JP2005285367A - Plasma generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize plasma production having high plasma space volume ratio over a plasma reactor volume and plasma production having high power efficiency. <P>SOLUTION: A grounding side electrode 3, a high-voltage side electrode 4 and a dielectric member 5 disposed between them are provided in the plasma reactor A, that is, a plasma processing chamber. The dielectric member 5 has a structure, in which a porous ceramic base material is covered with an inorganic dielectric material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a plasma generator, and more particularly to an atmospheric pressure plasma generator that generates plasma under normal pressure.

As a discharge method of a plasma generator for generating plasma, silent discharge, pulse discharge, creeping discharge, or ferroelectric pellet filling discharge is known. In any of these discharge methods, a predetermined space is brought into a plasma state by applying a voltage to an electrode located in the vicinity of the predetermined space at or near atmospheric pressure. For example, in a ferroelectric pellet filling discharge, a pellet-like ferroelectric is arranged between the ground-side electrode and the high-voltage side electrode, and a voltage is applied between the two electrodes, thereby causing a gap between the pellet-like ferroelectrics. Plasma is generated in the gap formed in the.
JP-A-8-321397

  However, in the above-described silent discharge, creeping discharge, or ferroelectric pellet filling discharge, the discharge space is very narrow for the reason of effectively generating the discharge. In particular, in a ferroelectric pellet-filled discharge, the pellet size is generally made relatively small in order to increase the discharge density. For this reason, the ferroelectric pellet occupies the plasma reactor volume. The volume is very large and the porosity, and thus the plasma space volume fraction, is very small. Moreover, in this structure, since the space | gap formed between pellets is small, when using to-be-processed gas distribute | circulating to plasma space and using it, there also exists a problem that a pressure loss becomes large. By increasing the pellet size, the porosity can be increased. However, in this case, there is a problem that it is difficult to obtain a high-density plasma space by increasing the voids generated between the pellet-like ferroelectrics.

  In addition, the conventional technology has a problem that since the volume of the ferroelectric portion is large, the ratio of power consumed by heat generation is large with respect to the power input to generate plasma, and the power efficiency with respect to discharge is poor. It was. Patent Document 1 discloses a structure in which a dielectric material in which a surface of a granular conductive material is coated with a ferroelectric substance is filled between a ground side electrode and a high voltage side electrode, and a voltage is applied between both electrodes to generate plasma. Thus, a technique has been disclosed in which the discharge start voltage is reduced as compared with the case where a dielectric formed only of a conventional ferroelectric material is used. However, the technique of Patent Document 1 cannot solve the above-described problems.

  Further, with respect to the above problems, it is conceivable to dispose a porous ceramic between the electrodes as a method for increasing the plasma space volume ratio with respect to the plasma reactor volume. However, when the porous ceramic disposed between the electrodes is made of a ferroelectric material such as barium titanate, the heat generation of electric power is concerned, and when the porous ceramic is made of a material having a low dielectric constant such as alumina, the discharge starting voltage is concerned. There is room for further improvement.

  The present invention has been made in view of the above problems in the prior art, and an object of the present invention is to provide a plasma generator that realizes plasma generation with a high plasma space volume ratio with respect to the plasma reactor volume, and further plasma generation with high power efficiency.

  To achieve the above object, a plasma generator according to an embodiment of the present invention includes a ground side electrode, a high voltage side electrode, and a dielectric member disposed between the ground side electrode and the high voltage side electrode. A plasma generator for generating plasma under normal pressure by applying a voltage between a ground side electrode and a high voltage side electrode, wherein the dielectric member has a structure in which a porous ceramic substrate is coated with an inorganic dielectric material It is characterized by having.

  In another embodiment of the present invention, the plasma generating apparatus is characterized in that the dielectric member has a structure in which a honeycomb-shaped ceramic substrate is coated with an inorganic dielectric substance.

  According to the plasma generator having the above configuration, the plasma space volume ratio with respect to the plasma reactor volume can be increased and the power efficiency can be increased without reducing the plasma density in the plasma space. In addition, compared with a configuration in which a porous ceramic member made of a single substance of a ferroelectric substance or a substance having a low dielectric constant is arranged between electrodes, it is possible to reduce the heat consumption of electric power and lower the discharge start voltage. .

