Carbon dioxide recovery system and carbon dioxide recovery method

Abstract

This carbon dioxide recovering system (1) comprises: a first adsorption tower (10) that accommodates a first adsorbent (14); and a second adsorption tower (40) that accommodates a second adsorbent (41). When the second adsorbent (41) comes into contact with a first concentrated gas supplied from the first adsorption tower (10), the second adsorbent (41) adsorbs carbon dioxide in the first concentrated gas. When heated in a second heating part (44), the second adsorbent (41) desorbs carbon dioxide adsorbed by the second adsorbent (41) and produces a second concentrated gas containing carbon dioxide desorbed from the second adsorbent (41) and having a carbon dioxide concentration higher than the first concentrated gas.

Description

Technical Field

[0001] The present disclosure relates to a carbon dioxide recovery system and a carbon dioxide recovery method.

Background Art

[0002] Carbon dioxide is regarded as a problem as a cause of global warming, and efforts to suppress the increase in carbon dioxide concentration are spreading worldwide. As one method of reducing the carbon dioxide concentration in the atmosphere, a technique called direct air capture (DAC) has been proposed. DAC is a technique for directly capturing carbon dioxide from the air. The carbon dioxide captured by DAC can be stored underground or used as a raw material for various compounds.

[0003] Patent Document 1 discloses a method for separating carbon dioxide from air by cyclic adsorption / desorption using an adsorbent. The method includes an adsorption step of adsorbing carbon dioxide to the adsorbent and a desorption step of desorbing carbon dioxide from the adsorbent. In the desorption step, the inside of the unit is evacuated until it becomes a vacuum state.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In DAC, since carbon dioxide is directly adsorbed from the air, a large amount of air is taken into the unit. Therefore, conventional DAC units are large and may require a lot of energy to reduce the pressure inside the unit until it becomes a vacuum state.

[0006] Therefore, an object of the present disclosure is to provide a carbon dioxide recovery system and a carbon dioxide recovery method capable of reducing the energy required for depressurization when desorbing carbon dioxide from an adsorbent.

Means for Solving the Problems

[0007] The carbon dioxide recovery system according to the present disclosure includes a first adsorption tower that houses a first adsorbent and includes a first heating unit that heats the first adsorbent, and a second adsorption tower that houses a second adsorbent and includes a second heating unit that heats the second adsorbent. When the first adsorbent comes into contact with air supplied from outside the first adsorption tower, it adsorbs carbon dioxide in the air. When heated by the first heating unit, it desorbs the carbon dioxide adsorbed on the first adsorbent, and generates a first concentrated gas that contains the carbon dioxide desorbed from the first adsorbent and has a higher carbon dioxide concentration than air. When the second adsorbent comes into contact with the first concentrated gas supplied from the first adsorption tower, it adsorbs carbon dioxide in the first concentrated gas. When heated by the second heating unit, it desorbs the carbon dioxide adsorbed on the second adsorbent, and generates a second concentrated gas that contains the carbon dioxide desorbed from the second adsorbent and has a higher carbon dioxide concentration than the first concentrated gas.

[0008] The second adsorption tower may have a smaller volume than the first adsorption tower.

[0009] The carbon dioxide recovery system may further include a depressurization unit that depressurizes the inside of the second adsorption tower.

[0010] The carbon dioxide recovery system may further include a gas supply unit that supplies at least one purge gas selected from the group consisting of air, hydrogen, water vapor, and inert gas into the second adsorption tower.

[0011] The bulk density of the second adsorbent may be equal to or greater than the bulk density of the first adsorbent.

[0012] The bulk density of the second adsorbent may be smaller than the bulk density of the first adsorbent.

[0013] The carbon dioxide recovery system further includes a concentration measurement unit that measures the carbon dioxide concentration in the first concentrated gas, and the first concentrated gas derived from the first adsorption tower may be introduced into the first adsorption tower according to the carbon dioxide concentration measured by the concentration measurement unit.

[0014] The carbon dioxide recovery method according to the present disclosure includes a step of adsorbing carbon dioxide in the air with a first adsorbent accommodated in a first adsorption tower by contact with air supplied from outside the first adsorption tower, a step of desorbing the carbon dioxide adsorbed on the first adsorbent by heating to generate a first concentrated gas containing the carbon dioxide desorbed from the first adsorbent and having a higher carbon dioxide concentration than air, a step of adsorbing the carbon dioxide in the first concentrated gas with a second adsorbent accommodated in a second adsorption tower by contact with the first concentrated gas supplied from the first adsorption tower, and a step of desorbing the carbon dioxide adsorbed on the second adsorbent by heating to generate a second concentrated gas containing the carbon dioxide desorbed from the second adsorbent and having a higher carbon dioxide concentration than the first concentrated gas.

Advantages of the Invention

[0015] According to the present disclosure, it is possible to provide a carbon dioxide recovery system and a carbon dioxide recovery method capable of reducing the energy required for depressurization when desorbing carbon dioxide from the adsorbent.

Brief Description of the Drawings

[0016]

Figure 1

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Figure 8

BEST MODE FOR CARRYING OUT THE INVENTION

[0017] Hereinafter, several exemplary embodiments will be described with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation and may be different from the actual ratios.

[0018] [Carbon Dioxide Recovery System] As shown in FIG. 1, the carbon dioxide recovery system 1 according to the present embodiment includes a first adsorption tower 10, an air supply unit 30, a second adsorption tower 40, and a recovery unit 70. In the carbon dioxide recovery system 1 according to the present embodiment, carbon dioxide in the air is adsorbed by the first adsorption tower 10, and the carbon dioxide adsorbed by the first adsorption tower 10 is concentrated and recovered by the second adsorption tower 40. Hereinafter, each component will be described in detail.

