Carbon dioxide recovery system and carbon dioxide recovery method

Abstract

To provide a carbon dioxide recovery system and a carbon dioxide recovery method that suppress decrease of water content in an absorbent, and can suppress accumulation of inorganic components in the absorbent even if reducing a used amount of high-purity water.SOLUTION: A carbon dioxide recovery system 1 comprises: a humidification part 20; a carbon dioxide absorption part 30; an absorbent recovery part 40 which recovers an absorbent L1 volatilized in the carbon dioxide absorption part 30; a high-purity water replenishment part 55 which replenishes high-purity water HW; an absorbent return flow channel 61 which returns a part of a recovery liquid L2 to which the high-purity water HW has been replenished to the carbon dioxide absorption part 30; and a flow rate adjustment part 62 which is provided in the absorbent return flow channel 61, and adjusts a flow rate of the recovery liquid L2 returned to the carbon dioxide absorption part 30 from the absorbent recovery part 40 through the absorbent return flow channel 61.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to carbon dioxide capture systems and methods. [Background technology]

[0002] Carbon dioxide is considered a problem as a cause of global warming, and there is a growing movement worldwide to curb the rise in carbon dioxide concentrations. One method proposed for reducing carbon dioxide concentrations in the atmosphere is a technology called direct air capture (DAC). DAC is a technology that directly captures carbon dioxide from the air. Carbon dioxide captured by DAC can be stored underground or used as a raw material for various compounds.

[0003] Patent Document 1 discloses a method for separating carbon dioxide from air by cyclic adsorption / desorption using an adsorbent. The method includes an adsorption step of adsorbing carbon dioxide onto the adsorbent and a desorption step of desorbing carbon dioxide from the adsorbent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6622302 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional technology uses solid adsorbents to adsorb carbon dioxide from the air, but the carbon dioxide concentration in the atmosphere is low, at around 400 ppm. Therefore, to capture a certain amount of carbon dioxide, a large amount of air must be processed. However, carbon dioxide capture methods using solid adsorbents are not easy to scale up.

[0006] On the other hand, it is also possible to use a method of absorbing carbon dioxide using a liquid absorbent. However, as mentioned above, a large amount of air needs to be processed to recover a certain amount of carbon dioxide. When a large amount of air is brought into contact with the absorption liquid, the water in the absorption liquid evaporates, and it is therefore necessary to replenish the absorption liquid with water. However, if low-purity water containing a large amount of inorganic components is supplied to the absorption liquid, the inorganic components continue to be concentrated, which may cause foaming of the absorption liquid or precipitation of the inorganic components. On the other hand, since high-purity water is more expensive than low-purity water, it is preferable to use a small amount of high-purity water.

[0007] Therefore, the present disclosure aims to provide a carbon dioxide recovery system and a carbon dioxide recovery method that can suppress the decrease in water content in the absorption solution and suppress the accumulation of inorganic components in the absorption solution even when the amount of high-purity water used is reduced. [Means for solving the problem]

[0008] A carbon dioxide capture system according to the present disclosure includes a humidifier that supplies water vapor generated from low-purity water to air. The carbon dioxide capture system includes a carbon dioxide absorption unit that absorbs carbon dioxide contained in air with an absorbing liquid through gas-liquid contact between the air and the absorbing liquid, and in which the water vapor comes into contact with the absorbing liquid. The carbon dioxide capture system includes an absorbing liquid recovery unit that recovers the absorbing liquid that has evaporated in the carbon dioxide absorption unit. The carbon dioxide capture system includes a high-purity water replenishment unit that replenishes the absorbing liquid recovered in the absorbing liquid recovery unit with high-purity water that is purer than the low-purity water, in accordance with the amount of recovery liquid containing the absorbing liquid in the absorbing liquid recovery unit. The carbon dioxide capture system includes an absorbing liquid return flow path that returns a portion of the recovery liquid replenished with high-purity water to the carbon dioxide absorption unit. The carbon dioxide capture system includes a flow rate adjustment unit that is provided in the absorbing liquid return flow path and adjusts the flow rate of the recovery liquid returned from the absorbing liquid recovery unit to the carbon dioxide absorption unit through the absorbing liquid return flow path. The carbon dioxide capture system includes a regeneration device that releases carbon dioxide absorbed by the absorbing liquid in the carbon dioxide absorption unit.

[0009] The humidifier may include a low-purity water level gauge that measures the liquid level of the low-purity water in the humidifier. The carbon dioxide capture system may include a low-purity water replenishment unit that adjusts the flow rate of low-purity water to be replenished to the humidifier in accordance with the liquid level of the low-purity water level gauge.

[0010] The humidifying unit may include a first gas-liquid contact unit through which air passes, and a first circulation system that circulates low-purity water and supplies the circulated low-purity water to the first gas-liquid contact unit.The carbon dioxide absorption unit may include a second gas-liquid contact unit through which air that has passed through the humidifying unit passes, a second circulation system that circulates absorption liquid and supplies the circulated absorption liquid to the second gas-liquid contact unit, and an absorption liquid level gauge that measures the liquid level of the absorption liquid in the second circulation system.The first circulation system may include a contact amount adjustment unit that adjusts the amount of low-purity water flowing through the first circulation system that comes into contact with air per unit time, based on the liquid level measured by the absorption liquid level gauge.

[0011] The humidifying section may include a first gas-liquid contact section through which air passes, and a first circulation system that circulates low-purity water and supplies the circulated low-purity water to the first gas-liquid contact section. The regeneration device may include a regeneration tower that strips carbon dioxide absorbed in the absorption liquid, and a heat exchanger that cools the carbon dioxide-containing gas by exchanging heat of the low-purity water circulated in the first circulation system with heat of the carbon dioxide-containing gas containing carbon dioxide discharged from the regeneration tower.

[0012] The regeneration device may include a regeneration tower that dissipates carbon dioxide absorbed in the absorption liquid, and a heat exchanger that cools the carbon dioxide-containing gas by exchanging heat of the absorption liquid flowing from the carbon dioxide absorption section to the regeneration tower with heat of the carbon dioxide-containing gas containing carbon dioxide discharged from the regeneration tower.

[0013] The humidifying section may include a first gas-liquid contact section through which air passes, a first circulation system that circulates low-purity water and supplies the circulated low-purity water to the first gas-liquid contact section, and a heating section that heats the low-purity water circulated in the first circulation system.

[0014] The carbon dioxide absorption unit may include a second gas-liquid contact unit through which the air that has passed through the humidification unit passes, a second circulation system that circulates the absorption liquid and supplies the circulating absorption liquid to the second gas-liquid contact unit, and an absorption liquid level gauge that measures the liquid level of the absorption liquid in the second circulation system. The humidification unit may adjust the amount of heat used to heat the low-purity water based on the liquid level measured by the absorption liquid level gauge.

[0015] The carbon dioxide recovery system may include a concentration measurement unit that measures the concentration of the absorbing solution in the air that has passed through the absorbing solution recovery unit.

[0016] The flow rate of the recovery liquid returned from the absorption liquid recovery section to the carbon dioxide absorption section may be adjusted according to the concentration measured in the concentration measurement section.

[0017] The high-purity water is pure water, and the low-purity water may be tap water, industrial water, or a mixture thereof.

[0018] High purity water may include water produced from a feedstock containing hydrogen and carbon dioxide stripped in a regenerator.

