DEVICE AND METHOD FOR HEATING A FLUID IN A PIPELINE USING THREE-PHASE CURRENT

Abstract

A device for heating a fluid, including at least one electrically conductive pipeline for accommodating the fluid, and at least one voltage source connected to a respective pipeline. The voltage source is designed to generate an electric current in the connected pipeline which heats the pipeline in order to heat the fluid. Each voltage source has M outer conductors, where M is a natural number greater than or equal to two. Each voltage source is designed to provide an AC voltage at the outer conductors, wherein those AC voltages are phase-shifted through 2/M with respect to one another, and wherein the outer conductors are electrically conductively connected to the pipeline such that a star circuit is formed.

Claims

1. Device for heating a fluid, comprising a plurality of electrically conductive pipelines for accommodating the fluid, and a plurality of voltage sources wherein one voltage source assigned to each pipeline, said voltage source being connected to the respective pipeline, wherein the respective voltage source is designed to generate an electric current in the respective pipeline which heats the respective pipeline in order to heat the fluid, wherein the respective voltage source has at least M outer conductors, where M is a natural number of greater than or equal to two, and wherein the respective voltage source is designed to provide an AC voltage at its outer conductors, wherein various AC voltages are phase-shifted with respect to one another through 2/M, and wherein the outer conductors of the respective voltage source are electrically conductively connected to the respective pipeline in such a way that a star circuit is formed, in which each outer conductor is electrically conductively connected to a neutral point of the star circuit over at least part of the respective pipeline.

2. Device according to claim 1, characterized in that the voltage sources each have a neutral conductor, wherein the respective neutral conductor is electrically conductively connected to the neutral point.

3. Device according to claim 1, characterized in that M is equal to three.

4. Device according to claim 1, characterized in that pipelines have M limbs, wherein each limb has a first and a second end section and a central section, which fluidically and electrically conductively connects the two end sections to one another.

5. Device according to claim 4, characterized in that the two end sections of the respective limb are electrically conductively connected to the neutral point.

6. Device according to claim 4, characterized in that the central connections of the limbs ( are each electrically conductively connected to the assigned outer conductor of the respective voltage source.

7. Device according to claim 4, characterized in that the second end section of a first limb is fluidically and electrically conductively connected to the first end section of a the second limb or is integrally formed on said first end section, and in that the second end section of the second limb is fluidically and electrically conductively connected to the first end section of a third limb or is integrally formed on said first end section, wherein the first end section of the first limb forms an inlet for feeding the fluid into the respective pipeline, and wherein the second end section of the third limb forms an outlet for allowing the fluid to pass out of the respective pipeline.

8. Device according to claim 4, characterized in that the limbs are not fluidically connected to one another and are designed to each conduct a fluid to be heated separately from one another.

9. Device according to claim 4, characterized in that the limbs are each in the form of a loop, wherein a central section of the respective limb forms an end of the respective loop, wherein in the region of the respective end, the respectively assigned outer conductor is electrically conductively connected to the respective limb.

10. Device according to claim 4, characterized in that the limbs each extend along a longitudinal axis, wherein the limbs have the same length along the respective longitudinal axis.

11. Device according to claim 4, characterized in that the end sections of the limbs of the respective pipeline are arranged in a central region, from which the limbs extend outwards along a radial direction.

12. Device according to claim 10, characterized in that the longitudinal axes of in each ease two adjacent limbs enclose an angle of 120.

13. Device according to claim 1, characterized in that a plurality of or all of the pipelines are fluidically connected in series with one another, such that the fluid can flow through said pipelines successively.

14. Device according to claim 1, characterized in that a plurality of or all of the pipelines are configured to be parallel, such that the fluid can be divided among the parallel pipelines.

