Gas replacement method and multi-shell tank

Abstract

Provided is a gas replacement method for replacing air or combustible gas inside a multi-shell tank with inert gas, the multi-shell tank comprising: a plurality of tanks including a first tank for storing liquefied gas and at least one second tank surrounding the first tank; and a heat-shielding layer that surrounds the first tank and is disposed in an inter-tank space between two tanks disposed facing each other among the plurality of tanks. The gas replacement method includes supplying an inert gas to a storage space which is the space within the first tank, replacing the air or combustible gas in the storage space with the inert gas, supplying the inert gas to a first inter-tank region which is a region located inside the heat-shielding layer in the inter-tank space, replacing the air or combustible gas in the first inter-tank region with the inert gas, supplying the inert gas to a second inter-tank region which is a region located outside the heat-shielding layer in the inter-tank space, and replacing the air or combustible gas in the second inter-tank region with the inert gas. The inert gas is supplied in parallel to at least two of the storage space, the first inter-tank region, and the second inter-tank region.

Description

Gas replacement method and multi-shell tank

[0001] The present disclosure relates to a gas displacement method and a multi-shell tank.

[0002] Patent Document 1 discloses a double-shell tank that includes an inner tank for storing liquefied gas and an outer tank that houses the inner tank.

[0003] International Publication No. 2020 / 202578

[0004] In a double-shell tank such as that described in Patent Document 1, the air present in the double-shell tank must be purged with an inert gas before storing liquefied gas in the double-shell tank. Furthermore, in a double-shell tank such as that described in Patent Document 1, the flammable gas present in the double-shell tank must be purged with an inert gas before personnel enter the double-shell tank for inspection or repair. However, Patent Document 1 does not describe the efficiency of the process of purging the air or flammable gas in the double-shell tank with an inert gas.

[0005] An object of the present disclosure is to provide a gas replacement method and a multi-shell tank that can efficiently replace the air or flammable gas inside a multi-shell tank with an inert gas.

[0006] One aspect of the present disclosure provides a gas replacement method for replacing air or flammable gas with an inert gas inside a multi-shell tank including a plurality of tanks, including a first tank for storing liquefied gas and at least one second tank surrounding the first tank, and an inter-tank space, which is a space between two opposing tanks among the plurality of tanks, and a thermal insulation layer surrounding the first tank, the gas replacement method comprising: supplying an inert gas to a storage space, which is a space within the first tank, to replace the gas in the storage space with the inert gas; supplying an inert gas to a first inter-tank region, which is a region of the inter-tank space located inside the thermal insulation layer, to replace the air or flammable gas in the first inter-tank region with the inert gas; and supplying an inert gas to a second inter-tank region, which is a region of the inter-tank space located outside the thermal insulation layer, to replace the air or flammable gas in the second inter-tank region with the inert gas, wherein the inert gas is supplied in parallel to at least two of the storage space, the first inter-tank region, and the second inter-tank region.

[0007] Another aspect of the present disclosure is a gas replacement method for replacing air or flammable gas inside a multi-shell tank including a first tank for storing liquefied gas and at least one second tank surrounding the first tank, and an insulation layer disposed in an inter-tank space, which is a space between two opposing tanks among the plurality of tanks, and surrounding the first tank, with an inert gas, the method comprising: supplying an inert gas to a storage space, which is a space within the first tank, to replace the air or flammable gas in the storage space with the inert gas; supplying an inert gas to a first inter-tank region, which is a region of the inter-tank space located inside the insulation layer, to replace the air or flammable gas in the first inter-tank region with the inert gas; and supplying an inert gas to a second inter-tank region, which is a region of the inter-tank space located outside the insulation layer, to replace the air or flammable gas in the second inter-tank region with the inert gas, wherein a volume of the second inter-tank region is larger than a volume of the first inter-tank region, The gas replacement method includes starting the supply of the inert gas to the storage space and the first inter-tank region after the supply of the inert gas to the second inter-tank region is stopped.

[0008] Yet another aspect of the present disclosure provides a gas replacement method for replacing air or flammable gas inside a multi-shell tank having a plurality of tanks including a first tank for storing liquefied gas and at least one second tank surrounding the first tank, with an inert gas, the method comprising: supplying an inert gas to a storage space, which is a space within the first tank, and replacing the air or flammable gas in the storage space with the inert gas; and supplying an inert gas to an inter-tank space, which is a space between two tanks arranged opposite each other among the plurality of tanks, and replacing the air or flammable gas in the inter-tank space with the inert gas, wherein a volume of the storage space is larger than a volume of the inter-tank space; the inert gas supplied to the storage space is a combustion gas; and the inert gas supplied to the inter-tank space is an inert gas different from the combustion gas.

[0009] Yet another aspect of the present disclosure provides a multi-shell tank comprising: a plurality of tanks including a first tank and at least one second tank surrounding the first tank; a thermal insulation layer disposed in an inter-tank space, which is a space between two opposing tanks of the plurality of tanks, and surrounding the first tank; a first supply pipe having one end disposed in a storage space, which is a space within the first tank, for supplying a combustion gas to the storage space; a second supply pipe having one end disposed in a first inter-tank region, which is a region of the inter-tank space located inside the thermal insulation layer, for supplying an inert gas different from the combustion gas to the first inter-tank region; a third supply pipe fluidly connecting the first supply pipe and the second supply pipe; and a fourth supply pipe branching off from the second supply pipe downstream of a connection between the second supply pipe and the third supply pipe, and having one end disposed in a second inter-tank region, which is a region of the inter-tank space located outside the thermal insulation layer, for supplying the combustion gas to the second inter-tank region.

[0010] According to the present disclosure, the air or flammable gas inside a multi-shell tank can be efficiently replaced with an inert gas.

