工矿自动化

Comprehensive prevention and control technology of coal spontaneous combustion in compound goaf of close distance coal seam

QIN Botao, GAO Yuan, SHI Quanlin, SHI Guoqing

2021, 47(9): 1-6. doi: 10.13272/j.issn.1671-251x.17837

<Abstract>(133) <HTML> (37) <PDF>(23)

Abstract:
In China, the occurrence of close distance coal seams accounts for a large proportion, and multiple goaf areas are easily connected to form compound goaf during mining. The compound goaf area is large. There are many air leakage areas and wide distribution range of residual coal, leading to the extremely serious coal spontaneous combustion disaster in compound goaf. In view of the rapid development of coal spontaneous combustion and the abnormal situation of CO and C2H4 pouring out from the compound goaf during the mining, this study comprehensively analyzes the factors such as air leakage source, air leakage sink, geological structure, residual coal during mining and characteristics of spontaneous combustion gas emission of coal, and determines the distribution range and development state of high temperature hidden danger of coal spontaneous combustion in compound goaf. The "two-step" comprehensive control plan for emergency control of hidden dangers and efficient management of hidden dangers is formulated. The combination of pressure equalization and leak plugging to reduce air leakage and nitrogen injection to dilute oxygen in goaf are adopted to achieve the effect of emergency control of hidden dangers. On this basis, effective measure areas of coal spontaneous combustion prevention and control are divided, and compound mud plugging, liquid CO2 cooling and three-phase foam covering oxygen isolation technology are adopted to achieve the goal of highly efficient control of hidden danger. The three-in-one comprehensive prevention and control technology system of "plugging and control velocity-inerting and cooling-covering and oxygen isolation" is constructed to completely eliminate the hidden danger of high temperature in compound goaf. After applying the above techniques, the volume fraction of C2H4 and CO in the compound goaf decreased from 72.1×10-6 and 3 912.6×10-6 to 0 and bellow 20×10-6 respectively. The results show that the proposed technology effectively eliminates the hidden danger of high temperature spontaneous combustion of coal in compound goaf and guarantees the safe and efficient mining of adjacent working face.

Monitoring and early warning technology of coal spontaneous combustion in coal mines: research status and intelligent development trends

ZHONG Xiaoxing, WANG Jiantao, ZHOU Kun

2021, 47(9): 7-17.. doi: 10.13272/j.issn.1671-251x.17841

<Abstract>(367) <HTML> (39) <PDF>(35)

Abstract:

Coal spontaneous combustion (CSC) is one of the main disasters in the process of coal mining. The rapid and precise monitoring of the characteristic parameters of CSC and the timely warning of the danger degree are important guarantees for achieving safe and efficient production in coal mines. The principle and research and application status of CSC monitoring and early warning technology are summarized from two aspects: CSC precursor information monitoring technology and prediction methods. And the main problems of the existing CSC monitoring and early warning technology are analyzed as follows. ① The integrated monitoring of CSC precursor information is greatly affected by underground environment. ② The construction of early warning index system and model is based on experiments, and is a bit tricky to correlate the actual scene. ③ There are few effective samples of CSC, and the prediction timeliness lacks advancement. Based on the development trend of coal mine intelligence, the research prospects of intelligent monitoring and early warning technology for CSC are proposed. ① It is suggested to establish a joint prediction model of CSC early warning and real-time forecast. ② It is proposed to develop a multi-source information fusion analysis method based on mechanism modeling and machine learning. ③ It is recommended to build a one-stop, visual and intelligent CSC monitoring and early warning platform for mines. It is expected to be beneficial to improve the ability of monitoring and early warning for CSC and enhance the intelligent development level of coal mines.

Research on intelligent regulation and control system and key technology of mine local ventilatio

CHENG Xiaozhi, WANG Kai, HAO Haiqing, CHEN Ruiding, WU Jianbin

2021, 47(9): 18-24.. doi: 10.13272/j.issn.1671-251x.17825

<Abstract>(191) <HTML> (29) <PDF>(23)

