Carbon dioxide liquefaction system

Abstract

To provide a carbon dioxide liquefaction system which can minimize energy required for liquefaction.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 gas containing carbon dioxide as a suction fluid, a carbon dioxide containing gas receiving line 75 through which the ejector 40 receives the gas containing carbon dioxide, and a liquefied carbon dioxide output line 78 which outputs liquefied carbon dioxide from the liquefied carbon dioxide drum 10 to the exterior.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] The present invention has been made to solve such problems, and has an object to provide a carbon dioxide liquefaction system that can minimize the energy required for liquefying carbon dioxide. [Means for solving the problem]

[0007] (1) The carbon dioxide liquefaction system according to the present invention comprises: 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; and a liquefied carbon dioxide discharge line that discharges the liquefied carbon dioxide from the liquefied carbon dioxide drum to the outside.

[0008] (2) In addition, the device described in (1) above is characterized by having an ejector heating means for heating the ejector.

[0009] (3) In addition, in the above (1) or (2), a refrigerant circulation line for circulating the refrigerant; a refrigerant pump disposed in the refrigerant circulation line to pressurize and discharge the refrigerant; and a refrigerant cooler that is disposed downstream of the refrigerant pump in the refrigerant circulation line and cools the refrigerant by heat exchange with LNG.

[0010] (4) In addition, in the device according to any one of (1) to (3) above, a re-liquefaction ejector using the liquefied carbon dioxide as a driving fluid and the gas in the gas layer of the liquefied carbon dioxide drum as a suction fluid; a re-liquefaction carbon dioxide circulation line branching from the carbon dioxide circulation line to supply liquefied carbon dioxide to the re-liquefaction ejector and to supply the fluid re-liquefied in the re-liquefaction ejector to the liquefied carbon dioxide drum; and a reliquefaction gas receiving line that receives gas from the gas layer of the liquefied carbon dioxide drum into the reliquefaction ejector.

[0011] (5) Furthermore, in the device described in any one of (1) to (4) above, a weir is disposed inside the liquefied carbon dioxide drum between the return port of the liquefied carbon dioxide circulation line and the inlet of the liquefied carbon dioxide circulation line, and causes the liquefied carbon dioxide inside the liquefied carbon dioxide drum to overflow and supply it to the inlet of the liquefied carbon dioxide circulation line.

[0012] (6) In addition, in the above-mentioned (1) to (5), the carbon dioxide-containing gas contains nitrogen and oxygen, a non-condensable gas discharge line for discharging nitrogen and oxygen accumulated in the gas layer of the liquefied carbon dioxide drum to the outside; a non-condensable gas discharge flow rate control valve disposed in the non-condensable gas discharge line for reducing the pressure and controlling the flow rate of the gas flowing through the non-condensable 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 non-condensable gas that has passed through the non-condensable gas discharge flow rate control valve in the non-condensable gas discharge line. [Effects of the Invention]

[0013] 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. [Brief explanation of the drawings]

[0014] [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. [Figure 5] FIG. 10 is a schematic diagram showing a carbon dioxide liquefaction system according to a fifth embodiment of the present invention. [Figure 6] FIG. 10 is a schematic diagram showing a carbon dioxide liquefaction system according to a sixth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] [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, and an ejector 40.

[0016] 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 .

[0017] 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.

[0018] 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.

[0019] 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 carbon dioxide gas from a 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 .

[0020] 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, 0.6 MPaG and −50° C., and is pressurized by the liquefied carbon dioxide pump 20 to, for example, 1.3 MPaG.

[0021] 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.

[0022] The liquefied carbon dioxide cooled by the liquefied carbon dioxide cooler 30 is supplied to the ejector 40, and a reduced pressure state is created by flowing at high speed through the small diameter portion inside the ejector 40 using Bernoulli's principle. Carbon dioxide gas at atmospheric pressure or low pressure is supplied from the gas receiving line 75 to the inside of the ejector 40 in a reduced pressure state.

