Carbon dioxide recovery system and method for operating carbon dioxide recovery system

Abstract

Provided is a carbon dioxide recovery system capable of reducing the possibility of occurrence of a phenomenon in which, when the circulation amount of an absorption liquid increases, the absorption liquid toward a release tower is not sufficiently heated or the temperature of the absorption liquid is not increased. The carbon dioxide recovery system comprises: a heat exchanger (30); and a reservoir device (40) that extracts, from the release tower (20), an absorption liquid from which at least a portion of carbon dioxide has been released, retains the extracted absorption liquid while heating the absorption liquid to a temperature higher than the temperature of the absorption liquid flowing from an absorption tower (10) to the release tower (20), and supplies the retained absorption liquid to the heat exchanger (30) without going through the release tower (20).

Description

Carbon dioxide capture system and method for operating the carbon dioxide capture system

[0001] The present disclosure relates to carbon dioxide capture systems and methods of operating carbon dioxide capture systems.

[0002] Plants such as thermal power plants and boiler facilities use cheap coal as fuel, and carbon dioxide (CO2) emissions contained in exhaust gases are becoming a problem. In addition, with the trend toward decarbonization, not only are CO2 emissions being reduced, but systems that capture the generated CO2 (carbon dioxide capture systems) are being installed in plants.

[0003] For example, a carbon dioxide capture system brings exhaust gas into contact with an amine-based absorbent in an absorption tower, causing the absorbent to absorb CO2 and produce a rich solution (an absorbent with a relatively high CO2 content). The carbon dioxide capture system also supplies the produced rich solution to a stripper tower, where it heats the rich solution to release the CO2 contained in the rich solution and produce a lean solution (an absorbent with a relatively low CO2 content). The carbon dioxide capture system then circulates the absorbent by supplying the lean solution to the absorption tower. At this time, a heat exchanger included in the carbon dioxide capture system heats the rich solution supplied from the absorption tower to the stripper tower with the lean solution returned from the stripper tower to the absorption tower, thereby promoting the stripping of carbon dioxide in the stripper tower. Related technology is disclosed in Patent Document 1.

[0004] JP 2016-187796 A

[0005] When the amount of exhaust gas emitted varies little, the amount of absorbent circulated between the absorption tower and the stripper tower can be approximately constant and presents no problem. However, for example, if the plant load increases and the amount of exhaust gas emitted increases, maintaining the amount of absorbent circulated may result in insufficient absorption of CO2 in the absorption tower or insufficient dissipation of CO2 in the stripper tower, and therefore the amount of absorbent circulated must be increased. However, if the amount of absorbent circulated increases suddenly, there is a possibility that the absorbent supplied to the stripper tower may not be sufficiently heated / heated by the heat exchanger. If such a phenomenon occurs, there is a possibility that the stripper tower may not be able to sufficiently dissipate CO2, and furthermore, the absorbent in the absorption tower may not be able to sufficiently absorb CO2.

[0006] The present disclosure has been made in consideration of the above circumstances, and aims to provide a carbon dioxide capture system and an operating method for a carbon dioxide capture system that can reduce the possibility of a phenomenon occurring in which the absorption liquid heading to the stripping tower is not sufficiently heated / increased in temperature when the amount of circulation of the absorption liquid increases.

[0007] In order to solve the above problems, the carbon dioxide capture system and the operating method of the carbon dioxide capture system of the present disclosure employ the following measures.

[0008] A carbon dioxide capture system according to one aspect of the present disclosure includes a heat exchanger that heats the absorption liquid flowing from an absorption tower, which absorbs carbon dioxide contained in a gas to be treated into an absorption liquid, to a stripper tower, which strips the carbon dioxide from the absorption liquid, using the absorption liquid flowing from the stripper tower to the absorption tower; and a storage device that removes the absorption liquid from which at least a portion of the carbon dioxide has been stripped from the stripper tower, stores the removed absorption liquid while heating it to a temperature higher than the temperature of the absorption liquid flowing from the absorption tower to the stripper tower, and supplies the stored absorption liquid to the heat exchanger without passing through the stripper tower.

[0009] A method for operating a carbon dioxide capture system according to one aspect of the present disclosure is a method for operating a carbon dioxide capture system that is equipped with a heat exchanger that heats the absorption liquid flowing from an absorption tower, which absorbs carbon dioxide contained in a gas to be treated into an absorption liquid, to a stripper tower, which strips the carbon dioxide from the absorption liquid, with the absorption liquid flowing from the stripper tower to the absorption tower, in which the absorption liquid from which at least a portion of the carbon dioxide has been stripped is removed from the stripper tower, and the removed absorption liquid is stored while being heated to a temperature higher than the temperature of the absorption liquid flowing from the absorption tower to the stripper tower, and the stored absorption liquid is supplied to the heat exchanger without passing through the stripper tower.

[0010] According to the present disclosure, it is possible to reduce the possibility of a phenomenon occurring in which the absorption liquid heading to the stripper tower is not sufficiently heated / increased in temperature when the circulation amount of the absorption liquid is increased.

[0011] 1 is a schematic configuration diagram of a carbon dioxide capture system according to an embodiment of the present disclosure. 2 is a schematic configuration diagram of a carbon dioxide capture system according to a modified example of an embodiment of the present disclosure.

