Site Trials of Ventilation Air Methane Enrichment with Two-Stage Vacuum, Temperature, and Vacuum Swing Adsorption

Abstract

Site trials of a two-stage vacuum, temperature, and vacuum swing adsorption (VTVSA) process using carbon fiber composites was, for the first time, carried out at an Australian coal mine to enrich ventilation air methane (VAM) in a safe manner. Four sets of tests were carried out with average inlet VAM concentrations ranging from 0.54 to 0.73 vol %, resulting in 4.34–4.94 vol % CH4 through the first stage and 27.62–35.89 vol % CH4 in the final product, which is overall a 44–63 times VAM enrichment. The average CH4 concentrations after the first stage were successfully maintained to be less than 5 vol % by regulating the initial vacuum pressure in response to the inlet VAM concentrations. The presence of CO2 in actual ventilation air, specifically the ratio of CO2 over CH4 concentrations, was found to associate with the methane recovery of the second stage, and CH4 and O2 concentrations in the final product. Compared to our previous results with simulated ventilation air, no effect of the presence of moisture in ventilation air on CH4 capture performance was found, confirming the adequacy of carbonaceous materials such as carbon fiber composites to be employed for VAM enrichment. In addition, oxygen concentrations in the final product for all tests were less than 10 vol %, enhancing the operational safety at coal mine sites.