Carbon dioxide recovery system and method for operating same

Abstract

Provided are a carbon dioxide recovery system with which it is possible to more efficiently collect an absorption liquid contained in exhaust gas, and a method for operating the carbon dioxide recovery system. A carbon dioxide recovery system (1A) comprises a refrigerant circulation system (30) configured to be provided with: a compressor (35) for compressing refrigerant; a radiator (31) for radiating heat from the refrigerant compressed by the compressor (35); an expansion valve (33) for expanding the refrigerant from which heat has been radiated by the radiator (31); and evaporators (32, 34) for evaporating the refrigerant expanded by the expansion valve (33). The evaporators (32, 34) cool a carbon-dioxide-containing exhaust gas discharged from a regeneration tower (20) for separating carbon dioxide contained in a gas being treated from an absorption liquid that has absorbed the carbon dioxide and regenerating the absorption liquid.

Description

Carbon dioxide capture system and its operating method

[0001] The present disclosure relates to a carbon dioxide capture system and a method for operating the same.

[0002] 2. Description of the Related Art In order to reduce carbon dioxide (CO2) emissions from thermal power plants and the like, systems for capturing generated CO2 (carbon dioxide capture systems) are being installed.

[0003] A carbon dioxide capture system, for example, brings flue gas into contact with an amine-based absorbent in an absorption tower, causing the absorbent to absorb CO2 and produce a rich solution (an absorbent with a relatively high CO2 content). The carbon dioxide capture system also supplies the produced rich solution to a regeneration tower, where it heats the rich solution to release the CO2 contained in the rich solution and produce a lean solution (an absorbent with a relatively low CO2 content). The carbon dioxide capture system then circulates the absorbent by supplying the lean solution to the absorption tower. At this time, a heat exchanger provided in the carbon dioxide capture system heats the rich solution supplied from the absorption tower to the regeneration tower with the lean solution returned from the regeneration tower to the absorption tower, thereby promoting the release of carbon dioxide in the regeneration tower. Related technologies are disclosed in Patent Documents 1 and 2.

[0004] JP 2015-24374 A JP 2015-163381 A

[0005] In recent years, attention has been focused on the environmental impact of absorbent solutions (e.g., amine-based absorbent solutions) used in carbon dioxide capture systems, and there is a demand for reducing the amount of absorbent solution discharged outside the system along with the gas to be treated. Conventional carbon dioxide capture systems are equipped with a device for recovering the absorbent solution contained in the gas to be treated, such as an inertial separation type mist collector, located at the top of the regeneration tower or downstream of the regeneration tower. However, inertial separation type mist collectors are unable to recover the absorbent solution in the gas phase corresponding to the saturated vapor pressure.

[0006] The present disclosure has been made in consideration of the above circumstances, and aims to provide a carbon dioxide recovery system and an operating method thereof that can more efficiently capture the absorption liquid contained in exhaust gas.

[0007] In order to solve the above problems, the carbon dioxide recovery system of the present disclosure comprises a refrigerant circulation system including a compressor that compresses a refrigerant, a radiator that dissipates heat from the refrigerant compressed by the compressor, an expansion valve that expands the refrigerant that has dissipated heat in the radiator, and an evaporator that evaporates the refrigerant expanded by the expansion valve, and the evaporator cools the exhaust gas containing the carbon dioxide that is discharged from a regeneration tower that separates the carbon dioxide from an absorption liquid that has absorbed carbon dioxide contained in the gas to be treated and regenerates the absorption liquid.

[0008] In addition, the method of operating a carbon dioxide capture system disclosed herein is a method of operating a carbon dioxide capture system equipped with a refrigerant circulation system including a compressor that compresses a refrigerant, a radiator that radiates heat from the refrigerant compressed by the compressor, an expansion valve that expands the refrigerant that has radiated heat in the radiator, and an evaporator that evaporates the refrigerant expanded by the expansion valve, and includes a discharge step of separating the carbon dioxide from an absorption liquid that has absorbed carbon dioxide contained in a gas to be treated and discharging an exhaust gas containing the carbon dioxide from a regeneration tower that regenerates the absorption liquid, and in the discharge step, the exhaust gas is cooled by the evaporator.

