Electric heating device for fluids

Abstract

To provide an electric heating device of fluid which can enhance heating efficiency of fluid and can miniaturize the heating device.SOLUTION: An electric heating device of fluid has a heating unit of a multiple pipe structure constituted by a plurality of conductive heating pipes, and a fluid to be heated therein is heated by the heating pipe whose temperature is raised by electricity-carrying heating. The electric heating device of fluid includes a) a fluid supply header, b) a fluid discharge header, c) a pipe end short-circuit electrode integrally formed with a wall on the heating unit side of the fluid header and short-circuiting both ends of the plurality of heating pipes one side by one side, and d) an electrical insulator provided between a body of the fluid header and the pipe end short-circuit electrode so as to insulate them from each other. Each of the heating pipes is arranged between the pipe end short-circuit electrodes facing with each other in such a manner that a heating pipe position in the heating unit is switched between the outside and the inside along a longitudinal direction of the heating pipe.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electric heating device for fluids, and more particularly to an electric heating device for fluids that has high heating efficiency and can be miniaturized.

Background Art

[0002] In recent years, for the purpose of countermeasures against global warming, efforts have been made to improve energy efficiency and convert to fuels with low carbon dioxide emissions. In the field of large-scale and high-capacity fluid heating devices, various types have been conventionally used. For example, heating devices such as boilers using combustion gas can be exemplified. However, heating devices such as boilers using combustion gas have a limit in efficiency, with even highly efficient ones being about 35%. In addition, in order to efficiently heat a fluid to a high temperature, it is necessary to increase the temperature of the combustion gas and the accompanying refractory heat insulation structure, resulting in an inevitable increase in the size and cost of the equipment.

[0003] Regarding both the miniaturization of such fluid heating equipment and the improvement of heating efficiency, it can be said that electric heating means that can input a large amount of power into a limited space is advantageous. For example, Patent Document 1 discloses an electric heating device 60 for fluids by induction heating as shown in (a) a longitudinal sectional view of FIG. 7 (however, the heating element 62 is described with only two simplified ones compared to the description in the cross-sectional view) and (b) a cross-sectional view. Specifically, the heating element 62 is composed of, for example, a non-magnetic tube 62a made of SUS304 and a magnetic tube 62b as a magnetic body made of, for example, SUS430. Both ends of the non-magnetic tube 62a are fixedly supported by tube support plates 64 and 66. Further, an induction heating coil 72 connected to an AC power source (not shown) is disposed around the outer periphery of the heating element 62. This induction heating coil 72 is interposed between a cylindrical inner heat insulating material 68 and an outer heat insulating material 70, and both ends of the inner heat insulating material 68 are positioned by being fixedly supported by the tube support plates 64 and 66. Fluid inlet headers 74 and fluid outlet headers 76 are provided on the tube support plates 64 and 66, respectively, and the heated fluid A, which is a gas or a liquid, is heated by passing through the non-magnetic tube 62a from the fluid inlet header 74 and is led to the fluid outlet header 76.

[0004] In the invention described in Patent Document 1, the magnetic tube 62b is in contact with the outer surface of the non-magnetic tube 62a through which the fluid to be heated A flows. The heat generated in the magnetic tube 62b by induction heating is conducted from the magnetic tube 62b to the non-magnetic tube 62a, and from the non-magnetic tube 62a to the fluid to be heated. As a result, the fluid to be heated does not come into contact with the magnetic tube 62b, which has inferior corrosion resistance compared to the non-magnetic tube 62a, thus improving corrosion resistance. Furthermore, by arranging multiple heating elements 62 parallel to each other and distributed at approximately equal intervals within the induction heating coil 72, it is possible to effectively heat the fluid to be heated while keeping the size of the electric heating device 60 of the fluid small.

[0005] Furthermore, Patent Document 2 discloses an electric heating device 80 for a fluid that uses electric heating, as shown in Figure 8. Its basic configuration, as shown in Figure 8(a), is a "one heating tube, one power supply" configuration consisting of a heating tube 82, a non-heating tube 84, a tube joint 86, and an AC power supply 88. The heating tube 82 is made of a metal that generates heat when electricity is applied. An AC power supply 88 that supplies current from one end to the other is connected to this heating tube 82. The non-heating tubes 84 are connected to both ends of the heating tube 82, have the same diameter as the heating tube 82, and form a flow path for the fluid to be heated. The tube joint 86 mechanically connects the heating tube 82 and the non-heating tubes 84, 84 to form a flow path and electrically insulates the heating tube 82 from the non-heating tubes 84, 84. Furthermore, if a support base is required to hold the heating tube 82, an electrical insulator 92 is interposed between the support base 90 and the heating tube 82, as shown in Figure 8(a).

[0006] Patent Document 2 also discloses embodiments for connecting multiple heating tubes 82, as shown in Figures 8(b) and 8(c). Figure 8(b) shows an example in which heating tubes 82 are connected using electrically insulating tube joints 86 and electrically connected using jumpers 94. Alternatively, heating tubes 82 may be connected using flanges that are both mechanically and electrically connected. Or, as shown in Figure 8(c), each heating tube 82 may be electrically insulated with a tube joint 86, and an AC power supply 88 may be provided for each heating tube 82.

