JP2000182799A - Inductive coupling plasma device and treating furnace using this - Google Patents

Abstract

PROBLEM TO BE SOLVED: To treat a to-be-treated material by suppressing heat loss caused by radiation energy from a high temperature to-be treated material and efficiently heating it. SOLUTION: An inductive coupling plasma device having an electric insulation discharge tube 1, a high frequency induction coil 2 coiled on the discharge tube 1, and a gas introducing part 4 is joined with a furnace vessel 21, gas introduced from the gas introducing part 4 into the discharge tube 1 is converted into plasma by supplying high frequency current to a high frequency induction coil 2, obtained plasma flame is applied to a to-be-treated material 30 to heat and melt it for treatment. A metal thin film made of 1 μm thick gold is formed on the inner surface of the discharge tube 1, and escape of radiation energy emitted from an opening of furnace vessel 21 to the outside is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inductively coupled plasma apparatus which generates thermal plasma using high frequency inductive coupling and is used for incineration and melting of waste.

[0002]

2. Description of the Related Art An inductively coupled plasma apparatus is an apparatus in which a high-frequency induction coil is wound coaxially around a discharge tube, a high-frequency current is applied to the high-frequency induction coil, and the gas introduced into the discharge tube is converted into plasma. .

FIG. 2 is a cross-sectional view showing the basic configuration of a conventionally used inductively coupled plasma apparatus. In FIG. 1, reference numeral 1 denotes a cylindrical discharge tube. The discharge tube 1 has a double structure of an insulating inner cylinder 1a and an insulating outer cylinder 1b, and is usually formed of quartz in consideration of electrical insulation and heat resistance. The discharge tube 1 is cooled by flowing a refrigerant through a gap between the insulating inner cylinder 1a and the insulating outer cylinder 1b. Reference numeral 2 denotes a high-frequency induction coil coaxially wound around the discharge tube 1, and the number of turns is usually 3 to 4 turns. 3 is a high frequency induction coil 2
This is a high-frequency power supply that supplies a high-frequency current to the power supply. Above the discharge tube 1, a gas introduction unit 4 having a nozzle for blowing gas supplied by the gas supply pipe 6 into the discharge tube 1 in a circumferential direction and a nozzle for blowing gas in a radial direction is arranged. .

In this configuration, a valve 7 is operated to first introduce helium gas as an ignition gas from a helium gas supply source 8 into a discharge tube 1 through a gas supply pipe 6 and a gas introduction section 4. Then, the output voltage of the high frequency power supply 3 is applied to the high frequency induction coil 2. The helium gas introduced into the discharge tube 1 is discharged by a capacitive coupling electric field formed by the high frequency induction coil 2. In the state where the helium gas is discharged, a plasma gas such as argon is introduced from the gas supply source 9 to maintain the discharge.
Next, the introduction of the helium gas is stopped, and the argon gas concentration in the discharge tube 1 is increased to shift to the arc plasma. The subsequent supply of energy to the plasma is performed by a high-frequency induction electric field generated by the high-frequency induction coil 2. This plasma is generally called inductively coupled plasma. The resulting plasma depends on the strength and shape of the electric field and the gas flow. Further, when it is desired to obtain a plasma other than argon, the plasma gas is supplied to the gas supply source 1.
0, and the method of gradually replacing the argon gas with the plasma gas by opening and closing the valve 7 is adopted.

[0005] Plasma has a high temperature of about 10,000 K and has a high capability as a heating source. Therefore, it is used for processing such as melting and decomposition of gas, liquid, and solid in the discharge tube plasma. Further, since the plasma is extremely high in temperature, the plasma expands rapidly, and the plasma flame (plasma flame) 20
In this state, it gushes out of the discharge tube 1. Utilizing the jetted plasma frame 20, heat treatment such as incineration or melting can be performed.

[0006]

When high-frequency inductively coupled plasma is used as a heat source for incineration, melting, and the like, the most common method is to introduce a plasma frame blown out from an inductively coupled plasma apparatus into a furnace and irradiate the object to be treated. It is commonly used. When this method is used, the object to be processed is heated by the irradiation of the plasma, and is incinerated or melted. However, at this time, the following problem occurs.

[0007] When the temperature of the object increases due to heating, the amount of energy released from the object increases in accordance with Planck's radiation law. The amount of radiant energy is represented by Stefan-Boltzmann's law and is given by the following equation.

