JPS6053240B2 - Freezing prevention device for the bottom ground of a low-temperature liquefied gas underground tank - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ground freezing prevention device near the bottom of an underground tank for storing low-temperature liquefied gas such as LNG or LPG.

In order to prevent the ground from freezing near the bottom of the underground tank, it is possible to flow a hot fluid under the concrete bottom slab to absorb the low heat, and then recover the heat-exchanged fluid to achieve the intended purpose. It has been proposed.

For the above purpose the following conditions must be met:

(a) Warm water should flow uniformly under the bottom slab and no dead water areas will be created.

This is because when a dead water area is formed, the water in that area freezes and the ground is cooled through the frozen area, causing frost heave. The conditions in (a) above shall be maintained for a long period of three or more years.

This is because new water constantly flows over a long period of time, causing limescale and
This is because if scale or the like adheres and causes clogging, the flow is obstructed and dead water areas are likely to be formed. I/→ It is desirable that the flow rate be as small as possible from an economic point of view, but for the purpose of heating with hot water, a minimum flow rate of about 40 Ihr is appropriate.

The above-mentioned freezing prevention devices for the ground under the bottom plate of underground tanks for storing low-temperature liquefied gas using hot water can be broadly classified into the following two types. (i) As previously proposed, a method of spreading gravel, crushed stones, cobblestones, etc. under the bottom slab to form a permeable layer and allowing water to flow into the permeable layer.

(11) A method of creating a culvert under the bottom slab and passing water through the culvert.

However, in the method (i) above, it is difficult to guarantee a uniform flow of water, and if the voids in the permeation layer become clogged due to long-term use, dead water areas are likely to occur. be. Next, the following types of hot water flow can be considered.

Central spout system (B) Peripheral spout system (C) Spiral system Figure 1 shows the above-mentioned (2) central spout system, in which flow is flowed from the pipe b disposed at the center of the lower part of the bottom plate a to the dividing wall c. Hot water is spouted into areas divided radially by the pipes, and the water is collected from water collection pipes d placed around the bottom of the bottom plate a.In order to obtain an even flow, 10 or more pipes are installed in each section. Since a large number of independent water collection pipes d are required and the flow rate of hot water is small, the flow velocity around the tank side wall e is approximately 0.1Tn! NlS
eC becomes extremely small, and at such a low flow rate, dead water,
It has the disadvantage that stagnation tends to occur.

Figure 2 shows an example of the above-mentioned (B) peripheral jetting method, in which nozzles f of pipe line b are arranged at predetermined intervals on the outer periphery of the lower part of the tank bottom plate a, and hot water is supplied from each nozzle f in a direction tangential to the tank peripheral wall. The water is collected by a water collecting pipe d installed at the center of the bottom of the tank bottom plate a, and a swirling flow is generated at the bottom of the bottom plate a. However, since the hot water flow rate is small, the water is collected in the area around the side wall of the tank. The flow velocity becomes extremely low, which tends to cause dead water and stagnation, and in order to obtain an even flow, many independent pipings are required, which complicates the piping, increases the number of pumps, and increases maintenance costs. There is.

In order to eliminate the drawbacks shown in Fig. 2, an arc-shaped header vibe g is connected to a pair of pipes b installed oppositely at the bottom of the bottom wall a of the tank, and a nozzle installed in the pipe g is connected to the bottom wall a of the tank. The idea is to gradually change the diameter of the nozzle, keep the speed of hot water jetted from each nozzle to the side wall e constant, and collect the same hot water into the central water collection pipe d, but changes over time in the diameter of the nozzle cannot be ignored. However, if there are fluctuations in the flow rate, it is impossible to maintain the jet velocity from the nozzles constant for all nozzles, as calculated. However, according to the above-mentioned (C) spiral system, the disadvantages of the above-mentioned systems are eliminated, a uniform flow of hot water is formed under the tank bottom plate, and the risk of clogging is avoided when the underdrain system (11) is used in combination. The present invention has been proposed with an eye to the fact that there is no such problem, and the present invention provides a single spiral piping system with a closed top surface extending over the entire lower part of the bottom plate of an underground tank for low-temperature liquefied gas. A bottom ground in an underground tank for low-temperature liquefied gas, characterized in that it is configured to have a pipe and flow a hot fluid for preventing ground freezing through the pipe. This relates to anti-freezing equipment.

