JPS6313075B2 - - Google Patents

Description

Detailed Description of the Invention The present invention utilizes the heat generated by the inner and outer tubes for heat retention in an electrically heated pipeline in which the inner and outer tubes generate heat as reciprocating conductors and the inner tube is used as a transport tube. The purpose is to reduce the temperature difference between the inner and outer pipes in order to reduce the strain caused by the difference in temperature, and also to minimize temperature fluctuations due to uneven heat retention in the pipeline along its length.

FIG. 1 is a longitudinal cross-sectional view of the pipeline of the present invention, and FIG. 2 is an enlarged view of section A in FIG.

In these figures, the inner pipe 1 is an electrically conductive pipe that transports a fluid 23, and 2 is its outer pipe,
It is made of steel tube, which is a ferromagnetic material. Reference numeral 3 denotes an AC power source, one of which is directly connected to the outer tube 2 at approximately the center portion 5 thereof, and the other terminal is connected to the outer tube 2 by a conductor 6 passing through a sealed insulating bushing 11 provided on the outer tube. Left terminal 4 is provided almost in the center of the inner tube.
connected to. The meaning of connecting the power supply almost to the center of the inner and outer tubes is, for example, by making the currents 8 and 9 that flow to the left and right as shown in Figure 2 as equal as possible, so that the heat generation on the left and right sides is equal; For example, the potentials at both ends of each unit, such as 17 and 18, should be made approximately equal, so that even if many units are electrically connected one after another without an insulating flange, the electrical values of each unit will not change as much as possible. It's for a reason. An electrical short circuit is prevented between the inner and outer tubes by an insulating spacer 20. Although FIG. 1 shows two units powered by AC power supplies 3 and 3', the number of units may be one or many. The length of one unit is usually from several tens of meters to several hundred meters. The inner and outer tubes of each unit are electrically connected at both ends (17, 18 for the power source 3 unit, 18, 19 for the power source 3' unit).

Now, in such an electric circuit, the current 10 from the AC power source 3 is divided into 8 and 9 using the inner and outer tubes as a circuit, but if the outer tube 2 is a ferromagnetic steel tube and its wall thickness t (cm) is , the resistivity ρ(Ω
cm), magnetic permeability μ, and power frequency f (Hz), the value called the skin depth S (cm) of alternating current is S=5030√ (cm) (1), whereas t>2S (2) When the relationship is as follows, the alternating current flowing through the outer tube 2 concentrates only near the inner skin of the tube and generates a lot of heat, and at the same time, substantially no voltage appears on the outer surface of the tube, and many Earthing or metal contact at these points will not generate currents that are harmful to human resources or that could ignite combustible gases. Therefore, such a circuit can be used as a heat generating circuit without particularly providing an electrical insulating layer on its outer periphery, and can be used to heat the fluid 23 and keep it warm.

When heating the fluid 23 from a cold state,
The heat generated in the inner tube 1 can be used as is for heating and heat retention, but in order to transfer the heat generated in the outer tube 2 to the fluid 23, it must pass through the gap 22 between the inner and outer tubes. Therefore, there is a temperature difference between the inner and outer tubes 1 and 2. In order to minimize this temperature difference, it is desirable to fill the gap 22, usually 10 to 30 mm, with a material that is electrically insulating but has better heat conductivity than air. The spacer 20 may also be used for heat transfer between the inner and outer tubes. Furthermore, if there is a large temperature difference between the inner and outer tubes, distortion will occur between the inner and outer tubes, so in order to prevent this, it is desirable to fill the gap 22 with the above-mentioned material. The type of filling material varies depending on the holding temperature of the pipeline, power supply voltage, etc., but it may be solid such as heat transfer cement if the power supply voltage is relatively low, up to several tens of volts. Holding temperature is 100
When the voltage is relatively low (below ℃) and high (above several hundred V), transformer oil can be used, and the holding temperature is
At temperatures above 100℃, ethylene glycol, silicone oil, and other known liquid heat media can be used. The thermal conductivity of liquid is around 0.2 KCal/mh°C, which is not very high, but at high temperatures, the apparent thermal conductivity becomes much larger than the above value due to the help of convection.

In the present invention, a filler is filled between the inner and outer tubes to improve heat transfer between them, so a heat insulating layer is placed on the outside of the outer tube to prevent the heat generated in these from escaping to the outside. is necessary. When a pipeline is buried in the soil, the soil may be used as it is as a heat insulating layer, but it is preferable to proactively provide a heat insulating layer such as foam or glass wool.

