Underground Coal Mining Environment Research Articles

Ventilation characteristics of double-forced air pipe ventilation in comprehensive mechanized excavation face and determination of its optimal parameters

ABSTRACT This study proposes a ventilation and dust control approach using double-forced air pipes at the tunnel excavation face, aiming to optimize the dust control and reduction measures for underground coal mining environment. We designed a physical model in proportion to the 11,139 excavation face in the Zhangji Coal Mine of China Huaihe Energy Holding Group Coal Company. To begin with, CFD numerical simulation was employed to unveil the basic laws of the double-forced air pipe ventilation approach, including airflow characteristics and dust concentrations. The orthogonal experimental method was then adopted to analyze the influence mechanism of installation location and airflow ratio of the double pipes on the dust density around the driver’s operating space. Results suggest that the double-forced air pipe ventilation can efficiently improve the airflow velocity at the excavation face, reaching 5.54 m/s. With the minimum dust density around the driver’s operating space as the optimal parameter standard and combined with the R value, the three factors in the orthogonal experiment can be sorted as: the distance between the forced ventilation pipe at the driver’s side and the excavation face (R = 206.91) > the distance between the forced ventilation pipe at the return air side and the excavation face (R = 171.72) > the airflow ratio of the two pipes (R = 77.52). The optimal combination is that the distance between the ventilation pipe at the driver’s side and the excavation face is 5 m, the distance between the ventilation pipe at the return air side and the excavation face is 5 m, and the airflow ratio of the two pipes is 6:4. In such a case, the dust density around the driver’s operating space is 48.21 mg/m3, achieving an ideal dust control effect.

Research on Coal Volume Detection and Energy-Saving Optimization Intelligent Control Method of Belt Conveyor Based on Laser and Binocular Visual Fusion

Real-time coal flow monitoring is crucial for efficient coal mine transportation. Traditional vision acquisition devices generate two-dimensional images that are not accurately identified in the complex underground coal mine environment, such as dust, water mist, and low light. In this paper, we propose a conveyor belt coal flow detection method that integrates laser scanning and binocular vision to address this problem. Our proposed method has several advantages over traditional approaches. Firstly, we calibrate the binocular camera using Zhang’s calibration method to enhance the accuracy of the system. Secondly, we extract the centerline of the laser stripe using the grayscale center of gravity method, which improves the system’s performance in complex environments. Thirdly, we calculate the cross-sectional area of the material accurately using the trapezoidal area accumulation method, and visualize it in two dimensions based on a single frame, while the point cloud data from multiple consecutive frames are visualized in a 3D model at a realistic scale. Finally, we use the continuous multi-frame cross-sectional area to calculate the current conveyor flow, and apply the BP neural network to establish an energy-saving optimization model for the belt conveyor. We also design a PLC fuzzy controller based on fuzzy control algorithms to adjust the belt’s operating speed intelligently according to the coal flow size, achieving energy-saving operation and intelligent control of the belt conveyor. Our experiments show that our method can accurately obtain coal volume and control the belt speed of the conveyor in real-time, making it an innovative and practical solution for coal flow detection and energy-saving operation in underground coal mines.

Study on PM diffusion and distribution of trackless rubber-tyred vehicle under different driving conditions in underground coal mining environment.

Particulate matter (PM) is one of the most harmful exhaust pollutants to human health. In this study, the PM diffusion and distribution emitted by trackless rubber-tyred vehicle under different driving conditions in coal mine were analyzed with numerical simulations and field measurements. The results show that when the vehicle velocity was constant, the PM concentration of the trackless rubber-tyred vehicle decreased with increasing distance from the exhaust pipe orifice. In addition, the proportion of PM with a concentration below 10mg/m3 was the highest owing to the influences of diffusion and airflow dilution. However, when the diffusion distance is less than 3m, the PM concentration far exceeds the occupational exposure limit (10mg/m3). In this case, underground personnel should stay away from the area near and along the exhaust pipe as far as possible. With increasing vehicle velocity, the PM concentration gradient at a diffusion distance of 0-6m showed the most significant slope. Besides, the concentration fluctuation of PM was the largest and relatively high when the diffusion distance was 5-15m. Therefore, the area 15m from the exhaust gas pipe opening of the trackless rubber-tyred vehicle should be controlled. In addition, the relative errors between the measured and numerical simulation results were mostly less than 10%, which proved that the numerical simulation results were reliable.

