Carbon dioxide recovery system and carbon dioxide recovery method

Abstract

The present invention provides an alternate technology capable of recovering carbon dioxide. This carbon dioxide recovery system comprises: a compressor that compresses a gas containing carbon dioxide and nitrogen; a tank that stores the compressed gas; a cooler that cools the carbon dioxide contained in the gas in the tank until the carbon dioxide turns into a solid; and a heater that heats the carbon dioxide, which has turned into a solid through cooling, until the carbon dioxide turns into a liquid. In a state in which the nitrogen contained in the gas in the tank is removed, the carbon dioxide recovery system heats the solid carbon dioxide and recovers the liquid carbon dioxide.

Description

Carbon dioxide capture system, carbon dioxide capture method

[0001] The present disclosure relates to a carbon dioxide capture system. This application is based on Japanese Patent Application No. 2024-047008 filed on March 22, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, technologies for capturing carbon dioxide have been proposed with the aim of achieving carbon neutrality. For example, Patent Document 1 discloses a carbon dioxide capture system including a cooling tower that cools a gas containing carbon dioxide by bringing the gas into contact with cooling water, an absorption tower that brings the gas cooled in the cooling tower into contact with an absorbing liquid to absorb the carbon dioxide into the absorbing liquid, a regeneration tower that heats the absorbing liquid that has absorbed carbon dioxide in the absorption tower to release the carbon dioxide from the absorbing liquid, and a heat pump that directly or indirectly heats the absorbing liquid in the regeneration tower with the heat of the cooling water.

[0003] Japanese Patent Application Laid-Open No. 2023-162661

[0004] In the carbon dioxide capture system described in Patent Document 1, carbon dioxide is absorbed in an absorption liquid, so there is a risk that components of the absorption liquid may be contained in the captured carbon dioxide, and there is therefore room for improvement. For this reason, there is a demand for other technologies that can capture carbon dioxide.

[0005] The present disclosure can be realized in the following forms.

[0006] (1) According to one aspect of the present disclosure, there is provided a carbon dioxide capture system. The carbon dioxide capture system includes a compressor that compresses a gas containing carbon dioxide and nitrogen, a tank that stores the compressed gas, a cooler that cools the carbon dioxide contained in the gas in the tank until it becomes a solid, and a heater that heats the cooled, solidified carbon dioxide until it becomes a liquid, and the solid carbon dioxide is heated and captured as liquid carbon dioxide in a state in which the nitrogen contained in the gas in the tank has been removed. This form of carbon dioxide capture system can capture carbon dioxide without using an absorption liquid.

[0007] (2) In the carbon dioxide capture system described in (1) above, a piston that reduces the volume of the gas phase may be provided in the tank. According to this form of carbon dioxide capture system, the volume of the gas phase can be reduced by the piston provided in the tank, so that an increase in the amount of carbon dioxide vaporized by heating can be suppressed, and as a result, a decrease in carbon dioxide capture efficiency can be suppressed.

[0008] (3) The carbon dioxide capture system described in (1) or (2) above may further include a liquid storage tank and an opening / closing unit that switches the communication state between the tank and the liquid storage tank, and the heater may include a first heater that heats the tank and a second heater that heats the liquid storage tank. The opening / closing unit may be opened to transfer carbon dioxide that has been partially liquefied by heating with the first heater to the liquid storage tank, and the opening / closing unit may be closed before heating with the second heater. This carbon dioxide capture system includes a first heater that heats the tank and a second heater that heats the liquid storage tank. Therefore, the carbon dioxide that has been partially liquefied in the tank can be heated in the liquid storage tank. As a result, the carbon dioxide can be heated and liquid carbon dioxide can be captured while removing nitrogen from the gas in the tank.

