Apparatus for forming a thermal process gas flow

Abstract

A heating element (1) is arranged in the device housing (2), which heating element has at least one flow channel (11) through or around which the process gas flows. At least one non-linearly wound electrical coil (3) connected to a voltage source is arranged in the housing (2), and / or at least two electrical coils (3a, 3b) are arranged one behind the other on the outside of the housing (2) and connected to the voltage source. The first electrical coil (3a) operates at a higher electrical power than the at least one additional electrical coil (3b). The number of turns of the electrical coil (3) is selected such that, at a first third of the length of the at least one heating element, the power that can be inductively coupled to the heating element is at least 25% greater than in the region of the outlet (6), or, using the at least one first electrical coil (3a) and an additional electrical coil (3b), the power that can be inductively coupled to the heating element is at least 25% greater than in the region of the outlet (6) through the first electrical coil (3a). The power that can be coupled to the heating element (1) is at least 25% more than in the region of the outlet (6).

Description

Technical Field

[0001] This invention relates to an apparatus for forming a hot process gas stream, which provides a hot gas flame for heating products and use in production processes. For example, the hot gas flame can be used to melt metals or glass, or for the heat treatment or heating of various components or materials.

[0002] The core of this invention lies in the induction heating of the heating element, the transfer of heat to the circulating process gas, and the use of this hot process gas. In this respect, this invention serves as a possible decarbonization replacement for gas burners.

[0003] This invention enables the use of electricity alone to provide heat and fully heat process gases to very high temperatures, replacing commonly used gas burners. Therefore, this invention facilitates the decarburization of heating systems. The device is particularly suitable for metallurgical processes. However, it can also be used in many other applications. Metallurgical processes include the melting and holding of metals or glass, heating in heat treatment furnaces, and heat treatment of any material, including bulk materials. Background Technology

[0004] Resistance-heated hot gas generators (hot air guns - hot air cannons) are also commonly used in the market, but their output is currently limited to a gas temperature of about 1000 °C and an output of about 100 kW.

[0005] By using inductive energy input, these power limits are significantly extended to temperatures exceeding 1000 °C and outputs in the MW range.

[0006] In addition, a burner is used to generate the required heat by oxidizing the fuel. A wide variety of hydrocarbons are used as fuel, which results in the release of CO2 during the oxidation process.

[0007] Thermally induced mechanical stress may occur when operating induction heating devices that are also used to heat fluids to higher temperatures. Large temperature differences between the inlet and outlet sides have adverse effects on the corresponding fluids. Summary of the Invention

[0008] Therefore, the object of the present invention is to propose the possibility of heating a process gas stream such that the process gas stream reaches a temperature of at least 1000 °C without releasing CO2, can achieve an efficiency of at least 30%, and the process gas is heated as uniformly as possible in the heating device.

[0009] According to the invention, this objective is achieved by a device having the features of claim 1. Advantageous embodiments and further embodiments of the invention can be achieved by the features described in the appended claims.

[0010] In the apparatus according to the invention, process gas flows from an inlet through a preferably hollow cylindrical shell made of refractory material to an outlet at a predetermined volumetric flow rate to form a hot process gas flow. A hot process gas flame is formed after the outlet. At least one heating element is arranged within the shell, the heating element being formed of a material that can be inductively heated, and having at least one flow channel therethrough through and / or around which the process gas flows. The term "through…material" should be understood to mean that the material of the heating element contains at least 90% by mass of a material that can be inductively heated.

[0011] The hollow shell is surrounded by at least one non-linearly wound electric coil, the number of turns of which decreases along the length of the coil from the inlet to the outlet.

[0012] At least one electric coil is connected to a voltage source through which an AC voltage or a pulsed DC voltage is applied to the electric coil.

[0013] The number of turns of the coil should be selected such that, in the first third of the length of the at least one heating element (measured from the process gas inlet), the power inductively coupled to the heating element is at least 25% greater than in the process gas outlet region. To this end, in the region where the coil is directly located or near the process gas inlet, the winding per unit length of the coil may be at least 20% more, preferably more than 30% more, than in the outlet region and the region near the outlet. Measured from the inlet, the winding should be at least 20% more, preferably more than 30% more, over at least 30% of the length of the corresponding coil. If there is more than one coil, the coil surrounding the heating element, at least in the inlet region, should have at least 20% more, preferably more than 30% more winding than at least one coil arranged downstream along the flow direction.

