Carbon dioxide recovery system

Abstract

To provide a carbon dioxide recovery system that can reduce the size of equipment and improve the efficiency of recovering carbon dioxide.SOLUTION: A carbon dioxide recovery system 10 includes: a first absorber 31a configured such that carbon dioxide contained in a target gas fed from a target gas source 90 through a first downstream gas passage 12a is absorbed into a solution; a second absorber 31b configured such that carbon dioxide contained in the target gas fed from the target gas source 90 through a second downstream gas passage 12b is absorbed into a solution; a first control valve 16a capable of changing a flow rate of the target gas in the first downstream gas passage 12a; and a second control valve 16b capable of changing a flow rate of the target gas in the second downstream gas passage 12b. A carbon dioxide absorption unit of the first absorber 31a and a carbon dioxide absorption unit of the second absorber 31b are different from each other in ability of absorbing carbon dioxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide capture system. [Background technology]

[0002] Conventionally, a carbon dioxide recovery system that recovers carbon dioxide from gas generated in a gas source such as a combustion facility has been known. The carbon dioxide recovery system includes a carbon dioxide absorption tower that absorbs carbon dioxide contained in the gas into a carbon dioxide absorbing solution, and a carbon dioxide stripper tower that heats the carbon dioxide absorbing solution to strip carbon dioxide from the carbon dioxide absorbing solution, and is configured so that the carbon dioxide absorbing solution is circulated between the carbon dioxide absorption tower and the carbon dioxide stripper tower.

[0003] The amount of carbon dioxide that a carbon dioxide capture system can capture is determined by the size of the carbon dioxide absorption tower and the carbon dioxide stripper tower. Therefore, the size of the carbon dioxide capture system equipment is determined by the maximum amount of carbon dioxide contained in the gas generated at the gas source. This makes it difficult to reduce the size of the carbon dioxide capture system equipment. Furthermore, because conventional carbon dioxide capture systems are operated to maintain constant the flow rate and heating amount of the carbon dioxide absorption solution, a decrease in the amount of gas generated at the gas source reduces the carbon dioxide capture efficiency (the ratio indicating the amount of carbon dioxide that can be captured relative to the energy consumed by the carbon dioxide capture system).

[0004] Patent Document 1 discloses a carbon dioxide capture system that includes multiple pairs of carbon dioxide absorption towers and carbon dioxide diffusion towers and is configured to maintain the gas flow rate in each pair of carbon dioxide absorption towers within an appropriate range. The carbon dioxide capture system disclosed in Patent Document 1 can improve the carbon dioxide capture efficiency in each pair. However, because the carbon dioxide capture system disclosed in Patent Document 1 includes multiple pairs of carbon dioxide absorption towers and carbon dioxide diffusion towers, the equipment becomes large.

[0005] Patent Document 2 discloses a carbon dioxide capture system including multiple carbon dioxide absorption towers and one carbon dioxide diffusion tower, in which gas is supplied from multiple gas sources to each of the multiple carbon dioxide absorption towers, and a carbon dioxide absorbing solution is circulated between the multiple carbon dioxide absorption towers and the single carbon dioxide diffusion tower. The carbon dioxide capture system disclosed in Patent Document 2 allows for a more compact facility compared to a configuration in which a carbon dioxide absorption tower and a carbon dioxide diffusion tower are provided for each gas source. However, with the carbon dioxide capture system disclosed in Patent Document 2, fluctuations in the amount of gas generated at each gas source make it difficult to maintain carbon dioxide capture efficiency throughout the system.

[0006] Patent Document 3 discloses a carbon dioxide capture system configured to return gas discharged from a carbon dioxide absorption tower (gas from which carbon dioxide has been removed) to the carbon dioxide absorption tower when the amount of gas generated in the gas source decreases. The carbon dioxide capture system disclosed in Patent Document 3 can improve operating efficiency and increase the amount of carbon dioxide absorbed. However, with the carbon dioxide capture system disclosed in Patent Document 3, there is a risk that the carbon dioxide capture efficiency will decrease when the amount of gas decreases. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-89478 [Patent Document 2] Japanese Patent Application Publication No. 2019-196885 [Patent Document 3] Japanese Patent Application Publication No. 2018-94919 Summary of the Invention

[0008] (Problem to be solved by the invention) In view of the above situation, one of the objects of the present invention is to provide a carbon dioxide recovery system that can improve the carbon dioxide recovery efficiency (or prevent or suppress a decrease) while miniaturizing the equipment, even when the amount of gas generated at the gas source fluctuates over time.

[0009] (Means for solving the problem) The carbon dioxide recovery system of the present invention comprises: a first carbon dioxide absorption unit connected to a gas source that generates a gas containing carbon dioxide via a first gas path, and configured so that carbon dioxide contained in the gas that flows from the gas source through the first gas path is absorbed in a carbon dioxide absorbing solution; a second carbon dioxide absorption unit that is connected to the gas source via a second gas path, that is configured so that carbon dioxide contained in the gas that flows in from the gas source through the second gas path is absorbed in a carbon dioxide absorbing solution, and that has a higher carbon dioxide absorption capacity than the first carbon dioxide absorption unit; a first gas valve provided in the first gas path and capable of changing a flow rate of the gas; a second gas valve provided in the second gas path and capable of changing a flow rate of the gas; Equipped with The first carbon dioxide absorbing unit and the second carbon dioxide absorbing unit are connected in series so that the carbon dioxide absorbing solution can flow therethrough.

[0010] According to the carbon dioxide capture system of the present invention, by opening the first gas valve and closing the second gas valve, gas can be supplied only to the first carbon dioxide absorption unit, by closing the first gas valve and opening the second gas valve, gas can be supplied only to the second carbon dioxide absorption unit, and by opening both the first gas valve and the second gas valve, gas can be supplied to both the first carbon dioxide absorption unit and the second carbon dioxide absorption unit. With this configuration, the first carbon dioxide absorption unit and the second carbon dioxide absorption unit can be operated according to the amount of gas generated in the gas source (gas flow rate), thereby preventing or suppressing a decrease in carbon dioxide capture efficiency. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a carbon dioxide capture system according to this embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of the first absorption tower and the second absorption tower of the carbon dioxide capture unit. [Figure 3] FIG. 3 is a flowchart showing the processing executed by the process control device. [Figure 4] FIG. 4 is a flowchart showing the processing executed by the process control device. [Figure 5] FIG. 5 is a flowchart showing the processing executed by the process control device. [Figure 6] FIG. 6 is a flowchart showing the process executed by the collection control device. [Figure 7] FIG. 7 is a flowchart showing the process executed by the collection control device. [Figure 8] FIG. 8 is a flowchart showing the process executed by the collection control device. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described. In the following description, the "carbon dioxide capture system" may be abbreviated as the "capture system," the "carbon dioxide capture device" may be abbreviated as the "capture device," and the "carbon dioxide absorption solution" may be abbreviated as the "solution." Furthermore, the gas from which carbon dioxide is captured (gas containing carbon dioxide) may be abbreviated as the "target gas." In the following description, unless otherwise specified, the "flow rate" of the target gas and solution refers to the flow rate per unit time.

[0013] <Configuration of collection system> 1 is a schematic diagram showing the configuration of a recovery system 10. As shown in Fig. 1, the recovery system 10 includes an upstream gas path 11, an upstream gas pump 12, an upstream gas flow meter 13, a first downstream gas path 14a, a second downstream gas path 14b, a first regulating valve 16a, a second regulating valve 16b, a first buffer 17a, a second buffer 17b, a first on-off valve 18a, a second on-off valve 18b, a first downstream gas pump 19a, a second downstream gas pump 19b, a first downstream gas flow meter 20a, a second downstream gas flow meter 20b, a pressure equalizing path 21, a process control device 22, and a recovery device 30.

[0014] The target gas source 90 is an example of a gas source of the present invention. The target gas source 90 is an apparatus that generates a gas containing carbon dioxide. For example, the target gas source 90 can be a metal melting furnace, a carburizing furnace, or a generator that uses the heat of combustion of fossil fuels (i.e., uses fossil fuels as fuel). In this case, the target gas is the combustion exhaust gas of the fossil fuel. Note that the number of devices in the target gas source 90 is not limited.

[0015] The upstream gas path 11, the first downstream gas path 14a, and the second downstream gas path 14b are paths for supplying the target gas generated in the target gas source 90 to the recovery device 30. One end of the upstream gas path 11 is connected to the target gas source 90. An upstream gas pump 12 and an upstream gas flow meter 13 are arranged on the upstream gas path 11. When the upstream gas pump 12 operates, it supplies (pressure-feeds) the target gas generated in the target gas source 90 from one end of the upstream gas path 11 to the other end. The configuration of the upstream gas pump 12 is not particularly limited, and various known gas supply pumps (blowers) can be used. The upstream gas flow meter 13 can measure the flow rate of the target gas flowing through the upstream gas path 11. The measurement value of the flow rate of the target gas by the upstream gas flow meter 13 is transmitted to a process control device 22, which will be described later.

[0016] The first downstream gas passage 14a is an example of a first gas passage of the present invention, and the second downstream gas passage 14b is an example of a second gas passage of the present invention. The first downstream gas passage 14a and the second downstream gas passage 14b are passages branching off from the upstream gas passage 11 at the other end of the upstream gas passage 11. One end of the first downstream gas passage 14a is connected to the other end of the upstream gas passage 11, and the other end of the first downstream gas passage 14a is connected to a first absorption tower 31a of a recovery device 30, which will be described later. One end of the second downstream gas passage 14b is connected to the other end of the upstream gas passage 11, and the other end of the second downstream gas passage 14b is connected to a second absorption tower 31b of the recovery device 30, which will be described later. The capacity (maximum flow rate of the target gas) of the second downstream gas passage 14b is larger than the capacity of the first downstream gas passage 14a.

[0017] In the first downstream gas path 14a, a first adjustment valve 16a, a first buffer 17a, a first on-off valve 18a, a first downstream gas pump 19a, and a first downstream gas flow meter 20a are arranged in this order from one end (the side closer to the upstream gas path 11, i.e., the upstream side of the target gas flow). In the second downstream gas path 14b, a second adjustment valve 16b, a second buffer 17b, a second on-off valve 18b, a second downstream gas pump 19b, and a second downstream gas flow meter 20b are arranged in this order from one end.

[0018] The first regulating valve 16a is an example of a first gas valve of the present invention, and the second regulating valve 16b is an example of a second gas valve of the present invention. The first regulating valve 16a is a valve capable of adjusting the flow rate of the target gas flowing through the first downstream gas path 14a. The second regulating valve 16b is a valve capable of adjusting the flow rate of the target gas flowing through the second downstream gas path 14b. For example, an electrically operated damper is applied to the first regulating valve 16a and the second regulating valve 16b. The first regulating valve 16a and the second regulating valve 16b are configured not only to be switched between open and closed, but also to be able to change the opening degree (in other words, the flow rate of the target gas) continuously or stepwise. The first regulating valve 16a and the second regulating valve 16b are controlled by a process control device 22, which will be described later.

[0019] The first buffer 17a and the second buffer 17b each include a pressure vessel capable of storing the target gas supplied from the target gas source 90 at a pressure higher than atmospheric pressure. The volume of the second buffer 17b (volume of the target gas that can be stored) is larger than the volume of the first buffer 17a. For example, the first buffer 17a includes one pressure vessel, and the second buffer 17b includes multiple pressure vessels that are the same as the pressure vessel of the first buffer 17a.

[0020] The first on-off valve 18a is a valve that opens and closes the first downstream gas path 14a. The second on-off valve 18b is a valve that opens and closes the second downstream gas path 14b. The first on-off valve 18a and the second on-off valve 18b only need to be able to open and close the first downstream gas path 14a and the second downstream gas path 14b, respectively (as long as they are switchable between an open state that allows the target gas to pass and a closed state that does not), and they do not need to be able to adjust their opening degrees continuously or in steps. Note that if the first downstream gas pump 19a and the second downstream gas pump 19b, which will be described later, are configured to "not allow the target gas to pass while not operating," the first on-off valve 18a and the second on-off valve 18b may not be provided.

[0021] The first downstream gas pump 19a is configured to operate to supply the target gas in the first downstream gas path 14a (which may also be referred to as the target gas accumulated in the first buffer 17a) to the first absorption tower 31a of the recovery device 30. The second downstream gas pump 19b is configured to operate to supply the target gas in the second downstream gas path 14b (which may also be referred to as the target gas accumulated in the second buffer 17b) to the second absorption tower 31b of the recovery device 30. The capacity of the second downstream gas pump 19b (the maximum amount of target gas that can be supplied per unit time) is greater than the capacity of the first downstream gas pump 19a. The configurations of the first downstream gas pump 19a and the second downstream gas pump 19b are not particularly limited, and various known gas supply pumps (blowers) can be used.

