JP2024062110A - Apparatus and method for electrically heating a fluid - Google Patents

Abstract

[Problem] To provide an electric heating device and an electric heating method for a fluid that enable high fluid heating efficiency and miniaturization of the heating device. [Solution] The present invention provides an electric heating device and an electric heating method for a fluid by electrical heating, in which a heating section is made of a multiple-pipe structure in which a large-cross-section heating tube is inserted into a small-cross-section heating tube, and an annular gap between the heating tubes, together with the inside of the innermost heating tube, serves as a fluid flow path for the heated fluid, and includes, as fluid flow path forming means for forming one fluid flow path going back and forth through the heating section, (1) a tube end support closing plate that supports the heating tube at both ends and provides electrical insulation while providing a sealed structure, (2) fluid introduction holes that are arranged at alternate end positions between one end and the other end of the heating tubes in the inner and outer directions and that connect the fluid flow paths on both sides of the tube wall to each other, and (3) a fluid inlet/outlet that is arranged at the end opposite the fluid introduction hole in the innermost heating tube and at a position equivalent to the fluid introduction hole in the outermost heating tube. [Selected Figure] Figure 1

Description

The present invention relates to an electric fluid heating device and an electric fluid heating method, and more particularly to an electric fluid heating device and an electric fluid heating method that have high heating efficiency and can be miniaturized.

In recent years, efforts to improve energy efficiency and switch to fuels with less carbon dioxide emissions have been promoted as a measure against global warming. In the field of large-scale, large-capacity fluid heating equipment, various types have been used up to now, and heating equipment such as boilers that use combustion gas are usually used to perform high-temperature heating of several hundred degrees. However, heating equipment such as boilers that use combustion gas not only requires large equipment, but also has the problem that even the most efficient heating equipment has a heating efficiency of around 35%, which means that there is a limit to how efficient it can be.

In order to address both the problems of miniaturizing the heating equipment and increasing the heating efficiency, an electric heating means capable of inputting 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 the longitudinal section (a) and transverse section (b) of FIG. 7. Specifically, the heating element 62 is composed of a non-magnetic tube 62a made of, for example, SUS304 and a magnetic tube 62b (62b1, 62b2, 62b3) made of, for example, SUS430 as a magnetic body. The non-magnetic tube 62a is formed with a curved portion 62c (62c1, 62c2) that curves the flow path of the heated fluid (arrow A) into a U-shape, and parallel portions extending in opposite directions on both sides of the curved portion 62c. The non-magnetic tube 62a passes through the induction heating coil 72 (a plane perpendicular to the coil axis) multiple times by extending in the opposite direction via the curved portion 62c. Three magnetic tubes (62b1, 62b2, 62b3) with an inner diameter substantially equal to the outer diameter of the non-magnetic tube 62a are arranged in the parallel portion of the non-magnetic tube 62a. Both ends of the non-magnetic tube 62a are fixed and supported in a state where they are inserted into holes formed in the plate-shaped tube support plates 64 and 66.

An induction heating coil 72 connected to an AC power source (not shown) is disposed around the outside of the heating element 62. The induction heating coil 72 is interposed between a cylindrical inner insulation material 68 and an outer insulation material 70, and is positioned by fixing both ends of the inner insulation material 68 to the tube support plates 64, 66. A fluid inlet header 74 and a fluid outlet header 76 are provided on the tube support plates 64, 66, respectively, and the heated gas or liquid fluid (arrow A) is heated through the fluid inlet header 74 and non-magnetic tube 62a before being directed to the fluid outlet header 76.

In the invention described in Patent Document 1, the magnetic tube 62b is in contact with the outer circumferential surface of the non-magnetic tube 62a through which the heated fluid (arrow A) flows, and the heat generated in the magnetic tube 62b by induction heating is thermally conducted from the magnetic tube 62b to the non-magnetic tube 62a, and from the non-magnetic tube 62a to the heated fluid. Therefore, the heated fluid does not come into contact with the magnetic tube 62b, which has inferior corrosion resistance compared to the non-magnetic tube 62a, and the corrosion resistance is improved. In addition, the non-magnetic tube 62a through which the heated fluid (arrow A) flows passes through the induction heating coil 72 multiple times. As a result, the same amount of heat can be obtained with one non-magnetic tube 62a as with multiple tubes, so there is no need to make the induction heating coil 72 longer or more frequent, or to make the non-magnetic tube 62a thicker. In addition, by reducing the number of non-magnetic tubes 62a, the temperature variation of the heated fluid (arrow A) is suppressed and temperature control becomes easier.

Patent Document 2 also discloses an electric heating device 80 for fluids by electrical heating as shown in FIG. 8. Its basic configuration is a "one heating tube, one power source" configuration, consisting of a heated tube 82, a non-heated tube 84, a tube joint 86, and an AC power source 88, as shown in FIG. 8(a). The heated tube 82 is made of a metal that generates heat when electricity is passed through it. An AC power source 88 that passes current from one end to the other end of the heated tube 82 is connected to the heated tube 82. The non-heated tube 84 is connected to both ends of the heated tube 82, has the same diameter as the heated tube 82, and forms a flow path for the heated fluid. The tube joint 86 mechanically connects the heated tube 82 and the non-heated tubes 84, 84 to form a flow path, and electrically insulates the heated tube 82 from the non-heated tubes 84, 84. If a support stand is required to hold the heating tube 82, an electrical insulator 92 is placed between the support stand 90 and the heating tube 82, as shown in FIG. 9(a).

