In order to increase the detection accuracy of coal dust and reduce the maintenance of the coal dust concentration sensor, in this paper, the electrostatic sensor of the plate-ring detection electrode was developed for the detection of coal dust concentration. Through the establishment of the three-dimensional finite element model of the plate-ring detection electrode and the simulation results of COMSOL, the superiority of the plate-ring detection electrode was demonstrated, and the basis for the structure design of the plate-ring detection electrode was provided. The plate-ring detection electrode and the processing circuit of the tiny electrostatic induction signal were designed. Electrostatic induction dust concentration sensor with plate-ring detection electrode was developed. Experiments and data analysis proved that the 1.5-order central moment of the electrostatic induction signal had a high degree of fit with the dust concentration value. The mathematical relationship between the electrostatic induction signal and the dust concentration was determined. The detection error of coal mine dust concentration sensor based on plate-ring detection electrode did not exceed 10%.

基于国内外矿井避难硐室环境控制技术的研究现状,比较了国内外关于避难硐室环境控制条款规定,探讨了环境控制参数的允许范围,并从建设成本及人员安全角度出发,分析了目前针对避难硐室空气品质控制技术和温度控制技术的不足,指出了未来避难硐室环境控制技术的研究方向:①制订合理的环境参数允许范围;②基于矿井压风的CO浓度多种控制技术的协同作用;③CO2 被动化学吸附技术;④多重复合控温技术.

The accurate determination of the height of a fractured zone is vital in preventing water inrush and reducing the risk of disasters. However, understanding the fractured zone height evolution process remains a significant challenge in mining activities. In this study, the caving characteristics of overlying strata were investigated experimentally to determine the height of a fractured zone based on the geological conditions of No. 4308 Face ChengZhuang Coal Mine, China. The fractured zone heights were compared with those measured using physical experiment, 3DEC simulation, and a time-dependent energy model, and their results were verified against one another. The gas drainage method was used to validate the mining-induced height evolution and boundary. The results showed that the height of the fractured zone exhibits a stepped increasing trend. It increases slowly at the beginning of strata collapse and when mining-induced fractures approach the key stratum. The key stratum considerably affects the evolution of fractured zone height and may also influence the destressed zone boundary in the horizontal direction. In the destressed zone with a lower height, longwall mining rapidly affects strata, and the gas stored in lower overlying strata, which is unstable due to the movement of strata, is released rapidly. The cross-measure boreholes can drainage more gas in the middle of the mining-induced fractured zone because of the relatively stable strata and penetrating fracture. Overall, the results provide references for assigning cross-measure boreholes and a high gas drainage gallery to ensure safe conditions in a coal mine.

A decrease in the viscosity of a solution of sodium carboxymethyl cellulose (CMC-Na) is a commonly encountered problem in coalbed methane (CBM) pressure measurement with an apron CMC-Na sealer and capsule CMC-Na sealer. Studies have shown that the factors that can reduce the CMC-Na solution viscosity include the hydrogen ion concentration index (pH), the environmental temperature, the drilling and sealing time, and the high-pressure CBM gas environment. In this study, a homemade instrument for measuring the viscosity of a CMC-Na solution under high pressure was used to determine the change laws of the viscosity under different conditions, and comparative tests were performed to investigate various factors affecting the viscosity. The best solution for stabilizing the viscosity was determined and effectively applied at a coal mine site, where an overall improvement in the viscosity behaviour was observed.

