Multi-shell tank, ship and gas pressure adjustment method

Abstract

To suppress condensation of a gas in a space outside of an inner tank for storing a low temperature liquid.SOLUTION: A multiple shell tank includes: an inner tank for storing a low temperature liquid inside; one or a plurality of outer tanks housing the inner tank; and a heat insulation space disposed between the inner tank and the outer tank and filled with a gas. A pressure of the gas in the heat insulation space is kept at less than a saturation vapor pressure of the gas in the heat insulation space at a reference temperature as a temperature determined on the basis of a temperature of the inner tank or a temperature of a space inside of the inner tank.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a multi-shell tank, a ship, and a gas pressure regulation method. [Background technology]

[0002] A multi-shell tank is known that has an inner vessel in which a cryogenic liquid is stored and an outer vessel that houses the inner vessel, and in which the insulated space between the inner vessel and the outer vessel is filled with a gas. For example, Patent Document 1 discloses a double-shell tank having an inner vessel and an outer vessel, in which the insulated space between the inner vessel and the outer vessel is filled with boil-off gas discharged from the inner vessel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-82889 Summary of the Invention [Problem to be solved by the invention]

[0004] When gas in the insulated space between the inner and outer vessels comes into contact with the inner vessel and condenses, the condensed liquid falls from the inner vessel to the outer vessel and then evaporates. When this liquefaction and vaporization of gas (absorption and evaporation of latent heat) is repeated, the heat input to the inner vessel increases due to the heat pipe effect. This phenomenon can occur not only in the space between the inner and outer vessels of a double-shelled tank, but also between the two outer vessels of a triple- or more-shelled tank.

[0005] Therefore, an object of the present invention is to provide a multi-shell tank, a ship, and a gas pressure adjustment method that can suppress condensation of gas in the space outside an inner tank in which a cryogenic liquid is stored. [Means for solving the problem]

[0006] In order to solve the above problems, DisclosureThe multi-shell tank according to one aspect of the present invention includes an inner tank in which a cryogenic liquid is stored, one or more outer tanks that accommodate the inner tank, and a heat-insulating space that is provided between the inner tank and the outer tank and is filled with a gas. ,before The pressure of the gas in the heat insulating space is determined based on the temperature of the inner vessel or the temperature of the space inside the inner vessel. of Maintained below the saturated vapor pressure of the gas and a pressure adjusting device configured to adjust the pressure of the gas in the thermal insulation space so as to .

[0007] According to the above configuration, the gas in the insulated space between the inner and outer vessels is maintained at a temperature lower than the saturated vapor pressure of the gas in the insulated space at a reference temperature corresponding to the temperature of the inner vessel or the temperature of the space inside the inner vessel. This allows the condensation temperature of the gas in the insulated space between the inner and outer vessels to be lower than the reference temperature. This prevents condensation of the gas in the insulated space between the inner and outer vessels.

[0008] Also, this Disclosure A multi-shell tank according to another aspect of the present invention includes an outer tank including an inner tank storing a cryogenic liquid therein, a first outer tank accommodating the inner tank, and a second outer tank accommodating the first outer tank, a first heat insulating space provided between the inner tank and the first outer tank, and a second heat insulating space provided between the first outer tank and the second outer tank and filled with a gas. ,before The pressure of the gas in the second insulating space is maintained below the saturated vapor pressure of the gas in the second insulating space at a reference temperature which is a temperature determined based on the temperature of the first outer vessel or the temperature of the first insulating space. and a pressure adjusting device configured to adjust the pressure of the gas in the second insulating space so as to .

[0009] According to the above configuration, the gas in the second insulation space between the first and second outer vessels is maintained at a temperature lower than the saturated vapor pressure of the gas in the second insulation space at the temperature of the first outer vessel or a reference temperature corresponding to the temperature of the first insulation space. This makes it possible to lower the condensation temperature of the gas in the second insulation space between the first and second outer vessels below the reference temperature. This makes it possible to suppress condensation of the gas in the second insulation space between the first and second outer vessels.

[0010] A ship according to one aspect of the present invention includes any one of the multi-shell tanks described above.

[0011] Furthermore, one aspect of the present invention provides a gas pressure adjustment method for adjusting the pressure of gas filled in an insulated space in a multi-shell tank having an inner tank storing a cryogenic liquid therein, one or more outer tanks that house the inner tank, and an insulated space provided between the inner tank and the outer tank and filled with gas, the method measuring the temperature of the inner tank or the temperature of the space inside the inner tank, setting the measured temperature or a temperature determined based on the multiple measured temperatures as a reference temperature, deriving the saturated vapor pressure of the gas in the insulated space at the reference temperature, and maintaining the pressure of the gas in the insulated space below the derived saturated vapor pressure.

[0012] According to the above method, the gas in the insulated space between the inner and outer vessels is maintained at a temperature lower than the saturated vapor pressure of the gas in the insulated space at a reference temperature corresponding to the temperature of the inner vessel or the temperature of the space inside the inner vessel. This makes it possible to lower the condensation temperature of the gas in the insulated space between the inner and outer vessels below the reference temperature. This makes it possible to suppress condensation of the gas in the insulated space between the inner and outer vessels.

[0013] Another aspect of the present invention provides a gas pressure adjustment method for a multi-shell tank, comprising an inner tank containing a cryogenic liquid, a first outer tank accommodating the inner tank, a second outer tank accommodating the first outer tank, a first insulated space provided between the inner tank and the first outer tank, and a second insulated space provided between the first outer tank and the second outer tank and filled with gas, the method adjusting the pressure of the gas filled in the second insulated space, the method measuring the temperature of the first outer tank or the temperature of the first insulated space, setting the measured temperature or a temperature determined based on multiple measured temperatures as a reference temperature, deriving the saturated vapor pressure of the gas in the second insulated space at the reference temperature, and maintaining the pressure of the gas in the second insulated space below the derived saturated vapor pressure.

[0014] According to the above method, the gas in the insulated space between the first and second outer vessels is maintained at a temperature lower than the saturated vapor pressure of the gas in the second insulated space at the temperature of the first outer vessel or a reference temperature corresponding to the temperature of the first insulated space. Therefore, the condensation temperature of the gas in the second insulated space between the first and second outer vessels can be lowered below the reference temperature. Therefore, condensation of the gas in the second insulated space between the first and second outer vessels can be suppressed. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a multi-shell tank, a ship, and a gas pressure adjustment method that can suppress condensation of gas in the space outside an inner tank in which a cryogenic liquid is stored. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic side view of a ship including a multi-shell tank according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the overall configuration of the multi-shell tank shown in FIG. [Figure 3] FIG. 3 is a flowchart showing the flow of gas pressure adjustment in the multi-shell tank shown in FIG. [Figure 4] FIG. 4 is a schematic diagram showing the overall configuration of a multi-shell tank according to a second embodiment of the present invention. [Figure 5] FIG. 5 is a schematic diagram showing the overall configuration of a multi-shell tank according to a third embodiment of the present invention. [Figure 6] FIG. 6 is a schematic diagram showing the overall configuration of a multi-shell tank according to a fourth embodiment of the present invention. [Figure 7] FIG. 7 is a schematic diagram showing the overall configuration of a multi-shell tank according to a fifth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this specification, the term "inside" means the side closer to the center of the space inside the inner vessel of the multi-shell tank, and the term "outside" means the side farther from the center of the space inside the inner vessel of the multi-shell tank.

