JP2022132263A - Air purification device - Google Patents

Abstract

To provide an air purification device which makes a distance that air to be treated passes through plasma constant.SOLUTION: An air purification device 10 has an atmospheric pressure plasma generation part 20 and an ozone removal part 30 arranged on its downstream, wherein the atmospheric pressure plasma generation part has a cylindrical plasma container 21 which is formed of a dielectric body and can pass air to be treated therethrough, a cylindrical or columnar internal electrode 22 which is arranged coaxially with the plasma container at a center of the plasma container, an annular external electrode 23 which is arranged coaxially with the plasma container on an outside surface of the plasma container, and a power source 25 for applying an AC voltage or a pulse voltage between the internal electrode and the external electrode.SELECTED DRAWING: Figure 2

Description

The present invention relates to an air purifier using dielectric barrier discharge.

2. Description of the Related Art Conventionally, air purifiers using dielectric barrier discharge have been known. Dielectric barrier discharge can be formed under atmospheric pressure, and when atmospheric pressure plasma is generated with oxygen-containing air, various active species and ozone are generated to sterilize bacteria floating in the air and kill viruses. It can inactivate and decompose volatile organic compounds (VOCs) in the air. Of these, active species such as hydroxyl radicals are more reactive than ozone and have a strong purifying action, but have a short lifespan. It is known.

In Patent Document 1, a plasma generating means is provided inside a housing that forms an air flow path, and the plasma generating means is configured by spirally winding a non-grounded electrode around a columnar grounded electrode via a dielectric film. An air cleaning device is described that generates a dielectric barrier discharge narrow gap plasma between electrodes.

In Patent Document 2, electrode panels in which at least a part of the discharge electrodes are covered with a dielectric are laminated, and a gas is flowed into the gap between the adjacent electrode panels to apply a voltage, thereby generating plasma by dielectric barrier discharge. An air purifier comprising a plasma panel stack that generates a is described.

Patent Document 3 discloses an elongated reactor in which air flows, an inner electrode positioned substantially concentrically within the reactor and covered with an insulating layer, and an inner electrode positioned on the inner surface of the reactor and covered with the insulating layer. An air cleaning and sterilizing device is described which has an outer electrode separated from the outer electrode and in which an electrical discharge is excited between the electrodes to create a plasma.

JP 2020-189172 A JP 2018-110648 A Japanese Patent Publication No. 2007-531597

In the air purifying device described in Patent Document 1, the generated ozone is expected to have a purifying effect. On the other hand, air passes near the plasma, but since the proportion of air passing through the plasma is limited, the purifying action of short-lived hydroxyl radicals and the like can hardly be used.

In the air purifier described in Patent Document 2, since the gas passes through the region where the plasma is generated between the electrode panels, it is possible to utilize the purifying action of short-lived hydroxyl radicals and the like. However, since the dielectric barrier discharge is formed between plate-shaped electrode panels with a large area, the position where the plasma is generated is not constant, and once the plasma is generated, it tends to become unstable. The numbers are also inconsistent. Therefore, the distance that the gas passes through the plasma is not constant.

In the air cleaning and sterilizing apparatus described in Patent Document 3, the air passes through the region where the plasma is generated in the elongated reactor, so compared to Patent Document 2, the entire amount of air passes through the plasma more reliably. It seems to do. However, since the electrodes are long, the position where the plasma is generated is not constant, as in Patent Document 2, and once the plasma is generated, it tends to be unstable. passes through the plasma is not constant.

If the distance through which the air to be treated passes through the plasma is not constant, it is necessary to provide a margin in the capacity of the device for the required purification effect, which inevitably increases the size of the device and consumes a large amount of power. Become. This is a particular problem when the air purifier is used at home. SUMMARY OF THE INVENTION It is an object of the present invention to provide an air purifier in which the distance through which air passes through plasma is constant.

The air purifier of the present invention has an atmospheric pressure plasma generating section and an ozone removing section arranged downstream thereof. The atmospheric pressure plasma generation unit is made of a dielectric material, and includes a cylindrical plasma container through which air to be processed can pass, and a cylindrical plasma container arranged coaxially with the plasma container at the center of the plasma container. Alternatively, a cylindrical internal electrode, an annular external electrode arranged coaxially with the plasma container on the outer surface of the plasma container, and a power source for applying an AC voltage or a pulse voltage between the internal electrode and the external electrode and

Here, downstream means downstream of the flow of air to be treated. With this structure, a disc-shaped atmospheric pressure plasma perpendicular to the axis of the plasma chamber is generated between the ring-shaped outer electrode and the inner electrode, and remains there. becomes constant. In addition, the purified air is discharged outside the apparatus after ozone that is harmful to the human body is removed by the ozone removal section.

