2021 Vol. 47, No. 2

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Research on alarm method of coal mine extraordinary accidents based on sound recognitio
SUN Jiping, YU Xingche
2021, 47(2): 1-5. doi: 10.13272/j.issn.1671-251x.17715
<Abstract>(122) <HTML> (25) <PDF>(21)
Abstract:
Coal mine gas and coal dust explosion will produce explosive sound. Coal and gas outburst will produce the sound of coal cannon and the supports will produce squeaking and cracking sound. Rock burst will produce huge rock breaking sound and vibrations. Coal mine water inrush will produce "hissing" water sound, and a large amount of water inrush will produce water flow sound. Coal mine roof fall will produce roof cracking sound, coal rock hitting the ground sound and support damage sound. According to the characteristics of the sound of extraordinary accidents in coal mines, the alarm methods of accidents of mine gas and coal dust explosion, coal and gas outburst, rock burst, water inrush and roof fall are proposed. The characteristics of the time domain and frequency domain of each accident sound are different from the characteristics of other sounds, and the sound can be monitored in real time by mine explosion-proof sound pickup equipment and system. Therefore, accidents can be sensed and alarmed through the intelligent analysis of the sound and the analysis of the characteristic parameters of the sound frequency, amplitude and short-term energy. By monitoring and analyzing the sound intensity and other characteristics of different monitoring locations, the sequence of occurrence and the damage sequence of explosion-proof sound pickup equipment, the accident location is able to be determined. Based on the characteristics of each accident, the accident identification method of multi-information fusion analysis is proposed to reduce the sound interference of coal fall from the working face, blasting operations, coal mining equipment, excavation equipment, transportation and lifting equipment, power supply equipment, emulsion pumps, water pumps and local ventilators. The paper discusses the advantages and disadvantages of different sound pickup equipment and proposes that the microphone arrays should be used for mine sound pickup equipment. Furthermore, the paper proposes a sound recognition classifier applicable to coal mine extraordinary accidents.
Design of high-power intrinsically safe power supply based on fault current change rate
KANG Qian, XU Chunyu, TIAN Muqin, SONG Jiancheng
2021, 47(2): 6-12. doi: 10.13272/j.issn.1671-251x.2020110035
<Abstract>(119) <HTML> (16) <PDF>(19)
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In order to solve the problems of low output power, poor protection effect, and slow dynamic response speed of existing intrinsically safe power supply, a high-power intrinsically safe power supply based on fault current change rate is designed. The intrinsically safe power supply is equivalent to an EC circuit, and the short-circuit fault characteristics of the EC circuit are analyzed as follows: the spark discharge current rises rapidly at the initial stage of the short-circuit, and the current change rate changes suddenly. By detecting the value of change rate of the fault current in the circuit after a short-circuit fault, it is able to predict the fault state in advance, trigger the protection function before the fault current reaching the protection threshold set by the conventional current protection method, and cut off the output circuit at the initial stage of the short-circuit fault so as to increase the output power of the intrinsically safe power supply. The high power intrinsically safe power supply includes 2 parts: the switching power supply and the intrinsically safe protection circuit. The switching power supply adopts flyback converter structure. The core of the control circuit is UC3842, and the core of the feedback circuit is optocoupler and three-terminal regulator TL431. The intrinsically safe protection circuit limits the energy of spark discharge according to the change rate of the fault current, and mainly includes a fault detection circuit, a comparison circuit, a self-recovery circuit, a soft start circuit and a drive circuit. The performance test results of the intrinsically safe power supply prototype show that the power factor of the intrinsically safe power supply is not less than 0.96 when the AC input voltage fluctuating in the range of 90 to 265 V, the output DC voltage ripple is within 20 mV, and the efficiency of the power supply is above 85%. The short-circuit test results show that the transient output energy of the intrinsically safe power supply after a short-circuit fault is 65 μJ, which meets the design requirements.
