Study on the Influence Mechanism of Hot Flue Gas Injection Pressure on the Wettability of Anthracite Coal: From the Perspective of Molecular Dynamics.

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A multicomponent wetting model of coal-water-methane-hot flue gas was hereby constructed to investigate the influence of complex components of hot flue gas on coal wettability. Besides, whether it is feasible to use the NIST method to capture the system pressure was verified from a microscopic perspective. Moreover, how the interaction energy and hydrogen bonds between water and coal, the spreading length of water nanodroplets in the X-direction, and the three-phase contact angle vary with the hot flue gas injection pressure were discussed. Here are the findings: (1) The absolute value of interaction energy between water and coal is negatively correlated with the pressure. In addition, the gradient of decrease shrinks continuously when the pressure rises. (2) As the pressure rises, a decline is monitored in both the number of hydrogen bonds and the spreading length of water nanodroplets in the X-direction, and a critical pressure value exists around 32.64 MPa, which divides the variation into two stages, i.e., rapid decrease and slow decrease. (3) The three-phase contact angle grows with the rise of pressure, and its critical pressure value is similar to that of number of hydrogen bonds and spreading length. In addition, it is found that the density of the gas adsorption layer augments as the pressure rises, which can be seen that a higher injection pressure is favorable for gas wetting. These research observations brought to light that appropriately raising the hot flue gas injection pressure can promote the transition of wetting mode from water wetting to gas wetting, which is of great benefit for relieving the water lock effect and effectively improving the transportation environment of gas.