Tank system, floating body, and method for transferring liquefied carbon dioxide

Abstract

To quickly transfer liquefied carbon dioxide in a tank to the outside while suppressing the generation of dry ice.SOLUTION: A tank system comprises a first tank, a second tank, a first discharge line, a connection line, a first transfer line, a first return line, and a switching unit. The first tank and the second tank are capable of storing liquefied carbon dioxide. The first discharge line is capable of discharging the liquefied carbon dioxide in the first tank to the outside of the first tank. The connection line connects the inside of the first tank and the inside of the second tank. The first transfer line is capable of transferring carbon dioxide gas in the first tank into the second tank. The first return line is capable of extracting carbon dioxide gas in the second tank, heating the carbon dioxide gas, and then returning the carbon dioxide gas to the second tank itself. The switching unit is capable of switching between transferring the carbon dioxide gas through the first transfer line and returning the carbon dioxide gas through the first return line.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a tank system, a floating body, and a method for transporting liquefied carbon dioxide. [Background technology]

[0002] For example, Patent Document 1 discloses a configuration in which a transfer device (natural gas transfer device) is provided for transferring liquefied gas (LNG: Liquefied Natural Gas) from a ship (import ship) equipped with a tank for storing the liquefied gas to an onshore facility (import terminal). In this configuration, the ship transfers the liquefied gas in the tank to the tank of the onshore facility. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2010-503132 Summary of the Invention [Problem to be solved by the invention]

[0004] When a ship is equipped with multiple tanks, each of the tanks is provided with a discharge pipe for discharging the liquefied gas from the tank to the outside and a pump for discharging the liquefied gas from the tank through the discharge pipe in order to transfer the liquefied gas from the tank to land-based facilities. In such a configuration, an alternative solution is required so that, even if the pump breaks down for some reason and becomes unusable, the liquefied gas in the tank whose pump cannot be used can be transferred to an onshore facility. One such alternative solution is a method of creating a pressure difference between the tanks, transferring the liquefied gas in the tank whose pump cannot be used to another tank whose pump can be used, and then transferring it to the onshore facility via the other tank.

[0005] However, when liquefied carbon dioxide is stored in a tank and an attempt is made to transfer the liquefied carbon dioxide to another tank by creating a pressure difference between the tanks, the pressure in the other tank gradually decreases and approaches the triple point due to the density difference between the liquefied carbon dioxide and carbon dioxide gas. When the pressure in the other tank falls below the triple point, dry ice may be generated. Therefore, when transferring liquefied carbon dioxide between multiple tanks as described above, it is necessary to occasionally stop the transfer of liquefied carbon dioxide between the tanks to restore the pressure in the other tank, which poses the problem of taking a long time to transfer the liquefied carbon dioxide out of the tank.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a tank system, a float, and a method for transporting liquefied carbon dioxide that can quickly transport liquefied carbon dioxide in a tank to the outside while suppressing the generation of dry ice. [Means for solving the problem]

[0007] In order to solve the above problems, the tank system according to the present disclosure comprises a first tank, a second tank, a first discharge line, a connection line, a first transfer line, a first return line, and a switching unit. The first tank and the second tank are capable of storing liquefied carbon dioxide. The first discharge line is capable of discharging the liquefied carbon dioxide in the first tank to the outside of the first tank. The connection line connects the inside of the first tank to the inside of the second tank. The first transfer line is capable of transferring carbon dioxide gas in the first tank into the second tank. The first return line is capable of extracting carbon dioxide gas from the second tank, heating it, and returning it to the second tank itself. The switching unit is capable of switching between transferring the carbon dioxide gas via the first transfer line and returning the carbon dioxide gas via the first return line.

[0008] A float according to the present disclosure comprises a float body and the above-described tank system provided on the float body.

[0009] A method for transferring liquefied carbon dioxide according to the present disclosure is a method for transferring liquefied carbon dioxide in a tank system as described above. The method for transferring liquefied carbon dioxide includes a step of transferring the liquefied carbon dioxide and a step of switching from transferring the carbon dioxide gas via the first transfer line to returning the carbon dioxide gas via the first return line. In the step of transferring liquefied carbon dioxide, the carbon dioxide gas in the first tank is transferred into the second tank through the first transfer line to increase the pressure in the second tank. In the step of transferring liquefied carbon dioxide, the liquefied carbon dioxide in the second tank is transferred into the first tank through the connection line due to a pressure difference between the pressure in the second tank and the pressure in the first tank. In the step of switching from transferring the carbon dioxide gas via the first transfer line to returning the carbon dioxide gas via the first return line, when the pressure in the first tank falls below a predetermined first threshold while the carbon dioxide gas in the first tank is being transferred to the second tank, the transfer of the carbon dioxide gas via the first transfer line is switched to returning the carbon dioxide gas via the first return line. [Effects of the Invention]

[0010] According to the tank system, float, and liquefied carbon dioxide transport method disclosed herein, liquefied carbon dioxide in the tank can be quickly transported to the outside while suppressing the generation of dry ice. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a plan view of a floating body equipped with a tank system according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram showing a tank system according to the first embodiment of the present disclosure, and is a cross-sectional view taken along line II-II in FIG. 1. [Figure 3] FIG. 2 is a diagram showing a state in which carbon dioxide gas is circulated through a first transfer line in the tank system according to the first embodiment of the present disclosure. [Figure 4]A diagram showing the state in which carbon dioxide gas is circulating through the first return line in the tank system according to the first embodiment of the present disclosure. [Figure 5] FIG. 10 is a diagram showing a state in which carbon dioxide gas is circulated through a second transfer line in the tank system according to the first embodiment of the present disclosure. [Figure 6] A diagram showing a state in which carbon dioxide gas is circulating through a second return line in a tank system according to the first embodiment of the present disclosure. [Figure 7] FIG. 1 is a flowchart showing the flow of a method for transferring liquefied carbon dioxide according to a first embodiment of the present disclosure. [Figure 8] FIG. 10 is a diagram showing a tank system according to a second embodiment of the present disclosure. [Figure 9] FIG. 10 is a diagram illustrating a hardware configuration of a control device according to a second embodiment of the present disclosure. [Figure 10] FIG. 10 is a functional block diagram of a control device according to a second embodiment of the present disclosure. [Figure 11] FIG. 10 is a diagram showing a state in which carbon dioxide gas is circulated through a first transfer line in a tank system according to a second embodiment of the present disclosure. [Figure 12] A diagram showing the state in which carbon dioxide gas is circulating through the first return line in the tank system according to the second embodiment of the present disclosure. [Figure 13] FIG. 10 is a diagram showing a state in which carbon dioxide gas is circulated through a second transfer line in a tank system according to a second embodiment of the present disclosure. [Figure 14] A diagram showing a state in which carbon dioxide gas is circulating through a second return line in a tank system according to a second embodiment of the present disclosure. [Figure 15] FIG. 10 is a diagram illustrating a tank system according to a modified example of an embodiment of the present disclosure. [Figure 16] FIG. 10 is a diagram illustrating a tank system according to a modified example of an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] First Embodiment Hereinafter, a tank system, a float, and a method for transferring liquefied carbon dioxide according to an embodiment of the present disclosure will be described with reference to FIGS. (Vessel configuration) 1, in this embodiment, a ship 1, which is a floating body, transports liquefied carbon dioxide. The ship 1 includes at least a hull 2 ​​as a floating body main body, and a tank system 10A.

[0013] (Hull configuration) The hull 2 ​​has a pair of side walls 3A, 3B, a bottom (not shown), and an upper deck 5 that form its outer hull. The side walls 3A, 3B have a pair of side shell plates that form the port and starboard sides, respectively. The bottom has a bottom shell plate that connects the side walls 3A, 3B. The upper deck 5 illustrated in this embodiment is a full-length deck that is exposed to the outside. A superstructure 7 having accommodation areas is formed on the hull 2. Note that the location of the superstructure 7 is merely an example, and it may be located, for example, on the bow 2a side of the hull 2. A cargo carrying compartment (hold) 8 is formed within the hull 2.

[0014] (Tank system configuration) FIG. 2 is a diagram showing the configuration of the tank system according to the first embodiment of the present disclosure, and is a cross-sectional view taken along line II-II in FIG. 2, the tank system 10A includes a first tank 11A, a second tank 11B, a first pressure detection unit 111A, a second pressure detection unit 111B, a first discharge line 13A, a second discharge line 13B, and a transfer piping unit 20A. In this first embodiment, the tank system 10A of the first embodiment will be described taking as an example a case where one tank system 10A is provided. Note that two or more tank systems 10A may be provided for one hull.

[0015] (First tank, second tank) Each of the first tank 11A and the second tank 11B is capable of storing liquefied carbon dioxide L. As shown in FIG. 1 , the first tank 11A and the second tank 11B are provided in the cargo carrying section 8. The first tank 11A and the second tank 11B may be provided above the upper deck 5. In this first embodiment, the first tank 11A and the second tank 11B are arranged, for example, at an interval in the fore-aft direction Da. The first tank 11A and the second tank 11B may be arranged side by side in the transverse direction Dw, for example. Although the first tank 11A and the second tank 11B each have a cylindrical shape extending in the horizontal direction, for example, the shape of each of the first tank 11A and the second tank 11B is not limited to a cylindrical shape and may be, for example, a spherical shape, a rectangular shape, or the like.

[0016] (First pressure detection unit, second pressure detection unit) 2, the first pressure detection unit 111A is attached to the first tank 11A and detects the pressure inside the first tank 11A. The second pressure detection unit 111B is attached to the second tank 11B and detects the pressure inside the second tank 11B.

[0017] (First discharge line) The first discharge line 13A discharges the liquefied carbon dioxide L in the first tank 11A to the outside of the first tank 11A. The first discharge line 13A sends the liquefied carbon dioxide L in the first tank 11A to, for example, a land facility, an offshore floating facility, another ship, etc. The first discharge line 13A includes an unloading pipe 131A and a pump 132A.

[0018] The discharge pipe 131A extends from the outside of the first tank 11A through the top of the first tank 11A and into the inside of the first tank 11A. One end of the discharge pipe 131A is arranged at a lower part inside the first tank 11A. The pump 132A is connected to one end of the discharge pipe 131A. The pump 132A sucks in liquefied carbon dioxide L inside the first tank 11A. The discharge pipe 131A sends out the liquefied carbon dioxide L sucked in by the pump 132A to the outside of the first tank 11A. The other end (not shown) of the discharge pipe 131A is arranged outside the first tank 11A. The other end of the discharge pipe 131A is connected to, for example, a bunkering station (not shown) or the like, and is arranged toward one of the shipboard sides 3A and 3B (for example, the shipboard side 3A), and is detachably connected to a connecting pipe (not shown) for connecting to a land facility, an offshore floating facility, another ship, etc.