Anomaly detection method of inspection video for coal mine underground roadway deformatio
YANG Chunyu, YUAN Xiaoguang
2021, 47(2): 13-17. doi: 10.13272/j.issn.1671-251x.17702
<Abstract>(112) <HTML> (14) <PDF>(22)
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When using intelligent video inspection technology for underground coal mine underground roadway deformation detection, the commonly used background difference algorithm cannot meet the requirements of inspection video background modeling due to the requirement of the input images having good temporal and spatial continuity. According to the characteristics of uniform speed, directional movement and periodic acquisition of video data of the deformation inspection robot in underground coal mine, an inspection video anomaly detection method is proposed. The method segments the inspection video with the inspection robot positioning information and extracts the corresponding key frames. Then the method establishes a background model based on the mean hash algorithm, and performs feature tracking on the frames in the background model to obtain correction. The method carries out a difference operation between the background model and the key frames to generate a binary mask and perform denoising and closed computing processing. Finally, the anomaly detection results are output and the key frames are updated. The experimental results show that the method can locate key frames and detect abnormal targets accurately under certain conditions, and the detection speed reaches about 50 frames/s.
Research on the application of direct current resistivity method in coal seam floor water inrush monitoring
LU Jingji
2021, 47(2): 18-25. doi: 10.13272/j.issn.1671-251x.2020080070
<Abstract>(181) <HTML> (27) <PDF>(11)
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The current researches on the application of direct current resistivity method in coal seam floor water inrush monitoring mainly focus on the resistivity response characteristics of the deformation and damage of the floor, and there are few researches on the resistivity change law of the dynamic development process of water channels. In order to solve the problem of floor water inrush in the North China coalfield, the direct current resistivity method is used to monitor the abnormal structure of floor water-bearing and water-conducting under the influence of mining. Firstly, the paper introduces the working principle of direct current resistivity monitoring system at coal working face and the automatic processing and interpretation method of monitoring data based on three-dimensional inversion of resistivity. Secondly, the paper constructs a geological model for monitoring the process of floor water inrush and carries out the numerical simulation study of the development process of floor water-bearing and water-conducting structures. Finally, the floor direct current resistivity monitoring test is carried out in the coal mine. The numerical simulation results show that the distribution range of abnormal structures of water bearing and water conducting along the survey line can be identified based on the resistivity three-dimensional inversion results. The development of abnormal structures can be inferred from the changing trend of resistivity over time. The low-resistance anomaly response gradually increases as the abnormal water bearing and water conducting structures developing upward, and the low-resistance anomaly increases gradually in the vertical direction. The results of the coal test show that the direct current resistivity monitoring successfully captures the process of water inrush from the floor of coal working face, and the time of abnormal changes in resistivity is earlier than the actual water inrush time of the working face. The low resistance response gradually increases before the increase of water inrush from the working face, which is basically consistent with the numerical simulation results. After the water inrush from the working face, the low resistance abnormality gradually weakens. The results show that the direct current resistivity method can be used for early warning of water inrush from the working face. However, determining the development height of the abnormal structure accurately requires a comprehensive interpretation combined with other monitoring methods.
Analysis of the influence of cable recovery method on long-distance power supply of fully mechanized working face
YAN Donghui, FAN Shengjun, HOU Gang, YANG Feiwen, RONG Xiang, WANG Yue, OUYANG Min
2021, 47(2): 26-31. doi: 10.13272/j.issn.1671-251x.17690
<Abstract>(182) <HTML> (22) <PDF>(9)
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The cable recovery operation will cause the cable structural deformation. Due to different recovery methods, there are different deformation states such as coil, reel and bending. Theses states cause differences in cable distribution parameters, which have influences on the main line voltage loss in long-distance power supply. The problems of existing analytical calculation of cable distribution parameters are complicated implementation process, limited extraction accuracy of distribution parameters and not being applicable to large deformation in the cable recovery process. In order to solve the above problems, this paper proposes a method to analyze the changes of cable distribution parameters in the process of cable recovery by using ANSYS and the working principle of monorail crane and cable car. The influence of cable car recovery method and monorail crane recovery method on cable distribution parameters and heat dissipation is analyzed. The influence of the cable recovery method on the long-distance power supply of the fully mechanized working face is analyzed by using ETAP. The analysis results show that the coil, reel, and bending deformation of the cable caused by the recovery operation will cause small changes in the capacitance value, the conductance value and the resistance value, and cause significant reduction of the inductance value. When the monorail recovery method is adopted, the cable deformation is greater and the inductance value per unit length is smaller with a drop of up to 29%. Compared with the cable car recovery method, the monorail crane recovery method has more advantages in terms of automation, cable heat dissipation and main line voltage loss. The changes in cable distribution parameters lead to changes in main line voltage loss. With the increase in cable recovery distance, the total voltage loss of each main line of the long-distance power supply system shows a decreasing trend as a whole. There is an increase in some parts of the main line, which influences the longest power supply distance and equipment carrying capacity.