[0018] First Embodiment FIG. 1 is a schematic side view of a ship 1 including a multi-shell tank 10A according to a first embodiment. The ship 1 is a liquefied gas carrier that transports cryogenic liquid. The ship 1 is equipped with a multi-shell tank 10A. The multi-shell tank 10A includes an inner tank 11 and an outer tank 12 that covers the inner tank 11. Cryogenic liquid is stored in a storage space R1 inside the inner tank 11. The outer tank 12 covers the inner tank 11, thereby forming a sealed insulated space R2 outside the inner tank 11 and inside the outer tank 12.

[0019] In this embodiment and the second to fourth embodiments described below, the inner tub 11 and the outer tub 12 are both spherical. The inner tub 11 and the outer tub 12 do not necessarily have to be spherical. For example, the inner tub 11 and the outer tub 12 may have a shape in which a short cylindrical body is sandwiched between an upper hemisphere, a horizontally placed cylindrical body, or a rectangular body. Alternatively, for example, the inner tub 11 and the outer tub 12 may have a shape that bulges 45 degrees above and / or below the center of the inner tub 11. The shapes of the inner tub 11 and the outer tub 12 may be similar or dissimilar to each other. The centers of the inner tub 11 and the outer tub 12 may coincide with each other, or they may not coincide with each other. For example, the center of the inner tub 11 may be eccentric to the center of the outer tub 12.

[0020] The upper part of the outer tub 12 is covered by a tank cover 13, and the remaining part of the outer tub 12 is covered by a retaining wall 14. The retaining wall 14 is, for example, a part of the hull 2. That is, the retaining wall 14 includes a pair of longitudinal bulkheads extending in the longitudinal direction on both sides of the outer tub 12 in the beam direction, an inner bottom plate extending in the longitudinal direction below the outer tub 12 and above the bottom shell plating of the hull 2, and the like.

[0021] The tank cover 13 and the retaining wall 14 are configured as a single housing structure 15 that houses the outer tub 12. By covering the outer tub 12 with the tank cover 13 and the retaining wall 14, an airtight space is formed inside the tank cover 13 and the retaining wall 14 and outside the outer tub 12. In other words, the tank cover 13 and the retaining wall 14 function as a single outer tub that further covers the outer tub 12. In this specification and claims, the outer tub of a multi-shell tank also includes a housing structure 15 configured with the tank cover and the retaining wall that functions as an outermost tub that forms an airtight space between itself and the inner outer tub.

[0022] The multi-shell tank 10A does not necessarily have to be installed as a cargo tank on the ship 1, but may also be installed as a fuel tank. Although Fig. 1 shows the ship 1 equipped with one multi-shell tank 10A, the ship 1 may be equipped with multiple multi-shell tanks 10A. When the ship 1 is equipped with multiple multi-shell tanks 10A, the bulkhead provided between two adjacent multi-shell tanks 10A is also included in the accommodation structure 15 covering the outer tank 12.

[0023] Fig. 2 is a schematic diagram showing the overall configuration of the multi-shell tank 10A shown in Fig. 1. Fig. 2 includes cross-sectional views of the inner vessel 11 and the outer vessel 12. However, the tank cover 13 and the retaining wall 14 are omitted from Fig. 2. As shown in Fig. 2, the inner vessel 11 separates a storage space R1 inside the inner vessel 11 in which a cryogenic liquid is stored, from an insulating space R2 outside the inner vessel 11 and inside the outer vessel 12. The gas layer in the upper part of the storage space R1 is filled with boil-off gas produced by vaporizing the cryogenic fluid in the storage space R1.

[0024] A heat insulating material is disposed in the heat insulating space R2. For example, the heat insulating material may be granular material such as perlite, or may be a heat insulating panel attached to the surface of the inner tank 11. The heat insulating space R2 is filled with gas. In this embodiment, the type of gas filled in the heat insulating space R2 is the same as the type of boil-off gas in the storage space R1. For example, the cryogenic liquid in the storage space R1 is liquefied hydrogen, and the gas in the heat insulating space R2 is hydrogen gas.

[0025] The multi-shell tank 10A is provided with an inlet passage 21 that introduces the boil-off gas in the inner tank 11, i.e., the boil-off gas in the storage space R1, into the thermally insulated space R2. The inlet passage 21 is provided with an inlet valve 22. The inlet valve 22 functions as a pressure regulator that adjusts the pressure of the gas in the thermally insulated space R2. For example, the inlet valve 22 is an on-off valve. However, the inlet valve 22 may be another type of valve, such as a pressure regulator valve. In this embodiment, the inlet valve 22 is controlled by a control device 33, which will be described later.

[0026] The multi-shell tank 10A also includes an exhaust passage 23 that guides gas within the insulated space R2 to the outside of the insulated space R2, and an exhaust device 24 provided on the exhaust passage 23. One end of the exhaust passage 23 is located within the insulated space R2, and the other end of the exhaust passage 23 is located outside the insulated space R2. The other end of the exhaust passage 23 is connected to another device. Examples of the other device include a propulsion engine, a power generation engine, a reliquefaction device, an incineration device, and a fuel cell. However, the other end of the exhaust passage 23 may be open to the atmosphere.

[0027] The exhaust device 24 functions as a pressure adjusting device that adjusts the pressure of the gas in the thermal insulation space R2. Examples of the exhaust device 24 include a compressor and an exhaust pump such as a vacuum pump. In this embodiment, the exhaust device 24 is controlled by a control device 33, which will be described later.

[0028] The multi-shell tank 10A also includes a relief passage 25 that guides gas within the insulated space R2 to the outside of the insulated space R2, and a relief valve 26 provided in the relief passage 25. One end of the relief passage 25 is located within the insulated space R2, and the other end of the relief passage 25 is located outside the insulated space R2. The other end of the relief passage 25 is connected to another device. Examples of the other device include a propulsion engine, a power generation engine, a reliquefaction device, an incineration device, and a fuel cell. The pressure around the other end of the relief passage 25 is near atmospheric pressure. The other end of the relief passage 25 may be open to the atmosphere.

[0029] The relief valve 26 functions as a pressure adjusting device that adjusts the pressure of the gas in the insulating space R2. For example, the relief valve 26 is an on-off valve. However, the relief valve 26 may be another type of valve, such as a pressure adjusting valve. In this embodiment, the relief valve 26 is controlled by a control device 33, which will be described later. Note that instead of providing the relief valve 26 in the relief path 25, a rupture disk or the like that does not involve control may be provided.

