Carbon dioxide liquefaction system

Abstract

To provide a carbon dioxide liquefaction system which can minimize energy required for liquefaction of carbon dioxide.SOLUTION: A carbon dioxide liquefaction system 1 has a liquefied carbon dioxide drum 10, a liquefied carbon dioxide circulation line, a liquefied carbon dioxide pump 20, a liquefied carbon dioxide cooler 30, an ejector 40 which is disposed in a flow in the rear of the liquefied carbon dioxide pump 20 in the liquefied carbon dioxide circulation line and functions with liquefied carbon dioxide output from the liquefied carbon dioxide pump 20 as a drive fluid and carbon dioxide containing gas as a suction fluid, a carbon dioxide containing gas receiving line 75 through which the ejector 40 receives the carbon dioxide containing gas, a liquefied carbon dioxide output line 78, a recycled gas line which reflux gas of a gas layer in the liquefied carbon dioxide drum 10 to the carbon dioxide containing gas receiving line 75, a carbon dioxide separation membrane 50 which is disposed in the recycled gas line and concentrates the carbon dioxide of the gas layer in the liquefied carbon dioxide drum 10, and a recycled gas flow control valve 83.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide liquefaction system for liquefying carbon dioxide. [Background technology]

[0002] There is a need for technology to liquefy gaseous carbon dioxide for the purpose of storage and transportation for CCS (Carbon dioxide Capture and Storage) and CCU (Carbon dioxide capture and utilization). Carbon dioxide can be liquefied at lower pressures at lower temperatures, so if it can be liquefied at low temperatures, the compression power required can be reduced, but a minimum pressure of 0.42 MPaG is required.

[0003] In this regard, Patent Document 1 discloses a technology for liquefying carbon dioxide by utilizing part of the cold energy of an air cryogenic separation unit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5932127 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 does not mention pressure, and so it is thought that the pressure is increased to at least 0.42 MPaG, and there is a process of compressing the carbon dioxide gas in the upstream. Generally, a compressor is used for such a compression process, but if the carbon dioxide gas is at atmospheric pressure, it needs to be compressed from atmospheric pressure to at least 0.42 MPaG, which requires a great deal of energy.

[0006] Furthermore, while CCS and CCU require a upstream process to separate carbon dioxide from combustion exhaust gases containing carbon dioxide, there is a need to reduce the energy required to capture carbon dioxide. Patent Document 1 does not disclose or suggest any technology that addresses such needs.

[0007] The present invention has been made to solve these problems, and has an object to provide a carbon dioxide liquefaction system that can minimize the energy required for separating and liquefying carbon dioxide. [Means for solving the problem]

[0008] (1) The carbon dioxide liquefaction system according to the present invention comprises: a liquefied carbon dioxide drum for storing liquefied carbon dioxide; a liquefied carbon dioxide circulation line through which liquefied carbon dioxide circulates, the liquefied carbon dioxide drum being a starting point; a liquefied carbon dioxide pump that is disposed downstream of the liquefied carbon dioxide drum in the liquefied carbon dioxide circulation line and that pressurizes and discharges the liquefied carbon dioxide stored in the liquefied carbon dioxide drum; a liquefied carbon dioxide cooler that is disposed in the liquefied carbon dioxide circulation line and cools the liquefied carbon dioxide discharged by the liquefied carbon dioxide pump by heat exchange with a refrigerant; an ejector that is disposed downstream of the liquefied carbon dioxide pump in the liquefied carbon dioxide circulation line, and that uses the liquefied carbon dioxide discharged by the liquefied carbon dioxide pump as a driving fluid and a carbon dioxide-containing gas as a suction fluid; a carbon dioxide-containing gas receiving line that receives the carbon dioxide-containing gas into the ejector; a liquefied carbon dioxide discharge line that discharges the liquefied carbon dioxide from the liquefied carbon dioxide drum to the outside; a recycle gas line for returning the gas in the gas layer of the liquefied carbon dioxide drum to the carbon dioxide-containing gas receiving line; a carbon dioxide separation membrane disposed in the recycle gas line for concentrating carbon dioxide in the gas layer of the liquefied carbon dioxide drum; and a recycle gas flow rate control valve that is disposed downstream of the carbon dioxide separation membrane in the recycle gas line and that reduces the pressure and controls the flow rate of the gas in the gas layer of the liquefied carbon dioxide drum.

