A membrane module and a method for its manufacture

Abstract: In conjunction with a method of producing a fluid purifier membrane module, sheets of membrane material are disposed in layers with intermediate spacer elements in a manner to obtain mutually alternating spaces for contaminated and purified fluid respectively, it is proposed, among other things, that mutually adjoining sheets of membrane material (12) are joined together in pairs in a manner to obtain membrane units (10) which include closed cavities (28), and that the membrane units (10) with associated spacer elements (18, 34) are arranged in a stack, and that the mutually facing outer surfaces of the membrane units are joined together in zones and in a fluid-tight fashion along at least one line (36) which extends through the walls of the membrane units, and that the membrane units are perforated along the line in a manner to obtain through the membrane units a passageway (32) which communicates with the cavities (28). The invention also relates to a membrane module produced in accordance with the method.

Description: The present invention relates to a method of producing a membrane module for fluid purifiers, wherein sheets of membrane material are disposed in layers with spacing elements placed therebetween, such as to obtain respective mutually alternating spaces or cavities in which contaminated and purified fluid are accommodated. The invention also relates to a membrane module produced in accordance with the method. According to one known method, the module is constructed of flat membrane sheets stretched between rigid support frames. Although this known method can be mechanized to a large extent, the resultant modules have low volume efficiency (active membrane surface area/module volume), primarily due to the thickness and sealing efficiency of the rigid frames. DE-A-25 37 389 discloses such a method having a filter membrane folded back and forth into a meander shape and having a single outlet common to the spaces defined in each fold of the membrane. Since, however, also in this case the filter membrane is stretched between rigid support frames, the resulting volume efficiency is low. According to another known method, the membrane module is produced by helically winding a plurality of membrane envelopes around a permeation tube. Although this method produces modules which have a high volume efficiency, it can only be mechanized to a small extent, since the task of helically winding and gluing the membrane envelopes must be carried out with extreme care in order to avoid folds and wrinkles on the inner surfaces of the envelopes, such folds and wrinkles causing the membrane material to rupture and therewith render it useless. Another problem encountered with these and other known membrane modules is the difficulty of readily placing the large number of spaces intended for accommodating purified fluid in fluid-tight communication with a fluid purifier outlet line that is common to all these spaces. Accordingly, an object of the present invention is to provide an improved membrane module and an improved method of the kind defined in the introduction which can be extensively mechanized, which will provide membrane modules of high volume efficiency, and with which the spaces intended for the purified fluid can be readily connected to an outlet line. This object is achieved with a method and membrane module of the aforesaid kind that have the features set forth in the following independent claims 1 and 4. According to one aspect of the invention, mutually adjacent sheets of membrane material are joined together in pairs to obtain a membrane unit which includes closed cavities, whereafter the membrane units are arranged in a stack. The mutually facing outer sides of the membrane units are then joined together at spaced zones or regions and in a fluidtight fashion along at least one line which extends through the stack. The membrane units are then perforated along said line in a manner to obtain through the membrane units a passageway which communicates with the cavities. A high degree of mechanization cane be achieved when the membrane units are formed continuously from a web of membrane material and the stack is created by multiple folding of the membrane units, since only one or a pair of web sections of membrane material need be worked and handled, for instance need be spot-welded and welded along longitudinal and transversal seams and folded during the manufacturing process. When the width of the membrane units is varied to obtain a stack of circular cross-section, the module can be adjusted to the shape of standardized pressure vessels for membrane modules. Other features of the invention and advantages afforded thereby will be evident from the claims and the following detailed description of a preferred exemplifying embodiment of the invention with reference to the accompanying drawings, in which FIG. 1 illustrates an end piece of a spread-out membrane module according to the invention, with parts of the module cut away and other parts folded up; FIG. 2 is an end view of part of a completed membrane module; and FIG. 3 is a schematic cross-sectional view in larger scale of a membrane module fitted to a pressure vessel, with parts of the module removed for illustration purposes. The out-spread membrane module of the embodiment illustrated in FIG. 1 is produced from a web of membrane material 12 which includes a thin membrane layer 14, for instance an osmosis material, which is joined to a thicker carrier sheet 16, for instance a sheet of nonwoven material, to