Modelling of gas flows in the goaf of retreating faces

Overview & Synopsis

In retreating faces, dilution of firedamp flowing out of the goaf area at the junction of face and retum roadway is problematic. Despite important flowrates and high CH4 drainage efficiencies, it has been observed that 2/3 of firedamp evacuated by the air stream concentrate in this particular place. So äs to progress in preventing such difficulties, it is necessary to better understand the repartition of gas fluxes in the goaf. This has obviously a benefit on firedamp drainage efficiency, but also on the choice of nitrogen injection points and flowrates in case of spontaneous combustion in the goaf. The use of a CFD code, PHOENICS, has allowed Simulation of circulation of three gases : air, CH4, and N2. Influence of the face dip on the repartition of CH4 patterns in the goaf area has been qualitatively demonstrated.