JP7515151B2 - Carbon dioxide recovery device and carbon dioxide recovery method - Google Patents

Description

This disclosure relates to a carbon dioxide capture device and a carbon dioxide capture method.

Apparatuses that separate carbon dioxide from gases that contain carbon dioxide are known (for example, Patent Documents 1 to 3). Patent Document 1 discloses a gas separation apparatus that separates carbon dioxide and water vapor from a mixed gas containing carbon dioxide and water vapor as main component gases. Patent Document 2 discloses a gas recovery apparatus that individually separates carbon dioxide and an inert gas from a mixed gas containing carbon dioxide and an inert gas as main components. Patent Document 3 discloses a gas separation system that includes a carbon dioxide separation membrane that separates carbon dioxide and a water vapor removal means that removes water vapor in the gas from which carbon dioxide has been separated.

International Publication No. 2012/086836 International Publication No. 2017/086293 JP 2017-221864 A

The present disclosure provides a carbon dioxide recovery device and a carbon dioxide recovery method that can easily recover gas in which the ratio of carbon dioxide to impurity gases has increased.

The carbon dioxide recovery device according to one aspect of the present disclosure includes a first processing unit arranged to separate a first supply space from a first processing space, and having a first separation unit that separates carbon dioxide contained in a raw gas supplied to the first supply space from impurity gases containing components other than carbon dioxide in the raw gas by either adsorption, absorption or permeation, and extracts at least a portion of the carbon dioxide contained in the raw gas and releases a first processing gas from the first processing space having a higher ratio of carbon dioxide to impurity gases than the raw gas, and a second processing unit arranged to separate a second supply space to which the first processing gas released by the first processing unit is supplied and the second processing space, and having a second separation unit that reduces water vapor contained in the first processing gas by either adsorption, absorption or permeation, and removes at least a portion of the water vapor contained in the first processing gas and releases a second processing gas having a higher carbon dioxide purity than the first processing gas. The second processing unit further has a regeneration gas supply unit that supplies a regeneration gas having a water vapor pressure lower than that of the first processing gas to the second processing space.

In this carbon dioxide recovery device, the first treatment gas in which the ratio of carbon dioxide contained in the raw gas to the impurity gas has increased is sent from the first treatment device to the second supply space of the second treatment device. In the second treatment device, a regeneration gas with a lower water vapor pressure than the first treatment gas is supplied to the second treatment space separated from the second supply space by the second separation device. As a result, the water vapor pressure of the second treatment gas is reduced while the water vapor is removed from the first treatment gas by the second separation device. The load of the device for sucking the second treatment gas from which at least a portion of the water vapor has been removed depends on the amount of water vapor contained in the second treatment gas. In the above recovery device, since the water vapor pressure of the second treatment gas is reduced, the required performance of the device for sucking the second treatment gas can be reduced. Therefore, it is possible to easily recover a gas in which the ratio of carbon dioxide contained in the raw gas to the impurity gas has increased.

The first processing unit may further include a water vapor supply unit that supplies a water vapor-containing gas containing water vapor to the first processing space. The first separation unit may include a separation membrane that selectively permeates carbon dioxide contained in the raw material gas. In this case, the water vapor-containing gas promotes the permeation of carbon dioxide through the separation membrane of the first separation unit. This makes it possible to efficiently separate carbon dioxide from the raw material gas.

The first processing section may further include a water vapor supply section that supplies a water vapor-containing gas containing water vapor to the first supply space. The first separation section may include a material that selectively adsorbs or absorbs carbon dioxide contained in the raw material gas. In this case, the water vapor-containing gas promotes the release of carbon dioxide stored in the material of the first separation section. This makes it possible to efficiently separate carbon dioxide from the raw material gas.

The temperature of the regeneration gas may be lower than the temperature of the water vapor-containing gas. In this case, the temperature of the second treatment gas is lowered to the same level as the temperature of the regeneration gas. This allows the performance requirements of the device for sucking in the second treatment gas to be further reduced, making it possible to more easily recover gas with an increased ratio of carbon dioxide to impurity gases.

The regeneration gas may be air. In this case, it is easy to supply the regeneration gas to the second treatment space.

The water vapor pressure of the second process gas may be lower than the saturated water vapor pressure of the second process gas. In this case, it is possible to reduce the performance requirements of the device for sucking the second process gas, compared to when the second process gas contains water vapor at the saturated water vapor pressure.

The recovery device may further include a suction section that sucks the gas in the first processing space. In this configuration, the water vapor pressure of the second processing gas is lowered in the second processing section, so the performance requirements of the suction section can be lowered compared to when the water vapor pressure is not lowered. This makes it possible to simplify the suction section.

The second separation section may include a separation membrane that selectively allows water vapor contained in the first process gas to pass through. In this case, it becomes possible to easily remove water vapor from within the first process gas.

A method for recovering carbon dioxide according to another aspect of the present disclosure includes a first step of extracting at least a portion of the carbon dioxide contained in the raw gas using a first separation section that separates the carbon dioxide contained in the raw gas from impurity gases containing components other than carbon dioxide in the raw gas by either adsorption, absorption, or permeation, thereby generating a first treated gas having a higher ratio of carbon dioxide to impurity gases than the raw gas, and a second step of removing at least a portion of the water vapor contained in the first treated gas using a second separation section that reduces the water vapor contained in the first treated gas by either adsorption, absorption, or permeation, thereby generating a second treated gas having a higher carbon dioxide purity than the first treated gas. In the second step, the second treated gas is generated by further using a regeneration gas having a water vapor pressure lower than that of the first treated gas.

In this carbon dioxide recovery method, a first separation section is used to generate a first treatment gas in which the ratio of carbon dioxide contained in the raw gas to the impurity gas is increased. Then, a second separation section that reduces the water vapor contained in the first treatment gas and a regeneration gas having a lower water vapor pressure than the first treatment gas are used to generate a second treatment gas. By using a regeneration gas with a lower water vapor pressure, the water vapor pressure of the second treatment gas can be reduced while removing water vapor from the first treatment gas by the second separation section. The load of the device for sucking the second treatment gas from which at least a portion of the water vapor has been removed depends on the amount of water vapor contained in the second treatment gas. In the above recovery method, the water vapor pressure of the second treatment gas can be reduced, and therefore the required performance of the device for sucking the second treatment gas can be reduced. Therefore, it is possible to easily recover a gas in which the ratio of carbon dioxide contained in the raw gas to the impurity gas is increased.