[0019] The first adsorption tower 10 is provided with an inlet 11 for introducing air into the first adsorption tower 10 and an outlet 12 for discharging the air in the first adsorption tower 10. Dampers are provided at the inlet 11 and the outlet 12. The air supply unit 30 is connected to the inlet 11 to supply air into the first adsorption tower 10. The air supply unit 30 may be a blower. When the inlet 11 and the outlet 12 are opened, external air is introduced into the first adsorption tower 10 from the inlet 11. The introduced air comes into contact with the first adsorbent 14 accommodated in the first adsorption tower 10 and is then discharged from the outlet 12.

[0020] Note that the air supply unit 30 may be connected to the air outlet 12 instead of the air inlet 11, and air may be supplied from the air inlet 11 into the first adsorption tower 10 by depressurizing the inside of the first adsorption tower 10. Further, in the carbon dioxide recovery system 1 according to the present embodiment, the first adsorbent 14 and air are brought into contact by forcibly supplying air into the first adsorption tower 10 by the air supply unit 30. However, instead of the air supply unit 30, air may be supplied into the first adsorption tower 10 by natural ventilation.

[0021] The first adsorption tower 10 houses the first adsorption section 13. The first adsorption section 13 is arranged with a gap from the side wall section of the first adsorption tower 10. The first adsorption section 13 includes the first adsorbent 14 and a support section 15 that supports the first adsorbent 14. The support section 15 includes a cylindrical outer wall 16 and a cylindrical inner wall 17 having a diameter smaller than that of the outer wall 16. The first adsorbent 14 is filled between the outer wall 16 and the inner wall 17, and the first adsorbent 14 is supported by the support section 15 so as to have a cylindrical shape. The opening on one end side of the cylindrical support section 15 is connected to the air inlet 11, and the opening on the other end side is blocked by a top plate 18. A plurality of holes 19 are provided in the outer wall 16 and the inner wall 17. Therefore, the air introduced from the air inlet 11 passes through the support section 15 while contacting the first adsorbent 14 from the inner wall 17 side toward the outer wall 16 side.

[0022] Note that the cylindrical first adsorbent 14 is arranged to extend in the vertical direction, but it may be arranged to extend in the horizontal direction. Further, in the present embodiment, air is passed from the inner wall 17 side toward the outer wall 16 side, but air may be passed from the outer wall 16 side toward the inner wall 17 side. Further, the shape of the first adsorbent 14 is not limited to a cylinder, and it may be a circular flat plate or a rectangular flat plate.

[0023] When the first adsorbent 14 comes into contact with the air supplied from the outside of the first adsorption tower 10, it adsorbs carbon dioxide in the air. The first adsorbent 14 may contain at least one selected from the group consisting of a porous body, an alkali metal, and an alkaline earth metal. These materials can efficiently adsorb carbon dioxide. The porous body may contain at least one selected from the group consisting of zeolite, alumina, silica, resin, clay, and activated carbon. The first adsorbent 14 containing an alkali metal may contain at least one of a carbonate of the alkali metal and a lithium transition metal composite oxide. The first adsorbent 14 containing an alkaline earth metal may contain an oxide of the alkaline earth metal or the like.

[0024] The first adsorbent 14 may include at least one of a porous body having a basic substance supported on its surface and a porous body whose surface is modified with a base. Such materials have a large specific surface area and high reactivity of the base with carbon dioxide, so it is possible to adsorb a large amount of carbon dioxide. The porous body described above may be used. Further, the basic substance may contain at least one amine compound selected from the group consisting of a primary amine compound, a secondary amine compound, and a tertiary amine compound. Further, the base for modifying the surface of the porous body may be an amino group. These materials can be obtained by immersing the porous body in the above-described amine compound and then drying it to support a basic substance on the surface of the porous body or modify it with a base. Alternatively, these materials can be obtained by using a chemical reaction such as a dealcoholization reaction between the porous body surface and the amine compound to modify the porous body with a basic substance.

[0025] The first adsorption tower 10 includes a first heating unit 20 that heats the first adsorbent 14. When the first adsorbent 14 is heated by the first heating unit 20, carbon dioxide adsorbed on the first adsorbent 14 is desorbed. Therefore, the first adsorbent 14 generates a first concentrated gas that contains carbon dioxide desorbed from the first adsorbent 14 and has a higher carbon dioxide concentration than the air supplied from outside the first adsorption tower 10. The first adsorption tower 10 is provided with a discharge port 23 for discharging the first concentrated gas, and the first concentrated gas is discharged from the first adsorption tower 10 through the discharge port 23 and introduced into the second adsorption tower 40.

[0026] The first heating unit 20 includes a power source 21 and a heating element 22 electrically connected to the power source 21. Then, when an electric current flows through the heating element 22 by the power source 21, the heating element 22 generates heat. The heating element 22 is embedded inside the first adsorbent 14. The heating element 22 only needs to be able to heat the first adsorbent 14, and may be provided so as to surround the periphery of the first adsorption part 13. The first heating unit 20 may include at least one selected from the group consisting of a band heater, a film heater, a plate heater, a sheathed heater, a tube heater, a hose heater, a plug heater, and a flange heater. Further, the first heating unit 20 may heat the first adsorbent 14 by circulating a heat medium such as steam through a conduit. Further, the first heating unit 20 may heat the first adsorbent 14 by at least one selected from the group consisting of induction heating, resistance heating, microwave heating, and millimeter wave heating.

