JPS6119880B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention is a method for storing low-temperature liquefied gases such as LNG and LPG, which are obtained by cooling and compressing substances such as methane and propane that are gases at normal temperature and pressure. Regarding the bottom freezing prevention structure of low temperature underground tanks.

Conventionally, storage tanks for low-temperature liquefied gas have been used to prevent damage from spreading in the unlikely event of a leak, spill, or destruction.
It is widely used from various viewpoints such as effective use of land. However, in low-temperature underground tanks, the surrounding soil freezes due to the low-temperature liquid inside the tank, and if this spreads over a wide area, it can have various effects on the side walls, bottom, nearby ground, structures, trees, etc. Therefore, it is necessary to control the freezing to within a certain range. In particular, if the soil directly below the tank bottom freezes, frost heaving may occur due to the expansion of frozen groundwater, and there is a risk that the entire tank may be lifted up or the tank may be destroyed due to uneven levitation. Additionally, if there is a large amount of groundwater, there is a risk that the water pressure will destroy the tank before it freezes.

As a countermeasure against this problem, the bottom freeze prevention structure of conventional low-temperature underground tanks has many holes in the pipe wall in the gravel layer 3 provided directly below the bottom plate 2 of the tank 1, as shown in Fig. 1. Hot water distribution pipe 4
A drainage central pipe 5, which also has a hole in the pipe wall, is buried slightly below that, hot water is supplied from the ground to the distribution pipe 4 through the water supply pipe 6, and hot water is injected into the gravel layer 3 to heat it. The required amount of water is pumped up along with groundwater through a central pipe 5 by a pump 6' installed on the ground, heated by a heater 7, and then supplied again to the distribution pipe 4 through a water supply pipe 6 by a pump 8, and the remaining water is sent to a branch pipe. The hot water was discharged from the pipe 9, and in this way hot water was circulated through the gravel layer under the tank bottom, and excess groundwater was pumped up to prevent the soil on the tank bottom from freezing. However, burying perforated distribution pipes and central pipes in a gravel layer is likely to cause corrosion, and there is also a possibility that accidents such as pipe clogging may occur. If an accident occurs in such a location, not only will the antifreeze function stop completely, but it will also be extremely difficult to repair it.

The purpose of this invention is to provide a structure for preventing freezing of the bottom of a low-temperature underground tank, which has a simple structure, is less prone to failure, is easy to maintain, and has high reliability, which solves the above-mentioned problems of the conventional ones. shall be.

To explain this invention based on drawings showing embodiments, in FIG. 2, a side wall 11 of a concrete cylindrical low temperature underground tank 10 is connected to a bottom plate
The bottom wall 13 is extended below the depth of the bottom wall 13 . The lower part of the cylindrical space surrounded by the inner surface of the hem wall 13 and the lower surface of the bottom plate 12 is a soil layer that is continuous with the soil 14 below it up to an appropriate height, and there is a soil layer between the upper surface and the lower surface of the bottom plate 12. A crushed stone tank 15 is formed and crushed stones 16 are filled in the bottom plate 12 and tank 1 to transfer the weight of the stored liquid to the soil and support it. A weir 17 of an appropriate height is provided around the crushed stone tank 15, and a water supply groove 18 is provided surrounding the outside thereof. The inside of the water supply groove 18 is made of coarse crushed stone 19
is filled, making it easier for water to flow.
At the center of the crushed stone tank 15, there is provided a water collection basin 20 whose circumferential wall has an upper surface slightly lower in height than the upper surface of the weir 17, and its interior is also filled with coarse crushed stones 19. Drainage pits 21, which are slightly deeper than the lower surface of the water collecting basin 20, are provided at appropriate locations around the low-temperature underground tank 1. A water supply port 22 is provided penetrating the skirt wall 13 from the water supply groove 18, and a water supply pipe 23 descending from the ground in the drainage pit 21 is a branch pipe provided on the side of the water supply port 22. Or connected to the seat. The opening in the drain pit of the main pipe of the water supply port 22 is closed with a blind flange 24. In addition, each drainage pit 21 and water collection basin 20
It is connected with the drain pipe 25. Drain pit 2
A water pump 26 is installed at the bottom of the drain pit 21 to drain water accumulated at the bottom of the pit, and a water pump 27 that runs through the drain pit 21 to the ground is connected to the discharge port of the pump. . The lift pipe 27 and the water supply pipe 23 are connected on the ground by a communication pipe 28, and a heater 29 is provided in the middle of the communication pipe 28 to heat the water within the pipe. Further, a branch pipe 30 is provided in the above-ground part of the pumping pipe. Although not shown in the figure, it goes without saying that each of the above-mentioned pipes is provided with valves and the like at necessary locations.

