Liquefied gas storage tank

Abstract

To provide a liquefied gas storage tank capable of reliably recovering low-temperature liquefied gas from a tank body even when a plurality of skeleton members is disposed inside the tank body.SOLUTION: A triple shell tank 1 comprises a tank body 1T having an inner wall that partitions a space for storing low-temperature liquefied gas, and a roof skeleton 6 that is disposed in the tank body 1T and supports a tank roof. A ring skeleton member 63P constituting a ring 63 of the roof skeleton 6 is disposed so as to form a retention wall 7 that creates a gas retention space 71 that is open at the bottom and closed at the top, in combination with an inner wall of a roof. A purge opening 64 is provided in a top part 63T of a flat plate part 631 of the ring skeleton member 63P, which connects the retention space 71 with an upper space 72 located above the retention space 71.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present disclosure relates to a liquefied gas storage tank for storing low-temperature liquefied gas. [Background technology]

[0002] A tank for storing low-temperature liquefied gas such as liquefied hydrogen or liquefied natural gas has a tank body with a thermal insulation structure. As a liquefied gas storage tank, a flat-bottom tank with a multi-shell structure is known. As a multi-shell tank, a tank with a triple-shell structure is known, which includes an inner tank, an intermediate tank surrounding the inner tank, and an outer tank surrounding the intermediate tank (for example, Patent Document 1).

[0003] In general, frame members are arranged in the tank body for various purposes. For example, frame members that constitute roof frames supporting the roofs of the inner tank, intermediate tank, and outer tank are arranged directly under the roofs. In addition, there are also frame members that constitute stairs for workers to enter the tank body, and an internal deck that is used for roof construction and remains in the tank body after completion. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 55-20937 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, when a liquefied gas storage tank is inspected, maintained, or dismantled, a purging operation is performed to completely recover the low-temperature liquefied gas and its vaporized gas remaining in the tank body before the inspection, maintenance, or dismantling of the tank. This is to prevent the vaporized gas vaporized from the low-temperature liquefied gas and the vaporized gas boiled off in the tank body from being randomly dispersed into the atmosphere. When the above-mentioned rib member is disposed in the tank body, the rib member may form a retention space for the vaporized gas. In this case, the above-mentioned purging operation may not completely recover the vaporized gas from the tank body.

[0006] An object of the present disclosure is to provide a liquefied gas storage tank that can reliably recover vaporized gas from the tank body even when multiple rib members are arranged inside the tank body. [Means for solving the problem]

[0007] A liquefied gas storage tank according to one aspect of the present disclosure includes a tank body having an inner wall that partitions a space for storing low-temperature liquefied gas, and a plurality of bone members arranged within the tank body, wherein at least one of the plurality of bone members is arranged to form, either by itself, in combination with other bone members, or in combination with the inner wall, a retention wall that creates a gas retention space that is open at the bottom and closed at the top, and a purge opening is provided at or near the upper end of the bone member constituting the retention wall, which connects the retention space to an upper space located above the retention space within the tank body. Effect of the Invention

[0008] According to the present disclosure, a liquefied gas storage tank can be provided that can reliably recover vaporized gas from the tank body even when multiple rib members are arranged inside the tank body. [Brief description of the drawings]

[0009] [Figure 1]FIG. 1 is a cross-sectional view showing a schematic diagram of a triple-shell tank according to one embodiment of the liquefied gas storage tank of the present disclosure. [Diagram 2] FIG. 2 is a plan view showing the roof frame supporting the tank roof. [Diagram 3] Figure 3(A) is a cross-sectional view of an example of a bone member that constitutes a roof bone, Figure 3(B) is a plan view showing the assembled state of an arch bone member and a ring bone member, and Figure 3(C) is a cross-sectional view along line IIIC-IIIC in Figure 3(B). [Figure 4] FIG. 4 is a cross-sectional view showing the internal condition of a triple-shell tank during normal operation. [Diagram 5] FIG. 5 is a cross-sectional view showing the internal condition of a triple-shell tank during maintenance, etc. [Figure 6] FIG. 6 is a cross-sectional view showing a retention space formed by combining the ring frame member and the outer tank roof. [Figure 7] FIG. 7(A) is a side view showing a ring bone member having a purge opening, which is an example of a bone member according to this embodiment, and FIG. 7(B) is a cross-sectional view taken along line VIIB-VIIB in FIG. 7(A) illustrating the purge flow when the ring bone member is applied. [Figure 8] FIG. 8 is a cross-sectional view showing a purge flow in a tank body in a triple-shell tank to which the ring frame member according to this embodiment is applied. [Figure 9] FIG. 9 is a cross-sectional view showing another example of a liquefied gas storage tank of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of a liquefied gas storage tank according to the present disclosure will be described in detail with reference to the drawings. The liquefied gas storage tank according to the present disclosure is a tank for storing low-temperature liquefied gas, and is a flat-bottom tank that is stationary on the ground. The stored liquefied gas may be, for example, liquefied hydrogen, liquid helium, liquid nitrogen, liquefied natural gas, or liquefied petroleum gas. In the following embodiment, a triple-shell tank is exemplified as an example of a liquefied gas storage tank. Of course, the liquefied gas storage tank according to the present disclosure may be a multi-shell tank other than a triple-shell tank, or a tank other than a flat bottom.