[0022] The first downstream gas flow meter 20a measures the flow rate of the target gas flowing through the first downstream gas path 14a. The second downstream gas flow meter 20b measures the flow rate of the target gas flowing through the second downstream gas path 14b. The measurement values of the flow rates of the target gas by the first downstream gas flow meter 20a and the second downstream gas flow meter 20b are transmitted to a process control device 22, which will be described later.

[0023] The pressure equalization path 21 is an example of a third gas path of the present invention. The pressure equalization path 21 is a path that connects a portion of the first downstream gas path 14a between the first adjustment valve 16a and the first buffer 17a and a portion of the second downstream gas path 14b between the second adjustment valve 16b and the second buffer 17b so that the target gas can pass through.

[0024] The process control device 22 controls the upstream gas pump 12, the first regulating valve 16a, the second regulating valve 16b, the first on-off valve 18a, the second on-off valve 18b, the first downstream gas pump 19a, and the second downstream gas pump 19b. The process control device 22 continuously acquires the target gas flow rate measured by the upstream gas flow meter 13, the target gas flow rate measured by the first downstream gas flow meter 20a, and the target gas flow rate measured by the second downstream gas flow meter 20b in real time. The process control device 22 is equipped with a computer including a CPU, ROM, RAM, a storage device (memory device), and an I / F (interface). The ROM of the process control device 22 pre-stores a computer program for controlling the devices. The CPU of the computer in the process control device 22 reads the computer program from the ROM, loads it into RAM (using the RAM as a work area), and executes the computer program. This allows control of the devices. The process control device 22 is also connected to a collection control device 70 of the collection device 30, which will be described later, via the I / F so as to be able to send and receive signals.

[0025] The recovery device 30 includes a first absorption tower 31a, a second absorption tower 31b, a first stripper tower 53a, a second stripper tower 53b, a rich solution path 40, a lean solution path 45, a solution path between the absorption towers 47, a solution path between the stripper towers 49, a heating circuit 60, and a recovery control device 70.

[0026] 2 is a schematic diagram showing the configuration of the first absorption tower 31a and the second absorption tower 31b of the recovery device 30. The first absorption tower 31a is an example of a first carbon dioxide absorption unit of the present invention, and the second absorption tower 31b is an example of a second carbon dioxide absorption unit of the present invention. The first absorption tower 31a and the second absorption tower 31b are configured so that the carbon dioxide contained in the target gas is absorbed into the solution by bringing the target gas into gas-liquid contact with the solution. The carbon dioxide absorption capacity of the second absorption tower 31b is higher than that of the first absorption tower 31a.

[0027] The first absorption tower 31a includes one absorption chamber 33, one rotating member 34, and a first driving force source 35a.

[0028] The absorption chamber 33 is a container having an internal space. The absorption chamber 33 is configured to be able to store a solution at its bottom, below the rotating member 34. The bottom of the absorption chamber 33 is provided with a gas inlet 331, which is an inlet for the target gas to receive the target gas from outside the absorption chamber 33, and a solution outlet 332, which is an outlet for discharging the solution stored at the bottom to the outside of the absorption chamber 33.

[0029] The rotating member 34 is a member that is disposed inside the absorption chamber 33 so as to be rotatable about an axis that is substantially parallel to the vertical direction. The rotating member 34 includes a rotating shaft 341, one gas-liquid contacting section 342, and one gas-liquid separating section 343. The rotating shaft 341, one gas-liquid contacting section 342, and one gas-liquid separating section 343 are joined to each other so as to rotate integrally.

[0030] The gas-liquid contact section 342 is a member that promotes the absorption of carbon dioxide by the solution by increasing the gas-liquid contact area between the target gas and the solution. The gas-liquid contact section 342 is a member that allows the solution to permeate and diffuse therein and allows the target gas to flow therethrough. The gas-liquid contact section 342 includes, for example, a container and a plurality (numerous) of fillers that are filled into the container. The container has a generally cylindrical shape with an open top and a closed bottom, and is formed from a plate material that allows liquid and gas to pass through, such as punched metal or a mesh plate. The filler is a member made of a material with a large specific surface area, such as a metal mesh, and is formed into a shape such as a sphere or a cylinder.

[0031] The gas-liquid separation unit 343 is disposed above the gas-liquid contact unit 342. The gas-liquid separation unit 343 is a member for separating the mist of the solution from the target gas. The gas-liquid separation unit 343 is a cylindrical container-shaped member (which can also be called a dome-shaped member) that is open on the bottom and closed on the sides and top.

[0032] The rotation shaft 341 of the rotating member 34 is provided with a solution introduction section 344, which is a solution inlet for receiving a solution from outside the absorption chamber 33, and a gas discharge section 345, which is a target gas outlet for discharging the target gas to the outside of the absorption chamber 33. The solution introduction section 344 is located above the rotation center of the gas-liquid contact section 342 so that the solution can be supplied to the rotation center on the upper surface of the gas-liquid contact section 342. The gas discharge section 345 is located at the rotation center and upper part inside the gas-liquid separation section 343 so that the target gas inside the gas-liquid separation section 343 can be discharged to the outside from the rotation center and upper part of the gas-liquid separation section 343.

[0033] The first driving power source 35a is a driving power source for rotating the rotating member 34. Various known electric motors are applied to the first driving power source 35a. The first driving power source 35a is controlled by the recovery control device 70, which will be described later.

[0034] The gas inlet 331 of the absorption chamber 33 of the first absorption tower 31a is connected to the other end of the first downstream gas path 14a. The solution inlet 344 of the rotating member 34 of the first absorption tower 31a is connected to one end of the lean solution path 45. The lean solution path 45 is a path for supplying the solution from the first stripper tower 53a to the first absorption tower 31a. A lean solution pump 46 is disposed on the lean solution path 45. The lean solution pump 46 operates to supply the solution from the first stripper tower 53a to the first absorption tower 31a.

[0035] One end of a first gas discharge path 311a is connected to the gas discharge section 345 of the rotating member 34 of the first absorption tower 31a. The first gas discharge path 311a is a path for discharging the target gas inside the absorption chamber 33 of the first absorption tower 31a to the outside of the absorption chamber 33. The other end of the first gas discharge path 311a is, for example, open to the atmosphere. One end of an inter-absorber solution path 47 is connected to the solution discharge section 332 of the absorption chamber 33 of the first absorption tower 31a. The inter-absorber solution path 47 is a path for feeding solution from the first absorption tower 31a to the second absorption tower 31b. An inter-absorber solution pump 48 is disposed on the inter-absorber solution path 47. When the inter-absorber solution pump 48 is operated, it feeds the solution accumulated at the bottom of the absorption chamber 33 of the first absorption tower 31a to the second absorption tower 31b.

[0036] The first absorption tower 31a operates as follows. The solution introduced into the absorption chamber 33 through the lean solution path 45 and the solution inlet 344 flows downward to the rotation center of the upper surface of the gas-liquid contact section 342. The solution then passes through the gas-liquid contact section 342, diffusing and penetrating radially outward and downward from the rotation center of the upper surface of the gas-liquid contact section 342 due to gravity and the centrifugal force of the rotation of the rotating member 34. The solution that has passed through the gas-liquid contact section 342 flows out from the bottom or side of the gas-liquid contact section 342 and accumulates at the bottom of the absorption chamber 33. The solution is then discharged to the outside of the absorption chamber 33 through the solution outlet 332.

[0037] The target gas that has flowed into the absorption chamber 33 from the first downstream gas path 14a and the gas inlet 331 flows into the gas-liquid contactor 342 from the bottom or side of the gas-liquid contactor 342. The target gas that has passed through the gas-liquid contactor 342 flows out from the top of the gas-liquid contactor 342 and flows into the gas-liquid separation section 343 from the lower side thereof. The target gas then passes through the gas-liquid separation section 343 and is discharged from the absorption chamber 33 through the gas discharge section 345 and the first gas discharge path 311a.

[0038] Carbon dioxide contained in the target gas is absorbed into the solution by gas-liquid contact between the solution and the target gas inside the gas-liquid contactor 342. Furthermore, when the target gas passes through the gas-liquid separator 343, gravity and the centrifugal force of the rotation of the rotating member 34 separate the mist of the solution contained in the target gas from the target gas.

[0039] The recovery control device 70 can switch the first absorption tower 31a between a stopped state and an operating state. The stopped state is a state in which the first driving power source 35a is stopped and the rotating member 34 of the first absorption tower 31a is not rotating. The operating state is a state in which the first driving power source 35a is operating and the rotating member 34 of the first absorption tower 31a is rotating.

[0040] The second absorption tower 31b includes a plurality of absorption chambers 33u, 33m, and 33d, a plurality of rotary members 34 rotatably disposed inside each of the absorption chambers 33u, 33m, and 33d, and a second driving force source 35b. The absorption chambers 33u, 33m, and 33d of the second absorption tower 31b have the same configuration as the absorption chambers 33 of the first absorption tower 31a. In this embodiment, the second absorption tower 31b is configured to include three absorption chambers 33u, 33m, and 33d. For ease of explanation, the three absorption chambers 33u, 33m, and 33d may be distinguished by being referred to as the lowest absorption chamber 33d, the middle absorption chamber 33m, and the uppermost absorption chamber 33u, respectively.

[0041] The three absorption chambers 33u, 33m, and 33d of the second absorption tower 31b are connected in series to allow the target gas to flow therethrough. Specifically, the gas inlet 331 of the lowest absorption chamber 33d is connected to the other end of the second downstream gas path 14b. The gas outlet 345 of the rotating member 34 of the lowest absorption chamber 33d is connected to the gas inlet 331 of the intermediate absorption chamber 33m via a lower gas path 52d. The gas outlet 345 of the rotating member 34 of the intermediate absorption chamber 33m is connected to the gas inlet 331 of the uppermost absorption chamber 33u via an upper gas path 52u. The gas outlet 345 of the uppermost absorption chamber 33u is connected to one end of a second gas outlet path 331b. The second gas outlet path 331b is a path for discharging the target gas to the outside of the second absorption tower 31b. The other end of the second gas outlet path 331b is, for example, open to the atmosphere.

[0042] Furthermore, the three absorption chambers 33u, 33m, and 33d of the second absorption tower 31b are connected in series to allow solution to flow therethrough. Specifically, the solution inlet 344 of the rotating member 34 of the uppermost absorption chamber 33u is connected to the other end of the inter-absorber solution path 47. The solution outlet 332 of the uppermost absorption chamber 33u and the solution inlet 344 of the rotating member 34 of the intermediate absorption chamber 33m are connected by an upper solution path 36u. An upper solution pump 37u is disposed on the upper solution path 36u. When the upper solution pump 37u is operated, it sends the solution accumulated at the bottom of the uppermost absorption chamber 33u to the rotating member 34 of the intermediate absorption chamber 33m.

[0043] The solution discharge port 332 of the intermediate-stage absorption chamber 33m and the solution introduction port 344 of the rotary member 34 of the lowest-stage absorption chamber 33d are connected to the lower-stage solution passage 36d. A lower-stage solution pump 37d is disposed on the lower-stage solution passage 36d. When the lower-stage solution pump 37d is operated, it sends the solution accumulated at the bottom of the intermediate-stage absorption chamber 33m to the rotary member 34 of the lowest-stage absorption chamber 33d. The solution discharge port 332 of the lowest-stage absorption chamber 33d is connected to one end of the rich solution passage 40. The rich solution passage 40 is a passage for sending the solution from the second absorption tower 31b to the first stripper tower 53a or the second stripper tower 53b. A rich solution pump 44 is disposed on the rich solution passage 40. When the rich solution pump 44 is operated, it sends the solution accumulated at the bottom of the lowest-stage absorption chamber 33d toward the first stripper tower 53a or the second stripper tower 53b.

[0044] Therefore, the target gas that flows into the lowermost absorption chamber 33d through the second downstream gas passage 14b passes through the lowermost absorption chamber 33d, the lower gas passage 52d, the intermediate absorption chamber 33m, the upper gas passage 52u, and the uppermost absorption chamber 33u, in that order, before being discharged through the second gas discharge passage 311b. The solution that flows into the uppermost absorption chamber 33u through the inter-absorber solution passage 47 passes through the uppermost absorption chamber 33u, the upper solution passage 36u, the intermediate absorption chamber 33m, the lower solution passage 36d, and the lowermost absorption chamber 33d, in that order, before being discharged through the rich solution passage 40. When the target gas and the solution pass through the gas-liquid contact section 342 of the rotating member 34 disposed inside the lowermost absorption chamber 33d, the intermediate absorption chamber 33m, and the uppermost absorption chamber 33u, carbon dioxide contained in the target gas is absorbed into the solution. The flow (movement) of the target gas and solution in each of the lowermost absorption chamber 33d, the intermediate absorption chamber 33m, and the uppermost absorption chamber 33u is the same as that in the first absorption tower 31a.

