Carbon dioxide capture device and carbon dioxide capture method

Abstract

To provide a carbon dioxide recovery device which recovers low-concentration carbon dioxide contained in ambient air and can obtain high-purity carbon dioxide in an economically advantageous method.SOLUTION: A carbon dioxide recovery device comprises an adsorption rotor 1 which contains an adsorbent that can reversibly adsorb and desorb carbon dioxide, and to which air containing carbon dioxide is supplied; a regenerative gas supply part 2 which supplies a regenerative gas of 60C or more and 120°C or less to the adsorption rotor 1; and a carbon dioxide recovery part 3 which separates carbon dioxide from the regenerative gas passed through the adsorption rotor 1 by amine absorption method and recovers the same, and is so configured that the regenerative gas, from which carbon dioxide has been separated by the carbon dioxide recovery part 3, is fed into the regenerative gas supply part 2 and is recycled. Further, the carbon dioxide recovery device comprises, in a regenerative gas circulation path, an oxygen removal part 4 for reducing concentration of oxygen contained in the regenerative gas.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 suppress the release of carbon dioxide into the atmosphere from the combustion of fossil fuels. On the other hand, since there are applications in which the use of fossil fuels is technically or economically unavoidable, there are growing expectations for direct air capture technology that captures carbon dioxide from the atmosphere.

[0003] Carbon dioxide can be converted into hydrocarbons such as methane by reacting 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 captured from the atmosphere, the resulting hydrocarbons, even if burned, will not increase the carbon dioxide concentration in the atmosphere throughout the entire process from fuel production to use, making them carbon-neutral.

[0004] Technologies for recovering carbon dioxide from flue gas are known. An amine absorption carbon dioxide removal system, 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 aqueous amine 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 a carbon dioxide recovery system from flue gas from a coal-fired power plant (Non-Patent Document 1).

[0005] The amine absorption method is advantageous when using the captured carbon dioxide as a raw material for fuel, etc., because it can capture high-purity (e.g., 99.5% or more) carbon dioxide. On the other hand, when capturing carbon dioxide from combustion exhaust gas in an amine aqueous solution, the carbon dioxide molecules pass through the gas-liquid interface, and it is necessary to promote gas-liquid contact in order to capture carbon dioxide efficiently. Therefore, a method is generally adopted in which an amine aqueous solution is allowed to flow down from the top of a packed tower filled with packing to increase the contact area, and the combustion exhaust gas is passed from the bottom to the top to cause countercurrent contact, but 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 compared to combustion exhaust gas (usually about 4% to 13%) is 100 to 300 times greater, 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 Documents 2 and 3). When a carbon dioxide adsorbent in which such a solid adsorbent is supported on a honeycomb-shaped carrier is used, a large amount of gas can be treated in a short time while suppressing pressure loss. The solid adsorbent adsorbs carbon dioxide at low temperatures and desorbs carbon dioxide at high temperatures, so that when air containing carbon dioxide is circulated at low temperatures, carbon dioxide is adsorbed by the solid adsorbent, and when high-temperature regeneration gas is circulated through the solid adsorbent, carbon dioxide is desorbed, resulting in a gas with an increased carbon dioxide concentration.

[0008] A carbon dioxide concentrating device is also known in which a honeycomb-shaped carrier is formed into a disk-shaped honeycomb rotor, and the rotation of the rotor repeatedly moves between the adsorption section and the regeneration section, thereby enabling continuous adsorption of carbon dioxide contained in the atmosphere and regeneration using a regeneration gas (Patent Document 1).

[0009] Known solid carbon dioxide adsorbents include adsorbents in which a porous carrier such as silica or activated carbon is supported with a large molecular weight amine, for example, polyethyleneimine, or weakly basic anion exchange resins, and these solid adsorbents are capable of adsorbing even dilute carbon dioxide in the atmosphere. However, it is usually impossible to recover high-purity carbon dioxide from these adsorbents at normal pressure and at temperatures lower than about 120°C. This is for the following reasons.

