Bio-methanation device and associated process

Abstract

The invention relates to a bio-methanation device (10) for a gas (8) containing CO and / or H2, the bio-methanation device being characterized in that it comprises: a first reactor (11) comprising a cavity (12), said first reactor being configured to be placed inside a liquid bath (13) comprising at least one bacterial population, such that, when the first reactor (11) is in contact with the liquid bath (13), a biofilm is formed around the cavity (12); an injector (7) for the gas (8) containing CO and / or H2 into the cavity (12), the biofilm being capable of carrying out a biological conversion of the gas containing CO and / or H2 into methane; a first CO2 injection device (14), configured to inject gaseous CO2 (9) into the liquid bath (13). Fig. 1

Description

Title of the invention: Bio-methanation device and associated method

[0001] The present invention relates to a device for bio-methanation of gas comprising H2 and / or CO, such as syngas. The invention also relates to a device for bio-methanation of a gas containing CO and / or H2. The device and the method of the invention are useful in the field of waste treatment, sludge treatment (in particular from wastewater treatment) and more generally what is called "Power to Gas conversion".

[0002] Methanation involves reacting hydrogen (H2), carbon monoxide (CO) and carbon dioxide (CO2) to generate methane (CH4) and water (H2O).

[0003] Chemical methanation processes with catalytic conversion are known. Such processes are nevertheless expensive and usually involve high pressures and temperatures. These disadvantages can be avoided by using the biological route to transform H2 and CO2 and / or CO into methane at normal temperatures and pressures.

[0004] Biological processes are also known, which could be considered as biocatalysis processes using microorganisms. Several mechanisms can be involved in the biomethanation reaction, depending on the populations of microorganisms involved. We can cite in particular three examples of bacterial populations making it possible to synthesize methane (CH4) from CO or H2 via three distinct mechanisms (see Navarro et al. Front. Microbiol. 7:1188).

[0005] Population 1: Carboxydotrophic Acetogens + Acetogenic Methanogens.

[0006] Reaction 1: 4CO + 2H2O -> CH3COOH + 2CO2

[0007] Reaction 2: CH3COOH -> CH4 + CO2

[0008] Overall Reaction: 4CO + 2H2O -> CH4 + 3CO2

[0009] Population 2: Homoacetogenic Bacteria + Acetogenic Methanogens or Hydrogenotrophic Methanogens

[0010] Reaction 1: 4H2 + 2CO2 -> CH3COOH + 2H2O

[0011] Reaction 2: CH3COOH -> CH4 + CO2

[0012] Reaction 3: 4H2 + CO2 -> CH4 + 2H2O

[0013] Overall Reaction: 4H2 + CO2 -> CH4 + 2H2O

[0014] Population 3: Carboxydotrophic Methanogens

[0015] Overall Reaction: 4CO + 2H2O -> CH4 + 3CO2

[0016] These various populations can of course coexist in the same reactor.

[0017] One of the well-known limitations of bio-methanation processes is the low solubility of carbon monoxide (CO) and dihydrogen (H2) in water, which limits the kinetics and / or yields of biological methanation processes. Various solutions have been explored in order to increase the transfer of these molecules into the reaction medium.

[0018] Thus, documents WO2013110186, US20160153008 and US20160230193 present methods comprising a step of circulating a pyrolysis gas (syngas) inside a digester. Such methods make it possible to implement methanation concomitant with the digestion reactions. However, such methods do not allow a selection of the microorganisms dedicated to methanation, and therefore limit the yield of the methanation.

[0019] Other solutions have been developed, which use a unit specific to the methanation step, which makes it possible, via selection pressure, to obtain a population of microorganisms specialized for methanation. We can notably cite document WO2018234058, which provides for the injection of a pyrolysis gas through a membrane positioned in the methanation reactor, in order to increase the contact surface between the gas and the reaction medium, and consequently the mass transfer and the yields. However, in such a system, the concentration of CO2 relative to the concentration of CO or H2 is not controlled: it results from the partial concentrations in the injected gas. Thus, the membranes are used in part to inject CO2, which is much more soluble in an aqueous medium than CO or H2.

[0020] There is therefore a need for improved methanation processes, particularly in terms of mass transfer of poorly soluble gases such as CO and H2, in terms of the use of membranes for the injection of said poorly soluble gases, in terms of overall conversion efficiency. Such improved processes would also make it possible to reduce the size of the methanation reactor.

