill materials was proposed in this study. The ABAQUS UMAT was used to develop the numerical calculation subroutine of the model. Finally, the rationality of the model was verified that simulated stress-strain curves of the backfill materials during the compaction process agree well with experiments. Based on the proposed constitutive model, the influence of three factors (the initial compaction rate of the filling body, the mining height, and the mining depth) on the key strata and surface subsidence was analyzed systematically. The results show that the initial compaction rate and the height of coal seams have significant influences on surface subsidence. When the thickness of topsoil is only changed and the structural composition and lithology of overburden are not changed, the mining depth has little influence on surface subsidence, but a significant influence on surface subsidence range. The influence of mining height and mining depth on the deformation of key strata of overburden and surface subsidence is approximately linear, while the influence of the initial compaction rate is nonlinear.

Method and Realization of Efficient Extraction of Basic Geological Data from Two-Dimensional Mine Drawings

In coal mining technology systems, it is very important to acquire, store, and represent basic geological data comprehensively and accurately. Based on the current working mode and information level in mining geology at coal mines, this paper proposes a process of building basic geological database for modeling of coal mines by using existing results’ data of mining geology and develops the efficient program for getting the basic geological data from the important 2D plane drawings’ achievement at mines, such as the contour maps of mine coal seam floors, geological cross-sections, underground drilling results, and geological survey results, based on AutoLISP, which is a programming language for the secondary development of AutoCAD. The obtained data in general text format is stored and managed by the MongoDB database, which realizes the storage, query, analysis, and correction of massive data of geological objects in the space of the underground coalmine. The application results show that compared with the previous data acquisition methods such as manual input and graphic transformation attribute, the extraction of spatial and attribute data from the existing mine 2D plane drawings by programming can effectively avoid the prominent problems such as artificial gross error, distortion of graph conversion, and different database structure, make the obtained spatial geological data more comprehensive, accurate, and effective, and, meanwhile, increase the rate by more than 60%, which plays an important role in data support for the construction of the geological modeling systems for transparent mines.

Research on Non-Pillar Coal Mining for Thick and Hard Conglomerate Roof

This article introduces a new non-pillar coal mining technology (i.e., Gob-side Entry Retaining by Roof Cutting (GERRC)) under the condition of thick and hard roofs. First, we theoretically analyzed the solution to the large suspension span of the thick and hard roof in coal mining. Three-Zone pre-split blasting design in non-pillar coal mining for thick and hard roofs was proposed, based on the principles of rock mechanics. After field experiments, the technology was successfully applied to the non-pillar coal mining of a huge thick conglomerate roof. This research supplements the non-pillar mining technology system. The proposed technologies and methods have strong applicability and have certain guiding significance for the safe and efficient mining of related coal mines.

Motion model and key parameters of overburden strata in longwall filling face

When the paste material is filled into the longwall working face of the coal mine, it firstly controls the movement of the overburden strata, thereby limiting the movement of the far field rock layer and reducing the subsidence. With this regard, the paste filling technology of the long-wall mining can address the limitation of “three down, one up” (mining under water body, building and rail, and on karst water body) technology in coal mining, thus improving the extraction rate of coal resource. To control the movement of the overburden strata near the working face, the prerequisite is to clarify the relationship among the parameters, including coal mining thickness, filling body thickness, filling step, filling body strength, etc. On this basis, this paper established an overall mechanical model of the filling body and surrounding rock, and determined the key technical parameters of the overburden movement, i.e., the filling rate, the strength of the filling body, and the filling step. Then, the influence of these parameters on the overburden movement and abutment pressure was analyzed through the numerical simulation method. The results show that at a higher filling rate, the overburden motion can be better controlled; the filling step only had a significant effect on the roof subsidence within the relevant step; as the early strength of the filling body was higher, the overburden subsidence was smaller and the abutment pressure in front of the face was better controlled. The research of overburden motion model and its key parameters have a good guiding significance for paste filling in the longwall face of coal mines.

