Method and device for electrically heating a stream of heat-transporting fluid
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- SYNHELION AG
- Filing Date
- 2024-08-06
- Publication Date
- 2026-06-17
Smart Images
Figure CH2024050039_20022025_PF_FP_ABST
Abstract
Description
[0001] Method and device for electrically heating a flow of heat-transporting fluid
[0002] The present invention relates to a method and a device for electrically heating a heat-transporting fluid comprising an IR-absorbing gas to at least 800°C.
[0003] Process heat with temperatures of 800°C or higher, up to 1300°C, is used in many applications. Such process heat is often transported via a heat-transporting fluid. Process heat is generated comparatively rarely in solar power plants and regularly by electric heating systems.
[0004] In solar power plants, receivers are used that are designed to reach temperatures of 1300°C. Solar radiation penetrates the structure of an absorber, heats it deeply, and thus heats the fluid passing through it via convection. This results in a virtually unpredictable, irregular heat distribution in the absorber structure, associated with mechanical problems and uneven heating of the fluid. Weather-dependent, fluctuating solar radiation can exacerbate these disadvantages. Therefore, it has been proposed to increasingly use absorption to heat the fluid in receivers. This has the advantage of resulting in a simpler receiver structure and mitigating irregular heat distribution and uneven heating of the fluid.
[0005] In addition to the rather rare, site-specific or weather-dependent solar power plants, electrical heating systems are widely used to heat gases used as heat-transporting fluids. As a standard, the absorption process for heat transfer, which is inherently possible, is avoided and forced convection is deliberately used, as disclosed, for example, in US Pat. No. 8,119,954. The design of these complex heating systems has many advantages, is sophisticated, and mechanical problems and the heat distribution in the fluid are fundamentally mastered by the expert.The operation of these electrical heating systems should continue to pose no problems even at temperatures of, for example, 1300°C, although at such temperatures there is an increasing risk that the fluid will corrode the heating systems, since the corrosion depends not only on the pairing of the material for the electrical heating elements and the heat-transporting fluid, but also on the temperature.
[0006] A disadvantage of the state-of-the-art electrical heating systems is that at higher temperatures, starting from 800°C and generally above 1000°C, the necessarily electrically conductive material of the resistance heating elements oxidizes easily, meaning that only inert gases or gases that are not corrosive to a particular material at these temperatures can be heated as a heat-transporting fluid.
[0007] Accordingly, it is the object of the present invention to provide a method for electrically heating both non-corrosive and corrosive gases, such as water vapor, to at least 800° C and a corresponding electrical heating device.
[0008] This object is achieved by a method having the features of claim 1 or by an electric heating device having the features of claim 17.
[0009] Because the heat-transporting fluid contains an infrared-absorbing gas and is exposed to the infrared radiation of an electrical heating device in an absorber chamber, heat transfer occurs predominantly through absorption, with the result that a structurally advantageously simplified electrical heating device is available, which in turn allows it to be modularly equipped with a protective gas arrangement for the resistance heating elements with only little additional structural effort in such a way that it can also be used on an industrial scale for a corrosive, heat-transporting fluid.
[0010] In addition to the stated object, it is also possible according to the invention to reach temperatures up to 1400 C, 1600 C or more, for which electrical heating devices for practical, even industrial, use have not been available so far, even for non-corrosive gases.
[0011] It follows that, according to the invention, non-corrosive gas such as CO2 and also corrosive gas such as water vapor can be heated to temperatures of more than 800°C up to the temperatures mentioned above, wherein for corrosive gas, a method or a design of the heating device according to the features of claims 5 and 27 is advantageous. Further preferred embodiments have the features of the remaining dependent claims.
[0012] The invention is described in more detail below with reference to the figures.
[0013] It shows:
[0014] Figure 1 schematically shows a known circuit in which a heat-transporting fluid circulates and is heated by an electric heating device,
[0015] Figure 2 schematically shows an embodiment of an electric heating device according to the invention,
[0016] Figures 3a to 3e schematically show various embodiments of an electric heating device according to the invention,
[0017] Figure 4 shows schematically an embodiment of the electric heating device modified for a corrosive gas,
[0018] Figure 5 schematically shows a further embodiment of an electric heating device for corrosive gas according to the invention,
[0019] Figure 6 shows schematically another embodiment of an electric heating device, and
[0020] Figure 7 schematically shows a method for separating protective gas present in a circuit of heat-transporting fluid of an electric heating device for corrosive gas according to the invention.
[0021] Figure 1 schematically shows a circuit known as such for a heat-transporting fluid with a fluid transport line 1, in which a heat-transporting fluid is transported in the direction of the arrow, heated to at least 800°C in an arrangement for heating the fluid, here an electric heating device 2 according to the invention, and fed to a consumer 3, where it releases its heat and is then fed back to the heating device 2 for further heating. The consumer 3, in turn, uses the heat obtained as process heat, which then allows its input and output, as is known to the person skilled in the art and symbolized by the arrows drawn at the consumer 3. The electric heating device 2 has a fluid supply connection 4 for the cold fluid (with the temperature T u ) and a fluid discharge connection 5 for the warm fluid (with the temperature T o), in addition electrical lines 6,6' for supplying the current required for heating the fluid from a symbolically indicated, suitable current source 7. It follows that the heat-transporting fluid is preferably guided in a circuit in which the arrangement for heating the fluid 2 and a consumer 3 for the heat of the heated fluid are located.
[0022] It should be noted that the method or electrical heating device according to the invention is not limited to use in a fluid circuit, although this is the main application.
[0023] Figure 2 shows a section through an arrangement according to the invention, designed as an electric heating device 10, for heating a heat-transporting fluid, with its fluid supply connection 4 and a collecting line having fluid collecting openings 11', designed here as a ring line 11, which serves as a collector for heated fluid and leads into a fluid output connection 5 (Figure 1a) omitted to reduce the load in the figure.
[0024] An infrared radiation device is designed as follows as a resistance heating element arrangement 12 (hereinafter the abbreviation "IR" is used for infrared): preferably concentrically arranged resistance heating elements 13 heat up during operation, ie when the power source 7 is activated, to a temperature of more than 800° C, up to, for example, 1200° C, 1400° C, 1600° C, 1800° C or more and thus emit the IR radiation 15 symbolized by the arrows via their surface 14 according to the black body model of physics.