In the present invention, as described above, the pipes are arranged in a spiral manner in one piping system across the lower part of the bottom plate of the underground tank for low-temperature liquefied gas, and hot water is allowed to flow through the spiral pipe. This prevents the ground at the bottom of the underground tank from freezing.
The hot fluid can be uniformly flowed over the entire lower part of the bottom plate with a single piping system and at a low flow rate.

Moreover, since the channel has a sufficiently wide cross section, there is no risk of blockage, clogging, or damage of the channel due to corrosion, limescale, etc. even after long-term use.

Note that the pipeline must withstand a huge overload from a structural mechanical point of view, but in the present invention, the pipeline is made of strong concrete, and when constructing it, a spiral pattern is first applied to the concrete. By constructing a concrete side wall, placing a precast concrete slab on top of it, and placing the bottom slab concrete using the same slab as the lower formwork, a strong concrete structure is created that prevents freezing of the ground at the bottom of the underground tank using hot fluid. The structure is designed to be able to withstand huge overload loads, and also to allow the tank bottom slab concrete to be placed quickly and without any problems. The present invention will be described below with reference to the illustrated embodiments.

1 is the side wall of a low-temperature liquefied gas underground tank, 2 is its bottom slab, and the crushed stone layer 3 with a floor formed in the ground at the bottom of the bottom slab 2
An asphalt concrete layer and a leveled concrete layer 5 are layered one after another on top of the leveled concrete layer 5, and a concrete pipe line 6 is constructed by a single spiral piping system over the entire area of the bottom slab 2. ing.

A precast concrete lid plate 8 is disposed above the side wall 7 of the pipe line 6, and the lower end of the hot water supply pipe 9 disposed along the outer periphery of the side wall 1 of the underground tank is connected to the concrete pipe bottom plate. Hot water is supplied to the starting point at the inner peripheral end of the pipe line 6, which is arranged in a single spiral pipe system that penetrates through the pipe line 16 and is located at the lower center of the bottom plate 2. A water collection section 10 arranged outside the underground tank is connected to the outer peripheral end of the tank 6, and a lower end of a water collection pipe 11 arranged parallel to the hot water supply pipe 9 is connected to the water collection section 10. It's communicating.

An asphalt mastic layer 12 is deposited on the top surfaces of the lid plate 8 and the side walls 7, and the concrete of the bottom plate 2 is placed on the layer 12. In the figure, 13 is a water stop wall, 14 is the roof of the underground tank, and 15 is a side heat fence.

Since the illustrated embodiment is configured as described above, a pump (not shown) is operated to connect the inner periphery of the pipe line 6 which is arranged in one spiral piping system from the hot water supply pipe 9. When supplied to the starting point, the same temperature water flows uniformly and spirally at a low flow rate over the entire lower part of the bottom plate 2, as shown by the arrow in Fig. 4.
The water whose temperature has been lowered by exchanging heat with the low temperature of the underground tank is collected from the outer peripheral end of the pipe 6 arranged in the single spiral piping system to the water collecting part 10, and then pumped (not shown). water is discharged through the water collection pipe 11 by activating the water pipe 11.

In this way, the warm water prevents the ground below the tank bottom plate 2 from freezing.

Although the present invention has been described above with reference to embodiments, the present invention is, of course, not limited to such embodiments, and can be modified in various ways without departing from the spirit of the present invention. .

[Brief explanation of drawings]

Figure 1A is a plan view showing an example of a hot water supply type for preventing freezing of the ground under the bottom plate of a low-temperature liquefied gas underground tank, Figure 1B is a longitudinal sectional view thereof, and Figure 2A is another example of the hot water supply type. FIG. 2B is a longitudinal sectional view thereof, FIG. 3A is a plan view showing still another example of the hot water supply type, and FIGS. 3B and 3C are enlarged portions of part X in FIG. 3A. FIG. 3D is a partial longitudinal sectional view of FIG. 3A, and FIG. 4 is a partial diagram showing an embodiment of the freezing prevention device for the bottom ground of a low-temperature liquefied gas underground tank according to the present invention. FIG. 5 is a longitudinal sectional view taken along line 1-1 in FIG. 4, and FIG. 6 is an enlarged view of part 2 in FIG. 2...Bottom plate, 6...Spiral conduit, 9.
...Hot water supply pipe, 11... Water collection pipe.

Claims (1)

[Claims] 1. A single spiral piping system is installed across the entire lower part of the bottom slab of an underground tank for low-temperature liquefied gas, and the system is configured to flow hot fluid for preventing ground freezing through the pipe. Freezing prevention device for the bottom ground of underground tanks for low-temperature liquefied gas.