Electric gas heater

Abstract

An electric gas heater comprising a bundle of a plurality of electrically conductive tubes for resistive heating. Electrical bridges are arranged between and attached to the electrically conductive tubes in a manner that provides within each set of tubes for an electric current from the external electric power supply to flow through the tubes of the respective set of tubes in series. Outlet-end electrical bridges are arranged between two adjacent tubes at or near their end portions facing towards their outlet openings and are configured to form a flexible or bendable electrical connection between the two adjacent tubes at or near their end portions. A portion of each of the outlet-end electrical bridges is helically wound around a portion of one of the tubes or both of the tubes to which it is attached in an electrically conductive manner.

Description

[0001] Electric Gas Heater

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to an electric gas heater.

[0004] BACKGROUND

[0005] Electric gas heaters are utilized in a variety of industrial applications. An important industrial application is process heating, wherein electric gas heaters are used to maintain specific temperatures required for industrial processes in sectors like chemical, petrochemical, and pharmaceutical industries. In the food and beverage industry, electric gas heaters are used in the production of food and beverages for processes such as pasteurization, sterilization, and other heat treatments. Electric gas heaters are suitable for the heating of many types of gases and gas mixtures from normal ambient air to highly explosive gases such as hydrogen, which, for examples, is used as a “clean fuel” in the steel industry in a heated state for the reduction of iron ore.

[0006] In general, electric gas heaters generate heat by resistive heating. A current is passed through electrically conductive members, such as heating wires, tubes or other electrically conductive parts, thereby resistively heating the members, and gas to be heated is passed along or through the heated members for heat transfer from the members to the gas. Compared to heating by combustion of fuels, electric heating, especially when sourced from renewable energy, greatly reduces process costs and the carbon footprint of the heating process. This is particularly important for energy-intensive industries, like steel production, considering increasing costs of fossil fuels and carbon dioxide emissions trading.

[0007] Furthermore, compared to heating by fuel combustion, the electric gas heating is valued for its efficiency and ability to reach the desired temperatures quickly and in a well-controlled manner. Moreover, the heating process is considered to be safer, especially when explosive gases are heated, and it reduces the risk of contamination or reaction that could compromise the quality of the end product.

[0008] US 927,173 discloses an electric air heater comprising a housing having a gas intake pipe in communication with the surrounding atmosphere for the inflow of air to be heated and a gas outlet pipe at the opposite side of the housing for the outflow of heated air. Within the housing, a large number of thin walled nickel tubes are mounted as resistive heating members through insulation in transverse sheet metal walls in a direction extending from the intake side to the outlet side of the housing. The nickel tubes are electrically connected in series in an uninterrupted conductor for electrical current. The ends of this conductor terminate in two binding posts mounted through insulation upon the housing. The heat produced by the nickel tubes upon resistive heating is given off to the air within and surrounding the tubes. If air is forced through the intake pipe, it flows partly through the tubes and partly through the space surrounding the tubes, and will become heated in consequence of the contact surface provided by the inner and outer surfaces of the heated nickel tubes.

[0009] FR 2664784 discloses a fluid heater comprising a bundle of tubes, which tubes are heated by resistance heating, are substantially parallel, and are connected electrically by linkage bars. The linkage bars support the tubes. The tubes transmit heat simultaneously via their inner and outer surfaces. The bundle of tubes may be combined with refractory bricks with which it defines annular spaces promoting heat transfer by convection.

[0010] US 4,233,494 discloses a throughflow heater for fluids, in particular, an air heater for use in regenerating a carbon-dioxide adsorber in an air-rectification system. Air is pumped from an upper chamber in a cylindrical housing through Ni-Cr steel heating tubes arranged in parallel groups to a lower chamber communicating with a carbon-dioxide adsorber. The tube groups are suspended at their upper ends from respective AI2O3 ceramic holder plates seated on flanges projecting into respective openings of a carrier plate in turn removably fastened to the inside of the housing. The tubes in each group are connected in series with one another to a power source, the lower ends of the tubes in a group being gripped by a form-fitted ceramic spacer slidably inserted into a pipe section aligned in a support plate with an associated opening in the upper carrier plate, thereby ensuring the electrical insulation of the tubes.

[0011] Electric gas heaters, especially those wherein a plurality of electrically conductive tubes are connected in series for resistive heating and wherein the gas is directed through the tubes, such as in US 4,233,494, usually comprise an inlet chamber and an outlet chamber with the inlet openings of the tubes being connected to and extending into the inlet chamber in a gastight manner for the inflow of gas from the inlet chamber. Gas is introduced into the inlet chamber, which acts as a manifold to distribute the gas into the plurality of resistively heated tubes. At the opposite end of the tubes, the outlet openings of each tube are connected to and extend into the outlet chamber in a gas-tight manner, wherein the outflowing gas is collected and guided for the intended further use of the heated gas. To provide stable support and connection of the tube ends to the inlet and outlet chambers, there is usually provided a supporting element, such as a support plate, with channels or bores through which the tube ends extend into the respective chamber and are mechanically fixed. The connection of the tube ends to the support plate channels or bores has to ensure electrical insulation of the conductive tubes from the support plate to avoid short circuit and must be gastight to ensure that the gas only flows into and through the tubes instead of flowing past them. However, to establish electrical connection of a group of tubes in series, electrical connectors are provided between the end regions of pairs of two neighbouring tubes.

[0012] In order to ensure proper operation of the electric gas heater it is important that the tubes of an electric gas heater are separated from each other. Therefore, positioning of the tubes of an electric gas heater is complicated and may require intricate positioning arrangements to fulfil both its positioning and electrical insulation requirements. Particularly, if an electric gas heater shall comprise a large number of parallel tubes, the suspension needs to be sufficiently strong in order to carry the weights of this large number of parallel tubes.

[0013] Known connectors for electrical connection of pairs of two adjacent tubes to establish electrical connection of a group of tubes in series consist of a rigid block of metal adapted to receive therethrough the tube ends of two adjacent heating tubes. The rigid connector block is secured to the tube ends, such as by welding to the outer surface of the tubes around the periphery of the holes or bores in the rigid connector block. Thereby, a reliable electrical connection is provided, and, at the same time, the rigid connector block ensures stable positioning and suspension of the tubes as well as distancing of the tubes to avoid short circuit by direct contact. The rigid connector blocks at opposite ends of the group of tubes are usually anchored with the support plates or flanges of the inlet and outlet chambers in a stable, gas-tight and electrically insulated manner.

