Carbon dioxide recovery method

Abstract

To provide a carbon dioxide recovery method which is applicable to a fixed bed type carbon dioxide recovery apparatus and does not require a drying process.SOLUTION: Introducing a raw material gas into one or more adsorption columns 2 filled with a carbon dioxide adsorbent represented by an amine-supported adsorbent in an adsorbent layer, and introducing the raw material gas into one or more adsorption columns 2,12 filled with the adsorbent; An operation cycle including an adsorption step of adsorbing carbon dioxide, a recovery step of desorbing and recovering carbon dioxide by introducing superheated steam, and a cooling step of cooling an adsorbent by introducing cooling gas is repeated, and in the adsorption step, a temperature of an adsorbent layer at the end of the adsorption step is set to be equal to or higher than a dew point of the superheated steam by reaction heat generated when carbon dioxide is adsorbed to an amine-supported adsorbent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide recovery method, and more particularly to a carbon dioxide recovery method in which carbon dioxide is separated and recovered from a raw material gas using a carbon dioxide adsorbent, typically an amine-supported adsorbent. [Background technology]

[0002] From the perspective of reducing greenhouse gas emissions, there is a need to build systems that can capture carbon dioxide from various emission sources such as thermal power plants, steel mills, cement factories, and boilers. Common commercial carbon dioxide capture devices use the chemical absorption process. Carbon dioxide capture devices that use the chemical absorption process absorb carbon dioxide by bringing an aqueous solution of amine compounds (aqueous amine solution) into gas-liquid contact with a feed gas containing carbon dioxide in an absorption tower, and then regenerating the aqueous amine solution with steam in a regeneration tower to capture carbon dioxide.

[0003] In a chemical absorption process using an aqueous amine solution, not only is carbon dioxide desorbed from the amine compound, but energy equivalent to the latent heat of vaporization of water is also consumed when carbon dioxide is desorbed. For this reason, a carbon dioxide capture device using an amine-supported adsorbent, in which an amine compound is supported on a porous carrier, is known (see Patent Document 1). Carbon dioxide adsorbents, such as amine-supported adsorbents, can adsorb carbon dioxide in the same way as aqueous amine solutions, but do not require the latent heat of vaporization of water when carbon dioxide is desorbed, thereby reducing the energy required for carbon dioxide capture.

[0004] Another method for desorbing carbon dioxide adsorbed on a carbon dioxide adsorbent involves introducing and heating a high-temperature regeneration gas. However, since the regeneration gas contains air components other than carbon dioxide, it is not possible to capture carbon dioxide at a high concentration. Therefore, a method for desorbing carbon dioxide by introducing water vapor is known. When water vapor is used, gas-liquid separation is easily possible after condensation, making it relatively easy to obtain high-concentration carbon dioxide. Therefore, this method is used in many carbon dioxide capture devices, including the carbon dioxide capture device described in Patent Document 1. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5820254 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the carbon dioxide capture device in Patent Document 1 uses a so-called moving bed system in which the amine-supported adsorbent is moved among an adsorption tower, a regeneration tower, a drying tower, and a cooling tower. Because movement is required using transport equipment, periodic maintenance with the interior open and a certain level of mechanical strength are required. Furthermore, friction and collisions between the amine-supported adsorbents occur, making the amine-supported adsorbent susceptible to deterioration.

[0007] Furthermore, carbon dioxide adsorption is hindered when the surface of a carbon dioxide adsorbent, such as an amine-supported adsorbent, is wet with condensed water. For this reason, the carbon dioxide recovery apparatus of Patent Document 1 must be provided with a drying step for drying the amine-supported adsorbent before introducing it into the adsorption tower, which requires heating gas and energy for drying.

[0008] Therefore, an object of the present invention is to provide a carbon dioxide recovery method that is applicable to a fixed-bed type carbon dioxide recovery device and does not require a drying step. [Means for solving the problem]

[0009] To achieve the above object, the present invention provides a carbon dioxide recovery method that involves introducing a feed gas, which is a mixed gas consisting of two or more gas components including carbon dioxide, into one or more adsorption columns whose adsorbent layers are filled with a carbon dioxide adsorbent, and separating and recovering carbon dioxide from the feed gas, the method comprising the steps of: an adsorption step of adsorbing the carbon dioxide in the feed gas onto the carbon dioxide adsorbent; a recovery step of introducing superheated steam into the adsorption columns to desorb the carbon dioxide adsorbed on the carbon dioxide adsorbent and recovering it as a recovered gas; and a cooling step of cooling the carbon dioxide adsorbent, wherein an operating cycle is repeated in which the adsorption step, the recovery step, and the cooling step are performed in this order, and during the adsorption step, the reaction heat generated by the adsorption of carbon dioxide onto the carbon dioxide adsorbent raises the temperature of the adsorbent layer at the end of the adsorption step to or above the dew point of the superheated steam. The carbon dioxide adsorbent is also characterized in that it is an amine-supported adsorbent.

