JP3100566B2 - Air cleaning method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the use of corona discharges generated by rapidly oscillating electric fields in indoor air.
It relates to a process for removing contaminants.

[0002]

2. Description of the Related Art Passing a contaminant-containing gas through a corona discharge region is known as a method for removing contaminants from the gas. A general description of this technology can be found at Puch
“Toxic Gas Decomposition by Su”
rface Discharge ”(Proceedings of the 1994 Internat
ional Conf. on Plasma Science, June, 1994, SantaF
e, New Mexico, paper No. 1E6, p. 88). Corona contaminant destruction methods for liquids are also assigned to Hughes Aircraft Company and are currently being handled by Hughes Electronics, Inc.
No. 5,959, “Corona Source for Producing Corona
Discharge and Fluid Waste Treatment with Corona Di
scharge ”(filed August 25, 1994).

The literature "Decomposition" by Yamamoto et al.
of Volatile Organic Compounds bya Packed Bed React
or and a Pulsed-Corona Plasma Reactor ”(Non-Therm
alPlasma Techniques for Pollution Control, NATO AS
I Series Vol.G34 Part B.Ed. by BM Penetrante and
SE Schultheis, Springer-Verlag Berlin Heidelbel
g, 1993, pp. 87-89), a brief high voltage pulse of about 120 to 130 nanoseconds is applied to the center conductor of a coaxial corona reactor through which gas flows. . Each pulse generates a corona discharge from the center wire, filling the reactor vessel with high energy electrons of about 5-10 keV. Similar systems are described in U.S. Pat. No. 4,695,358, in which, superimposed on pulse DC bias voltage of a positive DC voltage, streamer for thereby removing SO _x and NO _x from a gas stream Corona is generated. These processes are relatively inefficient.
With the selected reactor geometry, it is necessary to provide very short pulses to avoid arc breakdown between the electrodes. The pulse forming circuit loses about 1/2 of the power from the high voltage source in the charging resistor,
Additional energy is dissipated in the double spark gap. In addition, the capacitive load of the coaxial corona reactor must be charged. This charging energy is typically much greater than the energy used in the corona reaction itself and simply heats up after each pulse and does not contribute to the destruction of contaminants.

Attempts to use similar but different geometry reactors have been reported by Rosocha et al.
atment of Hazardous Organic Wastes Using Silent-Di
scharge Plasmas ”(Non-Thermal Plasma Techniques f
or Pollution Control, NATO ASI Series Vol.G34 Part
B. Ed. By BM Penetrante and SE Schultheis, Spr
inger-Verlag Berlin Heidelbelg, 1993, pp. 79-80), where a corona discharge is set up between the parallel plates. This system also suffers from inefficient pulse formation and a lack of certain energy because the charging energy of the reactor is not recovered.

[0005] The process of NO _x by plasma technology, RW
“ReactionKinetics for Flue” by Breault et al.
Gas Treatment of NO _x ”(Non-Thermal Plasma Techniq
uesfor Pollution Control, NATO ASI Series Vol.G34
Part B, 1993, p. 239). That document describes a NO _x reduction reaction sequence in a corona discharge reactor where plasma is generated by high voltage corona discharge.

[0006] The occurrence of corona has been reported by WCHinds.
(Aerosol Technology, John Wiley & Sons, Inc., 1982,
299-300). In the corona area,
The electrons bombard and collide with electrons from the gas molecules, thereby being accelerated to a velocity sufficient to produce cations and electrons. Within the corona region, this process occurs in a free-standing avalanche that creates a dense population of free electrons and cations around the electrodes, which is called a corona discharge. If the inner electrode is positive with respect to the outer electrode, the electrons move quickly to the inner electrode and the cations flow from the inner electrode to the outer electrode in a unipolar "ionic wind". When the inner electrode is negative with respect to the outer electrode, the cations move to the inner electrode and the electrons are repelled and driven to the outer electrode. As the speed of the electrons decreases as the strength of the electric field decreases, the electrons attach to the gas molecules and form anions, which flow across the tube.

