Operation method of liquefied gas storage tank and liquefied gas storage tank

Abstract

To prevent a powder thermal insulating material from being compacted when hotting up a liquefied gas storage tank.SOLUTION: A method for operating a liquefied gas storage tank (1) includes: an inner tank (4) for storing liquefied gas; an outer tank (3) for storing the inner tank (4) through a cold insulation layer (13); and a powder thermal insulating material (15) put into the cold insulation layer (13) in a state that a gap is generated between a roof (33) of the outer tank (3) and the cold insulation layer. The method includes: performing hotting up for removing liquefied gas from the inner tank (3) and causing the temperature of the inner tank (3) to get close to the room temperature; and performing powder fluidization for supplying gas to the cold insulation layer (13) and fluidizing the powder thermal insulation material (15) by the supplied gas at the time of the hotting-up.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to a liquefied gas storage tank in which a cold insulation layer between an outer tank and an inner tank is filled with powder insulation material. [Background technology]

[0002] The liquefied gas storage tank may be opened for maintenance or the like, as described in, for example, Patent Document 1 below. Specifically, in Patent Document 1, the following steps are performed before opening the liquefied gas storage tank (low-temperature tank): a step of draining the residual liquid in the inner tank, a step of draining the combustible gas (boil-off gas) from the tank using an inert gas such as nitrogen gas supplied from the outside after the residual liquid is drained, a step of raising the temperature of the inner tank using the same inert gas, and a step of introducing outside air into the inner tank after the temperature of the inner tank is raised. This creates an environment inside the tank that an operator can enter, making it possible to perform maintenance on the tank. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-25467 A Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, when a liquefied gas storage tank is opened, a process for raising the temperature of the inner tank beforehand is required. Hereinafter, this process is referred to as hot-up. When hot-up is performed, the temperature of the inner tank, which had dropped to about the same temperature as the liquefied gas during tank operation, rises to near room temperature. This causes the inner tank to expand, reducing the volume of the cold insulation layer between the inner tank and the outer tank. In cases where the volume of the cold insulation layer is reduced relatively significantly, the powder insulation material filled in the cold insulation layer may be compressed, and a large pressure that may buckle the inner tank may be applied to the inner tank.

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and aims to prevent powder insulation from being compacted when a liquefied gas storage tank is heated up. [Means for solving the problem]

[0006] In order to solve the above problems, an operating method according to one aspect of the present disclosure is a method of operating a liquefied gas storage tank having an inner tank for storing liquefied gas, an outer tank for accommodating the inner tank via an insulation layer, and powder insulation material filled in the insulation layer with a gap between the inner tank and the roof of the outer tank, and includes performing a hot-up process in which liquefied gas is removed from the inner tank to bring the temperature of the inner tank closer to room temperature, and performing powder fluidization during the hot-up process in which gas is supplied to the insulation layer and the supplied gas fluidizes the powder insulation material.

[0007] In addition, a liquefied gas storage tank according to another aspect of the present disclosure includes an inner tank for storing liquefied gas, an outer tank for accommodating the inner tank via a cold insulation layer, powder insulation material filled in the cold insulation layer with a gap formed between the inner tank and the roof of the outer tank, and a gas supply device capable of supplying gas to the cold insulation layer for fluidizing the powder insulation material. Effect of the Invention

[0008] According to the present disclosure, it is possible to prevent powder insulation from compacting when a liquefied gas storage tank is heated up. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view illustrating a schematic diagram of a liquefied gas storage tank according to an embodiment of the present disclosure. [Diagram 2] FIG. 4 is a schematic plan view showing the structure of a supply ring. [Diagram 3] FIG. 1 is a cross-sectional view showing a procedure (part 1) for hotting up the tank body. [Figure 4] FIG. 11 is a cross-sectional view showing the procedure (part 2) for hotting up the tank body. [Diagram 5] FIG. 4 is a cross-sectional view showing the procedure (part 3) for hotting up the tank body. [Figure 6] FIG. 11 is a cross-sectional view showing the procedure (part 4) for hotting up the tank body. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the liquefied gas storage tank of the present disclosure will be described in detail with reference to the drawings. The liquefied gas storage tank of the present disclosure is a tank for storing low-temperature liquefied gas. The stored liquefied gas is, for example, liquefied hydrogen, liquid helium, liquid nitrogen, liquefied natural gas, or liquefied petroleum gas. In the following embodiment, as an example of the liquefied gas storage tank, a flat-bottom cylindrical double-shell tank in which the liquefied gas stored is liquefied hydrogen is exemplified. Of course, the present disclosure is also applicable to double-shell tanks other than flat-bottom cylindrical tanks, or multi-shell tanks such as triple-shell tanks.

[0011] [Structure of liquefied gas storage tank] 1 is a cross-sectional view showing a schematic diagram of a liquefied gas storage tank 1 according to an embodiment of the present disclosure. As shown in the figure, the liquefied gas storage tank 1 is a tank for storing liquefied hydrogen (LH2), which is a cryogenic liquefied gas, and includes a ground-mounted tank body 2 erected on a tank foundation 10, a gas supply device 5 for supplying gas to the tank body 2, and a gas replacement device 6 for replacing the gas in the tank body 2.

