Device for capturing carbon dioxide (CO2)

Abstract

The invention relates to a device for capturing the carbon dioxide contained in a gas mixture by means of a liquid passing from a loading chamber to an unloading chamber. The conditions in the loading chamber force the carbon dioxide to pass from the gas mixture to the liquid and the conditions in the unloading chamber force it to be extracted therefrom. The loading of the carbon dioxide into the liquid is promoted by the temperature and pressure conditions and, where appropriate, by the addition of substances enabling crystallization or encapsulation of the carbon dioxide. The chambers can either consist of physically separate and interconnected containers, or consist of one and the same physical container where the closing and opening of valves allows the temporal transition from one state to another.

Description

[0001] Carbon dioxide (CO2) capture device

[0002] Scope of the invention

[0003] The present invention relates to a device and a method for capturing carbon dioxide (CO2).

[0004] Description of the state of the art

[0005] Carbon dioxide has become a major global problem because of the greenhouse effect it generates in the Earth's atmosphere. With the level of carbon dioxide in the atmosphere increasing rapidly in recent decades as a result of human activities, the greenhouse effect is intensifying and causing global climate change.

[0006] In order to limit the impact of human activities on climate change, one solution is to capture and sequester carbon dioxide to prevent it from being released into the atmosphere, or even to capture carbon dioxide already present in the atmosphere.

[0007] Various capture methods have been developed to meet this need, including chemical capture and cryogenic capture. Chemical capture involves passing gas containing carbon dioxide through chambers containing chemical compounds, such as amines or hydroxides, which react with the carbon dioxide. The carbon dioxide is then released by heating these compounds. Cryogenic capture involves cooling the carbon dioxide until it liquefies, allowing it to be separated from other gases by exploiting the different liquefaction temperatures of each gas.

[0008] These methods have the advantage of working well and having been mastered for a long time. However, they also have some drawbacks. For example, the gases containing the carbon dioxide that one wishes to extract may contain substances toxic to amines, leading to their degradation. Alternatively, the pH of these gases can also degrade the amines.

[0009] Cryogenic carbon capture is an interesting technique, but it is only economically viable for gases that already contain highly concentrated carbon dioxide. Otherwise, the technique requires significantly cooling the rest of the gas mixture. Examples include gases from oxy-combustion techniques (combustion in the presence of pure oxygen), which contain only carbon dioxide and water. However, the water must be removed before the carbon dioxide can be cooled.

[0010] All these techniques, however, have a high operating cost, particularly due to the energy required either to regenerate the compound (amines) by heating, or to cool the gases (cryogenics).

[0011] The present invention aims to address these difficulties by providing an economical CO2 capture solution that is also relatively insensitive to toxic compounds that may be present in the initial gas mixture. The present invention does not relate to a method for long-term carbon dioxide sequestration but only to its capture from an initial gas mixture.

[0012] Summary of the invention

[0013] The invention relates to a method for capturing carbon dioxide comprising the following steps: a gaseous mixture comprising carbon dioxide is injected into a loading chamber comprising a carbon dioxide capture liquid; the capture liquid becomes charged with carbon dioxide upon contact with the gaseous mixture in the loading chamber; the carbon dioxide-charged capture liquid is transferred to a discharge chamber; conditions are applied in the discharge chamber allowing the carbon dioxide captured by the capture liquid to be discharged to form a carbon dioxide-enriched gas; and the carbon dioxide-enriched gas is extracted from the discharge chamber.

[0014] The invention also consists of a device for capturing carbon dioxide comprising:

[0015] A carbon dioxide capture liquid, a loading chamber arranged to receive and contain the capture liquid and, said loading chamber comprising a gas inlet opening arranged to receive a gas mixture comprising carbon dioxide such that said gas mixture is in contact with said capture liquid, and a discharge chamber arranged to receive and contain the capture liquid from the loading chamber and, the discharge chamber comprising an outlet opening for extracting the gas discharged from said capture liquid into the discharge chamber.

[0016] The advantage of the invention is its ability to selectively capture carbon dioxide from a gaseous mixture containing varying concentrations of carbon dioxide and to extract this carbon dioxide in concentrated gaseous form. It is therefore a method for concentrating gaseous carbon dioxide from any gas containing carbon dioxide.

[0017] In the loading chamber, carbon dioxide can be loaded into the capture liquid by dissolving the carbon dioxide in the liquid, by enriching the capture liquid with liquid carbon dioxide bubbles, by adsorption of carbon dioxide by solid particles suspended in the capture liquid (e.g., amines), by precipitation of carbon dioxide forming a compound by binding to certain molecules present in the capture liquid (e.g., guanidine hydrochloride), and / or by encapsulation within clathrates where the carbon dioxide is enclosed within a structure made up of other molecules (e.g., guanidinium sulfate). These loading methods are not mutually exclusive and can be used simultaneously.

[0018] In the discharge chamber, the capture liquid is discharged as carbon dioxide by degassing, evaporation, desorption, disintegration, and / or decapsulation. Since the partial pressure of gaseous carbon dioxide in this discharge chamber is zero or very low, the carbon dioxide-enriched gas is then extracted from the discharge chamber through the outlet opening.

[0019] Loading and unloading chambers each refer to an enclosed space that may include fluid connections to the outside or to each other. Loading and unloading chambers can, for example, be either physically separate containers allowing the flow of the collection fluid from one to the other, or a single physical container where the transition from one "chamber" to the next occurs temporally, i.e., the same container alternately performs both functions. The physical conditions inside the container are modified so that it is first considered a "loading chamber" and then, subsequently, an "unloading chamber." These modifiable physical conditions include, for example, pressure, pH, and / or temperature.

