The present invention relates to a porous metallic membrane bundle for use in a filter module, and to a method of manufacturing the same. In particular, the invention provides a means of fitting small diameter tubular membranes into filter modules, and an effective alternative to welding of larger diameter membranes to module face plates.

BACKGROUND OF THE INVENTION

Porous filter membranes are used in numerous industries to separate particulates from fluid and gas. The membranes can be constructed from various materials including metal, plastic and ceramics. Stainless steel membrane technology was first developed more than twenty years ago, however, has not been widely implemented compared to other cross flow membranes, and is only typically used when other membranes fail.

The main reason for the slow market up take has been cost, when compared to say polysulfone or polyvinyl which sells for around 6% / m 2 and ceramic for around 25% / m 2 of the cost of metallic membrane. This is partly due to the raw material cost, however, the most expensive component is by far the high labour content.

A typical metallic membrane is manufactured by the known art of Isostatic Pressing. The green membrane produced is subsequently sintered, welded into the required lengths, coated with the appropriate inner membrane, and then re-fired. This process requires time and manpower which contribute to the significant costs.

Lumen standard commercial metallic membranes are produced having diameters of around 17- 19mm, which contributes to their expense and foot print. Smaller diameter metallic membranes would reduce the cost and foot print, and also provide other benefits, but they have not been developed to date. This is because of the difficulty associated with terminating bundles of small diameter tubular membranes for placement inside filter modules.

Large diameter membranes (12mm to 20mm) are typically bundled and welded to a filter module face plate. However, some filter modules may require many thousand smaller diameter tubes to be bundled, and it would be virtually impossible to weld them individually to a face plate. There are also a number of problems associated with the welding of metallic membranes in general, including but not limited to the following:

• When metallic membranes are welded together, a heat zone is produced adjacent to the weld. Because this area has been damaged due to heat and oxidation, it becomes more prone to corrosion; and

• Due to the high welding temperatures used (up to 2200°C), the fine inner coat that is the active membrane is damaged, causing a change in the micron size and porosity of the membranes. This then makes it impossible to classify the membrane as being "absolute", instead it can only be described as being "nominal". It is therefore an object of the present invention to overcome at least some of the aforementioned problems or provide the public with a useful alternative.

SUMMARY OF THE INVENTION

Therefore in one form of the invention there is proposed a metallic membrane bundle for use in a filter module, said metallic membrane bundle characterised by:

a plurality of tightly packed, tubular metallic membranes; and

end stop members adapted to hold said membranes in a tightly packed state inside said module.

Preferably said end stop members are formed by a potting compound moulded around ends of the tightly packed membranes.

In preference said potting compound is resin-based, thermoplastic, thermosetting, polyurethane, epoxy or any combination of cross -linking.

In preference said filter module includes a hollow casing.

Preferably an outer surface of each end stop member is shaped correspondingly with an inner surface of said filter module casing to enable a snug fit between the stop members and said inner surface. In preference the bundle further includes a means of allowing for expansion and contraction between said bundle and casing. Preferably each of said end stop members includes at least one O-ring groove for accommodating an O-ring, said O-ring adapted to form a seal between the end stop member and the filter module and constituting said means for allowing for expansion and contraction between said bundle and casing. In preference each metallic membrane includes a diameter of between 1 and 5mm.

Preferably each metallic membrane includes a diameter of between 3 and 20mm.

In preference each metallic membrane includes a diameter of more than 20mm.

In a further form of the invention there is proposed a filter module including at least one metallic membrane bundle as characterised in any one of the preceding claims. In a still further form of the invention there is proposed a method of producing a filter membrane bundle for use in a filter module, said method comprising the steps of:

(a) tightly packing a plurality of metallic membranes;

(b) selecting a suitable potting compound depending upon the filter module application;

(c) fitting a mould to one end of the tightly packed membranes; (d) filling the mould with the selected potting compound;

(e) repeating steps (c) and (d) on the opposite end of the bundle;

(f) curing the potting compound; and

(g) removing the moulds.

In a yet further form of the invention there is proposed a method of producing a filter membrane bundle for use in a filter module, said method comprising the steps of:

(a) tightly packing a plurality of metallic membranes;

(b) selecting a suitable potting compound depending upon the filter module application;

(c) fitting a mould to each end of the tightly packed membranes; (d) filling the moulds with the selected potting compound to thereby maintain the metallic membranes in said tightly packed state;

(e) curing the potting compound; and

(f) removing the moulds.

Preferably said filter module includes a substantially cylindrical casing into which said filter bundle is adapted to be fitted.

In preference said moulds are shaped to form said potting compound into a shape which allows for the moulded ends to fit snugly inside the filter module casing.

In preference the moulds are also shaped to form at least one O-ring groove on an outer surface of said potting compound, each groove adapted to accommodate an O-ring forming a seal between the bundle and the casing.

Preferably the potting compound selected is dependent upon the filter application. In preference, the compound is resin-based, thermoplastic, thermosetting, polyeurethane, epoxy or any combination of cross linking, and the type chosen is dependant upon whether the application requires high temperature, low temperature, food grade, oil resistant or chemical resistant compounds).

In a further form of the invention there is proposed a filter membrane bundle manufactured in accordance with the method defined above.