[0012] The tank body 2 is a flat-bottomed cylindrical double-shell tank, and includes an outer tank 3 and an inner tank 4 housed inside the outer tank 3. The outer tank 3 and the inner tank 4 are each formed in a circular shape when viewed from above, and are arranged concentrically. Liquefied hydrogen is stored in a storage space defined inside the inner tank 4.

[0013] The outer tank 3 is a sealed body made of metal such as carbon steel, and includes a disk-shaped outer tank bottom plate 31 laid on the upper surface of the tank foundation 10, a cylindrical outer tank side plate 32 erected from the periphery of the outer tank bottom plate 31, and an outer tank roof 33 that covers the upper opening of the outer tank side plate 32. The outer tank roof 33 is a dome-shaped roof with a convex spherical surface on the upper side.

[0014] The inner tank 4 is made of low-temperature steel such as austenitic stainless steel, nickel steel, or aluminum alloy, and is housed inside the outer tank 3. The inner tank 4 includes a disk-shaped inner tank bottom plate 41 having a smaller diameter than the outer tank bottom plate 31, a cylindrical inner tank side plate 42 standing on the periphery of the inner tank bottom plate 41, 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 that presents an upwardly convex spherical surface.

[0015] The upper layer of the inner tank 4 is a gas phase section SG. The gas phase section SG is a space filled with hydrogen gas (GH2) evaporated from the liquefied hydrogen, and is formed between the inner tank roof 43 and the liquid level S1 of the liquefied hydrogen (LH2).

[0016] A bottom cold insulation layer 11 is interposed between the inner tank bottom plate 41 and the tank foundation 10. The bottom cold insulation layer 11 is a heat insulating layer for suppressing heat input from the tank foundation 10 to the inner tank bottom plate 41. The bottom cold insulation layer 11 can be composed of a laminate of solid insulation materials such as foam glass and lightweight aerated concrete.

[0017] A cold insulation layer 13 is formed between the outer tank 3 and the inner tank 4. The cold insulation layer 13 is a gap (space) of a predetermined width formed between the inner tank 4 and the outer tank 3. That is, the cold insulation layer 13 includes a cylindrical ring-shaped side cold insulation layer 13a between the outer tank side plate 32 and the inner tank side plate 42, and a dome-shaped roof cold insulation layer 13b between the outer tank roof 33 and the inner tank roof 43. The cold insulation layer 13 has a function of suppressing heat input from the outside air to the inner tank side plate 42 and the inner tank roof 43.

[0018] The cold insulation layer 13 is filled with powder insulation material 15 to improve the cold insulation performance. The powder insulation material 15 is a fluid insulation material consisting of an aggregate of particles such as perlite and glass bubbles. In other words, the outer vessel 3 accommodates the inner vessel 4 via the cold insulation layer 13 filled with the powder insulation material 15.

[0019] The powder insulation material 15 is filled so as to occupy most of the cold insulation layer 13, except for a portion of the roof cold insulation layer 13b that contacts the outer tank roof 33. That is, an unfilled space NS where no powder insulation material 15 exists is formed in the roof cold insulation layer 13b. In the example of FIG. 1, the unfilled space NS is a ring-shaped space defined between the peripheral portion of the outer tank roof 33 and the upper surface of the powder insulation material 15. In other words, the powder insulation material 15 is filled in the cold insulation layer 13 in a state where a gap (unfilled space NS) is generated between the outer tank roof 33 and the powder insulation material 15.

[0020] The non-filled space NS is naturally formed during construction of the liquefied gas storage tank 1. That is, during construction of the liquefied gas storage tank 1, after the outer tank 3 and the inner tank 4 are constructed, the powder insulation material 15 is filled into the cold insulation layer 13 through a manhole or the like (not shown) formed in the outer tank 3. At this time, since the outer tank 3 and the inner tank 4 are at room temperature, when liquefied hydrogen is introduced into the inner tank 4 and the inner tank 4 is cooled, the inner tank 4 contracts with the cooling. This contraction of the inner tank 4 expands the volume of the cold insulation layer 13. Therefore, even if the powder insulation material 15 fills the cold insulation layer 13 almost without any gaps before the inner tank 4 contracts, a non-filled space NS is naturally formed in a part of the cold insulation layer 13. Note that the powder insulation material 15 gathers downward due to gravity, so the non-filled space NS is formed only in the upper end of the cold insulation layer 13, that is, in a part of the roof part cold insulation layer 13b that contacts the outer tank roof 33. In this way, the liquefied gas storage tank 1 necessarily has an unfilled space NS (gap) in the roof cold insulation layer 13b due to its structure or construction reasons.

[0021] The cold insulation layer 13 is filled with a seal gas. Specifically, the cold insulation layer 13 is filled with a gas corresponding to the liquid (liquefied hydrogen) in the inner tank 4, that is, hydrogen gas, as the seal gas. In this embodiment, the seal gas is hydrogen gas supplied from the gas phase section SG of the inner tank 4. That is, the hydrogen gas introduced from the gas phase section SG to the cold insulation layer 13 through a communication pipe 45 described later is used as the seal gas for the cold insulation layer 13.

