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

Abstract

To provide a carbon dioxide collection system that alleviates the possibility of occurrence of a phenomenon in which an absorption liquid flowing toward a desorption tower is not sufficiently heated or not sufficiently subjected to temperature rising in cases when a circulation amount of the absorption liquid increases.SOLUTION: A carbon dioxide collection system includes: a heat exchanger 30; and a storage device 40 for extracting an absorption liquid in which at least a portion of the carbon dioxide is desorbed, from a desorption tower 20, and for storing the extracted absorption liquid by heating it to reach a temperature that is higher than a temperature of an absorption liquid flowing from an absorption tower 10 toward the desorption tower 20, in order to supply the stored absorption liquid to the heat exchanger 30 without passing through the desorption tower 20.SELECTED DRAWING: Figure 1

Description

Technical Field

[0005] , , , , , ,

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

Background Art

[0002] Plants such as thermal power generation facilities and boiler facilities use, for example, inexpensive coal as fuel, and the emission of carbon dioxide (CO2) contained in the exhaust gas has become a problem. In addition, there is also a trend towards decarbonization, and not only reducing the amount of CO2 emissions but also systems for recovering generated CO2 (carbon dioxide recovery systems) are being installed in plants.

[0003] The carbon dioxide recovery system, for example, brings the exhaust gas into contact with an amine-based absorption liquid in an absorption tower to absorb CO2 into the absorption liquid to generate a rich solution (an absorption liquid with a relatively high CO2 content). Further, the carbon dioxide recovery system supplies the generated rich solution to a stripping tower, and heats the rich solution in the stripping tower to release the CO2 contained in the rich solution to generate a lean solution (an absorption liquid with a relatively low CO2 content). Then, the carbon dioxide recovery system performs a circulation of the absorption liquid by supplying the lean solution to the absorption tower. At this time, the rich solution supplied from the absorption tower to the stripping tower is heated and its temperature is raised by the lean solution returned from the stripping tower to the absorption tower by the heat exchanger provided in the carbon dioxide recovery system, thereby promoting the release of carbon dioxide in the stripping tower. Note that related technologies are disclosed in Patent Document 1.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When exhaust gas emissions fluctuate little, the circulation rate of the absorbent between the absorption tower and the decontamination tower can remain approximately constant without issue. However, if, for example, the plant load increases and exhaust gas emissions increase, maintaining the same absorption rate will result in insufficient CO2 absorption in the absorption tower or insufficient CO2 release in the decontamination tower. Therefore, it becomes necessary to increase the absorption rate. However, if the absorption rate increases rapidly, there is a possibility that the absorbent supplied to the decontamination tower will not be sufficiently heated or warmed up by the heat exchanger. If such a phenomenon occurs, the decontamination tower may not be able to release CO2 sufficiently, and furthermore, the absorption tower may not be able to absorb CO2 sufficiently.

[0006] This disclosure has been made in view of these circumstances and aims to provide a carbon dioxide capture system and a method for operating the carbon dioxide capture system that can reduce the possibility of a phenomenon occurring where the absorbent liquid heading to the evaporation tower is not sufficiently heated / heated when the circulation rate of the absorbent liquid increases. [Means for solving the problem]

[0007] To solve the above problems, the carbon dioxide capture system and the method of operating the carbon dioxide capture system of this disclosure employ the following means.

[0008] A carbon dioxide recovery system according to one aspect of the present disclosure includes a heat exchanger that heats the absorbent liquid moving from an absorption tower, which absorbs carbon dioxide contained in a gas to be treated into an absorbent liquid, to a diffusion tower, which releases the carbon dioxide from the absorbent liquid, with the absorbent liquid moving from the diffusion tower back to the absorption tower; and a storage device that removes the absorbent liquid from the diffusion tower, from which at least some of the carbon dioxide has been released, stores the removed absorbent liquid while heating it to a temperature higher than the temperature of the absorbent liquid moving from the absorption tower back to the diffusion tower, and supplies the stored absorbent liquid to the heat exchanger without passing through the diffusion tower.

