Carbon dioxide capture equipment

Abstract

To provide a carbon dioxide recovery device that deals with the fluctuation of a supplied carbon dioxide-containing gas while suppressing the large-sizing of the device.SOLUTION: A carbon dioxide recovery device includes: a carbon dioxide recovery portion recovering carbon dioxide from a carbon dioxide-containing gas supplied from a carbon dioxide-containing gas supply portion; and a carbon dioxide storage portion being connected to the carbon dioxide-containing gas supply portion in parallel with the carbon dioxide recovery portion, recovering carbon dioxide from a part of the carbon dioxide-containing gas supplied from the carbon dioxide-containing gas supply portion and storing carbon dioxide. The carbon dioxide storage portion has an upstream tank provided with an adsorbent adsorbing carbon dioxide and a downstream tank storing carbon dioxide discharged from the upstream tank in a gas state.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a carbon dioxide recovery device.

Background Art

[0002] Conventionally, a device for recovering carbon dioxide from exhaust gas discharged from a combustion furnace or the like is known. For example, Patent Document 1 discloses a technique for separating carbon dioxide from a gas containing carbon dioxide discharged from a combustion furnace or the like in a factory using a separator that houses an adsorbent.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In such a carbon dioxide recovery device, it is desired that the operation of recovering carbon dioxide can be continued without trouble not only when the amount of the supplied carbon dioxide-containing gas is in a steady state but also when the amount of the supplied carbon dioxide-containing gas fluctuates. However, in order to cope with such fluctuations in the supply amount of the carbon dioxide-containing gas, depending on the assumed fluctuation amount, it may be necessary to excessively increase the size of the carbon dioxide recovery device, which may be difficult to adopt. Such a problem is not limited to the configuration using a separator that houses an adsorbent, but is a common problem in devices for recovering carbon dioxide from a carbon dioxide-containing gas.

Means for Solving the Problems

[0005] The present disclosure can be realized in the following forms. (1) According to one embodiment of the present disclosure, a carbon dioxide recovery device is provided. This carbon dioxide recovery device includes a carbon dioxide recovery unit that recovers carbon dioxide from the carbon dioxide-containing gas supplied from a carbon dioxide-containing gas supply unit that is a source of the carbon dioxide-containing gas, and a carbon dioxide storage unit that is connected to the carbon dioxide-containing gas supply unit in parallel with the carbon dioxide recovery unit and recovers and stores carbon dioxide from a part of the carbon dioxide-containing gas supplied by the carbon dioxide-containing gas supply unit. The carbon dioxide storage unit includes an upstream tank provided with an adsorbent for adsorbing carbon dioxide, and a downstream tank for storing the carbon dioxide discharged from the upstream tank in a gaseous state. According to the carbon dioxide recovery device of this embodiment, by providing the carbon dioxide storage unit, it is possible to cope with fluctuations in the amount of the carbon dioxide-containing gas supplied to the carbon dioxide recovery device while suppressing the enlargement of the carbon dioxide recovery unit. Further, since the carbon dioxide storage unit includes an upstream tank provided with an adsorbent for adsorbing carbon dioxide and a downstream tank for storing the carbon dioxide discharged from the upstream tank in a gaseous state, the carbon dioxide storage unit can be downsized as compared with the case where it is configured only by a tank for storing carbon dioxide in a gaseous state. (2) The carbon dioxide recovery device of the above-described embodiment further includes a first control unit that controls the distribution amount of the carbon dioxide-containing gas supplied from the carbon dioxide-containing gas supply unit to the carbon dioxide recovery unit and the carbon dioxide storage unit. When the amount of the carbon dioxide-containing gas supplied by the carbon dioxide-containing gas supply unit is equal to or less than a preset value, which is the processable amount for the carbon dioxide recovery unit to recover carbon dioxide from the carbon dioxide-containing gas, the first control unit supplies the entire amount of the carbon dioxide-containing gas supplied by the carbon dioxide-containing gas supply unit to the carbon dioxide recovery unit. When the amount of the carbon dioxide-containing gas supplied by the carbon dioxide-containing gas supply unit exceeds the preset value, the first control unit supplies the amount of the carbon dioxide-containing gas equal to the preset value to the carbon dioxide recovery unit and supplies the excess amount of the carbon dioxide-containing gas over the preset value to the carbon dioxide storage unit. With such a configuration, within the range of the processable amount for the carbon dioxide recovery unit to recover carbon dioxide, since the carbon dioxide recovery unit is preferentially used for the recovery of carbon dioxide from the carbon dioxide-containing gas, the operation of recovering carbon dioxide from the carbon dioxide-containing gas can be made more stable. (3) In the carbon dioxide recovery device of the above-described embodiment, the carbon dioxide recovery unit may be a pressure / temperature swing adsorption device, and the upstream tank may be a pressure swing adsorption device. With such a configuration, by combining a pressure / temperature swing adsorption device with higher energy efficiency for carbon dioxide recovery and a pressure swing adsorption device with simpler device configuration and control, it is possible to increase the energy efficiency related to carbon dioxide recovery while suppressing the enlargement of the entire device. (4) The carbon dioxide recovery apparatus of the above-described embodiment further includes an air supply unit that supplies a sweep gas having a lower carbon dioxide concentration than the carbon dioxide-containing gas to the upstream tank in a direction opposite to the direction in which the carbon dioxide-containing gas flows in the upstream tank, and after the desorption step of desorbing carbon dioxide from the adsorbent in the upstream tank that has adsorbed carbon dioxide in the carbon dioxide-containing gas, prior to the adsorption step of supplying the carbon dioxide-containing gas to the upstream tank to adsorb carbon dioxide on the adsorbent, a second control unit that drives the air supply unit to supply the sweep gas to the upstream tank. With such a configuration, prior to the adsorption step, carbon dioxide can be desorbed from the downstream portion of the carbon dioxide-containing gas flow by the sweep gas in the adsorbent of the upstream tank. Therefore, the carbon dioxide concentration in the adsorption off-gas can be reduced at the start of the adsorption step. (5) In the carbon dioxide recovery apparatus of the above-described embodiment, the upstream tank includes a plurality of adsorption towers each provided with an adsorbent for adsorbing carbon dioxide, and the carbon dioxide recovery apparatus further includes a third control unit that switches the connection state of the pipes communicating with the plurality of adsorption towers. When the sweep gas is supplied to a first adsorption tower that is one of the plurality of adsorption towers, the third control unit may be provided to switch the connection state so as to guide the sweep off-gas discharged from the first adsorption tower to a second adsorption tower to which the carbon dioxide-containing gas is supplied. With such a configuration, since carbon dioxide in the sweep off-gas can be adsorbed by the second adsorption tower, the carbon dioxide recovery efficiency can be increased. (6) In the carbon dioxide recovery apparatus of the above-described embodiment, the upstream tank is an adsorption tower provided with an adsorbent for adsorbing carbon dioxide. At least one of the adsorption towers is in an adsorption step capable of receiving the supply of the carbon dioxide-containing gas and adsorbing carbon dioxide on the adsorbent, and at least one of the other adsorption towers is in a desorption step capable of desorbing carbon dioxide from the adsorbent. The downstream tank is provided with a pressure sensor for detecting the pressure inside the downstream tank. The carbon dioxide recovery apparatus further includes a fourth control unit for controlling the connection state of the pipes communicating with the plurality of adsorption towers and the downstream tank. When the pressure detected by the pressure sensor is lower than a predetermined lower limit value, carbon dioxide desorbed from the adsorption tower in the desorption step is guided to the downstream tank. When the pressure detected by the pressure sensor exceeds a predetermined upper limit value, the supply of carbon dioxide from the adsorption tower in the desorption step to the downstream tank is stopped. When the pressure detected by the pressure sensor is in the range of not less than the lower limit value and not more than the upper limit value, if the supply of carbon dioxide from the adsorption tower in the desorption step to the downstream tank has been stopped, the stopped state is maintained, and if the supply of carbon dioxide from the adsorption tower in the desorption step to the downstream tank is being performed, the supply of carbon dioxide is continued. It may be provided with a fourth control unit. With such a configuration, the downstream tank only needs to have a capacity capable of coping with fluctuations in the amount of carbon dioxide required for the carbon dioxide recovery apparatus. Therefore, the downstream tank for storing carbon dioxide in a gaseous state can be made smaller, and as a result, the entire carbon dioxide storage unit can be made smaller. (7) In the carbon dioxide recovery apparatus of the above-described embodiment, when it is determined that the adsorption state of carbon dioxide in the adsorption tower in the adsorption step has reached a predetermined maximum adsorption amount, the fourth control unit may stop the supply of the carbon dioxide-containing gas to the adsorption tower and switch the connection state so as to introduce the carbon dioxide-containing gas to another adsorption tower that has undergone the desorption step. With such a configuration, the adsorbent provided in the adsorption tower can be used efficiently, and the adsorption tower provided with the adsorbent can be made smaller. The present disclosure can be implemented in various forms other than those described above. For example, it can be implemented in the form of a carbon dioxide recycling system including a carbon dioxide recovery device, a carbon dioxide recovery method, a hydrocarbon production method, a control method for a carbon dioxide recovery device, a control method for a hydrocarbon production device, a computer program for causing a computer to execute these control methods, and the like.

