WO1996009118A1

WO1996009118A1 - Electrostatic air cleaner

Info

Publication number: WO1996009118A1
Application number: PCT/US1994/010656
Authority: WO
Inventors: Albert Barsimanto
Original assignee: Albert Barsimanto
Priority date: 1994-09-20
Filing date: 1994-09-20
Publication date: 1996-03-28
Also published as: AU7839094A

Abstract

An electro-mechanical electrostatic air cleaner (10) that combines a low air resistance dielectric fibrous filter material (18) such as polyester or glass which is positioned between and electrically charged by two electrically resistant carbon coated screens (12b, 14b) encased in an electrically insulated frame (12, 14). The screens (12b, 14b) are charged by a remotely mounted bi-polar power supply (22).

Description

ELECTROSTATIC AIR CLEANER DESCRIPTION TECHNICAL FIELD This invention relates generally to air filters and cleaners, and more specifically to an improved electrostatic-type air cleaner. BACKGROUND ART

Dust, pollen, smoke, smog, bacteria, virus, mold and odors are all comprised of particles which are suspended in the air. These airborne particles are small, ranging in size from .001 microns to 10 microns. Larger particles of 10 to 50 microns tend to settle out quickly while smaller particles, the main hazard to health, remain airborne.

These suspended particles can be removed from the air by either mechanical or electrical means. The most common mechanical techniques include fan/filter systems, gravity settling, centrifugal separation, and scrubbing.

In ordinary fan/filter systems air is drawn through a filter which mechanically traps particles in a web of synthetic or glass fibers. The efficiency of these filters is dependent on the filter surface area and the density of the web network. At low air resistance densities, these filters are pnly effective for large particles exceeding 10 microns. Fan/filter systems may also involve activated carbon and/or silica gel materials to remove odors. The efficiency and effectiveness of these approaches are grossly limited, so that scents or perfumes are often used to make the air smell "clean".

For small particle removal, a high efficiency, particle air (HEPA) filter having accordion-like pleats is used. These are expensive and used for special applications where a single pass efficiency is required, such as in hospitals and clean rooms, and they must be changed frequently before they become clogged and overburden the air circulation fan.

Electrical particle removal may be achieved by either electrostatic precipitation or open-air ion generation. Electronic deposition of particles is accomplished by charging the particles to be deposited with one polarity and grounding the objects on which the particles are to be deposited with the opposite polarity or common line ground.

The accepted theory of operation of a conventional electrostatic precipitation system involves air being drawn by a fan past an electrode that gives the airborne particles a relatively strong electric charge.

The air then passes by a set of parallel collector plates of opposite charge to which the particles are attracted and stick. Essentially, electrostatic precipitation uses electrical forces of charged bodies to separate particles from the air where the polarization forces are perpendicular to the direction of the air flow. This process is highly effective on small airborne pollutants ranging in size from 0.001 to 10 microns (0.0000003 to 0.0004 inches) . DISCLOSURE OF INVENTION

This invention relates to electrostatic precipitator filters in which the particle collecting element comprises a disposable fibrous dielectric material placed between two conductive screens, each of opposite polarity.

The inventive electrostatic precipitation air cleaner technology is unique and distinct in that collector plates are eliminated in favor of an inexpensive fibrous media placed in a bi-polarized electric field. The fibrous media becomes polarized by the electric field in the direction of the air flow, thereby attracting charged particles from the air to the fibrous media. This fibrous media has several times the collection capability and requires much less space than a conventional electrostatic precipitator. In addition, the fibrous network can secondarily function as a large particle filter, mechanically trapping the larger airborne particles, while maintaining low air resistance as required for all HVAC systems. In its simplest form the filter consists of a set of open screen conducting plates separated by a fibrous dielectric (i.e. non-electricity conducting) media such as fiberglass, polyester or foam. An electric field is formed by imposing an opposite charge on the plates through a high voltage power supply. Typically, the voltage imposed is a total of 14 kilovolts with a current not exceeding 6 milliamperes with a total power consumption not exceeding 0.6 watts. The filter is then placed upstream of a fan and air drawn through it.