[0025] The IR-radiating surface 14 formed by the individual surfaces of the heating elements 13 is directed into an absorber chamber 16, which extends over a length from one end, here the supply connection 4, to the other end, here the resistance heating element arrangement 12, and has a side wall 17 connecting them transversely to its ends, which side wall 17 has a cylindrical and a conical section. The fluid flows through the absorber chamber 16 in the direction of the arrows 18. The resistance heating element arrangement 12 thus forms, via the resistance heating elements 13, an IR radiation device having an IR-radiating surface 14 facing the absorber chamber 16. In other words, the IR-radiating surface 14 is designed, during operation, to release as completely as possible the heat generated by the resistance heating element arrangement 12 as IR radiation 15 into the absorber chamber 16.
[0026] The absorber chamber 16 from the supply connection 4 with an inlet temperature T u (which may be, for example, 600 °C or in another temperature range) in the direction of the arrows 18 now has an IR-absorbing gas which is exposed to the IR radiation 15, absorbs it and thus reaches the collecting openings 11' at a higher initial temperature T o heated. Regions of the IR-absorbing gas located close to the resistance heating elements 13 or the IR-radiating surface 14 absorb a large portion of the IR radiation 15, thereby heating up, and emitting IR radiation themselves according to the blackbody model, thus heating neighboring gas regions located upstream, approximately opposite the direction of arrows 18. The fluid present in the absorber chamber 16 can thus heat up against the flow direction toward the supply connection 4.
[0027] At the same time, the side wall 17 also heats up, partly by the IR radiation 15 of the resistance heating elements 13, partly by the IR radiation of the already heated IR-absorbing gas, and then, in turn, emits IR radiation into the absorber chamber 16 according to the blackbody model, so that it also contributes to the heating of the gas.
[0028] As an example, consider a point 17' of the side wall 17, which is reached by the IR beam 15' of the IR-radiating surface 14, is thus heated, and according to the blackbody model, in turn emits IR radiation 15*, which penetrates the absorber chamber 16. The IR radiation 15* reaches, for example, a volume element 18' of the IR-absorbing gas in the fluid, is absorbed by it, whereupon the volume element 18' heats up. If the fluid contains another, non-IR-absorbing gas in addition to the IR-absorbing gas (e.g., a protective gas, see the description below), the volume element 18' sooner or later collides with a volume element 19' of this non-IR-absorbing gas and heats it at the molecular level through the collision of the respective molecules.If the heat-transporting fluid contains other non-IR-absorbing gases in addition to the IR-absorbing gas, these also heat up due to the collision of the respective molecules, so that via the IR radiation 15 and the mixing of the gases, the entire fluid is finally heated directly and indirectly by the absorption of the IR radiation 15.
[0029] Furthermore, the fluid necessarily has contact with the warm side wall 17 and also with the surface 14 which radiates IR due to its high temperature, so that a subordinate convective heating of the fluid also occurs (subordinate, since it is not structurally supported - the structural design of the electrical heating device 10 is geared towards absorption).
[0030] The above-mentioned conditions are complex, so that during operation, a temperature distribution develops in the absorber chamber 16 which, although uniform, basically consists of a jumble of local, superheated or supercooled gas zones, which are caused more or less by the absorption of the IR radiation 15, 15* or by convective heat transfer at the wall 17 or the IR-radiating surface 14. It can now be seen that the heat transfer from the resistance heating elements 13 to the fluid is efficient if the proportion of heat transfer through absorption is increased, and that a significantly more uniform temperature distribution in the fluid, at least in the area of the collecting openings 11', can then be achieved. Among other things, the dimensions of the absorber chamber 16 and the IR-radiating surface 14 are determining parameters for this.
[0031] According to the invention, the heat transfer in an electric heating device 10 is reversed from the forced convection according to the prior art (achieved by a high ratio of the heated wall surface to the fluid volume to be heated) and a high IR absorption is sought, which is achieved by a large volume fraction of the fluid to be heated in comparison to the warm wall surface surrounding the fluid.
[0032] Taking into account the above-mentioned dimensions of the absorber chamber 16 and the IR-radiating surface 14, the skilled person can now adjust the flow velocity of the fluid, as a further determining parameter, to these dimensions such that the ratio x of the heating of the IR-absorbing gas by absorption of IR radiation compared to its total heating by absorption and convection is > 0.5, or reaches the value > 0.6, preferably > 0.7, particularly preferably > 0.8, and most preferably > 0.9. The heat distribution in the fluid is thus uniform, efficient, and almost completely uniform at the collection openings 11'.
[0033] It is advantageous that the construction of the electrical heating device 10, including the resistance heating element arrangement 12 designed as an IR radiation device, is quite simple and correspondingly cost-effective compared to conventional electrical heating devices and also has a significantly lower flow resistance, which contributes to efficiency, ie a higher degree of effectiveness.
[0034] It should be noted here that the heating power of the resistance heating elements 13 as such, ie the flux of the IR radiation 15, in a first approximation only has a subordinate influence on the ratio x, which is dominated by the mutual coordination of the dimensions of the absorber chamber 16, the IR-radiating surface 14 and the flow velocity. However, if stricter specifications regarding, for example, a desired starting temperature T oare maintained, the expert can preferably include the flow of IR radiation into the absorber chamber 16, which is determined by the heating power, in the quantities to be coordinated with one another as a further parameter.
[0035] The mutual coordination of the above-mentioned dimensions, the flow velocity, and, if applicable, the IR flow into the absorber chamber 16 can be carried out by a person skilled in the art in a specific case by simulation or by experiments. Preferably, the person skilled in the art will first determine the fluid, ie, the IR-absorbing gas, then, depending on the absorptivity of the IR-absorbing gas and the temperatures T u and T o the dimensions of the absorber chamber 16 and thus also of the IR radiating surface 14 and finally the flow velocity of the fluid through the absorber chamber 16.
[0036] With the above-described electric heating device 10, output temperatures T oof, as mentioned above, at least 800°C, but also higher temperatures such as at least 1000°C, 1200°C, 1400°C, or 1600°C or more, not only for small mass flows, but also for industrial applications. To avoid corrosion of the resistance heating elements 13 or their IR-radiating surface 14, their material and the type of gases in the fluid can be matched to one another. Therefore, the IR-radiating surface preferably comprises, for example, a high-temperature-resistant alloy of nickel-iron (NiFe), nickel-chromium (NiCr) and iron, chromium and aluminum (APN), silicon carbide or molybdenum disilicon MoSiz, the fluid comprises water vapor or carbon dioxide or a mixture thereof, or alternatively, the infrared-radiating surface (14) comprises silicon carbide and the fluid comprises carbon dioxide CO2 as the infrared-absorbing gas. Both the IR-emitting surface and the fluid can also be made of the materials mentioned.
