2023 Vol. 49, No. 2

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Academic Column of Editorial Board Member
Research on the safety threshold of radio wave explosion-proof
SUN Jiping, PENG Ming, PAN Tao, ZHANG Gaomin
2023, 49(2): 1-5. doi: 10.13272/j.issn.1671-251x.18072
<Abstract>(1206) <HTML> (135) <PDF>(80)
Abstract:
The powerful radio waves can ignite explosive gases. Therefore, it is necessary to reasonably set the radio wave explosion-proof safety power and energy threshold emitted by the radio transmitter to limit the radio wave power and energy emitted by the radio transmitter. The radio wave explosion-proof safety power and energy thresholds specified in European Standard CLC/TR 50427:2004 Assessment of inadvertent ignition of flammable atmospheres by radio-frequency radiation-Guide are the ignition power and energy threshold. The national standard GB/T 3836.1-2021 Explosive atmospheres-Part 1: Equipment-General requirements and the international standard IEC 60079-0:2017 Explosive atmospheres-Part 0: Equipment-General requirements directly cite the radio wave explosion-proof safe power and energy threshold specified in the European standard CLC/TR 50427:2004. But the continuous radio wave explosion-proof safe ignition power threshold is incorrectly modified as the product of the effective output power of the transmitter and the antenna gain. This leads to the reduction of the continuous radio wave explosion-proof safe transmission power threshold. Under certain transmission attenuation and reception sensitivity conditions, the wireless transmission distance is reduced. This is not conducive to the promotion and application of mine wireless communication system and personnel positioning system. Therefore, the safe power threshold for continuous radio wave explosion-proof specified in national standard GB/T 3836.1-2021 and international standard IEC 60079-0:2017 should be the ignition power threshold, not the product of the effective output power of the transmitter and the antenna gain.
Study on the technical specification of communication interface and protocol for intelligent mine
DING Zhen, SUN Jiping, ZHANG Fan, WANG Peng, HU Eryi, DENG Wenge, GAO Jing, ZHENG Yaotao, WANG Bo, GAO Qiuqiu, LI Ximin, QIAN Haijun, LIU Jianhua, QIAO Shaoli, BAO Zhen, YANG Yongsheng, YANG Zhenyu, LI Yuxue, LI Yuhan, SHAO Guangyao
2023, 49(2): 6-13. doi: 10.13272/j.issn.1671-251x.18061
<Abstract>(971) <HTML> (63) <PDF>(114)
Abstract:
At present, there are some problems in the construction of the intelligent mine, such as the non-uniform interface protocol and the formation of new "information island". They lead to the difficulty of data fusion and sharing in mines and the difficulty of realizing the high-quality development of intelligent mine. It is pointed out that the key problem of mine intelligent construction lies in the lack of standardized and unified data acquisition, transmission and sharing standards. According to the core specification, application specification, and operation and maintenance specification, the technology system of intelligent mine communication interface and protocol is designed. The communication interface and protocol model of intelligent mine is proposed. The perception layer, transmission layer and application layer of the model are defined. The model of intelligent mining equipment is constructed, and the communication interface is described formally. The intelligent mine data is divided into perception data, text data and audio-visual data. The message structures of the three kinds of data are defined. According to the current mining equipment, technology application and development direction, the intelligent mine data acquisition modes are divided into equipment direct acquisition, protocol conversion acquisition, and system transfer acquisition. The application scenarios of three data acquisition modes are pointed out. The acquisition and transmission process of perception data, text data, and audio-visual data are described. The technical specification of intelligent mine communication interface and protocol covers the whole process of mine data fusion communication. It provides unified interface mode and communication protocol specification for intelligent mine data acquisition, transmission, fusion and sharing. And it realizes interconnection and intercommunication among various systems of the mine.
Research on precise positioning technology and optimization method of mine moving targets
ZHENG Xuezhao, YAN Ruijin, CAI Guobin, WANG Baoyuan, HE Qinjian
2023, 49(2): 14-22. doi: 10.13272/j.issn.1671-251x.18020
<Abstract>(294) <HTML> (56) <PDF>(56)
Abstract:
The existing mine moving target positioning system has the problems of serious attenuation of underground wireless signal transmission, large non-line-of-sight error, complex underground electromagnetic environment, wide sensing range of dynamic and static targets, strong linkage of multi-system information fusion, etc. At present, the research on mine moving target precise positioning technology and optimization method does not comprehensively analyze the characteristics and technical requirements of the moving target accurate positioning service. It lacks a comprehensive comparison between the mainstream and emerging positioning technologies. In order to solve the above problems, the advantages and disadvantages of the common signal transmission technology and the positioning and ranging method applied in the mine moving target precise positioning system are analyzed. The radio positioning technology is pointed out to be a more suitable and feasible mine moving target precise positioning technology. This paper analyzes the research status and existing problems of the optimization method of the mine moving target precise positioning in China from four aspects: signal anti-collision technology, error elimination method, positioning result optimization method and fusion positioning technology. ① The comprehensiveness of the signal anti-collision algorithm still needs to be improved. ② The efficiency of ranging error control means needs to be improved. ③ The application of the fusion positioning method in the production site is not yet mature. ④ The auxiliary role of the system in emergency rescue is not fully played. In view of the shortcomings of the existing technology, the development trend of the mine moving target precise positioning technology is proposed: ① It is suggested to study the signal collision mechanism and post-conflict recovery mechanism in dynamic environment, and design a comprehensive signal anti-collision scheme. ② It is suggested to research precise, efficient and economical ranging error control scheme to save communication costs. ③ It is suggested to study dynamic positioning scheme design with deep integration of multiple positioning methods to improve the reliability, flexibility and applicability of the system. ④ It is suggested to study the multi-system linkage scheme and the emergency communication and positioning recovery mechanism in extreme cases, and give full play to the role of the system in emergency rescue.