[0019] The carbon dioxide capture method according to the present disclosure includes a step of supplying water vapor generated from low-purity water to air in a humidifying unit. The carbon dioxide capture method includes a step of absorbing carbon dioxide contained in the air with an absorbing liquid through gas-liquid contact between the air and the absorbing liquid in a carbon dioxide absorption unit, and contacting the water vapor with the absorbing liquid. The carbon dioxide capture method includes a step of recovering, in an absorbing liquid recovery unit, the absorbing liquid that has volatilized in the carbon dioxide absorption unit. The carbon dioxide capture method includes a step of replenishing, in a high-purity water replenishment unit, the absorbing liquid recovered in the absorbing liquid recovery unit with high-purity water having a higher purity than the low-purity water in accordance with the amount of recovery liquid containing the absorbing liquid in the absorbing liquid recovery unit. The carbon dioxide capture method includes a step of returning, in an absorption liquid return flow path, a portion of the recovery liquid replenished with high-purity water to the carbon dioxide absorption unit. The carbon dioxide capture method includes a step of adjusting, in a flow rate adjustment unit provided in the absorption liquid return flow path, the flow rate of the recovery liquid returned from the absorbing liquid recovery unit to the carbon dioxide absorption unit through the absorption liquid return flow path. The carbon dioxide recovery method includes a step of releasing carbon dioxide absorbed by an absorbing solution in a carbon dioxide absorption section in a regeneration device. [Effects of the Invention]

[0020] According to the present disclosure, it is possible to provide a carbon dioxide recovery system and a carbon dioxide recovery method that can suppress the decrease in water content in the absorption solution and suppress the accumulation of inorganic components in the absorption solution even when the amount of high-purity water used is reduced. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram illustrating a carbon dioxide capture system according to one embodiment. [Figure 2] FIG. 2 is a schematic diagram showing an absorber having a horizontal multi-stage structure according to one embodiment. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. [Figure 4] FIG. 1 is a schematic diagram illustrating a playback device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, several exemplary embodiments will be described with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios. In addition, in this specification, the length direction of the carbon dioxide absorbing device 10 will be described as the X direction, the width direction perpendicular to the X direction will be described as the Y direction, and the height direction perpendicular to the X direction and the X direction will be described as the Z direction.

[0023] FIG. 1 is a schematic diagram showing a carbon dioxide capture system 1 according to one embodiment. As shown in FIG. 1, the carbon dioxide capture system 1 according to this embodiment includes a carbon dioxide absorption device 10 and a regeneration device 70. Air G1 from the atmosphere is supplied to the carbon dioxide absorption device 10, and carbon dioxide in the air G1 is absorbed by the carbon dioxide absorption device 10. The air G2 from which carbon dioxide has been removed by the carbon dioxide absorption device 10 is discharged from the carbon dioxide absorption device 10. As will be described later, the absorption liquid from which carbon dioxide has been absorbed in the carbon dioxide absorption device 10 is sent to the regeneration device 70. In the regeneration device 70, carbon dioxide is released from the absorption liquid. The absorption liquid from which carbon dioxide has been released is returned to the carbon dioxide absorption device 10, and absorbs carbon dioxide again in the carbon dioxide absorption device 10.

[0024] 2 shows an embodiment of a horizontal multi-stage carbon dioxide absorption apparatus 10. As shown in FIG. 2, the carbon dioxide absorption apparatus 10 includes a container 11, a humidifying section 20, a carbon dioxide absorption section 30, an absorption liquid recovery section 40, a low-purity water replenishment section 50, a high-purity water replenishment section 55, and an absorption liquid return section 60.

[0025] The container 11 has a shape that is longer in the X direction than in the Z direction. The shape of the container 11 is a substantially quadrangular prism, and the cross section perpendicular to the X direction is substantially rectangular. The container 11 has a top plate 11t, a bottom plate 11b, and a pair of side walls 11s that extend along the X direction, which is the longitudinal direction, and a first end wall 11e1 and a second end wall 11e2 that are disposed at both ends in the X direction and are connected to the top plate 11t, the bottom plate 11b, and the pair of side walls 11s. The shape of the container 11 is not particularly limited, and for example, the container 11 may have a curved shape.

[0026] The container 11 is provided at one end in the X direction and has an air supply port 12 through which atmospheric air G1 is introduced. The container 11 is also provided at the other end in the X direction and has a gas outlet 13 through which the remaining air G2 from which carbon dioxide has been removed in the carbon dioxide absorbing device 10 is discharged. By providing the air supply port 12 and the gas outlet 13 in the X direction, the carbon dioxide absorbing device 10 can be made more compact than when a vertical absorption tower that is long in the vertical direction is used.

[0027] The air supply port 12 is provided with a filter 12a that removes foreign matter from the air G1. The gas outlet 13 is provided with an airflow generating unit 13a that generates an airflow in the container 11 so that the air G1 passes through the carbon dioxide absorbing device 10. The airflow generating unit 13a may be a blower or a fan. The airflow generating unit 13a may be provided in the air supply port 12, for example. Alternatively, an airflow may be generated in the container 11 by utilizing the flow pressure of the air G1 supplied from the outside, without using the airflow generating unit 13a. The gas outlet 13 is provided with a demister 13b to prevent microdroplets from being discharged from the gas outlet 13 together with the air G2. The demister 13b may include a mesh member such as a wire mesh or a porous member such as a perforated plate.

[0028] The humidifying unit 20, the carbon dioxide absorbing unit 30, and the absorbing liquid recovery unit 40 are housed in a container 11. The humidifying unit 20 is disposed between the air supply port 12 and the carbon dioxide absorbing unit 30. The carbon dioxide absorbing unit 30 is disposed between the humidifying unit 20 and the absorbing liquid recovery unit 40. The absorbing liquid recovery unit 40 is disposed between the carbon dioxide absorbing unit 30 and the gas discharge port 13.

[0029] The humidifying unit 20 supplies water vapor generated from low-purity water LW to the air G1. The purity of the water in the water vapor is high. Therefore, by supplying water vapor generated from low-purity water LW to the air G1, it is possible to supply high-purity water using low-purity water LW, which is less expensive than high-purity water HW. The humidifying unit 20 can vaporize the water in the low-purity water LW to generate water vapor by bringing the air G1 taken in from the air supply port 12 into contact with the low-purity water LW.

[0030] The low-purity water LW may be tap water, industrial water, or a mixture of these. These waters are easy to obtain and less expensive than the high-purity water HW, which allows for reduced operating costs for the carbon dioxide capture system 1. The low-purity water LW is water with a lower purity than the high-purity water HW. The low-purity water LW has a lower resistivity than the high-purity water HW. The resistivity of the low-purity water LW at 25°C may be greater than 0 MΩ·cm and less than 0.1 MΩ·cm, or may be 0.002 MΩ·cm or greater and 0.02 MΩ·cm or less.

[0031] The humidifying unit 20 includes a first gas-liquid contact unit 21, a first circulation system 22, a low-purity water level gauge 27, and a heating unit 28. The first circulation system 22 includes a liquid distributor 23, a liquid recovery port 24, a pipe 25, and a pump 26.

[0032] The first gas-liquid contact section 21 is configured to allow air G1 to pass through. As shown in FIG. 3 , the first gas-liquid contact section 21 according to this embodiment is configured such that multiple units, each of which has multiple plates 21a arranged in the Y direction, are stacked in the Z direction. The plates 21a are arranged in parallel to form gaps in a direction inclined relative to the Z direction. The formation of gaps along the inclined direction improves liquid dispersion in the X and Y directions, enabling the liquid to be evenly distributed in the first gas-liquid contact section 21. Furthermore, because the flow path is straight, the pressure loss of the air G can be reduced compared to random packing. Specifically, the plates 21a may be flat plates inclined relative to the Z direction, or corrugated plates with concave and convex portions alternately arranged in the X direction, with the ridges of the convex portions bent so as to be inclined relative to the Z direction. The ridges of adjacent corrugated plates may be arranged so as to intersect each other. This allows the parallel corrugated plates to maintain a regular arrangement without the need for spacers.

