Vertical skein of hollow fiber membranes and method of maintaining clean fiber surfaces while filtering a substrate to withdraw a permeate

In a gas-scrubbed assembly comprising, a microfiltration membrane device in combination with a gas-distribution means to minimize build-up of particulate deposits on the surfaces of hollow fiber membranes ("fibers") in said device, and to recover permeate from a multicomponent liquid substrate while leaving particulate matter therein, said membrane device comprising,

• a multiplicity of fibers, unconfined in a shell of a module, said fibers together having a surface area >1 m.sup.2, said fibers being swayable in said substrate, said fibers being subject to a transmembrane pressure differential in the range from about 0.7 kPa (0.1 psi) to about 345 kPa (50 psi), and each having a length >0.5 meter;
• a first and second header disposed in spaced-apart relationship within said substrate;
• said first header and said second header having opposed terminal end portions of each fiber sealingly secured therein, all open ends of said fibers extending from a permeate-discharging face of at least one header;
• permeate collection means to collect said permeate, sealingly connected in open fluid communication with a permeate-discharging face of each of said headers;
• and,
• means for withdrawing said permeate;
• and,
• said gas-distribution means is located within a zone near the base of said skein, having through-passages therein adapted to have sufficient gas flowed therethrough to generate enough bubbles flowing in a column of rising bubbles through and around said skein fibers, to keep surfaces of said fibers awash in bubbles;
• the improvement comprising,
• said fibers, said headers and said permeate collection means together forming a skein wherein said fibers are essentially vertically disposed and terminal end portions of individual fibers are potted in proximately spaced-apart relationship in cured resin;
• said first header being upper and disposed in vertically spaced-apart relationship above said second header at a fixed distance;
• each of said fibers having substantially the same length, said length being from at least 0.1% greater, to less than 5% greater than said fixed distance so as to permit restricted displacement of an intermediate portion of each fiber, independently of the movement of another fiber;
• and,
• said gas distribution means having through-passages therein to discharge a cleansing gas in an amount in the range from 0.47-14 cm.sup.3 /sec per fiber (0.001 scfm/fiber to about 0.03 scfm/fiber) in a column of bubbles which rise vertically substantially parallel to, and in contact with said fibers, movement of which is restricted within said column;
• whereby said permeate is essentially continuously withdrawn while concentration of said particulate matter in said substrate is increased.

In a process for maintaining the outer surfaces of hollow fiber membranes essentially free from a build-up of deposits of particulate material while separating a permeate from a multicomponent liquid substrate in a reservoir, said process comprising,

• submerging skein fibers within said substrate unconfined in a modular shell, said fibers being securely held in laterally opposed, spaced-apart first and second headers, said fibers having a transmembrane pressure differential in the range from about 0.7 kPa (0.1 psi) to about 345 kPa (50 psi), a total surface area >1 m.sup.2, and a length sufficiently greater than the direct distance between opposed faces of said first and second headers, so as to present said skein in a swayable configuration above a horizontal plane through the horizontal center-line of a header;
• mounting said headers in fluid-tight open communication with collection means to collect said permeate;
• flowing a fiber-cleansing gas through a gas-distribution means proximately disposed relative to said skein, within a zone near the base of said skein, and contacting surfaces of said fibers with sufficient physical impact of bubbles of said gas to maintain essentially the entire length of each fiber in said skein awash with bubbles and essentially free from said build-up;
• maintaining an essentially constant flux through said fibers substantially the same as an equilibrium flux initially obtained after commencing operation of said process;
• collecting said permeate in said collection means;
• and,
• withdrawing said permeate,
• the improvement comprising,
• introducing a cleansing gas in an amount in the range from 0.47-14 cm.sup.3 /sec per fiber (0.001 scfm/fiber to about 0.03 scfm/fiber) to generate a column of said bubbles alongside and in contact with outer surfaces of said fibers;
• deploying said skein fibers within said column in an essentially vertical configuration, with said headers in fixed spaced apart relationship at a fixed distance, said skein having fibers of substantially the same length and from at least 0.1% greater, to about 5% greater than said fixed distance, said fibers being independently swayable from side-to-side within a vertical zone of movement with terminal end portions of individual fibers potted in proximately spaced-apart relationship in cured resin;
• restricting movement of said fibers to said vertical zone defined by lateral movement of outer fibers in said skein;
• vertically gas-scrubbing said fibers' outside surfaces with bubbles which flow upward in contact with said surfaces;
• maintaining said surfaces substantially free from said deposits of particulate matter during a period when specific flux through said fibers has attained equilibrium;
• and,
• simultaneously, essentially continuously, withdrawing said permeate while increasing the concentration of said particulate material in said substrate.

A method of forming a header for a skein of a multiplicity of fibers, comprising,

• forming a stack of at least two superimposed essentially coplanar and similar arrays, each array comprising a chosen number of fibers supported on a support means having a thickness corresponding to a desired lateral spacing between adjacent arrays;
• holding the stack in a first liquid with terminal portions of the fibers submerged, until the liquid solidifies into a first shaped lamina, provided that the first liquid is unreactive with material of the fibers;
• pouring a second liquid over the first shaped lamina to embed the fibers to a desired depth, and solidifying the second liquid to form a fixing lamina upon the first shaped lamina, the second liquid also being substantially unreactive with either the material of the fibers or that of the first shaped lamina;
• forming a composite header in which terminal portions of the fibers are potted, the composite header comprising a laminate of a fugitive lamina of fugitive material and a contiguous finished header of fixing lamina;
• and,
• removing the first shaped lamina without removing a portion of the fixing lamina so as to leave the ends of the fibers open and protruding from the aft face of the header,
• whereby the open ends having a circular cross-section are exposed without cutting the fibers.

A header in which a multiplicity of hollow fiber membranes or "fibers" is potted, said header comprising,

• a molded body of arbitrary shape striated in a fixing lamina and a fugitive lamina, said fugitive lamina formed from a fugitive potting material and said fixing lamina formed from a fixing material;
• said fibers having terminal portions thereof potted in said fugitive potting material which when solidified plugs ends of said fibers, plugged ends having an essentially circular cross-section, said fugitive lamina maintaining said ends in closely spaced-apart substantially parallel relationship;
• said fugitive lamina having an aft face towards which said plugged ends protrude, and a fore face through which said fibers extend vertically;
• said fugitive lamina having said fixing lamina adhered thereto, said fixing lamina having a thickness sufficient to maintain said fibers in substantially the same spaced-apart relationship relative to one and another as the spaced-apart relationship in said lower portion.