Methane emission and control at Lingan Colliery

Abstract

Lingan mine is one of two underground collieries operated by the Cape Breton Development Corporation in Nova Scotia, Canada. The mine produces about 1.4 million tonnes of saleable bituminous coal from the 2.2 m thick Harbour Seam by advancing longwall method. The workings are submarine. The Harbour Seam is fourth in a sequence of eleven seams identified in the Sydney Coalfield. It is gassy and the gas emission increases with depth. Total gas emission at Lingan increased from about 29 m3 /tonne in 1978 when the workings were at a depth of about 400 m to the present 50 m3 /tonne at a depth of 600 m. The ventilation at Lingan is provided by a 1350 kW Sheldon Centrifugal fan with variable inlet vanes exhausting at a rate of 190 m3 /s and 450 mm w.g. Each wall is supplied with air in excess of 30m3/s. Because of the submarine workings, surface boreholes to control methane in gobs during longwall mining is not practical and dilution with ventilation alone is inadequate and costly. Hence, the cross-measure borehole technique was adopted in the Sydney Coalfield in the 1950's and the current practice was developed over the years by trial and error. The holes are drilled in the return gate, parallel to the faceline, at an angle of 50° - 600 to the horizontal, to a depth of 40 m with a 11 m standpipe cemented into it. The roof holes are spaced at 25 m and those in the floor at 50-75 m. The active holes, which could number to a maximum of fourteen at any one-time are connected to a 200 mm pipeline. Until April 1985, the pipeline was connected to vacuum pumps underground and the extracted methane was discharged at a point in the main return airway where the ventilation was sufficient to quickly dilute it to a safe level. However, the district methane pipelines are now connected to a main trunk pipeline and a new surface extraction plant capable of handling up to 120,000 m3 per day of gas at a vacuum of 465 mm of mercury. It is now contemplated not only to increase the number of methane drainage holes in each district to improve capture ratio, but also to extract methane from old workings. -A Sieger Methane Monitoring system is used on each wallface with automatic power cutoff at 1.25% methane. A computer based remote environmental monitoring system is now installed and is expected to be fully operational later this year. This will monitor wallface ventilation, fan performance and methane drainage on a continuous basis.