AU2012239391B2 - A support element for a filter and a filter unit including said support element - Google Patents

Description

AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention title: A support element for a filter and a filter unit including said support element The following statement is a full description of this invention, including the best method of performing it known to us: duwm A0121791416v11 120265033 1 A SUPPORT ELEMENT FOR A FILTER AND A FILTER UNIT INCLUDING SAID SUPPORT ELEMENT Field of the Invention [0001] The invention relates to a support element for a filter and a filter unit including said support element. In particular, the filter unit is for use in an industrial process. In one aspect, the invention relates to a support element for use with a pressure filter system used in the Bayer process for producing alumina from bauxite. Background of the Invention [00021 Any discussion of documents, acts, materials, devices, articles and the like in this specification is included solely for the purpose of providing a context for the present invention. It is not suggested or represented that any of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia or elsewhere before the priority date of each claim of this application. [0003] Pressure filters are used extensively in industrial processes for separating solids from liquids in mineral-bearing slurries. One such process applied on an industrial scale is the Bayer process used in producing alumina from bauxite, for eventual reduction to aluminium. A common pressure filter used in this process is the Kelly-type filter, described in US Patent No 869,372 to David J Kelly. This filter system provides a direct pressure filtration means of removal of insoluble bauxite residues - known as 'red mud' - from the alumina-bearing liquor. The Kelly system uses leaf-type filter units in a pressure vessel to remove the red mud particulate. [0004] A pressure filter unit generally consist of a frame holding one or more perforated panels. The filter frame supports a filter fabric (generally a cloth-like fabric) selected so that a filtrate-bearing suspension may be separated from a desired liquid (filtrate liquor) under pressure. The filter fabric is usually provided as a bag which envelops the frame and panels. The filter unit is installed within a pressure vessel in parallel with a plurality of other like filter units (either vertically or horizontally). In operation, slurry is pumped into the vessel under pressure so as to be pressed directly against the filter fabrics. The- filter frame and panels duwm A0121791416v1 1 120265033 2 therefore serve to support the filter fabric so as to resist the pressure of the applied slurry, thereby allowing the filtrate liquor to pass through the filter fabric. [0005] It is necessary to access or remove the filter units periodically to clean away the gradual build up of particulate residue from the filter fabric, eg. the red mud cake that builds up in the Bayer process. As this cake builds up on the fabric, the filtration rate decreases, at which the filter system must be drained and the filter elements washed, eg. by hosing down with caustic solution. These cleaning cycles are disruptive and costly to the overall operation. Although various solutions have been proposed in an attempt to improve the operational and/or technical performance of such pressure filter systems, many fail to offer sufficient improvement to warrant continued operational use in large scale industrial processes. In particular, it therefore important to maintain flow rates through the filter units at as high a level as possible when operating, to minimise the effect of the filter cleaning downtime on the overall process. Summary of the Invention [0006] According to a first aspect of the present invention there is provided a support element for supporting a filter material, the support element comprising: a frame arranged to carry at least one perforated support sheet, the frame and the perforated support sheet configured to support the filter material, the perforated support sheet having interstices orientated in a direction transverse to the plane of the sheet. [0007] When the support element is assembled with the filter material (preferably a filter fabric), a filter unit for use in a filtration process is provided. Such a filter unit may be, for example, configured for use as a pressure filter for use in an industrial process such as the Bayer process. In this process, a plurality of filters units are installed within a pressure vessel into which a filtrate-bearing suspension is pumped. In operation, the filtrate-bearing suspension is pressed against the filter material such that only the filtrate liquor passes therethrough, for further downstream processing. [0008] The filter material can be configured to completely surround the support element, eg. as a bag sealed around the frame of the support element. The properties of the filter material are selected to target the desired filtrate.