Research status and prospect of roadheader health management
LIU Songyong, LIU Qiang
2021, 47(2): 32-37. doi: 10.13272/j.issn.1671-251x.2020080068
<Abstract>(112) <HTML> (16) <PDF>(16)
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By analyzing and processing a large amount of monitoring data, the health management technology of roadheader grasps the operation condition of roadheader dynamically and predicts various failures so as to improve the safety of roadheader operation, reducing the accidents rate and losses, and reduce equipment maintenance costs. It is pointed out that the key technologies for health management of roadheader are working condition parameter extraction, full condition health management, remaining service life estimation and remote monitoring. The paper summarizes the current research status of four key technologies, and points out that the current research on the prediction of remaining service life of complex mechanical equipment does not consider the change of working conditions, remaining at the stage of theoretical simulation and laboratory test. If the technology is applied, the variable working conditions must be considered. The research directions of roadheader health management are proposed, including roadheader weak fault diagnosis method, roadheader monitoring multi-information fusion technology, roadheader heavy and maintenance parts life estimation method, oil contamination assessment and the application of digital twin technology in roadheader health management.
Analysis of the influence of mining thickness on the stability of surrounding rock of goaf-side roadway driving
YANG Zhen, YANG Yongliang, GUO Ruirui, GUO Aiwei, ZHAO Yangyang
2021, 47(2): 38-44. doi: 10.13272/j.issn.1671-251x.2020090032
<Abstract>(61) <HTML> (11) <PDF>(8)
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At present, in most coal mines, the coal pillar width of goaf-side roadway driving is determined by the average mining thickness. However, the thickness of the same coal seam could be varied greatly by various factors during the formation process. The large variation of mining thickness in the fully mechanized working face leads to large difference of surrounding rock deformation and complex damage mechanism of the goaf-side roadway driving. In order to solve the above problems, FLAC3D software is used to establish a roadway model so as to analyze the surrounding rock deformation and damage law under the average mining thickness, and determine the reasonable coal pillar width. When the average mining thickness is 18 m, on the side of the solid coal, the peak supporting pressure in the coal is positively correlated with the coal pillar width. Moreover, when the coal pillar width is greater than 8 m, the growth rate of the supporting pressure slows down. Therefore, the reasonable coal pillar width should be 8 m. This paper studies the influence of mining thickness on the stability of the surrounding rock of goaf-side roadway driving in the context of determined coal pillar width. The results show that when the coal pillar width is 8 m, with the increase of mining thickness, the shear damage area of roof increases, and the rock deformation range and the roof subsidence increase. However, the shear damage area of two sides and the distance between the two sides decrease. When the mining thickness is less than 18 m, the peak support pressure in the coal pillar is negatively correlated with the mining thickness. When the mining thickness is greater than 18 m, the peak support pressure in the coal pillar is positively correlated with the mining thickness, but the growth is small. According to the simulation analysis results, it is concluded that the increase of mining thickness is beneficial to the control of the surrounding rock along the two sides of the goaf roadway, but not beneficial to the roof maintenance. For areas with large mining thickness, anchor rods should be added to strengthen support in time. The actual application on site verifies the reliability and validity of the research in this paper.
