Carbon dioxide liquefier

Abstract

To provide a carbon dioxide liquefier for liquefying carbon dioxide while suppressing the freezing of carbon dioxide.SOLUTION: The carbon dioxide liquefier 1 includes a shell 11 in which carbon dioxide to be liquefied flows, at least one heat-transfer tube 12 disposed in the shell 11 and through which natural gas as a refrigerant for cooling the carbon dioxide flows, a baffle 14 disposed in the shell 11 so that the carbon dioxide flows in the same direction as the flow direction of the natural gas while meandering up and down, a liquid pool 17 provided adjacent to the shell 11 and in which liquefied carbon dioxide obtained by liquefying the carbon dioxide is stored, a temperature sensor SR1 provided in the liquid pool 17, and an inflow rate controller that adjusts the flow rate of the natural gas flowing into the heat-transfer tube 12 based on the temperature detected by the temperature sensor SR1 so that the carbon dioxide does not freeze.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] BACKGROUND ART Conventionally, it has been known to liquefy carbon dioxide by utilizing the cold energy of boil-off gas (BOG) obtained by vaporizing liquefied natural gas (LNG) (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2022 / 250078 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if carbon dioxide is cooled too much, it will freeze (become dry ice). When carbon dioxide freezes, it will no longer flow, and the carbon dioxide liquefaction device will no longer be able to continue operating.

[0005] An object of an embodiment of the present invention is to provide a carbon dioxide liquefaction device that liquefies carbon dioxide while suppressing freezing of carbon dioxide. [Means for solving the problem]

[0006] A carbon dioxide liquefaction device according to an aspect of the present invention comprises a shell through which carbon dioxide to be liquefied flows, at least one heat transfer tube arranged inside the shell and through which natural gas flows as a refrigerant for cooling the carbon dioxide, a baffle arranged inside the shell so that the carbon dioxide flows in a meandering pattern up and down in the same direction as the natural gas, a liquid reservoir arranged adjacent to the shell and in which liquefied carbon dioxide is accumulated, a first temperature sensor arranged in the liquid reservoir, and an inflow flow rate control unit that adjusts the flow rate of the natural gas flowing into the heat transfer tube based on a first temperature detected by the first temperature sensor so as to prevent the carbon dioxide from freezing. [Effects of the Invention]

[0007] According to an embodiment of the present invention, it is possible to provide a carbon dioxide liquefaction device that liquefies carbon dioxide while suppressing freezing of carbon dioxide. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a configuration diagram showing the configuration of a carbon dioxide liquefaction device according to a first embodiment of the present invention. [Figure 2] 1 is a configuration diagram showing the configuration of a carbon dioxide liquefaction system to which a carbon dioxide liquefaction device according to a first embodiment is applied. [Figure 3] FIG. 4 is a diagram showing the configuration of a carbon dioxide liquefaction device according to a second embodiment of the present invention. [Figure 4] 10 is a flowchart showing the flow of control by the control device of the carbon dioxide liquefaction device according to the second embodiment. [Figure 5] FIG. 10 is a diagram showing the configuration of a carbon dioxide liquefaction device according to a third embodiment of the present invention. [Figure 6] FIG. 10 is a configuration diagram showing the configuration of a carbon dioxide liquefaction device according to a fourth embodiment of the present invention. [Figure 7] FIG. 10 is a configuration diagram showing the configuration of a carbon dioxide liquefaction device according to a fifth embodiment of the present invention. [Figure 8] FIG. 10 is a diagram showing the configuration of a carbon dioxide liquefaction device according to a sixth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] (First embodiment) 1 is a diagram showing the configuration of a carbon dioxide liquefaction device 1 according to a first embodiment of the present invention. Note that the same parts in the drawings are given the same reference numerals, and duplicated explanations will be omitted where appropriate.

[0010] The carbon dioxide liquefaction device 1 is basically configured as a shell-and-tube heat exchanger in which a plurality of heat transfer tubes 12 (tubes) through which a refrigerant flows are arranged inside a shell 11 that forms the outer shape. The carbon dioxide liquefaction device 1 also employs a fixed tube plate type in which tube plates 13 for fixing the heat transfer tubes 12 are provided on both ends of the shell 11.

[0011] An example of the configuration of a carbon dioxide liquefaction system 10 to which the carbon dioxide liquefaction device 1 is applied will be described with reference to FIG.

[0012] The carbon dioxide liquefaction system 10 includes a carbon dioxide liquefaction device 1, a control device 2, a fuel cell 3, an LNG tank 4, a liquefied carbon dioxide tank 5, and an LNG pipeline.

[0013] The control device 2 controls the operation of the carbon dioxide liquefaction device 1. The control device 2 may control any device in the carbon dioxide liquefaction system 10. The control device 2 may be implemented as part of the carbon dioxide liquefaction device 1, or may be incorporated into the device to be controlled. Furthermore, the control device 2 may be realized by multiple devices, and control may be performed by separate devices for each function or role.

