KR840001122B1 - Induced current heating pipe - Google Patents

Abstract

The compact induced heat-generating pipe is useful for shorter bodies to be heated, such as small scale pipelines, the heat-generating pipe consisting of at least one set of two or three ferromagnetic pipes and an insulated wire passing therethrough and connected to an AC source, the respective pipes being electrically connected to each other at both the respective ends. The thickness of the pipes is between s and 1/25, where is s is the skin depth of AC. flowing through the pipes. The pipes of each set are brought into close proximity to each other. The length of the pipes is 1 Km or shorter.

Description

Simple Induction Current Heating Tube

1 is a cross-sectional schematic diagram showing the principle of a heating tube according to the present invention, and is a diagram showing a case where the power source is a single phase.

FIG. 2A is a diagram in which there is a gap between steel pipes in an induction current heating tube in which the thickness of the steel sheet is less than twice the depth of the skin of an alternating current.

Figure 2b is a diagram showing the relationship between the electric field distribution of the primary and secondary current and the magnetic field outside the tube, the thickness inside the tube in the absence of a gap according to the present invention.

Figure 3 is a longitudinal sectional view of the main portion of an embodiment of the present invention.

4 is a perspective view of one embodiment of the present invention in pipeline heating.

The present invention relates to an induction current heating tube and a heating structure using the same.

It is conventionally known as an induction skin current heating tube and is used for heating a pipeline. This heating tube is described in, for example, page 1578 of the 1978 edition of the Institute of Electrical Engineers Handbook, Japanese Patent Application Publication No. 46-588 (corresponding to US Patent No. 3515837). These heating tubes are: (1) two rows of single-phase alternating current and three rows of three-phase alternating current in the case of using three-phase alternating current. (2) two or three conductive ferromagnetic tubes, each of which is intended to be connected to each of the phases of the wires, each consisting of conductive ferromagnetic tubes having a form electrically connected to each other at both ends; The thickness of the ferromagnetic tube is more than twice the depth of the skin of the alternating current that must flow in the tube, and the main heat is generated by the current flowing concentrated in the inner skin of the ferromagnetic tube.

Conductive ferromagnetic tubes in the above-described induced skin current field heat pipes need to have a thickness of at least twice the depth of the skin of the alternating current as described above in order to prevent the alternating current flowing therefrom from appearing on the outer surface. There is this.

For example, to use commercial frequency (50Hz or 60Hz) as an AC power source for commercial steel pipes as the conductive ferromagnetic tube, the skin depth of the current is about 1 millimeter, so the thickness is 3 millimeters and the inner diameter is about 15 to 50 millimeters. Must use steel pipes. These heating steel pipes are suitable for heating insulation of pipelines of several kilometers in length and more than 10 centimeters in diameter, but are not suitable for heating insulation of small pipelines of less than one kilometer in length, especially from 10 to 100 meters in diameter and 5 centimeters in diameter or less. The following inconveniences occur.

(1) As the above-described heat generating steel pipes, that is, 3 millimeters thick and 15 to 50 millimeters in inner diameter, the secondary moment of the cross section is large, so the flexibility is small, and therefore, the contact between the two required for heat transfer to the transport main pipe is difficult. Welding was performed. However, welding requires special skills and cannot be used in the field where flammable gases are easily generated. Moreover, the use of welders in small pipelines is also uneconomical.

(The diameter of the exothermic steel pipe is larger than that of the transport main pipe, which is uneconomical because it requires a larger diameter shell insulation tube than in the case of using another kind of heating element having a small diameter.

Therefore, in order to eliminate such inconveniences, the outer diameter and thickness of the heating steel pipe may be reduced. That is, the curvature of the exothermic steel pipe becomes large in inverse proportion to the secondary moment of the cross section. The cross-sectional secondary moment is proportional to the difference between the fourth power of the outer diameter of the pipe and the fourth power of the inner diameter, and finally proportionally to the third power of the average diameter and the product of the thickness. It is possible by.

