Numerical investigations of methane flow characteristics on a longwall face Part I: Methane emission and base model results
The management of methane gas has always been a challenging issue for longwall operations. To improve the understanding of methane dispersion and flow characteristics on a longwall face, Computational Fluid Dynamics (CFD) modelling studies were conducted employing the longwall models developed recently. As a prerequisite of the CFD study, the methane emission rate was determined firstly taking advantage of a mathematical model whilst considering the decay of methane emission from different positions along the face, which was capable of estimating the methane emission from individual sources on the longwall face. Taking into account the impact of shearer position and cutting sequence on gas flow behaviour, calculations were carried out on the six CFD models representing six typical longwall operating scenarios respectively. Model results indicate that: 1) the methane concentration around the drums increases gradually as the shearer cuts from the maingate (MG) to tailgate (TG), and decreases as the shearer cuts back towards the MG; 2) the methane concentration at the TG drum is higher than it is at the MG drum in both cutting directions; 3) the monitored methane concentration at the tail end of the shearer body can be approximately two or three times lower than the maximum concentration around the TG drum; 4) the source of methane causing accumulation at TG is identified, i.e., the majority of methane trapped in the inner TG corner comes from the face emission while the methane accumulated at the upper TG corner is caused by goaf methane emission.