Carbon dioxide recovery device and carbon dioxide recovery method

Abstract

To provide a carbon dioxide recovery method and a carbon dioxide recovery device capable of obtaining high purity carbon dioxide by recovering low concentration carbon dioxide contained in the atmosphere by an economically advantageous method.SOLUTION: In a carbon dioxide recovery method, an air supply step of feeding air to an adsorption structure containing an adsorbent capable of reversibly adsorbing and desorbing carbon dioxide to cause the adsorption structure to adsorb carbon dioxide, a preheating step of feeding preheating gas to preheat the adsorption structure, and a regeneration step of feeding regeneration gas to desorb carbon dioxide from the adsorption structure to separate high-concentration carbon dioxide are repeated in this order, and an operation of moving water vapor from the preheating gas to the regeneration gas is performed by using difference in water vapor partial pressure between the preheating gas fed to a preheating zone in the preheating step and the regeneration gas fed to a regeneration zone in the regeneration step as a driving force.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide recovery apparatus and a carbon dioxide recovery method for recovering low-concentration carbon dioxide contained in the atmosphere to obtain high-purity carbon dioxide. [Background technology]

[0002] Global warming caused by carbon dioxide released during the combustion of fossil fuels has become a problem, and there is an urgent need to reduce the release of carbon dioxide into the atmosphere from fossil fuel combustion. On the other hand, there are applications where the use of fossil fuels is technically or economically unavoidable, and so expectations are rising for direct air capture technology, which recovers carbon dioxide from the atmosphere.

[0003] Carbon dioxide can be converted into hydrocarbons such as methane by reacting it with hydrogen. If the hydrogen is produced using electricity derived from renewable energy sources such as solar or wind power, and the carbon dioxide is collected from the atmosphere, the resulting hydrocarbons, even when burned, will not increase the atmospheric carbon dioxide concentration throughout the entire process from fuel production to use, making them carbon-neutral hydrocarbons.

[0004] Technologies for recovering carbon dioxide from flue gas are well known. Amine absorption carbon dioxide removal equipment, which brings flue gas into contact with an aqueous solution of an amine compound to remove most of the carbon dioxide contained in the flue gas, and heats the amine aqueous solution that has absorbed the carbon dioxide to recover high-purity carbon dioxide containing 99% or more carbon dioxide by volume, has been put to practical use as carbon dioxide recovery equipment for the flue gas of coal-fired power plants.

[0005] The amine absorption method can capture highly pure (e.g., 99.5% or higher) carbon dioxide, making it advantageous for using the captured carbon dioxide as a raw material for fuel and other purposes. However, when capturing carbon dioxide from combustion exhaust gas in an amine aqueous solution, the carbon dioxide molecules pass through the gas-liquid interface, and for efficient carbon dioxide capture, it is necessary to promote gas-liquid contact. Therefore, a commonly used method involves flowing an amine aqueous solution down from the top of a packed tower filled with packing to increase the contact area, and passing the combustion exhaust gas from the bottom to the top, resulting in countercurrent contact. However, this method has the problem of high gas pressure loss.

[0006] When capturing carbon dioxide contained in the atmosphere (approximately 400 ppm), the amount of gas that needs to be treated to capture the same amount of carbon dioxide is 100 to 300 times greater than that of combustion exhaust gas (usually about 4% to 13%), so the use of the amine absorption method, which results in a high gas pressure loss, is not practical.

[0007] Solid carbon dioxide adsorbents are known (Non-Patent Document 1). When a carbon dioxide adsorbent in which such a solid adsorbent is supported on a honeycomb carrier is used, it is possible to treat a large amount of gas in a short time while suppressing pressure loss. The solid adsorbent adsorbs carbon dioxide at low temperatures and desorbs carbon dioxide at high temperatures. Therefore, when air containing carbon dioxide is circulated at low temperatures, the carbon dioxide is adsorbed onto the solid adsorbent, and when high-temperature regeneration gas is circulated through the solid adsorbent, the carbon dioxide is desorbed, resulting in a gas with an increased carbon dioxide concentration.

[0008] A carbon dioxide concentrator is also known in which a honeycomb-shaped carrier is formed as a disc-shaped honeycomb rotor, and the rotation of the rotor moves the adsorption section and the regeneration section repeatedly, thereby continuously adsorbing carbon dioxide contained in the atmosphere and regenerating it using a regeneration gas (Patent Documents 1 to 3).

[0009] Known solid carbon dioxide adsorbents include those in which a porous carrier such as silica or activated carbon is supported with a high-molecular-weight amine, such as polyethyleneimine, or weakly basic anion exchange resins. These solid adsorbents are capable of adsorbing even dilute carbon dioxide in the atmosphere. However, due to thermodynamic limitations of adsorption, it is generally impossible to recover high-purity carbon dioxide from these adsorbents at temperatures lower than about 120°C under atmospheric pressure.

[0010] Carbon dioxide adsorbents undergo oxidative degradation in high-temperature, high-oxygen-containing atmospheres. In particular, amine-based adsorbents and weakly basic anion exchange resins rapidly deteriorate in air at temperatures above 120°C. Therefore, it is difficult to recover dilute carbon dioxide from the atmosphere and obtain high-purity carbon dioxide using the methods described in Patent Documents 1 to 3.

[0011] Patent Document 4 discloses a method for separating carbon dioxide from a gas mixture containing gaseous carbon dioxide and a gas other than carbon dioxide by cyclic adsorption / desorption using an adsorbent that adsorbs gaseous carbon dioxide.

