Carbon dioxide recovery system

Abstract

To provide a carbon dioxide absorption system capable of improving carbon dioxide recovery efficiency and energy efficiency.SOLUTION: A carbon dioxide recovery system 10 includes: a carbon dioxide recovery device 18 including a carbon dioxide absorption tower 21 which is configured to absorb carbon dioxide contained in gas fed through a gas route from a gas source in carbon dioxide absorption solution; a buffer tank 14 which is arranged on an object gas feeding route 12 and is configured to be capable of storing the gas; and a variable valve 15 capable of changing the flow rate of the gas to be fed to the carbon dioxide absorption tower 21 from the buffer tank 14.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a carbon dioxide recovery system.

Background Art

[0002] Conventionally, a carbon dioxide recovery apparatus including a carbon dioxide absorption tower and a carbon dioxide stripping tower has been known (see Patent Document 1 and Patent Document 2). The carbon dioxide absorption tower of such a carbon dioxide recovery apparatus is connected to a gas source and is configured such that a gas containing carbon dioxide fed from the gas source passes through the inside. Further, the carbon dioxide absorption tower and the carbon dioxide stripping tower are connected to each other so that a carbon dioxide absorption solution circulates. And such a carbon dioxide recovery apparatus is configured to recover carbon dioxide contained in the gas by absorbing carbon dioxide contained in the gas fed from the gas source into the carbon dioxide absorption solution in the carbon dioxide absorption tower and heating the carbon dioxide absorption solution in the carbon dioxide stripping tower to strip carbon dioxide from the carbon dioxide absorption solution.

[0003] Improvements in the carbon dioxide recovery efficiency (a ratio indicating the amount of recovered carbon dioxide relative to the amount of carbon dioxide contained in the gas) and energy efficiency (a ratio indicating the amount of recovered carbon dioxide relative to the energy consumption of the carbon dioxide recovery apparatus) are required for the carbon dioxide recovery apparatus. Since the amount of carbon dioxide that can be absorbed by the carbon dioxide absorption solution per unit volume is determined by the properties of the carbon dioxide absorption solution and the like, the relationship between the flow rate of the gas fed to the carbon dioxide absorption tower and the flow rate of the carbon dioxide absorption solution fed to the carbon dioxide absorption tower is preferably a predetermined target value. However, since the flow rate of the gas fed from the gas source varies over time, the relationship may deviate from the target value. In this case, if the flow rate of the gas is excessive with respect to the flow rate of the carbon dioxide absorption solution, the carbon dioxide recovery efficiency decreases. On the other hand, if the flow rate of the gas is too small with respect to the flow rate of the carbon dioxide absorption solution, the energy efficiency decreases.

[0004] Note that Patent Document 1 discloses a configuration for stably recovering carbon dioxide by adjusting the concentration of the carbon dioxide absorption solution to correspond to changes in the state of the gas. Patent Document 2 discloses a configuration for bringing the carbon dioxide recovery amount and the recovery efficiency closer to target values by controlling the circulation amount (flow rate) and the heating amount of the carbon dioxide absorption solution in accordance with changes in the measured values of the carbon dioxide recovery efficiency and the recovery amount. However, these patent documents do not disclose a configuration for controlling the gas flow rate in order to improve the carbon dioxide recovery efficiency or the energy efficiency (or to prevent or suppress a decrease).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] (Problems to be Solved by the Invention) In view of the above circumstances, one object of the present invention is to provide a carbon dioxide recovery apparatus capable of improving the carbon dioxide recovery efficiency and the energy efficiency (or preventing or suppressing a decrease) even when the amount of gas generated in the gas source varies over time.

[0007] (Means for Solving the Problems) The carbon dioxide recovery system of the present invention is connected via a gas path to a gas source that generates a gas containing carbon dioxide, and includes a carbon dioxide recovery apparatus including a carbon dioxide absorption tower configured to absorb carbon dioxide contained in the gas fed from the gas source through the gas path into a carbon dioxide absorption solution, a buffer tank disposed on the gas path and configured to be able to store the gas, A variable valve is disposed between the buffer tank in the gas path and the carbon dioxide absorption tower, and is capable of changing the flow rate of the gas fed from the buffer tank to the carbon dioxide absorption tower.

[0008] According to the present invention, by means of the buffer tank and the variable valve disposed on the downstream side of the buffer tank, it is possible to reduce the temporal variation in the flow rate of the gas fed to the carbon dioxide absorption tower. And, by reducing the temporal variation in the flow rate of the gas fed to the carbon dioxide absorption tower, it is possible to prevent a decrease in the carbon dioxide recovery efficiency (the ratio indicating the amount of carbon dioxide recovered with respect to the amount of carbon dioxide contained in the gas) and the energy efficiency (the ratio indicating the amount of carbon dioxide recovered with respect to the energy consumed by the carbon dioxide recovery apparatus).

[0009] In addition, in a configuration where a variable valve is provided on the downstream side of the buffer tank, it is possible to reduce the size of the buffer tank as compared with a configuration where a fixed throttle (fixed orifice) is provided on the downstream side of the buffer tank. That is, the flow rate of the gas passing through the fixed throttle is determined according to the internal pressure of the buffer tank. And, when the capacity of the buffer tank is small, the internal pressure of the buffer tank is likely to fluctuate. For this reason, in order to reduce the temporal variation in the flow rate of the gas passing through the fixed throttle, the capacity of the buffer tank must be increased. On the other hand, according to the present invention, since the flow rate of the gas fed to the absorption tower can be adjusted by the variable valve, the flow rate of the gas fed to the absorption tower is less affected by the internal pressure of the buffer tank. Therefore, even if the capacity of the buffer tank is reduced, it is possible to prevent or suppress the variation in the flow rate of the gas fed to the absorption tower, so that the size of the buffer tank can be reduced.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

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Figure 7

[0011] Hereinafter, embodiments of the present invention will be described. In the following description, the "carbon dioxide recovery system" may be abbreviated as the "recovery system", the "carbon dioxide recovery device" may be abbreviated as the "recovery device", the "carbon dioxide absorption tower" may be abbreviated as the "absorption tower", the "carbon dioxide emission tower" may be abbreviated as the "emission tower", and the "carbon dioxide absorption solution" may be abbreviated as the "solution". Further, unless otherwise specified, "flow rate" means "flow rate per unit time", and "heat quantity" means "heat quantity per unit time".

[0012] <Configuration of the Recovery System> FIG. 1 is a schematic diagram showing the configuration of the recovery system 10. As shown in FIG. 1, the recovery system 10 includes a target gas source 11, a target gas supply path 12, a target gas pump 13, a buffer tank 14, a variable valve 15, a target gas flow meter 16, a process control device 17, and a recovery device 18. The recovery system 10 is configured to absorb (recover) carbon dioxide contained in the gas generated in the target gas source 11 by the recovery device 18. Hereinafter, the gas generated in the target gas source 11 (the gas to be absorbed by carbon dioxide) may be referred to as the "target gas".

[0013] The target gas source 11 is applied with a device or facility that generates a gas containing carbon dioxide. For example, as the target gas source 11, a metal melting furnace and a carburizing furnace that utilize the combustion heat of fossil fuels (i.e., use fossil fuels as fuel) can be applied. In this case, the combustion exhaust gas of fossil fuels is the target gas. Note that in this embodiment, it is assumed that the carbon dioxide concentration of the target gas generated in the target gas source 11 is substantially constant and known.

