JP2006140063A - Microwave heating method and microwave heating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microwave heating method and a microwave heating apparatus for rapidly and uniformly heating a ceramic carrier with low power consumption. <P>SOLUTION: The method irradiating a microwave W to a microwave absorber 13 disposed in a cavity resonator to heat a ceramic carrier 14 with the absorber 13 carried thereon uses a microwave absorber containing a silicon carbide-based complex oxide as the absorber 13 and also uses a cuboid type cavity resonator 110 of a signal mode as the cavity resonator. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a microwave heating method and a microwave heating apparatus for heating a fluid such as gas or liquid using microwave energy.

In general, a purification process is performed on exhaust gas generated in an internal combustion engine such as a diesel engine or a gasoline engine from the viewpoint of environmental protection. The purification process is performed using an exhaust gas purification catalyst. However, when the internal combustion engine is started, the exhaust gas and the exhaust gas purification device are lower in temperature than the catalyst activation temperature of the exhaust gas purification catalyst when not warmed up. There may be a so-called cold emission in which higher concentrations of NO _x , HC, and the like are discharged than during steady operation in a warm-up state. From the viewpoint of environmental conservation, measures to prevent this cold emission are being studied.

  As a measure for preventing cold emission, there is a method of rapidly increasing the temperature of exhaust gas or the like. Conventionally, energization heating or an electric heater has been used, but such a method requires a large amount of power to heat the entire apparatus, and has a problem that it cannot be reduced in size and weight.

Therefore, as a method for solving such a problem, a method of heating only a necessary portion using microwave energy has been proposed. For example, a method is known in which an exhaust gas purifying apparatus carrying a microwave absorbing material is used in a heating chamber, and the microwave absorbing material is rapidly heated to near the catalyst activation temperature with a microwave. For example, in Patent Document 1, heat is generated by irradiating a microwave on a heating element in which a perovskite complex oxide such as La _1-x Sr _x CoO ₃ that is an electromagnetic wave absorption heating element is in direct contact with metal catalyst particles. A method for rapidly heating the body is described.

In addition, a method of separately arranging the microwave absorber and the exhaust gas purification catalyst is also known. That is, a microwave absorber is installed in front of the exhaust gas purification device carrying the exhaust gas purification catalyst, the microwave absorber heated by the microwave is brought into contact with the exhaust gas, and the temperature of the exhaust gas is changed to the activation temperature of the exhaust gas purification catalyst. This is a method of raising the temperature to the extent. As a microwave absorber disposed in front of the exhaust gas purification device, for example, Patent Document 2 describes a method using SiC whisker, and Non-Patent Document 1 describes a method using SiC fiber.
JP 7-49024 A JP-A-6-2535 SAE Paper 1999-01-2245

  However, in the heat generation method described in Patent Document 1, since the microwave absorber and the metal catalyst are in direct contact with each other, there is a possibility that the particles of the metal catalyst become coarse and the catalytic activity decreases. Further, in Patent Document 1, when a cylindrical cavity resonator is used as a heating chamber, multiple modes in which a large number of electric field modes exist are generated in the cylindrical cavity resonator. Control of internal resonance is difficult, and there is a problem that power consumption becomes large in order to realize sufficient rapid heating. Furthermore, due to the multiple modes in the cylindrical cavity resonator, the electric field strength varies depending on the location in the cavity resonator, and the temperature distribution of the heated object cannot be made sufficiently uniform.

  Also, in the heating methods described in Patent Document 2 and Non-Patent Document 1, when a cylindrical cavity resonator is used as a heating chamber, multiple modes are generated in the cavity resonator. There was a problem similar to the method described in 1.

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide a microwave heating method and a microwave heating apparatus that can rapidly and uniformly heat a ceramic carrier with low power consumption.

  In order to solve the above problems, the microwave heating method of the present invention heats the ceramic carrier carrying the microwave absorber by irradiating the microwave absorber disposed in the cavity resonator with the microwave. A microwave heating method, wherein a microwave absorber containing a silicon carbide-based composite oxide is used as the microwave absorber, and a single-mode rectangular parallelepiped cavity resonator is used as the cavity resonator. It is characterized by using.

According to the microwave heating method of the present invention, a microwave absorber containing a silicon carbide-based composite oxide having high microwave absorption characteristics is supported on a ceramic carrier disposed in a rectangular parallelepiped cavity resonator. Therefore, the temperature of the microwave absorber is rapidly raised by microwave irradiation with low power consumption. Thereby, the ceramic carrier can be heated rapidly. In the present invention, since the cavity resonator uses a single-mode rectangular cavity resonator (more preferably, TE _10n (n is an integer) single-mode rectangular resonator), The resonance in the cavity resonator can be sufficiently maintained. Moreover, even if the material and shape of the microwave absorber change, the electromagnetic field mode in the rectangular parallelepiped cavity resonator does not change, and the electromagnetic field distribution in the ceramic carrier can be made uniform. It is possible to heat the support uniformly. Therefore, according to the microwave heating method of the present invention, the ceramic carrier can be rapidly and uniformly heated with low power consumption, and the fluid is rapidly and uniformly heated by contacting the fluid with the ceramic carrier. Can do.

  In the microwave heating method of the present invention, it is preferable that the ceramic carrier has a large number of through holes for circulating a fluid, and the microwave absorber is supported on a wall surface that forms the through holes. .

