JP2013076560A - Microwave dryer and microwave drying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To selectively heat a lower layer portion of an agglomerate charged into a drying furnace using a microwave.SOLUTION: A microwave dryer is provided at a hot-air type drying furnace that makes hot air blast an object to be dried when the object to be dried is transported by a conveyer to thereby reduce moisture contained in the object to be dried, and has a microwave oscillator that oscillates a microwave for drying the object to be dried, and a plurality of coaxial antennas that are inserted in a layer of the object to be dried to a depth so that a heating range of the object to be dried heated by the microwave includes the lowermost layer of the layer of the object to be dried, and irradiates the object to be dried with microwaves, and at least two of the plurality of coaxial antennas are arranged at positions different from each other in a width direction of the drying furnace, and positions of the coaxial antennas adjacent to each other in the width direction of the drying furnace are different from each other in a transportation direction.

Description

  The present invention relates to a microwave drying apparatus and a microwave drying method.

  As the production of steel materials by electric furnaces becomes popular, the demand for scrap, which is the main raw material, is tightened, and the demand for reduced iron is increasing due to the demand for high-grade steel production in electric furnaces.

  As one of the methods for producing reduced iron, iron oxide raw materials such as powdered iron ore and iron-making dust are mixed with carbonaceous materials such as powdered coal and coke, for example, a lump such as pellets and briquettes. There is a method in which an agglomerated material is obtained, and this agglomerated material is charged into a reduction furnace such as a rotary hearth furnace and heated to a high temperature to reduce the iron oxide raw material to obtain solid metallic iron. In such a method, it is important to adjust the moisture content of the agglomerated material containing the iron oxide raw material and the carbonaceous material in order to increase the reduction rate of the agglomerated material.

  In the manufacturing process of reduced iron as described above, as a device for adjusting the moisture content of agglomerates, etc., a tunnel-shaped furnace for drying the material to be dried placed on a wire mesh conveyor by hot air (For example, refer to Patent Document 1 below.) Such a drying furnace dries the material to be dried by passing hot air from the top to the bottom of the furnace.

  Since the drying furnace as disclosed in Patent Document 1 is hot air drying by supplying hot air upward, the lower layer portion of the raw material to be dried (portion close to the wire mesh conveyor) Drying is delayed, and drying of the small block raw material located in the lower layer portion becomes insufficient. If the drying of the small block material is insufficient, the strength of the small block material is insufficient, and in the next step, the small block material is pulverized, resulting in a reduction in production yield. In addition, in order to prevent such a reduction in production yield, it is necessary to add various binders to be mixed with the small mass raw material, resulting in an increase in manufacturing cost.

  In addition, since the small lump material contains carbonaceous materials such as coal and coke, if the small lump material is heated too much, there is a risk of ignition, and it is difficult to improve the drying efficiency by raising the temperature of the hot air. is there. Therefore, from the viewpoint of preventing ignition, it is required to selectively heat the lower layer portion where moisture remains rather than the upper layer portion that is sufficiently dried.

  In addition to the drying furnace using hot air as described above, there has been proposed a drying furnace that irradiates microwaves into the free space of the drying chamber from the outside of the workpiece in order to assist drying by the heater ( For example, see the following Patent Document 2.)

JP-A-2005-113197 JP-A-6-347165

  In the manufacturing process of reduced iron as described above, the layer thickness of the agglomerated material to be dried in the drying furnace is as thick as about 200 mm or more. Therefore, as described in Patent Document 2, when microwaves are applied to the free space in the furnace, it is possible to cause the microwaves to act on the upper layer portion of the agglomerate layer. As will be described in detail, as a result of investigations by the present inventors, it has become clear that microwaves cannot be applied to the lower layer portion of the agglomerated material.

  In addition, since the conveyor for transporting the heavy agglomerate is a metal wire mesh, even if microwaves are irradiated from the back surface of the conveyor to the lower part of the agglomerate, the microwave is transmitted by the metal conveyor. Is reflected, and microwaves cannot be applied to the lower layer portion of the agglomerated material.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to selectively select a lower layer portion of an object to be dried charged in a drying furnace using a microwave. An object of the present invention is to provide a microwave drying apparatus and a microwave drying method that can be heated.

  In order to solve the above-described problem, according to a certain aspect of the present invention, when the object to be dried is transported by a conveyor, moisture contained in the object to be dried is reduced by blowing hot air against the object to be dried. A microwave drying apparatus installed in a hot-air drying furnace, comprising: a microwave oscillator that oscillates a microwave used for drying the object to be dried; and the object to be dried being conveyed. A heating range in which the object to be dried is heated by the microwave is inserted to a depth including the lowermost layer of the object to be dried, and the microwave is applied to the object to be dried. A plurality of coaxial antennas to be irradiated, and at least two of the plurality of coaxial antennas are arranged at different positions in the furnace width direction of the drying furnace and are adjacent to each other in the furnace width direction. Wherein the position of the conveying direction of the coaxial antenna is provided a microwave drying apparatus to differ from each other.

The plurality of coaxial antennas are preferably arranged in the furnace width direction at intervals such that the heating range of each of the coaxial antennas covers the entire furnace width direction of the drying furnace as the whole of the plurality of coaxial antennas. .

  The coaxial antenna has a center conductor that is a hollow metal tube and an outer peripheral conductor that is a hollow or solid metal tube provided further outside the center conductor, and the dried object layer of the center conductor The end on the side protrudes by a length corresponding to one-fourth of the wavelength of the microwave propagated in the coaxial antenna from the end on the layer to be dried side of the outer conductor. Is preferred.

  It is preferable that a tip of the coaxial antenna is provided with a ceramic cover formed of an inorganic material ceramic having a dielectric loss coefficient of less than 0.02.

  It is preferable that the positional relationship between the central conductor and the outer conductor of the coaxial antenna is fixed by a spacer formed of an inorganic material ceramic having a dielectric loss coefficient of less than 0.02.

  It is preferable to provide a vibration mitigation mechanism for mitigating vibration generated with the conveyance of the object to be dried on the coaxial antenna.

  As the vibration relaxation mechanism, a slide waveguide having a slide mechanism that enables axial sliding between the coaxial antenna and the microwave oscillator, or a flexible waveguide having a metal bellows portion. It is preferable to dispose at least one of the above.

  As the vibration relaxation mechanism, an elastic member is preferably provided on a part of the support that supports the coaxial antenna.

  It is preferable that the coaxial antennas are arranged in the transport direction so that the heating range is continuous in the transport direction.

  It is preferable that dustproof gas is introduced into the coaxial antenna, and a positive pressure is applied to the coaxial antenna.

