Liquefied gas storage tank unit

Abstract

A tank unit (U) comprising a plurality of tanks (1) for storing a liquefied gas, wherein each tank (1) is provided with an inner tank (11) that internally forms a storage space for the liquefied gas and an outer tank (15) that covers the inner tank (11) and, between said outer tank and the inner tank (11), forms a space filled with a vaporized gas of the liquefied gas, and wherein inner tank-to-outer tank space individual pipes (31) each connected to a space (17) between the inner and outer tanks of each tank (1), and inner tank-to-outer tank space shared pipes (33) connecting the plurality of individual pipes (31) are provided.

Description

Liquefied Gas Storage Tank Unit

[0001] The present disclosure relates to a liquefied gas storage tank unit.

[0002] Conventionally, a double-shell tank having an inner vessel and an outer vessel has been proposed as a tank for storing liquefied gas, such as cryogenic liquefied hydrogen. In the double-shell tank, a vacuum layer is formed between the inner and outer vessels, thereby achieving high thermal insulation (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2019-151291

[0004] However, if the space between the inner and outer tanks is made into a vacuum layer, it is difficult to actually manage the vacuum level when storing liquefied gas for a long period of time. Therefore, it is possible to fill the space between the inner and outer tanks with vaporized liquefied gas to be stored.

[0005] In a liquefied gas storage facility equipped with multiple such multi-layer tanks, it is desirable to simplify the piping structure used for supplying and discharging gas from the standpoints of reducing installation space, reducing piping costs, and improving operational efficiency.

[0006] An object of the present disclosure is to solve the above-mentioned problems by simplifying the piping structure in a tank unit having multiple liquefied gas storage tanks with a multi-layer structure.

[0007] In order to achieve the above object, the liquefied gas storage tank unit according to the present disclosure comprises: a plurality of tanks for storing liquefied gas, each tank having an inner tank that forms a storage space for the liquefied gas inside, and an outer tank that covers the inner tank and forms a space between the inner tank and the outer tank into which vaporized liquefied gas is filled; individual pipes for an inner-outer tank space connected to the inner-outer tank space of each tank; and a common pipe for an inner-outer tank space that connects the plurality of individual pipes for an inner-outer tank space.

[0008] 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.

[0009] 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 accompanying claims. In the accompanying drawings, the same reference numerals in multiple drawings indicate the same or corresponding parts.

[0023] Fig. 1 is a side view showing a schematic configuration of a liquefied gas storage tank unit according to an embodiment of the present disclosure. Fig. 2 is a plan view showing a schematic configuration of the liquefied gas storage tank unit of Fig. 1. Fig. 3 is a schematic view showing an example of operation of gas supply and gas discharge in the liquefied gas storage tank unit of Fig. 1. Fig. 4A is a schematic view showing an example of operation of gas supply and gas discharge in the liquefied gas storage tank unit of Fig. 1. Fig. 4B is a schematic view showing an example of the configuration of a switching mechanism provided in the liquefied gas storage tank unit of Fig. 1 and one operation example thereof. Fig. 4B is a schematic view showing another operation example of the switching mechanism of the liquefied gas storage tank unit shown in Fig. 4A.

[0010] A preferred embodiment of the present disclosure will now be described with reference to the drawings. Fig. 1 shows a liquefied gas storage tank unit (hereinafter simply referred to as a "tank unit") U according to one embodiment of the present disclosure. The tank unit U includes multiple tanks 1, four in this example, for storing liquefied gas.

[0011] 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. The liquefied gas storage ship in this embodiment is a liquefied gas carrier ship. In addition to liquefied gas carrier ships, 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.

[0012] 2, the tanks 1 are arranged such that their centers are aligned in a straight line in a plan view. Specifically, in this example, the tanks 1 are aligned along the longitudinal direction L of the ship S.

[0013] The liquefied gas 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.

