Liquid hydrogen tank and method for operating same

Abstract

This liquid hydrogen tank comprises: an inner tank in which liquid hydrogen is stored; an outer tank surrounding the inner tank; and a heat-insulating layer disposed in an inter-tank region between the inner tank and the outer tank, the heat-insulating layer covering the outer wall of the inner tank. In the liquid hydrogen tank, during storage when the inter-tank region is filled with hydrogen gas and liquid hydrogen is stored in the inner tank, an inter-tank pressure, which is the pressure in the inter-tank region, is lower than the saturated vapor pressure of hydrogen at a prescribed temperature.

Description

Liquid hydrogen tank and its operating method

[0001] The present disclosure relates to a liquid hydrogen tank for containing liquid hydrogen.

[0002] Conventionally, double-shell tanks have been known as liquefied gas tanks for storing low-temperature liquefied gas. The double-shell tank includes an inner tank and an outer tank surrounding the inner tank, and the inter-tank region between the inner and outer tanks is filled with gas. For example, Patent Document 1 discloses a double-shell tank having an inner tank and an outer tank, in which the space between the inner and outer tanks is filled with boil-off gas discharged from the inner tank. Furthermore, a heat insulating material is packed between the tanks.

[0003] International Publication No. 2020 / 202578

[0004] The gas between the tanks may condense and liquefy due to pressure fluctuations in the inter-tank region, etc. If the gas between the tanks liquefies, the tank components may fall below their allowable lower limit temperature, resulting in damage, deterioration of the insulation material placed between the tanks, or an increase in heat input due to the heat pipe effect.

[0005] The present disclosure has been made in consideration of the above circumstances, and its purpose is to suppress liquefaction of gas in the inter-tank region in a liquid hydrogen tank having an inner tank containing liquid hydrogen, an outer tank surrounding the inner tank, and the inter-tank region between the inner and outer tanks being filled with vaporized liquid hydrogen gas.

[0006] In order to solve the above problems, a liquid hydrogen tank according to one aspect of the present disclosure comprises an inner tank in which liquid hydrogen is stored, an outer tank surrounding the inner tank, and a thermal insulation layer disposed in an inter-tank region between the inner tank and the outer tank and covering the outer wall of the inner tank, wherein the inter-tank region is filled with hydrogen gas and, during storage with the liquid hydrogen stored in the inner tank, the inter-tank pressure, which is the pressure in the inter-tank region, is lower than the saturated vapor pressure of hydrogen at a predetermined temperature.

[0007] Furthermore, a method for operating a liquid hydrogen tank according to one aspect of the present disclosure is a method for operating a liquid hydrogen tank comprising an inner tank for storing liquid hydrogen, an outer tank surrounding the inner tank, and a thermal insulation layer disposed in an inter-tank region between the inner tank and the outer tank and covering the outer wall of the inner tank, wherein, during storage with hydrogen gas filled in the inter-tank region and the liquid hydrogen stored in the inner tank, the inter-tank pressure, which is the pressure in the inter-tank region, is maintained lower than the saturated vapor pressure of hydrogen at a predetermined temperature.

[0008] According to the present disclosure, in a liquid hydrogen tank having an inner tank containing liquid hydrogen, an outer tank surrounding the inner tank, and the inter-tank region between the inner and outer tanks filled with vaporized liquid hydrogen gas, liquefaction of the gas in the inter-tank region can be suppressed.

[0009] Fig. 1 is a vertical cross-sectional view showing a schematic configuration of a liquid hydrogen tank according to one embodiment of the present disclosure, and Fig. 2 is a vertical cross-sectional view showing a schematic configuration of a liquid hydrogen tank according to a modified example.

[0010] Next, an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a liquid hydrogen tank 1 according to one embodiment of the present disclosure. The liquid hydrogen tank 1 shown in FIG. 1 is a container for storing cryogenic liquid hydrogen. The liquid hydrogen tank 1 may be a cargo tank for storing liquid hydrogen as cargo, or a fuel tank for storing liquid hydrogen as fuel. The liquid hydrogen tank 1 may be mounted on a ship or a floating structure, or may be installed on land.