Brief Description of the Drawings

[0006]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

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Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0007] A. First Embodiment: (A-1) Overall Configuration of Carbon Dioxide Recycling System: FIG. 1 is an explanatory diagram showing a schematic configuration of a carbon dioxide recycling system 10 including a carbon dioxide recovery device 15 according to an embodiment of the present disclosure. The carbon dioxide recycling system 10 includes a carbon dioxide-containing gas supply unit 20, a carbon dioxide recovery device 15, a methanation reactor 22, and a methane tank 24.

[0008] The carbon dioxide-containing gas supply unit 20 is a source for supplying a carbon dioxide-containing gas containing carbon dioxide, and discharges the carbon dioxide-containing gas. The carbon dioxide-containing gas supply unit 20 is, for example, a combustion furnace in a factory. In this case, the discharged carbon dioxide-containing gas is combustion exhaust gas, which contains nitrogen, oxygen, water vapor, etc. in addition to carbon dioxide.

[0009] The carbon dioxide recovery device 15 is connected to the carbon dioxide-containing gas supply unit 20 by the first CO2-containing gas flow path 70, and recovers carbon dioxide from the carbon dioxide-containing gas supplied from the carbon dioxide-containing gas supply unit 20. A dehydration unit (not shown) may be provided in the first CO2-containing gas flow path 70 to reduce the moisture content in the carbon dioxide-containing gas. The carbon dioxide recovery device 15 includes a carbon dioxide recovery unit 30, a carbon dioxide storage unit 50, and a control unit 80. The first CO2-containing gas flow path 70 is connected to the carbon dioxide recovery unit 30, and the carbon dioxide recovered by the carbon dioxide recovery unit 30 is discharged into the first CO2 flow path 72. Also, a second CO2-containing gas flow path 74 is provided branching from the first CO2-containing gas flow path 70. The second CO2-containing gas flow path 74 is connected to the carbon dioxide storage unit 50, and the carbon dioxide recovered by the carbon dioxide storage unit 50 is discharged into the second CO2 flow path 76. The second CO2 flow path 76 merges into the first CO2 flow path 72. A three-way valve 78 is provided at the branch portion where the second CO2-containing gas flow path 74 branches from the first CO2-containing gas flow path 70, and the flow rate of the carbon dioxide-containing gas distributed from the first CO2-containing gas flow path 70 to the second CO2-containing gas flow path 74 is adjusted.

[0010] The three-way valve 78 is controlled by a control unit 80. The control unit 80 receives, for example, a detection signal from a flow rate sensor (not shown) provided in the first CO2-containing gas flow path 70, and acquires the flow rate of the CO2-containing gas supplied from the CO2-containing gas supply unit 20. Then, when the amount of the CO2-containing gas supplied by the CO2-containing gas supply unit 20 is equal to or less than a set value preset as a processable amount that the CO2 recovery unit 30 can recover CO2 from the CO2-containing gas, the three-way valve 78 is controlled so that the entire amount of the CO2-containing gas supplied by the CO2-containing gas supply unit 20 is supplied to the CO2 recovery unit 30. Further, when the amount of the CO2-containing gas supplied by the CO2-containing gas supply unit 20 exceeds the set value, the three-way valve 78 is controlled so that the amount of the CO2-containing gas equal to the set value is supplied to the CO2 recovery unit 30, and the excess amount of the CO2-containing gas over the set value is supplied to the CO2 storage unit 50. At this time, the control unit 80 functions as a "first control unit". The configurations of the CO2 recovery unit 30 and the CO2 storage unit 50 will be described in detail later.

[0011] The methanation reactor 22 is connected to the carbon dioxide recovery device 15 through the first CO2 flow path 72, and generates methane from the carbon dioxide supplied from the carbon dioxide recovery device 15. The methanation reactor 22 is also called the "fuel generation unit". The gas flowing through the first CO2 flow path 72 and used in the methanation reaction in the methanation reactor 22 is also called the "fuel gas". The methanation reactor 22 contains a methanation catalyst inside that promotes the methanation reaction to generate methane from carbon dioxide. As the methanation catalyst, for example, a catalyst containing ruthenium or nickel can be used. The methane generated in the methanation reactor 22 is once stored in the methane tank 24 and then supplied to the carbon dioxide-containing gas supply unit 20 and used for combustion in a combustion furnace or the like. Thereby, in the carbon dioxide-containing gas supply unit 20, a carbon dioxide-containing gas is generated from methane. Such a carbon dioxide-containing gas supply unit 20 is also called the "carbon dioxide generation unit". The carbon dioxide-containing gas generated in the carbon dioxide-containing gas supply unit 20 is supplied to the carbon dioxide recovery device 15 as described above, carbon dioxide is recovered, and the recovered carbon dioxide is used as a resource again.

[0012] (A-2) Configuration of Carbon Dioxide Recovery Device: In the carbon dioxide recovery device 15, the carbon dioxide recovery unit 30 mainly recovers carbon dioxide, and the carbon dioxide storage unit 50 additionally recovers carbon dioxide and stores carbon dioxide. Hereinafter, the configurations of the carbon dioxide recovery unit 30 and the carbon dioxide storage unit 50 will be sequentially described.

[0013] (A-2-1) Configuration of Carbon Dioxide Recovery Unit: FIG. 2 is an explanatory diagram showing the schematic configuration of the carbon dioxide recovery unit 30 provided in the carbon dioxide recovery device 15. The carbon dioxide recovery unit 30 includes separators 31a and 31b and a purge gas supply unit 33. In the following description, when the two separators 31a and 31b are not distinguished, they are simply referred to as "separator 31".

[0014] The separators 31a and 31b are formed in a cylindrical shape, and the adsorbents 32a and 32b are respectively accommodated inside. The adsorbents 32a and 32b are materials having carbon dioxide occlusion (adsorption) performance, and examples thereof include zeolite, activated carbon, and silica gel. In the carbon dioxide recovery unit 30 of the present embodiment, in one of the separators 31a and 31b, an adsorption step of adsorbing carbon dioxide in the carbon dioxide-containing gas to the adsorbent is performed, and in the other separator, a desorption step of desorbing carbon dioxide from the adsorbent that has adsorbed carbon dioxide is performed. FIG. 2 shows a state where the separator 31a is in the adsorption step and the separator 31b is in the desorption step. The carbon dioxide recovery unit 30 of the present embodiment is a pressure-thermal swing adsorption (PTSA) device that switches between the adsorption step and the desorption step by changing the pressure and temperature inside the separator provided with the adsorbent.

[0015] The first CO2-containing gas flow path 70 (see FIG. 1) through which the carbon dioxide-containing gas discharged from the carbon dioxide-containing gas supply unit 20 flows branches into CO2-containing gas branch paths 36a and 36b. The CO2-containing gas branch path 36a is connected to one end of the cylindrical separator 31a, and the CO2-containing gas branch path 36b is connected to one end of the separator 31b. In the following description, among both axial ends of each separator 31, the end to which the CO2-containing gas branch paths 36a and 36b, which are the sides where the carbon dioxide-containing gas flows in, are connected is referred to as the "one end", and the end on the different side is referred to as the "other end". CO2-containing gas valves 37a and 37b that are opened and closed by the control unit 80 are provided in each of the CO2-containing gas branch paths 36a and 36b. A discharge branch path 38a is connected to the other end of the separator 31a, and a discharge branch path 38b is connected to the other end of the separator 31b. The discharge branch paths 38a and 38b merge to form the adsorption off-gas path 40. Off-gas discharge valves 39a and 39b that are opened and closed by the control unit 80 are provided in each of the discharge branch paths 38a and 38b.

