Broken Coal Research Articles

Research on the annular distribution state of resin and design of anchoring synergistic device

The resin anchoring method promotes the development of high-strength bolt (cable bolt) support, which simplifies the construction process while ensuring that the high-strength support force of the bolt (cable bolt) can be effectively exerted. And with the increase of engineering depth and the complexity and variation of geological conditions, higher requirements are put forward for resin anchoring performance. In view of the influence of the annular distribution state of resin on the anchoring performance, with the main line of “optimizing the annular thickness, improving the mixing efficiency and increasing the degree of compactness”, through the comprehensive research method combining theoretical analysis, numerical simulation, laboratory test and field test, an anchoring synergistic device with simple and convenient operation were developed, the mechanism of the synergistic device was revealed, and the universality of synergistic anchoring was verified. The results show that the annular distribution of resin has a great influence on the anchoring performance, when the bolt is unconstrained, the annular thickness distribution of resin is uneven, and the mixing uniformity and the compactness of the anchoring section cannot be guaranteed, resulting in the reduction of anchorage force and the easy failure of anchorage. This device can center the bolt to ensure the uniform distribution of the annular thickness of the resin, which is helpful to break the resin sealing bag, improve the efficiency of stirring the resin, effectively prevent the spillage of the resin. Besides, it can also ensure the compactness of the anchoring section and strengthen the anchoring performance. Through laboratory tests and on-site verification, compared with normal construction, the anchorage force of the synergistic anchoring is increased by about 40 %, and the deformation of the roof is reduced by about 57.5 %. The research results enhance the understanding of the mechanism of the annular distribution state of resin on the anchoring performance, and carry out innovative attempts to solve the problem, which effectively form a relatively stable anchorage structure of the soft and broken surrounding rock on the surface, which has a certain theoretical reference value for ensuring the quality of resin anchoring engineering under the condition of soft and broken coal and rock mass.

Numerical Simulation Study on Vibration Characteristics and Influencing Factors of Coal Containing Geological Structure

Accurately determining the natural frequency of coal-containing geological structures is crucial for preventing mine dynamic disasters and utilizing vibration waves to break coal and enhance its permeability. Based on the modal theory of rock, vibration models of coal-containing geological structures, including layering and fractures are established. By analysis, the undamped vibration equation and its characteristic equation for both the layered coal system and the fractured coal system are derived. Subsequently, the Lanczos method is employed to solve the system’s vibration modes using ABAQUS. The effects of the layering position, layering thickness, layering physical properties, crack width, and crack length on the natural frequency and vibration response of coal-containing geological structures are investigated. The results indicate that when a single influencing factor is altered, the displacement response distribution of the coal body vibration system with geological structures remains essentially the same, and these single influencing factors have a minimal impact on the vibration displacement of the coal-containing geological structure. The natural frequency of the system decreases exponentially as the distance between the layering and the geometric center of the coal system with geological structures increases. The presence of layering in the coal system with geological structures significantly reduces the system’s natural frequency. The natural frequency of the coal system with geological structures increases in a power function manner as the layering elastic modulus increases. Conversely, the natural frequency decreases with an increase in crack length. When the change ranges of crack width and bedding thickness are the same, the natural frequency of the fractured coal body system exhibits more significant changes. The natural frequency of the coal system with geological structures initially decreases and then increases as bedding thickness and crack width increase. The trend in the natural frequency changes and the position of the extreme point are related to the ratio of the elastic modulus and density of the geological structure.

Самовоспламенение пылегазовоздушных смесей в атмосфере горных выработок

The underground mining of coal deposits is usually accompanied by manifestation of a number of negative factors, one of which is the presence of dust and gas-air mixtures consisting of fine coal dust, methane released from the broken coal and the air of the mine atmosphere. Despite modern methods and means of dust suppression and dust collection, it has not yet been possible to achieve complete neutralization of dust and gas-air mixtures in the atmosphere of mine workings. The negative effects of dust and gas-air mixtures can manifest themselves in different ways. On the one hand, deposits of coal dust in the worked-out spaces, under certain conditions, form foci of spontaneous combustion, which are the causes of endogenous fires. On the other hand, dust and gas-air mixtures are predisposed to ignition from external sources or to spontaneous ignition followed by combustion in the form of deflagration, which, under certain conditions, turns into detonation, spreading in the atmosphere of mine workings at supersonic speed. This article considers a nonstationary one-dimensional problem of selfignition of dust and gas-air mixtures in the air flows of mine workings. The temperature and the period of spontaneous ignition of dust-gas-air mixtures are found based on the solution of this problem, expressed numerically using the Geer method. An analysis of the mixture self-ignition process is performed and some patterns of the influence of the parameters of mixtures on the period of their self-ignition are revealed.