[0008]

E = εσT ⁴ [W / m ² ] (1) In equation (1), E is radiant energy, ε is emissivity, σ is Stefan-Boltzmann constant, and T is temperature (K). .

As described above, since the radiant energy increases in proportion to the fourth power of the temperature, most of the heat loss from the workpiece at a high temperature is due to the radiant energy. The saturation temperature of the object is determined by the balance between the incident energy from the plasma and the heat loss due to this radiation. Therefore,
In order to raise the temperature of the object to be processed to a high temperature region, it is necessary to suppress the loss due to the radiant energy. for that reason,
Generally, an object to be processed is processed in a closed furnace vessel formed of a material having excellent heat resistance and heat insulation. However, in a processing furnace using high-frequency inductively coupled plasma as a heating source,
It is necessary to provide the furnace container with an opening for introducing plasma from the inductively coupled plasma device, and heat loss due to radiant energy through this opening becomes a problem. Compared with the other methods, in the resistance heating furnace, the heat source is arranged in the furnace container, so that the furnace container can be a closed type. In addition, even in the same plasma method, when a DC arc is used, the plasma diameter is smaller than that of the high frequency inductively coupled plasma.
The opening of the furnace vessel may be small. On the other hand, it is inevitable that the diameter of the high-frequency inductively coupled plasma increases due to the principle of its generation, and the furnace vessel in which the plasma is incorporated must have a large opening. For this reason, in a processing furnace using an inductively coupled plasma apparatus, the radiant energy described above is emitted to the outside through a large opening provided in the furnace container, so that the heat loss is higher than that of a processing furnace of another type. However, there is a problem that is increased. That is, in a processing furnace using an inductively coupled plasma device, the inductively coupled plasma device is disposed at the opening of the furnace vessel and has a shape like a lid, but the discharge tube of the inductively coupled plasma device is formed of quartz. Therefore, it is almost transparent to the infrared region constituting the main part of heat radiation. Normally, cooling water is passed through the outside of the discharge tube, and the emissivity (and therefore the absorptance) of this water is as high as 0.95, and the radiant energy from the object is absorbed by this cooling water and Will be removed.

In order to increase the thermal efficiency of a processing furnace using an inductively coupled plasma apparatus, it is necessary to prevent the radiation energy from escaping to the outside of the discharge tube. As a material, radiant energy is absorbed by the discharge tube and transferred to the cooling water to be taken out, so that the heat loss cannot be reduced. Ceramics are heat-resistant and insulating materials applicable to the discharge tube. Ceramics generally have high emissivity, and the same results as described above are obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and in particular, has been made to reduce energy loss due to radiation of a processing furnace using an inductively coupled plasma apparatus.
An object of the present invention is to provide an inductively coupled plasma apparatus in which plasma energy is efficiently transmitted to an object to be processed and the object to be processed is heated and processed, and a processing furnace using the inductively coupled plasma apparatus.

[0012]

In order to achieve the above object, the present invention provides (1) an electric insulating discharge tube, a high-frequency induction coil wound around the discharge tube, and an upper portion of the discharge tube. In an inductively coupled plasma device configured to include a gas introduction unit disposed in the gas introduction unit, a gas is introduced into the discharge tube from the gas introduction unit, a high-frequency current flows through a high-frequency induction coil, and the introduced gas is turned into plasma. At least one of the inner surface and the outer surface of the discharge tube is coated with a thin film that reflects infrared light, for example, a metal deposition film, and the thickness t of the thin film is set to, for example, a high-frequency current. The thickness is smaller than the skin depth (δ) of the electromagnetic field determined by the frequency (f) and the resistivity (ρ) of the thin film as expressed by the following equation.

[0013]

Δ = (2ρ / (ωμ)) ^0.5 (2) In Equation (2), ω is an angular frequency, and therefore ω
= 2πf. Μ is the magnetic permeability of the thin film.

(2) Further, the inductively coupled plasma device of (1) is connected to an opening provided at one end of the furnace vessel to constitute a processing furnace, and the object to be processed stored in the furnace vessel is Heating, incineration, and melting are performed by a plasma frame generated by the inductively coupled plasma apparatus.

