Liquid hydrogen tank and method for operating same

Abstract

The liquid hydrogen tank is provided with: an inner tank for accommodating liquid hydrogen; an outer tank surrounding the inner tank; and a heat protection layer disposed in an inter-tank region between the inner tank and the outer tank and covering the outer wall of the inner tank. In the liquid hydrogen tank, when the inter-tank region is filled with hydrogen gas and the storage of liquid hydrogen is housed in the inner tank, the inter-tank pressure, which is the pressure of the inter-tank region, is lower than the saturated vapor of hydrogen at a predetermined temperature.

Description

Technical Field

[0001] The present disclosure relates to a liquid hydrogen tank for storing liquid hydrogen. Background Art

[0002] Conventionally, as a liquefied gas tank for storing low-temperature liquefied gas, a double-walled tank having an inner tank and an outer tank surrounding the inner tank, and a region between the inner tank and the outer tank filled with gas, is known. For example, Patent Document 1 discloses a double-walled tank having an inner tank and an outer tank, wherein the region between the inner tank and the outer tank in the double-walled tank is filled with boil-off gas exhausted from the inner tank. In addition, a heat insulating material is placed between the regions.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2020 / 202578 Summary of the invention

[0006] Problems to be solved by the invention

[0007] The gas filled in the tanks may condense and liquefy due to pressure fluctuations in the tank area, etc. If the gas in the tanks liquefies, the components of the tank may become below the allowable lower limit temperature of the components and be damaged, or the heat insulation material arranged in the tanks may deteriorate, or the heat input may increase due to the heat pipe effect.

[0008] The present disclosure has been completed in view of the above situation, and its purpose is to suppress liquefaction of gas in the inter-tank area in a liquid hydrogen tank having an inner tank for storing liquid hydrogen and an outer tank surrounding the inner tank, and the inter-tank area between the inner tank and the outer tank is filled with vaporized gas of liquid hydrogen.

[0009] Means for solving problems

[0010] In order to solve the above-mentioned problems, a liquid hydrogen tank in one embodiment of the present invention comprises: an inner tank, which stores liquid hydrogen; an outer tank, which surrounds the inner tank; and a heat-proof layer, which is arranged in an inter-tank area between the inner tank and the outer tank and covers the outer wall of the inner tank. When the inter-tank area is filled with hydrogen gas and the liquid hydrogen is stored in the inner tank, the inter-tank pressure, which is the pressure of the inter-tank area, is lower than the saturated vapor pressure of hydrogen at a specified temperature.

[0011] In addition, in an operating method of a liquid hydrogen tank of one embodiment of the present invention, the liquid hydrogen tank comprises: an inner tank that stores liquid hydrogen; an outer tank that surrounds the inner tank; and a heat-proof layer that is arranged in an inter-tank area between the inner tank and the outer tank and covers the outer wall of the inner tank, wherein when the inter-tank area is filled with hydrogen gas and the liquid hydrogen is stored in the inner tank, the inter-tank pressure, which is the pressure of the inter-tank area, is maintained lower than the saturated vapor pressure of hydrogen at a specified temperature.

[0012] Effects of the Invention

[0013] According to the present disclosure, in a liquid hydrogen tank having an inner tank containing liquid hydrogen and an outer tank surrounding the inner tank, and in which a region between the inner tank and the outer tank is filled with vaporized gas of liquid hydrogen, liquefaction of gas in the region between the tanks can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a vertical cross-sectional view showing a schematic structure of a liquid hydrogen tank according to one embodiment of the present disclosure.

[0015] Figure 2 It is a vertical cross-sectional view showing a schematic structure of a liquid hydrogen tank according to a modified example. DETAILED DESCRIPTION

[0016] Next, embodiments of the present disclosure will be described with reference to the drawings. Figure 1 It is a vertical cross-sectional view showing a schematic structure of a liquid hydrogen tank 1 according to one embodiment of the present disclosure. Figure 1 The liquid hydrogen tank 1 shown is a container for storing extremely low-temperature liquid hydrogen. The liquid hydrogen tank 1 can 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 can be carried on a ship or a floating structure, or can be set on the ground.