To augment the basic electrostatic approach an electrode may be placed upstream from the filter to charge incoming particles that would otherwise be neutral and remain uncaptured pollutants. Such an electrode may take the form of activated carbon (to assist in gas removal) and/or fibrous material (to act as a large particle prefilter) .

A major advantage of this bi-polar filter technology is the large increase in collection surface area of the fibrous media over a conventional set of flat parallel plates occupying the same space. The time between changing or cleaning the filter or plates, and the efficiency of this technology is well beyond that of conventional flat plate electrostatic precipitators.

In addition, the conventional precipitators, when dirty, tend to arc between the plates (producing ozone) which is a potential fire/explosion hazard in volatile atmospheres and which limits their use in many installations. In contrast, the inventive bi-polarized device, when dirty, will form a closed circuit which will reduce the effectiveness of the filter but lead to no arcing. The fibrous material is inexpensive and can be disposed of when contaminated whereas the plates must be cleaned and reused, posing potential health hazard to the person handling the plates.

As with all electronic filters, efficiency may be reduced as relative humidity increases. However, the inventive bi-polar filter is less effected by humidity than are conventional electrostatic precipitators which have a propensity for arcing at high humidities, whereas the bipolar filter device will not arc under such conditions. The inventive arrangement provides a configuration whereby air is simultaneously filtered (to remove both large and small particles - to .001 microns) and the air "treated" to: a. Neutralize ambient static (and on non- conductive surfaces); and b. Restore an increased level of balanced free air ions to the environment.

The net multiple effect of such a system has obvious benefits and multiple applications both for the occupants in the environment and more specifically, for the benefit of static sensitive equipment (such as computers). The inventive system may also have application in photo development labs, printing operations, semiconductor handling processes and in specific medical environments.

Accordingly, an object of this invention is to provide an air filter that is of elegant simplicity, compact, easy to install by the user, and which retrofits as a direct replacement, the ubiquitous, ordinary dust filter used in house furnaces and electrical air systems.

Another object of this invention is to provide the user with at least two options of different replacement filters: a. A permanent filter holder in which just the filter media is periodically replaced; and b. A fully disposable filter, frame and all, to eliminate or minimize physical contact with the collected matter.

Another object of this invention is to provide outboard visual monitoring using a neon light to confirm operation and/or to indicate that a filter change is required.

Another object of this invention is to provide a remote on/off switch to disengage the power source before replacing the filter.

Another object is to provide conductive screens which will not cause a static shock if touched directly. The preferred material provides conductivity with a minimum build-up of capacitance, has high electrical resistance properties, and may be used as a coating on polyester mesh screens.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a partially cutaway exploded perspective view of an electrostatic air cleaner of this invention. BEST MODE FOR CARRYING OUT THE INVENTION

The inventive air cleaner apparatus 10 preferably includes a two-piece frame 12, 14 constructed of a dielectric insulating material on at least three sides, so as to be electrically separate from any grounding source. The back and front members have openings 12a, 14a for the flow of an air stream passing through one side and exiting through the other side to a fan 16. Both sides have a conductive coated screen 12b, 14b between which a dielectric media 18 is sandwiched. The screens are electrodes of opposite polarity (negative to positive or positive to negative) . As air passes through the filter, small particles in the air stream are charged and attracted to the opposite polarity and lodge at random on the dielectric media surface 18 and held in place by the closed circuit of opposite polarity plates, and thus small particles are separated from the air stream. The electric charging of small particles causes rapid agglomeration, thus any particles that escape capture in the filter on the first pass, tend to get larger and are therefore more easily captured on a second pass or fall out of the air by gravity.

The conductive screens 12b, 14b are preferably coated with a carbon material which avoids capacitance build-up that could cause arcing, but is not limited to the use of high electrical resistance carbon. The electrical resistance material can be applied to a variety of certain plastic materials and/or certain fabrics. The use of high electrical resistance material for the conductive plates provides the following benefits: a. acts as a reduced capacitance; b. can be used as a resistor; c. no static shock on touch; d. no arcing (or vastly reduced arcing potential); and e. the screens can be varied in size (e.g., from sizes 3" x 3" in area to 25" x 25" in area) with little or no increase in capacitance buildup as would be the case if normal carbon materials or solid metal materials were used.

