Carbon dioxide fixation method and carbon dioxide fixation apparatus

Abstract

To provide a carbon dioxide fixation method which efficiently performs neutralization of cement in concrete sludge water, and allows an emission amount of carbon dioxide to be reduced.SOLUTION: A carbon dioxide fixation method includes: a gas supply step for introducing a carbon dioxide-containing gas A to concrete sludge water stored in a storage part; an introduction step for introducing a carbon dioxide-containing gas B having passed through the concrete sludge water, to a gas retention part provided above the storage part; and a gas circulation step for introducing a carbon dioxide-containing gas C containing the carbon dioxide-containing gas B, from the gas retention part into the concrete sludge water. In the gas circulation step, an introduction amount of the carbon dioxide-containing gas C introduced into the concrete sludge water, that is maintained is larger than a lead-out amount of the carbon dioxide-containing gas B lead out from the concrete sludge water to the gas retention part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide fixation method and a carbon dioxide fixation device. [Background technology]

[0002] A method for producing cement while suppressing carbon dioxide emissions at cement factories by immobilizing carbon dioxide contained in exhaust gases and the like in cement has been studied. Patent Document 1 describes a cement composition production system that immobilizes carbon dioxide in cement, the system comprising a means for supplying carbon dioxide to a mixture of water and cement. Patent Document 2 describes a method for immobilizing carbon dioxide in cement hydrate in a short period of time by injecting carbon dioxide into cement hydrate at an injection rate of 3600 kg / t·h or more and an injection amount of 600 kg / t or more. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-020598 [Patent Document 2] Japanese Patent Publication No. 2022-156508 Summary of the Invention [Problem to be solved by the invention]

[0004] Concrete sludge water generated from washing water in concrete mixers and the like is treated as industrial waste. Therefore, from the perspective of effective resource utilization, there is a demand for reusing concrete sludge water as mixing water for concrete. However, it is known that using concrete sludge water as mixing water accelerates the cement hydration reaction, resulting in slump loss, in which the fluidity of fresh concrete is lost over time during transportation, etc. Therefore, one known method for suppressing slump loss is to add a strong acid stabilizer, such as an oxycarboxylic acid, to the concrete sludge water to neutralize it and suppress the cement hydration reaction. However, adding a stabilizer requires controlling the amount of stabilizer added, which makes management complicated.

[0005] On the other hand, from the viewpoint of environmental protection, cement plants are required to reduce the emission of carbon dioxide contained in exhaust gases, etc. Therefore, the present disclosure provides a carbon dioxide fixation method and a carbon dioxide fixation device that can efficiently neutralize concrete sludge water and reduce carbon dioxide emissions. [Means for solving the problem]

[0006] One aspect of the present disclosure provides a carbon dioxide fixation method comprising: a gas supply step of introducing carbon dioxide-containing gas A into concrete sludge water contained in a storage section; an introduction step of introducing carbon dioxide-containing gas B that has passed through the concrete sludge water into a gas retention section provided above the storage section; and a gas circulation step of introducing carbon dioxide-containing gas C containing the carbon dioxide-containing gas B from the gas retention section into the concrete sludge water, wherein in the gas circulation step, the amount of carbon dioxide-containing gas C introduced into the concrete sludge water is maintained to be greater than the amount of carbon dioxide-containing gas B extracted from the concrete sludge water to the gas retention section.

[0007] In the carbon dioxide fixation method, the amount of carbon dioxide-containing gas C introduced into the concrete sludge water from the gas retention section is kept greater than the amount of carbon dioxide-containing gas B discharged from the concrete sludge water to the gas retention section, thereby circulating carbon dioxide and repeatedly introducing it into the concrete sludge water with high reliability. This allows the carbon dioxide and cement to continue reacting in the concrete sludge water in the storage section, thereby efficiently neutralizing the concrete sludge water and reducing carbon dioxide emissions.

[0008] One aspect of the present disclosure provides a carbon dioxide fixation device comprising: a storage section for storing concrete sludge water; a gas inlet section for introducing carbon dioxide-containing gas A into the concrete sludge water; a gas retention section above the storage section in which gas containing carbon dioxide-containing gas B that has passed through the concrete sludge water retains; and a gas circulation section for introducing carbon dioxide-containing gas C containing carbon dioxide-containing gas B from the gas retention section into the concrete sludge water, wherein the amount of carbon dioxide-containing gas C introduced into the concrete sludge water is maintained to be greater than the amount of carbon dioxide-containing gas B extracted from the concrete sludge water to the gas retention section.