[0023] Inside the ejector 40, the carbon dioxide gas supplied from the gas receiving line 75 mixes with the liquefied carbon dioxide, which is flowing at a high speed. 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 recovers to, for example, 0.6 MPaG, and the carbon dioxide gas in the mixed fluid is compressed and cooled, causing it to condense. At this time, the carbon dioxide gas is compressed while coming into contact with the liquefied carbon dioxide and being cooled, so the compression process of the carbon dioxide gas is close to isothermal compression, and therefore the carbon dioxide gas is compressed with high compression efficiency.

[0024] In the downstream of the ejector 40, the liquefied carbon dioxide flows through the ejector outlet line 74 towards the liquefied carbon dioxide drum 10, but if carbon dioxide gas that has not been completely condensed remains inside the ejector 40, it becomes a multiphase flow.

[0025] The liquefied carbon dioxide that flows into the liquefied carbon dioxide drum 10 becomes saturated at 0.6 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 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.

[0026] According to the carbon dioxide liquefaction system 1 of this embodiment, the reduced pressure state created by the ejector 40 can be utilized to accept and liquefy carbon dioxide at atmospheric pressure or low pressure, thereby eliminating or significantly reducing the compressor power required to pressurize the carbon dioxide.

[0027] 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.

[0028] [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 heater 110 that heats the ejector 40. The heater 110 is a general-purpose electric heater that adjusts the temperature of the ejector 40 so that it does not fall below a certain temperature.

[0029] 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.

[0030] In the ejector 40, since the liquefied carbon dioxide passes through a reduced-pressure space, albeit for an extremely short time, some of the liquefied carbon dioxide may evaporate, absorbing the latent heat of evaporation and cooling the unevaporated liquefied carbon dioxide. In this case, if the temperature drops below the solidification temperature of the liquefied carbon dioxide, solid carbon dioxide is produced, which may clog the ejector 40 or narrow the flow path, increasing pressure loss.

[0031] Therefore, in the carbon dioxide liquefaction system 100 of this embodiment, the electric heater 110 is used to maintain the part of the ejector 40 that is particularly in a reduced pressure state at a temperature higher than the solidification temperature of carbon dioxide, thereby preventing the solidification of carbon dioxide.

[0032] According to the carbon dioxide liquefaction system 100 of this embodiment, the electric heater 110 prevents the liquefied carbon dioxide from solidifying, thereby preventing problems such as blockages and enabling stable liquefaction of carbon dioxide.

[0033] In this embodiment, the heater 110 is described as a general-purpose electric heater, but a system in which heating is performed using a separately prepared heat medium may also be used. Also, a system in which part of the liquefied carbon dioxide discharged from the liquefied carbon dioxide pump 20 is used as a heat medium to prevent the temperature from falling below the solidification temperature of the carbon dioxide may also be used.

[0034] 2, the heater 110 is provided in the first embodiment shown in FIG. 1, but the heater 110 may also be provided in the third to sixth embodiments described later.

[0035] [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 the function of constantly cooling the refrigerant of the liquefied carbon dioxide cooler 30, for example, liquefied methane, to a constant temperature, and has as its main components a refrigerant pump 210, a refrigerant cooler 220, a refrigerant drum 230, a refrigerant cooler flow control valve 273, and a refrigerant cooler bypass flow control valve 275.

[0036] The refrigerant pump 210 is a general centrifugal pump, and discharges liquefied methane from a refrigerant pump inlet line 271 to a refrigerant pump outlet line 272 after increasing the pressure by the amount of pressure loss within the system.

[0037] The refrigerant cooler 220 is a typical shell-and-tube heat exchanger that cools liquefied methane by heat exchange between LNG supplied from an LNG supply line 281 and liquefied methane supplied from a refrigerant pump outlet line 272. Here, the LNG supply line 281 is, for example, an LNG delivery line or a branch line thereof at an LNG terminal, and LNG at a very low temperature (for example, about −150° C.) flows through the LNG supply line 281. The LNG that has cooled the liquefied methane in the refrigerant cooler 220 is discharged to an LNG discharge line 282 and then merges with, for example, the LNG delivery line.

