Warm-up method for tank and ship

Abstract

This warm-up method for a tank that is installed in a ship and stores liquefied hydrogen includes warming up the tank using hydrogen gas by pressurizing the hydrogen gas taken out from the tank, heating the pressurized hydrogen gas, and introducing the heated hydrogen gas into the tank. A part of the hydrogen gas taken out from the tank is sent to an outside facility.

Description

Tank warm-up method and ship

[0001] The present disclosure relates to a tank warm-up method and a ship.

[0002] Patent Document 1 describes a boil-off gas treatment system for a ship, which includes a liquefied gas storage tank for storing liquefied gas, a compressed gas supply means for supplying boil-off gas generated in the liquefied gas storage tank to gas-consuming equipment via a gas compressor, and a means for returning gas from the discharge side of the compressed gas supply means into the liquefied gas storage tank. Patent Document 1 describes that the liquefied gas storage tank is warmed up by returning the gas compressed by the gas compressor and having an increased gas temperature to the liquefied gas storage tank, and the boil-off gas is consumed by the gas-consuming equipment to suppress the pressure increase in the liquefied gas storage tank.

[0003] Japanese Patent Application Laid-Open No. 2019-056381 [[ID=II]]

[0004] In Patent Document 1, when liquefied hydrogen is used as the liquefied gas, it is assumed that hydrogen treatment equipment such as a boiler normally installed on a liquefied hydrogen carrier is used as the gas-consuming equipment. However, the processing capacity of hydrogen treatment equipment such as a boiler normally installed on a liquefied hydrogen carrier is often lower than the capacity required to process the hydrogen gas generated in the liquefied hydrogen storage tank within a predetermined time during warm-up. As a result, there is a problem that the time required for tank warm-up becomes long.

[0005] An object of the present disclosure is to provide a tank warm-up method and a ship that can shorten the time required for warm-up compared to the case where hydrogen gas generated in the tank is processed only inside the ship during the warm-up of a tank for storing liquefied hydrogen.

[0006] One aspect of the present disclosure provides a method for warming up a tank installed on a ship for storing liquefied hydrogen and hydrogen gas, the method comprising warming up the tank using hydrogen gas by pressurizing hydrogen gas taken out of the tank, heating the pressurized hydrogen gas, and introducing the heated hydrogen gas into the tank, wherein a portion of the hydrogen gas taken out of the tank is sent to an off-board facility.

[0007] According to this disclosure, when warming up a tank for storing liquefied hydrogen, the time required for warming up can be reduced compared to when the hydrogen gas generated in the tank is treated only on board the ship.

[0008] Figure 1 is a schematic diagram showing the configuration of a vessel according to one embodiment of the present disclosure. Figure 2 is a flowchart of a warm-up method according to one embodiment of the present disclosure. Figure 3 is a diagram illustrating the warm-up method according to one embodiment of the present disclosure. Figure 4 is a diagram illustrating the warm-up method according to one embodiment of the present disclosure. Figure 5 is a diagram illustrating the warm-up method according to one embodiment of the present disclosure.

[0009] A warm-up method and vessel according to one embodiment of this disclosure will be described below with reference to the attached drawings.

[0010] [Vessel Configuration] Figure 1 is a schematic diagram showing the configuration of vessel 1 according to this embodiment. Vessel 1 is a liquefied hydrogen carrier. Figure 1 shows vessel 1 docked at an offshore facility 2, such as a land base or an offshore base. The offshore facility 2 is, for example, a dock for repairing vessel 1 or for loading and unloading liquefied hydrogen. The offshore facility 2 includes a hydrogen gas processing facility for processing a large amount of hydrogen gas compared to boilers and the like that normally installed on vessel 1, and a nitrogen gas supply source for supplying nitrogen gas to vessel 1. Referring to Figure 1, vessel 1 includes a tank 10 and a circulation line 20.

[0011] Tank 10 is a cargo tank for storing liquefied hydrogen as cargo and hydrogen gas generated when liquefied hydrogen vaporizes. Tank 10 is equipped with a thermometer 11 for measuring the temperature inside the tank, a pressure gauge 12 for measuring the pressure inside the tank, and a hydrogen gas concentration meter 13 for measuring the hydrogen gas concentration inside the tank.

[0012] The circulation line 20 is a flow path that returns gas extracted from the tank 10 back to the tank 10. The circulation line 20 is composed of multiple pipes. The circulation line 20 has a first end 20a and a second end 20b located inside the tank 10. The first end 20a and the second end 20b are open inside the tank 10. The first end 20a is located at a higher position than the second end 20b. Gas from the tank 10 flows into the circulation line 20 via the first end 20a, and the gas that has flowed through the circulation line 20 is introduced into the tank 10 via the second end 20b. In the following description, the upstream of the gas flow in the circulation line 20 may be simply referred to as "upstream," and the downstream of the gas flow in the circulation line 20 may be simply referred to as "downstream."

[0013] The vessel 1 is equipped with a compressor 30, a first heater 31, and a second heater 32. The compressor 30, the first heater 31, and the second heater 32 are arranged on a circulation line 20. The compressor 30, the first heater 31, and the second heater 32 are arranged in the order of second heater 32, compressor 30, and first heater 31 from upstream to downstream in the circulation line 20.

[0014] The compressor 30 pressurizes the gas in the circulation line 20 and sends it toward the tank 10. In other words, the compressor 30 pressurizes the gas in the circulation line 20 and sends it toward the tank 10. The compressor 30 may also be used to return the boil-off gas generated in the tank 10 when liquefied hydrogen is loaded into the tank 10 to the off-board facility 2. When the compressor 30 is used to return the boil-off gas, the gas discharged from the compressor 30 may be returned to the off-board facility 2 through a branch line (not shown) that branches off downstream of the compressor 30 and upstream of the first heater 31 and is fluidically connected to the first manifold 62, which will be described later. The compressor 30 in this embodiment is a centrifugal compressor.

[0015] The first heater 31 is located on the circulation line 20. The first heater 31 is located downstream of the compressor 30. In other words, the first heater 31 is located on the discharge side of the compressor 30. The first heater 31 is pressurized by the compressor 30 and heats the gas flowing through the circulation line 20 toward the tank 10. The first heater 31 functions as an afterheater that heats the gas discharged from the compressor 30.

[0016] The second heater 32 is located on the circulation line 20. The second heater 32 is located upstream of the compressor 30. In other words, the second heater 32 is located on the suction side of the compressor 30. The second heater 32 functions as a preheater, preheating the gas supplied to the compressor 30.

[0017] The vessel 1 is equipped with a first bypass line 40 and a first valve 41.