[0009] (4) According to another aspect of the present disclosure, there is provided a carbon dioxide capture method. This carbon dioxide capture method includes a compression step of compressing a gas containing carbon dioxide and nitrogen, a cooling step of cooling the carbon dioxide contained in the gas after the compression step until it becomes solid, a removal step of removing the nitrogen contained in the gas after the cooling step, a heating step of heating the solid carbon dioxide until it becomes liquid, and a capture step of capturing the liquid carbon dioxide. According to this aspect of the carbon dioxide capture method, carbon dioxide can be captured without using an absorption liquid.

[0010] (5) In the carbon dioxide recovery method described in (4) above, the removal step may include a step of reducing the volume of the gas phase. According to this form of carbon dioxide recovery method, since the step of reducing the volume of the gas phase is included, an increase in the amount of carbon dioxide vaporized in the heating step can be suppressed, and as a result, a decrease in the carbon dioxide recovery efficiency can be suppressed.

[0011] (6) In the carbon dioxide capture method described in (4) or (5) above, the heating step may include a first heating step performed before the removal step and a second heating step performed after the removal step, and the first heating step may be a step of heating the carbon dioxide after the cooling step until a portion of the carbon dioxide becomes liquid, and the second heating step may be a step of heating the solid carbon dioxide, which has been partially liquefied by the first heating step, until it becomes liquid in a state in which nitrogen has been removed. According to this form of carbon dioxide capture method, the first heating step performed before the removal step and the second heating step performed after the removal step are included, and therefore the carbon dioxide that has been partially liquefied by the first heating step can be fully heated in the second heating step. As a result, it is possible to heat carbon dioxide and capture liquid carbon dioxide in a state in which nitrogen contained in the gas has been removed in the removal step.

[0012] The present disclosure can be realized in various forms, for example, a carbon dioxide capture device, a method for manufacturing a carbon dioxide capture device, a carbon dioxide production system, a carbon dioxide production device, a method for manufacturing carbon dioxide, etc.

[0013] Fig. 1 is an explanatory diagram for explaining a schematic configuration of a carbon dioxide capture system. Fig. 2 is an explanatory diagram for explaining the operation of the carbon dioxide capture system. Fig. 3 is an explanatory diagram for explaining a state change of carbon dioxide. Fig. 4 is a process diagram showing a carbon dioxide capture method. Fig. 5 is a schematic diagram showing the configuration of a main part of a carbon dioxide capture system of a second embodiment. Fig. 6 is a process diagram showing a carbon dioxide capture method.

[0014] A. First Embodiment (1) Carbon Dioxide Capture System FIG. 1 is an explanatory diagram illustrating a schematic configuration of a carbon dioxide capture system 100 according to an embodiment of the present disclosure. FIG. 2 is an explanatory diagram illustrating the operation of the carbon dioxide capture system 100. FIG. 3 is an explanatory diagram illustrating changes in the state of carbon dioxide. The carbon dioxide capture system 100 (hereinafter also referred to as "system 100") in this embodiment captures carbon dioxide from a gas containing carbon dioxide and nitrogen (hereinafter also referred to as "feed gas"). In addition to carbon dioxide and nitrogen, the feed gas may also contain water vapor and other gases. The feed gas is not particularly limited, but is preferably a combustion exhaust gas generated in a thermal power plant (not shown). The combustion exhaust gas is expected to be at atmospheric pressure and 100°C or higher.

[0015] The system 100 includes a heat exchanger 10, a compressor 20, a tank 30, a cooler 40, a heater 50, and a liquid storage tank 60. In FIG. 1, for ease of explanation, the flow of electricity is indicated by dashed arrows, the heat flow is indicated by solid arrows, and the material flow is indicated by hollow arrows. The system 100 of this embodiment is driven by electricity generated by thermal power generation or surplus renewable energy, but may be driven by any other type of electricity. The numbers indicated by circular letters in FIGS. 1 and 2 correspond to the state of matter at the point indicated by the number in FIG. 3. In FIG. 3, the pressure P of the raw material gas supplied to the system 100 is ０ is atmospheric pressure (0.101 MPa), and the volume fraction X of water contained in the raw material gas supplied to the system 100 Ｈ２Ｏ，０ The relationship between temperature and pressure is shown when ρ is 0.1. In Fig. 3, the total pressure of the gas is indicated by a thick solid arrow, and the partial pressure of carbon dioxide is indicated by a thick dashed arrow. Fig. 3 also shows the sublimation line, vaporization line, melting line, and triple point for carbon dioxide and water.