Patent Document 2 also discloses an embodiment in which multiple heating tubes 82 are connected together, as shown in Figures 8(b) and (c). Figure 8(b) shows an example in which the heating tubes 82 are connected together using electrically insulating tube joints 86, and electrically connected together using jumpers 94. Alternatively, the heating tubes 82 may be connected together using flanges that mechanically and electrically connect the heating tubes 82. Alternatively, as shown in Figure 8(c), each heating tube 82 may be electrically insulated by a tube joint 86, and an AC power source 88 may be provided for each heating tube 82.

In this way, 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 heated fluid, and the fluid flow path itself serves as a heat generating means to directly electrically heat the fluid, thereby making it possible to heat and increase the temperature of the fluid with high energy efficiency. As a specific experimental example of energy efficiency, an example is shown in which sludge slurry was passed at a flow rate of 80 liters/hour while passing an alternating current of 60 V and 180 A 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. In this experiment, the temperature could be raised by approximately 180°C from 20°C to 200°C, and it is said that 80 to 90% of the electrical energy given to the heating tube was used to heat the sludge slurry.

JP 2008-232606 A JP 2000-213807 A

However, when heating the heating element 62 (magnetic tube 62b) inside the solenoid-shaped induction heating coil 72 as described in Patent Document 1, there is a limit to improving the heating efficiency for the following reasons. This is because the magnetic flux generated by the induction heating coil 72 penetrates the surface layer of the heating element 62 (conductor) close to the induction heating coil 72 to cause an induced current, but as shown in Figure 7 (b), the part of the heating element 62 through which the effective magnetic flux penetrates and can effectively heat is limited. For example, the part of the heating elements (magnetic tubes) 62b1 and 62b3 facing the induction heating coil 72 is about half of the entire circumference, and the sides of 62b1 and 62b3 opposite the induction heating coil 72 and the central part 62b2 are away from the induction heating coil 72, making it difficult for the effective magnetic flux to penetrate and effective heating to occur. In addition, because the magnetic flux outside the induction heating coil 72 is freely radiated, there is a considerable amount of magnetic flux penetrating the surrounding metal other than the heating element 62. As a result, it is difficult to concentrate the magnetic flux on the material to be heated directly below the solenoid coil, and heating efficiency cannot be improved.

In addition, in the electric heating device 80 for fluids as described in Patent Document 2, heat is transferred from the heating tube 82 to the heated fluid only via the inner surface of the heating tube 82. Therefore, when performing high-temperature heating with such a heating device, it is necessary to extend the heating tube to increase the heat transfer area and ensure the heating time, which necessitates the extension of the heating tube. 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 is a limit to the miniaturization of the heating device according to the invention described in Patent Document 2.

The present invention was made in consideration of the above problems, and aims to provide an electric fluid heating device and an electric fluid heating method that can improve the heating efficiency of electric fluid heating and reduce the size of a large-capacity heating device.

[1] A multi-tube type fluid electric heating device using electrical heating, in which a plurality of electrically conductive heating tubes have cross sections that are approximately similar to each other, a heating tube having a small cross section is inserted into a heating tube having a large cross section without contacting each other to form a heating section having a multi-tube structure, and an annular gap between the heating tubes is used as a fluid flow path for a heated fluid together with an interior of the innermost heating tube,
(a) as a fluid flow path forming means for forming one fluid flow path together with a tube wall of the heating tube forming the annular gap,
(a1) a tube end support closing plate that supports each of the heating tubes at both ends and seals both ends while providing electrical insulation;
(a2) fluid introducing holes that are arranged at end positions that are staggered between one end and the other end of the heating tubes in the inner and outer directions and that connect the annular fluid flow paths on both sides in the inner and outer directions of the tube wall to each other;
(a3) a fluid inlet/outlet that is disposed at an end of an innermost heating tube among the heating tubes opposite to the fluid introducing hole, and that is disposed at a position corresponding to the fluid introducing hole in an outermost heating tube among the heating tubes;
1. An apparatus for electrically heating a fluid comprising:
[2] The electric heating device for a fluid according to [1], wherein the heating tubes constituting the heating portion of the multi-tube structure are divided into a plurality of heating tube groups each consisting of a plurality of heating tubes connected in an inner and outer direction, and a power supply circuit is provided for each of the heating tube groups.
[3] A power supply circuit for the heating tube constituting the heating portion of the multi-tube structure, or a power supply circuit for each of the plurality of heating tube groups constituting the heating portion of the multi-tube structure,
(b1) a single parallel power supply circuit in which power supply electrodes are electrically short-circuited to each other at one end and the other end of the heating section of the multi-tube structure, and the heating tubes are connected in parallel to a single power source;
(b2) a single series power supply circuit in which every other power supply electrode is electrically short-circuited at one end and the other end of the heating section of the multi-tube structure, and the heating tubes are connected in series to a single power source;
and,
(b3) a group of power supply circuits each consisting of a set of power supply circuits for one heating tube and one power source, in which the heating tubes constituting the heating portion of the multi-tube structure are each connected to one power source;
The electrical heating device for a fluid according to [1] or [2], wherein the electrical supply circuit is any one of the above.
[4] The electric heating device for a fluid according to any one of [1] to [3], wherein the heating tubes constituting the heating part of the multi-tube structure have at least some heat generation characteristics different from others between the heating tubes in the inner and outer directions having different cross-sectional outside dimensions, or between partial heating tubes having the same cross-sectional outside dimensions and joined to each other in the longitudinal direction.
[5] The electric heating device for a fluid according to any one of [1] to [4], wherein the heating tubes constituting the heating part of the multi-tube structure are either or both of the heating tubes in the inner and outer directions having different cross-sectional outside dimensions, and partial heating tubes having the same cross-sectional outside dimensions and joined to each other in the longitudinal direction, and have different unit heat values per predetermined unit area of the tube wall with either or both of a specific resistance and a cross-sectional area as variables.
[6] The electric heating device for a fluid according to any one of [1] to [5], wherein the shape of a substantially similar cross section of the heating tube is circular or polygonal.
[7] The electric heating device for a fluid according to any one of [1] to [6], wherein a vibration-proof member having an electrical insulating layer is disposed in the fluid flow path except for the fluid flow path in the innermost heating pipe.
[8] The electric heating device for a fluid according to any one of [1] to [7], wherein the heating tube has an electrically insulating layer on either or both of an inner circumferential surface and an outer circumferential surface.
[9] The electric heating device for a fluid according to any one of [1] to [8], wherein a heat insulating material is arranged on an outer peripheral surface of the outermost heating pipe.
[10] The electrically heating device for a fluid according to any one of [1] to [2], wherein a flexible conductor or a sliding contact that follows thermal deformation of the heating tube is provided at a connection portion between each of all of the power supply electrodes on at least one side of the heating section of the multi-tube structure and a power supply circuit side.
[11] An electrical heating device for a fluid described in any one of [1] to [10], wherein a fluid supply/discharge means for supplying and discharging the heated fluid is connected to one fluid inlet/outlet and the other fluid inlet/outlet of the fluid flow path, and comprises a fluid supply header and a fluid discharge header.
[12] The electric heating device for a fluid according to any one of [1] to [11], further comprising a control device that controls the input power to the heating tube based on physical quantities including at least the temperature and flow rate of the heated fluid, and on equipment capacity including at least the unit heat generation amount per unit area of the tube wall of the heating tube.
[13] A method for electrically heating a fluid, comprising heating a fluid to be heated using the electric heating device for a fluid according to any one of [1] to [12].

