Liquid hydrogen tank and its operating method

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

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 a cryogenic liquefied gas, a double-walled tank is known that includes an inner tank and an outer tank surrounding the inner tank, and the space between the inner tank and the outer tank is filled with gas. For example, Patent Document 1 discloses a double-walled tank having an inner tank and an outer tank, and the space between the inner tank and the outer tank in this double-walled tank is filled with boil-off gas discharged from the inner tank. Also, the space between the tanks is filled with a heat insulating material.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The gas filled in the space between the tanks may condense and liquefy due to pressure fluctuations in the space between the tanks or the like. When the gas between the tanks liquefies, the components of the tank may be damaged because they fall below the allowable lower limit temperature of the components, the heat insulating material arranged between the tanks may deteriorate, or the amount of heat input may increase due to the heat pipe effect.

[0005] In view of the above circumstances, the present disclosure has been made, and its object is to suppress the liquefaction of the gas in the space between the tanks in a liquid hydrogen tank in which an inner tank storing liquid hydrogen, an outer tank surrounding the inner tank, and the space between the inner tank and the outer tank are filled with the vaporized gas of liquid hydrogen.

Means for Solving the Problems

[0006] To solve the above problems, a liquid hydrogen tank according to one aspect of this disclosure is provided. An inner tank containing liquid hydrogen, The outer tank surrounds the inner tank, The system includes a heat-insulating layer disposed in the inter-tank region between the inner tank and the outer tank, which covers the outer wall of the inner tank. During storage, when the inter-tank region is filled with hydrogen gas and the inner tank contains the liquid hydrogen, 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 containing liquid hydrogen; an outer tank surrounding the inner tank; and a heat-insulating layer disposed in the inter-tank region between the inner tank and the outer tank and covering the outer wall of the inner tank, During storage, when the inter-tank region is filled with hydrogen gas and the inner tank contains the liquid hydrogen, the inter-tank pressure, which is the pressure in the inter-tank region, is maintained at a level lower than the saturated vapor pressure of hydrogen at a predetermined temperature. [Effects of the Invention]

[0008] According to this disclosure, in a liquid hydrogen tank comprising an inner tank containing liquid hydrogen, an outer tank surrounding the inner tank, and a region between the inner and outer tanks filled with vaporized liquid hydrogen gas, the liquefaction of the gas in the region between the tanks can be suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a vertical cross-sectional view showing a schematic configuration of a liquid hydrogen tank according to one aspect of the present disclosure. [Figure 2] Figure 2 is a vertical cross-sectional view showing the schematic configuration of a modified liquid hydrogen tank. [Modes for carrying out the invention]

[0010] Next, embodiments of the present disclosure will be described with reference to the drawings. Figure 1 is a vertical cross-sectional view showing a schematic configuration of a liquid hydrogen tank 1 according to one aspect of the present disclosure. The liquid hydrogen tank 1 shown in Figure 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 floating structure, or it may be installed on land.

[0011] The liquid hydrogen tank 1 comprises an inner tank 21 for containing 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-hulled tank, and may be a triple or multi-hulled tank having at least one tank surrounding 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 tank 21 and the outer tank 22 are spaced radially apart in 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-insulating layer 24 is placed in the inter-tank region 23. The heat-insulating layer 24 covers the outer wall of the inner tank 21 in the inter-tank region 23. The heat-insulating layer 24 is made of an insulating material, and examples of insulating materials include insulating panels, insulating sheets, and fibrous insulating materials. In this specification, the region between the outer wall of the inner tank 21 and the heat-insulating layer 24 in the inter-tank region 23 is referred to as the "annular region 25," and the region between the heat-insulating layer 24 and the inner wall of the outer tank 22 is referred to as the heat-insulating layer outer peripheral region 26. Here, the annular region 25 may be formed by a gap provided between the outer wall of the inner tank 21 and the heat-insulating layer 24, or it may be formed by voids or holes formed on the surface of the heat-insulating layer 24 facing the outer wall of the inner tank 21.

[0013] The inter-tank region 23 is filled with a gas of the same type 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 the vaporized gas produced when the liquid hydrogen L vaporizes inside the inner tank 21, or it may be a 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 independent spaces. On the other hand, the inter-tank region 23 can be (i) in which the annular region 25 and the outer peripheral region 26 of the heat-insulating layer are in communication, or (ii) in which the annular region 25 and the outer peripheral region 26 of the heat-insulating layer are independent spaces. If the heat-insulating layer 24 is an airtight layer, the annular region 25 and the outer peripheral region 26 of the heat-insulating layer become independent spaces. Therefore, the following describes the method for adjusting the pressure in the inter-tank region 23 of the liquid hydrogen tank 1 during storage in both cases (i) and (ii) above.