[0018] The first bypass line 40 is a flow path that allows gas flowing upstream of the first heater 31 in the circulation line 20 to flow downstream of the first heater 31 without passing through the first heater 31. The first bypass line 40 fluidly connects the upstream and downstream of the first heater 31. The first bypass line 40 is composed of multiple pipes. One end of the first bypass line 40 is fluidly connected to the circulation line 20 at a first connection 21 located upstream of the first heater 31. The other end of the first bypass line 40 is fluidly connected to the circulation line 20 at a second connection 22 located downstream of the first heater 31. The first connection 21 is located between the first heater 31 and the compressor 30 in the circulation line 20. In other words, the first connection 21 is located upstream of the first heater 31 and downstream of the compressor 30 in the circulation line 20. The second connection section 22 is located in the circulation line 20 between the first heater 31 and the second end 20b. In other words, the second connection section 23 is located in the circulation line 20 downstream of the first heater 31 and upstream of the second end 20b.

[0019] The first valve 41 is located on the first bypass line 40. The first valve 41 is a flow control valve that can adjust the flow rate by changing its opening. The first valve 41 may be able to adjust the flow rate continuously or in steps. The first valve 41 adjusts the flow rate of gas flowing through the first bypass line 40. By adjusting the flow rate of gas passing through the first bypass line 40, the flow rate of gas passing through the first heater 31 is adjusted.

[0020] The vessel 1 is equipped with a second bypass line 50 and a second valve 51.

[0021] The second bypass line 50 is a flow path that allows gas flowing upstream of the second heater 32 in the circulation line 20 to flow downstream of the second heater 32 without passing through the second heater 32. The second bypass line 50 fluidly connects the upstream and downstream of the second heater 32. The second bypass line 50 is composed of multiple pipes. One end of the second bypass line 50 is fluidly connected to the circulation line 20 at a third connection 23 located upstream of the second heater 32. The other end of the second bypass line 50 is fluidly connected to the circulation line 20 at a fourth connection 24 located downstream of the second heater 32. The third connection 23 is located in the circulation line 20 between the second heater 32 and the first end 20a. In other words, the third connection 23 is located in the circulation line 20 upstream of the second heater 32 and downstream of the first end 20a. The fourth connection section 24 is located in the circulation line 20 between the second heater 32 and the compressor 30. In other words, the fourth connection section 24 is located in the circulation line 20 downstream of the second heater 32 and upstream of the compressor 30.

[0022] The second valve 51 is located on the second bypass line 50. The second valve 51 is a flow control valve that can adjust the flow rate by changing its opening. The second valve 51 may be able to adjust the flow rate continuously or in steps. The second valve 51 adjusts the flow rate of gas flowing through the second bypass line 50. By adjusting the flow rate of gas passing through the second bypass line 50, the flow rate of gas passing through the second heater 32 is adjusted. The second valve 51 may also be an on / off valve.

[0023] The vessel 1 is equipped with a discharge line 60, a third valve 61, and a supply line 70.

[0024] The discharge line 60 branches off from the circulation line 20 and is a passage for discharging the gas flowing through the circulation line 20 to the outboard facility 2. One end of the discharge line 60 is fluidly connected to the circulation line 20 at the fifth connection 25, which is located upstream of the third connection 23. At the other end of the discharge line 60 is a first manifold 62, which is mechanically and fluidly connected to the piping 2a of the outboard facility 2. A flow meter 63 is located on the discharge line 60 to measure the flow rate of the gas flowing through the discharge line 60.

[0025] The third valve 61 is located on the discharge line 60. The third valve 61 is a flow control valve that can adjust the flow rate by changing its opening. The third valve 61 may be able to adjust the flow rate continuously or in steps. The third valve 61 adjusts the flow rate of the gas flowing through the discharge line 60.

[0026] The supply line 70 merges with the circulation line 20 and is a flow path for supplying gas supplied from the outboard facility 2 to the circulation line 20. One end of the supply line 70 is fluidly connected to the circulation line 20 at the sixth connection 26, which is located downstream of the second connection 22. At the other end of the supply line 70 is a second manifold 71 which is mechanically and fluidly connected to the piping 2b of the outboard facility 2.

[0027] The vessel 1 is equipped with a vent line 80, a fourth valve 81, and a venting device 82.

[0028] The vent line 80 branches off from the circulation line 20 and is a passage for sending the gas flowing through the circulation line 20 to the venting device 82. One end of the vent line 80 is fluidically connected to the circulation line 20 at the seventh connection part 27, which is located upstream of the fifth connection part 25. The other end of the vent line 80 is fluidically connected to the venting device 82.

[0029] The fourth valve 81 is located on the vent line 80. The fourth valve 81 is a flow control valve that can adjust the flow rate by changing its opening. The fourth valve 81 may be able to adjust the flow rate continuously or in steps. The fourth valve 81 adjusts the flow rate of the gas flowing through the vent line 80.

[0030] The venting device 82 discharges the gas in the circulation line 20 to the outside. In this embodiment, the venting device 82 is a vent mast for releasing the gas in the circulation line 20 into the atmosphere.

[0031] The vessel 1 is equipped with a control device 90. The control device 90 is electrically connected to a thermometer 11, a pressure gauge 12, a hydrogen gas concentration meter 13, a flow meter 63, a first valve 41, a second valve 51, a third valve 61, a fourth valve 81, a compressor 30, a first heater 31, and a second heater 32. Measurement data is input to the control device 90 from the thermometer 11, the pressure gauge 12, the hydrogen gas concentration meter 13, and the flow meter 63. Based on the measurement data input from the thermometer 11, the pressure gauge 12, the hydrogen gas concentration meter 13, and the flow meter 63, the control device 90 controls the operation of the first valve 41, the second valve 51, the third valve 61, the fourth valve 81, the compressor 30, the first heater 31, and the second heater 32. Furthermore, the control device 90 may control the operation of the first heater 31 based on the outlet temperature of the first heater 31, or control the operation of the second heater 32 based on the outlet temperature of the second heater 32. The pressure inside the tank 10 measured by the pressure gauge 12 of this embodiment is an example of the pressure related to the pressure inside the tank according to this disclosure. The pressure related to the pressure inside the tank according to this disclosure may be, for example, the pressure measured at any position upstream of the compressor 30 in the circulation line 20.

[0032] [Tank Warm-up Method] Figure 2 is a flowchart of the tank 10 warm-up method according to this embodiment. Figures 3 to 5 are diagrams illustrating the tank 10 warm-up method according to this embodiment. Warming up the tank 10 is performed in gas-free operation, in which the hydrogen gas in the tank 10 is replaced with an inert gas before inspection or repair of the ship 1, in order to raise the temperature of the tank 10 to a target temperature. The warm-up method according to this embodiment is performed by the control device 90 controlling the operation of the first valve 41, the second valve 51, the third valve 61, the fourth valve 81, the compressor 30, the first heater 31, and the second heater 32.

[0033] Referring to Figure 2, in step S1, the tank 10 is warmed up using hydrogen gas. At the start of step S1, most of the tank 10 is occupied by hydrogen gas. Also, at the start of step S1, the temperature inside the tank 10 is, for example, about -250°C. In step S1, as shown in Figure 3, the hydrogen gas taken out of the tank 10 is pressurized, the pressurized hydrogen gas is heated, and the heated hydrogen gas is introduced into the tank 10. In step S1, when the compressor 30 is started, the hydrogen gas in the tank 10 flows into the circulation line 20. The compressor 30 pressurizes the hydrogen gas flowing through the circulation line 20 and sends it towards the tank 10. The first heater 31 heats a portion of the hydrogen gas sent to the tank 10 by the compressor 30. The hydrogen gas heated and warmed by the first heater 31 is introduced into the tank 10, warming up the tank 10.

