Device and method for sequestering carbon dioxide (CO2)

Abstract

The application relates to a device and a method for sequestering carbon dioxide (CO2) in a container (5) placed at the bottom of a body of water (2) at a sufficient depth to maintain the carbon dioxide in the liquid state. The container (5) is connected by a pipe (4) to a source (3) of carbon dioxide for filling the container. The container can advantageously be connected to a platform (1) which allows it to be lowered into the body of water (2) and can be provided with a ballast so that the assembly has negative buoyancy.

Description

[0001] Device and method for carbon dioxide (CO2) sequestration

[0002] The present invention relates to a method for sequestering carbon dioxide in a container, whereby the container is immersed in a body of water to a depth equal to the liquid state depth of carbon dioxide, and carbon dioxide is transferred from a source to the container. It also relates to a device for sequestering carbon dioxide (CO2).

[0003] Such a method and device are known from Chinese patent CN 115076594. According to the known method, the container is immersed in a body of water at a depth of 3,000 meters or more. Carbon dioxide is injected in liquid form into the sediments of the seabed at a depth of at least 3,000 meters, allowing the carbon dioxide to be preserved at a density greater than that of the surrounding water, and therefore in a stable manner.

[0004] 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.

[0005] 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.

[0006] Various methods have been developed to address this need, including sequestration in old oil or gas wells, and injection into deep saline aquifers. While these methods offer promising possibilities, studies have revealed their limitations. The availability of suitable old oil or gas wells is not always sufficient, and not all deep saline aquifers have been thoroughly studied. Unexpected fissures or tectonic events can compromise the quality of sequestration, and given the massive quantities of carbon dioxide stored, in this case in a single location and area, the risk of a large-scale release into the atmosphere is significantly increased.However, carbon dioxide must be injected into the substrate, not left free on the seabed. This is necessary to prevent ocean acidification through the dissolution of carbon dioxide and its transformation into carbonic acid, and also to prevent the liquid dioxide from being carried uncontrollably by ocean currents. However, injecting carbon dioxide into the substrate presents a challenge in preserving it in liquid form. This is due to the progressive temperature increase with increasing depth of injection, which causes the carbon dioxide to expand and potentially rise to the surface. The formation of a "lid" of carbon dioxide hydrates is being considered to mitigate this problem, but the implementation parameters are complex to define satisfactorily given the multitude of possible substrate conditions (porosity, temperature, composition, etc.).

[0007] The present invention aims to address these difficulties by providing a long-term, stable, low-risk, inexpensive, and easy-to-implement carbon sequestration solution that meets humanity's significant carbon sequestration capacity needs. The present invention does not relate to methods of carbon dioxide capture, which are numerous, but only to its sequestration once captured.

[0008] The method according to the invention is characterized in that the container is immersed in a body of water at a depth equal to the liquid state depth of carbon dioxide and between 400 m and 2999 m, preferably between 400 m and 2950 m. Thus, the container is placed at a depth between the liquid state depth of CO2 and the negative buoyancy depth. A pipe can then be easily connected to the base of the container to fill it with CO2.

[0009] The carbon dioxide sequestration device according to the invention is characterized in that it comprises a container arranged to be positioned at a depth in a body of water such that the carbon dioxide is in a liquid state at the temperature and pressure of the water at that depth, which container is formed by a rigid casing.

[0010] Preferably, the rigid casing is formed from a geopolymer consisting of sands, sediments and / or aggregates bonded together by a binder, in particular a mineral binder that reacts with carbon dioxide. Preferably, the binder is obtained by polymerization of a silico-aluminate precursor in an alkaline medium.

[0011] A filling opening can, if necessary, be sealed by the substrate at the bottom of the water feature once the container is placed there, or the filling opening can be fitted with a siphon, possibly inverted, to prevent water from entering the container. In any case, the opening will tend to become naturally blocked quickly by the formation of carbon dioxide hydrates at the interface between the water and the carbon dioxide.

