Liquefied gas storage tank

Abstract

A tank (1) that stores a liquefied gas (LG) comprises: a tank body (3) that is provided with an inner vessel (11) forming, to the inside thereof, a storage space for the liquefied gas (LG), and an outer vessel (13) covering the inner vessel (11) and forming a space between the outer vessel (13) and the inner vessel (11), said space being filled with a gas (BG) that results from vaporization of the liquefied gas (LG); a communication passage (5) that communicates a space (15) in the inner vessel and a space (17) between the inner and outer vessels; a first valve (7) that is provided in the communication passage (5), and is set so as to open when the pressure of the space (17) between the inner and outer vessels has fallen to a prescribed value, or when the difference between said pressure and the pressure of the space (15) in the inner vessel has fallen to a prescribed value; and a second valve (9) that is provided in the communication passage (5) in series with the first valve (7), and is configured so as to be able to open and close the communication passage (5).

Description

Liquefied Gas Storage Tank

[0001] The present disclosure relates to liquefied gas storage tanks.

[0002] Conventionally, double-shell tanks having an inner tank and an outer tank have been proposed as tanks for storing liquefied gas, such as cryogenic liquefied hydrogen. In double-shell tanks, high thermal insulation can be achieved by providing a space (inter-tank space) outside the inner tank in which the liquefied gas is stored. The inter-tank space is generally a vacuum layer. However, this makes it difficult to manage in actual operation, such as maintaining a vacuum level when storing liquefied gas for a long period of time, and requires a high level of strength for the outer tank. Therefore, it has been proposed to introduce vaporized liquefied gas into the inter-tank space by, for example, connecting the space within the inner tank with the inter-tank space (see, for example, Patent Document 1).

[0003] International Publication No. 2020 / 202578

[0004] However, when vaporized gas is introduced into the space between the inner and outer tanks, the pressure in the space between the inner and outer tanks may rise excessively and exceed the saturated vapor pressure at the temperature of the space inside the inner tank, which may cause condensation of the gas near the wall surface of the inner tank. To prevent this, it is necessary to prevent excessive inflow of vaporized gas from the space inside the inner tank into the space between the inner and outer tanks.

[0005] The object of the present disclosure is to solve the above-mentioned problem by reliably blocking communication between the space within the inner tank and the space between the inner and outer tanks as necessary in a liquefied gas storage tank having a double structure.

[0006] In order to achieve the above object, the liquefied gas storage tank according to the present disclosure is a tank for storing liquefied gas, comprising: a tank body including an inner tank that forms a storage space for the liquefied gas inside, and an outer tank that covers the inner tank and forms an insulating layer between the inner tank and the outer tank, and in which the liquefied gas is filled; a communication passage that communicates the space inside the inner tank with the space between the inner and outer tanks; a first valve that is provided in the communication passage and is set to open when the pressure in the space between the inner and outer tanks drops to a predetermined value or when the difference in pressure with the space inside the inner tank drops to a predetermined value; and a second valve that is provided in the communication passage in series with the first valve and is configured to be able to open and close the communication passage.

[0007] Any combination of at least two features disclosed in the claims and / or the specification and / or the drawings is included in the present disclosure. In particular, any combination of two or more of the claims is included in the present disclosure.

[0008] The present disclosure will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are merely for illustration and explanation purposes and should not be used to define the scope of the present disclosure. The scope of the present disclosure is defined by the appended claims. In the accompanying drawings, the same reference numerals in multiple drawings indicate the same or corresponding parts. Fig. 1 is a schematic diagram showing an example of a liquefied gas storage tank according to an embodiment of the present disclosure. Fig. 2 is a schematic diagram showing an enlarged portion of the liquefied gas storage tank of Fig. 1, illustrating one mode of use of the tank. Fig. 3 is a schematic diagram showing an enlarged portion of the liquefied gas storage tank of Fig. 1, illustrating another mode of use of the tank.

[0009] A preferred embodiment of the present disclosure will be described below with reference to the drawings. Figure 1 shows a liquefied gas storage tank (hereinafter simply referred to as "tank") 1 according to one embodiment of the present disclosure. The tank 1 includes a tank body 3 that stores liquefied gas LG, a communication passage 5, a first valve 7, and a second valve 9, which will be described later.