[0021] The invention aims to overcome all or part of the problems cited above by proposing a modular bio-methanation device and bio-methanation method, decoupling the injection of CO2 from the injection of CO / H2.

[0022] To this end, the invention relates to a device for bio-methanation of a gas containing CO and / or H2, the bio-methanation device being characterized in that it comprises: - a first reactor comprising a cavity, said first reactor being configured to be placed inside a liquid bath comprising at least one bacterial population, such that, when the first reactor is in contact with the liquid bath, a biofilm is formed around the cavity; - an injector of the gas containing CO and / or H2 into the cavity, the biofilm being capable of carrying out a biological conversion of the gas containing CO and / or H2 into methane; - a first CO2 injection device, configured to inject gaseous CO2 into the liquid bath.

[0023] Advantageously, the bio-methanation device according to the invention comprises a generator of fine bubbles or microbubbles or nanobubbles comprising: - a first input connected to the first CO2 injection device; - a first outlet connected to the liquid bath, the fine bubble or microbubbles or nanobubbles generator being configured to deliver at the first outlet fine bubbles or microbubbles or nanobubbles of the CO2 injected at the first inlet.

[0024] Advantageously, the bio-methanation device according to the invention comprises a second injection device connected to the liquid bath, said second injection device being intended to inject sodium bicarbonate into the liquid bath.

[0025] Advantageously, the bio-methanation device according to the invention comprises a third gas injection device, preferably CO2, configured to intermittently inject said gas in gaseous form into the liquid bath, preferably in the form of fine bubbles or large bubbles.

[0026] Advantageously, the bio-methanation device according to the invention comprises: - a device for measuring the alkalinity and / or pH of the liquid bath, and / or - an analyzer of a gaseous composition at an outlet of the first reactor, and / Or - a probe for measuring the CO2 dissolved in the liquid bath, connected to the liquid bath and / or to the outlet of the first reactor and intended to determine a concentration of a control species in the liquid bath and / or at the outlet of the first reactor, the control species preferably being CO2, H2 or methane, the bio-methanation device further comprising a means for controlling the injection device as a function of the concentration of the control species determined. Advantageously, the first injection device and the third injection device (41) form a single injection device.

[0027] The invention also relates to a bio-methanation installation comprising: - an anaerobic digester configured to be fed by organic materials and to generate biogas, - a bio-methanation device as described previously, the anaerobic digester being connected to an outlet of the first reactor.

[0028] The invention also relates to a process for the bio-methanation of a gas containing CO and / or H2, the bio-methanation process being characterized in that it comprises the following steps: - a step of providing a first reactor placed inside a liquid bath comprising at least one bacterial population, said first reactor comprising a cavity in contact with the liquid bath, around which a biofilm is formed; - a step of injecting gas containing CO and / or H2 into the cavity; - a biological conversion step of the gas containing CO and / or H2 into methane by the biofilm; - a first stage of injecting gaseous CO2 into the liquid bath.

[0029] Advantageously, the bio-methanation process according to the invention comprises a step of generating fine bubbles or microbubbles or nanobubbles from the injected CO2.

[0030] Advantageously, the bio-methanation process according to the invention comprises a step of injecting sodium bicarbonate into the liquid bath.

[0031] Advantageously, the bio-methanation process according to the invention comprises a second stage of injecting gas, preferably CO2, intermittently and in gaseous form into the liquid bath, preferably in the form of fine bubbles or large bubbles.

[0032] Advantageously, the bio-methanation process according to the invention comprises: - a step of measuring the alkalinity of the liquid bath, and / or - a step of analyzing a gaseous composition at an outlet of the first reactor, and / or - a step of measuring the CO2 dissolved in the liquid bath, making it possible to determine a concentration of a control species in the liquid bath and / or at the outlet of the first reactor, the control species preferably being CO2, H2 or methane, - a step of controlling the injection step according to the concentration of the control species determined.

[0033] Advantageously, the bio-methanation process according to the invention comprises a step of feeding an anaerobic digester with the converted methane.

[0034] The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given as an example, a description illustrated by the attached drawing in which:

[0035] [Fig.l] schematically represents a sectional view of a bio-methanation device according to the invention;

[0036] [Fig.2] schematically represents a sectional view of another embodiment of a bio-methanation device according to the invention;

[0037] [Fig. 3] schematically represents a sectional view of another embodiment of a bio-methanation device according to the invention;

[0038] [Fig.4] schematically represents a sectional view of another mode of rea- use of a bio-methanation device according to the invention;

[0039] [Fig.5] schematically represents a sectional view of a bio-methanation installation according to the invention;

[0040] [Fig.6] schematically represents a flowchart of the steps of a bio-methanation process according to the invention.