[0010] If the site of the solid adsorbent that adsorbs carbon dioxide is designated as A, the adsorption of carbon dioxide is expressed by the following chemical reaction formula. A+CO2→ A·CO2(1)

[0011] If the equilibrium pressure of CO2 at 25°C is 10 Pa (corresponding to 100 ppm in the atmosphere) and the equilibrium pressure of CO2 at 125°C is 100 kPa (corresponding to 100% in the atmosphere), the Gibbs energy change of reaction (1) is -22.8 kJ / mol at 25°C and 0 kJ / mol at 125°C. In a narrow temperature range, the enthalpy change and entropy change of reaction (1) can be considered constant unless there is a phase change. Therefore, by solving the simultaneous linear equations consisting of the Gibbs energy changes at 25°C and 125°C, the enthalpy change and entropy change of reaction (1) are calculated as enthalpy change ΔH = -90.9 kJ / mol and entropy change ΔS = -228.3 J / (mol·K).

[0012] Regarding the adsorption reaction (1), if there exists an adsorbent A that exhibits the above-mentioned enthalpy change and entropy change, it is possible to adsorb CO2 from the atmosphere at 25°C, reduce the carbon dioxide concentration to 100 ppm, and recover normal pressure carbon dioxide by heating to 125°C. However, the standard entropy of CO2 (gas) at 25°C is 213.6 J / (mol·K), and if the entropy reduction due to the adsorption reaction (1) is 228.3 J / (mol·K), then the adsorption reaction (1) will cause a reduction in entropy that exceeds the standard entropy of CO2 (gas) at 25°C. The reduction in entropy due to the adsorption of gas molecules is due to the freezing of the translational motion of the gas molecules, and is generally about 50% to 70% of the standard entropy. A reduction in entropy that exceeds the standard entropy of the adsorbed molecules due to adsorption does not occur in normal adsorption phenomena. If a temperature higher than 125°C, for example 200°C, is used as the desorption temperature, it is possible to adsorb carbon dioxide in the atmosphere at 25°C and reduce it to 100 ppm, and to recover carbon dioxide at 100 kPa at 200°C, but in addition to requiring a higher temperature heat source for regeneration, there is a problem that thermal degradation of the solid adsorbent progresses. In particular, amine-based adsorbents and ion exchange resins are prone to thermal degradation in an atmosphere containing oxygen at high temperatures.

[0013] Patent Document 2 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.

[0014] Specifically, a method using a unit comprising an adsorptive structure with an adsorbent, the unit being evacuable to a vacuum pressure of up to 400 mbar abs, the adsorptive structure being heatable to a temperature of at least 80° C. for desorbing at least gaseous carbon dioxide, the unit being capable of passing a gas mixture through it 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 0.8-1.1 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 20-400 mbar abs and heating the adsorbent in the unit to a temperature in the range of 80-130°C, extracting at least the desorbed gaseous carbon dioxide from the unit and separating the gaseous carbon dioxide from the water by condensation in or downstream of the unit; (c) forcibly cooling the adsorbent at the pressure of step (b) to a temperature equal to or greater than 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 contact 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 steam injected during the entire step (b) to gaseous carbon dioxide released during the entire step (b) is less than 40:1.

[0015] In the method of this document, the adsorbent that has adsorbed carbon dioxide is heated to a temperature range of 80°C to 130°C, and the pressure is reduced to 20-400 mbar abs (approximately 0.02 atm to 0.4 atm), and superheated steam is allowed to coexist to lower the partial pressure of carbon dioxide, thereby desorbing carbon dioxide. In addition, the oxygen concentration is reduced by decompression and evacuation, so that thermal deterioration of the adsorbent in the desorption process can also be suppressed.

[0016] However, in order to perform carbon dioxide desorption by using superheated steam in combination, a large amount of steam is required, which increases the amount of energy required for carbon dioxide capture.

[0017] A method has been proposed in which desorption is performed at 90°C and 30 mbar while heating with an electric heater (Non-Patent Document 4), but this requires high equipment costs for the vacuum pump, and there is also the problem of a large amount of power consumption due to a large decrease in the efficiency of the vacuum pump in areas with a high degree of vacuum.

[0018] In addition, when carbon dioxide is desorbed by reducing 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 captured carbon dioxide will decrease due to air leakage.