[0014] The fuel cell 3 is a device that discharges the carbon dioxide liquefied by the carbon dioxide liquefaction device 1. The carbon dioxide liquefaction device 1 is not limited to the fuel cell 3 and can liquefy carbon dioxide discharged from any device.

[0015] The LNG tank 4 is a supply source that supplies natural gas as a refrigerant to the carbon dioxide liquefaction apparatus 1. For example, the LNG tank 4 supplies natural gas as fuel to the fuel cell 3. The LNG tank 4 may supply natural gas to any device. Here, the natural gas may be in a gaseous state, a liquefied state, or a critical state. Hereinafter, unless otherwise specified, the natural gas may be in any state.

[0016] The liquefied carbon dioxide tank 5 is a tank for storing the liquefied carbon dioxide liquefied by the carbon dioxide liquefaction device 1.

[0017] The LNG pipeline is a route for supplying natural gas from the LNG tank 4 to a destination. The LNG pipeline includes pipes R1 and R2 and valves 21 and 22. Pipe R1 forms a route through which natural gas flows from the LNG tank 4 to a destination, via the carbon dioxide liquefaction device 1. Pipe R2 forms a route through which natural gas flows from the LNG tank 4 to a destination, without passing through the carbon dioxide liquefaction device 1. Valve 21 adjusts the flow rate of natural gas flowing into pipe R1. Valve 22 adjusts the flow rate of natural gas flowing into pipe R2.

[0018] The carbon dioxide liquefaction apparatus 1 includes a shell 11, a plurality of heat transfer tubes 12, two tube plates 13, a plurality of baffles 14, two bonnets 15, an injection section 16, a liquid reservoir section 17, a discharge pump 18, a discharge valve 19, a nitrogen sensor SRN, and a temperature sensor SR1. The carbon dioxide liquefaction apparatus 1 is connected to a pipe R1 through which natural gas used as a refrigerant flows.

[0019] The valve 21 may be provided as part of the configuration of the carbon dioxide liquefaction apparatus 1. Furthermore, devices (valves, etc.) necessary for controlling the carbon dioxide liquefaction apparatus 1 may be part of the configuration of the carbon dioxide liquefaction apparatus 1. The same applies to the following embodiments.

[0020] The shell 11 is a cylindrical outer shell that covers the outside of the carbon dioxide liquefaction apparatus 1. Inside the shell 11, gaseous carbon dioxide is cooled and liquefied. Inside the shell 11, a plurality of heat transfer tubes 12, a tube plate 13, and a plurality of baffles 14 are arranged.

[0021] Natural gas, which serves as a refrigerant, flows through the heat transfer tubes 12, cooling the carbon dioxide on their outer surfaces. This allows heat exchange between the natural gas and the carbon dioxide. Any number of heat transfer tubes 12 may be provided, as long as there is at least one.

[0022] The tube sheet 13 is provided so as to close both ends of the shell 11. A plurality of holes are formed in the tube sheet 13. Ends of the heat transfer tubes 12 are connected and fixed to the respective holes.

[0023] The baffles 14 are partition plates that form a path for carbon dioxide to pass through the inside of the shell 11. The baffles 14 can be arranged in the following two ways. In one arrangement, the baffles 14 are arranged so that they completely separate the upper part of the shell 11 to prevent carbon dioxide from passing through, and leave a gap in the lower part of the shell 11 through which carbon dioxide can pass. In the other arrangement, the baffles 14 are arranged so that they completely separate the lower part of the shell 11 to prevent carbon dioxide from passing through, and leave a gap in the upper part of the shell 11 through which carbon dioxide can pass. These two arrangements are alternately adopted in the direction in which the heat transfer tubes 12 extend, and the baffles 14 are arranged. Due to the path formed by the baffles 14, the carbon dioxide to be cooled flows in a meandering pattern up and down in the same direction as the natural gas flows through the heat transfer tubes 12. Therefore, the carbon dioxide liquefaction system 1 is a parallel flow type in which the carbon dioxide to be cooled and the natural gas serving as a refrigerant flow in the same direction.

[0024] Bonnets 15 are provided at both ends of the shell 11 so as to cover the tube sheets 13. Natural gas enters one of the inlet bonnets 15, passes through the heat transfer tubes 12, and exits the other outlet bonnet. Hereinafter, the side where natural gas flows into the carbon dioxide liquefaction device 1 may be referred to as the "inlet side," and the side where natural gas is discharged from the carbon dioxide liquefaction device 1 may be referred to as the "outlet side."

[0025] The injection section 16 is a section for injecting carbon dioxide to be liquefied into the shell 11. The injection section 16 is provided on the upper part of the shell 11 on the inlet side for natural gas.