[0015] (i) When the annular region 25 and the outer peripheral region 26 of the heat-insulating layer are in communication. The pressure inside the inner tank 21 is referred to as "inner tank pressure P1," and the pressure in the inter-tank region 23 is referred to as "inter-tank pressure P3." Since the annular region 25 and the outer peripheral region 26 of the heat-insulating layer are in communication, the pressure in both of these regions is the inter-tank pressure P3.

[0016] During the initial setup 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 such that the inner tank pressure P1 is a predetermined standard inner tank pressure and the inter-tank pressure P3 is a predetermined standard inter-tank 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 in the gas phase portion of the inner tank 21, that is, the inner tank pressure P1. The inner tank safety valve 32 is configured to be opened when the inner tank pressure P1 exceeds a predetermined inner tank allowable pressure so that the inner tank pressure P1 does not exceed a predetermined inner tank design pressure, and to release the vaporized gas in the inner tank 21 to the outside. The inner tank allowable pressure is not higher than the inner tank design pressure and is sufficiently higher than the inner tank standard pressure.

[0018] The liquid hydrogen tank 1 includes a pressure regulating device 3 for regulating the pressure in the inter-tank region 23. The pressure regulating device 3 regulates the inter-tank pressure P3 to be lower than the inner tank pressure P1 and lower than the saturated vapor pressure of hydrogen at a predetermined temperature during storage of the liquid hydrogen tank 1. The pressure regulating device 3 according to the present 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 the outer tank 22 or a pipe or the like communicating with the inter-tank region 23. The inter-tank safety valve 33 is a valve that is closed during normal operation and is opened when the inter-tank pressure P3 exceeds the inter-tank allowable pressure, and corresponds to the first valve in the claims. The inter-tank safety valve 33 is a self-operated 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-operated automatic valve, and a control valve (i.e., a servo-operated automatic valve) or a manual valve that is opened when the inter-tank allowable pressure is exceeded by an actuator controlled by a control device may be used. When the inter-tank safety valve 33 is opened, the hydrogen gas G in the inter-tank region 23 is discharged to the outside of the liquid hydrogen tank 1 through the forced exhaust system, and the inter-tank pressure P3 decreases to below the inter-tank allowable pressure. The forced exhaust system may include a compressor for forcibly exhausting the hydrogen gas G, a discharge tower for safely discharging the hydrogen gas G to the atmosphere, and hydrogen fuel consumption equipment for consuming the hydrogen gas G as fuel or the like.

[0020] The allowable pressure between the tanks is lower than the standard pressure of the inner tank and lower than the saturated vapor pressure of hydrogen at a predetermined temperature. Here, the predetermined temperature is the temperature of the liquid hydrogen stored 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 gas G filled in the inter-tank region 23, and it may be not limited to the measured temperature but an estimated or set temperature between -259°C and -240°C. The allowable pressure between the tanks may be set to the assumed minimum value of the inner tank pressure P1. Since the inter-tank pressure P3 becomes a negative pressure less than 0 KPaG when the inner tank pressure P1 falls below 0 KPaG, the minimum value of the inner tank pressure P1 is higher than 0 KPaG, preferably higher than 5 KPaG. Thus, by adjusting so that the inter-tank pressure P3 does not exceed the predetermined allowable pressure between the tanks, liquefaction due to condensation of the hydrogen gas G in the inter-tank region 23 is prevented.

[0021] In the above, as shown in FIG. 2, the pressure adjustment device 3 may include a shut-off valve 37 provided in a pipe or the like communicating with the inter-tank region 23 separately from the inter-tank safety valve 33. Thereby, the liquid hydrogen tank 1 includes a first discharge passage which is a discharge passage of the hydrogen gas G from the inter-tank region 23 through the shut-off valve 37, and a second discharge passage which is a discharge passage of the hydrogen gas G from the inter-tank region 23 through the inter-tank safety valve 33. The first discharge passage and the second discharge passage are preferably independent of each other, and although these passages may merge on the way, it is preferable that they are independent of each other at least at the outlet from the inter-tank region 23. The shut-off valve 37 is closed during normal operation, and when opened, the hydrogen gas G in the inter-tank region 23 is released to the outside of the liquid hydrogen tank 1 through the first discharge passage. The shut-off valve 37 may be a manual valve operated by an operator or a control valve controlled to open and close by a control device.