According to the present invention, by forming the conductive heating tubes of the electric fluid heating device into a multi-tube structure and using the annular gaps between the heating tubes as a flow path for the heated fluid, it is possible to simultaneously secure a large heat transfer area and reduce the spatial size. Furthermore, by adopting electrical heating, unlike induction heating, there is no efficiency loss due to magnetic flux leakage in the first place, and it is possible to ensure high heating efficiency. As described above, the present invention can provide an electric fluid heating device and an electric fluid heating method using the same that can advantageously achieve the miniaturization of large-capacity fluid heating equipment by combining the spatial miniaturization of the heating device, including the expansion of the heat transfer area, and high electrical efficiency.

1 is a vertical cross-sectional view that shows a schematic view of an electric heating device 100 for a fluid according to a first embodiment. FIG. 2 is a vertical cross-sectional view that illustrates a schematic diagram of an electric heating device 110 for a fluid according to a modified example of the first embodiment. FIG. 13 is a vertical cross-sectional view that shows a schematic diagram of an electric heating device 120 for a fluid according to another modified example of the first embodiment. FIG. 13 is a vertical cross-sectional view that illustrates a schematic view of an electric heating device 130 for a fluid according to still another modified example of the first embodiment. FIG. 11 is a vertical cross-sectional view that shows a schematic view of an electric heating device 200 for a fluid according to a second embodiment. FIG. 11 is a vertical cross-sectional view that shows a schematic view of an electric heating device 300 for a fluid according to a third embodiment. 1A and 1B are schematic diagrams illustrating a conventional electric heating device for fluid by induction heating, in which (a) is a longitudinal sectional view and (b) is a transverse sectional view. 1A and 1B are schematic diagrams showing a conventional electrical heating device for a fluid by electrical heating, in which (a) an example of a basic configuration with one heating tube and one power source, (b) an example of a configuration with multiple heating tubes arranged in series, and (c) an example of a configuration with multiple basic configurations arranged in series.

The following describes in detail the embodiments of the present invention with reference to the drawings. In the embodiments described below, identical or common parts are given the same reference numerals in the drawings, and their description will not be repeated. Note that the present invention is not limited to the following embodiments.

(Embodiment 1)
Fig. 1 is a longitudinal sectional view that typically shows an electric heating device 100 for fluid according to the first embodiment. Fig. 2 is a longitudinal sectional view that typically shows an electric heating device 110 for fluid according to a modified example of the first embodiment. Fig. 3 is a longitudinal sectional view that typically shows an electric heating device 120 for fluid according to another modified example of the first embodiment. Fig. 4 is a longitudinal sectional view that typically shows an electric heating device 130 for fluid according to yet another modified example of the first embodiment. The electric heating device for fluid according to the first embodiment will be described with reference to Figs. 1 to 4.

As shown in FIG. 1, the fluid electric heating device 100 according to this embodiment is a multi-tube type fluid electric heating device that uses electrical heating. The multi-tube structure heating section (hereinafter also simply referred to as the heating section) 10 has multiple conductive heating tubes 10a with roughly similar cross sections, with the smaller cross-section heating tubes inserted without contact into the larger cross-section heating tubes. The annular gap between the heating tubes, together with the inside of the innermost heating tube, forms a fluid flow path for the heated fluid. The typical flow path spacing between the innermost heating tube and the annular flow path is, for example, about 2 to 3 mm in the case of heating for chemical reactions, and about 10 mm in the case of gas heating.

The electric heating device 100 for fluid according to this embodiment further includes (a) a fluid flow path forming means for forming one fluid flow path together with the heating tube 10a forming the annular gap. Specifically, the fluid flow path forming means further includes (a1) a tube end support closing plate 18, (a2) a fluid guide hole 30, and (a3) a fluid inlet/outlet 20.

