Fully-mechanized Mining Research Articles

A sensing system and solving method for dynamic detection of relative pose of hydraulic support group

The precise detection of the pose of hydraulic support groups is crucial for the construction of intelligent coal mines. Addressing current challenges in comprehensive position sensing of support groups, such as one-sided descriptions, missing information, and limited detection capabilities, this paper, based on the concept of digital twin, proposes a sensing system and solving method for dynamic detection of the relative pose of hydraulic support group. Initially, a relative pose detection model, based on the six-point localization principle, is proposed by combining existing sensor information. Then, a sensing system is designed, incorporating a photoelectric detection device for monitoring key position parameters and virtual sensors for determining pose information. Consequently, a method for dynamically deriving relative positions, driven by the fusion of real-virtual iterative solving, real-virtual error feedback, and iterative condition optimization, is established. Finally, a relative pose dynamic detection system for a hydraulic support prototype is constructed in a laboratory environment. Experimental results demonstrate that the sensor system and the relative position detection method designed in this paper achieve a relative position accuracy of over 95.32 % for the hydraulic support, with a dynamic reconstruction time of less than 0.2 s. This verifies the rationality of the sensor system and the feasibility and accuracy of the dynamic deduction method. To sum up, this work provides a theoretical foundation and technical support for the autonomous perception of hydraulic support group, autonomous frame adjustment between frames, and overall straightness adjustment. It also lays the groundwork for further research and the advancement of information-physical systems in the fully-mechanized mining face.

Research on “Playing Football” Type Roof Control in Fully-Mechanized Mining Face with a Super-Large Mining Height under the Background of 5G+ Big Data

With the increase of mining height at the working face, the influence range of roof fractures in the goaf increases, the advanced supporting pressure on the coal wall increases, ground pressure becomes more intense, and roof support becomes more difficult. Based on the analysis of ground pressure behavior in the first mining and caving stage, the normal mining stage, and the final mining breakthrough stage of the fully-mechanized mining face near 12,404, the relationship between conveyor current and coal speed is studied and compared. Based on the intelligent control system of the fully-mechanized mining face with a super-high mining height of 12,404 and the structure of the football team, the “playing football” roof control mode of the fully-mechanized mining face with super-high mining height under the background of 5G+ big data is put forward. The conclusions are as follows: In 12,404, the ground pressure was first mined. During normal mining, when the roof with a buried depth of more than 200 m is broken, the speed of the coal machine is kept within 12 m/min, and the full guard defends and controls the roof, pulling the lead frame through the area with severe ground pressure. When the roof is good, it is necessary to speed up the coal cutting and get rid of the pressure. When it is less than 200 m, it will overcome the local weighting, and show an offensive trend to speed up and increase production. In the final mining breakthrough stage, the speed of the coal machine should be controlled within 8 m/min, with attention to defense, guarding against roof leakage, and reducing waste rock.

Numerical studies on the effects of the hybrid cooling and dust suppression solution in hot fully-mechanized mining face

With the increasing depth of coal mining, the hot and humid environment at the mining faces is becoming more severe. Mining in these conditions, coupled with the hazardous effects of coal dust, poses a significant risk to the health of coal miners. To improve the working conditions in underground coal mines, this study proposes a hybrid solution that combines evaporative cooling and dust suppression in fully mechanized working faces. Numerical models of the mining face are also created to simulate the cooling effects of the proposed solution. Additionally, the migration laws of water droplets from the spray system are also studied. The results indicate that the proposed solution can effectively improve thermal environments and suppress coal dust. This research can enhance the workplace safety in underground coal mines and provide valuable insights for addressing high airflow temperatures and concentrated dust levels.

CM-YOLOv8: Lightweight YOLO for Coal Mine Fully Mechanized Mining Face.

With the continuous development of deep learning, the application of object detection based on deep neural networks in the coal mine has been expanding. Simultaneously, as the production applications demand higher recognition accuracy, most research chooses to enlarge the depth and parameters of the network to improve accuracy. However, due to the limited computing resources in the coal mining face, it is challenging to meet the computation demands of a large number of hardware resources. Therefore, this paper proposes a lightweight object detection algorithm designed specifically for the coal mining face, referred to as CM-YOLOv8. The algorithm introduces adaptive predefined anchor boxes tailored to the coal mining face dataset to enhance the detection performance of various targets. Simultaneously, a pruning method based on the L1 norm is designed, significantly compressing the model's computation and parameter volume without compromising accuracy. The proposed algorithm is validated on the coal mining dataset DsLMF+, achieving a compression rate of 40% on the model volume with less than a 1% drop in accuracy. Comparative analysis with other existing algorithms demonstrates its efficiency and practicality in coal mining scenarios. The experiments confirm that CM-YOLOv8 significantly reduces the model's computational requirements and volume while maintaining high accuracy.

