JP4036600B2 - Plasma decomposition apparatus and gas plasma decomposition method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas reforming reactor used for gas synthesis or gas decomposition, and more particularly, to a plasma decomposition apparatus and a gas plasma decomposition method for reforming harmful gases such as CO ₂ and NO _X utilizing plasma generation.
[0002]
[Prior art]
In today's highly industrialized society, various pollutants are harmful to human health. For example, pollutant gases such as NO _x , CO _x , and SO _x emitted from engines such as automobiles as pollutants. It is particularly problematic.
[0003]
It is necessary to decompose such gas into harmless gas before being released into the atmosphere. Conventionally, as a method for decomposing this harmful gas, for example, it is decomposed by plasma discharge or the like to reform the gas. Yes.
[0004]
For this reforming, for example, a gas reformer that is a plasma reactor that reforms a gas by using plasma generation has been proposed.
[0005]
As conventional gas reforming methods, the following methods (1) and (2) are generally proposed mainly depending on the properties of plasma generated between electrodes.
(1) A gas reforming method by local lightning-like concentrated discharge such as corona discharge, glow discharge, arc discharge, etc. generated by applying a voltage between opposed parallel metal electrodes.
(2) A gas reforming method by mist-like barrier discharge that is generated by applying a voltage after coating a dielectric on at least one surface of opposing parallel metal electrodes.
[0006]
[Problems to be solved by the invention]
However, the conventional method described above has the following problems.
[0007]
First, the former local concentrated discharge method has a problem that the plasma energy density is high, but the contact probability between the plasma and the reactive gas is low. As a result, the reactive gas passes through the discharge part without coming into contact with the plasma, and it is difficult to dramatically improve the reforming efficiency.
[0008]
On the other hand, the latter barrier discharge method has a problem that the plasma energy density is low although the contact probability with the reactive gas is high.
[0009]
As a result, it is effective for reforming reactive gases that require relatively low energy for reforming, such as ozone generation, but its plasma density is low for reforming stable gases with high decomposition energy. Have difficulty.
[0010]
Thus, in the conventional method, plasma reforming means for reforming with high efficiency has been proposed in reforming gases such as NO ₂ and CO ₂ which are generally stable with relatively high decomposition energy. Therefore, the advent of a highly efficient gas reforming technique is desired.
[0011]
In view of such circumstances, it is an object of the present invention to provide a plasma decomposition apparatus and a gas plasma decomposition method capable of improving gas reforming efficiency.
[0012]
[Means for Solving the Problems]
The first aspect of the present invention that solves the above-described problems includes a first plate-type electrode and a second plate-type electrode facing each other, a dielectric interposed between the two electrodes, An electric potential difference applying means for applying an electric potential difference therebetween, wherein fine metal particles covering the surface with a surface coverage of 20% to 60% are dispersed and deposited on the surface of the first electrode, and a high voltage is applied. And a plasma decomposition apparatus for generating a composite barrier discharge.
[0013]
According to a second aspect of the present invention, there is provided the plasma decomposition apparatus according to the first aspect, wherein the dielectric is laminated on the surface of the second electrode.
[0014]
According to a third aspect of the present invention, there is provided the plasma decomposition apparatus according to the first or second aspect, wherein the metal fine particles are metal fine particles having a high thermoelectron emission property.
[0015]
According to a fourth aspect of the present invention, in the third aspect, the metal fine particles are at least one selected from the group consisting of tungsten, platinum, thallium, niobium, nickel, zirconium, cesium, and barium. It is in the plasma decomposition apparatus.
[0016]
According to a fifth aspect of the present invention, in the plasma decomposition apparatus according to the first or second aspect, the metal fine particles are metal fine particles having a high secondary electron emission property.
[0017]
A sixth aspect of the present invention, in the first or second aspect, in the plasma decomposition unit, wherein the metal fine particles are high metal fine particles emissive low glow cathode drop voltage.
[0018]
According to a seventh aspect of the present invention, in the fifth or sixth aspect, at least the metal fine particles are selected from the group consisting of magnesium oxide, cesium composite, copper beryllium, silver magnesium, rubidium composite, and calcium oxide. The plasma decomposition apparatus is characterized by being one.
