Device for generating a hot process gas stream

Abstract

In this device, a process gas flows through a housing (2) with a predefinable volume flow rate from an inlet (5) to an outlet (6). Inside the housing (2) is at least one heating element (1) made of a material that can be heated by electrical induction and on which at least one flow channel (11) is provided. The housing (2) is enclosed by at least one nonlinear electrical coil (3) in which the number of turns decreases along the length of the coil (3) from the inlet (5) towards the outlet (6), and which is connected to an electrical voltage source. On the outside of the housing (2) at least two electrical coils (3a, 3b) can be arranged one after the other in the direction of flow of the process gas and connected to an electrical voltage source, wherein the first electrical coil (3a) is operated with a higher electrical power than the subsequently arranged at least one further electrical coil (3b).

Description

[0001] The invention relates to a device for generating a hot process gas stream, which provides a hot gas flare for heating products and for use in production processes. It can be used, for example, for melting metal or glass, or for heat treatment of various components or materials.

[0002] The core of the invention lies in the inductive heating of a heating element, the transfer of heat to the surrounding process gas, and the use of this hot process gas. In this respect, the invention serves as a potential decarbonized replacement for a gas burner.

[0003] The invention enables the provision of thermal energy and sufficient heating of a process gas to very high temperatures using only electrical energy, and also replaces conventional gas burners. It thus contributes to the decarbonization of heating systems. The device is particularly suitable for use in metallurgical processes. However, it can also be used in many other applications. These metallurgical processes preferably include the melting and holding of metals or glass at high temperatures, the heating of heat treatment furnaces, and the thermal treatment of any material, including bulk materials.

[0004] Hot gas generators based on electric resistance heating (hot air guns - hot air cannons) are also commonly used on the market, but their performance is currently limited to gas temperatures of approximately 1000 °C and outputs of approximately 100 kW.

[0005] These performance limits can be significantly extended to temperatures exceeding 1000 °C and power levels in the MW range by using inductive energy input.

[0006] Furthermore, burners that achieve the desired heat through the oxidation of a fuel are in use. Various hydrocarbon compounds are used as fuel in these burners, and the oxidation process releases CO2.

[0007] When operating inductively heated devices that heat fluids to higher temperatures, thermally induced mechanical stresses can occur. The large temperature differences between the inlet and outlet sides have a detrimental effect on the fluid in question.

[0008] It is therefore an object of the invention to provide possibilities for heating a process gas stream in which temperatures of at least 1000 °C are reached and no CO2 is released, an efficiency of at least 30% can be achieved and the process gas is heated as homogeneously as possible in a heating device.

[0009] According to the invention, this problem is solved with a device having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features specified in the dependent claims.

[0010] In the device according to the invention, a process gas flows through a preferably hollow cylindrical housing made of a refractory material, with a predefinable volume flow rate, from an inlet to an outlet, to form a hot process gas stream. A flare of the hot process gas forms after the outlet. Inside the housing, at least one heating element is arranged, which is made of a material that can be heated by electrical induction and has at least one flow channel through which the process gas flows and / or around. "Made of a material" here means that the material of the heating element contains at least 90% by mass of a material that can be heated by electrical induction.

[0011] The hollow housing is enclosed by at least one non-linearly wound electrical coil, in which the number of turns decreases along the length of the electrical coil from the inlet towards the outlet.

[0012] The at least one electrical coil is connected to an electrical voltage source, with which alternating voltage or a pulsed direct voltage is applied to the electrical coil.

[0013] The number of turns of the electrical coil should be selected such that, in the first third of the length of the at least one heating element, starting from the process gas inlet, at least 25% more power can be inductively coupled into the heating element than in the area of ​​the process gas outlet. For this purpose, in the area of ​​the electrical coil located directly at or near the process gas inlet, at least 20%, preferably more than 30%, more turns per unit length of the electrical coil may be present than in the area of ​​the outlet and the areas near the outlet. At least 20%, preferably more than 30%, more turns should be present over at least 30% of the length of the respective electrical coil, starting from the inlet.If there is more than one electrical coil, at least the electrical coil that surrounds the radiator in the area of ​​the inlet should have at least 20%, preferably more than 30%, more turns than at least one electrical coil arranged downstream in the direction of flow.