[0010] The method is also characterized in that the temperature of the adsorbent layer at the end of the cooling step is 50°C < the temperature of the superheated steam < 150°C. Preferably, the temperature of the superheated steam is 105°C to 150°C, and the pressure of the superheated steam is 10 to 300 kPa(g). Preferably, the carbon dioxide concentration in the raw material gas is 1 to 50%.

[0011] Furthermore, the cooling step is characterized in that a cooling gas is introduced into the adsorption cylinder to cool the carbon dioxide adsorbent, the direction in which the raw material gas is introduced into the adsorption cylinder being the same as the direction in which the cooling gas is introduced into the adsorption cylinder, and it is preferable that the raw material gas and the cooling gas are introduced from the lower side of the adsorption cylinder.

[0012] Furthermore, the present invention is characterized in that there are three or more adsorption columns, and when at least one adsorption column is performing the adsorption step, at least one of the other adsorption columns is performing the recovery step and at least one is performing the cooling step.Furthermore, the present invention is characterized in that a purging step is performed before the recovery step, in which a purge gas is introduced into the adsorption columns.Furthermore, it is preferable that the purge gas is a part of the recovery gas or the superheated steam. [Effects of the Invention]

[0013] The carbon dioxide capture method of the present invention can be applied to fixed-bed carbon dioxide capture devices, which allows for easier maintenance than moving-bed devices, and allows for long-term use without friction or collision between amine-supported adsorbents. Furthermore, by setting the temperature of the adsorbent layer at the end of the adsorption step to be equal to or higher than the dew point of the superheated steam, condensed water is not generated even when superheated steam is introduced into the adsorption column during the capture step, eliminating the need for a drying step and reducing the gas and energy required for drying. Furthermore, since the temperature of the adsorbent layer is in the range of 50°C to 150°C throughout the entire process, a high carbon dioxide adsorption capacity of the amine-supported adsorbent can be maintained. Furthermore, by providing three or more adsorption columns, carbon dioxide can be continuously captured, and by introducing a purging step, a higher concentration of carbon dioxide can be captured. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing an example of a carbon dioxide capture device to which a carbon dioxide capture method according to a first embodiment of the present invention can be applied. [Figure 2] FIG. 10 is a diagram showing an example of a carbon dioxide capture device to which a carbon dioxide capture method according to a second embodiment of the present invention can be applied. [Figure 3] FIG. 3 is a diagram showing an operation cycle of a carbon dioxide recovery method according to a second embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an example of a carbon dioxide capture apparatus to which a carbon dioxide capture method according to a first embodiment of the present invention, which will be described later, can be applied. As shown in FIG. 1, the carbon dioxide capture apparatus 10 is a so-called fixed-bed capture apparatus, and includes: an adsorption column 2 filled with an amine-supported adsorbent that adsorbs carbon dioxide in an internal adsorbent layer; a raw material gas supply line L1 that supplies raw material gas to the lower part of the adsorption column 2; an off-gas discharge line L2 through which carbon dioxide in the raw material gas is adsorbed in the adsorption column 2 and discharged as off-gas; a capture line L3 that recovers carbon dioxide from the inside of the adsorption column 2 from the lower part of the adsorption column 2; a superheated steam introduction line L4 that introduces superheated steam to the upper part of the adsorption column 2; a cooling gas introduction line L5 that introduces cooling gas to the lower part of the adsorption column 2; and a cooled off-gas discharge line L6 that discharges the cooled gas from the upper part of the adsorption column 2 as off-gas after cooling the inside of the adsorption column 2. Furthermore, a gas-liquid separator 3 that separates water and carbon dioxide gas is provided in the capture line L3.

[0016] The lines L1 to L6 are provided with on-off valves V1 to V6, respectively. The raw material gas is a mixed gas consisting of two or more gas components including carbon dioxide, and preferably a gas containing carbon dioxide and an air component such as oxygen or nitrogen as the main component. For example, it is exhaust gas containing 1 to 50% carbon dioxide from various emission sources such as thermal power plants, steel mills, and cement factories. The raw material gas supply line L1 may be provided with a blower for pressurizing the raw material gas as necessary. Furthermore, if the raw material gas contains impurities such as NOx and SOX, a pretreatment device such as a desulfurization / denitrification device may be provided.