[0030] The multi-shell tank 10A includes five thermometers 31, a pressure gauge 32, and a control device 33.

[0031] The five thermometers 31 measure the temperature of the storage space R1. The five thermometers 31 are provided at multiple locations within the storage space R1. Specifically, the five thermometers 31 are arranged in five regions obtained by vertically dividing the storage space R1 within the inner tank 11 into five equal parts. More specifically, the five thermometers 31 are arranged within a pipe tower (not shown). For example, the topmost of the five thermometers 31 is arranged in the gas layer within the inner tank 11 to measure the temperature of the boil-off gas, and the other four thermometers 31 are arranged in the liquid layer within the inner tank 11 to measure the temperature of the cryogenic liquid. The five thermometers 31 are communicably connected to a control device 33. Information on the temperatures measured by the five thermometers 31 is sent to the control device 33.

[0032] The pressure gauge 32 measures the pressure of the gas in the insulating space R2. The pressure gauge 32 is communicably connected to the control device 33. Information on the pressure measured by the pressure gauge 32 is sent to the control device 33.

[0033] The control device 33 is a so-called computer, and has an arithmetic processing unit such as a CPU, and storage units such as a ROM and RAM (neither of which are shown). The storage unit stores programs executed by the arithmetic processing unit, various fixed data, etc. The arithmetic processing unit transmits and receives data to and from external devices. In the control device 33, the arithmetic processing unit reads and executes a predetermined gas pressure adjustment program stored in the storage unit, thereby performing a gas pressure adjustment process for adjusting the gas pressure in the insulating space R2. The storage unit pre-stores correspondence relationship information indicating the relationship between the temperature and saturated vapor pressure of the gas whose pressure is to be adjusted.

[0034] The pressure of the gas in the insulating space R2 is maintained below the saturated vapor pressure Ps of the gas in the insulating space R2 at a reference temperature T. The reference temperature T is a temperature determined based on the temperatures measured by the five thermometers 31. In this embodiment, the lowest temperature among the temperatures measured by the five thermometers 31 is set as the reference temperature T.

[0035] The control device 33 adjusts the pressure of the gas in the insulating space R2 so that the pressure is maintained below the saturated vapor pressure Ps of the gas in the insulating space R2 at the reference temperature T. Specifically, the control device 33 controls the exhaust device 24 and / or the relief valve 26 so that the pressure P measured by the pressure gauge 32 is less than the saturated vapor pressure Ps of the gas in the insulating space R2 at the reference temperature T. More specifically, the control device 33 adjusts the pressure P measured by the pressure gauge 32 so that the pressure P is less than the saturated vapor pressure Ps of the gas in the insulating space R2 at the reference temperature T. up The exhaust device 24 and / or the relief valve 26 are controlled so that the pressure is equal to or less than (=Ps-ΔP1).

[0036] The control device 33 also determines whether the pressure P measured by the pressure gauge 32 is equal to or lower than the saturated vapor pressure Ps by a second differential pressure ΔP2. lowThe introduction valve 22 is controlled so that the second differential pressure ΔP2 is equal to or greater than (=Ps−ΔP2). The second differential pressure ΔP2 is greater than the first differential pressure ΔP1. The set lower limit pressure is preferably set to 1 kPa or greater.

[0037] The first differential pressure ΔP1 is preferably set in the range of 3 kPa or more and 70 kPa or less. The second differential pressure ΔP2 is preferably set in the range of 10 kPa or more and 100 kPa or less. The set upper limit pressure P up and the set lower limit pressure P low The difference between these two pressures, that is, the pressure difference obtained by subtracting the first pressure difference ΔP1 from the second pressure difference ΔP2, is preferably set within a range of 0 kPa or more and 30 kPa or less.

[0038] FIG. 3 is a flowchart showing the flow of the gas pressure adjustment process in the heat insulating space R2 in the multi-shell tank 10A shown in FIG.

[0039] In the gas pressure adjustment process, the control device 33 first acquires the temperatures measured by the five thermometers 31 from the five thermometers 31 (step S1).

[0040] The control device 33 determines the lowest temperature among the temperatures measured by the five thermometers 31 as the reference temperature T (step S2).

[0041] The control device 33 calculates the saturated vapor pressure Ps of the gas in the insulating space R2 at the determined reference temperature T (step S3). Correspondence information indicating the relationship between the temperature and saturated vapor pressure of the gas (hydrogen in this example) in the insulating space R2 is stored in advance in the memory unit of the control device 33. The calculation processing unit of the control device 33 uses the correspondence information stored in the memory unit to derive the saturated vapor pressure corresponding to the reference temperature T determined in step S2.

[0042] The control device 33 acquires the pressure P measured by the pressure gauge 32, that is, the gas pressure P in the insulating space R2, from the pressure gauge 32 (step S4).

[0043] The control device 33 determines whether the acquired pressure P is greater than the pressure obtained by subtracting a preset first differential pressure ΔP1 from the saturated vapor pressure Ps (step S5). Specifically, the control device 33 subtracts the preset first differential pressure ΔP1 from the saturated vapor pressure Ps derived in step S3 to obtain the set upper limit pressure P up Then, the control device 33 calculates whether the acquired pressure P is equal to or lower than the set upper limit pressure P up Determine whether it is greater than or equal to the value.

[0044] The acquired pressure P is the set upper limit pressure P up If it is determined that the pressure P is greater than the pressure P (step S5: YES), the control device 33 determines whether the acquired pressure P is a negative pressure (step S6).

[0045] When it is determined that the acquired pressure P is a negative pressure (step S6: YES), the control device 33 operates the exhaust device 24 so as to reduce the gas pressure in the heat insulating space R2 (step S7).

[0046] When it is determined that the acquired pressure P is not a negative pressure (step S6: NO), the control device 33 opens the relief valve 26 so as to reduce the gas pressure in the insulating space R2 (step S8).

[0047] The acquired pressure P is the set upper limit pressure P up If it is determined that the difference is not greater than the predetermined value (step S5: NO), the control device 33 stops the exhaust device 24 and closes the relief valve 26 (step S9). If the exhaust device 24 is already stopped, the control device 33 keeps the exhaust device 24 stopped. Also, if the relief valve 26 is already closed, the control device 33 keeps the relief valve 26 closed.

[0048] After steps S7, S8, and S9, the control device 33 determines whether the acquired pressure P is less than the pressure obtained by subtracting a preset second differential pressure ΔP2 from the saturated vapor pressure Ps (step S10). Specifically, the control device 33 subtracts the preset second differential pressure ΔP2 from the saturated vapor pressure Ps derived in step S3 to obtain the set lower limit pressure P lowThen, the control device 33 calculates whether the acquired pressure P is equal to or lower than the set lower limit pressure P low It is determined whether it is less than or equal to the value.

