GB2271726A

GB2271726A - Rotary drum filter

Info

Publication number: GB2271726A
Application number: GB9318706A
Authority: GB
Inventors: Arthur Hanson; Clifford Michael Spiller
Original assignee: HERCULES SYSTEMS Ltd; OPTIMA HOUSE Ltd
Current assignee: HERCULES SYSTEMS Ltd; OPTIMA HOUSE Ltd
Priority date: 1992-09-09
Filing date: 1993-09-09
Publication date: 1994-04-27
Anticipated expiration: 2013-09-09
Also published as: GB9219111D0; GB9318706D0; GB2271726B

Abstract

An outward flow rotary filter comprises a drum whose peripheral filtering surface is built up of a plurality of segments connected together, possibly by welding but preferably by bolts connecting their abutting flanges 20, which extend axially of the drum. Vanes which extend into the drum to lift the solid residue as the drum rotates may be clamped between flanges 20, but the drum interior surface is otherwise smooth. The filtering surface of each segment may comprise a perforate plate or parallel wedgewires, which may be angled relatively in adjacent segments or parts of a segment to present a herringbone pattern. Wedgewires are welded to supporting struts, perpendicular thereto, and to flanges 20 at their ends. Circumferential flanges on the ends of the drum may be bolted to further drum sections or to drive means. The drum is supported by external wheels and encloses a solids discharge chute leading to a rotary screw elevator. <IMAGE>

Description

Improvements Relating to Rotary Screens This invention relates to improvements in the design and performance of screens which are commonly used to separate liquids and solids. Typically but not exclusively said screens are used to separate solids from slurries and effluents which are introduced into the screens and typically the said screen will be in the form of a rotary screen.

At present, rotary screens are used for many processes where it is required that two substances be separated. In particular the system is of use for the removal of waste solids from slurries before said slurry is discharged into the public waste disposal system thereby preventing unnecessary pollution of the said public waste system. It has been found that the said rotary screens can be used to filter solids from the waste slurries and the rotary screen has been identified as being an important part of the waste purification process.

It is currently known that rotary screens are provided in the form of drums which are so disposed as to be rotatable about the longitudinal axis. The said drums typically comprise a series of hoops of wedge wire construction, the said hoops displaced circumferentially around the drum or a series of wedge wires displaced longitudinally of the drum or the said drum walls are formed from perforated plate. Where wedge wire has been used, it has been found that problems exist in maintaining the strength of the said drum walls such that they can withstand the impact of solids held within the drum during rotation of the drum. These solids have been found to knock the said wedge wires out of shape and hence the drum can become distorted or twisted around the longitudinal axis hence causing the efficiency of the drum to be reduced.

Normally the slurry to be sorted by the rotary screen is introduced into the centre of the drum and is continuously introduced at a set speed while the drum rotates. Rotation of the drum has the effect of breaking the solids in the slurry into smaller parts and of also allowing the liquid of the slurry to pass through the wedge wire or perforated walls with the solids held within the drum. The spacing of the wedge wires is dependant upon the particular material or slurry which is to be sorted and hence the spacing of the wedge wire dictates the size of solids which are to be allowed therethrough.A further disadvantage of the known rotary screens is that, as they are produced from continuous strips of wedge wire or from sections of wedge wire which are welded together to form the drum, the rotary screen is in effect one part and thus any damage to the screen can only be repaired by, at best, cutting free the damaged area and then again welding a new part in place and, at worst, by replacing the entire screen. This is an expensive and time consuming task and disadvantages the user in that to replace one damaged section requires the replacement of the entire rotary drum.

Once the slurry has been introduced into the centre of the rotary screen, it is found that considerable weight is carried in the rotary screen and the screen is supported by support means which are also designed to power the screen in its rotational movement. It has been found that if the support means fails, the drum, if loaded, can fall from its axis of rotation and if rotation continues destructive failure can occur causing damage to the screen and the -drive mechanism.

It is also known to provide protrusions inside the rotary screen which serve to break up the solids of the slurries to be separated into smaller parts and prevent said solids from wrapping around the inside of the said rotary screen and hence preventing further separation of solids and liquid.

Normally the protrusions or support members are required to be used to support the wedge wires which form the screen.

The conventional theory is therefore that when using screens formed of wedge wire, suppport members are required to strengthen the wedge wires, to hold the same at the required distance apart and also to provide sufficient strength to the wedge wires such that they can resist impact of solids and that the integrity of the drum can be maintained during use.