[0017] The liquid hydrogen tank 1 has an inner tank 21 for storing liquid hydrogen L and an outer tank 22 surrounding the inner tank 21. However, the liquid hydrogen tank 1 is not limited to a double-shell tank, and may be a multi-shell tank having three or more layers and having at least one tank surrounding the outer tank 22. In addition, when the liquid hydrogen tank 1 is mounted on a ship, the ship may also function as the outer tank 22.

[0018] The inner tank 21 and the outer tank 22 are separated in the radial direction of the liquid hydrogen tank 1, and an inter-tank region 23 is provided between the inner tank 21 and the outer tank 22. A heat-proof layer 24 is arranged in the inter-tank region 23. The heat-proof layer 24 covers the outer wall of the inner tank 21 in the inter-tank region 23. The heat-proof layer 24 is made of a heat-insulating material, and examples of the heat-insulating material include a heat-insulating plate, a heat-insulating sheet, and a fibrous heat-insulating material. In this specification, the area between the outer wall of the inner tank 21 and the heat-proof layer 24 in the inter-tank region 23 is referred to as an "annular region 25", and the area between the heat-proof layer 24 and the inner wall of the outer tank 22 is referred to as the heat-proof layer outer peripheral region 26. Here, the annular region 25 can be formed by a gap provided between the outer wall of the inner tank 21 and the heat-proof layer 24, or the annular region 25 can be formed by a gap or a hole formed on the surface of the heat-proof layer 24 opposite to the outer wall of the inner tank 21.

[0019] The intertank region 23 is filled with the same type of gas as the vaporized gas of the liquid hydrogen L stored in the inner tank 21, that is, hydrogen gas G. The hydrogen gas G may be a vaporized gas generated by vaporization of the liquid hydrogen L inside the inner tank 21, or may be a gas supplied from the outside of the liquid hydrogen tank 1. In the liquid hydrogen tank 1 during storage in a state where the inner tank 21 stores the liquid hydrogen L, the pressure of the intertank region 23 is adjusted so that the hydrogen gas G in the intertank region 23 does not liquefy due to condensation.

[0020] The interior of the inner tank 21 and the inter-tank area 23 are independent spaces. On the other hand, in the inter-tank area 23, there are cases where (i) the annular area 25 is connected to the outer peripheral area 26 of the heat-proof layer, and (ii) the annular area 25 and the outer peripheral area 26 of the heat-proof layer are independent spaces. If the heat-proof layer 24 is an airtight layer, the annular area 25 and the outer peripheral area 26 of the heat-proof layer become independent spaces. Therefore, the following is a method for adjusting the pressure of the inter-tank area 23 of the liquid hydrogen tank 1 during storage in the two shells of (i) and (ii) described above.

[0021] (i) When the annular region 25 is connected to the outer peripheral region 26 of the heat protection layer

[0022] The pressure inside the inner groove 21 is referred to as “inner groove pressure P1”, and the pressure in the inter-groove region 23 is referred to as “inter-groove pressure P3”. Since the annular region 25 is connected to the heat-proof layer outer peripheral region 26, the pressures in these regions are both the inter-groove pressure P3.

[0023] When the liquid hydrogen tank 1 is initially set to store liquid hydrogen L, the inner tank 21 is filled with liquid hydrogen L and the inter-tank area 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.

[0024] 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 of the inner tank 21, that is, the inner tank pressure P1. The inner tank safety valve 32 is configured to open when the inner tank pressure P1 exceeds the specified inner tank allowable pressure and release the gasified gas in the inner tank 21 to the outside so that the inner tank pressure P1 does not exceed the specified inner tank design pressure. The inner tank allowable pressure is less than the inner tank design pressure and sufficiently higher than the inner tank standard pressure.

[0025] The liquid hydrogen tank 1 has a pressure regulating device 3 for regulating the pressure of the inter-tank region 23. The pressure regulating device 3 regulates the inter-tank pressure P3 in the liquid hydrogen tank 1 during storage to be lower than the internal tank pressure P1 and lower than the saturated vapor pressure of hydrogen at a predetermined temperature. The pressure regulating device 3 of this embodiment includes an inter-tank safety valve 33, a connecting pipe 36, and a differential pressure safety valve 35.

