FR3043397A1 - COVER MODULE, DEVICE AND SYSTEM FOR METHANIZATION - Google Patents

Abstract

The invention relates to a cover module (120) for a methanation tank (110), said tank (110) being adapted to receive organic material (M) and comprising a bottom (112) and at least one wall (114). vertical cover defining an opening (116), said cover module (120) comprising a covering member (122) configured to extend into said opening (116), a central flotation unit (124) arranged on the one hand for supporting the covering element (122) at its central portion and secondly resting on organic matter (M) contained in the vessel (110), and a peripheral buoyancy unit (126) connected to the element covering (122) and configured both to hold it above the organic material (M) and to move vertically sealingly along the wall (114) of the tank (110) with the organic material (M) .

Description

COVER MODULE. DEVICE AND SYSTEM FOR METHANIZATION TECHNICAL FIELD AND OBJECT OF THE INVENTION

The present invention relates to the field of anaerobic digestion and more particularly relates to a covering module of a methanation tank. The cover module according to the invention allows in particular the capture of biogas resulting from the transformation of the fermentable fraction of manure-type livestock manure effluents into biogas.

STATE OF THE ART

Anaerobic digestion of organic matter is a known natural process that transforms organic matter, especially agricultural material, into biogas. The anaerobic digestion is carried out by biological degradation of the organic materials by a microbial consortium containing bacteria. It is thus known to transform into biogas the fermentable fraction of livestock effluents producing slurry such as, for example, bovine manure, palmiped, porcine, etc., by disposing these effluents in a manure pit built in the soil.

In order to make the pit at least partly watertight and to improve the efficiency of the anaerobic digestion, it is known to cover it with a flexible tarpaulin. Such a solution does not, however, capture the biogas resulting from the transformation of the fermentable fraction of livestock effluents. Also, when it is desired to collect the biogas resulting from the transformation of the fermentable fraction of livestock effluents, it is necessary to deposit the effluents in a methanizer.

A methanizer comprises in a known manner a tank called digester, in which the effluents are placed, and a biogas collection device. In a first type of methanizer, the vessel is of cylindrical shape, for example made of metal. The effluents are conveyed inside the tank through an inlet duct connected to one end of the tank and the biogas collection device is in the form of an outlet duct connected to the other end of the tank. tank. In a second type of methanizer, the tank is buried in the soil, the effluents are conveyed inside the tank through an inlet conduit, connected for example to the base of the tank, and the biogas collection device is in the form of a cover module mounted above the tank.

Thus, in a solution described in document EP0827681B1, the cover module comprises a flexible sheet mounted on a support frame and to which is connected a biogas outlet pipe. The support frame of the sheet comprises a plurality of metal posts fixed directly on the tank. In another solution, described in the patent application WO9828402A1, the covering module comprises a central post supporting a stretched cover so as to form a pyramid for guiding the biogas to the post where it is collected via a plurality of openings and of pipes.

Such solutions are complex and expensive to manufacture and assemble, which has significant disadvantages. In addition, in these solutions, the interior space of the tank is fixed so that the efficiency of the methanation varies with the volume of effluents contained in the tank. In particular, when there is little effluent in the tank, the volume of stagnant air above the effluents is such that the anaerobic digestion is slow and inefficient, which presents a significant disadvantage. In addition, in such solutions, the rainwater is either discharged and can not be reused, or flow into the tank and can represent up to 30% of the volume of the pit, which soaks organic matter and decreases the efficiency of anaerobic digestion. Finally, the conversion of a concrete slurry tank into a methanizer by the laying of a roofing module can generate mechanical stresses on the tank that were not planned during its design and cause de facto cracks in the roof. concrete, which presents a major drawback.

GENERAL PRESENTATION OF THE INVENTION The invention aims at solving at least part of these disadvantages by proposing a cover module solution which is at the same time simple, reliable, efficient, robust, inexpensive, easy and quick to assemble, in particular on a tank of an existing slurry tank, to capture the biogas produced by the transformation of the fermentable fraction of livestock effluents. For this purpose, the invention firstly relates to a module for covering a methanation tank, said tank being adapted to receive organic material and comprising a bottom and at least one vertical wall defining an opening, said module cover comprising a covering element configured to extend in said opening, a central flotation unit, arranged on the one hand to support the covering element at its central portion and on the other hand to rest on organic matter contained therein in the tank, and a peripheral buoyancy unit connected to the cover member and configured both to hold it above the organic material and to move vertically in a sealed manner along the wall of the tank with the organic material .

