Apparatus and method for treating a gas stream by membrane permeation, and installation comprising such an apparatus

Abstract

Installation and method for treating a feed gas stream (1) comprising carbon dioxide and methane by membrane permeation, said feed gas stream comprising at least 90 mol% carbon dioxide and between 0.5 and 10 mol% methane, and said apparatus comprising a compressor (8) configured to compress the feed gas stream (1) to a pressure between 2 barg and 16 barg, a membrane separation unit (3) configured to receive the feed gas stream (1) and to provide a permeate (2) and a retentate (4), a feed line (5) for the feed gas stream (1) to the membrane separation unit (3), and a retrieval line (9) for the retentate (4) configured to send the retentate (4) to a biogas production and / or storage unit. Abbreviated figure: Fig. 1

Description

Title of the invention: Apparatus and method for treating a gas stream by membrane permeation, and installation comprising such an apparatus

[0001] The invention relates to an apparatus and a method for treating a gas stream by membrane permeation, and an installation comprising such an apparatus.

[0002] The invention relates more particularly to a membrane permeation treatment apparatus for a feed gas stream comprising carbon dioxide and methane, said feed gas stream comprising at least 90 mol% of carbon dioxide, in particular at least 95 mol% or 97 mol% of carbon dioxide, and between 0.5 and 10 mol% of methane, in particular between 0.5 and 5 mol% or between 0.5 and 3 mol% of methane.

[0003] Biogas is the gas produced during the decomposition of organic matter in the absence of oxygen (anaerobic fermentation), also known as methanation. This can be a natural decomposition—as observed in marshes or municipal waste landfills—but biogas production can also result from the methanation of waste in a dedicated reactor, with controlled conditions, called a digester or digester, and then in a post-digester, similar to the digester but allowing the methanation reaction to progress further. Biogas is the gas produced during the decomposition of organic matter in the absence of oxygen (anaerobic fermentation), also known as methanation.This can be a natural degradation – as seen in marshes or household waste landfills – but biogas production can also result from the methanization of waste in a dedicated reactor, with controlled conditions, called a methanizer or digester, and then in a post-digester, similar to the digester and allowing the methanization reaction to be pushed further.

[0004] Biomass will be defined as any grouping of organic matter that can be transformed into energy through this methanization process, for example: sewage sludge, manure / slurry, agricultural residues, food waste...

[0005] The digester, that is, the reactor dedicated to the methanation of biomass, is a closed tank, heated or unheated (operation at a fixed temperature, between ambient temperature and 55°C), whose contents, consisting of biomass, are stirred continuously or sequentially. The conditions in the digester are anaerobic, and the generated biogas is found in the digester's headspace (gaseous space), where it is collected. Post-digesters are similar to digesters.

[0006] By virtue of its main constituents - methane and carbon dioxide - biogas is a powerful greenhouse gas; it also constitutes, in parallel, a valuable source of renewable energy in a context of dwindling fossil fuels.

[0007] Biogas mainly contains methane (CH4) and carbon dioxide (CO2) in varying proportions depending on the method of production, but also, in smaller proportions, water, nitrogen, hydrogen sulfide, oxygen, as well as other organic compounds in trace amounts.

[0008] Depending on the organic matter degraded and the techniques used, the proportions of the components differ, but on average biogas contains, on a dry gas basis, 30 to 75% methane, 15 to 60% CO2, 0 to 15% nitrogen, 0 to 5% oxygen and trace compounds.

[0009] Biogas is used in various ways. After light treatment, it can be used near the production site to provide heat, electricity or a mixture of both (cogeneration); the high carbon dioxide content reduces its calorific value, increases compression and transport costs and limits the economic interest of its use to this local application.

[0010] Further purification of biogas allows for its wider use; in particular, further purification of biogas makes it possible to obtain biogas purified to the specifications of natural gas, which can then be substituted for it; this purified biogas is called "biomethane." Biomethane thus complements natural gas resources with a renewable component produced within local areas; it can be used for exactly the same purposes as natural gas of fossil origin. It can supply a natural gas network, a vehicle refueling station, and it can also be liquefied for storage as liquefied natural gas (LNG).

[0011] The methods for utilizing biomethane are determined according to local contexts: local energy needs, potential for use as a biofuel, and the proximity of natural gas distribution or transmission networks, among other factors. By creating synergies between the various stakeholders operating in a region (farmers, industry, public authorities), biomethane production helps regions achieve greater energy independence.

