The occurrence of coal and gas outbursts is closely linked to the presence of tectonic coal. To study the pore structure characteristics and adsorption characteristics of different destruction types of coal, nondestructive coal, destructive coal, strongly destructive coal, pulverized coal, and fully pulverized coal are selected based on the coal and gas outburst mine identification specifications. The experimental methods used are liquid nitrogen adsorption, mercury intrusion porosimetry and CH₄ isothermal adsorption. The results show that the pore volume obtained by the Barrett–Joyner–Halenda method and the specific surface area increase with increasing destruction type. For all tested coal samples, the N₂ adsorption/desorption hysteresis loop is not closed when the relative pressure is low, indicating the existence of ink-bottle pores, an elastic structure of the coal and nitrogen affinity in the coal. With increasing tectonic stress, it becomes more advantageous to produce micropores. The pore volume obtained by the mercury intrusion porosimetry experiment increases with increasing destruction types except for the case of fully pulverized coal. High-pressure mercury causes pore deformation and collapse. When the f value is <0.5, the compression effect of the pores is obvious. The smaller the value of f is, the wider is the pore range affected by the high-pressure mercury. The degree of destruction is positively correlated with the porosity, specific surface area, and Langmuir volume. However, the degree of destruction is negatively correlated with the f value and mercury extrusion efficiency.

A comprehensive technology is proposed to realize fast and safe rock cross-cut coal uncovering (RCCCU) based on artificial freezing engineering method. This comprehensive technology includes four steps, namely, drilling a borehole, wetting the coal body by water injection, gas drainage and freezing the coal seam by liquid nitrogen injection. In this paper, the compressive strength, tensile strength and shear strength of frozen coal specimens are tested to obtain the mechanical parameters of the specimen. Then, for RCCCU under freezing temperatures, the outburst prevention effects are calculated and quantitatively analysed with regard to three aspects, namely, the enhancement of coal the mechanical properties, the reduction in the coefficient of outburst hazard (COH) in the distressed zone and the reduction in the interfacial elastic energy ratio (IEER) between the coal seam and the roof/floor. The results show that a considerable improvement in the mechanical properties of frozen coal and that the coal mechanical parameters, such as the compressive strength and the tensile strength, increase linearly with decreasing temperature. The coefficient of outburst hazard in the distressed zone decreases rapidly and drops from above 0.8 to below 0.3. The interfacial elastic energy ratio is greatly reduced from dozens of times of that of the roof/floor before freezing to several times of that of the roof/floor after freezing, which effectively weakens the sudden change of the elastic energy at the coal-rock interface.

Reduction of gas desorption capacity by cooling coal samples seems a feasible way to improve the accuracy of gas in place estimation. To find an efficient refrigeration mode for the freezing coring technology, the freezing tests for coal containing gas (at 0, 1.09, and 2.15 MPa) are separately conducted based on the precalculation of dry ice dose. The evolvement of coal temperature and gas pressure shows that under the catalysis of ethanol, the average cooling rate of coal gradually accelerates with the increased amount of ethanol (from 0 to 600 mL) in the early stage. Additionally when charging gas into the coal canister, the cooling rate of coal at each subzero temperature accelerates with the increased adsorption pressure of gas, and the low temperature preservation time (<0 °C) of coal is also prolonged. There is a good linear relationship between gas pressure and coal temperature, which indicates that the CH₄ adsorption and desorption in coal are basically reversible; but the desorption hysteresis is extensively observed, associated with the occurrence of numerous ink-bottle type micropores.

