Methods for cooling down and warming up liquefied gas storage tanks

Abstract

To reduce the time while inhibiting occurrence of stress in cooling down of a multiple heat-insulating structure tank for storage of a liquefied gas to reduce costs.SOLUTION: A method for cooling a tank for storing a liquefied gas, which includes an inner tank (3) and an outer tank (5), before the tank is filled with the liquefied gas, an object to be stored, includes: introducing a cooling liquefied gas (CH) into an inner tank internal space (7); measuring a temperature of the inner tank (3) and a temperature of the outer tank (5); and adjusting at least one of a temperature change speed of the inner tank (3) and a temperature change speed of the outer tank (5) based on a temperature difference between the temperature of the inner tank (3) and the temperature of the outer tank (5) to keep the temperature difference to a predetermined value or lower.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for cooling down and a method for warming up a liquefied gas storage tank.

Background Art

[0002] Conventionally, as a tank for storing a liquefied gas, for example, cryogenic liquefied hydrogen, it has been proposed to use a double-walled tank including an inner tank and an outer tank (see, for example, Patent Document 1).

[0003] Generally, when storing a cryogenic liquefied gas in a tank, in order to avoid rapidly cooling the tank by filling a large amount of the liquefied gas to be stored at one time into a tank at room temperature, before filling the liquefied gas to be stored, the tank is cooled in advance at a relatively low speed (hereinafter referred to as "cooling down"). Also, when it is necessary to empty the tank for maintenance or the like, after discharging the liquefied gas to be stored, the tank is heated (hereinafter referred to as "warming up").

Prior Art Documents

Patent Documents

[0004]

【Patent Document​​​​​​​​​​​However, in the case of tanks with a multi-layer thermal insulation structure, such as double-walled tanks for liquefied gases, due to their high thermal insulation properties, even when the tank is cooled at a relatively slow rate as described above, large temperature differences can occur depending on the location within the tank, potentially resulting in significant stress. To avoid this, conventional double-walled tanks require even slower cooling during the cool-down process, which takes a long time to cool the entire tank and necessitates a large amount of liquefied gas for cooling. Consequently, the cost of cool-down increases. Similar challenges exist for the warm-up of tanks with multi-layer thermal insulation structures.

[0006] The purpose of this disclosure is to reduce the time and cost while suppressing stress generation during the cool-down and warm-up of a multi-layer heat-insulating tank for liquefied gas storage, in order to solve the above-mentioned problems. [Means for solving the problem]

[0007] To achieve the above objective, the method for cooling down a liquefied gas storage tank according to this disclosure is: A method for cooling a tank, which has an inner tank and an outer tank for storing liquefied gas, before filling it with the liquefied gas to be stored, Introducing liquefied cooling gas into the internal space of the inner tank, The temperature of the inner tank and the temperature of the outer tank are measured, Based on the temperature difference between the temperature of the inner tank and the temperature of the outer tank, the temperature difference is maintained below a predetermined value by adjusting at least one of the temperature change rates of the inner tank and the outer tank. Includes.

[0008] The warm-up method for a liquefied gas storage tank relating to this disclosure is: A method for heating a tank, which has an inner tank and an outer tank, for storing liquefied gas, after the liquefied gas to be stored has been discharged, Introducing the first heating gas into the space inside the inner tank, Forcibly supplying a second heating gas to the space between the inner and outer tanks. The temperature of the inner tank and the temperature of the outer tank are measured, Based on the temperature difference between the temperature of the inner tank and the temperature of the outer tank, the temperature difference is maintained below a predetermined value by adjusting at least one of the temperature change rates of the inner tank and the outer tank. Includes. [Effects of the Invention]

