FR3114585A1 - Detection of pressure effects in an anaerobic digestion system - Google Patents

Abstract

The invention relates to a system (1) for the methanization of organic materials, said system (1) comprising a methanizer (10), a transport conduit (20), a safety conduit (30) shaped to store by gravity a volume of liquid in its lower part (30A) and a detector (50) configured to detect the displacement of the volume of liquid in the safety conduit (30) beyond a predetermined displacement threshold when the liquid is sucked from the part low (30A) through the connection portion in case of depression in the delivery conduit (30). Figure for the abstract: figure 1

Description

Detection of pressure effects in an anaerobic digestion system

The present invention relates to the field of methanation and relates more particularly to a methanation system and a method for controlling the pressure of the biogas circulating in such a system in order to protect said system, in particular its flexible membrane, in the event of depression or overpressure.

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 the fermentable fraction of livestock effluents into biogas by disposing these effluents in a methanizer.

A methanizer comprises a tank in which the effluents are placed, called a digester, and a biogas collection device, placed in said tank. In a known solution, the collection device comprises a flexible membrane, called a cover, which extends in the tank above the organic matter in order to concentrate the biogas produced by the fermentable fraction of the effluents by forming a dome. A transport pipe is fluidically connected to the cover in order to transport the biogas out of the methanizer to exploit it, for example in a cogeneration module or a storage module.

However, in this type of methanizer, it is observed that pressure effects can occur under the flexible membrane or in the conveying duct.

These effects can in particular be of the depression type when the cover is placed on the bottom of the tank, which can damage the flexible membrane, for example by tearing it, and prove to be dangerous if atmospheric air rushes into the methanizer. , thus presenting a risk of explosion or destruction of the anaerobic bacteria which could cause the methanation to stop.

These effects can also be of the overpressure type when the volume of biogas produced in the methanizer is greater than the volume of biogas evacuated from the device, which can lead to the escape of a quantity of biogas presenting a risk of explosion.

There is therefore a need for a solution making it possible to remedy these drawbacks at least in part, in particular at lower cost.

One of the aims of the invention is in particular to detect the effects of pressure such as a depression or an overpressure of the biogas circulating in the methanizer in order to protect said methanizer, in particular the flexible membrane, and the individuals operating in the environment. close to the digester. Another object of the invention is to trigger an alert when a depression or an overpressure has been detected in the delivery duct. Another object of the invention is to make it possible to avoid any leak of biogas in the event of depression or overpressure and to prohibit the introduction of air into the methanizer, a source of creation of an explosive atmosphere (ATEX) or destruction of anaerobic bacteria which can lead to the stoppage of methanisation.

• un méthaniseur comprenant une cuve de stockage de matières organiques et un module de couverture de ladite cuve, ledit module de couverture comprenant une membrane souple adaptée pour recouvrir les matières organiques placées dans la cuve afin de permettre leur méthanisation,
• un conduit d’acheminement relié fluidiquement au module de couverture afin d’évacuer le biogaz produit par le méthaniseur,
• un conduit de sécurité comprenant une partie basse, une portion de connexion reliée fluidiquement d’une part à la partie basse et d’autre part au conduit d’acheminement et un évent, ou canal d’aération, relié fluidiquement d’une part à la partie basse et d’autre part à l’atmosphère via un port d’aération poreux à l’air, ledit conduit de sécurité étant conformé pour stocker par gravité un volume de liquide dans la partie basse, notamment tant que la pression dans le conduit d’acheminement est comprise entre un seuil de surpression prédéterminé et un seuil de dépression prédéterminé,
• un détecteur configuré pour détecter le déplacement du volume de liquide dans le conduit de sécurité au-delà d’un (premier) seuil de déplacement prédéterminé lorsque le liquide est aspiré depuis la partie basse à travers la portion de connexion en cas de dépression dans le conduit d’acheminement, notamment dans le circuit de circulation de biogaz.