To study the effect of high temperature and high pressure on the adsorption characteristics of coking coal, Liulin coking coal and Pingdingshan coking coal were selected as the research objects, and isotherm adsorption curves at different temperatures and pressures were obtained by combining isotherm adsorption experiments and molecular dynamics methods. The effect of high temperature and high pressure on the adsorption characteristics of coking coal was analyzed, and an isothermal adsorption model suitable for high-temperature and high-pressure conditions was studied. The results show that the adsorption characteristics of deep coking coal can be well characterized by the molecular dynamics method. Under a supercritical condition, the excess adsorption capacity of methane decreases with the increase of temperature. With the increase of pressure, the excess adsorption capacity rapidly increases in the early stage, temporarily stabilizes in the middle stage, and decreases in the later stage. Based on the classical adsorption model, the adsorption capacity of coking coal under high-temperature and high-pressure environments is fitted. The fitting degree ranges from good to poor. The order is D-R > D-A > L-F >BET > Langmuir, and combined with temperature gradient, pressure gradient, and the D-R adsorption model, it can be seen that after 800 m deep in Liulin Mine and 400 m deep in Pingdingshan Mine, the adsorption capacity of coking coal to methane decreases with the increase of depth.

Addition of water to the coal is actually an isobaric imbibition process. To study the dynamic response characteristics of water and methane, the isobaric imbibition process was stimulated by a self-designed experimental device which can eliminate the reabsorbing phenomenon. The results indicate that adding water can displace absorbed gas. The displacement mechanism is attributed to the capillary effect and competitive adsorption during isobaric imbibition process. A competitive adsorption phenomenon exists between gas molecules and water molecules. Since oxygen-containing functional groups in coal and the hydrogen bond of water, water can easily occupy high-energy sites and only the low-energy sites are available for methane. The imbibition quantity increases with increasing water content or adsorption equilibrium pressure. Moreover, the imbibition quantity would reach a maximum value. The relationship between water content and maximum imbibition quantity or the maximum imbibition rate can be described by a Langmuir function under the same adsorption equilibrium pressure. The maximum imbibition quantity increases with increasing adsorption equilibrium pressure under the same water content, which also can be described by a Langmuir function. However, the maximum imbibition rate decreases with increasing adsorption equilibrium pressures under the same water content, which can be described by an exponential function. Compared to the adsorption equilibrium pressure, the water content has a greater effect on the imbibition quantity and imbibition rate. This study revealed the mechanisms of the dynamic response characteristics of water and methane during isobaric imbibition process based on the transformation form of Hagen–Poiseuille equation, adsorption force of coal and gas and adsorption force of coal and water, which can provide a new method to control gas in deep coal seams.

Pore space is the main desorption space for methane in coal; to study the effect of changes in pore structure on the desorption hysteresis effect of methane in coal under high-temperature and high-pressure conditions, the coking coal from Pingdingshan Twelve Mine was taken as the research object, and the isothermal adsorption and desorption curves were obtained and quantitatively analyzed at different temperatures and pressures by the help of isothermal adsorption and desorption experiments, combined with the pressed mercury experiments and the low-temperature liquid nitrogen adsorption experiments to test the pore structure of the coal samples before and after the adsorption and desorption tests. The pore structure of coal samples before and after the adsorption and desorption tests was tested by combining the mercury pressure test and the low-temperature liquid nitrogen adsorption test, and the influence of the change in the pore structure of coal samples after the high-temperature and high-pressure adsorption and desorption tests on the hysteresis effect of methane desorption was studied. The results showed that under the same pressure, the pore volume of coal samples increased with the increase in temperature, the pore-specific surface area showed a tendency to decrease, and the fractal dimension could well characterize the relationship between the pore structure and the pore surface of coal, in which the fractal dimension of the pores in the large pore size section gradually increased with the increase of temperature, and the fractal dimension in the small pore size section gradually decreased; there was a good correlation between the pore structure of the coal samples after the high-temperature and high-pressure adsorption and desorption tests and the hysteresis coefficient of desorption. The structural characteristics of the coal samples after adsorption and desorption hysteresis coefficient at high temperature and high pressure showed good correlation, i.e., the pore volume, the fractal dimension of the large pore size section, and the desorption hysteresis effect were negatively correlated, while the specific surface area, the fractal dimension of the small pore size section, and the desorption hysteresis effect were positively correlated.