ELECTRIC GAS FLOW HEATERS AND GAS FLOW HEATERS MANUFACTURING PROCESSES

Description

[0001] The invention relates to an electric gas flow heater for solid oxide cell technology comprising at least one cylindrical structure in which at least one channel for gas conduction is formed and at least one electric heating element is arranged in the channel of the cylindrical structure, wherein heat can be transferred from the electric heating element to a gas flowing through the channel for heating the gas and / or for achieving high gas temperatures.

[0002] Furthermore, the invention relates to a gas flow heater manufacturing method for producing an electric gas flow heater according to the invention for solid oxide cell technology.

[0003] The electric gas flow heater is designed specifically for vertical flow. Horizontal use is also possible. The typical temperature range is gas temperatures from 800 °C to 1200 °C, although the electric gas flow heater described here can also be used at significantly lower or even higher operating temperatures.

[0004] From the State of the art Different types of gas flow heaters with different manufacturing processes are known.

[0005] DE 10 2014 102 474 A1 discloses a gas flow heater in which an electric heating wire is guided through several individual channels. In this solution, the heating wire is stored in small ceramic tubes and electrically insulated. Due to this complex arrangement and the correspondingly complex manufacturing process, this type of gas flow heater is relatively expensive.

[0006] The European patent application with the file number EP20159612.9 discloses a correspondingly simpler manufacturing variant for a gas flow heater known from the prior art that is heated electrically. The heating element is made from a pre-bent heating wire, which is dipped in wax, which in turn forms a coating on the conductor. The wire, including the wax coating, is cast into concrete or a similar material, and the wax is then melted out, forming channels containing heating wires, thus enabling simpler production at reduced costs.

[0007] US Pat. No. 9,982,418 discloses a compact air heat exchanger / heating element for use in a portable vaporizer, wherein, in one arrangement, the heating element is a multilayer ceramic element with multiple internal conductive layers forming resistors. The heating element can be manufactured using low-temperature co-fired ceramic (LTCC) and printed circuit board (PCB).

[0008] According to WO 2016 / 172441, a heating element for an evaporator having a planar region with at least one filament is also known, wherein the filament forms an air channel through the planar region.

[0009] Also known in the art are meander-shaped heaters made of graphite that are bent into tubes. Solutions of this type are offered, for example, by SGL Carbon (see https: / / www.sglcarbon.com / loesungen / anwendung / hochtemperaturoefen / ).

[0010] Furthermore, heaters are known in the prior art in which a heating wire is arranged in a serpentine pattern around a core, with the core located in a channel. Solutions of this type are offered, for example, by Tutco Heating Solutions (see https: / / www.tutco.com / cartridge-heaters).

[0011] The Problems The main disadvantages of the electric gas flow heaters known in the state of the art are that the manufacture of the heating elements is both time-consuming and costly and that their installation or assembly is technically complicated.

[0012] Furthermore, they are difficult or even impossible to maintain or repair and are very complicated when it comes to achieving a uniform temperature at the end of the channel in which the gas is heated.

[0013] The present invention is based on the TaskThe aim is to provide an electric gas flow heater and a gas flow heater manufacturing process which enables the realization of both small and large, powerful gas heater heating elements with reduced manufacturing effort and which can be operated economically with reduced manufacturing costs.

[0014] Solved This object is achieved with a gas flow heater according to the main claim 1 and a gas flow heater manufacturing method according to the independent claim.

[0015] The electric gas flow heater for solid oxide cell technology has, according to the arrangement, at least one cylindrical structure in which at least one channel for gas conduction is formed and at least one electric heating element is arranged in the channel of the cylindrical structure, wherein heat can be transferred from the electric heating element to a gas flowing through the channel for heating the gas and / or for achieving high gas temperatures, and is characterized in that the electrical heating element has two or more spaced-apart, meander-like heating grid structure planes perpendicular to the flow direction of the channel, and the two or more spaced-apart, meander-like heating grid structure planes are arranged one after the other in the flow direction in the channel, wherein the individual spaced-apart, meander-like heating grid structure planes are connected to one another in a meandering manner via an electrically conductive intermediate connection, and the first and the last of the spaced-apart, meander-like heating grid structure planes have an electrical connector, and the cylindrical structure is designed on its inner wall to accommodate the two or more spaced-apart, meander-like heating grid structure planes.