3 [0009] Testing has determined that the orientation of the interstices of the perforated support sheet provides an increased effective open area offering less resistance than conventional mesh arrangements, so facilitating increased fluid flows therethrough. Pressure filters employing such support elements have been found to exhibit increased flows in the order of about 15-20% as compared with conventional pressure filter assemblies. Embodiments of the present invention can provide the following advantages: e The form of perforated support sheet reduces the risk of the filter material rupturing. Minimising the risk of such mechanical damage to the filter fabric is essential. " In a Kelly filter vessel, the same number of filters units as used with conventional filter assemblies can be installed without the need for modification. Furthermore, the pressure filter units of the invention may be installed using the same installation methods as conventionally used. * The pressure filter units of the invention are lighter and easier for operators to handle than conventional pressure filter units. * Standard filter fabrics may be employed thereby avoiding the need for specific customisation of materials. * The form of the perforated support sheet has also been found to help reduce scale build-up, ie. the gradual blocking of the interstices of the filter material. [0010] Embodiments of the first aspect of the present invention may comprise one or more of the following features: [0011] In one embodiment, the perforated support sheet comprises successive rows of shaped deformations which define the interstices. Each row may comprise repeating 'peak' and 'trough' formations of certain width which project outwardly from the plane of the sheet. The formations may be waveform (eg. sinusoidal) and may be substantially continuous along each row. [0012] The waveform shaping of the deformations of each row may be out of phase with the waveform shaping of the deformations of an adjacent row, preferably by 180o. A peak of one row and a trough of the subsequent row may duwm A0121791416v11 120265033 4 therefore define a single interstice of the sheet, ie. the trough and the peak are aligned, so as to define the periphery of the interstice. One peak deformation may therefore define part of two successive interstices, ie. one interstice formed either side of the peak deformation by way of the adjacent trough deformations of the two adjacent rows. [0013] Where the interstices are arranged in plural rows, the longitudinal axes of the rows will typically be parallel with one another. In this embodiment, the longitudinal axes of the rows will extend in a direction which is substantially parallel to the plane of the support sheet. [0014] The frame preferably carries two parallel perforated support sheets. [0015] The two perforated support sheets may be separated from one another by one or more separating members. In this way, the separation of the sheets defines a volume therebetween in which filtrate liquor may be received. [0016] Each separating member preferably comprises an elongate member positioned between the sheets. The two perforated support sheets and the elongate separating member are preferably positioned such that the elongate separating members are received within or between opposing peaks of the two sheets. [0017] In one arrangement, a plurality of separating members, provided as discrete elongate members segments, may be arranged in a staggered relationship so as to be spaced from one another (between the two support sheets) to help reduce impedance of the flow of filtrate liquor within the volume formed between the two support sheets. In this embodiment, a number of rows, each containing a number of separating members, are spaced across a substantial area of the sheets. Within each row, the separating members are axially aligned and regularly spaced from one another. The separating members in alternate rows may be offset from alignment with those of adjacent rows. In this way, impedance of filtrate liquor flow within the volume can be reduced due, at least in part, to the staggered nature of the separating members. It would be readily appreciated that a number of different spacing arrangements could be used for arranging the separating members relative to one another to help reduce impedance of the flow of filtrate liquor within the volume formed between the two support sheets. [0018] The frame may comprise a number of frame members assembled into a generally rectangular form. In alternative embodiments, the shape of the frame duwm A0121791416v11 120265033 5 may be varied in accordance with the cross-section of the vessel within which the frame is to be installed. [0019] Preferably, the frame includes one or more fluid outlets for egress of filtrate liquor. [0020] One or each frame member may be an elongate tube of uniform cross section, having apertures through which filtrate liquor can pass from the volume between the two perforated support sheets, the frame members in fluid connection to allow filtrate liquor to pass to said fluid outlet(s). The skilled reader will appreciate that the