[0012] Specifically, a method using a unit comprising an adsorptive structure with an adsorbent, the unit being evacuable to a vacuum pressure of 400 mbar abs or less, the adsorptive structure being heatable to a temperature of at least 80°C to desorb at least gaseous carbon dioxide, the unit being capable of flowing a gas mixture through and releasing it to contact the adsorbent therewith in an adsorption step, comprising the following sequence and repetition of said sequence: (a) in an adsorption step, contacting the gas mixture with an adsorbent and adsorbing at least gaseous carbon dioxide onto the adsorbent under ambient atmospheric pressure conditions in the range of 0.8 to 1.1 bar abs and ambient atmospheric temperature conditions in the range of -40 to 60°C; (b) in a desorption step, evacuating the unit to a pressure in the range of 20 to 400 mbar abs, heating the adsorbent in the unit to a temperature in the range of 80 to 130°C, extracting at least the desorbed gaseous carbon dioxide from the unit, and separating the gaseous carbon dioxide from water by condensation in or downstream of the unit; (c) forcibly cooling the adsorbent at the pressure of step (b) to a temperature above ambient atmospheric conditions and repressurizing the unit to ambient atmospheric conditions; In step (b), steam is injected into the unit, allowed to flow through, and contacted with the adsorbent under saturated steam conditions or superheated steam conditions at a superheated steam temperature of up to 130°C at the pressure level of the unit, and the molar ratio of the steam injected to the gaseous carbon dioxide released during the entire step (b) is less than 40:1.

[0013] In the method described in this document, the adsorbent that has adsorbed carbon dioxide is heated to a temperature in the range of 80 to 130°C, and the pressure is reduced to 20 to 400 mbar abs (approximately 0.02 to 0.4 atm), and the partial pressure of carbon dioxide is further reduced by adding superheated steam. Furthermore, because the oxygen concentration is reduced by the reduced pressure evacuation, thermal degradation of the adsorbent during the desorption process can also be suppressed.

[0014] However, the combined use of superheated steam to desorb carbon dioxide requires a large amount of steam, which increases the amount of energy required to capture carbon dioxide.

[0015] Furthermore, when carbon dioxide is desorbed under reduced pressure, it is necessary to carry out the desorption in a container that can withstand reduced pressure, which increases the equipment costs. In addition, it is inevitable that the concentration of the recovered carbon dioxide will decrease due to air leakage.

[0016] Patent Document 5 discloses a carbon dioxide recovery device that includes an adsorption rotor containing an adsorbent capable of reversibly adsorbing and desorbing carbon dioxide and to which air containing carbon dioxide is supplied, a regeneration gas supply unit that supplies a regeneration gas at 60°C or higher and 120°C or lower to the adsorption rotor, and a carbon dioxide recovery unit that separates and recovers carbon dioxide from the regeneration gas that has passed through the adsorption rotor by an amine absorption method, and the regeneration gas from which carbon dioxide has been separated in the carbon dioxide recovery unit is sent to the regeneration gas supply unit and recycled for reuse, and an oxygen removal unit that reduces the concentration of oxygen contained in the regeneration gas is provided in the circulation path of the regeneration gas.

[0017] According to this configuration, a large amount of air is treated with an adsorption rotor with low pressure loss to increase the carbon dioxide concentration in the regeneration gas, and then the carbon dioxide is recovered in a carbon dioxide separation section that uses an amine absorption method. This makes it possible to efficiently treat a large amount of air while recovering high-purity carbon dioxide. In this method, the regeneration of the adsorption rotor requires the supply of at least the sensible heat of the adsorption rotor and the heat of carbon dioxide desorption from the adsorption rotor. For example, if carbon dioxide is adsorbed from air at 25°C and the adsorption rotor is regenerated at 90°C, the sensible heat of the adsorption rotor is calculated by multiplying the heat capacity of the adsorption rotor by the temperature difference between regeneration and adsorption (65°C). The heat of carbon dioxide desorption is typically 60 to 90 kJ per mole of carbon dioxide. This heat requirement is met by the sensible heat of the regeneration gas. Of the heat required for the regeneration of the adsorption rotor, which is greater, the sensible heat of the adsorption rotor or the heat of carbon dioxide desorption from the adsorption rotor, depends on the amount of carbon dioxide adsorbed per unit mass of the adsorption rotor, but they usually account for roughly the same amount, and neither is dominant.

[0018] The only way to increase the sensible heat supply from the regeneration gas is to increase its temperature or flow rate. If the regeneration gas temperature is increased above 120°C, a higher-temperature heat source is required to heat the regeneration gas, and there is also the concern that the adsorption rotor may be thermally deteriorated due to exposure to high temperatures. Increasing the flow rate of the regeneration gas reduces the concentration of carbon dioxide contained in the regeneration gas that has passed through the adsorption rotor, raising concerns that the energy required to capture carbon dioxide in the amine absorption method may increase. Furthermore, desorption of water during the regeneration process is also a problem. Adsorbents that can reversibly adsorb carbon dioxide generally also reversibly adsorb water vapor. Therefore, when carbon dioxide-containing air is supplied to an adsorption rotor that adsorbs carbon dioxide, water vapor is also adsorbed unless the air containing carbon dioxide has extremely low humidity, for example, a relative humidity of less than 30%. If the water vapor partial pressure (or relative humidity) of the regeneration gas supplied during the regeneration process is low, desorption of water vapor will proceed in addition to carbon dioxide during the regeneration process, and the temperature of the adsorption rotor will drop, raising concerns that the adsorption rotor will not be fully regenerated.

[0019] Increasing the water vapor partial pressure (or relative humidity) of the regeneration gas is an effective way to avoid the above problems. Generally, the amount of water adsorbed by an adsorbent between room temperature and 100°C, the boiling point of water at normal pressure, varies depending on the relative humidity. Therefore, for example, if carbon dioxide is adsorbed from the air by an adsorbent at 25°C and a relative humidity of 50%, and then regenerated at 90°C, the relative humidity of the regeneration gas should be kept above 50%, and the water vapor partial pressure should be 35 kPa or higher. A simple way to increase the water vapor partial pressure of the regeneration gas is to mix low-pressure steam with the regeneration gas, but there is a concern that the energy required to generate the steam will increase, reducing the economic viability of carbon dioxide capture.