The inner diameter of the heating steel pipe is limited to the minimum value from the diameter of the insulated wire through. Compared to s at the depth of the so-called skin, which indicates the range in which an alternating current flows through this steel pipe in order to reduce the thickness t of another heating steel pipe,

t <2s

When it becomes, there is a risk of AC voltage appearing on the outer surface of the heating steel pipe.

The first object of the present invention is that the thickness of the conductive ferromagnetic tube is less than twice the depth of the skin of the alternating current flowing through the ferromagnetic tube, and the voltage appearing on the outer surface of the tube is substantially different from the induction skin current heating tube. It is to suppress the zero or safety to a degree that does not harm. A second object is to provide a heating device that is convenient for compact and small scale heating. A third object is to provide a structure of a heating element having good heat transfer without being welded to the heating element due to the material, environment, small scale, etc. of the heating element, or when it is not desirable.

t<2s의 관계로 있고 상기 2개 또는 3개의 강자성관의 상호로 밀접되어 있고 1조의 각 강자성관의 길이가 1킬로미터 이하인 것을 특징으로 하는 것이다.According to the present invention, when single phase AC is used as a power source, two rows of insulated wires are used when using three phase AC, and one end thereof is electrically connected to each other and the other end is connected to each phase of the AC power source. At least one conductive ferromagnetic tube, which is intended to be connected and consists of two or three conductive ferromagnetic tubes of substantially the same length each penetrated by a row of these wires, the ends of which are electrically connected In the induction current heating tube configured to form an independent secondary circuit for each group when there are a plurality of groups of the tube, the thickness t of the electric ferromagnetic tube is the depth of the skin of the alternating current flowing through the tube ( 0.5s against s)

It is characterized in that t <2s, the two or three ferromagnetic tubes are in close contact with each other, and each pair of ferromagnetic tubes has a length of 1 km or less.

Electrical connection of one end of the said 2nd or 3rd row insulated wire also includes the case where the edge part of the wire which was mutually disconnected was connected, and the case of one continuous wire from the beginning.

As a conductive ferromagnetic tube used in the present invention, a tube of an iron alloy containing ordinary steel and chromium is exemplified. For the sake of simplicity, the description will be made by contrasting the conductive ferromagnetic tubes with steel tubes.

The length of each steel pipe of one pair in this invention is enough to be 1 km or less from a viewpoint of safety. In order to be compact and convenient for transportation and assembly, the length of each steel pipe of one set should be only 10 meters, that is, 50 meters or less, so that two or three steel pipes are closely connected and zero impedance as possible at both ends in the factory or the like beforehand. It is good to weld them together so that they may be near. The lower limit of the length of each steel pipe in one tank may also be applied to the shape, length, and heating demand of the heating element (when this is small, there may be a space without a heating tube between adjacent tanks to adjust the installation density of the heating tube). But it will be about 0.5 meters. If it is made too short, the welding frequency of steel pipes will increase and the installation work of a heating pipe to a to-be-heated body will become cumbersome, and it is undesirable.

In the present invention, a form in which two (rows) or three (rows) of steel pipes in one tank are in close contact with each other and electrically connected at least at both ends thereof is as described above. It also includes a form as one tube having two or three coatings, in addition to the structure in which the mutually welded joints are preferably zero impedance. In the case of three phases, each tube as a close state of three (column) steel pipes is in close contact with two other tubes, and one of them is closely connected to one of the tubes, and these two tubes There may be cases where they do not touch each other. The former has the advantage that no electric current appears on the outer surface than the latter, but is inferior in terms of heat transfer to the heating object.

In the present invention, since the electric steel pipe is thinner than the conventional induction skin current heating tube, it is easy to bend and close to match the shape of the heating object, but a soft steel pipe may be used to make it easier to close.

In order for the heat generating tube of the present invention to be provided with good heat transfer to the heating element, a heat-resistant elastic material such as silicone rubber, heat-resistant rubber, and heat-resistant polyethylene may be inserted therebetween and tightened in a band from around them. Hereinafter, the present invention will be described with reference to the drawings.

