Carbon dioxide capture system and its operating method

Abstract

This invention provides a carbon dioxide recovery system and its operating method that can more efficiently collect absorbent liquid contained in exhaust gas. [Solution] The carbon dioxide recovery system 1A includes a refrigerant circulation system 30 comprising a compressor 35 for compressing a refrigerant, a heat exchanger 31 for releasing heat from the refrigerant compressed by the compressor 35, an expansion valve 33 for expanding the refrigerant released heat from the heat exchanger 31, and evaporators 32 and 34 for evaporating the refrigerant expanded by the expansion valve 33. The evaporators 32 and 34 cool the exhaust gas containing carbon dioxide discharged from the regeneration tower 20, which separates carbon dioxide from the absorbent liquid that has absorbed carbon dioxide contained in the gas to be treated and regenerates the absorbent liquid.

Description

Technical Field

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

Background Art

[0002] In order to reduce the carbon dioxide (CO2) emissions from thermal power generation facilities and the like, a system for recovering the generated CO2 (carbon dioxide recovery system) is being installed.

[0003] The carbon dioxide recovery system, for example, brings exhaust gas into contact with an amine-based absorbent in an absorption tower to absorb CO2 into the absorbent and generate a rich solution (an absorbent with a relatively high CO2 content). Further, the carbon dioxide recovery system supplies the generated rich solution to a regeneration tower, and heats the rich solution in the regeneration tower to release the CO2 contained in the rich solution and generate a lean solution (an absorbent with a relatively low CO2 content). Then, the carbon dioxide recovery system performs a circulation of the absorbent by supplying the lean solution to the absorption tower. At this time, the rich solution supplied from the absorption tower to the regeneration tower is heated and its temperature is raised by the lean solution returned from the regeneration tower to the absorption tower by a heat exchanger provided in the carbon dioxide recovery system, thereby promoting the dissipation of carbon dioxide in the regeneration tower. Note that related technologies are disclosed in Patent Documents 1 and 2.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, the environmental impact of absorbents (e.g., amine-based absorbents) used in carbon dioxide capture systems has attracted attention, and there is a need to reduce the amount of absorbent discharged outside the system along with the treated gas. Conventional carbon dioxide capture systems are equipped with devices to recover the absorbent contained in the treated gas, such as inertial separation type mist collectors, at the top of the regeneration tower or downstream of the regeneration tower. However, inertial separation type mist collectors cannot recover the absorbent in the gas phase corresponding to the saturated vapor pressure.

[0006] This disclosure is made in view of these circumstances and aims to provide a carbon dioxide recovery system and a method for operating the same that can more efficiently collect absorbent liquid contained in exhaust gas. [Means for solving the problem]

[0007] To solve the above problems, the carbon dioxide recovery system of the present disclosure comprises a refrigerant circulation system comprising a compressor for compressing a refrigerant, a heat exchanger for releasing heat from the refrigerant compressed by the compressor, an expansion valve for expanding the refrigerant released heat from the heat exchanger, and an evaporator for evaporating the refrigerant expanded by the expansion valve. The evaporator cools the exhaust gas containing carbon dioxide discharged from a regeneration tower that separates the carbon dioxide from an absorbent liquid that has absorbed carbon dioxide contained in the gas to be treated and regenerates the absorbent liquid.

[0008] Furthermore, the method for operating a carbon dioxide recovery system according to the present disclosure is a method for operating a carbon dioxide recovery system equipped with a refrigerant circulation system comprising a compressor for compressing a refrigerant, a radiator for releasing heat from the refrigerant compressed by the compressor, an expansion valve for expanding the refrigerant released heat from the radiator, and an evaporator for evaporating the refrigerant expanded by the expansion valve, wherein the method includes an exhaust step of discharging exhaust gas containing carbon dioxide from an absorbent liquid that has absorbed carbon dioxide contained in a gas to be treated, and discharging exhaust gas containing carbon dioxide from a regeneration tower that regenerates the absorbent liquid by separating the carbon dioxide, and in the exhaust step, the exhaust gas is cooled by the evaporator. [Effects of the Invention]

[0009] With the carbon dioxide capture system and operating method described herein, the exhaust gas containing carbon dioxide discharged from the regeneration tower can be cooled by a refrigerant circulating within the evaporator. Therefore, the temperature of the exhaust gas can be sufficiently reduced, allowing the absorbent liquid contained in the exhaust gas to be condensed and captured more efficiently. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram of a carbon dioxide capture system according to one embodiment of the present disclosure. [Figure 2] Figure 1 is a schematic diagram showing the radiators that make up the heat exchanger in the carbon dioxide capture system. [Figure 3] Figure 1 is a schematic diagram of the heat exchanger in the carbon dioxide capture system. [Figure 4] This is a schematic diagram of a carbon dioxide capture system relating to a modified embodiment of one embodiment of the present disclosure. [Figure 5] This is a schematic diagram of the carbon dioxide capture system for the comparative example. [Figure 6] Figure 5 is a schematic diagram showing the mist catcher in the carbon dioxide capture system. [Modes for carrying out the invention]

[0011] An embodiment of the carbon dioxide capture system and its operating method relating to this disclosure will be described below with reference to the drawings.

