JPS5944560B2 - Method for preventing cold temperatures in underground cryogenic tanks - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cold-heat prevention method for an underground low-temperature tank, and more particularly to a cold-heat prevention method for an underground low-temperature tank using heating by a heating wire.

Superconducting cables have received a lot of attention and research in recent years.

Superconducting cables can efficiently transmit power by cooling the cable with a refrigerant such as liquid helium or liquid nitrogen.If this superconducting cable is adopted in the future, a tank will be required to store a large amount of refrigerant. The tank is expected to be buried underground for safety and technical reasons. By the way, this low temperature tank buried underground has a refrigerant storage temperature of -200℃.
℃, structures in close proximity to the low-temperature tank will be affected by the cold heat from the low-temperature tank, and it is necessary to take countermeasures against this.

The purpose of the present invention is to solve these problems and to remove the influence of the cold temperature of the cryogenic tank on adjacent structures in the safest and most effective manner. Insert a heating wire and a filling liquid with good thermal conductivity into the pipe installed underground between the The feature is that by energizing this heating wire, the cold heat from the low-temperature tank can be prevented from damaging the structure.

Hot water circulation systems, steam circulation systems, etc. have been considered to achieve this purpose, but these systems require heating, storage, and circulation equipment for hot water, steam, etc., and there is a temperature difference between input and output. The difference makes the device complicated and difficult to control, so the inventors developed a system between the underground cryogenic tank and the structure adjacent to this tank in order to eliminate the influence of the cold heat of the cryogenic tank on the adjacent structure. We proposed a method for installing heating wires underground and energizing them.

Figure 1 shows the underground cross-sectional state showing the situation, and the cryogenic tank 2 buried underground 1 has a diameter of 50 to 70 m.
The metal pipes 2 are embedded perpendicularly to the ground at approximately equal intervals on concentric circles with a radius approximately 10 m larger than the outer circumference. A heating wire 4 is inserted into this metal pipe 2 to generate heat. Figures 2 and 3 show an apparatus for carrying out the method originally conceived by the inventors, and Figure 2 shows the connection status, Fig. 3 shows the structure of the connection part, which is a plastic lined pipe (
The heating wire 30 in the pipe 20 (hereinafter simply referred to as a pipe) is sealed with a packing 21, and the pipe 20 contains, for example, silicone oil, a mixture of propylene glycol and water, or a mixture of propylene glycol and water and its soil. A filling liquid 40 consisting of silicone oil added to the container is sealed.

A junction box 50 is attached to the upper part of the pedestal 11, and a lead wire 70 protected within a pipe 60 and a heating wire 30 are connected at a connecting portion 80. However, when this junction box 50 is installed in the air and nothing is filled in it, the conductor temperature increases due to the heat generated by the heating wire 30, and the ambient temperature (temperature of the junction box 50) rises to 40°C. ℃ or above 60℃
In addition, since the connection part 80 is installed in the air, heat dissipation is poor, and therefore the thermal resistance is high, and the conductor temperature is 130 to 15
The temperature could drop to 0 degrees Celsius, and it became clear that laying the cable in the air would pose major problems in terms of maintenance and safety.

The present invention was made based on such consideration, and the connection part between the heating wire and the lead wire, where the conductor temperature becomes high, is placed underground.
In addition to lowering the ambient temperature (from 60° C. to 25° C.), a filling liquid with good thermal conductivity is present around the connection portion to lower thermal resistance. Examples will be described below.

FIG. 4 shows an apparatus used in one embodiment of the present invention, and the same parts as in FIG.
The difference from the structure shown in the figure is that the connecting portion 90 between the heating wire 30 and the lead wire 70 is located in the filling liquid 40 underground.

For example, the heating wire 30 used here is made of copper, nickel alloy stranded wire, fluororesin insulated wire, or fluororesin sheathed wire, and the lead wire 70 is a copper conductor fluororesin insulated wire.The conductor resistance of the lead wire 70 is 1/20~ of the conductor resistance of hot wire 30
It is about 1/30. Further, the connecting portion 90 is formed by a method such as silver brazing using a crimp sleeve, silicone compound, or wrapping with adhesive Tetron tape. The heating wire 30 and the lead wire 70 are connected in advance before being inserted into the pipe 20, and then the filling liquid 40 is filled between the pipe 20 and the heating wire 30. In this way, the connection part 9 between the heating wire 30 and the lead wire 70
Since the filling liquid 40 is present around 0, heat transfer is improved, and since it is underground, the ambient temperature is low.In particular, since the pipe is buried around the low-temperature tank, the ground temperature is lower than in the general case. There is a possibility.

For example, when using a fluororesin-insulated fluororesin-sheathed cable with a heat output of 20 W/m, the temperature rise in the case of aerial installation as shown in Figure 3 is 94°C, whereas the ambient temperature is 40°C.
Then, the temperature inside the junction box will be 134°C.

Of this, 75% of thermal resistance (175% in 232℃ CTL/W)
℃CrL/w) is the heat dissipation resistance due to air. On the other hand, in the case of this embodiment shown in Fig. 4, the thermal resistance is approximately 80%.
(180℃Cm/W), so the temperature increase is 74℃, which is 99℃ assuming the ambient temperature is 25℃.
℃ and can be kept below 100℃.

Therefore, the heating wire configured in this way is energized to generate heat, supplying more heat than the amount of cold heat radiated to the surroundings from the low-temperature tank, and thereby suppressing the cold heat and dissipating it into the surroundings for a long time. The temperature can be maintained at 0°C or higher.

In addition, since the dangerous parts above the ground are located underground, it is possible to obtain safe equipment, and this is an effective method because there is no need for heating near or above the ground. Although this embodiment describes a heating wire inserted into a pipe installed underground around a low-temperature tank, it may also be installed around a structure adjacent to a low-temperature tank, or It can also be applied to the above ground extraction part of the heating wire when the heating wire is provided so as to surround the periphery of the tank.

Furthermore, although the above-mentioned embodiments have been described with respect to a low-temperature tank for a refrigerant used in a superconducting cable, the present invention can be similarly applied to this type of low-temperature tank.

As described above, the method for preventing cold heat in an underground buried low temperature tank according to the present invention makes it possible to remove the influence of cold heat of the low temperature tank on adjacent structures in the safest and most effective manner, and has great industrial effects.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the implementation status of one embodiment of the cold heat prevention method for an underground low temperature tank of the present invention, FIG. 2 is an explanatory diagram similarly showing the connection situation, and FIG. FIG. 4 is a cross-sectional view showing the structure of the connection between the heat generation wire and the lead wire used in the cooling prevention method of the present invention. 20: Plastic lined pipe, 30: Heating wire,
40: Filling liquid, 50: Junction box, 60:
Pipe, 70: Lead wire, 90: Connection part.

Claims (1)

[Claims] 1. Inserting a heating wire and a filling liquid with good thermal conductivity into a pipe installed underground between an underground low-temperature tank and a structure adjacent to the tank, and supplying power to the heating wire. A low-temperature underground buried structure characterized in that a lead wire and a heating wire are connected underground in the filling liquid, and the heating wire is energized to prevent cold heat from the tank from damaging the structure. How to prevent the tank from getting cold.