[0026] Liquid reservoir 17 is a portion where liquefied carbon dioxide accumulates. An inlet for the flow of liquefied carbon dioxide is provided in liquid reservoir 17 below the outlet side of shell 11. Liquid reservoir 17 is preferably provided below shell 11 so that liquefied carbon dioxide can easily flow in, but may be provided anywhere adjacent to shell 11.

[0027] The discharge pump 18 is a pump for discharging the liquefied carbon dioxide stored in the liquid reservoir 17 to the outside of the carbon dioxide liquefaction apparatus 1. Note that, as long as the liquefied carbon dioxide can be discharged to the outside of the carbon dioxide liquefaction apparatus 1, any device may be provided, not limited to the discharge pump 18, and if the liquefied carbon dioxide has its own pressure, the discharge pump 18 may not be necessary.

[0028] The discharge valve 19 is a valve for discharging nitrogen accumulated inside the shell 11. The discharge valve 19 is controlled based on the amount of nitrogen detected by the nitrogen sensor SRN. When the amount of nitrogen detected by the nitrogen sensor SRN exceeds a predetermined value, the discharge valve 19 is opened. For example, when the control device 2 determines that the nitrogen concentration in the upper interior of the shell 11 has reached a predetermined value (e.g., 5% to 15%) or higher, it outputs a command to open the discharge valve 19. Note that the discharge valve 19 does not necessarily have to be provided. For example, if the carbon dioxide to be liquefied does not contain nitrogen, there is no need to provide the discharge valve 19 and the nitrogen sensor SRN.

[0029] The nitrogen sensor SRN is a sensor for detecting the amount of nitrogen accumulated inside the shell 11. The detected value by the nitrogen sensor SRN is used to control the discharge valve 19. Note that any sensor may be provided, not limited to a sensor that detects nitrogen, as long as it can determine the amount of nitrogen inside the shell 11. For example, a sensor that detects carbon dioxide may be provided instead of the nitrogen sensor SRN, and the amount of nitrogen may be determined by estimating that the only gas other than carbon dioxide is nitrogen.

[0030] Temperature sensor SR1 is a sensor that detects the temperature of the liquefied carbon dioxide stored in liquid reservoir 17. Temperature sensor SR1 is provided inside or outside liquid reservoir 17. The value detected by temperature sensor SR1 is used to control the flow rate of natural gas flowing into carbon dioxide liquefaction device 1. For example, valve 21 provided in pipe R1 that flows natural gas into carbon dioxide liquefaction device 1 is controlled based on the temperature detected by temperature sensor SR1.

[0031] Next, the flow of carbon dioxide inside the carbon dioxide liquefaction device 1 will be described.

[0032] Gaseous carbon dioxide is injected from injection section 16 on the inlet side of carbon dioxide liquefaction apparatus 1. The injected carbon dioxide flows up and down along a path formed by baffles 14, meandering in the direction in which natural gas flows through heat transfer tubes 12. As a result, the carbon dioxide is cooled by the natural gas through heat transfer tubes 12 and gradually liquefied. The carbon dioxide becomes completely liquid by the time it reaches the end of shell 11 where outlet side tube sheet 13 is located. The liquefied carbon dioxide flows from shell 11 to liquid reservoir section 17.

[0033] Next, the control by the control device 2 of the carbon dioxide liquefaction device 1 will be described. The values ​​of temperature and the like described here vary depending on various factors such as the conditions of the carbon dioxide liquefaction device 1 and its surroundings. Specific values ​​are reference values ​​for the purpose of explanation and may not necessarily be accurate. Furthermore, various set values ​​such as temperature set in the carbon dioxide liquefaction device 1 can be corrected so that multiple controls do not adversely affect each other due to interference or the like. This also applies to the following embodiments.

[0034] Here, the carbon dioxide input to the carbon dioxide liquefaction apparatus 1 is assumed to be at 50°C, and the natural gas input to the carbon dioxide liquefaction apparatus 1 is assumed to be at -120°C. For example, the carbon dioxide may be controlled to 50°C using a cooler or the like before being input to the carbon dioxide liquefaction apparatus 1. Furthermore, the natural gas may be controlled to -120°C or higher using a heater or the like before being input to the carbon dioxide liquefaction apparatus 1.

[0035] Based on the value detected by the temperature sensor SR1, the control device 2 controls the amount of natural gas flowing into the carbon dioxide liquefaction device 1 so as to prevent the carbon dioxide in the shell 11 and the liquid reservoir 17 from freezing. For example, the control device 2 controls the temperature of the liquefied carbon dioxide that accumulates in the liquid reservoir 17 so that it falls within a certain temperature range where the carbon dioxide does not freeze.