[0022] As described above, when the liquid hydrogen tank 1 has two discharge channels from the inter-tank region 23, two levels of inter-tank allowable pressure are provided: a first inter-tank allowable pressure and a second inter-tank allowable pressure that is higher than the first inter-tank allowable pressure. Both the first and second inter-tank allowable pressures 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 allowable pressure. When the inter-tank pressure P3 exceeds the first allowable pressure, the on-off valve 37 is opened first, and the hydrogen gas G in the inter-tank region 23 is released to the outside through the first discharge channel. An inter-tank pressure sensor 38 for detecting the inter-tank pressure P3 is provided in the liquid hydrogen tank 1, and an alarm may be issued to notify the system when the pressure detected by the inter-tank pressure sensor 38 exceeds the first allowable pressure. If the opening of the on-off valve 37 does not cause the inter-tank pressure P3 to drop below the first allowable inter-tank pressure, and the inter-tank pressure P3 exceeds the second allowable inter-tank pressure, the inter-tank safety valve 33 is opened. With the opening of the on-off valve 37 and the inter-tank safety valve 33, hydrogen gas G is released to the outside through the first and second discharge channels, and the inter-tank pressure P3 drops to below the first allowable inter-tank pressure.

[0023] Returning to Figure 1, the connecting pipe 36 is a pipe that connects the gas phase portion in the inner tank 21 to 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 of the claims. The differential pressure safety valve 35 maintains the differential pressure between the inner tank pressure P1 and the inter-tank pressure P3 to be greater than 0 and less than or equal to the 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 connecting 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 the 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 region 23 and the inner tank 21 within an appropriate range and preventing excessive load on the components of the liquid hydrogen tank 1. The differential pressure safety valve 35 is a self-operating 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 differential pressure set value, controlled by an actuator controlled by a control device.

[0024] (ii) When the annular region 25 and the outer peripheral region 26 of the heat-insulating layer are independent spaces. Similarly, the liquid hydrogen tank 1 includes an internal tank pressure sensor 31, an internal 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 the other regions of the inter-tank region 23 (i.e., the outer peripheral region 26 of the heat-insulating layer). Here, the pressure in the annular region 25 of the inter-tank region 23 is defined as the annular pressure P2, and the pressure in the region of the inter-tank region 23 excluding the annular region 25 (i.e., the outer peripheral region 26 of the heat-insulating layer) is defined as the inter-tank pressure P3.

[0026] The annular region 25 is pre-filled with hydrogen gas G to achieve the annular standard pressure when the inner tank 21 is not filled with liquid hydrogen L or during initial setup. The annular pressure P2 will be lower than the annular standard pressure due to the coldness of the liquid hydrogen L contained in the inner tank 21 during loading, but it will never 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. By setting the annular standard pressure in this way, liquefaction due to condensation of hydrogen gas G in the annular region 25 is prevented.

[0027] If the inter-tank pressure P3 falls below the annular pressure P2, the heat-insulating layer 24 supported by the inner tank 21 may lift or the support may be damaged. Therefore, the inter-tank pressure P3 is adjusted to be equal to or greater than the annular pressure P2. As mentioned above, the annular pressure P2 is less than or equal to the annular standard pressure, so the inter-tank pressure P3 should be adjusted to be equal to or greater than the annular standard pressure. For example, the inter-tank standard pressure is set to a value equal to or greater 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 equal to or greater than the annular standard pressure.

[0028] [Summary] The liquid hydrogen tank 1 relating to item 1 of this disclosure is An inner tank 21 containing liquid hydrogen L, The outer tank 22 surrounds the inner tank 21, It comprises a heat-insulating layer 24 positioned in the inter-tank region 23 between the inner tank 21 and the outer tank 22, and covering the outer wall of the inner tank 21, During storage, when hydrogen gas G is filled in the inter-tank region 23 and liquid hydrogen L is contained in the inner tank 21, 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 with the above configuration, the hydrogen gas G filled in the inter-tank region 23 may decrease to substantially the same temperature as the liquid hydrogen L contained in the inner tank 21. Therefore, if the inter-tank pressure P3 becomes lower than the saturated vapor pressure at the temperature of the liquid hydrogen L stored in the inner tank 21, there is a risk that the hydrogen gas G in the inter-tank region 23 will condense. In the liquid hydrogen tank 1 with the above configuration, the inter-tank 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 in the inter-tank region 23 does not condense and liquefy even if its temperature decreases. Therefore, damage to tank components caused by the liquefaction of hydrogen gas G in the inter-tank region 23, deterioration of the heat-insulating layer 24 placed in the inter-tank region 23, and an increase in heat input due to the heat pipe effect can be suppressed.