[0010] In the illustrated example, the tank 1 is installed on a ship S, such as a liquefied gas storage ship. In this specification, the term "liquefied gas storage ship" refers to a ship that has the function of storing liquefied gas LG. The liquefied gas storage ship in this embodiment is a liquefied gas carrier. In addition to liquefied gas carriers, liquefied gas storage ships also include, for example, liquefied gas fuel ships and bunkering ships that supply liquefied gas to other ships. However, the tank 1 according to the present disclosure may also be installed in liquefied gas storage facilities other than ships, such as land-based liquefied gas storage facilities or plants that use liquefied gas.

[0011] The liquefied gas LG stored in the tank 1 is, for example, liquefied ammonia (LNH ３ , about -33°C), liquefied petroleum gas (LPG, about -45°C), liquefied ethylene gas (LEG, about -100°C), liquefied natural gas (LNG, about -160°C), liquefied hydrogen (LH2, about -250°C), and liquefied helium (LHe, about -270°C). In this embodiment, liquefied hydrogen is stored in tank 1.

[0012] The tank 1 is configured as a double-shell tank having an inner tank 11 and an outer tank 13. Specifically, the tank body 3 includes the inner tank 11, which defines a storage space 15 for liquefied gas LG (hereinafter referred to as the "inner tank space") inside, and the outer tank 13, which covers the inner tank 11 and defines a space 17 between the inner tank 11 and the outer tank 13, in which vaporized liquefied gas LG is filled (hereinafter referred to as the "inter-tank space") 17. The outer peripheries of the inner tank 11 and the outer tank 13 may each be covered with a heat insulating layer. This tank 1 is normally operated with vaporized liquefied gas sealed in the inter-tank space 17, which is an insulating layer.

[0013] In this embodiment, the tank body 3 has a main body portion 3a that stores the liquefied gas LG, and a dome portion 3b that protrudes upward from the main body portion 3a. In this example, the main body portion 3a is covered by a tank cover 23 that is part of the hull 21 of the ship S. An opening is formed in the top wall of the tank cover 23, through which the dome portion 3b is inserted. The dome portion 3b protrudes above the tank cover 23, i.e., is exposed, through the opening in the tank cover 23.

[0014] The dome portion 3b has a cylindrical sidewall 25 extending substantially vertically, and a substantially hemispherical lid 27 that closes the upper opening of the sidewall 25. Various types of piping, such as a plurality of transport pipes 29 for transporting (loading and unloading) the liquefied gas LG to and from the tank 1, are attached to the dome portion 3b. For simplification, only one transport pipe 29 is shown in the figure. In this embodiment, the transport pipe 29 passes through the lid 27 of the dome portion 3b in a substantially vertical direction.

[0015] In addition, the figure shows the above-mentioned transport pipe 29 as an example of a pipe that penetrates the dome portion 3b and extends to the outside of the tank 1, but such pipes include various types of pipes, such as a transport pipe for vaporized gas.

[0016] In this embodiment, a communication passage 5 is provided to communicate the inner tank space 15 with the inner-outer tank space 17. Vaporized gas BG of liquefied gas LG generated in the inner tank space 15 is introduced into the inner-outer tank space 17 at an appropriate timing via the communication passage 5. Although not shown, a gas introduction passage for introducing vaporized gas BG from an external liquefied gas source into the inner-outer tank space 17 may be provided connected to the communication passage 5 or independently of the communication passage 5.

[0017] In this embodiment, a first valve 7 is provided in the communicating passage 5. The first valve 7 is set to open when the pressure in the inner-outer tank space 17 drops to a predetermined value (hereinafter referred to as the "first predetermined pressure value") or when the difference between the pressure in the inner tank section 15 and the inner tank space 17 drops to a predetermined value (hereinafter referred to as the "first predetermined pressure difference"). Specifically, in the illustrated example, a safety valve is used as the first valve 7, which is set to automatically open when the pressure is equal to or greater than the first predetermined pressure difference. The first valve 7 is configured to open when the pressure in the inner-outer tank space 17 reaches the first predetermined pressure difference, and then close when the pressure in the inner-outer tank space 17 rises to a predetermined pressure difference (hereinafter referred to as the "second predetermined pressure difference") or less relative to the pressure in the inner tank space 15.

