Method for monitoring vacuum levels in hydrogen storage systems and liquefied hydrogen tanks

Abstract

This invention provides a hydrogen storage system and a method for monitoring the vacuum level of a liquefied hydrogen tank, which can detect a decrease in the vacuum level of a vacuum-insulated liquefied hydrogen tank at an earlier stage. [Solution] The hydrogen storage system is a hydrogen storage system equipped with a liquefied hydrogen tank for storing liquefied hydrogen, the liquefied hydrogen tank includes an outer tank and an inner tank installed within the outer tank at a position spaced apart from the inner surface of the outer tank, the inter-tank space between the outer tank and the inner tank is a vacuum, and the internal space of the inner tank where liquefied hydrogen is stored is vacuum-insulated from the outside, the hydrogen storage system is equipped with a pressure detector for detecting the pressure in the internal space and a processing circuit, the processing circuit determines that the vacuum level in the inter-tank space has decreased when the pressure in the internal space exceeds a reference value or is estimated to exceed a reference value, and outputs a predetermined vacuum level decrease signal.

Description

Technical Field

[0001] The present disclosure relates to a hydrogen storage system and a method for monitoring the degree of vacuum in a liquefied hydrogen tank.

Background Art

[0002] A liquefied hydrogen tank for storing liquefied hydrogen has a double-shell structure. That is, the liquefied hydrogen tank includes an outer tank and an inner tank, and the internal space of the inner tank where liquefied hydrogen is stored is vacuum-insulated from the outside due to the inter-tank space between the outer tank and the inner tank being vacuum.

[0003] In such a vacuum-insulated liquefied hydrogen tank, when a micropore is formed in the outer tank due to deterioration of the outer tank or the like, outside air enters the inter-tank space through the micropore, and the degree of vacuum decreases.

[0004] Patent Document 1 below discloses detecting the temperature of the outer surface of the outer tank or the temperature below the liquefied hydrogen tank with a thermometer, and determining that the degree of vacuum has decreased when the temperature becomes low.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] This is based on the following phenomenon: When outside air enters the space between the tanks through micropores formed in the outer tank, the outside air is cooled because the outer surface of the inner tank in contact with the liquefied hydrogen is at a low temperature, and liquefied air containing liquefied nitrogen, liquefied oxygen, etc. is generated in the space between the tanks. When the outer tank is cooled by the liquefied air generated in the space between the tanks, the outside air in contact with the outer surface of the outer tank is also cooled, and liquefied air containing liquefied nitrogen and liquefied oxygen is generated on the outer surface of the outer tank. As a result, the temperature of the outer surface of the outer tank and the temperature below the liquefied hydrogen tank decrease due to the liquefied air dripping from the outer surface of the outer tank. Therefore, a decrease in vacuum can be determined by detecting the temperature of the outer surface of the outer tank or the temperature below the liquefied hydrogen tank.

[0007] Thus, in the above-mentioned Patent Document 1, it is possible to detect a decrease in vacuum level after liquefied air has been generated on the outer surface of the outer tank. However, there is room for improvement in detecting the decrease in vacuum level earlier in the configuration of Patent Document 1.

[0008] This disclosure has been made in view of the above-mentioned problems, and aims to provide a hydrogen storage system and a method for monitoring the vacuum level of a liquefied hydrogen tank that can detect a decrease in the vacuum level of a vacuum-insulated liquefied hydrogen tank at an earlier stage. [Means for solving the problem]

[0009] A hydrogen storage system according to one aspect of the present disclosure is a hydrogen storage system comprising a liquefied hydrogen tank for storing liquefied hydrogen, wherein the liquefied hydrogen tank includes an outer tank and an inner tank installed within the outer tank at a position spaced apart from the inner surface of the outer tank, and the internal space of the inner tank in which the liquefied hydrogen is stored is vacuum-insulated from the outside by the inter-tank space between the outer tank and the inner tank being a vacuum, and the hydrogen storage system comprises a pressure detector for detecting the pressure in the internal space and a processing circuit, wherein the processing circuit determines that the vacuum level in the inter-tank space has decreased when the pressure in the internal space exceeds a reference value or is estimated to exceed a reference value, and outputs a predetermined vacuum level decrease signal.

[0010] Another embodiment of the present disclosure is a hydrogen storage system comprising a liquefied hydrogen tank for storing liquefied hydrogen, wherein the liquefied hydrogen tank is mounted on a ship and includes an outer tank and an inner tank installed within the outer tank at a position spaced apart from the inner surface of the outer tank, wherein the space between the outer tank and the inner tank is a vacuum, thereby providing vacuum insulation to the internal space of the inner tank where the liquefied hydrogen is stored from the outside, and the hydrogen storage system comprises a detector for detecting a predetermined parameter that changes with a change in the degree of vacuum in the space between the tanks, a water injector for injecting water or seawater into the outer tank, and a processing circuit, wherein the processing circuit outputs a command signal to activate the water injector when the value detected by the detector falls outside a normal range.

[0011] A vacuum monitoring method according to another aspect of the present disclosure is a method for monitoring the vacuum level in a liquefied hydrogen tank for storing liquefied hydrogen, wherein the liquefied hydrogen tank includes an outer tank and an inner tank installed within the outer tank at a position spaced apart from the inner surface of the outer tank, and the space between the outer tank and the inner tank is a vacuum, thereby vacuum-insulating the internal space of the inner tank in which the liquefied hydrogen is stored from the outside, and the vacuum monitoring method obtains the pressure of the internal space and determines that the vacuum level in the space between the tanks has decreased if the pressure of the internal space exceeds a reference value or is estimated to exceed a reference value. [Effects of the Invention]

[0012] According to this disclosure, a decrease in the vacuum level in a vacuum-insulated liquefied hydrogen tank can be detected at an earlier stage. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic diagram showing the general configuration of a hydrogen storage system according to Embodiment 1 of this disclosure. [Figure 2] Figure 2 is an illustrative diagram showing the state of the liquefied hydrogen tank shown in Figure 1 when a decrease in vacuum occurs. [Figure 3]Figure 3 shows an example of the injection piping for the water injector shown in Figure 1. [Figure 4] Figure 4 is a schematic diagram showing the general configuration of a hydrogen storage system according to Embodiment 2 of this disclosure. [Figure 5] Figure 5 shows the calculation block for determining vacuum level decrease in this embodiment. [Figure 6] Figure 6 is a schematic diagram showing the general configuration of a hydrogen storage system according to a modified example of Embodiment 1 of this disclosure. [Modes for carrying out the invention]

[0014] An embodiment will be described in detail below with reference to the drawings. In the following, the same or corresponding elements will be denoted by the same reference numerals throughout all the drawings, and redundant explanations will be omitted.