[0020] The loading chamber comprises the carbon dioxide capture liquid and a gas inlet opening arranged to receive a gas mixture containing carbon dioxide, such that said gas mixture is in contact with the capture liquid. This contact between the capture liquid and the gas mixture allows the capture liquid to be charged with carbon dioxide. If the invention is used to extract carbon dioxide already present in the atmosphere and the chambers are physically separated, then the loading chamber can be in direct contact with the atmosphere (ambient air), considered to be the gas mixture injected "naturally," through the inlet opening.Alternatively, the loading chamber may be equipped with at least one gas inlet pipe, allowing the gas mixture to be injected through the inlet opening and brought into contact with the capture liquid, for example by bubbling or passively, and at least one gas outlet pipe allowing the gas mixture to be extracted after the carbon dioxide has been extracted.

[0021] The discharge chamber is designed to receive and contain the collection fluid from the loading chamber and includes an outlet to extract the gas discharged from said collection fluid into the discharge chamber. The discharge chamber is inaccessible to the gas mixture from which the CO2 is to be extracted. This implies that, if the discharge chamber is physically separate from the loading chamber, the fluid connection between the two chambers is designed to prevent the gas mixture from entering the discharge chamber. If a single container performs both loading and unloading functions, valves are strategically actuated to prevent the gas mixture from entering the chamber during the unloading phase.This discharge chamber includes at least one outlet opening for extracting carbon dioxide from the discharge chamber. If the chambers are physically separated, the loading chamber will be equipped with at least one inlet pipe for the capture fluid and the discharge chamber with at least one outlet pipe for the capture fluid; these pipes may be connected to create a closed loop for the circulation of the capture fluid between the chambers. If both chambers consist of a single container, the capture fluid simply fills most of the container.

[0022] The method and device according to the invention consist either of bringing the atmosphere (ambient air), considered to be the gas mixture injected "naturally," into contact with the capture liquid in the loading chamber through the inlet opening (open chamber), or of injecting the gas mixture into the loading chamber via the gas inlet line, so that the carbon dioxide contained in the gas mixture can come into contact with the capture liquid to charge it with carbon dioxide (closed chamber). In the case of a closed loading chamber, the gas mixture depleted in carbon dioxide is extracted through the gas outlet line, and the carbon dioxide-charged capture liquid is allowed to pass into the discharge chamber. In the discharge chamber, the capture liquid is discharged as carbon dioxide by degassing, evaporation, desorption, disintegration, and / or decapsulation.The partial pressure of gaseous carbon dioxide in this discharge chamber being zero or very low, the gaseous carbon dioxide will then be extracted from the discharge chamber through the outlet opening. The zero or very low partial pressure of carbon dioxide in the discharge chamber is preferably achieved either by creating a vacuum in the discharge chamber using a vacuum pump connected to the outlet opening, or by injecting a fluid not containing carbon dioxide through an inlet pipe.

[0023] To improve the efficiency and therefore the energy and economic performance of the invention, it will be usefully implemented in an optimal manner. Indeed, the operation of loading carbon dioxide into the loading chamber and the operation of unloading carbon dioxide from the capture liquid into the unloading chamber are operations that can be quite slow, and all possible means must be used to make them as efficient and rapid as possible.

[0024] The parameters that influence the reactions in question are well known, and the present invention aims to manipulate these parameters to obtain the best possible yield. The parameters in question are:

[0025] • The contact surface between the gas mixture and the collection liquid

[0026] • The contact time between the gas mixture and the collection liquid

[0027] • The temperature

[0028] • The difference in partial pressure of carbon dioxide

[0029] • Total pressure (to a lesser extent but important in the case of clathrate formation to ensure their stability)

[0030] • Mechanical agitation

[0031] Indeed, for the partial pressure of carbon dioxide, the greater the difference, the greater and faster the transfer of carbon dioxide between the gas mixture and the capture liquid will be.

[0032] Regarding temperature, a low temperature will tend to promote the loading of the capture fluid with carbon dioxide, and a high temperature will tend to have the opposite effect. Preferably, the capture fluid is loaded at a temperature between -1 and 5 °C, preferably between 0 °C and 3 °C. Preferably, the discharge temperature is the same as or higher than the loading temperature.

[0033] The contact surface is important because the exchanges between the gas mixtures and the capture liquid take place via this surface, and the larger this surface area, the greater and faster the exchanges will be.

[0034] The contact time between the gas mixture and the capture liquid is also important because the exchanges are not immediate.

[0035] Finally, mechanical agitation does not particularly favor one direction over another, but the greater it is, the greater and faster the exchanges will be. Agitation therefore improves the kinetics of the exchanges. In a particular embodiment, the capture liquid is chosen so that carbon dioxide is readily soluble in it, while the other gases present in the gas mixture are only slightly soluble. A good example in many cases is water, as carbon dioxide is very soluble in water (Henry's constant at 25°C = 29.41 L·atm / mol), whereas the other gases frequently found in the gas mixture are relatively poorly soluble (nitrogen = 1639.34 L·atm / mol, hydrogen = 1282.05 L·atm / mol, and even oxygen = 769.23 L·atm / mol). Furthermore, water is abundant, inexpensive, non-toxic, and non-corrosive.