The present disclosure provides a carbon dioxide recovery device and a carbon dioxide recovery method that can easily recover gas in which the ratio of carbon dioxide to impurity gases has increased.

FIG. 1 is a schematic diagram showing an example of a carbon dioxide capture device. FIG. 2 is a schematic diagram showing another example of a carbon dioxide capture device. FIG. 3 is a schematic diagram showing another example of a carbon dioxide capture device. FIG. 4 is a schematic diagram showing another example of a carbon dioxide capture device. Fig. 5(a) is a diagram showing the flow of a carbon dioxide separation process that is the subject of calculation in the embodiment, and Fig. 5(b) is a table showing the prerequisites for calculation in the embodiment. Fig. 6(a) is a graph showing the pressure and temperature of the gas on the supply side and the process side in the module and the calculation results, and Fig. 6(b) is a table showing the comparison results of the water vapor concentration between the flash method and the membrane separation method.

One embodiment will be described below with reference to the drawings. In the description, identical elements or elements having the same functions are given the same reference numerals, and duplicate descriptions will be omitted.

[Carbon dioxide capture device]
FIG. 1 is a schematic diagram showing an example of a carbon dioxide capture device. The carbon dioxide capture device 1 shown in FIG. 1 is a device that captures carbon dioxide from a gas containing carbon dioxide. Specifically, the capture device 1 separates carbon dioxide contained in a gas supplied (hereinafter referred to as "raw material gas G0") to generate a gas having a higher carbon dioxide purity (concentration) than the raw material gas G0. As the raw material gas G0, for example, exhaust gas discharged after burning fuel in a factory, an agricultural heater, an engine such as an automobile, a gas heat pump, a boiler, a combustion-type water heater, or a power plant, indoor or outdoor air, or a fossil fuel reformed with water vapor is used.

Such a source gas contains carbon dioxide and an impurity gas containing components other than carbon dioxide. The impurity gas contains, for example, nitrogen, oxygen, or hydrogen. Alternatively, the source gas may contain the above-mentioned impurity gas in addition to carbon dioxide and water vapor. In the following, an example will be described in which the source gas contains carbon dioxide and water vapor, and an impurity gas containing components other than carbon dioxide and water vapor, and the components contained in the impurity gas are referred to as "impurity gas components."

When using combustion exhaust gas as the raw gas G0, the concentration of carbon dioxide contained in the raw gas (carbon dioxide in the raw gas) may be less than 40%. As an example, the concentration of carbon dioxide in the combustion exhaust gas may be 3% to 30%, 4% to 25%, or 5% to 20%. The concentration of carbon dioxide contained in the gas obtained by separating carbon dioxide using the recovery device 1 (hereinafter referred to as "separated gas Gc") may be, for example, 40% or more. As an example, the concentration of carbon dioxide in the separated gas Gc may be 60% or more, 70% or more, or 80% or more. In this disclosure, the concentration of carbon dioxide is a volume-based concentration under standard conditions (0°C, 1 atm). The recovery device 1 includes, for example, a first processing unit 10, a second processing unit 30, and an suction unit 50.

The first processing unit 10 extracts at least a portion of the carbon dioxide in the raw gas G0 to generate a first processing gas G1 having a higher ratio of carbon dioxide to impurity gases than the raw gas G0. That is, the ratio of carbon dioxide to impurity gases in the first processing gas G1 is higher than the ratio of carbon dioxide to impurity gases in the raw gas G0. The first processing unit 10 releases the generated first processing gas G1 toward the second processing unit 30. The first processing unit 10 has, for example, a first separation module 12 and a raw gas supply unit 22.

The first separation module 12 separates the carbon dioxide contained in the raw material gas G0 from the impurity gas contained in the raw material gas G0. The first separation module 12 includes, for example, a housing 14 and a first separation section 16. The housing 14 houses the first separation section 16 and forms an internal space. The first separation section 16 is a member that separates the carbon dioxide contained in the raw material gas G0 from the impurity gas by either adsorption, absorption, or permeation. The first separation section 16 is arranged to divide the internal space in the housing 14 into two spaces. Hereinafter, the space to which the raw material gas G0 is supplied of the pair of spaces separated by the first separation section 16 is referred to as the "supply space Vs1", and the other space is referred to as the "processing space Vd1". That is, the first separation section 16 is arranged to separate the supply space Vs1 (first supply space) and the processing space Vd1 (first processing space).

The first separation section 16 may include a separation membrane 18 that selectively allows carbon dioxide in the raw gas G0 to pass through. In the present disclosure, selectively allowing one component to pass through means allowing a portion of the gas to pass through such that the amount of the one component among the various components contained in the supplied gas is greater than the amount of the impurity gas components. The separation membrane 18 is a membrane that has a property that allows carbon dioxide, one of the various components contained in the raw gas G0, to pass through more easily than the impurity gas components. As the separation membrane 18, a membrane that has a property that allows carbon dioxide and water vapor, one of the various components contained in the raw gas G0, to pass through more easily than the impurity gas components (e.g., nitrogen, oxygen, and hydrogen, etc.) may be used. The separation membrane 18 may be made of an alkaline material.

The separation membrane 18 includes, for example, a monolayer membrane including gelling polymer particles having a basic functional group. The gelling polymer particles are polymer particles that have the property of swelling in water or a polar solvent to become gel-like fine particles. The gelling polymer particles may be, for example, particles of a neutral, alkaline, or acidic polymer compound impregnated with basic molecules. The thickness of the monolayer membrane including the gelling polymer particles may be less than 50 μm. The functional group included in the gelling polymer particles may be one or more functional groups selected from the group consisting of an amino group, an ammonium group, a carboxylic acid, and a sulfuric acid. The polymer compound constituting the gelling polymer particles may be a polymer of a monomer component including a monomer having a basic functional group or an acidic functional group. The basic molecule to be impregnated may include an amine-containing compound having a molecular weight of 61 to 10,000, and the pKa of the conjugate acid of the amine-containing compound may be 5 to 10. The basic molecule to be impregnated may have a hydroxyl group, a carboxylic acid group, or a sulfonic acid group. Alternatively, the basic molecule to be impregnated may have multiple amino groups or multiple hydroxyl groups.