[0009] A method for operating a carbon dioxide recovery system according to one aspect of the present disclosure is a method for operating a carbon dioxide recovery system that includes a heat exchanger that heats an absorbent liquid moving from an absorption tower, which absorbs carbon dioxide contained in a gas to be treated into an absorbent liquid, to a diffusion tower, which releases the carbon dioxide from the absorbent liquid, with the absorbent liquid moving from the diffusion tower to the absorption tower, wherein the absorbent liquid from which at least a portion of the carbon dioxide has been released is removed from the diffusion tower, the removed absorbent liquid is stored while being heated to a temperature higher than the temperature of the absorbent liquid moving from the absorption tower to the diffusion tower, and the stored absorbent liquid is supplied to the heat exchanger without passing through the diffusion tower. [Effects of the Invention]

[0010] According to this disclosure, it is possible to reduce the possibility that the absorbent liquid heading to the evaporation column will not be sufficiently heated or its temperature will not rise when the circulation rate of the absorbent liquid increases. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of a carbon dioxide capture system according to one embodiment of the present disclosure. [Figure 2] This is a schematic diagram of a carbon dioxide capture system relating to a modified embodiment of one embodiment of the present disclosure. [Modes for carrying out the invention]

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

[0013] [Regarding the overall structure] As shown in Figure 1, the carbon dioxide capture system 1 comprises an absorption tower 10, a emission tower 20, a heat exchanger 30, a storage device 40, and lines connecting these devices.

[0014] The absorption tower 10 is a device that chemically absorbs carbon dioxide contained in the exhaust gas (the gas to be treated) using an amine-based absorbent (hereinafter referred to as the "absorbent"). The lower part / bottom of the absorption tower 10 is a rich solution tank part 11 where a rich solution (an 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 part 11. The exhaust gas discharge line L1 is a line that supplies exhaust gas discharged from a plant such as a thermal power generation facility or a boiler facility to the absorption tower 10.

[0016] An exhaust gas cooler 91 is provided in the middle of 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. Examples of the cooling medium include in-plant cooling water used throughout the plant.

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

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

[0019] A rich solution supply part 22 is connected to the end of the rich solution line L12. The rich solution supply part 22 is a part that injects the rich solution supplied from the absorption tower 10 into the stripping tower 20, and is provided in the upper part inside the stripping tower 20. The rich solution sprayed from the rich solution supply unit 22 descends within the stripping tower 20 and, during the descent, at least a part of the carbon dioxide is released by being heated by the vapor (described later) generated in the reboiler 61.

[0020] In the middle of the rich solution line L12, a rich solution pump 81 and a rich solution valve 83 are provided. The rich solution pump 81 is a pump for sending the rich solution stored in the rich solution tank section 11 to the stripping 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 stripping tower 20 (rich solution supply unit 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. Note that the flow rate of the rich solution supplied to the stripping tower 20 (rich solution supply unit 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), a RAM (Random Access Memory), a ROM (Read Only Memory), and a computer-readable storage medium, etc. And a series of processes for realizing various functions are stored in a storage medium, etc. in the form of a program as an example. The CPU reads this program into the RAM, etc. and executes information processing and arithmetic processing, thereby realizing various functions. The program may be provided in various forms, such as being pre-installed on ROM or other storage media, being stored on a computer-readable storage medium, or being distributed via wired or wireless communication. Computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memory.

[0022] The lean solution tank section 21 of the evaporation tower 20 and the upper part of the absorption 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 absorption tower 10.

[0023] A lean solution supply unit 12 is connected to the end of the lean solution line L21. The lean solution supply unit 12 is the part that injects the lean solution supplied from the evaporation tower 20 into the absorption tower 10, and is located in the upper part of the absorption tower 10. The lean solution injected from the lean solution supply unit 12 descends through the absorption tower 10, and during the descent process, it comes into contact with the exhaust gas supplied from the exhaust 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 transferring the lean solution stored in the lean solution tank 21 to the absorption tower 10. The lean solution pump 71 is located downstream of the heat exchanger 30 in the lean solution line L21. The lean solution cooler 72 is a device that lowers the temperature of the lean solution flowing through the lean solution line L21 to the optimal temperature for chemical absorption performed in the absorption tower 10. Examples of cooling media include in-house cooling water. The lean solution cooler 72 is installed downstream of the lean solution pump 71 in the lean solution line L21. The lean solution valve 73 is a valve for changing the flow rate of the lean solution supplied to the absorption tower 10 (lean solution supply unit 12). The lean solution valve 73 is located in 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. Furthermore, 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 it becomes unnecessary to adjust the opening degree of the lean solution valve 73 (for example, it can be fully open at all times).