By the terms "to move in a sealed manner along the wall of the tank with the organic materials" is meant that the peripheral flotation unit, which is based on the organic materials, remains pressed against the wall as well when the volume organic matter is fixed only when it varies. By the terms "vertical" and "vertically" is meant parallel to the direction of the force of gravity.

The covering module according to the invention makes it possible to capture the biogas produced by the transformation of the fermentable fraction of organic materials such as livestock effluents. Such a cover module is simple and inexpensive to manufacture and assemble since it relies on organic matter and is not attached to the wall of the tank. In addition, since the cover module moves vertically with the organic materials, the interior space of the tank varies and adapts to the volume of organic matter, which improves the efficiency of the methanation. Such a cover module is also easy to adapt to any type of pit or liquid storage tank, in particular circular or rectangular, buried pit type made of concrete, metal or a geotextile material, for example of the EPDM type. The covering module according to the invention can thus advantageously be used with an existing slurry tank in order to transform it into a methanizer. Such a transformation is easy to perform and does not generate mechanical stresses on the tank and therefore no cracks in the concrete. The central flotation unit makes it possible to form, above the organic materials, a space sufficient to capture the biogas but limited to allow the methanization of organic matter. The peripheral flotation unit makes it possible to ensure the good coverage of the organic materials, especially when their volume varies. The joint use of a peripheral flotation unit and a central flotation unit thus allows both rapid methanization of organic matter and efficient collection of biogas.

According to a characteristic of the invention, the covering element comprises a flexible bottom wall, connected to the peripheral flotation unit and in which a plurality of biogas evacuation orifices produced by the organic materials are formed, and a wall upper fixed on the lower wall at its central part. The bottom wall has a shape at least partly frustoconical so as to guide the biogas towards the center of the covering element where it passes through the orifices formed in the lower wall, which preferably extends substantially horizontally at its central portion. .

Preferably, the cover module is arranged to retain the rainwater to prevent it from mixing with the organic materials, such a separation having the advantage of reducing the time and therefore the spreading costs. This reduces the spreading costs by capturing a large volume of rainwater. To this end, the peripheral flotation unit may have a thickness greater than that of the covering element so as to form a peripheral rim of retention of rainwater. Such storage of rainwater allows reuse for example for watering crops, and prevents them from flowing into the tank and soak organic materials.

Preferably, the peripheral flotation unit is attached to the bottom wall over its entire periphery to ensure the tightness of their connection.

Advantageously, the peripheral flotation unit is positioned and fixed on the bottom wall so as to maintain it on the organic materials.

According to one characteristic of the invention, the peripheral flotation unit comprises a ballasted skirt fixed on its periphery, preferably on its entire periphery, in order to press the peripheral buoyancy unit against the wall of the tank and thus ensure its vertical displacement in a sealed manner along the wall of the tank with the organic materials.

Advantageously, the weighted skirt comprises a sheath, attached to the periphery of the peripheral buoyancy unit, into which is inserted a mass which is, for example, in the form of a stainless steel tube, preferably conforming to the shapes of the wall of the tank.

Advantageously, the peripheral buoyancy unit is in the form of an annular buoy allowing to take the shape of a cylindrical vessel of circular section.

This ring buoy can be hollow and inflated with a gas such as, for example, air, which is inexpensive, or be solid, for example made of polystyrene.

In one embodiment, the central flotation unit is a single central float, for example inflated with a gas or made of polystyrene, simple and inexpensive.

In another embodiment, the central flotation unit comprises a plurality of central floats, for example inflated with a gas or made of polystyrene, in order to maintain the covering element securely while leaving sufficient space for the passage of biogas.

According to one aspect of the invention, the cover module further comprises biogas evacuation means connected to the upper wall in order to collect the biogas produced in the tank. The invention also relates to an anaerobic digestion device comprising a tank and a cover module as presented above, said tank being adapted to receive organic materials and comprising a bottom and at least one wall delimiting an opening, said cover module being disposed in the tank so as to extend into said opening.

Preferably, the device comprises an armature disposed at the bottom of the tank. Finally, the invention relates to an anaerobic digestion system comprising an anaerobic digestion device according to the preceding claim and an insertion module for organic materials in the tank.

Preferably, the system comprises a module for heating the organic materials, arranged at least partly in the tank.

Advantageously, the heating module comprises a set of heating pipes.