form a laminate. In the illustrated example, the web of membrane material 12 is folded in the longitudinal direction of the web along a line 24, so as to obtain a double-layer membrane web. As will be understood, the double-layer membrane web may also be formed by placing two webs of membrane material one upon the other. Placed between the two layers of the membrane web is a fluid permeable spacer sheet 18, which is also in web form and has a net or grid-like structure. The double-layer membrane web and the spacer sheet 18 enclosed therebetween are then joined together and sealed by welding, fusing, melt-gluing, gluing or taping the layers and sheet together along joining lines 20 and 22 in a manner to obtain a plurality of web-like, continuous membrane units 10, each having a closed cavity 28 (FIG. 3). The cavities 28 are thus delimited from the outer surfaces of the membrane material 12 and form spaces for the purified fluid or the fluid that is able to permeate through the membrane material 12 when a pressurized fluid acts on the outer surfaces of said material. The continuous string of membrane units 10 produced in the aforedescribed manner are then arranged in stacks, by folding the string of membrane units 10 towards one another along fold lines 26 that extend between adjacent transverse connecting lines 22. By positioning the fold lines 26 between the mutually adjacent joining lines 22, 22 and in spaced relationship with said lines, there is no risk that any rupture that may occur in the thin membrane layer 14 as a result of folding the layer will propagate to the actual membrane units 10. Although not shown, it is probable that the fold lines can be placed directly coincidental with a joining line or weld. Additional fluid permeable spacer sheets 34 are placed between the mutually facing outer surfaces of the membrane units 10 in the thus formed stack (FIG.S 2 and 3). Similar to the earlier described spacer sheets 18, the function of the further spacer sheets 34 is to hold the adjacent or adjoining sides of the membrane material 12 spaced from one another in the completed membrane module, so as to permit fluid to flow therebetween. As the membrane units 10 are folded, the mutually adjoining outer surfaces of the units are joined together at regions 30 in a fluid-tight and zone-wise fashion, said regions 30 lying on a line 36 which extends through or transversely to the completed stack. As when joining the material along the lines 20 and 22, joining of said adjacent outer surfaces can be effected by welding, melt-fusion, melt-gluing, gluing or taping. As will be evident from FIG. 3, each joining region or zone 30 extends through the thickness of associated spacer sheets 34. As shown in the framed region A in FIG. 3, the spacer sheets 34 may, alternatively, be provided beforehand with circular apertures around the line 36 in which O-rings 56 or optionally flat seals (not shown) are placed, these sealing devices, in turn, being clamped between the outer sides of the membrane units 10 in response to a pressure force applied externally to the stack, and therewith provide a fluid-tight join between said units. Subsequent to joining together the outer sides of the thus stacked membrane units 10 in the regions or zones 30, a throughpassing passageway 32 is formed through the membrane units along the line 36 that extends through the centre points of the joins 30. The passageway 36 can be provided in any suitable manner, for instance by punching or drilling, provided that the connections 38 to the closed cavities 28 formed by such perforation do not become blocked. This can be achieved by alternatively preparing the passageway 32 in a manner to provide openings 32' (FIG. 1) separately in the membrane material 12 prior to folding the material to the completed stack. The aforedescribed method steps in the manufacture of a membrane module are highly suited to a fully mechanized production process, which can be carried out roughly in accordance with the following non-limiting example: The webs of membrane material and spacer material (permeation spacers) 12, 18, 12 taken from respective rolls of material and mutually combined are first provided with the longitudinally extending and transversely extending joins 20 and 22, for instance in a welding station. Glue zones are then applied to the planned regions 30 on the outer surfaces of the membrane units. Ready-cut and optionally perforated (around the patches 30) pieces of spacer material (feed spacers) 34 are then positioned between adjoining membrane units 10, 10, whereafter these units are folded against one another and compressed so as to harden the joins 30. Finally, the completed membrane stack is drilled along the line 36 to provide the passageway 32. One open end of the passageway 32, or possibly both ends of said passageway, is/are connected to a connection pipe 40 (FIG. 3) which leads to an outgoing permeation fluid conduit (not shown), said conduit being connected in a suitable fluid-tight fashion to the associated outer side of an outer membrane unit 10. In the case of the FIG. 3 embodiment, the connector pipe 40 is provided with a flange 42 which is glued to a perimeter area of said outer surface around the mouth of the passageway 32. In the illustrated case, in which only one permeation fluid conduit shall be connected to the membrane module, the other orifice of the passageway 32 is sealed in a suitable manner by means of a fluid-tight plate or cloth 44 or some like device, as indicated in chain lines in FIG. 3. The completed membrane module is intended to be