CFD study of the effect of face ventilation on CH4 in returns and explosive gas zones in progressively sealed longwall gobs

The main purpose of coal mine ventilation design is to provide a sufficient quantity and quality of air to the workers and to dilute methane and other contaminants. It is generally perceived that additional air along the longwall face will improve methane dilution at the face and in the tailgate. However, computational fluid dynamics (CFD) modelling efforts at the Colorado School of Mines (CSM) under a National Institute for Occupational Safety and Health (NIOSH) funded research project have found that higher flow velocities along the longwall face will increase the pressure differential between the gob and longwall face and allow more methane to be swept from the gob into the active face and tailgate area, thereby diminishing the dilution effect. Increased pressure along the headgate side also allows more oxygen to ingress into the gob area, thereby increasing the amount of oxygen available to form explosive methane-Air mixtures in the gob and to support spontaneous combustion of the coal. In this paper, a parametric study is presented to discuss the effect of face air quantity on methane concentrations in the tailgate and formation of explosive gas zones (EGZs) in the gob. Counter to conventional wisdom, increased air quantities at the longwall face may increase the explosion hazard as they result in increased EGZ volumes in the gob, along with increased methane quantities in the tailgate return.