JPH11182797A - Cryogenic storage tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce cross-sectional force generated in a bottom plate by a temperature load, and to provide an economical structure by embedding a piping heater in concrete in the vicinity of the upper surface of the bottom plate, and holding an upper surface temperature of the bottom plate close to a freezing temperature by circulating a heating medium in the piping heater. SOLUTION: In a cryogenic storage tank 10, the peripheral edge of a bottom plate 1 and the lower end of a storage tank side wall 2 are formed as a rigidly joined structure. Plane spiral brine heater piping is arranged as a piping heater along a plane in the depth of D=1.5 m from the upper surface 1a of the bottom plate 1 so as to cover the whole surface of the bottom plate 1. A side part heater 20 is executed in the outside ground of the storage tank side wall 2, and the a side part heater 20 is arranged at installation intervals of about 5 deg. around the storage tank 10. In the cryogenic storage tank 10, as a result of heating the bottom plate upper part of the storage tank 10 by bottom surface heaters 11 and 12 laid in the vicinity of the bottom plate upper surface 1a, a freezing wire in a bottom plate position is smaller than a temperature load of the bottom plate 1 without the possibility of freezing the lower surface ground by pssing through a part between the bottom plate upper surface 1a and the heater 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-temperature storage tank, and more particularly to a low-temperature storage tank provided with a pipe heater in a bottom plate of an underground low-temperature storage tank such as an LNG underground storage tank.

[0002]

2. Description of the Related Art Conventionally, a storage tank for storing LNG (liquefied natural gas) is often a cylindrical underground storage tank made of reinforced concrete for disaster prevention and safety and harmony with the surrounding environment.
In this type of underground storage tank, the bottom of the storage tank is about 20 to
Since it reaches 60 m, the bottom plate is often subjected to a large pumping pressure due to groundwater. Under such conditions, many storage tanks having a strength plate structure in which the thickness of the bottom plate is sufficiently large so that the bottom plate can withstand this pumping pressure and resist bending.

[0003] Further, since the temperature of LNG in a cooled and liquefied state reaches -162 ° C, a heater is provided in the storage tank body or in the ground around the storage tank so as to prevent the surrounding ground from freezing due to the cold heat of the LNG. I have. These heaters are roughly divided into a bottom heater that warms the entire bottom plate,
And a side heater for warming the outer periphery of the side wall of the storage tank. In the case of the storage tank of the above-mentioned strength plate type structure, the thickness is about 5 to 10 m.
A piping heater and a crushed stone layer heater are often provided on the lower surface side of the bottom plate of a moderate strength plate. The piping heater is a heater buried in the concrete bottom slab and circulating a heating medium in the piping to prevent a temperature drop of the concrete body. On the other hand, a crushed stone layer heater is a heater in which crushed stones are stacked between the lower surface of a concrete bottom slab and the ground, and hot water flows through the crushed stone layer to indirectly heat the concrete slab.

FIG. 5 is a sectional view showing an example of a conventional LNG underground storage tank 50. As shown in FIG. As shown in the figure, a pumping pressure Wp by groundwater acts on the bottom plate. Storage tank 50 in FIG.
Has a strength plate structure in which the thickness of the bottom plate is large enough to resist the pumping pressure Wp. A crushed stone layer heater 52 constructed by laying crushed stones is provided below the bottom slab 51, and a piping heater 53 is provided in the bottom slab concrete near the lower surface. These heaters 52, 5
3 prevents the ground from freezing below the storage tank 50. For example, in the low-temperature storage tank 50 having this structure, the concrete surface temperature at the upper surface of the bottom slab 51 drops to -40 ° C, and the temperature of the crushed stone layer heater 52 is maintained at about 15 ° C.
In this state, the ground below the bottom slab 51 does not freeze. Also,
A side heater 55 is accommodated in a vertical hole drilled at a predetermined interval on the outer peripheral ground of the storage tank side wall 54. The operation of the side heater 55 controls the freezing of the ground around the storage tank side wall 54.

[0005]

As shown in FIG. 5, when a pipe heater 53 or a crushed stone heater 52 is installed on the lower surface of the bottom plate 51, the temperature difference between the upper and lower surfaces of the bottom plate 51 is 55.degree. (Difference between −40 ° C. and 15 ° C.), and a bending section force due to the temperature difference is generated in the bottom slab 51 that is constrained by the ground. That is, it is necessary to design a reinforcement arrangement so as to be able to resist the bending section force. At this time, if the bottom plate 51 and the lower end 54a of the side wall connected to the peripheral edge 51a of the bottom plate 51 are rigidly connected (rigidly connected), the amount of rebar at the center of the bottom plate 51 can be reduced. Reinforcing volume is required. In particular, there is a possibility that predetermined reinforcing bars cannot be formed on the side wall 54 having a small wall thickness.
Therefore, in the normal strength plate structure, as shown in FIG. 5, a joint portion 60 is provided between the bottom plate peripheral edge 51a and the side wall lower end 54a, and the both are pin-connected. Also in this case, it is necessary to arrange a large amount of reinforcing bars on the bottom slab 51 as a bending slab of simple peripheral support. In addition, installation work of a water stop plate (not shown) for supporting the joint and preventing water leakage at the joint 60 is required, leading to an increase in construction cost.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a low-temperature storage tank which solves the above-mentioned problems of the prior art, reduces the sectional force generated on the bottom plate by a temperature load, and realizes an economical structure. It is in.

