DE2636701A1 - AC-heating of pipes using skin effect - suitable for pipes conveying heavy oil - Google Patents

Abstract

Device is for heating a long body, esp. a pipe, made of an electrically conducting metal with magnetic properties, and through which a medium flows. A long, insulated conductor is laid on the outside of the pipe, but is not magnetically screened from the pipe, and a.c. is fed through the conductor and the pipe. The a.c. produces a skin effect generating heat in the pipe which is directly transferred to the flowing medium. The conductor may be flat metal strip insulated on all sides; alternatively, an extra insulating shields may be located round the conductor where the shield butts against the pipe. One embodiment uses two conductor wires located in resistance material which has a positive temp. coefft of resistance (P.T.C) so current flow is reduced as temp. increases, i.e. the material acts as a thermostat. Used e.g. for the inexpensive heating and insulation of a steel pipe through which heavy oil is pumped.

Description

Device for heat generation in one

elongated metal body The invention relates to a device for heat generation with an elongated body made of metal with magnetic properties and electrical conductivity, on the surface of which a medium is made to flow will. In particular, the invention is used in tube heating by alternating current.

The invention is based on an insulated, electrical conductor wire, the alternating current leads in a down conductor.

The alternating current flows through an adjacent and essentially parallel conductor, which has the shape of an elongated steel part and the return of the circuit results. The so-called skin effect develops in the process (Skin effect) in certain areas of the elongated steel part or conductor that is located in a band immediately adjacent to the wire. The effect arises by induction and magnetic effects. He calls out two essential appearances shows: a) A considerable reduction and localized contraction of the river path of the alternating current, both in depth and in width of the effective conduction path in relation to the cross-section of the steel wall concerns0 on this way it significantly increases the effective resistance of the steel conductor; b) at the same time an essential insulation ability is created against every electrical one Contact taking into account the steel cross-section in two dimensions (depth and width), especially on the surface, of both the inside and the tape also directed away from the outside. The proximity of the two conductors (outwards and backwards) and the actual electromagnetic shielding increases these effects even further and is the basis of the present system according to the invention.

An alternating current only flows along a certain band of the skin an elongated piece of steel, which is considered a very special conductor among such Conditions is.

It should be noted that the word steel is used here for any magnetic, electrically conductive material should stand. Steel is the most common such materials. As an example, consider a pipe that has a minimal Wall thickness of at least twice the skin depth. This is preferable about 3 mm or less for most steels O AC can be up to the distal end of the pipe flow through an adjacent, outboard one and insulated wire connected to the wall at the outer point0 based essentially all of the alternating current flows to the part on the skin effect the outer surface of the Robres back, which is immediately adjacent and parallel to the lead wire.

1 '1 eh 1 a This band of steel surface that is assigned to the wire, then the part that is called the skin effect conductor resistance can be designated. The rest of the surface of the pipe (inside and outside) is for practical considerations fully electrically isolated from any object that touched him. This considerable reduction in the effective cross-section of an electrical conductor, i.e. the entire pipe, is greatly enlarged by the effective resistance of what would otherwise be completely a conductor. the end this is the reason why pipes for oil or other liquids usually cannot Can be used as a conductor resistor because it has such a large cross-section compared to the usual copper wire conductor. According to the present invention the alternating current flow is limited to a narrow band of skin. The pipe calls you significantly increased resistance emerges, so that the newly proposed technique it allows such tubes to be used, alternating current resistance heating for which they would be completely unsuitable when using direct current.

It has been found that pipes according to U.S. Patent 3,777,117 compared to those of the present invention a much smaller resistance to have. This may be due to the fact that the skin effect is on the entire inside of the pipe is caused. Since alternating current only in the said band on one small part of the outer surface of such a pipe according to the present invention flows, is the inner wall of such a pipe for practical purposes completely isolated from alternating current and can even carry liquids that are electrical are conductive 0 Most of the outer pipe wall is also non-conductive, The pipe can be grounded and touched without causing an electric shock even if it is of considerable size. The pipe can be used for transport of liquids that have to be heated during transport or after a closure of the line must be re-heated, since this is essential reduced cross-section can be used, while maintaining the effective area of the conductor resistance has been reduced. Usually the escorted Liquid driven through the tube by a pump or other propellant. If there is such an insulated conductor wire along the length of a steel pipe element extends and is covered with a concave cover strip, all the heat of the alternating current developed within the pipe wall, namely in a band, facing the wire. This tape acts as a conductor resistance, the protective strip protects the wire0 The latter can be extruded from a thermoplastic synthetic resin Be0 In many cases, the wire can also be wound around and along the pipe as a helix be. The concave cover, if used, can again be made from an insulating material Material. The flow of the returning alternating current runs in the skin band facing the wire. The return flow follows the tape and the Shape of the wire, which can be much longer than the length of the pipe shortest distance measured. In using the invention, a nut liquid heated from the wall of the pipe. The liquid or the flowing gas becomes moved by pump, fan, transverse gravity or convention, etc. The steel body is heated by a conductor resistance due to the skin effect that limits is on an effective cross-section due to the skin effect and the close-up effect, which results in increased resistance and, as a result, heat generation.

Usually the steel body is a pipe and the useful fluid can be a liquid that is propelled through. In other cases, the steel body also have other shapes, for example planar, conical, spherical, etc. The useful fluid can be heated by conduction or bypassing.

Heating of pipes by skin effect according to the state of the art. Heating of long pipelines for heavy oils, the viscosity of which must be reduced known. Here, heated pipes with a low heat flow of at most 10 - 15 W used per 30 cm. In contrast, heaters offer due to the skin effect great advantages over the other systems, what steam or use other heating media.