[0009] The carbon dioxide capture system and operating method thereof disclosed herein can cool the exhaust gas containing carbon dioxide discharged from the regeneration tower using the refrigerant circulating in the evaporator, thereby sufficiently lowering the temperature of the exhaust gas and enabling the absorption liquid contained in the exhaust gas to be condensed and more efficiently captured.

[0010] Fig. 5 is a schematic configuration diagram of a carbon dioxide capture system according to an embodiment of the present disclosure. Fig. 6 is a schematic configuration diagram showing a radiator constituting a heat exchanger in the carbon dioxide capture system of Fig. 1. Fig. 7 is a schematic configuration diagram of a heat exchanger in the carbon dioxide capture system of Fig. 1. Fig. 8 is a schematic configuration diagram of a carbon dioxide capture system according to a modified example of an embodiment of the present disclosure. Fig. 9 is a schematic configuration diagram of a carbon dioxide capture system according to a comparative example. Fig. 10 is a schematic configuration diagram showing a mist catcher in the carbon dioxide capture system of Fig. 5.

[0011] Hereinafter, an embodiment of a carbon dioxide capture system and an operating method thereof according to the present disclosure will be described with reference to the drawings.

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

[0013] The absorption tower 10 is a facility that chemically absorbs carbon dioxide contained in flue gas (gas to be treated) into an absorption liquid (e.g., an amine-based absorption liquid). A packed bed 13 filled with packing is provided inside the absorption tower 10, which increases the gas-liquid contact efficiency between the absorption liquid and the flue gas. The lower / bottom portion of the absorption tower 10 serves as a rich solution tank section 11 in which a rich solution (absorption liquid that has absorbed carbon dioxide) is stored.

[0014] An exhaust gas discharge line L1 is connected to the lower part of the absorption tower 10 and above the rich solution tank section 11. The exhaust gas discharge line L1 is a line that supplies exhaust gas discharged from a plant such as a thermal power plant or a boiler plant to the absorption tower 10.

[0015] A prescrubber 91, a fan 92, and an exhaust gas cooler 93 are provided along the flue gas discharge line L1. The prescrubber 91 is a device that performs pretreatment on the flue gas to be introduced into the absorber 10, and removes soot and dust from the flue gas flowing through the flue gas discharge line L1. The fan 92 is a device that blows the flue gas flowing through the flue gas discharge line L1 into the lower part of the absorber 10. The flue gas cooler 93 is a device that lowers the temperature of the flue gas flowing through the flue gas discharge line L1 to a temperature optimal for the chemical absorption performed in the absorber 10. An example of the cooling medium is on-site cooling water used in various parts of the plant. The prescrubber 91, the fan 92, and the flue gas cooler 93 may be omitted as appropriate depending on the conditions (composition, temperature, pressure, etc.) of the flue gas to be treated.

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

[0017] The regeneration tower 20 is provided with a packed bed 23 filled with packing material inside, which increases the gas-liquid contact efficiency between the absorption liquid and the exhaust gas.

[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 (feed line) L12, and the rich solution stored in the rich solution tank section 11 is supplied to the regeneration tower 20.

[0019] A rich solution supply unit 22 is connected to an end of the rich solution line L12. The rich solution supply unit 22 is a unit that injects the rich solution supplied from the absorption tower 10 into the regeneration tower 20, and is provided at the upper part of the regeneration tower 20. The rich solution injected from the rich solution supply unit 22 descends within the regeneration tower 20, releasing at least a portion of the carbon dioxide during the process of descending.

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

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

[0022] The lean solution tank section 21 of the 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] An end of the lean solution line L21 is connected to a lean solution supply unit 12. The lean solution supply unit 12 is a unit that injects the lean solution supplied from the regeneration tower 20 into the absorption tower 10, and is provided 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 inside the absorption tower 10, and while passing through the packed bed 13 during the descending process, comes into contact with the flue gas supplied from the flue gas discharge line L1, thereby absorbing carbon dioxide.

