Search

Mine filling and tunnel spraying projects pose high requirements on the rheological properties of cement-based materials.The types, conditions of fine sands and the exposed environment have significant effects on the rheological properties.In this light, this paper uses coal gangue sand instead of quartz sand as the fine aggregate of cement-based material and investigates the effect of temperature and aggregate prewetting on the rheological properties of mortar and its mechanism.Results show that the shear stress-shear rate relationship of coal gangue mortar conforms to the characteristics of Herschel-Bulkley(H-B)model, with higher rheological index(higher than 1)and higher consistency than that of quartz sand mortar.The apparent viscosity of coal gangue mortar decreases with increasing temperature, but the effect of aggregate prewetting is not significant.The yield stress of coal gangue mortar at 30 ℃ is 2.99 Pa, 1.45 times higher than that at 10 ℃, and 2.13 times higher after prewetting.The thixotropic ring area of coal gangue mortar is higher than that of quartz sand mortar, and the thixotropic ring area of pre-wetting coal gangue mortar is 398.4 Pa/s, while that of dry coal gangue mortar is 283.3 Pa/s.The obtained results are expected to provide evidence for the rational utilization of coal gangue sand and the design and preparation of rheological materials served in complex environment.

China's intelligent mine construction is still in the early stage of development, which is seriously constrained by data trust problems such as low credibility of mine data, lack of trust mechanism in the data sharing process and the risk of data security and privacy leakage.To this end, this paper proposes an intelligent mine data trust model by drawing on the holistic approach to national security.Specifically, this study 1) offered a working definition of this model and proposed its underlying conceptions; 2) designed its technical architecture and analyzed the core technologies involved; 3) proposed the implementation strategies of the intelligent mine data trust model based on blockchain technology.This may lay the foundation for blockchain technology to empower intelligent mines and comprehensively enhance its efficiency and productivity, thus promoting the high-quality development of the coal industry.

Based on the engineering background of the ultra-close adjacent coal seam group in the deep part of Pingdingshan No.8 coal mine, this paper studies the reasonable layering of bottom pumping roadway under the mining condition of deep ultra-close seam. FLAC3D numerical model is used to simulate the evolution law of the plastic zone, stress field and displacement field of coal seam under different net rock distances between the roof of bottom pumping roadway and Ⅵ16-17 coal seam. The results show that when the net rock distance is 3 m or 5 m, the coal seam above the bottom drainage roadway can be divided into pressure relief zone, stress concentration zone and primary rock stress zone under the influence of mining. When the net rock distance is 8 m or more, the coal seam above the bottom drainage roadway can be divided into pressure relief zone and primary rock stress zone under the influence of mining. The optimal layout of bottom drainage roadway is 8-10 m distance from the retained net rock. After the bottom pumping roadway is mined, the position directly above the roadway has the best pressure relief effect, the coal body in this area is fully deformed, the gas control is easier, is conducive to the support and maintenance of the coal roadway in the later period, and is the best position to arrange the coal roadway. Field monitoring effectively verified the reliability of the bottom pumping roadway in the net rock distance to control the gas outburst risk of the working face near the deep seam group.

During the mining process of deep coal mining faces, they are often affected by strong mining dynamic pressure, resulting in strong mining pressure and significant deformation and damage of the surrounding rock of the roadway. Especially for isolated working faces, the dynamic pressure effect is more significant, and the difficulty of controlling the surrounding rock increases exponentially. In order to solve the problem of the influence of strong dynamic pressure on the control of surrounding rock in mining tunnels in deep isolated working faces, this paper takes 2308 working face as the research background and uses methods such as theoretical analysis, numerical simulation, and on-site verification. Firstly, the structural model of the surrounding rock in the tunnel is analyzed to determine the main factors affecting the stability of the surrounding rock in the working face. Further research will be conducted on the two options of coal pillar width and drilling pressure relief, and based on the actual deformation of the tunnel surrounding rock, the asymmetric support parameters of the tunnel surrounding rock will be determined to achieve a “unloading and support balance” collaborative control plan for the mining tunnel affected by strong dynamic pressure. After on-site practice verification, the displacement of the roof and floor of the 2308 working face roadway is 260 mm, and the displacement of the two sides is 471 mm. The integrity of the surrounding rock of the roadway is enhanced, and deformation is effectively controlled. The use of “unloading and support balance” has a significant control effect on the surrounding rock of tunnels affected by dynamic pressure.

Controlling the creep instability of the surrounding rock of the deep soft rock roadway is a necessary prerequisite to achieve safe mining operations. This paper takes Guqiao Coal Mine as the engineering background, uses experimental testing, theoretical analysis, industrial experiments, on-site monitoring and other methods to conduct in-depth research. The study results show that the strength of the surrounding rock of the deep roadway in Guqiao Coal Mine is weak, and it is easy to cause a significant decline in long-term strength, elastic modulus, cohesion and internal friction angle after immersion, rock softening, continuous expansion of floor loose zone and reduction of overall stability of surrounding rock; the special shape of internal and external bearing structure of surrounding rock is defined: approximate vertical ellipse, based on improving the stability of the bearing structure, the deep hole grouting technology of the bottom plate is proposed. The deep hole grouting of the bottom plate can quickly change the shape of the bearing structure and change the unstable approximate vertical ellipse shape into the approximate circular shape with high stability.

Aiming at the serious problem of dust pollution in coal mines, the OAPB automatic diverting acid solution of coal seams was studied to uniformly distribute acid, so as to improve the water content of coal bodies. In order to achieve better results in coal mines, this paper studied the effects of different anionic and cationic surfactants on the viscosity and wettability of self-diverting acid using methods such as viscosity, chargeability, and functional groups, explored the internal causes of performance changes, and optimized based on the test results. The results show that cationic surfactants can directly cause gel breaking of self-diverting acid, and the addition of anionic surfactants can increase the viscosity of self-diverting acid. SSA/SDBS has good wettability, with a minimum surface tension of 24.12 mN/m; SSA/SDBS-16 has an overall higher surface tension value, poor self-wetting performance, and weaker adsorption performance on the coal bodies. Through infrared experiments, it was found that OAPB molecules tended to form hydrogen bonds under the action of SSA/SDBS, and the percolation effect of self-diverting acid solution was verified through triaxial percolation experiments.

For the problem of retaining gangue bending and skewing in the process of hard roof cutting roadway, this paper takes the 11# coal 1105 working face haulage roadway of Qiuji Coal Mine as the object of study and builds the mechanical model of gangue retaining in the whole process. Then the stress and deformation of the retaining gangue structure under the impact and extrusion of gangue are simulated with the numerical calculation software ABAQUS, respectively. The results show that the hard roof caving gangue has obvious punching characteristics, which can easily lead to the lateral bending of the retaining gangue, especially the upper part of the I-steel in retaining gangue, and can effectively reduce the deformation of the I-steel by imposing a lateral constraint on the top of the I-steel. The metal mesh will deform and produce large tensile stress on the adjacent I-steel under the extrusion of gangue, which is easy to cause overall instability. The deformation of the steel mesh will be significantly reduced when the spacing between I-steels is 800 mm. A new gangue retaining support scheme is proposed. According to field monitoring, the deformation of the waste rock slope under the new scheme has been reduced by about 49 %, which is in line with production safety requirements.

Mine green filling plays an important role in the protection of ecological environment. In order to explore the development trend of green filling technology in mines at home and abroad in recent years, this paper uses CiteSpace to analyze the literatures on CNKI and WOS from 2004 to 2022, and studies the status quo and trend of green filling technology in mines by the number of publications, institutions, authors and keywords. The research shows that the attention on green filling technology in mines at home and abroad is increasing year by year, and China is in a leading position in this field. Its research focuses on filling materials, filling process, filling effect and environmental impact, etc. Data mining, acid mine drainage and edge computing are hot fields. The green filling technology in mine has a broad development prospect, but it still needs to solve the problems of material, process equipment and effect detection and evaluation to improve the level and effect of filling.

In order to explore the effects of pore size, aromatic lamellar stacking degree, aromatic lamellar ductility, gas temperature and gas pressure on the competitive adsorption of CH4 and CO2, the No.3 coal from Jincheng mining area was taken as the research object. The adsorption process of binary mixed gas of CH4 and CO2 in coal under different temperatures, pressures, pore diameters, aromatic lamellar stacking degrees and aromatic lamellar ductility was studied. The microstructure of coal was tested and analyzed based on industrial analysis and X-ray diffraction experiments. Molecular simulation of the process of gas mixture adsorption in coal using the Grand Canonical Monte Carlo (GCMC) method. The results shown that, the increase of gas pressure was favorable for adsorption, and the adsorption capacity of CO2 was close to saturation at a pressure of 5 MPa. The increase of temperature led to a decrease in the maximum adsorption capacity and adsorption heat of CO2 in coal. The increase of pore size led to the increase of CH4 adsorption capacity in coal, with the fastest increase in CH4 adsorption occurred when pore size increased from 1 nm to 2 nm. With the increase of aromatic lamellar stacking degree, the number of gas molecules adsorbed in coal did not change significantly, but CO2 adsorption capacity of per unit mass in coal decreased rapidly, and the CH4 adsorption capacity decreased slightly. With the increase of aromatic lamellar ductility, the number of CH4 molecules adsorbed in coal increased slowly and the number of CO2 molecules adsorbed increased rapidly, and the change of the two gases adsorption capacity in coal per unit mass was not significant. From the perspective of adsorption capacity and adsorption heat, CO2 is in a dominant position in the competitive adsorption process, so injecting CO2 into coal seam can effectively displace CH4. The results of this paper strengthened the molecular understanding of the adsorption of binary mixed gas of CH4 and CO2, which can lay a theoretical foundation for the enhancement of coalbed methane extraction by CO2 injection.

Under the trend of deep mining of coal resources, the problem of high temperature heat damage in mines is becoming increasingly serious, the heat source that causes high temperature heat damage in mines is actually sustainably used geothermal energy, extracting and utilizing geothermal energy from deep mines while mining coal is an innovative way to build green mines and reduce mine carbon dioxide emission. This paper summarizes the current situation of deep mineral and geothermal energy collaborative exploration at China and abroad, analyzes the feasibility in terms of processes and key equipment and finally proposes a system of coal-geothermal collaborative exploration. The system adopts closed cycle mode, including ground heat utilization system and underground extracting system, drilling horizontal holes and installing coaxial casing heat exchangers at the coal to extract the heat, and utilization of the extracted low-grade geothermal energy through the heat pump on ground. Adhering to the principle of “mining heat first and then mining” in terms of time and space coordination, the thermal mining face is divided in front of the mining work in advance, and two modes of sequential and alternating thermal mining are proposed to ensure that the thermal mining process does not interfere with the coal mining process. Analyzed key technologies including spatial collaborative design, coal seam drilling, efficient heat extraction, and intelligent monitoring and control. Conducted underground spatial collaborative design for coal mining and geothermal energy extraction, proposed a coaxial casing heat exchanger layout process based on coal seam water injection. Multiple combinations of quick assembly coaxial casing heat exchangers can be used to achieve efficient heat extraction. Building an intelligent monitoring and control platform and proposed relevant optimization models, building a heat extraction calculation model and propose an intelligent control heat extraction method. Simplify the heat transfer process of coal formations, construct a heat transfer model for heat extraction from coal to calculate and evaluate the heat capacity of the mining face based on its actual situation and the outlet airflow parameters. According to the heat transfer model, the initial temperature of coal, the coal transportation volume, and the outlet air flow temperature through mining face are the key parameters that determine the heat extraction from the coal. The heat extraction is the maximum when the moisture content of the air flow of the working face remains unchanged and the equivalent temperature of the air flow at the outlet of the working face is not higher than 28 ℃. The application of this system will converting heat damage of deep mine to useful resources, which not only solves the problem of heat damage of coal mining, but also realizes the comprehensive utilization of geothermal energy in deep mine.