Thin cables can be underneath their entire length due to the skin effect can be heated at favorable cost ratios.

The usual alternating current of 50 or 60 Hz as described in U.S. Patents 3,777,117 and 3,617,699 has been.

The facilities of these patents also use the skin effect when using different constructions and sizes of pipelines. operation and execution are based on the proximity effect, the current frequency and other parameters0 In particular, such factors affect the effective resistance the steel pipes. As the pipe size increases, the resistance must be increased, although the effective resistance of what a normal conductor would be very large.

Objects of development were also the construction data the materials, the conductor wires, their insulation under different conditions, fluids to be pumped using heating tubes for general purposes. The invention takes all of these aspects into account.

In a heating tube, an internal electrical wire forms a component of the AC circuit; the other end is at the end of the inside of the heating pipe. The return line of the circuit is the inner wall of the heating pipe; the outer wall Carries very little electricity if the steel pipe is more than twice the so-called effective Has a skin depth of about imm.

In ordinary steels, about three times this is sufficient, i.e. about 3.2 mm. The other connection to the AC power source is a point at the near end of the inner surface of the heating pipe, opposite the entrance of the insulated copper wire into the heating pipe, which carries the alternating current to the far end.

In the cited patents, improved heating pipes are given, which cause the pipe to adapt to the outer surface or to the wall of the oil line himself will. These constructions allow a much higher heat flow than before accepted. They also bring about savings in the cost of the pipe, the heating and the insulation, through suitable constructions the alternating current is passed through the multiple lengths of the pipe passed through spirally wound heat pipes instead a straight line, which would usually result in the least resistance.

An internal electrical wire or steel pipe instead of a copper wire for derivation was also used to provide further resistance for a second skin effect to create. The greater resistance develops even more heat.

In particular, very thick oil lines could also be used as heating lines act. Only one inner conductor is required, with a much lower investment cost and entertainment. By removing the position of the inner conductor from the pipe axis, the effective resistance of the "skin" of the oil pipe was increased considerably, which is essential with thick oil lines.

This can be attributed to the convergence effect that may change in use.

So far, the inner conductor or wire has been completely lengthwise enclosed in a steel tube.

Basics of the Invention The skin effect is a phenomenon with one AC circuit that limits the alternating current to iron and steel surfaces, which act as ohmic resistances and work in electromagnetic fields. Commercial AC frequencies between 50-60 Hz are used in other, neighboring Ladders used to create further magnetic and inductive effects. With suitable, known circuits, all three phases of a three-phase current can be achieved and use the frequency range of 10 - 1000 or more Hz, which is the case with conventional generators can be produced.

The electromagnetic flux around a wire carrying alternating current, expands until it meets a shield made of a different metal. According to In U.S. Patent 3,777,117, a conveyor pipe serves as a heating pipe, with an inner wire running along it the axis or on the bottom of the pipe.

To ensure that there is no power loss or exposure to high voltage alternating current of the inner tube go out, a minimum thickness of double or triple the Skin thickness (about 3 mm) for normal steels under normal Current conditions specified. There is no loss of energy in this case, even if the outside of the pipe is grounded or submerged in salt water. Usually an open one Pipe grounded at intervals. A cathodic protection system can be used where there is a risk of corrosion can be used without disturbing the skin effect.

Proximity Effect The proximity effect is a essential phenomenon in an electromagnetic field that arises when an alternating current through an inner wire conductor to the return of the circuit is connected, which is usually the steel wall of the pipe. This appearance was discussed in detail in U.S. Patent 3,777,177. An increase in the effective Resistance to twenty-five times the normal resistance could be achieved will.

Resulting from the combination of the skin effect with the approach effect different arrangements of line and return line in steel. Usually the steel ladder is a conveyor pipe whose effective resistance increases in practice must become. In the case of a circular conductor wire that is the outside of a steel pipe the effective resistance of the return line is substantially equal to that a skin effect ladder resistor that can be thought of as being cut out of the wall can imagine, with the usual skin thickness and an effective width of a narrow Band under and next to the pipe element on which the insulation is present.

The thickness of the insulation on the wire limits this effective distance of the wire from the pipe wall, as well as the shape of the wire cross-section. A flat one Conductor tape, which is held tightly against the outer pipe wall, with as little as possible Insulation thickness in between would result in the shortest distance. Here would be the convergence effect Most also, according to U.S. Patent 3,777,117, a flat wire, the rests against the inner surface of the pipe, resulting in the greatest effective resistance of the pipe wall. In the present invention, the convexity of the pipe wall is enhanced over the Wire compared an increase in resistance to the skin of the underlying tape to the concavity of the inner surface of the pipe wall.

This effect is due to the fact that in addition to the skin effect and the approximation effect there is still a shielding effect which is absent when the wire is intact is surrounded by the pipe.

It has been shown in individual cases that a flat wire «is desirable is that this is no more than five to twelve times the so-called penetration depth away from the pipe.

For normal steels this would be between 5 and 25 mm.

This includes the insulation thickness. The flatter the wire for a given cross-section, however, the stronger it must be for the same be electrical power and for the same reason is the width of the skin effect band all the greater which is generated by the electromagnetic flux0 in the in general, the effective width of the tape is equal to the sum of the width of the flat wire plus two to three times the depth of penetration on each side. The sum can i.e. wire width plus four to six times the penetration depth, this being depends on the actual distance of the wire conductor from the steel.