Mechanochemical evolution of coal microscopic groups: A new pathway for mechanical forces acting on coal spontaneous combustion

Coal spontaneous combustion (CSC) remains a significant threat to regional ecological environments. As coal mining operations extend deeper into the earth, the increasingly complex mechanical force conditions in deep-seated mines escalate the potential risk of CSC. Mechanical forces such as ground stress and mechanical cutting are traditionally believed to be linked to CSC through the following pathway: mechanical forces act → mechanical energy is input → mechanical crushing and pulverization occur → coal–oxygen contact area increases → CSC accelerates. Noteworthily, these forces do more than just physically break coal; they also trigger a mechanochemical effect (MCE) that alters coal's microscopic chemistry. However, an independent evaluation of its influence on CSC was lacking. This study characterized coal's microscopic chemical group responses to the MCE. It was found that the MCE led to the degradation of aliphatic side chains while enhancing the polycondensation of aromatic ring structures, indicating a synergistic effect. Additionally, an increase in oxygen-containing functional groups, such as alkyl/aryl ethers, suggested enhanced interactions of the coal microscopic groups with oxygen due to mechanical forces. Based on these findings, an MCE-modified coal macromolecular model was developed and molecular quantum mechanical calculations were conducted. The results indicated that the MCE boosted coal macromolecule reactivity, thus facilitating easier activation. These conclusions were validated through modern thermal analysis tests. Finally, this study proposed a new pathway of mechanical forces acting on CSC: mechanical forces act → mechanical energy is input → the MCE occurs → evolutions of the microscopic groups within coal are induced → Activity of coal molecules is enhanced → CSC accelerates.

Numerical modelling approach for estimation of a yield zone in the face of a deep longwall panel

In the Longwall mining method, the coal face is being supported with two-legged or four-legged shield supports which improve better roof control between the face and canopy tip. The development of load on the face increases with the face retreating rate or the increase of the overhung length behind the shield support and as a result, the coal face tends to yield/fail. The yield/failure zone in the face extends depending on intensity of developed load due to the depth of mining, panel size, height of excavation and geometry of the overhung. The broken coal from the yielded face may fall on the shearer, armoured flexible conveyor (AFC), shield supports or may hit the deployed manpower in the face and causes the face stoppage which in turn results in to the loss of the project. It is therefore, a study is conducted to understand the face yield/failure behaviour considering various geo-mining conditions based on input parameters such as main roof thickness, overhung length, and material type and setting load. This paper develops a unique statistical model to predict the yield/failure zone in the longwall face. For this purpose, a total of fifty-four (54) three-dimensional finite element models in ANSYS software are developed and analyzed considering Drucker-Prager failure criterion.

Comprehensive Gas Prevention and Control Technique for Mining the First Seam in Short-Distance Outburst Coal Seam Groups.

Coal and gas outbursts are a phenomenon whereby broken coal and gas suddenly erupt from the coal body into the mining space under pressure. The Diandong mining area is a group of close-range outburst coal seams in which the gas content is up to 20 m3/t and gas pressure can reach 3 MPa. Research has been conducted on engineering challenges such as advanced detection and prevention of interlayer excavation in close-range coal seam groups, improvement of gas extraction quality and efficiency in low-permeability coal seam groups, and traceability and evaluation of joint extraction of coal seam groups. Through this study, advanced detection technology with full coverage in front of the excavation working face has been constructed as well as advanced pre-extraction technology for adjacent coal seams and this coal seam in ultraclose layers. We have developed a method for achieving the standard of cross-layer fixed-point hole expansion and permeability enhancement for the first mining of coal seams in a coal seam group. A combined process of graded enhanced pre-extraction and segmented regulation and extraction was proposed, which included "fixed-point control section sealing pre-extraction of coal seam groups and secondary sealing and extraction of mining pressure relief orifice."