[0038] The refrigerant drum 230 is a typical vertical cylindrical container, and temporarily stores the liquefied methane obtained by cooling the liquefied carbon dioxide in the liquefied carbon dioxide cooler 30 in a saturated state.

[0039] Refrigerant cooler flow control valve 273 is a remotely controlled globe valve that adjusts the flow rate of liquefied methane supplied to refrigerant cooler 220. Refrigerant cooler bypass flow control valve 275 is a remotely controlled globe valve that adjusts the flow rate of liquefied methane supplied to 274.

[0040] 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 liquefied methane circulated by the refrigerant pump 210 is cooled by heat exchange with LNG in the refrigerant cooler 220, and the flow rate distribution is adjusted by the refrigerant cooler flow control valve 273 and the refrigerant cooler bypass flow control valve 275, so that the temperature of the liquefied methane supplied to the liquefied carbon dioxide cooler 30 is cooled to, for example, -55°C.

[0041] The cooled liquefied methane is supplied to the liquefied carbon dioxide cooler 30 via a refrigerant supply line 276, and cools the liquefied carbon dioxide discharged by the liquefied carbon dioxide pump 20 to, for example, −53° C. Thereafter, the liquefied methane is returned to the refrigerant drum via a refrigerant discharge line 277.

[0042] According to the carbon dioxide liquefaction system 200 of this embodiment, LNG discharged at an LNG terminal is used to supply the cold energy required to liquefy carbon dioxide, thereby making it possible to effectively utilize the cold energy of LNG that would previously have been discarded into the ocean or other environments.

[0043] Furthermore, since the carbon dioxide liquefaction system 200 according to this embodiment does not have a refrigerator for generating the cold heat required to liquefy carbon dioxide, it is possible to reduce the power costs required for the refrigerator.

[0044] In this embodiment, the refrigerant has been described as liquefied methane, but it is not limited to liquefied methane, and any refrigerant that can maintain a stable liquid state at a temperature that can supply cold enough to liquefy carbon dioxide, such as liquefied ethane, liquefied propane, or other fluorocarbon-based low-temperature refrigerants, can be selected appropriately according to the design conditions.

[0045] Furthermore, what is shown in Figure 3 is the first embodiment of Figure 1 to which a refrigerant drum 230 and the like have been added, but what has been added in this embodiment can also be added to the fourth to sixth embodiments in the same way.

[0046] [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 includes a re-liquefaction ejector 310 , an ejector flow rate adjustment valve 376 , a re-liquefaction ejector flow rate adjustment valve 372 , and a top gas flow rate adjustment valve 375 .

[0047] The re-liquefaction ejector 310 is a general ejector that creates a reduced pressure state using liquefied carbon dioxide supplied from a re-liquefaction ejector branch line 371 branching off from the ejector inlet line 73 as a driving fluid, and receives the top gas of the liquefied carbon dioxide drum 10 from a top gas receiving line 374.

[0048] The ejector flow rate control valve 376 and the reliquefaction ejector flow rate control valve 372 are remote-controlled globe valves, and adjust the flow rates of liquefied carbon dioxide supplied to the ejector 40 and the reliquefaction ejector 310. The top gas flow rate control valve 375 is a remote-controlled globe valve, and adjusts the flow rate of the top gas of the liquefied carbon dioxide drum 10 that is supplied to the reliquefaction ejector 310.

[0049] 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. In the gas layer of the liquefied carbon dioxide drum 10, the temperature increases as one moves further away from the gas-liquid interface toward the top, which causes an increase in the internal pressure of the liquefied carbon dioxide drum 10.

