vessel

Abstract

A ship has a hull, at least one double-shell tank mounted on the hull, having an inner tank storing liquefied gas and an outer tank covering the inner tank, at least one first discharge tower extending upward from the hull, at least one second discharge tower extending upward from the hull independently of the first discharge tower, a first discharge line connecting an upper portion in the inner tank and a tower interior of the first discharge tower, a second discharge line connecting the inner tank and an inter-tank region of the outer tank and a tower interior of the second discharge tower, and a pressure release device provided in the second discharge line, which is closed normally and opened when a pressure of the inter-tank region exceeds a prescribed inter-tank allowable value.

Description

Technical Field

[0001] This disclosure relates to ships equipped with double-hulled tanks as cargo tanks. Background Technology

[0002] It is known that ships equipped with double-hulled tanks as cargo tanks have long existed. A double-hulled tank has an inner tank for storing cryogenic fluids such as liquefied gas and an outer tank covering the inner tank. To improve insulation, a vacuum space is formed between the inner and outer tanks of the double-hulled tank, or it is filled with insulating material at atmospheric pressure. Patent Document 1 discloses an example of a liquefied gas transport ship equipped with double-hulled tanks as cargo tanks.

[0003] Patent Document 1 discloses a liquefied gas transport vessel having a cargo tank and a canister enclosing the cargo tank, with an inert gas sealed in the space between the cargo tank and the canister. The cargo tank has an inner tank for storing liquefied gas and an outer tank that ensures a vacuum space between the inner tank and the outer tank.

[0004] Typically, liquefied gas carriers have a pressure relief mechanism that maintains the internal pressure of the cargo tank at a value lower than its design pressure by appropriately venting the vaporized gas generated inside the cargo tank during navigation to the outside of the tank. The pressure relief mechanism generally has a discharge pipe connected to the top of the cargo tank and a pressure relief valve (safety valve) that releases vaporized gas from the cargo tank to the discharge pipe when the internal pressure of the cargo tank becomes excessive. The vaporized gas discharged to the outside of the cargo tank through the discharge pipe is either discharged from a height via a ventilation column, utilized as fuel, or reliquefied and returned to the cargo tank. For example, Patent Document 2 discloses a technique for discharging vaporized gas generated in a cargo tank storing liquefied hydrogen from a position above the top of the cargo tank via a discharge tower.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2014 / 203530

[0008] Patent Document 2: Japanese Patent Application Publication No. 2018-204721 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] In a double-shell tank storing liquefied petroleum gas (LPG), if a crack develops in the inner tank for some reason, the LPG inside the inner tank leaks into the area between the inner and outer tanks. The leaked LPG evaporates in the area between the tanks, increasing the pressure there. To prevent this, it is considered that ships equipped with double-shell tanks should have a pressure relief mechanism for the area between the inner and outer tanks, in addition to the pressure relief mechanism for the inner tank. Therefore, this application proposes a ship equipped with double-shell tanks that has a pressure relief mechanism for the area between the inner and outer tanks.

[0011] Methods for solving problems

[0012] One aspect of the vessel disclosed herein is characterized by comprising: a hull; at least one double-hulled tank mounted on the hull, having an inner tank for receiving liquefied gas and an outer tank covering the inner tank; at least one first discharge tower extending upward from the hull; at least one second discharge tower extending upward from the hull, independent of the first discharge tower; a first discharge line connecting the upper part of the inner tank to the interior of the first discharge tower; a second discharge line independent of the first discharge line and connecting the inter-tank region of the inner tank and the outer tank to the interior of the second discharge tower; and a pressure relief device disposed on the second discharge line, normally closed and open when the pressure in the inter-tank region exceeds a predetermined inter-tank allowable value.

[0013] In ships with the above-described structure, when liquefied gas immersed in the inter-tank area between the inner and outer tanks vaporizes, causing the pressure in the inter-tank area to rise, the vaporized liquefied gas is discharged from the inter-tank area through the second discharge line, thereby relieving pressure in the inter-tank area. Therefore, it is possible to prevent damage to the inner and outer tanks from excessive pressure.