[0019] In summary, the reality is that a carbon dioxide recovery apparatus and method for recovering low-concentration carbon dioxide contained in the atmosphere to obtain high-purity carbon dioxide have not yet been established. [Prior art documents] [Patent documents]

[0020] [Patent Document 1] JP 2017-154063 A [Patent Document 2] Patent No. 6622302 [Non-patent literature]

[0021] [Non-Patent Document 1] Nakagami, Energy and Resources, Vol. 40, No. 3, pp. 193-196 (2019) [Non-Patent Document 2] C.W.Jones et al., Chemical Reviews, Vol. 116, pp. 11840-11876 (2016) [Non-Patent Document 3] Yogo, Zeolite, Vol. 37, No. 2, pp. 47-58 (2020) [Non-Patent Document 4] Japan Science and Technology Agency, Center for Low Carbon Society Strategy, Cost and Evaluation of Direct Air Capture (DAC) Method for Carbon Dioxide (Vol. 2) (2021) Summary of the Invention [Problem to be solved by the invention]

[0022] In view of the above problems, the problem that the present invention aims to solve is to provide an economically excellent carbon dioxide recovery device and carbon dioxide recovery method for recovering low concentration carbon dioxide contained in the atmosphere and obtaining high-purity carbon dioxide. [Means for solving the problem]

[0023] In order to solve the above problems, the present invention provides 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 for supplying a regeneration gas having a temperature of 60° C. or higher and 120° C. or lower to the adsorption rotor; 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; 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. The carbon dioxide recovery device further includes an oxygen removal unit for reducing the concentration of oxygen contained in the regeneration gas, the oxygen removal unit being provided in a circulation path of the regeneration gas.

[0024] 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, so that it is possible to recover high-purity carbon dioxide while efficiently treating a large amount of air. In addition, since the oxygen concentration in the regeneration gas is kept lower than the oxygen concentration in the air, thermal deterioration of the adsorbent can be suppressed even when the temperature of the regeneration gas is high.

[0025] Furthermore, in the above invention, if the oxygen removal section comprises a hydrogen addition means for adding hydrogen to the regeneration gas, and an oxidation catalyst for catalytically oxidizing the hydrogen added by the hydrogen addition means through a reaction with oxygen contained in the regeneration gas, the concentration of oxygen contained in the adsorption rotor regeneration gas can be easily reduced with simple equipment.

[0026] Furthermore, in the above invention, if the adsorption rotor is configured to be installed under atmospheric pressure, the adsorption and desorption of carbon dioxide by the adsorption rotor can be performed under atmospheric pressure, which is more economical than the case where it is performed under reduced pressure.

[0027] In order to solve the above problems, the present invention provides a method for producing a liquid crystal display comprising: an adsorption step of contacting air containing carbon dioxide with an adsorption rotor containing an adsorbent capable of reversibly adsorbing and desorbing carbon dioxide at a temperature of 0°C or higher and 40°C or lower to adsorb the carbon dioxide contained in the air onto the adsorption rotor; a regeneration step of passing a regeneration gas at 60°C to 120°C through the adsorption rotor having adsorbed carbon dioxide, and recovering the regeneration gas containing 2% to 10% carbon dioxide by volume; a regeneration gas recovery step of contacting the regeneration gas recovered in the regeneration step with an aqueous amine solution to absorb carbon dioxide into the aqueous amine solution and recovering the regeneration gas containing 0.2% to 1% carbon dioxide on a volume basis; and a carbon dioxide recovery step of heating the amine aqueous solution having absorbed carbon dioxide to 100° C. or more and 150° C. or less to recover a gas containing 99% or more of carbon dioxide on a volumetric basis after dehydration, The present invention also provides a carbon dioxide recovery method in which the regeneration gas recovered in the regeneration gas recovery step is heated to 60° C. or higher and 120° C. or lower, and at least a portion of the oxygen is removed from the gas, followed by recycling the gas as the regeneration gas.

[0028] According to this method, 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 to 2% to 10% by volume, and then the carbon dioxide is recovered in a carbon dioxide recovery section that uses an amine absorption method, so that it is possible to recover high-purity carbon dioxide containing 99% or more carbon dioxide by volume after dehydration while efficiently treating a large amount of air. In addition, because the oxygen concentration in the regeneration gas is kept lower than that in the air, thermal deterioration of the adsorbent can be suppressed even when the temperature of the regeneration gas is high.

