JPH01193500A - Method for preventing foundation around cryounderground tank from freezing - Google Patents

Abstract

PURPOSE:To prevent a foundation around a cryounderground tank from freezing by making smaller a space between a heat fence and the outer wall of the tank as the depth becomes larger. CONSTITUTION:Rod-like heaters 2 constituting a heat fence are embedded slightly inclined to the vertical outer wall of a tank 1 so that a gap between the heat fence and the outer wall of tank 1 is made smaller as the depth becomes larger. Thus, the larger the depth is, the more heat reaches the outer wall of tank 1 from the heat fence, and the temperature gradient in the depth direction of the outer wall of tank 1 is lessened, so that the surface temperature of the outer wall of tank 1 can be maintained approximately at the freezing point irrespective of the depth and the freezing condition around the tank 1 can be prevented from expansion.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for preventing freezing of the ground surrounding a low-temperature underground tank for storing low-temperature substances such as liquefied natural gas.

(Prior Art) If no antifreeze measures are taken, for example, if liquefied natural gas is stored in an underground tank with a diameter of 50 m, the surrounding ground will freeze over an area of 100 m in diameter.

The frozen ground puts pressure on the outer walls of the tank, causing cracks in the tank. Therefore, for example, JP-A-54-1191
As disclosed in Publication No. 20, a heat fence consisting of buried piping for a heat medium such as hot water is provided to surround a low-temperature underground tank, and hot water is circulated through this heat fence to improve the surrounding ground. It is heated to prevent freezing.

(Problem to be solved by the invention) Conventionally, a heat fence was arranged vertically along the vertical outer wall of an underground tank, and the distance between the tank outer wall and the heat fence was constant. . When this heat fence was used to heat the surrounding ground, the temperature of the tank's outer wall remained almost constant; however, the temperature of the tank's outer wall became lower the deeper the tank went. There are three possible reasons for this:

■The closer it is to the ground, the greater the influence of outside temperature, and the shallower the tank, the higher the temperature on the outer wall of the tank.

■The insulation material attached to the outer wall of the tank needs to have higher strength toward the bottom, so materials with higher density are used. If this happens, the insulation of the lower part will be poor, and the cold heat inside the tank will easily reach the surrounding area. As a result, the temperature of the tank outer wall becomes lower as the depth increases.

■Depending on the structure of the heat fence, the surface temperature of the heat fence will be higher at the top, and the amount of heat reaching the outer wall of the tank will be higher at the shallower parts. As a result, the shallower the temperature of the tank outer wall, the higher it becomes.

The synergistic effect of the above causes causes a temperature difference in the depth direction of the tank outer wall, which leads to the following problems.

Of course, widespread freezing of the ground around tanks is harmful. However, the outer wall of the tank is kept below freezing (
This is desirable in order to keep the tank liquid-tight and air-tight.

Therefore, even if the surrounding ground is prevented from freezing by heating with the heat fence described above, it is necessary to keep the temperature of the tank outer wall as a whole below the freezing point and prevent the frozen state from spreading around the tank outer wall. desirable.

However, in the conventional technology, as described above, a temperature difference occurs in the depth (indeed, the temperature of the outer wall of the tank becomes lower).

Therefore, if settings are made to maintain the outer surface temperature of the tank outer wall at the freezing point in the deepest part, the outer surface temperature of the tank outer wall will be higher than the freezing point in the shallower parts, making it impossible to maintain the wall in a frozen state, resulting in poor liquid-tightness and air-tightness. becomes worse. Therefore, if the wall is set to completely freeze even in shallow areas, the frozen state will spread to the surrounding ground in deeper areas.

Furthermore, if the temperature difference in the depth direction of the outer wall of the tank is large, the temperature stress on the wall will also be large, which will cause problems in terms of the strength of the tank.

This invention was made in view of the above-mentioned conventional problems, and its purpose is to provide a method for preventing freezing of the ground surrounding a low-temperature underground tank, which makes it possible to reduce the temperature difference in the depth direction of the tank outer wall. It's about doing.