[0026] The inter-tank safety valve 33 is provided in the outer tank 22 or in the piping connected to the inter-tank area 23. The inter-tank safety valve 33 is a valve that is normally closed and opens when the inter-tank pressure P3 exceeds the inter-tank allowable pressure, which is equivalent to the first valve of the claim. The inter-tank safety valve 33 is a self-acting automatic valve that works by the force generated by the pressure of the fluid, the pilot pressure, and the spring pressure. However, the inter-tank safety valve 33 is not limited to a self-acting automatic valve, and a control valve (i.e., a self-acting automatic valve) or a manual valve that is opened by an actuator controlled by a control device when the inter-tank allowable pressure is exceeded can also be used. When the inter-tank safety valve 33 is opened, the hydrogen G in the inter-tank area 23 is released to the outside of the liquid hydrogen tank 1 via the forced exhaust system, and the inter-tank pressure P3 is reduced to below the inter-tank allowable pressure. In addition, the forced exhaust system may include a compressor that forcibly exhausts the hydrogen G, a release tower that safely releases the hydrogen G to the atmosphere, and a hydrogen fuel consumption device that consumes the hydrogen G as a fuel.

[0027] The inter-tank allowable pressure is lower than the standard pressure of the inner tank and lower than the saturated vapor pressure of hydrogen at a specified temperature. Here, the specified 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, the outer surface of the inner tank 21, or the temperature of the hydrogen G filled in the inter-tank area 23. It is not limited to the measured temperature, but can also be an estimated or set temperature between -259°C and -240°C. The inter-tank allowable pressure can be set to the assumed minimum value of the inner tank pressure P1. When the inner tank pressure P1 is lower than 0KPaG, the inter-tank pressure P3 becomes a negative pressure less than 0KPaG, so the minimum value of the inner tank pressure P1 is higher than 0KPaG, preferably higher than 5KPaG. In this way, by adjusting the inter-tank pressure P3 to not exceed the specified inter-tank allowable pressure, liquefaction caused by condensation of hydrogen G in the inter-tank area 23 is prevented.

[0028] In the above, if Figure 2As shown, the pressure regulating device 3 may also have an on-off valve 37 provided on a pipe or the like connected to the inter-tank area 23 in addition to the inter-tank safety valve 33. Thus, the liquid hydrogen tank 1 has two release flow paths, namely, a first release flow path as a release flow path for hydrogen gas G from the inter-tank area 23 through the on-off valve 37 and a second release flow path as a release flow path for hydrogen gas G from the inter-tank area 23 through the inter-tank safety valve 33. The first release flow path and the second release flow path are preferably independent of each other, and these flow paths may also merge in the middle, but are preferably independent of each other at least at the outlet from the inter-tank area 23. The on-off valve 37 is closed when stable, and when opened, the hydrogen gas G in the inter-tank area 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 that is controlled to open and close by a control device.

[0029] As described above, in the case where the liquid hydrogen tank 1 has two systems of release flow paths from the inter-tank area 23, the inter-tank allowable pressures of the first inter-tank allowable pressure and the second inter-tank allowable pressure higher than the first inter-tank allowable pressure are given. The first inter-tank allowable pressure and the second inter-tank allowable pressure are both values ​​lower than the saturated vapor pressure of hydrogen at a specified 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, first, the on-off valve 37 is opened to release the hydrogen G in the inter-tank area 23 to the outside through the first release flow path. It is also possible that the inter-tank pressure sensor 38 for detecting the inter-tank pressure P3 is provided on the liquid hydrogen tank 1, and when the pressure detected by the inter-tank pressure sensor 38 exceeds the first inter-tank allowable pressure, an alarm is sounded to notify the situation. Furthermore, when the inter-tank pressure P3 does not drop below the first inter-tank permissible pressure during the opening of the on-off valve 37 and the inter-tank safety valve 33 exceeds the second inter-tank permissible 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 is reduced to below the first inter-tank permissible pressure.

