WO2025067846A1 - Device for forming a hot process gas flow - Google Patents

Abstract

A heating element (1) having at least one flow channel (11), through or around which the process gas flows, is provided in the device housing (2). At least one non-linearly wound electric coil (3) that is connected to an electric voltage source is arranged in the housing (2), and/or at least two electric coils (3a, 3b) are successively arranged on the outer side of the housing (2) and connected to an electric voltage source. The first electric coil (3a) is operated at a higher electric power than the at least one additional electric coil (3b). The number of windings of an electric coil (3) is selected such that in the first third of the length of the at least one heating element, at least 25 % more power can be inductively coupled into the heating element than in the region of the output (6), or in the event that at least one first electric coil (3a) and an additional electric coil (3b) are used, by means of the first electric coil (3a) at least 25 % more power can be coupled into the heating element (1) than in the region of the output (6).

Description

Device for forming a hot process gas stream

The invention relates to a device for forming a hot process gas stream, with which a hot gas flare is provided for heating products and for use in production processes.

It can be used, for example, for melting metal or glass or for heat treatment or heating of various components or materials. The core of the invention lies in the inductive heating of a heater, 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.

The invention enables the provision of thermal energy and sufficient heating of a process gas up to very high temperatures using electrical energy alone, 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. Metallurgical processes include the melting and holding of metals or glass, the heating of heat treatment furnaces, and the thermal treatment of any material, including bulk materials.

Hot gas generators based on electrical 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 to power outputs of approximately 100 kW.

These performance limits are significantly extended to temperatures of over 1000 °C and power levels in the MW range by using inductive energy input.

Burners are also in use, where the desired heat is achieved by oxidizing a fuel. These use a variety of hydrocarbon compounds as fuel, which release CO2 during oxidation.

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 respective fluid. 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.

According to the invention, this object is achieved by a device having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features defined in the appended claims.

In the device according to the invention, a process gas flows through a preferably hollow-cylindrical housing made of a refractory material with a predeterminable volume flow from an inlet to an outlet to form a hot process gas stream. After the outlet, a flare of the hot process gas forms. Arranged inside the housing is at least one heating element made of a material that can be heated by electrical induction and on which at least one flow channel is present through which the process gas flows. By means of a material, it should be understood that the material of the heating element contains at least 90% by mass of a material that can be heated by electrical induction.

The internally hollow housing is enclosed by at least one non-linearly wound electrical coil, in which the number of turns is reduced over the length of the electrical coil, starting from the inlet towards the outlet.

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.

The number of turns of the electrical coil should be selected so that in the first third of the length of at least one radiator, from the inlet for the process gas at least 25% more power can be inductively coupled into the heater than in the area of the outlet for the process gas. For this purpose, in the area of the electrical coil arranged directly or close to the inlet for the process gas, there can be at least 20%, preferably greater than 30% more turns per length of the electrical coil than is the case in the area of the outlet and areas close to the outlet. At least 20%, preferably greater 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 encloses the heater in the area of the inlet should have at least 20%, preferably greater than 30% more turns than at least one electrical coil arranged downstream in the direction of flow.

In addition to changing the winding density of the coil, this effect can also be achieved by changing the cross-section or profile of the coil, or by changing the orientation of the coil profile. For example, an electrical coil can also have windings that are not rotationally symmetrical, but rather have windings with a polygonal cross-section. An electrical coil can also have different edge lengths, so that each electrical coil, for example, has a different height and width on its sides.

In an alternative according to the invention, at least two electrical coils can be arranged one after the other on the outside of the housing in the flow direction of the process gas, each connected to an electrical voltage source with which alternating voltage or a pulsed direct voltage is applied to the electrical coil. The first electrical coil, arranged in the inlet region, is operated with a higher electrical power than at least one further electrical coil arranged downstream of the first electrical coil in the flow direction of the process gas. Here, too, at least 25% more power should be able to be coupled into the heater in the inlet region than in the outlet region.

The introduction of more energy into the inlet side of the radiator than into the outlet side is advantageous, since The colder incoming process gas has a greater cooling effect on the at least one heating element than at the outlet where the heated process gas has reached operating temperature. In order to keep the temperature of the at least one heating element at least almost uniform despite the cooling effect of the heating process gas decreasing over the length, a different energy supply and thus different inductive heating of the element over the length is advantageous. This allows the entire length of the heating element to be fully utilized and the operating temperature to be reached more quickly, and temperature-related mechanical stresses in the heating element can be reduced or even completely avoided.