[0009] (2) In addition, in the device described in (1) above, a non-permeation gas discharge line for discharging non-permeation gas that has not permeated the carbon dioxide separation membrane to the outside; a non-permeate gas discharge flow rate control valve disposed in the non-permeate gas discharge line for reducing the pressure and regulating the flow rate of the gas flowing through the non-permeate gas discharge line; and a second liquefied carbon dioxide cooler that is disposed in the liquefied carbon dioxide circulation line and cools the liquefied carbon dioxide with the non-permeated gas that has passed through the non-permeated gas discharge flow rate control valve in the non-permeated gas discharge line.

[0010] (3) Furthermore, in the above (2), it is characterized in that it has a carbon dioxide-containing gas precooler that is arranged in the carbon dioxide-containing gas receiving line and cools the carbon dioxide-containing gas using the non-permeating gas that has passed through the second liquefied carbon dioxide cooler.

[0011] (4) In addition, in the device described in (1) above, a non-permeation gas discharge line for discharging non-permeation gas that has not permeated the carbon dioxide separation membrane to the outside; a non-permeate gas discharge flow rate control valve disposed in the non-permeate gas discharge line for reducing the pressure and regulating the flow rate of the gas flowing through the non-permeate gas discharge line; and a carbon dioxide-containing gas precooler that is disposed in the carbon dioxide-containing gas receiving line and cools the carbon dioxide-containing gas by the non-permeable gas that has passed through the non-permeable gas discharge flow rate control valve in the non-permeable gas discharge line.

[0012] (5) In the device described in (1) above, a non-permeation gas discharge line for discharging non-permeation gas that has not permeated the carbon dioxide separation membrane to the outside; a non-permeate gas discharge flow rate control valve disposed in the non-permeate gas discharge line for reducing the pressure and regulating the flow rate of the gas flowing through the non-permeate gas discharge line; and a recycle gas cooler disposed in the recycle gas line for cooling the recycle gas by the non-permeate gas that has passed through the non-permeate gas discharge flow rate control valve in the non-permeate gas discharge line.

[0013] (6) Furthermore, in the above (5), it is characterized in that it has a carbon dioxide-containing gas precooler that is arranged in the carbon dioxide-containing gas receiving line and cools the carbon dioxide-containing gas by the non-permeating gas that has passed through the recycle gas cooler. [Effects of the Invention]

[0014] In the present invention, an ejector is provided which is arranged downstream of the liquefied carbon dioxide pump in the liquefied carbon dioxide circulation line, and which uses the liquefied carbon dioxide discharged by the liquefied carbon dioxide pump as the driving fluid and the carbon dioxide-containing gas as the suction fluid, and the carbon dioxide-containing gas and liquefied carbon dioxide are mixed and liquefied in the ejector, so that carbon dioxide can be liquefied with minimal energy. Furthermore, a carbon dioxide separation membrane is provided in the recycle gas line to concentrate the carbon dioxide in the gas layer of the liquefied carbon dioxide drum, thereby improving the efficiency of recovering carbon dioxide. Furthermore, the differential pressure required for passing through the carbon dioxide separation membrane is obtained by pressure recovery downstream of the ejector, so the energy required for separating carbon dioxide can be reduced. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram showing a carbon dioxide liquefaction system according to a first embodiment of the present invention. [Figure 2] FIG. 4 is a schematic diagram showing a carbon dioxide liquefaction system according to a second embodiment of the present invention. [Figure 3]FIG. 10 is a schematic diagram showing a carbon dioxide liquefaction system according to a third embodiment of the present invention. [Figure 4] FIG. 10 is a schematic diagram showing a carbon dioxide liquefaction system according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] [Embodiment 1] First, the configuration and functions of the first embodiment of the present invention will be described with reference to FIG. The carbon dioxide liquefaction system 1 according to the first embodiment of the present invention includes a liquefied carbon dioxide drum 10, a liquefied carbon dioxide pump 20, a liquefied carbon dioxide cooler 30, an ejector 40, and a carbon dioxide separation membrane 50.

[0017] The liquefied carbon dioxide drum 10 is a vertical cylindrical drum that temporarily stores the liquefied carbon dioxide received from the ejector outlet line 74 .