[0011] [Overall structure of liquefied gas storage tank] 1 is a cross-sectional view showing a triple-shell tank 1 according to an embodiment of the present disclosure. Here, a triple-shell tank 1 for storing liquefied hydrogen LH as a low-temperature liquefied gas is shown as an example. The triple-shell tank 1 includes a tank body 1T including an outer tank 2, an intermediate tank 3, and an inner tank 4 erected on a tank foundation (not shown), a pump barrel 5 which is a structure for discharging the liquefied hydrogen LH from the tank body 1T, and a submerged pump P which is installed in a state immersed in the liquefied hydrogen LH inside the tank body 1T.

[0012] The tank body 1T is in the form of a flat-bottomed cylinder, and the outer tank 2, intermediate tank 3, and inner tank 4 all have a circular shape when viewed from above and are arranged concentrically. The inner tank 4 is a tank having an inner wall that partitions a space for actually storing liquefied hydrogen LH. The intermediate tank 3 surrounds the inner tank 4 via an inner cold insulation layer 11. The outer tank 2 surrounds the intermediate tank 3 via an outer cold insulation layer 12. The tank body 1T may be a tank having a shape other than a flat bottom, or may be a tank buried underground, etc.

[0013] The outer tank 2 is a sealed body made of metal such as carbon steel, and includes an outer tank bottom plate 21, an outer tank side plate 22, and an outer tank roof 23. The outer tank bottom plate 21 is laid directly on the tank foundation and has a disk-like shape. The outer tank side plate 22 stands upright from the periphery of the outer tank bottom plate 21 and has a cylindrical shape. The outer tank roof 23 is attached to the upper end of the cylindrical outer tank side plate 22 so as to close the upper opening of the outer tank side plate 22, and has a dome-like shape.

[0014] The intermediate tank 3 is a sealed body made of low-temperature steel such as austenitic stainless steel, nickel steel, or aluminum alloy, and includes an intermediate tank bottom plate 31, an intermediate tank side plate 32, and an intermediate tank roof 33. The intermediate tank bottom plate 31 has a disk-like shape with a smaller diameter than the outer tank bottom plate 21. The intermediate tank side plate 32 stands upright from the periphery of the intermediate tank bottom plate 31 and has a cylindrical shape. The intermediate tank roof 33 is attached to the upper end of the intermediate tank side plate 32 and has a dome-like shape.

[0015] The inner tank 4 is a sealed body made of low-temperature steel similar to the intermediate tank 3, and includes an inner tank bottom plate 41, an inner tank side plate 42, and an inner tank roof 43. The inner tank bottom plate 41 has a disk-like shape with a smaller diameter than the intermediate tank bottom plate 31. The inner tank side plate 42 stands upright from the periphery of the inner tank bottom plate 41 and has a cylindrical shape. The inner tank roof 43 is attached to the upper end of the inner tank side plate 42 and has a dome-like shape. Liquefied hydrogen LH is stored inside the inner tank 4. The upper layer of the inner tank 4 is a gas phase portion GH where hydrogen gas vaporized from the liquefied hydrogen LH accumulates.

[0016] Between the inner tank 4 and the intermediate tank 3, and between the intermediate tank 3 and the outer tank 2, there are formed gaps of a predetermined width that are used as heat insulating spaces. The gap between the inner tank 4 and the intermediate tank 3 is used as an inner cold insulation layer 11, and the gap between the intermediate tank 3 and the outer tank 2 is used as an outer cold insulation layer 12. The inner cold insulation layer 11 and the outer cold insulation layer 12 are filled with a powder insulation material to improve cold insulation. As the powder insulation material, for example, granular perlite can be used. In addition to the granular perlite, an insulation material such as glass wool may be filled in the areas between the side plates 22 and 32 and between the side plates 32 and 42 that surround the sides of the stored liquefied hydrogen LH.

