Method and system for fixing carbon dioxide

Abstract

To provide a fixation method of carbon dioxide which is excellent in fixation efficiency.SOLUTION: A fixation method of carbon dioxide of the disclosure includes: a step in which carbon dioxide in sea water is collected in a direct ocean capture (DOC) facility 1; a step in which mineral sources in sea water are concentrated in the DOC facility 1; a step in which the collected carbon dioxide is supplied to the mineral sources; a step in which carbon dioxide obtained at the outside of the DOC facility 1 is supplied to the mineral sources; and a step in which carbon dioxide collected in the DOC facility 1 and carbon dioxide supplied from the outside are mixed into the mineral sources to cause carbonation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method and system for immobilizing carbon dioxide. [Background technology]

[0002] Patent Document 1 discloses an electrodialysis system for recovering carbon dioxide (CO2), a greenhouse gas, from ocean water. The electrodialysis system in Patent Document 1 acidifies ocean water to recover the carbon dioxide. A separation membrane separates the carbon dioxide gas from the acidified liquid. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2022 / 99174 Summary of the Invention [Problem to be solved by the invention]

[0004] Carbon dioxide can be fixed by using mineral sources such as calcium (Ca) and magnesium (Mg). For example, carbon dioxide can be fixed by reacting the mineral source with carbon dioxide to form carbon dioxide. Calcium carbonate (CaCO3), magnesium carbonate (MgCO3) 3 Carbon dioxide can be fixed by producing carbonates such as Mg(CO3)2 or their double salts (CaMg(CO3)2).

[0005] There is a strong demand for the development of more efficient carbon dioxide fixation technologies. For example, Direct Ocean Capture (DOC) facilities can concentrate mineral sources for fixation. However, the amount of carbon dioxide obtained from seawater is small compared to the amount of magnesium and calcium. For example, the amount of calcium and magnesium obtained from seawater per unit volume is extremely large compared to the amount of carbon dioxide gas. Therefore, it is difficult to fix carbon dioxide efficiently.

[0006] The present disclosure has been made in view of the above-mentioned problems, and aims to provide a carbon dioxide fixation method and fixation system that can fix carbon dioxide efficiently. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, the following carbon dioxide fixation method and fixation system are provided.

[0008] The carbon dioxide fixation method according to the present disclosure includes the steps of recovering carbon dioxide from seawater at a DOC facility, concentrating a mineral source from the seawater at the DOC facility, supplying the recovered carbon dioxide to the mineral source, supplying carbon dioxide obtained outside the DOC facility to the mineral source, and mixing the carbon dioxide recovered at the DOC facility and carbon dioxide supplied from outside with the mineral source to carbonate it.

[0009] The carbon dioxide fixation system according to the present disclosure includes a recovery section in a DOC facility that recovers carbon dioxide from seawater, a seawater concentration section in the DOC facility that concentrates a mineral source from seawater, a supply section that supplies carbon dioxide obtained outside the DOC facility to the mineral source, and a fixation section that mixes the carbon dioxide supplied from the supply section with the mineral source to carbonate it. [Effects of the Invention]

[0010] According to the present disclosure, it is possible to provide a carbon dioxide fixation method and fixation system that can fix carbon dioxide efficiently. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing the overall configuration of a DOC facility. [Figure 2]FIG. 1 is a block diagram showing the overall configuration of an immobilization system according to a first embodiment. [Figure 3] FIG. 1 is a schematic diagram illustrating a bipolar membrane electrodialysis method. [Figure 4] 1 is a flowchart showing a method for immobilizing carbon dioxide. [Figure 5] FIG. 10 is a block diagram showing the overall configuration of an immobilization system according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the invention according to the claims is not limited to the following embodiments. Furthermore, not all of the configurations described in the embodiments are necessarily essential means for solving the problems. For clarity of explanation, the following description and drawings have been omitted and simplified as appropriate. In each drawing, the same elements are given the same reference numerals, and duplicate explanations are omitted as necessary.

[0013] Embodiment 1 The immobilization system according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing the overall configuration of a DOC facility 1. At least a part of a carbon dioxide (CO2) immobilization system 100 according to this embodiment is provided in the DOC facility 1.

[0014] As shown in Figure 1, the DOC facility 1 is a floating facility that floats on the sea. The DOC facility 1 is equipped with a water supply pipe 2, a collection facility 3, and a discharge pipe 4. The ends of the water supply pipe 2 and the discharge pipe 4 are submerged in the sea. The collection facility 3 floats on the sea.