[0011] The liquid hydrogen tank 1 comprises an inner tank 21 that contains liquid hydrogen L, and an outer tank 22 that surrounds the inner tank 21. However, the liquid hydrogen tank 1 is not limited to a double-shell tank, and may be a triple- or more-shelled tank that has at least one tank that surrounds the outer tank 22. Furthermore, if the liquid hydrogen tank 1 is mounted on a ship's hull, the ship's hull may function as the outer tank 22.

[0012] The inner vessel 21 and the outer vessel 22 are spaced apart in the radial direction of the liquid hydrogen tank 1, and an inter-vessel region 23 is provided between the inner vessel 21 and the outer vessel 22. A thermal insulation layer 24 is disposed in the inter-vessel region 23. The thermal insulation layer 24 covers the outer wall of the inner vessel 21 in the inter-vessel region 23. The thermal insulation layer 24 is made of a thermal insulating material, and examples of the thermal insulating material include a thermal insulating panel, a thermal insulating sheet, and a fibrous insulating material. In this specification, the region of the inter-vessel region 23 between the outer wall of the inner vessel 21 and the thermal insulation layer 24 is referred to as the "annular region 25," and the region between the thermal insulation layer 24 and the inner wall of the outer vessel 22 is referred to as the thermal insulation layer outer peripheral region 26. Here, the annular region 25 may be formed by a gap provided between the outer wall of the inner vessel 21 and the thermal insulation layer 24, or the annular region 25 may be formed by voids or holes formed in the surface of the thermal insulation layer 24 facing the outer wall of the inner vessel 21.

[0013] The inter-tank region 23 is filled with the same type of gas as the vaporized gas of the liquid hydrogen L contained in the inner tank 21, i.e., hydrogen gas G. The hydrogen gas G may be vaporized gas produced by vaporizing the liquid hydrogen L inside the inner tank 21, or may be gas supplied from outside the liquid hydrogen tank 1. When the liquid hydrogen tank 1 is stored with the liquid hydrogen L contained in the inner tank 21, the pressure in the inter-tank region 23 is adjusted so that the hydrogen gas G in the inter-tank region 23 does not liquefy due to condensation.

[0014] The interior of the inner tank 21 and the inter-tank region 23 are spaces independent of each other. On the other hand, the inter-tank region 23 may be (i) a case in which the annular region 25 and the thermal insulation layer outer peripheral region 26 are in communication with each other, or (ii) a case in which the annular region 25 and the thermal insulation layer outer peripheral region 26 are spaces independent of each other. If the thermal insulation layer 24 is an airtight layer, the annular region 25 and the thermal insulation layer outer peripheral region 26 will be spaces independent of each other. Therefore, the following describes a method for adjusting the pressure in the inter-tank region 23 of the liquid hydrogen tank 1 during storage in both of the above cases (i) and (ii).

[0015] (i) When the annular region 25 and the thermal insulation layer outer peripheral region 26 are in communication, the pressure inside the inner vessel 21 is referred to as the "inner vessel pressure P1," and the pressure in the inter-vessel region 23 is referred to as the "inter-vessel pressure P3." Because the annular region 25 and the thermal insulation layer outer peripheral region 26 are in communication, the pressures in these regions are both the inter-vessel pressure P3.

[0016] At the time of initial setting when liquid hydrogen L is stored in the liquid hydrogen tank 1, the inner tank 21 is filled with liquid hydrogen L and the inter-tank region 23 is filled with hydrogen gas G so that the inner tank pressure P1 is a predetermined inner tank standard pressure and the inter-tank pressure P3 is a predetermined inter-tank standard pressure.

[0017] The liquid hydrogen tank 1 is provided with an inner tank pressure sensor 31 and an inner tank safety valve 32. The inner tank pressure sensor 31 detects the pressure of the gas phase portion of the inner tank 21, i.e., the inner tank pressure P1. The inner tank safety valve 32 is configured to open when the inner tank pressure P1 exceeds a predetermined inner tank allowable pressure to release the vaporized gas in the inner tank 21 to the outside, so that the inner tank pressure P1 does not exceed a predetermined inner tank design pressure. The inner tank allowable pressure is equal to or lower than the inner tank design pressure and is sufficiently higher than the inner tank standard pressure.