[0016] In Fig. 2, the flow path through which the fluid is flowing is indicated by a thick line. As described above, the separator 31a is in the adsorption step. At this time, the carbon dioxide-containing gas supplied from the carbon dioxide-containing gas supply section 20 is supplied to the separator 31a via the first CO2-containing gas flow path 70 and the CO2-containing gas branch path 36a, and the carbon dioxide in the carbon dioxide-containing gas is adsorbed by the adsorbent 32a. Then, the adsorption off-gas, which is the remaining gas from which carbon dioxide has been separated, is discharged to the outside of the carbon dioxide recovery device 15, for example, into the atmosphere, via the discharge branch path 38a and the adsorption off-gas path 40.

[0017] A discharge branch path 41a is further connected to one end of the separator 31a, and a discharge branch path 41b is further connected to one end of the separator 31b. The discharge branch paths 41a and 41b merge to form the first CO2 flow path 72 (see Fig. 1) described above. CO2 discharge valves 42a and 42b that are opened and closed by the control unit 80 are provided in each of the discharge branch paths 41a and 41b. A pump 34 and a surge tank 35 that are driven and controlled by the control unit 80 are arranged in this order in the fluid flow direction in the first CO2 flow path 72. Further, in the carbon dioxide recovery section 30, a heat medium flow path 49 through which a heat medium for heating the adsorbents 32a and 32b flows is provided inside each of the separators 31a and 31b (however, in Fig. 2, only the heat medium flow path 49 through which the heat medium flows in the separator 31b is shown, and the description of the heat medium flow path 49 through which the heat medium flows in the separator 31a is omitted). The fluid flowing through the heat medium flow path 49 may be a high-temperature fluid that can raise the temperature of the adsorbents 32a and 32b to a temperature suitable for the desorption step. For example, if the heat medium flow path 49 is a flow path for circulating the heat medium between the methanation reactor 22 in which the methanation reaction, which is an exothermic reaction, proceeds and the separator 31, the energy consumed for heating the adsorbent in the desorption step can be reduced. The control unit 80 controls the flow state of the heat medium in the heat medium flow path 49 so that the heat medium is supplied only to the separator 31 in the desorption step by opening and closing a valve (not shown) provided in the heat medium flow path 49.

[0018] In FIG. 2, the flow path through which the fluid is flowing is indicated by a thick line. As described above, the separator 31b is in the desorption process. At this time, the pump 34 is driven and the CO2 discharge valve 42b is opened, so that the pressure inside the separator 31b is reduced. Further, the adsorbent 32b is heated by the heat medium flowing through the heat medium flow path 49. As a result, the carbon dioxide adsorbed on the adsorbent 32b is desorbed. The surge tank 35 provided in the first CO2 flow path 72 temporarily stores the carbon dioxide discharged by the desorption process and can absorb a part of the fluctuation in the flow rate of the carbon dioxide supplied from the carbon dioxide recovery unit 30 to the methanation reactor 22.

[0019] The purge gas supply unit 33 provided in the carbon dioxide recovery unit 30 of the present embodiment is a device for supplying a purge gas for promoting the desorption operation to the separator 31 in the desorption process. In the present embodiment, hydrogen is used as the purge gas, and the purge gas supply unit 33 is a hydrogen supply source. The purge gas supply unit 33 can be configured by, for example, a water electrolysis device, a hydrogen tank, or the like. As such a purge gas supply unit 33, a hydrogen supply source (not shown) that supplies hydrogen used in the methanation reaction to the methanation reactor 22 may be used. A purge gas branch path 44a provided with a purge gas supply valve 45a is connected to the other end of the separator 31a, and a purge gas branch path 44b provided with a purge gas supply valve 45b is connected to the other end of the separator 31b. The purge gas branch paths 44a and 44b merge on the upstream side to form a purge gas supply flow path 43, which is connected to the purge gas supply unit 33. As shown by the thick line flow path in FIG. 2, the purge gas is supplied from the purge gas supply unit 33 to the separator 31b in the desorption process through the purge gas supply flow path 43 and the purge gas branch path 44b.

[0020] By supplying purge gas to the separator 31 in the desorption step and flowing the purge gas over the adsorbent, carbon dioxide desorbed from the adsorbent is quickly removed from the vicinity of the adsorbent, and the partial pressure of carbon dioxide in the separator 31 is reduced by the purge gas, thereby increasing the efficiency of carbon dioxide desorption from the adsorbent. By using hydrogen as the purge gas, the fuel gas discharged from the separator 31 in the desorption step to the first CO2 flow path 72 will contain hydrogen together with carbon dioxide. The hydrogen contained in the fuel gas is used in the methanation reaction that produces methane using carbon dioxide in the methanation reactor 22. As described above, the methanation reactor 22 of the present embodiment includes a hydrogen supply source (not shown) that supplies hydrogen used in the methanation reaction to the methanation reactor 22. The control unit 80 calculates the carbon dioxide flow rate in the fuel gas supplied to the methanation reactor 22 and acquires the hydrogen flow rate supplied from the purge gas supply unit 33 to the separator 31. Then, the hydrogen supply source provided in the methanation reactor 22 is driven so that hydrogen in an amount insufficient as the hydrogen required for the methanation reaction is supplied to the methanation reactor 22 as the hydrogen contained in the fuel gas as the purge gas.

[0021] In FIG. 2, the carbon dioxide recovery unit 30 is provided with two separators 31, but it may be provided with one or three or more separators 31. Further, although only the adsorption step and the desorption step have been described above, in each separator 31, a step of performing other operations may be further executed. For example, a waste heat step of heating the adsorbent prior to the desorption step or a cooling step of cooling the adsorbent prior to the adsorption step may be performed. If the carbon dioxide recovery unit 30 is provided with a plurality of separators 31 and the steps are shifted between the plurality of separators so that any one of the separators 31 always performs the adsorption step and any one of the other separators 31 performs the desorption step, then in the carbon dioxide recovery unit 30, the operation of recovering and discharging carbon dioxide from the carbon dioxide-containing gas can be continuously performed.

[0022] (A-2-2) Configuration of Carbon Dioxide Storage Unit: FIG. 3 is an explanatory diagram showing a schematic configuration of a carbon dioxide storage unit 50 included in the carbon dioxide recovery device 15. The carbon dioxide storage unit 50 includes an upstream tank 69, a downstream tank 55, and a sweep gas supply unit 53. The upstream tank 69 includes adsorption towers 51a, 51b, and 51c. In the following description, when the three adsorption towers 51a, 51b, and 51c are not distinguished, they are simply referred to as "adsorption tower 51".

[0023] The adsorption towers 51a, 51b, and 51c are formed in a cylindrical shape, and adsorption materials 52a, 52b, and 52c are respectively accommodated inside. The adsorption materials 52a, 52b, and 52c are materials having carbon dioxide storage (adsorption) performance, and examples thereof include zeolite, activated carbon, and silica gel. The adsorption materials 52a, 52b, and 52c may be the same as or different from the adsorption materials 32a, 32b included in the separators 31a, 31b of the carbon dioxide recovery unit 30. In the present embodiment, the adsorption towers 51a, 51b, and 51c are devices having the same shape and the same capacity. In the carbon dioxide storage unit 50 of the present embodiment, in one of the adsorption towers 51a, 51b, and 51c, an adsorption step of adsorbing carbon dioxide in the carbon dioxide-containing gas to the adsorption material is performed, and in another one of the adsorption towers, a desorption step of desorbing carbon dioxide from the adsorption material that has adsorbed carbon dioxide is performed. In the remaining adsorption tower, a gas supply step of further reducing the amount of carbon dioxide adsorbed in the adsorption material is performed. In FIG. 3, the adsorption tower 51a is in the adsorption step, the adsorption tower 51b is in the desorption step, and the adsorption tower 51c is in the gas supply step.