[0034] In step S1, the first valve 41 is open. As a result, a portion of the hydrogen gas discharged from the compressor 30 is heated by the first heater 31 and returned to the tank 10, while the remaining hydrogen gas discharged from the compressor 30 passes through the first bypass line 40 and is returned to the tank 10 without being heated by the first heater 31. That is, at the second connection section 22 located downstream of the first heater 31, the hydrogen gas heated and warmed by the first heater 31 and the hydrogen gas that bypasses the first heater 31 and is not heated by the first heater 31 merge. At the second connection section 22, the relatively high-temperature hydrogen gas that has passed through the first heater 31 and the relatively low-temperature hydrogen gas that has flowed through the first bypass line 40 are mixed. As the opening of the first valve 41 increases, the flow rate of hydrogen gas flowing through the first bypass line 40 increases, while the flow rate of hydrogen gas passing through the first heater 31 decreases. As a result, the temperature of the hydrogen gas returned to tank 10 decreases as the opening of the first valve 41 increases. In other words, the amount of heat supplied to tank 10 decreases as the opening of the first valve 41 increases.

[0035] In step S1, the flow rate of hydrogen gas returned to the tank 10 without being heated by the first heater 31 is adjusted according to the pressure related to the pressure inside the tank 10. Specifically, the control device 90 controls the opening of the first valve 41 according to the pressure inside the tank 10 measured by the pressure gauge 12. Alternatively, the control device 90 may control the opening of the first valve 41 according to the pressure measured at any position upstream of the compressor 30 in the circulation line 20. The control device 90 adjusts the amount of heat supplied to the tank 10 by controlling the opening of the first valve 41 so that the pressure inside the tank 10 does not exceed the allowable pressure of the tank 10.

[0036] In step S1, the second valve 51 is fully open. As a result, in step S1, most of the hydrogen gas taken from the tank 10 into the circulation line 20 flows through the second bypass line 50 and is supplied to the compressor 30.

[0037] In step S1, the third valve 61 is open. As a result, some of the hydrogen gas removed from tank 10 is sent to the outboard facility 2, and the remaining hydrogen gas removed from tank 10 flows through the circulation line 20 and is returned to tank 10. The larger the opening of the third valve 61, the greater the flow rate of hydrogen gas through the discharge line 60, and the larger the amount of hydrogen gas removed from tank 10. Consequently, the larger the opening of the third valve 61, the lower the pressure inside tank 10.

[0038] In step S1, the flow rate of hydrogen gas sent to the outboard facility 2 is adjusted according to the pressure related to the pressure in tank 10. Specifically, the control device 90 controls the opening of the third valve 61 according to the pressure in tank 10 measured by the pressure gauge 12. Alternatively, the control device 90 may control the opening of the third valve 61 according to the pressure measured at any point upstream of the compressor 30 in the circulation line 20. The control device 90 adjusts the flow rate of hydrogen gas taken out of tank 10 by controlling the opening of the third valve 61 so that the pressure in tank 10 does not exceed the allowable pressure of tank 10.

[0039] The control device 90 controls the opening of the first valve 41 and the opening of the third valve 61 in accordance with the pressure related to the pressure inside the tank 10. In addition to or instead of the pressure related to the pressure inside the tank 10, the control device 90 may also control the opening of the first valve 41 and the opening of the third valve 61 in accordance with the flow rate of hydrogen gas flowing through the discharge line 60. Furthermore, the control device 90 may also control the discharge amount of the compressor 30 in accordance with the pressure related to the pressure inside the tank 10.

[0040] In step S1, the fourth valve 81 is closed, preventing the hydrogen gas taken from the tank 10 from being released into the atmosphere.

[0041] In step S1, if the following condition 1 is met as a result of warming up the tank 10 using hydrogen gas, the warm-up method proceeds from step S1 to step S2. In other words, if condition 1 is met in step S1, the warm-up of the tank 10 using hydrogen gas is completed, and the replacement of hydrogen gas in the tank 10 with replacement gas begins. In step S1, the control device 90 determines whether or not condition 1 is met. If the control device 90 determines that condition 1 is met, it terminates step S1 and starts step S2; if it determines that condition 1 is not met, it continues step 1.

[0042] <Condition 1> The temperature related to the temperature inside the tank 10 is at or above a predetermined first temperature. Here, in this embodiment, the first temperature is set to a temperature higher than the liquefaction temperature of the replacement gas (nitrogen gas in this embodiment). The first temperature is, for example, -180°C. In this embodiment, the temperature inside the tank 10 measured by the thermometer 11 is used as the temperature related to the temperature inside the tank 10 according to Condition 1. Alternatively, the temperature measured at any position upstream of the compressor 30 in the circulation line 20 may be used as the temperature related to the temperature inside the tank 10 according to Condition 1.

[0043] When step S1 ends, the warm-up method proceeds to step S2. In step S2, the hydrogen gas in tank 10 is replaced with a replacement gas. In step S2, the hydrogen gas in tank 10 is replaced with a replacement gas (nitrogen gas in this embodiment) having a gas density higher than the gas density of the hydrogen gas. In step S2, as shown in FIG. 4, nitrogen gas is supplied from the out-of-ship facility 2 to tank 10, and a mixed gas of hydrogen gas and nitrogen gas is discharged from tank 10 to the out-of-ship facility 2. At this time, the nitrogen gas is introduced into tank 10 through the second end 20b of the circulation line 20, and the hydrogen gas in tank 10 having a specific gravity smaller than that of the nitrogen gas is discharged into the circulation line 20 through the first end 20a located at a position higher than the second end 20b. That is, in step S2, replacement using the specific gravity difference between hydrogen gas and nitrogen gas is performed. In the early stage of the replacement of the hydrogen gas in tank 10 with the replacement gas, pure hydrogen gas is discharged from tank 10, in the middle stage of the replacement, a mixed gas of hydrogen gas and nitrogen gas is discharged from tank 10, and in the late stage of the replacement, pure nitrogen gas is discharged from tank 10. The nitrogen gas of this embodiment is an example of the replacement gas according to the present disclosure.

[0044] In step S2, the first valve 41, the second valve 51, and the fourth valve 81 are closed, and the third valve 61 is open. Thereby, the mixed gas taken out from tank 10 is sent to the out-of-ship facility 2 without returning to tank 10.

[0045] In step S2, the greater the opening degree of the third valve 61, the greater the flow rate of the mixed gas flowing through the discharge line 60, and the greater the amount of the mixed gas taken out from tank 10. As a result, the greater the opening degree of the third valve 61, the lower the pressure in tank 10.