(a1) The tube end support closing plate 18 supports and fixes each of the heating tubes 10a at both ends, maintaining a predetermined annular spacing between the heating tubes 10a in the inside-outside direction, and also functions as a wall that divides the end of the heating section 10 of the multi-tube structure. In addition, the tube end support closing plate 18 is electrically insulating to prevent electrical shorting between adjacent heating tubes 10a in the inside-outside direction, so as not to impede the formation of a power supply circuit connecting the heating tubes 10a and the power source 40. Furthermore, by forming a sealed structure between the tube end support closing plate 18 and the end of the heating tube 10a, the tube end support closing plate 18 can function as part of the fluid flow path wall.

(a2) The fluid introduction hole 30 is arranged at the end positions of the heating tubes 10a in the inner and outer directions, alternating between one end and the other end. This allows the annular fluid flow paths on both sides of the tube wall in the inner and outer directions to be connected to each other, enabling the fluid flow path to be turned back at the end of the heating tube 10a. In addition, (a3) the fluid inlet/outlet 20 is arranged at the end opposite the fluid introduction hole 30 in the innermost heating tube 11 of the heating tubes 10a, and is arranged at a position equivalent to the fluid introduction hole in the outermost heating tube 14 of the heating tubes 10a. In the example of this embodiment shown in FIG. 1, an example of a fluid flow path in which a fluid inlet 20a is arranged in the innermost heating tube 11 and a fluid outlet 20b is arranged in the outermost heating tube 14 is shown, but the flow path direction in which the heated fluid flows is not limited to this and may be the opposite direction.

The fluid electric heating device 100 according to this embodiment also has a fluid supply/discharge means (not shown) that is connected to one fluid inlet/outlet and the other fluid inlet/outlet of the fluid flow path, and supplies and discharges the heated fluid. This fluid supply/discharge means is preferably equipped with a known fluid supply header and a fluid discharge header in order to stably supply the heated fluid to the fluid flow path and discharge the heated fluid from the fluid flow path. In addition, the fluid supply header and the fluid discharge header are preferably connected to the energized heating tube 10a via a known insulating joint in order to ensure electrical insulation and allow the heated fluid to flow.

The heating tube 10a constituting the heating section 10 of the multi-tube structure according to this embodiment is not particularly limited in material, as long as it satisfies the requirements of being conductive, having heat resistance and corrosion resistance to withstand the heating temperature of the heated fluid, and being moldable into a tube body. A preferred material that satisfies such requirements is, for example, a known Cr alloy steel (including alloy steel with about 1 mass% Cr added to carbon steel, and even higher alloy Cr-based stainless steel). Another example of an alloy steel is Cr-Ni alloy steel (including alloy steel with about 0.2 to 1.0 mass% Cr and about 1.0 to 3.5 mass% Ni added to carbon steel, and even higher alloy Cr-Ni-based stainless steel). Another example is artificial graphite or conductive ceramics, which can withstand use at temperatures above 1000°C. These materials have a relatively high specific resistance, and are therefore preferred materials for heating tubes. As the conductive ceramics, known conductive ceramics such as SiC, TiC, or TiN may be used. In addition, depending on the fluid to be heated and the installation location, known high melting point metals such as tungsten and molybdenum or alloys of these may be used as necessary.

Furthermore, the heating tubes 10a constituting the heating section 10 of the multi-tube structure according to this embodiment may be made of the various materials exemplified above for each of the heating tubes 10a in the inner and outer directions having different cross-sectional outside dimensions. Also, the heating tubes 10a constituting the heating section 10 may be made of the various materials exemplified above for each of the partial heating tubes joined to each other in the longitudinal direction with the same cross-sectional outside dimensions. In this way, the heating tubes 10a can be made of a material having appropriate heat resistance and corrosion resistance for the entire length of the heating tube 10a or for each part, depending on each temperature range from the start to the end of heating in the fluid flow path. For example, in the relatively low temperature range from the room temperature range near the inlet of the fluid flow path to about 600 ° C, Cr alloy steel or the like can be used without problems in heat resistance and corrosion resistance. Furthermore, in the high temperature range up to about 1000 ° C, Cr-Ni stainless steel or the like can be used. At higher temperatures above 1000°C, artificial graphite or conductive ceramics such as SiC, TiC, or TiN can be used. In this way, by selecting materials according to the severity of the environment, the material cost of the heating tube 10a can be kept low.

The heating tube 10a according to this embodiment may have different unit heat generation amounts per unit area of the tube wall between the heating tubes 10a in the inner and outer directions having different cross-sectional external dimensions, with either or both of the resistivity and the cross-sectional area being variables. The heating tube 10a constituting the heating section 10 may have different unit heat generation amounts per unit area of the tube wall between partial heating tubes joined to each other in the longitudinal direction with the same cross-sectional external dimensions, with either or both of the resistivity and the cross-sectional area being variables. In this way, for example, the hit rate of the heating temperature can be increased by adopting a heating pattern in which the unit heat generation amount is increased from the early to middle heating stages and the unit heat generation amount is decreased in the later heating stages.

The heating section 10 of the multi-tube structure according to this embodiment is advantageous in terms of securing a large heat transfer surface (also called a heat generating surface or a heating surface) area under the same heating section volume conditions as the electric heating device 80 of the fluid consisting of a single-tube heating tube according to the conventional technology as shown in FIG. 8, for example. That is, in this embodiment, a heat transfer area as large as the inner and outer circumferential surfaces of the tube walls of the multiple heating tubes 10a inserted can be secured. In addition, in this embodiment, by making the tubes multi-tube, the heated fluid is forced to pass through a narrow space and is likely to become turbulent, so that the heat transfer capacity is improved. In order to enhance the heat transfer promotion by turbulence, the surface roughness of the tube wall of the heating tube 10a is made rough, or a shape that easily disturbs the fluid, such as unevenness or jagged edges, is given to the tube wall, so that the heat transfer efficiency can be further improved. Therefore, in the electric heating device 100 of the fluid according to this embodiment, the heating capacity can be significantly increased without increasing the size of the device. Conversely, according to the electric fluid heating device 100 of this embodiment, an electric fluid heating device consisting of a heating tube with a single-tube structure can be replaced with a smaller heating device without compromising the heating capacity.

