Multi-shell tank, ship and gas pressure adjustment method

Abstract

To keep a pressure of a gas layer in an inner tank low, while suppressing condensation of a gas in a space between the inner tank and an outer tank.SOLUTION: A multiple shell tank includes: an inner tank for storing a low temperature liquid inside; an outer tank housing the inner tank; and a housing structure housing the outer tank. A heat insulation space between the inner tank and the outer tank is filled with a gas of the kind same as a gas obtained by vaporization of the low temperature liquid, a pressure of a gas layer inside of the inner tank is higher than a pressure of the heat insulation space, and a pressure of the heat insulation space is lower than a pressure of a holding space between the outer tank and the housing structure.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] A multi-shell tank is known that has an inner tank in which a cryogenic liquid is stored and an outer tank that houses the inner tank, and in which a heat-insulating space between the inner tank and the outer tank is filled with a gas. For example, Patent Document 1 discloses a double-shell tank having an inner tank and an outer tank that is installed on a liquefied gas carrier. The heat-insulating space between the inner tank and the outer tank is filled with boil-off gas discharged from the inner tank. In addition, a holding space is formed around the outer tank by the tank cover and the hull. The holding space is also filled with gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 202578 Summary of the Invention [Problem to be solved by the invention]

[0004] When gas in the insulated space comes into contact with the inner vessel and condenses, the condensed liquid falls from the inner vessel into the outer vessel and then evaporates. If this liquefaction and vaporization of gas (absorption and evaporation of latent heat) is repeated, the amount of heat input to the inner vessel increases due to the heat pipe effect. For this reason, it is desirable to suppress gas condensation in the space outside the inner vessel.

[0005] Incidentally, the higher the pressure of the gas layer in the inner tank of a multi-shell tank, the higher the saturation temperature of the gas filling the gas layer in the inner tank, and thus the higher the temperature of the liquid layer in the inner tank. If the temperature of the liquid layer in the inner tank is high, for example when discharging the liquid in the inner tank during unloading, if the liquid temperature is higher than the requirement of the onshore receiving terminal, it becomes necessary to lower the liquid temperature in the inner tank. To lower the liquid temperature in the inner tank, the gas in the inner tank is usually discharged to lower the pressure, which results in a waste of gas in the inner tank. In addition, in order to keep the pressure of the gas layer in the inner tank high, the design pressure of the inner tank needs to be increased, which leads to an increase in costs due to an increase in the plate thickness of the multi-shell tank.

[0006] Therefore, an object of the present invention is to provide a multi-shell tank, a vessel, and a gas pressure adjustment method that make it possible to keep the pressure of the gas layer in the inner tank low while suppressing condensation of gas in the space between the inner tank and the outer tank. [Means for solving the problem]

[0007] In order to solve the above problems, a multi-shell tank according to one embodiment of the present invention comprises an inner tank having a cryogenic liquid stored therein, an outer tank that houses the inner tank, and a storage structure that houses the outer tank, and an insulated space between the inner tank and the outer tank is filled with the same type of gas as the gas vaporized from the cryogenic liquid, and the pressure of the gas layer in the inner tank is higher than the pressure of the insulated space, and the pressure of the insulated space is lower than the pressure of a retaining space between the outer tank and the storage structure.

[0008] According to the above configuration, the heat-insulating space between the inner vessel and the outer vessel is filled with the same type of gas as the gas vaporized from the low-temperature liquid in the inner vessel, and the pressure of the gas layer in the inner vessel is higher than the pressure of the heat-insulating space. Therefore, the pressure of the heat-insulating space can be made lower than the saturated vapor pressure of the gas in the heat-insulating space at the temperature of the liquid in the inner vessel. Therefore, condensation of the gas in the heat-insulating space can be suppressed.

[0009] In addition, the pressure in the insulating space is lower than the pressure in the holding space, so that even if the pressure in the holding space is limited, the pressure in the inner tank can be adjusted to be relatively low regardless of the pressure in the holding space.

[0010] Therefore, it is possible to keep the pressure of the gas layer in the inner tank low while suppressing condensation of gas in the insulating space, which is the space outside the inner tank.

[0011] A multi-shell tank according to another embodiment of the present invention comprises an inner tank having a cryogenic liquid stored therein, N outer tanks (N is an integer of 2 or more) that house the inner tank, and a storage structure that covers the Nth outermost tank from the inside among the N outer tanks and houses the N outer tanks, wherein N insulated spaces are formed between the inner tank and the outermost tank, separated by (N-1) outer tanks excluding the outermost tank, and a first insulated space that is the first from the inside among the N insulated spaces is filled with the same type of gas as the gas vaporized from the cryogenic liquid, and the pressure of the gas layer in the inner tank is higher than the pressure of the first insulated space, and the pressure of the first insulated space is lower than the pressure of a retaining space between the outermost tank and the storage structure.

[0012] According to the above configuration, the first insulation space from the inside is filled with the same type of gas as the gas vaporized from the low-temperature liquid in the inner tank, and the pressure of the gas layer in the inner tank is higher than the pressure of the first insulation space. Therefore, the pressure of the first insulation space can be made lower than the saturated vapor pressure of the gas in the first insulation space at the temperature of the liquid in the inner tank. Therefore, condensation of the gas in the first insulation space can be suppressed.

[0013] In addition, the pressure in the first insulation space is lower than the pressure in the holding space, so that even if the pressure in the holding space is limited, the pressure in the inner tank can be adjusted to be relatively low regardless of the pressure in the holding space.

[0014] Therefore, it is possible to keep the pressure of the gas layer in the inner tank low while suppressing condensation of gas in the first insulation space, which is the space outside the inner tank.

[0015] Furthermore, a ship according to one aspect of the present invention includes any one of the multi-shell tanks described above.

[0016] In addition, a gas pressure adjustment method according to one embodiment of the present invention provides a multi-shell tank comprising an inner tank having a cryogenic liquid stored therein, an outer tank housing the inner tank, and a storage structure housing the outer tank, in which an insulated space between the inner tank and the outer tank is filled with the same type of gas as the gas vaporized from the cryogenic liquid, by adjusting the pressure of the gas layer in the inner tank, the pressure of the insulated space, and the pressure of the retaining space so that the pressure of the gas layer in the inner tank is higher than the pressure of the insulated space, and the pressure of the insulated space is lower than the pressure of a retaining space between the outer tank and the storage structure.

[0017] According to the above method, the insulated space between the inner tank and the outer tank is filled with the same type of gas as the gas vaporized from the low-temperature liquid in the inner tank, and the pressure of the gas layer in the inner tank and the pressure of the insulated space are adjusted so that the pressure of the gas layer in the inner tank is higher than the pressure of the insulated space. Therefore, the pressure of the insulated space can be made lower than the saturated vapor pressure of the gas in the insulated space at the temperature of the liquid in the inner tank. Therefore, condensation of the gas in the insulated space can be suppressed.

[0018] In addition, the pressure in the insulating space and the pressure in the holding space are adjusted so that the pressure in the insulating space is lower than the pressure in the holding space, so that even if the pressure in the holding space is limited, the pressure in the inner tank can be adjusted to be relatively low regardless of the pressure in the holding space.