[0033] The first circulation system 22 circulates the low-purity water LW and supplies the circulated low-purity water LW to the first gas-liquid contactor 21. This configuration makes it possible to effectively utilize the low-purity water LW while promoting the generation of steam. The liquid distributor 23 is provided above the first gas-liquid contactor 21 and sprays the low-purity water LW into the first gas-liquid contactor 21. The liquid recovery port 24 is provided below the first gas-liquid contactor 21 and collects the low-purity water LW that has flowed down from the first gas-liquid contactor 21. The piping 25 connects the liquid distributor 23 and the liquid recovery port 24. The pump 26 is provided in the piping 25 and adjusts the flow rate of the low-purity water LW circulating in the first circulation system 22. In this embodiment, the low-purity water LW is supplied from the liquid distributor 23 to the first gas-liquid contactor 21 by driving the pump 26. The low-purity water LW is supplied from above the first gas-liquid contact section 21 and allowed to flow downward, thereby forming a liquid film in the first gas-liquid contact section 21. The low-purity water LW that has come into contact with the air G1 flows down the first gas-liquid contact section 21, and the low-purity water LW that has flowed down is supplied from the liquid recovery port 24 through the piping 25 to the liquid distributor 23. In this way, the low-purity water LW circulates through the liquid recovery port 24, the piping 25, and the liquid distributor 23 in this order.

[0034] The low-purity water level gauge 27 measures the liquid level of the low-purity water LW in the humidifying unit 20. The low-purity water level gauge 27 makes it possible to grasp the amount of low-purity water LW in the humidifying unit 20. Specifically, the low-purity water level gauge 27 measures the liquid level of the low-purity water LW that has flowed down from the first gas-liquid contactor 21 and accumulated at the bottom of the humidifying unit 20. The low-purity water level gauge 27 can be any known level gauge such as an electrode-type level gauge, a float-type level gauge, an ultrasonic-type level gauge, a capacitance-type level gauge, or a differential pressure-type level gauge.

[0035] The heating unit 28 heats the low-purity water LW circulating in the first circulation system 22. Heating the low-purity water LW can increase the amount of water vapor generated from the low-purity water LW. This increases the contact between the water vapor and the absorbing liquid L1, thereby suppressing a decrease in moisture content in the absorbing liquid L1. The heating unit 28 may adjust the amount of heat used to heat the low-purity water LW based on the liquid level measured by an absorption liquid level gauge 37 (described later). This configuration allows for more appropriate management of the amount of liquid in the absorbing liquid L1. The amount of heat used to heat the low-purity water LW can be controlled by a control unit 39 configured by a computer. The control unit 39 controls the amount of heat used to heat the low-purity water LW by the heating unit 28 in accordance with the liquid level measured by the absorption liquid level gauge 37, thereby adjusting the amount of water vapor generated from the low-purity water LW. In this embodiment, the heating unit 28 is provided in the pipe 25, and the heating unit 28 heats the low-purity water LW passing through the pipe 25. However, since the heating unit 28 only needs to be able to heat the low-purity water LW circulating in the first circulation system 22, the heating unit 28 may be provided in the first circulation system 22. The heat source for the heating unit 28 may include exhaust heat from facilities such as an adjacent power plant or factory, heat from a heat pump, or solar heat.

[0036] The first circulation system 22 may include a contact amount adjusting unit that adjusts the amount of low-purity water LW flowing through the first circulation system 22 that comes into contact with the air G1 per unit time. This configuration allows the amount of water vapor generated in the humidifying unit 20 to be adjusted. Therefore, by adjusting the amount of water vapor according to the amount of the absorbing liquid L1 in the carbon dioxide absorbing unit 30, it is possible to suppress a decrease in moisture content in the absorbing liquid L1. The contact amount adjusting unit may adjust the amount of low-purity water LW flowing through the first circulation system 22 that comes into contact with the air G1 per unit time, based on the liquid level measured by an absorption liquid level gauge 37 (described later). This configuration allows for more appropriate management of the amount of the absorbing liquid L1. The flow rate of the low-purity water LW can be controlled by a control unit 38 configured by a computer. The control unit 38 controls the contact amount adjusting unit according to the liquid level measured by the absorption liquid level gauge 37, thereby adjusting the amount of low-purity water LW flowing through the first circulation system 22 per unit time.

[0037] The contact amount adjusting unit may be a liquid distributor 23. The liquid distributor 23 may adjust the area of ​​the low-purity water LW that comes into contact with the first gas-liquid contact unit 21. For example, when the decrease in the amount of the absorption liquid L1 in the carbon dioxide absorbing unit 30 is small, the low-purity water LW may be brought into contact with only half of the first gas-liquid contact unit 21. On the other hand, when the decrease in the amount of the absorption liquid L1 in the carbon dioxide absorbing unit 30 is large, the low-purity water LW may be brought into contact with the entire first gas-liquid contact unit 21. When the liquid distributor 23 has a plurality of nozzles that can spray the low-purity water LW, the area of ​​the low-purity water LW that comes into contact with the first gas-liquid contact unit 21 can be adjusted by adjusting the number of nozzles that supply the low-purity water LW.

[0038] The contact amount adjustment unit may be a pump 26. The pump 26 may adjust the flow rate per unit time of the low-purity water LW circulating within the first circulation system 22. Specifically, the pump 26 may adjust the flow rate per unit time of the low-purity water LW that contacts the first gas-liquid contact unit 21. The amount of water vapor generated in the humidifying unit 20 can be adjusted simply by adjusting the flow rate of the low-purity water LW with the pump 26.

[0039] The container 11 has a lower partition wall 16. The lower partition wall 16 protrudes from the bottom plate 11b toward the top plate 11t at the boundary between the humidifying unit 20 and the carbon dioxide absorbing unit 30. A demister 17 is installed at the boundary between the humidifying unit 20 and the carbon dioxide absorbing unit 30. The demister 17 collects droplets of low-purity water LW traveling from the humidifying unit 20 toward the carbon dioxide absorbing unit 30 and prevents the droplets of low-purity water LW from moving toward the carbon dioxide absorbing unit 30 along with the air G1. The demister 17 may include a mesh member such as a wire mesh or a porous member such as a perforated plate. The demister 17 is installed closer to the humidifying unit 20 than the lower partition wall 16. This allows the droplets collected by the demister 17 to easily fall toward the humidifying unit 20.

[0040] The carbon dioxide absorbing unit 30 absorbs the carbon dioxide contained in the air G1 with the absorbing liquid L1 through gas-liquid contact between the air G1 and the absorbing liquid L1. Furthermore, water vapor comes into contact with the absorbing liquid L1 in the carbon dioxide absorbing unit 30. By contacting the water vapor with the absorbing liquid L1, the water vapor supplied from the humidifying unit 20 can suppress a decrease in moisture in the absorbing liquid L1.

[0041] The absorption liquid L1 may contain an alkaline aqueous solution. The alkaline aqueous solution may be an amine aqueous solution. This allows for efficient absorption of carbon dioxide. The amine aqueous solution may contain, for example, at least one selected from the group consisting of alkanolamines, hindered amines having an alcoholic hydroxyl group, piperazine, and piperazine derivatives. The alkanolamine may contain, for example, at least one selected from the group consisting of monoethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, diisopropanolamine, and diglycolamine. The hindered amine having an alcoholic hydroxyl group may contain, for example, at least one selected from the group consisting of 2-amino-2-methyl-1-propanol (AMP), 2-(ethylamino)ethanol (EAE), and 2-(methylamino)ethanol (MAE). The piperazine derivative may contain at least one selected from the group consisting of 2-methylpiperazine, 2-(aminomethyl)piperazine, 2,6-dimethylpiperazine, 2,5-dimethylpiperazine, and 2-(β-hydroxyethyl)piperazine. The absorbing liquid L1 may contain a tertiary amine. Tertiary amines are less likely to volatilize, making it easier to maintain a constant concentration in the absorbing liquid L1. The concentration of the amine compound in the alkaline aqueous solution may be, for example, 10% by mass to 50% by mass, from the viewpoints of the fluidity of the alkaline aqueous solution and suppression of consumption loss.

