Method for recovering carbon dioxide and carbon dioxide recovering system

Abstract

[Problem] To provide a process capable of separating and recovering carbon dioxide from a large amount of combustion exhaust gas in a manner that is space-saving and energy-saving. [Solution] Provided is a method for recovering carbon dioxide comprising: an absorption step in which a combustion exhaust gas including carbon dioxide is passed through a radial flow-type separation device provided with an absorbent material so that the absorbent material absorbs the carbon dioxide; and a release step in which steam is passed through the separation device to release the carbon dioxide from the absorbent material.

Description

Carbon dioxide recovery method and carbon dioxide recovery system

[0001] The present invention relates to a method for separating and recovering carbon dioxide from a gas containing carbon dioxide, and a carbon dioxide recovery system.

[0002] The problem of global warming due to rising atmospheric carbon dioxide concentrations has long been recognized. Reducing atmospheric carbon dioxide emissions has become an urgent priority. Along with automobile exhaust, two major sources of carbon dioxide emissions are waste incinerators and combustion exhaust gases from thermal power plants. Thermal power plants typically generate electricity by burning fossil fuels such as coal, oil, and natural gas to heat water in a boiler, producing high-temperature, high-pressure steam. This steam is then used to drive a steam turbine, which then rotates a generator directly connected to the turbine shaft. Recently, gas turbine power generation, which uses natural gas as fuel instead of a steam turbine, and combined-cycle power generation, which uses residual heat from the gas turbine's combustion exhaust gas to generate steam, have also been commercialized. These efforts have significantly improved the thermal efficiency and reduced the cost of thermal power generation. Furthermore, air pollution prevention technologies, such as dust removal, desulfurization, and denitrification, have already reached a significant level for treating combustion exhaust gases from these power plants. However, while there has been active research into reducing carbon dioxide emissions into the atmosphere, as mentioned above, from the perspective of switching from fossil fuels to renewable energy, there has not yet been sufficient research into post-combustion capture (PCC) of carbon dioxide from combustion exhaust gases.

[0003] In addition, recently, there has been a growing demand not only for the capture of carbon dioxide from combustion exhaust gas, but also for the utilization and storage (CCUS) of the captured carbon dioxide, and a technology has already been put into practical use in which carbon dioxide is separated and captured using an amine absorbent from the combustion exhaust gas of a coal-fired boiler, which has a carbon dioxide concentration of 13 to 14% by volume. However, the wet carbon dioxide absorption process using an amine absorbent has drawbacks in terms of the cost of renewable energy. Therefore, solid absorbents that can reduce the renewable energy required have been developed as carbon dioxide absorbents to replace aqueous amine solutions, and carbon dioxide separation and capture processes using these have been investigated. Non-Patent Documents 1 and 2 disclose technologies for capturing carbon dioxide using a fixed-bed reactor that uses a solid absorbent.

[0004] Japanese Patent Application Publication No. 11-147017

[0005] Chemical Engineering Journal 307 (2017) 273-282Ind. Eng. Chem. Res. 2021, 60,9906-9914

[0006] Carbon dioxide separation and capture processes that have been studied to date have primarily aimed to separate and capture the carbon dioxide (concentration of 13-14% by volume) contained in the flue gas from coal-fired boilers. In contrast, flue gas from oil-fired boilers has a carbon dioxide concentration of less than 10% by volume, and flue gas from natural gas-fired boilers and gas turbines has a carbon dioxide concentration of less than 6% by volume (usually 3-4% by volume). These have lower carbon dioxide concentrations than flue gas from coal-fired boilers, about one-half to one-quarter of the concentration. While this in itself contributes to reducing carbon dioxide emissions, capturing carbon dioxide from flue gas with such low carbon dioxide concentrations requires processing large amounts of flue gas.