Abstract:
At present, the automatic control method of mine local ventilation adopts manual adjustment of ventilator frequency, and relies on manual collection of air duct parameters, which lacks accurate and reliable monitoring methods to reflect the ventilation status and cannot provide a basis for accurate adjustment of air volume. In order to meet the demand for intelligent construction of local ventilation in mines, an intelligent regulation and control system for local ventilation in mines is proposed, and the overall design of the system is introduced in detail in terms of system composition, principle and function. Based on the real-time monitoring data of multiple sensors, a calculation method for local ventilation parameters and a ventilation system power consumption analysis method are proposed. By analyzing the dynamic distribution of air duct resistance, the air duct resistance and power consumption abnormalities are studied and quickly located. The monitoring parameters are used to simulate the air volume in advance to determine the best supply-demand matching control scheme. According to the law of gas emission from the working face, an intelligent air regulation scheme based on gas emission monitoring and ventilator frequency regulation gas diluting is proposed, and five local ventilator frequency conversion regulation rules are formulated to realize the intelligent matching of local ventilation supply and demand. The Bayesian network algorithm is used to diagnose the working status of local ventilators and sensor equipment, and the rough set and genetic algorithm are used to extract the characteristic samples and precursor information of the normal air supply and fault conditions of the local ventilation. The support vector machine is used to establish local ventilation fault decision-making rules, and local ventilation abnormality diagnosis and early warning model is established to realize the diagnosis and early warning of local ventilation status and development trend. Taking the local ventilation of a mine driving working face as an example, the calculation method of the ventilation parameters of the system has been verified, which provides the basic data for the diagnosis and early warning of local ventilation abnormalities.

Optimization design of mine regional ventilation system

LIU Kunlun, HAN Yaozhong, QIN Cunli, WANG Gang

2021, 47(9): 25-31. doi: 10.13272/j.issn.1671-251x.2021010081

<Abstract>(146) <HTML> (19) <PDF>(21)

Abstract:
Most of the existing ventilation system optimization designs focus on general mine ventilation systems, and there are few optimization designs for regional mine ventilation systems. In order to solve this problem and achieve balanced ventilation of the underground air network, taking the Wudong Coal Mine in Urumqi, Xinjiang as the research object, the stability of the regional ventilation system is analyzed and studied by using ventilation resistance measurement and ventilation network calculation method. The results are showed as follows. ① In Wudong Coal Mine, under the effect of the main ventilator pulling and natural wind pressure variation in the north and south regions, the air volume of +400 m horizontal track roadway is extremely unstable, and there is often less wind or even reverse wind flow. ② The efficiency of the main ventilator is low, the efficiency is 42% in the south region and 38% in the north region. The mine ventilation resistance value corresponding to the working condition point is lower than the resistance value in the high efficiency region. ③ The natural wind pressure of Wudong Coal Mine varies greatly in autumn and winter. The maximum fluctuation of natural wind pressure in the north region is about 65 Pa, which affects the stable operation of the main ventilator in the north region. The optimization design is proposed for the problems of the regional ventilation system of Wudong Coal Mine. It is proposed to construct ventilation facilities such as air walls and dampers at each production level in the north region, increase the ventilation resistance in the north region, and increase the air distribution volume in the south region according to the actual situation of the mine. Moreover, it is suggested to increase the negative pressure of the mine, add air volume adjustment facilities in the +400 m horizontal track main roadway, and strengthen the air volume monitoring of the roadway to avoid excessive air volume. After the implementation of the optimization scheme, the negative pressure in the north region is increased, which is beneficial to resist changes in natural wind pressure. After the resistance increase and adjustment at various levels in the north region, the mine resistance distribution is relatively reasonable and the air flow is relatively stable, which improves the safety and stability of the mine ventilation system. The efficiency of the main ventilator has also been significantly improved. The wind flow direction of the +400 m horizontal track roadway can be kept stable under the effect of the north-south pressure difference, and there is no more problems of less wind or reverse wind flow. The stability of the air volume has also been greatly increased. The air volume and pressure of other main wind locations are not abnormal. The operation stability of the main ventilator is improved, which proves the effectiveness of the optimization scheme.

Study on the mechanism of gas wind pressure induced wind flow oscillation after outburst disaster

ZHOU Aitao, HU Jiaying, WANG Kai, DU Chang'ang, LEI Huan

2021, 47(9): 32-37.. doi: 10.13272/j.issn.1671-251x.17832

<Abstract>(71) <HTML> (17) <PDF>(11)

Abstract:
The wind flow oscillation effect is an important characteristic of the post-disaster mine ventilation network, but there are few studies on the wind flow oscillation phenomenon and there is a lack of in-depth discussion on the wind flow oscillation characteristics. In order to solve the above problems, taking the parallel downward ventilation network as the research object, the oscillation effects of disaster wind flow and gas mass are studied.Based on the damped vibration theory, an open-loop airflow oscillation model is constructed and the Runge-Kuttamethod is used to solve the numerical problem in Matlab software so as to analyze the oscillation characteristics of the gas mass in the parallel roadway. As the initial wind speed increases, the amplitude of the gas mass increases and the impact range of gas in the parallel pipeline is expanded.A similar model of the actual roadway is established to simulate the change of wind speed in parallel roadways with time. The experimental results show that due to the effect of gas wind pressure and ventilator wind pressure, the wind speed repeatedly increases and decreases in the parallel roadways, i.e. wind flow oscillation phenomenon. When the initial wind speed increases from 0.35 m/s to 0.62 m/s, the wind flow oscillation time is shortened from 50 s to 35 s, and the maximum reverse wind speed is changed from -0.4 m/s to -0.12 m/s. This shows that the increase of the initial wind speed is more conducive to the diffusion and discharge of gas mass.The prevention and control measures of wind flow oscillation in parallel inclined gas accumulation shaft are proposed, including imposing wind-blocking measures on the air branch; strengthening local ventilation and increasing wind speed on the gas branch.