[0015] [Embodiment 1] Figure 1 is a schematic diagram showing the general configuration of a hydrogen storage system according to Embodiment 1 of the present disclosure. The hydrogen storage system 1A in this embodiment includes a liquefied hydrogen tank 2 for storing liquefied hydrogen. The liquefied hydrogen tank 2 includes an outer tank 3 and an inner tank 4 installed within the outer tank 3 at a position spaced apart from the inner surface of the outer tank 3. Liquefied hydrogen is introduced and stored in the internal space 6 of the inner tank 4. The inter-tank space 5 between the outer tank 3 and the inner tank 4 is maintained under vacuum. As a result, the internal space 6 of the inner tank 4 where the liquefied hydrogen is stored is vacuum-insulated from the outside.

[0016] In this embodiment, the liquefied hydrogen tank 2 is a marine tank mounted on a ship. In this embodiment, the liquefied hydrogen tank 2 is a horizontally oriented cylindrical shape, as shown in Figure 3, which will be described later. However, the liquefied hydrogen tank 2 may be a vertically oriented cylindrical shape. Alternatively, the liquefied hydrogen tank 2 may be spherical or substantially rectangular parallelepiped.

[0017] The ship in this embodiment uses the liquefied hydrogen stored in the liquefied hydrogen tank 2 as fuel for propulsion. Note that the liquefied hydrogen may also be used in a reciprocating engine, a boiler, or a fuel cell that generates shipboard electricity or serves as a heat source. For this reason, the hydrogen storage system 1A includes a first evaporator 7, a first feed pipe 8, and a second feed pipe 9. The first feed pipe 8 is connected between the lower part of the internal space 6 of the liquefied hydrogen tank 2 and the first evaporator 7. The second feed pipe 9 is connected between the first evaporator 7 and the engine 10.

[0018] The liquefied hydrogen in the liquefied hydrogen tank 2 is sent to the first evaporator 7 through the first feed pipe 8 and vaporized in the first evaporator 7. The hydrogen gas vaporized in the first evaporator 7 is supplied as fuel to the engine 10 through the second feed pipe 9.

[0019] Furthermore, the hydrogen storage system 1A includes a second evaporator 11, a third feed pipe 12, and a return pipe 13. The third feed pipe 12 is connected between the lower part of the internal space 6 of the liquefied hydrogen tank 2 and the second evaporator 11. The return pipe 13 is connected between the second evaporator 11 and the upper part of the internal space 6 of the liquefied hydrogen tank 2.

[0020] The liquefied hydrogen in the liquefied hydrogen tank 2 is sent to the second evaporator 11 through the third feed pipe 12 and vaporized in the second evaporator 11. The hydrogen gas vaporized in the second evaporator 11 is returned to the internal space 6 of the liquefied hydrogen tank 2 through the return pipe 13. Thereby, the pressure P in the internal space 6 of the liquefied hydrogen tank 2 increases, and a pushing pressure for pushing the liquefied hydrogen into the first evaporator 7 through the first feed pipe 8 can be generated.

[0021] Figure 2 is an illustrative diagram showing the state when a decrease in vacuum occurs in the liquefied hydrogen tank shown in Figure 1. In Figure 2, components other than the liquefied hydrogen tank 2 are not shown. As shown in Figure 2, if micropores H are formed in the outer tank 3 due to deterioration of the outer tank 3, outside air may enter the space between the tanks 5, potentially causing a decrease in vacuum. Note that Figure 2 shows an example where micropores H are formed at the top of the outer tank 3, but micropores H can be formed at any location on the outer tank 3.

[0022] When outside air enters the inter-tank space 5 through the micropores H formed in the outer tank 3, the outside air is cooled because the outer surface of the inner tank 4, which is in contact with the liquefied hydrogen, is at a low temperature, and liquefied air A1 containing liquefied nitrogen and liquefied oxygen is generated in the inter-tank space 5. When the outer tank 3 is cooled by the liquefied air A1 generated in the inter-tank space 5, the outside air in contact with the outer surface of the outer tank 3 is also cooled, and liquefied air A2 containing liquefied nitrogen and liquefied oxygen is generated on the outer surface of the outer tank 3. As a result, the temperature of the outer surface of the outer tank 3 decreases, and the temperature below the liquefied hydrogen tank 2 decreases due to the liquefied air A2 dripping from the outer surface of the outer tank 3.

[0023] Therefore, by measuring the temperature of the outer surface of the outer tank 3 and the temperature below the liquefied hydrogen tank 2, the generation of liquefied air A2 can be detected, and as a result, it can be detected that the vacuum level in the liquefied hydrogen tank 2 is decreasing. However, with this detection method, it is not possible to detect the decrease in vacuum level before the generation of liquefied air A2.

[0024] When the vacuum level in the inter-tank space 5 decreases, the vacuum insulation effect with the outside decreases, and the retention capacity of the liquefied hydrogen stored in the internal space 6 decreases. For this reason, it is desirable to detect the decrease in vacuum level as early as possible.

[0025] Furthermore, as in this embodiment, when the liquefied hydrogen tank 2 is a marine tank, a steel plate that receives stress on the hull as part of the ship's structure is installed below the liquefied hydrogen tank 2. If liquefied air A2 generated on the outer surface of the outer tank 3 drips onto such a steel plate, the steel plate will become extremely cold, and there is a risk that it will not be able to receive the proper stress due to low-temperature embrittlement. For this reason, in typical ships, a tray 14 to receive the liquefied air A2 is installed below the liquefied hydrogen tank 2, as shown in Figure 2. For example, the temperature of the surface of the tray 14 is measured as the temperature below the liquefied hydrogen tank 2.