[0036] In one particular embodiment, the chambers are physically separated and the loading chamber is open so that the collection fluid in this chamber is in direct contact with the atmosphere. In this case, the loading chamber has as large a surface area as possible with a minimal collection fluid height, so as to increase the contact area between the atmosphere and the collection fluid.

[0037] According to a particular embodiment, the gas mixture is injected onto the surface of the capture liquid and therefore the gas inlet pipe of the gas mixture opens onto the surface of the capture liquid.

[0038] In a preferred embodiment, the gas mixture is injected at the base of the collection liquid, i.e., below the surface of the collection liquid, preferably at the maximum depth of the collection liquid. Therefore, the gas inlet pipe for the gas mixture opens at the base of the collection liquid. By gravity, the gas mixture bubbles in the collection liquid, which improves the contact time and surface area between the gas mixture and the collection liquid. Ideally, there are several gas inlet pipes distributed across the surface of the loading chamber, or the gas inlet pipe(s) are connected to several nozzles inside the loading chamber, or a perforated plate is placed at the base of the loading chamber, and the gas inlet pipe(s) inject the gas mixture below the perforated plate.

[0039] All these embodiments are designed to increase the contact surface area between the gas mixture and the capture liquid by the formation of bubbles that rise through the capture liquid to the surface. The exchange of carbon dioxide between the gas mixture and the capture liquid occurs via the surface of each bubble, significantly increasing the total contact surface area compared to injecting the gas mixture directly onto the surface of the capture liquid.

[0040] The bubbles formed by the gas mixture passing through the perforations in the bottom of the loading chamber also prevent the accumulation at the bottom of the loading chamber of compounds, such as carbon dioxide hydrates or clathrates, when these are present in the liquid for selective CO2 capture, because these compounds will then be kept in motion in the capture liquid by the flow of bubbles.

[0041] In one particular embodiment, the size of the perforations in the bottom of the loading chamber that allow the gas mixture to pass through is defined to obtain an ideal bubble size. Since smaller bubbles rise more slowly in the collection liquid, the contact time is thus increased. The perforation size must achieve an optimum that takes into account the height of the collection liquid in the loading chamber and the rising speed of the bubbles.

[0042] If the collecting liquid is water, a bubble with a diameter of 0.1 mm rises at approximately 1.1 cm / s, and 5.5 cm / s for a bubble with a diameter of 0.5 mm. Between 1 mm and 1 cm in diameter, the rise is approximately 20 cm / s and increases further for bubble sizes larger than 1 cm, reaching approximately 60 cm / s for an 8 cm bubble. Beyond 10 cm, the bubbles are unstable and fragment into smaller bubbles.

[0043] In a specific embodiment, and to increase the rise time and thus the contact time between the gas mixture in bubble form and the collection liquid, one or more membranes porous to both the collection liquid and the gas mixture can be placed in the loading chamber. Ideally, the membranes are positioned horizontally to slow the rise of the bubbles while allowing the collection liquid to pass through easily. As the bubbles rise, they will be "hooked" by the membrane's pores, which increases both the rise time and the mechanical deformation of the bubble surface, and therefore the interactions between the gas mixture and the collection liquid. If porous membranes, such as a mesh, are placed at regular intervals in the loading chamber, this significantly increases the bubble rise time.Depending on the preferred uptake method(s), the desired interaction time may vary. For example, for dissolution in water, a contact time of 5 to 10 minutes is sufficient to reach equilibrium, whereas for clathrate formation, a contact time of 60 minutes or, ideally, 100 minutes is recommended.

[0044] In a specific embodiment, the viscosity of the collection fluid can be increased by adding a substance to slow the upward movement of bubbles within the fluid, thereby increasing the contact time between the gas mixture and the collection fluid. If the collection fluid is water, fibrous clays such as attapulgites or sepiolites can be added, for example, as they have the advantage of being relatively inert. Modifying the viscosity of the collection fluid must, of course, be taken into account when sizing the piping and pumps.

[0045] In one particular embodiment, the loading chamber is relatively tall so that the bubbles have a longer period of time to rise in the collection fluid before reaching the surface. For example, if the bubbles have a diameter of 1 mm, their ascent will occur at a speed of approximately 10 cm / s, and if the height of the collection fluid in the loading chamber is 10 meters, there will be contact between the bubble and the collection fluid for approximately 100 seconds. For example, by adding porous mesh membranes with a thickness of 5 centimeters every 10 centimeters, the bubble ascent time will be significantly increased, aiming for 30 minutes.

[0046] In one particular embodiment, the porous membranes are made of a material with good thermal conductivity, such as copper, so that they can also be used to cool or heat the capture fluid. Since clathrate formation is an exothermic reaction, this allows, for example, the heat produced by the reaction to be extracted in order to prevent the capture fluid from heating up. In another particular embodiment, the capture fluid is kept as cold as possible. The loading chamber, for example, includes a cooling system and / or the gas mixture is cooled before injection. It should be noted that the higher the carbon dioxide content of the gas mixture, the greater the efficiency obtained. The Earth's atmosphere currently (2024) contains approximately 400 ppm of carbon dioxide, or 0.04%.Industrial techniques that produce carbon dioxide often generate very rich exhaust gases, for example, around 10% for power plants and 15% to 25% for cement plants and hydrogen production facilities using methane. The optimal parameters for implementing the device according to the invention will obviously depend on the specific circumstances.