[0019] (Second discharge line) The second discharge line 13B discharges the liquefied carbon dioxide L in the second tank 11B to the outside of the second tank 11B. The second discharge line 13B sends the liquefied carbon dioxide L in the second tank 11B to, for example, a land facility, an offshore floating facility, another ship, etc. The second discharge line 13B includes an unloading pipe 131B and a pump 132B.

[0020] The discharge pipe 131B passes through the top of the second tank 11B from the outside of the second tank 11B and extends into the interior of the second tank 11B. One end of the discharge pipe 131B is disposed at the bottom of the second tank 11B. The pump 132B is connected to one end of the discharge pipe 131B. The pump 132B sucks in the liquefied carbon dioxide L in the second tank 11B. The discharge pipe 131B sends the liquefied carbon dioxide L sucked in by the pump 132B to the outside of the second tank 11B. The other end (not shown) of the discharge pipe 131B is disposed outside the second tank 11B. The other end of the lifting pipe 131B is connected to, for example, a bunkering station (not shown) and is positioned toward one of the sides 3A and 3B (for example, side 3A), and like the lifting pipe 131A, a connecting pipe (not shown) for connecting to land-based facilities, offshore floating facilities, other ships, etc. is detachably connected to it.

[0021] (Transport piping section) The transfer piping section 20A is configured to be able to transfer the liquefied carbon dioxide L in the second tank 11B into the first tank 11A when the pump 132B of the second discharge line 13B cannot be used due to, for example, a malfunction, etc. Furthermore, the transfer piping section 20A is configured to be able to transfer the liquefied carbon dioxide L in the first tank 11A into the second tank 11B when the pump 132A of the first discharge line 13A cannot be used due to, for example, a malfunction, etc.

[0022] The transfer piping section 20A has a liquid transfer pipe 21, a gas transfer pipe 22, a first connecting pipe (return pipe) 23, a second connecting pipe (first gas discharge pipe) 24, a compressor 31, a heater 32, and a switching section 120.

[0023] The liquid transfer pipe 21 communicates the liquid phase in the first tank 11A with the liquid phase in the second tank 11B. One end 21a of the liquid transfer pipe 21 opens to the lower part of the first tank 11A. The other end 21b of the liquid transfer pipe 21 opens to the lower part of the second tank 11B. An on-off valve 121 is provided midway along the liquid transfer pipe 21. The on-off valve 121 is capable of opening and closing the flow path in the liquid transfer pipe 21. In addition, the liquid transfer pipe 21 is provided with a pressure sensor 112 that detects the pressure inside the liquid transfer pipe 21. Here, the lower part of the first tank 11A and the lower part of the second tank 11B can refer to, for example, vertical positions equivalent to the vertical positions at which pumps 132A and 132B are installed inside the first tank 11A and the second tank 11B.

[0024] The gas transfer pipe 22 communicates the gas phase in the first tank 11A with the gas phase in the second tank 11B. One end 22a of the gas transfer pipe 22 opens to the upper part of the first tank 11A. The other end 22b of the gas transfer pipe 22 opens to the upper part of the second tank 11B. A first pressure-feeding section 30 is provided midway along the gas transfer pipe 22. The first pressure-feeding section 30 in the first embodiment includes a compressor 31 and a heater 32. The compressor 31 compresses carbon dioxide gas flowing through the gas transfer pipe 22 and sends the carbon dioxide from one of the first tank 11A and the second tank 11B to the other. The heater 32 heats the carbon dioxide gas flowing through the gas transfer pipe 22. In the first embodiment, the first pressure-feeding section 30 is arranged in this order from one end 22a to the other end 22b of the gas transfer pipe 22. The compressor 31 and the heater 32 may be arranged in the reverse order to that described above.

[0025] The gas transfer pipe 22 is provided with pressure sensors 113 and 114 for detecting the inlet pressure and outlet pressure of the compressor 31 .

[0026] One end 23a of the first connecting pipe 23 is connected to the top of the first tank 11A, and the other end 23b of the first connecting pipe 23 is connected to the gas transfer pipe 22 between the heater 32 and the second opening / closing valve 122B described later.

[0027] One end 24a of the second connecting pipe 24 is connected to the upper part of the second tank 11B. The other end 24b of the second connecting pipe 24 is connected to the gas transfer pipe 22 between the first on-off valve 122A and the compressor 31, which will be described later.

[0028] (Switching section) The switching unit 120 switches the flow mode (flow path) of the carbon dioxide gas in the transfer piping unit 20A. The switching unit 120 can switch between transferring the carbon dioxide gas G via the first transfer line 16A and returning the carbon dioxide gas G via the first return line 17A. The switching unit 120 can also switch between transferring the carbon dioxide gas G via the second transfer line 18A and returning the carbon dioxide gas G via the second return line 19A. The switching unit 120 illustrated in the first embodiment includes a first on-off valve 122A, a second on-off valve 122B, a third on-off valve 123, and a fourth on-off valve .

[0029] The first on-off valve 122A is provided between one end 22a of the gas transfer pipe 22 and the compressor 31. The second on-off valve 122B is provided between the heater 32 and the other end 22b of the gas transfer pipe 22. Each of the first on-off valve 122A and the second on-off valve 122B can open and close the flow path in the gas transfer pipe 22.

[0030] The third on-off valve 123 is provided midway through the first connecting pipe 23. The third on-off valve 123 is capable of opening and closing the flow path within the first connecting pipe 23. The fourth on-off valve 124 is provided midway through the second connecting pipe 24. The fourth on-off valve 124 is capable of opening and closing the flow path within the second connecting pipe 24.

[0031] Such transfer piping section 20A can switch the flow mode of carbon dioxide gas by switching the open / close states of first on-off valve 122A, second on-off valve 122B, third on-off valve 123, and fourth on-off valve 124. Transfer piping section 20A includes connection line 15, first transfer line 16A, first return line 17A, second transfer line 18A, and second return line 19A.

[0032] The connection line 15 connects the liquid phase inside the first tank 11A and the liquid phase inside the second tank 11B. The connection line 15 is equipped with a liquid transfer pipe 21. To circulate the liquefied carbon dioxide L through the connection line 15, the on-off valve 121 is opened. The connection line 15 can transfer the liquefied carbon dioxide L between the first tank 11A and the second tank 11B by utilizing the pressure difference between the pressure inside the first tank 11A and the pressure inside the second tank 11B. For example, when the pressure inside the first tank 11A is higher than the pressure inside the second tank 11B, the liquefied carbon dioxide L inside the first tank 11A is transferred into the second tank 11B through the connection line 15. On the other hand, when the pressure inside the second tank 11B is higher than the pressure inside the first tank 11A, the liquefied carbon dioxide L inside the second tank 11B is transferred to the first tank 11A through the connection line 15.

[0033] FIG. 3 is a diagram showing a state in which carbon dioxide gas is circulated through the first transfer line in the tank system according to the first embodiment of the present disclosure. 3, the first transfer line 16A is capable of transferring the carbon dioxide gas G in the first tank 11A into the second tank 11B. The first transfer line 16A includes a gas transfer pipe 22 and a first pressure-feeding unit 30.

[0034] To circulate carbon dioxide gas through the first transfer line 16A, the third on-off valve 123 and the fourth on-off valve 124 are closed, the first on-off valve 122A and the second on-off valve 122B are opened, and the compressor 31 is operated. The first transfer line 16A uses the compressor 31 to suck out carbon dioxide gas G from the first tank 11A and pumps it into the second tank 11B. The first transfer line 16A pressurizes (compresses) the carbon dioxide gas G with the compressor 31 and heats the carbon dioxide gas G with the heater 32, thereby expanding the carbon dioxide gas G in the first tank 11A and transferring it into the second tank 11B. Transferring the expanded carbon dioxide gas G into the second tank 11B in this manner increases the pressure in the second tank 11B.

[0035] FIG. 4 is a diagram showing a state in which carbon dioxide gas is circulated through the first return line in the tank system according to the first embodiment of the present disclosure. 4, the first return line 17A is capable of extracting and heating the carbon dioxide gas G from the second tank 11B and returning it to the second tank 11B itself. The first return line 17A includes a second connecting pipe 24, a portion of the gas transfer pipe 22, and a first pressure-feeding section 30. The first transfer line 16A, which is closer to the second tank 11B than the position where the second connecting pipe 24 is connected, also serves as the first return line 17A.

[0036] To circulate carbon dioxide gas through the first return line 17A, the first on-off valve 122A and the third on-off valve 123 are closed, the second on-off valve 122B and the fourth on-off valve 124 are opened, and the compressor 31 is operated. The first return line 17A uses the compressor 31 to suck out carbon dioxide gas G from the second tank 11B and supplies it to the first transfer line 16A, which is closer to the first tank 11A than the first pressure-feeding section 30. The carbon dioxide gas G supplied to the first transfer line 16A is pressurized by the compressor 31 and heated by the heater 32, and then returned to the second tank 11B. In this way, the carbon dioxide gas G sucked out from the second tank 11B is expanded and returned to the second tank 11B, thereby increasing the pressure in the second tank 11B.

[0037] FIG. 5 is a diagram showing a state in which carbon dioxide gas is circulated through the second transfer line in the tank system according to the first embodiment of the present disclosure. 5, second transfer line 18A is capable of transferring carbon dioxide gas G from second tank 11B into first tank 11A. Second transfer line 18A is composed of second connecting pipe 24 of first return line 17A, first connecting pipe 23 of second return line 19A, and first transfer line 16A including first compressing section 30 between a position of first transfer line 16A to which second connecting pipe 24 is connected and a position of first connecting pipe 23 to which first connecting pipe 23 is connected. Second transfer line 18A includes second connecting pipe 24, a portion of gas transfer pipe 22, and first compressing section 30.

[0038] To circulate carbon dioxide gas through the second transfer line 18A, the first on-off valve 122A and the second on-off valve 122B are closed, the third on-off valve 123 and the fourth on-off valve 124 are opened, and the compressor 31 is operated. The second transfer line 18A uses the compressor 31 to suck out carbon dioxide gas G from the second tank 11B and pumps it into the first tank 11A. The second transfer line 18A pressurizes (compresses) the carbon dioxide gas G with the compressor 31 and heats the carbon dioxide gas G with the heater 32, thereby expanding the carbon dioxide gas G in the second tank 11B and transferring it into the first tank 11A. Transferring the expanded carbon dioxide gas G into the first tank 11A in this manner increases the pressure inside the first tank 11A.

[0039] FIG. 6 is a diagram showing a state in which carbon dioxide gas is circulated through the second return line in the tank system according to the first embodiment of the present disclosure. 6, the second return line 19A is capable of extracting and heating the carbon dioxide gas G from the first tank 11A and returning it to the first tank 11A itself. The second return line 19A includes a gas transfer pipe 22 on the side closer to the first tank 11A than the position where the first connecting pipe 23 is connected, and a first connecting pipe 23. The first transfer line 16A on the side closer to the first tank 11A than the position where the first connecting pipe 23 is connected also serves as the second return line 19A.