[0014] In addition to changing the winding density of the coil, this effect can also be achieved by changing the cross-section of the coil, the outline of the coil, or the orientation of the coil outline.

[0015] For example, an electric coil can also have non-rotationally symmetric windings, but with a polygonal cross-section. Electric coils can also have different edge lengths, and thus, corresponding electric coils can, for example, have different lateral heights and widths.

[0016] In an alternative according to the invention, at least two coils may be arranged one after another outside the housing along the flow direction of the process gas, and each coil is connected to a voltage source through which an AC voltage or a pulsed DC voltage is applied to the coil. The first coil arranged in the inlet region operates with a greater electrical power than at least one additional coil arranged downstream of the first coil along the flow direction of the process gas. Similarly, the power that can be coupled to the heating element in the inlet region should be at least 25% greater than that in the outlet region.

[0017] It is advantageous to introduce more energy into the inlet region of the heating element compared to the outlet region, because the cooling effect of the cooler incoming process gas on the at least one heating element is greater than at the outlet where the heated process gas has already reached the operating temperature. Although the cooling effect of the heated process gas weakens along its length, it is advantageous to supply varying amounts of energy to inductively heat the element to different degrees along its length in order to maintain at least nearly uniform temperature of the at least one heating element. The entire length of the heating element can be used, the operating temperature can be reached more quickly, and temperature-related mechanical stresses in the heating element can be reduced or even completely avoided.

[0018] The process gas flows along the inner wall of the housing and the surface of the at least one heating element to heat it. The process gas can flow around and through the at least one heating element to heat the process gas along a flow path from inlet to outlet.

[0019] The housing and the at least one heating element should each be made of a material whose melting temperature is higher than the maximum temperature of the process gas being heated. The device is used to transfer heat energy, inductively introduced into the at least one heating element, to the process gas.

[0020] The at least one heating element should be made of a paramagnetic and high-temperature resistant material, with an advantageous passivated oxide layer on its surface. When air or other oxygen-containing gas mixtures are used as the process gas, this anti-oxidation layer protects the at least one heating element from further undesirable reactions at higher temperatures, particularly at the operating temperatures of hot gas flames formed with hot process gases, even above 1100 °C. This oxide layer should be formed at least on the surface in contact with or potentially in contact with the process gas.

[0021] The at least one heating element may be made of zirconium and / or alloys thereof and / or alloys whose main component is a refractory metal, particularly tantalum, tungsten, niobium or molybdenum, and other alloying elements, particularly chromium and / or titanium. Nickel-based alloys may also be used to manufacture the heating element. The base alloy contains at least 50% of the aforementioned metal by mass.

[0022] The minimum proportion of the corresponding chemical compounds, metals or alloys in the heating element material is 95% by mass.

[0023] For example, molybdenum, silicon, and / or tungsten, especially intermetallic compounds of molybdenum and silicon, may contain such additives. In particular, it may be 1%-2% aluminum by mass and <1% other elements by volume.

[0024] The heating element material may also contain carbides bonded to transition metals of Groups 4, 5 and 6 of the periodic table and / or nitrides bonded to transition metals of Group 4 and / or silicides bonded to transition metals of Groups 4, 5 and 6, particularly intermetallic compounds of molybdenum and silicon and / or molybdenum and tungsten, and / or compounds of silicon and tungsten and / or compounds of silicon and tungsten, and / or other additives.

[0025] The minimum proportion of the corresponding chemical compounds, metals or alloys in the heating element material is 95% by mass.

[0026] Prior to use, a protective oxide layer may be formed on the surface of the at least one heating element on the exterior of the device. 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 Celsius, or by treating the at least one heating element in a corrosive solution. The oxide layer on the surface of the at least one heating element should be dense and cover all surfaces in contact with the process gas. This is particularly applicable to internal or external flow channels and (one or more) side surfaces.

[0027] To heat the process gas, 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.

[0028] In the direction of process gas flow, the number of turns of the at least one electric coil can be continuously reduced along the length of the at least one electric coil.

[0029] Controlled induction heating of the heating element and process gas can also be achieved using at least two coils with different numbers of turns along their length, wherein the first coil arranged in the inlet region has a larger number of turns than the coils arranged downstream of the process gas flow direction or in the outlet region. Furthermore, the first coil can operate at a higher power than other coils arranged downstream of the process gas flow direction through the heating element.

