Cooling down methods for liquefied gas storage tanks

Abstract

To inhibit pressure drop of a space between inner and outer tanks in cooling down of a multiple heat-insulating structure tank for storage of a liquefied gas to maintain soundness of a tank structure.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 the liquefied gas to a space (9) between the inner and outer tanks if a pressure of the space (9) between the inner and outer tanks becomes a predetermined value or lower after introduction of the cooling liquefied gas (CH) starts.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Conventionally, as a tank for storing a liquefied gas, for example, a 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 once into the tank at room temperature, before filling the liquefied gas to be stored, the tank is pre-cooled at a relatively low speed (hereinafter referred to as "cooling down").

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the case of a tank having a multi-layer heat insulation structure such as a double-walled tank for liquefied gas, when the inner tank is cooled, the inner tank thermally contracts, so that the volume of the space between the inner and outer tanks relatively increases. Further, as the inner tank is cooled, the temperature of the space between the inner and outer tanks decreases. As a result, when the space between the inner and outer tanks is closed, the pressure in the space between the inner and outer tanks decreases, and if this pressure decrease becomes excessive, a large pressure is applied to the tank structure, and the soundness of the tank structure cannot be maintained.

[0006] An object of the present disclosure is to suppress a pressure decrease in the space between the inner and outer tanks during cooling of a multi-layer heat insulation structure tank for storing a liquefied gas and to maintain the soundness of the tank structure in order to solve the above 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, After the introduction of the liquefied cooling gas is started, if the pressure in the space between the inner and outer tanks falls below a predetermined value, the liquefied gas is supplied to the space between the inner and outer tanks. Includes. [Effects of the Invention]

[0008] According to the cooling method for liquefied gas storage tanks described herein, it is possible to suppress the pressure drop in the space between the inner and outer tanks during the cooling down of a multi-layer heat-insulating tank for liquefied gas storage, thereby maintaining the integrity of the tank structure. [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 one state during the 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 another state during the cooling of the inner tank in a cool-down method according to 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 one modified embodiment of one embodiment of the present disclosure. [Figure 2E] 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 2F]This is a schematic diagram showing the completed state of a cool-down method according to one embodiment of the present disclosure. [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 hydrogen 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 this on-off valve 19 is configured to open and close. The passage 11 is configured to be openable and closable. 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 inner space 7 and the space 9 between the inner and outer tanks, and the specific configuration that enables 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 source of hydrogen gas supply. 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] Also, in this 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 sensor elements for detecting the physical quantities (temperature, pressure) of the detection targets, various circuits for performing necessary processes such as signal conversion processing and arithmetic processing on the acquired detection amounts, 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, a transmission circuit for transmitting the output signal to the outside by wire or wirelessly, and the like. Note that as such temperature detection devices and pressure detection devices, devices 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.

[0017] The cooling method of the storage tank 1 configured as described above will be described in detail below.

[0018] In this embodiment, in the storage tank 1 in the initial state when starting the cooldown shown in FIG. 2A, the on-off valve 19 of the communication passage 11 is in the closed state, and in both the inner tank internal space 7 and the space 9 between the inner and outer tanks, for example, hydrogen gas at room temperature and atmospheric pressure (0 kPaG) exists. 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 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, the cooling hydrogen CH is sprayed into the inner tank internal space 7 using the sprayer 29.

[0019] [[ID=?]] By continuing to spray the cooling hydrogen CH in this state, the temperature of the inner tank 3 decreases. As the temperature of the inner tank 3 decreases, the space 9 between the inner and outer tanks is cooled by the cooling heat transmitted from the inner tank internal space 7 through the inner tank wall surface, and the temperature of the space 9 between the inner and outer tanks also decreases. Further, in the inner tank internal space 7, heat shrinkage associated with the cooling of the inner tank 3 and vaporization gas G1 generated by the vaporization of the cooling hydrogen CH are generated, and the pressure increases. On the other hand, in the space 9 between the inner and outer tanks, the pressure decreases due to the relatively increased volume due to the heat shrinkage of the inner tank 3 and the temperature decrease.