To this end, the subject of the invention is first of all a system for the methanation of organic materials, said system comprising:

• a methanizer comprising a storage tank for organic materials and a cover module for said tank, said cover module comprising a flexible membrane suitable for covering the organic materials placed in the tank in order to allow their methanization,
• a transport conduit fluidly connected to the cover module in order to evacuate the biogas produced by the methanizer,
• a safety conduit comprising a lower part, a connection portion fluidically connected on the one hand to the lower part and on the other hand to the delivery conduit and a vent, or aeration channel, fluidically connected on the one hand to the lower part and on the other hand to the atmosphere via an air-porous ventilation port, said safety conduit being shaped to store by gravity a volume of liquid in the lower part, in particular as long as the pressure in the routing conduit is between a predetermined overpressure threshold and a predetermined depression threshold,
• a detector configured to detect the displacement of the volume of liquid in the safety conduit beyond a (first) predetermined displacement threshold when the liquid is sucked from the lower part through the connection portion in the event of a depression in the delivery conduit, in particular in the biogas circulation circuit.

The fluidic connection of the vent of the safety conduit allows the displacement of the volume of liquid according to the variations in pressure of the biogas in the delivery conduit. The safety duct can easily be adapted to an existing methanization system that already has a methanizer and a transport duct. In addition, the use of such a safety conduit makes it possible to secure the system reliably and effectively in order to avoid any risk linked to excessive depression. Indeed, the volume of liquid stored in the lower part prevents the passage of biogas from the connection portion to the vent as long as said liquid is present in the lower part of the safety duct. Thus, in the event of significant depression, the liquid stored in the lower part is sucked through the connection portion towards the conveying duct. The displacement threshold is a liquid displacement limit placed on the safety duct which corresponds to a predetermined limit of depression tolerated in the circulation circuit of the biogas flow and beyond which the depression of the gases circulating in the duct d The transport of biogas presents a risk of damage to the methaniser, in particular a risk of tearing the flexible membrane of its cover module.

Preferably, the safety duct has a U-shape in order to easily retain the volume of liquid.

Preferably, the displacement threshold is located in the lower part of the safety conduit in order to detect the disappearance of the majority of the volume of liquid in the lower part.

As a variant, the displacement threshold can be located in the connection portion of the safety conduit.

As a further variant, the displacement threshold can be located in the vent of the safety duct.

Biogas can pass through the liquid volume in the event of overpressure and be vented to the atmosphere through the vent port. However, it may be advantageous to also detect such an overpressure. Thus, in one embodiment, the detector is configured to detect the displacement of the volume of liquid beyond a second predetermined displacement threshold in the safety conduit when the liquid has moved from the lower part into the vent due to overpressure. Indeed, in the event of overpressure, the biogas pushes the volume of liquid which then moves from the lower part towards the vent. The second overpressure threshold is a liquid displacement limit placed on the safety duct which corresponds to a predetermined overpressure limit tolerated in the transport duct and beyond which the pressure of the biogas becomes sufficiently high to present a danger for the system or its operators. Indeed, in the event of excessive overpressure, the system could present a risk of internal explosion, as long as the volume of liquid continues to fulfill its barrier function preventing the biogas from escaping. In this case, either the overpressure is evacuated through the volume of liquid and the aeration port into the atmosphere, or the overpressure is detected in order to be able, for example, to shut down the system to reduce the pressure of the biogas circulating in said system. .

Preferably, the second displacement threshold is located in the lower part of the safety duct in order to detect the disappearance of the majority of the volume of liquid in the lower part.

As a further variant, the second displacement threshold can be located in the vent of the safety duct.

Preferably, the ventilation port is located at a free end of the vent opening into the atmosphere, for example by being coincident with said free end.

In one embodiment, the ventilation port is made of a material porous to air or else comprises at least one orifice, preferably of small dimensions, in order to place the safety duct in communication with the atmosphere and thus allowing the displacement of the volume of liquid in the event of depression or overpressure while avoiding the evaporation of the liquid stored in the lower part. The ventilation port can be in the form of an orifice provided with a grid or a filter.

Advantageously, the aeration port includes a cap making it possible to obstruct the safety duct to prevent the volume of liquid from evaporating. The cap may be made of a material porous to air or else comprise at least one orifice, preferably of small dimensions, in order to place the safety conduit in communication with the atmosphere and thus allow the displacement of the volume of liquid in case of depression or overpressure while avoiding the evaporation of the liquid stored in the lower part.