[0041] For the sake of clarity, the same elements will have the same references in the different figures. For better visibility and for the sake of increased understanding, the elements are not always represented to scale.

[0042] [Fig.l] schematically represents a sectional view of a bio-methanation device 10 according to the invention. The bio-methanation device 10 of a gas 8 containing CO and / or H2 comprises: - a first reactor 11 comprising a cavity 12, said first reactor being configured to be placed inside a liquid bath 13 comprising at least one bacterial population, so that, when the first reactor 11 is in contact with the liquid bath 13, a biofilm is formed around the cavity 12; - an injector 7 of the gas 8 containing CO and / or H2 into the cavity 12, the biofilm being capable of carrying out a biological conversion of the gas containing CO and / or H2 into methane; - a first CO2 injection device 14, configured to inject gaseous CO2 9 into the liquid bath 13.

[0043] The cavity 12 can be seen as a growth support for the microbial biofilm inside which gas containing CO and / or H2 is injected in order to achieve a transfer of the gas by diffusion via the support. An example of a cavity can be a hollow fiber membrane or two plates arranged parallel to each other and comprising hollow channels between the plates. The gas containing CO and / or H2 is injected into the channels or hollow fibers. The gas diffuses by permeation through the cavity. The bacterial population attached to the cavity then accesses the gas inside the biofilm. There is biological conversion of the gas. In other words, the bio-methanation device aims to feed the biology to increase the production of methane. The gas containing CO and / or H2 is injected into the cavity and the biofilm grows around the cavity.

[0044] It is important to emphasize that the injector 7 injects the gas 8 containing the CO and / or the H2 into the cavity, while the first injection device 14 injects the gaseous CO2 9 into the liquid bath 13. This is therefore a differential injection of CO2 on the one hand and of CO and / or H2 on the other hand. The H2 and / or CO is thus injected into the lumen, that is to say the hollow space defined by the cavity 12, in order to maximize the concentration differential (and therefore the diffusion of the gas) on both sides of the cavity. Thanks to the device of the invention, the addition of CO2 to the liquid bath is controlled to the exact amount necessary. The injector 7 dedicated to the injection of CO2 makes it possible to control the quantity of CO2 introduced into the liquid bath 13. The bio-methanation device according to the invention differs from the known prior art for which the CO2 is often in excess due to an uncontrolled addition because it is carried out at the same time as the addition of CO and / or H2.

[0045] Preferably but still optionally, the bio-methanation device according to the invention may comprise a generator 21 of fine bubbles or microbubbles or nanobubbles, the generator 21 comprising: - a first input 22 connected to the first CO2 injection device 14; - a first outlet 23 connected to the liquid bath 13, the generator 21 of fine bubbles or microbubbles or nanobubbles being configured to deliver to the first outlet 23 fine bubbles or microbubbles or nanobubbles of the CO2 injected at the first inlet 22.

[0046] By fine bubbles, we mean bubbles coming from porous or membrane diffusers (typically made of elastomer equipped with holes of 0.5 to 2 mm in diameter) and generating a plume of bubbles whose average diameter at the genesis of the bubble is between 1 and 5 mm. Such bubbles can be obtained by a porous type generator. By microbubbles, we mean bubbles of very small size, of microscopic scale. By nanobubbles, we mean bubbles of nanoscopic scale. Microbubbles and nanobubbles can be obtained by a membrane pump type generator. It is the type of diffuser that defines the size of bubbles obtained. The distinction between the different categories of bubble sizes corresponds to a discretization of the worlds of nanobubbles (obtained with aerators and / or flotation), microbubbles (fat / oil flotation), fine bubbles (aeration) and large / medium bubbles (aeration, mixing).

[0047] The gas containing CO and / or H2 may also contain CO2. According to a particular embodiment, it is syngas (synthesis gas), in particular from a pyrolysis unit. According to a particular embodiment, it is syngas from the pyrolysis of: - organic deposit with low methanogenic potential (presence of lignin, excessive dryness, etc.); - organic deposit containing methanization inhibitors or regulated compounds (micro pollutants, toxic PAHs, PCBs, aromatic cycles, etc.); - Deposit with low degradation kinetics: • Long TSH (TSH is the abbreviation for hydraulic residence time), • High digester volume, • Large footprint.