[0012] These particular embodiments make it possible to avoid the use of non-mineral materials in the manufacture of the container in order to remain compliant with international regulations governing the disposal of waste on the seabed such as the London Convention of 1972 or the London Protocol of 1996. According to a particular embodiment, the pipeline, or at least its end, will be equipped with a heating element allowing the temperature of the pipeline to be maintained high enough to prevent the formation of carbon dioxide hydrates at that point which could obstruct the pipeline.

[0013] Preferably, the source will contain liquid carbon dioxide, but the device according to the invention also works if the source is gaseous; the carbon dioxide will liquefy in the container. However, since this phase change is exothermic, the container can only be filled more slowly to allow the heat produced to dissipate.

[0014] Preferably, the container is also connected to a platform placed on the surface of the body of water, equipped with a lifting device, allowing the container to be lowered into the body of water and, if necessary, to the bottom of it.

[0015] Preferably, the platform will be floating and can be moved so that the container can be placed in a specific location.

[0016] If necessary, the depth of the body of water will allow the pressure to increase the density of the liquid carbon dioxide so that it becomes greater than the density of the surrounding water, for example, approximately 2,999 meters in water at 3 degrees Celsius. This depth will be referred to as the "negative buoyancy depth" in the remainder of this document. In one particular embodiment, the container's shell is flexible and can deform to equalize the pressure between the inside and outside of the container. In another particular embodiment, the container's shell is rigid.

[0017] Preferably, so that the container's outer shell does not have to withstand excessively high pressure differences between the inside and outside, it will be filled with carbon dioxide to balance these pressures, for example by means of a valve placed at the junction of the pipe and the container and allowing carbon dioxide to pass into the container in order to balance the pressures.

[0018] Preferably, either the carbon dioxide source will be at a pressure greater than that prevailing at the maximum depth of the body of water, or a pump will be placed between the source and the pipe so that the pressure within the pipe is greater than that at the bottom of the body of water.

[0019] Optionally, the container will be provided with at least one valve which allows water to enter the container if the container is lowered by the platform to the bottom after filling, to equalize the pressure, liquid carbon dioxide being a compressible liquid and the gradual entry of water through the valve allowing to compensate for the compression of the carbon dioxide. According to a particular embodiment, the container's envelope is open in its lower part and it is the substrate of the bottom of the water feature which closes the container once the envelope is placed on the bottom.

[0020] According to a particular embodiment, the lower part of the envelope is provided with anchoring means, for example rods, allowing the envelope to be anchored in the substrate at the bottom of the body of water.

[0021] Preferably, if the container is intended to be placed at a final depth greater than or equal to its negative buoyancy depth, the piping should be connected to the container at its top so that, once the piping is separated from the container, carbon dioxide does not tend to escape. Preferably, a plug can be placed over the filling port if it is not fitted with a valve, or the filling port should be equipped with a siphon to prevent water from entering the container. In any case, the port will tend to become naturally blocked by the formation of carbon dioxide hydrates at the water-carbon dioxide interface. Preferably, if the container is intended to be placed at a final depth between its liquid state depth and its negative buoyancy depth, the piping should be connected to the container at its base.The container is preferably placed at a depth between 400 m and 2999 m, preferably between 400 m and 2950 m. The filling opening can be sealed by the substrate at the bottom of the body of water once the container is placed there, or the filling opening can be fitted with a (reverse) siphon to prevent water from entering the container. In any case, the opening will tend to become naturally blocked quickly by the formation of carbon dioxide hydrates at the interface between the water and the carbon dioxide.

[0022] In a particular embodiment, the container's outer shell is partially permeable to liquid carbon dioxide and / or water to allow gradual contact between the two liquids. This contact enables the formation of carbon dioxide hydrates on the shell's surface, which contributes to increasing the shell's impermeability to carbon dioxide over time and also to restoring this impermeability in the event of damage (perforations, cracks, etc.). Since the formation of carbon dioxide hydrates is an exothermic reaction, it is advantageous to modulate the shell's porosity to make the reaction gradual, allowing heat to be dissipated into the surrounding water without excessively raising the local temperature.

