JP2012167614A - Plasma generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma generating device for efficiently treating a gas when plasma is generated in the atmosphere by applying voltage on the gas containing a gas component to be treated.SOLUTION: The plasma generating device has a rod-like electrode to which power is supplied and a metal made cylindrical casing having an internal space into which the rod-like electrode is provided. An electrode side dielectric barrier layer is provided to the first end part of the rod-like electrode to be opposed to the first end surface of one of end parts of the cylindrical casing to protect the first end surface. A supply port for supplying the gas is provided to the first end surface of the cylindrical casing and a casing side dielectric barrier layer is provided to the first end surface of the cylindrical casing to cover the periphery of the supply port. When an edge part on the periphery in the first end of the rod-like electrode is projected on the first end surface of the cylindrical casing in parallel in the longitudinal direction, the edge part on the periphery is projected in a region on the casing side dielectric barrier layer or on the supply port.

Description

  The present invention relates to a plasma generator for generating a plasma at atmospheric pressure by applying a voltage to a gas containing a gas component to be processed.

  Today, in order to oxidize NO in exhaust gas exhausted from a diesel engine or the like, a processing apparatus using plasma generated in atmospheric pressure has been proposed.

  Conventionally, a plasma reactor has been proposed in which a high voltage of several kV is applied between electrodes to generate plasma, and this plasma is used to oxidize supplied NO (Non-patent Document 1). FIG. 11 shows the apparatus configuration of this plasma reactor. As shown in FIG. 11, the plasma reactor 10 includes a cylindrical dielectric glass tube 12, an electrode 16 wound around the outer peripheral surface of the dielectric glass tube 12, and a porous dielectric in the dielectric glass tube 12. A spherical pellet 22 made of a dielectric crystal disposed in a space where both sides are separated by body plates 18 and 20, and an AC power source 24 that applies an AC voltage of 60 Hz between the discharge electrode 14 and the electrode 16. .

  By applying a voltage between the discharge electrode 14 and the electrode 16, a high electric field is formed between the spherical pellets 22, and a micro discharge having a short period of nanosecond order is generated to generate non-equilibrium plasma. On the other hand, a nitrogen oxidizing gas containing NO flows through the gap between the spherical pellets 22 as a gas fluid in the dielectric glass tube 12. Therefore, the nitrogen oxidizing gas containing NO is oxidized using the plasma generated in the narrow gap between the spherical pellets 22 and is discharged from the dielectric glass tube 12. Thereby, it is supposed that the oxidation process of NO can be performed efficiently.

Further, a high-voltage plasma generator that efficiently processes a supplied gas by expanding a plasma generation region in the atmosphere is known (Patent Document 1).
Specifically, this apparatus is a long electrode that generates resonance by feeding a high-frequency signal and generates a high voltage by this resonance, and the feeding point of the AC signal is provided in the long middle portion. A first electrode to be formed, and a metal that covers the periphery of the first electrode and is provided with a gas flow supply port at a position spaced apart from at least one end of the first electrode on the extension of the first electrode A grounded second electrode connected to the casing, the first electrode being connected to the casing, in the vicinity of one end of the first casing and the first electrode. And a power supply device that supplies a signal having the same frequency as the resonance frequency when radiating. In this apparatus, plasma using a gas is generated in a region between the first electrode and the second electrode.

"Non-equilibrium plasma and chemical reaction process combined removal technology of nitrogen oxide gas (performance comparison between conventional and barrier plasma reactors), Toshiaki Yamamoto et al., Transactions of the Japan Society of Mechanical Engineers, 66-646B (2000), 1501- No. 1506

JP 2010-025049 A

  However, in the plasma reactor 10 disclosed in Non-Patent Document 1, since the spherical pellets 22 are arranged in the flow path through which the gas flows, it is difficult to ensure a sufficient flow rate due to flow path resistance or the like. In addition, since the micro discharge having a short period of nanosecond order is used, the efficiency of the oxidation treatment of NO is low. For this reason, it is desired to increase the plasma generation region and efficiently oxidize a lot of NO. In addition, since a voltage of several kV is applied for discharging, the power supply becomes large and it is difficult to configure a compact device.