[0048] [Fig. 2] schematically represents a sectional view of another embodiment of a bio-methanation device 20 according to the invention. The bio-methanation device 20 comprises a second injection device 31 connected to the liquid bath 13, said second injection device 31 being intended to inject sodium bicarbonate into the liquid bath 13. The sodium bicarbonate, by dissociation, produces soluble CO2. This avoids having to solubilize a gas. Alternatively, the second injection device 31 can be connected to an upstream reservoir in which the CO2 is generated from sodium bicarbonate in an acidic medium. Such a non-continuous injection of the excess reagent (CO2) makes it possible to avoid any unnecessary recirculation of the gas.

[0049] [Fig. 3] schematically represents a sectional view of another embodiment of a bio-methanation device 30 according to the invention. The bio-methanation device 30 comprises a third gas injection device 41, preferably CO2, configured to intermittently inject said gas in gaseous form into the liquid bath 13, preferably in the form of fine bubbles or large bubbles. The third gas injection device 41 is intended for scouring in the liquid bath 13. The gas thus injected makes it possible to at least partially sweep the biofilm to prevent the cavity from caking. Such an injection device avoids the use of a specific pump or mixing of the liquid bath which could damage the cavity (particularly when it is a membrane) and / or the biofilm, and thus negatively impact the performance of the biological treatment.Furthermore, such an injection device 41 reduces the operating expense costs associated with stirring. In one embodiment of the invention, the third injection device 41 can be positioned at the bottom of the cavity, and advantageously combined with the first CO2 injection device 14 as shown in [Fig. 3]. In another embodiment, the third injection device 41 can be positioned on the surface of the liquid bath. Finally, it is also possible to envisage two third injection devices 41, one at the bottom of the cavity and another on the surface of the liquid bath, the two devices 41 then being individually or not controllable.

[0050] In one embodiment, the first injection device 14 and the third injection device 41 form a single injection device. The injection device then makes it possible to combine the functions of supplying CO2 for the process and for scouring.

[0051] [Fig. 4] schematically represents a sectional view of another embodiment of a bio-methanation device 40 according to the invention. The bio-methanation device 40 comprises: - a device 51 for measuring the alkalinity and / or pH of the liquid bath 13, and / or - an analyzer 52 of a gaseous composition at an outlet of the first reactor 11, and / or - a measuring probe 53 of the CO2 dissolved in the liquid bath 13, connected to the liquid bath 13 and / or to the outlet of the first reactor 11 and intended to determine a concentration 54 of a control species in the liquid bath 13 and / or at the outlet of the first reactor 11, the control species preferably being CO2, H2 or methane, the bio-methanation device further comprising a means 55 for controlling the injection device 14, 41 as a function of the concentration 54 of the control species determined.

[0052] The addition of CO2 can thus be controlled by measuring alkalinity, in particular by direct measurement. This measurement can be carried out by an online sampler or analyzer (by titrimetry). This is for example an online sequential sampling analyzer which can use various automated analytical technologies to carry out the analysis. Alkalinity is a measure of the ability of water to neutralize acids. Alkaline compounds such as bicarbonates, carbonates and hydroxides remove hydrogen ions and lower the acidity of the water. This is done by combining the hydrogen ions to make new compounds. Total alkalinity is measured by measuring the amount of acid required to bring the sample to a specified pH endpoint. At this pH, all the alkaline compounds in the sample are "exhausted". The result is expressed in parts per million (ppm) or milligrams per liter (mg / 1) of calcium carbonate (CaCO3).It is also possible to calculate the alkalinity of the liquid bath by direct measurement of the conductivity. The addition of CO2 can also be controlled by measuring the alkalinity by measuring the pH in the liquid bath (indirect measurement).

[0053] The addition of CO2 can also be controlled based on the composition of the gas, or on a direct measurement of the CO2 in the liquid. Such control makes it possible to add just the right amount of CO2 to obtain optimal methanation efficiency.

[0054] The composition of the gas downstream of the first reactor 11 is obtained by the analyzer 52 of a gas composition at an outlet of the first reactor 11. The analyzer 52 may for example be an online biogas analyzer.

[0055] A control species is chosen in accordance with the chosen measuring means. Its concentration 54 is determined, and according to this value, the control means 55 controls the injection of CO2 into the bio-methanation device.

