FR3093731A1 - Cover module, methanization device and system - Google Patents

Abstract

The invention relates to a cover module (120) for a methanization tank (110), said tank (110) being adapted to receive organic materials (M) and comprising a bottom (112) and at least one wall (114). ) vertical delimiting an opening (116), said cover module (120) comprising a covering element (122) configured to extend into said opening (116) and a peripheral flotation unit (126) connected to the covering element ( 122) and configured both to hold it above the organics (M) and to move vertically in a sealed manner along the wall (114) of the vessel (110) with the organics (M). Figure for the abstract: figure 1

Description

Cover module, device and biogas system

The present invention relates to the field of methanization and more particularly relates to a cover module for a methanization tank. The cover module according to the invention allows in particular the capture of biogas resulting from the transformation of the fermentable fraction of slurry type livestock effluents into biogas.

State of the art

The methanization of organic matter is a known natural process that makes it possible to transform organic matter, in particular agricultural matter, into biogas. Methanation is carried out by biological degradation of organic matter by a microbial consortium including bacteria. It is thus known to transform into biogas the fermentable fraction of livestock effluents producing slurry such as, for example, bovine, waterfowl, porcine slurry, etc., by disposing these effluents in a slurry pit laid out in the ground.

In order to make the pit at least partly watertight and to improve the efficiency of the methanization, it is known to cover it with a flexible tarpaulin. However, such a solution does not capture the biogas resulting from the transformation of the fermentable fraction of livestock manure. Also, when one wishes 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 known manner, a tank called a digester, in which the effluents are placed, and a device for collecting biogas. In a first type of methanizer, the tank is cylindrical in shape, for example made of metal. The effluents are routed inside the tank through an inlet pipe connected to one end of the tank and the biogas collection device is in the form of an outlet pipe connected to the other end of the tank. In a second type of methanizer, the tank is buried in the ground, the effluents are conveyed inside the tank by an inlet pipe, connected for example to the base of the tank, and the biogas collection device comes 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 cover mounted on a support frame and to which is connected a biogas outlet conduit. The tarpaulin support frame comprises a plurality of metal posts fixed directly to the tank. In another solution, described in patent application WO9828402A1, the cover module comprises a central post supporting a cover stretched so as to form a pyramid allowing the biogas to be guided towards the post where it is collected via a plurality of orifices and of pipes.

Such solutions are complex and expensive to manufacture and assemble, which has significant drawbacks. In addition, in these solutions, the interior space of the tank is fixed so that the efficiency of 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 effluent is such that the methanization is slow and inefficient, which has a significant drawback. In addition, in such solutions, rainwater is either evacuated and therefore cannot be reused, or flows 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 pit into a methaniser by installing a cover module can generate mechanical stresses on the tank which were not foreseen during its design and de facto lead to cracks in the concrete, which has a major drawback.

The invention aims to solve these drawbacks at least in part 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 a pit. existing slurry, in order to capture the biogas produced by the transformation of the fermentable fraction of livestock effluents.

To this end, the invention firstly relates to a cover module for a methanation tank, said tank being adapted to receive organic matter and comprising a bottom and at least one vertical wall delimiting an opening, said module covering comprising a covering element configured to extend into said opening, a central buoyancy unit, arranged on the one hand to support the covering element at its central portion and on the other hand to rest on contained organic matter in the tank, and a peripheral flotation unit connected to the covering element and configured both to hold it above the organic materials and to move vertically in a sealed manner along the wall of the tank with the organic materials .

