Immobilization method of carbon dioxide, and immobilization system

Abstract

To provide an immobilization method of carbon dioxide which can efficiently immobilize carbon dioxide.SOLUTION: An immobilization method of carbon dioxide comprises the steps of: desalinating sea water to produce fresh water 13 and concentrated sea water 14; extracting NaOH or HCL from the sea water; adjusting pH of the sea water by use of NaOH or HCL; and supplying the concentrated sea water with gas including carbon dioxide to immobilize carbon dioxide to a mineral source contained in the concentrated sea water.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a recovery system for recovering carbon dioxide (CO2), which is a greenhouse gas. The recovery system in Patent Document 1 uses an amine-based compound as an absorption liquid for absorbing carbon dioxide gas contained in exhaust gas. The recovery system includes a treatment unit having an anion exchange membrane, a cation exchange membrane, and a bipolar membrane.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, a method for immobilizing carbon dioxide has been developed by using a mineral source such as calcium (Ca) or magnesium (Mg). For example, carbon dioxide can be immobilized by reacting carbon dioxide with a mineral source to carbonate it. Carbon dioxide can be immobilized by generating carbonates such as calcium carbonate (CaCO3), magnesium carbonate (MgCO 3 3), or double salts thereof (CaMg(CO3)2).

[0005] Seawater contains mineral sources such as calcium and magnesium. However, seawater has a problem that it cannot efficiently immobilize carbon dioxide because the concentration of the mineral source is low. Therefore, the development of a more efficient carbon dioxide immobilization technology is eagerly desired.

[0006] The present disclosure has been made in view of the above problems, and an object thereof is to provide a method for immobilizing carbon dioxide and an immobilization system that can efficiently immobilize carbon dioxide.

Means for Solving the Problems

[0007] In order to solve the above-described problems and achieve the object, the following method for immobilizing carbon dioxide and an immobilization system are provided.

[0008] The method for immobilizing carbon dioxide according to the present disclosure includes a step of desalinating seawater to produce fresh water and concentrated seawater, a step of extracting NaOH or HCl from the seawater, a step of adjusting the pH of the seawater using the NaOH or HCl, and a step of supplying a gas containing carbon dioxide to the concentrated seawater to immobilize carbon dioxide in the mineral source contained in the concentrated seawater.

[0009] In the above-described immobilization method, in the step of desalinating the seawater, the fresh water and the concentrated seawater may be separated using a reverse osmosis membrane.

[0010] In the above-described immobilization method, carbon dioxide gas contained in exhaust gas discharged from a factory or a plant may be supplied to the concentrated seawater.

[0011] In the above-described immobilization method, the fresh water may be used as cooling water for a factory or a plant that discharges exhaust gas.

[0012] The carbon dioxide immobilization system according to the present disclosure includes a desalination unit that desalinates seawater to produce fresh water, an extraction unit that extracts NaOH or HCl for adjusting the pH from the seawater, and an immobilization unit that supplies a gas containing carbon dioxide to the concentrated seawater to immobilize carbon dioxide in the mineral source contained in the concentrated seawater.

Effects of the Invention

[0013] According to the present disclosure, it is possible to provide a method for immobilizing carbon dioxide and an immobilization system that can efficiently immobilize carbon dioxide.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0015] 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. Also, not all of the configurations described in the embodiments are essential as means for solving the problems. For clarity of explanation, the following description and drawings are appropriately omitted and simplified. In each drawing, the same elements are denoted by the same reference numerals, and duplicate explanations are omitted as necessary.

[0016] Embodiment 1 The carbon dioxide immobilization system 100 will be described with reference to FIG. 1. FIG. 1 is a block diagram showing the overall configuration of the system. As shown in FIG. 1, the immobilization system 100 includes a desalination unit 10, a recovery unit 20, an extraction unit 30, an immobilization unit 40, and a gas supply unit 60. The desalination unit 10, the recovery unit 20, the extraction unit 30, the immobilization unit 40, and the gas supply unit 60 are connected by piping or the like. Seawater 5 is supplied to the desalination unit 10, the recovery unit 20, and the extraction unit 30. For example, a pump or the like sucks the seawater 5 in a shallow area of the sea. Then, the seawater 5 is supplied to the desalination unit 10, the recovery unit 20, and the extraction unit 30 through piping, respectively.