[0014] As shown in Figure 1, the tank 1 is configured as a double-shell tank having an inner tank 11 and an outer tank 13. Specifically, the tank 1 includes the inner tank 11, which defines a storage space for liquefied gas (hereinafter referred to as the "inner tank space") 15 inside, and the outer tank 13, which covers the inner tank 11 and defines a space between the inner tank 11 and the outer tank 13 (hereinafter referred to as the "inter-tank space") 17, into which vaporized liquefied gas is filled. The outer peripheries of the inner tank 11 and the outer tank 13 may each be covered with a thermal insulating layer. This tank 1 is normally operated with vaporized liquefied gas sealed in the inter-tank space 17, which is an insulating layer.

[0015] In this embodiment, the tank 1 has a main body 1a that stores liquefied gas, and a dome 1b that protrudes upward from the main body 1a. In this example, the main body 1a is covered by a tank cover 23 that is part of the hull 21 of the ship S. The dome 1b protrudes, i.e., is exposed, above the tank cover 23 through an opening formed in the top wall of the tank cover 23.

[0016] As shown in Figure 2, a flying passage, which is an installation passage 25 that extends in the arrangement direction of the multiple tanks 1, in the longitudinal direction L in this example, and spans the multiple tanks 1, is provided on the side of the dome portion 1b on the tank covers 23 of the multiple tanks 1. The installation passage 25 is a passage for crew members and workers of the ship S, and is also used to support piping, electrical wiring, and the like, which are connected to each tank 1, as described below. Note that in this example, tank covers 23 are provided that conform to the shape of each tank 1, and the installation passage 25 spans between and over these tank covers 23, but the configuration of the installation passage 25 is not limited to this. For example, if a tank cover 23 that has a shape that continuously covers the multiple tanks 1 is provided, the tank cover 23 may also serve as the installation passage 25.

[0017] Each tank 1 is provided with a vent mast 27, which is a gas release tower that releases vaporized gas filled in the tank 1 or generated in the tank 1 into the atmosphere from a position higher than the tank 1 when the pressure of the gas becomes high. However, the vent mast does not have to be provided directly on the tank 1, and may be provided at another location within the facility where the tank 1 is installed.

[0018] The piping structure of the tank unit U configured as above will be described in detail below.

[0019] 1, the tank unit U includes an individual pipe 31 for the inner / outer tank space connected to the inner / outer tank space 17 of each tank 1, and a common pipe 33 for the inner / outer tank space connecting multiple individual pipes 31 for the inner / outer tank space. The tank unit U further includes an individual pipe 35 for the inner tank connected to the inner space 15 of the inner tank of each tank 1, and a common pipe 37 for the inner tank connecting multiple individual pipes 35 for the inner tank.

[0020] In this embodiment, the individual pipes 31 for the inner / outer tank space include a first individual pipe 31A for the inner / outer tank space connected to an upper part of the inner / outer tank space 17, and a second individual pipe 31B for the inner / outer tank space connected to a lower part of the inner / outer tank space 17. In addition, the common pipes 33 for the inner / outer tank space include a first common pipe 33A for the inner / outer tank space connecting multiple individual pipes 31A for the first inner / outer tank space, and a second common pipe 33B for the inner / outer tank space connecting multiple individual pipes 31B for the second inner / outer tank space.

[0021] Note that, in the following, an example will be described in which there are two combinations of the common pipe 33 for the inner and outer tank interspace and the individual pipes 31 for the inner and outer tank interspace connected to each tank 1, as described above, but the number of combinations of the common pipe 33 for the inner and outer tank interspace and the individual pipes 31 for the inner and outer tank interspace connected to each tank 1 may be one, or three or more. Furthermore, in the following description, when it is not necessary to distinguish between the first common pipe 33A for the inner and outer tank interspace and the second common pipe 33B for the inner and outer tank interspace, they will be simply referred to as the "common pipe 33 for the inner and outer tank interspace." Similarly, when it is not necessary to distinguish between the first individual pipe 31A for the inner and outer tank interspace and the second individual pipe 31B for the inner and outer tank interspace, they will be simply referred to as the "individual pipe 31 for the inner and outer tank interspace."