[0014] Besides changing the winding density of the coil, this effect can also be achieved by changing the coil's cross-section, profile, or profile orientation. For example, an electrical coil can have windings that are not rotationally symmetrical but have polygonal cross-sections. Furthermore, an electrical coil can have different edge lengths, meaning that individual coils may have different heights and widths.

[0015] On the outside of the housing, either alone or additionally, at least two electrical coils can be arranged in series in the direction of process gas flow. Each coil can be connected to an electrical voltage source that applies alternating current or a pulsed direct current. The first electrical coil, located in the inlet area, is operated with a higher electrical power than at least one further electrical coil located downstream of the first. Here too, at least 25% more power should be able to be coupled into the heating element in the inlet area than in the outlet area.

[0016] Introducing more energy into the inlet area of ​​the radiator than into the outlet area is advantageous because the colder incoming process gas has a greater cooling effect on the radiator (or at least one element) at the inlet than at the outlet, where the heated process gas has reached operating temperature. To maintain a nearly homogeneous temperature across the radiator, despite the decreasing cooling effect of the warming process gas along its length, varying the energy input and thus the inductive heating of the radiator (or element) along its length is beneficial. This allows for full utilization of the radiator's entire length, faster attainment of operating temperature, and a reduction or even complete avoidance of temperature-related mechanical stresses within the radiator.

[0017] The process gas flows along the inner wall of the housing and the surface of at least one heating element to be heated. The process gas can both flow around and through the heating element, thereby heating the process gas along its flow path from inlet to outlet.

[0018] The housing and the at least one heating element should each be made of a material whose melting point is higher than the maximum temperature of the heated process gas. The device is intended to transfer the heat energy inductively introduced into the at least one heating element to a process gas.

[0019] The at least one heating element should be made of a paramagnetic and high-temperature resistant material, which advantageously has a passivating oxide layer on its surface. This durable oxide layer protects the at least one heating element, when using air or other oxygen-containing gas mixtures as process gas, from further undesirable reactions at higher temperatures, and especially at the operating temperature of the hot gas flare formed with the hot process gas, even at temperatures exceeding 1100 °C. The oxide layer should be present at least on the surfaces that are in contact with, or could be in contact with, the process gas.

[0020] The at least one heating element may be made of a nickel-based alloy and / or of zirconium and / or its alloys and / or an alloy with a refractory metal as its main component – ​​in particular tantalum, tungsten, niobium, or molybdenum – and other alloying elements, in particular chromium and / or titanium. The aforementioned metals must be present in a base alloy at a minimum of 50% by mass.

[0021] The protective oxide layer on the surface of the at least one heating element can be formed outside the device before use. This can be achieved by treating the at least one heating element in an oxygen-containing atmosphere, or preferably in an oxygen-containing atmosphere heated to several hundred degrees, or by treatment in a corrosive solution. The oxide layer on the surface of the at least one heating element should be continuous and cover all surfaces that come into contact with the process gas. This applies in particular to internal and external flow channels.

[0022] The process gas can flow along the inner wall of the housing and the outer surface of the heating element and / or through at least one flow channel of the at least one heating element to be heated.

[0023] The number of turns of the at least one electrical coil can be continuously reduced along the length of the at least one electrical coil in the direction of flow of the process gas.

[0024] Controlled inductive heating of the heating element and the process gas can also be achieved by at least two electrical coils with different numbers of turns along their length, wherein the first electrical coil, located in the inlet region, has a greater number of turns than an electrical coil located downstream in the process gas flow direction or in the outlet region. Additionally, the first electrical coil can be operated at a higher power than further electrical coils located downstream in the process gas flow direction through the heating element.

[0025] Controlled inductive heating of the heating element ensures that the incoming process gas is heated at a higher rate in the inlet area and subsequently at a lower rate towards the outlet. This prevents large temperature differences between the inlet and outlet areas of the process gas on at least one heating element.

[0026] If only one non-linear electrical coil is used in the device according to the invention, at least one additional electrical voltage supply for further electrical coils can be dispensed with. If at least two identical linear electrical coils are used, this has the advantage that standardized coils can be used.

[0027] The at least one radiator can be made of a nickel-based alloy and / or zirconium and / or its alloys and / or a refractory metal-based alloy – in particular a tantalum, tungsten, niobium, or molybdenum-based alloy. The respective metal or alloy must comprise a minimum of 95% by mass of the radiator material.

[0028] One or more radiators can be arranged as a bundle with at least three, preferably more than four, flow channels, or as a composite body inside the housing. Flow channels can preferably be tubular or hollow cylindrical.