Special of Digital Twin and Virtual Reality Technology of Intelligent Mine
Research on intelligent mine disaster digital twin based on industrial Internet
XING Zhen, HAN An, CHEN Xiaojing, CHEN Haijian, SHEN Yi
2023, 49(2): 23-30, 55. doi: 10.13272/j.issn.1671-251x.2022120050
<Abstract>(2314) <HTML> (82) <PDF>(168)
Abstract:
The comprehensive control of coal mine disasters is a key problem to be solved in the process of intelligent mine construction. It is an inevitable requirement for the construction of intelligent mines to realize the normalization control of coal mine disasters with the help of digital twin technology. Based on the connotation and essence of the digital twin, this paper analyzes the recognition rule of the digital twin and puts forward the application mode of digital twin technology in coal mine disaster research combining with data interactive process of mine disaster digital twin. Real-time monitoring is carried out by coal mine underground disaster monitoring sensor. The monitoring data is uploaded to the cloud through the edge communication module and cloud communication module. The digital twin numerical simulation software is deployed in the cloud. The monitoring data uploaded by the sensor is used as the initial condition parameter, boundary condition parameter and effect verification parameter. The best optimization parameters and solutions are sought through real-time simulation analysis and continuous trial and error. When the technical means are mature in the twin world, they can be used to analyze, judge and make decisions on the best parameters and solutions for virtual entities. The decision instructions can be sent to underground actuators to control the action of disaster prevention equipment. This paper discusses the practical application of digital twin enabling disaster predictive management and control from three aspects: disaster monitoring scheme optimization, disaster rehearsal and precise planning of disaster avoidance route, and post-disaster rescue scheme formulation and accident investigation. Based on the "cloud-pipe-edge-end" architecture of the industrial Internet, the digital twin service system for coal mine disasters is constructed. The key technologies of digital twin for mine disasters are analyzed. The technologies include intelligent sensing and execution equipment for coal mine disasters, simulation software for coal mine disasters and common support technologies. It is expected to provide reference for the construction of digital twin-enabling intelligent mines.
Straightness solution of the fully mechanized working face based on VR and DT technology
YAN Zewen, XIE Jiacheng, LI Suhua, SHEN Weidong, WANG Yirong, WANG Xuewen
2023, 49(2): 31-37. doi: 10.13272/j.issn.1671-251x.18066
<Abstract>(1909) <HTML> (63) <PDF>(68)
Abstract:
The straightness problem is one of the neck problems in the intelligent construction of the fully mechanized working face. The key to solve this problem is to obtain the position and posture of the scraper conveyor or hydraulic support group. At present, most of the research on the straightness of fully mechanized working face is to discuss the straightness of hydraulic support and scraper conveyor separately. There are problems such as high cost and difficulty in implementation. In order to solve this problem, based on virtual reality(VR) and digital twin(DT) technology, the method to solve the straightness problem of the fully mechanized working face is explored. The hydraulic support, floating connection mechanism and scraper conveyor are considered as a whole system. The straightness solution framework of the fully mechanized working face is built. There are mainly five steps: mechanism analysis, model construction, fusion deduction, reconstruction monitoring and predictive control. It is pointed out that the key to the analysis of the relative position relationship of the fully mechanized supporting equipment is the floating connection mechanism connecting the hydraulic support base and the scraper conveyor. According to the motion characteristics of the floating connection mechanism, it is simplified into a robot model and solved by forward and reverse motion. According to the real coal seam environment, the motion simulation model of fully mechanized mining support equipment based on joints is established in Unity3D, and the VR scene is constructed to realize virtual and real mapping. Through non-contact visual sensor, virtual sensor, virtual-real fusion and other technologies, the information of sensor and point cloud are fused to perform the position and posture deduction of support equipment. Using the technology of virtual and reality interaction, combined with a real physical scenario, a DT system is constructed to achieve virtual monitoring of the fully mechanized working face. The travel distance required to ensure straightness is predicted in the virtual scene and fed back to the physical scene for straightness control.