The monomer may include a substituted acrylamide monomer, an N-(aminoalkyl)acrylamide, or a carboxylic acid or sulfonic acid. In the monomer component, the ratio of the monomer having a carboxylic acid or sulfonic acid may be 1 to 95 mol %, or may be 5 to 95 mol %. The monomer component may include a monomer having a carboxylic acid or sulfonic acid and a monomer having a hydrophobic group. In this case, the molar ratio of the monomer having a carboxylic acid or sulfonic acid to the monomer having a hydrophobic group may be 1:95 to 95:5. The monomer having a carboxylic acid may be methacrylic acid or acrylic acid, and the monomer having a hydrophobic group may be an N-alkylacrylamide. Alternatively, the monomer having a sulfonic acid may be an acrylamide t-butylsulfonic acid or vinylsulfonic acid, and the monomer having a hydrophobic group may be an N-alkylacrylamide.

The first separation section 16 may further include a carrier 18a supporting the separation membrane 18. The carrier 18a may be a porous material (for example, a porous film). The monolayer membrane containing gelling polymer particles may be formed through a process in which an aqueous solution containing gelling polymer particles is applied to the surface of a porous film and the aqueous solution is dried. The gelling polymer particles may have a size that is large enough to block the surface pores contained in the porous carrier 18a. The particle diameter of the gelling polymer particles may be larger than the surface pores of the porous carrier 18a. The porous carrier 18a has a first surface and a second surface that are opposite to each other, and the surface pores on the first surface may be blocked by the polymer particles, and the surface pores on the second surface may not be blocked by the polymer particles. In this case, the separation membrane 18 and the carrier 18a may be arranged so that the first surface faces the supply space Vs1 and the second surface faces the treatment space Vd1. The carrier 18a may have a regular uneven structure on its surface that is sufficiently larger than the surface pores.

The raw gas supply unit 22 supplies the raw gas G0 to the supply space Vs1 of the first separation module 12. As described above, the raw gas supply unit 22 may supply post-combustion exhaust gas discharged from a factory or the like as the raw gas G0 to the supply space Vs1. The pressure of the supply space Vs1 to which the raw gas G0 is supplied from the raw gas supply unit 22 may be about 100 kPa (equivalent to 1 atmosphere). On the other hand, the pressure of the processing space Vd1 may be maintained at a pressure lower than the pressure of the supply space Vs1. For example, the pressure of the processing space Vd1 may be 50 kPa or less, or 20 kPa or less. The processing space Vd1 may be maintained in a substantially vacuum state. When the diameter of the polymer particles contained in the separation membrane 18 is larger than the pore diameter of the porous carrier 18a, the first separation unit 16 is less likely to be damaged by the pressure difference between the processing space Vd1 and the supply space Vs1.

The first processing unit 10 further includes a water vapor supply unit 24. The water vapor supply unit 24 supplies a gas containing water vapor to the processing space Vd1. The water vapor supply unit 24 supplies a gas containing water vapor (hereinafter referred to as "water vapor-containing gas Gs") to the processing space Vd1, thereby promoting the separation of carbon dioxide by the first separation unit 16 (permeation of carbon dioxide through the separation membrane 18). Specifically, the supply of the water vapor-containing gas Gs dilutes carbon dioxide in the processing space Vd1, and the partial pressure of carbon dioxide in the processing space Vd1 becomes lower than the partial pressure of carbon dioxide in the supply space Vs1. As a result, a larger amount of carbon dioxide is separated by the first separation unit 16 compared to the case where the water vapor-containing gas Gs is not supplied. The water vapor-containing gas used to promote the permeation of carbon dioxide through the separation membrane 18 is also called a sweep gas.

The temperature of the water vapor-containing gas Gs supplied from the water vapor supply unit 24 may be 25°C to 80°C. Alternatively, the temperature of the water vapor-containing gas Gs may be 30°C to 70°C, or 35°C to 65°C. The relative humidity of the water vapor-containing gas Gs may be 50% or more, 60% or more, or 70% or more. The water vapor-containing gas Gs supplied from the water vapor supply unit 24 may be generated by utilizing exhaust heat generated in a factory, etc.

The first separation module 12 releases the remaining gas Gd1 after carbon dioxide is extracted from the raw gas G0 from the supply space Vs1. The first separation module 12 may release the gas Gd1 from the supply space Vs1 to the outside. The first separation module 12 releases the gas (first processing gas G1) containing carbon dioxide separated in the processing space Vd1 (permeated from the supply space Vs1 to the processing space Vd1) from the processing space Vd1 toward the second processing unit 30. In addition to carbon dioxide, this first processing gas G1 contains water vapor in the raw gas G0 that has permeated the separation membrane 18 of the first separation unit 16 and water vapor in the water vapor-containing gas Gs from the water vapor supply unit 24. The relative humidity of the first processing gas G1 may be, for example, 50% or more, 60% or more, or 70% or more.

The second processing unit 30 removes at least a portion of the water vapor in the first processing gas G1 to generate a gas having a higher carbon dioxide purity than the first processing gas G1. Hereinafter, the gas generated by the second processing unit 30 and having a higher carbon dioxide purity than the first processing gas G1 will be referred to as the "second processing gas G2." The second processing unit 30 has a second separation module 32.

The second separation module 32 separates the carbon dioxide contained in the first processing gas G1 by removing at least a portion of the water vapor contained in the first processing gas G1. The second separation module 32 includes, for example, a housing 34 and a second separation section 36. The housing 34 houses the second separation section 36 and forms an internal space. The second separation section 36 is a member that reduces the water vapor contained in the first processing gas G1 by either adsorption, absorption, or permeation. The second separation section 36 is arranged to divide the internal space in the housing 34 into two spaces. Hereinafter, the space to which the first processing gas G1 is supplied of the pair of spaces separated by the second separation section 36 is referred to as the "supply space Vs2", and the other space is referred to as the "processing space Vd2". That is, the second separation section 36 is arranged to separate the supply space Vs2 (second supply space) and the processing space Vd2 (second processing space).

The second separation section 36 may include a separation membrane 38 that selectively allows water vapor in the first processing gas G1 to pass through. The separation membrane 38 is a membrane that has the property of allowing water vapor, one of the various components contained in the first processing gas G1, to pass through more easily than other components. The separation membrane 38 may be made of an ionic material.

