131 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/usunderground-coal-mine-ventilation-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. Figure 1. Schematic of an underground coal mine with dedicated drainage system and surface facilities for complex CMM energy recovery ( both: from drainage gas and VAM) (Courtesy of Green Gas International) The gas released from coal seams is a big problem for mining operations. The methane, which is stored in a micro-porous network of coal seams, was formed during a coalification process (Singh, Kumar, 2015; Baris, 2013). The higher rank coal, the more methane it contains (Kholod et al., 2020). Properly adapted ventilation is intended to reduce the concentration of methane per volume unit to a level, that guarantees the safety of workers. VAM is such a mixture of methane and air, where methane concentration is very lean, usually below 1 vol.%. The amount of methane released per 1 ton will be different at different mine locations. For example, in Poland, the amount of VAM emitted into the atmosphere per ton of extracted coal mined is over 9 m3 , in Indian gassy mines the value is more than 10 m3 (Singh, Mallick, 2015). It would be supposed that reducing the number of mines will solve the problem of VAM emissions, or at least reduce it. The problem of methane emission is still present even after decades of the coal mine abandonment (Kholod et al., 2020). Furthermore, it turned out that even a significant reduction of coal extraction and the number of mines does not lead to a reduction of VAM, what
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