[0007] Thus, according to the electric fluid heating device 80 described in Patent Document 2, the heating tube 82 constitutes at least a part of the flow path of the fluid to be heated, and the fluid flow path itself is used as a heating means to directly heat the fluid electrically, thereby enabling the fluid to be heated and raised in temperature with high energy efficiency. As a specific example of energy efficiency, an example is shown in which sludge slurry was flowed at a flow rate of 80 liters / hour through a heating tube made of stainless steel pipe with an inner diameter of 7 mm, an outer diameter of 10.5 mm, and a length of 8 m while an AC current of 60 V, 180 A was flowed through it. In this experiment, the temperature was raised from 20 °C to 200 °C, a rise of approximately 180 °C, and it was found that 80-90% of the electrical energy supplied to the heating tube was utilized to heat the sludge slurry. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2008-134041 [Patent Document 2] Japanese Patent Publication No. 2000-213807 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, when heating the heating element 62 (magnetic tube 62b) inside a solenoid coil-shaped induction heating coil 72 as described in Patent Document 1, there were limitations to improving the heating efficiency for the following reasons. This is because it is difficult to pass all of the magnetic flux generated by the induction heating coil 72 through to the heating element (conductor) inside the induction heating coil. The factors causing this decrease in efficiency will be explained in detail below with reference to Figure 7(b). (a) The magnetic flux generated in the induction heating coil 72 penetrates the surface of the heating element 62 adjacent to the induction heating coil 72 inside the induction heating coil 72, causing an induced current. However, due to the nature of the magnetic flux, the portion of the heating element 62 that contributes to heating is limited to about half a circumference on the induction heating coil 72 side. (i) On the other hand, among the heating elements 62 inside the induction heating coil 72, the outer heating element 62 has a side opposite to the induction heating coil 72 that is hidden in the shadow of the heating element 62 itself on the side of the induction heating coil 72, resulting in a reduced amount of effective magnetic flux penetration. Also, the central heating element 62 is generally far from the induction heating coil 72, and in addition, its arrangement, which hides it in the shadow of the outer heating element 62, results in a reduced amount of effective magnetic flux penetration. (c) Furthermore, since the magnetic flux on the outside of the induction heating coil 72 is freely radiated, a considerable amount of magnetic flux enters the surrounding metal other than the heating element 62. As described above, it is difficult to concentrate all of the magnetic flux generated by a solenoid-shaped induction heating coil onto the material being heated, and therefore there is a problem in that there are limitations to improving the heating efficiency of solenoid-shaped induction heating coils.

[0010] Furthermore, in the electric heating device 80 for fluids described in Patent Document 2, heat transfer from the heating tube 82 to the fluid to be heated occurs from the inner surface of the heating tube 82. Therefore, in order to efficiently heat at high temperatures of several hundred degrees Celsius with such a heating device, it is necessary to extend the heating tube to secure a larger heat transfer area. However, since extending the heating tube tends to lead to an increase in the size of the heating device, there is a problem in that there are limitations to miniaturizing the heating device according to the invention described in Patent Document 2.

[0011] In view of the above-mentioned problems, the present invention aims to provide an electric fluid heating device and a method for electric fluid heating that enable high-efficiency electric fluid heating, miniaturization of heating devices for large volumes of fluids, and reduction of temperature bias that tends to occur in AC heating of multiple heating tubes. [Means for solving the problem]

[0012] [1] A fluid electric heating device comprising a multi-tube heating section with multiple parallel conductive heating tubes, wherein the heating of the fluid to be heated is heated from the tube walls of the heating tubes, which are heated by the application of alternating current, The electric heating device for the aforementioned fluid, (a) A fluid supply header that distributes the fluid to be heated to each of the heating tubes, (b) A fluid discharge header for recovering the heated fluid from each of the heating tubes, (c) A tube end short-circuit electrode integrally formed with the heating section side wall of each of the fluid supply header and the fluid discharge header, which electrically short-circuits the ends of each of the multiple heating tubes one side at a time, (d) Between the main body of each of the fluid supply header and the fluid discharge header and the pipe end short-circuit electrode, an electrical insulator is provided to electrically insulate each other. Equipped with, Each of the aforementioned plurality of heating tubes is When the opposing surfaces of a pair of short-circuit electrodes at the ends of opposing tubes are divided into an inner region and an outer region in the direction of the heating section, which is the lateral direction of the heating tube, When one end of the heating tube is connected to either the inner region or the outer region of the short-circuit electrode at the tube end on that end side, The other end of the heating tube is arranged to be connected to either the inner or outer region of the short-circuit electrode at the tube end on that end side. An electric heating device for fluids.

[0013] [2] The electric fluid heating device according to [1], further comprising a conductive expander between one or both ends of the heating tube and one or both of the fluid supply header and the fluid discharge header, for absorbing thermal deformation of the heating tube.

[0014] [3] The electric heating device for fluid according to [1] or [2], wherein either the pipe end short-circuit electrode disposed in the fluid supply header or the fluid discharge header is a separate pipe end short-circuit electrode that is independent of the fluid supply header or the fluid discharge header and is combined with a flexible conductor to electrically short-circuit the end of the heating tube.