Although omitted in FIGS. 1 and 2, such pipelines usually have a heat insulating layer on the outside of the outer tube 2.
This heat insulation layer is inevitably uneven along the length of the pipeline, and even when the pipeline is above ground over its entire length and the ambient temperature is uniform, there is a temperature difference of about ±10% along the length of the pipeline. Can be done. Such temperature fluctuations can cause problems in sulfur pipelines where the transportable temperature range is as small as 140 to 160°C, especially when the flow is stagnant. Therefore, in order to avoid such temperature fluctuations, the filling material in the gap 22 is made into a liquid and is introduced into the pipeline from one end 14 using the pump 12 and piping 13 as shown in FIG.
5, the liquid is refluxed to the pump 12 through a device 21 which can provide some heating if necessary and which can purify or store the liquid, thereby reducing the temperature difference along the length of the pipeline.

Thus, when the fluid to be heated in the pipeline is at or near stagnation in the pipeline, a small amount of fluid is allowed to flow along the pipeline to equalize its temperature along the pipeline. A method for making the temperature uniform in the horizontal direction is described in Japanese Patent Publication No. 1983-21010, which was invented by the present inventor.
The present invention can be said to be an embodiment of the method, but in the present invention, the fluid is limited to an electrical insulator.

Now, the crossover pipe 16 in Fig. 1 is the electrical connection means 1.
If there is a hole in 8 that allows fluid to pass through, it is unnecessary. However, when assembling a pipeline by connecting prefabricated units, it may be convenient to make connections using such crossover piping possible.

As described above, although the method of the present invention is a direct current heating method to the pipeline, leakage of voltage and current to the outer surface of the pipeline can be limited, and moreover, it is possible to limit the leakage of voltage and current to the outer surface of the pipeline. This makes it possible to average, or balance, the temperatures of
In addition, if a heat-resistant liquid heating medium is used as the heat transfer material in the gap, the holding temperature of the pipeline can be increased to 350°C.
℃ and the upper limit of conventional electric heating pipelines is approx.
It can reach temperatures far exceeding 200℃.

[Brief explanation of the drawing]

FIG. 1 is a schematic longitudinal cross-sectional view of the pipeline of the present invention, and FIG. 2 is an enlarged view of section A in FIG. In these drawings, the numbers represent the following: 1 is an inner tube for transporting fluid, 2 is an outer tube that becomes part of the current path, 3 is an AC power source, 4 and 5 are connection terminals, 6 and 7
are connection conductors, 8, 9, and 10 are currents from an AC power supply, 11 is a sealed insulating bushing, 12 is a circulation pump, 13 is its piping, 14 and 15 are connection points between the piping 13 and the outer pipe, and 16 is a circulating fluid. Crossing piping, 17,
18 and 19 are electrical connections between the inner and outer tubes 1 and 2; 20 is an insulating spacer; 21 is a circulating fluid storage tank/cleaning device/heating device; 22 is an annular gap; and 23 is a transport fluid.

Claims (1)

[Scope of Claims] 1. A conductive inner tube through which a fluid that needs to be heated and kept warm is provided with an outer tube substantially concentric with the inner tube, and both ends of the inner and outer tubes are electrically connected to each other. An electrical terminal is provided in each central part, and a conductor connecting the inner tube terminal and the AC power source passes through an insulating bushing provided on the outer tube, thereby electrically connecting the two terminals of the inner and outer tubes and the AC power source terminal. The outer tube is made of a ferromagnetic steel tube, the wall thickness of which is at least twice the skin depth of the alternating current flowing through the outer tube, and the annular gap between the inner and outer tubes is provided with heat conductive material. Electric heating with a temperature equalizer, characterized in that it includes at least one pipeline unit filled with an electrically insulating material and provided with a heat insulating layer on the outside of the outer tube. pipeline. 2. The pipeline according to item 1, which includes two or more of the pipeline units connected together. 3. The pipeline according to item 1 or 2, wherein the material filling the annular gap between the inner and outer pipes of the pipeline unit is heat transfer cement. 4. In the pipeline described in item 1 or 2, a spacer is used to fill the annular gap between the inner and outer tubes of the pipeline unit, which has better thermal conductivity than air but is electrically insulating. The pipeline is filled at intervals. 5. The pipeline according to item 1 or 2, wherein the substance filling the annular gap between the inner and outer pipes of the pipeline unit is a fluid, preferably a liquid. 6. An outer tube is installed approximately concentrically with a conductive inner tube through which a fluid that needs to be heated and kept warm is installed, both ends of the inner and outer tubes are electrically connected, and an electrical terminal is installed approximately in the center of each of the inner and outer tubes. A conductor connecting the inner tube terminal and the AC power source passes through an insulating bushing provided on the outer tube, and the two terminals of the inner and outer tubes and the AC power source terminal are electrically connected to form an electric circuit. The outer tube is made of a ferromagnetic steel tube, the wall thickness of which is at least twice the skin depth of the alternating current flowing through the outer tube, and the annular gap between the inner and outer tubes has better heat conduction than air. However, it includes at least one pipeline unit filled with an electrically insulating fluid and provided with thermal insulation on the outside of the outer tube, so that the fluid flows in the length direction of the pipeline. Electric heating pipeline with temperature equalizer.