AU779598B2 - Intertank screen - Google Patents

Description

1 P/00/011 28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Name of Applicant: Actual Inventor Address for service is: Lycopodium Pty Ltd Bruno Ruggiero WRAY ASSOCIATES 239 Adelaide Terrace Perth, WA 6000 Attorney code: WR Invention Title: "Intertank Screen" Details of Associated Provisional Application No(s): PQ5132 The following statement is a full description of this invention, including the best method of performing it known to me:-

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-2- "Intertank Screen" Field of the Invention The present invention relates to the field of hydrometallurgical processing, and in particular to improvements in apparatus for leaching/adsorping/adsorbing values.

Background Art A typical mineral processing plant utilising leach/adsorption/adsorbtion processes for extracting metal values from a finely ground ore slurry consists of a series of leach/adsorption/adsorbtion tanks. The tanks are generally interconnected with launders to allow the slurry to gravitate through the tank train. Each tank is fitted with an intertank screen to retain the adsorpbent/adsorbent and an agitator to ensure uniform mixing. A wiper is associated with the intertank screen to prevent clogging of the screen by absorbent.

Pregnant slurry is introduced into the first tank and flows (either via gravity, pump or a combination of both) through the tank train. The adsorpbent/adsorbent is 15 introduced into the last tank of the train and advanced counter current to the slurry flow via airlift or pump to next upstream tank either batchwise or continuously. The adsorpbent/adsorbent is retained by the intertank screen within the upstream tank while the slurry gravitates back to the downstream tank.

The counter current process is repeated until the adsorpbent adsorbent reaches 20 the first tank, from where it is removed via airlift or pump for stripping. The slurry which discharges from the last tank is directed to tails (waste) disposal.

The purpose of the intertank screen is therefore twofold: to facilitate the counter current movement of the adsorpbent adsorbent; and to prevent the loss of loaded adsorpbent adsorbent to each downstream tank in turn and ultimately to tails disposal.

Historically, there have been several versions of intertank screens which have been used at some point or another, including but not limited to static screen, -3- Kambalda screen, vibrating screen, trommel, air swept cylindrical with bottom discharge, mechanically swept cylindrical with bottom discharge (also commonly known as a North Kalgurli screen and its various adaptations thereof), and mechanically swept cylindrical with top discharge (and its various adaptations thereof).

Irrespective of type however, all the intertank screens have been fitted with a filter screen generally referred to as a screen cloth (woven wire, wedgewire, or similar, of either stainless steel or polyurethane construction) whose aperture is significantly less than that of the adsorpbent adsorbent, thus retaining the adsorpbent adsorbent, while permitting the finely ground ore slurry to pass through.

To prevent clogging of the screen cloth, the cloth has usually been gently swept (agitated) with either air and or mechanical devices such as a wiper.

More recently, the industry has tended towards top discharge, mechanically swept, cylindrical screens in which the screen assembly is hinged to the intertank o launder and the mating flanges of the screen assembly and launder acting as seal to prevent leakage of the adsorpbent/adsorbent and entrainment thereof with the ore slurry. In view of perceived difficulties inter alia with retaining an effective seal with such an arrangement, the applicant has proposed an alternate 20 sealing system between the screen assembly and launder, which is the subject of the applicant's co-pending patent application PCT/AU99/00649, the contents of which are incorporated herein by cross-reference.

This invention is primarily concerned with top or bottom discharge, cylindrical screen assemblies described above, which have in the main relied upon gravity to progress flow of ground ore slurry through the tank train, however it will be appreciated from the following description that the invention may not be limited to screen assemblies of cylindrical configuration.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood -4to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Disclosure of the Invention In accordance with one aspect of the invention there is provided a screen assembly having an outlet for fluid communication with an ore slurry outlet in a leach tank, said screen assembly having a filter screen to allow undersize ore slurry to flow therethrough while restraining oversize material, wherein said screen assembly includes located in a position in the ore slurry flow pathway between said filter screen and toward or in said ore slurry outlet, impeller means to urge said undersize ore slurry through said outlet and draw said undersize ore slurry through said filter screen, and wherein ore slurry within said outlet is always in fluid communication with ore slurry discharged from said leach tank o whether the impeller means is operated or not.