[0029] In the above invention, oxygen can be removed from the regeneration gas by adding hydrogen to the regeneration gas, bringing the gas into contact with an oxidation catalyst, and reacting the hydrogen with the oxygen contained in the regeneration gas to convert it into water vapor. This makes it possible to easily reduce the concentration of oxygen contained in the adsorption rotor regeneration gas.

[0030] In the above invention, if the adsorption step and the regeneration step are performed under atmospheric pressure, the adsorption and desorption of carbon dioxide by the adsorption rotor can be performed under atmospheric pressure, which is more economical than performing the adsorption and desorption under reduced pressure. Effect of the Invention

[0031] According to the above-mentioned 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 description of the drawings]

[0032] [Figure 1] FIG. 1 is a diagram showing a configuration of a carbon dioxide capture device according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Hereinafter, embodiments of a carbon dioxide capture device and a carbon dioxide capture method according to the present invention will be described.

[0034] [Outline of carbon dioxide capture device] As shown in FIG. 1, the carbon dioxide capture device of this example contains an adsorbent capable of reversibly adsorbing and desorbing carbon dioxide, and is equipped with an adsorption rotor 1 to which air containing carbon dioxide is supplied, a regeneration gas supply unit 2 that supplies a regeneration gas at 60°C or higher and 120°C or lower to the adsorption rotor 1, and a carbon dioxide capture unit 3 that separates and captures carbon dioxide from the regeneration gas that has passed through the adsorption rotor 1 by an amine absorption method, and is configured so that the regeneration gas from which carbon dioxide has been separated in the carbon dioxide capture unit 3 is sent to the regeneration gas supply unit 2 and recycled, and is equipped with an oxygen removal unit 4 in the circulation path of the regeneration gas for reducing the concentration of oxygen contained in the regeneration gas.

[0035] [Adsorption rotor] The adsorption rotor 1 is supported rotatably around the axis and is configured to rotate at a constant speed in a predetermined direction (for example, the direction of the arrow X in FIG. 1). The adsorption rotor 1 is installed under atmospheric pressure. In the adsorption rotor 1, air containing carbon dioxide is supplied at a treatment position 1a, and the portion to which the air is supplied moves to a regeneration position 1b, to which a regeneration gas described later is supplied, by the rotation of the adsorption rotor 1. The base material of the adsorption rotor 1 may be any material as long as it has sufficient strength, is not easily deformed, and has a small specific heat capacity, but corrugated honeycomb made of ceramic paper, activated carbon fiber paper, heat-resistant organic fiber paper, etc. is preferable. The adsorption rotor 1 of this example adopts a corrugated honeycomb as the base material, and is configured so that the column direction of the columnar body constituting the honeycomb structure is approximately parallel to the rotation axis. In FIG. 1, air is supplied to the adsorption rotor 1 from one side of the column direction, and regeneration gas is supplied from the other side. The supply direction of the air and the supply direction of the regeneration gas may be the same.

[0036] The adsorbent capable of reversibly adsorbing and desorbing carbon dioxide may be any material capable of adsorbing carbon dioxide in the air when it is brought into contact with the air 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 K or Na are impregnated or supported on activated carbon, silica, alumina, or the like.

[0037] By bringing air containing carbon dioxide into contact with the adsorption rotor 1 at atmospheric pressure and at a temperature of 0° C. or higher and 40° C. or lower, the carbon dioxide contained in the air can be adsorbed (adsorption step).

[0038] [Regeneration gas supply section] The regeneration gas supplying section 2 heats the regeneration gas to 60°C or higher and 120°C or lower and supplies it to a portion of the adsorption rotor 1 located at the regeneration position 1b (hereinafter also referred to as the "regeneration portion of the adsorption rotor 1"), and is composed of a blower 21 and multiple heat exchangers 22, 23, and 24. In addition, in the regeneration gas supplying section 2, the regeneration gas supplied to the regeneration portion of the adsorption rotor 1 is supplied to an absorption tower 31 of the carbon dioxide capture section 3 described below, and then recovered, and is sent again to the regeneration portion of the adsorption rotor 1. In other words, the regeneration gas supplying section 2 has a circulation path that enables the cyclical use of the regeneration gas.