[0018] The liquid hydrogen tank 1 is equipped with a pressure regulating device 3 that adjusts the pressure in the inter-tank region 23. The pressure regulating device 3 adjusts the inter-tank pressure P3 in the liquid hydrogen tank 1 during storage so that it is lower than the inner tank pressure P1 and lower than the saturated vapor pressure of hydrogen at a predetermined temperature. The pressure regulating device 3 according to this embodiment includes an inter-tank safety valve 33, a connecting pipe 36, and a differential pressure safety valve 35.

[0019] The inter-tank safety valve 33 is provided in a pipe or the like connected to the outer tank 22 or the inter-tank region 23. The inter-tank safety valve 33 is normally closed and opens when the inter-tank pressure P3 exceeds the allowable inter-tank pressure, and corresponds to the first valve in the claims. The inter-tank safety valve 33 is a self-acting automatic valve that operates using forces generated by fluid pressure, pilot pressure, spring pressure, etc. However, the inter-tank safety valve 33 is not limited to a self-acting automatic valve, and may be a control valve (i.e., a passive automatic valve) that opens when the inter-tank pressure exceeds the allowable inter-tank pressure using an actuator controlled by a control device, or a manual valve. When the inter-tank safety valve 33 opens, hydrogen gas G in the inter-tank region 23 is released to the outside of the liquid hydrogen tank 1 via a forced exhaust system, and the inter-tank pressure P3 drops to or below the allowable inter-tank pressure. The forced exhaust system may include a compressor that forcibly exhausts hydrogen gas G, a release tower that safely releases hydrogen gas G into the atmosphere, and a hydrogen fuel consuming device that consumes hydrogen gas G as fuel, etc.

[0020] The allowable inter-vessel pressure is lower than the inner vessel standard pressure and lower than the saturated vapor pressure of hydrogen at a predetermined temperature. Here, the predetermined temperature refers to the temperature of liquid hydrogen contained in the inner vessel 21, the temperature of the inner surface of the inner vessel 21, the temperature of the outer surface of the inner vessel 21, or the temperature of the hydrogen gas G filled in the inter-vessel region 23. The predetermined temperature is not limited to an actually measured temperature, but may be an estimated or set temperature between −259°C and −240°C. The allowable inter-vessel pressure may be set to the expected minimum value of the inner vessel pressure P1. Because the inter-vessel pressure P3 becomes a negative pressure of less than 0 KPaG when the inner vessel pressure P1 falls below 0 KPaG, the minimum value of the inner vessel pressure P1 is higher than 0 KPaG, preferably higher than 5 KPaG. In this way, by adjusting the inter-vessel pressure P3 so as not to exceed the predetermined allowable inter-vessel pressure, liquefaction of the hydrogen gas G due to condensation in the inter-vessel region 23 is prevented.

[0021] In the above, as shown in FIG. 2 , the pressure regulating device 3 may include an on-off valve 37 provided in a pipe or the like connected to the inter-tank region 23, separate from the inter-tank safety valve 33. As a result, the liquid hydrogen tank 1 has two release flow paths: a first release flow path that is a flow path for releasing hydrogen gas G from the inter-tank region 23 through the on-off valve 37, and a second release flow path that is a flow path for releasing hydrogen gas G from the inter-tank region 23 through the inter-tank safety valve 33. The first and second release flow paths are preferably independent of each other, and although these flow paths may merge midway, they are preferably independent of each other at least at the outlet from the inter-tank region 23. The on-off valve 37 is normally closed, and when opened, hydrogen gas G in the inter-tank region 23 is released to the outside of the liquid hydrogen tank 1 via the first release flow path. The on-off valve 37 may be a manual valve operated by an operator, or a control valve whose opening and closing is controlled by a control device.

