Helium recovery from natural gas
Helium-containing natural gas is processed with three gas separation stages to produce a natural gas product and a Helium-containing gas that may be injected into the reservoir from which the Helium-containing natural gas is obtained. A permeate from the first gas separation membrane stage is compressed and fed to the second gas membrane stage. The permeate from the second gas separation membrane stage is recovered as the Helium-containing gas that may be injected into the reservoir. The non-permeate from the second gas separation membrane stage is fed to the third gas separation membrane stage. Non-permeates from the first and third gas separation stages are combined to produce a natural gas product. A permeate from the third gas separation membrane stage is combined with a non-permeate from the first gas separation membrane stage before it is compressed and fed to the second gas separation membrane stage.
1. A method of separating natural gas and Helium from a gas mixture, comprising the steps of:
separating Helium-containing natural gas at a first gas separation membrane into a first permeate and a first non-permeate, the Helium preferentially permeating over the natural gas at the first gas separation membrane;
compressing the first permeate to provide a compressed first permeate;
separating the compressed first permeate at a second gas separation membrane into a second permeate and a second non-permeate, the Helium preferentially permeating over the natural gas at the second gas separation membrane;
separating the second non-permeate at a third gas separation membrane into a third permeate and a third non-permeate, the Helium preferentially permeating over the natural gas at the third gas separation membrane;
combining the first and third non-permeates to provide a product natural gas stream; and
combining the first and third permeates upstream of the compressor.
2. The method of claim 1 , further comprising the step of injecting the second permeate into a natural gas reservoir from which the feed gas is ultimately obtained.
3. The method of claim 1 , wherein Helium is present in the Helium-containing natural gas at a concentration of less than 0.5 mol %.
4. The method of claim 1 , wherein a stream of the second permeate has a mass flow rate of no more than 3% of a mass flow rate of a stream of the Helium-containing natural gas separated at the first gas separation membrane.
5. The method of claim 1 , further comprising the step of purifying the second permeate stream to provide a Helium product gas having a Helium concentration of at least 99 mol %.