[0015] The water supply pipe 2 sucks in seawater 5 in a shallow area of the ocean and supplies it to the recovery facility 3. The water supply pipe 2 may be provided with a pump or the like for sucking in the seawater 5. The recovery facility 3 recovers carbon dioxide from the seawater. The recovery facility 3 has an immobilization system 100 that immobilizes the carbon dioxide absorbed in the seawater 5. The immobilization system 100 will be described later.

[0016] The seawater from which the carbon dioxide has been collected is discharged into the sea through a discharge pipe 4. The recovery facility 3 extracts carbon dioxide from the seawater 5, thereby reducing the carbon dioxide concentration in the seawater. The seawater with a low carbon dioxide concentration then returns to the sea through the discharge pipe 4. The recovery facility 3 can recover carbon dioxide from the seawater by fixing the carbon dioxide in a mineral source.

[0017] Fig. 2 is a block diagram showing the configuration of the immobilization system 100. As shown in Fig. 2, the immobilization system 100 includes a seawater concentrating section 10, a recovery section 20, an extraction section 30, an immobilization section 40, and a supply section 60. The seawater concentrating section 10, the recovery section 20, the extraction section 30, and the immobilization section 40 are provided in the DOC facility 1. The supply section 60 is provided in an external facility outside the DOC facility 1.

[0018] The seawater concentrating unit 10 is equipped with an RO (Reverse Osmosis membrane) 11 for concentrating seawater. The RO (Reverse Osmosis membrane) 11 is a reverse osmosis membrane that allows only water molecules to pass through and does not allow substances dissolved in water to pass through. When seawater passes through the RO membrane 11, it becomes fresh water 13. The fresh water 13 may be returned to the sea or may be used as cooling water, etc.

[0019] Furthermore, mineral sources such as calcium and magnesium are concentrated in seawater that does not pass through the RO membrane 11. The seawater with concentrated mineral sources is called concentrated seawater 14. In this way, by using the RO membrane 11, concentrated seawater and freshwater are produced. The concentrations of calcium and magnesium in the concentrated seawater are higher than those in seawater itself. The seawater concentrating unit 10 concentrates mineral sources such as calcium and magnesium from the seawater 5. The seawater concentrating unit 10 then supplies the concentrated seawater 14 to the immobilization unit 40.

[0020] The extraction unit 30 extracts sodium hydroxide 34 (hereinafter also referred to as NaOH) from the seawater 5. For example, the extraction unit 30 has an ion exchange membrane 31. Specifically, NaOH is extracted from the seawater 5 by electrodialysis using the ion exchange membrane 31. By using the electrodialysis method, NaOH is precipitated. The seawater from which NaOH has been extracted becomes desalinated seawater 33. The NaOH is supplied to the immobilization unit 40 to adjust the pH.

[0021] For example, NaOH and hydrogen chloride (HCl) are extracted by bipolar membrane electrodialysis (BMED) using an anion exchange membrane, a cation exchange membrane, and a bipolar membrane. Figure 3 is a schematic diagram illustrating an electrodialysis device 300 for bipolar membrane electrodialysis.

[0022] The storage tank 301 is a tank that stores seawater 5 containing sodium chloride (NaCl). The storage tank 301 is provided with an anode 302 and a cathode 303. The storage tank 301 is provided with an anion exchange membrane 311, a cation exchange membrane 312, and a bipolar membrane 313 between the anode 302 and the cathode 303. The anion exchange membrane 311, the cation exchange membrane 312, the bipolar membrane 313, the anion exchange membrane 311, and the cation exchange membrane 312 are arranged in this order from the anode 302 side.

[0023] Seawater containing NaCl is supplied to the compartment between the anion exchange membrane 311 and the cation exchange membrane 312. The anion exchange membrane 311 allows anions to pass through and blocks cations. ― passes through the anion exchange membrane 311 toward the anode 302 side. The cation exchange membrane 312 allows cations to pass through and blocks anions. + passes through the cation exchange membrane 312 toward the cathode 303 side.

[0024] The bipolar membrane 313 is an ion exchange membrane formed by bonding an anion exchange membrane 311 and a cation exchange membrane 312. The bipolar membrane 313 converts water molecules (HO) into H + and OH - It dissociates into H + moves into the compartment between the bipolar membrane 313 and the anion exchange membrane 311. - moves to the compartment between the cation exchange membrane 312 and the bipolar membrane 313. Thus, HCl is extracted from the compartment between the bipolar membrane 313 and the anion exchange membrane 311. NaOH is extracted from the compartment between the cation exchange membrane 312 and the bipolar membrane 313.