If a flat steel is used, the approach effect is strongest. This is especially true for flat wires, but can also be used with normal wires in Appearance. If flat steel wire is used as a conductor, the advantage is the Skin effect is taken into account in this and in the pipe wall. Is the flat steel stronger than twice the thickness of the skin, all the rest of the strength of the steel wall acts Tape as an insulator that becomes more effective with increasing thickness. That aspect the use of the shank as an insulator must be considered versus the use a usual insulation, which in any case somehow exists on the inner pipe have to be. Movement of the wire with respect to the pipe changes greatly the proximity effect, the pipe resistance and the heat generated.

Bb schirmunaa An electromagnetic positive, like that of an alternating current spawned in a lead wire is through an electrical conductor shielded. The shield reduces the penetration of the river into the steel wall. Shielding also affects the proximity effect, especially in the outer, convex pipe wall where an alternating current wire faces one of the elements.

In some cases it is desirable to use the width of the skin effect resistance to narrow in the pipe wall. It should be noted that the width is about twice the value of the skin depth and by this amount across the width of the wire This depends on the distance between the wire and the wall. In of this width the pipe wall carries alternating current on each side, with the value of Voltage and amperage decreases very rapidly at a distance from the side of the flat wire When the insulation that must be arranged around the flat wire is more than two or three times the value of the penetration depth on each side of the wire, it effectively isolates the pipe wall from each any contact or short circuit.

OBJECT OF THE INVENTION Objects of the invention are: lo reduction the effective width of the skin-effect conductor resistance and thus the magnification of resistance; 20 Use of a lead wire that is not enclosed by the steel pipe is, wherein the heating pipe at least partially from the wall of a conveyor pipe consists; 3o Simplification and cheapening of material and construction, including the thermal insulation for the pipelines and other heated surfaces; 4o Use of a guide wire, without a surrounding heating pipe, which does not come into contact stands with the medium that is conveyed through the line; 5. Using a simple, insulated conductor as the only element of a heating pipe as an additional part to the existing delivery line, which is arranged in the vicinity of the pipe wall; 6. Using a simple insulated wire next to a steel surface which can have any shape, using the skin effect resistance against the alternating current flow as a return line for the circuit; 7. Use a special conductor wire as a thermostat to regulate the heat supply and temperature of a steel surface, and thus of the guided liquid; 8. Oppression caused by thermal stresses in a steel structure, e.g. a conveyor line by welding a heating pipe; 9. Use of another adjacent pipe as a line for mutual skin heating; three adjacent Tubes are used for mutual heating, the three conductors of a three-phase circuit are used.

Embodiments of the invention are described with reference to the drawing The figures of the drawing show various schematic representations. In these Only alternating current is used in each of the pictures. In the circuit diagrams is the insulation of the wires not shown in the rule 0 The conveyed media are only indicated by arrows indicated to give the direction of flow. Pumps, special valves and the like are not shown.

Figs. 1 and 2 are cross sections of an ordinary insulated conductor which runs along the wall of a conveyor line and cover insulating hollow bodies the electric wire.

Fig0 3 is the cross section through an ordinary insulated wire on the outside of a delivery line.

Fig0 4 is the cross section through an insulated electrical wire of rectangular shape on the outside of a conveyor line, with means for enlarging the distance between the wire and the pipe.

Fig. 5 is a cross section through the insulated wire of Fig.

4, but with metal shielding strips embedded in the insulation are.

Figure 5A is a cross section parallel to the axis of a special conductor (Wire tube) that is electrically connected to a special steel body, also in Cross-section.

Fig. 5A is a cross section of the insulated wire in Fig. 4, but with protective metal strips embedded in insulation.

FIG. B is an enlargement of the cross section of the special wire in FIG Figure 5A, where the insulated wire lies outside a layer of thermal insulation.

Figure 6A is a cross section parallel to the axis of a special conductor (Tubular wire), which is electrically connected to a special steel body, also in cross sectionO Fig. 63 is a cross section at right angles to the axis in Fig. 6A.

Fig. 7 is a section through two conveyor lines, each also represents represents the guide wire for the other two in a three-phase circuit.

Fig. 8 is a section through three delivery lines, each of which also acts as a conductor for the other two in a three-phase circuit.

Fig. 9A is a plan view for a steel sheet heated by a simple one insulated conductor as a strand in an alternating current circuit and a derived The band of a skin effect conductor resistance is the return line.

Figure 9B is the cross-section of Figure 9A, with a medium being forcibly circulated against the surface of the steel sheet.

Fig. 10 is a diagram of an AC circuit in which an isolated Wire is spirally wrapped around a conveyor pipe.

Fig. 11 is a schematic of an AC circuit in which an isolated Wire on a pipe wall through a plastic coating of angled concave cross-section is protected.

Fig. 12 is a schematic of an AC circuit in which an isolated Wire on a pipe wall through a cuff with an angular cross-section is protected.

Fig. 13 is a schematic of an AC circuit in which an isolated Wire runs along part of a pipe wall.

FIG. 14 is a longitudinal view and circuit of FIG. 4.

Fig. 15 is a longitudinal view and circuit of Fig. 5A.

Fig. 16 is a longitudinal view and circuit of Fig. 5B.

Fig. 17 is a longitudinal view of the two tubes and circuit of Fig. 7th

Fig. 18 is a longitudinal view of the three tubes and circuit of Fig. 8th.