By the terms "moving in a sealed manner along the wall of the tank with the organic matter", it is meant that the peripheral flotation unit, which rests on the organic matter, remains pressed against the wall even when the volume of 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 cover module according to the invention makes it possible to capture the biogas produced by the transformation of the fermentable fraction of organic matter such as livestock effluents. Such a cover module turns out to be simple and inexpensive to manufacture and assemble since it rests on organic matter and is not fixed to the wall of the tank. In addition, since the cover module moves vertically with the organic matter, the interior space of the tank varies and adapts to the volume of organic matter, which improves the efficiency of the anaerobic digestion. Such a cover module is also easy to adapt to any type of pit or liquid storage tank, in particular circular or rectangular, of the buried pit type made of concrete, metal or a geotextile material, for example of the EPDM type. The cover module according to the invention can thus advantageously be used with an existing slurry pit 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 matter, a space sufficient to capture the biogas but limited to allow the methanization of the organic matter. The peripheral flotation unit ensures good coverage of 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 one characteristic of the invention, the covering element comprises a flexible lower wall, connected to the peripheral flotation unit and in which is formed a plurality of evacuation orifices for the biogas produced by the organic matter, and a wall upper fixed to the lower wall at its central part. The lower 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 the level of its central part .

Preferably, the cover module is arranged to retain rainwater in order to prevent it from mixing with organic matter, such separation having the advantage of reducing time and therefore spreading costs. This reduces spreading costs by capturing a large volume of rainwater.

To this end, the peripheral flotation unit may have a greater thickness than that of the covering element so as to form a peripheral edge for retaining rainwater. Such storage of rainwater makes it possible to reuse it, for example to water crops, and prevents it from flowing into the tank and soaking organic matter.

Preferably, the peripheral flotation unit is fixed to the lower wall over its entire periphery in order to ensure the proper sealing of their connection.

Advantageously, the peripheral flotation unit is positioned and fixed on the lower wall so as to hold it on the organic matter.

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

Advantageously, the weighted skirt comprises a sheath, fixed to the periphery of the peripheral flotation unit, in which is inserted a mass which is presented, for example, in the form of a stainless steel tube, preferably matching the shapes of the wall of the tank.

Advantageously, the peripheral flotation unit is in the form of an annular buoy making it possible to match the shape of a cylindrical tank of circular section.

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

In another embodiment, the central buoyancy unit comprises a plurality of central floats, for example gas-filled or made of polystyrene, in order to hold the covering element solidly 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 a methanization device comprising a tank and a cover module as presented above, said tank being adapted to receive organic matter and comprising a bottom and at least one wall delimiting an opening, said cover module being arranged in the tank so as to extend into said opening.

Preferably, the device comprises a frame placed at the bottom of the tank.

The invention finally relates to a methanization system comprising a methanization device as presented above and a module for inserting organic matter into the tank.

Preferably, the system comprises a module for heating organic materials, placed 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 in part at the bottom of the tank and/or on the wall of the tank.

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

Preferably again, the system comprises a module for recirculating the biogas, produced by the device, in the tank, the biogas then being preferably injected at the level of 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 in part at the bottom of the tank and/or on the wall of the tank.

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

According to one characteristic of the invention, the system comprises an organic matter extraction module.

Advantageously, the system comprises a surface water level regulation module. Such a module makes it possible to ensure that the volume of rainwater is both sufficient to allow movement by gravity in a sealed manner of the cover module along the wall(s) of the tank and limited to prevent the 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 methanation of organic matter in the tank in order to reuse it later.

Other characteristics and advantages of the invention will appear during the description which follows given with regard to the appended figures given by way of non-limiting examples and in which identical references are given to similar objects.

Description of figures

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

Figure 2 is a partial schematic perspective view, from above, of the methanization device of Figure 1.

Figure 3 is a partial schematic view from above and in perspective of the tank of the device of Figure 1 without a 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 a cover module.
Detailed description of at least one embodiment

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 rainwater in order to prevent it from mixing with said organic matter. Organic materials can be livestock effluents such as cattle, waterfowl, pig slurry, or any other organic material of which a fermentable fraction is capable of being transformed into biogas.

System 1

Referring to Figure 1, the system 1 according to the invention comprises a methanization device 10 and an insertion module 20 of organic matter M.

In the preferred embodiment illustrated in FIG. 1, the system 1 also 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.

Device 10

The methanization device 10 according to the invention comprises a tank 110 intended to receive organic materials 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 reinforcement 130 arranged at the bottom of the tank 110.