[0030] Controlled induction heating of the heating element can be used to ensure that the incoming process gas is heated in the inlet region, then heated at a higher heating rate, with the heating rate decreasing in the outlet direction. This avoids a large temperature difference between the inlet and outlet regions of the process gas at the at least one heating element.

[0031] If only one nonlinear coil is used in the device according to the invention, at least one additional power source for the other coils can be eliminated. If at least two identical linear coils are used, this has the advantage of using standardized coils.

[0032] One or more heating elements may be arranged as a bundle having at least three, preferably more than four flow channels, or arranged as a composite body within the housing. The flow channels are preferably tubular or hollow cylindrical.

[0033] The at least one heating element may be in the form of a straight tube bundle having at least three, preferably more than four, flow channels, wherein each flow channel is electrically insulated from each other and the intermediate space between each flow channel is filled in a non-conductive manner, and wherein the process gas to be heated flows around the outer surface of the tube bundle and through the internal flow channels.

[0034] Multiple heating elements can also be arranged in a non-contact, stacked, and electrically insulated manner, wherein at least three, preferably more than four, elements, such as conduits, are present within the housing. The flow channels through which the gas flows and the circumferential surfaces around which the gas flows are preferably tubular.

[0035] The heating element may also take the form of a bundle with at least three, preferably more than four, flow channels rotating in a spiral, wherein each flow channel is electrically insulated from the others and the intermediate space between each flow channel is filled in a non-conductive manner, and wherein the process gas to be heated flows around the outer surface of the bundle and through the internal flow channels.

[0036] The heating element may also be in the form of a cylinder, with at least three, preferably more than four, internal flow channels with a diameter greater than 2 mm extending in a straight line through the cylinder.

[0037] The heating element may also be in the form of a cylinder, with at least three, preferably more than four, internal flow channels passing through the cylinder, the internal flow channels having a diameter greater than 2 mm and extending in a straight line.

[0038] It may also have a cylindrical heating element with at least three, preferably more than four, internal flow channels passing through the cylinder, the internal flow channels having a diameter greater than 2 mm and rotating as a helix or designed as a coil.

[0039] Alternatively, the heating element can be designed in the form of multiple composite discs, with at least three, preferably more than four, internal flow channels passing through these composite discs. These flow channels have a minimum diameter of 2 mm and can extend vertically or obliquely relative to the end face.

[0040] The at least one heating element may also be arranged in the form of at least three, preferably more than four, straight tubes, each having a flow channel. This flow channel is formed by non-conductive, preferably ceramic, structures stacked within the housing to create a non-contact arrangement. The tubes are electrically insulated from each other and filled with a non-conductive material, and the process gas to be heated circulates around the flow channel. Other media, different from the process gas, may flow through the individual tubes in this arrangement. The media may be in any polymeric state. The non-conductive, preferably ceramic, structures need not exist along the entire length of the heating element arrangement; it is advantageous to have as few structural elements as possible along the length, for example, five structures per meter.

[0041] The diameter of a single internal flow channel should be greater than 2 mm. The non-contact stacked arrangement of at least three, preferably more than four, heating elements can almost completely fill the cross-sectional area of ​​the first inner shell.

[0042] For example, if the flow channel is not straight, but is, for example, in the form of a spiral, the length of the internal flow channel of at least one heat sink can be increased by a coil, which can be advantageously used to transfer heat to the process gas and allow for a corresponding reduction in the length of the heating element.

[0043] The shell can be made of quartz glass, Al2O3, ZrO2 or MgO or chemical compounds and / or mixtures of these materials.

[0044] A refractory sealing element can be arranged at the inlet of the process gas to prevent backflow of the heated process gas. This is particularly advantageous if the process gas is supplied through multiple housings nested within each other and surrounding the at least one heating element, as described below. This reduces energy loss, especially heat loss, and ensures that the process gas enters only through an inlet of appropriate size.

[0045] The housing containing the heating element may be surrounded by a second housing and / or a third housing, such that the process gas flows through the gap between the first housing and the second housing and / or the gap between the second housing and the third housing in a countercurrent or parallel flow manner to preheat the process gas.

[0046] The second and / or third housing may be provided with a reflective surface coating of titanium nitride, aluminum chromium nitride, or titanium aluminum nitride, or another coating that reflects electromagnetic radiation in the infrared wavelength range, which is not used or is only slightly used for induction heating.

