Method for storing liquefied hydrogen in ships

Abstract

To provide a liquid hydrogen storage method for a ship which enables reduction of an amount of liquid hydrogen consumed by evaporation when the interior of a liquid hydrogen tank mounted on a ship is cooled to a temperature at which liquid hydrogen is stored.SOLUTION: A liquid hydrogen storage method for a ship is used to store liquid hydrogen in a liquid hydrogen tank mounted on a ship. In the liquid hydrogen storage method, a refrigerant is introduced into the liquid hydrogen tank through a pipe inserted into the liquid hydrogen tank from an upper part to pre-cool the liquid hydrogen tank. Then, liquid hydrogen is introduced into the liquid hydrogen tank after pre-cooling.SELECTED DRAWING: Figure 2

Description

Technical Field

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[0001] The present disclosure relates to a method for storing liquefied hydrogen in a liquefied hydrogen tank mounted on a ship.

Background Art

[0002] When introducing liquefied hydrogen into a liquefied hydrogen tank, first, a step of removing oxygen and moisture in the liquefied hydrogen tank is necessary. This step aims to sufficiently lower the oxygen concentration in the liquefied hydrogen tank below the combustion conditions of flammable liquefied hydrogen, and to sufficiently lower the dew point in the liquefied hydrogen tank so that when the liquefied hydrogen tank becomes cold due to the introduction of liquefied hydrogen, residual water vapor does not condense on various valves or instruments provided in the liquefied hydrogen tank and cause malfunction.

[0003] Conventionally, after the step of removing oxygen and moisture, liquefied hydrogen has been introduced into the liquefied hydrogen tank. However, when introducing liquefied hydrogen, since the inside of the liquefied hydrogen tank is at room temperature, if liquefied hydrogen is directly introduced into the room-temperature liquefied hydrogen tank, there is a risk of cracks or deformation due to local thermal contraction in the liquefied hydrogen tank during storage of liquefied hydrogen. Regarding problems such as cracks or deformation of such low-temperature tanks, for example, in Patent Document 1 below, as a method for cooling a low-temperature tank, a step of cooling the low-temperature tank with the heat of vaporization of a liquefied gas and discharging the vaporized gas is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, even if the above method is applied to the introduction of liquefied hydrogen into a liquefied hydrogen tank, the liquefied hydrogen cannot be stored in the tank until it has cooled sufficiently after the introduction of liquefied hydrogen has begun. Instead, vaporized hydrogen gas is released to the outside and consumed.

[0006] In particular, increasing the capacity of a liquefied hydrogen tank increases the amount of liquefied hydrogen consumed for cooling the tank. Because liquefied hydrogen has a limited supply and a high unit price, the conventional method of cooling liquefied hydrogen tanks with liquefied hydrogen does not allow for cost reduction. Furthermore, since such liquefied hydrogen is flammable, the vaporized hydrogen gas must be safely treated in a combustion facility, and it is desirable to suppress the amount of hydrogen gas generated during tank cooling. In addition, if the tank pressure rises above the design pressure or combustion becomes impossible, it is necessary to release the gas into the atmosphere, and it is desirable to suppress the amount of gas released.

[0007] Furthermore, there are plans to transport liquefied hydrogen by sea using tanks mounted on ships. However, liquefied hydrogen tanks mounted on ships face greater constraints in order to ensure safety.

[0008] Therefore, the present disclosure aims to provide a method for storing liquefied hydrogen on a ship that can reduce the amount of liquefied hydrogen consumed by vaporization when cooling the inside of a liquefied hydrogen tank installed on a ship to the temperature at which the liquefied hydrogen is stored. [Means for solving the problem]

[0009] A method for storing liquefied hydrogen for ships according to one embodiment of the present disclosure is a method for storing liquefied hydrogen in a liquefied hydrogen tank installed on a ship, wherein a refrigerant is introduced into the liquefied hydrogen tank through a pipe inserted from the top of the liquefied hydrogen tank to precool the liquefied hydrogen tank, and the liquefied hydrogen is introduced into the liquefied hydrogen tank after precooling. [Effects of the Invention]

[0010] According to this disclosure, a method for storing liquefied hydrogen on a ship can be provided that reduces the amount of liquefied hydrogen consumed by vaporization when cooling the inside of a liquefied hydrogen tank on board a ship to the temperature at which the liquefied hydrogen is stored. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a diagram showing the schematic configuration of a ship in one embodiment of the present disclosure. [Figure 2] Figure 2 is a schematic diagram showing the piping control system to the liquefied hydrogen tank in the ship shown in Figure 1. [Figure 3] Figure 3 is a flowchart showing the method for storing liquefied hydrogen in the ship shown in Figure 1. [Figure 4] Figure 4 shows an image of the ship's navigation in this embodiment. [Modes for carrying out the invention]

[0012] An embodiment will be described below with reference to the drawings. Throughout the drawings, the same or corresponding elements are denoted by the same reference numerals, and redundant detailed descriptions are omitted.

[0013] Figure 1 is a diagram showing the schematic configuration of a vessel in one embodiment of the present disclosure. As shown in Figure 1, the vessel 100 is equipped with a plurality of liquefied hydrogen tanks 1 mounted on the hull 110. In the example of Figure 1, four liquefied hydrogen tanks 1 are arranged in a line along the longitudinal direction of the hull 110. Each liquefied hydrogen tank 1 includes a tank body 1A for storing liquefied hydrogen and a dome 1B projecting upward from the tank body 1A. However, the type and number of tanks are not limited.