[0011] FIG. 1 is a schematic diagram showing the configuration of a multi-shell tank according to an embodiment of the present disclosure. FIG. 2 is a diagram for explaining a gas replacement method according to an embodiment of the present disclosure. FIG. 3 is a diagram for explaining a gas replacement method according to an embodiment of the present disclosure. FIG. 4 is a diagram for explaining a gas replacement method according to a first modified example of an embodiment of the present disclosure. FIG. 5 is a schematic diagram showing the configuration of a multi-shell tank according to a second modified example of an embodiment of the present disclosure. FIG. 6 is a diagram for explaining a gas replacement method according to the second modified example of an embodiment of the present disclosure. FIG. 7 is a diagram for explaining a gas replacement method according to the second modified example of an embodiment of the present disclosure. FIG. 8 is a schematic diagram showing the configuration of a multi-shell tank according to a third modified example of an embodiment of the present disclosure. FIG. 9 is a diagram for explaining a gas replacement method according to the third modified example of an embodiment of the present disclosure. FIG. 10 is a schematic diagram showing the configuration of a multi-shell tank according to a fourth modified example of an embodiment of the present disclosure. FIG. 11 is a diagram for explaining a gas replacement method according to the fourth modified example of an embodiment of the present disclosure.

[0012] Hereinafter, a gas replacement method and a multi-shell tank according to the present disclosure will be described with reference to the accompanying drawings.

[0013] Fig. 1 is a schematic diagram showing the configuration of a multi-shell tank 1 according to one embodiment of the present disclosure. Referring to Fig. 1, the multi-shell tank 1 includes a first tank 10 for storing liquefied gas and a second tank 11 surrounding the first tank 10. The multi-shell tank 1 of this embodiment is a double-shell tank having two tanks, the first tank 10 and the second tank 11. The multi-shell tank 1 of this embodiment is a cargo tank installed on a ship and storing liquefied gas as cargo. The liquefied gas in this embodiment is liquefied hydrogen.

[0014] A storage space 12 for storing liquefied gas is defined inside the first tank 10. An inter-tank space 13 is defined between the first tank 10 and the second tank 11. The volume of the storage space 12 is larger than the volume of the inter-tank space 13.

[0015] The multi-shell tank 1 includes a thermal insulation layer 14 disposed in the inter-tank space 13. The thermal insulation layer 14 suppresses heat input to the first tank 10. The thermal insulation layer 14 surrounds the entire first tank 10. The thermal insulation layer 14 is disposed at an interval from the first tank 10. The thermal insulation layer 14 is disposed at an interval from the second tank 11.

[0016] The thermal insulation layer 14 divides the inter-tank space 13 into a first inter-tank region 13a and a second inter-tank region 13b. The first inter-tank region 13a is the region between the thermal insulation layer 14 and the first tank 10. The second inter-tank region 13b is the region between the thermal insulation layer 14 and the second tank 11. The volume of the second inter-tank region 13b is larger than the volume of the first inter-tank region 13a.

[0017] The heat insulating layer 14 includes a heat insulating panel 14a and a surface material 14b that protects the heat insulating panel 14a. The heat insulating panel 14a is exposed in the first inter-tank region 13a, and the surface material 14b is exposed in the second inter-tank region 13b.

[0018] The heat insulating panel 14a reduces heat input to the first tank 10. The heat insulating panel 14a is, for example, a urethane foam panel. In this embodiment, the heat insulating panel 14a includes a porous heat insulating material. The gaps or pores in the heat insulating panel 14a are included in the first inter-tank region 13a.

[0019] The surface material 14b covers the thermal insulation panel 14a from the side opposite the first tank 10, i.e., the second tank 11 side. The surface material 14b prevents gas present in the second inter-tank region 13b from contacting the thermal insulation panel 14a. This protects the thermal insulation panel 14a from the second tank 11 side. Specifically, even if gas containing a large amount of impurities, such as combustion gas, is present in the second inter-tank region 13b, the surface material 14b prevents the combustion gas from contacting the thermal insulation panel 14a, thereby protecting the thermal insulation panel 14a from contamination by the combustion gas. The surface material 14b is attached to the outer surface of the thermal insulation panel 14a on the second tank 11 side. The surface material 14b is made of, for example, aluminum or an aluminum alloy. The surface material 14b prevents gas in the second inter-tank region 13b from permeating into the first inter-tank region 13a. The surface material 14 b also functions as a heat shield that blocks radiant heat from reaching the first tank 10 .

[0020] The multi-shell tank 1 is provided with first to fourth supply pipes 20 to 23 for supplying gas to the storage space 12 and the inter-tank space 13, and first to fourth discharge pipes 30 to 33 for discharging gas from the storage space 12 and the inter-tank space 13.

[0021] In the following description, when there is no need to particularly distinguish between the first to fourth supply pipes 20 to 23 and the first to fourth discharge pipes 30 to 33, one of the first to fourth supply pipes 20 to 23 and the first to fourth discharge pipes 30 to 33 may be simply referred to as a pipe. In the following description, the upstream side in the flow direction of the gas flowing through the pipe may be simply referred to as the upstream side of the pipe, and the downstream side in the flow direction of the gas flowing through the pipe may be simply referred to as the downstream side of the pipe. The gas flows through the first to fourth supply pipes 20 to 23 toward the storage space 12 and the inter-tank space 13, and flows through the first to fourth discharge pipes 30 to 33 away from the storage space 12 and the inter-tank space 13.

[0022] The first supply pipe 20 is a pipe for supplying gas to the storage space 12. The first supply pipe 20 is used to supply combustion gas as an inert gas into the storage space 12. One end of the first supply pipe 20 is disposed in the storage space 12. One end of the first supply pipe 20 opens to the storage space 12. The combustion gas according to this embodiment is an example of the inert gas according to the present disclosure.

[0023] The second supply pipe 21 is a pipe for supplying gas to the first inter-tank region 13a. The second supply pipe 21 is mainly used to supply nitrogen gas as an inert gas to the first inter-tank region 13a. One end of the second supply pipe 21 is disposed in the first inter-tank region 13a. One end of the second supply pipe 21 opens to the first inter-tank region 13a. The nitrogen gas according to this embodiment is an example of an inert gas according to the present disclosure.

[0024] The third supply pipe 22 fluidly connects the first supply pipe 20 and the second supply pipe 21. One end of the third supply pipe 22 is connected to the first supply pipe 20 at a connection 24, and the other end of the third supply pipe 22 is connected to the second supply pipe 21 at a connection 25.

[0025] The fourth supply pipe 23 is a pipe for supplying gas to the second inter-tank region 13b. The fourth supply pipe 23 branches off from the third supply pipe 22. One end of the fourth supply pipe 23 is disposed in the second inter-tank region 13b. One end of the fourth supply pipe 23 opens into the second inter-tank region 13b. The other end of the third supply pipe 22 is connected to the third supply pipe 22 at a connection part 26.