Study on the Spontaneous Combustion Characteristics and Prevention Technology of Coal Seam in Overlying Close Goaf

ABSTRACT The short-distance coal seam group refers to the coal seams which has obvious mining influence on the adjacent coal seam during mining process. In the process of short-distance coal seam mining, there are a large number of cracks around the stope due to the mining stress, resulting in serious air leakage and high risk of spontaneous combustion. To mining the working face under the condition of overlying close goaf in Xutuan Coal Mine in Huaibei Mining area, the distribution of spontaneous combustion dangerous area in goaf was studied systematically with the help of engineering test, laboratory research and numerical simulation. Results show that a “Γ” distribution of high oxygen concentration area was found above the roadway of the goaf due to the effect of air leakage and coal seam space, the high spontaneous combustion risk area is close to the return airway. A three-dimensional distribution of the high spontaneous combustion risk area was formed in the composite goaf after mining in the lower coal seam face, the spontaneous combustion risk of the upper position is higher than that of the lower position. Besides, based on the pyrolysis-room temperature oxidation experiments of coal sample, it is considered that the inert environment and high temperature promote the production of active groups in coal and thus enhanced the oxidation ability of coal, mechanism of spontaneous combustion of residual coal in the overlying goaf was further revealed. Accordingly, the comprehensive fire prevention and fire extinguishing measures of nitrogen injection, leakage plugging and inhibitor injection are put forward. With the method of numerical simulation, it was found that nitrogen injection at the position of 50 m in the goaf can effectively reduce the spontaneous combustion risk in the compound goaf, and the injection of TEMPO inhibitor was put forward based on the secondary oxidation characteristics of residual coal. The research conclusion can provide theoretical guidance for the fire prevention technology of coal seam mining in the overlying close goaf.

Management of Excess Mined-Out Space of Quarry Fields of Coal Open Pit Mines

Regardless of the applied technology of coal mining, a technogenic resource of the open pit is formed – excess mined-out space. Excessive mined-out space should be understood as a part of the internal space of a pit that is not used for placing overburden in dumps. The excess mined-out space in the plan is limited by the following: on the flanks of the quarry field and along the uprising by the limiting contour of the quarry, along the inclination – by the possible position of the slope of the dump layer, as close as possible to the working area. The lower boundary corresponds to the position of the formed dumps, the upper one – to the marks of the dominant relief. The article presents a method for reducing the excess mined-out space by means of the patterns of spatial development of objects “quarry field – dump of overburden”.

Field and numerical investigation on the stability of coal pillars of gob-side entry driving with top coal

Determining the reasonable width of coal pillars is the key to the successful application of gob-side entry driving technology in coal mining. A comprehensive research method including numerical simulation, field monitoring, and theoretical analysis was proposed to determine the reasonable width of the coal pillars of gob-side entry with top coal based on a case study conducted in the Lugou Coal Mine, Henan Province, China. According to a comprehensive analysis of the stress distribution characteristics of the narrow coal pillar and the influence of the coal pillar width on the roadway deformation, the reasonable width of the coal pillar was determined to be 6 m with consideration of the stability of the coal pillar, roadway deformation, and coal recovery rate. Two principles for maintaining the stability of the gob-side entry with top coal were proposed, that is, strengthening the roof support to ensure top coal stability, and strengthening the support structure of the coal ribs to achieve collaborative control. Field monitoring indicated that the bolting support could effectively control the severe deformation of the roadway along the gob-side entry driving in the soft coal seam.

The comprehensive evaluation of coordinated coal-water development based on analytic hierarchy process fuzzy

Reasonable evaluation of the comprehensive effect of coordinated coal-water development is necessary for the sustainable development of ecologically vulnerable area. Taken Nalinhe mining area as the research area and focused on the thick coal seam mining, an evaluation index system of the comprehensive effect of coordinated coal -water development was proposed. The analytic hierarchy process modified by particle swarm optimization and fuzzy comprehensive evaluation method was adopted to determine the weights and grade thresholds of the evaluation indicators. The comprehensive effect of coordinated coal-water development for three typical thick coal seam mining technologies of layered mining, one-time full height mining and coal caving mining was evaluated. The results show that the priority of the evaluation index system is geological system, ecological environment system, natural system, and mining system. The comprehensive effect ratings corresponding to the three typical thick coal seam mining technologies in Nalinhe mining area are poor, excellent, and average respectively. The method and results can provide some references for the rational evaluation and selection and application of coordinated coal-water development in ecologically vulnerable areas.

Study on the mechanism of crack formation and the behavior of crack propagation of directional tension blasting in deep and high stress coal mine

Roadway safety is related to the high productivity and efficiency of coal mining, roof cutting and pressure releasing technology is one of the effective measures for roadway stability control. Under deep mining conditions,the stress condition around the blasthole is complex, and the expansion of directional crack will be affected by high ground stress. In this paper, Based on the engineering background of the roof Cutting and Pressure Relief Technology of Non-pillar Automatic Roadway Formation in guotun coal mine, the crack propagation mechanism and propagation evolution of deep rock under directional tension blasting were investigated. Based on the stress model of blasthole under the deep condition, the mechanical conditions of crack propagation under the action of directional detonation wave and high surrounding rock binding force are obtained theoretically; The mechanical model of directional blasting under the condition of stress constraint is established by using LS-DYNA numerical calculation software, the evolution characteristics of effective stress and the law of crack growth are analyzed; Finally, through the drilling peep and other technical means, the field measurement of the presplitting effect is carried out, which verifies the previous research results and puts forward the appropriate roof presplitting scheme. The results show that when the deep roof strata of Guotun coal mine adopt four hole continuous blasting and per blasthole charge of 2800g, the roof strata can form a continuous seam, and the Roof presplitting effect is the best.