[0024] A lean solution pump 71, a lean solution cooler 72, and a lean solution valve 73 are provided along the lean solution line L21. The lean solution pump 71 is a pump for sending the lean solution stored in the lean solution tank unit 21 to the absorber 10. The lean solution pump 71 is provided at a position on the lean solution line L21 downstream of the heat exchanger 31. The lean solution cooler 72 is a device for lowering the temperature of the lean solution flowing through the lean solution line L21 to a temperature range suitable for chemical absorption performed in the absorber 10. An example of the cooling medium is on-site cooling water. The lean solution cooler 72 is provided at a position on the lean solution line L21 downstream of the lean solution pump 71. The lean solution valve 73 is a valve for changing the flow rate of the lean solution supplied to the absorber 10 (lean solution supply unit 12). The lean solution valve 73 is provided at a location on the lean solution line L21 downstream of the lean solution cooler 72. The rotation speed of the lean solution pump 71 and the opening degree of the lean solution valve 73 are determined and adjusted by the control unit 2. The flow rate of the lean solution supplied to the absorption tower 10 (lean solution supply unit 12) may be changed by changing the rotation speed of the lean solution pump 71. In this case, the lean solution valve 73 can be omitted, or there is no need to adjust the opening degree of the lean solution valve 73 (for example, it is always fully open).

[0025] A heat exchanger (radiator) 31 constituting a refrigerant circulation system 30 (described later) is provided midway along the rich solution line L12 and the lean solution line L21. The heat exchanger 31 is a device that uses a refrigerant compressed by a compressor 35 (described later) as a heat source to heat the rich solution (absorption solution 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 dissipation in the regeneration tower 20, thereby promoting carbon dioxide dissipation 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 to be used as a radiator that dissipates heat from the refrigerant compressed by the compressor 35 using air cooling. In this case, a separate heat exchanger may be provided that uses the lean solution flowing through the lean solution line L21 as a heat source to heat the rich solution flowing through the rich solution line L12.

[0026] A heat exchanger (regenerative heat exchanger) 38 may be provided midway along 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 that shown in FIG. 1 . The heat exchanger 31 and the heat exchanger 38 may also be integrally configured. The heat exchanger 38 exchanges heat between the rich solution (the absorption liquid flowing from the absorber 10 to the regenerator 20) flowing through the rich solution line L12 and the lean solution (the absorption liquid flowing from the regenerator 20 to the absorber 10) flowing through the lean solution line L21. Heating the rich solution in the heat exchanger 38 raises the temperature of the rich solution to a temperature range suitable for carbon dioxide dissipation in the regenerator 20, thereby facilitating carbon dioxide dissipation in the regenerator 20. Furthermore, since the heat exchanger 38 can cool the lean solution, the temperature of the lean solution can be lowered to a temperature range suitable for carbon dioxide chemical absorption in the absorber 10, thereby facilitating carbon dioxide chemical absorption in the absorber 10. In addition, considering the possibility that the heat exchanger 38 alone may not be able to sufficiently 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 provided at the top of the regeneration tower 20. The heat exchanger 32 is a component of a refrigerant circulation system 30, which will be described later, and is a device that cools the exhaust gas containing carbon dioxide that is discharged from the regeneration tower 20. By cooling the exhaust gas containing carbon dioxide using the heat exchanger 32, the temperature of the exhaust gas can be sufficiently lowered, and the absorption liquid contained in the exhaust gas can be condensed. The structure of the heat exchanger 32 will be described in detail later.

[0028] A steam-water separator 40 is provided outside the regeneration tower 20 to separate condensed water and the like from the exhaust gas discharged from the top of the tower through the exhaust gas exhaust line L41. That is, the steam-water separator 40 is disposed downstream of the regeneration tower 20. The lower / bottom part of the steam-water separator 40 serves as a condensed water tank part 41 in which water and the like condensed in the steam-water separator 40 are stored.

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

[0030] An end of the condensed water recovery line L42 is connected to a condensed water supply unit 44. The condensed water supply unit 44 is a part that injects condensed water and the like supplied from the steam-water separator 40 into the regeneration tower 20, and is provided 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 steam-water 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 using the heat exchanger 34, the temperature of the exhaust gas can be sufficiently lowered, allowing the water vapor and absorbing liquid contained in the exhaust gas to condense. The exhaust gas discharged from the regeneration tower 20 is thus sufficiently cooled by the heat exchanger 34 of the steam-water separator 40, and the contained water vapor, absorbing liquid, etc. are condensed as much as possible. The condensed water, absorbing liquid, etc. are separated in the steam-water separator 40. The exhaust gas from which the water vapor, absorbing liquid, etc. have been separated is discharged from an exhaust gas discharge line L43 connected to the top of the steam-water separator 40. A pressure regulating valve 45 is provided in the exhaust gas discharge line L43, and the pressure inside the steam-water separator 40 is regulated. A pressure gauge 46 is provided in the exhaust gas discharge line L41 to check the pressure inside the steam-water separator 40. The pressure inside the steam-water separator 40 is controlled by a pressure regulating valve 45 and the pressure gauge 46 so as to prevent the evaporated absorption liquid from being discharged from the exhaust gas discharge line L43. The structure of the heat exchanger 34 will be described in detail later.