[0037] The above-mentioned alloy of iron, chromium, and aluminum is available under the brand name Kanthai® APM from Kanthai in Germany and is described in the "Resistance heating wire and resistance wire" section as a "powder-metallurgical, dispersion-strengthened, ferritic iron-chromium-aluminum alloy (FeCrAI alloy) for use at temperatures up to 1425°C." The first group of high-temperature-resistant metallic resistance alloys, such as APM, silicon carbide, or molybdenum disilicon, is therefore particularly suitable for fluid temperatures up to approximately 1200°C. The second group of materials, consisting of silicon carbide and molybdenum disilicon, is suitable for temperatures exceeding this temperature.
[0038] Specifically, initial temperatures T oof, for example, 1000° C and 1500° C or even 2000° C are interesting, whereby with increasing temperature the choice of materials for resistance heating elements decreases, since on the one hand the temperature resistance as such reaches a limit and on the other hand the susceptibility to corrosion increases significantly, so that with regard to the choice of material the starting temperature T o is relevant. In this regard, it should be added that, for example, highly absorbent water vapor (H2O) is advantageous as a heat-transporting fluid, since its high absorption allows a high mass flow to be achieved in an electric heating device according to the invention. However, water vapor is highly oxidizing, and therefore highly corrosive, as the temperature increases.
[0039] For an initial temperature in a lower temperature range, such as 1000°C, many material combinations (resistance heating elements / fluid) are available that are familiar to experts in the field of convective electric heating elements, whereby a protective gas is not required. These include, for example, the well-known and inexpensive iron-chromium-aluminum alloys, which can be operated with steam as the fluid.
[0040] For a starting temperature in a medium temperature range, such as 1500°C, the advantageous combination of iron-chromium-aluminum alloys and steam is no longer possible. Without a shielding gas, a combination of silicon carbide (SiC) and carbon dioxide (CO2) as a fluid is suitable, but rather expensive. A combination of molybdenum disilicon (MoSi2) and steam or carbon dioxide (CO2) as a fluid is also possible, with or without a shielding gas.
[0041] For an initial temperature of, for example, 1500°C, the advantageous water vapor can be used as a fluid with a protective gas if carbon dioxide (CO2) is used as the protective gas and silicon carbide (SiC) is used for the resistance heating elements. The reason for this is that the silicon carbide (SiC) forms a protective layer that is resistant to carbon dioxide (CO2) but not to water vapor. Another advantage of a combination of silicon carbide, water vapor, and carbon dioxide as a protective gas is that the carbon dioxide is also absorptive, which further supports rapid heating in the absorber chamber and thus a high volume flow. If a non-absorbing protective gas is desired in a specific case, argon (Ar) can be selected as the protective gas with water vapor as the fluid, for example, and graphite as the material for the resistance heating elements.It is also possible that the resistance heating element arrangement (12, 22, 32, 42, 52, 62, 92) comprises resistance heating elements made of silicon carbide and the infrared absorbing gas is carbon dioxide (CO2) or water vapor (H2O) with a protective gas, namely air (which is fundamentally very cost-effective even after any desired treatment with regard to dirt or moisture).
[0042] Alternatively, for high-temperature applications, molybdenum (Mo) alloys available on the market can be used as the material for the heating elements and hydrogen (H2) as the protective gas.
[0043] For an initial temperature in an upper temperature range, such as 2000°C, the choice of materials for the resistance heating elements appears limited. Graphite or tungsten alloys available on the market for high-temperature applications are generally possible, but are neither compatible with the inherently advantageous water vapor (H2O) nor with CO2, so a protective gas must be provided in these cases. Noble gases such as argon (Ar) are suitable as a protective gas for both graphite and tungsten alloys, although hydrogen (H2) can also be used for the latter. However, these materials for the resistance heating elements, which are suitable for 2000°C, corrode with water vapor (H2O) or carbon dioxide (CO2) even at 1000°C, so a protective gas arrangement can also make sense in this temperature range. A corresponding electric heating device would then be advantageously operable over a wide temperature range from 800°C to 2000°C.
[0044] Overall, it follows that the person skilled in the art must select the materials for the specific case (e.g. lower, middle or upper temperature range), but the electric heating device according to the invention is suitable for any material combination and any temperature range due to its simple construction, so that ultimately with regard to a desired fluid to be heated or the initial temperature T o In contrast to the state of the art, there are no restrictions. For example, in the above-mentioned state of the art, it is hardly possible, if at all, to simply modify this design for inert gas.
[0045] Finally, it should be noted that the flow direction does not necessarily have to be directed toward the IR-radiating surface 14, but can also be reversed. In this case, the direction of the arrows 18 would be reversed, and the openings designated as collection openings 11' in Figure 2 would serve to supply the fluid, and the fluid would be discharged via the connection designated as supply connection 4 in Figure 2. The skilled person can then adjust the dimensions, flow velocity, and, if appropriate, the IR flux into the absorber chamber 16 in the same way, as is the case with a flow direction according to the embodiment of Figure 2.
[0046] Regarding the structure of the electric heating device 10, according to the embodiment shown in Figure 1, it is preferred that the absorber chamber 16 has a length in the fluid flow direction between its ends and a side wall 17 connecting the ends transversely thereto, the IR-radiating surface 14 is at one end and either the supply or the output connection is at the same end, but opens into the side wall 17, and the other connection is provided at the opposite end and is preferably designed as a tapered connection. In Figure 1, for example, the upper region of the side wall 17 is conically drawn in, so that a tapered connection is formed. Furthermore, it is preferred that the resistance heating element arrangement 12 has concentrically arranged, annular heating elements 13, and the absorber chamber 17 preferably has a section adjoining these and which is cylindrical over part of its length.This results in a method for electrically heating a heat-transporting fluid comprising an IR-absorbing gas to at least 800 °C, characterized in that the fluid is passed through an absorber chamber 16 of an arrangement for heating the fluid, which arrangement is provided with an IR radiation device acting via an IR-radiating surface 14 into the absorber chamber 16, and wherein the dimensions of the absorber chamber 16, the IR-radiating surface 14 of the IR radiation device and the flow velocity of the fluid are coordinated with one another in such a way that the ratio x of the heating of the IR-absorbing gas in the absorber chamber 16 due to the absorption of infrared radiation 15,15* compared to its total heating by absorption and convection > 0.5, and wherein an IR radiation device with a resistance heating element arrangement 12 is used, the surface of which is designed as an IR-radiating surface 14 and the IR radiation 15,15* thus generated is directed into the absorber space 16.
