JPH09112873A - Microwave melting equipment - Google Patents

Abstract

(57) [Abstract] [Problem] The heating efficiency is poor, and there are various restrictions in designing the furnace, and it is necessary to adjust the impedance according to the change in the state of the material to be melted. A microwave generator (5) for generating microwaves using a gyrotron, a waveguide (6) for transmitting microwaves generated by the microwave generator, and a waveguide (6) provided at an end of the waveguide for transmission. Irradiator for irradiating microwave
4, a reflector antenna 15 that is provided so as to face the irradiator and focuses the microwave radiated from the irradiator to irradiate the object to be melted 4, and confine the microwave to heat and melt the object to be melted. Equipped with a melting furnace 8 for.

Description

Detailed Description of the Invention

[000l]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention irradiates a high power microwave generated by a gyrotron onto a radioactively contaminated concrete piece or a material to be melted such as incineration ash discharged from a refuse incinerator. , A microwave melting device for heating and melting the material to be melted.

[0002]

2. Description of the Related Art Since 2010, many nuclear power plant facilities currently in operation have reached the end of their lives. Moreover, the difficulty of locating a nuclear power plant is not expected to be resolved in the future, and it is desirable to be able to reconstruct the nuclear power plant in the same place in order to meet the ever-increasing power demand. For that purpose, the nuclear power plant facilities must be dismantled, and in order to reduce the radiation exposure during the dismantling as much as possible, it is essential to remove radioactive materials in advance.

Generally, nuclear power plant facilities (1.1 million kW
In the e-class) decommissioning measures, the ratio of the amount of concrete waste generated is 91.7% to 93.2%, which is more than 90% in any calculation, as shown in Table 1 below. The proportion of the portion of the concrete waste that becomes radioactive waste containing a large amount of radioactivity is 0.21% to 0.65%, which is less than 1% in any calculation. Other non-radioactive concrete wastes are reused after flushing, but the radioactive concrete wastes are planned to be deep-layered after volume reduction and solidification.

[0004]

[Table 1]

On the other hand, industrial waste tends to increase with changes in the industrial structure and development of economic activities. Although the recycling rate has been showing signs of improvement due to the growing awareness of global environmental problems in recent years, incineration and direct disposal still dominate waste disposal. Up until now, Japan's waste treatment policy has been to reduce the volume by incineration and stabilize it before landfilling it. In addition, it is difficult to secure a new disposal site for general waste to cope with the tight disposal amount, and further reduction of volume and detoxification are issues as a life extension measure.

The main component of concrete and incineration ash is silicon dioxide (SiO ₂ ), and its melting point is 1
414 ° C. Generally, objects with high melting points (1000-2
An electric furnace is used for melting at 500 ° C. Here, since a furnace by direct resistance heating or induction heating is not suitable for melting concrete pieces, incineration ash, etc., indirect resistance heating by radiation (resistance furnace) is often used. In this case, the operating temperature of the resistance furnace is determined by the allowable temperature rise of the heating element (nichrome wire, iron chrome wire, molybdenum wire, tungsten wire, etc.).

The construction of such a resistance furnace is shown in FIG. In the figure, 1 is a structure, 2 is a furnace wall made of refractory material, 3 is a heating element, and 4 is a melted material such as concrete pieces or incinerated ash.

Next, the operation will be described. As shown, this resistance furnace has a furnace wall 2 made of a refractory material in a structure 1, and a heating element 3 is arranged along the furnace wall 2.
When the melted material 4 such as concrete pieces or incinerated ash is put into the space inside the furnace wall 2 where the heating element 3 is arranged and the heating element 3 is energized, the heating element 3 generates heat. This generated heat is radiated to heat and melt the melted material 4 from the outside. The material 4 to be melted in this manner is reduced in volume, then solidified and disposed.

On the other hand, FIG. 3 is a conceptual diagram showing a conventional microwave melting apparatus. In the figure, 4 is a material to be melted, 5 is a microwave generator by a magnetron, 6 is a waveguide, 7 is an isolator, 8 is a resonator type melting furnace, 9 is a matching stub, 10 is a screw feeder, 11 is a It is an exhaust pipe, and the conventional microwave melting device is constituted by these.

