Helium Recovery through Inorganic Membranes Incorporated with a Nitrogen Rejection Unit

Abstract

Helium recovery and purification from a natural gas process is increasingly being investigated globally to address rising market demand, as traditional helium sources become depleted. Here, process simulations of two types of inorganic membranes were undertaken in Aspen HYSYS to investigate the possibility of recovering and purifying helium from the Nitrogen Rejection Unit (NRU) offgas close to the NRU’s operating temperature. The two membranes were a cobalt-silica membrane that has He/N2 selectivity through molecular sieving and a zeolite membrane that has N2/He selectivity at low temperatures, because of surface diffusion. Both membranes were able to achieve the desired He recovery and purification through a three-membrane-stage process, and for a feed of 4% He, the cobalt-silica membrane could achieve the same separation performance through a two-membrane-stage process above 340 K, because of increasing selectivity with temperature. In contrast, the zeolite membrane could not operate above 220 K, because of the loss of the surface diffusion mechanism. The difference in permeance of the two membranes significantly affected the membrane area, with the cobalt-silica membrane requiring three orders of magnitude more area than the zeolite membrane to recover and purify the same amount of helium. However, the zeolite membrane’s selectivity for N2 meant that the vast majority of the NRU offgas passed through the membrane into the permeate streams. Hence, to ensure a high helium recovery, the permeate streams from the second and third membrane stages must be recycled, resulting in permeate gas throughputs that are orders of magnitude higher than the cobalt-silica membrane process. This placed significant recompression duty on the zeolite membrane process, compared to the cobalt-silica process, and, as such, the zeolite membrane’s power duty for helium separation was at least five times greater than that of the cobalt-silica membrane. Hence, there is a tradeoff between the two inorganic membranes for helium recovery and purification, based on required membrane area and power demand.

Evaluation of Flowsheet Design Approaches to Improve Energy Efficiency in Multistage Membrane Processes to Recover Helium

“…Moreover, large-scale industrial vacuum equipment is not commonplace, and a vacuum pressure of 0.2 bar is probably the lowest practical vacuum pressure usually considered in the industry . Therefore, many previous membrane-based gas separation works including helium separation did not include a vacuum pump in the permeate side of the membrane as it required larger and more complicated equipment and larger membrane area as well. ,,,− …”

Helium separation using membrane technology: Recent advances and perspectives

“…Process simulation of membrane technology for helium recovery from natural gas or other industrial gas sources has been widely studied and reported in the literature [28,37,[179][180][181][182][183]. Hägg et al compared three different types of membranes (i.e., porous silica, CMS, and Matrimid) for their applicability in helium recovery processes [179].…”

Design and Optimization of a Novel Hybrid Membrane–Electrochemical Hydrogen Pump Process for Recovering Helium from NRU off Gas

“…Due to the similar molecular size and similar boiling points of hydrogen and helium, membrane processes and adsorption processes widely used in hydrogen separation [ 7 , 8 ] can also be applied to helium recovery and purification processes [ 9 ]. These processes offer alternative options for helium recovery that are more cost-effective and energy-efficient [ 10 , 11 , 12 , 13 ]. Hamedi et al [ 14 ] proposed a helium recovery process based on highly selective silicon dioxide membranes.…”