JP7734079B2 - Low-temperature underground tank - Google Patents

Description

This disclosure relates to cryogenic underground tanks.

A thin stainless steel membrane is attached to the entire surface of the bottom of a cryogenic underground tank that stores low-temperature liquefied gases such as LNG. This membrane has numerous corrugations with a convex cross-section. When the membrane is cooled by the low-temperature liquefied gas and contracts, each corrugation expands in response to the contraction of the membrane, preventing damage to the membrane.

The liquefied gas stored in the cryogenic underground tank is discharged to the outside by a pump barrel. The pump barrel extends vertically within the cryogenic underground tank and draws in the liquefied gas from a suction port located at the bottom. A pump barrel pit into which the lower end of the pump barrel is inserted may be formed at the bottom of the cryogenic underground tank (see Patent Document 1). By forming a pump barrel pit in the cryogenic underground tank, the amount of liquefied gas remaining after the liquefied gas is discharged can be reduced. The pump barrel pit is positioned to avoid the corrugations formed in the membrane.

Japanese Patent Application Laid-Open No. 2001-108198

When there is no liquefied gas stored in the low-temperature underground tank, workers may enter the pump barrel pit and perform work on the lower end of the pump barrel. To perform work efficiently, it is desirable for the pump barrel pit to be large. However, if the pump barrel pit is widened, the spacing between the corrugations around the pump barrel pit increases, and there is a risk that the membrane will not be able to withstand contraction due to cooling.

The present disclosure therefore aims to provide a low-temperature underground tank that has a spacious pump barrel pit and can suppress the expansion of corrugation spacing.

A cryogenic underground tank according to one embodiment of the present disclosure comprises a pump barrel pit into which a pump barrel is inserted, and a membrane that holds liquefied gas therein. The membrane includes a membrane opening hole through which the pump barrel passes and which has an area smaller than the horizontal cross section of the pump barrel pit, and multiple corrugations with a convex cross section, at least one of which passes over the pump barrel pit.

The above configuration makes it possible to provide a low-temperature underground tank with a spacious pump barrel pit and which can prevent the corrugation spacing from widening.

FIG. 1 is a vertical cross-sectional view of the bottom of a cryogenic underground tank. FIG. 2 is a plan view of the bottom of a cryogenic underground tank. FIG. 3 is a perspective view of the pump barrel pit and pit top plate.

The following describes a cryogenic underground tank 100 according to an embodiment. Figure 1 is a vertical cross-sectional view of the bottom of the cryogenic underground tank 100. The cryogenic underground tank 100 is partially or completely buried underground and stores low-temperature liquefied gas such as LNG. As shown in Figure 1, the cryogenic underground tank 100 comprises a pump barrel pit 10, a membrane 20, and a pit top plate 30. These components will be described in order below.

<Pump barrel pit>
The pump barrel pit 10 is a hole into which the lower end portion of the pump barrel 90 that dispenses liquefied gas is inserted. The pump barrel pit 10 is located at the bottom of the cryogenic underground tank 100, and is recessed downward and open upward. Figure 2 is a plan view of the bottom of the cryogenic underground tank 100. As shown in Figure 2, the pump barrel pit 10 is circular in plan view, and the horizontal cross section of the pump barrel pit 10 is also circular. As shown in Figure 1, the pump barrel pit 10 is defined by a pit body 11.

Figure 3 is a perspective view of the pit body 11 and the pit top plate 30, which will be described later. As shown in Figure 3, the pit body 11 is cup-shaped and includes a cylindrical side portion 12 and a bottom portion 13 located below the side portion 12. The pit body 11 is made of a metal, which has a smaller linear expansion coefficient than the material of the membrane 20, which will be described later. Therefore, when exposed to low-temperature liquefied gas, the pit body 11 is less likely to shrink than the membrane 20. The pit body 11 is made of a material such as 9% nickel steel or 36% nickel stainless steel, for example.

As shown in Figure 1, the pit body 11 is inserted into a recess formed in the concrete base slab 14, with cold insulation material 15 positioned between the pit body 11 and the base slab 14. The pit body 11 serves to prevent liquefied gas in the pump barrel pit 10 from leaking into the cold insulation material 15 and the base slab 14. Furthermore, because the horizontal cross section of the pump barrel pit 10, i.e., the horizontal cross section of the pit body 11, is circular, higher strength can be achieved compared to when the horizontal cross section is non-circular. As a result, the thickness of the pit body 11 can be reduced.