Coal is affected by the concentrated stress disturbance of mining, the disturbance of drilling hole formation, and the concentrated stress of coal shrinkage and splitting of gas desorption from the hole wall; these result in a large number of secondary cracks that collect and leak gas. As a result, it is difficult for the coal seam sealing process to meet engineering quality sealing requirements, which results in problems such as low gas concentration during the extraction process. In this paper, based on the analysis of coal pore and fissure characteristics, and in view of the current situation of gas drainage and sealing in this coal seam, combined with the existing grouting and sealing technology, it is proposed to use pressure grouting and sealing to realize the sealing of deep coal bodies in the hole wall. According to the field conditions, the experimental pressure sealing parameter index is as follows: theoretical sealing length L1 = 9.69 m, the sealing length L2 = 13.98 m is verified, and the final sealing length is determined to be 15 m; the sealing radius is determined to be 0.6 m; the cement slurry was prepared on site with a water: cement ratio of 2:1; PG = 0.43 MPa was calculated; the range of the slurry diffusion radius R was 93.4–176.6 cm; the grouting pressure was determined to be 0.516 MPa. Field application practice has proved that: (1) Under the same drilling parameters and sealing parameters, the gas drainage effect of drilling with pressure sealing is 2.3 times higher than that without pressure sealing; (2) Using traditional sealing technology for drilling holes, the gas extraction concentration is far lower than the sealing operation effect of using the pressure sealing process; (3) Reasonably extending the length of the gas extraction drilling and sealing is a basic guarantee for realizing a substantial increase in the gas extraction concentration; (4) Sealing with pressure leads to a reliable and stable hole process.

In order to further investigate the impacts of the water environment on the mechanical properties of rocks for an engineering project, taking the water-rich conditions in a coal mine as the engineering background, a series of tests were conducted, including the uniaxial compression test, the conventional triaxial compression test, and the constant axial pressure test on the cementitious sandstone. This was conducted along with the establishment of a multi-linear strain softening constitutive model. According to the tests, the following conclusions can be drawn. Firstly, as the water content increases, the weakening effect of water on the rock mass was obvious. Under various stress paths, the water weakened the rock body to various degrees. In other words, the weakening effect of water on the rock mass was either inhibited or promoted under different stress path conditions Secondly, under various stress paths, the turning point strength and strength variance rate of the rock mass’ mechanical properties decreased linearly with the increase of water content. This further proves that water has a weakening effect on the rock mass, showing that the failure of the specimen changes from brittleness to ductility. Thirdly, the test sample demonstrated different types of damages including the tensile failure, transformation from tensile-shear composite failure to shear failure, and expansion failure under three stress path conditions. In addition, the unloading process demonstrated some dynamic failure characteristics. The research aims to provide some foundational insights for the scientific design and safe construction of the mine and other underground engineering, especially rock mass engineering in the multi-water environment.

Coal mine methane (CMM) emissions from underground coal mines is becoming a global problem since it produces greenhouse gas contributing to global warming. It is critical to reduce low-concentration CMM(LCM) and ventilation air methane (VAM) emissions, which has become the focus to be solved urgently. One of the methods is utilizing this VAM as a fuel by mixing of CMM with the help of the porous burning system. In order to optimize the performance of a porous burning system composed of alumina particles, a series of complex porous media burners composed of two layers of alumina particles were proposed, after which a laboratory experimental system based on these burners was built. The lean-burn limits, lean-burn stabilization temperature and lean-burn fluctuation patterns of the burners built in this study were tested and reported in this paper. Results show that cylindrical burner with equal segment length of 3 mm diameter alumina particles at the upstream and 6 mm diameter alumina particles at the downstream is suitable for lean-burn with low flow rate, and cone burner with equal segment length of 3 mm diameter alumina particles at the upstream and 6 mm diameter alumina particles at the downstream is more suitable for lean-burn with high flow rate and low methane concentration, and the lean-burn limits for cone burner with volume methane concentration of 1.5% is obtained, which is the lowest lean-burn limit have reported at present.

Air quality and thermal environment of mine refuge chamber (MRC) are very important to determine the physical safety of refugees. Accurately assessing the environmental load and taking reasonable measures are critical to achieve the environmental control goals of MRC. In order to evaluate the metabolic parameters of occupants and the effectiveness of environmental control measures in a MRC, in this research, 50 adult men entered a MRC laboratory for an 8-h test. During the test, the compressed O2 cylinders and air purification devices were used to ensure the indoor air quality. The possibility of using chemical adsorbents to passively scrub CO2 and the performance of dehumidification by mine compressed air (MCA) were also investigated by simulation experiments. The results indicated that: (1) The per capita metabolic rates of O2, CO2 and heat during the refuge process are 0.34-0.37 L/min, 0.34 L/min and 117-128 W, respectively. (2) When Ca(OH)2 particles are used as CO2 adsorbent, the air purification device has both dehumidification and CO2 scrubbing functions, and three air purification devices could make the CO2 concentration below 0.8% with the relative humidity below 76%. When Ca(OH)2 particles are packaged to passively scrub CO2, the amount of adsorbent may increase significantly. (3) When MCA is used for dehumidification in a MRC, the air volume of 0.15 m3/min per capita could maintain the relative humidity close to 60%. (4) In the early stage of disaster avoidance, the indoor ambient temperature rises rapidly within 1 h followed by a slight increase.