[0012] Hereinafter, a carbon dioxide capture system and an operating method of the carbon dioxide capture system according to an embodiment of the present disclosure will be described with reference to the drawings.

[0013] [Overall Configuration] As shown in FIG. 1 , the carbon dioxide capture system 1 includes an absorption tower 10, a stripper tower 20, a heat exchanger 30, a storage device 40, and lines connecting these pieces of equipment.

[0014] The absorption tower 10 is a facility for chemically absorbing carbon dioxide contained in exhaust gas (gas to be treated) into an amine-based absorption liquid (hereinafter referred to as "absorption liquid"). The lower / bottom portion of the absorption tower 10 is a rich solution tank portion 11 in which a rich solution (absorption liquid that has absorbed carbon dioxide) is stored.

[0015] An exhaust gas discharge line L1 is connected to the lower part of the absorption tower 10 and above the rich solution tank section 11. The exhaust gas discharge line L1 is a line that supplies exhaust gas discharged from a plant such as a thermal power plant or a boiler plant to the absorption tower 10.

[0016] An exhaust gas cooler 91 is provided in the exhaust gas discharge line L1. The exhaust gas cooler 91 is a device that reduces the temperature of the exhaust gas flowing through the exhaust gas discharge line L1 to a temperature optimal for chemical absorption performed in the absorption tower 10. An example of the cooling medium is on-site cooling water used in various parts of the plant.

[0017] The stripper tower 20 is a facility for releasing carbon dioxide from the rich solution. The lower / bottom portion of the stripper tower 20 is a lean solution tank portion 21 in which a lean solution (absorption solution from which carbon dioxide has been released) is stored. The lean solution is an absorption solution that has a relatively lower carbon dioxide content than the rich solution. In other words, the rich solution is an absorption solution that has a relatively higher carbon dioxide content than the lean solution.

[0018] The rich solution tank section 11 of the absorption tower 10 and the upper part of the stripper tower 20 are connected by a rich solution line (feed line) L12, and the rich solution stored in the rich solution tank section 11 is supplied to the stripper tower 20.

[0019] A rich solution supply unit 22 is connected to an end of the rich solution line L12. The rich solution supply unit 22 is a unit that injects the rich solution supplied from the absorption tower 10 into the stripper tower 20, and is provided at the upper part of the stripper tower 20. The rich solution injected from the rich solution supply unit 22 descends inside the stripper tower 20, and in the process of descending, is heated by steam (described later) generated in the reboiler 61, thereby releasing at least a portion of the carbon dioxide.

[0020] A rich solution pump 81 and a rich solution valve 83 are provided along the rich solution line L12. The rich solution pump 81 is a pump for sending the rich solution stored in the rich solution tank section 11 to the stripper tower 20. The rich solution pump 81 is provided at a location on the rich solution line L12 upstream of the heat exchanger 30. The rich solution valve 83 is a valve for changing the flow rate of the rich solution supplied to the stripper tower 20 (rich solution supply section 22). The rich solution valve 83 is provided at a location on the rich solution line L12 downstream of the heat exchanger 30. The rotation speed of the rich solution pump 81 and the opening degree of the rich solution valve 83 are determined and adjusted by the control unit 2. The flow rate of the rich solution supplied to the stripper tower 20 (rich solution supply section 22) may be changed by changing the rotation speed of the rich solution pump 81. In this case, the rich solution valve 83 can be omitted, or there is no need to adjust the opening degree of the rich solution valve 83 (for example, it is always fully open).

[0021] The control unit 2 is composed of, for example, a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), and a computer-readable storage medium. A series of processes for realizing various functions is stored in a storage medium, for example, in the form of a program. The CPU reads this program into the RAM and executes information processing and arithmetic operations to realize various functions. The program may be pre-installed in a ROM or other storage medium, provided in a state stored in a computer-readable storage medium, or distributed via wired or wireless communication means. Examples of computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories.

[0022] The lean solution tank section 21 of the stripper tower 20 and the upper part of the absorber tower 10 are connected by a lean solution line (return line) L21, and the lean solution stored in the lean solution tank section 21 is supplied to the absorber tower 10.

[0023] An end of the lean solution line L21 is connected to the lean solution supply unit 12. The lean solution supply unit 12 is a part that injects the lean solution supplied from the stripper tower 20 into the absorption tower 10, and is provided at the upper part of the absorption tower 10. The lean solution injected from the lean solution supply unit 12 descends inside the absorption tower 10, and in the process of descending, comes into contact with the flue gas supplied from the flue gas discharge line L1, thereby absorbing carbon dioxide.

[0024] A lean solution pump 71, a lean solution cooler 72, and a lean solution valve 73 are provided along the lean solution line L21. The lean solution pump 71 is a pump for sending the lean solution stored in the lean solution tank unit 21 to the absorber 10. The lean solution pump 71 is provided at a location on the lean solution line L21 downstream of the heat exchanger 30. The lean solution cooler 72 is a device for lowering the temperature of the lean solution flowing through the lean solution line L21 to a temperature optimum for chemical absorption performed in the absorber 10. An example of the cooling medium is on-site cooling water. The lean solution cooler 72 is provided at a location on the lean solution line L21 downstream of the lean solution pump 71. The lean solution valve 73 is a valve for changing the flow rate of the lean solution supplied to the absorber 10 (lean solution supply unit 12). The lean solution valve 73 is provided at a location on the lean solution line L21 downstream of the lean solution cooler 72. The rotation speed of the lean solution pump 71 and the opening degree of the lean solution valve 73 are determined and adjusted by the control unit 2. The flow rate of the lean solution supplied to the absorption tower 10 (lean solution supply unit 12) may be changed by changing the rotation speed of the lean solution pump 71. In this case, the lean solution valve 73 can be omitted, or there is no need to adjust the opening degree of the lean solution valve 73 (for example, it is always fully open).