frame members may be of any suitable cross sectional profile, eg. circular, rectangular, etc. [0021] One or more of the frame members may be provided with openings configured to receive an edge of the or each perforated support sheet. Portions of the edge of the perforated support sheet or sheets are thus positioned within said frame members and are fastened thereto by way of any suitable fastening method. [0022] Alternatively or additionally an edge of the perforated support sheet may be fastened to the external surface of one or more of the frame members. A reinforcing element may be provided at this edge and preferably fastened to both the first frame member(s) and the sheet, so as to fasten an edge of the sheet to the frame. [0023] The invention provides a support element for supporting a filter material, the support element comprising at least one generally planar sheet having through-flow apertures formed by making a plurality of slit cuts in the sheet and deforming parts of the sheet between said slit cuts in a direction transverse to the plane of the sheet. [0024] The slit cuts are preferably straight line cuts, and in one form all of the slit cuts in a sheet are parallel. [0025] Put another way, the invention provides a support element for supporting a filter material, the support element comprising at least one generally planar sheet with a pattern of punched deformities in the sheet defining through flow apertures adapted to allow fluid flow therethrough in a direction other than normal to the plane of the sheet. duwm A0121791416v11 120265033 6 [0026] Preferably, substantially no material is removed from the sheet material in order to form the apertures. [0027] In a further aspect of the present invention, there is provided a filter unit for use in an industrial filter process, the filter unit comprising a support element as defined above, substantially enveloped by a filter material. [0028] The filter unit may be a pressure filter adapted for use as a Kelly leaf filter in a Bayer process for producing alumina from bauxite. [0029] The invention also provides a filtration system comprising a pressure vessel containing a plurality of the above-defined support elements, an inlet to the pressure vessel by which a filtrate-bearing suspension may be introduced, and an outlet connected to the support elements by which the filtrate liquor may be removed. Brief description of the Drawings [0030] The invention will now be further explained and illustrated, by way of example only, by reference to the accompanying drawings in which: [00311 Figure 1 is a schematic elevation view of one embodiment of the support element of the present invention. [0032] Figure 2 shows Section 'A' of the support element of Figure 1. [0033] Figure 3 shows Section 'B' of the support element of Figure 1. [0034] Figure 4 shows Section 'C' of the support element of Figure 1. [0035] Figure 5 shows a schematic perspective view of a corner section of the support element shown in Figure 1. [0036] Figure 6 shows a schematic elevation view of a further embodiment of the support element of the present invention. [0037] Figure 7 shows a schematic elevation view of an arrangement of the perforated support sheet used with the support element of Figure 6. duwm A0121791416v11 120265033 7 [00381 Figure 8 shows a perspective view of a portion of the perforated support sheet used with the embodiments of the support element shown in Figure 1 and Figure 6. [0039] Figure 9A shows a cross-sectional view of a portion of the perforated support sheet of Figure 8. [0040] Figure 9B shows a front view of a portion of the perforated support sheet of Figure 8. [0041] Figure 10 shows a filter system employing a Kelly-type pressure filter assembly in a Bayer process plant using a plurality of filter units of the invention. Detailed description [0042] One embodiment of a support panel 2 arranged in accordance with the present invention is shown in Figure 1. The support panel 2 is used for supporting a filter material (not shown, hereinafterfilterfabric) capable of filtering a filtrate liquor from a filtrate-bearing suspension. The support panel 2 comprises a frame 6 arranged to carry a perforated support sheet 16 whereby the frame and the sheet are configured to support the filter fabric thereabout so that the filtrate liquor may be received therethrough. The support sheet 16 comprises a plurality of interstices 17, each of which are orientated in a direction substantially normal to the effective plane of the support sheet (shown in detail in Figures 8, 9A and 9B). [0043] When the support panel 2 is assembled with the filter fabric, a filter unit for use in a filtration process is provided. Such a filter may be, for example, configured for use as a pressure filter (often referred to as a pressure leaf filter) for use in an industrial process such as the Bayer process - a process used for producing alumina from bauxite. In this process, a plurality of filter units are installed within a pressure vessel into which a filtrate-bearing suspension (referred to as a slurry) is pumped and placed under pressure. In operation, the slurry is