Reactor for carrying out a chemical reaction in a process fluid and method

Abstract

The invention relates to a reactor for carrying out a chemical reaction, which proceeds at least partially at a temperature of at least 500°C, in a process fluid using multiphase alternating current, comprising a reactor chamber, which is surrounded by thermally insulating reactor walls, and multiple substantially straight reaction tubes; wherein the reaction tubes run through the reactor chamber between at least one tube inlet opening and at least one tube outlet opening in mutually opposing reactor walls and consist of a material which allows electrical resistance heating; wherein two electrically conductive bridges, which are spaced from each other along the reaction tubes, are provided in the reactor chamber and connect the reaction tubes electrically conductively to each other; wherein electrically conductive current feed-in assemblies are provided, which extend through one or more feedin openings in one of the reactor walls, wherein each reaction tube is connected in an electrically conductive manner to one of the current feed-in assemblies, wherein each current feed-in assembly is connected electrically conductively to one of the reaction tubes between the bridges and is or can be connected to one of the phases of the alternating current.

Description

[0001] Description

[0002] Reactor for carrying out a chemical reaction in a process fluid and

[0003] Proceedings

[0004] The invention relates to a reactor for carrying out a chemical reaction in a process fluid using multiphase alternating current to heat the process fluid.

[0005] State of the art

[0006] A number of processes in the chemical industry utilize reactors in which one or more reactants are passed through heated reaction tubes and converted there, either catalytically or non-catalytically. The heating serves primarily to overcome the activation energy required for the chemical reaction to proceed. The reaction can be endothermic overall or, once the activation energy has been overcome, exothermic. The present invention particularly relates to strongly endothermic reactions.

[0007] Examples of such processes include steam cracking, various reforming processes, in particular steam reforming, dry reforming (carbon dioxide reforming), mixed reforming processes, alkane dehydrogenation processes, and the like. In steam cracking, the reaction tubes are guided through the reactor in the form of coils, which have at least one return bend in the reactor. In contrast, steam reforming typically uses tubes that run through the reactor without a return bend.

[0008] The invention is suitable for all such processes and reaction tube designs. For purely illustrative purposes, reference is made to the articles "Ethylene," "Gas Production," and "Propene" in Ullmann's Encyclopedia of Industrial Chemistry, for example, the publications of April 15, 2009, DOI: 10.1002 / 14356007.a10_045.pub2, December 15, 2006, DOI: 10.1002 / 14356007.a12_169.pub2, and June 15, 2000, DOI:

[0009] 10.1002 / 14356007. a22_211 . The reaction tubes of such reactors are conventionally heated using burners. The reaction tubes are guided through a combustion chamber in which the burners are also located.

[0010] Currently, there is increasing demand for synthesis gas and hydrogen produced with no or reduced local carbon dioxide emissions. However, this demand cannot be met, or can only be met to a limited extent, by processes that use fired reactors due to the rising cost of typically fossil fuels. Other processes are ruled out, for example, due to high costs. The same applies to the production of olefins and / or other hydrocarbons through steam cracking or the dehydrogenation of alkanes. Even in such cases, there is a desire for processes that, at least locally, emit lower amounts of carbon dioxide.

[0011] EP 3075704 A1 discloses a steam reforming furnace with reaction tubes guided through a combustion chamber. In addition to at least one burner, the reaction tubes are electrically heated by alternating current, with a collector located outside the combustion chamber serving as the star point. US 9347596 B2 relates to a device for electrically heating a pipeline system.

[0012] WO 2015 / 197181 A1 discloses a reactor in which a fluid flowing through a pipeline is heated. The electrically conductive pipeline is connected to multiple phases of an alternating current source, forming a star-point connection and generating heat according to the electrical resistance of the pipeline. The arrangement shown therein is particularly suitable for so-called multi-pass pipe geometries, i.e., the pipelines run back and forth in a serpentine line.

[0013] However, for single-pass pipe geometries, where the pipes to be heated run straight through the reactor, boundary conditions, particularly of an electrical and thermal nature, cannot be met with this known or similar arrangements. The object is therefore to provide an electrically heatable reactor that can meet electrical, thermal, and mechanical boundary conditions. This object is achieved by a reactor for carrying out a chemical reaction and a method having the features of the independent claims.

[0014] According to the invention, the power is fed into the reaction tubes to be heated between the electrically conductive bridges, i.e., bridges are arranged on both sides of the power feed, which electrically connect the reaction tubes. The electrically conductive bridges equalize the potential between the phases, so that electrical current flows from the reaction tubes via further process lines to other parts of a process plant in which the reactor is installed, which could lead to damage or hazards, are prevented or greatly suppressed. By arranging the bridges on both sides, this occurs on both the inlet and outlet sides. For single-fit tube geometries, this is advantageous compared to an arrangement with just a single bridge, since this would otherwise require complex electrical insulation of the reaction tubes from further process lines on one side.

[0015] At the same time, the arrangement according to the invention spatially spaced the power feed arrangements from the tube inlet and outlet openings, so that cooling elements can be mounted on the power feed arrangements, which must conduct high currents due to their application, without creating space conflicts with downstream process lines. In particular, hot reaction tubes or connected downstream process lines cannot negatively impact the cooling performance of such cooling elements. Regarding the mechanical design, there are also no space conflicts between the power feed arrangements, which comprise solid current-carrying elements due to the high currents involved, and downstream process lines.