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Preferably said impeller means comprises a rotary impeller.

15 Preferably said impeller is located entirely submerged in said ore slurry.

Preferably said impeller is located in a conduit which communicates with said outlet.

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Preferably said conduit is of circular cross-section, and said impeller has an axis extending with the axis of said conduit.

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Preferably said impeller has an axis substantially coaxial with the axis of said conduit.

The impeller may have a plurality of blades which have a pitch, so that rotation of the impeller urges ore slurry through said conduit toward said outlet, however a simpler and more preferred arrangement is one where the impeller discharges radially or at least with a radial component to its flow direction. This may be advantageously achieved in a most preferred form of the invention where the conduit is of frusto-conical shape with its broader diameter terminating in said outlet, with the impeller being located within the frusto-conical portion of said conduit and having blades sweeping said conduit. In this arrangement, the blades may have a pitch that extends with the axis of said impeller 900 coarse or maximum pitch the surfaces of the blades are co-planar with the axis of the impellor along any extent parallel with the axis of the impeller) and operate to urge said ore slurry outwardly (in the manner of a centrifugal impeller) to flow toward the broader diameter of said conduit. The blades most preferably prescribe a frusto-conical shape when the impeller is rotated, which shape corresponds approximately with that of the conduit, for greatest efficiency. The adoption of a blade assembly with a pitch that extends with the axis of the impeller simplifies construction of the impeller.

Preferably, the blades are curved so as to sweep the conduit with a trailing action.

Preferably said impeller is mounted on a drive shaft assembly driven from above.

Preferably filter screen is cylindrical in configuration and in use disposed with its axis vertical, one end of said filter screen being closed off to form a bottom of said screen assembly, with said outlet being located proximal to the other end of the screen assembly.

S 20 Preferably the drive shaft assembly extends toward said bottom, and has an •**°agitator mounted thereon proximal to said bottom to minimise settling and caking of said ore slurry at the bottom of said screen assembly.

Preferably said conduit extends down toward said bottom to a position proximal to said agitator. Alternatively a further conduit extends from said conduit to a position proximal to said agitator. Either arrangement results in the impeller drawing ore slurry up from a position proximal to said agitator.

Preferably said screen assembly includes agitator arms which travel around the outside of said filter screen, and are mounted to said drive shaft assembly for -6movement with said impeller. The agitator arms do not contact the filter screen, but create turbulence which helps to prevent oversize material from settling on and clogging the filter screen.

Preferably said screen assembly is intended to be received through said ore slurry outlet in said leach tank.

Preferably said screen assembly is intended to be received vertically through said ore slurry outlet in said leach tank.

Preferably said ore slurry outlet is accessible from above for insertion and extraction of said screen assembly.

Preferably said screen assembly is supported relative to said ore slurry outlet from a position located above said ore slurry outlet. In this manner, the only contact with said screen assembly below the level of the slurry (ie below the "water-line") is the contact between the seal and the outlet.

In a highly preferred form of the invention, the screen assembly includes a seal 15 means located around its periphery in a position to sealingly interfere with said ore slurry outlet, as is the case in the applicant's invention described in copending patent application PCT/AU99/00649.

In this arrangement, any one of the permutations for sealing the screen assembly to the ore slurry outlet described in co-pending patent application PCT/AU99/00649 can be employed. These include the inclusion of a peripheral flange on the screen assembly at a position commensurate with the position of said ore slurry outlet to locate and/or carry said seal means, where the seal means may extend peripherally beyond said flange to sealingly interfere with the ore slurry outlet. The seal means may comprise a seal formed of a resiliently 25 deformable material. The seal may be sandwiched between the flange and a clamping member, which may be a configuration substantially commensurate with the extent and configuration of the flange, with the seal also extending peripherally beyond said clamping member to sealingly interfere with said ore slurry outlet. The clamping member may be divided into a plurality of portions, for ease of handling.