  On the other hand, in the high-voltage plasma generator disclosed in Patent Document 1, the mesh electrode is provided as the second electrode so as to cover the gas supply port, whereby the mesh electrode on the supply port and the elongated electrode are provided. Plasma can be generated in a wide range. However, in this high-voltage plasma generator, plasma may not be generated uniformly and stably over a wide range, and gas may not be processed efficiently.

  In view of the above, an object of the present invention is to provide a plasma generator capable of efficiently processing a gas when a voltage is applied to a gas containing a gas component to be processed to generate a plasma at atmospheric pressure. .

One embodiment of the present invention is a plasma generator that generates plasma in an atmospheric pressure by applying a voltage to a gas containing a gas component to be processed. The device is
A rod-shaped electrode to which electric power is supplied to generate plasma;
A metal cylindrical housing provided with a long internal space in one direction, the rod-shaped electrode being provided in the internal space along the longitudinal direction of the internal space;
An electrode-side dielectric barrier layer provided at the first end of the rod-shaped electrode so as to protect the first end;
A supply port for supplying the gas provided on a first end surface of the cylindrical casing facing the electrode-side dielectric barrier layer;
A housing-side dielectric barrier layer provided on the first end face so as to surround the supply port.
In that case, when the electrode side circumferential upper edge portion in the cross-sectional shape of the first end portion of the rod-shaped electrode is projected on the first end surface of the cylindrical housing in parallel with the longitudinal direction, the electrode A side peripheral upper edge portion is projected onto a region on the housing side dielectric barrier layer or on the supply port.

  In the apparatus, plasma is generated with the casing side circumferential upper edge portion of the supply port as a counter electrode to the rod-shaped electrode, for example, the shortest distance from the electrode side circumferential upper edge portion to the casing side circumferential upper edge portion is It is preferable that the position is the same at each position of the electrode side circumferential upper edge portion.

  Furthermore, both the case side circumferential upper edge part and the electrode side circumferential upper edge part form an arc shape, and the center positions of the arc shape are both located on the same straight line parallel to the longitudinal direction. Is preferred.

  Further, it is preferable that a feeding point is provided at an intermediate portion in the longitudinal direction of the rod-shaped electrode, and a dielectric covers the periphery of at least a part of the rod-shaped electrode in the longitudinal direction.

  The second end surface opposite to the first end surface of the cylindrical housing is provided with a discharge port for exhausting gas, and the dielectric is formed between the dielectric and the side surface of the cylindrical housing. A gas flow path is provided so that a part of the internal space is formed therebetween, and a space between the dielectric and the cylindrical housing guides the gas supplied from the supply port to the discharge port It is preferable to form.

It is preferable that the relative permittivity of the dielectric is 10 or more, and the dielectric loss tangent of the dielectric is 5 × 10 ⁻⁴ or less.

  In addition, it is preferable that high-frequency power having a constant frequency is intermittently repeatedly supplied to the rod-shaped electrode, so that plasma is intermittently generated in the internal space.

  It is preferable that plasma is generated intermittently so as to surround the supply port with the electrode side circumferential upper edge portion and the housing side circumferential upper edge portion as electrodes.

  According to the above plasma generator, when a voltage is applied to a gas containing a gas component to be processed to generate plasma at atmospheric pressure, the gas can be processed efficiently.

It is a schematic block diagram of the plasma reactor which is the plasma generator of this embodiment. It is sectional drawing of the plasma reactor shown in FIG. It is a schematic block diagram of the electric power supply unit used for the plasma reactor of this embodiment. (A) is a figure which shows the RF signal which the RF oscillator of the electric power supply unit shown in FIG. 3 produces | generates, (b) is a figure which shows the rectangular pulse signal which a burst control signal generator produces | generates, (c ) Is a diagram showing a signal output from the amplitude modulator. It is a figure which shows the resonance state of the plasma reactor shown in FIG. It is a figure which shows typically an example of the change of the electric field strength measured with the electric field probe of the plasma reactor of this embodiment. It is a figure which shows the generation | occurrence | production position of the plasma generate | occur | produced with the plasma reactor of this embodiment. It is a figure which illustrates typically the relationship between the electric field strength when plasma generate | occur | produces by barrier discharge, and the energy of plasma. It is a figure which shows the modification of the plasma reactor of this embodiment. (A)-(c) is a figure which shows the result of having performed the process of the gas containing NOx in this embodiment on various conditions. It is a figure which shows the apparatus structure of the conventional plasma reactor.

