Cooling-down and warm-up methods for liquefied gas storage tanks

Abstract

A method for cooling a tank having an inner tank (3) and an outer tank (5) for storing liquefied gas before filling the liquefied gas to be stored comprises introducing a cooling liquefied gas (CH) into a space (7) inside the inner tank, measuring the temperature of the inner tank (3) and the temperature of the outer tank (5) respectively, and maintaining the temperature difference below a predetermined value by adjusting at least one of the rate of change of temperature of the inner tank (3) and the rate of change of temperature of the outer tank (5) based on the temperature difference between the temperature of the inner tank (3) and the temperature of the outer tank (5).

Description

Technology Field

[0001] [Related Application]

[0002] The present application claims priority to Japanese Patent Application No. 2022-046799 filed on March 23, 2022, and incorporates by reference the entirety thereof as part of the present application.

[0003] The present disclosure relates to a cooling down method and a warming up method for a liquefied gas storage tank. Background Technology

[0004] Conventionally, as a tank for storing liquefied gas, for example, cryogenic liquid hydrogen, it has been proposed to use a double-shell tank equipped with an inner tank and an outer tank (see, for example, Patent Document 1).

[0005] Generally, when storing low-temperature 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 into a tank at room temperature at once, the tank is cooled down at a relatively low speed in advance (hereinafter referred to as "cooling down") before filling the liquefied gas to be stored. In addition, if it is necessary to empty the tank for maintenance or other purposes, the tank is heated (hereinafter referred to as "warming up") after the liquefied gas to be stored is discharged. Prior art literature

[0006] Japanese Patent Publication No. 2019-151291 The problem to be solved

[0007] However, in the case of tanks with a multi-layer heat dissipation structure, such as double-shell tanks for liquefied gas, they possess high thermal insulation properties; therefore, as mentioned above, even if the tank is cooled at a relatively low speed, large temperature differences occur depending on the location within the tank, and as a result, there is a possibility of large stress occurring. To avoid this, in the cooling down of conventional double-shell tanks, measures such as cooling at an even lower speed are required, which takes a long time to cool the entire tank and requires a large amount of liquefied gas for cooling. Consequently, the cost required for cooling down increases. The same challenge exists regarding the warm-up of multi-layer heat dissipation structure tanks.

[0008] The purpose of the present disclosure is to reduce costs by reducing the time required for cooling down and warming up of a multi-layer heat dissipation structure tank for liquefied gas storage while suppressing the generation of stress, in order to solve the above-mentioned problem. means of solving the problem

[0009] To achieve the above objective, the cooling down method of a liquefied gas storage tank according to the present disclosure is,

[0010] A method for cooling a tank having an inner tank and an outer tank for storing liquefied gas before filling the liquefied gas to be stored,

[0011] Introducing cooling liquefied gas into the space inside the tank, and

[0012] Measuring the temperature of the inner tank and the temperature of the outer tank, respectively, and

[0013] Based on the temperature difference between the temperature of the inner tank and the temperature of the outer tank, maintaining the temperature difference at least one of the rate of change of temperature of the inner tank and the rate of change of temperature of the outer tank to keep the temperature difference below a predetermined value.

[0014] Includes

[0015] A method for warming up a liquefied gas storage tank according to the present disclosure is

[0016] A method of heating a tank having an inner tank and an outer tank for storing liquefied gas after discharging the liquefied gas to be stored,

[0017] Introducing a first heating gas into the space inside the tank, and

[0018] Forcibly supplying a second heating gas to the inner and outer tank space, and

[0019] Measuring the temperature of the inner tank and the temperature of the outer tank, respectively, and

[0020] Based on the temperature difference between the temperature of the inner tank and the temperature of the outer tank, maintaining the temperature difference at least one of the rate of change of temperature of the inner tank and the rate of change of temperature of the outer tank to keep the temperature difference below a predetermined value.

[0021] Includes

[0022] According to the cooling down and warm-up methods for a liquefied gas storage tank according to the present disclosure, the time can be shortened while suppressing the generation of stress during the cooling down and warm-up of a multi-layer heat dissipation structure tank for liquefied gas storage, thereby reducing costs.