The process gas flows along the inner wall of the housing and the surface of at least one heating element to heat it. The process gas can flow both around and through the at least one heating element, thereby heating the process gas along the flow path from inlet to outlet.

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

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

The at least one heating element may be made of zirconium and/or its Alloys and/or an alloy with the main component being a refractory metal—in particular tantalum, tungsten, niobium, or molybdenum—and other alloying elements, in particular chromium and/or titanium. A nickel-based alloy can also be used to manufacture a radiator. A base alloy contains at least 50% of these metals by mass.

The respective chemical compound, metal or alloy has a minimum proportion of 95% by mass of the radiator material.

For example, an intermetallic compound of molybdenum, silicon, and/or tungsten, and especially molybdenum and silicon, may contain such additives. These can include, in particular, 1% to 2% by mass of aluminum and < 1% by volume of other elements.

It may also contain a carbide which is bonded to a transition metal from group 4, 5 and 6 of the periodic table of elements and/or a nitride with a transition metal from group 4 and/or a silicide with a transition metal from group 4, 5 and 6, in particular an intermetallic compound of molybdenum and silicon and/or molybdenum, silicon and tungsten and/or further additives and/or a compound of silicon and carbon and/or further additives.

The respective chemical compound, metal or alloy has a minimum proportion of 95% by mass of the radiator material.

The protective oxide layer on the surface of the at least one heating element can be formed outside the device prior to use. This can be achieved by treating the at least one heating element in an oxygen-containing atmosphere, better still in an oxygen-containing atmosphere heated to several hundred degrees, or by treating it 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 particularly applies to internal or external flow channels and the lateral surface(s).

For heating purposes, 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.

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

Controlled inductive heating of the heater and the process gas can also be achieved by at least two electrical coils with different numbers of turns along their length, whereby the first electrical coil arranged in the inlet region has a greater number of turns than an electrical coil arranged downstream in the flow direction of the process gas or in the outlet region. In addition, the first electrical coil can be operated with greater power than other electrical coils arranged downstream in the flow direction of the process gas through the heater.

Through controlled inductive heating of the heater, the incoming process gas can be heated at a higher heating rate in the inlet area and then at a lower heating rate toward the outlet. This prevents large temperature differences between the inlet area and the outlet area of the process gas on at least one heater.

If only one non-linear electrical coil is used in the device according to the invention, at least one additional electrical power supply for additional electrical coils can be dispensed with. If at least two equally linear electrical coils are used, this has the advantage of being able to use standardized coils. One or more heating elements can be arranged inside the housing as a bundle with at least three, preferably more than four, flow channels or as a composite body. Flow channels can preferably be tubular or hollow cylindrical.

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 one another and the spaces between the individual flow channels 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.

Several heating elements can also be arranged inside the housing as a layered, contactless and electrically insulated arrangement with at least three, preferably more than four elements, such as tubes. The flow channels through which the flow occurs and, if applicable, the outer surface around which the flow occurs can preferably be tubular.

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 one another, and the spaces between the individual flow channels 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.

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 whose diameter is greater than 2 mm and the flow channels are designed to run in a straight line.

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 whose diameter is greater than 2 mm and the flow channels are designed to run in a straight line. It is also possible for a radiator in the form of a cylinder to be traversed by at least three, preferably more than four, internal flow channels whose diameter is greater than 2 mm and which rotate as a helix or are designed as turns.

Alternatively, a radiator can be designed in the form of several assembled discs which are traversed by at least three, preferably more than four, internal flow channels which have a minimum diameter of 2 mm and which can run at a right angle or at an angle to the end face.

The at least one heating element can also be in the form of an arrangement of at least three, preferably more than four straight tubes, each with a flow channel, which is layered within the housing by an electrically non-conductive, preferably ceramic structure, in a contactless layered manner. The individual tubes are electrically insulated from one another and contactless, and the spaces between the individual tubes are filled with electrically non-conductive material. The process gas to be heated flows around the free outer surface of the tubes and through the inner flow channel. Individual tubes of the arrangement can have other media flowing through them that differ from the process gas. The media can be in any state of aggregation. The electrically non-conductive, preferably ceramic structure does not have to be present over the entire length of the heating element arrangement; the smallest possible number of structural elements over the length is advantageous, for example 5 structures per meter of length.