Methane migration and explosive fringe localisation in retreating longwall panel under varied ventilation scenarios: a numerical simulation approach

Methane-based inflammable underground coal mine environment has led to catastrophic losses in the past. Migration of methane from the working seam and desorption region above and below the seam causes explosion hazard. In this study, the computational fluid dynamics (CFD)-based simulations of a longwall panel in a methane-rich inclined coal seam of the Moonidih mine in India established that the ventilation parameters greatlyinfluence themethane flow in the longwall tailgate and porous medium of the goaf. The field survey and CFD analysis revealed that methane accumulation on the "rise side" wall of the tailgate is attributable to the geo-mining parameters. Further, the turbulent energy cascade was observed to impact the distinct dispersion pattern along the tailgate. The numerical code was used to investigate the changes in ventilation parameters made to dilute the methane concentration in the longwall tailgate. Methane concentration in the tailgate outlet decreased from 2.4 to 1.5% as the inlet air velocity increased from 2 to 4m/s. The oxygen ingress into the goaf increased from 0.5 to 4.5 lps as thevelocity was increased, causing the explosive zone in the goaf to expand from 5 to 100m. Amongst all velocity variations, the lowest level of gas hazard was observed at an inlet air velocity of 2.5m/s. This study, thus, demonstrated the ventilation-based numerical method to assess the coexistence of gas hazard in the goaf and longwall workings. Moreover, it provided impetus to the necessity of novel strategies to monitor and mitigate the methane hazard in U-type longwall mine ventilation.

Dynamic Response Analysis of a Reinforced Concrete Structure in Underground Coal Mine Environment with Various Strata Conditions

Dynamic Response Analysis of a Reinforced Concrete Structure in Underground Coal Mine Environment with Various Strata Conditions

Genetic programming for prediction of heat stress hazard in underground coal mine environment

Working against nature and an uncertain environment makes underground mining a hazardous profession. Every year hundreds of miners lose their valuable lives due to mine hazards. Increasing demand for coal necessitates the extraction of coal at a higher rate. As a result, easily minable shallow coal deposits are depleting speedily, and in near future, deep-seated deposits will be left for mining by underground methods. With rising depth and deployment of high-capacity machines, increasing heat stress becomes a major hazard in the underground mine environment posing threat to the miners’ health, productivity and safety. Ignoring the effect of heat stress may lead to dangerous circumstances, even result in death. To avoid such unwanted event, it has become imperative to predict the heat stress to reduce its adverse impact in underground coal mines. Therefore, in this study a detailed field survey is conducted to collect the environmental data of three underground coal mines. Genetic programming (GP) is done to develop a relation between the environmental parameters and heat stress, by taking the mine survey data as input. A good correlation coefficient (R = 0.9816) is obtained between the GP predicted heat stress and actually measured heat stress, which indicates that GP can be effectively used to predict the heat stress in underground mines. A sensitivity analysis (SA) is done to determine the effect of input parameters on heat stress. The SA results revealed that all six input parameters have a considerable effect on the heat stress; however, the dry-bulb temperature has the highest effect (0.98) on heat stress.

Improving Workplace Environment of a Deep Underground Coal Mine with Multiseam Workings: An Alternative Approach

Improving Workplace Environment of a Deep Underground Coal Mine with Multiseam Workings: An Alternative Approach

Concurrent Solar-Illumination and Power Line Voice Communication for Indian Underground Coal Mines – An Experimental Study

The illumination systems in underground coal mines in India, generally operating in unfavourable, hazardous, and restricted environments, are badly in need of updating and revamping as they play a vital role in mine safety and productivity. Moreover, person-to-person communication in underground coal mines is very inadequate. In view of limited resources, the provision of illumination and communication using the same infrastructure forms an attractive proposition. As wireless communication is not a viable alternative because of the high attenuation profile there, wired personal communication employing the proposed DC distribution system along with LED illumination proves to be a very efficient and economical approach. The proposed technique establishes the design and implementation of the very low voltage DC (LVDC) power distribution system especially for mine illumination in consort with power line voice communication for underground coal mines. The environment of an Indian underground coal mine is simulated inside a sub-way tunnel and a suitable model designed. An experimental study is made to validate the technical aspects. The major contribution of the present work is a novel solution comprising of a low-cost mine-safe illumination system along with essential voice communication by the same underground infrastructure.