[0042] The carbon dioxide absorbing unit 30 has multiple regions including a first region 30a, a second region 30b, and a third region 30c that are allocated and arranged along the X direction of the container 11. In this embodiment, since the regions are arranged along the X direction, even if the carbon dioxide absorbing unit 30 has a multi-stage structure, it is less likely to be subjected to gravitational load, and a large amount of air G1 can be treated. The number of multiple regions in the carbon dioxide absorbing unit 30 is not particularly limited, and may be one, or the carbon dioxide absorbing unit 30 may have two or more multiple regions. The shape and size of each region may be the same or different. The multiple regions may be connected so that the carbon dioxide absorbing unit 30 has a branched structure, such as a Y-shape.

[0043] The vessel 11 has a plurality of upper partition walls 14 and a plurality of lower partition walls 15. The upper partition walls 14 each protrude from the top plate 11t toward the bottom plate 11b. The upper partition walls 14 prevent the air G1 from bypassing the second gas-liquid contact section 31 and flowing above the second gas-liquid contact section 31. The lower partition walls 15 protrude from the bottom plate 11b toward the top plate 11t. The lower partition walls 15 each face the upper partition walls 14 in the Z direction, with a space between them.

[0044] The carbon dioxide absorbing section 30 includes a second gas-liquid contact section 31, a second circulation system 32, and an absorbing liquid level gauge 37. The second gas-liquid contact section 31 is provided in each of a plurality of regions in the carbon dioxide absorbing section 30. The second gas-liquid contact section 31 is similar to the first gas-liquid contact section 21, and therefore description thereof will be omitted. That is, the second gas-liquid contact section 31 is configured so that air G1 that has passed through the humidifying section 20 passes through it. The second circulation system 32 circulates the absorbing liquid L1 and supplies the circulating absorbing liquid L1 to the second gas-liquid contact section 31. The second circulation system 32 includes a liquid distributor 33, a liquid recovery port 34, piping 35, and a pump 36. The second circulation system 32 is similar to the first circulation system 22 except that the absorbing liquid L1 is used instead of the low-purity water LW. That is, the liquid distributor 33, the liquid recovery port 34, the piping 35, and the pump 36 correspond to the liquid distributor 23, the liquid recovery port 24, the piping 25, and the pump 26, respectively. Specifically, the second circulation system 32 circulates the absorption liquid L1 and supplies the circulating absorption liquid L1 to the second gas-liquid contactor 31. With such a configuration, it is possible to improve the carbon dioxide absorption efficiency while effectively utilizing the absorption liquid L1.

[0045] A reflux pipe 82 is connected to the second circulation system 32 in the first region 30a. A supply pipe 81 is connected to the second circulation system 32 in the third region 30c. The absorption liquid L1 is supplied to the liquid distributor 33 in the first region 30a through the reflux pipe 82. The absorption liquid L1 supplied to the liquid distributor 33 is sprayed from the liquid distributor 33 in the first region 30a to the second gas-liquid contact section 31. The absorption liquid L1 flowing down from above the second gas-liquid contact section 31 along the surface of the second gas-liquid contact section 31 is stored at the bottom of the first region 30a and discharged from a liquid recovery port 34 to a pipe 35. The absorption liquid L1 is sent from the liquid recovery port 34 to the liquid distributor 33 by driving a pump 36, and is sprayed again from the liquid distributor 33 in the first region 30a to the second gas-liquid contact section 31. When the amount of the absorption liquid L1 stored at the bottom of the first region 30a exceeds a predetermined amount, it moves over the lower partition wall 15 from the bottom of the first region 30a to the bottom of the second region 30b. Similarly, when the amount of the absorption liquid L1 stored at the bottom of the second region 30b exceeds a predetermined amount, it moves over the lower partition wall 15 from the bottom of the second region 30b to the bottom of the third region 30c. The air G1 supplied to the carbon dioxide absorbing section 30 comes into gas-liquid contact with the absorption liquid L1 in the second gas-liquid contact section 31, and the carbon dioxide contained in the air G1 is absorbed by the absorption liquid L1. The absorption liquid L1 that has absorbed the carbon dioxide is sent to the regeneration device 70 from the liquid recovery port 34 of the third region 30c via the supply piping 81.

[0046] In this embodiment, the absorbing solution L1 passes through the carbon dioxide absorbing section 30 in the order of the first region 30a, the second region 30b, and the third region 30c. On the other hand, the air G1 passes through the carbon dioxide absorbing section 30 in the order of the third region 30c, the second region 30b, and the first region 30a. That is, since the direction in which the absorbing solution L1 passes through the carbon dioxide absorbing section 30 is opposite to the direction in which the air G1 passes through the carbon dioxide absorbing section 30, countercurrent contact is performed throughout the carbon dioxide absorbing section 30 as a whole.

[0047] The absorption of carbon dioxide is an exothermic reaction. However, the carbon dioxide concentration in the air G1 is low, at about 400 ppm, and the heat generated by the absorption of carbon dioxide is not significant. Furthermore, contact between the air G1 passing through the carbon dioxide absorption section 30 and the absorbing solution L1 vaporizes part of the absorbing solution L1, and the remaining absorbing solution L1 is cooled. This prevents the temperature of the absorbing solution L1 from rising excessively. Therefore, coolers for adjusting the temperature of the absorbing solution L1 do not need to be provided in the piping 35 and the reflux piping 82.

[0048] The absorption liquid level gauge 37 measures the liquid level of the absorption liquid L1 in the second circulation system 32. The absorption liquid level gauge 37 makes it possible to grasp the liquid amount of the absorption liquid L1 in the carbon dioxide absorption section 30. Specifically, the absorption liquid level gauge 37 measures the liquid level of the absorption liquid L1 that has flowed down from the second gas-liquid contact section 31 and accumulated at the bottom of the carbon dioxide absorption section 30. The absorption liquid level gauge 37 can be a known level gauge such as an electrode type level gauge, a float type level gauge, an ultrasonic type level gauge, a capacitance type level gauge, or a differential pressure type level gauge.

[0049] The absorbing liquid recovery section 40 recovers the absorbing liquid L1 that has volatilized in the carbon dioxide absorption section 30. By recovering the absorbing liquid L1 in the absorbing liquid recovery section 40, it is possible to prevent the absorbing liquid L1 from being released into the atmosphere. The absorbing liquid recovery section 40 has a plurality of regions including a first region 40a and a second region 40b that are allocated to be arranged along the X direction of the container 11.

