JP2014207195A - Microwave heating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microwave heating apparatus capable of allowing supplied gas and heating object to be sufficiently mixed while performing heat treatment of the heating object.SOLUTION: The microwave heating apparatus includes: a drum container that stores heating object 101; a rotation drive mechanism 111 that drives the drum container to rotate; a microwave generator 99 that emits microwave into the drum container; and a gas supply mechanism that supplies gas into the drum container. The gas supply mechanism has a gas injection port disposed facing to the inner wall of the drum container.

Description

  The present invention relates to a microwave heating apparatus.

  Microwave heating technology has been developed as a technology for warming food, and the household penetration rate of microwave ovens in Japan is 97.5% in 2009 (two or more households; nationwide consumption survey by the Ministry of Internal Affairs and Communications). , Has become one of the indispensable technologies in our lives.

Compared with conventional heating by far infrared rays or hot air, microwave heating is
-Since the substance is heated directly from the inside, the heating efficiency is good and high-speed heating is possible.

  -Selective heating is possible for materials such as polar substances that easily absorb microwaves.

  -Since the heating is from the inside of the material, the substance can be heated uniformly.

  ・ Because it is an energy transmission means by electromagnetic waves, it is hygienic without harming the work environment. Etc.

At present, from the above characteristics, it is industrially used in a wide range of fields such as drying of wood and the like, sterilization, sintering of ceramics, and synthesis of polymer materials. Among them, the microwave heating apparatus will be described using an example used for waste incineration. (For example, refer to Patent Document 1.)
FIG. 5 is an explanatory diagram showing the configuration of the microwave heating apparatus described in Patent Document 1. As shown in FIG. In the casing 2, a rotatable drum body 10 and a support roller 11 are provided. A plurality of stirring blades 19 are installed inside the drum body 10, and the waste 40 thrown into the drum body 10 is stirred. An inlet 31 as a gas supply system is connected to the lower part of the casing 2, and an exhaust gas purification means 35 is connected to the upper part of the casing 2. The microwave radiated from the magnetron 21 is applied to the waste 40 that is the object to be heated in the drum body 10. Thereby, the waste 40 can be heated.

JP 2004-183989 A

  However, in the above-described conventional configuration, since the inlet of the gas supply system is not provided toward the object to be heated, the gas is indirectly supplied to the object to be heated. There is a problem that the reaction with the supply gas is insufficient.

  The present invention solves the above-described conventional problems, and an object thereof is to provide a microwave heating apparatus in which a reaction between an object to be heated and a supply gas is sufficient.

  In order to achieve the above object, a microwave heating apparatus of the present invention includes a drum container that stores an object to be heated, a rotating mechanism that rotates the drum container, and a microwave generator that irradiates the drum container with microwaves. And a gas supply mechanism for supplying gas into the drum container, wherein the gas supply mechanism has a gas outlet provided facing the inner wall of the drum container.

  As described above, according to the present invention, it is possible to provide a microwave heating apparatus in which a reaction between an object to be heated and a supply gas is sufficient.

Schematic cross-sectional view of the microwave heating apparatus in the first embodiment Sectional schematic of the microwave heating apparatus in the other example of Embodiment 1 Sectional schematic of the microwave heating apparatus in further another example of Embodiment 1 Process diagram showing silicon wafer manufacturing and silicon recycling Schematic of the conventional microwave heating apparatus described in Patent Document 1

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
1 is a schematic cross-sectional view of a microwave heating apparatus according to Embodiment 1. FIG. In FIG. 1, a drum container 103 for storing an object to be heated 101 is installed in an oven 102 obliquely with its opening facing upward. A rotation mechanism 111 is connected to the drum container 103 and is rotatable. The drum container 103 is provided with fins 116 for stirring the article to be heated 101.

  A microwave generator 99 is connected to the oven 102, and microwaves are irradiated through the waveguide 107. The oven 102 is also provided with an air supply port 118 and an exhaust port 119 in order to improve the flow of gas generated during the heat treatment. Furthermore, a (radiation) thermometer 120 for measuring the temperature of the object to be heated 101 is installed.

  The gas supply mechanism 121 is installed such that the gas outlet 121 a for ejecting gas is located in the drum container 103 and facing the inner wall of the drum container 103.

  In order to heat the object to be heated 101 with this microwave heating apparatus, first, the object to be heated 101 is stored in the drum container 103 installed in the oven 102, and the drum container 103 is optimized by the rotation mechanism 111. Rotate at a reasonable speed. Thereby, the article to be heated 101 is agitated and mixed in the drum container 103 having the fins 116.