[0045] In this way, the second absorption tower 31b is configured so that the target gas delivered through the second downstream gas path 14b passes through the three absorption chambers 33u, 33m, and 33d in one direction, and the solution passes through in the opposite direction. The second absorption tower 31b is configured so that the target gas and the solution pass in opposite directions, and the target gas and the solution come into gas-liquid contact with each other at the gas-liquid contact sections 342 of the rotating members 34 rotatably arranged inside each of the three absorption chambers 33u, 33m, and 33d, thereby causing carbon dioxide contained in the target gas to be absorbed by the solution.

[0046] The rotary shaft 341 of the rotary member 34 disposed inside the lowermost absorption chamber 33d is connected to the second drive power source 35b. The rotary member 34 disposed inside the lowermost absorption chamber 33d and the rotary member 34 disposed inside the intermediate absorption chamber 33m are connected via a lower-stage clutch 38d. The rotary member 34 disposed inside the intermediate absorption chamber 33m and the rotary member 34 disposed inside the uppermost absorption chamber 33u are connected via an upper-stage clutch 38u.

[0047] The lower-stage clutch 38d and the upper-stage clutch 38u are configured to be switchable between a connected state that allows transmission of rotational power and a disconnected state that does not allow transmission of rotational power. The recovery control device 70 controls the second driving power source 35b, the lower-stage clutch 38d, and the upper-stage clutch 38u to switch the second absorption tower 31b between a stopped state, a first operating state, a second operating state, and a third operating state. The stopped state is a state in which all of the rotating members 34 are stopped. The first operating state is a state in which the rotating members 34 of the lowermost absorption chamber 33d are rotating, while the rotating members 34 of the intermediate absorption chamber 33m and the uppermost absorption chamber 33u are stopped. The second operating state is a state in which the rotating members 34 of the lowermost absorption chamber 33d and the intermediate absorption chamber 33m are rotating, while the rotating member 34 of the uppermost absorption chamber 33u is stopped. The third operating state is a state in which the rotary members 34 of all the absorption chambers 33u, 33m, 33d are rotating.

[0048] Specifically, the recovery control device 70 can put the second absorption tower 31b into an operation-stopped state by stopping the operation of the second driving power source 35b. The recovery control device 70 can put the second absorption tower 31b into a first operating state by operating the second driving power source 35b and disengaging the lower-side clutch 38d. The recovery control device 70 can put the second absorption tower 31b into a second operating state by operating the second driving power source 35b, engaging the lower-side clutch 38d, and disengaging the upper-side clutch 38u. The recovery control device 70 can put the second absorption tower 31b into a third operating state by operating the second driving power source 35b and engaging the lower-side clutch 38d and the upper-side clutch 38u.

[0049] The rich solution path 40 is a path for supplying the solution from the second absorption tower 31b to the first stripper tower 53a or the second stripper tower 53b. The rich solution path 40 includes an upstream section 41, a first downstream section 42a, a second downstream section 42b, and a solution path switching valve 43. One end of the upstream section 41 is connected to the solution discharge section 332 of the lowest absorption chamber 33d of the second absorption tower 31b, and the other end is connected to the solution path switching valve 43. One end of the first downstream section 42a is connected to the solution path switching valve 43, and the other end is connected to the first stripper tower 53a. One end of the second downstream section 42b is connected to the solution path switching valve 43, and the other end is connected to the second stripper tower 53b. The solution path switching valve 43 is a valve device configured to supply the solution supplied through the upstream section 41 to either the first downstream section 42a or the second downstream section 42b. A known three-way valve can be used for the solution path switching valve 43.

[0050] For ease of explanation, the "state in which the solution can be supplied to the first downstream section 42a (the upstream section 41 and the first downstream section 42a are in communication, and the upstream section 41 and the second downstream section 42b are not in communication)" of the solution path switching valve 43 may be referred to as the first state, and the "state in which the solution can be supplied to the second downstream section 42b (the upstream section 41 and the second downstream section 42b are in communication, and the upstream section 41 and the first downstream section 42a are not in communication)" may be referred to as the second state. The first state is an example of a first switching state of the present invention, and the second state is an example of a second switching state of the present invention. The recovery control device 70 is capable of switching the solution path switching valve 43 between the first state and the second state (it is capable of controlling the switching state).

[0051] The rich solution pump 44 is disposed on the rich solution path 40 closer to the second absorption tower 31b than the solution path switching valve 43, and is configured to operate to feed the solution from the second absorption tower 31b to the first stripper tower 53a or the second stripper tower 53b. The configuration of the rich solution pump 44 is not particularly limited, and various known electric liquid feed pumps can be used.

[0052] The first stripper tower 53a and the second stripper tower 53b are configured to strip carbon dioxide from the solution using heat transferred from a heating circuit 60, which will be described later. The other end of the first downstream section 42a of the rich solution path 40 is connected to the top of the first stripper tower 53a, and the other end of the second downstream section 42b of the rich solution path 40 is connected to the top of the second stripper tower 53b. The bottom of the second stripper tower 53b and the top of the first stripper tower 53a are connected by an inter-stripper tower solution path 49. The inter-stripper tower solution path 49 is a path for supplying solution from the second stripper tower 53b to the first stripper tower 53a. An inter-stripper tower solution pump 50 is disposed on the inter-stripper tower solution path 49. When the inter-stripper tower solution pump 50 is operated, it supplies the solution accumulated at the bottom of the second stripper tower 53b to the first stripper tower 53a. Furthermore, the other end of the lean solution path 45 is connected to the bottom of the second stripper tower 53b.

[0053] Therefore, when the solution path switching valve 43 is in the first state, the solution is fed from the second absorption tower 31b to the first stripper tower 53a, and the solution is not fed to the second stripper tower 53b. On the other hand, when the solution path switching valve 43 is in the second state, the solution is fed from the second absorption tower 31b to the second stripper tower 53b, and the solution that has passed through the second absorption tower 31b is fed to the first stripper tower 53a through the inter-stripper tower solution path 49.

[0054] Filler 54 is disposed inside first stripper tower 53a and second stripper tower 53b. Filler 54 is a member that promotes gas-liquid contact between the solution and the solution vapor. For filler 54, a member that is permeable to the solution and permeable to the solution vapor, such as a porous member or mesh member with a large specific surface area, is used. A first solution heating section 602a of a heating circuit 60 is connected to first stripper tower 53a, and a second solution heating section 602b of the heating circuit 60 is connected to second stripper tower 53b.

[0055] The heating circuit 60 is configured to heat a heating medium (e.g., a fluid such as oil) using exhaust heat from the target gas source 90 and provide heat for stripping carbon dioxide from the solution to the first stripper column 53a and the second stripper column 53b via the heated heating medium. The heating circuit 60 includes a heat recovery section 601, a first solution heating section 602a, a second solution heating section 602b, a main path 603, a first bypass path 604a, a second bypass path 604b, a first heating medium path switching valve 605, a second heating medium path switching valve 606, a third heating medium path switching valve 607, a fourth heating medium path switching valve 608, and a heating medium pump 609.

[0056] The heat recovery unit 601 is a device that heats a heating medium using exhaust heat from the target gas source 90. The heat recovery unit 601 includes a heat transfer path, such as a heat pipe, that transfers the exhaust heat from the target gas source 90, and a heater (a heat exchanger that exchanges heat between the working liquid of the heat pipe and the heating medium) that heats the heating medium using the heat transferred via the heat transfer path. Note that the specific configuration of the heat recovery unit 601 is not particularly limited as long as it can heat the heating medium for heating the solution using exhaust heat from the target gas source 90.

[0057] The first solution heating unit 602a is configured to receive a portion of the solution accumulating at the bottom of the first stripper tower 53a, heat the inflowing solution with the heat of a heating medium, and cause the heated solution and steam generated by heating to flow into the first stripper tower 53a. The second solution heating unit 602b is configured to receive a portion of the solution accumulating at the bottom of the second stripper tower 53b, heat the inflowing solution with the heat of a heating medium, and cause the heated solution and steam generated by heating to flow into the second stripper tower 53b. The first solution heating unit 602a and the second solution heating unit 602b each include a heat exchanger that exchanges heat between the heating medium and the solution. The solution heating capacity of the second solution heating unit 602b (the amount of heat that can be applied to the solution per unit time) is higher than the heating capacity of the first solution heating unit 602a.

[0058] The main path 603 is a circular (closed loop) path that connects the heat recovery section 601, the second solution heating section 602b, and the first solution heating section 602a so that the heating medium can circulate.

[0059] The first bypass path 604a is a path for preventing the heating medium from flowing through the first solution heating section 602a, and is a path provided in parallel to the first solution heating section 602a. For example, the first bypass path 604a branches off from the main path 603 at a first heating medium path switching valve 605 arranged on one side of the first solution heating section 602a (upstream side of the heating medium flow) and merges with the main path 603 at a second heating medium path switching valve 606 arranged on one side opposite the first solution heating section 602a (downstream side of the heating medium flow). The second bypass path 604b is a path for preventing the heating medium from flowing through the second solution heating section 602b, and is a path provided in parallel to the second solution heating section 602b. The second bypass path 604b branches off from the main path 603 at a third heating medium path switching valve 607 located on one side of the second solution heating section 602b, and merges with the main path 603 at a fourth heating medium path switching valve 608 located on the opposite side of the second solution heating section 602b.

[0060] The first heating medium path switching valve 605 and the second heating medium path switching valve 606 are switchable between a state in which the heating medium supplied from the heat recovery section 601 can pass through the first solution heating section 602a and a state in which the heating medium can pass through the first bypass path 604a (a state in which the heating medium cannot pass through the first solution heating section 602a). The third heating medium path switching valve 607 and the fourth heating medium path switching valve 608 are switchable between a state in which the heating medium supplied from the heat recovery section 601 can pass through the second solution heating section 602b and a state in which the heating medium can pass through the second bypass path 604b (a state in which the heating medium cannot pass through the second solution heating section 602b).

[0061] The heating medium pump 609 is arranged on the main path 603 and is configured to operate to cause the heating medium heated in the heat recovery section 601 to flow sequentially through the second solution heating section 602b or the second bypass path 604b, the first solution heating section 602a or the first bypass path 604a, and then return to the heat recovery section 601.

[0062] The recovery control device 70 controls the first heating medium path switching valve 605, the second heating medium path switching valve 606, the third heating medium path switching valve 607, and the fourth heating medium path switching valve 608 to switch the heating circuit 60 between a heating stop state, a first heating state, a second heating state, and a third heating state. The heating stop state is a state in which the heating medium can pass through the first bypass path 604a and the second bypass path 604b but cannot pass through the first solution heating section 602a and the second solution heating section 602b. When the heating circuit 60 is in the heating stop state, the solution is not heated in either the first solution heating section 602a or the second solution heating section 602b. The first heating state is a state in which the heating medium can pass through the first solution heating section 602a and the second bypass path 604b but cannot pass through the second solution heating section 602b. When the heating circuit 60 is in the first heating state, the solution is heated in the first solution heating section 602a, but not in the second solution heating section 602b. The second heating state is a state in which the heating medium can pass through the first bypass path 604a and the second solution heating section 602b, but cannot pass through the first solution heating section 602a. When the heating circuit 60 is in the second heating state, the solution is heated in the second solution heating section 602b, but not in the first solution heating section 602a. The third heating state is a state in which the heating medium can pass through the first solution heating section 602a and the second solution heating section 602b. When the heating circuit 60 is in the third heating state, the solution is heated in the first solution heating section 602a and the second solution heating section 602b.

[0063] The configuration of the heating circuit 60 is not limited to the above configuration. The heating circuit 60 may be configured to be switchable, under the control of the recovery control device 70, among a state in which the first solution heating unit 602a heats the solution and the second solution heating unit 602b does not heat the solution (first heating state), a state in which the second solution heating unit 602b heats the solution and the first solution heating unit 602a does not heat the solution (second heating state), and a state in which the first solution heating unit 602a and the second solution heating unit 602b heat the solution (third heating state).

[0064] A first recovery path 55a is connected to the top of the first stripper tower 53a, and one end of a second recovery path 55b is connected to the top of the second stripper tower 53b. The first recovery path 55a and the second recovery path 55b are paths for supplying the carbon dioxide stripped from the solution in the first stripper tower 53a and the second stripper tower 53b to the outside of the recovery device 30.

[0065] The lean solution path 45 is a path for supplying the solution from the first stripper tower 53a to the first absorption tower 31a. A lean solution pump 46 is disposed on the lean solution path 45. A solution heat exchanger 51 is disposed on the rich solution path 40 and the lean solution path 45. The solution heat exchanger 51 is configured to exchange heat between the solution flowing through the rich solution path 40 and the solution flowing through the lean solution path 45.

