Electric heating element, furnace and method for performing a chemical process and / or for heating a process medium

Abstract

The invention relates to an Electric heating element (30), in particular for arrangement in a furnace, configured to provide radiant heat, in particular to a heat sink (20). The electric heating element (30) comprises an electric resistance heating element (31) having in its cross section a width and a thickness, wherein the width is greater than the thickness, wherein the electric resistance heating element (31) comprises a middle section (31a), and two end sections (31b) on opposite sides of the middle section (31a) in a width direction (W) of the electric resistance heating element (31). An angle of each corner of at least one of the two end sections (31b) is greater than 90° and / or the outer surface of the at least one of the two end sections (31b) is a curved surface. The invention further relates to a furnace and a method for performing a chemical process and / or for heating a process medium.

Description

[0001] The invention relates to an electric heating element, a furnace and a method for performing a chemical process and / or for heating a process medium.Background

[0002] In a number of processes in various industries, heating is required for manufacturing of products.

[0003] For example, in the chemical industry, furnaces are used to heat one or more reactants that are passed through heated reaction tubes, in which the reactants undergo catalytic or non-catalytic reactions. The heating serves in particular to overcome the activation energy required for the chemical reaction to take place. The reaction can be endothermic or, after overcoming the activation energy, exothermic.

[0004] Examples of such processes are steam cracking, various reforming processes, in particular steam reforming, dry reforming (carbon dioxide reforming), mixed reforming processes, processes for dehydrogenating alkanes and the like. In steam cracking, the reaction tubes are guided through the reactor or furnace in the form of coils, which have at least one reverse bend in the reactor, whereas in steam reforming, reaction tubes running through the reactor without a reverse bend are typically used.

[0005] Further applications of the present invention are furnaces for performing a reverse water gas shift (RWGS) reaction of carbon dioxide and hydrogen to form carbon monoxide and water, dehydrogenation of oxygenates such as a reaction of methanol to formaldehyde and hydrogen, cleavage of ammonia to yield gaseous nitrogen and hydrogen, dehydrogenation of so-called liquid organic hydrogen carriers (LOHC) as known to the skilled person, and reforming of methanol and glycerol (as far as not already included by the term "reforming" used above).

[0006] Further, in steel making, the fabrication of direct reduced iron requires a reducing gas, containing hydrogen and / or carbon monoxide, to be heated to a predetermined temperature.

[0007] In many of these processes, fired reactor or heaters, in particular fired reactors or heaters burning fossil fuels, are used for heating.

[0008] At present, however, there is an increasing demand for production without or with reduced carbon dioxide emissions. This demand cannot be met by processes using fired reactors due to the use of (typically) fossil energy carriers. Other processes are ruled out due to high costs, for example the use of green hydrogen as energy source.

[0009] It was therefore proposed to support or replace the burners in corresponding reactors or heaters with electrical heating media. In addition to direct electrical heating, in which electricity is applied to the reaction tubes themselves, and other types of heating, which are not explained in detail here, there are also concepts for so-called indirect electrical heating.

[0010] Such indirect electrical heating can, as explained in WO2020 / 002326 A1, among others, but already known from earlier publications, be carried out using electrical radiant heating elements ("radiant heaters") which are suitable for heating to the high temperatures required for the reactions mentioned, such heating elements being arranged within the furnace in such a way that they are not in direct contact with the reaction or heatable tubes. The heat transfer takes place predominantly or exclusively in the form of radiant heat. The terms "indirect heating", "heating by means of radiant heat" and the like are therefore used synonymously below.

[0011] In high temperature heating with electric power, the electric heating element commonly features an electric resistance heating element. The electric resistance heating element's cross-section can be round ("wire"; and thereby symmetrical) for smaller applications but for higher energy applications flat rectangular cross-sections ("band") are preferable, as such an electric resistance heating element has various advantages. For example, due to the larger surface area (per unit volume of employed material), heat can be radiated with a better efficiency, i.e. at a lower gradient of heating element temperature versus heat sink (tube outer wall) temperature. Thus, the temperature of the heating elements decreases and lifetime increases.