A layer of steel wool, sharp conductive metal filings 20, or other material may be attached to the filter media 18 adjacent the upstream screen to intensify ionization, substantially improving collection efficiency in a single pass.

A carbon charcoal filter can be used as an electrode at one side or the other side or both sides. Electrifying a charcoal filter improves the residence time and efficiency for charcoal absorption of gasses attached to small particulate matter (e.g., carbon soot).

The power supply 22 produces equal values of opposite polarities to the respective plates for pre-fan filtration. The same power supply can provide post-fan bi-polar ionization through properly placed and spaced emitter electrodes to produce a static neutralizing field of varying field effect range depending on air volume and output voltages (static neutral). The power source is adapted to supply equal voltage for each polarity between 5KV and 10KV. A neon light array 24, 26 (one for each polarity) monitors output levels indicating the system is operating and when filter media should be replaced. The inventive apparatus may include an output control 28 - increasing or decreasing the output to provide optimal levels for varying thickness of filter media (e.g., 1" to 4") .

High voltage leads 30, 32 from the remote power supply 22 are attached to one of the opposite conductive screens 12b, 14b and held in place by the frame. The leads are instantly detachable from the power source as well as from the frame. The filter frame can be one of two different types: a. A permanent media holder which can be opened to remove a used filter and replaced with a new filter. b. A fully disposable filter, frame and all, which can be burned as is the routine in hospitals where filters may contain bacteria.

While the basic system is 1" thick (to retrofit and convert the ubiquitous 1" dust filter to an electronic electrostatic filter) , the principles apply to filters of any thickness, and allow a variety of "stages of processing" including: a. Basic: negative plate; dielectric, disposable media; positive plate. b. Ground - pre filter; negative plate; dielectric media; positive plate; media to ground. c. An ionization, pre-charge of the incoming air to a charcoal collector as a pre-filter followed by either of the above configurations. While the preferred embodiment utilizes a 1" thick electrostatic precipitator filter for installation in HVAC systems, other embodiments of the invention may be used in self contained air moving systems. For example, the inventive system may also be used in self contained air cleaners/static neutral products, both small and compact or large sizes with air movement from 50CFM to 300CFM. A filter cartridge with a removable plate for filter media replacement may be used in such self- contained systems. The filter plates are charged as the cartridge is fully inserted into a connector and disengaged as the filter cartridge is removed. Thus, the user cannot touch a charged filter.

While this invention has been described in connection with preferred embodiments thereof, it is obvious that modifications and changes may be made by those skilled in the art to which it pertains without departing from the spirit and scope of this invention. Accordingly, the scope of this invention is to be limited only by the appended claims.

Claims

ELECTROSTATIC AIR CLEANER CLAIMS What is claimed as invention is: 1. An air cleaner apparatus comprising: a frame member constructed of a dielectric material, said frame member having a first side and a second side; a first conductive screen member attached to said frame member first side; a second conductive screen member attached to said frame member second side; a dielectric filter media material interposed between said first conductive screen member and said second conductive screen member; a power supply adapted to provide opposite polarity high voltage to said first and second conductive screen members; wherein when said power supply is activated and said first and second conductive screen members are polarized, small particles in an air stream passing through said air cleaner apparatus are charged and attracted to the opposite polarity and lodge at random on the dielectric filter media material and held in place by the closed circuit of opposite polarity screens.

2. The air cleaner apparatus of claim 1 wherein said first and second conductive screen members are coated with a carbon material which avoids capacitance build-up.

3. The air cleaner apparatus of claim 1 wherein said power supply includes a neon light array to monitor output levels.

4. The air cleaner apparatus of claim 1 wherein said power supply includes an output control to increase or decrease the output to provide optimal levels for varying thickness of dielectric filter media material.

5. The air cleaner apparatus of claim 1 wherein said power supply includes a pair of high voltage leads from the power supply to each of said conductive screen members, and said leads are adapted to be detachable from said power supply as well as from said conductive screen members .

6. The air cleaner apparatus of claim 1 wherein said dielectric filter media material includes a layer of conductive metal filings to intensify ionization.

7. The air cleaner apparatus of claim 1 wherein said frame member is adapted to be opened to remove a used filter media material to be replaced with a new filter media material.