Heating pipes partially enclosed in steel All previous heating pipes, who used the skin effect for electrical heating were surrounded by and therefore completely surrounded by steel pipe, except for the ends that are not on the heater take part. This is especially true for the most common type where part of the heating pipe is also part of the delivery pipe. Here, completely enclosed means "a note on the longitudinal course of the pipe, as it is in a typical section at right angles to the Pipe axis would appear; and the whole perimeter of the steel is of uniform Metal; all joints are welded and ferromagnetic.

It has now been found that the steel wall, which gives the skin effect, In Fällenawo, part of the delivery pipe does not need to surround the threat Provides heat in part or all of the skin effects as defined in U.S. Patent 3,617 699 and application 107 5310 There are a number of advantages, mainly that the pipe does not heat up unevenly as a result of welds on the heating pipe, which could reduce its strength as a result of thermal stresses. It's convenient, desirable and economical, that portion of the AC return circuit within the delivery line to be separated as the main return line within a narrow strip of skin effect Conductor resistance, In the previously used heating pipe, isolated from the delivery pipe, but next to it and usually welded on (see U.S. Patents 3,329,3407 and 3,591,770) was the Skin effect resistance limited to the inner wall of the outer and insulated heating pipe. Although then there is contact, or usually a weld to the wall of the delivery pipe, no electricity could flow and no heat could be generated inside the wall of the conveyor pipe. This is based on the fact that, by definition, the The heating pipe was made of thick enough steel to allow electricity to flow and generate heat on the outer surface to avoid where there is contact with the delivery line; so no heat could are generated in the weld bead or in the pipe itself. The present invention relates the use of the insulated guide wire next to or in direct contact with the steel to be heated, usually the wall of the conveyor pipe, so that heat directly inside the steel wall itself, where otherwise the temperature is too low is.

Now the effective perimeter of the heating pipe has been reduced accordingly. This perimeter is the actual width of the "ribbon" of SkineSekt-Leiter and Resistance that carries the return alternating current. Hence, its cross-sectional area increases from when the "opening" remains the same because of the constancy of the penetration depth; and the resistance in the return line of the AC circuit becomes corresponding greater. The "opening" becomes 180 - for a flat steel plate - or larger 0 than 180 - for the outside of a pipe - then the tape is that main conductor simply the part of the adjacent steel surface or below the alternating current flow lies in the adjacent wire.

This consideration is very important when designing pipelines over greater distances, especially for large pipe diameters. In registration 107 361, now US Pat. No. 3,777,117, it was shown that with a suitable combination of skin and proximity effect, and appropriate frequency, the effective resistance of the steel pipe as the return line of the AC circuit can be varied up to a thousand times. By reducing the bandwidth for the skin effect conductor resistance after this Invention there is still a very large factor for increasing the resistance according to the invention.

Likewise, this invention can be used to target media that are outside flow from pipes to heat, and also other substances including solids be in contact with a heated steel body.

Application 107,351, now U.S. Patent 3,777,117, describes heating of media that are in contact with the walls of a combined stimulus and Conveyor pipe, either inside or outside. This heating tube can according to the invention can also be used when the wire is not inside the tube as described. In the same way, another piece of steel, pipe or other shape and no wire surround, with use the wire and take the return wire with you; and the form steel that carries the return line in the skin effect conductor resistor, then lies under the wire. This main warmer for a steel sheet or another Shape can have any shape the associated wire, and one on each side Form sheet of suitable thickness, and all three phases of the current can be used0 Heating with enclosed wire Fig. 1 shows the cross section of a heating pipe formed from the pipe wall 1, a skin effect conductor and resistor. Wire 3 with its insulation 4 lies along a pipe element and is covered with a concave Strip or shaped piece 2, made of plaster of paris or some other non-conductor. This can flanged or not, 6 to conform to the pipe wall. A thin joint 7 between the pipe and the two flanges of the cover strip extends over the whole Length of Both - The electrical connections are shown in Figure 11 and correspond those for heating pipe; the wire is on the near end with a clamp of AC power 5 connected at the far end of the outer tube face. The nearer end of the pipe is connected to the other terminal 5t of the alternating current. Lid 2 can be made of any non-magnetic and be a non-conductive material, such as a plastic. It is far enough around the tape of the pipe that lies under the wire as a skin effect conductor and resistor. The current density along the Pages of this volume are picking up quickly depends on the distance from the belt axis O The effective width mainly depends on the wire gauge, and therefore its actual distance from the steel and hence the insulation thickness. For round wire is the effective width of the skin effect conductor and resistance usually not more than 25 - 50 times the value of the penetration depth or skin depth. Heat generated in the pipe wall goes directly into the remainder of the wall and from there into the fluid.

Therefore, the arrangement of Fig. 1 with or without a plastic cover run along one or more parts of the pipeline the distance should be at least 100 times the penetration depth, the wire can also be around the Conveyor belt wrapped around in a helical shape with any pitch; however should the turns must be at least 100 times the penetration depth apart. This use a helical heating tube is described in more detail in U.S. Patent 3,617 699; this invention adds that using a simple insulated wire as a single ingredient in the pipe, in order to achieve the skin effect in conductors and resistance, which was previously known, was only for heating pipes along the entire length, with wire.

Likewise, any desired pattern can be applied to a steel body either flat or curved, as well as for various other heating purposes.

Fig. 2 shows some other plastic forms that are used as cover can serve. Here is a corner piece as described for Fig. 1. A standard version is comfortable; many other forms are possible. A plastic angle can be used as a screw body around a pipe, or on a flat sheet metal, as described for FIG. Fig. 10 shows the circuit diagram of the screw curve on the ear surface, either with or without cover.