[0019]
According to an eighth aspect of the present invention, there is provided the plasma decomposition apparatus according to any one of the first to seventh aspects, wherein a dispersion form of the metal fine particles is uniform dispersion or concentrated dispersion.
[0021]
A ninth aspect of the present invention, the potential difference applied between the opposing electrodes, it by generating plasma, the gas plasma decomposition method for decomposing a gas, the surface of one electrode, the surface of 20% A gas plasma decomposition method is characterized in that metal fine particles covered with a surface coverage of ˜60% are dispersed and deposited, a high voltage is applied, and a gas is decomposed while generating a composite barrier discharge.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, although embodiment of this invention is described, this invention is not limited to this.
[0023]
(First embodiment)
FIG. 1 shows a schematic diagram of a gas reformer according to the present embodiment. FIG. 2 is a perspective view of a metal electrode in which metal fine particles are dispersed and deposited on the surface.
[0024]
As shown in these drawings, the gas decomposition apparatus according to the present embodiment is provided with a ceramic decomposition container 12 that introduces a gas 11 and flows the gas 11 in a predetermined direction, and is disposed in the decomposition container 12. A metal flat plate electrode 14 which is a first electrode formed by dispersing and depositing metal fine particles 13 having a high thermoelectron emission property on the surface, and is opposed to the metal flat plate electrode 14 with a predetermined interval. AC voltage is applied between the metal flat plate electrode 15, which is the second electrode, the dielectric 16 covering the surface of the metal flat plate electrode 15, and the metal flat plate electrode 14 and the dielectric 16. Thus, the power supply unit 17 is configured to generate plasma discharge.
[0025]
Here, the metal fine particles 13 deposited and dispersed on the surface of the metal flat plate electrode 14 are metal fine particles having high thermionic emission properties, such as tungsten, platinum, thallium, niobium, nickel, zirconium, cesium, barium, and the like. Can be illustrated.
[0026]
A plurality of these materials may be used.
[0027]
The particle size of the metal fine particles 13 is not particularly limited as long as it is 500 μm or less, but it is more preferable to use ultrafine particles of 10 μm or less.
[0028]
Further, the ratio of the dispersion and deposition on the surface of the metal plate electrode 14 is preferably 60% or less, and the reforming efficiency is improved particularly at a coverage of 20 to 65%. This is preferable.
[0029]
If it exceeds 65%, the plasma energy density is too biased as shown in the examples to be described later, so that the discharge form is shifted to only one local concentrated discharge, and the probability of contact with gas is remarkably reduced. On the other hand, if it is less than 20%, the dispersion precipitation ratio of the metal fine particles is low, and the effects of the present invention cannot be exhibited.
[0030]
By using the metal flat plate electrode 14 in which the metal fine particles 13 having high thermionic emission properties are dispersed and deposited in this way, plasma discharge is performed to make the charge of the metal flat plate electrode 14 non-uniform, and the metal fine particles 13. A discharge column resembling local concentrated discharge is generated from the dispersed part of the plasma, thereby generating a composite barrier discharge based on the synergistic effect of fog-like barrier discharge and lightning-like local concentrated discharge, thereby improving the plasma energy level It becomes.
[0031]
As a result, in the reforming reaction by plasma of harmful gas contained in exhaust gas such as NO ₂ and CO ₂ that is generally stable and has relatively high decomposition energy, the contact frequency of the generated plasma and the generated plasma is referred to as barrier discharge. While maintaining a high probability of the same level, it is possible to maintain an energy index typified by the current density of the generated plasma at a high level similarly to the local concentrated discharge.
[0032]
Further, as in the present embodiment, the surface of the second metal flat plate electrode 15 that is one of the opposing electrodes is uniformly coated with the dielectric 16 so that a more stable and uniform barrier discharge can be achieved. In the metal flat plate electrode 14 that can be easily maintained and has the metal fine particles 13 with high thermionic emission properties dispersed and deposited on the surface, the metal fine particles 13 are locally distributed from the dispersed portion of the metal fine particles 13 toward the opposing dielectric 16. A plurality of discharge columns having a high current density similar to the flow column discharge are generated, and a composite barrier discharge becomes possible.
[0033]
(Second Embodiment)
In addition, by dispersing and precipitating metal fine particles having a high secondary electron emission property as the metal fine particles 13, the same as the case of dispersing and precipitating the metal fine particles having a high thermoelectron emission property according to the first embodiment described above. The effect of can be produced.