[0009] According to the cool-down and warm-up methods for liquefied gas storage tanks described herein, it is possible to reduce the time and cost while suppressing the generation of stress during the cool-down and warm-up of multi-layer heat-insulating tanks for liquefied gas storage. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view showing the schematic configuration of a liquefied gas storage tank to which a cool-down method according to one embodiment of this disclosure is applied. [Figure 2A] This is a schematic diagram showing the initial state before the start of a cool-down method according to one embodiment of this disclosure. [Figure 2B] This is a schematic diagram showing the state during cooling of the inner tank in a cool-down method according to one embodiment of the present disclosure. [Figure 2C] This is a schematic diagram showing the state in which temperature difference adjustment is being performed in a cool-down method according to one embodiment of the present disclosure. [Figure 2D] This is a schematic diagram showing the completed state of a cool-down method according to one embodiment of the present disclosure. [Figure 3A] This is a schematic diagram showing the state at the start of a warm-up method according to one embodiment of the present disclosure. [Figure 3B] This is a schematic diagram showing the state in which temperature difference adjustment is being performed in a warm-up method according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0011] Preferred embodiments of this disclosure will be described below with reference to the drawings. Figure 1 shows a liquefied gas storage tank (hereinafter simply referred to as "storage tank") 1 to which a cool-down method and a warm-up method according to one embodiment of this disclosure are applied. This storage tank 1 is a tank for storing liquefied gas and is configured as a double-shell tank comprising an inner tank 3 and an outer tank 5. In this specification, "cool-down" means cooling the storage tank 1 before filling it with the liquefied gas to be stored. In this specification, "warm-up" means heating the low-temperature storage tank 1 after discharging the liquefied gas to be stored in preparation for subsequent maintenance, etc.

[0012] In the embodiment described below, cryogenic (approximately -250°C) liquefied hydrogen is used as an example of the liquefied gas to be stored. However, the liquefied gas may be other types of gases, such as liquefied petroleum gas (LPG, approximately -45°C), liquefied ethylene gas (LEG, approximately -100°C), liquefied natural gas (LNG, approximately -160°C), or liquefied helium (LHe, approximately -270°C).

[0013] The storage tank 1 is installed on a ship, such as a liquefied hydrogen carrier. However, the liquefied hydrogen storage facility on which the storage tank 1 is installed is not limited to this example, as long as it is a facility with a structure and function capable of storing liquefied hydrogen. The liquefied hydrogen storage facility on which the storage tank 1 is installed may be, for example, a ship that uses liquefied hydrogen as propulsion fuel, a land-based liquefied hydrogen storage facility other than a ship, or a plant that utilizes liquefied hydrogen.

[0014] The storage tank 1 is configured as a double-walled tank having an inner tank 3 and an outer tank 5. Specifically, the inner tank 3 has an inner tank shell that forms a storage space for liquefied hydrogen (hereinafter referred to as the "inner tank inner space 7") inside it, and an inner tank heat insulation layer that covers the outer peripheral surface of the inner tank shell. The outer tank 5 has an outer tank shell that forms an inner and outer tank intermediate space 9, which is a heat insulation layer, between the outer tank 5 and the inner tank 3, and an outer tank heat insulation layer that covers the outer peripheral surface of the outer tank shell. Note that the locations where the heat insulation layers of the inner tank 3 and the outer tank 5 are installed are not limited to this example and are arbitrary. For example, the heat insulation layer may be installed so as to cover the inner peripheral surface of the outer tank shell. Also, one or both of the heat insulation layers of the inner tank 3 and the outer tank 5 may be omitted. This storage tank 1 is in steady operation with low-temperature hydrogen gas enclosed in the inner and outer tank intermediate space 9, which is a heat insulation layer.