Advantageously, the set of heating pipes is arranged at least partly at the bottom of the tank and / or on the wall of the tank.

Preferably, the heating pipe assembly is mounted on a frame of the device disposed at the bottom of the tank.

More preferably, the system comprises a biogas recirculation module, produced by the device, in the tank, the biogas then being preferably injected at the lower part of the tank.

Advantageously, the biogas recirculation module comprises a set of biogas diffusion pipes.

Advantageously, the set of biogas diffusion pipes is arranged at least partly at the bottom of the tank and / or on the wall of the tank.

Preferably, the assembly of biogas diffusion piping is mounted on a frame of the device, disposed at the bottom of the tank.

According to one characteristic of the invention, the system comprises a module for extracting organic matter.

Advantageously, the system comprises a module regulating the level of surface water. Such a module makes it possible to ensure that the volume of the rainwater is both sufficient to allow the gravity displacement in a sealed manner of the roofing module along the wall or walls of the tank and limited to prevent the water rain does not overflow into the tank.

Advantageously, the system comprises a biogas storage module. Such a module makes it possible to store biogas produced by the methanisation of the organic materials in the tank for later reuse. Other features and advantages of the invention will become apparent from the following description given with reference to the appended figures given by way of non-limiting examples and in which identical references are given to similar objects.

DESCRIPTION OF THE FIGURES

Figure 1 schematically illustrates an embodiment of the system according to the invention, the methanization device being shown in section.

FIG. 2 is a partial schematic view in perspective, from above, of the anaerobic digestion device of FIG.

Figure 3 is a partial schematic view from above and in perspective of the tank of the device of Figure 1 devoid of cover module.

Figure 4 is a partial schematic view from above and in perspective of another embodiment of the tank of the device of Figure 1 without cover module.

DETAILED DESCRIPTION OF THE INVENTION

Description of an embodiment of the system according to the invention

The system according to the invention makes it possible both to capture the biogas produced by the transformation of the fermentable fraction of organic matter and to collect the rainwater so as to prevent it from mixing with said organic matter. The organic materials may be livestock effluents such as cattle slurry, palmiped, pig, or any other organic material which a fermentable fraction is able to be converted into biogas. I. System 1

With reference to FIG. 1, the system 1 according to the invention comprises a methanation device 10 and an organic material insertion module 20.

In the preferred embodiment illustrated in FIG. 1, the system 1 further comprises a module 30 for extracting organic matter M, a module 40 for recirculating biogas, a module 50 for regulating the level of surface water E, a biogas storage module 60 and a heating module 70. 1) Device 10

The methanation device 10 according to the invention comprises a tank 110 intended to receive organic material M and a cover module 120 of said tank 110. In the preferred embodiment illustrated in FIGS. 1 to 3, the device 10 further comprises at least one armature 130 disposed at the bottom of the tank 110. a) Tank 110

In this nonlimiting example, the tank 110, or pit, comprises a body 110A and organic material inlet means M in said body 110A. The body 110A comprises a bottom 112 and at least one side wall 114 extending vertically from said bottom 112 and defining an opening 116 at its upper portion 110A-1. The body 110A can for example be buried in the ground and be made of concrete or geotextile or any other suitable material.

The inlet means make it possible to introduce the organic materials M inside the tank 110. Preferably, these inlet means are in the form of an inlet duct 118 opening into the interior of the tank. body 110A at its lower portion 110A-2. By the terms "lower", "upper" is meant as shown in Figure 1, that is to say for a device 10 in position of use.

In the example illustrated in Figures 1 and 3, the body 110A has a cylindrical shape of circular section of diameter DI and has a single side wall 114. In the example of Figure 4, the body 110A has a parallelepiped shape and has four side walls 114. b) Coverage module 120