[0017] The inner cold insulation layer 11 and the outer cold insulation layer 12 are filled with a predetermined seal gas. As the seal gas for the inner cold insulation layer 11, it is desirable to use hydrogen gas or helium gas. In this embodiment, a communication pipe 44 is arranged on the inner tank roof 43 to communicate the gas phase part GH of the inner tank 4 with the space of the inner cold insulation layer 11. Therefore, hydrogen gas, which is a vaporized gas of the liquefied hydrogen LH stored in the inner tank 4, can be used as the seal gas. In addition, by installing the communication pipe 44, the pressure of the inner cold insulation layer 11 and the gas phase pressure of the inner tank 4 can be set to be substantially the same. This makes it possible to suppress liquefaction or solidification of the seal gas of the inner cold insulation layer 11 due to the cold heat of the liquefied hydrogen LH stored in the inner tank 4. The outer cold insulation layer 12 is filled with an inert gas having a boiling point higher than that of hydrogen gas, such as nitrogen gas, as the seal gas. By filling the outer cold insulation layer 12 with the seal gas, it is possible to prevent the intrusion of air and moisture.

[0018] The pump barrel 5 is a cylinder installed so as to penetrate the tank body 1T vertically, and is an outlet pipe when discharging the liquefied hydrogen LH in the tank body 1T to the outside. The pump barrel 5 has an inner barrel space 50, which is an internal space through which the liquefied hydrogen LH flows. The lower end 51 of the pump barrel 5 is disposed near the inner tank bottom plate 41 of the tank body 1T and is immersed in the liquefied hydrogen LH. The upper end 52 of the pump barrel 5 is disposed at a predetermined height position, penetrating the inner tank roof 43, the intermediate tank roof 33, and the outer tank roof 23. The inner barrel space 50 extends vertically between the lower end 51 and the upper end 52, and has an inner diameter that allows the pump P to pass through.

[0019] The pump P is accommodated in the barrel space 50 near the lower end 51 of the pump barrel 5. A foot valve 53 is attached to the intake opening of the lower end 51. The pump P is placed on the foot valve 53. The foot valve 53 hangs down due to the weight of the pump P, and the intake opening of the lower end 51 is opened. As shown by the arrow in FIG. 1, the pump P takes in the liquefied hydrogen LH in the inner tank 4, increases the pressure, and sends the liquefied hydrogen LH to the barrel space 50. A discharge port 54 that discharges the liquefied hydrogen LH to the outside is protruded from the side near the upper end 52 of the pump barrel 5. When the pump P is operated, the liquefied hydrogen LH is discharged from the barrel space 50 through the discharge port 54.

[0020] The pump barrel 5 can also be used as a supply path for purge gas when purging the tank body 1T. When the triple-shell tank 1 is inspected, maintained, or dismantled, a purge operation is performed to completely recover hydrogen gas remaining in the tank body 1T before the inspection, maintenance, or dismantling. At this time, a purge gas having a higher density than hydrogen gas, such as nitrogen gas, is supplied to the tank body 1T, and the hydrogen gas is driven toward the tank roof side and discharged by utilizing the density difference. At this time, the purge gas is supplied from the discharge port 54. Of course, a separate supply path for supplying purge gas into the inner tank 4 may be provided without using the pump barrel 5. A separate purge gas supply path is secured for the space of the outer cold insulation layer 12.

[0021] [Roof bone] Although not shown in Fig. 1, the outer tank roof 23, intermediate tank roof 33, and inner tank roof 43 constituting the tank roof of each tank are supported by roof frames. Fig. 2 is a plan view showing the roof frame 6 that supports the tank roof from below. The roof frame 6 is formed by multiple frame members arranged inside the tank body 1T, and includes multiple arches 61, rafters 62, and rings 63.

[0022] The arch 61 is a frame member extending from the roof center 6A to the radially outward direction of the roof. A plurality of arches 61 are arranged radially at a predetermined interval in the circumferential direction of the roof. The rafter 62 is a frame member arranged between a pair of arches 61 so as to extend from the roof center 6A side toward the radially outward direction in the radially outer region of the roof where the interval between adjacent arches 61 is relatively wide. The ring 63 is an annular frame member connecting the plurality of arches 61 and the rafter 62. A plurality of rings 63 having different diameters are arranged concentrically. The outer peripheral ends of the arch 61 and the rafter 62 are connected to the upper end side of the outer tank side plate 22 (or the intermediate tank side plate 32, the inner tank side plate 42). The inner peripheral end of the arch 61 is connected to the ring 63 near the roof center 6A. The inner peripheral end of the rafter 62 is connected to the ring 63 near the radial center of the roof.

[0023] FIG. 3(A) is a cross-sectional view showing a bone member 6P constituting the roof frame 6. Most of the arch 61, rafter 62 and ring 63 are composed of bone members 6P having an H-shaped cross-sectional shape. The bone members 6P include a flat plate portion 631, an upper plate 632 and a lower plate 633. The flat plate portion 631 is a flat plate extending in a direction perpendicular to the upper plate 632 and the lower plate 633. When assembled as the roof frame 6, the flat plate portion 631 becomes a flat plate extending in a direction intersecting the outer tank roof 23, the intermediate tank roof 33 or the inner tank roof 43 in a cross-sectional view, for example, in the normal direction. The upper plate 632 is connected to the upper end side of the flat plate portion 631, and the lower plate 633 is connected to the lower end side of the flat plate portion 631, and each is a flat plate extending in a direction perpendicular to the flat plate portion 631.