[0009] The carbon dioxide fixation device maintains the amount of carbon dioxide-containing gas C introduced into the concrete sludge water from the gas retention section greater than the amount of carbon dioxide-containing gas B discharged from the concrete sludge water to the gas retention section, thereby circulating carbon dioxide and repeatedly introducing it into the concrete sludge water with high reliability. This allows the carbon dioxide and cement to continue reacting in the concrete sludge water in the storage section, thereby efficiently neutralizing the concrete sludge water and reducing carbon dioxide emissions. [Effects of the Invention]

[0010] The present disclosure can provide a carbon dioxide fixation method and a carbon dioxide fixation device that can efficiently neutralize cement in concrete sludge water and reduce carbon dioxide emissions. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a diagram for explaining the flow of a carbon dioxide-containing gas in a carbon dioxide fixation method. [Figure 2] FIG. 1 is a diagram showing an example of a carbon dioxide fixation device. [Figure 3] FIG. 10 is a graph showing the effect of carbon dioxide circulation on pH transition. [Figure 4] FIG. 1 is a graph showing the effect of the carbon dioxide supply rate on the pH transition. [Figure 5] FIG. 10 is a graph showing the effect of the presence or absence of a bubble generator on the pH transition. [Figure 6] FIG. 1 is a graph showing the effect of cement concentration on pH transition in concrete sludge water. [Figure 7] FIG. 1 is a graph showing the effect of temperature on pH transition of concrete sludge water. DETAILED DESCRIPTION OF THE INVENTION

[0012] Embodiments of the present disclosure are described below. However, the following embodiments are merely examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. The upper or lower limit of a numerical range specified in this disclosure may be replaced with any value shown in the examples. Furthermore, the upper and lower limits individually described may be combined in any desired manner. Unless otherwise specified, the materials or components exemplified in this disclosure may be used alone or in combination of two or more. The symbol "~" used in a numerical range indicates a numerical range that includes the upper and lower limits. For example, "X~Y" indicates a numerical range "greater than or equal to X and less than or equal to Y." In the description, identical elements or elements having the same function are designated by the same reference numerals, and redundant description is omitted. Furthermore, positional relationships such as up, down, left, and right used in the description are based on the positional relationships shown in the drawings unless otherwise specified.

[0013] A carbon dioxide fixation method according to one embodiment includes a gas supply step of introducing a carbon dioxide-containing gas A into concrete sludge water stored in a storage section, an introducing step of introducing carbon dioxide-containing gas B that has passed through the concrete sludge water into a gas retention section provided above the storage section, and a gas circulating step of introducing carbon dioxide-containing gas C containing carbon dioxide-containing gas B from the gas retention section into the concrete sludge water. By circulating the carbon dioxide-containing gas between the concrete sludge water and the gas retention section, this carbon dioxide fixation method can efficiently neutralize the sludge water and reduce carbon dioxide emissions.

[0014] The flow of carbon dioxide-containing gas in the carbon dioxide fixation method will be described using FIG. 1. First, carbon dioxide-containing gas A is introduced into concrete sludge water (hereinafter also referred to as "sludge water") 12 contained in storage section 10 via air bubble generator 50a. Then, carbon dioxide-containing gas B that has passed through sludge water 12 is introduced into gas retention section 20. The carbon dioxide-containing gas B introduced into gas retention section 20 mixes with another gas that has flowed into gas retention section 20 to form carbon dioxide-containing gas C. Carbon dioxide-containing gas C is introduced back into storage section 10 via air bubble generator 50b. By introducing another gas into gas retention section 20, the amount of carbon dioxide-containing gas C can be maintained greater than the amount of carbon dioxide-containing gas B. This allows carbon dioxide to continue circulating between storage section 10 and gas retention section 20 with high reliability. In this way, the concrete sludge water 12 in storage section 10 can be efficiently neutralized and the amount of carbon dioxide emitted to the outside of the system can be reduced.

[0015] FIG. 2 shows an example of a carbon dioxide fixation apparatus for performing a carbon dioxide fixation method. The carbon dioxide fixation apparatus 100 includes a storage unit 10 for storing concrete sludge water 12, a gas inlet unit 30 for introducing carbon dioxide-containing gas A into the concrete sludge water 12, a gas retention unit 20 above the storage unit 10 for retaining gas containing carbon dioxide-containing gas B that has passed through the concrete sludge water 12, and a gas circulation unit 40 for introducing carbon dioxide-containing gas C containing carbon dioxide-containing gas B from the gas retention unit 20 into the concrete sludge water 12. The carbon dioxide fixation apparatus 100 maintains a greater amount of carbon dioxide-containing gas C introduced into the concrete sludge water 12 than the amount of carbon dioxide-containing gas B extracted from the concrete sludge water 12 to the gas retention unit 20. This carbon dioxide fixation apparatus 100 can repeatedly introduce carbon dioxide into the concrete sludge water 12 with high reliability, thereby efficiently neutralizing the concrete sludge water 12 and reducing carbon dioxide emissions.

[0016] In the carbon dioxide fixation apparatus 100, the gas introduction section 30 has a carbon dioxide-containing gas storage section 80, a bubble generator 50a, and a tube 15 connecting these. The carbon dioxide-containing gas A in the carbon dioxide-containing gas storage section 80 is introduced into the sludge water 12 from the bubble generator 50a through the tube 15.

[0017] In the carbon dioxide fixation apparatus 100, the gas circulation section 40 has an air pump 70, an air bubble generator 50b, and a tube 17 connecting these. The air pump 70 sucks gas from the gas retention section 20 via a tube 16. The gas sucked by the air pump 70 is introduced again into the sludge water 12 as carbon dioxide-containing gas C from the air bubble generator 50b.