placed within a pressure vessel 50 of a fluid purifier (not shown), for instance a water purifier of the RO-type (reversed osmosis). In this case, the fold lines 26 are conveniently placed so that the completed membrane module will obtain a circular cross-section which coincides with the shape of the pressure vessel 50. Equalizing pieces 52, 54 of circular-segmental cross-section may optionally be mounted at the ends of the stack cross-section, wherein the flat sides of the equalizing pieces that face towards the membrane module function to hold the module in position with possible pressure force in the pressure vessel 50. The described inventive membrane module is intended to operate in the following manner when installed in the pressure vessel 50: A flow of pressurized fluid to be cleansed or purified is introduced axially into the elongated pressure vessel 50 through an inlet conduit, not shown. The pressurized fluid enters the module and penetrates to the outer sides of the membrane units 10, through the fluid permeable spacer sheets 34. As illustrated by the full arrows in FIG. 3, the pressurized fluid acts on all exposed outer surfaces of the membrane material 12, wherein the membrane sheet 14 (FIG. 1) allows permeation fluid or purified fluid to pass through to the cavities 28 of the membrane units 10 as a result of, for instance, reversed osmosis or some other filter effect, depending on the structure of the membrane layer. As indicated by the empty arrows in FIG. 3, purified fluid can only flow out to the passageway 32 through the connections 38, and exits from the pressure vessel through the fluid conduit 40 as process flow. That part of the axial flow through the pressure-vessel cross-section that is unable to penetrate through the membrane layer will exit as reject flow to the pressure vessel 50 outlet conduit, in a known manner not shown.

Claims: A method for producing a fluid purifier membrane module having a membrane material disposed in layers with alternating first and second flexible web-like spacer sheets placed therebetween forming mutually alternating spaces in the purifier for receiving respective unpurified and purified portions of a fluid to be purified in the purifier, said method comprising the steps of: disposing a pair of flexible web portions (12) of said membrane material face to face with said first web-like spacer (18) placed between the web portions; joining together the end portions of said pair of flexible web portions (12) at their perimeters to produce a continuous line of membrane units (10) each having a closed cavity (28) enclosing said first spacer sheet; arranging the membrane units (10) in a stack by multiple-folding said continuous line of membrane units (10) and placing said second web-like spacer sheet (34) between each fold of said multiple folding, whereby said spacer sheet (34) is sandwiched between the outer sides of said membrane units (10); the mutually adjoined outer surface of the membrane unit are joined together at regions (30), in a fluid tight manner, said regions (30) lying on a line (36) which extends through the membrane units in the stack; and forming a bore (32) through the membrane units (10) through said regions 30 along said line 36 for obtaining through the membrane units (10) a passageway (32) serially connecting said closed cavities (28), whereby said passageway (32) is being fluid tight sealed from the space outside the cavity (28). The method of claim 1, further comprising varying the width of the membrane units (10) in a manner to obtain a stack of circular cross-section. The method of claim 1, wherein said bore (32) through the membrane units (10) is formed by forming a bore through each said membrane unit prior to arranging the membrane units (10) in said stack. A fluid purifier membrane module, comprising a pair of flexible web portions (12) of membrane material disposed face to face, with a layer of a first web-like spacer (18) sandwiched therebetween, said web portions (12) being perimetrically joined, thereby providing a plurality of membrane units (10) disposed in a first line, each having a respective closed cavity (28) said first spacer (18) between of said pair of web portions (12); said line of membrane units (10) being folded back and forth upon itself at respective folds so as to provide a stack of said membrane units (10); a second web-like spacer sheet (34) being positioned between each said fold in said stack whereby said spacer sheets are sandwiched between the outer sides of the membrane units (10); the mutually adjoined outer surfaces of the membrane units are joined together at regions (30) in a fluid tight manner, said regions are lying on a second line (36), which extends through the membrane units in the stack, a bore forming a passageway (32) extending through said regions (30) of the membrane units (10) along said second line and serially connecting said closed cavities (28), whereby said first and second spacers (18,34) form mutually alternating spacers in said stack for respectively receiving unpurified and purified portions of a fluid to be purified in a purifier using said membrane module. The fluid purifier membrane module of claim 9, wherein said line of membrane units (10) are folded back and forth zigzag fashion, and outer faces of facially adjoining increments of said flexible web portions of said membrane material are joined together, thereby uniting said stack.

Inventors: HAGQVIST PETER, HAGQVIST, PETER
Applicants: ELECTROLUX AB, AKTIEBOLAGET ELECTROLUX
Application year: 1993
Main classification: B01D63
IPC codes: B01D63