[0016] As shown in FIG. 3 , the heat exchanger 10 lowers the temperature of the source gas by isobaric cooling. As shown in FIGS. 1 and 2 , the system 100 of this embodiment includes two heat exchangers 10, but the number of heat exchangers 10 may be one or three or more. The more upstream heat exchanger 10 lowers the temperature of the source gas by air cooling, i.e., by the ambient environment. The upstream heat exchanger 10 cools the source gas to, for example, about 40°C. The more downstream heat exchanger 10 is located downstream of the upstream heat exchanger 10 and further lowers the temperature of the source gas by liquefied carbon dioxide, nitrogen gas, or the like. In this embodiment, the downstream heat exchanger 10 utilizes cold energy extracted from the tank 30 or liquid storage tank 60, which will be described later. The downstream heat exchanger 10 cools the source gas to, for example, about 0°C. As a result, at least a portion of the water vapor contained in the source gas becomes liquid droplets 510 and is discharged as water through a discharge hole (not shown). In the example shown in FIG. 3, the final pressure P １ and the final pressure P in the downstream heat exchanger 10 ２ All of these are atmospheric pressure.

[0017] The compressor 20 is provided downstream of the heat exchanger 10. The compressor 20 compresses the raw material gas. As shown in FIG. 3, the compressor 20 compresses the raw material gas by isothermal compression. The raw material gas is pressurized by the compressor 20 to become a high-pressure gas. At this time, water vapor contained in the raw material gas turns into droplets 510 and is discharged as water through a discharge hole (not shown). As a result, it is expected that the amount of water vapor contained in the gas phase within the compressor 20 will be extremely small. Note that, as shown in FIG. 2, the compressor 20 may be provided with a compressor cooler 21 to suppress a temperature increase due to pressurization. The compressor cooler 21 is not particularly limited, and for example, a general-purpose heat exchanger or refrigerator may be used.

[0018] In FIG. 3, the volume fraction X of carbon dioxide contained in the gas ＣＯ２，０ The final total pressure P in the compressor 20 is 0.1. ３ whereas the final partial pressure of carbon dioxide P ３，ＣＯ２ Is, P３，ＣＯ２ =P ３ ・X ＣＯ２，０ In the system 100 of this embodiment, the final partial pressure P of carbon dioxide in the compressor 20 ３，ＣＯ２ , the final temperature T ３ Saturated vapor pressure P ３，ｓｔ By controlling the temperature T so that the temperature is as follows, it is possible to prevent the carbon dioxide from liquefying in the compressor 20. ３ is 0°C, the final temperature T ３ Saturated vapor pressure P ３，ｓｔ is 3.485 MPa, which is the saturated vapor pressure at 0° C. As will be described later, in the system 100 of this embodiment, it is preferable to sufficiently compress the gas in the compressor 20 in order to suppress a decrease in the carbon dioxide recovery efficiency.

[0019] As shown in Fig. 2, the tank 30 is provided downstream of the compressor 20. The tank 30 stores the gas compressed by the compressor 20. The tank 30 is formed with a discharge hole 31 for discharging nitrogen. In the system 100 of this embodiment, as will be described below, carbon dioxide is sublimated and solidified, and then heated and liquefied, in this order, within the tank 30.

[0020] The cooler 40 and the heater 50 are each provided adjacent to the tank 30. In this embodiment, the cooler 40 and the heater 50 cool and heat the tank 30 via a common brine (not shown). In this embodiment, the heat transfer surface 32 between the cooler 40 and the heater 50 in the tank 30 is formed along a substantially vertical direction. In this disclosure, the term "substantially vertical direction" is not limited to the vertical direction and also includes a direction intersecting the vertical direction at an angle of 10° or less. Note that the heat transfer surface 32 is not limited to the substantially vertical direction and may be formed along any direction.