The acceleration of the energy transition is driven by current geopolitical conflicts and climate and environmental challenges. It is crucial for China to construct a new energy system adapting to these changing circumstances for the sustainability, security, and stability of the energy supply system. At present, fossil fuels still dominate the China’s energy demand. There are energy security issues due to lacking oil and gas resources, and new energy technologies. China will still maintain a high dependence on coal energy in short term, consequently, prompting the clean and efficient conversion of coal is vital for developing a new energy system. In this paper, the specific connotations and develop direction of the new energy system are identified, and then the development status, opportunities and challenges of the China’s coal chemical industry in the new era are presented, also the suggestions for improving the technology of clean and efficient coal conversion and the future development of coal chemical industry are put forward. The new era has endowed the new energy system with more connotations, that is the future energy system should be characterized by “safe and efficient, clean and low-carbon, diverse and synergistic, and intelligent and accessible”. In addition, the new era will put forward higher requirements for the clean and efficient development of the coal industry.Although China has made significant achievements in the clean and efficient conversion of coal, the key technologies still need some breakthroughs.Combining the systematic understanding of the relationship between the transformation and development of the coal industry and the “dual carbon” goals, and in the context of the construction of a new energy system, the promotion of clean and efficient coal conversion is of great significance for social and economic development and helping to achieve the “dual carbon” goals. The key lies in strengthening the basic research of relevant disciplines and specialties in this field, as well as the innovative development of clean and efficient coal conversion technologies.

With the gradual development of coal mining into deep strata, the large deformation failure and strong dynamic impact disasters of surrounding rock caused by deep mining are becoming more and more serious. Under the complex geomechanical conditions including high ground stress, high ground temperature, high permeability, strong mining disturbance, strong rheology, and multi-field coupling, the stress field characteristics, rock fragmentation properties, strata movement and energy accumulation and release laws of deep mining areas are significantly different compared with those in shallow mining areas. In response to the rock mechanics issues in deep mining, this paper discusses the research progress made by the authors and team in three aspects: deep coal mining methods, failure mechanism and control of surrounding rock in deep roadway, and deep thermal disaster and geothermal utilization. The main results are as follows: ① the theory of balanced mining and the 110/N00 methodology for achieving balanced mining were proposed and applied in kilometer deep mines. ② The deep shaft construction mode with non-uniform pressure was proposed, and a SAP system to realize the stable lifting was developed. A mine construction method which can greatly reduce the roadway quantities and improve the coal recovery rate was invented. ③ Multiple experimental systems suitable for studying the macroscopic failure of deep soft rock under the effects of water, high temperature, high pressure, structural effects, multi-field coupling were developed. A supercomputing system capable of performing microscopic-level calculations was established. Based on the experimental results, the mechanism of large-scale deformation and failure of deep soft rock and its multi-scale mechanical properties were revealed. ④ An experimental system for simulating deep shock-type and strain-type rock bursts was built, and it was revealed that the rock burst is a nonlinear dynamic behavior in which energy is instantaneously released along the excavation-free surface. ⑤ The theory of excavation compensation support for deep roadway was proposed, and a NPR materials with extraordinary mechanical properties such as high constant resistance, high elongation, strong energy absorption, and impact resistance were invented. ⑥ A thermodynamic experimental system which can simulate deep high temperature, high humidity, and high-pressure environments was constructed, and a high temperature exchange machinery system (HEMS) for heat disaster treatment and heat source resource utilization was established. The above research achievements have been applied in the field of deep mining and can provide guidance for the complex rock mechanics problems faced by deep mining.

This paper analyzes the current situation and existing problems of coal roadway driving technologies and equipment, introduces the new mode, technology, equipment of coal roadway rapid driving with integrated drilling and anchoring and its underground applications. The bolting technologies and equipment with integrated drilling and anchoring are developed which include the integrated drilling and anchoring bolt, pumpable resin, drilling boom and drill rig as well as bolts cartridge with integrated drilling and anchoring, pump unit and intelligence control system. The new technology simplifies the traditional six-step rock bolting process to one continuous step. Rock bolting can be realized automatically by pressing button once and the operation time for installing a single bolt can be reduced from 5 to 6 minutes to 3 minutes. The technologies and equipment of automatic spraying support are developed which include high-strength, rapid setting, and deformable surface supporting spraying materials with a tensile strength exceeding 9 MPa, elongation at break exceeding 100%, and a bonding strength exceeding 3 MPa. The spraying system with 6-degree-of-freedom manipulator is developed which can automatically and rapidly spray during roadway driving. The dynamic monitoring technology and system for roadway surrounding rock deformation are developed during driving which can achieve a surface deformation monitoring of roadway in environments with dust, multiple interference, and low illumination. The monitoring accuracy can meet the requirements of the surrounding rock stability evaluation. A new partitioned parallel collaborative rapid driving mode of excavation, spraying, bolting and transport is proposed and a complete set of roadway rapid driving equipment with integrated drilling and anchoring is developed. The displacement and stability of the surrounding rock during the driving process at the Caojiatan Coal Mine in Shaanxi Province are monitored. In terms of time, more than 80% of the surrounding rock displacement had already occurred in 2 to 3 hours after the excavation of the roadway. In terms of space, more than 90% of the surrounding rock displacement had already occurred at a distance equivalent to twice the width of the roadway from the excavation face. Therefore, the roadway surrounding rock displacement caused by rapid driving can be completed in a short time, requiring timely and rapid support. The nearly 6 000 m roadway driving project has been completed in the 10-metre-extra-high fully mechanized mining face of the Caojiatan Coal Mine, and over 60 000 bolts with integrated drilling and anchoring are installed. The time for installing a single bolt, the number of supporting workers, and the labor intensity of workers have been significantly reduced. The driving speed, efficiency, and automation level have been significantly improved. The displacement of the experimental roadway roof is small. The roadway surrounding rock stability is good as well as the support effect. The coal roadway rapid driving technology and equipment with integrated drilling and anchoring have achieved a success in underground field test. It has the ability to achieve a monthly driving footage of 1500 to 2000 m for ultra-large cross-section coal roadways.

Under the background of “dual-carbon” goal and current technological conditions, coal, waste and carbon constitute an impossible triangle in the coal industry which severely constrains its green, low-carbon, and sustainable development. Adhering to the principles of treating waste with waste and returning the waste to where it comes from, with a focus on the three-dimensional perspectives of damage reduction in coal mining, the functional utilization of mining waste, and low-carbon disposal of carbon in mining industry, this paper explores a synergistic development path for coal, waste and carbon. It provides a comprehensive solution to unravel the impossible triangle and promote the overall green, low-carbon development of coal industry. The specific contributions of this work include: ① Clarifying the scientific connotation of damage reduction in coal mining, the spatial combination characteristics of aquifers in the ecologically fragile areas, the movement patterns of overlying strata under the application of coal mining damage reduction techniques, and the surface deformation patterns resulting from overlying strata damage; proposing the original technologies of drilling-backfilling-retention for section pillar extraction, narrow strip mining with backfill, and backfilling behind fully-mechanized longwall face aiming to address the challenges posed by damage reduction mining; ② Interpreting the scientific connotation of functional utilization for mining waste; clarifying the scientific issues related to the modification methods and mechanisms of magnesium-coal-based solid waste material, the mechanisms of synergistic interactions among diverse solid wastes, and the properties control of total solid waste backfilling materials. These efforts have led to the establishment of a key technological system for the functional utilization of solid waste, with a core focus on the modification of solid waste raw materials, the development of solid waste-based cementitious materials, and the preparation of solid waste based backfilling materials; ③ Elucidating the scientific connotation of low-carbon disposal of carbon with a scientific practical framework and implementation pathway; clarifying some scientific issues related to mineralization material preparation, storage space construction, CO2 storage and control mechanisms, the long-term environmental effects of CO2 storage, and reservoir stability in the low-carbon disposal process of carbon. The scientific issues related to mineralization material preparation, seal space key technologies such as fractured space CO2 storage and CO2 sequestration through coal mine carbon solidification are explicitly defined which results in a new model for achieving a low-carbon CO2 storage in coal mine goaf. Based on the green, low-carbon and sustainable development of coal industry, it is of great significance to collaboratively promote the damage reduction in coal mining, the functional utilization of mining waste, and the low-carbon disposal of carbon. This coordinated effort plays a crucial role in advancing the realization of the dual-carbon goal in the coal industry.

The coal industry is the ballast stone and stabilizer that supports the rapid development of China’s economy and society and ensures national energy security. It also undertakes the mission of ensuring energy supply and supporting the stable development of new energy. At present, the high-quality development of China’s coal industry has achieved some staged results, with remarkable achievements in energy supply, the continuous optimization of industrial structure, the significant improvement of scientific and technological innovation capabilities, and the continuous advance of green development and clean and efficient utilization. However, the current development level of the coal industry is far from meeting the national needs of Chinese-style modernization. The sustainable development is restricted by multiple factors. The digital technology and coal development and utilization have not yet been deeply integrated. The intelligent construction is still in the demonstration and cultivation stage. The green development is unbalanced and contradictory and prominent. The transformation and upgrading of the coal industry still has a long way to go. In view of the current development status and challenges of the coal industry, this paper proposes a synergistic development mode of digitalization, intelligentization and greenization (three -izations), clarifies the core connotation of new-quality coal productivity, constructs the overall framework of the synergistic development of new-quality coal productivity, and expounds the technical path for the transformation of the innovative allocation of production factors by digitalization, the breakthrough of key technologies led by intelligentization, and the deep transformation of traditional industries by greenization, i.e., by these three factors to generate new-quality coal productivity. Six major technical systems are proposed: through the research and development of the technical system of efficient data collection and in-depth governance of the whole industry chain, the data barriers among coal production, transportation, storage, marketing and use of the whole process are removed. Through the research and development of the knowledge map and intelligent decision-making and control technological system of the coal industry, the correlation relationship and value of the upstream and downstream business scenarios of the coal industry are deeply explored, so as to lay the foundation for the independent decision-making and intelligent control of the whole process of coal production and utilization. Also, the research should be carried out in terms of the intelligent-green-efficient development technological system of coal resources, the technical system of collaborative guarantee of safety in the coal industry, the technical system of ecological intelligent monitoring-early warning-restoration in mining areas, and the technical system of flexible development and clean and low-carbon utilization of coal, so as to realize the synergistic development of the whole industrial chain and the whole process of coal development and utilization, cultivate and form a new-quality coal productivity, and bring some fundamental changes and improvements to the overall image of the coal industry.