  By using a ceramic carrier having a large number of through holes, pressure loss due to the flow of fluid such as exhaust gas while ensuring a sufficient contact area between the fluid such as exhaust gas and the surface of the ceramic carrier on which the microwave absorber is supported Can be prevented from increasing.

  Further, the size of the introduction port for introducing the microwave and the inside of the rectangular parallelepiped cavity resonator so that the resonance in the rectangular parallelepiped cavity resonator is maintained during heating of the ceramic carrier. It is preferable to adjust the size of the cavity.

  Accordingly, even if the microwave absorption characteristics of the microwave absorber, the ceramic carrier, and the fluid change as the temperature rises, the size of the microwave inlet and / or the size of the cavity in the rectangular parallelepiped cavity resonator By adjusting the resonance, the resonance in the rectangular parallelepiped cavity can be sufficiently maintained at all times.

  In the present invention, the silicon carbide-based composite oxide contained in the microwave absorber is a composite oxide composed of Si, Zr, C and O elements, or Si, Ti, A composite oxide composed of C and O elements is preferred.

  Moreover, although the dielectric loss factor is an index representing the microwave absorption characteristics, the dielectric loss factor of the silicon carbide-based composite oxide is preferably 2 or more.

  By supporting the microwave absorber containing the silicon carbide-based composite oxide having a large dielectric loss factor on the ceramic carrier, the ceramic carrier can be heated more rapidly and uniformly with low power consumption.

  Here, the dielectric loss factor is a value defined by the product of the relative dielectric constant and the dielectric loss tangent, and varies depending on temperature, frequency, and the like. Therefore, in this specification, the dielectric loss factor means a dielectric loss factor of a dielectric measured under conditions of a temperature of 25 ° C. and a frequency of 2.45 GHz. This dielectric loss factor is used as an index representing the microwave absorption characteristics of the microwave absorber and the ceramic carrier. The larger the dielectric loss factor, the higher the microwave absorption property, and the smaller the dielectric loss factor. , The microwave absorption characteristics are lowered.

  On the other hand, the dielectric loss factor of the ceramic carrier is preferably 0.1 or less.

  By using a ceramic carrier having a low dielectric loss factor, that is, by suppressing the absorption of microwaves in the ceramic carrier, the absorption energy in the microwave absorber can be increased, and the ceramic carrier is more rapidly and Uniform heating is possible.

  Further, in the microwave heating method, the microwave absorber is disposed so as to include a position where the electric field strength is maximum in the rectangular parallelepiped cavity resonator, and the traveling direction is within the rectangular cavity resonator. It is preferable that the fluid be circulated and heated so as to be parallel to the direction of the electric field vector and to be in contact with the ceramic carrier.

  By arranging the ceramic carrier on which the microwave absorber is supported so as to include the position where the electric field strength is maximum, the microwave is efficiently absorbed by the microwave absorber and the ceramic carrier is heated more rapidly. Is done. In addition, by flowing the fluid through the ceramic carrier arranged in this manner so that the direction of the electric field vector in the rectangular parallelepiped cavity resonator is parallel to the traveling direction, the microwave irradiation direction and the traveling direction of the fluid Can be made orthogonal to each other, and there is no need to install a reflector in the direction of fluid flow. For this reason, an increase in pressure loss is prevented.

  A microwave heating apparatus according to the present invention is a microwave heating apparatus that irradiates a microwave absorber disposed in a cavity resonator with microwaves and heats a ceramic carrier carrying the microwave absorber. The microwave absorber includes a silicon carbide-based composite oxide, and the cavity resonator is a single-mode rectangular cavity resonator.

According to the microwave heating apparatus of the present invention, the ceramic carrier disposed in the rectangular parallelepiped cavity resonator carries the microwave absorber containing the silicon carbide composite oxide having high microwave absorption characteristics. Therefore, the temperature of the microwave absorber is rapidly raised by microwave irradiation with low power consumption. Thereby, the ceramic carrier can be heated rapidly. In the present invention, since the cavity resonator uses a single-mode rectangular cavity resonator (more preferably, TE _10n (n is an integer) single-mode rectangular resonator), The resonance in the cavity resonator can be sufficiently maintained. Moreover, even if the material and shape of the microwave absorber change, the electromagnetic field mode in the rectangular parallelepiped cavity resonator does not change, and the electromagnetic field distribution in the ceramic carrier can be made uniform. It is possible to heat the support uniformly. Therefore, according to the microwave heating apparatus of the present invention, the ceramic carrier can be rapidly and uniformly heated with low power consumption, and the fluid is rapidly and uniformly heated by bringing the fluid into contact with the ceramic carrier. Can do.

  In the microwave heating apparatus of the present invention, it is preferable that the ceramic carrier has a large number of through holes for circulating a fluid, and the microwave absorber is supported on a wall surface that forms the through holes. .

  By using a ceramic carrier having a large number of through holes, pressure loss due to the flow of fluid such as exhaust gas while ensuring a sufficient contact area between the fluid such as exhaust gas and the surface of the ceramic carrier on which the microwave absorber is supported Can be prevented from increasing.

  In the microwave heating apparatus of the present invention, the rectangular parallelepiped cavity resonator has an openable and closable microwave inlet, the inlet adjusting means for adjusting the size of the microwave inlet, and the rectangular parallelepiped cavity A cavity adjusting means for adjusting the size of the cavity in the cavity resonator, the inlet adjusting means and / or the resonance in the rectangular parallelepiped cavity resonator during the heating of the ceramic carrier, and / or It is preferable to further comprise control means for controlling the cavity adjusting means.