[0015] In this embodiment, a communication passage 11 that connects the inner tank inner space 7 and the inner and outer tank intermediate space 9 is provided. The communication passage 11 is configured to be openable and closable. In the illustrated example, specifically, a vapor gas discharge passage 13 that discharges the vapor gas (hereinafter simply referred to as the "vapor gas") G1 of the liquefied hydrogen generated in the inner tank inner space 7 to the outside of the storage tank 1, a hydrogen gas introduction passage 15 that introduces hydrogen gas (hereinafter referred to as the "external hydrogen gas") G2 from a hydrogen gas source (not shown) provided outside the storage tank 1 into the inner and outer tank intermediate space 9, and a connection passage 17 that connects the vapor gas discharge passage 13 and the hydrogen gas introduction passage 15 outside the storage tank 1 are provided. The communication passage 11 is formed by these vapor gas discharge passage 13, connection passage 17, and hydrogen gas introduction passage 15. Also, an on-off valve 19 is provided in the communication passage 11, and the communication passage 11 is configured to be openable and closable by this on-off valve 19. In this example, the on-off valve 19 is provided in the downstream portion of the connection point of the hydrogen gas introduction passage 15 with the connection passage 17, but the position and number of the on-off valves 19 are not limited to this example. Also, the on-off valve 19 may be a valve that can be manually opened and closed, or a valve that automatically opens and closes according to a set differential pressure.

[0016] Note that the specific configuration of the communication passage 11 between the inner tank inner space 7 and the space 9 between the inner and outer tanks, and the specific configuration enabling the opening and closing of the communication passage 11 are not limited to this example. Further, the above "hydrogen gas source" may have any configuration as long as it can be a supply source of hydrogen gas. Typically, it is a tank storing hydrogen gas, but for example, it may be a combination of a tank storing liquefied hydrogen and a vaporizer.

[0017] Furthermore, in the present embodiment, a device (hereinafter simply referred to as "gas supply device") 31 for forcibly feeding a cooling gas described later into the space 9 between the inner and outer tanks, such as a compressor or a blower, is provided in the communication passage 11. The gas supply device 31 is a device that moves gas by applying pressure to the gas, such as a turbo-type or positive-displacement compressor, blower, or fan. In the illustrated example, the gas supply device 31 is provided in the connection passage 17. Also, a cooling device 33 is provided on the communication passage 11, for example, on the hydrogen gas introduction passage 15. The cooling device 33 includes, for example, a temperature sensor for detecting the gas temperature, a cooling source such as a compression refrigerator or an absorption refrigerator, and a control circuit for controlling these. However, the cooling device 35 may be a device having a configuration other than the above, for example, a heat exchanger. Also, the gas supply device 31 and the cooling device 33 may be provided only as necessary according to the implementation modes of the cooling-down method and the warming-up method described later.

[0018] Also, in the present embodiment, an inner tank temperature detection device 21 for detecting the temperature of the inner tank 3, an inner tank inner space pressure detection device 23 for monitoring the pressure of the inner tank inner space 7, an inner and outer tank space temperature detection device 25 for detecting the temperature of the space 9 between the inner and outer tanks, and an inner and outer tank space pressure detection device 27 for detecting the pressure of the space 9 between the inner and outer tanks are provided. These detection devices include a sensor element for detecting the physical quantity (temperature, pressure) of the detection target, various circuits for performing necessary processes such as signal conversion processing and arithmetic processing on the acquired detection quantity, a memory for storing information necessary for these processes, a power source element such as a battery, or a power supply circuit for receiving power supply from the outside, and for transmitting the output signal to the outside by wire or wireless It is equipped with a transmission circuit, etc. Furthermore, other temperature and pressure detection devices may be provided to measure parts other than those mentioned above, such as an inner tank temperature detection device and an outer tank temperature detection device. Also, only the necessary temperature and pressure detection devices may be provided depending on the implementation of the cool-down and warm-up methods described later.

[0019] The method for cooling down the storage tank 1 configured in this way will be explained in detail below.

[0020] In this embodiment, in the initial state of the storage tank 1 at the start of the cool-down shown in Figure 2A, the on-off valve 19 of the communication passage 11 is open, and hydrogen gas at, for example, room temperature and atmospheric pressure (0 kPaG) is present in both the inner tank space 7 and the space between the inner and outer tanks 9. However, the temperature and pressure of the hydrogen gas in the initial state are not limited to room temperature and atmospheric pressure. From this state, as shown in Figure 2B, liquefied hydrogen for cooling (hereinafter simply referred to as "cooling hydrogen") CH is introduced into the inner tank space 7. In this example, cooling hydrogen CH is sprayed into the inner tank space 7 using a sprayer 29.

