Enrichment of Low-Quality Methane by Various Combinations of Vacuum and Temperature Swing Adsorption Processes

As an endeavor to reduce greenhouse gas emissions while harnessing an energy source, this paper applied various combinations of adsorption-based swing processes to enrich a wide range (3-30%) of low-quality coal mine methane (CMM) in air to a level that a direct utilization can be made by gas engine technology. Having honeycomb monolithic carbon fiber composites tuned for CMM enrichment, at least 5.3 and 3.5% CH4 were found to be required by one-and two-stage vacuum swing adsorption (VSA) processes, respectively, to obtain more than 9.0% CH4 in the product. As VSA alone, however, can give rise to a safety risk that the CH4 concentrations in the product are still in the explosive range, a one-stage vacuum, temperature, and vacuum swing adsorption (VTVSA) process was applied, enriching 3.0-8.6% CH4 up to 18.2-50.7% CH4 in the product and thus eliminating the safety concern. As a reference for other applications, 10.3-30.1% CMM streams can be enriched up to 57.5-86.9% through the one-stage VTVSA process. To minimize energy consumption with two fixed columns, VSA and VTVSA processes in the first and second columns, respectively, were applied, enriching 3.1 and 4.1% CH4 up to 31.6 and 37.3% CH4 in the product, respectively. In this paper, various adsorption-based technology options are provided for mine operators to enrich low-quality CMM and can be applied for other applications such as methane capture from abandoned landfill sites. Due to the explosive nature of the low-quality CH4 in air, this paper is the first to cover the enrichment of a wide range of low-quality CMM below 30% with an explosion-proof enrichment unit being capable of various vacuum and temperature swing adsorption processes.