[0019] Therefore, it is possible to keep the pressure of the gas layer in the inner tank low while suppressing condensation of gas in the insulating space, which is the space outside the inner tank.

[0020] In addition, a gas pressure adjustment method according to another aspect of the present invention provides a multi-shell tank comprising an inner tank having a cryogenic liquid stored therein, N outer tanks (N is an integer of 2 or more) that house the inner tank, and a storage structure that covers the N-th outermost tank from the inside among the N outer tanks and houses the N outer tanks, wherein N insulated spaces separated by (N-1) outer tanks excluding the outermost tank are formed between the inner tank and the outermost tank, and a first insulated space that is the first from the inside among the N insulated spaces is filled with the same type of gas as the gas vaporized from the cryogenic liquid, the pressure of the gas layer in the inner tank, the pressure of the first insulated space, and the pressure of the first insulated space are adjusted so that the pressure of the gas layer in the inner tank is higher than the pressure of the first insulated space and the pressure of the first insulated space is lower than the pressure of a holding space between the outermost tank and the storage structure.

[0021] According to the above method, the first insulation space from the inside is filled with the same type of gas as the gas vaporized from the low-temperature liquid in the inner tank, and the pressure of the gas layer in the inner tank and the pressure of the first insulation space are adjusted so that the pressure of the gas layer in the inner tank is higher than the pressure of the first insulation space. Therefore, the pressure of the first insulation space can be made lower than the saturated vapor pressure of the gas in the first insulation space at the temperature of the liquid in the inner tank. Therefore, condensation of the gas in the first insulation space can be suppressed.

[0022] In addition, the pressure in the first insulation space and the pressure in the holding space are adjusted so that the pressure in the first insulation space is lower than the pressure in the holding space. Therefore, even if the pressure in the holding space is limited, the pressure in the inner tank can be adjusted to be relatively low regardless of the pressure in the holding space.

[0023] Therefore, it is possible to keep the pressure of the gas layer in the inner tank low while suppressing condensation of gas in the first insulation space, which is the space between the inner tank and the outer tank. Effect of the Invention

[0024] According to the present invention, it is possible to provide a multi-shell tank, a vessel, and a gas pressure adjustment method that make it possible to keep the pressure of the gas layer in the inner tank low while suppressing condensation of gas in the space between the inner tank and the outer tank. [Brief description of the drawings]

[0025] [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. [Diagram 2] FIG. 2 is a schematic diagram showing the overall configuration of the multi-shell tank shown in FIG. [Diagram 3] FIG. 3 is a schematic diagram showing the overall configuration of a multi-shell tank according to a second embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing the overall configuration of a multi-shell tank according to a third embodiment of the present invention. [Diagram 5] FIG. 5 is a schematic diagram showing the overall configuration of a multi-shell tank according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this specification, the term "inner side" means the side closer to the center of the space in the inner tank of the multi-shell tank, and the term "outer side" means the side farther from the center of the space in the inner tank of the multi-shell tank.

[0027] 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 includes a multi-shell tank 10A. The multi-shell tank 10A includes an inner tank 11 and an outer tank 12 that accommodates the inner tank 11.

[0028] In this embodiment, both the inner tank 11 and the outer tank 12 are spherical. The inner tank 11 and the outer tank 12 do not necessarily have to be spherical. For example, the inner tank 11 and the outer tank 12 may have a shape in which a short cylinder is sandwiched between an upper hemisphere, a horizontal cylindrical shape, or a rectangular shape. Alternatively, for example, the inner tank 11 and the outer tank 12 may have a shape in which the inner tank 11 is bulged at an angle of 45 degrees above and / or below the center of the inner tank 11. The shapes of the inner tank 11 and the outer tank 12 may be similar or dissimilar to each other.

[0029] The multi-shell tank 10A does not necessarily have to be installed as a cargo tank on the ship 1, but may be installed as a fuel tank. In addition, although the ship 1 equipped with one multi-shell tank 10A is shown in Fig. 1, the ship 1 may be equipped with multiple multi-shell tanks 10A.

[0030] Fig. 2 is a schematic diagram showing the overall configuration of the multi-shell tank 10A shown in Fig. 1. Fig. 2 includes a cross-sectional view of the ship 1 perpendicular to the longitudinal direction of the ship. 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 tank cover 13 and the retaining wall 14 are configured as a single accommodation structure 15 that accommodates the outer tub 12.

[0031] The inner surface of the tank cover 13 faces the outer hull 12, and the outer surface of the tank cover 13 faces the atmosphere. The retaining wall 14 is, for example, a part of the hull 2. When the ship 1 is equipped with multiple multi-shell tanks 10A lined up in the longitudinal direction of the ship, the bulkhead provided between two adjacent multi-shell tanks 10A is also included in the accommodation structure 15 covering the outer hull 12.

[0032] A cryogenic liquid is stored in a storage space U inside the inner tank 11. The outer tank 12 covers the inner tank 11, thereby forming a sealed heat-insulating space V outside the inner tank 11 and inside the outer tank 12. A heat insulating material is disposed in the heat-insulating space V. The heat insulating material may be, for example, a granular material such as perlite, or a heat insulating panel attached to the surface of the inner tank 11. The accommodation structure 15 covers the outer tank 12, thereby forming a holding space W inside the accommodation structure 15 and outside the outer tank 12. That is, the inner tank 11 separates the storage space U from the heat-insulating space V, and the outer tank 12 separates the heat-insulating space V from the holding space W.

[0033] Moreover, at least a part of the accommodation structure 15 (specifically, the tank cover 13) separates the holding space W from the outside air.

[0034] The gas layer in the upper part of the storage space U is filled with boil-off gas produced by vaporizing the low-temperature fluid in the storage space U. A first BOG discharge passage 17 is connected to the inner tank 11. One end of the first BOG discharge passage 17 is disposed in the gas layer in the upper part of the storage space U, and the other end of the first BOG discharge passage 17 is connected to a gas consumption equipment 18 mounted on the hull 2. The gas consumption equipment 18 is, for example, a propulsion engine, a power generation engine, a reliquefaction device, a boiler, a GCU, a fuel cell, etc. A first BOG discharge valve 17a is provided in the first BOG discharge passage 17.

[0035] In this embodiment, the first BOG discharge valve 17a is a manual valve or a remotely operated valve that is operated to be opened by an operator. When the first BOG discharge valve 17a is opened, the boil-off gas in the inner tank 11 is sent to the gas consumption equipment 18 through the first BOG discharge path 17. Note that the first BOG discharge path 17 may be provided with a compressor or an exhaust pump that forcibly sends the boil-off gas from the inner tank 11 to the gas consumption equipment 18.

[0036] A second BOG discharge path 19 is connected to the inner tank 11. One end of the second BOG discharge path 19 is disposed in the upper air layer of the storage space U, and the other end of the second BOG discharge path 19 is open to the atmosphere. A second BOG discharge valve 19a is provided in the second BOG discharge path 19. The second BOG discharge valve 19a is a safety valve that opens when the pressure of the air layer in the inner tank 11 exceeds a first set upper limit pressure. Note that one end of the second BOG discharge path 19 does not have to be disposed in the upper air layer of the storage space U. For example, one end of the second BOG discharge path 19 may be connected to the middle of the first BOG discharge path 17.