[0032] The heat exchangers 32, 34 constituting the refrigerant circulation system 30 do not need to be provided in both the regenerator 20 and the steam-water separator 40. For example, it is also possible to provide an inertial separation type mist collector in place of either the heat exchanger 32 of the regenerator 20 or the heat exchanger 34 of the steam-water separator 40.

[0033] [Configuration of the refrigerant circulation system] The refrigerant circulation system 30 is configured to include a compressor 35 that compresses the refrigerant, a radiator (heat exchanger) 31 that radiates heat from the refrigerant compressed by the compressor 35, an expansion valve 33 that expands the refrigerant that has radiated heat in the radiator 31, and evaporators (heat exchangers) 32 and 34 that evaporate the refrigerant expanded by the expansion valve 33. These components that make up the refrigerant circulation system 30 are connected by respective lines.

[0034] That is, a refrigerant circulation line L31 connected to a refrigerant outlet of the compressor 35 is connected to the heat exchanger 31. The heat exchanger 31 is connected to a heat exchanger 34 of the steam-water separator 40 via a refrigerant circulation line L32 and an expansion valve 33. The heat exchanger 34 of the steam-water separator 40 is connected to a heat exchanger 32 of the regeneration tower 20 via a refrigerant circulation line L33. The heat exchanger 32 of the regeneration tower 20 is connected to a refrigerant inlet of the compressor 35 via a refrigerant circulation line L34.

[0035] [Configuration of the Heat Exchanger] The configuration of the heat exchanger 32 (34) according to this embodiment will be described with reference to FIGS. 2 and 3. The heat exchanger 32 includes at least one radiator 321, with tubes 322, each having fins 323 wrapped around its outer periphery, folded back alternately. A refrigerant flows through the tubes 322. That is, the heat exchanger 32 is a fin-tube 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 absorbing liquid contained in the exhaust gas condenses and impinges on the heat exchanger 32 (the tubes 322 and the fins 323). Droplets of water vapor and condensed absorbing liquid are formed (precipitated) on the surfaces of the fins 323 cooled by the refrigerant. As the condensed droplets grow, they fall downward. This allows the absorbing 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 configured to include multiple layers of radiators 321 shown in Fig. 2. Inside the radiator 321, tubes 322 with fins (not shown in Fig. 2) wound around their outer peripheries are provided in an alternately folded shape. As shown in Fig. 2, a refrigerant inlet to 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 configured to include multiple layers of the radiators 321 (cooling fins are shown) shown in Figure 2. Specifically, the heat exchanger 32 is configured by stacking multiple layers of the radiators 321 shown in Figure 2 that are laid on their sides. Exhaust gas containing carbon dioxide is introduced into the heat exchanger 32 from the bottom in Figure 3, the absorption liquid contained in the exhaust gas is removed in the heat exchanger 32, and the carbon dioxide is discharged to the top in Figure 3.

[0038] [Regarding Operation of the Carbon Dioxide Capture System] In the carbon dioxide capture system 1A configured as described above, the absorption liquid circulates between the absorption tower 10 and the regeneration tower 20. The operating method of the carbon dioxide capture system 1A of this embodiment includes a discharge step of discharging exhaust gas containing carbon dioxide from the regeneration tower 20, and in the discharge step, the exhaust gas is cooled by the evaporators 32, 34.

[0039] 5 is a schematic configuration diagram showing a carbon dioxide capture system 101 according to a comparative example. The carbon dioxide capture system 101 according to the comparative example does not include the refrigerant circulation system 30 of the present embodiment. Accordingly, the comparative example includes mist catchers 132, 134 instead of the heat exchangers 32, 34 of the present embodiment, and includes a water-cooled cooler 147 in the exhaust gas exhaust line L41 for cooling the exhaust gas. 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 or the like supplied from an external facility (for example, a plant in which a carbon dioxide capture system such as a thermal power plant or a boiler facility is installed) as a heat source to heat the absorption solution stored at the bottom of the regenerator 20. The absorption solution in the regenerator 20 is heated to release at least a portion of the carbon dioxide. In addition, a portion of the heated absorption solution heats the rich solution through heat exchange with the rich solution in a heat exchanger 38 installed in the lean solution line L21, and is then cooled before being supplied to the absorption tower 10.