[0014] However, these types of connectors have problems with the occurrences of tension and bending between electrically connected tubes due to unequal expansion or elongation, respectively, during resistive heating. This may lead to damage, especially at the connection sites, where two adjacent tubes are connected by a rigid block connector, and disruption of the electrical connection between the tubes and, in the worst case, to breakage of the tubes.

[0015] The aim of the disclosure is therefore to provide an electric gas heater, which overcomes the disadvantages of the prior art. SUMMARY OF THE DISCLOSURE

[0016] Hence, according to an aspect, the present disclosure provides an electric gas heater comprising: a bundle of a plurality of electrically conductive tubes for resistive heating, the plurality of electrically conductive tubes of the bundle forming one set of tubes or two or more sets of tubes, wherein the tubes of the bundle are arranged parallel to each other or substantially parallel to each other with respect to their axial extension and such that each tube is arranged with its conductive outer surface at a distance from the conductive outer surface of each other tube, wherein each tube has an inlet opening for the inflow of gas and an outlet opening for the outflow of gas. Electrical conductors are configured for connecting each set of tubes with an external electric power supply. Electrical bridges are arranged between and attached to the tubes of the plurality of electrically conductive tubes in a manner that provides within each set of tubes for an electric current from the external electric power supply to flow through the tubes of the respective set of tubes in series. Inlet-end electrical bridges provide an electrical connection between two adjacent tubes at or near their end portions facing towards their inlet openings and outlet-end electrical bridges provide an electrical connection between two adjacent tubes at or near their end portions facing towards their outlet openings. The outlet-end electrical bridges arranged between two adjacent tubes at or near their end portions facing towards their outlet openings are configured to form a flexible or bendable electrical connection between the two adjacent tubes at or near their end portions which allows for an axial movement of the end portions of the two adjacent tubes relative to each other while maintaining the electrical connection between them. A portion of each of the outlet-end electrical bridges is helically wound around a portion of one of the tubes or both of the tubes to which it is attached in an electrically conductive manner.

[0017] In this manner, due to the outlet-end helically wound bridges, during heating of the tubes, when the tubes are subjected to unequal expansion and / or elongation, transfer of tension and bending forces between electrically connected tubes via the outlet-end electrical bridges is significantly reduced. This so, in comparison with bridges extending straight between the outlet ends of the tubes, i.e. bridges that are rigid and stiff, such as being formed of a rigid block or plate of metal. Thus, damage to the tubes and / or to the electrical connection between the tubes is avoided in use of the electric gas heater.

[0018] Helically winding of the outlet-end electrical bridges around a portion of one of the tubes or both of the tubes provides a superior flexible or bendable electrical connection and length compensation between the two electrically connected tubes in the case of axial movement of their end portions relative to each other due to unequal expansion or elongation, respectively, while maintaining the electrical connection between the tubes.

[0019] More specifically, the portion or portions of each of the outlet-end electrical bridges which is helically wound around a portion of one of the tubes or both of the tubes act as one or two helical springs, which can be compressed and expanded independently to compensate for any occurring difference in length between the two tubes due to unequal expansion or elongation during use of the electric gas heater.

[0020] The electric gas heater comprises a bundle of a plurality of electrically conductive tubes for resistive heating. The tubes of the bundle are arranged parallel to each other or substantially parallel to each other with respect to their axial extension, and the inlet openings of the tubes are defined to be arranged at one end of the bundle and the outlet openings of the tubes are defined to be arranged at the opposite end of the bundle in axial direction. The electric gas heater is configured that gas to be heated is guided or flowed, respectively, through the tubes from the inlet opening towards the outlet opening of the tubes and in direct contact with inner surfaces of the tubes.

[0021] The electric gas heater is configured for the gas to flow through the tubes from their inlet openings to their outlet openings and in direct contact with inner surfaces of the tubes,

[0022] The electric gas heater may comprise a header, such as in the form of an inlet chamber, to receive the gas to be heated and guide it into the inlet openings of the tubes, during use of the electric gas heater.

[0023] Generally, the electric gas heater may be configured for use with large mass flow rates and high temperatures with a power rating in the Megawatt range. The electric gas heater may be utilized for heating of any type of gas, such as air, hydrogen, hydrocarbons and other gases to high temperatures, such as 400 to 1250°C or even higher. However, the gases may also have lower temperatures.

[0024] The electric gas heater may be suited to heat gas from low temperature, such as room temperature, or heat gas from already elevated temperature, such as from 300 to 900°C, to high temperatures. The number of tubes of the bundle of a plurality of electrically conductive tubes of the electric gas heater may be from 2 to 500 tubes, such as from 20 to 500 tubes, such as from 100 to 300 tubes.

[0025] According to embodiments, the tubes of the electric gas heater may be of the same type with respect to material and dimensions, such as inner diameter, wall thickness and length. The individual tubes of the bundle may have an inner diameter within a range from 7 to 30 mm, such as from 9 to 20 mm and / or a wall thickness within a range of from 1 to 3 mm, such as from 1.5 to 2.5 mm.

[0026] According to embodiments, the lengths of the individual tubes of the bundle may be within a range of from 0.5 to 10 m, or within a range of from 1 to 2.5 m. The temperature increase of the tubes during use of the electric gas heater results in a thermal expansion of the tube material, which primarily affects the lengths of the tubes. The length expansion depends on the coefficient of linear expansion of the respective tube material.

[0027] Due to the different positions of the tubes electrically connected in series within a set of tubes, the linear expansion of adjacent or neighbouring tubes electrically connected to each other may not be the same upon resistive heating. Different linear expansion of adjacent or neighbouring tubes may also result from the gas flow and how the tubes are positioned, for example, how close they are positioned to insulation.

[0028] According to embodiments, the bundle of the plurality of electrically conductive tubes forms one single set of tubes electrically connected in series. In these embodiments the single set of tubes represents the whole bundle of tubes.

