JP6225433B2 - Drying furnace and drying method - Google Patents

Description

  The present invention relates to a drying furnace and a drying method for drying an object to be dried by using hot air blowing and microwave irradiation in combination.

  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 from above, the lower layer portion (portion close to the wire mesh conveyor) of the small mass raw material that is to be dried is used. 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, there is a demand for selectively improving the drying of the lower layer portion where moisture remains, not the upper layer portion that is sufficiently dried.

  For example, as shown in Patent Document 2, there is an apparatus that has a stirring blade in a cylindrical drum and uniformly dries garbage using hot air and microwaves in combination.

  However, in drying a small lump raw material, a conveyor for conveying the small lump raw material, which is a heavy object, is necessary, and in the apparatus structure in which the object to be dried is lifted with a stirring blade as disclosed in Patent Document 2 above. In addition, it is impossible to transport the small mass raw material and drying is impossible. Although it may be possible if the stirring blade is made to have a considerable strength, a dryer having such a stirring blade is not practical because of high equipment costs.

  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 3.)

JP-A-2005-113197 JP 2001-56178 A 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 250 mm. Therefore, as described in Patent Document 3, when microwaves are applied to the free space in the furnace, it is possible to cause microwaves to act on the upper layer portion of the agglomerate layer. As will be described in detail, as a result of the examination by the present inventors, it was found that microwaves cannot act on the lower layer portion of the agglomerated material, and moisture in the layer direction cannot be dried uniformly. .

  In addition, the conveyor for conveying the agglomerated material that is heavy is a metal net, smaller than the agglomerated material, that is, a mesh of about 20 mm, so from the back surface of the conveyor to the lower layer part of the agglomerated material, Even if a microwave with a frequency of 2.45 GHz, which is a general microwave used in industrial heating, is irradiated, the microwave is reflected by the wire mesh, and the microwave 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 provide a moisture content in a layer direction of an object to be dried that is charged into a drying furnace using a microwave. It is an object of the present invention to provide a drying furnace and a drying method that can be dried so that the distribution of water is uniform.

In order to solve the above problems, according to an aspect of the present invention, there is provided a drying oven to reduce the moisture content of the material to be dried in bulk comprising iron oxide material and a reducing material, by laminating the material to be dried a mesh-like metal conveyor for conveying, waveguide for illuminating the hot air drying device blowing hot air to the object to be dried, a microwave oscillator which oscillates microwave, the microwave for the previous SL dried objects The to- be-dried object is laminated thicker than a range in which microwave heating penetrates, and the hot air drying device is disposed on the to-be-dried object from below the to-be-dried object. The hot air is blown over the waveguide, and the waveguide is provided with a drying furnace that irradiates the microwave to the object to be dried from above the object to be dried .

A plurality of the waveguides are provided so that a microwave irradiation range by the waveguide extends over the entire furnace width of the drying furnace, and at least two of the plurality of the waveguides have a furnace width of the drying furnace. It is preferable that they are arranged at different positions in the direction.

  The plurality of waveguides are arranged in the furnace width direction at intervals such that the heating range of each of the waveguides covers the entire furnace width direction of the drying furnace as the plurality of waveguides as a whole. Is preferred.

The waveguide includes a conveying direction position where blowing hot air to the stacked the material to be dried is completed, the conveying direction position in which the microwave irradiation is completed to laminated the material to be dried is matched Thus, it is preferable to arrange in the transport direction.

  At the position in the conveyance direction immediately before the microwave irradiation, the more the number of waveguides in series in the conveyance direction of the object to be dried, the more the moisture content remaining in the object to be dried is in the furnace width direction position. May be arranged.

  A ceramic cover made of an inorganic material ceramic having a dielectric loss coefficient of less than 0.02 is preferably provided at the tip of the waveguide.

  It is preferable that a dustproof gas is introduced into the waveguide, and a positive pressure is applied to the inside of the waveguide.

