OA18461A - Methanization device from solid biomass and corresponding biogas production process - Google Patents

Abstract

The present invention relates to an anaerobic digestion digester 7, intended for the production of biogas 25, comprising a tank 8, able to contain solid biomass 23, comprising at its upper part: at least one zone 9 for admitting the gas. solid biomass 23 and discharge of the residual digested solid biomass 19, on which a roof 10 is able to open and close, and at least one zone 9 'for discharging the biogas 25. The invention also relates to a process for producing biogas as well as a methanization installation implementing a main digestion unit 1 intended in particular to supply liquid digestate 5 to one or more methanization digesters 7 containing solid biomass 23, and to receive and store the biogas produced by the anaerobic digester (s) 7.

Description

Methanization device from solid biomass and corresponding biogas production process

The present invention relates to a methanization digester intended for the production of biogas comprising, at the level of the digester roof, a space for the introduction and evacuation of solid biomass.

The invention also relates to a process for the production of biogas as well as to an anaerobic digestion plant implementing a main digestion unit intended in particular to supply liquid digestate to several methanization digesters containing solid biomass.

For the purposes of the present invention, the term “solid biomass” is understood to mean organic materials of plant, animal, bacteriological or fungal origin, containing a level of dry matter greater than 12%, preferably greater than 15%, which allow the production of biogas.

The solid biomass can be fibrous, in particular straw, and / or heterogeneous, and / or contain undesirable elements, in particular pebbles, gravel, sand, barbed wire, twine, metal parts from agricultural tools or even plastic bags, packaging and packaging elements, or even urban waste, possibly poorly sorted.

Methanization (also called anaerobic digestion) is a natural biological process that involves the degradation of organic matter by several types of microorganisms, in particular bacteria, under controlled conditions and in the absence of oxygen.

Such a process leads, on the one hand, to the production of biogas, which corresponds to a gaseous mixture composed mainly of methane and carbon dioxide, and, on the other hand, to the production of a wet product rich in materials. partially stabilized organics called digestate, which can then be used as an organic amendment.

Biogas has the advantage of being a convertible gas into renewable energy and can, for example, be used in the production of electricity and / or heat or in the production of fuel. The biogas can also be injected into a natural gas network after purification.

The digestate can undergo a liquid / sotide phase separation treatment in which the solid fraction (called solid digestate) is richer in organic matter and phosphate elements and the liquid fraction (called liquid digestate) is richer in ammoniacal nitrogen and potassium . Liquid and solid digestates can be stored, and / or processed and / or applied separately.

Thus, the biological anaerobic digestion process makes it possible to recover organic materials, by producing renewable energy, and to reduce greenhouse gas emissions, by capturing the methane resulting from the degradation of these materials, and by replacing the use of 'fossil fuels and / or chemical fertilizers.

The organic materials, likely to produce biogas through anaerobic digestion, can be waste, for example from the agricultural and / or agro-industrial sector and / or be of urban origin. In particular, manure, from livestock farms, is an organic matter, derived from animal waste mixed with straw from litter, which is a major and particularly interesting source in the production of biogas. In this regard, anaerobic digestion in the agricultural sector from organic matter, in particular straw and / or manure, represents an activity that is developing more and more today.

Methanization is commonly carried out inside a reactor called a digester, most often corresponding to a tank, having a shape most often essentially cylindrical, but sometimes parallelepiped, vertical or horizontal, which is intended to contain organic matter. to be treated, in particular manure and / or straw and / or industrial waste, in order to produce biogas and digestate.

The different anaerobic digestion processes can be divided into two large families depending on the nature of the waste to be degraded, namely liquid methanization processes and dry methanization processes.

First, the liquid methanization process is generally implemented to treat waste whose mixture has an average dry matter content of less than 15%, corresponding for example to mixtures of liquid bucks or fats or mixtures. mainly composed of slurry. Such a process can also be used to treat solid organic material which has been mixed with water or liquid digestate.

The liquid methanization process consists in particular in conveying in a generally continuous manner the organic matter to be treated, most often by means of pumping systems or endless screws inside a digester which is generally hermetically closed by the 'intermediate a roof or a flexible membrane. The organic matter to be treated is continuously stirred inside the digester, often by one or more stirrers, which can be with propellers or blades, or sometimes by injections of gas, in particular of biogas, in order to avoid settling phenomena. biomass at the bottom of the digester and / or the phenomena of flotation and crusting of the biomass at the surface of the liquid in the digester, and to promote the formation of biogas and contact with micro-organisms. The digester can optionally be heated in temperatures between 20 and 60 ° C, in particular in temperatures between 35 and 55 ° C. The organic matter stays on average for several weeks in the digester, typically for a period ranging from 20 to 80 days.

The biogas produced during this anaerobic digestion reaction is generally stored at atmospheric pressure in a flexible waterproof membrane fixed above the digester. The membrane is then in the form of a dome containing a gas sky above the vertical wall of the digester. More rarely, the biogas can be stored in a gas meter, often a flexible storage bag located next to the digester.

This liquid methanization process has the particular drawback that the waste to be degraded can be difficult to handle and prepare for their transport to the digester and require a significant expenditure of energy to be stirred continuously inside the tank. digester.

In liquid methanization processes that include the introduction of solid organic materials, the solid organic materials are often crushed before being incorporated into the digestion tank in order to facilitate the flow of organic materials within the digester as well as their brewing. Sometimes solid organic material goes through a pre-sorting process to remove as many unwanted objects as possible.

This type of continuous liquid methanization process often presents difficulties in terms of feeding the biomass because it is often necessary to pre-treat the waste before its introduction into the digester, in particular by grinding the solid part of the biomass. and extracting unwanted material. In addition, the mixing system within the digester can be damaged due to the nature of organic matter or unwanted matter.

Secondly, the anaerobic digestion process, called by the dry route, is implemented to treat solid waste, the mixture of which has an average dry matter rate generally greater than 15%, in particular ranging from 15% to 40%, corresponding to example & manure, straw, industrial or urban waste, or heterogeneous biomass.

A first type of dry methanization process consists in continuously conveying, in particular by means of a hopper and an endless screw system, or more rarely a powerful pumping system, the solid organic materials to be treated. inside a digester, most often arranged horizontally. The solid organic materials to be treated are stirred, most often slowly, inside the digester which can also be heated at temperatures between 20 and 60 ° C, in particular at temperatures between 35 and 55 ° C.

In addition, solid organic materials are often crushed before being incorporated into the digestion tank to facilitate the flow of organic materials within the digester as well as their mixing. Sometimes solid organic materials are also pre-sorted to remove as many unwanted objects as possible.

This type of continuous dry methanization process often presents difficulties in terms of feeding the biomass because it is often necessary to pre-treat the waste before its introduction into the digester, in particular by grinding it and extracting the undesirable materials. . In addition, the mixing system within the digester can be damaged due to the nature of organic matter or unwanted matter.