[0047] For this purpose, the second or third housing may consist of at least two parts, such as half-shells, which can facilitate the formation of a reflective surface coating on the inner surface facing the heating element.

[0048] The temperature of the process gas exiting the outlet can be controlled by adjusting the process gas volume flow rate and / or operating the electrical power of at least one electric coil.

[0049] The geometry of the at least one heating element and / or inlet can be designed geometrically and / or by additional devices to maximize heat transfer between the at least one heating element and the process gas, particularly through turbulence in the process gas flow. For this purpose, contoured elements can be provided on the surfaces of the heating element onto which and / or around which the process gas flows.

[0050] The outlet can be designed geometrically and / or by means of the device to modify the flow of the hot process gas leaving the device, thereby maximizing heat transfer to any solids and / or melts and / or liquids and / or gases and / or plasmas in the discharged process gas flow. This can be achieved through the design of an outlet opening having at least one nozzle shape.

[0051] The outlet can be designed geometrically and / or by means of equipment to allow modification of the average flow rate of the process gas and / or the geometry of the process gas flow, particularly by means of nozzles with appropriate geometric design.

[0052] The length of the internal flow channel of the at least one heating element can be increased by winding a pipe, which can be used to facilitate heat transfer to the process gas.

[0053] The heating element can be designed in the form of at least one cylinder, with at least three, preferably more than four, internal flow channels passing through the cylinder. The internal flow channels can be straight, or, to increase their length, can be rotated as a helix or designed as a coil.

[0054] The diameter of a single internal flow channel should be greater than 2 mm.

[0055] The heating element can be designed as at least two composite discs, with at least three, preferably more than four, flow channels extending through these discs. The flow channels can be straight or angled relative to the end faces of the discs. The diameter of a single internal flow channel should be greater than 2 mm.

[0056] The ratio of the cross-sectional area of ​​the internal flow channel of the at least one heating element to the area of ​​the annular gap existing 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.

[0057] At least one heating element and flow channel should be tubular. One or more bodies may also have other geometries, including their internal free cross-sectional area and / or their surfaces. However, tubular shapes are advantageous in terms of flow and due to their relatively large surface area, which facilitates the heating of process gases.

[0058] The aforementioned heating element geometry, with additional contour elements (protrusions, recesses), can also be used to increase the total surface area of ​​at least one heating element. These can also be used to achieve beneficial turbulence in process gas flows.

[0059] Air can be used as a process gas, but another gas or gas mixture that is advantageous for the corresponding heating process can also be used. In particular, this includes inert gases, which can prevent the elements, materials, and objects to be heated from being affected.

[0060] In this invention, the temperature of the process gas exiting the outlet can be controlled by adjusting the process gas volumetric flow rate and / or operating the electrical power of at least one electric coil. To this end, the temperature of the process gas at the outlet can be determined and a control loop established.

[0061] The heat transferred depends on 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, and the temperature of the at least one heating element. Heat transfer from the heating element(s) to the flowing process gas is critical to efficiency.

[0062] The heat output of the apparatus can be controlled by the electrical power input, the quantity and pressure of the process gas flowing into the apparatus, and the flow temperature of the process gas entering the apparatus. Furthermore, as already mentioned, the process gas can be preheated inside or upstream of the apparatus. For example, an external preheating device can be used to preheat the process gas upstream of the apparatus. However, the heat contained within the gas can also be used to return the process gas to the apparatus. For this purpose, slightly cooled process gas from the heating zone that has already been used for heating can be drawn in and returned to the inlet of the apparatus after use.

[0063] The supply of process gas to the apparatus can be achieved by a compressor system for multiple apparatuses or a compressor associated with the apparatus according to the invention, which is preferably controllable or adjustable. Furthermore, flow conditions particularly favorable to heat transfer from the at least one heating element to the process gas can be configured in the process gas supply.

[0064] The geometry of the inlet of the process gas to be heated in the at least one heating element and / or device can be designed geometrically and / or by means of the device to maximize heat transfer between the at least one heating element and the process gas flow. This can be achieved, in particular, by swirling the process gas flow. For this purpose, contour elements can also be used that are capable of extending the path of the process gas along the surface of the at least one heating element for heating, and / or generating turbulence in the process gas flow.

[0065] The device may have an additional housing formed of fire-resistant material and surrounding one or more coils. This additional housing can protect against high temperatures.

