Helium is unique among all of the gases due to its extraordinary properties like the lowest boiling point, highest ionization potential, and chemical inertness. Due to the increase in demand, new ways of extracting helium from depleted natural gas sites, and geothermal pools are being explored. Non-cryogenic based purification techniques like adsorption and membrane separation are particularly attractive. The membrane separation process has the distinct advantage of separating bulk quantities of unwanted gas with high recovery. Due to the trade-off between permeability and selectivity, a single-stage membrane separation process cannot achieve high purity and high recovery simultaneously. Multi-stage membrane process requires compression of feed at each subsequent stage and also needs a large number of stages and compressors to achieve the target purification [2]. Pressure swing adsorption (PSA) is another widely used gas separation technology in various applications like hydrogen purification from steam methane reforming off the gas, and oxygen separation from air. Conventionally PSA is used to achieve high purities in the final product of the gas purification process. Hence, an alternative approach was designed to combine a single-stage membrane and a two-stage PSA process for helium purification. It is a 3-stage separation process with no inter-stage compressors. The objective of this work is to utilize the well-head feed gas pressure available at 40 bar to enrich helium from 1% to 95% purity with greater than 85% recovery.
We simulated a lab-scale single-stage hollow fiber membrane separation process with three different commercial membranes (Hyflon AD60X, Polyimide, and Polysulfone) using 1% He and 99 % N2 at 40 bar feed pressure. A parametric study was also performed by varying the permeate pressure (1 bar, 5 bar, 10 bar, 15 bar, and 20 bar) with different membranes. All the simulations were carried out using the gPROMS software package. Separation performance was evaluated and compared for all the cases by key performance indicators such as He purity and He recovery. The results from the simulations revealed that 1% He at a feed pressure of 40 bar can be enriched to 3 % He with greater than 95% recovery by maintaining a permeate pressure of 10 bar using a Polyimide membrane. Following that, a two-stage PSA process, validated using lab-scale experiments, was explored through rigorous dynamic modelling and optimization. The results obtained from this study were also compared with the three-stage membrane purification process reported in the literature [3].
References:
[1] Rufford, T. E.; Chan, K. I.; Huang, S. H.; May, E. F. Adsorp. Sci. Technol 2014, 32, 49–72.
[2] Alders, M.; Winterhalder, D.; Wessling, M. Sep Purif Technol 2017, 189, 433–440.
[3] Quader, M. A.; Rufford, T. E.; Smart, S. Separation and Purification Technology 2020, 236, 116269.