[0025] A heat exchanger 30 is provided in the middle of the rich solution line L12 and the lean solution line L21. The heat exchanger 30 is a device that uses the lean solution (absorbent liquid flowing from the evaporation tower 20 to the absorption tower 10) flowing through the lean solution line L21 as a heat source to heat the rich solution (absorbent liquid flowing from the absorption tower 10 to the evaporation tower 20) flowing through the rich solution line L12. By heating the rich solution in the heat exchanger 30, the temperature of the rich solution can be raised to near the optimal temperature for carbon dioxide emission in the diffusion tower 20, thereby promoting carbon dioxide emission in the diffusion tower 20. Conversely, by cooling the lean solution in the heat exchanger 30, the temperature of the lean solution can be lowered to near the optimal temperature for chemical absorption of carbon dioxide in the absorption tower 10, thereby promoting chemical absorption of carbon dioxide in the absorption tower 10. However, since the heat exchanger 30 alone may not be able to sufficiently cool the lean solution, the aforementioned lean solution cooler 72 is provided downstream of the heat exchanger 30 in the lean solution line L21.

[0026] A storage device 40 is provided at the lower part of the dispersion tower 20. The storage device 40 is a device that takes lean solution from the diffusion tower 20, stores the taken lean solution while heating it to a predetermined temperature or higher, and, in predetermined cases, supplies the stored lean solution to the heat exchanger 30 described later without passing through the diffusion tower 20. Details of the storage device 40 will be described later.

[0027] A reboiler 61 is installed at the lower part of the dispersion tower 20. The reboiler 61 is a separate device from 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 using steam supplied from external facilities (for example, plants such as thermal power plants and boiler facilities) as a heat source to heat a portion of the lean solution stored in the lean solution tank section 21 of the diffusion tower 20, thereby raising its temperature, and then supplies the heated lean solution and the generated steam to the diffusion tower 20. The steam supplied to the diffusion tower 20 is used to heat the rich solution, and the rich solution releases at least some of its carbon dioxide as it is heated.

[0028] [Regarding the configuration of the storage device] The storage device 40 is a device that takes lean solution from the diffusion tower 20, stores the taken lean solution while heating it to a predetermined temperature or higher, and, in predetermined cases, supplies the stored lean solution to the heat exchanger 30 without passing through the diffusion tower 20.

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

[0030] The buffer tank 41 is a tank (container) for storing the lean solution taken from the diffusion tower 20.

[0031] The buffer tank 41 is connected to the lean solution tank section 21 of the diffusion tower 20 via the extraction line L41. This allows the lean solution to be extracted from the lean solution tank section 21 and supplied to the buffer tank 41.

[0032] The buffer tank 41 is connected to the lean solution line L21 (the section of the lean solution line L21 upstream of the heat exchanger 30) via the supply line L42. In other words, the buffer tank 41 is connected to the heat exchanger 30 via the supply line L42 and the lean solution line L21. This allows the lean solution stored in the buffer tank 41 to be supplied 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 section 21 of the diffusion tower 20.

[0033] A heater 42 is provided in the buffer tank 41. The heater 42 is configured to heat the lean solution stored in the buffer tank 41. This ensures that the lean solution is stored at a temperature above a predetermined level. Examples of heaters 42 include electric heaters and those that use steam as a heat source. The predetermined temperature is a temperature at which the rich solution can be sufficiently heated in the heat exchanger 30, and is, for example, a temperature higher than the temperature of the absorbent liquid flowing from the absorption tower 10 to the decontamination tower 20, a temperature higher than the temperature of the absorbent liquid flowing from the decontamination tower 20 to the heat exchanger 30, and a temperature higher than the absorbent liquid stored in the lean solution tank section 21 of the decontamination tower 20. However, from the viewpoint of sufficiently and efficiently heating the rich solution in the heat exchanger 30, it is preferable that the predetermined temperature is higher than the temperature of the absorbent liquid flowing from the decontamination tower 20 to the heat exchanger 30 and a temperature higher than the absorbent liquid stored in the lean solution tank section 21 of the decontamination 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 to maintain the temperature of the lean solution at a predetermined temperature.

