Apparatus and method for treatment by membrane permeation of a gas flow, and Installation comprising such an apparatus

Abstract

An installation and method for membrane permeation treatment of a feed gas stream (1) comprising carbon dioxide and methane, said feed gas stream comprising at least 90 mol% of carbon dioxide and between 0.5 and 10 mol% of methane, and said apparatus comprising a compressor (8) configured to compress the feed gas stream (1) to a pressure of 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 conduit (5) for the feed gas stream (1) to the membrane separation unit (3), and a recycling conduit (9) for the retentate (4) configured to send the retentate (4) to a biogas production and / or storage unit. Abstract figure: Fig. 1

Description

Title of the invention: Apparatus and method for treatment by membrane permeation of a gas flow, and Installation comprising such an apparatus

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

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

[0003] Biogas is the gas produced during the degradation of organic matter in the absence of oxygen (anaerobic fermentation), also called methanization. It can be a natural degradation - it is observed in marshes or household waste dumps - but the production of biogas can also result from the methanization of waste in a dedicated reactor, the conditions of which are controlled, called a methanizer or digester, then in a post-digester, similar to the digester and allowing the methanization reaction to be pushed further. Biogas is the gas produced during the degradation of organic matter in the absence of oxygen (anaerobic fermentation), also called methanization.It can be a natural degradation - we observe it in marshes or household waste dumps - but the production of biogas can also result from the methanization of waste in a dedicated reactor, the conditions of which are controlled, called a methanizer or digester, then in a post-digester, similar to the digester and allowing the methanization reaction to be pushed further.

[0004] Biomass will be any group of organic materials that can be transformed into energy through this methanization process, for example: sludge from sewage treatment plants, manure / slurry, agricultural residues, food waste, etc.

[0005] The digester, that is to say the reactor dedicated to the methanization of biomass, is a closed tank, heated or not (operation at a fixed temperature, between ambient temperature and 55°C) and whose contents consisting of biomass are mixed, continuously or sequentially. The conditions in the digester are anaerobic and the biogas generated ends up in the head space of the digester (gaseous sky), where it is collected. Post-digesters are similar to digesters.

[0006] Due to its main constituents - methane and carbon dioxide - biogas is a powerful greenhouse gas; it also constitutes, at the same time, a significant source of renewable energy in a context of increasing scarcity of fossil fuels.

[0007] Biogas mainly contains methane (CH4) and carbon dioxide (CO2) in variable 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 degraded organic matter and the techniques used, the proportions of the components differ, but on average the biogas contains, on dry gas, 30 to 75% methane, 15 to 60% CO2, 0 to 15% nitrogen, 0 to 5% oxygen and trace compounds.

[0009] Biogas is used in different ways. After light treatment, it can be used close to the production site to provide heat, electricity or a mixture of the two (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 use.

[0010] Further purification of biogas allows its wider use, in particular, further purification of biogas makes it possible to obtain a purified biogas to the specifications of natural gas and which can be substituted for it; the biogas thus purified is "biomethane". Biomethane thus supplements natural gas resources with a renewable part produced in the heart of the territories; it can be used for exactly the same purposes as natural gas of fossil origin. It can supply a natural gas network, a vehicle filling station, it can also be liquefied to be stored in the form of liquid natural gas (LNG).

[0011] The methods of valorizing biomethane are determined according to local contexts: local energy needs, possibilities of valorization as biomethane fuel, existence near distribution networks or natural gas transport in particular. Creating synergies between the different actors working in a territory (farmers, industrialists, public authorities), the production of biomethane helps territories to acquire greater energy autonomy.

[0012] Several steps must be taken between the collection of biogas and the obtaining of biomethane, a final product capable of being compressed or liquefied.

[0013] In particular, several steps are necessary before the treatment which aims to separate the carbon dioxide to produce a purified methane stream. A first step consists of compressing the biogas which has been produced and conveyed to atmospheric pressure, this compression can be obtained - in a conventional manner - via a compressor. The following steps aim to rid the biogas of corrosive components such as hydrogen sulfide and volatile organic compounds (VOCs), the technologies used are conventionally pressure swing adsorption (PSA) and activated carbon trapping. Next comes the step of separating the carbon dioxide to ultimately produce methane at the purity required for its subsequent use.

[0014] Carbon dioxide is a contaminant typically present in natural gas, which often needs 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 the CO2 present in biogas, coming from landfill gas or from digesters of plant or animal waste.

[0015] It is preferable that the installations allowing the production of a gaseous flow enriched in methane can control the loss of methane.