Hereinafter, the plasma generator of the present invention will be described in detail based on this embodiment.
FIG. 1 is a schematic configuration diagram of a plasma reactor which is a plasma generating apparatus of the present embodiment. The plasma reactor supplies nitrogen oxidizing gas (NOx) into the plasma reactor, intermittently generates plasma near the gas supply port in the plasma reactor, and processes and discharges NOx using this plasma.
Specifically, the plasma generator mainly includes a rod-shaped electrode 100, a housing 110, and a power supply unit 140.

  The rod-shaped electrode 100 is a long rod-shaped electrode having a circular cross section. The rod-shaped electrode 100 extends along the longitudinal direction of the internal space (X direction in FIG. 1) so as to be separated from the inner wall surface of the internal space of the housing 110 in the internal space long in one direction of the housing 110. Provided. The rod-shaped electrode 100 is supplied with high-frequency signal power, and generates a high voltage when resonance occurs in the rod-shaped electrode 100. The rod-like electrode 100 of this embodiment is made of copper, but silver, aluminum, etc. are also preferably used.

A feeding point 102 for high-frequency signals is provided at an intermediate portion in the longitudinal direction of the rod-shaped electrode 100. A high frequency signal is applied as power from the feeder 118 to the feeding point 102. Assuming that the length of the rod-shaped electrode 100 in the longitudinal direction is 2 l, the feeding point 102 is located at a position slightly shifted from the center position of the rod-shaped electrode 100 in the longitudinal direction. When the distance from the longitudinal center position of the rod-shaped electrode 100 to a position where the feeding point 102 is provided to x _0, x ₀ satisfies the relation represented by the following formula (1).

Here, Z ₀₀ is a characteristic impedance of a power supply line that supplies power to the power supply point 102, and Z _C is a characteristic impedance when the rod-shaped electrode 100 is used as a transmission line. Further, when the coefficient indicating the energy loss of the equivalent capacitance C at the time of plasma generation in the plasma generator is χ, Q = 1 / χ.

The reason why the feeding point 102 is provided at a position slightly deviated from the center position in the longitudinal direction of the rod-shaped electrode 100 is to obtain impedance matching when feeding power to the plasma reactor. Similar to the AC dipole antenna, when the half length of the wavelength λ of the electromagnetic wave transmitted through the rod-shaped electrode 100 becomes the length 2l of the rod-shaped electrode 100, resonance of the lowest order mode occurs in the rod-shaped electrode 100, and high efficiency is achieved. A voltage is generated. Therefore, the length 21 of the rod-shaped electrode 100 is an important factor for determining the resonance frequency in the plasma reactor. In addition, since the rod-shaped electrode 100 is provided with a dielectric 105 around the rod-shaped electrode 100 as will be described later, the wavelength λ of the electromagnetic wave changes according to the dielectric constant of the dielectric 105, and there is no dielectric 105. The wavelength is different from the case.
In the present embodiment, the length 21 of the rod-like electrode 100 is set according to the dielectric constant of the dielectric 105 so as to generate a high voltage at a predetermined frequency in a frequency band of 100 MHz to 10 GHz.
One end portion (left end portion in FIG. 1) of the rod-shaped electrode 100 is opposed to one end surface (end surface of the left end portion in FIG. 1) of the housing 110 with the internal space interposed therebetween. An electrode-side dielectric barrier layer 104 is provided to protect the film. For the electrode-side dielectric barrier layer 104, a dielectric such as aluminum oxide is used, for example.