[0021] In this state, continuing to spray cooling hydrogen CH causes the temperature of the inner tank 3 to decrease. As the temperature of the inner tank 3 decreases, the temperature of the space between the inner and outer tanks 9 also decreases. In addition, in the inner tank space 7, vaporized gas G1 is generated from the vaporized cooling hydrogen CH, causing the pressure to rise, while in the space between the inner and outer tanks 9, the pressure decreases due to the temperature drop. As described above, since the connecting passage 11 is open, the vaporized gas G1 generated in the inner tank space 7 flows into the space between the inner and outer tanks 9 via the connecting passage 11 due to the pressure difference between the two spaces 7 and 9.

[0022] Furthermore, while the inner tank 3 is being cooled with the connecting passage 11 open, if the pressure difference between the two spaces exceeds a predetermined range, a pressure difference adjustment device may be used to adjust the pressure difference between the two spaces so that it remains within a predetermined range. For example, if the pressure in the space between the inner and outer tanks 9 is excessively low, the hydrogen gas supply device 31 may be used to supply vaporized gas G1 from the inner tank space 7 to the space between the inner and outer tanks 9. Alternatively, instead of or in addition to the forced supply of vaporized gas G1, external hydrogen gas G2 may be supplied to the space between the inner and outer tanks 9 from the hydrogen gas introduction passage 15. In the following description, the gas forcibly supplied in this manner to cool the space between the inner and outer tanks 9 will be collectively referred to as "cooling gas CG".

[0023] Furthermore, if cooling gas CG is forcibly supplied to the space between the inner and outer tanks 9 as described above, a discharge passage (not shown) for discharging the cooling gas CG from the space between the inner and outer tanks 9 may be provided to prevent the pressure in the space between the inner and outer tanks 9 from rising excessively.

[0024] Furthermore, although this embodiment describes an example in which the communication passage 11 is opened at the start of the cool-down, that is, from the start of the spraying of cooling hydrogen CH, the timing of opening the communication passage 11 is not limited to this. That is, the spraying of cooling hydrogen CH may be started with the communication passage 11 closed, and the communication passage 11 may be opened as needed to supply vaporized gas G1, such as when the pressure in the space between the inner and outer tanks 9 falls below a predetermined value.

[0025] During the cool-down process carried out in this manner, the temperature difference between the inner tank 3 and the outer tank 5 may become too large, leading to an excessive difference in the amount of thermal contraction of the constituent members and generating significant stress. To avoid this, in this embodiment, the temperature of the inner tank 3 and the temperature of the outer tank 5 are measured, and based on the temperature difference between the temperature of the inner tank 3 and the temperature of the outer tank 5 (hereinafter simply referred to as "temperature difference"), at least one of the temperature change rates of the inner tank 3 and the outer tank 5 is adjusted to maintain the temperature difference below a predetermined value. Here, "temperature of the inner tank 3" and "temperature of the outer tank 5" include the temperature of the inner space in contact with each tank, i.e., the temperature of the inner space 7 for the inner tank 3 and the temperature of the space 9 between the inner and outer tanks for the outer tank 5. Also, the "predetermined value" of the temperature difference here is, for example, The specified value is set based on the temperature difference at the start of normal operation of storage tank 1, and is, for example, a value greater than the temperature difference at the start of normal operation, such as around 150K. However, the specified value is not limited to this value.