Research on the application of digital twin in coal mine power grid
ZHAO Jianwen, MENG Xuhui
2023, 49(2): 38-46. doi: 10.13272/j.issn.1671-251x.2022040019
<Abstract>(2223) <HTML> (105) <PDF>(96)
Abstract:
Based on the basic concepts and connotations of digital twin, this paper analyzes the application advantages of digital twin technology in coal mine power grid. The operation management of the coal mine power grid is assisted by two means of synchronous entity operation status and digital simulation operation. The technology has the characteristics of data-driven, real-time update and synchronous feedback. The basic framework of the digital twin system of the coal mine power grid is proposed. The framework is composed of physical entity layer, digital twin model layer, user service management layer and data exchange layer. The operation mode of the digital twin system of the coal mine power grid is explored from two aspects of the physical entity and the digital twin model. This paper introduces the key technologies for establishing the digital twin system of the coal mine power grid. The technologies include digital twin model construction of coal mine power grid, intelligent data acquisition, intelligent communication based on 5G, digital twin intelligent database, and digital twin equipment intelligent management platform. The application scenarios of digital twin technology in the coal mine power grid are proposed. The scenarios include the condition evaluation of underground electrical equipment, fault location and protection of the coal mine power grid, intelligent monitoring of the coal mine power grid and intelligent inspection of underground lines. The digital twin technology is applied to the coal mine power grid to carry out dynamic simulation modeling on the state and operation of the coal mine power grid. On the one hand, the higher operation requirement of the current large-scale coal mine power grid relative to the ground power grid can be met. The safety of coal mine production can be guaranteed. On the other hand, the intelligent process of the coal mine power grid can be promoted. The efficient and reasonable utilization of data resources can be realized.
A three machine digital twin and collaborative modeling method for fully mechanized working face
LIU Qing, ZHANG Long, LI Tianyue, DU Pengfei
2023, 49(2): 47-55. doi: 10.13272/j.issn.1671-251x.2022120061
<Abstract>(1363) <HTML> (35) <PDF>(117)
Abstract:
The existing coal mine equipment digital twin modeling method mainly focuses on single equipment modeling. It lacks three machine coupling collaborative relationship analysis. In order to solve the above problems, the paper puts forward three machine digital twin and collaborative modeling method for fully mechanized working face. By adopting an intelligent modeling method, the method constructs agent-based models of a coal mining machine, a hydraulic support and a scraper conveyor which comprise a sensing unit, a control unit and an execution unit. The method constructs corresponding visual models according to a three-dimensional modeling process. The method drives the three-dimensional models to move by the intelligent models. The combination of the two forms a digital twin model of three machines. A discrete event modeling method is used to construct a collaborative process model covering the interaction process of the three machine digital twin model. The three machine mining process is sorted out according to the time sequence to form a three machine collaborative process time sequence table. The digital twin model is used to describe the state and behavior of the three machines in fully mechanized mining and to simulate the calculation at the individual level. The collaborative process model is used to represent the sequential action transformation between digital twin models and realize the deduction of the whole three machine collaborative process. The simulation of rocker lifting and lowering for the digital twin model of the shearer is carried out. The simulation results show that compared with the measured data of real equipment, the model error is small, an average error of rocker arm dip angle is 2.3°. The simulation of continuous column lifting action for the digital twin model of hydraulic support is carried out. The simulation results show good consistency between the model and real equipment. Compared with the measured data of the real equipment, the average angle error is 0.14° and the average stroke error is 6.3 mm. Combined with the actual production log of the coal mine, the virtual and real simulation experiment of the three machine collaborative model is carried out. The results show that the three machine digital twin model of the fully mechanized working face and real equipment realize mutual mapping. The simulation results are close to the real records. The three machine collaborative model can accurately reflect the collaborative mining process. The method of three machine digital twin and collaborative modeling for fully mechanized working face provides a new idea for the digital twin modeling of fully mechanized coal mining equipment and its collaborative relationship.
Digital twin system architecture and key technology of following process for fully mechanized mining
CUI Yao, LI Tianyue, YE Zhuang, LIU Junwei
2023, 49(2): 56-62, 76. doi: 10.13272/j.issn.1671-251x.18055
<Abstract>(1556) <HTML> (59) <PDF>(70)
Abstract:
The process design and parameter debugging of automatic following machine for fully mechanized mining are costly, time-consuming and cumbersome. In order to solve the above problems, the digital twin system architecture of following process for fully mechanized mining is proposed. The study analyzes the aspects of physical equipment, virtual and real interaction, twin data, mechanism model, simulation algorithm and process application. The key technologies such as the transmission and storage of the following process data, the playback of the following process history, the real-time following process twin deduction, the rehearsal simulation of following process, and the instruction scheduling of following process are described in detail. The paper puts forward the technical roadmap of the digital twin system of following process for fully mechanized machining. Through 10 Gigabit optical fiber ring network+5G communication, the shearer process action data is collected to the shearer host. The support process action data sent by the serial support controller is collected to the electrohydraulic control host. The process data is collected, classified and coded according to the action sequence as the data source for the playback of the process. At the same time, the host computer forwards the real-time reported following process data to the 3D digital twin system. The twin system deduces the following process in the 3D virtual scene. After the following process parameters are configured on the human-computer interface, the following process for fully mechanized mining can be previewed in the 3D scene. During the real-time mining process, the system will collect all kinds of sensor data and issue process scheduling instructions in combination with the rehearsal of error-free following process. The support controller is changed from a decision-maker to an executor to overcome the limitation of the limited computing power of the controller due to the lack of underground space. The field application results show that the digital twin system can provide technical reference for the process design, parameter configuration and simulation test of following process for fully mechanized mining. The system can shorten the development cycle of the following process from 14 days to 1 day, making the modification of the following process design more convenient. The system improves the following automation rate in working face to more than 90%.