Design of fuzzy PID controller for mine local ventilator optimized by improved genetic algorithm

HU Yelin, DENG Xiang, ZHENG Xiaoliang

2021, 47(9): 38-44.. doi: 10.13272/j.issn.1671-251x.2021030086

<Abstract>(121) <HTML> (26) <PDF>(17)

Abstract:
At present, the local ventilator control mainly uses traditional PID controllers. The parameters of the controller are fixed and selected based on experience. It is difficult to achieve the optimal combination of membership functions and fuzzy rules, which makes it difficult for the controller to meet the adaptive control requirements of local ventilator. In order to solve this problem, a fuzzy PID controller for mine local ventilator optimized by improved genetic algorithm is designed. In the improved genetic algorithm, the Euclidean distance is introduced to increase the diversity of the population, and the adaptive crossover and mutation probability are introduced to improve the convergence of the algorithm. In the encoding process, the proportional fraction is used to indirectly optimize the membership functions, which enables the improved genetic algorithm to optimize both the membership functions and fuzzy rules. The optimized membership functions and fuzzy rules are imported into the fuzzy PID controller. The controller can adaptively adjust the air volume of the local ventilator through the inverter according to the different working status of the local ventilator so as to realize the dynamic adjustment of the local ventilator. The simulation results show that compared with the traditional fuzzy PID controller, the improved fuzzy PID controller can basically achieve no overshoot, the rise time is shortened by 56.25%, and the stabilization time is shortened by 47.06%, which can better meet the control requirements of mine local ventilator.

Study on air flow control parameters of long-pressure and short-extraction ventilation air outlets in heading face

GONG Xiaoyan, PENG Gaogao, SONG Tao, FENG Xiong, CHEN Fei, LIU Hui, XIE Pei, XUE He

2021, 47(9): 45-52.. doi: 10.13272/j.issn.1671-251x.2021060008

<Abstract>(139) <HTML> (22) <PDF>(14)

Abstract:
The air flow at the air outlet cannot be dynamically adjusted according to the actual needs of the tunneling process under the long-pressure and short-extraction ventilation mode of the heading face, resulting in unreasonable air flow distribution and serious dust accumulation. The existing studies on the air flow distribution and dust reduction effect of long-pressure and short-extraction ventilation outlet at the heading face are only single analyses of the effect of the change of the air duct air outlet parameters on the air flow distribution and dust reduction effect in the heading face, without considering the interactive effect of each parameter on the dust field migration distribution. Moreover, there is no in-depth research on how the parameters of the air outlet can be changed comprehensively to achieve the optimal ventilation and dust reduction effect in different tunneling stages. In order to solve the above problems, taking the S1204 heading face of Shenmu Ningtiaota Mine in Yulin, Shaanxi Province as the research object, a finite element model of air flow control with variable air outlet parameters is established. The effect of the change of air duct air outlet parameters on the air flow and dust concentration migration distribution is simulated and analyzed. Through numerical analysis, the air outlet diameter, horizontal right deviation angle and vertical up deviation angle of the air duct are selected as the air flow dynamic control parameters of the air outlet, and the air speed and dust concentration data of the driver position and the pedestrian position on the return air side after the adjustment of different air flow control parameters are extracted. Through the niche genetic algorithm, the extracted air flow control data are mined and analyzed with the lowest dust concentration at the driver position and the pedestrian position on the return air side as the optimization object. And the optimal air flow control parameters are obtained for the closest distance of 5 m and the farthest distance of 10 m between the air outlet of S1204 heading face and the driving end face. At 5 m, the air outlet diameter is 1.1-1.2 m, the horizontal right deviation angle is 10-15°, and the vertical up deviation angle is 3-6°. At 10 m, the air outlet diameter is 0.8-0.9 m, the horizontal right deviation angle is 0-5° and vertical up deviation angle is 0-3°. A 1∶5 similar simulation test platform for intelligent control of air flow of the heading face of S1204 is built, and the optimal air flow control parameters are tested and analyzed. The results show that the dust concentration at the driver position is reduced by up to 52.3%, and the dust concentration at pedestrian position on the return air side is reduced by up to 60.6%, which verifies the accuracy of the optimal air flow control parameters.