[0027] The second adsorption tower 40 is provided with an inlet 42 for introducing the first concentrated gas. The outlet 23 of the first adsorption tower 10 and the inlet 42 of the second adsorption tower 40 are connected via a pipe 51. The pipe 51 is provided with an on-off valve 52, a first cooling section 54, a separation section 55, a concentration measurement section 56, and an on-off valve 57 in this order from the first adsorption tower 10. A pipe 58 branches from the pipe 51 between the concentration measurement section 56 and the second adsorption tower 40 and is connected to the inlet 24 provided in the first adsorption tower 10. The pipe 58 is provided with an on-off valve 59 and a blower 53. The outlet 43 of the second adsorption tower 40 and the inlet 24 of the first adsorption tower 10 are connected via a pipe 60. The pipe 60 is provided with an on-off valve 61. The outlet 48 of the second adsorption tower 40 and the recovery section 70 are connected via a pipe 71. The pipe 71 is provided with an on-off valve 72.

[0028] The blower 53 sucks the first concentrated gas in the first adsorption tower 10 so that the first concentrated gas flows in the pipe 51. When the on-off valve 52 and the on-off valve 59 are opened and the on-off valve 57 and the on-off valve 61 are closed, the blower 53 introduces the first concentrated gas from the inlet 24 into the first adsorption tower 10. When the on-off valve 52, the on-off valve 57, and the on-off valve 61 are opened and the on-off valve 59 and the on-off valve 72 are closed, the blower 53 introduces the first concentrated gas into the second adsorption tower 40.

[0029] The first cooling section 54 cools the first concentrated gas. By cooling the first concentrated gas in the first cooling section 54, the moisture in the first concentrated gas condenses.

[0030] The separation section 55 recovers the moisture condensed in the first cooling section 54 from the first concentrated gas. By removing the moisture from the first concentrated gas, it is possible to supply the dried first concentrated gas to the second adsorption tower 40. The separation section 55 may include a drain tank. The drain tank is provided with a thermometer, and the temperature of the water condensed in the drain tank may be measured.

[0031] The concentration measurement unit 56 measures the carbon dioxide concentration in the first concentrated gas. Then, the first concentrated gas derived from the first adsorption tower 10 may be introduced into the first adsorption tower 10 according to the carbon dioxide concentration measured by the concentration measurement unit 56. By introducing the first concentrated gas into the first adsorption tower 10 without passing through the second adsorption tower 40, the desorption of carbon dioxide remaining adsorbed on the first adsorbent 14 can be promoted, and the carbon dioxide concentration in the first concentrated gas can be increased. For example, when the carbon dioxide concentration is lower than a predetermined concentration, the first concentrated gas may be introduced into the first adsorption tower 10, and when the carbon dioxide concentration is higher than a predetermined concentration, the first concentrated gas may be introduced into the second adsorption tower 40. When it has been confirmed by preliminary experiments or the like that the carbon dioxide concentration in the first concentrated gas is higher than the desired concentration, the first concentrated gas may be introduced into the second adsorption tower 40 without measuring the concentration.

[0032] The second adsorption tower 40 houses a second adsorbent 41. The second adsorbent 41 adsorbs carbon dioxide in the first concentrated gas when it comes into contact with the first concentrated gas supplied from the first adsorption tower 10. The second adsorbent 41 may be filled in the flow path of the first concentrated gas. The second adsorbent 41 may be a structure such as a flat plate shape, a column shape, a polygonal column shape, an irregular shape, a powder shape, a particle shape, a spherical shape, an ellipsoidal shape, a conical shape, or a polygonal pyramid shape. As the second adsorbent 41, those exemplified as the first adsorbent 14 can be used. The first adsorbent 14 and the second adsorbent 41 may be of the same type or different types.

[0033] The second adsorption tower 40 is provided with a discharge port 43 for discharging the first concentrated gas that has come into contact with the second adsorbent 41. The discharge port 43 of the second adsorption tower 40 and the inlet 24 of the first adsorption tower 10 are connected via a pipe 60. By supplying the first concentrated gas that has come into contact with the second adsorbent 41 to the first adsorption tower 10 through the pipe 60, the amount of carbon dioxide moving from the first adsorbent 14 to the second adsorbent 41 can be increased.

[0034] The exposed area of the second adsorbent 41 on the inlet 42 side may be smaller than the exposed area of the first adsorbent 14 on the inlet 11 side. Thereby, the area where air contacts the first adsorbent 14 on the inlet 11 side is larger than the area where the first concentrated gas contacts the second adsorbent 41 on the inlet 42 side. Therefore, the flow path cross-sectional area of the air passing through the first adsorbent 14 is larger than the flow path cross-sectional area of the first concentrated gas passing through the second adsorption tower 40. Therefore, the air flow rate in the first adsorption tower 10 can be made larger than that in the second adsorption tower 40. On the other hand, the flow rate of the first concentrated gas flowing into the second adsorption tower 40 can be made small, and the time for the first concentrated gas to contact the second adsorbent 41 can be lengthened. Therefore, carbon dioxide can be easily concentrated in the second adsorption tower 40.