[0025] A heat exchanger 30 is provided midway along the rich solution line L12 and the lean solution line L21. The heat exchanger 30 is a device that uses the lean solution (the absorption liquid flowing from the stripper 20 to the absorber 10) flowing through the lean solution line L21 as a heat source to heat the rich solution (the absorption liquid flowing from the absorber 10 to the stripper 20) flowing through the rich solution line L12. By heating the rich solution with the heat exchanger 30, the temperature of the rich solution can be increased to a temperature close to the optimum temperature for carbon dioxide stripping in the stripper 20, thereby facilitating carbon dioxide stripping in the stripper 20. Conversely, by cooling the lean solution with the heat exchanger 30, the temperature of the lean solution can be decreased to a temperature close to the optimum temperature for carbon dioxide chemical absorption in the absorber 10, thereby facilitating carbon dioxide chemical absorption in the absorber 10. Note that, since the heat exchanger 30 alone may not be able to sufficiently cool the lean solution, the aforementioned lean solution cooler 72 is provided at a location on the lean solution line L21 downstream of the heat exchanger 30.

[0026] A storage device 40 is provided below the stripper tower 20. The storage device 40 is a device that extracts the lean solution from the stripper tower 20, stores the extracted lean solution while heating it to a predetermined temperature or higher, and, in a predetermined case, supplies the stored lean solution to a heat exchanger 30 (described later) without passing through the stripper tower 20. Details of the storage device 40 will be described later.

[0027] A reboiler 61 is provided at the bottom of the stripper tower 20. The reboiler 61 is a device independent of the storage device 40, and its function differs from that of the storage device 40. The reboiler 61 is a device that generates steam by heating and raising the temperature of a portion of the lean solution stored in the lean solution tank section 21 of the stripper tower 20 using steam or the like supplied from an external facility (for example, a plant such as a thermal power plant or a boiler facility) as a heat source, and supplies the heated lean solution and the generated steam to the stripper tower 20. The steam supplied to the stripper tower 20 is used to heat the rich solution, and the rich solution releases at least a portion of carbon dioxide by being heated.

[0028] [Configuration of the storage device] The storage device 40 is a device that extracts lean solution from the stripper tower 20, stores the extracted lean solution while heating it to a predetermined temperature or higher, and supplies the stored lean solution to the heat exchanger 30 without passing through the stripper tower 20 in a predetermined case.

[0029] The storage device 40 includes a buffer tank 41, an extraction valve 43, a supply pump 44, a supply valve 45, an extraction line L41, and a supply line L42.

[0030] The buffer tank 41 is a tank (container) that stores the lean solution extracted from the stripping tower 20 .

[0031] The buffer tank 41 is connected to the lean solution tank section 21 of the stripper tower 20 via an extraction line L41. This makes it possible to extract the lean solution from the lean solution tank section 21 and supply the extracted lean solution to the buffer tank 41.

[0032] The buffer tank 41 is connected to the lean solution line L21 (a portion of the lean solution line L21 upstream of the heat exchanger 30) via a supply line L42. That is, the buffer tank 41 is connected to the heat exchanger 30 via the supply line L42 and the lean solution line L21. This makes it possible to supply the lean solution stored in the buffer tank 41 to the heat exchanger 30. The supply line L42 directly connects the buffer tank 41 and the lean solution line L21, and does not pass through the lean solution tank portion 21 of the stripper tower 20.

[0033] The buffer tank 41 is provided with a heater 42. The heater 42 is configured to heat the lean solution stored in the buffer tank 41. As a result, the lean solution is stored at a temperature equal to or higher than a predetermined temperature. Examples of the heater 42 include an electric heater and a heater using steam as a heat source. The predetermined temperature is a temperature that can sufficiently heat at least the rich solution in the heat exchanger 30. For example, the predetermined temperature is a temperature higher than the temperature of the absorption solution flowing from the absorption tower 10 to the stripper tower 20, a temperature higher than the temperature of the absorption solution flowing from the stripper tower 20 to the heat exchanger 30, and a temperature higher than the absorption solution stored in the lean solution tank 21 of the stripper tower 20. However, from the viewpoint of sufficiently and efficiently heating the rich solution in the heat exchanger 30, the predetermined temperature is preferably a temperature higher than the temperature of the absorption solution flowing from the stripper tower 20 to the heat exchanger 30 and a temperature higher than the temperature of the absorption solution stored in the lean solution tank 21 of the stripper tower 20. The output of the heater 42 is determined and adjusted by the control unit 2. The control unit 2, for example, acquires the temperature of the lean solution stored in the buffer tank 41 using a temperature sensor (not shown) and adjusts the output of the heater 42 so as to maintain the temperature of the lean solution at a predetermined temperature.

