Cooling down methods for liquefied gas storage tanks

Abstract

To reduce the time needed to cool down 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); and supplying a temperature adjustment gas (TG) adjusted to an adjusted temperature range which is a predetermined temperature or higher to a space (9) between the inner and outer tanks through a temperature adjustment device (31).SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Conventionally, as a tank for storing 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 normal-temperature tank, 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").

Prior Art Documents

Patent Documents

[0004] [[ID=2​​​​​​​​​​​​​​​​​​​​​​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, A temperature-controlled gas, adjusted to a controlled temperature range above a predetermined temperature, is supplied to the space between the inner and outer tanks via a temperature control device. Includes. [Effects of the Invention]

[0008] The method for cooling down liquefied gas storage tanks according to this disclosure can shorten the time required to cool down multi-layer heat-insulating tanks for liquefied gas storage, thereby reducing costs. [Brief explanation of the drawing]

[0009] [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 during cooling of the inner tank in a cool-down method according to one modified embodiment of one embodiment of the present disclosure. [Figure 2D] This is a schematic diagram showing the state during cooling of the inner tank in a cool-down method according to another modification of one embodiment of the present disclosure. [Figure 2E] This is a schematic diagram showing the completed state of a cool-down method according to one embodiment of the present disclosure. [Figure 3] This is a schematic cross-sectional view showing an enlarged portion of the liquefied gas storage tank in Figure 1. [Modes for carrying out the invention]

[0010] 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 according to one embodiment of this disclosure is 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.

[0011] 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).

[0012] 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.

[0013] The storage tank 1 is configured as a double-shell 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 to be stored inside (hereinafter referred to as the "inner tank internal space 7") and an inner tank heat-insulating layer that covers the outer surface of the inner tank shell. The outer tank 5 has an outer tank shell that forms an inner-outer tank space 9, which is an insulating layer, between it and the inner tank 3, and an outer tank heat-insulating layer that covers the outer surface of the outer tank shell. Note that the locations where the heat-insulating layers of the inner tank 3 and outer tank 5 are installed are not limited to this example and are arbitrary; for example, the heat-insulating layer may be installed so as to cover the inner surface of the outer tank shell. Also, one or both of the heat-insulating layers of the inner tank 3 and outer tank 5 may be omitted. This storage tank 1 is operated on a steady basis with low-temperature hydrogen gas sealed in the inner-outer tank space 9, which is an insulating layer.

[0014] In this embodiment, a connecting passage 11 is provided that connects the inner tank space 7 and the space between the inner and outer tanks 9. The connecting passage 11 is configured to be openable and closable. Specifically, in the illustrated example, there is a vaporized gas discharge passage 13 that discharges vaporized gas (hereinafter simply referred to as "vaporized gas") G1 of liquefied hydrogen generated in the inner tank space 7 to the outside of the storage tank 1, a hydrogen gas introduction passage 15 that introduces hydrogen gas (hereinafter referred to as "external hydrogen gas") G2 from a hydrogen gas source (not shown) provided outside the storage tank 1 into the space between the inner and outer tanks 9, and a connecting passage 17 that connects the vaporized gas discharge passage 13 and the hydrogen gas introduction passage 15 outside the storage tank 1. The connecting passage 11 is formed by these vaporized gas discharge passage 13, connecting passage 17 and hydrogen gas introduction passage 15. In addition, an on-off valve 19 is provided in the connecting passage 11, and the connecting passage 11 is configured to be openable and closable by this on-off valve 19. In this example, an on-off valve 19 is provided in the portion of the hydrogen gas introduction passage 15 downstream of the connection point with the connecting passage 17, but the position and number of on-off valves 19 are not limited to this example. Furthermore, the on-off valve 19 may be a valve that can be opened and closed manually, or a valve that opens and closes automatically according to a set differential pressure.

[0015] Note that the specific configuration of the communication passage 11 between the inner tank space 7 and the space 9 between the inner and outer tanks, and the specific configuration that enables the communication passage 11 to be opened and closed are not limited to this example. Also, 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.