[0026] In this embodiment, as a method for adjusting the rate of temperature change of the inner tank 3, the rate at which cooling hydrogen CH is introduced into the inner tank 3 is adjusted. Specifically, the cooling rate of the inner tank 3 is reduced by decreasing the rate at which cooling hydrogen CH is introduced into the inner tank 3. Note that "decreasing the introduction rate" here includes stopping the introduction. In addition, as a method for adjusting the rate of temperature change of the outer tank 5, in this embodiment, the supply rate of cooling gas CG to the space between the inner and outer tanks 9 is adjusted. Specifically, the cooling rate of the outer tank 5 is increased by lowering the temperature of vaporized gas G1 and / or external hydrogen gas G2 in the space between the inner and outer tanks 9 using the cooling device 33, and increasing the supply rate of cooling gas CG using the gas supply device 31. The reduction in the cooling rate of the inner tank 3 and the increase in the cooling rate of the outer tank 5 may be performed individually or in combination. As an example, Figure 2C shows a state in which the spraying of cooling hydrogen CH into the inner tank 3 is stopped and the supply rate of cooling gas CG to the space between the inner and outer tanks 9 is increased.

[0027] The adjustment of the rate at which cooling hydrogen CH is introduced into the inner tank 3 is not limited to the above example, and may also include increasing the introduction rate if the inner tank 3 is not sufficiently cooled. Similarly, the adjustment of the supply rate of cooling gas CG to the space between the inner and outer tanks 9 is not limited to the above example, and may also include decreasing the supply rate if the outer tank 5 is overcooled. The method for adjusting at least one of the temperature change rate of the inner tank 3 and the temperature change rate of the outer tank 5 is not limited to the above example. For example, hydrogen gas at a temperature higher than the inner tank temperature may be supplied to the inner tank space 7.

[0028] Furthermore, in order to perform temperature difference control with high precision, predetermined locations are selected in the inner tank 3 and outer tank 5 to measure the respective temperatures. For example, a predetermined location capable of detecting the representative temperature of the inner tank 3 and a predetermined location capable of detecting the representative temperature of the outer tank 5 are selected. Here, "representative temperature" refers to the temperature that is considered to be the most appropriate representative of the temperature of the inner tank 3 and outer tank 5, respectively, based on the overall temperature distribution of each of the inner tank 3 and outer tank 5. An example of a "representative temperature" is the average value of the overall temperature distribution of the inner tank 3 and outer tank 5.

[0029] Other examples of locations where the temperature of the inner tank 3 and outer tank 5 can be measured include the connection points between the inner tank 3 and other components, and the connection points between the outer tank 5 and other components. Specifically, examples of connection points with other components where temperature measurement is performed include the connection points to the skirt, which is a cylindrical support member that supports the storage tank 1 relative to the hull, and the connection points to the pipe-shaped tower that protrudes vertically from the center of the storage tank 1. By measuring the temperature at the connection points with other components and adjusting the temperature difference, the connection state between the inner tank 3, outer tank 5 and other components can be effectively maintained.

[0030] Further examples of locations for measuring the temperature in the inner tank 3 and outer tank 5 include the inner spaces adjacent to each tank 3 and 5, namely the inner tank space 7 for the inner tank 3 and the space 9 between the inner and outer tanks for the outer tank 5. With this configuration, the temperature measurement locations used for the steady-state operation of the storage tank 1 can be utilized, eliminating the need for additional measuring devices.

[0031] The combination of locations where the temperature of the inner tank 3 and outer tank 5 is measured is not limited to the examples described above. For example, the temperature of the connection points with other components may be measured for the inner tank 3, and the temperature of the space 9 between the inner and outer tanks may be measured for the outer tank 5.

[0032] Furthermore, the devices used for measuring these temperatures may be, for example, the temperature detection devices described above, or they may be differential thermometers that output the temperature difference detected by individual temperature sensing elements.

[0033] In this way, by cooling the inner tank 3 with cooling hydrogen CH and supplying hydrogen gas to the space between the inner and outer tanks 9 as needed, the cooling of the space between the inner and outer tanks 9 and the outer tank 5 is promoted. This reduces the time required to cool down the entire storage tank 1 compared to simply cooling the inner tank 3 alone, thereby reducing costs. Furthermore, by maintaining the temperature difference between the inner tank 3 and the outer tank 5 below a predetermined value, the difference in thermal contraction of the constituent members can be suppressed.

