WO1999059706A1

WO1999059706A1 - An apparatus and a process for production of hollow fibre sections for hollow fibre modules

Info

Publication number: WO1999059706A1
Application number: PCT/DK1998/000192
Authority: WO
Inventors: Svend Andreas Geleff; Knud Søndertoft PEDERSEN
Original assignee: Hofimo Aps
Priority date: 1998-05-15
Filing date: 1998-05-15
Publication date: 1999-11-25
Also published as: AU7424898A

Abstract

The invention relates to an apparatus and a process for production of hollow fibre sections for hollow fibre modules. The apparatus comprises a casting matrix having an essentially horizontal perforated plate (1) in which a number of fibre-conveying perforations (2) are arranged in a predetermined pattern and a shoulder is provided around the fibre-conveying perforations, characterized in that the perforated plate comprises a number of slats (3) having essentially vertical grooves (4) to receive the hollow fibres and arranged in one or both sides, and wherein one or more resilient elements (5) are provided between neighbouring slats.

Description

AN APPARATUS AND A PROCESS FOR PRODUCTION OF HOLLOW FIBRE SECTIONS FOR HOLLOW FIBRE MODULES

FIELD OF THE INVENTION The present invention relates to an apparatus for production of hollow fibre sections for hollow fibre modules, and a process for production of hollow fibre sections for hollow fibre modules.

PRIOR ART

Hollow fibre modules are used in connection with exchange operations, separation operations and mixing operations within many industrial fields of activity. In heat exchange, heat is exchanged between two fluids of different temperature, whereby the temperature of the fluid having the lower temperature increases. By mass exchange, components are exchanged over a membrane. Mass exchange operations are e.g. dialysis (for instance an artificial kidney), direct osmosis, gas- gas-exchange and gas-fluid exchange (e.g. an oxygenator) . Examples of separation operations could be ultrafiltration, microfiltration, nanofiltration, reverse osmosis and gas permeation. By a mixing operation is e.g. meant humidifica ion or conditioning of air by providing aqueous vapour thereto.

In the present description and claims, the term "hollow fibre section" means the part of a hollow fibre module which comprises the hollow fibres, said hollow fibres being terminally provided with a plug-like means.

By the term "fluid" is in the present description and claims meant any gaseous or liquid material with flow properties sufficient for allowing passage through a hollow fibre module. By "liquid material" is meant both solutions and suspensions of solid. In the prior art, several processes for the manufacture of hollow fibre sections for hollow fibre modules are described, cf . e.g. GB-A-2 091 125, Japanese publication no 62-160,108, Swedish published specification no 397,638, US patents nos 3,697,635 and 4,769,146. Most of the processes disclosed in the prior art permit, however, no mass manufacturing of hollow fibre section in a simple manner, i.e. enabling automatization and with as few process steps as possible where each individual step can be carried out in a simple manner.

However, WO 95/33548 discloses a process for production of a hollow fibre module where the process in a simple manner can be automatized, such that the production of hollow fibre sections can be effected in one process step by an in-line method. This known process implies the provision of a casting matrix comprising a horizontal perforated plate in which a number of perforations are arranged in a predetermined pattern, continuous hollow fibres are conveyed through these perforations and a shoulder is provided around the perforations, a) a hardenable casting material is cast to form a cast plate, b) the cast plate with the embedded continuous hollow fibres is raised in a vertical direction to a desired distance from the perforated plate, c) the cast plate is cut in the horizontal plane to expose hollow fibre ends, d) steps a, b and c are repeated to form a hollow fibre section.

The use of this known process causes problems when dimensioning the perforations in the perforated plate through which the continuous fibres are conveyed. This is due to the mutually conflicting technical demands prevailing. On one hand, the perforations must have such a sufficiently large cross-sectional area that when raising the cast plate in step b) , the friction is under such a level which will deform or tear the hollow fibres. A cross-section of the perforation larger than that of the fibre is generally necessary because static electricity is created by conveying the hollow fibres in the perforations. On the other hand, the cross- sectional area of the perforations in relation to the cross-sectional area of the hollow fibres must be sufficiently small to prevent that the liquid casting mass under step a) flows, to any considerable extent, down in the cavity between the perforations and the hollow fibres. The object of the present invention is thus to overcome the above-stated drawbacks of the prior art according to WO 95/33548.