[0041] FIG. 6 is a schematic diagram showing the configuration of the mist catcher 132 (134) in the carbon dioxide capture system 101 of FIG. 5. The mist catcher 132 (134) is, for example, an inertial separation type mist collection device. As shown in FIG. 6, the mist catcher 132 is made up of multiple layers of uneven galvanized iron roof-like plates arranged with their longitudinal directions parallel to the gas flow. When exhaust gas flows in from below the mist catcher 132, the mist of the absorbing solution contained in the exhaust gas collides with the uneven shape of the plates due to the inertia of the plate, and droplets are formed on the surface of the plate. Then, as the droplets grow larger, they fall downward. This is how the mist of the absorbing solution contained in the exhaust gas is collected.

[0042] However, in the carbon dioxide capture system 101 of the comparative example, there was a limit to improving the capture rate of the absorbing liquid in the mist catchers 132, 134. That is, the mist catchers 132, 134 can only capture liquid mist, and cannot capture gaseous absorbing liquid. On the other hand, in this embodiment, the refrigerant circulation system 30 is introduced and heat exchangers (evaporators) 32, 34 are provided instead of the mist catchers 132, 134. This allows the absorbing liquid to be captured while cooling the exhaust gas, making it possible to condense and capture a portion of the gaseous absorbing liquid, thereby improving the capture rate of the absorbing liquid. Furthermore, this eliminates the need for the cooler 147 that was previously separate from the mist catchers 132, 134.

[0043] The actions and effects of the carbon dioxide capture system 1A according to the present embodiment described above will be described.

[0044] The carbon dioxide capture system 1A according to this embodiment includes a refrigerant circulation system 30, and evaporators 32, 34 cool the exhaust gas containing carbon dioxide discharged from the regeneration tower 20. Conventionally, the exhaust gas discharged from the regeneration tower 20 is passed through a mist catcher provided downstream of the regeneration tower 20 to capture the absorbing liquid contained in the exhaust gas. However, in this embodiment, the evaporators 32, 34 are provided instead of the mist catcher. This allows the exhaust gas containing carbon dioxide discharged from the regeneration tower 20 to be cooled by the refrigerant circulating through the evaporators 32, 34. Therefore, the temperature of the exhaust gas can be sufficiently lowered, allowing the absorbing liquid contained in the exhaust gas to condense and be more efficiently captured.

[0045] The finned tube heat exchanger has a finer mesh structure (with fins 323) than the mist catchers used conventionally, and therefore can more reliably cause the exhaust gas to collide with the evaporators 32, 34. This allows sufficient heat exchange between the exhaust gas and the refrigerant to cool the exhaust gas, thereby enabling the absorption liquid to be collected accurately and efficiently.

[0046] The carbon dioxide capture system 1A according to this embodiment is equipped with a refrigerant circulation system 30 and is configured to cool exhaust gas using evaporators 32, 34 through which a refrigerant flows. Therefore, compared to when a mist catcher is used, the cooling efficiency is higher due to the use of a refrigerant. Therefore, by providing the evaporators 32, 34 in the steam-water separator 40 located above the regeneration tower 20 and / or downstream of the regeneration tower 20, it is possible to eliminate the need for a heat exchanger for cooling exhaust gas that was previously provided between the regeneration tower 20 and the steam-water separator 40. This allows for a reduction in equipment.

[0047] In the carbon dioxide capture system 1A according to this embodiment, heat is dissipated to the absorption liquid supplied from the absorption tower 10, which absorbs carbon dioxide contained in the gas to be treated into the absorption liquid, to the regeneration tower 20, so that the absorption liquid can be heated by the refrigerant circulating in the radiator 31. This makes it possible to eliminate the need for a reboiler, which has conventionally been used to heat the absorption liquid. Furthermore, since the heat source for the reboiler is generally steam supplied from the plant in which the carbon dioxide capture system 1A is installed, eliminating the need for a reboiler also makes it possible to eliminate the need for a heat source such as steam. This makes it possible to suppress a decrease in efficiency of the entire plant.

