ABSTRACT: Methane is a powerful greenhouse gas and the principal component of natural gas. Coal seams often contain significant quantities of methane, and underground coal mines must ensure that methane released into the mine during coal extraction does not build to dangerous levels. This is accomplished in part through the use of large-volume ventilation systems that remove methane from the mine and release it to the atmosphere. Although the methane concentration exhausted is quite low (typically <1 percent), the volume of air that ventilation systems move is so great that they actually constitute the largest source of methane emissions from underground coal mines. Each year underground coal mines throughout the world emit more than 500 billion cubic feet of methane from their ventilation systems. An air pollution control technology, thermal oxidation using a flow-reversal reactor (TFRR), has emerged as a potential solution to ventilation air methane (VAM) emission mitigation. One manufacturer of TFRRs has demonstrated its oxidizer design (the VOCSIDIZER™) at coal mines in the United Kingdom and Australia. These demonstrations tested the technology’s effectiveness at oxidizing low-concentration methane, as well as its ability to tap the excess heat to produce steam for electric power generation. In early 2007, the first U.S. demonstration of this technology began operation at an abandoned mine in West Virginia. The project is designed to prove the technology’s operational robustness, its ability to reliably oxidize methane at concentrations typical of mine exhausts, and its safety. If the technology is employed at active underground coal mines, it offers the potential to mitigate substantial quantities of global methane emissions. This paper discusses global VAM emissions, options for the recovery and utilization of VAM, and existing projects such as WestVAMP in Australia and the ongoing U.S. VAM demonstration project.

     Introduction: Methane (CH4) released to the atmosphere from gassy underground coal mine ventilation systems constitutes a major source of greenhouse gas emissions. As concern over climate change grows worldwide, mitigating ventilation air methane (VAM) emissions is drawing increasing attention. Field demonstrations of VAM oxidation technology in the United Kingdom, Australia, and the U.S. have paved the way for the emergence of a new industry focused on capturing the energy embodied in VAM exhaust flows and putting it to beneficial use. With supplemental revenues potentially available from domestic and international carbon funds, the economics of VAM emission mitigation appear favorable. As a result, interest in implementing VAM emission mitigation technology in the U.S. and elsewhere is growing rapidly.
     Methane is formed over geologic time as the coalification process converts organic material into coal, and may be present both in coal seams as well as in adjacent rock strata. Deep underground coal mines may encounter substantial reservoirs of methane. Methane is released into the mine environment as coal is extracted, unless it has been removed prior to mining through the application of gas drainage techniques. Deep longwall operations, which are characterized by high extraction rates of often very gassy coal, can release substantial amounts of methane. This could constitute a dangerous situation since methane, the principal component of natural gas, is explosive at concentrations ranging from 5 to 15 percent in air.
      Coal mines are required to manage methane concentrations underground so that they do not approach the lower explosive limit of 5 percent, in order to ensure a safe environment for mine workers. In the U.S., if methane concentrations reach 1 percent in mine workings, specific response actions must be taken (per CFR 75.323 – Actions for Excessive Methane), which can be disruptive to mine productivity. Therefore, controlling methane in deep, gassy underground coal mines is an ongoing concern for mine operators, both in terms of ensuring worker safety as well as maximizing coal production and profitability.
      Two methane management approaches are available for gassy underground coal mines. Large-scale ventilation systems are employed to bring fresh air into the workings, where they dilute methane released during coal extraction and expel it from the mine into the atmosphere. At very gassy mines, however, the cost of operating a ventilation system large enough to handle high methane release rates can be cost prohibitive. In such circumstances, gas drainage can be employed to supplement the ventilation system. Drainage involves drilling boreholes into the coal seam (from the surface or within the mine), through which methane can be extracted from the coal before it is mined, or into the gob zone. Gob (or goaf) is the rubble area of broken rock that forms when the mine roof collapses as the longwall equipment advances during mining. Gob gas often continues to be released for extended periods after mining.