[0022] When the liquid hydrogen tank 1 has two release flow paths from the inter-tank region 23 as described above, two levels of inter-tank allowable pressure are provided: a first inter-tank allowable pressure and a second inter-tank allowable pressure higher than the first inter-tank allowable pressure. Both the first inter-tank allowable pressure and the second inter-tank allowable pressure are lower than the saturated vapor pressure of hydrogen at a predetermined temperature. The on-off valve 37 is set to open when the inter-tank pressure P3 exceeds the first allowable pressure, and the inter-tank safety valve 33 is set to open when the inter-tank pressure P3 exceeds the second inter-tank allowable pressure. When the inter-tank pressure P3 exceeds the first inter-tank allowable pressure, the on-off valve 37 is first opened, and the hydrogen gas G in the inter-tank region 23 is released to the outside through the first release flow path. An inter-tank pressure sensor 38 that detects the inter-tank pressure P3 may be provided in the liquid hydrogen tank 1, and an alarm may be issued to notify the user when the pressure detected by the inter-tank pressure sensor 38 exceeds the first inter-tank allowable pressure. When the on-off valve 37 is opened, the inter-tank pressure P3 does not decrease below the first inter-tank allowable pressure, and the inter-tank pressure P3 exceeds the second inter-tank allowable pressure, the inter-tank safety valve 33 is opened. By opening the on-off valve 37 and the inter-tank safety valve 33, the hydrogen gas G is released to the outside through the first release flow path and the second release flow path, and the inter-tank pressure P3 decreases to below the first inter-tank allowable pressure.

[0023] Returning to FIG. 1 , the connecting pipe 36 is a pipe connecting the gas phase in the inner tank 21 and the inter-tank region 23. The differential pressure safety valve 35 is a valve that opens and closes the flow path in the connecting pipe 36 and corresponds to the first valve in the claims. The differential pressure safety valve 35 maintains the differential pressure between the inner tank pressure P1 and the inter-tank pressure P3 greater than 0 and equal to or less than a differential pressure set value by introducing the vaporized gas from the inner tank 21 into the inter-tank region 23. For example, the differential pressure safety valve 35 is configured to open while the differential pressure between the inner tank pressure P1 and the inter-tank pressure P3 exceeds the differential pressure set value, thereby communicating the inner tank 21 and the inter-tank region 23 via the connecting pipe 36 and introducing the vaporized gas from the inner tank 21 into the inter-tank region 23. The differential pressure set value is an arbitrary value that suppresses condensation of hydrogen gas G in the inter-tank region 23. The differential pressure safety valve 35 maintains the differential pressure between the inner tank pressure P1 and the inter-tank pressure P3, thereby keeping the pressure difference between the inter-tank area 23 and the inner tank 21 within an appropriate range and preventing excessive load from being applied to the components of the liquid hydrogen tank 1. Note that the differential pressure safety valve 35 is a self-acting automatic valve that operates based on the differential pressure between the inner tank pressure P1 and the inter-tank pressure P3, but it may also be a control valve that opens when the differential pressure between the inner tank pressure P1 and the inter-tank pressure P3 exceeds a set differential pressure value using an actuator controlled by a control device.

[0024] (ii) When the annular region 25 and the thermal insulation layer outer peripheral region 26 are independent spaces, the liquid hydrogen tank 1 is similarly equipped with an inner tank pressure sensor 31, an inner tank safety valve 32, and a pressure regulating device 3. The pressure regulating device 3 includes an inter-tank safety valve 33, a connecting pipe 36, and a differential pressure safety valve 35.

[0025] In the inter-tank region 23, the annular region 25 is spatially independent from other regions of the inter-tank region 23 (i.e., the thermal insulation layer outer peripheral region 26). Here, the pressure in the annular region 25 of the inter-tank region 23 is referred to as annular pressure P2, and the pressure in the region of the inter-tank region 23 excluding the annular region 25 (i.e., the thermal insulation layer outer peripheral region 26) is referred to as inter-tank pressure P3.