研究岩石的热破裂和损伤机制在高放废物地质处置工程中越来越受到重视.以我国甘肃北山的高放废物处置库的花岗岩岩样为研究对象,采用低场核磁共振系统、MTS岩石力学试验机、倒置镜像光学显微镜对重点预选场址花岗岩的热稳定性开展室内试验研究.研究发现:①核磁共振T2谱图在0～ 400℃没有明显变化,当温度高于500℃时,T2谱图振幅显著增大且向右大幅移动,T2谱面积与孔隙率在加热过程中呈现幂率关系;②峰值应力随着温度和孔隙度的增加以幂律关系降低;③通过核磁共振成像(MRI)发现,温度低于500℃时质子密度分布均匀且没有发现明显的质子密度簇,说明岩石内部结构稳定.当温度高于500℃时,晶体裂纹和边界裂纹的产生致使出现大量的高质子密度区域,并随着温度持续升高质子密度高的微小区域融合成大的连通区域;④花岗岩岩样在不同温度条件下的核磁成像像素的概率密度函数都服从对数正态分布,当温度超过500℃,概率密度函数整体向右转移;⑤通过显微结构观察,500℃时在长石晶间和长石晶粒与石英晶粒间有边界裂纹产生,并在晶体内部出现少量的穿晶裂纹,当试样温度加热到600℃时,超过了石英α/β相变点,石英颗粒产生大面积透明状穿晶裂缝,同时伴随着明显的穿晶网络.

Abstract Low‐concentration gas is one of the most realistic and reliable supplementary or alternative energy sources of conventional natural gas, which has a wide range of applications. However, this gas is flammable and explosive during pipeline transportation and easily causes an explosion. In order to achieve safe transmission, the explosion characteristics and propagation law of low‐concentration gas are systematically studied through a large‐scale pipeline experimental system. We found that the peak pressure of low‐concentration gas explosion in pipeline has a quadratic function relationship with the propagation distance. Moreover, the peak pressure of gas explosion initially decreases from the explosion source, and then a turning point appears after a certain distance of propagation, which is followed by a sharp increase of peak pressure of gas explosion. The explosion pressure becomes maximum at the outlets of a pipeline. The arrival time of explosion flame is logarithmically relevant to propagation distance, while the speed of flame propagation gradually increases along with the increase of propagation distance. The flame propagation is faster at the exit point. In addition, the diameter of pipeline has also an important influence on the explosion propagation process of low‐concentration gas. So, the larger the diameter, the higher the explosion pressure. The explosion pressure of DN700 pipeline is obviously higher than that of DN500, and the explosion pressure rises faster; the speed of flame propagation of gas explosion in DN700 pipeline is also higher than that in DN500 pipeline. This study provides a theoretical reference for the prevention and control of explosion accidents in low‐concentration gas pipelines.

Simultaneous Localization and Mapping (SLAM) is an effective technique in the field of robot location and navigation. However, when the existing SLAM algorithm is applied in harsh terrain, such as the terrain found in coal mines, accuracy suffers, and on-line adaptive adjustment capability is poor. Furthermore, the system suffers from low robustness and is susceptible to random noise. In order to solve these problems, we propose an innovative Strong Tracking Second Order Central Difference SLAM (STSOSLAM) algorithm that combines a Strong Tracking Filter (STF), a Second-Order Central Differential Filter (SOCDF), and a Particle Filter (PF). The new algorithm utilizes the second order sterling interpolation formula to deal with the nonlinear system problem using the Cholesky decomposition technique, which propagates directly by using the covariance square root factor in the SLAM probabilistic estimation. This technique not only guarantees the positive definite property of the covariance matrix, but also reduces the truncation error of local linearization. In addition, STF is introduced into the algorithm. It updates every sigma point using an adaptive algorithm and obtains optimized filter gain through the STF online adjustment factor and suppresses uncertain noise and the influence of initial value selection. Through simulation and experiments, STSOSLAM algorithm shows much better performance in terms of estimation accuracy, robustness and reliability than FastSLAM2.0 and Central Difference FastSLAM (CDFastSLAM) algorithms, establishing the foundation of applying the STSOSLAM algorithm in the harsh terrain of coal mines.