[0034] Subsequently, as shown in Figure 2D, when the temperature of the inner tank 3 and the temperature of the space between the inner and outer tanks 9 have both decreased to the target temperature, the communication passage 11 is closed if it is open, and the spraying of cooling hydrogen CH is stopped to end the cool-down process.

[0035] In this embodiment, an example in which cool-down is performed using liquefied hydrogen for cooling has been described, but cool-down may also be performed using a liquefied gas other than liquefied hydrogen. For example, cool-down may be carried out in stages, such as introducing liquefied nitrogen from a state in which air is present in the inner tank 3, and then replacing the nitrogen with hydrogen.

[0036] The cool-down according to this embodiment is typically performed, for example, after the construction of the storage tank 1, after the construction of liquefied gas storage equipment such as a ship in which the storage tank 1 is installed, or before loading again after warming up the storage tank 1 for maintenance of the equipment or the storage tank 1. However, the cool-down method according to this embodiment can also be applied when the storage tank 1 is installed on a ship and is undergoing an empty voyage (ballast voyage) after unloading the liquefied gas from the storage tank 1. That is, during a ballast voyage, the temperature of the inner tank 3 may gradually rise, and in that case, the above cool-down method can be applied. When cooling down the storage tank 1 during a ballast voyage, for example, liquefied gas left in the inner tank 3 for cooling down without unloading is used, and the liquefied gas is transferred to the top of the tank by a supply device such as a pump installed in the inner tank 3 to perform the cool-down. If multiple storage tanks 1 are installed, liquefied gas or vaporized gas for cooling down may be supplied from other storage tanks 1.

[0037] Next, the method for warming up the storage tank 1 according to this embodiment will be described in detail below.

[0038] In this embodiment, when liquefied hydrogen is discharged from the storage tank 1 and the warm-up shown in Figure 3A begins, the on-off valve 19 of the communication passage 11 is closed in the initial state of the storage tank 1. In the inner tank space 7, for example, hydrogen gas exists at a slightly higher pressure than atmospheric pressure, for example, 5 kPaG, and a temperature of about 20 K, which is the freezing point. In the space between the inner and outer tanks 9, hydrogen gas exists in a steady-state operating state, for example, at a slightly lower pressure than atmospheric pressure, -10 kPaG, and a temperature of about 110 K. However, the temperature and pressure values ​​of the hydrogen gas in the initial state are not limited to the above examples. From this state, as shown in the figure, heating hydrogen gas (hereinafter referred to as "first heating gas") HG1 is supplied to the inner tank space 7 using the sprayer 29. The first heating gas may be supplied using another line connected to the inner tank 3 instead of the sprayer 29, for example, a line provided for supplying liquefied gas to the storage tank 1.

[0039] During the warm-up process, the temperature difference between the inner tank 3 and the outer tank 5 may become too large, resulting in an excessive difference in the amount of thermal contraction of the constituent members. In this embodiment, to avoid this, the temperature of the inner tank 3 and the temperature of the outer tank 5 are measured, and based on the temperature difference between the inner tank 3 and the outer tank 5 (hereinafter simply referred to as "temperature difference"), at least one of the temperature change rates of the inner tank 3 and the outer tank 5 is adjusted to maintain the temperature difference below a predetermined value. Here, the "predetermined value" of the temperature difference is set, for example, based on the temperature difference at the end of normal operation of the storage tank 1, and is a value greater than, for example, the temperature difference at the start of normal operation, for example, 1 It is approximately 50K. However, the "specified value" is not limited to this value.

[0040] As a method for maintaining the temperature difference below a predetermined value, in this embodiment, as shown in Figure 3B, the heating rate of the outer tank 5 is increased by supplying heating gas (hereinafter referred to as "second heating gas") HG2 to the space between the inner and outer tanks 9. The supply of the second heating gas HG2 to the space between the inner and outer tanks 9 is carried out, for example, via a dedicated heating gas supply passage 41. However, the supply of the second heating gas HG2 to the space between the inner and outer tanks 9 may also be carried out by bypassing the cooling device 33, for example, via a hydrogen gas introduction passage 15. In order to maintain the temperature difference below a predetermined value, at least one of the supply rate of the first heating gas to the inner tank space 7 and the supply rate of the second heating gas HG2 to the space between the inner and outer tanks 9 is adjusted.