[0029] The at least one heating element can be designed in the form of a straight tube bundle with at least three, preferably more than four, flow channels, in which the individual flow channels are electrically insulated from each other and the spaces between the individual flow channels are filled with an electrically non-conductive material, and in which the process gas to be heated flows around the outer surface of the bundle and through the inner flow channels.

[0030] A heating element can also be designed in the form of a bundle of at least three, preferably more than four, flow channels rotated as a helix, in which the individual flow channels are electrically insulated from each other, and the spaces between the individual flow channels are filled with an electrically non-conductive material, and in which the process gas to be heated flows around the outer surface of the bundle and through the inner flow channels.

[0031] A radiator can also be in the form of a cylinder, which is traversed by at least three, preferably more than four, internal flow channels, the diameter of which is greater than 2 mm and the flow channels are designed to run in a straight line.

[0032] A radiator can also be in the form of a cylinder, which is traversed by at least three, preferably more than four, internal flow channels, the diameter of which is greater than 2 mm and the flow channels are designed to run in a straight line.

[0033] It is also possible that a radiator in the form of a cylinder is traversed by at least three, preferably more than four, internal flow channels whose diameter is greater than 2 mm and which are rotated as a helix or formed as coils.

[0034] Alternatively, a radiator can be formed in the form of several composite discs, which are traversed by at least three, preferably more than four, internal flow channels that have a minimum diameter of 2 mm and which can run at right angles or at an angle to the front surface.

[0035] If flow channels are not straight but, for example, in the form of a helix, the length of the inner flow channels of the at least one heating element can be increased by the windings, which can be used advantageously for heat transfer to the process gas and makes it possible to reduce the length of the heating element accordingly.

[0036] A casing can be made of quartz glass, Al2O3, ZrO2 or MgO, or a chemical compound and / or a mixture of these materials.

[0037] A fire-resistant sealing element can be installed at the process gas inlet to prevent backflow of heated process gas. This is particularly advantageous when process gas, as explained below, is routed through several housings arranged inside one another and enclosing at least one heating element. This reduces energy and, in particular, heat losses, and ensures that the process gas enters exclusively through the appropriately sized inlet.

[0038] The housing in which the heating element is arranged can be enclosed by a second and / or a third housing, so that process gas flows through a gap between the first housing and the second housing and / or through a gap between the second housing and the third housing to preheat the process gas in countercurrent or cocurrent flow to the process gas flow.

[0039] A second housing and / or a third housing may be provided on their surfaces facing the heating element with a reflective surface coating of titanium nitride, or aluminum chromium nitride, or titanium aluminum nitride, or another coating reflecting electromagnetic radiation in the wavelength range of infrared light, which does not or only very slightly contributes to inductive heating.

[0040] For this purpose, a second or third housing can be assembled from at least two parts, for example half-shells, which can facilitate the formation of a reflective surface coating on the inner surfaces facing the radiator.

[0041] The temperature of the process gas exiting the outlet can be controlled by adjusting the process gas volume flow rate and / or the electrical power with which the at least one electrical coil is operated.

[0042] The geometry of the at least one heating element and / or the inlet can be designed geometrically and / or by means of additional apparatus such that the heat transfer between the at least one heating element and the process gas is maximized, in particular by turbulence of the process gas flow. For this purpose, surfaces on the heating element that are exposed to and / or around the process gas flow can be provided with contour elements.

[0043] The outlet can be geometrically designed and / or by means of an apparatus such that the flow of the hot process gas exiting the device is modified to maximize heat transfer to any solid, melt, liquid, gas, or plasma that may be located in the exiting process gas stream. This can be achieved by a design with at least one nozzle-shaped outlet opening.

[0044] The outlet can be geometrically and / or by means of an apparatus designed in such a way that the mean flow velocity of the process gas and / or the geometry of the process gas stream can be modified, in particular by means of a correspondingly geometrically designed nozzle.

[0045] The coiling of the pipes allows the length of the internal flow channels of the at least one heating element to be increased, which can be advantageously used for heat transfer to the process gas.

[0046] A radiator can be designed in the form of at least one cylinder traversed by at least three, preferably more than four, internal flow channels. The internal flow channels can be straight, or, to increase their length, be helically rotated or coiled.

[0047] The diameter of a single internal flow channel should be greater than 2 mm.