[0012] However, due to the sharper edges of band-like electric resistance heating elements, passivation of the electric resistance heating element material is favored compared to round electric resistance heating elements. This is due to the lower surface-to-volume ratio near the edges of the band-like cross section. For example, if the electric resistance heating elements is made of a material containing aluminium, the aluminium can diffuse from the interior of the electric resistance heating element and form a passivation layer, i.e. an Al 2 O 3 -layer, on the surface of electric resistance heating element. The passivation / corrosion mechanism in particular occurs at high temperatures (>900°C) and over a long time. However, the passivation layer also forms a protective barrier on the outer surface, such that further corrosion is reduced. Due to the geometry of the band-like electric resistance heating element however, the passivation layer can be spalled, leading to a removal of the protective layer and thus more passivation.

[0013] Further, upon dropping below a threshold aluminium content, respectively depletion of the aluminium reservoir in the electric resistance heating element, the electric resistivity changes dramatically and the electric resistance heating element as well as the whole circuit can fail and need to be replaced.

[0014] The present invention sets itself the task to improve the longevity of radiative heating elements for indirect heating furnaces.Disclosure of the invention

[0015] In view of this background, the present invention proposes an electric heating element, a furnace for performing a chemical process and / or heating a process medium and a corresponding method with the features of the independent patent claims. Embodiments are the subject of the dependent claims and the following description.

[0016] Conventional electric heating elements comprise an electric resistance heating element that has a band-like shape, i.e. a width that is larger than a thickness, for example an essentially rectangular cross-section. A current that flows through the electric resistance heating element generates heat due to the resistance of the electric resistance heating element, which is then radiated from the electric resistance heating element and used for heating.

[0017] As laid out above, due to the high temperature in which the electric heating element is applied, a passivation layer can be formed on the outer side of the electric resistance heating element. Thereby, the electric resistance heating element is depleted of the material used to form the passivation layer and, upon dropping below a threshold content, the electric resistivity changes dramatically and the electric resistance heating element and the electric heating element, respectively, fail and need to be replaced.

[0018] For example, electric resistance heating elements are commonly made of an alloy containing different components such as, in particular in high temperature applications, an alloy containing aluminium Al. Other materials in the alloy are, for example, iron, Fe, chrome, Cr, and / or nickel, Ni.

[0019] The most common point of failure are sharp edges, as the area containing these edges and corners has a high surface to volume ration and thus, the material reservoir per surface to form the passivation layer, that, once formed, also serves as a protection layer reducing further passivation, is low.

[0020] To overcome this problem, the invention proposes an electric resistance heating element geometry with larger angles, i.e. with corners that are less sharp compared to a rectangle of the same dimensions, or a curved surface at end sections of the electric resistance heating element in the width direction.

[0021] Thereby the surface to volume ratio in the region most prone to fail is decreased, increasing the material reservoir. Further, the formation of the protective passivation layer is improved and spalling of the protective layer is reduced, thus hindering further degradation. Both effects lead to an increased longevity of the electric resistance heating element.

[0022] In detail, the invention relates to an electric heating element, in particular for arrangement in a furnace, configured to provide radiant heat, in particular to a heat sink. The electric heating element comprises an electric resistance heating element having, in its cross section, a width and a thickness, wherein the width is greater than the thickness. The electric resistance heating element comprises, in a width direction of the electric resistance heating element, a middle section, and two end sections on opposite sides of the middle section in the width direction. An angle of the corners of at least one, in particular both, of the two end sections is greater than 90° and / or the outer surface of the at least one of the two end sections is a curved surface. The angle of the corner is herein defined as the angle between the inner sides of the end section and / or the inner side of the middle section and the inner side of the end section in a connecting area between the middle section and the end section. A curved surface is to be understood as a surface with no corners. An example for a curved surface is an electric resistance heating element with an essentially rectangular shape, but with rounded corners. The outer surface is a surface exposed to the exterior. For example, as the middle section and the end sections together, the outer surface refers only to the surface at which the middle section and the end sections are not joined together.