[0018] The liquefied carbon dioxide pump 20 is a centrifugal pump that receives liquefied carbon dioxide temporarily stored in the liquefied carbon dioxide drum 10 from a liquefied carbon dioxide pump inlet line 71, pressurizes the liquefied carbon dioxide, and discharges it to a liquefied carbon dioxide pump outlet line 72. The amount of pressure increase by the liquefied carbon dioxide pump 20 corresponds to the pressure loss in the system including the liquefied carbon dioxide cooler 30 and the ejector 40.

[0019] The liquefied carbon dioxide cooler 30 is a typical shell-and-tube heat exchanger, and cools the liquefied carbon dioxide received from the liquefied carbon dioxide pump outlet line 72 using a low-temperature refrigerant. The refrigerant is supplied from a refrigerant supply line 76 and is discharged to a refrigerant discharge line 77 after heat exchange.

[0020] The ejector 40 is a general ejector, which creates a reduced pressure state using liquefied carbon dioxide supplied from an ejector inlet line 73 as a driving fluid, and receives a carbon dioxide-containing gas from a carbon dioxide-containing gas receiving line 75 . After the ejector 40 , the liquefied carbon dioxide flows through the ejector outlet line 74 towards the liquefied carbon dioxide drum 10 .

[0021] The carbon dioxide separation membrane 50 is a membrane separation unit formed by stacking carbon dioxide separation membranes made of polymeric materials, and preferentially allows carbon dioxide to permeate from the carbon dioxide-containing gas supplied from the carbon dioxide separation membrane inlet line 81 and sends it to the carbon dioxide separation membrane outlet line 82. The gas layer in the liquefied carbon dioxide drum 10 is extracted into the carbon dioxide separation membrane inlet line 81, passes through the carbon dioxide separation membrane 50, is sent to the carbon dioxide separation membrane outlet line 82, is supplied to the carbon dioxide-containing gas receiving line 75, and is recycled. Therefore, the carbon dioxide separation membrane inlet line 81 and the carbon dioxide separation membrane outlet line 82 constitute the recycled gas line of the present invention.

[0022] Next, the operation of the carbon dioxide liquefaction system 1 according to this embodiment will be described. The carbon dioxide liquefaction system 1 circulates liquefied carbon dioxide within the system by operating the liquefied carbon dioxide pump 20 . Specifically, the liquefied carbon dioxide in the liquefied carbon dioxide drum 10 is sent to the liquefied carbon dioxide pump inlet line 71, passes through the liquefied carbon dioxide pump 20, the liquefied carbon dioxide pump outlet line 72, the liquefied carbon dioxide cooler 30, the ejector inlet line 73, the ejector 40 and the ejector outlet line 74, and is returned to the liquefied carbon dioxide drum 10. Therefore, the above-mentioned devices and lines constitute the liquefied carbon dioxide circulation line of the present invention. In the liquefied carbon dioxide drum 10, the liquefied carbon dioxide is stored at, for example, 0.9 MPaG and −50° C., and is pressurized by the liquefied carbon dioxide pump 20 to, for example, 1.6 MPaG.

[0023] The liquefied carbon dioxide pressurized by the liquefied carbon dioxide pump 20 is cooled in the liquefied carbon dioxide cooler 30 to a temperature range where it will not solidify, for example, -53°C, by a refrigerant supplied by cold heat generation equipment (e.g., a refrigerator) not shown.

[0024] The liquefied carbon dioxide cooled by the liquefied carbon dioxide cooler 30 is supplied to the ejector 40, and flows as a high-speed flow through the small diameter portion inside the ejector 40, thereby creating a reduced pressure state using Bernoulli's theorem.

[0025] As a result, the carbon dioxide-containing gas is supplied to the ejector 40 from the carbon dioxide-containing gas receiving line 75. In this embodiment, the carbon dioxide-containing gas is assumed to be, for example, a gas obtained by roughly separating carbon dioxide by passing it through a carbon dioxide separation membrane. The composition of the gas is, for example, 50% carbon dioxide with nitrogen and oxygen as excess gases.

[0026] Inside the ejector 40, the carbon dioxide-containing gas supplied from the carbon dioxide-containing gas receiving line 75 mixes with the high-speed flow of liquefied carbon dioxide. As the diameter inside the ejector 40 expands and the flow rate decreases, the pressure of the mixed fluid that has passed through the small-diameter portion of the ejector 40 is restored to, for example, 0.9 MPaG, and the carbon dioxide gas in the mixed fluid is compressed, cooled, and condensed. In addition, the nitrogen and oxygen are compressed and cooled as the pressure is restored. In this case, carbon dioxide, nitrogen, and oxygen are compressed while coming into contact with the liquefied carbon dioxide and being cooled, and therefore the compression process of these gases is close to isothermal compression, resulting in high compression efficiency.

