METHOD AND ARRANGEMENT FOR RECOVERING HELIUM

Abstract

A method for recovering helium from a feed gas mixture comprising helium, carbon dioxide and at least one of methane and nitrogen, and wherein at least a part of the feed gas mixture is subjected to a separation sequence including a membrane-based separation and an adsorption-based separation forming a helium product, wherein the the membrane based separation is performed using a first membrane separation step and a second membrane separation step, the membrane based separation and the separation sequence includes no further membrane separation steps, the adsorption based separation is performed using a pressure swing adsorption step, at least a part of the feed gas mixture is subjected to the first membrane separation step forming a first retentate and a first permeate. A corresponding arrangement is also provided.

Claims

1-12. (canceled)

13. A method for recovering helium from a feed gas mixture comprising helium, carbon dioxide and at least one of methane and nitrogen, wherein the feed gas mixture is subjected to a separation sequence including a membrane based separation and an adsorption based separation forming a helium product wherein the membrane based separation is performed using a first membrane separation step and a second membrane separation step, that the membrane based separation and the separation sequence includes no further membrane separation steps, that the adsorption based separation is performed using a pressure swing adsorption step, that at least a part of the feed gas mixture is subjected to the first membrane separation step forming a first retentate and a first permeate, that at least a part of the first permeate is subjected to a carbon dioxide removal step forming a gas mixture depleted in carbon dioxide, that at least a part of the gas mixture depleted in carbon dioxide is subjected to the second membrane separation step forming a second retentate and a second permeate, that at least a part of the second permeate is subjected to the pressure swing adsorption step forming a tail gas and the helium product, and that at least a part of the tail gas is recycled to a position between the first membrane separation step and the second membrane separation step in the separation sequence.

14. The method according to claim 13, wherein the feed gas mixture is obtained by submitting a starting gas mixture to a pretreatment comprising at least one of a removal of particles, a removal of liquids, a removal of heavy hydrocarbons, a removal of water, a removal of trace components including mercury, sulfur components and/or other trace components.

15. The method according to claim 13, wherein the starting gas mixture or the feed gas mixture is natural gas or obtained therefrom.

16. The method according to claim 13, wherein at least a part of the first retentate and/or at least a part of the second retentate are used in forming a further gas product poor in helium.

17. The method according to claim 13, wherein the first permeate or the part thereof being subjected to the carbon dioxide removal step is subjected to a first compression step and/or wherein the gas mixture depleted in carbon dioxide is or the part thereof subjected to the second membrane separation step is subjected to a second compression step and/or wherein the second permeate or the part thereof being subjected to the pressure swing adsorption step is subjected to a third compression step.

18. The method according to claim 17, wherein the tail gas or the part thereof being recycled is combined with the first permeate or with the part thereof being subjected to the carbon dioxide removal step is also subjected to the first compression step after being combined with the first permeate or with the part thereof being subjected to the carbon dioxide removal step.

19. The method according to claim 17, wherein the tail gas or the part thereof being recycled is subjected to a further compression step separate from the first compression step and is thereafter combined with the first permeate or with the part thereof being subjected to the carbon dioxide removal step.

20. The method according to claim 13, wherein the helium product is subjected to a compression and/or a liquefaction.

21. The method according to claim 16, wherein the further gas product is subjected to a compression and/or a liquefaction.

22. The method according to claim 13, wherein the feed gas mixture contains 0.1 to 5 mol-% helium and/or 0.5 to 60 mol-% of carbon dioxide and further comprises, in the part not formed by helium and carbon dioxide, at least 50 mol-% methane and/or nitrogen, wherein the first retentate and the second retentate contain less than 200 ppm helium, wherein the second permeate contains 20 to 40 mol-% helium and wherein the helium product contains 90 to 99.9999 mol-% helium.

23. An arrangement for recovering helium from a feed gas mixture comprising helium and carbon dioxide and at least one of methane and nitrogen, the arrangement comprising means for subjecting at least a part of the feed gas mixture to a separation sequence including a membrane based separation and an adsorption based separation forming a helium product wherein the membrane based separation comprises a first membrane separation step and a second membrane separation step, that the membrane based separation and the separation sequence includes no further membrane separation steps, that the adsorption based separation comprises a pressure swing adsorption step, that means are provided which are adapted to subject at least a part of the feed gas mixture to the first membrane separation step and to form a first retentate and a first permeate, that means are provided which are adapted to subject at least a part of the first permeate to a carbon dioxide removal step forming as gas mixture depleted in carbon dioxide, that means are provided to subject at least a part of the gas mixture depleted in carbon dioxide to the second membrane separation step and to form a second retentate and a second permeate, that means are provided which are adapted to subject at least a part of the second permeate to the pressure swing adsorption step and to form a tail gas and the helium product, and in that means are provided which are adapted to recycle a part of the tail gas at a position between the first membrane separation step and the second membrane separation step in the separation sequence.