The separation membrane 38 includes, for example, a monolayer membrane including gelling polymer particles having an acidic functional group. The thickness of the monolayer membrane including the gelling polymer particles may be less than 500 μm. The acidic functional group included in the gelling polymer particles may be one or more functional groups selected from the group consisting of a carboxyl group and a sulfate group, or a salt of the functional group and a cation. The polymer compound constituting the gelling polymer particles may be a polymer of a monomer component including a monomer having an acidic functional group. Examples of the polymer compound having a carboxyl group include a polymer compound including acrylic acid, methacrylic acid, acrylamido t-butylsulfonic acid, or vinylsulfonic acid as a constituent monomer. Examples of the cation include lithium ions, sodium ions, potassium ions, and magnesium ions.

The second separation section 36 may further include a carrier 38a that supports the separation membrane 38. The carrier 38a may be configured similarly to the carrier 18a (porous carrier 18a) that supports the separation membrane 18. The separation membrane 38 and the carrier 38a may be arranged so that the surface of the carrier 38a on which the separation membrane 38 is provided faces the space with the lower pressure between the supply space Vs2 and the processing space Vd2. The arrangement of the separation membrane 38 and the carrier 38a and the configuration of each surface of the separation membrane 38 and the carrier 38a may be changed based on the pressure difference between the supply space Vs2 and the processing space Vd2. For example, when the pressure of the supply space Vs2 is lower than the pressure of the processing space Vd2, the separation membrane 38 may be arranged closer to the supply space Vs2 than the carrier 38a.

The second processing unit 30 further has a regeneration gas supply unit 42. The regeneration gas supply unit 42 supplies the regeneration gas Gr, which has a lower water vapor pressure than the first processing gas G1, to the processing space Vd2. The temperature of the regeneration gas Gr may be lower than the temperature of the water vapor-containing gas Gs supplied by the water vapor supply unit 24 of the first processing unit 10. The relative humidity of the regeneration gas Gr may be, for example, 30% to 80%, 35% to 75%, or 40% to 70%. The temperature of the regeneration gas Gr may be, for example, 0°C to 45°C, 5°C to 40°C, or 10°C to 35°C.

The regeneration gas supply unit 42 may supply air as the regeneration gas Gr to the processing space Vd2. When the regeneration gas supply unit 42 supplies air as the regeneration gas Gr to the processing space Vd2, the temperature and relative humidity of the regeneration gas Gr described above are expressed as average values over a predetermined period (e.g., one day, one week, one month, or one year). The second separation module 32 releases gas Gd2 containing water vapor removed from the first processing gas G1 from the processing space Vd2. The second separation module 32 may release gas Gd2 to the outside. The second separation module 32 releases the gas (second processing gas G2) from which water vapor has been removed in the supply space Vs2 to the suction unit 50.

The suction unit 50 sucks gas in the processing space Vd1 of the first processing unit 10. The suction unit 50 may suck gas in the processing space Vd1 through the supply space Vs2. In this case, the processing space Vd1, the supply space Vs2, and the suction unit 50 may be connected to each other through a gas flow path. The suction unit 50 may be a compressor or a pump (e.g., a vacuum pump) that reduces the pressure of the processing space Vd1. In this case, the pressure of the processing space Vd1 and the supply space Vs2 decreases. The pressure of the processing space Vd1 may be maintained by the suction unit 50 at a value lower than the pressure of the supply space Vs1 (e.g., 50 kPa or less as described above).

The suction of gas by the suction unit 50 promotes the release of the first processing gas G1 from the processing space Vd1 and the release of the second processing gas G2 from the supply space Vs1. The suction unit 50 may suck in the second processing gas G2 and send the sucked second processing gas G2 to the outside of the recovery device 1 as a separated gas Gc. The suction unit 50 may also maintain the pressure in the water vapor supply unit 24 at a low value through the processing space Vd1. This makes it possible to efficiently generate water vapor in the water vapor supply unit 24. In order to adjust the amount of water vapor supplied to the processing space Vd1, a pressure adjustment valve or a flow rate adjustment valve may be provided between the water vapor supply unit 24 and the processing space Vd1. Alternatively, the amount of heat input to the water vapor supply unit 24 may be controlled. This control may adjust the amount of water vapor generated in the water vapor supply unit 24 (the amount of water vapor supplied to the processing space Vd1).

[Method of capturing carbon dioxide]
Next, as an example of a carbon dioxide recovery method, a recovery method using the above-mentioned recovery device 1 will be described. The recovery method using the recovery device 1 includes at least a step (first step) of generating a first processing gas G1 having a higher ratio of carbon dioxide to impurity gas than the raw material gas G0 by extracting at least a part of the carbon dioxide in the raw material gas G0 using a first separation section 16 that separates the carbon dioxide contained in the raw material gas G0 from the impurity gas by permeation. The recovery method also includes a step (second step) of generating a second processing gas G2 having a higher carbon dioxide purity than the first processing gas G1 by removing at least a part of the water vapor in the first processing gas G1 using a second separation section 36 that reduces the water vapor contained in the first processing gas G1 by permeation. In the step of generating the second processing gas G2, a regeneration gas Gr having a water vapor pressure lower than that of the first processing gas G1 is further utilized.

In more detail, first, in the first processing unit 10, the raw material gas G0 is supplied from the raw material gas supply unit 22 to the supply space Vs1 of the first separation module 12. In conjunction with the supply of the raw material gas G0, the processing space Vd1 of the first separation module 12 is depressurized by the suction unit 50, and the water vapor-containing gas Gs is supplied to the processing space Vd1 from the water vapor supply unit 24. Therefore, a difference in partial pressure of carbon dioxide occurs between the supply space Vs1 and the processing space Vd1, and at least a portion of the carbon dioxide contained in the raw material gas G0 supplied to the supply space Vs1 permeates the first separation unit 16 (separation membrane 18) and is sent to the processing space Vd1.

Since the processing space Vd1 is sucked by the suction section 50, the first processing gas G1 containing carbon dioxide and water vapor that has permeated the first separation section 16 flows from the processing space Vd1 toward the second processing section 30. Since the first processing gas G1 contains carbon dioxide selectively separated by the separation membrane 18 of the first separation section 16, the ratio of carbon dioxide to impurity gases in the first processing gas G1 is greater than the ratio of carbon dioxide to impurity gases in the raw material gas G0. The first processing gas G1 that has flowed to the second processing section 30 is supplied to the supply space Vs2 of the second separation module 32 in the second processing section 30.