[0050] The absorbing liquid recovery section 40 includes a third gas-liquid contact section 41, a third circulation system 42, and a high-purity water level gauge 47. The third gas-liquid contact section 41 is provided in each of the multiple regions in the absorbing liquid recovery section 40. The third gas-liquid contact section 41 is similar to the first gas-liquid contact section 21, and therefore description thereof will be omitted. That is, the third gas-liquid contact section 41 is configured so that air G1 that has passed through the carbon dioxide absorbing section 30 passes through it. The third circulation system 42 circulates the recovery liquid L2 and supplies the circulated recovery liquid L2 to the third gas-liquid contact section 41. The third circulation system 42 includes a liquid distributor 43, a liquid recovery port 44, a pipe 45, and a pump 46. The third circulation system 42 is similar to the first circulation system 22 except that the recovery liquid L2 is used instead of the low-purity water LW. That is, the liquid distributor 43, the liquid recovery port 44, the piping 45, and the pump 46 correspond to the liquid distributor 23, the liquid recovery port 24, the piping 25, and the pump 26, respectively. Specifically, the third circulation system 42 circulates the recovery liquid L2 and supplies the circulating recovery liquid L2 to the third gas-liquid contact section 41. With such a configuration, the recovery efficiency of the absorption liquid L1 in the absorption liquid recovery section 40 can be improved.

[0051] The volatilized absorbing liquid L1 contained in the air G1 is taken into the recovering liquid L2 by contact between the air G1 and the recovering liquid L2 sprayed from the liquid distributor 43. Therefore, the absorbing liquid recovery section 40 can recover the absorbing liquid L1 volatilized in the carbon dioxide absorption section 30. The concentration of the alkaline substance in the recovering liquid L2 (e.g., the concentration of the amine compound) may be 1 mass % or less. When the concentration of the alkaline substance in the recovering liquid L2 is low, the recovery efficiency of the absorbing liquid L1 can be improved. The air G2 that has passed through the absorbing liquid recovery section 40 is discharged from the gas outlet 13. It should be noted that the absorbing liquid recovery section 40 is not limited to the above-described configuration, and the volatilized absorbing liquid L1 may be recovered by cooling and coagulating it.

[0052] The height of the upper end of the lower partition wall 15 provided at the boundary position between the carbon dioxide absorbing section 30 and the absorbing liquid recovery section 40 may be higher than the upper ends of the lower partition walls 15 provided between the respective regions of the carbon dioxide absorbing section 30 and the lower partition walls 15 provided between the respective regions of the absorbing liquid recovery section 40. This makes it possible to prevent the absorption liquid L1 in the carbon dioxide absorbing section 30 from moving to the absorbing liquid recovery section 40 and the recovery liquid L2 in the absorbing liquid recovery section 40 from moving to the carbon dioxide absorbing section 30.

[0053] The high-purity water level gauge 47 measures the liquid level of the recovered liquid L2 in the third circulation system 42. The high-purity water level gauge 47 makes it possible to grasp the amount of the recovered liquid L2 in the absorbing liquid recovery section 40. Specifically, the high-purity water level gauge 47 measures the liquid level of the recovered liquid L2 that has flowed down from the third gas-liquid contact section 41 and accumulated at the bottom of the absorbing liquid recovery section 40. The high-purity water level gauge 47 can be a known level gauge such as an electrode-type level gauge, a float-type level gauge, an ultrasonic-type level gauge, a capacitance-type level gauge, or a differential pressure-type level gauge.

[0054] The low-purity water replenishment unit 50 replenishes the low-purity water LW to the humidification unit 20. By having the low-purity water replenishment unit 50 replenish the low-purity water LW to the humidification unit 20, the carbon dioxide capture system 1 can be operated continuously for an extended period of time. The low-purity water replenishment unit 50 includes a low-purity water replenishment passage 51 and a flow rate adjustment unit 52. The low-purity water replenishment passage 51 passes the low-purity water LW and supplies the low-purity water LW to the first circulation system 22 of the humidification unit 20. The flow rate adjustment unit 52 is provided in the low-purity water replenishment passage 51 and adjusts the flow rate of the low-purity water LW passing through the low-purity water replenishment passage 51. The flow rate adjustment unit 52 may adjust the flow rate of the low-purity water LW in accordance with the liquid level of the low-purity water level gauge 27.

[0055] The low-purity water replenishment unit 50 may adjust the flow rate of the low-purity water LW replenished to the humidifying unit 20 in accordance with the liquid level of the low-purity water level meter 27. This configuration can prevent a shortage of water vapor supplied from the humidifying unit 20 to the carbon dioxide absorbing unit 30. The flow rate of the low-purity water LW can be controlled by a control unit 29 configured by a computer. The control unit 29 controls the flow rate adjustment unit 52 in accordance with the liquid level of the low-purity water level meter 27, so that the flow rate of the low-purity water LW replenished to the humidifying unit 20 can be adjusted and supplied. The low-purity water replenishment unit 50 may replenish the low-purity water LW to the humidifying unit 20 when the liquid level of the low-purity water LW measured by the low-purity water level meter 27 is equal to or lower than a threshold value. The low-purity water replenishment unit 50 may replenish the low-purity water LW to the humidifying unit 20 intermittently or continuously. In order to improve the water quality of the humidifying section 20, a portion of the low-purity water LW in the first circulation system 22 may be discharged (blowed out). The amount of discharged water is preferably 10% by volume or less of the total amount of low-purity water LW circulating in the first circulation system 22, and more preferably 5% by volume or less.

[0056] The high-purity water replenishment unit 55 replenishes the absorbing liquid L1 recovered in the absorbing liquid recovery unit 40 with high-purity water HW, which has a higher purity than the low-purity water LW, in accordance with the amount of recovered liquid L2 containing the absorbing liquid L1 in the absorbing liquid recovery unit 40. The high-purity water replenishment unit 55 may adjust the flow rate of the high-purity water HW to be replenished to the absorbing liquid recovery unit 40 in accordance with the liquid level of the high-purity water level gauge 47. The high-purity water replenishment unit 55 includes a high-purity water replenishment flow path 56 and a flow rate adjuster 57. The high-purity water replenishment flow path 56 passes the high-purity water HW and supplies the high-purity water HW to the absorbing liquid recovery unit 40. The flow rate adjuster 57 is provided in the high-purity water replenishment flow path 56 and adjusts the flow rate of the high-purity water HW passing through the high-purity water replenishment flow path 56.

[0057] The flow rate adjuster 57 may adjust the flow rate of the high-purity water HW in accordance with the liquid level of the high-purity water level gauge 47. Such a configuration allows for more accurate management of the flow rate of the high-purity water HW. The flow rate of the high-purity water HW can be controlled by a control unit 48 configured by a computer. The control unit 48 controls the flow rate adjuster 52 in accordance with the liquid level of the high-purity water level gauge 47, so that the flow rate of the high-purity water HW to be replenished to the absorbing liquid L1 recovered in the absorbing liquid recovery unit 40 can be adjusted and supplied.

[0058] The high-purity water HW is water with a higher purity than the low-purity water LW. The content of inorganic components contained in the high-purity water HW is lower than that of the low-purity water LW. Therefore, by using the high-purity water HW, it is possible to prevent the concentration of inorganic components in the absorbing solution L1 from increasing even when the absorbing solution L1 is repeatedly circulated and used. This prevents the absorbing solution L1 from foaming and the inorganic components from precipitating. The high-purity water HW has a higher resistivity than the low-purity water LW. The high-purity water HW may be pure water. The high-purity water HW may be, for example, ion-exchanged water, soft water, distilled water, or RO water purified using an RO (reverse osmosis) membrane. The resistivity of the high-purity water HW at 25°C may be 0.1 MΩ·cm or more and 18.24 MΩ·cm or less, or may be 1 MΩ·cm to 10 MΩ·cm.