A dielectric 105 is provided around the rod electrode 100 along the longitudinal direction of the rod electrode 100. The dielectric 105 has a solid cylindrical shape provided such that a part of the internal space is formed between the dielectric 105 and the side surface of the housing 110, and as shown in FIG. A space between the casing 110 and the casing 110 is formed as a gas flow path 106 that guides a gas supplied from a supply port 114 described later to a discharge port 116 described later. The relative dielectric constant of the dielectric 105 is preferably 10 or more. The dielectric loss tangent of the dielectric 105 is preferably 5 × 10 ⁻⁴ or less. As such a dielectric 105, for example, a sintered body of aluminum oxide or titanium oxide is preferably used.
Note that, at the feeding point 102, power is fed through a hole formed in the dielectric 105 by a feeding line 118 connected to the power supply unit 140 via the connection terminal 120.

The casing 110 is a metal cylindrical casing having an internal space that is long in one direction and provided with a rod-shaped electrode 100 along the longitudinal direction (X direction) of the internal space. It is maintained at 0. The housing 110 is made of, for example, aluminum, but may be made of a metal such as silver or copper. Supply for supplying a gas to be treated including NOx to one end face (the end face at the left end in FIG. 1) of the casing 110 facing the end where the electrode-side dielectric barrier layer 104 is provided in the rod-shaped electrode 100. A mouth 114 is provided. A housing-side dielectric barrier layer 115 is provided on the end face provided with the supply port 114 so as to cover the periphery of the supply port 114.
The supply port 114 is connected to a supply pipe 130 that supplies a gas to be processed including NOx. For example, the supply pipe 130 is connected to an exhaust port such as a diesel engine.

The supply port 114 is not provided with a mesh electrode serving as a counter electrode of the rod-shaped electrode unlike the conventional high voltage plasma generator. Instead, the housing-side dielectric barrier layer 115 is provided on the wall surface so as to surround the periphery of the supply port 114.
A housing-side dielectric barrier layer 115 is provided on the end surface of the housing 110 so as to surround the supply port 114, and the electrode-side dielectric barrier is provided on the rod-like electrode 100 so as to face the end surface on which the housing-side dielectric barrier layer 115 is provided. The layer 104 is provided in order to generate a dielectric barrier discharge in a space between the casing-side circumferential upper edge portion of the supply port 114 and the electrode-side circumferential upper edge portion of the rod-shaped electrode 100 to stably generate plasma. It is.
For this reason, the electrode side circumferential upper edge portion at the end portion of the rod-shaped electrode 100 provided with the electrode-side dielectric barrier layer 104 is arranged in the longitudinal direction (in FIG. 1) on the end surface of the housing 110 provided with the supply port 114. When projected in parallel with the X direction, the above-mentioned electrode-side circumferential upper edge portion of the rod-shaped electrode 100 is projected onto the housing-side dielectric barrier layer 115 or the region of the supply port 114. That is, the electrode-side circumferential upper edge portion of the rod-shaped electrode 100 faces the housing-side dielectric barrier layer 115 surrounding the periphery of the supply port 114 in the housing 110 or the region of the supply port 114 in the X direction (longitudinal direction). .

  The casing side peripheral upper edge portion refers to a corner where the supply port 114 is formed by the end surface of the housing 110 and the wall surface of the hole connected to the supply port 114. Similarly, the electrode side circumferential upper edge portion is an angle formed by the end surface of the rod-shaped electrode 100 and the side surface of the rod-shaped portion.

Further, the housing side circumferential upper edge portion of the supply port 114 is a grounded counter electrode with respect to the rod-shaped electrode 100, and the shortest distance from the electrode side circumferential upper edge portion of the rod-shaped electrode 100 to the housing side circumferential upper edge portion of the supply port 114 is It is preferable that the same at each position of the electrode side circumferential upper edge portion in that plasma is stably generated by barrier discharge. The plasma at this time is generated in a cylindrical shape so as to surround the supply port 114.
The casing-side circumferential upper edge portion of the supply port 114 and the electrode-side circumferential upper edge portion of the rod-shaped electrode 100 both have an arc shape, and the center position of the arc shape is the same along the X direction in FIG. Positioning on a straight line is preferable in that cylindrical plasma is generated so as to surround the supply port 114 by barrier discharge. When the case side circumferential upper edge portion and the electrode side circumferential upper edge portion have sharp bent portions, plasma is concentrated around the bent portions and it becomes difficult to generate cylindrical plasma.