The cover module 120 is intended to rest on the organic material M contained in the tank 110. For the sake of clarity, the organic materials, referenced M in Figure 1, have not been shown in the figures (only the surface S organic matter M has been materialized). With reference to FIGS. 1 and 2, the cover module 120 is configured to cover the opening 116 of the tank 110 so as to conform to the shape of the wall or walls 114 of the tank 110 while allowing the formation of a space internal 123 biogas collection. Note that the shape of the cover module 120 is defined by the shape of the tank 110. It is thus circular in the example of Figures 1 to 3 and rectangular (not shown) in the case of the tank 110 illustrated in Figure 4. The cover module 120 of the tank 110 comprises a covering member 122, a central flotation unit 124, a peripheral flotation unit 126 and biogas outlet means. The covering element 122 extends into the opening 116 delimited by the wall or walls 114 of the tank 110. The covering element 122 is in the form of a capital and has a frustoconical section allowing, with the unit 124, to arrange an internal space 123 above the organic material M to collect the biogas. The covering element 122 comprises a flexible bottom wall 122A, connected to the peripheral flotation unit 126, and a flexible or rigid top wall 122B connected to the central portion 122A-1 of the bottom wall 122A. A plurality of orifices 122A-2 are formed in the central portion 122A-1 of the bottom wall 122A to guide and discharge the biogas produced by fermentation of organic matter M or by recirculation to a guide space 127 formed between the lower wall 122A and the upper wall 122B. The covering element 122 is configured to receive a volume of water called surface water E on the outer face 122A-3 of its bottom wall 122A. The mass of these surface waters E exerts a pressure which makes it possible both to ensure that the covering element 122 firmly bears on the organic materials M contained in the tank 110 and that the peripheral flotation unit 126 the covering or wall 114 of the tank 110. The covering element 122 may for example be made of polypropylene material or a thermally insulating material such as a thin insulator, for example ISOL CARGO® type, ISOL CONTENEUR® or TRISO SUPER 12. The central flotation unit 124 rests on the surface S of the organic material M contained in the tank 110 and is configured to support the covering element 122 at the central portion 122A-1 in order to hold it above organic matter M and thus form the internal space 123 for collecting biogas. This internal space 123 makes it possible to guide the biogas resulting from the methanization of the organic materials M towards the plurality of orifices 122A-2 formed in the central portion 122A-1 of the bottom wall 122A of the covering element 122. By the terms " "internal" and "external" means in relation to the inside or the outside of the tank 110. The central flotation unit 124 may comprise a single central float, for example annular, or, as illustrated in FIGS. Figures 1 and 3, a plurality of central floats, for example of parallelepiped shape. This or these floats can be inflated with a gas such as air or made of polystyrene or any material adapted to float on the organic material M and form the inner space 123.

Still with reference to FIG. 1, the peripheral flotation unit 126 is fixed to the inner face 122A-4 of the bottom wall 122A of the covering element 122. The peripheral flotation unit 126 matches the shape of the one or more 114 walls of the tank 110 to allow the methanization of organic materials M.

To do this, the peripheral flotation unit 126 comprises a weighted skirt 126A, fixed on its entire periphery, for pressing the peripheral flotation unit 126 against the inner face 114-1 of the side wall 114 of tank 110. In this non-limiting example, the weighted skirt 126A is made of a plastic material and comprises at its lower part a sleeve 126A-1 in which is inserted a mass 126A-2 which is, for example, in the form of 'a stainless steel tube. The peripheral flotation unit 126 holds the cover member 122 on the surface S of the organic material M while allowing both its vertical displacement in a sealed manner along the wall or walls 114 of the tank 110 when the volume of material organic M varies, in particular thanks to the weighted skirt 126A. The peripheral flotation unit 126 also allows the retention of the surface water E on the outer face 122A-3 of the covering element 122. For this purpose, the peripheral flotation unit 126 is sealed on the whole surface. the periphery of the covering member 122 and has a thickness greater than that of the covering member 122 so as to form a peripheral water surface retention edge E. The peripheral flotation unit 126 may be an annular peripheral float buoy type, hollow or full, for example inflated with a gas such as air or made of plastic, polystyrene or any suitable material. In this preferred example, the peripheral flotation unit 126 is in the form of a ring fixed at its lower part to the bottom wall 122A of the covering element 122.

The output means of the biogas are in this example in the form of an outlet duct 128 fixed to the upper part 122B of the covering element 122, the latter being perforated at its center to allow the biogas to flow through said outlet duct 128. c) Armature 130

In this nonlimiting example, the armature 130 allows in particular the support of a set of heating pipes and a set of biogas diffusion pipes as will be described hereinafter with reference to FIGS. 3 and 4, such support for making easy the insertion of new organic material M in the tank 110 via the inlet duct 118. The frame 130 also allows to support the cover module when there is little or no material organic M in the tank 110 to prevent it from extending on the bottom 112 of the tank. In the embodiment illustrated in FIGS. 1 and 3, the device 10 comprises an armature 130 and in the embodiment illustrated in FIG. 4, the device 10 comprises two armatures 130. In these examples, the armature (s) 130 comprise feet that allow an elevation so that the inlet conduit 118 M organic material opens under the set of heating pipes and / or set of biogas pipes diffusion. It goes without saying that, in other embodiments, the device 10 may not comprise armature 130 or comprise more than two armatures 130. When at least one armature 130 is present, it can be used to both to support a set of heating pipes or a set of biogas pipes or both. 2) Insertion module for organic materials 20