[0059] The absorbing liquid return section 60 includes an absorbing liquid return flow path 61, a flow rate adjuster 62, and a flow meter 63. The absorbing liquid return flow path 61 connects the absorbing liquid recovery section 40 and the carbon dioxide absorbing section 30. Specifically, the absorbing liquid return flow path 61 connects the piping 45 and the reflux piping 82. The absorbing liquid return flow path 61 returns a portion of the recovery liquid L2 replenished with high-purity water HW to the carbon dioxide absorbing section 30. The flow rate adjuster 62 is provided in the absorbing liquid return flow path 61, and adjusts the flow rate of the recovery liquid L2 returned from the absorbing liquid recovery section 40 to the carbon dioxide absorbing section 30 through the absorbing liquid return flow path 61. The flow meter 63 measures the flow rate of the recovery liquid L2 flowing through the absorbing liquid return flow path 61.

[0060] Increasing the flow rate of the recovery liquid L2 returned to the carbon dioxide absorption unit 30 increases the amount of replenishment of high-purity water HW, lowering the concentration of alkaline substances in the absorbing liquid recovery unit 40 and decreasing the concentration of the exhausted absorbing liquid L1. On the other hand, decreasing the flow rate of the recovery liquid L2 returned to the carbon dioxide absorption unit 30 decreases the amount of replenishment of high-purity water HW, increasing the concentration of alkaline substances in the absorbing liquid recovery unit 40 and increasing the concentration of the exhausted absorbing liquid L1. Therefore, the concentration of the exhausted absorbing liquid L1 can be adjusted by adjusting the flow rate of the recovery liquid L2 returned to the carbon dioxide absorption unit 30. Furthermore, since it is only necessary to replenish the minimum amount of high-purity water HW required depending on the required concentration, the amount of replenishment of high-purity water HW can be reduced.

[0061] The flow rate of the recovered liquid L2 to be returned can be controlled by a control unit 64 configured by a computer. The control unit 64 can adjust the flow rate of the recovered liquid L2 returned to the carbon dioxide absorption unit 30 by controlling the flow rate adjustment unit 62 based on the flow rate measured by the flow meter 63. By returning an appropriate amount of the recovered liquid L2 to the carbon dioxide absorption unit 30 by the absorption liquid return unit 60, the concentration of the absorption liquid L1 in the carbon dioxide absorption unit 30 can be appropriately controlled.

[0062] The regeneration device 70 strips the carbon dioxide absorbed by the absorption liquid L1 in the carbon dioxide absorption section 30. As shown in Figures 1 and 4, the regeneration device 70 includes a regeneration tower 71, a liquid supply section 72, a packing material 73, a circulation pipe 74, a reboiler 75, a demister 76, a supply pipe 81, a reflux pipe 82, a pump 83, a heat exchanger 84, a pump 85, and a gas-liquid separation section 90.

[0063] The supply pipe 81 connects the carbon dioxide absorbing apparatus 10 and the regeneration apparatus 70. A pump 83 is provided in the supply pipe 81. By driving the pump 83, the absorption liquid L1 that absorbs carbon dioxide is supplied from the carbon dioxide absorbing apparatus 10 to the regeneration apparatus 70. The reflux pipe 82 connects the regeneration apparatus 70 and the carbon dioxide absorbing apparatus 10. A pump 85 is provided in the reflux pipe 82. In addition, a heat exchanger 84 is provided in the supply pipe 81 and the reflux pipe 82. By driving the pump 85, the absorption liquid L1 from which carbon dioxide has been released is supplied from the regeneration apparatus 70 to the carbon dioxide absorbing apparatus 10.

[0064] The regeneration tower 71 strips the carbon dioxide absorbed in the absorption liquid L1. The regeneration tower 71 accommodates a liquid supply section 72, a packing material 73, and a demister 76. The absorption liquid L1 in the carbon dioxide absorption section 30 is heated by a heat exchanger 84 and supplied to the liquid supply section 72. The liquid supply section 72 is arranged above the packing material 73, and sprays the absorption liquid L1 onto the packing material 73. The absorption liquid L1 drips while stripping carbon dioxide and accumulates at the bottom of the regeneration tower 71. A circulation pipe 74 is connected to the bottom of the regeneration tower 71, and a reboiler 75 is provided on the circulation pipe 74. The absorption liquid L1 that accumulates at the bottom of the regeneration tower 71 is heated by the reboiler 75, and carbon dioxide is further stripped from the absorption liquid L1. The demister 76 is located above the liquid supply section 72, and the gas containing carbon dioxide released within the regeneration tower 71 passes through the demister 76, which removes minute droplets, and is discharged from a gas outlet located at the zenith of the regeneration tower 71.

[0065] Meanwhile, the absorption liquid L1 remaining at the bottom of the regeneration tower 71 is sent to the carbon dioxide absorbing section 30 through the reflux piping 82. At this time, the heat of the absorption liquid L1 passing through the supply piping 81 and the heat of the absorption liquid L1 passing through the reflux piping 82 are exchanged in the heat exchanger 84, so that the absorption liquid L1 passing through the supply piping 81 is heated and the absorption liquid L1 passing through the reflux piping 82 is cooled. The absorption liquid L1 supplied to the carbon dioxide absorbing section 30 comes into gas-liquid contact with air G1 in the atmosphere, and the carbon dioxide in the air G1 is again absorbed by the absorption liquid L1.

[0066] The gas-liquid separation unit 90 separates moisture from the gas containing carbon dioxide discharged from the regeneration tower 71. The gas-liquid separation unit 90 includes an exhaust pipe 91, a liquid feed pipe 92, a heat exchanger 93, a gas-liquid separator 94, and a pump 95. The exhaust pipe 91 connects the gas outlet of the regeneration tower 71 to the side of the gas-liquid separator 94, and the heat exchanger 93 is provided in the exhaust pipe 91. The liquid feed pipe 92 connects the bottom of the gas-liquid separator 94 to the regeneration tower 71, and the pump 95 is provided in the liquid feed pipe 92.

[0067] The gas containing a high concentration of carbon dioxide discharged from the gas outlet of the regenerator 70 passes through an exhaust pipe 91 and is cooled by a heat exchanger 93, and the absorbing liquid L1 contained in the gas is condensed. The condensed absorbing liquid L1 is separated in a gas-liquid separator 94 and supplied to the regenerator 70 from the gas-liquid separation section 90 through a liquid supply pipe 92 by driving a pump 95, and is returned to the absorbing liquid L1 at the bottom of the regenerator 71. The gas containing a high concentration of carbon dioxide contains, for example, 90% or more, 95% or more, or 99% or more carbon dioxide by volume of the dry matter excluding moisture.

[0068] The heat exchanger 93 may cool the carbon dioxide-containing gas by exchanging heat between the low-purity water LW circulating in the first circulation system 22 and the carbon dioxide-containing gas containing carbon dioxide discharged from the regeneration tower 71. With this configuration, the low-purity water LW can be used as, for example, a coolant for the heat exchanger 93, thereby reducing the amount of cooling water used.

[0069] The heat exchanger 93 may cool the carbon dioxide-containing gas by exchanging heat of the absorption liquid L1 flowing from the carbon dioxide absorption section 30 to the regeneration tower 71 with heat of the carbon dioxide-containing gas containing carbon dioxide discharged from the regeneration tower 71. Even with such a configuration, the absorption liquid L1 can be used as, for example, a cooling liquid for the heat exchanger 93, thereby reducing the use of cooling water.

[0070] The carbon dioxide capture system 1 may include a concentration measuring unit 100 that measures the concentration of the absorbing liquid L1 in the air G2 that has passed through the absorbing liquid recovery unit 40. By measuring the concentration of the absorbing liquid L1, it is possible to appropriately determine the amount of the recovery liquid L2 to be supplied from the absorbing liquid recovery unit 40 to the carbon dioxide absorbing unit 30. Note that if the amount of water to be supplied from the absorbing liquid recovery unit 40 to the carbon dioxide absorbing unit 30 is determined in advance by a preliminary experiment or the like, the concentration measuring unit 100 is not necessarily required.

