Installation and process for the production of purified methane

Abstract

The invention relates to an installation (1) for the production of purified methane from natural gas (2) and biogas (18) comprising, arranged in series in a gas circuit (100), a heavy hydrocarbon removal unit (3) and a CO2 removal unit (5), the heavy hydrocarbon removal unit (3) comprising a first inlet (4) intended to be connected to a gas source (2) comprising natural gas, a first outlet (6) of gas purified of heavy hydrocarbons, and a second outlet (8) of removed heavy hydrocarbons, the CO2 removal unit (5) comprising a first inlet (10) connected to the first outlet (6) of the heavy hydrocarbon removal unit (3), a first outlet (12) of gas with reduced CO2 content, and a second outlet (15) of effluent gas enriched in CO2,the installation (1) further comprising: - a biogas purification unit (9) including an inlet (16) intended to be connected to a biogas source (18) and a first outlet (20) of purified biogas connected to the first inlet (10) of the CO2 removal unit (5), the biogas purification unit (9) being configured to produce biogas or biomethane with a variable / determined CO2 concentration, and - a heavy hydrocarbon combustion heat production boiler (11) including a first inlet (22) connected to the second outlet (8) of the heavy hydrocarbon removal unit (3), the boiler (11) being configured to produce a thermal power determined according to the quantity of hydrocarbons removed and supplied by the heavy hydrocarbon removal unit (3),the boiler (3) being fluidly connected (23) to the CO2 removal unit (5) to supply the latter with thermal energy produced for CO2 removal. Abbreviated figure: Fig. 1,

Description

Title of the invention: Installation and method for producing purified methane

[0001] The present invention relates to an installation and a method for producing purified methane.

[0002] The invention relates more particularly to an installation for producing purified methane from natural gas and biogas comprising, arranged in series in a gas circuit, a heavy hydrocarbon removal unit and a CO2 elimination unit.

[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 observed in marshes or household waste dumps. The production of biogas can also result from the methanization of waste in a dedicated reactor, the conditions of which are controlled. This reactor is 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 is any group of organic matter that can be transformed into energy through this methanization process, for example, sewage treatment plant sludge, manure / slurry, agricultural residues, and food waste.

[0005] Biogas mainly contains methane (CH4) and carbon dioxide (CO2) in variable proportions depending on the method of production and the substrate but can also contain, in smaller proportions, water, nitrogen, hydrogen sulfide (H2S), oxygen, as well as other organic compounds, in trace amounts, including H2S, between 10 and 50,000 ppmv.

[0006] Depending on the degraded organic matter and the techniques used, the proportions of the components differ, but on average the biogas contains (in moles or volume) on dry gas, from 30 to 75% methane, from 15 to 60% carbon dioxide, from 0 to 15% nitrogen, from 0 to 5% oxygen and compounds in trace form.

[0007] Biogas can be recovered in different ways. After light treatment, it can be recovered 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 recovery to this local use.

[0008] Further purification of biogas allows its wider use, in particular, further purification of biogas makes it possible to obtain purified biogas with specific specifications of natural gas and which can be substituted for it. The biogas thus purified is called "biomethane". Biomethane thus supplements natural gas resources with a renewable portion 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 (bio-LNG).

[0009] Liquefaction installations for producing bio-LNG from natural gas in the network may in certain cases require a new configuration comprising two flows with different compositions, flow rates and pressures (natural gas and biogas).

[0010] Natural gas is generally distributed in high pressure networks (>40 barg) and has molecules unsuitable for liquefaction. We generally observe around 1 to 2 mol% of CO2 and long carbon chains (heavy hydrocarbons). Raw biogas is produced at low pressure (>~ 0 barg) and with a standard composition of 30 to 50 mol% of CO2. The remainder is largely composed of methane and some impurities (H2S, etc.). The raw biogas generated is generally improved into biomethane up to a CO2 level of 2 to 4 mol% in a process called "upgrading" (separation by membranes or washing with amines) to then be injected into a network, liquefied or compressed into a bottle for transport (CBG).