[0030] return Figure 1, the connecting pipe 36 is a pipe connecting the gas phase in the inner tank 21 and the inter-tank area 23. The differential pressure safety valve 35 is a valve that opens and closes the flow path in the connecting pipe 36, and is equivalent to the first valve in the claims. The differential pressure safety valve 35 keeps the differential pressure between the inner tank pressure P1 and the inter-tank pressure P3 greater than 0 and below the differential pressure setting value by introducing the gasified gas in the inner tank 21 into the inter-tank area 23. For example, the differential pressure safety valve 35 is configured to open during the period when the differential pressure between the inner tank pressure P1 and the inter-tank pressure P3 exceeds the differential pressure setting value, so that the inner tank 21 and the inter-tank area 23 are connected via the connecting pipe 36, and the gasified gas in the inner tank 21 is introduced into the inter-tank area 23. The differential pressure setting value is an arbitrary value that can suppress the condensation of the hydrogen gas G in the inter-tank area 23. By maintaining the differential pressure between the inner tank pressure P1 and the inter-tank pressure P3 by using the differential pressure safety valve 35, the pressure difference between the inter-tank region 23 and the inner tank 21 can be maintained within an appropriate range to prevent excessive loads from being applied to the components of the liquid hydrogen tank 1. In addition, the differential pressure safety valve 35 is a self-acting automatic valve that is actuated by the differential pressure between the inner tank pressure P1 and the inter-tank pressure P3, but it may also be a control valve that is opened by an actuator controlled by a control device when the differential pressure between the inner tank pressure P1 and the inter-tank pressure P3 exceeds the differential pressure setting value.

[0031] (ii) When the annular region 25 and the heat-protection layer outer peripheral region 26 are independent spaces

[0032] As described above, the liquid hydrogen tank 1 includes the inner tank pressure sensor 31 , the inner tank safety valve 32 , and the pressure regulating device 3 . The pressure regulating device 3 includes the inter-tank safety valve 33 , the connecting pipe 36 , and the differential pressure safety valve 35 .

[0033] In the inter-groove region 23, the annular region 25 is spatially independent from other regions of the inter-groove region 23 (i.e., the heat-proof layer outer peripheral region 26). Here, the pressure of the annular region 25 in the inter-groove region 23 is set to the annular pressure P2, and the pressure of the region other than the annular region 25 in the inter-groove region 23 (i.e., the heat-proof layer outer peripheral region 26) is set to the inter-groove pressure P3.

[0034] The annular region 25 is filled with hydrogen G in such a way that the annular standard pressure is pre-set when no liquid hydrogen L is contained in the inner tank 21 or when the annular standard pressure is set initially. The annular pressure P2 is lower than the annular standard pressure due to the hot and cold of the liquid hydrogen L contained in the inner tank 21 during loading, but will not be higher than the annular standard pressure. The annular standard 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 the measured temperature, but may be an estimated or set temperature between -259°C and -240°C. In this way, by setting the annular standard pressure, liquefaction caused by condensation of the hydrogen G in the annular region 25 is prevented.

[0035] If the inter-tank pressure P3 is lower than the annular pressure P2, the heat-proof layer 24 supported by the inner tank 21 may float or the supporting portion may be damaged, so the inter-tank pressure P3 is adjusted to be higher than the annular pressure P2. As described above, the annular pressure P2 is lower than the annular standard pressure, so it is sufficient to adjust the inter-tank pressure P3 to be higher than the annular standard pressure. For example, the inter-tank standard pressure is set to a value higher than the annular standard pressure, and the differential pressure setting value of the differential pressure safety valve 35 is set so that the inter-tank pressure P3 is higher than the annular standard pressure.

[0036] 〔Summarize〕

[0037] The liquid hydrogen tank 1 of the first item of the present disclosure comprises: an inner tank 21, which stores liquid hydrogen L; an outer tank 22, which surrounds the inner tank 21; and a heat-proof layer 24, which is arranged in the inter-tank area 23 between the inner tank 21 and the outer tank 22 and covers the outer wall of the inner tank 21. When the inter-tank area 23 is filled with hydrogen gas G and the inner tank 21 stores liquid hydrogen L, the inter-tank pressure P3, which is the pressure of the inter-tank area 23, is lower than the saturated vapor pressure of hydrogen at a specified temperature.