[0036] For example, the control device 2 controls the temperature of the liquefied carbon dioxide to be -50°C. Specifically, if the temperature detected by the temperature sensor SR1 is higher than -50°C, the control device 2 opens the valve 21 to increase the flow rate of the natural gas. If the temperature detected by the temperature sensor SR1 is lower than -50°C, the control device 2 closes the valve 21 to decrease the flow rate of the natural gas.

[0037] The control device 2 controls the temperature of the liquefied carbon dioxide so that it falls within a temperature range that includes an allowable temperature. Here, carbon dioxide freezes (becomes dry ice) at temperatures below -56.6°C. Therefore, the allowable temperature for the lower limit of the temperature range may be low, and the allowable temperature for the upper limit may be high. For example, the allowable temperature for the lower limit may be -1°C, and the allowable temperature for the upper limit may be +10°C, relative to the reference temperature. Specifically, if the temperature of the liquefied carbon dioxide is to be maintained at -50°C (reference temperature), the temperature range is set to be between -51°C and -40°C. The reference temperature may be set to any degree Celsius, as long as it allows carbon dioxide to remain in a liquid state without freezing.

[0038] In this embodiment, the control of the inflow rate of natural gas is described as being performed by operating the valve 21, but this is not limited to this, and any device may be controlled. For example, a pump or compressor that sends natural gas to the carbon dioxide liquefaction device 1 may be controlled, or a valve 22 provided on a pipe R2 that is separate from the pipe R1 connected to the carbon dioxide liquefaction device 1 may be controlled. Furthermore, when the inflow rate of natural gas is controlled by these devices, the valve 21 may or may not be used for the control.

[0039] According to this embodiment, by adopting a parallel flow type in which the carbon dioxide to be cooled and the natural gas refrigerant flow in the same direction, it is possible to prevent the carbon dioxide from freezing and liquefy it.

[0040] It is generally known that in heat exchangers, counterflow types, in which the object to be cooled and the refrigerant flow in opposing directions, have higher cooling efficiency than parallel flow types, in which the object to be cooled and the refrigerant flow in the same direction. In contrast, this embodiment uses a parallel flow type, which cools carbon dioxide at its lowest temperature with natural gas at a relatively high temperature. This reduces the possibility of carbon dioxide freezing compared to a counterflow type.

[0041] In addition, the temperature sensor SR1 installed in the liquid reservoir 17 monitors the temperature of the liquefied carbon dioxide and controls the flow rate of natural gas flowing into the carbon dioxide liquefaction device 1, thereby preventing carbon dioxide from freezing inside the carbon dioxide liquefaction device 1.

[0042] By providing the discharge valve 19 and the nitrogen sensor SRN, nitrogen that accumulates inside the carbon dioxide liquefaction device 1 can be discharged.

[0043] (Second embodiment) FIG. 3 is a configuration diagram showing the configuration of a carbon dioxide liquefaction device 1A according to a second embodiment of the present invention.

[0044] The carbon dioxide liquefaction apparatus 1A is configured by adding a valve 23, two temperature sensors SR2a and SR2b, and a pipe R3 to the carbon dioxide liquefaction apparatus 1 according to the first embodiment. These added devices may be provided separately from the configuration of the carbon dioxide liquefaction apparatus 1A. Other points are the same as those of the first embodiment.

[0045] A valve 23 for branching the piping is provided on the outlet side of the carbon dioxide liquefaction apparatus 1A. One of the two outlets branched by the valve 23 is connected to a pipe R1 that sends natural gas to a supply destination, and the other outlet is connected to a pipe R3. The outlet side of the pipe R3 is connected to the pipe R1 on the inlet side of the carbon dioxide liquefaction apparatus 1A. Therefore, the pipe R3 is a pipe that allows a portion of the natural gas discharged from the carbon dioxide liquefaction apparatus 1A to flow back into the carbon dioxide liquefaction apparatus 1A. By adjusting the aperture of the valve 23, the flow rate (branch flow rate) of natural gas that is branched from the natural gas discharged from the carbon dioxide liquefaction apparatus 1A and flows into the pipe R3 can be adjusted.

[0046] The temperature sensor SR2a is provided in a pipe near the natural gas outlet of the carbon dioxide liquefaction apparatus 1A, and measures the temperature (outlet temperature) of the natural gas discharged from the carbon dioxide liquefaction apparatus 1A.

[0047] The temperature sensor SR2b is provided in a pipe near the natural gas inlet of the carbon dioxide liquefaction apparatus 1A, and measures the temperature (inlet temperature) of the natural gas flowing into the carbon dioxide liquefaction apparatus 1A.

[0048] Referring to FIG. 4, the control by the control device 2 of the carbon dioxide liquefaction device 1A will be described.

[0049] The control device 2 controls the branch flow rate of the natural gas discharged from the carbon dioxide liquefaction device 1A by operating the valve 23 based on the temperatures detected by the two temperature sensors SR2a and SR2b.