[0025] As shown in Fig. 2, NaOH is supplied to the immobilization unit 40 to make the pH alkaline. NaOH may further be supplied to the recovery unit 20. HCl may also be supplied to the recovery unit 20 to make the pH acidic. The extraction unit 30 is not limited to electrodialysis, and may extract NaOH by electrolysis of seawater.

[0026] The capture unit 20 captures carbon dioxide 24 (hereinafter also referred to as CO2) from the seawater 5. The capture unit 20 includes an ion exchange membrane 21 for capturing CO2. For example, the capture unit 20 captures CO2 by electrodialysis using the ion exchange membrane 21. Bipolar membrane electrodialysis (BMED) using an anion exchange membrane, a cation exchange membrane, and a bipolar membrane can be used. Specifically, CO2 is captured using the technology described in Patent Document 1.

[0027] Furthermore, the recovery unit 20 can recover carbon dioxide 24 as CO2 gas by lowering the pH of the seawater. For example, the recovery unit 20 supplies HCl to the seawater 5 to make the seawater 5 acidic. Alternatively, the recovery unit 20 can convert carbon dioxide into carbonate ions by raising the pH of the seawater. In other words, supplying sodium hydroxide 34 to the seawater makes the seawater 5 alkaline. In this case, carbonate ions are generated. Therefore, if the seawater contains mineral sources such as Mg and Ca, they will precipitate as carbonates.

[0028] The supply unit 60 supplies a gas containing carbon dioxide (CO2) to the immobilization unit 40. For example, the supply unit 60 supplies carbon dioxide 64 contained in exhaust gas 62 generated in a factory 61 to the immobilization unit 40. For example, the factory 61 located on ground emits exhaust gas 62. The exhaust gas 62 is, for example, a combustion gas generated when a hydrocarbon fuel is combusted. The exhaust gas 62 contains carbon dioxide gas at a high concentration of, for example, 10 to 15%.

[0029] The absorbent 63 absorbs carbon dioxide gas contained in the flue gas 62. The absorbent 63 includes a solid adsorbent and a porous carrier. The solid adsorbent is supported on the porous carrier. When the flue gas 62 comes into contact with the absorbent 63, the absorbent 63 adsorbs the carbon dioxide in the flue gas 62. Here, the porous carrier supporting the solid adsorbent is not particularly limited, but may be, for example, coated on a substrate having a honeycomb structure.

[0030] The solid adsorbent is not particularly limited, but is, for example, a hydrophilic polymer, more specifically, an amine-based polymer such as polyethyleneimine, primary amine, secondary amine, or secondary alkanolamine.

[0031] In the supply unit 60, gas containing carbon dioxide 64 is extracted from the absorbent 63. For example, the absorbent 63 is placed under reduced pressure and heated. This causes the gas containing carbon dioxide 64 that has been absorbed in the absorbent 63 to be released. The carbon dioxide gas released from the absorbent 63 is supplied to the immobilization unit 40.

[0032] Gas containing carbon dioxide 64 from the supply unit 60 is supplied to the DOC facility 1 through piping or the like. By adjusting the heating temperature and pressure, gas having a desired carbon dioxide concentration can be extracted from the absorbent 63. By using the absorbent 63, the supply unit 60 can supply high-concentration carbon dioxide gas to the immobilization unit 40.

[0033] Here, the carbon dioxide gas contained in the exhaust gas 62 is supplied to the immobilization unit 40 via the absorbent 63, but the exhaust gas 62 may be supplied directly to the immobilization unit 40. For example, the exhaust gas 62 containing carbon dioxide gas may be supplied to the immobilization unit 40 through a pipe installed between the factory 61 and the immobilization unit 40.

[0034] As described above, the immobilization unit 40 is supplied with the concentrated seawater 14, carbon dioxide 24, and carbon dioxide 64. The immobilization unit 40 has a scrubber 41. The concentrated seawater 14, carbon dioxide 24, and carbon dioxide 64 are supplied to the scrubber 41. The scrubber 41 performs exhaust gas treatment using the concentrated seawater 14 containing carbon dioxide gas as a treatment liquid. The scrubber 41 mixes the carbon dioxide 24 and carbon dioxide 64 with the concentrated seawater 14 to immobilize the carbon dioxide. That is, the scrubber 41 reacts calcium and magnesium with the carbon dioxide to produce carbonate 44. That is, the scrubber 41 carbonates calcium and magnesium by mixing the carbon dioxide gas with the concentrated seawater 14.