[0014] In this embodiment, the dome 1B protrudes upward from the top of the tank body 1A. The dome 1B is equipped with a maintenance hatch that allows workers to enter the interior. Furthermore, various pipes that connect the inside and outside of the tank body 1A pass through the dome 1B.

[0015] The lower part of the tank body 1A is installed inside the hull 110. The upper part of the tank body 1A is covered by a tank cover 120. The tank cover 120 has an opening 120A through which the dome 1B passes. As a result, the liquefied hydrogen tank 1 is covered from the outside except for the dome 1B.

[0016] Figure 2 is a schematic diagram showing the piping control system to the liquefied hydrogen tank in the vessel shown in Figure 1. As shown in Figure 2, the vessel 100 stores liquefied hydrogen in the internal space 13 of the liquefied hydrogen tank 1. In the drawing, liquefied hydrogen is denoted as LH2. Before filling the internal space 13 with liquefied hydrogen, the vessel 100 has a function to remove oxygen and moisture present in the internal space 13 of the liquefied hydrogen tank 1 and to cool the internal space 13.

[0017] The liquefied hydrogen tank 1 has a double-shell structure to enhance thermal insulation. The tank body 1A has an outer tank 11 and an inner tank 12 housed in the outer tank 11 to form an internal space 13. As an example, the tank body 1A is formed in a spherical shape. That is, both the outer tank 11 and the inner tank 12 are formed in a spherical shape. An inter-tank space 14 is formed between the inner surface of the outer tank 11 and the outer surface of the inner tank 12. The inter-tank space 14 is maintained in a vacuum state, providing vacuum insulation to the internal space 13 from the outside of the liquefied hydrogen tank 1. The dome 1B also has a double-shell structure in a similar manner. However, the structure and thermal insulation method of the tank body 1A and the dome 1B are not limited to those described above.

[0018] Both the outer tank 11 and the inner tank 12 are constructed with pressure-resistant walls. For example, the outer tank 11 is constructed with higher pressure resistance than the inner tank 12 in order to withstand the differential pressure between atmospheric pressure and the pressure in the space between the tanks 14. However, the inner tank 12 may be constructed with higher pressure resistance than the outer tank 11. Multiple rods may be provided in the space between the tanks 14, spanning between the inner surface of the outer tank 11 and the outer surface of the inner tank 12.

[0019] The ship 100 includes a first introduction part 2 for introducing liquefied hydrogen into the liquefied hydrogen tank 1. The first introduction part 2 includes a manifold 21 for drawing in liquefied hydrogen from the outside, a discharge port 22 for discharging the drawn-in liquefied hydrogen within the liquefied hydrogen tank 1, and a first pipe 23 disposed between the manifold 21 and the discharge port 22. The discharge port 22 is disposed at the upper part of the internal space 13 of the liquefied hydrogen tank 1. The discharge port 22 has a spray nozzle shape or a small-diameter hole for spraying liquefied hydrogen within a predetermined range in the internal space 13 of the liquefied hydrogen tank 1.

[0020] The flow or non-flow of liquefied hydrogen can be switched by a first on-off valve 24 in the first pipe 23. Therefore, by connecting the manifold 21 to an external liquefied hydrogen introduction system and opening the first on-off valve 24, liquefied hydrogen is supplied into the internal space 13 of the liquefied hydrogen tank 1 through the first pipe 23 and the discharge port 22.

[0021] In this embodiment, the first introduction part 2 also functions as an introduction part for introducing liquefied nitrogen into the liquefied hydrogen tank 1. In the drawings, liquefied nitrogen is denoted as LN2. By connecting the manifold 21 to an external liquefied nitrogen introduction system and opening the first on-off valve 24, liquefied nitrogen is supplied into the internal space 13 of the liquefied hydrogen tank 1 through the first pipe 23 and the discharge port 22.

[0022] Furthermore, the ship 100 includes a second introduction part 3 for introducing low-temperature hydrogen gas obtained by vaporizing liquefied hydrogen into the liquefied hydrogen tank 1. In the drawings, low-temperature hydrogen gas is denoted as GH2. The second introduction part 3 includes a vaporizer 25 for vaporizing the liquefied hydrogen drawn from the manifold 21, and a second pipe 26 disposed between the manifold 21 and the discharge port 22. That is, the low-temperature hydrogen gas generated by the vaporizer 25 is discharged into the liquefied hydrogen tank 1 from the discharge port 22.

[0023] In this embodiment, the first pipe 23 and the second pipe 26 are connected to the third pipe 28 so as to converge outside the liquefied hydrogen tank 1. The third pipe 28 is inserted into the internal space 13 of the liquefied hydrogen tank 1 from above the tank body 1A through the dome 1B. Alternatively, a separate outlet for low-temperature hydrogen gas may be provided, in addition to the outlet 22 for liquefied hydrogen or liquefied nitrogen. The vaporizer 25 and the outlet 22 are connected by the second pipe 26.

