JP2005268129A - Plasma reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate malfunctions that although an indirect type reactor which discharges via a dielectrics is suitable for treating a large amount of gas, the electric discharge cannot be stabilized, and enhance stabilization and promote electric discharge efficiency in the plasma reactor. <P>SOLUTION: While electrodes 11, 12 are installed on both faces of the dielectrics 10, numerous gaps (discharging spaces) 13, 14 to make the gas flow contacting with the dielectrics 10 are installed in the both electrodes 11, 12 at a constant spacing, then at a position where no gap exists in one electrode for instance an anode 11, an electric discharge reaction part 15 is formed so that a gap 14 in the other electrode, for instance a cathode 12 is made to exist and to be positioned there, and afterwards this electric discharge reaction part 15 is laminated/housed into multiple stages in the main body of the reactor having an exhaust gas entrance on one side and an exhaust gas outlet on the other side to constitute the plasma reactor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a highly efficient and stabilized plasma reactor, more particularly, a plasma reactor in which a discharge is generated by applying a voltage, and more particularly a chemical reaction generated by applying a voltage, for example, diesel Treatment of gas containing solid particles and / or liquid particles such as black smoke treatment in exhaust gas (exhaust gas), treatment of gas such as Freon gas treatment and VOC treatment, production of useful products such as ozone generation, etc. The present invention relates to a discharge plasma reactor capable of decomposing toxic substances or generating useful substances, or converting physical energy, for example, electric energy into light energy.

Two types of plasma reactors have been developed so far for generating a discharge by applying a voltage, that is, (1) a direct discharge reactor and (2) an indirect discharge reactor via a dielectric (for example, (See Patent Documents 1, 2, and 3).
Japanese Patent Laid-Open No. 7-116460 (2nd page, FIG. 2) JP-A-4-247219 (2nd page, FIG. 2) Japanese Patent Laid-Open No. 5-115746 (2nd page, FIG. 2)

  In the above-described direct discharge reactor, a voltage can be directly applied between metal electrode pairs to discharge part or all of the gas. The electrode pair structure includes a structure in which an external electrode and an internal electrode are provided coaxially and concentrically as shown in FIG. 17, a needle-shaped electrode versus a needle-shaped electrode as shown in FIG. 20, and a needle-shaped electrode pair plate as shown in FIG. There are plate-shaped electrodes, plate-shaped electrodes versus plate-shaped electrodes as shown in FIG. Any of these can be classified according to the difference in the area and shape of the portion of the electrode that can be discharged, but the discharge gas is directly present between the electrode pair. Further, the discharge phenomenon, particularly the light emission associated with the discharge, varies depending on the applied voltage, the pressure of the discharge gas, and the temperature conditions. Corona discharge or glow discharge that shines in the vicinity of the electrodes, streamer discharge that partially shines between the electrodes, spark discharge or arc discharge that shines completely between the electrodes can be observed. Depending on conditions such as gas pressure and temperature, discharge often occurs only in a limited area between the electrodes, so that the discharge energy flows into the limited area and high energy injection density (per unit volume) Energy injection amount).

  On the other hand, in a discharge plasma reactor via a dielectric, a discharge can be generated in a wide range by installing a dielectric on one or both electrodes of an electrode pair. The electrode pair structure includes a linear electrode pair dielectric-cylindrical electrode as shown in FIG. 21, a packed layer structure in which electrodes are provided inside and outside of the packed layer as shown in FIG. 22, and a plate shape as shown in FIG. Electrode pair dielectric pair-plate-like electrode, plate-like electrode as shown in FIG. 23-dielectric vs. dielectric-plate-like electrode, a plate-like electrode on one side of the dielectric as shown in FIG. Creeping structures with electrodes have been developed. A discharge gas is discharged between the dielectric and one of the electrodes or between the dielectric and the dielectric. Depending on the applied voltage, gas pressure, and temperature conditions, many corona discharges and glow discharges are generated on the dielectric or electrode surface. Since the discharge energy is dispersed by the dielectric, the energy injection density is lower than that of the direct discharge reactor.