[0012] Several steps must be taken between the collection of biogas and the obtaining of biomethane, the final product suitable for compression or liquefaction.

[0013] In particular, several steps are necessary before the treatment aimed at separating the carbon dioxide to produce a purified methane stream. A first step consists of compressing the biogas that has been produced and conveyed at atmospheric pressure; this compression can be achieved—conventionally—using a compressor. The following steps aim to remove the corrosive components of hydrogen sulfide and volatile organic compounds (VOCs) from the biogas; the technologies used conventionally are pressure-controlled adsorption (PCA) and the Trapping on activated carbon. Next comes the step of separating the carbon dioxide to finally obtain methane at the purity required for its subsequent use.

[0014] Carbon dioxide is a contaminant typically present in natural gas, from which it is common to have to be removed. Various technologies are used for this purpose depending on the situation; among these, membrane technology is particularly effective when the CO2 content is high; it is therefore used to separate CO2 present in biogas, originating from landfill gas or from digesters of plant or animal waste.

[0015] It is preferable that installations enabling the production of a methane-enriched gas stream be able to control the loss of methane.

[0016] From there, a problem that arises is to provide a device to reduce the methane that goes out of the vent of a biogas purifier.

[0017] To this end, the apparatus according to the invention, which also conforms to the generic definition given in the preamble above, is essentially characterized in that it comprises a compressor configured to compress the feed gas stream to a pressure between 2 barg and 16 barg, preferably between 4 barg and 8 barg, a membrane separation unit configured to receive the feed gas stream and to provide a permeate and a retentate, a feed gas stream supplying duct to the membrane separation unit, and a retentate recycling duct configured to send the retentate to a biogas production and / or storage unit.

[0018] Such a device makes it possible to valorize a gaseous stream which is otherwise released into the atmosphere by the vent of a biogas scrubber and to reduce the loss of methane in a biomethane production process conforming to specifications, in particular for injection into a natural gas network.

[0019] According to one embodiment, the compressor is a variable speed compressor.

[0020] According to one embodiment, the supply duct for the gaseous feed includes at least the compressor, a pressure sensor configured to measure the pressure of the gaseous feed, a compressor speed variator and a loop for regulating and controlling the pressure of the gaseous feed.

[0021] According to one embodiment, the recycling conduit includes a valve.

[0022] According to one embodiment, the membrane separation unit comprises at least one membrane that is more permeable to carbon dioxide than to methane.

[0023] The invention further relates to a biomethane production plant comprising a biogas production and / or storage unit, a biogas purification unit for the biogas produced by the biogas production and / or storage unit, said biogas purification unit being configured to produce a first gas stream enriched in carbon dioxide and depleted in methane relative to the biogas and a second gas stream enriched in methane and depleted in carbon dioxide relative to biogas, and the membrane permeation treatment unit as described above, the feed line being connected to the biogas purification unit and configured to feed the first gas stream enriched in carbon dioxide and depleted in methane relative to biogas to the membrane separation unit, and the retentate recycling line being connected to the biogas production and / or storage unit.

[0024] According to one embodiment, the biogas production and / or storage unit is a digester or a post-digester or a gasometer.

[0025] According to one embodiment, the biogas purification unit comprises or is a PSA type unit and / or a scrubbing type unit, in particular a treatment unit using a scrubbing column, and / or a cryogenic distillation separation unit and / or a membrane permeation treatment unit comprising at least one membrane separation unit, for example, at least two membrane separation units.

[0026] According to one embodiment, the installation includes a recovery duct for the second gas stream enriched in methane and depleted in carbon dioxide compared to the biogas.

[0027] According to one embodiment, the second gaseous stream enriched in methane and depleted in carbon dioxide is biomethane, the final product.

[0028] The invention further relates to a process for treating a feed gas stream comprising carbon dioxide and methane by membrane permeation, said feed gas stream comprising at least 90 mol% carbon dioxide, in particular at least 95 mol% or 97 mol% carbon dioxide, and between 0.5 and 10 mol% methane, in particular between 0.5 and 5 mol% or between 0.5 and 3 mol% methane, and said process comprising a step of compressing the feed gas stream to a pressure between 2 and 16 barg, preferably between 4 and 8 barg, a step of feeding the compressed feed gas stream to the membrane separation unit,a step of treating the feed gas stream in the membrane separation unit to produce a permeate enriched in carbon dioxide and depleted in methane compared to the feed gas stream and a retentate enriched in methane and depleted in carbon dioxide compared to the feed gas stream, and a step of recycling the retentate to a biogas production unit and / or methane storage.