[0011] To produce methane of the necessary quality required for liquefaction, amine washing solutions or PTSA are commonly used to purify the methane stream comprising 1 to 4 mol% CO2 at the inlet of these units to 50 to 400 ppm called "polishing".

[0012] Heavy hydrocarbons must be evacuated so as not to freeze and clog the main heat exchanger of a liquefaction unit in the same way that CO2 does and

[0013] therefore stop the liquefaction process. The solutions for removing heavy hydrocarbons are not yet well defined in the market for small liquefaction units while for very large liquefaction units (>100 tpd of natural gas) the expensive solution of cryogenic distillation can be considered.

[0014] To produce purified methane of quality having between 0 and 400 ppm, in particular between 50 and 400 ppm, of CO2 from natural gas and biogas sources, the traditional solution is to mix the two incoming streams. The mixing is done after the removal of heavy hydrocarbons for the natural gas stream and after a standard "upgrading" (purification of raw biogas to produce biomethane containing 2 to 4% CO2) of the biogas with membranes. The mixing is carried out at the standard pressure for liquefaction of the biogas, i.e. the pressure achievable in a single compression unit and necessary for membrane purification (approximately 12 barg).

[0015] This approach, however, has the following drawbacks:

[0016] - Natural gas must be expanded from network pressure to pipeline pressure biomethane. A significant loss of energy (usable energy) would therefore be observed in this flow.

[0017] - The “upgrading” operation would have the standard CO2 rate (2 to 4 mol% at the outlet). This operation would not be optimized (i.e. neither adapted nor adaptable) to the amount of energy available for an additional purification operation. Such additional purification is for example amine washing, to achieve methane at the necessary quality required for liquefaction or "polishing", for example having a CO2 level of 50 to 400 ppm. The "upgrading" of raw biogas (the purification of raw biogas) has a strong economic impact on the installation since the membranes have a high investment cost while on its side the secondary "polishing" (the purification of the mixture of purified biogas and natural gas to achieve an even lower CO2 level), for example amine washing, requires a high heat operation cost (proportional to the CO2 level to be removed).

[0018] - The heat requirement for further CO2 removal would be constant. The amount of heavy hydrocarbons discharged by the natural gas process would not directly match the need.

[0019] An aim of the present invention is to overcome all or part of the drawbacks noted above.

[0020] The present invention provides an innovative plant and method for producing purified methane from two different sources of natural gas and biogas which makes it possible to optimize the methane purification operation. This optimization makes it possible to use the pressure of the natural gas network advantageously to increase the specific efficiency of the liquefier. It is also possible to optimize the biogas purification unit from the energy available by the heavy hydrocarbons extracted from the natural gas on the heavy hydrocarbon removal unit so that the energy required for additional CO2 removal is equal to the energy obtained by burning the heavy hydrocarbons.

[0021] The installation according to the invention, moreover in accordance with the generic definition given in the preamble above, is essentially characterized in that the heavy hydrocarbon removal unit comprises a first inlet intended to be connected to a gas source comprising natural gas, a first outlet for gas purified of heavy hydrocarbons, and a second outlet for removed heavy hydrocarbons. The CO2 removal unit comprises a first inlet connected to the first outlet of the heavy hydrocarbon removal unit, a first outlet for gas with a reduced CO2 content, and a second outlet for effluent gas enriched in CO2. The installation further comprises:

[0022] - a biogas purification unit comprising an inlet intended to be connected to a biogas source and a first purified biogas outlet connected to the first inlet (10) of the CO2 removal unit, the biogas purification unit being configured to produce biogas or biomethane with a variable / determined CO2 concentration, and

[0023] - a boiler for producing heat by combustion of heavy hydrocarbons comprising a first inlet connected to the second outlet of the heavy hydrocarbon removal unit, the boiler being configured to produce a thermal power determined as a function of the quantity of hydrocarbons removed and supplied by the heavy hydrocarbon removal unit, the boiler being fluidically connected to the CO2 removal unit to supply the latter with thermal energy produced for the removal of CO2.