[0016] From this, a problem that arises is to provide a device for reducing the methane that leaves the vent of a biogas purifier.

[0017] To this end, the apparatus according to the invention, moreover in accordance with 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 of 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 conduit for supplying the feed gas stream to the membrane separation unit, and a conduit for recycling the retentate configured to send the retentate to a biogas production and / or storage unit.

[0018] Such an apparatus makes it possible to recover a gas stream which is otherwise released into the atmosphere through the vent of a biogas purifier and to reduce the loss of methane in a specification-compliant biomethane production process, 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 conduit for the supply gas flow comprises at least the compressor, a pressure sensor configured to measure the pressure of the supply gas flow, a speed variator of the compressor and a loop for regulating and controlling the pressure of the supply gas flow.

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

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

[0023] The invention further relates to a biomethane production facility comprising a biogas production and / or storage unit, a unit for purifying the biogas from 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 the biogas, and the membrane permeation treatment apparatus as described above, the feed conduit 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 the biogas to the membrane separation unit, and the retentate recycling conduit 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 washing type unit, in particular a treatment unit by means of a washing 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 comprises a conduit for recovering the second gas flow enriched in methane and depleted in carbon dioxide compared to the biogas.

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

[0028] The invention further relates to a method for membrane permeation treatment of a feed gas stream comprising carbon dioxide and methane, said feed gas stream comprising at least 90 mol% of the carbon dioxide, in particular at least 95 mol% or 97 mol% of the carbon dioxide, and between 0.5 and 10 mol% of the methane, in particular between 0.5 and 5 mol% or between 0.5 and 3 mol% of the methane, and said method comprising a step of compressing the feed gas stream to a pressure between 2 and 16 barg, preferably between 4 barg 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 relative to the feed gas stream and a retentate enriched in methane and depleted in carbon dioxide relative 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 comprises 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 measurement of pressure and / or the opening position of a downstream valve, for example located at an outlet of the membrane separation unit.

[0031] According to one embodiment, the method comprises a step of controlling the pressure of the membrane separation unit.

[0032] The invention further relates to a method for producing biomethane 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 a biogas storage.

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

[0034] According to one embodiment, the first gas flow is compressed as a function of 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 method comprises a step of producing biogas in the biogas production unit.

[0036] According to one embodiment, the method comprises a step of pre-treatment of the biogas from the biogas production and / or storage unit before purification, to eliminate at least part of the water and / or hydrogen sulfide and / or volatile organic compounds present in the biogas.

[0037] According to one embodiment, the method comprises a step of compressing the biogas, in particular the pretreated biogas, before the purification step.

[0038] According to one embodiment, the method comprises a step of recovering the second gaseous flow enriched in methane and depleted in carbon dioxide compared to the biogas as biomethane, as a 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 appear on reading the description below. after, made with reference to the figures in which:

[0041] [Fig.l] represents a schematic and partial view illustrating an exemplary embodiment of the structure and operation of an apparatus according to the invention,

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

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

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

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

[0046] The feed gas stream 1 preferably comes from the vent of a biogas purifier, for example a PSA (“Pressure Swing Adsorption” in English) type unit and / or a washing type unit, in particular a treatment unit using a washing 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 apparatus 100 comprises a compressor 8 configured to compress the feed gas flow 1 to a pressure of 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 comprises 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 shown schematically in [Fig.l], the apparatus 100 comprises a membrane separation unit 3 and a supply conduit 5 for the supply gas flow 1 to the membrane separation unit 3.

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

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

[0052] The supply conduit 5 may comprise at least the compressor 8, a pressure sensor 7 configured to measure the pressure of the supply gas flow 1, a speed variator of the compressor 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 (intake pressure 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 valve for regulating the pressure of 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 feed gas flow 1 is compressed for example as a function of 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 relative to the feed gas stream 1.

[0057] Permeate 2 contains less than 0.5% methane. Permeate 2 can be recovered for subsequent 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 makes it possible to recover at least 99.5% of the methane in 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 apparatus 100 further comprises a conduit 9 for recycling the retentate 4 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 retentate outlet 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 comprise a valve 6 downstream of the membrane separation unit 3, for example at the retentate outlet 4.

[0064] Valve 6 allows the pressure in membrane separation unit 3 to be controlled, which allows CO2 to be separated from CH4 in 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 apparatus 100 described above.

[0066] The installation 200 comprises a unit 11 for producing and / or storing biogas, for example a digester and / or a post-digester and / or a gasometer, and a unit 13 for purifying the biogas 12 from the unit 11 for producing and / or storing biogas.