[0035] The bulk density of the second adsorbent 41 may be equal to or higher than the bulk density of the first adsorbent 14. When the bulk density of the second adsorbent 41 is larger than the bulk density of the first adsorbent 14, carbon dioxide can be adsorbed on the second adsorbent 41 at a higher density than on the first adsorbent 14. Therefore, since carbon dioxide can be concentrated more easily, the carbon dioxide recovery effect can be improved. On the other hand, when the bulk density of the first adsorbent 14 is smaller than the bulk density of the second adsorbent 41, the pressure loss in the first adsorption tower 10 can be made lower than the pressure loss in the second adsorption tower 40. Therefore, the air flow rate in the first adsorption tower 10 can be made larger than that in the second adsorption tower 40. Also, when the bulk density of the second adsorbent 41 is equal to the bulk density of the first adsorbent 14, since the same adsorbent can be used, it is not necessary to prepare separate adsorbents and the maintenance and management of the apparatus are simplified. On the other hand, the bulk density of the second adsorbent 41 may be smaller than the bulk density of the first adsorbent 14. Thereby, since the pressure loss of the second adsorbent 41 is reduced, the power of the blower 53 can be reduced. Also, by depressurizing the second adsorption tower 40 and purging with water vapor, carbon dioxide can be recovered efficiently.

[0036] The carbon dioxide adsorption capacity of the second adsorbent 41 may be equal to or greater than the carbon dioxide adsorption capacity of the first adsorbent 14. In this case, most of the carbon dioxide adsorbed in the first adsorption tower 10 can be adsorbed by the second adsorption tower 40. On the other hand, the carbon dioxide adsorption capacity of the second adsorbent 41 may be less than the carbon dioxide adsorption capacity of the first adsorbent 14. In this case, since the carbon dioxide adsorbed by the second adsorbent 41 easily reaches a saturated state, the finally obtained carbon dioxide concentration can be increased.

[0037] Note that the carbon dioxide adsorption capacity means the product of the carbon dioxide adsorption capacity per unit volume of the adsorbent and the volume of the adsorbent. That is, the carbon dioxide adsorption capacity of the first adsorbent 14 means the product of the carbon dioxide adsorption capacity per unit volume of the first adsorbent 14 [g_CO2 / L_adsorbent] and the volume of the first adsorbent 14 [L_adsorbent]. Similarly, the carbon dioxide adsorption capacity of the second adsorbent 41 means the product of the carbon dioxide adsorption capacity per unit volume of the second adsorbent 41 [g_CO2 / L_adsorbent] and the volume of the second adsorbent 41 [L_adsorbent]. Note that the adsorption capacity means the saturated adsorption capacity under the temperature in the adsorption atmosphere and the carbon dioxide partial pressure.

[0038] The volume of the first adsorbent 14 may be equal to or greater than the volume of the second adsorbent 41. The carbon dioxide concentration in the air introduced into the first adsorption tower 10 is about 400 ppm, which is lower than the concentration of the first concentrated gas introduced into the second adsorption tower 40. Therefore, by making the volume of the first adsorbent 14 larger than the volume of the second adsorbent 41 and making the surface area in contact with carbon dioxide larger than that of the second adsorbent 41, the recovery efficiency of carbon dioxide can be increased. The volume of the first adsorbent 14 may be twice or more, or five times or more, that of the second adsorbent 41.

[0039] The second adsorption tower 40 includes a second heating unit 44 that heats the second adsorbent 41. When the second adsorbent 41 is heated by the second heating unit 44, the carbon dioxide adsorbed by the second adsorbent 41 is desorbed. Therefore, the second adsorbent 41 generates a second concentrated gas that contains the carbon dioxide desorbed from the second adsorbent 41 and has a higher carbon dioxide concentration than the first concentrated gas.

[0040] The second heating unit 44 includes a power source 45 and a heating element 46 electrically connected to the power source 45. Then, when an electric current flows through the heating element 46 by the power source 45, the heating element 46 generates heat. The heating element 46 is embedded inside the second adsorbent 41. The heating element 46 only needs to be able to heat the second adsorbent 41 and may be provided so as to surround the second adsorbent 41. The second heating unit 44 may include at least one selected from the group consisting of a band heater, a film heater, a plate heater, a sheathed heater, a tube heater, a hose heater, a plug heater, and a flange heater. Further, the second heating unit 44 may heat the second adsorbent 41 by circulating a heat medium such as steam through a conduit. Further, the second heating unit 44 may heat the second adsorbent 41 by at least one selected from the group consisting of induction heating, resistance heating, microwave heating, and millimeter wave heating.

[0041] The carbon dioxide recovery system 1 may include a decompression unit 47 that decompresses the inside of the second adsorption tower 40. By decompressing the inside of the second adsorption tower 40 before the adsorption of carbon dioxide, the amount of carbon dioxide adsorbed by the second adsorbent 41 can be increased. Further, by decompressing the inside of the second adsorption tower 40 during the desorption of carbon dioxide, the desorption of carbon dioxide from the second adsorbent 41 can be promoted. Further, by decompressing the inside of the second adsorption tower 40 during the desorption of carbon dioxide, residual gases other than carbon dioxide can be reduced and the carbon dioxide concentration can be increased. The discharge side of the decompression unit 47 may be connected to a pipe 71 downstream of the on-off valve 72 and upstream of a second cooling unit 73 described later to pressurize the obtained high-concentration carbon dioxide mixed gas.

[0042] The second adsorption tower 40 may have a volume smaller than that of the first adsorption tower 10. When the volume of the second adsorption tower 40 is smaller than the volume of the first adsorption tower 10, the inside of the second adsorption tower 40 can be decompressed to a vacuum state with less energy than decompressing the inside of the first adsorption tower 10. Further, when the volume of the second adsorption tower 40 is small, the use of expensive dedicated components such as valves and dampers required to ensure a vacuum state can be reduced.