Tank 110

In this non-limiting example, the tank 110, or pit, comprises a body 110A and means for inlet of the organic matter M into said body 110A. The body 110A comprises a bottom 112 and at least one side wall 114 extending vertically from said bottom 112 and delimiting an opening 116 at its upper part 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 allow the organic materials M to enter inside the tank 110. Preferably, these inlet means are in the form of an inlet duct 118 opening inside the body 110A at its lower part 110A-2. By the terms “lower”, “upper”, is meant as represented in FIG. 1, that is to say for a device 10 in the position of use.

In the example illustrated in Figures 1 and 3, the body 110A has a cylindrical shape with a circular section of diameter D1 and has a single side wall 114. In the example of Figure 4, the body 110A has a parallelepipedal shape and has four side walls 114 .

Cover module 120

The cover module 120 is intended to rest on the organic materials M contained in the tank 110. For the sake of clarity, the organic materials, referenced M in FIG. 1, have not been shown in the figures (only the surface S organic matter M has materialized). Referring to Figures 1 and 2, the cover module 120 is configured to cover the opening 116 of the tank 110 so as to match 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 FIG. 4. The covering module 120 of the tank 110 comprises a covering element 122, a central flotation unit 124, a peripheral flotation unit 126 and biogas outlet means.

The covering element 122 extends in 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 central flotation 124, to arrange an internal space 123 above the organic matter M to collect the biogas. The covering element 122 comprises a flexible lower wall 122A, connected to the peripheral buoyancy unit 126, and an upper wall 122B, flexible or rigid, connected to the central part 122A-1 of the lower wall 122A. A plurality of orifices 122A-2 is formed in the central part 122A-1 of the lower wall 122A in order to guide and evacuate the biogas produced by fermentation of the organic matter M or by recirculation towards a guide space 127 formed between the bottom wall 122A and top wall 122B. The covering element 122 is configured to receive a volume of water called surface water E on the external face 122A-3 of its lower wall 122A. The mass of these surface waters E exerts a pressure which makes it possible to ensure both that the covering element 122 comes to rest firmly on the organic matter M contained in the tank 110 and that the peripheral flotation unit 126 marries the wall or walls 114 of the tank 110. The covering element 122 can for example be made of polypropylene material or of a thermally insulating material such as a thin insulator, for example of the ISOL CARGO®, ISOL CONTENEUR® or TRISO type. SUPER 12.

The central flotation unit 124 rests on the surface S of the organic materials M contained in the tank 110 and is configured to support the covering element 122 at the level of the central part 122A-1 in order to maintain it above the organic materials M and thus form the internal space 123 for collecting the biogas. This internal space 123 makes it possible to guide the biogas resulting from the methanation of the organic materials M towards the plurality of orifices 122A-2 formed in the central part 122A-1 of the lower wall 122A of the covering element 122. By the terms “ "internal" and "external" means relative to the interior or exterior of the tank 110. The central flotation unit 124 may comprise a single central float, for example annular, or else, as illustrated in the Figures 1 and 3, a plurality of central floats, for example of parallelepipedal shape. This or these floats can be inflated using a gas such as air or else made of polystyrene or any material suitable for floating on the organic materials M and forming the internal space 123.

Still with reference to FIG. 1, the peripheral flotation unit 126 is fixed to the internal face 122A-4 of the lower wall 122A of the covering element 122. The peripheral flotation unit 126 conforms to the shape of the walls 114 of the tank 110 in order to allow the methanization of the organic matter M.

To do this, the peripheral flotation unit 126 comprises a weighted skirt 126A, fixed over its entire periphery, making it possible to press the peripheral flotation unit 126 against the internal face 114-1 of the side wall 114 of the tank. 110. In this non-limiting example, the weighted skirt 126A is made of a plastic material and comprises at its lower part a sheath 126A-1 in which is inserted a mass 126A-2 which is presented, for example, in the form of a stainless steel tube.

The peripheral flotation unit 126 maintains the covering element 122 on the surface S of the organic materials M while at the same time allowing its vertical displacement in a sealed manner along the wall(s) 114 of the tank 110 when the volume of materials organic M varies, in particular thanks to the weighted skirt 126A.