[0012] [Carbon dioxide capture system] Hereinafter, one embodiment of this disclosure will be described with reference to Figures 1 to 3. As shown in Figure 1, the carbon dioxide recovery system 1A comprises an absorption tower 10, a regeneration tower 20, a heat exchanger 31, a refrigerant circulation system 30, and lines connecting these components.

[0013] The absorption tower 10 is a facility that chemically absorbs carbon dioxide contained in the exhaust gas (the gas to be treated) into the absorption liquid (for example, an amine-based absorption liquid). Inside the absorption tower 10, a packed bed 13 filled with packing materials is provided, enhancing the contact efficiency of the gas-liquid contact between the absorption liquid and the exhaust gas. The lower part / bottom of the absorption tower 10 is a rich solution tank part 11 where the rich solution (the absorption liquid that has absorbed carbon dioxide) is stored.

[0014] Above the lower part of the absorption tower 10 and above the rich solution tank part 11, an exhaust gas discharge line L1 is connected. The exhaust gas discharge line L1 is a line that supplies the exhaust gas discharged from plants such as thermal power generation facilities and boiler facilities to the absorption tower 10.

[0015] In the middle of the exhaust gas discharge line L1, a prescrubber 91, a fan 92, and an exhaust gas cooler 93 are provided. The prescrubber 91 is a device that performs pretreatment of the exhaust gas introduced into the absorption tower 10 and removes dust in the exhaust gas flowing through the exhaust gas discharge line L1. The fan 92 is a facility that blows the exhaust gas flowing through the exhaust gas discharge line L1 into the lower part of the absorption tower 10. The exhaust gas cooler 93 is a device that reduces the temperature of the exhaust gas flowing through the exhaust gas discharge line L1 to an optimal temperature for the chemical absorption performed in the absorption tower 10. Examples of the cooling medium include in-plant cooling water used throughout the plant. Note that the prescrubber 91, the fan 92, and the exhaust gas cooler 93 may be appropriately omitted according to the conditions (composition, temperature, pressure, etc.) of the exhaust gas to be treated. [[ID=Z6]]

[0016] The regeneration tower 20 is a facility that releases carbon dioxide from the rich solution. The lower part / bottom of the regeneration tower 20 is a lean solution tank section 21 where the lean solution (the absorption liquid from which carbon dioxide has been released) is stored. The lean solution is an absorption liquid that relatively has a lower carbon dioxide content than the rich solution. In other words, the rich solution is an absorption liquid that relatively has a higher carbon dioxide content than the lean solution.

[0017] Inside the regeneration tower 20, a packed bed 23 filled with packing is provided, and the contact efficiency of the gas-liquid contact between the absorption liquid and the exhaust gas is enhanced.

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

[0019] At the end of the rich solution line L12, a rich solution supply section 22 is connected. The rich solution supply section 22 is a part that injects the rich solution supplied from the absorption tower 10 into the regeneration tower 20, and is provided at the upper part inside the regeneration tower 20. The rich solution injected from the rich solution supply section 22 descends inside the regeneration tower 20 and releases at least a part of carbon dioxide during the descending process.

[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 regeneration tower 20. The rich solution pump 81 is provided at a location on the rich solution line L12 upstream of the heat exchanger 31. The rich solution valve 83 is a valve for changing the flow rate of the rich solution supplied to the regeneration 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 31. 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. Furthermore, the flow rate of the rich solution supplied to the regeneration 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 it becomes unnecessary to adjust the opening degree of the rich solution valve 83 (for example, it can be fully open at all times).

[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 are stored in the storage medium in the form of a program, for example. The CPU reads this program into the RAM and performs information processing and calculations to realize the 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 regeneration 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 regeneration tower 20 into the absorption tower 10, and is located in the upper part of the absorption tower 10 (above the packed bed 13). The lean solution injected from the lean solution supply unit 12 descends through the absorption tower 10, and as it descends and passes through the packed bed 13, 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 31 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 a temperature range suitable 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 (radiator) 31, which constitutes the refrigerant circulation system 30 described later, is provided in the middle of the rich solution line L12 and the lean solution line L21. The heat exchanger 31 is a device that uses the refrigerant compressed by the compressor 35 (described later) as a heat source to heat the rich solution (absorbent liquid flowing from the absorption tower 10 to the regeneration tower 20) flowing through the rich solution line L12. By heating the rich solution in the heat exchanger 31, the temperature of the rich solution can be raised to a temperature range suitable for carbon dioxide release in the regeneration tower 20, thereby promoting carbon dioxide release in the regeneration tower 20. Alternatively, the heat exchanger 31 may be configured not to heat the rich solution flowing through the rich solution line L12, but rather to act as a heat exchanger that dissipates the heat of the refrigerant compressed by the compressor 35 by air cooling. In this case, a separate heat exchanger can be provided to heat the rich solution flowing through the rich solution line L12 using the lean solution flowing through the lean solution line L21 as a heat source.