Intelligent identification method of mine fire video images based on YOLOv5

WANG Weifeng, ZHANG Baobao, WANG Zhiqiang, ZHANG Fangzhi, REN Hao, WANG Jing

2021, 47(9): 53-57.. doi: 10.13272/j.issn.1671-251x.17826

<Abstract>(216) <HTML> (29) <PDF>(36)

Abstract:
In order to solve the problems of video image distortion caused by uneven light distribution and low accuracy of fire identification in coal mines, an intelligent identification method of mine fire video images is proposed. The method uses YOLOv5 as the identification model and uses K-means algorithm to improve the traditional dark channel image defogging algorithm to defog the collected flame images and improve the identification accuracy of mine fire video images. In order to reduce the impact of static background on fire identification, the fusion algorithm of frame difference method and Gaussian mixture model is used to extract the characteristics of the dynamically evolved flame images, and the morphological processing algorithm is used to eliminate the gaps in the images so as to obtain more complete flame target images. The fire video image data set is annotated and input to the YOLOv5 algorithm model for training and testing. The results show that the average accuracy of the intelligent identification method of mine fire video images based on YOLOv5 is 92% with a loss function of 0.6, which is 9.6%, 13.5% and 4.9% higher than that of the traditional algorithms, Alexnet, VGG16 and Inceptionv3 respectively, indicating that this method has fast detection speed and high accuracy, and can improve the accuracy of mine fire identification effectively.

Comparative study on test methods of coal low-temperature oxidation kinetic parameters

HOU Fei, CAO Weihu, WANG Yi, ZHONG Xiaoxing

2021, 47(9): 58-64. doi: 10.13272/j.issn.1671-251x.17812

<Abstract>(80) <HTML> (22) <PDF>(8)

Abstract:
In order to solve the problem of the lack of comparative analysis of different coal low-temperature oxidation kinetic parameters test methods in existing studies, three test methods, Coats-Redfern method, q/m method and Starink iso-conversional method, are used to calculate coal low-temperature oxidation kinetic parameters respectively. The accuracy of the three methods is compared with coal oxidation self-heating reaction time and critical accumulative thickness of spontaneous combustion as comparative parameters. The adiabatic oxidation experiment, the multiple heating rate experiment and the constant temperature experiment of the coal sample under pure oxygen and poor oxygen conditions are carried out through an adiabatic oxidation device and a simultaneous thermal analyzer. Based on the results of the thermal analysis experiments, three methods are used to calculate coal low-temperature oxidation kinetic parameters. The coal oxidation self-heating reaction time and the critical accumulative thickness of spontaneous combustion are calculated based on the obtained kinetic parameters. The calculated results are compared with the measured coal oxidation self-heating reaction time and the actual thickness of residual coal in goaf to evaluate the accuracy of the three methods. The experimental results show the results as follows. ① The coal oxidation self-heating temperature change rate measured by the adiabatic oxidation experiment increases gradually with the time. The temperature calculated by the Coats-Redfern method hardly changes from 0-8 h (0-10 h for the q/m method), and the temperature increases rapidly after this time period. The temperature change trend obtained by the Starink iso-conversional method is similar to the measured result of adiabatic oxidation experiment. ② The actual thickness of residual coal in goaf is greater than the critical accumulative thickness calculated by the Coats-Redfern method. The critical accumulative thickness obtained by the q/m method exceeds the thickness of the coal seam where the working face is located, which is obviously inconsistent with the actual situation. The calculation results obtained by the Starink iso-conversional method are closer to the actual situation. ③ The prediction results obtained by the Starink iso-conversional method are closer to the measured results, indicating that the low-temperature coal oxidation kinetic parameters obtained by the Starink iso-conversional method are more accurate than the other two test methods.

Dynamic information perception and emergency isolation system for mine fire environment

XIAO Guoqiang, FAN Xinli, MA Li, LUO Wei, WU Mingming

2021, 47(9): 65-69.. doi: 10.13272/j.issn.1671-251x.17819

<Abstract>(126) <HTML> (24) <PDF>(15)

Abstract:
Fire area isolation is the main method to effectively control the development and spread of fire, which can cut off the reaction chain of secondary accidents and reduce the scope of fire impact. In order to solve the problem that the commonly used fire airtight isolation measures cannot provide real-time dynamic monitoring and forecasting of the airtight environment, a dynamic information perception and emergency isolation system for mine fire environment is designed. The monitoring nodes are arranged in the predetermined dangerous areas, and the environmental information of multiple measuring points are collected and transmitted to the ground monitoring platform through multi-parameter sensors and infrared cameras. When abnormal data is detected, the system alarms and controls the airtight isolation device to open through remote control to realize the airtight bag filling. The bag is expanded from the storage bin to the entire section through the preset slide rail drive system to realize emergency airtight isolation. Real-time monitoring of the internal air pressure of the bag is carried out through high-precision pressure sensors. When the internal pressure of the bag is lower than the lower limit of the safety range, the automatic air-filling device of the bag is activated to replenish the air volume of the bag. When the internal pressure reaches the upper limit of the set range, the device automatically stop inflation to enhance the airtight effect. Field test results show that the system achieves the functions of real-time collection and alarm of fire environment parameters, remote control of airtight isolation device, etc. The airtight bag can be opened within 5 min, and the pressure inside the airtight bag remains basically stable after stopping inflation, which meets the requirements of field applications.