[0034] An extraction valve 43 is provided in the extraction line L41. The extraction valve 43 is a valve for changing the flow rate of the lean solution supplied from the lean solution tank section 21 of the stripper tower 20 to the buffer tank 41. The opening degree of the extraction valve 43 is determined and adjusted by the control unit 2. For example, the control unit 2 acquires the liquid level of the lean solution stored in the lean solution tank section 21 of the stripper tower 20 using a level meter (not shown) and adjusts the opening degree of the extraction valve 43 so as to maintain the liquid level within a predetermined range. Note that a pump for sending the lean solution from the lean solution tank section 21 of the stripper tower 20 to the buffer tank 41 may be provided in the extraction line L41. The rotation speed of this pump is determined and adjusted by the control unit 2 based on at least one of the liquid level of the lean solution and the opening degree of the extraction valve 43. However, by installing the buffer tank 41 below the lean solution tank section 21 of the stripping tower 20, the lean solution can be sent without providing a pump.

[0035] A supply pump 44 and a supply valve 45 are provided along the supply line L42. The supply pump 44 is a pump for sending the lean solution stored in the buffer tank 41 to the lean solution line L21 and, ultimately, to the heat exchanger 30. The supply valve 45 is a valve for changing the flow rate of the lean solution supplied to the lean solution line L21 (heat exchanger 30). The supply valve 45 is provided at a location on the supply line L42 downstream of the supply pump 44. The rotation speed of the supply pump 44 and the aperture of the supply valve 45 are determined and adjusted by the control unit 2 based on, for example, the amount of circulating absorption solution corresponding to the plant load (i.e., the amount of exhaust gas discharged). Note that the flow rate of the lean solution supplied to the lean solution line L21 (heat exchanger 30) may be changed by changing the rotation speed of the supply pump 44. In this case, the supply valve 45 can be omitted, or there is no need to adjust the aperture of the supply valve 45 (for example, it is always fully open).

[0036] [Regarding Operation of the Carbon Dioxide Capture System] In the carbon dioxide capture system 1 configured as described above, the absorbing solution circulates between the absorption tower 10 and the stripper tower 20. The circulating flow of the absorbing solution is formed, for example, by the lean solution pump 71 and the rich solution pump 81. Therefore, the amount of the circulating absorbing solution is adjusted by the rotation speed of the lean solution pump 71 and the rotation speed of the rich solution pump 81.

[0037] The rich solution stored in the rich solution tank section 11 of the absorption tower 10 is led to the stripper tower 20 via the rich solution line L12. At this time, the rich solution is heated by the lean solution (the absorption liquid flowing from the stripper tower 20 to the absorption tower 10) as it passes through the heat exchanger 30 provided in the rich solution line L12, and the temperature of the rich solution increases. As the temperature of the rich solution increases, the stripper tower 20 promotes the stripping of carbon dioxide.

[0038] The rich solution introduced into the stripper tower 20 is injected into the stripper tower 20 from the rich solution supply unit 22. The injected rich solution descends within the stripper tower 20, and in the process of descending, is heated by steam generated in the reboiler 61 and rising within the stripper tower 20, thereby releasing at least a portion of the carbon dioxide, and is stored as a lean solution in the lean solution tank unit 21 located at the lower / bottom portion of the stripper tower 20. The released carbon dioxide is taken out from the top of the stripper tower 20, subjected to predetermined treatment in equipment not shown, and then stored in equipment not shown or utilized in equipment not shown.

[0039] The lean solution stored in the lean solution tank section 21 is introduced to the absorber 10 via the lean solution line L21. At this time, the lean solution is cooled by the rich solution (the absorption liquid flowing from the absorber 10 to the stripper 20) and its temperature is lowered as it passes through the heat exchanger 30 provided in the lean solution line L21. Furthermore, the lean solution is further cooled and its temperature is lowered as it passes through the lean solution cooler 72. As the temperature of the lean solution is lowered, the chemical absorption of carbon dioxide in the absorber 10 is promoted.

[0040] The lean solution introduced into the absorption tower 10 is injected into the absorption tower 10 from a lean solution supply unit 12. The injected lean solution descends within the absorption tower 10 and, in the process of descending, comes into contact with the flue gas introduced into the absorption tower 10 via the flue gas discharge line L1 and ascending within the absorption tower 10, thereby chemically absorbing carbon dioxide, and is stored as a rich solution in a rich solution tank unit 11 located at the lower / bottom portion of the absorption tower 10. The flue gas (treated gas) from which carbon dioxide has been removed is taken out from the top of the stripper tower 20.

[0041] This process is then repeated to continuously treat exhaust gas emitted from plants such as thermal power plants and boiler facilities.

[0042] However, there may be cases where the plant load increases suddenly, resulting in a sudden increase in the amount of exhaust gas emissions. In this case, maintaining the circulation rate of the absorption liquid may result in insufficient chemical absorption in the absorption tower 10 or in insufficient stripping of carbon dioxide in the stripping tower 20, and therefore it is necessary to increase the circulation rate of the absorption liquid. The circulation rate of the absorption liquid is adjusted by the rotation speed of the lean solution pump 71 and the rotation speed of the rich solution pump 81. The rotation speeds of the lean solution pump 71 and the rich solution pump 81 are determined and adjusted by the control unit 2, for example, depending on the plant load (i.e., the amount of exhaust gas emissions). If the circulation rate of the absorption liquid increases suddenly, a phenomenon may occur in which the absorption liquid heading to the stripping tower 20 is not sufficiently heated / heated by the heat exchanger 30. Therefore, the carbon dioxide capture system 1 according to this embodiment is provided with a storage device 40.