[0024] FIG. 3(B) is a plan view showing the assembled state of a pair of arch bone members 61P (or rafter bone members 62P and arch bone members 61P) constituting the arch 61 and a ring bone member 63P constituting the ring 63, and FIG. 3(C) is a cross-sectional view taken along line IIIC-IIIC in FIG. 3(B). The arch bone members 61P and rafter bone members 62P are H-shaped bone members having a predetermined length in the radial direction of the roof and curved along the dome shape of the roof. The ring bone member 63P is also an H-shaped bone member curved along the circumferential shape of the dome. The ring bone member 63P has a flat plate portion 631 having an upwardly convex arc shape in side view. The upper plate 632 and the lower plate 633 are also curved along the arc shape of the flat plate portion 631.

[0025] The ring bone member 63P is disposed so as to span between a pair of arch bone members 61P. One end of the ring bone member 63P is welded to one arch bone member 61P, and the other end of the ring bone member 63P is welded to the other arch bone member 61P. Scallops 63S consisting of notches to avoid crossing of weld lines are provided near both ends of the flat plate portion 631 of the ring bone member 63P. In addition to the examples shown in Figs. 3(B) and 3(C), the ring bone member 63P can also span between a pair of rafter bone members 62P, or between the arch bone member 61P and the rafter bone member 62P.

[0026] 3(B) and 3(C) show a fan-shaped outer tank roof plate 23P that constitutes part of the outer tank roof 23. The outer tank roof plate 23P is placed on the upper surface of the arch bone member 61P and the ring bone member 63P. The outer tank roof plate 23P may be welded to the arch bone member 61P and the ring bone member 63P, or may be supported by the bone members 61P, 63P without welding. The same applies to the roof plates that constitute the intermediate tank roof 33 and the inner tank roof 43.

[0027] [Inside the tank] Next, the internal condition of the triple-shell tank 1 will be described. Figure 4 is a cross-sectional view showing the internal condition of the tank body 1T during normal operation of the triple-shell tank 1. Liquefied hydrogen (LH2) is stored inside the inner tank 4. Hydrogen gas (H2) vaporized from the liquefied hydrogen accumulates in the upper layer of the inner tank 4.

[0028] The space of the inner cold insulation layer 11 between the inner tank 4 and the intermediate tank 3 and the internal space of the inner tank 4 are in communication with each other via a communication pipe 44. Therefore, hydrogen gas vaporized in the inner tank 4 enters the inner cold insulation layer 11 and functions as a seal gas. Nitrogen gas (N2) is sealed in the outer cold insulation layer 12 between the intermediate tank 3 and the outer tank 2 as a seal gas.

[0029] 5 is a cross-sectional view showing the internal state of the tank body 1T when the triple-shell tank 1 is in an irregular state. An example of an irregular state is when hydrogen gas remaining in the inner tank 4 and intermediate tank 3 is purged before maintenance, inspection, or dismantling of the triple-shell tank 1. On the other hand, the outer cold insulation layer 12 immediately inside the outer tank 2 is designed to assume that hydrogen gas has leaked from the intermediate tank 3.

[0030] During maintenance of the triple-shell tank 1, the liquefied hydrogen stored in the inner tank 4 is discharged through the pump barrel 5 and the discharge port 54 (see FIG. 1). Even after this discharge is completed, hydrogen gas (first gas), which is a vaporized gas of the liquefied gas, remains in the inner tank 4 and the inner cold insulation layer 11. In order to purge the hydrogen gas, a gas having a density greater than that of hydrogen gas, for example, nitrogen gas (second gas), is supplied into the tank body 1T as a purge gas. For example, a nitrogen gas supply source is connected to the discharge port 54 (supply path), and the nitrogen gas is supplied to the inner tank 4 through the pump barrel 5. Alternatively, if a supply path dedicated to purge gas is prepared, the purge gas is supplied to the inner tank 4 using the supply path.

[0031] When nitrogen gas is supplied to the inner tank 4, hydrogen gas, which is lighter than nitrogen gas, accumulates in the upper part of the inner tank 4 as shown in Fig. 5. The nitrogen gas accumulates below the upper part of the inner tank 4, and a lower nitrogen gas layer and an upper hydrogen gas layer are formed inside the inner tank 4. In addition, since the nitrogen gas also enters the inner cold insulation layer 11 through the communication pipe 44, the nitrogen gas accumulates in the lower layer and the hydrogen gas accumulates in the upper layer of the inner cold insulation layer 11. Therefore, the hydrogen gas can be discharged from the tank body 1T by providing one exhaust pipe that communicates the upper part of the inner cold insulation layer 11 with the outside, or by providing two exhaust pipes that communicate the upper part of the inner cold insulation layer 11 with the outside and the upper part of the inner tank 4 with the outside, respectively.