[0037] In this embodiment, the pressure of the gas layer in the inner tank 11 is maintained at a first set lower limit pressure or more and a first set upper limit pressure or less. For example, the first set lower limit pressure is atmospheric pressure. However, the first set lower limit pressure may be lower than atmospheric pressure.

[0038] For example, while the ship 1 is sailing, boil-off gas is generated in the inner tank 11 due to heat input. The generated boil-off gas is sent to the gas consuming equipment 18 through the first BOG discharge passage 17. When the consumption amount of boil-off gas in the gas consuming equipment 18 is small compared to the generation amount of boil-off gas in the inner tank 11, the pressure of the gas layer in the inner tank 11 increases. When the pressure of the gas layer in the inner tank 11 exceeds the first set upper limit pressure, the second BOG discharge valve 19a, which is a safety valve, opens and reduces the pressure of the gas layer in the inner tank 11 to less than the first set upper limit pressure. Preferably, the first set upper limit pressure is set within a range of, for example, a pressure higher than 5 kPa above atmospheric pressure and a pressure higher than 30 kPa above atmospheric pressure.

[0039] The heat insulating space V is filled with the same type of gas as the boil-off gas in the inner tank 11. The holding space W is filled with a type of gas different from the gas in the heat insulating space V and the boil-off gas in the inner tank 11. In this embodiment, for example, the cryogenic liquid in the storage space U is liquefied hydrogen, the gas filled in the heat insulating space V and the boil-off gas in the inner tank 11 are hydrogen gas, and the gas filled in the holding space W is nitrogen gas, inert gas, dry air, or the like.

[0040] The multi-shell tank 10A is provided with an introduction passage 21 for introducing the boil-off gas in the gas layer in the inner tank 11, i.e., the boil-off gas in the storage space U, into the thermal insulation space V. One end of the introduction passage 21 is disposed in the gas layer in the upper part of the storage space U, and the other end of the introduction passage 21 is disposed in the thermal insulation space V. The introduction passage 21 is provided with an introduction valve 22. For example, the introduction valve 22 is a valve that increases the pressure in the thermal insulation space V when the pressure in the thermal insulation space V falls below a second set lower limit pressure. In this embodiment, the introduction valve 22 is a manual valve or a remotely operated valve that is operated to be opened by an operator.

[0041] The multi-shell tank 10A also includes a discharge passage 23 that guides the gas in the thermal insulation space V to the outside of the thermal insulation space V. One end of the discharge passage 23 is disposed in the thermal insulation space V, and the other end of the discharge passage 23 is connected to a gas consumption equipment 18 outside the thermal insulation space V. The gas consumption equipment 18 may be, for example, a gas combustion unit (GCU), a propulsion engine, a power generation engine, a gas engine, a reliquefaction device, a boiler, a fuel cell, or the like. The gas consumption equipment 18 connected to the discharge passage 23 may be the same as the gas consumption equipment 18 connected to the first BOG discharge passage 17, or may be different. In this embodiment, the other end of the discharge passage 23 is maintained at a pressure lower than the pressure of the thermal insulation space V.

[0042] The discharge path 23 is provided with a discharge valve 24. In this embodiment, the discharge valve 24 is a valve that releases the pressure in the thermally insulated space V when the pressure in the thermally insulated space V exceeds a second set upper limit pressure. In this embodiment, the discharge valve 24 is a manual valve or a remotely operated valve operated by an operator, or a self-acting automatic valve (e.g., a safety valve) that is automatically opened when the pressure in the thermally insulated space V becomes equal to or higher than the second set upper limit pressure.

[0043] The pressure of the gas layer in the inner tank 11 is maintained at a pressure higher than the pressure of the insulating space V, which is maintained at a pressure lower than the pressure of the holding space W, and the pressure of the holding space W is maintained at or above atmospheric pressure. That is, in this embodiment, the pressure of the gas layer in the inner tank 11 and the pressure of the insulating space V satisfy the relationship of the following formula (A), the pressure of the insulating space V and the holding space W satisfy the relationship of the following formula (B), and the pressure of the holding space W and the atmospheric pressure satisfy the relationship of the following formula (C). Pa>Pb (A) Pc>Pb (B) Pc ≥ Po (C) Here, Pa is the pressure of the gas layer in the inner tank 11, Pb is the pressure of the insulating space V, Pc is the pressure of the holding space W, and Po is the atmospheric pressure.

[0044] Various devices are operated, set, or controlled so that the above formulas (A), (B), and (C) are satisfied. For example, the exhaust valve 24 is opened to reduce the pressure in the insulating space V so as to satisfy the above formula (A). For example, the exhaust valve 24 is opened to reduce the pressure in the insulating space V so as to satisfy the above formula (B). For example, a gas supply device 34 (described later) that supplies gas to the holding space W is operated to increase the pressure in the holding space W so as to satisfy the above formula (B) and / or formula (C).

[0045] In this embodiment, the pressure of the insulation space V is maintained at or above the second set lower limit pressure and at or below the second set upper limit pressure. When the pressure of the insulation space V falls below the second set lower limit pressure, the inlet valve 22 is opened to increase the pressure of the insulation space V to or above the second set lower limit pressure. When the pressure of the insulation space V exceeds the second set upper limit pressure, the exhaust valve 24 is opened to reduce the pressure of the insulation space V to below the second set upper limit pressure.

[0046] The second set upper limit pressure is set to be less than the pressure of the air layer in the storage space U and less than the pressure of the holding space W. Preferably, the second set upper limit pressure is set, for example, in a range of a pressure 30 kilopascals lower than atmospheric pressure or more and less than atmospheric pressure. More preferably, the second set upper limit pressure is set, for example, in a range of a pressure 30 kilopascals lower than atmospheric pressure or more and less than a value 5 kilopascals lower than the pressure of the air layer in the storage space U. The second set upper limit pressure may vary depending on the pressure of the air layer in the storage space U.

[0047] For example, when the first set lower limit pressure is equal to or higher than atmospheric pressure and the second set upper limit pressure is lower than atmospheric pressure, the relationship of formula (A) above is satisfied. Also, since the holding space W is filled with gas to be equal to or higher than atmospheric pressure, for example, when the second set upper limit pressure is lower than atmospheric pressure, the relationship of formula (B) above is satisfied.

[0048] The pressure of the gas layer in the inner tank 11 may be higher or lower than the pressure of the holding space W.

[0049] As described above, in the multi-shell tank 10A according to this embodiment, the insulated space V between the inner tank 11 and the outer tank 12 is filled with the same type of gas as the gas produced by vaporizing the low-temperature liquid in the inner tank 11, and the pressure of the gas layer in the inner tank 11 is higher than the pressure of the insulated space V. Therefore, the pressure of the insulated space V can be made lower than the saturated vapor pressure of the gas in the insulated space V at the temperature of the liquid in the inner tank 11. Therefore, condensation of the gas in the insulated space V can be suppressed.

[0050] In addition, in this embodiment, since the pressure in the holding space W is equal to or higher than atmospheric pressure, intrusion of outside air into the holding space W can be suppressed.

[0051] Furthermore, in this embodiment, since the pressure in the insulating space V is lower than the pressure in the holding space W, even if the pressure in the holding space W is maintained at or above atmospheric pressure, the pressure of the gas layer in the inner tank 11 can be adjusted to be relatively low regardless of the pressure in the holding space W.