[0026] Such trays 14 are sized according to the size of the liquefied hydrogen tank 2. Furthermore, the trays 14 are made of a material that is resistant to the extremely low temperatures caused by liquefied air A2, such as stainless steel. Thus, the installation of trays 14 increases the cost of ship equipment. For this reason, it is desirable to detect a decrease in vacuum before liquefied air A2 is generated.

[0027] Therefore, in this embodiment, the hydrogen storage system 1A includes a pressure detector 15 for detecting the pressure in the internal space 6 of the inner tank 4, and a processing circuit 16. The processing circuit 16 determines that the vacuum level in the inter-tank space 5 has decreased when the pressure P in the internal space 6 exceeds a reference value Po. When the processing circuit 16 determines that the vacuum level has decreased, it outputs a predetermined vacuum level decrease signal S.

[0028] The processing circuit 16 includes a computer such as a microcontroller, personal computer, or PLC (Programmable Logic Controller). More specifically, the processing circuit 16 includes a processor, memory, and peripheral circuits. The processor includes, for example, a CPU or MPU. The memory includes ROM, RAM, registers, non-volatile storage, etc. The peripheral circuits include input / output interfaces, etc. Furthermore, the processing circuit 16 may include input devices for user operation input and output devices such as monitors that output the control status.

[0029] The functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, dedicated processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuits. In this specification, a circuit, unit, means, or part is hardware that performs the enumerated functions, or hardware programmed to perform the enumerated functions. The hardware may be hardware disclosed herein, or other known hardware that is programmed or configured to perform the enumerated functions. If the hardware is a processor, which is considered a type of circuit, then the circuit, unit, or means is a combination of hardware and software, and the software is used to configure the hardware and / or the processor.

[0030] The memory stores the processing program. The processor reads the processing program from the memory and executes the above determination process based on that processing program.

[0031] The pressure detector 15 is positioned to detect the pressure near the inner surface of the upper part of the internal space 6. The upper part of the internal space 6 is filled with hydrogen gas, either by the generation of boil-off gas from the liquefied hydrogen stored in the internal space 6, or by the introduction of hydrogen gas vaporized in the second evaporator 11 into the internal space 6 through the return pipe 13.

[0032] When outside air enters the inter-tank space 5 through the micropores H formed in the outer tank 3, the vacuum level in the inter-tank space 5 decreases, reducing the vacuum insulation effect in the inter-tank space 5. As a result, the temperature of the inner tank 4 rises, accelerating the evaporation of liquefied hydrogen stored in the internal space 6. This causes the pressure P in the internal space 6 of the inner tank 4 to rise. In other words, the pressure P in the internal space 6 is a parameter that changes with the change in the vacuum level in the inter-tank space 5. Therefore, the processing circuit 16 can obtain the pressure P in the internal space 6 and determine that it is outside the normal range, i.e., the vacuum level in the inter-tank space 5 has decreased, if the pressure P exceeds the reference value Po.

[0033] This makes it possible to determine the decrease in vacuum in the vacuum-insulated liquefied hydrogen tank 2, regardless of whether or not liquefied air A2 is actually generated on the outer surface of the outer tank 3. The reference value Po of pressure P can be set based on a value corresponding to the lower limit of the allowable vacuum in the space between tanks 5. The reference value Po of pressure P is set to a value outside the normal range that is allowed during normal operation of the liquefied hydrogen tank 2.

[0034] Furthermore, when outside air enters the inter-tank space 5, it may take some time for the pressure P in the internal space 6 of the inner tank 4 to start rising and exceed the reference value Po. Therefore, the processing circuit 16 may determine that the vacuum level in the inter-tank space 5 has decreased when it is estimated that the pressure P in the internal space 6 exceeds the reference value Po.

[0035] For example, the processing circuit 16 calculates the increase in pressure P per unit time ΔP1 in the internal space 6. If the increase ΔP1 exceeds the reference value ΔP1o, the processing circuit 16 can determine that it is outside the normal range, that is, that the vacuum level in the space between the tanks 5 has decreased.

[0036] More specifically, even under normal operation, when the liquefied hydrogen tank 2 is properly vacuum-insulated, the liquefied hydrogen stored in the internal space 6 gradually evaporates, generating boil-off gas. As the amount of boil-off gas gradually increases, the pressure P in the internal space 6 gradually rises. On the other hand, if the vacuum level in the space between tanks 5 decreases and the vacuum insulation effect decreases, the amount of boil-off gas generated per unit time increases compared to normal operation.

[0037] Furthermore, the pressure P in the internal space 6 can be reduced by utilizing the liquefied hydrogen stored in the internal space 6. For example, the utilization of liquefied hydrogen includes supplying hydrogen fuel to the engine 10. The decrease in the amount of liquefied hydrogen in the internal space 6 due to the utilization of liquefied hydrogen is a factor that reduces the pressure P in the internal space 6. For this reason, during normal operation of the liquefied hydrogen tank 2, the change in the pressure P in the internal space 6 repeatedly consists of a pressure decrease due to the utilization of liquefied hydrogen and a pressure increase due to the generation of boil-off gas, and does not show a sudden pressure increase.

[0038] Therefore, if the increase in pressure ΔP1 per unit time in the internal space 6 is greater than what is expected under normal operation, it is highly probable that a decrease in the vacuum level in the inter-tank space 5 is occurring. Thus, if the increase in pressure P per unit time ΔP1 in the internal space 6 exceeds the increase limit ΔP1o, it is estimated that the pressure P in the internal space 6 exceeds the limit value Po. In this way, by determining that the vacuum level in the inter-tank space 5 is decreasing when the increase in pressure P per unit time ΔP1 in the internal space 6 exceeds the increase limit ΔP1o, a decrease in the vacuum level in the vacuum-insulated liquefied hydrogen tank 2 can be detected at an earlier stage.