[0056] As an illustration, in the case of the measuring probe 53 of the CO2 dissolved in the liquid bath 13, the control species is CO2. Its concentration 54 in the liquid bath is determined by the probe. Then this value of the concentration of CO2 in the liquid bath is compared to a CO2 concentration threshold. Above the threshold value (which means that there is too much CO2 in the system), the injection of CO2 in the liquid bath is stopped (or reduced) by means of the control means 55, until the concentration 54 of CO2 in the liquid bath is lower than the threshold value for this concentration.

[0057] The same principle can be applied for methane as a control species, downstream of the first reactor 11. The analyzer 52 of a gas composition downstream of the first reactor 11 determines the concentration 54 of methane downstream of the first reactor 11. The control means 55 controls the injection device 14, 41 as a function of the concentration 54 of methane determined in relation to a previously established methane concentration threshold (which can vary according to the operational conditions). If the concentration 54 of methane is lower than the threshold value, the CO2 injection device 14 and / or 41 is activated to contribute to the overall conversion of the gas 8 into methane.

[0058] The invention is based on two distinct and separate sources of CO2 and gas containing CO and / or H2. This makes it possible to control the supply ratio between the gases.

[0059] In addition, and as a result of the separation of the inlet gases, the flow rate of injected CO2 is discontinuous. It is therefore possible to completely control its supply and therefore avoid a surplus of CO2 which would require recirculation downstream of the CO2 to achieve the necessary purity of the gas.

[0060] A possible implementation of the bio-methanation device according to the invention is to carry out an injection of the gas containing H2 and / or CO inside the hollow material (i.e. in the cavity) continuously, or intermittently, and / or in batches. Based on the overall reactions involved (some of which are mentioned in the introduction), it is possible to regulate the gas supply in the device as a function of the partial pressure of dihydrogen (H2) and / or carbon monoxide (CO). The injection of CO2 by the first CO2 injection device 14 is preferably carried out discontinuously.

[0061] [Fig. 5] schematically represents a sectional view of a bio-methanation installation 50 according to the invention. The bio-methanation installation 50 comprises: - an anaerobic digester 61 configured to be fed with organic materials 62 and to generate biogas 63, - a bio-methanation device as described previously, the anaerobic digester 61 being connected to an outlet 64 of the first reactor 11. In other words, the anaerobic digester 61 is positioned downstream of the first reactor 11 and is in particular supplied by the methane converted by the bio-methanation device.

[0062] In the case of this installation, the analyzer 52 may be intended to analyze a gaseous composition in the gaseous airspace of the digester 61, and the control means 55 of the injection device 14 and / or 41 is controlled as a function of the concentration 54 of the control species determined in the gaseous airspace.

[0063] [Fig.6] schematically represents a flowchart of the steps of a bio-methanation process according to the invention.

[0064] The process for bio-methanation of gas 8 containing CO and / or H2 comprises the following steps: - a step 100 of providing a first reactor 11 placed inside a liquid bath 13 comprising at least one bacterial population, said first reactor 11 comprising a cavity 12 in contact with the liquid bath 13, around which a biofilm is formed; - a step 105 of injecting the gas 8 containing CO and / or H2 into the cavity 12; - a step 106 of biological conversion of the gas containing CO and / or H2 into methane by the biofilm; - a first step 110 of injecting gaseous CO2 into the liquid bath 13.

[0065] Step 105 of injecting gas 8 into the cavity can be carried out continuously, intermittently or in batches in order to regulate the production of methane.

[0066] Unless otherwise indicated, the different steps presented below are optional and can be combined in the process. In other words, they can be included individually or grouped in the bio-methanation process.

[0067] In another embodiment of the invention, the bio-methanation method comprises a step 120 of generating fine bubbles or microbubbles or nanobubbles of the injected CO2.

[0068] In an alternative embodiment, the bio-methanation process may comprise a step 130 of injecting sodium bicarbonate into the liquid bath 13. As a variant, step 130 may be a step of generating CO2 from sodium bicarbonate in an acidic medium.