[0034] A take-out valve 43 is provided in the middle of the take-out 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 diffusion tower 20 to the buffer tank 41. The opening degree of the extraction valve 43 is determined and adjusted by the control unit 2. The control unit 2, for example, acquires the liquid level of the lean solution stored in the lean solution tank section 21 of the diffusion tower 20 using a level gauge (not shown) and adjusts the opening degree of the extraction valve 43 to maintain the liquid level within a predetermined range. Furthermore, a pump may be installed in the middle of the extraction line L41 to transfer the lean solution from the lean solution tank section 21 of the diffusion tower 20 to the buffer tank 41. 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 diffusion tower 20, the lean solution can be transferred without installing 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 transferring the lean solution stored in the buffer tank 41 to the lean solution line L21 and, consequently, 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 located in the supply line L42, downstream of the supply pump 44. The rotational speed of the supply pump 44 and the opening degree of the supply valve 45 are determined and adjusted by the control unit 2 based on the amount of absorbent fluid circulated according to the plant load (i.e., the amount of exhaust gas discharged). Furthermore, 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 it becomes unnecessary to adjust the opening degree of the supply valve 45 (for example, it can be fully open at all times).

[0036] [Regarding the operation of the carbon dioxide capture system] In the carbon dioxide recovery system 1 configured as described above, the absorbent liquid circulates between the absorption tower 10 and the evaporation tower 20. The circulation flow of the absorbent liquid is formed, for example, by a lean solution pump 71 and a rich solution pump 81. Therefore, the amount of absorbent liquid circulated 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 guided to the evaporation tower 20 via the rich solution line L12. At this time, the rich solution is heated by the lean solution (the absorbent liquid moving from the evaporation tower 20 to the absorption tower 10) as it passes through the heat exchanger 30 provided in the rich solution line L12, causing its temperature to rise. This rise in temperature of the rich solution promotes the emission of carbon dioxide in the evaporation tower 20.

[0038] The rich solution, guided to the diffusion tower 20, is sprayed into the diffusion tower 20 from the rich solution supply unit 22. The injected rich solution descends through the diffusion tower 20, and as it descends, it is heated by the steam generated in the reboiler 61 and rising through the diffusion tower 20, releasing at least some carbon dioxide, and is stored as a lean solution in the lean solution tank section 21 at the bottom of the diffusion tower 20. The released carbon dioxide is removed from the top of the emission 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 21 is guided to the absorption tower 10 via the lean solution line L21. At this time, the lean solution is cooled and cooled by the rich solution (the absorbent liquid moving from the absorption tower 10 to the evaporation tower 20) as it passes through the heat exchanger 30 provided in the lean solution line L21. Furthermore, the lean solution is cooled and cooled further as it passes through the lean solution cooler 72. The cooling of the lean solution promotes the chemical absorption of carbon dioxide in the absorption tower 10.

[0040] The lean solution, which is guided into the absorption tower 10, is injected into the absorption tower 10 from the lean solution supply unit 12. The injected lean solution descends within the absorption tower 10, and during its descent, it chemically absorbs carbon dioxide by coming into contact with the exhaust gas that is guided into the absorption tower 10 via the exhaust gas discharge line L1 and rising within the absorption tower 10. The resulting rich solution is then stored as a rich solution in the rich solution tank section 11 located at the bottom of the absorption tower 10. The exhaust gas from which carbon dioxide has been removed (treated gas) is extracted from the top of the diffusion tower 20.

[0041] By repeating this process, exhaust gases emitted from plants such as thermal power plants and boiler facilities are continuously processed.

[0042] However, there are cases where the plant load increases rapidly, causing a sharp increase in exhaust gas emissions. In this case, if the absorption liquid circulation rate is maintained, carbon dioxide cannot be sufficiently chemically absorbed in the absorption tower 10 or sufficiently released in the decontamination tower 20, so it is necessary to increase the absorption liquid circulation rate. The absorption liquid circulation rate is adjusted by the rotation speed of the lean solution pump 71 and the rich solution pump 81. Furthermore, the rotation speed of the lean solution pump 71 and the rich solution pump 81 are determined and adjusted by the control unit 2, for example, according to the plant load (i.e., the amount of exhaust gas emitted). If the circulation rate of the absorbent liquid increases rapidly, there is a possibility that the absorbent liquid heading towards the evaporation tower 20 may not be sufficiently heated or heated up by the heat exchanger 30. Therefore, the carbon dioxide capture system 1 according to this embodiment is equipped with a storage device 40.

[0043] The buffer tank 41 of the storage device 40 constantly stores a lean solution at a predetermined temperature or higher. When the circulation rate of the absorbent liquid circulating between the absorption tower 10 and the evaporation 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. In contrast, if the circulation rate of the absorbent liquid between the absorption tower 10 and the evaporation 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 for rapid and sufficient heating of the absorbent liquid heading towards the evaporation tower 20.