[0039] In this embodiment, the hydrogen storage system 1A further includes an outer tank surface temperature detector 17 that detects the temperature T1 of the outer surface of the outer tank 3 as an external temperature detector for detecting the generation of liquefied air in the outer tank 3. As described above, the temperature T1 of the outer surface of the outer tank 3 is a parameter that changes with the change in the vacuum level in the space between tanks 5.

[0040] The processing circuit 16 determines that the temperature T1 detected by the outer tank surface temperature detector 17 is outside the normal range, i.e., that the vacuum level in the space between tanks 5 has decreased, if it is lower than the temperature reference value T1o. This allows for direct detection of the generation of liquefied air A2 on the outer surface of the outer tank 3. Furthermore, by performing both a determination based on the pressure P in the internal space 6 and a determination based on the temperature T1 on the outer surface of the outer tank 3, a decrease in the vacuum level in the liquefied hydrogen tank 2 can be detected more reliably.

[0041] In this embodiment, the hydrogen storage system 1A further includes a water injector 18 that injects water or seawater into the outer tank 3. The processing circuit 16 outputs a command signal to activate the water injector 18 as a vacuum level decrease signal S.

[0042] Figure 3 shows an example of the injection piping for the water injector shown in Figure 1. In the example in Figure 3, the injection piping 19 of the water injector 18 includes an upper pipe 19a, a middle pipe 19b, and a lower pipe 19c. Each of the pipes 19a, 19b, and 19c has two pipes in the width direction of the liquefied hydrogen tank 2, and each pipe extends in the longitudinal direction of the liquefied hydrogen tank 2. The upper pipe 19a is positioned diagonally above the outer surface of the outer tank 3 of the liquefied hydrogen tank 2. The middle pipe 19b is positioned lower than the upper pipe 19a and is located to the side of the outer tank 3. The lower pipe 19c is positioned below the outer tank 3.

[0043] Each pipe 19a, 19b, and 19c has a plurality of injection nozzles 19n. For example, the plurality of injection nozzles 19n are configured as spray nozzles that spray water or seawater in a mist. The upper pipe 19a sprays water or seawater downward or diagonally downward. The middle pipe 19b sprays water or seawater to the side. The lower pipe 19c sprays water or seawater upward or diagonally upward. In the example in Figure 3, the plurality of injection nozzles 19n are arranged perpendicular to the longitudinal direction of the liquefied hydrogen tank 2, that is, toward the circumferential surface of the cylindrical portion of the outer tank 3, but the plurality of injection nozzles 19n may be arranged along the longitudinal direction of the liquefied hydrogen tank 2. Note that the plurality of injection nozzles 19n only need to be arranged so that water or seawater spreads across the entire surface of the liquefied hydrogen storage system 1A, and are not limited to the arrangement in this embodiment.

[0044] The water injector 18 includes a pump that pressurizes water or seawater into the injection pipe 19. In the example in Figure 3, the water or seawater pressurized from the pump is sent to the respective pipes 19a, 19b, and 19c from a position on one longitudinal end of the liquefied hydrogen tank 2, as indicated by the upward arrow in Figure 3.

[0045] If the water injector 18 injects seawater, the water injector 18 may have a pump to draw up the seawater. If the water injector 18 injects water or seawater, the water injector 18 may have a tank to store the water or seawater.

[0046] According to the above configuration, if it is determined that the vacuum level in the space between the tanks 5 has decreased, water or seawater is sprayed onto the outer surface of the outer tank 3 by the water injector 18. This prevents the temperature T1 of the outer surface of the outer tank 3 from decreasing and suppresses the generation of liquefied air A2. Furthermore, even if liquefied air A2 has already been generated on the outer surface of the outer tank 3, the spraying of water or seawater can vaporize the liquefied air A2 again. Therefore, it is possible to prevent low-temperature liquefied air A2 from dripping down to the bottom of the liquefied hydrogen tank 2. For this reason, it is not necessary to install a tray 14 to receive the liquefied air A2 as shown in Figure 2.

[0047] In this embodiment, if the processing circuit 16 determines that the vacuum level in the inter-tank space 5 is decreasing, it is not necessary for the vacuum level in the inter-tank space 5 to actually be decreasing. The hydrogen storage system 1A in this embodiment can detect signs of a decrease in the vacuum level in the inter-tank space 5 and prevent liquefied air from being generated on the outer surface of the outer tank 3.

[0048] [Embodiment 2] Next, Embodiment 2 of the present disclosure will be described. Figure 4 is a schematic diagram showing the general configuration of a hydrogen storage system according to Embodiment 2 of the present disclosure. In the hydrogen storage system 1B shown in Figure 4, components similar to those in the hydrogen storage system 1A shown in Figure 1 are denoted by the same reference numerals and their descriptions are omitted.

[0049] In the hydrogen storage system 1B of this embodiment, the processing circuit 16 estimates the pressure Pe in the internal space 6 of the inner tank 4 from the state of the liquefied hydrogen stored in the internal space 6, and determines the decrease in the vacuum level in the space between tanks 5 by comparing it with the pressure P detected by the pressure detector 15. For this purpose, the hydrogen storage system 1B is equipped with an internal temperature detector 21, a liquid level detector 22, and flow rate detectors 23, 24.

[0050] The internal temperature detector 21 detects the temperature Tin of the internal space 6. The liquid level detector 22 detects the liquid level L of the liquefied hydrogen stored in the internal space 6. The flow rate detectors 23 and 24 detect the mass flow rate of liquefied hydrogen or hydrogen gas entering and leaving the internal space 6. In this embodiment, the flow rate detector includes a first flow rate detector 23 and a second flow rate detector 24.

[0051] The first flow detector 23 detects a first flow rate F1, which indicates the mass flow rate of hydrogen gas supplied from the first evaporator 7 to the engine 10. That is, the first flow rate F1 indicates the mass flow rate of hydrogen gas in the second supply pipe 9. The second flow detector 24 detects a second flow rate F2, which indicates the mass flow rate of hydrogen gas supplied from the second evaporator 11 to the internal space 6. That is, the second flow rate F2 indicates the mass flow rate of hydrogen gas in the return pipe 13.

