CFD modelling of longwall goaf gas flow to improve gas capture and prevent goaf self-heating

CFD models have been developed to investigate the longwall goaf gas flow patterns under different mining and geological control conditions. The longwall goaf was treated as porous regions and gas flow was modelled as a momentum sink added to the momentum equation. Gas desorption from the caved goaf and destressed coal seams within the mining disturbed area was modelled as additional mass sources in the continuity equation. These CFD models were developed according to specific longwall layouts and calibrated against field monitoring data. Two case studies were presented demonstrating the application of CFD modelling of goaf gas flow characteristics for improved goaf gas capture and the reduction of oxygen ingress into the goaf areas for self-heating prevention. Results from the case studies indicate that the optimum goaf drainage strategy would be a combination of shallow (near the face) and deep holes to improve the overall drainage efficiency and gas purity. For gassy longwall faces retreating against the seam dip, it is recommended to conduct cross-measure roof hole drainage targeting the fractured zones overlying the return corner, rather than high capacity surface goaf drainage deep in the goaf.