[0020] In this way, by closing the communication passage 11 at the initial stage of the cooldown and reducing the pressure in the space 9 between the inner and outer tanks, if the pressure in the space 9 between the inner and outer tanks is lower than the saturated vapor pressure in the inner tank 3 when the temperature in the inner tank internal space 7 reaches the liquefied gas temperature, condensation of the hydrogen gas in the space 9 between the inner and outer tanks can be prevented. On the other hand, an excessive decrease in the pressure in the space 9 between the inner and outer tanks is not preferable from the viewpoint of the soundness of the tank structure.

[0021] Therefore, in this embodiment, after starting the introduction of the liquefied hydrogen CH for cooling, when the pressure in the space 9 between the inner and outer tanks becomes equal to or lower than a predetermined value (hereinafter, this pressure is referred to as "first predetermined pressure"), as shown in FIG. 2C, a liquefied gas or a vaporization gas of the liquefied gas is introduced into the space 9 between the inner and outer tanks. In this example Hydrogen is supplied. Specifically, the connecting passage 11 is opened by opening the on / off valve 19 of the connecting passage 11. By opening the connecting passage 11, 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. The above first predetermined pressure is set based on the minimum allowable pressure of the space between the inner and outer tanks 9, taking into account the mechanical strength of the inner tank 3 and the outer tank 5, and is, for example, -20 kPaG.

[0022] Furthermore, while the inner tank 3 is being cooled with the connecting passage 11 open, if the pressure in the space between the inner and outer tanks 9 does not rise to a predetermined value, or 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, a device 31 for forcibly supplying hydrogen gas to the space between the inner and outer tanks 9 (hereinafter simply referred to as a "gas supply device") may be provided on the connecting passage 11, for example in the connecting passage 17, and the vaporized gas G1 from the inner tank space 7 may be supplied to the space between the inner and outer tanks 9 by this gas supply device 31. The gas supply device 31 is a device that moves gas by applying pressure to it, such as a turbo-type or positive displacement compressor, blower, or fan. 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 this case, as shown in Figure 2D as a modified example, the gas supply device 31 may be installed on the hydrogen gas introduction passage 15, and a bypass passage 15a may be provided for when the gas supply device 31 is not used.

[0023] Furthermore, if the pressure in the space between the inner and outer tanks 9 is excessively high, the hydrogen gas in the space between the inner and outer tanks 9 may be exhausted using an exhaust device 33, as shown in the modified example in Figure 2E. This exhaust device 33 can be installed on a specially provided exhaust passage 35, as shown in the same figure. However, the installation method of the exhaust device 33 is not limited to this example, and it may be installed, for example, in the middle of the hydrogen gas introduction passage 15. The "predetermined range" of the pressure difference between the inner tank space 7 and the space between the inner and outer tanks 9 is determined, for example, based on the set pressure of the safety valve installed in the inner tank 3. Note that it is not essential to install the exhaust device 33 in the exhaust passage 35. For example, if the pressure in the inner tank space 7 is kept higher than atmospheric pressure, the gas in the space between the inner and outer tanks 9 can be discharged only through the exhaust passage 35.

[0024] In this way, by cooling the inner tank 3 with cooling hydrogen CH and supplying hydrogen 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, the supply of hydrogen gas suppresses excessive pressure drops in the space between the inner and outer tanks 9, making it easier to maintain the minimum allowable pressure in the space between the inner and outer tanks 9, taking into account the mechanical strength of the inner tank 3 and the outer tank 5. This helps to maintain the integrity of the tank structure. Note that the substance supplied to the space between the inner and outer tanks 9 is not limited to the example of vaporized hydrogen gas G1, but may also be liquefied hydrogen.

[0025] Furthermore, if the temperature of the vaporized gas G1 and / or external hydrogen gas G2 introduced into the space between the inner and outer tanks 9 is not low enough to cool the space between the inner and outer tanks 9 to a first predetermined temperature, or if it is excessively low, a temperature control device (not shown) may be provided on the communication passage 11 (for example, the hydrogen gas introduction passage 15), and hydrogen gas whose temperature has been adjusted to approximately the first predetermined temperature using this temperature control device may be introduced into the space between the inner and outer tanks 9.

