FR3044563A1 - DEVICE AND METHOD FOR DECARBONATION OF BIOGAS - Google Patents

Abstract

The device (10) for decarbonating biogas comprises: - a first tank (105) for retaining a liquid volume comprising lime and water, comprising: - an inlet (110) for the liquid, - an inlet (115) for biogas in the liquid and - an outlet (120) for the liquid configured to release a portion of the liquid when the volume of liquid in the first vessel is greater than a predetermined maximum retention volume, - a second vessel (125). ), for retaining a liquid volume comprising lime and water, comprising: - an inlet (130) for liquid released by the first vessel, - an outlet (135) for decarbonated biogas and - an outlet (140) for the liquid, - a pipe (145) for recirculating the liquid exiting the second tank towards the first tank, - means (146) for recirculating the liquid leaving the second tank to the first tank, - a sensor (150) the pH of the liquid and a means (155) for supplying lime to the lime liquid when the pH of the liquid is below a predetermined set point.

Description

TECHNICAL FIELD OF THE INVENTION

The present invention is directed to a method and a device for decarbonating biogas. It applies, in particular, to the decarbonation of biogas produced by a physico-chemical or biological technique (bio-syngas, bio-sng) and in particular to biogas resulting from the methanisation of organic substrates.

STATE OF THE ART

Methanization of organic substrates is gaining renewed interest in France and Europe to produce biogas.

The biogas obtained contains mainly methane and carbon dioxide (CO2). The latter can constitute 25 to 50% of its total volume depending on the substrates used. This biogas must be purified and freed of its carbon dioxide as well as traces of hydrogen sulphide (H2S) in order to obtain a gas called "biomethane" of quality equivalent to natural gas.

Existing technologies such as wet scrubbing and amine scrubbing, membrane scrubbing or adsorption on materials are effective but hardly feasible for small on-farm installations or biogas flows can be less than 50 Nm3 / h. Similarly, cryogenic purification is expensive and difficult to envisage for flows below 80 Nm3 / h.

In addition, maintenance and direct exploitation of these technologies are not easy for a person without appropriate training, such as a farmer or a breeder.

Moreover, these technologies do not allow to trap the fraction of CO2 from purified biogas and this greenhouse gas is still often released to the atmosphere after separation.

Conventional biogas treatment techniques are mainly: - washing with water carried out in packed towers that can be relatively high and bulky, especially for small installations on the farm, - washing with amines, technology close to washing at water but using amines in the liquid phase to improve the transfer efficiency of CO2, - the adsorption of CO2 on support in fixed pressure bed or pressure swing adsorption (English " Pressure Swing Adsorption "), - Membrane technologies for separating methane and CO2, this technology has the advantage of requiring no chemical reagent but nevertheless requiring pretreatment of hydrogen sulphide (H2S) upstream of the membranes in order to protect them, - cryogenic purification, which is little used to treat biogas because of investment and operating costs. Eves.

Conventional decarbonation processes such as membrane treatments, water or amine washes or adsorption processes are relatively effective in purifying biogas, but expensive in terms of investment and exploitation. In the context of the purification of low-flow biogas, the main disadvantages of conventional solutions are the following: - washing with water and amines implement columns that may require a height and a large footprint, the structured or loose packings present in these columns clog up with time and their maintenance is not easy, their replacement at term represents a significant cost and requires the complete shutdown of the installation for maintenance, - the washing to amines requires a high energy consumption to regenerate the amines continuously in a boiler whose temperature is raised to more than 120 ° C, moreover, these hot spots may present a risk for the operating agent, - membrane technologies relatively recent have the advantage of not using any reagent, the term replacement of the membrane modules nevertheless representing ns a significant cost for biogas producers, - cryogenic purification is a biogas treatment technique with high investment and operating costs, especially for small biogas flows from a biogas on the farm. - Cryogenic purification is a sensitive technique and relatively difficult to exploit.

Finally, these technologies have the following common disadvantages: - their direct exploitation by a farmer or a farmer is not easy because these relatively complex processes require special technical skills and - they do not allow a trapping and recovery of CO2 gas so to limit its emission into the atmosphere.

OBJECT OF THE INVENTION

The present invention aims to remedy all or part of these disadvantages. For this purpose, according to a first aspect, the present invention is directed to a decarbonation device for biogas, which comprises: a first vessel for retaining a liquid volume comprising lime and water, comprising: an inlet for the liquid, - an inlet for biogas in the liquid and - an outlet for the liquid configured to release a part of the liquid when the volume of liquid in the first tank is greater than a predetermined maximum retention volume, - a second tank, for retain a liquid volume comprising lime and water, comprising: - an inlet for liquid released by the first tank, - a decarbonated biogas outlet and - an outlet for the liquid, - a liquid recirculation line out from the second tank to the first tank, - a liquid pH sensor and - a lime supply means to the liquid when the liquid pH is below a predetermined set value.

This device implements a decarbonation reaction of the biogas by neutralization in the liquid phase by lime Ca (OH) 2. This device is simple in design and can be easily operated by a biogas producer.

The chemical principle of decarbonation in the liquid phase by lime is a reliable and efficient solution. This principle also allows for a cost-effective solution for both investment and operating costs. Indeed, the proposed technique uses only one basic reagent, lime Ca (OH) 2 whose purchase cost in industrial quantities is about one hundred euros per ton. In addition, in terms of safety, the device has no hot spot.