This paper investigated the dynamic coupling heat transfer characteristics of rock and air in a Mine Refuge Chamber (MRC) under ventilation. In the current work, a comprehensive fifty-person MRC model combining human-body heat sources and ventilation is established, the proposed model is validated against available experimental data with deviation less than 4%. Furthermore, sensitivity analysis is performed to investigate the influence of several control parameters such as heating rate, ventilation and wall area in a MRC through using numerical simulation. Results indicated that: (i) the heat transfer process in a MRC will reach a stage of air temperature slow increase (ATSI) in less than 0.5 h. The air temperature rises linearly with the square root of time during the ATSI stage; (ii) for a MRC built in a sandstone seam with an initial rock temperature of less than 27 degrees C, the average air temperature will not exceed 35 degrees C in 96 h when the ventilation volume rate is 0.3 m(3)/min per person; (iii) the rate of temperature rise in MRC is proportional to the rate of heat generation, but it is inversely proportional to the thermal conductivity, density and thermal capacity of the rock, as well as the ventilation volume rate and the wall area; (iv) an empirical correlation for the MRC average air temperature is developed while the supply air temperature equals to the initial rock temperature.

A combined experimental and numerical study was performed to improve the performance of the ventilation system in a mine refuge chamber (MRC). In the experiment, CO2 cylinders and dispersion pipes were used to simulate the CO2 release of 50 people, and 0.1 L/min per person of fresh air was provided by an air compressor. A new analytical model for a 50-person MRC was proposed and validated against the experimental data. Sensitivity analysis was carried out to investigate the effects of several control factors. The results indicated the following: (1) The ventilation system layout has a significant influence on the CO2 concentration distribution in an MRC, while the uniformity of the CO2 concentration distribution in the MRC may not be effective with increased number of air inlets. (2) Under a well-arranged ventilation system in the 50-person MRC, the average CO2 concentration can be controlled at less than 0.5 % with a ventilation rate of 0.1 m(3) /min per person, and less than 0.2 % with a ventilation rate of 0.3 m(3) /min per person. (3) A quantitative correlation exists between the CO2 concentration and ventilation volume rate, as well as the CO2 release rate, for an MRC under a well-arranged ventilation system. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

In order to study the pore-forming process of the rotary jet and the particle size distribution of the coal cinder after breaking coal. According to the theory of maximum tensile strain and the theory of maximum shear stress, the failure criterion of coal under shear stress and tensile stress is obtained. Based on the strength of 3.65 MPa, elastic modulus of 185 MPa, size of 1 m×0.8 m×0.8 m coal similar material, the coal breaking experiment under different pump pressures was carried out; the coal cinder from broken coal was collected and the particle size analysis experiment was carried out. The results show that the external drilling jet breaks the coal drilling speed and the pore diameter increases with the increase of the pump pressure. In the pore-forming process, the forward jet breaks the coal, the backward jet reams, and the failure of coal is mainly caused by tensile stress and shear stress. The coal cinder particle size distribution is from 84 μm to 1 061 μm. The larger the pump pressure, the smaller the particle size of the coal cinder.