  Next, necessary gas types, gas flow rates and flow rates are set, and gas is supplied from the gas supply mechanism 121 into the drum container 103.

  Then, the microwave (electric power) generated by the microwave generator 99 is irradiated into the oven 102 (strictly, the drum container 103) through the waveguide 107, so that the heat treatment of the article to be heated 101 is started. Is done.

  In the first embodiment, since the gas ejection port 121a is installed in the drum container 103, it is possible to supply gas directly to the article to be heated 101 and promote efficient reaction.

  In addition, by appropriately adjusting the flow rate of the gas to be supplied, the stirring / mixing of the article to be heated 101 is further promoted as compared with the operation of the rotation and the fins 116 alone.

  In the first embodiment, the gas supply mechanism 121 is illustrated as a single pipe. However, a plurality of gas supply mechanisms 121 may be used. Moreover, the shape may be a shower plate shape in which a plurality of gas ejection ports 121a are provided in a block-shaped unit.

  Furthermore, in Embodiment 1, the heat treatment is performed at atmospheric pressure in the atmosphere, but may be performed under reduced pressure.

  Further, due to the cooling effect (temperature control: prevention of overheating) of the object to be heated 101 by the gas from the gas outlet 121a, the object to be heated 101 in which a substance having good microwave absorption and a bad substance are mixed is microscopic. A heat treatment exhibiting higher selectivity, such as preferential heating of a substance having good wave absorption, is possible.

  Here, more specifically, an example in which the microwave heating apparatus according to the first embodiment is applied for the purpose of removing carbon and water from powder or granular silicon containing carbon and water as main impurities will be described. . Carbon and water are substances having good microwave absorption, and powdered or granular silicon is a substance having poor microwave absorption.

  First, the manufacturing process of a solar cell or a semiconductor silicon wafer will be described with reference to FIG. First, initial silicon with few impurities is prepared in a silicon material preparation step (S110), and then an ingot is produced in an ingot production step (S120). The ingot is produced by the Czochralski (CZ) method or the like. The produced ingot is processed by the ingot processing / adhesion step (S130), and is bonded and fixed to the beam material. The ingot bonded and fixed to the beam material is sliced using a wire saw in the slicing step (S140). Thereafter, a silicon wafer is manufactured through a wafer cleaning step (S150).

  Next, the silicon recycling process (S200) will be described. In the silicon recycling process (S200), silicon sludge produced as a by-product in the slicing process (S140) is recovered in the recovery process (S210), and the microwave heating process (S220) and the melting / solidifying process (S230). Is a series of steps for producing silicon for recycling and returning to the ingot producing step (S120).

  In the slicing step (S140), silicon chips generated when processing the ingot are mixed with the beam material to which the ingot is bonded and water containing a coolant (organic system) and discharged in large amounts as silicon sludge. This silicon sludge is recovered as powdered silicon sludge by, for example, a filter press in the recovery step (S210). This powdery silicon sludge contains an organic carbon component which is a residual coolant component, an inorganic carbon component such as graphite, which is a material of a beam material, or abrasive grains of a wire saw, and a water component. The content of is also about 40% to 60% of the whole.

  The microwave heating apparatus according to the present embodiment is means for removing water components and reducing carbon components in the microwave heating step (S220) from the collected powdery silicon sludge. Here, organic and inorganic carbon components and water components contained in silicon sludge are substances that have a very good microwave absorption compared to silicon particles, and use the property of being instantaneously heated by microwaves. .

  First, the recovered silicon sludge (object to be heated 101) is charged into the drum container 103 of FIG. 1 as 1 to 5 kilograms, and the drum container 103 is rotated by the rotation mechanism 111 at a rotation speed of 3 to 20 rpm. At this time, in order to suppress an abnormal discharge phenomenon and partial overheating, the silicon sludge is crushed into granules of 5 mm or less by a crusher and then put into the drum container 103.

  Next, the flow rate and flow rate of the gas containing oxygen are set to desired values, and the gas is directly ejected from the gas supply mechanism 121 toward the silicon sludge stored in the drum container 103.

  Here, the microwave (electric power) generated by the microwave generator 99 is irradiated into the oven 102 (strictly, the drum container 103) through the waveguide 107, so that silicon that is the object to be heated 101 is obtained. The sludge heat treatment is started.

  When the heat treatment is started, the water component and the carbon component in the silicon sludge are heated by absorbing the microwave, and first, water vapor is generated and discharged from the exhaust port 119 to the outside of the oven 102. Thereafter, when the water component in the silicon sludge disappears, the carbon component in the silicon sludge is heated.