[0066] The collection control device 70 is a control device that controls each part (each device) of the collection device 30. The collection control device 70 is a device equipped with a computer including a CPU, ROM, RAM, a storage device, and an I / F. A computer program for controlling each part of the collection device 30 is stored in advance in the ROM of the collection control device 70. The CPU of the computer of the collection control device 70 then reads this computer program from the ROM, expands it in RAM (using the RAM as a work area), and executes this computer program. This realizes control of each part of the collection device 30. The collection control device 70 is also connected to the process control device 22 via the I / F so as to be able to send and receive signals.

[0067] As described above, the carbon dioxide absorption capacity of the second absorption tower 31b is higher than that of the first absorption tower 31a. "Carbon dioxide absorption capacity" refers to the amount of target gas that can be treated per unit time. Alternatively, carbon dioxide absorption capacity may be "the amount of carbon dioxide that can be absorbed per unit time from the target gas when the flow rates of the target gas and the solution are the same." There are no particular limitations on the ratio between the carbon dioxide absorption capacity of the first absorption tower 31a and the carbon dioxide absorption capacity of the second absorption tower 31b, but for example, it is preferable that the carbon dioxide absorption capacity of the second absorption tower 31b be at least twice the carbon dioxide absorption capacity of the first absorption tower 31a.

[0068] The first stripper tower 53a has a carbon dioxide stripping capacity corresponding to the carbon dioxide absorption capacity of the first absorption tower 31a. The second stripper tower 53b has a carbon dioxide stripping capacity corresponding to the carbon dioxide absorption capacity of the second absorption tower 31b. The carbon dioxide stripping capacity refers to the amount of solution that can be treated per unit time. It can also be said that the carbon dioxide stripping capacity is the amount of carbon dioxide stripped from a solution per unit time when the solution flow rate is the same. The carbon dioxide stripping capacity may also be the "amount of heat that can be given to the solution per unit time." The "carbon dioxide stripping capacity corresponding to the carbon dioxide absorption capacity of the first absorption tower 31a" can also be said to be the "carbon dioxide stripping capacity suitable for stripping carbon dioxide from the solution that has absorbed carbon dioxide in the first absorption tower 31a" or the "capacity to strip carbon dioxide in the right amount from the solution that has absorbed carbon dioxide in the first absorption tower 31a."

[0069] Since the carbon dioxide absorption capacity of the second absorption tower 31b is higher than the carbon dioxide absorption capacity of the first absorption tower 31a, the carbon dioxide diffusion capacity of the second stripper tower 53b is higher than the carbon dioxide diffusion capacity of the first stripper tower 53a. The capacity (maximum flow rate of the target gas) of the second downstream gas path 14b is larger than the capacity of the first downstream gas path 14a. The volume of the second buffer 17b is larger than the volume of the first buffer 17a. The capacity of the second downstream gas pump 19b is larger than the capacity of the first downstream gas pump 19a. The solution heating capacity of the second solution heating unit 602b is higher than the solution heating capacity of the first solution heating unit 602a.

[0070] The ratio of the carbon dioxide absorption capacity of the second absorption tower 31b to the carbon dioxide absorption capacity of the first absorption tower 31a, the ratio of the capacity of the second downstream gas path 14b to the capacity of the first downstream gas path 14a, the ratio of the volume of the second buffer 17b to the volume of the first buffer 17a, the ratio of the capacity of the second downstream gas pump 19b to the capacity of the first downstream gas pump 19a, and the ratio of the heating capacity of the second solution heating unit 602b to the heating capacity of the first solution heating unit 602a are determined according to the ratio of the carbon dioxide absorption capacity of the second absorption tower 31b to the carbon dioxide absorption capacity of the first absorption tower 31a. For example, if the ratio of the carbon dioxide absorption capacity of the second absorption tower 31b to the carbon dioxide absorption capacity of the first absorption tower 31a is "2", then each of these ratios is set to be "2".

[0071] <Recovery system operation> Next, the operation of the recovery system 10 will be described. The process control device 22 determines whether the amount of target gas generated in the target gas source 90 (the flow rate of the target gas delivered by the upstream gas pump 12) is less than the operational reference value, a small amount, a medium amount, or a large amount. Specifically, the process control device 22 acquires a measurement value of the flow rate of the target gas from the upstream gas flow meter 13. The process control device 22 then determines whether the acquired measurement value is less than the operational reference value, greater than or equal to the operational reference value and less than a first threshold value, greater than or equal to the first threshold value and less than a second threshold value, or greater than or equal to the second threshold value. The operational reference value, the first threshold value, and the second threshold value are values used to determine the flow rate of the target gas and are stored in advance in the ROM or storage device of the computer of the process control device 22. The operational reference value is a value used as a criterion for determining whether the target gas source 90 is operating. The first threshold value is a value greater than the operational reference value, and the second threshold value is a value greater than the first threshold value. Note that the specific values of the operational reference value, the first threshold value, and the second threshold value are not particularly limited and may be set as appropriate.

[0072] (1) When the flow rate of the target gas is below the standard operating value When the flow rate of the target gas is below the operational reference value, the target gas source 90 can be considered not to be operating. In this case, the process control device 22 closes the first regulating valve 16a, the first on-off valve 18a, the second regulating valve 16b, and the second on-off valve 18b. The process control device 22 also stops (does not operate) the first downstream gas pump 19a and the second downstream gas pump 19b. The recovery control device 70 keeps the first absorption tower 31a and the second absorption tower 31b in an inoperative state and keeps the heating circuit 60 in a heating-stopped state. However, regardless of the flow rate of the target gas, the recovery control device 70 circulates the solution by operating the rich solution pump 44, the lean solution pump 46, the inter-absorption tower solution pump 48, the upper-stage solution pump 37u, the lower-stage solution pump 37d, and the inter-stripping tower solution pump 50. Furthermore, the recovery control device 70 circulates the heating medium by operating the heating medium pump 609 regardless of the flow rate of the target gas.

[0073] (2) When the flow rate of the target gas is equal to or greater than the operation standard value and less than the first threshold value When the flow rate of the target gas is equal to or greater than the operation reference value and less than the first threshold, the target gas source 90 is operating but the flow rate of the target gas is small. In this case, the process control device 22 opens the first adjustment valve 16a and the first on-off valve 18a and closes the second adjustment valve 16b and the second on-off valve 18b. The process control device 22 also operates the first downstream gas pump 19a and stops (does not operate) the second downstream gas pump 19b. The recovery control device 70 also maintains the first absorption tower 31a in an operating state, the second absorption tower 31b in an inoperable state, the solution path switching valve 43 in a first state, and the heating circuit 60 in a first heating state.

[0074] As a result, the target gas generated in the target gas source 90 is delivered to the first absorption tower 31a via the upstream gas path 11 and the first downstream gas path 14a. The first buffer 17a arranged in the first downstream gas path 14a reduces fluctuations (pulsations) of the target gas delivered to the first absorption tower 31a. Furthermore, the first downstream gas path 14a and the second downstream gas path 14b are connected by a pressure equalization path 21. Therefore, the second buffer 17b arranged in the second downstream gas path 14b also functions as a buffer. This enhances the effect of reducing pulsations of the target gas delivered to the first absorption tower 31a.

[0075] The target gas fed to the first absorption tower 31a passes through the absorption chamber 33 of the first absorption tower 31a and is discharged to the outside of the first absorption tower 31a (i.e., the outside of the recovery device 30) through the first gas discharge path 311a. In addition, the solution fed to the first absorption tower 31a through the lean solution path 45 by operation of the lean solution pump 46 passes through the absorption chamber 33 of the first absorption tower 31a and is discharged from the first absorption tower 31a through the inter-absorber solution path 47. At this time, the solution and the target gas come into gas-liquid contact in the gas-liquid contact section 342 of the rotating member 34 arranged in the absorption chamber 33 of the first absorption tower 31a, whereby carbon dioxide contained in the target gas is absorbed into the solution.

[0076] The solution that has absorbed carbon dioxide is sent to the second absorption tower 31b through the inter-absorber solution path 47 by operation of the inter-absorber solution pump 48. The solution sent to the second absorption tower 31b then flows through the uppermost absorption chamber 33u, the intermediate absorption chamber 33m, and the lowermost absorption chamber 33d in this order. Note that because the target gas is not sent to the second absorption tower 31b, the solution does not absorb carbon dioxide while passing through the second absorption tower 31b. In addition, the second absorption tower 31b is maintained in an inoperative state, and the rotation of the rotating member 34 is stopped. The solution accumulated at the bottom of the lowermost absorption chamber 33d is sent through the rich solution path 40 toward the solution path switching valve 43 by operation of the rich solution pump 44. Because the solution path switching valve 43 is switched to the first state, the solution is sent to the first stripper tower 53a through the first downstream section 42a, but is not sent to the second stripper tower 53b.

[0077] The solution that flows into the first stripper tower 53a flows down through the packing material 54 arranged in the first stripper tower 53a and accumulates at the bottom of the first stripper tower 53a. A portion of the solution that accumulates at the bottom of the first stripper tower 53a flows into the first solution heating section 602a and is heated. The heated solution and steam generated by heating in the first solution heating section 602a flow into the first stripper tower 53a. The steam that flows into the first stripper tower 53a passes from bottom to top through the packing material 54. The solution flowing down through the packing material 54 comes into gas-liquid contact with the steam, heating the solution and causing carbon dioxide to strip from the solution. The carbon dioxide stripped from the solution is discharged from the first stripper tower 53a via the first recovery path 55a.

[0078] Since the heating circuit 60 is maintained in the first heating state, the heating medium heated in the heat recovery section 601 passes through the first solution heating section 602a but does not pass through the second solution heating section 602b. When the heating medium passes through the first solution heating section 602a, it exchanges heat with the solution delivered from the first stripper column 53a, thereby heating the solution.

[0079] In this way, when the flow rate of the target gas is small, the target gas is sent to the first absorption tower 31a, where carbon dioxide is absorbed. However, the target gas is not sent to the second absorption tower 31b. The solution discharged from the first absorption tower 31a is sent to the first stripper tower 53a, where carbon dioxide is stripped from the solution.

[0080] (3) When the flow rate of the target gas is equal to or greater than the first threshold and less than the second threshold When the flow rate of the target gas is equal to or greater than the first threshold and less than the second threshold, the flow rate of the target gas can be considered to be medium. In this case, the process control device 22 closes the first adjustment valve 16a and the first on-off valve 18a and opens the second adjustment valve 16b and the second on-off valve 18b. The process control device 22 also stops (does not operate) the first downstream gas pump 19a and operates the second downstream gas pump 19b. The recovery control device 70 also maintains the first absorption tower 31a in a stopped state, the second absorption tower 31b in a third operating state, the solution path switching valve 43 in a second state, and the heating circuit 60 in a second heating state.

[0081] As a result, the target gas generated in the target gas source 90 is delivered to the second absorption tower 31b through the upstream gas path 11 and the second downstream gas path 14b. The second buffer 17b arranged in the second downstream gas path 14b reduces fluctuations (pulsations) of the target gas delivered to the second absorption tower 31b. Furthermore, since the second downstream gas path 14b and the first downstream gas path 14a are connected by the pressure equalization path 21, the first buffer 17a arranged in the first downstream gas path 14a also functions as a buffer.

[0082] The target gas fed to the second absorption tower 31b flows through the lowest-stage absorption chamber 33d, the intermediate-stage absorption chamber 33m, and the highest-stage absorption chamber 33u in this order, and is discharged to the outside of the second absorption tower 31b through the second gas discharge path 311b. In addition, the solution is fed to the first absorption tower 31a by the operation of the lean solution pump 46, and the solution that has passed through the first absorption tower 31a is fed to the second absorption tower 31b by the operation of the inter-absorber solution pump 48 disposed in the inter-absorber solution path 47.

[0083] The solution fed to the second absorption tower 31b passes through the uppermost absorption chamber 33u and the intermediate absorption chamber 33m, and flows into the lowermost absorption chamber 33d, where it accumulates at the bottom. The target gas and the solution then come into gas-liquid contact in the gas-liquid contact sections 342 of the rotating members 34 of the uppermost absorption chamber 33u, the intermediate absorption chamber 33m, and the lowermost absorption chamber 33d, and carbon dioxide contained in the target gas is absorbed by the solution. Note that, because the target gas is not fed to the first absorption tower 31a, the solution does not absorb carbon dioxide as it passes through the first absorption tower 31a.

[0084] The solution that has absorbed carbon dioxide is discharged from the lowest absorption chamber 33d through the rich solution path 40 by operation of the rich solution pump 44. Because the solution path switching valve 43 is switched to the second state, the solution discharged from the lowest absorption chamber 33d passes through the upstream section 41 and the second downstream section 42b of the rich solution path 40 and is supplied to the second stripper tower 53b.