  Since the indirect discharge reactor via the dielectric has a larger amount of processing gas than the direct discharge reactor, the discharge is required to be stable and uniform with respect to the entire gas. However, in the conventional discharge reactor, since the discharge is easily edged, the discharge is partially developed. FIG. 5 shows the discharge principle of a conventional indirect discharge reactor. Depending on the applied voltage, positive or negative charges are generated on the surface of the dielectric 1. An electric field is generated in the negative charge and the positive electrode (anode) 2, during which the gas in the discharge space 3 can be discharged. However, if the discharge becomes uneven at the edge or the like, the surface of the dielectric 1 All negative charges generated in the flow at the edge. When the applied voltage is high, the dielectric 1 is destroyed and the discharge is in a state close to the direct type. 4 is a cathode.

  The problem to be solved is that an indirect reactor that discharges through a dielectric is suitable for processing a large-capacity gas, but the discharge cannot be stabilized.

  The present invention is characterized in that discharge characteristics through a dielectric are studied, and discharge is stabilized and made efficient by changing the structure of the electrode and the dielectric. In other words, the most important thing is that stable and uniform discharge is achieved by attaching electrodes on one side of the dielectric and alternately providing a basic structure with gaps (discharge spaces) through which gas passes. Features.

  In the plasma reactor of the present invention, electrodes are attached to both surfaces of a dielectric, and a large number of gaps (discharge spaces) for allowing gas to pass through the inner surface of the electrode or the outer surface of the dielectric are provided at regular intervals. It is characterized in that a discharge reaction portion is provided in such a manner that a gap on the other side exists and is located at a position where no gas exists.

  When the plasma reactor is actually configured, the discharge reaction sections are stacked and accommodated in multiple stages in a reactor body having an exhaust gas inlet on one side and an exhaust gas outlet on the other side.

In these plasma reactors, an uneven electrode or an uneven dielectric is provided in order to provide a gap. And it is preferable to make it the height of a convex part into 0.1-10 mm, and a width | variety as 0.1-500 mm.
Further, the dielectric is formed in any one of a plate shape, a tubular shape, and a spherical shape having a thickness of 0.01 mm to 10 mm made of any of metal oxide, ceramics, glass, plastic, silicon rubber, and the like. It is preferable to configure. The shape of the electrode is any one of a plate, a tube and a sphere.

These plasma reactors are adapted to cause a discharge between the electrode and the dielectric by applying a voltage to the electrodes attached to both sides of the dielectric. The voltage to be applied is that of a power supply that can apply any one of alternating current, positive direct current, negative direct current, positive pulse, and negative pulse to both electrodes of the dielectric. And it is preferable to make a peak voltage into the range of 1V-100kV. This discharge causes a chemical reaction in the gas passing through the gap.
The gas temperature is any one of room temperature, low temperature, and high temperature, and is preferably in a range where no liquid or solid is generated from the gas. The gas pressure introduced into the reactor body is 0.1 torr to 10 atm.

  In the plasma reactor of the present invention, energy is dispersed by the dielectric, the energy injection density is lowered, and a large area or large space discharge can be generated. In this case, since the occurrence of the discharge edging phenomenon is suppressed, there is an advantage that stable and uniform discharge can be obtained.

  The purpose of stabilizing and homogenizing the discharge in the indirect plasma reactor was realized by alternately providing gaps (discharge spaces) in the electrodes on both sides of the dielectric so as not to be at the same position.

Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and is appropriately modified. FIG. 1 shows a main part (basic unit) of a plasma reactor according to a first embodiment of the present invention.
Reference numeral 10 denotes a dielectric. An anode 11 and a cathode 12 are attached to both surfaces of the dielectric, and a gap (discharge space) 13 for allowing gas to pass through the anode 11 and the cathode 12 in contact with the dielectric 10; A number 14 is provided at regular intervals. Then, the discharge reaction portion 15 is formed so that the gap in the other electrode exists at the position where the gap in one electrode does not exist, that is, the position of the electrode in contact with the dielectric 10. The reactor includes the discharge reaction unit 15.

