JP2015056407A - Liquid plasma generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel plasma device which allows for compaction, light weight and low power consumption.SOLUTION: A liquid plasma generating device 1 performing dielectric barrier discharge includes an electrode 2 coated with a dielectric, a discharge section 10, an electrode 3 arranged to face the electrode 2 coated with a dielectric via the discharge section 10, and to separate the discharge section 10 from the liquid, while having a gas phase surface located on the discharge section 10 side, a liquid phase surface located on the liquid side, and a plurality of through holes 9 coupling the gas phase surface and the liquid phase surface, and a gas supply device for supplying gas to the discharge section 10, and formed the interface of gas and liquid in each through hole 9 in the electrode 3 having the plurality of through holes 9.

Description

It is an apparatus used in the field where a reaction product formed by non-equilibrium plasma is subjected to a chemical reaction to newly synthesize, modify, or decompose a substance. In particular, the characteristics are exhibited where the plasma region should be adjacent to the material to be treated by the plasma and should exist independently without intermingling with the untreated material. For example, in-liquid plasma treatment. In the liquid plasma, the plasma is formed in a single phase state in the liquid. Specifically, sterilization treatment in water purification plants, drinking water, food factories, semiconductor factories, liquid crystal factories, fish tanks, aquariums, etc.
Examples include decomposition of organic matter in contaminated water treatment, treatment of factory waste liquid, and material synthesis in solution. Examples of plasma treatment in gas include remote plasma CVD in which a plasma region and a reaction region are separated, and remote plasma surface treatment. It can also be used as an air purifier that decomposes pollutants in the atmosphere.

The first basic technology that forms the background of the present invention is a technology related to atmospheric pressure non-equilibrium dielectric barrier discharge plasma. This technology has already been put into practical use as an ozone generator and has a history of more than 150 years. Ozone is used on a large scale in final treatment at water purification plants and sludge volume reduction treatment at sewage treatment plants (see Non-Patent Document 1, for example). The ozone treatment apparatus uses air or oxygen as a raw material, transports ozone generated by atmospheric pressure dielectric barrier discharge by airflow, introduces it into treated water, and performs treatment by gas-liquid contact.

The second background art of the present invention is a submerged discharge technique. Technological development is progressing to form plasma in liquid to improve water quality and waste liquid treatment. The purpose is to decompose or sterilize persistent organic substances in aqueous solution. It is characterized by decomposing difficult-to-decompose organic substances such as dioxins that cannot be decomposed by ozone with hydroxy radicals (.OH) formed by the reaction between plasma and water. This is called an accelerated oxidation method, and other methods using ultraviolet rays, methods using hydrogen peroxide, and the like are known. The method of generating discharge plasma in liquid is roughly divided into direct current,
And those due to low frequencies and those due to high frequencies and microwaves. Examples of the former include underwater streamers by DC pulse discharge, arc discharge (see Non-Patent Document 2), and dielectric barrier discharge (see Patent Documents 1, 2, 3, and 4). In the case of dielectric barrier discharge, a method of actively interposing a gas and inducing a discharge plasma in the gas is used.
In patent document 1, discharge is induced on the water line of the surface of water and an electrode. In each of Patent Documents 2, 3, and 4, a structure in which a two-phase region composed of bubbles and water is sandwiched between electrodes is used. Examples of the latter include RF discharge and microwave discharge. Again, bubbles are used. The bubbles introduced or generated absorb the energy of electromagnetic waves and generate plasma (see Non-Patent Documents 3 and 4). Non-patent document 3 has reviewed the overall underwater discharge technology.

JP 2009-54567 “Water Purification by Plasmas: Which Reactors are Most Energy Efeeicient?” By Muhammad Arif Malik Plasma Chem Plasma orocess (2010) 30: 21-31 JP 2010-137212 A JP 2004-268003 A JP2009-114001

“Ozone and water treatment” (Nobuyoshi Kaiga, 2008, published by Gihodo Publisher) "Purification of Lakes by Pulsed Power Generated Underwater Streamer Discharge Plasma" (Akiyama Hidenori et al. J. Plasma Fusion Res. Vol.79, No.1 (2003) 26-30) "Formation and characteristics of underwater plasma" (Yasuoka Yasuoka et al., J. Plasma Fusion Res. Vol.84, No.10 (2008) 666-673) PLASMA CHEMISTRY by Alexander Fridman Published by Cambridge University Press 2008