[0071] The flow rate of the recovery liquid L2 returned from the absorbing liquid recovery unit 40 to the carbon dioxide absorbing unit 30 may be adjusted according to the concentration measured by the concentration measuring unit 100. With this configuration, the amount of water supplied from the absorbing liquid recovery unit 40 to the carbon dioxide absorbing unit 30 can be adjusted according to the operating conditions. Therefore, a more appropriate amount of the recovery liquid L2 can be returned from the absorbing liquid recovery unit 40 to the carbon dioxide absorbing unit 30. The flow rate of the returned recovery liquid L2 can be controlled by a control unit 64 configured by a computer. The control unit 64 controls the flow rate adjuster 62 based on the concentration measured by the concentration measuring unit 100, thereby adjusting the flow rate of the recovery liquid L2 returned to the carbon dioxide absorbing unit 30. By returning an appropriate amount of the recovery liquid L2 to the carbon dioxide absorbing unit 30 by the absorbing liquid returning unit 60, the concentration of the absorption liquid L1 in the carbon dioxide absorbing unit 30 can be more appropriately controlled.

[0072] The carbon dioxide capture system may include a reactor (not shown). The reactor may produce compounds from a raw material containing carbon dioxide released in the regeneration device 70. The reactor may produce hydrocarbons, for example, from a raw material containing hydrogen and the carbon dioxide obtained in the regeneration device 70 through a methanation reaction or a Fischer-Tropsch (FT) reaction. The hydrocarbons may include at least one of an alkane and an alkene. Specifically, the hydrocarbons may include at least one selected from the group consisting of methane, ethane, propane, butane, ethylene, propylene, 1-butene, 2-butene, isobutene, and 1,3-butadiene. These hydrocarbons can be effectively used as fuels such as city gas and sustainable aviation fuel (SAF), as well as chemical raw materials. The reactor may also produce carbon from a raw material containing hydrogen and the carbon dioxide obtained in the regeneration device 70. The reactor may be a single-stage or multi-stage reactor.

[0073] The high-purity water HW may include water produced from raw materials containing hydrogen and carbon dioxide stripped in the regeneration device 70. As described above, hydrocarbons, carbon, etc. can be produced from raw materials containing hydrogen and carbon dioxide stripped in the regeneration device 70. Meanwhile, in such a reaction, water is produced as a by-product. Because the purity of such water is high, it can be used as high-purity water HW, and by using such water as high-purity water HW, resources can be used effectively. The water produced in the reactor may be used directly as high-purity water HW, or may be subjected to water treatment before being used as high-purity water HW.

[0074] As described above, the carbon dioxide capture system 1 according to this embodiment includes a humidifier 20 that supplies water vapor generated from low-purity water LW to air G1. The carbon dioxide capture system 1 is equipped with a carbon dioxide absorption unit 30 that absorbs carbon dioxide contained in the air G1 with the absorbing liquid L1 through gas-liquid contact between the air G1 and the absorbing liquid L1, and brings the water vapor into contact with the absorbing liquid L1. The carbon dioxide capture system 1 is equipped with an absorbing liquid recovery unit 40 that recovers the absorbing liquid L1 that has evaporated in the carbon dioxide absorption unit 30. The carbon dioxide capture system 1 is equipped with a high-purity water replenishment unit 55 that replenishes the absorbing liquid L1 recovered in the absorbing liquid recovery unit 40 with high-purity water HW, which has a higher purity than the low-purity water LW, in accordance with the amount of the recovery liquid L2 containing the absorbing liquid L1 in the absorbing liquid recovery unit 40. The carbon dioxide capture system 1 is equipped with an absorbing liquid return flow path 61 that returns a portion of the recovery liquid L2, to which the high-purity water HW has been replenished, to the carbon dioxide absorption unit 30. The carbon dioxide capture system 1 includes a flow rate adjusting unit 62 that is provided in the absorbing liquid return flow path 61 and adjusts the flow rate of the recovery liquid L2 returned from the absorbing liquid recovery unit 40 to the carbon dioxide absorption unit 30 through the absorbing liquid return flow path 61. The carbon dioxide capture system 1 includes a regeneration device 70 that releases the carbon dioxide absorbed by the absorption liquid L1 in the carbon dioxide absorption unit 30.

[0075] The carbon dioxide capture method also includes a step of supplying water vapor generated from low-purity water LW to air G1 in the humidifying unit 20. The carbon dioxide capture method also includes a step of absorbing carbon dioxide contained in the air G1 with the absorbing liquid L1 through gas-liquid contact between the air G1 and the absorbing liquid L1 in the carbon dioxide absorption unit 30, and bringing the water vapor into contact with the absorbing liquid L1. The carbon dioxide capture method also includes a step of recovering, in the absorbing liquid recovery unit 40, the absorbing liquid L1 that has evaporated in the carbon dioxide absorption unit 30. The carbon dioxide capture method also includes a step of replenishing, in the high-purity water replenishing unit 55, the absorbing liquid L1 recovered in the absorbing liquid recovery unit 40 with high-purity water HW that is higher in purity than the low-purity water LW in accordance with the amount of the recovering liquid L2 containing the absorbing liquid L1 in the absorbing liquid recovery unit 40. The carbon dioxide capture method also includes a step of returning, in the absorbent return flow path 61, a portion of the recovering liquid L2 replenishing the high-purity water HW to the carbon dioxide absorption unit 30. The carbon dioxide recovery method includes a step of adjusting, in a flow rate adjustment unit 62 provided in the absorption liquid return flow path 61, the flow rate of the recovery liquid L2 returned from the absorption liquid recovery unit 40 to the carbon dioxide absorption unit 30 through the absorption liquid return flow path 61. The carbon dioxide recovery method includes a step of, in a regeneration device 70, stripping the carbon dioxide absorbed by the absorption liquid L1 in the carbon dioxide absorption unit 30.

[0076] The water used to prepare the absorption liquid L1 is preferably highly pure in order to maintain high carbon dioxide absorption properties and to prevent salt precipitation. Such pure water is more expensive than tap water. However, water vapor is replenished from the humidifying unit 20 to the absorption liquid L1 in the carbon dioxide absorption unit 30. Because the purity of the water vapor is high, the amount of pure water required to maintain the concentration of the absorption liquid L1 can be reduced.

[0077] On the other hand, simply supplying water vapor to the air G1 may not be enough to sufficiently reduce the amount of water evaporating from the absorbing solution L1. Therefore, the high-purity water replenishment unit 55 replenishes high-purity water HW to the absorbing solution recovery unit 40, and the recovery solution L2 is returned to the absorbing solution at a flow rate adjusted by the absorbing solution return flow path 61 and the flow rate adjuster 62, thereby making it possible to suppress a decrease in water content in the absorbing solution L1. Furthermore, since highly pure water is supplied to the absorbing solution L1, it is possible to suppress the accumulation of inorganic components in the absorbing solution L1.

[0078] Therefore, according to the carbon dioxide recovery system 1 and carbon dioxide recovery method of this embodiment, it is possible to suppress the decrease in water content in the absorption liquid L1 and to suppress the accumulation of inorganic components in the absorption liquid L1 even when the amount of high-purity water HW used is reduced.

[0079] In the present embodiment, an example has been described in which the carbon dioxide capture system 1 includes one carbon dioxide absorbing device 10 and one regenerating device 70. However, the carbon dioxide capture system 1 may include a plurality of carbon dioxide absorbing devices 10 and a number of regenerating devices 70 that is less than the number of carbon dioxide absorbing devices 10.