[0015] [4] An electric fluid heating device according to any one of [1] to [3], wherein each component from the fluid supply header through the heating section to the fluid discharge header is arranged in a sealed box filled with inert gas. [Effects of the Invention]

[0016] According to the present invention, a large heat transfer area can be secured by using a multi-tube structure for the heating tubes, and the heating tube side wall of the header that supplies or discharges the fluid to be heated and the tube end short-circuit electrodes that supply power in parallel to the heating tubes can be integrally configured to achieve miniaturization of the heating device. Furthermore, in the present invention, by employing energized heating, unlike induction heating, the efficiency reduction due to magnetic flux leakage is inherently small, and high heating efficiency can be ensured. Moreover, in the present invention, temperature deviations in the heating tubes caused by current unevenness that is likely to occur depending on the arrangement of the heating tubes when using an AC power supply can be eliminated, making it possible to heat uniformly. As described above, the present invention enables miniaturization of spatial heating devices, increased electrical efficiency, and enhanced heating capacity within the same facility space. Furthermore, it provides an electric fluid heating device that offers excellent controllability, making it less likely to cause current bias in the heating tubes and temperature deviations in the fluid, even in AC heating. [Brief explanation of the drawing]

[0017] [Figure 1]It is a diagram schematically showing the overall configuration along the flow path direction of the fluid electric heating device 1 according to the first embodiment. [Figure 2] It is a diagram schematically showing an example of the arrangement of the heating tubes 12 in the depth direction in FIG. 1 as viewed in the direction of the S-S cross-section arrow of FIG. 1. [Figure 3] It is a diagram schematically showing an example in which the arrangement of the heating tubes 12 of the fluid electric heating device according to the modification of the first embodiment is a rotationally symmetric arrangement in a cross-sectional arrow view equivalent to FIG. 2. [Figure 4] It is a diagram schematically showing the overall configuration along the flow path direction of the fluid electric heating device 2 according to the second embodiment. [Figure 5] It is a diagram schematically showing the overall configuration along the flow path direction of the fluid electric heating device 3 according to the third embodiment. [Figure 6] It is a diagram schematically showing the overall configuration along the flow path direction of the fluid electric heating device 4 according to the fourth embodiment. [Figure 7] It is a diagram schematically showing the fluid electric heating device by induction heating according to the prior art in (a) a longitudinal sectional view and (b) a transverse sectional view. [Figure 8] It is a diagram schematically showing the fluid electric heating device by energization heating according to the prior art in (a) a basic configuration example of one heating tube body and one power source, (b) a configuration example in which a plurality of heating tube bodies are arranged in series, and (c) a configuration example in which the basic configurations are arranged in series.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the embodiments shown below, the same or common parts are denoted by the same reference numerals in the drawings, and the description thereof will not be repeated. Note that the present invention is not limited to the following embodiments.

[0019] (First Embodiment) Figure 1 is a schematic diagram showing the overall configuration of the electric fluid heating device 1 according to the first embodiment, along the flow path direction. Figure 2 is a schematic diagram showing an example of the arrangement of the heating tubes 12 in the depth direction in Figure 1, viewed from the SS cross-sectional arrow in Figure 1. Figure 3 is a schematic diagram showing an example in which the arrangement of the heating tubes 12 of the electric fluid heating device according to a modification of the first embodiment is rotationally symmetrical, viewed from the same cross-sectional arrow as in Figure 2. The electric fluid heating device according to the first embodiment will be described with reference to Figures 1 to 3.

[0020] As shown in Figure 1, in the electric fluid heating device 1 according to the first embodiment, a plurality of parallel conductive heating tubes 12 form a multi-tube heating section (hereinafter also simply referred to as the heating section) 10. In each heating tube 12 of the heating section 10, the fluid to be heated A flowing inside is heated from the tube wall, which is heated by electric current.

[0021] The multi-tube heating section 10 according to this embodiment is advantageous in terms of securing a wide heat transfer surface (also called a heating surface or heating surface) compared to a conventional electric fluid heating device 80 consisting of a single-tube heating tube, such as the one shown in Figure 8, under the condition of equivalent heating section volume. In other words, in this embodiment, since multiple heating tubes 12 can be provided in the lateral direction of the flow path within the short length of the heating section 10, a wide heat transfer area, which is the sum of the inner circumferential surfaces of the multiple heating tubes 12, can be secured within the volume occupied by the heating section 10.

[0022] As described above, the electric fluid heating device 1 according to this embodiment can significantly increase heating capacity without increasing the size of the device. Conversely, the electric fluid heating device 1 according to this embodiment can also be used as a replacement for an electric fluid heating device consisting of a single-tube heating tube as shown in Figure 8, resulting in a smaller heating device without compromising heating capacity.