[0048] A radiator can be designed in the form of at least two composite discs, each traversed by at least three, preferably more than four, flow channels. The flow channels can be straight or angled relative to the end face of the disc. The diameter of a single internal flow channel should be greater than 2 mm.

[0049] The ratio of the cross-sectional area of ​​the inner flow channels of the at least one radiator to the area of ​​the annular gap that exists between the outer surface of the at least one radiator and the inner wall of the first casing should be between 1:2 and 4:1.

[0050] The at least one heating element and the flow channels should be tubular in shape. The element(s) could also have other geometries for their internal free cross-sectional areas and / or their surfaces. However, the tubular shape offers advantages in terms of fluid dynamics and because of the relatively large surface area, which contributes to heating the process gas.

[0051] It is also possible to supplement the aforementioned radiator geometries with contour elements (protrusions, indentations) to increase the total surface area of ​​at least one radiator. These can also be used to create a beneficial turbulence in the process gas flow.

[0052] Air, but also other gases or gas mixtures that may be advantageous for the respective heating process, can be used as the process gas. This includes, in particular, inert gases that can prevent any adverse effects on the elements, substances, and objects being heated.

[0053] In the invention, the temperature of the process gas exiting the outlet can be controlled by adjusting the process gas volume flow rate and / or the electrical power with which the at least one electrical coil is operated. For this purpose, the temperature of the process gas at the outlet can be determined, and a control loop can be established.

[0054] The amount of heat transferred is determined by the surface area of ​​the at least one heating element surrounded by the process gas, the surface area of ​​the internal flow channels, the number and length of the at least one heating element and the internal flow channels, and the temperature of the at least one heating element. The heat transfer from the heating element(s) to the flowing process gas is crucial for the efficiency.

[0055] The heating output of the device can be controlled via the electrical power input, the quantity and pressure of the process gas flowing into the device, and the inlet temperature of the process gas. Additionally, as already mentioned, the process gas can be preheated in or before the device. External preheating of the process gas before the device can be achieved, for example, using a resistance-heated device. However, it is also possible to recirculate the process gas back into the device, utilizing its heat. For this purpose, the process gas, which has already been used for heating and has cooled slightly, can be drawn from the heating zone after use and recirculated back into the device's inlet.

[0056] The process gas supply to the device can be achieved with a compressor system for multiple devices or with a compressor assigned to one of the devices according to the invention, which is preferably controllable or adjustable. Furthermore, a flow condition particularly favorable for heat transfer from the at least one heating element to the process gas can already be set in the process gas supply.

[0057] The geometry of the at least one heating element and / or the inlet for the process gas to be heated into the device can be designed geometrically and / or by means of an apparatus such that the heat transfer between the at least one heating element and the process gas flow is maximized. This can be achieved in particular by creating turbulence in the process gas flow. Contour elements that lengthen the path of the process gas along a surface of the at least one heating element used for heating and / or that create turbulence can also be used for this purpose.

[0058] The device may have an additional housing made of a fire-resistant material, which encloses the electrical coil(s) on the outside. This additional housing can serve as protection against high temperatures.

[0059] The exit of the process gas from the device can also be optimized for specific applications. For example, the exit can be geometrically designed and / or by means of a movable apparatus in such a way that the flow of the process gas is modified to maximize heat transfer to any solid, melt, liquid, gas, or plasma that may be placed in the exiting process gas stream.

[0060] Furthermore, the hot process gas outlet can be designed or configured to modify the velocity and / or shape of the process gas flow or flare. This can be achieved, for example, by means of at least one geometrically designed nozzle that can influence the cross-section, flow velocity, and / or direction of the hot process gas flow exiting the device.

[0061] The selection of the at least one electrical coil (design, electrical conductivity, and number of turns) and the frequency of the electrical voltage at which it is operated can be optimized taking into account the geometry and material of the radiator(s). For the optimal frequency for heating the at least one radiator, a ratio of three to five of the total diameter of the radiator to the current penetration depth δ can be assumed (d / δ = 3-5). The frequency and the electromagnetic properties of the radiator material are incorporated into the formula for the current penetration depth [according to Fasholz 1984] as follows: δ=503×ρμr×f δ [mm] = current penetration depth ρ[Ω mm2m] µ r = relative permeability f [Hz] = frequency

[0062] The formula above describes the current penetration depth. This value indicates the thickness up to which 86% of the induced energy is converted into heat. The remaining 14% is absorbed by deeper layers. Because of this, there is an optimized ratio between the overall diameter of the heating element and the current penetration depth for inductive heating. In addition to the frequency, this formula incorporates the temperature-dependent material properties of the object being heated, namely its specific electrical resistance and relative permeability.