The device also has the advantage of trapping all of the CO2 in the form of solid and stabilized calcium carbonate (CaCO 3). This inert material presents no health risk and can be valorized locally in agricultural composting with lime incinerators to stabilize the pH of acid soils, for example, or to bring to the soil an additional source of calcium and inorganic carbon. Residual calcium carbonate can also be used in local construction as backfill or in the form of lime plaster.

Finally, liquid recirculation and pH regulation allow the device to be automatically regulated without human intervention.

In embodiments, the device which is the subject of the present invention comprises an intermediate vessel, in the path of the liquid, downstream of the first vessel and upstream of the second vessel, for retaining a liquid volume comprising lime and water. water, comprising: - an inlet for liquid released by the first tank, - a biogas inlet, - a decarbonated biogas outlet and - an outlet for the liquid to the second tank.

These embodiments make it possible to improve the purity of the decarbonated biogas at the outlet of the device.

In embodiments, the first vessel has a decarbonated biogas outlet.

These embodiments allow an extraction, of the first tank, of the decarbonated biogas.

In embodiments, at least one decarbonated biogas outlet has a biogas shunt connected to a biogas inlet of at least one vessel.

These embodiments allow a recirculation of the gas leaving the device to at least one tank so as to improve its purity.

In embodiments, at least one decarbonated biogas outlet comprises means for measuring a quantity of carbon dioxide in the biogas leaving the tank associated with said outlet, the biogas supply of the bypass associated with said outlet being controlled according to the amount of carbon dioxide measured.

These embodiments allow a regulation of the quality of the decarbonation carried out by the device.

In embodiments, the biogas inlet is configured to inject the biogas into the first vessel at a rate of between five and sixty meters per second.

These embodiments avoid scaling of the biogas inlet, such scaling may damage or disable the device.

In embodiments, the liquid is lime water.

These embodiments allow the liquid to exhibit no solid particles.

In embodiments, the liquid is lime milk.

These embodiments allow a simplified embodiment of the liquid.

In embodiments, the maximum retention volume of the first tank is determined by an overflow wall having a predetermined height, the overflow of the liquid being effected to the second tank.

These embodiments allow an evacuation of decarbonated biogas by the surface of the liquid delimited by the maximum filling height of the tank defined by the height of the overflow wall. In this way, the release of the decarbonated biogas from the device does not require any specific extraction apparatus other than an outlet port positioned above the surface of the liquid.

In embodiments, the first and / or second vessel comprises calcium carbonate collection means positioned on a lower portion of said vessel.

These embodiments make it possible, on the one hand, to recover calcium carbonate formed outside the device and, on the other hand, to avoid filling the device with calcium carbonate.

In embodiments, the first vessel comprises: a first part comprising: the inlet for biogas in the liquid, the inlet for the liquid and an overflow wall of the liquid to a second part; part comprising: - a means of collecting calcium carbonate and - the outlet for the liquid.

These embodiments make it possible to maximize, for a minimum surface area of the device, the path traveled by the biogas in the first tank to achieve optimum decarbonation of this biogas.

In embodiments, the device that is the subject of the present invention comprises: an additional inlet for the liquid positioned on a lower part of the first part of the first tank; a means for opening / closing the liquid inlet; and - means for opening / closing the additional liquid inlet.

These embodiments allow the addition of water into the incoming liquid through the liquid inlet while the additional liquid inlet provides the recirculated liquid to the first vessel.

In embodiments, the device which is the subject of the present invention comprises a means for preventing scaling comprising: a means for inhibiting the means for supplying lime and a means for controlling the injection of water and biogas in the first tank. These embodiments make it possible to ensure the dissolution by CO2 of all the lime particles accumulated in the equipment.

According to a second aspect, the present invention relates to a decarbonation process of biogas, which comprises: a step of entering water into a first tank for retaining a volume of liquid comprising lime and water; a liquid entry step in the first tank, - a biogas entry step in the liquid in the first tank, - a liquid outlet step for releasing a part of the liquid when the volume of liquid in the first tank is greater than a predetermined maximum retention volume, - an inlet step, in a second tank, for retaining a liquid volume comprising lime and water, for the liquid released by the first tank, - a step outlet for decarbonated biogas, - an exit step for the liquid, - a step of recirculation of the liquid exiting the second tank towards the first tank, - a step of capturing the pH of the liquid and - a step of supplying lime to the liquid when the pH of the liquid is below a predetermined setpoint.

Since the aims, advantages and particular characteristics of the method which are the subject of the present invention being similar to those of the device which is the subject of the present invention, they are not recalled here.

BRIEF DESCRIPTION OF THE FIGURES Other advantages, aims and particular characteristics of the invention will emerge from the following nonlimiting description of at least one particular embodiment of the device and method for decarbonating biogas which are the subject of the present invention, in Referring to the accompanying drawings, in which: - Figure 1 shows schematically a first embodiment of the device of the present invention, - Figure 2 shows schematically a second particular embodiment of the device object of this FIG. 3 represents, schematically and in the form of a logic diagram, a particular sequence of steps of the method which is the subject of the present invention and FIG. 4 schematically represents a third particular embodiment of the device which is the object of the invention. present invention.

DESCRIPTION OF EXAMPLES OF EMBODIMENT OF THE INVENTION

This description is given in a nonlimiting manner, each feature of an embodiment being able to be combined with any other feature of any other embodiment in an advantageous manner.

It is already noted that the figures are not to scale.

The biogas described below can be of the type: - bio-SNG, - bio-syngas or - biogas resulting from the methanisation of organic compounds - and more generally any gas containing carbon dioxide.