[0041] The locations where the temperatures of the inner tank 3 and outer tank 5 are measured during the warm-up are the same as in the cool-down case described above. That is, for example, the temperatures of the representative temperatures of each tank 3 and 5 can be measured at predetermined locations where the representative temperatures of each tank 3 and 5 can be detected, at the connection points of each tank 3 and 5 to other components, and at the inner tank space 7 and the space between the inner and outer tanks 9, which are the inner spaces in contact with each tank 3 and 5.

[0042] Furthermore, it is preferable to supply the second heating gas HG2 to the space 9 between the inner and outer tanks after the temperature of the inner tank 3 has risen to a predetermined value or higher. Here, the "predetermined value" of the temperature of the inner tank 3 refers to a temperature at which there is no possibility of hydrogen gas condensation in the space 9 between the inner and outer tanks.

[0043] In this way, by heating the inner tank 3 with the first heating gas HG1 while supplying the second heating gas HG2 to the space between the inner and outer tanks 9, the temperature rise of the space between the inner and outer tanks 9 and the outer tank 5 is also promoted. Therefore, compared to simply heating the inner tank 3 alone, the time required to warm up the entire storage tank 1 can be shortened and costs can be reduced. Furthermore, by maintaining the temperature difference between the inner tank 3 and the outer tank 5 below a predetermined value, the difference in the amount of thermal contraction of the constituent members can be suppressed.

[0044] Figure 1 shows an example of a storage tank 1, specifically an independent double-hull tank formed separately from the hull. However, the cool-down and warm-up methods according to this embodiment are not limited to this example and can be applied to any type of storage tank. For example, the cool-down and warm-up methods according to this embodiment can also be applied to a type of storage tank formed integrally with the hull. Furthermore, the multi-layer structure of the storage tank may be triple-layer or more, and the cool-down and warm-up methods according to this embodiment can be applied to the internal space of the inner tank and any other inter-tank space of such a multi-layer structure.

[0045] As described above, according to the cool-down method of this embodiment, as shown in Figure 2B, by maintaining the temperature difference between the inner tank 3 and the outer tank 5 below a predetermined value by cooling the inner tank 3 with cooling hydrogen CH while supplying cooling gas CG to the space 9 between the inner and outer tanks, the generation of stress caused by the difference in thermal contraction between the constituent members can be suppressed, the time required for cool-down can be shortened, and costs can be reduced.

[0046] In the cool-down method according to this embodiment, the rate of temperature change of the inner tank 3 may be adjusted by reducing the spray rate of liquefied hydrogen CH for cooling into the inner tank 3. Alternatively, the rate of temperature change of the outer tank 5 may be adjusted by increasing the supply rate of cooling gas to the space 9 between the inner and outer tanks. This configuration allows for temperature difference adjustment with a simple structure.

[0047] In the cool-down method according to this embodiment, the temperature of the inner tank 3 and the outer tank 5 may be measured by measuring the temperature at a predetermined location where the representative temperatures of the inner tank 3 and the outer tank 5 can be detected. With this configuration, the temperature difference can be adjusted with high accuracy.

[0048] In the cool-down method according to this embodiment, the temperature of the inner tank 3 and the temperature of the outer tank 5 are measured. This can be done by measuring the temperature at each connection point between the inner tank 3 and the outer tank 5 and other components. With this configuration, the connection state between the inner tank 3, the outer tank 5 and other components can be effectively maintained by adjusting the temperature difference.