[0022] A resin-based heat insulating material 17 is disposed on the inner periphery of the side cold insulation layer 13a surrounding the inner tank side plate 42. The resin-based heat insulating material 17 is a cotton-like heat insulating material having a predetermined thickness in the radial direction of the tank body 2. For example, glass wool or rock wool is suitable as the resin-based heat insulating material 17. The resin-based heat insulating material 17 is in contact with the inner tank side plate 42 and is disposed in a limited portion of the radially inner side of the side cold insulation layer 13a. The outer region of the resin-based heat insulating material 17 in the side cold insulation layer 13a is occupied by the powder heat insulating material 15.

[0023] The inner tank roof 43 is provided with a communication pipe 45 (communication portion) that communicates the inside of the inner tank 4 with the cold insulation layer 13. 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 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 powder 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 cold insulation layer 13 and the pressure of the gas phase section SG of the inner tank 4.

[0024] The gas supply device 5 is a device that fluidizes the powder insulation material 15 by supplying gas to the cold insulation layer 13. The gas supply device 5 is used when hotting up the tank body 2 for maintenance or the like. Hotting up is a process in which liquefied hydrogen is removed from the inner tank 4 to bring the temperature of the inner tank 4 closer to room temperature. Details of hotting up will be described later.

[0025] The gas supply device 5 fluidizes the powder insulation material 15 by circulating hydrogen gas generated by vaporization of liquefied hydrogen, i.e., boil-off gas, inside and outside the tank body 2 and supplying it to the cold insulation layer 13. Specifically, the gas supply device 5 includes a blower 51 provided outside the tank body 2, a plurality of supply rings 52 arranged in multiple stages up and down in the side cold insulation layer 13a, an upstream pipe 53 connecting the inside of the inner tank 4 and the blower 51, and a downstream pipe 54 connecting the blower 51 and each supply ring 52.

[0026] FIG. 2 is a schematic plan view showing the structure of the supply ring 52. As shown in FIG. 1 and FIG. 2, the supply ring 52 is a ring-shaped pipe arranged at the outermost periphery of the side cold insulation layer 13a. That is, the supply ring 52 is formed so as to extend along the inner surface of the outer tank side plate 32 at a position close to the inner surface. The supply ring 52 has a large number of nozzle holes h1 that serve as outlets for hydrogen gas. The nozzle holes h1 are arranged in a line at a predetermined interval in the direction indicated by the arrow A1 along the inner and outer periphery of the supply ring 52, in other words, in the circumferential direction of the tank body 2. In other words, the nozzle holes h1 are distributed at various points on the circumferential surface of the supply ring 52 so that hydrogen gas is sprayed to a plurality of points separated in the circumferential direction of the side cold insulation layer 13a. The nozzle holes h1 are also distributed in the circumferential direction of the circle when the supply ring 52 is viewed in cross section, that is, in the direction perpendicular to the arrow A1. To prevent powder insulating material 15 from entering the inside of supply ring 52 through nozzle holes h1, each nozzle hole h1 is covered with a breathable filter made of glass wool or the like.

[0027] As shown in FIG. 1, in this embodiment, five supply rings consisting of first to fifth supply rings 52A to 52E are prepared as the multiple supply rings 52. The first to fifth supply rings 52A to 52E are arranged in the side cold insulation layer 13a in a state of being arranged at equal intervals in the vertical direction. Specifically, the first supply ring 52A, the second supply ring 52B, ... the fifth supply ring 52E are arranged in this order so that their heights decrease in that order. In other words, the first to fifth supply rings 52A to 52E are respectively distributed and arranged at different heights in the side cold insulation layer 13a so that the first supply ring 52A is the highest and the fifth supply ring 52E is the lowest. In the following description, when the first to fifth supply rings 52A to 52E are referred to without distinction, they are simply referred to as supply rings 52.

[0028] The upstream piping 53 is a piping that penetrates the inner tank roof 43 and the outer tank roof 33. That is, the upstream piping 53 is led out from the inside of the inner tank 4 to the outside of the outer tank 3 while penetrating the inner tank roof 43 and the outer tank roof 33, and is connected to a blower 51 outside the outer tank 3.

[0029] An upstream valve 55 is provided in the upstream piping 53. The upstream valve 55 is a valve for opening and closing the upstream piping 53, and is disposed outside the tank body 2. During normal operation in which liquefied hydrogen is stored in the tank body 2, the upstream valve 55 is maintained in a closed state.

[0030] The downstream piping 54 includes a main pipe 54a extending downstream from the blower 51, and a plurality of branch pipes 54b branching from the main pipe 54a to each supply ring 52. Each branch pipe 54b penetrates the outer tank side plate 32 to connect the main pipe 54a to each supply ring 52. In this embodiment, five supply rings 52 (first to fifth supply rings 52A to 52E) are prepared, and five branch pipes 54b are prepared correspondingly.