Research on health evaluation of mine ventilation system

REN Zihui, CHEN Zepeng, WU Xinzhong, QIAN Xiaoyu, LI Ang

2021, 47(9): 70-76.. doi: 10.13272/j.issn.1671-251x.2020120047

<Abstract>(75) <HTML> (18) <PDF>(19)

Abstract:
Most of the existing mine ventilation system health evaluation methods use constant weights. The evaluation results easily deviate from the actual situation and cannot reflect the real state of the system. At the same time, there are many indexes selected, and the weight of each index is low, which makes it difficult to detect the impact of some indexes abnormalities on the overall health of the system. Based on the actual operating conditions and health evaluation requirements of mine ventilation system, 21 influencing factors are selected as the health evaluation indexes to construct the health evaluation index system of mine ventilation system. Fuzzy comprehensive evaluation, analytic hierarchy process and variable weight theory are used comprehensively to carry out the health evaluation of mine ventilation system. The analytic hierarchy process is used to determine the weights of evaluation indexes, the Hardarmard product variable weight model based on membership degree is used to calculate the index weights. The maximum membership degree criterion of fuzzy comprehensive evaluation is used to determine the health degree of mine ventilation system. This method is used to evaluate the health of a coal mine ventilation system. The results show that the evaluation result of this method is consistent with the actual situation. Compared with the evaluation method based on constant weight, the weights of the evaluation index of this method can be adjusted according to the actual situation so as to make the evaluation result more objective. Moreover, this method amplifies the impact of unhealthy indexes and highlights the potential system safety hazards, which attracts the attention of relevant personnel.

Dynamic evaluation of mine ventilation quality based on FCE-AHP

JIN Hongmei, DANG Qi, LI Hong'an, LI Zhanli

2021, 47(9): 77-84.. doi: 10.13272/j.issn.1671-251x.2021050061

<Abstract>(107) <HTML> (19) <PDF>(10)

Abstract:
The existing evaluation method of mine ventilation system is to evaluate it as a whole from the overall perspective of mine ventilation system. The evaluation conclusions are static and comprehensive, which cannot precisely locate the ventilation situation in the wind range of the mine and discover its problems, and can not reflect the current state of ventilation quality in real time. In order to solve the above problems, a dynamic evaluation model of mine ventilation quality based on fuzzy comprehensive evaluation method-analytic hierarchy process(FCE-AHP) is established to evaluate the ventilation quality of coal mines in real time. Firstly, according to the requirements and functions of mine ventilation, the ventilation area is divided into five areas, namely, air inlet section, air return section, coal working face, heading face and chamber. And the corresponding evaluation index system is determined according to each type of ventilation area. Secondly, according to the evaluation index system, the data monitored in real time by the sensors of corresponding wind measuring points are obtained, the evaluation index weights of each area are determined by AHP. And the membership degree of the evaluation level belonging to the real-time monitoring data is calculated by the Cauchy distribution membership function. Finally, the rating weights are calculated by applying FCE, and the regional ventilation quality level is determined by the confidence recognition principle so as to complete the dynamic evaluation of the ventilation quality of each region. Taking the south wing of return airway of Dongtan Coal Mine as an example, the FCE-AHP model is used to evaluate the ventilation quality of Dongtan Coal Mine in real time. The evaluation results show that the ventilation quality is good and is consistent with the actual situation, which proves the reliability of the model. The FCE-AHP model can evaluate the ventilation quality of different ventilation areas of coal mines in real time based on the data monitored in real time, determine the safety level of coal mine ventilation quality, then achieve a comprehensive evaluation of mine ventilation quality, and provide a basis for improving the quality of coal mine ventilation systems.