[0024] Furthermore, embodiments of the invention may include one or more of the following features: - the CO2 removal unit includes or is an amine scrubbing unit, - the CO2 removal unit is configured to have a capacity to remove a determined quantity of CO2 from a gas stream, in particular an amine washing capacity, said capacity being a function of the thermal energy supplied by the boiler, - the installation is configured to measure or determine thermal energy produced by the boiler and supplied to the CO2 removal unit, - the installation is configured to modulate the level of biogas purification depending on the thermal energy produced by the boiler and supplied to the CO2 removal unit, - the boiler is configured to provide the heavy hydrocarbon removal unit with thermal energy, - the CO2 removal unit comprises a third gas outlet comprising a fuel and in that the boiler comprises a second fuel gas inlet connected to the third outlet of the CO2 removal unit, - the biogas purification unit is a membrane separation unit, - the installation includes a pipe intended to connect the first outlet of purified biogas to the natural gas network, and - the biogas purification unit includes a second CO2-rich gas outlet.

[0025] The invention also relates to a process for producing purified methane from natural gas and biogas, the process comprising: - a gas supply stage comprising natural gas to a unit of removal of heavy hydrocarbons, - a step of removing heavy hydrocarbons from said gas by the heavy hydrocarbon removal unit to produce a gas purified of heavy hydrocarbons, - a step of supplying the gas purified of heavy hydrocarbons to a CO2 removal unit, the CO2 removal unit ensuring CO2 removal by a process comprising heating, - a step of feeding a biogas purification unit with biogas, - a biogas purification step in the biogas purification unit for produce purified biogas, - a stage of supplying purified biogas to the CO2 elimination unit, - a combustion stage, in a boiler, of the removed heavy hydrocarbons by the heavy hydrocarbon removal unit, - a step of supplying the CO2 elimination unit with thermal energy produced by the combustion of heavy hydrocarbons, - a step of removing CO2 from the gas stream consisting of or comprising the sum of the gas purified of heavy hydrocarbons and the purified biogas, the step of removing CO2 being configured to reduce the CO2 concentration in the gas stream to a determined threshold,

[0026] in which the biogas purification step is configured to produce a purified biogas having a determined CO2 concentration, said concentration being chosen as a function of the total quantity of CO2 to be removed from the gas stream in the CO2 removal unit to reach the CO2 concentration threshold.

[0027] According to other possible particularities: - the total quantity of CO2 to be removed from the gas stream in the CO2 removal unit to reach the CO2 concentration threshold corresponds to the CO2 removal capacity of the removal unit, said capacity being determined by the thermal energy produced and supplied by the boiler, - the method comprises a step of determining the thermal energy produced by the boiler and available for the CO2 removal unit, and - the purified biogas is compressed to the pressure of the gas purified of heavy hydrocarbons and combined with the latter to constitute the gas stream supplied to the CO2 removal unit.

[0028] 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.

[0029] Other features and advantages will appear on reading the description below, given with reference to the figure.

[0030] [Fig.l] represents a schematic and partial view illustrating an example of rea- structural and operational development of an installation according to the invention.

[0031] The example of a purified methane production installation illustrated in [Fig. 1] comprises, arranged in series in a natural gas circuit 100, a unit 3 for removing heavy hydrocarbons and a unit 5 for removing CO2.

[0032] In one embodiment, the heavy hydrocarbon removal unit 3 comprises, for example, two (or more) adsorbent bottles arranged in parallel and operating alternately. The adsorbent comprises, for example, carbon filters that can be regenerated by heat. The adsorbent progressively adsorbs the heavier carbon species on its adsorption sites. The purified gas, i.e., freed from the compounds that occupy the adsorption sites of the adsorbent, circulates in a closed loop to regenerate the adsorbent without loss of methane. During the regeneration of the adsorbent of one bottle, another bottle is put into operation for removing heavy hydrocarbons. The adsorbent is calibrated to trap at least some of the C3 hydrocarbons (propane) and all heavier hydrocarbons (e.g. butane, pentane, hexane, aromatics (benzene, ethylbenzene, xylene, toluene, etc.), among others).Unit 3 for the removal of heavy hydrocarbons is, for example, a temperature and / or pressure swing adsorption unit or PTSA (Pressure-Temperature Swing Adsorption) with 2 to 3 adsorbent bottles arranged in parallel.