The diameter of a single inner flow channel should be greater than 2 mm. The contactless layered arrangement of the radiator, consisting of at least three, preferably more than four tubes, can almost completely fill the cross-sectional area of the first inner casing.

If flow channels are not designed in a straight line, but for example in the form of a helix, the length of the inner flow channels of at least one heating element can be increased by the windings, which is advantageous for the heat transfer to the process gas can be utilized and it allows the length of the radiator to be reduced accordingly.

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

A fireproof closure element can be arranged at the process gas inlet to prevent backflow of heated process gas. This is particularly advantageous when the process gas is guided through several housings, as explained below, which are arranged one inside the other and enclose at least one heating element. This reduces energy and, in particular, heat losses, and ensures that the process gas enters exclusively through the appropriately dimensioned inlet.

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 in countercurrent or cocurrent to the process gas flow to preheat the process gas.

A second housing and/or a third housing can be provided on their surfaces facing the heating element with a reflective surface coating made 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 serve, or only serves to a very small extent, for inductive heating.

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

The geometry of the at least one heating element and/or the inlet can be designed geometrically and/or by means of additional equipment in such a way that the heat transfer between the at least one heating element and the process gas can be maximized, in particular by swirling the process gas flow. For this purpose, surfaces on the heating element that are subject to and/or flowing around the process gas can be provided with contour elements.

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

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

Due to the windings of the tubes, the length of the inner flow channels of at least one heater can be increased, which can be advantageously used for heat transfer to the process gas.

A radiator can be designed in the form of at least one cylinder, which is traversed by at least three, preferably more than four, internal flow channels. The internal flow channels can straight or to increase their length, rotated as a helix or formed as a coil.

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

A radiator can be designed in the form of at least two assembled discs traversed by at least three, preferably more than four, flow channels. The flow channels can be straight or angled to the front surface of the disc. The diameter of an individual inner flow channel should be greater than 2 mm.

The ratio of the area of the cross section of the inner flow channels of the at least one heating element to the area of the annular gap present between the outer surface of the at least one heating element and the inner wall of the first housing should be between 1:2 and 4:1.

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

It is also possible to use the aforementioned heater geometries with additional contour elements (elevations, depressions) to increase the total surface area of at least one heater. These can also achieve a beneficial turbulence in the process gas flow.

The process gas can be air, but also another gas or gas mixture that may be advantageous for the respective heating process. This includes, in particular, inert gases that do not influence the elements, materials, and objects to be heated. can avoid.

In the invention, the temperature of the process gas exiting the outlet can be controlled by adjusting the process gas volume flow and/or the electrical power used to operate the at least one electrical coil. For this purpose, the temperature of the process gas at the outlet can be determined, thus establishing a control loop.

The amount of heat transferred is determined by the surface area of the at least one heating element around which the process gas flows, the surface area of the internal flow channels, the number and length of the at least one heating element and the internal flow channels, as well as 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 efficiency.

The heat output of the device can be controlled via the electrical power supplied, the quantity and pressure of the process gas flowing into the device, and the flow temperature of the process gas entering the device. In addition, as already mentioned, process gas can be preheated in or upstream of the device. External preheating of the process gas upstream of the device can be achieved, for example, using a resistance-heated device. However, it is also possible to recirculate process gas into the device using the heat it contains. For this purpose, the slightly cooled process gas that has already been used for heating can be sucked in from the heating zone after use and returned to the inlet of the device.

The process gas supply to the device can be achieved with a compressor system for multiple devices or with a compressor associated with the device according to the invention, which is preferably controllable or regulatable. Furthermore, a flow condition particularly favorable for heat transfer from the at least one heating element to the process gas can be set in the process gas supply. 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 in such a way 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 turbulence in the process gas flow. Contour elements that extend the path of the process gas along a surface of the at least one heating element used for heating and/or lead to turbulence can also be used for this purpose.

The device may include an additional housing made of a fireproof material that externally encloses the electrical coil(s). This additional housing can serve as protection against the high temperatures.

The process gas outlet from the device can also be optimized for specific applications. The outlet can be designed geometrically and/or by a movable device to modify the flow of the process gas in such a way that the heat transfer to any solid, melt, liquid, gas, and/or plasma present in the exiting process gas stream can be maximized.