[0020] In summary, the reality is that there is still room for improvement in carbon dioxide recovery devices and carbon dioxide recovery methods for recovering low-concentration carbon dioxide contained in the atmosphere and obtaining high-purity carbon dioxide. [Prior art documents] [Patent documents]

[0021] [Patent Document 1] Patent No. 5877922 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-175014 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-154063 [Patent Document 4] Patent No. 6622302 [Patent Document 5] Japanese Patent Publication No. 2023-45570 [Non-patent literature]

[0022] [Non-Patent Document 1] C.W. Jones et al., Chemical Reviews, Vol. 116, pp. 11840-11876 (2016) Summary of the Invention [Problem to be solved by the invention]

[0023] In view of the above problems, the problem that the present invention aims to solve is to provide an economically excellent carbon dioxide recovery apparatus and carbon dioxide recovery method for recovering low-concentration carbon dioxide contained in the atmosphere to obtain high-purity carbon dioxide. [Means for solving the problem]

[0024] In order to solve the above problems, the present invention provides: an adsorption structure containing an adsorbent capable of reversibly adsorbing and desorbing carbon dioxide; an air supply step of feeding air containing carbon dioxide and having a relative humidity of 30% to 100% and a temperature of 0°C to 40°C into the adsorptive structure to adsorb the carbon dioxide into the adsorptive structure, and then discharging the air with a reduced carbon dioxide concentration from the adsorptive structure; a preheating step of preheating the adsorption structure to 60°C or higher and 120°C or lower by supplying a preheating gas of 60°C or higher and 120°C or lower to the adsorption structure after the air supply step has been completed, and heating and circulating the preheating gas flowing out of the adsorption structure; a regeneration step in which a regeneration gas at 60°C or higher and 120°C or lower is fed into the adsorption structure after the preheating step, causing carbon dioxide to be desorbed from the adsorption structure, separating carbon dioxide from the carbon dioxide-enriched gas with an increased carbon dioxide concentration that has flowed out of the adsorption structure, and heating the gas from which the carbon dioxide has been separated to regenerate the adsorption structure while recycling it as the regeneration gas; and the above steps are repeated in this order, and water vapor is transferred from the heated preheating gas to the heated regeneration gas using the difference in water vapor partial pressure between the heated preheating gas fed into the preheating zone in the preheating step and the heated regeneration gas fed into the regeneration zone in the regeneration step as a driving force.

[0025] According to this method, a preheating step is provided between the air supply step, in which carbon dioxide is adsorbed from the air onto the adsorbent structure, and the regeneration step, in which carbon dioxide is desorbed from the adsorbent structure. Therefore, the sensible heat required to heat the adsorbent structure from a temperature of 0°C to 40°C during the air supply step to a temperature of 60°C to 120°C during the regeneration step is provided in the preheating step, separate from the regeneration step. This facilitates the production of a high-concentration carbon dioxide-enriched gas during the regeneration step. Furthermore, because water vapor is transferred from the heated preheating gas to the heated regeneration gas, the amount of water adsorbed by the adsorbent structure is reduced upon entering the regeneration step, and the water vapor partial pressure (or relative humidity) of the regeneration gas is increased. This suppresses the desorption of water vapor during the regeneration step, making it easier to maintain the temperature of the adsorbent structure during the regeneration step. Because the carbon dioxide concentration in the carbon dioxide-enriched gas is thus increased, the carbon dioxide capture method described above provides an economically advantageous method for recovering low-concentration carbon dioxide from the atmosphere and producing high-purity carbon dioxide.

[0026] A further characteristic feature of the carbon dioxide recovery method according to the present invention is that the operation of transferring the water vapor is carried out using a water vapor selective permeable membrane.

[0027] According to this configuration, there is almost no additional energy consumption except for a slight pressure loss occurring in the preheating gas and the regeneration gas when transferring the water vapor, and the operation of transferring the water vapor can be carried out continuously, so that it is possible to recover low-concentration carbon dioxide contained in the atmosphere and obtain high-purity carbon dioxide in an economically advantageous manner.

[0028] A further characteristic feature of the carbon dioxide recovery method according to the present invention is that the operation of transferring the water vapor is carried out using a water vapor adsorbent that selectively adsorbs water vapor.

[0029] According to this configuration, there is almost no additional energy consumption except for a slight pressure loss that occurs in the preheating gas and the regeneration gas when performing the operation of transferring water vapor, and therefore, it is possible to recover low-concentration carbon dioxide contained in the atmosphere and obtain high-purity carbon dioxide in an economically advantageous manner.

[0030] A further characteristic feature of the carbon dioxide recovery method according to the present invention is that the operation of transferring the water vapor is carried out using a desiccant rotor containing a water vapor adsorbent that selectively adsorbs water vapor.

[0031] According to this configuration, the pressure loss generated in the preheating gas and the regeneration gas during the operation of transferring the water vapor is extremely small, and there is almost no additional energy consumption. Furthermore, the operation of transferring the water vapor can be carried out continuously. Therefore, it is possible to recover low-concentration carbon dioxide contained in the atmosphere and obtain high-purity carbon dioxide in an economically advantageous manner.

[0032] A further characteristic feature of the carbon dioxide recovery method according to the present invention is that steam is further added from outside to the regeneration gas after the operation of transferring the steam.

[0033] According to this configuration, carbon dioxide desorption in the regeneration zone can be carried out under more advantageous conditions without adding excessive water vapor. Therefore, according to the carbon dioxide recovery method having the above configuration, it is possible to recover low-concentration carbon dioxide contained in the atmosphere and obtain high-purity carbon dioxide in an economically advantageous manner.

[0034] In order to solve the above problems, the present invention provides: an adsorption structure containing an adsorbent capable of reversibly adsorbing and desorbing carbon dioxide; a conveying means for passing the adsorption structure through at least three zones, i.e., an adsorption zone, a preheating zone, and a regeneration zone, which are divided by a flow path dividing means; an air supply unit having air feeding means for feeding air containing carbon dioxide, having a relative humidity of 30% to 100% and a temperature of 0°C to 40°C, into the inlet side of the adsorption zone, causing the carbon dioxide to be adsorbed by the adsorption structure passing through the adsorption zone, and discharging the air with a reduced carbon dioxide concentration from the outlet side; a preheating section having a preheating means and a preheating gas circulation means for supplying a preheating gas at 60°C or more and 120°C or less into an inlet side of the preheating zone to heat the adsorption structure and for circulating and utilizing the gas flowing out from an outlet side of the preheating zone; a regeneration section including a carbon dioxide separation means, a regeneration heating means, and a regeneration gas circulation means for feeding a regeneration gas at 60°C or higher and 120°C or lower into the inlet side of the regeneration zone, desorbing carbon dioxide from the adsorption structure, and separating and recycling carbon dioxide from a carbon dioxide-enriched gas with an increased carbon dioxide concentration that flows out from the outlet side of the regeneration zone; and a water vapor transfer means for transferring water vapor from the preheating gas to the regeneration gas using a difference in water vapor partial pressure between the preheating gas after heating and sent to the preheating zone in the preheating section and the regeneration gas after heating and sent to the regeneration zone in the regeneration section as a driving force.