[0032] The outer cold insulation layer 12 and the inner cold insulation layer 11 are isolated by the wall of the intermediate tank 3, so hydrogen gas does not normally enter the outer cold insulation layer 12. However, in the unlikely event that the intermediate tank 3 is damaged, hydrogen gas will enter the outer cold insulation layer 12 from the inner cold insulation layer 11. In this case, since nitrogen gas is present as a seal gas in the outer cold insulation layer 12, the hydrogen gas that has entered remains in the upper layer part of the outer cold insulation layer 12. Therefore, by providing an exhaust pipe that connects the upper layer part of the outer cold insulation layer 12 to the outside, the hydrogen gas that has entered the outer cold insulation layer 12 can be exhausted.

[0033] [Hydrogen gas retention space] As described above, by supplying a purge gas with a higher density than hydrogen gas to the tank body 1T, the difference in gas density can drive the hydrogen gas to the upper part of the tank body 1T and discharge it from the tank roof side. However, the roof frame 6 that supports the outer tank roof 23, intermediate tank roof 33, and inner tank roof 43 from below can cause hydrogen gas to accumulate in the tank body 1T. The areas where hydrogen gas accumulates are created by the ring frame members 63P that constitute the ring 63 assembled around the roof center 6A as the central point.

[0034] 6 is a cross-sectional view showing the retention space 71 formed by the combination of the ring frame member 63P and the outer tank roof 23. The ring frame member 63P is a frame member having an H-shaped cross section and arranged in a direction perpendicular to the radial direction of the outer tank roof 23. Moreover, the ring frame member 63P is arranged inclined toward the spherical center direction of the dome-shaped outer tank roof 23. In detail, the upper plate 632 of the ring frame member 63P abuts against the outer tank roof 23, and the flat plate portion 631 extends downward from the upper plate 632 along the spherical center direction.

[0035] The ring frame member 63P arranged in this manner forms a retention wall 7 in combination with the outer tank roof 23. In the example of FIG. 6, the retention wall 7 is formed by the flat plate portion 631 of the ring frame member 63P and a region of the inner wall of the outer tank roof 23 that is downward from the abutment position of the upper plate 632 and corresponds to the height width of the flat plate portion 631. The retention wall 7 forms a retention space 71 that is open at the bottom and closed at the top. This retention space 71 and the upper space 72 located above the retention space 71 via the flat plate portion 631 are isolated solely by the flat plate portion 631. For this reason, when a method of purging hydrogen gas by driving it upward as shown in FIG. 5 is adopted, a situation may occur in which hydrogen gas is trapped in the retention space 71 and cannot be purged. A similar retention space 71 is also formed by the ring frame member 63P and the intermediate tank roof 33 or the inner tank roof 43, and the same problem of hydrogen gas trapping may occur.

[0036] [Ring bone member according to the embodiment] Fig. 7(A) is a side view showing an example of a ring bone member 63P according to this embodiment, and Fig. 7(B) is a cross-sectional view taken along line VIIB-VIIB in Fig. 7(A). The ring bone member 63P has three purge openings 64, which are round holes drilled near the upper edge of the flat plate portion 631.

[0037] As explained based on FIG. 6, the flat plate portion 631 constitutes the retention wall 7 that creates the retention space 71. As explained previously based on FIG. 3(C), the flat plate portion 631 has an upwardly convex arc shape in side view. One of the purge openings 64 is drilled in the top 63T, which is the highest position of the flat plate portion 631. The purge opening 64 may be provided at or near the upper end of the bone member that constitutes the retention wall 7, and the purge opening 64 may be opened in the top 63T. However, if multiple purge openings 64 are provided, the gas release property is improved. In this embodiment, in addition to the purge opening 64 in the top 63T, purge openings 64 are also opened between the top 63T and the left and right scallops 63S. That is, three independent purge openings 64 are lined up along the upper edge of the flat plate portion 631.

[0038] FIG. 7(B) is also an explanatory diagram of the purge flow F when the ring frame member 63P having the purge opening 64 is applied. By drilling the purge opening 64, the retention space 71 on the left side of the flat plate portion 631 and the upper space 72 located above the retention space 71 in the space inside the tank body 1T are in a state of communication. Therefore, even if hydrogen gas rising toward the outer tank roof 23 enters the retention space 71 due to the density difference with the nitrogen gas, a purge flow F is formed toward the upper space 72 through the purge opening 64. Therefore, the hydrogen gas can flow toward the exhaust path installed on the outer tank roof 23 without being retained in the retention space 71, and the tank body 1T can be purged well.