[0026] Subsequently, if the pressure in the space between the inner and outer tanks 9 rises to a predetermined value, or if the temperature in the space between the inner and outer tanks 9 falls to a predetermined value, the on-off valve 19 may be closed, closing the communication passage 11 and stopping the supply of hydrogen gas to the space between the inner and outer tanks 9. By stopping the supply of hydrogen gas in this way, it is prevented that the pressure in the space between the inner and outer tanks 9 rises excessively and the temperature falls excessively, thereby preventing the condensation of hydrogen gas in the space between the inner and outer tanks 9, especially in the area near the inner tank 3. Even after the communication passage 11 has been closed, the supply of hydrogen gas may be restarted depending on the state of the space between the inner and outer tanks 9.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] According to the cool-down method of this embodiment described above, by cooling the inner tank 3 with liquefied hydrogen and supplying hydrogen gas to the space between the inner and outer tanks 9 as needed, the low-temperature vaporized gas G1 generated in the inner tank's internal space 7 is introduced into the space between the inner and outer tanks 9 as the pressure in the space between the inner and outer tanks 9 decreases. This promotes the cooling of the space between the inner and outer tanks 9 and the outer tank 5, thus shortening the time required to cool down the entire storage tank 1 and reducing costs compared to simply cooling only the inner tank 3. Furthermore, since the supply of hydrogen gas suppresses the pressure drop in the space between the inner and outer tanks 9, it becomes easier to maintain the minimum allowable pressure in the space between the inner and outer tanks 9, taking into account the mechanical strength of the inner tank 3 and the outer tank 5, and thus maintaining the integrity of the tank structure.

[0032] In the cool-down method according to this embodiment, the hydrogen gas supply may be performed by supplying vaporized gas G1 generated in the inner tank space 7 by opening the communication passage 11 between the space between the inner and outer tanks 9 and the space inside the inner tank 7. This makes it possible to supply hydrogen gas to the space between the inner and outer tanks 9 with a simple structure and at low cost by utilizing the cooling hydrogen.

[0033] In the cool-down method according to this embodiment, after supplying hydrogen gas to the space between the inner and outer tanks 9, the supply of hydrogen gas may be stopped if the pressure in the space between the inner and outer tanks 9 rises to a predetermined value, or if the temperature in the space between the inner and outer tanks 9 falls to a predetermined value. This prevents the pressure in the space between the inner and outer tanks 9 from rising excessively and the temperature from falling excessively, thus preventing the inner and outer tanks from rising excessively and falling excessively. Condensation of hydrogen gas in the intervening space 9 is prevented.

[0034] 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]

[0035] 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 Gas supply equipment CH4 liquefied gas for cooling G1 Vaporized gas G2 External hydrogen 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, After the introduction of the liquefied cooling gas begins, if the pressure in the space between the inner and outer tanks falls below a predetermined value, the liquefied gas, the vaporized gas of the liquefied gas, or hydrogen gas from a hydrogen gas source located outside the tank is supplied to the space between the inner and outer tanks. A temperature control device provided in the communication passage between the space between the inner and outer tanks and the space inside the inner tank adjusts the vaporized gas of the liquefied gas and / or the hydrogen gas to a predetermined temperature. including, Methods for cooling down liquefied gas storage tanks.

2. In the cool-down method described in claim 1, If, after supplying the liquefied gas, the vaporized gas of the liquefied gas, or the hydrogen gas to the space between the inner and outer tanks, the pressure in the space between the inner and outer tanks rises to a predetermined value, or the temperature in the space between the inner and outer tanks falls to a predetermined value, the supply of the liquefied gas or the vaporized gas of the liquefied gas is stopped. Cool-down methods.

3. In the cool-down method according to claim 1 or 2, Supplying the liquefied gas, the vaporized gas of the liquefied gas, or the hydrogen gas to the space between the inner and outer tanks includes supplying the vaporized gas generated in the inner tank space by opening the communication passage. Cool-down methods.

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