[0052] Therefore, the pressure of the gas layer in the inner tank 11 can be kept low while suppressing condensation of the gas in the insulating space V outside the inner tank 11.

[0053] In addition, in this embodiment, since the pressure in the insulation space V is lower than the pressure in the holding space W, it is possible to prevent the gas in the insulation space V from leaking into the holding space W in the event that the outer tank 12 is damaged.

[0054] In addition, in this embodiment, the boil-off gas in the storage space U can be introduced into the insulating space V through the introduction passage 21, so that even if the pressure in the insulating space V drops due to a temperature change in the holding space W or the like, the pressure in the insulating space V can be maintained at or above the second set lower limit pressure.

[0055] In addition, in this embodiment, since the gas in the heat insulation space V can be led to the outside of the heat insulation space V through the exhaust path 23, the pressure in the heat insulation space V can be reduced.

[0056] <Second embodiment> 3 is a schematic diagram showing the overall configuration of a multi-shell tank 10B according to the second embodiment. In this embodiment, the same or similar members as those in the first embodiment are denoted by the same reference numerals in the drawings, and detailed description thereof will be omitted.

[0057] In this embodiment, the pressure of the gas layer in the inner tank 11 is maintained at a pressure higher than the pressure of the insulating space V, which is maintained at a pressure lower than the pressure of the holding space W, and the pressure of the holding space W is maintained at or above atmospheric pressure.

[0058] However, in this embodiment, unlike the first embodiment, the introduction valve 22 and the exhaust valve 24 are control valves that are electrically or mechanically controlled. Also, in this embodiment, in addition to the exhaust valve 24, an exhaust device 25 is provided in the exhaust path 23. The exhaust device 25 is, for example, a compressor or an exhaust pump such as a vacuum pump. That is, the exhaust device 25 can forcibly exhaust the gas in the thermal insulation space V through the exhaust path 23. Therefore, the other end of the exhaust path 23 opposite to the thermal insulation space V does not need to be maintained at a pressure lower than the pressure of the thermal insulation space V. For example, the other end of the exhaust path 23 may be open to the atmosphere.

[0059] The multi-shell tank 10B also includes a control device 30, a first pressure gauge 31, a second pressure gauge 32, a third pressure gauge 33, and a gas supply device .

[0060] The control device 30 controls the inlet valve 22, the exhaust valve 24, the exhaust device 25, and the gas supply device 34. The control device 30 is communicatively connected to each of the exhaust valve 24, the exhaust device 25, and the gas supply device 34. The control device 30 is also communicatively connected to each of the first pressure gauge 31, the second pressure gauge 32, and the third pressure gauge 33.

[0061] The control device 30 is a so-called computer, and has an arithmetic processing unit such as a CPU, and a storage unit such as a ROM and a RAM (none of which are shown). The storage unit stores programs executed by the arithmetic processing unit, various fixed data, and the like. The arithmetic processing unit transmits and receives data to and from external devices. In the control device 30, 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 at least one of the gas pressure of the gas layer in the inner tank 11, the gas pressure of the insulating space V, and the gas pressure of the holding space W. The control device 30 may be composed of multiple computers. In this case, the control device 30 may control the introduction valve 22, the discharge valve 24, and the exhaust device 25 by distributed control through the cooperation of multiple computers, or may control the introduction valve 22, the discharge valve 24, and the exhaust device 25 individually.

[0062] The first pressure gauge 31 measures the pressure of the gas layer in the inner tank 11. The second pressure gauge 32 measures the pressure in the insulating space V. The third pressure gauge 33 measures the pressure in the holding space W. Information on the pressures measured by the first pressure gauge 31, the second pressure gauge 32, and the third pressure gauge 33 is sent to the control device 30.

[0063] The gas supply device 34 supplies the same type of gas as the gas filled in the holding space W to the holding space W. The gas supply device 34 supplies the gas to the holding space W, thereby increasing the gas pressure in the holding space W. In other words, the gas supply device 34 functions as a pressure boosting device for boosting the pressure in the holding space W.

[0064] The control device 30 controls the exhaust valve 24 and the exhaust device 25 so that the pressure measured by the second pressure gauge 32 is kept lower than the pressure measured by the first pressure gauge 31. That is, when the pressure measured by the second pressure gauge 32 becomes too high, the control device 30 opens the exhaust valve 24 and operates the exhaust device 25 to reduce the pressure in the insulating space V.

[0065] For example, when the second set upper limit pressure is set lower than the first set lower limit pressure, the control device 30 controls the exhaust valve 24 and the exhaust device 25 so that the exhaust valve 24 opens and the exhaust device 25 operates when the pressure measured by the second pressure gauge 32 exceeds the second set upper limit pressure. Alternatively, the control device 30 controls the exhaust valve 24 and the exhaust device 25 so that the exhaust valve 24 opens and the exhaust device 25 operates when the pressure difference between the pressure measured by the second pressure gauge 32 and the pressure measured by the first pressure gauge 31 becomes equal to or less than a predetermined value.

[0066] Furthermore, the control device 30 controls the introduction valve 22 so that the pressure measured by the second pressure gauge 32 becomes equal to or higher than the second set lower limit pressure.

[0067] Specifically, when the pressure measured by the second pressure gauge 32 falls below the second set lower limit pressure, the control device 30 opens the introduction valve 22 until the pressure measured by the second pressure gauge 32 becomes equal to or greater than the second set lower limit pressure. The control device 30 closes the introduction valve 22 when the pressure measured by the second pressure gauge 32 becomes equal to or greater than the second set lower limit pressure, or when the pressure measured by the second pressure gauge 32 becomes equal to or greater than the second set lower limit pressure, or when the pressure becomes equal to or greater than a predetermined pressure higher than the second set lower limit pressure.

[0068] The control device 30 controls the gas supply device 34 so that the pressure measured by the third pressure gauge 33 is maintained higher than the pressure measured by the second pressure gauge 32 and higher than the atmospheric pressure. That is, the control device 30 operates the gas supply device 34 so as to increase the pressure in the holding space W so as to satisfy the above formulas (B) and (C). The control device 30 may also control the exhaust valve 24 and the exhaust device 25 so that the pressure measured by the third pressure gauge 33 is higher than the pressure measured by the second pressure gauge 32. That is, the control device 30 may open the exhaust valve 24 and operate the exhaust device 25 so as to reduce the pressure in the insulating space V so as to satisfy the above formula (B).

[0069] In this embodiment, the same effects as in the first embodiment can be obtained.

[0070] In addition, in this embodiment, the control device 30 controls the introduction valve 22, so that when the pressure in the insulating space V drops due to a temperature change in the holding space W or the like, the pressure in the insulating space V can be adjusted in real time to be equal to or higher than the second set lower limit pressure.

[0071] In addition, in this embodiment, since the control device 30 controls the exhaust valve 24 and the exhaust device 25, even if the pressure in the insulated space V and / or the pressure of the gas layer in the inner tank 11 fluctuates, the pressure in the insulated space V can be adjusted in real time to be lower than the pressure of the gas layer in the inner tank 11.

