FR2972643A1 - Device, useful in an installation for recovery of methane and carbon dioxide from liquid and biogas under pressure, comprises a degassing tank, a degassing unit, and a reservoir containing a pressurized liquid - Google Patents

Abstract

The device (3) comprises a degassing tank (8), a degassing unit, and a reservoir containing a pressurized liquid. The degassing unit is configured such that it is adapted to allow an abrupt change of a pressure of the liquid under pressure at an outlet of the reservoir while providing a separation of liquid and carbon dioxide, and is formed by a conduit (9) that is connected to the reservoir at one end and opens at an opposite end into the degassing tank, a relaxation valve mounted on the conduit, and a mixer placed in the conduit. The device (3) comprises a degassing tank (8), a degassing unit, and a reservoir containing a pressurized liquid. The degassing unit is configured such that it is adapted to allow an abrupt change of a pressure of the liquid under pressure at an outlet of the reservoir while providing a separation of liquid and carbon dioxide, and is formed by a helicoidal conduit (9) that is connected to the reservoir at one end and opens at an opposite end into the degassing tank, a relaxation valve mounted on the conduit and a mixer placed in the conduit. The free liquid of carbon dioxide and extracted carbon dioxide is discharged from the degassing tank to an outlet conduit. The conduit extends along the degassing tank such that, in the outlet conduit, the carbon dioxide escapes and the liquid contained in the reservoir flows into the degassing tank, and extends around the degassing tank from a lower part to an upper part of the degassing tank. The reservoir is placed partially in the degassing tank so that the free liquid of carbon dioxide surrounds the reservoir on a part of its height. The degassing tank is partially buried. The carbon dioxide is derived from a biogas under pressure, and is dissolved in the pressurized liquid. The free liquid of carbon dioxide contained in the degassing tank is renewed in another reservoir by a pumping unit. Independent claims are included for: (1) an installation to recover carbon dioxide from biogas; and (2) a method for recovery of carbon dioxide from biogas.

Description

DEVICE FOR RECOVERING CARBON DIOXIDE FROM BIOGAS

The invention relates to a device for recovering carbon dioxide from a liquid. The invention also relates to a joint recovery facility for methane and carbon dioxide comprising said device. The invention finally relates to a method for jointly recovering methane and carbon dioxide using the recovery device.

The invention relates to the field of biogas recycling such as those from industry or agriculture. Biogas is a combustible gas resulting from the fermentation of organic waste of animal or plant origin in the absence of oxygen, which is mainly composed of methane and carbon dioxide.

Biogas recycling plants are known (WO2008 / 115079, EP2163293, WO2008 / 049613, WO2008 / 097304, WO2010 / 019763, WO2009 / 146805). These facilities aim to recover the methane contained in these biogases. Typically, the recovery of methane from biogas is carried out by means of a filling column which comprises a part called packing area through which circulates, under pressure and against the current, a liquid and biogas. The packing zone makes it possible to promote bringing the liquid and the biogas into contact over a large contact surface. Prior to this passage through the lining zone, the biogas is freed of its sulfur and is then pressurized. It is known that methane is very poorly soluble. Thus, when the sulfur-free and pressurized biogas enters the packing zone, there is a separation of the methane from the liquid. The methane is then extracted from the filling column, generally in the upper part of said column. Then, the liquid used to separate the methane from the rest of the biogas under pressure is then generally rejected in nature. This liquid contains carbon dioxide from biogas. Carbon dioxide dissolved in the liquid as the biogas passed through the packing area.

It is therefore one of the aims of the present invention to recycle this liquid comprising carbon dioxide so that it can not only extract the carbon dioxide that it contains but also to reuse this liquid once cleared of the dioxide. of carbon.

It is another object of the invention to recycle a biogas containing any other type of gas capable of being soluble. To do this, the invention provides a device for recovering carbon dioxide from a liquid containing dissolved carbon dioxide. For example, the carbon dioxide containing liquid comes from treated biogas after passing through a filling zone of a fill column as previously mentioned. This device according to the invention comprises a reservoir containing under pressure the same liquid. Degassing means are provided at the outlet of the reservoir to promote the extraction of carbon dioxide from the liquid. The liquid thus freed of carbon dioxide can then be recovered in a degassing tank for later use. Advantageously, the liquid reservoir comprising dissolved carbon dioxide may form part of the filling column. The liquid contained therein is derived from the passage of biogas and liquid through the packing area.