[0018] The carbon dioxide fixation apparatus 100 is equipped with an agitator blade 60 and a pH measuring device 90. Carbon dioxide-containing gases A, B, and C circulate between the storage section 10 and the gas retention section 20 through tubes 15, 16, and 17. Commercially available polyethylene terephthalate tubes can be used as the tubes. The carbon dioxide fixation apparatus 100 may also be equipped with a temperature adjustment unit that heats or cools the sludge water 12. The temperature adjustment unit may be, for example, a heater, a cooler, or a combination of these.

[0019] As defined in JIS A 5308, concrete sludge water 12 is a suspension of water obtained by removing coarse and fine aggregates from concrete washing water. While concrete sludge water generally contains a small amount of cement, concrete sludge water for cement-free concrete, which has been developed in recent years, does not contain cement. Concrete sludge water 12 does not necessarily contain cement. It may also be waste generated during the concrete manufacturing process, such as washing water from concrete mixers and truck agitators, or recovered from returned concrete. The type of cement is not particularly limited, and may include at least one selected from the group consisting of Portland cements such as ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, moderate-heat Portland cement, low-heat Portland cement, and sulfate-resistant Portland cement; blended cements such as blast-furnace cement, fly ash cement, and silica fume cement; and other cements such as ecocement, ultra-rapid-hardening cement, alumina cement, phosphate cement, and air-hardening cement.

[0020] The cement content in the sludge water 12 may be 20% by mass or less, 10% by mass or less, 6% by mass or less, or 3% by mass or less. When the cement content is within the above range, the viscosity of the sludge water 12 is reduced, and the carbon dioxide-containing gas can be thoroughly mixed throughout the sludge water 12. This further promotes the neutralization of the sludge water 12. The sludge water 12 recovered during the concrete production process may be used as is, or may be diluted with water so that the cement concentration falls within the above range.

[0021] The cement content in the sludge water 12 may be 0.01% by mass or more, or 0.1% by mass or more. If the cement content in the sludge water 12 is within the above range, the carbon dioxide and the cement can be reacted to sufficiently immobilize the carbon dioxide in the sludge water 12. For example, by immobilizing the carbon dioxide contained in the exhaust gas in the sludge water 12, it is possible to reduce the amount of carbon dioxide emitted into the atmosphere. The cement content in the sludge water 12 may be in the range of, for example, 0.01 to 20% by mass.

[0022] The concrete sludge contained in the sludge water may contain concrete components other than cement. Examples of concrete components other than cement include aggregate and admixture. The aggregate may be fine aggregate, coarse aggregate, or a combination of fine aggregate and coarse aggregate. The aggregate may also be natural aggregate, artificial aggregate, or recycled aggregate. The fine aggregate is not particularly limited and may include, for example, at least one selected from the group consisting of river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, slag fine aggregate, and lightweight fine aggregate. The coarse aggregate is not particularly limited and may include, for example, at least one selected from the group consisting of river gravel, mountain gravel, land gravel, sea gravel, crushed stone, slag coarse aggregate, and lightweight coarse aggregate. The admixture may include, for example, at least one selected from the group consisting of blast furnace slag, fly ash, silica fume, fine volcanic glass powder, metakaolin, expanding agent, fine limestone powder, calcium carbonate, air-entraining agent, water-reducing agent, air-entraining water-reducing agent, high-performance water-reducing agent, high-performance air-entraining water-reducing agent, superplasticizer, hardening accelerator, shrinkage-reducing agent, and rust inhibitor.

[0023] The gas supply process is a process of introducing carbon dioxide-containing gas A into sludge water 12 stored in storage section 10. There are no particular restrictions on the size of storage section 10, and it can be changed appropriately depending on the amount of sludge water 12 to be stored. A stirring blade 60 for stirring sludge water 12 may be installed inside storage section 10. By stirring sludge water 12, carbon dioxide-containing gas A can be sufficiently distributed throughout sludge water 12. This allows for more efficient neutralization of sludge water 12 and further reduction in carbon dioxide emissions.

[0024] In the gas supply step, carbon dioxide-containing gas A may be introduced into sludge water 12 via gas introduction section 30. Gas introduction section 30 has carbon dioxide-containing gas storage section 80, tube 15, and bubble generator 50a. By generating carbon dioxide-containing gas A stored in carbon dioxide-containing gas storage section 80 from bubble generator 50a, the carbon dioxide reacts with cement, more efficiently neutralizing sludge water 12 and further reducing carbon dioxide emissions.

[0025] The carbon dioxide-containing gas storage unit 80 is a unit that stores the carbon dioxide-containing gas A. The carbon dioxide-containing gas storage unit 80 may be, for example, a carbon dioxide cylinder containing high-purity carbon dioxide gas. From the viewpoint of resource reuse, the carbon dioxide-containing gas storage unit 80 may store factory exhaust gas or the like. Alternatively, the carbon dioxide-containing gas storage unit 80 may not be provided, and exhaust gas generated in a factory or the like may be introduced directly into the sludge water 12.