[0026] When the inner tank 21 does not contain liquid hydrogen L or during initial setup, the annular region 25 is pre-filled with hydrogen gas G to achieve the standard annular pressure. During loading, the annular pressure P2 becomes lower than the standard annular pressure due to the cold heat of the liquid hydrogen L contained in the inner tank 21, but never becomes higher than the standard annular pressure. The standard annular pressure is lower than the saturated vapor pressure of hydrogen at the temperature of the liquid hydrogen contained in the inner tank 21. Here, the temperature of the liquid hydrogen contained in the inner tank 21 is not limited to an actually measured temperature, but may be an estimated or set temperature between −259°C and −240°C. Setting the standard annular pressure in this manner prevents liquefaction of the hydrogen gas G due to condensation in the annular region 25.

[0027] If the inter-tank pressure P3 becomes lower than the annular pressure P2, the thermal insulation layer 24 supported by the inner tank 21 may be lifted or the support portion may be damaged. Therefore, the inter-tank pressure P3 is adjusted to be equal to or higher than the annular pressure P2. As described above, the annular pressure P2 is equal to or lower than the standard annular pressure, so the inter-tank pressure P3 may be adjusted to be equal to or higher than the standard annular pressure. For example, the standard inter-tank pressure is set to a value equal to or higher than the standard annular pressure, and the differential pressure setting value of the differential pressure relief valve 35 is set so that the inter-tank pressure P3 is equal to or higher than the standard annular pressure.

[0028] [Summary] The liquid hydrogen tank 1 according to the first item of the present disclosure comprises an inner tank 21 in which liquid hydrogen L is stored, an outer tank 22 surrounding the inner tank 21, and a thermal barrier layer 24 disposed in an inter-tank region 23 between the inner tank 21 and the outer tank 22 and covering the outer wall of the inner tank 21, wherein the inter-tank region 23 is filled with hydrogen gas G and the inner tank 21 stores liquid hydrogen L, and during storage, the inter-tank pressure P3, which is the pressure in the inter-tank region 23, is lower than the saturated vapor pressure of hydrogen at a predetermined temperature.

[0029] In the liquid hydrogen tank 1 configured as described above, the hydrogen gas G filled in the inter-chamber region 23 can drop to substantially the same temperature as the liquid hydrogen L contained in the inner tank 21. Therefore, if the inter-chamber pressure P3 becomes lower than the saturated vapor pressure at the temperature of the liquid hydrogen L stored in the inner tank 21, the hydrogen gas G in the inter-chamber region 23 may condense. In the liquid hydrogen tank 1 configured as described above, the inter-chamber pressure P3 is maintained at a value lower than the saturated vapor pressure of hydrogen at a predetermined temperature so that the hydrogen gas G does not condense and liquefy even if the temperature of the hydrogen gas G in the inter-chamber region 23 drops. This makes it possible to suppress damage to tank components due to liquefaction of the hydrogen gas G in the inter-chamber region 23, deterioration of the thermal insulation layer 24 arranged in the inter-chamber region 23, and an increase in heat input due to the heat pipe effect.

[0030] The liquid hydrogen tank 1 according to the second item is the liquid hydrogen tank 1 according to the first item, in which, during storage, the inter-tank pressure P3 is lower than the inner tank pressure P1, which is the pressure of the gas phase portion within the inner tank 21.

[0031] The temperature of the liquid hydrogen L in the inner tank 21 converges to a temperature corresponding to the inner tank pressure P1 (i.e., the saturation temperature at pressure P1). If the inter-tank pressure P3 is equal to or higher than the inner tank pressure P1, the saturation temperature of the hydrogen gas G in the inter-tank region 23 will be equal to or higher than the temperature of the liquid hydrogen L (= the temperature of the inner tank 21), and liquefaction of the hydrogen gas G will occur on the outer surface of the inner tank 21 in the inter-tank region 23. In contrast, in the liquid hydrogen tank 1 according to the present disclosure, by maintaining the inter-tank pressure P3 at a value lower than the inner tank pressure P1, the inter-tank pressure P3 is maintained at a value lower than the saturated vapor pressure at the temperature of the liquid hydrogen L contained in the inner tank 21. Therefore, with the liquid hydrogen tank 1 configured as described above, liquefaction due to condensation of the hydrogen gas G in the inter-tank region 23 is suppressed even if the temperature of the hydrogen gas G in the inter-tank region 23 drops. Therefore, damage to tank components caused by liquefaction of hydrogen gas G in the inter-tank region 23, deterioration of the thermal insulation layer 24 arranged in the inter-tank region 23, and an increase in heat input due to the heat pipe effect can be suppressed.