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

The selection of at least one electrical coil (design, electrical conductivity and number of turns) as well as the frequency of the electrical voltage with which it is operated can be optimized taking into account the geometry and material of the radiator(s). For the optimal frequency for heating at least one radiator with a cylindrical geometry, 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 following requirement for the ratio between the individual radiator diameter d and the current penetration depth [according to Benkowsky 1990] results in the frequency selection:

The frequency and the electromagnetic properties of the material of the radiator(s) are included in the formula for the current penetration depth [according to Fasholz 1984 and Benkowsky 1990] as follows:

1 px 10 ⁷

Ö = — X p - - 503

ö [mm] = Stromeindringtiefe 2 IT |i _r xf

ö [mm] = current penetration depth

p_r= relative Permeabilität f [Hz] = Frequenz P = specific electrical resistance

p _r = relative permeability f [Hz] = frequency

The above formula describes the current penetration depth. This number indicates the thickness up to which 86% of the induced energy is converted into heat. The remaining 14% is absorbed by deeper layers. Due to this fact, there is an optimized relationship between the total diameter of the heating element and the current penetration depth for inductive heating. In addition to the frequency, this formula also takes into account the temperature-dependent material properties of the body to be heated, such as the specific electrical resistance and relative permeability.

Compared to other electrical heating systems, the performance limits of the invention can be extended to applications at temperatures above 1000 °C and power outputs in the MW range. The invention will be explained in more detail below by way of example.

Showing:

Figure 1 shows an example of a device according to the invention with a non-linear electrical coil and a cylindrical heating element with a surface structure

Figure 2 a second example with two different electrical coils and a cylindrical heater and a possibility for preheating process gas

Figure 3 an example of a radiator made of a tube bundle

Figure 4 an example of a radiator made of a twisted tube bundle

Figure 5 an example of a radiator made of a cylinder with internal flow channels

Figure 6 shows an example of a radiator consisting of a cylinder with internal flow channels that are rotated.

Figure 7 shows an example of a radiator made up of several assembled discs with internal flow channels

Figure 8 an example of a non-linear wound electrical coil

Figure 9 an example of two electrical coils with different power

Figure 10 shows an example of a radiator variant consisting of a contactless layered arrangement of tubes in a square profile as a housing

Figure 11 shows an example of a radiator variant consisting of a contactless layered arrangement of tubes in a round tube as a housing In the example shown in Figure 1, process gas flows into an inlet 5 from a compressor (not shown) of the device. Along the outer surface, which has an exemplary spiral-shaped structure, and through the internal flow channels of the at least one heating element 1, the process gas flows through a housing 2 made of refractory material towards the outlet 6 of the device, where it can be used for subsequent further heating downstream of the outlet 6, utilizing the high temperature of the heating element 1. A structure on the surfaces over which the process gas flows can be advantageous for heat transfer compared to a smooth surface.

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 designed to be non-linear in order to introduce a different amount of energy into the at least one heating element 1 over its length. More energy is introduced inductively in the area of the inlet side of the at least one heating element 1 than in the area of the outlet side. The heating element 1 has a resistant, passivating oxide layer formed before use on its surfaces that come into contact with the process gas and is, in this case, formed, for example, from a nickel-based alloy or from 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. In a base alloy, the aforementioned metals are contained in a proportion of at least 50% by mass. These materials can also be used in the examples described below. In a nonlinear 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 heater 1 closest to the inlet 5 for the process gas than in regions of the electrical coil 3 further downstream toward the outlet 6. 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, which should preferably be done 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 heater 1.

A fireproof closure element 4 is arranged at the inlet 5 to prevent backflow of heated process gas.

The example shown in Figure 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 different power ratings are used. The first electrical coil 3a, located close to the inlet 5, has a higher winding density and is operated with a higher electrical power rating than a second electrical coil 3b or another electrical coil located closer toward the outlet 6.

After passing through the inlet 5, the process gas flows for preheating and insulating the electrical coils 3a and 3b, first in the gap between the second housing 7 and the third housing 8, then in the opposite direction in the gap between the second housing 7 and the first housing 2. From the aforementioned gap, the process gas now flows into the space between the surface of the heating element 1, which in the example is a cylindrical body, and the first housing 2, as well as through the internal flow channels of the heating element 1. Heating to the desired process temperature of the process gas takes place at these surfaces. The process gas reaches the outlet 6 through the intermediate space and the flow channels 11. 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.