FIG. 1, which is not to scale, shows a schematic view of an embodiment of the device 10 which is the subject of the present invention. This decarbonation device 10 of biogas comprises: a first tank 105, for retaining a volume of liquid comprising lime and water, comprising: an inlet 110 for the liquid; an inlet 115 for biogas in the liquid and - an outlet 120 for the liquid configured to release a portion of the liquid when the volume of liquid in the first tank 105 is greater than a predetermined maximum retention volume, - a second tank 125 for retaining a liquid volume comprising the lime and water, comprising: - an inlet 130 for liquid released by the first tank 105, - an outlet 135 for decarbonated biogas and - an outlet 140 for the liquid, - a pipe 145 for recirculating the liquid out of the second tank 125 to the first tank 105, a means 146 for recirculating the liquid from the second tank 125 to the first tank 105, a sensor 150 of the pH of the liquid and a means 155 for supplying lime to the liquid when the pH of the liquid is below a predetermined set point.

The liquid used by the device 10 is, for example, milk of lime. The milk of lime is a water supersaturated in lime presenting solid particles.

The lime provided by the means 155 for providing lime is: - solid lime, - lime water or - lime milk.

In variants, the device 10 comprises a means for preparing lime water and / or milk of lime configured to supply the means 155 for supplying lime. This means of preparation, not shown, is for example a water mixture tank and solid lime, the amount of solid lime inserted into the tank as a function of the pH of the captured liquid.

In other embodiments, the liquid is lime water. The lime water is saturated with lime at the threshold of solubility of Ca (OH) 2 and therefore has no solid particle. Lime water is the supernatant obtained after saturation and decantation of the milk of lime.

The first tank 105 is, for example, a closed and sealed volume configured to retain a predetermined volume of liquid. This first tank 105 is formed, in FIG. 1, of a base and side walls surrounding the base so as to define the volume of the tank 105.

The first tank 105 acts as a decarbonation compartment of the biogas by neutralization of the CO2 in aqueous phase. The decarbonation is carried out by contacting the biogas with a water saturated with lime or a milk of lime.

The carbon dioxide contained in the biogas changes from the gaseous phase to the basic aqueous phase by a conventional transfer mechanism. The hydroxide ions (OH-) provided by the lime make it possible to neutralize the dissolved CO2 by forming the hydrogen carbonate and bicarbonate ions in solution. The chemical reactions involved in the solubilization of CO2 and its neutralization are represented by the following acid-base equilibria: CC ^ tg) ^ CO2 (aq) H2O + CC> 2 (aq) <=> H2 CO3

## STR5 ## 11), conditions encountered in lime water and lime milk.

Carbonate and hydrogen carbonate ions from the solubilization and neutralization of CO2 in basic waters precipitate in the form of recoverable CaCC> 3 calcium carbonate.

This neutralization with lime also has the effect of eliminating to a certain extent the hydrogen sulphide present in the biogas.

H2S + OH- o HS- + H2O HS- + OH2 "S2 + H20

The sulfur precipitates are therefore likely to form, thus making it possible to eliminate all or part of the traces of H2S gas present in the biogas.

The device 10 constitutes a reactor for the chemical mechanisms described above. This device 10 makes it possible to bring the biogas into contact with the solution of water saturated with lime. After this contact phase, a purified biogas is obtained and a water settling phase makes it possible to recover the solid particles of calcium carbonate and lime incinerators at the bottom of the device 10. The inlet 110 for liquid is, for example, for example, a sealed pipe connected to a liquid injection valve in the first tank 105. This liquid inlet 110 is preferably positioned on a lower part of a wall, that is close to the lower part of the first one. tank 105.

When the first tank 105 is empty, the liquid entering the first tank 105 fills this first tank 105 until the predetermined maximum retention volume is reached by the volume of liquid in the first tank 105. The inlet 115 for biogas is, for example, formed of several hollow injection columns provided with orifices for injecting biogas into the liquid when the liquid fills the first tank 105.

In preferred embodiments, the inlet 115 for biogas is configured to inject the biogas into the first tank 105 at a speed of between five and sixty meters per second.

This speed is reached, for example, for a nominal injection flow of biogas in a line supplying the biogas at the inlet 115, by sizing orifices, in at least one column, so that the biogas velocity at the level of of these orifices is between five and sixty meters per second.

If the flow rate of biogas is variable, the sizing of the orifices is made according to the lowest operating rate of the device 10.

In variants, the biogas is stored in a tank (not shown) positioned upstream of the inlet 115 for biogas so that the biogas supplied to the inlet 115 for biogas has a pressure determined by the pressure at the inlet. inside the tank. This reservoir may also include a biogas pressurization means, such as a pump for example.

Once the maximum retention volume reached by the volume of liquid in the first tank 105, the liquid exits the first tank 105 through the outlet 120 of liquid. The outlet 120 is, for example, a pipe connecting the first tank 105 to the second tank 125. This pipe can be blocked, in variants, by a valve for example.

In preferred embodiments, the maximum retention volume of the first tank 105 is determined by an overflow wall 160 having a predetermined height, the overflow of the liquid being effected to the second tank 125 by overflow.

This overflow wall 160 is one of the walls constituting the periphery, relative to the base of the first tank 105. This wall 160 has a height less than the positioning height of a tank ceiling so that the maximum volume of liquid in the first tank 105 is less than the total volume of the first tank 105.

In this way, the biogas exits the liquid to fill a volume of the first tank 105 above the surface of the liquid.

In embodiments, such as that shown in Figure 2, the sizing of this volume for biogas is configured so that the biogas is driven by the liquid to the second tank.