[0043] The buffer tank 41 of the storage device 40 constantly stores lean solution at a predetermined temperature or higher. When the amount of absorption solution circulating between the absorption tower 10 and the stripper tower 20 is constant, the supply pump 44 is stopped and the supply valve 45 is closed to prevent the high-temperature lean solution stored in the buffer tank 41 from being supplied to the lean solution line L21. On the other hand, when the amount of absorption solution circulating between the absorption tower 10 and the stripper tower 20 increases, the supply valve 45 is opened and the supply pump 44 is operated to supply the high-temperature lean solution stored in the buffer tank 41 to the heat exchanger 30 via the lean solution line L21. This allows the absorption solution heading to the stripper tower 20 to be sufficiently heated quickly.

[0044] [Effects of this embodiment] The carbon dioxide capture system 1 according to this embodiment has the following effects.

[0045] The storage device 40 is provided, which extracts the absorption liquid from which at least a portion of the carbon dioxide has been stripped from the stripper tower 20, stores the extracted absorption liquid while heating it to a temperature higher than the temperature of the absorption liquid traveling from the absorption tower 10 to the stripper tower 20, and supplies the stored absorption liquid to the heat exchanger 30 without passing through the stripper tower 20. Therefore, when the circulation amount of the absorption liquid is increased in accordance with an increase in the amount of exhaust gas discharged due to an increase in the plant load, for example, the stored high-temperature absorption liquid can be supplied to the heat exchanger 30, thereby making it possible to quickly and sufficiently heat the absorption liquid traveling to the stripper tower 20. This reduces the possibility of the absorption liquid not being sufficiently heated / not being heated when the circulation amount of the absorption liquid is increased.

[0046] In addition, the storage device 40 has a buffer tank 41 for storing the absorption liquid, an extraction line L41 for guiding the absorption liquid from the stripper tower 20 to the buffer tank 41, a supply line L42 for guiding the absorption liquid from the buffer tank 41 to the heat exchanger 30, and a heater 42 for heating the absorption liquid stored in the buffer tank 41.Therefore, it is possible to extract a portion of the absorption liquid from which at least a portion of the carbon dioxide has been stripped from the stripper tower 20, store the extracted absorption liquid at a temperature higher than the temperature of the absorption liquid traveling from the absorption tower 10 to the stripper tower 20, and supply the stored absorption liquid to the heat exchanger 30 without passing through the stripper tower 20.

[0047] In addition, the control unit 2 determines the opening degree of the extraction valve 43 based on the liquid level of the absorption liquid stored in the lower part of the stripping tower 20, so that the amount of absorption liquid introduced into the buffer tank 41 can be changed in accordance with fluctuations in the liquid level, making it easy to control the liquid level of the absorption liquid stored in the lower part of the stripping tower 20.

[0048] Furthermore, since the storage device 40 has a supply pump 44 provided on the supply line L42, the absorption liquid can be efficiently supplied from the buffer tank 41.

[0049] In addition, since the control unit 2 determines the rotation speed of the supply pump 44 according to the amount of exhaust gas discharged, the flow rate of the high-temperature absorption liquid stored in the tank can be made to quickly follow the increase in the circulation amount of the absorption liquid in response to the increase in the amount of gas discharged to be treated.

[0050] In addition, the control unit 2 determines at least one of the rotation speed of the supply pump 44 and the opening degree of the supply valve 45 according to the amount of exhaust gas discharged, so that the supply amount of high-temperature absorption liquid stored in the buffer tank 41 can be made to quickly follow the increase in the circulation amount of absorption liquid in response to the increase in the amount of exhaust gas discharged.

[0051] [Variation 1] As shown in FIG. 2, the rich solution line L12 of the carbon dioxide capture system 1 according to Variation 1 branches downstream of the rich solution pump 81. In FIG. 2, the rich solution line L12 branches into three lines. A rich solution valve 83 is provided in each branched rich solution line L12. The control unit 2 adjusts the aperture of each rich solution valve 83 according to the total amount of rich solution flowing through the rich solution line L12. For example, when the circulating amount of the absorbent is small, the absorbent flows only through some, but not all, of the rich solution lines L12. When the circulating amount of the absorbent is large, the absorbent flows through all of the rich solution lines L12. This suppresses fluctuations in the flow rate of the absorbent flowing through each rich solution line L12, and maintains the speed of the absorbent sprayed from the rich solution supply unit 22 and descending within the stripper tower 20 within an optimal range for carbon dioxide release.

