Triple shell tank

Abstract

To enable purge processing of an inner cold insulation layer to be performed even in a situation where a manhole of an intermediate tank roof is closed.SOLUTION: A triple shell tank (1) includes: an inner tank (4) including an inner tank roof (43); an intermediate tank (3) including an intermediate tank roof (33) which covers the upper side of the inner tank roof (43); an outer tank (2) including an outer tank roof (23) which covers the upper side of the intermediate tank roof (33); a manhole (35) including a cylindrical body part (36) which extends upward in a state that a hole (H1) formed at the intermediate tank roof (33) is located at a bottom, and a lid part (37) which closes an upper end opening of the body part (36); and a nozzle (50) which is branched from the body part (36) of the manhole (35), extends upward, and penetrates through the outer tank roof (23).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a triple-shell tank including an inner vessel, an intermediate vessel, and an outer vessel. [Background technology]

[0002] The tank shown in Patent Document 1 below is known as a tank for storing low-temperature liquefied gas. Specifically, Patent Document 1 discloses a cylindrical double-shell tank equipped with an inner tank for containing liquefied gas, an outer tank for accommodating the inner tank, and a purging means for replacing gas in the space between the inner and outer tanks (hereinafter referred to as the cold insulation layer) with an inert gas. The purging means introduces an inert gas from the outside into the cold insulation layer, and uses the introduced inert gas to push the gas in the cold insulation layer out of the outer tank. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 156800 / 1983 Summary of the Invention [Problem to be solved by the invention]

[0004] Here, triple-shell tanks that further include an intermediate tank between the inner and outer tanks are sometimes used to store liquefied gas. In such triple-shell tanks, when a process (hereinafter referred to as a purging process) is performed to replace the gas in the outer cold insulation layer, which is the space between the outer and intermediate tanks, with a replacement gas, the replacement gas can be discharged to the outside, for example, through a manhole provided in the roof of the outer tank. However, when a purging process is performed on the inner cold insulation layer, which is the space between the inner and intermediate tanks, the same method cannot be applied. In other words, because the manhole in the roof of the intermediate tank is blocked during the purging process, the replacement gas cannot be discharged from the inner cold insulation layer through the manhole.

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and aims to provide a triple-shell tank that is capable of purging the inner cold insulation layer even when the manhole in the intermediate tank roof is closed. [Means for solving the problem]

[0006] In order to solve the above problem, a triple-shell tank according to one aspect of the present disclosure comprises an inner tank including an inner tank roof, an intermediate tank including an intermediate tank roof covering the upper part of the inner tank roof, an outer tank including an outer tank roof covering the upper part of the intermediate tank roof, a manhole including a cylindrical body extending upward with a hole formed in the intermediate tank roof as its base and a lid portion that closes the upper end opening of the body below the outer tank roof, and a nozzle that branches off from the body of the manhole, extends upward, and penetrates the outer tank roof. [Effects of the Invention]

[0007] According to the triple-shell tank of the present disclosure, the inner cold insulation layer can be purged even when the manhole in the intermediate tank roof is closed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing the structure of the upper part of a triple-shell tank according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is an enlarged cross-sectional view of a portion of the triple-shell tank. [Figure 3] FIG. 2 is a perspective view showing the structure of a purge pipe device. [Figure 4] FIG. 3 is a cross-sectional view showing a support structure of the purge pipe device. [Figure 5] FIG. 2 is a view equivalent to FIG. 1 showing the gas flow during air purging of the inner tank. [Figure 6] FIG. 2 is a diagram equivalent to FIG. 1 showing the gas flow during air purging of the inner cold insulation layer. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Triple-shell tank structure] Figure 1 is a cross-sectional view showing the structure of the upper part of a triple-shell tank 1 according to one embodiment of the present disclosure. The triple-shell tank 1 shown in this figure is a flat-bottomed cylindrical tank for storing liquefied hydrogen (LH), and comprises an outer tank 2 erected on a tank foundation (not shown), an intermediate tank 3 housed inside the outer tank 2, and an inner tank 4 housed inside the intermediate tank 3. The outer tank 2, intermediate tank 3, and inner tank 4 are all circular in top view and arranged concentrically. Liquefied hydrogen (LH) is stored inside the inner tank 4.

[0010] The outer tank 2 is a sealed body made of metal such as carbon steel, and includes a disk-shaped outer tank bottom plate laid on the top surface of the tank foundation, a cylindrical outer tank side plate 22 erected from the periphery of the outer tank bottom plate, and an outer tank roof 23 that closes the top opening of the outer tank side plate 22. The outer tank roof 23 is a dome-shaped roof with a convex spherical surface on the upward side.