With mining technology and mechanization degree being improving, fully mechanized caving mining technology (FCM) has become a main method for thick coal seam extraction in China. However, roof-coal caving characteristics in turn restrict its recovery efficiency, especially for the coal seam with complicated structure (CCS), that is, the coal seam comprises hard or soft coal and gangue. In order to explore the key factors influencing the roof-coal caving and recovery characteristics, related research work has been conducted as follows: firstly, a mechanical model of CCS has been established, which indicates the strength of the coal and gangue will directly affect the roof-coal recovery. Meanwhile, based on the geological settings of Qinyuan coal mine, numerical simulation on roof-coal caving law under different thicknesses of hard or soft coal and gangue has been performed using UDEC software. The results show that the maximum principal stress will increase with the increase of mining depth, making the roof-coal to break easily. Furthermore, the range of the plastic zone of the top coal and the damage degree of the top coal increase with the increase of mining depth. Physical modeling results show that when an extraction-caving ratio is 1, the number of times the coal arch forms is 0.43 at every caving, up to a maximum of 3; the number of times coal arch forms with an extraction-caving ratio of 2 is 4.65 times larger than that with an extraction-caving ratio of 1. The probability of coal arch formation with an extraction-caving ratio of 3 is minimal, about 0.4, which is due to that the arch span is large and the curvature is small, so it is difficult to form a stable arch structure. According to the mechanical characteristics of roof-coal in Qinyuan coal mine, deep-hole blasting technique has been used to reduce the fragments of roof-coal crushed. The results show that this technique can effectively improve the recovery of roof-coal.

Coalbed methane (CBM) production in the overlying strata of coal reservoirs is often hampered by the unknown distribution of the mining-induced fractures. Mining-induced fractures are CBM migration pathways in the fractured overlying strata, and the excavation of coal seams within a mine causes the CBM in adjacent coal seams to flow into the overlying strata. The mining-induced fracture field in the overlying strata is the best place from which this CBM is drained. Here, to better understand the distributions of vertical and horizontal fractures caused by excavation, we propose a novel approach to quantify the dimensions of vertical and horizontal fractures in fractured zones. In addition, we demonstrate that there are negligible changes in the dimensions of horizontal fractures and great changes in the dimensions of vertical fractures when there is an increase in the height of the fractured zone. We further demonstrate that mining-induced angles mainly concentrate on 0°–10°, 50°–70°, 110°–120° and 170°–180°, and larger width fractures exist in both sides and top due to the de-stressed effect and fractures in the middle of model close under mining-induced stress. The approach described here could be used to improve the accuracy of cross-measure borehole positioning and the efficiency of CBM drainage.

煤气化工艺生产中涉及的危险有害介质可能导致安全事故,造成人身伤害和财产损失.为更好的辨识、评估煤气化企业存在的安全生产风险及其危险程度,论文采取模糊综合评价理论,选取典型的煤气化工艺——某煤气化企业煤制甲醇生产过程为研究对象,构建合理的安全风险评价指标体系,并对某煤气化企业进行模糊综合安全评价.

以晋城矿区厚覆盖层下开采引起的地表移动为研究对象,在采煤工作面上方地表走向和倾向布置混凝土灌注测点,采用GPS快速静态定位测试与动态测试相结合的方法,对工作面回采后地表移动量进行了监测.采用MATLAB软件对地表移动数据进行分析,运用概率积分法得到工作面上方走向和倾向地表下沉曲线.结果表明,该区域内走向下沉最大值达4.692 m,倾向最大下沉值为4.043 m,充分采动后埋深采高之比与下沉量呈负相关关系;概率积分法对该区域内地表沉降预测较为准确,走向平均相对误差为4.7％;该区域地表下沉活跃期约130 d.

This paper proposes an innovative simultaneous localization and mapping (SLAM) algorithm which combines a strong tracking filter (STF), an unscented Kalman filter (UKF), and a particle filter (PF) to deal with the low accuracy of unscented FastSLAM (UFastSLAM). UFastSLAM lacks the capacity for online self-adaptive adjustment, and it is easily influenced by uncertain noise. The new algorithm updates each Sigma point in UFastSLAM by an adaptive algorithm and obtains optimized filter gain by the STF adjustment factor. It restrains the influence of uncertain noise and initial selection. Therefore, the state estimation would converge to the true value rapidly and the accuracy of system state estimation would be improved eventually. The results of simulations and practical tests show that strong tracking unscented FastSLAM (STUFastSLAM) has a significant improvement in accuracy and robustness.