JP2010137212A - Apparatus for generating plasma - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for generating plasma, in which a large quantity of harmful organic compounds in waste water or liquid waste are decomposed/removed efficiently and stably by a small power consumption without using expendable members. <P>SOLUTION: A bar-shaped electrode 1 covered with a dielectric 2 is inserted into a liquid and a dielectric barrier discharge 3 is formed in the atmosphere above a liquid level to decompose/remove harmful organic compounds in the liquid. The dielectric barrier discharge is used for saving the power consumption, atmospheric pressure plasma is used for making expendable members unnecessary and the bar-shaped electrode is used for keeping stable plasma even when the liquid level is fluctuated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a plasma generation method involving a liquid. In particular, it is applied to water treatment, waste liquid treatment, material synthesis involving liquids, and the treatment field.

There are roughly the following three plasma generation methods involving liquids. The first is to supply droplets to the gas phase discharge space, the second is discharge on the liquid surface, and the third is discharge in the liquid. The present invention relates to the second and third. As for the discharge on the liquid surface, a method has been shown in which both exist in contact with each other by devising the mutual arrangement of the plasma formed in the gas phase and the liquid surface (Non-Patent Document 1). On the other hand, the discharge in the liquid can be achieved by applying a high electric field to the acicular electrical station to cause dielectric breakdown of the liquid and inducing corona stream plasma, or by generating bubbles in the liquid by heating or ultrasonic waves, and generating electromagnetic waves there. There has been proposed a method of inducing plasma by irradiating with (Patent Documents 1 and 2).
Tohoku 2004-152523 JP 2006-253056 A Kitano: 66th JSAP, 9p-ZG-9 (2005) Brisset, J. et al. L. : J. Trace and Micropobe Technologies, 16, 363-370 (1998) In recent years, there has been a strong recognition of the need for environmental purification related to wastewater and waste liquid as well as CO2 emission reduction, and in particular, there is an increasing demand for the decomposition and removal of trace amounts of harmful organic compounds in groundwater, soil, sediment and industrial wastewater. Examples of harmful organic compounds include low-molecular organic chlorine compounds, dioxins, polychlorinated biphenyls, tetrachloroethylene, trichloroethylene, dichloroethylene, and organic phosphorus compounds. On the other hand, there are agglomeration, filtration, membrane separation, centrifugation, physical adsorption, oxidation, electrodialysis, microbial decomposition, etc. as methods of wastewater and waste liquid treatment. Of these, oxidation and physical adsorption are effective for decomposing and removing harmful organic compounds. Activated carbon is mainly used for physical adsorption, and photocatalyst, ozone, hydrogen peroxide, ultraviolet rays, and ultrasonic waves are used in combination for oxidation. Plasma involving liquids is a new method that is mainly used for oxidative decomposition of harmful organic compounds, particularly persistent organic substances.

  From the viewpoint of function and economy as a wastewater wastewater treatment device, it is required that harmful organic compounds are decomposed to wastewater standards, are low-cost, are as small as possible, and do not use reagents. . Activated carbon, photocatalyst, hydrogen peroxide, ultraviolet lamp, etc. are consumables. In addition, a large amount of power is consumed to generate ultrasonic waves and ultraviolet rays. Currently, a method using an ultraviolet lamp has been put into practical use. However, for the above reason, there is a problem of lower power consumption without using an ultraviolet lamp as a consumable member.

  Water or liquid is used as one electrode, a discharge gas is interposed between a counter electrode coated with a dielectric, and an electric field is applied between both electrodes to induce discharge in the gas. The liquid part is chemically treated with active species formed in the discharge space.

  Since the dielectric barrier discharge is used, the discharge current is intermittent, and the power consumption can be greatly reduced as compared with the conventional infrared lamp. By using the atmosphere in contact with water as the discharge gas, OH radicals with strong oxidizing power are formed, and harmful organic substances in water can be efficiently decomposed and removed. Further, since the treatment can be performed by inserting the dielectric-coated electrode into water or liquid, it can be performed in addition to the conventional aeration treatment.

  A plurality of rod-shaped electrodes coated with a dielectric are inserted into the water or liquid to be treated from the atmosphere. The electrode metal is preferably stainless steel with excellent environmental resistance. Silica-based glass is desirable because the dielectric covering the electrode is required to be a material that has good insulation against high voltages and is highly resistant to water, liquid, and air. . The dielectric constant is determined by the balance between the voltage division into the atmosphere and the wall charge accumulation effect. By making the length of the dielectric-coated electrode part immersed in water or liquid longer than the fluctuation range of the liquid level during the treatment, stable treatment can be performed at all times. The applied voltage may be an alternating current or pulse of several kilovolts with water or liquid as a reference potential, and the voltage value, frequency, on-duty, plasma formation and separation of the sustain period, etc., take into account the individual plasma formation conditions It is desirable to be determined.

  FIG. 1 shows a principle diagram of a processing apparatus equipped with a single electrode. (1) is a metal electrode, which is covered with glass (2) and is applied with an alternating electric field (4). (3) is water or liquid to be treated, and the potential is grounded. {Circle over (5)} shows the discharge region, where harmful organic components are decomposed and removed at the interface with water or liquid.

  FIG. 2 shows a processing apparatus using a sword-shaped electrode used in this embodiment. (7) is an insulating support for bundling and holding a plurality of rod-shaped electrodes, and (6) is a common electrode for supplying a voltage to each electrode. By arranging the electrodes densely in this way, the entire liquid surface can be covered with plasma. FIG. 3 shows light emission by atmospheric plasma formed on the water surface in this embodiment. In this example, ¼ inch SUS304 was used as the rod-shaped metal electrode, and the thickness of the coated silicate glass was 0.2 mm. The applied voltage was a rectangle of 3 KV width and duty 50, and the frequency was 1 KH. The liquid used was city water containing 10 mg / L of methylene blue, and the decolorization rate by plasma was measured. FIG. 4 shows the result. The energy time efficiency of methylene blue oxidative decomposition removal was determined from this example to be 0.1 mg / W / min, suggesting energy saving and high efficiency.

  Principle diagram of liquid level plasma generator   Kenyama liquid level plasma generator   Example of plasma obtained with Kenyama liquid level plasma generator   Decomposition result of methylene blue by Kenyama liquid level plasma generator

Explanation of symbols

(1) ... Metal electrode (2) ... Dielectric material (3) ... Plasma (4) ... Applied voltage (5) ... Non-treatment liquid (6) ... Common electrode (7) ▼ ... Kenyama electrode base

Claims (6)

A plasma is generated by applying an alternating electric field between both electrodes, with the metal coated with a dielectric as one electrode and the liquid as the other electrode, and by destroying the gas interposed between the two electrodes. Is applied to the liquid through the interface to modify the liquid. 2. The plasma generating apparatus according to claim 1, wherein the electrode covered with the dielectric is rod-shaped, has a length of 3 mm or more, and is inserted perpendicular to the liquid surface. The plasma generating apparatus according to claim 1 or 2, wherein a rod-shaped electrode covered with a plurality of dielectrics is supported by a common electrode. The metal electrode is made of any one of copper and copper alloy, stainless steel, aluminum and aluminum alloy, silicon and silicon alloy, chromium and chromium alloy, carbon steel and special steel other than stainless steel. Plasma generator. The plasma generator according to claim 3, wherein the dielectric is made of any one of an organic polymer, glass, and an oxide film of an electrode substrate. The plasma generating apparatus according to claim 3, wherein the dielectric is porous.