Experimental study on ignition of methane and coal dust on the surface of high temperature heat source

WANG Yi, WANG Haiyan, ZHANG Lei, HU Lang

2021, 47(9): 85-90. doi: 10.13272/j.issn.1671-251x.17823

<Abstract>(149) <HTML> (17) <PDF>(10)

Abstract:
The high temperature area of coal spontaneous combustion in coal mine goaf may cause methane/coal dust explosion. Therefore, it is necessary to carry out research on coal spontaneous combustion induced methane/coal dust explosion. The current research on the characteristics of methane/coal dust explosion based on the electric spark induced method cannot fully reflect the characteristics of methane/coal dust explosion induced by coal spontaneous combustion in the goaf. In order to solve this problem, the self-developed 40 L gas explosion equipment is used to study methane/coal dust explosion characteristics under the high temperature surface ignition of heat source. The results are showed as follows. ① The methane/coal dust explosion process obtained by the surface ignition method of the high-temperature heat source is consistent with that of methane/air explosion, which can be divided into 3 stages. ② The three explosion parameters of methane/coal dust (explosion pressure, pressure rise rate and explosion temperature) are consistent with the change law of methane concentration, that is, the parameters first increase with the increase of methane concentration, reach a peak and then decrease with the increase of methane concentration. When the methane concentration is less than the turning concentration, the three explosion parameters of methane/coal dust are greater than the corresponding explosion parameters of methane/air respectively. When the methane concentration is greater than the turning concentration, the three explosion parameters of methane/coal dust are less than the corresponding explosion parameters of methane/air respectively. Due to the addition of coal dust, the turning concentrations of the three explosion parameters of methane/air decrease from 11.5% to 9.5%, 10.5% and 9.5% respectively, and the peak values increase by 0.8%, 6.9% and 0.8% respectively, and decrease regularly. ③ Due to the different ignition methods, the explosion temperature change law is different. The explosion temperature rises again in the falling stage (stage III) after the methane/coal dust is detonated by the electric spark. The explosion temperature change law after detonation of methane/coal dust on the surface of high-temperature heat source remains the same as that before the addition of coal dust. ④ The coal dust ignition temperature prediction function is corrected, and the goodness of fit is improved by 20.05% after correction. Combined with the experimental data, the ignition temperature prediction function of coal dust in the ignition mode of the high temperature heat source surface is obtained.

Temperature rise characteristics of spontaneous combustion and oxidation ofcoal with different particle sizes under the effect of thermal-stress coupling

LIU Zejian, XU Yongliang, LYU Zhiguang, WU Jindong, LI Minjie

2021, 47(9): 91-95.. doi: 10.13272/j.issn.1671-251x.17805

<Abstract>(109) <HTML> (18) <PDF>(9)

Abstract:
The existing researches do not consider that coal of different particle sizes in the goaf is affected by the axial stress generated by the collapsed coal rock and the residual coal pillars, which will cause major changes in the coal permeability, fracture structure and other parameters, thereby affecting the temperature rise process of coal spontaneous combustion and oxidation. In order to study the temperature rise characteristics of spontaneous combustion and oxidation of coal with different particle sizes under the effect of thermal-stress coupling, the change law of the temperature rise rate, oxygen consumption rate and heat production rate of coal with different particle sizes is measured by using load-and-pressure coal spontaneous combustion characteristic parameter measuring device and a gas chromatograph. The experiment show the results as follows. ① The temperature rise rate of coal samples of different particle sizes under different uniaxial stresses has a consistent trend with the increase of temperature, and the overall trend is to increase first and then decrease. When the uniaxial stress is 2, 4, 6, 8 MPa, as the particle size of the coal sample increases, the maximum temperature rise rate first increases and then decreases. When the uniaxial stress is 10 MPa, the maximum temperature rise rate increases with the increase of particle size. ② The oxygen consumption rate of coal samples with different particle sizes increases rapidly and then increases slowly during the temperature rise process. The oxygen consumption rate of coal samples with different particle sizes generally tends to increase with the increase of uniaxial stress. ③ The overall heat production rate of coal samples with different particle sizes tends to remain stable first and then increase and then decrease during the temperature rise process. As the particle size of coal samples increases, the maximum heat production rate of coal samples under appropriate uniaxial stress is greater than that without uniaxial stress.

Study on the effect of gravity heat pipe arrangement onhigh temperature point of coal pile

YIN Pengcheng, TIAN Zhaojun, LU Yi, ZHANG Shengyuan, OU Yanping, SUN Kai, YANG Yihan

2021, 47(9): 96-100.. doi: 10.13272/j.issn.1671-251x.17813

<Abstract>(160) <HTML> (15) <PDF>(14)