  A tapered portion having a cross-sectional area that is perpendicular to the transport direction may be provided at an end of the coaxial antenna on the upstream side in the transport direction so as to go upstream in the transport direction.

  The microwave drying apparatus is configured such that the microwave impedance oscillated from the microwave oscillator and the microwave oscillation reflected between the microwave oscillator and the plurality of coaxial antennas are reflected in the drying furnace. It is preferable to further include an automatic matching device for matching with the impedance of the microwave toward the machine.

  The inorganic material ceramics may be selected from the group consisting of alumina, silicon nitride, sialon, aluminum nitride, boron nitride, and mixtures thereof.

  Moreover, in order to solve the said subject, according to another viewpoint of this invention, when conveying a to-be-dried object with a conveyor, the moisture contained in the to-be-dried object by spraying a hot air with respect to the to-be-dried object A microwave drying method implemented for a hot-air drying furnace for reducing the temperature of the object to be dried, the microwave being used for drying the object to be dried being oscillated and transported from the object to be dried A heating range in which the object to be dried is heated by the microwave with respect to the inside of the object layer from each of a plurality of coaxial antennas inserted to a depth including the lowest layer of the object layer to be dried. And at least two of the plurality of coaxial antennas are arranged at different positions in the furnace width direction of the drying furnace and are adjacent to each other in the furnace width direction. The position in the transport direction of fit the coaxial antenna is provided a microwave drying method different from each other.

  As described above, according to the present invention, the microwave irradiation member is inserted from above the layer to be dried to a predetermined position and irradiated with microwaves, so that the object to be dried charged in the drying furnace can be obtained. It becomes possible to selectively heat the lower layer portion.

It is explanatory drawing shown about the flow of the manufacturing method of a general reduced iron. It is explanatory drawing for demonstrating the state of the agglomerate in a drying furnace. It is explanatory drawing which showed the outline of the microwave drying method which concerns on embodiment of this invention. It is explanatory drawing for demonstrating the examination result regarding the heating method using a microwave. It is explanatory drawing for demonstrating the examination result regarding the heating method using a microwave. It is explanatory drawing which showed the structure of the microwave drying apparatus which concerns on the 1st Embodiment of this invention. It is explanatory drawing shown about the microwave irradiation member which concerns on the same embodiment. It is explanatory drawing shown about the microwave irradiation member which concerns on the same embodiment. It is explanatory drawing shown about the microwave irradiation member which concerns on the same embodiment. It is explanatory drawing shown about the microwave irradiation member which concerns on the same embodiment. It is explanatory drawing shown about the microwave irradiation member which concerns on the same embodiment. It is explanatory drawing shown about the modification of the microwave irradiation member which concerns on the same embodiment. It is explanatory drawing shown about the modification of the microwave irradiation member which concerns on the same embodiment. It is explanatory drawing shown about the modification of the microwave irradiation member which concerns on the same embodiment.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

(About manufacturing process of reduced iron)
Prior to describing the microwave drying apparatus and the microwave drying method according to the embodiment of the present invention, first, the manufacturing process of reduced iron will be described in detail with reference to FIG. Drawing 1 is an explanatory view for explaining the manufacturing process of reduced iron.

  First, iron oxide raw materials such as iron dust (iron oxide powder), iron ore, and powder ore, and reducing materials such as coal, coke, and fine carbon are stored in the hopper 1 and the like in advance. The iron oxide raw material and the reducing material are blended so as to have a preset blending ratio and charged into the pulverizer 2.

  A crusher 2 typified by a vibration mill such as a ball mill crushes the charged iron oxide raw material and the reducing material to a predetermined particle size while mixing them. The particle diameters of the iron oxide raw material and the reducing material after pulverization can be set to values suitable for a solid reduction furnace such as a rotary hearth furnace, a fluidized bed furnace, and a shaft furnace used for producing reduced iron. The mixture of the pulverized iron oxide raw material and the reducing material is conveyed to the kneader 3.

  The kneader 3 kneads the mixture pulverized to a predetermined particle size by the pulverizer 2. Moreover, the kneading machine 3 may perform a humidity control process for adding water to the mixture until the water content is suitable for a solid reduction furnace used for producing reduced iron. As an example of the kneading machine 3, for example, a mix muller can be cited. The mixture kneaded by the kneader 3 is conveyed to the molding machine 4.

  A molding machine 4 such as a pan pelletizer (dish granulator), a double roll compressor (briquette making machine), and an extrusion molding machine molds a mixture containing an iron oxide raw material and a reducing material, and agglomerates such as pellets. It is a chemical. Here, the agglomerated material refers to pellets, briquettes, extruded products that have been cut by extrusion molding, and granular materials / agglomerated materials such as mass-adjusted agglomerated materials. When the molding machine 4 is dried and heat-reduced, which will be described later, for example, when charged into the melting furnace 7 in the hot state, the above mixture is adjusted so as to have a size larger than the particle size so as not to be scattered by the rising gas flow in the furnace. Agglomerates. The produced agglomerated material is charged into the drying furnace 5.

  The drying furnace 5 dries the agglomerated material and has a moisture content suitable for the heating and reducing process described later (in other words, a moisture content suitable for each solid reduction furnace used for producing reduced iron: for example, 1% And so on. The agglomerated product having a predetermined moisture content is conveyed to a solid reduction furnace 6 to be described later.

  For example, the solid reduction furnace 6 such as a rotary hearth furnace (RHF), a fluidized bed furnace, a shaft furnace, etc., heats the agglomerate charged in a heating atmosphere such as an LNG burner or a COG burner. Reduce to iron reduced. The solid reduction furnace heats the agglomerate to, for example, about 1000 to 1300 ° C. to reduce the agglomerate and produce reduced iron. The manufactured reduced iron is conveyed to the melting furnace 7. In the melting furnace 7, the reduced iron produced in the solid reduction furnace 6 is melted to produce hot metal. The produced hot metal is processed into various steel products through a desulfurization / decarburization process, a secondary refining process, a continuous casting process, a rolling process, and the like.

(Outline of drying method using microwaves)
In the manufacturing process of reduced iron as described above, the drying furnace 5 is usually a tunnel-shaped furnace that dries the agglomerated material using hot air. Inside the drying furnace 5, normally, agglomerates such as briquettes are charged until the height reaches, for example, about 250 mm, and the inside of the furnace is conveyed by a mesh-like metal conveyor. Each agglomerated material to be conveyed has various sizes depending on the type of the reduction furnace or melting furnace, for example, a roughly spherical shape of about 10φ to 20φ, or 30φ to 50φ × thickness of about 25 mm. The load is about 300 kg / m ^{2 on} the mesh conveyor by being stacked up to about 250 mm in height. In the course of this conveyance, the moisture in the agglomerated material is removed by hot air, and the moisture content of the agglomerated material is controlled to a desired value. In addition, as described above, in order to prevent ignition of coal components contained in the agglomerated material, there is a restriction that the hot air used is about 200 ° C. or less.