In addition to the supply of the first processing gas G1 to the supply space Vs2, the processing space Vd2 of the second separation module 32 is supplied with the regeneration gas Gr from the regeneration gas supply unit 42. As a result, the second separation unit 36 (separation membrane 38) of the second separation module 32 removes water vapor from the first processing gas G1 supplied to the supply space Vs2. Specifically, a portion of the water vapor in the first processing gas G1 supplied to the supply space Vs2 permeates the second separation unit 36 (separation membrane 38) and is sent to the processing space Vd2. At this time, since the water vapor pressure of the regeneration gas Gr is lower than the water vapor pressure of the first processing gas G1, the water vapor pressure of the gas in the supply space Vs2 can be reduced to the same level as the water vapor pressure in the processing space Vd2. That is, the relative humidity of the gas in the supply space Vs2 can be less than 100%. In addition, since the temperature of the regeneration gas Gr is lower than the temperature of the water vapor-containing gas Gs, it can be lower than the temperature of the first processing gas G1. In this case, the gas in the supply space Vs2 is cooled by the regeneration gas Gr, so the temperature of the gas in the supply space Vs2 drops to approximately the same temperature as the regeneration gas Gr.

Since the supply space Vs2 is sucked by the suction section 50, the temperature is lowered by the second separation section 36, and the remaining second processing gas G2 after the water vapor is removed is sent from the supply space Vs2 toward the suction section 50. The amount of water vapor in the second processing gas G2 is lowered to a value lower than the saturated water vapor amount of the second processing gas G2 by the removal of water vapor by the second separation section 36. In addition, the temperature of the second processing gas G2 is lowered to a value lower than the temperature of the first processing gas G1 by the supply of the regeneration gas Gr to the processing space Vd2. The second processing gas G2 sucked by the suction section 50 is sent to the outside of the recovery device 1 as a separated gas Gc. The concentration (purity) of carbon dioxide in the second processing gas G2 is higher than the concentration (purity) of carbon dioxide in the first processing gas G1 by the removal of water vapor by the second separation section 36. As a result, the carbon dioxide concentration of the separated gas Gc discharged from the suction section 50 becomes higher than the carbon dioxide concentration of the raw gas G0 supplied to the recovery device 1. In other words, a gas in which carbon dioxide is concentrated (a gas in which the ratio of carbon dioxide to impurity gases is increased) is recovered by the recovery device 1.

[Modification 1]
In order to increase the ratio of carbon dioxide to impurity gases in the raw gas G0, the carbon dioxide recovery device may use a material that absorbs or adsorbs and releases carbon dioxide instead of a separation membrane that selectively permeates carbon dioxide. Fig. 2 is a schematic diagram showing another example of a carbon dioxide recovery device. In the carbon dioxide recovery device 1A shown in Fig. 2, the first separation section 16 of the first separation module 12 includes a material 18A that selectively adsorbs or absorbs carbon dioxide in the raw gas G0 instead of a separation membrane 18.

The first separation section 16 including the material 18A is arranged to separate the supply space Vs1 (first supply space) from the processing space Vd1 (first processing space) in the same manner as the first separation section 16 including the separation membrane 18. In this disclosure, selectively absorbing (adsorbing) one component means absorbing (adsorbing) a part of the gas so that the absorption (adsorption) amount of the one component among the various components contained in the supplied gas is greater than the absorption amount of the other components. The material 18A may be an adsorbent having a property that is more likely to adsorb carbon dioxide among the various components contained in the raw gas G0 than other components, or may be an absorbent having a property that is more likely to absorb carbon dioxide than other components. When the material 18A is an adsorbent, the material 18A may be made of activated carbon or silica gel.

When material 18A is an absorbent, material 18A may be composed of an alkaline material, similar to separation membrane 18. Material 18A includes, for example, polymer compound particles having an amino group. The polymer compound particles may be hydrogel particles. The polymer compound constituting the polymer compound particles may be a polymer of a monomer component including a monomer having an amino group. The monomer may include a substituted acrylamide monomer, may include an N-(aminoalkyl)acrylamide, or may include a tertiary amino group. In the monomer component, the proportion of the monomer having an amino group may be 5 to 99 mol %.

The monomer components may include a monomer having an amino group and a monomer having a hydrophobic group. In this case, the molar ratio of the monomer having an amino group to the monomer having a hydrophobic group may be 1:99 to 99:1. The monomer having an amino group may be N-(aminoalkyl)acrylamide, and the monomer having a hydrophobic group may be N-alkylacrylamide. The first separation section 16 may include a carrier 19A supporting the material 18A instead of the carrier 18a. In this case, the material 18A may be a film provided on the carrier 19A and containing gel particles of a polymer compound having an amino group. Alternatively, the material 18A may be a plurality of films containing gel particles formed in a layer on the carrier 19A. The carrier 19A may be a plate on a flat plate, a sheet, a foil, or a fiber aggregate. The carrier 19A may be a porous body or a honeycomb structure. The carrier 19A may be a powder of polymer compound fine particles, or may be particles obtained by granulating the powder. The powders and particles may contain fillers such as carbon or silica with a primary particle size of 100 nanometers or less.

In the recovery apparatus 1A, the water vapor supply unit 24 supplies a water vapor-containing gas Gs containing water vapor to the supply space Vs1. The gas in the processing space Vd1 is sucked by the suction unit 50, as in the recovery apparatus 1. Valves (not shown) may be provided in the gas flow path between the supply space Vs1 and the raw gas supply unit 22 and the gas flow path between the supply space Vs1 and the water vapor supply unit 24. Valves (not shown) may be provided in the gas flow path through which the gas Gd1 is discharged from the processing space Vd1 to the outside and in the gas flow path between the processing space Vd1 and the supply space Vs2 of the second processing unit 30. The open/closed states of these valves may be switched by a control device (not shown).

The carbon dioxide recovery method using the recovery device 1A exemplified above will be described. First, the raw gas G0 is supplied from the raw gas supply unit 22 to the supply space Vs1 of the first separation module 12. At this time, the supply of the water vapor-containing gas Gs from the water vapor supply unit 24 and the suction of the processing space Vd1 by the suction unit 50 are stopped. At least a portion of the carbon dioxide contained in the raw gas G0 supplied to the supply space Vs1 is absorbed (adsorbed) by the material 18A. The raw gas G0 is sent to the processing space Vd1 while the carbon dioxide is absorbed by the material 18A, and the remaining gas after the carbon dioxide is absorbed by the material 18A is discharged from the processing space Vd1 as gas Gd1. The above state continues for a predetermined period of time, and carbon dioxide is stored in the material 18A.