<Membrane>
The membrane 20 is a thin plate that extends over the surface of the bottom and sidewalls of the cryogenic underground tank 100 and holds the liquefied gas, which is the stored liquid, inside. The membrane 20 ensures airtightness and liquidtightness against the liquefied gas. As shown in FIG. 1 , at the bottom of the cryogenic underground tank 100, the membrane 20 is located above the bottom plate 14, and the cold insulation material 15 is located between the membrane 20 and the bottom plate 14. The membrane 20 serves to prevent the liquefied gas in the cryogenic underground tank 100 from leaking into the cold insulation material 15 and the bottom plate 14. The membrane 20 is made of a metal, such as SUS304.

As shown in FIG. 2, the membrane 20 includes a membrane opening 21 and numerous corrugations 22. The membrane opening 21 is located above the pump barrel pit 10, and the pump barrel 90 passes through it. The membrane opening 21 has an area smaller than the horizontal cross section of the pump barrel pit 10. Therefore, the area surrounding the membrane opening 21 is located above the pump barrel pit 10. Furthermore, if the vertical direction on the paper surface of FIG. 2 is referred to as the "first direction," and the horizontal direction on the paper surface perpendicular to the first direction is referred to as the "second direction," the membrane opening 21 is approximately rectangular, with the dimension Y in the first direction being greater than the dimension X in the second direction.

The corrugations 22 are convex cross-sectional portions formed on the membrane 20. The corrugations 22 expand when the membrane 20 is cooled by the liquefied gas and contracts, preventing damage to the membrane 20. The membrane 20 of this embodiment includes multiple corrugations 22 extending in a first direction and multiple corrugations 22 extending in a second direction. To prevent partial stress being applied to the membrane 20 when it contracts, it is desirable that the corrugations 22 extending in the first direction be positioned so that they are not spaced apart more than a certain distance in the second direction, and that the corrugations 22 extending in the second direction be positioned so that they are not spaced apart more than a certain distance in the first direction.

In this embodiment, of the numerous corrugations 22 included in the membrane 20, two corrugations 22 that are adjacent to both sides of the membrane opening hole 21 in the second direction and extend in the first direction pass over the pump barrel pit 10. In other words, these two corrugations 22 pass over the pump barrel pit 10 near the membrane opening hole 21. Therefore, the distance in the second direction between the two corrugations 22 that pass over the pump barrel pit 10 is smaller than the dimension of the pump barrel pit 10 in the second direction.

Furthermore, in this embodiment, the dimension Y in the first direction of the membrane opening hole 21 is larger than the dimension X in the second direction, so that there is a relatively large area at both ends of the membrane opening hole 21 in the first direction that does not interfere with the pump barrel 90. Therefore, workers can easily enter and exit the pump barrel pit 10 through this area.

In this embodiment, two corrugations 22 pass over the pump barrel pit 10, but the number may be one, or three or more. When at least one corrugation 22 is arranged to pass over the pump barrel pit 10, the increase in the spacing between adjacent corrugations 22 on either side of the pump barrel pit 10 (in this embodiment, the spacing in the second direction) can be suppressed. Therefore, even if the pump barrel pit 10 is enlarged, the increase in the spacing between the corrugations 22 can be suppressed.

<Pit top>
The pit top plate 30 is a member located on the pit main body 11. As shown in Figure 3, the pit top plate 30 is annular. The outer peripheral edge 31 of the pit top plate 30 is located outward from the side surface 12 of the pit main body 11, i.e., outward from the pump barrel pit 10. The inner peripheral edge 32 of the pit top plate 30 is located inward from the side surface 12 of the pit main body 11, i.e., above the pump barrel pit 10. Therefore, the top plate opening hole 33 formed by the inner peripheral edge 32 of the pit top plate 30 is located above the pump barrel pit 10, and the pump barrel 90 passes through it.

In this embodiment, the upper plate opening hole 33 of the pit upper plate 30 has the same shape and size as the membrane opening hole 21 of the membrane 20 (see Figure 2). Furthermore, the membrane opening hole 21 of the membrane 20 is located above the upper plate opening hole 33 of the pit upper plate 30. In other words, the pit upper plate 30 is in contact with the underside of the membrane 20 in the area surrounding the membrane opening hole 21. Therefore, the pit upper plate 30 is located above the pump barrel pit 10 of the membrane 20, suppressing distortion of the membrane 20 due to its own weight in this area.