Research on surface deformation law of closed mines based on SBAS-InSAR
YU Hao, CHEN Bingqian, KANG Jianrong, MEI Han
2021, 47(2): 45-51. doi: 10.13272/j.issn.1671-251x.2020110044
<Abstract>(269) <HTML> (11) <PDF>(13)
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After the mine is closed, the coal and rock mass undergoes weathering degradation and strength reduction under the action of various factors such as stress, groundwater and oxygen. Moreover, the stress and bearing capacity of the mining fractured rock mass is changed, which is likely to cause secondary deformation of the surface of the goaf. Most of the existing researches focus on the monitoring of surface deformation during the mining process, while there are few researches on the monitoring of surface deformation after mine closure. To investigate the surface deformation law of closed mines, 62 Sentinel-1A images from 2015-12-21 to 2019-12-24 and small baseline subset-interferometric synthetic aperture radar (SBAS-InSAR) technology are used to obtain the surface deformation results and deformation laws of the time series within 4 years of the closed mines in western Xuzhou (including Pangzhuang Mine, Jiahe Mine and Zhangxiaolou Mine). The research results show that the maximum surface subsidence rate in three mines is -48 mm/a, and the cumulative maximum subsidence in 4 years is 178 mm. The surface of the Jiahe Mine shows subsidence followed by uplift, while the surfaces of the Pangzhuang Mine and Zhangxiaolou Mine continue to sink. The maximum surface deformation of three coal mines within 4 years is 1.70 mm/m, and the maximum curvature deformation is -0.039 mm/m2. Through interpolation statistical calculations, the surface deformations which are greater than 10 mm of Pangzhuang Mine, Jiahe Mine and Zhangxiaolou Mine are 10.5, 13.7 and 11.6 km2 respectively, and they are increasing year by year.
Optimization of electromagnetic structure of magnetic levitation belt conveyor
HU Kun, JIANG Hao, JI Chenguang, PAN Ze
2021, 47(2): 52-57. doi: 10.13272/j.issn.1671-251x.2020050068
<Abstract>(77) <HTML> (9) <PDF>(5)
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The conventional magnetic levitation belt conveyor adopts the electromagnetic structure composed of permanent magnets and electromagnets, which has the problems of easy heat generation and high current loss under the working conditions with high demand of magnetic levitation support force. To solve this problem, an electromagnetic structure based on Halbach array is proposed in this study. The mathematical model of electromagnetic structure optimization is established with the maximum magnetic induction intensity of electromagnetic structure as the objective function and the size of electromagnetic structure and the range of magnetic induction intensity distribution as the constraints. When solving the mathematical model of electromagnetic structure optimization, the Teaching and Learning Optimization (TLBO) algorithm is easily to fall into the local optimum. To solve this problem, an improved TLBO algorithm is proposed so as to enhance the diversity and search ability of the population by introducing new populations through screening and improving the learning methods in the teaching stage and mutual learning stage. The test results show that the accuracy and stability of the improved TLBO algorithm are better than the standard TLBO algorithm. The improved TLBO algorithm is used to solve the electromagnetic structure optimization mathematical model of the magnetic levitation belt conveyor. The optimal electromagnetic structure parameters are obtained as follows: the height of a single permanent magnet in Halbach array is 7 mm, the width is 9 mm, and the number of permanent magnets is 7. The experimental results show that under the same size conditions, the maximum magnetic induction intensity of the Halbach array-based electromagnetic structure is increased by 47.69% compared with the permanent magnet-based electromagnetic structure.
Research on signal processing method of mine wire rope damage detectio
WANG Hongyao, WU Jiaqi, LI Changheng, TANG Wenjin, ZHANG Yanlin
2021, 47(2): 58-62. doi: 10.13272/j.issn.1671-251x.17677
<Abstract>(84) <HTML> (18) <PDF>(8)
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When using electromagnetic detection method to detect the damage of mine wire rope, the detection signal contains a lot of noise. Moreover, there are spikes and mutations interference, which increase the difficulty of damage identification. Therefore, it is necessary to reduce the noise of the original detection signal. The commonly used Fourier transform cannot process the operating wire rope detection signal. The wavelet transform has problems of poor translation invariance and frequency aliasing, which affect the detection accuracy. This paper proposes a method for mine wire rope damage detection based on dual-tree complex wavelet transform. Firstly, a dual-tree complex wavelet high and low pass filter is constructed by Q-shift method, and the original signal is decomposed by 3-layer dual-tree complex wavelet to obtain the high and low frequency signal components. Secondly, a soft threshold method with minimax variance is used to reduce the noise of the decomposed signal. Finally, the noise reduction signal is reconstructed. A wire rope damage detection test platform is built in the laboratory environment to verify the noise reduction performance of the wire rope damage detection signal processing method based on dual-tree complex wavelet transform. The results show that the method can reduce the number of spikes and mutations in the detection signal effectively and make the signal stable. The noise reduction effect is better than that of classical wavelet transform. The method increases the signal peak value at the singularity point, which is beneficial to the subsequent feature extraction.