[0027] In the downstream of the ejector 40, liquefied carbon dioxide flows through the ejector outlet line 74 towards the liquefied carbon dioxide drum 10, but if there is carbon dioxide gas that has not been completely condensed inside the ejector 40, this will also be included, and uncondensed nitrogen and oxygen will also be included in the gaseous state, resulting in a multiphase flow.

[0028] The liquefied carbon dioxide that flows into the liquefied carbon dioxide drum 10 becomes saturated at 0.9 MPaG and separates into a gas layer and a liquid layer. The amount of carbon dioxide held in the system increases as carbon dioxide gas is supplied from the carbon dioxide-containing gas receiving line 75. As a result, liquefied carbon dioxide is discharged from the liquefied carbon dioxide drum 10 to the outside via the liquefied carbon dioxide discharge line 78 in an amount equal to the amount of carbon dioxide gas that has been supplied.

[0029] Furthermore, nitrogen and oxygen do not condense, and therefore accumulate in the gas layer of the liquefied carbon dioxide drum 10 . Therefore, the gas layer in the liquefied carbon dioxide drum 10 is discharged to the outside of the drum by the recycle gas flow rate control valve 83 and the non-permeate gas discharge flow rate control valve 85 and is supplied to the carbon dioxide separation membrane 50 .

[0030] The carbon dioxide-enriched gas that has permeated the carbon dioxide separation membrane 50 is depressurized and its flow rate adjusted by the recycle gas flow control valve 83, and then supplied to the carbon dioxide-containing gas receiving line 75. The non-permeated gas that has not permeated the carbon dioxide separation membrane 50 is depressurized and its flow rate adjusted by the non-permeated gas discharge flow control valve 85, and then discharged to the outside via the non-permeated gas discharge line 84.

[0031] According to the carbon dioxide liquefaction system 1 of this embodiment, the reduced pressure created by the ejector 40 can be used to take in carbon dioxide-containing gas and liquefy the carbon dioxide, thereby reducing the energy required to separate the carbon dioxide.

[0032] Furthermore, according to the carbon dioxide liquefaction system 1 of this embodiment, the carbon dioxide-containing gas can be compressed during the pressure recovery process downstream of the ejector 40, so the compressor power required to pressurize the carbon dioxide can be reduced to zero or significantly reduced.

[0033] Furthermore, according to the carbon dioxide liquefaction system 1 of this embodiment, the pressure recovery process downstream of the ejector 40 described above is carried out while in contact with low-temperature liquefied carbon dioxide, which is close to isothermal compression, allowing for efficient compression.

[0034] Furthermore, according to the carbon dioxide liquefaction system 1 of this embodiment, non-condensable gases, nitrogen and oxygen, are extracted from the gas layer of the liquefied carbon dioxide drum 10, and carbon dioxide-enriched gas is produced by passing it through the carbon dioxide separation membrane 50, and then the gas is returned to the carbon dioxide-containing gas receiving line 75, thereby enabling carbon dioxide to be efficiently liquefied while minimizing the amount of carbon dioxide emitted to the outside.

[0035] Furthermore, the differential pressure required for passing through the carbon dioxide separation membrane 50 is obtained by pressure recovery downstream of the ejector 40, so that the energy required for separating carbon dioxide can be reduced.

[0036] In this embodiment, the carbon dioxide separation membrane 50 has been described as a membrane separation unit in which carbon dioxide separation membranes made of polymeric materials are stacked, but inorganic materials such as zeolite may also be used, or a hybrid type membrane of both may also be used, and these may be selected appropriately according to the design conditions.

[0037] [Embodiment 2] Next, the configuration and functions of the second embodiment will be described with reference to FIG. The same numbers are used for components having the same configurations and functions as those in the first embodiment. The carbon dioxide liquefaction system 100 according to the second embodiment has a second liquefied carbon dioxide cooler 110 disposed upstream of the liquefied carbon dioxide cooler 30 .