  A discharge port 116 for discharging the supplied gas is provided on the end surface of the cylindrical housing 110 opposite to the end surface on which the electrode-side dielectric barrier layer 104 is provided. A discharge pipe 132 that discharges gas is connected to the discharge port 116. A blower (not shown) is connected to the discharge pipe 132, and the gas inside the housing 110 is discharged to the atmosphere.

  The power supply unit 140 supplies power to the power supply point 102 intermittently (intermittently) with an AC signal having the same frequency as the resonance frequency of the rod-shaped electrode 100. In the approximate frequency range of the signal supplied by the power supply unit 140, the length of half of the wavelength λ of the transmission signal transmitted through the rod-shaped electrode 100 is the length 2l of the rod-shaped electrode 100, and resonance in the lowest order mode occurs. It is prescribed as follows.

FIG. 3 is a diagram illustrating a schematic configuration of the power supply unit 140. As shown in FIG. 3, the power supply unit 140 includes an RF oscillator 142, a variable attenuator 143, a burst control signal generator 144, an amplitude modulator 146, and an amplifier 148.
The RF oscillator 142 oscillates a continuous wave having a frequency of 100 MHz to 10 GHz and generates an RF signal. In the following description, the frequency at which the RF oscillator 142 oscillates is assumed to be f ₁ [Hz]. The frequency f ₁ oscillated by the RF oscillator 142 is adjusted based on the measurement result of the electric field probe 122. The RF signal generated by the RF oscillator 142 is output to the amplitude modulator 146 via the variable attenuator 143.
Note that the power supply unit 140 can also supply a signal having a frequency corresponding to the resonance frequency based on the intensity of the signal reflected by the connection terminal 120.
The variable attenuator 143 variably adjusts the signal level of the RF oscillator 142.

The burst control signal generator 144 generates a rectangular pulse signal at a predetermined frequency. In the following description, the pulse width of the rectangular pulse signal generated by the burst control signal generator 144 is W [seconds], and the frequency for generating the rectangular pulse signal is f ₂ [Hz]. Here, 1 / f ₁ <W <1 / f ₂ . The pulse width W of the rectangular pulse signal generated by the burst control signal generator 144 is such that the voltage of the rod-shaped electrode 100 that increases by feeding when a high-frequency signal having the same frequency as the resonance frequency of the rod-shaped electrode 100 is fed to the feeding point 102. It is set to be longer than the period until the plasma is generated by the barrier discharge after exceeding the insulation voltage.
Generally, when the pulse width W is too long, thermal plasma may be generated. When the thermal plasma is generated, heat is generated in the rod-shaped electrode 100, and NO or NO ₂ may be generated due to this. Therefore, the pulse width W is preferably set to a length that does not generate thermal plasma.
The rectangular pulse signal generated by the burst control signal generator 144 is output to the amplitude modulator 146.

The amplitude modulator 146 receives an RF signal generated by the RF oscillator 142. The amplitude modulator 146 receives the rectangular pulse signal generated by the burst control signal oscillator 144. The amplitude modulator 146 outputs the RF signal generated by the RF oscillator 142 only during the period of W [s] receiving the input of the rectangular pulse signal. In other words, the amplitude modulator 146 intermittently repeatedly outputs an AC signal having a frequency f ₁ [Hz] during W [s] with a period of 1 / f ₂ [s].
The amplifier 148 amplifies the signal output from the amplitude modulator 146. The signal amplified by the amplifier 148 is output to the connection terminal 120.

FIG. 4 is a diagram for explaining an example of a signal generated by the power supply unit 140. FIG. 4A is a diagram illustrating an example of an RF signal generated by the RF oscillator 142. FIG. 4B is a diagram illustrating an example of a rectangular pulse signal generated by the burst control signal generator 144. FIG. 4C is a diagram illustrating an example of a signal output from the amplitude modulator 146.
The power supply unit 140 of the present embodiment repeatedly supplies power to the feeding point 102 intermittently with an AC signal having the same frequency as the resonance frequency when the rod-shaped electrode 100 emits electromagnetic waves. Thereby, plasma is generated intermittently.

