1413 Figure 5. CSIRO VAMCAP: (a) two-stage temperature & vacuum adsorption (TVSA) process and (b) VAMCAP pilot unit installed at an Australian coal mine site. As shown in Figure 6, the average methane concentrations can be managed below 5 and over 25 vol% in the exhaust streams of the first and second stages, respectively, being avoided from the explosive range in a safe manner. The fundamental mechanism of the separation of methane from nitrogen and oxygen is the stronger affinity of methane over them towards carbon surfaces. Figure 6. Gas compositions of exhaust streams from (a) the first and (b) second stages. The VAMCAP prototype unit was designed, constructed and installed in accordance with relevant Australian Standards to enrich VAM up to a level that is beyond the methane explosive range. The results of site trials at an Australian coal mine site are summarized as below: • With average actual VAM concentrations of 0.57-0.73 vol%, the CH4 concentrations in the final product were 27.65-35.89 vol%, which is 44-63 times enrichment. • The average oxygen concentration in the final product was less than 10 vol%, enhancing the safe operation of the VAMCAP unit • The methane explosive range was successfully avoided during the enrichment process. • There was no sign of the negative effect of high humidity on VAM enrichment. CATAVAM Catalytic oxidation of CH4 completely to CO2 is an effective route to mitigate VAM emissions at a relatively low temperature. The use of a catalyst reduces the VAM mitigator operating temperature below 650 oC, which is well below the stone dust decomposition temperature of above 800-850 oC, thus avoiding
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