pressed against the filter units such that a target filtrate liquor passes through the filter fabric for further downstream processing. The filter fabric is arranged so as to surround the support panel 2 and is dimensioned as appropriate so as to exclude unwanted particulate from the suspension. duwm A0121791416v1 1 120265033 8 [00441 In the Bayer process, pressure filters are primarily 'polishing' filters used for filtering remaining amounts of unwanted particles from the filtrate bearing suspension or slurry. Over the cycle time, particulate from the suspension builds up on the surface of the filter fabric. This gradual build up or 'cake' has the effect of reducing the flow rate of filtrate liquor through the filter fabric. [0045] In the standard industrialised Bayer process, pressure filters (the design of which derives from the conventional Kelly filter traditionally used in the filtration step in the Bayer process) typically operate on a 8 to 10 hour cycle during which the flow rate slowly decreases as the filter fabric becomes increasingly congested due to cake build-up. When the filters are removed, the cake is discharged and the filter fabric washed. Although specific washing cycles used often vary from plant to plant, a wash cycle may, for example, comprise hot water washes for two cycles followed by a caustic wash on the third cycle. [0046] The arrangement of the interstices 17 of the support sheet 16 provides an increased effective open area offering less resistance than conventional mesh arrangements so as to facilitate increased fluid flows therethrough. Embodiments of the support sheet 16 (such as perforated sheet available from Gantois) have been found to improve flow rates in the order of about 15-20% as compared with conventional pressure filter assemblies. [0047] With reference to Figure 1, the frame 6 of the support panel 2 is assembled using four frame members 12a, 12b, 12c and 12d, and arranged in a substantially rectangular configuration. In one form, frame member 12a is an elongate tubular length of uniform circular cross-section (in the form of for example DN 65 SCH XS pipe) and the remaining frame members (12b, 12c, and 12d) are elongate tubular lengths of uniform rectangular cross-section (such as RHS 65 x 35 x 3 section). [0048] Frame member 12a further comprises outlets 24 and 26 in the form of pipe section secured (such as by welding) at or near its free ends (22, 23) so that filtrate liquor received during operation can be removed from frame 6 for further processing. [0049] The perforated support sheet 16 is provided by two like perforated support sheets 16a and 16b which are spaced parallel from one another by a plurality of separating members 20 (such as elongate rods). In one arrangement, the total size of each support sheet 16a, 16b is about 3.820m x 2.5m - whereby each support sheet is provided in the from of two 3.820m x 1.25m sheets. duwm A0121791416v11 120265033 9 [0050] The separating members 20 are configured in finite length (x,) segments (of about 300mm in length) and arranged in a staggered relationship relative to one another in the manner shown in Figure 1 ('horizontal' arrangement). As shown, the separating members 20 are aligned so as to be substantially parallel with one another and frame members 12a and 12c. The separating members 20 are each welded to one or both support sheets 16a and 16b and arranged such that the axis of each separating member 20 aligns substantially with direction W 1 shown (direction W, is substantially orthogonal to a given row of shaped formations of the support sheet 16a/b - see discussion further below). The arrangement of the separating members 20 is such that their respective elongate axes are substantially aligned in regularly spaced rows (proceeding substantially in direction W 2 ), with each row spaced from another by a distance x 2 (about 300mm). In each row, the separating members 20 are spaced end from end from each other at a distance x 3 (of about 300mm). As shown, each alternate row is indented from the adjacent rows by a nominal distance (such as the length of one separating member 20, eg. about 300mm). [0051] The separating members 20 are preferably rods 10mm in diameter and positioned between opposing peaks of the two perforated support sheets 16a, 16b. In this way, the separation of the support sheets 16a, 16b defines a volume therebetween in which filtrate liquor may be received. The arrangement of the separating members 20 is such so that the flow of the filtrate liquor encounters reduced impedance through substantially the full length of the frame while ensuring sufficient structural support is provided to the support sheets 16a, 16b. [0052] In view of the highly corrosive environment within which the filter units typically operate, the frame 12 and separating 20 members are of any appropriate material serving to minimise corrosion such as for example mild steel or stainless steel (using variants such as stainless steel 304, 316 and 316L). [0053] The skilled reader will appreciate that the separating members 20 could comprise elongate members of any cross-sectional shape and dimension