[0016] Specifically, a reactor is provided for conducting a chemical reaction in a process fluid using multiphase alternating current. The reactor comprises a reactor chamber surrounded by thermally insulating reactor walls and a plurality of essentially straight reaction tubes. The alternating current serves to electrically heat the reaction tubes and thus the process fluid flowing through the reaction tubes, providing energy for the chemical reaction. The fact that the reaction tubes and thus the process fluid are heated using alternating current should not preclude the possibility of additional heating, for example by increasing the cost of chemical energy sources. The chemical reaction is a chemical reaction that takes place at least partially at at least 500 °C.

[0017] The reaction tubes extend through the reactor chamber between at least one tube inlet and at least one tube outlet in opposing reactor walls and are made of a material that allows electrical resistance heating. The fact that the reaction tubes or their material are electrically heatable means that the material used for the reaction tubes, and in particular the sections between the bridges, is a material with electrical conductivity that is suitable for electrical heating. Examples are heat-resistant steel alloys, in particular heat-resistant chromium-nickel steel alloys. Such steel alloys can also be used for the bridges and the power supply arrangements, in particular their current-carrying elements.For example, materials with the standard designations GX40CrNiSi25-20, GX40NiCrSiNb35-25, GX45NiCrSiNbTi35-25, GX35CrNiSiNb24-24, GX45NiCrSi35-25, GX43NiCrWSi35-25-4, GX10NiCrNb32-20, GX50CrNiSi30-30, G-NiCr28W, G-NiCrCoW, GX45NiCrSiNb45-35, GX13NiCrNb45-35, GX13NiCrNb37-25, or GX55NiCrWZr33-30-04 according to DIN EN 10027, Part 1, "Materials", can be used. In particular, the material No. 1.4852 or No. 1.4852 Micro (GX40NiCrSiNb35-26) is suitable.

[0018] In the reactor chamber, two electrically conductive bridges are provided, spaced apart along the reaction tubes, which electrically connect the reaction tubes to each other. Electrically conductive power feed arrangements are provided, which extend through one or more feed openings (or power feed openings) in one of the reactor walls. Each power feed arrangement is electrically connected to one of the reaction tubes between the bridges and is connected or connectable to one of the phases of the alternating current. The electrically conductive connections (power feed point or contact point) of the power feed arrangements to the reaction tubes, as well as the bridges, are thus located within the reactor chamber. Each reaction tube is electrically connected to one of the power feed arrangements.The term "essentially straight" refers, on the one hand, to the fact that inlet and outlet headers may be provided in the reactor chamber between a bridge and the nearest reactor wall containing a tube inlet or outlet opening, respectively, connecting multiple reaction tubes into a single header. On the other hand, slight deviations from a straight line may occur between the bridges, i.e., each reaction tube should run within a circular cylinder with 10 times the diameter of the reaction tube between the bridges.

[0019] The reactor walls enclose or surround the reactor chamber, i.e. an area that is bounded in all spatial directions by at least one reactor wall. The reactor chamber is typically inerted. Generally, several individual walls are used for this purpose, which are joined together to enclose the reactor chamber; it could therefore also be referred to as a group of reactor walls. The enclosed area, and thus also the group of reactor walls, can have any volumetric shape, but preferably that of a quadrangular prism or a cylinder. The reactor walls can have sealed structural elements (such as feedthroughs or viewing windows), but also permanently open and / or closable openings as connections to other parts of the system, preferably for conditioning the atmosphere within the reactor wall, e.g. inlet nozzles for inert gas or outlet openings to a chimney tract.

[0020] Preferably, an electrical resistance of each of the bridges between two reaction tubes (i.e., the electrical resistance between two reaction tubes measured across the respective bridge) is smaller than an electrical reference resistance; wherein the reference resistance is equal to the electrical resistance (in the longitudinal direction of the reaction tubes) of one of the reaction tubes over a reference length; wherein the reference length is selected from: a distance between the two reaction tubes; a length of a reaction tube connection between an inlet or outlet header and a bridge connection at the inlet or outlet of the tube (i.e., the length of the reaction tube connection corresponds to the distance between the bridge and the inlet or outlet header). It is also conceivable to select a dimension of the bridge in the longitudinal direction (of the reaction tubes) as the reference length. Combinations of these selection options for the reference length are also possible, e.g.,by averaging or summation. More preferably, the ratio of the electrical resistance of the bridge (between the two reaction tubes) to the reference resistance is a maximum of 1 / 10, even more preferably a maximum of 1 / 50, most preferably a maximum of 1 / 100. In particular, this results in the electrical resistance of the bridges being lower than the electrical resistance of further process lines or of inlet and outlet headers, which, due to the relatively high temperatures still prevailing there, are typically made of the same or a similar material (in particular steel) as the reaction tubes and accordingly have comparable electrical conductivities. The effect of this is that the potential equalization and the resulting currents between the phases largely take place or flow via the bridges, and only small or no currents flow into further process lines outside the reactor.The reference resistance corresponds to the electrical resistance of a section (reference section) of a reaction tube with a length equal to the reference length. Since the multiple reaction tubes typically have the same dimensions (inner and outer diameter) and are made of the same material, the reference resistance is independent of which reaction tube is used to determine the reference resistance. The reference resistance can be easily calculated and / or measured.