[0021] The cooler 40 cools the carbon dioxide contained in the gas in the tank 30 until it solidifies. In other words, the cooler 40 sublimes and solidifies the carbon dioxide contained in the gas in the tank 30. While the cooler 40 is not particularly limited, a brine-type refrigerator is preferably used from the viewpoint of condensing the carbon dioxide into a film on the heat transfer surface 32. The cooler 40 cools the gas in the tank 30 to, for example, approximately −100°C. As a result, the carbon dioxide contained in the gas in the tank 30 sublimes and solidifies, and is separated from the gas phase as dry ice. That is, the carbon dioxide contained in the gas phase becomes solid. As a result, the total pressure of the gas phase in the tank 30 decreases, and the partial pressure of the carbon dioxide contained in the gas phase decreases. FIG. 2 schematically illustrates the carbon dioxide in the tank 30 as a vapor 520 of carbon dioxide contained in the gas phase, solid particles 530 of carbon dioxide that have been sublimated and solidified by cooling, and a solid film 540. The solid film 540 is formed by adhering to the heat transfer surface 32.

[0022] In this embodiment, a piston 33 that reduces the volume of the gas phase is provided within the tank 30. By operating the piston 33, the volume of the gas phase within the tank 30 can be reduced. As a result, when solid carbon dioxide, as described below, is heated, an increase in the amount of carbon dioxide vaporized can be suppressed, thereby suppressing a decrease in the carbon dioxide recovery efficiency. Furthermore, by operating the piston 33, nitrogen within the tank 30 can be easily discharged through the discharge hole 31 and removed from the tank 30. In the system 100 of this embodiment, when the carbon dioxide within the tank 30 is in a solid state, nitrogen contained in the gas within the tank 30 is discharged through the discharge hole 31. By discharging the nitrogen, the carbon dioxide within the tank 30 changes from a supercooled state to a saturated state in which solid and gas coexist.

[0023] FIG. 3 shows the final total pressure P of the gas in the tank 30 cooled by the cooler 40. ４ and the partial pressure of carbon dioxide P ４，ＣＯ２ and the final temperature T ４ Saturated vapor pressure P ４，ｓｔ As carbon dioxide solidifies, the volume fraction of carbon dioxide in the gas phase, XＣＯ２，０ When the partial pressure of carbon dioxide P ４，ＣＯ２ In the case of an isovolumetric change, the partial pressure of carbon dioxide P ４，ＣＯ２ As the total pressure P ４ The final total pressure P of the gas in the tank 30 cooled by the cooler 40 also decreases. ４ is expressed by the following formula: ４ =P ３ ×T ４ / T ３ × (1-X ＣＯ２，０ )

[0024] Final total pressure P ４ whereas the final partial pressure of carbon dioxide P ４，ＣＯ２ Is, P ４，ＣＯ２ =P ４ ・X ＣＯ２，０ In the system 100 of this embodiment, the final partial pressure P of the carbon dioxide cooled by the cooler 40 is ４，ＣＯ２ at the final temperature T ４ Saturated vapor pressure P ４，ｓｔ To achieve this, the final total pressure P ４ But, P ４ >P ４，ｓｔ / X ＣＯ２，０ It is preferable to sufficiently compress the gas in the compressor 20 so that the following condition can be satisfied. Here, the recovery rate (%) of carbon dioxide is expressed by the following formula: Recovery rate (%)={(P ４，ＣＯ２ -P ４，ｓｔ ) / P ４，ＣＯ２} x 100

[0025] From the viewpoint of improving the recovery rate of carbon dioxide, the final temperature T ４ Saturated vapor pressure P ４，ｓｔ It is preferable to make the temperature of the dew point sufficiently low.