[0026] The first to fourth supply valves 40 to 43 are respectively disposed on the first to fourth supply pipes 20 to 23. The first to fourth supply valves 40 to 43 open and close the corresponding first to fourth supply pipes 20 to 23. The first supply valve 40 is disposed on the first supply pipe 20 downstream of the connection part 24. The second supply valve 41 is disposed on the second supply pipe 21 downstream of the connection part 25. The third supply valve 42 is disposed on the third supply pipe 22 between the connection part 25 and the connection part 26.

[0027] The first discharge pipe 30 is a pipe for discharging gas from the storage space 12. One end of the first discharge pipe 30 is disposed in the storage space 12. One end of the first discharge pipe 30 opens to the storage space 12.

[0028] The second discharge pipe 31 is a pipe for discharging gas from the first inter-tank region 13 a. One end of the second discharge pipe 31 is disposed in the first inter-tank region 13 a. The second discharge pipe 31 opens into the first inter-tank region 13 a.

[0029] The third discharge pipe 32 fluidly connects the first discharge pipe 30 and the second discharge pipe 31. One end of the third discharge pipe 32 is connected to the first discharge pipe 30 by a connection 34, and the other end of the third discharge pipe 32 is connected to the second discharge pipe 31 at a connection 35.

[0030] The fourth discharge pipe 33 is a pipe for discharging gas from the second inter-tank region 13b. One end of the fourth discharge pipe 33 is disposed in the second inter-tank region 13b. One end of the fourth discharge pipe 33 opens into the second inter-tank region 13b. The other end of the fourth discharge pipe 33 is connected to the second discharge pipe 31 at a connection 36. The connection 36, at which the fourth discharge pipe 33 and the second discharge pipe 31 are connected, is located upstream of the connection 35, at which the second discharge pipe 31 and the third discharge pipe 32 are connected.

[0031] The first to fourth exhaust pipes 30 to 33 are respectively provided with corresponding first to fourth exhaust valves 50 to 53. The first to fourth exhaust valves 50 to 53 open and close the corresponding first to fourth exhaust pipes 30 to 33. The first exhaust valve 50 is provided on the first exhaust pipe 30 upstream of the connection 34. The second exhaust valve 51 is provided on the second exhaust pipe 31 upstream of the connection 36. The first exhaust pipe 30 is also provided with a fifth exhaust valve 54 that opens and closes the first exhaust pipe 30. The fifth exhaust valve 54 is provided on the first exhaust pipe 30 downstream of the connection 34. The second exhaust pipe 31 is also provided with a sixth exhaust valve 55 that opens and closes the second exhaust pipe 31. The sixth exhaust valve 55 is provided on the second exhaust pipe 31 downstream of the connection 35.

[0032] An inert gas generator 2 is disposed upstream of the first supply pipe 20. The inert gas generator 2 produces combustion gas as an inert gas by burning fuel. The combustion gas produced by the inert gas generator 2 of this embodiment has an oxygen concentration of 1% or less. The combustion gas produced by the inert gas generator 2 is supplied to the first supply pipe 20. The combustion gas supplied to the first supply pipe 20 is supplied to the storage space 12 (see FIG. 3). The combustion gas supplied to the first supply pipe 20 flows sequentially through the third supply pipe 22 and the fourth supply pipe 23, and is supplied to the second inter-tank region 13b (see FIG. 2).

[0033] A nitrogen gas generator 3 is disposed upstream of the second supply pipe 21. The nitrogen gas generator 3 produces nitrogen gas. The nitrogen gas generator 3 is a membrane separation type nitrogen gas generator. The nitrogen gas generator 3 of this embodiment can change the purity of the produced nitrogen gas within a range from 95% to 99.99% depending on the settings. The nitrogen gas produced by the nitrogen gas generator 3 is supplied to the second supply pipe 21. The nitrogen gas supplied to the second supply pipe 21 is supplied to the first inter-tank region 13a (see FIG. 3 ). The amount of impurities contained in the nitrogen gas produced by the nitrogen gas generator 3 is less than the amount of impurities contained in the combustion gas produced by the inert gas generator 2. Furthermore, the amount of nitrogen gas produced per unit time by the nitrogen gas generator 3 is less than the amount of combustion gas produced per unit time by the inert gas generator 2. The amount of nitrogen gas supplied from the nitrogen gas generator 3 to the second supply pipe 21 per unit time is less than the amount of combustion gas supplied from the inert gas generator 2 to the first supply pipe 20 per unit time.

[0034] A vent device 4 for discharging gas to the outside is disposed downstream of the first discharge pipe 30. The vent device 4 in this embodiment is a vent mast mounted on the ship. The vent device 4 is used to discharge air from the storage space 12 and the inter-tank space 13. The air in the storage space 12 flows through the first discharge pipe 30 and is discharged to the outside via the vent device 4. The air in the first inter-tank region 13a flows sequentially through the second discharge pipe 31, the third discharge pipe 32, and the first discharge pipe 30 and is discharged to the outside via the vent device 4. The air in the second inter-tank region 13b flows sequentially through the fourth discharge pipe 33, the second discharge pipe 31, the third discharge pipe 32, and the first discharge pipe 30 and is discharged to the outside via the vent device 4.

[0035] A combustion equipment 5 that combusts gas is disposed downstream of the second discharge pipe 31. In this embodiment, the combustion equipment 5 is, for example, a boiler. The combustion equipment 5 is used to combust the flammable gas discharged from the storage space 12 and the inter-tank space 13. The flammable gas discharged from the storage space 12 and the inter-tank space 13 is combusted by the combustion equipment 5, thereby being treated without being released into the atmosphere. The flammable gas in the storage space 12 flows sequentially through the first discharge pipe 30, the third discharge pipe 32, and the second discharge pipe 31 and is supplied to the combustion equipment 5. The flammable gas in the first inter-tank region 13a flows sequentially through the second discharge pipe 31 and is supplied to the combustion equipment 5. The flammable gas in the second inter-tank region 13b flows sequentially through the fourth discharge pipe 33 and the second discharge pipe 31 and is supplied to the combustion equipment 5.