Analysis Research
Research on cross interference and evaluation method of coal mine gas detection equipment
CHEN Yongran
2023, 49(2): 63-69, 93. doi: 10.13272/j.issn.1671-251x.17871
<Abstract>(177) <HTML> (42) <PDF>(25)
Abstract:
At present, coal mine underground gas detection equipment often causes false alarms or fails to alarm due to cross interference. There are potential safety hazards. There is no clear evaluation method for gas cross interference in current national or industry standards. In view of the above problems, combining with the actual underground environment gas type and volume fraction threshold in coal mines, the cross interference mechanism and characteristics of gas detection equipment based on the three commonly used principles of catalytic combustion, laser and electrochemistry are researched by using a combination method of theoretical analysis and experimental verification. The cross interference tests are designed and conducted. Combining with the common methods of gas detection equipment error testing in current standards, a gas detection equipment cross interference evaluation method based on the special gas environment in coal mines is proposed. The cross interference characteristics of the gas detection equipment are evaluated using the test method. By introducing cross interference gas samples, the cross interference value of the gas detection equipment is calculated. The value is compared with the highest precision of the equipment so as to determine if the non-target gas has a cross interference impact on the gas detection equipment. The test results show that cross interference of gas detection equipment is widespread. The methane detection equipment based on the catalytic combustion principle is easy to be interfered by sulfide and hydrogen under the specific gas environment conditions in the coal mine. Therefore, methane detection equipment should be avoided to be used in the gas environment containing hydrogen sulfide or sulfur dioxide for a long time. It will avoid poisoning or inhibiting the catalyst and affecting the measurement precision. Gas detection equipment based on the laser principle for detecting methane and acetylene is generally not affected by interference from common gases in coal mines and does not require cross interference testing. However, gas detection equipment based on the laser principle for detecting ethylene is affected by interference from methane gas. If it passes the cross interference evaluation, it can be used in a methane environment. If it fails, it should be clearly stated that the product cannot be used in environments containing methane. The cross interference characteristics of gas detection equipment based on the electrochemical principle are uncertain. It is necessary to determine the cross interference gas environment that can and cannot be used after the cross interference evaluation.
Experimental Research
Target detection of the fully mechanized working face based on improved YOLOv4
WANG Keping, LIAN Kaihai, YANG Yi, FEI Shumin
2023, 49(2): 70-76. doi: 10.13272/j.issn.1671-251x.2022070080
<Abstract>(369) <HTML> (103) <PDF>(43)
Abstract:
The accurate detection of key equipment and personnel in the fully mechanized working face is an important link to realize the information perception of intelligent coal mining. The traditional target detection algorithm realizes the target detection by extracting the features manually. But it is easily affected by the environment and it is not universal. The target detection algorithm based on the convolutional neural network can extract deep information adaptively. But the detection precision is not high, the network parameters are too many, and the calculation is too large in complex environment. In order to the above problems, an improved YOLOv4 model is proposed and applied to the target detection of the fully mechanized working face. In order to accurately detect targets in the complex environment of a fully mechanized working face, a residual self-attention module is integrated into the CSPDarkNet53 network. The capability of acquiring global information is enhanced while parameter sharing and efficient local information aggregation are ensured. The capability of expressing the features of key targets in an image is improved, and the target detection precision is further improved. In order to meet the requirement of high efficiency of target detection in the fully mechanized working face, depthwise-separable convolution is introduced to replace traditional convolution. The model parameter quantity and calculation quantity are reduced. It is beneficial to the industrial deployment of the model. And it improves target detection speed. The experimental results show that compared with YOLOv3, CenterNet and YOLOv4 models, the average precision of the improved YOLOv4 model is the highest, up to 92.59%. It has better balance in parameter quantity, calculation quantity and detection precision. It can accurately detect the target in the complex environment such as coal dust interference, uneven lighting and motion blur.
A pedestrian target detection method for underground coal mine based on image fusion and improved CornerNet-Squeeze
ZOU Sheng, ZHOU Libing, JI Liang, YU Zhengqian
2023, 49(2): 77-84. doi: 10.13272/j.issn.1671-251x.2022070001
<Abstract>(230) <HTML> (183) <PDF>(46)
Abstract:
In unmanned driving and security monitoring in the coal mine, detecting pedestrian targets is very important. But under the influence of special working conditions such as dim light, uneven illumination, complex background, and small and dense pedestrian targets, the pedestrian targets in the image have some problems such as few edge details, low signal-to-noise ratio and high similarity with the background. It is difficult to effectively identify the pedestrian targets under multi-scale occlusion. In order to solve the above problems, a pedestrian detection method for underground coal mine based on image fusion and improved CornerNet-Squeeze is proposed. The image collected by the infrared camera and depth camera is fused at the pixel level using the two-scale image fusion (TIF) algorithm. The morphological processing is carried out for the fused imoge to reduce background interference. Based on the CornerNet-Squeeze network, octave convolution (OctConv) is introduced into the hourglass type backbone network to process the high and low frequency information of image features, so as to enhance the image edge features and improve the detection capability of multi-scale pedestrians. The experimental results show the following points. ① The improved CornerNet-Squeeze model can effectively improve the detection precision of underground pedestrian while maintaining the real-time performance of the original algorithm on the data sets of range image, infrared image and fusion image. ② The detection precision of the model trained by the fusion image dataset is higher than that of the models trained by the infrared image dataset or the depth image dataset. The result shows that the fusion image can give full play to the advantages of the depth image and the infrared image, and is helpful to improve the detection precision of the model. ③ In the six scenes of different degrees of occlusion and multi-scale pedestrian target, the model trained by the improved CornerNet-Squeeze has the lowest pedestrian misdetection rate. ④ Compared with YOLOv 4, the average accuracy of the improved CornerNet-Squeeze algorithm on the COCO2014 pedestrian dataset is improved by 1.1%, and the detection speed is improved by 6.7%. ⑤ The improved CornerNet-Squeeze can effectively detect the small target in the image. The detection capability of the small target is obviously improved.