  As a result, even if the microwave absorption characteristics of the microwave absorber, the ceramic carrier and the fluid change as the temperature rises, the controller adjusts the inlet adjustment means and / or the cavity adjustment means while heating the ceramic carrier. By controlling so that the resonance in the rectangular parallelepiped cavity resonator is maintained, the size of the microwave introduction port and / or the size of the cavity in the rectangular parallelepiped cavity resonator is adjusted, and the rectangular parallelepiped cavity is adjusted. The resonance in the resonator can be maintained sufficiently at all times.

  In the present invention, the silicon carbide-based composite oxide contained in the microwave absorber is a composite oxide composed of Si, Zr, C, and O elements, or Si, Ti, from the viewpoint of microwave absorption characteristics. , C and O are preferable.

  The dielectric loss factor of the silicon carbide-based composite oxide is preferably 2 or more.

  By supporting the microwave absorber containing the silicon carbide-based composite oxide having a large dielectric loss factor on the ceramic carrier, the ceramic carrier can be heated more rapidly and uniformly with low power consumption.

  On the other hand, the dielectric loss factor of the ceramic carrier is preferably 0.1 or less.

  By using a ceramic carrier having a low dielectric loss factor, that is, by suppressing the absorption of microwaves in the ceramic carrier, the absorption energy in the microwave absorber can be increased, and the ceramic carrier is more rapidly and Uniform heating is possible.

  The microwave heating apparatus further includes a fluid transfer pipe for transferring a fluid, and the fluid transfer pipe has a traveling direction of the fluid parallel to a direction of an electric field vector in the rectangular parallelepiped cavity resonator. In the fluid transfer pipe, the ceramic carrier carrying the microwave absorber is arranged so as to include a position where the electric field strength in the rectangular parallelepiped cavity resonator is maximized. It is preferable that

  By arranging the ceramic carrier on which the microwave absorber is supported so as to include the position where the electric field strength is maximum, the microwave is efficiently absorbed by the microwave absorber and the ceramic carrier is heated more rapidly. Is done. In addition, by flowing the fluid through the ceramic carrier arranged in this manner so that the direction of the electric field vector in the rectangular parallelepiped cavity resonator is parallel to the traveling direction, the microwave irradiation direction and the traveling direction of the fluid Can be made orthogonal to each other, and there is no need to install a reflector in the direction of fluid flow. For this reason, an increase in pressure loss is prevented.

  According to the microwave heating method and the microwave heating apparatus of the present invention, the ceramic carrier can be rapidly and uniformly heated with low power consumption, whereby the fluid such as exhaust gas can be rapidly and uniformly heated.

  Hereinafter, preferred embodiments of a microwave heating method and a microwave heating apparatus of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

  FIG. 1 is a schematic view schematically showing a basic configuration of a preferred embodiment of the microwave heating apparatus of the present invention, and FIG. 2 is a perspective view showing a cavity resonator of the microwave heating apparatus shown in FIG. FIG. 3 is a cross-sectional view of the cavity resonator shown in FIG. 2 taken along line III-III.

  As shown in FIGS. 1 to 3, the microwave heating apparatus 100 according to the present embodiment includes a rectangular parallelepiped cavity resonator 110, a microwave supply unit 120 that supplies the microwave W into the rectangular parallelepiped cavity resonator 110, and The gas transfer pipe 130 is provided so as to pass through the rectangular parallelepiped cavity resonator 110 and transfers the exhaust gas F, and is disposed in the gas transfer pipe 130 in the rectangular parallelepiped cavity resonator 110 to pass the exhaust gas F. A heating element 140 for heating is mainly provided.

The rectangular parallelepiped cavity 110 is a rectangular parallelepiped metallic microwave introduction tube 1 used as a microwave W resonator. FIGS. 1 to 3 show an energy-concentrated single-mode rectangular parallelepiped. It is a cavity resonator, and is of TE _10n (Transverse Electric Wave, shown is n = 1) mode. The single-mode rectangular parallelepiped cavity resonator 110 is designed such that a standing wave S of ½ wavelength is generated in each of two directions perpendicular to the traveling direction of the microwave W in the cavity. Has been.

  The microwave introduction tube 1 should just be comprised with the metal, and stainless steel, aluminum, copper, brass etc. are used suitably as this metal, for example.

  A pair of variable coupling windows 2 are provided at one end of the microwave introduction tube 1 so as to be slidable in the direction of arrow A in FIG. 2. The microwave introduction port is formed by the pair of variable coupling windows 2 and the microwave introduction tube 1. 3 is formed. The size of the microwave inlet 3 can be adjusted by adjusting the distance between the pair of variable coupling windows 2. Connected to the variable coupling window 2 is a coupling window drive unit (for example, a motor) 4 that moves the variable coupling window 2 along the direction of arrow A in FIG. Although the specific configuration of the variable coupling window 2 is not particularly limited, a metal plate made of the same material as the microwave introduction tube 1 such as stainless steel, aluminum, copper, brass, or the like is preferably used for the variable coupling window 2. Is done.