[0014] Furthermore, in the ship with the above-described structure, the evaporated gas generated from the liquefied gas stored in the inner tank and the liquefied gas that leaks and vaporizes into the inter-tank area have independent discharge routes. That is, the discharge route for the evaporated gas in the inner tank is formed by the first discharge line and the first discharge tower, while the discharge route for the liquefied gas that leaks and vaporizes into the inter-tank area is formed by the second discharge line and the second discharge tower. Therefore, when depressurizing the inter-tank area, it is possible to prevent backflow of vaporized liquefied gas and external gas into the discharge route of the evaporated gas in the inner tank.

[0015] Invention Effects

[0016] According to this disclosure, it is possible to propose a vessel equipped with a double-shell tank, which has a pressure relief mechanism for the inter-tank area between the inner and outer tanks. Attached Figure Description

[0017] Figure 1 This is a side view showing the overall structure of a ship according to one embodiment of the present disclosure.

[0018] Figure 2 This is a cross-sectional view illustrating the structure of a double-hulled tank mounted on a ship.

[0019] Figure 3 This diagram illustrates the pressure relief mechanism of a ship. Detailed Implementation

[0020] Figure 1 A vessel 1 according to one embodiment of this disclosure is shown. The vessel 1 has a hull 2, two double-shell tanks 3 mounted on the hull 2, a first discharge tower 15 extending upwards from the hull 2, and a second discharge tower 16. The double-shell tanks 3 are storage tanks for transporting cryogenic fluids. In this embodiment, the double-shell tanks 3 are arranged along the length of the vessel, but they can also be arranged along the width of the vessel if the width is greater. Furthermore, the number of double-shell tanks 3 mounted on the hull 2 ​​can be one or more.

[0021] The two double-shelled tanks have substantially the same construction. For example... Figure 2 As shown, each double-shell tank 3 includes an inner tank 4 for storing goods and an outer tank 5 that encloses the inner tank 4. The inner tank 4 and the outer tank 5 are separated approximately equally, and an insulating layer enclosing the inner tank 4 is formed in the inter-tank region 30 between the inner tank 4 and the outer tank 5.

[0022] The insulation layer formed in the inter-slot region 30 can be a vacuum insulation layer. In this case, for example, the outer surface of the inner slot 4 is covered with a vacuum insulation material (e.g., a sheet formed by alternating layers of radiation shielding film and spacers), and a gap without any material is formed between the vacuum insulation material and the inner surface of the outer slot 5. Alternatively, the insulation layer can be formed by filling the inter-slot region 30 with insulation material. In this case, for example, pearlite as a granular insulation material is filled into the inter-slot region 30 between the inner slot 4 and the outer slot 5 under normal pressure or a depressurized atmosphere.

[0023] The cargo may be one of the following liquefied gases: liquefied petroleum gas (LPG, approximately -45°C), liquefied ethylene gas (LEG, approximately -100°C), liquefied natural gas (LNG, approximately -160°C), liquefied oxygen (LO2, approximately -180°C), liquefied hydrogen (LH2, approximately -250°C), and liquefied helium (LHe, approximately -270°C). However, the cargo does not necessarily have to be a liquid; it may also be a gas.

[0024] The inner tank 4 includes a horizontally elongated cylindrical inner tank body 41 and an inner tank top 42 protruding upward from the inner tank body 41. In this embodiment, the axial direction of the inner tank body 41 is parallel to the length direction of the ship. The axial direction of the inner tank top 42 is parallel to the vertical direction in this embodiment, but it may also be slightly inclined relative to the vertical direction.

[0025] The outer channel 5 comprises a horizontally elongated cylindrical outer channel body 51 and an outer channel top 52 protruding upward from the outer channel body 51. The outer channel body 51 surrounds the inner channel body 41. The outer channel top 52 surrounds the inner channel top 42. The axial direction of the outer channel body 51 is parallel to the ship's length direction, just like the inner channel body 41, and the axial direction of the outer channel top 52 is parallel to the vertical direction, just like the inner channel top 42. However, the inner channel body 41 and the outer channel body 51 do not necessarily have to be horizontally elongated cylindrical shapes; they can also be vertically elongated cylindrical shapes. Alternatively, the inner channel body 41 and the outer channel body 51 can be spherical, cubic, or cuboid.