[0026] Furthermore, a heat exchanger (regenerative heat exchanger) 38 may be provided in the middle of the rich solution line L12 and the lean solution line L21. In this case, the positional relationship between the heat exchanger 31 and the heat exchanger 38 is not limited to the configuration shown in Figure 1. Also, the heat exchanger 31 and the heat exchanger 38 may be integrally configured. The heat exchanger 38 performs heat exchange between the rich solution flowing through the rich solution line L12 (absorbent liquid moving from the absorption tower 10 to the regeneration tower 20) and the lean solution flowing through the lean solution line L21 (absorbent liquid moving from the regeneration tower 20 to the absorption tower 10). By heating the rich solution in the heat exchanger 38, the temperature of the rich solution can be raised to a temperature range suitable for carbon dioxide release in the regeneration tower 20, thereby promoting carbon dioxide release in the regeneration tower 20. Furthermore, since the lean solution can be cooled in the heat exchanger 38, the temperature of the lean solution can be lowered to a temperature range suitable for the chemical absorption of carbon dioxide in the absorption tower 10, thereby promoting the chemical absorption of carbon dioxide in the absorption tower 10. However, considering the possibility that the heat exchanger 38 alone may not be sufficient to cool the lean solution, the aforementioned lean solution cooler 72 may be provided in the lean solution line L21 downstream of the heat exchanger 38.

[0027] A heat exchanger (evaporator) 32 is installed at the top of the regeneration tower 20. The heat exchanger 32 is a component of the refrigerant circulation system 30, which will be described later, and is a device that cools the exhaust gas containing carbon dioxide discharged from the regeneration tower 20. By cooling the exhaust gas containing carbon dioxide with the heat exchanger 32, the temperature of the exhaust gas can be sufficiently reduced, and the absorbent liquid contained in the exhaust gas can be condensed. Details of the structure of the heat exchanger 32 will be described later.

[0028] Outside the regeneration tower 20, a gas-liquid separator 40 is provided to separate condensate and other substances from the exhaust gas discharged from the top of the tower through the exhaust gas exhaust line L41. In other words, the gas-liquid separator 40 is located downstream of the regeneration tower 20. The lower / bottom section of the gas-water separator 40 is a condensate tank section 41 where the water condensed in the gas-water separator 40 is stored.

[0029] A condensate recovery line L42 is connected to the lower part of the condensate tank section 41. A pump 43 is provided in the condensate recovery line L42. The pump 43 supplies the condensate stored in the condensate tank section 41 to the upper part of the regeneration tower 20 via the condensate recovery line L42.

[0030] A condensate supply unit 44 is connected to the end of the condensate recovery line L42. The condensate supply unit 44 is the part that injects condensate supplied from the gas-water separator 40 into the regeneration tower 20, and is located in the upper part of the regeneration tower 20 (above the rich solution supply unit 22).

[0031] A heat exchanger (evaporator) 34 is provided above the gas-liquid separator 40. The heat exchanger 34 is a component of the refrigerant circulation system 30, which will be described later, and is a device that cools the exhaust gas containing carbon dioxide discharged from the regeneration tower 20. By cooling the exhaust gas containing carbon dioxide with the heat exchanger 34, the temperature of the exhaust gas can be sufficiently reduced, so that the water vapor and absorbent liquid contained in the exhaust gas can be condensed. The exhaust gas discharged from the regeneration tower 20 is thus sufficiently cooled by the heat exchanger 34 of the gas-water separator 40, and the contained water vapor and absorbent liquid are condensed as much as possible. The condensed water and absorbent liquid are separated in the gas-water separator 40. The exhaust gas from which the water vapor and absorbent liquid have been separated is discharged from the exhaust gas discharge line L43 connected to the top of the gas-water separator 40. A pressure regulating valve 45 is provided in the exhaust gas discharge line L43 to regulate the pressure inside the gas-water separator 40. A pressure gauge 46 is provided in the exhaust gas exhaust line L41 to check the pressure inside the gas-water separator 40. The pressure inside the gas-liquid separator 40 is controlled by the pressure regulating valve 45 and the pressure gauge 46 to prevent the evaporated absorbent liquid from being discharged from the exhaust gas discharge line L43. Details of the structure of the heat exchanger 34 will be described later.

[0032] It is not necessary to provide the heat exchangers 32 and 34 that constitute the refrigerant circulation system 30 in both the regeneration tower 20 and the gas-liquid separator 40. For example, it is possible to replace either the heat exchanger 32 in the regeneration tower 20 or the heat exchanger 34 in the gas-liquid separator 40 with, for example, an inertial separation type mist collection device.

