Catalytic or thermal reversed flow combustion of coal mine ventilation air methane: What is better choice and when?

• Methane concentration range is divided into low (below 0.4%) and high (above 0.4%).
• Catalytic reactor is competitive to thermal in low concentrations while in high is not suitable.
• In low concentrations heat recovery is unprofitable – only greenhouse gas mitigation is effective.
• Heat recovery is attractive in high CH4 concentrations achieving environmental and energy effect.

The paper presents a comparison of the two options of reverse flow reactors destined for the utilization of coal mine ventilation air methane by catalytic (CFRR) or thermal (TFRR) combustion. It has been shown that both solutions have advantages and drawbacks. The use of the catalyst significantly decreases reactor temperature and makes the operation becomes to be autothermal for methane concentrations lower than in TFRR (even as low as over 0.06 vol.%). On the other hand when methane is combusted, particularly if average concentration is higher than ca. 0.4 vol.% the maximum temperature in the reactor appears to be too high for available cheap catalysts, while the use of the noble metals as active components (e.g. Pd) is not economically viable. Moreover lifetime of the catalysts is much lower than of the inactive heat exchange packing. For TFRR autothermicity threshold is higher (ca. 0.2 vol.%) but it enables cost-effective heat recovery if CH4 concentration is higher than approx. 0.4 vol.%. In conclusion, the paper states that for lower VAM concentrations, when only greenhouse gas mitigation is an aim of combustion CFRR can have some advantages over TFRR. Should the heat recovery be seriously taken into account the TFRR is economically and technically the most advantageous solution, however.

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