[0035] According to this configuration, a preheating section is provided between the air supply section, which adsorbs carbon dioxide from the air onto the adsorbent structure, and the regeneration section, which desorbs carbon dioxide from the adsorbent structure. The sensible heat required to heat the adsorbent structure from a temperature of 0°C to 40°C in the air supply section to a temperature of 60°C to 120°C in the regeneration section is provided in the preheating section, separated from the regeneration section. This facilitates the production of a high-concentration carbon dioxide-enriched gas in the regeneration section. Furthermore, because water vapor is transferred from the heated preheating gas to the heated regeneration gas, the amount of water adsorbed by the adsorbent structure upon entry into the regeneration section is reduced, and the water vapor partial pressure (or relative humidity) of the preheating gas is increased. This suppresses water vapor desorption in the regeneration section, making it easier to maintain the temperature of the adsorbent structure in the regeneration section, and facilitates the extraction of a carbon dioxide-enriched gas containing a high concentration of carbon dioxide in the regeneration section. As described above, because the carbon dioxide concentration in the carbon dioxide-enriched gas is increased, the carbon dioxide capture device described above can be used to recover low-concentration carbon dioxide from the atmosphere and obtain high-purity carbon dioxide in an economical manner.

[0036] A further characteristic feature of the carbon dioxide recovery device according to the present invention is that the water vapor transfer means is configured using a water vapor selective permeable membrane.

[0037] According to this configuration, there is almost no additional energy consumption except for a slight pressure loss in the preheating gas and the regeneration gas when transferring the water vapor, and the operation of transferring the water vapor is carried out continuously, so that this is an economically advantageous configuration that can recover low-concentration carbon dioxide contained in the atmosphere and obtain high-purity carbon dioxide.

[0038] A further characteristic feature of the carbon dioxide capture device according to the present invention is that the water vapor transfer means is configured using a water vapor adsorbent that selectively adsorbs water vapor.

[0039] According to this configuration, there is almost no additional energy consumption except for a slight pressure loss that occurs in the preheating gas and the regeneration gas when transferring the water vapor, and therefore this is an economically advantageous configuration that can recover low-concentration carbon dioxide contained in the atmosphere and obtain high-purity carbon dioxide.

[0040] A further characteristic feature of the carbon dioxide recovery apparatus according to the present invention is that the water vapor transfer means is configured using a desiccant rotor containing a water vapor adsorbent that selectively adsorbs water vapor.

[0041] According to this configuration, the pressure loss generated in the preheating gas and the regeneration gas during the operation of transferring the water vapor is extremely small, and there is almost no additional energy consumption. Furthermore, the operation of transferring the water vapor can be performed continuously. Therefore, with this economically advantageous configuration, low-concentration carbon dioxide contained in the atmosphere can be recovered and high-purity carbon dioxide can be obtained.

[0042] A further characteristic feature of the carbon dioxide recovery apparatus according to the present invention is that a steam addition means is provided on the path from the steam transfer means to the inlet of the regeneration zone in the regeneration section.

[0043] This configuration allows carbon dioxide desorption in the regeneration zone to be carried out under more favorable conditions without adding excessive water vapor. Therefore, a carbon dioxide recovery device having the above configuration can recover low-concentration carbon dioxide contained in the atmosphere and obtain high-purity carbon dioxide in an economically advantageous manner.

[0044] A further characteristic configuration of the carbon dioxide recovery system according to the present invention is that it includes a honeycomb rotor as the adsorption structure, and the conveying means rotates the honeycomb rotor to cause the carbon dioxide to pass through the adsorption zone, the preheating zone, and the regeneration zone in sequence.

[0045] According to this configuration, the rotation rate of the adsorptive structure can be increased, and therefore, carbon dioxide can be adsorbed and desorbed efficiently. [Effects of the Invention]

[0046] According to the above configuration, it is possible to recover low concentration carbon dioxide contained in the atmosphere and obtain high purity carbon dioxide in an economically advantageous manner. [Brief explanation of the drawings]

[0047] [Figure 1] 1 is a diagram showing a configuration example of a carbon dioxide recovery device of the present invention. [Figure 2] FIG. 10 is a diagram showing another example of the configuration of the carbon dioxide recovery device of the present invention. [Figure 3] FIG. 10 is a diagram showing another example of the configuration of the carbon dioxide recovery device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0048] Hereinafter, embodiments of the carbon dioxide recovery method and carbon dioxide recovery apparatus according to the present invention will be described.

[0049] The carbon dioxide recovery method of this example will be described. In the carbon dioxide recovery method of this example, an air supply step, a preheating step, and a regeneration step are repeatedly performed in this order on an adsorption structure containing an adsorbent capable of reversibly adsorbing and desorbing carbon dioxide, and water vapor is transferred from the preheating gas to the regeneration gas using the difference in water vapor partial pressure between the preheating gas used in the preheating step and the regeneration gas used in the regeneration step as a driving force.

[0050] The adsorbent capable of reversibly adsorbing and desorbing carbon dioxide may be any material capable of adsorbing carbon dioxide in the atmosphere when brought into contact with the atmosphere at a temperature between 0° C. and 40° C. Examples of such adsorbents include adsorbents in which tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), or polyethyleneimine (PEI) is supported on silica or activated carbon with a high specific surface area, adsorbents made of weakly basic anion exchange resins having primary or secondary amino groups as functional groups, and adsorbents in which carbonates or hydrogencarbonates of potassium or sodium are impregnated or supported on activated carbon, silica, alumina, or the like.

[0051] The adsorptive structure may contain an adsorbent capable of reversibly adsorbing and desorbing carbon dioxide, and may have a shape that allows the air supply step, preheating step, and regeneration step to be repeated in this order, such as a honeycomb-shaped substrate coated with the adsorbent, or a particulate substrate with a particle diameter of about 2 to 20 mm coated with the adsorbent. When using these, the air supply step, preheating step, and regeneration step may be repeated in this order while the adsorptive structure is being transported, or the position of the adsorptive structure may be fixed, and the circulating gas may be switched by switching a valve, and the air supply step, preheating step, and regeneration step may be repeated in this order. If the adsorption structure is configured in the shape of a honeycomb rotor, which is a rotationally symmetric disk having a flow path in the direction of the rotation axis, the air supply process, preheating process, and regeneration process can be repeated in this order while the adsorption structure is continuously rotated.