A second type of dry methanization process is a batch process, or in sheets. It consists in conveying, often by means of mechanical loading / unloading devices, for example of the bucket loader type, the solid organic materials inside methanization cells which are closed once filled. These cells are generally kinds of garages equipped with doors that are closed once loading has been completed. The organic matter is then sprayed or sprayed with liquid digestate, loaded with bacteria, in order to achieve a percolation leading to your production of biogas. Once your reaction is complete, the doors of each cell are opened in order to recover the solid digestate, generally by means of the same mechanical devices as for the loading. Such a process generally uses several methanization cells or digesters, fed in tarpaulins one after the other. In this process, your cells are generally intended to function mostly at the same time even if they have been fed at different times. The biogas, produced during the anaerobic digestion reaction, is most often stored separately in a gasometer, often a flexible storage bag located next to the digesters.

This type of dry batch methanation process poses the problem of managing biogas, which may be released into the atmosphere during the periods of filling and emptying of the methanization cells. In addition, the anaerobic digestion reaction is not suitably optimized because the biomass, introduced into these cells, is not mixed and often preferential paths of circulation of the liquid digestate in the solid biomass are formed, preventing good diffusion of the digestate. liquid within the solid biomass to be treated, and therefore preventing intimate contact between the bacteria and the biomass, significantly reducing the rate of degradation of the solid biomass.

Thus, organic materials & to be treated often raise difficulties during the various methanization processes because they have the drawback of comprising many undesirable elements and / or of being difficult to handle and / or to grind.

In fact, straw as well as manure, or even heterogeneous biomass, can contain pebbles, gravel, sand, barbed wire, twine, metal parts from agricultural tools or even plastic bags, elements of 'wrapping or packaging. Such elements are often difficult to separate from the biomass to be treated and can therefore seriously damage the installations making up the methanization unit. For example, these undesirable elements can damage the pumps, the worms and your grinders, thus leading to the partial or total replacement of wearing parts and / or main parts at high frequencies, generating high maintenance costs. .

In addition, straw and straw products, such as manure, small straw, corn stalks, etc., are delicate & to handle because the straw is abrasive, which can damage, degrade or wear out the equipment used in the field. during the different stages of the anaerobic digestion process (stages of grinding, sorting, pumping, pressing and / or mixing).

Such damage is therefore likely to lead to a decrease in your biogas production, or even to stop it, and to induce losses of profits and / or an increase in the maintenance and operating costs of the installation. .

In addition, once introduced, the straw and straw products are often difficult to stir in the digester, because they tend to float and / or settle and / or get tangled, which generates a significant expenditure of energy , especially high power consumption. Such energy expenditure has a negative impact on the profitability of the installation.

Thus, manure, straw and straw products are organic materials that can prove difficult to recover for methanization.

In order to remedy some of these drawbacks, patent application FR 2 990 951 describes in particular a process for preparing an anaerobic digestion substrate from solid fibrous biomass, such as manure and straw, comprising a step of dilution of biomass in a liquid, in particular water or liquid digestate, a hydrolysis step and a step for separating the suspended solids from the liquid so as to prepare a methanization substrate. In particular, this method comprises a step of grinding the biomass before or after dilution, for example carried out using a grinding pump. The purpose of this process is to remove the undesirable elements from the solid fibrous biomass by settling and, consequently, to optimize the preparation of the methanization substrate before carrying it out into the digester.

However, the solid fibrous biomass still too often remains difficult to handle during this process. In fact, the straw is complicated to compress, which can cause clamping and blocking problems at the level of pumps and presses and / or separation means.

Such a method also has the disadvantage of incurring significant energy expenditure in order to properly maintain the straw in suspension in the liquid during the dilution step. Indeed, it is observed that the straw tends to tangle, to agglomerate, to float and not to mix easily in the liquid.

In addition, this method does not adequately solve the problem that arises during the mixing of the biomass in the digester. In fact, the straw is still too difficult to stir in the digester because the latter floats on the surface and becomes tangled, which leads to a phenomenon of accumulation and crusting which prevents in particular the good circulation of the biogas within the tank, which complicates its recovery, and which can lead to the complete solidification of the solid biomass present in the digester and the paralysis of the latter.

Thus the various methanization units implemented at the present time have a number of drawbacks when they have to treat all or part of the solid biomasses.

In view of the foregoing, the object of the invention is in particular to make more efficient use of solid biomass while minimizing energy expenditure, by reducing operating personnel costs, by making the purchase and production unnecessary. '' installation of certain equipment for preparing and stirring solid biomass, by reducing the risk of damage to the installations making up the anaerobic digestion unit and by reducing the costs of maintenance and preparation of solid biomass.

A subject of the present invention is therefore in particular a methanization digester, intended for the production of biogas, comprising a tank, capable of containing solid biomass, comprising at its upper part: at least one biomass inlet zone solid and evacuation of the residual digested solid biomass, on which a roof is able to open and close, and at least one biogas evacuation zone. Preferably, these areas are separated from each other.

The intake zone, located in particular on at least part of the upper surface of the tank on which the roof opens and closes, allows the incorporation of solid biomass inside the tank and the evacuation of the solid biomass once the digestion is complete, that is to say the solid digestate (also called residual digested solid biomass). The roof of the digester is thus removable. The inlet area for incorporating and discharging the solid biomass is preferably separate from the biogas discharge area.

The inlet zone therefore makes it possible to introduce the solid biomass directly into the digester without having to carry out an operation of separation of the undesirable elements or a prior dilution in a liquid or a grinding, which makes it possible to reduce the investments in the equipment. preparation of solid biomass, reduce energy costs, maintenance and personnel and the risk of damage compared to conventional anaerobic digestion units.

In particular, the digester according to the invention makes it possible to dispense with a device for separating undesirable elements from the solid biomass, a grinding device and a device for stirring the biomass in the digester.

After introduction of the solid biomass, and closing of the roof, the digester tank is filled with liquid digestate, which is conveyed through one or more feed pumps, from a suitable digestion unit. storing liquid digestate and biogas (called the main digestion unit and which can be made up of one or more structures). After filling the tank, first with solid biomass, then with liquid digestate, methanization takes place by percolation of the liquid digestate through the solid biomass and diffusion of the liquid digestate into the solid biomass, which is completely submerged. (and optionally partially suspended), under anaerobic conditions within the digester tank.

The digestion of the solid biomass by percolation of the liquid digestate through the solid biomass and diffusion of the liquid digestate in the solid biomass eliminates the need to stir the mixture of solid biomass and liquid biomass in the tank of the ο digester, thus avoiding investments in mechanical agitation means and operating costs.

The biogas evacuation zone, located at the top of the digester, then makes it possible to recover a mixture of biogas and liquid digestate which will then be routed to the main digestion unit suitable for storing biogas and digestate liquid.

Preferably, the biogas discharge zone is located at the level of the upper surface of the digester tank.

Once the methanization is complete, an aerobic emptying of the liquid digestate contained in the digester tank is carried out, during which the vacant space left by this emptying is filled with air, and the access through the zone of The admission then makes it possible to easily recover the residual digested solid biomass, once the digestion is complete, while minimizing the energy expended during this operation. It is therefore a batch methanization process, or in a container.

In other words, the inlet zone constitutes an inlet and outlet for the solid biomass located at the level of the upper surface of the tank of the digester according to the invention.

Thus the digester according to the invention is connected, via a liquid digestate feed circuit and a biogas and liquid digestate discharge circuit, to a main digestion unit capable of containing biogas and liquid digestate. In this way, a permanent back and forth circulation of liquid digestate can be implemented between the digester and the main digestion unit.