[0043] The carbon dioxide recovery system 1 may include a gas supply unit 65 that supplies at least one purge gas selected from the group consisting of air, hydrogen, water vapor, and inert gas into the second adsorption tower 40. By supplying these purge gases into the second adsorption tower 40, the desorption of carbon dioxide from the second adsorbent 41 can be promoted. The gas supply unit 65 may be connected, for example, between the on-off valve 57 in the pipe 51 and the second adsorption tower 40.

[0044] When using air as the purge gas, ambient air can be used, so the cost required for the desorption of carbon dioxide can be reduced. Since water vapor condenses by cooling, when using water vapor as the purge gas, the desorbed carbon dioxide and moisture can be easily separated, and the carbon dioxide concentration can be increased. Since the inert gas has low reaction activity, when using an inert gas as the purge gas, carbon dioxide can be recovered in a state containing the inert gas without using a special separation device. When using hydrogen as the purge gas, a mixed gas of hydrogen and carbon dioxide can be obtained, and synthesis gas used for the hydrogenation reaction of carbon dioxide can be generated. Therefore, when using hydrogen as the purge gas, raw materials for various reaction steps such as methanation can be obtained. When using the recovered gas for, for example, methanation, hydrogen may be supplied into the second adsorption tower 40 so that the volume amount of carbon dioxide relative to hydrogen is 20% or more.

[0045] When the volume of the second adsorption tower 40 is smaller than the volume of the first adsorption tower 10, the inside of the second adsorption tower 40 can be purged with an amount less than that desorbed in the first adsorption tower 10. Therefore, the carbon dioxide in the second concentrated gas can be made higher. Also, when the volume of the second adsorption tower 40 is smaller than the volume of the first adsorption tower 10, since the inside of the second adsorption tower 40 can be easily heated, the energy for desorbing carbon dioxide can be reduced. Also, for example, when using water vapor as the purge gas, the energy required to remove the water vapor can be reduced.

[0046] The second adsorption tower 40 is provided with a lead-out port 48 for leading out the second concentrated gas. The lead-out port 48 of the second adsorption tower 40 and the recovery section 70 are connected via a pipe 71. An on-off valve 72, a second cooling section 73, and a compressor 74 are provided in this order in the pipe 71.

[0047] The second cooling section 73 cools the second concentrated gas passing through the pipe 71. The compressor 74 compresses the second concentrated gas and supplies the compressed second concentrated gas to the recovery section 70. As the compressor 74, a known compressor can be used. The recovery section 70 stores the second concentrated gas. The recovery section 70 may be a tank. Note that the carbon dioxide recovery system 1 may not include the recovery section 70, and the second concentrated gas generated in the second adsorption tower 40 may be supplied to a reactor (not shown) and directly used as a reaction raw material.

[0048] The pipe 71 may be provided with a concentration measurement section (not shown) for measuring the concentration of carbon dioxide in the second concentrated gas. Then, the second concentrated gas may be introduced into the first adsorption tower 10 according to the concentration of carbon dioxide measured by the concentration measurement section. For example, when the concentration of carbon dioxide is lower than a predetermined concentration, the second concentrated gas may be introduced into the first adsorption tower 10, and when the concentration of carbon dioxide is higher than the predetermined concentration, the second concentrated gas may be introduced into the recovery section 70. When the second concentrated gas is introduced into the first adsorption tower 10, the carbon dioxide concentration in the second concentrated gas may be increased by concentrating it again in the second adsorption tower 40.

[0049] [Carbon Dioxide Recovery Method] Next, the carbon dioxide recovery method according to the present embodiment will be described. The carbon dioxide recovery method according to the present embodiment includes a first adsorption step, a first desorption step, a second adsorption step, and a second desorption step.

[0050] (First Adsorption Step) As shown in FIG. 2, in the first adsorption step, carbon dioxide in the air is adsorbed by the first adsorbent 14 accommodated in the first adsorption tower 10 by contact with the air supplied from the outside of the first adsorption tower 10. In the first adsorption step, specifically, the inlet 11 and the outlet 12 are opened, and the on-off valves 52, 59, and 61 are closed. Then, the air outside the first adsorption tower 10 is supplied into the first adsorption tower 10 from the inlet 11 by the air supply unit 30. The air supplied into the first adsorption tower 10 is discharged from the first adsorption tower 10 through the outlet 12 after contacting the first adsorbent 14. The temperature in the first adsorption tower 10 in the first adsorption step is not particularly limited and may be normal temperature. The pressure in the first adsorption tower 10 in the first adsorption step is not particularly limited and may be normal pressure.

[0051] (First desorption step) As shown in FIG. 3, in the first desorption step, the carbon dioxide adsorbed on the first adsorbent 14 is desorbed by heating, and a first concentrated gas containing the carbon dioxide desorbed from the first adsorbent 14 and having a higher carbon dioxide concentration than air is generated. When the pressures are the same, the higher the temperature, the lower the adsorption amount of carbon dioxide with respect to the first adsorbent 14. Therefore, when the first adsorbent 14 is heated, carbon dioxide is desorbed from the first adsorbent 14, and a first concentrated gas containing the carbon dioxide desorbed from the first adsorbent 14 and having a higher carbon dioxide concentration than air is generated.