Furthermore, an arrangement whereby the uppermost of the clamping member and the flange has the greater overall external transverse size may be employed to give a greater purchase of the seal on insertion of the screen assembly, while reducing purchase on withdrawal of the screen assembly. Since the seal is sandwiched between said flange and the clamping member, and also extends peripherally beyond both to sealingly interfere with said ore slurry outlet, the insertion of the screen assembly causes the seal to interfere with the wall(s) of the ore slurry outlet and deflect upwards, while the seal can readily deflect in the opposite direction allowing for easy removal of the screen assembly from the outlet. As a result of reduced clearance between the uppermost member (of the clamping member and the flange) and the outlet, the sealing properties are improved. In a screen assembly where the clamping member is located above the flange, and where difficulty is encountered with obtaining a seal between the screen assembly and the ore slurry outlet, new clamping members may be fabricated with a greater overall diameter, to improve the sealing characteristics.

It will be understood that in an ore slurry outlet of a tank assembly, the flange may be peripherally provided therein, and the seal means mounted thereto, in a mechanical inversion of any of the arrangements described above.

As an alternative to the arrangement where the seal extends peripherally beyond said flange to sealingly interfere with said ore slurry outlet, said flange is arranged to mate with a corresponding internal flange located at said outlet. In this above alternative arrangement, the seal means may comprise machined mating surfaces of the flanges, a formed surface to create a line seal located on S. one or both contacting surfaces of the flanges, or a discrete seal which can be located between the flanges.

In accordance with a second aspect of the invention there is provided in a leach tank, a screen assembly as hereinbefore described, said leach tank having a launder connecting with said ore slurry outlet for discharge of said ore slurry to the next leach tank in a train of said leach tanks.

Preferably there is included a channel portion located between said outlet and said launder, said channel portion having a narrow end connecting with said outlet, and a wide end accessible from above to allow removal and replacement of said screen assembly from and to said leach tank, said channel portion tapering generally between said narrow end and said wide end.

Preferably said launder is fluidly connected to said channel portion through the wall thereof. In this manner, the slurry will exit upwardly from the screen assembly and enter the channel portion and flow across and out through said launder.

Brief Description of the Drawings The invention will now be described in the following description of one preferred embodiment thereof made with reference to the drawings in which: Figure 1 is a perspective view of a screen assembly, conical channel portion and launder according to the first embodiment; Figure 2 is a cross-section side elevation of the screen assembly, conical channel portion and launder of figure 1; ~Figure 3 is a cross-section side elevation of detail of the seal utilised in the embodiment; o Figure 4 is a cross-section side elevation of detail of an alternative seal which may be utilised in the embodiment; Figure 5 is a cross-section side elevation of detail of a further alternative seal which may be utilised in the embodiment; .Figure 6 is a plan view from above of the impeller utilised in the embodiment; and Figure 7 is a side view of the impeller of figure 6, and its drive shaft.

Best Mode(s) for Carrying Out the Invention Referring to figure 1, the embodiment is a screen assembly 11 and discharge 13 for a leach tank in a carbon-in-pulp gold extraction plant. It will of course be understood that while the embodiment is intended for use in carbon-in-pulp gold extraction, it may be used in any slurry hydrometallurgical application utilising leaching/adsorption/adsorbtion processes. As described in the preamble, the leach tank will be one of a series (often of six or seven), in which pulp moves progressively through activated carbon resident in each leach tank, the screen assembly 11 being provided with a filter screen 15 to retain the activated carbon in the leach tanks, while the finer slurry passes through the filter screen 15 and into the discharge 13, for transfer to the next leach tank in the series.

The parts list for items noted and illustrated in the embodiment is given in the following table: screen assembly 11 circular conical base member 49 discharge 13 sparge pipes 53 filter screen 15 outlet 55 (to discharge 13) circular ribs 17 frusto-conical channel 57 (of discharge 13) vertical bar 19 launder 59 (of discharge 13) bolts 21 wall 61 of frusto-conical channel 57) annular transverse flange 23 central tubular conduit 62 seal 25 clamping member 63 structural pipe members 27 second seal means 71 platform 29 frusto-conical portion 73 central axial tube 31 rotary impeller drive shaft 33 drive shaft 77 electric motor/gearbox 35 flange 79 25 wiper 37 agitator 81 .eee°: spaced vertical arms 39 blades 83 radial arms 41 circular plate 87 hoop 43 blades 89 coupling assembly 47 vanes 97 The screen assembly 11 is of cylindrical shape along its vertical axis, and the filter screen 15 is supported on a plurality of spaced circular ribs 17. The filter screen 15 is secured and tensioned in place by a vertical bar 19 which is received in a recess (not shown), so that as bolts 21 holding the vertical bar 19 are tightened, the filter screen 15 is tensioned across the vertical ribs.