[0033] [Regarding the configuration of the refrigerant circulation system] The refrigerant circulation system 30 comprises a compressor 35 for compressing the refrigerant, a heat exchanger 31 for releasing heat from the refrigerant compressed by the compressor 35, an expansion valve 33 for expanding the refrigerant that has been released heat by the heat exchanger 31, and evaporators (heat exchangers) 32 and 34 for evaporating the refrigerant that has been expanded by the expansion valve 33. Each of these components constituting the refrigerant circulation system 30 is connected by lines.

[0034] Specifically, the refrigerant circulation line L31 connected to the refrigerant outlet of the compressor 35 is connected to the heat exchanger 31. The heat exchanger 31 is connected to the heat exchanger 34 of the gas-liquid separator 40 via the expansion valve 33 through the refrigerant circulation line L32. The heat exchanger 34 of the gas-liquid separator 40 is connected to the heat exchanger 32 of the regeneration tower 20 via the refrigerant circulation line L33. The heat exchanger 32 of the regeneration tower 20 is connected to the refrigerant inlet of the compressor 35 via the refrigerant circulation line L34.

[0035] [Regarding the configuration of the heat exchanger] The configuration of the heat exchanger 32(34) according to this embodiment will be explained with reference to Figures 2 and 3. The radiator 321 is formed by a shape in which tubes 322, each with fins 323 wrapped around its outer circumference, are alternately folded back, and the heat exchanger 32 is equipped with at least one radiator 321. A refrigerant flows inside the tubes 322. In other words, the heat exchanger 32 is a fin-tube type heat exchanger through which a refrigerant flows. When exhaust gas containing carbon dioxide is introduced into the heat exchanger 32 from below, the exhaust gas is cooled by the refrigerant inside. At this time, the absorbent liquid contained in the exhaust gas condenses and collides with the heat exchanger 32 (tubes 322 and fins 323). Water vapor and condensed absorbent liquid droplets are formed (deposited) on the surface of the fins 323 cooled by the refrigerant. When the condensed droplets become large, they fall downwards. This allows the absorbent liquid contained in the exhaust gas to be collected, and carbon dioxide to be discharged from the top of the heat exchanger 32.

[0036] More specifically, the heat exchanger 32 is composed of multiple layers of radiators 321 as shown in Figure 2. Inside the radiators 321, tubes 322, each with fins (not shown in Figure 2) wrapped around its outer circumference, are arranged in an alternating folded shape. As shown in Figure 2, a refrigerant inlet into the tubes 322 is provided on one side of the radiator 321, and a refrigerant outlet from the tubes 322 is provided on the other side of the radiator 321.

[0037] Figure 3 is a schematic diagram of the heat exchanger 32 (34). The heat exchanger 32 is composed of multiple layers of the radiator 321 (with cooling fins shown) as shown in Figure 2. Specifically, the heat exchanger 32 is composed of multiple layers of the radiator 321 as shown in Figure 2, laid on their sides. Exhaust gas containing carbon dioxide is introduced into the heat exchanger 32 from the bottom in Figure 3, the absorbent liquid contained in the exhaust gas is removed in the heat exchanger 32, and carbon dioxide is discharged to the top in Figure 3.

[0038] [Regarding the operation of the carbon dioxide capture system] In the carbon dioxide recovery system 1A configured as described above, the absorbent liquid circulates between the absorption tower 10 and the regeneration tower 20. The operation method of the carbon dioxide recovery system 1A in this embodiment includes an exhaust step in which exhaust gas containing carbon dioxide is discharged from the regeneration tower 20, and in the exhaust step, the exhaust gas is cooled by evaporators 32 and 34.

[0039] Here, Figure 5 is a schematic diagram showing a carbon dioxide capture system 101 related to a comparative example. The comparative example carbon dioxide recovery system 101 does not have the refrigerant circulation system 30 of this embodiment. Accordingly, the comparative example is equipped with mist catchers 132 and 134 instead of the heat exchangers 32 and 34 of this embodiment, and a water-cooled cooler 147 for cooling the exhaust gas is provided in the exhaust gas exhaust line L41. In addition, a reboiler 111 is provided at the bottom of the regeneration tower 20.

[0040] The reboiler 111 is a device that uses steam supplied from an external facility (for example, a plant where a carbon dioxide capture system such as a thermal power plant or boiler facility is installed) as a heat source to heat and raise the temperature of the absorbent liquid stored at the bottom of the regeneration tower 20. The absorbent liquid in the regeneration tower 20 releases at least some of its carbon dioxide as it is heated. Furthermore, a portion of the heated absorption solution is supplied to the absorption tower 10 after being cooled by heat exchange with the rich solution in a heat exchanger 38 installed in the lean solution line L21, thereby heating the rich solution.