[0049] In the cool-down method according to this embodiment, the temperature of the inner tank 3 and the temperature of the outer tank 5 may be measured by measuring the temperature of the space inside the inner tank 7 and the space between the inner and outer tanks 9. With this configuration, the temperature measurement points used for the steady operation of the storage tank 1 can be used, eliminating the need for additional measuring devices, etc.

[0050] According to the warm-up method of this embodiment, by heating the inner tank 3 with the first heating gas HG1 while supplying the second heating gas HG2 to the space 9 between the inner and outer tanks, the temperature difference between the inner tank 3 and the outer tank 5 is maintained at or below a predetermined value. This suppresses differences in the amount of thermal shrinkage of the constituent members, shortens the time required for warm-up, and reduces costs.

[0051] As described above, preferred embodiments of the present disclosure have been explained with reference to the drawings, but various additions, modifications, or deletions are possible without departing from the spirit of the present disclosure. Therefore, such additions, modifications, or deletions are also included within the scope of the present disclosure. [Explanation of symbols]

[0052] 1. Liquefied gas storage tank 3 Inner tank 5 Outer tank 7. Inner chamber space 9 Space between inner and outer tanks 11 Communication path 29 Sprayer 33 Cooling device CG cooling gas CH4 liquefied gas for cooling G1 Vaporized gas G2 External hydrogen gas HG1 First heating gas HG2 Second heating gas

Claims

1. A method for cooling a tank, which has an inner tank and an outer tank for storing liquefied gas, before filling it with the liquefied gas to be stored, Introducing liquefied cooling gas into the internal space of the inner tank, The temperature of the inner tank and the temperature of the outer tank are measured, Based on the temperature difference between the temperature of the inner tank and the temperature of the outer tank, the temperature difference is maintained below a predetermined value by adjusting at least one of the temperature change rates of the inner tank and the outer tank. Includes, Measuring the temperature of the inner tank and the temperature of the outer tank, The temperature of a predetermined location where the representative temperature of the inner tank can be detected is measured, The temperature of a predetermined location where the representative temperature of the outer tank can be detected is measured, Includes, The aforementioned representative temperature is the average value of the overall temperature distribution of the inner tank and the outer tank, respectively. Methods for cooling down liquefied gas storage tanks.

2. In the cool-down method described in Claim 1, Adjusting at least one of the temperature change rate of the inner tank and the temperature change rate of the outer tank is This includes adjusting the rate at which the cooling liquefied gas is introduced into the internal space of the inner tank. Cool-down methods.

3. In the cool-down method according to claim 1 or 2, Adjusting at least one of the temperature change rate of the inner tank and the temperature change rate of the outer tank is This includes adjusting the rate at which cooling gas is supplied to the space between the inner and outer tanks. Cool-down methods.

4. In the cool-down method according to any one of claims 1 to 3, Measuring the temperature of the inner tank and the temperature of the outer tank, To measure the temperature of the connection point between the inner tank and other components, To measure the temperature of the connection point between the outer tank and other components, including Cool-down methods.

5. In the cool-down method according to any one of claims 1 to 4, Measuring the temperature of the inner tank and the temperature of the outer tank, To measure the temperature of the space inside the inner tank, Measuring the temperature of the space between the inner and outer tanks, including Cool-down methods.

6. A method for heating a tank, which has an inner tank and an outer tank, for storing liquefied gas, after the liquefied gas to be stored has been discharged, Introducing the first heating gas into the space inside the inner tank, The temperature of the inner tank and the temperature of the outer tank are measured, Based on the temperature difference between the temperature of the inner tank and the temperature of the outer tank, the temperature difference is maintained below a predetermined value by adjusting at least one of the temperature change rates of the inner tank and the outer tank. Includes, Measuring the temperature of the inner tank and the temperature of the outer tank, The temperature of a predetermined location where the representative temperature of the inner tank can be detected is measured, The temperature of a predetermined location where the representative temperature of the outer tank can be detected is measured, Includes, The aforementioned representative temperature is the average value of the overall temperature distribution of the inner tank and the outer tank, respectively. Method for warming up liquefied gas storage tanks.

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