Aiming at the development problems of deep coal reservoirs, such as deep burial, low permeability and complex stress field, this paper clarifies that the resource enrichment conditions, effective fracturing volume, effective horizontal section length, and good reservoir conditions are the key factors for high productivity on the basis of summarizing the exploration and development practice of the Daning-Jixian Block in the past five years. Under the guidance of the theory of “artificial gas reservoir” development, a technical system for the efficient development of deep coalbed methane was preliminarily established as follows. ① According to the reservoir resource conditions, structural preservation conditions and engineering fracturing conditions, a total of 11 indicators in three categories established the geological-engineering “dessert” evaluation standards of deep coalbed methane. ② Based on the techniques such as microstructural characterization, multi-scale fracture prediction, and 3D geological model construction, the quantitative and visual characterization of all elements of “geology + engineering” of deep coal seam was achieved. ③ Based on the guiding idea of “geological small scale, three-dimensional seismic microscale, drill along the target, less adjustment and fast drilling”, a three-stage geological-engineering geo-steering technology with an excellent design of pre-drilling trajectory, precise target entry and post-target fine-tuning as the core was developed.④ The optimization design of the five-in-one well network based on “in-situ stress field, natural fracture field, artificial fracture field, well type and orientation, well network and well spacing” realized the maximization of resource utilization and the maximization of gas field recovery. ⑤ According to the occurrence characteristics, seepage mechanism and production characteristics of deep coalbed methane, a reasonable production capacity evaluation and EUR prediction technology based on the rate-transient analysis method, the empirical production decline method, the numerical simulation method, and the empirical analogy method was formed. ⑥ Following to the design principle of “four-in-one” precision fracturing section and “fracture staggering + differentiation between fracturing segments”, a large-scale volumetric fracturing technology aimed at constructing artificial gas reservoirs was proposed.⑦ According to the characteristics of gas-water variation in gas wells, the optimal control technology of drainage and production in different production stages through the whole life cycle of wells was put forwarded. ⑧ Combined with the current progress of AI technology, and the characteristics of deep coalbed methane development law, gathering and transportation, the technology of gathering, transportation and digital intelligence integrating geological, engineering, and ground aspects was explored. Under the guidance of this achievement, 29 horizontal wells that have been put into production，with an initial production of 5×104−16×104 m3/d, an average of 10.2×104 m3/d, and the daily gas production of the block has exceeded 3 million cubic meters, which has important guiding significance for accelerating the large-scale production of deep coalbed methane in the eastern margin of the Ordos basin. Also the study establishes a reference and standard for the efficient development of similar resources.

The Xinjiang Uygur Autonomous Region has presented the expected resource conditions and work foundations for a large-scale coalbed methane (CBM) exploration and development, which shows that its CBM resources below the depth of 2000 m are 7.5 trillion m3, 450 CBM wells have been constructed, and the annual gas production has approached to 80 million m3. Xinjiang has put forward the goal of the annual CBM production of 2.5 billion m3 in 2025. Therefore, the large-scale and efficient development of CBM in Xinjiang has become an urgent and significant demand. In this paper, the main research progresses of Xinjiang CBM made in five key technical fields have been systematically summarized, including the CBM enrichment model and area optimization technology, the prediction and detection technology for sweet spot distribution, the technological strategy of the accelerated rolling development and rapid increase of reserves and productions, the geological adaptation technology system, and the cooperative exploration and development of CBM with coal, oil and gas. Then, the potential breakthrough directions have been analyzed and proposed. Research has shown that the coal reservoirs in Xinjiang show the unique geological characteristics of CBM, including widely developed multi-thick coal seams, low rank coal development, the frequent occurrence of steep coal seams, the significant deformation and structural control of coal bodies, complex hydrologic and outcrop conditions, and the gas-bearing and physical properties with three “low” (low gas content, methane concentration, and gas saturation) and five “high” (high gas intensity, porosity, stress change, reservoir pressure change, and permeability change). The Xinjiang CBM has multiple genetic types and enrichment models, including biogenic mechanism, thermogenic mechanism, and biogenic-thermogenic composite genetic mechanism, etc., and their corresponding enrichment models. Biogenic gas reservoirs or biogenic gas contribute widely. The distribution and occurrence patterns of CBM in Xinjiang show some significant differences between foreland basin and intermountain basin. Therefore, the first breakthrough direction is to innovate and form the scientific evaluation based on the principle of “two separation” (low-rank and middle- and high-rank; shallow and deep coal) and “two combination” (geological and engineering evaluation; multivariate data) and the precise target optimization technology based on “machine learning + three-dimensional geological modeling”. The sweet spot of deep CBM/CMG (coal measure gas) in Xinjiang is mainly the uplift of the depression in the basin, the depression of the uplift in the basin, and the slope around the basin margin. The potential well location is the structurally high position, and the potential reservoir is the fissure-developed primary structure coal seam or pore and fissure-developed coal bearing sand conglomerate reservoir. Then, the second breakthrough direction is the sweet spot prediction and exploration technology for deep CBM/CMG based on “new method of geophysics, rock physics and rock mechanics stratigraphy” and “new concept of geological and engineering sweet spot”. The basic principles of the accelerated rolling development are low-risk, short-cycle, high-efficiency, and multi-batch project deployment. The technical strategies of the rapid increase of CBM reserves and productions in the middle and shallow coal seams include the new well layout and construction in the new optimized block and the old well reconstruction for the increase of CBM production in the mature block. While this strategy for the deep coal seam is to give priority to deployment and development in the sweet spot in the deep but gentle slope in the large basin and the uplift in the basin. Then, the third breakthrough direction is the engineering deployment methods and technical strategies for the scientific accelerated rolling development, and efficient and rapid increase of the gas reserves and productions. The important progresses have been made in the engineering technologies of Xinjiang CBM, such as the differential optimization and deployment of the well type and pattern, the drilling and cementing with a low reservoir damage, the high reliability logging and well testing, the efficient staged fracturing with the multi-well types, and the drainage control with the low casing pressure and controlled pressure. The fourth breakthrough direction is to develop and construct a geological adaptability technology system for a large-scale and efficient exploration and development of CBM in Xinjiang. For the middle and shallow CBM and coal cooperative exploration and development, the gas extraction followed by coal mining, the co-extraction of CBM and coal, and the co-extraction of CBM and in-situ oil-rich coal should be conducted. For the deep CBM, oil, and gas cooperative exploration and development, the development of coal measure superimposed gas reservoir, the co-exploration and co-extraction of CBM and CMG, and the exploration and development of the whole petroleum system in coal-bearing sequence should be conducted. These cooperative exploration and development of deep CBM, oil, and gas is the fifth breakthrough direction, whose developments have been considered and explored. The results of this study are expected to provide the technical support and engineering decision reference for a large-scale and efficient exploration and development of CBM in Xinjiang.

With the increasing depth of coal mining, the stability control of surrounding rock in deep roadway has become one of major problems in the mining field, and the effect of surrounding rock control in deep roadway is directly related to the safe production and health of personnel in underground coal mines. The emergence of plastic zone after roadway excavation is the main reason for the stability of the surrounding rock of the roadway. From the perspective of the formation and expansion of the plastic zone, this paper discusses the intrinsic relationship between the roadway damage mode and the distribution of the plastic zone of surrounding rock on the basis of the results from collating and summarizing the existing roadway damage theory and the theory of the plastic zone of surrounding rock. It is believed that the control of the surrounding rock of roadway is essentially the process of controlling the formation and expansion of the plastic zone of surrounding rock. The expansion of the plastic zone of surrounding rock and the control effect of anchor support on the plastic zone of surrounding rock have become an important theoretical basis for the scientific and effective control of surrounding rock in roadway, and based on this, the authors propose the theory and technology for the stability control of surrounding rock in roadway. The results show that the plastic zone is the product of roadway excavation, and the formation and expansion of the plastic zone of surrounding rock is the result of mine pressure. For deep roadways, the appearance of the plastic zone of surrounding rock is inevitable. Scientific control of plastic zone requires a comprehensive understanding of the role played by the plastic zone in roadway surrounding rock. It is necessary to allow the surrounding rock to release the energy in the rock body through plastic failure, but also to prevent the disorderly expansion of the plastic zone. Therefore, in the process of controlling the surrounding rock of roadway, the self-bearing capacity of the surrounding rock should be given a full play as the main focus, and the support intervention should be supplemented. The control of plastic zone of surrounding rock in deep roadway is global and procedural. The control of the plastic zone of the surrounding rock in the whole life of roadway is divided into three stages. By regulating the shape of the plastic zone and inhibiting the expansion of the plastic zone, the stability control of the surrounding rock of deep roadway is realized.

The combination of water-jet and disc-cutter rock breaking is a key technology to improve the rock breaking efficiency of the full-face shaft boring machine and achieve the mechanized development of deep resources. It is a crux problem of selecting reasonable parameters for pre-cutting kerfs. In this paper, firstly, it examined the working characteristics of rock breaking with a disc-cutter driven by a conical cutter-head. Then, based on the cohesive element method, a discrete-continuous coupled numerical model for rock breaking with a disc-cutter under pre-cutting kerfs conditions was established. Comparing the intact rock mass, the influence of different pre-cut kerfs distances and depths on the stress and rock fragmentation characteristics of the rock breaking was analyzed. The three stage characteristics of dense core formation, blocky rock slag formation, and Hertz crack propagation during rock cutting with a disc-cutter were elaborated. The asymmetric fragmentation characteristics of the rock mass and the formation mechanism of rock slag in different regions were presented. Finally, a comprehensive analysis was conducted from four aspects: the force acting on the disc cutter, the rock breaking area, the specific energy consumption for rock breaking, and the degree of rock slag crushing, and the optimal range of distance and depth values for pre-cutting kerfs was determined. The research results indicate that the pre-cutting kerfs can significantly reduce the penetration force and lateral force during the rock breaking process of the SBM cutters. Compared with intact rock masses, the peak penetration force decreased by 44.0%−10.3%. The peak lateral force decreased by 35.2%−6.5%. When the spacing and depth of pre-cut kerfs are small, it will limit the range of rock breaking by the disc-cutter, and at the same time make the fragmentation of the rock mass smaller, resulting in an increase in specific energy consumption for rock breaking. As the pre-cut depth increases, the rock breaking volume first increases and then tends to be stabilized, while the specific energy consumption first decreases and then remains unchanged. Finally, it was determined that the cutting distance was 70−90 mm, and the best rock breaking effect was achieved when the cutting distance was 60−80 mm. The rock breaking volume was doubled compared to the case without cutting, and the specific energy consumption for rock breaking decreased by 69.2%. This provides a reference for the parameter design and determination of the cutter head.