[0017] The amine-supported adsorbent that is filled in the adsorbent layer of the adsorption column 2 and adsorbs carbon dioxide is an amine compound supported on a porous carrier such as silica or silica gel. Typical amine compounds supported on amine-supported adsorbents include tetraethylenepentamine, polyethyleneimine, monoethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, isopropanolamine, diethylenetriamine, triethylenetetramine, hexaethylenediamine, benzylamine, and morpholine.

[0018] It is known that the amount of carbon dioxide adsorbed by amine-supported adsorbents, which support amine compounds such as tetraethylenepentamine and polyethyleneimine, increases from around 50° C. and reaches a maximum at about 80 to 100° C. On the other hand, it is also known that the amine-supported adsorbents deteriorate when the temperature exceeds 150° C., and the amount of carbon dioxide adsorbed drops significantly.

[0019] The temperature of the superheated steam introduced into the upper part of the adsorption column 2 is 105°C to 150°C, and the pressure is 10 to 300 kPa(g). Examples of the cooling gas include the off-gas discharged from the off-gas discharge line L2 with its temperature lowered, ambient air blown in by a blower or the like, an inert gas such as nitrogen, and water vapor.

[0020] The carbon dioxide recovery method according to the first embodiment of the present invention uses the carbon dioxide recovery apparatus 10 configured as described above to repeat an operation cycle in which an adsorption step, a recovery step, and a cooling step are carried out in this order as follows.

[0021] [Adsorption process] With valves V1 and V2 open and the other valves closed, the raw gas is introduced into the adsorption column 2 via the raw gas supply line L1. The adsorbent layer, which is filled with an amine-supported adsorbent, is controlled to a temperature of 50 to 100°C at the end of the cooling process described below. Carbon dioxide in the raw gas is adsorbed by the amine-supported adsorbent, and the remaining components are discharged as off-gas through the off-gas discharge line L2. When the amine-supported adsorbent adsorbs carbon dioxide, the temperature of the adsorbent layer rises due to the heat of reaction. The adsorption process time is set so that the temperature of the adsorbent layer is above the dew point of superheated steam at the end of the adsorption process. To prevent deterioration of the amine-supported adsorbent, the adsorption process time is set so that the temperature does not exceed 150°C even if heat of reaction is generated by carbon dioxide adsorption. After the predetermined time has elapsed, valves V1 and V2 are closed.

[0022] [Recovery process] The on-off valves V3 and V4 are opened, and the other on-off valves are closed. Superheated steam is introduced from the top of the adsorption column 2 via the superheated steam inlet line L4, and the carbon dioxide adsorbed on the amine-supported adsorbent is desorbed. Because the temperature of the adsorbent layer is above the dew point of the superheated steam due to the above-mentioned adsorption process, there is no loss of heat from the superheated steam, and no condensed water is generated even when the superheated steam is introduced. In addition, the time for the recovery process is set so that the temperature of the adsorbent layer is raised above the temperature of the saturated water vapor pressure as the superheated steam is introduced. The desorbed carbon dioxide is sent together with the water vapor to the gas-liquid separator 3 on the recovery line L3, where the water and carbon dioxide gas are separated and recovered as carbon dioxide gas. After a predetermined time has elapsed, the on-off valves V3 and V4 are closed.

[0023] [Cooling process] The on-off valves V5 and V6 are opened, and the other on-off valves are closed. Cooling gas is introduced from the bottom of the adsorption column 2 via the cooling gas inlet line L5 to cool the adsorbent layer. The cooling step time is set so that the temperature of the adsorbent layer at the end of the cooling step is a predetermined temperature that is 50°C or higher and lower than the temperature of the superheated steam, preferably 100°C or lower. By setting the temperature within this range, the temperature at which the amine-supported adsorbent adsorbs carbon dioxide in the subsequent adsorption step is appropriately maintained, thereby achieving a high carbon dioxide adsorption capacity for the amine-supported adsorbent. Furthermore, since the temperature of the adsorbent layer is equal to or higher than the saturated steam pressure temperature in the recovery step, the generation of condensed water at the start of the cooling step is minimized. After the predetermined time has elapsed, the on-off valves V5 and V6 are closed.