Referring to figure 2, at the top of the filter screen 15, there is provided an annular transverse flange 23, extending around the cylindrical surface of the screen assembly 11, which receives a seal 25 (see figure 3 for finer detail).

Extending from and above the flange 23, four structural pipe members 27 extend to a platform 29, which sits atop the discharge 13, supporting and locating the screen assembly 11 relative to the discharge 13.

A central axial tube 31 runs from the top of the screen assembly 11, to the bottom thereof, and receives a drive shaft 33 connected to a 5kW electric motor and gearbox assembly 35 configured to run the drive shaft 33 at approximately revolutions per minute. The drive shaft 33 is connected to a wiper 37. The wiper 37 has three spaced vertical arms 39 supported from radial arms 41 welded to the lower end of the drive shaft 33. A hoop 43 secures spatially, the tops of the vertical arms 39. The drive shaft 33 has a coupling assembly 47 located at a position above the slurry level in the leach tank. There are no bearings or guides located lower down the drive shaft 33. This minimises maintenance which immersion might bring about. There is a clearance of approximately 30mm between the arms 39 and the filter screen 15. The purpose 20 of the wiper 37 is to disturb activated carbon which settles against the filter screen 15 under influence of the flow of slurry. The agitation prevents the filter S* screen 15 from becoming clogged with activated carbon.

The screen assembly 11 is closed at the bottom by a circular conical base member 49, which includes three upward blind holes (not shown), for receiving the upstanding legs of a support stand when the screen assembly is removed for maintenance. The circular conical member also includes an actuable plug member (not shown) which can be opened to drain the screen of fluid when it is desired to lift the screen assembly from the leach tank. Finally, sparge pipes 53 allow sparging down to dislodge any sedimentation from the inside of the base member 49. that may occur especially if the leach tank has been standing idle.

-11 The discharge 13 includes an outlet 55 of circular tubular configuration which connects at its upper end with the narrow end of a frusto-conical channel 57. A launder 59 (which is an open topped conduit) extends from the wall 61 of the frusto-conical channel 57 to carry slurry from the leach tank, to the next leach tank stage, for further processing. The flow path of slurry which has passed through the filter screen 15 is indicated by double line arrows in figure 2.

Internally, the screen assembly 11 includes a central tubular conduit 62 extending therewithin toward the base 49 thereof, to ensure that the region near the base 49 has flowing slurry. This assists to prevent the slurry settling as a sediment in the base 49 of the screen assembly 11.

It will be understood that the only fluid flow path from the leach tank to the discharge 13 must be through the filter screen 15, or there will be a loss of loaded activated carbon from the leach tank. To prevent loss of loaded activated carbon in this manner, the seal 25 extends from the flange 23, and sealingly contacts against the inner wall of the outlet 55. A clamping member 63 (refer to figure 3) of configuration commensurate with the external periphery of the flange 23 extends with the flange and is fastened with nuts 65 and bolts 67 (spaced evenly around the flange) to sandwich the seal 25 and thereby secure it in place.

The clamping member 63 is divided into four equal arcuate portions (not shown), 20 to reduce the weight of each piece for ease of handling, fitting, and removal. This also allows for removal and fitting of the clamping member.

The seal 25 is cut from soft natural rubber sheet of thickness between 8mm and 12mm (or thicker if it is desired to increase the sealing force), and is cut to a diameter exceeding the diameter of the outlet 55 by approximately 40mm. It will 25 be understood that changes may be made to the seal 25 as required, depending on the size of the space to be bridged between the flange 23 and the outlet The seal may be made from any resilient material that is inert to the reagents present in the leach tank, however, soft natural rubbers are the most preferred materials for the seal.

The screen assembly 11 is designed to be lifted out of the discharge 13 by a -12hoist. On lifting, the seal to the outlet 55 is broken, and the screen assembly 11 may be placed on a support stand for maintenance.

To refit the screen assembly 11, it is lowered vertically in place via the frustoconical channel 57 (which is open at the top to receive the screen assembly 11).