In preferred embodiments, the overflow wall 160 has a height configured so that the overflow area, corresponding to the outlet 120 for liquid, is at a high end of the height of the walls, in contact with the ceiling.

In preferred embodiments, such as that shown in FIG. 1, the first tank 105 comprises a calcium carbonate collection means 165 positioned on a lower part of said tank 105. This collecting means 165 is also intended for the collection of calcium carbonate. incense of lime.

This collecting means 165 is, for example, formed of a pipe whose inlet is positioned at the bottom end of a settling funnel forming the base of the first tank 105.

This pipe also comprises a valve which, in the open position, causes gravity to evacuate the calcium carbonate present in the decantation funnel.

The second vessel 125 is, for example, a volume configured to retain a predetermined volume of liquid. This second tank 125 is formed, in FIG. 1, of a lower part and lateral walls surrounding the lower part so as to define the predetermined maximum retention volume of the tank 125.

This second tank 125 comprises the inlet 130 for liquid released by the first tank 105. This inlet 130 is, for example, a pipe connecting the first tank 105 to the second tank 125.

Preferably, this second tank 125 comprises submerged slats (not shown) making it possible to accelerate the settling of the solid particles. Such slats are illustrated in FIG.

In preferred embodiments, such as that represented in FIG. 1, the inlet 130 is formed by the opening resulting from the height of the overflow wall 160 of the first tank 105. Preferably, this overflow wall 160 forms a walls of the second tank 125.

The outlet 135 for decarbonated biogas is, for example, a pipe positioned above the surface of the liquid when this liquid fills the maximum retention volume of the second tank 125.

The outlet 140 for the liquid is, for example, a pipe positioned on a wall of the second tank 125 defining the predetermined maximum retention volume as a function of the positioning of this pipe.

In preferred embodiments, the outlet 140 is formed by an overflow wall whose upper end is positioned at a lower height of the height of the inlet 130 for liquid. The liquid overflowing the overflow wall enters the recirculation line 145.

This overflow wall is one of the walls constituting the periphery, with respect to the lower part, or base, of the second tank 125. This wall has a height less than the height of positioning of a tank ceiling so that the maximum volume of liquid in the second tank 125 is less than the total volume of the second tank 125.

In this manner, the biogas exits the liquid to fill a volume of the second tank 125 above the surface of the liquid and exits through the exit 135 for biogas.

The recirculation pipe 145 is, for example, a sealed pipe connecting the liquid outlet 140 of the second tank 125 to the liquid inlet 110 of the first tank 105.

The means 146 for recirculating the liquid discharged from the second tank 125 to the first tank 105 is, for example, a pump.

In variants, the pipe 145 includes an outlet 147 for returning the recirculated water to the same outlet point as solids decanted and incinerated lime collected by a collection means, 165 and / or 170. These solids decanted, incuits of lime and recirculated waters out of the device 10 can be treated downstream.

The sensor 150 of the pH of the liquid is, for example, a pH probe positioned in the first tank 105, in the second tank 125 or in the recirculation line 145.

The lime supply means 155 is, for example, an automatic lime dispenser in powder form or in liquid form having an opening for dispensing lime into the liquid. This opening is controlled by an electronic control circuit, such a command being issued when the captured pH is less than a predetermined set value. The desired pH value is preferably greater than 12.

In preferred embodiments, such as that shown in FIG. 1, the second tank 125 comprises a calcium carbonate collection means 170 positioned on a lower part of said tank 125. This collection means 170 is also intended for the collection of calcium carbonate. incense of lime.

This collection means 170 is, for example, formed of a pipe whose inlet is positioned at the bottom end of a settling funnel forming the base of the second tank 125.

This pipe also comprises a valve which, in the open position, causes the gravity evacuation of the calcium carbonate positioned in the decantation funnel.

In preferred embodiments, each discharge valve of a collection means, 165 or 170, is actuated automatically and periodically according to a predetermined period or determined by a user.

FIG. 2, which is not to scale, shows a schematic view of one embodiment of the device 20 of the present invention. This biogas decarbonation device 20 comprises: a first tank 205, for retaining a volume of liquid comprising lime and water, comprising: an inlet 210 for the liquid; an inlet 215 for biogas in the liquid and - an outlet 220 for the liquid configured to release a portion of the liquid when the volume of liquid in the first tank 205 is greater than a predetermined maximum retention volume, - a second tank 225 for retaining a liquid volume comprising the lime and water, comprising: - an inlet 230 for liquid released by the first tank 205, - an outlet 235 for decarbonated biogas and - an outlet 240 for the liquid, - a pipe 245 for recirculating the liquid out of the second tank 225 to the first tank 205, a sensor 250 of the pH of the liquid and a means 255 for supplying lime to the liquid when the pH of the liquid is less than a predetermined set value.

The liquid used by the device 20 is, for example, milk of lime. The milk of lime is a water supersaturated in lime presenting solid particles. The lime provided by the means 255 for supplying lime is: - solid lime, - lime water or - lime milk.

In variants, the device 20 comprises a means for preparing lime water and / or milk of lime configured to supply the means 255 for supplying lime. This means of preparation, not shown, is for example a water mixture tank and solid lime, the amount of solid lime inserted into the tank as a function of the pH of the captured liquid.

In other embodiments, the liquid is lime water. The lime water is saturated with lime at the threshold of solubility of Ca (OH) 2 and therefore has no solid particle. Lime water is the supernatant obtained after saturation and decantation of the milk of lime.

The first vessel 205 is, for example, a sealed and sealed volume configured to retain a predetermined volume of liquid. This first tank 205 performs the same function as the first tank 105 described with reference to FIG.

