Ocean sequestration method for carbon dioxide

Abstract

To provide a method for sequestering carbon dioxide to the ocean while enhancing efficiency of contact between the carbon diode and an immobilizer and suppressing the acidification of the ocean resulting from dissolution of carbon dioxide supplied to an ocean floor.SOLUTION: There is provided a method for sequestering carbon dioxide to the ocean that is characterized in: supplying carbon dioxide hydrate and an immobilizer which chemically reacts with the carbon dioxide to produce an insoluble reaction product; and holding them on the ocean floor in contact. The immobilizer is preferably concrete including at least one of calcium oxide and calcium hydroxide.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for ocean sequestration of carbon dioxide that does not acidify the ocean.

Background Art

[0002] Conventionally, a method has been proposed in which carbon dioxide contained in exhaust gas is absorbed and immobilized by waste concrete materials (Patent Document 1). Calcium oxide and the like contained in concrete chemically react with carbon dioxide in the exhaust gas to produce calcium carbonate. At this time, carbon dioxide, which was a gas, is immobilized as solid calcium carbonate. In addition, a method has also been proposed in which carbon dioxide contained in the atmosphere is brought into contact with surface seawater, and the produced insoluble carbonate is allowed to settle by its own weight and immobilized in the deep sea (Patent Document 2).

[0003] However, these conventional methods have a problem that the reaction efficiency of immobilizing carbon dioxide is low because the concentration of carbon dioxide contained in exhaust gas or the atmosphere is low.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention provides a method for sequestering carbon dioxide in the ocean while increasing the contact efficiency between carbon dioxide and an immobilizing agent and suppressing ocean acidification caused by the dissolution of carbon dioxide supplied to the seabed.

Means for Solving the Problems

[0006] [1] A method for immobilizing carbon dioxide in the ocean, characterized by supplying carbon dioxide hydrate and an immobilizing agent that generates an insoluble reaction product by chemically reacting with carbon dioxide to the seabed and holding them on the seabed in a state where they are in contact with each other. [2] The method according to [1], wherein the shape of the immobilizing agent is gravel-like, granular, or powdery. [3] The method according to [1] or [2], wherein the immobilizing agent is a substance containing at least one of calcium oxide and calcium hydroxide. [4] The method according to any one of [1] to [3], wherein the immobilizing agent is concrete. [5] The method according to any one of [1] to [4], wherein the seabed is at a depth of 3000 m or deeper and is an environment in which carbon dioxide hydrate is formed by mixing with seawater when liquid carbon dioxide is supplied. [6] The method according to any one of [1] to [5], wherein the acidity of the carbon dioxide contained in the carbon dioxide hydrate is neutralized by the immobilizing agent, and the generated reaction product is adsorbed by the immobilizing agent, thereby suppressing the elution of carbon dioxide from the carbon dioxide hydrate supplied to the seabed into the ocean. [Advantages of the Invention]

[0007] In the method of the present invention, compared with the conventional method of bringing a gas containing carbon dioxide gas at a low concentration into contact with an immobilizing agent, a carbon dioxide hydrate having a high carbon dioxide concentration is brought into contact with the immobilizing agent, so that the contact efficiency between carbon dioxide and the immobilizing agent is increased. As a result, the reaction efficiency between carbon dioxide and the immobilizing agent is enhanced, and carbon dioxide can be efficiently immobilized. Therefore, it is possible to immobilize carbon dioxide on the seabed while suppressing the acidification of the ocean due to the elution of carbon dioxide supplied to the seabed. [Brief Description of the Drawings]

[0008]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0009] Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. The drawings used in the following description may show the characteristic parts enlarged for convenience of understanding, and the dimensional ratios of each component are not necessarily the same as the actual ones.

[0010] Fig. 1(a) shows a state where the immobilizing agent 1 is supplied to the seabed (seabed surface) F of the ocean O. The immobilizing agent 1 of the present embodiment is gravel of waste concrete dropped from a workboat S floating on the sea surface, and it sinks due to its own weight and accumulates on the seabed F.

[0011] The immobilizing agent 1 may be a substance that generates an insoluble reaction product by chemically reacting with carbon dioxide. From the viewpoint of installation on the seabed F, it is preferably a substance having a specific gravity heavier than water. From the viewpoint of enhancing the contact efficiency with carbon dioxide, it is preferable that the immobilizing agent 1 accumulates in a state with a large surface area. For example, it is preferably in the form of gravel, granules, or powder. Further, from the viewpoint that the reaction with carbon dioxide proceeds sufficiently in the sea, the immobilizing agent 1 is preferably a substance containing at least one of calcium oxide (CaO) and calcium hydroxide (Ca(OH)2). These chemical substances react with carbon dioxide to produce calcium carbonate (CaCO3), which is an insoluble carbonate in water. As a result of this neutralization reaction, the insoluble carbonate can be adsorbed to the immobilizing agent 1.

[0012] As a specific immobilizing agent 1, concrete is preferable, and waste concrete (waste concrete) is more preferable. Concrete can easily sink by its own weight and accumulate on the seabed F, and if it is in the form of crushed gravel, granules, or powder, a sufficient specific surface area for the reaction can be ensured. Furthermore, it is economical to utilize waste concrete.