[0040] To circulate carbon dioxide gas through the second return line 19A, the second on-off valve 122B and the fourth on-off valve 124 are closed, the first on-off valve 122A and the third on-off valve 123 are opened, and the compressor 31 is operated. The second return line 19A uses the compressor 31 to suck out carbon dioxide gas G from the first tank 11A and supplies it to the gas transfer pipe 22 that is closer to the first tank 11A than the position where the first connecting pipe 23 is connected. The carbon dioxide gas G supplied to the gas transfer pipe 22 is pressurized by the compressor 31 and heated by the heater 32, and then returned to the first tank 11A through the first connecting pipe 23. By expanding the carbon dioxide gas G and returning it to the first tank 11A in this way, the pressure inside the first tank 11A increases.

[0041] (Procedure for transporting liquefied carbon dioxide) In the tank system 10A, the liquefied carbon dioxide L in the first tank 11A and the second tank 11B is discharged to the outside through the first discharge line 13A and the second discharge line 13B. In the first tank 11A, the pump 132A of the first discharge line 13A discharges the liquefied carbon dioxide L in the first tank 11A to the outside of the first tank 11A through the discharge pipe 131A. In the second tank 11B, the pump 132B of the second discharge line 13B discharges the liquefied carbon dioxide L in the second tank 11B to the outside of the second tank 11B through the discharge pipe 131B. Note that the discharge of the liquefied carbon dioxide L from the first tank 11A and the discharge of the liquefied carbon dioxide L from the second tank 11B may be performed in parallel or sequentially.

[0042] If a malfunction occurs in either the pump 132A of the first tank 11A or the pump 132B of the second tank 11B while the liquefied carbon dioxide L in the first tank 11A or the second tank 11B is being discharged to the outside, the liquefied carbon dioxide is transferred between the first tank 11A and the second tank 11B using the procedure shown below.

[0043] FIG. 7 is a flowchart showing the flow of the method for transferring liquefied carbon dioxide according to the first embodiment of the present disclosure. As shown in Figure 7, the method S10 for transferring liquefied carbon dioxide L in the tank system 10A described above includes a step S11 of transferring liquefied carbon dioxide L, a step S12 of determining whether the pressure in the tank has dropped below a first threshold, a step S13 of switching from transferring carbon dioxide gas G to returning carbon dioxide gas G, a step S14 of determining whether the pressure in the tank has risen above a second threshold, a step S15 of switching from returning carbon dioxide gas G to transferring carbon dioxide gas G, and a step S16 of determining whether the transfer of liquefied carbon dioxide L has been completed. The method S10 for transferring liquefied carbon dioxide L in this embodiment is carried out by, for example, an operator.

[0044] In the following, for example, a case will be described in which a failure occurs in the pump 132B of the second tank 11B when the liquefied carbon dioxide L in the first tank 11A and the second tank 11B is being discharged to the outside. (If the pump in the second tank breaks down) In step S11 of transferring liquefied carbon dioxide L (hereinafter simply referred to as step S11), if a failure occurs in pump 132B of second tank 11B, liquefied carbon dioxide L in second tank 11B is transferred into first tank 11A. To achieve this, as shown in Fig. 3, carbon dioxide gas G in first tank 11A is transferred into second tank 11B through first transfer line 16A to pressurize the inside of second tank 11B. For this purpose, in step S11, on-off valve 121 is opened, third on-off valve 123 and fourth on-off valve 124 are closed, and first on-off valve 122A and second on-off valve 122B are opened, and compressor 31 is operated.

[0045] As a result, the first transfer line 16A sucks out the carbon dioxide gas G from the first tank 11A and pressure-feeds it toward the second tank 11B. At this time, the first transfer line 16A pressurizes (compresses) the carbon dioxide gas G with the compressor 31 and heats the carbon dioxide gas G with the heater 32, thereby expanding the carbon dioxide gas G in the first tank 11A. This increases the pressure in the second tank 11B, and increases the pressure difference between the first tank 11A and the second tank 11B. Due to the pressure difference between the first tank 11A and the second tank 11B, the liquefied carbon dioxide L in the second tank 11B is pushed out through the liquid transfer pipe 21 of the connection line 15 and transferred into the first tank 11A.

[0046] In step S12 (hereinafter simply referred to as step S12) of determining whether the pressure in the tank has fallen below a first threshold, the detection value of the first pressure detection unit 111A is monitored while the carbon dioxide gas G in the second tank 11B is being transferred into the first tank 11A in step S11. In step S12, it is determined whether the pressure in the first tank 11A has fallen below a preset first threshold based on the detection value of the first pressure detection unit 111A. This first threshold is preferably set to be equal to or higher than the triple point of carbon dioxide gas. If the detection value of the first pressure detection unit 111A is not lower than the first threshold value (No in step S12), step S11 continues, and step S12 is repeatedly performed at predetermined time intervals. If the detection value of the first pressure detection unit 111A is lower than the first threshold value (Yes in step S12), the process proceeds to step S13, in which the transfer of the carbon dioxide gas G is switched to the return of the carbon dioxide gas G.

[0047] In step S13 (hereinafter simply referred to as step S13) of switching from the transfer of carbon dioxide gas G to the return of carbon dioxide gas G, the transfer of carbon dioxide gas G via the first transfer line 16A is switched to the return of carbon dioxide gas G via the first return line 17A. Specifically, from the state shown in FIG. 3, as shown in FIG. 4, the first on-off valve 122A and the third on-off valve 123 are closed, and the second on-off valve 122B and the fourth on-off valve 124 are opened. As a result, carbon dioxide gas G is sucked out of the second tank 11B by the compressor 31 through the second connecting pipe 24 of the first return line 17A and supplied to the first transfer line 16A, which is closer to the first tank 11A than the first pumping section 30. The carbon dioxide gas G supplied to the first transfer line 16A is pressurized by the compressor 31, heated by the heater 32, and then returned to the second tank 11B. In this way, the carbon dioxide gas G sucked out from second tank 11B is expanded and returned to second tank 11B, thereby increasing the pressure inside second tank 11B. By increasing the pressure inside second tank 11B, a pressure difference between the pressure inside second tank 11B and the pressure inside first tank 11A is maintained, and the transfer of liquefied carbon dioxide L inside second tank 11B to first tank 11A continues through connection line 15. As a result, the amount of liquefied carbon dioxide L in first tank 11A increases, increasing the pressure inside first tank 11A and preventing it from approaching the triple point.

[0048] In step S14 (hereinafter simply referred to as step S14) of determining whether the pressure in the tank has exceeded a second threshold, the pressure in the second tank 11B is confirmed based on the detection value of the second pressure detection unit 111B, and it is determined whether the pressure has exceeded a predetermined second threshold. Here, the second threshold may be different from the first threshold. If the pressure in the second tank 11B is not higher than the preset second threshold value (No in step S14), step S13 continues. If the pressure in the second tank 11B is higher than the preset second threshold value (Yes in step S14), the process proceeds to step S15, where the carbon dioxide gas G is returned and the carbon dioxide gas G is transferred again.

[0049] In step S15 (hereinafter simply referred to as step S15) of returning the carbon dioxide gas G to the transfer of the carbon dioxide gas G, the state shown in FIG. 4 is returned to the state shown in FIG. 3, and the liquefied carbon dioxide L in the second tank 11B is transferred into the first tank 11A. To achieve this, as shown in FIG. 3, the third on-off valve 123 and the fourth on-off valve 124 are closed, and the first on-off valve 122A and the second on-off valve 122B are opened. This allows the state to be restored where the carbon dioxide gas G in the first tank 11A is pressurized by the compressor 31, heated by the heater 32, and then transferred into the second tank 11B through the first transfer line 16A. As a result, the second tank 11B is pressurized, and the liquefied carbon dioxide L in the second tank 11B continues to be transferred into the first tank 11A through the connection line 15.

[0050] In step S16 (hereinafter simply referred to as step S16) of determining whether the transfer of liquefied carbon dioxide L has been completed, it is determined whether the transfer of liquefied carbon dioxide L from the second tank 11B into the first tank 11A has been completed, for example, based on the detection value of pressure sensor 112. For example, if the detection value of pressure sensor 112 is equal to or less than a preset threshold, it can be determined that the transfer of liquefied carbon dioxide L from the second tank 11B into the first tank 11A through connection line 15 has been completed. Note that the determination of whether the transfer of liquefied carbon dioxide L has been completed may also be made based on, for example, a level gauge that detects the liquid level in second tank 11B. In this way, when the transfer of the liquefied carbon dioxide L is completed, the liquefied carbon dioxide L transferred from the second tank 11B into the first tank 11A is discharged through the first discharge line 13A.

[0051] Next, a case will be described in which, for example, a failure occurs in the pump 132A of the first tank 11A when the liquefied carbon dioxide L in the first tank 11A and the second tank 11B is being discharged to the outside. (If the pump in the first tank breaks down) For example, if a failure occurs in the pump 132A of the first tank 11A while the liquefied carbon dioxide L in the first tank 11A and the second tank 11B is being discharged to the outside, in step S11, the liquefied carbon dioxide L in the first tank 11A is transferred to the second tank 11B. To do this, as shown in Fig. 5, the carbon dioxide gas G in the second tank 11B is transferred to the first tank 11A through the second transfer line 18A, and the inside of the first tank 11A is pressurized. For this purpose, in step S11, the on-off valve 121 is opened, the first on-off valve 122A and the second on-off valve 122B are closed, and the third on-off valve 123 and the fourth on-off valve 124 are opened, and the compressor 31 is operated.

[0052] Then, the second transfer line 18A sucks out the carbon dioxide gas G in the second tank 11B through the second connecting pipe 24. At this time, the second transfer line 18A pressurizes (compresses) the carbon dioxide gas G with the compressor 31 and heats the carbon dioxide gas G with the heater 32, thereby expanding the carbon dioxide gas G in the second tank 11B. This increases the pressure in the first tank 11A, and increases the pressure difference between the first tank 11A and the second tank 11B. Due to the pressure difference between the first tank 11A and the second tank 11B, the liquefied carbon dioxide L in the first tank 11A is transferred into the second tank 11B through the liquid transfer pipe 21 of the connecting line 15.

[0053] In step S12, while the carbon dioxide gas G in the first tank 11A is being transferred to the second tank 11B in step S11, the detection value of the second pressure detection unit 111B is monitored. In step S12, it is determined based on the detection value of the second pressure detection unit 111B whether the pressure in the second tank 11B has become lower than a preset first threshold value. If the detection value of the second pressure detection unit 111B is not lower than the first threshold value (No in step S12), step S11 continues, and step S12 is repeatedly performed at predetermined time intervals. If the detection value of the second pressure detection unit 111B is lower than the first threshold value (Yes in step S12), step S13 is carried out.