[0021] The bridges are preferably made of the same material as the reaction tubes. This allows the reaction tubes to be connected to one another via the bridges in a heat-resistant manner, particularly by welding. Alternatively, the bridges are made of a material with higher electrical conductivity than the reaction tubes. Likewise, a cross-sectional area of ​​the bridges located between two reaction tubes, running parallel to the reaction tubes and perpendicular to the plane formed by the two reaction tubes, is preferably larger than a cross-sectional area of ​​a reaction tube wall perpendicular to the longitudinal axis of the tubes. These designs enable a low electrical resistance of the bridges relative to the reaction tubes.

[0022] Preferably, the reaction tubes are cast into at least one of the bridges and / or for at least one of the bridges, for each reaction tube, a reaction tube section is formed integrally (in one piece) with the bridge or an element of the bridge, wherein further reaction tube sections are more preferably connected to the bridge by welding.

[0023] Furthermore, at least one bridge preferably comprises first bridge elements, each of which is electrically conductively connected to one of the reaction tubes, and a second bridge element that electrically connects the first bridge elements, wherein the second bridge element consists of a material that has a higher electrical conductivity than a material from which the first bridge elements consist; wherein the first bridge elements preferably consist of the same material as the reaction tubes.

[0024] This design allows for a reduction in the electrical resistance of the bridges while maintaining the same geometric dimensions, thus improving the potential equalization between the reaction tubes. The material of the first bridge elements can be selected so that they can be connected to the reaction tubes in a simple and heat-resistant manner, for example, by welding. Therefore, the material of the reaction tubes is preferably used for the first bridge elements as well.

[0025] The second bridge element preferably has passages through which the reaction tubes extend and into which the first bridge elements are inserted in the form of a fit, in particular a press fit; wherein more preferably the material of the second bridge element has a lower coefficient of thermal expansion than the material of the first bridge elements. In particular, the material of the second bridge element can comprise molybdenum, tungsten, tantalum, niobium and / or chromium or consist largely of one of these materials or a combination thereof. Even more preferably, the second bridge element consists largely or entirely of molybdenum and / or the first bridge elements consist of the material of the reaction tubes.

[0026] In this embodiment, the second bridge element(s) consist at least partially of a material rich in molybdenum, tungsten, tantalum, niobium, and / or chromium, or is formed therefrom. In particular, the material has a higher specific electrical conductivity than the material from which the first bridge elements are formed.

[0027] By connecting the first bridge elements to the second bridge element by means of a press fit, a connection is created that is, in principle, detachable, which facilitates, for example, the replacement of reaction tubes. The different thermal expansion coefficients mean that the press fit occurs with increasing pressure as the temperature increases, thus improving the contact, particularly the electrical contact, between the first and second bridge elements. Molybdenum, for example, has a higher conductivity than steels, which are preferably used for the first bridge elements and the reaction tubes, and can also be used at the high temperatures prevailing in the reactor vessel.

[0028] The bridges are preferably designed as rigid components or assemblies, with at least one, and even more preferably each, of the bridges being designed as a single piece, in particular as a cast part. The rigid design provides additional relative fixation of the reaction tubes.

[0029] The one or more feed openings (for electrical connections) are preferably located in a reactor wall that runs between the reactor walls in which the at least one tube inlet opening and the at least one tube outlet opening are located; more preferably, the one or more feed openings have an elongated shape parallel to the longitudinal direction of the reaction tubes. The power feed arrangement can thus move with thermal expansion of the reaction tubes. The reactor wall in which the one or more feed openings are located is therefore a lateral reactor wall, i.e. a reactor wall that extends in the direction of the reaction tubes (e.g. parallel to them or at an angle, approximately < 20°, to them).

[0030] Cooling panels are preferably provided outside the reactor chamber, which are arranged adjacent to current-carrying elements of the power feed arrangements; the cooling panels preferably extend parallel to the longitudinal direction of the reaction tubes. The cooling panels are further preferably housed in an (inerted) connection chamber arranged on an outer side of the reactor wall in which the feed openings are located.

[0031] Preferably, the one or more feed openings are spatially separated from the at least one pipe inlet opening and from the at least one pipe outlet opening.

[0032] According to a preferred embodiment, the reactor comprises an alternating current source or alternating voltage supply that provides the alternating current or an alternating voltage. In particular, a neutral conductor can be provided for at least one, preferably for all, bridges, which connects the bridge to a star point of the alternating current source; further preferably, an electrical resistance of the bridges between two reaction tubes is smaller than the electrical resistance of the neutral conductor connected to the respective bridge; further preferably, a ratio of these resistances is a maximum of 1 / 5, more preferably a maximum of 1 / 20, most preferably a maximum of 1 / 50.

[0033] Preferably, the electrical resistance of the neutral conductor (between the bridge and the star point of the AC source) is smaller than the electrical reference resistance. This refers to the reference resistance introduced above in connection with the electrical resistance of the bridges. If different reference resistances are defined based on different reference lengths, one can be selected or an average of the reference resistances can be used.