[0038] The second liquefied carbon dioxide cooler 110 is a general shell-and-tube type heat exchanger, and cools the liquefied carbon dioxide by heat exchange with a gas that has been reduced in pressure from the non-permeable gas of the carbon dioxide separation membrane 50 . In Figure 2, the second liquefied carbon dioxide cooler 110 is arranged downstream of the liquefied carbon dioxide pump 20, but it may also be arranged upstream of the liquefied carbon dioxide pump 20 or downstream of the liquefied carbon dioxide cooler 30.

[0039] Next, the operation of the carbon dioxide liquefaction system 100 according to this embodiment will be described. The explanation of the same functions as those in the first embodiment will be omitted. Inside the liquefied carbon dioxide drum 10, nitrogen and oxygen accumulate in the gas layer of the liquefied carbon dioxide drum 10, causing an increase in the internal pressure. For this reason, the gas layer of the liquefied carbon dioxide drum 10 is discharged while its pressure is reduced and its flow rate is adjusted using the recycle gas flow control valve 83 and the non-permeate gas discharge flow control valve 85.

[0040] At this time, the temperature of the non-permeate gas flowing through the non-permeate gas discharge line 84 drops by several degrees Celsius to several tens of degrees Celsius due to the Joule-Thomson effect associated with the pressure reduction by the non-permeate gas discharge flow rate control valve 85, creating a temperature difference that is sufficient to cool the liquefied carbon dioxide in the second liquefied carbon dioxide cooler 110. The second liquefied carbon dioxide cooler 110 uses this temperature difference to cool the liquefied carbon dioxide.

[0041] According to the carbon dioxide liquefaction system 100 of this embodiment, the nitrogen and oxygen discharged from the liquefied carbon dioxide drum 10 can be reduced in pressure and temperature to contribute to cooling the liquefied carbon dioxide, so that carbon dioxide can be efficiently separated and liquefied even from gases containing non-condensable gases other than carbon dioxide while reducing the cooling energy required.

[0042] [Embodiment 3] Next, the configuration and functions of the third embodiment will be described with reference to FIG. The same numbers are used for components having the same configurations and functions as those in the first embodiment. The carbon dioxide liquefaction system 200 according to the third embodiment has a carbon dioxide-containing gas precooler 210 in the carbon dioxide-containing gas receiving line 75 .

[0043] The carbon dioxide-containing gas precooler 210 is a typical shell-and-tube type heat exchanger, and cools the carbon dioxide-containing gas flowing through the carbon dioxide-containing gas receiving line 75 by heat exchange with the non-permeating gas that has passed through the second liquefied carbon dioxide cooler 110.

[0044] Next, the operation of the carbon dioxide liquefaction system 200 according to this embodiment will be described. The explanation of the same functions as those in the first embodiment will be omitted. The temperature of the non-permeable gas obtained by cooling the liquefied carbon dioxide in the second liquefied carbon dioxide cooler 110 approaches the temperature of the liquefied carbon dioxide (for example, about -50°C), but remains low enough to cool gas at room temperature. In the carbon dioxide-containing gas precooler 210, the carbon dioxide-containing gas flowing through the carbon dioxide-containing gas receiving line 75 is cooled by heat exchange with the non-permeable gas that remains at a low temperature after cooling the liquefied carbon dioxide.

[0045] The carbon dioxide-containing gas flowing through the carbon dioxide-containing gas receiving line 75 is cooled in the carbon dioxide-containing gas precooler 210, and the resulting non-permeated gas is discharged to the outside.

[0046] According to the carbon dioxide liquefaction system 200 of this embodiment, the carbon dioxide-containing gas flowing through the carbon dioxide-containing gas receiving line 75 can be cooled by utilizing the cold energy of the non-permeable gas that has cooled the liquefied carbon dioxide in the second liquefied carbon dioxide cooler 110, thereby reducing the cold energy required to liquefy carbon dioxide and enabling efficient liquefaction of carbon dioxide.

[0047] In this embodiment, the non-permeable gas introduced into the carbon dioxide-containing gas precooler 210 has passed through the second liquefied carbon dioxide cooler 110, but the present invention is not limited to this and also includes an embodiment in which the non-permeable gas is supplied to the carbon dioxide-containing gas precooler 210 without passing through the second liquefied carbon dioxide cooler 110.

[0048] [Embodiment 4] Next, the configuration and functions of the fourth embodiment will be described with reference to FIG. The same numbers are used for components having the same configurations and functions as those in the first embodiment. The carbon dioxide liquefaction system 300 according to the fourth embodiment has a recycled gas precooler 310 in the carbon dioxide separation membrane outlet line 82 .