[0016] In this embodiment, a temperature adjustment device 31 for adjusting the temperature of the gas supplied to the space 9 between the inner and outer tanks is provided in the communication passage 11. Also, in the illustrated example, a device (hereinafter simply referred to as "gas supply device") 33 for forcibly feeding the gas to the space 9 between the inner and outer tanks, such as a compressor, is provided downstream of the temperature adjustment device 31 in the communication passage 11. The gas supply device 33 is a device that moves the gas by applying pressure to the gas, such as a turbo-type or positive-displacement compressor, blower, or fan. In the illustrated example, the temperature adjustment device 31 and the gas supply device 33 are provided in the connection passage 17. Note that in this example, the temperature adjustment device 31 is installed upstream of the gas supply device 33, but the arrangement of the temperature adjustment device 31 is not limited to this example. For example, the temperature adjustment device 31 may be installed downstream of the gas supply device 33, or may be installed on both the upstream and downstream sides. <——

[0017] Further, in the present 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 inter-tank space temperature detection device 25 for detecting the temperature of the inter-tank space 9, and an inter-tank space pressure detection device 27 for detecting the pressure of the inter-tank space 9 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 amount, a memory for storing information necessary for these processes, a power supply element such as a battery, or a power supply circuit for receiving power supply from the outside, a transmission circuit for transmitting the output signal to the outside by wire or wirelessly, and the like. In addition, as such a temperature detection device and pressure detection device, a device for measuring parts other than the above, for example, an inner tank temperature detection device or an outer tank temperature detection device may be provided. Further, only those necessary according to the implementation mode of the cooling method described later may be provided for these temperature detection devices and pressure detection devices.

[0018] The cooling method of the storage tank 1 configured as described above will be described in detail below.

[0019] In the present embodiment, in the storage tank 1 in the initial state when starting the cooling shown in FIG. 2A, the on-off valve 19 of the communication passage 11 is in an open state, and in both the inner tank internal space 7 and the inter-tank space 9, for example, hydrogen gas at normal temperature and atmospheric pressure (0 kPaG) exists. However, the temperature and pressure of the hydrogen gas in the initial state are not limited to normal temperature and atmospheric pressure. From this state, as shown in FIG. 2B, liquefied hydrogen for cooling (hereinafter, simply referred to as "cooling hydrogen") CH is introduced into the inner tank internal space 7. In this example, a sprayer 29 is used to spray the cooling hydrogen CH into the inner tank internal space 7.

[0020] 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.

[0021] As the cooldown progresses, the vaporized hydrogen gas G1 may reach extremely low temperatures of approximately 20K. Therefore, it is preferable to avoid localized rapid cooling of the inner tank 3 and outer tank 5, which form the space between the inner and outer tanks 9, by the extremely low-temperature vaporized gas G1. Furthermore, since the set temperature of the outer tank 5 during steady-state operation is higher than the set temperature of the inner tank 3, the design temperature of the outer tank 5 is higher than the design temperature of the inner tank 3. Therefore, it is preferable to ensure that the temperature of the outer tank 5 does not fall below the design temperature even during the cooldown. Accordingly, in this embodiment, after the introduction of the cooling gas CH is started, a temperature-controlled gas TG, adjusted to a controlled temperature range of a predetermined temperature or higher, is supplied to the space between the inner and outer tanks 9 via the temperature control device 31. Specifically, the vaporized gas G1 is supplied to the space between the inner and outer tanks 9 as a temperature-controlled gas TG via the temperature control device 31.

[0022] More specifically, in this embodiment, when the temperature of the vaporized gas G1 is below a predetermined temperature, the vaporized gas G1 is supplied to the space between the inner and outer tanks 9 as a temperature-regulating gas TG. Specifically, the vaporized gas G1 is heated by the temperature-regulating device 31 to a temperature above the predetermined temperature. On the other hand, when the temperature of the vaporized gas G1 exceeds the predetermined temperature, the vaporized gas G1 is supplied directly to the space between the inner and outer tanks 9. For example, when the cooling of the inner tank 3 has not progressed, the vaporized gas G1 is relatively hot, so the vaporized gas G1 is supplied directly to the space between the inner and outer tanks 9. When the cooling of the inner tank 3 has progressed, the temperature of the vaporized gas G1 decreases, so the vaporized gas G1 is heated by the temperature-regulating device 31.

[0023] Here, "supplying vaporized gas directly to the space between the inner and outer tanks" means supplying vaporized gas G1 to the space between the inner and outer tanks 9 without forcibly adjusting its temperature. That is, for example, the vaporized gas G1 may be passed through the temperature control device 31 with the temperature control function of the temperature control device 31 turned off, or, as shown in Figure 2C, a bypass passage 35 that bypasses the temperature control device 31 and a flow path switching device 37 may be provided in the communication passage 11 so that the vaporized gas G1 passes through the bypass passage 35. In the example shown in the figure, the bypass passage 35 is provided to bypass the temperature control device 31 and the gas supply device 33, but the bypass passage 35 may also be provided to bypass the temperature control device 31 and pass through the gas supply device 33.

