Gas separation: apparatus – Electric field separation apparatus – Including gas flow distribution means
Reexamination Certificate
2001-08-10
2003-02-04
Chiesa, Richard L. (Department: 1724)
Gas separation: apparatus
Electric field separation apparatus
Including gas flow distribution means
C055S486000, C055S521000, C055S524000, C055S528000, C055SDIG005, C055SDIG003, C095S059000, C096S069000, C264S484000, C264SDIG008, C264SDIG004, C442S414000
Reexamination Certificate
active
06514324
ABSTRACT:
TECHNICAL FIELD
This invention relates to filters cleanable by washing or vacuuming or the like for inlet air heating and air conditioning systems used in residential or commercial buildings and, more particularly, this invention relates to a washable electrostatic filter for such systems having an extended service life and improved efficiency.
BACKGROUND OF THE INVENTION
Inlet air filters for heating and air conditioning systems have been in use for decades. The inlet air or primary filter was originally intended to protect the heating coils and mechanical devices such as fans from damage by airborne particles. As the harmful effect of inhaled particles on human health became known, inlet air filters were designed to remove this particulate matter from the air.
The most popular prior art configuration is a thin, rectangular, disposable filter. The filter contains fiberglass, animal hair, fibrous foam or polymeric media or aluminum mesh encased in a cardboard or plastic frame. Prior art filters comprised polyester panels, urethane foam or latex coated animal hair. Recently, prior art filters containing static or passive electrostatic media have become available. Most residential resistance specifications require air filters to have an initial pressure drop of no more than 0.22 inches of water for an airflow rate of 300 feet per minute. The dust spot efficiency for typical prior art air filters tested using ASHRAE 52.1-1992 is 20% or less. The ASHRAE efficiencies of four types of commercially available filters follow:
TABLE 1
Area of Media
Filter Type
Square Feet
ASHRAE Efficiency
Fiberglass Throwaway
4.0
<20%
Electrostatic (Passive)
4.0
20%
Electrostatic (Fibers)
Up to 8.9
30%
Pleated Polyester Blend
Up to 6.0
25%
Minipleat
Up to 6.4
45% to 65%
When these filters are first placed in use across an air stream, they have a very low filtering efficiency. Typically, the exhaust or dust spot efficiency is about 8%. However, as dust particles are collected, the dust collection efficiency can increase to approximately 20%. At this point, the filter is ready to be replaced. Prior art filters are usually difficult to clean since the dust particles become embedded in the media.
Another current concern is the recognition that particles below 10 microns are not filtered by the cilia hairs in the nose and are therefore inhaled into a human lung. Fibrous particles such as asbestos and fiberglass are known to cause respiratory diseases. Most current inlet air filters for heating and air conditioning systems are not very efficient in capturing these small particles. Filters containing layers of electrostatic media perform better within this range of particles but these filters also become clogged. Since they cannot be efficiently cleaned they must be replaced.
U.S. Pat. No. 6,056,860 disclosed that pleating a washable electrostatic filter resulted in increased efficiency. Capture of particles was enhanced by the angle of approach to the pleated media and by the use of passive electrostatic netting in the multi-layer media. An electrostatic field is only present when air flows past the passive netting and induces charge on the surface of the netting.
The next generation of electrostatic type filter requires an efficiency boost, without increasing the amount of pressure it takes to push the air through the filter medium. Today, passive electrostatic filter medias work mainly on the principal of friction and inherent static electricity in the polymer to obtain their efficiencies. A company that manufactures static control equipment has stated that, contrary to popular belief, static electrification is never caused by just an air flow hitting a solid surface. In most cases, the filters contain layers of a polypropylene honeycombed netting, typically woven, formed from non-woven extruded, monofilament approximately 0.01 diameter and a central layer of a urethane foam or a high loft polyester which also contains some inherent static charges. In the more efficient static charged fiber filters, each fiber has both positive and negative charges. These fibers are 3 to 30 denier in size, or approximately 0.00049 to 0.00268 in. diameter. And usually these types of filters are expensive and are of a disposable type lasting about three months. These filters are known as an “Electret type” having efficiencies of approximately 34% dust spot.
The next generation of washable filters requires an increase in efficiency without increasing the pressure drop across the filter.
STATEMENT OF THE INVENTION
The efficiency of washable filters is further improved in accordance with this invention by adding active electrostatic materials to the polymeric netting, and/or central filter material and/or to the adhesive binder resins used to bond the fibers of the central filter layer of the filter. Preferred active electrostatic materials are charge control agents. The filters of the invention can have a flat or pleated configuration. Pleated filters result not only in increased efficiency but also lower initial resistance to flow. The life of the filter between cleanings is substantially increased and cleaning the filter is much easier. Another aspect of the invention is method and apparatus for forming and charging multiplayer washable filter media containing charge control agents.
In the filter of the invention, charge is not only induced on the surface of the netting or central layer, but is present throughout the bulk of the polymer fibers in the netting or the polymer fibers or foam in the central layer. The polymers are preferably non-conductive and contain from 0.5% to 15% preferably 1 to 10 percent by weight of the charge control agents. The polymers must have high melting and decomposition temperatures to survive the compounding, charging, pleating and other steps of manufacturing the filters. Suitable polymers are polyalkylene polymers having 2-6 carbon atoms such as polyethylene and polypropylene, linear polyamides such as Nylon®, polycarbonates, and polyurethanes. Polar polymers containing negative charge agents such as acrylic polymers, polymethacrylic acid or alkyl esters thereof, acrylic copolymers such as styrene-methylmethacrylate may be utilized.
Examples of charge control agents are compounds of organic or organometallic charge control compounds, inclusions compounds of cyclic polysaccharides, monoazo metal compounds, alkyl acrylate monomers, alkyl methacrylate monomers, calixarene compounds metallized with an alkali metal or an alkaline earth metal, rhodamine or xanthene-type dyes, polytetrafluoroethylene, alkylene, arylene, arylenealkylene, alkylenediarylene oxydialkylene or oxydiarylene polyacrylic and polymethacrylic acid compounds, organic titanates, quaternary phosphonium trihalozincate salts, organic silicone complex compounds, dicarboxylic acid compounds, cyclic polyethers or non-cyclic polyethers, cyclodextrin, complex salt compounds of amine derivatives, ditertbutylsalicicyclic acid, potassium tetaphenylborates, potassium bis borates, sulfonamides and metal salts thereof, alumina particles treated with silane coupling agents selected from the group consisting of dimethyl silicone compounds, azo dye, phthalic ester, quaternary ammonium salt, carbazole, diammonium and triammonium, hydrophobic silica and iron oxide, phenyl, substituted phenyl, naphthyl, substituted naphthyl, thienyl, alkenyl and alkylammonium complex salt compounds, sodium dioctylsulfosuccinate, sodium benzoate, zinc complex compounds, mica, monoalkyl and dialkyl tin oxides and urethane compounds, metal complex of salicyclic acid compound, oxazolidinones, piperazines, perfluroinated alkanes, fatty acid amides, oleophobic fluorochemical surfactants, Lecigran MT, nigrosine, fumed silica, carbon black, para-trifluoromethyl benzoic acid and ortho-fluoro benzoic acid, poly(styrene-co-vinylpyridinium toluene sulfonate), methyl or butyltriphenyl phosphonium-p-toluene sulfonate, complex aromatic amines, triphenylamine dyes and azine dyes, alkyldimethylbenzylammonium salts.
The charge control agents (“CCA”s) operate by tr
Chiesa Richard L.
Jacobs Marvin E.
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