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Improving the absorbed gas to active desorption and seepage and delaying gas drainage attenuation are considered as key methods for increasing drainage efficiency and gas output. According to the solid mechanics theory, the nonlinear Darcy seepage theory and thermodynamics, the heat-fluid-solid coupling model for gassy coal has been improved. The numerical model was founded from the improved multi-field coupling model by COMSOL Multiphysics and gas drainage by borehole down the coal seam enhanced by heat injection was modelled. The results show that the heatfluid-solid model with adsorption effects for gassy coal was well simulated by the improved multi-field model. The mechanism of coal seam gas desorption seepage under the combined action of temperature, stress and adsorption can be well described. Gas desorption and seepage can be enhanced by heat injection into coal seams. The gas drainage rate was directly proportional to the temperature of injected heat in the scope of 30-150°C and increasing in the whole modelled drainage process (0-1000 d). The increased level was maximum in the initial drainage time and decreasing gradually along with drainage time. The increasing ratio of drainage rate was maximum when the temperature raised from 30 to 60°C. Although the drainage rate would increase along with increasing temperature, when exceeding 60°C, the increasing ratio of drainage rate with rising temperature would decrease. Gas drainage promotion was more effective in coal seams with lower permeability than with higher permeability. The coal seam temperature in a 5 m distance surrounding the heat injection borehole would rise to around 60°C in 3 months. That was much less than the time of gas drainage in the coal mines in sites with low permeability coal seams. Therefore, it is valuable and feasible to inject heat into coal seams to promote gas drainage, and this has strong feasibility for coal seams with low permeability which are widespread in China.

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A novel carboxymethyl cellulose (CMC)-supported graphene oxide aerogel (CGOA) was fabricated from a cost-effective and abundant bituminous coal by a mild hydrothermal process and freeze-drying treatment. Such an aerogel has cross-linked graphene oxide layers supported by CMC, and therefore, displays high mechanical strength while having ultra-low density (8.257 mg·cm−3). The CGOA has a 3D interconnected porous structure, beneficial graphene framework defects and abundant oxygen-containing functional groups, which offer favorable diffusion channels and effective adsorption sites for the transport and adsorption of dye molecules. The adsorption performance of rhodamine B by an optimized CGOA shows a maximum monolayer adsorption capacity of 312.50 mg·g−1, as determined by Langmuir isotherm parameters. This CGOA exhibited a better adsorption efficiency (99.99%) in alkaline solution, and satisfactory stability (90.60%) after three cycles. In addition, adsorption experiments on various dyes have revealed that CGOA have better adsorption capacities for cationic dyes than anionic dyes.

For understanding acoustic emission (AE) activity and accumulation of micro-damage inside rock under pure tensile state, the AE signals has been monitored on the test of directly tension on two kinds of marble specimens. A tensile constitutive model was proposed with the damage factor calculated by AE energy rate. The tensile strength of marble was discrete obviously and was sensitive to the inside microdefects and grain composition. With increasing of loading, the tensile stress-strain curve obviously showed nonlinear with the tensile tangent modulus decreasing. In repeated loading cycle, the tensile elastic modulus was less than that in the previous loading cycle because of the generation of micro damage during the prior loading. It means the linear weakening occurring in the specimens. The AE activity was corresponding with occurrence of nonlinear deformation. In the initial loading stage which only elastic deformation happened on the specimens, there were few AE events occurred; while when the nonlinear deformation happened with increasing of loading, lots of AE events were generated. The quantity and energy of AE events were proportionally related to the variation of tensile tangent modulus. The Kaiser effect of AE activity could be clearly observed in tensile cycle loading. Based on the theory of damage mechanics, the damage factor was defined by AE energy rate and the tensile damage constitutive model was proposed which only needed two property constants. The theoretical stress-strain curve was well fitted with the curve plotted with tested datum and the two property constants were easily gotten by the laboratory testing. Int J Coal Sci Technol (2018) 5(3):295-304 https://doi.