[0052] Alternatively, the first flow detector 23 may detect the mass flow rate of liquefied hydrogen supplied from the internal space 6 to the first evaporator 7, i.e., the mass flow rate of liquefied hydrogen in the first supply pipe 8. Similarly, the second flow detector 24 may detect the mass flow rate of liquefied hydrogen supplied from the internal space 6 to the second evaporator 11, i.e., the mass flow rate of liquefied hydrogen in the third supply pipe 12. Furthermore, if the amount of hydrogen gas generated by the second evaporator 11 is constant or its change is within the error range, the mass flow rate F2 of hydrogen gas or liquefied hydrogen flowing through the second evaporator 11 may be stored in the memory of the processing circuit 16 as a predetermined fixed value.

[0053] Figure 5 shows the calculation block for determining vacuum level decrease in this embodiment. In this embodiment, the processing circuit 16 functions as the determination circuit 30 shown in Figure 5. The determination circuit 30 includes an adder 31, a subtractor 32, an estimated pressure calculation circuit 33, a comparison circuit 34, and integration circuits 35, 36, and 37.

[0054] The determination circuit 30 receives the boil-off gas amount G, the first flow rate F1, and the second flow rate F2 as input. The boil-off gas amount G is the amount of boil-off gas generated from the liquefied hydrogen stored in the internal space 6. The boil-off gas amount G is a predetermined fixed value based on the capacity of the liquefied hydrogen tank 2, etc. In this case, the memory of the processing circuit 16 stores this fixed value in advance. Alternatively, the boil-off gas amount G may be a predetermined value according to the pressure P of the internal space 6. In this case, the memory of the processing circuit 16 stores in advance a data table showing the boil-off gas amount G for the pressure P of the internal space 6. Generally, as the pressure P of the internal space 6 increases, the boil-off gas amount G increases.

[0055] The processing circuit 16 estimates the mass of hydrogen gas in the internal space 6 by obtaining the amount of boil-off gas G generated from the liquefied hydrogen stored in the internal space 6 and the mass flow rates F1 and F2 of liquefied hydrogen or hydrogen gas entering and leaving the internal space 6.

[0056] For this purpose, the integration circuit 35 integrates the amount of boil-off gas G from a predetermined timing. The predetermined timing is the timing at which the amount of boil-off gas G in the internal space 6 can be detected. For example, the predetermined timing is the timing when the liquefied hydrogen tank 2 is filled with liquefied hydrogen or when the ship carrying the liquefied hydrogen tank 2 departs port.

[0057] Similarly, the integration circuit 36 ​​integrates the first flow rate F1 detected from the first flow rate detector 23. In addition, the integration circuit 37 integrates the second flow rate F2 detected from the second flow rate detector 24.

[0058] The adder 31 adds the integrated value of the boil-off gas amount G and the integrated value of the second flow rate F2. The subtractor 32 subtracts the integrated value of the first flow rate F1 from the value output from the adder 31. The value output from the subtractor 32 is the estimated value of the mass Ft of hydrogen gas in the internal space 6. Note that the order of addition and subtraction is not limited to the example in Figure 5.

[0059] The estimated pressure calculation circuit 33 calculates the estimated pressure Pe of the internal space 6 using the mass Ft of hydrogen gas in the internal space 6 output from the subtractor 32, the liquid level L of liquefied hydrogen stored in the internal space 6 detected by the liquid level detector 22, and the temperature Tin of the internal space 6 detected by the internal temperature detector 21. The estimated pressure calculation circuit 33 calculates the volume V of the region occupied by hydrogen gas in the internal space 6 from the liquid level L of liquefied hydrogen.

[0060] For example, the memory of the processing circuit 16 stores a formula for calculating the volume V of the region above the liquid level L in the internal space 6, based on the liquid level L of the liquefied hydrogen. The pressure estimation circuit 33 calculates the volume V by substituting the liquid level L obtained from the liquid level detector 22 into the formula. Alternatively, the relationship between the liquid level L of the liquefied hydrogen and the volume V of the region above that liquid level L in the internal space 6 may be stored in the memory of the processing circuit 16 beforehand. In this case, the pressure estimation circuit 33 reads out the value of volume V corresponding to the liquid level L obtained from the liquid level detector 22.

[0061] The pressure estimation circuit 33 calculates the estimated pressure Pe in the internal space 6 using the equation of state, based on the volume V occupied by hydrogen gas in the internal space 6, the mass Ft of the hydrogen gas, and the temperature Tin of the internal space 6. The comparison circuit 34 compares the calculated estimated pressure Pe with the actual pressure P of the internal space 6 detected by the pressure detector 15. More specifically, the comparison circuit 34 calculates the difference ΔP2 between the actual pressure P and the estimated pressure Pe. The comparison circuit 34 determines whether the calculated difference ΔP2 exceeds the difference reference value ΔP2o. If the difference ΔP2 exceeds the difference reference value ΔP2o, the comparison circuit 34 determines that it is outside the normal range, i.e., that the vacuum level in the inter-tank space 5 has decreased, and outputs a vacuum level decrease signal S.

[0062] According to this embodiment, if the difference between the estimated pressure Pe during normal operation, which is estimated from the amount G of boil-off gas generated from the liquefied hydrogen stored in the internal space 6 of the liquefied hydrogen tank 2 and the mass flow rates F1 and F2 of liquefied hydrogen or hydrogen gas entering and leaving the internal space 6, and the actual pressure P detected by the pressure detector 15 is large, it is estimated that the pressure has deviated from the pressure range expected during normal operation and that a situation that would not normally occur during normal operation is occurring. In this way, by determining that the vacuum level in the inter-tank space 5 has decreased when the difference between the estimated pressure Pe and the actual pressure P is large, a decrease in the vacuum level in the vacuum-insulated liquefied hydrogen tank 2 can be detected at an earlier stage.