In this case, it is preferable to make the length of the facing discharge space larger than the length of the electrode in contact with the dielectric 10. For example, assuming that the length of the anode 11 in contact with the dielectric 10 is L _P and the length of the gap (discharge space) 14 facing this electrode portion is L _N , L _P > L _N is satisfied. . The gas flows through the gaps (discharge spaces) 13 and 14 so as to escape from the front side to the back side of the drawing.

  FIG. 2 shows, as an example, a mechanism for removing black smoke (including carbon-based particulate matter PM) in exhaust gas from a diesel engine. When exhaust gas is introduced into the discharge reaction section, PM16 in black smoke adheres to the surface of the dielectric 10, for example, an alumina plate, and PM16 in black smoke is oxidized by the generation of oxygen radicals or the like due to creeping discharge, resulting in exhaust gas. To be cleaned.

  In the main part of the plasma reactor shown in FIG. 1, uneven electrodes are used to form gaps (discharge spaces) 13 and 14. It is also possible to use a concavo-convex dielectric instead of the concavo-convex electrode. In this case, it is preferable that the height of the convex portion is 0.1 to 10 mm and the width is 0.1 to 500 mm.

  The dielectric may be any plate, 0.01 mm to 10 mm thick plate-like, tubular, spherical or the like made of metal oxide, ceramics, glass, plastic, silicon rubber, etc. Tubular ones are preferred. The shape of the electrode may be any of a plate, a tube and a sphere, but it is desirable to use a plate.

  In the main part of the plasma reactor configured as described above, by applying a voltage to the electrodes attached to both surfaces of the dielectric, a reaction occurs by causing a discharge between the electrode and the dielectric. In this case, the applied voltage is that of a power source that can apply any voltage such as alternating current, positive direct current, negative direct current, positive pulse and negative pulse to the both side electrodes of the dielectric, and the peak voltage ranges from 1 V to 100 kV. In particular, the peak voltage is preferably about 10 kV. A chemical reaction occurs in the gas passing through the gap due to the discharge by applying a voltage.

  The temperature of the gas introduced into the plasma reactor is one of room temperature, low temperature and high temperature, and it is desirable that the temperature be in a range where no liquid or solid is generated from the gas. The gas pressure introduced into the reactor main body can be 0.1 to 10 atm in vacuum, but it is desirable to set the pressure around normal pressure.

  FIG. 3 shows, as an example, a plasma reactor for treating the exhaust of a diesel engine. A reactor main body 20 has an exhaust inlet 21 at one end and an exhaust outlet 22 at the other end. In this reactor main body 20, the discharge reaction parts 15 shown in FIG. 1 are stacked and accommodated in multiple stages so that a large volume of exhaust gas can be treated. Reference numeral 23 is an anode, 24 is a cathode, and 25 is an alumina insulating tube. Other configurations are the same as those in FIG.

In the plasma reactor of the present invention, the discharge gaps are alternately provided to effectively disperse the discharge, thereby preventing a strong discharge such as a spark. FIG. 1 shows the principle. When the electrodes 11 and 12 are made uneven, by applying a voltage, charges are generated on the surface of the dielectric 10 in the opposite direction to the applied voltage polarity. Due to the action of this electric charge and the applied electric field, a discharge is generated in the gas in the space between the electrodes 11 and 12 and the dielectric 10 under a sufficiently high voltage condition. Let L _P be the area where the electrode and the dielectric are in contact, and L _N be the area where the electrode is not in contact with the dielectric. Under the condition of L _N > L _P , charge distribution on the dielectric surface occurs, and it is difficult for the charge to freely move to the dielectric surface. Therefore, even if one of the discharge spaces penetrates, the movement of all the charges on the dielectric surface to the penetrated portion is suppressed, and a strong discharge unlike the conventional discharger is difficult to occur.