Next, the operation will be described. The magnetron used for the microwave generator 5 has an oscillation frequency of 915 MHz and an output of 25 kW, for example. The microwave generated by the microwave generator 5 is guided to the melting furnace 8 by the waveguide 6 via the isolator 7, the matching stub 9, and the like. On the other hand, the melted material 4 is put into the melting furnace 8 by a predetermined amount by the screw feeder 10. Here, the melting furnace 8 is a resonator type, and the furnace itself plays a role of a resonator, and by placing the melted material 4 in a place where the electric field strength is strong, it can be melted. Water vapor and other gases generated when the melted material 4 is melted are exhausted to the outside through the exhaust pipe 11.

The isolator 7 absorbs reflected waves and protects the microwave generator 5. In addition, since the impedance changes significantly (the electric field distribution in the furnace also changes) with the state change of the melted object 4 (solid → liquid), the matching stub 9 is provided for impedance matching.

Note that, as a document in which a technique related to such a conventional microwave melting apparatus is described, there is, for example, Japanese Patent Publication No. 69-60880.

[0013]

Since the conventional melting furnaces for melting the material to be melted, such as radioactively contaminated concrete pieces and incinerator ash discharged from the refuse incinerator, are constructed as described above, There were problems as described below.

That is, in the resistance furnace, although it depends on the amount of material, the radiant heat from the heating element 3 heats the material to be melted 4 from its surface, so that the temperature of the material to be melted can be raised to the melting point. It takes a long time and the heating efficiency is low, and particularly when heating and melting a substance having poor heat transfer such as concrete pieces and incineration ash, there is a problem that the heating efficiency is further deteriorated.

On the other hand, the conventional microwave melting apparatus has an advantage that the microwave penetrates into the inside of the dielectric and directly heats the inside of the material to be melted 4, but since it is a resonator type, the length of the furnace is long. Is required to be an integral multiple of λ / 2 (λ is the wavelength of the microwave), which not only causes various restrictions on the selection of the furnace wall material and the installation position of the melted material, but also the melted material. There was a problem that the matching stub 9 for adjusting the impedance according to the state change of 4 was required.

The present invention has been made to solve the above-mentioned problems, and by focusing the high power microwave generated by the gyrotron and irradiating the object to be melted,
An object of the present invention is to obtain a microwave melting device with high heating efficiency, which is capable of dielectrically heating a material to be melted with a microwave having a high power density.

[0017]

A microwave melting apparatus according to the present invention is a microwave generator using a gyrotron for generating high power microwaves, and the microwaves are guided by a waveguide. It is transmitted to the melting furnace and irradiated by an irradiator provided at the end of the waveguide, and the irradiated microwave is focused by a reflector antenna arranged facing this irradiator to melt the melting furnace. The material to be melted inside is irradiated and heated to melt it.

The microwave melting apparatus according to the second aspect of the present invention is a beam converging type reflection device capable of moving the focal point of a microwave focused in a beam shape two-dimensionally or three-dimensionally as a reflector antenna. It uses a mirror antenna.

The microwave melting apparatus according to the third aspect of the present invention is provided with a reflector for returning the reflected wave generated by the impedance mismatch caused by the change in the state of the material to be melted to the melting furnace side.

In a microwave melting device according to a fourth aspect of the present invention, a reflector antenna is used which irradiates a microwave having a weak beam intensity which is not focused in a beam shape on the object to be melted.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. 1 is a conceptual diagram showing a microwave melting device according to a first embodiment of the present invention. In the figure, 4
Is a melted material such as concrete pieces and incineration ash that is disposed of after being melted, reduced in volume and solidified. Reference numeral 5 is a microwave generator for generating a microwave for dielectrically heating the melted material 4, and the same reference numeral is given to FIG. 3 in that a high power microwave is generated by using a gyrotron. Different from the conventional microwave generator shown in FIG.
Reference numeral 6 is a waveguide which is connected to the microwave generator 5 and transmits the high-power microwave generated by the microwave generator 5. Reference numeral 8 denotes a melting furnace for confining the microwaves transmitted by the waveguide 5 and heating the material 4 to be melted by insulating it from the outside. Here, the conventional microwave oven shown in FIG. 3 is used. Unlike the wave melting device, the electric field focusing type melting furnace is used instead of the resonator type. Reference numeral 11 is an exhaust pipe for exhausting water vapor and other gases generated in the melting furnace 8 when the melted material 4 is melted, and 12 is an inlet for charging the melted material 4 into the melting furnace 8. , 13 are outlets for taking out the melted material 4 which is solidified into glass and reduced in volume to the outside of the melting furnace 8.