[0023] The heating tubes 12 forming the multi-tube heating section 10 according to this embodiment are not limited in material as long as they satisfy requirements such as being electrically conductive, having heat resistance and corrosion resistance to withstand the heating temperature of the fluid to be heated, and being able to be formed into a tube. Preferred materials that satisfy such requirements include, for example, known Cr alloy steel (including alloy steel in which about 1 mass% of Cr is added to carbon steel, and even higher alloy Cr-based stainless steel). Other alloy steels include Cr-Ni alloy steel (including alloy steel in which about 0.2 to 1.0 mass% of Cr and about 1.0 to 3.5 mass% of Ni are added to carbon steel, and even higher alloy Cr-Ni-based stainless steel). Furthermore, carbon materials or conductive ceramics that can withstand use at temperatures exceeding 1000°C are also examples. These materials are preferred as heating tubes because they have relatively high resistivity. As for conductive ceramics, known conductive ceramics such as SiC can be used. In addition, depending on the fluid being heated, the installation location, etc., known high-melting-point metals such as tungsten and molybdenum, or alloys thereof, may be used as needed.

[0024] In the electric fluid heating device 1 according to this embodiment, (a) a fluid supply header 20 that distributes the fluid to be heated A to each of the heating tubes 12, and (b) a fluid discharge header 22 that recovers the fluid to be heated A from each of the heating tubes 12 are provided at both ends of the heating section 10 in the flow direction. Furthermore, (c) the walls of the fluid supply header 20 and the fluid discharge header 22 on the heating section 10 side are integrally configured with tube end short-circuit electrodes 30 that electrically short-circuit each end of the multiple heating tubes 12 and supply power in parallel to each heating tube 12. In this specification, the fluid supply header 20 and the fluid discharge header 22 together are sometimes referred to as the "fluid header".

[0025] The short-circuit electrode 30 at the end of the pipe and the header body 24 excluding the short-circuit electrode 30 are connected via a known electrical insulator 26 to form a sealed structure, thereby providing a header function similar to that of a known fluid header while insulating the heating section 10 from the fluid header and beyond. The header body 24 in this embodiment may be composed of the same structure and materials as a known fluid header corresponding to the header body 24, and a detailed explanation thereof is omitted. As described above, the single plate-shaped tube end short-circuit electrode 30, which also serves as a wall, can combine the functions of an individual electrode provided for each heating tube 12 in the conventional technology, a conductor that short-circuits each individual electrode, and a header wall, thereby contributing to a significant miniaturization of the heating device.

[0026] In the fluid electric heating device 1 according to this embodiment, the external power source is assumed to be an AC power supply 40. This is because AC power supplies are generally used as power sources due to their versatility, controllability, etc. In this embodiment, as shown in Figure 1, a parallel power supply circuit is employed, connecting the heating tubes 12 and the AC power supply 40 in parallel via tube end short-circuit electrodes 30 and electric wires. To configure this power supply circuit, the tube ends of the heating tubes 12 are electrically short-circuited at one end and the other end of the multi-tube heating section 10 by the tube end short-circuit electrodes 30. The electric fluid heating device 1 according to this embodiment can be controlled based on known techniques for controlling current, voltage, and power. Furthermore, the heating capacity of the electric heating device should be designed taking into account the resistance of each heating tube 12, the amount of heat generated, and the amount of temperature rise of the fluid to be heated.

[0027] In the electric fluid heating device 1 according to this embodiment, each of the multiple heating tubes 12 of the heating section 10 is connected so as to straddle both regions when the opposing surfaces of a pair of opposing tube end short-circuit electrodes 30 are divided into an inner region and an outer region in the inward-outward direction of the heating section 10 (lateral direction of the heating tube 12). That is, when one end of a heating tube 12 is connected to either the inner region or the outer region of the tube end short-circuit electrode 30 on that end side, the other end of the heating tube is connected to the other of the inner region or the outer region of the tube end short-circuit electrode 30 on that end side.

[0028] Figure 1 shows a specific example of the heating tube 12 according to this embodiment, which has first and second straight heating tube sections (also simply called heating tube straight sections) at both ends in the longitudinal direction, which are of approximately equal length and whose central axes are spaced a predetermined distance apart and are in a substantially parallel relationship. Furthermore, the heating tube 12 according to this embodiment shown in Figure 1 has a heating tube transition section between the first and second straight heating tube sections. Note that the shape of the heating tube, the dimensional ratio in the longitudinal direction, and the parallel relationship shown in Figure 1 are examples, and as described above, in this embodiment, it is sufficient that the requirements for the connection relationship between the heating tube 12 and the short-circuit electrode 30 at the end of the tube are met, and for example, the heating tube 12 may consist only of a curved section. In this embodiment, having the heating tubes 12 arranged in this manner makes it possible to avoid the problems that occur when heating with alternating current, as described below. Specifically, in the case of alternating current heating, problems of current distribution based on the inductance distribution of the heating tubes relative to the electrodes, such as overheating of the outer heating tube and underheating of the inner heating tube, which tend to occur between multiple heating tubes arranged parallel to each other between opposing electrodes, can be avoided in this embodiment.

[0029] Specifically, in this embodiment, a heating tube 12 connected to the outer region of one tube end short-circuit electrode 30 is connected to the inner region of the other tube end short-circuit electrode 30. Furthermore, a heating tube 12 connected to the inner region of one tube end short-circuit electrode 30 is connected to the outer region of the other tube end short-circuit electrode 30. This arrangement of heating tubes 12 averages the current distribution. As a result, the current flows almost uniformly among all heating tubes 12, eliminating differences in heating capacity and enabling uniform heating throughout the entire heating section 10. In addition, overheating of heating tubes 12 can be eliminated, preventing damage to the heating tubes 12. Moreover, since an averaged current flows through all heating tubes 12, heating controllability can be improved.

