Gas separation – Specific media material – With coating – impregnant – or bonding agent
Reexamination Certificate
2000-03-16
2002-05-14
Simmons, David A. (Department: 1724)
Gas separation
Specific media material
With coating, impregnant, or bonding agent
C055S487000, C055S527000, C055S528000, C055SDIG003, C055SDIG007, C055SDIG007
Reexamination Certificate
active
06387144
ABSTRACT:
BACKGROUND
The invention relates to filter media and filter assemblies for filtering fluid including air.
The invention arose during development efforts directed toward increasing filter life in filters exposed to high dust concentrations of dry and/or sooty and/or oily particles. Prior non-woven fibrous filter media use needling techniques to achieve required media thickness and solidity. During the process of needling, small holes are formed through the media. Such needle holes, formed in felted and other synthetic filter materials, promote the penetration of incoming and detached particles. These needle holes cause discontinuities in the filter media structure because they are relatively large pores compared to those in the bulk fiber matrix. The large pores offer a path of low resistance to the fluid flow. Because smaller pores are clogged faster by deposited particles, the velocity through the larger needle holes increases correspondingly. The holes caused by needle punching and the increased velocity therethrough thus create conditions for particle penetration and reentrainment. Consequently, both uncaptured and detached dust particles can penetrate the filter through such needle holes, leading to lower filter efficiency.
Further in the noted prior fibrous filter media, the fibers extend dominantly perpendicular to the flow direction of fluid through the filter media. In this type of orientation, the surface area of particle contact and adhesion with the fibers is small while the face surface area of particle clusters is large as captured dust particles build on each other. Sometimes dust particle aggregates form bridges between fibers. Such particle aggregates and bridges can be easily blown off, particularly if exposed to high fluid flow rates or pulsation. The particles form aggregates which can form particle bridges between fibers that block flow through the media and shorten filter life due to premature clogging. Furthermore, such particle aggregates and bridges are subject to instability and the noted break-off, particularly in areas adjacent the noted needle holes through which the air velocity increases. Such needle holes may be penetrated by an increased number of particles, which is undesirable because of such release and reentrainment of contaminant particles.
Contaminant cake stability is another problem in prior fibrous non-woven filter media. Because such media has very little rigidity and compression resistance, the contaminant cake which builds on the filter media can be easily dislodged in localized areas. The noted prior needling of such media improves rigidity and compression resistance when compared to air-laid nonwovens, however there is a need for additional stability of the contaminant dust cake to improve filtration performance. Furthermore, the noted needle holes cause the noted large pores which cause a nonuniform distribution of the dust cake, i.e. large craters at the pores, and dust cake particle agglomeration and bridging between fibers at areas between such needle hole pores.
SUMMARY
The present invention provides a simple and effective solution to the above noted and other filter problems. In one desirable aspect, the invention eliminates needling and the needle holes caused thereby in fibrous filter media, including non-woven media. This eliminates the noted large pores in the bulk fiber matrix at needle holes, which in turn eliminates the noted path of low restriction to the fluid flow and increased velocity therethrough, thus eliminating the noted penetration of uncaptured and detached reentrained dust particles through such needle holes, otherwise causing lower filter efficiency.
In another aspect, the surface area of particle adhesion and contact to fibers is increased and the face area of dust particle aggregates and bridging between fibers is reduced, preventing blockage to flow otherwise caused thereby, and reducing risk of reentrainment, and providing a more stable filtration process.
In another aspect, rigidity and compression resistance of the filter media is enhanced, increasing contaminant cake stability. In addition, the invention enables a more uniform distribution of a stable dust cake, including elimination of the noted craters otherwise formed at needle holes, and contaminant particle aggregates and bridging between fibers at areas between such craters, which in combination with the noted increased rigidity and compression resistance of the filter media, enhancing contaminant cake stability.
The present invention provides an improved method of filtering particles in fluid flowing along a given flow direction through filter media having a plurality of fibers, including an improved method for increasing capture of and retention of contaminant particles by the fibers of the filter media. In one aspect, the method includes, in combination: increasing residence dwell time of particles moving along the fibers to increase the chance of, and extend the time of, fiber-particle contact; increasing Brownian diffusion probability of particles diffusing to the fibers; increasing the spread of, and even loading of, particles along the fibers; reducing particle agglomeration and particle bridging between fibers which would otherwise block flow and be subject to instability and reentrainment if exposed to high flow rates or pulsation. The increased residence dwell time, increased Brownian diffusion, increased spread and evenness of particle loading, and reduction of particle agglomeration and bridging, is accomplished by orienting the fibers parallel to the fluid flow direction in combination with providing fibers of sufficient length along the flow direction such that residence dwell time is increased, Brownian diffusion is increased, spread and evenness of particle loading is increased, and particle agglomeration and bridging is reduced, all as compared to, and relative to, filter media fibers extending perpendicular to the fluid flow direction.
The contact surface area between the contaminant particles and their aggregates remains large, and the face area of the contaminant aggregates stays small during contaminant loading. This is a favorable condition for a stable filtration process.
A significant advantage of the invention is higher contaminant capacity due to favorable contaminant loading. In the noted prior art, contaminant accumulates on the fibers and aggregates on itself and also forms long and fragile bridges between fibers blocking fluid flow. In the present invention, contaminant particles forming the contaminant cake are distributed more evenly and uniformly along the entire fiber length. Contaminant loading is thus more evenly and uniformly distributed not only along a surface area along a plane perpendicular to the flow direction but also along a fiber length extending along a plane parallel to the flow direction. This uniformity of contaminant distribution along both planes provides decreased filter pressure drop and increased contaminant loading capability.
In a further desirable aspect, the invention increases rigidity and compression resistance of the fibrous filter media, including at low solidity, and enhances stability of the uniformly distributed contaminant cake, including resistance to reentrainment even if exposed to high flow rates or pulsation.
In preferred form, filter media construction is provided including a sheet of filter material having a thickness dimension between oppositely facing first and second sides for filtering particles in fluid flow therethrough along a flow direction perpendicular to the sheet and the first and second sides and parallel to the thickness dimension. The sheet is formed by an internal pleated subsheet of a plurality of fibers and having a plurality of pleats extending between first and second sets of pleat tips, the pleats extending parallel to the flow direction, the first set of pleat tips providing the first side of the sheet, and the second set of pleat tips providing the second side of the sheet. The pleats engage each other and are packed sufficiently tightly such that
Cady Daniel R.
Fallon Stephen L.
Jaroszczyk Tadeusz
Kallsen Kent J.
Morgan Jeffrey S.
Andrus Sceales Starke & Sawall LLP
Nelson Industries Inc.
Pham Minh-Chau T.
Simmons David A.
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