[0011] The intermediate tank 3 is a sealed body made of an appropriate metal material and is disposed inside the outer tank 2. The intermediate tank 3 includes a disk-shaped intermediate tank bottom plate having a smaller diameter than the outer tank bottom plate, a cylindrical intermediate tank side plate 32 standing upright from the periphery of the intermediate tank bottom plate, and an intermediate tank roof 33 that closes the upper opening of the intermediate tank side plate 32. The intermediate tank roof 33 is a dome-shaped roof with an upwardly convex spherical surface.

[0012] The inner tank 4 is made of low-temperature steel such as austenitic stainless steel and is disposed inside the intermediate tank 3. The inner tank 4 includes a disk-shaped inner tank bottom plate having a smaller diameter than the intermediate tank bottom plate, a cylindrical inner tank side plate 42 erected from the periphery of the inner tank bottom plate, and an inner tank roof 43 that closes the upper opening of the inner tank side plate 42. The inner tank roof 43 is a dome-shaped roof with an upwardly convex spherical surface.

[0013] The upper layer of the inner tank 4 is the gas phase LA. The gas phase LA is a space filled with hydrogen gas evaporated from the liquefied hydrogen LH, and is formed between the inner tank roof 43 and the liquid surface of the liquefied hydrogen LH.

[0014] A gap of a predetermined width is formed between the inner tank 4 and the intermediate tank 3, and between the intermediate tank 3 and the outer tank 2. Each gap functions as a cold insulation layer (thermal insulation space) that suppresses heat transfer from the outside air to the liquefied hydrogen LH. That is, the triple-shell tank 1 includes an inner cold insulation layer 11 between the inner tank 4 and the intermediate tank 3, and an outer cold insulation layer 12 between the outer tank 2 and the intermediate tank 3.

[0015] To improve the cold insulation properties, the inner cold insulation layer 11 and the outer cold insulation layer 12 are filled with granular insulation material 15. The granular insulation material 15 is a fluid insulation material made of an aggregate of particles such as perlite or glass bubbles.

[0016] The inner cold insulation layer 11 is filled with a seal gas. Specifically, the inner cold insulation layer 11 is filled with a gas corresponding to the liquefied hydrogen LH in the inner tank 4, i.e., hydrogen gas, as the seal gas. In this embodiment, the seal gas is hydrogen gas in the gas phase LA of the inner tank 4. That is, the hydrogen gas introduced into the inner cold insulation layer 11 from the gas phase LA through a connecting pipe 45, which will be described later, is used as the seal gas for the inner cold insulation layer 11.

[0017] The outer cold insulation layer 12 is filled with a seal gas different from that of the inner cold insulation layer 11. Specifically, the outer cold insulation layer 12 is filled with an inert gas, such as nitrogen gas, that has a higher boiling point than hydrogen gas, which is the seal gas of the inner cold insulation layer 11. Filling the outer cold insulation layer 12 with a seal gas improves the heat insulating performance.

[0018] A manhole 35 protrudes from the intermediate tank roof 33. The manhole 35 is a cylindrical body that connects the inner cold insulation layer 11 and the outer cold insulation layer 12, and is provided so as to protrude upward from the intermediate tank roof 33. The manhole 35 can be used, for example, to carry in and out equipment, for workers to enter and exit, and for filling with granular insulation material 15. In this embodiment, the manhole 35 is located at or near the top 33a of the intermediate tank roof 33, that is, the highest position of the dome-shaped intermediate tank roof 33.

[0019] As shown in FIG. 2, the manhole 35 includes a body 36 and a lid 37. The body 36 is a cylindrical member with a hole H1 formed in the top 33a of the intermediate tank roof 33 as its bottom. The upper end of the body 36 is located at a height between the intermediate tank roof 33 and the outer tank roof 23, and is spaced downward from the outer tank roof 23. A flange 36a extending radially outward is formed at the upper end of the body 36. The lid 37 is a disk-shaped member capable of closing the upper end opening of the body 36 and is detachably attached to the flange 36a. The lid 37 attached to the flange 36a closes the upper end opening of the body 36, thereby blocking communication between the inner cold insulation layer 11 and the outer cold insulation layer 12. When performing work using the manhole 35, the lid 37 is removed from the flange 36a to open the upper end opening of the body 36.

[0020] A purge nozzle 50 is connected to the body 36 of the manhole 35. The purge nozzle 50 is a pipe that branches off from the body 36 and extends upward, and is arranged to penetrate the outer tank roof 23. That is, as shown in FIG. 2, the purge nozzle 50 includes a branch pipe 51 that extends horizontally from the body 36, and a vertical pipe 52 that extends vertically from the tip of the branch pipe 51 to above the outer tank roof 23. The purge nozzle 50 corresponds to the "nozzle" in this disclosure.