Differences of Pyrolysis Products and Controlling Factors of Oil-Rich Coal with Different Grain Sizes under Fully-Mechanized Mining Conditions

Differences of Pyrolysis Products and Controlling Factors of Oil-Rich Coal with Different Grain Sizes under Fully-Mechanized Mining Conditions

Development and experimental study of a scaled model for dust dispersion in fully-mechanized mining face

Model experiment is one of the research methods for the fundamental theory of coal mine dust control. To address the current deficiencies in experiment development for research on dust migration rules, a scaled model for dust dispersion in a fully-mechanized mining face was constructed based on the design prototype of the 25211 mining face at the Hongliulin mine, using a similar theory. The model includes a mining face, a return airway, a haulage roadway, and a subsidiary roadway constructed using aluminum alloy profiles and tempered glass. The model uses U-shaped exhaust ventilation. The shearer, hydraulic support, and reverse loader are equipped with dust sources, and each dust source operates independently with distinct dust generation processes that do not interfere with each other. An experimental plan for dust diffusion during shearer dust generation was designed with a wind speed of 1.0 m/s. Preliminary model experiment was conducted based on this model. The results showed that the farther away from the dust source, the lower the dust concentration. The relative mass distribution and cumulative mass distribution of falling dust particles also showed that the farther away from the dust source, the smaller the particle size of the falling dust particles. The maximum size distribution decreased from 51.4 μm to 27.9 μm, and the average particle size decreased from 34.9 μm to 20.6 μm. The test model results were validated by field tests, indicating that the constructed model has good reliability. Finally, the critical areas for future research based on this model were proposed. The development of the model provides valuable experimental support for the theory of multi-source dust transportation in the airflow on the fully-mechanized mining face.

An AGCRN Algorithm for Pressure Prediction in an Ultra-Long Mining Face in a Medium–Thick Coal Seam in the Northern Shaanxi Area, China

Due to the increase in the length of the mining face, the pressure characteristics and spatial distribution in fully-mechanized mining faces are different from those in typical mining faces, which leads to great challenges in roof management and the intelligent control of ultra-long mining faces. Taking the ultra-long mining face of a medium–thick coal seam in the northern Shaanxi mining area as an example and using field monitoring data for the working resistance of the hydraulic supports, a non-linear prediction method was used to extract the features of the dynamic data sequence of the working resistance of the hydraulic supports, and a deep learning method was used to establish a pressure prediction model for ultra-long mining faces based on the adaptive graph convolutional recurrent network (AGCRN) algorithm. In the proposed model, the supports in the fully mechanized mining face were regarded as the logic nodes of a topological structure, while the time-series resistance data for the supports were regarded as data nodes on a graph. The AGCRN model was used to determine the spatiotemporal relationship between the working resistance data of adjacent hydraulic supports, thereby improving the accuracy of the proposed model. The MAE and MAPE were employed as performance evaluation indices. When the node-embedding dimension was set to 10 and the time window was set to 16, the corresponding MAE and MAPE values of the prediction model were the minimum values. Compared with the reference models (i.e., the BP, GRU, and DCRNN models), the MAE and MAPE of the AGCRN model were 38.75% and 23.49% lower, respectively, indicating that the AGCRN model effectively demonstrates high accuracy in predicting the working resistance of supports. The AGCRN model was applied in the prediction of the working resistance of the supports of the ultra-long fully mechanized mining face. The results revealed that the working resistance of the supports in the lower and upper areas was relatively small along the strike, whereas the working resistance of the supports in the middle area was large, exhibiting a zoning pattern of “low-high-low” in terms of the average working resistance. In conclusion, the proposed model provides data references for the state of the hydraulic supports, pressure identification, and intelligent control of the ultra-long mining faces of the medium–thick coal seams in northern Shaanxi.

Study on Dust Migration Law and Spray Dust Suppression Technology in Fully Mechanized Mining Face

To effectively solve the problem of high dust concentration during coal cutting and frame shifting in fully mechanized mining faces, based on the theory of gas–solid two-phase flow, a geometric model of a fully mechanized mining face was established by using COMSOL numerical simulation software. Simulations were performed for the movement characteristics of wind flow and the law of dust diffusion. Results show that the air flow at the junction of the working face, the air inlet, the hydraulic support moving area, and the vicinity of the shearer has accelerated movement, and the maximum wind speed zone of about 3 m/s can be formed. Under the influence of wind flow, dust particles above 35 μm settle faster, while dust particles below 35 μm are very vulnerable to the influence of wind flow, and the settling speed is slower. Using a custom experimental platform, the atomization characteristics and wind resistance of a pressure fan nozzle, a supersonic nozzle, and an ultrasonic nozzle were tested, and the nozzle that was suitable for the scheme was selected and applied in the field. Comparing the dust concentration before and after the application of the dust removal scheme at the sampling point, results show that the dust removal efficiency of the proposed scheme exceeds 85%, and the treatment effect is good.