[0026] The carbon dioxide-containing gas A may be 100% pure carbon dioxide gas, or may be a mixed gas containing carbon dioxide and a component other than carbon dioxide. The concentration of carbon dioxide contained in the carbon dioxide-containing gas A may be 1% by volume or more, 5% by volume or more, 10% by volume or more, or 20% by volume or more, from the viewpoint of promoting neutralization of the sludge water 12. Furthermore, from the viewpoint of ease of availability, the concentration of carbon dioxide may be 100% by volume or less, and from the viewpoint of safety, it may be 90% by volume or less, 80% by volume or less, 70% by volume or less, or 50% by volume or less. The concentration of carbon dioxide in the carbon dioxide-containing gas A may be, for example, 1 to 100% by volume.

[0027] The carbon dioxide-containing gas A may be an exhaust gas emitted from a factory or the like. From the viewpoint of further promoting the fixation of carbon dioxide, the carbon dioxide concentration in the exhaust gas may be 1% by volume or more, 5% by volume or more, 10% by volume or more, or 20% by volume or more. From the viewpoint of improving safety, the carbon dioxide concentration in the exhaust gas may be 100% by volume or less, 80% by volume or less, 60% by volume or less, or 40% by volume or less. The exhaust gas may be, for example, an exhaust gas generated in a cement manufacturing process (carbon dioxide concentration: about 20% by volume), an exhaust gas generated in a steelmaking process (carbon dioxide concentration: about 20% by volume), an exhaust gas generated in a thermal power generation process (carbon dioxide concentration: about 10% by volume), or a gas separated and recovered from these exhaust gases (carbon dioxide concentration: about 100% by volume). By using an exhaust gas as the carbon dioxide-containing gas A, the carbon dioxide contained in the exhaust gas emitted from the factory can be fixed, and carbon dioxide emissions can be further reduced.

[0028] In the gas supply step, the carbon dioxide-containing gas A may be introduced from a bubble generator 50a installed in the sludge water 12. The bubble generator 50a has pores and is a device that releases the carbon dioxide-containing gas A as fine bubbles. By releasing the carbon dioxide-containing gas A as fine bubbles, the contact area between the carbon dioxide and the sludge water 12 increases, further promoting the reaction between the carbon dioxide and cement. The average pore size of the pores in the bubble generator 50a may be 40 μm or less, 30 μm or less, or 20 μm or less, from the viewpoint of further promoting the reaction between the carbon dioxide and cement. Furthermore, from the viewpoint of ease of acquisition, the average pore size of the pores in the bubble generator 50a may be 5 μm or more, 7 μm or more, or 9 μm or more. The average value of the pores in the bubble generator may be, for example, 5 to 40 μm.

[0029] The bubble generator 50a may be, for example, an air stone. The shape of the air stone may be cylindrical, round, plate-shaped, or the like. The average pore diameter of the air stone is within the range of the average pore diameter of the pores of the bubble generator described above, and may be, for example, 5 to 40 μm. The number of air stones may be one, or two or more. The number of air stones used in the gas supply step may be three to five. As the air stone, for example, "ASM-80" (trade name, manufactured by Marine Tech Co., Ltd.) can be used.

[0030] The diameter of the bubbles of the carbon dioxide-containing gas A introduced from the bubble generator 50a into the sludge water 12 may be 70 to 120 μm, 75 to 110 μm, or 80 to 100 μm. When the diameter of the bubbles of the carbon dioxide-containing gas A is within this range, the bubbles of the carbon dioxide-containing gas A can be sufficiently miniaturized, further promoting the reaction between the carbon dioxide and cement.

[0031] The supply rate of the carbon dioxide-containing gas A may be 1 L / min or more, 2 L / min or more, or 4 L / min or more per 10.2 kg of sludge water, from the viewpoint of promoting the reaction with the cement in the sludge water 12. Furthermore, from the viewpoint of reducing the amount of carbon dioxide that passes through the sludge water without reacting, the supply rate of the carbon dioxide-containing gas A may be 30 L / min or less, 20 L / min or less, or 15 L / min or less per 10.2 kg of sludge water. The supply rate of the carbon dioxide-containing gas A may be, for example, 1 to 30 L / min per 10.2 kg of sludge water.

[0032] The carbon dioxide fixation method may include a temperature adjustment step of adjusting the temperature of the sludge water 12 in the storage unit 10. The temperature adjustment step may be performed at any time during the carbon dioxide fixation method. The temperature adjustment step may be a first temperature adjustment step using a temperature adjustment unit, or may be a second temperature adjustment step in which water (or other sludge water) having a temperature higher or lower than the temperature of the sludge water 12 is added to the storage unit 10. In the first temperature adjustment step, the temperature in the sludge water 12 can be adjusted using a temperature adjustment unit having, for example, a heater, a cooler, or a combination thereof.