  However, as a result of investigating the remaining state of moisture in the drying furnace by the present inventors, as schematically shown in FIG. 2, in the drying with hot air from above, the upper layer part of the agglomerate layer is dried. In the lower layer portion (portion close to the mesh conveyor), it was revealed that the residual amount of water is large, and the agglomerated material in the lower layer portion is often poorly dried. Due to such factors, the yield of the average drying rate of the agglomerated material decreases, and the drying time must be lengthened to increase the degree of drying.

  Therefore, the present inventors have intensively studied a method for selectively heating the lower layer portion of the agglomerate layer. For example, the following are the events that have become a concern in this study.

In other words, the floor surface of the drying furnace is a mesh-like conveyor using metal, so if microwaves are simply irradiated from below the conveyor, the irradiated microwaves are reflected by the conveyor and agglomerated. The chemical cannot be heated. It is also conceivable to change the material of the conveyor to a material that absorbs less microwaves, such as Teflon (registered trademark) or nylon, but such a material is more expensive than a metal mesh belt, The cost is high and the load of about 300 kg / m ² cannot be withstood. In addition, even when microwaves are irradiated from above, the agglomerate previously located in the lower layer may be heated by inverting the agglomerate layer in the drying furnace. However, if such an upside down is carried out, the agglomerated product may be crushed by colliding with each other, and the agglomerated product may be pulverized.

  Therefore, in order to sufficiently dry the agglomerated material under the condition that the material to be dried such as agglomerated material is moving in the furnace (that is, the material to be dried is not stationary). In addition, it is necessary to study a method that can efficiently irradiate the lower part of the agglomerate with high-power microwave of kW class, for example, while maintaining the wear resistance of the microwave irradiation member. It was.

  As a result, as schematically shown in FIG. 3, the agglomerate located in the lower layer by microwave heating is supplied to the lower layer part of the agglomerate layer without passing through the mesh conveyor. The inventors have conceived four types of methods capable of selectively heating the above.

  By using the drying method schematically shown in FIG. 3, the drying progress of the lower layer portion of the agglomerated layer is improved, the average drying rate of the agglomerated material is improved, and the drying time is shortened. As a result, productivity of the drying process can be improved.

  Prior to describing the microwave drying apparatus and the microwave drying method according to the embodiment of the present invention, various examination results on the method for drying an agglomerate using microwave heating by the present inventors will be described with reference to FIGS. This will be specifically described with reference to FIG.

<Examination of the range covered by microwave heating>
The present inventors conducted the following experiment in order to examine the range covered by microwave heating. FIG. 4 schematically shows an experimental apparatus for verifying the range covered by microwave heating when the agglomerate (briquette) is irradiated with microwaves from above.

  As shown in FIG. 4, the present inventors laminated an undried briquette (used in actual operation) of about 40φ × 20 mm on a metal container and placed it in the chamber. At this time, a thermocouple is inserted into a briquette located at a substantially central portion of the metal container, and between each layer (for example, between layer A and layer B, between layer B and layer C in the lower diagram of FIG. 4). ... etc.) was also equipped with a thermocouple to monitor the temperature rise. In addition, a 3.0 kW microwave oscillator capable of radiating a 2.45 GHz microwave, a power monitor capable of measuring the incident microwave output and reflected microwave output to the chamber, and reducing the reflected microwave For this purpose, a microwave output from the automatic aligner was irradiated from above the chamber through the waveguide. In this experiment, the microwave incident power was 600 W, and the microwave irradiation time was 60 seconds.

  As a result, in the thermocouple inserted in the briquette located in the layer A shown in the lower diagram of FIG. 4 and the thermocouple inserted between the layers A and B, a clear temperature rise was confirmed, and the briquette located in the layer B was confirmed. However, although it was not as high as the briquette located in the layer A, an increase in temperature was confirmed. However, in the briquettes located below the layer C, no temperature increase could be confirmed. This experimental result indicates that when microwaves are irradiated from above the agglomerated material, the range of heating by microwaves is at most from the outermost layer to the second layer.

By the way, the microwave energy P _abs per unit volume absorbed by the substance is expressed as the following Expression 11. As can be seen by referring to Equation 11 below, the microwave energy P _abs per unit volume absorbed by the substance to be heated (substance to be heated) depends on the conductivity, dielectric constant and permeability of the substance to be heated. You can see that Therefore, it can be said that P _abs represented by the following formula 11 is an amount related to the microwave absorption efficiency of the heated material.

Here, in Equation 11 above,
σ: Conductivity of heated material [S / m]
f: Microwave frequency [Hz]
ε ₀ : dielectric constant in vacuum [F / m]
ε ″: Imaginary part of relative permittivity of heated material μ ₀ : Permeability in vacuum [H / m]
μ ”: Imaginary part of relative permeability of heated material E: Electric field strength formed by microwave [V / m]
H: intensity of magnetic field formed by microwave [A / m]
π: Pi ratio.

  The values of the imaginary part ε ″ of the relative dielectric constant are collectively shown below for the iron oxide and carbon material (reducing material) that are the raw materials of the agglomerated material and the refractory furnace materials that are generally used.

Imaginary part of dielectric constant ε ”
Alumina, which is a typical refractory furnace material: 0.004 to 0.01
・ Powdered carbon powder: 10-50
・ Iron oxide: 0.1-10

  As is clear from the above, the iron oxide and carbon material used as the raw material for the agglomerate have a large value of the imaginary part ε ″ of the relative dielectric constant relative to the refractory furnace material generally used in a drying furnace or the like, The oxide and carbon material (reducing material) can absorb more microwave energy, and the value of alumina, which is a typical refractory furnace material, compared to the values of iron oxide and carbon powder, The value is about 1/1000, and it can be seen that the refractory furnace material does not absorb much microwave energy, so when the microwave is irradiated in the furnace in which the agglomerates are inserted, There is little energy supply to the furnace wall etc. which are coat | covered with the furnace material, and it becomes possible to raise only the temperature of the agglomerate which is a raw material efficiently, suppressing the raise in furnace temperature.

  However, in the experimental situation where the microwave as shown in FIG. 4 is irradiated to the free space in the furnace due to the characteristics as described above, the microwave irradiated from above is agglomerated in the upper layer region. It is considered that the microwave does not penetrate into the lower layer portion that needs to be supplied with heat to promote drying and is absorbed by the chemicals very well. Therefore, the present inventors, as in the prior art, heat the agglomerate located in the lower layer part when microwaves are irradiated from the furnace ceiling, side walls, or furnace bottom toward the space in the furnace. Judged that it is not possible.