Mine UWB radio frequency front-end electromagnetic co-simulation method based on ADS and HFSS
REN Wenqing
2023, 49(2): 85-93. doi: 10.13272/j.issn.1671-251x.18073
<Abstract>(297) <HTML> (50) <PDF>(32)
Abstract:
The radio frequency front-end is an important part of mine ultra-wideband (UWB) positioning system. Its electromagnetic performance affects positioning precision. At present, the RF front-end design of the UWB positioning system is generally simulated by ADS or HFSS for single device or chip. With the increasing frequency band of RF front-end design, the parasitic effect caused by three-dimensional structures such as discrete components and transmission lines has more and more influence on the performance of RF front-end circuits. It is necessary to study the electromagnetic co-simulation method of the board-level RF front-end. In order to solve the above problems, a mine UWB RF front-end electromagnetic co-simulation method based on ADS and HFSS is proposed. Firstly, the passive device is modeled by HFSS software. The corresponding snp file is obtained by directly simulating with HFSS software. Secondly, ADS software is used to build the schematic diagram of active devices, connect the parameter reading control with the schematic diagram, and import the snp file into the control. Finally, the schematic diagram is simulated in ADS, and the joint operation between ADS and HFSS is realized through S parameters as the medium to realize the joint simulation of UWB RF front-end electromagnetic characteristics. ADS and HFSS are used to co-simulate the active components, passive components and the whole board-level circuit of the UWB RF front-end. The test samples are made according to the simulation principle. The experimental results show that the co-simulation results match the measured results of the samples. It can be used for the design of the UWB RF front-end and the comprehensive test of electromagnetic performance. The RF front-end designed by the electromagnetic co-simulation method is made into a PCB sample and used in a UWB positioning system to test the positioning limit distance. The test results show that the RF front-end designed by the electromagnetic co-simulation method can completely meet the performance requirements of the actual product. It can accurately predict the effect of the actual product in the design stage, improve the design efficiency and reduce the design cost.
Low-carbon transportation scheduling of open-pit mine based on GWO-NSGA-Ⅱ hybrid algorithm
WEN Jiayan, WEN Haichao, CHENG Yang, LUO Shaomeng, HE Weichao
2023, 49(2): 94-101. doi: 10.13272/j.issn.1671-251x.2022080008
<Abstract>(226) <HTML> (57) <PDF>(19)
Abstract:
In order to improve truck transport efficiency, reduce carbon emissions and save transport costs in open-pit mines, pure electric trucks are taken as the research object. The objective function is transportation cost, total queuing time (including truck charging time, operation time and maintenance waiting time in the production process), and ore grade deviation. The constraints include the crushing capacity of the crushing site, mining capacity of the mining site, loading capacity, ore grade error limit, vehicle charging pile selection and charging limit. The optimization model of low carbon transportation scheduling of open-pit is established. The gray wolf optimization (GWO) and non-dominated sorting genetic algorithm-II (NSGA-II) have been used to solve the low-carbon transportation scheduling model for pure electric mining trucks in open-pit mines. The former is prone to get trapped in local optimum while the latter is likely to achieve a global optimum but converges slowly. In order to solve the above problems, a GWO-NSGA-II hybrid algorithm is proposed. The hybrid algorithm introduces three genetic operations of NSGA-II, selection, crossover and mutation, into the GWO algorithm to effectively prevent the algorithm from falling into local optimum. In order to improve the stability of the global convergence of the algorithm, hunting and attack operations are introduced into the elite retention strategy of NSGA-II. Five standard test functions are used to verify that the hybrid algorithm improves the stability while ensuring the convergence. The example analysis shows that, compared with NSGA-II and GWO, the hybrid algorithm improves the optimization speed by 48.7% and 27.1% respectively. The hybrid algorithm improves the optimization precision by 17.1% and 9.3% respectively. The hybrid algorithm reduces the number of trucks, carbon emissions, transportation distance and transportation costs.