[0013] FIG. 1(b) shows a state in which carbon dioxide hydrate 2 is supplied to the seabed F so as to come into contact with the immobilizer 1 deposited on the seabed F. The carbon dioxide hydrate 2 of the present embodiment is formed by liquid CO2 (liquid carbon dioxide) injected into the sea from the tip of a nozzle suspended in the sea from a workboat S floating on the sea surface. Since the specific gravity of liquid CO2 in the deep sea (at a depth of 3000 m or more) is slightly heavier than that of seawater, it stably deposits on the seabed F. At this time, at least the surface of the mass of liquid CO2 is mixed with seawater and is covered with a so-called hydrate film.

[0014] Generally, carbon dioxide becomes solid dry ice under the conditions of a temperature of -79.15°C or lower and normal pressure. However, when mixed with water, it is known to form hydrates at temperatures and pressures different from those under normal pressure. That is, carbon dioxide hydrate is formed when liquid CO2 is mixed with water under the conditions of a temperature of 10°C or lower and a pressure of 4.5 MPa or higher (environment). For example, in an environment at a depth of 3000 m or more, preferably at a depth of 3500 m or more, these conditions can be satisfied. The liquid CO2 used in the present invention is obtained by a known method.

[0015] FIG. 1(c) shows a state in which the immobilizer 1 and the carbon dioxide hydrate 2 are in contact with each other and are naturally mixed and held on the seabed F. Since there is the immobilizer 1 in contact with the carbon dioxide hydrate 2, the immobilizer 1 and carbon dioxide react to form an insoluble reaction product 3. This reaction can also be said to be a reaction in which the immobilizer 1 neutralizes the acidity of carbon dioxide. As a result of this reaction, carbon dioxide is adsorbed by the immobilizer 1, so that the elution of the carbon dioxide supplied to the seabed is suppressed. In the present invention, carbon dioxide can be immobilized on the seabed F while preventing this acidification.

[0016] In the embodiment described above, after depositing the immobilizing agent 1 on the seabed F, the carbon dioxide hydrate 2 is supplied in this order. However, the present invention is not limited to this order. The carbon dioxide hydrate 2 may be deposited on the seabed F first, and then the immobilizing agent 1 may be supplied, or the supply and deposition of the immobilizing agent 1 and the carbon dioxide hydrate 2 may be simultaneous.

[0017] <Aspen Simulation> In order to prove that the present invention is feasible, a simulation experiment was conducted to find out what differences there are in the reaction between carbon dioxide and calcium hydroxide under atmospheric pressure conditions and pressure conditions at a water depth of 3500 m. Fixed under the conditions of a temperature of 1 °C, seawater: 10,000 kg / h, CO2: 1,000 kg / h, and when the supply amount of calcium hydroxide was varied in the range of 0 to 2,000 kg / h, the pH of the seawater after the neutralization reaction was calculated. The results are shown in Figure 2. When the amount of calcium hydroxide was 0 kg / h, CO2 dissolved in the seawater and the pH became about 3. When the supply amount of calcium hydroxide was gradually increased and exceeded 1600 kg / h, the pH of the seawater showed neutral to alkaline. It was found that under both atmospheric pressure and pressure conditions at a water depth of 3500 m, the neutralization reaction of CO2 by calcium hydroxide occurred sufficiently, and the acidification of seawater by CO2 could be sufficiently suppressed.

[0018] Incidentally, the applicant of the present application has separately proposed a method for storing carbon dioxide hydrate at a position deeper than the seabed surface, so-called "underground carbon dioxide storage method". In this underground storage method, liquid CO2 is injected into the ground under the seabed, and the liquid CO2 moves upward by buoyancy. When it reaches a region with certain temperature and pressure conditions, carbon dioxide hydrate is generated, and it functions as a structure (shielding layer) that serves as a lid, physically suppressing the leakage of carbon dioxide into the sea and storing it stably. On the one hand, the present invention is a method of reacting carbon dioxide with an immobilizing agent by coexisting carbon dioxide hydrate with the immobilizing agent on the seabed, chemically suppressing the dissolution of the supplied carbon dioxide into the sea at the sea bottom, and stably retaining it. Therefore, the present invention is an invention having a completely different technical idea from the above-mentioned "method for underground storage of carbon dioxide".

Explanation of symbols

[0019] 1... Immobilizing agent, 2... Carbon dioxide hydrate, 3... Reaction product, F... Seabed, O... Ocean, S... Working ship

Claims

1. A method for sequestering carbon dioxide in the ocean, comprising supplying carbon dioxide hydrate and an immobilizing agent that forms an insoluble reaction product by reacting with carbon dioxide to the seabed and retaining them in contact with each other on the seabed.

2. The method according to claim 1, wherein the immobilizing agent is in the form of gravel, granules, or powder.

3. The method according to claim 2, wherein the immobilizing agent is a substance containing at least one of calcium oxide and calcium hydroxide.

4. The method according to claim 3, wherein the immobilizing agent is concrete.

5. The method according to claim 1, wherein the seabed is at a depth of 3000 m or more and is an environment in which carbon dioxide hydrate is formed by mixing with seawater when liquid carbon dioxide is supplied.

6. The method according to claim 1, wherein the acidity of the carbon dioxide contained in the carbon dioxide hydrate is neutralized by the immobilizing agent, and the generated reaction product is adsorbed by the immobilizing agent, thereby suppressing the elution of carbon dioxide from the carbon dioxide hydrate supplied to the seabed into the ocean.

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