Tubular membrane module

Abstract: A tubular membrane module for use in ultrafiltra­ tion or microfiltration has a bundle of membrane tubes that extend between inlet and return headers. The inlet header is fixed to one end of a tubular housing having a permeate outlet while the return header is free to float longitudi­ nally of the housing to accomodate dimensional changes in the tubes with respect to the housing. The tubes are sealed at their ends in sockets in respective potting collars but are mechanically secured and sealed to the headers. The sockets are undercut to protect the membranes from stripping due to fluid shear.

Description: This invention relates to so-called tubular membrane modules used in pressure-driven fluid concentration and/or separation processes. Examples of such processes are microfiltration, ultrafiltration and reverse osmosis. The term "tubular membrane module" is used to refer to a component which includes a series of permeable membranes of tubular configuration each supported on the inner surface of a porous pipe such as a glass fibre-reinforced fabric pipe. The pipes are enclosed within an outer housing having a permeate outlet. Fluid to be treated is passed through the pipes under pressure. Permeate passes through the membranes and pipes into the interior of the outer housing and leaves through the permeate outlet. US-A-4,707,261 (Ikeyama et al.) discloses a tubular membrane ultrafiltration module in which a plurality of water permeable non-woven fabric pipes are formed on the inside surface of an outer cylinder. The pipes are inserted into the outer cylinder in a closely bundled state and the spaces between the pipes and the outer cylinder at each end are filled with hardened synthetic resin to fix and seal the assembly. In other words, the ultrafiltration module provided by the Ikeyama invention essentially comprises a monolithic structure of non-woven fabric pipes set in an outer cylinder by means of a hardened synthetic resin. The invention relates to a tubular membrane module of a type known generally from EP-A-0 217 568, comprising a housing which includes a tubular shell having a closed first end and a permeate outlet, an inlet header sealed to the shell at a second end thereof, a second header disposed within the shell remote from the inlet header, and a plurality of membrane tubes extending between and sealed to the headers. Each tube comprises a porous pipe and a permeable membrane on the inner surface of the pipe. The inlet header has inlet and outlet ports, the return header having a return fluid passageway configured to permit fluid to flow through said membrane tubes in series from the inlet port to the outlet port. According to the invention, the ends of the membrane tubes are connected to respective tube potting collars having sockets in which the ends of the tubes are sealed. The thus-assembled membrane tubes and potting collars form a sub-assembly of the module which is connected in the module by attachment of the potting collars to the respective header. In this way, the second header can be made as a floating return header which fits closely within the shell but is free to move longitudinally with respect to the shell when the module is in use. This module offers a number of practical advantages in terms of economy of construction, in particular as regards pre-assembling of the tubes and potting collars, and fitting of these sub-assemblies in the module. At the same time, the use of a free-floating return header assembly minimizes stresses on the membrane tubes in service that would otherwise be caused by changes in the length of the tubes due to factors such as temperature variations if a fixed header were employed. In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which illustrate a particular preferred embodiment of the invention by way of example, and in which: Fig. 1 is a perspective view, partly exploded and partly broken away, of a tubular membrane module in accordance with a preferred embodiment of the invention; Fig. 2 is a vertical sectional view through the module of Fig. 1 as seen in the direction of arrow A; Fig. 3 and 4 are elevational views of the inner faces of the respective inlet and return headers of the module; Fig. 5 is a diagrammatic illustration showing the passageways in the inlet header superimposed on those of the return header; Fig. 6 is an elevational view of one of the tube potting collars used in the module; Fig. 7 is a sectional view on line 7-7 of Fig. 6; Fig. 7a is a detail view of the part of Fig. 7 circled at B; and, Fig. 8 is a view similar to Fig. 1 showing a module of extended length. The drawings show a tubular membrane module that was developed particularly for use in microfiltration and ultrafiltration. Referring first to Fig. 1, the principal components of the module are a housing generally indicated by reference numeral 20 and a series or "bundle" of spaced-apart membrane tubes 22 which extend between respective inlet and return headers 24 and 26 in the assembled module. Inlet and return pipes for fluid to be treated are indicated respectively at 28 and 30 in Fig. 1. Fig. 2 shows the assembled module. Housing 20 includes a plain tubular shell 32 which is closed at one end by an end cap 34 and at the other by the inlet header 24. In this particular embodiment, the shell 32 is a length of standard circular section PVC pipe. The end cap 34 is made of the same material and is permanently secured to shell 32 by a suitable solvent cement. Permeate outlets from housing 20 is provided by threaded ports 36 in shell 32. Inlet header 24 has the overall shape of a circular disc (see Fig. 3) of the same diameter as shell 32 and is secured across the end of the shell opposite end cap 34 (Fig. 2). The inlet header is mechanically attached and sealed to shell 32 by a VICTAULIC (TM) clamp generally denoted by reference numeral 38. Clamp 38 includes