Abstract:
The existing researches have concluded that the number of gravity heat pipes, insertion depth and angle, filling rate, working fluid will affect the distribution of the internal temperature field of coal pile. However, there are few researches on the optimal arrangement of gravity heat pipes in coal pile. In order to solve the above problems, based on the gravity heat pipe heat transfer theoretical model, the heat source is equivalent to a sphere, and the effect of gravity heat pipe arrangement on the high temperature point of coal pile is analyzed by a combination of numerical simulation and experiment, and the optimal arrangement of gravity heat pipe is derived. The numerical simulation results based on Comsol software show that the depth of gravity heat pipe insertion has greater effect on the temperature of the high-temperature heat source point inside coal pile than the inclination angle of gravity heat pipe insertion. Under the same angle, the greater the gravity heat pipe arrangement depth is, the better. This means that the closer to the heat source, the better. Under the same depth, when the gravity heat pipe arrangement angle is 60, 90, 45 and 30°, the cooling range decreases in order. When the insertion depth of gravity heat pipe is 60 cm and the insertion angle is 60°, the highest cooling range reaches 61.2 ℃, and the coal pile has the best cooling effect. The experimental results based on the coal storage pile heat transfer test bench show that the optimal arrangement of gravity heat pipes is consistent with the simulation results, and the overall trend of the cooling rate is similar to the simulation results. With the increase of the inclination angle, the cooling rate of heat pipe decreases first and then increases, and the cooling rate reaches the maximum when the inclination angle of heat pipe insertion reaches 60°.

Experimental study on the displacement of oxygen in coal with different particle sizes by inert gas

FANG Xiyang, YAO Haifei

2021, 47(9): 101-107.. doi: 10.13272/j.issn.1671-251x.17840

<Abstract>(97) <HTML> (16) <PDF>(11)

Abstract:
In order to reveal the effect of different inert gases in preventing coal spontaneous combustion and the law of flame retardation, the experiment of isothermal dynamic displacement of oxygen by inert gas in coal with different particle sizes is carried out, and the concentration of oxygen, displacement time, displacement volume, displacement rate and other parameters that characterize the displacement process of He, N2 and CO2 are analyzed. The experimental results are showed as follows.① The concentration change of oxygen displaced by inert gas can be divided into three stages. Firstly, the inert gas displaces the oxygen in the pipeline of the gas detector, and the volume fraction is about 21%. Secondly, the inert gas displaces free and partially adsorbed oxygen in the coal sample tank, and the oxygen concentration remains stable. Thirdly, the inert gas has completely replaced the free oxygen in the coal sample tank, and the oxygen concentration shows a negative exponential change. ② The time for different inert gases to displace oxygen in coal generally decreases as the particle size increases. The total time for CO2 to displace oxygen is the longest, followed by He, and N2 is the shortest. ③ For the same particle size, the amount of oxygen displacement shows an obvious inflection point. Before the inflection point, the amount of oxygen displacement basically increases linearly. After the inflection point, the amount of oxygen displacement increases slowly with time and finally remains stable. The accumulative amount of oxygen displacement under different inert gases decreases with the increase of particle size. The accumulative displacement of CO2 to oxygen is the largest, followed by He, and N2 is the smallest. ④ The oxygen displacement rate under the effects of different inert gases is characterized by first disorder and then stable decrease. Among them, the disorder stage of CO2 displacement is especially obvious. In the stable decrease stage of oxygen displacement rate, the rate of oxygen displacement basically decreases with the increase of particle size at the same time.

Coal mine safety intelligence and key technologies

WU Fusheng, BU Tengteng, WANG Lu

2021, 47(9): 108-112.. doi: 10.13272/j.issn.1671-251x.17833

<Abstract>(167) <HTML> (15) <PDF>(25)

Abstract:
Coal mine safety intelligence refers to the intelligent technology related to coal mine safety, which is a necessary technical means to realize the intelligent perception and accurate early warning of typical coal mine disasters, and is also an important support for coal mine safety production. The significance of coal mine safety intelligence to the development of coal industry is analyzed, and the research status and achievements of coal safety intelligence are summarized. In order to solve the problems of unclear technical system, less information fusion interaction and unbalanced technical development in the development of China's coal mine safety intelligence, the system architecture of coal mine safety intelligence is constructed, including the digitization of intelligent sensors, equipment IOT networking and safety fusion intelligence. This study clarifies the idea of relying on Coal Industry Internet to realize safety intelligence system construction and information fusion. Taking the key technologies of sensor digitization and reliability as the breakthrough point, this paper focuses on the analysis of the intelligent development of safety sensing technology. The digitization, networking, intelligence and other key technologies and their development ideas are proposed to promote the intelligent construction of coal mine safety and the high-quality development of coal industry.

Unmanned driving-oriented underground mine pedestrian detection method

LIU Beizhan, ZHAO Honghui, ZHOU Libing

2021, 47(9): 113-117.. doi: 10.13272/j.issn.1671-251x.17830

<Abstract>(122) <HTML> (20) <PDF>(10)

Abstract:
Pedestrian detection is a key technology for unmanned driving in underground coal mine, which is affected by uneven illumination, complex background, infrared interference, dim light and small and dense targets in images, etc. The existing methods are not ideal for detecting pedestrians in underground mines. In order to solve the above problems, a multi-sensor fusion method for underground mine pedestrian detection is proposed. This method uses a step-by-step multi-characteristic fusion method to fuse the image characteristics collected by the visible light sensor, infrared sensor and depth sensor to obtain richer image characteristics. On the basis of RetinaNet, Dense connection is added to ResNet to form a Dense-ResNet with a hierarchical connected structure, which is able to extract the deep image characteristics from the multi-sensor fusion results and enhance the detection capability of small targets. The experimental results show that multi-sensor fusion images can obtain richer target characteristics compared with a single image, which is beneficial to improve the target detection accuracy. Compared with RetinaNet, Dense-RetinaNet can improve the accuracy of multi-target and small target detection.