[0033] In one embodiment, the heavy hydrocarbon removal unit 3 may comprise at least one distillation column comprising a cold distillation solution for heavy hydrocarbons. The distillation column removes a hydrocarbon stream at a temperature between -10 and -120°C, in particular between -30 and -80°C.

[0034] The hydrocarbons removed may be in gaseous or liquid form.

[0035] The heavy hydrocarbon removal unit 3 comprises a first inlet 4 intended to be connected to a gas source 2 comprising natural gas, a first outlet 6 of gas purified of heavy hydrocarbons, and a second outlet 8 of removed heavy hydrocarbons. The gas source 2 is for example a natural gas network.

[0036] The CO2 removal unit 5 comprises a first inlet 10 connected to the first outlet 6 of the heavy hydrocarbon removal unit 3, a first outlet 12 for gas with reduced CO2 content and a second outlet 15 for effluent gas enriched in CO2.

[0037] The installation 1 comprises a biogas purification unit 9 which is arranged in series with the CO2 elimination unit 5 in a biogas circuit 200.

[0038] The biogas purification unit 9 comprises an inlet 16 intended to be connected to a source 18 of raw biogas, for example a digester, and a first outlet 20 of purified biogas, i.e. biogas having a higher concentration of CH4 and a lower concentration of CO2 than the raw biogas admitted to the inlet 16. The Purified biogas leaving the first outlet 20 has a variable degree of CO2, for example between 2 and 20%.

[0039] The first outlet 20 is connected to the first inlet 10 of the CO2 removal unit 5. The biogas purification unit 9 is configured to produce purified biogas or biomethane with a variable / determined CO2 concentration.

[0040] The biogas purification unit 9 may comprise any device capable of producing methane-enriched gas from raw biogas, the power of which may be regulated to produce methane-enriched gas with a variable / determined concentration of CO2. The biogas purification unit 9 may operate according to the principle of separation and / or adsorption and / or absorption. This may be, for example, a pressure swing adsorption (PSA) system, amine washing, water washing, physical organic washing, cryogenic distillation or membrane separation.

[0041] Preferably, the biogas purification unit 9 is a membrane permeation treatment unit (or a membrane separation unit).

[0042] The installation 1 comprises a boiler 11 for producing heat by combustion of heavy hydrocarbons. The boiler 11 comprises a first inlet 22 connected to the second outlet 8 of the heavy hydrocarbon removal unit 3. The first inlet 22 of the boiler 11 is configured to supply the boiler 11 with heavy hydrocarbons which exit via the second outlet 8 of the heavy hydrocarbon removal unit 3. The boiler 11 is configured to produce a thermal power determined as a function of the quantity of hydrocarbons removed and supplied by the heavy hydrocarbon removal unit 3. The boiler 11 is connected 23, for example by means of a heat transfer fluid, to the CO2 removal unit 5 to supply the latter with thermal energy produced for the removal of CO2.

[0043] The CO2 removal unit 5 is configured to have a capacity to remove a determined quantity of CO2 from a gas stream which is a function of the thermal energy supplied by the boiler 11.

[0044] The thermal energy produced by the combustion of heavy hydrocarbons in the boiler 11 provides the thermal energy necessary for the operation of the CO2 removal unit 5. That is to say, the CO2 removal capacity or the quantity of CO2 that can be removed from the gas stream introduced into the unit 5 depends on the quantity of heavy hydrocarbons removed by the heavy hydrocarbon removal unit 3. The total quantity of CO2 contained in the total gas stream admitted to the CO2 removal unit 5 is the sum of the CO2 contained in the gas coming from the gas source 2 after passing through the heavy hydrocarbon removal unit 3 and the CO2 contained in the purified biogas leaving the outlet 20 of the biogas purification unit 9.

[0045] The gas purified of heavy hydrocarbons leaves the hydrocarbon removal unit 3 heavy through the first outlet 6 and is supplied to the CO2 removal unit 5 via the first inlet 10.