[0023] Any combination of at least two configurations disclosed in the claims and / or the specification and / or the drawings is included in the present invention. In particular, any combination of two or more of each claim of the claims is included in the present invention. Brief explanation of the drawing

[0024] The present invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are for illustration and description only and are not intended to determine the scope of the invention. The scope of the invention is determined by the appended claims. In the accompanying drawings, the same part number in a plurality of drawings represents the same or substantial part. FIG. 1 is a cross-sectional view showing the schematic configuration of a liquefied gas storage tank to which a cooling-down method according to one embodiment of the present disclosure is applied. FIG. 2a is a schematic diagram showing the initial state prior to the start of a cooling down method according to one embodiment of the present disclosure. FIG. 2b is a schematic diagram showing the state during internal cooling in a cooling down method according to one embodiment of the present disclosure. FIG. 2c is a schematic diagram showing the state of performing temperature difference adjustment in a cooling down method according to one embodiment of the present disclosure. FIG. 2d is a schematic diagram showing the terminated state of a cooling down method according to one embodiment of the present disclosure. FIG. 3a is a schematic diagram showing the state at the start of a warm-up method according to one embodiment of the present disclosure. FIG. 3b is a schematic diagram showing the state of performing temperature difference adjustment in a warm-up method according to one embodiment of the present disclosure. Specific details for implementing the invention

[0025] Hereinafter, preferred embodiments of the present disclosure will be described with reference to the drawings. FIG. 1 shows a liquefied gas storage tank (hereinafter simply referred to as "storage tank") (1) to which a cooling down method and a warming up method according to one embodiment of the present disclosure are applied. This storage tank (1) is a tank for storing liquefied gas and is configured as a double-walled tank having an inner tank (3) and an outer tank (5). In addition, in the present specification, "cooling down" means cooling the storage tank (1) before filling the storage tank (1) with the liquefied gas to be stored. In addition, in the present specification, "warming up" means heating the low-temperature storage tank (1) after discharging the liquefied gas to be stored, in preparation for subsequent maintenance, etc.

[0026] In the embodiment described below, liquid hydrogen at a cryogenic temperature (approx. -250°C) is used as an example of the liquefied gas to be stored. However, the liquefied gas may be of other types of gas, such as liquefied petroleum gas (LPG, approx. -45°C), liquefied ethylene gas (LEG, approx. -100°C), liquefied natural gas (LNG, approx. -160°C), liquid helium (LHe, approx. -270°C), etc.

[0027] The storage tank (1) is installed on a vessel, for example, 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 having 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 vessel that uses liquefied hydrogen as propulsion fuel, a liquefied hydrogen storage facility on land other than a vessel, or a plant that uses liquefied hydrogen.

[0028] 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 section that forms a storage space for liquid hydrogen to be stored (hereinafter referred to as "inner tank space (7)") on its inner side, and an inner tank heat dissipation layer that covers the outer surface of the inner section. The outer tank (5) has an outer section that forms an inner-outer tank space (9), which is an insulating layer, between the inner tank (3) and the outer tank, and an outer tank heat dissipation layer that covers the outer surface of the outer section. Furthermore, the location where the heat dissipation layers of the inner tank (3) and the outer tank (5) are installed is not limited to this example and is arbitrary; for example, the heat dissipation layer may be installed to cover the inner surface of the outer section. Additionally, one or both of the heat dissipation layers of the inner tank (3) and the outer tank (5) may be omitted. This storage tank (1) is operated normally with low-temperature hydrogen gas sealed in the inner and outer space (9), which is an insulating layer.

[0029] In this embodiment, a connecting passage (11) is installed to connect the inner tank space (7) and the inner-outer tank space (9). The connecting passage (11) is configured to be openable and closable. In the illustrated example, specifically, a vaporized gas discharge passage (13) for discharging the vaporized gas (hereinafter simply referred to as "vaporized gas") (G1) of liquid hydrogen generated in the inner tank space (7) to the outside of the storage tank (1), a hydrogen gas introduction passage (15) for introducing hydrogen gas (hereinafter referred to as "external hydrogen gas") (G2) from a hydrogen gas source (not illustrated) installed outside the storage tank (1) into the inner-outer tank space (9), and a connecting passage (17) for connecting the vaporized gas discharge passage (13) and the hydrogen gas introduction passage (15) outside the storage tank (1) are installed. A communication channel (11) is formed by these vaporized gas discharge passage (13), connection passage (17), and hydrogen gas introduction passage (15). Additionally, an opening / closing valve (19) is formed in the communication channel (11), and the communication channel (11) is configured to be openable / closeable by this opening / closing valve (19). In this example, the opening / closing valve (19) is installed in the downstream portion of the connection point between the hydrogen gas introduction passage (15) and the connection passage (17), but the location and number of the opening / closing valves (19) are not limited to this example. Furthermore, the opening / closing valve (19) may be a valve that opens / closes automatically according to a set differential pressure, in addition to a valve that can be opened / closed manually.