[0047] In one particular embodiment, the gas mixture is compressed before being injected into the loading chamber. This compression increases the partial pressure of carbon dioxide within the mixture and, consequently, the partial pressure difference between the introduced gas mixture and the collection liquid in the loading chamber. It should be noted that the gas mixture produced in certain industrial processes is sometimes generated under pressure, as in the case of hydrogen production from natural gas (20 to 30 bar).

[0048] Ideally, the gas mixture will be compressed to a pressure sufficient for the carbon dioxide to be liquid at the temperature of the capture liquid, approximately 40 bar under normal temperature conditions. Indeed, compression will increase the temperature of the gas mixture, but it will cool upon contact with the capture liquid, and the carbon dioxide will tend to transition from a gaseous to a liquid or, in some cases, a supercritical state.

[0049] Ideally, the gas mixture will be compressed to a pressure such that the carbon dioxide has a density similar to that of the capture liquid at the capture liquid temperature and injection pressure, approximately 250 bar. This will allow the liquid carbon dioxide to rise slowly into the capture liquid and have time to dissolve or be adsorbed into it (or to pass, still in liquid form, into the discharge chamber).

[0050] Ideally, the mixture is compressed to a pressure sufficient to promote the formation of carbon dioxide clathrates at the temperature of the capture fluid. In pure water, this requires approximately 300 bar of pressure at a temperature of a few degrees. Ideally, if the capture fluid is water, it can contain substances that promote the formation of carbon dioxide hydrates so that the pressure required for hydrate formation is lower. Examples include substances such as THF (tetrahydrofuran) or TBAB (tetra-n-butylammonium bromide).

[0051] Ideally, the capture liquid includes substances that allow for the adsorption of carbon dioxide, precipitation by crystallization, or the formation of carbon dioxide clathrates.

[0052] The capture fluid may contain at least one guanidine salt. For example, in the case of an aqueous solution of guanidinium sulfate, clathrate formation begins at approximately 0.5 bar of partial pressure of carbon dioxide at a temperature of 20 degrees Celsius (and at 0.3 bar at 0 degrees Celsius). It will be beneficial to add sufficient guanidinium sulfate to the capture fluid so that it remains saturated. (If the capture fluid is water, saturation is reached at 72% by mass at 0 degrees Celsius and 75.7% by mass at 25 degrees Celsius).

[0053] Other guanidine salts have also shown their effectiveness in capturing carbon dioxide by crystallization, such as glyoxal-bis(iminoguanidine) which precipitates a hydrated compound.

[0054] Ideally, when the gas mixture is compressed before being introduced into the loading chamber, the gas outlet pipe and the gas inlet pipe of the loading chamber are fitted with a pressure exchanger so that the compression of the initial gas mixture is partially achieved by means of the pressure of the outlet gas mixture.

[0055] As it has been specified that a low temperature of the capture liquid in the loading chamber will tend to promote the loading of the capture liquid with carbon dioxide, the compressed gas mixture can usefully be cooled, for example by cooling fins, before injection into the loading chamber.

[0056] Since carbon dioxide loading operations are generally exothermic, it will be beneficial to cool both the gas mixture and the capture liquid in the loading chamber. Ideally, cooling the gas mixture will allow for the recovery and utilization of the heat thus captured. In one particular embodiment, the loading chamber will be equipped with mechanical agitators to stir the capture liquid.

[0057] Ideally, these mechanical agitators will be magnetic agitators rotating in the loading chamber without the need to drill into the loading chamber, increasing its resistance, particularly to the high pressures that may prevail there.

[0058] The dissolution of the gas mixture in the loading chamber can also be improved by passing ultrasound through the capture liquid and therefore, according to a particular embodiment, the loading chamber is equipped with an ultrasound source.

[0059] Depending on the intended use of the device according to the invention, the parameters will be adjusted. For example, if the goal is to extract carbon dioxide from the atmosphere, the focus will be on the extraction cost per ton, as the proportion of dioxide extracted is irrelevant. If industrial emissions are being treated, the focus will be on ensuring that the extracted proportion is sufficient to meet regulatory requirements while maintaining a minimum cost, which will also depend on the composition of the inlet mixture, its pressure, temperature, etc. The optimal parameters will therefore vary considerably.

[0060] According to a particular embodiment, the loading chamber may be present in several copies within the device according to the invention, and the gas mixture will pass successively through one chamber after another. This will allow, for example, achieving a desired minimum proportion of carbon dioxide. The first chambers may in this case be connected either in series or in parallel.

[0061] According to the invention, the capture liquid passes from the loading chamber to the discharge chamber to have the carbon dioxide it contains discharged there.

[0062] If the chambers are physically separated, the passage from one chamber to the other is achieved through at least one capture fluid line. The capture fluid lines must be positioned to prevent the gas mixture from passing from one chamber to the other. If the gas mixture is injected into the loading chamber as bubbles, these bubbles must be able to rise sufficiently in the capture fluid to avoid being carried through the passage. Depending on the type of carbon dioxide loading, the capture fluid lines will be positioned either at the top or bottom of the capture fluid level in the loading chamber, based on the maximum carbon dioxide concentration of the capture fluid. A pump should be installed on the capture fluid line between the chambers to ensure a sufficient flow rate of the capture fluid between them.