[0049] The acquired pressure P is the set lower limit pressure P low If it is determined that the pressure P is less than the set lower limit pressure P (step S10: YES), the control device 33 opens the introduction valve 22 so that the gas pressure in the heat insulating space R2 increases (step S11), and ends the gas pressure adjustment process. low If it is determined that the gas pressure is not less than the predetermined value (step S10: NO), the control device 33 closes the introduction valve 22 (step S12) and ends the gas pressure adjustment process. If the introduction valve 22 is already closed, the control device 33 keeps the introduction valve 22 closed.

[0050] The control device 33 repeats the gas pressure adjustment process of steps S1 to S12 to adjust the gas pressure in the heat insulating space R2 to the set lower limit pressure P low Above the set upper limit pressure P up Maintain within the following ranges:

[0051] As described above, in this embodiment, the gas in the insulating space R2 is maintained at a temperature lower than the saturated vapor pressure Ps of the gas in the insulating space R2 at the temperature of the inner tank 11 or the reference temperature T corresponding to the temperature inside the inner tank 11. Therefore, the condensation temperature of the gas in the insulating space R2 can be made lower than the reference temperature T. Therefore, condensation of the gas in the insulating space R2 between the inner tank 11 and the outer tank 12 can be suppressed.

[0052] In this embodiment, the gas pressure P in the heat insulating space R2 is set to a set upper limit pressure P that is lower than the saturated vapor pressure Ps by a first differential pressure ΔP1. up In this way, by providing a margin of the first differential pressure ΔP1 with respect to the saturated vapor pressure Ps, condensation of the gas in the insulating space R2 can be suppressed even if the reference temperature T fluctuates, such as immediately after the reference temperature T drops.

[0053] In this embodiment, the control device 33 controls the various pressure adjusting devices so that the pressure P measured by the pressure gauge 32 is less than the saturated vapor pressure Ps of the gas in the insulating space R2 at the reference temperature T. This makes it possible to monitor and adjust the pressure of the gas in the insulating space R2 in real time.

[0054] In this embodiment, the lowest temperature among the temperatures measured by the multiple thermometers 31 is determined as the reference temperature T. The lowest temperature on the outer surface of the inner tank 11 can be accurately predicted, and as a result, a gas pressure range in the insulation space R2 appropriate for suppressing condensation of gas in the insulation space R2 can be derived.

[0055] In addition, in this embodiment, the exhaust device 24 can exhaust the gas in the insulating space R2 to the outside of the insulating space R2, so that the pressure in the insulating space R2 can be reduced even if the gas pressure P in the insulating space R2 is negative pressure.

[0056] Furthermore, in this embodiment, when the gas pressure P in the thermal insulation space R2 is positive, the gas in the thermal insulation space R2 can be discharged to the outside of the thermal insulation space R2 by the relief valve 26. Therefore, the pressure in the thermal insulation space R2 can be reduced with little power.

[0057] In this embodiment, the gas in the heat insulating space R2 is kept at a set lower limit pressure P that is lower than the saturated vapor pressure Ps of the gas at the temperature of the inner vessel 11 or a reference temperature T corresponding to the temperature in the inner vessel 11 by a predetermined pressure (second differential pressure ΔP2). low This keeps the pressure difference between the storage space R1 and the thermal insulation space R2 in the inner tank 11 small while suppressing condensation of gas in the thermal insulation space R2. This reduces the strength required for the multi-shell tank 10A.

[0058] Second Embodiment 4 is a schematic diagram showing the overall configuration of a multi-shell tank 10B according to the second embodiment. In this embodiment and the third to fifth embodiments described later, the same or similar members as those in the first embodiment are designated by the same reference numerals in the drawings, and detailed description thereof will be omitted.

[0059] In the multi-shell tank 10B shown in Fig. 4, the type of gas filled in the insulation space R2 is different from the type of boil-off gas in the storage space R1. For example, the cryogenic liquid in the storage space R1 is liquefied hydrogen, and the gas in the insulation space R2 is nitrogen gas.

[0060] Furthermore, since the type of gas filled in the insulating space R2 and the type of boil-off gas in the storage space R1 are different from each other, the multi-shell tank 10B does not have an inlet passage 21 for introducing the boil-off gas in the storage space R1 into the insulating space R2, nor an inlet valve 22 provided in the inlet passage 21.

[0061] Furthermore, correspondence relationship information indicating the relationship between the temperature and saturated vapor pressure of the gas (nitrogen gas in this example) whose pressure is to be adjusted is stored in advance in the storage unit of the control device 33. The gas adjustment process of this embodiment is the same as the gas adjustment process described in the first embodiment except that steps S10 to S12 are omitted, and therefore description thereof will be omitted.

[0062] In this embodiment, the same effects as in the first embodiment can be obtained.

[0063] Third Embodiment Fig. 5 is a cross-sectional view showing the overall configuration of a multi-shell tank 40A according to a third embodiment. In the multi-shell tank 40A shown in Fig. 5, the outer tank 12, which covers the inner tank 11, is further covered by another outer tank 41. The outer tank 41 may be the storage structure 15 formed by the tank cover 13 and retaining wall 14 described above, or may be a separate member from the tank cover 13 and retaining wall 14, disposed outside the outer tank 12 and inside the tank cover 13 and retaining wall 14. In the following description, the outer tank 12 and the outer tank 41 covering it will be referred to as the first outer tank 12 and the second outer tank 41, respectively.

[0064] The second outer tank 41 covers the first outer tank 12, thereby forming a sealed heat-insulating space R3 outside the first outer tank 12 and inside the second outer tank 41. That is, the first outer tank 12 separates the heat-insulating space R2 inside the first outer tank 12 from the heat-insulating space R3 outside the first outer tank 12 and inside the second outer tank 41. In the following description, the heat-insulating space R2 between the inner tank 11 and the first outer tank 12, and the heat-insulating space R3 between the first outer tank 12 and the second outer tank 41 will be referred to as the first heat-insulating space R2 and the second heat-insulating space R3, respectively.

[0065] The first insulation space R2 and the second insulation space R3 are filled with a thermal insulator. Unlike the first and second embodiments, this embodiment adjusts the gas pressure in the second insulation space R3 between the first outer tank 12 and the second outer tank 41, rather than the gas pressure in the first insulation space R2 between the inner tank 11 and the first outer tank 12.

[0066] In this embodiment, the type of gas filled in the second insulation space R3 is different from the type of gas filled in the first insulation space R2. In this embodiment, for example, liquefied hydrogen is stored in the storage space R1, hydrogen gas is filled in the first insulation space R2, and nitrogen gas is filled in the second insulation space R3. However, the type of gas filled in the second insulation space R3 may be the same as the type of gas filled in the first insulation space R2. For example, hydrogen gas may be filled in both the first insulation space R2 and the second insulation space R3.