The inventive digester therefore makes it possible to recover solid biomass more efficiently by reducing investments in various equipment, energy costs, personnel costs and equipment maintenance, equipment wear and the risk of damage.

According to one characteristic of the invention, the digester is surmounted by a gripping means capable of allowing the supply of solid biomass and the removal of the residual digested solid biomass.

In other words, the gripping means is able to load the solid biomass into the digester and discharge the residual digested solid biomass, once digestion is complete, through the intake area of the digester.

The gripping means therefore makes it possible to grasp the solid biomass and incorporate it into the digester without having to carry out a step of sorting or prior separation of the undesirable elements liable to damage the installations making up the anaerobic digestion unit, and without having in performing a step of crushing or diluting the solid biomass.

The gripping means also makes it possible to recover the residual digested solid biomass once digestion is complete, that is to say the solid digestate, and to remove it from the digester.

Thus the gripping means makes it possible to feed and unload the digester from the top through the inlet zone (respectively outlet) located on at least part of the upper surface of the tank on which the roof closes.

The gripping device can also be used to open the roof of the digester before feeding the digester with solid biomass or discharging the solid digestate.

The gripping means can also be used to close the roof of the digester after the operations of feeding the digester with solid biomass or unloading of the solid digestate.

The gripping means is preferably a grapple capable of gripping the solid biomass by means of a plurality of hooks or a bucket capable of gripping the more pasty biomass by means of buckets.

According to one characteristic of the digester, the biogas discharge zone comprises at least one upper perforated separation element, located at the level of the upper part of the tank, capable of separating, on the one hand, the mixture composed of biogas and liquid digestate and on the other hand solid biomass.

The biogas evacuation zone therefore also makes it possible to evacuate liquid digestate by overflow.

In particular, the evacuation of the biogas can and is preferably done concomitantly with the recirculation of the liquid digestate to the main digestion unit.

Advantageously, the upper perforated separation element, capable of extracting the mixture based on biogas and liquid digestate, is a perforated pipe whose end is partially or totally closed.

According to another characteristic of the invention, the digester comprises at least one lower perforated separation element, located at the level of the lower part of the digester, in order to separate the liquid digestate and the solid biomass in particular during aerobic and anaerobic emptying of the digestate. liquid to the main digestion unit.

Preferably, the lower perforated separation elements, located at the lower part of the digester tank, are located upstream of the liquid digestate drain and evacuation system to the main digestion unit.

Preferably, the lower perforated separation element, located at the level of the lower part of the digester, is a perforated floor which can be located on all or part of the floor of the digester and / or is a perforated shell located in excess thickness on the ferrule or the vertical wall of the digester tank.

In particular, the perforated floor may correspond to a perforated ring partially occupying the floor of the digester, which makes it possible to minimize the risk of damage to the floor by the gripping means, in particular during the step of evacuating the solid digestate.

Preferably, the lower perforated divider is a perforated crown.

According to one characteristic of the invention, the digester comprises an opening provided with a valve capable of closing off or allowing the passage of air between the interior and the exterior of the digester tank and a valve intended to shut off or allow the circulation of biogas and liquid digestate between the digester and the main digestion unit.

The valve, suitable for closing off or allowing the passage of air between the inside and the outside of the digester tank, allows air to be introduced inside the digester, in particular at the time of putting into operation. implementation of an aerobic emptying step, and allows the air to be evacuated when filling the digester with liquid digestate after loading the digester with solid biomass.

The valve, capable of closing off or allowing the circulation of biogas and liquid digestate, allows you to circulate in the delivery circuits connected to the main digestion unit.

The main digestion unit can correspond to a digester capable of jointly storing liquid digestate and biogas or to two separate tanks capable of separately storing liquid digestate and biogas. In some cases, the main digestion unit may include several digesters capable of jointly storing liquid digestate and biogas or several separate tanks capable of separately storing liquid digestate and biogas.

The main digestion unit is separate from the digester according to the invention.

According to one characteristic of the invention, the roof capable of opening and closing located on the upper part of the digester can be surmounted by a cap making it possible to ensure better sealing of the roof and to avoid possible biogas leaks. . In some cases, this plug may be a liquid plug, the liquid may in particular be water or liquid digestate.

The subject of the invention is also a process for producing biogas comprising successively:

a step of supplying solid biomass, implemented by at least one gripping means, through an inlet and outlet zone located at the level of the upper part of a tank of a digester and on which a roof is able to open and close,

- a step of filling the digester tank with a liquid digestate to immerse the solid biomass and optionally suspend a portion of said solid biomass,

- a digestion step consisting of percolation of the liquid digestate through the solid biomass, and diffusion of the liquid digestate into the solid biomass, in order to bring the bacteria contained in the liquid digestate and the solid biomass into close contact, under anaerobic conditions, to generate and then recover the biogas through an evacuation zone located in the upper part of the digester,

- a step of aerobic emptying of the liquid digestate from the digester tank, during which the liquid digestate contained in the digester is emptied. Preferably, this emptying consists of pumping from the bottom of the digester tank to the main digestion unit through the lower separation element. During this step, the vacant space left by the discharge of the liquid digestate is filled with air from the outside of the tank. At the end of this step, the partially or fully digested solid biomass can come to rest on the bottom of the digester tank and / or on the lower separation element, and

- a step of evacuating the residual digested solid biomass after digestion, in other words the solid digestate, implemented by at least one gripping means, through the zone of admission of the solid biomass and evacuation of the biomass residual digested solid from the digester.

In other words, the digester tank is fed from above with solid biomass through an area over which the digester roof opens and closes.

The biogas production process therefore has the advantage of not requiring a step of preparation and / or separation of undesirable elements and / or of grinding and / or prior dilution of the solid biomass nor of requiring mixing of the biomass. solid 30 in the digester, which makes it possible to minimize the investments in equipment and the energy expenditure associated with such steps as well as the possible risks of damage to the equipment of the digester or to the equipment used during the process and to reduce the personnel and maintenance costs linked to the various steps avoided. ~

According to one characteristic, between the step of digestion of the solid biomass and the step of aerobic emptying of the liquid digestate, the process comprises at least the following steps:

- a step of anaerobic emptying of the liquid digestate from the digester tank, during which the liquid digestate, contained in the digester, is emptied. Preferably, this emptying consists of pumping from the bottom of the digester tank to the main digestion unit through the lower separation element. During this step, the vacant space left by the discharge of the liquid digestate is filled with biogas from the main digestion unit. At the end of this step, the partially or fully digested solid biomass comes to rest on the bottom of the digester tank, and

- a step of refilling the digester tank with liquid digestate. Preferably, the liquid digestate comes from the main digestion unit after anaerobic emptying.

According to one characteristic, between the step of refilling the digester tank with a liquid digestate and the step of aerobic emptying of the liquid biomass, the method further comprises at least one digestion step consisting of percolation of the digestate. liquid in the solid biomass and a diffusion of the liquid digestate in the solid biomass to generate and then recover the biogas through the biogas discharge zone located in the upper part of the digester.

In particular, the method includes a step of opening the roof of the digester before the feeding step in order to allow filling from the top of the digester tank with solid biomass.

The intake area is thus located on at least part of the upper surface of the tank on which the roof sc closes.

According to one embodiment, the method comprises a step of closing the roof on the intake area of the digester prior to the step of filling the tank with liquid digestate.

