Publisher's Synopsis
Until the early 1980s, mine face ventilation systems were designed for ventilating cutting depths up to 20 feet. Since that time, use of remotely operated mining machines have allowed cutting depths to increase to 40 ft, increasing concerns about the effects on methane levels at the mine face area. The principles for efficient methane control during deeper cutting remained the same, namely - Move a sufficient quantity of intake air from the end of the tubing or curtain to the face. - Mix intake air with methane gas liberated at the face. - Move methane contaminated air away from the face. However, when cutting to depths greater than 20 ft (known as deep-cut mining), airflow quantities reaching the face area often decreased because it was difficult to maintain tubing or brattice setback distances. Earlier research showed that use of machine-mounted scrubbers and water sprays increased airflow at the face area during deep cutting. NIOSH research examined how these and other factors affected face airflow. A full-scale ventilation test gallery was used to study how different operating conditions caused airflow patterns and methane distributions near the face to vary. The research results showed that during deep-cut mining - Without additional controls, only a small percentage of the air delivered to the end of the tubing or curtain reached the face area. - Operation of a machine-mounted scrubber increased airflow and reduced methane levels at the face area as long as the quantity of intake air delivered to the end of the curtain or tubing was not reduced. - Operation of water sprays did not significantly increase the volume of air reaching the face but did improve mixing of methane and intake air at the face. Methane monitoring requirements remained the same for deep cutting, but the possibility of rapidly changing conditions at the face increases the need for accurate estimates of face methane concentration. Research examined currently available instrumentation and sampling methods for monitoring methane at the face. In this report several practical guidelines are recommended for controlling and monitoring methane levels in the face areas of underground coal mines.