[0024] FIG. 4 is an explanatory diagram showing how the adsorption, desorption, and air supply processes are switched among the adsorption towers 51a to 51c. As shown in FIG. 4, cycle 1, cycle 2, and cycle 3 are repeated in this order, and in each adsorption tower 51, the adsorption process, the desorption process, and the air supply process are repeated in this order, and each adsorption tower 51 is in a different process from each other. FIG. 3 shows the state of cycle 1. In the present embodiment, the time for executing each of the adsorption process, the desorption process, and the air supply process is the same length, and cycles 1 to 3 are sequentially switched at predetermined time intervals. However, the time for each process may be made changeable. As described above, the carbon dioxide storage unit 50 of the present embodiment is supplied with the carbon dioxide-containing gas in excess of the set value set as the processable amount of carbon dioxide recovery in the carbon dioxide recovery unit 30 among the carbon dioxide-containing gas supplied from the carbon dioxide-containing gas supply unit 20. Therefore, when the amount of the carbon dioxide-containing gas supplied from the carbon dioxide-containing gas supply unit 20 is small, the adsorption tower 51 in the adsorption process may be in a state where it does not perform the adsorption operation without being supplied with the carbon dioxide-containing gas. The carbon dioxide storage unit 50 of the present embodiment is a pressure swing adsorption (PSA) device that switches between the adsorption process and the desorption process by changing the pressure in the adsorption tower provided with the adsorbent.

[0025] TwoThe second CO₂-containing gas flow path 74 (see FIG. 1) branching from the first CO₂-containing gas flow path 70 through which the carbon dioxide-containing gas flows branches into CO₂-containing gas branch paths 56a, 56b, and 56c. The CO₂-containing gas branch path 56a is connected to one end of the adsorption tower 51a formed in a cylindrical shape, the CO₂-containing gas branch path 56b is connected to one end of the adsorption tower 51b, and the CO₂-containing gas branch path 56c is connected to one end of the adsorption tower 51c. In the following description, among both axial ends of each adsorption tower 51, the end to which the CO₂-containing gas branch paths 56a, 56b, and 56c, which are the sides where the carbon dioxide-containing gas flows in, are connected is referred to as the "one end", and the end on the different side is referred to as the "other end". Each of the CO₂-containing gas branch paths 56a, 56b, and 56c is provided with a CO₂-containing gas valve 57a, 57b, or 57c that is opened and closed under the control of the control unit 80. Further, a discharge branch path 58a is connected to the other end of the adsorption tower 51a, a discharge branch path 58b is connected to the other end of the adsorption tower 51b, and a discharge branch path 58c is connected to the other end of the adsorption tower 51c. The discharge branch paths 58a, 58b, and 58c merge to form the adsorption off-gas path 60. Each of the discharge branch paths 58a, 58b, and 58c is provided with an off-gas discharge valve 59a, 59b, or 59c that is opened and closed under the control of the control unit 80.

[0026] In FIG. 3, the flow paths through which the fluid is flowing are shown by thick lines. As described above, the adsorption tower 51a is in the adsorption process. At this time, the carbon dioxide-containing gas supplied from the carbon dioxide-containing gas supply unit 20 is supplied to the adsorption tower 51a through the first CO₂-containing gas flow path 70, the second CO₂-containing gas flow path 74, and the CO₂-containing gas branch path 56a, and the carbon dioxide in the carbon dioxide-containing gas is adsorbed by the adsorbent 52a. Then, the adsorption off-gas, which is the remaining gas from which carbon dioxide has been separated, is discharged to the outside of the carbon dioxide recovery device 15, for example, into the atmosphere, through the discharge branch path 58a and the adsorption off-gas path 60.

[0027] At one end of each of the adsorption towers 51a, 51b, and 51c, discharge branch paths 61a, 61b, and 61c are further connected respectively. The discharge branch paths 61a, 61b, and 61c merge to form the aforementioned second CO₂ flow path 76. Each of the discharge branch paths 61a, 61b, and 61c is provided with CO₂ discharge valves 62a, 62b, and 62c that are opened and closed under the control of the control unit 80. In the second CO₂ flow path 76, a pump 54 driven and controlled by the control unit 80 and a downstream tank 55 are arranged in this order in the fluid flow direction. At the outlet of the downstream tank 55, a flow rate adjustment valve 55a for adjusting the amount of gas discharged from the downstream tank 55 is provided. Further, in the downstream tank 55, a pressure sensor 55b for detecting the pressure inside the downstream tank 55 is provided.

[0028] In FIG. 3, the flow paths through which the fluid is flowing are shown by thick lines. As described above, the adsorption tower 51b is in the desorption process. At this time, the pump 54 is driven and the CO₂ discharge valve 62b is opened, so that the inside of the adsorption tower 52b is depressurized. As a result, the carbon dioxide adsorbed on the adsorbent 52b is desorbed. The carbon dioxide discharged from the adsorption tower 51b, which is the upstream tank, is stored in the downstream tank 55 in a gaseous state. When the amount of carbon dioxide supplied from the carbon dioxide recovery unit 30 to the methanation reactor 22 is insufficient compared to the amount of carbon dioxide to be supplied to the methanation reactor 22, the flow rate adjustment valve 55a is driven and controlled, so that the insufficient amount of carbon dioxide is supplied from the downstream tank 55 to the methanation reactor 22.

[0029] The sweep gas supply unit 53 provided in the carbon dioxide storage unit 50 of the present embodiment is a device that supplies sweep gas to the adsorption tower 51 and is driven and controlled by the control unit 80. As the sweep gas, any gas with a sufficiently low carbon dioxide concentration and substantially no components adsorbed on the adsorbents 52a to 52c can be used. In the present embodiment, air, which can be used relatively inexpensively, is used as the sweep gas. The sweep gas supply unit 53 is also referred to as an "air supply unit".

[0030] At the other ends of the adsorption towers 51a, 51b, and 51c, there are connected sweep gas branch paths 64a, 64b, and 64c respectively, in which sweep gas supply valves 65a, 65b, and 65c that are opened and closed by the control unit 80 are provided. The sweep gas branch paths 64a, 64b, and 64c merge on the upstream side to form a sweep gas supply flow path 63, which is connected to the sweep gas supply unit 53. Further, at one end of the adsorption towers 51a, 51b, and 51c, there are connected sweep off-gas branch paths 67a, 67b, and 67c respectively, in which sweep off-gas valves 68a, 68b, and 68c that are opened and closed by the control unit 80 are provided. The sweep off-gas branch paths 67a, 67b, and 67c merge on the downstream side to form a sweep off-gas path 66.

[0031] In FIG. 3, the flow paths through which the fluid is flowing are indicated by thick lines. As described above, the adsorption tower 51c is in the air supply process. At this time, the sweep gas supplied from the sweep gas supply unit 53 is supplied to the adsorption tower 51c through the sweep gas supply flow path 63 and the sweep gas branch path 64c, and passes through the adsorbent 52c while desorbing the carbon dioxide remaining in the adsorbent 52c. Then, the sweep off-gas that has passed through the adsorbent 52c is discharged to the outside of the carbon dioxide recovery device 15, for example, into the atmosphere, through the sweep off-gas branch path 67c and the sweep off-gas path 66. Thus, after the desorption process, when driving the sweep gas supply unit 53 and performing control to supply the sweep gas to the adsorption tower 51 by opening and closing each valve related to the circulation of the sweep gas in the air supply process prior to the adsorption process, the control unit 80 functions as the "second control unit".

[0032] In the desorption process accompanied by reduced pressure in the adsorption tower 51, the carbon dioxide adsorbed on the adsorbent does not completely desorb, and a certain amount of carbon dioxide remains adsorbed on the adsorbent. When sweep gas is supplied to the adsorption tower 51 in the air supply process after the desorption process, due to the carbon dioxide partial pressure difference between the sweep gas and the adsorbent, the carbon dioxide remaining on the adsorbent desorbs and is mixed into the sweep gas. As a result, the carbon dioxide concentration in the sweep gas flowing through the adsorption tower 51 becomes higher towards the downstream side. Therefore, in the adsorbent, the amount of carbon dioxide adsorbed after the air supply process is less towards the upstream side of the sweep gas flow, that is, towards the other end side of the adsorption tower 51.

[0033] In FIG. 3, the carbon dioxide storage unit 50 is provided with three adsorption towers, but it may be provided with one or a plurality of adsorption towers other than three. Also, although only the adsorption process, desorption process, and air supply process have been described above, in each adsorption tower, a process of performing other operations may be further executed. If the carbon dioxide storage unit 50 is provided with a plurality of adsorption towers 51 and the processes are shifted between the plurality of adsorption towers so that any one of the adsorption towers always performs the adsorption process, the operation of recovering and storing the carbon dioxide-containing gas in an amount exceeding the processing capacity of the carbon dioxide recovery unit 30 to recover carbon dioxide can always be executed.