  According to the present invention, plasma generation with a high plasma space volume ratio and plasma generation with high power efficiency can be realized with respect to the plasma reactor volume.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. 1 and 2 are schematic views showing the configuration of a plasma generator according to an embodiment of the present invention, respectively. (A) and (b) are cross-sectional views along planes orthogonal to each other. FIG. 3 is a schematic view of a dielectric member used in the plasma generator of FIG. 4 and 5 are schematic views showing examples of the configuration of a gas processing apparatus using a plasma generator having the same configuration as that shown in FIGS. 1 and 2, respectively.

  The plasma generator shown in FIG. 1 performs a plasma treatment in which a ground side electrode 3 and a high voltage side electrode 4 for applying a voltage, and a dielectric member 5 disposed between the electrodes are disposed in the outer wall member 2. It has a plasma processing chamber A for execution, that is, a plasma reactor. The ground side electrode 3 and the high voltage side electrode 4 are provided in parallel with the dielectric member 5 interposed therebetween, that is, the plasma processing chamber A is configured as a parallel plate type plasma reactor. A plurality of ground-side electrodes 3 and high-voltage-side electrodes 4 are alternately provided with a plurality of dielectric members 5 sandwiched therebetween, and the plasma processing chamber A as a whole has the dielectric members 5 and the ground-side electrodes 3 sandwiching the dielectric members 5 and A plurality of plasma processing units constituted by the high-voltage side electrodes 4 are stacked.

  Although FIG. 1 shows a plasma processing chamber A having a rectangular shape, the shape of the plasma processing chamber A is not limited to this. The same applies to the following drawings.

  A gas inflow hole 2a for allowing a gas such as a gas to be processed to flow into the plasma processing chamber A is formed on one side surface of the plasma processing chamber A orthogonal to the ground side electrode 3 and the high voltage side electrode 4, and the opposite side. A gas outflow hole 2b for allowing a gas to flow out from the plasma processing chamber A is formed in the side wall of. The gas inflow hole 2a and the gas outflow hole 2b are provided at a plurality of locations corresponding to each dielectric member 5, and thus corresponding to each plasma processing unit.

  The side of the plasma processing chamber A where the gas inflow hole 2a is provided is provided with a gas introduction port 1 for introducing gas from outside the system, and a gas introduction part B for introducing the introduced gas to each gas inflow hole 2a. Is provided. Similarly, on the side of the plasma processing chamber A where the gas outflow hole 2b is provided, a gas exhaust port 1 for exhausting gas out of the system is provided, and the gas flowing out from each gas inflow hole 2b is discharged to the gas exhaust port. A gas discharge part C leading to 1 is provided.

  In the plasma processing apparatus of FIG. 1, each dielectric member 5 has a porous structure forming a three-dimensional network structure, and a gap in the network structure becomes a gas flow path. Although not shown in detail, the dielectric member 5 has a structure in which a porous ceramic base material is coated with an inorganic dielectric substance, and the porous ceramic base material is coated with an inorganic electric substance and then fired. It is formed by doing.

  At this time, the porous ceramic base material has a relative dielectric constant lower than that of the inorganic dielectric material, and the relative dielectric constant of the porous ceramic base material is desirably 50 or less. Preferred examples of such ceramics include alumina and zirconium oxide. On the other hand, the inorganic dielectric material is a ferroelectric material, and the relative dielectric constant of the inorganic dielectric material is desirably 1000 or more. Preferred specific examples of such inorganic dielectric materials include barium titanate and strontium titanate. However, these porous ceramic base materials and inorganic dielectric materials are not limited to the above materials, and other ceramics and ferroelectrics can be used as long as they satisfy the above conditions.

  The plasma generating apparatus shown in FIG. 2 has the same configuration as that shown in FIG. 1 except that the configuration of the dielectric member 15 is different. In FIG. A detailed description will be omitted.

  The dielectric member 15 in the plasma generator shown in FIG. 2 has a structure in which an inorganic dielectric material 22 is coated on a honeycomb-shaped ceramic substrate 21 as shown in FIG. It is formed by firing after coating the substance.