[0030] In this embodiment, the heating tube transition section 12b, which is provided between the straight heating tube sections 12a on both sides of the heating tube 12, is indispensable for the formation of the heating tube flow path, but its placement is not limited to within the plane that includes the straight heating tube sections 12a on both sides. For example, the heating tube transition section 12b may protrude out of the plane in a range where it does not come into contact with the surrounding heating tube 12 and the impedance does not change significantly.

[0031] Next, an example of the arrangement of the heating tube 12 within the heating section 10 of the fluid electric heating device 1 according to this embodiment will be described with reference to Figures 1 and 2. In the example shown in Figure 1, heating tubes 12i and 12iv, where the straight heating tube section 12a is outside the heating section 10 on the fluid supply side (lower side in the figure), transition to the inside of the heating section 10 on the fluid discharge side (upper side in the figure) via the heating tube transition section 12b. Conversely, heating tubes 12ii and 12iii, where the straight heating tube section 12a is inside the heating section 10 on the fluid supply side, transition to the outside of the heating section 10 on the fluid discharge side via the heating tube transition section 12b. This transition of the position of the straight heating tube section 12a on the flow direction projection plane can also be seen in Figure 2, which shows the view from the SS cross-section arrow in Figure 1.

[0032] In Figure 2, the straight sections 12a (upper part of Figure 1) on the fluid discharge side of the heating tubes 12 (12i to 12iv) are all depicted as circular shapes because they can be directly viewed in the SS cross-section view in Figure 1. The straight sections 12a (lower part of Figure 1) on the fluid supply side are depicted as semicircular outlines, excluding the semicircular portion that overlaps with the heating tube transition section 12b (see Figure 1), as long as they do not overlap with the straight sections 12a (upper part of Figure 1) on the fluid discharge side in the SS cross-section view in Figure 1. The heating tube transition section 12b, which is depicted as a straight or roughly spiral shape in Figure 2, also has arrows indicating the flow direction of the heated fluid A rising towards the viewer.

[0033] Figure 2 shows three patterns of arrangement of the heating tubes 12 in the depth direction of Figure 1, where two heating tubes 12 that are axially symmetrical with respect to each other in the flow direction appear to overlap at the heating tube transition section 12b in Figure 1. Figure 2(a) shows an example of arrangement where two heating tubes in the depth direction of Figure 1 are spaced apart from each other, with their heating tube center planes parallel, assuming a plane containing the central axes of the straight heating tube sections 12a at both ends of a single heating tube 12 (hereinafter also simply referred to as the heating tube center plane). Figure 2(b) shows an example of arrangement where the two heating tubes in the depth direction of Figure 1 intersect at the central axis position of the straight heating tube section 12a on one side of each heating tube. Figure 2(c) shows an example of arrangement where the two heating tubes in the depth direction of Figure 1 overlap, including the central axes of the straight heating tube sections 12a on both sides of each heating tube. In the case of Figure 2(c), it is preferable that the two heating tubes in the depth direction of Figure 1 have heating tube transition sections 12b that protrude out of the plane in opposite directions from the heating tube center plane (for example, roughly spiral in shape) so that they do not interfere with each other at the heating tube transition section 12b. Furthermore, in any of the arrangements shown in Figures 2(a) to (c), the effect of eliminating temperature deviations in the heating tubes due to current imbalances between them when using an AC power supply is equivalent. Therefore, the arrangement of the heating tubes 12 can be appropriately selected from any of the arrangements in Figure 2, depending on the size (heating capacity) of the heating tubes 12 within the heating section 10 in a limited space, the arrangement of the heating tubes 12, and the avoidance of interference with surrounding equipment.

[0034] Figure 3 is a schematic diagram showing the arrangement of heating tubes 12 in an electrically heated fluid heating device according to a modified example of the first embodiment, viewed from a cross-sectional perspective equivalent to that of Figure 2. The heating tubes 12 in Figure 3 are also the same as those in Figure 2, differing in that the arrangement of the heating tubes 12 is rotationally symmetrical. In Figure 3(a), eight heating tubes 12 are densely arranged in the heating section 10, with each heating tube 12 having its straight heating tube section 12a on both sides of the heating section 10 on the outside and inside. On the other hand, in Figure 3(b), two heating tubes 12 are treated as a pair, similar to Figure 2(c), and four pairs of heating tubes 12, totaling eight heating tubes 12, are densely arranged in the heating section 10, with each pair having its straight heating tube section 12a on the outside and inside of the heating section 10. As shown in Figure 3, when the heating tubes 12 are arranged in a rotationally symmetrical configuration, there is an advantage in that more heating tubes 12 can be installed compared to the case in Figure 2. However, in the cases of Figures 3(a) and (b), the effect of eliminating temperature deviations in the heating tubes due to current imbalances between heating tubes when using an AC power supply is the same as in the cases of Figures 2(a) to (c). Therefore, when designing the specific equipment, the choice of heating tube arrangement should be made appropriately based on the size (heating capacity) of the heating tubes 12 within the heating section 10 in a limited space, the arrangement of the heating tubes 12, and the avoidance of interference with surrounding equipment.