[0050] The overhead gas is supplied to the reliquefaction ejector 310 via the overhead gas receiving line 374, mixed with the liquefied carbon dioxide supplied from the reliquefaction ejector branch line 371, and reliquefied, and then returned to the liquefied carbon dioxide drum 10 via the reliquefaction ejector outlet line 373. The reliquefaction ejector branch line 371, the reliquefaction ejector 310, and the reliquefaction ejector outlet line 373 constitute the reliquefaction carbon dioxide circulation line of the present invention. By using the re-liquefaction ejector 310 to mix the gas at the top of the liquefied carbon dioxide drum 10 with the liquefied carbon dioxide and re-liquefy it, it is possible to suppress an increase in the internal pressure of the liquefied carbon dioxide drum 10.

[0051] According to the carbon dioxide liquefaction system 300 of this embodiment, the re-liquefaction ejector 310 can re-liquefy the gas at the top of the liquefied carbon dioxide drum 10, thereby suppressing an increase in the internal pressure of the liquefied carbon dioxide drum 10 and controlling the internal pressure of the liquefied carbon dioxide drum 10.

[0052] In particular, if the internal pressure of the liquefied carbon dioxide drum 10 is set as low as possible, for example, to about 0.6 MPaG, the saturation temperature will be about -50°C, which is close to the solidification temperature of liquefied carbon dioxide, which is about -56°C. Therefore, when the internal pressure of the liquefied carbon dioxide drum 10 increases, there is little room for temperature reduction in the liquefied carbon dioxide cooler 30, making it difficult to achieve the effect of suppressing pressure increase due to temperature reduction. In such cases, the pressure of the liquefied carbon dioxide drum 10 can be adjusted more quickly and with ample margin by extracting the relatively high-temperature top gas of the liquefied carbon dioxide drum 10 and re-liquefying it.

[0053] In the present embodiment, the branch line 371 for the reliquefaction ejector is branched off from the ejector inlet line 73. However, the reliquefaction ejector 310 may have a dedicated pump, cooler, and circulation line. Compared to the ejector 40, the reliquefaction ejector 310 has a higher suction gas pressure, so the required degree of decompression is lower, and as a result, the required differential pressure is also smaller. For this reason, if the flow rate of the liquefied carbon dioxide pump 20, which has a high head for the ejector 40, is increased for the reliquefaction ejector 310, the head would be wasted. If a pump dedicated to the reliquefaction ejector 310 is provided, the required head can be secured without excess or deficiency, allowing for efficient operation.

[0054] Moreover, what is shown in Figure 4 is the first embodiment of Figure 1 with the addition of a re-liquefaction ejector 310 and the like, but what is added in this embodiment can also be added to the fifth embodiment in the same way.

[0055] [Embodiment 5] Next, the configuration and functions of the fifth 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. Inside the ejector 40, the liquefied carbon dioxide is decompressed for a very short time, and as a result, solid carbon dioxide may be mixed into the ejector outlet line 74. If solid carbon dioxide enters the liquefied carbon dioxide drum 10 and is supplied as is to the liquefied carbon dioxide pump 20, this may damage the liquefied carbon dioxide pump 20. Therefore, the carbon dioxide liquefaction system 400 according to the fifth embodiment has weirs 411 and 412 provided inside the liquefied carbon dioxide drum 10 to prevent solid carbon dioxide from being supplied to the liquefied carbon dioxide pump 20.

[0056] Weirs 411 and 412 are both plate-shaped members and are installed inside the liquefied carbon dioxide drum 10. Weir 411 is structured so that its upper end is located above the liquid level and its lower end is spaced apart from the bottom of the liquefied carbon dioxide drum 10. Weir 412 is structured so that its lower end abuts against the bottom of the liquefied carbon dioxide drum 10 and so that liquefied carbon dioxide overflows from its upper end.

[0057] Next, the operation of the carbon dioxide liquefaction system 400 according to this embodiment will be described. The explanation of the same functions as those in the first embodiment will be omitted.