[0026] The heater 50 heats the carbon dioxide that has been solidified by cooling with the cooler 40 until it becomes a liquid. In other words, the heater 50 heats and liquefies the carbon dioxide that has been sublimated and solidified. The heater 50 of this embodiment is configured to include a heat exchanger that utilizes the exhaust heat of the combustion exhaust gas as the raw material gas, but is not limited to the exhaust heat of the combustion exhaust gas and may be configured in any way that can raise the temperature of the carbon dioxide, such as the atmosphere. The carbon dioxide that has become solid dry ice by sublimation and solidification is liquefied by heating with the heater 50, becoming liquefied carbon dioxide. Figure 2 shows the forms of carbon dioxide in the tank 30 as carbon dioxide vapor 520 contained in the gas phase and liquefied carbon dioxide 550, which is carbon dioxide liquefied by heating.

[0027] As shown in Figure 3, when carbon dioxide that has sublimated and solidified is heated, the temperature and pressure increase along the sublimation line. Carbon dioxide becomes liquid carbon dioxide when heated above the triple point to just above the triple point. In the system 100 of this embodiment, in order to prevent a decrease in the carbon dioxide recovery efficiency, heating by the heater 50 is stopped at a temperature just before the temperature begins to rise rapidly above the triple point temperature. Note that the final pressure of the gas in the tank 30 heated by the heater 50 is a value that corresponds to the balance between the final heating temperature, the volume of the tank 30, and the amount of carbon dioxide vaporized.

[0028] As shown in Figure 2, in the system 100 of this embodiment, the heat transfer surface 32 is formed in a substantially vertical direction, so that carbon dioxide that has become liquid as a result of heating can flow vertically downward under its own weight. As a result, the thickness of the liquid film on the heat transfer surface 32 can be made thinner, which improves heating efficiency and prevents a decrease in carbon dioxide recovery efficiency. In the system 100 of this embodiment, the liquid carbon dioxide is sent to the liquid storage tank 60. The liquid storage tank 60 stores the liquid carbon dioxide. Note that the liquid storage tank 60 may be omitted, and the recovered liquefied carbon dioxide may be used directly.

[0029] According to the system 100 of the first embodiment described above, carbon dioxide is sublimated and solidified by the cooler 40. Then, with nitrogen removed from the gas in the tank 30, the solid carbon dioxide is heated and liquefied by the heater 50, thereby recovering liquid carbon dioxide. Therefore, carbon dioxide can be recovered without using a carbon dioxide absorption liquid as in the conventional system. As a result, the inclusion of components of the absorption liquid in the recovered carbon dioxide can be prevented, thereby preventing a decrease in the purity of the carbon dioxide. Furthermore, since carbon dioxide can be recovered without using an absorption liquid, the absorption tower and regeneration tower included in conventional carbon dioxide recovery systems can be omitted. As a result, the operating energy required for absorption and regeneration can be eliminated, thereby preventing an increase in carbon dioxide recovery costs. Furthermore, since carbon dioxide can be recovered without using an absorption liquid, the cost required for developing an absorption liquid can be eliminated. Furthermore, since the heating of the absorption liquid can be omitted, a decrease in energy efficiency can be prevented. Furthermore, since carbon dioxide can be recovered without using an absorption liquid, the use of corrosion-resistant members that can withstand corrosion associated with heating the absorption liquid can be omitted, thereby preventing an increase in the manufacturing cost of the system.

[0030] Furthermore, since the system 100 of this embodiment can capture liquid carbon dioxide, a decrease in the transportation efficiency of the captured carbon dioxide can be suppressed compared to conventional carbon dioxide capture systems that capture high-pressure gaseous carbon dioxide. More specifically, for example, the need for truck transportation of carbon dioxide to remote locations such as CCS sites can be eliminated, thereby increasing applicability to CCUS demand and enabling the selection of a supply form according to demand. Furthermore, since the system 100 of this embodiment uses combustion exhaust gas generated at thermal power plants and the like as the feed gas, a decrease in carbon dioxide capture efficiency can be suppressed and zero emissions can be achieved for fossil fuel-based power sources. Furthermore, since the heater 50 utilizes the exhaust heat of the combustion exhaust gas, an increase in power consumption by the heater 50 can be suppressed.