[0017] The desalination unit 10 is, for example, a carbonization plant. The desalination unit 10 is equipped with an RO (Reverse Osmosis membrane) 11 for desalinating seawater 5. 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 water molecules in seawater pass through the RO membrane 11, fresh water 13 is obtained.

[0018] Furthermore, in the seawater that does not pass through the RO membrane 11, mineral sources such as calcium and magnesium are concentrated. The seawater in which the mineral source is concentrated is taken as concentrated seawater 14. By using the RO membrane 11, concentrated seawater 14 is generated when fresh water 13 is produced. The desalination unit 10 can separate seawater into concentrated seawater 14 and fresh water 13. In the concentrated seawater 14, the concentration of mineral sources such as calcium and magnesium is higher than that in seawater.

[0019] The concentrated seawater 14 produced in the desalination unit 10 is supplied to the immobilization unit 40. The fresh water 13 produced in the desalination unit 10 is supplied to the gas supply unit 60. The gas supply unit 60 is installed in a factory 61 or a plant, etc. In the factory 61, the fresh water 13 may be used as cooling water. For example, the fresh water 13 cools a heat source in the factory 61.

[0020] Note that the fresh water 13 is not limited to the factory 61 and may be supplied to various plants such as power generation plants, chemical plants, oil plants, gas plants, plant plants, ironmaking plants, and mining plants. Alternatively, at least a part of the fresh water 13 may be used as drinking water or water for plant cultivation. For example, the fresh water 13 is supplied to a plant factory or a plant plant and used for hydroponics, etc. Also, the facilities where the fresh water 13 is used are not particularly limited.

[0021] The extraction unit 30 extracts sodium hydroxide 34 (hereinafter also referred to as NaOH) from seawater 5. For example, the extraction unit 30 has an ion exchange membrane 31. Specifically, NaOH is extracted from seawater 5 by electrodialysis using the ion exchange membrane 31. By using the electrodialysis method, NaOH precipitates. The seawater from which NaOH has been extracted becomes desalinated seawater 33. NaOH is supplied to the immobilization unit 40 to adjust the pH.

[0022] For example, by bipolar membrane electrodialysis (BMED) using an anion exchange membrane, a cation exchange membrane, and a bipolar membrane, NaOH and hydrogen chloride (HCl) are extracted. FIG. 2 is a schematic diagram for explaining the electrodialysis apparatus 300 of the bipolar membrane electrodialysis method.

[0023] The storage tank 301 is a tank that stores seawater 5 containing sodium chloride (NaCl). An anode 302 and a cathode 303 are provided in the storage tank 301. Between the anode 302 and the cathode 303 in the storage tank 301, an anion exchange membrane 311, a cation exchange membrane 312, and a bipolar membrane 313 are installed. In order from the anode 302 side, 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.

[0024] 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 the passage of cations. Therefore, Cl in the seawater ― passes through the anion exchange membrane 311 toward the anode 302 side. The cation exchange membrane 312 allows cations to pass through and blocks the passage of anions. Therefore, Na in the seawater + passes through the cation exchange membrane 312 toward the cathode 303 side.

[0025] The bipolar membrane 313 is an ion exchange membrane formed by laminating an anion exchange membrane 311 and a cation exchange membrane 312. The bipolar membrane 313, upon application of a voltage, converts water molecules (H2O) into H+ and OH - dissociates into H + which moves to the compartment between the bipolar membrane 313 and the anion exchange membrane 311. OH - moves to the compartment between the cation exchange membrane 312 and the bipolar membrane 313. Therefore, 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.

[0026] As shown in FIG. 1, NaOH for making the pH alkaline is supplied to the immobilization unit 40. Further, NaOH may be supplied to the recovery unit 20. Also, HCl for making the pH acidic may be supplied to the recovery unit 20. The extraction unit 30 is not limited to the electrodialysis method, and NaOH may be extracted by electrolyzing seawater.