[0023] Thereby, the surface to volume ratio of the end sections can be reduced, increasing the available aluminium reservoir per surface area and reducing the surface area on which a passivation layer can be build. Further, due to the lack of sharp corners, splatting of this layer is reduced. Hence, the lifetime of the electric resistance heating element and correspondingly the electric heating as a whole is increased.

[0024] A width of each of the two end sections in particular amounts for less than or equal to 20% or less than or equal to 15% or less than or equal to 10% of the width of the electric resistance heating element.

[0025] In an embodiment, the electric resistance heating element contains aluminium, Al, in particular is made of an alloy further containing iron, Fe, chrome, Cr, and aluminium, Al. Aluminium and the mentioned alloy have a high melting point (from around 1425°C up to 1500°C) and suitable resistivity and temperature coefficient, so that the material can in particular be used in high-temperature applications, i.e. applications with temperatures above 800°C or 900°C.

[0026] In an embodiment, a cross-section of the electric resistance heating element is elliptical or oval. In particular, the cross-section of the electric resistance heating element is a cross-section in a plane parallel to the width direction and thickness direction, i.e. perpendicular to length direction of the electric resistance heating element. Due to the rounded end sections of the electric resistance heating element having an elliptic or oval cross-section, the end sections are rounded, thus having a reduced surface to volume ratio, increasing the available aluminium. Thereby, the lifetime of the electric resistance heating element can be easily increased.

[0027] In an embodiment, a cross-section of the middle section of the electric resistance heating element in the width direction is rectangular.

[0028] In an embodiment, at least one of the two end sections has a shape of a n-sided polygonal, where n is a positive integer equal to 3 or greater than or equal to 5, of a half-ellipse, a half-superellipse, in particular a half-hyperellipse, a half-circle, a partial circle or a full circle. In Cartesian coordinates x, y, the curve of a superellipse is defined by x a n + y b n = 1

[0029] Where n, a and b are positive numbers and a and b refer to the long and short axis, respectively. A hyperellipse is defined as a superellipse with n > 2 and resembles a rectangle with rounded corners, also called a squircle.

[0030] The polygons can be regular or irregular, as long as each corner has an angle of more than 90°. All of these shapes have rounded corners or corners with an angle of greater than 90° and thus, a reduced surface to volume ratio compared to a reference end section having a rectangular shape with the same thickness as the middle section and a width corresponding to the width of the end section. Thus, the aforementioned advantages can be achieved.

[0031] End sections having a shape as close to a full circle as possible, i.e. end sections being round up except for the part joint with the middle section, are particularly preferred, as the electric resistance heating element in this case combines the advantages of a band-type and a wire-type electric resistance heating element, i.e. has a large surface area for heat radiation and a low surface to volume ratio, in particular, the lowest surface to volume ratio for a given volume, at the corners leading to a large aluminium reservoir and stable passivation layer, thereby increasing the lifetime of the electric resistance heating element.

[0032] In an embodiment, a thickness of the two end sections is equal to or greater than a thickness of the middle section. In particular, when the end sections have a larger thickness than the middle section, as the amount of aluminium is increased, prolonging the lifetime of the electric resistance heating element.

[0033] In an embodiment, the electric resistance heating element comprises a plurality of reverse bends arranged along a first direction. In particular, the electric heating element can comprise one or more elongated suspension elements and the electric resistance heating element is guided at the reverse bends using one or more elongated suspension elements on a surface of which the electric resistance heating element rests. In particular, the elongated suspension elements can be arranged such that the electric resistance heating element forms a zig-zag-pattern.