Preferably, the vent port is configured to allow the lower part of the safety conduit to be filled with liquid.

In one embodiment, the vent includes a liquid inlet port and a sealing plug. This inlet orifice allows the lower part to be filled with liquid to prevent the passage of biogas. The plug makes it possible to seal this orifice against the passage of any gas.

Also advantageously, the safety conduit comprises an evacuation valve mounted in its lower part, preferably at the lowest point of the safety conduit, in order to allow the evacuation of the volume of liquid from the lower part of the safety conduit, especially when changing the fluid for maintenance purposes.

According to one aspect of the invention, the volume of liquid comprises a substance preventing the liquid from freezing in the safety conduit, that is to say a substance which does not freeze, preferably at temperatures above -5° C, preferably still higher than -15°C, to prevent the frozen liquid from damaging the system, in particular when the temperatures are slightly negative.

In one embodiment, the volume of liquid is a mixture consisting partly of water and of a substance preventing the liquid from freezing in the safety conduit, for example glycol, in particular food, which is both economical and easy maintenance. The proportion of water and glycol can for example be defined using a refractometer in order to guarantee that the mixture will not freeze at a given temperature, for example greater than or equal to -15°C.

According to one aspect of the invention, the system comprises at least one booster allowing the biogas to circulate in the transport conduit.

According to one characteristic of the invention, the detector is able to send a detection signal when said detector detects the liquid at or above the first displacement threshold or the second displacement threshold.

According to one characteristic of the invention, the system comprises a control module capable of receiving a detection signal from the detector when the volume of liquid has reached or exceeded the first displacement threshold or the second displacement threshold.

Preferably, the control module is capable of controlling the shutdown of at least the booster upon receipt of a detection signal sent by the detector in order in particular to avoid tearing the flexible membrane in the event of depression.

In one embodiment, the control module is configured to, upon receipt of the detection signal, emit an alert, for example of the sound or visual signal type, or to send an alert message, in particular to an operator.

According to one aspect of the invention, the detector comprises a float capable of floating on the surface of the volume of liquid and at least one sensitive element mounted on the safety conduit at the level of the (first) displacement threshold and which is capable of detecting the float when said float is in line with said sensitive element.

Advantageously, the detector is of the magnetic type in order to make the system both effective and inexpensive. In addition, it also allows measurements to be made in a non-intrusive manner, thus avoiding any possibility of liquid leakage from the detector.

Preferably, the flexible membrane is capable of forming a storage dome for the biogas resulting from the methanization while waiting for the biogas to be evacuated from the methanizer through the transport conduit.

In one embodiment, the system includes an activated carbon filter connected to the biogas delivery conduit.

Description of figures

Other characteristics and advantages of the invention will become apparent on reading the description which follows. This is purely illustrative and must be read in conjunction with the appended drawings on which:

Figure 1 schematically illustrates a first embodiment of the system according to the invention.

Figure 2 schematically illustrates a second embodiment of the system according to the invention.
Detailed description of at least one embodiment

The system according to the invention makes it possible both to produce biogas from organic matter in a secure manner by detecting any excessive depression, or even also any excessive overpressure, of the gases circulating in the system, in particular in order to stop the system if necessary. .

The organic materials can in particular be livestock effluents such as cattle, waterfowl, pig slurry, or any other organic material of which at least a fermentable fraction is capable of being transformed into biogas.

System 1

Referring to Figures 1 and 2, the system 1 according to the invention comprises a methanizer 10, a transport conduit 20, a safety conduit 30, a detector 50 and a control module 60. In this example, the system 1 further comprises a processing module 70 and a booster 80.

methanizer 10

The methanizer 10 comprises a tank 110 intended to receive organic materials (not visible in the figures) and a cover module 120 of said tank 110.

Tank 110

In this non-limiting example, the tank 110 comprises a bottom 112 and at least one side wall 114 extending vertically from said bottom 112 and delimiting an opening at its upper part. The tank 110 can for example be buried in the ground and be made of concrete or geotextile or any other suitable material.