SUMMARY OF THE INVENTION The present invention relates to an apparatus for production of hollow fibre sections for hollow fibre modules, comprising a casting matrix having an essentially horizontal perforated plate in which a number of fibre-conveying perforations are arranged in a prede- termined pattern and a shoulder is provided around the fibre-conveying perforations, characterized in that the perforated plate comprises a number of slats having essentially vertical grooves to receive hollow fibres and arranged in one or both sides, and wherein one or more resilient elements are provided between neighbouring slats.

The apparatus according to the invention has two extreme positions. The first extreme position is obtained as a result of loading the slats with a hori- zontal force perpendicular to the longitudinal direc- tion of the slats, whereby the resilient elements are pressed together such that the cross-sectional area of the fibre-conveying perforations which are at least partially limited by at least one groove is reduced. The second extreme position is reached as a result of a relief of the horizontal force perpendicular to the slats whereby the cross-sectional area is increased. The apparatus according to the invention can be operated at the two extreme positions and any position between them. The apparatus according to the invention can alternatively be designed in the way that the cross-sectional area is reduced when the applied force is relieved and that correspondingly, the cross-sectional area is increased when loaded with an applied force.

The cross-sectional area of the fibre-conveying perforations in the first extreme position is generally of such a size that a liquid casting mass cannot flow down in the interspace between the fibre-conveying perforations and the fibres. The cross-sectional area of the fibre-conveying perforations in the second extreme position is preferably of such a size that the fibres without any considerable friction can be passed through the fibre-conveying perforations. The slats are preferably designed in the way that on the top side in areas where there are no grooves, the edges adjoin each other in the first extreme position. Thus is obtained that during the cast of the cast plate, a coherent perforated plate is obtained such that the liquid casting mass does not flow down in the interspaces between the slats.

The slats are on one or both sides provided with vertical grooves through which the continuous hollow fibres are conveyed. The grooves in two neighbouring slats are preferably formed such that two grooves together define one fibre-conveying perforation. It is thus possible to design the grooves such that they correspond to one half of the shape of the hollow fibres. In case the fibres have an essentially circular cross-section, the grooves can thus be provided with semi-circular cross-section. When designing the fibre- conveying perforations so that they correspond to the shape of the fibres, it is possible to obtain a sealed fixing of the fibres during the cast in order to assure a predetermined position of the individual fibres in the cast plate and to prevent the liquid casting mass from flowing down.

The slats are kept together preferably by means of one or more guides to assure a correct position of the grooves so that they adjoin to form a fibre-conveying perforation. In the slats, one ore more guide holes are provided to receive guides. In particular, at least two guide holes are preferably arranged to receive guides to assure a uniform common movement of the slats during load and relief.

The slats can be manufactured from a material chosen at random. E.g. the slats can be manufactured from plastic, such as polyethylene, or a metal, such as iron or aluminium or alloys containing iron or alumin- ium. Metal is preferably used, especially aluminium in the cases where the hardening of the cast plate is most appropriately effected at a given temperature because of the good heat-conducting properties. If desired, at least on the topside facing the casting matrix, the slats can be covered with means to which the casting mass has only a minor tendency to bind. The slats can e.g. be covered with a layer of polytetrafluoroethylene

(PTFE) or a similar material. In the slats, cooling or heating elements can be provided in order to obtain an appropriate temperature during the solidification or hardening of the cast plate. As a heating element, e.g an electrically heated heating element can be used.

The grooves in the slats can, if desired, be coated or covered with a suitable material, e.g. a material with the ability to impede or prevent the formation of static electricity, a wear-resistant material or a material which reduces the friction.

The resilient element can comprise an arbitrary appropriate resilient material. The resilient element can e.g. be a metal spring or it can be manufactured completely or partially from an elastic rubber material. It is generally preferred to use such a resilient element which completely or partially consists of an elastic rubber material. The resilient element is in particular preferred to be an O-ring.