[0033] The temperature of the sludge water 12 may be 5°C or higher, 10°C or higher, 20°C or higher, or 30°C or higher from the viewpoint of promoting the neutralization reaction between carbon dioxide and the cement contained in the sludge water 12 and carbonating the cement to lower the pH. On the other hand, the temperature may be 50°C or lower or 40°C or lower from the viewpoint of dissolving carbon dioxide in the sludge water 12 to lower the pH of the sludge water. The temperature of the sludge water 12 can be adjusted appropriately depending on the stage of the reaction between carbon dioxide and cement. For example, immediately after the carbon dioxide is supplied to the sludge water 12, the reaction can be suppressed by keeping the temperature of the sludge water low (e.g., temperature T0), and the carbon dioxide can be dissolved in the water to quickly lower the pH. On the other hand, after the reaction has started, the temperature of the sludge water 12 can be set to, for example, temperature T1, which is higher than temperature T0, to promote the reaction between the cement and carbon dioxide and lower the pH of the sludge water 12 by carbonating the cement. Since the pH can be adjusted by adjusting the temperature of the sludge water 12 in this way, the neutralization of the sludge water 12 can be further promoted and the amount of carbon dioxide emitted can be further reduced.

[0034] The carbon dioxide-containing gas A passes through the sludge water 12 to become a carbon dioxide-containing gas B. The carbon dioxide-containing gas B is then introduced into a gas retention section 20 provided above the storage section 10. The gas retention section 20 and the storage section 10 may be provided in a single container, or may be provided in separate containers. In the case of separate containers, the storage section 10 and the gas retention section 20 may be connected by piping. There are no particular restrictions on the size of the gas retention section 20, and it can be adjusted appropriately depending on the size of the storage section 10 and the amount of carbon dioxide-containing gas B introduced.

[0035] A mesh member 18 may be provided between the storage section 10 and the gas retention section 20. The mesh member 18 may be provided on the surface of the sludge water 12 or may float on the water surface. By providing the mesh member 18, it is possible to introduce the carbon dioxide-containing gas B into the gas retention section 20 while suppressing foaming of the sludge water 12 caused by introducing gas into the sludge water 12. This improves safety.

[0036] The carbon dioxide contained in the carbon dioxide-containing gas A reacts with cement as it passes through the sludge water 12, whereby a portion of the carbon dioxide is fixed, and then passes through the sludge water 12. Therefore, the carbon dioxide concentration in the carbon dioxide-containing gas B is lower than the carbon dioxide concentration in the carbon dioxide-containing gas A.

[0037] The carbon dioxide concentration contained in the carbon dioxide-containing gas B may be 15% by volume or less, 10% by volume or less, 5% by volume or less, 4% by volume or less, or 3% by volume or less. The carbon dioxide concentration can be measured with a commercially available carbon dioxide concentration meter. If the carbon dioxide concentration of the carbon dioxide-containing gas B is within the above range, safety in the gas retention section 20 can be improved.

[0038] The carbon dioxide concentration in the gas retention section 20 may be less than 20% by volume, 15% by volume or less, 10% by volume or less, 5% by volume or less, 3% by volume or less, or 1% by volume or less. The carbon dioxide concentration can be measured using a commercially available carbon dioxide concentration meter. If the carbon dioxide concentration in the gas retention section 20 is within the above range, safety can be improved. For example, if the carbon dioxide concentration in the gas retention section 20 is 1% by volume or less, people can enter the gas retention section 20 and work there safely. This ensures work safety and simplifies factory safety management. In FIG. 1, safety can be further improved by introducing oxygen, air, or the like into the gas retention section 20.

[0039] In FIG. 1, the gas introduced into the gas retention section 20 may be a carbon dioxide-containing gas (e.g., the exhaust gas mentioned above) that contains carbon dioxide at a higher concentration than air, thereby enabling the sludge water 12 to be neutralized more efficiently.

[0040] In the gas circulation process, carbon dioxide-containing gas C containing carbon dioxide-containing gas B is introduced into sludge water 12 from gas retention section 20. Also, in the gas circulation process, the amount of carbon dioxide-containing gas C introduced into sludge water 12 is maintained greater than the amount of carbon dioxide-containing gas B discharged from sludge water 12 to gas retention section 20. By maintaining the amount of carbon dioxide-containing gas C introduced greater than the amount of carbon dioxide-containing gas B discharged, gas can be efficiently circulated between sludge water 12 and gas retention section 20. This allows the carbon dioxide contained in the carbon dioxide-containing gas to be circulated efficiently, thereby efficiently neutralizing sludge water 12 and reducing carbon dioxide emissions.

[0041] The carbon dioxide-containing gas C may contain carbon dioxide-containing gas B and a gas other than carbon dioxide-containing gas B by flowing a gas other than carbon dioxide-containing gas B into the gas retention section 20. By containing a gas other than carbon dioxide-containing gas B, the carbon dioxide-containing gas C may have a higher oxygen concentration than the carbon dioxide-containing gas B. This makes it possible to lower the carbon dioxide concentration in the gas retention section 20 than the carbon dioxide-containing gas B, thereby improving safety. The carbon dioxide-containing gas C may contain carbon dioxide-containing gas B and exhaust gases from factories, etc. By including exhaust gases, etc., waste can be effectively utilized.

