142 VAMCAP Due to low and variable VAM concentrations, additional energy input may be required to maintain stable and effective operation of VAM oxidation units such as VAMCAT and VAMMIT. Along with reducing fugitive emissions, VAM enrichment can be a beneficial option for providing the additional energy to the VAM oxidation units when required, acting as a buffer to stabilize methane concentrations. Amongst other technologies, it has been identified and demonstrated that adsorption technology with solid adsorbents is a viable and effective option for VAM enrichment [6,7]. In this regard, we have developed carbon composite adsorbents in a honeycomb monolithic structure to have a large geometric surface, a low-pressure drop, and a high dust and moisture tolerance. The composite adsorbents have high selectivity (about 9.5) of methane over nitrogen, and their performance on VAM enrichment is not affected in the presence of moisture [7,8]. Depending on the final product usage, it has been demonstrated that VAM can be enriched over 25 vol.% with a two-stage TVSA process. For a safety concern, any VAM enrichment process needs to avoid or eliminate the methane explosive range (5-15 vol.%). Figure 5 shows the prototype unit which is equipped with the two-stage TVSA process and installed at an Australian coal mine site. 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.
RkJQdWJsaXNoZXIy MTM0Mzk2