[0031] Each branch pipe 54b is provided with a downstream valve 56. That is, in this embodiment, the same number (five) of downstream valves 56 as the number of supply rings 52 are prepared to open and close each branch pipe 54b connected to the five supply rings 52. In other words, the downstream valves 56 include a first downstream valve 56A for opening and closing the branch pipe 54b for the first supply ring 52A, a second downstream valve 56B for opening and closing the branch pipe 54b for the second supply ring 52B, a third downstream valve 56C for opening and closing the branch pipe 54b for the third supply ring 52C, a fourth downstream valve 56D for opening and closing the branch pipe 54b for the fourth supply ring 52D, and a fifth downstream valve 56E for opening and closing the branch pipe 54b for the fifth supply ring 52E. In the following description, when the first to fifth downstream valves 56A to 56E are not to be distinguished from one another, they are simply referred to as downstream valves 56.

[0032] The blower 51 is a device for pumping hydrogen gas, and functions as a pressure source for circulating hydrogen gas inside and outside the tank body 2. As shown in FIG. 4 described later, the blower 51 draws up hydrogen gas in the inner tank 4 to the outside of the outer tank 3 through the upstream piping 53, and pumps the drawn-up hydrogen gas to each supply ring 52 (first to fifth supply rings 52A to 52E) through the downstream piping 54. Each supply ring 52 ejects hydrogen gas from its nozzle hole h1 to the side cold insulation layer 13a. The ejected hydrogen gas moves from the side cold insulation layer 13a to the roof cold insulation layer 13b, and further moves from the roof cold insulation layer 13b to the inside of the inner tank 4 through the communication pipe 45. The hydrogen gas in the inner tank 4 is sucked out again to the outside of the outer tank 3 by the blower 51. In this way, the blower 51 generates a circulation flow of hydrogen gas that goes from the inside of the inner tank 4 to the outside of the outer tank 3 and returns to the inner tank 4 again.

[0033] The circulating flow of hydrogen gas as described above fluidizes the powder insulation material 15 in the cold insulation layer 13. That is, while the circulating flow is being generated, hydrogen gas is sprayed from the numerous nozzle holes h1 in each supply ring 52 to the cold insulation layer 13, causing the powder insulation material 15 in the cold insulation layer 13 to become suspended in air, changing into a state having fluidity like that of a liquid.

[0034] The gas replacement device 6 is a device for replacing the gas in the tank body 2 with a safe gas during maintenance of the tank body 2. The gas replacement device 6 includes a replacement gas supply source 61 arranged outside the tank body 2, an inlet pipe 62 that communicates between the supply source 61 and the inside of the inner tank 4, an outlet pipe 63 that is led from the roof cold insulation layer 13b to the outside of the outer tank 3, a first valve 64 that can be opened and closed provided on the inlet pipe 62, and a second valve 65 that can be opened and closed provided on the outlet pipe 63. During normal operation when liquefied hydrogen is stored in the tank body 2, the first valve 64 and the second valve 65 are maintained in a closed state.

[0035] The replacement gas supplied from the supply source 61 may be of any type as long as it is an inert gas, but in this embodiment, nitrogen gas is used. The nitrogen gas supplied from the supply source 61 is introduced into the inner tank 4 through the inlet pipe 62. The introduced nitrogen gas drives the hydrogen gas (boil-off gas) remaining in the inner tank 4 into the cold insulation layer 13 through the communicating pipe 45, and is further discharged to the outside of the outer tank 3 through the outlet pipe 63. As a result, the gas in the inner tank 4 is replaced from hydrogen gas to nitrogen gas.

[0036] A discharge pipe 71 for discharging liquefied hydrogen from the tank body 2 is connected to the tank body 2. The discharge pipe 71 is led out from near the bottom of the inner tank 4 to the outside of the outer tank 3. A third valve 72 that can be opened and closed is provided on the discharge pipe 71. The third valve 72 is maintained in a closed state during normal operation of the tank body 2.

[0037] [Hot-up procedure] Next, we will explain the procedure for hotting up the tank body 2. Hotting up is a process for removing liquefied hydrogen from the inner tank 4 for maintenance or the like and bringing the inner tank 4 to room temperature, and is performed in the following procedure.

[0038] First, as shown in Fig. 3, liquefied hydrogen (LH2) is discharged from the tank body 2. That is, by opening the third valve 72, the liquefied hydrogen in the inner tank 4 is discharged to the outside of the tank body 2 through the discharge piping 71. As a result, the liquefied hydrogen disappears from the inner tank 4, and the inside of the inner tank 4 becomes occupied by boil-off gas, that is, hydrogen gas (GH2) generated by vaporization of the liquefied hydrogen.