[0029] According to further embodiments, the plurality of electrically conductive tubes of the bundle form two or more sets of tubes, wherein the total number of tubes of all sets of tubes amounts to the total number of tubes of the plurality of electrically conductive tubes of the bundle.

[0030] Independent whether the bundle of tubes forms one single set of tubes or forms two or more sets of tubes, in each set of tubes two of the tubes are connected to an external electric power supply by electrical conductors. The remaining tubes of the respective set of tubes are electrically connected in series for the electric power to flow through the tubes from one to the other of the two tubes connected to the external electric power supply. For the electrical connection in series within a set of tubes, a first tube connected to the external electric power supply by an electrical conductor at one end portion, for example at the inletend portion, is electrically connected to a neighbouring second tube within the set of tubes by an electrical bridge at the opposite end portions of the tubes, which in this case would be the outlet-end portions. The second tube connected to the first tube is then connected to a neighbouring third tube at its opposite end portion electrically connected to the second tube, which in this case would be the inlet-end portion, and so on, until the connections in series reach the final tube of the set of tubes, which is connected to the external electric power supply.

[0031] According to embodiments, the connections of the two tubes of a set of tubes connected to the external electric power supply by electrical conductors are arranged at the same side of both tubes, either at their inlet-end portions or their outlet-end portions. This means that each set of tubes electrically connected in series consists of an even number of tubes. According to one embodiment, the connections of the two tubes to the external electric power supply by electrical conductors are arranged at their inlet-end portions.

[0032] According to embodiments, the two or more sets of tubes of a bundle of a plurality of tubes are connected to the same external electric power supply.

[0033] In alternative embodiments, each set of tubes is connected to a separate external electric power supply, which allows for the electric power supplied to each set of tubes to be individually set. This may be desired or beneficial to adjust the temperature generated by resistive heating for each set of tubes individually. For example, different sets of tubes may exhibit different properties in the heating process if they consist of different numbers of tubes connected in series, which in turn would result in different total electric resistance and heating properties. This can be compensated for by adjusting the electric power supplied to each set of tubes individually. On the other hand, different temperatures may also be set for different sets of tubes, if desired.

[0034] In yet further embodiments, a group of one or more sets of tubes of the bundle are connected to one external electric power supply, and one or more further groups of one or more sets of tubes of the bundle are connected to one or more separate external electric power supplies. This allows for the electric power supplied to each group to be individually set with the options and advantages described above. To avoid short circuit, the tubes electrically connected in series at their inlet-end portions and outlet-end portions have no electrical contact between these connections along their axial extensions parallel to each other. The same applies for tubes of different sets of tubes. Electrical insulation of the tubes from each other may be achieved by proper positioning and suspension of the tubes with sufficient distance from each other, providing insulators between neighbouring tubes, providing insulating coatings or cover around the conducting surfaces of the tubes or a combination of these measures. According to embodiments, sleeves, preferably insulating ceramic spacer sleeves are arranged around portions of some or all of the tubes to provide spacing and / or insulation of adjacent tubes from each other.

[0035] The electrical conductors connecting two of the tubes of each set of tubes with an external electric power supply may be of any type known in the art for such connections, such as one or more of a plate, a pin, a clamp, a bar or a strip, such as a strip of braided or woven wires. The electrical conductors may be welded, brazed, screwed, or clamped to the relevant tubes. According to embodiments, the electrical conductors are welded to the conductive outer surfaces of the tubes at one of their end portions, such as at their inlet-end portions.

[0036] The external electric power supply may comprise mains power or may be connected to mains power via a transformer for adapting a voltage of electric current supplied to the electric gas heater.

[0037] For the electrical connection in series within a set of tubes, two neighbouring or adjacent tubes within the set of tubes are electrically connected by inlet-end electrical bridges at or near their end portions facing towards their inlet openings.

[0038] According to embodiments, the inlet-end electrical bridges are rigid and stiff, such as a rigid block or plate of metal, to ensures stable positioning and suspension of the tubes as well as distancing of the tubes at their inlet-end. The inlet-end electrical bridges may be anchored with a support plate or flange on the inlet-side of the electrical gas heater.

[0039] According to the present disclosure, the outlet-end electrical bridges for the electrical connection between two neighbouring or adjacent tubes at or near their end portions facing towards their outlet openings are configured to form a flexible or bendable electrical connection between the two adjacent tubes at or near their end portions which allows for an axial movement of the end portions of the two adjacent tubes relative to each other while maintaining the electrical connection between them. The present outlet-end electrical bridges overcome the problem of tension and bending between two electrically connected tubes due to unequal expansion or elongation, respectively, during resistive heating. With the present outlet-end electrical bridges damage, especially at the connection sites, and disruption of the electrical connection between the tubes and, in the worst case, breakage of the tubes can be avoided.

[0040] Advantageously, the electric gas heater of the present disclosure may be utilized with greater temperature differences and / or a greater degree of temperature modulation, as the pipes will be able to move and / or expand.

[0041] Furthermore, the electric gas heater of the present disclosure may be easier to produce, as it allows differences in lengths of the tubes to a certain extent.

[0042] According to embodiments, the outlet-end electrical bridges comprise or consist of one or more wires, strips or sheets of conductive material or a combination thereof.

[0043] The one or more wires, strips or sheets of conductive material are attached in an electrically conductive manner to the tubes to be electrically connected. The attachment of the outlet-end electrical connectors to the tubes in an electrically conductive manner is suitably made by welding, brazing, soldering, clamping, gluing or screwing. Attachment of the outlet-end electrical connectors to the tubes by welding is preferred, as it provides a stable and long-lasting connection with good electrical conduction between the tube and the outlet-end electrical connector.

[0044] According to embodiments, the end portions of each of the one or more outlet-end electrical bridges, such as wires, strips or sheets, are attached in an electrically conductive manner to one of each of the two adjacent tubes to be electrically connected. Attachment of the outletend electrical bridges to the tubes may be by welding to the outer surface of the tube.