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

[0045] The system includes a storage device 40 that removes the absorbent liquid from the evaporation tower 20, from which at least some of the carbon dioxide has been released, stores the removed absorbent liquid while heating it to a temperature higher than the absorbent liquid flowing from the absorption tower 10 to the evaporation tower 20, and supplies the stored absorbent liquid to the heat exchanger 30 without passing through the evaporation tower 20. For example, if the circulation rate of the absorbent liquid is increased due to an increase in exhaust gas emissions caused by an increase in plant load, the stored high-temperature absorbent liquid can be supplied to the heat exchanger 30 to quickly and sufficiently heat the absorbent liquid heading to the evaporation tower 20. This reduces the possibility that the absorbent liquid may not be sufficiently heated or its temperature may not rise when the circulation rate of the absorbent liquid is increased.

[0046] Furthermore, the storage device 40 includes a buffer tank 41 for storing the absorbent liquid, an extraction line L41 for guiding the absorbent liquid from the diffusion tower 20 to the buffer tank 41, a supply line L42 for guiding the absorbent liquid from the buffer tank 41 to the heat exchanger 30, and a heater 42 for heating the absorbent liquid stored in the buffer tank 41. Therefore, at least a portion of the absorbent liquid from which carbon dioxide has been released can be extracted from the diffusion tower 20, the extracted absorbent liquid can be stored at a temperature higher than the temperature of the absorbent liquid traveling from the absorption tower 10 to the diffusion tower 20, and the stored absorbent liquid can be supplied to the heat exchanger 30 without passing through the diffusion tower 20.

[0047] Furthermore, since the control unit 2 determines the opening degree of the extraction valve 43 based on the liquid level of the absorbent liquid stored at the bottom of the diffusion tower 20, the amount of absorbent liquid guided to the buffer tank 41 can be changed in accordance with fluctuations in the liquid level, making it easier to control the liquid level of the absorbent liquid stored at the bottom of the diffusion tower 20.

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

[0049] Furthermore, since the control unit 2 determines the rotation speed of the supply pump 44 according to the exhaust gas discharge volume, the flow rate of the high-temperature absorbent liquid stored in the tank can be quickly adjusted to match the increase in the circulation volume of the absorbent liquid corresponding to the increase in the discharge volume of the gas to be treated.

[0050] Furthermore, since 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 exhaust gas discharge volume, the supply volume of the high-temperature absorbent liquid stored in the buffer tank 41 can be quickly adjusted to match the increase in the circulation volume of the absorbent liquid corresponding to the increase in exhaust gas discharge volume.

[0051] [Example 1] As shown in Figure 2, the rich solution line L12 of the carbon dioxide recovery system 1 according to Modification 1 branches downstream of the rich solution pump 81. In Figure 2, the rich solution line L12 branches into three lines. In addition, rich solution valves 83 are provided in each of the branched rich solution lines L12. The control unit 2 adjusts the opening degree of each rich solution valve 83 according to the total amount of rich solution flowing through the rich solution line L12. For example, if the circulation rate of absorbent solution is low, the absorbent solution is flowed to only some of the rich solution lines L12, and if the circulation rate of absorbent solution is high, the absorbent solution is flowed to all of the rich solution lines L12. This suppresses fluctuations in the flow rate of absorbent solution flowing through each rich solution line L12 and maintains the velocity of the absorbent solution injected from the rich solution supply unit 22 and descending in the diffusion tower 20 within the optimal range for carbon dioxide release.

[0052] The rich solution line L12 may be branched downstream of the heat exchanger 30. If the rich solution line L12 branches 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 opening degree of each rich solution valve 83. For example, if the circulation rate of absorbent liquid is low, the absorbent liquid flows through only some of the rich solution lines L12, and if the circulation rate of absorbent liquid is high, the absorbent liquid flows through all of the rich solution lines L12. This suppresses fluctuations in the flow rate of absorbent liquid flowing through each rich solution line L12 passing through the heat exchanger 30, and maintains the velocity of the absorbent liquid flowing through each rich solution line L12 within the heat exchanger 30 within the range of the optimal velocity for heat exchange. To finely adjust the flow rate of the absorbent liquid through each rich solution line L12 passing through the heat exchanger 30, separate valves may be provided at each rich solution line L12 upstream of the heat exchanger 30. The opening degree of these valves is determined and adjusted by the control unit 2.