[0016] Preferably, the electric heating element can be constructed in one piece, in one piece, or from a single material. This virtually eliminates potential weak points during operation due to joining or connection errors and avoids additional assembly steps.

[0017] The cylindrical structure can be configured on the inside to accommodate the two or more spaced, meandering heating grid structure planes, preferably with an internal thread, particularly preferably with a double-start internal thread. The electric heating element can be inserted into or removed from the cylindrical structure by rotating the electric heating element relative to the cylindrical structure. The electric heating element can thus be screwed into the thread. In the assembled state, the individual heating grid structure planes are supported in the threads, establishing a linear contact between the heating grid structure planes and the threads.

[0018] A double-start thread on the inside of the cylindrical structure is advantageous over a single-start thread, as it prevents excessive bending of the heating grid structure planes and ensures good assembly.

[0019] The arrangement, particularly the spacing of the individual adjacent heating grid structure levels, is selected such that they mate with the internal thread of the cylindrical structure. Each level of the heating grid structure levels is held and supported by the internal thread.

[0020] The cylindrical structure can be formed as a single piece or as a single part, or as a multi-piece or multi-part structure. Preferably, the cylindrical structure can be formed from two half-shells that, when assembled, form the cylindrical structure. The use of half-shells facilitates the production of the cylindrical structure by molding or molding and sintering a green compact, since less complex semi-finished products can be used for molding, and post-processing can be avoided.

[0021] In an alternative embodiment, the cylindrical structure can be provided on its inner wall not with a thread for receiving the two or more spaced-apart, meander-shaped heating grid structure planes, but with an arrangement of grooves. The spacing of the grooves is selected such that it fits the spacing of the meander-shaped heating grid structure planes. Such an arrangement enables particularly simple assembly, namely by inserting or placing the electrical heating element into a first of the half-shells and then assembling the second half-shell with the first. The individual, spaced-apart, meander-shaped heating grid structure planes, which are connected to one another in a meander-like manner, can be arranged, in particular, equally spaced in the direction of flow.

[0022] The electric heating element may preferably have at least one of the features selected from the following features: The individual, spaced-apart, meander-shaped heating grid structure planes have a circular envelope; the individual, spaced-apart, meander-shaped heating grid structure planes are wider in their edge regions than in their inner regions; the conductor cross-section of the intermediate connections is significantly larger than the conductor cross-sections of the spaced-apart, meander-shaped heating grid structure planes.

[0023] Geometrically, the circular shape is particularly preferred, as it allows for the formation of a plane structure that can be inserted into the cylindrical structure for insertion into the thread. It is particularly advantageous if the round design is combined with the double-start thread on the inside of the cylindrical structure, as this ensures optimal screwability.

[0024] One advantage of the design in which the conductor cross-section in the edge regions of the meandering heating grid structure levels is larger than the conductor cross-sections of the inner heating conductors of the meandering heating grid structure levels is the increased service life. This is achieved because less heat energy is released there due to the larger conductor cross-section, so that the temperature of the heating grid structure levels in the contact area with the cylindrical structure is uncritical. The risk of local overheating due to poor heat dissipation at the contact points between the electrical heating element and the cylindrical structure is thus minimized without necessitating complex ceramic geometry. In the context of the design described above, conductor cross-section refers exclusively to the width of the electrical webs of the meander structure and not their height.The electric heating element is preferably formed from a sheet of substantially constant thickness, e.g. 0.7 mm or 1.0 mm.

[0025] The cylindrical structure can preferably be designed as an electrical insulator. This simultaneously provides electrical insulation and holds the electrical heating element in one structure.

[0026] Particularly preferably, the cylindrical structure is formed from technical ceramics and / or concrete and / or aluminum oxide.