(Means for Solving the Problems) Therefore, in the present invention, the distance between the heat fence and the outer wall of the tank is made smaller as the depth increases, or the flow velocity of the heat medium flowing through the heat fence is decreased as the depth becomes larger. The larger the depth, the greater the amount of heat transferred from the heat fence to the outer wall of the tank, thereby reducing the temperature difference in the depth direction of the outer wall of the tank.

(Function) In shallow areas, the distance between the heat fence and the outer wall of the tank is large, or the flow velocity of the heat medium is high, so the amount of heat transmitted to the outer wall is small. On the other hand, in a deep part, the distance is short or the flow rate of the heat medium is low, so the amount of heat reaching the outer wall of the tank from the heat fence increases. As a result, the temperature difference in the depth direction of the outer wall of the tank becomes smaller.

(Embodiment) FIG. 1 shows a first embodiment of the present invention. A heat fence is constructed by burying a large number of rod-shaped heaters 2 vertically so as to surround the circular outer wall of a tank 1 provided underground. The rod-shaped heater 2 has a double-tube structure consisting of an inner tube 2a with an open lower end and an outer tube 2b with a closed lower end. Hot water is supplied from the upper part of the inner tube 2a, and the hot water is supplied to the outer tube 2b.
is filled, and hot water comes out from the upper part of the outer tube 2b (.A large number of rod-shaped heaters 2 are connected by connecting pipes 3, 3, and a pump for circulating hot water and a heater for heating the hot water are installed (
(not shown) are connected in parallel.

Note that the heater 2 may be connected in series with the equipment.

A feature of this embodiment is that the rod-shaped heater 2 is buried at a slight angle to the vertical outer wall of the tank 1. At the lower end of the rod-shaped heater 2, the distance from the outer wall of the tank 1 is about 1 m, and near the ground, the distance between the rod-shaped heater 2 and the outer wall of the tank 1 is about 3 m. This rod-shaped heater 2
When hot water is circulated, heat is transmitted to the surrounding area.In the deep part, since the rod-shaped heater 2 and the tank 1 are close to each other, more heat is transmitted, and in the shallow part, from the rod-shaped heater 2 to the tank 1. relatively little heat is transferred to the As a result, the temperature difference in the depth direction due to the above-mentioned causes is corrected, and the temperature of the outer wall of the tank 1 becomes almost constant regardless of the depth. By appropriately setting the spacing between the rod-shaped heaters 2 and the temperature of the hot water circulated through them, the surface temperature of the outer wall of the tank 1 can be maintained at approximately the freezing point regardless of the depth, and the temperature around the tank can be maintained at approximately the freezing point. It is possible to create a situation that prevents the situation from spreading.

FIG. 2(A) shows a second embodiment of the present invention. In this embodiment, the rod-shaped heater 2 is buried parallel to the vertical outer wall of the tank 1, and the outer tube 2b of the rod-shaped heater 2
The thickness increases in three levels from top to bottom. Therefore, the distance between the outer tube 2b and the tank 1 is reduced in three steps from top to bottom.

In addition, the capacity of the outer tube 2b (which is also the heat capacity when filled with hot water) is larger at the lower part, and more heat reaches the lower outer wall of the tank 1 than the upper part, similar to the first embodiment described above. It is possible to prevent the frozen state from spreading to the surrounding ground, and to reduce the temperature difference in the depth direction of the outer wall of the tank to maintain the temperature of the outer surface at approximately the freezing point.

Further, in this embodiment, the thickness of the outer tube 2b is 3 from top to bottom.
Since the inner tube 2a becomes thicker in steps, the flow velocity of hot water discharged from the inner tube 2a decreases as the depth increases, so the amount of heat transferred from each rod-shaped heater 2 to the outer wall of the tank 1 increases as the depth increases. The same effects as in the first embodiment can also be obtained.