[0063] If the chambers are temporally separated, the transition from one to the other is achieved by modifying the physical conditions within the container. In this embodiment, the collection fluid lines connected to the container are equipped with valves for opening and closing them. When the container is used as a loading chamber, the carbon dioxide extraction line is closed, while the lines for injecting and extracting the original gas mixture are open. Once the carbon dioxide has been added to the collection fluid, the lines for injecting and extracting the gas mixture are closed, and the carbon dioxide extraction line is opened.The physical parameters will be modified (partial pressure of carbon dioxide, total pressure, temperature) so that the container moves from the "loading chamber" state to the "unloading chamber" state without physical displacement of the capture liquid.

[0064] According to a particular embodiment, the collection liquid will be only slightly compressible so that its volume and density change little when passing from one chamber to another. For example, it will be liquid water.

[0065] When the chambers are physically separated, if there is a pressure difference between the loading chamber and the unloading chamber, this must be taken into account.

[0066] In a particular embodiment, the discharge chamber will be positioned at a height that allows for pressure equalization through hydrostatic equilibrium. For example, if the collection fluid is water, the surface area of ​​the collection fluid in the discharge chamber will be approximately 10 meters greater than that in the loading chamber for every bar of pressure difference. For instance, if the loading chamber is under a pressure of 3 bar and the discharge chamber is under vacuum, the surface area of ​​the collection fluid in the discharge chamber must be at a height of 30 meters relative to the height of the collection fluid in the loading chamber.

[0067] According to a particular embodiment, in order to ensure hydrostatic balance between the chambers by the difference in height and if the pressure differences are significant, the discharge chamber will be very high and placed at the top of a height (mountain, building, mast, etc.) or the loading chamber will be placed very low, for example by using old mine shafts.

[0068] According to a particular embodiment and in the case where the chambers are physically separated, the passage of the capture liquid from the first to the discharge chamber will be equipped with a valve allowing the flow rate of the capture liquid to be adjusted so that it corresponds to the outlet flow rate of the capture liquid from the discharge chamber and, thus, prevent the pressure difference between the chambers from causing the discharge chamber to fill completely.

[0069] The discharge chamber according to the invention allows for the recovery of carbon dioxide by gaseous discharge, whether by degassing, evaporation, desorption, or release. It will therefore be equipped, at its top, with at least one pipe for collecting the gaseous carbon dioxide that escapes from the capture liquid.

[0070] To increase the efficiency of unloading into the unloading chamber, the chamber should contain only a very low partial pressure of carbon dioxide, preferably zero. This can be achieved either by placing the unloading chamber under vacuum or by containing only a gas mixture free of carbon dioxide.

[0071] In a particular embodiment, the discharge chamber is evacuated by a pump connected to the outlet opening. This pump creates a vacuum in the discharge chamber when the system is started up and also extracts carbon dioxide as it is discharged from the capture liquid.

[0072] In another particular embodiment, the discharge chamber contains a gas or gas mixture without carbon dioxide, which is injected into the discharge chamber through a gas inlet pipe. According to this particular embodiment, the outlet opening of the discharge chamber is also equipped with a pump for continuously extracting the carbon dioxide-enriched gas mixture.

[0073] If the discharge chamber contains a gas, it will preferably be inert, at least with regard to both the capture liquid and the carbon dioxide. For example, it could be nitrogen. In this particular embodiment, the outlet gas will be a mixture of inert gas and carbon dioxide at a more or less concentrated level.

[0074] In cases where a gas is injected into the discharge chamber, a specific embodiment allows this gas to be injected at the base of the discharge chamber, so that it rises into the collection liquid in the form of bubbles to increase the exchange surface area with the collection liquid (as in the loading chamber) and thus facilitate discharge. Ideally, the injection will be carried out through multiple nozzles and / or below a perforated plate to create a maximum number of bubbles.

[0075] If the discharge chamber is under vacuum, the outlet gas will be highly concentrated carbon dioxide, which will also contain a percentage of vapor from the capture liquid. Ideally, a capture liquid with a low vapor pressure, such as liquid water, should be used to maximize the proportion of carbon dioxide in the final gas.

[0076] According to a particular embodiment, the discharge chamber will be rather extended and will have a rather reduced height of collection liquid so as to reduce the total pressure in the bottom of the collection liquid in the discharge chamber, in order to increase the discharge.

[0077] In one particular embodiment, the discharge chamber will be equipped with a heating system to increase its temperature and / or that of the collection liquid. If the discharge chamber is open to the air, it will advantageously have a glazed top and black walls so that solar radiation can contribute to heating it. Heat recovered during loading into the loading chamber will be usefully supplied to the discharge chamber to compensate for the endothermic effect of unloading. In another particular embodiment, the discharge chamber will be equipped with mechanical agitators to increase unloading. Ideally, as in the loading chamber, these will be rotating magnetic agitators.Ideally, these agitators will also create an upward flow in the capture liquid in the discharge chamber in order to put the fraction of the capture liquid most charged with carbon dioxide as high as possible because that is where the pressure of the capture liquid due to its height is the lowest.

[0078] According to a particular embodiment, the discharge chamber will be equipped with an ultrasound generating system to increase discharge.

[0079] If the chambers are physically separated, the discharge chamber will be equipped with a collection fluid outlet pipe. Ideally, this collection fluid outlet pipe will connect to the collection fluid inlet pipe in the loading chamber so that the collection fluid circulates in a closed loop. If there is a pressure difference between the two chambers that is not compensated by hydrostatic equilibrium, a pump will be required to compress the collection fluid leaving the discharge chamber and bring it up to the pressure of the loading chamber.

