Bridge support and reduced feed spacers for spiral-wound elements
Embodiments of the invention provide replacements for a continuous layer of feed spacer mesh in spiral-wound reverse osmosis elements and replacing such mesh with discrete regions of feed spacer supporting the inlet and outlet ends of the element and a stiffening bridge feature to bridge between these regions at the tail end of each membrane leaf comprising the element during the element rolling process. The stiffening bridge feature prevents inward deflection of the inner layer of the membrane leaf during rolling, facilitating proper sealing of the adhesive through the permeate carrier to the adjacent membrane film using known membrane rolling techniques.
1. A method of producing a spiral wound element, comprising:
(a) providing a permeate carrier sheet having a length and width;
(b) providing a collection tube;
(c) providing a membrane sheet, having an active surface configured to provide selective fluid separation and an inactive surface opposite the active surface, and wherein the membrane sheet has feed spacing elements disposed on the active surface in regions near each of first and second opposing edges of the active surface, and wherein the membrane sheet has a stiffening bridge feature disposed on the active surface of the membrane sheet in a region near a third edge of the membrane sheet that is not one of the first and second opposing edges, wherein the membrane sheet has a width substantially equal to the width of the permeate carrier and a length substantially equal to about twice the length of the permeate carrier;
(d) folding the membrane sheet along a fold line extending along the width of the membrane sheet such that the active surface of the membrane sheet is inside the folded sheet;
(e) placing the folded membrane sheet such that the inactive surface is in contact with the permeate carrier, forming an element leaf having a first end near the fold of the membrane sheet and a second end opposite and parallel to the fold, with the first and second opposing edges folded and connecting the first and second ends, and having a first portion near the permeate carrier and a second portion separated from the permeate carrier by the first portion;
(f) applying adhesive to the membrane sheet, the permeate carrier, or a combination thereof, such that the adhesive extends across the membrane leaf near the third edge and near the first and second opposing edges;
(g) winding the element leaf around the collection tube, with the first end of the element leaf near the collection tube, forming a spiral wound element.
2. The method of claim 1 , further comprising curing the adhesive, then removing a portion of the spiral wound element corresponding to the first and second opposing edges of the element leaf, wherein the element leaf, after such removal, still has adhesive completely sealing the membrane sheet about the permeate carrier along the second end and the first and second opposing edges.
3. The method of claim 1 , wherein step (e) comprises placing the membrane sheet such that the stiffening bridge feature is with the second portion of the membrane sheet.
4. The method of claim 1 , wherein a central region of the active surface of the membrane sheet, between the feed spacing regions, is empty of feed spacing elements.
5. The method of claim 1 , wherein the stiffening bridge feature does not wrap around the third edge.
6. The method of claim 1 , wherein the stiffening bridge feature does not seal the permeate carrier at the second end of the element leaf.