Дегазация разрабатываемых пластов угля направленной трассы скважинами

The technology for conducting degassing work in the Russian mines is determined by the experience of half a century of using methods and means to reduce the methane abundance of excavation areas based on drilling wells along the developed and adjacent coal seams into mined-out spaces. The parameters of degassing and methane emission sources are legalized by the industry regulations, scientifically substantiated, and published in the scientific and practical works. The mines of the Kuznetsk coal basin and the Vorkuta deposit, mainly with high productivity of coal mining in the conditions of developing a suite of methane-bearing coal seams using complex mechanized faces were selected as objects of study: named after S.M. Kirov, named after V.D. Yalevsky (formerly «Kotinskaya»), Boldyrevsky coal seams (index 24) and seam 52. Gas hazard of the coal mines is determined by the volume of methane emissions, explosions of methane-air mixtures, loss of people life and is caused by the joint influence of natural, mining, organizational and subjective factors. The main indicator of gas hazard when developing a suite of methane-bearing coal seams is the absolute methane abundance of the excavation area. The method was used to predict the intensity of methane release from the exposed surface of a mined coal seam into the bottomhole space of the longwall and adjacent coal seams. Methane release from the exposed surface of a contiguous coal seam, subject to unloading from the rock pressure, was determined by analogy with the mined seam. The release of methane from the broken coal was established experimentally. When the working face unloads adjacent coal seams, the intensity of methane release from them into the working face is summed up.

Study and application of reasonable parameters for hydraulic punching of layer penetration boreholes in Changping Coal Mine

AbstractAiming at the application of hydraulic punching technology in soft, low permeability, and high gas coal seams in Changping Coal Mine, there are problems such as large workload, poor permeability enhancement effect, and the formation of “blank zones” in the pressure relief and permeability enhancement areas caused by workers' blind construction. By using a combination of theoretical analysis, numerical simulation, and on‐site practice, the threshold pressure for punching and breaking coal was calculated. The simulation analysis determined the reasonable key parameters for hydraulic punching through layered drilling, providing theoretical support for engineering applications; and the application effect of key parameters was investigated in the 5302 bottom extraction roadway of Changping Coal Mine. The research results show that the threshold value of incident pressure for punching and breaking coal in the No. 3 coal seam of Changping Coal Mine is 4.26 MPa, the reasonable hydraulic punching water pressure is 15 MPa, the punching angle is 60°, the diameter of the punching hole is not more than 0.8 m, and the punching time is 120 min; when the punching water pressure is lower than 4.0 MPa, effective coal flushing cannot be achieved. When the water pressure is between 4.0 and 15.0 MPa, the total amount of coal flushing is positively correlated with the punching water pressure; under the determined reasonable parameter punching conditions, the extraction influence radius is 8.9 m, the effective extraction radius is 5 m, and the average pure gas extraction volume is 0.089 m3/min. Under this parameter, hydraulic punching technology effectively improves the permeability characteristics of coal seams, which is conducive to long‐term gas extraction and has a significant effect on pressure relief and drainage promotion.

Damage Characteristics Caused by Deep-Hole Blasting near Normal Fault and Its Effects on Coal and Gas Outbursts

To understand the stability of coal and rock in areas of normal faults disturbed by the dynamic loads of blasting, the damage characteristics of coal and rock within a normal fault are investigated using similarity simulation tests. The mechanism for coal and gas outbursts within a normal fault is analyzed theoretically, and the results indicate that the maximum tensile stress in the vertical direction of the blasting hole in the normal-fault model is 1.17 times that in the no-fault model. The propagation of cracks near the blasting hole produces crushing circles, and more cracks are produced in the normal-fault model, causing severe damage to the coal seam and floor rock adjacent to the upper wall of the normal fault. Meanwhile, coal on the surface of the coal seam falls off. The cracks extend to the roof rock through the footwall of the normal fault. Cracks in the adjacent strata and coal seam interpenetrate those around the blasting hole, which is a potentially dangerous area for coal and gas outbursts. The cumulative damage caused by blasting vibrations increases the extent and scope of the damage to coal and rock, and broken coal and rock provide weak surfaces and gas flow channels that can lead to dynamic gas disasters. The research results will provide a theoretical basis for gas dynamic disasters induced by blasting disturbance in normal fault structures. Based on cases of coal and gas outbursts in the Didaoshenghe Coal Mine in Heilongjiang Province, China, an important reason for such incidents is considered to be the blasting areas of normal faults being disturbed by air-powered coal drilling.