[0039] The regeneration gas supply section 2 shown in FIG. 1 includes, as a plurality of heat exchangers, a heat exchanger 22 that heats the regeneration gas to be fed to the regeneration portion of the adsorption rotor 1 with steam, a heat exchanger 23 that preheats the regeneration gas before being fed to the heat exchanger 22 with the regeneration gas that has passed through the regeneration portion of the adsorption rotor 1, and a heat exchanger 24 that cools the regeneration gas that has passed through the adsorption rotor 1 and the heat exchanger 23 with cooling water before being fed to the absorption tower 31 of the carbon dioxide capture section 3 described later. In this way, by providing a plurality of heat exchangers 22, 23, and 24, it is possible to reduce energy consumption. For example, since the temperature of the regeneration gas at the outlet of the adsorption rotor 1 (the regeneration gas that has passed through the regeneration portion of the adsorption rotor 1) is usually 60° C. or higher, the energy required for heating the regeneration gas in the heat exchanger 22 can be reduced by exchanging heat with the regeneration gas that has left the absorption tower 31 of the carbon dioxide capture section 3 described later and has not yet been fed to the heat exchanger 22.

[0040] By supplying a regeneration gas to the regeneration point of the adsorption rotor 1 by this regeneration gas supply unit 2, the carbon dioxide adsorbed in the adsorption rotor 1 is desorbed from the adsorbent and recovered in the regeneration gas, thereby regenerating the adsorption rotor 1. The lower the concentration of carbon dioxide contained in the regeneration gas, the more efficiently the adsorption rotor 1 can be regenerated; however, since the carbon dioxide removal rate in the carbon dioxide recovery unit 3, which utilizes the amine absorption method described below, is usually in the range of about 80% to 95%, the regeneration gas usually contains 0.2% to 1% carbon dioxide on a volume basis.

[0041] The higher the temperature of the regeneration gas fed to the adsorption rotor 1, the shorter the time required to regenerate the adsorption rotor 1 and the higher the concentration of carbon dioxide captured in the regeneration gas. However, the higher the temperature, the more likely it is that the thermal degradation of the adsorbent will progress. Therefore, the heating temperature of the regeneration gas must be 60°C or higher and 120°C or lower, and is more preferably in the range of 75°C to 105°C.

[0042] The regeneration gas that has passed through the adsorption rotor 1 contains carbon dioxide desorbed from the adsorption rotor 1, and therefore contains 2% to 10% carbon dioxide on a volume basis.

[0043] According to this regeneration gas supply section 2, a regeneration gas containing 2% to 10% carbon dioxide by volume can be recovered by passing a regeneration gas at 60°C or higher and 120°C or lower through the adsorption rotor 1 that has adsorbed carbon dioxide under atmospheric pressure (regeneration process).

[0044] [Carbon Dioxide Recovery Section] The carbon dioxide recovery section 3 separates carbon dioxide from the regeneration gas, which has passed through the regeneration point of the adsorption rotor 1 and contains 2% to 10% carbon dioxide by volume, by utilizing an amine absorption method to obtain gas containing a high concentration of carbon dioxide, as well as gas containing 0.2% to 1% carbon dioxide by volume.

[0045] The carbon dioxide recovery section 3 can employ a carbon dioxide recovery method that utilizes a known amine absorption method, and for example, as shown in FIG. 1, is composed of an absorption tower 31, a regeneration tower 32, a gas-liquid separator 33, a circulation pump 34, and multiple heat exchangers 35, 36, 37, and 38.

[0046] In this carbon dioxide recovery section 3, an aqueous amine solution is caused to flow down from the top of the absorption tower 31, which is packed with a packing material to increase the geometric surface area, and at the same time, the gas to be treated, in this case a regeneration gas that has passed through the regeneration section of the adsorption rotor 1 and contains 2% to 10% carbon dioxide on a volumetric basis, is fed in from the bottom of the absorption tower 31, and the aqueous amine solution and the gas to be treated are brought into countercurrent contact, and the carbon dioxide contained in the gas to be treated is recovered in the aqueous amine solution.