[0036] 2 and 3 are diagrams illustrating the gas exchange method according to this embodiment. The following description will explain an example in which the gas exchange method according to this embodiment is applied to an inerting process that is performed after a ship that has undergone inspection or repair leaves the dock. The inerting process is a process in which the air in the multi-shell tank 1 is exchanged with an inert gas.

[0037] In the gas replacement method according to this embodiment, first, the air in the second inter-cell region 13b is replaced with an inert gas. A combustion gas is supplied to the second inter-cell region 13b, and air is discharged from the second inter-cell region 13b, thereby replacing the air in the second inter-cell region 13b with the combustion gas.

[0038] 2, with the fourth supply valve 43 open and the first to third supply valves 40 to 42 closed, combustion gas is supplied from the inert gas generator 2 to the first supply pipe 20, thereby supplying the combustion gas to the second inter-tank region 13b. Furthermore, with the third to fifth exhaust valves 52 to 54 open and the first, second, and sixth exhaust valves 50, 51, and 55 closed, air in the second inter-tank region 13b is exhausted to the outside via the vent device 4.

[0039] When the air in the second inter-cell region 13b is replaced with the inert gas and the oxygen concentration in the second inter-cell region 13b becomes equal to or lower than a predetermined threshold, the supply of combustion gas to the second inter-cell region 13b is stopped and gas replacement in the second inter-cell region 13b is completed.

[0040] When the gas replacement in the second inter-tank region 13b is completed, the air in the storage space 12 is replaced with the inert gas, and the air in the first inter-tank region 13a is also replaced with the inert gas. Combustion gas is supplied to the storage space 12 and air is discharged from the storage space 12, thereby replacing the air in the storage space 12 with the combustion gas. Furthermore, nitrogen gas is supplied to the first inter-tank region 13a and air is discharged from the first inter-tank region 13a, thereby replacing the air in the first inter-tank region 13a with nitrogen gas.

[0041] As shown in FIG. 3 , the supply of combustion gas to the storage space 12 and the supply of nitrogen gas to the first inter-tank region 13a are performed in parallel. With the first and second supply valves 40 and 41 open and the third and fourth supply valves 42 and 43 closed, combustion gas is supplied from the inert gas generator 2 to the first supply pipe 20, thereby supplying the combustion gas to the storage space 12. With the first and second supply valves 40 and 41 open and the third and fourth supply valves 42 and 43 closed, nitrogen gas is supplied from the nitrogen gas generator 3 to the second supply pipe 21, thereby supplying the nitrogen gas to the first inter-tank region 13a. In this embodiment, the purity of the nitrogen gas supplied to the first inter-tank region 13a is higher than 97%. Specifically, the purity of the nitrogen gas supplied to the first inter-tank region 13a is 99%.

[0042] The air in the storage space 12 and the first inter-tank region 13a is discharged to the outside through the vent device 4 by opening the first to third exhaust valves 50 to 52 and the fifth exhaust valve 54 and closing the fourth and sixth exhaust valves 53 and 55.

[0043] When the air in the storage space 12 is replaced with the inert gas and the oxygen concentration in the storage space 12 becomes equal to or lower than a predetermined threshold, the supply of combustion gas to the storage space 12 is stopped, and gas replacement in the storage space 12 is completed. Furthermore, when the air in the first inter-tank region 13a is replaced with the inert gas and the oxygen concentration in the first inter-tank region 13a becomes equal to or lower than a predetermined threshold, the supply of nitrogen gas to the first inter-tank region 13a is stopped, and gas replacement in the first inter-tank region 13a is completed. When both the gas replacement in the storage space 12 and the gas replacement in the first inter-tank region 13a are completed, the gas replacement method of this embodiment is completed.

[0044] In the above description, an example has been described in which the gas replacement method according to the present disclosure is applied to an inerting process. However, the gas replacement method according to the present disclosure may also be applied to a gas-freeing process, which is performed before a ship enters a dock for inspection or repair. The gas-freeing process is a process in which hydrogen gas in the multi-shelled tank 1 is replaced with an inert gas. In the above description of the inerting process, the term "inerting process" is replaced with the term "gas-freeing process," "air" is replaced with the term "hydrogen gas," and "oxygen concentration" is replaced with the term "hydrogen gas concentration." Furthermore, the gas discharged from the multi-shelled tank 1 is supplied to the combustion equipment 5 instead of the vent device 4. This allows the gas replacement method according to the present embodiment to be applied to the gas-freeing process.

[0045] The gas replacement method according to this embodiment has the following advantages.

[0046] In the gas replacement method according to this embodiment, the inert gas is supplied to at least two of the storage space 12, the first inter-tank region 13a, and the second inter-tank region 13b (in this embodiment, the storage space 12 and the first inter-tank region 13a) in parallel. Therefore, the air or flammable gas inside the multi-shell tank 1 can be replaced with the inert gas more efficiently than in the case where the inert gas is sequentially supplied to the storage space 12, the first inter-tank region 13a, and the second inter-tank region 13b, for example.

[0047] When a thermal barrier 14 is provided in the inter-tank space 13, as in the multi-shell tank 1 of this embodiment, sufficient airtightness may not be ensured between the first inter-tank region 13a and the second inter-tank region 13b. In this case, if inert gas is supplied to the first inter-tank region 13a, which has a relatively small volume, before replacing the air or flammable gas in the second inter-tank region 13b, which has a relatively large volume, with inert gas, the air or flammable gas in the second inter-tank region 13b may flow into the first inter-tank region 13a while the air or flammable gas in the first inter-tank region 13a is being replaced with inert gas. As a result, the replacement of the air or flammable gas in the first inter-tank region 13a with inert gas may not be performed efficiently. In contrast, in the gas replacement method of this embodiment, the supply of inert gas to the first inter-tank region 13a is started after the supply of inert gas to the second inter-tank region 13b is stopped. Therefore, the air or flammable gas in the first inter-tank region 13a can be replaced with the inert gas more efficiently than when the supply of the inert gas to the first inter-tank region 13a is started before the replacement of the air or flammable gas in the second inter-tank region 13b with the inert gas is completed.

[0048] According to the gas replacement method of this embodiment, an inert gas (nitrogen gas in this embodiment) different from the combustion gas is supplied to the first inter-tank region 13a where the heat insulating panel 14a is exposed, thereby preventing the heat insulating panel 14a from being contaminated by the combustion gas.