[0014] The target gas supply path 12 is a path for supplying the target gas generated in the target gas source 11 to the recovery device 18. One end of the target gas supply path 12 is connected to the target gas source 11, and the other end is connected to the absorption tower 21 of the recovery device 18 described later. On the target gas supply path 12, in order from the side closer to the target gas source 11 (i.e., in order from the upstream side of the flow of the target gas), a target gas pump 13, a buffer tank 14, a variable valve 15, and a target gas flow meter 16 are arranged.

[0015] The target gas pump 13 is configured to feed (specifically, pump under pressure) the target gas generated in the target gas source 11 to the buffer tank 14 when it operates. The configuration of the target gas pump 13 is not particularly limited, and various electric air supply pumps are applicable.

[0016] The buffer tank 14 is configured to be able to store the target gas supplied from the target gas source 11 at a pressure higher than atmospheric pressure. For example, the buffer tank 14 is configured to be able to store the target gas at a pressure of about several tens of kPa at most. Note that the configuration of the buffer tank 14 is not particularly limited, and various known pressure vessels are applicable. A pressure gauge 19 (barometer) is provided on the buffer tank 14. The pressure gauge 19 is configured to continuously measure the internal pressure (atmospheric pressure) of the buffer tank 14 in real time. A known pressure gauge (barometer) is applied to the pressure gauge 19.

[0017] The variable valve 15 is arranged between the buffer tank 14 and the recovery device 18 (i.e., on the downstream side of the target gas flow as seen from the buffer tank 14), and is configured to be able to adjust the flow rate of the target gas fed from the buffer tank 14 to the recovery device 18 (which flows into the absorption tower 21 described later of the recovery device 18). Note that the variable valve 15 is configured to be able to continuously or stepwise change not only the switching between opening and closing but also the opening degree (in other words, the flow rate of the target gas). The configuration of the variable valve 15 is not particularly limited, and various known valve devices can be applied.

[0018] The target gas flowmeter 16 is configured to continuously measure in real time the flow rate of the target gas fed from the buffer tank 14 to the recovery device 18 (in other words, flowing into the absorption tower 21 of the recovery device 18). A known gas flowmeter is applied to the target gas flowmeter 16.

[0019] The process control device 17 is configured to be able to continuously acquire in real time the measurement result of the flow rate of the target gas by the target gas flowmeter 16 (hereinafter, may be referred to as the "gas flow measurement value") and the measurement result of the internal pressure of the buffer tank 14 by the pressure gauge 19 (hereinafter, may be referred to as the "pressure measurement value"), and is configured to be able to control the opening degree of the variable valve 15. Further, the process control device 17 is configured to be able to control the target gas pump 13. The process control device 17 is a device provided with a computer including a CPU, a ROM, a RAM, a storage device (memory device), and an I / F (interface). A computer program for controlling the variable valve 15 and the target gas pump 13 is pre-stored in the ROM of the process control device 17. Then, the CPU of the computer of the process control device 17 reads out this computer program from the ROM and expands it in the RAM (using the RAM as a work area) to execute this computer program. Thereby, the control of the variable valve 15 and the target gas pump 13 is realized. Further, the process control device 17 is connected to be able to transmit and receive signals to and from the recovery control device 28 of the recovery device 18 described later via the I / F.

[0020] The recovery device 18 includes an absorption tower 21, a stripping tower 22, a reboiler 23, a first solution path 24, a first solution pump 25, a second solution path 26, a second solution pump 27, a solution flow meter (not shown), and a control device 28. For convenience of explanation, the control device 28 of the recovery device 18 may be referred to as the "recovery control device 28".

[0021] The absorption tower 21 is configured to absorb carbon dioxide contained in the target gas into the solution by bringing the solution into gas-liquid contact with the target gas. Inside the absorption tower 21, a packing material, which is a member that promotes gas-liquid contact between the solution and the target gas, is disposed. The packing material is a member through which the solution can penetrate and the target gas can pass, and is, for example, a porous member or a mesh member having a large specific surface area. One end of the target gas supply path 12 and one end of the target gas discharge path 31 are connected to the absorption tower 21. The target gas discharge path 31 is a path for discharging the target gas (sometimes referred to as off-gas) from which carbon dioxide has been absorbed in the absorption tower 21 to the outside of the absorption tower 21. The other end of the target gas discharge path 31 is, for example, open to the atmosphere. Also, one end of the first solution path 24 and one end of the second solution path 26, which will be described later, are connected to the absorption tower 21.

[0022] The stripping tower 22 is configured to strip carbon dioxide from the solution. Inside the stripping tower 22, a packing material, which is a member that promotes gas-liquid contact between the solution and the vapor of the solution, which will be described later, is disposed. The packing material is a member through which the solution can penetrate and the vapor of the solution can pass, and is, for example, a porous member or a mesh member having a large specific surface area. The reboiler 23 is connected to the stripping tower 22, and one end of the carbon dioxide recovery path 32 is connected to the stripping tower 22. The reboiler 23 is an example of the heating device of the present invention. The reboiler 23 is configured to heat a part of the solution accumulated in the stripping tower 22 to generate vapor and supply the generated vapor to the stripping tower 22. The carbon dioxide recovery path 32 is a path for recovering the carbon dioxide stripped from the solution in the stripping tower 22. The other end of the carbon dioxide recovery path 32 is connected to a carbon dioxide storage facility (not shown) or the like.

[0023] The first solution path 24 is a path for feeding the solution from the absorption tower 21 to the stripping tower 22. The first solution pump 25 is arranged on the first solution path 24 and is configured to feed the solution from the absorption tower 21 to the stripping tower 22 by operating. The second solution path 26 is a path for feeding the solution from the stripping tower 22 to the absorption tower 21. One end of the second solution path 26 is connected to the absorption tower 21 and the other end is connected to the stripping tower 22. The second solution pump 27 is arranged on the second solution path 26 and is configured to feed the solution from the stripping tower 22 to the absorption tower 21 by operating. Further, a solution heat exchanger 29 is provided on the first solution path 24 and the second solution path 26. The solution heat exchanger 29 is configured to perform heat exchange between the solution flowing through the first solution path 24 and the solution flowing through the second solution path 26. The first solution path 24, the first solution pump 25, the second solution path 26, and the second solution pump 27 are examples of the carbon dioxide absorption solution circulation section of the present invention.

[0024] The solution flowmeter (not shown in the figure) is configured to continuously measure in real time the flow rate of the solution circulating through the absorption tower 21, the first solution path 24, the stripping tower 22, and the second solution path 26 of the recovery device 18, in other words, the flow rate of the solution passing through the absorption tower 21. Hereinafter, the flow rate of the solution measured by the solution flowmeter may be referred to as the solution flowmeter measurement value. Note that the configuration of the solution flowmeter is not particularly limited.

[0025] The recovery control device 28 controls the reboiler 23, the first solution pump 25, and the second solution pump 27. Also, the recovery control device 28 can continuously acquire the solution flow rate measurement value from the solution flow meter in real time. The recovery control device 28 is a device including a computer having a CPU, a ROM, a RAM, a storage device, and an I / F. In the ROM of the recovery control device 28, a computer program for controlling each part of the recovery device 18 including the reboiler 23, the first solution pump 25, and the second solution pump 27 is stored in advance. Then, the CPU of the computer of the recovery control device 28 reads out this computer program from the ROM, expands it in the RAM (using the RAM as a work area), and executes this computer program. Thereby, the control of the recovery device 18 is realized. Also, the recovery control device 28 is connected to be able to transmit and receive signals to and from the process control device 17 via the I / F.