[0046] In step S2, the flow rate of the mixed gas returned to the outboard facility 2 is adjusted according to the pressure related to the pressure in the tank 10. Specifically, the control device 90 controls the opening degree of the third valve 61 according to the pressure in the tank 10 measured by the pressure gauge 12. Alternatively, the control device 90 may control the opening degree of the third valve 61 according to the pressure measured in the flow path through which the mixed gas taken out from the tank 10 flows toward the first manifold 62. The control device 90 controls the opening degree of the third valve 61 to adjust the flow rate of the mixed gas taken out from the tank 10 so that the pressure in the tank 10 does not exceed the allowable pressure of the tank 10.

[0047] In addition to or instead of the pressure related to the pressure in the tank 10, the control device 90 may control the opening degree of the third valve 61 according to the flow rate of the mixed gas flowing through the discharge line 60.

[0048] In step S2, the temperature of the nitrogen gas supplied from the outboard facility 2 is higher than the temperature related to the temperature in the tank 10. The temperature of the nitrogen gas supplied from the outboard facility 2 may be, for example, the same as the outside air temperature. Thereby, even in the replacement of the hydrogen gas in the tank 10 with nitrogen gas, the tank 10 is warmed up, so that the time required for the tank 10 to complete the warming up can be shortened. In the present embodiment, the temperature in the tank 10 measured by the thermometer 11 is used as the temperature related to the temperature in the tank 10. Alternatively, as the temperature related to the inside of the tank 10, the temperature measured in the flow path through which the mixed gas taken out from the tank 10 flows toward the first manifold 62 may be used.

[0049] In step S2, the nitrogen gas supplied from the outboard base 2 is nitrogen gas obtained by vaporizing liquid nitrogen. Generally, since impurities such as moisture are removed at the stage of cooling and liquefying nitrogen gas, liquid nitrogen is of high purity. Therefore, the dew point temperature of the nitrogen gas obtained by vaporizing liquid nitrogen is lower than, for example, the dew point temperature of the nitrogen gas immediately after being manufactured in the factory. Thereby, when nitrogen gas is supplied to the tank 10, it is possible to suppress the occurrence of condensation in the tank 10.

[0050] In step S2, if the following conditions 2 and 3 are met as a result of the hydrogen gas in tank 10 being replaced with the replacement gas, the warm-up method proceeds from step S2 to step S3. In other words, when conditions 2 and 3 are met in step S2, the replacement of hydrogen gas in tank 10 with the replacement gas is completed, and the warm-up of tank 10 using the replacement gas is started. In step S2, the control device 90 determines whether the following conditions 2 and 3 are met. If the control device 90 determines that conditions 2 and 3 are met, it terminates step S2 and starts step S3; if it determines that conditions 2 and 3 are not met, it continues step 2.

[0051] <Condition 2> The temperature related to the temperature inside the tank 10 is at or above a predetermined second temperature. Here, in this embodiment, the second temperature is set to a temperature higher than the lowest temperature at which the compressor 30 can operate using the displacement gas in design / operational terms. In this embodiment, the temperature inside the tank 10 measured by the thermometer 11 is used as the temperature related to the temperature inside the tank 10 in relation to condition 2. Alternatively, the temperature measured in the flow path through which the mixed gas taken out of the tank 10 flows toward the first manifold 62 may be used as the temperature related to the temperature inside the tank 10 in relation to condition 2.

[0052] <Condition 3> The hydrogen gas concentration in tank 10 is below a predetermined hydrogen gas concentration. In this embodiment, the predetermined hydrogen gas concentration is set to a range in which, when the gas in tank 10 is released into the atmosphere, no explosion will occur due to a chemical reaction between the hydrogen contained in the released gas and the oxygen contained in the atmosphere.

[0053] Once step S2 is completed, the warm-up method proceeds to step S3. Referring to Figure 5, in step S3, the tank 10 is warmed up using displacement gas. Step S3 is performed away from the outboard facility 2 (shown in Figure 1). In step S3, as shown in Figure 5, nitrogen gas taken out of tank 10 is pressurized, the pressurized nitrogen gas is heated, and the heated nitrogen gas is introduced into tank 10. Specifically, in step S3, when the compressor 30 is started, the nitrogen gas in tank 10 flows into the circulation line 20. The second heater 32 may heat the nitrogen gas flowing through the circulation line 20. The compressor 30 pressurizes the nitrogen gas flowing through the circulation line 20 and sends it towards tank 10. The first heater 31 heats a portion of the nitrogen gas sent to tank 10 by the compressor 30. The tank 10 is warmed up when the nitrogen gas heated and warmed by the first heater 31 is introduced into tank 10.

[0054] In step S3, the first valve 41 is open. As a result, a portion of the nitrogen gas discharged from the compressor 30 is heated by the first heater 31 and returned to the tank 10, while the remaining nitrogen gas discharged from the compressor 30 passes through the first bypass line 40 and is returned to the tank 10 without being heated by the first heater 31. That is, at the second connection section 22 located downstream of the first heater 31, the nitrogen gas heated and warmed by the first heater 31 and the nitrogen gas that bypasses the first heater 31 and is not heated by the first heater 31 merge. At the second connection section 22, the nitrogen gas at a relatively high temperature that has passed through the first heater 31 and the nitrogen gas at a relatively low temperature that has flowed through the first bypass line 40 are mixed. As the opening of the first valve 41 increases, the flow rate of nitrogen gas flowing through the first bypass line 40 increases, while the flow rate of nitrogen gas passing through the first heater 31 decreases. As a result, the temperature of the nitrogen gas returned to tank 10 decreases as the opening of the first valve 41 increases. In other words, the amount of heat supplied to tank 10 decreases as the opening of the first valve 41 increases.

[0055] In step S3, the flow rate of nitrogen gas returned to the tank 10 without being heated by the first heater 31 is adjusted according to the pressure related to the pressure inside the tank 10. Specifically, the control device 90 controls the opening of the first valve 41 according to the pressure inside the tank 10 measured by the pressure gauge 12. Alternatively, the control device 90 may control the opening of the first valve 41 according to the pressure measured at any position upstream of the compressor 30 in the circulation line 20. For example, the control device 90 may control the opening of the first valve 41 according to the pressure measured upstream of the seventh connection 27 in the circulation line 20. The control device 90 controls the opening of the first valve 41 to adjust the amount of heat supplied to the tank 10 so that the pressure inside the tank 10 does not exceed the allowable pressure of the tank 10.

[0056] In step S3, the second valve 51 is closed. As a result, in step S3, all of the nitrogen gas taken from the tank 10 to the circulation line 20 is supplied to the compressor 30 through the second heater 32.

[0057] In step S3, the control device 90 controls the opening of the second valve 51 according to the temperature inside the tank 10. If the gas density of the nitrogen gas supplied to the compressor 30 is excessively high, the load on the motor driving the compressor 30 may increase. For this reason, the compressor 30 has an operating temperature range set for the temperature of the supplied gas that takes into account the load on the motor. The control device 90 may close the second valve 51 if the temperature inside the tank 10 is below the lowest temperature in the operating temperature range, and may open the second valve 51 if the temperature is above the lowest temperature in the operating temperature range.

