133 implementation of any known and available technology or being developed technology to an industrial scale. The first of those is the flow rate, the scale of which does not enable the process to be limited to only one apparatus. Moreover, the air exhausted by the mine ventilation shaft contains nearly completely-saturated water vapor, which will pose problems in any industrial process. In the case of catalysts, the humidity will inhibit oxidation (Liu et al., 2013; Haojie et al., 2015) by covering active places on the catalyst bed. In other cases, when the ambient temperature will be lower than the temperature of VAM exhausted from the ventilation shaft excess moisture will condense out in pipes and other apparatus. The risk caused by a large amount of dust may increase the flow resistance in devices filled with a fixed bed or decrease the efficiency of the catalyst by clogging its key areas on the surface. A major problem in the utilization of VAM is the content of methane. An even greater problem is the possibility of its variability and significant difference between the maximum and minimum value from the one measure point. In the case of very large differences obtained on one ventilation shaft, the selection of the method of utilization of such a mixture becomes difficult. Intensive interest in the problem of methane utilization from mine ventilation air appeared in the last decade of the previous century. It was due to the establishment of the Intergovernmental Panel on Climate Change (IPCC) in 1988 and the requirements of the Kyoto Protocol signed in 1997 (UNFCC. Tex of the Kyoto Protocol. Accesed on 15th June 2021). Moreover, it was realized that due to very high flow rates of ventilation air low methane concentration in VAM causes high methane emission to the atmosphere. According to (Cashdollar et al., 200), global methane emission in this way amounts to 16 billion m3 per year. This amount is close to the annual consumption of natural gas e.g. in Poland since domestic consumption in 2018 reached 17.2 billion m3 (excluding exports). A good classification of the ways of using this fuel can be found in the review (Su et al., 2005). However only underlined technologies in Figure 2, are considered. Figure 2. Scheme of combustion technologies of VAM. The analysed methods are divided into two basic categories:
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