[0034] In an embodiment, at least one of the end sections of the electric resistance heating element, in particular bot of the end sections, is arranged in an eccentrically with the middle section, i.e. such that the middle points of the middle section and the end sections are not in line along the width direction. For example, when circular end sections are used, the circular end sections can be shifted in the thickness direction, such that the middle section is flush with a lower part of the end sections.

[0035] Thereby, the arrangement of the electric resistance heating elements on suspension elements can be improved

[0036] The electric resistance heating elements can, for example, be fabricated by sintering, fabricating separate end sections and a middle section and welding the end sections to the middle section, honing the edges of a band-shaped electric resistance heating element to form end sections with the desired shape, squeeze the middle section from a rectangular or band cross section or a combination of the proposed methods .

[0037] The invention further relates to a furnace for performing a chemical process and / or heating a process medium. The furnace comprises a plurality of walls defining an interior volume of the furnace, one or more heat sinks at least partially arranged in the interior volume of the furnace, and one or more electric heating elements according to any embodiment as described above and are arranged in the interior volume of the furnace and configured to provide radiant heat to heat the one or more heat sinks.

[0038] With regard to further features and advantages of the electric heating element and embodiments thereof, reference is expressly made to the above explanations concerning the furnace proposed according to the invention and its embodiments, since these apply to this in the same way.

[0039] The one or more electric heating elements can, for example, be arranged on an inner surface of one or more walls of the furnace. In particular, when the electric heating element comprises elongated suspension elements on which the electric resistance heating band rests, a longitudinal axis of each of the one or more suspension elements is oriented in parallel to a normal vector to the inner surface of the wall on which the one or more electric heating element are arranged or wherein a longitudinal axis of each of the one or more suspension elements is oriented in parallel to the inner surface of the wall on which the one or more electric heating element are arranged.

[0040] Alternatively, the electric resistance heating element can simple be supported on metallic hooks anchored within the refractory wall (for electric insulation) comprising the same advantages.

[0041] In an embodiment, the one or more heat sinks are tubes or reaction tubes (in the following generally "tubes") that are at least partially arranged in the interior volume of the furnace. Thereby, one or more reactants can be passed through the correspondingly heated tubes, where they are catalytically or non-catalytically reacted in a chemical reaction. It is also possible to pass a process medium to be heated through the correspondingly heated tubes.

[0042] Alternatively, the heat sink can be a product that needs to be annealed and is placed inside the furnace for that purpose.

[0043] The one or more tubes can be guided through the furnace in any desired manner, in particular with or without one or more reversal points or reversal bends, wherein the reversal points or reversal bends can be arranged inside or outside the interior of the furnace. For example, the one or more tubes can be arranged in a single row in a vertically arranged plane or a plane parallel to one of the side walls, respectively. A multi-row arrangement in an intermediate area between two side walls is also possible.

[0044] In particular, the one or more tubes can have a (total) length of 3 to 100 m and / or a diameter of 20 to 200 mm. Furthermore, the individual tubes can be designed in sections in two or more parallel strands with reduced tube diameters. For example, the multi-strand section is arranged close to the inlet to the furnace in order to provide the longest possible tube wall surface in this area. Further downstream, this arrangement combines the initially parallel strands into a common strand, preferably with a larger tube diameter. In this example, the tube consists of the two or more parallel strands, the joint and the combined strand. Conversely, it is also possible in principle to provide a multi-strand design of the tube at the end or in a middle area, with intermediate splitting sections and possibly additional joining sections. The tubes can also be filled with a suitable catalyst material and / or an inert material, depending on the type of reaction.

