JPS5911079B2 - Installation method for underground heater wires - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for installing heater wires vertically buried underground.

In recent years, in order to control the freezing of soil damage around underground tanks that store low-temperature liquids such as liquefied natural gas, heater wires 3 have been buried underground 2 around tanks 1, as shown in Figure 1. things are being done.

By the way, in the conventional heater wire of this kind, a heating element of the same resistance is used as a resistance wire, and the part extending above the ground is connected to a cold lead part, and then connected to a power supply lead wire. However, when such a cold lead connection method is used, the temperature distribution of the heater wire 3 shows the highest temperature in the underground part near the ground surface, as shown in FIG.

That is, the temperature distribution around the low-temperature tank 1 is such that the frozen area 4 is limited to the very vicinity of the tank 1 at the ground surface due to heat dissipation and suppression of the ground temperature, and the diameter of the frozen area 4 increases as the depth increases. Therefore, the temperature distribution of the heater wire 3 is kept relatively low in the deep part, but near the surface, the influence of the cold temperature of the tank 1 is small and the groundwater is also small compared to the deep part. Earthquake 2 has high thermal resistance and exhibits quite high temperatures. In addition, the area very close to the ground shows a slightly lower temperature due to heat dissipation and suppression of atmospheric temperature.

(In Fig. 2, 5 shows the temperature distribution on the surface of the heater wire 3 in winter, and 6 shows the temperature distribution on the surface of the heater wire 3 in summer.The vertical axis is the depth m of the underground 2, and the horizontal axis is The temperature is °C.

) By the way, the capacity of the heater wire 3 is determined by the temperature at the high temperature point, that is, the maximum temperature near the earth's surface, which has the drawback that it cannot be used truly effectively.

Also, in the area near the surface of the earth, this amount of heat was unnecessary and wasted. Furthermore, when connecting to the cold lead part T on the ground surface, the distance to the connection part 9 with the power supply lead wire 8 is short, making it difficult to sufficiently release the heat of the heater wire 3, and the conductor of the cold lead part T Considerations such as increasing the size were necessary.

Furthermore, since the area around the tank 1 is generally an explosion-proof area, it was desired that the tank 1 be drawn out at the lowest temperature possible. In view of the above points, the present invention has been made with the object of providing a method for installing underground heater wires, which eliminates ineffective hot spots and allows heater wires to be used effectively and efficiently. The gist of this is that when a heater wire is buried vertically underground and a lead wire that supplies power to the heater wire, the connecting part of the heater wire is A method for installing an underground heating wire is characterized in that the heating wire is placed deeper than the location underground where the temperature distribution shows the highest temperature.

Generally, this type of heater wire is connected to the power supply lead wire via a cold lead. In that case, the connection between the heater wire and the lead wire is the connection between the heater wire and the cold lead. It refers to the department.

As the heater wire, MI wire, fluororesin insulated wire, etc. are used.

When burying a heater wire vertically underground, it is common to bury a protection tube underground in advance and insert the heater wire into it. It is preferable to include a filler from the viewpoint of heat conduction.

Next, an embodiment of the method of the present invention will be further described with reference to the accompanying drawings.

3 and 4 show the state of the connecting portion 10 of the heater wire 3 used in the method of the present invention with the cold lead portion 7. In FIG. 3, the heater wire is 3. For example, an alloy wire of copper and nickel is connected to a cold lead wire 7, such as a copper wire, by welding, and then the heater wire 3 and the cold lead wire 7 are manufactured as an MI type wire by wire drawing.

FIG. 4 shows a connection 10 of a cold lead wire 7 made of a copper conductor or a thick low-resistance alloy to the manufactured heater wire 3.
This is what I did.

FIG. 5 shows an embodiment of the method of the present invention. For example, when 10 KW is applied to one heater wire 3, in the conventional method, that is, when the heater wire 3 is extended to the ground and buried, the method shown in FIG. As shown, there are hot spots at a depth of 2 to 5 meters, reaching temperatures of over 180 degrees Celsius, while in the deep layers
The temperature was as low as 0°C, and there was a considerable temperature difference.

In the case of the present invention, by installing the connection part 10 between the heater wire 3 and the cold lead wire 7 at a position of 5 m underground,
As shown in curves 5 and 6, the maximum temperature could be kept at around 150°C.

Although the current flowing through the heater is limited by the portion exhibiting the highest temperature, the current carrying capacity can be increased by lowering the portion exhibiting the highest temperature (hot spot) as in this embodiment. Also, if the connection is in the air, it is difficult to expect a large temperature drop because the cold lead is short and heat is transferred from the high-temperature heater, but by placing the connection underground, Heat transfer to the ground is also considered, and since it has a large heat capacity, it is useful for lowering the temperature.

In the conventional method and in this example, the terminal temperature was about 100°C when a lead wire of about 1 m was installed by going out into the air and replacing it with a cold lead part, but at a depth of 0.5 m. If a cold lead section is installed and taken out, 17
r! At the end of the clay ivy, the temperature is around 30℃, and the ambient temperature is 15-2
It became clear that the temperature was not too high compared to 0°C, and that the effect was extremely large.

In this example, the heater wire has been explained as being buried vertically, but it is not limited to the case where it is installed completely vertically, but it is also possible to install it in an L-shape or U-shape by passing through the bottom of the tank. It may also be installed diagonally in the depth direction, and is not limited to this embodiment.

The above-described facility method of the present invention can eliminate hot spots that restrict use, and can use the entire heater wire with increased capacity.

Also, if the current is the same, there will be no high temperature part, so
You can expect a long life. The temperature of the terminal part can be reduced and the life of the lead wire can be extended.

Furthermore, since it does not reach extremely high temperatures, there is no need to lower the temperature of the terminal through forced cooling such as wind cooling, making it possible to provide a safe terminal even in explosion-proof areas, and its industrial value is extremely high. There is something.

[Brief explanation of the drawing]

Figure 1 is a diagram explaining the installation outline of an underground low temperature tank and heater wire, Figure 2 is a diagram explaining the temperature distribution of the conventional heater wire,
FIGS. 3 and 4 are longitudinal cross-sectional views showing examples of heater wires used in the method of the present invention, and FIG. 5 is an explanatory view showing the temperature distribution of the heater wires installed by the facility method of the present invention. . 1...Underground cryogenic tank, 2...Earth damage, 3...Heater wire, 4...Frozen area, 5...Winter Temperature distribution curve on the surface of the heater wire in summer, 6 Temperature distribution curve on the surface of the heater wire in summer, 7 Cold lead part, 8
...Power supply lead wire, 9...Connection part between cold lead part and power supply lead wire, 10...
・Connection part between heater wire and cold lead part.

Claims (1)

[Claims] 1. The connection part between the heater wire buried vertically underground and the lead wire that supplies power to the heater wire shall be connected to the highest temperature in the temperature distribution of the heater wire when the heater wire is extended to the ground and buried. A method for installing an underground heater wire, characterized in that it is placed at a deeper position than the underground position shown.