Numerical Simulation Study on the Multi-Physical Field Response to Underground Coal and Gas Outburst under High Geo-Stress Conditions

Based on thermal–fluid–solid coupling law in coal and gas outburst, a multi-physical field numerical analysis model is built for the whole outburst process. The response laws of stress, gas pressure, temperature, and seepage in different areas and different time nodes around coal and rock mass in the coal and gas outburst under high stress condition are discussed. Research results show: Firstly, the stress response law of the coal and rock mass around the burst hole is initial vibration–sudden attenuation–late stability. Secondly, the gas pressure response law in different areas is that the gas pressure response rate decreases gradually with the increase of the distance from the outburst. Thirdly, the adsorbed gas contained in the broken coal near the outburst port is desorbed rapidly and expands to do work, and the temperature changes dramatically after outburst occurs. In contrast, with the increase of stress, the proportion of elastic potential in total coal and gas outburst energy increases, and the proportion of elastic potential is positively correlated with stress. The critical gas pressure under the energy condition of coal and gas outburst decreases with the increase of stress. It illustrates that the lower gas pressure can also meet the energy condition of coal and gas outburst under high stress.

Построение и реализация термической модели горения в рудничной атмосфере метановоздушной смеси с учетом ее кинетики

At the coal deposits exploitation by using underground methods, as a rule, negative factors that reduce coal production and miners' safety exhibit. These factors include, first of all, methane emitted from the broken coal and the coal dust as an inevitable result of work of headers and cleansing combines. Interacting with the atmosphere of mines, methane and coal dust generate dust- and dust-gas-aerial mixtures where thermophysical and chemical processes take place. First of all, these processes are combustion and detonation that until recently were included into the category of highly hazardous accidents. Based on the assumptions of single-stage chemical reaction of combustion and ideal gas agents and reaction products, an attempt to construct a math model of combustion of aeromethane mixture, considering the kinetics of chemical reaction of the origin agents. Three justified simplifying suggestions are made. The first implies that the pressure derivative is negligibly small in relation to the temperature derivative. The second implies that the area of laminar combustion consists of two zones: the mixture is being heated in one of them, and the combustion chemical reaction takes place in the other. The third implies that the temperature of mixture’s ignition does not significantly differ from the end temperature of the mixture at the completion of combustion reaction. A boundary value problem for the ordinary non-linear differential equation of the second order is set. Considering the simplifying assumptions, this was reduced to the linear equation whose solution is found in quadrature. The formulas describing combustion process have been developed. The dependences of the rate of laminar combustion on a number of mixture’s properties are established.

Comparative investigation of the damage of coal subjected to pure water jets, ice abrasive water jets and conventional abrasive water jets

This paper firstly proposed using ice abrasive water jets (IAWJs) to slot coal seam to ensure the safe exploitation of coal mines. The performances of IAWJs, pure water jets (PWJs) and conventional abrasive water jets (CAWJs) breaking coal were simulated and compared using the coupled SPH-FEM methodology. The findings indicate that the breaking performance of coal samples subjected to abrasive water jets are more obvious than those of coal samples subjected to PWJs, while the performance achieved by CAWJs is slightly more evident than that by IAWJs. Most of the ice particles transformed into pure water after impacting and then flowed away with the backflow, while many abrasives remained in the coal under CAWJ impact. The specific energy consumption of breaking coal by IAWJs is obviously lower than that consumed by PWJs and CAWJs. Accordingly, it can be inferred that IAWJ is a promising technology in coal slotting applications

Adaption of Theoretical Adsorption Model on Coal: Physical Structure

With the motivation to investigate the role of coal physical structure on the adsorption performance of coal reservoir, 18 different types of coal samples with different coal structures were collected from six coal profiles of four production mines located at China. The adsorption characteristics of CH4 on coal samples with different coal structures were examined, and then experimental results were fitted and analyzed by the Langmuir model and the adsorption potential model (D-R and D-A). The prominent factors in terms of adsorption capacity of coal with different coal structures and its adaptability to the model were discussed. Results indicate the following: a) under the condition of a similar coal rank, the adsorption performance of coal is governed by coal rock composition and adsorption heat, the effect of structural deformation on the adsorption performance of coal is not obvious; b) the Langmuir model has a certain adaptability to coal samples with different coal structures, while the D-R model is evidently not suitable to describe coal samples with scaly coal, part of broken coal with small vitrinite content; c) the D-A model has a high adaptability to coal samples with various coal structure types, and the stronger the coal deformation is, the higher the accuracy is.