According to the invention, one or more resilient elements are provided between neighbouring slats. The resilient element or elements can be arranged on arbitrary places, e.g. in the intermediate area between two grooves or around the guide. The resilient element is preferably arranged around the guide.

The guide hole is preferably provided with a recess to receive the resilient element, especially an O-ring. The O-ring is appropriately of such a size that it fits tightly to the guide to assure the position of the O-ring.

When using a large number of slats to form the perforated plate, the slats are advantageously divided in sections. When diving in two or more sections, the strain on the outer fibres is less by the movement of the slats, so that a damage of the fibres is avoided.

The fibre-conveying perforations in the perforated plate are arranged in a predetermined pattern depending on the intended use and design of the finished hollow fibre module. The fibre-conveying perforations are preferably provided in such a pattern that these fibre- conveying perforations are spaced essentially evenly relative to the nearest neighbouring fibre-conveying perforations. The distance between the fibre-conveying perforations can, measured from periphery to periphery, be from 0.1 to 100 times the radius of the fibre- conveying perforations, preferably ^-2 times the radius of the fibre-conveying perforations.

Besides the perforated plate, the casting matrix comprises a shoulder arranged around the fibre-conveying perforations. The shoulder is meant to prevent the liquid casting mass from flowing out of the matrix. The height of the shoulder is thus at least as large as the thickness of the cast plate formed. The geometrical form of the final cast plate is thus defined by the casting matrix comprising the perforated plate and the shoulder. The geometrical form shaped by the casting matrix can be any form suitable for the intended use of the hollow fibre section. The form can thus e.g. describe a circle, an oval, a polygon or any other appropriate geometrical form.

The hardenable casting mass used can be supplied to the casting matrix in any appropriate way. The liquid casting mass is preferably supplied to the casting matrix through inlets in one or more of the slats or through inlets in the shoulder. To facilitate the removal of the completely or partially hardened casting mass from the casting matrix, the casting matrix can, if desired, be covered with a release agent. The release agent can e.g. be supplied to the casting matrix through inlets in the shoulder or inlets in one or more of the slats.

The invention relates furthermore to a process for production of hollow fibre section for hollow fibre modules, characterized by (1) providing a casting matrix comprising an essentially horizontal perforated plate in which a number of fibre-conveying perforations are arranged in a predetermined pattern and a shoulder around the fibre- conveying perforations, which perforated plate comprises a number of slats with essentially vertical grooves arranged in one or both sides in which endless fibres are provided in the grooves, one or more resilient elements being provided between neighbouring slats,

(2) loading the slats with an essentially horizontal force essentially perpendicular to the longitudinal direction of the slats so that the resilient elements are pressed together and the cross-sectional area of the fibre-conveying perforations are reduced,

(3) casting a casting mass with the ability to solidify or harden in the casting matrix to form a solid cast plate,

(4) relieving the horizontal force which affects the resilient element to increase the cross-sectional area of the fibre-conveying perforations,

(5) raising the cast plate with the embedded continuous hollow fibres in a vertical direction to a desired distance from the perforated plate, (6) cutting the cast plate in the horizontal plane to expose hollow fibre ends,

(7) repeating step (2) to step (6) for the formation of a hollow fibre section, whereby step 2) and step 6) , if desired, can be effected simultaneously or in reverse order.

Through each fibre-conveying perforation, a small number of hollow fibres are preferably provided, e.g. less than 10 hollow fibres per perforation. It is especially preferred that only one hollow fibre is present in each fibre-conveying perforation. The hollow fibres may be of any material and have any form suitable for the intended object of the final hollow fibre module. For heat exchange in heat exchangers, the material can e.g. be metal, glass or another material with good heat-conducting properties. For dialysis, ultrafiltration, reverse osmosis and gas separation, the fibres may completely or partially consist of polymeric materials (e.g. cellulose acetate, polysulphone, polyamide, etc.) and/or ceramic mate- rials. The materials used for the hollow fibres may have a porous or non-porous structure, a prerequisite for mass exchange being, however, that the material used has a porous structure.