The borehole transient electromagnetic method is used to detect the long-range water-bearing bodies around the borehole wall by using the advanced water exploration borehole in the heading roadway, which avoids the “one’s opinion in one hole” because the normal logging methods can only detect the rock layer of the borehole wall. At present, because of the whole space effect, the current borehole transient electromagnetic method cannot distinguish the orientation of abnormal bodies by the received single-component response, and it can approximate the orientation of abnormal bodies by multi-component response, but it is difficult to precisely locate and interpret the profiles by the visual and effective means such as imaging. Based on the theory of borehole transient electromagnetic method and azimuthal electromagnetic logging, this paper proposes a borehole transient electromagnetic positioning method with azimuthal coil scanning detection. The azimuth coil is used as the detection device to reduce the mutual inductance of the coil and enhance the detection effect of the borehole transient electromagnetic method. At the same time, by changing the rotation angle of the coil, the borehole wall is scanned by 360° to form a radial all-round detection of the borehole, aiming at a precise localization and profile interpretation of low-resistance abnormal bodies in the rock mass at the periphery of the borehole wall. Firstly, the authors derive an analytical expression for the mutual inductance of an azimuth coil, discuss the effect of azimuth angle on azimuth coil mutual inductance, and determine the optimum azimuth angle by numerical calculation. Secondly, a full-space 3D geological-geophysical model of the borehole with homogeneous medium and low-resistance abnormal bodies are established respectively and the numerical simulation of transient electromagnetic field is carried out. The multi-component response characteristics of the azimuthal coil scanning detection transient electromagnetic response are analyzed, and the law of transient electromagnetic response of azimuthal coil scanning detection is summarized, and the borehole transient electromagnetic positioning method with azimuthal coil scanning detection is determined. Namely, through the transient electromagnetic response characteristics of the axial and radial directions of the borehole, the position of the low-resistance abnormal bodies in the rock body at the periphery of the borehole wall is determined. Finally, by establishing the geological-geophysical model with two low-resistance bodies and using azimuth coils set to the best azimuth angle for numerical experiments, it is verified that the method can intuitively and effectively determine the orientation of low resistance abnormal bodies. The study shows that the azimuth coil scanning detection results of the borehole transient electromagnetic method can better reflect the transient electromagnetic field anomaly caused by the low-resistance abnormal bodies in the rock body at the periphery of the borehole wall, and the resolution of the full-space apparent resistivity imaging results is high. Based on the transient electromagnetic response characteristics of the axial and radial directions of the borehole, the borehole transient electromagnetic positioning method with azimuthal coil scanning detection has a high resolution and localization accuracy for the low-resistance abnormal bodies in the rock body at the periphery of the borehole wall. The research results provide a theoretical basis for the practical application of the borehole transient electromagnetic positioning method with azimuthal coil scanning detection.

The mining industry is a sector aimed at the safe, efficient, green development, and clean, efficient, low-carbon utilization of mineral resources, serving as a foundational industry for economic and social development. In order to make mining development more economical, consider a more comprehensive range of factors, and optimize the design and development processes, in the late 1950s, operations research and computer technology were introduced into mining engineering, giving rise to a new discipline known as mining systems engineering. In its early stages, mining systems engineering primarily focused on the optimization of mining production processes and the use of computers in mine design, excavation planning, information processing, and application software development, with a predominant emphasis on open-pit mining as the research object. In recent years, research in mining systems engineering has closely integrated with big data, artificial intelligence, network technology, and has achieved fruitful results in areas such as mining information network construction, logistics systems, intelligent mining, equipment management, and safety management. This paper provides a detailed exposition of the origin and development process of mining systems engineering, with a chronological narrative based on international conferences on the application of operations research and computers in mining (APCOM), particularly the fifteen national conferences on mining systems engineering that have taken place. It objectively summarizes the developmental process and evolution of research content in mining systems engineering. Using the CNKI database as the data foundation, current research employs cluster analysis to study the publication volume, research objects, and their changes in mining systems engineering over the past 20 years. The future development of mining systems engineering should focus on the integration of systems science thinking with modern mining technology, establishing scientific systems and their boundaries, such as scientific mining systems, mine lifecycle systems, intelligent mine systems, and other eight major systems. The development of mining systems engineering will increasingly emphasize innovation and application in aspects such as digitization, intelligence, sustainable development, informatization, and automation, while continually expanding its application areas to achieve optimized, efficient, green, and low-carbon mining development.

The structure and stress environment of the surrounding rock at the longwall mining area in the steeply dipping coal seam are alienated, and the composition factors and disaster modes of the ”support and surrounding rock” system in the working face are affected. This leads to some frequent safety accidents in the working face, low coal extraction rate, and high roadway excavation rate. This paper analyzes the mining mechanics behavior of surrounding rock of in the steeply dipping coal seam and proposes a technological concept of partial backfill non-pillar mining in the longwall faces of steeply dipping coal seam. During the process of advancing the working face, partial backfill is carried out along the inclined direction in the lower part of the goaf. The filling body not only forms a gob-side roadway with the support effect of the roadway side, but also eliminates the protection coal pillar, achieving a non-pillar mining. At the same time, the length of the filling and compaction area at the lower dip of the working face is increased, enhancing the stability of the ”support and surrounding rock” system of the working face. Based on the characteristics of the longwall mining area in the steeply dipping coal seam, the partial backfill process of the steeply dipping coal seam paste was optimized and determined. And the partial backfill recovery system and mining and filling process in the steeply dipping coal seam were designed. By using a combination of theoretical analysis, simulation experiments, and numerical calculations, the regulatory mechanism of partial backfill on the mechanical behavior of surrounding rock at the longwall mining area in the steeply dipping coal seam was analyzed. The results show that the filling body affects the deformation and failure of the main roof rock beam, as well as the bearing characteristics of the coal and rock mass on the lower side of the mining area. The deformation of the main roof and the roof of the head entry, as well as the constraints on the coal and rock mass on the lower side of the head entry, all decrease with the increase of filling length. In order to prevent the hanging roof disaster in the unfilled area of the goaf, the filling length should not exceed 1/3 of the working face length. The partial backfill body restricts the fracture of the roof in the lower area of the working face, reduces the formation layer of the critical zone of the overlying rock, forms a stable roadway, and reduces the deformation of the surrounding rock gob-side roadway retained. At the same time, the length of the filling area at the lower part of the working face increases, and the length of the unstable area of the middle and upper surrounding rock structures decreases, improving the stability of the ”support and surrounding rock” system. The filling body changes the stress transmission path of the surrounding rock in the mining area, bearing part of the overlying rock load. The side abutment pressure on the lower side of the working face and the front advanced pressure both decrease with the increase of filling length, and the front support pressure in the lower filling area of the working face has the greatest decrease. The stress state of the gob-side roadway and the working face is improved. Technology of partial backfill non-pillar mining in the longwall faces of steeply dipping coal seam has the advantages of effectively improving resource recovery rate, reducing the roadway drivage ratio, alleviating the tension of mining and replacement, and strengthening the stability of the ”support and surrounding rock” system in the working face. It is of great scientific significance for guiding the green, safe, and efficient mining in the steeply dipping coal seam.

With the gradual transfer of shallow coal mining to deep coal mining in China, the rock burst disasters are becoming an increasingly serious problem. In the process of rock burst mechanism cognition to rock burst prevention engineering, the primary task is to clarify the main factors of rock burst and to identify its risk level. In this paper, four kinds of objective factors i.e., coal rock impact tendency, mining depth, hard roof and geological structure, and three kinds of human factors i.e., coal pillar, goaf and mining unloading effect, were proposed. And the disaster evolution mechanism of each factor was discussed in detail. In terms of objective controlling factors, the impact tendency is the inherent attribute of coal/rock to accumulate deformation energy and induce impact failure. The mining depth is positively correlated with the deformation energy accumulated in the surrounding rock of the roadway, which is an essential condition for the occurrence of rock burst. The impact dynamic load and kinetic energy formed by large-scale hard roof periodic fracture are the 'fuse' to rock burst. The influence of geological structure on rock burst is significant. For fault structure, the two walls will relatively ‘rebound’ under the sudden unloading caused by mining disturbance. And the equivalent elastic modulus of the thinning area of the coal seam becomes larger, and the advanced abutment pressure is distributed in a 'double peak' pattern, which expands the impact influence range. In terms of subjective controlling factors, coal pillar is a high stress concentration area, and its size, dip angle and relative position will directly affect the probability and strength of rock burst. The goaf will induce a sudden release of energy accumulated in the stress concentration area, especially under large mining height and insufficient roof collapse conditions. Mining unloading will lead to the rapid “migration” of the stress concentration area and release a large amount of energy stored in the coal/rock, which is an important external inducement of rock burst. On this basis, the differences of main control factors of rock burst disaster in the main rock burst mining area, such as Xinwen, Luxi, Erdos, Binchang, Xinjiang and Gansu were compared and analyzed. The study emphasized the importance of identifying the main control factors and their influence degree of rock burst from an entire mine, a panel to a working face. Also, it constructed the engineering management path of rock burst from energy-reducing, energy-releasing, energy-damping to energy-resisting.

Aiming at the real problems such as the occurrence of coal and gas outburst and based on the hypothesis of comprehensive action of coal and gas outburst, a method of gas hydration and solidification to prevent coal and gas outburst is proposed. The core of this method is to solidify the gas in coal seam to form gas hydrate, which can not only reduce the gas pressure, but also improve the coal strength, so as to reduce or eliminate the risk of coal and gas outburst. Based on the idea of “coal and gas outburst prevention using hydrate”, the test of gas hydrate formation in coal and the in-situ test of the mechanical property-permeability of gas hydrate bearing coal have been performed, with the numerical modeling technique of the triaxial compression of the gas hydrate bearing coal proposed. The techniques are implemented by comprehensively applying the methods of theoretical analysis, development of testing equipment, indoor test and numerical analysis. In terms of coal and gas outburst prevention, the thermodynamic and kinetic conditions of gas hydrate formation are its theoretical basis, the stable storage of gas hydrate is its technical precondition, and the reduction of gas pressure and the improvement of mechanical properties are its key measures. This paper focuses on the cross mechanics related to the gas hydrate bearing coal. The results show that: ① the theoretical framework of gas solidification technology by the hydrate method for outburst prevention has been initially formed, and the meso-mechanism of improving the mechanical characteristics of coal before and after gas hydration has been preliminarily explored by means of the numerical simulation. ② At present, it has been confirmed that the hydrate formation in coal can not only reduce the gas pressure, but also improve its mechanical properties. High saturation can obviously improve the peak strength of coal. ③ Gas hydrate formation experiences three stages: rapid, slow and stable stage. Additionally, the formation of hydrate will cause the gas seepage channel in the coal to be blocked, resulting in a decrease in its permeability. ④ High gas pressure and high CH4 concentration not only help to increase the saturation but also delay hydrate decomposition, which is conducive to the stable existence of the hydrate. However, a large number of repetitive experiments are still needed to verify the reliability of the method to build up a generalized database. By analyzing current research findings, the limitations and challenges that still exist are discussed, with further research interests pointed out.