[0034] Returning to FIG. 1, the control unit 80 provided in the carbon dioxide recovery device 15 is composed of a so-called microcomputer equipped with a CPU, ROM, RAM, etc. that execute logical operations, and drives and controls the entire carbon dioxide recovery device 15. The control unit 80 is electrically connected to the valves provided in each of the above-described flow paths, the sensors (temperature sensors, flow rate sensors, pressure sensors, etc.) provided in each part, the pumps 34, 54, the purge gas supply unit 33, the sweep gas supply unit 53, etc., and drives and controls each part such as valves and pumps based on the measured values from the sensors.

[0035] The carbon dioxide recovery device 15 of the present embodiment configured as described above includes a carbon dioxide recovery unit 30 that recovers carbon dioxide from a carbon dioxide-containing gas, and a carbon dioxide storage unit 50 that is connected to the carbon dioxide-containing gas supply unit 20 in parallel with the carbon dioxide recovery unit 30 and recovers and stores carbon dioxide from a part of the carbon dioxide-containing gas supplied by the carbon dioxide-containing gas supply unit 20. With such a configuration, by providing the carbon dioxide storage unit 50, it becomes possible to cope with fluctuations in the amount of carbon dioxide-containing gas supplied to the carbon dioxide recovery device 15 while suppressing an increase in the size of the carbon dioxide recovery unit 30. That is, since a part of the operation of recovering carbon dioxide from the carbon dioxide-containing gas supplied to the carbon dioxide recovery device 15 can be performed by the carbon dioxide storage unit 50, it is not necessary to provide the carbon dioxide recovery unit 30 so as to be able to handle the maximum amount of the fluctuating carbon dioxide-containing gas, and the carbon dioxide recovery unit 30 can be made smaller, simplifying the configuration of the entire device.

[0036] At this time, the carbon dioxide storage unit 50 includes an upstream tank 69 having an adsorption tower 51 provided with an adsorbent for adsorbing carbon dioxide, and a downstream tank 55 for storing the carbon dioxide discharged from the upstream tank 69 in a gaseous state. With such a configuration, it becomes possible to adsorb and store a part of the carbon dioxide recovered by the carbon dioxide storage unit 50 on the adsorbent. Therefore, the carbon dioxide storage unit 50 provided in addition to the carbon dioxide recovery unit 30 can be made smaller than the case where the carbon dioxide storage unit 50 is composed only of a tank for storing carbon dioxide in a gaseous state.

[0037] Further, in the present embodiment, the three-way valve 78 is driven so that the carbon dioxide-containing gas exceeding the processing capacity of the carbon dioxide recovery unit 30 to recover carbon dioxide among the carbon dioxide-containing gas flowing through the first CO2-containing gas flow path 70 flows into the second CO2-containing gas flow path 74. In this way, within the range of the processing capacity of the carbon dioxide recovery unit 30 to recover carbon dioxide, since the carbon dioxide recovery unit 30 is preferentially used, the operation of recovering carbon dioxide from the carbon dioxide-containing gas can be made more stable.

[0038] Furthermore, in the present embodiment, the carbon dioxide recovery unit 30 is a pressure and temperature swing adsorption (PTSA) apparatus, and the upstream tank 69 of the carbon dioxide storage unit 50 is a pressure swing adsorption (PSA) apparatus. In the adsorption process and the desorption process, the PTSA apparatus that varies both pressure and temperature can reduce the energy required for carbon dioxide recovery compared to the PSA apparatus that varies only pressure. This is because the PTSA apparatus can reduce the energy consumed due to pressure fluctuations. Also, as in the present embodiment, when using the heat generated by the methanation reaction in the methanation reactor 22 to vary the temperature of the carbon dioxide recovery unit 30, the energy consumed due to temperature fluctuations can be reduced. However, the PTSA apparatus that varies both pressure and temperature has a more complex device configuration than the PSA apparatus and is generally more costly. Therefore, the adverse effects of the increase in the size of the device caused by increasing the device capacity can be greater. In the present embodiment, most of the process of recovering carbon dioxide from the carbon dioxide-containing gas is performed using the highly energy-efficient PTSA apparatus, and the process of the temporary increase in the amount of the carbon dioxide-containing gas is performed using the PSA apparatus with a simpler device configuration. Therefore, while coping with fluctuations in the amount of the carbon dioxide-containing gas, it is possible to improve the energy efficiency of the entire device and suppress the increase in the size of the entire device. In particular, as described above, since the carbon dioxide recovery unit 30 is preferentially used within the range of the processing capacity for recovering carbon dioxide, the effect of improving the energy efficiency of the entire device can be enhanced.

[0039] Furthermore, according to the present embodiment, in each adsorption tower 51 of the upstream tank 69 of the carbon dioxide storage unit 50, an air supply process is performed after the desorption process, and in the adsorption tower 51 of the air supply process, a sweep gas is flowed in a direction opposite to the direction of the flow of the carbon dioxide-containing gas in the adsorption process. Therefore, at the start of the adsorption process, the concentration of carbon dioxide in the adsorption off-gas discharged from the adsorption tower 51 in the adsorption process can be reduced, that is, the leakage of carbon dioxide from the adsorption tower 51 in the adsorption process can be suppressed.

[0040] Figs. 5 and 6 are explanatory diagrams showing changes in the carbon dioxide concentration in the adsorption off-gas discharged in the adsorption step. Fig. 5 shows the state of the adsorption off-gas discharged from the adsorption tower 51 of the present embodiment in which the air supply step is performed prior to the adsorption step, and Fig. 6 shows the state of the adsorption off-gas discharged from the adsorption tower in which the adsorption step is performed after the desorption step without performing the air supply step. In Figs. 5 and 6, the horizontal axis represents the elapsed time from the start of the adsorption step, and the vertical axis represents the carbon dioxide concentration in the sweep off-gas. As shown in Fig. 5, when the air supply step is performed, from the start of the adsorption step until the breakthrough point, that is, until the adsorbent breaks through by adsorbing carbon dioxide, the carbon dioxide concentration in the adsorption off-gas becomes almost zero. On the other hand, when the air supply step is not performed, as shown in Fig. 6, from the start of the adsorption step, the adsorption off-gas contains a certain amount of carbon dioxide, and carbon dioxide leakage occurs.

[0041] This is considered to be because at the end of the desorption step, the adsorbent is in a state where a small amount of carbon dioxide is adsorbed. In the desorption step involving depressurization as in the present embodiment, it is considered that the residual amount of carbon dioxide is relatively uniform throughout the adsorbent. When the adsorption step is started with carbon dioxide remaining in the adsorbent in this way, since the amount of carbon dioxide remaining in the entire adsorbent is small, the carbon dioxide partial pressure difference between the carbon dioxide-containing gas supplied to the adsorption tower 51 and the adsorbent becomes large, and the carbon dioxide in the carbon dioxide-containing gas is adsorbed by the adsorbent on the upstream side of the carbon dioxide-containing gas flow in the adsorption tower 51. By adsorbing carbon dioxide on the upstream side in this way, on the downstream side of the carbon dioxide-containing gas flow in the adsorption tower 51, the gas flowing through the adsorption tower 51 becomes a gas with an extremely low carbon dioxide concentration and carbon dioxide partial pressure. As a result, in the downstream part of the adsorption tower 51, the carbon dioxide partial pressure of the gas is lower than that of the adsorbent, and the carbon dioxide remaining in the adsorbent desorbs into the gas, causing carbon dioxide leakage into the adsorption off-gas as shown in Fig. 6.

[0042] In this embodiment, in the air supply step, the sweep gas is flowed in a direction opposite to the direction of the flow of the carbon dioxide-containing gas in the adsorption step. In this air supply step, in the adsorption tower 51, at least on the upstream side of the sweep gas flow, that is, on the downstream side of the carbon dioxide-containing gas flow in the adsorption step, the carbon dioxide remaining in the adsorbent can be desorbed. Therefore, at the start of the adsorption step, when a gas in which carbon dioxide is adsorbed on the upstream side of the carbon dioxide-containing gas flow and the carbon dioxide partial pressure becomes extremely low flows, on the downstream side of the carbon dioxide-containing gas flow, the remaining carbon dioxide is prevented from desorbing and leaking out, and the recovery efficiency of carbon dioxide can be increased.