In the ozone generator and the ozone treatment apparatus, improvement of energy efficiency is a problem.
The amount of ozone derived from the chemical reaction (formula 1) is 1.25 g / Wh, but the actual amount of ozone generated by dielectric barrier discharge using oxygen as the raw material is about 0.05 to 0.07 g / Wh. Yes, its energy efficiency

3 / 2O2 → O3 ΔH = 1.5eV (1)

Is 4% to 6%. When air is used as a raw material, it is 2% to 3%, and nitrogen contributes to the three-body reaction. The largest cause of low energy efficiency is due to the reaction mechanism, but up to 30% of theoretical efficiency can be expected by referring to theoretical and experimental results (see Non-Patent Document 4). However, the efficiency is further reduced when it becomes a practical machine. The cause is decomposition and extinction of ozone during transportation from the production field to the reaction field. The main factor is the decomposition of ozone molecules due to collision with the transport pipe wall and other particles, and further the promotion of decomposition due to temperature rise. In practical systems, additional power loads such as gas circulation pumps and coolers are greater, and the energy efficiency of the system is further reduced. When energy efficiency is reduced, the equipment becomes large, and its practical application is limited to large plants.

The problem in submerged or submerged discharge is to reduce the power supply capacity and expand the plasma reaction region. The dielectric breakdown electric field strength of water is 1 MV / cm or more. In order to generate streamer discharge in water by DC pulse discharge, it is necessary to supply a voltage of 20 KV or higher even if the electric field concentration effect is used. And in order to expand a discharge reaction area | region, it is necessary to expand an electrode area. Therefore, the power supply capacity is large and the apparatus is currently large.
Discharging is facilitated by introducing bubbles into the water. In the case of dielectric barrier discharge, the starting voltage can be reduced, but in order to do so, it is necessary to keep the distance between the electrodes short and stably obtain a structure in which bubbles are bridged between the electrodes. The barrier discharge is considered to be a stable streamer corona discharge, and the required discharge starting voltage is lower than the value (Vs) given by Paschen's equation (2 equation).

Vs = Bpd / ln (Apd / ln (1 + 1 / γ)) (2)

A, B: Constant
p: pressure γ: γ coefficient
d: Discharge gap length

However, in the previously reported dielectric barrier discharge in liquid, as shown in the prior patents 1, 2, 3, and 4, a method of sandwiching a two-phase mixed region of bubbles and liquid with an electrode is used. According to this method, it is necessary to increase the load capacity and form a two-phase flow with external power. In addition, it is a condition for the discharge to have a structure in which bubbles are cross-linked between the electrodes, but it is difficult to obtain this constantly. On the other hand, in high frequency discharge, Vs decreases due to charge trapping in the bubbles, but the absorption of high frequency power by the plasma increases and the power supply capacity increases.

In view of the above existing technology, the problems to be solved by the present invention are set as follows.
1) Stable and steady generation of discharge plasma in dielectric barrier discharge in liquid, and
2) the plasma is in contact with the liquid, and
3) Small size, light weight and low power consumption.

In order to solve the above problems, in the conventional method, the gas-liquid two-layer mixed phase is sandwiched between the barrier discharge electrodes, whereas a gas-phase single space is separated and formed in the liquid phase using the discharge electrodes. In addition, the contact between the plasma and the liquid was ensured through the pores provided through the electrodes.

The power supply capacity of the in-liquid plasma generator was reduced, and the size and weight were reduced. As a result, it is possible to cope with processing in a local field, and it is easy to construct a processing system according to the processing amount and environment. In addition, it has become possible to use plasma in liquids as a consumer device. Compared with the conventional ozone treatment apparatus, the energy efficiency was improved and the effect of accelerated oxidation was imparted.

Configuration diagram of discharge electrode in liquid Conceptual diagram of dielectric barrier discharge in liquid Structure of low voltage side discharge electrode 1 Structure of low voltage side discharge electrode 2 Configuration diagram of high-voltage side discharge electrode Conceptual diagram of in-liquid plasma processing system Conceptual diagram of plasma treatment in liquid in piping High voltage generation circuit Methylene blue dye decomposition results Emission spectroscopy results of underwater plasma Structural diagram of discharge electrode B using porous material Structure diagram of discharge electrode B using microfabricated silicon substrate

