JP6020844B2 - Submerged plasma device and liquid purification system - Google Patents

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 is adjacent to the material to be processed by the plasma and should exist independently without being mixed with the object to be processed. 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., decomposition of organic matter in contaminated water treatment, treatment of factory waste liquid, synthesis of materials in solution, Etc. In the plasma treatment in the gas, remote plasma CVD in which the plasma region and the reaction region are separated, remote plasma surface treatment, and the like can be given. 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 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 in that a hardly decomposable organic substance such as dioxin that cannot be decomposed by ozone is decomposed by 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. Methods for generating discharge plasma in a liquid are roughly classified into those using direct current and low frequency, and those using high frequency and microwave. Examples of the former include underwater streamers by DC pulse discharge, arc discharge (see Non-Patent Document 4 ), and dielectric barrier discharge (see Patent Documents 1, 2, and 3 ). 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 each of Patent Documents 1 , 2 , and 3 , 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 introduced or generated bubbles absorb the energy of the electromagnetic wave to generate plasma (see Non-Patent Documents 2 and 3 ). Non-patent document 2 reviews the overall underwater discharge technology.

JP 2010-137212 A JP 2004-268003 A JP 2009-11001 A

"Ozone and water treatment" (Nobuyoshi Kaiga, 2008, published by Gihodo Publisher) "Formation of underwater plasma and its characteristics" (Yasuoka Yasuoka et al., J. PlasmaFusionRes.Vol.84, No.10 (2008) 666-673) Published by CambridgeUniversityPress by PLASMACHEMISTRYAlexanderFridman 2008 `` WaterPurificationbyPlasmas: WhichReactorsareMostEnergyEfeeicient? '' By MuhammadArifMalik PlasmaChemPlasmaprocess (2010) 30: 21-31

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 (Chemical Formula 1 ) is 1.25 g / Wh, but in an actual machine, the amount of ozone generated by dielectric barrier discharge using oxygen as a raw material is 0.05 g / Wh to 0.07 g. / Wh, and its energy efficiency
(Chemical formula 1) 3/2 O ₂ → O ₃ ΔH = 1.5 eV
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 the theoretical efficiency can be expected by referring to the results of theory and experiment (see Non-Patent Document 3 ). 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. To generate a streamer discharge in water by a DC pulse discharge, the even using an electric field concentration effect required voltage supply over 20 k V at present. 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 dielectric barrier discharge is considered to be a stable streamer corona discharge, and the required discharge start voltage is lower than the value (Vs) given by Paschen's equation (Equation 1 ).
( Expression 1) Vs = Bpd / ln (Appd / ln (1 + 1 / γ))
A, B: constant p: pressure γ: γ coefficient d: distance between electrodes However, in the reported dielectric barrier discharge in liquid, as shown in Patent Documents 1 , 2, and 3 , two phases of bubbles and liquid A method of sandwiching the mixed region with electrodes 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 bubbles, but the absorption of high frequency power by 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) It is possible to generate discharge plasma stably and constantly in dielectric barrier discharge in liquid, 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 the gas phase single space is separated using an electrode having a plurality of through holes in the liquid phase. Formed. Further, the contact between the plasma and the liquid was ensured through a through hole provided through the electrode.

  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.

It is a figure which shows a dielectric barrier discharge plasma apparatus in a liquid . It is a figure which shows a part of electrode part of a dielectric barrier discharge plasma apparatus in a liquid . It is a figure which shows the structure of the electrode which has a some through-hole. It is a figure which shows the structure of the electrode which has a some through-hole. It is a figure which shows the structure of the electrode coat | covered with the dielectric material. It is a figure which shows the state currently used in the liquid It is a figure which shows the state currently used in piping . It is a figure which shows a high voltage generation circuit It is a figure which shows a methylene blue pigment decomposition result It is a figure which shows the emission spectroscopy result of underwater plasma . It is a figure which shows the structure of the electrode which has several through-holes using a porous material . It is a figure which shows the structure of the electrode which has several through-holes using the silicon substrate which performed the microfabrication so that it may have a through-hole .