[0034]
That is, by dispersing and depositing metal fine particles having high secondary electron emission properties as the metal fine particles 13, a plurality of discharge columns with high current density similar to local concentrated discharge are generated during the barrier discharge, thereby realizing a composite barrier discharge. Will be.
[0035]
Here, as the fine metal particles having a high secondary electron emission property, materials such as magnesium oxide, cesium composite, copper beryllium, silver magnesium, rubidium composite, and calcium oxide are preferable.
[0036]
A plurality of these materials may be used.
[0037]
(Third embodiment)
In a gas reforming reactor, metal fine particles with high thermionic emission properties can also be dispersed by dispersing and precipitating metal fine particles with a low glow cathode drop voltage and high electron emission properties on the surface of the metal plate electrode. The same effect as that of the case can be obtained.
[0038]
That is, by dispersing and depositing metal fine particles 13 having a low glow cathode fall voltage and a high electron emission property as the metal fine particles 13, a plurality of discharge columns having a high current density similar to the local concentrated discharge are generated during the barrier discharge. Barrier discharge can be realized.
[0039]
Here, as the fine metal particles having a low glow cathode fall voltage and a high electron emission property, materials such as magnesium oxide, cesium composite, copper beryllium, silver magnesium, rubidium composite, and calcium oxide are preferable.
[0040]
A plurality of these materials may be used.
[0041]
In this way, in a composite barrier discharge in which multiple discharge columns resembling local concentrated discharge with strong light intensity are mixed during the barrier discharge, the reaction gas in contact with the multiple discharge columns reacts with high efficiency due to high plasma energy. A part of the reaction gas that has progressed and is in contact with the barrier discharge also reacts, and other gases are pre-excited to be more easily reacted.
[0042]
In addition, by controlling the particle size and dispersion density of the fine metal particles dispersed and deposited on the metal surface, the size and quantity of the plurality of discharge columns generated during the barrier discharge, that is, the plasma energy density of the discharge part can be controlled. By appropriately installing this at a plasma energy density that matches the reaction gas system for reforming purposes, a low-power and high-efficiency plasma reforming reaction can be realized.
[0043]
Hereinafter, although the suitable Example of this invention is described, this invention is not limited to these Examples at all.
[0044]
Example 1
Using an apparatus as shown in FIG. 1, the ratio of depositing and precipitating metal fine particles with high thermionic emission properties on the surface is changed, and NO _x gas due to the difference in composite barrier discharge due to the coverage of metal fine particles with high thermionic emission properties. Was subjected to a decomposition test.
[0045]
Here, tungsten having a metal particle diameter of 5 μm was used as the metal fine particles having a high thermionic emission property on the surface.
[0046]
FIG. 3 shows the relationship between the surface coverage of the fine metal particles having high thermionic emission properties and the NO _x gas decomposition rate.
[0047]
The particle diameter of the metal fine particles is 5 μm, and when the coverage is 0%, the conventional apparatus is used.
[0048]
As shown in FIG. 3, it was found that the NO _x decomposition efficiency was good when the surface coverage was in the range of 20 to 65%.
[0049]
(Example 2)
Instead of the NO _x gas in Example 1, CO ₂ was used as the gas to be decomposed, and the same measurement was performed.
[0050]
The result is shown in FIG.
[0051]
As shown in FIG. 4, it was found that the CO ₂ decomposition efficiency was good when the surface coverage was in the range of 20 to 65%.
[0052]
(Example 3)
In the dissociation of CO ₂ in Example 2, and the particle size of the fine metal particles while varying measures the gas reforming rate.
[0053]
The surface coverage was 60%.
[0054]
The result is shown in FIG.
[0055]
As shown in FIG. 5, when the surface coverage is constant, the number of lightning-like discharges that occur as the metal particle size is smaller increases and the probability of contact with CO ₂ gas increases. Turned out to improve.
[0056]
Example 4
Next, when CO ₂ was decomposed in Example 2, the gas reforming rate due to the difference in the dispersion form of the metal fine particles was measured.
[0057]
As the form of dispersion, the metal fine particles 13 were intensively dispersed on the surface of the metal plate electrode 14 and the case where the metal fine particles 13 were uniformly dispersed were carried out.