[0058] In step S3, the third valve 61 is closed. Also in step S3, the fourth valve 81 is open, and a portion of the nitrogen gas removed from the tank 10 is released into the atmosphere via the vent device 82.

[0059] In step S3, the flow rate of nitrogen gas sent to the venting device 82 is adjusted according to the pressure related to the pressure in the tank 10. Specifically, the control device 90 controls the opening of the fourth valve 81 according to the pressure in the tank 10 measured by the pressure gauge 12. Alternatively, the control device 90 may control the opening of the fourth valve 81 according to the pressure measured at any point upstream of the compressor 30 in the circulation line 20. For example, the control device 90 may control the opening of the fourth valve 81 according to the pressure measured upstream of the seventh connection 27 in the circulation line 20. The control device 90 controls the opening of the fourth valve 81 to adjust the flow rate of nitrogen gas taken out of the tank 10 so that the pressure in the tank 10 does not exceed the allowable pressure of the tank 10.

[0060] In step S3, the warm-up of the tank 10 using the replacement gas is completed when the following condition 4 is met as a result of the warm-up of the tank 10 using the replacement gas. In step S3, the control device 90 determines whether or not condition 4 is met. If the control device 90 determines that condition 4 is met, it terminates step S3, while if it determines that condition 4 is not met, it continues step S3.

[0061] <Condition 4> The temperature related to the temperature inside the tank 10 is equal to or greater than the third temperature. Here, the third temperature is the target temperature for warming up the tank 10. The third temperature is, for example, 5°C. In this embodiment, the temperature inside the tank 10 measured by the thermometer 11 is used as the temperature related to the temperature inside the tank 10 according to condition 4. Alternatively, the temperature measured at any position upstream of the compressor 30 in the circulation line 20 may be used as the temperature related to the temperature inside the tank 10 according to condition 4.

[0062] In step S3, when the warm-up of the tank 10 using the displacement gas is completed, the warm-up method is terminated.

[0063] [Effects] The warm-up method according to this embodiment provides the following effects.

[0064] (1) The tank 10 warm-up method according to this embodiment is a warm-up method for a tank 10 installed on a ship 1 and storing liquefied hydrogen and hydrogen gas, and includes warming up the tank 10 using hydrogen gas by pressurizing the hydrogen gas taken out of the tank 10, heating the pressurized hydrogen gas, and introducing the heated hydrogen gas into the tank 10, and a portion of the hydrogen gas taken out of the tank 10 is sent to an outboard facility 2.

[0065] During the warm-up of tank 10, when heated hydrogen gas is introduced into tank 10, the pressure inside tank 10 increases. Therefore, it is necessary to process a portion of the hydrogen gas inside tank 10 (hereinafter referred to as excess hydrogen gas) so that the pressure inside tank 10 does not exceed the allowable pressure of tank 10. The processing capacity of hydrogen processing equipment such as boilers normally installed on liquefied hydrogen carriers is often lower than the capacity required to process the excess hydrogen gas inside tank 10 within a predetermined time during the warm-up of tank 10. In this case, the processing capacity of the excess hydrogen gas limits the amount of heat input into tank 10 by hydrogen gas, which can prolong the warm-up time of tank 10. In other words, the processing of excess hydrogen gas can become a bottleneck during the warm-up of tank 10. In contrast, according to the warm-up method of this embodiment, a portion of the hydrogen gas inside tank 10 is sent to the offshore facility 2, so that the excess hydrogen gas inside tank 10 can be processed by the hydrogen processing equipment of the offshore facility 2. As a result, the time required to warm up the tank 10 can be reduced compared to the case where the excess hydrogen gas in the tank 10 is processed only on board the ship.

[0066] (2) The method for warming up the tank 10 according to this embodiment includes warming up the tank 10 using hydrogen gas, supplying a replacement gas (in this embodiment, nitrogen gas) having a higher gas density than the hydrogen gas in the tank 10 to the tank 10, discharging the mixed gas containing the hydrogen gas and replacement gas from the tank 10 to replace the hydrogen gas in the tank 10 with the replacement gas, pressurizing the replacement gas taken out of the tank 10 and sending it back to the tank 10, heating the replacement gas sent to the tank 10, and returning the heated replacement gas to the tank 10, thereby warming up the tank 10 using the replacement gas.

[0067] When warming up the tank 10 to the target temperature using only hydrogen gas, as the tank 10 warms up and the temperature of the hydrogen gas rises and the gas density decreases, depending on the type of compressor 30, it may not be possible to obtain the discharge pressure necessary to return the hydrogen gas extracted from the tank 10 back to the tank 10. In such cases, it becomes necessary to add compressors 30, which increases the cost of the ship 1. In contrast, according to the warm-up method of this embodiment, after warming up the tank 10 using hydrogen gas, the hydrogen gas in the tank 10 is replaced with nitrogen gas, and the tank 10 is warmed up using the replacement gas. This makes it possible to warm up the tank 10 while suppressing an increase in the cost of the ship 1 by, for example, using hydrogen gas to warm up the tank 10 in the extremely low temperature range (e.g., below -180°C) where the necessary discharge pressure can be obtained even with hydrogen gas, and using a replacement gas with a higher gas density than hydrogen gas to warm up the tank 10 in the temperature range where the necessary discharge pressure cannot be obtained with hydrogen gas.

[0068] (3) In the tank 10 warm-up method according to this embodiment, the displacement gas is supplied to the tank from the offshore facility 2, and the mixed gas discharged from the tank is returned to the offshore facility 2.

[0069] For example, when using nitrogen gas as the replacement gas, as in the warm-up method for tank 10 according to this embodiment, it is assumed that the nitrogen gas supplied to tank 10 is produced by a nitrogen gas generator normally installed on the ship 1. However, the nitrogen gas supply capacity of the nitrogen gas generator is often lower than the nitrogen gas supply capacity required to complete the replacement of hydrogen gas in tank 10 with nitrogen gas within a predetermined time. In this case, the nitrogen gas supply capacity limits the rate at which hydrogen gas in tank 10 is replaced with nitrogen gas, which can increase the time required for the replacement of hydrogen gas in tank 10 with nitrogen gas. In contrast, according to the warm-up method according to this embodiment, nitrogen gas is supplied to tank 10 from an external facility 2. Typically, the nitrogen gas supply capacity of the external facility 2 is higher than the nitrogen gas supply capacity of a nitrogen gas generator normally installed on the ship 1. Therefore, compared to the case where the nitrogen gas supplied to tank 10 is produced only onboard, the time required for the replacement of hydrogen gas in tank 10 with nitrogen gas can be shortened.