The frusto-conical shape of the channel 57 assists in guiding the screen assembly 11 into the outlet 55. Once the platform 29 is located on the top of the discharge 13, the seal 25 will seal with the outlet 55 (since the parts are dimensioned to locate the seal 25 vertically coincident with the outlet 55). It will be understood that where it is desired to site the platform 29 on the leach tank rather than on top of the discharge 13 (top of the channel 57), it is a simple matter to fabricate the screen assembly 11 with structural pipe members 27 (or other structure of the required length so that the seal 25 is in correct alignment with the outlet Referring to figure 4, an alternative sealing arrangement is disclosed. The sealing arrangement in figure 4 differs from the sealing arrangement shown in figure 3, in that the clamping member 63 has an outer edge 65 which extends closer to the wall of the outlet 55, reducing the rubber flexibility and hence oooo S•creating a greater sealing force, causing the seal to get a greater "purchase" on the wall. This arrangement should not interfere greatly with the force required to 20 break the seal when removing the screen assembly 11, since the distance between the flange 23 and the wall of the outlet 55 is the same as in the first •ooo• embodiment. In both arrangements of figures 3 and 4, the distance between the flange 23 and the wall of the outlet 55 is in the order of 20mm. The sealing arrangement of figure 4 can be employed as a "fix" where due to unforseen problems an adequate seal cannot be obtained with the arrangement shown in figure 3. In such circumstances, it is a simple matter to fabricate new clamping members 63 with the required increased diameter, to replace the original oooo• S•clamping members.

Referring to figure 5, a further alternative sealing arrangement is shown. The sealing arrangement of figure 5 differs from that shown in figure 3, in that there is -13provided a double seal arrangement, a second seal means 71 having like numbered parts and construction as the first seal means, the second seal means 71 being located below the first seal means. This embodiment would be utilised where operational difficulties which might lead to failure of either of the sealing arrangements shown in figures 3 and 4 is encountered. As will be understood, one of the features of the larger diameter in the clamping member 63 in the first (upper) seal means may be utilised in further embodiments where difficulties are encountered in the field, where due to unforseen problems an adequate seal cannot be obtained.

Referring back to figure 2, extending above the central tubular conduit 62 (toward the launder 59) is a frusto-conical portion 73 of the conduit, which frusto-conical portion 73 contains a rotary impeller 75 to form an impeller means. The central tubular conduit 62 and frusto-conical portion 73 together form an outlet for the screen assembly 11, to discharge slurry through the outlet 55 into the discharge 13 and launder 59. The impeller 75 is supported from a drive shaft 77 which is attached to the coupling assembly 47, for rotation of the drive shaft 77 with the drive shaft 33 (thus the impeller 75 rotates with the wiper 37). The drive shaft 77 extends down to and almost reaches the top of the conical base member 49.

Mounted to the bottom of the drive shaft 77 on a flange 79 is a bladed agitator S 20 81, the blades 83 of which have a pitched portion 85, and sweep close to the surface of the conical base member 49, in order to disperse any slurry which •"might otherwise settle on the member 49. The agitator 81 has four blades 81 in e* total.

Referring to figures 6 and 7, further detail of the drive shaft 77 and impeller 75 is shown. The impeller 75 is closed on its top by a circular plate 87 which in this embodiment has a diameter of 1070mm. The impeller 75 has four blades 89 which extend down from the plate 87 at 900 pitch (ie with the axial extent of the drive shaft 77). Each blade 89 has an arcuate length of 765mm, and the blades together prescribe a maximum rotational diameter of 1300mm at their upper tips 91 and 670mm at their lower tips 93. The lower inclined surface 95 of the blades 89 sweeps closely to the frusto-conical portion 73 of the conduit, and a discharge for slurry is provided in the area between the periphery of the circular plate 87 -14and the circle swept by the upper tips 91 of the blades 89.

Finally, referring to figure 2, located between the impeller 75 and the launder 59, in the fluid flow pathway, are a number of vertical vanes 97, provided to direct radial flow from the impeller 75, into the launder 59. The vanes 97 may be rotated about a vertical axis by rotation of a vertical pipe 99 to which they are attached. This allows for adjustment of the deflection of the flow of fluid from the impeller 75 to the launder 59.