[0026] The hull 2 ​​has two upward-opening cargo holds 21. The cargo holds 21 are arranged along the length of the ship and are separated from each other by bulkheads 22. Furthermore, the lower part of a double-shell tank 3 is inserted inside the interior of each cargo hold 21.

[0027] Inside each cargo hold 21, a pair of saddles 25, separated from each other along the ship's length, are provided. The saddles 25 support the outer main body 51 of the outer trough 5 of the double-shell tank 3. Additionally, a pair of support members 35 are provided between the inner trough 4 and the outer trough 5 of the double-shell tank 3 to support the inner trough main body 41. In this embodiment, the support members 35 are located at the same position as the saddles 25, but the support members 35 may also be located at a different position than the saddles 25.

[0028] A canister 6 is disposed above each double-shell tank 3. Each canister 6 covers the corresponding double-shell tank 3 from above, and forms a retaining space 7 filled with inert gas between itself and the hull 2. The outer tank body 51 of the aforementioned outer tank 5 is located below the canister 6, and the top 52 of the outer tank penetrates through the canister 6.

[0029] Nitrogen, argon, or other inert gases can be used as the inert gas filling the holding space 7. The inert gas prevents negative pressure formation in the holding space 7 and condensation on the surface of the double-shell tank 3. In particular, when the liquefied gas stored in the inner tank 4 is liquefied hydrogen, the inert gas filling the holding space 7 also prevents the formation of liquefied oxygen around the double-shell tank 3. However, a gas other than an inert gas (e.g., dry air) can also be filled into the holding space 7. Alternatively, the holding space 7 can be left empty, and the gas inside can be ordinary air.

[0030] The inner tank top 42 and the outer tank top 52 are sections for collecting various pipes such as liquefied gas transmission pipes and electrical pipes, and for these pipes (not shown) to pass through. A partition member 33 is disposed between the inner tank top 42 and the outer tank top 52. This partition member 33 is used to maintain most of the tank area 30 as a vacuum when a maintenance opening is formed in the outer tank top 52. The partition member 33 divides the tank area 30 into an upper area 31 that encloses the inner tank top 42 and a lower area 32 that completely encloses the inner tank body 41.

[0031] exist Figure 2 In this configuration, the dividing member 33 is disposed between the peripheral walls of the inner tank top 42 and the outer tank top 52 and has a flat annular shape, but the position and shape of the dividing member 33 can be appropriately changed. For example, the dividing member 33 can also be disposed between the tops of the inner tank top 42 and the outer tank top 52 and has a cylindrical shape.

[0032] An upper vacuum gauge 91 and an upper pressure gauge 93 are installed in the upper region 31. The upper vacuum gauge 91 detects the vacuum level in the upper region 31. The upper pressure gauge 93 detects the pressure in the upper region 31. A lower vacuum gauge 92 and a lower pressure gauge 94 are installed in the lower region 32. The lower vacuum gauge 92 detects the vacuum level in the lower region 32. The lower pressure gauge 94 detects the pressure in the lower region 32. In this way, by installing vacuum gauges and pressure gauges in the upper region 31 and the lower region 32 respectively, not only can a vacuum be detected, but the pressure in the upper region 31 and the lower region 32 can also be detected over a relatively wide range.

[0033] [First pressure relief mechanism 10A]

[0034] The ship 1 of this embodiment has a first pressure relief mechanism 10A for depressurizing the inner tank 4. The first pressure relief mechanism 10A is configured to discharge the evaporated gas retained in the upper part of the inner tank 4 into the atmosphere through a first discharge tower 15 in the event that the pressure in the inner tank 4 (hereinafter referred to as "inner tank pressure") exceeds a preset first allowable pressure.

[0035] In this embodiment, the first discharge tower 15 is approximately I-shaped, extending vertically, and has a discharge outlet at its upper end that opens upwards towards the atmosphere. Furthermore, since the vaporized gas of liquefied petroleum gas is flammable, the location of the discharge outlet of the first discharge tower 15, which releases the vaporized gas, is specified as being "at a horizontal distance of at least 10 meters from living areas, office areas, and ignition sources, and at a height of at least 6 meters above a pedestrian walkway within 4 meters," and is located in a place isolated from ignition sources and crew members on the ship.

