Abstract
Recovery and treatment of methane from coal mine ventilation air methane (VAM) with cost-effective technologies have been an ongoing challenge due to low methane concentrations. In this study, a type of coconut shell-based active carbon was employed to enrich VAM with a three-bed vacuum pressure swing adsorption unit. A new vacuum exhaust step for the VPSA process was introduced. The results show that the vacuum exhaust step can increase the methane concentration of the product without changing adsorption and desorption pressure. Under laboratory conditions, the concentration of product increased from 0.4% to 0.69% as the vacuum exhaust ratio increased from 0 to 3.1 when the feed gas concentration was 0.2%. A 500 m³/h pilot-scale test system for VAM enrichment was built rendering good correlation with the laboratory results in terms of the vacuum exhaust step. By using a two-stage three-bed separation unit, the VAM was enriched from 0.2% to over 1.2%.
Highlights
Coal mine methane is a form of natural gas extracted from coal beds, which is formed together with coal during coalification
Methane emitted from coal mines makes up approximately 8% of the world’s anthropogenic methane emissions, which comprises 17% of all anthropogenic greenhouse gas emissions [4]
Most fugitive coal mine methane is emitted as mine ventilation air methane (VAM) at low concentrations of below 1%, which makes up 70% of the methane emissions in the coal mining processes
Summary
Coal mine methane is a form of natural gas extracted from coal beds, which is formed together with coal during coalification. Lean-burn combustion turbine technologies can generate power, operating on a higher methane concentration (between 0.8% and 1.6%), such as the carbureted gas turbine (CGT) by Energy. Lean-burn combustion turbine technologies may require additional supplementary fuel for stable operation depending on the VAM concentration [14]. VAM can be enriched to 5 times higher than the feed gas at the end of the vacuum step, previous work studied only one adsorption bed. Ouyang [26] modified coconut shell-based carbon adsorbents, the separation factor of CH4 /N2 is 6.18, showing that VAM can be enriched from 0.42% to 1.09% by vacuum pressure swing adsorption (VPSA). The other step is co-current depressurization; this step allows the low concentration heavy component gas to flow out from the top of the adsorption bed [31,32,33]. Comparisons with experimental results as well as practically-oriented analyses for further applications will be shown
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