[0039] The flat plate portion 631 is provided with a scallop 63S, which is a kind of opening. However, the scallop 63S is arranged at both ends of the flat plate portion 631, which is the joint with the arch frame member 61P or the rafter frame member 62P, that is, the welded portion. On the other hand, since the flat plate portion 631 has an upwardly convex arc shape, the opening of the scallop 63S alone will trap hydrogen gas near the top portion 63T. However, in this embodiment, since the purge opening 64 is drilled in the top portion 63T, the trapping of the hydrogen gas can be suppressed. Furthermore, since the purge openings 64 are drilled on both sides of the top portion 63T, the purging of hydrogen gas from the retention space 71 is further promoted.

[0040] The purge opening 64 can be formed in various forms other than the form exemplified in Fig. 7(A). For example, although Fig. 7(A) illustrates the purge opening 64 as a round hole, it may be a rectangular or triangular opening. There is no particular limitation on the arrangement of the purge opening 64 as long as the opening is arranged at or near the apex 63T and does not significantly reduce the strength of the ring bone member 63P. Also, a slit-shaped long hole extending left and right along the upper edge of the flat plate portion 631 may be opened in the region including the apex 63T, and this may be used as the purge opening 64.

[0041] [Tank body purging example] 8 is a cross-sectional view showing the purge flow in the tank body 1T in the triple-shell tank 1A to which the ring frame member 63P according to this embodiment is applied. The outer tank roof 23, intermediate tank roof 33, and inner tank roof 43 of the tank body 1T are each supported by a roof frame 6 including a ring frame member 63P having a purge opening 64. The inside of the tank body 1T shows a state in which the replacement with nitrogen gas (N2) progresses and hydrogen gas (H2) is driven to the upper part of the tank body 1T, similar to the example shown in FIG. 5 above.

[0042] The triple-shell tank 1A is provided with a first exhaust passage 24 and a second exhaust passage 34 provided on the roof of the tank body 1T. The first exhaust passage 24 is a pipe that is erected on or near the top of the outer tank roof 23 and connects the outer cold insulation layer 12 to the outside. The first exhaust passage 24 is equipped with a first opening / closing valve 25 that is always "closed" during tank operation and "opened" during maintenance, etc. The second exhaust passage 34 is equipped with a second opening / closing valve 35 that is always "closed" during tank operation and "opened" during maintenance, etc. The second exhaust passage 34 is equipped with a second opening / closing valve 35 that is always "closed" during tank operation and "opened" during maintenance, etc.

[0043] As the supply of nitrogen gas from the supply path (not shown) to the inner tank 4 and the outer cold insulation layer 12 progresses, hydrogen gas flows upward due to the density difference and is discharged to the outside of the tank from the first exhaust path 24 and the second exhaust path 34, whose on-off valves 25, 35 are respectively "open". At this time, the ring frame member 63P blocks the flow of the hydrogen gas. However, since the ring frame member 63P is provided with the purge opening 64, the hydrogen gas does not stagnate at the location where the ring frame member 63P is arranged.

[0044] Specifically, a purge flow F11 is formed from the inner tank 4 toward the second exhaust passage 34 through the communicating pipe 44. The purge flow F11 includes a flow passing through the purge opening 64 of the ring frame member 63P supporting the inner tank roof 43. A purge flow F12 is also formed in the inner cold insulation layer 11 (intermediate tank 3) toward the second exhaust passage 34, including a flow passing through the purge opening 64. In the outer cold insulation layer 12 (outer tank 2), a purge flow F13 is formed toward the first exhaust passage 24, including a flow passing through the purge opening 64. By the above-mentioned purge flows F11, F12, and F13, the hydrogen gas in the tank body 1T is discharged to the outside and collected.

[0045] According to the triple-shell tank 1 according to the present embodiment described above, the ring frame member 63P of the roof frame 6 is disposed in the tank body 1T so as to form the retention space 71. However, even if hydrogen gas enters the retention space 71 due to the supply of nitrogen gas by the purging operation, the ring frame member 63P has a purge opening 64, so that the hydrogen gas can escape from the retention space 71 to the upper space 72. Moreover, the purge opening 64 is drilled in the top of the flat plate portion 631 that is inclined toward the spherical center of the tank roof and has a convex arc shape. Therefore, the purging operation that discharges hydrogen gas from the tank roof side due to the density difference with nitrogen gas does not allow hydrogen gas to remain in the retention space 71, and the hydrogen gas can be reliably recovered from the tank body 1T.