  The honeycomb-shaped ceramic substrate 21 is formed by alternately laminating a corrugated sheet-shaped ceramic that can be bent into a corrugated shape and a flat sheet-shaped ceramic. The ceramic material constituting the honeycomb-shaped ceramic substrate 21 has a relative dielectric constant lower than that of the inorganic dielectric substance, and the relative dielectric constant of the honeycomb-shaped ceramic substrate 21 is desirably 50 or less. Preferable specific examples of such a ceramic material include alumina and zirconium oxide. The inorganic dielectric material 22 is a ferroelectric material, and the relative dielectric constant of the inorganic dielectric material 22 is desirably 1000 or more. Preferable specific examples of such an inorganic dielectric material 22 include barium titanate and strontium titanate. However, the honeycomb-shaped ceramic base material 21 and the inorganic dielectric material 22 are not limited to the above materials, and other ceramics and ferroelectrics can be used as long as the above conditions are satisfied. .

  A plasma generator having a parallel plate type plasma reactor shown in each of FIGS. 1 and 2 is, for example, a gas processing apparatus as shown in FIGS. It can be used to detoxify the gas to be treated by plasma treatment. In each gas processing apparatus shown in FIGS. 4 and 5, an introduction pipe provided with a fan 12 for circulating a gas to be processed in the gas introduction port 1 of the plasma generator having the same configuration as shown in FIGS. 13 is connected, and a discharge pipe 14 for discharging the processed gas is connected to the gas discharge port 6. A high voltage power supply 11 is connected between the ground side electrode 3 and the high voltage side electrode 4. 4 and 5 has the same configuration as that shown in FIGS. 1 and 2 except that the number of plasma processing units is different. The number of plasma processing units is not limited to that shown in the figure, and can be changed as appropriate.

  The gas processing by these gas processing apparatuses is performed as follows. That is, the fan 12 is started, and the gas to be processed flows from the gas introduction part B into each plasma processing unit in the plasma processing chamber A and flows through each plasma processing unit while being in contact with the dielectric members 5 and 15. At that time, a voltage is applied between the ground side electrode 3 and the high voltage side electrode 4 by the high voltage power source 11. As a result, a discharge is generated in the dielectric member gap space under normal pressure and the gap wall surface in each plasma processing unit to generate plasma, and the plasma is decomposed and rendered harmless by this plasma. In this manner, the gas that has been rendered harmless by plasma processing in each plasma processing unit flows out to the gas discharge part C and is discharged out of the system through the gas discharge port 6.

  According to the present embodiment described above, in the plasma processing chamber A, that is, the plasma reactor, the porosity can be increased and a high plasma space volume ratio can be obtained without greatly reducing the plasma density, and power efficiency can be obtained. Can be increased. In addition, compared with a configuration in which a porous ceramic member made of a single substance of a ferroelectric substance or a substance having a low dielectric constant is arranged between electrodes, it is possible to reduce the heat consumption of electric power and lower the discharge start voltage. .

  The parallel plate type plasma reactor can also be configured as shown in FIG. In the configuration shown in FIG. 6, a ground side electrode 23 and a high voltage side electrode 24 having a mesh structure capable of passing gas are provided on both sides of the dielectric member 5. In this configuration, the gas to be processed is circulated in a direction perpendicular to the ground-side electrode 23 and the high-voltage side electrode 24 as shown by arrows in the drawing. At this time, a dielectric member 15 having a honeycomb structure may be disposed between the ground-side electrode 23 and the high-voltage side electrode 24. In this case, the dielectric member 15 is connected to the surface on the ground-side electrode 23 side and the high-voltage side electrode. The gas is allowed to flow between the electrode 24 and the surface on the electrode 24 side.

  The plasma processing of the gas to be processed by the parallel plate type plasma reactor shown in FIG. 6 is executed as follows, for example. That is, a gas to be processed such as a gas containing a volatile harmful substance is allowed to flow from one side of the ground side electrode 23 and the high voltage side electrode 24, and at that time, the high voltage power source 11 causes the ground side electrode 23 and the high voltage side electrode 24 to flow. A voltage is applied between As a result, discharge occurs in the dielectric member gap space and the gap wall surface under normal pressure to generate plasma, and the plasma is decomposed and rendered harmless by this plasma. Thus, the gas that has been rendered harmless by the plasma treatment in the plasma reactor flows out from the other side of the ground side electrode 23 and the high voltage side electrode 24 and is discharged out of the system.