The embodiment will be specifically described with reference to the accompanying drawings. FIG. 1 shows a submerged discharge electrode 1 according to the present invention.
FIG. The discharge part 10 is a space sandwiched between the discharge electrode A2 and the discharge electrode B3, and the gap length is 1 mm or less. Desirably 0.5 mm ± 0.1 mm is appropriate.
The confidentiality of the space surrounded by the electrode support substrate 18 and the discharge electrode B3 is maintained by the O ring 16,
The gas that is the raw material of the plasma is guided to the pressure adjustment chamber 12 by the gas introduction tube 7, and the electrode support substrate 18
The gas is introduced into the discharge unit 10 through the gas inlet 8 provided in the. After becoming plasma gas in the discharge part 10, it is discharged into the liquid from the gas-liquid contact port 9 provided in the discharge electrode B3. At this time, the plasma contacts the liquid at the gas-liquid contact port 9. The intrusion of the liquid into the discharge unit 10 can be achieved by adjusting the gas pressure by the pressure adjusting valve 11. By providing the pressure adjusting chamber 12, the adjustment becomes easier.

It is one of the most important matters in the present invention to keep the liquid level in the gas-liquid contact port 9 and prevent the liquid from entering the discharge part 10. When the liquid penetrates and wets the electrode surface, if the liquid is conductive, an electric field is not generated in the bubble 20 due to negative shielding. As shown in FIG. 2, even if the discharge part 10 is partially formed, the other counter electrode surface is short-circuited with the conductive liquid, which increases the load capacity and the power supply capacity. Pressure adjustment is indispensable to prevent liquid from entering. At the same time, the opening diameter of the gas-liquid contact port 9 must be appropriately determined. As a result of repeated experiments, it was found that it is reasonable that the aperture diameter is not more than the gap length between the electrodes. FIG. 3 shows a cross-sectional view of the discharge electrode B3. Usually, the electrode is used while being grounded. The discharge electrode B3 may be coated with a dielectric, but since it has an opening, it is desirable that the discharge electrode B3 be a metal material that has conductivity, good thermal conductivity, good corrosion resistance, and good workability. . Specifically, Al alloy,
Stainless steel, nickel alloy, titanium alloy and the like can be used. It is also possible to use composite materials. Specifically, a plastic resin or ceramic plate provided with a hole and coated with a conductive thin film can be used. If the opening diameter is too small, there is a concern that liquid may enter due to surface tension. In order to prevent this, as shown in FIG. 4, it is effective to incline the side wall so that the diameter of the gas-liquid contact port 9 increases from the liquid phase surface 32 toward the gas phase surface 31. This is also effective in reducing pressure loss.

FIG. 5 shows a cross-sectional structure of the discharge electrode A2. Usually, a high voltage is applied to the electrode. The electrode is composed of a metal part 34 and a dielectric part 33, to which a power supply wiring A4 is connected. The discharge surface 35 side of the dielectric part 33 is preferably as thin as possible so that the voltage applied to the discharge part 10 is increased, but the dielectric strength, thickness controllability, mechanical strength, and ease of processing are taken into consideration. To be determined. It is desirable that the dielectric support surface 36 be thicker in order to reduce load capacitance and avoid application of a high voltage to the electrode support substrate 18. The material of the metal part 34 may have a small difference in thermal expansion coefficient from the dielectric, good adhesion to the dielectric, easy processing, and connection to the power supply wiring A4 by processing. It is a necessary condition. As a result of the experimental study, the conditions for forming by thermocompression bonding using soda-lime glass as the dielectric and ferritic tenres steel (SUS403 series) or martensitic stainless steel (SUS410 series) as the metal were found. At this time, the dielectric thickness on the discharge surface 35 side is
The dielectric thickness on the support surface side 36 was 0.5 mm and 20 mm. The thickness of the stainless steel plate is 0.5m.
m. In addition, ceramics may be used as a dielectric, and a semiconductor may be used as a conductive material instead of metal. A film forming method such as plating, CVD, vapor deposition, thermal oxidation, or printing may be used as a forming method.

The electrode support substrate 18 and the side wall 15 are required to have good insulation against high voltage. Usually, a resin with good processability is used, but ceramics may be used. In particular, the electrode support substrate 18 is required to have resistance to plasma. In addition, a material having good heat resistance is preferable in consideration of the temperature rise of the discharge electrode A2 due to discharge. In water treatment, it is desirable that there is no deformation at least at 100 ° C. Specifically, a fluorine resin, a polyacetal resin, a polyphenylene sulfide resin, or the like is used. The upper plate 14 must be made of an insulating resin or ceramic when using a metal bolt / nut 19. When an insulating coupling method is used instead of the metal bolt / nut 19, a metal material such as an aluminum alloy or stainless steel can be used.