[0036] The first pressure relief mechanism 10A includes: a first discharge line 45 connecting the upper part of the inner tank 4 and the first discharge tower 15; a first pressure relief valve (inner tank pressure relief valve) 46 provided on the first discharge line 45; a heating line 47 connecting the lower part of the inner tank 4 and the first discharge line 45; a heater 48 for heating the liquefied gas passing through the heating line 47; an on / off valve 49 provided on the heating line 47; an inner tank pressure gauge 95 for detecting the pressure inside the inner tank 4; and a first control device (inner tank control device) 60A. In this embodiment, the first discharge line 45 connects the top of the inner tank top 42, which is the highest position inside the inner tank 4, to the lower end of the first discharge tower 15.

[0037] The first control device 60A activates the first pressure relief valve 46 and the on / off valve 49 based on the internal tank pressure detected by the internal tank pressure gauge 95. The first control device 60A continuously monitors the internal tank pressure detected by the internal tank pressure gauge 95. When the internal tank pressure exceeds a first permissible value, the first control device 60A performs a first pressure relief control, opening the first pressure relief valve 46 and the on / off valve 49. Furthermore, the first control device 60A also monitors the internal tank pressure during the first pressure relief control. When the internal tank pressure during the first pressure relief control is below a first reference value (first reference value < first permissible value), the first pressure relief valve 46 and the on / off valve 49 are closed, ending the first pressure relief control. The first permissible value is the permissible value for the internal tank, and the first reference value is the reference value for the internal tank.

[0038] When the first pressure relief valve 46 is opened, the evaporated gas of liquefied petroleum gas (LPG) flows from the top of the inner tank 4 to the first discharge line 45. When the on / off valve 49 is opened, LPG flows from the lower part of the inner tank 4 to the heating line 47. The LPG flowing into the heating line 47 is heated by the heater 48 to a temperature higher than that of the evaporated gas in the inner tank 4. The vaporized LPG heated by the heating line 47 flows into the first discharge line 45, whereby the evaporated gas becomes hotter than when it was at the top of the inner tank 4 and flows into the first discharge tower 15. The evaporated gas flowing into the first discharge tower 15 rises within the first discharge tower 15 and is discharged to the atmosphere from the upper end of the first discharge tower 15.

[0039] Thus, in the first pressure relief mechanism 10A, when the pressure inside the inner tank 4 becomes too high, the evaporated gas is discharged to the outside from the inner tank 4 through the first discharge tower 15, thereby relieving the pressure in the inner tank 4. In addition, the evaporated gas discharged to the atmosphere through the first discharge tower 15 is at a higher temperature than when it is inside the inner tank 4, which suppresses the generation of liquid air near the discharge outlet of the first discharge tower 15.

[0040] [Second pressure relief mechanism 10B]

[0041] The vessel 1 of this embodiment has a second pressure relief mechanism 10B, independent of the first pressure relief mechanism 10A. The second pressure relief mechanism 10B is configured such that, in the event that liquefied gas leaks into the inter-tank region 30 between the inner tank 4 and the outer tank 5 of the double-shell tank 3, causing the pressure in the inter-tank region 30 (hereinafter referred to as the "inter-tank pressure") to exceed a predetermined second allowable pressure, the liquefied gas that has leaked into the inter-tank region 30 and vaporized will be discharged to the atmosphere through a second discharge tower 16. In this embodiment, the second discharge tower 16 is independent of the first discharge tower 15. The discharge outlet of the second discharge tower 16 is also located, like the first discharge tower 15, in a location isolated from the vessel's ignition sources and crew.

[0042] The second pressure relief mechanism 10B includes: a second discharge line 81 connecting the outer tank top 52 of the outer tank 5 and the second discharge tower 16; a second pressure relief valve (inter-tank pressure relief valve) 83 installed on the second discharge line 81; a third discharge line 82 connecting the outer tank body 51 of the outer tank 5 and the second discharge line 81; a third pressure relief valve 84 installed on the third discharge line 82; an upper vacuum gauge 91 and an upper pressure gauge 93 that detect the pressure in the upper region 31; a lower vacuum gauge 92 and a lower pressure gauge 94 that detect the pressure in the lower region 32; an inert gas supply line 85 connecting the inert gas source 87 and the second discharge line 81; a supply valve 86 installed on the inert gas supply line 85; and a second control device (inter-tank control device) 60B. The second discharge line 81 is completely independent of the first discharge line 45.