[0023] According to a particular method of implementation, the envelope is made of concrete.

[0024] In a particular embodiment, the casing is made of geopolymer consisting of sands, sediments and / or aggregates bound by a binder. Preferably, the casing will be made of recycled mineral materials.

[0025] In one particular embodiment, the liner is formed from the substrate of the water feature itself, which is aspirated and filtered, and then mixed with a binder. Preferably, the binder is a mineral binder, in particular one containing sodium silicate or reacting with carbon dioxide, such as sodium silicate or a feldspar such as anorthite. In this particular case, the diffusion of liquid carbon dioxide through the liner will tend to harden the liner and, in the event of a crack, seal it. In another particular embodiment, the liner may contain or be coated with a substance that promotes the formation of carbon dioxide hydrates. This substance may also be mixed with the liquid carbon dioxide or the ballast fluid. The substance may, for example, be THF (tetrahydrofuran) or TBAB (tetra-n-butylammonium bromide).

[0026] According to a particular embodiment, the container can also be connected to a weight serving as ballast or be initially filled with a fluid serving as ballast.

[0027] In one embodiment, this fluid can, for example, be brine. In this case, the container contains less than 20% brine. Advantageously, it contains less than 10% brine. Even more advantageously, it contains less than 5% brine.

[0028] According to another particular embodiment, the container can also be connected to a reservoir of a fluid that can serve as ballast.

[0029] According to another particular embodiment, the container can be made of or covered with a mineral substance similar to that of the bottom of the body of water in order to integrate with the seabed.

[0030] According to one embodiment, the container does not include an outlet drain.

[0031] The invention also consists of a method of carbon dioxide sequestration characterized in that: a container (5) is immersed in a body of water at a depth at least equal to the liquid state depth, the container being connected to a pipe (4) itself connected to a carbon dioxide source (3) and carbon dioxide is transferred from the source (3) to the container (5) in order to fill the container (5) with carbon dioxide via the pipe (4).

[0032] The attached drawings illustrate embodiments of the invention:

[0033] Figure 1 shows, in cross-section, the device according to the invention.

[0034] Figure 2 shows, in cross-section, a variant of this device.

[0035] Figure 3 shows, in cross-section, another variant of this device.

[0036] Figure 4 shows the device with a siphon placed at the top of the container. Figure 5 shows the device with a siphon placed at the bottom of the container. With reference to the drawings, the device comprises a container (5) connected by a pipe (4) to a carbon dioxide source (3) and immersed in a body of water (2) at least at a depth allowing the carbon dioxide to remain in a liquid state, taking into account the temperature and pressure of the water at that depth.

[0037] In a preferred embodiment according to Figure 1, the container (5) is connected to the pipeline via a valve (6).

[0038] In a preferred embodiment according to Figure 1, the container (5) is also connected to a platform (1) which allows the container (5) to be placed at the desired location on the bottom of the body of water. This location is situated at a depth between 400 m and 2999 m, preferably between 400 m and 2950 m.

[0039] In a preferred embodiment according to Figure 2, the container (5) is connected to a ballast weight (7), of sufficient mass to compensate for the buoyancy of the container filled with liquid carbon dioxide at the depth of the end of the pipeline.

[0040] In another preferred embodiment as shown in Figure 3, the depth of the water chamber (2) is greater than the negative buoyancy depth, and the pipeline (4) allows this depth to be reached. If the pressure at this depth is greater than that of the liquid carbon dioxide source connected to the platform, the platform is equipped with a pump (8) to inject the liquid carbon dioxide into the container at the negative buoyancy depth.