Study on spontaneous combustion law of residual coal in goaf under the condition of gas extraction in the low-level roadway
FAN Jiafeng
2023, 49(2): 102-108, 124. doi: 10.13272/j.issn.1671-251x.2022070031
<Abstract>(836) <HTML> (59) <PDF>(20)
Abstract:
The gas extraction in the low-level roadway in the coal seam roof is an important technical measure to solve the problem of gas concentration exceeding the limit in the upper corner of the working face. But the high-flow mixed extraction in the low-level roadway causes serious air leakage in goaf and increases the risk of spontaneous combustion of residual coal. At present, there are few studies on the synergistic effect of low-level roadway layout and extraction flow on the spontaneous combustion of residual coal in goaf. According to the actual situation of gas extraction in existing goaf with the low-level roadway in 10106 working face of Jiajiagou Coal Mine, a three-dimensional fluid-solid-thermal multi-field coupling numerical model of heterogeneous goaf is established by COMSOL software. The spontaneous combustion law of residual coal in goaf induced by gas extraction in the low-level roadway is analyzed by numerical simulation. The results show that gas extraction in the low-level roadway can reduce the gas concentration in the upper corner of the working face. The gas extraction flow rate is proportional to the maximum width of the spontaneous combustion oxidation zone and the maximum temperature of goaf. With the increase of gas extraction flow rate, the maximum width of the spontaneous combustion oxidation zone and the maximum temperature of goaf will increase. But too high gas extraction pressure will cause the air near the upper corner to "flow back" to the goaf. This will increase the risk of spontaneous combustion of residual coal in goaf. When the gas extraction flow rate of low-level roadway is constant, the smaller the dislocation distance is, the larger the maximum width and the maximum temperature of the spontaneous combustion oxidation zone in goaf are. Combined with the numerical simulation results and engineering practice, it is determined that the dislocation distance in the low-level roadway of Jiajiagou Coal Mine is 15 m. The gas extraction flow rate is 45 m3/min. The gas volume fraction in the upper corner is 0.875% and the maximum width of the spontaneous combustion oxidation zone in goaf is 59.14 m. The scheme effectively solves the problem of gas concentration exceeding the limit in the upper corner. The risk area of spontaneous combustion of residual coal in goaf is not significantly increased.
Study on spontaneous combustion characteristics of coking coal with different pre-oxidation degrees after CO2 cooling
WANG Qingguo, ZHOU Liang, QIN Ruxiang, LIU Zhen, YANG Yanyan
2023, 49(2): 109-114, 156. doi: 10.13272/j.issn.1671-251x.2022060020
<Abstract>(165) <HTML> (56) <PDF>(9)
Abstract:
In view of the problem of coal spontaneous combustion and re-ignition by reducing the oxidation of coal with inert gas, most of the existing studies are related to the coal low-temperature oxidation process and the coal re-ignition process. The spontaneous combustion characteristics of coal secondary oxidation after reducing inert gas temperature are less covered. In order to solve the above problems, taking coking coal as an example, the spontaneous combustion characteristics of coking coal oxidized at different temperatures after CO2 cooling and secondary oxidation are explored through the low-temperature oxidation experiment. The coking coal is pre-oxidized by GC-4000A temperature-programmed equipment at 70, 110, 150 ℃ respectively. The oxygen consumption rate, CO production rate, CO2 concentration and apparent activation energy of coking coal during the secondary oxidation process are analyzed after cooling to 30 ℃ with CO2 gas and dry air respectively. The experimental results show that at the same pre-oxidation temperature, compared with the dry air cooling, the change rule of related parameters of coking coal cooled by CO2 is basically the same. In the early stage of secondary oxidation, because of coking coal absorbs a lot of CO2, CO2 hinders the contact between coal and O2, the oxygen consumption rate and CO production rate decrease. The apparent activation energy increases, and the oxidation of coking coal decreases. As the CO2 resolves, CO2 cooling also affects the later reaction of pre-oxidized coking coal, which reduces the spontaneous combustion risk of pre-oxidized coking coal during the whole reaction process. When the pre-oxidation temperature is different, the pre-oxidation coking coal at 70 ℃ and 110 ℃ has a small amount of CO2 adsorption in the early stage. This leads to no change in oxygen consumption rate, CO production rate and apparent activation energy. When the pre-oxidized coking coal at 150 ℃ is cooled to 30 ℃, the coking coal has more CO2 adsorption, resulting lower the oxygen consumption rate and CO production rate. With the increase of activation energy, more energy is required. The coal oxygen reaction is more difficult. The risk of spontaneous combustion is also reduced. Therefore, when there is a danger of oxidation and spontaneous combustion of coal in the coal mine, it is necessary to inject CO2 for a long time to reduce the possibility of secondary oxidation and re-ignition when the mining area is reopened.