[0034] Preferably, a phase shift between each two different phases of the alternating current, expressed as a radian, is 2TT k / M, where k is an integer in the range from 1 to M-1.

[0035] Preferably, all feedthroughs through the reactor walls, i.e. in particular the pipe inlets, pipe outlets and the (power) feedthroughs, are made gas-tight by means of suitable devices, such as a sealing bellows. Such a gas-sealing device is designed to be electrically insulating so that there is no electrical contact between the component being passed through and the respective reactor wall. If cooling panels are arranged in a connection chamber, a gas-tight design of the feedthroughs is not necessary. The connection chamber should then be gas-tight with respect to the environment. This design is useful, for example, when sealing elongated feedthroughs (to accommodate longitudinal movement due to thermal expansion of the reaction tubes) is difficult. The pipe inlets and outlets should be designed to be gas-tight.

[0036] Preferably, the ratio of the two distances of a power feed arrangement to the two bridges is in the range from 0.25 to 1. More preferably, the ratio of the two distances is in the range from 0.25 to 0.8, preferably in the range from 0.25 to 0.7. The contact point, i.e., the point at which the power feed arrangement is connected to the reaction tube, can thus be arranged asymmetrically with respect to the bridges. In other words, the contact point in such an embodiment divides the section of the reaction tube located between the two bridges into two tube sections of different lengths. This enables a different heat input into the two tube sections and thus improved process control.

[0037] The chemical reaction can be a chemical reaction that takes place at least partially at a temperature in the range from 200°C to 1700°C, in particular from 300°C to 1400°C or from 400°C to 1100°C. The chemical reaction is preferably a chemical reaction that takes place at least partially at a temperature of at least 500°C, more preferably of at least 700°C, in particular at least partially in a temperature range from 500°C or 700°C to 1100°C. The electrical voltages / currents provided are suitable for providing corresponding heating outputs. The reactor and the power source are likewise configured to carry out chemical reactions at these temperatures and provide corresponding heating outputs.Preferably, the chemical reaction is one of the following: steam cracking, steam reforming, dry reforming (dry reforming, carbon dioxide reforming), propane dehydrogenation, and generally reactions with hydrocarbons which are carried out at least partially at more than 500°C.According to the invention, a method for carrying out a chemical reaction in a process fluid, which reaction takes place at least partially at a temperature of at least 500°C, is proposed, wherein a reactor according to one of the preceding claims is used, wherein the process fluid is passed through the reaction tubes of the reactor and is heated by means of electrical resistance heating using multiphase alternating current; wherein the chemical reaction is preferably one of the following reactions: steam cracking, steam reforming, dry reforming, propane dehydrogenation, a reaction with hydrocarbons which is carried out at least partially at more than 500°C.

[0038] The present invention will initially be described below with reference to reaction tubes and reactors used for steam cracking or steam reforming. However, the invention can also be used in other reactor types. In general, as mentioned, the reactor proposed according to the invention can be used to carry out all endothermic chemical reactions.

[0039] The invention is further explained below with reference to the accompanying figures, which illustrate embodiments of the present invention.

[0040] Short description of the characters

[0041] Figure 1 shows a reactor connected to an alternating current source according to a preferred embodiment of the invention;

[0042] Figures 2A and 2B show cross-sections of one-piece bridges and their connection to reaction tubes according to preferred embodiments of the invention;

[0043] Figure 3 shows a cross-section of a multi-part bridge according to another preferred embodiment of the invention;

[0044] Figure 4 schematically shows a power feed arrangement according to an embodiment of the invention; and Figures 5A and 5B schematically show reactors in which cooling panels are provided for cooling the power feed arrangements according to a preferred embodiment.

[0045] Detailed character description

[0046] In the figures, structurally or functionally corresponding elements are illustrated with identical or similar reference symbols and, for the sake of clarity, are not explained repeatedly. In some cases, only one of the elements that appear multiple times is provided with a reference symbol.

[0047] Figure 1 shows a reactor 100 according to the invention according to a preferred embodiment. The reactor comprises reactor walls 12o, 12u, 12r, 12l that surround a reactor chamber 10; the reactor walls thus form a reactor vessel (or a reactor box), the interior of which represents the reactor chamber. Furthermore, the reactor comprises a plurality of reaction tubes 22 that run linearly through the reactor chamber 10, running between tube inlet openings 14 and tube outlet openings 15 formed in the lower reactor wall 12u and the upper reactor wall 12o, respectively. Furthermore, collecting lines referred to as inlet headers and outlet headers (not shown) can be provided, which fluidically connect the reaction tubes to one another on the inlet side and the outlet side, respectively. These inlet headers and outlet headers can be arranged outside the reactor chamber, i.e., on the side of the reactor walls facing away from the reactor chamber, or in the reactor chamber.In the latter case, they are each arranged between one of the bridges and the reactor wall closest along the reaction tubes.