[0030] Furthermore, the specific configuration of the passageway (11) between the inner tank space (7) and the inner and outer tank space (9), and the specific configuration that enables the passageway (11) to be opened and closed, are not limited to this example. In addition, the "hydrogen gas source" can be any configuration that can serve as a source of hydrogen gas, and typically it is a tank that stores hydrogen gas, but for example, it can be a combination of a tank that stores liquid hydrogen and a vaporizer.

[0031] In addition, in this embodiment, a device (hereinafter simply referred to as a "gas supply device") (31) for forcibly supplying cooling gas, such as a compressor or a blower, to the inner and outer space (9), which will be described later, is installed in the connecting passage (11). The gas supply device (31) is a device that moves gas by applying pressure to the gas, such as, for example, a turbo-type or volumetric compressor, a blower, or a fan. In the illustrated example, the gas supply device (31) is installed in the connecting passage (17). In addition, a cooling device (33) is installed on the connecting passage (11), for example, on the hydrogen gas introduction passage (15). The cooling device (33) is equipped with, for example, a temperature sensor that detects the gas temperature, a cooling source such as a compression refrigerator or an absorption refrigerator, and a control circuit that controls them. However, the cooling device (35) may be a device with a configuration other than that described above, for example, a heat exchanger. Also, the gas supply device (31) and the cooling device (33) may be installed only as necessary according to the implementation of the cooling down method and warming up method described later.

[0032] In addition, in this embodiment, an inner tank temperature detection device (21) for detecting the temperature of the inner tank (3), an inner tank internal space pressure detection device (23) for monitoring the pressure of the inner tank internal space (7), an inner tank inter-space temperature detection device (25) for detecting the temperature of the inner tank inter-space (9), and an inner tank inter-space pressure detection device (27) for detecting the pressure of the inner tank inter-space (9). This detection device is equipped with a sensor element for detecting a physical quantity (temperature, pressure) of a detection target, various circuits for performing necessary processing such as signal conversion processing and calculation processing on the acquired detection quantity, a memory for storing information necessary for this processing, a power element such as a battery or a power circuit for receiving power supply from the outside, and a transmission circuit for transmitting an output signal to the outside via wired or wireless means. Furthermore, as such a temperature detection device and pressure detection device, a device for measuring parts other than those described above, such as an inner tank temperature detection device or an outer tank temperature detection device, may be installed. In addition, these temperature detection devices and pressure detection devices may be installed only as necessary according to the implementation of the cooling down method and warming up method described later.

[0033] The method for cooling down the storage tank (1) configured in this way will be explained in detail below.

[0034] In this embodiment, in the initial state of the storage tank (1) at the time of initiating the cooling down shown in FIG. 2a, the opening / closing valve (19) of the connecting passage (11) is open, and hydrogen gas at room temperature and atmospheric pressure (0 kPaG) exists in both the inner tank space (7) and the inner / outer tank space (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, liquid hydrogen for cooling (hereinafter simply referred to as "cooling hydrogen") (CH) is introduced into the inner tank space (7) as shown in FIG. 2b. In this example, cooling hydrogen (CH) is sprayed into the inner tank space (7) using a sprayer (29).

[0035] In this state, by continuing to spray cooling hydrogen (CH), the temperature of the inner tank (3) decreases. As the temperature of the inner tank (3) decreases, the temperature of the space between the inner and outer tanks (9) also decreases. Furthermore, in the space inside the inner tank (7), vaporized gas (G1) is generated as cooling hydrogen (CH) vaporizes, 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 space inside the inner tank (7) flows into the space between the inner and outer tanks (9) through the connecting passage (11) due to the pressure difference between the two spaces (7, 9).