After carbon dioxide is stored in the material 18A, the supply of the raw material gas G0 from the raw material gas supply unit 22 and the discharge of the gas Gd1 from the processing space Vd1 to the outside are stopped, and the water vapor-containing gas Gs is supplied from the water vapor supply unit 24 to the supply space Vs1, and the flow path between the processing space Vd1 and the supply space Vs2 of the second processing unit 30 is opened. As a result, the water vapor-containing gas Gs supplied to the supply space Vs1 sends the carbon dioxide stored in the material 18A to the processing space Vd1, and the gas containing carbon dioxide after being sent to the processing space Vd1 is supplied to the supply space Vs2 as the first processing gas G1. Since the first processing gas G1 contains the carbon dioxide stored in the material 18A, the ratio of carbon dioxide to impurity gases is higher than that of the raw material gas G0. In the second processing unit 30 and the suction unit 50, the second processing gas G2 and the separated gas Gc are generated and sent out in the same manner as in the above-mentioned recovery device 1.

[Modification 2]
The carbon dioxide recovery device may include a plurality of second processing units and a plurality of suction units in order to remove at least a portion of the water vapor in the first processing gas G1. FIG. 3 is a schematic diagram showing another example of a carbon dioxide recovery device. The carbon dioxide recovery device 1B shown in FIG. 3 includes a second processing unit 30a and a second processing unit 30b instead of the second processing unit 30, and includes a suction unit 50a and a suction unit 50b instead of the suction unit 50. The second processing units 30a and 30b are each configured similarly to the second processing unit 30, and the suction units 50a and 50b have the same function as the suction unit 50. In the recovery device 1B, the pressure of the supply space Vs2 decompressed by the suction unit 50b may be higher than the pressure of the supply space Vs2 decompressed by the suction unit 50a.

The carbon dioxide recovery method using the recovery device 1B will be described. As with the recovery device 1 illustrated in FIG. 1, the first processing gas G1 is supplied from the first processing unit 10 (first separation module 12) to the supply space Vs2 of the second processing unit 30a. In the second separation module 32 of the second processing unit 30a, at least a portion of the water vapor in the first processing gas G1 is removed by the second separation unit 36 to generate a second processing gas G21. The purity of carbon dioxide in the second processing gas G21 is higher than that of the first processing gas G1. The gas in the supply space Vs2 of the second processing unit 30a is sucked in and compressed by the suction unit 50a to become the second processing gas G21 with increased carbon dioxide partial pressure and water vapor pressure. The second processing gas G21 is supplied to the supply space Vs2 of the second processing unit 30b.

In the second separation module 32 of the second processing unit 30b, the second separation unit 36 removes at least a portion of the water vapor in the second processing gas G21 to generate the second processing gas G22. The purity of the carbon dioxide in the second processing gas G22 is higher than the purity of the carbon dioxide in the second processing gas G21. The second processing gas G22 is sucked from the supply space Vs2 of the second processing unit 30b by the suction unit 50b, and the gas is sent to the outside of the recovery device 1B as a separated gas Gc.

The recovery device 1B may further include one or more separate second processing units 30 and one or more separate suction units 50. In the recovery device 1A illustrated in FIG. 2, second processing units 30a, 30b and suction units 50a, 50b may be provided instead of the second processing unit 30 and suction unit 50. In the recovery device 1B described above, the amount of water vapor removed from the first processing gas G1 can be made larger than in the recovery devices 1 and 1A. Alternatively, the performance per suction unit (e.g., compressor) can be made smaller than in the recovery devices 1 and 1A.

[Other Modifications]
In the above-mentioned recovery device 1, 1A, the second treatment unit 30 reduces the water vapor contained in the first treatment gas G1 by the separation membrane 38, but instead of the separation membrane 38, a material (absorbent or adsorbent) that selectively adsorbs or absorbs the water vapor contained in the first treatment gas G1 may be included. Even in this case, the regeneration gas supply unit 42 may supply the regeneration gas Gr to one space (treatment space) of a pair of spaces separated by the absorbent (adsorbent) in the second treatment unit 30. Such an absorbent may include a film, powder, or particle containing gelling polymer particles having an acidic functional group, or may include a film, powder, or particle containing both a salt of a gelling polymer particle having an acidic functional group and a salt of a gelling polymer microparticle having a basic functional group. The absorbent may be supported on a carrier such as a porous material, and may include a filler such as carbon black or fumed silica.

[Effects of the embodiment]
In the carbon dioxide recovery device 1 described above, the first processing gas G1 in which the ratio of impurity gases contained in the raw material gas G0 is reduced and the ratio of carbon dioxide is increased is sent from the first processing unit 10 to the supply space Vs2 of the second processing unit 30. Then, the regenerated gas Gr, which has a lower water vapor pressure than the first processing gas G1, is supplied to the processing space Vd2 separated from the supply space Vs2 by the second separation unit 36. As a result, the water vapor pressure of the second processing gas G2 is reduced to below the saturated water vapor pressure while the water vapor is removed from the first processing gas G1 by the second separation unit 36. The load on the device for sucking the second processing gas G2 depends on the water vapor pressure (amount of water vapor) contained in the second processing gas G2. In the above recovery device 1, since the water vapor pressure of the second processing gas G2 is reduced, the required performance of the device for sucking the second processing gas G2 can be reduced. Therefore, it is possible to easily recover a gas in which the ratio of carbon dioxide to impurity gases contained in the raw material gas G0 is increased.

In the above embodiment, the first processing unit 10 of the recovery device 1 further includes a water vapor supply unit 24 that supplies a water vapor-containing gas Gs containing water vapor to the processing space Vd1. The first separation unit 16 includes a separation membrane 18 that selectively permeates carbon dioxide contained in the raw material gas G0. In this case, the water vapor-containing gas Gs promotes the permeation of carbon dioxide through the separation membrane 18 of the first separation unit 16. Therefore, it becomes possible to efficiently separate carbon dioxide from the raw material gas G0.

In the above embodiment, the first processing unit 10 of the recovery device 1A further has a water vapor supply unit 24 that supplies a water vapor-containing gas Gs containing water vapor to the supply space Vs1. The first separation unit 16 includes a material 18A that selectively adsorbs or absorbs carbon dioxide contained in the raw material gas G0. In this case, the water vapor-containing gas Gs promotes the release (desorption) of carbon dioxide stored in the material 18A of the first separation unit 16. Therefore, it becomes possible to efficiently separate carbon dioxide from the raw material gas G0.