[0022] In this embodiment, the common pipe 33 for the inner and outer tank spaces and the common pipe 37 for the inner tank are connected above the multiple tanks 1. Specifically, in this example, the common pipe 33 for the inner and outer tank spaces and the common pipe 37 for the inner tank are connected above the tank cover 23. More specifically, in this example, as shown in FIG. 2 , the common pipe 33 for the inner and outer tank spaces and the common pipe 37 for the inner tank are arranged above the installation passage 25, and the two common pipes 33, 37 are connected above the installation passage 25 via a common pipe connecting pipe 41. The common pipe connecting pipe 41 is provided with an on-off valve (not shown). Note that the position at which the common pipe 33 for the inner and outer tank spaces and the common pipe 37 for the inner tank are connected is not limited to above the installation passage 25 and may be, for example, above the tanks 1.

[0023] In operating the double-structure tank 1 used in this embodiment, it is useful to provide a communication passage between the inner tank space 15 and the inner / outer tank space 17 and open / close this communication passage as needed, for example, to adjust pressure. As in this example, by connecting the common pipe 33 for the inner / outer tank space and the common pipe 37 for the inner tank and providing an open / close valve on the common pipe connection pipe 41 connecting them, it becomes possible to open and close the communication passage between the inner tank space 15 and the inner / outer tank space 17 for multiple tanks 1 collectively, rather than for each tank 1. Furthermore, by connecting the common pipe 33 for the inner / outer tank space and the common pipe 37 for the inner tank above multiple tanks 1, the distance between the two common pipes 33, 37 can be shortened, thereby reducing installation space and simplifying the connection structure. Furthermore, connecting the two common pipes above the tank cover 23 or above the installation walkway 25 facilitates installation and provides stable support for the connection. The above-mentioned communication passage between the inner tank space 15 and the inner / outer tank space 17 may be provided for each tank 1 .

[0024] The common pipe 33 for the inner / outer tank interspaces and the plurality of individual pipes 31 for the inner / outer tank interspaces are connected outside the tank 1. Specifically, in this example, each individual pipe 31 for the inner / outer tank interspaces and the common pipe 33 for the inner / outer tank interspaces are connected above the tank cover 23. More specifically, in this example, each individual pipe 31 for the inner / outer tank interspaces and the common pipe 33 for the inner / outer tank interspaces are connected above the installation passage 25. Connecting the common pipe 33 for the inner / outer tank interspaces and the individual pipes 31 for the inner / outer tank interspaces outside each tank 1 can facilitate installation work. Furthermore, connecting the common pipe 33 for the inner / outer tank interspaces and the individual pipes 31 for the inner / outer tank interspaces above the tank cover 23 or above the installation passage 25 can further facilitate installation work and enable stable support of the connection portion.

[0025] In this embodiment, the common pipe 33 for the inner and outer tank spaces is connected to the vent mast 27. A common pipe 37 for the inner tank is also connected to the vent mast 27. In the illustrated example, the common pipe 33 for the inner and outer tank spaces is connected to only one of the multiple vent masts 27 (in this example, the vent mast 27 of the tank 1 located at the third position from the front).

[0026] Note that, when the common pipe 33 for the inner and outer tank spaces and the common pipe 37 for the inner tank are provided to connect to a plurality of tanks 1 as in this embodiment, the vent masts 27 may be provided to only some of the tanks 1. Furthermore, when a plurality of vent masts 27 are provided, the common pipe 33 for the inner and outer tank spaces may be connected to any of the vent masts 27. Furthermore, the common pipe 33 for the inner and outer tank spaces may be connected to all or some of the plurality of vent masts 27.

[0027] By connecting the common pipe 33 for the inner and outer tank spaces to the vent mast 27, the connection structure with the vent mast 27 can be simplified compared to when the inner and outer tank spaces 17 of each tank 1 are connected to the vent mast 27 of each tank 1. However, connecting the common pipe 33 for the inner and outer tank spaces to the vent mast 27 is not essential.

[0028] When two common pipes 33 for the spaces between the inner and outer tanks, namely, the first common pipe 33A for the spaces between the inner and outer tanks and the second common pipe 33B for the spaces between the inner and outer tanks, are provided as in this embodiment, one common pipe 33 for the spaces between the inner and outer tanks can be used to supply gas to the spaces between the inner and outer tanks 17, and the other common pipe 33 for the spaces between the inner and outer tanks can be used to exhaust gas from the spaces between the inner and outer tanks 17. By using both common pipes 33 for the spaces between the inner and outer tanks in this manner, gas replacement in the spaces between the inner and outer tanks 17 can be performed efficiently.