The degassing means are more precisely formed by a conduit, an expansion valve mounted on the conduit and a mixer housed in said conduit. The duct is mounted on the tank to open in the upper part of the tank. In a preferred example of the invention, the reservoir is formed by a lower part of the filling column. The expansion valve is opened by means of a control box which is connected to the expansion valve. When the expansion valve is open, the pressurized liquid comprising the dissolved gas leaves the reservoir through the conduit. The mixer is activated by means of the control box which is also connected to said mixer. In the duct, the liquid is subjected to turbulence by the mixer. Gas bubbles are formed due to the pressure drop created by the expansion valve and due to turbulence. As the liquid is discharged through the conduit, the liquid is discharged into gas. At the outlet of the conduit, liquid free of gas and gas escape into the degassing tank. The liquid freed from carbon dioxide and recovered at the outlet of the duct is stored in the degassing tank. The freed liquid can be used to spray said lining area at the top of said fill column. The invention therefore relates to a device for recovering carbon dioxide from a pressurized liquid containing dissolved carbon dioxide, said device comprising - a degassing tank, - degassing means, and - a reservoir containing the liquid under pressure, the degassing means being configured in such a way that they allow a sudden change in the pressure of the pressurized liquid at the outlet of the reservoir while ensuring a separation of the liquid and the carbon dioxide, the liquid free of dioxide of carbon and the extracted carbon dioxide being poured into the degassing tank at the outlet of the conduit.

The dissolved carbon dioxide may preferentially come from a biogas. The liquid in which the carbon dioxide is dissolved is preferably water. But any other type of liquid could be suitable such as aqueous solutions of soda, amines or lime and more generally basic solutions. The device according to the invention also has the following characteristics: the degassing means are formed by a duct connected to the tank at one end and opening at an opposite end in the degassing tank, an expansion valve mounted on the duct, a mixer placed in the duct, the duct extending along the degassing tank so that at the outlet of said duct, the carbon dioxide escapes and the liquid contained in the tank flows into the tank degassing in a form freed of carbon dioxide. - The duct is helical in shape extending around the degassing tank from a lower part to an upper part of said degassing tank. - The tank is placed partially in the degassing tank so that the liquid freed of carbon dioxide surrounds the tank over part of its height. the carbon dioxide comes from a biogas previously pressurized and the carbon dioxide of which has been dissolved in pressurized liquid. - The liquid free of carbon dioxide contained in the degassing tank is returned to the tank by a pumping means. By carbon dioxide-free liquid is meant liquid no longer containing carbon dioxide or liquid containing a trace amount of carbon dioxide. By trace is meant carbon dioxide or other compound which makes carbon dioxide or the compound difficult to detect. The tank may or may not be immersed in the degassing tank. - The degassing tank is at least partially buried. In a preferred embodiment of the invention, the tank is immersed in the degassing tank and the degassing tank is buried. In this embodiment of the invention, the liquid contained in the degassing tank can thus be maintained at a stable temperature. This stable temperature also maintains a stable temperature of the water contained in the degassing tank and the water contained in the tank. More specifically, the maintenance of this water contained in the reservoir at this stable temperature is conducive to the maintenance of carbon dioxide in a dissolved form. The device according to the invention may advantageously be part of a methane recovery plant from biogas to form a facility for the joint recovery of methane and carbon dioxide from biogas. The degassed liquid stored in the degassing tank can be pumped in order to spray the filling column above the packing area. In addition, the degassing tank can be placed around a foot of the filling column. The foot of the column forming the liquid reservoir containing dissolved gas from biogas.

The invention therefore also relates to an installation for recovering carbon dioxide from biogas, said installation comprising the recovery device described above. The installation according to the invention furthermore has the following characteristic: it comprises a methane recovery device, said device comprising a filling column enclosing, in the upper part, a packing zone for extracting under pressure methane from a liquid mixed with the biogas, and containing, in the lower part, the tank containing the pressurized liquid free of methane and containing dissolved carbon dioxide. The invention thus advantageously provides a facility for joint recovery of methane and compact carbon dioxide. Such an installation is advantageously monobloc and stable.