an annular seal member 40 which encircles the joint line between shell 32 and inlet header 24, and an outer bracket indicated at 42 which embraces the seal member 40 and which has inwardly directed flanges that engage in respective grooves 44 and 46 in header 24 and shell 32. As can be seen from Fig. 1, bracket 42 is in fact made up of two C-shaped members 42a and 42b which are bolted together. Return header 26 also has the overall shape of a circular disc but is of somewhat less diameter than the inlet header 24. Return header is sized to fit closely within the shell 32 of module housing 20 but is free to float longitudinally of the module, as indicated by the arrow 48 in Fig. 2. The two headers 24, 26 are both moulded in a PVC material and are shaped to provide on their respective inner surfaces return fluid passageways configured to permit fluid to flow through the membrane tubes 22 in series. Referring more specifically to Figs. 3 and 4, the inner surface of inlet header 24 is shown in Fig. 3 and is denoted by reference numeral 24a while the inner surface of return header 26 is shown in Fig. 4 and is denoted 26a. Inlet header 24 has respective inlet and outlet ports 50 and 52 which communicate with the inlet and outlet pipes 28 and 30 respectively shown in Fig. 1 when the module is in use. The return fluid passageways are individually denoted by reference numeral 54 and it will be seen that three such passageways are provided in the case of inlet header 24. Return header 26 has no ports but has four return fluid passageways individually denoted at 56. Fig. 5 is an artificial view in the direction of arrow C in Fig. 2 and shows in full lines the ports 50, 52 (Fig. 3) and return passageways 54 of the inlet header 24 super-imposed on the passageways 56 of the return header 26 (which are shown in dotted lines). This view illustrates quite graphically how the ports and passageways cooperate to provide for series flow of fluid through the membrane tubes 22. It will of course be appreciated that Fig. 5 shows the ports and passageways of inlet header 24 in mirror image as compared with Fig. 3 because those ports and passageways are illustrated as they would be seen in the direction of arrow C (i.e. from the outer end of inlet header 24). It will also be appreciated that the particular configuration of ports and passageways shown in the drawings is designed to accomodate eight membrane tubes arranged with one tube at the centre and the remainder equiangularly spaced around the centre tube. The number of tubes and, consequently, the configuration and arrangement of return fluid passageways may of course vary. In another practical embodiment, a module having twenty tubes is provided. At opposite ends of the bundle of tubes potting collars are used to couple the tubes to the respective headers. The potting collars are identical and are individually denoted by reference numeral 58 in Fig. 2. One of those collars is shown separately in Figs. 6, 7 and 7a. Again, the component is a disc-shaped PVC moulding. As seen in Fig. 7, the potting collar has an inner face 60 at which the tubes are coupled to the collar, and an outer face 62 which bears against the inner face of the relevant header 24 or 26 in the assembled module. The inner face 60 of the collar is formed with a series of sockets 64 for receiving the membrane tubes. The sockets are of course arranged in a configuration corresponding to the configuration of the tubes in the bundle; that is, with a single centre tube and seven further tubes equiangularly spaced around the centre tube as shown in Fig. 6. Referring back to Fig. 7, each socket 64 has an annular blind end 66 for closely receiving an end portion of one of the tubes 22. A port 68 of smaller diameter than and located within the blind end portion 64 of the socket provides communication between the interior of the tube and the header in the assembled module. Fig. 7a shows an enlarged detail of part of the annular blind end of one of the sockets 66 and part of one of the tubes 22 in place in the socket. The tubes are sealed into the sockets by an appropriate epoxy resin. It will be seen from Fig. 7a that the blind end 66 of socket 64 in effect forms an undercut with respect to the port 68, leaving a shoulder 70 between the port and the tube. Shoulder 70 is radiussed at 70a to facilitate insertion of the tubes into the sockets. Shoulder 70 in effect protects the tube from the effects of fluid shear caused by fluid entering the tube 22 from the port 68 under pressure. The fluid shear effect could otherwise cause the membrane to be stripped from the inner surface of tube 22. In Fig. 7a, the membrane is denoted by reference numeral 72 and is illustrated as having an exaggerated thickness. The membrane is cast on to the inner surface of a glass fibre-reinforced fabric pipe 74 by a technique that is well-known in the art. The pipe itself has not been illustrated in detail since it too may be of conventional form. For example, the pipe may comprise several layers of spirally wound fabric tapes. These may be filament wound with glass fibres impregnated with a suitable thermosetting plastic resin, when extra strength is required. Referring back to Fig. 2, it will be appreciated that the use of the potting collars 58 allows the bundle of tubes and collars to be preformed as a sub-assembly to which the respective headers 24 and 26 are subsequently attached. In this particular embodiment, mechanical attachment is used. Specifically, a series of socket-headed cap screws which are individually denoted by reference numeral 76 in Fig. 2 are inserted through preformed holes in the respective headers and driven into the respective potting collars in the manner of self-tapping screws. Preformed holes in the two headers for receiving the screws are indicated at 78 in the case of inlet header 24 (Fig. 3) and at 80 in the case of return header 26 (Fig. 4). A neoprene gasket is used between each header and potting collar in the assembled module; the two gaskets are indicated at 82 in Fig. 2. Fig. 2 also shows tube support baffles or "spiders" 84 which may be used between the potting collars to help protect against sagging or deflection of the tubes due to the weight of fluid, internal pressure or temperature. These "spiders" are essentially thin PVC discs having an external diameter slightly less than the internal diameter of the housing shell 32, and each of which is formed with a series of holes for receiving membrane tubes. The holes are dimensioned so that the spiders can frictionally fit onto the tubes. In a very short module, the spiders may be unnecessary, while in longer modules two or even more spiders may be necessary. By way of example, the module 20 shown in the drawings may have an overall nominal length of approximately 2 metres. It will be appreciated that, since the tubes are not made of the same material as the shell, the overall length of the tubes may vary with respect to the shell in response to varying temperature conditions. The fact that the return header 26 is free to float longitudinally accomodates this variation without imposing stresses on the tubes in service. It will also be appreciated that the particular design of the module is economic in the sense that it permits the use of standard pipe sizes for the shell 32. Fig. 8 illustrates that it is possible to multiply the capacity of the module by simply using a longer tube for the shell 32 and bolting together end to end two or more sub-assemblies each comprising a series of tubes and a pair of potting collars. Primed reference numerals have been used in Fig. 8 to denote parts that correspond with parts shown in the previous views. Thus, it will be seen that two potting collars 58' of a pair of tube bundle sub-assemblies are bolted together face to face with respective inlet and return headers 24' and 26' at opposite ends of the assembly. The potting collars are preformed with holes for receiving such bolts, as indicated at 84 in Figs. 6 and 7. It will be understood from Fig. 8 that the facility for the return header 26' to float longitudinally of the shell 32' is particularly important in an extended module of this form.

Claims: A tubular membrane module comprising a housing (20) which includes a tubular shell (32) having a closed first end and a permeate outlet (36), an inlet header (24) sealed to said shell (20) at a second end thereof, a second return header (26) disposed within said shell (20) remote from said inlet header (24), and a plurality of membrane tubes (22) extending between and sealed to said headers (24,26), each tube (22) comprising a porous pipe (74) and a permeable membrane (72) on the inner surface of said pipe, said inlet header (24) having inlet and outlet ports (50,52), and at least said return header (26) having a return fluid passageway (56) configured to permit fluid to flow through said membrane tubes (22) in series from said inlet port (50) to said outlet port (52), characterised in that : the ends of the membrane tubes (22) are connected to respective tube potting collars (58) having sockets (64) in which the ends of the tubes are sealed, said membrane tubes (22) and potting collars (58) forming a sub-assembly of the module which is connected in the module by attachment of the potting collars (58) to the respective header (24,26); and said second header (26) is a floating return header which is sized to fit closely within said shell (20) but is free to move longitudinally with respect to the shell when the module is in use. A module as claimed in claim 1, wherein each potting collar (58) is mechanically coupled in pressure-tight fashion to an inner face (24a, 26a) of the respective header, and at least an inlet end portion of each membrane tube (22) is sealed in a socket (64) having an annular blind end (66) closely receiving said end portion of the respective tube (22), and a port (68) of smaller diameter than and within said blind end (66) providing communication between the interior of the tube (22) and the header (24,26), whereby the membrane (72) on the tube (22) is protected from fluid shear caused by fluid entering the tube from the header under pressure. A module as claimed in claim 1 or 2, wherein the module comprises a plurality of said sub-assemblies of membrane tubes and potting collars coupled together end-to-end between said inlet and return headers (24',26'), the tubes (22') in respective sub-assemblies being aligned with one another, and wherein said tubular shell (32') comprises a length of plastic tubing selected to accommodate said sub-assemblies. A module as claimed in claim 1, wherein said shell (32) comprises a length of standard plastic pipe, and wherein said inlet header (24) has the overall shape of a disc of substantially the same external diameter as the diameter of the shell and is coupled to the shell over said second end by an external clamp (38) which includes an annular seal (40) encircling the joint between the shell and the inlet header, and a bracket (42) enclosing said seal (40). A module as claimed in claim 1, wherein said shell (32) comprises a length of plastic tube, and wherein said inlet and return headers (24,26) each comprise a disc-shaped plastic moulding. A module as claimed in claim 1, further comprising at least one membrane tube support baffle (84) disposed in said shell (32) between the headers (24,26), the tubes (22) passing through the baffle (84) and the baffle (84) being dimensioned to fit closely within said shell.

Inventors: APOSTOLACHE RADU, KOEHLER PAUL B, LANGERAK ROBERT WILLIAM, TONELLI FERNANDO A, APOSTOLACHE, RADU, KOEHLER, PAUL B., LANGERAK, ROBERT WILLIAM, TONELLI, FERNANDO A.
Applicants: ZENON ENVIRONMENTAL INC, ZENON ENVIRONMENTAL INC.
Application year: 1989
Main classification: B01D63
IPC codes: B01D63