Based on this idea, the distance between the outer tube 2b and the tank 1 as shown in FIG. 2(A) remains unchanged, and
), the heaters 2 may be installed at constant intervals.

FIG. 3 shows a fourth embodiment of the invention. Here, continuous hot water pipes 4 are spirally arranged to surround the tank 1 to form a heat fence, and hot water is circulated through the hot water pipes 4 from a pump/heater equipment 5. As shown in the figure, the winding diameter of the hot water pipe 4 is small at the deeper part and becomes larger as it becomes shallower. Therefore, in the deep part, the distance between the outer wall of the tank 1 and the hot water pipe 4 is small, and in the shallow part, this distance is large. As a result, the same effects as the first and second embodiments described above are achieved.

(Effects of the Invention) As explained in detail above, in the method for preventing freezing of the ground around a low-temperature underground tank according to the present invention, the distance between the heat fence buried so as to surround the underground tank and the outer wall of the tank is reduced to a depth. The larger the depth, the smaller the heat fence, and the larger the depth, the more heat is transferred from the heat fan to the tank outer wall, thereby reducing the temperature difference in the depth direction of the tank outer wall. It maintains almost the entire area at freezing point, keeps the wall in a frozen state, maintains liquid and airtightness, and facilitates the desired heating state to prevent the frozen state from spreading to the surrounding soil. can be produced.

The flow rate of the heat medium flowing through the heat fence is made smaller as the depth increases, so that the larger the depth, the more heat is transferred from the heat fence to the outer wall of the tank. A similar effect can be obtained by reducing the temperature difference.

[Brief explanation of the drawing]

Figures 1 (A) and (B) are a plan view and a vertical sectional view of essential parts showing the first embodiment of the present invention, Figure 2 is a schematic diagram showing the second and third embodiments, and Figure 3 is the same. It is a schematic diagram showing a fourth example. 1... Low temperature underground tank 2... Rod heater 2 a... Inner pipe 2 b.
...Outer pipe -3...Connecting pipe 4
... Hot water pipe 5 ... Pump heater equipment patent applicant Obayashi Corporation Agent
Person Patent Attorney - Color Ken Interpolation
Patent Attorney Masatoshi Matsumoto Figure 1 (A) (B) Figure 2 (A) CB) Procedural amendment (spontaneous) March 9, 1985 2, Title of invention: Prevention of freezing of the ground surrounding low-temperature underground tanks Method 3, relationship with one person making an amendment Patent applicant address 3-37 Kyobashi, Higashi-ku, Osaka-shi, Osaka Name Name
Obayashi Gumi Co., Ltd.↓1 Agent address: 7th floor, Rokin Shinbashi Building, 2-12-7 Shinbashi, Minato-ku, Tokyo Name (8768) Patent attorney Matsumoto
Masari 4゜te 1), 5. Attached drawing 6 of the specification subject to amendment and attached drawing Figure 1 (A) of the specification of contents of amendment are replaced with attached drawings. Figure 1 (A)

Claims (2)

[Claims] (1) In a method for preventing freezing by providing a heat fence formed by burying heat medium piping so as to surround a low-temperature underground tank, and using the heat fence to warm the surrounding ground, the above-mentioned heat fence and the above-mentioned tank The distance from the outer wall of the tank is made smaller as the depth increases, so that the larger the depth is, the more heat is transferred from the heat fence to the outer wall of the tank, thereby reducing the temperature difference in the depth direction of the outer wall of the tank. A method for preventing freezing of the ground surrounding low-temperature underground tanks. (2) In a method of installing a heat fence consisting of buried heat medium pipes surrounding a low-temperature underground tank, and using this heat fence to warm the surrounding ground and prevent freezing, the water flows through the heat fence. The flow velocity of the heat medium is made smaller as the depth increases, so that as the depth increases, the amount of heat transferred from the heat fence to the outer wall of the tank increases, thereby reducing the temperature difference in the depth direction of the outer wall of the tank. A method for preventing freezing of the ground around low-temperature underground tanks.