[0038] In the liquid hydrogen tank 1 of the above structure, the hydrogen gas G filled in the inter-tank area 23 can be reduced to a temperature substantially the same as that of the liquid hydrogen L stored in the inner tank 21. Therefore, if the inter-tank pressure P3 is in a state 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-tank area 23 may condense. In the liquid hydrogen tank 1 of the above structure, the inter-tank pressure P3 is maintained at a value lower than the saturated vapor pressure of hydrogen at a predetermined temperature, so that even if the temperature of the hydrogen gas G in the inter-tank area 23 is reduced, the hydrogen gas G will not condense but liquefy. Therefore, it is possible to suppress damage to the tank components caused by the liquefaction of the hydrogen gas G in the inter-tank area 23, degradation of the heat protection layer 24 arranged in the inter-tank area 23, and increase in heat input caused by the heat pipe effect.

[0039] The liquid hydrogen tank 1 according to claim 2 is the liquid hydrogen tank 1 according to claim 1, wherein during storage, the inter-tank pressure P3 is lower than the inner tank pressure P1 which is the pressure of the gas phase portion in the inner tank 21 .

[0040] The temperature of the liquid hydrogen L in the inner tank 21 converges to the temperature corresponding to the inner tank pressure P1 (i.e., the saturation temperature of the pressure P1). Here, it is assumed that if the inter-tank pressure P3 is greater than the inner tank pressure P1, the saturation temperature of the hydrogen G in the inter-tank region 23 becomes greater than the temperature of the liquid hydrogen L (= the temperature of the inner tank 21), and liquefaction of the hydrogen G occurs on the outer surface of the inner tank 21 in the inter-tank region 23. In contrast, in the liquid hydrogen tank 1 of 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, according to the liquid hydrogen tank 1 having the above-mentioned structure, even if the temperature of the hydrogen G in the inter-tank region 23 is reduced, liquefaction caused by condensation of the hydrogen G in the inter-tank region 23 can be suppressed. Therefore, it is possible to suppress damage to tank components due to liquefaction of the hydrogen gas G in the inter-tank region 23, degradation of the heat-proof layer 24 disposed in the inter-tank region 23, and increase in heat input due to the heat pipe effect.

[0041] The liquid hydrogen tank 1 according to item 3 is the liquid hydrogen tank 1 according to item 1 or 2, 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 .

[0042] According to the liquid hydrogen tank 1 of the above structure, 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 stored in the inner tank 21. Therefore, even if the temperature of the hydrogen gas G filled in the inter-tank area 23 decreases, liquefaction caused by condensation of the hydrogen gas G can be prevented.

[0043] The liquid hydrogen tank 1 of item 4 is the liquid hydrogen tank 1 according to any one of items 1 to 3, wherein the liquid hydrogen tank 1 comprises a pressure regulating device 3 for regulating the inter-tank pressure P3.

[0044] The liquid hydrogen tank 1 of item 5 is based on the liquid hydrogen tank 1 of item 4, wherein the pressure regulating device 3 has a first valve that releases the hydrogen gas G in the inter-tank area 23 to the outside when the inter-tank pressure P3 exceeds a specified inter-tank allowable 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.

[0045] According to the liquid hydrogen tank 1 of the fourth and fifth items, it is possible to prevent the liquefaction of the hydrogen gas G in the inter-tank region 23 without depending on the operation of the operator. The first valve described above corresponds to the inter-tank safety valve 33 in the above embodiment.

[0046] The liquid hydrogen tank 1 of item 6 is a liquid hydrogen tank 1 according to any of items 1 to 5, wherein the inter-tank area 23 includes an airtight annular area 25 filled with hydrogen G between the inner tank 21 and the heat protection layer 24, and during storage, the pressure P2 of the annular area 25 is lower than the inner tank pressure P1.

[0047] Thus, even if the temperature of the hydrogen gas G filling the annular region 25 decreases, liquefaction due to condensation of the hydrogen gas G can be prevented.

[0048] The liquid hydrogen tank 1 according to item 7 is the liquid hydrogen tank 1 according to item 6, wherein the pressure P2 of the annular region 25 is lower than the pressure P3 of the inter-tank region 23 excluding the annular region 25 .

[0049] This can prevent the heat-insulating layer 24 and its supporting member from being damaged or the heat-insulating layer 24 from being lifted up.

[0050] The liquid hydrogen tank 1 according to item 8 is the liquid hydrogen tank 1 according to item 4, wherein the pressure regulating 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.

[0051] In this way, by managing the differential pressure between the interior of the inner tank 21 and the inter-tank region 23 within the differential pressure setting value, it is possible to prevent damage to the tank components due to excessive differential pressure.