[0048] Each of the reaction tubes 22 is electrically connected to a power feed arrangement 18, which extends through a feed opening 16 in a lateral reactor wall 12r. For this purpose, corresponding contact passages can be provided on the reaction tubes, which are electrically connected to rod-shaped elements 64, which are included in the power feed arrangements and serve as current-carrying (electrically conductive) elements. The rod-shaped elements 64 extend through the reactor wall. The power feed arrangements are in turn connected to the phases or phase terminals U, V, W, of a multi-phase alternating current source 50, so that one of the phases is fed into each reaction tube. Preferably, the alternating current source has 3 phases, as shown, and the number of reaction tubes is 3 or a multiple thereof, e.g.N-3, where N is an integer greater than or equal to 2, wherein each of the phases is connected to one of the reaction tubes via a respective power feed arrangement, or wherein, if the number of reaction tubes is a multiple N of 3, each phase is connected to N reaction tubes via respective power feed arrangements. Of course, a number other than 1 of phases and reaction tubes (or multiples thereof) other than 3 is also conceivable. The contact point of the connection of the power feed arrangements to the reaction tubes can be located asymmetrically with respect to the bridges for at least one power feed arrangement (for different power feed arrangements independently of one another), ie the tube section of the respective reaction tube located between the bridges can be asymmetrically divided (not shown).

[0049] In general, the number of phases is therefore M, where M is an integer greater than 1. The phase shifts between the phases are preferably chosen so that the voltages or currents cancel each other out at a star point, i.e. the phase shift between any two phases can be expressed in radians (unit rad) as 2 -k / M, or in degrees as 360°-k / M, where k is an integer in the range from 1 to M-1. For three phases, this is 2p / 3 or 4p / 3, corresponding to 120° or 240°. The phase difference between two consecutive phases is then obtained with k=1, i.e. as 2p / M. This choice is advantageous because, when the phases are loaded symmetrically, the alternating voltages of the different phases at the bridges cancel each other out.

[0050] The AC power source 50 is shown primarily for the purpose of understanding the invention and to illustrate how the multiphase AC power can be provided; it is not a necessary component of the invention. This power can be provided, for example, by a production facility in which the reactor is or will be installed.

[0051] A suitable alternating current source 50 can be designed as follows, e.g. as an alternating current transformer, in particular as a high-current transformer. The primary side, i.e. the alternating current supply to the alternating current source 50, comes, e.g. from a public supply network or a generator. A primary-side alternating voltage can typically be several hundred to several thousand volts, e.g. 400 V, 690 V or 1.2 kV. At least one further transformer (not shown) (possibly at least one regulating transformer which makes it possible to control the secondary-side alternating voltage or to set it within a certain voltage range) may be interposed between the primary side of the power source 50 and any public supply network or generator in order to obtain a suitable input voltage for the high-current transformer.Instead of or in addition to this at least one intermediate transformer, the input voltage or the resulting heating power can also be adjusted using one or more thyristor power controllers. The phase lines or phase terminals U, V, W are provided on the secondary side, to which the phases of the alternating current are supplied. The secondary side alternating voltage can conveniently be in the range up to 300 V, approximately less than 150 V or less than 100 V, and even less than or equal to 50 V is possible. The secondary side is galvanically isolated from the primary side.

[0052] In the reactor chamber 10, two electrically conductive bridges 30 are provided, which are electrically conductively connected to the reaction tubes 22; each bridge is connected to all the reaction tubes here. The connection to the reaction tubes is made at points that are spaced apart from one another along the reaction tubes, i.e. along their longitudinal direction (i.e., the direction in which the process fluid can flow). In circuit terms, the bridges 30 form star points, and could therefore be referred to as star bridges. If a multiple N of the number of phases M of reaction tubes is present (i.e., NM), two spaced-apart electrically conductive bridges can be provided for each of these multiples, each connected to M reaction tubes, or only two spaced-apart bridges can be provided, each of which is then connected to all the reaction tubes. Combinations are also conceivable.

[0053] The power feed arrangements 18 or their current-carrying elements 64 are connected to the reaction tubes between the two bridges 30. Here, for example, approximately in the middle between the bridges. More generally, a distance ratio, i.e. the ratio of the two distances of a power feed arrangement 18 to the two bridges 30 (more precisely, the ratio of the smaller of these distances to the larger one), should be in the range from 0.25 (one distance four times as large as the other) to 1 (distances of equal size). Preferably, this ratio is in the range from 0.5 to 1, more preferably in the range from 0.8 to 1. According to another preferred embodiment, this ratio is in the range from 0.25 to 0.8, more preferably in the range from 0.25 to 0.7. This ratio can be different for different reaction tubes, but it is preferably the same for all reaction tubes.Different distances between the current feed arrangements and the bridges (distance ratios other than one) result in different current intensities and thus in different heat inputs into the two pipe sections between the current feed arrangement and the two bridges. This can be used to influence the chemical reaction.