[0024] The flow of low-temperature hydrogen gas through the second piping 26 is switched on or off by the second on-off valve 27. Therefore, by connecting the external liquefied hydrogen introduction system to the manifold 21 and opening the second on-off valve 27, low-temperature hydrogen gas is supplied into the internal space 13 of the liquefied hydrogen tank 1 through the vaporizer 25, the second piping 26, and the discharge port 22.

[0025] Furthermore, the vessel 100 is equipped with a discharge pipe 32 for discharging gas from the internal space 13 of the liquefied hydrogen tank 1. The gas flowing through the discharge pipe 32 may include oxygen, nitrogen, or hydrogen. In the drawings, nitrogen gas is denoted as GN2. The discharge pipe 32 is arranged such that one end is located above the internal space 13 of the liquefied hydrogen tank 1 and the other end is located outside. The vessel 100 is equipped with a first measuring instrument 33 for measuring the oxygen concentration in the discharge pipe 32 and a second measuring instrument 34 for measuring the hydrogen concentration in the discharge pipe 32. The flow of gas through the discharge pipe 32 is switched on or off by a third on-off valve 35. The discharge pipe 32 may be divided into different pipes depending on the gas being discharged.

[0026] The vessel 100 is equipped with a controller 5 for switching the piping through which the fluids are flowing. The controller 5 acquires measurement results from measuring instruments 33 and 34 and controls the opening and closing of valves 24, 27, and 35 based on these results. The controller 5 is configured as a processing circuit having a processor, volatile memory, non-volatile memory, and I / O interface, etc.

[0027] The functions of the elements disclosed herein can be performed using circuits or processing circuits that include general-purpose processors, dedicated processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, 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, or means 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 or processor.

[0028] Figure 3 is a flowchart illustrating the liquefied hydrogen storage method in the vessel shown in Figure 1. At the start of the liquefied hydrogen storage method in this embodiment, the internal space 13 of the liquefied hydrogen tank 1 is at room temperature and contains oxygen, nitrogen, and water vapor. In addition, the pressure in the internal space 13 is adjusted in advance so that the dew point temperature of the internal space 13 reaches a predetermined value.

[0029] First, as step S1, a pre-cooling process is performed in which the inside of the liquefied hydrogen tank 1 is pre-cooled using liquefied nitrogen. In the pre-cooling process, with the external liquefied nitrogen introduction system connected to the manifold 21, the controller 5 closes the second on-off valve 27 and opens the first on-off valve 24 and the third on-off valve 35. As a result, liquefied nitrogen is introduced into the liquefied hydrogen tank 1 through the liquefied nitrogen introduction system, the first piping 23, and the third piping 28 inserted into the inside of the liquefied hydrogen tank 1 from the top. This pre-cools the liquefied hydrogen tank 1. Furthermore, the liquefied nitrogen introduced into the liquefied hydrogen tank 1 removes oxygen and moisture from inside the liquefied hydrogen tank 1.

[0030] The liquefied nitrogen introduced during the precooling process and the low-temperature nitrogen gas vaporized by cooling the internal space 13 have a higher specific gravity than the residual air in the internal space 13, i.e., oxygen and nitrogen at room temperature. Therefore, the liquefied nitrogen and low-temperature nitrogen gas accumulate from the bottom of the internal space 13, pushing the residual air upwards. As a result, the residual air is discharged from the discharge pipe 32 located at the top of the internal space 13, enabling efficient oxygen removal.

[0031] Furthermore, once a predetermined amount of liquefied nitrogen has been introduced into the liquefied hydrogen tank 1, the first shut-off valve 24 may be closed, and the connection between the manifold 21 and the liquefied nitrogen introduction system may be disconnected. In this case, the ship 100 will be able to navigate with the liquefied nitrogen stored in the liquefied hydrogen tank 1.

[0032] When oxygen removal is complete, for example, when the oxygen concentration falls below a predetermined first reference value Th1, the internal space 13 becomes a low-temperature nitrogen gas atmosphere, which is created when the introduced liquid nitrogen vaporizes through heat exchange with the internal space 13. At this time, the temperature of the internal space 13 becomes a first pre-cooling temperature, which is somewhat higher than the boiling point of nitrogen. The first pre-cooling temperature is, for example, about -180°C.

[0033] In step S2, the controller 5 determines whether the oxygen concentration measured by the first measuring instrument 33 has fallen below the first reference value Th1. The first reference value Th1 is set to the value when the oxygen concentration in the internal space 13 is sufficiently lower than the combustion conditions for liquefied hydrogen. The combustion conditions for setting the first reference value Th1 are determined according to the dew point temperature set in advance in the internal space 13.

[0034] If the oxygen concentration measured by the first measuring instrument 33 falls below the first reference value Th1, step S2 is determined to be Yes, and the process proceeds to step S3. Step S3 is a nitrogen removal process that removes low-temperature nitrogen gas from the internal space 13 of the liquefied hydrogen tank 1. In the nitrogen removal process, the controller 5 closes the first on-off valve 24 and opens the second on-off valve 27 and the third on-off valve 35, with the manifold 21 connected to the external liquefied hydrogen introduction system. The vaporizer 25 vaporizes the liquefied hydrogen introduced from the manifold 21 and generates low-temperature hydrogen gas at a predetermined temperature. The low-temperature hydrogen gas generated in the vaporizer 25 is introduced into the liquefied hydrogen tank 1 through the second pipe 26 and the third pipe 28. As the low-temperature hydrogen gas is introduced into the liquefied hydrogen tank 1, the nitrogen gas in the internal space 13 of the liquefied hydrogen tank 1 is discharged to the outside through the discharge pipe 32. Therefore, the nitrogen gas in the internal space 13 is removed.