[0080] According to a particular embodiment, the discharge chamber may be equipped with one or more membranes through which the collection liquid must pass on its way to the outlet of the discharge chamber, this or these membranes also increasing the discharge.

[0081] In one particular embodiment, if the chambers are separated by time, it will be useful to use multiple containers so that some are used as loading chambers while others are used as unloading chambers. This allows for more continuous processing of the gas mixture.

[0082] In a particular embodiment, the loading / collection chamber will include, on the one hand, a vertical section at the top of which will be the injection pipe for the gas mixture and in which the collection liquid will undergo a downward movement at a speed greater than the upward velocity of the bubbles in the collection liquid. If the collection liquid is water of normal viscosity, this upward velocity will depend on the size of the bubbles but will not exceed 60 cm per second and will be lower if the water temperature is lower. In this particular embodiment, the loading chamber will also include a horizontal section for recovering the remaining original gas mixture after collection.

[0083] This particular embodiment has the advantage of compressing the original gas mixture by increasing hydrostatic pressure, thereby increasing the partial pressure of carbon dioxide within it. Indeed, the deeper the liquid descends, the more its hydrostatic pressure tends to increase (by approximately 1 bar per 10 meters if the liquid is water), and this pressure increase will cause a corresponding increase in the pressure of the gas mixture inside the bubbles by reducing their size.

[0084] According to a preferred embodiment of this particular design, the diameter of the vertical portion of the loading chamber increases as the liquid descends, thereby decreasing the velocity of the collection liquid within it. Since the upward velocity of the bubbles is related to their size, which decreases with increasing pressure, the upward velocity of the bubbles decreases as the liquid descends. Slowing the downward velocity of the liquid thus increases the contact time between the bubbles and the liquid without allowing the bubbles to rise faster than the liquid descends.

[0085] A significant portion of the system's operating costs is related to friction between the collection fluid and the chamber and pipe walls; therefore, it is advisable to minimize these forces as much as possible. In one particular embodiment, the device's interior walls are lined with diamond- or oval-shaped scales ranging in size from 100 micrometers to 5 millimeters. The ideal size depends on the collection fluid and its flow velocity, and in the case of water, is most often around 1 millimeter. These scales tend to reduce friction and thus lower the cost of circulating the collection fluid. Detailed description of the invention

[0086] The invention will now be explained in more detail, with the help of the attached drawings, on which:

[0087] Figure 1 schematically shows, in cross-section, the device according to the invention with physically separated chambers.

[0088] Figure 2 schematically illustrates, in cross-section, the device according to the invention with temporally separated chambers within a single container.

[0089] Figure 3 is a block diagram of a method for capturing carbon dioxide according to the invention.

[0090] Figure 4 schematically shows, in cross-section, the device according to the invention with physically separated chambers and an essentially vertical loading chamber where the injection of gas mixture occurs at the top.

[0091] Referring to this drawing, the device comprises a loading chamber (1) connected to a discharge chamber (2) by a pipe (3). Both the loading and discharge chambers contain a collection fluid (4), circulating in a closed loop between the chambers via a pump (5). The collection fluid (4) exits the discharge chamber (2) through an outlet pipe (6) and enters the loading chamber (1) through an inlet pipe (7). The collection fluid is water saturated with guanidinium sulfate, which readily forms carbon dioxide clathrates at ambient temperature and pressure.

[0092] A pressurized gas mixture containing carbon dioxide is introduced into the loading chamber (1) through an inlet opening via a gas inlet pipe (8), located at the base of the loading chamber (1) and beneath a perforated plate (9). This plate forces the gas mixture to form bubbles (10) that rise into the collection fluid of the loading chamber (1). During this ascent through the collection fluid, the gas mixture bubbles release their carbon dioxide content into the collection fluid. The carbon dioxide-depleted gas mixture is then extracted from the loading chamber (1) through a gas outlet pipe (11).

[0093] The carbon dioxide-enriched capture fluid passes from the loading chamber (1) to the discharge chamber (2) via the pipe (3) and the pump (5). In the discharge chamber (2), the capture fluid (4) is discharged as carbon dioxide by the vacuum (12) created by the vacuum pump (14), as well as by the action of two mechanical agitators (15) rotating at the bottom of the discharge chamber, and by ultrasound produced in the discharge chamber (2) by an ultrasonic generator (16). The shape of the discharge chamber is noteworthy: initially tall and narrow to increase the upward flow of the capture fluid from the loading chamber and ensure the removal of clathrates, it then widens to provide a large exchange surface with a minimal capture fluid height.

[0094] The ultra-concentrated carbon dioxide that escapes from the capture liquid (4) is sucked up by the vacuum pump (14) to be extracted from the discharge chamber (2) through an outlet opening by the outlet pipe (13).

[0095] The pressure difference between the chambers is compensated here by the hydrostatic equilibrium obtained by the difference in height between the surfaces of the collection liquid.

[0096] The difference compared to the device illustrated in Fig. 1 is that there is only one container, and the pipes connected to it are fitted with valves (17) that allow them to be opened or closed. The collection liquid in the container can therefore, depending on the opening and closing of the valves and the variation in conditions within the container, be alternately in a "loading chamber" or a "discharging chamber".