[0007]

In order to achieve the above object, the present invention provides an underground low-temperature storage tank in which a bottom plate has a strength plate structure, wherein a pipe heater is buried in concrete near an upper surface of the bottom plate. A heating medium is circulated in the pipe heater to keep the upper surface temperature of the bottom plate close to the freezing temperature.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the low-temperature storage tank according to the present invention will be described below with reference to the accompanying drawings. FIG.
Shows a sectional view of the low-temperature storage tank 10 of the present invention. In the low-temperature storage tank 10 of the present invention, the periphery of the bottom plate 1 and the lower end of the storage tank side wall 2 have a rigid structure. Further, a flat spiral spiral heater pipe as a pipe heater is installed along the plane to a depth of D = 1.5 m from the upper surface 1a of the bottom plate 1 so as to cover the entire surface of the bottom plate 1. More specifically, the brine heater pipes 11 and 12 are composed of two systems of pipes 11 and 12 which are arranged in a plane spiral as shown in the schematic plan view shown in FIG. In the present embodiment, one end 11a of a first-system brine heater pipe 11 indicated by a solid line in FIG.
After a half circle around the outer circumference from the path entrance 15, it extends linearly to the center position, and further spirally from the center to the vicinity of the outer periphery,
The pipe is formed with a distance of about 3 m from the adjacent pipe, and reaches the route outlet 16. On the other hand, the second-system brine heater piping 12 shown by the broken line has the same shape so as to be located at an intermediate position between the piping intervals of the first system. As described above, the two systems of the spiral spiral brine heater pipes 11 and 12 are connected to the bottom plate 1.
The concrete temperature near the upper surface 1a of the bottom slab can be sufficiently increased by installing the slab at a predetermined depth. As a heating medium for the brine heater pipes 11 and 12, warm water, an ethylene glycol aqueous solution, or the like is preferable.
Generally, the installation depth of the brine heater pipes 11 and 12 is set according to the thickness of the slab. However, it is usually preferable to set the depth to 0.5 m to 2 m from the upper surface 1a of the slab. The temperatures of the brine heater pipes 11 and 12 are preferably set so that the temperature of the bottom plate upper surface 1a is -2 to -10C. As the pipe shape, in addition to the flat spiral shape described above, a pipe shape in which a folded portion is provided at an end of a parallel pipe, or the like can be used.

On the other hand, the side heater 20 is installed in the ground outside the storage tank side wall 2 as shown in FIG.
In the present embodiment, a side heater 20 is provided around the storage tank 10.
Are arranged at intervals of about 5 °.

Here, the temperature distribution of the low-temperature storage tank 10 of the present invention and the conventional low-temperature storage tank 50 when LNG is full will be described. FIG. 4 shows a low-temperature storage tank 1 shown in FIG. 1 as a comparative example.
The configuration of the low-temperature storage tank 50 having the same scale as that of the bottom plate and the bottom hot water heater 52 provided on the lower surface of the bottom plate, and a freezing line (0 ° C. isotherm) obtained by temperature analysis in the low-temperature storage tank 50 are shown. As shown in the figure, the ground below the bottom slab can be maintained at a temperature equal to or higher than the freezing temperature by operating the bottom surface hot water heater 52.
The temperature of the bottom plate upper surface 51a is -4 due to the influence of the cold heat of LNG.
0 ℃, the temperature difference between the top and bottom of the bottom plate is about 55 ℃
Becomes For this reason, a large temperature load acts on the bottom plate 51. On the other hand, in the low-temperature storage tank 10 shown in FIG. 1, a freezing line as a result of heating the upper part of the bottom plate of the storage tank 10 by the bottom heaters 11 and 12 arranged near the bottom plate upper surface 1a is shown. The freezing line at the bottom slab position passes between the top surface 1a of the bottom slab and the heater 11, and there is no risk of freezing of the lower ground at this time. In addition, the temperature difference between the upper and lower surfaces of the bottom plate 1 is about 20 ° C., and the temperature load acting on the bottom plate 1 can be reduced.

By laying the bottom plate heater at the above-mentioned position, the temperature stress of the bottom plate can be reduced in the design of a low-temperature storage tank having a strength plate structure, and the amount of reinforcement in the bottom plate can be greatly reduced. In addition, the amount of reinforcement of the bottom plate, which is increased when the bottom plate and the lower end of the side wall are rigidly connected, can be greatly reduced by laying the bottom plate heater at the above-described position. Further, since the joint is eliminated by adopting the rigid connection structure, ancillary equipment such as a bearing and a water stop plate becomes unnecessary, and an economical low-temperature storage tank can be provided. In the above description, a heating method of circulating a liquid heating medium is shown for each heater, but it goes without saying that a resistance heating method such as a heating wire or other various heating means can be selected.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration and a freezing line of an embodiment of a low-temperature storage tank according to the present invention.

FIG. 2 is a schematic plan view showing an arrangement example of a bottom heater of the low-temperature storage tank.

FIG. 3 is a cross-sectional view showing a configuration of a conventional low-temperature storage tank and a freezing line.

FIG. 4 is a sectional view showing an example of the configuration of a conventional low-temperature storage tank.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bottom plate 2 Storage tank side wall 10 Low temperature storage tank 11 and 12 Piping heater 20 Side heater

Claims (1)

[Claims] An underground low-temperature storage tank in which a bottom plate has a strength plate structure, wherein a pipe heater is buried in concrete near an upper surface of the bottom plate, and a heating medium is circulated in the pipe heater to circulate a heating medium. A low-temperature storage tank characterized in that the temperature is kept close to the freezing temperature.