1402 1. CONTEXT AND PROBLEM STATEMENT Methane is a potent greenhouse gas (GHG) with a global warming potential (GWP) 28-36 times that of CO2 for a 100-year timescale (IPCC, 2016; US EPA, 2017b). It is a potent precursor to air pollution, contributing to ozone formation, which itself causes serious health problems. It also has a short residence time in the atmosphere with a GWP 84 times higher than CO2 over 20 years. Therefore, reducing methane emissions contributes to relatively fast (within our lifetimes !) improving air quality and slowing down climate change and can be achieved cost-effectively, exploiting new business opportunities as methane is a valuable energy source. In the EU, 53% of anthropogenic methane emissions come from agriculture, 26% from waste, and 19% from energy. The coal mining industry is estimated to account for 11% of global methane emissions from human activities (U.S. EPA, 2019). However, many scholars argue that current estimates of methane emissions from fossil fuels are underestimated. For example, Schwietzke et al. found that “fossil fuel methane emissions are 60-110 greater than current estimates” (Schwietzke et al.,2016). Similarly, Miller et al. show that global methane emissions might be 1.5 times greater than estimated by a U.S. inventory study (Miller et al.,2013). Coal mine methane (CMM) is a term given to the methane gas produced or emitted in association with coal mining activities, either from the coal seam itself or from other gassy formations underground. The amount of CMM generated at a specific operation depends on the productivity of the coal mine, the gassiness of the coal seam and any underlying and overlying formations, operational variables, and geological conditions. CMM can be captured by dedicated drainage systems that augment the mine's ventilation system and if NOT it is emitted into the mine environment and exhausted from the mine shafts along with ventilation air as Ventilation Air Methane (VAM). The large amounts of methane released during mining are subject to concerns about adequate mine ventilation to ensure worker safety. However, they also can create opportunities to generate energy if this gas is captured and utilized properly. CMM captured underground is transported to the ground surface using special drainage systems (UNECE, 2016. Best Practice Guidance for Effective Methane Drainage and Use in Coal Mines. Available at: https://www.unece.org/fileadmin/DAM/energy/se/pdfs/cmm/pub/UNECE.BPG.pdf) connected to surface (mostly, but sometimes also underground) compressor stations where mixture (40-50%) of methane with air constitutes fuel-ready to use in all sorts of gas engines to produce electricity and heat. This sort of fuel (on average globally, about 30% of methane released during mining operations) can be recognized as “low hanging fruit” to utilize for energy purposes, which is quite contrary to VAM (on average globally, about 70% of methane released during mining operations). VAM constitutes the rest of emitted methane and must, for safety reasons, be diluted to safe values (0-0.75%) and removed with the ventilation air to the atmosphere. The release of methane from ventilation shafts is critical to ensure the safety of mine workers. VAM, if captured, can be used for combustion in thermal reactors, which is the only globally known technology for the economical use of methane https://www.epa.gov/cmop/us-underground-coal-mineventilation-air-methane-exhaust-characterization. Even though that VAM installations have low efficiency compared with installations using gas engines and thus, they can not be economically compared – the challenging target of huge GHGs’ emissions mitigation to be achieved if VAM emissions are effectively handled has been for many years and still is the ambition for many industrial and scientific parties including ProVAM project consortium partners.
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