The permeability coefficient of coal seams is a key parameter that judges the difficulty of gas flow in coal seams. In the current calculation formula for the permeability coefficient of coal seams, the coefficient of the nonlinear partial differential equation with variable pressure is assumed to be a constant, which leads to significant errors in the theoretical derivation results and results in significant deviations in the permeability coefficient measured on site. To solve the inaccurate determination problem of the coal seam permeability coefficient, this paper derived the process of using the radial flow rate method to test the coal seam permeability coefficient, and pointed out the problems of this method during the derivation process. Based on the Langmuir's gas content and Darcy's law, a dimensionless model was established, and the model solution results were inverted and fitted. A new calculation formula for the coal seam permeability coefficient was obtained, which was verified by on-site drilling data. The current testing method for coal seam permeability coefficient was revised, and an accurate and reliable new method for calculating the coal seam permeability coefficient was proposed. The results indicate that using a parabolic equation to represent the coal seam gas content and treating variable p1.5 as a constant to derive the coal seam permeability coefficient calculation formula is equivalent to fitting the gas content into a proportional relationship with the square of pressure. There are theoretical problems and significant errors in actual calculations. Using the Langmuir dimensionless model to calculate Y' for inversion fitting can solve the shortcomings of current calculation methods. When the product of the adsorption constant b and the original gas pressure p0 (the dimensionless original gas pressure) is different, the function curve of the dimensionless gas emission velocity Y' and the dimensionless time Fo' is significantly different. Therefore, the permeability coefficient calculation formula containing the dimensionless original gas pressure was obtained. When the coal seam and drilling conditions are constant, the values of the coal seam permeability coefficient λ calculated from the gas emission volume at different times have a good reproducibility. The new on-site measurement method for the permeability coefficient of coal seams is completely the same as the current method without adding additional workload. However, the new calculating method is more accurate and reliable.

China’s total carbon emissions are approximately 11 billion tons, with around 40% of CO2 being produced by the coal-fired power plants (CFPP). Therefore, reducing carbon emissions from the CFPP is critical in achieving the Dual-Carbon target. This paper focused on the advancements in the low-carbon/carbon-neutral fuel substitution technologies (such as biomass, sludge, hydrogen/ammonia, etc.) and the CCUS (carbon capture, utilization and storage). The CFPP coupled with biomass includes direct and indirect coupling, but are subject to the supply and price of biomass feedstock. To address these challenges, a comprehensive “planting-harvesting-transportation-storage-pretreatment-combustion” approach was recommended to ensure an effective control throughout the entire chain. Initial pilot test on a 660 MW CFPP revealed a substantial reduction in CO2 emissions by 772500 tons annually. The high-water content of municipal sludge, reaching up to 80%, necessitates drying prior to entering the boiler. Current steam drying and flue gas drying technologies entail substantial investment and operational costs, with the dried sludge still retaining high water content and associated problems such as odor. Consequently, the blending ratio in the CFPP remains below 8%. A sludge carbonization technology based on a biomass heat source can address these challenges, which allows for the direct production of odorless sludge char in sewage plants with a calorific value of about 10.26 MJ/kg. This technology enables an increased blending ratio in the CFPP to 20%−30%, thereby significantly reducing coal consumption and CO2 emissions. The blending of hydrogen/ammonia necessitates addressing the issues of ammonia escape and NOx emission under high blending ratios. Experiments for co-firing of coal and ammonia were conducted on 300 MW and 600 MW CFPP in China to address the challenges of ammonia escape and NOx emissions under high blending ratios. The results showed that combustion control can achieve a higher NH3 burn-up rate with a slight increase in NOx emissions. However, the commercialization of hydrogen/ammonia blending in the CFPP is constrained by the cost of hydrogen and ammonia. The commercialization of pre-combustion decarbonization technology, such as IGCC, faces significant limitations due to high costs. Several foreign demonstration projects were discontinued. The construction costs and equipment reliability are crucial for promoting the commercialization of this technology. Carbon capture technologies in combustion processes include oxygen-enriched combustion and chemical chain combustion. The power generation efficiency of atmospheric oxyfuel combustion is lower by 8%−12% compared to air combustion due to the energy consumption associated with air separation and recycling processes. Transitioning from atmospheric oxyfuel combustion to pressurized oxyfuel combustion can further increase the net power generation efficiency. Notably, China has constructed the world’s largest 4 MW chemical-looping combustion (LCL) demonstration plant. The LCL also has a potential application in the gasification industry. Post-combustion carbon capture predominantly employs the solution absorption technology, while the solid adsorption technology offers a lower regeneration energy consumption. However, some challenges remain in reducing energy consumption and costs to facilitate the large-scale commercialization of this technology.

Coal-fired power generation is an important guarantee for the energy security in China, but a large amount of CO2 is emitted from flue gas. At the same time, a large amount of fly ash is also generated. The CO2 mineralization by fly ash and its product utilization are able to achieve the goals of solid waste treatment and long-term CO2 storage. At present, there are still some shortcomings in the CO2 mineralization technology by fly ash, such as low mineralization efficiency, long reaction time, and small processing capacity. The corresponding key scientific issues and technical bottlenecks need to be addressed urgently. In this paper, the basic principle of CO2 mineralization by fly ash is briefly introduced. The influencing mechanisms of different reaction conditions on alkali metal ion leaching and CO2 mineralization are analyzed. The advantages and disadvantages of three processes, namely the CO2 direct mineralization reaction process, the alkali metal pre-leaching process, and the CO2 pre-absorption process, are compared. The key technology of CO2 mineralization by fly ash is proposed, including the efficient alkali metal ion leaching, the enhanced CO2 mineralization reaction process, the intelligent equipment for fly ash mineralization CO2, and the comprehensive evaluation of mineralization effect. The physical and chemical properties of its mineralization products are clarified. And the utilization of its mineralization products is explored. Finally, three key scientific issues are summarized, including the rapid leaching of alkali metal ions from fly ash and the efficient mineralization of CO2, the multiphase mixing and reaction laws in large CO2 mineralization reactors, and the control mechanism of the mineralization product properties. The research direction of the entire chain including basic research, key technology and equipment development, and engineering application is proposed, providing a reference for the efficient mineralization of flue gas CO2 by fly ash and the utilization of its products, which is of great significance for achieving the carbon neutrality goal and utilization of solid waste.

Under the carbon peaking and carbon neutrality strategy, biomass has attracted much attention due to its characteristics of regeneration, low pollution and zero carbon emissions. The imperfects of biomass, such as the loose structure and low energy density, can be effectively solved by briquetting, and the resulted fuel pellets can be used as a substitute for fossil fuels, which is of great significance for the construction of new energy system. In the paper, the influencing factors of the hot briquetting process of biomass were summarized, and the evolution behavior and binding mechanism of biomass particles during the hot briquetting process were analyzed and discussed. Biomass briquetting process mainly includes cold briquetting and hot briquetting. Compared with cold briquetting process of biomass, hot briquetting with lower energy consumption can produce the biomass fuel pellets with higher quality. The moisture content (4%−15%) of the raw biomass has greater influence, the briquetting temperature (70−150 ℃) has relatively smaller effect on the density of the fuel pellets, and the briquetting pressure (60−130 MPa) and the particle size ( < 2.5 mm) of the raw material show the different impact on the density of the fuel pellets from different biomass. During the hot process, cellulose mainly plays the role of supporting skeleton, hemicellulose and lignin play the role of binder. In the microcosmic process of hot briquetting process, the inertia movement and subsequent viscoelastic-plastic deformation of the biomass particles occur and the mechanical interlock is formed between the particles. The brittle particles are broken and the natural viscous components are released, and thus, the bridge linkage between the particles is formed under the integrated effects of moisture, temperature and pressure. Mechanical interlocking and bridging reduce the distance between biomass molecules and promote the generation of intermolecular forces. Based on the above-mentioned mechanism of the hot briquetting of biomass, the quality of the resulted fuel pellets can be improved by biomass component adjustment, biomass blending or hydrothermal pretreatment. In the future, the molecular dynamics simulation method will be used to investigate the biomass briquetting process to obtain the molecular bonding mechanism of biomass components, which is conducive to further exploring the hot briquetting mechanism of biomass, and provide important guiding significance for the preparation of fuel pellets and molding materials from biomass.

The sheave is an important part of a mine hoisting system. Once it fails, it will not only affect the production efficiency of coal mine, but also cause some safety risks. Poor lubrication is one of the main causes of sheave failure. In view of the low efficiency and difficulty in ensuring the uniformity and timeliness of lubrication caused by the current manual lubrication method commonly used in coal mines, this paper presented a new intelligent lubrication system for sheave bearings and implemented it on-site application. First of all, starting from sheave structure and considering the different operating modes of the sheave shaft end rolling bearing and the traveling wheel sliding bearing, it was proposed to use a combination of automatic lubrication and manual assistance to lubricate the sheave bearing. Through a real-time monitoring of the lubrication system, it realized the intelligent distribution function of single pump and multiple points with different grease amounts, and also provided the waste grease recovery function to avoid damage to bearings by waste oil. Then, an intelligent control strategy based on the identification of abnormal lubrication status was studied, and the lubrication cycle and lubrication amount of the system were adjusted based on the judgment results of the lubrication status. Subsequently, considering the impact of lubrication status identification accuracy on system operation results, an intelligent identification model of lubrication status based on the combination of Locality Preserving Projections (LPP) and Support Vector Data Description (SVDD) was constructed. In view of the problem that the number of neighboring points in the feature dimensionality reduction method will seriously affect the dimensionality reduction effect, it was proposed to use the information entropy difference between the high and low dimensional feature sets of the sample set as the objective function, and apply the particle swarm optimization algorithm to optimize the parameters of the LPP algorithm. The model was verified using on-site measured data. The results show that the proposed method can effectively identify the abnormal state of the sheave bearing, and the identification accuracy can reach 82% under on-site working conditions. Finally, an on-site application study of the intelligent lubrication system for pulley bearings was conducted in a coal mine. A single pump was used to lubricate four pulleys. The results show that the lubrication system can obtain its own operating parameters in real time and achieve remote control, ensure the continuation and uniformity of the lubrication effect, and meet the actual requirements of the mine site.