[0021] The inside of the manhole 35 leading to the inner cold insulation layer 11 and the outside of the outer tank 2 are connected to each other via the above-mentioned purge nozzle 50. Hereinafter, the outside of the outer tank 2 will be abbreviated to "outside of the tank." In other words, the purge nozzle 50 is a pipe that connects the inner cold insulation layer 11 to the outside of the tank. The purge nozzle 50 is used as a discharge route for the gas to be replaced during a purge process (details of which will be described later) in which the gas in the inner cold insulation layer 11 is replaced with a replacement gas.

[0022] A first valve 53 is attached to the vertical pipe 52 of the purge nozzle 50. The first valve 53 is a valve that opens and closes the purge nozzle 50, and is disposed outside the outer tank 2.

[0023] As shown in FIG. 1, multiple manholes 25 protrude from the outer tank roof 23. Each manhole 25 is a cylindrical body that connects the outer cold insulation layer 12 to the outside of the tank (outside air), and is provided so as to protrude upward from various locations on the outer tank roof 23. In this embodiment, the multiple manholes 25 include one central manhole 25A located at the top 23a of the dome-shaped outer tank roof 23, and multiple peripheral manholes 25B located at the shoulder 23b of the outer tank roof 23 radially outward from the central manhole 25A. Like the manhole 35 of the intermediate tank roof 33 described above, each manhole 25A, 25B can be used to perform at least one of the following tasks: carrying in and out equipment, allowing workers to enter and exit the tank, and filling the granular insulation material 15.

[0024] 2, the central manhole 25A includes a cylindrical body 26 that extends upward from a hole H2 formed in the top 23a of the outer tank roof 23, and a lid 27 that closes the upper end opening of the body 26. The lid 27 is detachably attached to a flange 26a at the upper end of the body 26. Although not shown in detail, the structure of the peripheral manhole 25B is basically the same as that of the central manhole 25A.

[0025] As shown in Figures 1 and 2, the inner tank roof 43 is provided with a communication pipe 45 that connects the interior of the inner tank 4 with the inner cold insulation layer 11. The communication pipe 45 is a circular pipe with a relatively short axial length in the vertical direction, and is provided so as to penetrate the top 43a of the dome-shaped inner tank roof 43. A breathable filter 46 is attached to the upper end of the communication pipe 45. The filter 46 is made of a material that can block the flow of the granular insulation material 15 while allowing the flow of gases such as hydrogen gas. Such a communication pipe 45 plays a role in balancing the pressure of the inner cold insulation layer 11 and the pressure of the gas phase portion LA of the inner tank 4.

[0026] The communicating pipe 45 is aligned vertically with the manholes 35, 25A of the intermediate tank roof 33 and the outer tank roof 23. That is, the manhole 35 of the intermediate tank roof 33 is located directly above the communicating pipe 45, and the central manhole 25A of the outer tank roof 23 is located directly above the manhole 35. In other words, the communicating pipe 45, the manhole 35, and the central manhole 25A are aligned vertically along the center line of the triple-shell tank 1.

[0027] Here, the triple-shell tank 1 of this embodiment is equipped with a plurality of pipes penetrating the roof portion in addition to the above-mentioned purge nozzle 50 penetrating the outer tank roof 23. Specifically, as shown in Fig. 1, the triple-shell tank 1 is equipped with a plurality of purge pipe devices 60 that connect the inner cold insulation layer 11 to the outside of the tank, and a BOG pipe 70 that connects the inside of the inner tank 4 to the outside of the tank.

[0028] The BOG piping 70 is a piping for extracting hydrogen gas (boil-off gas) generated by vaporization of liquefied hydrogen LH from the gas phase LA of the inner tank 4. The BOG piping 70 is installed so as to penetrate the outer tank roof 23, the intermediate tank roof 33, and the inner tank roof 43, and connects the gas phase LA of the inner tank 4 to the outside of the tank. The boil-off gas extracted through the BOG piping 70 can be re-liquefied, for example, by a liquefier and returned to the inner tank 4, or can be supplied as fuel gas to a demand destination such as a power generation facility. In this embodiment, the BOG piping 70 is also used as a supply route for replacement gas during purging of the inner tank 4 and the inner cold insulation layer 11. Such a BOG piping 70 corresponds to the "supply pipe" in this disclosure.

[0029] A third valve 71 is attached to the BOG pipe 70. The third valve 71 is a valve that opens and closes the BOG pipe 70, and is disposed outside the outer tank 2.