[0007] The carbon dioxide separation and capture process using a fixed-bed reactor with a solid absorbent, as disclosed in Non-Patent Documents 1 and 2, is an excellent method in itself with low renewable energy costs. However, when this process is added to an existing thermal power plant (including gas turbine power generation and combined cycle power generation) fueled by oil or natural gas, for example, it is necessary to increase the space for the fixed-bed reactor to process large amounts of gas, and to increase the flow rate of the combustion exhaust gas in the fixed-bed reactor. As a result, the operating cost per unit of carbon dioxide captured increases. Furthermore, there may be limited space, making it difficult to install a new carbon dioxide separation and capture plant of the scale required to process all of the combustion exhaust gas. Furthermore, there is a limit to the increase in the flow rate of the combustion exhaust gas in the fixed-bed reactor. The present invention has been made in consideration of the above problems. Specifically, the present invention aims to solve the problem of providing a process that can separate and capture carbon dioxide from large amounts of combustion exhaust gas in a space-saving and energy-saving manner.

[0008] A carbon dioxide recovery method according to one embodiment of the present invention is characterized by comprising an absorption step of passing a combustion exhaust gas containing carbon dioxide through a radial flow type separation device equipped with an absorbent material to cause the carbon dioxide to be absorbed by the absorbent material, and a release step of passing steam through the separation device to cause the carbon dioxide to be released from the absorbent material.

[0009] Furthermore, a carbon dioxide capture system according to another aspect of the present invention is characterized by comprising a radial flow type separation device equipped with an absorbent material, a first conduit for guiding combustion exhaust gas containing carbon dioxide to the separation device, and a second conduit for guiding steam to the separation device.

[0010] A process is provided that can separate and capture carbon dioxide from large amounts of combustion exhaust gas in a space-saving and energy-saving manner.

[0011] It is a cross-sectional view showing an example of a radial flow type separation device that can be preferably used in the method according to the present invention. It is a conceptual diagram showing an example of a process for separating and capturing carbon dioxide from combustion exhaust gas by applying the method according to the present invention. It is a schematic diagram for explaining an example of the configuration of a carbon dioxide separation and capture plant that implements the method according to the present invention.

[0012] The method according to the present invention is a method for separating and recovering carbon dioxide from a gas mixture containing carbon dioxide, particularly from combustion exhaust gas under atmospheric pressure. The method according to the present invention is a space-saving and energy-saving method particularly suited to separating and recovering carbon dioxide from combustion exhaust gas from a gas turbine in a gas turbine power plant or combined cycle power plant fueled by natural gas, and has the advantage that it is relatively easy to install a plant for separating and recovering carbon dioxide from combustion exhaust gas, for example, as an addition to an existing power plant.

[0013] In the method according to the present invention, SA-VSA (Steam Assisted Vacuum Swing Adsorption) using an absorbent is used to separate and capture carbon dioxide from a gas mixture containing carbon dioxide, particularly from a combustion exhaust gas under atmospheric pressure. ２ To recover carbon dioxide from a gas mixture with a low carbon dioxide concentration (CO 2 concentration of 10% by volume or more), an amine absorption method using an aqueous monoethanolamine solution or the like as an absorption liquid is usually used. ２ concentration is less than 10% by volume), for example, combustion exhaust gas (CO ２ In particular, when recovering carbon dioxide from solid waste (concentration less than 6% by volume), the amine absorption method requires the use of an amine that binds carbon dioxide more firmly, which increases the cost required for heating during regeneration and the cost for replenishing and replacing degraded amines. For this reason, it is preferable to use a solid absorbent material as the absorbent, which has the advantage of being superior in carbon dioxide absorption and release characteristics (especially release characteristics) and, because it does not contain water, there is no need to include the latent heat of vaporization of water in the heating energy during regeneration.

[0014] Suitable solid absorbents for this purpose include granular inorganic porous carriers, such as porous silica, prepared by supporting a polyamine compound. Granular porous silica can be obtained, for example, by adding a pore-expanding agent such as trimethylbenzene to an acetic acid-acidic aqueous solution of a hydrophilic polymer (e.g., Sigma-Aldrich P-123) and thoroughly mixing it. Then, an aqueous sodium silicate solution is added and gently mixed at room temperature for 24 hours. The mixture is then allowed to stand at 100°C for 24 hours, filtered, washed, and the resulting solid is dried at 80°C for 2 days. The resulting dried solid is then calcined in air at 550°C for 4 hours, and the resulting powder is granulated to a particle size of approximately 2 mm. The resulting granular porous silica is dispersed in, for example, methanol, and an appropriate polyamine compound (e.g., tetraethylenepentamine with protected functional groups) is added to the dispersion to impregnate the porous silica with the polyamine compound. The resulting mixture is then dried, yielding a granular porous silica supported with the polyamine compound (see Non-Patent Document 1).