Heating with the lid removed Fig. 3 is a cross section of the simplest Form of the invention and shows a wire, insulated as usual, on the outer surface of the pipe along a pipe part, screw or other desired shape. The electrical circuit is again as in Fig. 13 and the return line with the skin action conductor and resistor lies below the point of passage of the electromagnetic flow into the outer surface of the steel pipe, depending on the proximity effect and skin effect, depending on the wire thickness and insulation thickness. The wire in the circuit diagram can either run along a pipe element or as a screw in Fig. 10, or some other pattern with a suitable spacing on the pipe wall be used.

The wire by itself can also be used to carry heat in a steel body which is not a pipe, as in Figs. 1 and 2.

A valuable variety of the common wire in Fig. 3 is the flattened one isolated wire or tape in Fig. 4, the width of which is greater than the thickness. For the purpose of best utilization of the proximity effect, i.e. the minimum width of the skin effect conductor and resistance, and maximum resistance, should be the effective center of the conductor if possible be close to the pipe wall. You can get close to this by using a flat wire or metal band. However, if this one gets wider, it will lie under a wider one Band of steel skin for reflux with correspondingly reduced resistance in that Return steel ladder.

The most favorable ratio of these dimensions depends on the electrical Properties of these circuits0 The electrical insulation is used in the usual Way used. If you make it wider than otherwise necessary, i.e. 2 to 6 times the penetration depth on both sides of the wire band, it covers the whole band of return conductivity and isolates it against mechanical contact and shock or short circuit.

This use is best suited for the use of heat insulation of the delivery pipe, because it is the least over the pipe.

Fig. 14 is an elevation of Fig. 4 also showing normal wire routing; Special fittings 14, 15 and 16 are described below. The ladder is normal made of copper or aluminum, but steel can also be used, especially as a Tape, whereby heat is generated by conduction losses or by the skin effect, is transmitted from the steel conductor through the insulation to the pipe wall. When the steel belt is thicker than the effective depth of penetration, or skin thickness, is only the skin thickness essential for the AC line O larger Thickness of the steel band becomes electrical insulation. According to application, now US Patent 3,777,117, growing the insulating effect of steel very quickly (as an exponential function) in contrast to the linear function for ordinary isolators.

Fig. 5A is a modification of Fig. 4 and also has a protective edge 8 on each side of the flaehead to reduce the effective volume of skin conductor. Therefore, the tape cannot go beyond a certain width to a part to expose the pipe surface in which a substantial part of the current flows. These Protective strips are surrounded by the molded insulation and can either be individual be, thin Eupfer or aluminum strips or from a bundle of metal fibers or wires. Each protects the steel pipe and determines the range of the Skin effect of the conductor and resistance underneath. An elevation of Fig. 5A and a Circuit diagrams are in Fig. 15.

Figure 5B is an enlarged cross-section of this particular flat wire in a molded or drawn insulator of suitable material. This can be used are as in Fig.

5A and previous, directly on the pipe wall. However, this form of Wire can be used as the rest in this invention, particularly as shown in Fig. 3 and 4 outside of the usual thermal insulation, as shown in Fig. 5B with the usual circuit diagram in Fig. 16. The thermal insulation has the usual thickness from 1 to 6 and the conductor wire is simply on the outside and conducts the current back, while the useful heat is generated in the skin effect conductor and Resistance below and inside the pipe wall.

The guide wire as a thermostat The guide wire that is a branch of a AC circuit with return through a band of skin effect conductor and resistor, can advantageously be formed from a special insulation resistance cable that with increasing temperature of resistance increases and the passage of current throttles0 It usually consists of a pair of wires in an EabA with a special material between the two wires. This special material can be a synthetic plastic be with a special filler; and the whole has high specific electrical Resistance compared to that of the wires and increases its specific electrical Resistance, its ability to generate heat diminishes as it increases Temperature. Such a substance has a positive temperature coefficient (P.T00.). Therefore, the special cable is its own thermostat or supply regulator for AC power equipment in existing technology. External insulation covers both the parallel wires and the tnsulator and resistor in between, made of PTC material0 So far, the Always keep both wires on one end of the cable with an AC or DC power source tied together. Once the temperature of the cable and the special insulator and resistance rises between the two wires, the takes Conductivity. The flow of current between the two conductor resistance wires and through them themselves decreases. When the heat supply decreases, the cable cools down to a temperature is reached where the conductivity of the conductor resistance, which is evenly distributed is about the length of the two wires, again increasing, more current flows and the circuit repeats itself0 This well-known type of cable heating always had its two parallel ones Wires on each side of the PTU fabric, the same at the conductor resistance End was connected to the source of power.

It has now been found that when using this heating cable with a slightly different circuit than the guide wire of a skin effect heating system, the thermostatic control not only takes place in the cable itself as before, but that at the same time current flow and heat generation in the return line of the circuit be controlled, i.e. the part of the resistance and conductor that is due to the effect of the skin is present in the adjacent steel body.