[0053] [Differentiation 2] In the modified example 2, the lean solution line L21 of the carbon dioxide recovery system 1 branches downstream of the lean solution cooler 72. In Figure 2, the lean solution line L21 branches into three lines. Lean solution valves 73 are provided in each of the branched lean solution lines L21. The control unit 2 adjusts the opening of the lean solution valve 73 according to the total amount of lean solution flowing through the lean solution line L21. For example, if the circulation rate of the absorbent solution is low, the absorbent solution is flowed to only some of the lean solution lines L21, and if the circulation rate of the absorbent solution is high, the absorbent solution is flowed to all of the lean solution lines L21. This suppresses fluctuations in the flow rate of the absorbent solution flowing through each lean solution line L21, and maintains the velocity of the absorbent solution injected from the lean solution supply unit 12 and descending in the absorption tower 10 within the optimal range for chemical absorption of carbon dioxide.

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

[0055] A carbon dioxide recovery system (1) according to a first aspect of the present disclosure includes: a heat exchanger (30) that heats the absorbent liquid moving from an absorption tower (10) that absorbs carbon dioxide contained in a gas to be treated into an absorbent liquid to a diffusion tower (20) that releases the carbon dioxide from the absorbent liquid with the absorbent liquid moving from the diffusion tower (20) to the absorption tower (10); and a storage device (40) that takes out the absorbent liquid from which at least a portion of the carbon dioxide has been released from the diffusion tower (20), stores the taken-out absorbent liquid while heating it to a temperature higher than the temperature of the absorbent liquid moving from the absorption tower (10) to the diffusion tower (20), and supplies the stored absorbent liquid to the heat exchanger (30) without passing through the diffusion tower (20).

[0056] The system includes a storage device (40) that removes the absorbent liquid from the evaporation tower (20) from which at least some of the carbon dioxide has been released, stores the removed absorbent liquid while heating it to a temperature higher than the absorbent liquid heading from the evaporation tower (10) to the evaporation tower (20), and supplies the stored absorbent liquid to the heat exchanger (30) without passing through the evaporation tower (20). For example, if the circulation rate of the absorbent liquid is increased due to an increase in the amount of treated gas discharged caused by an increase in the plant load, the absorbent liquid heading to the evaporation tower (20) can be quickly and sufficiently heated by supplying the stored high-temperature absorbent liquid to the heat exchanger (30). This reduces the possibility that the absorbent liquid may not be sufficiently heated or its temperature may not rise when the circulation rate of the absorbent liquid is increased.

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

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

[0059] A carbon dioxide recovery 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 absorbent liquid, an extraction line (L41) for leading the absorbent liquid from the evaporation tower (20) to the tank (41), a supply line (L42) for leading the absorbent liquid from the tank (41) to the heat exchanger (30), and a heater (42) for heating the absorbent liquid stored in the tank (41).

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

[0061] A carbon dioxide recovery system (1) according to a fourth aspect of the present disclosure, in a third aspect, comprises a control unit (2), the storage device (40) having a valve (43) provided in the extraction line (L41), and the control unit (2) determines the degree of opening of the valve (43) based on the liquid level of the absorbent liquid stored in the lower part of the diffusion tower (20).

[0062] The control unit (2) determines the opening degree of the valve (43) based on the liquid level of the absorbent liquid stored at the bottom of the diffusion tower (20). Therefore, the amount of absorbent liquid guided to the tank (41) can be changed in accordance with fluctuations in the liquid level, making it easy to control the liquid level of the absorbent liquid stored at the bottom of the diffusion tower (20).

[0063] In any of the second to fourth embodiments of the carbon dioxide capture system (1) according to the fifth aspect of this disclosure, the storage device (40) has a pump (44) provided in the supply line (L42).

[0064] Since the storage device (40) has a pump (44) installed in the supply line (L42), the absorbent liquid can be efficiently supplied from the tank (41).

[0065] A carbon dioxide recovery system (1) according to a sixth aspect of this disclosure, in a fifth aspect, includes a control unit (2), the control unit (2) determines the rotation speed of the pump (44) according to the discharge amount of the gas to be treated.