[0045] According to embodiments, one end portion of each of the one or more outlet-end electrical bridges is attached in an electrically conductive manner to one of the two adjacent tubes, and the other end portion of the respective outlet-end electrical bridge is attached in an electrically conductive manner to another outlet-end electrical bridge, which is attached in an electrically conductive manner to the other one of the two adjacent tubes. According to embodiments, the outlet-end electrical bridge between two tubes consist of one single wire, strip or sheet with each end-region of the bridge being attached to one of the two tubes to be connected.

[0046] According to further embodiments, the outlet-end electrical bridge between two tubes comprises two or more wires, strips or sheets with each of the two end-regions of each wire, strip or sheet being attached to one of the two tubes to be connected. By providing two or more wires, strips or sheets for the connection of two tubes, a failure or disruption of the connection of attachment one of the wires, strips or sheets from one or both of the tubes can be balanced or compensated by the remaining wire(s), strip(s) or sheet(s) to maintain the electrical connection and to avoid failure of the entire electrical connection in series of the whole set of tubes.

[0047] According to embodiments, each wire, strip or sheet is attached to one of the two tubes in an electrically conductive manner, such as by welding, and, starting from the attachment site the wire, strip or sheet is helically wound about a region of said tube towards the outlet-end of the tube or in opposite direction. The wire, strip or sheet is then further guided to the neighbouring tube to be electrically connected, again helically wound about a region of said neighbouring tube, and attached to said tube in an electrically conductive manner.

[0048] Thus, each one of the two tubes is able to expand or elongate along its lengthwise extension relative to the helically wound wire, strip, or sheet. Moreover, any difference in expansion or elongation between the two tubes affects the length of the respective portions of the helically wound wire, strip, or sheet around each of the two tubes, which are compressed or expanded accordingly.

[0049] According to embodiments, each wire, strip or sheet is attached to one of the tubes in an electrically conductive manner, such as by welding, and, starting from the attachment site, the wire, strip or sheet is helically wound about a distance around both neighbouring tubes to be electrically connected towards their outlet-ends or in opposite direction. The wire, strip or sheet is then attached to the other tube in an electrically conductive manner.

[0050] Thus, again, as discussed above, each one of the two tubes is able to expand or elongate along its lengthwise extension relative to the helically wound wire, strip, or sheet. Any difference in length due to expansion or elongation between the two tubes results in compression or expansion of the helically wound wire, strip, or sheet around the two tubes. In the electric gas heater, the tubes consist of an electrically conducting material for active resistive heating or more than one electrically conducting material for active resistive heating. According to embodiments, the electrically conducting material of the tubes is selected from the group consisting of iron-chromium-aluminium alloys (FeCrAI alloys), nickel-based alloys, nickel-chromium alloys (NiCr alloys), nickel-chromium-iron alloys (NiCrFe alloys) or compositions based on molybdenum (Mo) disilicide and / or tungsten (W) disilicide.

[0051] According to embodiments, at least the electrically conductive part of the tubes consists of one single material for active resistive heating. In an aspect of the disclosure the electrically conducting material is the same in all tubes. According to further embodiments, different tubes may be manufactured from different electrically conducting materials, which may be useful to adjust the heating properties of different tubes within a series of electrically connected tubes and / or between different sets of tubes of the bundle.

[0052] According to embodiments, the electrically conductive part of the tubes consists of two or more different materials, each of them being electrically conductive and suitable for resistive heating. The two or more different materials may be coated or laminated onto each other forming the tube wall.

[0053] According to embodiments, the electrically conducting material of the tubes is an aluminium oxide forming material, such as iron chromium aluminium alloy comprising at least 3 wt% aluminium. The aluminium oxide will form a protective layer and thereby, the tubes may withstand both high temperatures and other harsh environmental conditions and thus, may enable heating of gas to high temperatures. Example of such material is the material sold by the company Kanthal under the tradename Kanthal® APMT and Kanthal® APM.

[0054] According to embodiments, the electric gas heater comprises a housing possessing an inlet chamber and an outlet chamber, wherein the electric gas heater is configured for the gas to flow through the plurality of electrically conductive tubes of the bundle from the inlet chamber to the outlet chamber, and wherein the inlet opening of each tube of the bundle is connected to the inlet chamber for the inflow of gas from the inlet chamber and the outlet opening of each tube of the bundle is connected to the outlet chamber for the outflow of gas into the outlet chamber.

[0055] According to embodiments, the inlet opening of each tube of the bundle is connected to the inlet chamber in a gas-tight manner. According to further embodiments, the outlet opening of each tube of the bundle is connected to the outlet chamber in a gas-tight manner. During use of the electric gas heater, a stream of gas to be heated is charged into the inlet chamber, and the inlet chamber acts as a manifold for distributing a collective gas stream to the individual tubes. The outlet chamber acts as a manifold for converging gas that has been heated in the individual tubes into one collective gas stream.

[0056] The electric gas heater may be utilised for heating gas to be used in an industrial process, e. g. as an energy carrier and / or as a heat source.

[0057] The electric gas heater provides directly electrically heated tubes and thereby directly energized tubes, which do not require any additional heating elements and thus, provide basis for an uncomplicated construction of the gas heater. The gas heater is of a simple construction requiring few different components. Although the heater may comprise hundreds of individual tubes, the tubes may be of a limited number of different kinds.

[0058] According to a further aspect of the disclosure, there is provided a bundle of a plurality of electrically conductive tubes for resistive heating, the plurality of electrically conductive tubes of the bundle forming one set of tubes or two or more sets of tubes. The electrically conductive tubes of the bundle are arranged parallel to each other or substantially parallel to each other with respect to their axial extension and such that each tube is arranged with its conductive outer surface at a distance from the conductive outer surface of each other tube. Each electrically conductive tube has an inlet opening for the inflow of gas and an outlet opening for the outflow of gas. Electrical bridges are arranged between and attached to the electrically conductive tubes of the plurality of electrically conductive tubes in a manner that provides within each set of tubes for an electric current to flow through the tubes of the respective set of tubes in series. Inlet-end electrical bridges provide an electrical connection between two adjacent tubes at or near their end portions facing towards their inlet openings and outlet-end electrical bridges provide an electrical connection between two adjacent tubes at or near their end portions facing towards their outlet openings. The outlet-end electrical bridges arranged between two adjacent tubes at or near their end portions facing towards their outlet openings are configured to form a flexible or bendable electrical connection between the two adjacent tubes at or near their end portions which allows for an axial movement of the end portions of the two adjacent tubes relative to each other while maintaining the electrical connection be-tween them. A portion of each of the outlet-end electrical bridges is helically wound around a portion of one of the tubes or both of the tubes to which it is attached in an electrically conductive manner. As discussed above with reference to the electric gas heater, in this manner, the helical winding of the outlet-end electrical bridges around a portion of one of the tubes or both of the tubes provides a superior flexible or bendable electrical connection and length compensation between the two electrically connected tubes in the case of axial movement of their end portions relative to each other due to unequal expansion or elongation, respectively, while maintaining the electrical connection between the tubes.