[0015] Carbon dioxide separation and recovery using SA-VSA is performed by alternately repeating an absorption process in which a carbon dioxide-containing gas to be treated is brought into contact with an absorbent material under normal pressure to absorb and capture the carbon dioxide contained in the gas, and a release process in which the absorbent material, which has absorbed carbon dioxide, is brought into contact with low-temperature steam under reduced pressure to release the carbon dioxide. In SA-VSA, the absorbent material is placed under normal pressure during the absorption operation and under reduced pressure during the release operation, so these operations are performed in an airtight container. The gas-solid contact operation between the gas to be treated and the solid absorbent material in the absorption process can be performed using various types of systems, such as a packed bed, moving bed, or fluidized bed. However, if the carbon dioxide concentration in the gas to be treated is low and it is desired to achieve almost zero carbon dioxide leakage into the gas after treatment, a packed bed system with high contact efficiency and minimal channeling is preferred. On the other hand, the gas-solid contact operation between steam and the solid absorbent in the release process is performed using the same packed bed system as the absorption process, because the steam flow rate is significantly slower than the flow rate of the gas to be treated, and therefore a moving bed or fluidized bed system cannot be used.

[0016] The method according to the present invention is characterized by its ability to treat a large amount of gas to be treated in the absorption step. When the space velocity GHSV of the gas to be treated in the absorption step is set to about 2,000 to 6,000 / h, the aspect ratio of the packed bed ([layer thickness] / [cross-sectional area of ​​flow path]) is set to about 1,500 mm (average superficial column reference linear velocity of about 0.5 m / s) in order to reduce the pressure loss associated with the energy required to pressurize the gas to be treated, which is at atmospheric pressure, using a blower or the like. １／２) must be significantly reduced. However, increasing the cross-sectional area of ​​the flow path (i.e., the cross-sectional area of ​​the bed) to reduce the aspect ratio of the packed bed may result in a too large installation area (footprint) for a conventional packed bed in which the treated gas flows vertically. This is not a problem if space for installing a carbon dioxide capture system can be secured from the start on a large site, but when a carbon dioxide capture system is retrofitted to an existing power plant, there is often limited installation space. In such cases, if the packed bed is designed so that gas passes horizontally (horizontal flow type), the cross-sectional area of ​​the flow path can be expanded vertically without expanding the installation area. Typical horizontal flow packed bed types are the leaf (flat) type (parallel flow type) and the tubular type (radial flow type). The leaf (flat) type refers to a type in which the packed bed is arranged as an upright hollow flat plate, and the fluid passes horizontally and parallel through the packed bed. On the other hand, a radial flow type refers to a type in which a packed bed is arranged in an upright cylindrical tube, and a fluid passes through the packed bed horizontally and radially from the inside to the outside or from the outside to the inside of the tube. In either type, multiple packed beds can be arranged in a single large airtight container, or a single packed bed can be arranged in a single airtight container. When arranging a single packed bed in a single airtight container, the most compact and space-saving method is to house a radial flow type packed bed in a cylindrical airtight container. Furthermore, since the packed bed in the radial flow type is arranged in a tubular shape, it has the advantage of having higher pressure resistance than a leaf (flat) type in which the packed bed is arranged in a flat plate shape. In the present invention, from the perspective of strength when treating a large amount of gas to be treated at high speed by vacuuming, the packed bed of the absorbent material is preferably a radial flow type. It is preferable that the layer thickness of the packed bed be as thin as possible, specifically, 3,000 mm or less, in order to suppress pressure loss.