[0050] Here, the temperature of the carbon dioxide input to the carbon dioxide liquefaction device 1A is 50°C. In this case, in order to raise the carbon dioxide inside the carbon dioxide liquefaction device 1A above its melting point (-56.6°C), the outlet temperature of the natural gas needs to be -63.2°C or higher.

[0051] The control device 2 controls the inlet temperature of the natural gas to be in the range of -140°C to -100°C, and the outlet temperature of the natural gas to be in the range of -62°C to -55°C. When the inlet or outlet temperature of the natural gas is to be increased, the control device 2 operates the valve 23 to increase the branched flow rate of the natural gas. When the inlet or outlet temperature of the natural gas is to be decreased, the control device 2 operates the valve 23 to decrease the branched flow rate of the natural gas. Specifically, the control device 2 performs control as follows.

[0052] The control device 2 adjusts the branch flow rate of the natural gas so that the outlet temperature of the natural gas becomes −60° C. (step S101).

[0053] When the outlet temperature of the natural gas becomes -60°C, if the inlet temperature of the natural gas is -140°C or higher, the branched flow rate of the natural gas is maintained as is (No in step S102, step S106). On the other hand, if the inlet temperature of the natural gas is lower than -140°C, the control device 2 adjusts the branched flow rate of the natural gas so that the outlet temperature of the natural gas becomes -62°C or higher and the inlet temperature of the natural gas becomes -140°C or higher (Yes in step S102, step S103).

[0054] The control device 2 adjusts the branch flow rate of the natural gas until the outlet temperature of the natural gas becomes −62° C. or higher and the inlet temperature of the natural gas becomes −140° C. or higher (No in step S105, step S103).

[0055] If the outlet temperature of the natural gas becomes less than -62°C and less than -140°C before the outlet temperature of the natural gas becomes -62°C or higher and the inlet temperature of the natural gas becomes -140°C or higher, the control device 2 stops the operation of the carbon dioxide liquefaction device 1A (Yes in step S104, step S107). This is because there is a high possibility that the carbon dioxide will freeze at this time.

[0056] When the outlet temperature of the natural gas becomes −62° C. or higher and the inlet temperature of the natural gas becomes −140° C. or higher, the control device 2 maintains the branch flow rate of the natural gas as it is (Yes in step S105, step S106).

[0057] According to this embodiment, in addition to the effects of the first embodiment, the following effects can be obtained.

[0058] A portion of the natural gas discharged from the carbon dioxide liquefaction apparatus 1A is configured to flow back into the carbon dioxide liquefaction apparatus 1A, and by controlling the flow rate of the natural gas that is flowed back into the carbon dioxide liquefaction apparatus 1A, the temperature of the natural gas flowing through the heat transfer tubes 12 inside the carbon dioxide liquefaction apparatus 1A can be adjusted. This makes it possible to prevent the carbon dioxide from freezing inside the carbon dioxide liquefaction apparatus 1A.

[0059] (Third embodiment) FIG. 5 is a configuration diagram showing the configuration of a carbon dioxide liquefaction device 1B according to a third embodiment of the present invention.

[0060] The carbon dioxide liquefaction device 1B is the same as the first embodiment except that the two bonnets 15 in the carbon dioxide liquefaction device 1 are replaced with two bonnets 15B and a valve 24 and a temperature sensor SR3 are added. Other points are the same as those in the first embodiment.

[0061] The interior of the bonnet 15B is divided into two chambers, an upper chamber and an lower chamber. Natural gas flows into the two chambers inside the inlet bonnet 15B separately from two pipes branching off from the inlet pipe R1. The natural gas that flows into the upper chamber of the inlet bonnet 15B flows through the heat transfer tubes 12 provided in the upper half of the shell 11, where the injection port 16 is provided, and is discharged into the upper chamber of the outlet bonnet 15B. The natural gas that flows into the lower chamber of the inlet bonnet 15B flows through the heat transfer tubes 12 provided in the lower half of the shell 11, where the carbon dioxide outlet is provided, and is discharged into the lower chamber of the outlet bonnet 15B. The natural gas that flows into the two chambers of the outlet bonnet 15B is discharged from the separate pipes and flows into the pipe R1, which joins the separate pipes.

[0062] Valve 24 is provided on the pipe through which natural gas flows into the chamber below inlet bonnet 15B. When valve 24 closes, the flow of natural gas into the chamber below inlet bonnet 15B is stopped. Valve 24 is a device for urgently stopping the flow of natural gas when there is a possibility that carbon dioxide may freeze.