Reference numeral 14 is an irradiator which is provided at the tip of the waveguide 6 and irradiates high-power microwaves transmitted from the microwave generator 5 through the waveguide 6. A beam focusing reflector antenna (reflector antenna) 15 is installed so as to face the irradiator 14 and sharply focuses the high-power microwave radiated from the irradiator 14 into a beam and irradiates the object to be melted 4. Reference numeral 16 denotes an antenna driving unit for driving the beam focusing type reflecting mirror antenna 15 to move the focus position of the focused microwave beam two-dimensionally or three-dimensionally. The beam focusing reflector antenna 15 includes a circular waveguide for transmitting the TE0n mode, a parabolic mirror whose focal axis is the tube axis of the circular waveguide,
In the symmetry plane of this parabolic mirror, a rotary parabolic mirror whose axis θ forms an angle θ with the tube axis facing inward from the opening of the circular waveguide is given by the following formula (1): Is equipped with. The antenna drive unit 16 also includes a mechanism for rotating the parabolic mirror about its mirror axis and a mechanism for moving the parabolic mirror in parallel along the mirror axis.

Θ = sin ⁻¹ (k _cn / k) k _cn = χ′0n / a, k = 2π / λ ₀ (1) where χ′0n: J′0 (χ) N root of = 0 a: Waveguide radius λ ₀ : Free space wavelength

Reference numeral 17 denotes a high-power microwave that is focused into a beam by the beam-focusing reflector antenna 15 and irradiates the object 4 to be melted, which is a reflected wave generated by impedance mismatching accompanying a change in the state of the object 4 to be melted. It is a reflector for returning to the melting furnace 8 side. Reference numeral 18 is a gyrotron power supply that supplies power for oscillating the gyrotron used in the microwave generator 5, and 19 is a gyrotron cooler that cools the gyrotron that has been heated by microwave oscillation. . In addition, the inlet 12, the outlet 13, the antenna driving device 16, the gyrotron power supply 18, the gyrotron cooling device 19, etc. of the melted material 4 are
It is installed in another place and is remotely controlled by a remote control device (not shown).

Next, the operation will be described. When melting the melted material 4 using the microwave melting device configured as described above, first, the melted material 4 such as low-level radioactive waste (concrete piece) or refuse incineration ash is conveyed by the belt conveyor. It is charged into the melting furnace 8 through the charging port 12. Next, power is supplied from the gyrotron power supply 18 to cause the gyrotron of the microwave generator 5 to oscillate, the generated high-power microwave is guided into the melting furnace 8 by the waveguide 6, and the irradiator 14 is used. The beam converging-type reflecting mirror antenna 15 arranged to face it is irradiated with it. Next, the antenna driving unit 16 is operated to control the beam focusing reflection mirror antenna 15, and the beam focusing reflection mirror antenna 15 is rotated and translated. As a result, the high-power microwave is sharply focused and irradiated in a beam shape in a predetermined range in the melting furnace 8, and further, the focused microwave beam is scanned to be introduced into the melting furnace 8. The material 4 to be melted is caused to generate heat from the inside by its dielectric loss and melted. Since water vapor and other gases are generated when the melted material 4 is melted, they are processed by an exhaust device (not shown) connected to the exhaust pipe 11. After the concrete pieces and the incineration ash in the melting furnace 8 are melted and a certain period of time has passed, the solidified material which is solidified into a glass is taken out of the melting furnace 8 through the outlet 13 and disposed of. As a result, the volume of the melted material 4 is reduced to about 1/7 due to solidification into glass and evaporation of water and gas components.

Next, the heat generation amount per unit volume when the conventional magnetron and the gyrotron of the present invention are used as the microwave generation source will be compared and explained.
Here, when the microwave is applied to the irradiated body 4 such as concrete which is a dielectric or incineration ash, the heat generation amount P per unit volume inside the dielectric is expressed by the following equation (2).

