COMBINED MEMBRANE-PRESSURE SWING ADSORPTION METHOD FOR RECOVERY OF HELIUM

Abstract

A method of obtaining helium from a process gas. The process gas is at a pressure less than 15 bar to a first membrane separation stage having a first membrane more readily permeable for helium than for at least one other component in the process gas. A first retentate stream is fed to a second membrane separation stage having a second membrane more readily permeable for helium than for at least one other component in the process gas. Helium is separated from a first helium-containing permeate stream using a pressure swing adsorption to obtain a helium-containing product stream. A second helium-containing permeate stream is recycled to the first membrane separation stage. A purge gas from the pressure swing adsorption is also recycled to the first membrane separation stage.

Claims

1. Method of obtaining helium from a helium-containing process gas, having at least the following steps: a) feeding a helium-containing process gas to a compression, said helium-containing process gas having a pressure of less than 15 bar, preferably of less than 10 bar, b) feeding the process gas that leaves the compression to a prepurifying unit in which the troublesome components are removed; c) guiding the process gas removed from the troublesome components to a first membrane separation stage having a first membrane which is more readily permeable for helium than for at least one further component present in the process gas; d) guiding a first retentate stream that has not passed through the first membrane to a second membrane separation stage having a second membrane which is more readily permeable for helium than for at least one farther component present in the process gas; e) separating helium from a first helium-containing permeate stream that has passed through the first membrane by means of pressure swing adsorption to produce a helium-containing product stream; and f) recycling a second helium-containing permeate stream that has passed through the second membrane to the first membrane separation stage, and recycling a purge gas from the pressure swing adsorption to the first membrane separation stage.

2. Method according to claim 1, characterized in that a temperature swing adsorption or a reaction, especially a thermal oxidation, is conducted in the prepurifying unit.

3. Method according to claim 1, characterized in that the process gas is a manufacturing offgas from a manufacturing process for production of an electronic and/or semiconductor element, the troublesome components to be removed in said prepurification including at least one of the following components: H.sub.2, a hydrocarbon, H.sub.2O, CO.sub.2, a sulphur compound, a silane, a phosphine, arsine, a halogenated hydrocarbon, a fluorine gas, especially SF6 or NF3, a metal hydride.

4. Method according to claim 1, characterized in that a second retentate stream that has not passed through the second membrane is used for regeneration of an adsorber used in the temperature swing adsorption.

5. Method according to claim 1, characterized in that a second retentate stream that has not passed through the second membrane is expanded to perform work, especially with generation of electrical energy.

6. Method according to claim 1, characterized in that the helium content of the first permeate stream is not less than 25% by volume, and/or in that the helium content of the product stream is not less than 95% by volume, especially not less than 99% by volume.

7. Method according to claim 1, characterized in that the helium-containing process gas has a helium content of more than 0.1% by volume, preferably of more than 0.5% by volume.

Description

[0036] The invention described above is elucidated in detail hereinafter against the technical background in question with reference to the accompanying drawings, which show preferred embodiments. The FIGURE shows:

[0037] FIG. 1: a method according to the invention for separating helium from a process gas and a helium separation plant according to the invention.

[0038] FIG. 1 shows a plant 1 according to the invention. If a process gas to be treated is an offgas from a manufacturing process or a manufacturing line 25, especially for production of electronic elements and/or semiconductor elements, the plant is also referred to as helium recovery plant 24 and may comprise the manufacturing process or the manufacturing line 25.

[0039] The process gas/offgas is fed to a compressor 22 via a feed conduit 20 and is compressed therein and optionally prepurified downstream of the compressor 22, especially by means of a temperature swing adsorption 23. Subsequently, the optionally prepurified process gas is fed via a first process gas inlet 8 to a first membrane separation stage 2, specifically on the first retentate side 6. A process gas fraction having a high helium content which can pass through the first membrane 4 arrives on the first permeate side 12 and exits there as the first permeate stream via the first permeate stream outlet 14 and is fed to the pressure swing adsorption unit 16 via the first permeate stream conduit 27.

[0040] The proportion of the process gas which does not pass through the first membrane 4 in the first membrane separation stage 2, i.e. is ultimately retained by the membrane 4, remains on the first retentate side 6 and is discharged as first retentate stream via the first retentate stream outlet 10. Via the first retentate stream conduit 26, the first retentate stream is then introduced via the second process gas inlet 9 into the second membrane separation stage 3, namely to the second retentate side 7. The process gas which passes through the second membrane 5 arrives on the second permeate side 13 and flows through the second permeate outlet 15 as the second permeate stream into the first recycle conduit 28, through which the second permeate stream is fed back to the feed conduit 20 or to the first membrane separation stage 2, preferably upstream of the compressor 22.

[0041] The process gas component in the second membrane separation stage 3 which does not pass through the second membrane 5 is removed as the second retentate stream through the second retentate stream outlet 11 and the first offgas conduit 30. This (low-helium) offgas can especially be used for purging adsorbers of the temperature swing adsorption 23.

[0042] The first permeate stream is introduced into the pressure swing adsorption unit 16 via the first permeate stream conduit 27 and via the third process gas inlet 17. A purge gas obtained in the pressure swing adsorption is introduced back into the feed conduit 20 or the first membrane separation stage 2, preferably upstream of the compressor 22, via the purge gas outlet 18 and via the second recycle conduit 29, here by means of the first recycle conduit 28. The first permeate stream which has been purified further by pressure swing adsorption is dispensed via the product gas outlet 19 as product gas or pure helium gas, preferably with a helium content of more than 95% by volume, more preferably more than 99% by volume, and can be sent to a further use via the product gas conduit 21. A tail gas from the temperature swing adsorption 23 is removed via a second offgas conduit 31.

LIST OF REFERENCE NUMERALS

[0043]

TABLE-US-00001 1 Helium separation plant 2 First membrane separation stage 3 Second membrane separation stage 4 First membrane 5 Second membrane 6 First retentate side 7 Second retentate side 8 First process gas inlet 9 Second process gas inlet 10 First retentate stream outlet 11 Second retentate stream outlet 12 First permeate side 13 Second permeate side 14 First permeate stream outlet 15 Second permeate stream outlet 16 Pressure swing adsorption unit 17 Third process gas inlet 18 Purge gas outlet 19 Product gas outlet 20 Feed conduit 21 Product gas conduit 22 Compressor stage 23 Prepurifying unit 24 Helium recovery plant 25 Manufacturing line 26 First retentate stream conduit 27 First permeate stream conduit 28 First recycle conduit 29 Second recycle conduit 30 First offgas conduit 31 Second offgas conduit