Air cleaning device

Details Air cleaning device Air cleaning device

2002-02-05

2004-06-15

Chiesa, Richard L. (Department: 1724)

Gas separation: apparatus

Electric field separation apparatus

Including gas flow distribution means

C055SDIG003, C096S016000, C096S069000, C096S070000, C096S097000, C096S099000

Reexamination Certificate

active

06749669

ABSTRACT:

This invention relates to an air-cleaning device for reducing aerosol concentrations in a confined space such as a factory, shed, greenhouse, hall, shopping mall or room.
High aerosol concentrations can pose a health hazard through breathing the suspended particles.
In farming high aerosol concentrations are found in situations such as poultry sheds and intensive pig rearing sheds etc., the health of both workers and animals is at risk.
In industry a variety of processes such as welding, grinding, smelting and use of internal combustion engines in confined spaces all produce high polluting aerosol concentrations in enclosed spaces.
In social and domestic situations, aerosol pollution is produced by tobacco smoking. Sneezing can produce aerosols of bacteria and viruses. Allergy producing pollen is found in high concentrations at various times of the year. Dust mite allergen particles are produced when making up beds and enter the air as an aerosol.
Conventional air cleaners remove particles from the air by trapping them either in filters (filtration air cleaners (FAC's)) or by collecting them on plates (electrostatic precipitation air cleaners (ESPAC's)). The filters or plates may then be disposed of, washed or replaced.
U.S. Pat No. 4234324 discloses an electrostatic air filter comprising closely spaced planar electrodes of conductive material separated by corrugated spacers at edges thereof.
The disadvantages associated with FAC's are:
1. The efficiency of the filter often drops off markedly with time.
2. The pressure drop across the filter is often high and so requires a powerful fan.
3. The powerful fans are often noisy and consume considerable power.
4. The filters need to be regularly replaced.
The advantages associated with ESPAC's are:
1. Lower pressure drop.
2. Low noise and low power.
3. Washable collection plates.
The disadvantages associated with ESPAC's are:
1. Costly shielding of the high voltage metal collecting plates. The user needs to be protected from the possibility of electrical shock from the high voltage power supply (typically several kilovolts). Even when the power supply is switched off, there is danger of shock from stored electrical charge on the plates. The plates need to be removed for cleaning and so a safety interlock is usually provided to automatically discharge the plates before gaining access to them.
2. Loss of efficiency and generation of ozone caused by electrical breakdown and leakage between the metal plates.
3. The plates need to be relatively widely spaced to reduce electrical breakdown in the air between the plates. This reduces efficiency.
An object of the present invention is to provide a practical device for use in removing particles from an air or gas stream substantially without the disadvantages associated with ESPAC's.
According to a first aspect of the invention there is provided a particle precipitation device for removing particles entrained in a gas stream comprising an array of passages through which the gas stream can pass relatively freely, the passages being provided enclosed by plastics walls, means for urging the gas stream through the array, the plastics walls having areas of conductive material in contact therewith and externally of the passages, and means for applying high and low electrical potentials alternately to isolated areas of the conductive material to provide charged sites in the array for collecting particles from the gas stream.
According to a second aspect this invention provides a particle precipitation device for removing particles entrained in a gas stream comprising an array of passages through which the gas stream can pass relatively freely, the passages being enclosed by plastics walls having electret properties, means for urging the gas stream through the array, whereby particles are collected from the gas stream in the passages.
The passages are preferably provided by fluted plastics sheet preferably having conductive material on opposite external faces thereof. The fluted plastics sheets may, for example, be overlaid one on top of the other, folded in concertina fashion, formed into a spiral, or in a concentric array.
Alternatively, the passages may be provided by plastics tubes arranged side by side. The plastics tubes may be of rectangular cross-section or of circular cross-section.
Yet again the passages may be formed between walls of corrugated plastics sheet or between flat plastics sheets and corrugated conductive material.
The plastics material used in the invention is preferably of polypropylene, polyethylene or a copolymer thereof. Although other plastics materials such as PVC, PET, PTFE and polycarbonate may also be suitable.
For embodiments of the first aspect of the invention the areas of conductive material are preferably of high impedance material but may be of low impedance material. Alternate plastics sheets may have respectively areas of high impedance material and low impedance material thereon.
The high impedance material is preferably cellulose based material, such as paper. Alternative high impedance materials include paint or ink or anti-static coatings.
The low impedance material may be selected from metal sheet, metal film, carbon based films and carbon based paints.
The conductive material is preferably spaced inwardly from edges of the plastics walls except where connection is made to the means for applying potential thereto.
Preferred embodiments of the invention further comprise means for electrically charging particles in the gas stream prior to the array of passages. Such means may be corona discharge means or radioactive ionisation means.
Preferred embodiments of the first aspect of the invention comprise alternate layers of fluted plastics sheet conductive material at high and low electrical potentials, wherein the conductive material is spaced inwardly from edges of the plastics sheets to induce leakage of high voltage and hence ion leakage for charging particles entering the device. The areas of low electrical potential are preferably at ground potential.
High impedance material used in the invention preferably has a thin film resistivity in the range of 10
9
to 10
11
ohms per square.
Devices of the first aspect of the invention preferably comprise a high voltage power supply for powering the high electrical potential areas and a connection lead between the power supply and those areas made of insulated high impedance material.
Devices of preferred embodiments of the invention further comprise means for ionising the gas stream as it leaves the array. The means for ionising the gas steam as it leaves the array preferably comprises a primary corona discharge emitter and a secondary corona discharge emitter at a lower potential to the primary emitter. The primary emitter is preferably connected to high negative potential whilst the secondary emitter is preferably earthed. The primary emitter is preferably a needle having a sharp tip and the secondary emitter is preferably a needle having a relatively blunt tip.
In preferred embodiments of the second aspect of this invention the plastics walls are electrically charged prior to inclusion in the device. The plastics walls may be charged by means of electrodes applied to opposite sides of the walls with a high voltage difference applied thereto. Alternatively, the plastics walls may be charged by applying an electric field at a higher temperature and then cooling to a lower temperature in the presence of the electric field. The plastics walls may also be charged by moving the plastics walls between a high potential corona discharge on one side and an earthed conductive plate on the other side.
In another preferred embodiment of the second aspect of the invention the plastics walls may be provided by faces of fluted plastics sheet material and charging may be by means of filling the flutes with a conductive liquid connecting the flute insides to ground potential and outer faces of the sheet material to high negative and positive potentials respectively.
Another means of charging the pl

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