Getting the most from gas

MANY mines in the United States that have ventured into utilisation of Coal Mine Methane (CMM) have reaped financial benefits ranging from lowering mine operational costs to a very lucrative secondary revenue source on gas sales.
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Borehole methane drainage installation site near Adgwe, Alabama.

Angie Tomlinson

Published in the December 2005 American Longwall Magazine

Not be confused with Coal Bed Methane (CBM) – high quality methane contained in coal seams – CMM is a subset of CBM and is released from the coal seams and surrounding rock strata during the process of coal mining.

This includes abandoned or closed mines, ventilation air methane, and degasification systems, also known as “drainage systems”, where vertical and horizontal wells are employed to capture methane in advance of, during and post mining operations. Gas quality varies from pipeline to low grade.

New developments include technologies to utilise even the dilute levels of methane from ventilation air methane (VAM) sources. Although not popular yet in the US, VAM containing methane levels as low as 0.5% can be combusted to provide thermal energy for coal drying, water heating and mine air heating at the site.

Most mines have ventured down the path of selling CMM to natural gas pipeline systems. Methane is the major component of natural gas and the technology is readily available to provide a consistent quality product to the end-user.

Gas from abandoned mines and degasification systems can have contaminants scrubbed and BTU levels enriched when necessary for pipeline injection.

With this in mind, Pennsylvania-based manufacturer Rel-Tek Corporation has capitalised on the relatively-new CMM market with the introduction of its monitor – WellBoss. The technology continuously monitors the methane and/or oxygen content of the gas well stream.

In the case where levels vary above or below pre-determined values, a controlling circuit sends a signal to a servo valve that adjusts until the respective gas components regain acceptable values. Sensors maintain tight accuracy through automatic calibration utilities, Rel-Tek said.

“In essence the WellBoss eliminates trips to the well for spot quality checks,” the company said.

“Utilisation of coal mine methane offers many economic and environmental benefits and would also serve as one of many components to ensure our energy independence.”