[0030] The multiple purge pipe devices 60 are pipes used as discharge routes for the gas to be replaced during purging of the inner cold insulation layer 11. Each purge pipe device 60 is disposed in a region radially outwardly spaced from the shoulder portion 33b of the intermediate tank roof 33, i.e., the top portion 33a of the intermediate tank roof 33. In this embodiment, the multiple purge pipe devices 60 include a first purge pipe device 60A and a second purge pipe device 60B that are radially spaced apart. The first purge pipe device 60A is disposed near the outermost periphery of the intermediate tank roof 33, and the second purge pipe device 60B is disposed radially inwardly of the first purge pipe device 60A.

[0031] The first purge pipe device 60A and the second purge pipe device 60B have basically the same structure except for their different diameters. FIG. 3 is a perspective view showing the structure of each purge pipe device 60A, 60B. As shown in this figure, the first purge pipe device 60A (second purge pipe device 60B) includes a base pipe 61 and multiple nozzle pipes 62. The base pipe 61 is a ring-shaped pipe arranged along the underside of the intermediate tank roof 33. The nozzle pipe 62 is a pipe extending upward from the base pipe 61. In this embodiment, two nozzle pipes 62 are provided, extending upward from two positions on the base pipe 61 that face each other across the center. The nozzle pipes 62 correspond to the "additional nozzles" in this disclosure.

[0032] The base pipe 61 includes a plurality of short pipes 64 arranged alternately along a predetermined circumference and a plurality of vent joints 65. That is, the plurality of arc-shaped short pipes 64 are arranged along the circumference, and adjacent short pipes 64 are connected to each other via vent joints 65, thereby forming a ring-shaped base pipe 61 as a whole. The diameter of the base pipe 61 of the first purge pipe device 60A is larger than the diameter of the base pipe 61 of the second purge pipe device 60B (see FIG. 1).

[0033] The ventilation joints 65 are permeable cylinders made primarily of, for example, glass wool, and connect adjacent short pipes 64 with a gap between them. This gap functions as an opening for introducing gas into the base pipe 61. In other words, the base pipe 61 has air intake ports S1 for introducing gas at multiple locations around the circumference that correspond to the ventilation joints 65. The ventilation joints 65 are made of a material that allows gas to flow into these air intake ports S1, while preventing the granular insulation material 15 from flowing into the air intake ports S1.

[0034] 4, each base pipe 61 of the first and second purge pipe devices 60A, 60B is supported on the intermediate tank roof 33 via a support 67. The support 67 is fixed to the roof frame 38 of the intermediate tank roof 33, and supports the ring-shaped base pipe 61 below the intermediate tank roof 33.

[0035] More specifically, the intermediate tank roof 33 includes the roof ribs 38 and roof panels 39 that form the ceiling surface. The roof ribs 38 are members that form the framework of the intermediate tank roof 33 and are arranged to extend circumferentially and radially along the underside of the roof panels 39. That is, the roof ribs 38 include a plurality of ring-shaped first frame elements 38a arranged concentrically and a plurality of second frame elements 38b that extend radially outward from the center of the roof. The support 67 can be fixed to either the first frame element 38a or the second frame element 38b, but this embodiment illustrates a case in which the support 67 is fixed to the ring-shaped first frame element 38a.

[0036] The nozzle pipe 62 extends upward from the base pipe 61 and penetrates the roof panel 39. The inside of the base pipe 61 and the outside of the tank are connected to each other via the nozzle pipe 62. Here, the base pipe 61 is formed with the above-mentioned multiple intake ports S1, and therefore, by connecting the base pipe 61 to the outside of the tank via the nozzle pipe 62, a discharge route for gas from the intake port S1 to the outside of the tank is secured.

[0037] 1 and 3, each nozzle pipe 62 of the first and second purge pipe devices 60A, 60B is attached with a second valve 63. The second valve 63 is a valve that opens and closes the nozzle pipe 62, and is disposed outside the outer tank 2.

[0038] As shown in FIG. 1, the triple-shell tank 1 further includes a gas inlet pipe 73 and a gas outlet pipe 74 .

[0039] The gas introduction pipe 73 is provided so as to penetrate the outer tank side plate 22. One end of the gas introduction pipe 73 opens to the outer cold insulation layer 12. The other end of the gas introduction pipe 73 is drawn out to the outside of the outer tank 2 and connected to a gas supply source not shown. The gas supply source supplies replacement gas during purging of the outer cold insulation layer 12. The supplied replacement gas is introduced into the outer cold insulation layer 12 through the gas introduction pipe 73.