[0029] Specifically, as will be explained below, it is possible to efficiently perform gas replacement by utilizing the difference in specific gravity between the supplied gas and the discharged gas. Here, hydrogen gas HG, which is the gas to be stored in this embodiment and which is filled into the space between the inner and outer chambers 17 during normal operation, is used as an example of a gas with a lower specific gravity, and nitrogen gas NG, which is used for inerting, is used as an example of a gas with a higher specific gravity.

[0030] 3A , as described above, the first inner-outer tank interspace individual piping 31A is connected to the upper part of the inner-outer tank interspace 17, and the second inner-outer tank interspace individual piping 31B is connected to the lower part of the inner-outer tank interspace 17. Therefore, by supplying hydrogen gas from the first inner-outer tank interspace common piping 33A to which the first inner-outer tank interspace individual piping 31A is connected, and connecting the second inner-outer tank interspace common piping 33B to which the second inner-outer tank interspace individual piping 31B is connected to a nitrogen gas source, hydrogen gas HG, which has a low specific gravity, is supplied from above, and nitrogen gas NG, which has a high specific gravity, is discharged from below, thereby easily replacing the nitrogen gas NG atmosphere with hydrogen gas HG. Conversely, when replacing the hydrogen gas HG atmosphere with a nitrogen gas NG atmosphere, as shown in Fig. 3B , nitrogen gas NG is supplied via the lower second inner-outer tank-interspace individual pipe 31B and the connected second inner-outer tank-interspace common pipe 33B, while hydrogen gas HG is discharged via the upper first inner-outer tank-interspace individual pipe 31A and the connected first inner-outer tank-interspace common pipe 33A. In this way, the supply and discharge roles of the first inner-outer tank-interspace common pipe 33A and the second inner-outer tank-interspace common pipe 33B can be easily interchanged. Note that a switching mechanism 45, described below, is not shown in Figs. 3A and 3B.

[0031] Furthermore, in this embodiment, as shown in Fig. 4A, each tank 1 is provided with a switching mechanism 43 that switches the flow path between the first inner-outer-tank space individual piping 31A and the second inner-outer-tank space individual piping 31B. Specifically, the switching mechanism 43 is composed of a flow path switching pipe 45 that connects the first inner-outer-tank space individual piping 31A and the second inner-outer-tank space individual piping 31B, and a plurality of valves arranged around the flow path switching pipe 45. In the illustrated example, two flow path switching pipes, a first flow path switching pipe 45A and a second flow path switching pipe 45B, are provided as the flow path switching pipe 45. The second flow path switching pipe 45B connects a portion upstream of the connection between the first inner-outer-tank space individual piping 31A and the first flow path switching pipe 45A and a portion downstream of the connection between the second inner-outer-tank space individual piping 31B and the first flow path switching pipe 45A. On-off valves 47 are provided in the first flow path switching pipe 45A, the second flow path switching pipe 45B, the first individual pipe 31A between the inner and outer tanks at a connection portion between the two flow path switching pipes 45A and 45B, and the second individual pipe 31B at a connection portion between the two flow path switching pipes 45A and 45B. In the following description, these on-off valves will be referred to as the first on-off valve 47A to the fourth on-off valve 47D, in that order.

[0032] By providing a flow path switching mechanism 43 configured as described above, while fixing the supply and discharge roles of the common pipes 33A, 33B for the spaces between the inner and outer tanks, it is possible to switch between the supply and discharge side flow paths of the first individual pipe 31A for the spaces between the inner and outer tanks and the second individual pipe 31B for the spaces between the inner and outer tanks by opening and closing these on-off valves 47. For example, in the configuration shown in Fig. 4A, an example will be described in which the roles of the first common pipe 33A for the spaces between the inner and outer tanks and the second common pipe 33B for the spaces between the inner and outer tanks are fixed as a supply pipe and a discharge pipe, respectively.