[0063] In this embodiment as well, the hydrogen storage system 1B is equipped with an outer tank surface temperature detector 17 that detects the temperature T1 of the outer surface of the outer tank 3. The processing circuit 16 determines that the vacuum level in the inter-tank space 5 is decreasing when the temperature T1 detected by the outer tank surface temperature detector 17 is lower than the temperature reference value T1o. This makes it possible to directly detect that liquefied air A2 is being generated on the outer surface of the outer tank 3. Furthermore, by performing both a determination based on the pressure P of the internal space 6 and a determination based on the temperature T1 of the outer surface of the outer tank 3, a decrease in the vacuum level in the liquefied hydrogen tank 2 can be detected more reliably.

[0064] In this embodiment as well, the hydrogen storage system 1B is equipped with a water injector 18 that injects water or seawater into the outer tank 3. The processing circuit 16 outputs a command signal to activate the water injector 18 as a vacuum level decrease signal S. This prevents a decrease in the temperature T1 of the outer surface of the outer tank 3 and suppresses the generation of liquefied air A2.

[0065] In this embodiment as well, when the processing circuit 16 determines that the vacuum level in the inter-tank space 5 is decreasing, it is not necessary for the vacuum level in the inter-tank space 5 to actually decrease. The hydrogen storage system 1B in this embodiment can detect signs of a decrease in the vacuum level in the inter-tank space 5 and prevent liquefied air from being generated on the outer surface of the outer tank 3.

[0066] [Differentiation] Next, modifications of Embodiments 1 and 2 described above will be explained. Figure 6 is a schematic diagram showing the general configuration of a hydrogen storage system according to a modification of Embodiment 1 of this disclosure. In the hydrogen storage system 1C shown in Figure 6, components similar to those in the hydrogen storage system 1A shown in Figure 1 are denoted by the same reference numerals and their descriptions are omitted. In the example of Figure 6, a modification of Embodiment 1 shown in Figure 1 is illustrated, but this modification is also applicable to Embodiment 2 shown in Figure 4.

[0067] In this modified example, the hydrogen storage system 1C has a tray 14 installed below the liquefied hydrogen tank 2. Furthermore, the hydrogen storage system 1C is equipped with a tray surface temperature detector 20 that detects the surface temperature T2 of the tray 14, instead of the outer tank surface temperature detector 17 in Embodiment 1, as an external temperature detector for detecting the generation of liquefied air in the outer tank 3.

[0068] As described above, if liquefied air is generated on the outer surface of the outer tank 3, the liquefied air will drip downward from the outer surface of the outer tank 3. By installing the tray 14 below the liquefied hydrogen tank 2, it is possible to prevent the ship's structure below the liquefied hydrogen tank 2 from becoming extremely cold due to the dripping liquefied air.

[0069] Furthermore, when liquefied air is dripped onto tray 14, the surface temperature T2 of tray 14 decreases. Therefore, the surface temperature T2 of tray 14 can be said to be a parameter that changes with the change in vacuum level in the space between chambers 5.

[0070] The processing circuit 16 determines that the temperature T2 detected by the tray surface temperature detector 20 is outside the normal range, i.e., that the vacuum level in the space between the tanks 5 has decreased, if it is lower than the temperature reference value T2o. This allows for direct detection of liquefied air A2 being dropped onto the surface of the tray 14. Furthermore, by performing both a determination based on the pressure P in the internal space 6 and a determination based on the surface temperature T2 of the tray 14, a decrease in the vacuum level in the liquefied hydrogen tank 2 can be detected more reliably.

[0071] In this modified example, a configuration is shown in which a tray surface temperature detector 20 is provided instead of an outer tank surface temperature detector 17. However, the hydrogen storage system may also be equipped with both an outer tank surface temperature detector 17 and a tray surface temperature detector 20.

[0072] While embodiments of this disclosure have been described above, this disclosure is not limited to the embodiments described above, and various improvements, changes, and modifications are possible without departing from the spirit of this disclosure.

[0073] [Other embodiments] For example, the determination in Embodiment 1 and the determination in Embodiment 2 may be used in combination. For example, the processing circuit 16 may determine that the vacuum level in the space between the tanks 5 has decreased if at least two of the following conditions are met: the pressure P in the internal space 6 exceeds a reference value Po; the increase amount ΔP1 of the pressure P in the internal space 6 per unit time exceeds a reference increase value ΔP1o; the difference ΔP2 of the pressure P in the internal space 6 with respect to the estimated pressure Pe exceeds a reference difference value ΔP2o; the temperature T1 of the outer surface of the outer tank 3 is lower than a reference temperature value; and the temperature T2 of the surface of the tray 14 is lower than a reference temperature value.

[0074] For example, the pressure P in the internal space 6 can change due to factors other than a decrease in the vacuum level of the inter-tank space 5, as described above. Therefore, if only one of the three conditions described above using the pressure P in the internal space 6 is met, it is possible that the meeting of that condition is not due to a decrease in the vacuum level of the inter-tank space 5.

[0075] Therefore, the processing circuit 16 may combine one condition using the pressure P of the internal space 6 with other conditions using the pressure P of the internal space 6 or conditions using the external temperatures T1 and T2, and determine that the vacuum level of the inter-tank space 5 has decreased when both conditions are met. For example, the processing circuit 16 may determine that the vacuum level of the inter-tank space 5 has decreased when the increase amount ΔP1 per unit time of the pressure P of the internal space 6 exceeds the increase amount reference value ΔP1o, and the difference ΔP2 of the pressure P of the internal space 6 with the estimated pressure Pe exceeds the difference reference value ΔP2o.

[0076] Furthermore, for example, the processing circuit 16 may determine that the vacuum level in the inter-tank space 5 has decreased if the difference ΔP2 between the pressure P in the internal space 6 and the estimated pressure Pe exceeds the difference reference value ΔP2o, and the temperature T1 of the outer surface of the outer tank 3 is lower than the temperature reference value T1o. When determining the decrease in vacuum level based on whether both the condition using pressure P and the condition using external temperatures T1 and T2 are met, the temperature reference values ​​T1o and T2o used in the condition determination using external temperatures T1 and T2 may be set to higher temperatures than when determining the decrease in vacuum level based only on the condition determination using external temperatures T1 and T2. This makes it possible to reliably and early detect a decrease in vacuum level in the liquefied hydrogen tank 2.