[0040] A fourth valve 75 is attached to the gas introduction pipe 73. The fourth valve 75 is a valve that opens and closes the gas introduction pipe 73, and is disposed outside the outer vessel 2.

[0041] The gas exhaust pipe 74 is provided so as to penetrate all of the outer tank side plate 22, the intermediate tank side plate 32, and the inner tank side plate 42. One end of the gas exhaust pipe 74 opens into the interior of the inner tank 4, and the other end of the gas exhaust pipe 74 is drawn out to the outside of the outer tank 2. During purging of the inner tank 4, the gas to be replaced in the inner tank 4 is exhausted to the outside through the gas exhaust pipe 74.

[0042] A fifth valve 76 is attached to the gas exhaust pipe 74. The fifth valve 76 is a valve that opens and closes the gas exhaust pipe 74, and is disposed outside the outer tank 2.

[0043] [Purge Process] During construction or maintenance of the triple-shell tank 1, a purging process may be performed to replace the gas present in the inner tank 4, inner cold insulation layer 11, and outer cold insulation layer 12 with a predetermined replacement gas (purge gas). A specific example of this purging process is described below. At the start of the purging process, the inner tank 4, inner cold insulation layer 11, and outer cold insulation layer 12 are each filled with air. At the start of the purging process, the inner cold insulation layer 11 and outer cold insulation layer 12 are each filled with granular insulation material 15, and the manhole 35 in the intermediate tank roof 33 is closed. With the manhole 35 closed, i.e., with the top opening of the body 36 of the manhole 35 closed by the lid 37, communication between the inner cold insulation layer 11 and the outer cold insulation layer 12 is blocked, and the cold insulation layers 11 and 12 are independent spaces.

[0044] In this embodiment, the purging process of the inner tank 4, the inner cold insulation layer 11, and the outer cold insulation layer 12 includes a process of replacing air with nitrogen gas and a process of replacing nitrogen gas with hydrogen gas. Hereinafter, the former process of replacing air with nitrogen gas will be referred to as "air purging," and the latter process of replacing nitrogen gas with hydrogen gas will be referred to as "N2 purging."

[0045] FIG. 5 is a diagram showing the gas flow during air purging of the inner tank 4. As shown in this figure, during air purging of the inner tank 4, nitrogen gas (N2) is supplied to the inner tank 4 through the BOG piping 70, and air is discharged from the inner tank 4 through the gas exhaust pipe 74. To achieve this gas flow, in this embodiment, the third valve 71 attached to the BOG piping 70 and the fifth valve 76 attached to the gas exhaust pipe 74 are both opened. Meanwhile, the first valve 53 and the second valve 63 are closed. Then, when nitrogen gas is supplied from the BOG piping 70 in this state, the air present in the inner tank 4 is pushed out by the nitrogen gas and led to the gas exhaust pipe 74, through which it is discharged to the outside of the tank. As a result, the gas in the inner tank 4 is replaced with nitrogen gas.

[0046] After the air purge of the inner tank 4 is completed as described above, the inner cold insulation layer 11 is then purged with air. FIG. 6 is a diagram showing the gas flow during the air purge of the inner cold insulation layer 11. As shown in this figure, during the air purge of the inner cold insulation layer 11, nitrogen gas (N2) is supplied to the inner tank 4 through the BOG piping 70, and air is discharged from the inner cold insulation layer 11 through the purge nozzle 50 and the purge pipe device 60. To achieve this gas flow, in this embodiment, the first valve 53 attached to the purge nozzle 50, the second valve 63 attached to each nozzle pipe 62 of the purge pipe device 60, and the third valve 71 attached to the BOG piping 70 are all opened. Meanwhile, the fifth valve 76 is closed. In this state, nitrogen gas is supplied from the BOG piping 70, and the nitrogen gas is introduced into the inner cold insulation layer 11 through the inner tank 4 and the connecting pipe 45. The introduced nitrogen gas pushes the air present in the inner cold insulation layer 11 out of the tank through the purge nozzle 50 and the purge pipe device 60.

[0047] That is, in this embodiment, there are two routes for discharging air from the inner cold insulation layer 11: a first route passing through the purge nozzle 50, and a second route passing through the purge pipe device 60 (base pipe 61 and nozzle pipe 62). In the first route, the air enters the body portion 36 of the manhole 35 of the intermediate tank roof 33, which is in a closed state, and is then guided from the body portion 36 to the purge nozzle 50, and is further discharged to the outside of the tank through the purge nozzle 50. In the second route, the air is introduced into the base pipe 61 through multiple intake ports S1 (FIG. 3), and is then discharged from the base pipe 61 to the nozzle pipe 62 to the outside of the tank. As a result, the gas in the inner cold insulation layer 11 is replaced with nitrogen gas.