[0017] On the other hand, the release step according to the present invention is characterized by being able to minimize steam consumption. To release carbon dioxide from the absorbent that absorbed carbon dioxide in the absorption step, a vessel containing a packed bed is evacuated to reduce the total pressure to less than 1 atmosphere, and steam is simultaneously introduced and passed through the packed bed. Using a horizontal-flow packed bed allows carbon dioxide to be absorbed while suppressing pressure loss, but if drift occurs within the airtight vessel, pressure loss increases. Therefore, it is desirable to suppress drift as much as possible. In the release step, it is preferable to minimize steam consumption as much as possible from the perspective of reducing energy costs. However, if the volumetric flow rate of steam is reduced for this purpose, drift is likely to occur within the airtight vessel. Therefore, in order to increase the volumetric flow rate and suppress drift, it is necessary to introduce steam under reduced pressure. In SA-VSA, the primary operation in the release step is essentially reducing the pressure by evacuating, with the introduction of steam being merely a secondary operation. The technical significance of introducing steam is that when carbon dioxide absorbed in the absorbent is released due to reduced pressure, the latent heat of release is lost from the absorbent, and this is compensated for by the sensible heat and latent heat of condensation of the steam. In other words, introducing steam in the release process is thought to have the effect of preventing excessive cooling of the absorbent and maintaining a constant temperature when carbon dioxide is simultaneously released from the absorbent due to reduced pressure in VSA (vacuum swing adsorption), thereby maintaining continuous release and promoting release. In particular, when a horizontal flow-type packed bed is used, the structure of the equipment makes it difficult to indirectly heat the packed bed in the airtight container, so direct heating using the sensible heat of steam is important. From this perspective, it is preferable that at least a portion of the introduced steam condenses within the packed bed and transfers its latent heat of condensation to the packed bed. During the release process, the atmosphere surrounding the packed bed is reduced in pressure below 1 atmosphere, and if the temperature of the introduced steam is 100°C or higher, the steam will not condense within the packed bed until the temperature drops below the dew point (less than 100°C) under the reduced pressure conditions. Therefore, it is preferable that the temperature of the introduced steam be less than 100°C. This "steam below 100°C" is called "low-temperature steam."In practice, the total pressure in the release step is preferably reduced to 10 to 45 kPaA (the last "A" means absolute pressure) by a steam total pressure control mechanism, and the temperature of the steam introduced is more preferably less than 80°C. The mass of carbon dioxide contained in the steam after passing through the separation device is defined as t. ＣＯ２ The mass of water contained in the steam after passing through the separation device is t Ｈ２Ｏ From the viewpoint of efficient operation energy, the release process is Ｈ２Ｏ / t ＣＯ２ It is preferable that the method further includes controlling the amount of steam supplied to the separation device by the steam amount control mechanism so that the ratio of the steam amount to the steam amount is within a range of 0.5 to 1.8, for example.

[0018] Figure 1 is a cross-sectional schematic diagram showing an example of a radial flow separation apparatus preferably used in the method of the present invention. Figure 1(a) shows a vertical cross-section of the apparatus, and Figure 1(b) shows a horizontal cross-section of the apparatus taken along line A-A' in Figure 1(a). The separation apparatus 1 of Figure 1 comprises a vertical cylindrical shell container 10, a cylindrical inner pipe 11, and a cylindrical outer basket 12 arranged coaxially therein, and an absorbent material packed between them forms a tubular packed bed 13 extending vertically (referred to as the first direction). Inside the packed bed 13 (inside the cylindrical inner pipe 11) is a cylindrical central space 14 that serves as a first flow path. Outside the packed bed 13 (outside the cylindrical outer basket 12), there is a tubular peripheral space 15 that serves as a second flow path between the packed bed 13 and the inner wall of the shell container 10. The central space (first flow path) 14 and the peripheral space (second flow path) 15 have a first gas inlet / outlet 16 and a second gas inlet / outlet 17 at their lower ends, respectively, and the cylindrical inner pipe 11 and the cylindrical outer basket 12 are each configured to be gas permeable, and the cylindrical central space (first flow path) 14 and the cylindrical peripheral space (second flow path) 15 are configured to sandwich the packed bed 13 via the cylindrical inner pipe 11 and the cylindrical outer basket 12, thereby forming a gas flow path from the first gas inlet / outlet 16 via the central space (first flow path) 14, the packed bed 13, and the peripheral space (second flow path) 15 to the second gas inlet / outlet 17, or a gas flow path from the second gas inlet / outlet 17 via the peripheral space (second flow path) 15, the packed bed 13, and the central space (first flow path) 14 to the first gas inlet / outlet 16. The gas to be treated may flow in from the first gas inlet / outlet 16 and out from the second gas inlet 17, or may flow in the opposite direction. Furthermore, as will be described in detail later, when releasing the carbon dioxide absorbed in the absorbent (i.e., regenerating the absorbent), a method of introducing steam in the same direction as the flow of the gas to be treated (cocurrent regeneration method) can be used, or a method of introducing steam in the opposite direction to the flow of the gas to be treated (countercurrent regeneration method) can be used. Depending on the direction of flow of the gas to be treated in the absorption step and the direction of flow of steam in the release step, conduits (not shown) for leading out the combustion exhaust gas that leads the carbon dioxide are switchably connected to the first gas inlet / outlet 16 and the second gas inlet / outlet 17.The second conduit is also connected to a steam amount control mechanism (not shown) that controls the amount of steam supplied to the separation device.