  Further, a movable short-circuit member 5 is provided in the microwave introduction tube 1 on the side opposite to the variable coupling window 2 so as to be slidable in the longitudinal direction of the microwave introduction tube 1 (in the direction of arrow B in FIG. 2). Yes. The size of the cavity in the rectangular parallelepiped cavity resonator 110 is adjusted by sliding the movable short-circuit member 5 in the direction of arrow B in FIG. Although the specific configuration of the movable short-circuit member 5 is not particularly limited, a metal plate made of the same material as the microwave introduction tube, for example, stainless steel, aluminum, copper, brass, or the like is preferably used for the movable short-circuit member 5. The The movable short-circuit member 5 is connected to a short-circuit member drive unit 6 (for example, a motor) that moves the movable short-circuit member 5 in the direction of arrow B in FIG.

  The coupling window drive unit (for example, motor) 4 is connected to a control device (control means) 7, and the short-circuit member drive unit 6 is connected to the control device 7. Here, the control device 7 adjusts the amount of movement of the variable coupling window 2 via the coupling window driving unit 4 so as to obtain an optimum coupling state according to the type, flow rate, temperature, and the like of the exhaust gas F, The amount of movement of the movable short-circuit member 5 along the arrow B direction in FIG. 2 is adjusted via the short-circuit member driving unit 6. Specifically, the control device 7 moves the variable coupling window 2 and the movable short-circuit member 5 so that an optimum resonance state is maintained in the rectangular parallelepiped cavity resonator 110 during heating of the ceramic carrier described later. Is appropriately controlled.

  The pair of variable coupling windows 2, the coupling window drive unit 4, and the control device 7 constitute the inlet adjustment means used in the present invention. The movable short-circuit member 5, the short-circuit member driving unit 6, and the control device 7 constitute a cavity adjusting means used in the present invention.

  The microwave supply means 120 includes a microwave oscillator 8 that oscillates the microwave W, a coaxial cable 9 that transmits the microwave W oscillated by the microwave oscillator 8, and power transmission through the waveguide to the coaxial cable 9. A coaxial-waveguide converter 10 for conversion and a directional coupler 11 are provided.

  In the present invention, the microwave refers to a radio wave of 0.3 to 30 GHz band (wavelength 10 mm to 1 m), and includes radio waves called so-called centimeter wave and ultra-short wave. The microwave oscillator 8 may suffice as long as it oscillates microwaves in the above-mentioned frequency band. Usually, a magnetron, a klystron, a Gunn diode, or the like is used.

  The coaxial-waveguide converter 10 is connected to the microwave introduction port 3 of the rectangular parallelepiped cavity resonator 110, and a microwave oscillator 8 is connected via a coaxial cable 9 in which a directional coupler 11 is further installed. It is connected. The directional coupler 11 is connected to the control device 7, and the microwave reflectance {(reflected power / incident power) × 100} from the rectangular parallelepiped cavity resonator 110 measured by the directional coupler 11. The variable coupling window 2 and the movable short-circuit member 5 are configured to be controlled by the control device 7 so that is minimized. When the microwave is used at a high output, the microwave oscillator 8 and the microwave inlet 3 are provided with a directional coupler 11 instead of the coaxial-waveguide converter 10 and the coaxial cable 9. It is preferable that they are connected by a waveguide. Note that the microwave reflectance from the rectangular parallelepiped cavity resonator 110 is preferably maintained at 10% or less.

  The gas transfer pipe 130 passes through the microwave introduction pipe 1 constituting the rectangular parallelepiped resonator 110. Specifically, the gas transfer pipe 130 extends in a direction orthogonal to the traveling direction of the microwave W. The gas transfer pipe 130 is composed of a heating pipe 130a in which the exhaust gas F is heated and a metal pipe 130b connected to both sides of the heating pipe 130a, and microwaves in the rectangular parallelepiped cavity resonator 110 are exposed to the outside. It has a structure that does not leak. A heating element 140 that absorbs the microwave W to generate heat and heats the exhaust gas F is accommodated in the heating tube 130a. The metal tube 130b is for introducing the exhaust gas F into the heating tube 130a or for circulating the exhaust gas F heated in the heating tube 130a. Examples of the metal constituting the metal tube 130b include stainless steel and aluminum. Copper or the like is used. Further, a seal (not shown) is provided between the heating pipe 130a and the metal pipe 130b so that the exhaust gas F does not leak.

  Such a heating tube 130a is preferably made of a material that easily transmits microwaves and has high heat resistance, and is made of a ceramic tube such as high-purity alumina, mullite, cordierite, zirconia, magnesia, or boron nitride. Preferably used. Further, the periphery of the gas transfer pipe 130 is covered with a heat insulating material 12, and such a heat insulating material 12 is preferably one that easily transmits microwaves, and a heat insulating material made of ceramic fibers such as heat-resistant alumina fiber is suitable. Used.

  The gas transfer pipe 130 is disposed between the variable coupling window 2 and the movable short-circuit member 5 so that a heating element 140 described later includes a position of a quarter wavelength of the standing wave S from the variable coupling window 2. It is preferable.

  The heating element 140 will be described with reference to FIG. FIG. 4 is a partial cross-sectional view of the heating element 140.

  As shown in FIG. 4, the heating element 140 includes a microwave absorber 13 and a ceramic carrier 14 that supports the microwave absorber 13.

  The ceramic carrier 14 may be a woven fabric or a nonwoven fabric made of a fibrous material, but preferably has a porous body and a structure having a large number of through holes 15. In the present embodiment, the ceramic carrier 14 has a monolith shape. That is, the ceramic carrier 14 has a large number of through-holes 15 for circulating the exhaust gas. The through-hole 15 extends in a direction parallel to the extending direction of the heating tube 130a so that the exhaust gas F can easily pass through and the pressure loss is as small as possible. A microwave absorber 13 is carried on the wall surface forming the through hole 15.