[0059] According to some embodiments, the outlet-end electrical bridges between two adjacent tubes at or near their end portions facing towards their outlet openings may comprise or may consist of one or more wires, strips or sheets of conductive material or a combination thereof. In this manner, suitably shaped outlet-end electrical bridges may be provided for them to be helically wound about the adjacent tubes.

[0060] According to some embodiments, each wire, strip or sheet is attached to one of the two adjacent tubes in an electrically conductive manner, and starting from the attachment site the wire, strip or sheet may be helically wound about a region of said one tube towards the outlet-end of the tube or in an opposite direction. The wire, strip or sheet then may be further guided to the neighbouring tube to be helically wound about a region of said neighbouring tube and is attached to said neighbouring tube in an electrically conductive manner. In this manner, as discussed above, each one of the two tubes is able to expand or elongate along its lengthwise extension relative to the helically wound wire, strip, or sheet. Moreover, any difference in expansion or elongation between the two tubes affects the length of the respective portions of the helically wound wire, strip, or sheet around each of the two tubes, which are compressed or expanded accordingly.

[0061] According to some embodiments, each wire, strip or sheet is attached to one of the two adjacent tubes in an electrically conductive manner, and starting from the attachment site, the wire, strip or sheet may be helically wound about a distance around the two adjacent tubes to be electrically connected towards their outlet-ends or in an opposite direction. The wire, strip or sheet is attached to the other tube of the two adjacent tubes in an electrically conductive manner. In this manner, Thus, again, as discussed above, each one of the two tubes is able to expand or elongate along its lengthwise extension relative to the helically wound wire, strip, or sheet. Any difference in length due to expansion or elongation between the two tubes results in compression or expansion of the helically wound wire, strip, or sheet around the two tubes. A further aspect of the disclosure relates to a furnace comprising at least one electric gas heater or at least one bundle of tubes according to any one of aspects and / or embodiments as discussed herein.

[0062] A further aspect of, the disclosure relates to a method for heating a gas in an electric gas heater according to any one of aspects and / or embodiments as discussed herein, the method comprising the steps of:

[0063] - supplying a gas to the inlet openings of the plurality of electrically conductive tubes of the bundle and conducting the gas through the electrically conductive tubes to the outlet openings of the electrically conductive tubes,

[0064] - supplying electric current to each set of the electrically conductive tubes of the bundle in order to heat the electrically conductive tubes,

[0065] - continue with conducting the gas through the electrically conductive tubes to the outlet openings of the electrically conductive tubes, and

[0066] - leading the gas from the outlet openings of the electrically conductive tubes.

[0067] BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figures 1-7 schematically illustrate embodiments of outlet-end electrical connectors for the electrical connection between two neighbouring tubes near their end portions facing towards their outlet openings in accordance with the present disclosure.

[0069] Figures 8a - 8c schematically illustrate an electric gas heater comprising a bundle of a plurality of electrically conductive tubes.

[0070] Figure 9 illustrates a method for heating a gas in an electric gas heater.

[0071] DETAILED DESCRIPTION

[0072] Aspects and embodiments will be described in more detail below with reference to exemplifying embodiments and the accompanying drawings. The disclosure is however not limited to the exemplifying embodiments discussed and / or shown in the drawings, but may be varied within the scope of the appended claims. Furthermore, the drawings shall not be considered drawn to scale as some features may be exaggerated in order to more clearly illustrate aspects and / or embodiments. Like numbers refer to like elements throughout. Well-known functions or constructions will not necessarily be shown and / or described in detail for brevity and / or clarity. Figures 1 to 7 schematically illustrate embodiments of outlet-end electrical bridges 5 for the electrical connection between two neighbouring tubes 2 near their outlet-end portions 7 facing towards their outlet openings 4 of an electric gas heater in accordance with the present disclosure. The electric gas heater may be an electric gas heater 1 as discussed below with reference to figures 8a - 8c. The illustrations of figures 1 to 4 are to be understood schematically in that the tubes of the electric gas heater are usually longer than shown herein in their axial extension relative to the dimensions of the shown outlet-end portions 7 of the tubes 2, where the outlet-end electrical bridges 5 are arranged. Therefore, figures 1 to 4 also show the inlet openings 3 and inlet-end portions 6 of the tubes 2 for illustrative purposes.

[0073] In the embodiments of figures 1 to 4, the outlet-end electrical bridges 5 between the two tubes consist of one single flexible and / or bendable wire 17, with each end-region of the wire 17 being attached to the tubes 2 to be electrically connected.

[0074] Inlet-end electrical bridges 9 are discussed below with reference to figures 8a - 8c.

[0075] In the embodiment shown in figure 1 , one end of the wire 17 is attached to a first of the two tubes near its outlet-end opening 4 in an electrically conductive manner by welding. Starting from the attachment site at the first tube 2 the wire is helically wound around the outlet-end portion 7 of said tube 2 about a distance towards the inlet-end portion 6 of the tube 2, and is then further guided to the neighbouring tube 2 to be electrically connected, again helically wound around the outlet-end portion 7 of said neighbouring tube 2 about a distance towards the outlet-end of said tube 2, and is attached to said tube 2 near its outlet-end opening 4 in an electrically conductive manner by welding.