Preferably, said external electrode is torus-shaped. This is because the lines of electric force are concentrated, so that plasma can be generated with less energy (current value).

Preferably, a plurality of the external electrodes are provided at intervals in the axial direction of the plasma container. With this structure, more disk-shaped plasma is generated, and the distance through which the air to be processed passes through the plasma can be increased.

Preferably, the air purifying device further includes a reaction tank for retaining air between the atmospheric pressure plasma generating section and the ozone removing section. As a result, the time during which ozone can react with contaminants in the air can be lengthened, and the purification effect of ozone can be enhanced.

Preferably, the ozone removal section has a fluidized bed of an ozone decomposition catalyst. As a result, the ozone decomposition reaction rate can be increased and the size of the apparatus can be reduced.

More preferably, the ozone removing unit further includes a second power source for generating an AC electric field within the fluidized bed. As a result, by rotating ozone, which is a polar molecule, the decomposition rate of ozone can be further increased.

A dielectric barrier discharge is formed in a portion with a high density of lines of electric force. According to the air purifier of the present invention, a dielectric barrier discharge is always formed at a fixed position between the annular outer electrode and the inner electrode, and a disk-shaped atmospheric pressure plasma perpendicular to the axis of the plasma container is generated. Therefore, the distance that the air passing through the plasma chamber passes through the plasma becomes constant. As a result, there is no need to allow a large margin in the capacity of the device for the required purification effect, and the device can be made smaller and consume less power.

It is a figure showing the whole air cleaner composition of one embodiment. It is a figure which shows the structure of the plasma generation part of the air cleaner of one Embodiment. A: vertical sectional view including the axis, B: side view seen from the downstream side. It is a figure which shows the structure of the plasma generation part of the air cleaner of one Embodiment. A: vertical sectional view including the axis, B: side view seen from the downstream side. It is a figure which shows the structure of the ozone removal part of the air cleaner of one Embodiment.

Referring to FIG. 1, an air purifier 10 of the present embodiment includes an atmospheric pressure plasma generating section 20 that forms dielectric barrier discharge to generate atmospheric pressure plasma, a reaction vessel 42, an ozone removal section 30, and a collection unit. and a dust filter 46 . Each part is connected by a vent pipe 40 through which air flows. Air A to be treated is taken into the apparatus 10 through an intake port 41, pollutants and the like are removed, and the air is discharged out of the apparatus through an outlet port 47. be done. In this specification, the term "removal of contaminants" is used in the sense of including all of sterilization of bacteria, inactivation of viruses, and decomposition of VOCs.

Referring to FIG. 2, atmospheric pressure plasma generation unit 20 includes a cylindrical plasma container 21 through which air A passes, an internal electrode 22 arranged coaxially with the plasma container at the center of the plasma container, and a plasma container. It has an annular outer electrode 23 arranged coaxially with the plasma chamber on the outer surface of the plasma chamber, and a power source 25 for applying an AC voltage between the inner electrode and the outer electrode.

The plasma chamber 21 is cylindrical and made of a dielectric. The type of dielectric is not particularly limited, and various types of glass, ceramics, and the like can be used.

The internal electrode 22 is inserted through the center of the plasma container 21 , supported by a spacer 24 and arranged coaxially with the plasma container 21 . The shape of the internal electrode is cylindrical or columnar.

The external electrode 23 is arranged coaxially with the plasma container 21 on the outer surface of the plasma container 21 . The shape of the external electrode is an annular shape that goes around the outer surface of the plasma chamber in the circumferential direction. The shape of the external electrode may be, for example, a torus shape (doughnut shape) or a short cylindrical shape in which a belt-like conductor is wrapped around the plasma chamber.

When a voltage is applied between the internal electrode 22 and the external electrode 23, a dielectric barrier discharge is formed in the portion where the electric line of force density is high. When the external electrode is torus-shaped, a dielectric barrier discharge is formed between the internal electrode and the inner circumference of the torus that is closest to the internal electrode. A piece of disk-shaped plasma P having a cross section perpendicular to the axis of the plasma container 21 is generated. Further, when the outer electrode is torus-shaped, the lines of electric force are concentrated between the inner circumference of the torus and the inner electrode, so plasma is generated with less energy (current value). For this reason, in order to suppress power consumption during plasma generation, it is preferable to form the external electrode in a torus shape.

When the external electrode has a torus shape, the thickness of the metal wire forming the electrode is such that the minor diameter of the torus (diameter of two circles appearing in the cross section including the axis) is preferably 0.3 mm or more, more preferably 0.3 mm. .5 mm or more. This is because if the metal wire is too thin, the life of the electrode will be shortened. On the other hand, the small diameter of the torus (the diameter of the two circles appearing in the cross section containing the axis) is preferably 5 mm or less, more preferably 3 mm or less. This is because even if the metal wire is thicker than this, there is no particular merit, and it becomes an obstacle to miniaturization of the electrode portion.