[0063] With this invention, the performance limits can be extended compared to other electric heating systems to include applications at temperatures above 1000 °C and power outputs in the MW range.

[0064] The invention will be explained in more detail below by way of example.

[0065] This shows: Fig. 1 An example of a device according to the invention with a nonlinear electrical coil and a cylindrical heating element with a surface structure Fig. 2. A second example with two different electrical coils and a cylindrical heating element and a possibility for preheating process gas. Fig. 3. An example of a radiator made from a tube bundle Fig. 4. An example of a radiator made from a twisted bundle of tubes Fig. 5. An example of a radiator made from a cylinder with internal flow channels. Fig. 6 An example of a radiator made from a cylinder with internal flow channels that are rotated. Fig. 7 An example of a radiator made of several composite discs with internal flow channels. Fig. 8. An example of a non-linearly wound electrical coil Fig. 9. An example of two electrical coils with different power ratings

[0066] At the in Fig. In the example shown, process gas flows into an inlet 5 from a compressor (not shown) of the device. The process gas flows along the outer surface, which has an exemplary helical structure, and through the internal flow channels of the at least one heating element 1, through a housing 2 made of refractory material, towards the outlet 6 of the device. There, it can be used for further heating downstream of the outlet 6, utilizing the high temperature of the heating element 1. A structured surface exposed to the process gas can be advantageous for heat transfer compared to a smooth surface.

[0067] The housing 2 is made of ceramic, e.g., Al₂O₃ or ZrO₂, and is enclosed by at least one electrical coil 3, so that the at least one heating element 1 arranged inside it can be heated by electrical induction. In this case, the electrical coil 3 is non-linear in order to introduce varying amounts of energy into the at least one heating element 1 along its length. More energy is inductively introduced at the inlet end of the at least one heating element 1 than at the outlet end. The heating element 1 has a durable, passivating oxide layer on its surfaces that come into contact with the process gas, formed prior to use, and is, for example, made of a nickel-based alloy, or of zirconium, or a zirconium alloy, or an alloy with a refractory metal as the base element—in particular, a tantalum, tungsten, niobium, or molybdenum-based alloy.The aforementioned metals are present in a base alloy with a minimum mass of 50%. These materials can also be used in the examples described below. In a non-linear electrical coil, the number of turns of the electrical coil 3 varies along its length. In the invention, the number of turns of the electrical coil 3 is greater in the region of the heating element 1, which is located closest to the inlet 5 for the process gas, than in regions of the electrical coil 3 located further downstream towards the outlet 6.

[0068] The at least one electrical coil 3 is connected to an electrical voltage source (not shown) whose power and frequency can be controlled or regulated, preferably depending on the desired final temperature of the process gas after the outlet 6. The frequency of the electrical voltage should be matched to the geometry and material of the heating element 1.

[0069] A fire-resistant sealing element 4 is arranged at the inlet 5 to prevent backflow of heated process gas.

[0070] The in Fig. Example 2 shows a device that enables preheating of the process gas while simultaneously providing additional thermal insulation. In this example, two electrical coils with different winding densities and power ratings are used. The first electrical coil 3a, located near the inlet 5, has a higher winding density and is operated at a higher electrical power than a second electrical coil 3b or any other electrical coil located closer to the outlet 6.

[0071] After passing through inlet 5, the process gas flows for preheating and insulation of the electrical coils 3a and 3b, first in the gap between the second housing 7 and the third housing 8, and then in the opposite direction in the gap between the second housing 7 and the first housing 2. From this gap, the process gas now flows into the space between the surface of the heating element 1, which in this example is a cylindrical body, and the first housing 2, as well as through the internal flow channels of the heating element 1. The process gas is heated to the desired process temperature at these surfaces. Through the space and the flow channels 11, the process gas reaches outlet 6. In this example, the electrical coils 3a and 3b are enclosed by a ceramic housing 9. Such a housing 9 can, in principle, be present in the invention and thus also in the other examples.