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Optionally, the gripping means can also open and possibly close the roof of the digester.

The liquid digestate is then introduced inside the tank through one or more feed pumps from the main digestion unit capable of storing biogas and liquid digestate.

According to one embodiment, after the step of filling the tank with the solid biomass to be treated and with the liquid digestate, the valve, capable of closing off or allowing the passage of air between the inside and the outside of the tank. digester tank is closed so that the methanization reaction takes place under anaerobic conditions.

The percolation step leads, at the level of the upper part of the digester, to the formation of a flow of biogas and liquid digestate.

Percolation is ensured by the implementation of one or more circulation pumps located between the main digestion unit and the digester tank.

In particular, the circulation pump (s) make it possible to ensure a pressure of the liquid digestate on the solid biomass forcing it to pass through it which promotes intimate contact between the bacteria contained in particular in the liquid digestate and the solid biomass to be degraded.

Percolation is accompanied by diffusion of the liquid digestate into the solid biomass, which is promoted by the pressure exerted by the pumping of the liquid digestate on the solid biomass. This diffusion promotes intimate contact between the bacteria and the solid biomass to be treated.

In addition, the pumping and forced circulation of the liquid digestate between the main digestion unit and the digester have the advantage of circulating a very large quantity of liquid digestate through a smaller volume of solid biomass to be treated, which limits the risks of acidosis in the digester, around the solid biomass to be treated.

In fact, in other methanization processes, too large quantities of biomass to be treated in the digester can lead to an excessive acidogenesis reaction, which can cause acidification of the liquid digestate, or acidosis, which results in partial or even total inhibition. , methanogenesis and therefore methane production. In synthesis, such a reaction is provoked when the production of volatile fatty acids, induced by acidogenic bacteria, is greater than the capacity of conversion of these fatty acids into methane by methanogenic bacteria.

According to one embodiment, the method comprises, at the time of the discharge of the biogas to the main digestion unit and of the recirculation of the liquid digestate to the main digestion unit, a separation step, implemented by means of at least one upper perforated separation element, preferably a perforated pipe or a perforated ceiling, allowing both to extract the mixture composed of biogas and liquid digestate towards the main digestion unit and to retain in the digester the solid fibrous biomass which is in suspension in the tank.

In particular, during the anaerobic digestion phase, the valve for closing or allowing the circulation of biogas and liquid digestate is opened in order to circulate the biogas and digestate to the main digestion unit. The valve is located in particular downstream of the upper separation element and upstream or on the biogas and liquid digestate delivery circuits.

According to one embodiment, the step of anaerobic emptying of the liquid digestate is implemented by emptying the tank of the liquid digestate from the bottom, which causes the solid biomass to settle at the bottom of the tank and makes it possible to eliminate the paths preferential percolation as well as the pockets of biogas blocked in the biomass.

The anaerobic emptying step can be performed by aspirating the liquid digestate through the pump (s) located between the digester tank and the main digestion unit.

The suction of the liquid digestate can preferably take place downstream of the lower perforated member to prevent the solid biomass from being carried along with the liquid digestate towards the main digestion unit.

The anaerobic emptying step allows the biogas from the main digestion unit to fill the entire volume released in the tank replacing the liquid digestate which is sucked by the pump to the main digestion unit.

After the anaerobic emptying step, a step of refilling the tank with liquid digestate is again implemented in order to continue the methanization reaction.

In the same way as before, the digestion step leads to the formation of biogas, recovered through the upper perforated separation element located at the level of the upper part of the digester.

According to one embodiment, the step of aerobic emptying of the liquid digestate from the digester tank is carried out at the end of the anaerobic digestion cycle.

Such a step is implemented by closing the valve making it possible to block or circulate the biogas and the liquid digestate, and by opening the valve making it possible to block or introduce air into the digester and by emptying the tank. liquid digestate from the bottom of the digester tank to the main digestion unit.

The aerobic emptying step is carried out by aspirating the liquid digestate through the pump (s) located between the digester tank and the main digestion unit.

The suction of the liquid digestate can preferably take place downstream of the perforated element to prevent the solid biomass from being carried along with the liquid digestate towards the main digestion unit.

The aerobic emptying step allows air from outside to fill the entire volume released in the replacement tank with liquid digestate which is sucked by the pump to the main digestion unit.

According to one embodiment, the method comprises a step of opening the roof to the solid biomass intake area prior to the step of removing the solid digestate, corresponding to your residual digested solid biomass after methanization.

The step of removing the residual digested solid biomass can be carried out by means of the gripping means capable of gripping the residual digested solid biomass after anaerobic digestion.

Such a step has the advantage of being able to take place in complete safety after the aerobic emptying of the liquid digestate, in the absence of contact with the biogas.

The invention also relates to a biogas production system, comprising at least one digester as defined above, which is or are connected by means of a liquid digestate supply circuit and a liquid digestate circuit. evacuation of biogas and liquid digestate, to at least one main digestion unit capable of containing biogas and liquid digestate.

In other words, the biogas production system corresponds to an anaerobic digestion installation implementing a main digestion unit intended to supply liquid digestate to one or more anaerobic digestion process (s), as defined above, and recovering the biogas produced by this or these different digesters.

Alternatively, the main digestion unit (s) can each be made up of two separate structures, one intended to contain mainly liquid digestate, the other intended to contain mainly biogas.

The main digestion unit is different from the digester according to the invention.

Preferably, the biogas discharge and liquid digestate recirculation circuit to the main digestion unit comprises a circuit suitable for conveying biogas and a circuit suitable for conveying liquid digestate.

Preferably, the evacuation circuit comprises a separation pot capable of separating the biogas and the liquid digestate.

The main digestion unit does not contain solid biomass or in very low amounts.

The main digestion unit can have a complementary function of producing biogas. In fact, during the digestion step, the recirculation of the liquid digestate from the digestor (s) to the main digestion unit, after percolation of the liquid digestate in the solid biomass, can cause entrainments with the liquid digestate of fine materials. undigested solids and / or volatile fatty acid entrainments which have not had time to be transformed into biogas in the digestor. Under these conditions, the residual anaerobic digestion of these materials occurs in the main digestion unit.

As indicated above, the main digestion unit can be made up of one or more structures.

Other advantages and characteristics of the invention will become apparent on examining the detailed description of an embodiment of the invention which is in no way limiting, and the accompanying drawings, in which:

- Figure 1 schematically shows a sectional view of the digester, according to the invention, connected to a main digestion unit jointly storing biogas and liquid digestate,

- Figures 2 to 9 schematically show sectional views of the digester during the different stages of the biogas production process,

- Figure 10 shows schematically a top view of a digester according to the invention,

- Figure 11 shows schematically a view of the digester, according to the invention, connected to a main digestion unit composed of two structures,

- Figure 12 schematically illustrates a top view of a biogas and digestate production system comprising a main digestion unit capable of supplying liquid digestate to a plurality of digesters, in accordance with the present invention, and of storing the biogas in origin of said digesters.

In Figure 1 is shown schematically, a main digestion unit I, composed of a single structure, and a digester 7 according to the invention.

The main digestion unit I comprises a tank 3, having an essentially cylindrical shape, filled with liquid digestate 5, which is surmounted by a sealed membrane 2 constituting a gas storage space 4, which is filled with biogas 25. The membrane 2 therefore occupies the upper part of the main digestion unit I, thus forming a dome containing a gaseous sky. Tank 3 corresponds to a reserve of liquid digestate 5.