  Between the microwave oscillator and the waveguide, the impedance of the microwave oscillated from the microwave oscillator and the impedance of the microwave reflected in the drying furnace and directed to the microwave oscillator It is preferable to further include an automatic aligner for performing the above.

  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 above-mentioned problem, according to another aspect of the present invention, there is provided a drying method in a drying furnace for reducing the moisture content of a massive object to be dried containing an iron oxide raw material and a reducing material , which has a mesh shape. of using a metal conveyor, wherein the step of transporting by stacking material to be dried, only with blowing hot air to the material to be dried using a hot-air drying apparatus, and generating microwaves using the microwave generator, guide Irradiating the object to be dried with a wave tube, and the object to be dried is laminated thicker than a range in which microwave heating penetrates. The hot air is blown onto the object to be dried from below the object to be dried through the metal conveyor, and the waveguide applies the microwave to the object to be dried from above the object to be dried. An irradiation drying method is provided.

  As described above, according to the present invention, hot air is blown over the conveyor from below on the object to be dried, and the microwave irradiation member provided above the object layer is irradiated with microwaves, It becomes possible to uniformly dry the moisture of the material to be dried charged in the drying furnace in the layer direction.

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 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 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 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 hot air. It is explanatory drawing for demonstrating the examination result regarding the heating method using a hot air. It is explanatory drawing for demonstrating the examination result regarding the heating method using a hot air. 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 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 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 embodiment of this invention. It is explanatory drawing which showed the outline of the microwave drying apparatus which concerns on embodiment of this invention. It is explanatory drawing shown about the modification of the waveguide which irradiates the microwave which concerns on the embodiment. It is explanatory drawing shown about the modification of the waveguide which irradiates the microwave which concerns on the embodiment. It is explanatory drawing shown about the modification of the waveguide which irradiates the microwave which concerns on the 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 drying furnace 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 or the like heats the agglomerated material charged in a heating atmosphere such as an LNG burner or a COG burner. Reduced to iron. 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. It is of a size. By laminating such agglomerates to a height of about 250 mm, a load of about 300 kg / m ² is applied to the mesh conveyor. 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.

  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 portion of the agglomerate layer is dried, but the lower layer It was revealed that the amount of moisture remaining was large at the site (the site close to the mesh conveyor), and the agglomerated material at the lower site was 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.

  Then, the present inventors examined the method of improving the drying of the agglomerate layer on the leeward side of the hot air and drying the layer direction uniformly. For example, the following issues are considered.

That is, since the floor surface of the drying furnace is a mesh-like conveyor using metal, when the microwave is simply irradiated from below the conveyor as schematically shown in FIG. It is reflected by the conveyor and the agglomerated material cannot be heated. It is also conceivable to change the material of the conveyor to a material that absorbs less microwaves, such as Teflon or nylon, but such a material cannot withstand a load of about 300 kg / m ² . 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.

  Also, as schematically shown in FIG. 4, when microwaves are irradiated from above the agglomerate layer, the range of heating by the microwave is at most from the outermost layer to the second layer. It has been clarified in the examination described below that only the upper layer portion of the agglomerate layer is heated and does not contribute to the drying of the lower layer portion of the agglomerate layer and the uniform distribution of water content.

  Therefore, it is necessary to devise a method of heating uniformly over the entire thickness of the agglomerated layer by hot air and microwaves. Therefore, the present inventors first analyzed and experimented in detail the heating behavior of the agglomerates by microwaves. Prior to describing the drying furnace according to the embodiment of the present invention, various examination results for the method of drying an agglomerate using microwave heating by the present inventors will be described with reference to FIGS. I will explain it.

<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. 5 schematically shows an experimental apparatus for verifying the range covered by microwave heating when the agglomerated material (briquette) to be dried is irradiated with microwaves from above. .