[0035] In the multi-tube heating section 10 according to this embodiment, the heating tubes 12 are arranged in a way that takes into account the effect of eliminating temperature deviations in the heating tubes due to current imbalances between the heating tubes when using the above-mentioned AC power supply, and the heating tubes 12 may be bundled together in a manner that does not short-circuit each other. This is preferable because it can suppress heat loss due to heat dissipation to the surroundings. In this case, the heating tubes located on the inside of the bundled heating tubes will have almost no heat loss because their surfaces are surrounded by other heating tubes, and the main heat loss will be limited to heat dissipation from the outer surface of the heating tube located on the outermost periphery. Furthermore, in order to suppress heat loss due to heat dissipation from the heating tubes 12 to the surroundings, each heating tube 12, or the entire bundle of heating tubes 12, may be covered with a known insulating material. As the known insulating material here, insulating materials such as ceramic fibers with low thermal conductivity can be used. Alternatively, the entire heating section 10 may be placed inside an insulated case.

[0036] In this embodiment, when viewed as a unit of 12 heating tubes, turbulence is easily generated because the flow direction changes at the heating tube transition section 12b. Also, when viewed as a whole, the heating section 10 is multi-tube, so the fluid to be heated A is forced to pass through narrow spaces, which also easily generates turbulence, thus improving heat transfer capacity. In addition, to enhance heat transfer promotion by turbulence, the heat transfer efficiency can be further improved by making the surface roughness of the tube walls of the heating tubes 12 rougher or by adding shapes to the tube walls that easily cause fluid turbulence, such as irregularities. As an example of typical dimensions for the flow path of the fluid to be heated A inside the heating tubes 12, the inner diameter is preferably several millimeters to several tens of millimeters, and should be determined considering the processing volume, heating temperature, pressure loss, etc.

[0037] The cross-sectional shape of the heating tube 12 is preferably circular or polygonal. A circular shape is advantageous in terms of manufacturing the heating tube 12 and avoiding flow deviations compared to other shapes. Similarly, a polygonal shape is also relatively advantageous in terms of manufacturing the heating tube 12 and avoiding flow deviations. Among polygonal shapes, a square shape is preferable because it is relatively easy to maximize the space of the heating section 10 while avoiding interference with surrounding equipment when the installation space for the electric heating device is limited.

[0038] Furthermore, the heating tube 12 may have an electrical insulating layer on its inner surface. By providing such an electrical insulating layer, electrically conductive fluids to be heated can also be heated by electric current. The material of this electrical insulating layer is not particularly limited as long as it satisfies requirements such as having electrical insulating properties, as well as heat resistance and corrosion resistance to withstand the heating temperature of the fluid to be heated. For example, known materials and coating methods such as a chromium oxide film formed by high-temperature oxidation of a chromium-containing steel tube, or insulating oxide ceramics such as alumina formed by high-temperature oxidation after coating with molten aluminum, may be used. Furthermore, the exterior surface should be fitted with an insulating and heat-insulating coating that also provides thermal insulation.

[0039] Furthermore, in this embodiment, there is a control device (not shown) that controls the power supplied to the heating tube 12 based on physical quantities including at least the temperature and flow rate of the fluid to be heated A, and the equipment capacity including at least the unit heat generation per unit area of ​​the tube wall of the heating tube 12. This control device controls the power supplied from the AC power supply 40 to the heating tube 12, thereby energizing the heating tube 12 and heating the fluid flowing inside the tube. It is also preferable that this control device has a function to issue an alarm and / or cut off the power in the event of an abnormality or emergency such as overheating of the heating tube, based on temperature measurement data at the monitoring point of the heating tube. Note that the control device here may be a known control device including an arithmetic unit, memory device, input / output device, etc., and a detailed explanation thereof is omitted.

[0040] It is preferable to measure predetermined physical quantities, including the temperature and flow rate of the fluid A to be heated, used for heating control, near the inlet and / or outlet of the fluid A to be heated in the multi-tube heating section 10. This is because the measurement results of the physical quantities of the fluid A to be heated near the inlet and / or outlet can contribute to improving the accuracy of the temperature control of the fluid to be heated by feedforward control and / or feedback control of the power supply, such as input power, current, and voltage. In the case of electric heating, since the control response is high, it is also possible to measure the physical quantities of the fluid A to be heated only near the inlet of the fluid to be heated in the multi-tube heating section 10 and perform only feedforward control. The equipment capacity, including the unit heat generation per unit area of ​​the tube wall of the heating tube 12, is used as basic data for controlling the power supply, such as input power, current, and voltage, to the heating tube 12 in both the feedback control and feedforward control described above. Examples of means for measuring the temperature of the fluid A to be heated here include temperature measurement using a thermocouple, which is a known method. Furthermore, examples of means for measuring the flow rate of the heated fluid A include known electromagnetic flow meters, impeller-type flow meters, ultrasonic flow meters, and differential pressure flow meters (orifice flow meters).