[0052] The liquid hydrogen tank 1 of item 9 is the liquid hydrogen tank 1 of item 8, wherein the pressure regulating device 3 comprises: a connecting pipe 36 connecting the gas phase of the inner tank 21 and the inter-tank region 23; and a second valve that, when the differential pressure between the inner tank pressure P1 and the inter-tank pressure P3 exceeds the differential pressure setting value, introduces the gasified gas of the gas phase of the inner tank 21 into the inter-tank region 23 through the connecting pipe 36. The second valve corresponds to the differential pressure safety valve 35 in the above embodiment.

[0053] In the liquid hydrogen tank 1 of the above structure, the differential pressure between the inner tank 21 and the inter-tank region 23 is managed independently of the operator's operation. In addition, the inter-tank pressure P3 can be adjusted based on the relative relationship between the inner tank pressure P1 and the inter-tank pressure P3 without measuring the inter-tank pressure P3.

[0054] In the operation method of the liquid hydrogen tank 1 of item 10 of the present disclosure, the liquid hydrogen tank 1 comprises: an inner tank 21, which stores liquid hydrogen L; an outer tank 22, which surrounds the inner tank 21; and a heat-proof layer 24, which is arranged in the inter-tank area 23 between the inner tank 21 and the outer tank 22 and covers the outer wall of the inner tank 21, wherein, when the inter-tank area 23 is filled with hydrogen gas G and the inner tank 21 stores liquid hydrogen L, the inter-tank pressure P3, which is the pressure of the inter-tank area 23, is maintained lower than the saturated vapor pressure of hydrogen at a specified temperature.

[0055] In addition, the operating method of the liquid hydrogen tank 1 of item 11 is based on the operating method of the liquid hydrogen tank 1 of item 10, wherein, during storage, when the inter-tank pressure P3 exceeds a specified inter-tank allowable pressure that is lower than the saturated vapor pressure of hydrogen at a specified temperature, hydrogen gas G is released from the inter-tank area 23 to reduce the inter-tank pressure P3 to less than the inter-tank allowable pressure.

[0056] According to the operating method of the liquid hydrogen tank 1 of the tenth and eleventh items, by maintaining the inter-tank pressure P3 at a value lower than the saturated vapor pressure of hydrogen at a predetermined temperature, even if the temperature of the hydrogen gas G in the inter-tank region 23 decreases, liquefaction due to condensation of the hydrogen gas G can be suppressed. Therefore, damage to the tank components caused by liquefaction of the hydrogen gas G in the inter-tank region 23, deterioration of the heat protection layer 24 disposed in the inter-tank region 23, and increase in heat input due to the heat pipe effect can be suppressed.

[0057] The operating method of the liquid hydrogen tank 1 of item 12 is based on the operating method of the liquid hydrogen tank 1 of item 10, wherein, during storage, when the inter-tank pressure P3 exceeds a prescribed first inter-tank allowable pressure lower than the saturated vapor pressure of hydrogen at a prescribed 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 lower than the saturated vapor pressure of hydrogen at a prescribed temperature and higher than the first inter-tank allowable pressure, hydrogen gas G is released from the inter-tank region 23 through the first release flow path and the second release flow path, so that the inter-tank pressure P3 is reduced to less than the first inter-tank allowable pressure. The first release flow path corresponds to the release flow path for releasing 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 for releasing hydrogen gas G from the inter-tank region 23 through the inter-tank safety valve 33 in the above embodiment.

[0058] According to the operating method of the liquid hydrogen tank 1, the hydrogen gas G can be released from the inter-tank area 23 of the liquid hydrogen tank 1 in two stages: a first stage using the first release flow path and a second stage using the first release flow path and the second release flow path.