[0046] In this embodiment, the triple-shell tank 1 is exemplified as a liquefied gas storage tank. Instead, the present disclosure can be applied to a double-shell tank having an inner tank and an outer tank, for example, to obtain the same effect. In this case, too, an opening similar to the above-mentioned purge opening 64 may be provided in the ring bone members of the roof bones that support the inner tank roof and the outer tank roof, respectively.

[0047] [Other embodiments] In the above embodiment, the ring frame member 63P of the roof frame 6 is exemplified as a frame member that forms the retention space 71 (see FIG. 6) that retains gas, and an example is shown in which the purge opening 64 is provided in the ring frame member 63P. Inside the tank body 1T, there are other frame members, combinations of multiple frame members, or combinations of frame members and tank inner walls that can form the retention space 71. Such frame members may also be provided with purge openings.

[0048] 9 is a cross-sectional view showing a liquefied gas storage tank 100 according to another embodiment. A deck 81 and an internal staircase 82 are assembled inside the liquefied gas storage tank 100. The deck 81 is assembled as a scaffold for construction of the tank roof, and remains inside the tank body even after completion of construction. The internal staircase 82 is a turn-around staircase for workers to enter and exit the inner bottom of the tank, and is provided with a landing 83 at the turn-around portion. The deck 81 and the internal staircase 82 are facilities that are generally provided in many liquefied gas storage tanks.

[0049] The internal staircase 82 including the deck 81 and the landing 83 is often made of C-shaped steel 84 (frame member) as shown in FIG. 9. The C-shaped steel 84 is generally laid with its opening facing downward. Therefore, when hydrogen gas in the tank is purged using nitrogen gas as the purge gas, the C-shaped steel 84 is likely to form a retention space 710 that holds the hydrogen gas. In consideration of this, a purge opening 85 is provided in the horizontal plate located at the upper end when the C-shaped steel 84 is laid. This allows the retention space 710 inside the C-shaped steel 84 to be in communication with the space above it through the purge opening 85. Therefore, it is possible to prevent hydrogen gas from being retained in the retention space 710 during the purging operation.

[0050] Purge openings may be provided not only in the deck 81 and the internal staircase 82, but also in various accessories present in the tank body 1T. For example, retention spaces in which hydrogen gas accumulates may be formed in accessories such as stiffeners, which are stiffening materials for the inner tank side plate 42, the connecting pipe 44 near the joint between the connecting pipe 44 and the inner tank roof 43, or the bulkhead structure disposed between the inner tank roof 43 and the intermediate tank roof 33. Alternatively, retention spaces may be formed by combining accessories with frame members. Therefore, purge openings may be provided in such accessories as well.

[0051] [Summary of this disclosure] The specific embodiments described above include disclosures having the following configurations.

[0052] A liquefied gas storage tank according to a first aspect of the present disclosure includes a tank body having an inner wall that partitions a space for storing low-temperature liquefied gas, and a plurality of bone members arranged within the tank body, wherein at least one of the plurality of bone members is arranged to form a retention wall that creates a gas retention space that is open at the bottom and closed at the top, either by the bone member alone, in combination with other bone members, or in combination with the bone member and the inner wall, and a purge opening is provided at or near the upper end of the bone member constituting the retention wall, which connects the retention space with an upper space located above the retention space within the tank body.

[0053] According to the above liquefied gas storage tank, the frame members are disposed in the tank body so as to form a retention space. However, even if a situation occurs in which vaporized gas of low-temperature liquefied gas enters the retention space, the frame members have purge openings, so the vaporized gas can escape from the retention space to the upper space. Moreover, the purge openings are opened at or near the upper end of the frame members constituting the retention wall. Therefore, when the vaporized gas is discharged from the tank roof side, the structure can be made such that the vaporized gas is not allowed to remain in the retention space.

[0054] The liquefied gas storage tank of the second aspect is a liquefied gas storage tank of the first aspect, wherein the tank body includes a cylindrical side panel, a roof covering the upper opening of the side panel, and a roof rib supporting the roof from below, the roof ribs including a plurality of arches or rafters arranged radially from the center of the roof and rings arranged concentrically, and the rib members are ring rib members arranged between adjacent arches or between the arches and the rafters and constituting the rings.

[0055] According to the second aspect, a purge opening is drilled in a ring bone member that constitutes a part of the roof bone. Therefore, the retention space formed by the presence of the ring bone member can be communicated with the space above the roof bone through the purge opening. Therefore, the entrapment of vaporized gas by the ring bone member can be suppressed.

[0056] The liquefied gas storage tank of the third aspect is the liquefied gas storage tank of the second aspect, wherein the roof has a dome-shaped shape, the ring frame member includes a flat plate portion extending in a direction intersecting the roof in a cross-sectional view and having an upwardly convex arc shape in a side view, the flat plate portion being arranged at an angle toward the spherical center of the roof, and the purge opening is drilled in the top of the arc-shaped flat plate portion.