Integrated Management System for Coal Mine Locomotive Transportation

<p>Combined with the reconstruction project of underground locomotive transportation system in Guqiao Coal Mine of Huainan Mining Group, the dissertation studies the comprehensive management system of coal mine locomotive transportation. The accuracy of ZigBee wireless positioning technology is improved through Gaussian filtering to make it applicable to more complex underground coal mine environment. Frequency conversion control is used in the motor control circuit to realize real-time calculation of the running speed of the locomotive. By analyzing the control scheme of the turnout and traffic lights, the explosion isolation and essential safety control sub-station suitable for gas mine are designed. Communication platform construction of the system is realized through wireless base station of Benan mine and industrial network of coal mine. System relevant data can be uploaded to the ground dispatching center in real time, so that the scheduling staff can reasonably arrange the scheduling tasks in a timely manner. The optimized logistics management and storage management system makes the material dispatching and transportation more reasonable and scientific. Through the analysis of the running data, the construction and personnel management of the locomotives are realized.</p>

Bending Behavior of Corroded H-Shaped Steel Beam in Underground Environment

To investigate the residual bending strength of a corroded H-shaped steel beam in an underground coal mining environment, the law governing the degradation of the mechanical properties of corroded steel was first investigated through tensile testing. Subsequently, a four-point bending test was conducted on corroded H-shaped steel beams. The influence of the corrosion rate and sustained loading ratio on the residual bending performance of a corroded H-beam was investigated. The results reveal that the uniform corrosion and uneven corrosion of the steel occurred simultaneously. Additionally, pits with a small size appeared on the steel surface and the number of these pits increased with the corrosion time. Four different fracture modes were observed after the tensile test, and the yield strength and ultimate strength of the corroded steel decreased as the corrosion rate increased. In the bending test, the failure mode of the corroded H-shaped steel beam was not changed by the corrosion. The bearing capacity, stiffness, and ductility of the corroded H-shaped steel beams decreased with the increase in the corrosion rate, and the sustained loading further decreased the bearing capacity. Finally, a simple method for assessing the yield load and ultimate load of corroded H-shaped steel beams is proposed.

Mine Machine Radar Sensor for Emergency Escape

This paper presents the results of recent work to develop and trial a mine machine radar sensor for underground coal mine vehicles. There is an urgent industry need for an integrated solution to the problem of operating an underground vehicle in conditions of dense ambient dust and/or smoke, such as may occur in underground coal mines after a fire or explosion. Under these conditions, sensors such as cameras and lidar offer limited assistance due to their inability to penetrate thick dust. Thermal infrared can penetrate dust but still results in poor vision, as there is insufficient temperature contrast between the tunnel walls and the ambient air. Microwave radar sensors are able to penetrate the dust, and suitable radar sensors have been developed for use in the automation industry. Adapting such sensors for use in an underground coal mining environment was the focus of this research effort, and involved trialing a suitable sensor in dust and smoke chambers as well as trials in an underground coal mine with introduced dust. Data processing and the development of a suitable user interface were key aspects of the research. Since any sensor would have to operate in an explosive atmosphere, a related research work developed a flameproof dielectric enclosure to allow the use of the radar in the mine environment.

Design and Evaluation of the Roof Bolt Corrosion Test System in a Simulated Underground Coal Mine Environment

Corrosion of steel roof support systems can cause potential premature failure of the support, thus adversely affecting the excavation stability and rock-related safety. An in-house corrosion test system was designed and developed to test full-length roof bolts for material performance based on tensile load capacity and strength under different corrosive conditions found underground. The roof bolts tested are also used to identify the possible corrosion mechanisms that influenced the bolts’ performance over time. Initially, the most commonly used bolt material in the USA, the ASTM A615 grade 60 steel roof bolts, was tested with and without stresses in a simulated underground coal mining environment for approximately 6 months, and the results are discussed. Localized corrosion forms such as crevice and pitting were mainly observed after testing. The stressed and unstressed roof bolts with and without threads that were tested in alkaline coal mine corrosive environment for 6 months passed their load-bearing capacity as per ASTM F432 test standards. From the results, it is concluded that this test protocol could be applicable to test the material performance of different roof bolt metallurgies and coatings with desired modifications to the proposed methodology for the specific underground mine environment. This paper mainly discusses the test system and protocol and shortcomings of the system and makes recommendations based on the observations and results.