[0049] The recycle gas precooler 310 is a typical shell-and-tube heat exchanger, which cools the carbon dioxide-enriched gas flowing through the carbon dioxide separation membrane outlet line 82 by heat exchange with a gas that has been reduced in pressure from the non-permeable gas of the carbon dioxide separation membrane 50. 4, the recycled gas precooler 310 is disposed upstream of the recycled gas flow rate control valve 83, but it may also be disposed downstream of the recycled gas flow rate control valve 83. Because the pressure of the gas that has permeated the carbon dioxide separation membrane 50 drops by the amount of the pressure difference, the temperature drop due to the Joule-Thomson effect is smaller for the recycled gas flow rate 83 than for the non-permeate gas discharge flow rate control valve 85. For this reason, even if the recycled gas precooler 310 is disposed downstream of the recycled gas flow rate control valve 83, the recycled gas can be cooled.

[0050] Next, the operation of the carbon dioxide liquefaction system 300 according to this embodiment will be described. The explanation of the same functions as those in the first embodiment will be omitted. The temperature of the non-permeating gas of the carbon dioxide separation membrane 50 is lower by several degrees Celsius to several tens of degrees Celsius than the temperature of the gas layer in the liquefied carbon dioxide drum 10 due to the Joule-Thomson effect associated with the pressure reduction in the recycle gas flow rate control valve 83. In the recycle gas precooler 310, the carbon dioxide-enriched gas flowing through the carbon dioxide separation membrane outlet line 82 is cooled by heat exchange with this gas.

[0051] The non-permeable gas obtained by cooling the carbon dioxide-enriched gas flowing through the carbon dioxide separation membrane outlet line 82 in the recycle gas precooler 310 is introduced into the carbon dioxide-containing gas precooler 210 and cools the carbon dioxide-containing gas flowing through the carbon dioxide-containing gas receiving line 75.

[0052] According to the carbon dioxide liquefaction system 300 of this embodiment, the temperature of the non-permeable gas in the carbon dioxide separation membrane 50 is lowered by reducing the pressure using the non-permeable gas discharge flow control valve 85, thereby cooling the carbon dioxide-enriched gas flowing through the carbon dioxide separation membrane outlet line 82. The cooled carbon dioxide-enriched gas is further reduced in temperature by pressure reduction using the recycle gas flow control valve 83, and then merges with the carbon dioxide-containing gas flowing through the carbon dioxide-containing gas receiving line 75. This allows low-temperature carbon dioxide-containing gas to be supplied to the ejector 40, reducing the cooling load on the carbon dioxide, and by supplying more of the carbon dioxide-containing gas to the ejector 40 because the gas density has increased due to cooling, carbon dioxide can be liquefied with less energy.

[0053] In addition, the non-permeable gas obtained by cooling the carbon dioxide-enriched gas flowing through the carbon dioxide separation membrane outlet line 82 in the recycle gas precooler 310 is introduced into the carbon dioxide-containing gas precooler 210 and cools the carbon dioxide-containing gas flowing through the carbon dioxide-containing gas receiving line 75, thereby further reducing the cooling load on the carbon dioxide and enabling the carbon dioxide to be liquefied with even less energy.

[0054] In this embodiment, a configuration is shown in which the non-permeable gas that has passed through the recycle gas precooler 310 is introduced into the carbon dioxide-containing gas precooler 210, but the present invention also includes a configuration in which the non-permeable gas that has passed through the recycle gas precooler 310 is not introduced into the carbon dioxide-containing gas precooler 210. [Industrial Applicability]

[0055] The present invention can be used as a carbon dioxide liquefaction system that can minimize the energy required for separating and liquefying carbon dioxide. [Explanation of symbols]

[0056] 1, 100, 200, 300 Carbon dioxide liquefaction system 10 drums of liquefied carbon dioxide 20 Liquefied carbon dioxide pump 30 Liquefied carbon dioxide cooler 40 Ejector 50 Carbon dioxide separation membrane 71 Liquefied carbon dioxide pump inlet line 72 Liquefied carbon dioxide pump outlet line 73 Ejector inlet line 74 Ejector outlet line 75 Carbon dioxide-containing gas receiving line 76 Refrigerant supply line 77 Refrigerant discharge line 78 Liquefied carbon dioxide delivery line 81 Carbon dioxide separation membrane inlet line 82 Carbon dioxide separation membrane outlet line 83 Recycle gas flow control valve 84 Non-permeate gas discharge line 85 Non-permeate gas discharge flow control valve 110 Second liquefied carbon dioxide cooler 210 Carbon dioxide-containing gas precooler 310 Recycle gas precooler