  As shown in FIG. 5, the present inventors laminated an undried briquette (used in actual operation) of about 40φ × 20 mm on a metal container (cylindrical container) and placed it in the chamber. In the cylindrical container, as shown in FIG. 6, undried briquettes were laminated over 6 layers. At this time, thermocouples were inserted into the briquettes 1 to 6 located in the central part of the metal container shown in FIG. 6 so that the temperature increase could be monitored. In addition, a 3.0 kW microwave oscillator capable of irradiating a microwave of 2.45 GHz, a power monitor capable of measuring an incident microwave output to the chamber and a reflected microwave output, and to reduce the reflected microwave The auto-matching device (auto tuner) was connected with a waveguide, and the microwave output from the auto-matching device was irradiated from above the chamber through the waveguide. In this experiment, the microwave incident power was 880 W, and the microwave irradiation time was 5 minutes.

  The measurement result of temperature is shown in FIG. In the thermocouple inserted in the briquette 6 located in the uppermost layer shown in FIG. 6, a clear temperature rise was confirmed, and in the briquette 5 located in the second layer from the upper layer, a temperature rise was confirmed although not as much as the briquette 6. It was. However, the briquette located in the lower layer could not confirm the temperature rise. 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]
ε0: Dielectric constant in vacuum [F / m]
ε ″: Imaginary part of relative permittivity of heated material μ0: 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, It is possible to absorb more microwave energy in the oxide and the carbon material (reducing material).

  However, in the experimental situation of irradiating the free space in the furnace with microwaves as shown in FIG. 5, the microwaves irradiated from above are absorbed very well by the agglomerates located in the upper layer part, It is considered that the microwave does not penetrate into the lower layer portion that requires heat supply for promoting drying. Therefore, when the microwave is irradiated from the furnace ceiling portion toward the space in the furnace, the agglomerate located in the lower layer portion cannot be heated.

  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.

In the above equation 12, tan δ can be calculated as (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 size is about 0.5 cm, and therefore the effective heating range δ _eff by microwave heating is about 5 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.

  In FIG. 7, a slight temperature increase is also observed in briquettes 1, 2, 3, and 4. However, from the above examination, these temperature increases are not due to direct action of microwaves, but are due to heat transfer from the upper briquette. It can be said that it is a thing.

  In order to uniformly dry the moisture amount in the layer direction of the agglomerated layer, it is necessary to selectively irradiate the undried portion of the agglomerated layer with microwaves. Assuming that microwaves are irradiated from above the agglomerate layer, it is necessary to create a distribution in which an undried portion exists in the upper layer of the agglomerate layer by drying with hot air alone. Therefore, as a result of further studies based on the knowledge obtained by the experiments as described above, the present inventors blow hot air into the agglomerate layer from below the drying furnace through the conveyor, I thought of a method that creates a distribution in which the lower layer part of the material is dried and the upper layer part is undried, creating a situation in which a large amount of undried agglomerated raw material remains in the microwave heating range. is there.

  Conventionally, in drying agglomerates, the drying method in which hot air is blown through the conveyor from below the agglomerate layer has poor drying efficiency due to loss of heat in the conveyor, and the advantage of adopting drying with hot air alone is also motivated Does not exist. However, in combination with drying by microwave irradiation from above the agglomerate layer, hot air drying through a conveyor is an effective method for uniformly drying the moisture distribution in the layer direction.

  Therefore, the drying behavior by blowing hot air from below the agglomerate layer was investigated using the apparatus shown in FIG. Connected to the lower part of the metal container (cylindrical container) is a pipe for blowing hot air created by a blower and a heater, and the bottom is meshed to simulate the metal conveyor installed in the drying furnace 5 It was. In this experiment, the hot air temperature was 120 ° C., the hot air flow rate was 30 L / min, and the hot air drying time was 60 minutes. In the cylindrical container, as shown in FIG. 9, undried briquettes were laminated over six layers.

  The temperature measurement results are shown in FIG. The temperature gradually increased from the briquette 1 located in the lowermost layer shown in FIG. 9, and the temperature increase tended to gradually decrease as the upper layer was reached.