Furthermore, as described above, two corrugations 22 pass over the pump barrel pit 10, and the pit top plate 30 contacts the underside of the membrane 20 in the area corresponding to the two corrugations 22. In other words, the pit top plate 30 covers the corrugations 22 from below. This prevents liquefied gas stored in the low-temperature underground tank 100 from leaking through the two corrugations 22 into the ice pack 15 and bottom slab 14. In this embodiment, the pit top plate 30 is supported on the bottom slab 14 via support members 34.

<Effects of the embodiment>
As described above, the low-temperature underground tank according to the embodiment comprises a pump barrel pit into which a pump barrel is inserted, and a membrane that holds liquefied gas therein, and the membrane includes a membrane opening hole through which the pump barrel passes and which has an area smaller than the horizontal cross section of the pump barrel pit, and a number of corrugations with a convex cross section, at least one of which passes over the pump barrel pit.

With this configuration, at least one corrugation passes over the pump barrel pit, so even if the pump barrel pit is widened, the gap between adjacent corrugations on either side of the pump barrel pit can be prevented from widening.

In addition, the low-temperature underground tank according to this embodiment further includes a pit upper plate that contacts the underside of the membrane in an area that includes the corrugation that passes over the pump barrel pit.

With this configuration, the pit body covers the corrugation that passes over the pump barrel pit from below, preventing liquefied gas stored in the low-temperature underground tank from leaking through the corrugation into the ice insulation and bottom slab.

In addition, in the low-temperature underground tank according to this embodiment, the pit top plate is annular and contacts the underside of the membrane in an area surrounding the membrane opening, with its outer periphery located outward from the pump barrel pit and its inner periphery located above the pump barrel pit.

With this configuration, the pit top plate supports the area of the membrane located above the pump barrel pit and is submerged in liquid, so it is only necessary to suppress distortion due to the membrane's own weight in that area, and no reinforcing structure is required to support the liquid pressure.

In addition, in the low-temperature underground tank according to the embodiment, the material of the pit body that defines the pump barrel pit has a smaller linear expansion coefficient than the material of the membrane.

It is difficult to form corrugations in the pit body like in the membrane, so if the pit body is made of the same material as the membrane, it will deform significantly due to cooling. In contrast, with the above configuration, the pit body material has a smaller linear expansion coefficient than the membrane material, which helps to suppress deformation of the pit body and, ultimately, minimize the impact on the membrane.

In addition, in the low-temperature underground tank of this embodiment, the horizontal cross section of the pump barrel pit is circular.

This configuration improves the strength of the pump barrel pit and allows the thickness of the pit body to be reduced compared to when the horizontal cross section of the pump barrel pit is not circular.

In addition, in the low-temperature underground tank according to the embodiment, the dimension of the membrane opening hole in a first direction, in which the corrugation passing over the pump barrel pit extends, is larger than the dimension in a second direction perpendicular to the first direction.

This configuration makes it possible to increase the area of the membrane openings while preventing the gap between adjacent corrugations on either side of the pump barrel pit from widening. This makes it easier for workers to enter and exit the pump barrel pit.

10 Pump barrel pit 11 Pit body 20 Membrane 21 Membrane opening hole 22 Corrugation 30 Pit top plate 31 Outer periphery 32 Inner periphery 90 Pump barrel 100 Cryogenic underground tank

Claims (6)

a pump barrel pit into which the pump barrel is inserted;
a membrane for holding a liquefied gas therein;
The membrane includes a membrane opening hole through which the pump barrel passes and which is smaller in area than the horizontal cross section of the pump barrel pit, and a number of corrugations with a convex cross section, at least one of which passes over the pump barrel pit. The cryogenic underground tank described in claim 1, further comprising a pit top plate in contact with the underside of the membrane in an area including the corrugation passing over the pump barrel pit. The cryogenic underground tank described in claim 2, wherein the pit top plate is annular and in contact with the underside of the membrane in an area surrounding the membrane opening, with its outer periphery located outward from the pump barrel pit and its inner periphery located above the pump barrel pit. A low-temperature underground tank as described in any one of claims 1 to 3, wherein the material of the pit body defining the pump barrel pit has a linear expansion coefficient smaller than that of the material of the membrane. A cryogenic underground tank as described in any one of claims 1 to 4, wherein the horizontal cross section of the pump barrel pit is circular. A low-temperature underground tank as described in any one of claims 1 to 5, wherein the dimension of the membrane opening hole in a first direction, which is the direction in which the corrugation passing over the pump barrel pit extends, is larger than the dimension in a second direction perpendicular to the first direction.