[0046] Advantageously, the pressure of the gas coming from the gas source 2 remains constant, for example at 45 barg. This pressure is kept high or constant during all the stages of the purification process (a stage of removing heavy hydrocarbons from said gas by the heavy hydrocarbon removal unit 3, a stage of supplying the gas purified of heavy hydrocarbons to a CO2 removal unit 5 and a stage of removing CO2).

[0047] In parallel, the biogas purification unit 9 is supplied with raw biogas 18 via the inlet 16 in which the biogas is purified to produce a purified biogas having a higher CH4 concentration and a lower CO2 concentration than the raw biogas admitted at the inlet 16. The purified biogas exits the first outlet 20 and is supplied to the CO2 removal unit 5 via the first inlet 10.

[0048] The gas purified of heavy hydrocarbons and the purified biogas can be fed to the CO2 removal unit 5 via the first inlet 10 independently, i.e. the two gas streams are combined only inside the unit. Alternatively, and as illustrated, the gas purified of heavy hydrocarbons and the purified biogas can be combined upstream of the CO2 removal unit 5, for example by connecting a conduit for the gas purified of heavy hydrocarbons and a conduit for the purified biogas, and fed to the unit 5 as a combined gas stream.

[0049] Advantageously, the purified biogas is compressed to the pressure of the gas from the gas source 2, for example to 45 barg, before being supplied to the CO2 removal unit 5 or before being combined with the gas purified of heavy hydrocarbons upstream of the CO2 removal unit 5.

[0050] The installation 1 is configured to modulate the level of purification of the biogas as a function of the thermal energy produced by the boiler 11 and supplied to the CO2 elimination unit 5.

[0051] To produce purified methane having a predetermined CO2 concentration and exiting through the outlet 12 of the CO2 removal unit 5, the total CO2 content in the gas stream admitted to the unit 5 is adjusted as a function of the thermal energy available by the combustion of heavy hydrocarbons within the boiler 11. The total CO2 content / quantity / concentration admitted to the CO2 removal unit 5 is in particular adjusted by varying the degree of purification of the raw biogas in the biogas purification unit 9. The degree of biogas purification conditions the level of CO2 concentration in the purified biogas exiting the outlet 20 of the biogas purification unit 9.

[0052] The operation of the biogas purification unit 9 is optimized according to the energy available by the combustion of the heavy hydrocarbons extracted on the unit 3 removal of heavy hydrocarbons. Plant 1 is configured so that the energy required to operate unit 5 for removing CO2 from the gas stream to reach a given threshold is equal to the energy obtained by the combustion of heavy hydrocarbons.

[0053] The CO2 rate at the outlet of the biogas purification unit 9, i.e. the molar concentration of CO2 in the biomethane, is determined by a function linked to a certain number of parameters. A single optimum of energy efficiency is found as a function of the molar flow rates of the gas comprising the natural gas and the raw biogas as well as the concentrations of heavy hydrocarbons in the gas comprising the natural gas and of CO2 in the raw biogas. Thus, the installation 1 according to the invention makes it possible to vary / modulate the degree of purification of the biogas in order to optimize the energy efficiency and the equipment costs (“CAPEX”) linked to the biogas purification unit 9.

[0054] For example, the biogas purification unit 9 is a membrane permeation treatment unit comprising one or more membrane separation units. Each membrane separation unit (also called a "stage") may comprise one or more membranes connected in parallel. Several membrane stages (typically between 2 and 4) are necessary to achieve the purification rate of approximately 2% of CO2 at the outlet of the unit 9. Less extensive purification makes it possible to reduce this number of stages, for example from 1 to 2.

[0055] In an exemplary implementation of the invention, the biogas purification unit 9 may operate in a fixed mode in which the biogas purification level is predetermined / fixed. This is applicable for example when the flow rate and composition of the gas stream from the source 2, in particular the quantity of heavy hydrocarbons supplied to the boiler 11 is previously known.