[0035] The temperature of the low-temperature hydrogen gas is within a predetermined range, including the temperature at the end of the pre-cooling process. For example, if the temperature at the end of the pre-cooling process is -180°C, the temperature of the low-temperature hydrogen gas is set to -180±10°C. This reduces the temperature difference between the oxygen removal process and the subsequent nitrogen removal process, thereby preventing the liquefaction or solidification of nitrogen while maintaining the cooling state inside the liquefied hydrogen tank 1.

[0036] Once nitrogen removal is complete, for example, when the hydrogen concentration exceeds a predetermined second reference value Th2, the internal space 13 becomes a low-temperature hydrogen gas atmosphere. At this time, the temperature of the internal space 13 becomes a second pre-cooling temperature, which is equivalent to or somewhat higher than the temperature at which the low-temperature hydrogen gas was introduced. The second pre-cooling temperature is, for example, approximately -180°C to -160°C.

[0037] In step S4, the controller 5 determines whether the hydrogen concentration measured by the second measuring instrument 34 has risen above the second reference value Th2. The second reference value Th2 is set to the value when the nitrogen concentration in the internal space 13 is sufficiently low.

[0038] If the hydrogen concentration measured by the second measuring instrument 34 becomes higher than the second reference value Th2, step S4 is determined to be Yes, and the process proceeds to step S5. Step S5 is a liquefied hydrogen introduction process in which liquefied hydrogen is introduced into the internal space 13 of the liquefied hydrogen tank 1 after pre-cooling from which oxygen and nitrogen have been removed. The controller 5 closes the second on-off valve 27 from the state in the nitrogen removal process, while opening the first on-off valve 24. As a result, liquefied hydrogen is introduced into the internal space 13 of the liquefied hydrogen tank 1 through the liquefied hydrogen introduction system, the first piping 23, and the third piping 28 inserted into the interior from the top of the liquefied hydrogen tank 1. As liquefied hydrogen is introduced into the liquefied hydrogen tank 1, the low-temperature hydrogen gas in the internal space 13 of the liquefied hydrogen tank 1 is discharged to the outside through the discharge piping 32, and liquefied hydrogen is stored in the internal space 13.

[0039] Liquefied hydrogen is sprayed from a first discharge port 22 located at the top of the internal space 13. The liquefied hydrogen introduced from the top of the internal space 13 further cools the inside of the internal space 13 to a temperature at which liquefied hydrogen can be stored, that is, a liquefied hydrogen storage temperature near the boiling point of liquefied hydrogen, which is -252.6°C.

[0040] The internal space 13 is cooled to a temperature near that which is suitable for storing liquefied hydrogen, so that the liquefied hydrogen is stored in the internal space 13 without vaporizing.

[0041] According to the above method, before introducing liquefied hydrogen into the liquefied hydrogen tank 1 mounted on the ship 100, liquefied nitrogen is introduced into the liquefied hydrogen tank 1 through pipes 23 and 28 inserted from the top of the liquefied hydrogen tank 1, thereby pre-cooling the inside of the liquefied hydrogen tank 1. Therefore, when introducing liquefied hydrogen into the liquefied hydrogen tank 1, the amount of liquefied hydrogen consumed to cool the liquefied hydrogen tank 1 is reduced. Consequently, the amount of liquefied hydrogen consumed by vaporization when cooling the inside of the liquefied hydrogen tank 1 to the temperature at which the liquefied hydrogen is stored can be reduced. Furthermore, according to the above method, since the inside of the liquefied hydrogen tank 1 is cooled in stages, localized thermal contraction of the liquefied hydrogen tank 1 can be made less likely. In addition, by using liquefied nitrogen to cool the inside of the liquefied hydrogen tank 1 from room temperature to a first pre-cooling temperature close to the boiling point of liquefied nitrogen, the cooling efficiency, including the cost of manufacturing the refrigerant, can be made higher compared to when liquefied hydrogen or low-temperature hydrogen gas is used to cool from room temperature to the first pre-cooling temperature.

[0042] Furthermore, for safety reasons, the liquefied hydrogen tank 1 installed on the ship 100 has an upper dome 1B that protrudes from the tank cover 120, so that the connection between the piping for introducing liquefied hydrogen and the liquefied hydrogen tank 1 is in an exposed space outside the ship. The rest of the tank, excluding the dome 1B, is covered by the hull 110 and the tank cover 120. By limiting the connection route to the internal space 13 of the liquefied hydrogen tank 1 to the upper dome 1B, even if flammable hydrogen leaks from the dome 1B or its surrounding piping and other ancillary equipment, it will easily diffuse outside the ship, preventing the accumulation of flammable hydrogen on the ship 100. In response to these constraints on the ship 100, pre-cooling of the liquefied hydrogen tank 1 can be achieved while adhering to the safety constraints of the liquefied hydrogen tank 1 installed on the ship 100 by introducing liquefied nitrogen through piping 23, 28 inserted into the interior from the top of the liquefied hydrogen tank 1.