[0027] In a further preferred variant, the electric heating element is designed without a support structure, so that the electric heating element is mounted exclusively in the thread of the cylindrical structure. This represents a significant manufacturing advantage, since only the heating element and the cylindrical structure need to be manufactured and then joined together.

[0028] In a further preferred variant, the adjacent heating grid structure planes of the meandering heating grid structure planes are shaped such that the openings of the individual heating grid structure planes are not aligned with each other with respect to the flow direction. In a further preferred variant, the meandering heating grid structure planes are provided with diffuser elements that are formed integrally with the individual heating grid structure planes, in one piece, or made of a single material. The arrangement of the openings of the individual planes and the diffuser elements can influence the flow of the gas to be heated and the heat input into the gas, thus optimizing the temperature distribution in the gas.

[0029] The electric heating element can be made, in particular, of VDM ®< Aluchrom W, Kanthal ®< APM, or another aluminum-containing ferritic chromium steel for use at temperatures up to 1250°C. However, other alloys are also conceivable that exhibit sufficiently high dimensional stability in the selected temperature range and, preferably during operation and in the presence of oxygen, form a surface-protecting oxide layer.

[0030] The cylindrical structure can be designed with openings such that connecting means for electrically contacting the connectors of the first or last heating grid structure level can be passed through these openings and electrically connected to them, so that the electrical heating element can be supplied with an electrical energy source via them.

[0031] In principle, it can be said that the gas flow heater described here essentially consists of two functional components, namely the cylindrical structure and the electrical heating element in a double meander shape, namely once in the plane perpendicular to the flow direction and once along the flow direction.

[0032] According to the method, the gas flow heater manufacturing method for producing an electric gas flow heater according to the invention for solid oxide cell technology comprises at least the following steps: a) Producing the cylindrical structure; b) Producing the electrical heating element by bending using the following steps: Producing a blank by punching and / or lasering and / or cutting from a sheet metal, whereby meandering heating grid structure planes connected to one another via intermediate connections are formed; Bending the blank in the region of the intermediate connections by 180° in each case, so that a cylindrical structure is created from plane-parallel meandering heating grid structure planes, the spacing of which is maintained by the intermediate connections; c) Assembling the gas flow heater using the following steps: Screwing or inserting the electrical heating element into the cylindrical structure; and Electrically contacting the electrical heating element.

[0033] The cylindrical structure can be manufactured by molding or molding and sintering a green compact. This process makes it possible to manufacture a corresponding gas flow heater cost-effectively and with as few process steps as possible. In particular, the dimensioning can be achieved by adjusting the number of levels of the heating grid structure. Furthermore, the separate production of the heating element and cylindrical structure also enables location-independent individual production of the two components, whereby they only need to be screwed together during final assembly, i.e. the electric heating element into the cylindrical structure. The process also enables the production of a three-dimensional heating element in which the principle of series connection is used exclusively. Parallel connections, which would require the use of higher currents, are avoided.

[0034] In the following, embodiments of the invention are described with reference to the accompanying drawings in the Image description described in detail, which are intended to explain the invention and are not to be considered limiting: They show: Fig. 1 a schematic representation of a blank of the electric heating element in cut or punched form; Fig. 2 a schematic representation of the blank of the electric heating element from Fig. 1 in meandering folded form in side view; Fig. 3 a schematic representation of the Fig. 2 shown meandering folded electric heating element in isometric view; Fig. 4 a schematic representation of an alternative blank of the electric heating element in cut or punched form, with additional webs provided for handling during the manufacturing process; Fig. 5 a schematic representation of the Fig. 4shown now meander-folded electric heating element in an isometric view; Fig. 6 a schematic representation of the cylindrical structure in a sectional side view; Fig. 7 a schematic representation of an installed electric heating element in a cylindrical structure in a plan view; Fig. 8 a schematic representation of an installed electric heating element in a cylindrical structure in a sectional side view; and Fig. 9 a schematic representation of the assembled electric gas flow heater in an isometric view; and Fig. 10 a schematic representation of an alternative embodiment of the electric gas flow heater in an exploded view.