Coal gasification fine slag (CGFS) has high utilization value, but the low recovery rate of residue carbon greatly restricts its resource utilization. The oil agglomeration separation method has obvious advantages in the CGFS separation process, but its separation efficiency is severely limited by the symbiotic structure of carbon and ash. In order to break through the bottleneck problem of residue carbon separation and enrichment technology by oil agglomeration method, the effects of ultrasonic time, ultrasonic power, fluid shear time and their interaction on oil agglomeration and separation were investigated in this paper. Combined with BET, particle size distribution, FT-IR, XPS and SEM-EDS analysis methods, the strengthening mechanism of ultrasonic cavitation and fluid shear (UC-FS) pretreatment on oil agglomeration separation was revealed. The results show that when the ultrasonic power is 270 W, the ultrasonic treatment time is 29 min, and the fluid shear time is 23 min, the concentrate with ash content of 9.55% and the tailings with ash content of 91.51% can be obtained, and the combustible recovery rate can be increased to 90.54%. Ultrasonic cavitation gradually loosens the original dense carbon ash structure, and promotes the development of the pore structure of CGFS in coordination with the scouring effect of fluid shear, which increases the dissociation degree of carbon ash particles and thus reduces the ash content of concentrate. UC-FS pretreatment can effectively increase the proportion of hydrophobic groups such as C—C, C=C and C—H on the surface of carbon residue, increase its contact angle from 110.34° to 121.16°, and further expand the difference of hydrophilic and hydrophobic properties on the surface of carbon and ash particles, thus improving the effect of oil agglomeration separation. The mechanism of UC-FS synergistic pretreatment to improve the efficient separation of carbon ash particles is mainly attributed to the micro-abrasive effect generated by the coupling of ultrasonic cavitation bubbles and fine-grained microspheres. This study can provide theoretical basis and technical guidance for the separation and utilization of CGFS.

In view of the natural endowment of mercury in fossil fuels and mineral resources, as well as the mercury emission controlling and regulating in the energy and resource utilization processes, the research and development on the mercury continuous emissions monitoring system (Hg-CEMS) with proprietary intellectual property rights is the most important requirement in science and technology in China. As a critical component of the Hg-CEMS system, the flue gas pretreatment system is a core technology that limits the development and application of the Hg-CEMS technology in China. This paper presents a comprehensive review of the research progress in the four key modules of the Hg-CEMS flue gas pretreatment technology, including the dilution sampling, Hg0/Hg2+ separation, Hg2+ reduction and Hg2+ calibration gas generation. Firstly, the dilution sampling techniques are highlighted in their characteristics and principles. The working principles, structures, and design considerations of the critical parameters for both critical hole and thermal dilution injectors are summarized. Emphasis is focused on the connection of numerical simulation with the optimal design methodology for the thermal dilution injector and critical hole. Secondly, regarding the Hg0/Hg2+ separation technology, various partitioning methodologies encompassing the wet absorption separation, physical adsorption separation and chemical adsorption separation are discussed. Particular attention is given to the separation and adsorption efficiency of the advanced dry chemical adsorption techniques involving the novel selective adsorbents of KCl and CaO with their updated theoretical and experimental outcomes under practical operating conditions. Thirdly, in aspect of the Hg2+ reduction technology, a comparative analysis of wet chemical reduction, low-temperature reduction and high-temperature reduction techniques is expatiated. Particular focus is on the active components of solid-state reducing agents, the impact of temperature on the reduction of divalent mercury, and the detrimental influences of flue gas components on the re-oxidation of the reduced elemental mercury in the low-temperature reduction techniques. An in-depth investigation of the impact of filler materials, acidic gas components and acid removal techniques on the reduction of divalent mercury in the high-temperature reduction techniques is highlighted. Finally, facing the technical problems, a solid generation method of the Hg2+ calibration gas is invented and its industrial utilization feasibility is verified in chemistry and experiments. In conjunction with the current status of research and application of the Hg-CEMS technology, the research technical routs, the solutions to some problems and development prospect for the above-mentioned four key modules are put forward.

In view of the uniqueness of the occurrence conditions of coal resources in Xinjiang and the fragility of the ecological environment in the coal occurrence area, it is urgent to develop coal resources in Xinjiang scientifically. Therefore, in this paper, the geological occurrence conditions, hydrogeological conditions, physical geography and ecological environment conditions of coal resources in Xinjiang were briefly discussed, and the exploitation potential of coal resources was analyzed. The results show that the coal resources in Xinjiang are extremely abundant, with an estimated coal resource of 2.19 trillion tonnes in the entire region, accounting for more than 40% of the total estimated coal resources in China. There are 24 coal fields in Xinjiang with estimated resource levels exceeding 10 billion tonnes, of which 5 have estimated resource levels exceeding 100 billion tonnes, 8 have estimated resource levels between 40 billion−100 billion tonnes, and 11 have estimated resource levels between 10 billion−40 billion tonnes. Among the potential coal resources, shallow resources below 1000 meters account for 52.8%. The main coal rank of Xinjiang’s coal resources is low-rank bituminous coal and medium-rank bituminous coal, fol-lowed by high-rank bituminous coal in middling coal rank coal, while lignite in low-rank coal, ultra-high rank bituminous coal in middling coal rank coal and anthracite in high-rank coal have extremely limited distribution range and quantity, accounting for a very low proportion of the total resources. Taking into account the transportation of coal from Xinjiang, the transmission of electricity from Xinjiang, the transmission of natural gas from the west to the east, and the local coal chemical industry plan, it is expected that Xinjiang’s coal production capacity will exceed 800 million tonnes by 2035. On this basis, an ecological environment carrying capacity evaluation index system was constructed, and the ecological environment carrying capacity of the five major coal mining areas planned and constructed in Xinjiang was evaluated. The results show that the overall ecological environment carrying capacity of the coal resource areas in Xinjiang is at a medium to low level, and the average ecological environment carrying capacity of the five major coal mining areas is ranked as Yili (0.42)>Kubai (0.38)>Hefeng (0.31)>Zhundong (0.25)>Tuha (0.22). It shows a decreasing trend from west to east. In response to the conditions and potential of coal resource development in Xinjiang, strategies have been proposed to optimize the layout of coal resource development, promote mining technology upgrading, promote intelligent mining technology, strengthen the concept of green mining, and expand diversified channels for coal utilization.

The hydraulic support precise pushing and fast follow-up is the key technical support to realize intelligent mining of working face. In order to realize intelligent mining, the precise pushing of hydraulic support is equivalent to the precise position control of valve-controlled cylinder system in coal mine environment, and fast follow-up of hydraulic support need to be realized through follow-up process, liquid supply with stable pressure, fast support movement, etc. Aiming at the precise advancing technology of hydraulic support, it is pointed out that the mature precise position control technology of valve control in related fields can be used for reference. This paper summarizes the research achievements of the electro-hydraulic proportional valve, high-speed on-off valve and electromagnetic directional valve control cylinder position control technology. This paper also summarizes the problems existing in the application of above achievements in the field of coal mines. It is proposed that the precise pushing of hydraulic support can be realized by developing large-flow high-pressure water-based electro-hydraulic proportional valve suitable for the underground environment and developing the intelligent optimization control algorithm. Aiming at the fast follow-up technology of hydraulic support, it is pointed out that the current automatic follow-up of hydraulic support is slow due to unreasonable follow-up process, unstable liquid supply system, and unreasonable support moving process. It is easy to appear the situation of not moving in place and losing support. The related research achievements of improving the follow-up speed are summarized from three aspects: optimizing the follow-up process, supplying liquid with stable pressure, and fast pushing support. The following points are pointed out. At present, the follow-up process cannot be dynamically adjusted according to the speed of the shearer, and the automatic follow-up based on equipment perception is still at the theoretical stage. Optimizing the structure and control algorithm of the liquid supply system is the main way to realize the liquid supply with stable pressure in the working face. But it can not effectively solve the problem of pressure and flow stability at the end of the hydraulic support when the multi-support cooperates. Improving the structure of the hydraulic system is the main way to achieve fast support pushing. But there are some problems such as the large pressure drop when high-pressure oil is transmitted over a long distance, the pipe explosion at the high-pressure point, and the difficulty of pipeline layout caused by increasing the pipe diameter. In view of the above problems, it is proposed to realize the precise pushing and fast follow-up of hydraulic support from four aspects: the constant pressure control of the working face liquid supply system, the improvement of the control precision of hydraulic support pushing, the guarantee of the automatic follow-up effect of hydraulic support, and the improvement of the whole follow-up speed of the working face. It is pointed out that the development trends of precise pushing and fast follow-up technology of the hydraulic support are centralized-distributed agile and efficient liquid supply, improvement of the edge computing capacity of hydraulic support controller, enhancement of adaptability of follow-up control strategy to stope environment, dynamic coupling and follow-up control of stope and equipment.hancement of adaptability of follow-up control strategy to stope environment, dynamic coupling and follow-up control of stope and equipment.

This paper introduces the application and research status of the intelligent gangue sorting robot. This paper points out that the intelligent gangue sorting robot is mainly based on the principle of X-ray and image identification. And the high-pressure pneumatic sorting and truss robot grasping sorting are used to separate coal and gangue. The sorting actuators are mainly truss type, parallel type and series type of intelligent gangue sorting robot. The sorting actuators have fast response speed and often separate the gangue in the form of 'pulling' and 'grasping'. In the process of belt transportation, the compatibility of different gangue sizes and the optimization of movement path need to be considered in the 'pulling' of the intelligent gangue sorting robot. And the working space of the manipulator and the bearing capacity of the robot need to be considered in the 'grasping'. This paper analyzes the key technologies such as deep learning-based coal and gangue identification, unstructured multi-constraint environment-oriented motion planning of gangue sorting manipulator, force feedback-based active compliance control of manipulator and multi-arm cooperative sorting task allocation strategy and control. These technologies are used for intelligent gangue sorting robot to effectively realize gangue sorting in complex on-site environment. This paper points out that coal and gangue identification technology based on deep learning is one of the key technologies of gangue sorting robot. It still needs further research on the efficient construction method of coal gangue data set, improving the generalization of coal gangue identification algorithm, and the real-time optimization of coal gangue identification algorithm. Combined with the demand of field application and intelligent robot development, the future research directions of intelligent gangue sorting robot are pointed out. In the complex environment on site, it is suggested to improve the robustness and adaptability of the coal gangue identification algorithm. It is suggested to develop intelligent sensing and control technology for complex environment and high-precision three-dimensional pose estimation technology for gangue. It is suggested to develop intelligent gangue picking technology of gangue picking robot based on force position hybrid control. It is suggested to research intelligent gangue sorting robot underground gangue sorting technology.

The underground coal mine transportation system can be divided into the main transportation system and the auxiliary transportation system according to the different transportation objects. This paper expounds the status of the bottom equipment and system intelligent technology of the main and auxiliary transportation systems in the underground coal mine in China. This study also analyzes the problems existing in the intelligent technology of the main and auxiliary transportation systems from the aspect of the top planning, standard system and single machine intelligent technology. The three key technologies of intelligent main transportation system are introduced, including distributed communication control technology of belt conveyor based on full digital FCS (fieldbus control system), enhanced protection technology of belt conveyor based on multi-sensor fusion of machine audio and vision, and coordinate economic operation control technology of coal flow. The two key technologies of intelligent auxiliary transportation system are also introduced, including management and control integration technology of underground coal mine auxiliary transportation based on industrial Internet architecture, vehicle-to-everything and unmanned driving technology in underground coal mine. Combined with the requirements of Coal mine intelligent construction guide (2021 edition) for intelligent main coal flow transportation system and intelligent auxiliary transportation system, this paper expounds the intelligent development trend and goal of main transportation system and auxiliary transportation system of underground coal mine from the short term and medium and long term. At present, the research of the main transportation system of underground coal mine in China should focus on the enhanced protection and detection technology of belt conveyor based on multi-sensor fusion of machine audio and vision, intelligent inspection robot technology, etc. And the research of the auxiliary transportation system should focus on the fine closed-loop control and advanced auxiliary driving technologies.