[0043] Note that the sweep off-gas discharged in the air supply step may contain carbon dioxide. However, in the air supply step, since it is sufficient to sufficiently reduce the amount of carbon dioxide remaining in the adsorbent on the upstream side of the sweep gas flow, the flow rate of the sweep gas can be made sufficiently smaller than the flow rate of the carbon dioxide-containing gas supplied to the adsorption tower 51 in the adsorption step. Therefore, by performing the air supply step, the amount of carbon dioxide leaking out from the adsorption tower 51 can be suppressed.

[0044] In the adsorption tower 51 of the carbon dioxide storage unit 50, similar to the separator 31 of the carbon dioxide recovery unit 30, by flowing purge gas in the desorption step, the amount of carbon dioxide remaining in the adsorbent can be reduced, and without performing the air supply step, it is also possible to suppress the leakage of carbon dioxide at the start of the adsorption step. However, when purge gas is supplied in the desorption step, the gas obtained in the desorption step will contain the purge gas in addition to carbon dioxide. When hydrogen is used as the purge gas, the hydrogen mixed with carbon dioxide as the purge gas can be used in the methanation reaction in the methanation reactor 22. However, when purge gas is used in both the carbon dioxide recovery unit 30 and the carbon dioxide storage unit 50, the control of the amount of hydrogen to be supplied as the shortage for the methanation reaction in the methanation reactor 22 (control of the ratio of carbon dioxide to hydrogen in the methanation reactor 22) becomes complicated and may be difficult to adopt. Therefore, from the perspective of simplifying the control of the entire carbon dioxide recycling system 10, it is desirable to perform the air supply step in the upstream tank 69 of the carbon dioxide storage unit 50 as in this embodiment. Also, if the amount of carbon dioxide leakage at the start of the adsorption step is within the allowable range, it may not be necessary to perform the air supply step.

[0045] B. Second Embodiment: FIG. 7 is an explanatory diagram showing the schematic configuration of the carbon dioxide storage unit 150 of the second embodiment. The carbon dioxide storage unit 150 is used in place of the carbon dioxide storage unit 50 in a system similar to the carbon dioxide recycling system 10 of the first embodiment. In the second embodiment, the same reference numerals are given to the parts common to the first embodiment. In FIG. 7, similar to FIG. 3, the adsorption tower 51a is in the adsorption step, the adsorption tower 51b is in the desorption step, and the adsorption tower 51c is in the air supply step, and the flow paths through which the fluid flows are shown by thick lines. The adsorption tower 51c in the air supply step where the sweep gas is supplied is also called the "first adsorption tower", and the adsorption off-gas 1a in the adsorption step where the carbon dioxide-containing gas is supplied is also called the "second adsorption tower".

[0046] In the carbon dioxide storage unit 150, the sweep-off gas passage 66 is connected to the second CO2-containing gas passage 74. Therefore, in the state of cycle 1 shown in FIG. 7, the sweep-off gas containing carbon dioxide discharged from the adsorption tower 51c (the first adsorption tower) in the air supply process is guided to the adsorption tower 51a (the second adsorption tower) via the second CO2-containing gas passage 74 and the CO2-containing gas branch passage 56a. As a result, the carbon dioxide in the sweep-off gas is adsorbed by the adsorbent 52a in the adsorption tower 51a. In this way, when performing control to switch the connection state of the pipes communicating between the adsorption towers so as to guide the sweep-off gas discharged from the adsorption tower 51 in the air supply process to the adsorption tower 51 in the adsorption process, the control unit 80 functions as a "third control unit".

[0047] With such a configuration, in order to adsorb the carbon dioxide in the sweep-off gas in another adsorption tower 51a in the adsorption process, the amount of carbon dioxide released to the outside during the air supply process can be suppressed, and the carbon dioxide recovery efficiency in the carbon dioxide recovery device 15 can be improved.

[0048] C. Third Embodiment: In the first and second embodiments, in each adsorption tower 51 provided in the carbon dioxide storage unit 50, as shown in FIG. 4, the adsorption process, the desorption process, and the air supply process were set to the same time, and the cycle was changed at predetermined time intervals. However, a different configuration may be used. Hereinafter, as a third embodiment, the desorption operation in the adsorption tower 51 in the desorption process is controlled so that the pressure inside the downstream tank 55 is within a specific range, and when it is determined that the degree of carbon dioxide adsorption in the adsorption tower 51 in the adsorption process has reached a breakthrough state, a configuration for changing the cycle will be described. In the third embodiment, that the adsorption tower 51c is in the desorption process means a state in which the operation of desorbing carbon dioxide from the adsorbent is possible after the adsorption process, and not only the state in which the pump 54 is driven and the CO2-containing gas valve 57c is opened, but also the state in which the CO2-containing gas valve 57c is closed and waiting for the desorption operation to be performed when the valve is opened is included. Hereinafter, based on the same structure as the carbon dioxide storage unit 50 of the first embodiment, the operation of the third embodiment will be described.

[0049] FIG. 8 is a flowchart showing a desorption process control routine executed by the control unit 80 of the third embodiment. This routine is activated when any one of the three adsorption towers 51 (hereinafter described as adsorption tower 51b) enters the desorption process, and is repeatedly executed until the desorption process of this adsorption tower 51b is completed. In this way, when controlling the desorption process, specifically, when controlling the connection state of the pipes communicating with the adsorption tower 51b and the downstream tank 55, the control unit 80 functions as the "fourth control unit".

[0050] When this routine is activated, the CPU of the control unit 80 acquires the detection signal of the pressure sensor 55b provided in the downstream tank 55, and compares the pressure Pt in the downstream tank 55 with the threshold value min which is the lower limit value of the pressure in the downstream tank 55 (step S100). In this embodiment, a threshold value max which is the upper limit value is preset together with the threshold value min which is the lower limit value of the pressure in the downstream tank 55. The threshold value min and the threshold value max are defined as reference values for ensuring the accuracy of adjusting the flow rate of the gas discharged from the downstream tank 55 by setting the pressure in the downstream tank 55 within the range of these lower limit values or more and upper limit values or less.

[0051] If it is determined in step S100 that the pressure Pt in the downstream tank 55 is less than the threshold value min which is the lower limit value of the pressure in the downstream tank 55 (step S100: YES), the control unit 80 starts the desorption operation of the adsorption tower 51b (step S110), that is, drives the pump 54 and opens the CO2 discharge valve 62b. As a result, the supply of the carbon dioxide desorbed in the adsorption tower 51b to the downstream tank 55 is started. At this time, if the flow rate of the carbon dioxide supplied to the downstream tank 55 exceeds the flow rate of the carbon dioxide discharged from the downstream tank 55, the pressure Pt in the downstream tank 55 will increase.

[0052] Thereafter, the control unit 80 compares the pressure Pt in the downstream tank 55 with a threshold value max which is the upper limit value of the pressure in the downstream tank 55 (step S120). When it is determined that the pressure Pt in the downstream tank 55 exceeds the threshold value max (step S120: YES), the control unit 80 stops the desorption operation (step S130) and ends this routine. In step S130, the CO2 discharge valve 62b is closed. Thereby, the supply of carbon dioxide from the adsorption tower 51b to the downstream tank 55 is stopped. Thereafter, when the supply of carbon dioxide from the downstream tank 55 to the methanation reactor 22 is performed, the pressure Pt in the downstream tank 55 decreases.

[0053] In step S120, when it is determined that the pressure Pt in the downstream tank 55 is equal to or less than the threshold value max (step S120: NO), the control unit 80 continues the desorption operation (step S160). Then, steps S120 and S160 are repeated until it is determined in step S120 that the pressure Pt in the downstream tank 55 exceeds the threshold value max.

[0054] In step S100, when it is determined that the pressure Pt in the downstream tank 55 is less than the threshold value min (step S100: NO), the control unit 80 determines whether the adsorption tower 51b is in the desorption operation (step S140). When it is determined that it is in the desorption operation (step S140: YES), the control unit 80 proceeds to step S120, continues the desorption operation until the pressure Pt in the downstream tank 55 exceeds the threshold value max (step S160), and stops the desorption operation when the pressure Pt in the downstream tank 55 exceeds the threshold value max (step S130).