15. Method for heating a fluid using a device comprising a plurality of electrically conductive pipelines for accommodating the fluid and a plurality of voltage sources, wherein one voltage source is assigned to each pipeline, said voltage source being connected to the respective pipeline, wherein the respective voltage source is designed to generate an electric current in the respective pipeline which heats the respective pipeline in order to heat the fluid, and wherein the respective voltage source has at least M outer conductors, where M is a natural number of greater than or equal to two, and wherein the respective voltage source is designed to provide an AC voltage at its outer conductors, wherein various AC voltages are phase-shifted with respect to one another through 2/M, and wherein the outer conductors of the respective voltage source are electrically conductively connected to the respective pipeline in such a way that a star circuit is formed in which each outer conductor is electrically conductively connected to a neutral point of the star circuit over at least part of the respective pipeline, the method, wherein the fluid flows through the pipelines of the device and is heated in said pipelines by virtue of the pipelines being heated by a polyphase alternating current flowing in the pipelines, such that Joulean heat is generated in the pipelines, and is transferred to the fluid to heat said fluid as it flows through the pipelines.

16. Method according to claim 15, characterized in that a hydrocarbon to be cracked thermally, or a mixture of hydrocarbons, is heated as fluid.

17. Method according to claim 16, characterized in that water or steam is heated as fluid, wherein steam is heated to a reactor inlet temperature of 550 C. to 700 C., and is added to the hydrocarbon to be cracked.

18. Method according to claim 15, characterized in that a preheated mixture of hydrocarbons and steam is heated as fluid in order to crack the hydrocarbons.

19. Method according to claim 15, characterized in that combustion air from a reformer furnace is preheated as to a temperature of 200 C. to 800 C.

20. Method according to claim 15, characterized in that the pipelines are reaction tubes of a reformer.

21. Method according to claim 19, characterized in that the temperature is 400 C. to 700 C.

Description

[0071] Further features and advantages of the present invention will be explained in the description of exemplary embodiments with reference to the figures, in which:

[0072] FIG. 1 shows a schematic illustration of a pipeline of a device according to the invention;

[0073] FIG. 2 shows a further development of the embodiment shown in FIG. 1;

[0074] FIG. 3 shows a further schematic illustration of a pipeline of a device according to the invention;

[0075] FIG. 4 shows an illustration of an arrangement of a plurality of pipelines of a device according to the invention;

[0076] FIG. 5 shows a schematic illustration of the interconnection of the outer conductors and the neutral conductor in the case of a TN network; and

[0077] FIG. 6 shows a schematic illustration of the interconnection of the outer conductors in the case of an IT network.

[0078] First, for reasons of simplicity, embodiments of the invention are illustrated below with reference to a pipeline 100. The measures illustrated using a pipeline can in this case naturally in each case be applied to a plurality of pipelines 100.

[0079] As shown in FIG. 1, in the case of direct heating with three-phase current of a pipeline 100 in a device 1 according to the invention for heating a fluid F, a neutral point S can be provided. In this case, the three phases L1, L2 and L3 of a three-phase system or of a three-phase voltage source 2 (cf. FIG. 5) are connected to the limbs 101, 102, 103 of the pipeline 100 and preferably the N conductor (neutral conductor), if provided, is connected to the neutral point S. In the case of solid or low-resistance grounding of the N connection or the neutral point S of the voltage source 2 to ground (PE), as is conventional in power supply, and in the case of a connection of the neutral conductor N to the neutral point S of the pipeline 100, it is possible to dispense with grounding of the neutral point S at the pipeline 100.

[0080] As shown in FIGS. 5 and 6, the invention can be applied both as part of a network comprising (preferably three) outer conductors and a neutral conductor (for example TN network) and for a network without a neutral conductor (for example IT network).