[0067] The multi-shell tank 40A includes an exhaust passage 43 that guides gas within the second insulated space R3 to the outside of the second insulated space R3, and an exhaust device 44 provided on the exhaust passage 43. One end of the exhaust passage 43 is located within the second insulated space R3, and the other end of the exhaust passage 43 is located outside the second insulated space R3. The other end of the exhaust passage 43 is connected to another device. Examples of the other device include a propulsion engine, a power generation engine, a reliquefaction device, an incineration device, and a fuel cell. The other end of the exhaust passage 43 may be open to the atmosphere.

[0068] The exhaust device 44 functions as a pressure adjusting device that adjusts the pressure of the gas in the second insulation space R3. Examples of the exhaust device 44 include a compressor and an exhaust pump such as a vacuum pump. In this embodiment, the exhaust device 44 is controlled by the control device 33, which will be described later.

[0069] The multi-shell tank 40A also includes a relief passage 45 that guides gas in the second insulation space R3 to the outside of the second insulation space R3, and a relief valve 46 provided in the relief passage 45. One end of the relief passage 45 is located within the second insulation space R3, and the other end of the relief passage 45 is located outside the second insulation space R3. The other end of the relief passage 45 is connected to another device. Examples of the other device include a propulsion engine, a power generation engine, a reliquefaction device, an incineration device, and a fuel cell. The pressure around the other end of the relief passage 45 is near atmospheric pressure. The other end of the relief passage 45 may be open to the atmosphere.

[0070] The relief valve 46 functions as a pressure adjusting device that adjusts the pressure of the gas in the second insulation space R3. For example, the relief valve 46 is an on-off valve. However, the relief valve 46 may be another type of valve, such as a pressure adjusting valve. In this embodiment, the relief valve 46 is controlled by a control device 33, which will be described later.

[0071] The multi-shell tank 40A includes five thermometers 51, a pressure gauge 52, and a control device 33.

[0072] The five thermometers 51 measure the temperature in the first insulating space R2. The five thermometers 51 are provided at multiple locations in the first insulating space R2. Specifically, the five thermometers 51 are arranged in five regions obtained by dividing the first insulating space R2 into five equal parts in the vertical direction. The five thermometers 51 are communicably connected to the control device 33. Information on the temperatures measured by the five thermometers 51 is sent to the control device 33.

[0073] The pressure gauge 52 measures the pressure of the gas in the second insulating space R3. The pressure gauge 52 is communicably connected to the control device 33. Information on the pressure measured by the pressure gauge 52 is sent to the control device 33.

[0074] In this embodiment, in the control device 33, a gas pressure adjustment process for adjusting the gas pressure in the second insulation space R3 is performed by having the calculation processing unit read and execute a predetermined gas pressure adjustment program stored in the memory unit.

[0075] The pressure of the gas in the second insulating space R3 is maintained below the saturated vapor pressure Ps of the gas in the second insulating space R3 at a reference temperature T. The reference temperature T is a temperature determined based on temperatures measured by the five thermometers 51. In this embodiment, the lowest temperature among the temperatures measured by the five thermometers 51 is set as the reference temperature T.

[0076] The control device 33 adjusts the pressure of the gas in the second insulating space R3 so that the pressure is maintained below the saturated vapor pressure Ps of the gas in the second insulating space R3 at the reference temperature T. Specifically, the control device 33 controls the exhaust device 44 and / or the relief valve 46 so that the pressure P measured by the pressure gauge 52 is less than the saturated vapor pressure Ps of the gas in the second insulating space R3 at the reference temperature T. More specifically, the control device 33 adjusts the pressure P measured by the pressure gauge 52 so that the pressure P is less than the saturated vapor pressure Ps of the gas in the second insulating space R3 at the reference temperature T. up The exhaust device 44 and / or the relief valve 46 are controlled so that the pressure is equal to or less than (=Ps-ΔP1).

[0077] The gas pressure adjustment process in this embodiment can be explained by replacing steps S1 to S9 of the gas pressure adjustment process in the first embodiment with the storage space R1 as the first insulated space R2, the insulated space R2 as the second insulated space R3, the exhaust device 24 as the exhaust device 44, the relief valve 26 as the relief valve 46, the thermometer 31 as the thermometer 51, and the pressure gauge 32 as the pressure gauge 52. Therefore, a detailed explanation of the gas pressure adjustment process in this embodiment will be omitted.

[0078] In this embodiment, the gas in the second insulation space R3 is maintained at a temperature lower than the saturated vapor pressure Ps of the gas at a reference temperature T corresponding to the temperature of the first outer tank 12 or the temperature in the first insulation space R2. This makes it possible to lower the condensation temperature of the gas in the second insulation space R3 below the reference temperature T. This makes it possible to suppress condensation of the gas in the second insulation space R3 between the first outer tank 12 and the second outer tank 41.

[0079] <Fourth embodiment> Fig. 6 is a schematic diagram showing the overall configuration of a multi-shell tank 40B according to a fourth embodiment. As shown in Fig. 6, the multi-shell tank 40B of this embodiment is a combination of the configurations of the first and third embodiments.

[0080] That is, similar to the first embodiment, the multi-shell tank 40B includes an inner tank 11, an outer tank 12, an inlet passage 21, an inlet valve 22, an exhaust passage 23, an exhaust device 24, a relief passage 25, a relief valve 26, five thermometers 31, a pressure gauge 32, and a control device 33. Also, similar to the third embodiment, the multi-shell tank 40B includes an outer tank 41, an exhaust passage 43, an exhaust device 44, a relief passage 45, a relief valve 46, five thermometers 51, and a pressure gauge 52.

[0081] In this embodiment, the type of gas filled in the first insulation space R2 is the same as the type of boil-off gas in the storage space R1 but is different from the type of gas filled in the second insulation space R3. In this embodiment, for example, liquefied hydrogen is stored in the storage space R1, hydrogen gas is filled in the first insulation space R2, and nitrogen gas is filled in the second insulation space R3. However, the type of gas filled in the first insulation space R2 and the type of boil-off gas in the storage space R1 may be different from each other. Furthermore, the type of gas filled in the second insulation space R3 may be the same as the type of gas filled in the first insulation space R2. For example, hydrogen gas may be filled in both the first insulation space R2 and the second insulation space R3.

[0082] In this embodiment, a gas pressure adjustment process for adjusting the gas pressure in the first insulation space R2 and a gas pressure adjustment process for adjusting the gas pressure in the second insulation space R3 are performed by having the calculation processing unit read and execute a predetermined gas pressure adjustment program stored in the storage unit in the control device 33. That is, the gas pressure adjustment process for adjusting the gas pressure in the first insulation space R2 and the gas pressure adjustment process for adjusting the gas pressure in the second insulation space R3 are the same as the gas pressure adjustment processes in the first and third embodiments, respectively, and therefore detailed description thereof will be omitted.