As a variant, the tank 3 may have a cubic or parallelepiped shape.

The tank 3 can be made from steel, concrete or any other material while the waterproof membrane 2 can be made from a polymer, in particular polyethylene, polypropylene or polyvinyl chloride.

Alternatively, your waterproof membrane 2 can be surmounted by at least one additional membrane so that air is sandwiched between the additional membrane and the waterproof membrane 2.

The main digestion unit I is connected to a digester 7, according to the invention, by means of a pipe 6b on which a pump 6a is mounted. The digester 7 comprises a tank 8, of substantially cylindrical shape, provided with an inlet port 9, having an area less than or equal to the total area of the upper part of the tank 8, on which a removable roof 10 is. suitable for closing and / or opening. As a variant, the tank 8 may have an essentially cubic or parallelepipedal shape.

At the periphery of the inlet orifice 9, the vessel 8 comprises a ring 11 which projects outwardly with respect to the upper surface 12 of the vessel 8. The projecting ring may represent a position in stopper making it possible to maintain the removable roof 10 when it is in the raised position. The projecting crown 11 can also form a safety wall or a separating wall making it possible to protect the elements located outside the crown 11, in particular during the step of feeding and removing the biomass. The crown 11 may represent an enclosure in which will be located a plug ensuring the waterproofing of the roof (shown in Figure 4). Such a plug can be liquid or solid. In the embodiment illustrated in Figure I, the removable roof 10 is open allowing air to flow through the inlet 9 and into the interior of the vessel 8.

The pump 6a makes it possible not only to supply the digester 7 with liquid digestate 5 coming from the main digestion unit 1 but also to empty the liquid digestate 5 located inside your tank 8 to the main digester 1. In the embodiment illustrated in figure 1, the pipe 6b connects the tank 3, filled with liquid digestate 5, of the main digestion unit 1, to the tank 8 of the digester 7, which is empty.

Thus, the pipe 6b corresponds to a supply pipe, during the stage of filling tank 8 with liquid digestate 5, and to a drain pipe for tank 8 during the anaerobic and aerobic emptying stages.

The tank 8 comprises, at its upper part, an upper perforated separation element 13, preferably a perforated pipe, projecting from the inside to the edge of the tank 8. The perforated separation element upper 13 is positioned outside the crown 11.

The upper perforated divider 13 includes a plurality of interstices 13 ’.

The upper perforated separation element 13 is connected to a pipe 14 on which is mounted a valve 15 located upstream of a separation pot 14c, which is connected to two separate circuits 14a and 14b which are connected at their end to the 'main digestion unit 1. The pipe 14 makes it possible to recover a fluid coming from the upper perforated separation element 13 and the valve 15 makes it possible to close off or allow the circulation of the fluid in the delivery circuit 14. The valve 15 is in the closed position in Figure 1.

The circuit 14a, intended to convey mainly the biogas, is located above the circuit 14b, intended to mainly convey the liquid digestate, which facilitates the transfer of the various fluids.

The pot 14c, mounted on the routing circuit 14, allows the biogas to be separated more efficiently from the liquid digestate when they are extracted from your tank 8 through the separation element 13.

In Figure 1, the pot 14c contains liquid digestate 5 from a previous cycle of methanization.

The circuit 14b can include a circulation pump (not shown in FIG. 1) in order to facilitate the routing of the liquid digestate.

The upper perforated separation element 13 is therefore located in a zone 9 for discharging the biogas, located at the level of the upper part of the tank 8 of the digester 7.

In Figure 1, there has been shown, in cross section, only one perforated separation element 13, but preferably a plurality of perforated separation elements 13a, 13b, 13c etc. can be mounted on line 14.

Alternatively, the upper perforated separation element 13 can be located laterally at the level of the upper part of the tank 8 (not shown in Figure 1). In this case, the zone 9 * can correspond to a protuberance located laterally on the vertical part of the upper part of the tank 8 and the zone 9 could cover the whole of the upper surface of the digester 7.

The tank 8 also includes a pipe 16 which protrudes outwardly from the upper surface 12 of the tank 8. The pipe 16 is open to the outside which allows air to be channeled inside. of the tank 8 of the digester 7 or to evacuate it to the outside of the tank 8. The valve 17, mounted on the pipe 16, makes it possible to make possible or prevent the introduction or evacuation of the atr inside the tank 8. The piping 16 is located in zone 9 '.

As a variant, the pipe 16 can be located laterally at the level of the upper part of the wall of the tank 8.

In Figure 1 is shown the air 24 which is located both outside and inside the vessel 8.

The tank 8 also comprises, at its lower part, a lower perforated separation element 18, preferably a perforated floor partially or totally occupying the bottom of the tank 8. Thus the lower perforated separation element 18 may correspond to a perforated floor. perforated crown partially occupying the bottom of the tank 8.

Alternatively, the lower perforated separation element 18 can correspond to a vertical element located in excess of the shell or of the part of the vertical wall of the tank 8. The lower perforated separation element 18 can also correspond to any other. type of perforated element located upstream of the pipe 6b, during aerobic or anaerobic emptying operations of the liquid digestate from tank 8 of digester 7 to tank 3 of main digestion unit 1.

The separation element 18 comprises a plurality of interstices 18 * in order to allow the liquid digestate 5 to circulate during the anaerobic and aerobic emptying steps of the digester 7 while retaining the solid digestate in the tank 8 of the digester 7.

In the embodiment illustrated in FIG. 1, your tank 8 comprises, at its walls, residues of digested solid biomass 19, resting on the perforated element 18 and / or on the bottom of the tank 8, which can be from a previous anaerobic digestion cycle.

Alternatively, at the start of the anaerobic digestion cycle, the tank 8 can be empty and contain no residual digested solid biomass at its walls.

In Figure 1, a grapple 20 is positioned above the inlet 9 of the tank 8 and is suspended on an overhead crane 22 by means of a cable or a rope which may be made of steel. . The grapple 20, as shown, comprises a plurality of hooks 21 and is controlled from the overhead crane 22.

Alternatively, the grab 20 corresponds to a bucket having a plurality of buckets.

Figures 2 to 8 show the successive steps of a biogas production process according to the invention.

Figure 2 schematically shows the step of filling tank 8 of digester 7 with solid biomass 23, in particular fibrous and / or heterogeneous, using the grab 20.

During this step, the removable roof 10 is in the raised position, that is to say in the open position. The grapple 20 makes it possible to seize the solid biomass 23 stored outside the digester 7 in order to deposit it inside the tank 8 of the digester 7. In other words, the grab 20 makes it possible to feed, by the top, the tank 8 of the digester 7, made of solid biomass 23, through the inlet port 9 which is located at the level of the upper surface 12 of the tank 8 of the digester 7. Thus the inlet port 9 constitutes an admission zone for your solid biomass 23.

The grapple 20 makes it possible to grab the solid biomass 23 possibly containing undesirable elements, such as pebbles, gravel, sand, barbed wire, twine, metal parts 20 coming from agricultural tools or even plastic bags, without having need to carry out prior sorting, or grinding, or dilution of the solid biomass in a liquid.