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

[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 of pressure P1). If the inter-tank pressure P3 is equal to or greater 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 greater than the temperature of the liquid hydrogen L (= 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 this 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 saturation vapor pressure at the temperature of the liquid hydrogen L contained in the inner tank 21. Therefore, with the liquid hydrogen tank 1 configured above, 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 in the inter-tank region 23 is suppressed. Therefore, damage to tank components caused by the liquefaction of hydrogen gas G in the inter-tank region 23, deterioration of the heat-insulating layer 24 placed 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 relating to the third item is a liquid hydrogen tank 1 relating to the first or second item in which 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] With the liquid hydrogen tank 1 configured as described above, 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. Therefore, even if the temperature of the hydrogen gas G filled in the inter-tank region 23 decreases, liquefaction due to condensation of the hydrogen gas G can be prevented.

[0034] The liquid hydrogen tank 1 relating to item 4 is a liquid hydrogen tank 1 relating to any of items 1 to 3, and is equipped with a pressure adjustment device 3 for adjusting the inter-tank pressure P3.

[0035] The liquid hydrogen tank 1 relating to item 5 is the liquid hydrogen tank 1 relating to item 4, and the pressure regulating 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] According to the liquid hydrogen tank 1 relating to items 4 and 5, liquefaction of hydrogen gas G in the inter-tank region 23 can be prevented regardless of operator operation. The first valve described above corresponds to the inter-tank safety valve 33 in the above embodiment.

[0037] The liquid hydrogen tank 1 relating to item 6 is a liquid hydrogen tank 1 relating to any of items 1 to 5, wherein the inter-tank region 23 includes an airtight annular region 25 filled with hydrogen gas G between the inner tank 21 and the heat-insulating layer 24, and during storage, the pressure P2 in the annular region 25 is lower than the inner tank pressure P1.

[0038] This prevents liquefaction due to condensation of the hydrogen gas G filling the annular region 25, even if the temperature of the hydrogen gas G decreases.

[0039] In the liquid hydrogen tank 1 relating to item 7, the pressure P2 in the annular region 25 is lower than the pressure P3 in the inter-tank region 23 excluding the annular region 25.

[0040] This prevents damage to the heat-insulating layer 24 and its supporting members, as well as the lifting of the heat-insulating layer 24.

[0041] In the liquid hydrogen tank 1 relating to item 8, 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.

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

[0043] The liquid hydrogen tank 1 relating to item 9 is the same as the liquid hydrogen tank 1 relating to item 8, and the pressure regulating device 3 has a connecting pipe 36 that connects the gas phase portion 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 a differential pressure setting value, introduces the vaporized gas from the gas phase portion 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.

[0044] In the liquid hydrogen tank 1 with the above configuration, the differential pressure between the inside of the inner tank 21 and the inter-tank region 23 is controlled independently of operator operation. Furthermore, 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.

[0045] A method for operating a liquid hydrogen tank 1 according to item 10 of this disclosure comprises an inner tank 21 containing liquid hydrogen L, an outer tank 22 surrounding the inner tank 21, and a heat-insulating layer 24 arranged in the inter-tank region 23 between the inner tank 21 and the outer tank 22 and covering the outer wall of the inner tank 21. During storage, when hydrogen gas G is filled in the inter-tank region 23 and liquid hydrogen L is contained in the inner tank 21, the 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 for the liquid hydrogen tank 1 related to item 11 is the same as the operating method for the liquid hydrogen tank 1 related to item 10, but when the inter-tank pressure P3 exceeds a predetermined allowable inter-tank pressure that is lower than the saturated vapor pressure of hydrogen at a predetermined temperature during storage, hydrogen gas G is released from the inter-tank region 23 to reduce the inter-tank pressure P3 to below the allowable inter-tank pressure.

[0047] According to the operating method of the liquid hydrogen tank 1 described in items 10 and 11, 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 due to condensation of hydrogen gas G in the inter-tank region 23 even if the temperature of hydrogen gas G decreases. Therefore, damage to tank components caused by the liquefaction of hydrogen gas G in the inter-tank region 23, deterioration of the heat-insulating layer 24 placed in the inter-tank region 23, and an increase in heat input due to the heat pipe effect can be suppressed.