[0007] Corona forms groups (H, OH, O, etc.)
It ultimately forms ozone (O ₃ ). Ozone is highly reactive and destroys volatile organic compounds (VOCs) and oxidizes organisms such as bacteria, bacteria, viruses and spores. The groups OH and O also oxidize all VOCs and organisms very effectively. In addition, particulate materials such as dust and cigarette smoke are also charged when they collide with charged ions.

[0008] A high voltage D is applied so as to charge the fine particles.
An indoor contaminant treatment system that uses a C electric field and provides another high frequency electric field to agglomerate particles is described in the CRS document "COSATRON" (Product Literature, 1993). Another electric field requires a separate power supply with different power generation characteristics, and another set of electrodes, one generating ions to charge the particles and the other aggregating the charged particles.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a simple and efficient indoor air treatment apparatus having a simple structure for generating ions for charging particles with a set of electrodes and aggregating the charged particles. To provide.

[0010]

SUMMARY OF THE INVENTION The present invention provides an indoor air treatment unit that uses a corona discharge generated by a rapidly oscillating electric field.

[0011] The air cleaning method of the present invention generates an oscillating electric field.
To generate a corona discharge that releases the free charge.
The air containing the pollutant particles is transmitted through the Rona discharge,
A free charge is applied to the contaminant particles to charge them,
The above-mentioned oscillating electric field was supplied to the contaminated material fine particles, which were charged
Aggregates the contaminant particulates into larger sized particles,
Characterized by removing large size particles by filtration with a filter

In one embodiment, the power supply generates a high voltage, pulse modulated, sinusoidal signal to generate a high intensity, rapidly oscillating electric field that induces a corona discharge in the reactor. The power supply is controlled by a computerized controller that monitors the concentration levels of the contaminants in the air with one or more pollution sensors and provides the power supply with the desired signal characteristics for processing the contaminants. To generate a power having

The rapidly oscillating electric field in the corona discharge reactor also causes the charged particulate material to agglomerate. Free ions generated by the corona discharge charge particulate materials such as smoke and dust. When the charged particulate materials pass through a rapidly oscillating electric field, they aggregate into large particles, which are filtered by a conventional dust filter after the air passes through a corona discharge reactor.

An advantage of the present invention is that only one power supply is used because the same oscillating electric field used to generate free ions to charge the particulate material is also used to aggregate those particulate materials. Only the device and one set of electrodes are required.

[0015] These and other features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, taken in conjunction with the accompanying drawings.

[0016]

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a corona discharge reactor to remove indoor gaseous contaminants and particulate matter.
And methods for destroying volatile organic compounds (VOCs) and organisms.

According to the present invention, in one embodiment of the present invention shown schematically in FIG. 1, the corona discharge reactor 2 has an inlet conduit 4 in which a fan 6 for flowing air to the reactor is located. Have been. Either a single-chamber configuration or a multi-chamber configuration can be installed in the corona discharge reactor 2. In a preferred embodiment, which enhances all processing of the air passing through the reactor 2, the reactor has a number of reactor elements 8 arranged in parallel with one another in the air flow. Each reactor element has a chamber containing an inner electrode 10 and is closed by an outer electrode 12. The inner electrode 10 and the outer electrode 12 are connected to a power supply 14, which is a reactor element 8
Supply high power electricity to generate plasma in the chamber. The high voltage difference between the inner and outer electrodes creates a strong electric field in each chamber.