Depending on its dry matter content, a liquid fraction of the biomass 23 may possibly flow from the grapple at the time of the step of feeding tank 8.

As a variant, the grapple 20 can also be used to open the removable roof 10 to deposit it next to the tank 8 or further, and to close it subsequently.

The solid biomass 23 sc is then found inside the tank 8 and rests on the bottom and / or all or part of the lower perforated separation element 18.

The interstices 18 ’of the lower perforated separation element have a size small enough to prevent the biomass 23 from entering the piping 6b during the anaerobic and aerobic emptying steps of the tank 8.

The feeding step is stopped from the moment when the quantity of solid biomass 23 introduced is considered sufficient to start the methanization.

When the step of filling the tank 8 with solid biomass 23 is completed, the removable roof is closed so as to completely seal the inlet port 9.

Thus, FIG. 3 illustrates the tank 8 of the digester 7, after closing the removable roof 10, which is filled with liquid digestate 5, conveyed through the feed pump 6a, coming from the tank 3 of the unit. of main digestion I. In particular, in FIG. 3, the liquid digestate 5 is conveyed at the level of the lower part of the tank 8 under the perforated element 18 and circulates through the interstices 18 'of the floor 18.

The tank 8 of the digester 7 can also be filled with liquid digestate 5 through an inlet located in an area located above the lower perforated element 18.

Thus, the tank 8 can be filled with liquid digestate 5 which does not pass through the lower perforated element 18.

Alternatively, the liquid digestate 5 can also be routed through an inlet located at any other location in the tank 8.

During this step of filling tank 8 with liquid digestate 5, valve 17 is left in the open position so that the air, present in tank 8, is evacuated from digester 7 via the pipe 16. In Figure 3 is shown schematically, the air 24 which escapes from the pipe 16 during the filling with liquid digestate 5 of the tank 8. The valve 15 is closed so that the air 24 does not flow to the main digestion unit 1.

The solid biomass 23, and possibly the residual digested solid biomass 19 resulting from a previous anaerobic digestion cycle, is then found immersed in the liquid digestate 5 inside the tank 8. In the embodiment illustrated in FIG. 3 , the solid biomass 23 and the residues of digested biomass 19 are found mixed together.

The level of the liquid digestate 5 in the tank 3 of the main digester 1 decreases while it increases inside the tank 8 5 expelling the air, located inside the tank 8, which escapes through through the pipe 16. The filling step will be considered to be completed when the level of the liquid digestate 5 has reached and slightly exceeded the level of the valve 17, and that all of the air contained in the tank 8 will have been evacuated.

In Figure 3 is shown, on the one hand, the direction of circulation of the liquid digestate 5 inside the tank 8 of the digester 7 which reflects the increase in level in the tank 8 and, on the other hand, the direction of circulation 27 which illustrates the drop in the level of the liquid digestate 5 inside the main digestion unit 1.

In addition, the direction of flow 27 of the liquid digestate 5 is shown inside the piping 6b.

According to FIG. 4, once the tank 8 has been filled with the liquid digestate 5, the valve 17 is closed so as to place the digester 7 under anaerobic conditions, that is to say to prevent any introduction of air. in tank 8, while valve 15 is open in order to collect the biogas and liquid digestate mixture.

FIG. 4 therefore represents the step of digestion of the biomass 23 under anaerobic conditions. During this step, biogas is formed in tank 8.

Percolation of the liquid digestate 5 & through the biomass 23 is carried out by pumping the liquid digestate 5 cn from the main digestion unit 1. The percolation takes place through the solid biomass 23 so that the most possible large part of the solid biomass 23 is brought into intimate contact with the bacteria contained in the liquid digestate 5 and thus can react during digestion. In FIG. 4 is shown schematically the flow of liquid digestate 5 circulating, by ascending vertical percolation, through all of the solid biomass 23.

According to FIG. 4, preferably, the supply of liquid digestate 5 continues throughout the whole digestion step so that the liquid digestate 5 continues to flow through the solid biomass 23, which decreases the risk of occurrence of. unwanted point chemical or biological reactions in certain places of the solid biomass heap 23, such as acidosis for example, which could alter the quality of the bacterial flora.

However, the supply of liquid digestate 5 can be, in certain cases, temporarily or permanently interrupted, in particular towards the end of the anaerobic digestion cycle, when the chemical and biological reactions are less virulent.

During this step, a process of diffusion of the liquid digestate 5 into the solid biomass 23 occurs. Such a diffusion process is favored, on the one hand, by the immersion of the solid biomass 23 in the liquid digestate 5 and, on the other hand, by the pressure of the liquid digestate 5 on the solid biomass 23 which results from the action of the pump 6a.

In the embodiment of FIG. 4, the solid fibrous biomass 23 breaks up during the percolation of the liquid digestate 5 through the solid biomass 23 and the diffusion of the liquid digestate 5 into the solid biomass 23.

The biogas 25 and the liquid digestate 5 are extracted through the interstices 13 'of the upper perforated separation element 13 while the solid biomass 23 remains immersed in the tank 8. The mixture of biogas 25 and liquid digestate 5, circulating through the upper perforated separation element 13, is shown schematically in Figure 4.

The biogas and liquid digestate are routed together in circuit 14 to the separation vessel 14c. In FIG. 4, after separation of the biogas 25 and the liquid digestate 5, the pipe 14a mainly conveys the biogas 25 while the pipe 14b mainly conveys the liquid digestate 5.

In Figure 4 is shown the level 5a of the liquid digestate 5 in the separation pot 14c. Liquid digestate 5 is found

418461 routed in a routing circuit 14b corresponding to a liquid digestate overflow pipe. The liquid digestate 5 present in the circuit 14b is conveyed to the tank 3, filled with liquid digestate 5, of the main digester 1. In FIG. 4, the liquid digestate 5 injected into your tank 8 of the digester 7, by the Through the pump 6, is recirculated by overflow, by means of the routing circuit 14b, in the tank 3 of the main digester 1. The direction of circulation of the liquid digestate 5 is represented by the arrows 27.

Optionally, the presence of a circulation pump (not shown in Figure 4) mounted on the circuit 14b allows the liquid digestate 5 to be sucked through the upper perforated separation element 13.

The biogas 25 is for its part conveyed in the circuit 14a to the main digester 1, in particular at a level close to the sealed membrane 2, which level is preferably higher than the maximum level of storage of the liquid digestate 5 in the tank. 3 of the main digestion unit 1.

Thus the upper perforated separation element 13 is located in an evacuation zone 9 ’of the biogas 25 which is located at the level of the upper part of the digestion tank 8.

In other words, zone 9 ’constitutes the evacuation space for liquid digestate 5 and biogas 25.

In addition, zone 9 ’constitutes the space for evacuating or introducing air into tank 8.

The digestion step makes it possible to produce biogas without necessarily having to implement a solid biomass mixing step 23, which makes it possible to reduce investments in mixing and agitation equipment and to reduce energy expenditure and maintenance generally related to this step.

In accordance with Figure 4, a plug 26 can be positioned on the removable roof 10 of the tank 8 so as to exert pressure in order to better ensure its tightness and its good closure during the digestion step.