[0041] Figure 6 is a schematic diagram showing the mist catcher 132 (134) in the carbon dioxide capture system 101 of Figure 5. The mist catcher 132 (134) is, for example, an inertial separation type mist collection device. As shown in Figure 6, the mist catcher 132 consists of multiple layers of plates with a corrugated iron roof-like uneven shape, with their longitudinal directions parallel to the gas flow. When exhaust gas flows into the mist catcher 132 from below, the mist of the absorbent liquid contained in the exhaust gas collides with the uneven shape of the plates due to its inertia, forming droplets on the surface of the plates. As the droplets grow larger, they fall downwards. This mechanism allows for the collection of the mist of the absorbent liquid contained in the exhaust gas.

[0042] However, in the comparative example carbon dioxide recovery system 101, there was a limit to improving the collection rate of the absorbent liquid by the mist catchers 132 and 134. That is, the mist catchers 132 and 134 can only collect liquid mist, and cannot collect gaseous absorbent liquid. On the other hand, in this embodiment, a refrigerant circulation system 30 is introduced and heat exchangers (evaporators) 32 and 34 are provided instead of the mist catchers 132 and 134. By collecting the absorbent liquid while cooling the exhaust gas, it becomes possible to condense and collect a portion of the gaseous absorbent liquid, thereby improving the collection rate of the absorbent liquid. Furthermore, this eliminates the need for the cooler 147, which was separate from the mist catchers 132 and 134.

[0043] The functions and effects of the carbon dioxide capture system 1A according to this embodiment, as described above, will now be explained.

[0044] The carbon dioxide recovery system 1A according to this embodiment is equipped with a refrigerant circulation system 30, and the evaporators 32 and 34 cool the exhaust gas containing carbon dioxide discharged from the regeneration tower 20. Conventionally, the absorbent liquid contained in the exhaust gas was collected by passing the exhaust gas discharged from the regeneration tower 20 through a mist catcher installed downstream of the regeneration tower 20. On the other hand, in this embodiment, evaporators 32 and 34 are provided instead of a mist catcher. As a result, the exhaust gas containing carbon dioxide discharged from the regeneration tower 20 can be cooled by the refrigerant circulating in the evaporators 32 and 34. Therefore, the temperature of the exhaust gas can be sufficiently reduced, and the absorbent liquid contained in the exhaust gas can be condensed and collected more efficiently.

[0045] The fin-tube heat exchanger has a finer mesh structure (with fins 323) than conventional mist catchers, allowing it to more reliably collide exhaust gas with evaporators 32 and 34. This enables sufficient heat exchange between the exhaust gas and the refrigerant, cooling the exhaust gas and allowing for accurate and efficient collection of the absorbent liquid.

[0046] The carbon dioxide recovery system 1A according to this embodiment is equipped with a refrigerant circulation system 30 and is configured to cool exhaust gas with evaporators 32 and 34 through which refrigerant flows. Therefore, the cooling efficiency is higher than when a mist catcher is used because refrigerant is used. Accordingly, by providing evaporators 32 and 34 in the gas-liquid separator 40 located at the top of the regeneration tower 20 and / or downstream of the regeneration tower 20, the heat exchanger for exhaust gas cooling that was conventionally provided between the regeneration tower 20 and the gas-liquid separator 40 can be eliminated. This makes it possible to reduce the amount of equipment.

[0047] In the carbon dioxide recovery system 1A according to this embodiment, the absorbent liquid supplied from the absorption tower 10, which absorbs carbon dioxide contained in the gas to be treated, to the regeneration tower 20 can be heated by the refrigerant circulating in the radiator 31 by releasing heat into the absorbent liquid. This eliminates the need for a reboiler, which was conventionally used to heat the absorbent liquid. Furthermore, since the heat source for a reboiler is generally steam supplied from the plant where the carbon dioxide recovery system 1A is installed, eliminating the need for a reboiler eliminates the need for a heat source such as steam. This suppresses a decrease in the overall efficiency of the plant.

[0048] [Differentiation] Next, details of a modified carbon dioxide capture system 1B according to this embodiment will be explained with reference to Figure 4. This modified example differs from the embodiment in that a thermometer 84 is provided in the rich solution line L12, and a bypass line L35, a bypass valve 36, and a thermometer 37 are provided in the refrigerant circulation system 30. Components identical to those in this embodiment are denoted by the same reference numerals, and their detailed descriptions are omitted.

[0049] In this modified example, as shown in Figure 4, a bypass line L35 is provided that connects the upstream side of the expansion valve 33 in the refrigerant circulation line L32 to the refrigerant circulation line L33, bypassing the expansion valve 33 and the heat exchanger 34. A bypass valve 36 is also provided in the bypass line L35. By opening the bypass valve 36, it becomes possible to supply the refrigerant that has been heated in the heat exchanger 31 to the heat exchanger 32 of the regeneration tower 20 without expanding it in the expansion valve 33.