[0052] The rich solution line L12 may branch at a location downstream of the heat exchanger 30. When the rich solution line L12 branches at a location downstream of the rich solution pump 81 and multiple rich solution lines L12 pass through the heat exchanger 30, the control unit 2 adjusts the aperture of each rich solution valve 83. For example, when the circulating amount of the absorbent is low, the absorbent flows through only some of the rich solution lines L12, not all of them, and when the circulating amount of the absorbent is high, the absorbent flows through all of the rich solution lines L12. This suppresses fluctuations in the flow rate of the absorbent flowing through each rich solution line L12 passing through the heat exchanger 30, and maintains the speed of the absorbent flowing through each rich solution line L12 within the heat exchanger 30 within an optimal speed range for heat exchange. To finely adjust the flow rate of the absorbent flowing through each rich solution line L12 passing through the heat exchanger 30, a separate valve may be provided in each rich solution line L12 upstream of the heat exchanger 30. The aperture of the valve is determined and adjusted by the control unit 2.

[0053] [Variation 2] The lean solution line L21 of the carbon dioxide capture system 1 according to Variation 2 branches downstream of the lean solution cooler 72. In the example shown in FIG. 2, the lean solution line L21 branches into three lines. A lean solution valve 73 is provided in each of the branched lean solution lines L21. The control unit 2 adjusts the aperture of the lean solution valve 73 depending on the total amount of lean solution flowing through the lean solution line L21. For example, when the amount of circulating absorbent is small, the absorbent flows through only some of the lean solution lines L21, but not all of them. When the amount of circulating absorbent is large, the absorbent flows through all of the lean solution lines L21. This reduces fluctuations in the flow rate of the absorbent flowing through each lean solution line L21, and maintains the speed of the absorbent sprayed from the lean solution supply unit 12 and descending within the absorber 10 within an optimal range for chemical absorption of carbon dioxide.

[0054] [Additional Note] The carbon dioxide capture system 1 and the operating method of the carbon dioxide capture system 1 according to one embodiment of the present disclosure described above can be understood, for example, as follows.

[0055] A carbon dioxide capture system (1) according to a first aspect of the present disclosure includes a heat exchanger (30) that heats, with the absorption liquid flowing from the stripper tower (20) to the absorption tower (10), the absorption liquid from which at least a portion of the carbon dioxide has been stripped, and a storage device (40) that extracts the absorption liquid from which at least a portion of the carbon dioxide has been stripped from the stripper tower (20), stores the extracted absorption liquid while heating it to a temperature higher than the temperature of the absorption liquid flowing from the absorption tower (10) to the stripper tower (20), and supplies the stored absorption liquid to the heat exchanger (30) without passing through the stripper tower (20).

[0056] The storage device (40) extracts the absorption liquid from which at least a portion of the carbon dioxide has been stripped from the stripper tower (20), stores the extracted absorption liquid while heating it to a temperature higher than the temperature of the absorption liquid flowing from the absorption tower (10) to the stripper tower (20), and supplies the stored absorption liquid to the heat exchanger (30) without passing through the stripper tower (20). Therefore, when the circulation amount of the absorption liquid is increased in accordance with an increase in the amount of discharge of gas to be treated due to an increase in the plant load, for example, the stored high-temperature absorption liquid can be supplied to the heat exchanger (30), thereby enabling sufficient heating of the absorption liquid flowing to the stripper tower (20) to be quickly performed. This reduces the possibility of the phenomenon occurring in which the absorption liquid is not sufficiently heated / increased in temperature when the circulation amount of the absorption liquid is increased.

[0057] In the carbon dioxide capture system (1) according to the second aspect of the present disclosure, in the first aspect, the temperature of the absorption liquid stored in the storage device (40) is higher than the temperature of the absorption liquid flowing from the stripper tower (20) to the heat exchanger (30) or higher than the temperature of the absorption liquid stored in the bottom (21) of the stripper tower (20).

[0058] The temperature of the absorption liquid stored in the storage device (40) is set to a temperature higher than the temperature of the absorption liquid flowing from the stripper (20) to the heat exchanger (30) or higher than the temperature of the absorption liquid stored in the bottom (21) of the stripper (20), so that the absorption liquid can be heated sufficiently and efficiently in the heat exchanger (30).

[0059] In the carbon dioxide capture system (1) according to a third aspect of the present disclosure, in the first or second aspect, the storage device (40) includes a tank (41) for storing an absorption liquid, an extraction line (L41) for guiding the absorption liquid from the stripper tower (20) to the tank (41), a supply line (L42) for guiding the absorption liquid from the tank (41) to the heat exchanger (30), and a heater (42) for heating the absorption liquid stored in the tank (41).

[0060] The storage device (40) includes a tank (41) for storing the absorption liquid, an extraction line (L41) for guiding the absorption liquid from the stripper tower (20) to the tank (41), a supply line (L42) for guiding the absorption liquid from the tank (41) to the heat exchanger (30), and a heater (42) for heating the absorption liquid stored in the tank (41). Therefore, a part of the absorption liquid from which at least a part of the carbon dioxide has been stripped is extracted from the stripper tower (20), and the extracted absorption liquid is stored at a temperature higher than the temperature of the absorption liquid flowing from the absorption tower (10) to the stripper tower (20), and the stored absorption liquid can be supplied to the heat exchanger (30) without passing through the stripper tower (20).

[0061] The carbon dioxide capture system (1) according to the fourth aspect of the present disclosure is the third aspect, and includes a control unit (2), wherein the storage device (40) has a valve (43) provided in the extraction line (L41), and the control unit (2) determines the opening degree of the valve (43) based on the liquid level of the absorption liquid stored in the lower part of the stripper tower (20).

