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 CH 4 isothermal adsorption. The results show that the pore volume obtained by the Barrett-Joyner-Halenda method and the specific surface area increase with increasing
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.
Coal seam degasification by in‐seam drilling borehole is one of the popular techniques for coal mine methane (CMM) control. How to address the conflict between borehole numbers and drainage durations always arouses researchers’ interests. Furthermore, since coal has anisotropy structures, how the anisotropy feature of coal associated with bedding and cleat structure affects the influence radius of the drainage borehole has rarely been considered. In order to address the above‐mentioned issues, this work not only conducted underground in‐situ measurement of the borehole influence radius within 200 days in an anisotropy coal seam at Jiulishan coal mine in China, but also modeled the influence radius evolvement around borehole in an anisotropy coal seam using finite‐element based COMSOL package. The underground in‐situ measurement revealed an anisotropy feature of borehole influence radius associated with coal bedding and cleat structures. The influence radius of borehole parallel to the bedding plane in butt cleat direction is much larger than that perpendicular to the bedding plane. Ten permeability measurements of coal show that the permeability of coal parallel to the bedding plane in butt cleat direction is higher than that perpendicular to the bedding plane. Simulation results of the gas transport model in coal are consistent with underground in‐situ measurement in determining the influence radius of drainage borehole in the anisotropy coal seam. Based on modeling results, the ellipse influence area of borehole in an anisotropy coal seam is proposed, and the relationship between the influence radius of borehole and drainage time is obtained. On the basis of these findings, the proper in‐seam borehole arrangements for a specific mining panel at different drainage durations are determined. The finding of this work will be fundamental for addressing the conflict between minimizing the cost of borehole arrangement and increasing coal mining productions by adjusting CMM drainage durations.
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
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