[0072] Different types of inductively heated heating elements 1 can be used in the devices already shown to heat a process gas. The one in Fig. The example shown in Figure 3 features an exemplary heating element 1. Several straight tubes, acting as flow channels 11, are bundled together and can be heated by electrical induction. Process gas flows over the outer surface 10 of the bundle forming the heating element 1 and through the inner flow channels 11.

[0073] Another example is the one in Fig. Four radiators are shown. In radiator 1, several tubes are bundled together as flow channels 11 and additionally rotated in a helical shape. The process gas flows along the outer surface 10 of the bundle and through the tubes to be heated. The extended path of the inner flow channels 11 and the turbulence generated by the coils allow for improved heat transfer from radiator 1 to the process gas.

[0074] The in Fig. Example 5 shows a heating element 1 shaped like a cylinder. The cylinder is traversed by several internal, straight flow channels 11. In addition to the outer surface 10, the inner surfaces of the flow channels 11 also constitute a surface on which the process gas is heated. In comparison to the first two heating element examples, heating element 1 consists of Fig. 5 only from one body, which is advantageous for heat conduction in radiator 1.

[0075] The example according to Fig. Figure 6 also represents a cylindrical heating element 1 whose outer surface 10 is exposed to the process gas flow. In this example, the internal flow channels 11 are formed as a helix or coils. The extended flow path and the turbulence generated by the coils allow for improved heat transfer from the heating element 1 to the process gas. This type of heating element 1 can be manufactured, for example, by casting or additive manufacturing.

[0076] Another example of a cylindrical radiator 1 is shown in Fig. Figure 7 represents several composite disks, which are traversed by straight or angled bores serving as flow channels. The composite disks, with the internal flow channels 11 used for heat transfer and the outer surface 10, form a cylinder whose overall length can be extended as desired by adding further disks.

[0077] An example of a non-linearly wound electrical coil 3 is in Fig. Figure 8 illustrates this. The electrical coil 3 has a higher winding density (number of turns per unit length of the coil) in the region at the inlet 5 than in the region at the outlet 6. The amount of induced energy can be controlled by compressing and stretching the windings of the electrical coil 3. The number of turns per unit length is greater in the region of the inlet 5 than towards the outlet 6. This allows for greater heating of the at least one heating element 1, located inside the housing 2, in the areas where the cooling effect of the heating process gas is greater.

[0078] Another example of a possible coil arrangement for the homogeneous heating of at least one radiator 1 is shown in Fig.Figure 9 is shown as a combination of two electrical coils 3a and 3b. In this example, a higher power is applied to the first electrical coil 3a than to the second electrical coil 3b. This ensures that the at least one heating element 1, which is arranged in the housing 2, is heated homogeneously despite the different cooling effects of the process gas flowing from the inlet 5 to the outlet 6.

[0079] In tests, with an effective power of approximately 9 kW used for inductive heating, a non-preheated process gas was heated to a temperature of over 1100 °C.

[0080] In the figures, identical elements are marked with the same reference symbols.