[0050] Furthermore, a thermometer 37 is provided downstream of the point where the refrigerant circulation line L33 merges with the bypass line L35. This allows the control unit 2 to check the temperature of the thermometer 37 and adjust the opening of the bypass valve 36 according to the temperature of the heat exchanger 32 located at the top of the regeneration tower 20 (specifically, the temperature of the refrigerant circulating inside it). Thus, it is possible to control the temperature of the heat exchanger 32 so that it does not drop too low.

[0051] In this modified example, a thermometer 84 is provided in the rich solution line L12, which is downstream of the heat exchanger 31 and upstream of the rich solution valve 83. As a result, the control unit 2 controls the compression ratio of the refrigerant based on the temperature detected by the thermometer 84. Specifically, the control unit 2 is configured to control the compression ratio of the refrigerant by the compressor 35 via a motor 39 that rotates the compressor 35, so that the absorbent liquid supplied to the regeneration tower 20 can be heated to a predetermined temperature. The predetermined temperature is the temperature at which carbon dioxide can be reliably separated from the absorbent liquid after it has been supplied to the regeneration tower 20.

[0052] The functions and effects of the carbon dioxide capture system 1B related to this modified example, as described above, will now be explained.

[0053] In the carbon dioxide recovery system 1B according to this modified example, heat exchangers 32 and 34 are provided in a gas-liquid separator 40 located at the top of the regeneration tower 20 and downstream of the regeneration tower 20, and the refrigerant circulation system 30 has a bypass line L35 that sends the refrigerant that has been heated by the heat exchanger 31 to the heat exchanger 32 located at the top of the regeneration tower 20, bypassing the expansion valve 33. Therefore, the refrigerant before it is expanded by the expansion valve 33 can be sent to the heat exchanger 32 located at the top of the regeneration tower 20 via the bypass line L35. In addition, a bypass valve 36 is provided in the bypass line L35, and the control unit 2 is configured to adjust the opening degree of the bypass valve 36 according to the temperature of the heat exchanger 32 located at the top of the regeneration tower 20. Therefore, it is possible to control the temperature of the heat exchanger 32 so that it does not drop too low. This prevents the temperature of the heat exchanger 32 from dropping too low, which would cool the exhaust gas to the point where the absorbent liquid in the regeneration tower 20 condenses, and the absorbent liquid would reabsorb carbon dioxide.

[0054] In the carbon dioxide recovery system 1B according to this modified example, the control unit 2 is configured to control the compression of the refrigerant by the compressor 35 so that the absorbent liquid supplied to the regeneration tower 20 can be heated to a predetermined temperature according to the thermometer 84 installed in the rich solution line L12. Therefore, the absorbent liquid supplied to the regeneration tower 20 can be reliably heated to a sufficient temperature. This allows for more reliable separation of the absorbent liquid and carbon dioxide.

[0055] <Note> The carbon dioxide capture system and its operating method described in the embodiments above can be understood, for example, as follows. A carbon dioxide recovery system (1A, 1B) according to a first aspect of this disclosure comprises a refrigerant circulation system (30) comprising a compressor (35) for compressing a refrigerant, a heat exchanger (31) for releasing heat from the refrigerant compressed by the compressor, an expansion valve (33) for expanding the refrigerant released heat from the heat exchanger, and evaporators (32, 34) for evaporating the refrigerant expanded by the expansion valve. The evaporators cool the exhaust gas containing carbon dioxide discharged from a regeneration tower (20) that separates the carbon dioxide from an absorbent liquid that has absorbed carbon dioxide contained in the gas to be treated and regenerates the absorbent liquid.

[0056] The carbon dioxide recovery system of this disclosure is equipped with a refrigerant circulation system, and the evaporator cools the exhaust gas containing carbon dioxide discharged from the regeneration tower. Conventionally, the absorbent liquid contained in the exhaust gas was collected by passing the exhaust gas discharged from the regeneration tower through a mist catcher installed downstream of the regeneration tower. In contrast, this disclosure uses an evaporator instead of a mist catcher. This allows the exhaust gas containing carbon dioxide discharged from the regeneration tower to be cooled by a refrigerant circulating within the evaporator. Therefore, the temperature of the exhaust gas can be sufficiently reduced, allowing the absorbent liquid contained in the exhaust gas to be condensed and collected more efficiently.

[0057] In the first embodiment, the carbon dioxide recovery system according to a second aspect of the present disclosure is a finned tube heat exchanger through which the refrigerant flows, and which exchanges heat between the exhaust gas released from the regeneration tower and the refrigerant.

[0058] Fin-tube heat exchangers have a finer mesh structure (with fins) than conventional mist catchers, allowing them to more reliably collide exhaust gases with the evaporator. This enables sufficient heat exchange between the exhaust gas and the refrigerant, cooling the exhaust gas and allowing for accurate and efficient collection of absorbent liquid.