  As schematically shown in FIG. 11, if microwaves are irradiated from above the agglomerate layer in a situation where hot air is blown into the briquette from below, the upper undried region as shown in the following experiment On the other hand, it is possible to improve drying by microwave and to dry the agglomerated layer with a uniform amount of moisture in the layer direction.

  Therefore, it was confirmed that the water content in the layer direction can be made uniform by blowing hot air from below the agglomerate layer and irradiating microwaves from above the agglomerate layer with the apparatus shown in FIG. At this time, a 3.0 kW microwave oscillator capable of irradiating a 2.45 GHz microwave, a power monitor capable of measuring an incident microwave output to the chamber and a reflected microwave output, and a method for reducing the reflected microwave An automatic matching device (auto tuner) was connected to the waveguide, and the microwave output from the automatic matching device was irradiated from above the chamber through the waveguide. In addition, a pipe for blowing hot air generated by a blower and a heater is connected to the lower part of the metal container, and the bottom surface has a mesh structure to simulate a metal conveyor installed in the drying furnace 5. In this experiment, the hot air temperature was 120 ° C., the hot air flow rate was 30 L / min, and the hot air drying time was 60 minutes. The microwave incident power was 880 W, and the microwave irradiation time was 5 minutes at the end of hot air drying.

  The measurement result of temperature is shown in FIG. A temperature increase was observed from briquette 1 located in the lowermost layer shown in FIG.

  FIG. 15 shows the water content of each briquette after the experiment. The moisture content after the experiment has a distribution that reflects the temperature rise of each briquette. In the hot air alone drying from the bottom, the drying proceeds well in the lower layer of the briquette layer, and in the microwave alone drying from the top The drying is progressing well in the upper layer of the briquette layer. Furthermore, it was shown that the distribution of water content in the direction of the briquette layer approaches uniformly by performing drying by combining hot air drying from below and microwave drying from above.

  In producing the agglomerated product, starch-based paste such as corn starch is used as a binder to achieve the required strength. However, the starch paste becomes stronger as it is dried. 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, the microwave used in the drying furnace 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. In the embodiment of the present invention described below, the frequency of electromagnetic waves is not particularly limited. For example, the IMS band is 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 a frequency belonging to the 24 GHz band (24.0 GHz to 24.25 GHz), or an ISM band, but an 915 MHz band (902 MHz to 928 MHz) or the like with an inexpensive oscillator can be appropriately selected. However, since the penetration of the microwave into the object to be heated is proportional to the wavelength of the microwave as expressed by the above equation 12, the penetration depth δ in the 915 MHz band and the 2.45 GHz band is in the above microwave. The raw briquettes can be heated from the upper layer to a deeper depth. In addition, 915 MHz and 2.45 GHz have the equipment cost of the present invention that requires a high output of kW class because of the low cost of the apparatus and the ability to radiate a high output up to several tens of kW with one oscillator. However, it can be introduced at a low cost. For this reason, the microwave device used in the present invention is preferably one that can oscillate 915 MHz or 2.45 GHz microwave.

(Embodiment)
Subsequently, a drying furnace according to an 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 drying furnace according to the present embodiment will be described in detail with reference to FIG. FIG. 16 is an explanatory diagram for explaining a configuration of a drying furnace according to the present embodiment.

  The microwave drying apparatus installed in the drying furnace according to the present embodiment is a process in which a powder or small block raw material (substance to be dried) is conveyed by a metal mesh conveyor from below the raw material. It is used for a hot air type tunnel drying furnace that reduces the moisture contained in the raw material by blowing hot air through the shape conveyor and passing the hot air from the lower side to the upper side of the raw material. This microwave drying apparatus is installed in a drying furnace so that microwaves can be applied to the raw material from above the raw material to be dried.

  The microwave drying apparatus 10 according to the present embodiment mainly includes a microwave oscillator 101, a circulator 103, and an automatic matching unit 107, and these devices are connected by a waveguide. Above the raw material in the drying furnace, connected to these devices, a microwave irradiation waveguide 111 (hereinafter also simply referred to as a waveguide 111) for irradiating the raw material layer with microwaves. ) Is installed.