[0049] Nitrogen gas having a purity of 97% is typically used as the nitrogen gas supplied to the venting device 4, which is the vent mast, or as the nitrogen gas used to replace the flammable gas inside the cargo and fuel gas piping. According to the replacement method of this embodiment, the purity of the nitrogen gas used to replace the air or flammable gas in the first inter-tank region 13a is higher than 97%, so that the air or flammable gas in the first inter-tank region 13a can be replaced with nitrogen gas more efficiently than when the air or flammable gas in the first inter-tank region 13a is replaced with nitrogen gas having a purity of 97%, which is typically used on ships.

[0050] [Modifications] The present disclosure is not limited to the configurations described in the above embodiments, and various modifications are possible.

[0051] [First Modification] In the above embodiment, after the supply of the inert gas to the second inter-tank region 13b is stopped, the inert gas is supplied in parallel to the storage space 12 and the first inter-tank region 13a. However, as in the first modification of the above embodiment shown in FIG. 4 , the inert gas may be supplied in parallel to all of the storage space 12, the first inter-tank region 13a, and the second inter-tank region 13b.

[0052] [Second Modification] In the above embodiment, the fourth supply pipe 23 branches off from the third supply pipe 22. However, as in a second modification of the above embodiment shown in FIG. 5 , the fourth supply pipe 23 may branch off from the second supply pipe 21. In the second modification, the fourth supply pipe 23 branches off from the second supply pipe 21 downstream of the connection 25 between the second supply pipe 21 and the third supply pipe 22. One end of the fourth supply pipe 23 is disposed in the second inter-tank region 13b. One end of the fourth supply pipe 23 opens into the second inter-tank region 13b. The other end of the fourth supply pipe 23 is connected to the second supply pipe 21 at the connection 27. The connection 27, at which the fourth supply pipe 23 and the second supply pipe 21 are connected, is located downstream of the connection 25, at which the second supply pipe 21 and the third supply pipe 22 are connected. The second supply valve 41 is disposed in the second supply pipe 21 downstream of the connection 27. In the second modified example, the supply of combustion gas to the storage space 12 and the supply of nitrogen gas to the first inter-tank region 13a are preferably performed in parallel. Furthermore, the supply of combustion gas to the storage space 12 and the supply of nitrogen gas to the first inter-tank region 13a are preferably started after the supply of combustion gas to the second inter-tank region 13b has stopped. In the second modified example, as shown in FIG. 6 , first, combustion gas is supplied from the inert gas generator 2 to the second inter-tank region 13b to replace the air or flammable gas in the second inter-tank region 13b with the combustion gas. Then, as shown in FIG. 7 , combustion gas is supplied from the inert gas generator 2 to the storage space 12 to replace the air or flammable gas in the storage space 12 with the combustion gas. Furthermore, in parallel with the gas replacement in the storage space 12, nitrogen gas is supplied from the nitrogen gas generator 3 to the first inter-tank region 13a to replace the air or flammable gas in the first inter-tank region 13a with nitrogen gas.

[0053] When combustion gas is supplied to the second inter-tank region 13b through the fourth supply pipe 23 branching from the third supply pipe 22 as in the above embodiment, the piping length required to supply the combustion gas to the second inter-tank region 13b is long, which may increase the manufacturing cost of the multi-shell tank 1. In contrast, in the multi-shell tank 1 according to the second modification, combustion gas is supplied to the second inter-tank region 13b through the fourth supply pipe 23 branching from the second supply pipe 21. The second supply pipe 21 is a pipe for supplying inert gas to the first inter-tank region 13a, which together with the second inter-tank region 13b constitutes the inter-tank space 13, and is therefore typically positioned closer to the second inter-tank region 13b than the third supply pipe 22. Therefore, the length of the fourth supply pipe 23 can be shorter than when the fourth supply pipe 23 branches from the third supply pipe 22. This prevents the piping length required to supply combustion gas to the second inter-tank region 13b from increasing, thereby suppressing an increase in the manufacturing cost of the multi-shell tank 1.

[0054] [Third Modification] In the above embodiment, a thermal insulation layer 14 is provided in the inter-tank space 13. However, as in a third modification of the above embodiment shown in Fig. 8, a thermal insulation layer may not be provided in the inter-tank space 13. In the fourth modification, the multi-shell tank 1 does not include the fourth supply pipe 23, the fourth supply valve 43, the fourth discharge pipe 33, and the fourth discharge valve 53 (shown in Fig. 1). In the third modification, the inert gas supplied to the storage space 12 may be a combustion gas, and the inert gas supplied to the inter-tank space 13 may be nitrogen gas. In the third modification, as shown in Fig. 9, the supply of combustion gas to the storage space 12 and the supply of nitrogen gas to the inter-tank space 13 are preferably performed in parallel.

[0055] In the third modification, an inert gas generator 2 is used as a combustion gas supply source, and a nitrogen gas generator 3 is used as a supply source of an inert gas different from the combustion gas. The amount of combustion gas supplied from the inert gas generator 2 is greater than the amount of nitrogen gas supplied from the nitrogen gas generator 3. According to the gas replacement method of the third modification, the air or flammable gas in the multi-shell tank 1 can be efficiently replaced with the inert gas by supplying the combustion gas from the inert gas generator 2 to the storage space 12, which has a relatively large volume, and supplying the nitrogen gas from the nitrogen gas generator 3 to the inter-chamber space 13, which has a relatively small volume. Furthermore, in the third modification, the supply of the combustion gas to the storage space 12 and the supply of the nitrogen gas to the inter-chamber space 13 are performed in parallel. This allows the air or flammable gas in the multi-shell tank 1 to be efficiently replaced with the inert gas, compared to a case in which the supply of the combustion gas to the storage space 12 and the supply of the nitrogen gas to the inter-chamber space 13 are performed sequentially.