[0032] The liquid hydrogen tank 1 according to the third item is the liquid hydrogen tank 1 according to the first or second item, wherein the predetermined temperature is the temperature of the liquid hydrogen contained in the inner tank 21, the temperature of the inner surface of the inner tank 21, or the temperature of the outer surface of the inner tank 21.

[0033] According to the liquid hydrogen tank 1 having the above configuration, the inter-tank pressure P3 is maintained at a value lower than the saturated vapor pressure of hydrogen at the temperature of the liquid hydrogen L contained in the inner tank 21, so that even if the temperature of the hydrogen gas G filled in the inter-tank region 23 drops, liquefaction of the hydrogen gas G due to condensation can be prevented.

[0034] The liquid hydrogen tank 1 according to the fourth aspect is the liquid hydrogen tank 1 according to any one of the first to third aspects, and further includes a pressure adjusting device 3 for adjusting the inter-vessel pressure P3.

[0035] The liquid hydrogen tank 1 according to the fifth item is the liquid hydrogen tank 1 according to the fourth item, in which the pressure adjustment device 3 has a first valve that releases hydrogen gas G in the inter-tank region 23 to the outside when the inter-tank pressure P3 exceeds a predetermined allowable inter-tank pressure that is lower than the saturated vapor pressure of hydrogen at the temperature of the liquid hydrogen L contained in the inner tank 21.

[0036] The liquid hydrogen tank 1 according to the fourth and fifth aspects can prevent liquefaction of the hydrogen gas G in the inter-cell region 23 without relying on operator operation. The first valve corresponds to the inter-cell safety valve 33 in the above embodiment.

[0037] The liquid hydrogen tank 1 according to the sixth item is the liquid hydrogen tank 1 according to any one of the first to fifth items, in which the inter-vessel region 23 includes an airtight annular region 25 filled with hydrogen gas G between the inner vessel 21 and the thermal insulation layer 24, and during storage, the pressure P2 in the annular region 25 is lower than the inner vessel pressure P1.

[0038] This prevents the hydrogen gas G from condensing and becoming liquefied even if the temperature of the hydrogen gas G filled in the annular region 25 drops.

[0039] The liquid hydrogen tank 1 according to the seventh item is the liquid hydrogen tank 1 according to the sixth item, in which the pressure P2 in the annular region 25 is lower than the pressure P3 in the inter-vessel region 23 excluding the annular region 25.

[0040] This prevents damage to the thermal insulation layer 24 and its supporting members, and prevents the thermal insulation layer 24 from floating up.

[0041] The liquid hydrogen tank 1 according to the eighth item is the liquid hydrogen tank 1 according to the fourth item, in which the pressure adjustment device 3 maintains the differential pressure between the inner tank pressure P1 and the inter-tank pressure P3 at or below a predetermined differential pressure setting value.

[0042] In this way, by controlling the differential pressure between the interior of the inner tank 21 and the inter-tank region 23 to be within the set differential pressure value, damage to the tank components caused by an excessive differential pressure can be prevented.

[0043] The liquid hydrogen tank 1 according to the ninth item is the liquid hydrogen tank 1 according to the eighth item, wherein the pressure adjustment device 3 includes a connecting pipe 36 connecting the gas phase part of the inner tank 21 to the inter-tank region 23, and a second valve that introduces vaporized gas from the gas phase part of the inner tank 21 into the inter-tank region 23 through the connecting pipe 36 when the pressure difference between the inner tank pressure P1 and the inter-tank pressure P3 exceeds a set pressure difference. The second valve corresponds to the differential pressure safety valve 35 in the above embodiment.

[0044] In the liquid hydrogen tank 1 configured as described above, the pressure difference between the inside of the inner vessel 21 and the inter-vessel region 23 is managed without relying on operator operation. Furthermore, the inter-vessel pressure P3 can be adjusted based on the relative relationship between the inner vessel pressure P1 and the inter-vessel pressure P3 without measuring the inter-vessel pressure P3.