The data acquisition of intelligent mine is based on ubiquitous perception and cannot be separated from the basic technical support of industrial Internet of things and big data. This paper analyzes the current situation of coal mine automation and monitoring data acquisition technology and platform, that is, the lack of identity marks of the perception node, data not being shared, system maintenance difficulties, system software smokestack construction and data fusion difficulties. This paper proposes the process and key technologies of intelligent mine basic information acquisition based on industrial Internet of things, including low-power ubiquitous perception technology, perception node identification and data sharing technology, long-term maintenance-free technology, data hierarchical interaction and fusion technology, etc. On this basis, the structure and design concept of the intelligent mine basic information platform based on private cloud deployment is proposed. Only one set of distributed software platform based on microservice technology can solve the problem of the collection, classification and storage, interaction, fusion and analysis of all kinds of automation data in the entire mine, and realizes the linkage control with the control execution devices. Through the establishment of a unified technology and service system, including a unified technology architecture and technology stack, unified master data, unified data storage mechanism, unified data model, unified authority and user interface mode, it is ensured that multiple businesses integration can be realized under the same software platform. By establishing a unified data acquisition mode based on the Internet of things, that is, loading and adapting different protocol drivers, data acquisition by professional systems of different manufacturers is realized. Through the establishment of a unified data processing and storage mechanism, data fusion and release mechanism, it is able to provide consistent data sources for intelligent mines.

The data middle platform is the data base of intelligent coal mine construction and the foundation of coal mine big data application. This paper proposes the idea of intelligent coal mine data middle platform construction, including data aggregation, data development, data storage, data asset management and data service. This study designs the intelligent coal mine data middle platform architecture, analyzes the data standard specification, big data basic support, data aggregation, data development, data resource pool, data asset management, data service, operation and maintenance guarantee and other function modules of the data middle platform. This paper discusses the solutions of key technologies such as large concurrency and low latency data processing, data classification and storage, data governance, and the construction of big data-based coal mine disaster-risk model in the process of building an intelligent coal mine data middle platform. The application shows that the intelligent coal mine data middle platform realizes data aggregation, data development, as well as the data classification and storage of various perception data, basic data and management data, data asset management, data modeling, model training and data services, etc. The platform makes the multi-source heterogeneous data of coal mines change from data resources to data assets, provides applications such as scheduling decision, disaster risk analysis, equipment health diagnosis and preventive maintenance based on big data, and solves the problems of serious information silos, difficult data integration and low level of intelligent analysis in coal mines.

Most of the existing studies on CO2 replacement for CH4 are focused on microscopic gas injection replacement mechanism and macroscopic replacement efficiency influencing factors, and most of the studies are theoretical analysis at the model level or multiple factor analysis at the simulation test level. There are few physical simulation experiments and quantitative analysis. In order to solve the above problems, by using CO2 replacement for CH4 experiment system, this paper studies the seepage diffusion evolution law and time-varying characteristics of CO2 replacement for CH4 in coal during the replacement process at different injection pressures. This paper analyzes the change law of CO2 and CH4 concentrations at the gas outlet, the accumulated CH4 replacement volume and the replacement ratio during the whole process. Physical simulation experiments are used to investigate the influence of gas injection pressure on the replacement efficiency and make the quantitative analysis. The experiments results show that: ① The CO2 and CH4 gas concentration change trends at different injection pressures are basically the same, which can be divided into three stages, including the original equilibrium stage, the dynamic equilibrium stage and the new equilibrium stage. As the gas injection pressure increases, the time of CO2 and CH4 gas breaking the original equilibrium stage is gradually shortened, the time of the dynamic equilibrium stage increases, and the time of the new equilibrium stage is about the same. ② At different injection pressures, the accumulated CH4 replacement volume increases with the increase of gas injection time, and the increase rate is fast at first and then slow, and becoming a fixed value at last. The gas injection pressure increases from 0.6 MPa to 1.4 MPa, the accumulated CH4 replacement volume increases, the replacement ratio decreases from 4.99 to 4.10, and the replacement efficiency increases. When the gas injection pressure is 1.4 MPa, the replacement ratio is the smallest and the replacement efficiency is the best. This conclusion can provide a reference for the theoretical study of CO2-ECBM related technologies and the selection of related process parameters for technical implementation in low permeability coal seams.

The 5G communication system used in coal mines must obtain a safety mark certificate. In order to better promote the intelligent construction of coal mines and the development of 5G technology in coal mines, help the companies to understand the technical requirements of coal mine 5G communication system and inspection requirements in advance, shorten the review period, this paper studies the safety technical requirements and inspection methods of coal mine 5G communication system. The safety technical requirements of coal mine 5G communication systems are discussed in terms of basic requirements, networking requirements, 5G communication technology requirements, explosion-proof safety requirements and anti-interference requirements. Moreover, relevant suggestions are made for the issues that need to be focused on. In terms of the coal mine 5G communication system, this paper focuses on the system networking mode discrimination, core network inspection and anti-interference performance inspection. In terms of 5G base stations and terminals, this paper focuses on the inspection of 5G technical indicators and explosion-proof safety requirements. The issues such as coal mine 5G communication system management issues, 5G base station multi-antenna power superposition threshold power calculation issues, anti-interference technical difficulties, the technical requirements and inspection methods of transmission rate and delay, the inspection of antenna-integrated base stations, and the problems of 5G upstream and downstream bandwidth in mines are also discussed in this paper.

The current research on intelligent coal mines focuses on top-level design, theoretical architecture, core technologies, control platforms, construction routes, standard development and evaluation systems, etc. There is no research on the technical research before and after the release of The guiding opinions on accelerating the development of intelligent coal mines. Intelligent coal mines are technology-intensive and capital-intensive, and need to be guided by policies to form a joint force which brings the government, academia, industry, finance and users together. Using CNKI (China National Knowledge Infrastructure) as a tool, this paper analyzes the current status of intelligent coal technology research, hot spots of concern and major research institutions. This paper summarizes the current status of intelligent coal mine policy development at the national level and in major coal-producing provinces such as Guizhou, Shandong and Shanxi. Although there are slight differences in the starting point and implementation progress of intelligent coal mines, all provinces have issued guiding documents in terms of implementation methods and acceptance and grading, and have made attempts to develop standards and establish innovative R&D centers to accelerate the pace of intelligent coal mine research and construction.

Mine unmanned vehicles are needed to reduce the number of coal mine underground operating personnel and to build safe, efficient, green and intelligent mines. The characteristics of mine unmanned vehicles are summarized as following points. The positions of underground operating personnel in coal mine are comprehensively identified. All mine vehicles are controlled. Mine track transportation equipment only needs one-dimensional positioning. The lighting condition is poor. The wireless transmission attenuation is large. There is no satellite signal. The electromagnetic environment is complex. The characteristics also include electrical explosion-proof, humid environment and water spray and dust. This paper analyzes the technical characteristics of mine vehicle positioning, such as ultrasonic positioning, laser position, radio positioning(including RFID, ZigBee, UWB, WiFi6, 5G), inertial navigation, simultaneous localization and mapping(SLAM), odometer and so on. This study puts forward a joint positioning method of mine vehicle, which is based on UWB and supplemented by inertial navigation, odometer and SLAM. This paper analyzes the technical characteristics of obstacle identification and distance measurement of mine unmanned vehicle, such as laser radar, millimeter wave radar, infrared camera, visible light camera, visible light binocular vision camera and so on. This study puts forward a multi-information fusion method of obstacle identification and distance measurement of mine unmanned vehicle. The method is mainly based on laser radar, supplemented by millimeter wave radar, infrared camera, visible light camera, visible light binocular vision camera and ultrasonic radar. When the road condition is complex and the automatic driving can not make decisions, the mine unmanned vehicle needs to automatically switch to the ground remote control mode. In view of the above situation, it is pointed out that the mine unmanned vehicle ground remote control technology based on 5G is the preferred scheme. However, the mine 5G wireless communication system has the problems of small wireless coverage radius and high cost. Therefore, it is suggested to study the application of WiFi7 in the mine vehicle ground remote control.

The accuracy of mine ultrasonic gas flowmeter needs to be improved. The cross-correlation detection signal has 'signal hopping' phenomenon and affects the measurement precision of ultrasonic transit time. In order to solve the above problems, this paper proposes an automatic tracking method of reference waveform of mine ultrasonic gas flowmeter. While calculating the ultrasonic transit time, the cross-correlation operation is carried out between the ultrasonic reference waveform and the real-time received signal waveform. The reliability of the cross-correlation detection is calculated. The reliability effective threshold value and the reference waveform update threshold value are set. The reliability of the cross-correlation coefficient is evaluated so as to determine whether the reference waveform is updated. When the reliability is less than the effective threshold, it is determined that the received signal is invalid, and the ultrasonic signal is re-sent. When the reliability is greater than the update threshold, it is determined that the received signal waveform is highly consistent with the reference waveform. There is no need to update the reference waveform. When the reliability is between the effective threshold and the update threshold, it is determined that the received signal is valid. And the original reference waveform is replaced with the current received signal waveform to realize automatic tracking of the reference waveform. This paper analyzes the two kinds of waveform changes of ultrasonic received signal which may cause ultrasonic transit time error of one waveform period. The waveform changes are continuous envelope deformation and instantaneous envelope distortion. The change of gas flow rate, temperature and pressure will lead to the continuous change of received signal envelope. Spike pulses, random signals and periodic interference may cause instantaneous envelope distortion of the ultrasonic received signal. The instantaneous envelope distortion can be divided into three cases, severe distortion of the main peak, slight distortion of the main peak and non-main peak distortion. The experimental results show that under the influence of different flow velocity, temperature, pressure and noise, the relative error of ultrasonic gas flowmeter is less than ±1.0%. The results meet the measurement requirement of precision level 1.0. The automatic tracking method of reference waveform provides a guarantee for the accuracy and reliability of flow measurement.

