Electric heating – Metal heating – By arc
Reexamination Certificate
2001-05-07
2004-08-10
Van, Quang T. (Department: 3742)
Electric heating
Metal heating
By arc
C219S121520, C219S121400, C156S345480
Reexamination Certificate
active
06774335
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma reactor for performing gas modification reaction so as to synthesize or decompose gas, and to a method for modifying gas. More particularly, the invention relates to a plasma reactor and a method for modifying gas for performing gas modification reaction with high efficiency by employing complex plasma discharge.
2. Background Art
Conventionally, there have been known gas modification methods employing discharge.
An example of the known methods is a method for plasma-treating a contaminant gas of a harmful substance; e.g., NO
X
, VOC (volatile organic compound) gas, or ethylene by employing silent discharge so as to purify the gas.
The aforementioned silent discharge is a type of discharge which is attained by applying AC high voltage to two planar electrodes which face opposite each other and which sandwich a dielectric layer formed of an insulating substance. The silent discharge uniformly disperses between the electrodes even at ambient pressure.
Among the methods for modifying gas by plasma, typically employed methods are categorized, in accordance with the nature of the plasma induced between the electrodes, into the following two types:
1. Gas modification methods employing localized and concentrated discharge such as corona discharge, glow discharge, or arc discharge, which is induced by applying voltage between a pair of electrodes facing opposite each other, and
2. Gas modification methods employing barrier discharge, which is induced by forming a dielectric body on at least a metallic electrode surface and, subsequently applying voltage between the electrodes.
Japanese Patent Application Laid-Open (kokai) No. 6-106025 discloses an exhaust-gas-purifying apparatus for removing NO contained in exhaust gas. The exhaust-gas-purifying apparatus employs an exhaust-gas-purification catalyst and a plasma reactor in combination. In fact, there are disclosed (ibid.) one apparatus employing a plasma reactor in which lightning-like concentrated discharge is induced through the application of AC voltage between a pair of electrodes, and another apparatus employing a plasma reactor in which barrier discharge is induced by applying AC voltage between a pair of electrodes, at least one of which is coated with a dielectric body.
However, concentrated discharge of high plasma energy density disadvantageously attains contact with a reaction gas at low probability. In contrast, barrier discharge that attains contact with reaction gas at high probability has a disadvantageously low plasma energy density.
SUMMARY OF THE INVENTION
In view of the foregoing, the present inventors have conducted extensive studies in an effort to elevate the plasma energy level over a region between the electrodes, and have found that the collision frequency of molecules of a gas introduced for treatment can be enhanced by complex barrier discharge; i.e., combination of mist-like barrier discharge and lightning-like localized and concentrated discharge, to thereby enhance the gas reaction efficiency.
Accordingly, in one aspect of the present invention, there is provided a plasma reactor for modifying gas by plasma, characterized by comprising
a first planar electrode and a second planar electrode, the two electrodes facing opposite each other approximately in parallel;
a dielectric body inserted between the first and the second electrodes; and
a complex barrier discharge-generating means for providing a predetermined electric potential difference between the first and the second electrodes; wherein the first and the second electrodes are provided so as to apply complex plasma discharge to the gas to be treated fed between the electrodes, to thereby modify the gas.
The ratio of the width (W) to the length (L) of the first and second electrodes may be predetermined in accordance with modification reaction of the gas to be treated, the width (W) being approximately perpendicular to the direction for feeding the gas to be treated and the length (L) being along the direction.
The relationship between W and L may be adjusted to W≧L when the modification reaction is a single-step reaction, or the relationship between W and L may be adjusted to W≦L when the modification reaction includes multiple reaction steps.
Positions of voltage application to the first and the second electrodes may be offset from a central position with respect to the direction of the flow of the gas to be treated.
The positions of voltage application to the first and the second electrodes may differ from each other with respect to the direction of the flow of the gas to be treated.
The reactor may be provided for treatment of a gas of a substance which has a low dissociation energy and can be decomposed by low-density plasma.
The reactor may be provided for treatment of NO
X
.
The positions of voltage application to the first and the second electrodes may be identical to each other with respect to the direction of the flow of the gas to be treated; face opposite each other; and are offset upstream from a central position with respect to the direction of the flow of the gas to be treated.
The reactor may be provided for treatment of a gas of a substance which has a high dissociation energy and can be decomposed by high-density plasma.
The reactor may be provided for treatment of CO
2
fed to the reactor.
A plurality of projections may be formed on one or both surfaces of the dielectric body.
A plurality of units may be stacked, the units being formed from the first and the second electrodes and the dielectric body inserted between the electrodes.
The units may adjacent to each other share at least one electrode.
The projections formed on the surface of the dielectric body may have a cross-sectional shape selected from the group of a rhombus, a polygon, a circle, and an ellipse.
The projections formed on the surface of the dielectric body may be of different heights.
The dielectric body may be not in contact with at least one of the first and the second electrodes.
The dielectric body may be in contact with the first and the second electrodes.
Metallic microparticles may be dispersively deposited on the surface of the first electrode, to thereby induce complex barrier discharge through the application of high voltage.
The dielectric body may be stacked on the surface of the second electrode.
The metallic microparticles may have a high thermoelectron-emission property.
The metallic microparticles may be formed of at least one metal selected from the group consisting of tungsten, platinum, thallium, niobium, nickel, zirconium, cesium, and barium.
The metallic microparticles may have a high secondary-electron-emission property.
The metallic microparticles may provide a small glow-cathode-fall-voltage and have a high secondary-electron-emission property.
The metallic microparticles may be formed of at least one species selected from a group consisting of magnesium oxide, cesium-containing material, copper-beryllium, silver-magnesium, rubidium-containing material, and calcium oxide.
The metallic microparticles may be dispersed in a uniform manner or a localized manner.
The surface coverage by the dispersively deposited metallic microparticles may be 20-60%.
In another aspect of the present invention, there is provided a method for modifying gas by plasma, characterized by comprising
feeding the gas to be treated into a space between the first and the second electrodes, and
applying complex plasma discharge to the gas, to thereby cause gas modification reaction, the plasma being provided by a plasma reactor comprising a first planar electrode and a second planar electrode, the two electrodes facing opposite each other approximately in parallel; a dielectric body inserted between the first and the second electrodes; and a complex barrier discharge-generating means for providing a predetermined electric potential difference between the first and the second electrodes.
The ratio of the width (W) to the length (L) of the first and second electrodes may be p
Ando Kazuo
Dosaka Kenji
Fujishiro Hideyuki
Kotani Koji
Torii Minoru
Hokushin Corporation
Sughrue & Mion, PLLC
Van Quang T.
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