Experimental study on characteristics of strain and acoustic emission in the process of coal rock expansion and fracture
LI Jie, QIU Liming, YIN Shan, LIU Yang, TONG Yongju
2021, 47(2): 63-69. doi: 10.13272/j.issn.1671-251x.2020110052
<Abstract>(172) <HTML> (64) <PDF>(7)
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In order to solve the problem that there are few researches on the acoustic emission characteristics in the process of coal rock expansion and fracture, experiments on coal rock expansion and fracture are carried out to analyze the change law of strain and acoustic emission signals during the whole process of coal rock expansion and fracture. The results show that: ① the coal-rock expansion and fracture process can be divided into micro-fracture stage (Ⅰ), macro-fracture generation and expansion stage (Ⅱ) and splitting stage (Ⅲ). ② the strain evolution of coal and rock samples in the expansion process is consistent, showing the trend of 'slow change→acceleration→extreme value'. However, the acoustic emission signals of the two samples at each stage are quite different. ③ the acoustic emission ringing counts are more abundant in the coal samples at stages Ⅰ and Ⅱ, and the cumulative ringing counts increase exponentially near stage Ⅲ; while the acoustic emission ringing counts are less in the rock samples at stages Ⅰ and Ⅱ, and the cumulative ringing counts show a 'sudden increase - calm' trend near stage Ⅲ. ④ there is deformation localization in the process of both coal and rock expansion and fracture. The sudden change of strain variation coefficient and the increase of acoustic emission peak frequency range can be used as the precursor characteristics of coal rock expansion,fracture and instability. The research results can provide a basis for monitoring and early warning of coal rock fractures and other projects.
Study on the change law of temperature and mechanical properties of coal body in uncovering coal seam in low temperature freezing cross-cut
ZHOU Zhen, ZHAI Cheng
2021, 47(2): 70-74. doi: 10.13272/j.issn.1671-251x.2020070028
<Abstract>(140) <HTML> (12) <PDF>(5)
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In order to study the change law of temperature and mechanical properties of coal body in uncovering coal seam in low-temperature freezing cross-cut, U-shaped copper tubes are pre-buried and frozen with liquid nitrogen during the preparation of coal samples. The characteristics of internal and surface temperature and stress-strain changes of coal samples under different freezing times are analyzed by temperature measurement, infrared thermal imaging and uniaxial compression. The test results show that with the increase of freezing time, the internal and surface temperatures of coal samples show a decreasing trend. The lowest surface temperature of coal samples is located near the U-shaped copper tube, and the highest surface temperature of coal samples is located at the boundary of coal samples. In the compaction stage, with the increase of freezing time, the strain of coal samples gradually decreases and the compaction stage shortens. In the elastic deformation stage and yield stage, with the increase of freezing time, the maximum stress and elastic modulus of coal samples both increase.