Analysis of heat dissipation performance of mine inverter based on the integrated model
WANG Yue, SHI Han, RONG Xiang, JIANG Dezhi
2023, 49(2): 115-124. doi: 10.13272/j.issn.1671-251x.18017
<Abstract>(187) <HTML> (48) <PDF>(18)
Abstract:
The space of the mine inverter is closed. The internal power device itself will produce a lot of heat in the operation process, which is easy to produce thermal degradation and thermal failure. In the existing research, a certain power device or a radiator of the mine inverter is analyzed independently. The heat exchange effect among the power device or the radiator is not considered. The combination with the running state of the mine inverter is not close enough. Therefore, the deviation between the heat generation and heat transfer processes and the actual situation is large. This reduces the accuracy and comprehensiveness of the heat dissipation performance analysis. In order to the above problems, taking the 630 kW/1 140 V four-quadrant mine inverter as the research object, the heat dissipation performance of the mine inverter is analyzed based on integrated model . A topological model of the main circuit of the mine inverter considering equivalent resistance is established. The electrical characteristics of the bus bar and the cable, the charge/discharge resistance, the absorption resistance, the IGBT module and the output reactor are analyzed, and the power loss is calculated. The cooling system of the inverter is optimized by forced water cooling + air cooling + natural cooling. The IGBT module and the absorption resistor are arranged on the substrate of the water-cooling radiator. The fan is configured to accelerate the heat exchange efficiency of the output reactor, and other power devices dissipate heat naturally. Based on the integrated model, the temperature field characteristics and heat transfer characteristics of the mine inverter are numerically simulated and analyzed. The correctness of the temperature field simulation based on the integrated model and the effectiveness of the heat dissipation design are verified by building the loading test platform of mineing inverter . The results show the following points. ① Under the heat transfer of conduction, convection and radiation of the internal power devices, the temperature of the flameproof enclosure is higher than the ambient temperature. The lowest temperature is 36 ℃. The temperature of the rear substrate is higher than that of the other flameproof surfaces, and the highest temperature can reach 70 ℃. The temperature of the internal components of the mine inverter is not higher than 80 ℃, which is far lower than the specified value of relevant standards. The mine inverter has good heat dissipation performance. The temperature of IGBT module is the highest, the temperature of the bus bar assembly is the second, and the temperature of the DC filter capacitor assembly is the lowest. ② The power device in the process of charging has a larger loss. But because of the short charging time, the loss will not cause severe changes in temperature. The instantaneous temperature of the power device is not more than 59 ℃. The maximum instantaneous temperature of the discharge resistance can reach 267 ℃, and the action time above 100 ℃ is 200 seconds. The high-temperature impact resistance of the trapezoidal aluminum shell resistor can meet the application scenario. It does not form a thermal stress cycle, and will not produce thermal breakdown and thermal failure. ③ The temperature of each power device tends to be stable gradually after 2-3 h. The experimental and simulation results of each calibration temperature measurement point keep good consistency in the overall trend.
Bearing fault diagnosis based on harmonic matching compensation and keyless phase order tracking
WU Jie, LU Zhenlian, MA Hongru, ZHU Yanfang, WU Yaochun, XUE Xiaofeng, JIANG Kuosheng
2023, 49(2): 125-133, 140. doi: 10.13272/j.issn.1671-251x.17983
<Abstract>(172) <HTML> (77) <PDF>(23)
Abstract:
The vibration signals of the bearings of coal mine machanical equipment under the working conditions of strong impact and heavy load show strong transient non-stationary and local nonlinear features. It is difficult to identify the fault features by the classical time-domain statistical analysis method and the global domain transformation method. The traditional order tracking method has the problems of inconvenient equipment installation and difficulty in obtaining instantaneous frequency. The traditional keyless phase order tracking method estimates the instantaneous frequency with low precision under the condition of severe speed fluctuation. This leads to poor fault identification effect. To solve these problems, a new method of bearing fault diagnosis based on harmonic matching compensation and keyless phase order tracking is proposed. Firstly, the time-frequency analysis method based on harmonic matching compensation is used to process the bearing vibration signal and estimate the instantaneous frequency accurately. Secondly, the Vold-Kalman filtering method is used to adaptively extract the harmonic component signal. Thirdly, the Hilbert transform is used to calculate the instantaneous phase of the harmonic. The mapping relationship between the time domain and angle domain is obtained, so as to complete the resampling of the original time domain signal in the angle domain. Finally, the resampled signals are processed by fast Fourier transform (FFT). The fault features of the bearing are identified by analyzing the envelope order spectrum. The simulation and experimental results show that the maximum relative error between the estimated instantaneous frequency and the actual value is less than 1%. The feature order of bearing fault is accurate and obvious, which can effectively diagnose the bearing fault.
Study on permeability characteristics of caved coal and rock in goaf
YANG Xiaochen, JIA Nan, ZHANG Xiaoming, SASAKI Kyuro
2023, 49(2): 134-140. doi: 10.13272/j.issn.1671-251x.2022090015
<Abstract>(180) <HTML> (46) <PDF>(17)
Abstract:
The seismic method is often used to analyze the correlation between porosity and permeability of caved coal and rock in goaf. Most of the existing studies adopt the effective medium theory, which convert the anisotropy and inhomogeneity of caved coal and rock in goaf into equivalent medium parameters. The influence of particle size, porosity, spatial characteristics and other factors on the seismic wave is less considered. Taking the caved coal and rock in goaf as the research object, the broken coal and rock samples are prepared according to the actual particle gradation and porosity of the caved coal and rock in goaf. The porosity and wavelength-particle size ratio of the caved coal and rock samples are verified to be consistent with those of the caved coal and rock in the actual goaf. On this basis, the influence of coal and rock particle size, porosity and seismic wave frequency on wave velocity, amplitude attenuation coefficient and permeability is analyzed through experiments.The P-wave velocity in broken coal and rock decreases with the increase of porosity, increases with the increase of particle size, and is less affected by seismic wave frequency. The amplitude attenuation coefficient increases with porosity and decreases with the increase of particle size, and is more easily affected by seismic wave frequency when porosity is larger. The permeability of broken coal and rock increases with the increase of porosity and particle size. According to the Kozney-Carman equation, the permeability prediction formula of coal and rock in goaf is established based on the experimental results. The calculated permeability of caved coal and rock in goaf is 1 225× 10−12-178 930×10−12 m2. In order to eliminate the influence of particle size on the amplitude attenuation coefficient of seismic wave and the permeability of coal and rock samples, the amplitude attenuation coefficient of unit wavelength (amplitude attenuation factor) is proposed. The empirical relationship between the amplitude attenuation factor and the permeability is obtained by least square fitting. The study provides a thought for preliminarily judging the permeability of caved coal and rock in goaf.