The peripheral flotation unit 126 also allows the retention of surface water E on the outer face 122A-3 of the covering element 122. To this end, the peripheral flotation unit 126 is fixed in a sealed manner on the entire from the periphery of the covering element 122 and has a thickness greater than that of the covering element 122 so as to form a peripheral edge for retaining surface water E.

The peripheral flotation unit 126 can be an annular peripheral float of the buoy type, hollow or solid, for example inflated with a gas such as air or made of plastic material, polystyrene or any suitable material. In this preferred example, peripheral flotation unit 126 is in the form of a ring attached at its bottom to bottom wall 122A of covering member 122.

The biogas outlet means are in this example in the form of an outlet pipe 128 fixed to the upper part 122B of the covering element 122, the latter being perforated at its center to allow the biogas to circulate through it. said outlet duct 128.

Frame 130

In this non-limiting example, the frame 130 allows in particular the support of a set of heating pipes and a set of biogas diffusion pipes as will be described below with reference to Figures 3 and 4, such support making it easy to insert new organic materials M into the tank 110 via the inlet duct 118. The reinforcement 130 also makes it possible to support the cover module when there are no or few materials organic M in the tank 110 to prevent it from spreading on the bottom 112 of the tank. In the embodiment illustrated in Figures 1 and 3, the device 10 comprises an armature 130 and in the embodiment illustrated in Figure 4, the device 10 comprises two armatures 130. In these examples, the armature(s) 130 comprise feet which allow an elevation so that the inlet duct 118 of the organic matter M emerges under the set of heating pipes and/or the set of biogas diffusion pipes. It goes without saying that, in other embodiments, the device 10 could comprise no frame 130 or comprise more than two frames 130. When at least one frame 130 is present, this can be used both to support a set of heating pipes or a set of biogas diffusion pipes or both.

Organic material insertion module 20

The module 20 for inserting the organic materials M is configured to cause the organic materials M to circulate as far as the inlet duct 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 a pump for injecting organic materials M into the tank 110 via the inlet pipe 118. It will be noted that the pump could optionally be used reversibly to empty the tank 110 via inlet conduit 118.

Organic material extraction module 30

The extraction module 30 of the organic materials M makes it possible to carry out all or part of the emptying of the tank 110. To this end, the extraction module 30 comprises an extraction conduit 310 passing through the bottom 112 of the tank 110 and a pump 320 making it possible to extract or suck the organic materials M from the inside towards the outside of the tank 110, for example via a buried evacuation pipe (not shown). As a variant, the extraction duct 310 can be arranged in the tank 110 so as not to cross the bottom 112 (or the walls 114) of the tank 110 to avoid piercing it.

Biogas recirculation module 40

The biogas recirculation module 40 makes it possible to reinject the biogas produced by the tank 110 at the level of the lower part 110A-2 of the tank 110 in order to improve the methanation process. Such 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 effective agitation, 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 conduit 128 of the cover module 110 and, on the other hand, via an injection conduit 420 of the biogas, to a set of biogas diffusion pipes 430 mounted on the frame 130 and in which are formed orifices making it possible to diffuse the biogas in the organic matter M. It will be noted that advantageously, the set of pipes for diffusion of biogas 430 can itself constitute all or part of the armature 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 grinder pump making it possible to diffuse bubbles in a laminar flow of slurry.

Surface Water Level Control Module 50

Still with reference to FIG. 1, the regulation module 50 makes it possible to regulate the level of surface water E resting on the outer face 122A-3 of the covering element 122. Such regulation may consist in taking part of the water from surface E to maintain their level below the peripheral buoyancy unit 126 so that the surface waters E do not overflow the covering member 122 onto the organic matter, thereby keeping the organic matter M sufficiently dry to allow spreading on agricultural crops. Such regulation can also consist of pouring water or any suitable liquid onto the cover module 120 when part of the surface water E has evaporated or has been taken off to water agricultural crops. To this end, the regulation module 50 can be connected to a reservoir or to a water distribution network.

Biogas storage module 60

The biogas storage module 60 can for example take the form of a gas holder and makes it possible to store the biogas produced by the tank 110 and routed via the outlet conduit 128.