[0055] In step S140, if it is determined that the desorption operation is not in progress (step S140: NO), the control unit 80 maintains a standby state without performing the desorption operation (step S150). Then, it returns to step 100 again and performs the operations after step S100 described above. As a result, in the adsorption tower 51b of the desorption process, when the pressure Pt in the downstream tank 55 becomes less than the threshold value min, the desorption operation is performed until the pressure Pt reaches the threshold value max, and carbon dioxide is supplied from the adsorption tower 51b to the downstream tank 55. When the pressure Pt in the downstream tank 55 exceeds the threshold value max, the desorption operation is stopped until the pressure Pt becomes less than the threshold value min. In this way, the pressure Pt in the downstream tank 55 is maintained within the range of the threshold value min or more and the threshold value max or less.

[0056] FIG. 9 is a flowchart showing an adsorption process control routine executed by the control unit 80 of the third embodiment. This routine is activated every time the cycle shown in FIG. 4 is switched and is executed to determine the timing of the cycle switch. Hereinafter, the case where the adsorption tower 51a switches to cycle 1 in the adsorption process will be described.

[0057] When this routine is activated, the CPU of the control unit 80 starts the adsorption operation for the adsorption tower 51a (step S200). Specifically, the CO2-containing gas valve 57a and the off-gas discharge valve 59a are opened to supply the carbon dioxide-containing gas to the adsorbent 52a of the adsorption tower 51a. Thereafter, the control unit 80 determines whether the adsorbent 52a has reached the breakthrough state, that is, whether the adsorbent 52a has adsorbed carbon dioxide and reached the breakthrough state (step S210).

[0058] The determination in step S210 can be made as follows. For example, a temperature sensor (such as a thermocouple) for measuring the temperature of the adsorbent is provided at the other end of the adsorbent 52a, that is, at the downstream part of the carbon dioxide-containing gas flow. When the measured temperature becomes equal to or higher than a reference temperature predetermined as the reference for the breakthrough state, it can be determined that the breakthrough state has occurred. Further, a carbon dioxide concentration sensor may be provided in the adsorption off-gas passage 60, and when the carbon dioxide concentration in the adsorption off-gas becomes equal to or higher than a predetermined reference value, it may be determined that the breakthrough state has occurred. Alternatively, a flow rate sensor is provided in the second CO2-containing gas flow path 74, and the control unit 80 integrates the flow rate detected by the flow rate sensor to calculate the amount of the carbon dioxide-containing gas supplied to the adsorption tower 51a. When the amount of the supplied carbon dioxide-containing gas exceeds a predetermined reference amount, it may be determined that the breakthrough state has occurred.

[0059] When it is determined that the breakthrough state has occurred (step S210: YES), the control unit 80 ends this routine and switches from cycle 1 to cycle 2. When it is determined that the breakthrough state does not exist (step S210: NO), the control unit 80 continues the adsorption operation (step S220) and continues the adsorption operation until it is determined in step S210 that the breakthrough state has occurred.

[0060] In the third embodiment, the desorption operation is started based on the condition that the pressure Pt in the downstream tank 55 becomes less than the lower limit value, and the desorption operation is stopped based on the condition that the pressure exceeds the upper limit value. Then, when the adsorption state of carbon dioxide in the adsorption tower in the adsorption process breaks through, the cycle is switched. Therefore, the downstream tank 55 only needs to have a capacity capable of coping with fluctuations in the amount of carbon dioxide required by the methanation reactor 22. In the third embodiment, even if the amount of the carbon dioxide-containing gas supplied to the carbon dioxide storage unit 50 is excessive with respect to the amount of carbon dioxide required by the methanation reactor 22, the carbon dioxide supplied to the carbon dioxide storage unit 50 is adsorbed and stored in the adsorption tower in the adsorption process. Therefore, the downstream tank 55 for storing carbon dioxide in a gaseous state can be made smaller, and as a result, the entire carbon dioxide storage unit 50 can be made smaller.

[0061] In the third embodiment, when the adsorption tower in the adsorption step reaches the breakthrough state, the cycle is switched. However, a different configuration may be used. For example, similar to the first and second embodiments, the cycle may be switched when a predetermined reference time has elapsed. However, if the cycle is switched when the adsorption tower in the adsorption step reaches the breakthrough state, the adsorbent provided in the adsorption tower 51 can be used efficiently. Also, unlike the case of switching the cycle based on the elapsed time, for example, it is not necessary to set the capacity of the adsorption tower 51 so as to be able to handle the maximum value of the carbon dioxide-containing gas that can be supplied during the reference time, and the adsorption tower 51 can be downsized.

[0062] D. Other Embodiments: In each of the above-described embodiments, the adsorbent provided in the separator 31 of the carbon dioxide recovery unit 30 and the adsorption tower 51 of the carbon dioxide storage unit 50 is an adsorbent that adsorbs carbon dioxide by physical adsorption. However, a different configuration may be used. For example, a chemisorbent such as a solid absorbent in which an amine is supported on a porous material may be used.

[0063] In each of the above-described embodiments, the separators 31 in the carbon dioxide recovery unit 30 or the adsorption towers 51 in the carbon dioxide storage unit 50 are the same in shape and the same in capacity. However, they may be different in shape and capacity from each other.

[0064] In each of the above-described embodiments, the carbon dioxide recovery unit 30 is a device that recovers carbon dioxide from a carbon dioxide-containing gas using an adsorbent. However, a different configuration may be used. For example, the carbon dioxide recovery unit 30 may include a carbon dioxide permeable membrane that selectively permeates carbon dioxide and a tank that stores carbon dioxide in a gaseous state, and store the carbon dioxide separated by the carbon dioxide permeable membrane in the tank. Even in such a case, by combining the carbon dioxide recovery unit 30 and the carbon dioxide storage unit 50, a similar effect of downsizing the carbon dioxide recovery unit 30 can be obtained.

[0065] In each of the above-described embodiments, when the amount of the carbon dioxide-containing gas supplied by the carbon dioxide storage unit 50 exceeds the set value set as the processable amount in the carbon dioxide recovery unit 30, the carbon dioxide-containing gas in excess of the set value is recovered and stored. However, a different configuration may be adopted. For example, even when the amount of the carbon dioxide-containing gas supplied by the carbon dioxide supply unit 20 is less than the set value, if the amount of carbon dioxide required by the methanation reactor 22 is less than the amount of the carbon dioxide-containing gas supplied by the carbon dioxide supply unit 20, a part of the carbon dioxide-containing gas supplied to the carbon dioxide recovery device 15 may be recovered and stored in the carbon dioxide storage unit 50.

[0066] In each of the above-described embodiments, the carbon dioxide recovery device 15 is included in the carbon dioxide recycling system 10. However, a different configuration may be adopted. The carbon dioxide recovery device 15 only needs to receive the supply of the carbon dioxide-containing gas and recover carbon dioxide. The carbon dioxide recovered by the carbon dioxide recovery device 15 may be used for applications other than methane production. For example, it can be used to produce other hydrocarbon fuels including hydrocarbons such as ethane and propane other than methane, or alcohols such as methanol. Further, the hydrocarbon fuel produced from the recovered carbon dioxide without recycling the carbon dioxide may be used for applications other than those involving the generation of the carbon dioxide-containing gas supplied to the carbon dioxide recovery device 15. Furthermore, the carbon dioxide recovered by the carbon dioxide recovery device 15 may be used for applications other than the production of hydrocarbon fuels.

[0067] The present disclosure is not limited to the above-described embodiments and the like, and can be realized in various configurations without departing from the gist thereof. For example, the technical features in the embodiments corresponding to the technical features in each form described in the summary of the invention can be appropriately replaced or combined in order to solve some or all of the above-described problems or to achieve some or all of the above-described effects. Further, if the technical feature is not described as essential in this specification, it can be appropriately deleted.