The organic material insertion module M is configured to circulate the organic materials M to the inlet conduit 118 so that they enter the interior of the tank 110. For this purpose and in this example, the insertion module 20 is in the form of an injection pump organic material M in the tank 110 via the inlet conduit 118. Note that the pump could optionally be used reversibly to empty the tank 110 via the inlet duct 118. 3) Extraction module for organic matter 30

The extraction module 30 of the organic matter M makes it possible to completely or partially empty the tank 110. For this purpose, the extraction module 30 comprises an extraction duct 310 passing through the bottom 112 of the tank 110 and a pump 320 for extracting or aspirating the organic material M from the inside to the outside of the tank 110, for example by a buried drainage pipe (not shown). Alternatively, the extraction duct 310 may be arranged in the tank 110 so as not to cross the bottom 112 (or the walls 114) of the tank 110 to avoid drilling. 4) Bioeaz recirculation module 40

The biogas recirculation module 40 makes it possible to reinject biogas produced by the tank 110 at the lower part 110A-2 of the tank 110 in order to improve the methanation process. Such a recirculation makes it possible to lower the temperature of the biogas by heat exchange with the organic matter M contained in the tank and allows an effective stirring thus avoiding the formation of crusts on the surface which would be detrimental to the rise of the biogas.

To do this, the recirculation module 40 comprises in this example a biogas recirculation pump 410 connected, on the one hand, to the outlet duct 128 of the cover module 110 and, on the other hand, via an injection duct 420 of the biogas, to a set of biogas diffusion piping 430 mounted on the frame 130 and in which are formed orifices for diffusing the biogas in the organic matter M. It will be noted that advantageously, the set of piping of The diffusion of biogas 430 can itself constitute all or part of the reinforcement 130. The injection of the biogas can be done by bubble diffusers or by one or more Venturi diffusers placed at the outlet of a dilacerator pump making it possible to diffuse bubbles in a laminar flow of slurry. 5) Regulation module for surface water level 50

Still with reference to FIG. 1, the regulation module 50 makes it possible to regulate the level of the surface waters E lying on the outer face 122A-3 of the covering element 122. Such a regulation can consist in taking up part of the surface E to maintain their level below the peripheral flotation unit 126 so that the surface water E does not overflow the covering element 122 on organic matter, which keeps the organic material M sufficiently dry to allow spreading on agricultural crops. Such a regulation may also consist of pouring water or any suitable liquid on the roofing module 120 when part of the surface water E has evaporated or has been taken to water agricultural crops. For this purpose, the regulation module 50 can be connected to a reservoir or a water distribution network. 6) bioeaz 60 storage module

The biogas storage module 60 may for example be in the form of a gasometer and can store the biogas produced by the tank 110 and conveyed via the outlet conduit 128. 7) Heating module 70

The heating module 70 is used to heat the organic matter M contained in the tank 110 to accelerate their methanation. The heating module 70 of the organic materials M comprises a heat generator (not shown) preferably placed outside the tank 110 and at least one heating pipe assembly 710 connected to the heat generator and mounted at least in part. on the armature (s) 130. The heating pipe assembly 710 may allow the circulation of a heating liquid or may consist of metal resistors. It will be noted that, advantageously, the set of heating pipes 710 may itself constitute all or part of the armature 130. In the example illustrated in FIGS. 1 and 3, the heating pipe assembly 710 is mounted on the armature 130 and also extends at least in part along the wall 114 of the tank 110. In the example illustrated in Figure 4, two sets of heating piping 710 are used, each of these two assemblies 710 being mounted on a frame 130 and also extending at least partly along the wall 114 of the tank 110. The invention will now be described in its implementation. II. Implementation of the invention

First, when the tank 110 is empty, the cover module 120 rests on the heating pipe assembly 710 and the set of biogas diffusion pipes 430 mounted on the frame 130 disposed on the bottom 112 of the body 110A of the tank 110. The introduction F1 of organic matter M inside the tank 110 is carried out by the pump of the insertion module 20 via the inlet duct 118. Water, or any liquid adapted, can be placed on the outer face 122A-3 of the covering member 122 so as to exert a force for pressing the peripheral flotation unit 126 against both the inner face 114-1 of the side wall 114 of the 110A body and organic matter contained in the tank 110, thus sealing the device 10 sufficiently to allow methanization of organic matter M.

