Coal dust is a great threat to coal mine workers' health and safety in coal mine production. Wet dust removal is one of the effective dust removal methods. As a solid, coal has different rough surfaces, which have a certain effect on the wetting effect of coal. In this paper, three coal samples with different surface wettability are used as the research objects. Phase-field interface tracking method is used to simulate the wetting of droplets on rough surfaces. From the simulation results, it can be concluded that the influence of the rough interface on the contact angle of the droplets is in accordance with the change rule described in the Wenzel model. As the roughness increases, the contact angle of the hydrophilic lignite surface gradually decreases. As the roughness increases, the contact angle of hydrophobic coking coal gradually increases. The change trend of the contact on the surface of weakly hydrophilic anthracite coal is the same as that of lignite. Due to the local and global differences, the contact angles obtained from the numerical model are slightly different from the values calculated from the Wenzel model.
There are many karst collapse columns in coal seam roof in the southern coal field in China, which are different from those in coal seam floor in the northern coal field, due to the stratum characteristics. The karst collapse column in coal seam roof tends to reactivate and conduct water and induce the serious water inrush disaster, when the karst collapse column communicates with the overlying aquifer. In order to reveal the evolution mechanism of water-conducting channel of collapse column in karst mining area of southwest China, the aquifers and water inflow rule in 1908 working face in Qianjin coal mine are analyzed. Besides, the particle size distribution and mineral component of collapse column are researched by the X-ray diffraction test and the screening method, which are the basis for researching the water inrush mechanism in karst collapse column. On this basis, the water inrush of roof collapse column under the influence of mining is researched by establishing the numerical calculation model with the UDEC numerical software. The results show that the water flowing into the 1908 working face comes from the Changxing formation aquifer and Yulongshan formation aquifer above the coal seam, and the proportion of coarse particles and fine particles in collapse column is 89.86% and 10.14%, respectively. With the advance of working face, the water-conducting channel connected the working face with the aquifer, or the surface is formed by collapse pits, karst caves, and collapse column. The research results can be treated as an important basis for the water-preserved mining in southern coal field in China.
Although the impact of Karst Collapse Pillars (KCPs) on water inrush has been widely recognized and studied, few have investigated the fluid-solid interaction, the particles migration inside KCPs, and the evolution feature of water inrush channels. Moreover, an effective approach to reliably predict the water inrush time has yet to be developed. In this work, a suite of fully coupled governing equations considering the processes of water flow, fracture erosion, and the change of rock permeability due to erosion were presented. The inverse velocity theory was then introduced to predict the water inrush time under different geological and flow conditions. The impact of four different controlling factors on the fracture geometry change, water flow, and inrush time was discussed in detail. The results showed that the inverse velocity theory was capable of predicting the occurrences of water inrush under different conditions, and the time of water inrush had a power relationship with the rock heterogeneity, water pressure, and initial particle concentration and an exponential relationship with the initial fracture apertures. The general approach developed in this work can be extended to other engineering applications such as the tunneling and tailing dam erosion.
In order to supply benefits for safe production of coal underground and efficient exploitation of coalbed methane, a self‐developed gas seepage experimental device considering gas adsorption and desorption was proposed to study the seepage properties of gas‐saturated coal in this paper. A series of gas seepage experiments under different loading conditions were carried out to investigate the change rules of permeability of gas‐saturated coal. The experimental results covered the significant effects of confining pressure, gas pressure, temperature change, creep stress, and complete stress‐strain process on the seepage laws of gas‐saturated coal. The experimental results showed that the permeability of gas‐saturated coal is strongly sensitive to the effective stress and decreases with the increase of the effective stress. Under the fixed confining pressure, the permeability of gas‐saturated coal showed an obvious Klinkenberg effect, but the Klinkenberg effect would no longer be evident once the gas pressure was larger than 1.0 MPa. And the change law of permeability of gas‐saturated coal with temperature was mainly reflected in the comprehensive effect of thermal stress and effective stress on the control of pore deformation. Under the complete stress‐strain loading conditions, the change rules of permeability were mainly dependent on the failure mode of gas‐saturated coal. And the change rules of permeability, for the condition of triaxial creep stress, were relied on the stage of creep deformation. The deformation at decay creep stage was responsible for a steady permeability after the failure of gas‐saturated coal, while the deformation at nondecay creep stage was responsible for a rapid increase of permeability after the failure of gas‐saturated coal. The results in this work can offer some helpful suggestions for efficiently exploring coalbed methane in the future.
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