[0070] When replacing the hydrogen gas in tank 10 with replacement gas, it is necessary to process the mixed gas containing the hydrogen gas and replacement gas discharged from tank 10. The processing capacity of hydrogen processing equipment, such as boilers, typically installed on liquefied hydrogen carriers such as ship 1 according to this embodiment is often lower than the capacity required to process the mixed gas discharged from tank 10 within a predetermined time during the replacement of hydrogen gas in tank 10 with replacement gas. In this case, the processing capacity of the mixed gas limits the rate at which the hydrogen gas in tank 10 is replaced with replacement gas, which can increase the time required for the replacement of hydrogen gas in tank 10. In other words, the processing of the mixed gas discharged from tank 10 can become a bottleneck in the replacement of hydrogen gas in tank 10. In contrast, according to the warm-up method of this embodiment, the mixed gas discharged from tank 10 is sent to the offshore facility 2, so the mixed gas can be processed by the hydrogen processing equipment at the offshore facility 2. As a result, the time required for the replacement of hydrogen gas in tank 10 with replacement gas can be shortened compared to the case where the mixed gas in tank 10 is processed only onboard the ship.

[0071] (4) In the tank 10 warm-up method according to this embodiment, when replacing the hydrogen gas in the tank 10 with the replacement gas, the temperature of the replacement gas supplied to the tank 10 is higher than the temperature related to the temperature inside the tank 10.

[0072] According to the warm-up method of this embodiment, the temperature of the tank 10 can be raised even when replacing the hydrogen gas in the tank 10 with a replacement gas. As a result, the time required to warm up the tank 10 can be shortened compared to the case where the temperature of the replacement gas supplied to the tank 10 is below the temperature related to the temperature inside the tank 10.

[0073] (5) During the warm-up of the tank 10 using hydrogen gas, a portion of the hydrogen gas taken out of the tank 10 is returned to the tank 10 without being heated, and the flow rate of the hydrogen gas returned to the tank 10 without being heated is adjusted according to the pressure related to the pressure inside the tank 10.

[0074] If all of the hydrogen gas extracted from tank 10 is heated and returned to tank 10, the amount of heat input to tank 10 may become excessively large, causing the pressure in tank 10 to become excessively high. In contrast, according to the warm-up method of this embodiment, a portion of the hydrogen gas extracted from tank 10 is returned to tank 10 without being heated, thus reducing the amount of heat input to tank 10 compared to the case where all of the hydrogen gas extracted from tank 10 is heated and returned to tank 10. As a result, it is possible to prevent the pressure inside tank 10 from becoming excessively high. Furthermore, since the flow rate of the hydrogen gas returned to tank 10 without being heated is adjusted according to the pressure related to the pressure inside tank 10, it is possible to prevent the pressure inside tank 10 from becoming excessively high.

[0075] (6) In the tank 10 warm-up method according to this embodiment, when warming up the tank 10 using hydrogen gas, the flow rate of hydrogen gas sent to the outboard facility 2 is adjusted according to the pressure related to the pressure inside the tank 10.

[0076] According to the warm-up method of this embodiment, the flow rate of hydrogen gas discharged from the tank 10 and returned to the offshore facility 2 is adjusted according to the pressure related to the pressure inside the tank 10. Therefore, it is possible to ensure a sufficient flow rate of hydrogen gas used for warming up the tank 10 while suppressing the pressure inside the tank 10 from becoming excessively high.

[0077] (7) In the tank 10 warm-up method according to this embodiment, when the temperature related to the temperature inside the tank 10 becomes higher than the liquefaction temperature of the replacement gas during the warm-up of the tank 10 using hydrogen gas, the warm-up of the tank 10 using hydrogen gas is terminated and the replacement of the hydrogen gas inside the tank 10 with the replacement gas is started.

[0078] According to the warm-up method of this embodiment, when replacing the hydrogen gas in the tank 10 with the replacement gas, it is possible to suppress the liquefaction of the replacement gas within the tank 10.

[0079] (8) In the tank 10 warm-up method according to this embodiment, the replacement gas is an inert gas, and when the hydrogen gas concentration in the tank 10 falls below a predetermined hydrogen gas concentration during the replacement of hydrogen gas in the tank 10 with the replacement gas, the replacement of hydrogen gas in the tank 10 with the replacement gas is terminated and the warm-up of the tank 10 using the replacement gas is started.

[0080] According to the warm-up method of this embodiment, since the substitution gas is an inert gas, the hydrogen gas in the tank 10 can be replaced with the substitution gas, thereby creating an inert atmosphere inside the tank 10. Furthermore, according to the warm-up method of this embodiment, when the replacement of the hydrogen gas in the tank 10 with the substitution gas is completed, the hydrogen gas concentration in the tank 10 is below a predetermined hydrogen gas concentration. For this reason, for example, by setting the predetermined hydrogen gas concentration to a range within which no explosion occurs due to a chemical reaction between the hydrogen contained in the mixed gas and the oxygen contained in the atmosphere, it is not necessary to perform a gas-free operation to create an inert atmosphere inside the tank 10 after the warm-up method of this embodiment. As a result, it is possible to suppress an increase in the idle time of the ship 1.

[0081] (9) In the warm-up method according to this embodiment, when the temperature related to the temperature inside the tank 10 reaches a predetermined temperature or higher during the replacement of hydrogen gas in the tank 10 with the replacement gas, the replacement of hydrogen gas in the tank 10 with the replacement gas is terminated and the warm-up of the tank 10 using the replacement gas is started.

[0082] (10) In the warm-up method according to this embodiment, when replacing the hydrogen gas in the tank 10 with the replacement gas, the flow rate of the mixed gas returned from the tank 10 to the outboard facility 2 is adjusted according to the pressure related to the pressure in the tank 10.

[0083] According to the warm-up method of this embodiment, the flow rate of the mixed gas returned from the tank 10 to the outboard facility 2 is adjusted according to the pressure related to the pressure inside the tank 10, thereby preventing the pressure in the tank 10 from becoming excessively high.

[0084] (11) In the warm-up method according to this embodiment, during the warm-up of the tank 10 using the replacement gas, a portion of the replacement gas taken out of the tank 10 is discharged to the outside, and the flow rate of the replacement gas discharged to the outside is adjusted according to the pressure related to the pressure inside the tank 10.

[0085] According to the warm-up method of this embodiment, the flow rate of the replacement gas discharged from the tank 10 to the outside is adjusted according to the pressure related to the pressure inside the tank 10. Therefore, it is possible to ensure the flow rate of replacement gas used for warming up the tank 10 while suppressing the pressure inside the tank 10 from becoming excessively high.

[0086] (12) In the warm-up method according to this embodiment, when warming up the tank 10 using replacement gas, a portion of the replacement gas taken out of the tank 10 is heated before it is pressurized, and the flow rate of the replacement gas heated before it is pressurized is adjusted according to the temperature inside the tank 10.