[0062] The control unit (2) determines the opening degree of the valve (43) based on the liquid level of the absorption liquid stored in the lower part of the stripping tower (20), and therefore, the amount of absorption liquid introduced into the tank (41) can be changed in accordance with fluctuations in the liquid level, making it easy to control the liquid level of the absorption liquid stored in the lower part of the stripping tower (20).

[0063] A carbon dioxide capture system (1) according to a fifth aspect of the present disclosure is any one of the second to fourth aspects, wherein the storage device (40) has a pump (44) provided in the supply line (L42).

[0064] The storage device (40) has a pump (44) provided in the supply line (L42), so that the absorption liquid can be efficiently supplied from the tank (41).

[0065] The carbon dioxide capture system (1) according to the sixth aspect of the present disclosure is the fifth aspect, and is provided with a control unit (2), and the control unit (2) determines the rotation speed of the pump (44) according to the emission amount of the gas to be treated.

[0066] The control unit (2) determines the rotation speed of the pump (44) according to the discharge amount of the gas to be treated, and therefore the supply amount of the high-temperature absorption liquid stored in the tank (41) can be made to quickly follow the increase in the circulation amount of the absorption liquid in response to the increase in the discharge amount of the gas to be treated.

[0067] The carbon dioxide capture system (1) according to the seventh aspect of the present disclosure is the fifth aspect, and includes a control unit (2), wherein the storage device (40) has a valve (45) provided in the supply line (L42), and the control unit (2) determines at least one of the rotation speed of the pump (44) and the opening degree of the valve (45) according to the discharge amount of the gas to be treated.

[0068] The control unit (2) determines at least one of the rotation speed of the pump (44) and the opening degree of the valve (45) according to the discharge amount of the gas to be treated, and therefore the supply amount of the high-temperature absorption liquid stored in the tank (41) can be made to quickly follow the increase in the circulation amount of the absorption liquid corresponding to the increase in the discharge amount of the gas to be treated.

[0069] A carbon dioxide capture system (1) according to an eighth aspect of the present disclosure is in any of the first to seventh aspects, and includes a control unit (2), a plurality of return lines (L21) that guide the absorption liquid to the absorption tower (10), and a valve (73) provided in each of the return lines (L21), and the control unit (2) determines the opening degree of each of the valves (73) in accordance with the total amount of the absorption liquid guided to the absorption tower (10).

[0070] The absorber (10) includes a plurality of return lines (L21) that guide the absorbing liquid to the absorber (10) and a valve (73) provided in each return line (L21), and the control unit (2) determines the opening degree of each valve (73) according to the total amount of the absorbing liquid guided to the absorber (10), thereby suppressing fluctuations in the flow rate of the absorbing liquid flowing through each return line (L21). For example, when the circulation amount of the absorbing liquid is small, the absorbing liquid is caused to flow only through some, but not all, of the return lines (L21), and when the circulation amount of the absorbing liquid is large, the absorbing liquid is caused to flow through all of the return lines (L21), thereby suppressing fluctuations in the flow rate of the absorbing liquid flowing through each return line (L21). This makes it possible to maintain the speed of the absorbing liquid descending in the absorber (10) within an optimum range for the chemical absorption of carbon dioxide.

[0071] The carbon dioxide capture system (1) according to a ninth aspect of the present disclosure, in the first to eighth aspects, includes a control unit (2), a plurality of forward lines (L12) that guide the absorption liquid to the stripper tower (20), and a valve (83) provided in each of the forward lines (L12), and the control unit (2) determines the opening degree of each of the valves (83) according to the total amount of the absorption liquid guided to the stripper tower (20).

[0072] The system includes a plurality of feed lines (L12) that guide the absorbing liquid to the stripper tower (20) and a valve (83) provided in each feed line (L12), and the control unit (2) determines the opening degree of each valve (83) according to the total amount of the absorbing liquid guided to the stripper tower (20), thereby suppressing fluctuations in the flow rate of the absorbing liquid flowing through each feed line (L12). For example, when the circulation amount of the absorbing liquid is small, the absorbing liquid is caused to flow only through some, but not all, of the feed lines (L12), and when the circulation amount of the absorbing liquid is large, the absorbing liquid is caused to flow through all of the feed lines (L12), thereby suppressing fluctuations in the flow rate of the absorbing liquid flowing through each feed line (L12). This makes it possible to maintain the speed of the absorbing liquid descending in the stripper tower (20) within an optimal range for releasing carbon dioxide.

[0073] A carbon dioxide capture system (1) according to a tenth aspect of the present disclosure is the ninth aspect, wherein the plurality of forward lines (L12) pass through the heat exchanger (30).

[0074] Since the plurality of forward lines (L12) pass through the heat exchanger (30), fluctuations in the flow rate of the absorbing liquid flowing through each of the forward lines (L12) passing through the heat exchanger (30) can be suppressed. For example, when the circulation rate of the absorbing liquid is small, the absorbing liquid is caused to flow through only some of the forward lines (L12) but not all of them, and when the circulation rate of the absorbing liquid is large, the absorbing liquid is caused to flow through all of the forward lines (L12), thereby suppressing fluctuations in the flow rate of the absorbing liquid flowing through each of the forward lines (L12) passing through the heat exchanger (30). This makes it possible to maintain the speed of the absorbing liquid flowing through each of the forward lines (L12) inside the heat exchanger (30) within a speed range optimal for heat exchange.