[0026] <Basic Operation of the Recovery System> Next, the basic operation of the recovery system 10 will be described. The target gas generated in the target gas source 11 is temporarily stored in the buffer tank 14 by being fed (pressurized) to the buffer tank 14 by the operation of the target gas pump 13. The target gas stored in the buffer tank 14 is fed to the absorption tower 21 of the recovery device 18 through the variable valve 15 by the internal pressure of the buffer tank 14 when the variable valve 15 is in the open state. The process control device 17 continuously acquires the gas flow rate measurement value from the target gas flow meter 16 in real time, and controls the opening degree of the variable valve 15 based on the acquired gas flow rate measurement value so that the flow rate of the target gas fed to the absorption tower 21 approaches the target gas flow rate (it can also be said to maintain the target gas flow rate). Thereby, the flow rate of the target gas fed to the absorption tower 21 stabilizes at the target gas flow rate or a flow rate close to the target gas flow rate.

[0027] The target gas flowing out of the buffer tank 14 flows into the absorption tower 21. Also, inside the absorption tower 21, a solution flows in due to the operation of the second solution pump 27 of the recovery device 18. Then, the target gas and the solution that have flowed into the absorption tower 21 come into gas-liquid contact, and carbon dioxide contained in the target gas is absorbed by the solution. The target gas after carbon dioxide has been absorbed is discharged outside the absorption tower 21 (in other words, outside the recovery device 18) through the target gas discharge path 31. The solution that has absorbed carbon dioxide accumulates at the bottom of the absorption tower 21, and the solution that has accumulated at the bottom of the absorption tower 21 is fed from the absorption tower 21 to the stripping tower 22 through the first solution path 24 by the operation of the first solution pump 25. The solution flowing through the first solution path 24 is heated by exchanging heat with the solution flowing through the second solution path 26 in the solution heat exchanger 29, and then flows into the inside of the stripping tower 22.

[0028] The solution that has flowed into the inside of the stripping tower 22 flows down inside the stripping tower 22 and accumulates at the bottom of the stripping tower 22. A part of the solution that has accumulated at the bottom of the stripping tower 22 flows into the reboiler 23 and is heated in the reboiler 23. The vapor generated in the reboiler 23 flows into the inside of the stripping tower 22 and then rises from the bottom of the stripping tower 22. At that time, the vapor and the solution come into gas-liquid contact (countercurrent contact). As a result, the solution is heated and carbon dioxide is stripped from the solution. In this way, the stripping tower 22 is configured such that carbon dioxide is stripped from the solution by the heat applied to the solution in the reboiler 23 (in other words, such that a "reaction in which the solution strips carbon dioxide" occurs).

[0029] The carbon dioxide stripped from the solution is discharged outside the stripping tower 22 (in other words, discharged from the recovery device 18) through the carbon dioxide recovery path 32. Note that a demister, a condenser, or the like for removing the vapor of the solution (for separating carbon dioxide and the vapor of the solution) may be provided in the carbon dioxide recovery path 32.

[0030] The solution accumulated at the bottom of the stripping tower 22 is fed from the stripping tower 22 to the absorption tower 21 through the second solution path 26 by the operation of the second solution pump 27. Then, the solution flowing through the second solution path 26 is cooled by exchanging heat with the solution flowing through the first solution path 24 in the solution heat exchanger 29. As a result, the solution reaches a temperature suitable for the absorption of carbon dioxide. Then, the solution flows into the absorption tower 21.

[0031] In this way, due to the operations of the first solution pump 25 and the second solution pump 27, the solution circulates in the order of the absorption tower 21, the first solution path 24, the stripping tower 22, and the second solution path 26. And while circulating, the solution repeatedly undergoes the reaction of absorbing carbon dioxide contained in the target gas in the absorption tower 21 and releasing the absorbed carbon dioxide in the stripping tower 22.

[0032] <Specific Operations of the Recovery System> Next, the specific operations of the recovery system 10 will be described. As the specific operations of the recovery system 10, a first operation, a second operation, and a third operation are shown.

[0033] (First Operation) The recovery system 10 preferably operates to stably recover carbon dioxide from the target gas. Specifically, it is preferable that the carbon dioxide recovery efficiency (the ratio indicating the amount of recovered carbon dioxide to the amount of carbon dioxide contained in the target gas) and the energy efficiency (the ratio indicating the amount of recovered carbon dioxide to the energy consumed by the recovery device 18) are each maintained at or above the target value. Also, from the perspective of energy conservation, it is preferable that the flow rate of the solution circulating through the recovery device 18 and the amount of heat applied to the solution in the reboiler 23 have little change over time.

[0034] On the other hand, the amount of the target gas generated per unit time in the target gas source 11 varies according to the operating conditions of the target gas source 11. When the flow rate of the target gas fed to the absorption tower 21 of the recovery device 18 varies over time, the carbon dioxide recovery efficiency or the energy efficiency may decrease. For example, since the amount of carbon dioxide that can be absorbed by the solution per unit volume is determined by the characteristics of the solution (type of solute and concentration of the solution), etc., when the flow rate of the target gas becomes excessive relative to the flow rate of the solution, the solution cannot absorb all the carbon dioxide contained in the target gas, and as a result, the carbon dioxide recovery efficiency decreases. On the other hand, when the flow rate of the target gas becomes too small relative to the flow rate of the solution, the amount of carbon dioxide that can be recovered decreases, so the energy efficiency decreases.

[0035] The first operation is an operation of maintaining the flow rate of the solution and the amount of heat applied to the solution by the reboiler 23 substantially constant, and maintaining the flow rate of the target gas fed from the buffer tank 14 to the absorption tower 21 substantially constant. In the storage device of the computer of the process control device 17, a target gas flow rate, which is the target value of the flow rate of the target gas, is stored in advance. The target gas flow rate in the first operation is a fixed value (constant value). The target gas flow rate is a value such that the carbon dioxide recovery efficiency is equal to or higher than the target value, and is defined in advance according to the characteristics of the solution and the flow rate of the solution, etc.

[0036] The recovery control device 28 controls the outputs of the first solution pump 25 and the second solution pump 27 so that the flow rate of the circulating solution becomes substantially constant while the recovery device 18 is operating. In other words, the recovery control device 28 controls the outputs of the first solution pump 25 and the second solution pump 27 so as to approach the target solution flow rate, which is a predefined target value (it can also be said that the target solution flow rate is maintained). Further, the recovery device 18 controls the output of the reboiler 23 so that the amount of heat applied to the solution by the reboiler 23 becomes substantially constant. In other words, the recovery device 18 controls the output of the reboiler 23 so as to maintain the target heat amount, which is a predefined target value (it can also be said that the recovery device 18 controls the output of the reboiler 23 so as to approach the target heat amount).

[0037] On the one hand, the process control device 17 continuously and in real time executes a process of acquiring a gas flow measurement value from the target gas flowmeter 16 and determining whether the acquired gas flow measurement value is equal to the target gas flow. Then, when the acquired gas flow measurement value is equal to the target gas flow, the process control device 17 maintains the opening degree of the variable valve 15 as it is. When the gas flow measurement value is lower than the target gas flow, the process control device 17 increases the opening degree of the variable valve 15. When the gas flow measurement value is higher than the target gas flow, the process control device 17 decreases the opening degree of the variable valve 15. Note that the process control device 17 may change the opening degree of the variable valve 15 stepwise or continuously.

