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In order to explore the research trends of thermodynamic disaster in coal mine, based on the perspective of information visualization, 2 845 related papers published in CNKI database from 2002 to 2021 were used as data sources, and CiteSpace was used to conduct scientific measurement analysis on the number of papers, authors, institutions and keywords. The research shows that the research on thermodynamic disaster in coal mine generally shows three stages: slow growth, steady growth and stable development. DENG Jun, WANG Deming, YU Minggao, WEN Hu are the main core authors in this field. China University of Mining and Technology, Xi’an University of Science and Technology, Liaoning Technical University, China University of Mining & Technology（Ｂｅｉｊｉｎｇ） are the main research institutions in this field. Hot keywords mainly focus on gas explosion, coal spontaneous combustion, numerical simulation, mined-out area, etc. The research emphasis in this field is mainly embodied in the research of spontaneous combustion characteristics of coal and gas explosion, in which numerical simulation is an important research method. At present, there are few studies on coal mine thermal power compound disasters and disaster monitoring and early warning. In the future, the research on these two aspects can be strengthened.

In order to quantitatively characterize the effect of carbon dioxide fracturing on the pore structure of coal, the M8 coal seam of Dayun Coal Mine was used as the research object to carry out carbon dioxide fracturing. Four groups of coal samples were tested by mercury injection and scanning electron microscope, and fractal characteristics were combined to analyze the coal samples before and after cracking. The results show that carbon dioxide fracturing has a significant effect on coal pores. Mercury injection test results show that the pore volume, average pore diameter and porosity of coal samples all increase, and the specific pore surface area will increase within the range of about 1 m close to the cracking hole, and then the cracking effect will be weakened with the propagation of the cracking impact. The fractal dimensions of the four groups of coal samples were calculated by the mercury pressing experiment and the electron microscope scanning experiment. After cracking, the fractal dimensions were all smaller than that of the raw coal. The fractal dimension of 4 groups of coal samples is 1# < 2# < 3# < YM from small to large. The results indicate that carbon dioxide cracking can promote the development of pore structure and the connectivity between pores in coal samples.

The evolution characteristics of pores and fractures in coal after liquid carbon dioxide (CO2) phase change are important factors that determine the permeability increase effect. Therefore, it is critical to correctly understand the influences of liquid CO2 phase change on pores and fractures in coal. The changes of adsorption and desorption isotherm, pore size, pore volume, and specific surface area of fractured coal and fractured coal were compared by low temperature liquid nitrogen adsorption experiment. In addition, a scanning electron microscope was adopted to observe fracture characteristics of fractured and unfractured coal samples and analyze changes in the connectivity and fracture development. Experimental results show that the fractured coal samples exhibit better hysteresis loops and a larger proportion of gas desorption than the unfractured ones. Fractured coal samples contain more developed pores and fractures compared with unfractured ones, and their fragmentation degree, pore diameter, fracture width, and connectivity of pores and fractures are also better. Besides, the closer the samples from the fracturing boreholes are, the better the fracturing effect. This indicates that liquid CO2 phase change can effectively enhance the gas transport capacity in pores and fractures in coal. The research results provide a solid basis for the better application of liquid CO2 phase‐change fracturing to the prevention of coal and gas outburst disasters and the realization of efficient gas extraction in deep coal seams. [ABSTRACT FROM AUTHOR]

We select a representative coal mine in Guizhou Province as the research object, conduct on-site investigation and data collection, adopt Romanian occupational accident and occupational disease risk assessment method (MLSP method), International Mining and Metals Committee occupational health risk assessment model (ICMM model) and occupational hazard operation class-ification method. These three occupational health risk assessment methods were used for health risk assessment, and the advantages and disadvantages of the three models were compared and analyzed. The results show that the MLSP model determines that the coal mine worker’s exposure to dust is a medium risk level; the ICMM model quantitative method determines that the coal mine worker’s exposure to dust is an intolerable risk level, and the ICMM model matrix method determines that the health risk the coal miner’s exposure to dust is medium risk or low risk; the occupational disease hazard operation classification method determines that the coal mine worker’s risk level of exposure to dust is Class I mild hazard operation. According to the research status of the coal mine enterprise, the risk management measures are proposed from the government, the enterprise itself and the coal miners.

Liquid carbon dioxide (CO2) phase change fracturing (LCPCF) is an innovative technique to improve the efficiency of gas drainage from low-permeability coal seams of high gas content. However, fracture sprouting, extension and displacement changes of coal under LCPCF need further study, and corresponding field tests are also lacking. Therefore, a mechanical model based on the thermodynamic theory of CO2 phase change is developed in this paper. Then, the pressure change characteristics, crack propagation and displacement change of coal subjected to LCPCF were analyzed through numerical simulation. In addition, the permeability-enhancing effect of the field LCPCF test was analyzed. The results obtained from the numerical simulation show that during the LCPCF process, the crack-generation process changes with pressure as follows: microfracture–numerous microfractures–major macrofracture–macrofractures. During the development of fractures, the stress is incompletely symmetrically distributed in coal centered on the fracturing borehole. The failure occurs stochastically in the coal in the vicinity of the fracturing borehole at first, and then it gradually propagates to the inner seam of coal as the gas pressure increases. The following result can be obtained from field experiments: the permeability coefficient of coal seams after increasing the permeability through LCPCF is 2.60~3.97 times that of coal seams without presplitting. The average concentration of gas extracted in coal seams within the zone having undergone an increase in permeability through liquid CO2 fracturing is 2.14 times greater than that within the zone without presplitting. The average pure amount of gas extracted within the zone having undergone an increase in permeability through LCPCF is 3.78 times greater than that within the zone without presplitting. By comparing coal seams before and after fracturing in the field test, it can be seen that the LCPCF presents a favorable effect in increasing the permeability of low-permeability coal seams. This provides an effective approach for increasing the permeability of coal seams in coal mines with similar geological conditions. [ABSTRACT FROM AUTHOR]