[0024] The carbon dioxide recovery method of the first embodiment of the present invention repeatedly performs an operation cycle in which the above-mentioned adsorption process, recovery process, and cooling process are performed in that order. During this operation, the temperature is controlled so that the temperature of the adsorbent layer at the end of the adsorption process is equal to or higher than the dew point of superheated steam and equal to or lower than 150°C, and the temperature of the adsorbent layer at the end of the cooling process is equal to or higher than 50°C and lower than the superheated steam temperature. Furthermore, the temperature of the adsorbent layer at the end of the recovery process is controlled so that it is equal to or higher than the temperature of saturated steam pressure.

[0025] In this carbon dioxide recovery method, the temperature of the adsorbent layer at the end of the adsorption process, i.e., at the start of the recovery process, is above the dew point of the superheated steam, so no condensed water is generated even when superheated steam is introduced in the recovery process. Furthermore, the temperature of the adsorbent layer at the end of the recovery process, i.e., at the start of the cooling process, is above the temperature of the saturated steam pressure, so only a small amount of condensed water is generated when the cooling gas is introduced. Therefore, the amine-supported adsorbent is not covered with condensed water throughout the entire process. This eliminates the need for a drying process, reducing the gas and energy required for drying.

[0026] Furthermore, since the temperature of the adsorbent at the start of the adsorption process is 50°C to 100°C, a high carbon dioxide adsorption capacity can be obtained, particularly for amine-supported adsorbents that support amine compounds such as tetraethylenepentamine and polyethyleneimine. Furthermore, since the adsorption process is performed so that the adsorbent layer does not exceed 150°C, the amine-supported adsorbent does not deteriorate. Therefore, the amine-supported adsorbent can maintain a high carbon dioxide adsorption capacity.

[0027] In the first embodiment, the cooling gas is introduced from the bottom side of the adsorption column 2, along with the feed gas. However, the cooling gas may be introduced from the opposite side of the feed gas introduction direction. However, during the adsorption process, the temperature of the adsorbent layer rises due to the generation of reaction heat from carbon dioxide adsorption. Because the temperature of the adsorbent layer on the feed gas introduction side is higher, if the cooling gas is introduced from the opposite side of the feed gas, the temperature of the adsorbent layer may exceed the amine agent degradation temperature in the adsorption process unless the entire adsorbent layer is cooled. On the other hand, because the generation of reaction heat on the side opposite the feed gas introduction (the upper side of the adsorption column 2 in the first embodiment) is low, introducing the cooling gas from the same direction as the feed gas eliminates the need to cool the entire adsorbent layer. This reduces the amount of cooling gas and the power required for the vacuum pump. Note that condensation may occur when the cooling gas is introduced. If the cooling gas is introduced from the top side of the adsorption column 2, the condensed water may descend down the adsorbent layer and accumulate at the bottom. When the cooling gas is introduced from the bottom side of the adsorption column 2, even if condensed water is generated at the bottom, it does not affect the amine-supported adsorbent at the top. Therefore, it is preferable to introduce the cooling gas, like the raw material gas, from the lower side of the adsorption column 2. When a cooling gas that is not saturated with water is used, the drying of the amine-supported adsorbent can be minimized, and a high carbon dioxide adsorption amount can be maintained.

[0028] Furthermore, although the cooling process of the first embodiment involves introducing a cooling gas, by closing the on-off valve V5, opening the on-off valve V6, and closing the other on-off valves, and exhausting the gas using a vacuum pump installed downstream of the cooling off-gas exhaust line L6, the temperature of the adsorbent layer can be lowered and cooled by the effects of pressure reduction and desorption of the adsorbate without introducing a cooling gas.

[0029] The carbon dioxide capture method according to the first embodiment uses an amine-supported adsorbent, which significantly reduces the energy consumed for sensible heat and latent heat of vaporization during the regeneration step of the chemical absorption process, compared to a chemical absorption process using an aqueous amine solution. Furthermore, as described above, suppressing the generation of condensed water throughout the entire process reduces the risk of amine leakage from the amine-supported adsorbent. Furthermore, since this carbon dioxide capture method can be applied to fixed-bed carbon dioxide capture systems, wear and tear on the amine-supported adsorbent can be minimized compared to moving-bed capture systems, enabling long-term use. Moving-bed systems require moving parts inside the system to move the amine-supported adsorbent, which requires periodic maintenance that requires the interior to be opened, whereas fixed-bed systems do not. Therefore, the carbon dioxide capture method according to the present invention reduces the frequency and cost of maintenance.