[0085] The solution that flows into the second stripper tower 53b flows down through the packing material 54 arranged in the second stripper tower 53b and accumulates at the bottom of the second stripper tower 53b. A portion of the solution that accumulates at the bottom of the second stripper tower 53b flows into the second solution heating section 602b and is heated. The solution heated in the second solution heating section 602b and the steam generated by heating flow into the second stripper tower 53b. The steam that flows into the interior of the second stripper tower 53b passes through the packing material 54 from bottom to top. Then, the solution flowing down the packing material 54 comes into gas-liquid contact with the steam, heating the solution and causing carbon dioxide to strip from the solution. The carbon dioxide stripped from the solution is discharged from the second stripper tower 53b via the second recovery path 55b.

[0086] At this time, since the heating circuit 60 is switched to the second heating state, the heating medium heated in the heat recovery section 601 passes through the second solution heating section 602b but does not pass through the first solution heating section 602a. Then, when the heating medium passes through the second solution heating section 602b, it exchanges heat with the solution delivered from the second stripper column 53b, thereby heating the solution.

[0087] The solution accumulated at the bottom of the second stripper tower 53b is sent to the first stripper tower 53a through the inter-stripping tower solution path 49 by the operation of the inter-stripping tower solution pump 50. The solution sent to the first stripper tower 53a flows down through the packing material 54 arranged inside the first stripper tower 53a and accumulates at the bottom of the first stripper tower 53a. Note that, since no heating medium is supplied to the first solution heating section 602a, the solution accumulated at the bottom of the second stripper tower 53b is not heated. For this reason, the reaction of carbon dioxide stripping from the solution hardly occurs in the second stripper tower 53b.

[0088] The solution accumulated at the bottom of the first stripper tower 53a is fed by the operation of the lean solution pump 46 through the lean solution path 45 toward the first absorption tower 31a.

[0089] In this way, when the flow rate of the target gas is medium, the target gas is sent to the second absorption tower 31b, where carbon dioxide is absorbed. However, the target gas is not sent to the first absorption tower 31a. The solution discharged from the second absorption tower 31b is sent to the second stripper tower 53b, where carbon dioxide is stripped from the solution.

[0090] (4) When the flow rate of the target gas is equal to or greater than the second threshold value When the flow rate of the target gas is equal to or greater than the second threshold, the flow rate of the target gas can be considered to be large. In this case, the process control device 22 opens all of the first adjustment valve 16a, the first on-off valve 18a, the second adjustment valve 16b, and the second on-off valve 18b. The process control device 22 also operates the first downstream gas pump 19a and the second downstream gas pump 19b. The recovery control device 70 maintains the first absorption tower 31a in an operating state, the second absorption tower 31b in a third operating state, the solution path switching valve 43 in the second state, and the heating circuit 60 in a third heating state.

[0091] As a result, the target gas generated in the target gas source 90 is supplied to the first absorption tower 31a through the upstream gas path 11 and the first downstream gas path 14a, and is also supplied to the second absorption tower 31b through the upstream gas path 11 and the second downstream gas path 14b. Furthermore, the lean solution pump 46 is operated to supply the solution to the first absorption tower 31a. Then, the target gas and the solution come into gas-liquid contact in the gas-liquid contact section 342 of the first absorption tower 31a, thereby absorbing carbon dioxide contained in the target gas into the solution. The target gas from which carbon dioxide has been absorbed in the first absorption tower 31a is discharged to the outside through the first gas discharge path 311a. Furthermore, the solution from which carbon dioxide has been absorbed in the first absorption tower 31a accumulates at the bottom of the absorption chamber 33 of the first absorption tower 31a and is supplied to the second stripper tower 53b through the inter-absorber solution path 47 by the operation of the inter-absorber solution pump 48.

[0092] The target gas fed to the second absorption tower 31b flows through the lowest absorption chamber 33d, the intermediate absorption chamber 33m, and the uppermost absorption chamber 33u, in that order. The solution fed to the second stripper tower 53b via the inter-absorption tower solution path 47 flows through the uppermost absorption chamber 33u, the intermediate absorption chamber 33m, and the lowermost absorption chamber 33d, in that order. The target gas and the solution come into gas-liquid contact in the gas-liquid contact sections 342 of the uppermost absorption chamber 33u, the intermediate absorption chamber 33m, and the lowermost absorption chamber 33d, thereby absorbing carbon dioxide contained in the target gas into the solution. The target gas from which carbon dioxide has been absorbed in the gas-liquid contact section 342 of the uppermost absorption chamber 33u is discharged to the outside via the second gas discharge path 311b. The solution that has absorbed carbon dioxide in the lowest absorption chamber 33d accumulates at the bottom of the lowest absorption chamber 33d and is fed towards the solution path switching valve 43 through the rich solution path 40 by the operation of the rich solution pump 44.

[0093] Because the solution path switching valve 43 is maintained in the second state, the solution delivered from the lowest absorption chamber 33d passes through the upstream section 41 and the second downstream section 42b of the rich solution path 40 and is delivered to the second stripper tower 53b. The solution that flows into the second stripper tower 53b flows down through the packing material 54 and accumulates at the bottom. A portion of the solution that accumulates at the bottom flows into the second solution heating section 602b and is heated. The heated solution and the steam generated by heating in the second solution heating section 602b flow into the second stripper tower 53b and pass through the packing material 54 from bottom to top. The solution flowing down through the packing material 54 comes into gas-liquid contact with the steam, heating the solution and causing carbon dioxide to strip from the solution. The carbon dioxide stripped from the solution is discharged from the second stripper tower 53b via the second recovery path 55b.

[0094] The solution accumulated at the bottom of the second stripper tower 53b is sent to the first stripper tower 53a through the inter-stripping tower solution path 49 by the operation of the inter-stripping tower solution pump 50. The solution that flows into the first stripper tower 53a flows down through the packing material 54 and accumulates at the bottom. A portion of the solution that accumulates at the bottom flows into the first solution heating section 602a and is heated. The heated solution and steam generated by heating in the first solution heating section 602a flow into the first stripper tower 53a and pass through the packing material 54 from bottom to top. The solution flowing down through the packing material 54 comes into gas-liquid contact with the steam, heating the solution and causing carbon dioxide to strip from the solution. The carbon dioxide stripped from the solution is discharged from the first stripper tower 53a via the first recovery path 55a.

[0095] The solution accumulated at the bottom of the first stripper tower 53a is fed by the operation of the lean solution pump 46 through the lean solution path 45 toward the first absorption tower 31a.

[0096] In this way, when the flow rate of the target gas is large, the target gas is supplied to the first absorption tower 31a and the second absorption tower 31b, and carbon dioxide is absorbed in the first absorption tower 31a and the second absorption tower 31b. Then, the solution that has passed through the first absorption tower 31a and the second absorption tower 31b is supplied to the first stripper tower 53a and the second stripper tower 53b, and carbon dioxide is stripped from the solution in the first stripper tower 53a and the second stripper tower 53b.

[0097] Since the heating circuit 60 is switched to the third heating state, the heating medium heated in the heat recovery section 601 passes through the second solution heating section 602b and the first solution heating section 602a. Therefore, the solution is heated in both the second solution heating section 602b and the first solution heating section 602a.

[0098] This configuration can improve the carbon dioxide capture efficiency (the ratio of the amount of carbon dioxide captured to the energy consumed by the capture system 10). In particular, even when the flow rate of the target gas fluctuates, a decrease in the carbon dioxide capture efficiency can be prevented or suppressed. That is, when the flow rate of the target gas is low, only the first solution heating unit 602a is operated, and only the first driving force source 35a of the first absorption tower 31a is operated. When the flow rate of the target gas is medium, only the second solution heating unit 602b is operated, and only the second driving force source 35b of the second absorption tower 31b is operated. Therefore, when the flow rate of the target gas is low or medium, energy consumption can be reduced compared to a configuration in which both the first absorption tower 31a and the second absorption tower 31b and both the first stripper tower 53a and the second stripper tower 53b are operated. As such, this embodiment can reduce energy consumption depending on the flow rate of the target gas.

[0099] Furthermore, in this embodiment, the carbon dioxide absorption capacity of the second absorption tower 31b is higher than the carbon dioxide absorption capacity of the first absorption tower 31a, and therefore the carbon dioxide absorption capacity of the carbon dioxide capture system 10 is lowest when the target gas is supplied only to the first absorption tower 31a, next lowest when the target gas is supplied only to the second absorption tower 31b, and highest when the target gas is supplied to both the first absorption tower 31a and the second absorption tower 31b. The energy consumption of the capture system 10 is lowest when the target gas is supplied only to the first absorption tower 31a, the first absorption tower 31a is in the operating state, the second absorption tower 31b is in the stopped state, and the heating circuit 60 is in the first heating state, next lowest when the target gas is supplied only to the second absorption tower 31b, the first absorption tower 31a is in the stopped state, the second absorption tower 31b is in the third operating state, and the heating circuit 60 is in the second heating state, and most frequently when the target gas is supplied to the first absorption tower 31a and the second absorption tower 31b, the first absorption tower 31a is in the operating state, the second absorption tower 31b is in the third operating state, and the heating circuit 60 is in the third heating state. Thus, the capture system 10 according to this embodiment can increase the carbon dioxide capture efficiency by gradually changing the carbon dioxide absorption capacity depending on the amount of target gas supplied from the target gas source 90 (i.e., the amount of gas generated in the target gas source 90).

[0100] Furthermore, if the carbon dioxide absorption capacities of the first absorption tower 31a and the second absorption tower 31b are different from each other, the number of stages can be increased when changing the carbon dioxide absorption capacity of the recovery system 10 in stages. That is, if the carbon dioxide absorption capacities of the first absorption tower 31a and the second absorption tower 31b are the same, the carbon dioxide absorption capacity of the recovery system 10 will be the same when only the first absorption tower 31a is operating and when only the second absorption tower 31b is operating. Therefore, with this configuration, the overall carbon dioxide absorption capacity of the recovery system 10 can be changed in two stages: when either the first absorption tower 31a or the second absorption tower 31b is operating, or when both are operating. In contrast, according to this embodiment, the overall carbon dioxide absorption capacity of the recovery system 10 can be changed in three stages: when only the first absorption tower 31a is operating, when only the second absorption tower 31b is operating, and when both the first absorption tower 31a and the second absorption tower 31b are operating. Therefore, it is possible to flexibly respond to fluctuations in the flow rate of the target gas.

[0101] Furthermore, when the first absorption tower 31a and the second absorption tower 31b are connected in series via the inter-absorber solution path 47, the configuration of the recovery system 10 can be simplified compared to when they are connected in parallel. That is, when the first absorption tower 31a and the second absorption tower 31b are connected in parallel, a mechanism for distributing the solution between the first absorption tower 31a and the second absorption tower 31b and a mechanism for adjusting the amount of solution distributed to the first absorption tower 31a and the second absorption tower 31b are required. In contrast, when the first absorption tower 31a and the second absorption tower 31b are connected in series, such mechanisms are not required.

[0102] Furthermore, because the first downstream gas path 14a is provided with the first buffer 17a and the second downstream gas path 14b is provided with the second buffer 17b, fluctuations in the flow rate of the target gas delivered to the first absorption tower 31a and the second absorption tower 31b are prevented or suppressed. This prevents or suppresses fluctuations in the carbon dioxide absorption rate of the solution. In particular, this prevents or suppresses delivery of target gas containing more carbon dioxide than the solution can absorb to the first absorption tower 31a and the second absorption tower 31b. This reduces the amount of carbon dioxide discharged from the recovery device 30 without being absorbed. Furthermore, because the first downstream gas path 14a and the second downstream gas path 14b are connected by the pressure equalization path 21, both the first buffer 17a and the second buffer 17b function as buffers that temporarily store the target gas, whether the target gas is delivered only to the first absorption tower 31a or only to the second absorption tower 31b. This means that the buffer capacities can be increased. Therefore, with this configuration, it is possible to enhance the effect of preventing or suppressing fluctuations in the flow rate of the target gas fed to the first absorption tower 31a and the second absorption tower 31b.

[0103] When the flow rate of the target gas is large, the process control device 22 may adjust the apertures of the first regulating valve 16a and the second regulating valve 16b in accordance with the flow rate of the target gas. In this case, the process control device 22 maintains the flow rate of the target gas fed to the first absorption tower 31a at a constant flow rate, and varies the flow rate of the target gas fed to the second absorption tower 31b. In addition, the recovery control device 70 switches the first absorption tower 31a between a first operating state, a second operating state, and a third operating state in accordance with the flow rate of the target gas.