[0035] For example, the scrubber 41 has a tank for storing the concentrated seawater 14, an inlet connected to it for introducing carbon dioxide gas, and a nozzle for generating bubbles. By operating the scrubber 41, carbon dioxide is immobilized in mineral sources contained in the concentrated seawater 14. That is, carbonates 44 such as calcium carbonate (CaCO3), magnesium carbonate (MgCO3), and calcium magnesium carbonate (CaMg(CO3)2) are produced. This makes it possible to immobilize carbon dioxide 24 contained in the seawater and carbon dioxide 64 contained in the air.

[0036] The immobilization unit 40 immobilizes carbon dioxide in mineral sources contained in the concentrated seawater 14. The concentrated seawater 14 has higher concentrations of calcium and magnesium than ordinary seawater. Because the concentrated seawater 14 has a high concentration of mineral sources, carbon dioxide can be immobilized efficiently.

[0037] A supply unit 60 located in an external facility of the DOC facility 1 supplies gas containing carbon dioxide to the immobilization unit 40. The supply unit 60 supplies gas with a high carbon dioxide concentration to the scrubber 41. The scrubber 41 mixes the carbon dioxide gas with the concentrated seawater 14 to carbonate it. The immobilization unit 40 can efficiently immobilize carbon dioxide into calcium and magnesium. The mixed liquid containing a high concentration of carbon dioxide gas is treated in the scrubber 41. Therefore, carbonates such as calcium carbonate, magnesium carbonate, and calcium magnesium carbonate can be efficiently produced.

[0038] For example, the amount of carbon dioxide 24 recovered from only seawater 6 in the DOC facility 1 is small compared to the mineral source. The supply unit 60 can make up for the shortage by supplying the carbon dioxide 24 from an external source. In other words, carbon dioxide 64 is supplied from an external facility to compensate for the excess mineral source obtained from seawater 5. This allows the excess mineral source to be used for immobilization. Since carbon dioxide can be immobilized efficiently, the amount of carbon dioxide reduction can be increased.

[0039] Furthermore, the immobilization unit 40 is supplied with NaOH extracted in the extraction unit 30. By supplying NaOH to the concentrated seawater 14, the pH of the mixed solution can be adjusted. NaOH may be supplied to the concentrated seawater 14 in the form of a solid or an aqueous solution. Here, NaOH is added to the concentrated seawater 14 so that the pH of the concentrated seawater 14 becomes 12 or higher. The scrubber 41 generates bubbles in the mixed solution obtained by mixing the concentrated seawater 14 with NaOH and carbon dioxide gas.

[0040] By making the pH of the mixed solution alkaline, carbon dioxide can be efficiently immobilized. The higher the pH of the mixed solution, the lower the solubility of carbonates. In particular, when the pH is 12 or higher, the solubility becomes extremely low. Therefore, NaOH is added to the concentrated seawater 14 so that the pH of the mixed solution becomes 12 or higher. This allows a larger amount of carbonates 44 to be precipitated from the concentrated seawater, thereby enabling efficient immobilization of carbon dioxide. Calcium carbonate, magnesium carbonate, etc. may also be used as industrial raw materials. Alternatively, they may be stored underground or in the sea as carbonate minerals.

[0041] 4 is a flowchart showing a method for immobilizing carbon dioxide. First, the seawater concentrating unit 10 concentrates seawater 5 (S11). The seawater concentrating unit 10 concentrates mineral sources in the seawater 5 using an RO membrane 11. The seawater concentrating unit 10 supplies concentrated seawater 14, in which the mineral sources have been concentrated, to the immobilizing unit 40.

[0042] Next, the recovery unit 20 recovers carbon dioxide 24 from the seawater 5 and supplies it to the mineral source (S12). The recovery unit 20 may supply the carbon dioxide as a gas, or may supply the carbon dioxide gas as a liquid dissolved in the seawater 5.

[0043] The supply unit 60 supplies carbon dioxide to the mineral source from outside the DOC facility 1 (S13). Here, the supply unit 60 supplies carbon dioxide gas contained in exhaust gas 62 emitted from a factory 61 to the immobilization unit 40.

[0044] The immobilization unit 40 immobilizes the carbon dioxide in the mineral source (S14). Specifically, the scrubber 41 processes the concentrated seawater 14 containing carbon dioxide. The scrubber 41 mixes the concentrated seawater 14 with the carbon dioxide 24, 64 to produce carbonates. In this way, the carbon dioxide can be immobilized efficiently.