Study on the Stage Failure Mechanism and Stability Control of Surrounding Rock of Repeated Mining Roadway

China is one of the leading countries in the mining and utilization of coal resources, and the problems of coal-mining technology and safety have been concerned by the world, while the serious deformation and destruction of surrounding rock and the difficulty of support have brought inconvenience to the mining of coal resources due to repeated mining. This paper takes the actual engineering 22205 mining roadway in Buertai mine as the research background, through the combination of numerical simulation and field measurement. In this paper, the stress environment, plastic zone, and surrounding rock deformation in the advancing process of coal-mining face are studied, and the stress evolution law of surrounding rock in repeated mining roadway is obtained. It is clarified that the surrounding rock deformation is the failure mechanism under the combined action of principal stress difference and stress direction deflection. As a result, the surrounding rock of the roadway is asymmetrically deformed and destroyed, and the corresponding surrounding rock control scheme is put forward. The results show that the influence of repeated mining on roadway stress environment can be divided into four stages with the mining process: the stability stage of mining influence, the expansion stage of primary mining, the stable stage after primary mining, and the expansion stage of second mining. At the same time, the shape changes of the plastic zone and the displacement monitoring results of the monitoring are analyzed, and the results are obtained; the stage of stress change is suitable, and combined with the failure characteristics of surrounding rock in each stage, it is put forward that reinforcement measures should be taken in the stable stage after mining; the specific reinforcement scheme is determined according to the expansion form of plastic zone and field measurement. The on-site monitoring shows that there is no roof fall accident during the use of the roadway, which ensures the safety in production.

Physical simulation experiment on prevention and control of water inrush disaster by backfilling mining under aquifer

Solid backfill coal mining technology can be safely and efficiently used to exploit coal resources under aquifers, without causing harm to the water resources and the environment. Nevertheless, the mechanism of fracture development and seepage channel or pathway control in the key aquiclude strata (KAS) in backfill coal mining under fluid–solid coupling have not been studied. Based on the similarity theory of fluid–solid coupling physical simulation, this study involves experimental evaluation of similar materials and characteristics of composite KAS, backfill body, and aquifer. Subsequently, we designed and employed three experimental models for physical simulation, corresponding to backfill materials’ compaction ratios (BMCRs) of 0%, 65%, and 80% using the geological conditions of mining face No. 101 under the aquifer in the Wugou coal mine. Fracture evolution laws, mining-induced deformation, and stress distribution characteristics of composite KAS with different BMCRs are studied. The backfill body can effectively weaken the influence of mining stress, such as the maximum subsidence, sinking speed, initial or periodic fracture damage area of the composite KAS, inhibiting the formation of seepage cracks and water inrush channels. The increase in the BMCR plays an important role in the closure and repair of developed fractures.

The Sustainable Development of Aged Coal Mine Achieved by Recovering Pillar-Blocked Coal Resources

China faces the problem of depletion of its coal resources, and a large number of mines are becoming aged mines. Demand for coal, however, still increases due to the growth of China’s economy. Energy shortage might restrict the sustainability of China’s national economy. As one contribution to a solution, this paper proposes the innovative exploitation method of solid backfill coal mining (SBCM) technology to exploit parts of pillar-blocked (residual coal pillar resources under industrial square, RCPRIS) that protect industrial facilities. Thus, blocked coal resources may be converted into mineable reserves that improve the recovery ratio of mine resources. Also, waste would be removed from the surface reducing hazards of environmental pollution. Based on the case of the Baishan Coal Mine in Anhui, China, numerical simulation is used to study the size of shaft-protecting coal pillars (SPCP) required at different backfill ratios. Results show that the disturbance to a shaft caused by exploitation decreases with the increase of the backfill ratio. When using SBCM to exploit RCPRIS under the condition of 80% backfill ratio, compared with the caving method, a lot of pillar-blocked coal resources would be freed. The life of Baishan Coal Mine would be prolonged, resulting in appreciable social, environmental, and economic benefits.