In addition, in the heating section 10 of the multi-tube structure according to this embodiment, the heat loss due to heat dissipation to the surroundings can be essentially kept low. This is because, in the multi-tube structure, except for the outermost heating tube 14, the other heating tubes 10a (the innermost heating tube 11 and the intermediate heating tubes 12, 13) are surrounded on their outer periphery by the other heating tubes 10a. That is, in this embodiment, the heat loss from the heating tube 10a is mainly due to heat dissipation from the outer periphery of the outermost heating tube 14, and in the other heating tubes 10a, the outer periphery also becomes the heating surface of the heated fluid, so there is almost no heat loss.

The reason why the heating tubes 10a constituting the heating section 10 of the multi-tube structure have substantially similar cross sections is to make the annular gaps between the heating tubes 10a adjacent in the inner and outer directions substantially the same at any circumferential position of the heating tubes 10a. This makes it possible to form a fluid flow path in which the heated fluid flows stably without causing variations in flow speed or drift. In addition, it is also possible to avoid sparks that occur when the heating tubes 10a heated by electricity come into contact with each other and short-circuit electrically. In addition, when the heated fluid is a gas and the amount of heat (amount of temperature rise) along the flow path direction is large and the cross-sectional area of the fluid flow path does not change along the flow path direction, the volume expansion of the heated fluid may cause a gradual increase in the flow speed of the heated fluid along the flow path direction, which may cause a problem. In such a case, in order to offset the effect of the increase in speed, the cross-sectional area of the heating tubes 10a may be gradually enlarged along the flow path direction while maintaining a substantially similar cross-sectional shape.

The approximately similar cross-sectional shape of the heating tube 10a is preferably circular or polygonal. This is because a circular shape is more advantageous than other shapes in terms of manufacturing the heating tube 10a, forming an annular fluid flow path, and avoiding drift. Similarly to the circular shape, a polygonal shape is also relatively advantageous in terms of manufacturing the heating tube 10a, forming an annular fluid flow path, and avoiding drift. Furthermore, 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.

In the fluid flow paths except for the fluid flow path in the innermost heating tube 11, it is preferable to provide anti-vibration members 56 having an electrically insulating layer to prevent lateral vibration of the heating tubes 10a on both sides. When there is concern about contact between the heating tubes due to vibration of the heating tube caused by electromagnetic force and fluid flow, or thermal deformation of the heating tube, this anti-vibration member 56 can more reliably make the gap between the adjacent heating tubes 10a in the inner and outer directions approximately the same at any position. In addition, this anti-vibration member 56 can be used to maintain the flow path width that gradually expands in the flow path direction even when the cross-sectional area of the heating tube 10a is gradually expanded along the flow path direction as a measure against the gradual increase in the speed of the heated fluid along the flow path direction due to the volume expansion of the heated fluid. In addition, the size, position, and number of anti-vibration members 56 and other conditions for their placement in the flow path are sufficient for the purpose of vibration prevention, so the anti-vibration members 56 do not become a factor that impedes the flow of the heated fluid. In addition, the anti-vibration member 56 is provided with a refractory material or ceramics having a known electrically insulating layer to prevent the heating tubes 10a on both sides, which are independently energized, from being electrically shorted to each other. There are no particular limitations on the other constituent materials of the anti-vibration member 56, so long as they meet the requirements of having heat resistance, corrosion resistance, and chemical reactivity resistance to withstand the heating temperature of the heated fluid, and can be molded into components.

It is also preferable to provide an electrical insulating layer on either or both of the inner and outer circumferential surfaces of the heating tube 10a. This is because such an electrical insulating layer can prevent problems such as sparks caused by contact between the electrically heated heating tubes 10a or bursting of the heating tube. In addition, by providing such an electrical insulating layer, it is possible to heat the electrically conductive fluid to be heated by electrical heating. The material of this electrical insulating layer is not particularly limited as long as it satisfies the requirements of electrical insulation, heat resistance and corrosion resistance to withstand the heating temperature of the heated fluid. For example, a known material and coating method such as spraying insulating oxide ceramics such as alumina may be used.

As shown in FIG. 1, the fluid electric heating device 100 according to this embodiment has a power supply electrode 50, a power source 40, and a power supply circuit connecting them to supply power to the heating tube 10a. The power supply electrode 50 is disposed on each of the tube walls at one end and the other end of the heating tube 10a. This allows the effective heating range between the power supply electrodes 50 at both ends of the heating tube 10a to be almost the entire tube wall of the heating tube 10a. In addition, it is preferable that the power supply electrode 50 is disposed so as to penetrate the tube end support closing plate 18 in constructing the power supply circuit. Although not shown, a temperature measuring means such as a thermocouple is provided for the heating tube or the heated fluid of the present invention, and the temperature of the heating tube and the temperature of the heated fluid are controlled by controlling the input power, current, and voltage of the power source.

The power source 40 supplies power to one or more heating tubes 10a through the power supply electrode 50. The power source 40 here may be a DC power source or an AC power source. If uniformity of the current distribution in the heating tube is required, a DC power source that is not affected by the skin effect is preferable. Conversely, if the purpose is to heat the surface of the heating tube by the skin effect or if the equipment cost of the power source is important, an AC power source is preferable. The heating frequency band in the case of an AC power source may be the same heating frequency band of 1 kHz to 400 kHz as in the case of normal induction heating, and if the skin effect is to be suppressed, a heating frequency of less than 1 kHz, which is a lower frequency band, is preferable. This is because an AC power source with a heating frequency band of less than 1 kHz is likely to have advantages such as a small effect of the skin effect on the current distribution in the heating tube and low power source costs.