  By the way, when the microwave is absorbed by the material due to dielectric loss, the energy of the microwave is converted into heat, and as a result, the material that has absorbed the microwave is heated. At this time, how much the microwave penetrates into the substance can be calculated by the following equation 12.

Here, in the above equation 12,
δ: microwave penetration depth [cm]
λ: wavelength of microwave in free space [cm]
ε ': relative permittivity of the substance (real part)
tan δ: the dielectric loss tangent of the substance.
Further, tan δ can be calculated by (ε _r ′ / ε _r ″) using the dielectric constant ε _r ′ and the dielectric loss coefficient ε _r ″ of the substance.

As a result of further experiments by the present inventors, the briquette is a lump of 30φ to 50φ × thickness 25 mm, and there is a gap between each briquette, and in the briquette being transported, the gap between each briquette Since the state changes, the microwave heating range is expanded, and the range up to 10 times the penetration depth δ obtained by Equation 12 is an effective heating range (hereinafter also referred to as δ _eff ). It became clear. When the penetration depth δ is calculated from the physical property values of the briquette, the magnitude is about 1 cm, so the effective heating range δ _eff by microwave heating is about 10 cm. Therefore, it was also clarified that microwave irradiation from the side face cannot heat the entire lower layer of the drying furnace having a width of about 2 to 2.5 m and a transport distance of about 20 to 30 m used in the operation.

  Therefore, as a result of further studies based on the knowledge obtained by the experiments as described above, the present inventors have come up with a microwave irradiation method capable of heating the entire lower layer portion of the drying furnace. The inventors have arrived at a microwave drying apparatus and a microwave drying method as described below.

  FIG. 5 is a graph schematically showing the relationship between the moisture content (%) after drying the agglomerated material and the crushing strength of the agglomerated material. In producing the agglomerated material, starch-based paste such as corn starch is used as a binder to achieve the required strength. The starch-based paste increases in strength as it is dried as illustrated in FIG. . Therefore, the crushing strength of the agglomerated product can be increased without changing the binder amount by improving the drying rate of the entire agglomerated product by the method described below. As a result, it is possible to reduce the amount of agglomerated material that cannot be used by being crushed during transportation, and the yield can be improved. Further, by improving the drying rate, it is possible to reduce the amount of the binder to be added in order to obtain the same strength, and thus it is possible to reduce the manufacturing cost.

(About the microwave used)
Next, a microwave used in the microwave drying apparatus and the microwave drying method according to the embodiment of the present invention will be briefly described.

  The microwave generally refers to an electromagnetic wave having a wavelength of 1 mm to 1 m and a frequency of 300 MHz to 300 GHz. However, as noted in the method for heating an agglomerate according to the present embodiment, when microwaves are used as heating means (so-called microwave heating is performed), microwaves are so-called ISM (Industry- Science-Medical) refers to an electromagnetic wave in a frequency band belonging to the band.

  In the embodiment of the present invention described below, there is no particular limitation as long as the electromagnetic wave has a frequency belonging to the IMS band. For example, a 2.45 GHz band (2.40 GHz to 2.50 GHz), a 5.8 GHz band (5. 725 GHz to 5.875 GHz) and frequencies belonging to the 24 GHz band (24.0 GHz to 24.25 GHz) can be selected as appropriate. However, since the penetration of microwaves into the object to be heated is proportional to the wavelength of the microwaves as represented by the above equation 12, the penetration depth δ in the 2.45 GHz band is one for the microwaves in the ISM band. The raw material briquette can be heated over the entire number of coaxial antennas or waveguides and the entire width of the drying furnace. In addition, 2.45 GHz is widely used for microwave ovens and other microwave heating applications, and the device is inexpensive, and it is possible to radiate high power up to several tens of kW with one oscillator. Also, the equipment cost of the present invention that requires a large output of kW class can be introduced at a lower cost than the other two frequency devices. For this reason, the ISM band microwave device used in the present invention is preferably capable of oscillating 2.45 GHz microwave.

(First embodiment)
Subsequently, the microwave drying apparatus and the microwave drying method according to the first embodiment of the present invention will be described in detail with reference to FIGS.

<About the configuration of the microwave dryer>
First, the configuration of the microwave drying apparatus according to the present embodiment will be described in detail with reference to FIG. FIG. 6 is an explanatory diagram for explaining the configuration of the microwave drying apparatus according to the present embodiment.

  The microwave drying apparatus 10 according to the present embodiment blows hot air from above the raw material and passes the hot air from the upper side to the lower side of the raw material in the process of conveying the powder or small block raw material by a mesh conveyor. Thus, it is used for a hot-air type tunnel drying furnace that reduces moisture contained in the raw material.

  As shown in FIG. 6, the microwave drying apparatus 10 according to the present embodiment mainly includes a microwave oscillator 101, a circulator 103, an automatic matching unit 107, and a microwave irradiation member 109. Are connected by a waveguide 111. In FIG. 6, a support mechanism for supporting each member such as the microwave guiding member 109 and the waveguide 111 is not shown.

  The microwave oscillator 101 is a device that oscillates a microwave having a frequency belonging to, for example, an ISM band. The microwave oscillator 101 is preferably a device capable of oscillating microwaves having a kW class output. For example, a microwave having a frequency belonging to a 2.45 GHz band is output to the circulator 103 described later by the microwave oscillator 101. As this microwave oscillator 101, a publicly known one can be appropriately selected and used.

  The circulator 103 performs a microwave progress control using, for example, a magnet, so that the microwave input to the circulator 103 is changed from the incident wave output from the microwave oscillator 101 to the automatic matching unit 107 described later. It separates into the reflected wave that has returned. The circulator 103 guides the separated incident microwave toward the automatic matching unit 107 described later, and guides the reflected microwave toward the isolator 105 side. Thereby, the reflected microwave can be absorbed by a dummy load (for example, water) provided in the isolator 105 and can be prevented from returning to the microwave oscillator 101 side. By providing such a circulator 103, the microwave drying apparatus 10 according to the present embodiment can output a stable microwave. As this circulator 103, a known circulator can be appropriately selected and used.

  The automatic matching unit 107 reduces the reflected wave from the load side by matching the impedance on the incident side with the impedance on the load side (that is, the raw material layer side made of agglomerated material), and the reflected wave is almost zero. It is a device. The automatic matching unit 107 measures the phase and intensity of the reflected electric field and automatically performs impedance matching, thereby realizing the reduction of the reflected wave as described above.