[0033] 4A , the upper first inner-outer tank space individual piping 31A can be used as a supply piping, and the lower second inner-outer tank space individual piping 31B can be used as a discharge piping, by opening the third on-off valve 47C and the fourth on-off valve 47D and closing the other on-off valves 47. In this case, for example, hydrogen gas HG, which has a low specific gravity, can be supplied from the upper side, and nitrogen gas NG, which has a high specific gravity, can be discharged from the lower side, thereby easily replacing the nitrogen gas NG atmosphere with hydrogen gas HG.

[0034] 4B , by opening the first on-off valve 47A and the second on-off valve 47B and closing the other on-off valves 47, the upper first individual pipe 31A for the inner-outer tank space can be used as a pipe for discharging the target gas G, and the lower second individual pipe 31B for the inner-outer tank space can be used as a pipe for supplying the target gas G. In this case, for example, hydrogen gas HG, which has a low specific gravity, can be discharged from the upper side, and nitrogen gas NG, which has a high specific gravity, can be supplied from the lower side, thereby easily replacing the nitrogen gas NG atmosphere with hydrogen gas HG.

[0035] The specific configuration of the switching mechanism 43 is not limited to the illustrated example. For example, instead of providing the on-off valve 47, a flow path switching valve may be provided at each connection between the flow path switching pipe 45 and each of the individual pipes 31A, 31B.

[0036] By using this switching mechanism 43, the supply and discharge roles can be easily switched between the upper first individual pipe 31A for the inner-outer tank interspace and the lower second individual pipe 31B for the inner-outer tank interspace without changing the supply and discharge roles between the first common pipe 33A for the inner-outer tank interspace and the second common pipe 33B for the inner-outer tank interspace. Therefore, with a simple configuration, gas replacement in the inner-outer tank interspace 17 can be efficiently performed by utilizing the difference in specific gravity of the gases. However, the above operation is merely an example, and the pressure in the tank 1 may be adjusted using only one of the individual pipes used for supply or discharge, for example.

[0037] In the illustrated example, the entire inner-outer-tank space 17 is a single space, with the first inner-outer-tank space individual piping 31A and the second inner-outer-tank space individual piping 31B disposed on the upper and lower sides, respectively. However, the inner-outer-tank space 17 may also be divided into multiple partial spaces, for example, vertically. Here, division includes not only division into mutually sealed spaces, but also cases where the spaces are partitioned so that gas does not substantially flow in or out, even if they are not sealed. When the inner-outer-tank space 17 is divided in this manner, the first inner-outer-tank space individual piping 31A and the second inner-outer-tank space individual piping 31B may be disposed on the upper and lower sides, respectively, of each divided partial space.

[0038] In this embodiment, the multiple individual pipes 31 for the inner and outer tank interspaces shown in FIG. 1 are configured to be able to communicate with each other via the common pipe 33 for the inner and outer tank interspaces. Furthermore, the common pipe 33 for the inner and outer tank interspaces is provided with a common on-off valve 49 that can open and close the gap between the multiple inner and outer tank interspaces 17, which are connected by the common pipe 33 for the inner and outer tank interspaces and the individual pipes 31, and the external space. Note that the "external space" here includes not only the atmosphere but also various devices that utilize or treat gas discharged from the common pipe 33 for the inner and outer tank interspaces, such as vent pipes and combustion treatment devices. This configuration allows all of the multiple individual pipes 31 for the inner and outer tank interspaces to be connected via the common pipe 33 for the inner and outer tank interspaces, allowing operations such as the gas replacement described above to be performed collectively for multiple tanks 1, rather than for each tank 1. This simplifies the control process for the inner and outer tank interspaces 17 of multiple tanks 1. Furthermore, it is possible to reduce the number of components, such as detection devices and various valves, required for pressure monitoring and pressure control of the inner and outer tank interspaces 17 of multiple tanks 1. Although not shown, the common pipe 37 for the inner tank may also be provided with an on-off valve and connected to various devices such as the combustion treatment device described above.