[0056] In another example of implementation of the invention, the installation can be configured to modulate the level of purification of the biogas in a dynamic mode as a function of the quantity of heavy hydrocarbons removed by the heavy hydrocarbon removal unit 3 or of the thermal energy produced by the boiler 11 supplied to the CO2 removal unit 5.

[0057] The installation 1 may comprise a device for continuously measuring or analyzing the quantity of heavy hydrocarbons supplied to the boiler 11 or the thermal energy produced by the boiler 11 and supplied to the CO2 removal unit 5. The installation 1 may comprise a member for sending a signal to the biogas purification unit 9 from the value measured / analyzed by the measuring or analyzing device. The biogas purification unit 9 may be configured to receive said signal making it possible to adjust the purification level so that the quantity of CO2 remaining in the biomethane (treated biogas) at the outlet of the purification unit 9 is regulated so that the thermal power required for the elimination of CO2 at a given threshold of the gas admitted into the CO2 elimination unit 5 corresponds to the thermal power generated by the combustion of heavy hydrocarbons in the boiler 11.

[0058] Preferably, the CO2 removal unit 5 comprises or is an amine washing unit. In the case where the CO2 removal unit 5 is an amine washing unit, the thermal power required for the removal of CO2 corresponds to the thermal power required for the regeneration of the amines. The CO2 removal unit 5 is thus configured to have an amine washing capacity as a function of the thermal energy supplied by the boiler 11.

[0059] In an exemplary implementation of the invention, the boiler 11 is configured to provide the heavy hydrocarbon removal unit 3 with thermal energy 25, for example by means of a heat transfer fluid. The thermal energy produced by the combustion of the heavy hydrocarbons in the boiler 11 may be supplied in part 25 to the heavy hydrocarbon removal unit 3 and in part 23 to the CO2 removal unit 5. The excess energy after having provided the energy necessary for the CO2 removal 5 may be supplied for the at least partial removal 3 of the heavy hydrocarbons.

[0060] As seen in [Fig.l], for this purpose, the CO2 removal unit 5 may comprise a third outlet 14 for gas comprising a fuel and the boiler 11 may comprise a second inlet 24 for fuel gas connected to the third outlet 14 of the CO2 removal unit 5. The CO2 removal unit 5 (in particular when it is an amine scrubbing unit) may be purged (“flashed”) to remove CO2 with a stream comprising residual hydrocarbons. This gas comprising a fuel which leaves the third outlet 14 of the CO2 removal unit 5 may be supplied to the boiler 11 via the second inlet 24.

[0061] The installation 1 may comprise a pipe, for example a bypass, intended to also connect the first outlet 20 of purified biogas to the natural gas network. The purified biogas leaving the first outlet 20 of the biogas purification unit 9 may have the specification of biomethane sufficient to be reinjected into the natural gas network.

[0062] The biogas purification unit 9 may comprise a second outlet 28 for CO2-rich gas.

Claims

1. Claims Installation (1) for producing purified methane from natural gas (2) and biogas (18) comprising, arranged in series in a gas circuit (100), a unit (3) for removing heavy hydrocarbons and a unit (5) for removing CO2, the unit (3) for removing heavy hydrocarbons comprising: - a first inlet (4) intended to be connected to a gas source (2) comprising natural gas, - a first outlet (6) of gas purified of heavy hydrocarbons, and - a second outlet (8) of removed heavy hydrocarbons, the CO2 elimination unit (5) comprising: - a first inlet (10) connected to the first outlet (6) of the heavy hydrocarbon removal unit (3), - a first outlet (12) of gas with reduced CO2 content, and - a second outlet (15) of effluent gas enriched in CO2, the installation (1) further comprising: - a biogas purification unit (9) comprising an inlet (16) intended to be connected to a biogas source (18) and a first outlet (20) of purified biogas connected to the first inlet (10) of the CO2 removal unit (5), the biogas purification unit (9) being configured to produce biogas or biomethane with a variable / determined CO2 concentration, and - a boiler (11) for producing heat by combustion of heavy hydrocarbons comprising a first inlet (22) connected to the second outlet (8) of the heavy hydrocarbon removal unit (3), the boiler (11) being configured to produce a thermal power determined as a function of the quantity of hydrocarbons removed and supplied by the heavy hydrocarbon removal unit (3), the boiler (11) being fluidically connected (23) to the CO2 removal unit (5) to supply the latter with thermal energy produced for the removal of CO2.