Description of Symbols

[0068] 10…Carbon dioxide recycling system 15…Carbon dioxide recovery device 20…Carbon dioxide-containing gas supply section 22…Methanation reactor 24…Methane tank 30…Carbon dioxide recovery section 31, 31a, 31b…Separator 32a, 32b…Adsorbent 33…Purge gas supply section 34…Pump 35…Surge tank 36a…CO2-containing gas branch path 36b…CO2-containing gas branch path 37a…CO2-containing gas valve 38a, 38b…Discharge branch path 39a, 39b…Off-gas discharge valve 40…Adsorption off-gas path 41a, 41b…Discharge branch path 42a, 42b…CO2 discharge valve 43…Purge gas supply flow path 44a, 44b…Purge gas branch path 45a, 45b…Purge gas supply valve 49…Heat medium flow path 50, 150…Carbon dioxide storage section 51, 51a~51c…Adsorption tower 52a~52c…Adsorbent 53…Sweep gas supply section 54…Pump 55…Downstream tank 55a…Flow rate adjustment valve 55b…Pressure sensor 56a~56c…CO2-containing gas branch path 57a~57c…CO2-containing gas valve 58a~58c…Discharge branch path 59a~59c…Off-gas discharge valve 60…Adsorption off-gas path 61a~61c…Discharge branch path 62a~62c...CO2 exhaust valve 63...Sweep gas supply passage 64a~64c...Sweep gas branch 65a~65c...Sweep gas supply valve 66...Sweep off gas passage 67a~67c...Sweep off gas branch 68a~68c...Sweep off gas valve 69...Upstream tank 70...First CO2-containing gas flow path 72...First CO2 flow path 74...Second CO2-containing gas flow path 76...Second CO2 flow path 78...Three-way valve 80...Control unit

Claims

1. A carbon dioxide recovery device, comprising: a carbon dioxide recovery unit that recovers carbon dioxide from the carbon dioxide-containing gas supplied from a carbon dioxide-containing gas supply unit that is a source of the carbon dioxide-containing gas; a carbon dioxide storage unit that is connected to the carbon dioxide-containing gas supply unit in parallel with the carbon dioxide recovery unit and stores the carbon dioxide recovered from a part of the carbon dioxide-containing gas supplied by the carbon dioxide-containing gas supply unit; a first control unit that controls the distribution amount of the carbon dioxide-containing gas supplied from the carbon dioxide-containing gas supply unit to the carbon dioxide recovery unit and the carbon dioxide storage unit; The carbon dioxide storage unit includes an upstream tank provided with an adsorbent for adsorbing carbon dioxide and a downstream tank for storing the carbon dioxide discharged from the upstream tank in a gaseous state. When the amount of the carbon dioxide-containing gas supplied by the carbon dioxide-containing gas supply unit is equal to or less than a preset value that is the processable amount by which the carbon dioxide recovery unit can recover carbon dioxide from the carbon dioxide-containing gas, the first control unit supplies the entire amount of the carbon dioxide-containing gas supplied by the carbon dioxide-containing gas supply unit to the carbon dioxide recovery unit. When the amount of the carbon dioxide-containing gas supplied by the carbon dioxide-containing gas supply unit exceeds the preset value, the first control unit supplies the amount of the carbon dioxide-containing gas equal to the preset value to the carbon dioxide recovery unit and supplies the excess amount of the carbon dioxide-containing gas over the preset value to the carbon dioxide storage unit. A carbon dioxide recovery device.

2. A carbon dioxide recovery device, comprising: a carbon dioxide recovery unit that recovers carbon dioxide from the carbon dioxide-containing gas supplied from a carbon dioxide-containing gas supply unit that is a source of the carbon dioxide-containing gas; a carbon dioxide storage unit that is connected to the carbon dioxide-containing gas supply unit in parallel with the carbon dioxide recovery unit and stores the carbon dioxide recovered from a part of the carbon dioxide-containing gas supplied by the carbon dioxide-containing gas supply unit; The carbon dioxide storage unit includes an upstream tank provided with an adsorbent for adsorbing carbon dioxide and a downstream tank for storing the carbon dioxide discharged from the upstream tank in a gaseous state. The carbon dioxide recovery unit is a pressure / temperature swing adsorption device, and the upstream tank is a pressure swing adsorption device. A carbon dioxide recovery device.

3. A carbon dioxide recovery device, comprising: ​ ​ ​ ​ A carbon dioxide recovery unit that recovers carbon dioxide from the carbon dioxide-containing gas supplied from a carbon dioxide-containing gas supply unit that is a source of the carbon dioxide-containing gas, A carbon dioxide storage unit that is connected to the carbon dioxide-containing gas supply unit in parallel with the carbon dioxide recovery unit and stores carbon dioxide recovered from a part of the carbon dioxide-containing gas supplied by the carbon dioxide-containing gas supply unit, Comprising, The carbon dioxide storage unit includes an upstream tank provided with an adsorbent for adsorbing carbon dioxide, and a downstream tank for storing the carbon dioxide discharged from the upstream tank in a gaseous state, The carbon dioxide recovery device further includes, A gas supply unit that supplies a sweep gas having a lower carbon dioxide concentration than the carbon dioxide-containing gas to the upstream tank in a direction opposite to the direction in which the carbon dioxide-containing gas flows in the upstream tank, After the desorption step of desorbing carbon dioxide from the adsorbent of the upstream tank that has adsorbed carbon dioxide in the carbon dioxide-containing gas, prior to the adsorption step of supplying the carbon dioxide-containing gas to the upstream tank to adsorb carbon dioxide to the adsorbent, the gas supply unit is driven to supply the sweep gas to the upstream tank. A second control unit, Carbon dioxide recovery device.

4. The carbon dioxide recovery device according to claim 3, The upstream tank includes a plurality of adsorption towers provided with an adsorbent for adsorbing carbon dioxide, The carbon dioxide recovery device further includes a third control unit that switches the connection state of a pipe communicating with the plurality of adsorption towers. When the sweep gas is supplied to a first adsorption tower that is one of the plurality of adsorption towers, the sweep off-gas discharged from the first adsorption tower is supplied to a second adsorption tower to which the carbon dioxide-containing gas is supplied. A third control unit that switches the connection state so as to guide the gas, Carbon dioxide recovery device.

5. A carbon dioxide recovery device, A carbon dioxide recovery unit that recovers carbon dioxide from the carbon dioxide-containing gas supplied from a carbon dioxide-containing gas supply unit that is a source of the carbon dioxide-containing gas, A carbon dioxide storage unit that is connected to the carbon dioxide-containing gas supply unit in parallel with the carbon dioxide recovery unit and stores carbon dioxide recovered from a part of the carbon dioxide-containing gas supplied by the carbon dioxide-containing gas supply unit, Comprising, The carbon dioxide storage unit includes an upstream tank provided with an adsorbent for adsorbing carbon dioxide, and a downstream tank for storing the carbon dioxide discharged from the upstream tank in a gaseous state. The upstream tank is an adsorption tower provided with an adsorbent for adsorbing carbon dioxide. At least one of the adsorption towers is in an adsorption step capable of receiving the supply of the carbon dioxide-containing gas and adsorbing carbon dioxide on the adsorbent, and at least one of the other adsorption towers is in a desorption step capable of desorbing carbon dioxide from the adsorbent. The upstream tank includes a plurality of adsorption towers. The downstream tank is provided with a pressure sensor for detecting the pressure inside the downstream tank. The carbon dioxide recovery device further includes a fourth control unit for controlling the connection state of a pipe communicating with the plurality of adsorption towers and the downstream tank. When the pressure detected by the pressure sensor is lower than a predetermined lower limit value, the carbon dioxide desorbed from the adsorption tower in the desorption step is guided to the downstream tank. When the pressure detected by the pressure sensor exceeds a predetermined upper limit value, the supply of carbon dioxide from the adsorption tower in the desorption step to the downstream tank is stopped. When the pressure detected by the pressure sensor is in the range of not less than the lower limit value and not more than the upper limit value, if the supply of carbon dioxide from the adsorption tower in the desorption step to the downstream tank has been stopped, the stopped state is maintained, and if the supply of carbon dioxide from the adsorption tower in the desorption step to the downstream tank is being carried out, the fourth control unit is provided to continue the supply of carbon dioxide. Carbon dioxide recovery device.

6. The carbon dioxide recovery device according to claim 5, When it is determined that the adsorption state of carbon dioxide in the adsorption tower in the adsorption step has reached a predetermined maximum adsorption amount, the fourth control unit stops the supply of the carbon dioxide-containing gas to the adsorption tower and switches the connection state so as to guide the carbon dioxide-containing gas to another adsorption tower that has undergone the desorption step. Carbon dioxide recovery device.

7. A carbon dioxide recycling system, The carbon dioxide recovery device according to any one of claims 1 to 6, A fuel generation unit that generates a hydrocarbon-based fuel using the carbon dioxide supplied from the carbon dioxide recovery device. Energy is extracted from the hydrocarbon-based fuel generated by the fuel generation unit, and a carbon dioxide-containing gas is generated. As the carbon dioxide-containing gas supply unit, a carbon dioxide generation unit that supplies the generated carbon dioxide to the carbon dioxide recovery device, A carbon dioxide recycling system comprising.

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