FIG. 4 shows the main part (basic unit) of the plasma reactor according to the second embodiment of the present invention, where the dielectric is made uneven. In the case where the dielectric 10a has an uneven shape, by applying a voltage, a charge is generated on the surface of the dielectric opposite to the applied voltage polarity. Due to the action of this electric charge and the applied electric field, discharge is generated in the gas in the space between the electrodes 11a and 12a and the dielectric 10a under the condition that the voltage is sufficiently high. Electrode and the dielectric are in contact area S _P, the area of the electrode and the dielectric and is not in contact space and S _N. In terms of S _N> S _P, since occurring greater than when the charge distribution of the dielectric surface has an electrode uneven, that the charges move freely on the dielectric surface it becomes more difficult. Therefore, even if one of the discharge spaces penetrates, the movement of the charges on the dielectric surface to all the penetrated portions is suppressed, and a strong discharge unlike the conventional discharger hardly occurs. Reference numerals 13a and 14a denote gaps (discharge spaces). Other configurations and operations are the same as those in the first embodiment.

  As Example 1, an experiment was conducted on a discharge in an alternating plasma reaction discharge. The structure of the main part of the alternating plasma reaction discharger is shown in FIGS. 6 is a front view, FIG. 7 is a rear view, and FIG. 8 is a cross-sectional view. After digging grooves 31 (width 6 x depth 0.3 x length 150 mm) on both sides of an alumina plate 30 (150 x 150 x thickness 3 mm), a net-like metal electrode 32 such as a stainless steel net (SUS304, 110 x 110 x thickness approx. 0.25 mm, 60 mesh) was attached on each side. The pulse voltage of these two stainless steel nets was applied in the air, and the state of discharge was recorded in the dark room with an Olympus digital camera E-10 (aperture: 2.4, exposure time 8 seconds). The discharge voltage was measured with a voltage probe (EP-50K, Pulse Electronics Technology Co., Ltd.), and the discharge current was measured with a current probe (Model 2-1.0, Stragenes) and an oscilloscope (TDS754D, Tektronix). EP-10K10 (Pulse Electronics Technology Co., Ltd.) was used as the pulse power source.

The discharge voltage and current waveform during one pulse at a pulse frequency of 4 kHz are shown in FIGS. The voltage is boosted to the peak voltage in about 1 microsecond and drops to near zero V within about 10 microseconds. The discharge current between the anode and the cathode increased to around 1 A with increasing voltage and then decreased.
When the state of the discharge of the reactor shown in FIGS. 6 to 7 was photographed and observed from the front, stable discharge was uniformly seen in the discharge gap formed by the groove of the stainless steel mesh and the alumina plate. Even when the front face was an anode or a cathode, a uniform discharge was obtained.

As Example 2, an experiment was conducted on diesel black smoke treatment using an alternating plasma reactor. A diesel exhaust black smoke treatment system using an alternating plasma reactor is shown in FIG. An experiment was conducted by attaching an alternating plasma reactor 34 to an exhaust pipe 33 of a diesel engine.
FIG. 13 shows the structure of the alternating plasma reactor 34, and FIG. 14 shows the basic unit around the alumina plate 30. This basic unit includes one alumina plate 30, two metal electrodes 35 and four glass spacers 36 shown in FIGS. The groove 31 on the surface of the alumina plate is perpendicular to the engine exhaust flow direction. A similar groove was provided on the back side of the alumina plate having a groove width of 6 mm, a depth of 0.5 mm, a length of 150 mm, and a distance between the grooves of 4 mm. The groove on the front surface and the groove on the back surface have the positional relationship described in [0008]. The metal electrode 35 (110 × 110 × 2 mm) was made of steel, and 13 grooves 37 having a width of 5 mm, a depth of 0.5 mm, and a length of 110 mm were dug on the surface in the exhaust gas flow direction. The distance between the grooves was 3 mm. A similar groove was provided on the back surface. Glass spacers 36 (20 × 110 × 2 mm) were attached to both sides of the metal electrode 35 for electrical insulation. One metal electrode was the anode and the other metal electrode was the cathode. Thirteen such basic units were manufactured and set in a reactor as shown in FIG. The insufficient space above and below the reactor was filled with a plate-like alumina packed bed 38. Reference numeral 39 denotes an alumina insulating tube. Other configurations are the same as those in FIG.