The casting mass used may be of any suitable type having the ability to solidify. The casting material may e.g. be melted metal, a material containing cement or a curable polymeric material . The curable polymeric material can e.g. be an epoxy resin.

It is of importance not to damage the fibres essentially during the embedment thereof in the cast plate, for which reason care should be taken to prevent the casting mass used from destroying the fibres essentially during processing, e.g. by melting or dissolution thereof. In cases where heat is developed or removed during the hardening or solidification of the cast plate, this heat can be drained by passing a cooler fluid, such as air, through the fibres. By an appropriate choice of the flow velocity in the hollow fibres, an approximate- ly constant temperature of the casting mass can thus be obtained during hardening or solidification.

After casting and complete or partial solidification or hardening of the cast plate, the cast plate is loosened from the casting matrix and subsequently raised. The completely or partially hardened cast plate is appropriately loosened from the casting matrix by both relieving the applied force and raising the cast plate simultaneously or in smaller phases and relatively slowly. If the applied force is released to soon and too strongly, it may entail such a large movement of the slats that the embedded fibres are damaged. It may further be advantageous to start the raising of the cast plate while this still has a certain suppleness. The solid cast plate formed is cut horizontally, usually in such a way that the thickness of the cast plate is halved. This cutting may be performed in any suitable way, e.g. by means of a saw or a hot wire, or the cast plate may be cleft with an axe-like tool. It is important to cut the cast plate such that essential- ly all hollow fibre ends are exposed to allow a fluid to pass freely and unimpededly through the fibres.

When the hollow fibres are of a resilient material, it may be advantageous to provide the hollow fibre section with supporting means during the produc- tion process to increase the mechanical strength of the hollow fibre section. Such supporting means may e.g. be in the form of a through-going rigid rod connected with the cast plates .

In the production of the hollow fibre section according to the invention, it is intended to keep the fibres straight during the casting process, such that each fibre has essentially the same length, whereby intimate physical contact between the fibres is avoided. This is an advantage, as in areas where the fibres are in physical contact, there will be no noticeable mass or heat transport between the fluid flowing around the fibres and the fluid flowing within the fibres. It is an object to prevent the fibres in the hollow fibre section essentially from mutual physical contact, in such a way that by use of the final module containing the hollow fibre section, an essentially unimpeded flow in a predetermined direction relative to the fibres is attained. The unimpeded flow is an important factor in order to obtain an optimum exploitation of the membrane area available.

By the process according to the invention, a hollow fibre section can be obtained where the distance between a given fibre and the nearest neighbouring fibres is essentially constant. An essentially uniform flow pattern is thus obtained for the fluid flowing around the fibres and consequently a uniform treatment hereof .

The hollow fibre section obtained by the process according to the invention can be further processed to a finished hollow fibre module. By this further processing, the hollow fibre section is provided with a mantle fitting tightly to the periphery of the cut cast plates, said mantle being provided with pipe stubs for inlet and outlet of fluid. The ends are provided with end pieces having a stub for inlet and outlet, respectively, of fluid to the hollow fibres. In order to fasten the ends of the mantle to the cut cast plates, any technique known to the person skilled in the art can be used. E.g. the mantle and the cut cast plates can be soldered, welded or glued together.

If desired, the mantle may be fastened to the cut cast plates as a part of a continuous in-line process. After the cutting of the cast plate, the hollow fibre section can be introduced into a cylinder with a clear corresponding to the cast plate and a length at least corresponding to that of the hollow fibre section following which the cast plates may be fastened to the ends of the cylinder. BRIEF DESCRIPTION OF THE DRAWING

In the following the invention will be explained in detail with reference to the drawing, in which

Fig. 1 shows the perforated plate seen from above, Fig. 2 shows the perforated plate seen obliquely from above,

Fig. 3 shows three slats seen from above,

Fig. 4 shows a slat cut at the line IV,

Fig. 5 shows a cross-section of a portion of the perforated plate in a relieved condition,

Fig. 6 shows a cross-section of a portion of the perforated in a loaded condition.