[0018] In this embodiment, a second valve 9, separate from the first valve 7, is further provided in series with the first valve 7 on the communicating passage 5. The second valve 9 is configured as a valve that can open and close the communicating passage 5. The second valve 9 is provided for the purpose of closing the communicating passage 5 when, after the first valve 7 has opened, the pressure in the inner-tank space 15 has decreased to a second predetermined pressure difference or less with respect to the pressure in the inner-outer-tank space 17, but the first valve 7 does not close.

[0019] Specifically, in this embodiment, the second valve 9 is configured as a remotely controlled valve. The remotely controlled valve may be any type of valve that is electrically opened and closed by a control signal, such as an electric valve, a solenoid valve, or a diaphragm-operated valve. By using a remotely controlled valve as the second valve 9, the second valve 9 can be closed in a short time after it is detected that the first valve 7 is not closed when it should be. However, the second valve 9 does not have to be a remotely controlled valve. In other words, the second valve 9 may be a valve that can be closed by direct operation.

[0020] In this example, the second valve 9 is provided on the primary side of the first valve 7. With this configuration, the second valve 9 is closed upstream of the first valve 7, so that communication between the inner tank space 15 and the inner-outer tank space 17 can be more reliably blocked. However, the second valve 9 may also be provided on the secondary side of the first valve 7. In the illustrated example, only one second valve 9 is provided, but multiple second valves 9 may also be provided. In that case, the second valve 9 may be provided on both the primary side and the secondary side of the first valve 7. In addition, multiple communication passages 5 and multiple first valves 7 may also be provided.

[0021] In this embodiment, a gas exhaust path 31 is provided to exhaust gas in the space between the inner and outer tanks 17 to the outside of the tank 1. The gas exhaust path 31 is provided with a third valve 33 that is set to open when the pressure reaches a predetermined level or higher. The third valve 33 is configured as a safety valve that automatically opens when the pressure reaches a predetermined level or higher. By providing the third valve 33 in the gas exhaust path 31, it is possible to prevent the pressure in the space between the inner and outer tanks 17 from becoming excessive. However, the third valve 33 may be omitted.

[0022] As shown in FIG. 1 , in this embodiment, the tank 1 includes an inner tank space pressure detector 35 for detecting the pressure in the inner tank space 15, an inner-external tank space pressure detector 37 for detecting the pressure in the inner-external tank space 17, an inner tank space temperature detector 39 for detecting the temperature in the inner tank space 15, and an inner-external tank space temperature detector 41 for detecting the temperature in the inner-external tank space 17. These detectors include a sensor element for detecting the physical quantity (pressure, temperature) to be detected, various circuits for performing necessary processing such as signal conversion and arithmetic processing on the acquired detected quantity, memory for storing information necessary for these processing, a power supply element such as a battery or a power supply circuit for receiving power from an external source, and a transmission circuit for transmitting output signals to the outside via wired or wireless communication. In addition to these detectors, the tank 1 may be provided with various other detectors necessary for the operation of the tank 1. Furthermore, the detectors 35, 37, 39, and 41 illustrated above are not required; only those necessary for the operation of the tank 1 may be provided.

[0023] By providing the second valve 9, after the first valve 7 is opened as shown in FIG. 2A , the vaporized gas BG in the inner tank space 15 flows into the inner-outer tank space 17, causing the pressure in the inner-outer tank space 17 to rise to or below the second predetermined pressure difference relative to the pressure in the inner tank space 15, and the communicating passage 5 remains open even when it should not be closed or when an attempt to close it manually fails to do so. In such a case, the second valve 9 can close the communicating passage 5 as shown in FIG. 2B , thereby preventing the pressure in the inner-outer tank space 17 from excessively rising above the predetermined operating pressure.

[0024] If the pressure in the space between the inner and outer tanks 17 rises excessively, the pressure in the space between the inner and outer tanks 17 may exceed the saturated vapor pressure at the temperature of the space within the inner tank 15, potentially causing gas condensation near the wall of the inner tank 11 in the space between the inner and outer tanks 17. This may result in a decrease in the insulating performance of the space between the inner and outer tanks 17 or in condensation of gas around the outer tank 13 due to a drop in the temperature of the outer tank 13. Furthermore, in the present embodiment, when the third valve 33 is provided in the gas discharge path 31 of the space between the inner and outer tanks 17, if the communicating passage 5 remains open as shown in FIG. 2A , the pressure in the space between the inner and outer tanks 17 may reach the operating pressure of the third valve 33, potentially causing vaporized gas BG to continue to be released to the outside via the third valve 33. Closing the communicating passage 5 using the second valve 9 can avoid this situation, as shown in FIG. 2B .