[0043] Furthermore, according to the above method, after liquid nitrogen is introduced but before liquid hydrogen is introduced, low-temperature hydrogen gas, which is vaporized liquid hydrogen, is introduced, thereby removing the vaporized nitrogen during oxygen removal. As a result, it becomes unnecessary to use liquid hydrogen for nitrogen removal, and thus the consumption of liquid hydrogen can be reduced.

[0044] Furthermore, in the conventional method, where room-temperature nitrogen is introduced to remove oxygen from the liquefied hydrogen tank 1, and then liquefied hydrogen is introduced to remove the nitrogen, there is a risk that some of the nitrogen filling the liquefied hydrogen tank 1 will cool rapidly, causing localized solidification or liquefaction of the nitrogen. If nitrogen solidifies or liquefies in the liquefied hydrogen tank 1, localized thermal contraction of the liquefied hydrogen tank 1 is likely to occur at the location where the solidified or liquefied nitrogen occurs. In contrast, with the above method, since liquid nitrogen is introduced to remove oxygen from the liquefied hydrogen tank 1, the liquefied hydrogen tank 1 is filled with low-temperature nitrogen gas at the stage when low-temperature hydrogen gas is introduced. Therefore, the rapid cooling of nitrogen due to the introduction of low-temperature hydrogen gas can be suppressed, and localized solidification or liquefaction of nitrogen can be prevented.

[0045] Furthermore, by introducing liquid nitrogen at a higher temperature than liquid hydrogen when the inside of the liquid hydrogen tank 1 is at or near room temperature, the thermal shock caused by direct contact between the liquid hydrogen and the inner surface of the liquid hydrogen tank 1 can be suppressed. In addition, by introducing liquid nitrogen before introducing liquid hydrogen, the rapid cooling of the liquid hydrogen tank 1 can be suppressed compared to when liquid hydrogen is introduced directly. Therefore, damage to the liquid hydrogen tank 1 due to cooling can be reduced.

[0046] In conventional methods, when the internal space 13 of the liquefied hydrogen tank 1 is cooled from room temperature using liquefied hydrogen, the amount of liquefied hydrogen required to cool it to the liquefied hydrogen storage temperature increases as the volume of the internal space 13 increases. On the other hand, according to this embodiment, the amount of liquefied hydrogen required to cool it to the liquefied hydrogen storage temperature can be reduced to, for example, about 1 / 5 of that required by conventional methods.

[0047] In this embodiment, although the amount of nitrogen required increases compared to the conventional method, the cost of introducing nitrogen, especially liquid nitrogen, is lower than the production and maintenance costs of liquid hydrogen, thus enabling overall system cost reduction.

[0048] Furthermore, as the size of the liquefied hydrogen tank 1 increases, the amount of liquefied hydrogen released into the atmosphere increases significantly with conventional methods, becoming a non-negligible issue. Also, as the size of the liquefied hydrogen tank 1 increases, the aforementioned problem of nitrogen solidification or liquefaction becomes more apparent with conventional methods. In contrast, with the implementation configuration of this embodiment, even if the liquefied hydrogen tank 1 is enlarged, the increase in the amount of hydrogen released into the atmosphere can be effectively suppressed, and nitrogen solidification or liquefaction can be prevented. Therefore, even if the liquefied hydrogen tank 1 is enlarged, the increase in the amount of liquefied hydrogen consumed can be suppressed, and the inside of the liquefied hydrogen tank 1 can be appropriately cooled.

[0049] As described above, the pre-cooling process can be carried out while the vessel 100 is underway. Figure 4 shows an image of the vessel's navigation in this embodiment. For example, the vessel 100 sails between a first port P1 that receives the liquefied hydrogen transported by the vessel 100 and a second port P2 that supplies liquefied hydrogen to the vessel 100. For example, the second port P2 has an onshore liquefied hydrogen storage facility F2 where liquefied hydrogen is stored, such as a cargo handling base. The liquefied hydrogen storage facility F2 corresponds to the external liquefied hydrogen introduction system described above.

[0050] While the vessel 100 is anchored at the second port P2, at least a nitrogen removal process using hydrogen gas and a liquefied hydrogen introduction process are carried out. After liquefied hydrogen is introduced into the liquefied hydrogen tank 1 at the second port P2, the vessel 100 sails from the second port P2 to the first port P1 with the liquefied hydrogen stored in the liquefied hydrogen tank 1. At the first port P1, where the liquefied hydrogen is received, the liquefied hydrogen stored in the liquefied hydrogen tank 1 is removed, and the liquefied hydrogen tank 1 of the vessel 100 is empty during the voyage from the first port P1 to the second port P2.

[0051] Since the number of liquefied hydrogen storage facilities F2 is limited, it is desirable that the period during which a vessel 100 is docked at the second port P2, that is, the period during which a single vessel 100 occupies the second port P2, be short. On the other hand, if the internal space 13 of the liquefied hydrogen tank 1 is at room temperature or higher than the temperature at which a predetermined amount of liquefied hydrogen can be loaded when the vessel 100 arrives at the second port P2, then in addition to these two processes, the above-mentioned pre-cooling process must also be carried out at the second port P2.