FIG. 5 is a diagram for explaining a resonance state when a high-frequency signal having the same frequency as the resonance frequency of the rod-shaped electrode 100 is fed to the feeding point 102. As shown in FIG. 5, when a high-frequency signal having the same frequency as the resonance frequency is fed to the feeding point 102, resonance that maximizes the voltage occurs at both ends of the rod-shaped electrode 100. A voltage _{Vout of} several kV is generated at both ends of the rod electrode 100.
As described above, the feeding point 102 is displaced by a distance x ₀ of the formula (1) with respect to the center position of the rod-shaped electrode 100. The ratio of the voltage V _out at both ends of the rod-shaped electrode 100 to the voltage V _{in at the} feeding point 102 is expressed as 1 / sin {x ₀ / (2l)} using x ₀ / (2l) determined by the equation (1). Is done.

FIG. 6 is a diagram showing a change in the electric field strength of the rod-shaped electrode 100 measured by the electric field probe 122. The waveforms shown in FIG. 6 are the state A in which the electric field is increased by supplying power, the state B in which the barrier discharge is started, and the rectangular pulse signal is OFF as shown in FIG. A state C in which the generated electric field attenuates is shown. In state B, barrier discharge occurs and plasma is generated. Therefore, plasma is intermittently generated each time power is supplied with a 1 / f ₂ [s] period.

  FIG. 7 is a view showing the generation position of the plasma P. As shown in FIG. The plasma P is generated in a cylindrical shape so as to surround the supply port 114 in a space between the housing side edge portion of the supply port 114 and the electrode side edge portion of the rod-shaped electrode 100. In addition, since the barrier discharge and the plasma are generated between the case-side dielectric barrier 115 and the electrode-side dielectric barrier layer 104 provided at the edges of each other, stable plasma generation is realized. In particular, since cylindrical plasma is generated, the gas generated before the gas such as NOx that has passed through the supply port 114 flows before flowing into the gas flow path 106 is surely crossed. Therefore, the gas processing efficiency using plasma is improved.

  FIG. 8 is a diagram schematically illustrating the relationship between electric field strength and plasma energy when plasma is generated by barrier discharge. As shown in FIG. 8, when the dielectric 105 is provided around the rod-shaped electrode 100 (electric field curve D), the dielectric 105 is compared with the case where the dielectric is not provided around the rod-shaped electrode 100 (electric field curve E). Therefore, the time to reach the limit of the barrier discharge is long, but the plasma energy D ′ generated in the case of the electric field curve D is larger than the plasma energy E ′ generated in the case of the electric field curve E. For this reason, the plasma reactor of this embodiment can generate large energy by generating plasma once. Therefore, the plasma reactor of this embodiment can efficiently process a gas such as NOx.

When the dielectric 105 is provided on the rod-shaped electrode 100, the time average value of the energy density of the electromagnetic wave accumulated for a certain period is expressed by the following formula (2). In order to increase the average value of this energy density, it is preferable to increase the relative dielectric constant ε _r . Thus, in this embodiment, the relative dielectric constant is preferably 10 or more.

Average value of energy density = 1/2 · (ε _r · ε ₀ ) · E ₀ ² (2)
(E ₀ is the lower limit value of the electric field in the barrier discharge)

Further, when the electric field of the electromagnetic wave in the dielectric 105 has only a component in the y direction (direction orthogonal to the x direction in FIG. 1), Ey which is the y component of the electric field is expressed by the following formula (3). The energy density of electromagnetic waves from this electric field is expressed by the following equation (4).
Ey = E0 e ^{i (ωt−kx)} (3)
(Ω = 2πf ₁ , k is a wave vector, and x is a position vector.)
Average value of energy density of electromagnetic wave ∝ e ^{-2ωnjz / c} (4)
(N _j is the imaginary part of ε _r ^1/2 (ε _r is the complex dielectric constant), and c is the speed of light.)
Therefore, in order to increase the average value of the energy density of the electromagnetic wave, n _j is decreased, more specifically, the dielectric loss tangent of the dielectric 105 (= tan δ = ε ″ / ε ′: ε ′ and ε ″). It is preferable to reduce the real part and the imaginary part of the complex dielectric constant of the dielectric 105. Accordingly, the dielectric loss tangent of the dielectric 105 is preferably 5 × 10 ⁻⁴ or less.