[0039] Next, as shown in FIG. 4, the gas supply device 5 is used to circulate hydrogen gas (GH2) inside and outside the tank body 2. That is, the upstream valve 55 is opened, and at least one of the first to fifth downstream valves 56A to 56E is opened, and in this state, the blower 51 is operated. As a result, hydrogen gas is sucked up from the inner tank 4 to the outside of the outer tank 3 through the upstream piping 53, and the sucked up hydrogen gas is introduced into the cold insulation layer 13 through the downstream piping 54 and the supply ring 52. The hydrogen gas introduced into the cold insulation layer 13 is returned to the inside of the inner tank 4 through the communication pipe 45. In this way, a circulation flow of hydrogen gas is generated that goes from inside the inner tank 4 to the outside of the outer tank 3 and returns to the inner tank 4 again.

[0040] The above-mentioned operation of circulating hydrogen gas fluidizes the powder insulation material 15 filled in the cold insulation layer 13. That is, hydrogen gas introduced into the supply ring 52 from the downstream piping 54 is sprayed from the numerous nozzle holes h1 of the supply ring 52 into the cold insulation layer 13, thereby fluidizing (suspending) the powder insulation material 15. Although details will be described later, such fluidization of the powder insulation material 15 serves to prevent consolidation of the powder insulation material 15 that may be caused by the expansion of the inner tank 4 accompanying heating up.

[0041] Here, in this embodiment, the hydrogen gas is sequentially ejected from a plurality of (five) supply rings 52 having different heights so that the powder insulation material 15 is fluidized from the top. That is, the first downstream valve 56A, the second downstream valve 56B, ..., the fifth downstream valve 56E are opened in this order so that the supply of hydrogen gas is sequentially started from the high position to the low position of the side cold insulation layer 13a. At this time, when the second and subsequent valves are opened, the valves that have already been opened before are kept open so that the number of open valves increases over time. As a result, the hydrogen gas is ejected from the first supply ring 56A, the second supply ring 56B, ..., the fifth supply ring 52E in this order, and finally, as shown in FIG. 5, hydrogen gas is ejected from all the supply rings 56A to 56E. In this way, the higher the supply ring 52 is, the earlier the hydrogen gas is ejected, so that the powder insulation material 15 is fluidized from the top, and finally, the powder insulation material 15 is fluidized as a whole.

[0042] Moreover, the circulation of hydrogen gas by the gas supply device 5 described above gradually increases the temperature of the hydrogen gas. That is, in the process of circulation of hydrogen gas, the hydrogen gas is repeatedly compressed by the blower 51. Also, the hydrogen gas receives heat input from the outside air when passing through the piping outside the tank body 2, that is, the downstream part of the upstream piping 53 and the downstream piping 54. The temperature of the hydrogen gas gradually increases due to such compression by the blower 51 and heat input from the outside air. As the temperature of the hydrogen gas increases, the temperature of the inner tank 4 increases, and the tank body 2 is heated up.

[0043] As described above, the circulation of hydrogen gas by the gas supply device 5 has the effect of raising the temperature of the inner vessel 4 while fluidizing the powder insulation material 15. The circulation of hydrogen gas continues until the temperature of the inner vessel 4 rises sufficiently and approaches room temperature, at which point it is stopped. For example, if the gas supply device 5 is provided with a temperature sensor that detects the temperature of the circulating hydrogen gas, it is possible to stop the circulation of hydrogen gas when the temperature of the hydrogen gas detected by this temperature sensor rises to a predetermined threshold value close to room temperature. To stop the circulation of hydrogen gas, the operation of the blower 51 is stopped, and the upstream valve 55 and the first to fifth downstream valves 56A to 56E are all closed.

[0044] When the circulation of hydrogen gas is stopped, the gas in the tank body 2 is replaced from hydrogen gas (GH2) to nitrogen gas (GN2) using the gas replacement device 6 as shown in FIG. 6. That is, with the first valve 64 and the second valve 65 both open, nitrogen gas is supplied from the supply source 61 to the inner tank 4 through the inlet pipe 62. The supplied nitrogen gas pushes the hydrogen gas present in the inner tank 4 from the inner tank 4 through the communication pipe 45 to the cold insulation layer 13. The hydrogen gas in the cold insulation layer 13 is pushed by the nitrogen gas to the outlet pipe 63 and is discharged to the outside of the tank body 2 through the outlet pipe 63. As a result, the gas in the inner tank 4 and the cold insulation layer 13 is replaced from hydrogen gas to nitrogen gas.

[0045] By replacing the gas inside the tank body 2 with nitrogen gas in the above manner, it becomes possible to open the tank body 2 and perform maintenance. For example, a manhole provided in the outer tank 3 is opened, and air is introduced into the tank body 2 through the manhole. This allows workers to enter the tank body 2, making it possible to perform maintenance on the tank body 2.

[0046] [Effects] As described above, in this embodiment, when the tank body 2 is heated up, hydrogen gas is supplied to the cold insulation layer 13 using the gas supply device 5, thereby fluidizing the powder insulation material 15 in the cold insulation layer 13. This configuration has the advantage that it is possible to prevent the powder insulation material 15 from being consolidated during the hot-up.