DPM flow pattern of LHD in underground mines with different ventilation conditions

Diesel-operated Load Haul Dumper (LHD) vehicles are commonly used in underground coal mines. Despite their value as utility vehicles, the main drawback of these vehicles is that they generate diesel particulate matter (DPM), a known carcinogenic agent. In this work, an attempt is made to model DPM flows generated by LHDs in an underground coal mine environment for different DPM flow and intake air flow directions. The field experiments are conducted and used to validate the computational fluid dynamics (CFD) models and used to map the DPM flow patterns. The results obtained show that if DPM and the intake air co-flow (flow in the same direction), DPM is confined predominantly in the middle of the roadway. To the contrary, if the DPM and intake air counter-flow (flow in the opposite directions), the DPM spread occurs throughout the entire cross-section of the roadway. In the latter case, the operator will be more susceptible to exposure to high concentrations of DPM. Overall, the DPM concentration decreases with an increase in the intake air velocities. For co-flow for intake air velocities of 2 m/s, 3 m/s, and 4 m/s, the DPM concentrations at 50 m downstream of the vehicles are 39 µg/m3, 23 µg/m3, and 19 µg/ m3, respectively. The DPM concentration is also influenced by the DPM temperature at the source. For the DPM temperatures of 30 oC, 40 oC, 50 oC, and 60 oC, the DPM concentrations at 50 m downstream of the source are 43 µg/m3, 34 µg/m3, 12 µg/m3, and 9 µg/m3, respectively.

Distribution characteristics and ecological risk assessment of polycyclic aromatic hydrocarbons (PAHs) in underground coal mining environment of Xuzhou

Polycyclic aromatic hydrocarbons (PAHs) in underground mining environment pose serious threats to groundwater and surface ecological environment with the migration and flow of mine water. We collected 26 underground samples from six mines of Xuzhou, including coal, mine water, and underground sludge, to measure the 16 PAHs, aiming to investigate the contamination level, distribution, and possible sources and to estimate the ecological risks of PAHs. Results showed that the concentrations of 16-PAHs (mean value) in the coal, mine water, and underground sludge were 15.87 μg/g, 0.82 μg/L, and 10.63 μg/g, respectively. There was a significant difference in the number of rings between different coals, and 2-3 ring PAHs occupied the majority of PAHs in mine water, which was determined by the Kow of PAHs. Coal and underground sludge contained more carcinogenic PAHs than mine water. And the main carcinogenic PAHs in coal were BaA, BbF, and InP, and for underground sludge were BbF, CHr, and BaP. Risk quotient (RQ) was used to evaluate the ecological risk of mine drainage, showing that PAHs in mine water were generally at medium-high risk levels. This study highlights the PAHs pollution problems in underground mining environment, particularly the potential ecological risks of mine drainage in Xuzhou.

A Search-and-Rescue Robot System for Remotely Sensing the Underground Coal Mine Environment.

This paper introduces a search-and-rescue robot system used for remote sensing of the underground coal mine environment, which is composed of an operating control unit and two mobile robots with explosion-proof and waterproof function. This robot system is designed to observe and collect information of the coal mine environment through remote control. Thus, this system can be regarded as a multifunction sensor, which realizes remote sensing. When the robot system detects danger, it will send out signals to warn rescuers to keep away. The robot consists of two gas sensors, two cameras, a two-way audio, a 1 km-long fiber-optic cable for communication and a mechanical explosion-proof manipulator. Especially, the manipulator is a novel explosion-proof manipulator for cleaning obstacles, which has 3-degree-of-freedom, but is driven by two motors. Furthermore, the two robots can communicate in series for 2 km with the operating control unit. The development of the robot system may provide a reference for developing future search-and-rescue systems.

Study on Coal Mine Gas Monitoring System Based on Arduino

Aimed at the frequency gas accident of coal mine, we designed a coal mine gas monitoring system based on Arduino microcontroller. The MQ-4 gas sensor was used to collect gas concentration, wireless ZigBee was used to transfer data of gas concentration to PC. The system can display gas concentration real-timely by LCD and use SD card to store the data. The system will send out sound and light alarm when the gas concentration overruns. Industrial tests have been carried out in Wuyang coal mine. Results show that gas monitoring system can well adapt to environment of underground coal mine and the measurement is accurate. The system is real-time monitoring and early warning. It has the characteristics of low power consumption, low cost, wireless, good market prospect.