[0027] The recovery unit 20 recovers carbon dioxide 24 (hereinafter also referred to as CO2) from seawater 5. The recovery unit 20 is provided with an ion exchange membrane 21 for recovering CO2. For example, the recovery unit 20 recovers CO2 by an electrodialysis method using the ion exchange membrane 21. A bipolar membrane electrodialysis method (BMED) using an anion exchange membrane, a cation exchange membrane, and a bipolar membrane can be used. Specifically, the technique described in International Publication No. 2022 / 99174 is used to recover CO2.

[0028] Also, the recovery unit 20 can recover carbon dioxide 24 as CO2 gas by lowering the pH of seawater. For example, the recovery unit 20 supplies HCl to seawater 5 to make seawater 5 acidic. Alternatively, the recovery unit 20 raises the pH of seawater so that carbon dioxide becomes carbonate ions. That is, by supplying sodium hydroxide 34 to seawater, seawater 5 becomes alkaline. In this case, carbonate ions are generated. Therefore, if seawater contains a mineral source such as Mg or Ca, it precipitates as a carbonate.

[0029] In the gas supply unit 60, a gas containing carbon dioxide (CO2) is supplied to the immobilization unit 40. Specifically, in the factory 61, exhaust gas 62 is being discharged. The exhaust gas 62 is, for example, combustion gas generated when a hydrocarbon-based fuel is burned. The exhaust gas 62 contains carbon dioxide gas at a high concentration of, for example, 10 - 15%.

[0030] The exhaust gas 62 is supplied to the immobilization unit 40. Here, 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. Alternatively, carbon dioxide gas may be supplied to the immobilization unit 40 via an adsorbent or an absorbent.

[0031] As described above, concentrated seawater 14 and exhaust gas 62 are supplied to the immobilization unit 40. The immobilization unit 40 has a scrubber 41. The concentrated seawater 14 and the exhaust gas 62 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.

[0032] For example, the scrubber 41 has a tank for storing the concentrated seawater 14, an inlet for introducing the exhaust gas 62, and nozzles for generating bubbles, etc. By the operation of the scrubber 41, carbon dioxide is immobilized on the mineral source 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 generated.

[0033] The immobilization unit 40 immobilizes carbon dioxide on the mineral source contained in the concentrated seawater generated during desalination. In the concentrated seawater 14, the concentrations of calcium and magnesium are higher than those in normal seawater. Since the concentration of the mineral source is high in the concentrated seawater 14, carbon dioxide can be efficiently immobilized.

[0034] The gas supply unit 60 supplies a gas containing carbon dioxide gas to the immobilization unit 40. The gas supply unit 60 supplies exhaust gas 62 with a high carbon dioxide concentration to the scrubber 41. Therefore, the immobilization unit 40 can efficiently immobilize carbon dioxide to calcium or magnesium. A mixed solution containing a high-concentration carbon dioxide gas is processed in the scrubber 41. Therefore, carbonates such as calcium carbonate, magnesium carbonate, and calcium magnesium carbonate can be efficiently produced.

[0035] Furthermore, NaOH extracted by the extraction unit 30 is supplied to the immobilization unit 40. 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 a solid state or in an aqueous solution state. Here, NaOH is added to the concentrated seawater 14 so that the pH of the concentrated seawater 14 becomes 12 or more. The scrubber 41 generates bubbles in the mixed solution in which NaOH and the exhaust gas 62 are mixed with the concentrated seawater 14.

[0036] 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 the carbonate. In particular, when the pH becomes 12 or more, 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 more. As a result, more carbonate 44 can be precipitated from the concentrated seawater, so that carbon dioxide can be efficiently immobilized. Calcium carbonate, magnesium carbonate, etc. may be used as industrial raw materials. Alternatively, they may be stored in the ground or in the sea as carbonate minerals.

[0037] Figure 3 is a flowchart showing a method for immobilizing carbon dioxide. First, the desalination unit 10 desalinates seawater 5 (S11). The desalination unit 10 generates fresh water 13 and concentrated seawater 14 using the RO membrane 11.

[0038] Next, the extraction unit 30 extracts NaOH or HCl from the seawater 5 (S12). Here, as described above, the electrodialysis device 300 etc. extract NaOH and HCl.