[0030] In the first embodiment, an amine-supported adsorbent is used as the carbon dioxide adsorbent. However, similar effects can be obtained by using a hydrophobic adsorbent such as activated carbon, cerium, zirconia, or high-silica zeolite, since the generation of condensed water is suppressed.

[0031] To improve the quality of the recovered carbon dioxide, a device for removing moisture and trace impurities may be installed in the recovery line L3. Furthermore, since the drain discharged from the gas-liquid separator 3 contains dissolved carbon dioxide, the dissolved carbon dioxide may be discharged by heating or the like and recovered. Alternatively, the water containing carbon dioxide may be used for culturing microalgae, etc. [Example]

[0032] As Example 1, a carbon dioxide recovery method according to a first embodiment of the present invention was carried out under the following conditions: A raw material gas with a carbon dioxide concentration of 30%, a temperature of 60°C, and a pressure of 50 kPa (g) was introduced into adsorption column 2. The time for each step was set so that the temperature of the adsorbent layer would be 60°C at the start of the adsorption step (at the end of the cooling step).

[0033] In the adsorption step, carbon dioxide is adsorbed onto the amine-supported adsorbent, generating reaction heat, and at the end of the adsorption step, the temperature of the entire adsorbent layer reaches approximately 115°C. 110℃ Superheated steam at a pressure of 20 kPa (g) was introduced to desorb the carbon dioxide adsorbed on the amine-supported adsorbent.

[0034] [Comparative Example 1] As a comparative example, the same carbon dioxide recovery method was carried out under the following conditions: A raw material gas with a carbon dioxide concentration of 30%, a temperature of 30°C, and a pressure of 50 kPa (g) was introduced into adsorption column 2. The time for each step was set so that the temperature of the adsorbent layer at the start of the adsorption step (at the end of the cooling step) would be 30°C.

[0035] In the adsorption step, carbon dioxide is adsorbed onto the amine-supported adsorbent, generating reaction heat, and at the end of the adsorption step, the temperature of the entire adsorbent layer reaches approximately 85°C. Compared to Example 1, the temperature of the adsorbent layer was lower, so 20% more amine-supported adsorbent was required. In addition, in the recovery step, the temperature 110℃ Superheated steam at a pressure of 20 kPa (g) was introduced to desorb the carbon dioxide adsorbed on the amine-supported adsorbent. Furthermore, in the case of Comparative Example 1, the temperature of the superheated steam introduced during the recovery process was lower than the dew point of the superheated steam, so condensed water was generated in the early stage of the recovery process. If the superheated steam was allowed to continue to flow, the condensed water would evaporate, but 15% more steam was required compared to Example 1.

[0036] Fig. 2 is a diagram showing an example of a carbon dioxide capture apparatus to which a carbon dioxide capture method according to a second embodiment of the present invention, which will be described later, can be applied. Unlike the carbon dioxide capture apparatus 10 shown in Fig. 1, the carbon dioxide capture apparatus 20 shown in Fig. 2 is a three-cylinder type, having three adsorption columns 12. By using two or more adsorption columns, it is possible to continuously perform the processes of adsorbing carbon dioxide in the raw material gas and desorbing and recovering the carbon dioxide adsorbed on the amine-supported adsorbent.

[0037] As shown in Figure 2, carbon dioxide capture device 20 includes three adsorption columns 12 (adsorption columns 12a, 12b, and 12c) whose adsorbent layers are filled with an amine-supported adsorbent. It receives a feed gas from a feed gas supply source, adsorbs carbon dioxide in the feed gas within adsorption columns 12, and discharges it as off-gas. It also introduces superheated steam from the top of adsorption columns 12 and recovers carbon dioxide from the bottom of adsorption columns 12. Cooling gas is also introduced from the bottom of adsorption columns 12. The recovered CO2-rich gas, which has a high carbon dioxide concentration, is temporarily stored in capture tank 14, and a portion of it is introduced as purge gas from the bottom of adsorption columns 12 and discharged from the top as CO2 purge off-gas.

[0038] The specific piping configuration of the carbon dioxide capture device 20 is as follows: Each adsorption column 12 (12a, 12b, 12c) is provided with a lower pipe L17 (L17a, L17b, L17c) at its lower end, and an upper pipe L18 (L18a, L18b, L18c) at its upper end.

[0039] A raw material gas supply line L21 connected to a raw material gas supply source branches into raw material gas supply branch lines L21a, L21b, and L21c. The raw material gas supply branch line L21a is connected to the lower pipe L17a of adsorption column 12a, the raw material gas supply branch line L21b is connected to the lower pipe L17b of adsorption column 12b, and the raw material gas supply branch line L21c is connected to the lower pipe L17c of adsorption column 12c.