[0047] An electric heating device 10 according to the invention for heating a heat-transporting fluid containing an IR-absorbing gas to at least 800 °C thus has a supply connection 4 for the cold fluid to be supplied and an outlet connection 5 for the heated fluid to be led away from it, and an arrangement for heating fluid passed through the heating device 10, wherein the latter has an absorber chamber 16 and an IR radiation device designed as a resistance heating element arrangement 12, the surface of which is designed as an IR-radiating surface 14 facing the absorber chamber in order to emit the heat generated by the resistance heating element arrangement 12 as IR radiation 15, 15* into the absorber chamber 16 during operation, wherein furthermore the dimensions of the absorber chamber 16 and those of the IR-radiating surface 14 are coordinated with one another in such a way thatthat during operation, at a predetermined flow velocity of the fluid through the absorber chamber 16, the ratio x of the heating of the IR-absorbing gas due to the absorption of infrared radiation 15.15* to its total heating by absorption and convection in the absorber chamber is > 0.5.
[0048] In Figure 2 and other figures, the electric heating device 10 is oriented vertically, although this is not mandatory. In a specific case, a person skilled in the art can arrange it in any position, such as horizontally or obliquely, or even upside down, so that the output connection of the heating device 10 shown in Figure 2 points downward. Figure 3a schematically shows a section through an embodiment of an electric heating device 20 with a modified resistance heating element arrangement 22, which has rod-shaped resistance heating elements 23 and cylindrical IR-radiating surfaces 24. The absorber chamber 26, adapted to the resistance heating elements 23, is provided with a rectangular side wall 27. Side channels 21, 21' extend opposite one another and enclosing the rod-shaped resistance heating elements 23 across their spacing, along the opposite wall sections 27, 27' of the side wall 27 that forms the absorber chamber 26.The side channels 21, 21' are connected to a supply connection for the heat-transporting fluid, omitted to reduce the volume of the figure. The fluid enters the absorber chamber 26 according to the arrows 28 and leaves it again through the outlet connection 25. For the sake of completeness, Figure 3a also shows a point 17' on the wall of the absorber chamber 26, which is heated by the IR radiation 15 of the rod-shaped heating elements 23 and in turn generates IR radiation 15*, which enters the absorber chamber 26.
[0049] This arrangement has the advantage that the resistance heating element arrangement 20 preferably has rod-shaped, parallel-arranged resistance heating elements 23, wherein the absorber chamber 26 preferably has a rectangular section adjoining these over part of its length.
[0050] Figure 3b schematically shows a section through an embodiment of an electric heating device 30 with a modified resistance heating element arrangement 32, which also has rod-shaped, parallel resistance heating elements 33 with IR-radiating surfaces 34, which, however, are not arranged at one end of the absorber chamber 36, which here has a cylindrical side wall 37, but rather within it, penetrating it across its entire length. A supply connection 4 is located on one side of the absorber chamber 36, and an output connection 5 is located on the other side, so that the fluid flows through the resistance heating elements 33 in the direction of the arrows 38, absorbing the IR radiation from the IR-radiating surfaces 34. The figure shows that a flow component of the flowing fluid lies transversely to the length of the resistance heating elements.Symbolically, with only one resistance heating element 33', the power supply with the electrical lines 6, 6' and the power source 7 is indicated, whereby the power supply naturally supplies all resistance heating elements 33 with power in an operational state.
[0051] Preferably, the absorber chamber 36 is interspersed with parallel, rod-shaped resistance heating elements 33, the surfaces of which form the IR-radiating surface 34, and wherein the supply 4 and the output connection 5 are arranged such that a flow component of the fluid flowing through lies transversely to the length of the resistance heating elements 33.
[0052] Figure 3c schematically shows a section through an embodiment of an electric heating device 40 with a resistance heating element arrangement 42, which is designed analogously to that of Figure 3b and has rod-shaped resistance heating elements 43 penetrating the absorber chamber 46 over its entire dimensions. The absorber chamber 46 has parallel walls here, and the fluid flowing through it according to the arrows 48 flows almost laminarly in the region of the resistance heating elements 43, which supports uniform absorptive heating of the fluid.
[0053] Figure 3d schematically shows a section through an embodiment of an electric heating device 50 with a modified resistance heating element arrangement 52, wherein the absorber chamber 56 preferably has a length in the fluid flow direction 58 between its ends formed by the supply connection 4 and the output connection 5 and, transversely thereto, a side wall 57 connecting the ends, which narrows towards the ends in sections 59, 59', preferably in a funnel shape, and wherein the resistance heating elements 53 are arranged in the one funnel-shaped narrowing region 59 or 59'. This arrangement has the advantage of a very simple construction.
[0054] Figure 3e shows a schematic section through an embodiment of an electric heating device 60 in which the absorber space 66 is divided into several, here three, chambers 66', 66" and 66'" arranged one behind the other in the direction of flow, wherein the supply connection 4 for each chamber 66', 66" and 66'" has an associated ring line 61', 61", 61'" formed from local supply connections, via which the fluid is distributed to openings 11' and through these into the interior of the respective chamber 66', 66" and 66'". Each chamber 66', 66" and 66'" has a resistance heating element arrangement 62', 62", 62'" with resistance heating elements 63. Each of the chambers 66', 66" and 66"' heats the fluid flowing according to the arrows 68', 68" and 68'" in the same manner as described for the heating device 20 (Figure 2), but the chambers 66" and 66'" additionally receive already at least partially heated fluid via the intermediate output connections 65' and 65".
[0055] The advantage of this arrangement is the large IR-radiating surface area provided by the large number of resistance heating elements 63 in relation to the total volume of the absorber chamber 66, which is nevertheless designed for maximum absorption with minimal convection. This allows even for high temperatures T o of the fluid at the output section 5, resistance heating elements 63 with materials are used whose maximum operating temperature is comparatively little above the output temperature T o , with the correspondingly comparatively low flux of IR radiation into the respective chambers 66', 66" and 66'" (the radiation intensity of the black body increases with the fourth power of the temperature in K). A small difference between the operating temperature of the resistance heating elements 63 and the output temperature T o For example, at low temperature T oThe advantage is that simple or inexpensive materials can be used. Furthermore, this arrangement has the advantage of small transverse dimensions and is nevertheless suitable for operation with a protective gas arrangement; see the description below. This results in an electric heating device in which several local supply connections 61', 61", 61'" are arranged on the absorber chamber 66, and the resistance heating element arrangement has several IR radiation devices, each arranged one behind the other in the flow direction 68 of the fluid, such that each IR radiation device is assigned to a local supply connection and heats fluid flowing into it from this.