  As a black smoke generation source, a 4-cylinder, direct-injection diesel engine with a total displacement of 2 L was used. After a part of the exhaust gas from the engine was diluted with air at 150 ° C., the amount of black smoke generated was measured using a black smoke monitor (TEOM105, Rupprecht & Patanick). The experiment was performed at an engine condition of 3.8 kW at 1 krpm. Under this condition, the amount of black smoke discharged from the engine was about 1.5 g / hour. 20 minutes after starting the engine, the peak pulse voltage was around 4.5 kV, the pulse frequency was 30 kHz under the condition of 2 kHz, 10 minutes under the condition of 4 kHz, 40 minutes in total, and then the engine was stopped. When the surface of the alumina plate in the reactor was photographed and observed with a digital camera, it was found that the trace of discharge between the groove portion of the alumina plate and the edge portion of the groove of the metal electrode occurred uniformly. On the other hand, instead of the grooved alumina plate shown in FIGS. 6-8, a grooved alumina plate and a metal net (expanded metal, small mesh (2), Okutani Metal Works) were used, and a photograph of the plate after discharge was taken. As a result of photographing and observing, strong and weak discharges were observed, and further, no discharge was observed. That is, a uniform and stable discharge could not be obtained.

  As Example 3, further experiments were conducted on diesel black smoke treatment using an alternating plasma reactor. In order to efficiently treat diesel exhaust black smoke, it is important to discharge uniformly. In addition, even if the discharge electric field is made uniform, the discharge cannot be made uniform, so it is also important to forcibly generate the discharge. Therefore, an experiment was conducted using a steel plate punched from the metal electrode shown in FIG. Punch hole diameter: 5 mm, distance between hole centers: 8 mm, 60 ° plover, plate thickness: 0.8 mm. A total of two punched steel plates were used as one electrode. An alumina plate was inserted into the two steel plates, and the electrode thickness was adjusted to 2 mm. A total of 20 units were set in the plasma reactor 34 of FIG. The engine conditions were the same as in Example 2. From 20 minutes after the engine was started, the pulse voltage was changed and the discharge of black smoke was measured while discharging. FIG. 15 shows the relationship between the black smoke removal rate at a pulse frequency of 2 kHz and the peak value of the applied pulse voltage. It can be seen that the black smoke removal rate increased as the pulse voltage increased.

  As Example 4, an experiment was conducted on diesel black smoke treatment using an alternating plasma reactor, and the effect of removing black smoke after starting the engine was considered. After the diesel engine is cold started, a lot of black smoke is emitted from the engine. FIG. 16 shows the reaction of Example 3 when no plasma reactor is installed in the engine exhaust pipe (no reactor), and when the reactor of Example 3 is installed but there is no discharge (with reactor and no discharge). This shows the amount of black smoke discharged (monitor measured value) when a vessel was installed and discharge was performed before the engine was started (with reactor and with discharge). In the case without the reactor, the discharge amount of the black smoke had a peak value of 5 mg / h. However, in the case of the discharge with the reactor, this peak value could be reduced to 2.2 mg / h. Thereafter, it was found that in the case of discharge, the amount of black smoke emitted was smaller than in other cases.