In preferred embodiments, such as that shown with reference to FIG. 2, the first tank 205 comprises: a first portion 275, called the first contact chamber, comprising: the inlet 215 for biogas in the liquid; the inlet 210 for the liquid and - a wall 280 for overflow of the liquid to a second portion 285, - the second portion 285, said second contact chamber, comprising: - means 265 for collecting calcium carbonate and - the outlet 220 for the liquid.

The first part 275 is, for example, a volume for receiving the liquid and the biogas. One of the side walls 280 forming, together with a base and a ceiling, the volume, is said to "overflow", that is to say that the height of this wall 280 relative to the base is less than the maximum height of the volume forming the first part. In this way, once the liquid reaches the point of maximum height of the overflow wall 280, the liquid is poured into the second portion 185 by overflow.

The second portion 285 is, for example, a volume for receiving liquid and biogas formed by sidewalls, a base and a ceiling.

Preferably, this second portion 285 has a wall which extends from the ceiling towards the base and which has a width such that, on the extension height of this wall, the wall extends from one edge to the other of the second part 285. In this way this wall acts as an obstacle for the flow of liquid which is forced to bypass this wall. Thus, the path traveled by the liquid and the biogas is increased, which improves the transfer time of the carbon dioxide to the aqueous solution of lime.

In preferred embodiments, the device 20 comprises: - an additional inlet 290 for the liquid positioned on a lower part of the first part of the first tank, - a means 295 for opening / closing the liquid inlet and a means 300 for opening / closing the additional liquid inlet. The inlet 210 for liquid is, for example, a sealed pipe connected to a liquid injection valve in the first tank 205, this injection valve acting as an opening / closing means 295. The inlet 210 is connected to the recirculation pipe 245. The additional inlet 290 for the liquid is, for example, a sealed line connected to a liquid injection valve in the first tank 205, this injection valve acting as an opening / closing means 300. The inlet 290 additional is connected to the recirculation pipe 245 by a bypass.

Preferably, a water injection pipe 320 is positioned between the branch providing the additional inlet 290 and the inlet 210 for liquid. This water injection pipe 320 acts as a water inlet of the device, this water can be potable and allows extra water in the circuit. This water also allows internal cleaning of the system during maintenance stops. This water injection pipe 320 comprises an opening / closing valve controlled by an electronic control circuit or by a level pear float.

When the first vat 205 is empty, the liquid entering the first vat 205 fills this first vat 205 until the predetermined maximum retention volume is reached by the volume of liquid in the first vat 205. The entry 215 for biogas is, for example, formed of several hollow injection columns provided with orifices for injecting biogas into the liquid when the liquid fills the first tank 205.

In preferred embodiments, the biogas inlet 215 is configured to inject the biogas into the first vessel 205 at a velocity of between five and sixty meters per second.

This speed is reached, for example, for a nominal injection flow of biogas in a pipe supplying the biogas at the inlet 215, by sizing orifices, in at least one column, so that the speed of the biogas at the of these orifices is between five and sixty meters per second.

If the flow of biogas is variable, the sizing of the orifices is made according to the lowest operating flow rate of the device 20.

In variants, the biogas is stored in a tank (not shown) positioned upstream of the inlet 215 for biogas so that the biogas supplied to the entry 215 for biogas has a pressure determined by the pressure at the inlet. inside the tank. This reservoir may also include a biogas pressurization means, such as a pump for example.

Once the maximum retention volume reached by the volume of liquid in the first tank 205, the liquid exits the first tank 205 through the outlet 220 of liquid. The outlet 220 is, for example, a pipe connecting the first tank 205 to the second tank 225. This pipe can be blocked, in variants, by a valve for example.

In preferred embodiments, the maximum retention volume of the first tank 205 is determined by an overflow wall 260 having a predetermined height, the overflow of the liquid being effected towards the second tank 225.

This overflow wall 260 is one of the walls constituting the periphery, with respect to the lower part, or base, of the first tank 205. This wall 260 has a height less than the positioning height of a tank ceiling. so that the maximum volume of liquid in the first tank 205 is less than the total volume of the first tank 205.

In this way, the biogas exits the liquid to fill a volume of the first tank 205 not filled by the liquid and positioned in height relative to the surface of the liquid.

In embodiments, such as that shown in FIG. 2, the sizing of this biogas volume is configured so that the biogas is entrained by the liquid towards the second tank 225.

In preferred variants, the overflow wall 260 has a height configured so that the overflow area, corresponding to the outlet 220 for liquid, is at a high end of the height of the walls, in contact with the ceiling.

In preferred embodiments, such as that represented in FIG. 2, the first tank 205 comprises a calcium carbonate collection means 265 positioned on a lower part of said tank 205. This collection means 265 is also intended for the collection of calcium carbonate. incense of lime.

This collecting means 265 is, for example, formed of a pipe whose inlet is positioned at the bottom end of a settling funnel forming the base of the first tank 205.

This pipe also comprises a valve which, in the open position, causes the gravity evacuation of the calcium carbonate positioned in the decantation funnel.

The second vessel 225 is, for example, a volume configured to retain a predetermined volume of liquid. This second tank 225 is formed, in FIG. 2, of a lower part and side walls surrounding the lower part so as to define the predetermined maximum retention volume of the tank 225.

This second tank 225 comprises the inlet 230 for liquid released by the first tank 205. This inlet 230 is, for example, a pipe connecting the first tank 205 to the second tank 225.

Preferably, this second vessel 225 comprises submerged slats 226 for accelerating the settling of the solid particles.