[0019] When the gas to be treated is introduced through the first gas inlet / outlet 16, the gas introduced through the first conduit flows upward through the central space (first flow path) 14, gradually penetrating the packed bed 13 and absorbing carbon dioxide while passing through the peripheral space (second flow path) 15, and then flows downward through the peripheral space (second flow path) 15, and the treated gas is discharged through the second gas inlet 17. Here, in the first flow path (central space), the upward speed decreases as the treated gas gradually escapes, but the pressure remains approximately constant from bottom to top (because there are no areas along the way that cause pressure loss). Similarly, in the second flow path (peripheral space), the downward speed increases as the treated gas gradually adds, but the pressure remains approximately constant from top to bottom. Therefore, the pressure difference between the first flow path (central space) 14 and the second flow path (peripheral space) 15 is approximately uniform from the bottom to the top of the packed bed 13, and the flow rate passing through the packed bed 13 is approximately uniform from the bottom to the top. When the gas to be treated is introduced through the second gas inlet / outlet 17, the gas flow direction is reversed, but the gas flow velocity and pressure are the same as when the gas to be treated is introduced through the first gas inlet / outlet 16. However, if the difference in the cross-sectional areas (flow path cross-sectional areas) of the first flow path (central space) 14 and the second flow path (peripheral space) 15 in the direction perpendicular to the first direction becomes large, the flow velocity ascending through the first flow path (central space) 14 and the flow velocity descending through the second flow path (peripheral space) 15 will differ significantly. Therefore, even if the pressure difference on both sides of the packed bed is uniform from the bottom to the top, it is thought that uneven flow will be more likely to occur. For this reason, it is preferable that the ratio of the horizontal cross-sectional area of ​​the central space (first flow path) 14 to the cross-sectional area of ​​the peripheral space (second flow path) 15 in a direction perpendicular to the first direction is approximately 1, specifically, 0.8 or more and 1.25 or less.

[0020] 1, the first gas inlet / outlet 16 and the second gas inlet / outlet 17 are provided at the bottom of the first flow path 14 and the second flow path 15, respectively, but both may be provided at the top, or one may be provided at the top and the other at the bottom. When both are provided at the top, the only difference is that the piping for the gas to be treated and the piping for the treated gas are at the top rather than the bottom, and the same can be said about the gas flow within the apparatus when both are provided at the bottom. However, if one is provided at the top and the other at the bottom, the flow direction in the first flow path and the flow direction in the second flow path will be the same, and the way in which the flow velocity ascending or descending through the first flow path changes vertically will be opposite to the way in which the flow velocity ascending or descending through the second flow path changes vertically (gradually slowing down on the inlet side and gradually increasing on the outlet side). Therefore, even if the horizontal cross-sectional areas of the central space and the peripheral space are made approximately equal, the flow velocities on both sides of the packed bed cannot be made approximately equal throughout the entire length from the bottom to the top. Therefore, it is thought that flow bias is likely to occur regardless of the ratio of the horizontal cross-sectional areas of the central space and the peripheral space. For these reasons, it is preferable to provide the first gas inlet / outlet and the second gas inlet / outlet at the ends on the same side of the first and second flow paths.