[0077] Furthermore, although the above embodiment illustrates a configuration equipped with a water injector 18 that sprays water or seawater into the outer tank 3, the water injector 18 may be omitted if there are no structures below the liquefied hydrogen tank 2 that would be damaged by extremely low temperatures. Also, as shown in the example in Figure 6, if a tray 14 is installed, a water supply device that supplies water or seawater to the tray 14 may be installed instead of, or in addition to, the water injector 18. By supplying water or seawater to the tray 14, the liquefied air A2 that has dripped onto the tray 14 can be vaporized again.

[0078] Furthermore, in the above embodiment, the example given is that the vacuum level decrease signal S output by the processing circuit 16 when it determines that the vacuum level in the inter-tank space 5 has decreased is a command signal to activate the water injector 18, but the invention is not limited to this. The vacuum level decrease signal S may also be a signal that activates a predetermined alarm device such as a speaker or lamp. Such an alarm device may be installed near the liquefied hydrogen tank 2, or it may be installed in the wheelhouse of a ship or the control room of a facility. The vacuum level decrease signal S may also be a signal that sends a warning signal or warning email to a computer terminal operated by an administrator. The processing circuit 16 may simultaneously output multiple types of signals, such as those exemplified above, as the vacuum level decrease signal S to predetermined output targets. An operator who learns that the vacuum level has decreased via an alarm device or the like may manually operate the water injector 18.

[0079] Furthermore, in the above embodiment, an example was given in which the processing circuit 16 uses both a determination based on the pressure P of the internal space 6 and a determination based on the external temperatures T1 and T2. However, the processing circuit 16 does not necessarily have to perform a determination based on the external temperatures T1 and T2.

[0080] Furthermore, although the above embodiment shows an example where the liquefied hydrogen tank 2 is a marine tank, it is not limited to this. For example, the liquefied hydrogen tank 2 may be a storage tank installed in a bunkering facility where liquefied hydrogen is temporarily stored before being introduced into a marine tank.

[0081] [Summary of this disclosure] [Item 1] A hydrogen storage system according to one aspect of the present disclosure is a hydrogen storage system comprising a liquefied hydrogen tank for storing liquefied hydrogen, wherein the liquefied hydrogen tank includes an outer tank and an inner tank installed within the outer tank at a position spaced apart from the inner surface of the outer tank, and the internal space of the inner tank in which the liquefied hydrogen is stored is vacuum-insulated from the outside by the inter-tank space between the outer tank and the inner tank being a vacuum, and the hydrogen storage system comprises a pressure detector for detecting the pressure in the internal space and a processing circuit, wherein the processing circuit determines that the vacuum level in the inter-tank space has decreased when the pressure in the internal space exceeds a reference value or is estimated to exceed a reference value, and outputs a predetermined vacuum level decrease signal.

[0082] According to the above configuration, when outside air enters the space between the tanks, the pressure inside the inner tank rises, and a decrease in the vacuum level in the space between the tanks is determined. This makes it possible to determine a decrease in the vacuum level in a vacuum-insulated liquefied hydrogen tank regardless of whether liquefied air is actually generated on the outer surface of the outer tank. Therefore, a decrease in the vacuum level in a vacuum-insulated liquefied hydrogen tank can be detected at an earlier stage.

[0083] [Item 2] In the hydrogen storage system of item 1, the processing circuit may calculate the increase in pressure in the internal space per unit time, and if the increase exceeds a standard increase value, it may be determined that the vacuum level in the space between the tanks has decreased. This allows for earlier detection of a decrease in the vacuum level in a vacuum-insulated liquefied hydrogen tank.

[0084] [Item 3] The hydrogen storage system of item 1 or 2 comprises an internal temperature detector for detecting the temperature of the internal space, a liquid level detector for detecting the liquid level of liquefied hydrogen stored in the internal space, and a flow rate detector for detecting the mass flow rate of liquefied hydrogen or hydrogen gas entering and leaving the internal space. The processing circuit estimates the mass of hydrogen gas in the internal space by obtaining the amount of boil-off gas generated from the liquefied hydrogen stored in the internal space and the mass flow rate of liquefied hydrogen or hydrogen gas entering and leaving the internal space. It calculates the volume of the region occupied by hydrogen gas in the internal space from the liquid level of liquefied hydrogen stored in the internal space. It calculates the estimated pressure of the internal space from the volume, mass, and temperature of the internal space. If the difference between the pressure of the internal space detected by the pressure detector and the estimated pressure exceeds a differential reference value, it may be determined that the vacuum level in the inter-tank space has decreased. According to this, if there is a large difference between the estimated pressure during normal operation, which is estimated from the amount of boil-off gas generated from the liquefied hydrogen stored in the internal space of the liquefied hydrogen tank and the flow rate of liquefied hydrogen or hydrogen gas entering and leaving the internal space, and the actual pressure detected by the pressure detector, it is estimated that the pressure has deviated from the pressure range expected during normal operation, and a situation that would not normally occur during normal operation is occurring. In this way, by determining that the vacuum level in the space between the tanks has decreased when there is a large difference between the estimated pressure and the actual pressure, it is possible to detect a decrease in the vacuum level in a vacuum-insulated liquefied hydrogen tank at an earlier stage.

[0085] [Item 4] Any of the hydrogen storage systems described in items 1 to 3 includes an external temperature detector that detects the temperature of the outer surface of the outer tank or the temperature of the surface of a tray installed below the liquefied hydrogen tank. The processing circuit may determine that the vacuum level in the space between the tanks has decreased when the temperature detected by the external temperature detector is lower than a temperature reference value. This allows for direct detection of the generation of liquefied air on the outer surface of the outer tank. Furthermore, by performing both a determination based on the pressure in the internal space and a determination based on the external temperature, a decrease in the vacuum level in the liquefied hydrogen tank can be detected more reliably.

[0086] [Item 5] In any of the hydrogen storage systems described in items 1 to 4, the liquefied hydrogen tank may be a marine tank mounted on a ship.