[0052] Therefore, a pre-cooling process can be carried out during the voyage from the first port P1 to the second port P2. That is, the ship 100 sails to the second port P2 with liquefied nitrogen introduced into the liquefied hydrogen tank 1. For example, if the first port P1 has a liquefied nitrogen storage facility F1, liquefied nitrogen is introduced into the liquefied hydrogen tank 1 while the ship 100 is anchored at the first port P1. The liquefied nitrogen storage facility F1 corresponds to the external liquefied nitrogen introduction system described above.

[0053] According to this, the internal space 13 of the liquefied hydrogen tank 1 is pre-cooled by the time the ship 100 arrives at the second port P2, where the liquefied hydrogen storage facility F2 that supplies liquefied hydrogen to the liquefied hydrogen tank 1 is located. This shortens the time from when the ship 100 arrives at the second port P2 until liquefied hydrogen is introduced into the liquefied hydrogen tank 1. Furthermore, since pre-cooling is performed while the ship 100 is sailing at sea, it is not necessary for the ship to remain anchored at the first port P1 after introducing liquefied nitrogen there and while pre-cooling is performed. Therefore, the transport cycle of liquid hydrogen between the first port P1 and the second port P2 can be shortened.

[0054] Furthermore, the location where liquefied nitrogen is introduced into the liquefied hydrogen tank 1 does not have to be the first port P1 where the liquefied hydrogen is received. For example, liquefied nitrogen may be introduced into the liquefied hydrogen tank 1 when the ship is anchored in a third port different from the first port P1 and the second port P2. In this case, the ship 100 sails empty from the first port P1 to the third port. At the third port, the ship 100 introduces liquefied nitrogen into the liquefied hydrogen tank 1 and sails from the third port to the second port P2 while pre-cooling with liquefied nitrogen. After the ship 100 arrives at the second port P2, liquefied hydrogen is introduced into the liquefied hydrogen tank 1. The ship 100 sails from the second port P2 to the first port P1, thereby transporting liquefied hydrogen from the second port P2 to the first port P1.

[0055] Furthermore, the location where liquefied nitrogen is introduced into the liquefied hydrogen tank 1 does not have to be a fixed liquefied nitrogen storage facility F1 in the port. For example, in a port without a liquefied nitrogen storage facility F1, liquefied nitrogen transported to the port by a liquefied nitrogen transport vehicle such as a tanker truck or liquefied nitrogen transported by another vessel may be introduced into the liquefied hydrogen tank 1. Also, the liquefied nitrogen storage facility F1 or the liquefied hydrogen storage facility F2 may be installed on land or at sea.

[0056] Typically, the vessel 100 undergoes regular maintenance every 2.5 or 5 years. In such cases, it enters a dry dock for maintenance. Before entering the dry dock, it is warmed up, and the liquefied hydrogen tank 1 is placed in a nitrogen gas atmosphere or an air atmosphere. After entering the dry dock, if loading is to be carried out again, it is necessary to replace the liquefied hydrogen tank 1 with nitrogen gas, then with hydrogen gas, and then perform a cool-down. According to this embodiment, by introducing liquefied nitrogen at the third port where it is introduced, pre-cooling can be performed while replacing with nitrogen gas, and then the cool-down with liquefied hydrogen can be performed at the second port P2.

[0057] Furthermore, if the vessel 100 is equipped with multiple liquefied hydrogen tanks 1, one of the liquefied hydrogen tanks 1 may be pre-cooled with liquefied nitrogen at the third port, and liquefied nitrogen may be stored in the liquefied hydrogen tank 1. In addition, while the vessel 100 is sailing from the third port to the second port P2, liquefied nitrogen may be supplied from the liquefied hydrogen tank 1 containing the stored liquefied nitrogen to the other liquefied hydrogen tanks 1, and the liquefied nitrogen may be sprayed into the other liquefied hydrogen tanks 1 to pre-cool them.

[0058] Furthermore, precooling with liquid nitrogen is not necessarily required before introducing liquefied hydrogen. For example, after the construction of the vessel 100 or after the completion of periodic maintenance, precooling may be performed by introducing liquid nitrogen at the third port before introducing liquefied hydrogen, and then cooling down with liquefied hydrogen may be performed at the second port P2. On the other hand, after introducing liquefied hydrogen at the second port P2, the vessel 100 may transport liquefied hydrogen between the first port P1 and the second port P2 multiple times during the period until the next periodic maintenance without precooling with liquid nitrogen.

[0059] Furthermore, the vessel 100 may remain anchored at sea for a predetermined period with liquefied nitrogen stored in the liquefied hydrogen tank 1. For example, if the port where the liquefied nitrogen storage facility F1 is installed is close to the second port P2, the vessel may be anchored in the vicinity of the second port P2 so that pre-cooling is completed. For example, the anchoring period is determined based on the assumed temperature of the internal space 13 of the liquefied hydrogen tank 1 at the end of the pre-cooling process, the rate of temperature decrease per unit time in the internal space 13 due to liquefied nitrogen, and the distance from the anchoring point of the vessel 100 to the second port P2.