[0031] (2) Carbon Dioxide Capture Method Fig. 4 is a process diagram showing a carbon dioxide capture method. This carbon dioxide capture method may be realized using the above-described carbon dioxide capture system 100. The carbon dioxide capture method in this embodiment includes a compression step (process P110), a cooling step (process P120), a removal step (process P130), a heating step (process P140), and a capture step (process P150) in this order.

[0032] In the compression process (process P110), a gas containing carbon dioxide and nitrogen is compressed. In the cooling process (process P120), the carbon dioxide contained in the gas after the compression process (process P110) is cooled until it becomes solid. In the removal process (process P130), the nitrogen contained in the gas after the cooling process (process P120) is removed. In this embodiment, the removal process (process P130) includes a process (process P135) of reducing the volume of the gas phase. In this process, the volume of the gas phase is reduced using a piston or the like. In the heating process (process P140), the solid carbon dioxide is heated until it becomes liquid in a state where the nitrogen has been removed. In the recovery process (process P150), the liquid carbon dioxide is recovered.

[0033] According to the carbon dioxide recovery method described above, by including the above steps, it is possible to recover liquid carbon dioxide. Therefore, carbon dioxide can be recovered without using a carbon dioxide absorption liquid as in the conventional method. Furthermore, by including the step of reducing the volume of the gas phase (step P135), it is possible to prevent an increase in the amount of carbon dioxide vaporized in the heating step (step P140), and therefore it is possible to prevent a decrease in the carbon dioxide recovery efficiency.

[0034] B. Second Embodiment (1) Carbon Dioxide Capture System Figure 5 is a schematic diagram showing the configuration of the main parts of a carbon dioxide capture system 100a of the second embodiment. The carbon dioxide capture system 100a of the second embodiment (hereinafter also referred to as "system 100a") differs from the system 100 of the first embodiment mainly in that it includes a heater 50a instead of the heater 50 and in that it further includes an opening / closing unit 70a. Components similar to those of the first embodiment are given the same reference numerals, and detailed description thereof will be omitted. Figure 5 shows the general configuration of the tank 30, cooler 40, heater 50a, liquid storage tank 60a, and opening / closing unit 70a of the system 100a.

[0035] The heater 50a in the system 100a of the second embodiment includes a first heater 51a that heats the tank 30 and a second heater 52a that heats the liquid storage tank 60a. The first heater 51a is provided adjacent to the tank 30. In this embodiment, the first heater 51a heats the tank 30 via brine 90a that is also used with the cooler 40. In this embodiment, the heat transfer surface 32 between the cooler 40 and the first heater 51a in the tank 30 is also formed along a substantially vertical direction. The first heater 51a slightly heats the carbon dioxide that has been sublimated and solidified in the tank 30 by the cooler 40. As a result, a solid film 540 of carbon dioxide that had been formed and adhered to the heat transfer surface 32 is liquefied on the heat transfer surface 32 and peels off from the heat transfer surface 32. In other words, the first heater 51 a heats the tank 30 to such an extent that the solid film 540 of carbon dioxide peels off from the heat transfer surface 32 .

[0036] The second heater 52a is provided adjacent to the liquid storage tank 60a. In this embodiment, the heat transfer surface 62a between the second heater 52a and the liquid storage tank 60a is formed along the bottom surface of the liquid storage tank 60a. Note that the heat transfer surface 62a is not limited to the bottom surface of the liquid storage tank 60a, and may be formed along any surface, such as a wall surface of the liquid storage tank 60a.