[0057] According to a third aspect, the ring frame member includes a flat plate portion that is inclined toward the spherical center of the tank roof and has a convex arc shape. With such a shape of the ring frame member, the vaporized gas tends to remain near the top of the arc-shaped flat plate portion. In view of this, the purge opening is drilled in the top of the flat plate portion. This further suppresses the entrapment of the vaporized gas by the ring frame member.

[0058] The liquefied gas storage tank of the fourth aspect is the liquefied gas storage tank of the first to third aspects, further comprising a supply passage for supplying a second gas having a density greater than that of a first gas stored in the tank body into the tank body, and an exhaust passage provided on the roof of the tank body for discharging the first gas based on the density difference when the second gas is supplied into the tank body in which the first gas is stagnating.

[0059] According to the fourth aspect, the first gas can be discharged from the tank body by utilizing the density difference between the first gas and the second gas. At this time, since the exhaust path from the retention space to the upper space is secured by the purge opening, the first gas can be prevented from remaining in the retention space. That is, when a gas (second gas) having a higher density than a vaporized gas (first gas) of a low-temperature liquefied gas is supplied into the tank body and the vaporized gas is driven toward the tank roof side by the gas density difference and discharged, the vaporized gas can be prevented from remaining in the retention space.

[0060] The liquefied gas storage tank of the fifth aspect is the liquefied gas storage tank of the first aspect, wherein the tank body includes an attachment other than the frame member, and a retention area in which a gas retention space that is open at the bottom and closed at the top is created by a combination of the frame member and the attachment, and a purge opening is provided in the attachment that constitutes the retention area.

[0061] According to the fifth aspect, since the accessory is also provided with a purge opening, retention of vaporized gas within the tank body can be further suppressed. [Explanation of symbols]

[0062] 1. Triple-shell tank (liquefied gas storage tank) 1T tank body 2 Outer tank 21, 22, 23 Outer tank bottom plate, outer tank side plate, outer tank roof 24 First exhaust duct (exhaust duct) 3 Intermediate tank 31, 32, 33 Intermediate tank bottom plate, intermediate tank side plate, intermediate tank roof 34 Second exhaust duct (exhaust duct) 4 Inner tank 41, 42, 43 Inner tank bottom plate, inner tank side plate, inner tank roof (inner wall) 5 Pump barrel (supply line) 54 Delivery port (supply route) 6 Roof frame 6 (frame member) 61 Arch 62 Laughter 63 Ring 63P Ring bone member 63T Apex (top of bone member) 631 Flat plate section (flat plate section with arc shape) 64 Purge opening 7 Retention wall 71 Retention space 72 Upper space 84 C type steel (bone component) 85 Purge opening LH Liquefied hydrogen (low temperature liquefied gas) H2 Hydrogen gas (first gas) N2 Nitrogen gas (second gas)

Claims

1. A tank body having an inner wall that defines a space for storing low-temperature liquefied gas; a plurality of rib members disposed within the tank body; At least one of the plurality of bone members is arranged to form a retention wall that creates a gas retention space that is open at the bottom and closed at the top, either by the bone member alone, in combination with other bone members, or in combination with the bone member and the inner wall; A liquefied gas storage tank, wherein a purge opening is provided at or near the upper end of the bone member constituting the retention wall, connecting the retention space with an upper space located above the retention space within the tank body.

2. 2. The liquefied gas storage tank according to claim 1, The tank body includes a cylindrical side plate, a roof that closes an upper opening of the side plate, and a roof frame that supports the roof from below, The roof frame includes a plurality of arches or rafters arranged radially from the center of the roof and a ring arranged concentrically, A liquefied gas storage tank, wherein the bone members are ring bone members arranged between adjacent arches or between the arches and the rafters and form the ring.

3. 3. The liquefied gas storage tank according to claim 2, The roof has a dome shape; the ring frame member includes a flat plate portion extending in a direction intersecting the roof in a cross-sectional view and having an upwardly convex arc shape in a side view, the flat plate portion being disposed at an angle toward a spherical center of the roof, A liquefied gas storage tank, wherein the purge opening is drilled in the top of the arc-shaped flat plate portion.

4. The liquefied gas storage tank according to any one of claims 1 to 3, a supply path for supplying a second gas having a density greater than that of the first gas stored in the tank body into the tank body; The liquefied gas storage tank further includes an exhaust passage provided on the roof of the tank body, which exhausts the first gas based on the density difference when the second gas is supplied into the tank body in which the first gas is stagnating.

5. 2. The liquefied gas storage tank according to claim 1, The tank body includes an attachment other than the frame member, and a retention area in which a gas retention space that is open at the bottom and closed at the top is created by a combination of the frame member and the attachment, A liquefied gas storage tank, wherein a purge opening is provided in the attachment that constitutes the retention area.

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