[0021] The absorbent that absorbed carbon dioxide in the absorption step is regenerated by releasing the absorbed carbon dioxide in the subsequent release step, and is then used again to absorb carbon dioxide in the next absorption step. In the release step, the entire space within the shell vessel 1, including the packed bed and the first and second flow paths, is depressurized by a vacuum pump serving as a steam total pressure control mechanism. The vacuum pump is connected to either the first or second gas inlet / outlet to perform evacuation. Meanwhile, steam is introduced from the gas inlet / outlet not connected to the vacuum pump and flows through the same flow path as the gas to be treated. As mentioned above, if the flow direction of the gas to be treated in the absorption step and the flow direction of the steam in the release step are the same, this is called cocurrent release (cocurrent regeneration), and if they are opposite, this is called countercurrent release (countercurrent regeneration). Countercurrent regeneration is preferable in the release step because countercurrent regeneration is superior to cocurrent regeneration in terms of release efficiency and purity of the released carbon dioxide. Although the mass flow rate of steam in the release step is much smaller than the mass flow rate of the gas to be treated in the absorption step, the total pressure, including the steam, in the shell vessel is preferably reduced to 10 to 45 kPaA (approximately 0.1 to 0.45 atm) in the release step, so the volumetric flow rate is not so small, and it is considered that the flow rate changes in the first and second flow paths are similar to those in the absorption step. However, since the total pressure is lower in the release step, it is considered that drift is more likely to occur in the release step than in the absorption step. Therefore, it is preferable to provide the first gas inlet / outlet and the second gas inlet / outlet at the same end of the first and second flow paths, even more so than in the absorption step. That is, in the present invention, the separation device preferably has a gas inlet for introducing combustion exhaust gas or steam and a gas outlet for discharging combustion exhaust gas or steam at the same end of the first and second flow paths extending in the first direction.

[0022] 2 is a conceptual diagram showing an example of the case where carbon dioxide is separated and captured from combustion exhaust gas of a power plant by applying the method according to the present invention. The combustion exhaust gas from the power plant is discharged into the atmosphere from a chimney, but at least a portion of it is extracted from a flue and guided by a flue gas blower (booster) 100 to a carbon dioxide separation and capture plant (PCC plant) 200 which implements the method according to the present invention, where the carbon dioxide contained in the combustion exhaust gas is separated and captured and then returned to the flue. The regenerating steam used in the carbon dioxide separation and capture plant (PCC plant) 200 may be supplied from a steam supply facility of a thermal power plant equipped with the power plant in order to reduce construction costs and operation costs. The captured carbon dioxide is CO ２ It is compressed by compressor 300 and then stored or put to useful use.

[0023] Figure 3 is a schematic diagram illustrating an example of the configuration of a carbon dioxide separation and capture system (PCC plant) 200 for implementing the method of the present invention, including the separation device 1 (1A, 1B) that forms the core of the PCC plant 200 and its associated equipment. In Figure 3, two separation towers 1A and 1B are used, and the system is programmed so that one tower is in the absorption process while the other is in the release process, thereby enabling continuous carbon dioxide separation and capture by alternating between the absorption and release processes. However, three or more separation towers may also be used, and some of the towers may be programmed so that the other towers are in the release process and the absorption process, allowing continuous carbon dioxide separation and capture by rotating these towers. The combustion exhaust gas extracted from the flue is pressurized by a flue gas blower (booster) 100 and enters a scrubber unit 400, where it is cleaned with wash water before being introduced into the separation tower 1A, which is in the absorption process. The gas, after passing through a packed bed of absorbent to capture carbon dioxide, is returned to the flue. 3 omits the flow of combustion exhaust gas in separation tower 1A, and does not specifically show that combustion exhaust gas flows in from the top of the separation device and flows out from the bottom. Meanwhile, it shows that low-temperature, low-pressure steam is introduced into separation device 1B in the release step, the pressure inside separation device 1B is reduced to release carbon dioxide, and the released carbon dioxide is extracted from the separation device together with the steam, after which the steam accompanying the carbon dioxide flow is separated as drain, and the remaining carbon dioxide is recovered. At least a portion of the low-temperature, low-pressure steam introduced into separation device 1B may be supplied from a thermal power plant.