2. Installation (1) according to claim 1, characterized in that the CO2 removal unit (5) comprises or is an amine washing unit.

3. Installation (1) according to claim 1 or 2, characterized in that the CO2 removal unit (5) is configured to have a capacity to remove a determined quantity of CO2 from a gas flow, in particular an amine washing capacity, said capacity being a function of the thermal energy supplied by the boiler (11).

4. Installation (1) according to any one of claims 1 to 3, characterized in that it is configured to measure or determine the thermal energy produced by the boiler (11) and supplied to the CO2 elimination unit (5).

5. Installation (1) according to any one of claims 1 to 4, characterized in that it is configured to modulate the level of purification of the biogas as a function of the thermal energy produced by the boiler (11) and supplied to the CO2 elimination unit (5).

6. Installation (1) according to any one of claims 1 to 5, characterized in that the boiler (11) is configured to supply the heavy hydrocarbon removal unit (3) with thermal energy (25).

7. Installation (1) according to any one of claims 1 to 6, characterized in that the CO2 elimination unit (5) comprises a third outlet (14) for gas comprising a fuel and in that the boiler (11) comprises a second inlet (24) for fuel gas connected to the third outlet (14) of the CO2 elimination unit (5).

8. Installation (1) according to any one of claims 1 to 7, characterized in that the biogas purification unit (9) is a membrane separation unit.

9. Installation (1) according to any one of claims 1 to 8, characterized in that it comprises a pipe intended to connect the first outlet (20) of purified biogas to the natural gas network.

10. Installation (1) according to any one of claims 1 to 9, characterized in that the biogas purification unit (9) comprises a second outlet (28) for CO2-rich gas.

11. A method for producing purified methane from natural gas and biogas, the method comprising: - a gas supply step comprising natural gas (2) to a heavy hydrocarbon removal unit (3), - a step of removing heavy hydrocarbons from said gas by the heavy hydrocarbon removal unit (3) to produce a gas purified of heavy hydrocarbons, - a step of supplying the gas purified of heavy hydrocarbons to a CO2 removal unit (5), the CO2 removal unit (5) ensuring CO2 removal by a process comprising heating, - a step of feeding a biogas purification unit (9) with biogas (18), - a biogas purification step in the biogas purification unit (9) to produce a purified biogas, - a step of supplying purified biogas to the CO2 elimination unit (5), - a combustion step, in a boiler (11), of the heavy hydrocarbons removed by the heavy hydrocarbon removal unit (3), - a step of supplying (23) to the CO2 elimination unit (5) the thermal energy produced by the combustion of heavy hydrocarbons, - a step of eliminating CO2 within the gas stream consisting of or comprising the sum of the gas purified of heavy hydrocarbons and the purified biogas, the step of eliminating CO2 being configured to reduce the CO2 concentration in the gas stream to a determined threshold, wherein the biogas purification step (9) is configured to produce a purified biogas having a determined CO2 concentration, said concentration being chosen as a function of the total quantity of CO2 to be removed from the gas stream in the CO2 removal unit (5) to reach the CO2 concentration threshold.

12. Method according to claim 11, characterized in that the total quantity of CO2 to be removed from the gas flow in the CO2 removal unit (5) to reach the CO2 concentration threshold corresponds to the CO2 removal capacity of the removal unit (5), said capacity being determined by the thermal energy produced and supplied by the boiler (11).

13. Method according to claim 11 or 12, characterized in that it comprises a step of determining the thermal energy produced by the boiler (11) and available for the CO2 elimination unit (5).

14. Method according to any one of claims 11 to 13, characterized in that the purified biogas is compressed to the pressure of the gas purified of heavy hydrocarbons and combined with the latter to constitute the gas flow supplied to the CO2 elimination unit (5).

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