[0035] The following exemplary further embodiments are not necessarily intended to be limiting, but rather represent specific embodiments and are intended to explain the invention disclosed here: First, a blank of the electrical heating element is manufactured, whereby a structure is punched or cut from a 1 to 0.7 millimeter thick sheet metal, for example using a laser. This manufacturing step can be carried out using CNC technology, for example. This creates a flat meandering structure as a band made up of several segments that are circular with respect to their envelopes, i.e., the individual heating grid structure levels, which are connected to one another by intermediate connections or webs (cf. Fig. 1 ). The meanders of the individual heating grid structure levels are punched or cut in such a way that the conductor cross-section relative to the circle centre in the outer area is larger than the conductor cross-section of the inner heating conductors (cf. Fig. 7). Following cutting, the blank is deburred using standard methods (not shown). At the intermediate joints or webs, the blank is bent 180° to create a cylinder stack of superimposed, parallel meander sheets, whose spacing, for example, of approximately 3 mm, is maintained by the webs (see Figures 2 and 3 ).

[0036] Alternatively, the individual heating grid structure levels can be cut individually and welded together. This would result in a strip-shaped blank, but rather individual circular sheet segments.

[0037] To facilitate production, webs for handling during the manufacturing process can be attached to the heating grid structure levels (see Figures 4 and 5 opposite Figures 1 and 3 ) which are separated after bending or welding or before assembly (step c).

[0038] The finished electrical heating element is then inserted into the cylindrical structure (see Fig. 6 ), whereby this can be done in particular by screwing or turning (cf. Figures 7, 8 and 9 ). The cylindrical structure, which also serves as an insulator, is in Fig. 6 shown and provided with an internal thread.

[0039] The cylindrical structure can alternatively be formed from two half-shells which, when put together, form the cylindrical structure (cf. Fig. 10 ).

[0040] In an alternative embodiment, the cylindrical structure can have an arrangement of grooves on its inner wall for receiving the two or more spaced meander-shaped heating grid structure planes (cf. Fig. 10). This design enables particularly simple assembly, namely by inserting or placing the electric heating element into a first of the half-shells and then assembling the second half-shell with the first.

[0041] With regard to further optimization options, the following is explained: During production of the blank for the electrical heating element, it is possible to design corresponding heating grid structure levels or regions thereof with different dimensions, so that, for example, thicker conductor cross-sections in certain defined regions can release different amounts of heat to the passing gas. Furthermore, the flow can also be specifically influenced by cutting or punching out adjacent heating grid structure levels (and pre-selecting them during welding) in such a way that the openings of adjacent heating grid structure levels do not coincide with one another with regard to the flow direction. The individual heating grid structure levels can also have diffuser elements that do not establish contact between the individual conductors but influence the flow to increase turbulence (not shown).

[0042] This individual design can vary from level to level of the heating grid structure, so that by specifically influencing the flow, a homogeneously heated gas is ultimately discharged from the gas flow heater, which is then made available for further processing. The channel structure inside can be varied in this way, resulting in corresponding homogenization. In particular, this allows for great variability in the design of the channel and support structure that can be formed in this way. Channel structures can be designed inside, which can then have a positive influence on the heating of the flowing gas. However, complex internal channel structures can also be created, for example to calm flows or to deliberately make them turbulent.Using computer simulations, such bottlenecks for the gas flow can be calculated and adjusted accordingly, as this depends on many factors such as gas inlet area, gas outlet area, flow rate, etc.

[0043] The individual heating conductors of the meandering electrical heating elements can be arranged at varying densities. In a special variant, an inhomogeneous distribution of heating conductors in a single plane can be realized, which can counteract potentially uneven gas heating, for example, in the edge areas of the heater. For this purpose, the heater and the heating elements can be designed according to the flow profiles.