[0037] The opening / closing unit 70a switches the communication state between the tank 30 and the liquid storage tank 60a. When the opening / closing unit 70a is open, the tank 30 and the liquid storage tank 60a are in a communication state, and when the opening / closing unit 70a is closed, the tank 30 and the liquid storage tank 60a are not in a communication state. Therefore, when the opening / closing unit 70a is closed, the liquid storage tank 60a is in a sealed state. In this embodiment, the opening / closing unit 70a is formed by a shutter provided in the flow path between the tank 30 and the liquid storage tank 60a, but it may be formed by any member such as a valve.

[0038] In the system 100a of this embodiment, first, the carbon dioxide that has been partially liquefied by heating with the first heater 51a is transferred to the liquid storage tank 60a by opening the opening / closing unit 70a. Then, after closing the opening / closing unit 70a, heating is performed with the second heater 52a. In order to prevent a decrease in the carbon dioxide recovery efficiency, heating with the second heater 52a is preferably performed in a state where carbon dioxide has accumulated from the tank 30 to such an extent that the volume of the gas phase in the liquid storage tank 60a is sufficiently small. In the system 100a of this embodiment, the main heating of the carbon dioxide is performed in the liquid storage tank 60a, so the volume of the gas phase during the main heating can be easily reduced. Therefore, in the system 100a of this embodiment, the piston 33 in the tank 30 may be omitted.

[0039] The system 100a of the second embodiment described above includes the first heater 51a for heating the tank 30 and the second heater 52a for heating the liquid storage tank 60a. Therefore, carbon dioxide that has fallen off the heat transfer surface 32 of the tank 30 can be fully heated in the liquid storage tank 60a. As a result, solid carbon dioxide can be heated to recover liquid carbon dioxide while removing nitrogen from the gas in the tank 30. Furthermore, the volume of the gas phase generated when liquefying carbon dioxide in the liquid storage tank 60a can be easily reduced, further reducing the decrease in carbon dioxide recovery efficiency. Furthermore, since the opening / closing unit 70a can seal the liquid storage tank 60a, cooling by the cooler 40 and heating by the second heater 52a can be performed simultaneously. As a result, the decrease in carbon dioxide recovery efficiency can be further reduced.

[0040] (2) Carbon Dioxide Capture System FIG. 6 is a process diagram showing a carbon dioxide capture method. This carbon dioxide capture method may be realized using the carbon dioxide capture system 100a described above. In the carbon dioxide capture method of the second embodiment, the heating step is divided into two steps. In the carbon dioxide capture method of the second embodiment, detailed explanations of steps that are the same as those in the carbon dioxide capture method of the first embodiment will be omitted. The carbon dioxide capture method of the second embodiment includes a compression step (step P110), a cooling step (step P120), a first heating step (step P141a), a removal step (step P130a), a second heating step (step P142a), and a capture step (step P150).

[0041] The first heating step (step P141a) is performed before the removing step (step P130a). In the first heating step (step P141a), the carbon dioxide after the cooling step (step P120) is heated until part of the carbon dioxide becomes liquid. The first heating step (step P141a) is performed by a first heater 51a.

[0042] The removal step (step P130a) removes nitrogen contained in the gas after the cooling step (step P120) and the first heating step (step P141a). In this embodiment, the removal step (step P130a) is achieved by the liquid storage tank 60a and the opening / closing unit 70a. More specifically, carbon dioxide that has been partially liquefied by the first heating step (step P141a) is transferred to the liquid storage tank 60a, and then the opening / closing unit 70a is closed to seal the liquid storage tank 60a, thereby removing the nitrogen contained in the gas.

[0043] The second heating step (step P142a) is performed after the removal step (step P130a). In the second heating step (step P142a), the solid carbon dioxide, which has been partially liquefied in the first heating step (step P141a), is heated until it becomes liquid in a state in which nitrogen has been removed in the removal step (step P130a). The second heating step (step P142a) is performed by the first heater 51a.