2021, 47(2): 75-79. doi: 10.13272/j.issn.1671-251x.17668
<Abstract>(113) <HTML> (8) <PDF>(10)
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Numerical simulation study on the influence of surface air leakage in shallow thick coal seam on coal spontaneous combustion in goaf
XING Zhen
2021, 47(2): 80-87. doi: 10.13272/j.issn.1671-251x.2020100018
<Abstract>(140) <HTML> (17) <PDF>(11)
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The shallow thick coal seam in the western mine area in China usually adopts the extraction ventilation method. The surface air leakage makes the wind flow disorderly, and the oxygen of the air penetrates the goaf and interacts with the residual coal in goaf to oxidize the coal. Therefore, the coal spontaneous combustion is likely to occur, and the harmful gas such as carbon monoxide exceeds the standard, causing seriously effects on the normal mining of the mine. At present, field measurements, theoretical analysis and experimental research methods are generally used to analyze the gas concentration field and temperature field of coal spontaneous combustion in goaf caused by surface air leakage. However, the spontaneous combustion experiment of surface air leakage is relatively complex. It is difficult to use theoretical analysis and experimental research methods to obtain the influence law of surface air leakage on coal spontaneous combustion in goaf from a three-dimensional perspective.In order to solve the above problems, according to the characteristics of shallow thick coal seam in northwest China, a three-dimensional numerical calculation model is established. Combined numerical simulation and field measurement methods are used to analyze the distribution of "three zones" in the surface air leakage goaf area of shallow thick coal seam. The methods also analyze the distribution law of O2 concentration field, CO concentration field, temperature field and pressure field in goaf under different working conditions. Moreover, the field validation is carried out by the ZD5 coal mine fire multi-parameter monitoring device. The results show that the distribution of the "three zones" and the O2 concentration field in goaf are greatly affected by the surface air leakage. It is found that O2 is easily accumulated at the top of the goaf, which changes the gas flow field distribution in goaf. The concentration range of high volume fraction O2 (volume fraction 18%-23%) in goaf is 0-270 m along the strike direction of the goaf and 3-20 m along the vertical direction of the goaf. In particular, O2 is sufficient in the range of 0-80 m along the strike direction of the goaf and 3-8 m along the vertical direction of the goaf. In this area, there is a certain amount of residual coal and heat is not easily dissipated, raising the risk of coal spontaneous combustion. The pressure at the corner of return air roadway in goaf is the smallest, -10 Pa, the pressure at the return air roadway outlet is the lowest, and the pressure at the air inlet is the highest. The pressure gradually increases along the inclined direction, the vertical direction and the strike direction. The temperature distribution is similar to the CO distribution in goaf. The goaf floor is little affected by the air leakage from the surface, but largely affected by the corner of the intake air roadway of the working face. The heat accumulation and CO accumulation are basically the same as the situation of no air leakage. From the middle of the goaf, the temperature and CO are mainly affected by the surface air leakage, presenting an "O" ring distribution. At the top of the goaf,the temperature and CO reach maximum values at the junction of each fracture zone and the goaf, then decrease along both sides. The maximum value appears at the junction of the deepest fracture zone and the goaf.
Buck circuit fault diagnosis method based on digital twi
XIA Ling, JIANG Yuanyuan, ZHANG Jie, SUN Quan, WEI Nianwei, ZHANG Shuting
2021, 47(2): 88-92. doi: 10.13272/j.issn.1671-251x.2020070063
<Abstract>(415) <HTML> (14) <PDF>(16)
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In order to address the problems of large calculation and low accuracy of Buck circuit fault diagnosis methods, a buck circuit fault diagnosis method based on digital twin is proposed. Firstly, the digital twin model of Buck circuit is established by Matlab/Simulink software platform, and the initial parameters of the digital twin model are set according to the nominal values of Buck circuit components.Secondly, the acquired Buck circuit output voltage signal and operation state are mapped into the digital twin model, and the objective functionsare established according to the digital twin model and the output voltage of Buck circuit. The Levenberg-Marquart algorithm is used toiterate and optimize the objective functions to achieve the digital twin modelupdate so as to realize the parameter estimation of Buck circuit components. Finally, the estimated parameters obtained from the digital twin model are compared with the nominal values of Buck circuit components. When the difference between the two exceeds 20% of the nominal values, it is indicated that the component is invalid and the Buck circuit fault diagnosis is obtained. The experimental results show that the proposed method has high estimation accuracy and diagnostic reliability for Buck circuit component parameters.