[0052] [Air supply process] In the air supply step, air containing carbon dioxide at a relative humidity of 30% to 100% is brought into contact with the adsorptive structure at atmospheric pressure at a temperature of 0°C to 40°C, thereby adsorbing the carbon dioxide contained in the air. During this process, air with a reduced carbon dioxide concentration flows out from the outlet side of the adsorptive structure. Whether water is adsorbed from the air to the adsorptive structure or desorbed from the adsorptive structure to the air depends on the amount of water adsorbed by the adsorptive structure at the start of the air supply step, but the adsorptive structure after the air supply step contains an amount of adsorbed water that corresponds to the relative humidity of the air.

[0053] [Preheating process] In the preheating step, a preheating gas at 60° C. or more and 120° C. or less is fed into the adsorption structure to heat the adsorption structure and preheat it to 60° C. or more and 120° C. or less. The gas flowing out from the outlet side of the adsorption structure is recycled and fed again into the inlet side of the adsorption structure. Depending on the temperature of the adsorption structure and the carbon dioxide concentration in the circulating gas, carbon dioxide may be desorbed from the adsorption structure or may be adsorbed onto the adsorption structure. However, once the operation is repeated and the operation has stabilized and reached a steady state, the amount of carbon dioxide adsorbed by the adsorption structure at the start of the preheating step will be the same as the amount of carbon dioxide adsorbed by the adsorption structure at the end of the preheating step, and therefore the amount of carbon dioxide adsorbed by the adsorption structure does not appear to increase or decrease during the preheating step.

[0054] The carbon dioxide concentration in the circulating gas in the preheating step (if the preheating step is not performed continuously by moving the adsorption structure, the concentration at the end of the step) is usually 2% to 10% (volume basis, the same applies below). Since the purpose of this step is to preheat the adsorptive structure to the temperature required for the subsequent regeneration step, it is necessary to circulate a gas with a heat capacity that matches the heat capacity of the adsorptive structure. The required amount of gas to circulate depends on the heat capacity of the adsorptive structure, but it is appropriate to feed the amount of gas into the adsorptive structure at approximately 300 to 3,000 times the volume of the adsorptive structure.

[0055] [Regeneration process] In the regeneration process, a regeneration gas at 60°C to 120°C is fed into the adsorption structure to desorb carbon dioxide from the adsorption structure, and high-purity carbon dioxide is separated by a carbon dioxide separation means from the carbon dioxide-enriched gas with an increased carbon dioxide concentration that flows out of the adsorption structure. The gas from which the carbon dioxide has been separated is recycled and fed again through the inlet side of the adsorption structure. The carbon dioxide concentration in the carbon dioxide-enriched gas varies depending on the temperature of the regeneration gas, but is typically 2% to 10% (volume basis, the same applies below). When the carbon dioxide concentration is low, the efficiency of carbon dioxide separation in the carbon dioxide separation means decreases and the required energy also increases. In this case, it is preferable to increase the temperature of the regeneration gas within a range not exceeding 120°C. Conversely, when the carbon dioxide concentration is high, the temperature of the regeneration gas may be decreased within a range not falling below 60°C, which not only reduces energy consumption in the regeneration process but also suppresses deterioration of the adsorption structure.

[0056] [Operation to transfer water vapor] For example, if no water vapor transfer operation is performed, carbon dioxide is adsorbed from the air onto an adsorbent at 25°C and 50% relative humidity, and then the adsorbent is preheated to 90°C. The water vapor partial pressure in the circulating gas during the preheating process is approximately 35 kPa, which corresponds to the water vapor partial pressure at 90°C and 50% relative humidity. On the other hand, the gas after carbon dioxide separation in the regeneration process typically contains water vapor equivalent to the saturated water vapor pressure at the temperature during carbon dioxide separation. If the carbon dioxide separation process is performed at a temperature between 35°C and 50°C, the water vapor partial pressure will be approximately 6 to 12 kPa. Therefore, the water vapor partial pressure of the regeneration gas is significantly lower than that of the preheating gas. Therefore, water vapor can be transferred from the preheating gas to the regeneration gas using a water vapor selective permeable membrane or a water vapor selective adsorbent (an example of a water vapor adsorbent).

[0057] When a water vapor selective permeable membrane is used, the preheating gas after heating and the regeneration gas after heating are brought into contact with each other through the water vapor selective permeable membrane, thereby transferring water vapor from the preheating gas to the regeneration gas. The water vapor selective permeable membrane is required to have high water vapor permeability and low carbon dioxide permeability, and a polymer membrane such as a polyimide membrane can be used.

[0058] When a water vapor selective adsorbent is used, the preheating gas after heating and the regeneration gas after heating are alternately brought into contact with the water vapor selective adsorbent by switching the gas flow path with a valve, etc., thereby transferring water vapor from the preheating gas to the regeneration gas. The water vapor selective adsorbent is required to have a large adsorption capacity for water vapor and a low adsorption capacity for carbon dioxide, and for example, silica gel or various zeolites can be used. It is also possible to use a honeycomb rotor (desiccant rotor) coated with a water vapor selective adsorbent, and by rotating the desiccant rotor, alternately bring the heated preheating gas and the heated regeneration gas into contact with the desiccant rotor. This simple mechanism allows water vapor to be transferred continuously from the preheating gas to the regeneration gas, and the pressure loss is low, making it particularly economically advantageous.

[0059] When the operation of transferring water vapor is carried out appropriately, the difference in water vapor partial pressure between the preheating gas and the regeneration gas can be reduced to 10 kPa or less, more preferably 5 kPa or less, and even more preferably 2 kPa or less.