In preferred embodiments, such as that represented in FIG. 2, the inlet 230 is formed by the opening resulting from the height of the overflow wall 260 of the first tank 205. Preferably, this overflow wall 260 forms a walls of the second tank 225.

The exit 235 for decarbonated biogas is, for example, a pipe positioned above the surface of the liquid when this liquid fills the maximum retention volume of the second tank 225.

The outlet 240 for the liquid is, for example, a pipe positioned on a wall of the second tank 225 defining the predetermined maximum retention volume as a function of the positioning of this pipe.

In preferred embodiments, the outlet 240 is formed by an overflow wall whose upper end is positioned at a lower height of the height of the inlet 230 for liquid. The liquid overflowing from the overflow wall enters the recirculation pipe 245.

This overflow wall is one of the walls constituting the periphery, with respect to the lower part, or base, of the second tank 225. This wall has a height less than the positioning height of a tank ceiling so that the maximum volume of liquid in the second tank 225 is less than the total volume of the second tank 225.

In this way, the biogas comes out of the liquid to fill a volume of the second tank 225 not filled by the liquid and positioned in height relative to the surface of the liquid and out through the exit 235 for biogas.

The recirculation pipe 245 is, for example, a sealed pipe connecting the outlet 240 for liquid from the second tank 225 to the liquid inlet 210 of the first tank 205.

The means 246 for recirculating the liquid exiting the second tank 225 to the first tank 205 is, for example, a pump.

In variants, the pipe 245 has an outlet 247 making it possible to return the recirculated water to the same outlet point as the decanted solids and lime incinerators collected by means of collection, 265 and / or 270. These solids decanted, incinerated lime and recirculated waters out of the device 20 can be treated downstream.

In variants, the device 20 comprises a biogas injection means in the recirculation conduit 245 for acidifying the recirculated lime water.

The sensor 250 of the pH of the liquid is, for example, a pH probe positioned in the first tank 205, in the second tank 225 or in the recirculation line 245.

The lime supply means 255 is, for example, an automatic lime dispenser in powder form having an opening for dispensing lime into the liquid. This opening is controlled by an electronic control circuit, such a command being issued when the captured pH is less than a predetermined set value. The desired pH value is preferably greater than twelve.

In preferred embodiments, such as that represented in FIG. 2, the second tank 225 comprises a means 270 for collecting calcium carbonate positioned on a lower part of said tank 225. This collection means 270 is also intended for the collection of calcium carbonate. incense of lime.

This collecting means 270 is, for example, formed of a pipe whose inlet is positioned at the bottom end of a settling funnel forming the base of the second tank 225.

This pipe also comprises a valve which, in the open position, causes the gravity evacuation of the calcium carbonate positioned in the decantation funnel.

In preferred embodiments, each discharge valve of a collection means, 265 or 270, is actuated automatically and periodically at a predetermined period or determined by a user or by a measurement of solids level.

In preferred embodiments, the device 20 comprises a means 305 for preventing scaling comprising: a means 310 for inhibiting the means 255 for supplying lime and a means 315 for controlling the injection of water and of biogas in the first tank 205.

The prevention means 305 is, for example, an electronic control circuit which periodically emits a descaling control of the device 20. When such a command is issued, an electronic control circuit, forming an inhibition means 310, prevents the supply device 255 to supply lime to the circulating liquid in the device 20. Then, an electronic control circuit, forming an injection control means 315, controls the injection of water into the water injection pipe 320 by opening the opening / closing valve attached to this pipe 320.

The descaling is carried out by rinsing the equipment with carbonated water, that is to say water saturated with biogas, without addition of lime. This phase of preventive cleaning can be automated at a daily frequency and does not require any intervention of the user. This cleaning is intended to ensure the dissolution by CO2 of all the lime particles accumulated in the device 20. The regular rinsing does not require any particular reagent except those already implemented by the device 20.

FIG. 3 shows a particular flow diagram of the process of the present invention. This biogas decarbonation process comprises: a liquid inlet step 405 in the first tank; a biogas inlet stage 410 in the liquid in the first tank; a liquid outlet stage 415 for releasing the liquid. a part of the liquid when the volume of liquid in the first tank is greater than a predetermined maximum retention volume, - an inlet stage 420, in a second tank, for retaining a liquid volume comprising lime and water. water, for the liquid released by the first tank, a decarbonated biogas exit step 425, an exit stage 430 for the liquid, a liquid recirculation stage 435 from the second tank to the first tank, a step 440 for capturing the pH of the liquid and a step 445 for supplying lime to the liquid when the pH of the liquid is less than a predetermined reference value.

This method is implemented, for example, by one of the devices, 10 or 20, described with reference to Figures 1 or 2.

FIG. 4 diagrammatically shows a third particular embodiment of the device 40 which is the subject of the present invention. This device 40 for decarbonating biogas comprises: a first tank 510, for retaining a volume of liquid comprising lime and water, comprising: an inlet 505 for the liquid; a inlet 570 for biogas in the liquid and - an outlet 511 for the liquid configured to release a part of the liquid when the volume of liquid in the first tank is greater than a predetermined maximum retention volume, - an intermediate tank (515), in the path of the liquid, in downstream of the first tank and upstream of the second tank, for retaining a liquid volume comprising lime and water, comprising: an inlet (516) for liquid released by the first tank (510); inlet (575) for biogas, - an outlet (550) for decarbonated biogas and - an outlet (517) for the liquid to the second tank (520), - a second tank 520, for retaining a liquid volume containing lime and water, comprising: - an entr e 521 for liquid released by the intermediate vessel, - a 585 outlet for decarbonated biogas and - an outlet 522 for the liquid, - a pipe 525 for recirculating the liquid out of the second tank to the first tank, - a means 546 for recirculation liquid discharged from the second tank to the first tank; a sensor 526 for the pH of the liquid; and a means 560 for supplying lime to the liquid when the pH of the liquid is below a predetermined set point.