[0045] A method for operating a liquid hydrogen tank 1 according to a tenth item of the present disclosure is a method for operating a liquid hydrogen tank 1 comprising an inner tank 21 that contains liquid hydrogen L, an outer tank 22 that surrounds the inner tank 21, and a thermal insulation layer 24 that is disposed in an inter-tank region 23 between the inner tank 21 and the outer tank 22 and covers the outer wall of the inner tank 21, wherein, during storage when the inter-tank region 23 is filled with hydrogen gas G and the inner tank 21 contains liquid hydrogen L, an inter-tank pressure P3, which is the pressure in the inter-tank region 23, is maintained lower than the saturated vapor pressure of hydrogen at a predetermined temperature.

[0046] Furthermore, the operating method of the liquid hydrogen tank 1 according to the eleventh item is the operating method of the liquid hydrogen tank 1 according to the tenth item, in which, during storage, when the inter-tank pressure P3 exceeds a predetermined inter-tank allowable pressure which is lower than the saturated vapor pressure of hydrogen at a predetermined temperature, hydrogen gas G is released from the inter-tank region 23 to reduce the inter-tank pressure P3 to below the inter-tank allowable pressure.

[0047] According to the operating methods for the liquid hydrogen tank 1 relating to the tenth and eleventh items, the inter-tank pressure P3 is maintained at a value lower than the saturated vapor pressure of hydrogen at a predetermined temperature, thereby suppressing liquefaction of the hydrogen gas G due to condensation even if the temperature of the hydrogen gas G in the inter-tank region 23 drops. This makes it possible to suppress damage to tank components due to liquefaction of the hydrogen gas G in the inter-tank region 23, deterioration of the thermal insulation layer 24 disposed in the inter-tank region 23, and an increase in the amount of heat input due to the heat pipe effect.

[0048] The operating method of the liquid hydrogen tank 1 according to the twelfth item is the operating method of the liquid hydrogen tank 1 according to the tenth item, wherein, during storage, when the inter-tank pressure P3 exceeds a predetermined first inter-tank allowable pressure that is lower than the saturated vapor pressure of hydrogen at a predetermined temperature, hydrogen gas G is released from the inter-tank region 23 through the first release flow path, and when the inter-tank pressure P3 exceeds a second inter-tank allowable pressure that is lower than the saturated vapor pressure of hydrogen at the predetermined temperature and higher than the first inter-tank allowable pressure, hydrogen gas G is released from the inter-tank region 23 through the first and second release flow paths, thereby reducing the inter-tank pressure P3 to below the first inter-tank allowable pressure. The first release flow path corresponds to the release flow path that releases hydrogen gas G from the inter-tank region 23 through the on-off valve 37 in the above embodiment. The second release flow path corresponds to the release flow path that releases hydrogen gas G from the inter-tank region 23 through the inter-tank safety valve 33 in the above embodiment.

[0049] According to the above-described method of operating the liquid hydrogen tank 1, hydrogen gas G can be released from the inter-tank region 23 of the liquid hydrogen tank 1 in two stages: a first stage using the first release flow path, and a second stage using both the first release flow path and the second release flow path.

[0050] The functions performed by the controller described herein may be implemented in circuitry or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), CPUs (Central Processing Units), conventional circuits, and / or combinations thereof, programmed to perform the described functions. Processors include transistors and other circuits and are considered circuitry or processing circuitry. A processor may also be a programmed processor that executes a program stored in memory. In this specification, a circuit, unit, or means is hardware that is programmed to perform or executes the described functions. The hardware may be any hardware disclosed herein or any hardware known to be programmed to perform or execute the described functions. When the hardware is a processor, which is considered a type of circuitry, the circuit, means, or unit is a combination of hardware and software used to configure the hardware and / or processor.

[0051] The foregoing discussion of the present disclosure has been presented for purposes of illustration and description and is not intended to limit the present disclosure to the form disclosed herein. For example, in the foregoing detailed description, various features of the present disclosure are grouped together in a single embodiment for the purpose of streamlining the disclosure, but some of the features may also be combined. Furthermore, the features included in the present disclosure may be combined into alternative embodiments, configurations, or aspects other than those discussed above.