First, in Fig. 1, (1) is a single-phase AC power supply, (2) is in series with the pipes of the steel pipes (3) and (4) and the tanks of (3 ') and (4'), and the AC power source (1) Insulated wire to be connected.

The pairs of steel pipes (3) and (4) and the groups of (3 ') and (4') are closely related to each other (in Fig. 1, the principle is made clear so that the two steel pipes are shown in between). Independent secondary currents i _2, which are connected as close to zero impedance as possible electrically at at least two places in both pipes (5), (6) and (7), (8), and a secondary circuit is formed in each group independently. , i ₂ 'is supposed to flow. It is convenient that the electrical connection is made by welding in advance at the factory. This welding may span the entire length of the tight portion. Alternatively, one steel pipe having two coatings may be used instead. In FIG. 1, two sets of (3), (4) and (3 ') and (4') are shown. For example, when the heating element is long as a pipeline, a plurality of pairs are required depending on the length. . In FIG. 1, the case of the single-phase AC power supply is shown, but of course, in the case of the three-phase AC power supply, three steel pipes are required.

As in the present invention, when the thickness of the steel pipe is less than twice the depth of the skin of the alternating current flowing therethrough, the leakage voltage appears on the outer surface of the conductive ferromagnetic tube unless special consideration is given to the skin current heating tube. In the present invention, in order to reduce the leakage voltage to a degree that substantially does not compromise the zero to safety, employing an induction current heating tube, one or three columns of steel pipes are in close contact with each other to reduce the length of a set of steel pipes by 1 km or less (preferably 10 meters or less).

The reason why the voltage appearing on the outer surface of the steel pipe in the heat generating tube according to the present invention does not actually become a problem is as follows.

2a and 2b show, for example, the correlation between the longitudinal cross-sections of the first and second steel pipes 3 and 4 with the side where the steel pipe surfaces are opposed to each other and the insulated wire 2 passing through the steel pipe. Doing. In these figures, the thickness of the steel pipes 3 and 4 is t to s, and the interval between the steel pipes 3 and 4 is zero in FIG. 2A and zero in FIG. 2B (in the case of the present invention). I am doing it.

If the primary current flowing through the insulated wire 2 is i ₁ and the secondary current flowing through the steel pipes 3 and 4 is i ₂ , i ₂ is the thickness t of the steel pipes 3 and 4. It is the integral value between (0-t) of the current density of.

This current density is equivalent to the electrical conductivity of the electric pipe generated within the thickness of the steel pipes (3) and (4) as the electrical conductivity of the steel pipe, and the electric strength (e) of the electric field is the primary current i ₁ and its frequency. , Material, dimensions and mutual positional relationship of steel pipes (3) and (4), for example, are determined by g.

The strength H of the external magnetic field of the steel pipes 3 and 4 is proportional to (i ₁ -i ₂ ). In other words

to be.

2S의 경우에는Like conventional skin current heating tube

In the case of 2S

Therefore, as in the case of Fig. 2a, even if there are gaps g between the steel pipes 3 and 4, the magnetic field H in this gap is almost zero, and the electric field e on the surface of the steel pipes 3 and 4 is almost zero. ₂ degrees became almost zero and it was safe to use as a heating tube.

However, in the present invention, since the thickness t of the steel pipes 3 and 4 is t <2S, for example, t = S, (i ₁ -i ₂ ) becomes large and the magnetic field H cannot be made almost zero. The electric field e ₂ on the surface of the steel pipe is proportional to the total amount gH of the alternating magnetic flux in the gap. In other words

to be. Thus, the new first condition is to make g 2 zero to make e ₂ as small as possible, that is, to close the steel pipes (3) and (4) and to connect both ends to zero impedance as much as possible. It's foolish. The electric field distribution e in the thickness t of the steel pipes 3 and 4 when the first condition (g → 0 and the electrical connection at both ends) is applied is shown in FIG. 2B. The electric field e ₂ on the outer surfaces of the steel pipes 3 and 4 shown in FIG. 2B is almost zero.