In preferred embodiments, such as that shown in FIG. 4, the first tank 510 has an outlet 545 for decarbonated biogas.

In preferred embodiments, such as that represented in FIG. 4, at least one outlet, 545, 550 and / or 585, for decarbonated biogas comprises a bypass, 535 and / or 540, for biogas connected to an inlet, 570, 575 and / or 580, for biogas of at least one tank, 510, 515 and / or 520.

In preferred embodiments, such as that shown in FIG. 4, at least one outlet, 545 and / or 550, for decarbonated biogas comprises a means, 547 and / or 548, of measuring a quantity of carbon dioxide in the biogas leaving the tank, 510 and / or 515, associated with said outlet, the biogas supply of the bypass associated with said outlet being controlled according to the amount of carbon dioxide measured.

As is understood, this device 30 for decarbonating a gas comprises three tanks, 510, 515 and 520, nicknamed contact chambers.

The first tank 510 comprises: a water inlet 505, a recirculated liquid inlet 565, a biogas inlet 570 configured so that the biogas is diffused into the liquid contained in the tank 510, a decarbonated biogas outlet 545 positioned outside the liquid contained in the tank 510, - an outlet 511 for liquid to the intermediate tank 515 and - an outlet for decanted and incinerated solids positioned at the base of the tank 510. The inlet 570 for biogas is supplied with biogas by a biogas inlet pipe 530 and a pipe 535 for recirculating all or part of the biogas exiting via the decarbonated biogas outlet 545 or via a decarbonated biogas outlet 550 of the second tank 515.

This 535 recirculation pipe may include an automatic or manual opening / closing mechanism.

This recirculation line 535 may comprise a recirculation means, such as a pump for example, decarbonated biogas in line 535.

The liquid outlet to the intermediate tank 515 is formed by a side wall of the first tank 510 whose height relative to the base of the tank 510 is less than the total height of the tank 510. Thus, the maximum volume of The liquid in the vessel is determined by the height of the side wall so that any excess volume is poured over the intermediate vessel 515.

Intermediate tank 515 comprises: an inlet for liquid discharged from the first tank 510; a inlet 575 for biogas configured so that the biogas is diffused into the liquid contained in the intermediate tank; a 550 outlet for decarbonated biogas positioned outside the tank; the liquid contained in the intermediate tank 515, an outlet 517 for liquid to the second tank 520 and an outlet for decanted and incinerated solids positioned at the base of the intermediate tank 515.

By decarbonated biogas is meant the biogas injected into the first tank and, by passage through the liquid, lost all or part of the carbon dioxide that it contained. The inlet 575 for biogas is supplied with biogas by the recirculation line 535 of all or part of the biogas discharged through the inlet 530 for biogas, via the outlet 545 for decarbonated biogas or via an outlet 550 for decarbonated biogas of the tank 515. intermediate. The recirculation of decarbonated biogas aims to lower the proportion of carbon dioxide present in the biogas by successive passages in the tanks containing the liquid. Recirculation of the biogas can also be carried out from the other tanks, depending on the proportion of carbon dioxide in the decarbonated gas that is to be obtained.

The liquid outlet to the third tank 520 is formed by a side wall of the intermediate tank 515 whose height relative to the base of the intermediate tank 515 is less than the total height of the intermediate tank 515. Thus, the maximum volume of liquid in the intermediate tank is determined by the height of the side wall so that any excess volume is discharged by overflow in the second tank 520.

The second tank 520 comprises: an inlet 521 for liquid discharged from the intermediate tank 515, a biogas inlet 580 configured so that the biogas is diffused into the liquid contained in the second tank 520, a decarbonated biogas outlet 585 positioned. out of the liquid contained in the second tank 520, - an outlet to the liquid recirculation pipe 525 to the first tank 510 and - an outlet for decanted and incinerated solids positioned at the base of the second tank 520. The inlet 580 for biogas is fed with biogas by a recirculation line 540 of all or part of the biogas output by the exit 550 for decarbonated biogas or by a 545 outlet for decarbonated biogas of the first tank 510.

This recirculation pipe 540 may comprise an automatic or manual opening / closing mechanism.

This recirculation pipe 540 may comprise a recirculation means, such as a pump, for example, decarbonated biogas in line 540.

The outlet towards the recirculation pipe 525 is formed, for example, by a side wall of the second tank 520 whose height relative to the base of the second tank 520 is less than the total height of the second tank 520. , the maximum volume of liquid in the second tank 520 is determined by the height of the side wall so that any excess volume is poured by overflow into the recirculation line 525.

In particular embodiments, the device 40 further comprises a lime tank 555 configured to supply lime to a mixer 560 in which water is present to form lime water or milk of lime. lime. A quantity of liquid thus formed is injected into the second tank 520 as a function of a value representative of the pH measured in the recirculation line 525 or in one of the tanks 510, 515 and / or 520.

Preferably: the biogas is injected into the first tank 510 so as to be partially decarbonated by the liquid present in this first tank 510; the partially decarbonated biogas leaves the first tank 510 via the exit 545 for decarbonated biogas, this partially decarbonated biogas enters the recirculation pipe 535 and is injected into the intermediate tank 515, the biogas advantageously decarbonated by the liquid present in this intermediate tank 515 leaves the intermediate tank 515 through the outlet 550 for decarbonated biogas and this biogas d The decarbonated advantage enters the recirculation line 540 and is injected into the second tank 520; the biogas is decarbonated by the liquid present in the second tank 520 and leaves the device 40 via the outlet 585.