[0056] Figure 4 shows schematically a section through an embodiment of an electric heating device 70 which corresponds to that of Figure 2 with two differences.
[0057] The first difference is that the flow direction of the fluid is reversed, as already mentioned above as a possible alternative in the description of Figure 2. The fluid thus flows into the absorber chamber 16 via the ring line 11 according to the arrows 71 and leaves it via the outlet connection 5, which is now located at the end of the absorber chamber 16 opposite the resistance heating element arrangement 12. The second difference is that a protective gas arrangement 72 for the resistance heating element arrangement 12 with a protective gas supply line arrangement 73 is preferably provided, which opens in the region of the IR-radiating surface 14 such that, during operation, protective gas escaping from it flows around the IR-radiating surface 14, forming a protective gas region 74 and thus operatively sealing it against fluid to be heated in the absorber chamber 16.The protective gas arrangement 72 allows the provision of a fluid with at least one gas component that corrodes the respective resistance heating elements 13 upon contact at their operating temperature. In detail, the individual line sections 73' of the protective gas supply line arrangement 73 open at the heating elements 13 and thus flow along their IR-radiating surfaces toward the absorber chamber 16. The protective gas forms a cushion above the IR-radiating surface 14 and below the openings 11', thus forming the protective gas region 74 and preventing fluid entering through the openings 11' from reaching the IR-radiating surface 14.
[0058] Although in the embodiment shown, both the shielding gas and the fluid flow toward the output port 5, mixing, albeit slight, of the shielding gas with the fluid in the shielding gas region 74 cannot be ruled out and is determined by the specific design of the heating device 70 or the shielding gas arrangement 72. Therefore, if necessary, a skilled person can provide a maintenance interval for the maintenance or replacement of the resistance heating elements 13, so that the IR-emitting surface 14 is operatively sealed by the shielding gas region 74 during the maintenance interval. "Operational" thus includes slight corrosion occurring over time, which does not impair the intended function of the IR-emitting surface 14 during the maintenance interval.
[0059] This results in a method according to which a protective gas is preferably supplied to the IR radiation device in the region of the IR-radiating surface 14 in such a way that it flows around it in the region of possible contact with the fluid and thus forms a protective gas region 74 which operatively protects the IR-radiating surface from contact with the heat-transporting fluid.
[0060] The protective gas can be IR transparent or IR-absorbing. For example, a material with ohmic resistance, preferably graphite, molybdenum, or tungsten, can be used as the material for the resistance heating elements (and thus for the IR-radiating surface), oxidizing and thus corrosive water vapor H2O or carbon dioxide (CO2), or a mixture thereof, can be used as the fluid, and an inert gas can be used as the protective gas, preferably argon (Ar) or helium (He). e), i.e., IR-transparent, inert gases. It is also possible, for example, to use silicon carbide (SiC) as the material for the resistance heating elements (and thus for the IR-radiating surface 14) with silicon carbide-corrosive H2O or CO2, with carbon dioxide (CO2) being used as the protective gas, which is IR-absorbing.
[0061] Figure 5 shows a schematic section through an embodiment of an electric heating device 80, which is identical to that of Figure 4, but has a modified shielding gas arrangement 82, which, although corresponding to that of Figure 4 with regard to the shielding gas supply, is additionally provided with a shielding gas return arrangement 84. This arrangement has shielding gas return openings 81' arranged in the shielding gas region 74 and below the fluid openings 11', as well as a shielding gas return ring line 81 connected to these.
[0062] Shielding gas supplied to the shielding gas area 74 via the shielding gas supply line arrangement 73 can now be withdrawn through the openings 81', discharged via the ring line 81, and, for example, guided into a shielding gas return line (not shown to reduce the load in the figure), which in turn opens into the shielding gas supply line arrangement 73, thus resulting in a shielding gas circuit. This results in a process in which preferably at least a portion of the shielding gas is discharged from the shielding gas area 74 while still in the shielding gas area. Furthermore, an electric heating device 80 is provided, the shielding gas arrangement 82 of which has a shielding gas return arrangement 84 leading away from the shielding gas area.
[0063] Figure 6 shows a schematic section through an embodiment of an electric heating device 90 constructed according to the principle of the heating device 20 (Figure 2), with a modified fluid supply connection 91, a modified resistance heating element arrangement 92 and a modified protective gas arrangement 93. Apart from that, the heating device 90 is, as mentioned, basically constructed, for example, according to Figure 2 or one of the other corresponding embodiments.
[0064] The fluid supply connection 91 has a number of end pipes 94 with orifices 94' extending into the absorber chamber 16, which branch off from a fluid distributor 95, so that the fluid can be advantageously distributed over the entire cross-section of the absorber chamber 16. Fluid flows into the distributor 95 according to the arrow 95'.
[0065] The resistance heating element arrangement 92 is designed as a plate 97 provided with a pattern of openings 96 for protective gas. This plate forms one end of the absorber chamber 16 and its IR-radiating surface 98 is directed into the absorber chamber 16. To reduce the burden on the figure, the power connection for the resistance heating element arrangement 92 has been omitted. The correspondingly plate-shaped IR-radiating surface 98 advantageously acts uniformly on the absorber chamber 16.
[0066] The shielding gas supply arrangement 93 has a shielding gas supply line 99 into which shielding gas flows from a shielding gas source according to the arrow 100, reaches a distribution chamber 101 and from there flows around the IR-radiating surface 98 through the openings 92, so that the shielding gas region 102 shown in dashed lines is formed, which extends from the IR-radiating surface 98 to just below the openings 94' of the end pipes 98 releasing the fluid.
[0067] The embodiment shown in Figure 6 can be easily equipped by a person skilled in the art with a shielding gas return arrangement 84 (Figure 5) (not shown in the figure) by arranging shielding gas return openings 81' (Figure 5) in the absorber chamber 16 in the shielding gas region 102, at the upper end, and connecting them to a shielding gas return ring line 81 (Figure 5). A shielding gas circuit can then be formed by connecting the shielding gas return arrangement to the shielding gas supply line 99.