  Here, the microwave absorber 13 contains a silicon carbide-based composite oxide. The silicon carbide-based composite oxide is a composite oxide in which silicon carbide is dissolved in an inorganic oxide. The silicon carbide-based composite oxide is composed of a composite oxide composed of Si, Zr, C, and O elements, or Si, Ti, C, and O elements from the viewpoint of having excellent microwave absorption characteristics. A composite oxide is preferable. Moreover, the microwave absorber 13 may contain 2 or more types of silicon carbide type complex oxides, and may contain 1 type, or 2 or more types of silicon carbide type complex oxides and silicon carbide.

A composite oxide composed of elements of Si, Zr, C and O has the following composition formula:
Si _x Zr _y C _z O _w
X is preferably 50 to 60, y is preferably 0.5 to 5, z is preferably 30 to 40, and w is preferably 5 to 20.

The composite oxide composed of Si, Ti, C and O elements has the following composition formula:
Si _x Ti _y C _z O _w
X is preferably 50 to 60, y is preferably 0.5 to 5, z is preferably 30 to 40, and w is preferably 5 to 20.

  The dielectric loss factor of the silicon carbide-based composite oxide is preferably 2 or more, and more preferably 5 or more. When the dielectric loss factor of the silicon carbide-based composite oxide is smaller than 2, the microwave energy is not sufficiently absorbed and the temperature is not increased sufficiently rapidly. The dielectric loss factor of the silicon carbide-based composite oxide is preferably 30 or less.

  The shape of the microwave absorber 13 is not particularly limited as long as it can be supported on the ceramic carrier 14. However, in the step of supporting the microwave absorber 13 on the ceramic carrier 14, the shape of the slurry containing the microwave absorber 13 is not limited. In view of the general use of a solution, a powder is preferable.

  When the dielectric loss factor of the silicon carbide based composite oxide is 2 or more, the dielectric loss factor of the ceramic carrier 14 supporting the microwave absorber 13 is preferably 0.1 or less, and 0.02 or less. It is more preferable. When the ceramic carrier 14 has a monolithic shape as in the present embodiment, the microwave absorber 13 is present inside the ceramic carrier 14. Therefore, when the dielectric loss factor of the ceramic carrier 14 exceeds 0.1, the microwave permeability of the ceramic carrier 14 is low, and the irradiated microwave energy is absorbed by a part of the ceramic carrier 14, so that microwave absorption is achieved. The microwave energy absorbed by the body 13 tends to be excessively small.

  The ceramic carrier 14 is preferably made of a material having heat resistance because it is rapidly heated by the microwave absorber 13. The ceramic carrier 14 is not particularly limited as long as it is a material having low microwave absorption characteristics and heat resistance, but is composed of magnesia, alumina, silica, cordierite, mullite, or a composite material using a mixture of these. Of these, cordierite and mullite are particularly preferable.

  Next, a microwave heating method using the above-described microwave heating apparatus 100 will be described.

  First, the microwave oscillator 8 is operated in the microwave heating apparatus 100. Then, a microwave W is generated by the microwave oscillator 8, and the microwave W is transmitted through the coaxial cable 9, and after being mode-converted by the coaxial-waveguide converter 10, a rectangular parallelepiped type air is introduced from the microwave inlet 3. It is introduced into the body resonator 110. The microwave W enters the cavity of the rectangular parallelepiped cavity resonator 110 by the traveling wave from the microwave introduction port 3 toward the movable short-circuit member 5 and the reflected wave from the movable short-circuit member 5 toward the microwave introduction port 3. A standing wave S of ½ wavelength is generated in each of two directions perpendicular to the traveling direction.

  At this time, the microwave W is irradiated to the heating element 140 stored in the heating tube 130 a of the gas transfer tube 130 in the rectangular parallelepiped cavity resonator 110.

  At this time, the microwave W passes through the ceramic carrier 14 and is irradiated to the microwave absorber 13. Here, the microwave absorber 13 includes a silicon carbide-based composite oxide that is superior in microwave absorption characteristics as compared with conventional SiC. For this reason, the microwave W is efficiently absorbed and converted into heat, and the temperature of the microwave absorber 13 is increased rapidly and with low power consumption by microwave irradiation. Thereby, the ceramic support | carrier 14 can be heated rapidly and uniformly. In the microwave heating apparatus 100, since the cavity resonator uses the single-mode rectangular cavity resonator 110, the resonance in the rectangular cavity resonator 110 can be sufficiently maintained. . Even if the material and shape of the microwave absorber 13 change, the electromagnetic field mode in the rectangular parallelepiped cavity resonator 110 does not change, and the electromagnetic field distribution in the ceramic carrier 14 can be made uniform. Therefore, the ceramic carrier 14 can be heated uniformly. Therefore, according to the microwave heating apparatus 100, the ceramic carrier 14 can be heated rapidly and uniformly with low power consumption.

  Therefore, when the exhaust gas is circulated in the gas transfer pipe 130, the exhaust gas passes through the through hole of the heating element 140, so that the exhaust gas F contacts the microwave absorber 13 and the exhaust gas F is heated rapidly and uniformly. It will be.