Ina yet further form of the invention there is proposed a filter membrane module including a casing inside which is housed a filter membrane bundle manufactured in accordance with the method defined above.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawings, which are incorporated in and constitute a part of this

specification, illustrate several implementations of the invention and, together with the description, serve to explain the advantages and principles of the invention. In the drawings:

Figure 1 illustrates a perspective view of a potted metallic membrane module in

accordance with the present invention; Figure 2 illustrates a perspective view of a plurality of tightly packed, small diameter metallic membranes;

Figure 3 illustrates a perspective and end view of a bundle of tightly packed metallic

membranes of Figure 2 after having been terminated at their ends using a potting compound;

Figure 4 illustrates an enlarged cross sectional view of one end of the bundle of Figure 3;

Figure 5 illustrates a perspective and view of a bundle of tightly packed metallic

membranes of Figure 2 after having been terminated at their ends using a potting compound in accordance with a second aspect of the invention; and

Figure 6 illustrates an enlarged cross sectional view of one end of the bundle of Figure 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description of the invention refers to the accompanying drawings.

Although the description includes exemplary embodiments, other embodiments are possible, and changes may be made to the embodiments described without departing from the spirit and scope of the invention. Wherever possible, the same reference numbers will be used throughout the embodiments and the following description to refer to the same and like parts.

The present invention relates to a filter module 10 which houses metallic membranes 12 having a lumen diameter from as low as 3mm (to 20mm or greater). The invention further relates to a method of terminating bundles 14 of such small diameter membranes 12 for use in filter modules

10.

In brief, small diameter metallic membranes are preferably constructed as follows:

(a) metal powders of various sieve sizes (depending on micron finish required) are mixed with various binders and are either heated or cooled depending on the binder selected;

(b) the mix is then extruded using specially designed die heads (single or multi head dies) of various diameters from 3mm to 20mm or greater; (c) as the membrane is extruded from the die head the material is cured using a heating or cooling source, again depending on the binder selected (typically either hot air, induction heating or a cooling media);

(d) the membranes are cut to length and by the known art of sintering are sintered; (e) an inner coating is applied to the membranes either in a high vacuum furnace or a low hydrogen continuous furnace; and

(f) the membranes are re-sintered.

Turning now to Figure 1, there is shown a filter module 10 including a bundle 14 of small diameter metallic membranes 12 encased inside the module 10 in accordance with the present invention.

It is to be understood that the filter module 10 is depicted like so to assist the reader in understanding the present invention, and that such filter modules may well include additional features and appear quite different in reality. The important feature of the module 10 is that it includes a hollow body or casing 16 which houses the aforementioned bundle 14 of metallic membranes as will be described in more detail below. The filter 10 need not be cylindrical, but could be any other cross sectional shape.

Figure 2 illustrates a bundle 14 prior to being inserted into the module 10, and it can be seen that it is made up of a plurality of tightly packed, tubular metallic membranes 12. Figures 3-4 show how the bundle 14 is held in position at ends thereof by stop members 18. It is envisaged that larger diameter modules could hold up to thousands of these tightly packed, small diameter membranes 12.

The stop members 18 are an important feature of the invention because they provide a unique alternative to welding the ends of each membrane to a module end plate (not shown), a method which is not possible for smaller diameter metallic membranes. Each bundle 14 is formed by the following steps:

(a) tightly packing a plurality of metallic membranes into a similar configuration to that shown in the embodiment of Figure 2; (b) selecting a suitable potting compound depending upon the filter application (potting compounds tend to be resin-based, thermoplastic, thermosetting, polyeurethane, epoxy or any combination of cross linking, and are available in different types depending on whether the application requires high temperature, low temperature, food grade, oil resistant or chemical resistant compounds);

(c) fitting a mould (not shown) to one end of the tightly packed membranes, and filling the mould with the selected potting compound;

(d) repeating step (b) on the opposite end of the bundle (alternatively, this end could be terminated simultaneously); and (e) curing the potting compound, and removing the moulds.

To create each stop member 18 shown in Figures 3-4, the mould used (not shown) is of a cylindrical construction having an internal diameter slightly smaller than the internal diameter of filter module hollow body 16. This ensures that once the bundle is constructed, it can be inserted into the module such the stop members 18 fit snugly inside the hollow body 16. Some filters may require a water-tight seal between each of the stop members 18 and the inside surface of the filter module hollow body 16. Figures 5-6 illustrate a bundle 20 of metallic membranes 12 including stop members 22 according to a second embodiment of the invention. Each stop member 22 includes a pair of O-ring grooves 24 for accommodating O-rings (not shown) in a configuration which provides a seal between the compound and the filter module. A person skilled in the art would realize that to create the O-ring grooves 24, the potting compound mould (not shown) includes a pair of annular shoulders (not shown) on its inside surface suitably shaped to form the grooves 24 when the mould is filled.

This O-ring configuration also assists in allowing for expansion and contraction between the membrane bundle 20 and the outer casing 16. It is to be understood that other methods could be used to seal the compound to the casing, provided it too allows for expansion and contraction.

The final step in assembling the filter membrane modules 10 is by fitting the bundle of lumen 14/20 into the outer casing 16. The present invention thus enables the use of small diameter membranes of 3mm or greater diameter in filter modules, which in the past could not be used. There are a number of benefits in using such metallic membranes, including:

• increased surface area in the same size module (up to 10 times the surface area);

• increased shear providing better self cleaning of the membrane;

• smaller circulation pumps required to move liquid through the filter and hence less power consumption;

• smaller hold-up volume, reducing waste;

• reduced manufacturing costs;

• reduced land fill due to long life expectancy of membrane, which is in excess of 10 years.

Further advantages and improvements may very well be made to the present invention without deviating from its scope. Although the invention has been shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope and spirit of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus.

In any claims that follow and in the summary of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprising" is used in the sense of "including", i.e. the features specified may be associated with further features in various embodiments of the invention.