[0043] The second control device 60B can also be shared with the first control device 60A of the first pressure relief mechanism 10A. Furthermore, the functions of the control devices 60A and 60B disclosed in this specification can be executed using circuits or processing circuits including general-purpose processors, special-purpose processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, and / or combinations thereof configured or programmed to perform the disclosed functions. A processor includes transistors or other circuits and is therefore considered a processing circuit or circuit. In this disclosure, a circuit, unit, or component is hardware that performs the listed functions, or hardware programmed to perform the listed functions. The hardware can be the hardware disclosed in this specification, or other known hardware programmed or configured to perform the listed functions. Where the hardware is a processor considered a type of circuit, the circuit, component, or unit is a combination of hardware and software, with the software used in the structure of the hardware and / or processor.

[0044] The second control device 60B activates the second pressure relief valve 83 and the supply valve 86 based on the pressure in the upper region 31 detected by the upper vacuum gauge 91 and the upper pressure gauge 93. The second control device 60B continuously monitors the pressure in the upper region 31 detected by the upper vacuum gauge 91 and the upper pressure gauge 93. When the pressure in the upper region 31 exceeds a second allowable value, the second control device 60B performs a second pressure relief control, opening the second pressure relief valve 83 and the supply valve 86. During the second pressure relief control, the second control device 60B continues to monitor the pressure in the upper region 31. When the pressure in the upper region 31 during the second pressure relief control is below a second reference value (second reference value < second allowable value), the second pressure relief valve 83 and the supply valve 86 are closed, ending the second pressure relief control. Furthermore, the second allowable value is an allowable value for inter-tank use, and the second reference value is a reference value for inter-tank use. Generally speaking, the design pressure resistance of the outer tank 5 is lower than that of the inner tank 4, so there is no special limitation. However, the second allowable value can be smaller than the first allowable value, and the second reference value can be smaller than the first reference value.

[0045] When the second pressure relief valve 83 opens, the vaporized liquefied gas flows from the upper region 31 into the second discharge line 81. When the supply valve 86 opens, inert gas flows from the inert gas source 87 into the second discharge line 81. The inert gas flowing into the second discharge line 81 dilutes the vaporized liquefied gas flowing in the second discharge line 81. The diluted vaporized liquefied gas flows into the second discharge tower 16, rises within the second discharge tower 16, and is discharged to the atmosphere from the upper end of the second discharge tower 16.

[0046] The second control device 60B activates the third pressure relief valve 84 and the supply valve 86 based on the pressure in the lower region 32 detected by the lower vacuum gauge 92 and the lower pressure gauge 94. The second control device 60B continuously monitors the pressure in the lower region 32 detected by the lower vacuum gauge 92 and the lower pressure gauge 94. When the pressure in the lower region 32 exceeds a second allowable value, the second control device 60B performs a third pressure relief control, opening the third pressure relief valve 84 and the supply valve 86. During the third pressure relief control, the second control device 60B continues to monitor the pressure in the lower region 32. When the pressure in the lower region 32 falls below a second reference value during the third pressure relief control, the third pressure relief valve 84 and the supply valve 86 are closed, ending the third pressure relief control.

[0047] When the third pressure relief valve 84 is opened, the vaporized liquefied gas flows from the lower region 32 through the third discharge line 82 to the second discharge line 81. When the supply valve 86 is opened, inert gas flows from the inert gas source 87 to the second discharge line 81. The inert gas flowing into the second discharge line 81 dilutes the vaporized liquefied gas flowing in the second discharge line 81. The diluted vaporized liquefied gas flows into the second discharge tower 16, rises within the second discharge tower 16, and is discharged to the atmosphere from the upper end of the second discharge tower 16.

[0048] Thus, in the second pressure relief mechanism 10B, when the pressure in the upper region 31 and / or the lower region 32 is too high, the vaporized liquefied gas is discharged to the outside from the upper region 31 and / or the lower region 32 through the second discharge tower 16, thereby relieving the pressure in the upper region 31 and / or the lower region 32.