[0048] 5 and 6, air purging of the outer cold insulation layer 12 is performed in parallel with the air purging of the inner tank 4 and inner cold insulation layer 11. During this air purging of the outer cold insulation layer 12, nitrogen gas (N2) is supplied to the outer cold insulation layer 12 through the gas inlet pipe 73, and air is discharged from the outer cold insulation layer 12 through the manhole 25 in the outer tank roof 23. To achieve this gas flow, in this embodiment, the fourth valve 75 attached to the gas inlet pipe 73 is opened, and the manhole 25 in the outer tank roof 23 is opened. Then, when nitrogen gas is supplied from the gas inlet pipe 73 in this state, the air present in the outer cold insulation layer 12 is pushed by the nitrogen gas into the manhole 25 and discharged to the outside of the tank through the upper end opening of the manhole 25. As a result, the gas in the outer cold insulation layer 12 is replaced with nitrogen gas.

[0049] The air purging of the outer cold insulation layer 12 as described above does not necessarily have to be performed simultaneously with the air purging of the inner tank 4 and the inner cold insulation layer 11, and the air purging of both may be performed at different times.

[0050] After the air purge of the inner tank 4, the inner cold insulation layer 11, and the outer cold insulation layer 12 is completed as described above, an N2 purge is then performed to replace the nitrogen gas with hydrogen gas. The procedure is the same as that shown in Figures 5 and 6, except that hydrogen gas is used instead of nitrogen gas as the replacement gas. This N2 purge replaces the nitrogen gas in each of the gases in the inner tank 4, the inner cold insulation layer 11, and the outer cold insulation layer 12 with hydrogen gas.

[0051] [Action and effect] As described above, in this embodiment, the manhole 35 is provided in the intermediate tank roof 33, and the purge nozzle 50, which branches off from the body 36 of this manhole 35 and extends upward, penetrates the outer tank roof 23. This configuration has the advantage that the inner cold insulation layer 11 can be purged even when the manhole 35 of the intermediate tank roof 33 is closed, making it easier to purge the inner cold insulation layer 11.

[0052] When purging the inner cold insulation layer 11, the manhole 35 of the intermediate tank roof 33 is already closed, so even if replacement gas is supplied to the inner cold insulation layer 11, the upper opening of the manhole 35 cannot be used as an outlet for the replacement gas. In contrast, in this embodiment, the purge nozzle 50 branching off from the body 36 of the manhole 35 penetrates the outer tank roof 23, so that the replacement gas that has entered the body 36 is discharged from the body 36 to the outside of the outer tank 2, i.e., the outside of the tank, through the purge nozzle 50. In this way, the addition of the purge nozzle 50 ensures a route from the manhole 35 to the outside of the tank, so that the body 36 of the closed manhole 35 can be used as part of the discharge route, and the replacement gas can be discharged to the outside of the tank through the purge nozzle 50 branching off from the body 36, thereby facilitating purging of the inner cold insulation layer 11.

[0053] In addition, in this embodiment, a manhole 35 is provided at the top 33a of the dome-shaped intermediate tank roof 33, so that the gas to be replaced can be discharged from the top 33a, where the gas to be replaced tends to collect, to the outside of the tank through the manhole 35 and the purge nozzle 50, thereby preventing the gas to be replaced from remaining in the inner cold insulation layer 11 without being replaced and increasing the gas replacement rate of the inner cold insulation layer 11.

[0054] In other words, in this embodiment, the purge nozzle 50 branches off from the manhole 35 located in the center of the intermediate tank roof 33. Therefore, compared to, for example, a case where a nozzle is provided near the manhole 35 without branching off from it, it is possible to prevent the nozzle inlet from being misaligned with the center of the roof, and the gas to be replaced inside the tank can be discharged to the outside evenly.

[0055] In addition, in this embodiment, a purge pipe device 60 including a nozzle pipe 62 that penetrates both the intermediate tank roof 33 and the outer tank roof 23 is provided on the shoulder portion 33b of the intermediate tank roof 33.Therefore, using the purge pipe device 60 and the above-mentioned purge nozzle 50, the gas to be replaced can be discharged from multiple radially dispersed locations, thereby improving the efficiency of the purging process of the inner cold insulation layer 11.

[0056] In addition, in this embodiment, the purge pipe device 60 includes a base pipe 61 that is disposed between the intermediate tank roof 33 and the inner tank roof 43 and has multiple air intake ports S1, and a nozzle pipe 62 that extends upward from the base pipe 61 and penetrates the intermediate tank roof 33 and the outer tank roof 23. Such a configuration has the advantage of further improving the efficiency of the purging process.