Study on dust pollution suppression of mine wind-assisted spray device based on orthogonal test and CFD simulation

To solve the problem of high-concentration coal dust pollution in a fully mechanized working face, and based on the principle of mechanical wind-assisted negative pressure suction of dust-laden air flow combined with spray dust reduction, a new wind-assisted spray device was investigated. The nozzle of the device was optimized through experimental investigation of the macroscopic characteristics of the spray field. Based on the actual situation of the fully mechanized mining face, a numerical simulation of the wind-assisted spray device was carried out and combined with an orthogonal test. It was shown that when the spray device deviates by 30°, the spray pressure is 6 MPa, and the air output is 90 l/min, resulting in a more efficient spray field. Finally, the wind-assisted spray device was used in the 22,104 fully-mechanized mining face of Shangwan Coal Mine, China, and the dust concentration was monitored at measuring points before and after the spraying device was switched on. The concentration of total dust and respirable dust at the shearer driver's position decreased to 104.2 mg/m³ and 68.3 mg/m³, respectively, and the dust removal efficiency reached 88.31% and 83.45%, respectively, which effectively suppressed the high-concentration coal dust pollution in the working face.

Intelligent decision method for the position and attitude self-adjustment of hydraulic support groups driven by a digital twin system

The hydraulic support group is often skewed during the propulsion process, but the existing technology cannot autonomously adjust its position and attitude according to the actual working conditions. This paper proposes an intelligent decision method for the position and attitude self-adjustment of hydraulic support groups driven by a digital twin system. The method reconstructs the position and attitude of the hydraulic support, completes virtual decision-making, virtual execution and strategy optimization for the adjustment behavior in the virtual space, and finally derives the optimal control command to reversely control the real support to achieve the self-adjustment of the position and attitude of the support. First, the full position and attitude parameter matrix and the 3D workspace are defined to describe the position and attitude of the hydraulic support, and a pose analysis method of the hydraulic support group is proposed based on the lengths of the column and balance jack. Second, the method of predicting the ideal pose of the support, the synergistic method of the adjustment device, and the method for the calculation of its elongation are studied. Finally, a digital twin system facing physical support prototypes was built in a laboratory environment, and three key experiments were carried out for the virtual reconstruction of the support pose, the intelligent decision-making and virtual execution of the adjustment behavior, and the autonomous adjustment of the physical prototype based on virtual decision-making results. The experimental results show that virtual decision-making can effectively guide the real adjustment behavior, and the applicability and influencing factors of the adjustment effect are further studied. The proposed method compensates for the vacancy of hydraulic support self-adjustment technology, and can provide a reference for the intelligent control of fully-mechanized mining equipment.

Research on a Carbon Emission Calculation Model and Method for an Underground Fully Mechanized Mining Process

With the ratification of the Paris Agreement at the Paris Climate Conference, reducing carbon emissions has become a global interest. Coal is one of the main industries causing carbon emissions; thus, quantifying carbon emissions from coal mining is an important step in reducing these emissions. Firstly, based on the life cycle idea, in this paper, we define the Carbon Emission Boundary of the fully mechanized coal mining method. Secondly, the carbon emission accounting model (B-R model) of fully mechanized coal mining is established, which includes the total amount of carbon emissions and the carbon emissions of each mining link during the mining process. The Fifth-II mining area of the Jinda Coal Mine in Tengzhou City is taken as an example. We collect the relevant data on carbon emissions in the mining process of the Jinda Coal Mine, and the B-R model is used to obtain the carbon emissions in the mining process of this mining area. Finally, the feasibility of the B-R model is further verified according to the international authoritative carbon emission IPCC calculation method and the China Coal Production Enterprises Greenhouse Gas Emissions Accounting Methodology and Reporting Guide. The results show that the B-R model in this paper is feasible and that the greatest amount of carbon emissions arises from the coal breaking link and coal transportation, which provides a basis for other coal mines to calculate carbon emissions. The B-R model lays a foundation for coal mines to formulate a carbon emission reduction system.