The tank 110 has in this example a cylindrical shape of circular section and has a single side wall 114 . In any other embodiment, the tank 110 could have another shape, for example parallelepipedic, comprising four side walls.

Cover module 120

The cover module 120 is intended to close the open part of the tank 110 in order to cover the organic materials present in the tank 110 and thus allow their methanization. More specifically, the cover module 120 is configured to cover the upper opening of the tank 110 by matching the shape of the wall 114 and by authorizing the formation of an internal space allowing the biogas to be collected in order to evacuate it through the transport conduit 20.

It will be noted that the shape of the cover module 120 is defined by the shape of the tank 110. It is thus of circular shape in the example of the figures, in a non-limiting manner.

Preferably, cover module 120 includes a flexible membrane extending over the organic materials. The flexible membrane is capable of forming a dome above the organic matter as illustrated in the figures in order to concentrate the biogas produced by the fermentation of said organic matter.

Delivery conduit 20

The inlet of the transport conduit 20 is fluidically connected to the cover module 120 of the methanizer 10 in order to evacuate the biogas produced in the tank of the methanizer 20 and stored under the cover module 120.

In this example, the transport pipe 20 is fixed to the central part of the membrane, the latter being perforated in its center to allow the biogas to circulate through said transport pipe 20 to the treatment module 70 which is therefore connected to the outlet of the routing conduit 20.

In this example, the conveying conduit 20 further comprises a vacuum valve 21 making it possible, when it is open, to lower the pressure of the biogas prevailing in the conveying conduit 20. This vacuum valve 21 is able to be controlled remotely by the control module 60.

safety conduit 30

The safety duct 30 comprises a lower part 30A, a connection portion 30-1 and a vent (or ventilation channel) 30-2.

The safety conduit 30 is shaped to store by gravity in its lower part 30A a volume of liquid, preferably glycol water, making it possible to block the biogas as long as the pressure in the conveying conduit 20, and in extenso in the safety conduit 30, is between a predetermined overpressure threshold and a predetermined depression threshold.

In the embodiments illustrated in the figures, the safety duct 30 is shaped like a U and is fluidically connected by one branch of the U (connection portion 30-1) to the routing duct 20, the other branch of the U ( vent 30-2) being connected to the atmosphere. In another embodiment, the safety conduit 30 could have any other suitable shape.

The connection portion 30-1 makes it possible to fluidically connect the lower part 30A and the routing duct 20.

The vent 30-2 is fluidically connected on the one hand to the lower part 30A and on the other hand to the atmosphere via a ventilation port 32 porous to the air in order to allow the displacement of the volume of liquid in case depression or overpressure. The ventilation port 32 is preferably located high up, for example at more than 3 m, away from any personnel or source of ignition.

Vent port 32 is located at the free end of vent 30-2 leading to the atmosphere. Preferably, the free end of the vent 30-2 is provided with a filter that is porous to air but blocks solid particles such as, in particular, rubble and dust, thus preventing them from entering the safety duct 30.

Advantageously, in the first embodiment illustrated in FIG. 1, the ventilation port 32 is configured to allow the passage of a liquid making it possible to fill the lower part 30A of the safety conduit 30 with liquid.

In the second embodiment illustrated in FIG. 2, the vent 30-2 comprises, between its junction with the lower part 30A and the ventilation port 32, a liquid inlet orifice 31 making it possible to fill the lower part 30A of the safety conduit 30 with the volume of liquid.

In this second embodiment, the liquid inlet orifice 31 is provided with a plug 33. The plug 33 can be sealed or else be made of a porous material in order to allow air to circulate, for example through one or more orifices, while avoiding the evaporation of the liquid contained in the lower part 30A.

The safety conduit 30 comprises an evacuation valve 34 mounted in its lower part 30A, preferably at the lowest point of said lower part 30A, in order to allow the evacuation of the volume of liquid from the lower part 30A, in particular by case of changing the volume of liquid for maintenance purposes.

Detector 5 0

The detector 50 makes it possible to detect that the level of liquid in the safety conduit 30 reaches a first displacement threshold synonymous with excessive depression and to alert the control module 60 if necessary in order to stop the operation of the booster 80 which contributes to depression.