[0060] Furthermore, the vessel 100 may be equipped with a liquefied nitrogen tank for storing liquefied nitrogen. In addition to the introduction of liquefied nitrogen into the liquefied hydrogen tank 1 while the vessel is anchored in the first port P1, or alternatively, while the vessel is sailing with liquefied nitrogen stored, liquefied nitrogen may be sprayed from the liquefied nitrogen tank through the manifold 21, the first pipe 23, and the third pipe 28 at predetermined timings from the discharge port 22.

[0061] 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.

[0062] For example, in the above embodiment, an example was shown in which liquefied nitrogen is circulated in the first pipe 23 through which liquefied hydrogen is circulated. That is, in the above embodiment, the liquefied hydrogen circulation pipe and the liquefied nitrogen circulation pipe are common pipes, but this is not limited to this. For example, the liquefied hydrogen circulation pipe and the liquefied nitrogen circulation pipe may be arranged independently. Also, in the above embodiment, an example was given in which the end of the discharge pipe 32 is located in the upper part of the liquefied hydrogen tank 1, but the position of the end of the discharge pipe 32 is not limited to this. Furthermore, instead of the discharge pipe 32 that discharges nitrogen gas, oxygen gas, and hydrogen gas, pipes for discharging nitrogen gas and oxygen gas and pipes for discharging hydrogen gas may be arranged independently. In this case, the positions of the ends of each discharge pipe may be different from each other. For example, the end of the discharge pipe for discharging residual air when nitrogen is introduced may be located in the upper part of the liquefied hydrogen tank 1, and the end of the discharge pipe for discharging nitrogen gas when hydrogen is introduced may be located in the lower part of the liquefied hydrogen tank 1.

[0063] Furthermore, although the above embodiment illustrates a configuration in which liquid nitrogen or liquid hydrogen is sprayed from the discharge port 22 into the internal space 13 of the liquid hydrogen tank 1, the invention is not limited to this configuration. For example, the piping for the flow of liquid nitrogen or liquid hydrogen may have a discharge port other than the discharge port 22. If the liquid nitrogen or liquid hydrogen is not sprayed from the discharge port 22, the liquid nitrogen or liquid hydrogen may be discharged from a different discharge port.

[0064] Furthermore, although the above embodiment illustrates a configuration in which liquefied nitrogen is introduced from an external liquefied nitrogen introduction system via the manifold 21, the invention is not limited to this. For example, the ship 100 may be equipped with a liquefied nitrogen tank for storing liquefied nitrogen, and liquefied nitrogen may be introduced from the liquefied nitrogen tank to the liquefied hydrogen tank 1. For example, the liquefied nitrogen tank installed on the ship 100 may be smaller than the liquefied hydrogen tank 1.

[0065] Furthermore, in the above embodiment, the low-temperature hydrogen gas introduced in the nitrogen removal process is generated by vaporizing liquefied hydrogen in the vaporizer 25, but this is not limited to this. For example, when liquefied hydrogen is used as a refrigerant in another facility, the low-temperature hydrogen gas generated by heat exchange between the liquefied hydrogen and the object to be cooled in that facility may be introduced into the internal space 13 of the liquefied hydrogen tank 1 from the first piping 23. In this case, the vaporizer 25, the second piping 26, and the second on-off valve 27 may be omitted.

[0066] Furthermore, in the above embodiment, the first measuring instrument 33 for measuring oxygen concentration is provided inside the discharge pipe 32, but the first measuring instrument 33 may be provided inside the internal space 13. Similarly, in the above embodiment, the second measuring instrument 34 for measuring hydrogen gas concentration is provided inside the discharge pipe 32, but the second measuring instrument 34 may be provided inside the internal space 13.

[0067] Furthermore, while the above embodiment exemplifies a pre-cooling process in which liquid nitrogen is introduced from a state in which the internal space 13 of the liquid hydrogen tank 1 is at room temperature and contains oxygen, nitrogen, and water vapor, the embodiment is not limited to this. For example, oxygen may be removed before the pre-cooling process by introducing nitrogen gas before introducing liquid nitrogen.

[0068] Furthermore, in the above embodiment, an example was given in which low-temperature hydrogen gas is introduced after introducing liquid nitrogen but before introducing liquid hydrogen, but the introduction of low-temperature hydrogen gas is not required. Also, precooling with low-temperature nitrogen gas may be performed instead of precooling with liquid nitrogen. In other words, the refrigerant used for precooling may be either liquid nitrogen or low-temperature nitrogen gas.

[0069] Furthermore, although a spherical liquefied hydrogen tank 1 was exemplified in the above embodiment, the shape of the liquefied hydrogen tank 1 is not particularly limited, and can be cylindrical, rectangular, or the like. Also, the type of liquefied hydrogen tank 1 is not particularly limited, for example, a self-supporting spherical type.