sufficient to space and support sheets 16a and 16b from one another when under operational pressure. It will be also understood that the volume between support sheets 16a, 16b is of sufficient dimension so that filtrate liquor can flow (under pressure) toward frame member 12a so to exit the support panel 2 at either of outlets 24, 26. [0054] Figures 3 and 4 show the construction arrangement used to secure support sheets 16a, 16b with respective frame members. Frame members 12b, duwm A0121791416v11 120265033 10 12c and 12d are each configured with appropriately dimensioned laser cut slots 32 (laser cut for example) provided on their internal facing side (when assembled) and into which corresponding edge regions (such as tabs) of support sheets 16a, 16b are received and accommodated within. For example, each slot 32 may be 350mm in length and spaced apart along the internal length of frame members 12b, 12c, 12d, in intervals of about 100mm. Thus, the edge of each sheet is effectively tabbed (as is illustrated in Figure 7) so that each tab portion can be received by corresponding slots formed in the frame members. [0055] In an alternate embodiment, the arrangement may be such that one or more of the separating members 20 (either wholly or a portion thereof) resides within the tubular section of a respective frame member. [0056] Frame members 12b, 12c and 12d are arranged so that the volume between support sheets 16a, 16b fluidly connects with frame member 12a by way of one or more apertures 36 provided therein. With reference to Figure 5, an end of frame member 12d is secured at or near end 22 of frame member 12a, substantially about aperture 36. Thus, the end of the frame member 12d is secured to frame member 12a such that aperture 36 opens into the tubular hollow of frame member 12d. A similar arrangement is provided for the connection between frame member 12b at end 23 of frame member 12a. The frame 6 is therefore arranged with support sheets 16a, 16b so that filtrate liquor flows toward the periphery of the frame (generally toward frame members 12b, 12c and 12d) so as it may flow toward and into first frame member 12a by way of aperture 36. [0057] Figure 2 shows an arrangement used to fasten support sheets 16a, 16b to frame member 12a when arranged as that shown in Figure 1. Support sheets 16a, 16b are arranged so as to abut the periphery of frame member 12a, and are sandwiched between substantially flat elongate reinforcing members 30a and 30b (such as 50mm x 5mm flat metal strips), each secured (for example by welding) to frame member 12a (on its external surface) and the edge of the respective support sheets 16a, 16b. [0058] In another form (shown in Figure 6 - an example of a 'vertical' filter arrangement), all frame members (12a', 12b', 12c', 12d') of frame 6' are provided in the from of standard RHS 100 x 50 x 4 or RHS 65 x 35 x 3 sections. The corners of each frame member are mitred, V-prepped, butt welded and ground flush so as all are in fluid connection with each other so filtrate liquor may flow toward and out through one of outlets 24', 26'. In the form shown, outlets 24', 26' are duwm A0121791416v11 120265033 11 provided in the form of discrete lengths of appropriately sized pipe section which are inserted and secured within respective ends of frame member 12a'. Each frame member comprises regularly spaced slots to accommodate respective edge (or tabbed) portions of the perforated support sheets 16a', 16b' as described. [0059] It will be appreciated by the skilled person that the staggered arrangement of the separating members 20' for the 'vertical' filter configuration is similar to that previously for the 'horizontal' arrangement described but is effectively rotated 90*, as is the orientation of the perforated support sheets 16a', 16b' (as shown in Figure 7). [0060] Support sheets 16a, 16b are formed using a metal pressing or punching process which provides a repeating pattern of shaped deformations which are aligned substantially normal to the effective plane of the respective sheet (or out of-plane with each respective sheet). With reference to Figures 8, 9A and 9B, each support sheet 16a, 16b comprises successive rows of the shaped deformations which provide the interstices 17 of the support sheet 16. The shaped deformations may be waveform (eg. sinusoidal) and may be substantially continuous along each row which is aligned substantially with direction W 2 . In this regard, each row comprises repeating 'peak' 40 and 'trough' 46 deformations of finite width. When assembled with frame 6, the two support sheets 16a,16b and the separating members 20 are positioned such that the separating members are received within or between opposing peaks 40 of the two sheets. [0061] The waveform behaviour of each row is preferably out of phase with that of an adjacent row such that a peak 40 of one row is adjacent a trough 46 of the succeeding row. Adjacent rows are out of phase with one another by 180'. As such, a peak 40 of one row, and a trough 46 of the subsequent row, both define a single interstice 17 of the sheet 16, ie. the trough 46 and peak 40 deformations are aligned