[0056] [Fourth Modification] In the above embodiment, the thermal insulation layer 14 including the thermal insulation panels 14a is disposed in the inter-tank space 13, and the thermal insulation layer 14 divides the inter-tank space 13 into the first inter-tank region 13a and the second inter-tank region 13b. However, the present disclosure is not limited to this. As shown in a fourth modification in FIG. 10 , the thermal insulation layer 14 may include a porous thermal insulation material, a powdered thermal insulation material, or a fibrous thermal insulation material filled in the inter-tank space 13, instead of the thermal insulation panels 14a and the surface material 14b. In the fourth modification, the multi-shell tank 1 does not include the fourth supply pipe 23, the fourth supply valve 43, the fourth discharge pipe 33, and the fourth discharge valve 53 (shown in FIG. 1 ). Examples of the porous thermal insulation material include urethane foam. Examples of the powdered thermal insulation material include granular perlite. Examples of the fibrous thermal insulation material include glass wool. In the fourth modification, the inter-tank space 13 includes voids or holes in the thermal insulation layer 14. In the fourth modification, the inert gas supplied to the storage space 12 is combustion gas, and the inert gas supplied to the inter-tank space 13 is nitrogen gas. The purity of the nitrogen gas supplied to the inter-tank space 13 may be higher than 97%, for example, 99%. In the fourth modification, as shown in FIG. 11 , it is preferable that the supply of combustion gas to the storage space 12 and the supply of nitrogen gas to the inter-tank space 13 are performed in parallel.

[0057] According to the gas replacement method of the fourth modification, the inert gas supplied to the inter-tank space 13 is nitrogen gas. This prevents the thermal barrier layer 14 from being contaminated by impurities contained in the inert gas, compared to when the inert gas supplied to the inter-tank space 13 is a combustion gas. Furthermore, according to this modification, the purity of the nitrogen gas used to replace the air or flammable gas in the inter-tank space 13 is higher than 97%, so the air or flammable gas in the inter-tank space 13 can be replaced with nitrogen gas more efficiently than when nitrogen gas with a purity of 97% is used to replace the air or flammable gas in the inter-tank space 13. Furthermore, in the fourth modification, the supply of combustion gas to the storage space 12 and the supply of nitrogen gas to the inter-tank space 13 are performed in parallel. This allows the air or flammable gas in the multi-shell tank 1 to be replaced with inert gas more efficiently than when the supply of combustion gas to the storage space 12 and the supply of nitrogen gas to the inter-tank space 13 are performed sequentially.

[0058] [Other Modifications] In the above description, an example has been described in which the inert gas is supplied to the storage space 12 and the first inter-tank region 13a in parallel, but the inert gas may also be supplied to the storage space 12 and the second inter-tank region 13b in parallel. Also, the inert gas may also be supplied to the first inter-tank region 13a and the second inter-tank region 13b in parallel.

[0059] In the above description, an example has been described in which the supply of inert gas to the storage space 12 and the first inter-tank region 13a is started after the supply of inert gas to the second inter-tank region 13b is stopped, but the supply of inert gas to the first inter-tank region 13a may be started before the supply of inert gas to the second inter-tank region 13b is stopped. Also, for example, the supply of inert gas to the first inter-tank region 13a may be started after the supply of inert gas to the second inter-tank region 13b is started.

[0060] In the above description, the nitrogen gas used to replace the air or combustible gas in the first inter-tank region 13a has a purity of more than 97%, but it may have a purity of 97% or less.

[0061] In the above description, the nitrogen gas generator 3 is an example of a membrane separation type nitrogen gas generator, but it may also be a pressure swing adsorption type nitrogen gas generator.

[0062] In the above description, the multi-shell tank 1 is installed on a ship, but the multi-shell tank 1 may be installed on a floating structure or a land base. In the above description, the multi-shell tank 1 is installed as a cargo tank, but the multi-shell tank 1 may be installed as a fuel tank that stores liquefied gas as fuel.

[0063] In the above description, an example was described in which the liquefied gas was liquefied hydrogen, but the liquefied gas according to the present disclosure may be liquefied natural gas (LNG) or liquefied petroleum gas (LPG).

[0064] In the above description, the inert gas different from the combustion gas is nitrogen gas, but the inert gas different from the combustion gas may be other inert gas such as helium gas. Depending on the type of inert gas different from the combustion gas, another inert gas generator such as a helium generator may be used instead of the nitrogen gas generator 3.

[0065] In the above description, an example was given in which the heat insulating panel 14a was a urethane foam panel, but the heat insulating panel 14a may be another heat insulating panel such as a phenolic foam panel, an aerogel panel, or a glass wool panel.

[0066] In the above description, an example has been described in which the multi-shell tank 1 is a double-shell tank, but the multi-shell tank 1 may be a multi-shell tank with three or more shells, in which an additional tank is provided outside the second tank 11. By interpreting the relationship between the first tank 10 and the second tank 11 in the above description as the relationship between two tanks arranged opposite each other among three or more tanks, the present disclosure can be applied to a multi-shell tank with three or more shells.

[0067] In the above description, an example has been described in which the thermal insulation panel 14a is exposed in the first inter-tank region 13a and the surface material 14b is exposed in the second inter-tank region 13b, but the surface material 14b may be exposed in the first inter-tank region 13a and the thermal insulation panel 14a may be exposed in the second inter-tank region 13b. In other words, the surface material 14b may cover the thermal insulation panel 14a from the side of the first tank 10. In this case, it is preferable to use combustion gas as the inert gas supplied to the first inter-tank region 13a and nitrogen gas as the inert gas supplied to the second inter-tank region 13b.

[0068] The foregoing discussion of the present disclosure has been presented for purposes of illustration and description and is not intended to limit the present disclosure to the form or forms disclosed herein. For example, in the foregoing description, various features of the present disclosure are grouped together in a single embodiment for the purpose of concisely describing the disclosure, but it should be understood that certain of the various features may also be combined.

[0069] [Additional Notes] The gas replacement method and multi-shell tank according to the present disclosure provide the following aspects.

[0070] [Aspect 1] A gas replacement method for replacing air or flammable gas with an inert gas inside a multi-shell tank comprising a plurality of tanks, including a first tank for storing liquefied gas and at least one second tank surrounding the first tank, and a thermal insulation layer disposed in an inter-tank space between two opposing tanks of the plurality of tanks and surrounding the first tank, the gas replacement method comprising: supplying an inert gas to a storage space, which is a space within the first tank, to replace the air or flammable gas in the storage space with the inert gas; supplying an inert gas to a first inter-tank region, which is a region of the inter-tank space located inside the thermal insulation layer, to replace the air or flammable gas in the first inter-tank region with the inert gas; and supplying an inert gas to a second inter-tank region, which is a region of the inter-tank space located outside the thermal insulation layer, to replace the air or flammable gas in the second inter-tank region with the inert gas; wherein the inert gas is supplied in parallel to at least two of the storage space, the first inter-tank region, and the second inter-tank region.