[0029] According to one embodiment, the step of compressing the feed gas flow includes a step of measuring the pressure of the feed gas flow before compression.

[0030] According to one embodiment, the feed gas flow is compressed as a function of the pressure measurement and / or opening position measurement of a downstream valve, for example located at an outlet of the membrane separation unit.

[0031] According to one embodiment, the process includes a pressure control step of the membrane separation unit.

[0032] The invention further relates to a biomethane production process comprising a step of supplying biogas from the biogas production and / or storage unit to the biogas purification unit, a step of purifying the biogas from the biogas production and / or storage unit in the biogas purification unit to produce a first gas stream enriched in carbon dioxide and depleted in methane relative to the biogas and a second gas stream enriched in methane and depleted in carbon dioxide relative to the biogas, a step of compressing the first gas stream to a pressure between 2 barg and 16 barg, preferably between 4 barg and 8 barg, a step of feeding the first compressed gas stream to the membrane separation unit,a step of treating the first gas stream in the membrane separation unit to produce a permeate enriched in carbon dioxide and depleted in methane compared to the first gas stream and a retentate enriched in methane and depleted in carbon dioxide compared to the first gas stream, and a step of recycling the retentate to the production unit and / or biogas storage.

[0033] According to one embodiment, the first gas flow compression step includes a step of measuring the pressure of the first gas flow before compression.

[0034] According to one embodiment, the first gas flow is compressed according to the pressure measurement and / or the opening position of a downstream valve, for example located at an outlet of the membrane separation unit.

[0035] According to one embodiment, the process includes a biogas production step in the biogas production unit.

[0036] According to one embodiment, the process includes a pretreatment step of the biogas from the biogas production and / or storage unit before purification, to remove at least some of the water and / or hydrogen sulfide and / or volatile organic compounds present in the biogas.

[0037] According to one embodiment, the process includes a step of compressing the biogas, in particular pre-treated biogas, before the purification step.

[0038] According to one embodiment, the process includes a step of recovering the second gas stream enriched in methane and depleted in carbon dioxide relative to biogas as biomethane, as the final product.

[0039] The invention may also relate to any alternative device or method comprising any combination of the above or below features within the scope of the claims.

[0040] Other features and advantages will become apparent upon reading the description below. then, made with reference to the figures in which:

[0041] [Fig. 1] represents a schematic and partial view illustrating an example of the structure and operation of a device according to the invention,

[0042] [Fig.2] represents a schematic and partial view illustrating an example of a Structural and operational design of an installation according to the invention.

[0043] In all figures, the same references refer to the same elements.

[0044] In this detailed description, the following are examples. The fact that the description refers to one or more embodiments does not mean that the features apply only to a single embodiment. Simple features from different embodiments can also be combined and / or interchanged to provide other embodiments.

[0045] The membrane permeation treatment apparatus 100 is suitable for receiving a feed gas stream 1 comprising carbon dioxide and methane. The feed gas stream 1 comprises at least 90 mol% carbon dioxide and between 0.5 and 10 mol% methane. More particularly, the feed gas stream 1 comprises at least 95 mol% carbon dioxide and between 0.5 and 5 mol% methane. More particularly, the feed gas stream 1 comprises at least 97 mol% carbon dioxide and between 0.5 and 3 mol% methane. Even more particularly, the feed gas stream 1 comprises at least 99.5 mol carbon dioxide and up to 0.5 mol methane.

[0046] The feed gas stream 1 preferably comes from the vent of a biogas scrubber, for example a PSA (“Pressure Swing Adsorption”) type unit and / or a scrubbing type unit, in particular a treatment unit using a scrubbing column, and / or a cryogenic distillation separation unit and / or a membrane permeation treatment unit comprising at least one membrane separation unit, for example, at least two units or at least three membrane separation units.

[0047] The device 100 includes a compressor 8 configured to compress the feed gas stream 1 to a pressure between 2 barg and 16 barg, preferably between 4 barg and 8 barg. The compressor 8 is, for example, a variable speed compressor.