[0041] In the embodiment shown in Figure 4, the pipeline is also connected to another tank (9) containing a fluid denser than water at the depth of the liquid state, and allowing the container to be partially filled in order to serve as ballast (10). For example, sand or salt.

[0042] In one embodiment of the invention, the body of water is a sea or ocean with a depth between 400 m and 2999 m, preferably between 400 m and 2950 m, such that the pressure compressing the carbon dioxide at this depth increases its density so that it becomes (significantly) greater than the surrounding seawater. In one embodiment of the invention, the pipeline is sufficiently robust to serve as a lifting cable, and the pipeline itself is used both to fill the container and to lower it into the water.

[0043] In a preferred embodiment of the invention according to Figure 5, the container will be equipped with a siphon (13) at its top, and the pipe will be attached to the end of this siphon. If the container is placed at a depth at least equal to its negative buoyancy depth, this limits water penetration into the container, thereby promoting the formation of carbon dioxide hydrates in the siphon to seal it.

[0044] In a preferred embodiment of the invention according to Figure 6, the container is equipped with a siphon (13) at its base, and the piping is attached to the end of this siphon. If the container is placed at a depth at least below its negative buoyancy depth, this limits water penetration into the container, thus promoting the formation of carbon dioxide hydrates in the siphon to seal it. The method according to the invention allows the device to be operated. It consists of connecting the container to the end of the piping, with the entire assembly placed at a depth at least equal to the liquid state depth. By connecting the liquid carbon dioxide source to the container via the piping, the container will fill with liquid carbon dioxide if the pressure of the source is greater than the pressure at the filling depth.Otherwise, the pump is necessary to create this pressure difference and allow filling.

[0045] According to one embodiment of the method according to the invention, the connection of the container to the end of the pipeline can be made at the height of the platform, the whole being then lowered to the filling depth.

[0046] According to another embodiment of the method according to the invention, the container is lowered to the filling depth where the end of the pipe is located and they are connected at that point.

[0047] If the filling depth is less than the negative buoyancy depth, the container may need to be ballasted to compensate for the positive buoyancy of the carbon dioxide inside. This ballast can be the container itself, an external weight attached to the container, or a fluid denser than the surrounding water, injected into the container either before or during the filling process.

[0048] According to one embodiment of the method according to the invention, the container can be filled near the surface and then released so that it sinks to the bottom of the body of water.

[0049] According to another preferred embodiment of the method according to the invention, the container can be lowered by means of a lifting device, such as a winch, equipped with a cable which will then allow, once the container has been placed at the bottom of the body of water, the external ballast to be raised in order to be reused.

[0050] According to another embodiment of the method according to the invention, the filling depth is greater than the negative buoyancy depth, and a pump is used to fill the container via the pipeline. In this latter case, no ballast is necessary (if the container's shell has a density greater than that of water).

[0051] According to another preferred embodiment of the method according to the invention, the container is lowered gradually by the lifting device to the bottom of the body of water, and the valve connecting the pipe to the container allows for its gradual filling during the descent. This makes it possible to balance the internal and external pressures of the container while maximizing the amount of carbon dioxide contained within the container at the final depth. Indeed, since carbon dioxide is a compressible liquid, it will compress more and more during the descent, and the same volume of container will therefore hold more as the pressure increases.

[0052] If carbon dioxide is injected into the container before it reaches the liquid depth, the carbon dioxide injected through the pipeline will transition to a gaseous state. This will effectively balance the internal and external pressures applied to the container (5), but particular attention must be paid during the descent once the liquid depth is reached, as this is when a large amount of liquid carbon dioxide will need to be injected to maintain pressure balance. Subsequently, the amount of carbon dioxide required for injection during the rest of the descent will be reduced.

[0053] It is also possible to fill the container with carbon dioxide before immersing it. Alternatively, a fluid denser than the surrounding water can be injected into the container, either before the carbon dioxide transfer or during the transfer process. This helps to equalize the pressure applied to the container.