[0042] An air pump 70 can be used to introduce the carbon dioxide-containing gas C into the sludge water 12. A commercially available air pump can be used. The air pump is used to suck in gas containing the carbon dioxide-containing gas B contained in the gas retention section 20 and supply it to the sludge water 12 as the carbon dioxide-containing gas C. In this way, the carbon dioxide in the carbon dioxide-containing gas C supplied to the sludge water 12 can react with the cement in the sludge water 12 and be immobilized. In addition, since a portion of the carbon dioxide-containing gas C introduced in the gas circulation step passes through the sludge water 12, the passed gas is introduced again into the gas retention section 20 as the carbon dioxide-containing gas B. In this way, the introduction step and the gas circulation step can be repeated with high reliability, and carbon dioxide can be circulated between the sludge water 12 and the gas retention section 20.

[0043] In the gas circulation step, carbon dioxide-containing gas C may be introduced into sludge water 12 via gas circulation section 40. Gas circulation section 40 has air pump 70, tube 17, and air bubble generator 50b. By generating carbon dioxide-containing gas C sucked from gas retention section 20 by air pump 70 from air bubble generator 50b, the carbon dioxide reacts with cement, more efficiently neutralizing sludge water 12 and further reducing carbon dioxide emissions.

[0044] The bubble generator 50b may be the same as the bubble generator 50a described above. The bubble generator 50b may also be an air stone. The air stone may be the same as that described for the bubble generator 50a described above. The bubble generators 50a and 50b may be used in both the gas supply process and the gas circulation process. In this case, both the carbon dioxide-containing gas A and the carbon dioxide-containing gas C are supplied to the sludge water 12 as fine bubbles, thereby more efficiently neutralizing the sludge water 12 and further reducing the amount of carbon dioxide emissions.

[0045] The method may include a pH measurement step in which the pH is measured as an indicator of the carbonation of the sludge water. The pH measurement step can be performed by placing a pH measuring device, such as a pH meter, in the sludge water. Neutralization may be completed when the pH of the sludge water reaches approximately 7, i.e., when it becomes neutral. The sludge water after neutralization can be reused as concrete mixing water. The pH of the sludge water after neutralization may be 5.5 to 7.0, or 6.0 to 7.0. Because carbon dioxide is a weak acid, the pH does not drop too much even if carbon dioxide is continuously introduced into the sludge water. Therefore, when carbon dioxide is used as a substitute for a stabilizer for sludge water, the amount of stabilizer added can be more easily controlled than when a strong acid stabilizer is used, simplifying the operation.

[0046] Although several embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments.

[0047] The present disclosure includes the following several embodiments. [1] A gas supply step of introducing a carbon dioxide-containing gas A into the concrete sludge water contained in the container; an introducing step of introducing the carbon dioxide-containing gas B that has passed through the concrete sludge water into a gas retention section provided above the storage section; a gas circulation step of introducing a carbon dioxide-containing gas C containing the carbon dioxide-containing gas B from the gas retention section into the concrete sludge water, A carbon dioxide fixation method, wherein in the gas circulation process, the amount of carbon dioxide-containing gas C introduced into the concrete sludge water is maintained to be greater than the amount of carbon dioxide-containing gas B extracted from the concrete sludge water to the gas retention section. [2] The carbon dioxide fixation method according to [1], which comprises a temperature adjustment step of adjusting the temperature of concrete sludge water. [3] The carbon dioxide fixation method described in [1], wherein the temperature adjustment step includes at least one of a first temperature adjustment step using a temperature adjustment unit and a second temperature adjustment step of adding water having a temperature higher or lower than the temperature of the concrete sludge water to the storage unit. [4] The carbon dioxide fixation method according to any one of [1] to [3], wherein in the gas supply step and the gas circulation step, the carbon dioxide-containing gas A and the carbon dioxide-containing gas C are introduced from a bubble generator installed in the concrete sludge water and having pores with an average pore diameter of 5 to 40 μm. [5] The bubble generator has an air stone, The carbon dioxide fixation method according to [4], wherein the air stone has an average pore size of 5 to 40 μm. [6] The carbon dioxide fixation method according to [5], wherein the diameter of the bubbles of the carbon dioxide-containing gas A and the carbon dioxide-containing gas C introduced from the air stone into the concrete sludge water is 70 to 120 μm. [7] The carbon dioxide fixation method according to any one of [1] to [6], wherein the carbon dioxide concentration in the gas retention portion is less than 20% by volume. [8] The carbon dioxide fixation method according to any one of [1] to [7], wherein the carbon dioxide-containing gas C has a higher oxygen concentration than the carbon dioxide-containing gas B. [9] The carbon dioxide fixation method according to any one of [1] to [8], further comprising a pH measurement step of measuring pH as an index of carbonation of the concrete sludge water.

[10] A storage unit for storing concrete sludge water; a gas introduction section for introducing a carbon dioxide-containing gas A into the concrete sludge water; a gas retention section above the storage section in which gas containing carbon dioxide-containing gas B that has passed through the concrete sludge water retains; a gas circulation section that introduces the carbon dioxide-containing gas C containing the carbon dioxide-containing gas B from the gas retention section into the concrete sludge water, A carbon dioxide fixation device that maintains an amount of carbon dioxide-containing gas C introduced into the concrete sludge water that is greater than the amount of carbon dioxide-containing gas B that is discharged from the concrete sludge water to the gas retention section.