[0045] Using tubes, the furnace can particularly be provided for performing a steam cracking process, various reforming processes, in particular steam reforming, dry reforming (carbon dioxide reforming), mixed reforming processes, processes for the dehydrogenation of alkanes and the like. The furnace can further be a cracking furnace, a reforming furnace, a direct reduced iron (DRI) furnace etc. In general, the furnace is suitable for all types of reactions in which a feed mixture is passed in a gaseous state through the one or more tubes heated from the outside to corresponding temperature levels and thereby converted. The furnace is also suitable for heating process media only, e.g. upstream of a reactor.

[0046] In an embodiment, the one or more heat sinks are heated to a temperature level, between 0 °C and 1,200 °C, in particular between 300 °C and 1,050 °C, in particular between 400 °C and 950 °C. The temperature level can in particular be identical or comparable to a fired furnace or to other electrically heated furnaces. The temperature levels cover a comparatively wide temperature range, as, in case of tubes, the corresponding tubes always have a not inconsiderable temperature gradient ("cold" inlet and "hot" outlet, especially with increasing coking).

[0047] While furnace according to the invention is concerned with radiant heat from electric heating elements, this does not exclude the possibility that other types of heating may also be used, for example direct heating, in which the tubes themselves are used as electrical resistors to generate heat, inductive heating or, in further furnaces, heating using burners. In any case, in addition to the radiant heat, some of the heat provided by a corresponding heating element can also be transferred to the tubes by convection.

[0048] Therefore, the use of indirect electrical heating, i.e. the use of radiant heat provided by means of electrical heating elements, does not exclude the presence of additional electrical or non-electrical heating. In particular, it can further be possible to vary the contributions of the types of electrical and, in particular, non-electrical heating over time, for example depending on the supply and price of electricity or the supply and price of non-electrical energy carriers.

[0049] In an embodiment, the furnace is partially or fully thermally insulated, i.e. the plurality of walls may in particular be lined with a material that is thermally resistant at the stated temperatures. In particular, at least 90%, 95% or 99% of surface are of the walls can be provided with thermally insulating material. The present invention is further not limited to the use of exactly one furnace but can in particular also be used in arrangements with different furnaces.

[0050] The invention further relates to a method for performing a chemical process and / or for heating a process medium in a furnace, the furnace comprising a plurality of walls defining an interior volume of the furnace, one or more heat sinks arranged in the inner volume of the furnace, and one or more electric heating elements according to any of the previously described embodiments, arranged in the interior volume of the furnace and configured to provide radiant heat to heat the heat sink. The furnace can in particular be a furnace according to any of the previously described embodiments.

[0051] The same advantages as for the furnace and the electric heating element apply accordingly to the method.Short description of the Figures

[0052] Embodiments of the invention are described below purely by way of example with reference to the accompanying drawing, wherein Figure 1 shows a side view of a furnace according to an embodiment of the present invention, Figure 2 shows a front view of an electric heating element according to an embodiment of the present invention, Figures 3 and 3b each show a cross-section of an electric resistance heating element according to an embodiment of the present invention, and Figures 4a to 4f show cross-sections of an electric resistance heating element according to an embodiment of the present invention. Embodiments of the invention

[0053] The embodiments described below are described solely for the purpose of assisting the reader in understanding the claimed and previously explained features. They are merely representative examples and are not intended to be exhaustive and / or limiting with respect to the features of the invention. It is to be understood that the advantages, embodiments, examples, functions, features, structures and / or other aspects described above and below are not to be considered limitations of the scope of the invention as defined in the claims or limitations of equivalents to the claims, and that other embodiments may be used and modifications may be made without departing from the scope of the claimed invention.

[0054] Different embodiments of the invention may include, comprise, consist of, or consist essentially of other useful combinations of the described elements, components, features, parts, steps, means, etc., even if such combinations are not specifically described herein. In addition, the disclosure may include other inventions that are not currently claimed but that may be claimed in the future, particularly if they are encompassed by the scope of the independent claims.