Different types of inductively heated heaters 1 can be incorporated into the devices already shown for heating a process gas. The example shown in Figure 3 has an exemplary heater 1. Several straight tubes as flow channels 11 are combined in a bundle and can be heated by electrical induction. Process gas flows over the outer surface 10 of the bundle, which forms the heater 1, and through the inner flow channels 11.

Another example is the heater 1 shown in Figure 4. In the heater 1, several tubes are bundled as flow channels 11 and additionally rotated in a helix. 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 windings enable improved heat transfer from the heater 1 to the process gas.

The example shown in Figure 5 has a heater 1 configured as a cylinder. The cylinder is traversed by several internal, linear flow channels 11. In addition to the outer surface 10, the internal surfaces of the flow channels 11 also represent a surface on which the process gas is heated. Compared to the first two heater examples, the heater 1 in Figure 5 consists of only one body, which is advantageous for heat conduction within the heater 1.

The example shown in Figure 6 also represents a cylindrical heater 1, around whose outer surface 10 the process gas flows. In this example, the internal flow channels 11 are configured as a helix or coils. The extended flow path and the turbulence generated by the coils allow for improved heat transfer from the heater 1 to the process gas. This type of heater 1 can be manufactured, for example, by casting or additive manufacturing.

Another example of a cylindrical radiator 1 is shown in Figure 7 in the form of several assembled discs, which are traversed by straight or angled holes as flow channels. ten discs, with the inner flow channels 11 used for heat transfer and the shell surface 10, form a cylinder which can be extended as desired in its total length by adding further discs.

An example of a non-linearly wound electrical coil 3 is shown in Figure 8. The electrical coil 3 has a greater winding density (number of turns per length of the electrical coil) in the area at the inlet 5 than in the area at the outlet 6. By compressing and stretching the windings of the electrical coil 3, the amount of induced energy can be controlled. The number of turns per length is greater in the area of the inlet 5 than in the direction of the outlet 6. This makes it possible to heat the at least one heating element 1, which is located inside the housing 2, more strongly in the areas where the cooling effect of the heating process gas is greater.

Another example of a possible coil arrangement for homogeneous heating of the at least one heating element 1 is shown in Figure 9 as a combination of two electrical coils 3a and 3b. In this example, a higher power is introduced into the first electrical coil 3a than into the second electrical coil 3b. As a result, the at least one heating element 1, which is arranged in the housing 2, is heated homogeneously despite the varying cooling effect of the process gas flowing from the inlet 5 to the outlet 6.

The example shown in Figure 10 for several heating elements 1 in a housing 2 is designed as a contactless layered arrangement of straight tubes. In the heating elements 1, several tubes, each with a flow channel 11 and a jacket surface 10, are layered contactlessly to one another and arranged in a defined manner separated from one another by an electrically non-conductive structure 12. The process gas flows through the flow channels 11 for heating and along the jacket surface 10 without contact with contact points of the structure 12 for the defined arrangement. For optimized utilization of the cross-section, a rounded square tube can be used as the surrounding housing 2. The structure 12 serves for electrical insulation as well as the defined arrangement of the individual tubes and is In the example shown, the electrically non-conductive structure is represented as a grid-like structure made up of insulation elements connected perpendicular to one another.

Another example is the heating element arrangement shown in Figure 11. In this arrangement, several heating elements 1 are arranged as straight tubes in a tubular housing 2, layered in contact with one another by an electrically non-conductive structure 12. The process gas flows through the flow channels 11 to be heated and along the casing surface 10 without contact with the electrically non-conductive structure 12. In the example shown, the structure 12 for the defined arrangement of the heating elements 1 in the housing 2 is a uniform stacking of elements with a hexagonal cross-section; however, other arrangements with polygons in various housing geometries are also possible. In a form not shown, the flow channels 11 can also have polygonal cross-sections.

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

In the figures, identical elements are identified and labeled with the same reference symbols.