As the organic materials M fill the tank 110, they move with them the cover module 120 upwards, in particular via the central flotation unit 124, the peripheral flotation unit 126 remaining pressed against the inner face 114-1 of the side wall 114 so as to allow the continuation of methanation. The biogas produced during methanization of the organic matter M is then guided F2 to the bottom wall 122A and passes through the plurality of orifices 122A-2 to the guide space 127 and the outlet conduit 128 which routes it F3 then to the storage module 60 (F4) and / or the recirculation module 40 (F5) which routes it via the injection conduit 420 to the set of biogas diffusion pipes 430 which diffuses it F6 in the organic materials M to allow agitation and thus improve the methanation process.

In operation of the device 10, the regulation module 50 of the level of the surface water E acts to maintain said level constant. In other words, when the volume and therefore the water level E on the surface of the covering element 122 increases, for example with rain, when the device 10 is placed outside, the regulation module 50 pumps a part surface water E to prevent the weight of water E from deforming the covering element 122 and overflow on organic matter M. Similarly, when the volume and therefore the level of water E on the surface of the covering element 122 decreases, for example by evaporation, the control module 50 discharges water on the covering element 122 in order to maintain the level of the surface water E at its useful level.

When the volume of the organic material M varies, for example during an insertion via the insertion module 20 or a drain via the extraction module 30, the cover module 120 moves vertically with the organic material M.

Finally, it should be noted that the present invention is not limited to the examples described above and is capable of numerous variants accessible to those skilled in the art. In particular, the shape and dimensions of the device 10, in particular of the tank 110, the cover module 120 and the armature 130, the extraction module 20, the extraction module 30, the recirculation module 40, the Regulator module 50, biogas storage module 60 and heating module 70 as shown in the figures so as to illustrate an embodiment of the invention and the materials used can not be interpreted as limiting.

Claims (10)

1. Covering module (120) of an anaerobic digestion tank (110), said tank (110) being adapted to receive organic material (M) and comprising a bottom (112) and at least one wall (114) vertical portion defining an aperture (116), said cover module (120) comprising a cover member (122) configured to extend into said aperture (116), a central buoyancy unit (124) arranged on one hand to support the covering element (122) at its central portion and secondly to rest on organic matter (M) contained in the vessel (110), and a peripheral flotation unit (126) connected to the covering element (122) and configured both to maintain it above the organic material (M) and to move vertically sealingly along the wall (114) of the tank (110) with the organic material (M). The covering module (120) according to claim 1, wherein the covering member (122) comprises a flexible bottom wall (122A) connected to the peripheral buoyancy unit (126) and in which a plurality of orifices (122A-2) for discharging the biogas produced by the organic materials (M), and an upper wall (122B) attached to the bottom wall (122A) at its central portion (122A-1). 3. Covering module (120) according to one of claims 1 and 2, wherein the peripheral flotation unit (126) is attached to the bottom wall (122A) over its entire periphery. 4. Covering module (120) according to one of claims 1 to 3, wherein the peripheral flotation unit (126) is in the form of an annular buoy. The covering module (120) according to one of claims 1 to 4, wherein the peripheral flotation unit (126) comprises a weighted skirt (126A) fixed on its periphery to press the peripheral flotation unit ( 126) against the wall (114) of the tank (110) and thus ensure its vertical displacement sealingly along the wall (114) of the tank (110) with the organic material. 6. Cover module (120) according to one of claims 1 to 5, wherein the central flotation unit (124) is a single central float. Cover module (120) according to one of claims 1 to 5, the central flotation unit (124) comprises a plurality of central floats. 8. A methanation device (10) comprising a tank (110) and a cover module (120) according to one of claims 1 to 7, said tank (110) being adapted to receive organic material (M) and comprising a bottom (112) and at least one wall (114) defining an opening (116), said cover module (120) being disposed in the vessel (110) so as to extend into said opening (116). 9. An anaerobic digestion system (1) comprising a methanation device (10) according to claim 8, a module (20) for the insertion of organic matter (M) into the tank (110) and a heating module (70). organic material (M) disposed at least partly in the vessel (110). 10. System (1) according to claim 9, comprising a module (40) for recirculating the biogas produced by the device (10) in the tank (110).