[0066] The process gas outlet of the device can also be optimized for any application purpose. Therefore, the outlet can be designed geometrically and / or by means of movable equipment so that the flow of the process gas is modified so that heat transfer to any solids and / or melts and / or liquids and / or gases and / or plasmas placed in the discharged process gas flow can be maximized.

[0067] Furthermore, the outlet of the hot process gas can be designed with an appropriate geometry or by means of equipment to modify the velocity and / or shape of the process gas flow or the process gas flame. For example, this can be achieved by at least one appropriately geometrically designed nozzle that can accordingly affect the cross-section, velocity, and / or direction of the hot process gas flow exiting the device.

[0068] Considering the geometry and material of one or more heating elements, the selection (design, conductivity, and number of turns) of at least one electric coil and the frequency of its operating voltage can be optimized. For the optimal frequency to heat at least one heating element with a cylindrical geometry, it can be assumed that the ratio of the total diameter of the heating element to the current penetration depth δ is 3 to 5 (d / δ = 3-5). When selecting the frequency, the ratio between the diameter d of a single heating element and the current penetration depth has the following requirements [according to Benkowsky 1990]:

[0069] The frequency of (one or more) heating elements and the electromagnetic properties of the materials are contained in the formula for the current penetration depth [according to Fasholz 1984 and Benkowsky 1990], as follows: , , , , .

[0070] The above formula describes the current penetration depth. This value indicates that up to a certain thickness, 86% of the induced energy is converted into heat. The remaining 14% is absorbed by deeper layers. Due to this fact, for induction heating, there exists an optimized ratio between the total diameter of the heating element and the current penetration depth. In addition to frequency, the temperature-dependent material properties of the heated body are also included in the formula in the form of resistivity and relative permeability.

[0071] Compared to other electric heating systems, this invention allows for applications where performance limits can be extended to temperatures above 1000 °C and outputs in the MW range. Attached Figure Description

[0072] The invention will now be explained in more detail with examples.

[0073] The following is shown: Figure 1 An example of a device according to the invention includes a nonlinear electric coil and a cylindrical heating element having a surface structure. Figure 2 The second example has two different electric coils and cylindrical heating elements, as well as the option to preheat process gases; Figure 3 Example of a heating element made of tube bundles; Figure 4 Example of a heating element made of twisted tube bundles; Figure 5 Example of a heating element consisting of a cylinder with internal flow channels; Figure 6 Example of a heating element consisting of a cylinder with a rotating internal flow channel; Figure 7 Example of a heating element consisting of multiple composite panels with internal flow channels; Figure 8 Example of a non-linearly wound electric coil; Figure 9 Example of two electric coils with different rated power; Figure 10 Example of a heating element variant, which consists of non-contact stacked pipes arranged within a square outline that forms a housing; Figure 11 Example of a heating element variant consisting of non-contact stacked pipes within a circular pipe that serves as a housing. Detailed Implementation

[0074] exist Figure 1In the example shown, process gas flows from the compressor (not shown) of the apparatus into inlet 5. The process gas flows over the sleeve surface of the housing 2 made of refractory material (with an exemplary spiral structure) and through the internal flow channel of at least one heating element 1 toward the outlet 6 of the apparatus, whereby the process gas can be subsequently further heated downstream of outlet 6 by the high temperature of the heating element 1. The structure on the surface over which the process gas flows can facilitate heat transfer compared to a smooth surface.

[0075] The housing 2 is made of ceramic (e.g., Al2O3 or ZrO2) and is surrounded by at least one electric coil 3, such that at least one heating element 1 disposed therein can be heated by induction. In this case, the electric coil 3 has a non-linear design to introduce varying amounts of energy into the at least one heating element 1 along its length. More energy is induced in the inlet-side region of the at least one heating element 1 than in the outlet-side region. On its surface in contact with the process gas, the heating element 1 has a durable passivated oxide layer formed before use, in this case, formed of, for example, a nickel-based alloy or zirconium or zirconium alloy or an alloy based on a refractory metal (particularly tantalum-based, tungsten-based, niobium-based, or molybdenum-based alloy). The base alloy contains at least 50% by mass of the metal. These materials can also be used in the examples described below. In the non-linear electric coil, the number of turns of the electric coil 3 varies along its length. In this invention, the number of turns of the electric coil 3 in the region of the heating element 1 closest to the inlet 5 of the process gas is greater than the number of turns of the electric coil 3 in the region arranged further downstream along the direction of the outlet 6.