Application Research on Coal Mining Technology in Fully Mechanized Mining Face

Application Research on Coal Mining Technology in Fully Mechanized Mining Face

Study on the coupling migration law of airflow-respiratory dust of an 8-m high fully-mechanized mining face

8-m super-high fully mechanized mining face has been successfully applied in China, which has brought many difficulties to dust control. The main reason is that the mining height increases and the dust distribution and evolution law are quite different. Targeting the 12,513 fully-mechanized mining face in Bulianta Coal Mine of China in this paper. The spatial evolution of airflow-respiratory dust of an 8-m high fully-mechanized mining face is analyzed using numerical simulation and underground measurement methods. The results reveal that the numerical and measured results are consistent. At the working range from 15 m in front of the shearer to 30 m behind it, the wind speed increases with an average rise of 70% on the coal cutting side. The airflow diffusion at the working face is primarily longitudinal and partly transverse. Along the airflow direction, the respiratory dust concentration in the pedestrian space first increases and decreases, followed by a marginal increase and gradual decrease，and the dust concentration increased with the increase of height, the migration distance of dust particles was directly proportional to time, and the smaller dust particles were prone to transverse diffusion. In the range of 20–30 m from the downwind side of the shearer, the transverse diffusion of coal cutting dust and the dust produced by support coal falling show conversion, leading to the increase of dust concentration. Under the same dust production intensity, compared with ordinary mining height, with the increase of mining height, the influence range of dust diffusion is wider, the floating duration is longer, and the space dust concentration will be reduced, and the support coal falling dust is the main dust pollution source in pedestrian space. The results reveal that the numerical and measured results are consistent, and obtained the relationship of spatial evolutions of respiratory dust

Application of Gas Drainage Technology in Fully Mechanized Mining Face under Influence of Adjacent Layers

Application of Gas Drainage Technology in Fully Mechanized Mining Face under Influence of Adjacent Layers

Research and Application of Recovery Technology in Fully Mechanized Mining Face under Complex Geological Conditions

Research and Application of Recovery Technology in Fully Mechanized Mining Face under Complex Geological Conditions

Instability mechanism of surrounding rock chain structure in steeply inclined thick seam mining

In view of the difficulty of fully-mechanized mining in steeply inclined coal seam with thickness of 4 to 8 m, the horizontal section short wall fully-mechanized caving mining method is innovatively proposed. In the No. 3-3c steeply inclined coal seam of a Coal Mine, the single roadway integrated with excavation and recovery is arranged as working face, the pillar on sides of roadway is recovered ahead by spiral drilling machine, and the top coal is recovered by the vertical and horizontal self-moving supports. The Z-type ventilation is formed by constructing a ventilation roadway along the side of gob. Through theoretical analysis, numerical calculation and physical similarity simulation, the main mining parameters, including sectional height and ratio of mining height to caving height, were determined, and the characteristics of roof movement evolution, floor failure and sliding and the generalization of surrounding rock bearing structure were revealed. The results show that the effect of coal caving is better when the section height is 10 m and the ratio of mining height to caving height is 2.85. The cross-layer multi-ladder voussoir structure is formed by transformation and migration of the critical layer, and the failure and slip modes of floor are extruding-translation, extruding-underdraught and extruding-upthrust in different areas of horizontal sublevel caving stope. Roof, pillar and floor are interrelated to form the Roof-Pillar-Floor (R-P-F) chain structure. When the height of section with three sublevels is 30 to 45 m, the mutual conversion of strong and weak chains between structural units can be cut effectively in mining process, and the impact disaster caused by the roof falling over great extent and the instability of pillar can be prevented. The new mining method proposed and studied above provides the technological and theoretical basis for the safe and efficient production of such coal seams, and is of great significance to the sustainable development of coal in Xinjiang province and even western China.

Reasonable Arrangement of High-Level Orientation Extraction Boreholes of Pressure Relief Gas in Overlying Strata under High-Strength Fully Mechanized Mining in Low-Gas-Thick-Coal Seam

In order to solve the problem of pressure relief gas control under high-strength fully mechanized top-coal caving in low-gas-thick-coal seams, this paper studies the evolution of overburden structures and the distribution characteristics of fissure fields during the initial and stable period of working face by physical simulation and numerical analysis. The mathematical model of coupling between mining fracture field and pressure relief gas field is established. The results reveal the distribution characteristics of pressure relief gas field that considers mining-induced fissure field. According to the distribution of mining gas accumulation area, the high directional long boreholes have been put forward to control the pressure relief gas in goafs, and the effect has been tested. The results show that the initial pressure and three periodic pressures occurred from the cutting hole to 135 m in the initial mining period of the working face. The height of collapse zone developed to 22 m, and fracture height developed to 75 m. The development height of caving zone is stable at 25∼27 m, and the development height of fissure zone is stable at 75∼95 m. The process and distribution of pressure relief gas flow in goaf are obtained by solving the numerical model of pressure relief gas flow in mining fissure field. The gas accumulation area is located within 25∼55 m from return laneway and 25∼50 m from the roof of coal seam. After the implementation of high directional long drilling gas drainage technology in the initial mining period and the stable mining period, good results have been obtained in the gas control, where the average concentration of gas extraction is 5.8%, the average gas flow rate is 0.71 m3/min, and the gas concentration in upper corner and return air is less than 0.8%. The results can provide a reference for pressure relief gas control under similar conditions.

