(622a) Helium Purification from Depleted Natural Gas Sites By Pressure Swing Adsorption

Helium is a non-renewable gas and it is indispensable in several modern technologies involving health, medicine, space, and nuclear research. The helium market has undergone several global shortages in recent years due to fluctuations in helium production. Helium is typically separated from helium-rich natural gas using cryogenic distillation integrated into an LNG plant. As helium is running out, and worldwide demand is predicted to exceed current production levels, extraction of helium from unconventional sources like depleted natural gas sites, small natural gas sites, geothermal pools, and hot springs is being explored. For small gas reservoirs that have moderate production capacity, the cryogenic process is not suitable. The adsorption process, specifically in the form of pressure swing adsorption (PSA) is explored as a replacement to the conventional cryogenic distillation for helium purification.

Sources such as depleted natural gas sites consist of a bulk quantity of nitrogen and trace amounts of helium (0.5%-10 vol%) and no hydrocarbons [1]. The gas from these gas reservoirs is available at high pressures of 40 bar. Thus, a high-pressure 5-step PSA process is designed and explored for He purification from depleted natural gas sites. At first, dynamic column breakthrough (DCB) experiments were performed on an experimental test rig with Zeolite-5A adsorbent using 100% N₂, 75% N₂, and 50% N₂ [2]. The DCB results provided information regarding the equilibrium and kinetic parameters, which were then used for the modeling of the PSA process. Following this, a non-isothermal PSA model was developed to simulate the process dynamics of dynamic column breakthrough and the PSA cycle configuration. The DCB model developed, agreed with the experimental results.

An experimental test rig consisting of three beds filled with Zeolite 5A adsorbent was then used to perform a 5-step PSA process. A series of PSA experiments with atmospheric regeneration was designed to perform a parametric study by varying adsorption time, feed pressure, feed velocity, and feed composition. The pressure histories, and inlet and outlet mass flow during each step were recorded and analyzed. The experiments resulted in a He purity and recovery of 95%, and 90%, respectively, for the feed containing 10% He .The experiments are well in agreement with the results of the non-isothermal PSA model with an average deviation of less than 5% between simulated and experimental product purities, recoveries, and productivities. The results are also compared with the dual reflux (DR) PSA cycle 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.Wilkins, N. S.; Rajendran, A. Adsorption 2019, 25, 115–133.

3.Weh, G. Xiao, E. Sadeghi Pouya, E. F. May, Sep.Purif. Technol. 2022, 450, 137894