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

Moisture content of brown coal has a pronounced impact on O-2 diffusion during coal oxidation. The transport behaviour of O-2 in dry and hydrated brown coal matrix with 10, 20, and 30wt% moisture contents have been studied by molecular dynamics ( MD) simulations at 298.15K and 0.1 MPa. By analysing the diffusion characteristics of O-2, it is found that the diffusion process results from jumps of O-2 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 O-2 molecule. In addition, O-2 molecule prefers to reside in the available water-poor coal cavity and unoccupied region of water-rich cavity according to the estimated binding energies.