VAM Enrichment with a Two-stage Adsorption Process

Treatment of ventilation air methane (VAM) with cost-effective technologies has been an on-going challenge due to its high volumetric flow rate with low and variable methane concentrations. As part of CSIRO's approaches to tackle the challenges, this project is about VAM enrichment with CSIRO's carbon composites to support gas utilisation technologies such as gas engines and lean burn turbines for power generation. The ACARP project C19054 demonstrated that 5 or 11 times VAM enrichment was achievable with a single-stage VAM adsorption process, depending on operational conditions. As of today, this is the best performance achieved in VAM enrichment technologies worldwide. With these successful outcomes, this project, as an extension of the ACARP project C19054, aimed to achieve further VAM enrichment up to more than 25 vol.% methane in the final product, employing a two-stage adsorption process. The aim (> 25 vol.% CH4) in this project was accomplished with identification of further improvement options.

The initial scope was to utilise the existing large-scale test unit that was used for ACARP C19054, modifying the unit to accommodate another column for the two-stage adsorption process. At the early stage of this project, with an intension for future mine site trials, a strong need was identified to construct a new test unit that complies with mine site standards and regulations, which was supported by industry monitors. Consequently, extra tasks and costs were devoted to this project, including HAZOP study, hazardous area classification, and design, construction and installation of a new test unit in accordance with Australian standards and mine site regulations.

After the HAZOP study and hazardous area classification, a new VAM enrichment unit with a two-stage adsorption process was designed in 3D with SolidWorks and constructed, consisting of two fixed columns filled with carbon fibre composites, a heating/cooling system, a gas monitoring system and a control system. As one of the issues identified from ACARP C9054 was a slow heating process for temperature swing, the second column was made out of copper and brass to enhance heat transfer with a suitable thermal fluid for both heating and cooling. The heating process for the first column was improved by about 3.8 times with the selected thermal fluid at given conditions. Also the composite temperatures in the second column were increased almost double times faster than those in the first column. Overall, about 7.1 times improvement was achieved with the thermal fluid in the second column, compared to the time with hot air in the first column. Two sets of gas monitoring systems with SIL 2 were designed and fabricated. Operational safety features were implemented in the control and monitoring system in case of power failure or emergency.

As methane is a safety hazard that may fall into an explosive atmosphere, in the course of VAM enrichment, special precautions and preventative measures were taken during the design and construction phases as well as for normal operation and emergency. Particularly, the functional specification document (FSD) of the VAM enrichment unit was prepared to clearly identify the operating parameters, including the start-up, operating and shutdown sequences as well as emergency procedures.