[0054] In step S13, as shown in FIG. 6, the transfer of carbon dioxide gas G via the second transfer line 18A is switched to the return of carbon dioxide gas G via the second return line 19A. Specifically, the second on-off valve 122B and the fourth on-off valve 124 are closed, and the first on-off valve 122A and the third on-off valve 123 are opened. As a result, carbon dioxide gas G is sucked out of the first tank 11A by the compressor 31 through the second return line 19A, pressurized by the compressor 31, heated by the heater 32, and then returned to the first tank 11A. By expanding the carbon dioxide gas G and returning it to the first tank 11A in this manner, the pressure in the first tank 11A can be increased. By increasing the pressure in the first tank 11A, a pressure difference between the pressure in the first tank 11A and the pressure in the second tank 11B is ensured, and the transfer of liquefied carbon dioxide L from the first tank 11A to the second tank 11B via the connection line 15 is continued. As a result, the amount of liquefied carbon dioxide L in the second tank 11B increases, which increases the pressure in the second tank 11B and prevents it from approaching the triple point.

[0055] In step S14, it is determined whether or not the pressure in the first tank 11A is lower than a predetermined second threshold value based on the detection value of the first pressure detection unit 111A. If the pressure in the first tank 11A is not higher than the preset second threshold value (No in step S14), step S13 continues. If the pressure in the first tank 11A is higher than the preset second threshold value (Yes in step S14), the process proceeds to step S15.

[0056] In step S15, the state shown in FIG. 6 is returned to the state shown in FIG. 5, and the liquefied carbon dioxide L in the first tank 11A is transferred into the second tank 11B. To achieve this, as shown in FIG. 5, the first on-off valve 122A and the second on-off valve 122B are closed, and the third on-off valve 123 and the fourth on-off valve 124 are opened. This allows the state to be restored so that the carbon dioxide gas G in the second tank 11B is pressurized by the compressor 31, heated by the heater 32, and then transferred into the first tank 11A through the second transfer line 18A. As a result, the inside of the first tank 11A is pressurized, and the liquefied carbon dioxide L in the first tank 11A continues to be transferred into the second tank 11B through the connection line 15.

[0057] In step S16, it is determined whether or not the transfer of the liquefied carbon dioxide L in the first tank 11A into the second tank 11B has been completed, for example, based on the detection value of the pressure sensor 112. When the detection value of the pressure sensor 112 is equal to or lower than a preset threshold value, the transfer of the liquefied carbon dioxide L in the first tank 11A into the second tank 11B through the connection line 15 has been completed. Note that the determination of whether or not the transfer of the liquefied carbon dioxide L has been completed may be made, for example, based on a level gauge that detects the liquid level in the first tank 11A. In this way, when the transfer of the liquefied carbon dioxide L is completed, the liquefied carbon dioxide L transferred from the first tank 11A to the second tank 11B is discharged through the second discharge line 13B.

[0058] (Action and effect) In the tank system 10A, ship 1, and liquefied carbon dioxide transfer method S10 of the first embodiment, the switching unit 120 can switch from transferring carbon dioxide gas G via the first transfer line 16A to returning carbon dioxide gas G via the first return line 17A. The first return line 17A can extract carbon dioxide gas G from the second tank 11B, heat it, and return it to the second tank 11B itself. This allows the transfer of liquefied carbon dioxide L from the second tank 11B to the first tank 11A to continue without extracting carbon dioxide gas G from the first tank 11A, which is the transfer destination, when the pressure of the first tank 11A, which is the transfer destination, approaches the triple point. This allows the liquefied carbon dioxide L to be rapidly transferred to the outside while suppressing the generation of dry ice in the first tank 11A.

[0059] In the first embodiment, the first transfer line 16A, which is closer to the second tank 11B than the position where the second connecting pipe 24 is connected, also serves as the first return line 17A. This makes it possible to suppress an increase in the number of parts.

[0060] Furthermore, in the first embodiment, the carbon dioxide gas G passing through the first pumping section 30 is compressed by the compressor 31 and heated by the heater 32. Therefore, in addition to the temperature increase of the carbon dioxide gas G when compressed by the compressor 31, the temperature of the carbon dioxide gas G can be further increased by the heater 32. This increases the pressure in the second tank 11B and increases the pressure difference between the first tank 11A and the second tank 11B. Therefore, the liquefied carbon dioxide L in the second tank 11B can be successfully transferred into the first tank 11A through the connection line 15.

[0061] Furthermore, in the first embodiment, the switching unit 120 can switch from transferring carbon dioxide gas G via the second transfer line 18A to returning carbon dioxide gas G via the second return line 19A. The second return line 19A can extract carbon dioxide gas G from the first tank 11A, heat it, and return it to the first tank 11A itself. This makes it possible to continue transferring liquefied carbon dioxide L from the first tank 11A to the second tank 11B without extracting carbon dioxide gas G from the second tank 11B, which is the transfer destination, when the pressure of the second tank 11B, which is the transfer destination, approaches the triple point. This makes it possible to quickly transfer the liquefied carbon dioxide L from the first tank 11A to the second tank 11B while suppressing the generation of dry ice in the second tank 11B.

[0062] In the first embodiment, the first transfer line 16A, including the first pumping section 30 between the position where the second connecting pipe 24 is connected and the position where the first connecting pipe 23 is connected, also serves as the second transfer line 18A. This makes it possible to suppress an increase in the number of parts.

[0063] Second Embodiment Next, a second embodiment of the tank system, float, and liquefied carbon dioxide transfer method according to the present disclosure will be described. The second embodiment described below differs from the first embodiment only in that it includes a control device. Therefore, the same parts as those in the first embodiment will be denoted by the same reference numerals and will not be described again. FIG. 8 is a diagram showing a tank system according to a second embodiment of the present disclosure. As shown in FIG. 8, the tank system 10B of the ship 1 in this embodiment includes a first tank 11A, a second tank 11B, a first discharge line 13A, a second discharge line 13B, a transfer piping section 20A, and a control device 60. The first pressure detection section 111A, the second pressure detection section 111B, and the pressure sensors 112 to 114 provided in the transfer piping section 20A each output their detection signals to the control device 60.

[0064] (Hardware configuration diagram) FIG. 9 is a diagram illustrating a hardware configuration of a control device according to the second embodiment of the present disclosure. 9, the control device 60 has a computer including a processor 61 such as a CPU (Central Processing Unit), a ROM 62 (Read Only Memory), a RAM 63 (Random Access Memory), a storage 64 such as an HDD (Hard Disk Drive), and a signal transmitting / receiving module 65. The signal transmitting / receiving module 65 receives detection signals from the first pressure detection unit 111A, the second pressure detection unit 111B, and the pressure sensors 112-114.

[0065] (Function block diagram) FIG. 10 is a functional block diagram of a control unit according to the second embodiment of the present disclosure. As shown in FIG. 10, a processor 61 of a control device 60 executes a program stored in advance in a ROM 62, a storage 64, or the like, thereby realizing the functional configurations of a signal receiving unit 70, a switching control unit 71, and a signal output unit 72.

[0066] The signal receiving unit 70 receives detection signals from the first pressure detecting unit 111A, the second pressure detecting unit 111B, and the pressure sensors 112 to 114 via a signal transmitting / receiving module 65 which is hardware.

[0067] The switching control unit 71 controls the operation of the switching unit 120 based on the detection results of the first pressure detection unit 111A, the second pressure detection unit 111B, and the pressure sensors 112-114.

[0068] Fig. 11 is a diagram showing a state in which carbon dioxide gas is circulated through a first transfer line in a tank system according to a second embodiment of the present disclosure. Fig. 12 is a diagram showing a state in which carbon dioxide gas is circulated through a first return line in a tank system according to a second embodiment of the present disclosure. In the second embodiment, when the pressure in the first tank 11A detected by the first pressure detection unit 111A becomes lower than a preset first threshold while carbon dioxide gas G is being transferred from the first tank 11A to the second tank 11B via the first transfer line 16A, the switching control unit 71 causes the switching unit 120 to switch from transferring carbon dioxide gas G via the first transfer line 16A to returning carbon dioxide gas G via the first return line 17A, as shown in Fig. 11. Furthermore, when carbon dioxide gas G is being extracted from the second tank 11B via the first return line 17A, heated, and returned to the second tank 11B itself, the switching control unit 71 causes the switching unit 120 to switch from returning carbon dioxide gas G via the first return line 17A to transferring carbon dioxide gas G via the first transfer line 16A, as shown in Fig. 12.

[0069] Fig. 13 is a diagram showing a state in which carbon dioxide gas is circulated through a second transfer line in a tank system according to a second embodiment of the present disclosure. Fig. 14 is a diagram showing a state in which carbon dioxide gas is circulated through a second return line in a tank system according to a second embodiment of the present disclosure. When the pressure in the second tank 11B detected by the second pressure detection unit 111B becomes lower than a preset first threshold value while the carbon dioxide gas G in the second tank 11B is being transferred to the first tank 11A via the second transfer line 18A, the switching control unit 71 causes the switching unit 120 to switch from transferring the carbon dioxide gas G via the second transfer line 18A to returning the carbon dioxide gas G via the second return line 19A, as shown in Fig. 13. Furthermore, when the carbon dioxide gas G in the first tank 11A is being extracted, heated, and returned to the first tank 11A via the second return line 19A, and the pressure in the first tank 11A becomes lower than a preset second threshold value, the switching control unit 71 causes the switching unit 120 to switch from returning the carbon dioxide gas G via the second return line 19A to transferring the carbon dioxide gas G via the second transfer line 18A, as shown in Fig. 14.

[0070] The signal output unit 72 outputs a command signal to the switching unit 120 and the compressor 31 to control the operations of the switching unit 120 and the compressor 31 under the control of the switching control unit 71 .

[0071] (Procedure for transporting liquefied carbon dioxide) In the tank system 10B, the liquefied carbon dioxide L in the first tank 11A and the second tank 11B is discharged to the outside through the first discharge line 13A and the second discharge line 13B. If a malfunction occurs in either the pump 132A of the first tank 11A or the pump 132B of the second tank 11B while the liquefied carbon dioxide L in the first tank 11A or the second tank 11B is being discharged to the outside, the control device 60 receives a signal indicating that the pump 132A or the pump 132B is not operating normally. When the control device 60 receives a signal indicating that the pump 132A or the pump 132B is not operating normally, the control device 60 performs control to transfer the liquefied carbon dioxide between the first tank 11A and the second tank 11B in the following procedure based on a preset program.

[0072] As shown in Figure 7, the method S20 for transferring liquefied carbon dioxide L in the tank system 10B of the second embodiment described above includes a step S21 for transferring liquefied carbon dioxide L, a step S22 for determining whether the pressure in the tank has dropped below a first threshold value, a step S23 for switching from transferring carbon dioxide gas G to returning carbon dioxide gas G, a step S24 for determining whether the pressure in the tank has risen above a second threshold value, a step S25 for switching from returning carbon dioxide gas G to transferring carbon dioxide gas G, and a step S26 for determining whether the transfer of liquefied carbon dioxide L has been completed.