[0063] The temperature sensor SR3 is a sensor for detecting the temperature of the carbon dioxide immediately before it is discharged into the liquid reservoir 17. The temperature sensor SR3 is provided near the carbon dioxide outlet to the liquid reservoir 17 of the shell 11. For example, the temperature sensor SR3 is provided on a heat transfer tube 12 arranged in the lower half of the shell 11, between the outlet-side tube sheet 13 and the baffle 14 closest to the outlet. Any number of temperature sensors SR3 may be provided. The temperature detected by the temperature sensor SR3 is used to operate the valve 24.

[0064] Next, the operation of the carbon dioxide liquefaction apparatus 1B in an emergency will be described. The control device 2 constantly measures the temperature of the carbon dioxide based on the value detected by the temperature sensor SR3. When the control device 2 determines that the temperature detected by the temperature sensor SR3 is below a predetermined temperature (for example, -55°C), it outputs a command to close the valve 24. When multiple temperature sensors SR3 are provided, the control device 2 may close the valve 24 when the temperature detected by at least one of the temperature sensors SR3 is below the predetermined temperature.

[0065] When valve 24 closes, the inflow of natural gas into the lower chamber of inlet bonnet 15B stops. As a result, natural gas does not flow through heat transfer tubes 12 in the lower half of shell 11, and carbon dioxide is not cooled in the lower half of shell 11. This prevents the carbon dioxide from freezing. Meanwhile, natural gas continues to flow into the upper chamber of inlet bonnet 15B, and therefore the carbon dioxide continues to be cooled in the upper part of shell 11.

[0066] When the control device 2 determines that the temperature detected by the temperature sensor SR3 has reached a predetermined temperature (for example, -50 degrees) or higher, it outputs a command to open the valve 24. Natural gas again flows through the heat transfer tubes 12 in the lower half of the shell 11. This causes the carbon dioxide liquefaction device 1B to return to normal liquefaction operation.

[0067] According to this embodiment, in addition to the effects of the first embodiment, the following effects can be obtained.

[0068] If there is a risk of carbon dioxide freezing, the carbon dioxide liquefaction device 1B can take emergency measures to prevent the carbon dioxide from freezing by preventing natural gas from flowing through some of the heat transfer tubes 12 of the shell 11.

[0069] Here, the carbon dioxide is in the coolest state immediately before flowing into the liquid reservoir 17. The entrance of the carbon dioxide to the liquid reservoir 17 is located below the shell 11. Therefore, by preventing cooling below the shell 11, it is possible to prevent the carbon dioxide from freezing inside the carbon dioxide liquefaction device 1B.

[0070] Note that the heat transfer tubes 12 through which the flow of natural gas stops when the valve 24 is closed are not limited to the heat transfer tubes 12 arranged in the lower half of the shell 11. It is sufficient that the flow of natural gas stops in some of all of the heat transfer tubes 12 when the valve 24 is closed. Furthermore, the closure of the valve 24 may stop the flow of natural gas in some of all of the heat transfer tubes 12 arranged in the lower half of the shell 11, or in the heat transfer tubes 12 arranged in the upper half of the shell 11. Therefore, the bonnet 15B does not need to have an upper chamber and a lower chamber separated exactly in the middle, and the upper chamber and the lower chamber may be different sizes.

[0071] (Fourth embodiment) FIG. 6 is a configuration diagram showing the configuration of a carbon dioxide liquefaction apparatus 1C according to a fourth embodiment of the present invention.

[0072] The carbon dioxide liquefaction apparatus 1C is the same as the carbon dioxide liquefaction apparatus 1A according to the second embodiment as long as the configuration according to the third embodiment is added to the carbon dioxide liquefaction apparatus 1A according to the second embodiment.

[0073] Next, the operation of the carbon dioxide liquefaction apparatus 1C will be described.

[0074] As in the first embodiment, the control device 2 controls the inflow rate of natural gas flowing into the carbon dioxide liquefaction device 1C based on the temperature detected by the temperature sensor SR1 provided in the liquid reservoir 17. In this way, the control device 2 controls the temperature of the liquefied carbon dioxide stored in the liquid reservoir 17, preventing the carbon dioxide from freezing.

[0075] As in the second embodiment, the control device 2 is configured to allow a portion of the natural gas discharged from the carbon dioxide liquefaction device 1C to flow back into the carbon dioxide liquefaction device 1C, and adjusts the internal temperature of the carbon dioxide liquefaction device 1C by controlling the flow rate of the natural gas to be re-introduced based on temperature sensors SR2a and SR2b installed near the natural gas inlet and outlet of the carbon dioxide liquefaction device 1C, respectively.

[0076] As in the third embodiment, the control device 2 urgently prevents the carbon dioxide from freezing inside the carbon dioxide liquefaction device 1C based on the temperature detected by the temperature sensor SR3 provided near the carbon dioxide outlet to the liquid reservoir 17 of the shell 11. Specifically, when the control device 2 determines that the temperature detected by the temperature sensor SR3 has fallen below a predetermined temperature, it closes the valve 24 to stop the natural gas from flowing through the heat transfer tubes 12 in the lower half of the shell 11.