In this embodiment, as one of the power supply circuits connecting the heating tube 10a and the power source 40 via the power supply electrode 50, the conductor (bus bar, electric wire, etc.) 51, and the electric wire 52, a single parallel power supply circuit (b1) in which the heating tube 10a is connected in parallel to a single power source 40 as shown in FIG. 1 is adopted. In addition, in this embodiment, as another power supply circuit connecting the heating tube 10a and the power source 40 via the power supply electrode 50, the conductor 51, and the electric wire 52, a single series power supply circuit (b2) in which the heating tube 10a is connected in series to a single power source 40 as shown in FIG. 2 may be adopted. To configure these power supply circuits, in (b1), the power supply electrodes 50 are electrically shorted to each other at one end and the other end of the heating section 10 of the multi-tube structure. In addition, in (b2), the power supply electrodes 50 are electrically shorted to every other end of the heating section 10 of the multi-tube structure. In any of the power supply circuits, heating control of the electric fluid heating device 100 (110) according to this embodiment can be performed based on known technology for controlling current, voltage, power, etc. Whether to use parallel or series connection can be designed taking into account the resistance of each heating tube, the amount of heat generated, the amount of temperature rise of the heated fluid, etc.

In this embodiment, it is preferable to provide a control device (not shown) that controls the input power to the heating tube 10a based on the physical quantities including at least the temperature and flow rate of the heated fluid, and the equipment capacity including at least the unit heat generation amount per unit area of the tube wall of the heating tube 10a. This control device allows the heating tube 10a to be electrically heated while controlling the power input from the power source 40 to the heating tube 10a. Looking at the entire heating section 10 with a multi-tube structure, the outermost heating tube 14 heats the heated fluid from the tube wall on the inside of the tube while controlling the input power, and all heating tubes other than the outermost heating tube 14 (the innermost heating tube 11 and the intermediate heating tubes 12 and 13) heat the heated fluid flowing on both sides of the tube wall. The control device here may be a known control device including a calculation device, a storage device, an input/output device, etc., and a detailed description thereof will be omitted.

It is preferable that the predetermined physical quantities, including the temperature and flow rate of the heated fluid, used for heating control are measured near the inlet and/or outlet of the heated fluid of the heating section 10 of the multi-tube structure. This is because the measurement results of the physical quantities of the heated fluid near the inlet and/or outlet can contribute to high accuracy of the heated fluid temperature control by feedforward control and/or feedback control to the power source such as input power, current, and voltage. In addition, since the control response is high in electric heating, the physical quantities of the heated fluid may be measured only near the inlet of the heated fluid of the heating section 10 of the multi-tube structure, and only feedforward control may be performed. The equipment capacity, including at least the unit heat generation amount per unit area of the tube wall of the heating tube 10a, is used as basic data for controlling the power source such as input power, current, and voltage to the heating tube 10a in both the above feedback control and feedforward control. Examples of temperature measurement means for the heated fluid and the heating tube here include temperature measurement using a known thermocouple. Examples of flow rate measurement means for the heated fluid include known electromagnetic flow meters, impeller flow meters, ultrasonic flow meters, and differential pressure flow meters (orifice flow meters).

As shown in FIG. 3, the electric fluid heating device 120 according to this embodiment may be configured so that the outer peripheral surface of the outermost heating tube 14 is covered with a heat insulating material 58. The outer peripheral surfaces of the other heating tubes (the innermost heating tube 11 and the intermediate heating tubes 12 and 13) other than the outermost heating tube 14 are surrounded by the other heating tubes 10a and become the flow path of the heated fluid, so there is no concern about heat loss, whereas heat dissipation from the outer peripheral surface of the outermost heating tube 14 directly results in heat loss. In addition, in order to protect the equipment around the heating section 10 of the multi-tube structure, it is preferable to reduce heat dissipation from the outer peripheral surface of the outermost heating tube 14. As the heat insulating material, a known heat insulating material such as ceramic fiber with low thermal conductivity can be used.

In this embodiment, as in the fluid electric heating device 130 shown in FIG. 4, even if the heating tube 10a constituting the heating section 10 of the multi-tube structure thermally expands or contracts depending on the heating conditions, a means for avoiding disconnection troubles in the power supply circuit may be provided. For example, a flexible conductor 54 or a sliding contact (not shown) that follows the thermal deformation of the heating tube 10a may be provided at least in the range of the thermal deformation of the heating tube 10a at the connection part between each of all the power supply electrodes 50 on at least one side of the heating section 10 of the multi-tube structure and the power supply circuit side. This is preferable because the heating tube 10a constituting the heating section 10 of the multi-tube structure can follow the deformation and position change of the electrode part even if it thermally expands or contracts depending on the heating conditions. The flexible conductor is a so-called braided wire, a water-cooled cable, a spring-type conductor, etc., which can absorb thermal expansion or thermal contraction by flexibly bending even when the conductor itself is subjected to an external force. A sliding contact is a well-known contact such as a carbon brush that can follow thermal expansion or contraction by sliding between the contact on the power supply side and the contact on the power receiving side while maintaining a certain level of pressure and contact area and maintaining a current-carrying state.