In the above embodiment, the temperature of the regenerated gas Gr is lower than the temperature of the water vapor-containing gas Gs. In this case, the temperature of the second treatment gas G2 is lowered to the same temperature as the regenerated gas Gr. Therefore, the performance requirements of the device for sucking the second treatment gas G2 can be further reduced, and it becomes possible to more easily recover gas with an increased ratio of carbon dioxide to impurity gases.

In the above embodiment, the regeneration gas Gr is air. In this case, it is easy to supply the regeneration gas Gr to the treatment space Vd2.

In the above embodiment, the water vapor pressure of the second process gas G2 is smaller than the saturated water vapor pressure of the second process gas G2. In this case, it is possible to reduce the performance requirements of the device for sucking the second process gas G2 compared to when the second process gas G2 contains water vapor at the saturated water vapor pressure.

The recovery device 1, 1A according to the above embodiment includes an suction section 50 that sucks in the gas in the processing space Vd1. In this configuration, the water vapor pressure of the second processing gas G2 is lowered in the second processing unit 30, so the performance requirements of the suction section 50 can be lowered compared to when the water vapor pressure is not lowered. This makes it possible to simplify the suction section 50.

In the above embodiment, the second separation section 36 includes a separation membrane 38 that selectively transmits water vapor contained in the first processing gas G1. In this case, it becomes possible to easily remove water vapor from the first processing gas G1.

In the carbon dioxide recovery method using the recovery apparatus 1, 1A, 1B according to the above embodiment, the first separation section 16 is used to increase the ratio of carbon dioxide contained in the raw gas G0 to the impurity gas (carbon dioxide is separated or concentrated), thereby generating the first processing gas G1. Then, the second separation section 36 that reduces the water vapor contained in the first processing gas G1 and the regeneration gas Gr having a lower water vapor pressure than the first processing gas G1 are used to generate the second processing gas G2. By using the regeneration gas Gr having a lower water vapor pressure, the water vapor pressure of the second processing gas G2 can be reduced while removing water vapor from the first processing gas G1 by the second separation section 36. The load of the device for sucking the second processing gas G2 depends on the amount of water vapor contained in the second processing gas G2. In the above recovery method, the water vapor pressure of the second processing gas G2 can be reduced, so that the required performance of the device for sucking the second processing gas G2 can be reduced. Therefore, it is possible to easily recover a gas in which the ratio of carbon dioxide contained in the raw gas G0 to the impurity gas has increased.

As another device or method for recovering carbon dioxide after separating it (e.g., concentrating it), a device or method is considered in which the treated gas from which carbon dioxide has been separated (e.g., concentrated) in the first processing unit 10 is recovered via a heat exchanger, a gas-liquid separator, and a compressor. In this device or method, the heat exchanger, gas-liquid separator, and compressor are arranged in this order from upstream, and the treated gas is cooled in the heat exchanger, thereby liquefying some of the water vapor in the treated gas. Then, the gas-liquid separator separates some of the liquefied water vapor (moisture) from the remaining gas containing carbon dioxide, and the separated gas containing carbon dioxide is sucked in by the compressor.

In this device or method, the processing gas can be cooled to a temperature similar to that of the cooling gas by the heat exchanger, but the cooled gas contains a saturated amount of water vapor. Since the performance required of the compressor increases depending on the amount of water vapor in the gas to be sucked by the compressor, a compressor that sucks in the gas containing carbon dioxide (gas with a saturated amount of water vapor) separated by the gas-liquid separator requires high performance and large power. In contrast, in the recovery device 1 and recovery method of the above embodiment, gas with a low relative humidity (below the saturated amount of water vapor) is generated in the second separation section 36 of the second processing section 30, so the performance required of the compressor can be reduced.

Although the embodiment of the present disclosure has been described above, the present disclosure is not limited to the above embodiment. The heat exchanger and gas-liquid separator used in the other device or method described above may be used in combination with one or more second processing units (second separation modules). FIG. 4 is a schematic diagram showing another example of a carbon dioxide recovery device. The recovery device 1C shown in FIG. 4 differs from the recovery device 1B shown in FIG. 3 in that it further includes a heat exchanger 62 and a gas-liquid separator 64 provided between the first processing unit 10 and the second processing unit 30a. The recovery device 1C also differs from the recovery device 1B in that the suction unit 50a is disposed between the first processing unit 10 and the second processing unit 30a (downstream of the gas-liquid separator 64), and the suction unit 50b is disposed between the second processing unit 30a and the second processing unit 30b. In addition, another suction unit (not shown) may be provided further downstream of the downstream second separation module 32. In the recovery device 1C shown in FIG. 4, it is also possible to reduce the load on each suction unit. In the recovery device 1, 1A shown in Figures 1 and 2, the suction section 50 (heat exchanger 62 and gas-liquid separator 64) may also be disposed between the first processing section 10 and the second processing section 30.

In the above-mentioned recovery apparatus 1, 1A, the water vapor-containing gas Gs is supplied to the processing space Vd1 or the supply space Vs1 of the first processing unit 10 by the water vapor supply unit 24, but the first processing unit 10 does not have to have the water vapor supply unit 24. In this case, the first processing gas G1 sent to the second processing unit 30 that removes water vapor from the gas contains water vapor that is contained in the raw material gas G0 and has passed through the first separation unit 16 (separation membrane 18 or material 18A).

The temperature of the regeneration gas Gr supplied by the regeneration gas supply unit 42 may be approximately the same as the temperature of the water vapor-containing gas Gs supplied from the water vapor supply unit 24 in the first processing unit 10, or may be higher than the temperature of the water vapor-containing gas Gs. The regeneration gas supply unit 42 may supply a gas other than air. For example, the regeneration gas supply unit 42 may include a humidity regulator capable of adjusting humidity, and may supply a gas having a humidity adjusted by the humidity regulator to the processing space Vd2 as the regeneration gas Gr.

[Evaluation results]
The present disclosure will now be described in more detail with reference to examples, but the present disclosure is not limited to the following examples. In the following examples, the removal performance in the case of using a separation membrane module (the above-mentioned second separation module 32) capable of selectively separating water vapor is evaluated by calculation.

