METHOD OF RECOVERYING A LOW CONCENTRATION GAS USING TWO MEMBRANE STAGES WITH A SECOND STAGE REFLUX

摘要

A first gas present at low concentration in a source gas is recovered from the source gas at a relatively high recovery using first and second gas separation membrane stages. The second stage permeate gas is divided into first and second portions. The first portion is a first product gas a majority of which is the first gas. The second portion and the permeate gas from the first stage are both fed to the compressor and then to the second stage gas separation membrane. The second stage non-permeate gas is combined with the source gas and fed to the first gas separation membrane stage. The first gas separation membrane separates that combined gas into the permeate (which is combined with the second portion as explained above) and a non-permeate. The first stage non-permeate is the second product gas mainly comprised of the second gas. The invention is particularly applicable to natural gas containing Helium.