[0038] According to the first operation, even when the flow rate of the target gas fed from the target gas source 11 to the buffer tank 14 varies over time, it is possible to reduce the temporal variation in the flow rate of the target gas fed from the buffer tank 14 to the absorption tower 21 of the recovery device 18 (passing through the absorption tower 21). Therefore, the flow rate of the target gas passing through the absorption tower 21 can be maintained at or near the target gas flow rate. That is, in a configuration without the buffer tank 14, when the amount of the target gas generated in the target gas source 11 (the flow rate of the target gas fed from the target gas source 11) decreases, even if the opening degree of the variable valve 15 is increased, the flow rate of the target gas fed to the absorption tower 21 of the recovery device 18 may be less than the target gas flow rate. In contrast, in a configuration where the recovery system 10 includes the buffer tank 14, even when the amount of the target gas generated in the target gas source 11 temporarily decreases, the target gas temporarily stored in the buffer tank 14 is fed to the absorption tower 21 of the recovery device 18. Therefore, it is possible to prevent or suppress the flow rate of the target gas fed to the absorption tower 21 of the recovery device 18 from becoming less than the target gas flow rate.

[0039] When the variable valve 15 is arranged on the downstream side of the buffer tank 14, compared with the configuration in which a fixed throttle (fixed orifice) is provided, the effect of preventing or suppressing the temporal variation of the target gas fed from the buffer tank 14 to the absorption tower 21 of the recovery device 18 can be enhanced. Therefore, the effect of preventing or suppressing the decrease in the carbon dioxide recovery efficiency can be enhanced. That is, when the flow rate of the target gas fed from the target gas source 11 to the buffer tank 14 varies over time, the internal pressure of the buffer tank 14 also varies over time. For this reason, in the configuration where a fixed throttle is arranged on the downstream side of the buffer tank 14, the flow rate of the target gas fed from the buffer tank 14 to the absorption tower 21 of the recovery device 18 also varies over time in response to the temporal variation of the internal pressure of the buffer tank 14. On the other hand, when the variable valve 15 is arranged on the downstream side of the buffer tank 14, even when the internal pressure of the buffer tank 14 varies over time, by adjusting (changing) the opening degree of the variable valve 15, the temporal variation of the flow rate of the target gas fed from the buffer tank 14 to the absorption tower 21 of the recovery device 18 can be prevented or suppressed.

[0040] Also, according to the configuration in which the variable valve 15 is provided on the downstream side of the buffer tank 14, the buffer tank 14 can be downsized compared with the configuration in which a fixed throttle (fixed orifice) is provided on the downstream side of the buffer tank 14. That is, the flow rate of the target gas passing through the fixed throttle is determined according to the internal pressure of the buffer tank 14. And when the capacity of the buffer tank 14 is small, the internal pressure of the buffer tank 14 is likely to vary. For this reason, in order to reduce the temporal variation of the flow rate of the target gas passing through the fixed throttle, the capacity of the buffer tank 14 has to be increased. On the other hand, according to the present embodiment, since the flow rate of the target gas fed to the absorption tower 21 is adjusted by the variable valve 15, the flow rate of the target gas fed to the absorption tower 21 is less affected by the internal pressure of the buffer tank 14. Therefore, even if the capacity of the buffer tank 14 is reduced, the temporal variation of the flow rate of the target gas fed to the absorption tower 21 can be reduced, so that the buffer tank 14 can be downsized.

[0041] Furthermore, the absorption tower 21 of the recovery device 18 can be downsized. That is, since the fluctuation in the flow rate of the gas fed to the absorption tower 21 can be reduced, the peak value of the flow rate of the gas fed to the absorption tower 21 can be lowered. For this reason, since the internal volume of the absorption tower 21 can be made smaller, the recovery device 18 can be downsized.

[0042] Next, the processes executed by the process control device 17 will be described. FIG. 2 is a flowchart showing the processes executed by the process control device 17. The computer program for executing this process is stored in advance in the ROM or storage device of the computer of the process control device 17. Then, the CPU (hereinafter simply abbreviated as "CPU") of the computer of the process control device 17 reads this computer program from the ROM or storage device and repeatedly executes it at a predetermined cycle. Thereby, the first operation is realized.

[0043] In step S101, the CPU acquires the gas flow rate measurement value from the target gas flow meter 16. Then, the CPU proceeds to step S102.

[0044] In step S102, the CPU determines whether the acquired gas flow rate measurement value is equal to the target gas flow rate. If the gas flow rate measurement value is equal to the target gas flow rate, the CPU temporarily ends this series of processes. In this case, the CPU does not change the opening degree of the variable valve 15. On the other hand, if the acquired gas flow rate measurement value is different from the target gas flow rate, the CPU proceeds to step S103.

[0045] In step S103, the CPU determines whether the acquired gas flow rate measurement value is greater than or less than the target gas flow rate. Then, if the acquired gas flow rate measurement value is greater than the target gas flow rate, the CPU proceeds to step S104, and if the acquired gas flow rate measurement value is less than the target gas flow rate, the CPU proceeds to step S105.

[0046] In step S104, the CPU reduces the opening degree of the variable valve 15. On the other hand, in step S105, the CPU increases the opening degree of the variable valve 15. Then, the CPU returns the process to step S102 (it may also return the process to step S101).

[0047] According to such a process, the first operation is realized.

[0048] FIG. 3 is a graph showing an example of the flow rate of the target gas fed from the target gas source 11 to the buffer tank 14 (denoted as "upstream flow rate" in FIG. 3) and the flow rate of the target gas fed from the buffer tank 14 to the absorption tower 21 when the first operation is executed (denoted as "downstream flow rate" in FIG. 3). As shown in FIG. 3, the flow rate of the target gas fed from the target gas source 11 to the buffer tank 14 varies with time. In contrast, the temporal variation in the flow rate of the target gas fed from the buffer tank 14 to the absorption tower 21 is reduced compared to the temporal variation in the flow rate of the target gas fed from the target gas source 11 to the buffer tank 14. In particular, it is prevented or suppressed that the peak value of the flow rate of the target gas fed from the target gas source 11 to the buffer tank 14 exceeds the target gas flow rate. Thus, according to the first operation, the temporal variation in the flow rate of the target gas fed from the buffer tank 14 to the absorption tower 21 can be reduced. Therefore, the flow rate of the target gas fed from the buffer tank 14 to the absorption tower 21 can be maintained at or near the target gas flow rate.

[0049] (Second operation) Next, the second operation will be described. The second operation is an operation of setting the target gas flow rate according to the flow rate of the target gas fed from the buffer tank 14 to the absorption tower 21, and controlling the flow rate of the solution and the amount of heat applied to the solution by the reboiler 23 according to this target gas flow rate.

[0050] The process control device 17 continuously and in real time executes the process of acquiring the gas flow measurement value from the target gas flowmeter 16 and calculating the moving average of the acquired gas flow measurement value. Then, the process control device 17 sets the target gas flow according to the moving average of the gas flow measurement value. Specifically, at the start of operation of the recovery system 10 (when the target gas pump 13 starts operating), the process control device 17 sets the target gas flow to a preset initial value (default value). After the start of operation of the recovery system 10, the process control device 17 calculates the moving average of the gas flow measurement value as described above. When the difference between the calculated moving average and the currently set target gas flow becomes equal to or greater than a predetermined threshold value, the process control device 17 sets the value of the target gas flow according to the calculated moving average. That is, when the moving average decreases (when the flow rate of the target gas decreases), the target gas flow is decreased. Also, when the pressure measurement value becomes equal to or greater than a preset value (when the flow rate of the target gas increases), the process control device 17 increases the target gas flow. Note that the period of the moving average is not particularly limited.