[0060] [Outline of carbon dioxide capture equipment] As shown in FIG. 1, the carbon dioxide recovery device A of this example is equipped with an adsorption structure (not shown) containing an adsorbent material capable of reversibly adsorbing and desorbing carbon dioxide, an adsorption zone 11, a preheating zone 12, and a regeneration zone 13, and a transport means (not shown) for transporting the adsorption structure through the adsorption zone 11, the preheating zone 12, and the regeneration zone 13, all mounted on a honeycomb rotor 1. The carbon dioxide recovery device A also includes an air supply section 110 that feeds air containing carbon dioxide at a temperature of 0°C or higher and 40°C or lower into the adsorption zone 11 and discharges air with a reduced carbon dioxide concentration, a preheating section 120 that feeds a preheating gas at a temperature of 60°C or higher and 120°C or lower into the preheating zone 12 and heats the adsorption structure, a regeneration section 130 that feeds a regeneration gas at a temperature of 60°C or higher and 120°C or lower into the regeneration zone 13 and desorbs carbon dioxide from the adsorption structure and separates the carbon dioxide, and a desiccant rotor 2 that is provided between the preheating section 120 and the regeneration section 130 and serves as water vapor transfer means that uses the difference in water vapor partial pressure between the preheating gas and the regeneration gas as a driving force to transfer water vapor from the preheating section to the regeneration section.

[0061] [Transportation means] The conveying means may be any means that circulates the adsorption structure by passing it through the three sections of the adsorption zone, preheating zone, and regeneration zone at a predetermined speed, and then passing it through the adsorption zone again. In this example, a motor attached to a honeycomb rotor, which is an adsorption structure, rotates the honeycomb rotor.

[0062] [Honeycomb rotor] The substrate of the honeycomb rotor 1 can be made of any material as long as it is sufficiently strong, resistant to deformation, and has a small specific heat capacity. However, corrugated honeycomb made from ceramic paper, activated carbon fiber paper, heat-resistant organic fiber paper, etc. is preferred. The honeycomb rotor 1 of this example uses a corrugated honeycomb as the substrate, and is configured so that the columns constituting the honeycomb structure are aligned approximately parallel to the rotation axis. In Figure 1, air is supplied to the honeycomb rotor 1 from one side of the columns, and preheating gas and regeneration gas are supplied from the other side. However, these supply directions may be the same or opposite. The honeycomb rotor 1 is supported rotatably around its axis and is configured to rotate at a constant speed in a predetermined direction (for example, the direction of the arrow in Figure 1) by a conveying means such as a motor. If you focus on a specific part of the honeycomb rotor 1, as it rotates, it moves sequentially through the adsorption zone 11, preheating zone 12, and regeneration zone 13, and returns to its original position after one rotation of the honeycomb rotor 1. The honeycomb rotor 1 contains an adsorbent capable of reversibly adsorbing and desorbing carbon dioxide.

[0063] [Flow path dividing means] The flow path dividing means can be formed, for example, by abutting a thin metal plate or the like extending radially from the rotation axis of the honeycomb rotor 1 against the honeycomb rotor 1 directly or via a flexible and slidable resin or the like. Each flow path is formed by dividing a roughly fan-shaped area consisting of two radially extending sides plus the outer periphery of the honeycomb.

[0064] [Air supply section] The air supply unit 110 is equipped with an air supply means (not shown) that supplies air containing carbon dioxide, with a relative humidity of 30% to 100% and a temperature of 0°C to 40°C, to the inlet side of the adsorption zone 11. Air with a reduced carbon dioxide concentration flows out from the outlet side of the adsorption zone 11. The air supply means can be any type of fan or blower, regardless of its configuration, as long as it can supply carbon dioxide-containing air to the adsorption zone 11 at atmospheric pressure and a temperature of 0°C to 40°C. However, since a large amount of air must be supplied, it is preferable to use a pressurized ventilation fan, as it requires less power and is economical.

[0065] [Preheating section] The preheating section 120 has a configuration in which a gas circulation path C1 passing through the preheating zone 12 is provided with preheating gas circulation means 121 (e.g., a blower) for circulating gas in the gas circulation path C1 and preheating heating means 122 (e.g., a heat exchanger) for heating the gas in the gas circulation path C1. The preheating section 120 is configured to send preheating gas at a temperature of 60°C to 120°C to the inlet side of the preheating zone 12 to heat the honeycomb rotor 1, and to heat the gas via the preheating gas circulation means 121 (e.g., a blower) and the preheating heating means 122 (e.g., a heat exchanger) before sending it to the inlet side of the preheating zone 12. In other words, the preheating section 120 is configured to be able to recycle the gas flowing out from the outlet side of the preheating zone 12.

[0066] [Playback Department] The regeneration unit 130 is configured to include a gas circulation path C2 passing through the regeneration zone 13, a regeneration gas circulation means 133 (e.g., a blower) for circulating gas through the gas circulation path C2, a carbon dioxide separation means 134 for separating carbon dioxide from the gas in the gas circulation path C2, and a regeneration heating means 135 (e.g., a heat exchanger) for heating the gas in the gas circulation path C2. The regeneration unit 130 is configured to feed a regeneration gas at a temperature of 60°C to 120°C into the inlet side of the regeneration zone 13, desorb carbon dioxide from the honeycomb rotor 1, and separate high-purity carbon dioxide from the carbon dioxide-enriched gas with an increased carbon dioxide concentration that flows out from the outlet side of the regeneration zone 13 in the carbon dioxide separation means 134. The remaining gas is then heated via the regeneration heating means 135 and sent to the inlet side of the regeneration zone 13. In other words, the regeneration unit 130 is configured to recycle the gas that flows out from the outlet side of the regeneration zone 13 as a regeneration gas.