[0104] Specifically, when the flow rate of the target gas is equal to or greater than the second threshold and less than the third threshold, the process control device 22 sets the aperture of the second adjustment valve 16b to "small." The third threshold is a value greater than the second threshold. When the flow rate of the target gas is equal to or greater than the third threshold and less than the fourth threshold, the process control device 22 sets the aperture of the second adjustment valve 16b to "medium," which is greater than the "small" aperture. The fourth threshold is a value greater than the third threshold. Furthermore, when the flow rate of the target gas is equal to or greater than the fourth threshold, the process control device 22 sets the aperture of the second adjustment valve 16b to "large," which is greater than the "small" and "medium" apertures. At this time, the process control device 22 adjusts the aperture of the first on-off valve 18a so that the amount of target gas fed to the first absorption tower 31a is maintained at a predetermined target value (constant value). The target value for the flow rate of this target gas is a value that makes the carbon dioxide absorption rate in the first absorption tower 31a (the ratio indicating the amount of carbon dioxide absorbed to the amount of carbon dioxide contained in the target gas fed to the first absorption tower 31a) equal to or greater than a predetermined target value. Note that the specific values of the third threshold, the fourth threshold, and the target value for the flow rate of the target gas are not particularly limited and are set as appropriate. Similarly, the specific values of the opening degrees "small," "medium," and "large" are not particularly limited and are set as appropriate.

[0105] Then, when the flow rate of the target gas is equal to or greater than the second threshold and less than the third threshold, the recovery control device 70 maintains the second absorption tower 31b in the first operating state. When the flow rate of the target gas is equal to or greater than the third threshold and less than the fourth threshold, the recovery control device 70 maintains the second absorption tower 31b in the second operating state. When the flow rate of the target gas is equal to or greater than the fourth threshold, the recovery control device 70 maintains the second absorption tower 31b in the third operating state. Note that the recovery control device 70 maintains the heating circuit 60 in the third heating state in either case.

[0106] With this configuration, the load on the second driving force source 35b can be reduced according to the flow rate of the target gas, thereby reducing the energy consumption of the second driving force source 35b. Furthermore, by maintaining a constant flow rate of the target gas fed to the first stripper tower 53a, it is possible to prevent a decrease in the carbon dioxide absorption efficiency in the first stripper tower 53a. Therefore, it is possible to enhance the effect of improving (or preventing or suppressing a decrease in) the carbon dioxide recovery efficiency.

[0107] <Processes performed by the process control device and the recovery control device> Next, the processing executed by the process control device 22 and the collection control device 70 will be described. Figures 3, 4, and 5 are flowcharts showing the processing executed by the computer of the process control device 22. A computer program for executing this processing is stored in advance in the ROM or storage device of the computer of the process control device 22. The CPU of the computer of the process control device 22 (hereinafter simply referred to as "CPU") reads this computer program from the ROM or storage device and repeatedly and continuously executes it at a predetermined cycle.

[0108] In step S101, the CPU acquires the measurement value of the flow rate of the target gas by the upstream gas flow meter 13. Then, the CPU advances the process to step S102.

[0109] In step S102, the CPU determines whether the measured value of the flow rate of the target gas is less than the standard operating value. If the measured value is less than the standard operating value, the CPU proceeds to step S103. If the measured value is equal to or greater than the standard operating value, the CPU proceeds to step S105.

[0110] In step S103, the CPU transmits the determination result of the measurement value to the collection control device 70. Then, the CPU advances the process to step S104.

[0111] In step S105, the CPU closes the first adjusting valve 16a, the first on-off valve 18a, the second adjusting valve 16b, and the second on-off valve 18b (if they are in a closed state, they are kept closed), and stops the first downstream gas pump 19a and the second downstream gas pump 19b (if they are stopped, they are kept stopped).The CPU then temporarily ends this series of processes.

[0112] In step S105, the CPU determines whether the measured value of the flow rate of the target gas is less than the first threshold. If the measured value is less than the first threshold, the CPU proceeds to step S106. If the flow rate of the target gas is not less than the first threshold (if it is equal to or greater than the first threshold), the CPU proceeds to step S108.

[0113] In step S106, the CPU transmits the determination result of the measurement value to the collection control device 70. Then, the CPU advances the process to step S107.

[0114] In step S107, the CPU opens the first regulating valve 16a and the first on-off valve 18a (if they are open, it keeps them open), and operates the first downstream gas pump 19a (if they are operating, it continues operating). Meanwhile, the CPU closes the second regulating valve 16b and the second on-off valve 18b (if they are closed, it keeps them closed), and stops the second downstream gas pump 19b (if they are stopped, it continues to be stopped). As a result, the target gas is supplied to the first stripping tower 53a, but not to the second stripping tower 53b. The CPU then temporarily terminates this series of processes.

[0115] In step S108, the CPU determines whether the measured value of the flow rate of the target gas is equal to or greater than the first threshold and less than the second threshold. If the measured value is equal to or greater than the first threshold and less than the second threshold, the CPU proceeds to step S109. If the measured value is not equal to or greater than the first threshold and less than the second threshold (in other words, if the measured value is equal to or greater than the second threshold), the CPU proceeds to step S1111.

[0116] In step S109, the CPU transmits the determination result of the measurement value to the collection control device 70. Then, the CPU advances the process to step S110.

[0117] In step S110, the CPU opens the second regulating valve 16b and the second on-off valve 18b (if they are open, it keeps them open), and operates the second downstream gas pump 19b (if they are operating, it continues operating). Meanwhile, the CPU closes the first regulating valve 16a and the first on-off valve 18a (if they are closed, it keeps them closed), and stops the first downstream gas pump 19a (if they are stopped, it continues to be stopped). As a result, the target gas is supplied to the second stripping tower 53b, but not to the first stripping tower 53a. The CPU then temporarily terminates this series of processes.

[0118] In step S111, the CPU transmits the determination result of the measurement value to the collection control device 70. Then, the CPU advances the process to step S112.

[0119] In step S112, the CPU opens the first regulating valve 16a, the first on-off valve 18a, the second regulating valve 16b, and the second on-off valve 18b (or keeps them open if they are open), and operates the first downstream gas pump 19a and the second downstream gas pump 19b (or continues operating them if they are operating). As a result, the target gas is supplied to the first stripping tower 53a and the second stripping tower 53b. The CPU then proceeds to step S113.

[0120] In step S113, the CPU determines whether the measured value of the flow rate of the target gas is less than a third threshold. If the flow rate of the target gas is less than the third threshold, the CPU proceeds to step S114. If the flow rate of the target gas is not less than the third threshold, the CPU proceeds to step S115.

[0121] In step S114, the CPU changes the opening degree of the first adjusting valve 16a to "small" (if it is "small", it is kept at "small"), and then the CPU temporarily ends this series of processes.

[0122] In step S115, the CPU determines whether the flow rate of the target gas is equal to or greater than the third threshold and less than the fourth threshold. If the flow rate of the target gas is equal to or greater than the third threshold and less than the fourth threshold, the CPU proceeds to step S116. If the flow rate of the target gas is not equal to or greater than the third threshold and less than the fourth threshold (in other words, if the flow rate of the target gas is equal to or greater than the fourth threshold), the CPU proceeds to step S117.

[0123] In step S116, the CPU changes the opening degree of the first adjusting valve 16a to "medium" (if it is "medium", it is maintained at "medium"), and then the CPU temporarily ends this series of processes.

[0124] In step S117, the CPU changes the opening degree of the first adjusting valve 16a to "large" (if it is "large", it is kept at "large"), and then the CPU temporarily ends this series of processes.

[0125] 6, 7, and 8 are flowcharts showing the processing executed by the computer of the collection control device 70. A computer program for executing this processing is stored in advance in the ROM or storage device of the computer of the collection control device 70. The CPU of the computer of the collection control device 70 (hereinafter simply referred to as "CPU") reads this computer program from the ROM or storage device and executes it repeatedly and continuously at a predetermined cycle.

[0126] In step S201, the CPU determines whether or not a signal indicating the determination result of the measurement value of the flow rate of the target gas has been received from the process control device 22. If no signal has been received, the CPU temporarily ends this series of processes. If a signal has been received, the CPU proceeds to step S202.

[0127] In step S202, the CPU determines whether the measured value of the flow rate of the target gas is less than the operation standard value. If the measured value is less than the operation standard value, the CPU proceeds to step S203. If the flow rate of the target gas is not less than the operation standard value, the CPU proceeds to step S204.

[0128] In step S203, the CPU stops the first driving power source 35a and the second driving power source 35b (if they are stopped, they continue to be stopped). The CPU also switches the solution path switching valve 43 to the first state (if it is in the first state, it maintains the first state). Furthermore, the CPU controls the first heating medium path switching valve 605, the second heating medium path switching valve 606, the third heating medium path switching valve 607, and the fourth heating medium path switching valve 608 to change the heating circuit 60 to a heating stopped state (if it is in the heating stopped state, it maintains the heating stopped state). Then, the CPU temporarily ends this series of processes.

[0129] In step S204, the CPU determines whether the measured value of the flow rate of the target gas is less than the first threshold. If the measured value is less than the first threshold, the CPU proceeds to step S205. If the flow rate of the target gas is not less than the first threshold (if it is equal to or greater than the first threshold), the CPU proceeds to step S206.

[0130] In step S205, the first driving force source 35a is operated (if it is operating, it continues to operate), and the second driving force source 35b is stopped (if it is stopped, it continues to be stopped). The CPU also switches the solution path switching valve 43 to the first state (if it is in the first state, it maintains the first state). Furthermore, the CPU changes the heating circuit 60 to the first heating state (if it is in the first heating state, it maintains the first heating state). Then, the CPU temporarily ends this series of processes.

[0131] In step S206, the CPU determines whether the measured value of the flow rate of the target gas is equal to or greater than the first threshold and less than the second threshold. If the measured value is equal to or greater than the first threshold and less than the second threshold, the CPU proceeds to step S207. If the measured value is not equal to or greater than the first threshold and less than the second threshold (if the measured value is equal to or greater than the second threshold), the CPU proceeds to step S208.

[0132] In step S207, the CPU operates the second driving power source 35b (continues operation if it is operating) and stops the first driving power source 35a (continues stopping if it is stopped). The CPU also switches the solution path switching valve 43 to the second state (maintains the second state if it is in the second state). The CPU also changes the heating circuit 60 to the second heating state (maintains the second heating state if it is in the second heating state). The CPU also switches the lower-stage clutch 38d and the upper-stage clutch 38u to the continuous state (maintains the continuous state if it is in the continuous state). The CPU then temporarily ends this series of processes.

[0133] In step S208, the first driving force source 35a and the second driving force source 35b are operated (if they are operating, they continue to operate). The CPU also switches the solution path switching valve 43 to the second state (if they are in the second state, they maintain the second state). Furthermore, the CPU changes the heating circuit 60 to the third heating state (if they are in the third heating state, they maintain the third heating state). The CPU then proceeds to step S209.

[0134] In step S209, the CPU determines whether the measured value of the flow rate of the target gas is less than a third threshold. If the flow rate of the target gas is less than the third threshold, the CPU proceeds to step S210. If the flow rate of the target gas is not less than the third threshold (if it is equal to or greater than the third threshold), the CPU proceeds to step S211.

[0135] In step S210, the CPU switches the lower stage clutch 38d and the upper stage clutch 38u to a disengaged state (if they are in a disengaged state, they are maintained in the disengaged state), and then the CPU temporarily ends this series of processes.

[0136] In step S211, the CPU determines whether the measured value of the flow rate of the target gas is equal to or greater than the third threshold and less than the fourth threshold. If the measured value is equal to or greater than the third threshold and less than the fourth threshold, the CPU proceeds to step S212. If the measured value is not equal to or greater than the third threshold and less than the fourth threshold (if the measured value is equal to or greater than the fourth threshold), the CPU proceeds to step S213.

[0137] In step S212, the CPU switches the lower-stage clutch 38d to the connected state (if it is in the connected state, it maintains the connected state), and switches the upper-stage clutch 38u to the disconnected state (if it is in the disconnected state, it maintains the disconnected state).The CPU then temporarily ends this series of processes.

[0138] In step S213, the CPU switches the lower stage clutch 38d and the upper stage clutch 38u to the continuous state (if they are in the continuous state, they are maintained in the continuous state), and then the CPU temporarily ends this series of processes.

[0139] When such processing is executed, the above-described operation is realized. When the flow rate of the target gas is equal to or greater than the second threshold, the CPU of the recovery control device 70 switches the lower-stage clutch 38d and the upper-stage clutch 38u between on and off depending on the flow rate of the target gas, but this configuration is not limited to this. For example, when the flow rate of the target gas is equal to or greater than the second threshold, the CPU of the recovery control device 70 may switch the lower-stage clutch 38d and the upper-stage clutch 38u to the connected state (i.e., after step S208, the CPU may omit the processing of steps S209 and S211 and proceed to the processing of step S213).