Such an installation can be provided on any farm thus making the owner self-sufficient in fuel management. Finally, a subject of the invention is a process for recovering carbon dioxide from biogas by means of the installation as described above, said process comprising the following steps: starting up an expansion valve and of a mixer, then - recovery of the carbon dioxide and the liquid freed of carbon dioxide in the degassing tank. The method also has the following steps - prior to the preceding steps, pressurizing a biogas, - filling a filling zone of a device for recovering methane by the pressurized biogas and by a liquid under pressure, and recovering the methane on one side and the liquid from the passage through the packing zone on the other side. - Pump the liquid free of carbon dioxide to introduce it into the packing area. The start of the expansion valve is therefore performed after recovery of the liquid from the passage through the packing area. These steps make it possible to combine the recovery of methane and carbon dioxide using a one-piece and stable structure. As previously mentioned, a carbon dioxide-free liquid is a liquid that no longer contains carbon dioxide or liquid containing a trace amount of carbon dioxide.

The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These are presented only as an indication and in no way limitative of the invention. The figures show: FIGS. 1a, 1b, 1c: Various schematic longitudinal sectional representations of an installation for recovering carbon dioxide, according to the invention, and FIG. 2: A schematic representation in cross-section of the FIG. installation for recovering carbon dioxide according to one of Figures la, lb and lc, according to the invention.

Figures 1a, 1b and 1c illustrate an installation 1 for recovering carbon dioxide (CO2) according to the invention. The carbon dioxide can come from a biogas or any other source. By biogas is meant combustible gas resulting from the fermentation of organic waste of animal or vegetable origin in the absence of oxygen, which is mainly composed of methane and carbon dioxide. In a preferred embodiment of the invention, this recovery plant 1 comprises a methane recovery device (CH4) and a carbon dioxide recovery device 3 from the biogas, FIGS. 1a, 1b and 1c. Such an installation 1 allows a joint recovery of methane and carbon dioxide while being compact and stable. The methane recovery device 20 comprises a filling column 2. This filling column 2 is pressurized. The filling column 2 has a packing zone 4 which forms a labyrinth through which a pressurized liquid passes through against the flow, and the biogas is also pressurized. The liquid is usually water. With the pressurization and the packing zone 4, it is desired that the water and the biogas can be in contact with each other over a larger possible contact area.

Methane is a gas that is very slightly soluble while carbon dioxide is very soluble. Thus, after contacting the water and the biogas through the packing zone 4, the methane is discharged at the top of the filling column 2 while the soluble carbon dioxide is dissolved in the water.

In the example illustrated in FIGS. 1a, 1b and 1c, the recovery device 3 is part of the installation 1. But this recovery device 3 could be independent of the methane recovery device 20. The recovery device 3 of the Carbon dioxide has a first reservoir. In the exemplary embodiment of the invention, the first reservoir is formed by a lower portion of the filling column 2 or water foot 6, Figure 1c. The water foot 6 is a place in the filling column 2 which is located in the lower part 7 of said column 2, away from the upper part 5 of said column 2. The water foot 6 receives and stores the water under pressure loaded with carbon dioxide and which is recovered after passing through the packing zone 4. But the first tank could be any other type of container containing pressurized liquid loaded with carbon dioxide obtained by any other type of after the passage through the packing zone 4. In fact, the first tank may not be part of the recovery installation 1. The recovery device 3 also comprises a second tank 8 or degassing tank 8 This degassing tank 8 may preferably be placed around the foot of water 6, FIG. With such an arrangement of the degassing tank 8 around the water foot 6, the recovery installation can be advantageously compact and stable. More precisely, the filling column 2 is immersed in its lower part 7 in the degassing tank 8 and more particularly at the location of the filling column 2 where the water charged with carbon dioxide is stored. The recovery device 3 also comprises a duct 9, an expansion valve 10 and a mixer 11. The duct 9 has a generally circular section but could be of any other section, for example of square or rectangular section, FIGS. 1a, 1b. , 1c and 2. The conduit 9 is sealed. The duct 9 extends along a wall of the degassing tank 8 helically from a bottom 19 of the degassing tank 8 to an upper portion 12 of said degassing tank 8. The bottom 19 of the degassing tank 8 is a place against which the water foot 6 is placed by the lower part 7 of the filling column 2.