• ** "

The stopper 26 may be a liquid stopper consisting of clear water or liquid digestate which may come from the liquid digestate reserve 5 from the main digestion unit 1 and / or from leaks in the roof 10 coming from the tank 8. The cap 26 may be covered by means of a cover, a closed double-walled roof or a plastic cover, in particular a plastic sheet. Preferably, the upper level of the liquid plug 26 will be the same as the level of overflow of the liquid digestate 5 in the separation pot 14c, towards the circulation pipe 14b.

Alternatively, the separation of the biogas 25 and the liquid digestate 5 can be carried out without the presence of a separation pot 14c, or even without the presence of several delivery pipes 14a or 14b. In this case, the separation of the biogas 25 and the liquid digestate 5 would take place in the main digestion unit 1.

During the digestion step, the solid biomass 23 is immersed in the liquid digestate 5 and can partly float at the top of the tank 8, be partly in suspension in the middle of the tank 8 or partly settle and be found in bottom of tank 8.

In FIG. 5 is schematically represented the step of anaerobic emptying of the liquid digestate 5 from the tank 8 of the digester 7, to the tank 3 of the main digestion unit 1, by emptying the liquid digestate 5 via the pump 6a and keeping the valve 17 in the closed position while the valve 15 is in the open position.

The emptying step makes it possible, by compacting the solid biomass 23 partially digested following the digestion and diffusion step at the bottom of the digester 7, to eliminate any preferential percolation paths as well as any pockets of biogas, blocked. in the biomass 23. Thus the biogas 25, located in the circuit 14a, circulates from the main digestion unit 1 towards the interior of the tank 8 of the digester 7, passing through the upper perforated separation element 13. The biogas thus fills the space left vacant by the emptying of the liquid digestate 5. During this emptying step, the biomass

I ° "solid 23 descends towards the bottom of the tank 8 in the direction of the lower perforated separation element 18, and finally settles on the bottom of the tank 8 and / or on the lower perforated separation element

18.

In Figure 5 is shown the direction of flow of biogas 25 in circuit 14 towards tank 8 as well as the direction of flow 27 of liquid digestate 5 towards tank 3 of the main digestion unit I.

The lower perforated separation element 18 has the advantage of allowing the liquid digestate 5 to pass through at the time of anaerobic emptying by retaining the partially digested solid biomass 23 in the tank 8. The lower perforated separation element 18 therefore makes it possible to separate the liquid digestate 5, allowing it to circulate, and the solid biomass 23 which makes it possible not to risk clogging the feed pump 6a and not to introduce digestate. solid 23 in main digestion unit 1.

During the anaerobic emptying step, the liquid stopper 26 can be partially or totally emptied, in particular to prevent excessive pressure from being exerted on the roof 10. The discharged liquid part can be emptied inside the tank 8. digester 7, or else be stored in a storage place for later use, or be transferred to another digestion tank, or finally be evacuated to any other destination.

After the anaerobic emptying of the tank 8, a new step of filling the tank 8 with liquid digestate 5 is implemented as shown in Figure 6. The filling step is identical to the previous filling step è l ' except that the valve 17 is in the closed position and the valve 15 is in the open position.

In accordance with Figure 7, once the filling step is complete, the solid biomass digestion step 23 is again implemented in order to continue the production of biogas

25.

"* · ·

In the same way as above, the biogas 25, resulting from the digestion step, is mainly conveyed through the routing circuit 14a to the main digestion unit i.

Once the digestion step is complete, that is to say at the end of the cycle after approximately 20 to 80 days, an aerobic emptying step of the tank 8 of the digester 7 is implemented as illustrated in Figure figure 8.

The aerobic emptying step is implemented by closing the valve 15 in order to prevent any introduction of biogas 25 inside the digestion tank 8, and by opening the valve 17 in order to introduce the air 24 to the interior of the digestion tank 8 by replacing the liquid digestate 5 discharged and by pumping the liquid digestate 5 through the pump 6a through the lower perforated separation element 18 in order to discharge the liquid digestate 5 towards the main digestion unit 1 tank 3.

This step makes it possible to drain the liquid digestate from the digestion tank 8 while avoiding the presence of biogas in the tank 8, which makes it possible to minimize the leaks / releases of biogas into the atmosphere at the time of the subsequent implementation of the step of removing the residual solid biomass 19 after digestion, that is to say the solid digestate.

In this figure, the level of the liquid digestate 5 decreases and the air 24 gradually enters the interior of the tank 8 of the digester 7 cn filling the space left vacant by the emptying of the liquid digestate 5.

FIG. 9 describes the step of removing the residual digested solid biomass 19, once the digestion is complete, by the grapple 20. In particular, the removable roof 10 is raised so that the grapple 20 can be actuated at through the inlet 9 of the tank 8. In this way, the grab 20 makes it possible to seize the residual digested solid biomass 19, once the digestion is complete, so as to evacuate it either towards a storage zone, a treatment area or transport vehicle.

In the embodiment illustrated in FIG. 9, the grapple 20 grasps the residual digested solid biomass 19 in the tank 8 of the digester 7, possibly leaving residues of digested solid biomass 19 at the level of the walls or the bottom of the tank.

8.

Residues of digested solid biomass 19 can be left at the walls, or in the bottom of the tank 8, or else on the lower separation element 18, because they can constitute a good substrate, very rich in bacteria which will be likely to act during the next anaerobic digestion cycle.

Thanks to the previous aerobic emptying step, the step of 10 recovery of the residual digested solid biomass 19 after anaerobic digestion, corresponding to the solid digestate, can be carried out in complete safety while minimizing the risks of biogas being released into the atmosphere as well. that the risks of bringing people, the grapple and equipment located outside the digestion tank 8 into contact with the biogas.

Thus the inlet 9 of the tank 8 represents both an admission zone for the solid biomass 23 before anaerobic digestion as well as an evacuation zone for the residual digested solid biomass 19 after anaerobic digestion, called solid digestate

In other words, the inlet 9 of the tank 8 constitutes a space for introducing the solid biomass and removing the residual digested solid biomass.

In FIG. 10 is shown schematically a top view of the tank 8 of the digester 7, according to the invention, comprising an inlet orifice 9 constituting an inlet zone for the solid biomass 23 and a zone of evacuation of the residual digested solid biomass 19 after methanization reaction.

The digester 7 also has a zone 9 for discharging the biogas 25 and for introducing and discharging air.

The upper part of the tank 8, in its biogas discharge space 9 ', is provided with several upper perforated separating elements 13a, 13b, 13c and 13d, preferably perforated pipes, which are protruding extending from inside to the upper edge of the tank 8.

The upper perforated separation elements 13a, 13b, 13c, and 13d are connected to a pipe 14 comprising a separation pot

14c connected to two separate circuits 14a and 14b which are connected to the main digestion unit 1 (not shown in FIG. 10).

Circuit 14a constitutes a general pipe mainly conveying biogas and circuit 14b constitutes a general pipe conveying mainly liquid digestate.

As indicated above, during the digestion step, a mixture of biogas 25 and liquid digestate 5 is extracted 10 through the upper perforated separation elements 13a, 13b, 13c, 13d and is fed into the pipe 14.

The liquid digestate 5 is then routed mainly in the circuit 14b to the liquid digestate reserve 5 of a main digestion unit 1 and the biogas 25 is found mainly routed in the circuit 14a to the gas storage space 4 main digestion unit 1.