[0072] Furthermore, in this embodiment, since the control device 30 controls the gas supply device 34, even if the pressure in the insulating space V and / or the pressure in the holding space W fluctuates, the pressure in the holding space W can be adjusted in real time to be higher than the pressure in the insulating space V.

[0073] <Third embodiment> Fig. 4 is a schematic diagram showing the overall configuration of a multi-shell tank 10C according to the third embodiment. In this embodiment, the same or similar members as those in the first and second embodiments are given the same reference numerals in the drawings, and detailed description is omitted. In addition, the multi-shell tanks 10C and 10D in this embodiment and the fourth embodiment described later are provided with a first BOG discharge passage 17, a first BOG discharge valve 17a, a second BOG discharge passage 19, and a second BOG discharge valve 19a, as in the first embodiment, but these are omitted in Figs. 4 and 5 for simplicity of the drawings.

[0074] As shown in Fig. 4, the multi-shell tank 10C includes a plurality of thermometers 35 and a gas supply device 34. For simplicity of illustration, only one of the plurality of thermometers 35 is shown in Fig. 4.

[0075] The multiple thermometers 35 measure the temperature in the insulating space V, which is a space one space inside the holding space W. The multiple thermometers 35 are provided at multiple locations in the holding space W. The multiple thermometers 35 are communicatively connected to the control device 30. Information on the temperatures measured by the multiple thermometers 35 is sent to the control device 30.

[0076] The multi-shell tank 10C also includes a relief passage 41 that guides gas in the holding space W to the outside of the holding space W, and a relief valve 42 provided in the relief passage 41. One end of the relief passage 41 is disposed in the holding space W, and the other end of the relief passage 41 is open to the atmosphere. The relief valve 42 is communicatively connected to the control device 30. The relief valve 42 is controlled by the control device 30.

[0077] In this embodiment, as in the second embodiment, the pressure of the gas layer in the inner tank 11 and the pressure of the insulating space V satisfy the relationship of the above formula (A), the pressure of the insulating space V and the pressure of the holding space W satisfy the relationship of the above formula (B), and the pressure of the holding space W and the atmospheric pressure satisfy the relationship of the above formula (C).

[0078] In addition, in this embodiment, the control device 30 adjusts the gas pressure in the holding space W so that condensation of the gas in the holding space W is suppressed.

[0079] Specifically, the control device 30 derives a reference temperature T corresponding to the temperature of the outer tank 12 or the temperature in the insulated space V from the temperatures measured by the multiple thermometers 35. In this embodiment, the control device 30 derives the minimum temperature among the temperatures measured by the multiple thermometers 35 as the reference temperature T.

[0080] Then, the control device 30 adjusts the pressure of the gas in the holding space W so as to maintain the pressure below the saturated vapor pressure Ps of the gas in the holding space W at the derived reference temperature T. That is, the memory unit of the control device 30 pre-stores correspondence relationship information indicating the relationship between the temperature and saturated vapor pressure related to the gas in the holding space W, and the control device 30 derives the saturated vapor pressure Ps of the gas in the holding space W at the derived reference temperature T. Then, when the pressure measured by the third pressure gauge 33 is equal to or higher than the saturated vapor pressure Ps, the control device 30 opens the relief valve 42 so that the pressure measured by the third pressure gauge 33 becomes less than the saturated vapor pressure Ps.

[0081] The control device 30 performs the same control as in the second embodiment, except for the control based on the temperature of the thermometer 35.

[0082] In this embodiment, the same effects as in the first and second embodiments can be obtained.

[0083] In this embodiment, the pressure of the gas in the holding space W is adjusted so as to be maintained below the saturated vapor pressure Ps of the gas in the holding space W at the derived reference temperature T. Therefore, the dew point of the gas in the holding space W can be made lower than the reference temperature T, and as a result, condensation of the gas in the holding space W can be suppressed.

[0084] The control device 30 does not need to determine the minimum temperature among the temperatures measured by the multiple thermometers 35 as the reference temperature T, and may determine the average temperature of the temperatures measured by the multiple thermometers as the reference temperature, or may determine a temperature derived from the temperatures measured by the multiple thermometers using a predetermined calculation formula as the reference temperature T. Also, only one thermometer 35 may be provided in the insulating space V, and its temperature may be set as the reference temperature T. Also, the one or more thermometers 35 may measure the surface temperature of the outer tank 12.

[0085] Alternatively, relief valve 42 may be a safety valve that is not controlled by controller 30 .

[0086] <Fourth embodiment> 5 is a schematic diagram showing the overall configuration of a multi-shell tank 10D according to a fourth embodiment. In this embodiment, the same or similar members as those in the first embodiment are denoted by the same reference numerals in the drawings, and detailed description thereof will be omitted.

[0087] As shown in Fig. 5, the multi-shell tank 10D includes an outer tank 16 (hereinafter referred to as "second outer tank 16") that covers the first outer tank 12 between the outer tank 12 (hereinafter referred to as "first outer tank 12") and the storage structure 15. An upper portion of the second outer tank 16 is covered by a tank cover 13, and the remaining portion of the second outer tank 16 is covered by a retaining wall 14. That is, the second outer tank 16 covers the storage structure 15.

[0088] A cryogenic liquid is stored in a storage space U inside the inner tank 11. The first outer tank 12 covers the inner tank 11, thereby forming a first insulation space V1 that is sealed outside the inner tank 11 and inside the outer tank 12. A heat insulating material is arranged in the first insulation space V1. The second outer tank 16 covers the first outer tank 12, thereby forming a second insulation space V2 that is sealed outside the first outer tank 12 and inside the second outer tank 16. A heat insulating material is also arranged in the second insulation space V2. In addition, the accommodation structure 15 covers the second outer tank 16, thereby forming a holding space W inside the tank cover 13 and the holding wall 14 and outside the second outer tank 16.

[0089] That is, the inner tank 11 separates a storage space U inside the inner tank 11 in which a cryogenic liquid is contained, from a first insulated space V1 outside the inner tank 11 and inside the outer tank 12, the first outer tank 12 separates the first insulated space V1 from a second insulated space V2 outside the first outer tank 12 and inside the second outer tank 16, and the second outer tank 16 separates the second insulated space V2 from a holding space W outside the second outer tank 16 and inside the storage structure 15.

[0090] The gas layer in the upper part of the storage space U is filled with boil-off gas obtained by vaporizing the low-temperature fluid in the storage space U. The first insulation space V1 and the second insulation space V2 are filled with the same type of gas as the boil-off gas in the inner tank 11. The holding space W is filled with a type of gas different from the gas in the first insulation space V1 and the second insulation space V2 and the boil-off gas in the inner tank 11. In this embodiment, for example, the low-temperature liquid in the storage space U is liquefied hydrogen, the boil-off gas obtained by vaporizing the low-temperature fluid in the storage space U and the gas filled in the first insulation space V1 and the second insulation space V2 are hydrogen gas, and the gas filled in the holding space W is nitrogen gas, inert gas, dry air, or the like.