This novel connection, shown in Fig. 6A in longitudinal section and in Figo 6B in cross section, the purpose of a steel body 1 is to be heated by skin effect conductor resistance in ribbon form, caused by the flow of alternating current in the parallel conductor wires 3 'and 3 "with the common electrical Isolation 40 (purpose the wires are shown in elevation for clarity). The special insulator resistance material (with PTC) in this case is shown as a synthetic resin with a special one Filler. It is part of a molded cable between the two Wire and lies within the overall insulation. Any such system can be used when it electrically connects the two wires, evenly over their entire length in order to increase the resistance between the wires and to reduce the current flow when the cable is heated. The composition this material, 11 and the type of electrical connection between the two Wires 3 'and 3 "is neither part of the invention nor the fact that the electrical resistance and therefore the heat developed in this special material, is used for heating the steel body 1, as is the "conduction loss" each other lead wire. Furthermore, as in other embodiments according to this invention, the lead wires, here 3 'and 3 ", can be made from a good conductor such as copper or aluminum or steel, a middle conductor or resistance wire, a bad conductor. In any case, the wires will be more or less electrical resistance and heat generation than the so-called conduction loss is equivalent to. This heat is beneficial in the steel body 1 and increases by the Skin effect formed.

Basically, the two parallel wires behave 3 ' and 3 "with the special insulator 11 like single element ladder more ordinary Type and convey alternating current from the (+) end of the alternating current source to the spot 6 at the far end of the steel body 1 back through the skin effect tape resistance conductor at 1 and from there through the connecting wire 13 to the other (-) end of the alternating current.

If the system and especially the special insulator resistor 11 When warmed, its resistance to the flow of alternating current and its flow increases is decreased.

Less heat is generated than so-called conduction loss as in the ordinary Use of this type of cable for direct heating of cables. (Normally Both ends of two wires are connected directly from one end of the cable to the AC end points and one is not connected to the pipe like in this new schematic).

In this invention, the electrical conductivity is decreased of the insulator-resistance material 11 as well as the electrical flow, not only in this return line of the diagram, but also in the skin effect ladder resistance band of the adjacent steel body that forms the return line as soon as heating occurs. The thermostatic effect of the cable itself (as it has been used so far) can do so many times over are strengthened by controlling the flow of current from the skin effect and the corresponding Heat effect inside the pipe or other steel body.

FIGS. 6A and 6B show the steel to be heated in section 1 with the adjacent twin-wire cables. Apparently, the bundle of cables can be inside or lie outside a pipe wall, this steel cross-section can also have a different shape as a pipe wall, as further discussed for other wire conductors this one Invention. The cable bundle can also have plastic covers, as in Fig. 1 or 2, as shown, for the purpose of insulation or as protection for the band of skin effect conductor resistance underneath. Also, the cable bundle can usually be molded with the flat side of the Insulation against the steel body can be accommodated in order to improve the aforementioned Proximity effect.

Heating with a further pipe as a conductor Fig. 7 shows schematically a cross-section through two conveyor pipes 31 and 91 ', each of which as adjacent Head serving for the other. An elevation and circuit diagram are shown in FIG as a mutual arrangement of wire and skin effect conductor resistance. Number 31 indicates the combination of conductors 3 and 1 for the steel tube, as both functions were taken over here by the conveyor pipe. An electrical insulator 4 is in Scheme as a flat band of suitable material, indicated adjacent to both tubes, but such a tape can also be attached to the surface of one or both tubes or it can be around the perimeter of the space between the almost tangent pipes be shaped. Its purpose is the skin effects of the Xeiter resistance bands in the To insulate the steel wall of the individual pipes from one another; one is the outer conductor of the circuit and the other 31 'acts as a return line.

The endpoints of the AC power source are shown at 5 and near End at 31 for 5 and for 31 'at 5'. A bridging line connects electrically the far ends of the two tubes together at 6 for 31, and 6 'for 31'. Of the circuit thus formed carries alternating current from point 5 to the near end, then through and out of the skin band at 31t to the near end, then to point 5 '.

Both pipes are heated by the heat that is developed in the bands of skin effect conductor resistance in the part of the walls that are closest to the rest of the length and each band acts as a common conductor in the creation of the electromagnetic flux for the skin effect and proximity effect in the other conductor, because of the space requirements of the two convex tube walls of the opposite one Pipes, the tape in each pipe can become wider than desired. One can see the skin effects With these conductor strips reduce by two thin strips of conduct the metal 8 embedded in the insulation as shown; see Figures 5A and 5B.

While 31 and 31 'are shown as cross sections of conveyor pipes, what the useful application of this part of the invention may be, so may others Steel bodies or longitudinal strips can be used with equal success; and the warmed liquid can exit outside the two bodies instead of going through the pipes like in Fig. 7. If means are provided to separate the bodies (pipe etc0) further apart To place, the skin effect and the proximity effect serve to establish the effective resistance of the circuit to enlarge and less heat is developed, as in Fig. 4 for an ordinary one Lead wire is shown. While usually the use of bodies is the same Cross-section will be desired, in other cases unequal length bodies in substantially parallel arrangement have better effect. The only thing that matters is that they are next to each other.

Fig. 8 is, on a larger scale, the system of Fig. 7 applied to a Three-phase power source with three steel tubes of equal length, each of which has a band of Has skin effect ladder resistance.

Each belt acts as a guide wire for making the corresponding one Ribbon skin effect conductor resistance in the pipe opposite. Again, there is isolation provided, 4, here as a uniform fitting, between each line of contact of the pipe pair in question; and again shielding can be provided in the insulators although not shown in FIG. 8.

The AC circuit for Fig. 8 is shown in Fig. 18 and is analogous to that in Fig. 17, expanded for three-phase current, where each phase is 1200 opposite the two other lies. The three endpoints 5, 5 'and Fjn of the rotary power source are indicated as small circles at the ends of the three wires 13, 13 'and 13 ", the are connected to the adjacent pipe ends 31, 31 'and 31n. The far ends of each three tubular wire combinations are connected by connecting wires between 6 and 6 ', 6' and 6 "also 6" and 6 ', although two of these three connections also would be enough. This is how the usual star connection is established at the far ends of 31 ', 31 "and 31"' with balanced load for each of the three equal pipes.