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

[0067] A carbon dioxide recovery system (1) according to a seventh aspect of the present disclosure, in a fifth aspect, comprises a control unit (2), the storage device (40) having a valve (45) provided in the supply line (L42), and the control unit (2) determines at least one of the rotational 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, so that the supply amount of the high-temperature absorbent liquid stored in the tank (41) can be quickly adjusted to match the increase in the circulation amount of the absorbent liquid in response to the increase in the discharge amount of the gas to be treated.

[0069] A carbon dioxide recovery system (1) according to the eighth aspect of the present disclosure, in any of the first to seventh aspects, comprises a control unit (2), a plurality of return lines (L21) that lead the absorbent liquid to the absorption tower (10), and valves (73) provided in each of the return lines (L21), wherein the control unit (2) determines the opening degree of each valve (73) according to the total amount of absorbent liquid led to the absorption tower (10).

[0070] The system includes multiple return lines (L21) that lead the absorbent liquid to the absorption tower (10), and valves (73) provided in each return line (L21). The control unit (2) determines the opening degree of each valve (73) according to the total amount of absorbent liquid led to the absorption tower (10), thereby suppressing fluctuations in the flow rate of the absorbent liquid flowing through each return line (L21). For example, if the amount of absorbent liquid circulating is small, the absorbent liquid is flowed through only some of the return lines (L21), while if the amount of absorbent liquid circulating is large, the absorbent liquid is flowed through all of the return lines (L21), thereby suppressing fluctuations in the flow rate of the absorbent liquid flowing through each return line (L21). This makes it possible to maintain the velocity of the absorbent liquid descending in the absorption tower (10) within the range optimal for the chemical absorption of carbon dioxide.

[0071] A carbon dioxide recovery system (1) according to the ninth aspect of this disclosure comprises, in the first to eighth aspects, a control unit (2), a plurality of supply lines (L12) that lead the absorbent liquid to the diffusion tower (20), and valves (83) provided in each of the supply lines (L12), wherein the control unit (2) determines the opening degree of each valve (83) according to the total amount of absorbent liquid led to the diffusion tower (20).

[0072] The system includes multiple supply lines (L12) that lead the absorbent liquid to the evaporation tower (20), and valves (83) provided in each supply line (L12). The control unit (2) determines the opening degree of each valve (83) according to the total amount of absorbent liquid led to the evaporation tower (20), thereby suppressing fluctuations in the flow rate of the absorbent liquid flowing through each supply line (L12). For example, if the circulation rate of the absorbent liquid is low, the absorbent liquid is flowed through only some of the supply lines (L12), while if the circulation rate of the absorbent liquid is high, the absorbent liquid is flowed through all of the supply lines (L12), thereby suppressing fluctuations in the flow rate of the absorbent liquid flowing through each supply line (L12). This makes it possible to maintain the velocity of the absorbent liquid descending within the evaporation tower (20) within the optimal range for carbon dioxide release.

[0073] In the carbon dioxide recovery system (1) according to the tenth aspect of this disclosure, in the ninth aspect, a plurality of supply lines (L12) pass through the heat exchanger (30).

[0074] Since multiple supply lines (L12) pass through the heat exchanger (30), fluctuations in the flow rate of the absorbent liquid flowing through each supply line (L12) passing through the heat exchanger (30) can be suppressed. For example, when the amount of absorbent liquid circulating is small, the absorbent liquid can be flowed through only some of the supply lines (L12), while when the amount of absorbent liquid circulating is large, the absorbent liquid can be flowed through all of the supply lines (L12), thereby suppressing fluctuations in the flow rate of the absorbent liquid flowing through each supply line (L12) passing through the heat exchanger (30). This makes it possible to maintain the velocity of the absorbent liquid flowing through each supply line (L12) inside the heat exchanger (30) within the range of the optimal velocity for heat exchange.

[0075] A method for operating a carbon dioxide recovery system (1) according to an eleventh aspect of the present disclosure is a method for operating a carbon dioxide recovery system (1) comprising an absorption tower (10) that absorbs carbon dioxide contained in a gas to be treated into an absorbent liquid, and a heat exchanger (30) that heats the absorbent liquid moving from the absorption tower (20) to the absorption tower (10) with the absorbent liquid moving from the absorption tower (20) to the absorption tower (10), wherein the absorbent liquid from which at least a portion of the carbon dioxide has been released is taken out of the absorption tower (20), the taken out absorbent liquid is stored while being heated to a temperature higher than the temperature of the absorbent liquid moving from the absorption tower (10) to the absorption tower (20), and the stored absorbent liquid is supplied to the heat exchanger (30) without passing through the absorption tower (20). [Explanation of symbols]