[0047] During normal operation when liquefied hydrogen is stored in the tank body 2, the inner tank 4 in contact with the liquefied hydrogen is in an extremely low temperature state close to the temperature of the liquefied hydrogen. When hot-up is performed from this state, the temperature of the inner tank 4 rises significantly to a temperature close to room temperature, which causes the inner tank 4 to expand. On the other hand, the outer tank 3 in contact with the outside air is in a state close to room temperature both before and after hot-up. Therefore, when the inner tank expands due to hot-up, the volume of the cold insulation layer 13 between the outer tank 3 and the inner tank 4 is reduced by that amount, and the powder insulation material 15 in the cold insulation layer 13 may be compacted. In contrast, in this embodiment, hydrogen gas is supplied to the cold insulation layer 13 during hot-up to fluidize the powder insulation material 15, so that even if the volume of the cold insulation layer 13 is reduced due to the expansion of the inner tank 4, the powder insulation material 15 can be released from a high pressure area to a low pressure area in the cold insulation layer 13, and the powder insulation material 15 can be prevented from being compacted. In addition, by preventing consolidation of the powder insulation material 15, the large stress associated with the consolidation can be prevented from being applied to the inner tank 4, thereby preventing a situation in which the stress causes the inner tank 4 to buckle, for example.

[0048] Furthermore, in this embodiment, resin-based insulation material 17 is arranged in the side cold insulation layer 13a, and the cushioning effect of this resin-based insulation material 17 reduces the pressure of the powder insulation material 15, making it possible to prevent compaction of the powder insulation material 15 with a higher probability.

[0049] In this embodiment, the gas supply device 5 is provided with a plurality of supply rings 52 arranged in multiple tiers up and down within the cold insulation layer 13 (side cold insulation layer 13a), and a large number of nozzle holes h1 for spraying hydrogen are formed in each supply ring 52. With this configuration, hydrogen gas can be supplied to the cold insulation layer 13 from a large number of points spaced apart in the height direction and circumferential direction, and the powder insulation material 15 within the cold insulation layer 13 can be appropriately fluidized.

[0050] Particularly in this embodiment, downstream valves 56 are provided in the branch pipes 54b connected to each supply ring 52, and the downstream valves 56 are controlled so that hydrogen gas ejection starts in sequence starting from the supply ring 52 located at the highest position. With this configuration, the powder insulation material 15 in the cold insulation layer 13 is fluidized in sequence from the top, so that the powder insulation material 15 over a wide range can be fluidized uniformly.

[0051] The powder insulation material 15 in the lower part of the cold insulation layer 13 is subjected to a larger pressure due to its own weight than the powder insulation material 15 in the upper part of the cold insulation layer 13. Therefore, the powder insulation material 15 is more difficult to fluidize in the lower part than in the upper part of the cold insulation layer 13. On the other hand, the powder insulation material 15 in the upper part of the cold insulation layer 13 is subjected to a smaller pressure due to its own weight and is close to the non-filled space NS of the powder insulation material 15 formed near the outer tank roof 33, so it is relatively easy to fluidize. In such a situation, if hydrogen gas starts to be ejected simultaneously from multiple supply rings 52 with different heights, the powder insulation material 15 may be fluidized only in the upper part of the cold insulation layer 13, and the powder insulation material 15 may not be fluidized in the lower part of the cold insulation layer 13. For example, in the lower part of the cold insulation layer 13, a phenomenon called channeling may occur in which a gas passage like an ant nest is formed in the powder insulation material 15. When channeling occurs, the gas path becomes fixed, making it impossible to fluidize the powder insulation material 15.

[0052] In contrast, in this embodiment, the hydrogen gas starts to be ejected from the supply ring 52 located at a higher position in order, so that the powder insulation material 15 can be fluidized in order from the upper part of the cold insulation layer 13 where fluidization is likely to occur. If the powder insulation material 15 is fluidized in the upper part of the cold insulation layer 13, the powder insulation material 15 adjacent to the lower side of this fluidized region is also likely to be fluidized. Therefore, by fluidizing the powder insulation material 15 in order from the top as in this embodiment, it is possible to gradually expand the fluidized range of the powder insulation material 15 while preventing the above-mentioned phenomenon such as channeling from occurring, and ultimately to uniformly fluidize most of the powder insulation material 15.

[0053] In this embodiment, the gas supply device 5 for supplying hydrogen gas to the cold insulation layer 13 includes the supply ring 52 arranged in the cold insulation layer 13, a blower 51 arranged outside the tank body 2, an upstream pipe 53 connecting the blower 51 and the inside of the inner tank 4, and a downstream pipe 54 connecting the blower 51 and the supply ring 52. With this configuration, the hydrogen gas sucked out from the inner tank 4 to the outside of the outer tank 3 is supplied to the cold insulation layer 13, and the supplied hydrogen gas can be returned from the cold insulation layer 13 to the inner tank 4 through the communication pipe 45 penetrating the inner tank 4. In this way, when a circulation flow of hydrogen gas is generated that goes from the inside of the inner tank 4 to the outside of the outer tank 3 and returns to the inner tank 4 again, it becomes unnecessary to separately supply gas for fluidizing the powder insulation material 15 from the outside of the tank body 2. In addition, since the temperature of the hydrogen gas increases in the process of circulating the hydrogen gas, the fluidization of the powder insulation material 15 and the heating up of the tank body 2 can be carried out in parallel.