[0048] [Modification] Next, details of a carbon dioxide capture system 1B according to a modification of the present embodiment will be described with reference to Fig. 4. This modification differs from the present embodiment in that a thermometer 84 is provided in the rich solution line L12, and that a bypass line L35, a bypass valve 36, and a thermometer 37 are provided in the refrigerant circulation system 30. The same components as those in the present embodiment are denoted by the same reference numerals, and detailed descriptions thereof will be omitted.

[0049] 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 and bypasses the expansion valve 33 and the heat exchanger 34. In addition, a bypass valve 36 is provided in the bypass line L35. This allows the refrigerant that has dissipated heat in the heat exchanger 31 to be supplied to the heat exchanger 32 of the regeneration tower 20 without being expanded by the expansion valve 33 by opening the bypass valve 36.

[0050] Furthermore, a thermometer 37 is provided downstream of the junction with the bypass line L35 in the refrigerant circulation line L33. This allows the control unit 2 to check the temperature on the thermometer 37 and adjust the opening of the bypass valve 36 according to the temperature of the heat exchanger 32 provided in the upper part of the regeneration tower 20 (specifically, the temperature of the refrigerant flowing therethrough). Therefore, the temperature of the heat exchanger 32 can be controlled so as not to drop too much.

[0051] In this modification, a thermometer 84 is provided in the rich solution line L12 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. That is, the control unit 2 is configured to control the compression ratio of the refrigerant by the compressor 35 via the motor 39 that rotates the compressor 35 so that the temperature of the absorption liquid supplied to the regeneration tower 20 can be raised to a predetermined temperature. The predetermined temperature is a temperature at which carbon dioxide can be reliably separated from the absorption liquid after the absorption liquid is supplied to the regeneration tower 20.

[0052] The actions and effects of the carbon dioxide capture system 1B according to this modified example described above will be described.

[0053] In the carbon dioxide capture system 1B according to this modification, heat exchangers 32 and 34 are provided in the upper part of the regeneration tower 20 and in the steam-water separator 40 disposed downstream of the regeneration tower 20. The refrigerant circulation system 30 has a bypass line L35 that sends the refrigerant that has dissipated heat in the heat exchanger 31 to the heat exchanger 32 disposed in the upper part of the regeneration tower 20, bypassing the expansion valve 33. Therefore, the refrigerant before being expanded in the expansion valve 33 can be sent to the heat exchanger 32 disposed in the upper part 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 disposed in the upper part of the regeneration tower 20. Therefore, the temperature of the heat exchanger 32 can be controlled so as not to drop too low. This prevents the temperature of the heat exchanger 32 from dropping too low, which would cool the exhaust gas to the extent that the absorbing liquid in the regeneration tower 20 condenses, thereby preventing the absorbing liquid from reabsorbing carbon dioxide.

[0054] In the carbon dioxide capture system 1B according to this modification, the control unit 2 is configured to control the compression of the refrigerant by the compressor 35 in accordance with the thermometer 84 provided in the rich solution line L12 so that the temperature of the absorbing solution supplied to the regenerator 20 can be raised to a predetermined temperature. Therefore, the absorbing solution to be supplied to the regenerator 20 can be reliably heated to a sufficient temperature. This makes it possible to more reliably separate the absorbing solution and carbon dioxide.

[0055] <Additional Notes> The carbon dioxide capture system and its operating method described in the above-described embodiments can be understood, for example, as follows: A carbon dioxide capture system (1A, 1B) according to a first aspect of the present disclosure includes a refrigerant circulation system (30) including a compressor (35) that compresses a refrigerant, a radiator (31) that radiates heat from the refrigerant compressed by the compressor, an expansion valve (33) that expands the refrigerant that has radiated heat in the radiator, and an evaporator (32, 34) that evaporates the refrigerant expanded by the expansion valve, and the evaporator cools the carbon dioxide-containing exhaust gas discharged from a regeneration tower (20) that separates carbon dioxide from an absorption liquid that has absorbed carbon dioxide contained in a gas to be treated and regenerates the absorption liquid.