  Therefore, when the microwave heating apparatus 100 is applied to an engine such as an automobile and the gas transfer pipe 130 is an exhaust pipe, if the catalyst 150 is disposed on the downstream side of the heating element 140 (see FIG. 3), the exhaust gas rapidly and It is heated to a temperature equal to or higher than the catalyst activation temperature. For this reason, phenomena such as cold emission occurring in the initial stage of warm-up operation in an automobile or the like can be sufficiently suppressed, which can contribute to environmental conservation.

  Further, in the microwave heating apparatus 100, the gas transfer pipe 140 is between the variable coupling window 2 and the movable short-circuit member 5, and the heating element 140 has a quarter wavelength of the standing wave S from the variable coupling window 2. It arrange | positions so that the position separated only by the length may be included. For this reason, the microwave absorber 13 will be arrange | positioned so that the intensity | strength of the electric field E in the rectangular parallelepiped cavity resonator 110 may include the maximum position. Therefore, the microwave W is efficiently absorbed by the microwave absorber 13 and an improvement in energy efficiency is achieved.

  Further, since the gas transfer tube 130 extends in a direction orthogonal to the traveling direction of the microwave W, the traveling direction of the exhaust gas F substantially coincides with the direction of the electric field E in the rectangular parallelepiped cavity resonator 110. Therefore, it is not necessary to install a reflector in the traveling direction of the exhaust gas F. For this reason, an increase in pressure loss can be prevented.

  Furthermore, in the microwave heating apparatus 100 of the present embodiment, the microwave reflectance {(reflected power / incident power) × 100} from the rectangular parallelepiped cavity resonator 110 is measured by the directional coupler 11, and the microwave The variable coupling window 2 and the movable short-circuit member 5 are controlled by the control device 7 so that the wave reflectance is minimized. That is, when the dielectric characteristics of the microwave absorber 13 and the heated exhaust gas F change with temperature rise and resonance in the rectangular parallelepiped cavity resonator 110 cannot be taken (changes), the rectangular parallelepiped cavity resonator 110 The reflected microwave increases and the microwave reflectivity increases. Therefore, the state of resonance in the rectangular parallelepiped cavity resonator 110 is monitored by measuring the microwave reflectance with the directional coupler 11, and the variable coupling window 2 and the movable coupling window 2 are movable so that the microwave reflectance is minimized. By controlling the short-circuit member 5 and adjusting the size of the microwave inlet and / or the size of the cavity in the cavity resonator, the resonance in the rectangular parallelepiped cavity resonator 110 is always maintained in an optimum state. Is done.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

That is, in the above embodiment, a TE ₁₀₁ single-mode rectangular parallelepiped cavity resonator is designed as a cavity resonator so that a standing wave of 1/2 wavelength is generated in the microwave traveling direction. Although used, the present invention is not limited to this, and a TE _10n mode in which a plurality of standing waves exist in the traveling direction of the microwave may be used.

  Further, in the above-described embodiment, the inlet adjustment means and / or the control means by the control means so that the optimum resonance state in the rectangular parallelepiped cavity resonator 110 is maintained according to the type, flow rate, temperature, etc. of the exhaust gas F. Although the cavity adjusting means is controlled, the inlet adjusting means, the cavity adjusting means, and the control means are not necessarily required. According to the microwave absorber 13 disposed in the rectangular parallelepiped cavity resonator 110, the microwave absorption characteristics of the ceramic carrier 14, the microwave absorption characteristics of the exhaust gas F to be heated, and the heating conditions, the microwave inlet By optimizing and fixing the size and the size of the cavity in the rectangular parallelepiped cavity 110, the rectangular parallelepiped type can be provided without the inlet adjusting means, the cavity adjusting means, and the control means for controlling them. Resonance can be sufficiently maintained in the cavity resonator 110.

  Moreover, in the said embodiment, although waste gas is used as a fluid, it may replace with waste gas and may use a liquid. In this case, the liquid can be heated rapidly and uniformly.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
The powder of the silicon carbide based composite oxide was synthesized from polycarbosilane having an organosilicon polymer as a precursor. A metal alkoxide containing Zr was added to polycarbosilane and reacted at about 220 ° C. to polymerize polymetallocarbosilane. Thereafter, infusibilization treatment was performed at about 180 ° C. in the atmosphere, and further, firing was performed at 1300 to 1500 ° C. in an inert gas. Thus, a silicon carbide based composite oxide powder (hereinafter referred to as “Si—Zr—C—O powder”) having an elemental composition ratio represented by Si ₅₅ Zr ₁ C ₃₅ O ₉ was obtained. It was confirmed by a chemical analysis method using infrared absorption that the Si—Zr—C—O powder was a silicon carbide composite oxide having the above elemental composition ratio.

  On the other hand, a cordierite monolith having a cylindrical shape with a diameter of 50 mm and a length of 10 mm as a ceramic carrier and a dielectric loss factor of 0.01 is prepared, and the Si—Zr—C—O powder is obtained by the following method. It was carried on the cell wall surface forming the through hole. First, a binder was mixed with Si—Zr—C—O powder to form a slurry, a monolith was immersed in this slurry, and a slurry containing Si—Zr—C—O powder was uniformly applied to the cell wall of the monolith. The outer peripheral surface of the monolith was masked so that the slurry was not applied. A monolith in which the slurry is applied to the cell wall surface is dried at 110 ° C. for 24 hours and then calcined at 500 ° C. for 1 hour to obtain a monolith carrying Si—Zr—C—O powder (hereinafter referred to as “heating element”). Obtained.