[0087] In the warm-up of tank 10 using replacement gas, if the gas density of the replacement gas is excessively high, the load on the motor driving the compressor 30 increases. In contrast, according to the warm-up method of this embodiment, a portion of the replacement gas taken out of tank 10 is heated before being pressurized by the compressor 30. Therefore, compared to the case where all of the replacement gas taken out of tank 10 is supplied to the compressor 30 without being heated, the gas density supplied to the compressor 30 can be reduced. As a result, the load on the motor can be reduced during the warm-up of tank 10 using replacement gas. Furthermore, according to the warm-up method of this embodiment, the flow rate of the replacement gas heated before being pressurized is adjusted according to the temperature inside tank 10. For example, when the temperature inside tank 10 has risen sufficiently and the load on the motor of the compressor 30 is within an appropriate range, the warm-up of tank 10 using replacement gas can be efficiently performed by reducing the flow rate of the replacement gas heated before being pressurized.

[0088] (13) In the warm-up method according to this embodiment, the displacement gas is nitrogen gas obtained by vaporizing liquefied nitrogen.

[0089] Generally, liquid nitrogen is of high purity because impurities such as water are removed during the cooling and liquefaction process of nitrogen gas. For this reason, the dew point temperature of nitrogen gas obtained by vaporizing liquid nitrogen is lower than, for example, the dew point temperature of nitrogen gas immediately after production at a factory. By using nitrogen gas obtained by vaporizing liquid nitrogen as a displacement gas, it is possible to suppress the occurrence of condensation inside the tank 10 when nitrogen gas is supplied to the tank 10.

[0090] (14) The ship 1 includes a tank 10 for storing liquefied hydrogen, a circulation line 20 for returning gas taken out of the tank 10 to the tank 10, a compressor 30 located on the circulation line for sending gas taken out of the tank 10 to the tank 10, a first heater 31 located on the circulation line 20 downstream of the compressor 30 for heating the gas sent to the tank 10, a discharge line 60 branching off from the circulation line 20 and being fluidly connected to an outboard facility 2, a third valve 61 located on the discharge line 60 for adjusting the flow rate of gas flowing through the discharge line 60, and a control device 90 for controlling the opening degree of the third valve 61 in accordance with the pressure related to the pressure inside the tank 10.

[0091] According to the vessel of this embodiment, a portion of the hydrogen gas in the tank 10 can be sent to the offshore facility 2. Therefore, during the warm-up of the tank 10, the excess hydrogen gas in the tank 10 can be processed by the hydrogen treatment equipment of the offshore facility 2. As a result, the time required for the warm-up of the tank 10 can be shortened compared to the case where the excess hydrogen gas in the tank 10 is processed only on board the ship. In addition, since the flow rate of the gas flowing through the discharge line 60 is adjusted according to the pressure related to the pressure in the tank 10, it is possible to suppress the pressure in the tank 10 from becoming excessively high.

[0092] [Modifications] This disclosure is not limited to the configurations described in the embodiments above, and various modifications are possible.

[0093] In the above embodiment, an example was described in which the tank 10 is a cargo tank, but the tank 10 may also be a fuel tank that contains liquefied hydrogen as fuel.

[0094] In the above embodiment, the tank 10 warm-up method included warming up the tank 10 using hydrogen gas, replacing the hydrogen gas in the tank 10 with a replacement gas, and warming up the tank 10 using the replacement gas. However, the tank 10 warm-up method according to the present disclosure is not limited to this. The tank 10 warm-up method according to the present disclosure may include only warming up the tank 10 using hydrogen gas.

[0095] In the above embodiment, when replacing the hydrogen gas in the tank 10 with the replacement gas, the temperature of the replacement gas supplied to the tank 10 was higher than the temperature related to the temperature inside the tank 10, but this is not limited to this. When replacing the hydrogen gas in the tank 10 with the replacement gas, the temperature of the replacement gas supplied to the tank 10 may be lower than or equal to the temperature related to the temperature inside the tank 10.

[0096] In the above embodiment, the discharge line 60 was fluidly connected to the circulation line 20 at a fifth connection 25 located upstream of the compressor 30 in the circulation line 20, but the disclosure is not limited thereto. For example, the discharge line 60 may be fluidly connected to the circulation line 20 at a connection located downstream of the compressor 30 and upstream of the first heater 31. In other words, the discharge line 60 may branch off from the circulation line 20 downstream of the compressor 30 and upstream of the first heater 31. In this case, for example, the discharge line 60 may be used as a return line used to return boil-off gas generated in the tank 10 when the compressor 30 loads liquefied hydrogen into the tank 10 to the off-board facility 2.

[0097] In the above embodiment, a flow meter 63 was placed on the discharge line 60, but it is not necessary for a flow meter 63 to be placed on the discharge line 60.

[0098] In the above embodiment, the second heater 32 was located on the circulation line 20, but the second heater 32 does not have to be located on the circulation line 20. In this case, the ship 1 does not have to be equipped with the second bypass line 50 and the second valve 51.

[0099] In the above embodiment, an example was described in which nitrogen gas obtained by vaporizing liquefied nitrogen is used as the replacement gas according to the disclosure, and the nitrogen gas is supplied from an external facility 2. However, the replacement gas according to the disclosure is not limited to nitrogen gas, and may be any gas having a higher gas density than the hydrogen gas in the tank 10. For example, the replacement gas according to the disclosure may be combustion gas produced by an inert gas generator (IGG). In this case, it is preferable to treat the combustion gas with an exhaust gas treatment device such as a scrubber to lower the dew point temperature of the combustion gas.

[0100] [Note] The warm-up method and vessel relating to this disclosure provide the following embodiments.

[0101] [Aspect 1] A method for warming up a tank installed on a ship for storing liquefied hydrogen and hydrogen gas, comprising: pressurizing hydrogen gas taken out of the tank; heating the pressurized hydrogen gas; and introducing the heated hydrogen gas into the tank, wherein a portion of the hydrogen gas taken out of the tank is sent to an off-board facility.

[0102] [Aspect 2] The method according to aspect 1, which includes warming up the tank using hydrogen gas, supplying the tank with a replacement gas having a higher gas density than the hydrogen gas in the tank, discharging the mixed gas containing the hydrogen gas and the replacement gas from the tank to replace the hydrogen gas in the tank with the replacement gas, pressurizing the replacement gas taken out of the tank, heating the pressurized replacement gas, and introducing the heated replacement gas into the tank to warm up the tank using the replacement gas.

[0103] [Aspect 3] The method according to aspect 2, wherein the displacement gas is supplied from the offshore facility to the tank, and the mixed gas discharged from the tank is returned to the offshore facility.

[0104] [Aspect 4] The method according to aspect 2 or 3, wherein, in replacing the hydrogen gas in the tank with a replacement gas, the temperature of the replacement gas supplied to the tank is higher than the temperature related to the temperature inside the tank.

[0105] [Aspect 5] The method according to any one of aspects 1 to 4, wherein, in the warm-up of the tank using hydrogen gas, a portion of the hydrogen gas taken out of the tank is returned to the tank without being heated, and the flow rate of the hydrogen gas returned to the tank without being heated is adjusted according to the pressure related to the pressure inside the tank.

[0106] [Aspect 6] The method according to any one of aspects 1 to 5, wherein, in the warm-up of the tank using hydrogen gas, the flow rate of hydrogen gas sent to the outboard facility is adjusted according to the pressure related to the pressure inside the tank.