In this example, the detector 50 is a magnetic sensor comprising a float 51 and a sensitive element 52.

In an embodiment not shown, the system 1 may comprise, in addition to the aforementioned elements, a second sensitive element (not shown) mounted for example on the vent 30-2 and corresponding to a second predetermined displacement threshold in order to detect a displacement of the volume of liquid from the lower part 30A towards the vent 30-2, synonymous with an excessive overpressure of the biogas in the system.

In one embodiment, the system 1 can comprise a single sensitive element 52 adjusted to detect both an excessive depression and an excessive overpressure, for example by being mounted in the lower part 30A of the safety duct 30. In other words, in In this case, the first displacement threshold and the second displacement threshold coincide.

In the example illustrated, the float 51 is placed in the safety conduit 30 and is able to float on the surface of the volume of liquid stored in the safety conduit 30, in this example on the side of the connection portion 30-2 of the safety duct 30. Alternatively, the float 51 could for example be placed on the side of the vent 30-2.

Still in this example, the sensitive element 52 is mounted at the level of the lower part 30A of the safety conduit 30 and is configured to detect the float 51 when said float 51 is located in line with said sensitive element 52, at the level of the first threshold of predetermined displacement. The first predetermined displacement threshold corresponds to a predetermined limit of depression tolerated in the delivery duct 30 and beyond which the membrane risks being damaged. This first displacement threshold can for example be determined empirically using a device for measuring the pressure of the biogas in the transport conduit 20 by knowing the level of admissible pressure so as not to tear the membrane.

The sensitive element 52 (and the second sensitive element if present) is configured to send a detection signal to the control module 60 when the float 51 has been detected.

In other embodiments, the float 51 and the sensing element 52 (and the second sensing element if applicable) could be placed differently. For example, the float 51 could be placed on the liquid surface located on the side of the vent 30-2 (in the absence of overpressure or depression) and the sensitive element 52 could be placed in the vent 30- 2 in order to detect an and an excessive depression.

Control module 60

The control module 60 is configured to receive a detection signal sent by the detector 50 when the sensitive element 52 detects the float 51 and to control the stopping of the booster 80 following the reception of such a detection signal. As a variant or in addition, the control module 60 can be configured to, upon receipt of the detection signal, emit an audible or visual signal or send a message, for example an operator of the system 1 who can then order the shutdown of the system 1, in particular the booster 80.

The control module 60 can be connected to the sensitive element 52 (and to the second sensitive element if applicable) by wire or wirelessly.

The control module 60 can also be configured to, upon receipt of an alert signal sent by the detector 50 in the event of overpressure, open the vacuum valve 21 in order to reduce the pressure of the biogas in the transport conduit 20 , then close the vacuum valve 21 when the pressure of the biogas has returned to an acceptable level, below a predetermined reference pressure threshold, for example 10 millibars.

The booster 80 or the boosters 80 when there are several of them are arranged in the biogas circulation circuit, for example in the transport pipe 20, in order to allow the circulation of the flow of biogas from the methanizer 10, in particular in the direction of the processing module 70. The control module 60 is configured to control, preferably automatically, the shutdown of the booster(s) 80 when a detection signal has been received from the detector 50.

M processing module 7 0

The treatment module 70 makes it possible to treat the biogas produced by the methanizer 10. For example, the treatment module 70 can be an activated carbon filter making it possible to desulphurize the biogas produced by the methanizer 10 in order for example to allow its combustion. in a cogeneration module and thus produce electricity and heat. The processing module 70 can also be a cogeneration module, a biogas storage tank or any other known biogas processing module.

Implementation of the invention

During the production of biogas by the methanizer 10, the biogas circulates from the methanizer 10 in the transport conduit 20 towards the treatment module 70.

When the gases circulating in the system 1 are under depression, for example when the membrane rests at the bottom of the tank 110, the liquid containing in the lower part 30A of the safety duct 30 is sucked up by said depression.

In doing so, the float 51 descends in the lower part 30A until it reaches the sensitive element 52 which detects it and, preferably, sends a detection signal to the control module 60.