Again, the three longitudinal bodies of FIG. 8, like that of FIG. 7 other than tubular. Their cross-sections can be the same or different and the fluids to be heated can lie wholly or partly against the outer surfaces and the distance between them can be adjusted in pairs to increase the resistance for the alternating current flowing through the circuit for a couple, with regulation the heat generated in the resistors.

Heating of non-tubular steel bodies Figures 9A and 9B show schematically a sheet steel, here assumed to be flat, although every other surface, how cylindrical, conical, spherical or otherwise uneven can be used. The surface can be part of the heater and then means can be provided to move a fluid to be heated against the surface.

The steel sheet 1, the wall of the conveyor pipe in the rest Corresponds to pictures, has attached an insulated wire 3, Of the Wire can also have a steel or plastic lid, as in Figures 1 and 2, again with narrow slots cover and steel, essentially parallel with the wire and on the back. The surface of the steel sheet can be covered uniformly with wire in different patterns; straight, curved or otherwise. However, should no part of wire is closer to another than about 50 to 100 times the Value of the penetration depth. One end of the wire is connected to the steel sheet Point 9; and at a remote point, the wire separates from the sheet for the purpose Connect to an end point (-) of the AC power source. The other endpoint (+) of the AC current is connected to the steel sheet at a point 10 near the point where the isolation ends.

All other embodiments of this invention, including all of them Other pictures shown can also be attached to one or more steel bodies that do not have any Pipe walls are to be attached in connection with the circuit diagram in Fig. 9A and 9B and the conveying medium can rest on any surface of the steel body; see arrows in Figures 9A and 9B.

Attachment of Wires and Coatings Numerous means are available for holding the pipe wall or plate on the insulated conductor wires in the various Images, also for the coatings in Figs. 1 and 2. All are earlier for similar ones Purposes and they do not form part of this invention. To be able to hold on Wires, screw connections, Use glue, putty, etc. None should significantly interfere with the thermal insulation that is normal in conveyor lines, whether prefabricated or under construction.

When prefabricating heat-insulated and covered pipe lengths Wire connections provided for electrical connection after welding the pipe joints.

Electrical insulation Substances for the electrical insulation of wire conductors are discussed in U.S. Patents 3,617,699 and 3,777,117. The insulation of the wire conductors according to this invention offers fewer problems than the simultaneous registration because of the lower temperature and the absence of contact with the pumped liquid, when the wire is outside the tubes.

Also are the temperatures which the insulation of the lead wires must be able to withstand, much lower than those found in conventional tubular heating wires Heat generated outside the pipe and ile must go through the insulation with sufficient high temperature to transfer the heat into the pipe wall. According to this invention the heat is essentially generated in the pipe wall itself and only that of the relatively small line loss of the steel, copper or aluminum conductor must through the insulation can be routed to the pipe wall. Accordingly, there is a lower temperature in insulation and less difficulty in design and operation.

Sometimes the temperatures used are high, especially if that Pipe is pre-insulated and pre-coated in the factory and then a special insulation is made used. This can be applied to the pipe wall as mineral insulation, as mentioned above, or designed as glass fiber, impregnated for high temperatures, insulating resin or other will. The wire, preferably in ribbon form, can then be placed on the tube outside of the electrical insulation and add further insulation as desired.

Thermal insulation Iyp and structure of the thermal insulation of a pipeline which is heated in this way is outside of this invention.

However, it has been found that pipelines that are already thermally insulated were, by means of the usual materials and not against electromagnetic flux effectively shielded are also heated by the method of this invention can be, namely through the insulation.

For example, if an electrical conductor is outside the electrical Insulation is applied and the circuit is connected as usual, heating a band of skin effect-ladder resistance effectively the underlying steel Pipe wall, i.e. the whole pipe and then its contents. This is by no means so effective as if the wire were next to the pipe wall, because practically all of the line loss is lost to the environment instead of heating the pipe itself.

However, this system can be used in an existing insulated pipeline Use in an emergency or when only little heating time is required per year. In such cases, the wasteful use of electricity can become negligible. The wire can be used either parallel to the axis or in screw form0 The insulation cover of Fig0 1 and 2 can be recycled; but the flat wires of Figures 4 and 5 are not so advantageous at this distance from the pipe wall. Most of the time, the simple insulated wire in Fig. 3 is used, although Fig. 5B shows the application of a flat conductor.

In this individual case, the efficiency can be improved if the Wire is placed on top of the insulation, especially if the pipe is high but close to it Floor lies. Then the whole circumference acts as a shield against the magnetic field from the conductor wire the reason and the resulting power losses. The same applies to a limited extent for other wires that lie directly on the pipe wall 0 variable resistance and Heat consumption As already mentioned, changes with the position of the conductor wire in relation to the pipe the proximity effect and the resistance of the skin effect conductor and resistance0 If the Wire or pipe can be moved relative to each other, so that an alternating current circuit is formed, the resistance, the generated heat and the temperature change. In some cases you can Pipe or wire during operation move appropriate means against each other.

Fig. 4 shows such a means; and Fig. 14 shows the circuit. A lever arm is attached to the insulation 4o. The other end of the lever arm swings in a bearing block 16 and is attached to the pipe wall 1 by welding.