[0049] As described above, the vessel 1 of this embodiment includes: a hull 2; at least one double-shell tank 3 mounted on the hull 2, having an inner tank 4 for receiving liquefied gas and an outer tank 5 covering the inner tank 4; at least one first discharge tower 15 extending upward from the hull 2; at least one second discharge tower 16 extending upward from the hull 2 ​​independently of the first discharge tower 15; a first discharge line 45 connecting the upper part of the inner tank 4 and the interior of the first discharge tower 15; a second discharge line 81 independently of the first discharge line 45 connecting the inter-tank region 30 of the inner tank 4 and the outer tank 5 and the interior of the second discharge tower 16; and a pressure relief device (a second pressure relief valve 83 in this embodiment) provided on the second discharge line 81, which is normally closed and opens when the pressure in the inter-tank region 30 exceeds a predetermined second allowable value (inter-tank allowable value). In addition, in the ship 1 of this embodiment, the inter-slot area 30 is divided into multiple areas (upper area 31 and lower area 32), and each of the multiple areas is connected to the second discharge line 81.

[0050] According to the above-described structure of the vessel 1, when the pressure in the inter-tank region 30 between the inner tank 4 and the outer tank 5 rises due to the liquefied gas entering and vaporizing, the vaporized liquefied gas is discharged from the inter-tank region 30 through the second discharge line 81, thereby relieving the pressure in the inter-tank region 30. Therefore, it is possible to prevent the inner tank 4 and the outer tank 5 from being damaged by excessive pressure.

[0051] Furthermore, the evaporated gas from the inner tank 4 and the vaporized liquefied gas from the inter-tank region 30 have independent discharge routes. That is, the discharge route for the evaporated gas from the inner tank 4 is formed by the first discharge line 45 and the first discharge tower 15, while the discharge route for the vaporized liquefied gas leaking into the inter-tank region 30 is formed by the second discharge line 81 and the second discharge tower 16. Therefore, when depressurizing the inter-tank region 30, it is possible to prevent the vaporized liquefied gas and external gas from flowing back into the discharge route of the evaporated gas from the inner tank 4.

[0052] Furthermore, the vessel 1 of this embodiment includes: a first pressure relief valve (inner tank pressure relief valve) 46, which is provided at the first discharge line 45; an inner tank pressure gauge 95, which detects the pressure inside the inner tank 4; and a first control device (inner tank control device) 60A, which controls the first pressure relief valve 46 such that when the detected pressure inside the inner tank 4 exceeds a first allowable value (inner tank allowable value), the first pressure relief valve 46 is opened, and then when the detected pressure inside the inner tank 4 becomes a predetermined first reference value (inner tank reference value) lower than the first allowable value, the first pressure relief valve 46 is closed.

[0053] Therefore, the first pressure relief mechanism 10A used in the inner tank 4 can operate automatically. Furthermore, in the vessel 1 of this embodiment, the first pressure relief mechanism 10A used in the inner tank 4 can operate independently of the second pressure relief mechanism 10B used in the inter-tank region 30. However, the first pressure relief mechanism 10A and the second pressure relief mechanism 10B can also operate simultaneously.

[0054] Furthermore, the vessel 1 in this embodiment includes: a tank pressure gauge that detects the pressure in the tank area 30; and a second control device (tank control device) 60B that controls a second pressure relief valve 83 such that when the detected pressure in the tank area 30 exceeds a second allowable value, the second pressure relief valve 83 is opened, and then closed when the detected pressure in the tank area 30 becomes a predetermined second reference value (tank allowable value) lower than the second allowable value. Additionally, in the above embodiment, the upper vacuum gauge 91, lower vacuum gauge 92, upper pressure gauge 93, and lower pressure gauge 94 correspond to the tank pressure gauge.

[0055] In this way, the second pressure relief mechanism 10B used in the inter-tank area 30 can operate automatically. In addition, in the ship 1 of this embodiment, the second pressure relief mechanism 10B used in the inter-tank area 30 can operate independently of the first pressure relief mechanism 10A used in the inner tank 4.

[0056] Furthermore, the ship 1 of this embodiment has an inert gas supply line 85 that supplies inert gas to the second discharge line 81.

[0057] Therefore, the vaporized liquefied gas discharged to the atmosphere through the second discharge tower 16 is diluted by an inert gas, thus enabling the vaporized liquefied gas to be discharged more safely.