  The object to be dried by the microwave drying apparatus 10 according to the present embodiment is a small lump raw material such as an agglomerated material being conveyed in the drying furnace 5. Therefore, the contact state between the moving small lump material and the microwave irradiation member 109 to be described later constantly changes, and the impedance on the load side changes, so that the microwave irradiation efficiency changes. By providing an automatic matching unit 107 and realizing automatic matching processing according to the impedance on the load side, it is possible to stably and efficiently irradiate the raw material layer with microwave energy from the microwave irradiation member 109 described later. It becomes.

  The microwave irradiation member 109 is a member that irradiates the microwave to the lower layer portion of the raw material layer in order to selectively heat the lower layer portion of the raw material layer made of agglomerated material in the hot air drying furnace 5. The configuration of the microwave irradiation member 109 will be described in detail later.

  The waveguide 111 is a tube that guides a microwave to a desired location. The shape of the waveguide 111 may be appropriately determined in consideration of the waveguide characteristics of the microwave, etc., and the waveguide 111 itself also depends on the frequency and output intensity of the microwave to be used. A well-known thing can be selected suitably.

<Configuration of microwave irradiation member>
Next, the configuration of the microwave irradiation member according to the present embodiment will be described in detail with reference to FIGS. 7-11 is explanatory drawing shown about the microwave irradiation member which concerns on this embodiment.

  As shown in FIG. 7, in the present embodiment, as the microwave irradiation member 109, the converter 121 connected by the automatic matching unit 107 and the waveguide 111, the coaxial antenna 123 connected to the converter 121, Is used.

  The converter 121 is a device that converts the microwave guided in the waveguide 111 so as to propagate through the coaxial antenna 123. The converter 121 can be used by appropriately selecting a known device.

  The coaxial antenna 123 is inserted from above the drying furnace 5 into the raw material layer made of agglomerated material that is conveyed in the depth direction of the drawing in FIG. In FIG. 7, only one of the coaxial antennas 123 inserted into the drying furnace 5 is shown for easy understanding, but the drying furnace 5 includes a plurality of coaxial antennas 123. Inserted from above. The coaxial antenna 123 is inserted so as to be substantially perpendicular to the bottom surface of the drying furnace 5 formed of a mesh conveyor. Moreover, in order to reduce the conveyance resistance of the agglomerated material, the coaxial antenna 123 may be inclined and installed so that the lower end is directed to the downstream side in the conveyance direction of the raw material layer.

FIG. 8 is an explanatory diagram for explaining the coaxial antenna 123 according to the present embodiment.
As shown in FIG. 8, the coaxial antenna 123 has a two-layer structure including a central conductor 123a and an outer peripheral conductor 123b surrounding the central conductor 123a. Here, as is clear from the cross-sectional view along the line AA in FIG. 8, the central conductor 123a is formed using a solid rod-shaped metal, and the outer peripheral conductor 123b is a hollow metal tube. Formed. The central conductor 123a may be formed using a hollow metal tube instead of a solid rod-like metal. Further, as is clear from the cross-sectional view taken along the line BB in FIG. 8, a spacer that holds the center conductor 123a in a part of the outer conductor 123b and fixes the positional relationship between the center conductor 123a and the outer conductor 123b. 123c is provided.

Further, coaxial antenna 123, the tip of the center conductor 123a is formed so as to protrude from the tip of the outer peripheral conductor 123b by a distance _{L 3.} The length of the protrusion distance L _{3 is} a length represented by λ ′ / 4 when the wavelength of the microwave propagated in the coaxial antenna 123 is λ ′. Microwaves propagated in the coaxial antenna 123 are radiated from the periphery of the protruding portion.

  Since the microwave is guided inside the coaxial antenna 123, the cross-sectional shape and the cross-sectional size of the central conductor 123a have a shape and size capable of guiding a microwave having a desired frequency and intensity. For example, it is preferable to make the cross-sectional shape a rectangular shape or a circular shape as shown in FIG. Further, the cross-sectional shape of the outer peripheral conductor 123b is not particularly limited, but is preferably a circular shape as shown in FIG. 8 in order to reduce the conveyance resistance of the agglomerated material.

  The coaxial antenna 123 (especially the outer conductor 123b) is made of copper so that the cross-sectional shape is strong enough to prevent buckling deformation due to the load in consideration of the load per unit surface received from the agglomerated material being conveyed. It is manufactured using various metals such as (Cu), aluminum (Al), nonmagnetic austenitic stainless steel (SUS), and alloys containing these. Further, when the coaxial antenna 123 itself is fixed to the upper part (for example, the ceiling) of the place where the drying furnace 5 is installed, the coaxial antenna itself undergoes a buckling deformation under the load from the agglomerate, It is preferable to have strength that does not bend in the transport direction. The central conductor 123a of the coaxial antenna 123 can be formed using the same metal as that of the outer peripheral conductor 123b.

In addition, since the microwave output from the coaxial antenna 123 is set to be in the order of kW, if a substance having a high electrolytic density and a dielectric loss is used as the material of the spacer 123c, the spacer 123c becomes a microwave. May absorb and self-heat. Moreover, since the use atmosphere of the coaxial antenna 123 is assumed to be 100 ° C. to 200 ° C., a support plate made of Teflon (registered trademark) or the like cannot be used. Therefore, the spacer 123c is preferably formed using a ceramic having a low dielectric loss (for example, a ceramic having a dielectric loss coefficient ε _r ″ of less than 0.02). As an example of such a ceramic, alumina (Al ₂ O ₃ ), silicon nitride (Si ₃ N ₄ ), sialon (SiAlON, chemical formula: Si ₃ N ₄ .Al ₂ O ₃ ), aluminum nitride (AlN), boron nitride (BN), etc. The spacer 123c may be manufactured by using alone, or the spacer 123c may be manufactured by mixing these ceramics.

  The inside of the raw material layer of the drying furnace 5 has a temperature of about 80 ° C. or higher at the lower layer portion and is in a high temperature and high humidity state having a humidity close to about 100%, and the agglomerated material is moving under such conditions. . Therefore, in order to prevent the occurrence of arcing due to moisture entering the inside of the coaxial antenna 123, and to prevent the dust from entering the inside of the coaxial antenna 123, a dust-proof gas such as dry air, dry nitrogen or dry argon is used. Is preferably introduced into the hollow coaxial antenna 123 (the central conductor 123a and the outer conductor 123b) so that a positive pressure is applied to the coaxial antenna 123.

