JPH11156145A - Gas decomposition disposal method and apparatus for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas decomposition disposal method and apparatus wherein decomposition efficiency is improved by maintaining stable discharge with a low power. SOLUTION: In a method of effecting gas decomposition disposal by applying electric field between an external electrode 1 having a honeycomb structure and an internal electrode 2 located at a center of a cell of the honeycomb structure in order that a gas flowing through the cell of the honeycomb structure undergo plasma excitation, a solid dielectric 3 is disposed on an electrode- opposite face of the outer electrode 1 and/or the internal electrode 2. The solid dielectric 3 is a metal oxide film made of a mixture of 5-50 wt.% of titanium oxide and 50-95 wt.% of aluminum oxide or a metal oxide film containing zirconium oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for decomposing a harmful gas such as nitrogen oxides, sulfur oxides, volatile organic compounds and the like by plasma excitation.

[0002]

2. Description of the Related Art In recent years, environmental concerns have been raised, and many methods for decomposing harmful gases such as nitrogen oxides, sulfur oxides, and volatile organic compounds have been proposed. Especially corona discharge,
The technology to decompose harmful gas using plasma discharge etc.
It is attracting attention as being clean and capable of coping with low-concentration harmful gases. On the other hand, the above-described processing method using discharge requires input of high energy, and the improvement of processing efficiency and the balance of input power have been the keys to practical application.

[0003] For example, Japanese Patent Application Laid-Open No. 7-26562 discloses a method using a combination of a honeycomb electrode and a wire electrode.
Japanese Patent Application Laid-Open No. HEI 2-15024 discloses a technique using a solid dielectric. However, there was still a need to reduce power consumption and improve processing efficiency.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a gas decomposition treatment method and apparatus for improving the decomposition efficiency by maintaining stable discharge at low power.

[0005]

According to the gas decomposition treatment method of the present invention, an electric field is applied between an external electrode having a honeycomb structure and an internal electrode located at the center of a cell of the honeycomb structure, whereby the honeycomb structure is formed. A method for performing gas decomposition treatment by exciting a gas flowing in a cell by plasma, characterized in that a solid dielectric is disposed on an electrode facing surface of an external electrode and / or an internal electrode.

The external electrodes and the internal electrodes can be made of ordinary metals. The external electrode is generally called a honeycomb structure, and a typical example is a combination of a plurality of rectangular cylinders having a regular hexagonal cross section. The internal electrode may be located at the center of the cell of the honeycomb structure formed by the external electrode, and preferably has no irregularities on the surface. An internal electrode shaped along the external electrode, that is, an internal electrode of a hexagonal prism may be located at the center of a regular hexagonal prismatic cell.

[0007] The solid dielectric is disposed on the electrode-facing surface of both the external electrode and the internal electrode, or on either electrode surface of the external electrode or the internal electrode. It is preferable to dispose them on both opposing surfaces. In addition, when disposed on both opposing surfaces, the distance between the solid dielectrics should be substantially parallel, and when disposed on one opposing surface, the distance between the electrodes and the solid dielectric should be substantially parallel. Is more preferred.

Examples of the solid dielectric include plastics such as polytetrafluoroethylene and polyethylene terephthalate, glass, metal oxides such as silicon dioxide, aluminum oxide, zirconium dioxide and titanium dioxide, and double oxides such as barium titanate. No.

The solid dielectric has a relative dielectric constant (25).
° C environment, the same applies hereinafter) is preferably 2 or more,
More preferably, it is 10 or more. As a particularly preferred example, a metal oxide film mixed with 5 to 50% by weight of titanium oxide and 50 to 95% by weight of aluminum oxide, or
A metal oxide film containing zirconium oxide may be used. The thickness of the coating is preferably from 10 to 1000 μm.

[0010]

FIG. 1 is a perspective view of an apparatus according to the present invention.
The gas to be processed flows in the direction shown in the figure, is plasma-excited while passing through the inside of the honeycomb cell, and is converted into a harmless form or a form easily collected. In the apparatus of the present invention, ammonia, a denitrifying desulfurizing agent such as lime, or blowing a fixing agent,
The harmful gas can be fixed by known means such as providing a bag filter at the end of the flow path of the apparatus of the present invention.