While flowing a gas containing NOx through such a casing 110, the power of the high-frequency signal as shown in FIG. By feeding the high-frequency signal once, the rod-shaped conductor 100 resonates to cause a barrier discharge between the electrode-side circumferential upper edge portion of the rod-shaped electrode 100 and the casing-side circumferential upper edge portion. Cylindrical plasma is generated so as to surround the periphery of 114. At this time, plasma can be stably generated by constantly supplying a gas flow. Here, “stable” means that the cylindrical plasma is surely generated every time the high-frequency signal is repeatedly fed.
Since the rod-like electrode 100 is provided with the dielectric 105, as shown in FIG. 8, it takes a long time for the electric field to reach the barrier discharge, but the energy of the plasma generated by this discharge is high. For this reason, the cylindrical plasma is surely generated each time the high-frequency signal is repeatedly fed.
The gas processed by the plasma passes through the gas flow path 106 and is discharged from the discharge port 116. The treated gas is treated with plasma, so that harmful NO is treated with NO ₂ or N ₂ and contains almost no NO.

  In the present embodiment, the dielectric 105 is provided in all parts along the longitudinal direction of the rod-shaped electrode 100 as shown in FIG. 1, but the dielectric 105 does not necessarily need to cover the entire rod-shaped electrode 100. For example, as shown in FIG. 9, the dielectric 105 may cover the periphery of a part of the rod-shaped electrode 100 in the longitudinal direction. Even in such a form, the energy of the generated plasma can be increased compared to the conventional case, and a stable cylindrical plasma can be generated.

FIGS. 10A to 10C are diagrams showing the results of processing gas containing NOx under various conditions in the form in which the dielectric 105 is arranged as shown in FIG.
The diameter of the rod-shaped electrode 100 was 12 mm, the outer diameter of the dielectric 105 was 40 mm, and the length of the rod-shaped electrode 100 in the X direction was 270 mm. The diameter of the supply port 114 of the housing 110 was 4 mm. As the dielectric 105, aluminum oxide was used (relative permittivity approximately 10, dielectric loss tangent 4 × 10 ⁻⁴ ). The electrode-side dielectric barrier layer 104 and the housing-side dielectric barrier layer 115 were made of aluminum oxide sintered bodies having thicknesses of 3 mm and 1 mm, respectively. In addition, the distance in the X direction from the end of the rod-shaped electrode 100 where the electrode-side dielectric barrier layer 104 is provided to the position where the supply port 114 is provided was 0.5 mm. Further, the oscillation frequency f ₁ of the RF oscillator 142 was set to 400 MHz, W was set to 1 μsec, and the frequency of feeding high-frequency power was variously changed.

On the other hand, as the gas to be treated, NO gas in the gas discharged when 5 to 20 liters per minute of a gas containing NO (approximately 230 ppm), N ₂ (90%), and O ₂ (about 10%) is flowed. The concentration of was measured. The gas flow rates are 5 liters, 15 liters and 20 liters per minute in order from FIGS. 10 (a), (b) and (c). Figure 10 (a) ~ (c) takes a repetition frequency f ₂ for intermittently feeding a high-frequency signal on the horizontal axis is a graph taking the NO concentration in the gas after treatment on the vertical axis. For comparison, a measurement result of a conventional plasma reactor in which the dielectric 105 is not provided is also shown.

As shown in FIGS. 10A to 10C, by providing the dielectric 105, the NO concentration is lower at the same repetition frequency than the case of the conventional plasma reactor in which the dielectric 105 is not provided. It is possible to reduce the repetition frequency to be substantially zero.
From this, it can be seen that by providing the dielectric 105, gas treatment using plasma can be performed efficiently.