(Method of calculation)
The target gas for removing water vapor was the permeate gas (gas on the processing space side) under the conditions that had been used as the reference case for the calculation of carbon dioxide separation membranes up to now. Figure 5(a) shows the process flow that was the subject of the calculation, and the table in Figure 5(b) shows the prerequisites for the calculation, such as the characteristics of the water vapor separation membrane used in the calculation and the gas flow rate. "Case 1" shown in Figures 5(a) and 5(b) shows the condition in which the permeate gas of the carbon dioxide separation membrane was directly introduced into the water vapor separation membrane, and "Case 2" shows the condition in which the permeate gas was flushed at 40°C and the compressed gas was introduced into the water vapor separation membrane. The material balance in the composition membrane separation module was calculated using a differential equation that sets the permeation flow rate of the membrane, and the energy balance was calculated using a differential equation that takes into account the enthalpy change due to gas permeation in the membrane and heat transfer through the membrane, and the amount of water vapor removed was calculated by solving both simultaneously using Matlab.

(result)
FIG. 6(a) shows an example of calculation of the gas partial pressure and gas temperature on the supply side and permeation side in the module in case 2. It is confirmed that water vapor is removed by the partial pressure difference between the permeation and non-permeation sides of the membrane, and the gas temperature drops from about 343K to 305K, and it can be seen that the heat exchanger and gas-liquid separator can be omitted. FIG. 6(b) shows a comparison of the water vapor removal rate with the flash operation. In case 1, although the gas to be treated contains a lot of water vapor, the partial pressure difference between the water vapor and the sweep gas (regeneration gas) is small due to the low total pressure, and it can be seen that the water vapor cannot be removed. In contrast, in case 2, although the total pressure is about twice as high, water vapor is removed by membrane separation, and the water vapor concentration can be lowered compared to the flash method, and further, by increasing the sweep gas flow rate from 200 mol/s to 300 mol/s, the water vapor concentration was reduced from 21% to 14%. This indicates that dehydration using a membrane module is effective for gases pressurized to a certain extent, and that it has the potential to significantly reduce the energy required and costs compared to the flash method.

The present disclosure provides a carbon dioxide recovery device and recovery method that can easily recover gas in which the ratio of carbon dioxide to contaminant gases has increased.

1, 1A, 1B, 1C... carbon dioxide recovery device, 10... first processing section, 16... first separation section, 18... separation membrane, 18A... material, 24... water vapor supply section, 30... second processing section, 36... second separation section, 38... separation membrane, 42... regeneration gas supply section, 50... suction section, Vs1, Vs2... supply space, Vd1, Vd2... processing space, G0... raw material gas, G1... first processing gas, G2... second processing gas, Gs... water vapor-containing gas, Gr... regeneration gas.

Claims (9)

a first processing unit that is disposed so as to separate a first supply space and a first processing space, the first processing unit having a first separation unit that separates carbon dioxide contained in a raw material gas supplied to the first supply space from an impurity gas containing components of the raw material gas other than carbon dioxide, and that extracts at least a portion of the carbon dioxide contained in the raw material gas and releases a first processing gas from the first processing space, the first processing gas having a higher ratio of carbon dioxide to the impurity gas than the raw material gas;
a second processing unit that is disposed to separate a second supply space to which the first processing gas discharged by the first processing unit is supplied from a second processing space, the second processing unit having a second separation unit that reduces water vapor contained in the first processing gas by any one of adsorption, absorption, or permeation, and that removes at least a portion of the water vapor contained in the first processing gas and discharges a second processing gas having a higher carbon dioxide purity than the first processing gas;
a suction unit that suctions gas within the first processing space,
the first separation section includes a separation membrane that selectively allows carbon dioxide contained in the raw material gas to permeate therethrough,
The carbon dioxide recovery apparatus, wherein the second treatment section further includes a regeneration gas supply section that supplies a regeneration gas having a water vapor pressure lower than that of the first treatment gas to the second treatment space. The suction unit suctions gas in the first processing space through the second supply space,
The recovery device includes:
a third processing unit that is disposed to separate a third supply space to which the second processing gas sucked by the suction unit is supplied and a third processing space, the third processing unit having a third separation unit that reduces water vapor contained in the second processing gas by any one of adsorption, absorption, or permeation, and removes at least a portion of the water vapor contained in the second processing gas and releases a third processing gas having a higher carbon dioxide purity than the second processing gas;
a second suction unit that sucks the third process gas;
The recovery device of claim 1 further comprising: the suction unit is provided between the first processing space and the second supply space,
The recovery device includes:
a second suction unit that sucks the second process gas;
a third processing unit that is disposed to separate a third supply space to which the second process gas sucked by the second suction unit is supplied and a third processing space, the third processing unit having a third separation unit that reduces water vapor contained in the second process gas by any one of adsorption, absorption, or permeation, and removes at least a portion of the water vapor contained in the second process gas and releases a third process gas having a higher carbon dioxide purity than the second process gas;
The recovery device of claim 1 further comprising: The recovery apparatus according to claim 1 , wherein the first processing section further comprises a water vapor supply section that supplies a water vapor-containing gas that contains water vapor to the first processing space. 5. The recovery apparatus of claim 4 , wherein the temperature of the regeneration gas is lower than the temperature of the water vapor-containing gas. The recovery apparatus according to any one of claims 1 to 5 , wherein the regeneration gas is air. The recovery apparatus according to claim 1 , wherein the water vapor pressure of the second process gas is lower than a saturated water vapor pressure of the second process gas. The recovery device according to any one of claims 1 to 7, wherein the second separation section includes a separation membrane that selectively allows water vapor contained in the first treatment gas to pass through. a first step of extracting at least a portion of the carbon dioxide contained in the raw material gas supplied to the first supply space using a first separation unit that is disposed to separate a first supply space and a first processing space and that separates carbon dioxide contained in the raw material gas from an impurity gas that contains components of the raw material gas other than carbon dioxide, thereby generating a first processing space in which a ratio of carbon dioxide to the impurity gas is higher than that of the raw material gas;
a second step of removing at least a portion of the water vapor contained in the first process gas using a second separation section that reduces the water vapor contained in the first process gas by any one of adsorption, absorption, or permeation, thereby generating a second process gas having a higher carbon dioxide purity than the first process gas;
a suction step of suctioning the gas in the first processing space by a suction part,
the first separation section includes a separation membrane that selectively allows carbon dioxide contained in the raw material gas to permeate therethrough,
A method for recovering carbon dioxide, wherein in the second step, the second treated gas is produced by further using a regeneration gas having a water vapor pressure lower than that of the first treated gas.

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