24. The arrangement according to claim 11, comprising means adapted to perform a method for recovering helium from a feed gas mixture comprising helium, carbon dioxide and at least one of methane and nitrogen, wherein the feed gas mixture is subjected to a separation sequence including a membrane based separation and an adsorption based separation forming a helium product wherein the membrane based separation is performed using a first membrane separation step and a second membrane separation step, that the membrane based separation and the separation sequence includes no further membrane separation steps, that the adsorption based separation is performed using a pressure swing adsorption step, that at least a part of the feed gas mixture is subjected to the first membrane separation step forming a first retentate and a first permeate, that at least a part of the first permeate is subjected to a carbon dioxide removal step forming a gas mixture depleted in carbon dioxide, that at least a part of the gas mixture depleted in carbon dioxide is subjected to the second membrane separation step forming a second retentate and a second permeate, that at least a part of the second permeate is subjected to the pressure swing adsorption step forming a tail gas and the helium product, and that at least a part of the tail gas is recycled to a position between the first membrane separation step and the second membrane separation step in the separation sequence.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0033] FIG. 1 illustrates an arrangement according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWING

[0034] FIG. 1 schematically illustrates an arrangement 100 according to an embodiment of the invention in form of a simplified process diagram. The following explanations likewise relate to a corresponding method.

[0035] In the arrangement 100, which is adapted to perform a method according to the present invention, a feed stream A containing helium at least one of methane and nitrogen, e.g. natural gas or a gas mixture formed from natural gas, is subjected to a pretreatment 1 of the kind mentioned before, forming a feed gas mixture B. As mentioned, the pretreatment is entirely optional. At least a part of the feed gas mixture B which also contains helium and at least one of methane and nitrogen is subjected to a separation sequence which is designated 10 in total.

[0036] The separation sequence 10 includes a membrane-based separation and an adsorption-based separation, wherein that the membrane-based separation is performed using a first membrane separation step 11 and a second membrane separation step 14. The adsorption-based separation is performed using a pressure swing adsorption step 16. A carbon dioxide removal step 13 is and optionally a first compression step 12 is provided as a part of the separation sequence as well.

[0037] In the embodiment shown, at least a part of the feed gas mixture B is subjected to the first membrane separation step 11 forming a first retentate C and a first permeate D. At least a part of the first permeate D is subjected to carbon dioxide removal unit step 13, forming a gas mixture depleted in carbon dioxide (without specific reference numeral). At least a part of the gas mixture depleted in carbon dioxide is subjected to the second membrane separation step 14 forming a second retentate E and a second permeate F. At least a part of the second permeate F is subjected to the pressure swing adsorption step 16 forming a tail gas G and a helium product H.

[0038] As also shown, at least a part of the tail gas G is combined with the first permeate D or the part thereof being subjected to the carbon dioxide removal unit step 13. As mentioned, no further membrane-based separation is be performed according to the present invention. As shown, at least a part of the first retentate C and/or of the second retentate E are used in forming a natural gas product K.

[0039] As mentioned, in the embodiment shown in FIG. 1, the first permeate D or the part thereof being subjected to the carbon dioxide removal unit step 13 is subjected to a first compression step 12 and/or the second permeate F or the part thereof being subjected to the pressure swing adsorption step 16 is subjected to a compression step 15, previously referred to as “third” separation step. Additionally, the gas mixture depleted in carbon dioxide in the carbon dioxide removal unit step 13 may be compressed (in a “second” compression step). In the embodiment shown, the tail gas G or the part thereof being combined with the first permeate D or with the part thereof being subjected to the carbon dioxide removal unit step 13 is also subjected to the first compression step 12 after being combined with the first permeate D or with the part thereof being subjected to the carbon dioxide removal unit step 13.

[0040] The feed gas mixture B, in the embodiment shown, shall comprise carbon dioxide, at least a part of the carbon dioxide being transferred to the first permeate D which is at least in part subjected to a carbon dioxide removal step 13.