[0040] Off-gas discharge branch lines L22a, L22b, and L22c extend from the off-gas discharge line L22, and the off-gas discharge branch line L22a is connected to the upper pipe L18a of the adsorption column 12a, the off-gas discharge branch line L22b is connected to the upper pipe L18b of the adsorption column 12b, and the off-gas discharge branch line L22c is connected to the upper pipe L18c of the adsorption column 12c.

[0041] Branch recovery lines L23a, L23b, and L23c extend from the recovery line L23. Branch recovery line L23a is connected to the lower pipe L17a of adsorption column 12a, branch recovery line L23b is connected to the lower pipe L17b of adsorption column 12b, and branch recovery line L23c is connected to the lower pipe L17c of adsorption column 12c. A gas-liquid separator 13 is also provided in the recovery line L23 to separate water and carbon dioxide gas. The carbon dioxide gas separated by the gas-liquid separator 13 is recovered and stored in recovery tank 14 as CO2-rich gas with a high carbon dioxide concentration.

[0042] Superheated steam introduction branch lines L24a, L24b, and L24c extend from the superheated steam introduction line L24. The superheated steam introduction branch line L24a is connected to the upper pipe L18a of the adsorption column 12a, the superheated steam introduction branch line L24b is connected to the upper pipe L18b of the adsorption column 12b, and the superheated steam introduction branch line L24c is connected to the upper pipe L18c of the adsorption column 12c.

[0043] Cooling gas inlet branch lines L25a, L25b, and L25c extend from the cooling gas inlet line L25. The cooling gas inlet branch line L25a is connected to the lower pipe 17a of the adsorption column 12a, the cooling gas inlet branch line L25b is connected to the lower pipe 17b of the adsorption column 12b, and the cooling gas inlet branch line L25c is connected to the lower pipe 17c of the adsorption column 12c.

[0044] Cooled off-gas discharge branch lines L26a, L26b, and L26c extend from the cooled off-gas discharge line L26. The cooled off-gas discharge branch line L26a is connected to the upper pipe L18a of the adsorption column 12a, the cooled off-gas discharge branch line L26b is connected to the upper pipe L18b of the adsorption column 12b, and the cooled off-gas discharge branch line L26c is connected to the upper pipe L18c of the adsorption column 12c.

[0045] The purge gas introduction line L27 connected to the recovery tank 14 is provided with a gas pump 15, and extends branched into purge gas introduction branch lines L27a, L27b, and L27c downstream of the gas pump 15. The purge gas introduction branch line L27a is connected to the lower pipe L17a of the adsorption column 12a, the purge gas introduction branch line L27b is connected to the lower pipe L17b of the adsorption column 12b, and the purge gas introduction branch line L27c is connected to the lower pipe L17c of the adsorption column 12c.

[0046] Purge-offgas discharge branch lines L28a, L28b, and L28c extend from the purge-offgas discharge line L28. The purge-offgas discharge branch line L28a is connected to the upper pipe L18a of the adsorption column 12a, the purge-offgas discharge branch line L28b is connected to the upper pipe L18b of the adsorption column 12b, and the purge-offgas discharge branch line L28c is connected to the upper pipe L18c of the adsorption column 12c.

[0047] Furthermore, the raw material gas supply branch lines L21a, L21b, and L21c are respectively equipped with on-off valves Va1, Vb1, and Vc1, and the off-gas discharge branch lines L22a, L22b, and L22c are respectively equipped with on-off valves Va2, Vb2, and Vc2.

[0048] The recovery branch lines L23a, L23b, and L23c are respectively equipped with on-off valves Va3, Vb3, and Vc3. The superheated steam introduction branch lines L24a, L24b, and L24c are respectively equipped with on-off valves Va4, Vb4, and Vc4.

[0049] The cooling gas inlet branch lines L25a, L25b, and L25c are respectively equipped with on-off valves Va5, Vb5, and Vc5. The cooling off-gas outlet branch lines L26a, L26b, and L26c are respectively equipped with on-off valves Va6, Vb6, and Vc6.

[0050] The purge gas inlet branch lines L27a, L27b, and L27c are respectively fitted with on-off valves Va7, Vb7, and Vc7, and the purge off-gas outlet branch lines L28a, L28b, and L28c are respectively fitted with on-off valves Va8, Vb8, and Vc8.