When the external electrode 29 has a short cylindrical shape as shown in FIG. 3, the density of the electric lines of force is high near the two open ends of the cylinder, so that the lines pass through the two open ends and are perpendicular to the axis of the plasma vessel 21 . Two disk-shaped plasmas P having a uniform cross section are generated (FIG. 3A).

When the external electrode is cylindrical, its length (length in the axial direction of the plasma chamber) is preferably 3-20 mm, more preferably 5-10 mm. This is because if the cylindrical shape becomes too long, the lines of electric force connecting the external electrode and the internal electrode become sparse throughout, and the plasma may not be formed in a disk shape. On the other hand, if the cylindrical shape is too short, it becomes difficult to process during manufacturing. Also, the thickness of the electrode is preferably 0.2 mm or more, more preferably 0.5 mm or more. This is because if the electrode is too thin, the life of the electrode will be shortened. On the other hand, the thickness of the electrode is preferably 3 mm or less, more preferably 1 mm or less. This is because there is no particular merit even if the metal wire is thicker than this.

The following description continues assuming that the outer electrode is torus-shaped (23 in FIG. 2), but equally applies if the outer electrode is short cylindrical (29 in FIG. 3).

Returning to FIG. 2, preferably, a plurality of external electrodes 23 are provided at intervals in the axial direction of the plasma container 21 . As a result, one or two disk-shaped plasmas P are generated for each external electrode, so the number of disk-shaped plasmas generated in the plasma chamber increases, and the distance through which air passes through the plasma becomes longer. .

A power supply 25 applies an alternating voltage between the internal electrode 22 and the external electrode 23 . For example, the internal electrode 22 is grounded and an AC voltage is applied to the external electrode 23 . The magnitude of the voltage is set to a magnitude sufficient to form a dielectric barrier discharge, and the electric field strength between the two electrodes exceeds about 35 kV/cm, which is the dielectric breakdown electric field strength of air. The frequency of the alternating voltage is preferably about 3 kHz to about 5 kHz, particularly preferably about 4 kHz. This is because by setting such a frequency, ions are less likely to diffuse and a dielectric barrier discharge is stably formed. Also, a DC pulse voltage may be applied between the electrodes instead of the AC voltage.

By applying an AC voltage from the power supply 25, a dielectric barrier discharge is formed between the internal electrode 22 and the external electrode 23, atmospheric pressure plasma is generated, and active species such as hydroxyl radicals and ozone are generated. In addition, when the air flowing through the plasma container 21 contains nitrogen, short-wavelength ultraviolet light with high sterilizing power is emitted.

When a plurality of external electrodes 23 are provided, preferably, a switch 26 is interposed between the power source 25 and each external electrode 23 so that the number of external electrodes to which voltage is applied can be adjusted. As a result, the number of external electrodes to be operated can be increased or decreased according to usage conditions, and power consumption can be minimized for a desired purification effect. For example, when the system is operated all night at bedtime, the number of external electrodes to be activated can be reduced to suppress power consumption, and when the odor is strong, the number of external electrodes to be activated can be increased to improve the purification effect.

Returning to FIG. 1, preferably, the reaction vessel 42 is arranged between the atmospheric pressure plasma generating section 20 and the ozone removing section 30 . Since the air emitted from the atmospheric pressure plasma generating part stays in the reaction tank, the contact time between the ozone and the contaminants can be lengthened, and the decomposition of the contaminants can be promoted. Ozone has a longer life than active species such as hydroxyl radicals, but its reaction rate with contaminants is slow. can be done. The reaction tank may be provided with stirring means for stirring the air in the tank.

Referring to FIG. 4 , in ozone removal unit 30 , ozone decomposition catalyst 32 is sealed inside cylindrical container 31 .

As the ozone decomposition catalyst 32, various known catalysts such as activated carbon, manganese catalyst, silver-cobalt catalyst, and Calolite can be used. Since ozone is also harmful to the human body, it is necessary to provide an ozone removal unit to decompose it so that it is not discharged from the device 10 . Since active species such as hydroxyl radicals have a short life, they disappear within the atmospheric pressure plasma generating section 20 and do not flow downstream.

The ozone decomposition catalyst 32 may be supported on a carrier and used in the form of a filter, but is preferably used by forming a fluidized bed of the ozone decomposition catalyst. In FIG. 4, a particulate ozone decomposition catalyst 32 is sealed inside a container 31 . A fluidized bed of the ozone decomposition catalyst is formed by air A flowing in from below and exiting from above. By using the fluidized bed of the ozone decomposition catalyst, the ozone decomposition reaction rate can be increased and the size of the apparatus can be reduced. In addition, by adjusting the amount of catalyst charged and changing the contact time between the catalyst and ozone, it is possible to easily adjust the processing capacity of the ozone removal section. not grow much. Activated carbon is preferably used as the ozone decomposition catalyst that forms the fluidized bed. This is because it has a low specific gravity and easily forms a fluidized bed.