[0091] The multi-shell tank 10D includes an introduction passage 21 and an introduction valve 22 provided in the introduction passage 21, as in the first embodiment. In this embodiment, the introduction passage 21 and the introduction valve 22 are referred to as the first introduction passage 21 and the first introduction valve 22, respectively. The first introduction passage 21 introduces the boil-off gas in the storage space U into the first insulation space V1 between the inner tank 11 and the first outer tank 12. One end 21a of the first introduction passage 21 is disposed in the air layer in the upper part of the storage space U, and the other end of the first introduction passage 21 is disposed in the first insulation space V1. For example, the first introduction valve 22 is a valve that increases the pressure in the first insulation space V1 when the pressure in the first insulation space V1 falls below the second set lower limit pressure. In this embodiment, the first introduction valve 22 may be a manual valve or a remotely operated valve operated to be opened by an operator, or may be a control valve that is electrically or mechanically controlled.

[0092] A second inlet passage 51 branches off from the first inlet passage 21 between the end 21a of the gas layer in the upper part of the storage space U and the first inlet valve 22. The second inlet passage 51 introduces the boil-off gas introduced through the first inlet passage 21 into the second insulating space V2 between the first outer tank 12 and the second outer tank 16. One end of the second inlet passage 51 is connected to a position between the end 21a of the gas layer in the upper part of the storage space U in the first inlet passage 21 and the first inlet valve 22, and the other end of the second inlet passage 51 is disposed in the second insulating space V2.

[0093] The second introduction passage 51 is provided with a second introduction valve 52. For example, the second introduction valve 52 is a valve that increases the pressure in the second insulation space V2 when the pressure in the second insulation space V2 falls below a second set lower limit pressure. In this embodiment, the second introduction valve 52 may be a manual valve or a remote control valve that is operated to be opened by an operator, or may be a control valve that is electrically or mechanically controlled.

[0094] Similarly to the first embodiment, the multi-shell tank 10D also includes a discharge passage 23 and a discharge valve 24 provided in the discharge passage 23. In this embodiment, the discharge passage 23 and the discharge valve 24 are referred to as a first discharge passage 23 and a first discharge valve 24, respectively. One end of the first discharge passage 23 is disposed in the first insulation space V1, and the other end of the first discharge passage 23 is connected to a gas consumption facility 18 outside the first insulation space V1.

[0095] The first discharge valve 24 is a valve that releases the pressure in the first insulation space V1 when the pressure in the first insulation space V1 exceeds a second set upper limit pressure. In this embodiment, the first discharge valve 24 is a manual valve or a remote control valve operated by an operator, or a self-acting automatic valve (e.g., a safety valve) that is automatically opened when the pressure in the first insulation space V1 becomes equal to or higher than the second set upper limit pressure.

[0096] The multi-shell tank 10D also includes a second discharge passage 53 and a second discharge valve 54 provided in the second discharge passage 53. The second discharge passage 53 guides the gas in the second insulation space V2 to the outside of the second insulation space V2. One end of the second discharge passage 53 is disposed in the second insulation space V2, and the other end of the second discharge passage 53 is connected to the gas consumption equipment 18 outside the second insulation space V2. In addition, when the gas filled in the second insulation space V2 is nitrogen gas or the like, the other end of the second discharge passage 53 does not have to be connected to the gas consumption equipment 18. In this case, the other end of the second discharge passage 53 may be open to the atmosphere. In addition, in this embodiment, the other end of the second discharge passage 53 is maintained at a pressure lower than the pressure of the second insulation space V2.

[0097] The second exhaust valve 54 is a valve that releases the pressure in the second insulating space V2 when the pressure in the second insulating space V2 exceeds a second set upper limit pressure. The second exhaust valve 54 is a manual valve or a remotely operated valve operated by an operator, or a self-operated automatic valve (e.g., a safety valve) that is automatically opened when the pressure in the second insulating space V2 becomes equal to or higher than the second set upper limit pressure. The set upper limit pressure at which the second exhaust valve 54 opens may be different from the set upper limit pressure at which the first exhaust valve 24 opens.

[0098] The pressure of the gas layer in the inner tank 11 is maintained at a pressure higher than the pressure of the first insulation space V1, which is maintained at a pressure lower than the pressure of the holding space W, which is maintained at or above atmospheric pressure.

[0099] That is, in this embodiment, the pressure of the gas layer in the inner tank 11 and the pressure of the first insulation space V1 satisfy the relationship of the following formula (D), the pressure of the first insulation space V1 and the pressure of the holding space W satisfy the relationship of the following formula (E), and the pressure of the holding space W and atmospheric pressure satisfy the relationship of the following formula (F). Pa>Pb1 (D) Pc>Pb1 (E) Pc ≥ Po (F) Here, Pa is the pressure of the gas layer in the inner tank 11, Pb1 is the pressure of the first of the two insulating spaces from the inside, Pc is the pressure of the holding space W, and Po is the atmospheric pressure.

[0100] The pressure in the second insulation space V2 is preferably lower than the pressure in the holding space W. This is because, in the event that the second outer tank 16 is damaged, the gas in the second insulation space V2 can be prevented from leaking into the holding space W.

[0101] Various devices are operated, set, or controlled so that the above formulas (D), (E), and (F) are satisfied. For example, the first exhaust valve 24 is opened to reduce the pressure in the first insulation space V1 so as to satisfy the above formula (D). For example, the first exhaust valve 24 is opened to reduce the pressure in the first insulation space V1 so as to satisfy the above formula (E). For example, the above-mentioned gas supply device 34 and the like are operated to increase the pressure in the holding space W so as to satisfy the above formula (E) and / or formula (F).

[0102] As described above, in the multi-shell tank 10D according to this embodiment, the first insulation space V1 is filled with the same type of gas as the gas vaporized from the cryogenic liquid in the inner tank 11, and the pressure of the gas layer in the inner tank 11 is higher than the pressure of the first insulation space V1. Therefore, the pressure of the first insulation space V1 can be made lower than the saturated vapor pressure of the gas in the first insulation space V1 at the temperature of the liquid in the inner tank 11. Therefore, condensation of the gas in the first insulation space V1 can be suppressed.

[0103] In addition, in this embodiment, since the pressure in the holding space W is equal to or higher than atmospheric pressure, intrusion of outside air into the holding space W can be suppressed.

[0104] In addition, the pressure in the first insulation space V1 is lower than the pressure in the holding space W. Therefore, even if the pressure in the holding space W is maintained at or above atmospheric pressure, the pressure in the inner tank 11 can be adjusted to be relatively low regardless of the pressure in the holding space W.

[0105] Therefore, the pressure of the gas layer in the inner tank 11 can be kept low while suppressing condensation of the gas in the first insulation space V1 outside the inner tank 11.

[0106] <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.

[0107] For example, the configurations of the above first to fourth embodiments can be combined as appropriate.

[0108] The gas supply device 34 described in the second and third embodiments may be provided in the multi-shelled tanks 10A, 10D of the first and fourth embodiments. The relief passage 41 and relief valve 42 described in the third embodiment may be provided in the multi-shelled tanks 10A, 10B, 10D of the first, second, and fourth embodiments.

[0109] Moreover, the multi-shell tank 10D of the first and fourth embodiments may be provided with the control device 30 described in the second and third embodiments. In this case, the control device 30 may control at least one of the inlet valve 22, the exhaust valve 24, and the gas supply device 34.

[0110] The number of outer vessels included in the multi-shell tank is not limited to that described in the above embodiment. For example, the number of outer vessels may be three or more.