  The features and effects of the present invention will be more specifically described below with reference to Examples, Comparative Examples 1 and 2, but the present invention is not limited to these Examples.

In Examples and Comparative Examples 1 and 2, gas treatment devices having different configurations were used to perform a treatment for detoxifying a gas containing a volatile substance as follows.
(Example)
FIG. 7 shows a schematic configuration diagram of a gas processing apparatus using a plasma generator used in the examples. In this gas processing apparatus, a plasma generator having a parallel plate type plasma reactor having the same configuration as that shown in FIG. 1 was used. A gas introduction pipe 13 connected to the gas introduction port 1 of the plasma generator extends from the gas cylinder 8 to be processed and is provided with a gas flow rate regulator 9. An analytical instrument 10 is connected to the gas exhaust pipe 14 connected to the gas exhaust port 6. A high voltage power source 11 is connected between the ground side electrode 3 and the high voltage side electrode 4 of the plasma generator. As the dielectric member 5, a porous alumina base material coated with barium titanate (relative permittivity ε = 1600) and fired at 1250 ° C. was used. The porosity of the dielectric member 5 as a whole, that is, the porosity is 80%.

  A plasma reactor having an internal volume of 30 mL, a size of the high voltage side electrode 2 and the ground side electrode 3 of 50 mm × 30 mm × 10 mm, and a distance between electrodes of 10 mm was used. As the analytical instrument 10, a gas detector tube (manufactured by Gastec) was used.

Using this gas treatment apparatus, 10 ppm ammonia gas was passed at a flow rate of 6 L / min, and the applied voltage was changed from 15 kVp-p to 23 kVp-p to perform plasma treatment. When the gas after the discharge treatment was analyzed, the ammonia concentration was about 0 ppm to 7 ppm, and the treatment rate was 30% to 100%. The power consumption was 1.0 W to 4.0 W.
(Comparative Example 1)
In Comparative Example 1, the gas processing apparatus having the configuration shown in FIG. 8 was used. The plasma generator shown in FIG. 9 is used for the gas processing apparatus shown in FIG. This plasma generator differs from that of the embodiment shown in FIG. 7 in that a dielectric member 25 having a plurality of spherical dielectrics is used. As the dielectric, granular barium titanate (particle size = 3 mmφ, relative permittivity ε = 1600) was used. The porosity of the dielectric member 25 as a whole is 26%. The internal volume of the plasma reactor, the sizes of the high-voltage side electrode 2 and the ground-side electrode 3, and the analytical instrument 10 used are the same as in the example.

Using this gas treatment apparatus, ammonia treatment was conducted in the same manner as in the example, and plasma treatment was performed by changing the applied voltage. When the gas after the discharge treatment was analyzed, the ammonia concentration was about 0 ppm to 9.5 ppm, and the treatment rate was 5% to 100%. The power consumption was 1.0 W to 6.7 W.
(Comparative Example 2)
In Comparative Example 2, the gas processing apparatus having the configuration shown in FIG. 9 was used. The gas processing apparatus shown in FIG. 9 is the same as that shown in FIG. 7 in that the dielectric member 35 is composed only of the porous ceramic substrate in the plasma generator shown in FIG. 1 and is not coated with an inorganic dielectric substance. It is different from the gas processing apparatus of the comparative example shown. The internal volume of the plasma reactor, the sizes of the high-voltage side electrode 2 and the ground-side electrode 3, and the analytical instrument 10 used are the same as in the example.

Using this gas treatment apparatus, ammonia treatment was conducted in the same manner as in the example, and plasma treatment was performed by changing the applied voltage. When the gas after the discharge treatment was analyzed, the ammonia concentration was about 0 ppm to 9 ppm, and the treatment rate was 10% to 100%. The power consumption was 1.0 W to 4.0 W.
(Evaluation)
The results obtained in Examples and Comparative Examples 1 and 2 are shown as graphs in FIGS. FIG. 11 is a graph showing the results relating to the change in the ammonia treatment rate relative to the power consumption obtained in the example and the comparative examples 1 and 2, and FIG. 12 shows the results relating to the change in the ammonia treatment rate relative to the applied voltage. FIG. 13 is a graph showing the results relating to the change in power consumption with respect to the applied voltage.