[0071] According to the gas replacement method of Aspect 1, the inert gas is supplied to at least two of the storage space, the first inter-tank region, and the second inter-tank region in parallel, which allows the air or flammable gas in the multi-shell tank to be replaced with the inert gas more efficiently than when the inert gas is sequentially supplied to the storage space, the first inter-tank region, and the second inter-tank region, for example.

[0072] [Aspect 2] A gas replacement method for replacing air or flammable gas with inert gas in a multi-shell tank comprising a plurality of tanks, including a first tank for storing liquefied gas and at least one second tank surrounding the first tank, and a thermal insulation layer disposed in an inter-tank space, which is a space between two opposing tanks among the plurality of tanks, and surrounding the first tank, the method comprising: supplying inert gas to a storage space, which is a space within the first tank, to replace the air or flammable gas in the storage space with the inert gas; supplying inert gas to a first inter-tank region, which is a region of the inter-tank space located inside the thermal insulation layer, to replace the air or flammable gas in the first inter-tank region with the inert gas; and supplying inert gas to a second inter-tank region, which is a region of the inter-tank space located outside the thermal insulation layer, to replace the air or flammable gas in the second inter-tank region with the inert gas, wherein a volume of the second inter-tank region is greater than a volume of the first inter-tank region, a gas replacement method, wherein the supply of the inert gas to the storage space and the first inter-tank region is started after the supply of the inert gas to the second inter-tank region is stopped.

[0073] When a thermal barrier is provided in the inter-tank space, as in the invention of Aspect 2, sufficient airtightness between the first inter-tank region and the second inter-tank region may not be ensured. In this case, if inert gas is supplied to the first inter-tank region, which has a relatively small volume, before replacing the air or flammable gas in the second inter-tank region, which has a relatively large volume, with inert gas, the air or flammable gas in the second inter-tank region may flow into the first inter-tank region while replacing the air or flammable gas in the first inter-tank region with inert gas. As a result, replacement of the air or flammable gas in the first inter-tank region with inert gas may not be performed efficiently. In contrast, in the gas replacement method of Aspect 2, the supply of inert gas to the first inter-tank region is initiated after the supply of inert gas to the second inter-tank region is stopped. Therefore, the air or flammable gas in the first inter-tank region can be replaced with inert gas more efficiently than, for example, when the supply of inert gas to the first inter-tank region is initiated before replacing the air or flammable gas in the second inter-tank region with inert gas.

[0074] [Aspect 3] The gas replacement method according to Aspect 1 or 2, wherein the thermal insulation layer comprises a thermal insulation panel and a surface material that protects the thermal insulation panel from the first tank side or the opposite side to the first tank, the inert gas supplied to the storage space and the areas of the first inter-tank region and the second inter-tank region where the surface material is exposed is a combustion gas, and the inert gas supplied to the areas of the first inter-tank region and the second inter-tank region where the thermal insulation panel is exposed is an inert gas different from the combustion gas.

[0075] According to the gas replacement method of Aspect 3, by supplying an inert gas other than the combustion gas, such as nitrogen gas, to the area of ​​the first inter-tank region and the second inter-tank region where the heat protection panel is exposed, contamination of the heat protection panel by the combustion gas can be suppressed.

[0076] [Aspect 4] The gas replacement method according to Aspect 3, wherein the inert gas supplied to the areas of the first inter-tank region and the second inter-tank region where the thermal insulation panels are exposed is nitrogen gas.

[0077] [Aspect 5] The gas replacement method for replacing the air inside the multi-shell tank with an inert gas according to Aspect 4, wherein the purity of the nitrogen gas is higher than 97%.

[0078] When a multi-shell tank is installed on a ship, a nitrogen gas generator typically installed on the ship can be used as a nitrogen gas supply source. In this case, nitrogen gas with a purity of 97% is typically used for supplying to the vent mast or for replacing flammable gas in cargo and fuel gas piping. According to the gas replacement method of Aspect 5, the purity of the nitrogen gas used to replace the air in the first inter-tank region or the second inter-tank region is higher than 97%, so that the air in the first inter-tank region or the second inter-tank region can be replaced with nitrogen gas more efficiently than when nitrogen gas with a purity of 97% typically used on ships is used to replace the air in the first inter-tank region or the second inter-tank region.

[0079] [Aspect 6] A gas replacement method for replacing air or flammable gas inside a multi-shell tank equipped with a plurality of tanks including a first tank for storing liquefied gas and at least one second tank surrounding the first tank, with an inert gas, the gas replacement method comprising: supplying an inert gas to a storage space, which is a space within the first tank, and replacing the air or flammable gas in the storage space with the inert gas; and supplying an inert gas to an inter-tank space, which is a space between two tanks arranged opposite each other among the plurality of tanks, and replacing the air or flammable gas in the inter-tank space with the inert gas, wherein a volume of the storage space is larger than a volume of the inter-tank space; the inert gas supplied to the storage space is a combustion gas; and the inert gas supplied to the inter-tank space is an inert gas different from the combustion gas.

[0080] When a multi-shell tank is installed on a ship, an inert gas generator normally installed on the ship can be used as a supply source of combustion gas, and a nitrogen gas generator normally installed on the ship can be used as a supply source of an inert gas different from the combustion gas. Furthermore, the amount of combustion gas supplied from the inert gas generator is usually greater than the amount of nitrogen gas supplied from the nitrogen gas generator. In the gas replacement method according to Aspect 6, the combustion gas is supplied to a storage space having a relatively large volume, and an inert gas different from the combustion gas, such as nitrogen gas, is supplied to the inter-tank space having a relatively small volume, thereby enabling efficient replacement of the air or flammable gas in the multi-shell tank with the inert gas.

[0081] [Aspect 7] The gas replacement method according to Aspect 6, wherein the multi-shell tank includes a thermal insulation layer including a porous thermal insulation material, a powdered thermal insulation material, or a fibrous thermal insulation material filled in the inter-tank space, the inert gas supplied to the inter-tank space is nitrogen gas, and the purity of the nitrogen gas is higher than 97%.