[0052] In the first desorption step, specifically, the inlet 11, the outlet 12, the on-off valves 52, 59, and 61 are closed, and the first adsorbent 14 is heated by the first heating unit 20. When the first concentrated gas is generated, the on-off valve 52 is opened and discharged from the first adsorption tower 10 through the outlet 23. The desorption of carbon dioxide may be promoted by supplying air into the first adsorption tower 10 by the air supply unit 30. The first concentrated gas passes through the pipe 51 and is introduced into the second adsorption tower 40 from the inlet 42.

[0053] As shown in FIG. 4, in the first desorption step, the first concentrated gas may be introduced into the first adsorption tower 10 according to the concentration of carbon dioxide measured by the concentration measurement unit 56. For example, when the carbon dioxide concentration in the first concentrated gas is lower than a predetermined concentration, the first concentrated gas may be introduced into the first adsorption tower 10. Specifically, when the carbon dioxide concentration in the first concentrated gas is lower than a predetermined concentration, the on-off valve 52 and the on-off valve 59 are opened, and the on-off valve 57 and the on-off valve 61 are closed. Thereby, since the first concentrated gas passes through the first adsorption tower 10 again, desorption of carbon dioxide adsorbed on the first adsorbent 14 is promoted, and the carbon dioxide concentration in the first concentrated gas can be increased. The first concentrated gas may pass through the first adsorption tower 10 repeatedly. The first concentrated gas may pass through the first adsorption tower 10 a plurality of times, for example, three or more times. And when the carbon dioxide concentration in the first concentrated gas becomes equal to or higher than a predetermined concentration, the first concentrated gas may be introduced into the second adsorption tower 40.

[0054] (Second Adsorption Step) In the second adsorption step, carbon dioxide in the first concentrated gas is adsorbed by the second adsorbent 41 accommodated in the second adsorption tower 40 by contact with the first concentrated gas supplied from the first adsorption tower 10. As shown in FIG. 5, in the second adsorption step, the first concentrated gas that has contacted the second adsorbent 41 may be supplied to the first adsorption tower 10. In this case, the on-off valve 52, the on-off valve 57, and the on-off valve 61 are opened, and the inlet 11, the outlet 12, the on-off valve 59, and the on-off valve 72 are closed. By supplying the first concentrated gas to the first adsorption tower 10 again, the amount of carbon dioxide moving from the first adsorbent 14 to the second adsorbent 41 can be increased.

[0055] That is, the first concentrated gas that has contacted the second adsorbent 41 is introduced into the first adsorption tower 10 through the pipe 60 and contacts the first adsorbent 14. Since the carbon dioxide concentration of the gas supplied to the first adsorption tower 10 is lowered by the adsorption of carbon dioxide by the second adsorbent 41, the gas that has contacted the first adsorbent 14 promotes the desorption of carbon dioxide adsorbed on the first adsorbent 14. The first concentrated gas that has contacted the first adsorbent 14 is supplied to the second adsorption tower 40 again, and carbon dioxide in the first concentrated gas is adsorbed by the second adsorbent 41.

[0056] (Second detachment process) As shown in FIG. 6, in the second detachment process, carbon dioxide adsorbed on the second adsorbent 41 is desorbed by heating, and a second concentrated gas containing carbon dioxide desorbed from the second adsorbent 41 and having a higher carbon dioxide concentration than the first concentrated gas is generated. In the second detachment process, the on-off valve 57, the on-off valve 61, and the on-off valve 72 are closed, and the second adsorbent 41 is heated by the second heating unit 44. When the second adsorbent 41 is heated, carbon dioxide is desorbed from the second adsorbent 41, and a second concentrated gas containing carbon dioxide desorbed from the second adsorbent 41 and having a higher carbon dioxide concentration than the first concentrated gas is generated.

[0057] As shown in FIG. 7, when the second concentrated gas is generated, the on-off valve 72 is opened, and purge gas is supplied from the gas supply unit 65 to the second adsorption tower 40. The purge gas promotes the desorption of carbon dioxide from the second adsorbent 41. The second concentrated gas is led out from the second adsorption tower 40 through the outlet 48 and recovered by the recovery unit 70 via the pipe 71.

[0058] As described above, the carbon dioxide recovery system 1 according to the present embodiment includes a first adsorption tower 10 that houses the first adsorbent 14 and includes a first heating unit 20 that heats the first adsorbent 14, and a second adsorption tower 40 that houses the second adsorbent 41 and includes a second heating unit 44 that heats the second adsorbent 41. When the first adsorbent 14 comes into contact with air supplied from the outside of the first adsorption tower 10, the first adsorbent 14 adsorbs carbon dioxide in the air. When the first adsorbent 14 is heated by the first heating unit 20, the carbon dioxide adsorbed on the first adsorbent 14 is desorbed, and a first concentrated gas containing carbon dioxide desorbed from the first adsorbent 14 and having a higher carbon dioxide concentration than air is generated. When the second adsorbent 41 comes into contact with the first concentrated gas supplied from the first adsorption tower 10, the second adsorbent 41 adsorbs carbon dioxide in the first concentrated gas. When the second adsorbent 41 is heated by the second heating unit 44, the carbon dioxide adsorbed on the second adsorbent 41 is desorbed, and a second concentrated gas containing carbon dioxide desorbed from the second adsorbent 41 and having a higher carbon dioxide concentration than the first concentrated gas is generated.