[0055] Explanations relating to devices, apparatuses, arrangements, systems, etc., according to embodiments of the present invention may also apply to methods, processes, methods, etc., according to embodiments of the present invention, and vice versa. Elements, process steps, etc. which are identical, have the same effect, correspond to each other in their function, are structurally identical or comparable, etc. may be indicated by identical reference signs.

[0056] Figure 1 shows a side view of a furnace 100 according to an embodiment of the present invention, in particular a cut through the furnace 100 along the yz-plane. The furnace 100 a plurality of walls 11, 12, 13, 14 in which six electric heating elements 30 are arranged in an interior volume 15 of the furnace 100, three on an inner surface of a front-end wall 11 of the furnace 100 next to each other in the z-direction and three on an opposite back-end wall 12 of the furnace 100 next to each other in the z-direction. Between the front-end wall 11 and the back-end wall 12 of the furnace 100, one or more heat sinks 20 (only one heat sink 20 can be seen) are at least partially arranged in the interior volume 15 of the furnace 100. The one or more heat sinks 20 are for example tubes arranged in a row in the x-direction (only one tube can be seen). While here only one row of tubes is arranged in the furnace 100, it is also possible to arrange more than one row of tubes in the furnace 100 next to each other in the y-direction. The tubes enter the furnace through a bottom wall 13 and exits the furnace 100 through the top wall 14. The tubes can for example be provided with a reverse point outside the furnace 100 and enter the furnace 100 again from the top wall 14 and exit the furnace via the bottom wall 13. While in the provided figures show tubes as heat sinks 20, it is pointed out that other heat sinks 20 can also be provided in the furnace 100.

[0057] During operation of the furnace 100, a reactant of the chemical reaction or process medium to be heated is guided through the tubes. In order to perform the chemical reaction, the temperature level in the heat sink 20 has to reach a temperature between 400 °C and 1,500 °C, in particular between 450 °C and 1,300 °C, furthermore in particular between 500 °C and 1,200 °C. To achieve the necessary temperature level, a current is passed through the electric heating elements 30, in particular the electric resistance heating element 31 of the electric heating elements 30 to generate heat in the electric resistance heating element 31 which is radiated towards the heat sink 20 or the tubes, respectively, arranged in the interior volume of the furnace 100 and heats the reactant or process medium inside the tubes.

[0058] Figure 2 shows front view of a section of an electric heating element 30 according to an embodiment of the present invention. In the front view, the length direction L and the thickness direction T of the electric resistance heating element 31 extends in parallel to the xz-plane, wherein the thickness direction is perpendicular to the length direction. The width direction W extends in parallel to the y-direction.

[0059] As can be seen in Figure 2, the electric resistance heating element 31 comprises a plurality of reverse bends 31a arranged along the x-direction, wherein two rows of reverse bends 31c are formed distanced apart in the z-direction. Further, the two rows of reverse bends 31c are arranged in a staggered fashion with regard to one another. In the region of reverse bends 31a, the electric resistance heating element 31 rests on elongated suspension elements 32, that, for example, can comprise a metallic core surrounded by an insulating material.

[0060] The electric resistance heating element 31 can, for example, be made of or contain an alloy comprising aluminium, chrome and iron.

[0061] Figures 3a and 3b each show a cross-section of an electric resistance heating element according to an embodiment of the present invention. In Figures 3a and 3b, the width direction W extends in parallel to the y-direction, the thickness direction T extends in parallel to the x-direction and the length direction L extends in parallel to the z-direction.

[0062] The electric resistance heating element 31 comprises a middle section 31a and two end sections 31b, which are arranged on either end of the middle section 31a in the width direction W. In particular, the end sections 31b constitute less than 20% or less than 15% or less than 10% of the total width of the electric resistance heating element 31. The middle section 31a further has a rectangular cross-section and each end section 31b has the shape of a partial circle when viewed in the xy-plane. The shape of a fully circular end sections is shown with dotted lines. Further, the diameter of the circular end sections 31b is larger than the thickness of the middle section 31a, thereby increasing the material reservoir in the end sections 31b most prone to failure because of depletion.