[0036] In addition, while cooling the inner tank (3) with the flue 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 falls within the predetermined range. For example, if the pressure in the space between the inner and outer tanks (9) is excessively low, a hydrogen gas supply device (31) may be used to supply the vaporized gas (G1) from the inner tank space (7) to the space between the inner and outer tanks (9). Alternatively, instead of the forced supply of the vaporized gas (G1), or additionally, 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 that is forcibly supplied to cool the space between the inner and outer tanks (9) in this manner is collectively referred to as "cooling gas (CG)."

[0037] In addition, as described above, when cooling gas (CG) is forcibly supplied to the inner and outer space (9), a discharge passage (not shown) for discharging cooling gas (CG) from the inner and outer space (9) may be installed to prevent the pressure in the inner and outer space (9) from rising excessively.

[0038] In addition, in this embodiment, an example was described in which the passage (11) is opened at the start of cooling down, that is, at the start of spraying cooling hydrogen (CH), but the timing of opening the passage (11) is not limited to this. That is, the spraying of cooling hydrogen (CH) is started while the passage (11) is closed, and the passage (11) may be opened and vaporized gas (G1) supplied as needed, such as when the pressure in the space between the inner and outer passages (9) becomes below a predetermined value.

[0039] In the cooling down process performed in this manner, the temperature difference between the inner tank (3) and the outer tank (5) may become excessively large, resulting in a large stress due to an excessive difference in the amount of thermal shrinkage of the constituent members. To avoid this, in this embodiment, the temperature of the inner tank (3) and the temperature of the outer tank (5) are measured separately, 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 rate of the inner tank (3) and the temperature change rate of the outer tank (5) is adjusted to maintain the temperature difference below a predetermined value. Here, the "temperature of the inner tank (3)" and the "temperature of the outer tank (5)" include the temperature of the inner space in contact with each tank, that is, for the inner tank (3), the temperature of the space inside the inner tank (7), and for the outer tank (5), the temperature of the space between the inner and outer tanks (9). In addition, the "predetermined value" of the temperature difference here is set based on, for example, the temperature difference at the start of normal operation of the storage tank (1), and is, for example, a value greater than the temperature difference at the start of normal operation, for example, about 150K. However, the "predetermined value" is not limited to this value.

[0040] As a method for adjusting the rate of temperature change of the inner tank (3), in this embodiment, the rate of introduction of cooling hydrogen (CH) into the inner tank (3) is adjusted. Specifically, the cooling rate of the inner tank (3) is reduced by lowering the rate of introduction of cooling hydrogen (CH) into the inner tank (3). And, "lowering the rate of introduction" 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 rate of supply of cooling gas (CG) to the space between the inner and outer tanks (9) is adjusted. Specifically, the temperature of the vaporized gas (G1) and / or external hydrogen gas (G2) into the space between the inner and outer tanks (9) is lowered by the cooling device (33), and the rate of supply of cooling gas (CG) is increased by using the gas delivery device (31), thereby increasing the cooling rate of the outer tank (5). The reduction in the cooling speed of the inner tank (3) and the increase in the cooling speed of the outer tank (5) may be carried out by either one alone or by combining both. As an example, FIG. 2c shows a state in which the spraying of cooling hydrogen (CH) into the inner tank (3) is stopped and the supply speed of cooling gas (CG) into the space (9) between the inner and outer tanks is increased.

[0041] Furthermore, the adjustment of the introduction rate of cooling hydrogen (CH) into the inner tank (3) is not limited to the above-described examples, and includes, for example, increasing the introduction rate when the cooling of the inner tank (3) is insufficient. Likewise, the adjustment of the supply rate of cooling gas (CG) into the space between the inner and outer tanks (9) is not limited to the above-described examples, and includes, for example, decreasing the supply rate when the outer tank (5) is excessively cooled. The method of 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-described examples. For example, hydrogen gas at a higher temperature than the inner tank temperature may be supplied to the space (7) inside the inner tank.

[0042] In addition, since temperature difference control is performed with high precision, for the inner tank (3) and the outer tank (5), a specific location capable of detecting the representative temperature of the inner tank (3) and a specific location capable of detecting the representative temperature of the outer tank (5) are selected as the location for measuring each temperature. Here, "representative temperature" refers to a temperature that is considered to most appropriately represent the temperature of the inner tank (3) and the outer tank (5) when viewed from the overall temperature distribution of the inner tank (3) and the outer tank (5), respectively. As an example of "representative temperature," the average value of the overall temperature distribution of the inner tank (3) and the outer tank (5) can be cited.

