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 % CH 4 through the first stage and 27.62−35.89 vol % CH 4 in the final product, which is overall a 44−63 times VAM enrichment. The average CH 4 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 CO 2 in actual ventilation air, specifically the ratio of CO 2 over CH 4 concentrations, was found to associate with the methane recovery of the second stage, and CH 4 and O 2 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 CH 4 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.

Will It Be Possible to Put into Practice the Mitigation of Ventilation Air Methane Emissions? Review on the State-of-the-Art and Emerging Materials and Technologies

“…It was shown that the measured values were different between the examined objects, but also depended on the currently conducted mining works (see Table 1). As reported by other sources, the VAM flow rate can achieve even 600 m 3 /s [19,20] and daily dust loading can reach 232 kg [21]. It should be considered that all mentioned parameters generate huge technical problems in the implementation of any known and available technology or currently being developed technology to an industrial scale.…”

Enrichment of low concentration methane: an overview of ventilation air methane

“…86 Very recently they have successfully carried out site trials of a two-stage VTVSA process using carbon fiber composites for VAM enrichment at an Australian coal mine. 7…”

“…Porous carbon materials, including high surface area activated carbons (ACs), 114,115 activated carbon fibers (ACFs), 92,116 and carbon molecular sieves (CMSs), 117,118 have been extensively studied as the adsorbents in adsorption based processes for low concentration CH 4 recovery from unconventional natural gases 115,119,120 and VAM enrichment. 7,77,84–86 Table 3 summarizes the textural properties, CH 4 adsorption capacity, CH 4 /N 2 selectivity and CO 2 /CH 4 selectivity of porous carbon materials under ambient conditions unless otherwise specified.…”

“…In this respect, the adsorbent (carbon fiber composites) used in the site study for VAM enrichment by Bae et al shows that the presence of moisture in ventilation air has no effect on CH 4 capture. 7 It is important to investigate the effect of water vapor on the adsorption performance of other porous carbon materials (with high CH 4 adsorption capacity and high CH 4 /N 2 selectivity) that are potentially useful for VAM enrichment.…”

“…The VAM gas mixture is characterized by large volume (200-385 m 3 s À1 ), the majority being air (nitrogen $79%, oxygen $20%, carbon dioxide 0.13-0.19% and small amounts of other gases), low and changeable VAM concentration (0.1-1.5%), high relative humidity (70-100%) and high dust loading (0.13-4.47 mg m À3 ). 4,7 VAM contributes about 60-70% of total CH 4 emissions from coal mining activities. 6,8 Therefore, the utilization of VAM can not only reduce greenhouse gas emissions, but also provide extra economic benets to the mining industry.…”