Since this tank bottom freeze prevention structure is configured as described above, the hot water heated by the heater 29 is supplied to the water supply groove 18 through the communication pipe 28, the water supply pipe 23, and the water supply port 22, and the water level is When the hot water reaches the top of the weir 17, it flows over the weir 17 and into the crushed stone tank 1.
Flows into 5. There, heat exchange is performed with the crushed stones 16 to heat the crushed stones 16, and the water whose temperature has decreased flows into the water collecting basin 20, passes through the drain pipe 25, and collects at the bottom of the drain pit 21. The water pump 26 is operated continuously and pumps the water accumulated in the pit to the ground via the water pipe 27. The pumped water is transferred to the connecting pipe 28
The water is heated by the heater 29 and flows through the above-mentioned path again. In this way, each of the above-mentioned components forms a circulation system, and warm water at a constant level is constantly circulated in the crushed stone tank 15, keeping the crushed stone at an appropriate temperature and preventing the soil below the tank bottom from freezing. It can be prevented. If there is a large amount of underground water flowing out and the water level exceeds a predetermined water level, the water level will be detected and the excess water will be discharged from the branch pipe 30 to the outside of the circulation system.
By providing a hot water supply pipe (not shown), it is also possible to constantly supply a fixed amount of hot water to the crushed stone tank 15.

Now, the commonly used low-temperature underground tanks have a diameter of about 60 m, and it is quite difficult to finish the top surface of the weir 17 to exactly the same level. Furthermore, changes over time may cause unevenness in the height of the cough. If the height of the weir is uneven, water will flow in only from low places, and the crushed stone 1
No. 6 cannot be heated evenly, and complete anti-freezing is inhibited. So, as shown in Figure 3, cough 17
It is preferable to provide slits 31 at appropriate intervals around the entire circumference so that hot water uniformly flows into the crushed stone tank 15 from all the slits. Further, as shown in FIG. 4, it is also possible to provide an opening 32 of an appropriate size instead of the slit. Chips of crushed stone, soil particles, scale, etc. that have accumulated in the water inlet 22 and drain pipe 25 due to long-term use can be easily cleaned from inside the drain pit using a tube cleaner or the like by removing the blind flange 24 of the water inlet. be able to. Further, although the drain pipe 25 is buried in the soil, unlike the distribution pipe 4 and the central pipe 5 used in the above-mentioned conventional device, it simply drains water from the water collection basin to the drain pit 21. Since it is not necessary to make many holes in the pipe wall, it is suitable for using plated pipes or lined pipes with good corrosion resistance, and since they are advantageous in terms of strength, it is suitable to use corrosion-resistant pipes such as hard vinyl chloride pipes. It is also possible to use tubes made of superior materials.

As explained above, according to the present invention, with a simple structure, it is possible to always uniformly heat the entire bottom of the tank to prevent freezing, and it is also easy to clean the skirt walls and pipes buried in the soil. This makes it possible to avoid suspension of functions due to corrosion and blockage, making it possible to reliably prevent damage to the tank due to freezing of the soil directly under the tank bottom or frost heaving, which also contributes to environmental conservation. There are significant effects such as contributing to

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing a typical example of a conventional low-temperature underground tank bottom freeze prevention structure, Fig. 2 is a sectional view showing an embodiment of the present invention, and Fig. 3 is a sectional view of a part of the main part of the weir. FIG. 4 is a perspective view showing a part of the alternative plan in cross section. 10... Low temperature underground tank, 12... Bottom, 1
4... Soil, 15... Crushed stone tank, 16... Crushed stone, 1
7...Weir, 18...Water supply groove, 20...Drainage basin, 21...Drain pit, 22...Water supply port, 23
... Water supply pipe, 25 ... Drain pipe, 26 ... Lifting pump, 27 ... Lifting pipe, 28 ... Connection pipe, 29 ...
heater.

Claims (1)

[Claims] 1. In a low-temperature underground tank where hot water is circulated through gaps such as sand and gravel directly under the tank bottom plate to heat the soil below the tank bottom plate and prevent it from freezing, the bottom plate and the soil are connected to each other over almost the entire area of the tank bottom plate. a crushed stone tank provided between the two, a suitable number of drainage pits provided around the tank and reaching approximately the same level as the bottom of the crushed stone tank, and a weir provided surrounding the crushed stone tank; It has a water supply groove provided around the outer periphery of the weir and a water collection chamber provided in the crushed stone tank,
Hot water from the ground is supplied to the water supply groove from near the bottom of the drainage pit via the water supply pipe, and flows into the crushed stone tank over the weir.On the other hand, the water in the crushed stone tank collected by the water collection basin is passed through the drain pipe. The water is stored in a drainage pit, pumped to the ground using a water pump, heated, and then returned to the water supply pipe for recirculation, thereby constantly circulating hot water at a constant level within the stone crushing tank. Anti-freezing structure at the bottom of low-temperature underground tanks.