[0058] The preferred embodiments of the present invention have been described above. However, without departing from the spirit of the present invention, modifications to the specific structure and / or function of the above embodiments may also be included in the present invention. For example, the above structure may be modified as follows.

[0059] For example, in the ship 1 described above, a first pressure relief valve 46 is used as an example of a pressure relief device installed on the first discharge line 45; a second pressure relief valve 83 is used as an example of a pressure relief device installed on the second discharge line 81; and a third pressure relief valve 84 is used as an example of a pressure relief device installed on the third discharge line 82. However, these pressure relief devices are not limited to valves that operate under the control of control devices 60A and 60B. For example, spring-loaded safety valves or rupture plates can also be used as pressure relief devices.

[0060] In addition, in the ship 1 of the above embodiment, the inter-slot area 30 is divided into multiple spaces (upper area 31 and lower area 32), but the dividing member 33 may be omitted so that the inter-slot area 30 is a continuous space.

[0061] Label Explanation

[0062] 1: Ship; 2: Hull; 3: Double-shell tank; 4: Inner tank; 5: Outer tank; 10A: First pressure relief mechanism; 10B: Second pressure relief mechanism; 15: First discharge tower; 16: Second discharge tower; 45: First discharge line; 46: First pressure relief valve (pressure relief valve for inner tank); 60A: First control device (control device for inner tank); 60B: Second control device (control device for inter-tank use); 81: Second discharge line; 82: Third discharge line; 83: 84: 85: 86: 87: 88: 88: 89: 80: 81: 82: 83: 84: 85: 86: 87 ...9: 80: 81: 82: 83: 84: 85: 86: 89: 80: 89: 80: 81: 82: 83: 84

Claims

1. A ship having: hull; At least one double-shell tank, mounted on the hull, having an inner tank for receiving liquefied gas and an outer tank covering the inner tank; At least one first-row tower extends upward from the hull; At least one second discharge tower, independent of the first discharge tower, extends upward from the hull; The first discharge line connects the upper part of the inner tank to the inside of the first discharge tower; The second discharge line connects the inter-tank region of the inner tank and the outer tank to the interior of the second discharge tower, forming a discharge route for the vaporized gas of the liquefied gas independent of the first discharge line; and A pressure relief device, located at the second discharge line, is normally closed and opens when the pressure in the inter-tank region exceeds a specified inter-tank allowable value. The discharge route for the evaporated gas of the liquefied gas discharged from the inner tank is formed by the first discharge line and the first discharge tower, and the discharge route for the vaporized gas of the liquefied gas that leaks into the inter-tank area is formed by the second discharge line and the second discharge tower. The evaporated gas in the inner tank and the vaporized gas in the inter-tank region have independent discharge routes. When the inter-tank region is depressurized, the vaporized gas in the inter-tank region is discharged directly to the atmosphere through the second discharge line and the second discharge tower without flowing back to the discharge route of the evaporated gas in the inner tank.

2. The vessel according to claim 1, wherein, The pressure relief device is a pressure relief valve for use between tanks. The vessel also has: A pressure gauge is used to detect the pressure in the inter-tank region; and A tank control device controls the tank pressure relief valve such that when the detected pressure in the tank area exceeds the allowable value for the tank, the tank pressure relief valve is opened, and then when the detected pressure in the tank area becomes a predetermined tank reference value lower than the allowable value for the tank, the tank pressure relief valve is closed.

3. The vessel according to claim 1 or 2, wherein, The vessel also has an inert gas supply line that supplies inert gas to the second discharge line.

4. The vessel according to claim 1 or 2, wherein, The slot area is divided into multiple regions, and each region is connected to the second discharge line.

5. The vessel according to claim 1 or 2, wherein, The vessel also has: An inner tank pressure relief valve is provided at the first discharge line; An inner tank pressure gauge detects the pressure within the inner tank; and An inner tank control device controls the inner tank pressure relief valve such that when the detected pressure in the inner tank exceeds a predetermined allowable value for the inner tank, the inner tank pressure relief valve is opened, and then when the detected pressure in the inner tank becomes a predetermined reference value for the inner tank that is lower than the allowable value for the inner tank, the inner tank pressure relief valve is closed.

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