[0054] [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 without departing from the spirit and scope of the present disclosure.

[0055] For example, a heater for heating hydrogen gas may be added to the upstream piping 53 or the downstream piping 54 in the gas supply device 5. By adding a heater, the rate at which the temperature of the hydrogen gas circulating inside and outside the tank body 2 increases can be increased, and the time required to heat up the tank body 2 can be shortened.

[0056] In the above embodiment, the powder insulation material 15 is fluidized and the temperature of the inner vessel 4 is raised (hot-up) by generating a circulating flow of hydrogen gas circulating inside and outside the tank body 2, but the gas used for fluidization and hot-up is not limited to hydrogen gas. For example, in a situation where the internal temperature of the inner vessel 4 is equal to or higher than the boiling point of nitrogen (approximately -196°C), nitrogen gas may be used for fluidization and hot-up.

[0057] The resin-based insulation material 17 arranged in the cold insulation layer 13 (side cold insulation layer 13a) may be omitted. If the powder insulation material 15 can be sufficiently fluidized by gas supply, compaction of the powder insulation material 15 can be prevented even without the resin-based insulation material 17.

[0058] In the above embodiment, an example in which the present disclosure is applied to a double-shelled liquefied gas storage tank 1 having an outer tank 3 and an inner tank 4 has been described, but the present disclosure can also be applied to a liquefied gas storage tank having an additional tank outside the outer tank, that is, a triple-shelled tank having an inner tank, an outer tank that houses the inner tank, and an outermost tank that houses the outer tank. The present disclosure can also be applied to such a triple-shelled tank in order to prevent the powder insulation material in the cold insulation layer between the inner tank and the outer tank from being compacted during heating up.

[0059] [summary] The above embodiment and its modifications include the following disclosures.

[0060] An operating method according to a first aspect of the present disclosure is a method of operating a liquefied gas storage tank comprising an inner tank for storing liquefied gas, an outer tank for accommodating the inner tank via an insulation layer, and powder insulation material filled in the insulation layer with a gap between the inner tank and the roof of the outer tank, and includes performing a hot-up process in which liquefied gas is removed from the inner tank to bring the temperature of the inner tank closer to room temperature, and performing powder fluidization in which gas is supplied to the insulation layer during the hot-up and the powder insulation material is fluidized by the supplied gas.

[0061] According to this first aspect, when the tank is heated up, gas is supplied to the cold insulation layer to fluidize the powder insulation material, so that even if the volume of the cold insulation layer is reduced due to the expansion of the inner tank accompanying the hot-up, the powder insulation material can escape from high pressure areas to low pressure areas in the cold insulation layer, preventing the powder insulation material from being consolidated. Also, by preventing the powder insulation material from being consolidated, it is possible to prevent the large stress associated with the consolidation from being applied to the inner tank, and it is possible to prevent, for example, a situation in which the stress causes the inner tank to buckle.

[0062] In the operating method according to a second aspect, in the first aspect, the gas is supplied to the cold insulation layer from a plurality of points spaced apart in a circumferential direction in the powder fluidization.

[0063] According to the second aspect, the powder insulating material can be appropriately fluidized by utilizing gas supplied from a plurality of points in the circumferential direction.

[0064] In the operating method according to a third aspect, in the first or second aspect, in the powder fluidization, the gas is supplied to the cold insulation layer from a plurality of points spaced apart in a height direction.

[0065] According to the third aspect, the powder insulation material can be appropriately fluidized by utilizing gas supplied from a plurality of positions in the height direction.

[0066] In an operating method according to a fourth aspect, in the third aspect, during powder fluidization, the timing at which the gas supply starts is varied depending on the height of the gas supply point, so that the lower the height of the gas supply point is, the later the start of the gas supply is.

[0067] The powder insulation material in the upper part of the cold insulation layer is more easily fluidized than the powder insulation material in the lower part of the cold insulation layer. Also, if the powder insulation material in the upper part of the cold insulation layer is fluidized, the powder insulation material adjacent to the lower side of this fluidized area is also more easily fluidized. Therefore, when the powder insulation material is fluidized from the top, as in the fourth embodiment, the fluidized range of the powder insulation material can be gradually expanded, and ultimately most of the powder insulation material can be uniformly fluidized.

[0068] In an operating method according to a fifth aspect, in the first to fourth aspects, during the powder fluidization, gas sucked out from the inner tank to the outside of the outer tank is supplied to the cold insulation layer, and the supplied gas is returned from the cold insulation layer to the inner tank via a communication part penetrating the inner tank.

[0069] In the fifth embodiment, when a circulating flow of gas is generated that flows from inside the inner tank to outside the outer tank and then back to the inner tank, it is not necessary to separately supply gas from outside the tank to fluidize the powder insulation material. In addition, since the temperature of the gas increases during the gas circulation process, the powder insulation material can be fluidized and the tank can be heated up in parallel.