[0073] In the following, for example, a case will be described in which a failure occurs in the pump 132B of the second tank 11B when the liquefied carbon dioxide L in the first tank 11A and the second tank 11B is being discharged to the outside. (If the pump in the second tank breaks down) In step S21 of transferring liquefied carbon dioxide L (hereinafter simply referred to as step S21), if a malfunction occurs in pump 132B of second tank 11B, control device 60 confirms that the free space in second tank 11B is greater than the liquid volume of liquefied carbon dioxide L in first tank 11A, and then transfers liquefied carbon dioxide L from second tank 11B to first tank 11A. To do this, as shown in FIG. 11 , carbon dioxide gas G from first tank 11A is transferred to second tank 11B through first transfer line 16A, and the inside of second tank 11B is pressurized. In step S21, on-off valve 121 is opened, third on-off valve 123 and fourth on-off valve 124 are closed, and first on-off valve 122A and second on-off valve 122B are opened, and compressor 31 is operated.

[0074] As a result, the first transfer line 16A sucks out the carbon dioxide gas G from the first tank 11A and pressure-feeds it toward the second tank 11B. At this time, the first transfer line 16A pressurizes (compresses) the carbon dioxide gas G with the compressor 31 and heats the carbon dioxide gas G with the heater 32, thereby expanding the carbon dioxide gas G in the first tank 11A. This increases the pressure in the second tank 11B, and increases the pressure difference between the first tank 11A and the second tank 11B. Due to the pressure difference between the first tank 11A and the second tank 11B, the liquefied carbon dioxide L in the second tank 11B is pushed out through the liquid transfer pipe 21 of the connection line 15 and transferred into the first tank 11A.

[0075] In step S22 (hereinafter simply referred to as step S22) of determining whether the pressure inside the tank has fallen below a first threshold, while the carbon dioxide gas G inside the second tank 11B is being transferred into the first tank 11A in step S21, the switching control unit 71 monitors the detection value of the first pressure detection unit 111A. In step S22, the switching control unit 71 determines whether the pressure inside the first tank 11A has fallen below a preset first threshold based on the detection value of the first pressure detection unit 111A. This first threshold is preferably set to be equal to or higher than the triple point of carbon dioxide gas. If the detection value of the first pressure detection unit 111A is not lower than the first threshold value (No in step S22), the switching control unit 71 continues step S21 and repeatedly executes step S22 at predetermined time intervals. If the detection value of the first pressure detection unit 111A is lower than the first threshold value (Yes in step S22), the switching control unit 71 proceeds to step S23 to switch from transferring carbon dioxide gas G to returning carbon dioxide gas G.

[0076] In step S23 (hereinafter simply referred to as step S23) of switching from the transfer of carbon dioxide gas G to the return of carbon dioxide gas G, the switching control unit 71 switches from the transfer of carbon dioxide gas G via the first transfer line 16A to the return of carbon dioxide gas G via the first return line 17A. Specifically, from the state shown in FIG. 11 , as shown in FIG. 12 , the first on-off valve 122A and the third on-off valve 123 are closed, and the second on-off valve 122B and the fourth on-off valve 124 are opened. As a result, carbon dioxide gas G is sucked out of the second tank 11B by the compressor 31 through the second connecting pipe 24 of the first return line 17A and supplied to the first transfer line 16A, which is closer to the first tank 11A than the first pumping unit 30. The carbon dioxide gas G supplied to the first transfer line 16A is pressurized by the compressor 31, heated by the heater 32, and then returned to the second tank 11B. In this way, the carbon dioxide gas G sucked out from second tank 11B is expanded and returned to second tank 11B, thereby increasing the pressure inside second tank 11B. By increasing the pressure inside second tank 11B, a pressure difference between the pressure inside second tank 11B and the pressure inside first tank 11A is maintained, and the transfer of liquefied carbon dioxide L inside second tank 11B to first tank 11A continues through connection line 15. As a result, the amount of liquefied carbon dioxide L in first tank 11A increases, increasing the pressure inside first tank 11A and preventing it from approaching the triple point.

[0077] In step S24 (hereinafter simply referred to as step S24) of determining whether the pressure inside the tank is higher than a second threshold value, the switching control unit 71 checks the pressure inside the second tank 11B based on the detection value of the second pressure detection unit 111B, and determines whether the pressure has become higher than a predetermined second threshold value. If the pressure in the second tank 11B is not higher than the preset second threshold value (No in step S24), the switching control unit 71 continues step S23. If the pressure in the second tank 11B is higher than the preset second threshold value (Yes in step S24), the switching control unit 71 proceeds to step S25, where the carbon dioxide gas G is returned and returned to being transferred.

[0078] In step S25 (hereinafter simply referred to as step S25) of returning the carbon dioxide gas G to the transfer of the carbon dioxide gas G, the switching control unit 71 controls the switching unit 120 to return from the state shown in FIG. 12 to the state shown in FIG. 11, and transfers the liquefied carbon dioxide L in the second tank 11B into the first tank 11A. To do this, as shown in FIG. 11, the switching control unit 71 closes the third on-off valve 123 and the fourth on-off valve 124 and opens the first on-off valve 122A and the second on-off valve 122B. This allows the state to be restored so that the carbon dioxide gas G in the first tank 11A is pressurized by the compressor 31, heated by the heater 32, and then transferred into the second tank 11B through the first transfer line 16A. As a result, the second tank 11B is pressurized, and the liquefied carbon dioxide L in the second tank 11B continues to be transferred into the first tank 11A through the connection line 15.

[0079] In step S26 (hereinafter simply referred to as step S26) of determining whether the transfer of liquefied carbon dioxide L has been completed, the switching control unit 71 determines whether the transfer of liquefied carbon dioxide L from the second tank 11B into the first tank 11A has been completed, for example, based on the detection value of the pressure sensor 112. If the detection value of the pressure sensor 112 is equal to or less than a preset threshold, it can be determined that the transfer of liquefied carbon dioxide L from the second tank 11B into the first tank 11A through the connection line 15 has been completed. Note that the determination of whether the transfer of liquefied carbon dioxide L has been completed may also be made by the switching control unit 71, for example, based on a level gauge or the like that detects the liquid level in the second tank 11B. In this way, when the transfer of the liquefied carbon dioxide L is completed, the liquefied carbon dioxide L transferred from the second tank 11B into the first tank 11A is discharged through the first discharge line 13A.

[0080] Here, when liquefied carbon dioxide L in first tank 11A is being transferred to second tank 11B through liquid transfer pipe 21 of connection line 15, control device 60 monitors the detection signal from first pressure detection unit 111A. When the pressure in first tank 11A detected by first pressure detection unit 111A exceeds a preset upper limit set value, control device 60 stops the operation of compressor 31 to prevent the pressure in first tank 11A from rising excessively.

[0081] (If the pump in the first tank breaks down) FIG. 13 is a diagram showing a state in which carbon dioxide gas is circulated through the second transfer line in the tank system according to the second embodiment of the present disclosure. For example, if a failure occurs in the pump 132A of the first tank 11A while the liquefied carbon dioxide L in the first tank 11A and the second tank 11B is being discharged to the outside, step S21 is performed to transfer the liquefied carbon dioxide L in the first tank 11A into the second tank 11B. To do this, as shown in Fig. 13, carbon dioxide gas G in the second tank 11B is transferred into the first tank 11A through the second transfer line 18A, and the inside of the first tank 11A is pressurized. For this purpose, the switching control unit 71 opens the on-off valve 121, closes the first on-off valve 122A and the second on-off valve 122B, and opens the third on-off valve 123 and the fourth on-off valve 124, and operates the compressor 31.

[0082] Then, the second transfer line 18A sucks out the carbon dioxide gas G from the second tank 11B through the second connecting pipe 24, pressurizes (compresses) it, and heats it, thereby expanding the carbon dioxide gas G in the second tank 11B. This increases the pressure in the first tank 11A, and increases the pressure difference between the first tank 11A and the second tank 11B. Due to the pressure difference between the first tank 11A and the second tank 11B, the liquefied carbon dioxide L in the first tank 11A is transferred into the second tank 11B through the liquid transfer pipe 21 of the connecting line 15.

[0083] In step S22, while the carbon dioxide gas G in the first tank 11A is being transferred to the second tank 11B in step S21, the switching control unit 71 monitors the detection value of the second pressure detection unit 111B. In step S22, the switching control unit 71 determines whether the pressure in the second tank 11B has become lower than a preset first threshold value based on the detection value of the second pressure detection unit 111B. If the detection value of the second pressure detection unit 111B is not lower than the first threshold value (No in step S22), the switching control unit 71 continues step S21 and repeatedly executes step S22 at predetermined time intervals. If the detection value of the second pressure detection unit 111B is lower than the first threshold value (Yes in step S22), the switching control unit 71 carries out step S23.

[0084] FIG. 14 is a diagram showing a state in which carbon dioxide gas is circulated through the second return line in the tank system according to the second embodiment of the present disclosure. In step S23, the switching control unit 71 switches from the transfer of carbon dioxide gas G through the second transfer line 18A to the return of carbon dioxide gas G through the second return line 19A, as shown in FIG. 14 . Specifically, the switching control unit 71 closes the second on-off valve 122B and the fourth on-off valve 124 and opens the first on-off valve 122A and the third on-off valve 123. As a result, carbon dioxide gas G is sucked out of the first tank 11A by the compressor 31 through the second return line 19A, pressurized by the compressor 31, heated by the heater 32, and then returned to the first tank 11A. By expanding the carbon dioxide gas G and returning it to the first tank 11A in this manner, the pressure in the first tank 11A can be increased. By increasing the pressure in the first tank 11A, a pressure difference between the pressure in the first tank 11A and the pressure in the second tank 11B is ensured, and the transfer of liquefied carbon dioxide L from the first tank 11A to the second tank 11B through the connection line 15 is continued. As a result, the amount of liquefied carbon dioxide L in the second tank 11B increases, which increases the pressure in the second tank 11B and prevents it from approaching the triple point.

[0085] In step S24, the switching control unit 71 determines whether or not the pressure in the first tank 11A is lower than a predetermined second threshold value based on the detection values ​​of the first pressure detection unit 111A and the second pressure detection unit 111B. If the pressure in the first tank 11A is not higher than the preset second threshold value (No in step S24), the switching control unit 71 continues step S23. If the pressure in the first tank 11A is higher than the preset second threshold value (Yes in step S24), the switching control unit 71 proceeds to step S25.

[0086] In step S25, the switching control unit 71 returns the state shown in FIG. 14 to the state shown in FIG. 13, and the liquefied carbon dioxide L in the first tank 11A is transferred into the second tank 11B. To do this, as shown in FIG. 13, the switching control unit 71 closes the first on-off valve 122A and the second on-off valve 122B and opens the third on-off valve 123 and the fourth on-off valve 124. This allows the state to be restored so that the carbon dioxide gas G in the second tank 11B is pressurized by the compressor 31, heated by the heater 32, and then transferred into the first tank 11A through the second transfer line 18A. As a result, the inside of the first tank 11A is pressurized, and the liquefied carbon dioxide L in the first tank 11A continues to be transferred into the second tank 11B through the connection line 15.