[0107] [Aspect 7] The method according to any one of aspects 2 to 6 (Aspects 5 and 6 refer to aspect 2), wherein, during the warm-up of the tank using hydrogen gas, when the temperature related to the temperature inside the tank becomes higher than the liquefaction temperature of the replacement gas, the warm-up of the tank using hydrogen gas is terminated and the replacement of the hydrogen gas inside the tank with the replacement gas is started.

[0108] [Aspect 8] The method according to any one of aspects 2 to 7 (Aspects 5 and 6 refer to aspect 2), wherein the replacement gas is an inert gas, and when the hydrogen gas concentration in the tank falls below a predetermined hydrogen gas concentration during the replacement of hydrogen gas in the tank with the replacement gas, the replacement of hydrogen gas in the tank with the replacement gas is terminated and the tank is warmed up using the replacement gas.

[0109] [Aspect 9] The method according to any one of aspects 2 to 8 (Aspects 5 and 6 refer to aspect 2), wherein when the temperature related to the temperature inside the tank reaches a predetermined temperature or higher during the replacement of hydrogen gas in the tank with replacement gas, the replacement of hydrogen gas in the tank with replacement gas is terminated and the tank is warmed up using the replacement gas.

[0110] [Aspect 10] The method according to any one of aspects 2 to 9 (with respect to aspects 5 and 6, aspect 2 is incorporated by reference) wherein, in replacing the hydrogen gas in the tank with a replacement gas, the flow rate of the mixed gas returned from the tank to the off-board facility is adjusted according to a pressure related to the pressure in the tank.

[0111] [Aspect 11] The method according to any one of aspects 2 to 10 (Aspects 5 and 6 refer to aspect 2), wherein, in the warm-up of the tank using displacement gas, a portion of the displacement gas taken out of the tank is discharged to the outside, and the flow rate of the displacement gas discharged to the outside is adjusted according to the pressure related to the pressure inside the tank.

[0112] [Aspect 12] The method according to any one of aspects 2 to 11 (with respect to aspects 5 and 6, aspect 2 is referenced), wherein in the warm-up of the tank using displacement gas, a portion of the displacement gas taken out from the tank is heated before it is pressurized, and the flow rate of the displacement gas heated before it is pressurized is adjusted according to the temperature inside the tank.

[0113] [Aspect 13] The method according to any one of aspects 2 to 12 (with respect to aspects 5 and 6, refer to aspect 2), wherein the displacement gas is nitrogen gas obtained by vaporizing liquid nitrogen.

[0114] [Aspect 14] A ship comprising: a tank for storing liquefied hydrogen; a circulation line for returning gas taken out of the tank to the tank; a compressor disposed on the circulation line for sending gas taken out of the tank to the tank; a heater disposed downstream of the compressor on the circulation line for heating the gas sent to the tank; a discharge line branching off from the circulation line and fluidly connectable to an offshore facility; a valve disposed on the discharge line for adjusting the flow rate of gas flowing through the discharge line; and a control device for controlling the opening degree of the valve in accordance with a pressure related to the pressure in the tank.

Claims

1. A method for warming up a tank installed on a ship for storing liquefied hydrogen and hydrogen gas, comprising warming up the tank using hydrogen gas by pressurizing the hydrogen gas taken out of the tank, heating the pressurized hydrogen gas, and introducing the heated hydrogen gas into the tank, and sending a portion of the hydrogen gas taken out of the tank to an off-board facility.

2. The method according to claim 1, comprising warming up the tank using hydrogen gas, supplying the tank with a replacement gas having a higher gas density than the hydrogen gas in the tank, discharging the mixed gas containing the hydrogen gas and the replacement gas from the tank to replace the hydrogen gas in the tank with the replacement gas, and after replacing the hydrogen gas in the tank with the replacement gas, pressurizing the replacement gas taken out of the tank, heating the pressurized replacement gas, and introducing the heated replacement gas into the tank to warm up the tank using the replacement gas.

3. The method according to claim 2, wherein the replacement gas is supplied from the offshore facility to the tank, and the mixed gas discharged from the tank is returned to the offshore facility.

4. The method according to claim 2, wherein, in the replacement of hydrogen gas in the tank with a replacement gas, the temperature of the replacement gas supplied to the tank is higher than the temperature related to the temperature inside the tank.

5. The method according to claim 1, wherein, in the warming up of the tank using hydrogen gas, a portion of the hydrogen gas taken out of the tank is returned to the tank without being heated, and the flow rate of the hydrogen gas returned to the tank without being heated is adjusted according to the pressure inside the tank.

6. The method according to claim 1, wherein, in the warm-up of the tank using hydrogen gas, the flow rate of hydrogen gas supplied to the outboard facility is adjusted according to a pressure related to the pressure inside the tank.

7. The method according to claim 2, wherein, during the warm-up of the tank using hydrogen gas, when the temperature related to the temperature inside the tank becomes higher than the liquefaction temperature of the replacement gas, the warm-up of the tank using hydrogen gas is terminated and the replacement of the hydrogen gas inside the tank with the replacement gas is started.

8. The method according to claim 2, wherein the replacement gas is an inert gas, and when the hydrogen gas concentration in the tank falls below a predetermined hydrogen gas concentration during the replacement of hydrogen gas in the tank with the replacement gas, the replacement of hydrogen gas in the tank with the replacement gas is terminated and the tank is warmed up using the replacement gas.

9. The method according to claim 2, wherein, in the replacement of hydrogen gas in the tank with a replacement gas, when the temperature related to the temperature inside the tank reaches a predetermined temperature or higher, the replacement of hydrogen gas in the tank with a replacement gas is terminated and the tank is warmed up using the replacement gas is started.

10. The method according to claim 2, wherein, in the replacement of hydrogen gas in the tank with a replacement gas, the flow rate of the mixed gas returned from the tank to the offshore facility is adjusted according to a pressure related to the pressure in the tank.

11. The method according to claim 2, wherein, in the warm-up of the tank using a replacement gas, a portion of the replacement gas taken out of the tank is discharged to the outside, and the flow rate of the replacement gas discharged to the outside is adjusted according to the pressure related to the pressure inside the tank.

12. The method according to claim 2, wherein, in the warm-up of the tank using a replacement gas, a portion of the replacement gas taken out of the tank is heated before it is pressurized, and the flow rate of the replacement gas heated before it is pressurized is adjusted according to the temperature inside the tank.

13. The method according to claim 2, wherein the displacement gas is nitrogen gas obtained by vaporizing liquid nitrogen.

14. A ship comprising: a tank for storing liquefied hydrogen; a circulation line for returning gas taken from the tank back to the tank; a compressor located on the circulation line for sending gas taken from the tank back to the tank; a heater located downstream of the compressor on the circulation line for heating the gas sent to the tank; a discharge line branching off from the circulation line and fluidly connectable to an offshore facility; a valve located on the discharge line for adjusting the flow rate of gas flowing through the discharge line; and a control device for controlling the opening degree of the valve in accordance with a pressure related to the pressure in the tank.

Images