The high frequency electric field is generated by the power supply 14 in high voltage pulses. The pulse may be a gated sine wave 50 as shown in FIG.
B) has any of the pulse modulation waveforms as shown in FIG. The gated sine wave has a pulse repetition frequency f _pulse and the sine wave has an oscillating frequency f _osc . The pulse repetition frequency f _pulse is about 0.1 to 100
kHz, and f _osc is f _pulse
Is preferably about 5 to 10 times. Each pulse has a duration of pulse width τ. Corona discharge reactor
The average power supplied to 2 can be adjusted by changing the pulse duty cycle, which is defined as the product of pulse width τ and pulse repetition frequency f _pulse . Depending on the application, the power required to generate the corona discharge may be less than the power required to process the exhaust gases from the internal combustion engine,
The voltage difference between each pair of inner and outer electrodes must be sufficiently large, that is, generally in the range of about 5 to 15 kV to produce a corona discharge.

The power supply 14 is designed to produce fixed or variable power to optimize the treatment of contaminants. In a variable power supply, the characteristics of any pulse-modulated sinusoidal or gated sinusoidal voltage signal, such as voltage level, pulse width, pulse repetition frequency and oscillation frequency, are varied to adjust the average power of the signal. Can be For example, changing the pulse width and / or pulse repetition frequency changes the duty cycle, thereby affecting the average power for corona generation. In a preferred embodiment, the power supply 14 is controlled by a computerized controller responsive to inputs from one or more contaminant sensors 18, 20, 22 that sense the amount of contaminants in the air before and after processing. Is done. Preferably, at least one sensor 18 is located in the inlet conduit 4 for sensing the contaminant content in the untreated air. If the amount of the detected pollutant increases, the control device 16
14 instructs to increase power to generate a larger corona discharge. If the pollutant level drops, the power is reduced to keep the energy constant.

FIG. 3 shows a preferred embodiment of a corona discharge reactor having a number of reactor elements 8 arranged in parallel in the passage of the air flow, while in FIG. One more detailed diagram is shown. Each reactor element 8 is defined by the internal space of a hollow cylindrical dielectric 32 formed of a material having a low loss angle (tan δ) at the vibration frequency. Although the cylindrical dielectric may have various cross-sectional shapes, in a corona discharge reactor having a large number of reactor elements, the reactor elements 8 are packed tightly spatially and strongly supported mechanically. Are preferably regular hexagons so that they can be arranged adjacent to each other. Hollow cylindrical dielectric
32 has an inner surface 34 and an outer surface 36. Inside surface
34 defines an individual reactor chamber 42 containing at least one inner electrode formed from a conductive material.
The inner electrode 10 is preferably located along the vertex of the inner surface 34. A layer of conductive material surrounds the outer surface of the dielectric and forms outer electrode 12. When a positive voltage is applied to the outer electrode with respect to the inner electrode 10, an electric field is generated in the reactor chamber 42 as shown in FIG.
Is generated. The electric field charges the dielectric 32, thereby creating a positive charge 46 on its inner surface 34. If the strength of the electric field is high enough, a corona discharge will occur, thereby creating a free charge in the reactor chamber.

In the corona region of the reactor, positive and negative charges are generated. When the inner electrode 10 is at a positive voltage peak with respect to the outer electrode 12, as shown in FIG. 5b, the direction of the electric field lines 44 'is opposite to that shown in FIG. A negative charge 46 'is formed on the inner dielectric surface 34. The high voltage electric field resulting from the high voltage oscillation operating at f _osc shown in FIG. 2 a or b causes the electrons from the gas molecules to collide and collide, thereby producing cations and electrons. The electrons are accelerated to a sufficient speed. The electrons attach to the gas molecules to form negative ions, which flow across the reactor chamber.

The corona discharge generates electrons which react with molecules in the gas to generate groups such as H, OH and O, thereby forming ozone (O ₃ ). Ozone is a highly reactive oxidant, VOCs and bacteria, bacteria,
It is effective for destroying viruses and spores.