[0057] That is, a plurality of intake ports S1 are formed in the base pipe 61 located between the intermediate tank roof 33 and the inner tank roof 43, and the gas to be replaced can be taken into the base pipe 61 from various locations in the inner cold insulation layer 11 through these plurality of intake ports S1. Also, a nozzle pipe 62 penetrating the intermediate tank roof 33 and the outer tank roof 23 is connected to the base pipe 61, and the gas to be replaced taken into the base pipe 61 can be discharged through this nozzle pipe 62 to the outside of the outer tank 2, i.e., to the outside of the tank. In this way, in this embodiment, by using the plurality of intake ports S1 formed in the base pipe 61 as intake ports for the gas to be replaced, the gas to be replaced can be taken in from multiple locations dispersed in the circumferential or radial direction and discharged to the outside of the tank, and the efficiency of the purging process of the inner cold insulation layer 11 can be further improved.

[0058] In this embodiment, the inner tank roof 43 is provided with the communicating pipe 45, and the BOG piping 70 is provided to communicate the inside of the inner tank 4 with the outside of the tank (the outside of the outer tank 2). Therefore, the inner tank 4 can be purged with replacement gas supplied from the BOG piping 70 to the inner tank 4, and the inner cold insulation layer 11 can be purged with replacement gas introduced from the inner tank 4 to the inner cold insulation layer 11 through the communicating pipe 45. In other words, the common BOG piping 70 can serve as both a supply route for replacement gas for purging the inner tank 4 and a supply route for replacement gas for purging the inner cold insulation layer 11.

[0059] In addition, in this embodiment, the manhole 35 of the intermediate tank roof 33 is located directly above the connecting pipe 45 of the inner tank roof 43, and the central manhole 25A of the outer tank roof 23 is located directly above the manhole 35.Therefore, when transporting equipment, etc. into or out of the inner tank 4, for example, the equipment can be transported in or out straight in the vertical direction using each manhole 35, 25A and the connecting pipe 45, thereby improving the workability of the transport.

[0060] [Variations] Although the preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the present disclosure.

[0061] For example, in the above embodiment, when purging the inner cold insulation layer 11, the replacement gas supplied from the BOG piping 70 to the inner tank 4 is introduced into the inner cold insulation layer 11 through the connecting pipe 45, but a separate pipe may be provided to supply the replacement gas directly to the inner cold insulation layer 11.

[0062] In the above embodiment, a purge pipe device 60 was prepared that included a purge nozzle 50 that branches off from the manhole 35 and extends upward, as well as a ring-shaped base pipe 61 and a nozzle pipe 62 that extends upward from it.However, as for the discharge pipe other than the purge nozzle 50, it is sufficient if there is at least a nozzle (additional nozzle) that penetrates the intermediate tank roof 33 and the outer tank roof 23 radially outside the manhole 35, and something equivalent to the base pipe 61 is not required.

[0063] In the above embodiment, the triple-shell tank 1 for storing liquefied hydrogen LH is taken up as an example of a triple-shell tank, but the present disclosure is broadly applicable to triple-shell tanks for storing low-temperature liquefied gases, and the storage object is not limited to liquefied hydrogen. For example, the present disclosure can also be applied to triple-shell tanks for storing low-temperature liquefied gases such as liquid helium, liquid nitrogen, and liquefied natural gas.

[0064] In the above embodiment, a flat-bottomed cylindrical triple-shell tank 1 including an outer tank 2, an intermediate tank 3, and an inner tank 4 is used as an example of a triple-shell tank, but the present disclosure is broadly applicable to triple-shell tanks including at least three tanks, and can also be applied to triple-shell tanks other than flat-bottomed cylindrical tanks. Alternatively, the present disclosure may be applied to a multi-shell tank having three or more shells including three or more (e.g., four) tanks.

[0065] [summary] The above-described embodiment and its modifications include the following disclosures.

[0066] The triple-shell tank according to the first aspect of the present disclosure comprises an inner tank including an inner tank roof, an intermediate tank including an intermediate tank roof covering the upper part of the inner tank roof, an outer tank including an outer tank roof covering the upper part of the intermediate tank roof, a manhole including a cylindrical body extending upward from a hole formed in the intermediate tank roof as its base and a lid portion that closes the upper end opening of the body below the outer tank roof, and a nozzle that branches off from the body of the manhole, extends upward, and penetrates the outer tank roof.