  The microwave oscillator 101 is a device that oscillates a microwave having a frequency of 300 MHz to 300 GHz. The microwave oscillator 101 is preferably a device capable of oscillating microwaves having a kW class output. By this microwave oscillator 101, for example, a microwave having a frequency belonging to a band of 915 MHz or 2.45 GHz is applied to the waveguide 111 for irradiating the raw material layer in which the raw material to be dried is laminated. Will be output. 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 returns from the incident wave output from the microwave oscillator 101 and the automatic matching unit 107 described later. Separated into reflected waves. 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. As a result, the reflected microwave can be absorbed by a dummy load (for example, water) provided in the isolator 105 and not returned 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. For this reason, when the state of the moving small lump material changes and the impedance on the load side fluctuates, the microwave irradiation efficiency fluctuates. In this case, an automatic matching unit 107 is provided to automatically irradiate the raw material layer with the microwave energy from the waveguide 111 for irradiating the microwave, and the automatic matching unit 107 is adjusted to the impedance on the load side. A matching process may be performed.

  The waveguide connecting each device is a metal hollow tube that guides microwaves to a desired location. The shape of the waveguide may be determined as appropriate in consideration of the waveguide characteristics of the microwave, and the waveguide itself is also known depending on the frequency and output intensity of the microwave used. A thing can be selected suitably.

<About the structure of the waveguide for microwave irradiation>
Next, the configuration of the waveguide for irradiating the microwave according to the present embodiment will be described in detail with reference to FIGS. 17 to 20 are explanatory views showing a waveguide for irradiating microwaves according to the present embodiment.

  As illustrated in FIG. 17, in this embodiment, the waveguide 111 installed above the raw material layer (above the thickness direction of the raw material layer) is used as a microwave irradiation member. The cross-sectional shape of the waveguide 111 for irradiating the microwave (the cross-sectional shape in the direction parallel to the conveying direction of the raw material layer) and the size of the cross-section are to guide the microwave having a desired frequency and intensity For example, the cross-sectional shape is preferably rectangular (rectangular waveguide) or circular (circular waveguide).

  Inside the drying furnace 5, the hot air blown from below the raw material layer forms a dust environment above the raw material layer. Moreover, the furnace has a temperature of about 80 ° C. or higher 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 dust entering the inside of the waveguide 111 and to prevent moisture from entering the inside of the waveguide 111, dry air, dry nitrogen, dry argon, etc. It is preferable to introduce dustproof gas into the hollow waveguide so that a positive pressure is applied to the waveguide 111.

  Further, as illustrated in FIG. 18, a dustproof plate 112 made of ceramics is provided as a ceramic cover at the tip of the waveguide 111 for irradiating microwaves, and microwaves are emitted from the periphery of the dustproof plate. It is preferable to do so. Here, as shown in FIG. 18, the shape of the dustproof plate is a rectangular parallelepiped when the cross-sectional shape of the waveguide 111 is rectangular, and is cylindrical when the cross-sectional shape of the waveguide 111 is circular. It is preferable.

The dust-proof plate 112 is formed using an inorganic material ceramic that absorbs less microwaves as a heating source and can be used even in a high-temperature and high-humidity state. The inorganic material ceramics used for the dustproof plate 112 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 dustproof plate 112 may be manufactured by using these inorganic material ceramics alone, or the dustproof plate 112 may be manufactured by mixing these inorganic material ceramics.

  When the furnace width of the drying furnace 5 is wide and the agglomerate cannot be heated uniformly in the furnace width direction of the drying furnace 5 with only the single waveguide 111, the agglomerate is uniformly distributed in the furnace width direction of the drying furnace 5. In order to heat, for example, as shown in FIG. 19, at least two of the plurality of waveguides 111 are preferably arranged at different positions in the furnace width direction of the drying furnace.