The duct 9 extends in a helical manner, preferentially outside, around and along the wall formed by the degassing tank 8, from the bottom 19 of the tank 8 to the upper part 12 of the same tank 8. arrangement of the duct 9 makes it possible to optimize the space and contributes to forming a compact, one-piece and stable installation. Alternatively, the duct 9 may extend in the same way inside and along the wall of the degassing tank 8. The duct 9 is inserted by one of its ends at a discharge orifice 13 formed by the foot of water 6, Figure 1a. This discharge orifice 13 is formed at the lower portion 7 of the same foot of water 6 and near the bottom 19 of the degassing tank 8. The conduit 9 opens at an end opposite to the upper part 12 of the tank degassing 8. A pipe 14 may be placed at the orifice 13 and then connected to the pipe 9, Figure 2. The expansion valve 10 is mounted on the pipe 14 and / or on the pipe 9, Figure 2. The expansion valve 10 makes it possible to reduce the pressure at which the charged water is subjected to the interior of the water foot 6. In one example, the charged water is at a pressure of between 7 and 10 bars. Preferably, the charged water is at a pressure of 7 bar. The pressure to which the charged water is subjected must be at least equal to a pressure which makes it possible to dissolve the carbon dioxide in the water and to maintain the carbon dioxide thus dissolved in the water.

The mixer 11 is mounted in the duct 9, downstream of the expansion valve 10, FIG. 2. The mixer is a static mixer. The mixer 11 creates a turbulence zone inside the conduit 9. The mixer 11 facilitates the release of carbon dioxide from the water. The turbulence creates carbon dioxide bubbles that as they progress through the conduit 9, eventually associate with each other to form a single volume of carbon dioxide. The discharged water is then discharged into the degassing tank 8 and the carbon dioxide is released in the upper part 12 of the degassing tank 8. The pipe 9 thus extends over a minimum length allowing all the water from the foot of water 6 to be completely cleared of carbon dioxide. The dimensions of the degassing tank 8 will depend on the length of the pipe 9 necessary to obtain this result. They also depend on the desired water buffer volume for the absorption operation performed in the filling column 2.

The process for recovering carbon dioxide using the device 3 is carried out as follows. The water containing dissolved carbon dioxide is transferred from the water foot 6 to the degassing tank 8 by passing through the degassing pipe 9, the expansion valve 10 and the mixer 11. The expansion valve 10 and the mixer 11 are activated by means of a control box (not shown) connected to the valve 10 and to the mixer 11. Then, carbon dioxide and carbon dioxide-freed water leave the conduit 9 to be respectively discharged in the upper part 12 of the degassing tank 8 and to be stored in the degassing tank 8. The water thus disposed of and stored can then be used for later use. The escape of the carbon dioxide is shown schematically in FIGS. 1a and 1b by bubbles forming in the liquid contained in the degassing tank 8. The recovery device 3 can advantageously be part of the recovery installation 1. In particular, in the example illustrated in Figures 1a, 1b, 1c and 2, the water foot 6 is part of said installation 1. This installation 1 according to the example 1a, lb, 1c and 2 also includes the recovery device Such an installation 1 thus makes it possible to treat biogas in order to jointly recover methane and carbon dioxide. The installation 1 further comprises, in a known manner, a desulfurization device 15 and a compressor 16, FIG. Such an installation 1 according to the invention is compact and allows autonomous production of methane and carbon dioxide.

The production of methane and carbon dioxide from biogas B is therefore carried out as follows. The biogas B enters through the device 15 to rid the biogas of its sulfur. Generally it is used iron filings. Then the biogas removed from its sulfur is pressurized with the compressor 16. Once pressurized, the biogas removed is inserted through the filling column 2.

After passage of the biogas through the packing zone 4, the methane is extracted through the top 5 of the filling column 2 and the carbon dioxide contained in the biogas is dissolved in water. Then the water containing the carbon dioxide is then collected in the foot of water 6, in the lower part 7 of the filling column 2. The water containing dissolved carbon dioxide is then transferred from the water foot 6 to the degassing tank 8 by passing through the degassing pipe 9, the expansion valve 10 and the mixer 11 as previously mentioned.