The embodiment will be specifically described with reference to the accompanying drawings. FIG. 1 shows a sectional structural view of a submerged dielectric barrier discharge plasma apparatus 1 according to the present invention. The discharge part 10 is a space sandwiched between the electrode 2 covered with a dielectric and the electrode 3 having a plurality of through holes , 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 electrode 3 having a plurality of through holes is maintained by the O-ring 17 , but the gas as the plasma raw material is guided to the pressure adjustment chamber 12 by the gas introduction tube 7. Then, the gas is introduced into the discharge unit 10 from the gas inlet 8 provided in the electrode support substrate 18. After becoming plasma gas in the discharge part 10, it is discharged | emitted in the liquid from the through-hole 9 provided in the electrode 3 which has a several through-hole . At this time, the plasma comes into contact with the liquid through the through hole 9. The penetration of the liquid into the discharge unit 10 can be achieved by adjusting the gas pressure by the pressure adjustment 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 through-hole 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, no electric field is generated in the bubble 20 due to negative shielding. As shown in FIG. 2, even if bubbles 20 are generated in part and discharge occurs , the other counter electrode surface is short-circuited with the conductive liquid, so that the load capacity increases and the power supply capacity increases. Pressure adjustment is indispensable to prevent liquid from entering. At the same time, the opening diameter of the through hole 9 must be appropriately determined. As a result of repeated examinations, it was found that it is reasonable that the aperture diameter is not more than the distance between the electrodes. FIG. 3 shows a cross-sectional view of the electrode 3 having a plurality of through holes . Usually, the electrode is used while being grounded. Since the electrode 3 having a plurality of through holes has openings, it is desirable that the electrode 3 be a metal material that is conductive, has good thermal conductivity, good corrosion resistance, and good workability. Specifically, Al alloy, stainless steel, nickel alloy, titanium alloy, or 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 through-hole 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 electrode 2 covered with a dielectric . 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 portion 33 is desirably as thin as possible so that the voltage applied to the discharge portion 10 is increased, but considering the dielectric strength, thickness controllability, mechanical strength, and ease of processing. To be determined. The support surface 36 side of the dielectric portion 33 is desirably thick in order to reduce the load capacity 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 was 0.5 mm, and the dielectric thickness on the support surface 36 side was 20 mm. The plate thickness of the stainless steel plate was 0.5 mm. In addition, ceramics may be used as a dielectric, and a semiconductor may be used as a conductive substance 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, in view of the temperature rise of the electrode 2 covered with a dielectric due to discharge, a material having good heat resistance is preferable . 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 to be processed 21 is filled in the liquid treatment tank 26 in which the submerged dielectric barrier discharge plasma apparatus 1 is mounted, and gas is supplied from the gas supply device 24 to the submerged dielectric barrier discharge plasma apparatus 1 through the gas introduction pipe 7. It is sent. Plasma is generated in the submerged dielectric barrier discharge plasma apparatus 1, and the plasma comes into contact with the liquid 21, and the generated plasma reaction product such as active species is sent into the liquid 21 as bubbles 20 . The bubble 20 floats and diffuses in the liquid 21 , 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 submerged dielectric barrier discharge plasma apparatus 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 cell 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 a form in which the liquid dielectric barrier discharge plasma apparatus 1 is used in a local field. The submerged dielectric barrier discharge plasma apparatus 1 is inserted into the pipe 28, and 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 21 is subjected to plasma processing. As shown in the figure, the in- liquid dielectric barrier discharge plasma apparatus 1 can be installed at a specific point such as a liquid retention site.

FIG. 8 shows a high-voltage driving circuit used in carrying out the present invention. The oscillation circuit is a Wien bridge circuit, and the oscillation frequency and gain are adjusted with a variable resistor. Oscillation frequency used in this embodiment was 26 k Hz. The size of the metal part of the electrode 2 covered with the dielectric 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 distance between the electrodes was 0.5 mm. Electrode support board 18, upper plate 14, and side walls 15 were prepared using the polyacetal resin plate. The power source used was a rectified commercial 100 VAC, and the winding ratio of the high voltage transformer was 1:28. Discharge voltage 2.8 k V, 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 with 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 obtained efficiency is about 2 to 3 times higher than the result of the reported pulse corona discharge (see Non-Patent Document 3 ). FIG. 10 shows the results of emission spectroscopy of underwater plasma measured in the present example in comparison with atmospheric plasma. In the discharge in water, the generation of hydroxy radicals is clearly observed.

FIGS. 11 and 12 show the structures of the electrode 3 having a plurality of through holes , each of which includes a porous material and a silicon substrate that has been finely processed so as to have through holes . 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 liquid dielectric barrier discharge plasma device 2 electrode covered with dielectric 3 electrode having a plurality of through holes 4 power supply wiring A
5 Power supply wiring B
6 Insulating tube 7 Gas introducing tube 8 Gas introducing port 9 Through hole 10 Discharge portion 11 Pressure adjusting valve 12 Pressure adjusting chamber 13 Introducing tube 14 Upper plate 15 Side wall 16 Flange 17 O-ring 18 Electrode supporting substrate 19 Bolt / nut 20 Bubble 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 Pipe 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 material 38 Silicon substrate finely processed to have through-holes

Claims (9)

A submerged plasma apparatus for performing dielectric barrier discharge,
A first electrode coated with a dielectric and having no through-hole;
A discharge part;
A second electrode made of metal, arranged to face the first electrode and separate the discharge part from the liquid via the discharge part, and is located on the discharge part side ; a gas phase surface substantially entirely to contact with the gas, situated on the side of the liquid, and a liquid phase surface substantially entirely to contact with liquid, and the liquid phase surface and the gas phase surface A second electrode having a plurality of through holes to be coupled;
A gas supply device that supplies gas to the discharge portion from the discharge portion side of the second electrode, and forms an interface between the gas and the liquid in a through-hole in the second electrode;
A submerged plasma apparatus.   The in-liquid plasma apparatus according to claim 1, wherein each of the first electrode and the second electrode has a flat plate shape.   The in-liquid plasma apparatus according to claim 1 or 2, wherein an opening size of each of the plurality of through holes is smaller than an inter-electrode distance defined by the first electrode and the second electrode.   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. The plurality of through holes, the aperture size of the gas phase side is larger than the aperture size of the liquid-phase side, liquid plasma apparatus according to any one of claims 1 to 4. Comprises a pressure adjusting chamber connected to said discharge portion, liquid plasma apparatus according to any one of claims 1 to 5. Wherein the first electrode by applying a voltage between the second electrode comprises an electrical circuit configured to perform a dielectric barrier discharge, liquid plasma apparatus according to any one of claims 1 to 6. The in-liquid plasma apparatus according to any one of claims 1 to 7 , 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. . Fluid purification system using a liquid plasma apparatus according to any one of claims 1 to 8.

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