Claims

Patent claims 1. Device for forming a hot process gas stream for melting and keeping metals, including glass, heating heat treatment furnaces and thermally treating any material, including bulk materials, in which a process gas with temperatures of at least 1000 °C flows through a housing (2) made of a refractory material with a predeterminable volume flow from an inlet (5) to an outlet (6), and in the interior of the housing (2) at least one heating element (1) is arranged, which is formed from a material that can be heated by means of electrical induction and on which at least one flow channel (11) is present, through which the process gas flows or around, and the internally hollow housing (2) is enclosed by at least one non-linearly wound electrical coil (3), in which the number of turns over the length of the electrical coil (3) is reduced 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 the alternating voltage or a pulsed direct voltage is applied to the electrical coil (3), and/or at least two electrical coils (3a, 3b) are arranged one after the other on the outside of the housing (2) in the flow direction of the process gas and are each 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; wherein the number of turns of an electrical coil (3) is selected such that in the first third of the length of the at least one heating element, starting from the inlet (5) for the process gas, at least 25% more power can be inductively coupled into the heating element than in the region of the outlet (6) for the process gas, or when using at least one first electrical coil (3a) and a further electrical coil (3b) which is arranged downstream of the first electrical coil (3a) in the flow direction of the process gas, at least 25% more power can be coupled into the heating element (1) in the region of the inlet (5) by means of the first electrical coil (3a) than in the region of the outlet (6). 2. Device according to claim 1, characterized in 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 in that 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 in that the number of turns of the at least one electrical coil (3) decreases continuously 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 in that a controlled inductive heating of the heating element (1) is achievable, and the process gas, through at least two electrical coils (3a, 3b) with different numbers 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) is arranged, is heatable and there are at least 20% more turns per length of the electrical coil near the inlet (5) for the process gas than the number of turns in the area of the outlet (6) and areas close to the outlet. 6. Device according to one of the preceding claims, characterized in that the at least one heating element (1) consists of a nickel-based alloy, 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 in that the material from which the at least one heating element (1) is formed is a carbide with a transition metal from group 4, 5 and 6 of the periodic table of elements and/or a nitride with a transition metal from group 4 and/or a silicide with a transition metal from group 4, 5 and 6, in particular an intermetallic compound of molybdenum and silicon and/or molybdenum, silicon and tungsten and/or further additives and/or a compound of silicon and carbon and/or further additives. 8. Device according to one of the preceding claims, characterized in that one or more heating elements (1) is/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/are arranged 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 is circulated around the outer surface of the bundle and flows 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) rotating 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) is designed in the form of a cylinder, which is traversed by at least three, preferably more than four inner 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) is designed in the form of a cylinder, which is traversed by at least three, preferably more than four inner flow channels (11), the diameter of which is greater than 2 mm and which rotate as a helix or are designed as turns, or the A heating element (1) in the form of several assembled discs, which are traversed by at least three, preferably more than four, internal flow channels (11), which have a minimum diameter of 2 mm and which can run at right angles or at an angle to the end face. Or at least three, preferably more than four heating elements (1) in the form of an arrangement of elements layered in a defined pattern that are contactless with one another and have an internal flow channel (11), in which the individual heating elements (1) are electrically insulated from one another and arranged in a defined manner by an electrically non-conductive structure, preferably ceramic (12), and the spaces between the individual heating elements (1) are filled with electrically non-conductive material. and in which the process gas to be heated flows around the outer surface (10) of the heating elements (1) which is not in contact with the structure (12) and through the inner flow channels (11). 9. Device according to one of the preceding claims, characterized in that the housing (2) is formed from quartz glass, Al2O3, ZrO2 or MgO or a chemical compound and/or a mixture of these materials. 10. Device according to one of the preceding claims, characterized in that a fire-resistant closure element (4) is arranged at the inlet (5) for the process gas to prevent backflow of heated process gas. 11. Device according to one of the preceding claims, characterized in 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. 12. Device according to one of the preceding claims, characterized in that 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 aluminum chromium nitride, or titanium aluminum nitride, or another coating reflecting electromagnetic radiation in the wavelength range of infrared light, which coating is not used for inductive heating. 13. Device according to one of the preceding claims, characterized in that the temperature of the process gas emerging from the outlet is controlled 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, is controllable. 14. Device according to one of the preceding claims, characterized in that 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. 15. Device according to one of the preceding claims, characterized in that the outlet (6) is designed geometrically and/or by an apparatus in such a way that the flow of the process gas is modified in such a way 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. 16. Device according to one of the preceding claims, characterized in that the outlet (6) is designed geometrically and/or by an apparatus in such a way 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.