Molecular dynamics simulation of oxygen diffusion in dry and water-containing brown coal

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Moisture content of brown coal has a pronounced impact on O2 diffusion during coal oxidation. The transport behaviour of O2 in dry and hydrated brown coal matrix with 10, 20, and 30 wt% moisture contents have been studied by molecular dynamics (MD) simulations at 298.15 K and 0.1 MPa. By analysing the diffusion characteristics of O2, it is found that the diffusion process results from jumps of O2 molecules between adjacent cavities in the coal matrix. With the increase of moisture content, the swelling extent of coal matrix increases in the range of 10–30 wt%, resulting in increased cavity volume, cavity interconnectivity, and mobility of coal macromolecule. These factors are all beneficial to the transport process of O2 molecule. In addition, O2 molecule prefers to reside in the available water-poor coal cavity and unoccupied region of water-rich cavity according to the estimated binding energies.