so to define the interstice 17. Therefore, the plane in which each interstice 17 resides is normal to the effective plane of the support sheet 16 thereby providing a three dimensional component to the sheet - as opposed to a conventional woven mesh sheet in which the interstices are generally co-planar with the sheet and therefore broadly substantially two dimensional in nature. A single peak 40 deformation therefore defines two interstices 17, ie. one interstice 17 either side of a peak 40 deformation formed by way of the adjacent trough 46 deformations of the two adjacent (prior and succeeding) rows. [0062] Support sheets 16a, 16b may be exemplified by a perforated sheet currently available from Gantois. In this form, the repeating peak 40 and trough duwm A0121791416v11 120265033 12 46 deformations have a wavelength (refer reference w in Figure 9A) of about 12mm, a peak to trough dimension (a) of about 6mm, and a radius of curvature (r) of about 4.1mm. Furthermore, the width (reference t in Figure 9B) of each row is in the order of 3.25mm. It will be readily appreciated by the skilled reader that the above dimensions are not specific and may be varied as appropriate without departing from the core aspects of the invention. [0063] It will be appreciated that the support sheet 16 may be formed from any planar sheet of any appropriate material in which the through-flow apertures are formed by making a plurality of slit cuts in the sheet and using any appropriate pressing machinery to deform the parts of the sheet between the slit cuts in a direction which is transverse to the plane of the sheet. [0064] The skilled reader will appreciate that the shape of the deformities serve to define through-flow apertures which are adapted to facilitate fluid flow therethrough and which have a substantial through flow component which is aligned in a direction which is substantially parallel to the plane of the sheet. [0065] As the interstices 17 of each support sheet 16a, 16b are out-of-plane, their effect serves to increase the available open area than compared with conventional two dimensional woven mesh sheets, while retaining sufficient structural integrity to ensure appropriate support is provided to the filter fabric when under operational pressure. Furthermore, the deformations of the support sheet 16 can be readily conformed with by the filter fabric helping to, at least in part, reduce the risk of the fabric rupturing or tearing, ie. reducing abrasive or other contact with the filter fabric while increasing fluid flow therethrough. This allows standard filter fabrics to be readily used thereby reducing the need for specific customisation. In addition, the geometry of the deformations has been found to help reduce scale build-up (the gradual blocking of the interstices of the filter fabric) on the filter fabric. [0066] Figure 10 shows a plurality of filter units 50, each comprising a support panel 2 enveloped in or otherwise covered on both sides by cloth filter fabric, in place in a Kelly-type pressure filter assembly 60, illustrating an application of the present invention. The filter elements 50 are mounted in a parallel horizontal series as shown in a filtration apparatus 62 with a movable body shell 64 having a cylindrical body 66 and end plates 68 and 70. [00671 In closed position (shown in dashed lines) the assembly provides a closed filter press system. In this position, filtrate-bearing suspension is duwm A0121791416v11 120265033 13 introduced under pressure into the shell 64 via inlet pipe 72 on end plate 68 and the filter units 50 connect by way of outlets 24, 26 through a manifold system (not shown) to a filtrate liquor outlet pipe 74. [00681 Once the filter cake on. the filter elements has built up to a certain level, body shell 64 can thus be slid out on wheels 76 travelling on rails 78 by way of a motive means 80. In this open position (solid lines) the filter units 50 are exposed so that they may be washed by a suitable washing means (not shown) to remove the filter cake. [00691 An alternative arrangement may mount the set of filter units 50 on a support means which can be withdrawn from the interior of a stationary body shell 64 for washing. [0070] Various advantages be realised by the present invention. The same number of filters as used in conventional designs may be installed in a standard Kelly filter system without the need for any modification. The filter elements of the invention are lighter and easier for operators to handle than conventional pressure elements. The same installation and disassembly methods as used with conventional Kelly filter designs may be employed. [0071] It is to be noted that, throughout the description and claims of this specification, the word 'comprise' and variations of the word, such as 'comprising' and 'comprises', is not intended to exclude other variants or additional components, integers or steps. [0072] Modifications and improvements to the invention will be readily apparent to those skilled in the art. Such modifications and improvements are intended to be within the scope of this invention. duwm A0121791416v11 120265033