[0111] In the above embodiment, the introduction passage 21 and the introduction valve 22 do not necessarily have to be provided.

[0112] In addition, in the above first to fourth embodiments, the cryogenic liquid in the inner tank 11 is liquefied hydrogen, but the cryogenic liquid in the inner tank 11 is not limited to this. For example, the cryogenic liquid in the storage space U may be liquefied natural gas, and the gas filled in the insulating space V (or V1) and the boil-off gas in the inner tank 11 may be natural gas.

[0113] In addition, in the above first to third embodiments, the holding space W is filled with a type of gas different from the gas in the insulating space V and the boil-off gas in the inner tank 11, but the holding space W may be filled with the same type of gas as the gas in the insulating space V and the boil-off gas in the inner tank 11.

[0114] In the fourth embodiment, the second insulation space V2 is filled with the same type of gas as the boil-off gas in the inner tank 11 and the gas in the second insulation space V2, but the second insulation space V2 may be filled with a different type of gas from the boil-off gas in the inner tank 11 and the gas in the second insulation space V2. In the fourth embodiment, the holding space W is filled with a different type of gas from the gas in the first insulation space V1 and the second insulation space V2 and the boil-off gas in the inner tank 11, but the holding space W is filled with the same type of gas as one or both of the gas in the insulation space V and the boil-off gas in the inner tank 11. For example, the gas filled in the first insulation space V1 may be hydrogen gas, the gas filled in the second insulation space V2 may be nitrogen gas, and the gas filled in the holding space W may be nitrogen gas, inert gas, dry air, or the like.

[0115] In the above embodiment, the pressure in the holding space W is maintained at atmospheric pressure or higher, but the pressure in the holding space W may be maintained at a pressure lower than atmospheric pressure.

[0116] The first BOG discharge valve 17a does not have to be a valve that is operated to be opened by an operator, and may be a valve that is controlled by, for example, a control device as described in the second embodiment.

[0117] In the above embodiment, the multi-shell tank is provided on a ship, but the multi-shell tank may be installed on land.

[0118] The multi-shell tank of the present invention can also be applied to a membrane tank. That is, in a membrane tank, the primary membrane that contains the cryogenic liquid corresponds to the inner tank of the present invention, the secondary membrane that covers the primary membrane corresponds to the outer tank of the present invention, and the hull that contains the primary and secondary membranes corresponds to the containing structure of the present invention. In this case, a heat insulating material is disposed in the heat insulating space between the primary membrane and the secondary membrane and in the holding space between the secondary membrane and the hull, respectively, and the pressure and weight of the cryogenic liquid in the primary membrane are supported by the hull via the heat insulating material in the heat insulating space and the heat insulating material in the holding space. The heat insulating space between the primary membrane and the secondary membrane is filled with the same type of gas as the gas that the cryogenic liquid is vaporized into, and the pressure of the gas layer in the primary membrane is higher than the pressure of the heat insulating space, and the pressure of the heat insulating space is lower than the pressure of the holding space between the secondary membrane and the hull.

[0119] A multi-shell tank according to a first aspect, comprising an inner tank in which a cryogenic liquid is stored, an outer tank that houses the inner tank, and a housing structure that houses the outer tank, wherein an insulating space between the inner tank and the outer tank is filled with the same type of gas as the gas produced by vaporizing the cryogenic liquid, and a pressure of a gas layer in the inner tank is higher than a pressure of the insulating space, and the pressure of the insulating space is lower than a pressure of the holding space, At least a portion of the storage structure may face the atmosphere on a side opposite the holding space, and the pressure in the holding space may be equal to or higher than atmospheric pressure.

[0120] According to this configuration, since the pressure in the holding space is equal to or higher than atmospheric pressure, it is possible to prevent outside air from entering the holding space.

[0121] Here, if the pressure in the insulating space is higher than the pressure in the holding space, which is equal to or higher than atmospheric pressure, the relationship between the pressure Pa of the air layer in the inner tank, the pressure Pb of the insulating space, the pressure Pc of the holding space, and the atmospheric pressure Po is expressed by the following equation. Pa>Pb>Pc≧Po However, when the pressures Pa, Pb, and Pc are adjusted in this way, it becomes necessary to set the pressure of the inner tank relatively higher than the atmospheric pressure. In order to keep the pressure of the gas layer in the inner tank high, as described above, it is not preferable because it leads to an increase in costs due to the consumption of gas in the inner tank during unloading and an increase in the plate thickness of the multi-shelled tank. In contrast, with the multi-shelled tank of the first embodiment, the pressure in the insulating space is lower than the pressure in the holding space, so the pressure in the inner tank can be adjusted to be relatively low (e.g., close to atmospheric pressure) regardless of the pressure in the holding space.

[0122] The multi-shell tank of the first aspect may further include a discharge passage for guiding the gas in the thermal insulation space to the outside of the thermal insulation space, and a discharge valve and / or an exhaust device provided in the discharge passage. With this configuration, the thermal insulation space can be depressurized.

[0123] The multi-shell tank of the first aspect may further include a first pressure gauge for measuring the pressure of the gas layer in the inner tank, a second pressure gauge for measuring the pressure of the insulated space, and a control device for controlling the exhaust valve and / or the exhaust device so that the pressure measured by the second pressure gauge is kept lower than the pressure measured by the first pressure gauge. With this configuration, even if the pressure of the insulated space and / or the pressure of the gas layer in the inner tank fluctuates, the pressure of the insulated space can be adjusted in real time to be lower than the pressure of the gas layer in the inner tank.

[0124] The multi-shell tank of the first aspect may include an inlet passage for introducing the boil-off gas of the gas layer in the inner tank into the thermal insulation space, and an inlet valve provided in the inlet passage, and the control device may control the inlet valve so that the pressure measured by the second pressure gauge becomes equal to or higher than a set lower limit pressure. With this configuration, when the pressure in the thermal insulation space decreases due to a temperature change in the holding space or the like, the pressure in the thermal insulation space can be adjusted in real time to be equal to or higher than the second set lower limit pressure.

[0125] The multi-shell tank of the first embodiment may further include a second pressure gauge that measures the pressure in the insulating space, a third pressure gauge that measures the pressure in the holding space, a gas supply device that supplies the same type of gas as that filled in the holding space W to the holding space W, and a control device that controls the gas supply device so that the pressure measured by the third pressure gauge is kept higher than the pressure measured by the second pressure gauge. With this configuration, even if the pressure in the insulating space and / or the pressure in the holding space fluctuates, the pressure in the holding space can be adjusted in real time to be higher than the pressure in the insulating space.

[0126] The multi-shell tank of the first aspect may include one or more thermometers for measuring the temperature of the outer tank or the temperature of the insulated space, and the pressure of the gas in the holding space may be maintained below the saturated vapor pressure of the gas in the holding space at a reference temperature that is determined based on the temperature measured by the one thermometer or the temperatures measured by the multiple thermometers. With this configuration, the dew point of the gas in the holding space can be made lower than the reference temperature, and as a result, condensation of the gas in the holding space can be suppressed.