[0063] By having a circular shape, the surface to volume ratio of the end sections 31b can be reduced, thereby increasing the amount of available aluminium for forming the passivation layer while still maintaining an aluminium content inside the electric resistance heating element 31 suitable for using the electric resistance heating element 31 for heating. Further, as no sharp edges, i.e. edges with an angle below 90°, are present in the electric resistance heating element 31, splatting of the passivation layer that also serves as a protective layer and prevents further passivation, is reduced or prevented. Thereby, the lifetime of the electric resistance heating element 31 can be increased.

[0064] In Figure 3a, the middle points of the two end sections 31b are in line with the middle point of the middle section 31a in the width direction.

[0065] In contrast, Figure 3b shows an eccentric arrangement of the end sections 31b, where the middle points of the end sections 31b are in line with one another, but not in line with the middle point of the middle section 31a. In particular, the end sections 31b are flush with one side of the middle section 31a. Thereby, assembly of the electric resistance heating element 31 on the elongated suspension elements 32, as the side of the middle section 31a can be arranged that is flush with the end sections 31b can easily be arranged thereon.

[0066] Figures 4a to 4f show various cross-sections of an electric resistance heating element according to an embodiment of the present invention. In Figures 4a to 4f, the width direction W extends in parallel to the y-direction, the thickness direction T extends in parallel to the x-direction and the length direction L extends in parallel to the z-direction.

[0067] In Figure 4a, the middle section 31a has a rectangular shape and the end sections 31b have a triangular shape, wherein the width of the baseline of the triangle is the same as the thickness of the middle section 31a and a width in the width direction W that constitutes to less than 20% or less than 15% or less than 10% of the total width of the electric resistance heating element 31.

[0068] Figure 4b shows an electric resistance heating element 31 with a rectangular middle section 31a and end sections 31b that are half-circles. Similar to Figure 4a, the diameter of the half-circular end sections 31b is the same as the width of the electric resistance heating element 31 or the middle section 31a and the end sections 31b each have a width that constitutes to less than 10% of the total width of the electric resistance heating element 31.

[0069] Figure 4c shows another example of a shape of the end sections 31b. Similar to the previous examples, the middle section 31a has a rectangular shape. The end sections 31b each have the shape of a hyper-ellipse, in particular a squircle, i.e. are essentially rectangular with rounded corners.

[0070] Figures 4d and 4e each show an electric resistance heating element 31 with a rectangular middle section 31a and end sections 31b that have an essentially hexagonal shape (as can be seen by the dotted lines). Due to the fixture of the end sections 31b to the middle section 31a, the end sections 31b do not constitute the full hexagon, but the sides facing the middle section 31a are fused with the middle section 31a.

[0071] In Figure 4d, the hexagonal end sections 31b have the same thickness as the middle section 31a and the electric resistance heating element 31, respectively, while in Figure 4e, the thickness of the hexagonal end sections 31b is larger than the thickness of the electric resistance heating element 31. Due to the larger size of the hexagonal end section 31b in Figure 4e, a larger amount of material, e.g. aluminium is present in the end sections 31b, thus increasing the material reservoir and prolonging the lifetime of the electric resistance heating element 31.

[0072] Figure 4f shows an electric resistance heating element 31 with an overall elliptical cross-section. As can be seen, in case of an elliptical electric resistance heating element 31, the end sections 31b have curved outer surface of each of the end section is a curved surface. Thereby, the surface to volume ratio at the end sections can be reduced and the lifetime of the electric resistance heating element 31 is increased.