The carbon dioxide and the water freed of carbon dioxide leave the duct 9 to be respectively discharged in the upper part 12 of the degassing tank 8 and stored in the degassing tank 8. The water thus disposed of and stored can then be reused for spraying the filling column 2 in the upper part 5. For this, pumping means 17 may be provided such as for example a pump 17 to collect the water removed from the degassing tank 8 to the upper part 5 of the column Thus, the dimensions of the degassing tank 8 will also depend on the buffer volume of water desired for the absorption operation performed in the filling column 2 and necessary for the operation of the pump 17. As previously mentioned , the escape of carbon dioxide is shown schematically in Figure 1 by bubbles. Advantageously, the degassing tank 8 may be buried in order to regulate the temperature of the discharged water contained in said degassing tank 8. Advantageously, the water foot 6 can be immersed in the degassing tank 8 thus buried. The water charged with carbon dioxide present in the water foot 6 can thus be maintained at a temperature between 10 ° C and 25 ° C, to ensure that the carbon dioxide remains in a state dissolved in said water. Between the lining zone 4 and the water foot 6 is a layer of a retaining material 18, FIGS. 1a, 1b and 1c. Through this layer 18 pass carbon dioxide-laden water drops recovered after passing through the packing zone 4. This layer of material 18 has the particularity of making it possible to slow down the speed with which the drops of water charged with carbon dioxide flow through the filling column 2 to fall on the water contained in the foot of water 6. By slowing this speed of movement, each of the drops of water is preserved from a possible contaminating the ambient gas by incorporating microbubbles of said ambient gas. Indeed, the ambient gas can be loaded with biogas that would not have been rid of methane. This contamination by the creation of microbubbles of said ambient gas can therefore be effected at the moment of impact of the drop of water on the water. By avoiding an abrupt impact of the drop of water on the water by reducing its speed of movement, the drop of water is unlikely to be contaminated. Preferably, this layer of retentative material 18 is reticulated foam.

Claims (12)

CLAIMS1 - Device for recovering (3) carbon dioxide from a pressurized liquid containing dissolved carbon dioxide, said device comprising - a degassing tank (8), - degassing means (9,10,11 ), and - a reservoir (6) containing the pressurized liquid, the degassing means being configured in such a way that they allow a sudden change in the pressure of the pressurized liquid at the outlet of the reservoir while ensuring separation of the liquid and carbon dioxide, the carbon dioxide-free liquid and the extracted carbon dioxide being poured into the degassing tank at the outlet of the conduit. 2 - Device according to claim 1, wherein the degassing means are formed by - a duct (9) connected to the tank at one end and opening at an opposite end in the degassing tank, - an expansion valve (10) mounted on the conduit, - a mixer (11) placed in the conduit, the conduit extending along the degassing tank so that at the outlet of said conduit, the carbon dioxide escapes and the The liquid contained in the tank is discharged into the degassing tank in a form free of carbon dioxide. 3 - Device according to claim 2, wherein the conduit is of helical shape extending around the degassing tank from a lower part to an upper part of said degassing tank. 4 - Device according to one of claims 2 to 3, wherein the reservoir is placed partially in the degassing tank so that the carbon dioxide-free liquid surrounds the tank over a portion of its height. 5 - Device according to one of claims 1 to 4, wherein the degassing tank is at least partially buried. 6 - Device according to one of claims 1 to 5, wherein the carbon dioxide comes from a biogas previously pressurized and whose carbon dioxide was dissolved in pressurized liquid. 7 - Device according to one of claims 1 to 6, wherein the liquid free of carbon dioxide contained in the degassing tank is returned to another tank (2) by a pumping means (17). 8 - Installation (1) for recovering carbon dioxide from biogas, said installation comprising the recovery device according to one of claims 1 to 7. 9 - Installation according to claim 8, characterized in that it also comprises a methane recovery device (20) comprising a filling column (2) containing, in the upper part, a packing zone (4) for extracting under pressure methane from a liquid mixed with the biogas, and containing, in the lower part, the tank containing the pressurized liquid free of methane and containing dissolved carbon dioxide. 10 - Process for recovering carbon dioxide from biogas by means of the installation according to one of claims 8 to 9, said process comprising the following steps - starting an expansion valve (10) and a mixer (11) and then - recovery of the carbon dioxide and the carbon dioxide-free liquid in the degassing tank. 11 - Process according to claim 10, characterized in that, prior to the preceding steps, it comprises the following stages - pressurization of a biogas, - filling of a packing area (4) of a recovery device methane (20) by pressurized biogas and pressurized liquid, and - recovery of methane on one side and liquid from the passage through the packing area on the other side. 12 - Process according to claim 11, characterized in that it comprises the following step - pump the liquid free of carbon dioxide from the degassing tank to introduce it into the packing area.