The first condition is that e ₂ is limited to a small amount, but if it is still not sufficient, the second condition is to limit the length 1 of each pair of steel pipes (3), (4) or (3 '), (4'). As the independent secondary circuits, leakage voltages of the electric field e ₂ , that is, the steel pipes 3, 4 or 3 ', 4', etc., are integrated in the direction so as not to become large.

Only the closest part of e ₂ becomes completely zero. Therefore, when the cross section of the outer surfaces of the steel pipes 3 and 4 is circular, only the point of contact is in the cross section, and there is some leakage magnetic flux in the space between the other steel pipes. However, in the results of the experiment, even if the cross-section of the steel pipe is circular, the length of the cable is less than 1km, especially several hundred meters, there is no electric shock to the human body or arcing with other metal objects. Therefore, when the pipe wall forming the boundary between the coatings 35 and 36 is long, such as the steel pipe having the cross-sectional structure shown in FIG. 3, since the leakage magnetic flux is small, the length of the steel pipe can be safely increased.

In the above, the case of using two ferromagnetic steel pipes (3) and (4) has been described. However, in order to satisfy the above conditions, for example, as shown in FIG. The use of one steel pipe 34 having two corresponding coatings 35 and 36 can also be considered. Of course, the coating has three power supplies in three phases.

In addition, in the first case, the steel pipes 3 and 4 form secondary induction circuits in FIGS. 1 and 2, and when the thickness t is close to zero (t ↑ 0), e → 0 i ₂ → 0 can not play the role of heating steel pipe. Therefore, the lower limit of t is determined by itself in the sense that it is a heating tube. If it is too thin, not only heat generation but also mechanical protection tube of insulated wire cannot play its role.

4 shows a case in which the heat generating tube of the present invention is applied to heating insulation of a pipeline. In Fig. 4, numerals 1 to 8 have the same meanings as in Fig. 1, but 9 is a pipeline requiring heating and insulation, and 10 is a steel pipe 3, 4 which constitutes an induction heating tube. ) Or (3 '), (4') and the tightening band is tightened by inserting the heat-resistant elastic material 11 between the pipeline (9) and (13) is a heat insulating layer.

FIG. 3 shows a partial cross section of the heat insulation pipe line as shown in FIG. 4, but in this case, as described above, one steel pipe 34 having two coatings instead of the pair of light tubes 3 and 4 is used. have.

As shown in FIG. 3 and FIG. 4, the outer dimensions of the steel pipes 3, 4, or 34 should be large in a direction parallel to the surface of the transport main pipe 9 and small in a right angle. By this means, the inner diameter of the thermos should not be unnecessarily enlarged or the heat transfer area should be made small, and the cross-sectional secondary moment in the direction of the main pipe should not be increased (that is, to improve the flexibility in the direction of the main pipe).

Claims (1)

When single-phase AC is used as the power source, it is two rows of insulated wires when three-phase AC is used. One end thereof is electrically connected to each other, and the other end is intended to be connected to each phase of the AC power source. And at least one conductive ferromagnetic tube having two or three conductive ferromagnetic tubes of substantially equal length, each of which is penetrated by a row of these wires, having an electrically connected form. When there are a plurality of sets of the pipes, the ferromagnetic pipes (3, 4 3 ') in an induction current heating tube in which an independent secondary circuit is formed for each group with respect to a common primary circuit constituted by the insulated wire. 0.5 s with respect to the depth S of the surface of the alternating current i ₂ , i ₂ ′ flowing through the tube

there is a relationship of t <2s, the two or three rows of ferromagnetic tubes (3, 4 3 ', 4' 34) are closely connected to each other, and a set of ferromagnetic tubes (3, 4 3 ', 4'; 34) Induction current heating tube, characterized in that the length of less than 1km.

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