When the pressure of the biogas circulating in the transport conduit 20 increases, the biogas causes the displacement of the volume of liquid stored in the lower part 30A of the safety conduit 30 in the direction of the vent 30-2 of the safety conduit 30. Thus, the level of the volume of liquid located on the side of the connection portion 30-1 of the safety conduit 30 drops so that the float 51 descends into the safety conduit 30.

In the embodiment in which the system 1 is also capable of detecting an overpressure, when the pressure is such that the float 51 reaches the second predetermined displacement threshold, in line with the sensitive element 52 (or a second sensitive element), the sensitive element 52 detects the float 51 and, preferably, sends an alert signal to the control module 60.

Upon receipt of the detection signal, the control module 60 controls the shutdown of the booster(s) 80 of the system 1 and possibly triggers an alert intended for an operator, for example by sending a alert message or by emission of an audible or visual alarm. As a variant or in addition, the control module 60 can, in the event of overpressure, automatically open the depression valve 21 or control the methanizer 10 in order to reduce the pressure of the flow of biogas in the transport pipe 20 and avoid any danger. of explosion.

Finally, it should be noted that the present invention is not limited to the examples described above and is capable of numerous variants accessible to those skilled in the art. In particular, the shape and dimensions of the methanizer 10, in particular of the tank 110 and of the cover module 120, of the routing duct 20, of the safety duct 30 and of the detector 50 as shown in the figures so as to illustrate a embodiment of the invention as well as the materials used cannot be interpreted as limiting.

Claims (10)

System (1) for the methanization of organic materials, said system (1) comprising:

• a methanizer (10) comprising a tank (110) for storing organic materials and a cover module (120) of said tank (110), said cover module (120) comprising a flexible membrane adapted to cover the organic materials placed in the tank (110) in order to allow their methanization,
• a transport conduit (20) fluidically connected to the cover module (120) in order to evacuate the biogas produced by the methanizer (10),
• a safety conduit (30) comprising a lower part (30A), a connection portion (30-1) fluidically connected on the one hand to the lower part (30A) and on the other hand to the routing conduit (20) and a vent (30-2) fluidically connected on the one hand to the lower part (30A) and on the other hand to the atmosphere via a ventilation port (32) porous to the air, said safety duct ( 30) being shaped to store a volume of liquid by gravity in the lower part (30A),
• a detector (50) configured to detect the displacement of the volume of liquid in the safety conduit (30) beyond a predetermined displacement threshold when the liquid is sucked from the lower part (30A) through the connection portion (30-1) in the event of depression in the delivery duct (20).

Anaerobic digestion system (1) according to claim 1, in which the safety conduit (30) has a U-shape. Anaerobic digestion system (1) according to any one of the preceding claims, in which the aeration port (32) is located at a free end of the vent (30-2) opening into the atmosphere. Anaerobic digestion system (1) according to any one of the preceding claims, in which the aeration port (32) comprises an air-porous filter or plug. Methanisation system (1) according to any one of the preceding claims, in which the vent (30-2) comprises a liquid inlet orifice (31) and a leaktight plug (33). Methanisation system (1) according to any one of the preceding claims, in which the safety conduit (30) comprises an evacuation valve (34) mounted in its lower part (30A). Anaerobic digestion system (1) according to any one of the preceding claims, in which the volume of liquid comprises a substance preventing the liquid from freezing in the safety conduit (30). Anaerobic digestion system (1) according to any one of the preceding claims, comprising at least one booster (80) allowing the biogas to circulate in the transport pipe (20). Anaerobic digestion system (1) according to the preceding claim, in which the detector (50) is able to send a detection signal when the volume of liquid has exceeded the displacement threshold, said system (1) comprising a control module (60 ) adapted to receive said detection signal and to control the shutdown of the at least one booster (80). Methanisation system (1) according to any one of the preceding claims, in which the detector (50) comprises a float (51) capable of floating on the surface of the volume of liquid and at least one sensitive element (52) capable of detecting said float (51) when the float (51) is in line with said sensitive element (52), at the level of the predetermined displacement threshold.