[0056] The carbon dioxide capture system disclosed herein includes a refrigerant circulation system, and an evaporator cools the exhaust gas containing carbon dioxide discharged from the regeneration tower. Conventionally, the exhaust gas discharged from the regeneration tower is passed through a mist catcher installed downstream of the regeneration tower to capture the absorbing liquid contained in the exhaust gas. In contrast, the present 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 the refrigerant circulating within the evaporator. Therefore, the temperature of the exhaust gas can be sufficiently lowered, allowing the absorbing liquid contained in the exhaust gas to condense and be more efficiently captured.

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

[0058] The finned tube heat exchanger has a finer mesh structure (finned structure) than the mist catcher used in the past, which allows the exhaust gas to collide with the evaporator more reliably. This allows for sufficient heat exchange between the exhaust gas and the refrigerant, cooling the exhaust gas, and allowing for accurate and efficient collection of the absorption liquid.

[0059] A carbon dioxide capture system according to a third aspect of the present disclosure is the first or second aspect, wherein the evaporator is provided in an air-water separator (40) arranged above the regeneration tower and / or downstream of the regeneration tower.

[0060] The carbon dioxide capture system disclosed herein is equipped with a refrigerant circulation system and is configured to cool exhaust gas using an evaporator through which a refrigerant flows. Therefore, compared to systems using a mist catcher, the cooling efficiency is higher due to the use of a refrigerant. Therefore, by providing an evaporator in the steam-water separator located above the regeneration tower and / or downstream of the regeneration tower, the heat exchanger for cooling exhaust gas that was previously provided between the regeneration tower and the steam-water separator can be eliminated. This allows for a reduction in equipment.

[0061] The carbon dioxide recovery system according to a fourth aspect of the present disclosure is the third aspect, and further includes a control unit (2), wherein the evaporator is provided in an upper part of the regeneration tower and in the steam-water separator, and the refrigerant circulation system has a bypass line (L35) that sends the refrigerant that has had heat dissipated in the radiator to the evaporator provided in the upper part of the regeneration tower, bypassing the expansion valve, and a bypass valve (36) is provided in the bypass line, and the control unit adjusts the opening degree of the bypass valve according to the temperature of the evaporator provided in the upper part of the regeneration tower.

[0062] In the carbon dioxide capture system disclosed herein, evaporators are provided in the upper part of the regeneration tower and in the steam-water separator located downstream of the regeneration tower. The refrigerant circulation system includes a bypass line that sends refrigerant that has been heat-dissipated in the radiator to the evaporator located in the upper part of the regeneration tower, bypassing the expansion valve. Therefore, refrigerant before being expanded in the expansion valve can be sent to the evaporator located in the upper part of the regeneration tower via the bypass line. The bypass line also includes a bypass valve, and the control unit is configured to adjust the opening of the bypass valve depending on the temperature of the evaporator located in the upper part of the regeneration tower. This allows for control so that the evaporator temperature does not drop too low. This prevents the evaporator temperature from dropping too low, which would cool the exhaust gas to the point where the absorbing liquid condenses in the regeneration tower, causing the absorbing liquid to reabsorb carbon dioxide.

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

[0064] In the carbon dioxide capture system disclosed herein, heat is dissipated into the absorption liquid supplied from the absorption tower, which absorbs carbon dioxide contained in the gas to be treated, into the absorption liquid, which is supplied to the regeneration tower, and the absorption liquid can be heated by the refrigerant circulating in the radiator. This eliminates the need for a reboiler, which has traditionally been used to heat the absorption liquid. Furthermore, since the heat source for the reboiler is generally steam supplied from the plant in which the carbon dioxide capture system is installed, eliminating the need for a reboiler also eliminates the need for a heat source such as steam. This prevents a decrease in the efficiency of the entire plant.

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

[0066] In the carbon dioxide capture system of the present disclosure, the control unit controls the compression of the refrigerant by the compressor in accordance with the temperature of the rich solution line so that the absorbent supplied to the regeneration tower can be heated to a predetermined temperature. This ensures that the absorbent supplied to the regeneration tower can be reliably heated to a sufficient temperature. This allows for more reliable separation of the absorbent and carbon dioxide.

[0067] A method for operating a carbon dioxide capture system according to a seventh aspect of the present disclosure is a method for operating a carbon dioxide capture system having a refrigerant circulation system including a compressor that compresses a refrigerant, a radiator that radiates heat from the refrigerant compressed by the compressor, an expansion valve that expands the refrigerant that has radiated heat in the radiator, and an evaporator that evaporates the refrigerant expanded by the expansion valve, the method comprising a discharge step of separating carbon dioxide from an absorption liquid that has absorbed carbon dioxide contained in a gas to be treated and discharging an exhaust gas containing the carbon dioxide from a regeneration tower that regenerates the absorption liquid, and in the discharge step, the exhaust gas is cooled by the evaporator.