[0039] The immobilization unit 40 adjusts the pH of the seawater (S13). For example, by supplying NaOH to the concentrated seawater 14, the concentrated seawater 14 becomes alkaline. Here, it is preferable to add NaOH so that the pH of the mixed solution becomes 12 or more. Also, in the recovery unit 20, the pH of the seawater 5 may be adjusted. For example, HCl is added to the seawater 5 in order to extract carbon dioxide as a gas. As a result, the seawater 5 becomes acidic.

[0040] The immobilization unit 40 supplies the exhaust gas 62 to the concentrated seawater 14 to immobilize carbon dioxide in the mineral source (S14). Specifically, the scrubber 41 processes the concentrated seawater 14 containing the exhaust gas 62 to generate carbonate. By doing so, carbon dioxide can be efficiently immobilized.

[0041] Embodiment 2 The immobilization method and the immobilization system according to Embodiment 2 will be described with reference to FIG. 4. FIG. 4 is a block diagram showing the overall configuration of the immobilization system. In Embodiment 2, the configuration of the gas supply unit 60 is different from that in Embodiment 1. Since the configurations other than the gas supply unit 60 are the same as those in Embodiment 1, the description thereof will be omitted as appropriate.

[0042] The gas supply unit 60 has a gas concentration unit 65. The gas concentration unit 65 takes in the atmosphere and concentrates the carbon dioxide gas in the atmosphere. The gas concentration unit 65 has, for example, a separation membrane that separates carbon dioxide gas. The separation membrane is formed of a polymer membrane, an ionic liquid membrane, or the like. The separation membrane selectively permeates carbon dioxide. A plurality of separation membranes may be arranged in multiple stages in the gas concentration unit 65. In this way, the gas concentration unit 65 generates a concentrated gas 66 in which the carbon dioxide gas is concentrated. The concentrated gas 66 is a gas containing carbon dioxide gas at a concentration higher than the carbon dioxide gas concentration in the atmosphere.

[0043] And the gas supply unit 60 supplies the concentrated gas 66 generated in the gas concentration unit 65 to the immobilization unit 40. Also, the fresh water 13 generated in the desalination unit 10 is supplied to the plant 71 and the plant 72. The fresh water 13 is used as cooling water in the plant 71. It may be used for cultivating the plant 72. Further, the fresh water 13 may be used as drinking water 73.

[0044] Note that in the immobilization system 100 of the present embodiment as well, as shown in the first embodiment, the exhaust gas 62 from the factory 61 or the plant 71 may be supplied to the immobilization unit 40. Further, the gas concentration unit 65 may concentrate the carbon dioxide gas in the exhaust gas to generate the concentrated gas 66.

[0045] Note that the present disclosure is not limited to the above-described embodiments, and can be appropriately modified without departing from the gist.

Explanation of Reference Numerals

[0046] 100 Immobilization system 10 Desalination unit 11 RO membrane 13 Fresh water 14 Concentrated seawater 20 Recovery unit 21 Ion exchange membrane 23 Decarbonated seawater 24 Carbon dioxide 30 Extraction unit 31 Ion exchange membrane 40 Immobilization unit 41 Scrubber 60 Gas supply unit 61 Factory 62 Exhaust gas

Claims

1. generating fresh water and concentrated seawater by desalinating seawater; extracting NaOH or HCl from the seawater; adjusting the pH of the seawater using the NaOH or HCl; and fixing carbon dioxide to a mineral source contained in the concentrated seawater by supplying a gas containing carbon dioxide to the concentrated seawater. A method for fixing carbon dioxide, comprising the steps of:

2. The fixing method according to claim 1, wherein, in the step of desalinating the seawater, the fresh water and the concentrated seawater are separated using a reverse osmosis membrane.

3. The fixing method according to claim 1 or 2, wherein carbon dioxide gas contained in exhaust gas discharged from a factory or a plant is supplied to the concentrated seawater.

4. The fixing method according to claim 3, wherein the fresh water is used as cooling water for a factory or a plant that discharges exhaust gas.

5. a desalination unit that desalinates seawater to produce fresh water and concentrated seawater; an extraction unit that extracts NaOH or HCl for pH adjustment from the seawater; a fixing unit that fixes carbon dioxide to a mineral source contained in the concentrated seawater by supplying a gas containing carbon dioxide to the concentrated seawater. A carbon dioxide fixing system comprising:

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