[0051] The carbon dioxide recovery method of the second embodiment of the present invention uses carbon dioxide recovery apparatus 20 configured as described above, and is configured to repeat the following adsorption process, purging process, recovery process, and cooling process in a predetermined order and at predetermined time intervals in each of adsorption cylinders 12a, 12b, and 12c.

[0052] [Adsorption process] In the adsorption step, the on-off valve Va1 (or Vb1 or Vc1) and the on-off valve Va2 (or Vb2 or Vc2) are opened, and the raw material gas is introduced into the adsorption column 12a (or 12b or 12c) from the bottom side via the raw material gas supply branch line L21a (or L21b or L21c). Carbon dioxide in the raw material gas is adsorbed by the amine-supported adsorbent, and the remaining components are discharged as off-gas from the off-gas discharge branch line L22a (or L22b or L22c).

[0053] [Purge process] In the purging step, the on-off valves Va7 (or Vb7 or Vc7) and Va8 (or Vb8 or Vc8) are opened, and a portion of the recovered gas stored in the recovery tank 14 is introduced into the adsorption column 12a (or 12b or 12c) from the lower side via the purge gas inlet branch line L27a (or L27b or L27c). The remaining components adsorbed to the amine-supported adsorbent and the components remaining in the adsorption column 12a are discharged as purge-off gas from the purge-off gas outlet branch line L28a (or L28b or L28c).

[0054] [Recovery process] In the recovery step, the on-off valves Va3 (or Vb3 or Vc3) and Va4 (or Vb4 or Vc4) are opened, and superheated steam is circulated through the superheated steam inlet branch line L24a (or L24b or L24c), thereby desorbing the carbon dioxide adsorbed in the amine-supported adsorbent and regenerating the amine-supported adsorbent. The desorbed carbon dioxide is sent to the gas-liquid separator 13 via the recovery branch line L23a (or L23b or L23c), where it is recovered and stored in the recovery tank 14 as a recovered gas (CO2-rich gas with a high carbon dioxide concentration).

[0055] [Cooling process] In the cooling step, the on-off valves Va5 (or Vb5 or Vc5) and Va6 (or Vb6 or Vc6) are opened, and the cooling gas is circulated from the lower side of the adsorption column 12a through the cooling gas inlet branch line L25a (or L25b or L25c), thereby cooling the amine-supported adsorbent. The cooled cooling gas is discharged from the cooled off-gas outlet branch line L26a (or L26b or L26c).

[0056] The temperature settings of the adsorbent layer in the adsorption process, recovery process, and cooling process in the second embodiment are the same as those in the first embodiment. In the carbon dioxide recovery method according to the second embodiment, adsorption column 12a, adsorption column 12b, and adsorption column 12c each repeatedly perform one cycle of "adsorption process, purging process and recovery process, cooling process" → "purging process and recovery process, cooling process, adsorption process" → "cooling process, adsorption process, purging process, and recovery process" to transition between processes (see FIG. 3). Note that while FIG. 3 shows the time for each process, this is merely an example.

[0057] In each adsorption column, the adsorption step, recovery step, and cooling step are performed in this order, as in the first embodiment, but the second embodiment differs in that a purge step is performed before the recovery step. The purpose of the purge step is to discharge the remaining components adsorbed to the amine-supported adsorbent at the end of the adsorption step and the impurities (e.g., oxygen and nitrogen) in the gas remaining in the adsorption column together with the purge-off gas to the outside of the system before the recovery step so that these remaining components and impurities do not become mixed into the recovery gas in the recovery step. If a portion of the recovery gas is used as the purge gas, the inside of the adsorption column is replaced with recovery gas with a high carbon dioxide concentration. Therefore, a higher concentration of carbon dioxide can be recovered in the recovery step after the purge step.

[0058] If three or more adsorption columns are used, as in the second embodiment, one of the adsorption columns is performing the recovery process, so carbon dioxide can be recovered continuously. As in the first embodiment, the second embodiment also does not require a drying process. When carbon dioxide is continuously recovered using a fixed-bed carbon dioxide recovery device with two or more columns, as in the second embodiment, the elimination of the drying process shortens the time for the adsorption process, making it possible to reduce the amount of amine-supported adsorbent and the size of the adsorption columns.

[0059] In the second embodiment, a part of the recovered gas is used as the purge gas, but superheated steam introduced in the recovery step can also be used.