[0076] At least one electric coil 3 is connected to a voltage source (not shown) whose power and frequency can be controlled or regulated, preferably according to the desired final temperature of the process gas after outlet 6. The frequency of the voltage should be matched with the geometry and material of the heating element 1.

[0077] The refractory sealing element 4 is arranged at the inlet 5 to prevent the backflow of heated process gas.

[0078] Figure 2 The example shown illustrates a device capable of preheating process gases while simultaneously providing additional thermal insulation. In this example, two coils with different winding densities and different powers are used. The first coil 3a, positioned closer to inlet 5, has a higher winding density and operates at a higher power than the second coil 3b or another coil positioned closer to outlet 6.

[0079] After passing through inlet 5, the process gas, for preheating and insulation of the coils 3a and 3b, first flows through the gap between the second housing 7 and the third housing 8, and then flows in the opposite direction through the gap between the second housing 7 and the first housing 2. The process gas now flows from the aforementioned gap into the space between the surface of the heating element 1 (cylinder in this example) and the first housing 2, and flows through the flow channel inside the heating element 1. It is heated to the desired process temperature on these surfaces. The process gas passes through the intermediate space and flow channel 11 to reach outlet 6. In this example, the coils 3a and 3b are enclosed in a ceramic housing 9. Such a housing 9 can exist in principle in this invention, and therefore can also exist in other examples.

[0080] Different types of induction heating elements 1 can be used in the apparatus shown for heating process gases. Figure 3 The example shown has an exemplary heating element 1. A plurality of straight tubes, which serve as flow channels 11, are bundled together and can be heated by inductance. Process gas flows over the outer surface 10 of the tube bundle forming the heating element 1 and through the internal flow channels 11.

[0081] Another example is Figure 4 The heating element 1 is shown. In this heating element 1, multiple pipes are bundled together to form a flow channel 11, and can also rotate as a helical body. Process gas flows along the outer surface 10 of the tube bundle and heats it by flowing through the pipes. Due to the extended path of the internal flow channel 11 and the turbulence generated by the winding, better heat transfer from the heating element 1 to the process gas can be achieved.

[0082] Figure 5 The example shown has a heating element 1 designed as a cylinder. Multiple internal straight flow channels 11 extend through this cylinder. In addition to the outer surface 10, the inner surfaces of the flow channels 11 also represent the surfaces on which the process gas is heated. Compared to the previous two heating element examples, Figure 5 The heating element 1 in the heating element consists of only one main body, which is beneficial for heat conduction in the heating element 1.

[0083] Figure 6 The example also shows a cylindrical heating element 1, with process gas flowing around its outer surface 10. In this example, the internal flow channel 11 rotates in a spiral or forms a coil. Better heat transfer from the heating element 1 to the process gas can be achieved due to the longer flow path and the turbulence generated by the winding. This type of heating element 1 can be produced, for example, by casting or additive manufacturing.

[0084] Another example of cylindrical heating element 1 is as follows: Figure 7As shown, multiple composite disks are perforated by straight or oblique holes to serve as flow channels. The assembled disks, along with the internal flow channels 11 for heat transfer and the outer surface 10, form a cylinder, the total length of which can be extended by adding more disks as needed.

[0085] An example of a nonlinearly wound coil 3 is as follows: Figure 8 As shown. The 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 coil 3. From the region at the inlet 5, the number of turns per unit length is greater than the number of turns along the direction of the outlet 6. This allows at least one heating element 1 located inside the housing 2 to achieve a greater degree of heating in the region where the cooling effect of the heating process gas is stronger.

[0086] Another example of a possible coil arrangement for uniformly heating at least one heating element 1 is as follows: Figure 9 As shown, this is a combination of two coils 3a and 3b. In this example, the power applied to the first coil 3a is higher than the power applied to the second coil 3b. Therefore, although the cooling effect of the process gas flowing from inlet 5 to outlet 6 is different, at least one heating element 1 arranged in the housing 2 is heated uniformly.

[0087] Figure 10 The example shown in the housing 2 is designed as a non-contact stacked arrangement of straight tubes. Each of these heating elements 1 consists of multiple tubes stacked without contact, each having a flow channel 11 and a sheath surface 10, and separated from each other by a non-conductive structure 12. For heating, process gas flows through the flow channel 11 and along the side surface 10 without contacting the contact points of the structure 12 that defines the arrangement. To optimize the use of the cross-section, circular or square tubes can be used as the surrounding housing 2. The structure 12 serves as electrical insulation and defines the arrangement of the individual tubes, shown in the example as a mesh structure composed of insulating elements (non-conductive structures) connected at right angles to each other.