FIG. 6 shows a system diagram of the liquid processing apparatus according to the present invention. The liquid treatment tank 26 to which the in-liquid discharge electrode 1 is attached is filled with the non-treatment liquid 19, and gas is sent from the gas supply device 24 to the liquid discharge electrode 1 through the gas introduction tube 7. Plasma is generated in the discharge electrode 1 in the liquid, and the plasma comes into contact with the liquid 19, and the generated plasma reaction product such as active species becomes bubbles 18 to form the liquid 19.
Sent out. The bubble 18 floats and diffuses in the liquid 18, passes through the filter 27, and is discharged to the outside. The filter 27 is provided to capture harmful substances in the exhaust gas. The electric power for discharge is supplied from the high voltage power supply 25 to the in-liquid discharge electrode 1 through the power supply wiring A4 and the power supply wiring B5. The power source may be a commercial power source 29 or a solar battery 30. When the liquid processing apparatus is installed outdoors and continuous operation is desired, power supply by the solar cell 30 provided with an auxiliary power supply is reasonable as an ecosystem. In the case of a liquid processing apparatus using ozone, the gas supply device 24 is a blower pump or an oxygen supply device, and the filter 27 is an ozone decomposition filter.

FIG. 7 shows an embodiment in which liquid discharge is performed in a local field. The submerged discharge electrode 1 is inserted into the pipe 28, and electric power and gas as a plasma raw material are fed from the power supply wiring A4, the power supply wiring B5, and the gas introduction pipe 7, and the liquid 19 is subjected to plasma treatment. As shown in the figure, an electrode can be installed at a specific point such as a liquid retention site.

FIG. 8 shows a high-voltage drive circuit used when implementing the present invention. The oscillation circuit is a Wien bridge circuit, and the oscillation frequency and gain are adjusted with a variable resistor. The oscillation frequency used in this embodiment was 26 kHz. The size of the metal part of the discharge electrode A was 2 cm × 2 cm, the discharge surface side dielectric thickness was 1 mm, the support substrate side dielectric thickness was 20 mm, and the dielectric electrode capacitance was 20 pF. Ferritic stainless steel was used as the metal part, and a soda lime glass plate was used as the dielectric part. The discharge gap length was 0.5 mm. Electrode support base 18
The upper plate 14 and the side wall 15 were made using a polyacetal resin plate. Power supply is commercial 100VAC
The winding ratio of the high-voltage transformer was 1:28. The discharge voltage was 2.8 kV and the apparent power was 10 W. An air pump having a discharge rate of 3500 cc / min was used as the gas supply device 24.

Using these, the whole was constructed as shown in FIG. 6, and the dye methylene blue was decolorized. FIG. 9 shows the change over time of the spectral transmission characteristics of the treatment liquid. The methylene blue decomposition energy efficiency calculated from this result was calculated to be 0.180 g / kWh. The chemical reaction is caused by the action of oxidizing active species generated by the discharge plasma. The required efficiency is about 2 to 3 times higher than that of the previously reported pulse corona discharge (see Non-Patent Document 4).
FIG. 10 shows the results of emission spectroscopy of the underwater plasma measured in the present example in comparison with the atmospheric plasma. In the discharge in water, the generation of hydroxy radicals is clearly observed.

FIGS. 11 and 12 show the structures of the discharge electrode B having a porous material and a microfabricated silicon substrate as part of the constituent members, respectively. In any structure, good discharge characteristics were obtained. In the case of the porous material, good discharge was realized in any of bulk, powder, and fiber. In this case, if each material is non-conductive, the liquid to be treated which is an electrolyte ensures conductivity and becomes an electrode.

In the area of liquid treatment, it can be used as an energy efficient ozone water treatment device, specifically, a water treatment device or a sewage treatment device. It can also be used as a sludge volume reduction device after biological treatment with good energy efficiency. Similarly, it can be used for sterilization treatment in aquariums and pools. Furthermore, it can be used for sterilization treatment in complicated pure water pipes in semiconductor and liquid crystal factories and in local fields in food factories and hospitals. It can also be used for wastewater treatment at plating plants, wastewater treatment at cleaning plants, and wastewater treatment at chemical plants. Furthermore, it can be used as a consumer device for sterilization of water storage tanks, disinfection in water supply and drainage pipes, and removal of organic substances. In addition, an ecosystem using a solar cell as a power source can be realized for sterilization treatment of water for outdoor installation such as well water. Furthermore, it can utilize for manufacture of ozone water for disinfection and cleaning.