[11] The carbon dioxide fixation device according to

[10] , which is provided with a temperature control unit that heats or cools the concrete sludge water. [Example]

[0048] The present disclosure will be described in more detail below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0049] Example 1 A carbon dioxide fixation device 100 as shown in FIG. 2 was fabricated by the following procedure. A carbon dioxide cylinder containing high-purity carbon dioxide was prepared as the carbon dioxide-containing gas storage section 80. A container large enough to integrate the storage section 10 and the gas retention section 20 was also prepared. Commercially available PET tubes (inner diameter: 7 mm) were prepared as the tubes 15, 16, and 17. After connecting the tube 15 to the carbon dioxide cylinder, the connected tube 15 was placed inside the storage section 10, and the tube was branched to attach four air stones (product name: "ASM-80", manufactured by Marine Tech Co., Ltd.) to the ends as bubble generators 50a. The air stones were placed at the bottom of the storage section 10. In this manner, the gas introduction section 30 was fabricated.

[0050] Tube 16 was placed in gas retention section 20 and connected to tube 17 via air pump 70. Tube 17 was branched inside storage section 10, and four air stones (product name: "ASM-80", manufactured by Marine Tech Co., Ltd.) were attached to the tip as bubble generators 50b. The air stones were placed at the bottom of storage section 10. In this way, gas circulation section 40 was prepared. A pH measuring device 90 (pH meter) and stirring blades 60 connected to a stirrer were placed inside storage section 10. Note that no lid was provided on gas retention section 20, and gas retention section 20 was not sealed.

[0051] A simulated concrete sludge water 12 was prepared in the storage section 10 by mixing 10 kg of water and 200 g of cement. After preparation, a mesh member 18 was placed on the surface of the concrete sludge water 12. Carbon dioxide gas was introduced into the concrete sludge water from a carbon dioxide cylinder, and the air pump 70 was started to circulate the carbon dioxide-containing gas. The carbon dioxide supply rate from the carbon dioxide cylinder was set to 5 L / min, the temperature of the concrete sludge water to 20°C, and the rotation speed of the stirring blade to 400 rpm. The change in pH over time (seconds) after the introduction of carbon dioxide was measured using a pH meter. The measurement results are shown in Figure 3.

[0052] (Comparative Example 1) Except for not starting the air pump 70, the pH was measured over time using a pH meter after the introduction of carbon dioxide in the same manner as in Example 1. The measurement results are shown in FIG.

[0053] As shown in Figure 3, it was confirmed that the pH of Example 1, in which carbon dioxide gas was circulated using the air pump 70, decreased more quickly than that of Comparative Example 1, in which carbon dioxide gas was not circulated. Therefore, it was confirmed that circulating carbon dioxide promotes the carbonation of cement and makes it possible to efficiently neutralize concrete sludge water. Furthermore, since the air pump 70 was not started in Comparative Example 1, the carbon dioxide-containing gas B that passed through the sludge water was released directly into the atmosphere from the gas retention section 20. On the other hand, in Example 1, the carbon dioxide-containing gas B was circulated into the sludge water 12 in the storage section 10, so the amount of carbon dioxide emitted into the atmosphere could be reduced.

[0054] <Evaluation of the effect of gas supply speed> (Comparative Example 2) Except for changing the supply rate of carbon dioxide gas from the carbon dioxide cylinder to 2 L / min, the pH was measured over time using a pH meter after the introduction of carbon dioxide gas in the same manner as in Comparative Example 1. The measurement results are shown in Figure 4.

[0055] (Comparative Example 3) The same procedure as in Comparative Example 1 was used, except that the supply rate of carbon dioxide gas from the carbon dioxide cylinder was set to 10 L / min, and the pH was measured over time using a pH meter after the introduction of carbon dioxide gas. The measurement results are shown in Figure 4. As shown in Figure 4, it was confirmed that increasing the amount of carbon dioxide supplied can promote the neutralization of concrete sludge water. However, in this case, unreacted carbon dioxide gas will be released into the atmosphere.

[0056] <Evaluation of the effect of the presence or absence of a bubble generator> (Reference example 1) The pH was measured over time using a pH meter after the introduction of carbon dioxide gas in the same manner as in Comparative Example 1, except that air stones serving as bubble generators 50a and 50b were not attached to the tip of the tube. The measurement results are shown in Figure 5. As shown in Figure 5, it was confirmed that the neutralization of concrete sludge water can be promoted by using air stones to atomize the carbon dioxide-containing gas A.

[0057] <Evaluation of the effect of cement concentration> (Reference example 2) The same procedure as in Comparative Example 1 was used, except that concrete sludge water was prepared by mixing 300 g of cement with 10 kg of water, and the pH was measured over time using a pH meter after the introduction of carbon dioxide gas. The measurement results are shown in Figure 6. As shown in Figure 6, it was confirmed that the decrease in pH of the sludge water became more gradual as the cement concentration increased.

[0058] <Evaluation of the effect of sludge water temperature> (Reference example 3) The pH was measured over time using a pH meter after the introduction of carbon dioxide gas in the same manner as in Comparative Example 1, except that the water used to prepare the concrete sludge water was heated to a temperature of 37°C. The measurement results are shown in Figure 7.