[0087] In step S26, the switching control unit 71 determines whether or not the transfer of the liquefied carbon dioxide L in the first tank 11A into the second tank 11B has been completed, for example, based on the detection value of the pressure sensor 112. If the detection value of the pressure sensor 112 is equal to or less than a preset threshold value, the transfer of the liquefied carbon dioxide L in the first tank 11A into the second tank 11B through the connection line 15 has been completed. Note that the determination of whether or not the transfer of the liquefied carbon dioxide L has been completed may be made, for example, based on a level gauge that detects the liquid level in the first tank 11A. In this way, when the transfer of the liquefied carbon dioxide L is completed, the liquefied carbon dioxide L transferred from the first tank 11A to the second tank 11B is discharged through the second discharge line 13B.

[0088] When liquefied carbon dioxide L in second tank 11B is being transferred to first tank 11A through liquid transfer pipe 21 of connection line 15, control device 60 monitors the detection signal from second pressure detection unit 111B. When the pressure in second tank 11B detected by second pressure detection unit 111B exceeds a preset upper limit set value, control device 60 stops the operation of compressor 31 to prevent the pressure in second tank 11B from rising excessively.

[0089] Furthermore, the control device 60 monitors detection signals from the pressure sensors 113 and 114 while the compressor 31 is operating. If the ratio of the inlet pressure of the compressor 31 detected by the pressure sensor 113 to the outlet pressure of the compressor 31 detected by the pressure sensor 114 becomes an abnormal value, the control device 60 stops the operation of the compressor 31. At this time, the control device 60 may maintain the differential pressure between the first tank 11A and the second tank 11B by closing the first on-off valve 122A, the second on-off valve 122B, the third on-off valve 123, and the fourth on-off valve 124. This allows the start-up time of the compressor 31 to be shortened upon recovery.

[0090] (Action and effect) In the tank system 10B, ship 1, and liquefied carbon dioxide transfer method S20 of the second embodiment, in addition to the effects of the first embodiment, when the pressure in the first tank 11A falls below a first threshold, the control device 60 can automatically switch from transferring carbon dioxide gas G via the first transfer line 16A to returning carbon dioxide gas G via the first return line 17A. Similarly, when the pressure in the second tank 11B falls below a first threshold, the control device 60 can automatically switch from transferring carbon dioxide gas G via the second transfer line 18A to returning carbon dioxide gas G via the second return line 19A. Therefore, as in the first embodiment, when the pressure in the first tank 11A or the second tank 11B approaches the triple point, the extraction of carbon dioxide gas G from the first tank 11A or the second tank 11B, which are the transfer destinations, is automatically stopped, while the transfer of liquefied carbon dioxide L can be automatically continued using the pressure difference between the tanks. This allows for rapid transfer of liquefied carbon dioxide L while reducing the burden on the operator.

[0091] Furthermore, in the second embodiment, when the pressure in the second tank 11B becomes lower than the second threshold value, the control device 60 can automatically switch from returning the carbon dioxide gas G through the first return line 17A to transferring the carbon dioxide gas G through the first transfer line 16A. Therefore, the burden on the operator can be further reduced.

[0092] (First Modification of the Embodiment) In each of the above embodiments, the transfer piping section 20A is provided with a set of first compression section 30 (compressor 31 and heater 32), and the first transfer line 16A and the first return line 17A share the first compression section 30, but this is not limited to this. FIG. 15 is a diagram showing a tank system according to a first modified example of the embodiment of the present disclosure. 15, the transfer piping section 20C of the tank system 10C transfers the liquefied carbon dioxide L in the second tank 11B into the first tank 11A when the pump 132B of the second discharge line 13B cannot be used, for example, due to a malfunction, etc. The transfer piping section 20C has a first transfer line 16C, a first return line 17C, and a switching section 120C.

[0093] The first transfer line 16C is capable of transferring carbon dioxide gas G from the first tank 11A to the second tank 11B. The first transfer line 16C includes a gas transfer pipe 22 and a first compression unit 30. The first compression unit 30 includes a compressor 31 and a heater 32. The first transfer line 16C is provided with a first on-off valve 122A and a second on-off valve 122B as a switching unit 120C. The first on-off valve 122A is provided between one end 22a of the gas transfer pipe 22 and the compressor 31. The second on-off valve 122B is provided between the heater 32 and the other end 22b of the gas transfer pipe 22.

[0094] To circulate carbon dioxide gas through the first transfer line 16C, the first on-off valve 122A and the second on-off valve 122B are opened, and the compressor 31 is operated. The first transfer line 16C uses the compressor 31 to suck out carbon dioxide gas G from the first tank 11A and pumps it toward the second tank 11B. The first transfer line 16C pressurizes (compresses) the carbon dioxide gas G with the compressor 31 and heats the carbon dioxide gas G with the heater 32, thereby expanding the carbon dioxide gas G in the first tank 11A and transferring it into the second tank 11B. Transferring the expanded carbon dioxide gas G into the second tank 11B in this manner increases the pressure inside the second tank 11B.

[0095] The first return line 17C is capable of returning the carbon dioxide gas G in the second tank 11B to the second tank 11B. The first return line 17C includes a first circulation pipe 201 and a second pumping section 200.

[0096] The first circulation pipe 201 is capable of returning the carbon dioxide gas G in the second tank 11B to the inside of the second tank 11B via the outside of the second tank 11B. The first circulation pipe 201 is provided outside the second tank 11B, independently of the first transfer line 16C. One end 201a and the other end 201b of the first circulation pipe 201 are each connected to the upper part of the second tank 11B.

[0097] The second pumping section 200 is provided midway through the first circulation pipe 201. The second pumping section 200 includes a compressor 231 and a heater 232. The first return line 17C is provided with a fifth on-off valve 212A and a sixth on-off valve 212B as a switching section 120C. The fifth on-off valve 212A is provided between one end 201a of the first circulation pipe 201 and the compressor 231. The sixth on-off valve 212B is provided between the heater 232 and the other end 201b of the first circulation pipe 201.

[0098] To circulate carbon dioxide gas through the first return line 17C, the fifth on-off valve 212A and the sixth on-off valve 212B are opened, and the compressor 231 is operated. The first return line 17C uses the compressor 231 to suck out and compress the carbon dioxide gas G from the second tank 11B, and returns the gas to the second tank 11B. The first return line 17C pressurizes (compresses) the carbon dioxide gas G with the compressor 231 and heats the carbon dioxide gas G with the heater 232, thereby expanding the carbon dioxide gas G in the second tank 11B and returning it to the second tank 11B. By returning the expanded carbon dioxide gas G to the second tank 11B in this manner, the pressure inside the second tank 11B increases.

[0099] The switching unit 120C includes a first on-off valve 122A, a second on-off valve 122B, a fifth on-off valve 222A, and a sixth on-off valve 222B. The switching unit 120C switches the flow mode (flow path) of the carbon dioxide gas in the transfer piping unit 20C by opening and closing the first on-off valve 122A, the second on-off valve 122B, the fifth on-off valve 222A, and the sixth on-off valve 222B. The switching unit 120C can switch between transferring the carbon dioxide gas G via the first transfer line 16C and returning the carbon dioxide gas G via the first return line 17C.

[0100] Although Figure 15 only shows the configuration for transferring carbon dioxide gas G from the first tank 11A to the second tank 11B, a configuration for transferring carbon dioxide gas G from the second tank 11B to the first tank 11A may also be provided in a similar manner.

[0101] According to this configuration, by providing the first return line 17C with the first circulation pipe 201 and the second pumping unit 200 in addition to the first pumping unit 30, it is possible to extract and heat the carbon dioxide gas G from the second tank 11B and return it to the second tank 11B itself. This increases the pressure in the second tank 11B, increasing the pressure difference between the pressure in the first tank 11A and the pressure in the second tank 11B, and allows the liquefied carbon dioxide L in the second tank 11B to be sent to the inside of the first tank 11A through the connection line 15. Even with this configuration, it is possible to quickly transfer the liquefied carbon dioxide L from the tank to the outside while suppressing the generation of dry ice.

[0102] (Second Modification of the Embodiment) FIG. 16 is a diagram showing a tank system according to a modified example of the embodiment of the present disclosure. As shown in FIG. 16, the transfer piping section 20D of the tank system 10D transfers the liquefied carbon dioxide L in the second tank 11B into the first tank 11A when the pump 132B of the second discharge line 13B cannot be used, for example, due to a malfunction. The transfer piping section 20D in this second modification includes a bypass pipe 301 in the gas transfer pipe 22 constituting the first transfer line 16D. The bypass pipe 301 is provided in the gas transfer pipe 22 so as to bypass the compressor 31A and the heater 32A. The bypass pipe 301 is connected to the gas transfer pipe 22 via a connecting pipe 302 between one end 22a of the gas transfer pipe 22 and the first on-off valve 122A. The bypass pipe 301 is connected to the gas transfer pipe 22 via a connecting pipe 303 between the other end 22b of the gas transfer pipe 22 and the second on-off valve 122B.

[0103] A compressor 31B and a heater 32B are provided midway along the bypass pipe 301. A first on-off valve 322A serving as the switching unit 120D is provided between the compressor 31B and the position where the bypass pipe 301 is connected to the connecting pipe 302. A second on-off valve 322B serving as the switching unit 120D is provided between the heater 32B and the position where the bypass pipe 301 is connected to the connecting pipe 303. An on-off valve 323 serving as the switching unit 120D is provided midway along the connecting pipe 302. An on-off valve 324 serving as the switching unit 120D is provided midway along the connecting pipe 303.

[0104] The compressor 31B and heater 32B provided in the bypass pipe 301 are provided as spares for the compressor 31A and heater 32A provided in the gas transfer pipe 22 of the first transfer line 16D. When at least one of the compressor 31A and heater 32A provided in the gas transfer pipe 22 is unavailable due to a malfunction, maintenance, or the like, the first on-off valve 122A and the second on-off valve 122B are closed, and the first on-off valve 322A, the second on-off valve 322B, and the on-off valves 323 and 324 are opened. As a result, the first transfer line 16D passes the carbon dioxide gas G through the compressor 31B and heater 32B provided in the bypass pipe 301, where the carbon dioxide gas G is pressurized and heated.

[0105] The transfer piping section 20D in this modified example further includes a first connecting pipe 333 and a second connecting pipe 334. One end 333a of the first connecting pipe 333 is connected to the upper part of the first tank 11A. The other end 333b of the first connecting pipe 333 is connected between the first on-off valve 322A and the on-off valve 323. An on-off valve 325 serving as the switching section 120D is provided midway along the first connecting pipe 333. One end 334a of the second connecting pipe 334 is connected to the upper part of the second tank 11B. The other end 334b ​​of the second connecting pipe 334 is connected at the other end of the bypass pipe 301 between the second on-off valve 322B and the on-off valve 324. An on-off valve 326 serving as the switching section 120D is provided midway along the second connecting pipe 334.