Structure optimization design of transmission system of shearer cutter based on genetic algorithm

As one of the mainstream equipment of fully mechanized mining equipment, shearer is a large complex system with the functions of breaking coal and transporting coal. It is an important milestone for China’s coal industry to move towards modernization and mechanization. In order to adapt to the complex working environment and better meet the needs of social development, the optimization of spatial structure and bearing capacity of coal machine has become the focus of research. Based on genetic algorithm, taking MG500/1170-AWD1 electric haulage shearer as an example, this paper takes the weight function of maximizing the bearing capacity and minimizing the volume as the optimization objective to optimize the structure of the cutting part transmission system, and analyses the rationality of the scheme by comparing the objective function before and after optimization, so as to provide technical support for the R & D department.

ПРО РОЗРОБКУ ЗАГАЛЬНОЇ МЕТОДИКИ ДЛЯ ПРОГНОЗУ НЕБЕЗПЕЧНИХ ВЛАСТИВОСТЕЙ ВУГІЛЬНИХ ШАХТОПЛАСТІВ

Purpose: to establish a quantitative effect on the dust-generating ability of mine layers of the degree of metamorphic transformations of fossil coals, mining-geological and mining conditions of mining operations and to provide proposals for the development of a general methodology for predicting other hazardous properties of mine layers. Methodology: research is based on the experience of using regulatory documents and analysis of the results of experimental and calculated data on dust formation of fine fractions for various observation conditions. Results: based on the analysis of statistical models of shallow and steeply dipping mine layers by groups of their dustiness, the effect of specific dust release, dust content in broken coal, moisture and thickness of the seams was established. Of all the possible factors that determine the specific dust release, the main ones are the design features of mining machines. The yield of small grades when tested by the falling weight method can serve as an indicator of the strength of coal. The use of such methods eliminates the errors caused by determining the degree of coal change during the transition from its actual destruction by a coal mining machine to the reference mode. The use of carbon content as one of the main indicators of the degree of metamorphism makes it possible to analyze the level of influence of both the sum of the remaining main components of the organic mass (hydrogen, nitrogen, sulfur, oxygen) and their separate influence. In order to bring the state of coal as close as possible to production conditions, it is necessary to additionally take into account moisture, mineral inclusions and their composition. The petrographic composition and some physical and mechanical properties are reliably characterized by the vitrinite reflectance index. The extreme limits of influence on dust formation of the design features of mass-produced combines differ by 43.4 times. The influence of metamorphic transformations at the extreme limits of the yield of the 1-0 mm class when testing coals in a pile driver is estimated by a difference of 5.6 times. The release of volatile substances taken as the main indicator of the degree of metamorphism in the normative base for the safe conduct of mining operations does not unambiguously characterize the gradation of mine layers according to their dustiness groups. The thickness of the mines being developed and the angles of occurrence do not determine their tendency to dust formation, but are the main criteria for choosing mining equipment for crushing coal in the massif. The general methodology for predicting the hazardous properties of coal mine layers, using the example of their dust-forming ability, should take into account the influence of factors of three blocks – metamorphic transformations, mining and geological and mining technical conditions. Scientific novelty: for the first time, a quantitative assessment of the effect on the dust-generating capacity of mine layers of a combination of factors of metamorphic transformation of fossil coals, mining-geological and mining-technical conditions of mining operations has been established. Practical value: the results obtained make it possible to substantiate and develop a general methodology for predicting the hazardous properties of mine layers, which will contribute to improving the regulatory framework for the safe conduct of mining operations.