[0054] The bridges 30 are advantageously designed such that their electrical resistance is small compared to that of the reaction tubes. This is to be understood in the sense that the electrical resistance measured across a bridge between two reaction tubes is smaller than the electrical resistance of a section or reference section of the reaction tubes with a specific length, wherein the electrical resistance is determined (calculated and / or measured) along the length. The electrical resistance of the reference section forms a reference resistance.Preferably, one of the following comparison sections is used: a comparison section having a length equal to the distance between the two reaction tubes; a comparison section having a length equal to a dimension of the bridge in the longitudinal direction of the reaction tubes; a comparison section having a length equal to a length of a reaction tube connection between an inlet or outlet header and a bridge connection at the inlet or outlet of the tube; or a comparison section having a length equal to a distance of the bridge to a reactor wall in which the tube inlet or outlet openings are located, wherein the bridge is located between this reactor wall and the connection points of the power feed arrangements to the reaction tubes.Preferably, the ratio between the electrical resistance measured across the bridge and the electrical resistance of the comparison section is a maximum of 1 / 10, more preferably a maximum of 1 / 50, and most preferably a maximum of 1 / 100. Furthermore, optional neutral conductors N are shown, which connect the bridges to a star point of the power source. The neutral conductors are advantageously designed such that their electrical resistance (between the bridge and the power source) is greater than the electrical resistance of the bridges between two reaction tubes and less than the electrical resistance of the above comparison section.

[0055] The bridges can, in principle, be components that have passages for the reaction tubes. Contact between the reaction tubes running through these passages and the bridges can then be achieved, for example, by means of a press fit. It is also possible to cast the reaction tubes into the bridges.

[0056] Alternatively, it is preferably provided that passages through the bridges themselves are sections of the reaction tubes; in other words, that sections of the reaction tubes are formed integrally with the bridges. The other reaction tube sections are then connected to these sections by welding. Corresponding embodiments are shown in Figures 2A, 2B, and 3.

[0057] Figures 2A and 2B show, in a cross-sectional view, one-piece bridges 30a, 30b and their connection to reaction tubes 22 according to preferred embodiments. In Figure 2A, the bridge 30a is formed by a plate through which passages 32 extend in the longitudinal direction. The side surfaces of the bridge or plate, which lie opposite one another in the longitudinal direction, are flat, thus forming planes without projections apart from the passages. The geometry and dimensions of the passages 32 correspond to or are identical to the geometry and dimensions of the inner side 34 of the reaction tubes 22. In the case of reaction tubes that are rotationally symmetrical about the longitudinal axis, the passages are therefore circular, with their diameter being equal to the inner diameter of the reaction tubes. The bridge is connected to the reaction tube sections located outside the bridge by welding, i.e. by weld seams 36, so that the passages 32 run flush with the inner sides 34.The passages 32 thus form sections of the reaction tubes.

[0058] The embodiment of Figure 2B is essentially similar to the embodiment of Figure 2A, with the difference that here, projections 33 are provided on the side surfaces of the bridge 30b. Their geometry and dimensions are identical to the geometry and dimensions of the wall of the reaction tubes 22 (more precisely, the reaction tube sections located outside the bridge). In rotationally symmetrical reaction tubes, the inner and outer diameters of the projections are therefore equal to the inner and outer diameters of the reaction tubes. These projections extend the passages beyond the side surfaces, so to speak. The reaction tube sections located outside the bridge are connected to the end faces of the projections by weld seams 36.

[0059] Figure 3 shows, in a cross-sectional view, a preferred, multi-part bridge 30c. This comprises, corresponding to the number of reaction tubes, a plurality of first bridge elements 38 and a second bridge element 40. Each of the first bridge elements 38 has a passage 42 in the longitudinal direction, the geometry and dimensions of which are identical to the geometry and dimensions of the inner side 44 of one of the reaction tubes 22. Reaction tube sections outside the bridge 32c are connected to the respective first bridge element 38 by welding (weld seams 46) such that the passage is aligned with them. The outer side 48 of the first bridge elements runs parallel to the longitudinal direction. A radial thickness of the first bridge elements, i.e. a distance between the passage and the outer side of the bridge elements, is preferably constant in the circumferential direction. Radial direction and circumferential direction are to be understood with reference to the longitudinal direction defined by the reaction tubes.Deviating from this, the outside can also have a different geometry.

[0060] The second bridge element 40, which here, by way of example, is essentially a plate, has stepped passages 49 running in the longitudinal direction, wherein one region (one step) of the passages is adapted in its geometry and dimensions to the outer side of the first bridge elements such that the first bridge elements can be inserted into these regions by means of a fit, in particular a press fit. Another region (another step) of the passages has a geometry and dimensions such that, on the one hand, the reaction tube section welded to the respective first bridge element fits through this region, and, on the other hand, the respective first bridge element does not fit through it. The second bridge element can therefore rest on the first bridge elements in the arrangement shown and is thus secured even if there is no press fit.

[0061] Preferably, the second bridge element is made of a different material from the material of the first bridge elements. Further preferably, the material of the second bridge element (e.g., molybdenum or a molybdenum alloy) has a higher electrical conductivity and a lower thermal expansion coefficient than the material of the first bridge elements (e.g., a high-temperature-resistant Cr-Ni steel).

[0062] The first bridge elements could also be designed analogously to Figure 2B (not shown), i.e., projections could be provided that extend the passages and whose geometry and dimensions are similar to the walls of the reaction tubes. The reaction tube sections outside the bridge are then welded to the end faces of the projections. It is also possible for the reaction tubes to be cast into the first bridge elements.

[0063] Instead of a plurality of first bridge elements, a single first bridge element can also be used, which spans the plurality of reaction tubes (and is connected to them) and is connected to a single second bridge element. Referring to Figure 3, the first bridge elements could be connected, for example, at their lower end to form a single first bridge element, so that this single first bridge element can still be fitted into the second bridge element as shown. This ensures that even in the cold state, with possibly reduced contact between the two (first and second) bridge elements, a minimum potential equalization can take place via the first bridge element, which is further improved with increasing temperature and improved contact with the second bridge element.