Claims

1. Electric heating element (30), in particular for arrangement in a furnace, configured to provide radiant heat, in particular to a heat sink (20), the electric heating element (30) comprising: an electric resistance heating element (31) having in its cross section a width and a thickness, wherein the width is greater than the thickness, wherein the electric resistance heating element (31) comprises a middle section (31a), and two end sections (31b) on opposite sides of the middle section (31a) in a width direction (W) of the electric resistance heating element (31), characterized in that an angle of each corner of at least one of the two end sections (31b) is greater than 90° and / or the outer surface of the at least one of the two end sections (31b) is a curved surface.

2. Electric heating element (30) according to claim 1, wherein the angle of the corners of both of the two end sections (31b) is greater than 90° and / or the outer surface of the at least one of the two end sections (31b) is a curved surface.

3. Electric heating element (30) according to claim 1 or 2, wherein the electric resistance heating element (31) contains aluminium, Al, in particular is made up of an alloy containing aluminium, Al, iron, Fe, chrome, Cr.

4. Electric heating element (30) according to any of claims 1 to 3, wherein the cross-section in a plane parallel to the width direction (W) and a thickness direction (T) of the electric resistance heating element (31) is elliptical or oval.

5. Electric heating element (30) according to any of claims 1 to 3, wherein the cross-section of the middle section (31a) of the electric resistance heating element (3a) in a plane parallel to the width direction (W) and the thickness direction (T) is rectangular.

6. Electric heating element (30) according to any of claims 1 to 5, wherein at least one of the two end sections (31b) has the shape of a n-sided polygonal, where n is a positive integer equal to 3 or greater than or equal to 5, of a half-ellipse, a half-superellipse, in particular a half-squircle, a half-circle, a partial circle or a full circle.

7. Electric heating element (30) according to any of claims 1 to 6, wherein a thickness of the two end sections (31b) is equal to or greater than a thickness of the middle section (31a).

8. Electric heating element (30) according to any of claims 1 to 7, wherein a width of each of the two end sections (31b) amounts for less than or equal to 20% or less than or equal to 15% or less than or equal to 10% of the width of the electric resistance heating element (31).

9. Electric heating element (30) according to any of claims 1 to 8, wherein the electric resistance heating element (31) comprises a plurality of reverse bends (31c) arranged along a first direction, particularly wherein the electric heating element (30) comprises one or more elongated suspension elements and the electric resistance heating element (31) is guided at the reverse bends (31c) using one or more elongated suspension elements (32) on a surface of which the electric resistance heating element (31) rests.

10. Electric heating element (30) according to any of claims 1 to 9, wherein at least one of the end sections (31b), in particular both end sections (31b), are arranged eccentrically with regard to the middle section (31a).

11. Furnace (100) for performing a chemical process and / or heating a process medium, wherein the furnace (100) comprises: a plurality of walls (11, 12, 13, 14) defining an interior volume (15) of the furnace (100), one or more heat sinks (20) at least partially arranged in the interior volume (15) of the furnace (100), and one or more electric heating elements (30) according any of claims 1 to 10 arranged in the interior volume (15) of the furnace (100) and configured to provide radiant heat to the one or more heat sinks (20).

12. Furnace (100) according to claim 11, wherein the one or more heat sinks (20) are one or more tubes that are at least partially arranged in the interior volume (15) of the furnace (100).

13. Furnace (100) according to any of claims 11 or 12, wherein the furnace (100) is at least partially, in particular fully, thermally insulated.

14. Method for performing a chemical process and / or for heating a process medium in a furnace (100), the furnace (100) comprising: a plurality of walls (11, 12, 13, 14) defining an interior volume (15) of the furnace (100), a plurality of walls (11, 12, 13, 14) defining an interior volume (15) of the furnace (100), one or more heat sinks (20) at least partially arranged in the interior volume (15) of the furnace (100), and one or more electric heating elements (30) according any of claims 1 to 10 arranged in the interior volume (15) of the furnace (100) and configured to provide radiant heat to the one or more heat sinks (20).

15. Method according to claim 14, wherein the furnace (100) is a furnace (100) according to any of claims 11 to 13.

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