The air A flowing into the ozone removing section 30 is heated to 40° C. or higher by a heater 34 provided in front of the inlet of the ozone removing section. As a result, the adsorption of water vapor in the air, which lowers the activity of the ozone decomposition catalyst 32, can be suppressed. Moreover, when a metal oxide catalyst such as manganese oxide is used, it is possible to prevent the accumulation of peroxides that cause a decrease in catalytic activity.

The ozone removing section 30 preferably has an electrode 35 and a second power supply 36 for generating an AC electric field in the fluidized bed of the ozone decomposition catalyst. Since ozone is a polar molecule, the alternating electric field can rotate the ozone molecules, increasing the rate of decomposition. The strength of the alternating electric field shall be such that no discharge occurs. The frequency of the alternating electric field is preferably about 2 kHz or higher.

Returning to FIG. 1, an ozone sensor 45 is provided at the outlet of the ozone removing unit 30. When the ozone concentration is higher than a predetermined concentration, the valve 44 is operated to allow the air to flow through the recirculation pipe 43 into ozone. It is returned to the remover. Various impurities and dust of the ozone decomposition catalyst 32 are removed from the air from which ozone has been removed by a dust collection filter, and the air is discharged from the outlet 47 to the outside of the apparatus 10 .

The operation of the air purification device 10 of this embodiment will be explained again.

The air A to be treated first enters the atmospheric pressure plasma generating section 20 . Active species such as hydroxyl radicals generated by the atmospheric pressure plasma P, ozone, and ultraviolet luminescence promote removal reactions of contaminants and the like.

Since a disc-shaped plasma P perpendicular to the axis is generated in the plasma container 21 of the atmospheric pressure plasma generation part, the air flowing through the plasma container always passes through the plasma, and is caused by active species such as hydroxyl radicals having a short life. is also strongly purified. The generated plasma is always generated only at a fixed position such as the central part or both ends of the external electrode in the axial direction according to the shape of the external electrode, and the number of plasmas existing at a certain point is always constant. The distance that air passes through the plasma is always constant. If a plurality of external electrodes are provided in the axial direction, the number of disk-shaped plasmas P is increased, and the distance through which air passes through the plasma is lengthened.

The air A that has passed through the atmospheric pressure plasma generating section 20 contains ozone generated in the atmospheric pressure plasma generating section and is further purified by the ozone. The ozone is decomposed in the ozone removal unit 30 , and purified and detoxified air A is discharged from the device 10 .

The present invention is not limited to the above-described embodiments, and various modifications are possible within the technical scope of the invention.

INDUSTRIAL APPLICABILITY The air purifier of the present invention can be suitably used for sterilization and deodorization of the air in refrigerators and refrigerating rooms as well as in human living spaces.

REFERENCE SIGNS LIST 10 air purifier 20 atmospheric pressure plasma generator 21 plasma container 22 internal electrode 23 external electrode 24 spacer 25 power supply 26 switch 29 external electrode 30 ozone removal unit 31 container 32 ozone decomposition catalyst 34 heater 35 electrode 36 second power supply 40 ventilation pipe 41 Inlet 42 Reaction tank 43 Reflux pipe 44 Valve 45 Ozone sensor 46 Dust collection filter 47 Outlet A Air P Atmospheric pressure plasma

Claims (6)

Having an atmospheric pressure plasma generation unit and an ozone removal unit arranged downstream thereof,
The atmospheric pressure plasma generation unit is
A cylindrical plasma container made of a dielectric and through which the air to be processed can pass;
a cylindrical or cylindrical internal electrode arranged coaxially with the plasma container at the center of the plasma container;
an annular external electrode arranged coaxially with the plasma container on the outer surface of the plasma container;
a power supply that applies an alternating voltage or a pulse voltage between the internal electrode and the external electrode;
air purifier. wherein the external electrode is torus-shaped;
The air cleaning device according to claim 1. A plurality of the external electrodes are provided at intervals in the axial direction of the plasma container,
The air cleaner according to claim 1 or 2. further comprising a reaction tank for retaining air between the atmospheric pressure plasma generation unit and the ozone removal unit;
The air purification device according to any one of claims 1-3. wherein the ozone removal unit has a fluidized bed of an ozone decomposition catalyst;
The air purification device according to any one of claims 1-4. The ozone removal unit further has a second power supply for generating an AC electric field in the fluidized bed,
The air cleaning device according to claim 5.

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