[0082] According to the gas replacement method of Aspect 7, by supplying nitrogen gas to the inter-chamber space, contamination of the thermal insulation layer by combustion gas can be suppressed. Furthermore, since the purity of the nitrogen gas used to replace the air or flammable gas in the inter-chamber space is higher than 97%, the air or flammable gas in the inter-chamber space 13 can be replaced with the inert gas more efficiently than when the air or flammable gas in the inter-chamber space is replaced with nitrogen gas having a purity of 97%, which is normally used on ships.

[0083] a first supply pipe having one end disposed in a storage space within the first tank, the first supply pipe being for supplying a combustion gas to the storage space; a second supply pipe having one end disposed in a first inter-tank region, the inter-tank space being a region located inside the thermal insulation layer, the second supply pipe having one end disposed in a first inter-tank region, the inter-tank space being a region located inside the thermal insulation layer, the second supply pipe having one end disposed in a first inter-tank region, the inter-tank space being a region located inside the thermal insulation layer, the second supply pipe having one end disposed in a first inter-tank region, the inter-tank space being a region located outside the thermal insulation layer, the second supply pipe having one end disposed in a second ...

[0084] For example, if combustion gas is supplied to the second inter-tank region through a pipe branching from the third supply pipe, the length of piping required to supply the combustion gas to the second inter-tank region becomes long, which may increase the manufacturing cost of the multi-shell tank. In contrast, in the multi-shell tank described in Aspect 8, the combustion gas is supplied to the second inter-tank region through a fourth supply pipe branching from the second pipe for supplying inert gas to the first inter-tank region, which together with the second inter-tank region constitutes the inter-tank space. Therefore, the length of piping required to supply the combustion gas to the second inter-tank region can be shortened compared to when combustion gas is supplied to the second inter-tank region through a pipe branching from the third supply pipe.

Claims

1. A gas replacement method for replacing air or flammable gas inside a multi-shell tank comprising a plurality of tanks, including a first tank for storing liquefied gas and at least one second tank surrounding the first tank, and an insulation layer disposed in an inter-tank space between two opposing tanks of the plurality of tanks, the inter-tank space being the space between the first tank and surrounding the first tank, the method comprising: supplying inert gas to a storage space, which is the space within the first tank, and replacing the air or flammable gas in the storage space with the inert gas; supplying inert gas to a first inter-tank region, which is a region of the inter-tank space located inside the insulation layer, and replacing the air or flammable gas in the first inter-tank region with the inert gas; and supplying inert gas to a second inter-tank region, which is a region of the inter-tank space located outside the insulation layer, and replacing the air or flammable gas in the second inter-tank region with the inert gas; wherein the inert gas is supplied in parallel to at least two of the storage space, the first inter-tank region, and the second inter-tank region.

2. A gas replacement method for replacing air or flammable gas with inert gas in a multi-shell tank comprising a plurality of tanks, including a first tank for storing liquefied gas and at least one second tank surrounding the first tank, and an insulation layer disposed in an inter-tank space between two opposing tanks of the plurality of tanks and surrounding the first tank, the method comprising: supplying inert gas to a storage space, which is a space within the first tank, and replacing the air or flammable gas in the storage space with the inert gas; supplying inert gas to a first inter-tank region, which is a region of the inter-tank space located inside the insulation layer, and replacing the air or flammable gas in the first inter-tank region with the inert gas; and supplying inert gas to a second inter-tank region, which is a region of the inter-tank space located outside the insulation layer, and replacing the air or flammable gas in the second inter-tank region with the inert gas; wherein the volume of the second inter-tank region is greater than the volume of the first inter-tank region; the supply of the inert gas to the storage space and the first inter-tank region is started after the supply of the inert gas to the second inter-tank region is stopped.

3. A gas replacement method according to claim 1 or 2, wherein the heat insulation layer comprises a heat insulation panel and a surface material that protects the heat insulation panel from the first tank side or the side opposite to the first tank, the inert gas supplied to the storage space and the areas of the first inter-tank region and the second inter-tank region where the surface material is exposed is a combustion gas, and the inert gas supplied to the areas of the first inter-tank region and the second inter-tank region where the heat insulation panel is exposed is an inert gas different from the combustion gas.

4. A gas replacement method according to claim 3, wherein the inert gas supplied to the first inter-tank region and the second inter-tank region where the heat insulating panel is exposed is nitrogen gas.

5. A gas replacement method for replacing the air inside the multi-shell tank with an inert gas, according to claim 4, wherein the purity of the nitrogen gas is higher than 97%.

6. A gas replacement method for replacing air or flammable gas inside a multi-shell tank having a plurality of tanks including a first tank for storing liquefied gas and at least one second tank surrounding the first tank, with an inert gas, the method comprising: supplying an inert gas to a storage space, which is a space within the first tank, and replacing the air or flammable gas in the storage space with the inert gas; supplying an inert gas to an inter-tank space, which is a space between two tanks arranged opposite each other among the plurality of tanks, and replacing the air or flammable gas in the inter-tank space with the inert gas; wherein the volume of the storage space is larger than the volume of the inter-tank space; the inert gas supplied to the storage space is a combustion gas; and the inert gas supplied to the inter-tank space is an inert gas different from the combustion gas.

7. The gas replacement method according to claim 6, wherein the multi-shell tank is provided with a thermal insulation layer containing a porous thermal insulation material, a powdered thermal insulation material, or a fibrous thermal insulation material filled in the inter-tank space, the inert gas supplied to the inter-tank space is nitrogen gas, and the purity of the nitrogen gas is higher than 97%.

8. A multi-shell tank comprising: a plurality of tanks including a first tank and at least one second tank surrounding the first tank; a thermal insulation layer disposed in an inter-tank space, which is the space between two opposing tanks of the plurality of tanks, and surrounding the first tank; a first supply pipe having one end disposed in a storage space, which is the space within the first tank, for supplying combustion gas to the storage space; a second supply pipe having one end disposed in a first inter-tank region, which is a region of the inter-tank space located inside the thermal insulation layer, for supplying an inert gas different from the combustion gas to the first inter-tank region; a third supply pipe fluidly connecting the first supply pipe and the second supply pipe; and a fourth supply pipe branching off from the second supply pipe downstream of a connection between the second supply pipe and the third supply pipe, and having one end disposed in a second inter-tank region, which is a region of the inter-tank space located outside the thermal insulation layer, for supplying the combustion gas to the second inter-tank region.

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