[0068] Another embodiment of a protective gas return arrangement, not shown in the figures, consists in the end pipes 94 of the fluid supply connection 91 (Figure 6) being double-walled, such that an inner pipe is connected to an annular outer pipe. The inner pipes are then connected to the distributor 95, and the outer pipes to the distributor chamber 101. Accordingly, fluid is then supplied to the absorber chamber through the inner pipes, while the outer pipes draw in protective gas near the opening and discharge it from the electric heating device via these pipes.
[0069] As mentioned above in the description of Figure 2, the electrical heating device does not have to be in a vertical position, so that the resistance heating element arrangement is in an upright position and radiates from bottom to top, as is the case, for example, with the heating device 70 (Figure 4). An inverted position is also possible, see, for example, the heating device 50 (Figure 3d) with downward-radiating resistance heating elements 53, which is oriented upside down with respect to the heating device 70. Of course, in view of the simple construction principle, the electrical heating device 50 can also be provided with a protective gas arrangement, analogous to the protective gas arrangement 72 (Figure 4), in that a protective gas supply line arrangement supplies protective gas to the individual resistance heating elements 53 (for the sake of completeness, it should be noted that the person skilled in the art can also readily devise a protective gas return arrangement - e.g.analogous to the protective gas return arrangement 84 of Figure 5).
[0070] If, for example, steam is used as the fluid, it is advantageous, with regard to the protective gas, to provide argon (Ar) as the protective gas in an arrangement with upward-radiating heating devices (see, for example, Figures 3a, 4, 5, 6). On the other hand, for an overhead arrangement such as that shown in Figure 3d, it is then sensible to use hydrogen (H2) as the protective gas. The reason lies in the molecular weight of the protective gas in relation to that of the fluid: in a temperature range of 500 °C to 2500 °C, for the same temperature interval, the molecular weight of water is higher than that of hydrogen (or helium) and lower than that of argon (or CO2 or air).
[0071] The temperature of the protective gas and that of the fluid near the protective gas area (see, for example, the protective gas area 74 of Figure 4 or the protective gas area 102 of Figure 6) are in fact quite close to each other during operation, in a same temperature interval in the sense of the previous section: the ratio of the molecular weights does not change when the electric heating device is operated at different set temperatures T o is driven.
[0072] The advantage of these combinations of shielding gas and fluid is that when the heating device is positioned upright, the fluid is lighter and the shielding gas heavier, resulting in less efficient mixing, allowing the shielding gas to perform its function better. Conversely, when the heating device is positioned upside down, the lighter shielding gas remains more in the upper region of the absorber chamber, thus better protecting the resistance heating elements arranged above. This results in a process in which the shielding gas and the fluid preferably have different densities, with the shielding gas region in the absorber chamber being positioned at the bottom when the density of the shielding gas is higher, and at the top when the density of the shielding gas is lower.For an electric heating device, it follows that the shielding gas supply lines are spaced vertically from the output connection and that the shielding gas supply lines are arranged below the supply connection for the heat-transporting fluid if its molecular weight is smaller than that of the shielding gas, and above if its molecular weight is larger than that of the shielding gas.
[0073] Figure 7 shows a diagram 110 with a circuit 111 for heat-transporting fluid, which in the embodiment shown is coupled to a circuit for protective gas 112, symbolized by the circulating arrow 112', the flow direction of which is indicated by the direction of the arrow 112'. A fluid transport line 1 (see also Figure 1) connects, in the flow direction symbolized by the arrow 1', an electrical heating device 113, designed, for example, according to the heating device 70 of Figure 4 or according to the heating device 90 of Figure 6, to a consumer 3 (see also Figure 1). A branch 114 is provided behind the consumer, in which branch a line branch 115 of the fluid line 1 leads to a separation station 116 and, downstream of this, re-enters the circuit line 1 at a junction 117.
[0074] From the separation station 116, a protective gas line 118 for protective gas separated in the separation station in the circuit 112 leads back into the heating device 113 and thus supplies it with protective gas.
[0075] This results in a method in which preferably the fluid flowing through the absorber chamber is enriched with protective gas originating from the protective gas region, the enriched fluid is led through the absorber chamber and away from it, and downstream protective gas originating from the protective gas region is separated from the fluid again, wherein the fluid is led back to the absorber chamber in a fluid circuit and preferably the protective gas is led back to the IR-radiating surface in a protective gas circuit.PA 29 Furthermore, a heating device is provided, wherein the fluid discharge connection with its supply connection are closed via a fluid transport line in a circuit which has a consumer for the heat of the heated fluid, wherein a branch line is also provided, which preferably branches off from the circuit line at a branch after the consumer, to a separation station designed for the separation of the protective gas from the fluid and after this downstream after the branch and before the supply connection back into the circuit line.
[0076] In diagram 110, the molar mass flows are plotted at the location of the arrows: I denotes the inflow of I mole of shielding gas into the heating device 113, for example, through the shielding gas supply line arrangement 73 (Figure 4) or through the shielding gas supply line arrangement 93 (Figure 6). The fluid is thus enriched with I mole of shielding gas as it passes through the heating device 113.
[0077] M denotes the flow of M mol of protective gas and fluid through the absorber chamber 16 of the heating device 113 or the consumer 3, where the M mol includes the enrichment of the fluid with I mol of protective gas. The total proportion of protective gas is N mol, since the fluid already contains a proportion of L mol of protective gas before entering the heating device 113. This proportion of L is intentional and essential for the efficiency of the fluid circuit 111; see the following description.
[0078] C denotes the flow of C mol through branch 115 of fluid line 1 to the separation station 116, which in turn releases the shielding gas from the fluid via the shielding gas line 118 into the shielding gas circuit 112 and only fluid via the line branch 115 into the union 117 and thus back into the fluid line 1.
[0079] If the protective gas content in the fluid is to be prevented from continuously increasing during operation of the heating device 113, the ongoing enrichment of protective gas of I mol must correspond to the continuously separated portion of protective gas, ie the flow of separated protective gas through the line 118 must be I mol.
[0080] If the fluid flowing into the heating device 113 did not contain any protective gas, the entire fluid flow would have to be passed through the separation station 116 in order to separate the supplied protective gas again. Since the fluid flowing into the heating device 113 already contains a proportion of K mol of protective gas, the Shielding gas concentration after the heating device 113 k = There is thus a partial flow of C mol of protective gas, which already contains I mol of protective gas, so that for the separation of the protective gas in the separation station 116 only the energy expenditure for the partial flow of C mol and not for the entire fluid flow of M mol is incurred. A simple calculation shows that then
[0081] IN THE
[0082] C = —. The energy saving is particularly illustrative when using steam as a fluid and argon as a protective gas: in the separation station 116, the argon is then separated by condensation of the steam, whereupon the water is heated again at the branch 117 to the inlet temperature T uwhich, even with recuperation of the condensation waste heat, leads to energy losses and thus to a reduced efficiency of the fluid circuit 112. With a smaller fluid or vapor flow passed through the separation station 116, these energy losses are smaller and the efficiency of the fluid circuit 112 correspondingly greater. The person skilled in the art can now, in the specific case, specify a predetermined proportion of L mol of protective gas in the fluid flow. This means that, preferably during operation, the fluid upstream of the supply connection has a predetermined proportion of protective gas. Furthermore, it is preferred that the protective gas is separated from the fluid by condensation of the other components of the fluid.