It is a schematic block diagram of the principal part (basic unit) of the plasma reactor by 1st Embodiment of this invention. It is explanatory drawing which shows the removal mechanism of the black smoke in exhaust_gas | exhaustion of a diesel engine. FIG. 1 illustrates a plasma reactor for processing exhaust gas from a diesel engine as an example, in which the configuration illustrated in FIG. 1 is stacked. It is a schematic block diagram of the principal part of the plasma reactor by the 2nd Embodiment of this invention. It is a schematic block diagram which shows an example of the principal part of the conventional plasma reactor. 1 is a front view of a main part of a plasma reactor used in Example 1. FIG. It is the same rear view. FIG. 4 is a graph showing a discharge voltage waveform during one pulse in Example 1. 3 is a graph showing an anode current waveform in one pulse in Example 1. 3 is a graph showing a cathode current waveform in one pulse in Example 1. It is a system diagram of the black smoke generation and measurement apparatus in Example 2. 6 is an explanatory view showing the structure of a plasma reactor used in Example 2. FIG. It is a perspective view which shows the basic unit (principal part) of the plasma reactor shown in FIG. It is a graph which shows the relationship between the black smoke removal rate and peak pulse voltage in Example 3. It is a graph which shows the black smoke removal effect after the engine cold start in Example 4. It is composition explanatory drawing which shows an example of the conventional direct type | mold discharge reactor. It is composition explanatory drawing which shows the other example of the conventional direct discharge reactor. It is composition explanatory drawing which shows the other example of the conventional direct discharge reactor. It is composition explanatory drawing which shows the further another example of the conventional direct discharge reactor. It is composition explanatory drawing which shows an example of the conventional indirect discharge reactor. It is structure explanatory drawing which shows the other example of the conventional indirect discharge reactor. It is structure explanatory drawing which shows the other example of the conventional indirect discharge reactor. It is structure explanatory drawing which shows the other example of the conventional indirect discharge reactor. It is structure explanatory drawing which shows the further another example of the conventional indirect discharge reactor.

Explanation of symbols

10, 10a Dielectric 11, 11a Anode 12, 12a Cathode 13, 13a, 14, 14a Gap (discharge space)
15, 15a Discharge reaction part 16 PM (particulate matter) in black smoke
20 Reactor body 21 Exhaust inlet 22 Exhaust outlet 23 Anode 24 Cathode 25 Alumina insulating tube 30 Alumina plate 31 Groove 32 Reticulated metal electrode 33 Exhaust tube 34 Plasma reactor 35 Metal electrode 36 Glass spacer 37 Groove 38 Plate-shaped alumina packed layer 39 Alumina Insulation tube

Claims (10)

  Electrodes are attached to both surfaces of the dielectric, and a large number of gaps for allowing gas to pass therethrough are provided on the inner surface of the electrode or the outer surface of the dielectric, and the gap on the other side is located at a position where there is no gap on one side. A plasma reactor comprising a discharge reaction portion configured to exist and be positioned.   A plasma reactor, wherein the discharge reaction section according to claim 1 is stacked and accommodated in a reactor body having an exhaust gas inlet on one side and an exhaust gas outlet on the other side.   To provide the gap, an uneven electrode or an uneven dielectric is provided, and the height of the convex portion is 0.1 to 10 mm and the width is 0.1 to 500 mm. The plasma reactor as described.   The dielectric is formed into any one of a plate shape, a tubular shape, and a spherical shape having a thickness of 0.01 mm to 10 mm made of any of metal oxide, ceramics, glass, plastic, silicon rubber, and the like. The plasma reactor according to 2 or 3.   The plasma reactor according to any one of claims 1 to 4, wherein a shape of the electrode is any one of a plate, a tube and a sphere.   The plasma reactor according to any one of claims 1 to 5, wherein a discharge is caused between the electrode and the dielectric by applying a voltage to the electrodes attached to both surfaces of the dielectric.   The voltage to be applied is that of a power source that can apply any one of AC, positive DC, negative DC, positive pulse, and negative pulse to both electrodes of the dielectric, and the peak voltage is in the range of 1V to 100kV. 6. The plasma reactor according to item 6.   The plasma reactor according to any one of claims 1 to 7, wherein a chemical reaction occurs in the gas passing through the gap by electric discharge.   The plasma reactor according to any one of claims 1 to 8, wherein the gas temperature is one of room temperature, low temperature and high temperature, and is in a range in which no liquid or solid is generated from the gas. The plasma reactor according to any one of claims 1 to 9, wherein a gas pressure introduced into the reactor main body is 0.1 torr to 10 atm.