[0043] As other examples of locations for measuring the temperature in the inner tank (3) and the outer tank (5), connection points with other members in the inner tank (3) and connection points with other members in the outer tank (5) can be cited. Specifically, as examples of connection points with other members for measuring the temperature, there may be a connection point with a skirt, which is a tubular support member that supports the storage tank (1) against the hull, or a connection point with a pipe-shaped tower that protrudes vertically from the center of the storage tank (1). By measuring the temperature at the connection point with other members and adjusting the temperature difference, the connection state between the inner tank (3), the outer tank (5), and other members can be effectively maintained.

[0044] As another example of a temperature measurement location in each of the inner tank (3) and outer tank (5), an inner space in contact with each tank (3, 5), namely, an inner tank space (7) for the inner tank (3) and an inner-outer tank space (9) for the outer tank (5), can be cited. With this configuration, the temperature measurement location used for normal operation of the storage tank (1) can be utilized, so the addition of a measuring device, etc., becomes unnecessary.

[0045] Furthermore, the combination of locations for measuring the temperature in the inner tank (3) and the outer tank (5) is not limited to the examples described above. That is, for example, the temperature of the connection point with another member 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).

[0046] In addition, the device used for measuring these temperatures may be, for example, a temperature detection device as described above, or a temperature difference thermometer that outputs the temperature difference detected by individual temperature detection elements.

[0047] 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. Therefore, compared to the case where only the inner tank (3) is cooled, the time required for cooling down the entire storage tank (1) is shortened, thereby reducing costs. In addition, 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 shrinkage of the components can be suppressed.

[0048] After that, as shown in FIG. 2d, when the temperature of the inner tank (3) and the temperature of the space between the inner and outer tanks (9) have each dropped to the target temperature, if the flue (11) is in an open state, it is closed and the spraying of cooling hydrogen (CH) is stopped to end the cooling down.

[0049] In this embodiment, an example of performing cooling down using liquid hydrogen for cooling has been described, but cooling down may be performed using a liquefied gas other than liquid hydrogen. For example, cooling down may be performed in stages, such as introducing liquid nitrogen from a state where air is present in the inner tank (3) and then replacing the nitrogen with hydrogen.

[0050] Cooling down according to the present embodiment is typically performed, for example, after the storage tank (1) is dried, after the liquefied gas storage facility, such as a ship on which the storage tank (1) is installed, is dried, or before loading again after warming up the storage tank (1) for maintenance of the facility or the storage tank (1). However, the cooling down method according to the present embodiment can also be applied when the storage tank (1) is installed on a ship and the liquefied gas inside the storage tank (1) is unloaded during a ballasted voyage. That is, during a ballasted voyage, the temperature of the inner tank (3) may gradually rise, and in that case, the cooling down method can be applied. And, for cooling down the storage tank (1) during ballast voyage, for example, liquefied gas left in the inner tank (3) for cooling down without being discharged is used, and cooling down is performed by transferring the liquefied gas to the top of the tank by a supply device such as a pump installed in the inner tank (3). If multiple storage tanks (1) are installed, liquefied gas or vaporized gas for cooling down may be supplied from other storage tanks (1).

[0051] Next, a method for warming up a storage tank (1) according to the present embodiment will be described in detail below.

[0052] In this embodiment, liquid hydrogen is discharged from the storage tank (1), and in the initial state of the storage tank (1) at the time of initiating the warm-up shown in FIG. 3a, the opening / closing valve (19) of the connecting passage (11) is closed. In the inner tank space (7), hydrogen gas exists at a temperature of about 20K, which is the freezing point, for example, under a pressure slightly higher than atmospheric pressure, for example, 5kPaG. In the inner-outer tank space (9), hydrogen gas exists at a temperature of about 110K, which is a normal operating state, for example, under a pressure slightly lower than atmospheric pressure, for example, -10kPaG. However, the values ​​of the temperature and pressure of the hydrogen gas in the initial state are not limited to the above examples. From this state, as shown in the figure, hydrogen gas for heating (hereinafter referred to as "first heating gas") (HG1) is supplied to the inner tank space (7) using a sprayer (29). The first heating gas may be supplied using a different line connected to the inner tank (3) other than the sprayer (29), for example, a line installed to supply liquefied gas to the storage tank (1).