[0083] In this embodiment, the same effects as those in the first and third embodiments can be obtained.

[0084] Fifth Embodiment 7 is a schematic diagram showing the overall configuration of a multi-shell tank 60 according to a fifth embodiment. In this embodiment, the multi-shell tank 60 is a membrane-type tank installed on a ship.

[0085] The multi-shell tank 60 includes a primary membrane 61 that contains a cryogenic liquid, a secondary membrane 62 that covers the primary membrane 61, and an inner hull 63 that further covers the secondary membrane 62. The inner hull 63 is part of the hull of the ship.

[0086] A cryogenic liquid is stored in a storage space R1 inside the primary membrane 61. A sealed first insulation space R2 (so-called inter-barrier space (IBS)) is formed between the primary membrane 61 and the secondary membrane 62. A thermal insulator is arranged in the first insulation space R2. A sealed second insulation space R3 (so-called insulation space (IS)) is formed between the secondary membrane 62 and the inner hull 63. A thermal insulator is arranged in the second insulation space R3. In this embodiment, the primary membrane 61 functions as an inner tank in which a cryogenic liquid is stored, the secondary membrane 62 functions as an outer tank that houses the primary membrane 61 as the inner tank, and the inner hull 63 functions as an outer tank that further covers the secondary membrane 62 as the outer tank.

[0087] The primary membrane 61 and the secondary membrane 62 do not themselves have the strength to support the pressure and weight of the cryogenic liquid in the primary membrane 61. The pressure and weight of the cryogenic liquid in the primary membrane 61 are supported by the hull via the insulating material in the first insulating space R2 and the insulating material in the second insulating space R3.

[0088] In this embodiment, for example, liquefied hydrogen is stored in the storage space R1, hydrogen gas is filled in the first heat insulation space R2, and nitrogen gas is filled in the second heat insulation space R3.

[0089] In this embodiment, as in the first embodiment, the gas pressure in the first insulating space R2, which is immediately outside the storage space R1, is adjusted. The method for adjusting the gas pressure in the first insulating space R2 is substantially the same as the method for adjusting the gas pressure in the insulating space R2 in the first embodiment. That is, as in the first embodiment, the multi-shell tank 60 includes an exhaust path 23, an exhaust device 24, a relief path 25, a relief valve 26, five thermometers 31, a pressure gauge 32, and a control device 33. The gas pressure adjustment method is substantially the same as in the first embodiment, so a description thereof will be omitted.

[0090] In this embodiment, the same effects as in the first embodiment can be obtained.

[0091] <Other embodiments> The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention.

[0092] For example, in the above embodiment, the lowest temperature among the temperatures measured by the multiple thermometers 31 (or 51) was determined as the reference temperature T, but the method of determining the reference temperature in the present invention is not limited to this. For example, the average temperature of the temperatures measured by the multiple thermometers may be determined as the reference temperature. For example, in the first, second, fourth, and fifth embodiments, the lowest temperature on the outer surface of the inner tank 11 or 61 may be estimated using a predetermined calculation formula from the temperatures measured by the multiple thermometers 31, and the estimated temperature may be set as the reference temperature T. For example, in the third embodiment, the lowest temperature on the outer surface of the first outer tank 12 may be estimated using a predetermined calculation formula from the temperatures measured by the multiple thermometers 51, and the estimated temperature may be set as the reference temperature T.

[0093] In the first, second, fourth, and fifth embodiments, five thermometers 31 are provided in the interior space of the inner tank 11, but the number of thermometers is not limited to this. For example, one thermometer may be provided in the inner tank 11, and the temperature measured by that thermometer may be used as the reference temperature. Even if multiple thermometers are provided in the inner tank 11, only the temperature measured by a predetermined thermometer (e.g., the thermometer located at the bottom) may be used to determine the reference temperature. Furthermore, the one or more thermometers in the present invention do not necessarily need to measure the temperature inside the inner tank, but may instead measure the temperature of the inner tank (e.g., the surface temperature of the inner tank). Similarly, in the third embodiment, the number of thermometers 51 provided in the first insulation space R1 is not limited to five, and the thermometer 51 may measure the temperature of the first outer tank 12 (e.g., the surface temperature of the first outer tank 12).

[0094] In the above embodiment, the first differential pressure ΔP1, the second differential pressure ΔP2, and the set upper limit pressure P up and the set lower limit pressure P low Although a preferred range of values ​​has been shown for the difference between the set lower limit pressure P low The lower limit pressure P may not be set based on the derived saturated vapor pressure Ps. lowmay be a preset design pressure allowed by the structural strength of the multi-shell tank. One or both of the first differential pressure ΔP1 and the second differential pressure ΔP2 may be a preset fixed value or may be changed depending on the derived saturated vapor pressure Ps.

[0095] The pressure around the other end of the relief passage 25, 45 does not have to be near atmospheric pressure, but may be near a predetermined pressure that deviates from atmospheric pressure. In this case, in step S6 of the gas adjustment process shown in FIG. 3, the control device 33 may determine whether the acquired pressure P is less than the predetermined pressure.

[0096] In the above embodiment, the pressure regulating device is an exhaust device, a relief valve, and an introduction valve, but the pressure regulating device is not limited to these. The multi-shelled tank may include only one of the exhaust device and the relief valve as a pressure regulating device for reducing the pressure in the insulated space. Furthermore, the multi-shelled tank may include a gas supply device other than the introduction valve as a pressure regulating device for supplying gas to the insulated space to increase the pressure therein.

[0097] Further, the exhaust path 23 and the relief path 25 may be provided with check valves to prevent backflow of gas into the (first) insulation space R2, and the exhaust path 43 and the relief path 25 may be provided with check valves to prevent backflow of gas into the second insulation space R3. Further, the introduction path 21 may be provided with a check valve to prevent backflow of gas into the storage space R1.

[0098] The multi-shell tank of the present invention does not need to be equipped with the control device 33. That is, the gas pressure regulating method of the present invention does not need to be electrically controlled by a computer, but may be performed by an operator or the like. In this case, in the first, second, fourth, and fifth embodiments, the pressure regulating device that regulates the gas pressure in the insulated space between the inner and outer vessels may be a manual type controlled by an operator, or may be a mechanical control valve whose settings can be changed by an operator.

[0099] For example, before the ship 1 departs port, an operator may measure the temperature of the inner tank or inside the inner tank, determine a reference temperature based on the measured temperature, and derive the saturated vapor pressure of the gas to be filled in the insulated space between the inner tank and the outer tank from the determined reference temperature. Then, the operator may fill the insulated space with gas so that the gas pressure in the insulated space is maintained below the derived saturated vapor pressure of the gas in the insulated space.