Claims (15)

1. A support element for supporting a filter material, the support element comprising: a frame arranged to carry at least one perforated support sheet, the frame and the perforated support sheet configured to support the filter material, the perforated support sheet having interstices orientated in a direction transverse to the plane of the sheet.

2. A support element according to claim 1, wherein the interstices provide through-flow apertures, formed by making a plurality of slit cuts in the sheet and deforming parts of the sheet between said slit cuts in a direction transverse to the plane of the sheet.

3. A support element according to claim 2, wherein the slit cuts are straight line cuts.

4. A support element according to claim 3, wherein the slit cuts are parallel.

5. A support element according to any preceding claim, wherein the perforated support sheet comprises successive rows of shaped deformations whose form defines said interstices of the sheet.

6. A support element according to claim 5, wherein each row of the perforated support sheet comprises repeating peak and trough formations projecting outwardly from the plane of the sheet.

7. A support element according to claim 5 or claim 6, wherein the shaped deformations of each row are out of phase with those of an adjacent row such that the peak deformation of one row and a trough deformation of the subsequent row define a single interstice of the support sheet.

8. A support element according to any preceding claim, wherein the frame includes one or more outlets for egress of filtrate liquor.

9. A support element according to any preceding claim, wherein the frame carries two parallel perforated support sheets separated from one another by one or more separating members so as to define a volume therebetween in which filtrate liquor may be received. 15

10. A support element according to claim 9, wherein the frame comprises a number of frame members assembled into a generally rectangular form, one or each frame member having apertures through which filtrate liquor can pass from the volume between the two perforated sheets, the frame members in fluid connection to allow filtrate liquor to pass to the or each outlet.

11. A support element for supporting a filter material, the support element comprising at least one generally planar sheet with a pattern of punched deformities in the sheet defining through-flow apertures adapted to allow fluid flow therethrough in a direction other than normal to the plane of the sheet.

12. A support element according to claim 11, wherein substantially no material is removed from the sheet material in order to form said apertures.

13. A filter unit for use in an industrial filter process, the filter unit comprising a support element as defined in any preceding claim, substantially enveloped by a filter material.

14. A filter unit according to claim 13, being a pressure filter adapted for use as a Kelly leaf filter in a Bayer process for producing alumina from bauxite.

15. A filtration system comprising a pressure vessel containing a plurality of support elements according to any one of claims 1 to 12, an inlet to the pressure vessel by which a filtrate-bearing suspension may be introduced, and an outlet connected to the support elements by which filtrate liquor may be removed.