[0069] In an advantageous embodiment, the bio-methanation method comprises a second step 140 of injecting gas, preferably CO2, intermittently and in gaseous form into the liquid bath 13, preferably in the form of fine bubbles or large bubbles. This second step 140 makes it possible to inject gaseous CO2 (or for example biogas, or methane or any other gas not interfering with the downstream process of valorization of the biogas produced in the digester) into the liquid bath of the first reactor 11 for scouring (or cleaning) in the liquid bath. This second injection step makes it possible to prevent the microorganisms from clumping on the cavity. This avoids having to stir the liquid medium (for example by injecting a stream of pressurized water) which could damage the membranes / biofilms. In addition, this step 140 reduces the operating costs which would be associated with stirring the liquid bath.The gas injected during the second step 140 may be injected intermittently (for example at a frequency of once per day or once . per week) via fine or large bubbles (for example, the injected gas is sent via diffusers to create bubbles) to carry out scouring instead of having a medium agitation system. In one embodiment of the invention, the second injection step 140 can be carried out at the bottom of the cavity, and advantageously combined with the first CO2 injection step 110. In another embodiment, the second injection step 140 can be carried out on the surface of the liquid bath. Finally, it is also possible to envisage two injection steps 140, one carried out at the bottom of the cavity and another carried out on the surface of the liquid bath, which can be controlled individually or not.

[0070] According to another embodiment of the invention, the bio-methanation process according to the invention comprises: - a step 150 of measuring the alkalinity of the liquid bath 13, and / or - a step 160 of analyzing a gaseous composition at an outlet of the first reactor 11 (preferably in the gaseous airspace of a digester coupled downstream of the first reactor), and / or - a step 170 of measuring the CO2 dissolved in the liquid bath 13, making it possible to determine a concentration 54 of a control species in the liquid bath 13 and / or at the outlet of the first reactor 11, the control species preferably being CO2, H2 or methane, - a step 180 of controlling the injection step 110, 140 as a function of the concentration 54 of the determined control species.

[0071] As explained previously, the invention is based on a differential injection of CO2 and H2 and / or CO with two actions on the bio-methanation process.

[0072] On the one hand, the invention relates to the CO2 process in which the addition of CO2 is controlled to the exact amount necessary by the alkalinity (by direct or indirect measurement via pH measurement) or based on the composition of the gas downstream of the first reactor 11, or based on a direct measurement of the CO2 in the liquid bath 13. This control of the quantity of CO2 injected into the liquid bath minimizes any downstream separation treatment. Indeed, the CO2 is almost systematically in excess and available in the liquid medium via the alkalinity. This avoids recirculating gas or having to purify it downstream.

[0073] On the other hand, the invention can also relate to scouring, preferably by CO2. There are several ways of controlling the need for scouring: - Alkalinity: When a drop in alkalinity is observed, this means that CO2 is accumulating (it is therefore unconsumed CO2); - The break in slope on H2 consumption (with for example a flow meter positioned at an H2 / CO inlet of the cavity) due to a lack of local CO2, indicating a loss of biofilm activity which may be linked to an excessively thick biofilm; - Measurement of CH4 and / or CO2 in the biogas produced downstream in the digester indicating an increase in CO2 or with a decreasing CH4 / CO2 ratio.

[0074] The study of these parameters makes it possible to identify when it is necessary to trigger a gas injection step for scouring.

[0075] It emerges that by following at least one of these parameters, it is possible to control the injection of CO2 into the liquid bath for biological conversion and the injection of gas (including CO2) for scouring.

[0076] Finally, the bio-methanation process according to the invention may comprise a step 190 of feeding an anaerobic digester with the converted methane. This step aims to enrich the digester with methane.

[0077] The invention makes it possible to increase the conversion of organic matter with low methanogenic potential but high PCI by carrying out the bio-methanation of the syngas; resulting from the gasification or pyrolysis of this same organic matter. The invention makes it possible to optimize the mass transfer of the syngas (CO and / or H2) as well as the overall conversion efficiency which is more than 90%. In addition, the proposed coupling makes it possible to reduce the size of the first reactor (and therefore to reduce the associated operating costs).

[0078] It will more generally appear to those skilled in the art that various modifications can be made to the embodiments described above, in light of the teaching which has just been disclosed to them. In the following claims, the terms used should not be interpreted as limiting the claims to the embodiments set out in the present description, but should be interpreted to include all equivalents which the claims are intended to cover by virtue of their wording and the prediction of which is within the reach of those skilled in the art based on their general knowledge.