Heating module 70

The heating module 70 makes it possible to heat the organic materials M contained in the tank 110 in order to accelerate their methanization. The heating module 70 for the organic materials M comprises a heat generator (not shown) preferably placed outside the tank 110 and at least one set of heating pipes 710 connected to the heat generator and mounted at least partially on the reinforcement(s) 130. The set of heating pipes 710 can allow the circulation of a heating liquid or else be made up of metal resistors. It will be noted that advantageously, the set of heating pipes 710 can itself constitute all or part of the armature 130. In the example illustrated in FIGS. 1 and 3, the set of heating pipes 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 FIG. 4, two sets of heating pipes 710 are used, each of these two sets 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.

Implementation of the invention

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

As the organic materials M fill the tank 110, they move the cover module 120 upwards with them, in particular via the central flotation unit 124, the peripheral flotation unit 126 remaining pressed against the internal face 114-1 of the side wall 114 so as to allow the continuation of the methanation. The biogas produced during the methanization of the organic matter M is then guided F2 towards the lower wall 122A and passes through the plurality of orifices 122A-2 to the guide space 127 then to the outlet duct 128 which carries it F3 then to the storage module 60 (F4) and/or to 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 organic materials M in order to allow agitation and thus improve the methanization process.

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

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

Finally, it should be noted that the present invention is not limited to the examples described above and is susceptible to 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, of the cover module 120 and of the frame 130, of the extraction module 20, of the extraction module 30, of the recirculation module 40, of the regulation module 50, the biogas storage module 60 and the heating module 70 as shown in the figures so as to illustrate an embodiment of the invention as well as the materials used cannot be interpreted as limiting.

Claims (10)

Cover module (120) of a biogas tank (110), said tank (110) being suitable for receiving organic materials (M) and comprising a bottom (112) and at least one vertical wall (114) delimiting an opening (116), said cover module (120) comprising a cover member (122) configured to extend into said opening (116) and a peripheral flotation unit in the form of a ring buoy (126) connected to the covering element (122) and configured both to hold it above the organic materials (M) and to move vertically in a sealed manner along the wall (114) of the tank (110) with the organic materials (M). Cover module (120) according to claim 1, in which the covering element (122) comprises a flexible lower wall (122A), connected to the peripheral buoyancy unit (126) and in which is formed a plurality of openings (122A-2) for evacuating the biogas produced by the organic matter (M), and an upper wall (122B) fixed to the lower wall (122A) at its central part (122A-1). Cover module (120) according to one of Claims 1 and 2, in which the peripheral flotation unit (126) is fixed to the bottom wall (122A) over its entire periphery. Cover module (120) according to one of Claims 1 to 3, in which the peripheral flotation unit (126) comprises a weighted skirt (126A) fixed around its periphery, preferably over its entire periphery, in order to to press the peripheral flotation unit (126) against the wall (114) of the tank (110) and thus to ensure its vertical displacement in a sealed manner along the wall (114) of the tank (110) with the organic materials. Cover module (120) according to the preceding claim, in which the weighted skirt (126A) comprises a sheath, fixed to the periphery of the peripheral flotation unit (126), in which a mass is inserted. Covering module (120) according to one of Claims 1 to 5, comprising a central flotation unit (124), arranged on the one hand to support the covering element (122) at the level of its central portion and on the other leaves to rest on organic matter (M) contained in the tank (110). A cover module (120) according to the preceding claim, wherein the central flotation unit (124) comprises a single central float or a plurality of central floats. Methanization 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 materials (M) and comprising a bottom ( 112) and at least one wall (114) delimiting an opening (116), said cover module (120) being arranged in the tank (110) so as to extend into said opening (116). Methanization system (1) comprising a methanization device (10) according to claim 8, a module (20) for inserting organic materials (M) into the tank (110) and a heating module (70) for the organic materials (M) arranged at least partly in the tank (110). System (1) according to claim 9, comprising a module (40) for recirculating the biogas, produced by the device (10), in the tank (110).