According to the above (1), thermal radiation is reflected on the thin film surface, and escape to the outside of the plasma device is suppressed. The radiant energy is returned into the furnace vessel, and is repeatedly absorbed and radiated by the wall material of the furnace vessel, and finally absorbed by the object. As the thin film, it is desirable to use a metal vapor-deposited film of gold or the like having a high reflectance (and thus a low emissivity and absorptance).

Further, since the plasma in the discharge tube is generated by an induction electromagnetic field generated by a high-frequency induction coil wound outside the discharge tube, if a thin film that obstructs the induction electromagnetic field is disposed on the discharge tube, a predetermined Plasma cannot be obtained. FIG. 3 is a characteristic diagram showing an electric field attenuation characteristic in a metal film. Gold (ρ = 2.44 × 10 ⁻⁸ Ωm) having a suitable reflectance as a coating material for a discharge tube is used for induction plasma generation. Frequency 13.56 MHz, 4 MHz, 450
This shows the characteristics in the case of kHz. As can be seen from FIG. 3, when the thickness of the thin film is increased, the electric field is blocked, and a predetermined plasma cannot be obtained. The measure to measure the degree of this shielding is the skin depth. Gold for thin film material, frequency for
When the skin depth (δ) is calculated using Equation (2) at 450 kHz, it is 117 μm. FIG. 3 shows that the skin depth indicates the thickness at which the electric field intensity is reduced to 37%.

When coating the discharge tube with a thin film, attention must be paid to eddy current loss that occurs in the thin film. An eddy current corresponding to the magnitude of the electromagnetic field is generated in the metal thin film, and a loss is determined by the magnitude of the eddy current and the resistance of the thin film. This loss becomes smaller as the metal thin film becomes thinner. FIG. 4 shows the heat generated by the eddy current generated in the thin film of gold as a function of the film thickness. The calculation conditions are: frequency: 13.56 MHz, 4 MHz, 450 kHz, applied magnetic field strength;
7.5 kA / m, winding length of induction coil; 100 m. In addition,
This applied magnetic field intensity is a value that takes into account the operating conditions of the actual induction plasma device. As can be seen from FIG. 4, if the thickness of the gold thin film is 1 μm or less, the eddy current loss in this thin film is expected to be 1 kW or less. The input energy of the induction plasma device at this operating condition is about 50 kW, and the effect is negligible if the eddy current loss is 1 kW or less.
According to Infrared Technology, No. 9 (1984), p. 70, the change in reflectance depending on the thickness of the gold coating is as shown in the following table.

[0018]

[Table 1] From this table, it can be seen that a reflectance of 97.7% can be obtained if the film thickness is 1 μm. As described above, when the film thickness is set to 1 μm as in the above (1), a sufficient reflection effect on heat radiation can be obtained, and the loss occurring in the thin film can be suppressed to a small value. Therefore, the thermal efficiency of the inductively coupled plasma device is improved. Also, as in the above (2),
If a processing furnace is configured by combining a furnace container with this inductively coupled plasma apparatus, the thermal efficiency of the processing furnace will be improved.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a longitudinal sectional view showing an embodiment of a processing furnace using an inductively coupled plasma apparatus of the present invention. FIG. In FIG. 1, the high-frequency induction coil 2 is connected to a high-frequency inverter power supply (not shown), and the rated output frequency of this power supply is 450 kHz. The configuration of the inductively coupled plasma device including the high frequency induction coil 2 is basically the same as the configuration of the conventional device shown in FIG. 2, and the inner radius of the discharge tube 1 is 85 mm. The difference between the inductively coupled plasma apparatus shown in FIG. 1 and the conventional apparatus is a metal thin film 11 provided on the inner surface of the discharge tube 1. The metal thin film 11 is coated by a vacuum evaporation method, and has a thickness of 1 μm.

At the lower part of the inductively coupled plasma apparatus, a furnace container 21 for storing a workpiece 30 such as incineration ash is disposed, and is connected to the inductively coupled plasma apparatus through an opening having the same inner radius as that of the discharge tube 1. Are linked. The furnace container 21 has a workpiece supply port 2 for introducing a workpiece 30 such as incineration ash.
3. A melt outlet 24 for allowing the melted workpiece 30 to flow out and a gas outlet 25 for exhaust gas discharge are provided. Further, a plasma transport pipe 22 for guiding the plasma frame 20 ejected from the inductively coupled plasma apparatus to the workpiece 30 is connected to the opening. The incineration ash and the like are continuously supplied into the furnace container 21 from the processing object supply port 23, and are heated and melted by the heat of the plasma frame 20 ejected from the inductively coupled plasma device. The obtained melt overflows from the melt outlet 24 and is continuously taken out.