(Dielectric loss factor measurement)
The dielectric loss factor of the Si—Zr—C—O powder obtained as described above was measured as follows. That is, the dielectric loss factor was measured using the perturbation method, and obtained from the change in the half-value width of the resonance waveform when the sample in the rectangular parallelepiped cavity resonator 110 was inserted. The results are shown in Table 1.

(Monolith microwave heating characteristics evaluation test)
Next, the heating element obtained as described above was placed in a rectangular parallelepiped cavity resonator 110 of the microwave heating apparatus shown in FIGS. More specifically, the heating element 140 having a cylindrical shape is inserted into the heating tube 130a, and the position where the electric field intensity in the rectangular parallelepiped cavity resonator 110 is maximum coincides with the center of the cross-sectional circle of the heating element 140. In addition, the heating element 140 and the heating tube 130a are connected to the rectangular parallelepiped resonator so that the direction of the through hole 15 of the monolith and the direction of the electric field vector in the rectangular parallelepiped cavity 110 are parallel to each other. 110. Then, the microwave oscillator 8 was operated to irradiate the heating element 140 with microwaves, and the temperature rise profile of the ceramic carrier at this time was measured to evaluate the microwave heating characteristics of the monolith. The results are shown in FIG. Here, in the microwave heating characteristic evaluation test, the temperature was the temperature inside the monolith. FIG. 5 shows a temperature rise profile of the ceramic carrier when the microwave output is 500 W as a result of the microwave heating characteristic test. Table 1 also shows the time required to heat the ceramic carrier constituting the heating element from room temperature 25 ° C. to 500 ° C. for each case where the microwave output is 300 W and 500 W, as a result of the microwave heating characteristic test. It was.

The components of the microwave heating apparatus other than the heating element 140 were as follows.
Cavity resonator: TE ₁₀₁ single mode cuboid resonator, copper, cavity dimensions 110 mm × 55 mm × 75 mm;
-Heating tube: High-purity alumina tube (purity 99.6%), inner diameter 50 mm, length 55 mm
・ Heat insulation: Made of alumina fiber ・ Microwave generation means: Magnetron oscillator, frequency 2.45 GHz
・ Coaxial-wave conduit converter ・ Directional coupler ・ Control circuit: Automatic control by personal computer so that reflectivity is zero ・ Variable coupling window: Made of brass ・ Variable short circuit board: Made of brass

(Example 2)
A silicon carbide system in which the elemental composition ratio is represented by Si ₅₂ Ti ₂ C ₃₀ O ₁₆ in the same manner as in Example 1 except that a metal alkoxide containing Ti is used instead of a metal alkoxide containing Zr. A composite oxide powder (hereinafter referred to as “Si—Ti—C—O powder”) was obtained. It was confirmed by a chemical analysis method using infrared absorption that the Si—Ti—C—O powder was a silicon carbide-based composite oxide having the above elemental composition ratio.

  Then, the dielectric loss factor of the Si—Ti—C—O powder was measured in the same manner as in Example 1. The results are shown in Table 1. Further, a heating element was obtained in the same manner as in Example 1 except that Si—Ti—C—O powder was used instead of the Si—Zr—C—O powder. By measuring the temperature rise profile of the ceramic carrier for the heating element thus obtained in the same manner as in Example 1, the microwave heating characteristics of the monolith were evaluated. The results are shown in FIG. FIG. 5 shows the temperature rise profile of the ceramic carrier when the microwave output is 500 W, as a result of the microwave heating characteristic test, as in Example 1. Also, in Table 1, as in Example 1, as a result of the microwave heating characteristic test, the ceramic carrier constituting the heating element was heated from room temperature 25 ° C. to 500 ° C. for each case where the microwave output was 300 W and 500 W. The time required to do is shown.

(Comparative Example 1)
A heating element was obtained in the same manner as in Example 1 except that a commercially available SiC powder was used instead of the Si—Zr—C—O powder as the microwave absorber. The microwave heating characteristics of the monolith were evaluated by measuring the temperature rise profile of the ceramic carrier for the heating element obtained as described above in the same manner as in Example 1. The results are shown in FIG.

  The dielectric loss factor of the commercially available SiC powder was as shown in Table 1.

FIG. 5 shows the temperature rise profile of the ceramic carrier when the microwave output is 500 W, as a result of the microwave heating characteristic test, as in Example 1. Also, in Table 1, as in Example 1, as a result of the microwave heating characteristic test, the ceramic carrier constituting the heating element was heated from room temperature 25 ° C. to 500 ° C. for each case where the microwave output was 300 W and 500 W. The time required to do is shown.

  As shown in Table 1, the time required to heat the monoliths of Examples 1 and 2 from 25 ° C. to 500 ° C., which is near the catalyst activation temperature of the exhaust gas purifying catalyst, etc., when the microwave output is 500 W, respectively. 5 seconds and 11 seconds, and the monolith could be heated very rapidly. On the other hand, when the monolith of Comparative Example 1 carrying SiC powder was used, the time required under the same conditions was 19 seconds.

  Further, in the graph of the temperature rise profile plotted in FIG. 5, the more linear the slope of the graph, the smaller the change in the dielectric loss factor of the microwave absorber due to the temperature. It was found that the entire monolith was heated uniformly without local overheating, so-called temperature runaway. The temperature rise profile graphs of Examples 1 and 2 are linear over the entire temperature measurement range, ie, from 25 ° C. to about 890 ° C. in Example 1 and from 25 ° C. to about 780 ° C. in Example 2. It was found that the entire monolith was heated uniformly. On the other hand, the graph of the temperature rise profile of Comparative Example 1 is linear in the range from 25 ° C. to about 400 ° C., but the slope of the graph tends to rise above 400 ° C. Uneven heating and temperature runaway occurred outside.