[0106] In the transfer piping section 20D, the first on-off valve 122A, the second on-off valve 122B, and the on-off valves 323 and 324 are closed, and the first on-off valve 322A, the second on-off valve 322B, and the on-off valves 325 and 326 are opened, thereby forming a first return line 17D. The first return line 17D uses the compressor 31B to suck out carbon dioxide gas G from the second tank 11B through a first connecting pipe 333. The sucked carbon dioxide gas G is pressurized and heated by the compressor 31B and the heater 32B, which serve as a second compression section 300 provided in the bypass pipe 301, and is returned to the second tank 11B through a second connecting pipe 334. According to the second modified example, the first return line 17D can be configured by effectively utilizing the compressor 31B and the heater 32B that are provided as spares.

[0107] (Other embodiments) The above describes in detail the embodiments of the present disclosure with reference to the drawings, but the specific configuration is not limited to this embodiment, and design changes and the like are also included within the scope that does not deviate from the gist of the present disclosure. In the above embodiment, in steps S14 and S24 for determining whether the pressure inside the tank has become higher than the second threshold, if the pressure inside the tank is higher than a preset second threshold, the process is switched back from returning the carbon dioxide gas G to transferring the carbon dioxide gas G. However, this is not limited to this. For example, in steps S14 and S24, the pressure difference between the pressure inside the second tank 11B and the pressure inside the first tank 11A may be confirmed based on the detection values ​​of the first pressure detection unit 111A and the second pressure detection unit 111B, and if the pressure difference is smaller than a predetermined reference pressure difference, the process may be switched back from returning the carbon dioxide gas G to transferring the carbon dioxide gas G.

[0108] Furthermore, in the above embodiment, the configurations of the tank systems 10A to 10D are shown, but the configuration of each part can be changed as appropriate. Furthermore, in the above embodiment, the configuration of the hull 2 ​​is shown, but the configuration of each part can be changed as appropriate.

[0109] Furthermore, in the above embodiment, the tank systems 10A to 10D are configured to be provided on the ship 1, but the tank systems 10A to 10D may also be provided on the floating body of an offshore floating facility, a liquefied gas storage facility on land, or the like.

[0110] <Additional Notes> The tank systems 10A to 10D, the floating body 1, and the method for transferring liquefied carbon dioxide L described in each embodiment can be understood, for example, as follows.

[0111] (1) The tank systems 10A to 10D according to the first aspect comprise a first tank 11A and a second tank 11B capable of storing liquefied carbon dioxide L, a first discharge line 13A capable of discharging the liquefied carbon dioxide L in the first tank 11A to the outside of the first tank 11A, a connection line 15 connecting the inside of the first tank 11A with the inside of the second tank 11B, first transfer lines 16A, 16C capable of transferring carbon dioxide gas G in the first tank 11A into the second tank 11B, first return lines 17A, 17C capable of extracting and heating carbon dioxide gas G in the second tank 11B and returning it to the second tank 11B itself, and a switching unit 120 capable of switching between transferring the carbon dioxide gas G via the first transfer lines 16A, 16C and returning the carbon dioxide gas G via the first return lines 17A, 17C.

[0112] In the tank systems 10A to 10D, the liquefied carbon dioxide L in the first tank 11A can be discharged to the outside of the first tank 11A through a first discharge line 13A. When the liquefied carbon dioxide L in the second tank 11B cannot be discharged to the outside of the second tank 11B, the carbon dioxide gas G in the first tank 11A is transferred to the second tank 11B through first transfer lines 16A and 16C. This increases the pressure in the second tank 11B, creating a pressure difference between the pressure in the first tank 11A and the pressure in the second tank 11B. Due to the pressure difference between the pressure in the first tank 11A and the pressure in the second tank 11B, the liquefied carbon dioxide L in the second tank 11B is sent to the inside of the first tank 11A through the connection line 15. Furthermore, when the pressure in first tank 11A approaches the triple point, switching unit 120 switches from transferring carbon dioxide gas G via first transfer lines 16A and 16C to returning carbon dioxide gas G via first return lines 17A and 17C. Carbon dioxide gas G in second tank 11B is extracted, heated, and returned to second tank 11B via first return lines 17A and 17C. This increases the pressure in second tank 11B, increasing the pressure difference between the pressure in first tank 11A and the pressure in second tank 11B. As a result, liquefied carbon dioxide L in second tank 11B is transferred into first tank 11A through connection line 15. In this way, liquefied carbon dioxide L in the tank can be rapidly transferred to the outside while suppressing the generation of dry ice.

[0113] (2) The tank systems 10A and 10B according to the second aspect are the tank systems 10A and 10B of (1), wherein the first transfer line 16A is provided with a first compression section 30 that compresses the carbon dioxide gas G toward the second tank 11B using a compressor 31, the first return line 17A is provided with a first gas discharge pipe 24 that can supply the carbon dioxide gas G in the second tank 11B to the first transfer line 16A that is closer to the first tank 11A than the first compression section 30, and the first transfer line 16A that is closer to the second tank 11B than the position where the first gas discharge pipe 24 is connected also serves as the first return line 17A.

[0114] As a result, the first transfer line 16A, which is closer to the second tank 11B than the position where the first gas discharge pipe 24 is connected, also serves as the first return line 17A. Therefore, the carbon dioxide gas G transferred from the first tank 11A to the second tank 11B through the first transfer line 16A is compressed by the first compression unit 30. In addition, the carbon dioxide gas G taken out of the second tank 11B and returned to the second tank 11B itself through the first return line 17A is compressed by the first compression unit 30. In this way, the first compression unit 30 can be shared by the first transfer line 16A and the first return line 17A, which can prevent an increase in equipment costs.

[0115] (3) The tank systems 10A and 10B according to the third aspect are the tank systems 10A and 10B of (2), in which the first pumping section 30 includes a compressor 31 for compressing the carbon dioxide gas G and a heater 32 for heating the carbon dioxide gas G.

[0116] As a result, the carbon dioxide gas G passing through the first pumping section 30 is compressed by the compressor 31 and expanded by being heated by the heater 32. By expanding the carbon dioxide gas G by the first pumping section 30, the pressure in the second tank 11B can be increased, and the pressure difference between the pressure in the first tank 11A and the pressure in the second tank 11B can be increased. As a result, the liquefied carbon dioxide L in the second tank 11B can be successfully transferred into the first tank 11A through the connection line 15.

[0117] (4) A tank system 10C according to a fourth aspect is the tank system 10C of (1), wherein the first transfer line 16C is provided with a first compression section 30C that compresses the carbon dioxide gas G toward the second tank 11B using a compressor 31, and the first return line 17C is provided with a first circulation pipe 201 that can return the carbon dioxide gas G in the second tank 11B to the second tank 11B via the outside of the second tank 11B, and a second compression section 200 that is provided midway along the first circulation pipe 201 and compresses the carbon dioxide gas G in the second tank 11B using a compressor 31 and returns it to the second tank 11B.

[0118] Thus, by providing the first return line 17C with the first circulation pipe 201 and the second pumping unit 200 in addition to the first pumping unit 30C, it is possible to extract and heat the carbon dioxide gas G from the second tank 11B and return it to the second tank 11B itself. This increases the pressure in the second tank 11B, increasing the pressure difference between the pressure in the first tank 11A and the pressure in the second tank 11B, and allows the liquefied carbon dioxide L in the second tank 11B to be sent to the inside of the first tank 11A through the connection line 15. Even with this configuration, it is possible to quickly transfer the liquefied carbon dioxide L from the tank to the outside while suppressing the generation of dry ice.

[0119] (5) The tank system 10C according to the fifth aspect is the tank system 10C of (4), wherein at least one of the first pumping section 30C and the second pumping section 200 includes a compressor 31 for compressing the carbon dioxide gas G and a heater 32 for heating the carbon dioxide gas G.

[0120] As a result, the carbon dioxide gas G passing through at least one of the first pumping section 30C and the second pumping section 200 is compressed by the compressor 31 and expanded by being heated by the heater 32. This causes the carbon dioxide gas G to expand, increasing the pressure in the second tank 11B and increasing the pressure difference between the pressure in the first tank 11A and the pressure in the second tank 11B.

[0121] (6) The tank system 10A, 10B relating to the sixth aspect is any one of the tank systems 10A, 10B of (1) to (5), and further includes a second discharge line 13B capable of discharging the liquefied carbon dioxide L in the second tank 11B to the outside of the second tank 11B, a second transfer line 18A capable of transferring the carbon dioxide gas G in the second tank 11B into the first tank 11A, and a second return line 19A capable of extracting the carbon dioxide gas G in the first tank 11A, heating it, and returning it to the first tank 11A itself, and the switching unit 120 is capable of switching between transferring the carbon dioxide gas G via the second transfer line 18A and returning the carbon dioxide gas G via the second return line 19A.

[0122] This allows the liquefied carbon dioxide L in the second tank 11B to be discharged to the outside of the second tank 11B through the second discharge line 13B. When the liquefied carbon dioxide L in the first tank 11A cannot be discharged to the outside of the first tank 11A, the carbon dioxide gas G in the second tank 11B is transferred to the first tank 11A through the second transfer line 18A. This increases the pressure in the first tank 11A, and the pressure difference between the pressure in the second tank 11B and the pressure in the first tank 11A increases. Due to the pressure difference between the pressure in the second tank 11B and the pressure in the first tank 11A, the liquefied carbon dioxide L in the first tank 11A is sent to the inside of the second tank 11B through the connection line 15. Furthermore, when the pressure in the second tank 11B approaches the triple point, the switching unit 120 switches from transferring the carbon dioxide gas G through the second transfer line 18A to returning the carbon dioxide gas G through the second return line 19A. In the second return line 19A, carbon dioxide gas G is extracted from the first tank 11A, heated, and returned to the first tank 11A itself. This increases the pressure in the first tank 11A, increasing the pressure difference between the pressure in the second tank 11B and the pressure in the first tank 11A, and the liquefied carbon dioxide L in the first tank 11A is sent to the inside of the second tank 11B through the connection line 15. In this way, it is possible to quickly transfer the liquefied carbon dioxide L in the tank to the outside while suppressing the generation of dry ice.

[0123] (7) The tank systems 10A and 10B according to the seventh aspect are the tank systems 10A and 10B of (6), wherein the first transfer line 16A includes a first compression section 30 that compresses the carbon dioxide gas G toward the second tank 11B using a compressor 31, the first return line 17A includes a first gas discharge pipe 24 that can supply the carbon dioxide gas G in the second tank 11B to the first transfer line 16A that is closer to the first tank 11A than the first compression section 30, and the second return line The second transfer line 18A is equipped with a return pipe 23 that can return the carbon dioxide gas G pressurized by the first compression section 30 into the first tank 11A, and the second transfer line 18A is composed of the first gas discharge pipe 24 of the first return line 17A, the return pipe 23 of the second return line 19A, and the first transfer line 16A including the first compression section 30 between the position of the first transfer line 16A where the first gas discharge pipe 24 is connected and the position of the return pipe 23 where the first transfer line 16A is connected.