[0081] FIG. 5 shows the three outer conductors L1, L2, L3 and the neutral conductor N of the voltage source 2, as are provided, for example, in a TN network. The neutral point S of the voltage source 2, to which the neutral conductor N is electrically conductively connected, is in this case grounded via a resistor R.sub.N, wherein in particular R.sub.N=0 may hold true (solid grounding) or low-resistance, for example. Z.sub.1, Z.sub.2, Z.sub.3 represent the loads or impedances which are formed by the at least one pipeline 100 or the limbs 101, 102, 103 thereof The latter are interconnected at the neutral point S of the load or pipeline 100, wherein the neutral conductor N is electrically conductively connected to the neutral point S. In the case of solid operational grounding of the neutral point S of the voltage source 2 (R.sub.N=0), grounding of the neutral point S can be dispensed with, but is preferably provided.

[0082] FIG. 6 shows a three-conductor network (for example IT network), in which there is no neutral conductor N. In this case, the neutral point S, which is formed by the interconnection of the impedances Z.sub.1, Z.sub.2, Z.sub.3, is preferably solidly grounded.

[0083] Without any restriction to generality, three outer conductors L1, L2, L3 and a neutral conductor N are assumed below. However, it is possible to dispense with the neutral conductor N (see above) or to vary the number of outer conductors (see above).

[0084] Specifically, a first limb 101 of the pipeline 100, starting from a first end section 101a or from the inlet 3, via which fluid F is fed into the pipeline 100, extends along a longitudinal axis A to a return bend of a central section 101b of the first limb 101, from where the central section 101b of the first limb 101 extends back to a second end section 101c, which is arranged adjacent to the first end section 101a in a central region B. The second end section 101c of the first limb 101 becomes a first end section 102a of the second limb 102, which, in a similar manner, extends over a return bend of its central region 102b to a second end section 102c of the second limb 102, which in turn becomes a first end section 103a of the third limb 103, which, in a similar manner, extends over a return bend of its central section 103b to a second end section 103c, at which an outlet 4 for allowing the (heated) fluids F to pass out of the pipeline 100 is provided. The three longitudinal axes A of the loop-shaped limbs 101, 102, 103 are preferably arranged in the form of a star, as shown in FIG. 1, i.e. in each case two adjacent limbs 101, 102; 102, 103; 103, 101 enclose an angle of 120.

[0085] In this case, a contact K to an outer conductor LI, L2 or L3 of a three-phase current source 2 is provided at each return bend of a central section 101b, 102b, 103b of a loop 101, 102, 103, respectively, wherein the end sections 101a, 101c, 102a, 102c, 103a, 103c are connected to the neutral point S via contacts Q. In this case, preferably end sections 101c, 102a; 102c, 103a of the limbs 101, 102, 103 which are connected to one another are connected to the neutral point S or to the neutral conductor N via a contact Q at the transition between the respective end sections.

[0086] The arrangement shown in FIG. 1 can naturally also be used in the case of generally M phases, where M is a natural number greater than or equal to two. Then, correspondingly M limbs are provided and interconnected as described above.

[0087] Furthermore, as shown in FIG. 2, the limbs 101, 102, 103 can be formed separately from one another in the arrangement shown in FIG. 1, with the result that individual fluid flows F, F, F can flow through said limbs independently of one another. The first end sections 101a, 102a, 103a can in this case be in the form of inlets for the fluid flows F, F and the second end sections 101c, 102c, 103c can be in the form of outlets for the fluid flows, wherein those end sections 101a, 102a, 103a and 101c, 102c, 103c are in turn connected to the neutral point S.

[0088] FIG. 3 shows a variation of the profile of the limbs 101, 102, 103, wherein said limbs now run next to one another, in contrast to FIG. 1.

[0089] This configuration in principle enables an arrangement of a plurality of pipelines 100 of the type shown in FIG. 3 next to one another, as is shown in FIG. 4, wherein in this case the individual limbs 101, 102, 103 each run outwards in the radial direction R starting from a central region B, in which the individual end sections are arranged, and are connected to the neutral point S there. The return bends of the individual loop-shaped limbs 101, 102, 103 are now further outwards in the radial direction R on an imaginary circle and are in each case connected to one phase L1, L2 or L3 of a three-phase current source 2.