The charge generated by the corona discharge, as shown in FIG. 5a, is effective in treating particulate materials such as dust, tobacco smoke and pollen. Fine particles in media such as smoke generally cannot be filtered through conventional filters of fibrous material. The free charge generated by the corona discharge in the reactor chamber collides with fine particles, which are basically dielectric materials, and gives them a charge. As the charged particles flow downstream, they are exposed to a rapidly oscillating electric field, which causes them to agglomerate and form particles that are large enough to be trapped by ordinary fiber material filters. The electric field applied to the particles for agglomeration is the same as for generating a corona discharge. The charged particles have an oscillation frequency f _osc
When passing through high intensity and rapidly oscillating electric fields, they oscillate with the electric field, thereby increasing the possibility of aggregation. In the preferred embodiment shown in FIG.
A conventional fibrous material filter 24 is located downstream of the reactor element to filter out large agglomerated particles.

FIG. 6 shows the progress of the agglomeration process in which the charged fine particles 52 are turned into large particles 54 that can be filtered by the filter 24 of fibrous material. The inner electrode 10 and outer electrode 12, when energized, create a rapidly oscillating electric field that is used for both corona discharge and aggregation of charged particles. In this configuration, only one set of electrodes and one power supply are needed to perform corona generation and particle aggregation.

Further, a sensor is provided between the output of the reactor element 8 and the filter 24 to sense the amount of particles prior to filtration.
An outlet conduit 20 is located and downstream of the filter 24 for sensing the amount of particulate material and other contaminants after filtration.
It is desirable that another sensor 22 be disposed in 26. Reactor element for oxidizing VOCs and organisms
Generated in 8, it is preferable that any of the sensors 20, 22 are provided to sense the full amount of are preferably O ₃ broken during the oxidation reaction is thereby excess O ₃ outlet conduit 26 Do not enter. The controller 16 compares the amount of particulate material before and after filtration and characterizes the signal generated by the power supply 14 to enhance the aggregating capacity of the particulate material and the processing of other contaminants such as VOCs and organisms. To fit. The power supply device 14 is a corona discharge reactor 2 is adjusted to produce enough O ₃ to oxidize the VOC and organisms effectively, at the same time, the unpleasant odor upon exiting from the reactor itself Prevents excessive generation of contaminant O ₃ .

While one embodiment of the present invention has been shown and described, many modified and alternative embodiments can be made by those skilled in the art. Such modified and alternative embodiments can be made without departing from the spirit and scope of the invention, as defined in the following claims.

[Brief description of the drawings]

FIG. 1 is a block diagram of a corona discharge indoor air treatment system.

FIG. 2 is a voltage vs. time diagram of a typical gated sinusoidal waveform generated by the power supply and a typical pulse modulated sine waveform generated by the power supply.

FIG. 3 is a sectional view of a corona reactor according to the present invention having a number of reactor chambers.

FIG. 4 is a detailed cross-sectional view of one of the corona discharge chambers shown in FIG.

FIG. 5 is a cross-sectional view similar to FIG. 3, but showing the electric field lines and positive charges in the reactor chamber, similar to this cross-sectional view, but with the direction of the electric field lines reversed; FIG. 4 is another cross-sectional view with a negative charge in the chamber.

FIG. 6 is a cross-sectional view of the reactor chamber and the fiber material filter, showing the state of aggregating and the state of filtration of the particulate material in progress.

──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Weldon E. Williamson Seastar Drive 6424, Malibu, California 90265, U.S.A. , South Juanita Avenue (no address), apartment 14 (56) References JP-A-5-86841 (JP, A) JP-A-4-322718 (JP, A) JP-A-9-99211 ( JP, A) JP-A-9-329015 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53/32 B01D 51/00 B01D 51/02

Claims (1)

(57) [Claims] 1. A corona discharge that generates an oscillating electric field to release free charges, transmits air containing contaminant fine particles through the corona discharge, and gives the free charges to the contaminant fine particles to charge them. The charged contaminant particles generate the corona discharge.
At the same time a large dimension are aggregated into particles of air cleaning method characterized by removing particles of aggregated large dimension and filtered by the filter and charged by the oscillating electric field that.