In the present embodiment, a space is provided between the outer surface of the dielectric 105 and the side surface of the housing 110, and the flow path 106 is formed in this space, but the dielectric 105 is filled up to the side surface of the housing 110 to fill the flow path. 106 may not be formed. In this case, a discharge port may be provided on the side surface of the housing 110 at a position in the X direction where the cylindrical plasma is generated. By filling the dielectric 105 so as to be in contact with the side surface of the housing 110, the energy of generated plasma can be further increased.
Further, in this embodiment, the rod-shaped electrode 100 has a uniform circular cross section, but the cross section is circular in the vicinity of the end on the side facing the supply port 114, and the cross sections of the other portions are rectangular or polygonal. Or an ellipse etc. may be sufficient.

  As mentioned above, although the plasma generator of this invention was demonstrated in detail, this invention is not limited to the said embodiment, Of course, in the range which does not deviate from the main point of this invention, you may make a various improvement and change. is there.

DESCRIPTION OF SYMBOLS 100 Rod-shaped electrode 102 Feed point 104 Electrode side dielectric barrier layer 105 Dielectric 106 Gas flow path 110 Case 114 Supply port 116 Discharge port 118 Feed line 120 Connection terminal 122 Electric field probe 130 Supply tube 132 Discharge tube 140 Power supply unit 142 RF Oscillator 143 Variable attenuator 144 Burst control signal generator 146 Amplitude modulator 148 Amplifier

Claims (8)

A plasma generator for generating a plasma at atmospheric pressure by applying a voltage to a gas containing a gas component to be processed,
A rod-shaped electrode to which electric power is supplied to generate plasma;
A metal cylindrical housing provided with a long internal space in one direction, the rod-shaped electrode being provided in the internal space along the longitudinal direction of the internal space;
An electrode-side dielectric barrier layer provided at the first end of the rod-shaped electrode so as to protect the first end;
A supply port for supplying the gas provided on a first end surface of the cylindrical casing facing the electrode-side dielectric barrier layer;
A housing-side dielectric barrier layer provided on the first end face so as to surround the supply port;
When the electrode-side circumferential upper edge portion in the cross-sectional shape of the first end portion of the rod-shaped electrode is projected on the first end surface of the cylindrical housing in parallel with the longitudinal direction, An edge portion is projected onto a region on the housing-side dielectric barrier layer or on the supply port.   Plasma is generated with the casing side circumferential upper edge portion of the supply port as a counter electrode to the rod-shaped electrode, and the shortest distance from the electrode side circumferential upper edge portion to the casing side circumferential upper edge portion is the electrode side circumferential upper edge. The plasma generator according to claim 1, which is the same at each position of the portion.   The case side circumferential upper edge portion and the electrode side circumferential upper edge portion both form an arc shape, and the center positions of the arc shape are both located on the same straight line parallel to the longitudinal direction. Or the plasma generator of 2. A feeding point is provided in an intermediate portion in the longitudinal direction of the rod-shaped electrode,
The plasma generator according to any one of claims 1 to 3, wherein the rod-shaped electrode is covered with a dielectric around at least a part of the rod-shaped electrode in the longitudinal direction. The second end surface opposite to the first end surface of the cylindrical housing is provided with a discharge port for discharging gas.
The dielectric is provided such that a part of the internal space is formed between the dielectric and a side surface of the cylindrical casing, and a space between the dielectric and the cylindrical casing is provided. The plasma generator according to claim 4, wherein a gas flow path that guides the gas supplied from the supply port to the discharge port is formed. 6. The plasma generating apparatus according to claim 4, wherein the dielectric has a relative dielectric constant of 10 or more, and a dielectric loss tangent of the dielectric is 5 × 10 ⁻⁴ or less.   The plasma generator according to any one of claims 1 to 6, wherein plasma is intermittently generated in the internal space by intermittently and repeatedly supplying high-frequency power having a constant frequency to the rod-shaped electrode. The plasma according to any one of claims 1 to 7, wherein plasma is intermittently generated so as to surround the supply port with the electrode side circumferential upper edge portion and the housing side circumferential upper edge portion as electrodes. Generator.

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