[0076] 1. Carbon dioxide capture system 2 Control Unit 10 Absorption Towers 11 Rich Solution Tank Section 12. Lean solution supply unit 20 Radiation towers 21 Lean solution tank section 22 Rich Solution Supply Unit 30 heat exchanger 40 Storage device 41 Buffer Tank (Tank) 42 Heater 43. Take-out 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 Emission Line L12 Rich solution line (supply line) L21 Lean solution line (return line) L41 Extraction Line L42 supply line

Claims

1. A heat exchanger heats the absorbent liquid, which flows from an absorption tower that absorbs carbon dioxide contained in the gas to be treated into an absorbent liquid, to a diffusion tower that releases the carbon dioxide from the absorbent liquid, with the absorbent liquid flowing from the diffusion tower back to the absorption tower. A storage device that removes an absorbent liquid from which at least some carbon dioxide has been released from the emission tower, stores the removed absorbent liquid while heating it to a temperature higher than the temperature of the absorbent liquid flowing from the absorption tower to the emission tower, and supplies the stored absorbent liquid to the heat exchanger without passing through the emission tower, Equipped with, The absorbent liquid that heats the absorbent liquid flowing from the absorption tower to the radiation tower is the absorbent liquid supplied from the storage device to the heat exchanger. Carbon dioxide capture system.

2. The temperature of the absorbent liquid stored in the storage device is A temperature higher than the temperature of the absorbent liquid flowing from the aforementioned diffusion tower to the aforementioned heat exchanger, or A higher temperature than the absorbent liquid stored at the bottom of the aforementioned diffusion tower. It is said that The carbon dioxide capture system according to claim 1.

3. The storage device is Tank for storing absorbent liquid, A take-off line that guides the absorbent liquid from the diffusion tower to the tank, A supply line that guides the absorbent liquid from the tank to the heat exchanger, A heater for heating the absorbent liquid stored in the aforementioned tank. It has A carbon dioxide capture system according to claim 1 or 2.

4. Equipped with a control unit, The storage device has a valve provided in the extraction line, The control unit determines the opening degree of the valve based on the liquid level of the absorbent liquid stored in the lower part of the diffusion tower. The carbon dioxide capture system according to claim 3.

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

6. Equipped with a control unit, The control unit determines the rotation speed of the pump according to the discharge volume of the gas to be treated. The carbon dioxide capture system according to claim 5.

7. Equipped with a control unit, The storage device has a valve provided in the supply line, The control unit determines at least one of the pump's rotation speed and the valve's opening degree according to the discharge amount of the gas to be treated. The carbon dioxide capture system according to claim 5.

8. Control unit and Multiple return lines that guide the absorbent liquid to the absorption tower, A valve provided in each of the aforementioned return lines, Equipped with, The control unit determines the opening degree of each valve according to the total amount of absorbent liquid supplied to the absorption tower. A carbon dioxide capture system according to claim 1 or 2.

9. Control unit and Multiple supply lines that guide the absorbent liquid to the aforementioned diffusion tower, Each of the aforementioned supply lines is provided with a valve, Equipped with, The control unit determines the opening degree of each valve according to the total amount of absorbent liquid guided to the diffusion tower. A carbon dioxide capture system according to claim 1 or 2.

10. Multiple of the aforementioned supply lines pass through the heat exchanger. The carbon dioxide capture system according to claim 9.

11. A method for operating a carbon dioxide recovery system, comprising a heat exchanger that heats the absorbent liquid flowing from an absorption tower, which absorbs carbon dioxide contained in the gas to be treated into an absorbent liquid, to a diffusion tower, which releases the carbon dioxide from the absorbent liquid, with the absorbent liquid flowing from the diffusion tower back to the absorption tower, The absorbent liquid from which at least some of the carbon dioxide has been released is taken out of the emission tower, The extracted absorbent liquid is stored while being heated to a temperature higher than the temperature of the absorbent liquid flowing from the absorption tower to the emission tower. The stored absorbent liquid is supplied to the heat exchanger without passing through the diffusion tower. The absorbent liquid supplied to the heat exchanger heats the absorbent liquid moving from the absorption tower to the emission tower, The absorbent liquid that flows from the absorption tower to the emission tower is heated and then supplied to the absorption tower. Operating procedures for a carbon dioxide capture system.

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