[0051] Thereafter, the process control device 17 continuously executes the process of "setting the value of the target gas flow according to the calculated moving average when the difference between the calculated moving average of the gas flow measurement value and the currently set target gas flow becomes equal to or greater than the threshold value". Then, the process control device 17 controls the opening degree of the variable valve 15 so that the target gas fed from the buffer tank 14 to the absorption tower 21 approaches the target gas flow. Also, each time the process control device 17 sets the target gas flow (each time the target gas flow is changed), the process control device 17 transmits the set target gas flow to the recovery control device 28 of the recovery device 18.

[0052] When the recovery control device 28 of the recovery device 18 receives the target gas flow rate from the process control device 17, it calculates a target solution flow rate, which is the target value of the solution flow rate such that the ratio of the solution flow rate to the target gas flow rate (L / G ratio) becomes the target L / G ratio. Then, the recovery control device 28 of the recovery device 18 controls the outputs of the first solution pump 25 and the second solution pump 27 so that the actual flow rate of the solution approaches the target solution flow rate (or maintains the target solution flow rate). Furthermore, the recovery control device 28 of the recovery device 18 sets a target heat quantity, which is the target value of the heat quantity applied to the solution corresponding to the target solution flow rate. Then, the recovery control device 28 of the recovery device 18 controls the output of the reboiler 23 so that the heat quantity applied to the solution by the reboiler 23 approaches the target heat quantity (or maintains the target heat quantity).

[0053] That is, the amount of carbon dioxide that can be absorbed by the solution per unit volume is determined according to the characteristics of the solution (such as the type and concentration of the solute). Therefore, the preferred flow rate of the solution for improving the carbon dioxide recovery efficiency (specifically, for example, the flow rate that can absorb the total amount of carbon dioxide contained in the target gas) is determined according to the flow rate of the target gas. Also, the heat quantity applied to the solution to dissipate carbon dioxide from the solution is determined according to the flow rate of the solution. Thus, the L / G ratio, which is the preferred solution flow rate for the flow rate of the target gas fed to (passing through) the absorption tower 21, is stored in advance in the storage device of the recovery control device 28 as the target L / G ratio. At the same time, the "heat quantity applied to the solution corresponding to the preferred solution flow rate (in other words, the output of the reboiler 23)" is also stored in advance in the storage device of the recovery control device 28 of the recovery device 18.

[0054] Then, the recovery control device 28 of the recovery device 18 sets a target solution flow rate corresponding to the received target gas flow rate from the target gas flow rate and the target L / G ratio stored in the storage device. At the same time, the recovery control device 28 of the recovery device 18 sets a target heat quantity corresponding to the set target gas flow rate.

[0055] According to such a configuration, the same effects as those of the first operation can be achieved. Furthermore, according to such a configuration, the effect of preventing or suppressing temporal fluctuations in the flow rate of the target gas supplied to the absorption tower 21 can be enhanced. Specifically, when the target gas flow rate is a fixed value, if the moving average of the gas flow rate measurement value becomes small, the flow rate of the gas supplied from the buffer tank 14 to the absorption tower 21 may become smaller than the target gas flow rate. In contrast, in the second operation, when the moving average of the gas flow rate measurement value becomes small, the process control device 17 reduces the target gas flow rate according to the moving average. Thereby, it is possible to prevent or suppress the flow rate of the gas supplied from the buffer tank 14 to the absorption tower 21 from becoming smaller than the target gas flow rate.

[0056] Also, according to such a configuration, the effect of reducing the size of the buffer tank 14 can be enhanced. That is, when the state where the flow rate of the target gas supplied from the target gas source 11 is large continues, the amount of the target gas temporarily stored in the buffer tank 14 increases. For this reason, when the temporal fluctuations in the flow rate of the target gas are large, it is necessary to increase the capacity of the buffer tank 14. In the second operation, when the moving average of the gas flow rate measurement value supplied to the absorption tower 21 becomes high, the process control device 17 increases the flow rate of the target gas supplied from the buffer tank 14 to the absorption tower 21 according to the increase in the moving average. Thereby, since the amount of gas that must be stored in the buffer tank 14 can be decreased, the effect of reducing the size of the buffer tank 14 can be enhanced.

[0057] Here, a configuration in which the process control device 17 sets the value of the target gas flow rate according to the moving average of the gas flow rate measurement value has been shown, but it is not limited to such a configuration. That is, the process control device 17 may set a value different from the moving average of the gas flow rate measurement value as the value of the target gas flow rate. In short, when the moving average of the gas flow rate measurement value becomes low, the process control device 17 may lower the value of the target gas flow rate, and when the pressure measurement value becomes equal to or higher than a predetermined value, the process control device 17 may increase the value of the target gas flow rate. In short, the process control device 17 may set the value of the target gas flow rate according to the calculated moving average of the gas flow rate measurement value. In this case, the target gas flow rate may be a value having a positive correlation with the moving average of the gas flow rate measurement value.

[0058] Next, the processes executed by the process control device 17 and the recovery control device 28 will be described. FIG. 4 is a flowchart showing the process executed by the process control device 17. FIG. 5 is a flowchart showing the process executed by the recovery control device 28. A computer program for executing the process shown in FIG. 5 is stored in advance in the ROM or storage device of the computer of the recovery control device 28. Then, the CPUs of the process control device 17 and the recovery control device 28 read out these computer programs from the ROM or storage device, respectively, and repeatedly execute them continuously at a predetermined cycle. Thereby, the second operation is realized.

[0059] The process executed by the process control device 17 is as follows.

[0060] In step S201, the CPU acquires a gas flow rate measurement value from the target gas flow meter 16. Then, the CPU proceeds to step S202.

[0061] In step S202, the CPU calculates the moving average of the acquired gas flow rate measurement value. Then, the CPU proceeds to step S203.

[0062] In step S203, the CPU calculates the difference between the calculated moving average and the acquired gas flow measurement value. Then, the CPU proceeds with the process to step S204.

[0063] In step S204, the CPU determines whether the absolute value of the calculated difference is greater than or equal to the threshold value. If the absolute value of the difference exceeds the threshold value, the CPU proceeds with the process to step S205. On the other hand, if the absolute value of the difference is less than the threshold value, the CPU temporarily ends this series of processes.

[0064] In step S205, the CPU sets the target gas flow rate corresponding to the calculated moving average. Then, the CPU proceeds with the process to step S206.

[0065] In step S206, the CPU determines whether the gas flow measurement value (or the moving average) is equal to the target gas flow rate. If the gas flow measurement value is not equal to the target gas flow rate, the CPU proceeds with the process to step S207. On the other hand, if the gas flow measurement value is equal to the target gas flow rate, the CPU temporarily ends this series of processes.

[0066] In step S207, it is determined whether the gas flow measurement value is higher or lower than the target gas flow rate. If the gas flow measurement value is higher than the target gas flow rate, the CPU proceeds with the process to step S208. On the other hand, if the gas flow measurement value is lower than the target gas flow rate, the CPU proceeds with the process to step S209.

[0067] In step S206, the CPU decreases the opening degree of the variable valve 15. On the other hand, in step S207, the CPU increases the opening degree of the variable valve 15. Then, the CPU returns the process to step S206.

[0068] The process executed by the recovery control device 28 is as follows.

[0069] In step S301, the CPU determines whether it has received the target gas flow rate from the process control device 17. If not received, the CPU temporarily ends this series of processes. That is, in this case, the CPU maintains the solution flow rate (outputs of the first solution pump 25 and the second solution pump 27) and the amount of heat applied to the solution (output of the reboiler 23) without change. If received, the CPU advances the process to step S302.

[0070] In step S302, the CPU calculates the L / G ratio indicating the ratio of the solution flow rate measurement value to the target gas flow rate from the received target gas flow rate and the solution flow rate measurement value obtained from the solution flow meter. Then, the CPU advances the process to step S303.