At this time, the carbon component that has become a high temperature by absorbing the microwave efficiently causes a combustion reaction with the gas containing oxygen ejected from the gas ejection port 121a, and generates an organic gas containing CO or CO ₂ . The generated organic gas is efficiently transferred from the exhaust port 119 to the outside of the oven 102 in combination with the rotation of the drum container 103 and the action of the fins 116 and the effect of an appropriate flow rate by the gas ejected from the gas ejection port 121a. Well discharged.

  On the other hand, silicon has poor microwave absorption, so the temperature rise due to direct heating by microwave is small, but contact with high temperature carbon that has absorbed microwave promotes oxidation by indirect temperature rise. Concerned. On the other hand, in the present embodiment, high-temperature carbon can be efficiently discharged from the drum container 103, so that opportunities for contact with silicon can be reduced. Further, the cooling effect by directly jetting the gas from the gas jet port 121a to the silicon sludge makes it possible to effectively suppress the temperature rise of the silicon, thereby suppressing the oxidation of the silicon and producing high-quality recycling silicon. You can get it.

  By performing the above steps for several minutes to several tens of minutes, the carbon concentration can be reduced to about 0.1 at% while suppressing the progress of oxidation of silicon in the silicon sludge to about several percent.

  In addition, even a substance with poor microwave absorption, such as silicon, is likely to absorb microwaves as the temperature of the substance increases, resulting in a heating phenomenon. According to the microwave heating apparatus, since the gas can be directly ejected to the object to be heated 101 by the gas ejection port 121a, a substance having a poor microwave absorbability can be kept at a low temperature.

  In addition, sludge generated at the time of manufacturing a substrate such as sapphire, gallium nitride (GaN), or gallium arsenide (GaAs) can be recycled in the same manner by using this microwave heating apparatus, and heating of the recycled material is possible. This makes it possible to efficiently remove impurities having good microwave absorption such as carbon.

Note that the substance having good microwave absorption (first substance) is a polar substance, a substance having a dielectric loss angle (Tan δ) of 0.01 or more, or a substance having a conductivity of 10 ⁻² or more and 10 ⁴ or less. Indicates. In addition, the substance having a poor microwave absorption (second substance) is a substance different from any of the above. An object to be heated including both the first substance and the second substance is suitable for processing with the microwave heating apparatus according to this embodiment. In this case, only the first substance can be heated without causing thermal damage to the second substance.

  It is desirable to further include a cooling mechanism 140 that cools the gas supplied from the gas supply mechanism 121 to the drum container 103. This is because it is possible to further suppress the temperature rise of a substance having poor microwave absorption such as silicon. In the present embodiment, the cooling mechanism 140 has a function of cooling the gas introduced into the gas supply mechanism 121. It is more preferable that the cooling mechanism 140 cools not only the gas but also the gas supply mechanism 121 itself. This is because the temperature increase of the gas supply mechanism 121 itself can be prevented to suppress the absorption of microwaves, and the efficient heating of the article to be heated 101 can be promoted.

  Here, another example of the gas supply mechanism will be described. FIG. 2A is a schematic sectional view showing a drum container 203 and a gas supply mechanism 221 in another example, and FIG. 2B is a schematic plan view thereof. The same structure as in FIG.

  The feature of this example is that the gas supply mechanism 221 is arranged at the bottom of the drum container 203. Specifically, a pipe as a gas path in the gas supply mechanism 221 is arranged inside the rotating shaft of the drum container 203, this pipe projects from the bottom of the drum container 203, and the tip of the pipe is a desired one in the drum container 203. The gas jet port 221a is configured to be brought into contact with the object to be heated 101 in the drum container 203 by bending toward the inner wall.

  In this example, since the gas ejection port 221a is installed in contact with the object to be heated 101, the reaction between the object to be heated 101 and the gas is more efficiently promoted. Furthermore, stirring and mixing of the article to be heated 101 is promoted more efficiently. In addition, a temperature increase of a substance having a poor microwave absorbability can be further suppressed with respect to an object to be heated 101 in which a substance having a good microwave absorbability and a bad substance are mixed. In this case, it is preferable that the gas ejection port 221a is disposed so as to be buried in the article to be heated 101. Gas can be ejected from the inside of the article to be heated 101, and the above-described effects can be further enhanced.

  In addition, since the gas supply mechanism 221 is disposed at the bottom of the drum container 203, the opening of the drum container 203 can be widened, and the workability of loading / collecting the article to be heated 101 is improved.

  In FIG. 2, the gas supply mechanism 221 is illustrated as a single pipe, but a plurality of gas supply mechanisms 221 may be provided. Moreover, the shape may be a shower plate shape in which a plurality of ejection holes are provided in the block-shaped unit. In addition, although the bending angle and direction of the pipe of the gas supply mechanism 221 are 90 degrees and downward, respectively, other angles and directions may be used.