[0048] The operating method for the liquid hydrogen tank 1 according to item 12 is the same as the operating method for the liquid hydrogen tank 1 according to item 10, but during storage, when the inter-tank pressure P3 exceeds a predetermined first allowable inter-tank 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 through the first discharge channel, and when the inter-tank pressure P3 exceeds a second allowable inter-tank pressure which is lower than the saturated vapor pressure of hydrogen at a predetermined temperature and higher than the first allowable inter-tank pressure, hydrogen gas G is released from the inter-tank region 23 through the first and second discharge channels to reduce the inter-tank pressure P3 to less than the first allowable inter-tank pressure. The first discharge channel corresponds to a discharge channel that releases hydrogen gas G from the inter-tank region 23 through the on-off valve 37 in the above embodiment. The second discharge channel corresponds to a discharge channel 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 operating method for 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 discharge channel, and a second stage using the first and second discharge channels.

[0050] The functions realized by the control devices described herein may be implemented in a circuit 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 realize the described functions. A processor, including transistors and other circuits, is considered a circuit or processing circuitry. A processor may be a programmed processor that executes a program stored in memory. In this specification, circuitry, unit, and means are hardware programmed to realize or perform the described functions. Such hardware may be any hardware disclosed herein, or any hardware known to be programmed to realize or perform the described functions. If such hardware is a processor that is considered a type of circuitry, then such circuitry, means, or unit is a combination of hardware and software used to constitute such hardware and / or processor.

[0051] The discussions of this disclosure described above are presented for illustrative and explanatory purposes only and are not intended to limit the disclosure to the forms disclosed herein. For example, in the detailed description above, various features of the disclosure are grouped into a single embodiment for the purpose of streamlining the disclosure, but some of the features may be combined. Also, some of the features included in this disclosure may be combined into alternative embodiments, configurations, or aspects other than those discussed above.

Claims

1. An inner tank containing liquid hydrogen, The outer tank surrounds the inner tank, The system includes a heat-insulating layer disposed in the inter-tank region between the inner tank and the outer tank, which covers the outer wall of the inner tank. When the inter-tank region is filled with hydrogen gas and the inner tank contains the liquid hydrogen during storage, 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. Liquid hydrogen tank.

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

3. The predetermined temperature is the temperature of the liquid hydrogen contained 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. A liquid hydrogen tank according to claim 1 or 2.

4. The system includes a pressure regulating device for adjusting the pressure between the tanks. A liquid hydrogen tank according to claim 1.

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

6. The inter-tank region includes an airtight annular region filled with hydrogen gas between the inner tank and the heat-insulating layer. During storage, the pressure in the annular region is lower than the pressure in the inner tank. A liquid hydrogen tank according to claim 1 or 2.

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

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

9. The pressure regulating device includes a connecting pipe that connects the gas phase portion of the inner tank to the inter-tank region, and a second valve that, when the differential pressure between the inner tank pressure (which is the pressure in the gas phase portion of the inner tank) and the inter-tank pressure exceeds the differential pressure setting value, introduces the vaporized gas from the gas phase portion of the inner tank into the inter-tank region through the connecting pipe. A liquid hydrogen tank according to claim 8.

10. A method for operating a liquid hydrogen tank comprising an inner tank for containing liquid hydrogen, an outer tank surrounding the inner tank, and a heat-insulating layer disposed in the inter-tank region between the inner tank and the outer tank and covering the outer wall of the inner tank, During storage, when the inter-tank region is filled with hydrogen gas and the inner tank contains the liquid hydrogen, the inter-tank pressure, which is the pressure in the inter-tank region, is kept lower than the saturated vapor pressure of hydrogen at a predetermined temperature. Operating procedures for liquid hydrogen tanks.

11. During storage, if the inter-tank pressure exceeds a predetermined allowable inter-tank pressure that is 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 below the allowable inter-tank pressure. A method for operating a liquid hydrogen tank according to claim 10.

12. During storage, if the inter-tank pressure exceeds a predetermined first allowable inter-tank pressure that is lower than the saturated vapor pressure of hydrogen at the predetermined temperature, the hydrogen gas is released from the inter-tank region through the first discharge channel. If the inter-tank pressure exceeds a second allowable inter-tank pressure that is lower than the saturated vapor pressure of hydrogen at the predetermined temperature and higher than the first allowable inter-tank pressure, the hydrogen gas is released from the inter-tank region through the first and second discharge channels to reduce the inter-tank pressure to below the first allowable inter-tank pressure. A method for operating a liquid hydrogen tank according to claim 10.

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