[0100] For example, if the pressure adjustment device is manual, when the pressure value of the gas in the insulated space measured by the pressure gauge exceeds a set upper limit pressure that is lower than the derived saturated vapor pressure by a first differential pressure, the operator may operate the manual pressure adjustment device so that the pressure value of the gas in the insulated space becomes equal to or lower than the set upper limit pressure.

[0101] Alternatively, for example, if the pressure adjustment device is a mechanical control valve, the operator may change the setting of the mechanical control valve so that the pressure is less than the saturated vapor pressure of the gas in the thermal insulation space. For example, if the relief valve 26 in the above embodiment is a mechanical control valve that opens in response to the pressure of the gas in the thermal insulation space, the operator may set the set pressure at which the relief valve 26 opens to less than the derived saturated vapor pressure (for example, equal to or less than a set upper limit pressure that is lower than the derived saturated vapor pressure by a first differential pressure).

[0102] After the ship departs port, it is not necessary to adjust the gas pressure in the insulated space. For example, by adjusting the gas pressure in the insulated space in advance during gas filling so that it can be maintained throughout the voyage at or below a set upper limit value that is lower by the first differential pressure than the saturated vapor pressure of the gas at the reference temperature during gas filling, it is possible to suppress condensation of the gas in the insulated space even if the temperature inside the inner tank fluctuates while the ship is sailing.

[0103] As with the pressure adjustment of the heat-insulating space between the inner and outer tanks described above, the pressure adjustment of the heat-insulating space between the two outer tanks does not have to be performed by a computer, but may be performed by an operator, etc. For example, in the third and fourth embodiments described above, the pressure adjustment device that adjusts the gas pressure in the heat-insulating space between the first and second outer tanks may be a manual type, or may be a mechanical control valve whose settings can be changed by an operator.

[0104] The configurations of the first to fifth embodiments can be combined as appropriate. For example, in the fifth embodiment, the multi-shelled tank 60 is shown in which the gas pressure in the first insulation space R2 is adjusted. However, the multi-shelled tank 60 may be configured so that the gas pressure in the second insulation space R3 is adjusted instead of or in addition to adjusting the gas pressure in the first insulation space R2. That is, the multi-shelled tank 60 may include the exhaust path 43, the exhaust device 44, the relief path 45, the relief valve 46, the five thermometers 31, and the pressure gauge 52 shown in the third and fourth embodiments, instead of or in addition to the exhaust path 23, the exhaust device 24, the relief path 25, the relief valve 26, the five thermometers 31, and the pressure gauge 32.

[0105] The number of outer tanks provided in a multi-shell tank is not limited to that described in the above embodiment. For example, in a multi-shell tank having three or more outer tanks, the "first outer tank" in the present invention does not have to be the outer tank closest to the inner tank, but may be the second outer tank or later from the inside, and the "second outer tank" may be the third outer tank or later from the inside.

[0106] The cryogenic liquid stored in the inner tank is not limited to that described in the above embodiment. For example, the cryogenic liquid stored in the inner tank may be liquefied hydrogen, liquefied natural gas, liquefied nitrogen, liquefied helium, etc. For example, the gas filled between the inner tank and the outer tank or between the two outer tanks may be hydrogen gas, natural gas, nitrogen gas, helium, dry air, etc. The types of gas filled in both the space where the temperature is measured and the space where the pressure is adjusted based on the reference temperature may be the same or different.

[0107] In the above embodiment, the multi-shell tank is provided on a ship, but the multi-shell tank may also be installed on land.

[0108] A first aspect of the multi-shell tank comprises an inner tank storing a cryogenic liquid therein, one or more outer tanks accommodating the inner tank, and an insulated space filled with gas provided between the inner tank and the outer tank, wherein the pressure of the gas in the insulated space is maintained below the saturated vapor pressure of the gas in the insulated space at a reference temperature determined based on the temperature of the inner tank or the temperature of the space inside the inner tank. The multi-shell tank may further comprise one or more thermometers measuring the temperature of the inner tank or the temperature of the space inside the inner tank, and the reference temperature may be determined based on the temperature measured by the one thermometer or the temperatures measured by the multiple thermometers.

[0109] The outer vessel may include a first outer vessel and a second outer vessel that houses the first outer vessel, the insulated space may be a first insulated space provided between the first outer vessel and the inner vessel, the multi-shell tank may include a second insulated space provided between the first outer vessel and the second outer vessel and filled with a gas, the reference temperature may be a first reference temperature, and the pressure of the gas in the second insulated space may be maintained below the saturated vapor pressure of the gas in the second insulated space at a second reference temperature that is a temperature determined based on the temperature of the first outer vessel or the temperature of the first insulated space.

[0110] According to the above configuration, the gas in the first insulation space between the first outer vessel and the second outer vessel is maintained at a temperature lower than the saturated vapor pressure of the gas in the second insulation space at the temperature of the first outer vessel or a reference temperature corresponding to the temperature of the first insulation space. Therefore, the condensation temperature of the gas in the second insulation space between the first outer vessel and the second outer vessel can be lowered below the reference temperature, thereby suppressing condensation of the gas in the second insulation space. Therefore, condensation of the gas in the first insulation space between the inner vessel and the first outer vessel can be suppressed while suppressing condensation of the gas in the second insulation space.

[0111] The multi-shell tank of the first aspect described above may be provided with one or more second thermometers that measure the temperature of the first outer tank or the temperature of the first insulated space, and the reference temperature may be a temperature determined based on the temperature measured by the one second thermometer or the temperatures measured by the multiple second thermometers.

[0112] The multi-shell tank of the first aspect may further include a pressure gauge that measures the pressure of the gas in the insulated space, a pressure regulator that adjusts the pressure of the gas in the insulated space, and a control device that controls the pressure regulator so that the pressure measured by the pressure gauge is less than the saturated vapor pressure of the gas in the insulated space at the reference temperature, thereby enabling real-time monitoring and adjustment of the gas pressure in the insulated space.

[0113] In the multi-shell tank of the first aspect, the plurality of thermometers may be provided at a plurality of locations inside the inner tank, and the control device may determine the lowest temperature among the temperatures measured by the plurality of thermometers as the reference temperature, thereby deriving a gas pressure range in the insulated space appropriate for suppressing condensation of gas in the insulated space.

[0114] The multi-shell tank of the first aspect may further include an exhaust passage connecting the inside and outside of the insulated space, and the pressure regulating device may include an exhaust device that is provided in the exhaust passage and that, when activated, exhausts the gas in the insulated space to the outside of the insulated space. This allows the pressure inside the insulated space to be reduced even when the gas pressure P in the insulated space is negative.

[0115] The multi-shell tank of the first aspect may further include an exhaust passage connecting the inside and outside of the insulated space, and the pressure regulating device may include a relief valve provided in the exhaust passage and opening to release gas from the insulated space to the outside of the insulated space, thereby making it possible to easily reduce the pressure inside the insulated space when the gas pressure inside the insulated space is positive.