[0077] According to this embodiment, in addition to the effects of the second embodiment, like the third embodiment, it is possible to take emergency measures to prevent carbon dioxide from freezing.

[0078] (Fifth embodiment) FIG. 7 is a diagram showing the configuration of a carbon dioxide liquefaction device 1D according to a fifth embodiment of the present invention.

[0079] The carbon dioxide liquefaction apparatus 1D is the carbon dioxide liquefaction apparatus 1 according to the first embodiment, to which a heater 20 and a temperature sensor SR3 according to the third embodiment have been added. Other points are the same as those of the first embodiment.

[0080] As in the third embodiment, the temperature sensor SR3 is provided near the outlet of carbon dioxide to the liquid reservoir 17 of the shell 11. However, in this embodiment, the temperature sensor SR3 may be disposed in the upper half of the shell 11.

[0081] The heater 20 is a device for urgently heating the carbon dioxide to prevent the carbon dioxide from freezing. The heater 20 is provided near the carbon dioxide outlet to the liquid reservoir 17 of the shell 11. For example, the heater 20 is an electric heating wire. The electric heating wire is wound around the heat transfer tube 12 in a coil shape.

[0082] The heater 20 is not limited to an electric heating wire and may be any device that can heat carbon dioxide so that it can liquefy or vaporize it from a frozen state. For example, the heater heats in the range of 0°C to 50°C. The heater 20 is preferably installed at a position slightly away from the temperature sensor SR3 so as not to directly heat the temperature sensor SR3.

[0083] Next, the operation of the carbon dioxide liquefaction apparatus 1D will be described. In addition to the operation of the carbon dioxide liquefaction apparatus 1 according to the first embodiment, the carbon dioxide liquefaction apparatus 1D performs the following emergency operation.

[0084] The control device 2 prevents the carbon dioxide from freezing inside the carbon dioxide liquefaction device 1D in an emergency based on the temperature detected by the temperature sensor SR3 provided near the carbon dioxide outlet to the liquid reservoir 17 of the shell 11.

[0085] Specifically, when the control device 2 determines that the temperature detected by the temperature sensor SR3 has fallen below a predetermined temperature (for example, -55°C), it outputs a command to heat the heater 20. If multiple temperature sensors SR3 are provided, the control device 2 may cause the heater 20 to heat when the temperature detected by at least one of the temperature sensors SR3 falls below the predetermined temperature. Heating the carbon dioxide with the heater 20 prevents the carbon dioxide from freezing.

[0086] Furthermore, even if the carbon dioxide is in a frozen state, it can be liquefied or vaporized. Therefore, the temperature of the carbon dioxide (the temperature detected by the temperature sensor SR3) that is the condition for starting heating by the heater 20 may be a temperature at which the carbon dioxide may be frozen (for example, −57° C.).

[0087] According to this embodiment, in addition to the effects of the first embodiment, the following effects can be obtained.

[0088] When there is a risk of the carbon dioxide freezing, the carbon dioxide liquefaction device 1D can take emergency measures to prevent the carbon dioxide from freezing by heating the heater 20 provided inside the shell 11.

[0089] Furthermore, even if the carbon dioxide is in a frozen state (dry ice), it can be thawed. Therefore, even if the carbon dioxide freezes inside the carbon dioxide liquefaction device 1D, the operation of the carbon dioxide liquefaction device 1D can be continued without interruption by heating the carbon dioxide with the heater 20.

[0090] (Sixth embodiment) FIG. 8 is a configuration diagram showing the configuration of a carbon dioxide liquefaction apparatus 1E according to a sixth embodiment of the present invention.

[0091] The carbon dioxide liquefaction apparatus 1E is obtained by adding the heater 20 according to the fifth embodiment to the carbon dioxide liquefaction apparatus 1C according to the fourth embodiment. In other respects, it is the same as the fourth embodiment.

[0092] Here, a configuration will be described in which the same temperature sensor SR3 is used to control the heater 20 and the valve 24, but the heater 20 and the valve 24 may each use a separate temperature sensor SR3.

[0093] Next, the operation of the carbon dioxide liquefaction apparatus 1E will be described. In addition to the operation of the carbon dioxide liquefaction apparatus 1C according to the fourth embodiment, the following emergency operation is performed.

[0094] The control device 2 emergency prevents the carbon dioxide from freezing inside the carbon dioxide liquefaction device 1E based on the temperature detected by the temperature sensor SR3 provided near the carbon dioxide outlet to the liquid reservoir 17 of the shell 11.