  Here, another example of the gas supply mechanism will be described. FIG. 3A is a schematic cross-sectional view showing a drum container 303 and a gas supply mechanism 321 in still another example, and FIG. 3B is a schematic plan view thereof. Here, the same structure as in FIG.

  The feature of this example is that the gas supply mechanism 321 is arranged along the fins 316. Specifically, a pipe which is a gas path of the gas supply mechanism 321 is arranged inside the rotation shaft of the drum container 303, the pipe protrudes from the bottom part in the drum container 303, and the bottom part and the side surface of the fin 316 are disposed. Arrange the pipes along. Further, the pipe is bent at a position in the middle of the fin 316 and arranged so that the gas outlet 321a which is the tip of the pipe faces the center of the drum container 303.

  Due to this feature, the gas from the gas ejection port 321a is directly ejected to the object to be heated 101 lifted by the fins 316, so that the reaction between the object to be heated 101 and the gas is more efficiently promoted.

  In addition, by appropriately adjusting the flow rate of the gas to be ejected, the stirring / mixing of the article to be heated 101 is more efficiently promoted as compared with the action of the fins 316 alone. In addition, a temperature increase of a substance having a poor microwave absorbability can be further suppressed with respect to an object to be heated 101 in which a substance having a good microwave absorbability and a bad substance are mixed. Also in this example, there is an advantage that the opening of the drum container 303 can be widened, and the workability of loading / collecting the article to be heated 101 is improved.

  In addition, although the gas ejection port 321a was shown in FIG. 3 as three per one fin 316, if the installation is possible, there will be no restriction | limiting in number. In addition, the angle of bending of the pipe of the gas supply mechanism 321 is 90 degrees with respect to the major axis direction of the fin 316, but other angles may be used.

  Note that the gas supply mechanism 321 (121, 221) is preferably made of a material that transmits microwaves, such as quartz. Even when the gas supply mechanism 321 (121, 221) is disposed in the drum container 303 (103, 203), the microwave from the microwave generator 99 is efficiently transmitted without being shielded by the gas supply mechanism 321. This is because the object to be heated 101 can be irradiated.

  In the present embodiment, since the gas from the gas supply mechanism 321 (121, 221) is directly injected to the object to be heated 101, the object to be heated 101 is scattered, and the drum container 303 (103, 203). I am worried about jumping out of. In order to prevent this, it is preferable to provide a lid at the opening of the drum container 303 (103, 203). Installing this lid so as to cover the lower half of the opening is effective in preventing the heated object 101 from jumping out.

  The present invention can be used in heat treatment processes in various industrial fields, such as a material recycling process for solar cells and semiconductors, and a synthesis of functional materials and polymer materials.

99 Microwave generator 101 Object to be heated 102 Oven 103, 203, 303 Drum container 107 Waveguide 111 Rotating mechanism 116, 316 Fin 118 Air supply port 119 Exhaust port 120 Thermometer 121, 221, 321 Gas supply mechanism 121a, 221a , 321a Gas outlet 140 Cooling mechanism

Claims (11)

A drum container for storing an object to be heated;
A rotating mechanism for rotating the drum container;
A microwave generator for irradiating microwaves into the drum container;
A gas supply mechanism for supplying gas into the drum container,
The microwave heating apparatus according to claim 1, wherein the gas supply mechanism includes a gas outlet provided to face the inner wall of the drum container. The microwave heating device according to claim 1, wherein the gas ejection port is located in the drum container. The microwave heating apparatus according to claim 1 or 2, wherein the gas ejection port is in contact with the object to be heated in the drum container. The microwave heating device according to any one of claims 1 to 3, wherein the gas outlet is buried in the object to be heated in the drum container. The microwave heating device according to any one of claims 1 to 4, wherein the gas supply mechanism is provided so as to protrude from a bottom portion of the drum container. Fins for stirring the object to be heated are provided in the drum container,
The microwave heating apparatus according to claim 1, wherein the gas supply mechanism is disposed along the fin. The microwave heating device according to claim 1, further comprising a cooling mechanism that cools the gas supplied from the gas supply mechanism. The microwave heating apparatus according to claim 7, wherein the cooling mechanism cools the gas supply mechanism. The microwave heating apparatus according to any one of claims 1 to 8, wherein the gas supply mechanism is made of a substance that transmits microwaves. The microwave heating device according to claim 1, wherein the gas supply mechanism is made of quartz. The microwave heating device according to claim 1, further comprising a lid that covers a lower portion of the opening of the drum container.

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