[0097] With reference to Figure 3, a method for capturing carbon dioxide includes the following steps:

[0098] (A) A gaseous mixture comprising carbon dioxide is injected into a loading chamber comprising a carbon dioxide capture liquid,

[0099] (B) the capture liquid becomes charged with carbon dioxide upon contact with the gas mixture in the loading chamber,

[0100] (C) the carbon dioxide-laden capture liquid is transferred into a discharge chamber, (D) conditions are applied in the discharge chamber allowing the carbon dioxide captured by the capture liquid to be discharged to form a carbon dioxide-enriched gas, and

[0101] (E) The carbon dioxide-enriched gas is extracted from the discharge chamber,

[0102] A concrete example of implementation

[0103] Here is a detailed, quantified explanation of a practical implementation of the device according to the invention, applied to capturing carbon dioxide generated during the combustion of natural gas (methane, formula CH4) from the air. This energy production method is used, for example, in gas-fired power plants, according to the formula: CH4 + 2O2 => CO2 + 2H2O (+ energy). We will detail here the situation for capturing carbon dioxide from a standard 400 MW gas-fired power plant producing 800,000 MWh annually and emitting 320,000 tons of carbon dioxide per year.

[0104] When natural gas is burned in the presence of air composed of 79% nitrogen and 21% oxygen (by volume), the exhaust gas from these installations contains nitrogen, which reacts very little, as well as carbon dioxide and water vapor. In practice, this is approximately 73% nitrogen, 9% carbon dioxide, and 18% water vapor. The water vapor can be removed by condensation, which cools the exhaust gas to ambient temperature and pressure, leaving a mixture of 73 parts nitrogen (89%) and 9 parts carbon dioxide (11%).

[0105] If the goal is to capture 90% of the carbon dioxide produced, the device according to the invention will use water at nearly 0 degrees Celsius containing guanidine sulfate as the capture liquid, and an inlet gas mixture compressed to at least 31 bar so that the 10% of uncaptured carbon dioxide always represents more than 0.34 atmospheres of partial pressure of carbon dioxide at a temperature of 0 degrees Celsius. In practice, we will compress the mixture even further to increase the exchange between the gas mixture and the capture liquid, to 50 bar. The volume of the loading chamber must be sufficient to contain the initial gas mixture for a sufficient time to allow carbon dioxide capture while also containing enough capture liquid. For example, in the case of a 400 MW gas-fired power plant producing 320 MW of CO2, the volume of the inlet chamber must be sufficient to hold the initial gas mixture for a sufficient period to allow carbon dioxide capture, while also containing enough capture liquid.To produce 1,000 tonnes of carbon dioxide per year, and to absorb 90% of the carbon dioxide produced, this carbon dioxide must be kept in contact with the gas mixture for approximately 90 minutes. Since the power plant generates 400 MWh of electricity per hour, it releases approximately 160 tonnes of carbon dioxide per hour, which, at a pressure of 50 bar and 0 degrees Celsius, corresponds to a volume of approximately 4,850,000 liters of gaseous carbon dioxide. As carbon dioxide represents only 11% of the total volume, the total volume to be treated is therefore 45 million liters of gaseous mixture, or 45,000 m³. Because the mixture must remain in the loading chamber for 90 minutes, 22,500 m³ of gaseous mixture are required continuously.

[0106] If at all times we want at least twice as much collection fluid as gas mixture, we therefore also need at least 54,000 m³ of collection fluid, resulting in a total loading chamber volume of at least 76,500 m³. The gas mixture will be injected at the base of the loading chamber under a plate perforated with 1 mm diameter holes, and since the rise time of a 1 mm diameter bubble is approximately 10 cm / s, and this can be slowed down by placing a series of horizontal membranes in the loading tank to achieve an actual rise speed of approximately 1 cm / s, the time of 90 minutes, or 5,400 seconds, represents 5,400 cm, or a total required height of 54 m. To have the total volume required, you need at least 1,416 m2 of loading chamber surface area, or, let's say, a width of 15m over a length of 100m.

[0107] The capture fluid must pass from one chamber to the other quickly enough to ensure it always contains sufficient guanidine sulfate available to form clathrates without slowing down the capture process, and also to prevent the heat released during clathrate formation (approximately 15 kJ / mol of captured carbon dioxide) from excessively raising the temperature of the capture fluid. We will assume a transit time of 90 minutes for the capture fluid, representing 54,000 m³ in 5,400 seconds, or 10 m³ per second, as it passes from the loading chamber to the discharge chamber.

[0108] Since we will capture 90% of 480 tonnes of carbon dioxide in 90 minutes, this represents 10,909,090 moles of carbon dioxide which, through clathrate encapsulation, produces 15.7 kJ / mol, or approximately 171 billion joules, or 41 billion calories. This heat is absorbed by 54,000 m³ of capture fluid, resulting in a temperature increase of less than one degree Celsius (approximately 0.8 degrees), which will have a negligible impact on the system. Furthermore, the carbon dioxide concentration after capture, 432 tonnes per 54,000 m³ of fluid, or less than one-hundredth of a gram of carbon dioxide per cm³ of capture fluid, is also very low compared to the fluid's absorption capacity of approximately 0.2 g per cm³.

[0109] As mentioned above, the pipeline connecting the loading chamber to the discharge chamber must allow a flow rate of 10 m³ / s of capture fluid. Given the pressure difference between the chambers of 45 bar (i.e., 50 bar initial pressure minus the pressure drop caused by carbon dioxide capture), the flow velocity will be approximately 95 m / s. The pipeline connecting the chambers must therefore have a diameter of at least 37 cm. A larger diameter is preferred, but a valve should be installed on the pipeline to allow for precise control of the capture fluid flow rate between the chambers.