[0024] The temperature-regulating gas TG may be supplied to the space between the inner and outer tanks 9 by force using a gas supply device 33. In this case, the temperature-regulating gas TG supplied to the space between the inner and outer tanks 9 is discharged to the outside of the storage tank 1, for example, via a discharge passage 39. The discharge passage 39 has an inlet near the bottom of the space between the inner and outer tanks 9, passes through the space between the inner and outer tanks 9, and discharges the cooling gas CG to the outside of the storage tank 1 from an outlet located at the top of the space between the inner and outer tanks 9, for example, near the top. A gas compressor or exhaust pump for discharge may be appropriately installed in the discharge passage 39.

[0025] The space between the inner and outer tanks 9 may be provided with upper and lower safety valves to prevent the pressure in the storage tank 1 from exceeding an acceptable range. Furthermore, the control device may control the gas supply device 33, the discharge passage 39, the on-off valve 19, etc., thereby controlling the gas supply to the space between the inner and outer tanks 9 and the exhaust from the space between the inner and outer tanks 9 according to the pressure.

[0026] Instead of supplying vaporized gas G1, or in addition to it, external hydrogen gas G2 may be supplied from the hydrogen gas introduction passage 15 to the space between the inner and outer tanks 9 as temperature control gas TG. In this case, as shown as a modified example in Figure 2D, a temperature control device 31 may be provided on the hydrogen gas introduction passage 15, and a bypass passage 15a may be provided for when the temperature control device 31 is not used. Also, when supplying external hydrogen gas G2 to the space between the inner and outer tanks 9 as temperature control gas TG, the supply of temperature control gas TG may be started before the introduction of cooling hydrogen CH into the inner tank space 7 begins.

[0027] In this embodiment, the "predetermined temperature" is the set temperature (for example, 110K) of the space between the inner and outer tanks 9 during steady-state operation of the storage tank 1. The "adjustable temperature range" is set to a range that does not hinder the cooling of the space between the inner and outer tanks 9, for example, 110K or more and 120K or less. The temperature of the vaporized gas G1 used as the reference for temperature adjustment may be the value obtained by directly measuring the temperature of the vaporized gas G1 flowing through the communication passage 11, or the value obtained by measuring the temperature of the inner tank 3 may be used.

[0028] Furthermore, if the temperature of the vaporized gas G1 and / or external hydrogen gas G2 introduced into the space 9 between the inner and outer tanks is not sufficiently low, the temperature difference between the inner and outer tanks may become too large during the cool-down process, resulting in an excessive difference in the amount of thermal contraction of the constituent materials. To avoid this, the cooling rate of the outer tank 5 may be adjusted by adjusting the temperature of the temperature-regulating gas TG and the flow rate of the temperature-regulating gas TG using the temperature control device 31, so that the temperature difference between the inner tank 3 and the outer tank 5 remains below a predetermined value during the cool-down process. The predetermined value of the temperature difference between the inner tank 3 and the outer tank 5 is, for example, the value set as the temperature difference at the start of normal operation of the storage tank.

[0029] The temperature control device 31 used in this embodiment may be any device that has the function of adjusting the temperature of the liquefied gas. For example, the temperature control device 31 includes a temperature sensor for detecting the gas temperature, an electrically driven heater, a switch for turning the heater on and off, and a control circuit for controlling these. However, the temperature control device 31 may be a device with a configuration other than that described above, such as a heat exchanger or a device that adjusts the temperature by mixing gases of different temperatures.

[0030] In this embodiment, an example was described 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. However, the timing of opening the communication passage 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, for example, when the pressure in the space between the inner and outer tanks 9 falls below a predetermined value. At that time, vaporized gas G1 may be supplied to the space between the inner and outer tanks 9 as temperature adjustment gas TG.

[0031] In this way, by cooling the inner tank 3 with cooling hydrogen CH while supplying temperature-controlled gas TG to the space between the inner and outer tanks 9, the inner tank 3 and the outer tank 5 are rapidly cooled locally, and the cooling of the space between the inner and outer tanks 9 and the outer tank 5 is promoted while avoiding the temperature of the outer tank 5 falling below the design temperature. Therefore, the time required to cool down the entire storage tank 1 can be shortened and costs reduced compared to simply cooling the inner tank 3 alone.