[0076] In the embodiment shown in figure 2, one end of the wire 17 is attached to a first of the two tubes 2 distant from its outlet-end opening 4, helically wound around the outlet-end portion 7 of said tube 2 about a distance towards the outlet-end of the tube 2, is then further guided to the neighbouring tube 2 to be electrically connected, again helically wound around the outletend portion 7 of said neighbouring tube 2 about a distance towards the inlet-end portion 6 of said tube 2, and is attached to said tube 2 distant from its outlet-end opening 4 in an electrically conductive manner by welding.

[0077] In the embodiments shown in figures 3 and 4, the wire 17 is attached to one of the two tubes near its outlet-end opening 4, helically wound around the outlet-end portions 7 of both neighbouring tubes 2 about a distance towards the inlet-end portions 6 of the tubes 2, and is then distant from its outlet-end openings 4 either attached to the same tube 2, to which the opposite (starting) end of the wire 17 is attached (figure 3), or to the other tube 2 (figure 4) in an electrically conductive manner by welding.

[0078] Figures 5 to 7 show embodiments, wherein the outlet-end electrical bridge 5 between two tubes 2 comprises strips 17’, instead of wire. At each of two tubes 2, one end of each of two strips 17’ is attached to the respective tube 2 distant from its outlet opening 4 by welding. The two strips 17’ are helically wound side by side around the outlet-end portion 7 of the respective tube towards its outlet-end opening 4. Near the outlet-end openings 4 of two tubes 2, each end portion of the strips 17’ is connected to an end portion of a strip 17’ attached to the respective neighbouring tube 2 by welding. However, instead of attaching the ends of the strips 17’ to each other between the two tubes to be connected, longer strips may be utilized and helically wound around the outlet-end portions 7 of both tubes, similar to the use of the wire shown in figures 1 and 2.

[0079] In the embodiments shown in figures 5 to 7 insulating ceramic spacer sleeves 8 are arranged around portions of the tubes 2 to provide spacing and insulation of neighbouring tubes from each other to avoid short circuit.

[0080] Figure 7 shows a bundle 11 of a plurality of electrically conductive tubes 2 forming three sets of tubes 2. Each set of tubes is separately connected with an external electric power supply by electrical conductors (not shown). The outlet-end electrical bridges 5 are arranged between and attached to the electrically conductive tubes 2 in a manner that the tubes within each set of tubes are electrically connected in series for an electric current to flow from a first electrical conductor connected to the external electric power supply through the series of tubes of the respective set of tubes to a second electrical conductor connected to the external electric power supply.

[0081] By providing two or more wires or strips 17, 17’ side by side for the connection of two tubes 2, as shown in figures 5 to 7, a failure or disruption of the connection or detachment of the wires or strips 17, 17’ from one or both of the tubes can be balanced or compensated by the remaining wire(s) or strip(s) to maintain the electrical connection and to avoid failure of the entire electrical connection in series of the whole set of tubes. Flexibility may also be varied by the diameter of the wire or the width of strip. In order to meet any required conductive cross-sectional area, it may be required to use a number of outlet-end electrical bridges 5 in parallel. The electrical bridges 5 may be positioned in parallel as since in any contact they will have the same electrical potential which means there will be essentially no risk for shorting out. The outlet-end electrical bridges 5, exemplified by the embodiments illustrated in figures 1 to 7, form a flexible or bendable electrical connection between two adjacent tubes at or near their end portions 7 which allows for an axial movement of the end portions of the two tubes relative to each other while maintaining the electrical connection between them. The present outletend electrical bridges 5 overcome the problem of tension and bending between two electrically connected tubes due to unequal expansion or elongation, respectively, during resistive heating. With the present outlet-end electrical bridges damage, especially at the connection sites, and disruption of the electrical connection between the tubes and, in the worst case, breakage of the tubes can be avoided.

[0082] In alternative embodiments, the bundle 11 of a plurality of electrically conductive tubes 2 may form a different number of sets than three sets, such as one, two, or more than three sets of tubes 2.

[0083] Figures 8a - 8c schematically illustrate an electric gas heater 1 comprising a bundle 11 of a plurality of electrically conductive tubes 2. Figure 8a shows an isometric see-through view of the electric gas heater 1 , figure 8b shows a top view of the electric gas heater 1 , and figure 8c shows a section along the electric gas heater 1.

[0084] The electrically conductive tubes 2 are electrically connected to each other via outlet-end electrical bridges 5 arranged between two neighbouring tubes 2 near their outlet-end portions 7 according to any one of the embodiments discussed above with reference to figures 1 - 7.

[0085] End portions 6 of tubes 2 facing towards inlet opening 3 of the tubes are shown in figures 8a - 8c and most clearly visible in figure 8b. Inlet-end electrical bridges 9 provide an electrical connection between two adjacent tubes 2 at or near their end portions 6 facing towards their inlet openings 3.

[0086] The inlet-end electrical bridges 9 are rigid and stiff, to ensures stable positioning and suspension of the tubes 2 as well as distancing of the tubes at their inlet-ends. The inlet-end electrical bridges 9 are supported by and / or anchored to a support plate 13 or flange of the electrical gas heater 1.

[0087] The bundle 11 of tubes 2 of the electric gas heater 1 shown in figures 8a - 8b forms one set of tubes 2. Two electrical conductors 10 are provided for connecting the set of tubes 2 with an external electric power supply 12. Alternatively, the bundle 11 of tubes 2 may form more than one set of tubes, such as e.g. three sets of tubes as discussed above with reference to figure 7. In such embodiments one or more further electrical conductors 10 may be provided for connecting each set of tubes 2 with one or more external electric power supplies. For instance, three electrical conductors may supply three phase electric power in a Y- or delta-configuration to three sets of tubes 2.

[0088] In illustrated embodiments of the electric gas heater 1 , the number of electrically conductive tubes 2 of the set of tubes 2 is an even number of tubes 2. Accordingly, since the tubes 2 are connected in series with the set of tubes 2, the electrical conductors 10 configured for connecting the tubes 2 with the external electric power supply 12 are arranged at one axial end portion of the set of tubes 2, either at the end portion 6 facing towards the inlet openings 3 of the tubes 2 as shown in figures 8a - 8b or at the end portion 7 facing towards the outlet openings 4 of the tubes 2.