Figs. 1 and 2 show an apparatus comprising a perforated plate 1 in which a number of vertical fibre-conveying perforations 2 are provided in a pattern. A number of slats 3 are provided in such a way that two grooves 4 in neighbouring slats form a fibre-conveying perforation. A shoulder (not shown) is arranged around the fibre-conveying perforations to form a casting matrix. The slats are situated on two guides 7. In the perforated plate, holes 9 are arranged for fastening in a fixture. During operation of the apparatus, an essentially horizontal force affects essentially perpendicular to the longitudinal direction of the slats.

Fig. 3 shows three slats arranged next to each other. The slats are provided with vertical grooves 4 with a semi-circular cross-section. Two grooves in neighbouring slats form a fibre-conveying perforation. The slats are provided with guide holes 8 to receive a guide 7 (not shown) . Around the guide hole, a recess 9 is arranged to receive an O-ring 5 of rubber. From Fig. 4 it appears that a recess is provided on each side of the debouchment of the guide hole. Figs. 5 and 6 show a cross-section of a portion of the perforated plate broken at the line IV in Fig. 3. Fig. 5 shows the apparatus in a relieved condition, and Fig. 6 shows the apparatus in a loaded condition. The slats 3 are arranged next to each other and the guide 7 is arranged in the guide holes 8. In the recesses 9, O-rings 5 are received. In a relieved condition, an interspace is provided between the edges 6 on the top side of the slats, whereas the edges in a loaded condition adjoin each other.

When loading the apparatus with a horizontal force perpendicular to the longitudinal direction of the slats, the O-rings 5 are pressed together. When this force is subsequently relieved, the resilient effect of the O-rings entails that the slats move from each other. In a corresponding way, the cross-sectional area of the fibre-conveying perforations will be smaller when the apparatus is influenced by a horizontal force perpendicular to the longitudinal direction of the slats. When relieving the force, the cross-sectional areal is increased.

Claims

C L A I M S

1. An apparatus for production of hollow fibre sections for hollow fibre modules, comprising a casting matrix having an essentially horizontal perforated plate (1) in which a number of fibre-conveying perforations (2) are arranged in a predetermined pattern and a shoulder is provided around the fibre-conveying perforations, c h a r a c t e r i z e d in that the perforated plate comprises a number of slats (3) having essentially vertical grooves (4) to receive the hollow fibres and arranged in one or both sides, and wherein one or more resilient elements (5) are provided between neighbouring slats.

2. An apparatus according to claim 1, c h a r a c- t e r i z e d in that the edges (6) on the top side of the slats adjoin each other in an extreme position.

3. An apparatus according to claim 1, c h a r a ct e r i z e d in that grooves in neighbouring slats define the fibre-conveying perforations.

4. An apparatus according to any of the claims 1- 3, c h a r a c t e r i z e d in that the slats are kept together by one or more guides (7) .

5. An apparatus according to claim 4, c h a r a ct e r i z e d in that the slats are provided with one or more guide holes (8) to receive guides.

6. An apparatus according to claim 5, c h a r a ct e r i z e d in that the guide holes are provided with a recess (9) to receive the resilient element.

7. An apparatus according to any of the preceding claims, c h a r a c t e r i z e d in that the resilient element completely or partially consists of rubber .

8. A process for production of hollow fibre sections for hollow fibre modules, c h a r a c t e r - i z e d by (1) providing a casting matrix comprising an essentially horizontal perforated plate in which a number of fibre-conveying perforations are arranged in a predetermined pattern and a shoulder around the fibre- conveying perforations, which perforated plate comprises a number of slats with essentially vertical grooves arranged in one or both sides in which endless fibres are provided in the grooves, one or more resilient elements being provided between neighbouring slats,

(3) casting a casting mass having the ability to solidify or harden in the casting matrix to form a solid cast plate,

(4) relieving the horizontal force which affects the resilient element, to increase the cross-sectional area of the fibre-conveying perforations,

9. A process according to claim 8, c h a r a ct e r i z e d in that during the solidification or hardening in step (3) a fluid with a cooler temperature than the casting mass is passed through the fibres.