Research on stability control technology of surrounding rock along goaf roadway with water intrusion in isolated island working face

LIU Xi

2021, 47(9): 118-125.. doi: 10.13272/j.issn.1671-251x.2021030089

<Abstract>(69) <HTML> (17) <PDF>(8)

Abstract:
At present, there are few researches on the reasonable coal pillar design under the condition of accumulated water weakened surrounding rock in the goaf of isolated island working face. Only simplified analysis or theoretical researches are conducted from one aspect such as the influencing factor of weakened bearing strength of coal pillar by accumulated water, simplified model of conventional stress of coal pillar, laboratory determination of accumulated water weakened coal pillar strength, etc. The effect of surrounding rock control along goaf roadway is poor. In order to solve this problem, the I020908 return airway of Qipanjing Coal Mine of China Energy Mengxi Coal Chemical Co., Ltd. is studied as the engineering background. In order to solve the problem of serious deformation of the surrounding rock along the goaf roadway under the condition of accumulated water weakening in the goaf of the isolated working face, the physical and mechanical parameters of the coal rock mass under the two conditions of dryness and water absorption saturation are determined by indoor physical and mechanical experiments using laboratory measurements and numerical calculations and analysis methods. Based on the measured parameters, FLAC3D numerical software is used to establish a numerical calculation model for the weakening of surrounding rock, which analyzes the evolution law of lateral support stress and the distribution characteristics of plastic zone in the surrounding rock in the roadway under the condition of accumulated water in the goaf. The mechanical model of accumulated water weakened coal pillar is established and a reasonable coal pillar width of 6-12 m under the accumulated water condition is determined. In order to solve the problem of roof falling and rib spalling caused by the water intrusion of the coal pillar of the return airway, a technical scheme for the stability control of surrounding rock along goaf roadway with water intrusion in isolated island working face is proposed. When the width of coal pillar is 6 m, the anchor cable reinforced support of the roadway can effectively control the large deformation of the surrounding rock of the roadway. The deformation of the surrounding rock of the roadway tends to be stable within 52 d after using the reinforced support. The maximum displacement of the roof and floor is about 200 mm, and the maximum displacement of the two sides is about 130 mm, which is 85.6% lower than the displacement of the surrounding rock under the original support condition. The control effect of the surrounding rock of the roadway is better.

Research on discharge spark safety of equivalent receiving antenna of underground metal structure

LIU Xiaoyang, MA Xinyan, TIAN Zijian, CHEN Wei, WANG Shuai, HU Zongqun

2021, 47(9): 126-130.. doi: 10.13272/j.issn.1671-251x.2021040106

<Abstract>(60) <HTML> (13) <PDF>(10)

Abstract:
The metal structures distributed in underground coal mine roadways can be equivalent to the receiving antenna to absorb electromagnetic wave energy and release the energy in the form of discharge sparks under specific conditions. The accumulated energy has the risk of igniting explosive gas. In order to solve the problem, the conditions of ignition of gas by discharge spark when the metal structure is equivalent to the receiving antenna are analyzed, and the calculation expression of the maximum power that can be absorbed by the discharge spark as load is derived. It is concluded that when the gas volume fraction is 8.5% and the metal structure is equivalent to the receiving antenna, the maximum allowable power that the discharge spark will not ignite the gas is 2.8 W. Wireless Insite electromagnetic simulation software is used to simulate the maximum power that can be absorbed by the discharge spark as load under different working conditions of the radio frequency equipment. The results show that the greater the output power of radio frequency equipment, the lower the working frequency of radio frequency equipment, the closer the metal structure to radio frequency equipment, the greater the load maximum power that can be absorbed, the greater the potential safety hazard of gas ignited by discharge spark. When the minimum safety distance between the transmitting antenna of the radio frequency equipment and the metal structure is 0.1 m, the discharge sparks generated by the radio frequency electromagnetic radiation energy in the frequency band below 800 MHz of the radio frequency equipment have the possibility of igniting gas. The discharge sparks generated by the radio frequency electromagnetic radiation energy in the frequency band above 890 MHz of the radio frequency equipment in the metal structure are intrinsically safe and will not ignite gas.

2021 Vol. 47, No. 9

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