[0067] According to this first aspect, a nozzle branching from the body of the manhole in the intermediate tank roof penetrates the outer tank roof, and the gas to be replaced that enters the body of the manhole is discharged from the body to the outside of the outer tank, i.e., the outside of the tank, through the nozzle. In this way, the addition of the nozzle ensures a route from the manhole to the outside of the tank, and the body of the closed manhole can be used as part of the discharge route, allowing the gas to be discharged to the outside of the tank through the nozzle branching from the body. This facilitates purging of the inner cold insulation layer, which is the space between the outer tank and the intermediate tank.

[0068] A triple-shell tank according to a second aspect is the same as the first aspect, except that the intermediate tank roof is formed in a dome shape, and the manhole is provided at the top of the intermediate tank roof.

[0069] According to the second aspect, the gas to be replaced can be discharged to the outside of the tank through the manhole and nozzle from the top of the intermediate tank roof where the gas to be replaced tends to collect, thereby preventing the gas to be replaced from remaining in the inner cold insulation layer without being replaced, and increasing the gas replacement rate of the inner cold insulation layer.

[0070] The triple-shell tank of the third aspect is the same as that of the second aspect, and further comprises an additional nozzle provided on the shoulder of the intermediate tank roof radially outward from the manhole and penetrating both the intermediate tank roof and the outer tank roof.

[0071] According to this third aspect, an additional nozzle is provided on the shoulder of the intermediate tank roof, and by using this additional nozzle and the nozzle described above, the gas to be replaced can be discharged from multiple locations dispersed in the radial direction, thereby improving the efficiency of the purging process of the inner cold insulation layer.

[0072] The triple-shell tank of the fourth aspect is the same as that of the first to third aspects, and further includes a connecting pipe connecting the inner cold insulation layer, which is the space between the inner tank and the intermediate tank, to the inside of the inner tank, and a supply pipe connecting the inside of the inner tank to the outside of the outer tank.

[0073] According to the fourth aspect, the inner tank can be purged by the replacement gas supplied from the supply pipe to the inner tank, and the inner cold insulation layer can be purged by the replacement gas introduced from the inner tank through the connecting pipe to the inner cold insulation layer. That is, a common supply pipe can serve as both the supply route of the replacement gas for purging the inner tank and the supply route of the replacement gas for purging the inner cold insulation layer.

[0074] The triple-shell tank of the fifth aspect is the fourth aspect, wherein the connecting pipe is arranged to penetrate the inner tank roof, and the manhole is arranged in the intermediate tank roof at a position directly above the connecting pipe.

[0075] According to this fifth aspect, for example, when carrying equipment into or out of the inner tank, the equipment can be carried in or out straight in the vertical direction using the manhole and the connecting pipe, thereby improving the workability of the carrying in and out. [Explanation of symbols]

[0076] 1. Triple-shell tank 2 Outer tank 3 Intermediate tank 4 Inner tank 23 Outer tank roof 33 Intermediate tank roof 33a (Top of intermediate tank roof) 33b (intermediate tank roof) shoulder 35 Manhole 36 Torso 37 Lid 43 Inner tank roof 45 Communication pipe 50 Purge nozzle (nozzle) 62 Nozzle pipe (additional nozzle) 70 BOG piping (supply pipe) H1 (Intermediate tank roof) hole

Claims

1. an inner tank including an inner tank roof; an intermediate tank including an intermediate tank roof covering an upper portion of the inner tank roof; An outer tank including an outer tank roof covering the upper part of the intermediate tank roof; a manhole including a cylindrical body portion extending upward from a hole formed in the intermediate tank roof as a bottom, and a lid portion closing an upper end opening of the body portion below the outer tank roof; A triple-shell tank comprising: a nozzle that branches off from the body of the manhole, extends upward, and penetrates the outer tank roof.

2. The triple-shell tank according to claim 1, The intermediate tank roof is formed in a dome shape, The manhole is provided at the top of the intermediate tank roof.

3. The triple-shell tank according to claim 2, A triple-shell tank further comprising an additional nozzle provided on a shoulder of the intermediate tank roof radially outwardly away from the manhole and penetrating both the intermediate tank roof and the outer tank roof.

4. The triple-shell tank according to any one of claims 1 to 3, A communication pipe that communicates an inner cold insulation layer, which is a space between the inner tank and the intermediate tank, with the inside of the inner tank; A triple-shell tank further comprising a supply pipe communicating between the interior of the inner tank and the outside of the outer tank.

5. The triple-shell tank according to claim 4, The communication pipe is provided so as to penetrate the inner tank roof, The manhole is provided in a position on the intermediate tank roof directly above the communicating pipe.

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