[0083] It should be emphasized that one advantage of the absorptive electric heating device lies in the possible design diversity, which is not available with prior art electric heating devices. The absorber chamber can be designed in different ways, as can the resistance heating element arrangement, the resistance heating elements themselves and their arrangement in the absorber chamber; the respective electric heating device is always simple in design and cost-effective to manufacture. This also applies to a protective gas arrangement and, if applicable, a protective gas return arrangement: these are also structurally simple and can be easily and suitably arranged in the electric heating device without additional effort. Individual features of the embodiments shown in the figures can be combined in practically any way, depending on the specific requirements of the case.
Claims
Patent claims 1. A method for electrically heating a heat-transporting fluid comprising an infrared-absorbing gas to at least 800 °C, characterized in that the fluid is passed through an absorber chamber (16, 26, 36, 46, 56, 66) of an arrangement for heating the fluid, which is provided with an infrared radiation device acting via an infrared-radiating surface (14) into the absorber chamber (16, 26, 36, 46, 56, 66), and wherein the dimensions of the absorber chamber (16, 26, 36, 46, 56, 66), the infrared-radiating surface (14) of the infrared radiation device and the flow velocity of the fluid are coordinated with one another in such a way that the ratio x of the heating of the infrared-absorbing gas in the absorber chamber (16, 26, 36, 46, 56, 66) due to the absorption of infrared radiation compared to its total heating by absorption and convection > 0.5, and wherein an infrared radiation device with a resistance heating element arrangement (12, 22, 32, 42, 52, 62, 92) is used, which has a surface designed as an infrared-radiating surface (14), and wherein the infrared radiation thus generated is directed into the absorber space (16, 26, 36, 46, 56, 66).
2. The method according to claim 1, wherein the infrared absorbing gas is a heteropolar gas and preferably one or a mixture of the gases CO2, water vapor, CH4, NH3, CO, SO2, SO3, HCl, NO, and NO2, particularly preferably a mixture with water vapor and CO2 is used.
3. Method according to claim 1, wherein the fluid is guided in a circuit in which the arrangement for heating the fluid and a consumer (3) for the heat of the heated fluid are located.
4. The method according to claim 2, wherein the infrared radiating surface (14) comprises a high-temperature resistant alloy of iron, chromium and aluminum, silicon carbide or molybdenum disilicon, the fluid comprises water vapor or carbon dioxide or a mixture thereof, 5. The method according to claim 1, wherein a protective gas is supplied to the infrared radiation device in the region of the infrared-radiating surface (14) in such a way that it flows around it in the region of possible contact with the fluid and thus forms a protective gas region (74,102) which operatively protects the infrared-radiating surface (14) from contact with the heat-transporting fluid.
6. The method according to claim 1 or 5, wherein a temperature-resistant material with ohmic resistance is used as the material for the infrared-radiating surface 14, preferably silicon carbide (SiC) or graphite (C), or molybdenum (Mo) or tungsten (W), further a heat-transporting fluid which comprises water vapor (H2O) or carbon dioxide (CO2) or a mixture thereof and preferably an inert gas as a protective gas, preferably argon (Ar) or hydrogen (H2) or carbon dioxide (CO2).
7. The method according to claim 5, wherein at least a portion of the protective gas is removed from the protective gas region (74,102) while still in the latter.
8. The method according to claim 5, wherein the fluid flowing through the absorber chamber (16, 26, 36, 46, 56, 66) is enriched with protective gas supplied in the region of the infrared-radiating surface (14), the enriched fluid is guided through the absorber chamber (16, 26, 36, 46, 56, 66) and away from it, and downstream the supplied protective gas is separated from the fluid again, the fluid being guided in a fluid circuit (111) back to the absorber chamber (16, 26, 36, 46, 56, 66) and preferably the protective gas in a protective gas circuit (112) back to the infrared-radiating surface (14).
9. The method according to claim 5 or 8, wherein the heat-transporting fluid has a predetermined proportion (L) of protective gas before entering the arrangement for heating the fluid.
10. The method according to claim 8, wherein the separation of the protective gas from the fluid occurs by condensation of the other components of the fluid.
11. The method according to claim 8, wherein the separation of the protective gas from the fluid takes place after the consumer (3) 12. The method according to claim 5, wherein silicon carbide is used as the material for the infrared radiating surface (14), a heat-transporting fluid comprises water vapor or a mixture of water vapor and carbon dioxide, and the protective gas comprises carbon dioxide.
13. The method according to claim 1, wherein the flux of infrared radiation into the absorber chamber (16, 26, 36, 46, 56, 66) is further included in the quantities to be coordinated with one another.
14. The method according to claim 1, wherein the ratio x is 0.6, preferably > 0.7, particularly preferably > 0.8 and most preferably > 0.
9.
15. The method according to claim 5, wherein the protective gas and the fluid have a different density, and wherein in the vertical direction the protective gas region (74,102) in the absorber chamber (16,26,36,46,56,66) is arranged at the bottom when the density of the protective gas is greater, and at the top when the density of the protective gas is lower.
16. The method according to claim 1, wherein the fluid is heated to at least 1000°C, preferably 1200°C, more preferably 1400°C, or most preferably 1600°C or more.