[0059] (Reference example 4) The pH was measured over time using a pH meter after the introduction of carbon dioxide gas in the same manner as in Comparative Example 1, except that the water used to prepare the concrete sludge water was cooled to prepare concrete sludge water with a temperature adjusted to 5.2°C. The measurement results are shown in Figure 7.

[0060] (Reference example 5) The pH was measured over time using a pH meter after the introduction of carbon dioxide gas in the same manner as in Comparative Example 1, except that the water used to prepare the concrete sludge water was cooled and the temperature of the concrete sludge water was adjusted to 7°C. The measurement results are shown in Figure 7.

[0061] As shown in Figure 7, the pH of concrete sludge water decreased rapidly immediately after the introduction of carbon dioxide gas. However, after a certain time had passed since the introduction of carbon dioxide gas, the pH reversed, and the pH tended to decrease as the temperature increased. This is thought to be because, at low temperatures, the reaction between carbon dioxide and cement was slow, and the rate at which carbon dioxide dissolved in water was faster than the neutralization reaction, resulting in a decrease in pH. On the other hand, at high temperatures, carbon dioxide was less soluble in water, but the neutralization reaction proceeded, resulting in the formation of carbon dioxide and a decrease in pH after a certain time. This demonstrates that the pH of concrete sludge water can be adjusted by adjusting the temperature of the sludge water. Therefore, it was confirmed that the pH could be reduced more quickly, i.e., the carbon dioxide could be immobilized more efficiently, by first circulating carbon dioxide gas at temperature T1 after the introduction of carbon dioxide gas, followed by a second circulating carbon dioxide gas at temperature T2, which was higher than temperature T1. [Industrial Applicability]

[0062] According to the present disclosure, it is possible to provide a carbon dioxide fixation method and a carbon dioxide fixation device that can efficiently neutralize concrete sludge water and reduce carbon dioxide emissions. [Explanation of symbols]

[0063] 100...carbon dioxide fixation device, 10...storage section, 20...gas retention section, 30...gas introduction section, 40...gas circulation section, 50a, 50b...bubble generator, 60...agitating blade, 70...air pump, 80...carbon dioxide-containing gas storage section, 90...pH measuring device, 15, 16, 17...tube, 12...concrete sludge water (sludge water), 18...mesh member

Claims

1. a gas supplying step of introducing a carbon dioxide-containing gas A into the concrete sludge water contained in the container; an introducing step of introducing the carbon dioxide-containing gas B that has passed through the concrete sludge water into a gas retention section provided above the storage section; a gas circulation step of introducing a carbon dioxide-containing gas C containing the carbon dioxide-containing gas B from the gas retention section into the concrete sludge water, A carbon dioxide fixation method in which, in the gas circulation process, the amount of carbon dioxide-containing gas C introduced into the concrete sludge water is maintained greater than the amount of carbon dioxide-containing gas B extracted from the concrete sludge water to the gas retention section.

2. 2. The carbon dioxide fixation method according to claim 1, further comprising a temperature adjustment step of adjusting the temperature of the concrete sludge water.

3. 3. The carbon dioxide fixation method according to claim 2, wherein the temperature adjustment step includes at least one of a first temperature adjustment step using a temperature adjustment unit and a second temperature adjustment step of adding water having a temperature higher or lower than that of the concrete sludge water to the storage unit.

4. 4. The carbon dioxide fixation method according to claim 1, wherein in the gas supply step and the gas circulation step, the carbon dioxide-containing gas A and the carbon dioxide-containing gas C are introduced from a bubble generator installed in the concrete sludge water and having pores with an average pore diameter of 5 to 40 μm.

5. The bubble generator has an air stone, 5. The carbon dioxide fixation method according to claim 4, wherein the air stone has an average pore size of 5 to 40 μm.

6. 6. The carbon dioxide fixation method according to claim 5, wherein the diameters of the bubbles of the carbon dioxide-containing gas A and the carbon dioxide-containing gas C introduced from the air stone into the concrete sludge water are 70 to 120 μm.

7. 4. The carbon dioxide fixation method according to claim 1, wherein the carbon dioxide concentration in the gas retention portion is less than 20% by volume.

8. 4. The carbon dioxide fixation method according to claim 1, wherein the carbon dioxide-containing gas C has a higher oxygen concentration than the carbon dioxide-containing gas B.

9. The carbon dioxide fixation method according to any one of claims 1 to 3, further comprising a pH measurement step of measuring pH as an index of carbonation of the concrete sludge water.

10. a storage section for storing concrete sludge water; a gas inlet for introducing a carbon dioxide-containing gas A into the concrete sludge water; a gas retention section above the storage section in which gas containing carbon dioxide-containing gas B that has passed through the concrete sludge water is retained; a gas circulation section that introduces the carbon dioxide-containing gas C containing the carbon dioxide-containing gas B from the gas retention section into the concrete sludge water, A carbon dioxide fixation device that maintains an amount of carbon dioxide-containing gas C introduced into the concrete sludge water that is greater than the amount of carbon dioxide-containing gas B that is discharged from the concrete sludge water to the gas retention section.

11. The carbon dioxide fixation device according to claim 10, further comprising a temperature adjustment unit that heats or cools the concrete sludge water.

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