[0044] Should the electric heating element need to be replaced over time due to material fatigue, it can be easily unscrewed from the cylindrical housing and a new electric heating element inserted. Gas heating can also be optimized in the same way, as the inventive solution, using CNC-supported processes, allows for rapid validation of simulated temperature distributions of the gas flow heater.

[0045] Possible applications can be seen particularly in the field of solid oxide cell technology or the steel industry, since high gas temperatures must be achieved in both areas of application.

[0046] The above-mentioned embodiments are intended to explain the invention, but do not necessarily limit its scope.

Claims

1. Electric gas flow heater for solid oxide cell technology comprising at least one cylindrical structure in which at least one channel for gas conduction is formed and at least one electric heating element is arranged in the channel of the cylindrical structure wherein heat can be transferred from the electric heating element to a gas flowing through the channel to heat the gas and to achieve gas temperatures of 800°C to 1200°C, wherein - the electric heating element has two or more spaced meander-like heating grid structure planes perpendicular to the flow direction of the channel, and - the two or more spaced meander-like heating grid structure planes are arranged one after the other in the channel in the direction of flow, the individual spaced meander-like heating grid structure planes being connected to one another in a meander-like manner via an electrically conductive intermediate connection in each case and the first and the last of the spaced meander-like heating grid structure planes having an electrical connector, and - the cylindrical structure is designed on its inner wall to accommodate the two or more spaced meander-like heating grid structure levels.

2. Electric gas flow heater according to claim 1, characterized in that the electric heating element is formed in one piece or is one piece or is one piece made of one material.

3. Electric gas flow heater according to claim 1 or 2, characterized in that the cylindrical structure is formed on the inside for receiving the two or more spaced-apart meander-like heating grid structure planes with - an internal thread, particularly preferably with a double-threaded internal thread, wherein the electric heating element can be inserted into or removed from the cylindrical structure by a rotary movement of the electric heating element relative to the cylindrical structure, or - an arrangement of grooves, whereby the electric heating element can be inserted into or removed from the cylindrical structure when the two-part half-shell design of the cylindrical structure is open.

4. Electric gas flow heater according to one of the preceding claims, characterized in that the spaced meander-like interconnected individual meander-like heating grid structure planes are arranged equally spaced in the direction of flow.

5. Electric gas flow heater according to one of the preceding claims, characterized in that the electric heating element has at least one of the features selected from the following features: - the individual spaced meandering heating grid structure planes have a circular envelope; - the individual spaced meandering heating grid structural levels are wider in their edge areas than in their inner areas; - the conductor cross-section of the intermediate connections is significantly larger than the conductor cross-sections of the spaced meandering heating grid structural levels.

6. Electric gas flow heater according to one of the preceding claims, characterized in that the cylindrical structure is designed as an insulator.

7. Electric gas flow heater according to one of the preceding claims, characterized in that the cylindrical structure is formed of technical ceramics and / or concrete and / or aluminum oxide.

8. Electric gas flow heater according to one of the preceding claims, characterized in that the electric heating element is designed without a support structure, so that the electric heating element is mounted exclusively in the receptacle of the cylindrical structure.

9. Electric gas flow heater according to one of the preceding claims, characterized in that the adjacent heating grid structural planes are shaped such that their openings do not coincide with each other with respect to the direction of flow and / or the heating grid structural planes are provided with diffuser elements.

10. A gas flow heater manufacturing method for manufacturing an electric gas flow heater for solid oxide cell technology according to any one of the preceding claims, comprising at least the following steps: a) manufacturing the cylindrical structure; b) manufacturing the electric heating element by bending by means of the following steps: - Producing a blank by punching and / or lasering and / or cutting from a sheet metal, wherein meander-like heating grid structure planes connected to each other via intermediate connections are formed; - Bending the blank by 180° in each case in the area of the intermediate connections, so that a cylindrical structure of plane-parallel meandering heating grid structure planes is formed, the spacing of which is maintained by the intermediate connections; c) Assembly of the gas flow heater by means of the following steps: - screwing or inserting the electric heating element into the cylindrical structure; and electrically contacting the electric heating element.