The upper part of the tank 8, in its biogas discharge space 9 ', is also provided with one or more openings 16, allowing the introduction or the discharge of air during certain phases of aerobic loading of the tank. liquid digestate or aerobic discharge of liquid digestate 5.

In Figure 11 is shown schematically a digester 7, according to the invention, connected to a main digestion unit composed of two separate structures.

In accordance with this figure, the main digestion unit comprises a first structure 41, which corresponds to a tank 42 containing liquid digestate 5 surmounted on the surface by a small amount of biogas 25. The second structure 43 corresponds to a gasometer capable of storing biogas 25.

The two structures 41 and 43 are interconnected by a pipe 44.

Thus the main digestion unit is able to store separately mainly biogas 25 and mainly liquid digestate 5.

. ··.

In Figure 11, the conveyor circuit 14 comprises a separation pot 14c connected to two separate circuits 14a and 14b which are connected to the main digestion unit. In particular, the routing circuit 14b is connected to the tank 42 at the level of the liquid digestate reserve 5 and the routing circuit 14a is connected to the upper part of the structure 42 in a zone not comprising any digestate liquid 5. As an alternative, the routing circuit 14b can be connected to the upper part of the structure 42 in a zone not comprising any liquid digestate 5.

As previously indicated, during the digestion step, a mixture of biogas 5 and liquid digestate 25 is extracted through the upper perforated separation element 13 ’and is routed through piping 14.

The liquid digestate is then routed mainly in the circuit 14b to the liquid digestate reserve 5 of the tank 42.

As for the biogas 5, it circulates mainly in the circuit 14a and passes through the structure 41, in a zone which does not include liquid digestate 5, to be conveyed, through the pipe 44, to the gasometer 43.

In this way, the structure 41 comprises, on the surface of the liquid digestate 25, a small amount of biogas 5 coming from the circuit 14a connecting the digester 7 and the main digestion unit 41.

FIG. 12 schematically represents a top view of a system or of a biogas production installation comprising the main digestion unit 1 capable of being supplied by overflow with liquid digestate, via a routing circuit 14b, by a plurality of digesters 7 fed from above with solid biomass by means of a grapple 20 mounted on an overhead crane 22.

The main digestion unit I is also supplied with biogas via a delivery circuit 14a following the production of biogas in each digester 7.

The main digestion unit 1 is not, or very slightly, supplied with solid biomass 23 during the anaerobic digestion process but advantageously constitutes a liquid digestate reserve 5 and a biogas storage space 25.

The liquid digestate reserve 5 is therefore used to supply the digesters 7 and the biogas storage space 25 is used to recover the biogas 25 from the various digesters 7.

During the methanization process considered as a whole, the grab 20 circulates through the different digesters 7 in order to feed them from above with solid biomass 23.

Likewise, the grapple 20 circulates through the various digesters 7 in order to recover from the top the residual digested solid biomasses 19, or solid digestates, at the end of the anaerobic digestion cycle.

Claims (11)

1. Bloga2 production system (25) comprising: - at least one main digestion unit (1), consisting of one or more structures, capable of containing biogas (25) and 5 liquid digestate (5), - at least one methanization digester (7), intended for the production of biogas (25), comprising a tank (8), capable of containing solid biomass (23), and comprising at its upper part: at least a solid biomass intake zone (9) 10 (23) and evacuation of the residual digested solid biomass (19), on which a roof (10) is able to open and close, and at least one zone (9 *) for evacuating the biogas (25); - said biogas discharge zone (9 ') comprising at least one upper perforated separation element (13, 13a, 13b, 13c, 13d), 15 located at the level of the upper part of the tank, capable of separating, on the one hand, a mixture composed of biogas (25) and liquid digestate (5) and, on the other hand, solid biomass (23) , - said anaerobic digestion digester (7) being surmounted by a gripping means (20) capable of allowing the supply of the 20 solid biomass (23) and the evacuation of the residual digested solid biomass (19), • said digester being connected, by means of a supply circuit (6b) in liquid digestate (5) and by means of a circuit (14) for discharging biogas (25) and liquid digestate (5) to said main digestion unit (1). 2. System according to claim 1, characterized in that the gripping means (20) is a grapple (21) comprising a plurality of hooks or a bucket comprising buckets. 3. System according to claim 1 or 2, characterized in that the upper perforated separation element (13, 13a, 13b, 13c, 13d) is a perforated pipe, the end of which is partially or totally closed. 4 Γ ⁴ ** 4. System according to any one of the preceding claims, characterized in that said digester (7) comprises at least one lower perforated separation element (18), located at the level of the lower part of the tank (8), suitable for separate liquid digestate 5 (5) solid biomass (23). 5. System according to claim 4, characterized in that the lower perforated separation element (18) is a perforated floor. 6. System according to any one of the preceding claims, characterized in that said digester (7) comprises a 10 opening (16) provided with a valve (17), capable of closing off or allowing the passage of air (24) between the inside and the outside of the tank (8) of the digester (7) and a valve (15 ), located on a routing circuit (14), capable of closing off or allowing the circulation of biogas (25) and liquid digestate (5) between the digester (7) and a main digestion unit (I). 7. System according to any one of the preceding claims, characterized in that said digester (7) comprises a liquid plug (26) positioned on the roof (10) of the tank (8). 8. System according to any one of the preceding claims, characterized in that the main digestion unit (l) consists of two separate structures, one intended to contain mainly liquid digestate (5), the other intended to contain mainly biogas (25). 9. System according to any one of the preceding claims, characterized in that the evacuation circuit (14) comprises a circuit (14a) suitable for conveying biogas (25) and a circuit (14b) suitable for conveying digestate. liquid (25). 10. A method of producing biogas (25) comprising at least the following successive steps: 30 - a step of supplying solid biomass (23), implemented by at least one gripping means (20), through an inlet and outlet zone (9) located at the level of the upper part of 'a tank (8) of a digester (7), as defined in "f' ·· '*" claim 1, and on which a roof (10) is able to open and close, - a step of filling the tank (8) of the digester (7) with a liquid digestate (5) to immerse the solid biomass (23), • 5 - a digestion step, consisting of percolation of the liquid digestate (5 ) through the solid biomass (23) and diffusion of the liquid digestate (5) in the solid biomass (23) under anaerobic conditions to generate and then recover the biogas (25) through an evacuation zone (9 * ), located in the upper part 10 of said digester (7), and - a step of aerobic emptying of the liquid digestate (5) from the tank (8) of the digester (7), and »a step of removing the residual digested solid biomass (19), implemented by at least one means of gripping 15 (20), through the zone (9) of the digester (7). i I. A process for producing biogas (25) according to claim 10, characterized in that it further comprises between the digestion step and the step of aerobic emptying of the liquid digestate (5) at least the following steps: 20 - a step of anaerobic emptying of the liquid digestate (5) from the tank (8) of the digester (7), and - a step of refilling the tank (8) of the digester (7) with a liquid digestate (5) after anaerobic emptying. 12. A method of producing biogas (25), according to claim 11, characterized in that it further comprises, after the step of refilling the tank (8) of said digester (7) with a liquid digestate. (5), at least one digestion step, consisting of percolation of the liquid digestate (5) through the solid biomass (23) and of a diffusion of the liquid digestate (5) into the solid biomass (23) 30 - to generate and then recover the biogas (25) through the zone (9 *).