Claims

[1] Device for forming a hot process gas flow, in which a process gas flows through a housing (2) made of a refractory material with a predeterminable volume flow from an inlet (5) to an outlet (6) and at least one heating element (1) is arranged inside the housing (2) and is made of material that can be heated by means of electrical induction and on which at least one flow channel (11) is provided through which the process gas flows or around it, and the internally hollow housing (2) is enclosed by at least one non-linearly wound electrical coil (3), in which the number of turns is reduced over the length of the electrical coil (3) starting from the inlet (5) towards the outlet (6), and the at least one electrical coil (3) is connected to an electrical voltage source with which alternating voltage or a pulsed direct voltage is applied to the electrical coil (3), and / or on the outside of the housing (2) in the flow direction of the process gas, at least two electrical coils (3a, 3b) are arranged one after the other and each is connected to an electrical voltage source with which alternating voltage or a pulsed direct voltage is applied to the electrical coil (3a, 3b), wherein the first electrical coil (3a), which is arranged in the region of the inlet (5), is operated with a greater electrical power than at least one further electrical coil (3b) arranged downstream of the first electrical coil (3a) in the flow direction of the process gas. [2] Device according to claim 1, characterized by that a passivating oxide layer is formed on surfaces of the heating element (1) which are in contact with process gas. [3] Device according to one of the preceding claims, characterized bythat the process gas flows along the inner wall of the housing (2) and the outer surface (10) of the heating element (1) and / or through at least one flow channel (11) of the at least one heating element (1) for its heating. [4] Device according to one of the preceding claims, characterized by that the number of turns of the at least one electrical coil (3) continuously decreases over the length of the at least one electrical coil (3) in the flow direction of the process gas. [5] Device according to one of claims 1 to 3, characterized bythat a controlled inductive heating of the heating element (1) can be achieved, and the process gas can be heated by at least two electrical coils (3a, 3b) with a different number of turns over their length, wherein the first electrical coil (3a) arranged in the region of the inlet (5) has a greater number of turns than an electrical coil (3b) arranged subsequently or in the region of the outlet (6). [6] Device according to claim 1, characterized by that the at least one heating element (1) is formed from a nickel-based alloy and / or from zirconium and / or its alloys and / or a refractory metal-based alloy - in particular a tantalum-, tungsten-, niobium-, or molybdenum-based alloy. [7] Device according to one of the preceding claims, characterized bythat one or more heating elements (1) are arranged as a bundle with at least three, preferably more than four flow channels (11) or as a composite body in the interior of the housing (2) or the at least one heating element (1) is designed in the form of a straight tube bundle with at least three, preferably more than four flow channels (11), in which the individual flow channels (11) are electrically insulated from one another and the spaces between the individual flow channels (11) are filled with electrically non-conductive material, and in which the process gas to be heated flows around the outer surface of the bundle and through the inner flow channels (11) or the heating element (1) is designed in the form of a bundle of at least three, preferably more than four, flow channels (11) rotated as a helix, in which the individual flow channels (11) are electrically insulated from one another and the spaces between the individual flow channels (11) are filled with electrically non-conductive material, and in which the process gas to be heated flows around the outer surface (10) of the bundle and through the inner flow channels (11) or the heating element (1) in the form of a cylinder, which is traversed by at least three, preferably more than four internal flow channels (11), the diameter of which is greater than 2 mm and the flow channels (11) are designed to run in a straight line or the heating element (1) in the form of a cylinder which is traversed by at least three, preferably more than four, internal flow channels (11) whose diameter is greater than 2 mm and which rotate as a helix or are designed as turns or the heating element (1) is designed in the form of several assembled discs which are traversed by at least three, preferably more than four, inner flow channels (11) which have a minimum diameter of 2 mm and which can run at a right angle or at an angle to the end face. [8] Device according to one of the preceding claims, characterized by that the housing (2) is made of quartz glass, Al2O3, ZrO2 or MgO or a chemical compound and / or a mixture of these materials. [9] Device according to one of the preceding claims, characterized bythat a fireproof closure element (4) is arranged at the inlet (5) for the process gas to prevent backflow of heated process gas. [10] Device according to one of the preceding claims, characterized by that the housing (2) is enclosed by a second (7) and / or a third housing (8), so that process gas flows through a gap between the first housing (2) and the second housing (7) and / or through a gap between the second housing (7) and the third housing (8) in countercurrent or cocurrent to the process gas flow to preheat the process gas. [11] Device according to one of the preceding claims, characterized bythat a second housing (7) and / or a third housing (8) is provided on its surfaces facing towards the heating element (1) with a reflective surface coating made of titanium nitride, or aluminium chromium nitride, or titanium aluminium nitride, or another coating which reflects electromagnetic radiation in the wavelength range of infrared light and which does not serve for inductive heating. [12] Device according to one of the preceding claims, characterized by that the temperature of the process gas emerging from the outlet can be regulated by adjusting the process gas volume flow and / or the electrical power with which the at least one electrical coil (3, 3a, 3b) is operated. [13] Device according to one of the preceding claims, characterized bythat the geometry of the at least one heating element (1) and / or the inlet (5) is designed geometrically and / or by additional equipment in such a way that the heat transfer between the at least one heating element (1) and the process gas is maximized, in particular by swirling the process gas flow. [14] Device according to one of the preceding claims, characterized by that the outlet (6) is designed geometrically and / or by an apparatus such that the flow of the process gas is modified such that the heat transfer to any solid and / or melt and / or liquid and / or gas and / or plasma placed in the exiting process gas stream is maximized. [15] Device according to one of the preceding claims, characterized bythat the outlet (6) is designed geometrically and / or by an apparatus such that the average flow velocity of the process gas and / or the geometry of the process gas flow is modified, in particular by means of a correspondingly geometrically designed nozzle.

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