Study on the oxidation and heating characteristics of residual coal in goafs under different air-leakage conditions

The spontaneous combustion of broken coal is one of the main causes for mine safety accidents in goafs. To determine the effect of different air-leakage conditions on the spontaneous combustion of leftover coal, the air-leakage passage of the goaf was designed based on the principle of Sudoku grid in an inflammable coal seam. The temperature rise during the auto-ignition oxidation of coal was studied using a self-built experimental platform. By changing the air-flow rate, the laws of the change in the oxygen consumption rate and the heat release intensity with the coal temperature were analyzed. Results show that the oxygen consumption rate had three obvious peaks at 48?C, 75?C, and 105?C, respectively. Above 80?C, spontaneously combustion of the experimental coal samples began. The exothermic intensity increased exponentially with the rise of temperature. Furthermore, an exponential relationship was observed between the air supply at the working face and the spontaneous combustion of broken coal in the goaf. In addition, the increase in air supply in the fully-mechanized mining face increased the width of the oxidation zone.

Rib Spalling 3D Model for Soft Coal Seam Faces with Large Mining Height in Protective Seam Mining: Theoretical and Numerical Analyses

Fully-mechanized mining of coal face with a large cutting height is generally jeopardized by rib spalling disaster in the working face. Preventive measures based on undisturbed coal seam conditions fail to provide safe predictions, as large-scale fractures in soft coal face frequently appear before excavation due to mining-induced stresses. This paper investigates a case study of the Paner Mine 11224 working face in the Huainan mine area, China, which features an overlying protected layer in the protective seam mining. To simulate the failure process in such a mine, we elaborated a simplified physical-mechanical model of a coal wall that underwent shear failure and sliding instability, in compliance with the triangular prism unit criterion. Similar simulation experiments, theoretical calculations, and borehole monitoring were used to comprehensively analyze the overburden fracture and movement after mining the lower protective seam. The development height of three overburden zones was determined, and the characteristics of the protected layer affected by mining were obtained. The results show that the failure is mainly related to the roof load, coal cohesion, internal friction angle, coal seam inclination, and sidewall protecting force. The key to limiting the frictional sliding of a slip body is to reduce the roof load and increase the sliding coefficient and cohesion of the main control weak surface (MCWS). Besides, a self-developed three-dimensional numerical calculation software RFPA3D (Realistic Fracture Process 3D Analysis), which considered the rock heterogeneity, was used to reproduce a weak triangular prism’s progressive failure process. The numerical simulation results agreed with the fracture pattern predicted by the theoretical model, which accurately described the rib spalling mechanisms in a soft coal face with a large cutting height and a protective layer.

Strata behavior and control strategy of backfilling collaborate with caving fully-mechanized mining

Abstract This article analyzes the technical difficulties in full-section backfill mining and briefly introduces the technical principle and advantages of backfilling combined with caving fully mechanized mining (BCCFM). To reveal the strata behavior law of the BCCFM workface, this work establishes a three-dimensional numerical model and designs a simulation method by dynamically updating the modulus parameter of the filling body. By the analysis of numerical simulation, the following conclusions about strata behavior of the BCCFM workface were drawn. (1) The strata behavior of the BCCFM workface shows significant nonsymmetrical characteristics, and the pressure in the caving section is higher than that in the backfilling section. φ has the greatest influence on the backfilling section and the least influence on the caving section. C has a significant influence on the range of abutment pressure in the backfilling section. (2) There exits the transition area with strong mine pressure of the BCCFM workface. φ and C have significant effect on the degree of pressure concentration but little effect on the influence range of strong mine pressure in the transition area. (3) Under different conditions, the influence range of strong mine pressure is all less than 6 m. This article puts forward a control strategy of mine pressure in the transition area, which is appropriately improving the strength of the transition hydraulic support within the influence range (6 m) in the transition area according to the pressure concentration coefficient. The field measurement value of Ji15-31010 workface was consistent with numerical simulation, which verifies the reliability of control strategy of the BCCFM workface.