[0064] Figure 4 schematically shows a partial view of an exemplary power feed arrangement 18 connected to a reaction tube 22 extending through a reactor chamber 10. The power feed arrangement 18 comprises an electrically conductive rod-shaped element 64 extending through a feed opening 16 in a reactor wall 12 (for example, the reactor wall 12r of Figure 1). The feed opening 16 is preferably lined with an electrically insulating material 68.

[0065] The power feed arrangement 18 is electrically connected to the reaction tube 22 in a contact passage 62. This is preferably designed, as shown, as a thickened portion of the reaction tube, with the rod-shaped element 64 being integrally formed with the thickened portion, i.e., integrally connected to the reaction tube. During production, for example, the contact passage 62 and the rod-shaped element 64 can be manufactured as a single-piece cast part and then connected to the reaction tube by welding. As an alternative to the single-piece design, the power feed arrangement could also be connected to the reaction tube by means of a sleeve that runs around the reaction tube. The rod-shaped element 64 merges into a power feed pin 65, to which, for example, two busbars or stranded wires 66 are attached for connecting one of the phases (such as U, V, W in Figure 1) of a multi-phase alternating current source.

[0066] Furthermore, a bellows arrangement 70 can optionally be provided, which ensures a gas-tight seal of the reactor chamber 10 against the environment and at the same time a mobility (for example for thermal compensation movements) of the rod-shaped elements 64 relative to the reactor wall 12.

[0067] Figures 5A and 5B sketch preferred embodiments in which a cooling arrangement comprising cooling panels 81 is provided for cooling the power feed arrangements 18. The cooling arrangement is accommodated, for example, in a connection chamber 80 arranged outside the reactor chamber. In both cases, the arrangement of the reaction tubes 22 in the reactor chamber surrounded by the reactor wall 12 and their connection to the bridges 30 and the power feed arrangements 18 corresponds to that shown in Figure 1. The reaction tubes are each electrically conductively connected to the power feed arrangements 18 at contact passages 62 (for example, with rod-shaped elements enclosed therein, as in Figure 4) and extend through one of the reactor walls, i.e., through feed openings not shown in detail.

[0068] The cooling panels 81 housed in the connection chamber 80 are arranged such that they are adjacent to and parallel to current-carrying elements of the feed devices 18 (rod-shaped elements 64). In particular, the panels are each located between two current-carrying elements or rod-shaped elements 64. In this way, heat conducted out of the reactor by the feed devices and heat generated by electrical currents in the feed devices can be dissipated. A cooling fluid preferably flows through the cooling panels.

[0069] The two figures differ in that the feed openings are arranged in different reactor walls, and the feed devices 18 or the rod-shaped elements 64 extend through different reactor walls, respectively. In Figure 5A, this is the left reactor wall (in the figure). More generally, a reactor wall that extends parallel to the longitudinal direction defined by the reaction tubes; it could therefore just as easily be the right, front, or rear reactor wall. The connection chamber 80 is arranged on the left reactor wall outside the reactor space. The cooling panels 81 are arranged parallel to the longitudinal direction. A longitudinal movement of the feed devices 18 in the longitudinal direction relative to the cooling panels 81, which are normally not movable, is therefore possible. Such a longitudinal movement of the feed devices, which are typically rigidly connected to the reaction tubes, can result from the thermal expansion of the reaction tubes.The support or suspension of the feed devices is preferably designed to be flexible, allowing longitudinal movement. Each feed opening should preferably have an elongated shape, i.e., its longitudinal dimension should be larger than its transverse dimension, with both dimensions being understood to be parallel to the reactor wall. The left, right, front, and rear reactor walls can generally be considered the lateral reactor walls.

[0070] In Figure 5B, the feed devices, more precisely rod-shaped elements 64, are guided through the lower reactor wall; the upper reactor wall would also be possible. The rod-shaped elements 64 thus run parallel to the longitudinal direction. The feed devices 18 here comprise further electrically conductive rod-shaped elements 64', which are connected on the one hand to the rod-shaped elements 64 running through the reactor wall, and on the other hand to the reaction tubes 22. These further rod-shaped elements 64' run parallel to the lower reactor wall here, but could also run obliquely. Here, too, the feed devices 18 are preferably flexibly supported or suspended.

[0071] As can be seen from the embodiments of Figures 5A and 5B, the present invention makes it possible to arrange the feed openings away from the inlet and outlet openings, so that current-carrying elements of the current feed arrangements are not additionally heated by hot continuing process lines and effective cooling of the current feed arrangements is made possible.

Claims

Patent claims 1. Reactor (100) for carrying out a chemical reaction, at least partially at a temperature of at least 500 °C, in a process fluid using multiphase alternating current, comprising a reactor chamber (10) surrounded by thermally insulating reactor walls (12o, 12u, 12r, 121) and several substantially straight reaction tubes (22); wherein the reaction tubes extend through the reactor chamber in opposing reactor walls between at least one tube inlet opening (14) and at least one tube outlet opening (15) and are made of a material that allows electrical resistance heating; wherein two electrically conductive bridges (30) are provided in the reactor chamber spaced apart from each other along the reaction tubes, which electrically connect the reaction tubes to each other;wherein electrically conductive current feed arrangements (18) are provided which extend through one or more feed openings (16) in one of the reactor walls, wherein each reaction tube is electrically conductively connected to one of the current feed arrangements (18), wherein each current feed arrangement is electrically conductively connected between the bridges to one of the reaction tubes and is connected or connectable to one of the phases (U, V, W) of the alternating current.