Experience Exchange
Research on key technology of intelligent fully mechanized caving face construction in Baode Coal Mine
WU Xicang, ZHANG Xueliang, RUAN Jinlin, WANG Zhiqiang
2023, 49(2): 141-148. doi: 10.13272/j.issn.1671-251x.2022060103
<Abstract>(257) <HTML> (44) <PDF>(39)
Abstract:
The current research achievements in the construction of intelligent fully mechanized caving face lack systematic implementation case for a specific fully mechanized caving face. In order to solve this problem, The 81309 intelligent fully mechanized caving face of Baode Coal Mine, CHN Energy Shendong Coal Group Co.,Ltd. is taken as the research background. Based on the configuration of hydraulic support electro-hydraulic control system and fully mechanized mining automation system, the key technologies such as equipment upgrading and transformation, limited transparent mining model building, intelligent coal drawing process decision-making, optimization of coal gangue recognition method, and multi-mode fusion integrated control are introduced in detail. ① The localization upgrading and transformation of the electric control system of the shearer is carried out. The inertial navigation system is installed. The optical fiber composite cable/5G communication is supported to realize efficient and stable transmission of attitude and control data of shearer. The equipment train can be pulled and moved by 1 - 2 persons by adopting step-type self-shift equipment train and pipe and cable expansion device. ② The iterative correction on the geological model in the data source of the intelligent planning center is carried out. The limited transparent mining geological model is formed through a series of conversions and multi-source heterogeneous data fusion. ③ In view of the sequential coal caving mode of "one cut, one caving and two rounds" in the 81309 working face, 10 intelligent fully mechanized caving mining stages and the corresponding actions and time of shearer, fully mechanized caving hydraulic support, front and rear scraper conveyor are constructed. The automatic mining and drawing in the middle and automatic mining in the triangle coal area are realized. ④ The intelligent coal gangue recognition system of fully mechanized caving is built by combining the vibration coal gangue recognition and video coal gangue recognition technology. ⑤ With the SAM-type fully mechanized mining automation control system as the hub, an intelligent centralized control system is constructed by integrating the electro-hydraulic control of hydraulic support, video monitoring, electric control of shearer and centralized control of pump stations of three machines. The intelligent fully mechanized caving face with adaptation in all links of "mining, support, recognition, caving and transportation" based on transparent mining has been initially built. The debugging results show that the middle part of 81309 fully mechanized caving face can realize the automatic control of 4 coal cutters in a single shift. The hydraulic support can realize the functions of the automatic following machine and pulling frame, linkage receiving and extension guard / expansion beam, and automatic pushing and sliding. The intelligent centralized control system can start and stop the production system with one key, and monitor the equipment operation data in real-time.
Fault detection method for belt conveyor idler
WU Guoping
2023, 49(2): 149-156. doi: 10.13272/j.issn.1671-251x.2022100022
<Abstract>(276) <HTML> (66) <PDF>(43)
Abstract:
The existing fault detection methods for belt conveyor idler have the problems of low recognition precision, poor anti-interference capability and inability to operate stably over a long period of time. In order to solve the above problems, a fault detection method for belt conveyor idler based on time-frequency-MFCC(TFM) and multi-input one-dimensional convolutional neural network (MI-1DCNN) is proposed. Firstly, the pickup collects the audio signal of the coal conveyor idler running along the line. The dB 4 wavelet unbiased risk estimation threshold noise reduction method is used to preprocess the signal to eliminate the background noise and improve the signal-to-noise ratio. Secondly, the time domain, frequency domain and Mel frequency cepstrum coefficient (MFCC), and the first and second order difference coefficient of the noise reduction audio signal are normalized respectively, and finally assembled to obtain the feature TFM. Finally, that TFM signals are input into a MI-1DCNN model with a multi-scale convolution kernel. The feature fusion is carried out at the end of a network channel. The classification and identification of the normal idler and the fault idler are completed through a Softmax function. The TFM-MI-1DCNN model is tested with the audio signal samples of coal conveyor idler collected in a coal mine. The results show that the average recognition accuracy of the fault idler is 98.65%. The average recognition accuracy is improved by 1.50% and 1.03% compared to the improved wavelet threshold denoising-backpropagation-radial basis function network and MFCC-K-nearest neighbor algorithm-support vector machine. The false detection rate is only 0.194%. The results of field application show that the average dentification accuracy of the proposed method is 98.4%, indicating that the proposed method is suitable for field application.

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