The current researches on the application of direct current resistivity method in coal seam floor water inrush monitoring mainly focus on the resistivity response characteristics of the deformation and damage of the floor, and there are few researches on the resistivity change law of the dynamic development process of water channels. In order to solve the problem of floor water inrush in the North China coalfield, the direct current resistivity method is used to monitor the abnormal structure of floor water-bearing and water-conducting under the influence of mining. Firstly, the paper introduces the working principle of direct current resistivity monitoring system at coal working face and the automatic processing and interpretation method of monitoring data based on three-dimensional inversion of resistivity. Secondly, the paper constructs a geological model for monitoring the process of floor water inrush and carries out the numerical simulation study of the development process of floor water-bearing and water-conducting structures. Finally, the floor direct current resistivity monitoring test is carried out in the coal mine. The numerical simulation results show that the distribution range of abnormal structures of water bearing and water conducting along the survey line can be identified based on the resistivity three-dimensional inversion results. The development of abnormal structures can be inferred from the changing trend of resistivity over time. The low-resistance anomaly response gradually increases as the abnormal water bearing and water conducting structures developing upward, and the low-resistance anomaly increases gradually in the vertical direction. The results of the coal test show that the direct current resistivity monitoring successfully captures the process of water inrush from the floor of coal working face, and the time of abnormal changes in resistivity is earlier than the actual water inrush time of the working face. The low resistance response gradually increases before the increase of water inrush from the working face, which is basically consistent with the numerical simulation results. After the water inrush from the working face, the low resistance abnormality gradually weakens. The results show that the direct current resistivity method can be used for early warning of water inrush from the working face. However, determining the development height of the abnormal structure accurately requires a comprehensive interpretation combined with other monitoring methods.

At present, there are more researches on the concept and development plan of intelligent mines, and less researches on the intelligent construction results and key technologies. Based on the 5-layer technical structure of intelligent mine construction, taking the intelligent construction of Daliuta Coal Mine as an example, the paper discusses the intelligent construction and effectiveness in terms of fully mechanized mining, excavation, transportation, power supply, water supply and drainage systems. A total of about 100 fixed mine positions are canceled, and more than 200 operators are reduced. The construction helps to reduce the labor costs by 40 million yuan/a, save the industrial water and electricity consumption by 30%, improve the equipment utilization by 5%, and increase the total workforce efficiency by 10%. It is pointed out that the key points of intelligent mine construction are broadening the network channel, unifying the interfaces of various subsystems, ensuring the associated equipment safe and reliable, and hiring professional personnel teams. This paper summarizes the current difficulties in the intelligent mine construction and discusses the key technologies to be tackled. The technologies include automatic coal cutting, personnel detection of mobile equipment, wireless sensing, centralized refueling, intelligent security inspection at the mine entrance and unmanned driving.

Coal mine gas and coal dust explosion will produce explosive sound. Coal and gas outburst will produce the sound of coal cannon and the supports will produce squeaking and cracking sound. Rock burst will produce huge rock breaking sound and vibrations. Coal mine water inrush will produce 'hissing' water sound, and a large amount of water inrush will produce water flow sound. Coal mine roof fall will produce roof cracking sound, coal rock hitting the ground sound and support damage sound. According to the characteristics of the sound of extraordinary accidents in coal mines, the alarm methods of accidents of mine gas and coal dust explosion, coal and gas outburst, rock burst, water inrush and roof fall are proposed. The characteristics of the time domain and frequency domain of each accident sound are different from the characteristics of other sounds, and the sound can be monitored in real time by mine explosion-proof sound pickup equipment and system. Therefore, accidents can be sensed and alarmed through the intelligent analysis of the sound and the analysis of the characteristic parameters of the sound frequency, amplitude and short-term energy. By monitoring and analyzing the sound intensity and other characteristics of different monitoring locations, the sequence of occurrence and the damage sequence of explosion-proof sound pickup equipment, the accident location is able to be determined. Based on the characteristics of each accident, the accident identification method of multi-information fusion analysis is proposed to reduce the sound interference of coal fall from the working face, blasting operations, coal mining equipment, excavation equipment, transportation and lifting equipment, power supply equipment, emulsion pumps, water pumps and local ventilators. The paper discusses the advantages and disadvantages of different sound pickup equipment and proposes that the microphone arrays should be used for mine sound pickup equipment. Furthermore, the paper proposes a sound recognition classifier applicable to coal mine extraordinary accidents.

At present, in most coal mines, the coal pillar width of goaf-side roadway driving is determined by the average mining thickness. However, the thickness of the same coal seam could be varied greatly by various factors during the formation process. The large variation of mining thickness in the fully mechanized working face leads to large difference of surrounding rock deformation and complex damage mechanism of the goaf-side roadway driving. In order to solve the above problems, FLAC3D software is used to establish a roadway model so as to analyze the surrounding rock deformation and damage law under the average mining thickness, and determine the reasonable coal pillar width. When the average mining thickness is 18 m, on the side of the solid coal, the peak supporting pressure in the coal is positively correlated with the coal pillar width. Moreover, when the coal pillar width is greater than 8 m, the growth rate of the supporting pressure slows down. Therefore, the reasonable coal pillar width should be 8 m. This paper studies the influence of mining thickness on the stability of the surrounding rock of goaf-side roadway driving in the context of determined coal pillar width. The results show that when the coal pillar width is 8 m, with the increase of mining thickness, the shear damage area of roof increases, and the rock deformation range and the roof subsidence increase. However, the shear damage area of two sides and the distance between the two sides decrease. When the mining thickness is less than 18 m, the peak support pressure in the coal pillar is negatively correlated with the mining thickness. When the mining thickness is greater than 18 m, the peak support pressure in the coal pillar is positively correlated with the mining thickness, but the growth is small. According to the simulation analysis results, it is concluded that the increase of mining thickness is beneficial to the control of the surrounding rock along the two sides of the goaf roadway, but not beneficial to the roof maintenance. For areas with large mining thickness, anchor rods should be added to strengthen support in time. The actual application on site verifies the reliability and validity of the research in this paper.

Compared with single coal seam or other coal seam group, the mining process of the close-distance coal seam group is more likely to be affected by the stress of the adjacent seam. Moreover, the gas is more likely to gush into the coal seam through the developed fissures, causing gas accumulation on the working face of the mining seam. The existing gas control research for close-distance coal seam group mainly focuses on the determination of single measure parameters and effect analysis, without in-depth research of the relationship between gas management measures in time and space. The researches on the optimal combination of comprehensive gas management measures, the basis for determining specific parameters and the effect analysis after the measures being taken are not sufficient enough. In order to solve the above problems, taking the 81403 fully mechanized working face of No.1 Coal Mine of Yangquan Coal Industry (Group) Co., Ltd. as the research object, the paper analyzes the stress distribution and evolution process of mining under the conditions of close-distance coal seam group through numerical simulation. The research studies the overlying rock destruction and fissures development change law, and proposes that the main sources of gas on the 81403 fully mechanized working face are coal seam desorption gas, pressure relief gas in upper adjacent coal seam and goaf gas, etc. Based on the different gas emission sources and characteristics, the paper proposes the gas extraction measures of bedding pre-extraction + high extraction roadway+high borehole+buried pipes in the extraction area. Before mining, pre-extraction is applied to reduce the amount of coal seam desorption gas. High extraction roadway and high borehole are used to deal with gas gush from adjacent coal seam. Buried pipes are used to control local gas accumulation in the upper corner. The measures form a comprehensive management system in time and space so as to achieve the purpose of gas control. Practical application results show that the gas extraction rate reaches 89.9% on the working face, and the gas volume fraction of the return airway and upper corner is kept below 1%, ensuring the safe mining of the working face.

This paper, taking the Chinese and English literature of mine safety and digital mine safety management from 1999 to 2019 as the research object, using Citespace visualization software as the research tool, systematically sorted out and analyzed the highly cited literature from the number of documents, research topics, major scholars and research institutions, keywords and keyword centrality. The results show that: papers on mine safety from the perspective of digital mines account for about 20 % of the research papers in the field of mine safety, and show an upward trend year by year, indicating that the related research of digital mines in the field of safety management has always been a hot spot in this field; Most cited Chinese documents are theoretical methods or management studies, while highly cited foreign documents are mostly engineering and technical studies, indicating that there are certain differences between Chinese and foreign academic journals. 61.9 % of the authors of foreign literature are from China, which shows that Chinese scholars have made a great contribution to the research in this field. It also shows that Chinese scholars have taken theoretical method research, management research, and engineering technology research into account at the same time. Current research at home and abroad has a high degree of concentration, strong research intensity, and strong forward-looking nature. It has basically realized the combination of emerging technologies and the safety management of digital mines, which provides the necessary theoretical support for the application and development of digital mines in mine safety management.

Mine moving target positioning system provides location-based services for intelligent construction of coal mines. However, most of the traditional mine positioning systems use single or combined communication technologies between positioning beacons and positioning tags with inflexible structure, limited coverage, low robustness and limited positioning accuracy. Using single or combined ranging technology, the optimal ranging technology cannot be selected adaptively according to different usage scenarios. For the position solution algorithm is fixed, the optimal solution algorithm cannot be selected adaptively according to different usage scenarios and signal changes. Hence, a new paradigm for all source mine positioning service is proposed, which can dynamically select the optimal combination of devices that meets current needs from all available positioning signal measurement devices according to the changes of the positioning environment and the target bearing platform. The paradigm can select the optimal combination of algorithms from the available ranging algorithms, positioning solving algorithms and result optimization algorithms adaptively to calculate the optimal position of the target node. In this study, all source mine positioning system architecture is designed, the available positioning signal measurement devices in mines and the types of measurement attribute values that can be used for positioning are discussed, and the functional differences of positioning servers between single mine positioning and all source mine positioning are compared. This paper discusses three key technologies in all source mine positioning service: unified positioning framework technology, which aims to meet the modular, combined and expandable needs of all source positioning; all source positioning information fusion technology, which organizes the measured attribute values to improve positioning accuracy; communication and positioning integration technology, which simplifies the design of all source mine positioning system and improves positioning accuracy through the positioning capability of wireless communication network itself. This paper proposes the implementation architecture of a terminal-edge-cloud based all source mine positioning system in order to fit in with the mainstream construction mode of intelligent coal mine and reduce the implementation difficulty and system cost significantly.

At present, remote peer-to-peer firmware updates have been implemented in the multi-layer heterogeneous network of coal mines, but the firmware of devices at all levels cannot be directly updated from the ground control host. The maintenance workload is relatively large when the sensors are distributed and the number is large, thus a remote firmware update method for multi-layer heterogeneous network of coal mines with unlimited levels and multiple links is proposed. The method is proposed that the host sends the firmware and its routing, and devices at all levels parse the routing, forward the firmware or update itself. The update process can display its progress information. The characteristic features of the firmware data in multilayer heterogeneous networks is transferring through multiple devices and links to reach the target device. This paper is proposing that the core of realizing remote firmware updates in multi-layer heterogeneous networks lies in routeing description. Moreover, this paper studies the method and process of realizing routing description by using JS object notation (JSON) from three aspects: device property description, network topology construction and firmware routeing description. The lower and upper computer software design method for implementing remote firmware updates of multi-layer heterogeneous networks in coal mines is introduced. A four-layer heterogeneous network experimental system containing Ethernet, RS485 bus and CAN bus is built, and the feasibility and stability of the JSON routing description based remote firmware update method for multi-layer heterogeneous networks in coal mines is verified by the statistics of the success rate and update time of each layer device firmware update.