[0032] Subsequently, as shown in Figure 2E, 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.

[0033] In this embodiment, as shown in Figure 1, a deflection plate 41 is provided to deflect the temperature-regulating gas TG introduced into the space 9 between the inner and outer tanks. Specifically, as shown in Figure 3, the deflection plate 41 is positioned opposite the supply port 43 for the temperature-regulating gas TG in the space 9 between the inner and outer tanks, and is arranged approximately perpendicular to the direction of outflow of the temperature-regulating gas TG. The deflection plate 41 is supported at a distance from the outer surface of the inner tank 3 or the inner surface of the outer tank 5 via a support member (not shown) protruding from the outer surface of the inner tank 3 or the inner surface of the outer tank 5. The temperature-regulating gas TG flowing out from the supply port 43 collides with the deflection plate 41, is dispersed in various directions along the surface of the deflection plate 41, and then diffuses into the space 9 between the inner and outer tanks. In this way, by providing the deflection plate 41, it is prevented that the temperature-regulating gas TG flowing out from the supply port 43 concentrates on and collides with a part of the inner tank 3 or the outer tank 5 that constitutes the storage tank 1, and that part is cooled locally. The number of supply ports 43 to the space between the inner and outer tanks 9 is not limited to the one shown in the figure, but may be multiple. If there are multiple supply ports 43, the deflection plates 41 may be provided for all or some of the supply ports 43. The shape of the deflection plates 41 is not limited to the flat plate shape shown in the example, as long as it can disperse the temperature control gas TG that flows out from the supply ports 43. However, the deflection plates 41 may be omitted. Also, the gas blown onto the deflection plates 41 is not limited to the cooling gas CG, but may be any gas of any temperature introduced into the space between the inner and outer tanks 9.

[0034] 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.

[0035] 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 method according to this embodiment is not limited to this example and can be applied to any type of storage tank. For example, the cool-down method according to this embodiment can also be applied to a 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 method 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.

[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] According to the cool-down method of this embodiment described above, by supplying temperature-controlled gas TG to the space between the inner and outer tanks 9 while cooling the inner tank 3 with cooling hydrogen CH, the inner tank 3 and the outer tank 5 are rapidly cooled locally, and the cooling of the space between the inner and outer tanks 9 and the outer tank 5 is promoted while avoiding the temperature of the outer tank 5 falling below the design temperature. Therefore, the time required to cool down the entire storage tank 1 can be shortened and costs can be reduced compared to simply cooling the inner tank 3 alone.

[0038] In the cool-down method according to this embodiment, the vaporized gas generated in the inner tank space may be introduced into the temperature control device 31 and supplied to the space between the inner and outer tanks 9 as the temperature control gas TG. This allows for the supply of temperature control gas TG to the space between the inner and outer tanks 9 at a low cost using a simple structure and by utilizing the liquefied cooling gas.

[0039] In the cool-down method according to this embodiment, if the temperature of the vaporized gas G1 is below the predetermined temperature, the vaporized gas G1 may be supplied to the space 9 between the inner and outer tanks as a temperature-regulating gas TG. This prevents the inner tank 3 and the outer tank 5 from being excessively cooled, for example, to a set temperature in design.

[0040] In the cool-down method according to this embodiment, a deflection plate may be provided in the space 9 between the inner and outer tanks, and the temperature-regulating gas TG may be injected toward the deflection plate. With this configuration, the temperature-regulating gas TG is prevented from concentrating and colliding with a part of the inner tank 3 or outer tank 5 that constitute the storage tank 1, thereby preventing localized cooling of that part.

[0041] 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]

[0042] 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 31 Temperature adjustment device 41 Deflection plate CH4 liquefied gas for cooling G1 Vaporized gas G2 External hydrogen gas TG temperature control 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, A temperature-controlled gas, adjusted to a controlled temperature range above a predetermined temperature, is supplied to the space between the inner and outer tanks via a temperature control device. Includes, The supply of the temperature-regulating gas includes introducing the vaporized gas generated in the inner tank space into the temperature-regulating device and supplying it as the temperature-regulating gas to the space between the inner and outer tanks, When the temperature of the vaporized gas is below the predetermined temperature, the vaporized gas is supplied to the space between the inner and outer tanks as the temperature-regulating gas. Methods for cooling down liquefied gas storage tanks.

2. In the cool-down method described in claim 1, This includes providing a deflection plate in the space between the inner and outer tanks and injecting the temperature control gas toward the deflection plate. Cool-down methods.

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