In the present treatment furnace, the melting temperature of the incinerated ash of the object 30 is about 1700 ° C.
From 0, the energy radiated through the opening to the inductively coupled plasma device side can be as much as 10 kW. Since the plasma flame output of the inductively coupled plasma device is about 50 kW, about 20% will be released by heat radiation from the opening. In the conventional inductively coupled plasma device, this radiant energy is transmitted to the cooling water through the discharge tube 1 and causes a large energy loss. In the configuration of the present embodiment, since the metal thin film 11 is provided on the inner surface of the discharge tube 1 as described above, the heat radiation from the opening is effectively reflected by the metal thin film 11 and stays inside. Therefore, heat radiation loss is greatly reduced. Further, since the metal thin film 11 has a thickness of 1 μm, the eddy current loss generated in the metal thin film 11 is small and negligible. Although the metal thin film 11 is formed of gold in this embodiment, it is apparent that the same effect can be obtained by using another metal having a high reflectance.

In this embodiment, the metal thin film 11 is disposed on the inner surface of the discharge tube 1, but may be disposed on the outer surface. The discharge tube 1 has a double tube structure as in the conventional example shown in FIG. 2, and when cooling water is passed through the gap, the discharge tube 1 is placed on the inner surface or outer surface of the insulating inner tube 1a inside the cooling water. It should be arranged.

[0023]

As described above, according to the present invention, (1) the inductively coupled plasma apparatus is configured as described in claim 1, 2 or 3; By incinerating and melting the material to be treated in combination with a container, heat loss due to heat radiation is effectively suppressed, reducing heat loss by as much as 20%, and inductively coupled plasma that can supply plasma energy extremely efficiently. The device was obtained.

(2) If the processing furnace is constructed by combining the above-mentioned inductively coupled plasma apparatus with a furnace vessel as in claim 4, the heat insulation performance of the induction plasma method is equivalent to that of other melting furnaces. Thus, a processing furnace having the same is obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of a processing furnace using an inductively coupled plasma apparatus of the present invention.

FIG. 2 is a sectional view showing a basic configuration of a conventionally used inductively coupled plasma apparatus.

FIG. 3 is a characteristic diagram showing an electric field attenuation characteristic in a metal film.

FIG. 4 is a characteristic diagram showing a film thickness dependency of a calorific value due to an eddy current generated in a metal film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulation pipe 2 High frequency induction coil 3 High frequency inverter power supply 4 Gas introduction part 11 Metal thin film 20 Plasma frame 21 Furnace vessel 22 Plasma transport pipe 23 Processing object supply port 24 Melt outlet 25 Gas exhaust port 30 Processing object

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05B 7/18 H05B 7/18 EF term (Reference) 3K061 AA18 AB03 AC03 CA14 DB20 3K084 AA09 AA15 BA07 4K046 AA01 AA03 BA10 CC05 CD02 CD04 5C034 CC07 CC19

Claims (4)

[Claims] An electric insulating discharge tube, a high-frequency induction coil wound around the discharge tube, and a gas introduction portion disposed above the discharge tube. In an inductively coupled plasma device that introduces a gas into a high-frequency induction coil and causes a high-frequency current to flow through the high-frequency induction coil to convert the introduced gas into plasma, at least one of the inner and outer surfaces of the discharge tube has An inductively coupled plasma device characterized by being coated with a thin film that reflects light. 2. The inductively coupled plasma apparatus according to claim 1, wherein the thickness of the thin film is smaller than the skin depth of an electromagnetic field determined by the frequency of the high-frequency current and the conductivity of the thin film. Inductively coupled plasma device. 3. An inductively coupled plasma apparatus according to claim 1, wherein said thin film is made of a metal deposited film. 4. An inductively coupled plasma device according to claim 1, wherein said inductively coupled plasma device is connected to an opening provided at one end of a furnace vessel, and an object to be processed stored in said furnace vessel is subjected to said induction. A processing furnace that heats, incinerates, and melts with a plasma flame generated by a combined plasma device.