[0067] Known carbon dioxide separation equipment can be used for the carbon dioxide separation means 134, for example, carbon dioxide separation equipment using an amine absorption method. Typically, the carbon dioxide-rich gas contains 2% to 10% carbon dioxide on a volume basis. In the carbon dioxide separation means 134, the carbon dioxide-rich gas is separated into a gas containing high-purity carbon dioxide of 99% or more on a volume basis, and a gas containing 0.2% to 1% carbon dioxide on a volume basis. The latter gas is heated by the regeneration heating means 135 and recycled for reuse. In a known amine absorption carbon dioxide separation system, the gas to be treated (carbon dioxide-rich gas in this example) is brought into contact with an aqueous amine solution to absorb the carbon dioxide contained in the gas to be treated into an amine absorbing solution. The absorbing solution is then heated to recover high concentrations of carbon dioxide. The temperature when the gas to be treated is brought into contact with the amine absorbing solution is typically 35°C to 50°C. Carbon dioxide separation systems that use a solid absorbing agent carrying amines instead of an absorbing solution are also known. However, the higher the temperature, the lower the carbon dioxide absorption efficiency. Therefore, the temperature when carbon dioxide is absorbed from the gas to be treated is typically 50°C or lower. Therefore, as long as known carbon dioxide separation systems are used, the water vapor partial pressure of the remaining gas (gas containing 0.2% to 1% carbon dioxide by volume) after recovering high-purity carbon dioxide from a carbon dioxide-rich gas (gas containing 2% to 10% carbon dioxide by volume) will not exceed the saturated water vapor pressure at 50°C. As mentioned above, in known carbon dioxide separation equipment, the higher the temperature, the lower the carbon dioxide absorption efficiency. Meanwhile, the temperature of the carbon dioxide-rich gas flowing out from the honeycomb rotor 1 is usually in the range of 60°C to 120°C. Therefore, the carbon dioxide-rich gas flowing out from the honeycomb rotor 1 is preferably first passed through a heat recovery heat exchanger 131 to recover heat, and then further cooled, if necessary, using a heat exchanger 132 with cooling water before being passed through a regeneration gas circulation means 133.

[0068] [Water vapor transfer means] The carbon dioxide recovery apparatus A of this example is equipped with a desiccant rotor 2 as a water vapor transfer means. The base material of the desiccant rotor 2 can be any material as long as it is sufficiently strong, resistant to deformation, and has a small specific heat capacity, but corrugated honeycomb made from ceramic paper, activated carbon fiber paper, heat-resistant organic fiber paper, or the like is preferred. The desiccant rotor 2 of this example uses a corrugated honeycomb as the base material and is configured so that the column direction of the columns that make up the honeycomb structure is approximately parallel to the rotation axis. The desiccant rotor 2 is rotatably supported around its axis, and is configured to rotate at a constant speed in a predetermined direction (for example, the direction of the arrow in FIG. 1). The temperatures of the preheating gas leaving the preheating means 122 and the regeneration gas leaving the regeneration heating means 135 are approximately the same, ranging from 60°C to 120°C. The water vapor partial pressure of the regeneration gas leaving the regeneration heating means 135 is lower than that of the preheating gas leaving the preheating heating means 122. Therefore, water vapor desorbs from the desiccant rotor 2 in the water desorption section 22, through which the heated regeneration gas passes before being sent to the regeneration zone in the regeneration step. Conversely, water vapor adsorbs to the desiccant rotor in the water adsorption section 21, through which the heated preheating gas passes before being sent to the preheating zone in the preheating step. Therefore, as the desiccant rotor 2 rotates, water vapor moves from the preheating section 120 to the regeneration section 130. Since the desorption of water vapor from the desiccant rotor is accompanied by endothermic heat and the adsorption of water vapor onto the desiccant rotor is accompanied by exothermic heat, some temperature change may occur in both the preheating gas and the regeneration gas before and after the desiccant rotor. If this becomes a problem, the heat capacity of the desiccant rotor may be made sufficiently large, or the temperature of the regeneration gas at the outlet of the regeneration heating means 135 may be made higher than the temperature of the preheating gas at the outlet of the preheating heating means 122.

[0069] [Another embodiment] [1] In the above example configuration, a desiccant rotor 2 is provided as the water vapor transfer means, but instead of the desiccant rotor 2, a water vapor selective permeation device 3 equipped with a water vapor selective permeation membrane 24 may be provided as the water vapor transfer means, as shown in Figure 2.

[0070] [2] In the above example, in the regeneration step, the carbon dioxide-enriched gas flowing out of the regeneration zone 13 is separated and recovered in the carbon dioxide separation means 134, and the remaining gas is heated by the regeneration heating means 135. Furthermore, the water vapor selective permeation device 3 simply transfers water vapor from the preheating section 120 before circulating it to the regeneration zone 13. However, as shown in Figure 3, the regeneration gas may be circulated to the regeneration zone 13 after steam is added by a steam addition device 4 that adds steam (water vapor) to the regeneration gas leaving the desiccant rotor 2 so that the relative humidity of the regeneration gas fed to the honeycomb rotor 1 in the regeneration step is higher than the relative humidity of the preheating gas fed to the honeycomb rotor 1 in the preheating step. When the water vapor concentration in the circulating gas is increased by the addition of steam, the adsorption of water vapor to the adsorbent in the regeneration zone 13 is facilitated. Since the adsorption of water vapor is accompanied by heat generation, it becomes easy to maintain a high temperature of the honeycomb rotor 1 in the regeneration zone 13, and it becomes easy to recover a highly concentrated carbon dioxide-rich gas from the regeneration zone 13.

[0071] [3] In the above example, one preheating zone 12 was provided. However, the preheating zone 12 may be divided into multiple zones, and the temperature of the gas fed into the zone may be changed. For example, a method may be adopted in which 60°C gas is fed into the first preheating zone and heated to about 55°C, and then 95°C gas is fed into the second preheating zone and heated to about 90°C. When waste heat is present in different temperature ranges, dividing the zones in this way may allow for more effective use of the waste heat. Note that when the preheating zone 12 is divided into multiple zones, the operation of transferring steam to the regeneration zone is performed between the preheating zone with the highest temperature.

[0072] [4] In the above example, the preheating zone 12 and the regeneration zone 13 are assumed to be in completely independent gas circulation paths, except for the transfer of water vapor by the water vapor transfer means. The pressure in each zone remains approximately atmospheric pressure even when operation reaches a steady state. However, the pressure in each zone may be slightly increased or decreased from atmospheric pressure due to heating, cooling, gas desorption, etc. If the pressure in each zone becomes significantly increased from atmospheric pressure, there is a risk of the circulating gas leaking into the atmosphere. If the pressure in each zone becomes significantly decreased from atmospheric pressure, there is a risk of the atmosphere leaking into the circulating gas. In this case, the gas circulation paths of each zone may be connected with very thin connecting pipes to equalize the pressure. Because the carbon dioxide concentration of the gas circulating through the preheating zone 12 is typically high, approximately 2% to 10%, it is recommended that the connecting pipe between the gas circulation path of the preheating zone 12 and the gas circulation path of the regeneration zone 13 be connected to the outlet side of the regeneration zone 13.