The lever arm moves around a pin 15 in the bearing for a rotary movement to execute. A number of such arms along the insulated wire 4 move it off the pipe through to the arc shown. The electromagnetic field changes with it increasing distance and also with the angle against the tube with the rectangular wire 4 and the skin effect conductor and resistor can increase its resistance many times over by swinging the lever arm and the wire 3 away from the pipe wall to accordingly to reduce the development of heat in the pipe.

If the wire is made of steel with a skin effect conductor resistance band for the current, the change and the control area can be expanded even more. When the conveyor tube moves against the wire, or against another Conveyor pipe where the skin effect conductor and resistor along the adjacent surface the concurrent lengths arises, the effect is the same and the most important thing is that resistance increase and control of heat input by separating the both branches of the AC circuit can be reached.

Claims (18)

Pa tent claims 9 device for generating heat with an elongated Body made of metal with magnetic properties and electrical conductivity, on the surface of which a medium is made to flow, characterized by an elongated electrical conductor that electrically insulates but not opposite the outer surface of the body is magnetically shielded, and along its entire length applied directly to the body, an AC power source having a first and a second connection (end point), an electrical connection between the first connection and the front (first) end of the body, an electrical connection between the second terminal and the front (first) end of the electrical conductor and an electrical connection between the rear (second) end of the body and the rear (second) end of the electrical conductor to form an alternating current circuit from the second terminal of the AC power source through the electrical conductor and back through the body to the first terminal of the AC power source, with in the body near the electrical conductor, concentrated in a band-shaped zone (longitudinal band), a current flows (skin effect or skin effect), which generates heat in the body, which is at least partially transferred directly to the medium. 2. Device according to claim 1, characterized in that the body is a pipe through which the medium flows while touching the inner surface is brought. 3. Device according to claim 1, characterized in that one Cover made of electrically insulating material attached over the electrical conductor is, the band-shaped acting as a conductor and resistor for the skin effect Zone of the body is electrically isolated. 4. Device according to claim 1, characterized in that the body has a flattening for better support of the electrical conductor. 5. Device according to claim 1, characterized in that the electrical Head is a metal strip that is insulated and wider along its entire length than is thick. 6. Device according to claim 1, characterized in that between a heat insulating layer is arranged on the conductor and the body. 7. Device according to claim 1, characterized by an electrical Conductor made up of two adjacent and substantially parallel wires, means for electrical connection between the first and the second wire made of a material with high electrical resistance compared with that of wires, and higher resistance at a higher temperature, an electrical connection between the second connection the AC power source and the end of the first wire near the front end of the Body and the alternating current connection, an electrical connection between the rear end of the body and the second wire, spaced from the electrical Connect the first wire to the AC terminal to form an AC circuit through the conductor from the second terminal of the AC power source through the first Wire and through the electrical conduit between the first wire to the second wire and through the second wire to electrical connection to the rear end of the body, with the temperature dependence of the resistance and the high specific Resistance between the first and the second wire increases the flow of alternating current Throttle the temperature in the line between the first and the second wire and so that Heat generation and decrease the temperature in the body. 8. Device according to claim 7, characterized in that the body is a pipe through which the medium flows while touching the inside of the pipe is brought. 9. Device according to claim 7, characterized in that the body on its outer surface in the area of the electrical conductor over its entire length is flattened. 10. Device according to claim 1, characterized in that the conductor made of metal with magnetic properties and electrical conductivity is. 11. Device according to claim 10, characterized in that both the body and the conductor have the same cross-section. 12. Device for generating heat, characterized by three tubes made of metal with magnetic properties and electrical conductivity, which all three are arranged close together, but each of which is electrically isolated is opposite the outer surfaces of the other two, a three-phase power source with three Infeed or end points, means for electrical connection of the front end of the first pipe with the first feed point, the front end of the second Tube with the second feed point and the front end of the third tube with the third feed point, means for electrical connection of the rear Ends of all three pipes in a star connection to create a three-phase circuit, with which a first Single-phase alternating current from the first feed-in point through the wall of the first tube in a longitudinal band opposite the wall of the second Tube and flows in a longitudinal band opposite the wall of the third tube second single phase alternating current from the second endpoint through the wall of the second tube in a longitudinal band opposite the wall of the first tube and in a longitudinal band opposite the wall of the third tube flows a third single-phase alternating current from the third End point through the wall of the third pipe in a longitudinal band opposite the wall of the first tube and flows in a longitudinal band opposite the wall of the second tube and each of these three currents through the star connection at the rear ends of the through three pipes and finally back to the other two entry points the walls of the other two tubes flow in longitudinal bands, with skin effect currents and at least some of the heat generated in each tube is transmitted directly to the medium. 13. Device according to claim 12, characterized in that each Tube has a wall thickness of at least twice the thickness of the skin through which the Alternating current flows for warming up. 14. Device according to claim 12, characterized in that the Cross-section of each of the three tubes is the same and their centers are equidistant from each other lie. 15. Device according to claim 2, characterized in that the conductor is laid on a three-dimensional curved line on the pipe wall. 16. Device according to claim 1, characterized in that the electrical The conductor is laid on a helical line on the pipe. i aa 17. Device according to claim 1, characterized by means for changing the assignment (the distance) of the electrical conductor to the body over at least a portion of the common length for enlargement the resistance in the skin-effect conductor and to nosselung the flow of alternating current or heat generation. 18. Device according to claim 1, characterized by insulation on at least one side of the electrical conductor between the body and the electrical conductors to shield the body from the electromagnetic field, which is generated as a result of the flow of alternating current.