Design of pipeline flow meter based on ultrasonic time difference method
MA Jian, LI Zefang, ZHANG Desheng
2021, 47(2): 93-97. doi: 10.13272/j.issn.1671-251x.2021010022
<Abstract>(93) <HTML> (18) <PDF>(11)
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The traditional gas flow meter used in gas pipelines in coal mines has problems like blocking failure. The flow meter based on ultrasonic time difference method has high measurement accuracy and good repeatability of measurement results. However, it is not suitable for gas extraction pipeline flow measurement. Moreover, it is difficult to design ultrasonic driver circuit and signal processing circuit separately. Based on the characteristics of coal mine gas extraction pipelines, a pipeline flow meter based on ultrasonic time difference method is designed. In the context of fixed propagation distance, the propagation time of ultrasonic waves emitted by ultrasonic transducer in the fluid is functionally related to the gas flow rate. The product of the flow rate and the cross-sectional area of the pipeline is the flow, hence the pipeline gas flow is indirectly obtained. The pipeline flow meter uses a low-power microprocessor STM32F103 as the core control element, and uses the automatic differential flight time measurement method inside the time-to-digital conversion chip MAX35104 to calculate the ultrasonic wave downstream and upstream flow propagation time. The gas flow rate, instantaneous flow and cumulative flow are calculated through the propagation time. The test results show that the maximum absolute error of the pipeline flow meter based on ultrasonic time difference method is 0.15 m/s and the maximum repeatability error is 0.17%. The performance meets the requirements of level 2 accuracy in JJG 1030—2007 Verification Regulations Ultrasonic Flowmeters and also meets the requirements of the ultrasonic wind speed sensor basic error requirements in MT 448—2008 Wind speed sensor for mine.
Optimal measures for gas control on fully mechanized working face of close-distance coal seam group
XUE Yanping
2021, 47(2): 98-103. doi: 10.13272/j.issn.1671-251x.2020060055
<Abstract>(125) <HTML> (13) <PDF>(7)
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Compared with single coal seam or other coal seam group, the mining process of the close-distance coal seam group is more likely to be affected by the stress of the adjacent seam. Moreover, the gas is more likely to gush into the coal seam through the developed fissures, causing gas accumulation on the working face of the mining seam. The existing gas control research for close-distance coal seam group mainly focuses on the determination of single measure parameters and effect analysis, without in-depth research of the relationship between gas management measures in time and space. The researches on the optimal combination of comprehensive gas management measures, the basis for determining specific parameters and the effect analysis after the measures being taken are not sufficient enough. In order to solve the above problems, taking the 81403 fully mechanized working face of No.1 Coal Mine of Yangquan Coal Industry (Group) Co., Ltd. as the research object, the paper analyzes the stress distribution and evolution process of mining under the conditions of close-distance coal seam group through numerical simulation. The research studies the overlying rock destruction and fissures development change law, and proposes that the main sources of gas on the 81403 fully mechanized working face are coal seam desorption gas, pressure relief gas in upper adjacent coal seam and goaf gas, etc. Based on the different gas emission sources and characteristics, the paper proposes the gas extraction measures of bedding pre-extraction + high extraction roadway+high borehole+buried pipes in the extraction area. Before mining, pre-extraction is applied to reduce the amount of coal seam desorption gas. High extraction roadway and high borehole are used to deal with gas gush from adjacent coal seam. Buried pipes are used to control local gas accumulation in the upper corner. The measures form a comprehensive management system in time and space so as to achieve the purpose of gas control. Practical application results show that the gas extraction rate reaches 89.9% on the working face, and the gas volume fraction of the return airway and upper corner is kept below 1%, ensuring the safe mining of the working face.
Design and implementation of clock synchronization scheme for mine distributed acquisition system
AN Sai
2021, 47(2): 104-108.. doi: 10.13272/j.issn.1671-251x.2020090005
<Abstract>(112) <HTML> (15) <PDF>(12)
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Due to its accuracy and application limitations, single clock synchronization technology can not meet the high-precision and high-reliability clock synchronization accuracy requirements of the mine distributed acquisition system. In order to solve the above problems, a three-level coordinated clock synchronization scheme based on Beidou+IEEE 1588V2+local backup clock is proposed. The T600-BDGOCXC Beidou timing server is selected to be deployed on the ground as the master clock to provide absolute clock with nanosecond precision for the system. The STM32F407+DP83848 and PTPd protocol stack are used to implement the acquisition nodes that support IEEE 1588V2 protocol. The absolute clock of Beidou is synchronized to each acquisition node through the mine ring network. The local backup clock is implemented by using the STM32F407 internal RTC (Real-time Clock), which provides each acquisition node with time stamp initial value with second-level precision, so that each acquisition node can synchronize with the master clock in the shortest time. The test results show that the clock synchronization precision is 162 ns after 1 min when the Beidou timing server and the acquisition nodes are directly connected through the switch. The clock synchronization precision is 565 ns when the Beidou timing server and the acquisition nodes are connected through the three-level switch. When the Beidou timing server fails, the acquisition node with high priority is upgraded to be the master clock and provides timing for the remaining acquisition nodes with strong reliability.