P = 5/9 × ε _r × tan δ × f × E ² × 10 ⁻¹⁰ (W / m ³ ) ... (2) where ε _r : relative permittivity of material tan δ : Dielectric loss tangent of material f: Microwave frequency (Hz) E: Electric field strength (V / m)

From the above equation (2), the microwave frequency,
It can be seen that the larger the relative permittivity and dielectric loss tangent of the substance, the electric field strength, and the like, the larger the amount of heat P generated per unit volume.

Using this as a microwave generation source, the magnetron of 915 MHz and 25 kW described above and 28
The following is a comparison when a gyrotron of GHz and 10 kW is used. Here, the relative permittivity ε _r and the dielectric loss tangent tan δ of concrete are 3 to 30 GHz.
Is almost constant (note that, as a typical value, ε _r = 4, ta
nδ = about 0.05. However, there is also a report that tan δ rapidly increases as the temperature rises). Regarding the electric field strength at which the microwave can be transmitted to the melting furnace 8 without causing the discharge in the waveguide 6,
Considering the discharge limit, the upper limit value at 915 MHz is 275 kV / m, and the upper limit value at 28 GHz is 1350 kV / m.

Now, with the relative permittivity ε _r and the dielectric loss tangent tan δ being constant, the heat generation amounts P1 and P2 at 915 MHz and 28 GHz are compared and examined. From the above equation (2), the ratio P2 / P1 of both heat generation amounts is P2 / P1 = (f2 / f1) × (E2 / E1) ² = (28 / 0.915) × (1350/275) ² = 737. Actually, as described above, the dielectric loss tangent tan δ rapidly increases with the temperature rise. Therefore, in such a case,
It is expected that the ratio of this heat generation amount will be further increased.

Therefore, as the microwave generator 5,
When a gyrotron with an oscillating frequency of 28 GHz is used, the amount of heat generated per unit volume is 737, compared with the case of using a magnetron with an oscillating frequency of 915 MHz.
More than double. Further, since the microwave heating is heating from the inside of the material to be melted 4 rather than heating from the outside such as in an electric furnace, it has a characteristic that uniform heating and rapid heating can be performed, and the heating efficiency can be improved. A high microwave melting device can be provided.

In the microwave melting apparatus according to the first embodiment, an electric field focusing type furnace is used as the melting furnace 8. In this melting furnace 8 as well, the state change of the material 4 to be melted (solid → liquid). It is conceivable that the impedance mismatch will occur and the reflected wave will increase. That is, when the material to be melted 4 is irradiated with microwaves, the material to be melted 4 is heated from the inside, and when the temperature rises to 1000 ° C. or higher, the electrical resistivity begins to decrease and becomes about several Ωcm at about 1400 ° C. On the other hand, the impedance of the waveguide 5 is usually about 400Ω, and it is assumed that the reflected wave of the microwave increases due to the impedance mismatch. In the melting furnace 8 according to the first embodiment, a reflector 17 is arranged between the irradiator 14 and the waveguide 6 in order to stabilize the operation of the gyrotron. This reflector 17 returns the reflected wave of a mode other than the TE0n mode generated by the impedance mismatching accompanying the change of the state of the melted material 4 to the melting furnace 8 side again and melts it for melting the melted material 4. I am making it available.

As described above, since the melting furnace 8 is an electric field focusing type furnace, as in the case of a resonator type furnace, the furnace length depending on the wavelength of the microwave, the furnace design regarding the installation location of the material 4 to be melted, etc. In addition, the reflected wave reflected from the melted object 4 is returned to the melting furnace 8 side by the reflector 17 so that the energy of the high-power microwave generated by the gyrotron is transferred to the melted object 4 of the melted object 4. It can be effectively used for melting.

Embodiment 2 In the first embodiment, the case where the microwave radiated from the irradiator 14 is sharply focused into a beam by the beam focusing reflector antenna 15 and radiated to the melted object 4 has been described. Is larger by one digit, it is possible to obtain a predetermined power density even with a broad beam with a reduced degree of focusing. That is, the microwave generator 5 outputs, for example, 100 k
When a high-power gyrotron exceeding W is used, the beam focusing reflector antenna 15 does not sharply focus the microwave into a beam, but a broad beam is applied to the melted material 4, In this case, since the irradiation range of the beam to the melted object is wide, the melting efficiency becomes better than that in the first embodiment.