  From FIG. 11, it can be seen that the power consumption for obtaining a processing rate of 100% was 4.0 W in the example, whereas that in Comparative Example 1 was 6.7 W. In other words, it can be seen that in the example, the power consumption can be suppressed to 40% as compared with Comparative Example 1.

  From FIG. 11, it can be seen that the comparative example 2 and the example have substantially the same ammonia treatment rate when the power consumption is made the same. However, it can be seen from FIG. 12 that in the example, the applied voltage can be suppressed compared to the comparative example. That is, in the example, by using a dielectric member coated with barium titanate as the inorganic dielectric material, the applied voltage during the treatment was lower than that of Comparative Example 2 using the non-coated member. It can be seen that

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram of the plasma generator of one Embodiment of this invention, FIG. 1 (a) and FIG.1 (b) are sectional drawings along a mutually perpendicular | vertical surface, respectively. It is a schematic diagram of the plasma generator of other embodiment of this invention, and Fig.2 (a) and FIG.2 (b) are sectional drawings along a mutually perpendicular | vertical surface, respectively. 3A and 3B are schematic views of a dielectric member used in the plasma generator of FIG. 2, in which FIG. 3A is a perspective view and FIG. 3B is a partially enlarged front view. It is a block diagram of the gas processing apparatus using the plasma generator of the structure equivalent to FIG. It is a block diagram of the gas processing apparatus using the plasma generator of the structure equivalent to FIG. It is a schematic diagram of the plasma generator of further another embodiment of this invention. It is a block diagram of the gas processing apparatus used in the Example. It is a block diagram of the gas treatment apparatus used in the comparative example 1. It is a schematic diagram of the plasma generator used in the comparative example 1, and Fig.9 (a) and FIG.9 (b) are sectional drawings along a mutually perpendicular | vertical surface, respectively. It is a block diagram of the gas processing apparatus used in the comparative example 2. It is a graph which shows the result which concerns on the change of the ammonia process rate with respect to power consumption obtained by the Example and the comparative example 1 and the comparative example 2. FIG. It is a graph which shows the result which concerns on the change of the ammonia process rate with respect to the applied voltage obtained by the Example and the comparative example 1 and the comparative example 2. FIG. It is a graph which shows the result which concerns on the change of the power consumption with respect to the applied voltage obtained by the Example, the comparative example 1, and the comparative example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Ground side electrode 4 High voltage side electrode 5,15 Dielectric material 21 Honeycomb-shaped ceramic base material 22 Inorganic dielectric material

Claims (7)

A grounding electrode, a high voltage side electrode, and a dielectric member disposed between the ground side electrode and the high voltage side electrode are provided, and a voltage is applied between the ground side electrode and the high voltage side electrode. A plasma generator for generating plasma under normal pressure,
The plasma generating apparatus, wherein the dielectric member has a structure in which a porous ceramic base material is coated with an inorganic dielectric material.   The plasma generating apparatus according to claim 1, wherein the inorganic dielectric material is a ferroelectric material, and is fired after being coated on the porous ceramic substrate.   3. The plasma generating apparatus according to claim 1, wherein the porous ceramic base material is made of a material having a three-dimensional network structure and having a relative dielectric constant lower than that of the inorganic dielectric substance. A grounding electrode, a high voltage side electrode, and a dielectric member disposed between the ground side electrode and the high voltage side electrode are provided, and a voltage is applied between the ground side electrode and the high voltage side electrode. A plasma generator for generating plasma under normal pressure,
The plasma generating apparatus, wherein the dielectric member has a structure in which a honeycomb-shaped ceramic base material is coated with an inorganic dielectric material.   The honeycomb-shaped ceramic substrate has a structure in which a sheet-shaped ceramic that can be bent is corrugated to form a corrugated shape, and the flat sheet-shaped ceramic is laminated alternately. The plasma generator according to claim 4.   The plasma generating apparatus according to claim 4 or 5, wherein the inorganic dielectric material is a ferroelectric material, and is fired after being coated on the honeycomb-shaped ceramic substrate.   The plasma generating apparatus according to any one of claims 4 to 6, wherein the honeycomb-shaped ceramic substrate is made of a material having a relative dielectric constant lower than that of the inorganic dielectric substance.

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