2. Reactor according to claim 1, wherein an electrical resistance of each of the bridges between two reaction tubes is less than an electrical reference resistance; wherein the reference resistance is equal to the electrical resistance of one of the reaction tubes over a reference length; wherein the reference length is selected from: a distance between the two reaction tubes, and a length of a reaction tube connection between an inlet or outlet header and a bridge connection at the inlet or outlet. Pipe exit; wherein the ratio of the bridge resistance to the reference resistance is preferably a maximum of 1 / 10, more preferably a maximum of 1 / 50, most preferably a maximum of 1 / 100.

3. Reactor according to one of the preceding claims, wherein the bridges are made of the same material as the reaction tubes or of a material with higher of electrical conductivity than the reaction tubes; and / or wherein a cross-sectional area of ​​the bridges lying between two reaction tubes, running parallel to the reaction tubes and perpendicular to the plane formed by the two reaction tubes, is larger than a cross-sectional area of ​​a wall of the reaction tubes perpendicular to the longitudinal axis of the tubes.

4. Reactor according to one of the preceding claims, wherein the reaction tubes are cast into at least one of the bridges; and / or wherein, for at least one of the bridges, a reaction tube section is formed integrally with the bridge or an element of the bridge for each reaction tube; wherein further reaction tube sections are preferably connected to the bridge by welding.

5. Reactor according to one of the preceding claims, wherein at least one bridge (30c) comprises first bridge elements (38), each of which is electrically connected to one of the reaction tubes, and a second bridge element (40) which electrically connects the first bridge elements, wherein the second bridge element is made of a material having a higher electrical conductivity than a material of which the first bridge elements are made; wherein preferably the first bridge elements are made of the same material as the reaction tubes.

6. Reactor according to claim 5, wherein the second bridge element has stepped passages (49) through which the reaction tubes pass and into which the first bridge elements are inserted in the form of a fit, in particular an interference fit.

7. Reactor according to claim 6, wherein the material of the second bridge element has a lower coefficient of thermal expansion than the material of the first bridge elements, wherein preferably the second bridge element consists mostly or entirely of molybdenum, tungsten, tantalum, niobium and / or chromium and / or the first bridge elements consist of the material of the reaction tubes.

8. Reactor according to one of the preceding claims, wherein the bridges are designed as rigid components or assemblies, wherein preferably at least one, preferably each, of the bridges is designed in one piece, in particular as a casting.

9. Reactor according to one of the preceding claims, wherein the one or more feed openings are located in a reactor wall which runs between the reactor walls in which the at least one pipe inlet opening or the at least one pipe outlet opening is located.

10. Reactor according to claim 9, wherein the one or more feed openings have an elongated shape parallel to the longitudinal direction of the reaction tubes.

11. Reactor according to one of the preceding claims, wherein cooling panels are provided outside the reactor space, which are arranged adjacent to current-carrying elements of the power supply arrangements; wherein the cooling panels preferably extend parallel to the longitudinal direction of the reaction tubes.

12. Reactor according to one of the preceding claims, wherein the one or more feed openings are spatially separated from the at least one pipe inlet opening and from the at least one pipe outlet opening.

13. Reactor according to one of the preceding claims, further comprising an alternating current source (50) which provides the alternating current.

14. Reactor according to claim 13, wherein a neutral conductor (N) is provided for at least one, preferably for all, bridges, which connects the bridge to a star point of the AC power source; wherein preferably an electrical resistance of the bridges between two reaction tubes is smaller than the electrical resistance of the neutral conductor connected to the respective bridge; wherein further preferably a ratio of these resistances is at most 1 / 5, more preferably at most 1 / 20, most preferably at most 1 / 50.

15. Reactor according to claim 14, if, depending on claim 2, the electrical resistance of the neutral conductor is less than the reference resistance.

16. Reactor according to one of the preceding claims, wherein a phase shift between any two different phases of the alternating current, expressed as radians, is 2TT k / M, where k is an integer in the range from 1 to M-1.

17. Reactor according to one of the preceding claims, wherein the ratio of the two distances of a power feed arrangement (18) to the two bridges (30) is in the range of 0.25 to 1.

18. Reactor according to claim 17, wherein the ratio of the two distances is in the range of 0.25 to 0.8, preferably in the range of 0.25 to 0.

7.

19. A method for carrying out a chemical reaction in a process fluid, at least partially at a temperature of at least 500 °C, wherein a reactor according to one of the preceding claims is used, wherein the process fluid is passed through the reaction tubes of the reactor and is heated by electrical resistance heating using multiphase alternating current; wherein the chemical reaction is preferably one of the following reactions: steam cracking, steam reforming, dry reforming, propane dehydrogenation, a reaction with hydrocarbons, which is carried out at least partially at more than 500 °C.