COMPUTER MODELING OF COAL SEAM BLASTING

The authors discuss the mechanism of breaking coal by blasting with a view to optimizing this method of dynamic treatment of coal and improving drilling-and-basting performance. A combination model of high gassy coal is used to describe the connection between coal breaking by blasting and subsequent gas liberation. This model and the smoothed-particle hydrodynamics method are used to study evolution of damage zones and stress–strain behavior of coal in the neighborhood of a blasthole after explosion. The research findings help predict coal response to the dynamic impact.

Microcrack evolution and permeability enhancement due to thermal shocks in coal.

To understand the effects of thermal shock on microcrack propagation and permeability in coal, thermal shock tests were conducted on coal specimens by using a constant temperature drying oven (105 °C) and a SLX program controlled cryogenic tank. The growth and propagation of microcracks were measured with computer tomography (CT) scanning and scanning electron microscope (SEM) tests. Results showed that thermal shocks improved the permeability of coal significantly. Notably, the permeability of coal after thermal shocks increased from 211.31% to 368.99% and was positively correlated with temperature difference. CT scanning images revealed that thermal shocks increased the crack number, crack volume and crack width as well as smoothened and widened the gas flow paths, thereby enhancing coal permeability. Moreover, SEM images showed that heating-cooling shocks created more new microcracks, forming more complex crack propagation paths and better connectivity among microcracks in coal compared to cooling shocks. We proposed a crack propagation criterion for coal to explain the mechanism of crack failure and propagation during thermal shocks. Our experiment results and theoretical analysis indicate that the heating-cooling shock is more effective in damaging and breaking coal than the cooling shock. Thus, it can be used as an alternative approach to enhance coal permeability in the production of coalbed methane (CBM).

Analysis of Statistics on Methane Release in High-Production Coal Faces in Kuzbass

The statistical analysis results on methane release in coal faces in Kuzbass are presented. The parabolic curves of methane release have maximums as regard to feed velocity and productivity of shearer. Methane release from broken coal is an inverse proportional function of linear hyperbolic dependence and has maximum as regard to feed velocity and productivity of shearer. The analysis of the found methane release from broken coal shows that methane release reduces as a quadratic dependence with decreasing drum rotation speed and number of picks per cutting line, and increases also as a quadratic dependence with growing thickness of coal seam and shearer web width.

Mechanical and Heterogeneous Properties of Coal and Rock Quantified and Mapped at the Microscale

Due to the impossibility of obtaining intact standard experimental samples, it is difficult to test the mechanical properties of soft and broken coal and rock obtained from deep coal mines. So, an advanced experimental technology based on a small sample volume, nanoindentation technology, was introduced and used to measure the mechanical parameters of them. By using the averaging method, the hardness of shale, mudstone and coal are 1191.90 MPa, 674.95 MPa and 424.30 MPa, respectively; their elastic moduli are 20.39 GPa, 11.72 GPa and 5.47 GPa; and their fracture toughness were 1.66 MPa·m0.5, 1.28 MPa·m0.5 and 0.77 MPa·m0.5. These three mechanical parameters were used to quantify and map the heterogeneous properties of coal and rock for convenience and accuracy. For example, the inter quartile range (IQR) of the hardness of shale, mudstone, and coal are 1502.10 MPa, 1016.20 MPa and 54.64 MPa, respectively, meaning that coal has the best homogeneity among them. Nanoindentation technology provides researchers with a convenient method to conduct mechanical experiments at the microscale.

The Porosity Dynamic Model of the Compacted Broken Coal

In order to study the dynamic change law of the porosity of the compacted broken coal under different axial stress loading, based on the environment of the broken and compacted coal in the gob, aiming at the influence of the porosity on the spontaneous combustion of the coal, combined with the fractal theory, the fractal model of the porosity of the broken coal is established. A self‐designed “testing device for permeability evolution and spontaneous combustion characteristics of crushed coal under pressure” is used to carry out axial loading test on selected coal samples in the gob. By comparing and analyzing the calculated results of void dynamic evolution model and experimental data, it is found that the relative error of void dynamic evolution model is between 2.8% and 6.2%, which meets the engineering needs. According to the stress‐strain curve, initial accumulation state parameters, fractal dimension of initial crushing, and particle size distribution, the change of porosity under different compacted conditions can be predicted by the model, which has certain significance for identifying the change of compacted broken coal porosity and analyzing the process of coal spontaneous combustion and oxidation.