[0090] Each pipeline 100 is in this case assigned to a three-phase current source 2, which is preferably arranged above the limbs and is arranged radially further inwards than the return bends. As a result, the feed lines to S (or N) and L1, L2, L3 can be minimized. The pipelines 100 have in each case three loop-shaped limbs 101, 102, 103, whose return bends are each connected to one of the outer conductor phases L1, L2 or L3 of the assigned voltage source 2.

[0091] For reasons of clarity, only one pipeline 100 is denoted in FIG. 4. The pipeline sections 100 shown in FIG. 4 can, as illustrated, be arranged in series such that the fluid F can flow through said sections successively. However, it is also possible for a divider to be provided in the central region B, which divides the fluid F among the individual pipelines 100, each comprising the three limbs 101, 102, 103, so that the fluid F flows through said limbs parallel to one another. Thereafter, the (heated) fluid F can be combined again and supplied for further use thereof.

[0092] In the examples described above, the three-phase current in the limbs 101, 102, 103 generates Joulean heat in each case owing to the electrical resistance of the limbs 101, 102, 103, which Joulean heat is transferred to the fluid F flowing in the limbs 101, 102, 103, wherein said limbs are heated.

[0093] Naturally, the arrangement shown in FIGS. 3 and 4 can likewise be generalized for M phases (M is greater than or equal to two).

[0094] The configuration of a three-phase direct heating shown in FIGS. 1 to 4 or the star-shaped arrangement of the individual limbs 101, 102, 103 shown therein is not absolutely necessary, however. In general, any geometric arrangement of pipelines 100 or limbs 101, 102, 103 is conceivable. The method according to the invention or the device 1 according to the invention can be applied in principle for all pressures, temperatures, dimensions, etc.

[0095] In the technical implementation, stainless steels are preferred over carbon steels for the pipelines 100 owing to the higher resistivity. Furthermore, the feed line of the polyphase or three-phase alternating current is preferably embodied with a markedly lower resistance than the pipeline conducting the fluid F in order to minimize the generation of heat of the feed line since this is generally undesirable.

[0096] The solution according to the invention can advantageously be applied, in particular when heating media which cause a reduction of dielectric strength (for example coking in the case of cracking furnaces). There is a comparatively low risk in this case of an undesired current flow, with the result that it is even possible to dispense with a switch-off device as mentioned at the outset.

[0097] Furthermore, there is the possibility of controlling the heating in the in each case three limbs 101, 102, 103 by virtue of the current flow of the respective phases L1, L2, L3 being set correspondingly (this also applies in the case of M phases, where M is greater than or equal to two).

[0098] In principle, the heating according to the invention of a fluid can be used for all media in electrically conductive pipelines. In the case of liquids which are very good conductors (in comparison with the electrical conductivity of the pipeline), this fact needs to he incorporated in the calculation of the current flow, if appropriate. The geometric profile of the pipelines or pipeline sections is advantageously flexible and can be matched to the respective requirements, Furthermore, the pipeline material can be matched to the process requirements. Currents, voltages and the frequency can be selected appropriately for the geometry and are not subject to any basic limitation. The maximum achievable temperature is limited by the pipeline material used.

List of Reference Symbols

[0099] 1 Device [0100] 2 Three-phase current source [0101] 3 Inlet [0102] 4 Outlet [0103] 100 Pipeline [0104] 101, 102, 103 Limb [0105] 101a, 102a, 103a First end section [0106] 101b, 102b, 103b Central section [0107] 101c, 102c, 103c Second end section [0108] L1, L2, L3 Outer conductor [0109] B Central region [0110] N Neutral conductor [0111] K, Q Electrical contacts [0112] F, F, F Fluid [0113] A Longitudinal axis [0114] R Radial direction [0115] S Neutral point [0116] S Neutral point of voltage source