17. Electric heating device (2,10,20,30,40,50,60,70,80,90,113) for heating a heat-transporting fluid containing an infrared-absorbing gas to at least 800 0C, with a supply connection 4 for cold fluid to be supplied thereto and an output connection (5, 25) for heated fluid to be led away from it, and with an arrangement for heating fluid passed through the heating device (2, 10, 20, 30, 40, 50, 60, 70, 80, 90, 113), characterized in that it comprises an absorber chamber (16, 26, 36, 46, 56, 66) and an infrared heating element designed as a resistance heating element arrangement (12, 22, 32, 42, 52, 62, 92). Radiation device, the surface of which is designed as an infrared-radiating surface (14) facing the absorber chamber (16, 26, 36, 46, 56, 66) in order to emit the heat generated by the resistance heating element arrangement (12, 22, 32, 42, 52, 62, 92) as infrared radiation into the absorber chamber (16, 26, 36, 46, 56, 66) during operation, wherein further the dimensions of the absorber chamber (16, 26, 36, 46, 56, 66) and those of the infrared-radiating surface (14) are matched to one another in such a way that, during operation, at a flow velocity of the fluid through the absorber chamber (16, 26, 36, 46, 56, 66), the ratio x of the heating of the infrared-absorbing gas due to the absorption of infrared radiation compared to its total heating by absorption and convection in the absorber chamber (16, 26, 36, 46, 56, 66) is > 0.
5.
18. Electric heating device (2,10,20,30,40,50,60,70,80,90,113) according to claim 17, wherein the ratio x is 0.6, preferably > 0.7, particularly preferably > 0.8 and most preferably > 0.
9.
19. Electric heating device (2,10,20,30,40,50,60,70,80,90,113) according to claim 17, wherein the infrared absorbing gas is a heteropolar gas or gas mixture, preferably a gas or a mixture of several gases of the gases CO2, water vapor, CH4, NH3, CO, SO2, SO3, HCl, NO, and NO2, particularly preferably a mixture with water vapor and CO2.
20. Electric heating device (2,10,20,30,40,50,60,70,80,90,113) according to claim 17, wherein the resistance heating element arrangement (12,22,32,42,52,62, 92) comprises resistance Has heating elements made of silicon carbide and the infrared absorbing gas is carbon dioxide (CO2) or water vapor (H2O) with a protective gas, namely carbon dioxide (CO2) or argon (Ar).
21. Electric heating device (2,10,20,30,40,50,60,70,80,90,113) according to claim 17, wherein the absorber chamber (16,26,36,46,56,66) has a length in the fluid flow direction between its ends and a side wall (17,37,57) connecting the ends transversely thereto, the infrared radiating surface (14) is formed at one end and either the supply (4) or the output connection (5) is formed at the same end, but opening into the side wall (17,37,57) and the other connection (5,4) is provided at the opposite end and is preferably formed as a narrowing connection (5,4).
22. Electric heating device (2, 10, 20, 30, 40, 50, 60, 70, 80, 90, 113) according to claim 21, wherein the resistance heating element arrangement (12, 22, 32, 42, 52, 62, 92) comprises concentrically arranged, annular resistance heating elements (13), and the Absorber chamber (16,26,36,46,56,66) preferably has a section adjoining it which is cylindrical over part of its length.
23. Electric heating device (2,10,20,30,40,50,60,70,80,90,113) according to claim 21, wherein the resistance heating element arrangement (12,22,32,42,52,62, 92) has rod-shaped, parallel arranged resistance heating elements (23) and the absorber chamber (16,26,36,46, 56,66) preferably has a rectangular section adjoining these over part of its length.
24. Electric heating device (2,10,20,30,40,50,60,70,80,90,113) according to claim 17, wherein the absorber chamber (16,26,36,46,56,66) is interspersed with parallel arranged, rod-shaped resistance heating elements (23), the surfaces of which form the infrared-radiating surface (14), and wherein the supply (4) or the output connection (5) are arranged such that a flow component of the fluid flowing through lies transversely to the length of the resistance heating elements (23).
25. Electric heating device (2,10,20,30,40,50,60,70,80,90,113) according to claim 17, wherein the absorber chamber (56) has a length in the fluid flow direction between its ends and transversely thereto a side wall (57) connecting the ends, which narrows towards the ends in sections 59,59', preferably in a funnel shape, and wherein the resistance heating elements (53) are arranged in one or both of the sections 59,59'.
26. Electric heating device (60) according to claim 17, wherein a plurality of local supply connections are arranged on the absorber chamber (66) and the resistance heating element arrangement (62, 62', 62") has a plurality of infrared radiation devices, each arranged one behind the other in the flow direction (68) of the fluid, such that each infrared radiation device is assigned to a local supply connection and heats fluid flowing therefrom. TI. Electric heating device (2, 10, 20, 30, 40, 50, 60, 70, 80, 90, 113) according to claim 17, wherein a protective gas arrangement (72, 82, 93) is provided for the infrared radiating surface (14), which has a protective gas supply line arrangement (73, 93) which opens in the region of the infrared radiating surface, such that during operation escaping protective gas flows around the infrared radiating surface (14) forming a protective gas area (74,102) and thus operatively seals it against fluid to be heated in the absorber chamber (16,26,36,46,56,66).
28. Electric heating device (2,10,20,30,40,50,60,70,80,90,113) according to claim 11, wherein the protective gas arrangement (72,82,93) has a protective gas return arrangement (84) leading away from the protective gas region (74,102).
29. Electric heating device (2, 10, 20, 30, 40, 50, 60, 70, 80, 90, 113) according to claim 11, wherein the output connection (5) for the fluid is closed with its supply connection (4) via a fluid transport line (1) in a circuit which has a consumer (3) for the heat of the heated fluid, wherein a branch line (115) is further provided which preferably branches off from the circuit line (1) at a branch (114) after the consumer (3), to a separation station (116) designed for the separation of the protective gas from the fluid and after this downstream after the branch (114) and before the supply connection (4) leads back into the circuit line (1).
30. Electric heating device (2,10,20,30,40,50,60,70,80,90,113) according to claim 11, wherein, during operation, the fluid upstream of the supply connection (4) has a predetermined proportion of protective gas (L).
31. Electric heating device (2,10,20,30,40,50,60,70,80,90,113) according to claim 11, wherein the separation station (116) is connected to the protective gas supply line arrangement (4) and is designed to convey the separated protective gas into the protective gas supply line arrangement (4) during operation.
32. Electric heating device (2,10,20,30,40,50,60,70,80,90,113) according to claim 11, wherein the protective gas supply lines (4,118) are spaced apart from the output connection (5) in the vertical direction and wherein the protective gas supply lines are arranged below the supply connection (4) for the heat-transporting fluid if its molecular weight is smaller than that of the protective gas, and above it if its molecular weight is greater than that of the protective gas.
3. Electric heating device (2,10,20,30,40,50,60,70,80,90,113) according to claim 17, wherein the resistance heating element arrangement (12,22,32,42,52,62, 92) comprises resistance Heating elements made of silicon carbide and the infrared absorbing gas is carbon dioxide (CO2) or water vapor (H2O) with a protective gas, namely air.