[0035]

As described above, according to the first aspect of the present invention, a high-power microwave is generated by a microwave generator using a gyrotron, and the microwave is guided by a waveguide in a melting furnace. And irradiate it from an irradiator provided at its end, and the irradiated microwave is focused by a reflector antenna arranged facing this irradiator and irradiates the material to be melted in the melting furnace. Since it is configured as described above, it is possible to perform microwave heating (heating that utilizes the fact that the irradiated microwave penetrates into the melted material and is absorbed by the melted material due to dielectric loss and converted to heat). Therefore, the material to be melted can be heated from the inside, not from the outside such as in an electric furnace, so that uniform heating and rapid heating of the material to be melted are possible, and the heating efficiency is high. A microwave melting device is obtained On the other hand, there is no need to adjust the impedance according to the change in the state of the melted object, and like the resonator type melting furnace, the furnace length that depends on the wavelength of the microwave and the installation location of the melted object, etc. The effect is that there are no restrictions on the design.

According to the second aspect of the invention, as the reflector antenna, a beam focusing reflector antenna capable of moving the focus of the beam-focused microwave in a two-dimensional or three-dimensional manner is used. Since it was configured to
It is possible to irradiate microwaves that are sharply focused into a beam shape anywhere in the melting furnace, and it is also possible to scan the microwave beam, which efficiently heats the material to be melted put into the melting furnace. There is an effect that it can be melted.

According to the third aspect of the present invention, a reflector is provided so that the reflected wave reflected from the melted material is returned to the melting furnace side due to impedance mismatch caused by the change in the state of the melted material. Therefore, there is an effect that the gyrotron can be protected and the energy of the high-power microwave generated by the gyrotron can be effectively used for melting the material to be melted.

According to the fourth aspect of the present invention, since the reflector antenna is configured to irradiate a broad beam to the melted object, when a microwave is generated using a high output gyrotron. Since the material to be melted can be irradiated over a wide range, there is an effect that the material to be melted can be more efficiently melted.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a microwave melting device according to a first embodiment of the present invention.

FIG. 2 is a conceptual diagram showing a melting device using a conventional resistance furnace.

FIG. 3 is a conceptual diagram showing a conventional microwave melting device.

[Explanation of symbols]

4 melted object, 5 microwave generator, 6 waveguide, 8
Melting furnace, 14 irradiator, 15 beam focusing reflector antenna (reflector antenna), 17 reflector.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location H05B 6/64 H05B 6/64 H (72) Inventor Fumitake Sato 2-2 Marunouchi, Chiyoda-ku, Tokyo No. 3 Sanryo Electric Co., Ltd. (72) Inventor Kazuhisa Itami 2-32 Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Co., Ltd. (72) Hiroyuki Asano 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Co., Ltd. (72) Inventor, Ito Naito 2-3-3 Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Co., Ltd.

Claims (4)

[Claims] 1. A microwave generator for generating a microwave using a gyrotron, a waveguide connected to the microwave generator for transmitting the microwave generated by the microwave generator, and a waveguide for the microwave. An irradiator provided at an end portion of the wave tube for irradiating the microwave transmitted from the microwave generator through the waveguide, and an irradiator provided so as to face the irradiator and irradiate from the irradiator. A microwave melting device comprising: a reflector antenna for focusing the irradiated microwaves and irradiating the object to be melted; and a melting furnace for confining the microwaves to heat and melt the object to be melted. 2. The reflector antenna is a beam focusing reflector antenna capable of two-dimensionally or three-dimensionally moving the position of the focal point of the microwave focused by the reflector antenna in a beam shape. The microwave melting device according to claim 1. 3. A reflector is provided for returning to the melting furnace the reflected wave generated by the impedance mismatching of the microwave radiated to the material to be melted due to the state change of the material to be melted. The microwave melting apparatus according to claim 1, which is characterized in that. 4. The microwave melting apparatus according to claim 1, wherein the reflector antenna irradiates the material to be melted with a broad beam over a wide range.