Surface properties of pulverized coal and its effects on coal mine methane adsorption behaviors under ambient conditions

Methane adsorption characteristics of six Chinese pulverized coals were analyzed systemically. The maximum vitrinite reflectance values of the coal samples are within the range of 0.59% to 2.35% with varying maceral composition. Textures of the coal samples were characterized by N2 adsorption method at 77K. Particle surface morphologies were measured by scanning electron microscopy (SEM). The fine chemical structures on coal surface were analyzed by FTIR and Raman spectra. Methane adsorption isotherms were measured at simulated ambient environment of underground coal mine (298K and 1atm) and the Langmuir model was used to fit the experimental data. From the results, it can be seen that the nature of the isotherms varied widely for the selected six coal samples. Langmuir model is of the correct qualitative form to represent methane adsorption isotherms on the pulverized coal at ambient pressure environment. Methane adsorption parameters (VL and PL) present significant non-linear correlations with the increasing of coal maceral and proximate compositions. Ash has a negative impact on methane adsorption for all coals. About 1% increase in ash contents may reduce the methane adsorption capacities of 1.46cm3/g on the average. With the increase of maximum vitrinite reflectance values (R0,max), the Langmuir volume (VL) present first a decreasing and then an increasing trend after the maximum vitrinite reflectance values (R0,max) exceed 1.2%. However, Langmuir pressure (PL) presents a decreasing trend with the increase of the maximum vitrinite reflectance, which indicates that methane seems to show a faster adsorption rate and higher affinity to the surface of coal with higher vitrinite contents. Furthermore, coals with larger specific surface area and richer-aromatic structures always have higher methane adsorption capacities. Research results may have important significance for understanding the mechanism of coal and methane coupling interactions in hybrid mixtures.

Identifying underground coal mine displacement through field and laboratory laser scanning

The ability to identify ground movements in the unique environment of an underground coalmine is explored through the use of laser scanning. Time-lapse scans were performed in an underground coal mine to detect rib surface change after different volumes of coal were removed from the mine ribs. Surface changes in the rib as small as 57 cm3 were detected through analysis of surface differences between triangulated surfaces created from point clouds. Results suggest that the uneven geometry, coal reflectance, and small movements of objects and references in the scene due to ventilation air do not significantly influence monitoring ability. Time-lapse scans were also performed on an artificial coal rib constructed to allow the researchers to control deformation and error precisely. A test of displacement measurement precision showed relative standard deviations of 3200 pts/m2. Changing the distance and angle of incidence of the artificial coal rib to the scanner had little impact on the accuracy of results beyond the expected reduction due to a smaller point density of the target area. The results collected in this study suggest that laser scanning can be a useful, comprehensive tool for measuring ground change in an underground coal mining environment.

Design of the Coal Mining Transient Electromagnetic Receiver with A Large Dynamic Range

Considering the influence of the transient process of transient electromagnetic receiving coil on the early signals detection of the secondary field, as well as the great change and the various decay rates in different periods of the secondary field signals, which will affect the secondary field signal collection, we aim at designing a new receiver with the variable stored program control receiving coil, prefixed amplifying circuit, programmable amplifying circuit and high-performance analog-to-digital conversion circuit according to the underground coal mining environment, in which we apply the different sampling interval software and self-adaptive filtering algorithm to eliminate the influence of transient process and filter out the 50Hz power line interference, thus to increase the data collection ability and improve the detection result. The whole device is suitable for underground coal mining environment with a small volume.

Modeling the pipe umbrella roof support system in a Western US underground coal mine

Weak roof conditions in underground coal mines are a common occurrence and cause significant problems in delaying production. This work presents innovative way of using directional drilling method for roof support in weak sandstone conditions other than conventional method such as bolting, trussing, and cribbing methods. This paper presents a conceptual model of pipe umbrella roof support methods intended for employment in the underground coal mining environment over a single entry of a development section.The design methodology was evaluated by examining a case study of a western U.S. coal mine, and its specific geologic conditions. This work used extensive literature reviews and laboratory test results of the mine. Geotechnical laboratory testing was performed for a weak sandstone channel material that occurs in large extents at the mine for input into numerical models. 2D and 3D models in FLAC were developed.These models utilize beam elements embedded in the continuum model. Results from the modeling showed that bending moments vary in the embedded beams based on the pipe spacing and the diameter of the pipes. A design criterion for a pipe umbrella system was based on the developed bending moment due to undermining and the commonly used flexure formula for bending stress. A safety factor approach was used in this paper for the design of a pipe umbrella system.