It can also be used in the area of gas processing. As a remote plasma apparatus, reduction treatment using hydrogen and oxidation treatment using oxygen are possible, and therefore, it is used for surface treatment without ion damage before the interface formation. Specifically, surface treatment before solder connection, functional interface formation process of a semiconductor device in a semiconductor or liquid crystal process, and the like. If reduced pressure is introduced, it can be applied as a remote plasma CVD apparatus and can be used for thin film formation in semiconductor and flat panel display processes. It can be used as an air cleaner as a consumer device.

1 ・ ・ ・ Discharge electrode in liquid, 2 ・ ・ ・ Discharge electrode A, 3 ・ ・ ・ Discharge electrode B, 4 ・
・ ・ Power supply wiring A, 5 ・ ・ ・ Power supply wiring B, 6 ・ ・ ・ Insulation tube, 7 ・ ・ ・ Gas introduction pipe, 8 ・ ・ ・ Gas introduction port, 9 ・ ・ ・ Gas-liquid contact port, 10 ・ ・ ・Discharge part,
11 ・ ・ ・ Pressure regulating valve, 12 ・ ・ ・ Pressure regulating chamber, 13 ・ ・ ・ Introducing pipe, 14 ・
.. Upper plate, 15 ... side wall, 16 ... flange, 17 ... О ring,
18 ... Electrode support substrate, 19 ... Bolts and nuts, 20 ... Air bubbles,
21 ・ ・ ・ Liquid, 22 ・ ・ ・ Electrode metal part, 23 ・ ・ ・ Electrode dielectric part, 24 ・
・ ・ Gas supply device, 25 ・ ・ ・ High voltage power supply, 26 ・ ・ ・ Liquid treatment tank, 27 ・ ・ ・
Filter, 28 ... Piping, 29 ... Commercial power supply, 30 ... Solar cell, 31 ... Gas phase surface, 32 ... Liquid phase surface, 33 ... Dielectric part, 34 ...
・ Metal part, 35 ・ ・ ・ Discharge surface, 36 ・ ・ ・ Support surface, 37 ・ ・ ・ Porous part, 38 ・ ・ ・ Micro-processed silicon substrate part

Claims (11)

A submerged plasma apparatus for performing dielectric barrier discharge,
An electrode coated with a dielectric;
A discharge part;
An electrode disposed to face the electrode covered with the dielectric via the discharge part and to separate the discharge part from the liquid, the gas phase surface located on the discharge part side; and An electrode having a liquid phase surface located on the liquid side and having a plurality of through holes connecting the gas phase surface and the liquid phase surface;
A gas supply device for supplying a gas to the discharge unit, and forming an interface between the gas and the liquid in each through hole in the electrode having the plurality of through holes;
A submerged plasma apparatus.   2. The in-liquid plasma apparatus according to claim 1, wherein both the electrode covered with the dielectric and the electrode having the plurality of through holes are flat.   3. The liquid according to claim 1, wherein an opening size of each of the plurality of through holes is smaller than an inter-electrode distance defined by the electrode covered with the dielectric and the electrode having the plurality of through holes. Medium plasma device.   The in-liquid plasma apparatus according to any one of claims 1 to 3, wherein an opening size of each of the plurality of through holes is smaller than 0.5 mm.   5. The in-liquid plasma apparatus according to claim 1, wherein the electrode having the plurality of through holes includes a silicon substrate that is finely processed to have through holes. 6.   6. The in-liquid plasma device according to claim 1, wherein the plurality of through holes have an opening size on a gas phase surface side larger than an opening size on a liquid phase surface side.   The in-liquid plasma apparatus according to claim 1, wherein the electrode having the plurality of through holes includes a porous material.   The in-liquid plasma apparatus in any one of Claim 1 to 7 provided with the pressure regulation chamber connected with the said discharge part.   9. The electric circuit according to claim 1, further comprising an electric circuit configured to apply a voltage between the electrode covered with the dielectric and the electrode having the plurality of through holes to perform dielectric barrier discharge. The in-liquid plasma apparatus of description.   The in-liquid plasma apparatus according to any one of claims 1 to 9, further comprising a tank that at least temporarily accommodates the liquid in a stationary or fluid state and contacts the liquid with the liquid phase surface of the second electrode. .   A liquid purification system using the in-liquid plasma device according to claim 1.

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