Claims

Claims

1. A bio-methanation device (10, 20, 30, 40, 50) for a gas (8) containing CO and / or H2, the bio-methanation device being characterized in that it comprises: - a first reactor (11) comprising a cavity (12), said first reactor being configured to be placed inside a liquid bath (13) comprising at least one bacterial population, so that, when the first reactor (11) is in contact with the liquid bath (13), a biofilm is formed around the cavity (12); - an injector (7) for the gas (8) containing CO and / or H2 into the cavity (12), the biofilm being capable of carrying out a biological conversion of the gas containing CO and / or H2 into methane; - a first CO2 injection device (14), configured to inject gaseous CO2 (9) into the liquid bath (13).

2. Bio-methanation device (10, 20, 30, 40, 50) according to claim 1, comprising a generator (21) of fine bubbles or microbubbles or nanobubbles comprising: - a first inlet (22) connected to the first CO2 injection device (14); - a first outlet (23) connected to the liquid bath (13), the generator (21) of fine bubbles or microbubbles or nanobubbles being configured to deliver to the first outlet (23) fine bubbles or microbubbles or nanobubbles of the CO2 injected at the first inlet (22).

3. Bio-methanation device (20, 30, 40) according to claim 1 or 2, comprising a second injection device (31) connected to the liquid bath (13), said second injection device (31) being intended to inject sodium bicarbonate into the liquid bath (13).

4. Bio-methanation device (30, 40) according to any one of claims 1 to 3, comprising a third gas injection device (41), preferably CO2, configured to intermittently inject said gas in gaseous form into the liquid bath (13), preferably in the form of fine bubbles or large bubbles.

5. Bio-methanation device (40) according to any one of the claims- indications 1 to 4, including: - a device (51) for measuring the alkalinity and / or pH of the liquid bath (13), and / or - an analyzer (52) of a gaseous composition at an outlet (64) of the first reactor (11), and / or - a measuring probe (53) of the CO2 dissolved in the liquid bath (13), connected to the liquid bath (13) and / or to the outlet (64) of the first reactor (11) and intended to determine a concentration (54) of a control species in the liquid bath (13) and / or at the outlet of the first reactor (11), the control species preferably being CO2, H2 or methane, the bio-methanation device further comprising a means of controlling (55) the injection device (14, 41) as a function of the concentration (54) of the control species determined.

6. Bio-methanation device (20, 30, 40) according to claim 4 or 5, wherein the first injection device (14) and the third injection device (41) form a single injection device.

7. Bio-methanation installation (50) comprising: - an anaerobic digester (61) configured to be fed with organic materials (62) and to generate biogas (63), - a bio-methanation device (10, 20, 30, 40) according to any one of claims 1 to 6, the anaerobic digester (61) being connected to an outlet (64) of the first reactor (11).

8. A method for the bio-methanation of a gas (8) containing CO and / or H2, the bio-methanation method being characterized in that it comprises the following steps: - a step (100) of providing a first reactor (11) placed inside a liquid bath (13) comprising at least one bacterial population, said first reactor comprising a cavity (12) in contact with the liquid bath (13), around which a biofilm is formed; - a step (105) of injecting the gas (8) containing CO and / or H2 in the cavity (12); - a step (106) of biological conversion of the gas containing CO and / or H2 into methane by the biofilm; - a first step (110) of injecting the gaseous CO2 into the liquid bath (13).

9. Bio-methanation method according to claim 8, comprising a step (120) of generating fine bubbles or microbubbles or nanobubbles of the injected CO2.

10. Bio-methanation method according to claim 8 or 9, comprising a step (130) of injecting sodium bicarbonate into the liquid bath (13).

11. Bio-methanation process according to any one of claims 8 to 10, comprising a second step (140) of injecting gas, preferably CO2, intermittently and in gaseous form into the liquid bath (13), preferably in the form of fine bubbles or large bubbles.

12. Bio-methanation method according to any one of claims 8 to 11, comprising: - a step (150) of measuring the alkalinity of the liquid bath (13), and / or - a step (160) of analyzing a gaseous composition at an outlet of the first reactor (11), and / or - a step (170) of measuring the CO2 dissolved in the liquid bath (13), making it possible to determine a concentration (54) of a control species in the liquid bath (13) and / or at the outlet of the first reactor (11), the control species preferably being CO2, H2 or methane, - a step (180) of controlling the injection step (110, 140) as a function of the concentration (54) of the determined control species.

13. A bio-methanation process according to any one of claims 8 to 12, comprising a step (190) of feeding an anaerobic digester with the converted methane.

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