  Moreover, since the front-end | tip part (especially protrusion part of the center conductor 123a) of the coaxial antenna 123 collides with what agglomerated material and the agglomerated material pulverized, and friction arises between these, protection It is preferable to do. Therefore, as shown in FIGS. 7 and 8, it is preferable to provide a ceramic cover 125 at the tip of the coaxial antenna 123 to protect the tip of the coaxial antenna 123.

The ceramic cover 125 uses an inorganic material ceramic that has a low absorption of microwaves as a heating source, can be used even in a high temperature and high humidity state, and has strength, wear resistance, and workability that can withstand contact with the agglomerated material. It is formed. The inorganic material ceramic used for the ceramic cover 125 preferably has a dielectric loss coefficient ε _r ″ related to microwave absorption characteristics of less than 0.02. The dielectric loss coefficient ε _r ″ is less than 0.02. This makes it possible to suppress self-heating of the inorganic material ceramics due to microwave absorption.

Examples of such inorganic material ceramics include alumina (Al ₂ O ₃ ), silicon nitride (Si ₃ N ₄ ), sialon (SiAlON, chemical formula: Si ₃ N ₄ · Al ₂ O ₃ ), aluminum nitride (AlN), Examples include boron nitride (BN). The ceramic cover 125 may be manufactured by using these inorganic material ceramics alone, or the ceramic cover 125 may be manufactured by mixing these inorganic material ceramics.
Here, the shape of the ceramic cover 125 may be a half dome shape as shown in FIG. 7 or a cylindrical shape.

  In this embodiment, the coaxial antenna 123 is inserted from above the drying furnace 5 to such a depth that the heating range of the coaxial antenna 123 reaches the lowest layer of the raw material layer. By inserting the coaxial antenna 123 into the raw material layer in this way, it is possible to selectively heat the agglomerate located in the lower layer portion of the raw material layer by the microwave energy irradiated from the tip of the coaxial antenna 123. Become.

  That is, in this embodiment, the microwave is radiated inside the raw material layer (lower layer part), so that most of the radiated microwave energy is absorbed by the raw material around the radiation point and used for heating the raw material. It is a heating method with high energy efficiency of heating.

  In the present embodiment, when a plurality of coaxial antennas 123 that are the microwave irradiation members 109 are disposed in the width direction of the drying furnace 5, the agglomerated material is disposed in the furnace width direction of the drying furnace 5 by the plurality of disposed coaxial antennas 123. In order to heat uniformly, at least two of the plurality of coaxial antennas 123 are arranged at different positions in the furnace width direction of the drying furnace.

  In addition, in order to prevent the arranged coaxial antennas 123 from becoming a resistance to the flow of the agglomerated material, for example, as shown in FIG. 9, conveyance of coaxial antennas at positions adjacent to each other in the projection view shown in FIG. The direction position should not be the same. That is, in the view of the drying furnace 5 shown in FIG. 9, the width direction of the drying furnace 5 is divided into five regions A to E for convenience, the feed direction of the raw material layer is the X direction, The width direction is the Y direction. In this case, in the present embodiment, the coaxial antennas 123 are distributed and arranged so that the X-direction positions of the coaxial antennas 123 belonging to adjacent regions (for example, the region A and the region B) are not the same.

  In the present embodiment, when a plurality of coaxial antennas 123 are arranged in the width direction of the drying furnace 5, for example, when the drying furnace 5 is viewed in the transport direction as shown in the projection view of FIG. 10. The coaxial antennas 123 are preferably arranged at intervals such that the ranges (heating ranges) heated by the respective coaxial antennas 123 cover substantially the entire width of the drying furnace 5. At this time, it is preferable to determine the arrangement interval of the coaxial antennas 123 so that the heating ranges of the coaxial antennas 123 overlap each other. In other words, the maximum width of the heating range by the single coaxial antenna 123 is L, the width of the drying furnace 5 is W, and the number of coaxial antennas in the width direction of the drying furnace 5 in the projection view shown in FIG. In this case, it is preferable to determine the maximum number of coaxial antennas in the width direction of the drying furnace 5 so as to satisfy L × N ≧ W.

Specifically, when 10 times the microwave penetration depth δ shown in the above equation 12 is considered as the effective heating range δ _eff , the maximum width L of the heating range by the single coaxial antenna 123 is 2 ×. It is preferable to determine the arrangement interval in the width direction of the coaxial antenna 123 so that δ _{eff and} the distance between the respective coaxial antennas adjacent in the width direction is L or less. By arranging the coaxial antennas 123 at such intervals, the agglomerated material for the entire width of the drying furnace can be heated evenly.

  When the interval between the plurality of coaxial antennas is larger than L, the heating range by the microwave does not reach the entire width of the furnace, and heating unevenness of the agglomerated raw material is generated in the width direction of the furnace. It is not desirable to be connected. However, since the drying of the raw material is improved in the portion heated by the microwave, the drying as the average value of the entire raw material is improved according to the number of inserted coaxial antennas.

  Also, if the efficiency of hot air drying in the furnace width direction is different as the characteristics of the drying furnace, insert a coaxial antenna only in the part where drying efficiency is inferior and drying of the agglomerated raw material is delayed, and microwave irradiation Is also effective.

  Further, how the coaxial antennas 123 are arranged is not particularly limited. For example, the coaxial antennas 123 are coaxial so that the deviation can be eliminated based on knowledge about the residual moisture unevenness in the drying furnace 5. What is necessary is just to determine the arrangement | positioning position of an antenna. Therefore, for example, in FIG. 9, a plurality of coaxial antennas 123 may be disposed in the same region.

  For example, as shown in FIG. 11, a tapered portion 127 whose width becomes narrower toward the upstream side in the transport direction may be provided on the end of the coaxial antenna 123 on the upstream side in the transport direction. By providing such a tapered portion 127, it becomes possible to further reduce the agglomerated material transport resistance by the coaxial antenna 123. Further, the tapered portion 127 may be provided not only on the end portion on the upstream side in the transport direction of the coaxial antenna 123 but also on the end portion on the downstream side in the transport direction.

  The microwave drying apparatus 10 and the microwave drying method according to the first embodiment of the present invention have been described in detail above with reference to FIGS.

<Modification of First Embodiment>
Next, a modification of the microwave irradiation member according to the first embodiment of the present invention will be described with reference to FIGS. 12 to 13B. FIGS. 12-13B is explanatory drawing for demonstrating the modification of the microwave irradiation member which concerns on the 1st Embodiment of this invention.

[Method of disposing the coaxial antenna in the material layer conveying direction]
First, a method for arranging the coaxial antenna according to the present modification in the raw material layer transport direction will be described with reference to FIG.