Next, mainly based on FIG. 1, a method for electrically heating a fluid using the electric heating device 100 for a fluid according to this embodiment will be described. In this embodiment, as shown in FIG. 1, the heated fluid is supplied from the inlet of one fluid flow path of the heating section 10 of the multi-tube structure, that is, the fluid inlet 20a provided at one end of the innermost heating tube 11. The heated fluid that has flowed to the other end of the innermost heating tube 11 passes through a fluid introduction hole 30 provided in the tube wall at the end of the innermost heating tube 11, moves to an adjacent fluid flow path, and turns back and flows to the fluid introduction hole 30 provided at the other end of the intermediate heating tube 12. In this way, the heated fluid flows back and forth through the multiple layers of annular fluid flow paths in the heating section 10 of the multi-tube structure to the fluid outlet 20b provided at the end of the outermost heating tube 14. The end position of the fluid outlet 20b provided at the end of the outermost heating tube 14 differs in positional relationship with the fluid inlet 20a between FIG. 1 and FIG. 6, but is common in that it is provided at the end opposite to the end on the side of the fluid introduction hole 30 provided in the adjacent intermediate heating tube 12 (13). Also, the direction in which the heated fluid flows is not limited to the example in FIG. 1, and it may flow in the opposite direction to that in FIG. 1.

In this embodiment, the heating tubes 10a (the innermost heating tube 11, the intermediate heating tube 12, and the outermost heating tube 14) that form the fluid flow path are electrically heated, and the tube walls become heat generating surfaces and act as heating surfaces, so that the heated fluid is efficiently heated while passing through the fluid flow path. Looking more closely, the outermost heating tube 14 heats the heated fluid from the tube wall on the inside of the tube, and all heating tubes 10a except the outermost heating tube 14 heat the heated fluid flowing on both sides of the tube wall.

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

Specific examples of applications for heating the heated fluid include, but are not limited to, preheating fuel and combustion air sent to a combustion device, or heating heavy oil and atomization steam for heavy oil atomization.

(Embodiment 2)
Fig. 5 is a vertical cross-sectional view that typically shows an electric heating device 200 for fluid according to embodiment 2. The electric heating device 200 for fluid according to embodiment 2 will be described with reference to Fig. 5 .

As shown in FIG. 5, the fluid electric heating device 200 according to the second embodiment differs from the fluid electric heating device according to the first embodiment in the power supply circuit connecting the heating tube 10a and the power source 40. Specifically, the fluid electric heating device 200 differs from the first embodiment in that (b3) the heating tubes 10a constituting the heating section 10 of the multi-tube structure are each connected to one power source 40, and the device is provided with a group of power supply circuits consisting of a set of power supply circuits for one heating tube and one power source. The example shown in FIG. 5 is an example in which a group of power supply circuits is formed by a set of three power supply circuits for one heating tube and one power source, such as the innermost heating tube 11 and a dedicated power source 41, the intermediate heating tube 12 and a dedicated power source 42, and the outermost heating tube 14 and a dedicated power source 44. The other configurations are almost the same as those of the first embodiment.

Even when configured as described above, the fluid electric heating device 200 according to the second embodiment can achieve substantially the same effects as the fluid electric heating device according to the first embodiment.

In addition, a dedicated power source 40 (41, 42, 43) is provided for each heating tube 10a, so that detailed heating control for each heating tube 10a can be achieved, enabling even more precise heating control for the entire heating section 10 with a multi-tube structure.

(Embodiment 3)
Fig. 6 is a vertical cross-sectional view that typically shows an electric fluid heating device 300 according to embodiment 3. The electric fluid heating device 300 according to embodiment 3 will be described with reference to Fig. 6 .

As shown in FIG. 6, the fluid electric heating device 300 according to the third embodiment has the following differences when compared with the fluid electric heating devices according to the first and second embodiments. That is, this embodiment differs from the first and second embodiments in that the heating tubes 10a constituting the heating section 10 of the multi-tube structure are divided into a plurality of heating tube groups, each of which is made up of a plurality of heating tubes connected in the inner and outer directions, and each heating tube group is provided with a parallel power supply circuit. The other configurations are substantially the same as those of the first and second embodiments.

In the example shown in FIG. 6, the heating tubes 10a constituting the heating section 10 of the multi-tube structure are divided into two heating tube groups: the innermost heating tube 11 and the intermediate heating tube 12 form a small cross-section heating tube group 15, and the intermediate heating tube 13 and the outermost heating tube 14 form a large cross-section heating tube group 16, which continues from the innermost heating tube 11 and the intermediate heating tube 12 and the outermost heating tube 14. A power supply 45 for the small cross-section heating tube group is connected to the small cross-section heating tube group 15, and a power supply 46 for the large cross-section heating tube group is connected to the large cross-section heating tube group 16 by parallel power supply circuits.

Note that the example shown in FIG. 6 is just one example, and in this embodiment, each heating tube group is provided with any one of (b1) a parallel power supply circuit, (b2) a series power supply circuit, and (b3) a group of power supply circuits. For example, a separate power supply circuit may be provided for each heating tube group, resulting in all three types of power supply circuits being provided. Also, in the example shown in FIG. 6, two intermediate heating tubes 12 and 13 are shown, but more intermediate heating tubes may be provided.

Even when configured as described above, the fluid electric heating device 300 according to embodiment 3 provides substantially the same effects as the fluid electric heating devices according to embodiments 1 and 2.

In addition, since a dedicated power source 40 (45, 46) is provided for each heating tube group, the heating control of the entire heating section 10 with a multi-tube structure can be made even more precise through detailed heating control for each heating tube group.

Various embodiments of the fluid electric heating devices 100, 110, 120, 130, 200, and 300 according to the present invention have been described above, but these may be connected in series or in parallel in the flow path direction with the same or different embodiments. This increases the freedom of facility design, such as optimizing the heating capacity of the fluid electric heating device on the upstream and downstream sides within the limited installation space of the heating device.