[0071] In step S303, the CPU determines whether the L / G ratio is equal to a predefined target L / G ratio. If the L / G ratio is equal to the target L / G ratio, the CPU temporarily ends this series of processes. In this case, the CPU maintains the solution flow rate (outputs of the first solution pump 25 and the second solution pump 27) and the amount of heat applied to the solution (output of the reboiler 23) without change. If the L / G ratio is not equal to the target L / G ratio, the CPU advances the process to step S304.

[0072] In step S304, the CPU calculates (sets) the target solution flow rate based on the target L / G ratio and the target gas flow rate. Further, the CPU calculates (sets) the target heat amount based on the calculated target solution flow rate. Then, the CPU advances the process to step S305.

[0073] In step S305, the CPU adjusts the outputs of the first solution pump 25 and the second solution pump 27 so that the solution flow rate approaches (or matches) the target solution flow rate. Also, the CPU adjusts the output of the reboiler 23 so that the amount of heat applied to the solution approaches (or matches) the target heat amount. Then, the series of processes is temporarily ended.

[0074] According to these processes, the second operation is realized.

[0075] FIG. 6 is a graph showing an example of the flow rate of the target gas fed from the target gas source 11 to the buffer tank 14 and the flow rate of the target gas fed from the buffer tank 14 to the absorption tower 21 when the second operation is executed. Note that the period P in FIG. 6 is a period in which the target gas flow rate (moving average) has decreased compared to other periods, so the target gas flow rate is lowered. As shown in FIG. 6, the flow rate of the target gas fed from the target gas source 11 to the buffer tank 14 varies over time. In contrast, the change over time in the flow rate of the target gas fed from the buffer tank 14 to the absorption tower 21 is reduced compared to the change over time in the flow rate of the target gas fed from the target gas source 11 to the buffer tank 14. Thus, according to the second operation, the change over time in the flow rate of the target gas fed from the buffer tank 14 to the absorption tower 21 can be reduced.

[0076] (Third operation) Next, the third operation will be described. The third operation is an operation of predicting the flow rate of the target gas by using a production plan that defines the operating status of the target gas source 11 and setting a target value according to the predicted flow rate.

[0077] The production plan defines the operating schedule of the target gas source 11. For example, if the target gas source 11 is a metal melting furnace, the time during which the burner for melting the metal operates is defined in advance. Since the amount of the target gas generated per unit time in the target gas source 11 is determined according to the operating status of the burner, the flow rate of the target gas and its change over time can be predicted from the production plan.

[0078] Note that the production plan is stored in advance in the storage device of the process control device 17. However, the target gas source 11 may be provided with a control device (not shown) and the production plan may be stored in this control device. In this case, the process control device 17 and the control device of the target gas source 11 are connected so as to be able to transmit and receive signals to and from each other, and the process control device 17 receives the production plan from the control device of the target gas source 11.

[0079] The process control device 17 sets a target gas flow rate based on the production plan of the target gas source 11. For example, the process control device 17 calculates the amount of the target gas generated per unit time in the target gas source 11 from the production plan of the target gas source 11, and sets the calculated amount as the target gas flow rate. Then, each time the process control device 17 sets the target gas flow rate, it transmits the set target gas flow rate to the recovery control device 28. Further, the process control device 17 continuously and in real time executes a process of acquiring a gas flow measurement value from the target gas flow meter 16 and determining whether the acquired gas flow measurement value is equal to the target gas flow rate. Then, when the acquired gas flow measurement value is equal to the target gas flow rate, the process control device 17 maintains the opening degree of the variable valve 15 as it is, when the gas flow measurement value is lower than the target gas flow rate, it increases the opening degree of the variable valve 15, and when the gas flow measurement value is higher than the target gas flow rate, it decreases the opening degree of the variable valve 15, and continuously executes this process in real time.

[0080] Here, a configuration is shown in which the amount of the target gas generated per unit time calculated from the production plan of the target gas source 11 is used as the target gas flow rate, but the target gas flow rate is not limited to such a value. That is, the process control device 17 may set a value different from the amount of the target gas generated per unit time to be calculated as the value of the target gas flow rate. In short, the process control device 17 may lower the value of the target gas flow rate when the moving average of the gas flow measurement value decreases, and increase the value of the target gas flow rate when the pressure measurement value becomes equal to or higher than a predetermined value. In other words, the process control device 17 may set the value of the target gas flow rate according to the amount of the target gas generated per unit time calculated from the production plan. In this case, the target gas flow rate may be a value having a positive correlation with the amount of the target gas generated per unit time.

[0081] The operation of the recovery control device 28 in the third operation is substantially the same as the operation of the recovery control device 28 in the second operation. That is, when the recovery control device 28 of the recovery device 18 receives the target gas flow rate from the process control device 17, it calculates the target solution flow rate, which is the target value of the solution flow rate such that the ratio of the solution flow rate to the target gas flow rate (L / G ratio) becomes the target L / G ratio. Then, the recovery control device 28 of the recovery device 18 controls the outputs of the first solution pump 25 and the second solution pump 27 so that the actual flow rate of the solution approaches the target solution flow rate (or maintains the target solution flow rate). Further, the recovery control device 28 of the recovery device 18 sets the target heat amount, which is the target value of the heat amount applied to the solution corresponding to the target solution flow rate. Then, the recovery control device 28 of the recovery device 18 controls the output of the reboiler 23 so that the heat amount applied to the solution by the reboiler 23 approaches the target heat amount (or maintains the target heat amount).

[0082] According to such a configuration, the same effects as those in the second operation can be achieved.

[0083] Next, the process executed by the process control device 17 will be described. FIG. 7 is a flowchart showing the process executed by the process control device 17.

[0084] In step S401, the CPU refers to the production plan and sets the target gas flow rate. Then the CPU transmits the set target gas flow rate to the recovery control device 28. Then, the CPU proceeds with the process to step S402. Steps S402 to S406 are the same as steps S101 to S105 in the first operation (see FIG. 2). Therefore, the description will be omitted.

[0085] Also, the process executed by the CPU of the recovery control device 28 is substantially the same as the process executed by the CPU of the recovery control device 28 to realize the second operation (see FIG. 5). Therefore, the description will be omitted. According to such a process, the third operation is realized.

[0086] <Summary of the Embodiment> The carbon dioxide recovery system 10 according to this embodiment is connected to a gas source (target gas source 11) that generates a gas containing carbon dioxide (target gas) via a gas path (target gas supply path 12), and is configured such that carbon dioxide contained in the gas (target gas) fed from the gas source (target gas source 11) through the gas path (target gas supply path 12) is absorbed by a carbon dioxide absorption solution. A carbon dioxide recovery device 18 including a carbon dioxide absorption tower 21, a buffer tank 14 disposed on the gas path (target gas supply path 12) and configured to be able to store the gas (target gas), and a variable valve 15 disposed between the buffer tank 14 and the carbon dioxide absorption tower 21 of the gas path (target gas supply path 12), and capable of changing the flow rate per unit time of the gas (target gas) fed from the buffer tank 14 to the carbon dioxide absorption tower 21.

