Effect of Vacuum Process on Enrichment of Low-Concentration Coal Mine Methane by Adsorption

The massive emission of low-concentration coal mine methane (CMM) has resulted in the ineffective utilization of a large amount of energy methane and caused environmental pollution. The gas mixture used in the study consisted of methane (CH4) 12% and nitrogen (N2) 88%. The adsorbent was coconut activated carbon. This paper uses the adsorption method to conduct enrichment research on 12% low-concentration CMM. Firstly, the variation in methane gas concentration under different desorption methods was studied by numerical simulation, and the desorption methods suitable for increasing methane concentration were analyzed. A three-bed VPSA CMM separation experimental device was built, and three enrichment processes of feed gas pressurization, exhaust gas pressurization, and vacuum exhaust (VE) were studied. The results show that using the three-bed vacuum pressure swing adsorption (VPSA) process can effectively enrich low-concentration CMM. Under the adsorption pressure of 110 kPa and the desorption pressure of 10 kPa, 12% of CMM can be enriched to more than 25%, with a recovery rate higher than 80%. The exhaust process can significantly increase the product gas concentration. The product gas concentration increased by 18.2%, with the product rising from 22.5% to 26.6% when the extraction step increased from 0 s to 8 s. This research may provide reliable fundamental data for industrial-scale low-concentration CMM enrichment.