[0089] The electric gas heater 1 comprises a housing 14 possessing an inlet chamber 15 (schematically indicated) and an outlet chamber 16. The inlet chamber 15 is delimited from the outlet chamber 16 by the support plate 13 for supporting the tubes 2 in the heater 1.

[0090] The housing 14 may comprise a supporting structure, such as a shell and / or structure of beams, and insulation material for insulating the high temperatures prevailing within the electric gas heater 1 during use thereof.

[0091] In the illustrated embodiment, the housing 14 has a rectangular cross section. The housing 14 may have any appropriate alternative cross section suited for the bundle 11 of tubes to be arranged therein.

[0092] The electric gas heater 1 , during use thereof, is configured for the gas to flow through the plurality of electrically conductive tubes 2 of the bundle 11 , from the inlet chamber 15 to the outlet chamber 16. The gas is heated by the resistively heated tubes 2 as is flows through the tubes 2. The inlet opening 3 of each tube 2 of the bundle 11 is connected to the inlet chamber 15 for the inflow of gas from the inlet chamber 15. The outlet opening 4 of each tube 2 of the bundle 11 is connected to the outlet chamber 16 for the outflow of gas into the outlet chamber 16.

[0093] Heating of the gas in the electric gas heater 1 may be performed in accordance with the method 100 discussed below with reference to figure 9. Figs. 8a - 8c also relate to a furnace. The furnace may comprise at least one electric gas heater 1 or at least one bundle 11 of tubes 2 as discussed herein. In the furnace, the electric gas heater 1 or the at least one bundle 11 of tubes 2 is utilised to heat a gas within the furnace. The furnace comprises a supporting structure and insulation material, similarly to the housing 14 of the electric gas heater 1 discussed above, for at least temporarily containing matter within the furnace.

[0094] Figure 9 illustrates a method 100 for heating a gas in an electric gas heater. The electric gas heater is an electric gas heater 1 as discussed herein. Accordingly, in the following, reference is also made to the discussion of figures 1 - 8c.

[0095] The method 100 comprises the steps of:

[0096] - Supplying 102 a gas to the inlet openings 2 of the plurality of electrically conductive tubes 2 of the bundle 11 and conducting the gas through the electrically conductive tubes 2 to the outlet openings 4 of the electrically conductive tubes 2. Thus, the gas to be heated is transferred to, and through, the tubes 2.

[0097] - Supplying 104 electric current to each set of the electrically conductive tubes 2 of the bundle 11 in order to heat the electrically conductive tubes 2. Thus, the tubes 2 are resistively heated for the gas flowing through the tubes 2 to be heated by the tubes 2. The step of supplying 104 electric current to each set of the electrically conductive tubes 2 may be initiated prior to, or simultaneously with the step of supplying 102 a gas to the inlet openings 2.

[0098] - Continue with conducting 106 the gas through the electrically conductive tubes 2 to the outlet openings 4 of the electrically conductive tubes 2. Thus, a continuous heating of the gas is established.

[0099] - Leading 108 the gas from the outlet openings 4 of the electrically conductive tubes 2. In this manner, the heated gas may be conducted to a subsequent process step or to an intended end use thereof.

[0100] Reference Numbers

[0101] 1 electric gas heater

[0102] 2 electrically conductive tubes

[0103] 3 inlet opening

[0104] 4 outlet opening

[0105] 5 outlet-end electrical bridge

[0106] 6 end portion of tube facing towards the inlet opening

[0107] 7 end portion of tube facing towards the outlet opening

[0108] 8 insulating ceramic spacer sleeve

[0109] 9 inlet-end electrical bridge

[0110] 10 electrical conductors

[0111] 11 bundle of tubes

[0112] 12 external electric power supply

[0113] 13 support plate

[0114] 14 housing

[0115] 15 inlet chamber

[0116] 16 outlet chamber

[0117] 17, 17’ wire, strip or sheet

Claims

CLAIMS1 . An electric gas heater (1) comprising: a bundle of a plurality of electrically conductive tubes (2) for resistive heating, the plurality of electrically conductive tubes (2) of the bundle forming one set of tubes or two or more sets of tubes, wherein the electrically conductive tubes of the bundle are arranged parallel to each other or substantially parallel to each other with respect to their axial extension and such that each tube (2) is arranged with its conductive outer surface at a distance from the conductive outer surface of each other tube, wherein each electrically conductive tube (2) has an inlet opening (3) for the inflow of gas and an outlet opening (4) for the outflow of gas, wherein electrical conductors (10) are configured for connecting each set of tubes with an external electric power supply, wherein electrical bridges (9, 5) are arranged between and attached to the electrically conductive tubes (2) of the plurality of electrically conductive tubes (2) in a manner that provides within each set of tubes for an electric current from the external electric power supply to flow through the tubes of the respective set of tubes in series, wherein inlet-end electrical bridges (9) provide an electrical connection between two adjacent tubes at or near their end portions (6) facing towards their inlet openings (3) and outlet-end electrical bridges (5) provide an electrical connection between two adjacent tubes at or near their end portions (7) facing towards their outlet openings (4), wherein the outlet-end electrical bridges (5) arranged between two adjacent tubes at or near their end portions (7) facing towards their outlet openings (4) are configured to form a flexible or bendable electrical connection between the two adjacent tubes at or near their end portions (7) which allows for an axial movement of the end portions (7) of the two adjacent tubes (2) relative to each other while maintaining the electrical connection between them,and wherein a portion of each of the outlet-end electrical bridges (5) is helically wound around a portion of one of the tubes (2) or both of the tubes (2) to which it is attached in an electrically conductive manner.

2. The electric gas heater of claim 1 , wherein the outlet-end electrical bridges (5) between two adjacent tubes at or near their end portions (7) facing towards their outlet openings (4) comprise or consist of one or more wires, strips or sheets (17, 17’) of conductive material or a combination thereof.

3. The electric gas heater of any one of the preceding claims, wherein the electric gas heater is configured for the gas to flow through the electrically conductive tubes (2) from the inlet opening (3) to the outlet opening (4) and in direct contact with inner surfaces of the tubes (2).