  From the above results, it was confirmed that the ceramic carrier can be rapidly and uniformly heated with low power consumption according to the microwave heating method and the microwave heating apparatus of the present invention. Therefore, rapid and uniform heating of a fluid such as exhaust gas can be expected by using the microwave heating method and the microwave heating apparatus of the present invention.

It is a schematic diagram which shows the basic composition of suitable one Embodiment of the microwave heating apparatus of this invention. It is a perspective view which shows the cavity resonator which comprises the microwave heating apparatus shown in FIG. It is sectional drawing along the III-III line of the cavity resonator shown in FIG. It is a fragmentary sectional view which shows one Embodiment of the ceramic support | carrier with which the microwave absorber was carry | supported. It is a graph which shows the heating characteristic in the heating characteristic evaluation test in Example 1, 2, and the comparative example 1 with the microwave output of 500W.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Microwave introduction tube, 2 ... Variable coupling window (introduction port adjustment means), 3 ... Microwave introduction port, 4 ... Coupling window drive part (introduction port adjustment means), 5 ... Movable short circuit board (cavity adjustment means), DESCRIPTION OF SYMBOLS 6 ... Short-circuit plate drive part (cavity adjustment means), 7 ... Control apparatus (control means), 13 ... Microwave absorber, 14 ... Ceramic carrier, 110 ... Cuboid cavity resonator, 130a ... Heating tube (fluid transfer) Tube), W ... microwave, F ... exhaust gas (fluid), E ... electric field vector.

Claims (16)

A microwave heating method of irradiating a microwave absorber disposed in a cavity resonator with microwaves and heating a ceramic carrier carrying the microwave absorber,
Microwave heating using a microwave absorber containing a silicon carbide-based composite oxide as the microwave absorber, and using a single-mode rectangular cavity resonator as the cavity resonator Method.   The microwave according to claim 1, wherein the ceramic carrier has a large number of through holes for allowing fluid to flow, and the microwave absorber is supported on a wall surface forming the through holes. Heating method.   The size of the inlet for introducing the microwave and the cavity in the rectangular parallelepiped resonator so that the resonance in the rectangular parallelepiped resonator is maintained during the heating of the ceramic carrier. The microwave heating method according to claim 1, wherein the size of the microwave is adjusted.   The microwave heating method according to any one of claims 1 to 3, wherein the silicon carbide-based composite oxide includes Si, Zr, C, and O elements.   The microwave heating method according to any one of claims 1 to 3, wherein the silicon carbide-based composite oxide includes Si, Ti, C, and O elements.   The microwave heating method according to any one of claims 1 to 5, wherein the silicon carbide-based composite oxide has a dielectric loss factor of 2 or more.   The microwave heating method according to claim 1, wherein the ceramic carrier has a dielectric loss factor of 0.1 or less.   The microwave absorber is disposed so as to include a position where the electric field strength is maximum in the rectangular parallelepiped resonator, and the traveling direction is parallel to the direction of the electric field vector in the rectangular resonator. The microwave heating method according to any one of claims 1 to 7, wherein a fluid is circulated and heated so as to be in contact with the ceramic carrier. A microwave heating apparatus for irradiating a microwave absorber disposed in a cavity resonator with microwaves and heating a ceramic carrier carrying the microwave absorber,
The microwave absorber includes a silicon carbide-based composite oxide, and the cavity resonator is a single-mode rectangular parallelepiped resonator.   10. The microwave according to claim 9, wherein the ceramic carrier has a plurality of through holes for allowing fluid to flow, and the microwave absorber is supported on a wall surface forming the through holes. Heating device. The rectangular parallelepiped cavity resonator has a microwave inlet that can be opened and closed,
An inlet adjusting means for adjusting the size of the microwave inlet;
Cavity adjusting means for adjusting the size of the cavity in the rectangular parallelepiped cavity resonator;
The apparatus further comprises control means for controlling the introduction adjusting means and / or the cavity adjusting means so that resonance in the rectangular parallelepiped cavity resonator is maintained during heating of the ceramic carrier. Item 11. The microwave heating apparatus according to Item 9 or 10.   The microwave heating apparatus according to any one of claims 9 to 11, wherein the silicon carbide-based composite oxide includes Si, Zr, C, and O elements.   The microwave heating apparatus according to any one of claims 9 to 11, wherein the silicon carbide-based composite oxide is composed of elements of Si, Ti, C, and O.   The microwave heating device according to any one of claims 9 to 13, wherein a dielectric loss factor of the silicon carbide-based composite oxide is 2 or more.   The microwave heating device according to any one of claims 9 to 14, wherein a dielectric loss factor of the ceramic carrier is 0.1 or less. The rectangular parallelepiped cavity resonator includes a fluid transfer pipe for transferring a fluid;
The fluid transfer pipe is arranged so that the fluid traveling direction is parallel to the direction of the electric field vector in the rectangular parallelepiped cavity resonator,
The ceramic carrier carrying the microwave absorber is disposed in the fluid transfer pipe so as to include a position where the electric field strength in the rectangular parallelepiped cavity resonator is maximized. The microwave heating device according to any one of claims 9 to 15.

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