[0059] The functions implemented by the control device described in this specification may also be installed in a circuit system (circuitry) or a processing circuit (processing circuitry) including a general-purpose processor, a special-purpose processor, an integrated circuit, ASICs (Application Specific Integrated Circuits), a CPU (Central Processing Unit), an existing circuit and / or a combination thereof, which is programmed to implement the functions described. The processor includes transistors and other circuits and is regarded as a circuit system (circuitry) or a processing circuit (processing circuitry). The processor may also be a programmable processor (programmed processor) that executes a program stored in a memory. In this specification, a circuit system (circuitry), a unit, and a component are hardware programmed in a manner to implement the described functions or hardware that is executed. The hardware may also be all the hardware disclosed in this specification, or all the hardware that is programmed to implement the described functions, or all the hardware known as the executed hardware. In the case where the hardware is a processor of a type that is regarded as a circuit system (circuitry), the circuit system (circuitry), component or unit is a combination of hardware and software used to constitute the hardware and / or processor.

[0060] The above discussion of the present disclosure is presented for the purpose of illustration and description, and is not intended to limit the present disclosure to the methods disclosed in this specification. For example, in the above detailed description, various features of the present disclosure are summarized into one embodiment for the purpose of rationalizing the present disclosure, but several of the multiple features may be combined. In addition, the multiple features included in the present disclosure may also be combined with alternative embodiments, structures or methods other than those described above.

Claims

1. A liquid hydrogen tank, comprising: an inner tank containing liquid hydrogen; an outer tank surrounding the inner tank; and a heat protection layer, which is arranged in the inter-groove region between the inner groove and the outer groove and covers the outer wall of the inner groove, When the inter-tank region is filled with hydrogen gas and the liquid hydrogen is stored in the inner tank, the inter-tank pressure, which is the pressure of the inter-tank region, is lower than the saturated vapor pressure of hydrogen at a predetermined temperature.

2. The liquid hydrogen tank according to claim 1, wherein: During the storage, the inter-tank pressure is lower than the inner tank pressure which is the pressure of the gas phase portion in the inner tank.

3. The liquid hydrogen tank according to claim 1 or 2, wherein: The predetermined temperature is the temperature of the liquid hydrogen stored in the inner tank, the temperature of the inner surface of the inner tank, or the temperature of the outer surface of the inner tank.

4. The liquid hydrogen tank according to any one of claims 1 to 3, wherein: The liquid hydrogen tank has a pressure regulating device for regulating the inter-tank pressure.

5. The liquid hydrogen tank according to claim 4, wherein: The pressure regulating device includes a first valve for releasing the hydrogen gas in the inter-cell region to the outside when the inter-cell pressure exceeds a predetermined inter-cell allowable pressure that is lower than the saturated vapor pressure of hydrogen at the predetermined temperature.

6. The liquid hydrogen tank according to any one of claims 1 to 5, wherein: The inter-groove region includes a gas-tight annular region filled with the hydrogen gas between the inner groove and the heat protection layer. During the storage, the pressure of the annular region is lower than the pressure of the inner tank.

7. The liquid hydrogen tank according to claim 6, wherein: During the storage, the pressure of the annular region is lower than the pressure of the inter-groove region excluding the annular region.

8. The liquid hydrogen tank according to claim 4, wherein: The pressure regulating device maintains a differential pressure between the pressure of the inner tank and the inter-tank pressure at or below a predetermined differential pressure setting value.

9. The liquid hydrogen tank according to claim 8, wherein: The pressure regulating device comprises: a connecting pipe connecting the gas phase portion of the inner tank with the inter-tank region; and and a second valve for introducing the vaporized gas in the gas phase portion of the inner tank into the inter-tank region through the connecting pipe when the differential pressure between the inner tank pressure and the inter-tank pressure exceeds the differential pressure setting value.

10. A method for operating a liquid hydrogen tank, The liquid hydrogen tank has: an inner tank containing liquid hydrogen; an outer tank surrounding the inner tank; and a heat protection layer, which is arranged in the inter-groove region between the inner groove and the outer groove and covers the outer wall of the inner groove, in, When the inter-tank region is filled with hydrogen gas and the liquid hydrogen is stored in the inner tank, the inter-tank pressure, which is the pressure of the inter-tank region, is maintained lower than the saturated vapor pressure of hydrogen at a predetermined temperature.

11. The method for operating a liquid hydrogen tank according to claim 10, wherein: During the storage, when the inter-tank pressure exceeds a predetermined inter-tank allowable pressure lower than the saturated vapor pressure of hydrogen at the predetermined temperature, the hydrogen gas is released from the inter-tank region to reduce the inter-tank pressure to less than the inter-tank allowable pressure.

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

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