[0039] The common pipe 33 for the space between the inner and outer tanks, which connects the plurality of individual pipes 31 for the space between the inner and outer tanks, may be either the first common pipe 33A for the space between the inner and outer tanks or the second common pipe 33B for the space between the inner and outer tanks. If a problem occurs with one of the common pipes 33 for the space between the inner and outer tanks, the other may be used as a backup.

[0040] However, it is not essential to maintain constant communication between the common pipe 33 for the inner and outer tank spaces and the inner and outer tank spaces 17 of each tank 1, and for example, by providing an on-off valve in each individual pipe 31 for the inner and outer tank spaces, communication between the common pipe 33 for the inner and outer tank spaces and the inner and outer tank spaces 17 of each tank 1 may be blocked as necessary. Furthermore, if a malfunction occurs in a certain tank 1, communication with only that tank 1 may be blocked.

[0041] A gas supply source for the gas to be introduced into the inner / outer tank space 17, such as hydrogen gas HG or an inert gas in this example, is connected to the end of the inner / outer tank space common piping 33 used for gas supply. When the gas discharged from the inner / outer tank space 17 is to be used for another purpose, the device for that purpose, such as a heat exchanger, is connected to the end of the inner / outer tank space common piping 33 used for gas discharge.

[0042] 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.

[0043] According to the liquefied gas storage tank unit U of this embodiment described above, by providing individual pipes 31 for the inner and outer tank spaces connected to the inner and outer tank spaces 17 of each tank 1 and a common pipe 33 for the inner and outer tank spaces connecting multiple individual pipes 31 for the inner and outer tank spaces, it is possible to simplify the piping structure of the tank unit U which includes multiple liquefied gas storage tanks 1 having a multi-layer structure.

[0044] In the liquefied gas storage tank unit U according to this embodiment, the common pipe 33 for the inner-outer tank space and the common pipe 37 for the inner tank may be connected above the plurality of tanks 1. With this configuration, the distance between the two common pipes 33, 37 can be shortened, thereby reducing the installation space and simplifying the connection structure.

[0045] In the liquefied gas storage tank unit U according to this embodiment, at least one of the multiple tanks 1 may be provided with a vent mast 27, and the common pipe 33 for the inner and outer tank spaces may be connected to the vent mast 27. With this configuration, the connection structure with the vent mast 27 can be simplified compared to when the inner and outer tank spaces 17 are connected to the vent mast 27 of each tank 1 for each tank 1.

[0046] In the liquefied gas storage tank unit U according to this embodiment, the individual pipes 31 for the inner and outer tank interspaces may include a first individual pipe 31A for the inner and outer tank interspaces connected to an upper portion of the inner and outer tank interspace 17 and a second individual pipe 31B for the inner and outer tank interspaces connected to a lower portion of the inner and outer tank interspace 17, and the common pipes 33 for the inner and outer tank interspaces may include a first common pipe 33A for the inner and outer tank interspaces connecting a plurality of the individual pipes 31A for the first inner and outer tank interspaces and a second common pipe 33B for the inner and outer tank interspaces connecting a plurality of the individual pipes 31B for the second inner and outer tank interspaces. With this configuration, as explained with reference to Figures 3A and 3B, a gas with a low specific gravity is supplied or discharged from the upper side, and a gas with a high specific gravity is supplied or discharged from the lower side, so that the supply and discharge roles can be easily interchanged between the first common pipe 33A for the inner and outer tank interspaces and the second common pipe 33B for the inner and outer tank interspaces. This makes it possible to efficiently perform gas replacement by utilizing the difference in specific gravity between the supplied gas and the discharged gas.

[0047] In the liquefied gas storage tank unit U according to this embodiment, a switching mechanism 43 that switches the flow path between the first inner-outer-tank space individual piping 31A and the second inner-outer-tank space individual piping 31B may be provided in each tank 1. With this configuration, as explained with reference to Figures 4A to 4B, while the supply and discharge roles of the inner-outer-tank space common piping 33A, 33B are fixed, the supply and discharge roles of the first inner-outer-tank space individual piping 31A and the second inner-outer-tank space individual piping 31B are interchanged, thereby enabling efficient gas replacement that takes advantage of the difference in specific gravity of the gases.