[0067] The biogas 12 from the biogas production and / or storage unit 11 may be pretreated in a pretreatment unit before being supplied to the biogas purification unit 13 to remove at least a portion of the water and / or hydrogen sulfide and / or volatile organic compounds present in the biogas 12. Preferably, the pretreated biogas may be compressed before being introduced into the biogas purification unit 13 to a pressure necessary for purification of the biogas 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 relative to the biogas 12 and a second gas stream 20 enriched in methane and depleted in carbon dioxide relative to the biogas 12 supplied to this unit 13. The biogas purification unit 13 comprises an inlet connected to the biogas production and / or storage unit 11, an outlet for the first gas stream 1 and an outlet for 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 comprise or be a PSA type unit and / or a washing type unit, in particular a treatment unit by means of a washing 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% of carbon dioxide and between 0.5 and 10 mol% of methane. More particularly, the first gas stream 1 comprises at least 95 mol% of carbon dioxide and between 0.5 and 5 mol% of methane. More particularly, the first gas stream 1 comprises at least 97 mol% and between 0.5 and 3 mol% of methane. Even more particularly, the first gas stream comprises at least 99.5 mol% of carbon dioxide and up to 0.5 mol% of methane.

[0071] The installation 200 may comprise a recovery conduit 19 for the second gas flow 20 enriched in methane and depleted in carbon dioxide compared to the biogas 12. The recovery conduit 19 comprises in particular an upstream end connected to the outlet of the second gas flow 20.

[0072] The second gas stream 20 may be recovered as a final product. In particular, the second gas stream 20 is biomethane at the purity required for its subsequent 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 flow 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 flow 1 leaving the biogas purification unit 13 is supplied via 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 of 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 as a function of 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 retentate outlet 4 of 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

Claims

1. Apparatus (100) for membrane permeation treatment of a feed gas stream (1) comprising carbon dioxide and methane, said feed gas stream comprising at least 90 mol% of the carbon dioxide, in particular at least 95 mol% or 97 mol% of the carbon dioxide, and between 0.5 and 10 mol% of the methane, in particular between 0.5 and 5 mol% or between 0.5 and 3 mol% of the methane, and said apparatus comprising: - a compressor (8) configured to compress the feed gas stream (1) to a pressure of 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 conduit (5) for the feed gas stream (1) feed gas (1) to membrane separation unit (3),and - a recycling conduit (9) for the retentate (4) 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 conduit (5) for the supply gas flow comprises at least the compressor (8), a pressure sensor (7) configured to measure the pressure of the supply gas flow (1), a speed variator of the compressor (8) and a regulation and control loop (10) for the pressure of the supply gas flow (1).

3. Apparatus (100) according to claim 1 or 2, characterized in that the recycling conduit (9) comprises 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. Installation (200) for producing biomethane comprising: - a unit for producing and / or storing (11) biogas (12), - a unit for purifying (13) the biogas from the unit production and / or storage unit (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 conduit (5) being connected to the biogas purification unit (13) and configured to feed 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 recycling conduit (9) of the retentate (4) being connected to the biogas production and / or storage unit (11).

6. Installation (200) according to claim 5, characterized in that the unit (11) for producing and / or storing biogas 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 washing type unit, in particular a treatment unit by means of a washing 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.

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

9. A method of membrane permeation treatment of a feed gas stream (1) comprising carbon dioxide and methane, said feed gas stream comprising at least 90 mol% of the carbon dioxide, in particular at least 95 mol% or 97 mol% of the carbon dioxide, and between 0.5 and 10 mol% of the methane, in particular between 0.5 and 5 mol% or between 0.5 and 3 mol% of the methane, and said method using 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 relative to the feed gas stream (1) and a retentate (4) enriched in methane and depleted in carbon dioxide relative to the feed gas stream (1), and - a step of recycling the retentate (4) to a biogas production unit and / or a methane storage.

10. Method according to claim 9, characterized in that the step of compressing the feed gas flow (1) comprises a step of measuring (7) the pressure of the feed gas flow (1) before compression, the feed gas flow (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 step of pressure control of the membrane separation unit (3).

12. A method of producing biomethane using the installation (200) according to any one of claims 5 to 11, said method comprising: - a step of supplying the 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. Method according to claim 12, characterized in that the step of compressing the first gas flow (1) comprises a step of measuring the pressure of the first gas flow (1) before compression, the first gas flow (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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