[0059] In the third aspect of the present disclosure, the carbon dioxide recovery system is provided in the first or second aspect, wherein the evaporator is located in a gas-liquid separator (40) positioned above and / or downstream of the regeneration tower.

[0060] The carbon dioxide recovery system of this disclosure is equipped with a refrigerant circulation system and is configured to cool exhaust gases by an evaporator through which refrigerant flows. Therefore, the cooling efficiency is higher than when using a mist catcher because refrigerant is used. Accordingly, by providing an evaporator in the gas-liquid separator located at the top of the regeneration tower and / or downstream of the regeneration tower, the heat exchanger for exhaust gas cooling that was conventionally provided between the regeneration tower and the gas-liquid separator can be eliminated. This makes it possible to reduce the amount of equipment.

[0061] A carbon dioxide recovery system according to a fourth aspect of the present disclosure, in a third aspect, comprises a control unit (2), the evaporator being located at the top of the regeneration tower and the gas-liquid separator, the refrigerant circulation system having a bypass line (L35) that sends the refrigerant, which has been heated by the heat exchanger, to the evaporator located at the top of the regeneration tower, bypassing the expansion valve, the bypass line being provided with a bypass valve (36), and the control unit adjusting the opening degree of the bypass valve according to the temperature of the evaporator located at the top of the regeneration tower.

[0062] In the carbon dioxide recovery system of this disclosure, the evaporator is provided in a gas-liquid separator located at the top of the regeneration tower and downstream of the regeneration tower, and the refrigerant circulation system has a bypass line that sends the refrigerant, which has been heated by the radiator, to the evaporator located at the top of the regeneration tower, bypassing the expansion valve. Therefore, the refrigerant can be sent to the evaporator located at the top of the regeneration tower via the bypass line before it is expanded by the expansion valve. In addition, a bypass valve is provided in the bypass line, and the control unit is configured to adjust the opening degree of the bypass valve according to the temperature of the evaporator located at the top of the regeneration tower. Therefore, it is possible to control the temperature of the evaporator so that it does not drop too low. This prevents the exhaust gas from being cooled to the point where the absorbent liquid in the regeneration tower condenses due to the evaporator temperature dropping too low, and prevents the absorbent liquid from reabsorbing carbon dioxide.

[0063] In the fifth aspect of the present disclosure, the carbon dioxide recovery system, in any of the first to fourth aspects, has a heat radiator that radiates heat to the absorbent liquid supplied from the absorption tower (10), which absorbs the carbon dioxide contained in the gas to be treated, to the regeneration tower.

[0064] In the carbon dioxide capture system disclosed herein, the absorbent liquid, which absorbs carbon dioxide contained in the gas to be treated, is heated by a refrigerant circulating within a radiator by releasing heat into the absorbent liquid supplied from the absorption tower to the regeneration tower. This eliminates the need for a reboiler, which was conventionally used to heat the absorbent liquid. Furthermore, since the heat source for a reboiler is generally steam supplied from the plant where the carbon dioxide capture system is installed, eliminating the need for a heat source such as steam eliminates the need for a reboiler. This suppresses a decrease in the overall efficiency of the plant.

[0065] A carbon dioxide recovery system according to a sixth aspect of the present disclosure, in a fifth aspect, comprises a control unit (2), the control unit controls the compression of the refrigerant by the compressor so that the absorbent liquid supplied to the regeneration tower can be heated to a predetermined temperature.

[0066] In the carbon dioxide recovery system of this disclosure, the control unit is configured to control the compression of the refrigerant by the compressor so that the absorbent liquid supplied to the regeneration tower can be heated to a predetermined temperature according to a thermometer installed in the rich solution line. Therefore, the absorbent liquid supplied to the regeneration tower can be reliably heated to a sufficient temperature. This allows for more reliable separation of the absorbent liquid and carbon dioxide.

[0067] A method for operating a carbon dioxide recovery system according to a seventh aspect of this disclosure is a method for operating a carbon dioxide recovery system equipped with a refrigerant circulation system comprising a compressor for compressing a refrigerant, a radiator for releasing heat from the refrigerant compressed by the compressor, an expansion valve for expanding the refrigerant released heat from the radiator, and an evaporator for evaporating the refrigerant expanded by the expansion valve, wherein the method includes an exhaust step of discharging an exhaust gas containing carbon dioxide from an absorbent liquid that has absorbed carbon dioxide contained in a gas to be treated, by separating the carbon dioxide from the absorbent liquid and regenerating the absorbent liquid, and in the exhaust step, the exhaust gas is cooled by the evaporator.