[0053] In the process of warming up in this manner, the temperature difference between the inner tank (3) and the outer tank (5) may become excessively large, resulting in an excessive difference in the amount of thermal shrinkage of the components. In this embodiment, to avoid this, the temperature of the inner tank (3) and the temperature of the outer tank (5) are measured separately, 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 rate of the inner tank (3) and the temperature change rate of 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 based on, for example, the temperature difference at the end of normal operation of the storage tank (1), and is, for example, a value greater than the temperature difference at the start of normal operation, for example, about 150K. However, the above "predetermined value" is not limited to this value.

[0054] As a method for maintaining the temperature difference below a predetermined value, in this embodiment, as shown in FIG. 3b, the heating gas (hereinafter referred to as "second heating gas") (HG2) is supplied to the space between the inner and outer tanks (9) to increase the heating rate of the outer tank (5). The supply of the second heating gas (HG2) to the space between the inner and outer tanks (9) is carried out, for example, through a dedicated heating gas supply path (41). However, the supply of the second heating gas (HG2) to the space between the inner and outer tanks (9) may be carried out, for example, by bypassing the cooling device (33) through 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 space inside the inner tank (7) and the supply rate of the second heating gas (HG2) to the space between the inner and outer tanks (9) is adjusted.

[0055] In the warm-up, the location for measuring the temperature of each of the inner tank (3) and the outer tank (5) is the same as in the case of the cooling-down described above. That is, for example, a predetermined location where the representative temperature of each tank (3, 5) can be detected, a connection location with other members of each tank (3, 5), an inner tank space (7) that is an inner space in contact with each tank (3, 5), and a temperature of the space between the inner and outer tanks (9) can be measured.

[0056] In addition, it is preferable to supply the second heating gas (HG2) to the space between the inner and outer tanks (9) after the temperature of the inner tank (3) has risen above a predetermined value. 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 between the inner and outer tanks (9).

[0057] In this way, by heating the inner tank (3) with the first heating gas (HG1) and 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 the case where only the inner tank (3) is heated, the time required for warming up the entire storage tank (1) can be shortened, thereby reducing costs. In addition, by maintaining the temperature difference between the inner tank (3) and the outer tank (5) below a predetermined value, the difference in thermal shrinkage of the constituent members can be suppressed.

[0058] Also, FIG. 1 shows an example of a storage tank (1) in which an independent double-sided tank formed independently of the hull is shown, but the cooling down method and warming up method according to the present embodiment are not limited to this example and can be applied to any type of storage tank. For example, the cooling down method and warming up method according to the present embodiment can also be applied to a type of storage tank formed integrally with the hull. In addition, the multi-layer structure of the storage tank may be a triple-layer structure or more, and the cooling down method and warming up method according to the present embodiment can be applied to any space between the inner tank of such a multi-layer structure and any other tank space.

[0059] According to the cooling down method according to the embodiment described above, as shown in FIG. 2b, by cooling the inner tank (3) with cooling hydrogen (CH) and supplying cooling gas (CG) 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 a value below a predetermined value, thereby suppressing the occurrence of stress caused by the difference in thermal shrinkage between the components and also reducing the time required for cooling down, thereby reducing costs.

[0060] In the cooling down method according to the present embodiment, the rate of change in temperature of the inner tank (3) may be adjusted by lowering the rate of introduction of cooling liquid hydrogen (CH₄) into the inner tank (3). Additionally, the rate of change in temperature of the outer tank (5) may be adjusted by increasing the rate of supply of cooling gas to the space (9) between the inner and outer tanks. With this configuration, the temperature difference can be adjusted with a simple structure.

[0061] In the cooling down method according to the present embodiment, the temperature of the inner tank (3) and the temperature of the outer tank (5) may be measured by measuring the temperature at a predetermined location where each representative temperature of the inner tank (3) and the outer tank (5) can be detected. With this configuration, the temperature difference can be adjusted with high precision.

