Liquid purification or separation – Recirculation – Serially connected distinct treating or storage units
Reexamination Certificate
2002-06-25
2004-01-27
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Recirculation
Serially connected distinct treating or storage units
C210S257200, C210S636000, C210S650000, C210S321800, C210S333100, C210S333010
Reexamination Certificate
active
06682652
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a membrane device which is an improvement on a frameless array of hollow fiber membranes and a method of maintaining clean fiber surfaces while filtering a substrate to withdraw a permeate, which is also the subject of U.S. Pat. No. 5,248,424; and, to a method of forming a header for a skein of fibers. The term “vertical skein” in the title (hereafter “skein” for brevity), specifically refers to an integrated combination of structural elements including (i) a multiplicity of vertical fibers of substantially equal length; (ii) a pair of headers in each of which are potted the opposed terminal portions of the fibers so as to leave their ends open; and, (iii) permeate collection means held peripherally in fluid tight engagement with each header so as to collect permeate from the ends of the fibers.
The term “fibers” is used for brevity, to refer to “hollow fiber membranes” of porous or semipermeable material in the form of a capillary tube or hollow fiber. The term “substrate” refers to a multicomponent liquid feed. A “multicomponent liquid feed” in this art refers, for example, to fruit juices to be clarified or concentrated; wastewater or water containing particulate matter; proteinaceous liquid dairy products such as cheese whey, and the like. The term “particulate matter” is used to refer to micron-sized (from 1 to about 44 &mgr;m) and sub-micron sized (from about 0.1 &mgr;m to 1 &mgr;m) filterable matter which includes not only particulate inorganic matter, but also dead and live biologically active microorganisms, colloidal dispersions, solutions of large organic molecules such as fulvic acid and humic acid, and oil emulsions.
The term header is used to specify a solid body in which one of the terminal end portions of each one of a multiplicity of fibers in the skein, is sealingly secured to preclude substrate from contaminating the permeate in the lumens of the fibers. Typically, a header is a continuous, generally rectangular parallelpiped of solid resin (thermoplastic or thermosetting) of arbitrary dimensions formed from a natural or synthetic resinous material. In the novel method described hereinbelow, the end portions of individual fibers are potted in spaced-apart relationship in cured resin, most preferably by “potting” the end portions sequentially in at least two steps, using first and second potting materials. The second potting material (referred to as “fixing material”) is solidified or cured after it is deposited upon a “fugitive header” (so termed because it is removable) formed by solidifying the first liquid. Upon removing the fugitive header, what is left is the “finished” or “final” header formed by the second potting material. Of course, less preferably, any prior art method may be used for forming finished headers in which opposed terminal end portions of fibers in a stack of arrays are secured in proximately spaced-apart relationship with each other.
The '424 patent required potting the opposed ends of a frameless array of fibers and dispensed with the shell of a module; it was an improvement on two preceding configurations disclosed in U.S. Pat. Nos. 5,182,019, and 5,104,535, each of which used frameless arrays and avoided potting the fibers. The efficiency of gas-scrubbing a '424 array was believed to be due, at least in large part, to a substantial portion of the fibers of the fibers in the array lying in transverse relationship to a mass of rising bubbles, referred to herein as a “column of rising bubbles”, so as to intercept the bubbles. Specific examples are illustrated in FIGS. 9, 9A, 10 and 11 of the '424 patent.
A '424 “array” referred to a bundle of arcuate fibers the geometry of which array was defined by the position of a pair of transversely spaced headers in which the fibers were potted. In the '424 array, as in the array of this invention, each fiber is free to move independently of the others, but the degree of movement in the '424 is unspecified and arbitrary, while in the vertical skein of this invention, movement is critically restricted by the defined length of the fibers between opposed headers. Except for their opposed ends being potted, there is no physical restraint on the fibers of a skein. To avoid confusion with the term “array” as used for the '424 bundle of arcuate fibers, the term “skein fibers” is used herein to refer to plural arrays. An “array” in this invention refers to plural, essentially vertical fibers of substantially equal lengths, the one ends of each of which fibers are closely spaced-apart, either linearly in the transverse (y-axis herein) direction to provide at least one row, and typically plural rows of equidistantly spaced apart fibers. Less preferably, a multiplicity of fibers may be spaced in a random pattern. Typically, plural arrays are potted in a header and enter its face in a generally x-y plane (see FIG. 5). The width of a rectangular parallelpiped header is measured along the x-axis, and is the relatively shorter dimension of the rectangular upper surface of the header; and, the header's length, which is its relatively longer dimension, is measured along the y-axis.
This invention is particularly directed to relatively large systems for the microfiltration of liquids, and capitalizes on the simplicity and effectiveness of a configuration which dispenses with forming a module in which the fibers are confined. As in the '424 patent, the novel configuration efficiently uses a cleansing gas, typically air, discharged near the base of a skein to produce bubbles in a specified size range, and in an amount large enough to scrub the fibers, and to cause the fibers to scrub themselves against one another. Unlike in the '424 system, the fibers in a skein are vertical and do not present an arcuate configuration above a horizontal plane through the horizontal center-line of a header. As a result, the path of the rising bubbles is generally parallel to the fibers and is not crossed by the fibers of a vertical skein. Yet the bubbles scrub the fibers. The restrictedly swayable fibers, because of their defined length, do not get entangled, and do not abrade each other excessively, as is likely in the '424 array. The defined length of the fibers herein minimizes (i) shearing forces where the upper fibers are held in the upper header, (ii) excessive rotation of the upper portion of the fibers, as well as (iii) excessive abrasion between fibers. The fibers of this invention are confined so as to sway in a “zone of confinement” (or “bubble zone”) through which bubbles rise along the outer surfaces of the fibers. The side-to-side displacement of an intermediate portion of each fiber within the bubble zone is restricted by the fiber's length. The bubble zone, in turn, is determined by one or more columns of vertically rising gas bubbles, preferably of air, generated near the base of a skein.
Since there is no module in the conventional sense, the main physical considerations which affect the operation of a vertical skein in a reservoir of substrate relate to intrinsic considerations, namely, (a) the fiber chosen, (b) the amount of air used, and (c) the substrate to be filtered. Such considerations include the permeability and rejection properties of the fiber, the process flow conditions of substrate such as pressure, rate of flow across the fibers, temperature, etc., the physical and chemical properties of the substrate and its components, the relative directions of flow of the substrate (if it is flowing) and permeate, the thoroughness of contact of the substrate with the outer surfaces of the fibers, and still other parameters, each of which has a direct effect on the efficiency of the skein. The goal is to filter a slow moving or captive substrate in a large container under ambient or elevated pressure, but preferably under essentially ambient pressure, and to maximize the efficiency of a skein which does so (filters) practically and economically.
In the skein of this invention, all fibers in the plura
Behmann Henry
Henshaw Wayne
Mahendran Mailvaganam
Pedersen Steven
Bereskin & Parr
Fortuna Ana
Zenon Environmental Inc.
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