[0070] A liquefied gas storage tank according to a sixth aspect of the present disclosure comprises an inner tank for storing liquefied gas, an outer tank for accommodating the inner tank via a cold insulation layer, powder insulation material filled in the cold insulation layer with a gap formed between the inner tank and the roof of the outer tank, and a gas supply device capable of supplying gas to the cold insulation layer for fluidizing the powder insulation material.

[0071] According to this sixth aspect, when the tank is heated up, the powder insulation material in the cold insulation layer can be fluidized using a gas supply device, thereby preventing compaction of the powder insulation material that may be caused by the expansion of the inner tank due to hot-up.

[0072] A seventh aspect of the liquefied gas storage tank is related to the sixth aspect, wherein the gas supply device includes a supply ring having a plurality of nozzle holes serving as an outlet for the gas inside the cold insulation layer.

[0073] According to the seventh aspect, the powder insulating material can be appropriately fluidized by gas ejected from a plurality of nozzle holes in the supply ring arranged in the cold insulation layer.

[0074] The liquefied gas storage tank according to an eighth aspect is the seventh aspect, wherein the gas supply device includes a plurality of the supply rings disposed at different heights inside the cold insulation layer.

[0075] According to this eighth aspect, by starting the gas ejection from the supply ring located at a higher position, for example, the powder insulation material can be fluidized from the top, and ultimately most of the powder insulation material can be fluidized uniformly.

[0076] A liquefied gas storage tank according to a ninth aspect is the liquefied gas storage tank according to the seventh or eighth aspect, wherein the inner tank includes a communication portion that connects its interior with the cold insulation layer, and the gas supply device includes the supply ring, a blower that pressurizes gas, an upstream piping that connects the interior of the inner tank with the blower, and a downstream piping that connects the blower with the supply ring.

[0077] According to the ninth aspect, by operating the blower, gas can be sucked from the inner tank to the outside of the outer tank and supplied to the cold insulation layer, and the supplied gas can be returned from the cold insulation layer to the inner tank through the communication part penetrating the inner tank. That is, a circulating flow of gas can be generated that goes from inside the inner tank to the outside of the outer tank and returns to the inner tank again. [Explanation of symbols]

[0078] 1. Liquefied gas storage tank 3 Outer tank 4 Inner tank 5 Gas supply equipment 13 Cold layer 15 Powder insulation material 45 Communication pipe (communication part) 51 Blower (pressure source) 52 Supply Ring 53 Upstream piping 54 Downstream piping h1 nozzle hole

Claims

1. A method for operating a liquefied gas storage tank including an inner tank for storing liquefied gas, an outer tank for accommodating the inner tank via a cold insulation layer, and a powder insulation material filled in the cold insulation layer with a gap formed between the inner tank and a roof of the outer tank, comprising: A hot-up process is performed to bring the temperature of the inner tank closer to room temperature by removing liquefied gas from the inner tank; and A method for operating a liquefied gas storage tank, the method including, during the hot-up, supplying gas to the cold insulation layer and performing powder fluidization in which the supplied gas fluidizes the powder insulation material.

2. The method for operating a liquefied gas storage tank according to claim 1, In the powder fluidization, the gas is supplied to the cold insulation layer from a plurality of points spaced apart in a circumferential direction.

3. The method for operating a liquefied gas storage tank according to claim 1, In the powder fluidization, the gas is supplied to the cold insulation layer from a plurality of points separated in a vertical direction.

4. The method for operating a liquefied gas storage tank according to claim 3, In the powder fluidization, the timing of starting the supply of the gas is varied depending on the height of the supply point, so that the lower the height of the gas supply point is, the later the start of the supply of the gas is.

5. In the method for operating a liquefied gas storage tank according to any one of claims 1 to 4, In the powder fluidization, gas sucked from the inner tank to the outside of the outer tank is supplied to the cold insulation layer, and the supplied gas is returned from the cold insulation layer to the inner tank via a communication part that penetrates the inner tank, in this method of operating a liquefied gas storage tank.

6. an inner tank for storing liquefied gas; an outer tank that accommodates the inner tank via a cold insulation layer; A powder insulation material filled in the cold insulation layer with a gap between the powder insulation material and the roof of the outer tank; A liquefied gas storage tank equipped with a gas supply device capable of supplying gas to the cold insulation layer for fluidizing the powder insulation material.

7. 7. The liquefied gas storage tank according to claim 6, The gas supply device is a liquefied gas storage tank including a supply ring having a plurality of nozzle holes serving as outlets for the gas inside the cold insulation layer.

8. 8. The liquefied gas storage tank according to claim 7, The gas supply device is a liquefied gas storage tank including a plurality of the supply rings disposed at different heights within the cold insulation layer.

9. The liquefied gas storage tank according to claim 7 or 8, The inner tank includes a communication part that communicates the inside of the inner tank with the cold insulation layer, The gas supply device includes the supply ring, a blower that pressure-transfers the gas, an upstream piping that connects the inside of the inner tank to the blower, and a downstream piping that connects the blower to the supply ring.

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