[0054] Preferably, the rigid casing is formed from a geopolymer consisting of sands, sediments, and / or aggregates bonded together by a binder, in particular a mineral binder that reacts with carbon dioxide. This type of geopolymer is particularly well-suited to the environment in which the container will be placed and is highly resistant to carbon dioxide; the binder is preferably obtained by polymerization of a silico-aluminate precursor in an alkaline medium.

[0055] The rigid liner that forms part of the container is partially permeable to liquid carbon dioxide and / or water. This allows the carbon dioxide to react with the material present in the body of water and thus form a liner around the container. This is particularly true when the rigid liner is made from sands and sediments from the body of water.

[0056] The envelope contains and / or is preferably coated with a substance that promotes the formation of carbon dioxide hydrates, in particular a substance that includes tetrahydrofuran and / or tetra-n-butylammonium bromide. This contributes to the envelope's airtightness.

[0057] If necessary, the container may include a concrete casing. Concrete is an inexpensive material that is highly water-resistant.

Claims

DEMANDS 1. Method of sequestration of carbon dioxide in a container (5) according to which the container is immersed in a body of water at a depth equal to the liquid state depth of carbon dioxide and carbon dioxide is transferred from a source to the container, characterized in that the container is immersed in the body of water at a depth of between 400 meters and 2,999 meters, preferably between 400 meters and 2,950 meters.

2. Method according to claim 1, characterized in that carbon dioxide is transferred to the container (5) from the beginning of the immersion of the container (5) so as to balance the internal and external pressures applied to the container (5).

3. Method according to any one of claims 1 to 2, characterized in that a fluid denser than the surrounding water at the water feature is injected into the container, either before the transfer of carbon dioxide, or as it occurs during this transfer.

4. Method according to any one of claims 1 to 3, characterized in that the container (5) is manufactured, before its immersion, by means of a substrate present in the water body (2) and to which a binder is added, in particular a binder obtained by polymerization of a silico-aluminate precursor in an alkaline medium.

5. Method according to any one of claims 1 to 4, characterized in that the container is filled using a pump (8) placed on a pipe (3) connected to the container in order to increase the filling pressure of the container (5).

6. Carbon dioxide sequestration device comprising a container (5) arranged to be positioned at a depth in a body of water such that carbon dioxide is in a liquid state at the temperature and pressure of the water at that depth, characterized in that the container is formed by a rigid shell.

7. Device according to claim 6, characterized in that the rigid casing is formed by a geopolymer consisting of bound sands, sediments and / or aggregates between them by a binder, in particular a binder containing sodium silicate or reacting with carbon dioxide.

8. Device according to claim 6 or 7, characterized in that the rigid envelope is partially permeable to liquid carbon dioxide and / or water.

9. Device according to any one of claims 6 to 8, characterized in that the rigid envelope is made from sands and sediments from the body of water.

10. Device according to any one of claims 6 to 9, characterized in that the device is provided with a siphon (13) one end of which is connected either to a top of the container or to a base of the container, another end of the siphon being arranged to be connected to a conduit arranged to be connected to a carbon dioxide source.

11. Device according to any one of claims 6 to 9, characterized in that the envelope contains and / or is coated with a substance promoting the formation of carbon dioxide hydrates, in particular a substance which comprises tetrahydrofuran and / or tetra-n-butylammonium bromide.

12. Device according to any one of claims 7 to 11, characterized in that the binder is obtained by polymerization of a silico-aluminate precursor in an alkaline medium.

13. Device according to any one of claims 6 or 12, characterized in that a ballast (7) is associated with the container (5) and whose weight is sufficient to compensate for the buoyancy of the container (5) filled with carbon dioxide.

14. Device according to any one of claims 1 to 6, characterized in that the container comprises a concrete shell.

15. Device according to any one of claims 6 to 14 characterized in that the container is open in its lower part and that the container (5) is closed when it is placed on the bottom of the body of water.

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