[0062] In the cooling down method according to the present embodiment, the temperature of the inner tank (3) and the temperature of the outer tank (5) may be measured by measuring the temperature of each connection point with other members in the inner tank (3) and the outer tank (5). With this configuration, the connection state between the inner tank (3), the outer tank (5) and other members can be effectively maintained by adjusting the temperature difference.

[0063] In the cooling down method according to the present 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 (7) inside the inner tank and the space (9) between the inner and outer tanks. With this configuration, the temperature measurement location used for normal operation of the storage tank (1) can be utilized, so the addition of a measuring device, etc., becomes unnecessary.

[0064] According to the warming-up method of the present embodiment, by heating the inner tank (3) with a first heating gas (HG1) and supplying a 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 a value below a predetermined value, thereby suppressing the difference in thermal shrinkage of the constituent members and also shortening the time required for warming up, thereby reducing costs.

[0065] As described above, preferred embodiments of the present disclosure have been explained with reference to the drawings; however, various additions, changes, or deletions are possible without departing from the spirit of the present disclosure. Accordingly, such additions or deletions are also included within the scope of the present disclosure. Explanation of the symbols

[0066] 1: Liquefied gas storage tank 3: Supportive wife 5: Support from the husband 7: Household space 9: Inner and outer space 11: Chimney 29: Sprayer 33: Cooling device CG: Cooling gas CH: Cooling liquefied gas G1: Vaporized gas G2: External hydrogen gas HG1: First heating gas HG2: Second heating gas

Claims

Claim 1 A method for cooling a tank having an inner tank and an outer tank for storing liquefied gas before filling the liquefied gas to be stored, comprising the steps of: introducing a cooling liquefied gas into the space inside the inner tank; supplying the cooling liquefied gas into the space between the inner and outer tanks; and measuring the temperature of the inner tank and the temperature of the outer tank, respectively. A cooling down method for a liquefied gas storage tank, comprising: a step of maintaining the temperature difference below a predetermined value by adjusting at least one of the rate of change of temperature of the inner tank and the rate of change of temperature of the outer tank based on the temperature difference between the temperature of the inner tank and the temperature of the outer tank; wherein the step of measuring the temperature of the inner tank and the temperature of the outer tank, respectively, comprises measuring the temperature at a predetermined location where the representative temperature of the inner tank can be detected and measuring the temperature at a predetermined location where the representative temperature of the outer tank can be detected, and wherein the representative temperature is the average value of the total temperature distribution of the inner tank and the outer tank, respectively. Claim 2 A cooling down method according to claim 1, wherein the step of adjusting at least one of the temperature change rate of the inner tank and the temperature change rate of the outer tank includes adjusting the rate of introduction of the cooling liquefied gas into the space inside the inner tank. Claim 3 A cooling down method according to claim 1 or 2, wherein the step of adjusting at least one of the temperature change rate of the inner tank and the temperature change rate of the outer tank includes adjusting the cooling gas supply rate to the space between the inner and outer tanks. Claim 4 A cooling down method according to claim 1 or 2, wherein the step of measuring the temperature of the inner tank and the temperature of the outer tank, respectively, includes measuring the temperature of a connection point with another member in the inner tank and measuring the temperature of a connection point with another member in the outer tank. Claim 5 A cooling down method according to claim 1 or 2, wherein the step of measuring the temperature of the inner tank and the temperature of the outer tank, respectively, includes measuring the temperature of the space inside the inner tank and measuring the temperature of the space between the inner and outer tanks. Claim 6 A method for warming up a liquefied gas storage tank having an inner tank and an outer tank for storing liquefied gas, wherein the method comprises: a step of introducing a first heating gas into the space within the inner tank; a step of supplying a second heating gas into the space between the inner and outer tanks; a step of measuring the temperature of the inner tank and the temperature of the outer tank, respectively; and a step of maintaining the temperature difference to be less than or equal to a predetermined value by adjusting at least one of the rate of change of temperature of the inner tank and the rate of change of temperature of the outer tank based on the temperature difference between the temperature of the inner tank and the temperature of the outer tank; wherein the step of measuring the temperature of the inner tank and the temperature of the outer tank, respectively, includes measuring the temperature at a predetermined location where the representative temperature of the inner tank can be detected and measuring the temperature at a predetermined location where the representative temperature of the outer tank can be detected, and wherein the representative temperature is the average value of the total temperature distribution of the inner tank and the outer tank, respectively. Claim 7 delete

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