[0059] The carbon dioxide recovery method according to this embodiment includes a step of adsorbing carbon dioxide in the air with the first adsorbent 14 accommodated in the first adsorption tower 10 by contact with the air supplied from the outside of the first adsorption tower 10. The above method includes a step of desorbing the carbon dioxide adsorbed on the first adsorbent 14 by heating, and generating a first concentrated gas containing the carbon dioxide desorbed from the first adsorbent 14 and having a higher carbon dioxide concentration than air. The above method includes a step of adsorbing the carbon dioxide in the first concentrated gas with the second adsorbent 41 accommodated in the second adsorption tower 40 by contact with the first concentrated gas supplied from the first adsorption tower 10. The above method includes a step of desorbing the carbon dioxide adsorbed on the second adsorbent 41 by heating, and generating a second concentrated gas containing the carbon dioxide desorbed from the second adsorbent 41 and having a higher carbon dioxide concentration than the first concentrated gas.

[0060] FIG. 8 is a graph showing the relationship between the carbon dioxide partial pressure and the carbon dioxide adsorption capacity when the adsorbent is at a high temperature and a low temperature. As shown in FIG. 8, the greater the carbon dioxide partial pressure, the greater the adsorption capacity of the adsorbent. However, the carbon dioxide concentration in the air is about 400 ppm, and the carbon dioxide partial pressure is not high. Therefore, even if the carbon dioxide is desorbed by heating after adsorbing the carbon dioxide in the air with the adsorbent to generate the first concentrated gas, it is not possible to obtain a first concentrated gas having a sufficiently high carbon dioxide concentration. On the other hand, when the carbon dioxide in the first concentrated gas is adsorbed again by the adsorbent, since the adsorbed amount of carbon dioxide increases, a second concentrated gas having a high carbon dioxide concentration can be obtained by desorbing the carbon dioxide by heating.

[0061] Therefore, according to the carbon dioxide recovery system 1 and the carbon dioxide recovery method according to this embodiment, the energy required for depressurization can be reduced when desorbing carbon dioxide from the adsorbent.

[0062] In addition, in the carbon dioxide recovery system 1 according to this embodiment, an example in which the first adsorption tower 10 and the second adsorption tower 40 have different configurations has been described. However, the first adsorption tower 10 and the second adsorption tower 40 may have the same configuration.

[0063] Also, in the carbon dioxide recovery system 1 according to the present embodiment, the blower 53 is provided in the pipe 58. However, the position where the blower 53 is provided is not particularly limited, and the blower 53 may be provided in the pipe 51 or the pipe 58.

[0064] Also, in the present embodiment, the first concentrated gas is configured to flow from the upper side to the lower side of the second adsorption tower 40. However, the first concentrated gas may be configured to flow from the lower side to the upper side of the second adsorption tower 40.

[0065] Also, in the present embodiment, an example in which the carbon dioxide recovery system 1 includes one first adsorption tower 10 has been described. However, the carbon dioxide recovery system 1 may include a plurality of first adsorption towers 10 provided in parallel. Thereby, for example, while carbon dioxide is being adsorbed in one first adsorption tower 10, carbon dioxide can be desorbed in the other first adsorption tower 10. Therefore, the carbon dioxide recovery efficiency by the carbon dioxide recovery system 1 can be improved.

[0066] Also, in the carbon dioxide recovery system 1 according to the present embodiment, an example in which carbon dioxide is recovered using two adsorption towers, i.e., the first adsorption tower 10 and the second adsorption tower 40, has been described. However, the carbon dioxide recovery system 1 may include three or more adsorption towers. The carbon dioxide recovery system 1 may include, for example, a first adsorption tower 10 that generates a first concentrated gas, a second adsorption tower 40 that concentrates the first concentrated gas to generate a second concentrated gas, and a third adsorption tower (not shown) that concentrates the second concentrated gas to generate a third concentrated gas.

Example

[0067] Hereinafter, the present embodiment will be described in more detail with the following examples, but the present embodiment is not limited to these examples.

[0068] An adsorbent was filled into a cylindrical container provided with an inlet and an outlet. The weight of the filled adsorbent was 1.7 g. As the filler, Lewatit (registered trademark) VP OC 1065 of Lanxess was used. The adsorbent is a porous body having a polymer as a matrix and having a primary amine as a functional group. Further, a heater for heating the adsorbent was attached to the outer periphery of the container.

[0069] Next, as Operation 1, the temperature inside the container was set to 25°C, and air having a carbon dioxide concentration of 0.04% by volume was passed through the container at a flow rate of 3.8 slm, and carbon dioxide in the air was adsorbed by the adsorbent.

[0070] After Operation 1, as Operation 2, the temperature inside the container was set to 140°C, and air having a carbon dioxide concentration of 0.04% by volume was passed through the container at a flow rate of 0.05 slm, and carbon dioxide was desorbed from the adsorbent.

[0071] After Operation 2, as Operation 3, the temperature inside the container was set to 25°C, and air having a carbon dioxide concentration of 0.04% by volume was passed through the container at a flow rate of 3.8 slm, and carbon dioxide in the air was adsorbed by the adsorbent.

[0072] After Operation 3, as Operation 4, the temperature inside the container was set to 25°C, and a gas having a carbon dioxide concentration of 10% by volume was passed through the container at a flow rate of 0.5 slm, and carbon dioxide in the gas was adsorbed by the adsorbent.

[0073] After Operation 4, as Operation 5, the temperature inside the container was set to 140°C, and air having a carbon dioxide concentration of 0.04% by volume was passed through the container at a flow rate of 0.05 slm, and carbon dioxide was desorbed from the adsorbent.

[0074] [Evaluation] The peak carbon dioxide concentration in the gas obtained in Operations 2 and 5 was measured. Also, the adsorption amount and desorption amount of carbon dioxide with respect to the adsorbent were measured. These results are shown in Table 1.