[0068] The carbon dioxide recovery system used in this disclosure is equipped with a refrigerant circulation system, and the evaporator cools the exhaust gas containing carbon dioxide discharged from the regeneration tower. Conventionally, the absorbent liquid contained in the exhaust gas was collected by passing the exhaust gas discharged from the regeneration tower through a mist catcher installed downstream of the regeneration tower. In contrast, this disclosure uses an evaporator instead of a mist catcher. This allows the exhaust gas containing carbon dioxide discharged from the regeneration tower to be cooled by a refrigerant circulating within the evaporator. Therefore, the temperature of the exhaust gas can be sufficiently reduced, allowing the absorbent liquid contained in the exhaust gas to be condensed and collected more efficiently. [Explanation of symbols]

[0069] 1A, 1B Carbon Dioxide Capture System 2 Control Unit 10 Absorption Towers 11 Rich Solution Tank Section 12. Lean solution supply unit 13 Filled bed 20 Regeneration Tower 21 Lean solution tank section 22 Rich Solution Supply Unit 23 Filled bed 30 Refrigerant circulation system 31 Heat exchanger (radiator) 32 Heat exchanger (evaporator) 321 Radiator 322 Tube 323 Fin 33 Expansion valve 34. Heat exchanger (evaporator) 35 Compressor 36 Bypass valve 37 Thermometer 38 Heat exchanger (regenerative heat exchanger) 39 Motor 40 Steam water separator 41 Condensate Tank Section 43 pumps 44 Condensate Water Supply Unit 45 Pressure Regulating Valve 46 Pressure gauge 71 Lean Solution Pump 72 Lean Solution Cooler 73 Lean Solution Valve 81 Rich Solution Pump 83 Rich Solution Valve 84 Thermometer 91 Press Club 92 Fans 93 Exhaust gas cooler L1 Exhaust Gas Emission Line L12 Rich solution line (supply line) L21 Lean solution line (return line) L31, L32, L33, L34 Refrigerant circulation line L35 Bypass Line L41 Exhaust Gas Line L42 Condensate Recovery Line L43 Exhaust Gas Release Line

Claims

1. The refrigerant circulation system comprises a compressor for compressing the refrigerant, a heat sink for releasing heat from the refrigerant compressed by the compressor, an expansion valve for expanding the refrigerant released heat from the heat sink, and an evaporator for evaporating the refrigerant expanded by the expansion valve. The evaporator cools the exhaust gas containing carbon dioxide discharged from the regeneration tower, which separates the carbon dioxide from the absorbent liquid that has absorbed the carbon dioxide contained in the gas to be treated and regenerates the absorbent liquid. The evaporator is provided in the steam-liquid separator located at the top of the regeneration tower and downstream of the regeneration tower. Equipped with a control unit, The refrigerant circulation system has a bypass line that sends the refrigerant, which has been heated by the heat exchanger, to the evaporator located at the top of the regeneration tower, bypassing the expansion valve. A bypass valve is provided in the bypass line. The control unit is a carbon dioxide recovery system that adjusts the opening degree of the bypass valve according to the temperature of the evaporator located at the top of the regeneration tower.

2. The carbon dioxide recovery system according to claim 1, wherein the evaporator is a fin-tube type heat exchanger through which the refrigerant flows, and heat is exchanged between the exhaust gas discharged from the regeneration tower and the refrigerant.

3. The carbon dioxide recovery system according to claim 1 or 2, wherein the heat radiator dissipates heat to the absorbent liquid supplied from the absorption tower, which absorbs the carbon dioxide contained in the gas to be treated, to the regeneration tower.

4. Equipped with a control unit, The carbon dioxide recovery system according to claim 3, wherein the control unit controls the compression of the refrigerant by the compressor so that the absorbent liquid supplied to the regeneration tower can be heated to a predetermined temperature.

5. In a method for operating a carbon dioxide recovery system comprising a refrigerant circulation system comprising a compressor for compressing a refrigerant, a heat sink for releasing heat from the refrigerant compressed by the compressor, an expansion valve for expanding the refrigerant released heat from the heat sink, and an evaporator for evaporating the refrigerant expanded by the expansion valve, The system includes an exhaust process in which an exhaust gas containing carbon dioxide is discharged from a regeneration tower that separates the carbon dioxide from an absorbent liquid that has absorbed the carbon dioxide contained in the gas to be treated, thereby regenerating the absorbent liquid, and the exhaust gas is discharged from the regeneration tower. The evaporator is provided in the steam-liquid separator located at the top of the regeneration tower and downstream of the regeneration tower. The refrigerant circulation system has a bypass line that sends the refrigerant, which has been heated by the heat exchanger, to the evaporator located at the top of the regeneration tower, bypassing the expansion valve. A bypass valve is provided in the bypass line. In the discharge process, the exhaust gas is cooled by the evaporator. A method for operating a carbon dioxide recovery system, wherein in the discharge process, the opening degree of the bypass valve is adjusted according to the temperature of the evaporator located at the top of the regeneration tower.

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