[0073] [5] In the above example, the process immediately returns to the air circulation process after the regeneration process is completed. However, this is not limited to this configuration, and a pre-cooling process may be provided between the regeneration process and the air circulation process. When the carbon dioxide recovery apparatus A has a pre-cooling process, a pre-cooling zone 14 is provided between the regeneration zone 13 and the adsorption zone 11 of the honeycomb rotor 1, and a pre-cooling gas of 0°C to 60°C is fed to cool the honeycomb to 60°C or below. The gas flowing out from the outlet side of the pre-cooling zone 14 is circulated after cooling and then fed again from the inlet side of the pre-cooling zone 14. In the pre-cooling process, a gas-liquid separation process may be performed to separate condensed water, if necessary, and heat may be recovered from the gas flowing out from the outlet side of the pre-cooling zone 14 and used for heating in the pre-heating process.

[0074] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, as long as no contradictions arise. Furthermore, the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited to these, and can be modified as appropriate within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

[0075] The present invention can be used as an apparatus and method for recovering low-concentration carbon dioxide contained in the atmosphere to obtain high-purity carbon dioxide. [Explanation of symbols]

[0076] 1: Honeycomb rotor 11: Adsorption zone 12: Preheating zone 13: Play Zone 120: Preheating section 121: Preheating gas circulation means 122: Preheating means 130: Playback section 131: Regeneration gas cooling means (heat recovery heat exchanger) 132: Regeneration gas cooling means (heat exchanger using cooling water) 133: Regenerative gas circulation means 134: Carbon dioxide separation means 135:Heating means for regeneration 2: Desiccant rotor (means of transporting water vapor) 21: Water adsorption part 22:Water desorption part 3: Water vapor selective permeation device (water vapor transfer means) 24: Selective water vapor permeable membrane

Claims

1. an adsorption structure containing an adsorbent capable of reversibly adsorbing and desorbing carbon dioxide; an air supplying step of feeding air containing carbon dioxide and having a relative humidity of 30% to 100% and a temperature of 0°C to 40°C into the adsorptive structure to cause the adsorptive structure to adsorb carbon dioxide, and then discharging the air with a reduced carbon dioxide concentration from the adsorptive structure; a preheating step of feeding a preheating gas at 60°C or higher and 120°C or lower into the adsorptive structure after the air supply step, and heating and circulating the preheating gas flowing out of the adsorptive structure to preheat the adsorptive structure to 60°C or higher and 120°C or lower; a regeneration step of feeding a regeneration gas at 60°C or higher and 120°C or lower into the adsorption structure that has completed the preheating step, desorbing carbon dioxide from the adsorption structure, separating carbon dioxide from the carbon dioxide-enriched gas that has flowed out of the adsorption structure and has an increased carbon dioxide concentration, and heating the gas from which the carbon dioxide has been separated to regenerate the adsorption structure while circulating and reusing it as the regeneration gas, and repeating these steps in this order; and

2. 2. The carbon dioxide recovery method according to claim 1, wherein the operation of transferring the water vapor is carried out using a water vapor selective permeable membrane.

3. 2. The carbon dioxide recovery method according to claim 1, wherein the operation of transferring the water vapor is carried out using a water vapor adsorbent that selectively adsorbs water vapor.

4. 2. The carbon dioxide recovery method according to claim 1, wherein the operation of transferring the water vapor is carried out using a desiccant rotor containing a water vapor adsorbent that selectively adsorbs water vapor.

5. 5. The carbon dioxide recovery method according to claim 1, wherein further water vapor is added from outside to the regeneration gas after the operation of transferring the water vapor has been performed.

6. an adsorption structure containing an adsorbent capable of reversibly adsorbing and desorbing carbon dioxide; a conveying means for passing the adsorption structure through at least three zones, i.e., an adsorption zone, a preheating zone, and a regeneration zone, which are divided by a flow path dividing means; an air supply unit having air feeding means for feeding air containing carbon dioxide, having a relative humidity of 30% to 100% and a temperature of 0°C to 40°C, into the inlet side of the adsorption zone, causing the carbon dioxide to be adsorbed by the adsorption structure passing through the adsorption zone, and discharging the air with a reduced carbon dioxide concentration from the outlet side; a preheating section having a preheating means and a preheating gas circulation means for supplying a preheating gas at 60°C or more and 120°C or less into an inlet side of the preheating zone to heat the adsorption structure and for circulating and utilizing the gas flowing out from an outlet side of the preheating zone; a regeneration section including a carbon dioxide separation means, a regeneration heating means, and a regeneration gas circulation means for supplying a regeneration gas at 60°C or higher and 120°C or lower to an inlet side of the regeneration zone, desorbing carbon dioxide from the adsorption structure, and separating and recycling carbon dioxide from a carbon dioxide-enriched gas with an increased carbon dioxide concentration that flows out from an outlet side of the regeneration zone; and a water vapor transfer means for transferring water vapor from the preheating gas to the regeneration gas using a difference in water vapor partial pressure between the preheating gas after heating and sent to the preheating zone in the preheating section and the regeneration gas after heating and sent to the regeneration zone in the regeneration section as a driving force.

7. 7. The carbon dioxide recovery device according to claim 6, wherein the water vapor transfer means is configured using a water vapor selective permeable membrane.

8. 7. The carbon dioxide recovery system according to claim 6, wherein the water vapor transfer means is constructed using a water vapor adsorbent that selectively adsorbs water vapor.

9. 7. The carbon dioxide recovery system according to claim 6, wherein the water vapor transfer means is configured using a desiccant rotor containing a water vapor adsorbent that selectively adsorbs water vapor.

10. The carbon dioxide recovery apparatus according to any one of claims 6 to 9, wherein a steam addition means is provided on a path from the steam transfer means to an inlet of the regeneration zone in the regeneration section.

11. 11. The carbon dioxide recovery apparatus according to claim 10, wherein the adsorption structure is a honeycomb rotor, and the transport means rotates the honeycomb rotor to pass the adsorption zone, the preheating zone, and the regeneration zone in sequence.

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