[0140] <Summary of the embodiment> (1) The carbon dioxide capture system 10 according to this embodiment is a first carbon dioxide absorption unit (first absorption tower 31a) connected to a gas source (target gas source 90) that generates a gas containing carbon dioxide via a first gas path (first downstream gas path 14a), and configured so that carbon dioxide contained in the gas (target gas) that flows from the gas source (target gas source 90) through the first gas path (first downstream gas path 14a) is absorbed in a carbon dioxide absorbing solution; a second carbon dioxide absorption unit (second absorption tower 31b) connected to the gas source (target gas source 90) via a second gas path (second downstream gas path 14b), configured so that carbon dioxide contained in the gas (target gas) flowing from the gas source (target gas source 90) through the second gas path (second downstream gas path 12b) is absorbed in a carbon dioxide absorbing solution, and having a higher carbon dioxide absorption capacity than the first carbon dioxide absorption unit (first absorption tower 31a); a first gas valve (first adjustment valve 16a) that is provided in the first gas path (first downstream gas path 14a) and is capable of changing the flow rate of the gas (target gas); a second gas valve (second adjustment valve 16b) that is provided in the second gas path (second downstream gas path 14b) and is capable of changing the flow rate of the gas (target gas); Equipped with The first carbon dioxide absorbing section (first absorption tower 31a) and the second carbon dioxide absorbing section (second absorption tower 31b) are connected in series so that the carbon dioxide absorbing solution can flow therethrough.

[0141] According to the carbon dioxide capture system 10 of this embodiment, by opening the first gas valve (first adjustment valve 16a) and closing the second gas valve (second adjustment valve 16b), gas can be supplied only to the first carbon dioxide absorption unit (first absorption tower 31a); by closing the first gas valve (first adjustment valve 16a) and opening the second gas valve (second adjustment valve 16b), gas can be supplied only to the second carbon dioxide absorption unit (second absorption tower 31b); and by opening both the first gas valve (first adjustment valve 16a) and the second gas valve (second absorption tower 31b), gas (target gas) can be supplied to both the first carbon dioxide absorption unit (first absorption tower 31a) and the second carbon dioxide absorption unit (second absorption tower 31b). With this configuration, the first carbon dioxide absorption unit (first absorption tower 31a) and the second carbon dioxide absorption unit (second absorption tower 31b) can be operated according to the amount of gas (flow rate of the target gas) generated in the gas source (target gas source 90), thereby improving the carbon dioxide recovery efficiency or preventing or suppressing a decrease in the efficiency.

[0142] In particular, because the second carbon dioxide absorption unit (second absorption tower 31b) has a higher carbon dioxide absorption capacity than the first carbon dioxide absorption unit (first absorption tower 31a), the overall carbon dioxide absorption capacity of the carbon dioxide capture system 10 is lowest when the gas (target gas) is supplied only to the first carbon dioxide absorption unit (first absorption tower 31a), next lowest when the gas (target gas) is supplied only to the second carbon dioxide absorption unit (second absorption tower 31b), and highest when the gas (target gas) is supplied to both the first carbon dioxide absorption unit (first absorption tower 31a) and the second carbon dioxide absorption unit (second absorption tower 31b). Therefore, according to the carbon dioxide capture system 10 of this embodiment, the carbon dioxide absorption capacity can be changed in stages depending on the amount of gas supplied from the gas source (target gas source 90) (i.e., the amount of gas generated in the target gas source 90), thereby increasing the carbon dioxide capture efficiency.

[0143] Furthermore, when the first carbon dioxide absorption unit (first absorption tower 31a) and the second carbon dioxide absorption unit (second absorption tower 31b) are configured to be connected in series so that the carbon dioxide absorbing solution can flow, the configuration of the carbon dioxide capture system 10 can be simplified compared to a configuration in which they are connected in parallel. That is, when a plurality of carbon dioxide absorption units (first absorption tower 31a, second absorption tower 31b) are connected in parallel, a mechanism for distributing the carbon dioxide absorbing solution to each carbon dioxide absorption unit (first absorption tower 31a, second absorption tower 31b) and a mechanism for adjusting the amount of the carbon dioxide absorbing solution distributed to each carbon dioxide absorption unit (first absorption tower 31a, second absorption tower 31b) are required. In contrast, when a plurality of carbon dioxide absorption units (first absorption tower 31a, second absorption tower 31b) are connected in series, such mechanisms are not required.

[0144] (2) In the carbon dioxide capture system 10 according to this embodiment, The first carbon dioxide absorption section (first absorption tower 31a) comprises one carbon dioxide absorption chamber (absorption chamber 33), and a first gas-liquid contact section (gas-liquid contact section 342) that is rotatably disposed inside the one carbon dioxide absorption chamber (absorption chamber 33) and configured to allow the gas to pass therethrough and the carbon dioxide absorbing solution to permeate therethrough, and is configured to absorb carbon dioxide contained in the gas by bringing the carbon dioxide absorbing solution into contact with the gas (target gas) delivered through the first gas path (first downstream gas path 14a) in the first gas-liquid contact section (gas-liquid contact section 342), The second carbon dioxide absorption section (second absorption tower 31b) includes a plurality of carbon dioxide absorption chambers (uppermost absorption chamber 33u, intermediate absorption chamber 33m, and lowermost absorption chamber 33d) and a plurality of second gas-liquid contact sections (gas-liquid contact sections 342) rotatably disposed inside each of the plurality of carbon dioxide absorption chambers (uppermost absorption chamber 33u, intermediate absorption chamber 33m, and lowermost absorption chamber 33d) and configured to allow the gas to pass therethrough and the carbon dioxide absorbing solution to permeate therethrough, and the gas (target gas) delivered through the second gas path (second downstream gas path 14b) is absorbed by the plurality of carbon dioxide absorption chambers. The plurality of carbon dioxide absorption chambers (top-stage absorption chamber 33u, middle-stage absorption chamber 33m, and bottom-stage absorption chamber 33d) are connected in series with each other so that the carbon dioxide absorbing solution passes through the plurality of carbon dioxide absorption chambers (top-stage absorption chamber 33u, middle-stage absorption chamber 33m, and bottom-stage absorption chamber 33d) in one direction, and the carbon dioxide absorbing solution passes through the plurality of carbon dioxide absorption chambers (top-stage absorption chamber 33u, middle-stage absorption chamber 33m, and bottom-stage absorption chamber 33d) in the opposite direction to the one direction while coming into contact with the gas (target gas) in each of the plurality of second gas-liquid contact sections (gas-liquid contact sections 342), thereby absorbing the carbon dioxide contained in the gas (target gas).

[0145] According to this configuration, the area of gas-liquid contact between the carbon dioxide absorbing solution and the target gas can be increased by the first gas-liquid contact section (gas-liquid contact section 342) and the second gas-liquid contact section (gas-liquid contact section 342). Therefore, the absorption rate of carbon dioxide by the carbon dioxide absorbing solution can be increased compared to a conventional carbon dioxide capture system equipped with a carbon dioxide absorption tower inside which a filler is fixed.

[0146] Specifically, when the flow rate of the gas (target gas) is small, carbon dioxide is absorbed only in the first carbon dioxide absorption unit (first absorption tower 31a), when the flow rate of the gas (target gas) is medium, carbon dioxide is absorbed only in the second carbon dioxide absorption unit (second absorption tower 31b), and when the flow rate of the gas (target gas) is large, carbon dioxide can be absorbed in both the first carbon dioxide absorption unit (first absorption tower 31a) and the second carbon dioxide absorption unit (second absorption tower 31b). In this way, since it is possible to operate one or both of the first carbon dioxide absorption unit (first absorption tower 31a) and the second carbon dioxide absorption unit (second absorption tower 31b) depending on the flow rate of the target gas, it is possible to prevent or suppress a decrease in the carbon dioxide recovery efficiency even when the flow rate of the target gas fluctuates.

[0147] (3) The carbon dioxide capture system 10 according to this embodiment is The gas passage is provided with a third gas passage (pressure equalization passage 21) that connects a position in the first gas passage (first downstream gas passage 14a) between the first gas valve (first adjustment valve 16a) and the first carbon dioxide absorption section (first absorption tower 31a) and a position in the second gas passage (second downstream gas passage 14b) between the second gas valve (second adjustment valve 16b) and the second carbon dioxide absorption section (second absorption tower 31b) so that gas can flow therethrough.

[0148] According to this configuration, when the target gas is supplied only through the first gas path (first downstream gas path 14a), the second gas path (second downstream gas path 14b) functions as a buffer. Similarly, when the target gas is supplied only through the second gas path (second downstream gas path 14b), the first path (first downstream gas path 14a) functions as a buffer. Therefore, fluctuations (pulsations) in the flow rate of the gas (target gas) can be reduced, thereby preventing or suppressing fluctuations in the carbon dioxide absorption rate by the carbon dioxide absorbing solution. In particular, even if the amount of target gas generated in the gas source (target gas source 90) temporarily increases, the amount of target gas supplied to the first carbon dioxide absorbing unit (first absorption tower 31a) or the second carbon dioxide absorbing unit (second absorption tower 31b) can be prevented or suppressed from exceeding the carbon dioxide absorption capacity of the first carbon dioxide absorbing unit (first absorption tower 31a) or the second carbon dioxide absorbing unit (second absorption tower 31b). This reduces the amount of carbon dioxide emitted from the carbon dioxide capture system 10 without being absorbed by the carbon dioxide absorbing solution.

[0149] (4) In the carbon dioxide capture system 10 according to this embodiment, a first buffer (first buffer 17a) capable of temporarily storing the gas (target gas) is provided between the first gas valve (first adjustment valve 16a) of the first gas path (first downstream gas path 14a) and the first carbon dioxide absorption unit (first absorption tower 31a); A second buffer (second buffer 17b) capable of temporarily storing the gas (target gas) is provided between the second gas valve (second adjustment valve 16b) of the second gas path (second downstream gas path 14b) and the second carbon dioxide absorption section (second absorption tower 31b).

[0150] According to this configuration, the first buffer (first buffer 17a) and the second buffer (second buffer 17b) can prevent or suppress fluctuations in the flow rate of the gas (target gas) supplied to the first carbon dioxide absorption unit (first absorption tower 31a) and the second carbon dioxide absorption unit (second absorption tower 31b). Therefore, fluctuations in the carbon dioxide absorption rate by the carbon dioxide absorbing solution can be prevented or suppressed. Furthermore, because the first gas path (first downstream gas path 14a) and the second gas path (second downstream gas path 14b) are connected by the third gas path (pressure equalization path 21), the effect of preventing or suppressing fluctuations in the carbon dioxide absorption rate can be enhanced. That is, both the first buffer (first buffer 17a) and the second buffer (second buffer 17b) function as buffers whether only the first gas path (first downstream gas path 14a) or only the second gas path (second downstream gas path 14b) is used. Therefore, since the capacity of the buffer can be increased, it is possible to enhance the effect of preventing or suppressing fluctuations in the flow rate of the gas (target gas) fed to the first carbon dioxide absorption section (first absorption tower 31a) or the flow rate of the gas (target gas) fed to the second carbon dioxide absorption section (second absorption tower 31b), and therefore it is possible to enhance the effect of preventing or suppressing fluctuations in the absorption rate of carbon dioxide by the carbon dioxide absorbing solution.

[0151] (5) The carbon dioxide capture system 10 according to this embodiment is The control device (process control device 22) is configured to open the first gas valve (first adjustment valve 16a) and close the second gas valve (second adjustment valve 16b) when the flow rate of the gas (target gas) delivered from the gas source (target gas source 90) is less than a first threshold, close the first gas valve (first adjustment valve 16a) and open the second gas valve (second adjustment valve 16b) when the flow rate of the gas (target gas) is equal to or greater than the first threshold and less than a second threshold that is greater than the first threshold, and open both the first gas valve (first adjustment valve 16a) and the second gas valve (second adjustment valve 16b) when the flow rate of the gas is equal to or greater than the second threshold.

[0152] According to this configuration, the gas (target gas) is supplied to one or both of the first carbon dioxide absorption section (first absorption tower 31a) and the second carbon dioxide absorption section (second absorption tower 31b) depending on the amount of gas (target gas) generated in the gas source (target gas source 90). Therefore, an appropriate flow rate of the gas (target gas) can be supplied to each of the first carbon dioxide absorption section (first absorption tower 31a) and the second carbon dioxide absorption section (second absorption tower 31b), thereby improving the carbon dioxide recovery efficiency. Specifically, when the flow rate of the gas (target gas) is small (less than the first threshold), only the first carbon dioxide absorption unit (first absorption tower 31a) is operated; when the flow rate of the gas (target gas) is medium (not less than the first threshold and less than the second threshold), only the second carbon dioxide absorption unit (first absorption tower 31a) is operated; and when the flow rate of the gas (target gas) is large (not less than the second threshold), both the first carbon dioxide absorption unit (first absorption tower 31a) and the second carbon dioxide absorption unit (second absorption tower 31b) are operated.This makes it possible to change the energy consumption according to the flow rate of the gas (target gas), thereby improving the carbon dioxide recovery efficiency.