[0025] In this embodiment, the first valve 7 and the second valve 9 are located above the base end 3ba of the dome portion 3b, i.e., above the boundary between the main body portion 3a and the dome portion 3b. More specifically, in this embodiment, the first valve 7 and the second valve 9 are located to the side of the dome portion 3b.

[0026] Specifically, in this example, a portion of the communicating pipe forming the communicating passage 5 is exposed to the outside of the dome portion 3b from the sidewall 25 of the portion of the dome portion 3b that protrudes upward from the tank cover 23. The first valve 7 and the second valve 9 are provided in this exposed portion of the communicating passage 5 located on the side of the dome portion 3b. As described above, the transport pipe 29 for the liquefied gas LG penetrates upward from the cover 27 of the dome portion 3b. This is because it is preferable to efficiently arrange the piping and piping accessories such as various valves in the limited space of the dome portion 3b, to arrange piping with a pipe diameter necessary to transport the liquefied gas LG, which is the cargo of the tank 1, within the required loading and unloading time, and to simplify the piping structure as much as possible. In this case, by arranging the communicating passage 5 and the various valves provided in the communicating passage 5 on the side of the dome portion 3b, the piping above the tank 1 can be efficiently arranged. Although it is not essential to arrange the first valve 7 and the second valve 9 in this manner, it is preferable that at least one of the first valve 7 and the second valve 9 be located to the side of the dome portion 3b.

[0027] The locations of the first valve 7 and the second valve 9 are not limited to the examples described above. For example, one or both of the first valve 7 and the second valve 9 may be located above the dome portion 3b, or may be located below the base end 3ba of the dome portion 3b.

[0028] In this embodiment, the third valve 33 is also located above the base end 3ba of the dome portion 3b of the tank 1, specifically, to the side of the dome portion 3b. However, the location of the third valve 33 is not limited to this example. The location of the transport pipe 29 is not limited to the example shown. Also, it is not essential to provide the dome portion 3b on the tank 1.

[0029] In the operating method of the tank 1 according to the present embodiment, when the first valve 7 is open, the second valve 9 is closed based on the pressure or temperature in at least one of the inner tank space 15 and the inner / outer tank space 17. Specifically, the second valve 9 can be closed based on a determination that the first valve 7 is not closed as set, for example, based on a pressure value detected by either or both of the inner tank space pressure detection device 35 and the inner / outer tank space pressure detection device 37 shown in FIG. 1 . Instead of or in addition to pressure detection, the second valve 9 can be closed based on a temperature value detected by either or both of the inner tank space temperature detection device 39 and the inner / outer tank space temperature detection device 41. In this way, by determining based on at least one of the pressure and temperature in the inner tank space 15 and / or the inner / outer tank space 17, the second valve can be closed at an appropriate time.

[0030] 1 shows an example of the tank 1, which is an independent double-hull tank 1 formed independently from the hull 21, but the configuration of the tank 1 is not limited to this example and may be any type of multiple heat-insulating tank 1. For example, the tank 1 may be a type of tank 1 formed integrally with the hull 21. Furthermore, the multiple heat-insulating structure of the tank 1 may be a triple- or more-walled structure.

[0031] According to the liquefied gas storage tank 1 of this embodiment described above, in addition to the first valve 7, the connecting passage 5 is provided with the second valve 9 that can be operated to close if the first valve 7 does not close.Therefore, if the pressure in the space between the inner and outer tanks 17 rises to a level below a second predetermined pressure difference with respect to the pressure in the space within the inner tank 15 after the first valve 7 is opened, and the connecting passage 5 remains open, such as in the case where the connecting passage 5 does not close even though it should, or where it cannot be closed even when an attempt is made to close it manually, the second valve 9 can be used to close the connecting passage 5, thereby preventing the pressure in the space between the inner and outer tanks 17 from rising excessively beyond the predetermined operating pressure.

[0032] In the liquefied gas storage tank 1 according to this embodiment, the second valve 9 may be a remotely controlled valve. With this configuration, the second valve 9 can be closed in a short time after it is detected that the first valve 7 is not closed when it should be.