FIG. 2 is a diagram showing an example of installation of a solid dielectric. 2A shows an example in which the solid dielectric 3 is provided only on the internal electrode 2, and FIG. 2B shows an example in which both the external electrode 1 and the internal electrode 2 are covered with the solid dielectric 3. The distance between the electrode indicated by l in the figure and the opposing surface formed by the solid dielectric or the solid dielectric is preferably 5 to 30 mm. If it is less than 5 mm, the efficiency of the flow path of the gas to be treated is poor.

In the present invention, a gas flowing through the external electrode cell having the honeycomb structure is plasma-excited by applying an electric field between the external electrode and the internal electrode to perform a gas decomposition process. From the viewpoint of stabilizing the discharge state and performing continuous processing for a long time, the voltage rise time is 100 μs or less, and the electric field intensity is 1 to 100 kV / c.
It is preferable to apply a pulsed electric field having a frequency of 1 to 100 kHz. The pulse voltage waveform is impulse type,
Examples thereof include a square pulse type, a modulation type, and a single wave pulse type in which a voltage is applied to either the positive or negative polarity side, and are not particularly limited.

The use of a high-speed pulse electric field that satisfies the pulse rise time, electric field strength, and frequency is extremely effective in stabilizing the discharge state and improving the gas decomposition efficiency. Here, the rise time refers to a time during which the voltage change is continuously positive.

Preferably, the pulse duration in the pulse electric field is 500 μs or less. 500
If the time exceeds μs, it becomes difficult to stabilize the discharge state. More preferably, it is 3 μs to 200 μs. The pulse duration refers to a continuous ON time in a pulse electric field formed by repetition of ON and OFF.

FIG. 3 shows an equivalent circuit diagram of a power supply when such a pulsed electric field is applied. SW in FIG. 3 is a semiconductor element functioning as a switch. By using a semiconductor device having a turn-on time and a turn-off time of 500 ns or less as the switch,
The electric field strength as described above is 1 to 100 kV / cm,
In addition, a high-voltage and high-speed pulse electric field having a pulse rise time of 100 μs or less can be realized.

[0016]

According to the present invention, a honeycomb-structured electrode is employed, and the solid dielectric is provided between the electrodes, so that a large amount of gas to be processed can be continuously processed for a long time with low power consumption. Can be done. Furthermore, by using a high-speed pulse electric field with a fast rise at a specific frequency, the discharge state can be further stabilized, and stable processing can be performed with high decomposition efficiency.

[0017]

[Brief description of the drawings]

FIG. 1 is a perspective view of an example of a gas decomposition processing apparatus.

FIG. 2 is an explanatory diagram of an example of setting a solid dielectric in a gas decomposition processing apparatus.

FIG. 3 is an equivalent circuit diagram of a power supply that generates a pulse electric field.

[Explanation of symbols]

 1 external electrode 2 internal electrode 3 solid dielectric 4 power supply

Claims (5)

[Claims] An electric field is applied between an external electrode having a honeycomb structure and an internal electrode located at the center of a cell of the honeycomb structure to excite a gas flowing in the cell of the honeycomb structure into plasma. A method for performing a gas decomposition treatment, wherein a solid dielectric is provided on an electrode facing surface of an external electrode and / or an internal electrode. 2. The gas decomposition treatment method according to claim 1, wherein the solid dielectric and the external electrode or the internal electrode, or the solid dielectrics face each other with a substantially parallel interval therebetween. 3. The method according to claim 1, wherein the solid dielectric is titanium oxide 5 to 50.
3. A metal oxide film mixed with 50% by weight of aluminum oxide and 50 to 95% by weight of aluminum oxide, or a metal oxide film containing zirconium oxide.
The gas decomposition treatment method according to 1. 4. A voltage rising time between an external electrode and an internal electrode is 100 μs or less, and an electric field intensity is 1 to 100 kV /
The gas decomposition treatment method according to any one of claims 1 to 3, wherein a pulse electric field having a frequency of 1 cm to 100 kHz is applied. 5. An external electrode having a honeycomb structure, an internal electrode located at the center of a cell of the honeycomb structure, and a power supply for applying an electric field between the external electrode and the internal electrode, wherein the external electrode and / or the electrode of the internal electrode are provided. A gas decomposition treatment apparatus, wherein a solid dielectric is provided on an opposite surface, and the solid dielectrics face each other, or the solid dielectric and an external electrode or an internal electrode face each other with a substantially parallel interval therebetween.