[0153] (6) The carbon dioxide capture system 10 according to this embodiment is a first carbon dioxide stripper unit (first stripper tower 53a) and a second carbon dioxide stripper unit (second stripper tower 53b) that are connected to the first carbon dioxide absorption unit (first absorption tower 31a) and the second carbon dioxide absorption unit (second absorption tower 31b) so that the carbon dioxide absorbing solution can flow therethrough; a path switching valve (solution path switching valve 43) that switches the path of the carbon dioxide absorbing solution so that the carbon dioxide absorbing solution flows to either or both of the first carbon dioxide stripping section (first stripping tower 53a) and the second carbon dioxide stripping section (second stripping tower 53b); The system includes a heating circuit 60 including a first heating unit (first solution heating unit 602a) that heats the carbon dioxide absorbing solution inside the first carbon dioxide stripping unit (first stripping tower 53a), and a second heating unit (second solution heating unit 602b) that has a higher heating capacity for the carbon dioxide absorbing solution than the first heating unit (first solution heating unit 602a) and heats the carbon dioxide absorbing solution inside the second carbon dioxide stripping unit (second stripping tower 53b), and is switchable among a first heating state in which the carbon dioxide absorbing solution is heated by the first heating unit (first solution heating unit 602a), a second heating state in which the carbon dioxide absorbing solution is heated by the second heating unit (second solution heating unit 602b), and a third heating state in which the carbon dioxide absorbing solution is heated by both the first heating unit (first solution heating unit 602a) and the second heating unit (second solution heating unit 602b).

[0154] According to this configuration, the heating state can be switched depending on the flow rate of the gas (target gas), thereby improving (preventing or suppressing a decrease in) the carbon dioxide recovery efficiency. That is, when the flow rate of the gas (target gas) is low or medium, the carbon dioxide absorbing solution is heated in only one of the first carbon dioxide stripping section (first stripping tower 53a) or the second carbon dioxide stripping section (second stripping tower 53b), thereby reducing energy consumption depending on the flow rate of the gas (target gas). On the other hand, when the flow rate of the gas (target gas) is high, the carbon dioxide absorbing solution is heated in both the first carbon dioxide stripping section (first stripping tower 53a) and the second carbon dioxide stripping section (second stripping tower 53b), thereby reducing the carbon dioxide remaining without being stripped from the carbon dioxide absorbing solution.

[0155] (7) The carbon dioxide capture system 10 according to this embodiment is When the flow rate of the gas (target gas) delivered from the gas source (target gas source 90) is less than a first threshold value, the first gas valve (first adjustment valve 16a) is opened, the second gas valve (second adjustment valve 16b) is closed, and the heating circuit 60 is switched to the first heating state; When the flow rate of the gas is equal to or greater than a first threshold value and less than a second threshold value that is greater than the first threshold value, the first gas valve (first adjustment valve 16a) is closed, the second gas valve (second adjustment valve 16b) is opened, and the heating circuit 60 is switched to the second heating state; When the flow rate of the gas is equal to or greater than the second threshold, the control device (process control device 22, recovery control device 70) opens both the first gas valve (first adjustment valve 16a) and the second gas valve (second adjustment valve 16b) and switches the heating circuit 60 to the third heating state.

[0156] This configuration can achieve the same effect as (6) above. Furthermore, this configuration can control the energy consumption in the first heating section (first solution heating section 602a) and the second heating section (second solution heating section 602b) depending on the flow rate of the gas (target gas) (more specifically, the amount of carbon dioxide absorbed in the carbon dioxide absorbing solution). Therefore, the carbon dioxide recovery efficiency can be improved.

[0157] (8) The control device (recovery control device 70) of the carbon dioxide capture system 10 according to this embodiment controls the switching state of the path switching valve (solution path switching valve 43) so that, when the flow rate of the gas (target gas) delivered from the gas source (target gas source 90) is less than the first threshold value, the switching state of the path switching valve (solution path switching valve 43) is set to a first switching state (first state) in which the carbon dioxide absorbing solution flows only to the first carbon dioxide stripping section (first stripping tower 53a), and, when the flow rate of the gas (target gas) delivered from the gas source (target gas source 90) is equal to or greater than the first threshold value, the switching state of the path switching valve (solution path switching valve 43) is set to a second switching state (second state) in which the carbon dioxide absorbing solution flows to both the first carbon dioxide stripping section (first stripping tower 53a) and the second carbon dioxide stripping section (second stripping tower 53b).

[0158] According to this configuration, when the flow rate of the target gas is small, the carbon dioxide absorbing solution is heated only in the first carbon dioxide stripper (first stripper tower 53a), when the flow rate of the target gas is medium, the carbon dioxide absorbing solution is heated only in the second carbon dioxide stripper (second stripper tower 53b), and when the flow rate of the target gas is large, the carbon dioxide absorbing solution is heated in both the first carbon dioxide stripper tower (first stripper tower 53a) and the second carbon dioxide stripper tower (second stripper tower 53b). Therefore, the amount of energy consumed by the carbon dioxide capture device 30 can be changed according to the flow rate of the target gas (in other words, the amount of carbon dioxide absorbed by the carbon dioxide absorbing solution). Therefore, the carbon dioxide capture efficiency can be improved.

[0159] Although the embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the above-described embodiments. The present invention can be modified in various ways without departing from the spirit of the invention, and such modifications are also included in the technical scope of the present invention.

[0160] For example, in the above embodiment, the first absorption tower 31a includes one absorption chamber 33, and the second absorption tower 31b includes three absorption chambers (the uppermost absorption chamber 33u, the middle absorption chamber 33m, and the lowermost absorption chamber 33d). However, the present invention is not limited to this configuration. That is, the number of absorption chambers included in each of the first absorption tower 31a and the second absorption tower 31b is not limited. The key is that the first absorption tower 31a and the second absorption tower 31b only need to have different carbon dioxide absorption capacities. Similarly, the first stripper tower 53a and the second stripper tower 53b only need to have different carbon dioxide stripping capacities (heating capacities for the carbon dioxide absorbing solution), and the specific difference or ratio is not particularly limited.

[0161] In addition, in the above embodiment, the heating circuit 60 is configured to heat the heating medium using the exhaust heat from the target gas source 90, and the solution is heated by the heating medium, but the heating circuit 60 is not limited to this configuration. For example, the heating circuit 60 may be provided with a heating device that heats the heating medium instead of the heat recovery unit 601 that uses exhaust heat or residual heat as described above, or in addition to the heat recovery unit 601. Furthermore, the heating circuit 60 may be provided with a heating device that heats the carbon dioxide absorbing solution without using a heating medium. [Explanation of symbols]

[0162] 10...carbon dioxide capture system, 14a...first downstream gas path, 14b...second downstream gas path, 16a...first regulating valve, 16b...second regulating valve, 17a...first buffer, 17b...second buffer, 21...pressure equalization path, 22...process control device, 30...carbon dioxide capture device, 31a...first absorption tower, 31b...second absorption tower, 33...absorption chamber, 33u...topmost absorption chamber, 33m...intermediate absorption chamber, 33d...bottommost absorption chamber, 34...rotating element, 40...rich solution path path, 41...upstream portion, 42a...first downstream portion, 42b...second downstream portion, 43...solution path switching valve, 45...lean solution path, 53a...first stripper tower, 53b...second stripper tower, 60...heating circuit, 70...recovery control device, 90...target gas source, 342...gas-liquid contact section, 602a...first solution heating section, 602b...second solution heating section, 605...first heating medium path switching valve, 606...second heating medium path switching valve, 607...third heating medium path switching valve, 608...fourth heating medium path switching valve

Claims

1. a first carbon dioxide absorption unit connected to a gas source that generates a gas containing carbon dioxide via a first gas path, and configured so that carbon dioxide contained in the gas that flows from the gas source through the first gas path is absorbed in a carbon dioxide absorbing solution; a second carbon dioxide absorbing unit that is connected to the gas source via a second gas path, that is configured so that carbon dioxide contained in the gas that flows in from the gas source through the second gas path is absorbed in the carbon dioxide absorbing solution, and that has a higher carbon dioxide absorption capacity than the first carbon dioxide absorbing unit; a first gas valve provided in the first gas path and capable of changing a flow rate of the gas; a second gas valve provided in the second gas path and capable of changing a flow rate of the gas; Equipped with The carbon dioxide recovery system, wherein the first carbon dioxide absorption unit and the second carbon dioxide absorption unit are connected in series so that the carbon dioxide absorbing solution can flow through them.

2. 2. The carbon dioxide capture system of claim 1, the first carbon dioxide absorption unit comprises one carbon dioxide absorption chamber and a first gas-liquid contact unit that is rotatably disposed inside the one carbon dioxide absorption chamber and configured to allow the gas to pass therethrough and the carbon dioxide absorbing solution to permeate therethrough, and is configured so that the carbon dioxide absorbing solution comes into contact with the gas delivered through the first gas path in the first gas-liquid contact unit, thereby absorbing carbon dioxide contained in the gas; the second carbon dioxide absorption unit comprises a plurality of carbon dioxide absorption chambers, and a plurality of second gas-liquid contact sections that are rotatably disposed inside each of the plurality of carbon dioxide absorption chambers and configured to allow the gas to pass through the interior thereof and the carbon dioxide absorbing solution to permeate therein; and the plurality of carbon dioxide absorption chambers are connected in series to one another so that the gas delivered through the second gas path passes through the plurality of carbon dioxide absorption chambers in one direction, and the carbon dioxide absorbing solution passes through the plurality of carbon dioxide absorption chambers in the direction opposite to the one direction, thereby coming into contact with the gas in each of the plurality of second gas-liquid contact sections, thereby absorbing the carbon dioxide contained in the gas.

3. 2. The carbon dioxide capture system of claim 1, A carbon dioxide capture system comprising a third gas path that allows gas to flow between a position in the first gas path between the first gas valve and the first carbon dioxide absorption unit and a position in the second gas path between the second gas valve and the second carbon dioxide absorption unit.

4. 4. The carbon dioxide capture system of claim 3, a first buffer capable of temporarily storing the gas is provided between the first gas valve and the first carbon dioxide absorption unit in the first gas path; a second buffer capable of temporarily storing the gas is provided between the second gas valve and the second carbon dioxide absorption unit in the second gas path;

5. The carbon dioxide recovery system according to any one of claims 1 to 4, a control device that opens the first gas valve and closes the second gas valve when the flow rate of the gas delivered from the gas source is less than a first threshold, closes the first gas valve and opens the second gas valve when the flow rate of the gas is equal to or greater than the first threshold and less than a second threshold that is greater than the first threshold, and opens both the first gas valve and the second gas valve when the flow rate of the gas is equal to or greater than the second threshold.

6. The carbon dioxide recovery system according to any one of claims 1 to 4, a first carbon dioxide dissipation unit and a second carbon dioxide dissipation unit connected to the first carbon dioxide absorption unit and the second carbon dioxide absorption unit so that the carbon dioxide absorbing solution can flow therethrough; a path switching valve that switches the path of the carbon dioxide absorbing solution so that the carbon dioxide absorbing solution flows to either or both of the first carbon dioxide dissipation section and the second carbon dioxide dissipation section; a heating circuit including a first heating unit that heats the carbon dioxide absorbing solution inside the first carbon dioxide dissipation unit, and a second heating unit that has a higher heating capacity for the carbon dioxide absorbing solution than the first heating unit and heats the carbon dioxide absorbing solution inside the second carbon dioxide dissipation unit, and that is configured to be switchable between a first heating state in which the carbon dioxide absorbing solution is heated by the first heating unit, a second heating state in which the carbon dioxide absorbing solution is heated by the second heating unit, and a third heating state in which the carbon dioxide absorbing solution is heated by both the first heating unit and the second heating unit; A carbon dioxide capture system comprising:

7. 7. The carbon dioxide capture system of claim 6, when a flow rate of the gas delivered from the gas source is less than a first threshold, opening the first gas valve, closing the second gas valve, and switching the heating circuit to the first heating state; when the flow rate of the gas is equal to or greater than the first threshold and less than a second threshold that is greater than the first threshold, closing the first gas valve, opening the second gas valve, and switching the heating circuit to the second heating state; a control device that opens both the first gas valve and the second gas valve and switches the heating circuit to the third heating state when the flow rate of the gas is equal to or greater than the second threshold value.

8. 8. The carbon dioxide capture system of claim 7, The control device A carbon dioxide recovery system that controls the switching state of the route switching valve so that, when the flow rate of the gas delivered from the gas source is less than the first threshold value, the switching state of the route switching valve is set to a first switching state in which the carbon dioxide absorbing solution flows only to the first carbon dioxide dissipation section, and, when the flow rate of the gas delivered from the gas source is equal to or greater than the first threshold value, the switching state of the route switching valve is set to a second switching state in which the carbon dioxide absorbing solution flows to both the first carbon dioxide dissipation section and the second carbon dioxide dissipation section.

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