However, the process described above is not limiting, and the biogas leaving a tank can be redirected to the biogas inlet of any tank, including the tank from which the biogas is discharged.

As understood by reading the foregoing description, the present invention makes it possible to implement: a simple and robust design method that can be automated to feed it and the preparation of reagents, such as lime powder, lime milk, and water from the network, - a compact process that can be easily set up to treat small flows in the case of small on-farm biogas plants, - a device with no hot surface and with a relatively low risk level, - the trapping and stabilization of CO2 gas in the form of calcium carbonate reducing the emission of greenhouse gases, and - the easy recovery of the by-product from the process and composed mainly of CaCC> 3 calcium carbonate and lime incuits Ca (OH) 2. These residues do not present any particular health risk and are easily recoverable locally as an agricultural amendment on acid soils or under construction.

Claims (14)

1. Device (10, 20, 40) for decarbonating biogas, characterized in that it comprises: a first tank (105, 205, 510) for retaining a liquid volume comprising lime and water , comprising: - an inlet (110, 210, 505) for the liquid, - an inlet (115, 215, 570) for biogas in the liquid and - an outlet (120, 220, 511) for the liquid configured to release a liquid. part of the liquid when the volume of liquid in the first tank is greater than a predetermined maximum retention volume, - a second tank (125, 225, 520), for retaining a liquid volume comprising lime and water, comprising: - an inlet (130, 230, 521) for liquid released by the first vessel, - an outlet (135, 235, 585) for decarbonated biogas and - an outlet (140, 240, 522) for the liquid, - a pipe (145, 245, 525) for recirculating the liquid exiting the second tank towards the first tank; means (146, 246, 546) for recirculating the liquid output from the second tank to the first tank, - a sensor (150, 250, 526) of the pH of the liquid and - a means (155, 255, 560) for supplying lime to the liquid when the pH of the liquid is less than a predetermined set value. 2. Device (40) according to claim 1, which comprises a tank (515) intermediate, in the path of the liquid, downstream of the first vessel and upstream of the second vessel, for retaining a liquid volume containing lime and water, comprising: - a liquid inlet (516) released by the first tank (510), - a biogas inlet (575), - a decarbonated biogas outlet (550) and - an outlet (517) for the liquid to the second tank (520). 3. Device (40) according to one of claims 1 or 2, wherein the first vessel (510) comprises an outlet (545) for decarbonated biogas. 4. Device (40) according to one of claims 1 to 3, wherein at least one outlet (545, 550, 585) for decarbonated biogas comprises a bypass (535, 540) for biogas connected to an inlet (570, 575 , 580) for biogas of at least one tank (510,515,520). 5. Device according to claim 4, wherein at least one outlet (545, 550) for decarbonated biogas comprises means (547, 548) for measuring a quantity of carbon dioxide in the biogas leaving the tank (510, 515) associated with said output, the biogas feed of the bypass associated with said outlet being controlled according to the amount of carbon dioxide measured. 6. Device (10, 20) according to one of claims 1 to 5, wherein the inlet (115, 215) for biogas of the first tank (105, 205) is configured to inject the biogas into the first tank to a speed of between five and sixty meters per second. 7. Device (10, 20) according to one of claims 1 to 6, wherein the liquid is lime water. 8. Device (10, 20) according to one of claims 1 to 6, wherein the liquid is milk of lime. 9. Device (10, 20) according to one of claims 1 to 8, wherein the maximum retention volume of the first vessel (105, 205) is determined by a wall (160, 260) of overflow having a predetermined height , the overflow of the liquid being effected to the second tank (125, 225). 10. Device (10, 20) according to one of claims 1 to 9, wherein the first and / or second vessel (105, 205, 125, 225) comprises means (165, 265, 170, 270) of collecting calcium carbonate positioned on a lower portion of said tank. 11. Device (20) according to claim 10, wherein the first tank (205) comprises: - a first portion (275) comprising: - the inlet (215) for biogas in the liquid, - the inlet (210) for the liquid and - a wall (280) for overflowing the liquid to a second portion (285), - the second part comprising: - means (265) for collecting calcium carbonate and - the outlet (220) for the liquid . 12. Device (20) according to claim 11, which comprises: - an additional inlet (290) for the liquid positioned on a lower part of the first part of the first tank (205), - means (295) for opening / closing the liquid inlet and - means (300) for opening / closing the additional liquid inlet. 13. Device (20) according to one of claims 1 to 12, which comprises means (305) for preventing scaling comprising: - means (310) for inhibiting the means (255) for providing lime and means (315) for controlling the injection of water and biogas into the first tank (205). 14. Process (30) for decarbonating biogas, characterized in that it comprises: a step (405) for entering liquid into the first vessel; a step (410) for introducing biogas into the liquid in the first vat, - a step (415) for discharging the liquid to release a part of the liquid when the volume of liquid in the first vat is greater than a predetermined maximum retention volume, - a step (420) of entry, in a second tank, for retaining a liquid volume comprising lime and water, for the liquid released by the first tank, - a step (425) for decarbonated biogas outlet, - a step (430) of output for the liquid, a step (435) for recirculating the liquid exiting the second tank to the first tank, a step (440) for capturing the pH of the liquid and a step (445) for supplying lime to the liquid when the pH of the liquid is below a predetermined set point.