[0087] According to this embodiment, even when the amount of gas (target gas) generated per unit time at the gas source (target gas source 11) varies over time, the buffer tank 14 and the variable valve 15 disposed on the downstream side of the buffer tank 14 can reduce the temporal variation in the flow rate of the gas (target gas) fed to the carbon dioxide absorption tower 21. That is, if the configuration is such that the buffer tank 14 is not provided, the flow rate per unit time of the gas (target gas) fed to the carbon dioxide absorption tower 21 varies in accordance with the temporal variation in the amount of gas (target gas) generated per unit time at the gas source (target gas source 11). In contrast, if the configuration is such that the buffer tank 14 is provided, the buffer tank 14 can absorb the temporal variation in the amount of gas (target gas) generated per unit time at the gas source (target gas source 11), so that the temporal variation in the flow rate of the gas (target gas) fed to the carbon dioxide absorption tower 21 can be reduced.

[0088] Furthermore, when the configuration is such that a variable valve 15 capable of changing the flow rate of the gas (target gas) is provided on the downstream side of the buffer tank 14, the temporal variation in the flow rate of the gas (target gas) fed to the carbon dioxide absorption tower 21 can be reduced as compared with the configuration in which a fixed throttle (fixed orifice) is provided. That is, in the configuration in which a fixed throttle is provided on the downstream side of the buffer tank 14, the flow rate per unit time of the gas (target gas) passing through the fixed throttle (that is, the flow rate per unit time of the gas (target gas) fed to the carbon dioxide absorption tower 21) varies according to the internal pressure of the buffer tank 14. On the other hand, when the configuration is such that the variable valve 15 is provided, by controlling (adjusting) the opening degree of the variable valve 15 according to the internal pressure of the buffer tank 14, the temporal variation in the flow rate of the gas (target gas) fed to the carbon dioxide absorption tower 21 can be reduced.

[0089] And, by reducing the temporal variation in the flow rate per unit time of the gas (target gas) fed to the carbon dioxide absorption tower 21, a decrease in the carbon dioxide recovery efficiency (the ratio indicating the amount of carbon dioxide recovered with respect to the amount of carbon dioxide contained in the target gas) and the energy efficiency (the ratio indicating the amount of carbon dioxide recovered with respect to the energy consumed by the carbon dioxide recovery device 18) can be prevented. That is, since the amount of carbon dioxide that can be absorbed by the solution per unit volume is determined by the characteristics of the solution and the like, when the flow rate of the gas (target gas) becomes excessive with respect to the flow rate of the solution, the solution cannot absorb all the carbon dioxide contained in the target gas, and as a result, the carbon dioxide recovery efficiency decreases. On the other hand, when the flow rate of the target gas becomes too small with respect to the solution, the absolute amount of carbon dioxide that can be recovered decreases, so the energy efficiency decreases. In contrast, according to the present embodiment, since the flow rate per unit time of the gas (target gas) fed to the carbon dioxide absorption tower 21 can be maintained at an appropriate flow rate, a decrease in the carbon dioxide recovery efficiency and the energy efficiency can be prevented or suppressed.

[0090] Also, when configured such that a variable valve 15 is provided on the downstream side of the buffer tank 14, the buffer tank 14 can be made smaller compared to a configuration where a fixed throttle (fixed orifice) is provided on the downstream side of the buffer tank 14. That is, the flow rate of the gas (target gas) passing through the fixed throttle per unit time is determined according to the internal pressure of the buffer tank 14. And when the capacity of the buffer tank 14 is small, the internal pressure of the buffer tank 14 tends to fluctuate. For this reason, in order to reduce the temporal variation in the flow rate of the gas (target gas) passing through the fixed throttle per unit time, the capacity of the buffer tank 14 has to be increased. On the other hand, according to the present embodiment, since the flow rate of the gas (target gas) fed to the carbon dioxide absorption tower 21 per unit time can be adjusted by the variable valve 15, the flow rate of the gas (target gas) fed to the carbon dioxide absorption tower 21 per unit time is less affected by the internal pressure of the buffer tank 14. Therefore, even if the capacity of the buffer tank 14 is reduced, the variation in the flow rate of the gas (target gas) fed to the carbon dioxide absorption tower 21 per unit time can be reduced, so that the buffer tank 14 can be made smaller.

[0091] The carbon dioxide recovery system 10 according to the present embodiment includes a process control device 17 that controls the opening degree of the variable valve 15 so that the flow rate of the gas (target gas) fed from the buffer tank 14 to the carbon dioxide absorption tower 21 per unit time approaches a target value (target gas flow rate).

[0092] According to such a configuration, fluctuations in the carbon dioxide recovery efficiency and energy efficiency can be prevented or suppressed. For this reason, carbon dioxide can be recovered stably.

[0093] A configuration can be applied in which the target value (target gas flow rate) is a fixed value defined in advance.

[0094] According to such a configuration, a decrease and fluctuation in the carbon dioxide recovery efficiency and energy efficiency can be prevented or suppressed with simple control.

[0095] The carbon dioxide recovery system 10 according to this embodiment is disposed between the buffer tank 14 and the carbon dioxide absorption tower 21 in the gas path (target gas supply path 12), and includes a gas flow meter (target gas flow meter 16) that measures the flow rate of the gas (target gas) per unit time. The process control device 17 may be configured to set the target value (target gas flow rate) based on the moving average of the measurement result (gas flow measurement value) of the flow rate of the gas per unit time measured by the gas flow meter (target gas flow meter 16).

[0096] The process control device 17 may be configured to lower the target value (target gas flow rate) as the moving average of the flow rate (gas flow measurement value) of the gas (target gas) per unit time measured by the gas flow meter (target gas flow meter 16) decreases.

[0097] According to such a configuration, the effect of reducing the temporal variation of the flow rate per unit time of the gas (target gas) fed to the carbon dioxide absorption tower 21 can be enhanced. That is, when the moving average of the flow rate (gas flow measurement value) of the gas (target gas) per unit time becomes low, it may become impossible to prevent or suppress the flow rate of the gas (target gas) fed from the buffer tank 14 to the carbon dioxide absorption tower 21 from becoming lower than the target value (target gas flow rate). Therefore, when the moving average of the flow rate (gas flow measurement value) of the gas (target gas) fed to the carbon dioxide absorption tower 21 becomes low, the target value (target gas flow rate) is lowered according to the moving average. Thereby, it is possible to prevent or suppress the flow rate of the gas (target gas) fed from the buffer tank 14 to the carbon dioxide absorption tower 21 from becoming lower than the target value (target gas flow rate).

[0098] Furthermore, when the internal pressure of the buffer tank 14 becomes equal to or higher than a predetermined value, the configuration may be such that the target value (target gas flow rate) is increased. According to such a configuration, the effect of reducing the size of the buffer tank 14 can be enhanced. That is, if the state where the flow rate of the gas (target gas) fed from the gas source (target gas source 11) per unit time continues to be high, the amount of the target gas temporarily stored in the buffer tank 14 increases. For this reason, when the fluctuation in the flow rate of the gas (target gas) per unit time is large, it is necessary to increase the capacity of the buffer tank 14. Therefore, when the moving average of the flow rate (gas flow rate measurement value) of the gas (target gas) fed to the carbon dioxide absorption tower 21 per unit time becomes high, the flow rate of the gas fed from the buffer tank 14 to the carbon dioxide absorption tower 21 per unit time is increased according to the moving average. Thereby, since the amount of gas that must be stored in the buffer tank 14 can be reduced, the effect of reducing the size of the buffer tank 14 can be enhanced.

[0099] A configuration can be applied in which the process control device 17 sets the target value (target gas flow rate) based on a production plan indicating the operating status of the gas source (target gas source 11).

[0100] According to such a configuration, the process control device 17 can predict the temporal fluctuation in the flow rate of the target gas fed to the carbon dioxide absorption tower 21 per unit time. For this reason, the temporal fluctuation in the flow rate of the gas (target gas) per unit time can be suppressed.