4. The electric gas heater of any one of the preceding claims, wherein the end portions of each of the one or more outlet-end electrical bridges (5) are attached in an electrically conductive manner to one of each of the two adjacent tubes.

5. The electric gas heater of any one of the preceding claims, wherein one end portion of each of the one or more outlet-end electrical bridges (5) is attached in an electrically conductive manner to one of the two adjacent tubes, and the other end portion of the respective outlet-end electrical bridge (5) is attached in an electrically conductive manner to another outlet-end electrical bridge (5), which is attached in an electrically conductive manner to the other one of the two adjacent tubes.

6. The electric gas heater of any one of the preceding claims, wherein the attachment of the outlet-end electrical bridges (5) to the tubes in an electrically conductive manner is made by welding, brazing or soldering.

7. The electric gas heater of any one of the preceding claims, wherein the tubes (2) consist of an electrically conducting material for active resistance heating or more than one electrically conducting material for active resistance heating, and wherein the electrically conducting material is the same in all the tubes (2) or different and is selected from the group consisting of iron-chromium-aluminium alloys (FeCrAI alloys), nickel-based alloys, nickel-chromium alloys (NiCr alloys), nickel-chromium-iron alloys (NiCrFe alloys) or a compositions based on molybdenum (Mo) disilicide and / or tungsten (W) disilicide .

8. The electric gas heater of any one of the preceding claims, wherein the number of electrically conductive tubes (2) forming a set of tubes within the bundle of tubes (2) is an even number of tubes (2), and wherein the electrical conductors configured for connecting the tubes (2) of the set of tubes with an external electric power supply are arranged at one axial end portion of the set of tubes, either at the end portion (6) facing towards the inlet openings (3) of the tubes or at the end portion (7) facing towards the outlet openings (4) of the tubes.

9. The electric gas heater of any one of the preceding claims, wherein insulating ceramic spacer sleeves (8) are arranged around portions of some or all of the tubes to provide spacing and / or insulation of adjacent tubes from each other.

10. The electric gas heater of any one of the preceding claims comprising a housing (14) possessing an inlet chamber (15) and an outlet chamber (16), wherein the electric gas heater is configured for the gas to flow through the plurality of electrically conductive tubes (2) of the bundle (11) from the inlet chamber to the outlet chamber, and wherein the inlet opening (3) of each tube (2) of the bundle is connected to the inlet chamber for the inflow of gas from the inlet chamber and the outlet opening (4) of each tube of the bundle is connected to the outlet chamber for the outflow of gas into the outlet chamber.

11. A bundle (11) of a plurality of electrically conductive tubes (2) for resistive heating, the plurality of electrically conductive tubes (2) of the bundle forming one set of tubes or two or more sets of tubes, wherein the electrically conductive tubes of the bundle are arranged parallel to each other or substantially parallel to each other with respect to their axial extension and such that each tube (2) is arranged with its conductive outer surface at a distance from the conductive outer surface of each other tube, wherein each electrically conductive tube (2) has an inlet opening (3) for the inflow of gas and an outlet opening (4) for the outflow of gas, wherein electrical bridges (9, 5) are arranged between and attached to the electrically conductive tubes (2) of the plurality of electrically conductive tubes (2) in a manner that provides within each set of tubes for an electric current to flow through the tubes of the respective set of tubes in series, wherein inlet-end electrical bridges (9) provide an electrical connection between two adjacent tubes at or near their end portions (6) facing towards their inlet openings (3) and outlet-end electrical bridges (5) provide an electrical connection between two adjacent tubes at or near their end portions (7) facing towards their outlet openings (4),wherein the outlet-end electrical bridges (5) arranged between two adjacent tubes at or near their end portions (7) facing towards their outlet openings (4) are configured to form a flexible or bendable electrical connection between the two adjacent tubes at or near their end portions (7) which allows for an axial movement of the end portions (7) of the two adjacent tubes (2) relative to each other while maintaining the electrical connection between them, wherein a portion of each of the outlet-end electrical bridges (5) is helically wound around a portion of one of the tubes (2) or both of the tubes (2) to which it is attached in an electrically conductive manner.

12. The bundle (11) of claim 11 , wherein the outlet-end electrical bridges (5) between two adjacent tubes at or near their end portions (7) facing towards their outlet openings (4) comprise or consist of one or more wires, strips (17, 17’) of conductive material or a combination thereof.

13. The bundle (11) of claim 12, wherein each wire, strip or sheet (17, 17’) is attached to one of the two adjacent tubes (2) in an electrically conductive manner, and starting from the attachment site the wire, strip or sheet (17, 17’) is helically wound about a region of said one tube (2) towards the outlet-end (7) of the tube (2) or in an opposite direction, wherein the wire, strip or sheet (17, 17’) is then further guided to the neighbouring tube (2) to be helically wound about a region of said neighbouring tube (2), and attached to said neighbouring tube (2) in an electrically conductive manner.

14. The bundle (11) of claim 13, wherein each wire, strip or sheet (17, 17’) is attached to one of the two adjacent tubes (2) in an electrically conductive manner, and starting from the attachment site, the wire, strip or sheet (17, 17’) is helically wound about a distance around the two adjacent tubes (2) to be electrically connected towards their outlet-ends (7) or in an opposite direction, and wherein the wire, strip or sheet (17, 17’) is attached to the other tube (2) of the two adjacent tubes (2) in an electrically conductive manner.

15. A method (100) for heating a gas in an electric gas heater (1) according to any one of claims 1 - 10, the method (100) comprising the steps of:- supplying (102) a gas to the inlet openings (3) of the plurality of electrically conductive tubes (2) of the bundle and conducting the gas through the electrically conductive tubes (2) to the outlet openings (4) of the electrically conductive tubes (2),- supplying (104) electric current to each set of the electrically conductive tubes (2) of the bundle in order to heat the electrically conductive tubes (2),- continue with conducting (106) the gas through the electrically conductive tubes (2) to the outlet openings (4) of the electrically conductive tubes (2), and- leading (108) the gas from the outlet openings (4) of the electrically conductive tubes (2).

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