[0075] A method for operating a carbon dioxide capture system (1) according to an eleventh aspect of the present disclosure is a method for operating a carbon dioxide capture system (1) including a heat exchanger (30) that heats, with absorption liquid flowing from an absorption tower (10), which absorbs carbon dioxide contained in a gas to be treated, to a stripper tower (20), which strips the carbon dioxide from the absorption liquid, the absorption liquid flowing from the stripper tower (20) to the absorption tower (10), in which the absorption liquid from which at least a portion of the carbon dioxide has been stripped is extracted from the stripper tower (20), and the extracted absorption liquid is stored while being heated to a temperature higher than the temperature of the absorption liquid flowing from the absorption tower (10) to the stripper tower (20), and the stored absorption liquid is supplied to the heat exchanger (30) without passing through the stripper tower (20).

[0076] REFERENCE SIGNS LIST 1 Carbon dioxide capture system 2 Control unit 10 Absorption tower 11 Rich solution tank unit 12 Lean solution supply unit 20 Stripper tower 21 Lean solution tank unit 22 Rich solution supply unit 30 Heat exchanger 40 Storage device 41 Buffer tank (tank) 42 Heater 43 Extraction valve 44 Supply pump 45 Supply valve 61 Reboiler 71 Lean solution pump 72 Lean solution cooler 73 Lean solution valve 81 Rich solution pump 83 Rich solution valve 91 Exhaust gas cooler L1 Exhaust gas discharge line L12 Rich solution line (forward line) L21 Lean solution line (return line) L41 Extraction line L42 Supply line

Claims

1. A carbon dioxide recovery system comprising: a heat exchanger that heats the absorption liquid flowing from an absorption tower, which absorbs carbon dioxide contained in a gas to be treated into an absorption liquid, to a stripper tower, which strips the carbon dioxide from the absorption liquid, using the absorption liquid flowing from the stripper tower to the absorption tower; and a storage device that removes the absorption liquid from which at least a portion of the carbon dioxide has been stripped from the stripper tower, stores the removed absorption liquid while heating it to a temperature higher than the temperature of the absorption liquid flowing from the absorption tower to the stripper tower, and supplies the stored absorption liquid to the heat exchanger without passing through the stripper tower.

2. The carbon dioxide recovery system according to claim 1, wherein the temperature of the absorption liquid stored in the storage device is higher than the temperature of the absorption liquid flowing from the stripper tower to the heat exchanger, or higher than the temperature of the absorption liquid stored at the bottom of the stripper tower.

3. The carbon dioxide recovery system according to claim 1 or 2, wherein the storage device comprises: a tank for storing the absorption liquid; an extraction line for guiding the absorption liquid from the stripper tower to the tank; a supply line for guiding the absorption liquid from the tank to the heat exchanger; and a heater for heating the absorption liquid stored in the tank.

4. A carbon dioxide capture system as described in claim 3, further comprising a control unit, wherein the storage device has a valve provided in the extraction line, and the control unit determines the opening degree of the valve based on the liquid level of the absorption liquid stored in the lower part of the stripping tower.

5. The carbon dioxide capture system according to claim 3, wherein the storage device includes a pump provided in the supply line.

6. The carbon dioxide capture system according to claim 5, further comprising a control unit, wherein the control unit determines the rotation speed of the pump according to the amount of gas to be treated that is discharged.

7. A carbon dioxide capture system as described in claim 5, further comprising a control unit, wherein the storage device has a valve provided in the supply line, and the control unit determines at least one of the rotation speed of the pump and the opening degree of the valve according to the emission amount of the gas to be treated.

8. A carbon dioxide recovery system as described in claim 1 or 2, comprising: a control unit; a plurality of return lines that guide the absorption liquid to the absorption tower; and a valve provided on each of the return lines, wherein the control unit determines the opening degree of each of the valves according to the total amount of the absorption liquid guided to the absorption tower.

9. A carbon dioxide capture system as described in claim 1 or 2, comprising: a control unit; a plurality of forward lines that guide the absorption liquid to the stripping tower; and a valve provided on each of the forward lines, wherein the control unit determines the opening degree of each of the valves according to the total amount of absorption liquid guided to the stripping tower.

10. The carbon dioxide capture system according to claim 9, wherein a plurality of said feed lines pass through said heat exchanger.

11. A method for operating a carbon dioxide recovery system equipped with a heat exchanger that heats the absorption liquid flowing from an absorption tower, which absorbs carbon dioxide contained in a gas to be treated into an absorption liquid, to a stripper tower, which strips the carbon dioxide from the absorption liquid, with the absorption liquid flowing from the stripper tower to the absorption tower, the method comprising: removing the absorption liquid from which at least a portion of the carbon dioxide has been stripped from the stripper tower; storing the removed absorption liquid while heating it to a temperature higher than the temperature of the absorption liquid flowing from the absorption tower to the stripper tower; and supplying the stored absorption liquid to the heat exchanger without passing through the stripper tower.

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