Providing impeller means integral with the screen assembly and driven from the same drive as the wiper arms, assists in the flow of slurry through the tank train.

Particularly, the provision of the impeller means increases the capacity of the screen (especially useful in upgrade situations where a similar screen, less the pump means, would otherwise need to be replaced), and/or assists in maintaining the flow of slurry between tanks (especially useful in slurries which are characterised by poor flow qualities.

It should be appreciated that the scope of the invention is not limited to the specific embodiments described, and that changes may be made that will fall within the scope of the invention. Particularly, any dimensions given in this description are provided for illustrative purposes and assistance as to the scale of the embodiment, and variations from these dimensions may be made.

Claims (14)

1. A screen assembly having an outlet for fluid communication with an ore slurry outlet in a leach tank, said screen assembly having a filter screen to allow undersize ore slurry to flow therethrough while restraining oversize material, wherein said screen assembly includes located in a position in the ore slurry flow pathway between said filter screen and toward or in said ore slurry outlet, impeller means to urge said undersize ore slurry through said outlet and draw said undersize ore slurry through said filter screen, and wherein ore slurry within said outlet is always in fluid communication with ore slurry discharged from said leach tank whether the impeller means is operated or not. *o i2. A screen assembly as claimed in claim 1 wherein said impeller means *i comprises a rotary impeller.

3. A screen assembly as claimed in claim 2 wherein said impeller is located entirely submerged in said ore slurry.

4. A screen assembly as claimed in claim 2 or 3 wherein said impeller is :I o; located in a conduit which communicates with said outlet. S" 5. A screen assembly as claimed in claim 4 wherein said conduit is of circular cross-section, and said impeller has an axis extending with the axis of said conduit.

6. A screen assembly as claimed in claim 5 wherein said impeller has an axis substantially coaxial with the axis of said conduit.

7. A screen assembly as claimed in claim 6 wherein the conduit is of frusto- conical shape with its broader diameter terminating in said outlet, with the impeller being located within the frusto-conical portion of said conduit and having blades sweeping said conduit. -16-

8. A screen assembly as claimed in claim 7 wherein the blades have a pitch extending with the axis of said impellor, and operate to urge said ore slurry outwardly to flow toward the broader diameter of said conduit.

9. A screen assembly as claimed in claim 8 wherein the blades are curved so as to sweep the conduit with a trailing action. A screen assembly as claimed in any one of claims 2 to 9 wherein said impeller is mounted on a drive shaft assembly driven from above.

11. A screen assembly as claimed in claim 10 wherein filter screen is cylindrical in configuration and in use disposed with its axis vertical, one end of said filter screen being closed off to form a bottom of said screen assembly, with said outlet being located proximal to the other end of the screen assembly, and wherein the drive shaft assembly extends toward said bottom, and has an agitator mounted thereon proximal to said bottom to minimise settling and caking of said ore slurry at the bottom of said screen assembly.

12. A screen assembly as claimed in claim 11 wherein said conduit extends down toward said bottom to a position proximal to said agitator.

13. A screen assembly as claimed in claim 11 wherein a further conduit extends from said conduit to a position proximal to said agitator.

14. A screen assembly as claimed in claim 11 wherein said screen assembly includes agitator arms which travel around the outside of said filter screen, and are mounted to said drive shaft assembly for movement with said impeller. In a train of leach tanks, a leach tank having a screen assembly as claimed in any one of the preceding claims, said leach tank having a launder connecting with said ore slurry outlet for discharge of said ore slurry to the next leach tank in said train of leach tanks. -17-

16. In said train of leach tanks as claimed in claim 15, a channel portion located between said outlet and said launder, said channel portion having a narrow end connecting with said outlet, and a wide end accessible from above to allow removal and replacement of said screen assembly from and to said leach tank, said channel portion tapering generally between said narrow end and said wide end.

17. In said train of leach tanks as claimed in claim 16, said launder being fluidly connected to said channel portion through the wall thereof.

18. A screen assembly having an impeller substantially as herein described with reference to the drawings. .~cJ R~, S C Dated this Fifteenth day of January 200 U LYCOPODIUM PTY LTD Applicant Wray Associates Perth, Western Australia Patent Attorneys for the Applicant ooooe a