[0075]

Table 1

[0076] As shown in Table 1, the carbon dioxide concentration of the gas obtained from the outlet increased from 30% in Operation 2 to 100% in Operation 5. From these results, it can be seen that by repeating adsorption and desorption as in Operations 1 to 5, the carbon dioxide concentration of the desorbed gas can be increased. In this example, it was confirmed that by using the same adsorption device and adsorbent, the peak concentration of carbon dioxide can be concentrated from 30% to 100%. However, it is considered that carbon dioxide can be concentrated even when the volume of the adsorption device used in Operations 1 and 2 is smaller than that of the adsorption device used in Operations 4 and 5. Therefore, as in the above-described embodiment, it can be seen that by using a plurality of adsorption towers, carbon dioxide in the air can be recovered without depressurizing the inside of the adsorption tower. Similarly, it can be seen that by performing two-stage adsorption and desorption, carbon dioxide in the air can be recovered without depressurizing the inside of the adsorption tower.

[0077] The entire contents of Japanese Patent Application No. 2021-190128 (filing date: November 24, 2021) are incorporated herein by reference.

[0078] Although some embodiments have been described, it is possible to modify or deform the embodiments based on the above disclosure. All the components of the above embodiments and all the features described in the claims may be individually extracted and combined as long as they do not conflict with each other.

[0079] The present disclosure can contribute to, for example, Goal 7, "Ensure access to affordable, reliable, and sustainable modern energy for all," and Goal 13, "Take urgent action to combat climate change and its impacts," of the Sustainable Development Goals (SDGs) led by the United Nations.

Explanation of Reference Numerals

[0080] 1 Carbon dioxide recovery system 10 First adsorption tower 14 First adsorbent 20 First heating unit 40 Second adsorption tower 41 Second adsorbent 44 Second heating section 47 Pressure reduction section 65 Gas supply section

Claims

1. A first adsorption tower including a first heating unit that houses a first adsorbent and heats the first adsorbent; A second adsorption tower including a second heating unit that houses a second adsorbent and heats the second adsorbent; and comprising: When the first adsorbent comes into contact with air supplied from outside the first adsorption tower, it adsorbs carbon dioxide in the air. When heated in the first heating unit, it desorbs the carbon dioxide adsorbed on the first adsorbent, generates a first concentrated gas containing the carbon dioxide desorbed from the first adsorbent and having a higher carbon dioxide concentration than the air; When the second adsorbent comes into contact with the first concentrated gas supplied from the first adsorption tower, it adsorbs carbon dioxide in the first concentrated gas. When heated in the second heating unit, it desorbs the carbon dioxide adsorbed on the second adsorbent, generates a second concentrated gas containing the carbon dioxide desorbed from the second adsorbent and having a higher carbon dioxide concentration than the first concentrated gas; The first concentrated gas that has come into contact with the second adsorbent is supplied to the first adsorption tower to come into contact with the first adsorbent, and promotes the desorption of the carbon dioxide adsorbed on the first adsorbent, a carbon dioxide recovery system.

2. The carbon dioxide recovery system according to claim 1, wherein the second adsorption tower has a smaller volume than the first adsorption tower.

3. The carbon dioxide recovery system according to claim 1 or 2, further comprising a pressure reducing unit that reduces the pressure inside the second adsorption tower.

4. The carbon dioxide recovery system according to claim 1 or 2, further comprising a gas supply unit that supplies at least one purge gas selected from the group consisting of air, hydrogen, water vapor, and inert gas into the second adsorption tower.

5. The carbon dioxide recovery system according to claim 1 or 2, wherein the bulk density of the second adsorbent is equal to or greater than the bulk density of the first adsorbent.

6. The bulk density of the second adsorbent is smaller than the bulk density of the first adsorbent. The carbon dioxide recovery system according to claim 1 or 2.

7. The carbon dioxide recovery system further includes a concentration measurement unit that measures the carbon dioxide concentration in the first concentrated gas. The first concentrated gas derived from the first adsorption tower is introduced into the first adsorption tower according to the carbon dioxide concentration measured by the concentration measurement unit. The carbon dioxide recovery system according to claim 1 or 2.

8. The gas supplied from the second adsorption tower and contacted with the first adsorbent is supplied to the second adsorption tower. Carbon dioxide in the gas supplied from the second adsorption tower and contacted with the first adsorbent is adsorbed by the second adsorbent. The carbon dioxide recovery system according to claim 1 or 2.

9. A step of adsorbing carbon dioxide in the air by the first adsorbent accommodated in the first adsorption tower by contact with air supplied from the outside of the first adsorption tower. A step of desorbing the carbon dioxide adsorbed on the first adsorbent by heating to generate a first concentrated gas containing carbon dioxide desorbed from the first adsorbent and having a higher carbon dioxide concentration than the air. A step of adsorbing carbon dioxide in the first concentrated gas by the second adsorbent accommodated in the second adsorption tower by contact with the first concentrated gas supplied from the first adsorption tower. A step of desorbing the carbon dioxide adsorbed on the second adsorbent by heating to generate a second concentrated gas containing carbon dioxide desorbed from the second adsorbent and having a higher carbon dioxide concentration than the first concentrated gas. The first concentrated gas contacted with the second adsorbent is supplied to the first adsorption tower to contact with the first adsorbent to promote desorption of carbon dioxide adsorbed on the first adsorbent. A carbon dioxide recovery method including the above steps.

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