[0048] The apparatus 100 includes at least one membrane separation unit 3 configured to receive the feed gas stream 1 and to provide a permeate 2 and a retentate 4.

[0049] As schematically shown in [Fig.1], the apparatus 100 comprises a membrane separation unit 3 and a supply conduit 5 for the supply gas stream 1 to the membrane separation unit 3.

[0050] The supply conduit 5 includes an upstream end configured to be connected to a source of the supply gas flow 1. The source of the gas flow 1 The feed is preferably the vent of a biogas scrubber. The feed duct 5 further includes a downstream end connected to an inlet of the membrane separation unit 3.

[0051] The membrane separation unit 3 includes an inlet connected to the downstream end of the feed duct 5 to receive the feed gas stream 1, a retentate outlet 4 and a permeate outlet 2.

[0052] The supply conduit 5 may include at least the compressor 8, a pressure sensor 7 configured to measure the pressure of the supply gas flow 1, a compressor speed variator 8 and a loop 10 for regulating and controlling the pressure of the supply gas flow 1.

[0053] The compressor 8, for example thanks to the pressure sensor 7 measuring the upstream pressure (pressure at the inlet for example), takes the gas flow 1 and maintains this upstream pressure around atmospheric pressure by accelerating or slowing down the compression thanks to its speed variator.

[0054] A valve 6, in particular a pressure regulating valve for the feed gas stream 1, may be provided, for example at the retentate outlet 4 of the membrane separation unit 3, to compress the gas stream 1 through the compressor 8 to a pressure for example between 2 barg and 16 barg, preferably between 4 barg and 8 barg.

[0055] The supply gas flow 1 is compressed for example according to the pressure measurement and / or the opening position of the valve 6.

[0056] The membrane separation unit 3 is configured to receive the compressed feed gas stream 1 and to provide a permeate 2 and a retentate 4. The permeate 2 is enriched in carbon dioxide and depleted in methane compared to the feed gas stream 1.

[0057] Permeate 2 contains less than 0.5% methane. Permeate 2 can be recovered for further CO2 recovery or released into the atmosphere.

[0058] The retentate 4 is enriched in methane and depleted in carbon dioxide relative to the feed gas stream 1. For example, the retentate 4 contains at least 99.5% of the methane contained in the feed gas stream 1.

[0059] The membrane separation unit 3 allows at least 99.5% of the methane to be recovered from the feed gas stream 1.

[0060] The membrane separation unit 3 may comprise one or more membranes more permeable to carbon dioxide than to methane.

[0061] The device 100 further includes a retentate 4 recycling conduit 9 configured to send the retentate 4 to a biogas production and / or storage unit.

[0062] The recycling conduit 9 comprises an upstream end connected to the outlet of the retentate 4 of the membrane separation unit 3 and a downstream end configured to be connected to a biogas production and / or storage unit, for example a digester and / or a post-digester and / or a gasometer.

[0063] The recycling conduit 9 may include a valve 6 downstream of the membrane separation unit 3, for example at the retentate outlet 4.

[0064] Valve 6 allows the pressure in the membrane separation unit 3 to be controlled, which allows CO2 to be separated from CH4 in the membrane separation unit 3.

[0065] The installation 200 shown in [Fig.2] is an example of a biomethane production installation comprising the membrane permeation treatment unit 100 described above.

[0066] The installation 200 includes a unit 11 for the production and / or storage of biogas, for example a digester and / or a post-digester and / or a gasometer, and a unit 13 for the purification of biogas 12 from the unit 11 for the production and / or storage of biogas.

[0067] The biogas 12 from the biogas production and / or storage unit 11 can be pre-treated in a pre-treatment unit before being supplied to the biogas purification unit 13 to remove at least some of the water and / or hydrogen sulfide and / or volatile organic compound(s) present in the biogas 12. Preferably, the pre-treated biogas can be compressed before being introduced into the biogas purification unit 13 to a pressure necessary for biogas purification in the purification unit 13.

[0068] The biogas purification unit 13 is configured to produce a first gas stream 1 enriched in carbon dioxide and depleted in methane compared to the biogas 12 and a second gas stream 20 enriched in methane and depleted in carbon dioxide compared to the biogas 12 supplied to this unit 13. The biogas purification unit 13 includes an inlet connected to the biogas production and / or storage unit 11, an outlet of the first gas stream 1 and an outlet of the second gas stream 20. The outlet of the first gas stream 1 is, for example, the vent of the biogas purification unit 13.