[0047] The amine aqueous solution having absorbed carbon dioxide is sent to the regeneration tower 32, heated to 100°C to 150°C by heat exchange using low-pressure steam or the like as a hot heat source in the heat exchanger 36, releases the absorbed carbon dioxide, and is cooled by heat exchange using the amine aqueous solution sent from the absorption tower 31 as a cold heat source in the heat exchanger 35 and heat exchange using cooling water as a cold heat source in the heat exchanger 37, and is returned to the absorption tower 31. The carbon dioxide released from the amine aqueous solution in the regeneration tower 32 is cooled together with the water vapor in the regeneration tower 32 by heat exchange using cooling water as a cold heat source in the heat exchanger 38, sent to the gas-liquid separator 33, and separated from water in the gas-liquid separator 33 and recovered. The carbon dioxide thus recovered is usually 99% or more, and preferably has a purity of 99.5% or more.

[0048] Amines that can be used in the aqueous amine solution include monoethanolamine (MEA), methyldiethanolamine (MDEA), and 2-ethylaminoethanol (EAE). By appropriately selecting the heating temperature in the regeneration tower 32 and the flow rate of the aqueous amine solution, carbon dioxide can be removed from the regeneration gas containing 2% to 10% carbon dioxide by volume, to obtain a gas containing 0.2% to 1% carbon dioxide by volume.

[0049] According to the carbon dioxide recovery section 3, the regeneration gas recovered in the regeneration step (the regeneration gas containing 2% to 10% carbon dioxide by volume) is brought into contact with an aqueous amine solution to absorb carbon dioxide into the aqueous amine solution, and a regeneration gas containing 0.2% to 1% carbon dioxide by volume can be recovered (regeneration gas recovery step). In addition, the aqueous amine solution that has absorbed carbon dioxide can be heated to 100°C to 150°C to recover a gas containing 99% or more carbon dioxide by volume after dehydration (carbon dioxide recovery step).

[0050] [Oxygen removal section] The oxygen remover 4 reduces the concentration of oxygen contained in the regenerating gas within the circulation path of the regenerating gas.

[0051] Using nitrogen instead of air as the regeneration gas not only suppresses thermal deterioration of the adsorbent when carbon dioxide is desorbed from the adsorption rotor 1 (when the adsorption rotor 1 is regenerated), but also reduces the amount of oxygen dissolved in the aqueous amine solution in the carbon dioxide capture section 3, thereby suppressing deterioration of the aqueous amine solution and reducing operating costs. However, in a carbon dioxide capture method that uses the adsorption rotor 1 to perform adsorption and regeneration continuously, it is difficult to completely eliminate air leaking in from gaps in the adsorption rotor 1, and even if nitrogen is filled and operation is started, it is unavoidable that it will be gradually replaced by air.

[0052] Therefore, in the present invention, an oxygen removal section 4 for reducing the concentration of oxygen contained in the regeneration gas is provided in the circulation path of the regeneration gas, so that the oxygen concentration of the regeneration gas is kept constant at a level sufficiently lower than that of air.

[0053] It is known that the reaction between hydrogen and oxygen starts near room temperature when an oxidation catalyst carrying a precious metal such as Pt is used, and proceeds at a sufficient rate at 60°C or higher. For example, as shown in FIG. 1, if hydrogen is added from a hydrogen supply unit 41 (hydrogen addition means) to the regeneration gas returned from the carbon dioxide capture unit 3 and sent again to the regeneration point of the adsorption rotor 1, and the gas is heated to 60°C or higher before passing through an oxidation catalyst 42 housed in a container, the added hydrogen can react with the oxygen contained in the regeneration gas to convert it into water vapor. Therefore, the oxygen concentration in the regeneration gas can be reduced, and the regeneration gas can be further heated by the heat of combustion of hydrogen.

[0054] The oxidation catalyst is preferably Pt supported on an inorganic oxide carrier such as alumina, titania, or zirconia, and Pd or Rh may be added as a promoter if necessary. The shape of the oxidation catalyst is not important, but the use of a honeycomb catalyst in which catalytic components are coated on a honeycomb carrier made of cordierite or stainless steel foil is advantageous because of the small pressure loss.

[0055] The amount of hydrogen added can be set appropriately taking into consideration the amount of air leaking into the circulation path, but is usually set to about 0.05 to 0.3% by volume relative to the regeneration gas.