[0024] 1 Separation device 1A First separation device 1B Second separation device 10 Outer shell vessel 11 Inner cylindrical pipe 12 Outer cylindrical basket 13 Packed bed 14 Central space (first flow path) 15 Peripheral space (second flow path) 16 First gas inlet / outlet 17 Second gas inlet / outlet 100 Flue gas blower (booster) 200 Carbon dioxide separation and capture plant 300 CO ２ Compressor 400 Scrubber Unit

Claims

1. A method for recovering carbon dioxide, comprising: an absorption step of passing a combustion exhaust gas containing carbon dioxide through a radial flow type separation device equipped with an absorbent material to absorb the carbon dioxide into the absorbent material; and a release step of passing steam through the separation device to release the carbon dioxide from the absorbent material.

2. A method for recovering carbon dioxide as described in claim 1, wherein the concentration of carbon dioxide in the combustion exhaust gas is 10 volume % or less.

3. A method for recovering carbon dioxide as described in claim 1, wherein the separation device has a first flow path through which the combustion exhaust gas or the steam flows before passing through the absorbent material, and a second flow path through which the combustion exhaust gas or the steam flows after passing through the absorbent material, both of the first flow path and the second flow path extending in a first direction, and the separation device has a gas inlet section for introducing the combustion exhaust gas or the steam and a gas outlet section for discharging the combustion exhaust gas or the steam, at ends on the same side of the first flow path and the second flow path extending in the first direction.

4. The method for recovering carbon dioxide described in claim 1, wherein the separation device has a first flow path through which the combustion exhaust gas or the steam flows before passing through the absorbent material, and a second flow path through which the combustion exhaust gas or the steam flows after passing through the absorbent material, the first flow path and the second flow path both extend in a first direction, and a ratio of a cross-sectional area of ​​the second flow path in a direction perpendicular to the first direction to a cross-sectional area of ​​the first flow path in a direction perpendicular to the first direction is 0.8 or more and 1.25 or less.

5. The mass of carbon dioxide contained in the steam after passing through the separation device is t ＣＯ２ The mass of water contained in the steam after passing through the separation device is t Ｈ２Ｏ When the release step is performed, t Ｈ２Ｏ / t ＣＯ２ The method for recovering carbon dioxide according to claim 1 , further comprising controlling the ratio of the β-amino acid to the β-amino acid so as to be within a range of 0.5 to 1.

8.

6. A method for recovering carbon dioxide as described in claim 1, wherein the release step includes controlling the total pressure of the steam supplied to the separation device to be 10 kPaA or more and 45 kPaA or less.

7. A carbon dioxide capture system comprising a radial flow type separator having an absorbent material, a first conduit for conducting flue gas containing carbon dioxide to said separator, and a second conduit for conducting steam to said separator.

8. A carbon dioxide capture system as described in claim 7, wherein a flow path through which the combustion exhaust gas guided from the first conduit or the steam guided from the second conduit flows within the separation device extends in a first direction, and the separation device has a gas inlet for introducing the combustion exhaust gas or the steam and a gas outlet for discharging the combustion exhaust gas or the steam, at an end on the same side in the first direction.

9. The carbon dioxide capture system described in claim 7, wherein the separation device has a first flow path through which the combustion exhaust gas or the steam flows before passing through the absorbent material, and a second flow path through which the combustion exhaust gas or the steam flows after passing through the absorbent material, the first flow path and the second flow path both extend in a first direction, and a ratio of a cross-sectional area of ​​the second flow path in a direction perpendicular to the first direction to a cross-sectional area of ​​the first flow path in a direction perpendicular to the first direction is 0.8 or more and 1.25 or less.

10. The carbon dioxide capture system according to claim 7, further comprising a steam amount control mechanism for controlling the amount of steam supplied to the separation device.

11. The carbon dioxide capture system according to claim 7, further comprising a steam total pressure control mechanism for controlling the total pressure of the steam supplied to the separation device.

Images