[0069] The biogas purification unit 13 may include or be a PSA type unit and / or a scrubbing type unit, in particular a treatment unit using a scrubbing column, and / or a cryogenic distillation separation unit and / or a membrane permeation treatment unit comprising at least one membrane separation unit, for example, at least two membrane separation units.

[0070] The first gas stream 1 comprises at least 90 mol% carbon dioxide and between 0.5 and 10 mol% methane. More particularly, the first gas stream 1 comprises at least 95 mol% carbon dioxide and between 0.5 and 5 mol% methane. More particularly, the first gas stream 1 comprises at least 97 mol% and between 0.5 and 3 mol% of methane. More specifically, the first gas stream comprises at least 99.5 mol% carbon dioxide and up to 0.5 mol% methane.

[0071] The installation 200 may include a recovery duct 19 for the second gas stream 20 enriched in methane and depleted in carbon dioxide relative to the biogas 12. The recovery duct 19 includes in particular an upstream end connected to the outlet of the second gas stream 20.

[0072] The second gas stream 20 can be recovered as an end product. In particular, the second gas stream 20 is biomethane of the purity required for its further use, for example for injection into a natural gas network.

[0073] As illustrated, the upstream end of the supply conduit 5 is connected to the outlet of the first gas stream 1, in particular the vent of the biogas purification unit 13, and the downstream end of the supply conduit 5 is connected to the inlet of the membrane separation unit 3.

[0074] The first gas stream 1 exiting the biogas purification unit 13 is fed through the supply conduit 5 to the membrane separation unit 3 of the membrane permeation treatment apparatus 100.

[0075] The first gas stream 1 is compressed to a pressure between 2 barg and 16 barg, preferably between 4 barg and 8 barg, by the compressor 8, before being introduced into the membrane separation unit 3. Preferably, the pressure of the first gas stream 1 is measured before compression. The feed gas stream 1 is compressed, for example, according to the pressure measurement 7 and / or the opening position of a downstream valve 6, for example located at an outlet, in particular the retentate outlet 4, of the membrane separation unit 3.

[0076] The first compressed gas stream 1 is treated in the membrane separation unit 3 and separated into permeate 2 enriched in carbon dioxide and depleted in methane compared to the first gas stream 1 and into retentate 4 enriched in methane and depleted in carbon dioxide compared to the first gas stream 1.

[0077] The pressure of the membrane separation unit 3 can be controlled by a valve 6 located downstream of the membrane separation unit 3, for example at the retentate outlet 4.

[0078] As shown schematically, the recycling conduit 9 comprises an upstream end connected to the outlet of the retentate 4 from the membrane separation unit 3 and a downstream end connected to the biogas production and / or storage unit 11. The retentate 4 is recycled to the biogas production and / or storage unit 11 via the recycling conduit 9.

Claims

Demands

1. Apparatus (100) for treating a feed gas stream (1) comprising carbon dioxide and methane by membrane permeation, said feed gas stream comprising at least 90 mol% carbon dioxide, in particular at least 95 mol% or 97 mol% carbon dioxide, and between 0.5 and 10 mol% methane, in particular between 0.5 and 5 mol% or between 0.5 and 3 mol% methane, and said apparatus comprising: - a compressor (8) configured to compress the feed gas stream (1) to a pressure between 2 barg and 16 barg, preferably between 4 barg and 8 barg, - a membrane separation unit (3) configured to receive the feed gas stream (1) and to provide a permeate (2) and a retentate (4), - a feed duct (5) for the gas stream feeding (1) to the membrane separation unit (3),and - a retentate (4) recycling conduit (9) configured to send the retentate (4) to a biogas production and / or storage unit.

2. Apparatus (100) according to claim 1, characterized in that the compressor (8) is a variable speed compressor and in that the supply duct (5) of the supply gas stream comprises at least the compressor (8), a pressure sensor (7) configured to measure the pressure of the supply gas stream (1), a speed variator of the compressor (8) and a regulation and control loop (10) of the pressure of the supply gas stream (1).

3. Device (100) according to claim 1 or 2, characterized in that the recycling conduit (9) includes a valve (6).

4. Apparatus (100) according to any one of claims 1 to 3, characterized in that the membrane separation unit (3) comprises at least one membrane more permeable to carbon dioxide than to methane.

