Gas separation: processes – Filtering
Reexamination Certificate
2001-05-31
2004-04-06
Smith, Duane (Department: 1724)
Gas separation: processes
Filtering
C095S278000, C095S280000, C055S302000, C055S484000, C055S486000, C055S487000, C055S495000, C055S498000, C055S510000, C055S527000, C055S528000
Reexamination Certificate
active
06716274
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a filter arrangement and filtration method. More specifically, it concerns an arrangement for filtering particulate material from a gas flow stream, for example, an air stream. The invention also concerns a method for achieving the desirable removal of particulate material from such a gas flow stream.
The present invention is an on-going development of Donaldson Company Inc., of Minneapolis, Minn., the assignee of the present invention. The disclosure concerns continuing technology development related, in part, to the subjects characterized in U.S. Pat. Nos. B2 4,720,292; Des 416,308; 5,613,992; 4,020,783; and 5,112,372. Each of the patents identified in the previous sentence is also owned by Donaldson, Inc., of Minneapolis, Minn.; and, the complete disclosure of each is incorporated herein by reference.
The invention also relates to polymer materials can be manufactured with improved environmental stability to heat, humidity, reactive materials and mechanical stress. Such materials can be used in the formation of fine fiber such as microfibers and nanofiber materials with improved stability and strength. As the size of fiber is reduced the survivability of the materials is increasingly more of a problem. Such fine fiber are useful in a variety of applications. In one application, filter structures can be prepared using this fine fiber technology. The invention relates to polymers, polymeric composition, fiber, filters, filter constructions, and methods of filtering. Applications of the invention particularly concern filtering of particles from fluid streams, for example from air streams and liquid (e.g. non-aqueous and aqueous) streams. The techniques described concern structures having one or more layers of fine fiber in the filter media. The compositions and fiber sizes are selected for a combination of properties and survivability.
BACKGROUND OF THE INVENTION
Particulate matter suspended in a gas is encountered in many industries. In some industries, such particulate matter is a valuable product, for example, starch, that is to be recovered. For others, such as the metal working industry, the particulate matter may be simply dust to be removed from the air. Systems for cleaning an air or gas stream laden with particulate matter include air filter assemblies that have filter elements disposed in a housing. The filter element may be a bag or sock of a suitable fabric or pleated paper. Cleaning is accomplished by periodically pulsing a brief jet of pressurized air into the interior of the filter element to reverse the air flow through the filter element. Such air filter assemblies are disclosed in, for example, U.S. Pat. No. 4,218,227 and U.S. Pat. No. 4,395,269, which patents are incorporated by reference herein.
Venturi elements are sometimes used to direct the jet of pressurized air into the filter element and to recover pressure energy as air exits the filter element. Often, the inlet end of the Venturi element is either outside the filtering chamber or extends into the interior of the filter element. For example, U.S. Pat. No. 4,218,227 discloses mounting a Venturi with the inlet of the Venturi element resting on the side of the partition of the filter chamber opposite the filter element. U.S. Pat. No. 3,942,962 discloses a Venturi element with the Venturi inlet portion extending into the interior of the filter element.
The invention relates to polymeric compositions with improved properties that can be used in a variety of applications including the formation of fibers, microfibers, nanofibers, fiber webs, fibrous mats, permeable structures such as membranes, coatings or films. The polymeric materials of the invention are compositions that have physical properties that permit the polymeric material, in a variety of physical shapes or forms, to have resistance to the degradative effects of humidity, heat, air flow, chemicals and mechanical stress or impact.
In making non-woven fine fiber filter media, a variety of materials have been used including fiberglass, metal, ceramics and a wide range of polymeric compositions. A variety of techniques have been used for the manufacture of small diameter micro- and nanofibers. One method involves passing the material through a fine capillary or opening either as a melted material or in a solution that is subsequently evaporated. Fibers can also be formed by using “spinnerets” typical for the manufacture of synthetic fiber such as nylon. Electrostatic spinning is also known. Such techniques involve the use of a hypodermic needle, nozzle, capillary or movable emitter. These structures provide liquid solutions of the polymer that are then attracted to a collection zone by a high voltage electrostatic field. As the materials are pulled from the emitter and accelerate through the electrostatic zone, the fiber becomes very thin and can be formed in a fiber structure by solvent evaporation. As more demanding applications are envisioned for filtration media, significantly improved materials are required to withstand the rigors of high temperature 100° F. to 250° F. and up to 300° F., high humidity 10% to 90% up to 100% RH, high flow rates of both gas and liquid, and filtering micron and submicron particulates (ranging from about 0.01 to over 10 microns) and removing both abrasive and non-abrasive and reactive and non-reactive particulate from the fluid stream.
Accordingly, a substantial need exists for polymeric materials, micro- and nanofiber materials and filter structures that provide improved properties for filtering streams with higher temperatures, higher humidities, high flow rates and said micron and submicron particulate materials. A variety of air filter or gas filter arrangements have been developed for particulate removal. However, in general, continued improvements are sought.
SUMMARY OF THE INVENTION
Herein, general techniques for the design and application of air filter arrangements are provided. The techniques include preferred filter media. In general, the preferred media concern utilization, within an air filter, of barrier media, typically pleated media, and fine fiber, to advantage. The filter media includes at least a micro- or nanofiber web layer in combination with a substrate material in a mechanically stable filter structure. These layers together provide excellent filtering, high particle capture, efficiency at minimum flow restriction when a fluid such as a gas or liquid passes through the filter media. The substrate can be positioned in the fluid stream upstream, downstream or in an internal layer. A variety of industries have directed substantial attention in recent years to the use of filtration media for filtration, i.e. the removal of unwanted particles from a fluid such as gas or liquid. The common filtration process removes particulate from fluids including an air stream or other gaseous stream or from a liquid stream such as a hydraulic fluid, lubricant oil, fuel, water stream or other fluids. Such filtration processes require the mechanical strength, chemical and physical stability of the microfiber and the substrate materials. The filter media can be exposed to a broad range of temperature conditions, humidity, mechanical vibration and shock and both reactive and non-reactive, abrasive or non-abrasive particulates entrained in the fluid flow. Further, the filtration media often require the self-cleaning ability of exposing the filter media to a reverse pressure pulse (a short reversal of fluid flow to remove surface coating of particulate) or other cleaning mechanism that can remove entrained particulate from the surface of the filter media. Such reverse cleaning can result in substantially improved (i.e.) reduced pressure drop after the pulse cleaning. Particle capture efficiency typically is not improved after pulse cleaning, however pulse cleaning will reduce pressure drop, saving energy for filtration operation. The filtration media can be cleaned using vibration-cleaning methods wherein the media is vibrated to loosen particulate that has co
Gogins Mark A.
Weik Thomas M.
Donaldson & Company, Inc.
Greene Jason M.
Merchant & Gould P.C.
Smith Duane
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