[0088] Another example is Figure 11 The heating element arrangement is shown. Multiple heating elements 1 are arranged as straight tubes within a tubular housing 2, and are not in contact with each other via a non-conductive structure 12. For heating, process gas flows through a flow channel 11 and along the sheath surface 10 without contacting the non-conductive structure 12. In the example shown, the structure 12 defining the arrangement of the heating elements 1 within the housing 2 is a uniform stack of elements with a hexagonal cross-section, but other arrangements with polygonal shapes and different housing geometries are also possible. In forms not shown, the flow channel 11 may also have a polygonal cross-section.

[0089] For example, in the test, the process gas that was not preheated was heated to a temperature above 1100 °C, with an effective output of about 9 kW for induction heating.

[0090] In the figures, the same elements are designated and labeled with the same reference numerals.

Claims

1. An apparatus for forming a hot process gas stream, said hot process gas stream being used for melting and holding hot metals, including glass, for heating heat treatment furnaces, and for heat treating any material, including bulk materials, wherein, Process gas at a temperature of at least 1000°C flows from the inlet (5) through the shell (2) made of refractory material to the outlet (6) at a predetermined volumetric flow rate. At least one heating element (1) is disposed inside the housing (2), the at least one heating element being formed of a material capable of being heated inductively, and at least one flow channel (11) is present on the at least one heating element, through which the process gas flows or around the flow channel, and The hollow housing (2) is surrounded by at least one non-linearly wound electric coil (3), wherein the number of turns of the at least one electric coil decreases along the length of the electric coil (3) from the inlet (5) toward the outlet (6), and the at least one electric coil (3) is connected to a voltage source through which an AC voltage or a pulsed DC voltage is applied to the electric coil (3). and / or At least two coils (3a, 3b) are arranged one after another outside the housing (2) along the flow direction of the process gas, and each coil is connected to a voltage source through which an AC voltage or a pulsed DC voltage is applied to the coils (3a, 3b), wherein, The first coil (3a) arranged in the region of the inlet (5) operates with a greater electrical power than at least one additional coil (3b) arranged downstream of the first coil (3a) along the flow direction of the process gas; wherein, The number of turns of the coil (3) is selected such that, starting from the inlet (5) of the process gas, the power induced to the heating element in the first third of the length of the at least one heating element is at least 25% greater than that in the region at the outlet (6) of the process gas. When at least one first coil (3a) and another coil (3b) arranged downstream of the first coil (3a) along the flow direction of the process gas are used, the power coupled to the heating element (1) through the first coil (3a) in the region of the inlet (5) is at least 25% greater than that in the region of the outlet (6).

2. The apparatus according to claim 1, characterized in that, A passivated oxide layer is formed on the surface of the heating element (1) that is in contact with the process gas.

3. The apparatus according to any one of the preceding claims, characterized in that, The process gas flows along and / or through at least one flow channel (11) of the at least one heating element (1) to be heated on the inner wall of the housing (2) and the outer peripheral surface (10) of the heating element (1).

4. The apparatus according to any one of the preceding claims, characterized in that, In the flow direction of the process gas, the number of turns of the at least one electric coil (3) continuously decreases along the length of the at least one electric coil (3).

5. The apparatus according to any one of claims 1 to 3, characterized in that, By setting at least two coils (3a, 3b) with different turns distributed along their length, controlled induction heating of the heating element (1) and the process gas can be achieved. The first coil (3a) arranged in the region of the inlet (5) has a larger number of turns than the coil (3b) arranged in the downstream region or the outlet (6), and is thus able to be heated. The number of turns per unit length of the coil near the inlet (5) of the process gas is at least 20% greater than that in the area of ​​the outlet (6) and the area near the outlet.

6. The apparatus according to any one of the preceding claims, characterized in that, The at least one heating element (1) is composed of a nickel-based alloy, zirconium and / or an alloy thereof and / or a refractory metal-based alloy, wherein the refractory metal-based alloy is in particular a tantalum-based, tungsten-based, niobium-based or molybdenum-based alloy.