[0045] The pH of the seawater may be adjusted in the collection step of step S12 or the immobilization step of step S14. For example, the extraction unit 30 supplies NaOH to the concentrated seawater 14, thereby making the concentrated seawater 14 alkaline. Here, it is preferable to add NaOH so that the pH of the mixed liquid becomes 12 or higher. The collection unit 20 may also adjust the pH of the seawater 5. For example, HCl is added to the seawater 5 to extract carbon dioxide as a gas. This makes the seawater 5 acidic.

[0046] The facility that emits the exhaust gas is not limited to a factory. In other words, carbon dioxide 64 may be supplied from various plants, such as a power plant, a chemical plant, an oil plant, a gas plant, a plant for steel making, or a mining plant, in addition to the factory 61.

[0047] Embodiment 2 An immobilization method and an immobilization system according to the second embodiment will be described with reference to Fig. 5. Fig. 5 is a block diagram showing the overall configuration of the immobilization system. In the second embodiment, the configuration of the supply unit 60 is different from that of the first embodiment. The configuration other than the supply unit 60 is the same as that of the first embodiment, and therefore description thereof will be omitted where appropriate.

[0048] The supply unit 60 supplies carbon dioxide from the DAC facility 66 to the immobilization unit 40. The DAC facility 66 concentrates, for example, carbon dioxide gas in the atmosphere. The DAC facility 66 has a fan for collecting air, a separation membrane for separating carbon dioxide gas, and the like. The separation membrane is formed of a polymer membrane, an ionic liquid membrane, or the like. The separation membrane selectively allows carbon dioxide to pass through. In the DAC facility 66, separation membranes may be arranged in multiple stages. In this way, the DAC facility 66 supplies concentrated carbon dioxide gas. The carbon dioxide 64 is a gas containing carbon dioxide gas at a higher concentration than the carbon dioxide gas concentration in the atmosphere.

[0049] The supply unit 60 then supplies the carbon dioxide 64 as a gas to the immobilization unit 40. A gas containing concentrated carbon dioxide gas is supplied to the immobilization unit 40. The carbon dioxide 64 from the DAC facility is mixed with the concentrated seawater 14 to produce carbonates 44. This allows the immobilization unit 40 to immobilize the carbon dioxide 24 contained in the seawater and the carbon dioxide 64 contained in the air into the mineral source.

[0050] In the immobilization system 100 of this embodiment, as shown in the first embodiment, carbon dioxide contained in the exhaust gas 62 from a factory 61 or the like may be supplied to the immobilization unit 40. In other words, there may be two or more external facilities that supply carbon dioxide. Carbon dioxide gas may be supplied to the immobilization unit 40 from two or more different facilities, or carbon dioxide gas may be supplied to the immobilization unit 40 from two or more locations in one facility.

[0051] The present disclosure is not limited to the above-described embodiments and can be modified as appropriate without departing from the spirit of the present disclosure. The present disclosure also contributes to carbon neutrality, decarbonization, and the Sustainable Development Goals (SDGs). [Explanation of symbols]

[0052] 100 Immobilization System 10 Seawater concentration section 11 RO membrane 13 Freshwater 14 Concentrated seawater 20 Collection Department 21 Ion exchange membrane 23 Decarbonated seawater 24 Carbon dioxide 30 Extraction part 31 Ion exchange membrane 40 Immobilization part 41 Scrubba 60 Supply section 61 Factory 62 Exhaust gas 63 Absorbent material 64 Carbon dioxide 66 DAC Facilities

Claims

1. Recovering carbon dioxide from seawater at a Direct Ocean Capture (DOC) facility; Concentrating mineral sources in seawater at the DOC facility; providing the recovered carbon dioxide to the mineral source; supplying carbon dioxide obtained outside the DOC facility to the mineral source; and mixing the carbon dioxide recovered in the DOC facility and carbon dioxide supplied from an external source with the mineral source to carbonate the carbon dioxide.

2. 2. The immobilization method according to claim 1, wherein carbon dioxide obtained from outside the DOC facility is supplied to the mineral source as a gas having a carbon dioxide concentration higher than that of the atmosphere.

3. 3. The immobilization method according to claim 1, wherein the carbon dioxide obtained from outside the DOC facility is carbon dioxide gas contained in exhaust gas from a plant or factory.

4. 3. The fixation method according to claim 1, wherein the carbon dioxide obtained from outside the DOC facility is supplied from a DAC (Direct Air Capture) facility.

5. At the DOC facility, a capture unit that captures carbon dioxide from seawater; In the DOC facility, a seawater concentrating section that concentrates mineral sources from seawater; a supply section that supplies the mineral source with carbon dioxide obtained outside the DOC facility; an immobilization unit that mixes the carbon dioxide supplied from the supply unit with the mineral source to carbonate the carbon dioxide.

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