[0044] According to the carbon dioxide capture method of the second embodiment, the method includes a first heating step (process P141a) performed before the removal step (process P130a) and a second heating step (process P142a) performed after the removal step (process P130a). Therefore, the carbon dioxide that has been partially liquefied by the first heating step (process P141a) can be fully heated in the second heating step (process P142a). As a result, the carbon dioxide can be heated and liquid carbon dioxide can be captured in a state in which nitrogen contained in the gas has been removed by the removal step (process P130a). When the carbon dioxide capture method of the second embodiment is repeatedly performed, the cooling step (process P120) and the second heating step (process P142a) may be performed simultaneously. According to this embodiment, a decrease in the carbon dioxide capture efficiency can be further suppressed.

[0045] C. Modifications The configurations of the systems 100 and 100a in the above-described embodiments are merely examples and can be modified in various ways. For example, in the system 100 of the first embodiment, the cooler 40 and the heater 50 cool and heat the tank 30 via a common brine (not shown). However, they may each cool and heat the tank 30 via an independent brine. Similarly, in the system 100a of the second embodiment, the cooler 40 and the first heater 51a cool and heat the tank 30 via a common brine 90a. However, they may each cool and heat the tank 30 via an independent brine 90a. The cooler 40 and the heater 50 are not limited to a brine system and may be of any type. For example, the liquid storage tank 60a of the second embodiment may be provided with a piston that reduces the volume of the gas phase. The systems 100 and 100a in the above-described embodiments may be configured to include any other configuration, and the carbon dioxide capture method may be configured to include any other process.

[0046] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in each embodiment corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0047] 10...heat exchanger, 20...compressor, 21...compressor cooler, 30...tank, 31...discharge hole, 32...heat transfer surface, 33...piston, 40...cooler, 50, 50a...heater, 51a...first heater, 52a...second heater, 60, 60a...liquid storage tank, 62a...heat transfer surface, 70a...opening / closing part, 90a...brine, 100, 100a...carbon dioxide capture system (system), 510...liquid droplets, 520...steam, 530...solid particles, 540...solid membrane, 550...liquefied carbon dioxide

Claims

1. A carbon dioxide capture system comprising: a compressor that compresses a gas containing carbon dioxide and nitrogen; a tank that stores the compressed gas; a cooler that cools the carbon dioxide contained in the gas in the tank until it becomes a solid; and a heater that heats the carbon dioxide that has become solid by cooling until it becomes a liquid, wherein the carbon dioxide capture system heats the solid carbon dioxide and captures liquid carbon dioxide in a state in which the nitrogen contained in the gas in the tank has been removed.

2. A carbon dioxide capture system according to claim 1, wherein a piston for reducing the volume of the gas phase is provided within the tank.

3. A carbon dioxide capture system as defined in claim 1 or claim 2, further comprising: a liquid storage tank; and an opening / closing unit that switches the communication state between the tank and the liquid storage tank, wherein the heater has a first heater that heats the tank and a second heater that heats the liquid storage tank, and wherein carbon dioxide that has been partially liquefied by heating with the first heater is transferred to the liquid storage tank by opening the opening / closing unit, and then heating with the second heater is carried out after the opening / closing unit is closed.

4. A carbon dioxide recovery method comprising: a compression step of compressing a gas containing carbon dioxide and nitrogen; a cooling step of cooling the carbon dioxide contained in the gas after the compression step until it becomes a solid; a removal step of removing the nitrogen contained in the gas after the cooling step; a heating step of heating the solid carbon dioxide until it becomes a liquid; and a recovery step of recovering the liquid carbon dioxide.

5. A method for recovering carbon dioxide according to claim 4, wherein the removing step includes a step of reducing the volume of the gas phase.

6. A carbon dioxide recovery method according to claim 4 or 5, wherein the heating step includes a first heating step carried out before the removal step, and a second heating step carried out after the removal step, wherein the first heating step is a step of heating the carbon dioxide after the cooling step until part of the carbon dioxide becomes liquid, and the second heating step is a step of heating the solid carbon dioxide, part of which has become liquid by the first heating step, in a state in which nitrogen has been removed, until it becomes liquid.

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