PSA for Separating N2 & He from Natural Gas


Many of the gas reserves destined to supply the generation of LNG plants now under construction contain sufficient nitrogen that cryogenic distillation is required at the end of the train to ensure the LNG product meets the shipping specification of less than 1 % N2. Very large savings in capital and operational costs, as well as greenhouse emissions would be realised if this parasitic N2 could be removed earlier in the processing stages so that downstream equipment could be reduced in size and the refrigeration duty lowered. However, separating N2 and CH4 is extremely challenging because of their molecular similarities. A provisional patent for a novel adsorbent with a world-record CH4 /N2 selectivity was recently filed by Li and May, who characterised its adsorption capacity and kinetics from -30 to 60°C, to 50 bar and with a range of gas compositions; this is a first key outcome of Li’s ARC DECRA project. Such data can be used to design industrial scale pressure-swing adsorption (PSA) cycles with Aspen Adsorption software, which are validated against cycle data produced using UWA’s pilot-scale PSA rig. Contributions to the design of the PSA rig were made by Rufford who is also conducting an ARC DECRA project on the capture of helium. Global demand for helium is rapidly increasing for use in medical scanning, arc welding, and as an inert gas in chemical analysis and synthesis. Cryogenic natural gas processing and hence LNG plants are essential to the modern production of helium. The UQ-based PhD student will help Rufford develop novel adsorbent materials for helium capture from the CH4-N2 mixtures at the tail-end of LNG plants, before travelling to UWA to test the best ones. This PSA rig will be used for cyclic testing of the novel adsorbent materials developed through both ARC DECRAs. The PhD will also use the Aspen software to develop up-scaled designs for the deployment of these novel PSA processes.

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