[0056] [Another embodiment] [1] In the above example, in order to reduce energy consumption, a heat exchanger is used to perform heat exchange as appropriate, but this is not limited to this and may be a configuration in which heat exchange is not performed.

[0057] [2] In the above example, the oxygen removal unit 4 is configured to include the hydrogen supply unit 41 and the oxidation catalyst 42. However, this is not limited to this, and any configuration may be used as long as it can reduce the oxygen concentration contained in the regeneration gas.

[0058] [3] In the above example, the adsorption rotor 1 is installed under atmospheric pressure, and the adsorption of carbon dioxide contained in the air by the adsorption rotor 1 (adsorption process) and the regeneration of the adsorption rotor 1 by desorption of carbon dioxide from the adsorption rotor 1 (regeneration process) are performed under atmospheric pressure, but this is not limiting. The adsorption rotor 1 does not necessarily have to be installed under atmospheric pressure, and the adsorption rotor 1 may be housed in a container that allows for reduced pressure within an economical range, in which case the adsorption process and regeneration process may be performed under reduced pressure within an economical range.

[0059] 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, provided that no contradiction arises. Furthermore, the embodiments disclosed in this specification are merely examples, and the embodiments of the present invention are not limited thereto, and can be appropriately modified within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

[0060] INDUSTRIAL APPLICABILITY The present invention can be used as an apparatus and method for recovering low-concentration carbon dioxide contained in the atmosphere and obtaining high-purity carbon dioxide. [Explanation of symbols]

[0061] 1: Adsorption rotor 2: Regeneration gas supply section 21: Blower 22,23,24: Heat exchanger 3: Carbon dioxide capture section 31: Absorption tower 32: Regeneration Tower 33: Gas-liquid separator 34: Circulation pump 35,36,37,38: Heat exchanger 4: Oxygen removal section 41: Hydrogen supply unit (hydrogen addition means)

Claims

1. 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 for supplying a regeneration gas having a temperature of 60° C. or higher and 120° C. or lower to the adsorption rotor; 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; 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. The carbon dioxide recovery apparatus further comprises an oxygen removal unit in a circulation path of the regeneration gas for reducing the concentration of oxygen contained in the regeneration gas.

2. 2. The carbon dioxide recovery apparatus according to claim 1, wherein the oxygen removal section comprises a hydrogen addition means for adding hydrogen to the regeneration gas, and an oxidation catalyst for catalytically oxidizing the hydrogen added by the hydrogen addition means through a reaction with oxygen contained in the regeneration gas.

3. The carbon dioxide recovery apparatus according to claim 1 or 2, wherein the adsorption rotor is installed under atmospheric pressure.

4. an adsorption step of contacting air containing carbon dioxide with an adsorption rotor containing an adsorbent capable of reversibly adsorbing and desorbing carbon dioxide at a temperature of 0° C. or higher and 40° C. or lower to adsorb the carbon dioxide contained in the air onto the adsorption rotor; a regeneration step of passing a regeneration gas at 60° C. or higher and 120° C. or lower through the adsorption rotor having adsorbed carbon dioxide, and recovering the regeneration gas containing 2% to 10% carbon dioxide by volume; a regeneration gas recovery step of contacting the regeneration gas recovered in the regeneration step with an aqueous amine solution to absorb carbon dioxide into the aqueous amine solution and recovering the regeneration gas containing 0.2% to 1% carbon dioxide on a volume basis; a carbon dioxide recovery step of heating the aqueous amine solution having absorbed carbon dioxide to 100° C. or more and 150° C. or less to recover a gas containing 99% or more of carbon dioxide on a volume basis after dehydration, A carbon dioxide recovery method comprising heating the regeneration gas recovered in the regeneration gas recovery step to 60° C. or higher and 120° C. or lower, removing at least a portion of the oxygen, and recycling the gas as the regeneration gas.

5. 5. The carbon dioxide recovery method according to claim 4, wherein the removal of oxygen from the regeneration gas is carried out by adding hydrogen to the regeneration gas, bringing the gas into contact with an oxidation catalyst, and reacting the hydrogen with the oxygen contained in the regeneration gas to convert it into water vapor.

6. The method for recovering carbon dioxide according to claim 4 or 5, wherein the adsorption step and the regeneration step are carried out under atmospheric pressure.

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