  Further, as shown in FIG. 19, it is preferable to arrange the waveguides 111 at intervals such that the range (heating range) heated by each waveguide 111 covers the entire furnace width direction of the drying furnace 5. . At this time, it is preferable to determine the arrangement interval of the waveguides 111 so that the heating ranges of the respective waveguides 111 overlap each other.

  Specifically, since the heating efficiency of the agglomerated raw material is proportional to the square of the electric field strength, the electric field strength of the microwave from each waveguide 111 is obtained by electromagnetic field analysis using a finite element method or the like. The time average of the electric field strength at the intermediate portion of the wave tube 111 (intermediate portion between the waveguides adjacent to each other in the furnace width direction) is 63% or more of the time average of the electric field strength directly under each waveguide 111. If the furnace width direction distances of the respective waveguides 111 adjacent to each other in the furnace width direction are determined, the variation of the heating efficiency in the furnace width direction of the drying furnace 5 becomes ± 20% or less. It is preferable to arrange the waveguides 111 at such intervals. The electromagnetic field analysis method is not particularly limited, and any known method can be used.

  When the interval between the plurality of waveguides is larger than the interval determined above, uneven heating of the agglomerated raw material is generated in the furnace width direction, which leads to uneven drying of the raw material. 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 waveguides.

  In addition, as the characteristics of the drying furnace, the thickness of the raw material layer in the furnace width direction may be different, or the hot air flow rate may be distributed and the efficiency of hot air drying may be different in the furnace width direction. At this time, the position in the furnace width direction where the raw material layer is thick, or the position in the furnace width direction where the air volume is small and the drying efficiency is inferior and the moisture content remaining in the agglomerated raw material is large, compared to other positions. It is considered that the amount of water remaining in the agglomerated raw material increases. Therefore, the moisture remaining in the agglomerated raw material such as the position in the furnace width direction where the raw material layer is thick, or the position in the furnace width direction where the air volume is small and the drying efficiency is inferior and the water content remaining in the aggregating raw material is large It is also effective to install a large number of waveguides 111 in series along the furnace length direction and irradiate microwaves as the position in the furnace width direction increases.

  Further, how to arrange each waveguide 111 is not particularly limited. For example, based on knowledge about the uneven state of residual moisture in the drying furnace 5, the unevenness can be eliminated. What is necessary is just to determine the arrangement | positioning position of a waveguide. Therefore, for example, as shown in FIG. 20, a plurality of waveguides 111 may be provided in the same region in the furnace width direction.

  The position where the waveguide 111 is installed with respect to the furnace length direction of the drying furnace 5 (the conveying direction of the raw material layer) is preferably a position where the temperature of the agglomerated material is highest. In the drying of hot air alone, the amount of heat given to the agglomerated product by the hot air is expressed by the following equation (13).

Here, in the above equation 13,
Q: Heat flow per unit area [W / m ² ]
Ta: Hot air temperature [K]
Tb: surface temperature of agglomerated material [K]
h: Heat transfer coefficient [W / m ² K]
ε: Emissivity σ: Stefan Boltzmann coefficient [W / m ² K ⁴ ]
It is.

  As apparent from the above equation 13, as the agglomerated material is heated by the hot air and the surface temperature of the agglomerated material approaches the hot air temperature, the thermal energy from which the agglomerated material is obtained decreases.

  On the other hand, the energy given to the agglomerated material by the microwave is obtained by Equation 11, and does not depend on the temperature of the agglomerated material and hot air. Therefore, when heating agglomerates using hot air and microwaves, it is assumed that the total amount of heat given to the agglomerates by hot air and the total energy given to the agglomerates by microwaves are constant. Rather than irradiating the agglomerate with microwaves before the drying furnace where the temperature of the agglomerate is still sufficiently increased by hot air, microwaves are applied to the agglomerate while the agglomerate is sufficiently heated by the hot air. When irradiated, the sum of the hot air and microwave energy from which the agglomerated material is obtained is the largest, and the temperature of the agglomerated material is also the highest, so that drying proceeds most. This is because, when combined with heating with hot air and heating with microwaves at a position where the temperature increase of the agglomerates with hot air is still sufficiently performed, the temperature of the agglomerates is increased by heating with microwaves, This is because the amount of heat absorbed by the agglomerated material is reduced by the amount of heating by the microwave.