The practice of rock burst disaster prevention and control in the stress concentration area of Zhangshuanglou Coal Mine
ZHANG Lei
2021, 47(2): 109-115. doi: 10.13272/j.issn.1671-251x.2020080010
<Abstract>(73) <HTML> (14) <PDF>(9)
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The current pressure relief blasting methods are only for the coal seam roof, and there are few researches on the roof-coal-floor synergistic pressure relief blasting management, especially for the rock burst disaster prevention and control in the hard and thick sandstone roof overburden area. In order to solve the above problems, taking the 74101 working face of Zhangshuanglou Coal Mine of Jiangsu Xukuang Energy Co., Ltd. as the engineering background, this study analyzes the rock burst disaster inducing factors from the aspects of mining layout, coal rock burst tendency and sandstone overburden area stress concentration degree. This study reveals the reasons for the rock burst disaster induced by the sudden instability of coal rock mass. It is proposed that the local high stress concentration, caused by the geological conditions such as abnormal sandstone overburden area of roof, fault geological structure and hard fine sandstone of floor, is the main cause of rock burst disaster. The CT inversion technology of mine rock burst vibration wave is used to accurately detect the high rock burst risk area of 74101 working face: the transportation lane side is 75 m along the roadway and the extended working face is 60 m elliptical area; the track lane side is 60 m along the roadway and the extended working face is 80 m elliptical area. Aiming at the targeted high stress concentration areas, a precise "roof-coal-floor" synergistic pressure relief blasting technology is proposed to relieve pressure in the rock burst risk area of 74101 working face and adopt micro-seismic monitoring methods and on-site observation methods to evaluate the effect of pressure relief and rock burst prevention. The results show that after pressure relief blasting, the daily cumulative energy of mine rock burst in the hard and thick sandstone overburden area of 74101 working face is reduced from 1.57×104 J to below 104 J and the vibration frequency is reduced by 50%. Moreover, the characteristics of mine rock burst are low energy and low frequency, and rock burst risk is significantly reduced. Therefore, it is verified that the synergistic pressure relief blasting technology is applicable to the prevention and control of rock burst disasters in the hard and thick sandstone overburden area of Zhangshuanglou Coal Mine.
Construction practice and key technologies of intelligent mine
REN Wenqing, GAO Xiaoqiang
2021, 47(2): 116-120. doi: 10.13272/j.issn.1671-251x.2020100042
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Abstract:
At present, there are more researches on the concept and development plan of intelligent mines, and less researches on the intelligent construction results and key technologies. Based on the 5-layer technical structure of intelligent mine construction, taking the intelligent construction of Daliuta Coal Mine as an example, the paper discusses the intelligent construction and effectiveness in terms of fully mechanized mining, excavation, transportation, power supply, water supply and drainage systems. A total of about 100 fixed mine positions are canceled, and more than 200 operators are reduced. The construction helps to reduce the labor costs by 40 million yuan/a, save the industrial water and electricity consumption by 30%, improve the equipment utilization by 5%, and increase the total workforce efficiency by 10%. It is pointed out that the key points of intelligent mine construction are broadening the network channel, unifying the interfaces of various subsystems, ensuring the associated equipment safe and reliable, and hiring professional personnel teams. This paper summarizes the current difficulties in the intelligent mine construction and discusses the key technologies to be tackled. The technologies include automatic coal cutting, personnel detection of mobile equipment, wireless sensing, centralized refueling, intelligent security inspection at the mine entrance and unmanned driving.

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