Methane Abatement
Technology Landscape in Methane Abatement
Methane is absorbed in the coal mass and trapped in the matrix of a coal seam and the surrounding strata. Once released it is a more potent greenhouse gas than carbon dioxide. The greenhouse potency of methane is approximately 84 times more powerful than CO2 over 20 years, and 28 times more powerful over 100 years (Stocker, 2014). According to the Ember Climate Think Tank (Assan, 2022), Australian coal mine methane contributes 74Mt CO2-e 20yr each year whereas the annual emission from vehicles in Australia is 44Mt CO2-e 20yr. Globally, coal mine methane emissions make up approximately 8% of all anthropogenic methane emissions in UNFCCC Annex I countries, which ranks fourth after agriculture, waste, and the energy sectors (EPA, 2019).
Coal mine methane can be released, captured, or abated through various mechanisms described here.
Natural fractures in the strata.
Open cut mining.
Underground mining gas drainage holes.
Underground coal mine ventilation systems.
Abandoned mines.
Where possible the methane should be captured and processed through separation for use in gas powered energy and domestic and industrial heating applications rather than released or flared into the atmosphere. On this note, flaring (combustion) is an abatement technique that has long been used via an enclosed flaring stack at the surface. This provides a solution where capturing or transporting the methane is not economic or available.
Ventilation Air Methane (VAM) abatement is starting to become more prominent, although currently being less effective and much more expensive than gas drainage. This involves capturing the low-concentration methane (usually <2%) from the mine ventilation airways. The Regenerative Thermal Oxidizer (RTO) is commercially available for effective abatement of low concentration VAM. Lean-fuel turbines and Regenerative Catalytic Oxidizers (RCO) are two other technologies being developed for VAM abatement.
The most effective way to control the release and abate methane from a coal seam is through pre-mining gas drainage holes. Ideally, when pre-drainage is efficient, mine ventilation is a minimum source of methane emissions. Unfortunately, the current coal mining operations do not reflect this ideal and immediate and meaningful gains in methane abatement are currently available. Importantly, methane concentrations and processes at pre-drainage are comparatively more efficient and effective than methane abatement ventilation methods. Considering the substantial expense and advanced technologies required for VAM abatement, enhancing methane drainage system efficiency can yield a significant reduction in abatement costs.
Challenges and Opportunities in Methane Abatement for the Mining Industry
The reason for gas drainage contributing poorly to methane mitigation is that mines typically only conduct enough drainage to adhere to safety requirements. As it stands, gas drainage in mines can be only a small percentage of the total gas content and at best 50% as reported to Mining3 by some select mines. In the USA, the EPA Coalbed Methane Outreach Program (Sources of Coal Mine Methane, 2023) notes that drained methane gas accounts for only approximately 4.3% of coal mine methane, while ventilation air methane contributes to around 60%. Nonetheless, pre-mine drainage yields exceptionally high-quality gas with methane concentrations surpassing 90%, rendering it amenable to combustion.
If mines applied an extensive drainage program, then in practice methane emissions from the mine could be reduced by 30 to 50%, and theoretically up to 80%" (UNECE) (Best Practice Guidance for Effective Management of Coal Mine Methane at National Level: Monitoring, Reporting, Verification and Mitigation, 2021).
A key problem that exists lies in the inefficiency and ineffectiveness of coal bed methane pre-mining drilling and drainage methods. Although they are two separate operations, drilling, and drainage both contribute to poor methane drainage performance at mines. Drilling is often encumbered with poor drilling conditions, and irregular and unstable boreholes are common at coal mines. It is also common for a mine to encounter unexplained problematic events inside the borehole that results in poor gas drainage. A paucity of information currently exists during the drilling and drainage stages to help a mine identify the cause of the poor performance and take ameliorative action. If the coal mining industry is to be pushed towards conducting extensive drainage programs, then we first need to fix the inefficiencies that exist in drilling and drainage practices. Otherwise very costly drilling programs will be implemented that fail to produce the drainage targets that need to be achieved.
Mining3 has a 25-year history successfully developing and investigating technologies for coal seam drilling and methane drainage and is strategically positioned to help solve some of the key problems that currently exist.
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