[0058] If solid carbon dioxide is mixed in with the liquefied carbon dioxide received from the ejector outlet line 74, the movement of the solid carbon dioxide moving on the liquid surface is restricted by the weir 411. The solid carbon dioxide whose movement is restricted has a greater specific gravity than the liquefied carbon dioxide and so settles, and is heated and melted in the process of settling. The solid carbon dioxide that moves in its solid form from the lower end of the weir 411 to the weir 412 side is restricted in its movement by the weir 411, where it is heated and melted. Because the lower end of the weir 412 abuts against the bottom surface of the liquefied carbon dioxide drum 10, the solid carbon dioxide does not exceed the weir 412 and remains in the upstream of the weir 412, where it is heated and further melted.

[0059] According to the carbon dioxide liquefaction system 400 of this embodiment, even if solid carbon dioxide is produced in the ejector 40, the solid carbon dioxide can be reliably melted by the weirs 411 and 412 of the liquefied carbon dioxide drum 10. As a result, the carbon dioxide liquefaction system 400 can stably liquefy carbon dioxide while minimizing the risk of trouble caused by solid carbon dioxide.

[0060] 5 is obtained by adding weirs 411 and 412 to the first embodiment of FIG. 1, but what has been added in this embodiment can also be added to the sixth embodiment in the same way.

[0061] [Embodiment 6] Next, the configuration and functions of the sixth 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 500 of embodiment 6 is designed to cool the liquefied carbon dioxide supplied to the liquefied carbon dioxide cooler 30 by utilizing the cold energy of the top gas discharged from the liquefied carbon dioxide drum 10, and has a second liquefied carbon dioxide cooler 510, a top gas discharge line 571, and a top gas discharge flow rate control valve 572.

[0062] The second liquefied carbon dioxide cooler 510 is a typical shell-and-tube type heat exchanger that is arranged upstream of the liquefied carbon dioxide cooler 30 and cools the liquefied carbon dioxide by heat exchange with the depressurized gas from the top of the liquefied carbon dioxide drum 10. In Figure 6, the second liquefied carbon dioxide cooler 510 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.

[0063] The top gas discharge flow rate control valve 572 is a typical remotely operated globe valve provided on the top gas discharge line 571, which reduces the pressure of the top gas in the liquefied carbon dioxide drum 10 and adjusts the flow rate, and discharges it outside the system.

[0064] Next, the operation of the carbon dioxide liquefaction system 500 according to this embodiment will be described. The explanation of the same functions as those in the first embodiment will be omitted. If the gas received by the ejector 40 contains non-condensable gases other than carbon dioxide, such as nitrogen or oxygen, the carbon dioxide is liquefied by adjusting the internal pressure and temperature of the liquefied carbon dioxide drum 10, taking into account the partial pressure of carbon dioxide.

[0065] On the other hand, nitrogen and oxygen, which do not liquefy under the carbon dioxide liquefaction conditions, accumulate in the gas layer of the liquefied carbon dioxide drum 10, causing an increase in the internal pressure. For this reason, the flow rate is adjusted while the pressure is reduced by the top gas discharge flow control valve 572, and the nitrogen and oxygen are discharged to the outside of the system.

[0066] At this time, due to the Joule-Thomson effect accompanying the pressure reduction by the overhead gas discharge flow rate adjustment valve 572, the temperatures of the nitrogen and oxygen are lowered by several degrees Celsius to several tens of degrees Celsius below the gas layer temperature in the liquefied carbon dioxide drum 10, and a temperature difference sufficient to cool the liquefied carbon dioxide is generated. This temperature-lowered overhead gas cools the liquefied carbon dioxide in the second liquefied carbon dioxide cooler 510 by utilizing the temperature difference, and is then discharged from the cooled gas discharge line 573.