[0124] As a result, the first transfer line 16A, including the first pumping section 30 between the position of the first transfer line 16A to which the first gas discharge pipe 24 is connected and the position of the return pipe 23, also serves as the second transfer line 18A. Carbon dioxide gas G transferred from the second tank 11B to the first tank 11A through the second transfer line 18A is pumped by the first pumping section 30. In addition, carbon dioxide gas G taken out of the first tank 11A and returned to the first tank 11A itself through the second transfer line 18A is pumped by the first pumping section 30. In this way, the first pumping section 30 can be shared by the first transfer line 16A and the second transfer line 18A, thereby suppressing an increase in equipment costs.

[0125] (8) The tank system 10B according to the eighth aspect is any one of the tank systems 10B of (1) to (7), and further includes a control device 60 that controls the operation of the switching unit 120 and a first pressure detection unit 111A that detects the pressure in the first tank 11A. When the pressure in the first tank 11A detected by the first pressure detection unit 111A becomes lower than a predetermined first threshold value while the carbon dioxide gas G in the first tank 11A is being transferred to the second tank 11B via the first transfer line 16A, the control device 60 switches, via the switching unit 120, from transferring the carbon dioxide gas G via the first transfer line 16A to returning the carbon dioxide gas G via the first return line 17A.

[0126] As a result, when the pressure in the first tank 11A falls below a first threshold value, the control device 60 can automatically switch from transferring carbon dioxide gas G via the first transfer line 16A to returning carbon dioxide gas G via the first return line 17A.

[0127] (9) The tank system 10B according to the ninth aspect is the tank system 10B of (8), further comprising a second pressure detection unit 111B that detects the pressure inside the second tank 11B, and when the pressure inside the second tank 11B detected by the second pressure detection unit 111B becomes smaller than a predetermined second threshold value while the control device 60 is extracting, heating, and returning carbon dioxide gas G from the second tank 11B through the first return line 17A to the second tank 11B itself, the control device 60 switches, via the switching unit 120, from returning the carbon dioxide gas G through the first return line 17A to transferring the carbon dioxide gas G through the first transfer line 16A.

[0128] This allows automatic switching from returning carbon dioxide gas G via the first return line 17A to transferring carbon dioxide gas G via the first transfer line 16A when the pressure in the second tank 11B becomes lower than the second threshold value.

[0129] (10) A floating body 1 according to a tenth aspect includes a floating body main body 2 and a tank system 10A, 10B of any one of (1) to (9) provided on the floating body main body 2.

[0130] With this configuration, it is possible to provide a floating body 1 equipped with tank systems 10A and 10B that can quickly transfer the liquefied carbon dioxide L in the tanks to the outside while suppressing the generation of dry ice. Examples of the floating body 1 include a ship and an offshore floating facility. Examples of the floating body main body 2 include the hull of a ship and the floating body main body 2 of an offshore floating facility.

[0131] (11) The method for transferring liquefied carbon dioxide L according to the eleventh aspect is a method S10, S20 for transferring liquefied carbon dioxide L in any one of the tank systems 10A, 10B of (1) to (9), and includes steps S11, S21 of transferring carbon dioxide gas G in the first tank 11A into the second tank 11B through the first transfer line 16A to increase the pressure in the second tank 11B, and transferring the liquefied carbon dioxide L in the second tank 11B into the first tank 11A through the connection line 15 due to the pressure difference between the pressure in the second tank 11B and the pressure in the first tank 11A, and steps S13, S23 of switching from transferring the carbon dioxide gas G via the first transfer line 16A to returning the carbon dioxide gas G via the first return line 17A when the pressure in the first tank 11A becomes lower than a predetermined first threshold value while the carbon dioxide gas G in the first tank 11A is being transferred into the second tank 11B.

[0132] In these methods S10 and S20 for transferring liquefied carbon dioxide L, if the pressure in second tank 11B falls below a preset first threshold while carbon dioxide gas G in second tank 11B is being transferred into first tank 11A, the system switches from transferring carbon dioxide gas G via first transfer line 16A to returning carbon dioxide gas G via first return line 17A. This increases the pressure in second tank 11B, increasing the pressure difference between the pressure in first tank 11A and the pressure in second tank 11B, and liquefied carbon dioxide L in second tank 11B is sent into first tank 11A through connection line 15. In this way, it is possible to quickly transfer liquefied carbon dioxide L from the tank to the outside while suppressing the generation of dry ice. [Explanation of symbols]

[0133] 1... Ship (floating body) 2...Hull (floating body) 2a…bow 2b…stern 3A, 3B...Side 5...Upper deck 7...Superstructure 8...Cargo compartment 10A~10D...Tank system 11A...First tank 11B...Second tank 13A...First discharge line 13B...Second discharge line 15...Connection line 16A, 16C, 16D...First transfer line 17A, 17C, 17D...First return line 18A...Second transfer line 19A...Second return line 20A, 20C, 20D…Transfer piping section 21…Liquid transfer pipe 21a…one end 21b...other end 22...Gas transfer pipe 22a...one end 22b...other end 23...First connecting pipe (return pipe) 23a…one end 23b...other end 24...Second connecting pipe (first gas exhaust pipe) 24a…one end 24b...other end 30, 30C...First pumping section 31, 31A, 31B...Compressor 32, 32A, 32B…heater 60...Control device 61...Processor 62...ROM 63...RAM 64…Storage 65...Signal transmission / reception module 70...Signal receiving unit 71...Switching control unit 72...Signal output section 111A...First pressure detection unit 111B...Second pressure detection unit 112~114...Pressure sensor 120, 120C, 120D...Switching section 121...Shut-off valve 122A...First shut-off valve 122B...Second on-off valve 123...Third on-off valve 124...Fourth on-off valve 131A, 131B...unloading pipes 132A, 132B...Pump 200, 300...Second pumping section 201…First circulation pipe 201a…One end 201b...other end 212A, 222A... Fifth on-off valve 212B, 222B... Sixth on-off valve 231...Compressor 232…heater 301...Bypass pipe 302, 303…Connecting pipe 322A...First shut-off valve 322B...Second on-off valve 323~326...Shut-off valve 333...First connecting pipe 333a...one end 333b...other end 334...Second connecting pipe 334a...one end 334b...other end G...carbon dioxide gas L...liquefied carbon dioxide

Claims

1. a first tank and a second tank capable of storing liquefied carbon dioxide; a first discharge line capable of discharging the liquefied carbon dioxide in the first tank to the outside of the first tank; a connection line connecting the inside of the first tank and the inside of the second tank; a first transfer line capable of transferring carbon dioxide gas in the first tank into the second tank; a first return line capable of extracting and heating the carbon dioxide gas in the second tank and returning it to the second tank itself; a switching unit capable of switching between transferring the carbon dioxide gas through the first transfer line and returning the carbon dioxide gas through the first return line; A tank system comprising:

2. the first transfer line includes a first compression section that compresses the carbon dioxide gas toward the second tank using a compressor, the first return line includes a first gas discharge pipe capable of supplying the carbon dioxide gas in the second tank to the first transfer line closer to the first tank than the first pumping unit, The tank system according to claim 1, wherein the first transfer line, which is closer to the second tank than the position where the first gas exhaust pipe is connected, also serves as the first return line.

3. The tank system according to claim 2 , wherein the first pumping unit includes a compressor that compresses the carbon dioxide gas and a heater that heats the carbon dioxide gas.

4. the first transfer line includes a first compression section that compresses the carbon dioxide gas toward the second tank using a compressor, The first return line is a first circulation pipe capable of returning the carbon dioxide gas in the second tank to the inside of the second tank via the outside of the second tank; a second pressure-feeding section that is provided in the middle of the first circulation pipe and that compresses the carbon dioxide gas in the second tank using a compressor and returns the gas to the second tank. The tank system of claim 1 .

5. At least one of the first pumping unit and the second pumping unit includes a compressor that compresses the carbon dioxide gas and a heater that heats the carbon dioxide gas.

5. The tank system of claim 4.

6. a second discharge line capable of discharging the liquefied carbon dioxide in the second tank to the outside of the second tank; a second transfer line capable of transferring the carbon dioxide gas in the second tank into the first tank; a second return line capable of extracting and heating the carbon dioxide gas in the first tank and returning it to the first tank itself; The switching unit is The transfer of the carbon dioxide gas through the second transfer line and the return of the carbon dioxide gas through the second return line can be switched. The tank system of claim 1 .

7. the first transfer line includes a first compression section that compresses the carbon dioxide gas toward the second tank using a compressor, the first return line includes a first gas discharge pipe capable of supplying the carbon dioxide gas in the second tank to the first transfer line closer to the first tank than the first pumping unit, The second return line is a return pipe capable of returning the carbon dioxide gas pressure-fed by the first pressure-fed unit into the first tank; The second transfer line the first gas discharge pipe of the first return line, the return pipe of the second return line, and the first transfer line including the first pressure-feeding section between a position of the first transfer line to which the first gas discharge pipe is connected and a position of the first transfer line to which the return pipe is connected.

7. The tank system of claim 6.

8. a control device that controls the operation of the switching unit; a first pressure detection unit that detects the pressure in the first tank, When the pressure in the first tank detected by the first pressure detection unit becomes lower than a preset first threshold value while the carbon dioxide gas in the first tank is being transferred to the second tank through the first transfer line, the control device switches, by the switching unit, from transferring the carbon dioxide gas through the first transfer line to returning the carbon dioxide gas through the first return line.

3. A tank system according to claim 1 or 2.

9. Further, a second pressure detection unit is provided to detect the pressure in the second tank, When the pressure in the second tank detected by the second pressure detection unit becomes higher than a preset second threshold value while the carbon dioxide gas in the second tank is being extracted, heated, and returned to the second tank itself via the first return line, the control device switches, by the switching unit, from returning the carbon dioxide gas via the first return line to transferring the carbon dioxide gas via the first transfer line.

9. The tank system of claim 8.

10. A floating body; The tank system according to claim 1 or 2, which is provided on the floating body; A floating body comprising:

11. A method for transferring liquefied carbon dioxide in the tank system according to claim 1 or 2, a step of transferring the carbon dioxide gas in the first tank into the second tank through the first transfer line to increase the pressure in the second tank, and transferring the liquefied carbon dioxide in the second tank into the first tank through the connecting line due to the pressure difference between the pressure in the second tank and the pressure in the first tank; and when the pressure in the first tank becomes lower than a preset first threshold value while the carbon dioxide gas in the first tank is being transferred to the second tank, switching from transferring the carbon dioxide gas through the first transfer line to returning the carbon dioxide gas through the first return line. A method for transporting liquefied carbon dioxide.

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