[0127] A multi-shell tank according to a second aspect, comprising an inner tank in which a cryogenic liquid is stored, N outer tanks (N is an integer of 2 or more) that house the inner tank, and a housing structure that covers an outermost tank that is an Nth tank from the inside among the N outer tanks and houses the N outer tanks, wherein N insulated spaces are formed between the inner tank and the outermost tank, the N spaces being partitioned by (N-1) of the outer tanks excluding the outermost tank, a first insulated space that is a first space from the inside among the N insulated spaces is filled with the same type of gas as the gas produced by vaporizing the cryogenic liquid, and a pressure of a gas layer in the inner tank is higher than a pressure of the first insulated space, and the pressure of the first insulated space is lower than a pressure of the holding space, At least a portion of the storage structure may face the atmosphere on a side opposite the holding space, and the pressure in the holding space may be equal to or higher than atmospheric pressure.

[0128] According to this configuration, since the pressure in the holding space is equal to or higher than atmospheric pressure, it is possible to prevent outside air from entering the holding space.

[0129] Here, if the pressure in the first insulation space is higher than the pressure in the holding space, which is equal to or higher than atmospheric pressure, the relationship between the pressure Pa of the gas layer in the inner tank, the pressure Pb1 of the first insulation space, the pressure Pc of the holding space, and the atmospheric pressure Po is expressed by the following equation. Pa>Pb1>Pc≧Po In this case, it becomes necessary to set the pressure in the inner tank relatively higher than the atmospheric pressure. However, in the multi-shell tank of the second embodiment, since the pressure in the first insulation space is lower than the pressure in the holding space, the pressure in the inner tank can be adjusted to be relatively low (e.g., close to the atmospheric pressure) regardless of the pressure in the holding space.

[0130] The multi-shell tank of the second aspect may further include one or more thermometers for measuring the temperature of the outermost tank or the temperature of the Nth insulating space, and the pressure of the gas in the holding space may be maintained below the saturated vapor pressure of the gas in the holding space at a reference temperature determined based on the temperature measured by the one thermometer or the temperatures measured by the multiple thermometers. With this configuration, the dew point of the gas in the holding space can be made lower than the reference temperature, and as a result, condensation of the gas in the holding space can be suppressed.

[0131] In the multi-shell tank of the second embodiment, the N insulating spaces may be filled with the same type of gas as the gas obtained by vaporizing the cryogenic liquid.

[0132] Alternatively, in the multi-shell tank of the second embodiment, the second to Nth insulated spaces from the inside out of the N insulated spaces may be filled with a type of gas different from the gas vaporized from the cryogenic liquid. [Explanation of symbols]

[0133] 1: Ship 10A, 10B, 10C, 10D: Multi-shell tanks 11: Inner tank 12: Outer tank 13: Tank cover 14: Retaining wall 15: Housing structure 16: Outer tank 21:Introduction path 22: Inlet valve 23:Exhaust channel 24: Discharge valve 25: Exhaust system 30: Control device 31: First pressure gauge 32: Second pressure gauge 33: 3rd pressure gauge 34: Gas supply equipment 35:Thermometer 41: Escape route 42: Relief valve 51: 1st discharge path 52: First exhaust valve 53:Second discharge path 54: Second exhaust valve U: Storage space V: Insulated space V1: First insulation space V2: Second insulation space W: Holding space

Claims

1. An inner tank having a cryogenic liquid stored therein; an outer tank that accommodates the inner tank; A housing structure for housing the outer tank, a heat insulating space between the inner vessel and the outer vessel is filled with the same type of gas as the gas vaporized from the cryogenic liquid; A multi-shell tank, wherein the pressure of the gas space in the inner tank is higher than the pressure of the insulated space, and the pressure of the insulated space is lower than the pressure of a holding space between the outer tank and the storage structure.

2. At least a portion of the storage structure faces the atmosphere on a side opposite the holding space, 2. The multi-shell tank of claim 1, wherein the pressure in said holding space is equal to or greater than atmospheric pressure.

3. An exhaust passage for guiding gas in the thermal insulation space to the outside of the thermal insulation space; 3. The multi-shell tank according to claim 1 or 2, further comprising a discharge valve and / or an exhaust device provided in the discharge passage.

4. a first pressure gauge that measures a pressure of the gas layer in the inner tank; A second pressure gauge that measures the pressure in the insulating space; 4. The multi-shell tank according to claim 3, further comprising: a control device that controls the exhaust valve and / or the exhaust device so that the pressure measured by the second pressure gauge is kept lower than the pressure measured by the first pressure gauge.

5. an introduction passage for introducing the boil-off gas of the gas layer in the inner tank into the thermal insulation space; an introduction valve provided in the introduction path, 5. The multi-shell tank according to claim 4, wherein the control device controls the introduction valve so that the pressure measured by the second pressure gauge becomes equal to or higher than a set lower limit pressure.

6. A second pressure gauge that measures the pressure in the insulating space; a third pressure gauge that measures the pressure in the holding space; A gas supply device that supplies the same type of gas as the gas filled in the holding space W to the holding space W; and a control device that controls the gas supply device so that the pressure measured by the third pressure gauge is kept higher than the pressure measured by the second pressure gauge.

7. An inner tank having a cryogenic liquid stored therein; N outer tanks (N is an integer of 2 or more) that accommodate the inner tanks; a housing structure that covers an N-th outermost tank from the inside of the N outer tanks and houses the N outer tanks, Between the inner tank and the outermost tank, N heat insulating spaces are formed, the N spaces being partitioned by (N-1) outer tanks excluding the outermost tank, and a first heat insulating space, which is the first space from the inside among the N heat insulating spaces, is filled with the same type of gas as the gas obtained by vaporizing the cryogenic liquid, A multi-shell tank, wherein the pressure of the gas space in the inner tank is higher than the pressure of the first insulation space, and the pressure of the first insulation space is lower than the pressure of a holding space between the outermost tank and the storage structure.

8. A ship comprising a multi-shell tank according to any one of claims 1 to 7.

9. A multi-shell tank comprising an inner tank in which a cryogenic liquid is stored, an outer tank for accommodating the inner tank, and a housing structure for accommodating the outer tank, wherein a heat-insulating space between the inner tank and the outer tank is filled with a gas of the same type as the gas produced by vaporizing the cryogenic liquid, A gas pressure adjustment method, comprising adjusting the pressure of the gas layer in the inner tank, the pressure of the insulating space, and the pressure of the retaining space so that the pressure of the gas layer in the inner tank is higher than the pressure of the insulating space, and the pressure of the insulating space is lower than the pressure of a retaining space between the outer tank and the storage structure.

10. A multi-shell tank comprising an inner tank in which a cryogenic liquid is stored, N outer tanks (N is an integer of 2 or more) that house the inner tank, and a housing structure that covers an outermost tank that is an Nth tank from the inside among the N outer tanks and houses the N outer tanks, wherein N insulated spaces are formed between the inner tank and the outermost tank by (N-1) outer tanks excluding the outermost tank, and a first insulated space that is a first space from the inside among the N insulated spaces is filled with a gas of the same type as the gas produced by vaporizing the cryogenic liquid, A gas pressure adjustment method, comprising adjusting the pressure of the gas layer in the inner tank, the pressure of the first insulation space, and the pressure of the retaining space so that the pressure of the gas layer in the inner tank is higher than the pressure of the first insulation space, and the pressure of the first insulation space is lower than the pressure of a retaining space between the outermost tank and the containing structure.

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