The time t during which the agglomerated material transported inside the drying furnace 5 is heated by the microwaves radiated from one coaxial antenna 123 according to this modification is the heating range (2 × δ) of the coaxial antenna 123. _eff ) is W (mm) and the agglomerated material transport speed is V [mm / sec], which is approximately (W / V) seconds.

  On the other hand, when a microwave is guided using a coaxial antenna, the diameter of the coaxial antenna is set to be small so that a plurality of propagation modes do not occur inside the antenna and the microwave transmission efficiency is maintained. Often accompanied by conditions related to the wavelength of the wave. As a result, it is difficult to set the diameter of the coaxial antenna 123 to an arbitrary size. Therefore, it is conceivable that the heating time t becomes a certain value.

  In order to sufficiently dry the agglomerate with microwaves during such a predetermined time, it is conceivable to use a microwave with a high output intensity as one of the measures. However, the agglomerates that exist around the coaxial antenna and are heated by microwaves are not necessarily heated uniformly because of differences in heating depending on the position of the agglomerates. In addition, when trying to obtain drying in a short time using a high-power microwave, some agglomerates may be overheated and the volatile components contained in the agglomerates may ignite. is there. Therefore, in order to sufficiently dry the agglomerate by microwave, the microwave is used so that the agglomerate does not overheat, and the microwave action time is lengthened to promote drying. It is important to plan.

  Therefore, in the present modification, for example, as shown in FIG. 12, the coaxial antenna 123 is arranged side by side in the material layer conveyance direction so that the heating range of the coaxial antenna 123 continues in the material layer conveyance direction. By adopting such an arrangement method of the coaxial antenna, it is possible to lengthen the section where the microwave is irradiated, and thus, it is possible to lengthen the action time of the microwave on the agglomerated material. .

  Here, the arrangement method of the coaxial antennas 123 in the transport direction is not particularly limited as long as the heating ranges of the coaxial antennas 123 adjacent to each other in the transport direction are continuous. They may be in contact or separated from each other. In addition, when arrange | positioning adjacent coaxial antenna 123 apart, it is preferable to provide a cover etc. so that an agglomerate may not block in the space between adjacent coaxial antennas 123. FIG.

  FIG. 12 illustrates the case where two coaxial antennas 123 are continuously arranged in the transport direction. However, three or more coaxial antennas 123 may be continuously arranged in the transport direction. Needless to say.

[Vibration relaxation mechanism]
Next, with reference to FIGS. 13A and 13B, a technique for mitigating vibration generated in the coaxial antenna 123 accompanying the transport of the agglomerated material will be described.

  In the microwave drying apparatus 10 according to the first embodiment of the present invention and the modification thereof, the agglomerated material is stacked on a mesh conveyor to form a raw material layer, and then conveyed from the upper part to the lower part of the raw material layer. For the drying furnace that dries the agglomerate by passing hot air toward the same, insert the coaxial antenna 123 from above the drying furnace and irradiate the raw material layer lower layer with microwaves, and the corresponding part It is a device that promotes drying.

  At this time, the coaxial antenna 123 inserted from above the drying furnace 5 is subjected to a stress that varies as the agglomerated material is conveyed. The stress acting on the coaxial antenna fluctuates because the transport speed by the mesh conveyor is not constant but slightly fluctuates, and the density of the agglomerates is not strictly uniform, so the agglomeration contacting the coaxial antenna It is conceivable that the state of the chemical compound changes from moment to moment with the conveyance. When such fluctuating stress acts on the coaxial antenna 123, the coaxial antenna 123 is vibrated in the raw material layer conveyance direction. When considering long-term use of the coaxial antenna under such circumstances, there is a concern that such vibration may cause fatigue damage of the waveguide 111 and the coaxial antenna 123.

  Therefore, in the microwave drying apparatus 10 according to the present modification, a vibration mitigation mechanism for mitigating vibrations generated along with the transportation of the agglomerated material is installed in the waveguide 111 located on the upstream side of the converter 121. To do. Examples of such a vibration relaxation mechanism include the following two types of mechanisms.

  As a first vibration mitigation mechanism, a waveguide having a mechanism for mitigating vibration may be provided in the waveguide 111 that guides the microwave generated by the microwave oscillator 101.

  As a waveguide including a mechanism for reducing vibration, for example, a waveguide having a slide mechanism that enables sliding in the central axis direction of the waveguide (hereinafter referred to as a slide waveguide), or a microwave. For example, a waveguide having a bellows portion formed of a metal material capable of being guided (more preferably, a metal material similar to the waveguide) (hereinafter referred to as a flexible waveguide).

  Since the slide waveguide has a slide mechanism, it can expand and contract in the central axis direction of the waveguide, so that vibration substantially parallel to the central axis direction of the waveguide can be mitigated. In addition, since the flexible waveguide has a metal bellows portion, it can be bent in a direction substantially orthogonal to the central axis direction of the waveguide. On the other hand, it is possible to mitigate vibrations in a direction substantially perpendicular to the direction.

  Further, as the second vibration relaxation mechanism, an elastic member may be provided on a part of the support that supports the coaxial antenna 123 that is a microwave irradiation member. By providing an elastic member such as a spring mechanism or a rubber member on a part of the support, vibration generated in the coaxial antenna 123 supported by the support can be reduced by the elastic member.

  By providing the vibration mitigation mechanism as described above, it becomes possible to mitigate vibrations generated along with the transportation of the agglomerated material, and to prevent the waveguide 111 and the coaxial antenna 123 from being fatigued. it can.

  FIG. 13A shows that a flexible waveguide 161 is installed as a first vibration mitigating mechanism with respect to the waveguide 111 positioned on the upstream side of the converter 121, and one of the supports 163 is used as a second vibration mitigating mechanism. An example in which an elastic member 165 made of, for example, a spring mechanism is provided in the part is shown.

  In the example shown in FIG. 13A, the waveguide 111 extending from the microwave oscillation mechanism such as the microwave oscillator 101, the circulator 103, and the automatic matching unit 107 is located upstream of the converter 121. In addition, a flexible waveguide 161 is installed in a part of the waveguide extending in the vertical direction. As described above, the flexible waveguide 161 relieves vibrations in a direction substantially orthogonal to the axial direction of the waveguide, and therefore is inserted into the drying furnace 5 as shown in FIG. 13A. Therefore, it is preferable to be installed in a part of the waveguide 111 provided in a substantially vertical direction.

  In FIG. 13A, an elastic member 165 including a spring mechanism is provided on a part of a support body 163 that supports the coaxial antenna 123 and extends in the horizontal direction. The spring mechanism is a mechanism that relieves stress by expanding and contracting the spring in the direction of the central axis of the spring.