[0041] Next, a method for electrically heating a fluid using the fluid electric heating device 1 according to this embodiment will be described based on Figure 1. In this embodiment, as shown in Figure 1, the fluid to be heated A is supplied to each of the fluid flow paths in the four heating tubes 12 via the fluid supply header 20. The fluid to be heated A then passes through the fluid flow paths formed by the four heating tubes 12 in the multi-tube heating section 10, and is heated by the electric current, becoming a heating surface, and is heated from the tube walls of the heating tubes 12 that act as heating surfaces. The heated fluid to be heated A is discharged from each of the four heating tubes 12, collected by the fluid discharge header 22, and discharged outside the fluid electric heating device 1 system. In the example shown in Figure 1, only four heating tubes 12 are shown, but more heating tubes 12 may be provided.

[0042] In the heating control of the fluid A to be heated, a control device (not shown) controls the power input to the heating unit 10 based on physical quantities such as the target heating temperature and heating flow rate, as well as the equipment capacity such as the unit heat generation of the heating tube 12. In addition, it is preferable to perform feedback control based on the temperature and flow rate of the fluid A to be heated after heating.

[0043] Specific examples of applications for heating the fluid A to be heated include, but are not limited to, preheating fuel and combustion air supplied to a combustion device, or heating heavy oil and atomizing vapor for heavy oil atomization.

[0044] (Second embodiment) Figure 4 is a schematic diagram showing the overall configuration of the fluid electric heating device 2 according to the second embodiment, along the flow path direction. The fluid electric heating device 2 according to the second embodiment will be described with reference to Figure 4.

[0045] As shown in Figure 4, the electric fluid heating device 2 according to the second embodiment differs from the electric fluid heating device 1 according to the first embodiment mainly in that an expansion joint 28 is arranged between one end of the heating tube 12 on the fluid supply side and the fluid supply header 20. The other configurations of the second embodiment are substantially the same as those of the first embodiment.

[0046] Even when configured as described above, the electric fluid heating device 2 according to the second embodiment can obtain substantially the same effects as the electric fluid heating device 1 according to the first embodiment.

[0047] In addition, in this embodiment, the expansion joint 28, which is disposed between one end of the heating tube 12 on the fluid supply side and the fluid supply header 20, can advantageously avoid the effects of thermal expansion or contraction of the heating tube 12 depending on the heating conditions. Specifically, this expansion joint 28 can prevent rupture of the heating tube 12, interruption of the power supply circuit, deformation and damage to the fluid header including the tube end short-circuit electrode 30, and thereby further improve the maintainability and durability of the equipment.

[0048] In the example shown in Figure 4, the expansion joint 28 is positioned between one end of the heating tube 12 on the fluid supply side, where the temperature of the heated fluid A is low, and the fluid supply header 20. This is a preferred configuration because it allows for a relaxation of the heat resistance requirements for the expansion joint 28. However, this embodiment is not limited to this configuration, and the expansion joint 28 may be positioned between one end of the heating tube 12 on the fluid discharge side and the fluid discharge header 22. Furthermore, the expansion joint 28 may be positioned between both ends of the heating tube 12 and both the fluid supply header 20 and the fluid discharge header 22.

[0049] Here, the expansion joint 28, together with the heating tube 12, is part of the energizing circuit and therefore must be conductive; for example, a known metal bellows can be used. Furthermore, since the inside of the expansion joint 28 is also a fluid passage for the heated fluid A, it must be airtight to prevent leakage of the heated fluid. Similarly, it is preferable to use conductive metal packing to ensure airtightness between the heating tube 12 and the tube end short-circuit electrodes 30 on both sides of the expansion joint 28.

[0050] (Third embodiment) Figure 5 is a schematic diagram showing the overall configuration of the fluid electric heating device 3 according to the third embodiment, along the flow path direction. The fluid electric heating device 3 according to the third embodiment will be described with reference to Figure 5.

[0051] As shown in Figure 5, the electric fluid heating device 3 according to the third embodiment differs from the electric fluid heating device 2 according to the second embodiment mainly in the configuration of the pipe end short-circuit electrodes 30 and 32 on the fluid supply header 20 side. Specifically, the third embodiment differs from the second embodiment in that the pipe end short-circuit electrode 30 is separated from the fluid supply header 20, and a separate type pipe end short-circuit electrode 32 is formed by combining an individual pipe end electrode 34, a flexible conductor 36, and a main connecting conductor 38. The main connecting conductor 38 is a fixed conductor made of a copper plate, copper pipe, or cable, etc., installed at a distance from the heating pipe 12, to which the flexible conductor is connected. A flexible conductor is a so-called braided wire, water-cooled cable, spring-type conductor, etc., which can absorb thermal expansion or contraction by flexibly bending even when subjected to external force.

[0052] In addition to these main configuration differences, in the third embodiment, the fluid supply header 20 is a conventional type without the pipe end short-circuit electrode 30 which is integrally formed with the wall portion on the heating section 10 side. Furthermore, there are subordinate differences, such as the positional relationship between the heating tube 12 of the expansion joint 28 and the pipe end short-circuit electrodes 30 and 32 being reversed between the second and third embodiments. However, these are due to the main structural changes to the pipe end short-circuit electrodes 30 and 32 mentioned above and are not significant differences between the second and third embodiments. The other configurations of the third embodiment are substantially the same as those of the second embodiment.

[0053] Even when configured as described above, the electric fluid heating device 3 according to the third embodiment can obtain substantially the same effects as the electric fluid heating device 2 according to the second embodiment.