5. Biomethane production installation (200) comprising: - a biogas production and / or storage unit (11) (12), - a biogas purification unit (13) from the unit production and / or storage (11) of biogas, said biogas purification unit (13) being configured to produce a first gas stream (1) enriched in carbon dioxide and depleted in methane relative to the biogas (12) and a second gas stream (20) enriched in methane and depleted in carbon dioxide relative to the biogas (12), and - the membrane permeation treatment apparatus (100) according to any one of claims 1 to 4, the feed line (5) being connected to the biogas purification unit (13) and configured to supply the first gas stream (1) enriched in carbon dioxide and depleted in methane relative to the biogas (12) to the membrane separation unit (3), and the retentate (4) recycling line (9) being connected to the biogas production and / or storage unit (11).

6. Installation (200) according to claim 5, characterized in that the biogas production and / or storage unit (11) is a digester or a post-digester or a gasometer.

7. Installation (200) according to claim 5 or 6, characterized in that the biogas purification unit (13) comprises or is a PSA type unit and / or a scrubbing type unit, in particular a scrubbing column treatment unit, and / or a cryogenic distillation separation unit and / or a membrane permeation treatment unit comprising at least one membrane separation unit, for example, at least two membrane separation units.

8. Installation (200) according to any one of claims 5 to 7 characterized in that it comprises a recovery duct (19) for the second gas stream (20) enriched in methane and depleted in carbon dioxide relative to the biogas (12).

9. A method for treating a feed gas stream (1) comprising carbon dioxide and methane by membrane permeation, said feed gas stream comprising at least 90 mol% carbon dioxide, in particular at least 95 mol% or 97 mol% carbon dioxide, and between 0.5 and 10 mol% methane, in particular between 0.5 and 5 mol% or between 0.5 and 3 mol% methane, and said method utilizing the apparatus (100) according to any one of claims 1 to 4 and comprising: - a step of compressing the feed gas stream (1) to a pressure between 2 barg and 16 barg, preferably between 4 barg and 8 barg, - a step of feeding the compressed feed gas stream (1) to the membrane separation unit (3), - a step of treating the feed gas stream (1) in the membrane separation unit (3) to produce a permeate (2) enriched in carbon dioxide and depleted in methane compared to the feed gas stream (1) and a retentate (4) enriched in methane and depleted in carbon dioxide compared to the feed gas stream (1), and - a step of recycling the retentate (4) to a biogas production unit and / or a methane storage facility.

10. A method according to claim 9, characterized in that the step of compressing the feed gas stream (1) includes a step of measuring (7) the pressure of the feed gas stream (1) before compression, the feed gas stream (1) being compressed for example as a function of the pressure measurement (7) and / or the opening position of a valve (6) downstream, for example located at an outlet of the membrane separation unit (3).

11. Method according to claim 9 or 10, comprising a pressure control step of the membrane separation unit (3).

12. A biomethane production process using the installation (200) according to any one of claims 5 to 11, said process comprising: - a step of supplying biogas (12) from the biogas production and / or storage unit (11) to the biogas purification unit (13), - a step of purifying the biogas (12) from the biogas production and / or storage unit (11) in the biogas purification unit (13) to produce a first gas stream (1) enriched in carbon dioxide and depleted in methane relative to the biogas (12) and a second gas stream (20) enriched in methane and depleted in carbon dioxide relative to the biogas (12), - a step of compressing the first gas stream (1) to a pressure between 2 barg and 16 barg, preferably between 4 barg and 8 barg, - a step of feeding the first compressed gas stream (1) to the membrane separation unit (3), - a step of treating the first gas stream (1) in the membrane separation unit (3) to produce a permeate (2) enriched in carbon dioxide and depleted in methane compared to the first gas stream (1) and a retentate (4) enriched in methane and depleted in carbon dioxide compared to the first gas stream (1), and - a step of recycling the retentate (4) to the production unit (11) and / or a biogas storage.

13. A method according to claim 12, characterized in that the step of compressing the first gas stream (1) includes a step of measuring the pressure of the first gas stream (1) before compression, the first gas stream (1) being compressed for example as a function of the pressure measurement (7) and / or the opening position of a valve (6) downstream, for example located at an outlet of the membrane separation unit (3).

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