Sanitary spiral wound filtration cartridge
Sanitary elements and cartridges of high performance are described which utilize a thin surrounding tubular shell with an exterior textured surface. Through the use of an overwrap material of particular design and by wrapping an assemblage of sheets of semipermeable membrane material, permeate carrier material and feed spacer material using a high tension, a spirally wound crossflow filtration element is constructed which has a substantially cylindrical outer surface of closely controlled OD that smoothly fits within such shell and which resists telescoping as a result of its radial compression.
1. A method of making a spiral wound membrane cartridge of about 7.9 in. diameter for a sanitary application, which method comprises the steps of:
providing a central permeate collection tube and a plurality of sheets of feed spacer material, permeate carrier material, and semipermeable membrane filtration material, said membrane filtration material sheets each having a length about twice as long as said other sheets and being folded approximately in half,
adhesively attaching each of said permeate carrier sheets between half-sheets of two different semipermeable membrane filtration sheets along both longitudinal side edges of said permeate carrier sheet and across the free end edge thereof to create 3-ply leaves,
disposing a feed spacer sheet between each two facing half-sheets of different filtration membrane material, which feed spacer sheet is of bi-planar construction and formed of two groups of parallel filaments,
spirally wrapping said plurality of sheets about said central permeate collection tube to form an assemblage,
following curing of said adhesive, partially unrolling said spiral wound assemblage and trimming a free end edge of each of the 3-ply leaves to provide an adhesive-filled end edge surface,
affixing overwrap material sheeting to an end portion of one of said feed spacer sheets which feed spacer sheet is juxtaposed in surface to surface contact with facing membrane filtration sheets within said spiral wound assemblage, said overwrap material sheeting having a substantially greater tensile strength than the feed spacer, which greater tensile strength is at least about 1250 N/m in the longitudinal direction,
tightly re-winding said plurality of sheets of said partially unrolled assemblage about said central permeate collection tube with said overwrap sheeting attached to one feed spacer sheet to create several wraps of overwrap sheeting around the spiral wound assemblage, while applying gradually increasing tension to at least 7 lbf/in (1250 N/m) to said overwrap sheeting to thereby tighten the wrapped assemblage about said central permeate collection tube and place the assemblage of sheets in radial compression,
joining two juxtaposed regions of said overwrap sheeting to each other in surface to surface contact to retain the resultant tightly wrapped final filtration element in substantially cylindrical form having a selected outer diameter, and
associating a thin tubular shell having a textured exterior surface with said tightly wrapped element to provide a filtration cartridge designed to allow a controlled bypass flow of liquid feed between a pressure vessel interior surface and said textured exterior surface of said shell.
2. The method according to claim 1 wherein said overwrap sheeting is wrapped about said assemblage for at least about four total wraps while applying said tension to provide the desired tightness in said element and then slightly unwrapped to an extent which provides a precise selected outer diameter before joining said overwrap sheeting to itself and severing said sheeting adjacent said joint.
3. The method according to claim 2 wherein said overwrap material, which is joined to an end portion of one of said feed spacer sheets, encircles said assemblage at least about 1½ times in the tightly wrapped final filtration element.
4. The method according to claim 1 wherein said feed spacer sheet and said overwrap sheeting are made of thermoplastic polymeric materials and are joined via heat-sealing and wherein said adhesive is a two-part epoxy or polyurethane adhesive.
5. The method according to claim 1 wherein said feed spacer sheet material and said overwrap sheeting material are each made of two groups of spaced apart parallel strands which groups are arranged substantially perpendicular to each other and wherein the two groups of strands are bi-planar in said feed spacer material and that the two groups of strands in said overwrap sheeting material have a planar arrangement.
6. A method of making a spiral wound membrane cartridge of about 7.9 in. diameter for a sanitary application, which method comprises the steps of:
providing a central permeate collection tube and a plurality of sheets of feed spacer material, permeate carrier material, and semipermeable membrane filtration material,
attaching each of said permeate carrier sheets between two sheets of semipermeable membrane filtration material along both longitudinal side edges of said permeate carrier sheet and across a free outer end edge thereof with a curable adhesive to create 3-ply leaves,
disposing a feed spacer sheet between each two 3-ply leaves, which feed spacer sheet is of bi-planar construction and formed of two groups of parallel filaments,
spirally wrapping said plurality of feed spacer sheets and 3-ply leaves about said central permeate collection tube to form an assemblage,
partially unrolling said spiral wound assemblage following curing of said adhesive,
affixing overwrap material sheeting to an end portion of one of said feed spacer sheets in said partially unrolled assemblage, which feed spacer sheet is juxtaposed in surface to surface contact with facing membrane filtration sheets within said spiral wound assemblage, said overwrap material sheeting having a planar construction which has an at least about 1.5 times higher resistance to cross flow therethrough than the bi-planar feed spacer sheet and which has a tensile strength of at least about 1250 N/m in the longitudinal direction that is greater than the tensile strength of the feed spacer sheet,
then tightly re-winding said partially unrolled assemblage about said central permeate collection tube with said overwrap sheeting affixed to one feed spacer sheet to create several wraps of overwrap sheeting around the spiral wound assemblage, while applying gradually increasing tension to at least 7 lbf/in (1250 N/m) to said overwrap sheeting, to thereby tighten the wrapped assemblage containing said cured adhesive about said central permeate collection tube with multiple encircling wraps of said overwrap material and place the assemblage of sheets in radial compression,
unwrapping said tightened wrapped assemblage while maintaining said tension until a precise outer diameter is reached and then joining two juxtaposed regions of said overwrap sheeting to each other in surface to surface contact to retain the resultant tightly wrapped final filtration element in substantially cylindrical form having said precise outer diameter, and
associating a thin tubular shell having a textured exterior surface with said tightly wrapped element to provide a filtration cartridge designed to allow a controlled bypass flow of liquid feed between a pressure vessel interior surface and said textured exterior surface of said shell.
7. The method according to claim 6 wherein said overwrap sheeting is wrapped about said assemblage for at least about four total wraps while applying said tension to provide the desired tightness in said element.
8. The method according to claim 7 wherein said overwrap material sheeting is severed at a location such that said overwrap material, encircles said assemblage at least about 1½ times in the tightly wrapped final filtration element of precise outer diameter.
9. The method according to claim 6 wherein said feed spacer sheet and said overwrap sheeting are made of thermoplastic polymeric materials and are joined via heat-sealing and wherein said adhesive is a two-part epoxy or polyurethane adhesive.