[0080] In this embodiment, the carbon dioxide absorbing unit 30 has three regions, but it may have at least one region, and may have a plurality of regions, for example, four or more regions. Furthermore, the absorbing liquid recovery unit 40 has two regions, but it may have at least one region, and may have a plurality of regions, for example, three or more regions. Furthermore, the carbon dioxide absorbing apparatus 10 may be provided with an acid washing unit that brings the acidic liquid into gas-liquid contact downstream of the absorbing liquid recovery unit 40. The acid washing unit can recover the absorbing liquid L1 so that the concentration of the absorbing liquid L1 discharged from the carbon dioxide absorbing apparatus 10 is low, such as 0.1 ppm or less.

[0081] Although several embodiments have been described, the embodiments can be modified or varied based on the above disclosure. All components of the above embodiments and all features described in the claims may be individually extracted and combined, unless they contradict each other.

[0082] This disclosure can contribute, for example, to Goal 13 of the United Nations-led Sustainable Development Goals (SDGs), "Take urgent action to combat climate change and its impacts." [Explanation of symbols]

[0083] 1. Carbon dioxide capture system 10 Carbon dioxide absorber 20 Humidification unit 21 First gas-liquid contact section 22 First Circulation System 27 Low purity water level gauge 28 Heating section 30 Carbon dioxide absorption section 31 Second gas-liquid contact section 32 Second Circulation System 37 Absorption liquid level gauge 40 Absorbent recovery section 50 Low purity water replenishment section 55 High purity water replenishment section 61 Absorbent liquid return flow path 62 Flow rate adjustment section 70 Playback device 71 Regeneration Tower 93 Heat exchanger 100 Concentration measurement section L1 Absorbent L2 recovery liquid LW Low purity water HW High purity water

Claims

1. a humidifying unit that supplies water vapor generated from low-purity water to air; a carbon dioxide absorption section in which carbon dioxide contained in the air is absorbed by the absorption liquid through gas-liquid contact between the air and the absorption liquid, and the water vapor is brought into contact with the absorption liquid; an absorbing liquid recovery unit that recovers the absorbing liquid volatilized in the carbon dioxide absorption unit; a high-purity water replenishment unit that replenishes the absorbing liquid recovered in the absorbing liquid recovery unit with high-purity water having a purity higher than that of the low-purity water in accordance with the amount of recovered liquid containing the absorbing liquid in the absorbing liquid recovery unit; an absorbing liquid return flow path that returns a portion of the recovered liquid replenished with the high-purity water to the carbon dioxide absorbing unit; a flow rate adjusting unit that is provided in the absorbing liquid return flow path and adjusts the flow rate of the recovered liquid returned from the absorbing liquid recovery unit to the carbon dioxide absorption unit through the absorbing liquid return flow path; a regeneration device that releases the carbon dioxide absorbed by the absorbing liquid in the carbon dioxide absorption unit; A carbon dioxide capture system comprising:

2. the humidifying unit includes a low-purity water level meter that measures the liquid level of the low-purity water in the humidifying unit; The carbon dioxide capture system according to claim 1, further comprising a low-purity water replenishment unit that adjusts the flow rate of the low-purity water to be replenished to the humidification unit in accordance with the liquid level of the low-purity water level meter.

3. the humidifying unit includes a first gas-liquid contact unit through which the air passes, and a first circulation system that circulates the low-purity water and supplies the circulated low-purity water to the first gas-liquid contact unit, the carbon dioxide absorption unit includes a second gas-liquid contact unit through which the air that has passed through the humidification unit passes, a second circulation system that circulates the absorption liquid and supplies the circulating absorption liquid to the second gas-liquid contact unit, and an absorption liquid level gauge that measures the liquid level of the absorption liquid in the second circulation system, 3. The carbon dioxide capture system according to claim 1, wherein the first circulation system includes a contact amount adjustment unit that adjusts an amount of low-purity water flowing through the first circulation system that comes into contact with the air per unit time, based on the liquid level measured by the absorption liquid level gauge.

4. the humidifying unit includes a first gas-liquid contact unit through which the air passes, and a first circulation system that circulates the low-purity water and supplies the circulated low-purity water to the first gas-liquid contact unit, The playback device a regeneration tower that releases carbon dioxide absorbed in the absorption liquid; a heat exchanger that cools the carbon dioxide-containing gas by exchanging heat of the low-purity water circulating in the first circulation system with heat of the carbon dioxide-containing gas containing carbon dioxide discharged from the regeneration tower; 3. The carbon dioxide capture system of claim 1 or 2, comprising:

5. The playback device a regeneration tower that releases carbon dioxide absorbed in the absorption liquid; a heat exchanger that cools the carbon dioxide-containing gas by exchanging heat of the absorption liquid flowing from the carbon dioxide absorption unit to the regeneration tower with heat of the carbon dioxide-containing gas containing carbon dioxide discharged from the regeneration tower; 3. The carbon dioxide capture system of claim 1 or 2, comprising:

6. 3. The carbon dioxide capture system according to claim 1, wherein the humidifying unit includes a first gas-liquid contact unit through which the air passes, a first circulation system that circulates the low-purity water and supplies the circulated low-purity water to the first gas-liquid contact unit, and a heating unit that heats the low-purity water circulated in the first circulation system.

7. the carbon dioxide absorption unit includes a second gas-liquid contact unit through which the air that has passed through the humidification unit passes, a second circulation system that circulates the absorption liquid and supplies the circulating absorption liquid to the second gas-liquid contact unit, and an absorption liquid level gauge that measures the liquid level of the absorption liquid in the second circulation system, The carbon dioxide capture system according to claim 6 , wherein the humidifying unit adjusts the amount of heat used to heat the low-purity water based on the liquid level measured by the absorption liquid level gauge.

8. The carbon dioxide capture system according to claim 1 or 2, further comprising a concentration measuring unit that measures a concentration of the absorbing liquid in the air that has passed through the absorbing liquid recovery unit.

9. The carbon dioxide recovery system according to claim 8, wherein a flow rate of the recovery liquid returned from the absorption liquid recovery section to the carbon dioxide absorption section is adjusted according to the concentration measured by the concentration measurement section.

10. 3. The carbon dioxide recovery system according to claim 1, wherein the high-purity water is pure water, and the low-purity water is tap water, industrial water, or a mixture thereof.

11. 3. The carbon dioxide recovery system according to claim 1, wherein the high-purity water includes water produced from a raw material containing hydrogen and carbon dioxide released by the regeneration device.

12. supplying water vapor generated from low-purity water to air in a humidifying section; a step of absorbing carbon dioxide contained in the air with the absorbing liquid through gas-liquid contact between the air and the absorbing liquid in a carbon dioxide absorption unit, and contacting the water vapor with the absorbing liquid; recovering the absorbing liquid volatilized in the carbon dioxide absorption unit in an absorbing liquid recovery unit; a step of replenishing the absorbing liquid recovered in the absorbing liquid recovery section with high-purity water having a purity higher than that of the low-purity water in a high-purity water replenishing section in accordance with the amount of recovered liquid containing the absorbing liquid in the absorbing liquid recovery section; a step of returning a portion of the recovered liquid replenished with the high-purity water to the carbon dioxide absorbing unit in an absorption liquid return flow path; a step of adjusting, in a flow rate adjusting unit provided in the absorbing liquid return flow path, a flow rate of the recovered liquid returned from the absorbing liquid recovery unit to the carbon dioxide absorption unit through the absorbing liquid return flow path; a step of releasing the carbon dioxide absorbed in the absorbing liquid in the carbon dioxide absorption unit in the regeneration device; A method for capturing carbon dioxide, comprising:

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