Claims

1. a liquefied carbon dioxide drum for storing the liquefied carbon dioxide; a liquefied carbon dioxide circulation line through which liquefied carbon dioxide circulates, the liquefied carbon dioxide drum being a starting point; a liquefied carbon dioxide pump that is disposed downstream of the liquefied carbon dioxide drum in the liquefied carbon dioxide circulation line and that pressurizes and discharges the liquefied carbon dioxide stored in the liquefied carbon dioxide drum; a liquefied carbon dioxide cooler that is disposed in the liquefied carbon dioxide circulation line and cools the liquefied carbon dioxide discharged by the liquefied carbon dioxide pump by heat exchange with a refrigerant; an ejector that is disposed downstream of the liquefied carbon dioxide pump in the liquefied carbon dioxide circulation line, and that uses the liquefied carbon dioxide discharged by the liquefied carbon dioxide pump as a driving fluid and a carbon dioxide-containing gas as a suction fluid; a carbon dioxide-containing gas receiving line that receives the carbon dioxide-containing gas into the ejector; a liquefied carbon dioxide discharge line that discharges the liquefied carbon dioxide from the liquefied carbon dioxide drum to the outside; a recycle gas line for returning the gas in the gas layer of the liquefied carbon dioxide drum to the carbon dioxide-containing gas receiving line; a carbon dioxide separation membrane disposed in the recycle gas line for concentrating carbon dioxide in the gas layer of the liquefied carbon dioxide drum; a recycle gas flow rate control valve that is arranged downstream of the carbon dioxide separation membrane in the recycle gas line and that reduces the pressure and adjusts the flow rate of the gas in the gas layer of the liquefied carbon dioxide drum.

2. a non-permeation gas discharge line for discharging non-permeation gas that has not permeated the carbon dioxide separation membrane to the outside; a non-permeate gas discharge flow rate control valve disposed in the non-permeate gas discharge line for reducing the pressure and regulating the flow rate of the gas flowing through the non-permeate gas discharge line; a second liquefied carbon dioxide cooler that is disposed in the liquefied carbon dioxide circulation line and cools the liquefied carbon dioxide with the non-permeate gas that has passed through the non-permeate gas discharge flow rate control valve in the non-permeate gas discharge line.

3. The carbon dioxide liquefaction system described in claim 2, characterized in that it further comprises a carbon dioxide-containing gas precooler arranged in the carbon dioxide-containing gas receiving line and cooling the carbon dioxide-containing gas using the non-permeating gas that has passed through the second liquefied carbon dioxide cooler.

4. a non-permeation gas discharge line for discharging non-permeation gas that has not permeated the carbon dioxide separation membrane to the outside; a non-permeate gas discharge flow rate control valve disposed in the non-permeate gas discharge line for reducing the pressure and regulating the flow rate of the gas flowing through the non-permeate gas discharge line; 2. The carbon dioxide liquefaction system according to claim 1, further comprising: a carbon dioxide-containing gas precooler disposed in the carbon dioxide-containing gas receiving line, which cools the carbon dioxide-containing gas using the non-permeable gas that has passed through the non-permeable gas discharge flow rate control valve in the non-permeable gas discharge line.

5. a non-permeation gas discharge line for discharging non-permeation gas that has not permeated the carbon dioxide separation membrane to the outside; a non-permeate gas discharge flow rate control valve disposed in the non-permeate gas discharge line for reducing the pressure and regulating the flow rate of the gas flowing through the non-permeate gas discharge line; a recycle gas cooler disposed in the recycle gas line for cooling the recycle gas with non-permeate gas that has passed through the non-permeate gas discharge flow rate control valve in the non-permeate gas discharge line.

6. The carbon dioxide liquefaction system according to claim 5, further comprising a carbon dioxide-containing gas precooler disposed in the carbon dioxide-containing gas receiving line and cooling the carbon dioxide-containing gas by the non-permeate gas that has passed through the recycle gas cooler.

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