[0087] [Item 6] The hydrogen storage system of item 5 is equipped with a water injector that sprays water or seawater into the outer tank, and the processing circuit may output a command signal to activate the water injector as a vacuum level decrease signal. This prevents the temperature of the outer surface of the outer tank from decreasing and suppresses the generation of liquefied air. Furthermore, even if liquefied air has already been generated on the outer surface of the outer tank, the liquefied air can be vaporized again by spraying water or seawater.

[0088] [Item 7] Another embodiment of the present disclosure is a hydrogen storage system comprising a liquefied hydrogen tank for storing liquefied hydrogen, wherein the liquefied hydrogen tank is mounted on a ship and includes an outer tank and an inner tank installed within the outer tank at a position spaced apart from the inner surface of the outer tank, wherein the space between the outer tank and the inner tank is a vacuum, thereby providing vacuum insulation to the internal space of the inner tank where the liquefied hydrogen is stored from the outside, and the hydrogen storage system comprises a detector for detecting a predetermined parameter that changes with a change in the degree of vacuum in the space between the tanks, a water injector for injecting water or seawater into the outer tank, and a processing circuit, wherein the processing circuit outputs a command signal to activate the water injector when the value detected by the detector falls outside a normal range.

[0089] [Item 8] A vacuum monitoring method according to another aspect of the present disclosure is a method for monitoring the vacuum level in a liquefied hydrogen tank for storing liquefied hydrogen, wherein the liquefied hydrogen tank includes an outer tank and an inner tank installed within the outer tank at a position spaced apart from the inner surface of the outer tank, and the space between the outer tank and the inner tank is a vacuum, thereby vacuum-insulating the internal space of the inner tank in which the liquefied hydrogen is stored from the outside, and the vacuum monitoring method obtains the pressure of the internal space and determines that the vacuum level in the space between the tanks has decreased if the pressure of the internal space exceeds a reference value or is estimated to exceed a reference value. [Explanation of symbols]

[0090] 1A, 1B, 1C Hydrogen Storage System 2. Liquefied hydrogen tank 3 Outer tank 4 Inner tank 5 Space between tanks 6. Interior space 15. Pressure detector 16 Processing Circuit 17,20 External temperature detector 18 water injector 21 Internal temperature detector 22 Liquid level detector 23,24 Flow detector

Claims

1. A hydrogen storage system equipped with a liquefied hydrogen tank for storing liquefied hydrogen, The liquefied hydrogen tank includes an outer tank and an inner tank installed within the outer tank at a position spaced apart from the inner surface of the outer tank, wherein the space between the outer tank and the inner tank is a vacuum, and the internal space of the inner tank where the liquefied hydrogen is stored is vacuum-insulated from the outside. The aforementioned hydrogen storage system is A pressure detector for detecting the pressure in the internal space, A processing circuit is provided, The processing circuit determines that the vacuum level in the inter-tank space is decreasing when the pressure in the internal space exceeds a reference value or is estimated to exceed a reference value, and outputs a predetermined vacuum level decrease signal, in a hydrogen storage system.

2. The hydrogen storage system according to claim 1, wherein the processing circuit calculates the amount of increase per unit time in the pressure of the internal space, and determines that the vacuum level in the space between the tanks has decreased when the amount of increase exceeds a reference value.

3. An internal temperature detector for detecting the temperature of the internal space, A liquid level detector for detecting the liquid level of liquefied hydrogen stored in the internal space, The system includes a flow detector that detects the mass flow rate of liquefied hydrogen or hydrogen gas entering and leaving the internal space, The aforementioned processing circuit is By obtaining the amount of boil-off gas generated from the liquefied hydrogen stored in the internal space and the mass flow rate of liquefied hydrogen or hydrogen gas entering and leaving the internal space, the mass of hydrogen gas in the internal space is estimated. The volume of the region occupied by hydrogen gas in the internal space is calculated from the liquid level of the liquefied hydrogen stored in the internal space. The estimated pressure of the internal space is calculated from the volume, mass, and temperature of the internal space. The hydrogen storage system according to claim 1, wherein it is determined that the vacuum level in the inter-tank space has decreased when the difference between the pressure in the internal space detected by the pressure detector and the estimated pressure exceeds a differential reference value.

4. The system includes an external temperature detector that detects the temperature of the outer surface of the outer tank or the temperature of the surface of a tray installed below the liquefied hydrogen tank. The hydrogen storage system according to claim 1, wherein the processing circuit determines that the vacuum level in the space between the tanks has decreased when the temperature detected by the external temperature detector is lower than a temperature reference value.

5. The hydrogen storage system according to any one of claims 1 to 4, wherein the liquefied hydrogen tank is a marine tank installed on a ship.

6. The outer tank is equipped with a water injector that sprays water or seawater, The hydrogen storage system according to claim 5, wherein the processing circuit outputs a command signal to activate the water injector as the vacuum level reduction signal.

7. A hydrogen storage system equipped with a liquefied hydrogen tank for storing liquefied hydrogen, The liquefied hydrogen tank is mounted on a ship and includes an outer tank and an inner tank installed within the outer tank at a position spaced apart from the inner surface of the outer tank, wherein the space between the outer tank and the inner tank is a vacuum, and the internal space of the inner tank in which the liquefied hydrogen is stored is vacuum-insulated from the outside. The aforementioned hydrogen storage system is A detector that detects a predetermined parameter that changes due to a change in the vacuum level in the space between the tanks, A water injector for spraying water or seawater into the outer tank, A processing circuit is provided, The processing circuit is a hydrogen storage system that outputs a command signal to activate the water injector when the value detected by the detector falls outside the normal range.

8. A method for monitoring the vacuum level in a liquefied hydrogen tank for storing liquefied hydrogen, The liquefied hydrogen tank includes an outer tank and an inner tank installed within the outer tank at a position spaced apart from the inner surface of the outer tank, wherein the space between the outer tank and the inner tank is a vacuum, and the internal space of the inner tank where the liquefied hydrogen is stored is vacuum-insulated from the outside. The vacuum level monitoring method is, The pressure of the internal space is obtained, A vacuum level monitoring method for determining that the vacuum level in the inter-tank space has decreased when the pressure in the internal space exceeds a standard value or is estimated to exceed a standard value.

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