[0048] In the liquefied gas storage tank unit U according to this embodiment, the common pipe 33 for the inner-outer tank space and the plurality of individual pipes 31 for the inner-outer tank space may be connected to each other outside the tank 1. This configuration can facilitate the piping installation work.

[0049] In the liquefied gas storage tank unit U according to this embodiment, the plurality of individual pipes 31 for the inner and outer tank spaces are configured to be able to communicate with each other via the common pipe 33 for the inner and outer tank spaces, and a common on-off valve 49 that can open and close the common pipe 33 for the inner and outer tank spaces and the external space may be provided on the common pipe 33 for the inner and outer tank spaces. With this configuration, the control process for the inner and outer tank spaces 17 of the plurality of tanks 1 can be simplified.

[0050] 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.

[0051] DESCRIPTION OF SYMBOLS 1 Liquefied gas storage tank 1 11 Inner tank 13 Outer tank 15 Space inside inner tank 17 Space between inner and outer tanks 27 Vent mast 31 Individual piping for space between inner and outer tanks 31A Individual piping for first space between inner and outer tanks 31B Individual piping for second space between inner and outer tanks 33 Common piping for space between inner and outer tanks 33A Common piping for first space between inner and outer tanks 33B Common piping for second space between inner and outer tanks 35 Individual piping for inner tank 37 Common piping for inner tank 43 Switching mechanism 49 Common on-off valve U Liquefied gas tank unit

Claims

1. A plurality of tanks for storing liquefied gas, A plurality of tanks, each of which includes an inner tank that defines a storage space for the liquefied gas thereinside, and an outer tank that covers the inner tank and defines a space between the inner tank and the outer tank into which vaporized gas of the liquefied gas is filled; Individual piping for the inner and outer tank spaces connected to the inner and outer tank spaces of each tank; A common pipe for the space between the inner and outer tanks that connects a plurality of the individual pipes for the space between the inner and outer tanks; A liquefied gas storage tank unit comprising:

2. The liquefied gas storage tank unit according to claim 1, further comprising: An individual piping for the inner tank connected to the space inside the inner tank of each tank; an inner tank common pipe connecting the plurality of inner tank individual pipes; Equipped with the common pipe for the inner and outer tank spaces and the common pipe for the inner tank are connected above the plurality of tanks; Liquefied gas storage tank unit.

3. The liquefied gas storage tank unit according to claim 1 or 2, In addition, it is equipped with a bent mast, The common pipe for the inner and outer tank spaces is connected to the vent mast. Liquefied gas storage tank unit.

4. The liquefied gas storage tank unit according to claim 1 or 2, the individual piping for the inner and outer tank spaces includes a first individual piping for the inner and outer tank spaces connected to an upper portion of the inner and outer tank spaces and a second individual piping for the inner and outer tank spaces connected to a lower portion of the inner and outer tank spaces, the common pipe for the inner and outer tank spaces includes a first common pipe for the inner and outer tank spaces connecting the plurality of first individual pipes for the inner and outer tank spaces, and a second common pipe for the inner and outer tank spaces connecting the plurality of second individual pipes for the inner and outer tank spaces, Liquefied gas storage tank unit.

5. The liquefied gas storage tank unit according to claim 4, In each tank, a switching mechanism is provided for switching a flow path between the first individual pipe for the inner and outer tank spaces and the second individual pipe for the inner and outer tank spaces. Liquefied gas storage tank unit.

6. The liquefied gas storage tank unit according to claim 1 or 2, the common pipe for the inner and outer tank spaces and the individual pipes for the inner and outer tank spaces are connected to the outside of the tank; Liquefied gas storage tank unit.

7. The liquefied gas storage tank unit according to claim 1 or 2, The individual pipes for the inner and outer tank spaces are configured to be able to communicate with each other via the common pipe for the inner and outer tank spaces, a common on-off valve capable of opening and closing between the common pipe for the inner and outer tank spaces and the external space is provided in the common pipe for the inner and outer tank spaces; Liquefied gas storage tank unit.