[0054] In addition, since the short-circuit electrode 32 at the end of the tube is a separate type, the short-circuit electrode 32 will no longer be affected by the thermal deformation of the heating tube 12. This makes it possible to further improve the stability of current flow, the maintainability and durability of the equipment, etc.

[0055] (Fourth embodiment) Figure 6 is a schematic diagram showing the overall configuration of the fluid electric heating device 4 according to the fourth embodiment, along the flow path direction. The fluid electric heating device 4 according to the fourth embodiment will be described with reference to Figure 6.

[0056] As shown in Figure 6, the electric fluid heating device 4 according to the fourth embodiment has the following differences compared to the electric fluid heating device 3 according to the third embodiment. Specifically, the electric fluid heating device 4 according to the fourth embodiment differs from the third embodiment in that each component part from the fluid supply header 20 through the heating unit 10 to the fluid discharge header 22 is arranged in a sealed box 50 filled with an inert gas B such as nitrogen gas. The other configurations are substantially the same as those of the third embodiment.

[0057] Even when configured as described above, the electric fluid heating device 4 according to the fourth embodiment can achieve substantially the same effects as the electric fluid heating device according to the third embodiment.

[0058] In addition, since the electric fluid heating device 4 according to the fourth embodiment has all of its main components arranged inside a sealed box 50 filled with an inert gas B such as nitrogen gas, it becomes possible to safely heat even flammable fluids A that pose a risk of ignition or explosion. Furthermore, by installing a flammable gas detector inside this sealed box or at the outlet and linking it to the power control device, safety measures such as emergency shutdown of the power supply can be implemented in the initial stages of a flammable gas leak. Furthermore, the heating efficiency of the seal box 50 can be further improved by incorporating an insulating structure.

[0059] The various embodiments of the electric fluid heating devices 1, 2, 3, and 4 according to the present invention have been described above. These devices may be arranged in series or in parallel in the flow direction, either with identical embodiments or with different embodiments. This increases the flexibility of equipment design, such as optimizing the heating capacity of the electric fluid heating devices on the upstream and downstream sides within a limited space for heating devices. [Explanation of Symbols]

[0060] 1, 2, 3, 4 Electric heating devices for fluids 10. Multi-tube heating section 12, 12i, 12ii, 12iii, 12iv heating tube 12a Straight heating pipe section 12b Heating tube transition section 20 Fluid supply headers 22 Fluid discharge header 24 Header body 26 Electrical insulators 28 Telescoping 30. Short-circuit electrode at the end of the tube (integrated type) 32. Short-circuit electrode at the end of the tube (separable type) 34 Individual tube end electrode 36 Flexible Conductors 38 Main connecting conductor 40 AC power supply 50 sealed boxes 60. Electric heating devices for fluids 62 Heating element 62a non-magnetic tube 62b magnetic tube 64, 66 Pipe support plate 68 Interior insulation 70 Exterior insulation 72 Induction heating coil 74 Fluid Inlet Header 76 Fluid outlet header 80. Electric heating devices for fluids 82 Heating tube 84 Unheated pipe 86 Pipe joints 88 AC power supply 90 Support stand 92 Electrical insulators 94 Jumper A Heated fluid B Inert gas

Claims

1. An electric heating device for fluids, comprising a heating section with multiple parallel conductive heating tubes forming a multi-tube structure, and heating of the fluid to be heated from the tube walls of the heating tubes, which are heated by the application of alternating current, The electric heating device for the aforementioned fluid, (a) A fluid supply header that distributes the fluid to be heated to each of the heating tubes, (b) A fluid discharge header for recovering the heated fluid from each of the heating tubes, (c) A tube end short-circuit electrode integrally formed with the heating section side wall of each of the fluid supply header and the fluid discharge header, which electrically short-circuits the ends of each of the multiple heating tubes one side at a time, (d) Between the main body of each of the fluid supply header and the fluid discharge header and the pipe end short-circuit electrode, an electrical insulator is provided to electrically insulate each other. Equipped with, Each of the aforementioned plurality of heating tubes is When the opposing surfaces of a pair of short-circuit electrodes at the ends of opposing tubes are divided into an inner region and an outer region in the direction of the heating section, which is the lateral direction of the heating tube, When one end of the heating tube is connected to either the inner region or the outer region of the short-circuit electrode at the tube end on that end side, The other end of the heating tube is arranged to be connected to either the inner or outer region of the short-circuit electrode at the tube end on that end side. An electric heating device for fluids.

2. The electric fluid heating device according to claim 1, further comprising a conductive expander between one or both ends of the heating tube and one or both of the fluid supply header and the fluid discharge header, for absorbing thermal deformation of the heating tube.

3. The electric heating device for fluid according to claim 1 or claim 2, wherein either the pipe end short-circuit electrode disposed in the fluid supply header or the fluid discharge header is a separate type pipe end short-circuit electrode that is independent of the fluid supply header or the fluid discharge header and is combined with a flexible conductor to electrically short-circuit the end of the heating tube.

4. An electric fluid heating device according to claim 1 or claim 2, wherein each component from the fluid supply header through the heating section to the fluid discharge header is arranged in a sealed box filled with inert gas.

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