[0116] In the multi-shell tank of the first aspect, the insulated space may be filled with the same type of gas as the gas inside the inner tank, the multi-shell tank may have an inlet passage for introducing the gas inside the inner tank into the insulated space, and the pressure regulating device may include an inlet valve provided in the inlet passage. This allows the gas pressure inside the insulated space to be adjusted using the gas inside the inner tank.

[0117] In the multi-shell tank of the first aspect, the control device may control the pressure regulating device so that the pressure measured by the pressure gauge is less than the saturated vapor pressure of the gas in the insulated space at the reference temperature and equal to or greater than a lower limit pressure that is lower than the saturated vapor pressure by a predetermined pressure. This makes it possible to suppress condensation of the gas in the insulated space while maintaining a small pressure difference between the interior of the inner tank and the insulated space. This reduces the strength required of the multi-shell tank. [Explanation of symbols]

[0118] 1: Ship 2: Hull 10A: Multi-shell tank 10B: Multi-shell tank 11: Inner tank 12: Outer tank 13: Tank cover 14: Retaining wall 15: Housing structure 21:Introduction path 22: Inlet valve 23: Exhaust duct 24: Exhaust system 25: Escape route 26: Relief valve 31:Thermometer 32: Pressure gauge 33: Control device 40A: Multi-shell tank 40B: Multi-shell tank 41: Outer tank 43: Exhaust duct 44: Exhaust system 45: Escape route 46: Relief valve 51: Thermometer 52: Pressure gauge 60: Multi-shell tank 61: Primary membrane (inner tank) 62: Secondary membrane (outer tank) 63: Inner hull (outer tank)

Claims

1. an inner tank storing a cryogenic liquid therein; One or more outer tanks that house the inner tank; a heat insulating space provided between the inner tank and the outer tank and filled with gas; a pressure regulating device configured to adjust the pressure of the gas in the insulated space so that the pressure of the gas in the insulated space is maintained below the saturated vapor pressure of the gas in the insulated space at a reference temperature, which is a temperature determined based on the temperature of the inner tank or the temperature of the space inside the inner tank.

2. the multi-shell tank is provided with one or more thermometers for measuring the temperature of the inner tank or the temperature of the space inside the inner tank; 2. The multi-shell tank according to claim 1, wherein the reference temperature is a temperature determined based on the temperature measured by the one thermometer or the temperatures measured by the plurality of thermometers.

3. The outer tank includes a first outer tank and a second outer tank that accommodates the first outer tank, the heat insulating space is a first heat insulating space provided between the first outer tank and the inner tank, the multi-shell tank includes a second insulating space provided between the first outer shell and the second outer shell and filled with a gas, the reference temperature is a first reference temperature, 3. The multi-shell tank according to claim 1, wherein the pressure of the gas in the second insulating space is maintained below the saturated vapor pressure of the gas in the second insulating space at a second reference temperature, which is a temperature determined based on the temperature of the first outer vessel or the temperature of the first insulating space.

4. the multi-shell tank is provided with one or more second thermometers that measure the temperature of the first outer tank or the temperature of the first insulating space; 4. The multi-shell tank according to claim 3, wherein the reference temperature is a temperature determined based on the temperature measured by the one second thermometer or the temperatures measured by the plurality of second thermometers.

5. a pressure gauge that measures the pressure of the gas in the thermal insulation space; 5. The multi-shell tank according to claim 1, further comprising: a control device that controls the pressure regulating device so that the pressure measured by the pressure gauge is less than the saturated vapor pressure of the gas in the insulated space at the reference temperature.

6. the plurality of thermometers are provided at a plurality of locations inside the inner tank, 6. The multi-shell tank according to claim 5, wherein the control device determines the lowest temperature among the temperatures measured by the plurality of thermometers as the reference temperature.

7. an exhaust path for guiding gas in the heat-insulating space to the outside of the heat-insulating space; 7. The multi-shell tank according to claim 5, wherein the pressure regulating device includes an exhaust device provided in the exhaust path.

8. a relief passage for guiding gas in the heat insulating space to the outside of the heat insulating space; 8. The multi-shell tank according to claim 5, wherein the pressure regulating device includes a relief valve provided in the relief path.

9. The heat insulating space is filled with the same type of gas as the gas inside the inner tank, the multi-shell tank includes an introduction passage for introducing gas inside the inner tank into the thermally insulated space, 9. The multi-shell tank according to claim 5, wherein the pressure regulating device includes an inlet valve provided in the inlet passage.

10. 10. The multi-shell tank according to claim 5, wherein the control device controls the pressure regulating device so that the pressure measured by the pressure gauge is less than the saturated vapor pressure of the gas in the insulated space at the reference temperature and is equal to or greater than a set lower limit pressure that is lower than the saturated vapor pressure by a predetermined pressure.

11. an inner tank storing a cryogenic liquid therein; an outer tank including a first outer tank that houses the inner tank and a second outer tank that houses the first outer tank; a first heat insulating space provided between the inner tank and the first outer tank; a second insulation space provided between the first outer tank and the second outer tank and filled with a gas; a pressure regulating device configured to adjust the pressure of the gas in the second insulated space so that the pressure of the gas in the second insulated space is maintained below the saturated vapor pressure of the gas in the second insulated space at a reference temperature, which is a temperature determined based on the temperature of the first outer tank or the temperature of the first insulated space.

12. A ship comprising a multi-shell tank according to any one of claims 1 to 11.

13. A gas pressure regulating method for a multi-shell tank including an inner tank storing a cryogenic liquid therein, one or more outer tanks accommodating the inner tank, and an insulated space provided between the inner tank and the outer tank and filled with a gas, the method comprising: measuring the temperature of the inner tank or the temperature of the space inside the inner tank; The measured temperature or a temperature determined based on the measured temperatures is set as a reference temperature; Deriving a saturated vapor pressure of the gas in the thermal insulation space at the reference temperature; A gas pressure adjusting method for maintaining the pressure of the gas in the heat-insulating space at a level lower than the derived saturated vapor pressure.

14. A gas pressure regulating method for a multi-shell tank including an inner tank storing a cryogenic liquid therein, a first outer tank accommodating the inner tank, a second outer tank accommodating the first outer tank, a first insulating space provided between the inner tank and the first outer tank, and a second insulating space provided between the first outer tank and the second outer tank and filled with a gas, the method comprising: measuring the temperature of the first outer tank or the temperature of the first insulating space; The measured temperature or a temperature determined based on the measured temperatures is set as a reference temperature; Deriving a saturated vapor pressure of the gas in the second insulating space at the reference temperature; A gas pressure adjusting method for maintaining the pressure of the gas in the second insulating space at a level lower than the derived saturated vapor pressure.

15. The set lower limit pressure is 1 kPa or more.

11. The multi-shell tank of claim 10.

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