Claims

1. an inner tank for accommodating liquid hydrogen; An outer tank surrounding the inner tank; a thermal barrier layer disposed in an inter-tank region between the inner tank and the outer tank and covering an outer wall of the inner tank, during storage in which the inter-chamber region is filled with hydrogen gas and the inner chamber contains liquid hydrogen, an inter-chamber pressure, which is the pressure in the inter-chamber region, is lower than a saturated vapor pressure of hydrogen at a predetermined temperature; Liquid hydrogen tank.

2. During the storage, the inter-tank pressure is lower than an inner tank pressure which is a pressure of a gas phase portion in the inner tank.

2. The liquid hydrogen tank according to claim 1.

3. the predetermined temperature is a temperature of the liquid hydrogen contained in the inner tank, a temperature of the inner surface of the inner tank, or a temperature of the outer surface of the inner tank; 3. A liquid hydrogen tank according to claim 1 or 2.

4. A pressure adjusting device for adjusting the inter-tank pressure is provided.

3. A liquid hydrogen tank according to claim 1 or 2.

5. the pressure regulating device has a first valve that releases the hydrogen gas in the inter-chamber region to the outside when the inter-chamber pressure exceeds a predetermined allowable inter-chamber pressure that is lower than a saturated vapor pressure of hydrogen at the predetermined temperature.

5. The liquid hydrogen tank according to claim 4.

6. The inter-vessel region includes an airtight annular region filled with the hydrogen gas between the inner vessel and the thermal barrier layer, During the storage, the pressure in the annular region is lower than the pressure in the inner vessel.

3. A liquid hydrogen tank according to claim 1 or 2.

7. During the storage, the pressure in the annular region is lower than the pressure in the inter-vessel region excluding the annular region; 7. The liquid hydrogen tank according to claim 6.

8. The pressure regulating device maintains a pressure difference between the pressure in the inner tank and the pressure between the tanks at a predetermined pressure difference set value or less.

5. The liquid hydrogen tank according to claim 4.

9. the pressure regulating device includes a connecting pipe connecting the gas phase part of the inner tank and the inter-tank region, and a second valve configured to introduce vaporized gas from the gas phase part of the inner tank through the connecting pipe into the inter-tank region when a pressure difference between the inner tank pressure and the inter-tank pressure exceeds the differential pressure setting value.

9. The liquid hydrogen tank according to claim 8.

10. 1. A method for operating a liquid hydrogen tank comprising an inner tank for accommodating liquid hydrogen, an outer tank surrounding the inner tank, and a thermal barrier layer disposed in an inter-tank region between the inner tank and the outer tank and covering an outer wall of the inner tank, comprising: During storage in which the inter-chamber region is filled with hydrogen gas and the inner chamber contains liquid hydrogen, an inter-chamber pressure, which is the pressure in the inter-chamber region, is maintained lower than a saturated vapor pressure of hydrogen at a predetermined temperature. How to operate a liquid hydrogen tank.

11. during the storage, when the inter-cell pressure exceeds a predetermined inter-cell allowable pressure which is lower than the saturated vapor pressure of hydrogen at the predetermined temperature, the hydrogen gas is released from the inter-cell region to reduce the inter-cell pressure to below the inter-cell allowable pressure; A method for operating a liquid hydrogen tank according to claim 10.

12. during the storage, when the inter-cell pressure exceeds a predetermined first inter-cell allowable pressure that is lower than the saturated vapor pressure of hydrogen at the predetermined temperature, the hydrogen gas is released from the inter-cell region through a first release flow path, and when the inter-cell pressure exceeds a second inter-cell allowable pressure that is lower than the saturated vapor pressure of hydrogen at the predetermined temperature and higher than the first inter-cell allowable pressure, the hydrogen gas is released from the inter-cell region through the first release flow path and the second release flow path, thereby reducing the inter-cell pressure to less than the first inter-cell allowable pressure; A method for operating a liquid hydrogen tank according to claim 10.