  Therefore, the installation position of the waveguide 111 with respect to the furnace length direction of the drying furnace 5 where the temperature of the agglomerated material becomes the highest is the latter stage of the drying furnace 5 (the latter stage in the furnace length direction), and hot air is blown onto the agglomerated substance. It is preferable that the conveyance direction position at which the agglomeration ends coincides with the conveyance direction position at which the microwave irradiation to the agglomerated material ends. By installing the waveguide 111 at such a position, the supply of energy by hot air and the supply of energy by microwaves are completed simultaneously.

  The drying furnace according to the embodiment of the present invention has been described in detail above with reference to FIGS.

  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 111 Waveguide 112 Dust-proof board

Claims (10)

A drying furnace for reducing the moisture content of a mass to be dried containing an iron oxide raw material and a reducing material ,
A mesh-like metal conveyor that conveys the object to be dried by stacking,
A hot air drying device for blowing hot air on the object to be dried;
And micro-wave oscillator for oscillating a microwave,
A waveguide for irradiating the microwave to the front SL material to be dried,
Have
The object to be dried is laminated thicker than the range where microwave heating penetrates,
The hot air drying device blows the hot air over the metal conveyor from below the object to be dried,
The drying furnace characterized in that the waveguide irradiates the object to be dried with the microwave from above the object to be dried . A plurality of the waveguides,
The drying furnace according to claim 1, wherein at least two of the plurality of waveguides are arranged at different positions in the furnace width direction of the drying furnace. The plurality of waveguides are arranged in the furnace width direction at intervals such that the heating range of each of the waveguides covers the entire furnace width direction of the drying furnace as the plurality of waveguides as a whole. The drying furnace according to claim 2, wherein: The waveguide includes a conveying direction position where blowing hot air to the stacked the material to be dried is completed, the conveying direction position in which the microwave irradiation is completed to laminated the material to be dried is matched The drying furnace according to any one of claims 1 to 3, wherein the drying furnace is arranged in the transport direction. At the position in the conveying direction immediately before the microwave irradiation, the more the number of waveguides arranged in series in the conveying direction of the object to be dried, the more the amount of moisture remaining in the object to be dried is in the furnace width direction position. The drying furnace according to any one of claims 1 to 4, wherein the drying furnace is provided. The ceramic cover made of an inorganic material ceramic having a dielectric loss coefficient of less than 0.02 is provided at a tip portion of the waveguide, according to any one of claims 1 to 5. Drying oven. The dust-proof gas is introduced into the inside of the waveguide, and a positive pressure is applied to the inside of the waveguide. The drying oven described. Between the microwave oscillator and the waveguide, the impedance of the microwave oscillated from the microwave oscillator and the impedance of the microwave reflected in the drying furnace and directed to the microwave oscillator The drying furnace according to any one of claims 1 to 7, further comprising an automatic aligner that performs the operation. The drying furnace according to claim 6, wherein the inorganic material ceramics is selected from the group consisting of alumina, silicon nitride, sialon, aluminum nitride, boron nitride, and a mixture thereof. A drying method in a drying furnace that reduces the moisture content of a mass to be dried containing an iron oxide raw material and a reducing material ,
Using a mesh metal conveyor, the step of laminating and transporting the object to be dried,
Installing blowing hot air to the material to be dried using a hot-air drying apparatus, a step of irradiating the microwaves with respect to generating microwaves, the material to be dried using a waveguide with a microwave oscillator ,
Including
The object to be dried is laminated thicker than the range where microwave heating penetrates,
The hot air drying device blows the hot air over the metal conveyor from below the object to be dried,
The drying method according to claim 1, wherein the waveguide irradiates the object to be dried with the microwave from above the object to be dried .