[0060] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention. For example, the number of adsorption columns is not necessarily limited to one or three, and the present invention can be applied to any number of adsorption columns, including two, four, or more. Furthermore, the purging step is not an essential step, and does not have to be performed in every cycle. [Explanation of symbols]

[0061] 2...adsorption column, 3...gas-liquid separator, 10...carbon dioxide capture device, 12 (12a, 12b, 12c)...adsorption column, 13...gas-liquid separator, 14...recovery tank, 15...gas pump, 20...CO2 capture device, V1 to V6...opening and closing valves, Va1, Vb1, Vc1, Va2, Vb2, Vc2, Va3, Vb3, Vc3, Va4, Vb4, Vc4, Va5, Vb5, Vc5, Va6, Vb6, Vc6, Va7, Vb7, Vc7, Va8, Vb8, Vc8...opening and closing valves, L1...raw material gas supply line, L2...off-gas discharge line, L3...recovery line, L4...superheated steam introduction line, L5...cooling gas introduction line, L6...cooling off-gas discharge line, L17 (L17a, L17b, L17c)...lower piping, L18 (L18a, L18b, L18c)...upper piping, L21... Raw material gas supply line, L21a, L21b, L21c... raw material gas supply branch line, L22... off-gas discharge line, L22a, L22b, L22c... off-gas discharge branch line, L23... recovery line, L23a, L23b, L23c... recovery branch line, L24... superheated steam introduction line, L24a, L24b, L24c... superheated steam introduction branch line, L25... cooling gas introduction line, L25a, L25b, L25c... cooling gas introduction branch line, L26... cooling off-gas discharge line, L26a, L26b, L26c... cooling off-gas discharge branch line, L27... purge gas introduction line, L27a, L27b, L27c... purge gas introduction branch line, L28... purge off-gas discharge line, L28a, L28b, L28c... purge off-gas discharge branch line

Claims

1. A carbon dioxide recovery method comprising introducing a raw material gas, which is a mixed gas consisting of two or more gas components including carbon dioxide, into one or more adsorption columns having an adsorbent layer filled with a carbon dioxide adsorbent, and separating and recovering carbon dioxide from the raw material gas, an adsorption step of adsorbing carbon dioxide in the raw material gas onto the carbon dioxide adsorbent; a recovery step of introducing superheated steam into the adsorption column to desorb the carbon dioxide adsorbed in the carbon dioxide adsorbent and recovering it as a recovered gas; a cooling step of cooling the carbon dioxide adsorbent; Including, an operation cycle in which the adsorption step, the recovery step, and the cooling step are performed in this order is repeated; In the adsorption step, the temperature of the adsorbent layer at the end of the adsorption step is raised to a dew point of superheated steam or higher by reaction heat generated when carbon dioxide is adsorbed onto the carbon dioxide adsorbent. A carbon dioxide recovery method characterized by:

2. 2. The method for recovering carbon dioxide according to claim 1, wherein the carbon dioxide adsorbent is an amine-supported adsorbent.

3. 50°C≦temperature of the adsorbent layer at the end of the cooling step<temperature of the superheated steam≦150°C 2. The carbon dioxide recovery method according to claim 1 .

4. 2. The method for recovering carbon dioxide according to claim 1, wherein the temperature of the superheated steam is 105°C to 150°C.

5. 2. The carbon dioxide recovery method according to claim 1, wherein the pressure of the superheated steam is 10 to 300 kPa (g).

6. 2. The method for recovering carbon dioxide according to claim 1, wherein the carbon dioxide concentration in the raw material gas is 1 to 50%.

7. the cooling step includes introducing a cooling gas into the adsorption column to cool the carbon dioxide adsorbent; 2. The carbon dioxide recovery method according to claim 1, wherein the direction in which the raw material gas is introduced into the adsorption column is the same as the direction in which the cooling gas is introduced into the adsorption column.

8. 8. The carbon dioxide recovery method according to claim 7, wherein the raw material gas and the cooling gas are introduced into the adsorption column from a lower side thereof.

9. 8. The carbon dioxide recovery method according to claim 1, wherein there are three or more adsorption columns, and when at least one adsorption column is performing the adsorption process, at least one of the other adsorption columns is performing the recovery process and at least one is performing the cooling process.

10. 10. The carbon dioxide recovery method according to claim 9, further comprising the step of: conducting a purging step of introducing a purge gas into the adsorption column before the recovery step.

11. 11. The carbon dioxide recovery method according to claim 10, wherein the purge gas is a part of the recovery gas.

12. 11. The carbon dioxide recovery method according to claim 10, wherein the purge gas is the superheated steam.

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