7. The apparatus according to any one of the preceding claims, characterized in that, The material forming the at least one heating element (1) is: Carbides containing transition metals from Groups 4, 5 and 6 of the periodic table and / or nitrides containing transition metals from Group 4 and / or silicides containing transition metals from Groups 4, 5 and 6, especially intermetallic compounds of molybdenum and silicon, and / or intermetallic compounds of molybdenum, silicon and tungsten, and / or other additives, and / or compounds of silicon and carbon, and / or other additives.

8. The apparatus according to any one of the preceding claims, characterized in that, One or more heating elements (1) within the housing (2) are arranged as a bundle having at least three, preferably more than four flow channels (11), or arranged as a composite body. or The at least one heating element (1) is in the form of a straight tube bundle having at least three, preferably more than four, flow channels (11), wherein each flow channel (11) is electrically insulated from each other and the intermediate space between each flow channel (11) is filled in a non-conductive manner, and wherein the process gas to be heated flows around the outer surface of the tube bundle and through the internal flow channels (11). or The heating element (1) is in the form of a bundle of at least three, preferably more than four, flow channels (11) rotating as a helix, wherein each flow channel (11) is electrically insulated from each other, and the intermediate space between each flow channel (11) is filled in a non-conductive manner, and wherein the process gas to be heated flows around the outer surface (10) of the bundle and through the internal flow channels (11). or The heating element (1) is in the form of a cylinder, through which at least three, preferably more than four flow channels (11) pass, the flow channels (11) having a diameter greater than 2 mm and extending in a straight line. or The heating element (1) is in the form of a cylinder, through which at least three, preferably more than four, internal flow channels (11) pass, the flow channels having a diameter greater than 2 mm and rotating as a helix or forming a winding. or The heating element (1) is in the form of multiple composite discs, with at least three, preferably more than four, internal flow channels (11) passing through the multiple composite discs. The minimum diameter of the internal flow channels is 2 mm and they can extend perpendicularly or obliquely relative to the end face. or The at least three, preferably more than four heating elements (1) are stacked in a defined pattern as non-contact elements and have internal flow channels (11), wherein each heating element (1) is preferably electrically insulated from each other by ceramic (12) and arranged in a defined manner by a non-conductive structure, and the intermediate space between each heating element (1) is filled in a non-conductive manner, and wherein the process gas to be heated flows around the outer surface (10) of the heating element (1) that does not contact the structure (12) and flows through the internal flow channels (11).

9. The apparatus according to any one of the preceding claims, characterized in that, The shell (2) is formed of quartz glass, Al2O3, ZrO2 or MgO, or chemical compounds of these materials, and / or mixtures of these materials.

10. The apparatus according to any one of the preceding claims, characterized in that, A fire-resistant sealing element (4) is arranged at the inlet (5) of the process gas to prevent the heated process gas from flowing back.

11. The apparatus according to any one of the preceding claims, characterized in that, The housing (2) is surrounded by a second housing (7) and / or a third housing (8), such that the process gas flows through the gap between the first housing (2) and the second housing (7) and / or the gap between the second housing (7) and the third housing (8) in a countercurrent or parallel flow manner to preheat the process gas.

12. The apparatus according to any one of the preceding claims, characterized in that, The second housing (7) and / or the third housing (8) are coated with a reflective surface coating of titanium nitride, aluminum chromium nitride, or titanium aluminum nitride, or another coating that reflects electromagnetic radiation in the infrared wavelength range, on their surfaces facing the heating element (1), and these coatings are not used for induction heating.

13. The apparatus according to any one of the preceding claims, characterized in that, The temperature of the process gas flowing out of the outlet can be adjusted by adjusting the volumetric flow rate of the process gas and / or by operating the electrical power of the at least one electric coil (3, 3a, 3b).

14. The apparatus according to any 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 means of additional equipment such that the heat transfer between the at least one heating element (1) and the process gas is maximized, particularly by means of the turbulence of the process gas flow.

15. The apparatus according to any one of the preceding claims, characterized in that, The outlet (6) is designed geometrically and / or by means of equipment such that the flow of the process gas is modified to maximize heat transfer to any solid and / or melt and / or liquid and / or gas and / or plasma in the discharged process gas flow.

16. The apparatus according to any one of the preceding claims, characterized in that, The outlet (6) is designed geometrically and / or by means of equipment such that the average flow rate of the process gas and / or the geometry of the process gas flow are modified, particularly by means of nozzles with appropriate geometric design.

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