[0033] In the liquefied gas storage tank 1 according to this embodiment, the second valve 9 may be provided on the primary side of the first valve 7. With this configuration, the second valve 9 is closed on the upstream side of the first valve 7, so that communication between the inner tank space 15 and the inner-outer tank space 17 can be more reliably blocked.

[0034] In the liquefied gas storage tank 1 according to this embodiment, the tank body 3 may have a main body portion 3a that stores the liquefied gas LG and a dome portion 3b that protrudes upward from the main body portion 3a, and the first valve 7 and the second valve 9 may be located above a base end 3ba of the dome portion 3b. Furthermore, at least one of the first valve 7 and the second valve 9 may be located to the side of the dome portion 3b. This configuration allows for efficient use of the space around the tank 1, including the arrangement of other piping, such as piping for gas transport, provided in the tank 1.

[0035] The liquefied gas storage tank 1 according to this embodiment may be provided with a gas discharge path 31 for discharging gas in the inner-outer tank space 17 to the outside, and a third valve 33 provided in the gas discharge path 31 and set to open when the pressure in the inner-outer tank space 17 reaches or exceeds a predetermined value. This configuration can more reliably prevent the pressure in the inner-outer tank space 17 from becoming excessively high.

[0036] The method for operating the liquefied gas storage tank 1 according to this embodiment is a method for operating the above-described liquefied gas storage tank 1, and includes, when the first valve 7 is open, closing the second valve 9 based on at least one of the pressure and temperature in at least one of the inner tank space 15 and the inner-outer tank space 17. According to this configuration, the second valve can be closed at an appropriate timing by making a determination based on at least one of the pressure and temperature in the inner tank space 15 and / or the inner-outer tank space 17.

[0037] As described above, the preferred embodiments of the present disclosure have been described with reference to the drawings, but various additions, modifications, and deletions can be made without departing from the spirit of the present disclosure. Therefore, such additions, modifications, and deletions are also included in the scope of the present disclosure.

[0038] REFERENCE SIGNS LIST 1 Liquefied gas storage tank 3 Tank body 3a Body portion 3b Dome portion 3ba Base end of dome portion 5 Communication passage 7 First valve 9 Second valve 11 Inner tank 13 Outer tank 15 Space inside inner tank 17 Space between inner and outer tanks BG Vaporized gas LG Liquefied gas

Claims

1. A tank for storing liquefied gas, a tank body including an inner tank that defines a storage space for the liquefied gas inside, and an outer tank that covers the inner tank and defines a space between the inner tank and the outer tank into which the vaporized gas of the liquefied gas is filled; a communication passage that communicates a space within the inner tank with a space between the inner and outer tanks; a first valve provided in the communication passage and configured to open when the pressure in the inner / outer tank space drops to a predetermined value or when a pressure difference between the inner tank space and the inner tank space drops to a predetermined value; a second valve provided in the communication passage in series with the first valve and configured to open and close the communication passage; A liquefied gas storage tank comprising:

2. 2. The liquefied gas storage tank of claim 1, wherein the second valve is a remotely operated valve.

3. 3. The liquefied gas storage tank according to claim 1 or 2, wherein the second valve is provided on the primary side of the first valve.

4. The liquefied gas storage tank according to claim 1 or 2, The tank body has a main body portion which is a portion for accommodating the liquefied gas, and a dome portion which protrudes upward from the main body portion, The first valve and the second valve are located above a base end of the dome portion. Liquefied gas storage tank.

5. 5. The liquefied gas storage tank according to claim 4, At least one of the first valve and the second valve is located to the side of the dome portion. Liquefied gas storage tank.

6. The liquefied gas storage tank according to claim 1 or 2, further comprising: a gas exhaust passage for exhausting gas in the space between the inner and outer tanks to the outside; a third valve provided in the gas exhaust passage and configured to open when the pressure in the space between the inner and outer tanks becomes equal to or higher than a predetermined value; A liquefied gas storage tank comprising:

7. A method for operating a liquefied gas storage tank according to claim 1 or 2, comprising the steps of: and closing the second valve based on at least one of a pressure and a temperature of at least one of the space inside the inner tank and the space between the inner and outer tanks when the first valve is open. How to operate a liquefied gas storage tank.