[0110] The discharge chamber will have sufficient surface area to allow the capture liquid to release its carbon dioxide during its transit time. Since discharge will be faster than loading, a transit time of 90 minutes will be sufficient. The volume of capture liquid will therefore be 54,000 m³, and the chamber dimensions in our example will be 1 m high (liquid level) by 54,000 m² (surface area), or 54 m wide and 100 m long.

[0111] Finally, a pipeline will return the collection fluid to the loading chamber, and this pipeline will also carry 10 m³ per second to maintain a constant level of the collection fluid in each chamber. This pipeline will need to be equipped with pumps to increase the pressure of the passing collection fluid by approximately 45 bar. The pipeline will be sized accordingly, depending on the power of the available pumps.

[0112] The discharge chamber will be equipped with a pipeline to collect the nearly pure carbon dioxide being discharged. This pipeline will be fitted with a vacuum pump capable of absorbing the 80 kg of carbon dioxide discharged per second. Maintaining a maximum pressure of 0.1 bar in the discharge chamber, this equates to a carbon dioxide extraction volume of 400 m³ per second. Presumably, several pipelines and pumps distributed across the surface of the discharge chamber will be required. The discharge of the carbon dioxide will cause a drop in the temperature of the collection fluid of a similar magnitude, approximately 0.8 degrees Celsius.

[0113] Figure 4 schematically shows, in cross-section, a device according to the invention with physically separated chambers and a substantially vertical loading chamber where the gas mixture injection occurs at the top. The elements designating the same aspects as in Figure 1 are designated by the same reference numbers.

[0114] The loading / collection chamber (1) comprises two parts: a vertical section at the top of which is a gas mixture injection pipe (8) and in which the collection liquid (4) undergoes a downward movement at a speed greater than the upward velocity of the bubbles in the collection liquid. If the collection liquid is water of normal viscosity, this upward velocity will depend on the bubble size but will not exceed 60 cm per second and will be lower if the water temperature is lower. According to this particular embodiment, the loading chamber (1) also includes a horizontal section for recovering the remaining original gas mixture after collection.

[0115] This particular embodiment has the advantage of compressing the original gas mixture by increasing hydrostatic pressure, thereby increasing the partial pressure of carbon dioxide within it. Indeed, the deeper the liquid descends, the more its hydrostatic pressure tends to increase (by approximately 1 bar per 10 meters if the liquid is water), and this pressure increase will cause a corresponding increase in the pressure of the gas mixture inside the bubbles by reducing their size.

Claims

Demands 1. Method for forming, in a device, a gas enriched in carbon dioxide, which device comprises a loading chamber having a vertical part and a horizontal part, a discharge chamber and a capture liquid circulating in the loading chamber and the discharge chamber, said method comprising the following steps: a gaseous mixture, in the form of bubbles, comprising carbon dioxide into the capture liquid through a pipe located in the upper part of the vertical part, the capture liquid present in the vertical part is subjected to a downward movement at a speed greater than the upward speed of the bubbles present in the gaseous mixture present in the capture liquid in the vertical part, the capture liquid is allowed to become charged with carbon dioxide by contact with the bubbles of the gaseous mixture in the vertical part of the loading chamber,The collection liquid is transferred to the horizontal chamber; the remaining gas mixture not collected by the collection liquid is released from the horizontal section; the carbon dioxide-laden collection liquid is transferred to the discharge chamber; conditions are applied in the discharge chamber to induce the collection liquid to discharge as carbon dioxide, forming a carbon dioxide-enriched gas; and the carbon dioxide-enriched gas is then released from the discharge chamber.

2. A method for forming, in a device, a carbon dioxide-enriched gas according to claim 1, wherein the velocity of the capture liquid is decreased as it descends in the vertical part by passing it through the vertical part whose diameter increases as it descends.

3. Method for forming, in a device, a gas enriched in carbon dioxide according to any one of the preceding claims, wherein the gas mixture is compressed to obtain a partial pressure of CO2 of at least 34 kPa measured at 0°C, injected at a pressure above 40 bars.

4. Method for forming, in a device, a gas enriched in carbon dioxide according to any one of the preceding claims, wherein the capture liquid is cooled.

5. Method for forming, in a device, a carbon dioxide-enriched gas according to any one of the preceding claims, wherein the liquid is an aqueous solution comprising at least one guanidine salt such as guanidine sulfate, guanidine hydrochloride and / or guanidine acetate.

6. Method for forming, in a device, a gas enriched in carbon dioxide according to any one of the preceding claims, wherein the liquid is an aqueous solution comprising substances enabling adsorption of carbon dioxide, precipitation by crystallization or the formation of carbon dioxide clathrates.

7. Method for forming, in a device, a gas enriched in carbon dioxide according to any one of the preceding claims, wherein ultrasound is applied to the capture liquid during the loading and / or unloading of the liquid with carbon dioxide.

8. Method for forming, in a device, a gas enriched in carbon dioxide according to any one of the preceding claims, wherein the liquid is agitated during the loading and / or unloading of the liquid in carbon dioxide. Tl 9. Method for forming, in a device, a carbon dioxide-enriched gas according to any one of the preceding claims, wherein the discharge chamber is placed under vacuum to decrease the partial pressure of carbon dioxide during the carbon dioxide discharge step.

10. Method for forming, in a device, a gas enriched in carbon dioxide according to any one of the preceding claims, wherein the capture liquid is heated in the discharge chamber.

Images