Mining Publication: Ventilating the Box Cut of a Two-Pass 40-ft Extended Cut
On a continuous miner coal face methane concentrations are affected by the quantity of fresh intake air reaching the face. When mining the box cut on a 12.2m (40ft) two-pass extended cut face, the continuous miner is always at the point of deepest penetration, and the operation of the machine -mounted dust scrubber and water spray system improve the flow of fresh air at the end of the box cut. The Pittsburgh Research Laboratory (PRL) of the National Institute for Occupational Safety and Health conducted a full scale study to answer this question. Tests were run to determine how much ventilation air reaches the end of the box cut with the continuous miner at three locations in the 40 ft slab cut, and 6.1 m (20ft) into the slab cut. During these tests, methane gas was uniformly released at the end of the 40 ft box cut. Methane concentrations measured 0.3 m (1 ft) from the roof and face of the box cut were used to estimate face airflow quantities. Fresh air flow rates of 1.89 and 4.72 m3/sec (4000 and 10,000 cfm), scrubber flow rates of 4,000 and 10,000 cfm, water spray pressures of 0 and 827 kPa (0 and 120 psi), and a blowing curtain setback position of 15.2 (50 ft) were used during these tests. To improve ventilation to the end of the 40 ft box cut when the continuous miner was starting the 40 ft slab cut an 20 ft in the slab cut, the blowing curtain was advanced from its 50-ft setback to locations 40 ft and the 8.5 m (28 ft) from the face.