10 Heating section with multi-tube structure 10a Heating tube 11 Innermost heating tube 12, 13 Intermediate heating tube 14 Outermost heating tube 15 Group of small cross-section heating tubes 16 Group of large cross-section heating tubes 18 Tube end support closing plate 20 Fluid inlet/outlet 20a Fluid inlet 20b Fluid outlet 30 Fluid guide hole 40 Power source 41 Power source for innermost heating tube 42 Power source for intermediate heating tube 44 Power source for outermost heating tube 45 Power source for group of small cross-section heating tubes 46 Power source for group of large cross-section heating tubes 50 Power supply electrode 51 Conductor (bus bar, electric wire)
52 Electric wire 54 Flexible conductor 56 Vibration prevention member (spacer)
Description of the Related Art 58 Insulation material 60 Fluid electric heating device 62 Heating element 62a Non-magnetic pipe 62b, 62b1, 62b2, 62b3 Magnetic pipe 62c, 62c1, 62c2 Curved portion 64, 66 Pipe support plate 68 Inner insulation material 70 Outer insulation material 72 Induction heating coil 74 Fluid inlet header 76 Fluid outlet header 80 Fluid electric heating device 82 Heated pipe body 84 Non-heated pipe body 86 Pipe joint 88 AC power source 90 Support base 92 Electrical insulator 94 Jumper 100, 110, 120, 130, 200, 300 Fluid electric heating device

Claims (13)

A multi-tube type fluid electric heating device using electrical heating, comprising a plurality of electrically conductive heating tubes each having a cross section substantially similar to one another, a heating tube having a smaller cross section being inserted into a heating tube having a larger cross section without contacting each other to form a heating section having a multi-tube structure, and an annular gap between the heating tubes, together with an interior of the innermost heating tube, is used as a fluid flow path for a fluid to be heated,
(a) as a fluid flow path forming means for forming one fluid flow path together with a tube wall of the heating tube forming the annular gap,
(a1) a tube end support closing plate that supports each of the heating tubes at both ends and seals both ends while providing electrical insulation;
(a2) fluid introducing holes that are arranged at end positions that are staggered between one end and the other end of the heating tubes in the inner and outer directions and that connect the annular fluid flow paths on both sides in the inner and outer directions of the tube wall to each other;
(a3) a fluid inlet/outlet that is disposed at an end of an innermost heating tube among the heating tubes opposite to the fluid introducing hole, and that is disposed at a position corresponding to the fluid introducing hole in an outermost heating tube among the heating tubes;
1. An apparatus for electrically heating a fluid comprising: The fluid electric heating device according to claim 1, in which the heating tubes constituting the heating section of the multi-tube structure are divided into a plurality of heating tube groups each consisting of a plurality of heating tubes connected in the inner and outer directions, and a power supply circuit is provided for each heating tube group. A power supply circuit for the heating tube constituting the heating portion of the multi-tube structure, or a power supply circuit for each of the plurality of heating tube groups constituting the heating portion of the multi-tube structure,
(b1) a single parallel power supply circuit in which power supply electrodes are electrically short-circuited to each other at one end and the other end of the heating section of the multi-tube structure, and the heating tubes are connected in parallel to a single power source;
(b2) a single series power supply circuit in which every other power supply electrode is electrically short-circuited at one end and the other end of the heating section of the multi-tube structure, and the heating tubes are connected in series to a single power source;
and,
(b3) a group of power supply circuits each consisting of a set of power supply circuits for one heating tube and one power source, in which the heating tubes constituting the heating portion of the multi-tube structure are each connected to one power source;
3. The electric heating device for fluid according to claim 1 or 2, wherein the electric supply circuit is any one of the above. The electric heating device for fluids according to claim 1 or 2, wherein the heating tubes constituting the heating portion of the multi-tube structure have at least some heat generating characteristics different from the others between the heating tubes in the inner and outer directions having different cross-sectional external dimensions, or between partial heating tubes with the same cross-sectional external dimensions joined to each other in the longitudinal direction. The heating tubes constituting the heating section of the multi-tube structure are either or both of the heating tubes in the inner and outer directions having different cross-sectional outside dimensions, and partial heating tubes with the same cross-sectional outside dimensions joined to each other in the longitudinal direction, and each of these has a different unit heat value per unit area of the tube wall with either or both of the resistivity and the cross-sectional area as variables. The electric heating device for fluids according to claim 1 or 2. The fluid electric heating device according to claim 1 or 2, wherein the shape of the approximately similar cross section of the heating tube is circular or polygonal. The electric heating device for fluid according to claim 1 or 2, in which a vibration-stopping member having an electrically insulating layer is disposed in the fluid flow path except for the fluid flow path in the innermost heating tube. The fluid electric heating device according to claim 1 or 2, wherein the heating tube has an electrically insulating layer on either or both of its inner and outer circumferential surfaces. The electric heating device for fluids according to claim 1 or 2, in which a heat insulating material is provided on the outer peripheral surface of the outermost heating tube. The fluid electric heating device according to claim 1 or 2, wherein a flexible conductor or sliding contact that follows the thermal deformation of the heating tube is provided at the connection between each of all power supply electrodes on at least one side of the heating section of the multi-tube structure and the power supply circuit side. The electric heating device for fluid according to claim 1 or 2, wherein the fluid supply/discharge means for supplying and discharging the heated fluid, which is connected to one fluid inlet/outlet and the other fluid inlet/outlet of the fluid flow path, comprises a fluid supply header and a fluid discharge header. The electric heating device for fluid according to claim 1 or 2, further comprising a control device that controls the input power to the heating tube based on physical quantities including at least the temperature and flow rate of the heated fluid, and the equipment capacity including at least the unit heat generation amount per unit area of the tube wall of the heating tube. A method for electrically heating a fluid, comprising heating a fluid to be heated by using the electrically heating device for a fluid according to claim 1 or 2.

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