Integration of hybrid membrane-distillation processes to recover helium from pre-treated natural gas in liquefied natural gas plants

Abstract

We used Aspen HYSYS V.10 simulations and techno-economic analysis to evaluate the potential of four hybrid membrane-cryogenic distillation flowsheets for the direct recovery helium from nitrogen and methane in pre-treated natural gas (i.e., CO2, H2S, and water removed from the gas). The study aims to increase energy efficiency and reduce the cost of helium recovery from natural gas by better integration of the helium recovery unit (HeRU) with the nitrogen rejection unit (NRU) and methane production. Our results demonstrate that a flowsheet (Design # d) with a distillation column that produces a 90 mol% He overhead stream that is further purified in a single-stage membrane unit can produce grade-A helium with better than 99 mol% He purity at a specific helium breakeven price (SHBP) of $67.72/MSCF of He product. This hybrid flowsheet leads to the lowest SHBP because (i) it reduces the separation load in the HeRU column, (ii) provides a high He concentration feed to the membrane unit, and (iii) does not require recompression of the HeRU overhead stream to feed the membrane unit because the pressure of the feed gas is not let down to close to atmospheric pressure as in a conventional NRU-HeRU flowsheet. This type of hybrid distillation-membrane process may also be of interest in other gas separations that currently only use cryogenic distillation such as oxygen and argon production from air, CO2 capture, and olefin/paraffin separation.