[0067] According to the carbon dioxide liquefaction system 500 of this embodiment, even if the carbon dioxide gas received by the ejector 40 contains non-condensable gases such as nitrogen and oxygen, the non-condensable gases can be reduced in pressure and temperature to contribute to cooling the liquefied carbon dioxide, so that carbon dioxide-containing gas can be received and only carbon dioxide can be efficiently liquefied while reducing cooling energy. [Industrial Applicability]

[0068] The present invention can be used as a carbon dioxide liquefaction system that can liquefy carbon dioxide with minimal energy. [Explanation of symbols]

[0069] 1, 100, 200, 300, 400, 500 Carbon dioxide liquefaction system 10 liquefied carbon dioxide drums 20 Liquefied carbon dioxide pump 30 Liquid carbon dioxide cooler 40 Ejector 71 Liquefied carbon dioxide pump inlet line 72 Liquefied carbon dioxide pump outlet line 73 Ejector inlet line 74 Ejector outlet line 75 Gas receiving line 76 Refrigerant supply line 77 Refrigerant discharge line 78 Liquefied carbon dioxide delivery line 110 Heater (electric heater) 210 Refrigerant pump 220 Refrigerant cooler 230 Refrigerant drum 271 Refrigerant pump inlet line 272 Refrigerant pump outlet line 273 Refrigerant cooler flow control valve 274 Refrigerant cooler bypass line 275 Refrigerant cooler bypass flow control valve 276 Refrigerant supply line 277 Refrigerant discharge line 281 LNG supply line 282 LNG discharge line 310 Reliquefaction Ejector 371 Branch line for reliquefaction ejector 372 Flow control valve for reliquefaction ejector 373 Reliquefaction ejector outlet line 374 Top gas receiving line 375 Top gas flow control valve 376 Ejector flow control valve 411, 412 Weir 510 Second liquefied carbon dioxide cooler 571 Top gas exhaust line 572 Top gas discharge flow control valve 573 Cooling gas discharge line

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.

2. 2. The carbon dioxide liquefaction system according to claim 1, further comprising an ejector heating means for heating the ejector.

3. a refrigerant circulation line through which the refrigerant circulates; a refrigerant pump disposed in the refrigerant circulation line to pressurize and discharge the refrigerant; 2. The carbon dioxide liquefaction system according to claim 1, further comprising: a refrigerant cooler disposed downstream of the refrigerant pump in the refrigerant circulation line, the refrigerant being cooled by heat exchange with LNG.

4. a re-liquefaction ejector that uses the liquefied carbon dioxide as a driving fluid and the gas in the gas layer of the liquefied carbon dioxide drum as a suction fluid; a re-liquefaction carbon dioxide circulation line branching from the carbon dioxide circulation line to supply liquefied carbon dioxide to the re-liquefaction ejector and to supply the fluid re-liquefied in the re-liquefaction ejector to the liquefied carbon dioxide drum; 2. The carbon dioxide liquefaction system according to claim 1, further comprising: a reliquefaction gas receiving line that receives gas from the gas layer of the liquefied carbon dioxide drum into the reliquefaction ejector.

5. The carbon dioxide liquefaction system described in claim 1, characterized in that it has a weir arranged inside the liquefied carbon dioxide drum between the return port of the liquefied carbon dioxide circulation line and the inlet of the liquefied carbon dioxide circulation line, which overflows the liquefied carbon dioxide inside the liquefied carbon dioxide drum and supplies it to the inlet of the liquefied carbon dioxide circulation line.

6. the carbon dioxide-containing gas includes nitrogen and oxygen; a non-condensable gas discharge line for discharging nitrogen and oxygen accumulated in the gas layer of the liquefied carbon dioxide drum to the outside; a non-condensable gas discharge flow rate control valve disposed in the non-condensable gas discharge line for reducing the pressure and controlling the flow rate of the gas flowing through the non-condensable gas discharge line; The carbon dioxide liquefaction system described in claim 1, characterized in that it further comprises a second liquefied carbon dioxide cooler that is arranged in the liquefied carbon dioxide circulation line and cools the liquefied carbon dioxide using non-condensable gas that has passed through the non-condensable gas discharge flow rate control valve in the non-condensable gas discharge line.

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