[0058]
FIG. 6 shows a dispersion state diagram of a metal electrode in which metal fine particles are dispersed and deposited on the surface.
[0059]
The particle size of the metal fine particles was 5 μm.
[0060]
The result is shown in FIG.
[0061]
As shown in FIG. 7, the discharge state shifts to the local concentrated discharge when the metal fine particles are concentrated and dispersed (see FIG. 6A) and when the metal fine particles are uniformly dispersed (see FIG. 6B). Until then, it was found that the CO ₂ reforming rate increased with the increase in coverage.
[0062]
The difference in the dispersion state of the metal fine particles appears as a difference in the surface coverage that shifts to local concentrated discharge, and it turns out that the concentration shifts to 35% in the case of concentrated dispersion and 65% in the case of uniform dispersion. did.
[0063]
When the coverage is low, the decomposition rate is higher in the form of concentrated dispersion at about 20 to 25. However, uniform dispersion is better at 25% or more thereafter, so that uniform dispersion is preferable as a whole. It has been found.
[0064]
【The invention's effect】
According to the present invention, metal fine particles are dispersed and deposited on the surface of one of the opposing electrodes, so that when a high voltage is applied, a composite barrier discharge is generated, and gases such as CO ₂ and NO _X are decomposed with high efficiency. can do.
[Brief description of the drawings]
FIG. 1 is a schematic view of a gas reformer of the present invention.
FIG. 2 is a perspective view of a metal electrode in which metal fine particles are dispersed and deposited on the surface.
FIG. 3 is a graph showing the relationship between the surface coverage of metal fine particles having high thermionic emission properties and the NO _x gas decomposition rate.
FIG. 4 is a graph showing the relationship between the surface coverage of the fine metal particles having high thermionic emission properties and the CO ₂ gas decomposition rate.
FIG. 5 is a graph showing the relationship between the particle diameter of metal fine particles having high thermionic emission properties and the CO ₂ gas decomposition rate.
FIG. 6 is a dispersion state diagram of a metal electrode in which metal fine particles are dispersed and deposited on the surface.
FIG. 7 is a graph showing the relationship between the surface dispersion state of metal fine particles having high thermionic emission properties and the CO ₂ gas decomposition rate.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Gas 12 Decomposition | disassembly container 13 Metal particulate 14 Metal flat plate electrode 15 Metal flat plate electrode 16 Dielectric 17 Power supply unit

Claims (9)

A first flat plate electrode and a second flat plate electrode facing each other, a dielectric interposed between the two electrodes, and a potential difference applying means for applying a potential difference between the two electrodes;
Plasma formed by dispersing and depositing metal fine particles covering the surface with a surface coverage of 20% to 60% on the surface of the first electrode, and applying a high voltage to generate a composite barrier discharge. Disassembly equipment.   2. The plasma decomposing apparatus according to claim 1, wherein the dielectric is laminated on the surface of the second electrode.   3. The plasma decomposing apparatus according to claim 1, wherein the metal fine particles are metal fine particles having a high thermoelectron emission property.   4. The plasma decomposition apparatus according to claim 3, wherein the metal fine particles are at least one selected from the group consisting of tungsten, platinum, thallium, niobium, nickel, zirconium, cesium, and barium.   3. The plasma decomposing apparatus according to claim 1, wherein the metal fine particles are metal fine particles having a high secondary electron emission property.   3. The plasma decomposing apparatus according to claim 1, wherein the metal fine particles are metal fine particles having a low glow cathode fall voltage and a high electron emission property.   7. The plasma according to claim 5, wherein the metal fine particles are at least one selected from the group consisting of magnesium oxide, cesium composite, copper beryllium, silver magnesium, rubidium composite, and calcium oxide. Disassembly equipment.   The plasma decomposition apparatus according to claim 1, wherein a dispersion form of the metal fine particles is uniform dispersion or concentrated dispersion. In a gas plasma decomposition method for decomposing a gas by applying a potential difference between opposing electrodes to generate plasma,
Metal fine particles covering the surface with a surface coverage of 20% to 60% are dispersed and deposited on the surface of one electrode, and a high voltage is applied to decompose the gas while generating a composite barrier discharge. Gas plasma decomposition method.

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