[0095] As in the third embodiment, when the control device 2 determines that the temperature detected by the temperature sensor SR3 has fallen below a predetermined temperature (for example, −55° C.), it outputs a command to close the valve 24. This stops the flow of natural gas through the heat transfer tubes 12 in the lower half of the shell 11, and stops the cooling of the carbon dioxide in the lower half of the shell 11.

[0096] If the temperature detected by the temperature sensor SR3 does not rise sufficiently or drops further even after the valve 24 is closed, the control device 2 starts heating with the heater 20, as in the fifth embodiment. This prevents or thaws (defrosts) the carbon dioxide from freezing.

[0097] The closing of the valve 24 and the heating of the heater 20 may be performed simultaneously, or the valve 24 may be closed after the heating of the heater 20 has started.

[0098] According to this embodiment, in addition to the effects and advantages of the fourth embodiment, the effects and advantages of the fifth embodiment can be obtained. For example, in addition to the normal operation of liquefying carbon dioxide, the carbon dioxide liquefaction apparatus 1E can take two types of emergency measures in response to freezing of carbon dioxide: closing the valve 24 and heating with the heater 20. The carbon dioxide liquefaction apparatus 1E may close the valve 24 to prevent the carbon dioxide from freezing, and may heat with the heater 20 if the carbon dioxide freezes.

[0099] In this embodiment, a configuration has been described in which the heater 20 according to the fifth embodiment is added to the carbon dioxide liquefaction apparatus 1C according to the fourth embodiment, but the heater 20 according to the fifth embodiment may also be added to the carbon dioxide liquefaction apparatus 1A, 1B according to the second or third embodiment.

[0100] It is to be understood that additional advantages and modifications may readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. [Explanation of symbols]

[0101] 1...carbon dioxide liquefaction device, 2...control device, 3...fuel cell, 4...LNG tank, 5...liquefied carbon dioxide tank, 10...carbon dioxide liquefaction system, 11...shell, 12...heat transfer tube, 13...tube sheet, 14...baffle, 15...bonnet, 16...injection section, 17...liquid reservoir section, 18...discharge pump, 19...discharge valve, 21, 22...valve, R1, R2...piping, SR1...temperature sensor, SRN...nitrogen sensor

Claims

1. A shell inside which the carbon dioxide to be liquefied flows, At least one heat transfer tube disposed inside the shell and through which natural gas flows as a refrigerant for cooling the carbon dioxide; a baffle arranged inside the shell so that the carbon dioxide flows up and down in a meandering manner in the same direction as the natural gas; a liquid reservoir provided adjacent to the shell and configured to store liquefied carbon dioxide; a first temperature sensor provided in the liquid reservoir; an inflow flow rate control unit that adjusts the flow rate of the natural gas flowing into the heat transfer tube based on the first temperature detected by the first temperature sensor so that the carbon dioxide does not freeze; A carbon dioxide liquefaction device comprising:

2. an inlet temperature sensor for measuring an inlet temperature of the natural gas before it enters the heat transfer tube; an outlet temperature sensor for measuring an outlet temperature of the natural gas discharged from the heat transfer tube; a branch pipe branching off from a pipe through which the discharged natural gas flows, for allowing a portion of the natural gas discharged from the heat transfer tubes to flow again into the heat transfer tubes; a branch flow rate control unit that controls the flow rate of the natural gas flowing into the branch pipe so as to adjust the temperature of the natural gas flowing through the heat transfer tube based on the inlet temperature measured by the inlet temperature sensor and the outlet temperature measured by the outlet temperature sensor; 2. The carbon dioxide liquefaction device according to claim 1, further comprising:

3. a valve for stopping the inflow of the natural gas into some of the heat transfer tubes; a second temperature sensor provided inside the shell; a valve control unit that controls operation of the valve based on the second temperature detected by the second temperature sensor; 2. The carbon dioxide liquefaction device according to claim 1, further comprising:

4. The liquid reservoir is provided in a lower portion of the shell, The part of the heat transfer tubes is a heat transfer tube arranged in the lower half of the shell.

4. The carbon dioxide liquefaction device according to claim 3,

5. a third temperature sensor provided inside the shell; a heater provided inside the shell for heating the carbon dioxide; a heater control unit that controls heating of the heater based on a third temperature detected by the third temperature sensor; 2. The carbon dioxide liquefaction device according to claim 1, further comprising:

6. The heater is an electric heating wire wound around the heat transfer tube. The carbon dioxide liquefaction device according to claim 5,

7. a nitrogen content sensor for determining the amount of nitrogen accumulated inside the shell; a nitrogen discharge valve for discharging nitrogen accumulated inside the shell to the outside; a nitrogen discharge control unit that opens the nitrogen discharge valve based on the amount of nitrogen determined by the nitrogen amount sensor, and controls the nitrogen to be discharged to the outside of the shell; 2. The carbon dioxide liquefaction device according to claim 1, further comprising:

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