[0068] The carbon dioxide capture system used in the present disclosure is equipped with a refrigerant circulation system, and an evaporator cools the exhaust gas containing carbon dioxide discharged from the regeneration tower. Conventionally, the exhaust gas discharged from the regeneration tower is passed through a mist catcher installed downstream of the regeneration tower to capture the absorbing liquid contained in the exhaust gas. However, in the present disclosure, an evaporator is installed instead of the mist catcher. This allows the exhaust gas containing carbon dioxide discharged from the regeneration tower to be cooled by the refrigerant circulating within the evaporator. Therefore, the temperature of the exhaust gas can be sufficiently lowered, allowing the absorbing liquid contained in the exhaust gas to condense and be more efficiently captured.

[0069] DESCRIPTION OF SYMBOLS 1A, 1B Carbon dioxide recovery system 2 Control unit 10 Absorption tower 11 Rich solution tank unit 12 Lean solution supply unit 13 Packed bed 20 Regeneration tower 21 Lean solution tank unit 22 Rich solution supply unit 23 Packed 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 Condensed water tank unit 43 Pump 44 Condensed 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 Presscrubber 92 Fan 93 Exhaust gas cooler L1 Exhaust gas discharge line L12 Rich solution line (feed line) L21 Lean solution line (return line) L31, L32, L33, L34 Refrigerant circulation line L35 Bypass line L41 Exhaust gas exhaust line L42 Condensed water recovery line L43 Exhaust gas discharge line

Claims

1. A carbon dioxide recovery system comprising a refrigerant circulation system including a compressor that compresses a refrigerant, a radiator that radiates heat from the refrigerant compressed by the compressor, an expansion valve that expands the refrigerant that has radiated heat in the radiator, and an evaporator that evaporates the refrigerant expanded by the expansion valve, wherein the evaporator cools exhaust gas containing the carbon dioxide that is discharged from a regeneration tower that separates the carbon dioxide from an absorption liquid that has absorbed the carbon dioxide contained in the gas to be treated and regenerates the absorption liquid.

2. The carbon dioxide recovery system described in claim 1, wherein the evaporator is a fin-tube heat exchanger through which the refrigerant flows, and exchanges heat between the exhaust gas released from the regeneration tower and the refrigerant.

3. A carbon dioxide recovery system as described in claim 1 or 2, wherein the evaporator is provided in an air-water separator located above the regeneration tower and / or downstream of the regeneration tower.

4. A carbon dioxide recovery system as described in claim 3, further comprising a control unit, wherein the evaporator is provided at the top of the regeneration tower and at the steam-water separator, the refrigerant circulation system has a bypass line that sends the refrigerant that has had heat dissipated in the radiator to the evaporator provided at the top of the regeneration tower, bypassing the expansion valve, and a bypass valve is provided in the bypass line, and the control unit adjusts the opening of the bypass valve according to the temperature of the evaporator provided at the top of the regeneration tower.

5. A carbon dioxide recovery system as described in claim 1 or 2, wherein the radiator radiates heat to the absorption liquid supplied to the regeneration tower from an absorption tower that absorbs the carbon dioxide contained in the gas to be treated into the absorption liquid.

6. A carbon dioxide recovery system as described in claim 5, further comprising a control unit, which controls the compression of the refrigerant by the compressor so that the absorption liquid supplied to the regeneration tower can be heated to a predetermined temperature.

7. A method for operating a carbon dioxide capture system equipped with a refrigerant circulation system including a compressor that compresses a refrigerant, a radiator that radiates heat from the refrigerant compressed by the compressor, an expansion valve that expands the refrigerant that has radiated heat in the radiator, and an evaporator that evaporates the refrigerant expanded by the expansion valve, the method comprising a discharge step of separating carbon dioxide from an absorption liquid that has absorbed carbon dioxide contained in a gas to be treated and discharging the carbon dioxide-containing exhaust gas from a regeneration tower that regenerates the absorption liquid, and in the discharge step, cooling the exhaust gas by the evaporator.

Images