[0070] Furthermore, in the above embodiment, an example was given of cooling the inside of the liquefied hydrogen tank 1 in order to store liquefied hydrogen in the liquefied hydrogen tank 1. Conversely, nitrogen gas may be supplied when heating the inside of the liquefied hydrogen tank 1 to return the internal space 13 of the liquefied hydrogen tank 1 to a nitrogen atmosphere. For example, hydrogen gas remaining in the liquefied hydrogen tank 1 is taken out from the discharge pipe 32, and then circulated again from the manifold 21 to the second pipe 26 to be heated by the vaporizer 25, which is a heat exchanger, and then reintroduced into the liquefied hydrogen tank 1. After the temperature of the internal space 13 of the liquefied hydrogen tank 1 rises to a temperature at which nitrogen does not liquefy, nitrogen gas is introduced into the liquefied hydrogen tank 1. This makes it possible to heat the internal space 13 of the liquefied hydrogen tank 1 while replacing the hydrogen atmosphere with a nitrogen atmosphere. Thus, instead of warming up the liquefied hydrogen tank 1 to near room temperature with hydrogen gas during maintenance, using nitrogen gas allows the warm-up and the gas replacement process from hydrogen gas to nitrogen gas to be carried out simultaneously, thus enabling the process of warming up the tank and creating a nitrogen gas atmosphere to be carried out quickly. Furthermore, the heating of the hydrogen gas or nitrogen gas used for warm-up is not limited to the vaporizer 25, but may be carried out by other heaters within the ship 100.

[0071] [Summary of this disclosure] A method for storing liquefied hydrogen for ships according to one aspect of the present disclosure is a method for storing liquefied hydrogen in a liquefied hydrogen tank installed on a ship, wherein a refrigerant is introduced into the liquefied hydrogen tank through a pipe inserted from the top of the liquefied hydrogen tank to precool the liquefied hydrogen tank, and the liquefied hydrogen is introduced into the liquefied hydrogen tank after precooling.

[0072] According to the above method, before introducing liquefied hydrogen into the liquefied hydrogen tank installed on the ship, a refrigerant is introduced into the liquefied hydrogen tank through piping inserted from the top of the tank, thereby pre-cooling the inside of the liquefied hydrogen tank. As a result, the amount of liquefied hydrogen consumed to cool the liquefied hydrogen tank when introducing liquefied hydrogen into it is reduced. Consequently, the amount of liquefied hydrogen consumed by vaporization when cooling the inside of the liquefied hydrogen tank to the temperature at which the liquefied hydrogen is stored can be reduced.

[0073] Furthermore, for safety reasons, liquefied hydrogen tanks installed on ships are completely enclosed except for the top. To overcome these constraints on ships, pre-cooling of the liquefied hydrogen tank 1 can be achieved while adhering to the safety constraints of liquefied hydrogen tanks installed on ships by introducing a refrigerant through piping inserted into the interior from the top of the liquefied hydrogen tank.

[0074] The refrigerant may be liquid nitrogen. Alternatively, the refrigerant may be low-temperature nitrogen gas obtained by vaporizing the liquid nitrogen.

[0075] After introducing the liquefied nitrogen or the low-temperature nitrogen gas and before introducing the liquefied hydrogen, low-temperature hydrogen gas, which is obtained by vaporizing the liquefied hydrogen, may be introduced. By introducing low-temperature hydrogen gas after introducing the liquefied nitrogen or low-temperature nitrogen gas and before introducing the liquefied hydrogen, the nitrogen vaporized during oxygen removal is removed. This eliminates the need to use liquefied hydrogen for nitrogen removal, thus reducing the consumption of liquefied hydrogen.

[0076] The vessel may sail to a liquefied hydrogen storage facility where the liquefied hydrogen is stored with the refrigerant introduced into the liquefied hydrogen tank, and then introduce the liquefied hydrogen into the liquefied hydrogen tank at the liquefied hydrogen storage facility.

[0077] According to this system, the internal space of the liquefied hydrogen tank is pre-cooled before the ship arrives at the liquefied hydrogen storage facility that supplies the liquefied hydrogen to the tank. This shortens the time from when the ship arrives at the liquefied hydrogen storage facility until the liquefied hydrogen is introduced into the tank. Furthermore, because pre-cooling is performed while the ship is sailing at sea, the transport cycle of liquid hydrogen between the receiving and supplying locations can be shortened.

[0078] The refrigerant may be introduced into the liquefied hydrogen tank while the vessel is moored at a location separate from the liquefied hydrogen storage facility. Since the refrigerant is introduced into the liquefied hydrogen tank at a location separate from the liquefied hydrogen storage facility, the mooring period at the liquefied hydrogen storage facility can be shortened. [Explanation of symbols]

[0079] 1. Liquefied hydrogen tank 23. First Piping 26. Second Piping 28. Third Piping 100 ships F1 Liquefied Nitrogen Storage Facility F2 Liquefied Hydrogen Storage Facility

Claims

1. A method for storing liquefied hydrogen in a liquefied hydrogen tank installed on a ship, A refrigerant is introduced into the liquefied hydrogen tank through piping inserted from the top of the liquefied hydrogen tank into the interior. With the refrigerant introduced into the liquefied hydrogen tank, the vessel is sailed to a liquefied hydrogen storage facility where the liquefied hydrogen is stored, thereby pre-cooling the liquefied hydrogen tank. A method for storing liquefied hydrogen for ships, comprising introducing the liquefied hydrogen into a liquefied hydrogen tank after pre-cooling in the aforementioned liquefied hydrogen storage facility.

2. The method for storing liquefied hydrogen for a ship according to claim 1, wherein the refrigerant is introduced into the liquefied hydrogen tank while the ship is moored at a location separate from the liquefied hydrogen storage facility.

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