  As shown in FIG. 13A, the ends of the microwave oscillation mechanism and the support 163 are fixed to a strong member such as a wall. In addition, by installing the flexible waveguide 161 and the elastic member 165 as described above, the converter 121 and the coaxial antenna 123 positioned downstream of the flexible waveguide 161 and in front of the elastic member 165 are structured. Separated and can move freely to some extent. In addition, it is preferable to provide an embedding material 167 for maintaining the airtightness of the drying furnace 5 while allowing the coaxial antenna 123 to move to some extent while inserting the coaxial antenna 123 into the drying furnace 5.

  FIG. 13B shows an example in which a slide waveguide 169 is installed instead of the flexible waveguide 161 shown in FIG. 13A. As described above, the slide waveguide 169 relaxes the vibration in the axial direction of the waveguide, and as shown in FIG. 13B, the slide waveguide 169 extends in a substantially horizontal direction on the upstream side of the converter 121. It is preferable to be installed in a part of the waveguide 111.

  13A and 13B illustrate the case where one of the flexible waveguide 161 and the slide waveguide 169 is provided for one waveguide 111, the flexible waveguide 161 and the slide are illustrated. A waveguide 169 may be used in combination. 13A and 13B illustrate the case where one flexible waveguide 161, elastic member 165, and slide waveguide 169 are used, these members are illustrated as one waveguide 111 and coaxial antenna 123. A plurality of them may be installed.

  13A and 13B illustrate the case where the flexible waveguide 161 or the slide waveguide 169 and the elastic member 165 are used together, but depending on the agglomerated material transport speed, the elastic member Instead of using 165, only the flexible waveguide 161 or the slide waveguide 169 may be provided.

  13A and 13B, the mechanism for structurally separating the coaxial antenna that receives the fluctuating stress has been described. However, the entire coaxial antenna 123 including the microwave oscillation mechanism is made movable to reduce vibration. It is also possible to do so.

  In the above, the modification of the microwave irradiation member which concerns on the 1st Embodiment of this invention was demonstrated, referring FIGS. 12-13B.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Microwave dryer 101 Microwave oscillator 103 Circulator 105 Isolator 107 Automatic matching device 109 Microwave irradiation member 121 Converter 123 Coaxial antenna 123a Center conductor 123b Outer periphery conductor 123c Spacer 125 Ceramics cover 127 Tapered part 161 Flexible waveguide 163 Support Body 165 Elastic member 167 Embedding material 169 Slide waveguide

Claims (14)

A microwave drying apparatus installed in a hot-air drying furnace that reduces moisture contained in the material to be dried by transporting the material to be dried by hot air when the material is conveyed by a conveyor. And
A microwave oscillator that oscillates a microwave used to dry the object to be dried;
A heating range in which the object to be dried is heated by the microwave is inserted into the inside of the object layer to be dried that is transported to a depth including the lowest layer of the object to be dried, and A plurality of coaxial antennas for irradiating the microwaves with respect to the dry matter;
With
At least two of the plurality of coaxial antennas are arranged at different positions in the furnace width direction of the drying furnace,
The microwave drying apparatus according to claim 1, wherein positions of the coaxial antennas adjacent to each other in the furnace width direction are different from each other in the transport direction. The plurality of coaxial antennas are arranged in the furnace width direction such that the heating range of each of the coaxial antennas covers the whole furnace width direction of the drying furnace as the whole of the plurality of coaxial antennas. The microwave drying apparatus according to claim 1. The coaxial antenna is
A central conductor which is a hollow or solid metal tube;
An outer peripheral conductor which is a hollow metal tube provided further outside the central conductor;
Have
The end portion of the center conductor on the object layer side is one fourth of the wavelength of the microwave propagated in the coaxial antenna than the end portion of the outer conductor on the object layer side. The microwave drying apparatus according to claim 1, wherein the microwave drying apparatus protrudes by a corresponding length. 4. The ceramic cover according to claim 1, wherein a ceramic cover made of an inorganic material ceramic having a dielectric loss coefficient of less than 0.02 is provided at a distal end portion of the coaxial antenna. Microwave dryer. The center conductor and the outer peripheral conductor of the coaxial antenna are fixed to each other by a spacer formed of an inorganic material ceramic having a dielectric loss coefficient of less than 0.02. 3. The microwave drying apparatus according to 3. The microwave drying apparatus according to any one of claims 1 to 5, wherein the coaxial antenna is provided with a vibration mitigation mechanism for mitigating vibration generated along with the conveyance of the object to be dried. . As the vibration relaxation mechanism, a slide waveguide having a slide mechanism that enables axial sliding between the coaxial antenna and the microwave oscillator, or a flexible waveguide having a metal bellows portion. At least any one of these is arrange | positioned, The microwave drying apparatus of Claim 6 characterized by the above-mentioned. The microwave drying apparatus according to claim 6 or 7, wherein an elastic member is provided as a part of a support that supports the coaxial antenna as the vibration relaxation mechanism. The microwave drying apparatus according to any one of claims 1 to 8, wherein the coaxial antennas are arranged side by side in the transport direction so that the heating range is continuous in the transport direction. 10. The dust-proof gas according to claim 1, wherein a dustproof gas is introduced into the coaxial antenna, and a positive pressure is applied to the coaxial antenna. Microwave dryer. The taper portion in which an area of a cross section perpendicular to the transport direction becomes smaller toward the upstream side in the transport direction is provided at an end portion on the upstream side in the transport direction of the coaxial antenna. The microwave drying apparatus of any one of these. Between the microwave oscillator and the plurality of coaxial antennas, the impedance of the microwave oscillated from the microwave oscillator, and the microwave reflected in the drying furnace and directed to the microwave oscillator The microwave drying apparatus according to any one of claims 1 to 11, further comprising an automatic matching device for matching with impedance. The microwave drying apparatus according to claim 4 or 5, wherein the inorganic material ceramics is selected from the group consisting of alumina, silicon nitride, sialon, aluminum nitride, boron nitride, and a mixture thereof. This is a microwave drying method implemented in a hot-air drying furnace that reduces moisture contained in the material to be dried by conveying the material to be dried with hot air when the material to be dried is conveyed by a conveyor. And
Oscillates a microwave used to dry the object to be dried;
A plurality of heating ranges in which the object to be dried is heated by the microwave are inserted to the depth including the lowermost layer of the object to be dried, with respect to the inside of the object to be dried composed of the object to be dried being conveyed. Each of the coaxial antennas irradiates the microwave to the layer to be dried,
At least two of the plurality of coaxial antennas are arranged at different positions in the furnace width direction of the drying furnace,
The microwave drying method, wherein positions of the coaxial antennas adjacent to each other in the furnace width direction are different from each other in the transport direction.

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