[0101] The carbon dioxide recovery device 18 a heating device (reboiler 23) that heats the carbon dioxide absorption solution that has absorbed carbon dioxide in the gas (target gas) in the carbon dioxide absorption tower 21, a carbon dioxide emission tower 22 configured to emit carbon dioxide from the carbon dioxide absorption solution by the heat applied to the carbon dioxide absorption solution by the heating device (reboiler 23), A carbon dioxide absorption solution circulation section (first solution path 24, first solution pump 25, second solution path 26, and second solution pump 27) that circulates the carbon dioxide absorption solution between the carbon dioxide absorption tower 21 and the carbon dioxide emission tower 22, A recovery control device 28 that controls the heating device (reboiler 23) and the carbon dioxide absorption solution circulation section (first solution pump 25 and second solution pump 27), is provided, The recovery control device 28 controls the amount of heat applied to the carbon dioxide absorption solution by the heating device (reboiler 23) and the flow rate per unit time of the carbon dioxide absorption solution passing through the carbon dioxide absorption tower 21 by the carbon dioxide absorption solution circulation section (first solution pump 25 and second solution pump 27) based on the target value (target gas flow rate). Such a configuration can be applied.

[0102] According to such a configuration, the flow rate of the carbon dioxide absorption solution and the amount of heat per unit time applied to the carbon dioxide absorption solution by the heating device (reboiler 23) can be set to appropriate values according to the flow rate per unit time of the gas (target gas) fed to the carbon dioxide absorption tower 21. Therefore, it is possible to prevent or suppress a decrease in the carbon dioxide recovery efficiency and to prevent or suppress a decrease in the energy efficiency.

[0103] The recovery control device 28 controls the flow rate per unit time of the carbon dioxide absorption solution passing through the carbon dioxide absorption tower 21 so as to approach the L / G ratio (target L / G ratio), which is a ratio indicating the flow rate per unit time of the carbon dioxide absorption solution with respect to the flow rate per unit time of the gas (target gas) specified in advance, and controls the amount of heat applied to the carbon dioxide absorption solution by the heating device (reboiler 23) based on the flow rate per unit time of the carbon dioxide absorption solution. Such a configuration can be applied.

[0104] According to such a configuration, a liquid-gas ratio (target liquid-gas ratio) at which the carbon dioxide recovery efficiency becomes equal to or higher than the target value is specified in advance, and the flow rate of the carbon dioxide absorption solution with respect to the target gas flow rate is controlled so as to approach this target liquid-gas ratio, thereby preventing or suppressing fluctuations in the carbon dioxide recovery efficiency and the energy efficiency.

[0105] As described above, the embodiments of the present invention have been explained. However, the technical scope of the present invention is not limited to the above embodiments. The present invention can be variously modified without departing from the gist thereof, and these are also included in the technical scope of the present invention.

[0106] For example, the configuration of the recovery device 18 is not limited to the configuration shown in the above embodiment. The recovery device 18 may have a configuration including a carbon dioxide absorption tower 21 configured to bring the target gas and the carbon dioxide absorption solution into gas-liquid contact, a carbon dioxide emission tower 22 configured to emit carbon dioxide from the carbon dioxide absorption solution by the heat applied to the carbon dioxide absorption solution by a heating device, and a carbon dioxide absorption solution circulation unit configured to circulate the carbon dioxide absorption solution between the carbon dioxide absorption tower 21 and the carbon dioxide emission tower 22.

[0107] Also, the type of solution applied to the recovery device 18 is not limited. Various known solutions such as, for example, an aqueous amine solution can be applied to the solution.

[0108] In the above embodiment, the carbon dioxide concentration of the target gas is regarded as being substantially constant, and a configuration for controlling the flow rate of the target gas per unit time is shown. However, the present invention is not limited to such a configuration. For example, a configuration for controlling the flow rate of the target gas per unit time based on the carbon dioxide concentration of the target gas may be adopted. In this case, the recovery system 10 includes a carbon dioxide concentration meter for measuring the carbon dioxide concentration of the target gas, and the process control device 17 calculates the carbon dioxide concentration of the target gas from the measured value by the target gas flow meter 16 and the measured value by the carbon dioxide concentration meter. Then, the process control device 17 controls the opening degree of the variable valve 15 so that the flow rate of carbon dioxide per unit time becomes the target value.

Explanation of Symbols

[0109] 10…Carbon dioxide recovery system, 11…Target gas source, 12…Target gas supply path, 13…Target gas pump, 14…Buffer tank, 15…Variable valve, 16…Target gas flow meter, 17…Process control device, 18…Carbon dioxide recovery device, 21…Carbon dioxide absorption tower, 22…Carbon dioxide emission tower, 23…Reboiler, 24…First solution path, 25…First solution pump, 26…Second solution path, 27…Second solution pump 28…Recovery control device

Claims

1. A carbon dioxide recovery device comprising a carbon dioxide absorption tower connected via a gas path to a gas source that generates a gas containing carbon dioxide, and configured such that carbon dioxide contained in the gas fed from the gas source through the gas path is absorbed by a carbon dioxide absorption solution; A buffer tank disposed on the gas path and configured to store the gas; A variable valve disposed between the buffer tank and the carbon dioxide absorption tower in the gas path and configured to change the flow rate of the gas fed from the buffer tank to the carbon dioxide absorption tower; A carbon dioxide recovery system comprising the above.

2. The carbon dioxide recovery system according to Claim 1, further comprising a process control device configured to control the opening degree of the variable valve so that the flow rate of the gas fed from the buffer tank to the carbon dioxide absorption tower approaches a target value.

3. The carbon dioxide recovery system according to Claim 2, wherein the target value is a predefined fixed value.

4. The carbon dioxide recovery system according to Claim 2, further comprising a gas flow meter disposed between the buffer tank and the carbon dioxide absorption tower in the gas path and configured to measure the flow rate of the gas, wherein the process control device sets the target value based on the measurement result of the flow rate of the gas measured by the gas flow meter.

5. The carbon dioxide recovery system according to Claim 4, wherein the process control device lowers the target value as the moving average of the flow rate of the gas measured by the gas flow meter decreases.

6. The carbon dioxide recovery system according to Claim 2, The carbon dioxide recovery system, wherein the process control device sets the target value based on a production plan indicating the operating status of the gas source.

7. The carbon dioxide recovery system according to any one of claims 4 to 6, wherein the carbon dioxide recovery device includes a heating device that heats the carbon dioxide absorption solution that has absorbed carbon dioxide contained in the gas, a carbon dioxide emission tower configured to emit carbon dioxide from the carbon dioxide absorption solution by the heat applied to the carbon dioxide absorption solution by the heating device, a carbon dioxide absorption solution circulation unit that circulates the carbon dioxide absorption solution between the carbon dioxide absorption tower and the carbon dioxide emission tower, a recovery control device that controls the heating device and the carbon dioxide absorption solution circulation unit, and is provided with wherein the recovery control device controls the amount of heat applied to the carbon dioxide absorption solution by the heating device or the flow rate of the carbon dioxide absorption solution passing through the carbon dioxide absorption tower by the carbon dioxide absorption solution circulation unit based on the target value.

8. The carbon dioxide recovery system according to claim 7, wherein the recovery control device controls the flow rate of the carbon dioxide absorption solution passing through the carbon dioxide absorption tower so as to approach the L / G ratio, which is a ratio indicating the flow rate of the carbon dioxide absorption solution with respect to the flow rate of the gas defined in advance, and controls the amount of heat applied to the carbon dioxide absorption solution by the heating device based on the flow rate of the carbon dioxide absorption solution.

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