Furthermore the provision of support members has conventionally been viewed as being necessary on the inside face of the drum and as such considerable time and effort has been spent in attempting to specify the minimum spacing of adjacent support bars and hence greatest strength which is possible without adversely affecting the sieving of the slurry.

The aim of this invention is to provide improvements to the construction of the rotary screen and the drive and supports therefore, such that the use of the screen is improved, the efficiency of said screen is improved and the cost of replacement of parts upon damage is also improved to the user.

The present invention relates to a rotary screen for the separation of materials, said screen comprising a drum mounted to be rotatably driven about its longitudinal axis wherein the wall of said drum is formed from a series of segments, each of said segments formed at least partially from a plurality of wires of wedge shaped cross section, said segments joined together to form the wall of the said drum and wherein intermediate the edges of at least one of said segments there is provided a plurality of spaced apart support members passing over and attached to said wedge wires to provide support therefor.

Preferably the said support members will be provided on the external surface of the wedge wires in the segment.

Typically said segments will be shaped such that when a series of said segments are fixed to each other, the drum will have the form of a cylinder; said cylinder having a substantially circular cross section.

The segments may in one embodiment have each of the longitudinal edges thereof welded to an edge of an adjacent segment to form the drum wall. Preferably each of said segments will be provided with flanges along the longitudinal edges thereof and said flanges will be provided with means such that adjacent flanges can be connected together to form the wall of the drum. Typically said segments will be joined together by means of bolts passing through the adjacent flanges and spaced along the length of the flanges.

Preferably the flanges will be provided such that the interior face thereof is substantially flush with the interior wall of the drum formed by the wedge shaped wires.

Typically the ends of the wedge shaped wires in the segment will be welded to the vertical face of the flange at a position such that the faces of the wedge wire facing to the interior of the drum are substantially flush with the interior face of the flange.

In one preferred embodiment there is provided between at least one pair of adjacent segment flanges a lifting stave which is fitted and maintained in position between the said flanges such that a portion of the said stave protrudes inwardly of the drum wall.

In one embodiment each of said segments is partially formed by a series of wedge wires which are displaced at an angle to the flanges of said segments.

Preferably said segments will be joined in sequence such that a "herringbone effect", is produced.

Said herringbone effect will be produced by the mounting of adjacent segments with the angle of the wedge wire in one of said segments being the negative angle of the angle of the wedge wire on the adjacent segments. The herringbone can in one embodiment be reproduced within one segment of the said rotary drum wall by the welding of wedge wire or by the provision of subsegments within the segment, each adjacent subsegment having wedge wire mounted at a different angle to that of the other subsegment.

In one embodiment each of said segments will be provided with a series of stiffener flats running perpendicularly to the flanges.

In a further aspect of the invention there is provided a series of segments so joined as to form a rotary drum wall wherein upon damage occuring to one of said segments it is possible to remove and replace the said damaged segment without the necessity to remove the remaining segments forming said drum wall.

In a further aspect of the invention there is provided a series of support wheels between which the said rotary screen is mounted wherein said series of support wheels includes at least one of said support wheels mounted below the axis of rotation of said rotary screen.

Said support wheels serve to increase the dynamic balance of the drum when in use and also preferably provide an anti destruct feature such that in the event of failure of the one of the upper support wheels the drum is prevented from dropping from its central axis of rotation, by the support wheels mounted below the axis of rotation.

In a further aspect of the invention there is provided a rotary screen for the separation of materials, said screen comprising a rotatably mounted drum wherein the walls of said drum are formed from a plurality of segments and each of said segments is formed at least partially of perforated plate and wherein there is provided location means along each of the longitudinal edges of the segments to allow said segments to be joined together to form the wall of the drum.

In one embodiment each of said segments is partially formed by perforated plates which have a series of perforations therein to allow liquid to pass therethrough In a further aspect of the invention there is provided an adaptable rotary drum wall wherein in the event of damage to the screening drum or a change to the screening specification where an increase or decrease in the available void area is required by changing the slot dimension of the wedge wire screens, there is provided an adaptive aspect wherein the segmented and bolted construction of the screen wall assembly enables the individual wall segments to be removed and replaced without dismantling the entire unit.

Typically the construction of the rotary screen will be based on a modular system wherein each element can be fixed to and removed from the body of the screen. Typically the drive outlet and inlet means will all be individual modules.

A specific embodiment of the invention will now be described with reference to the accompanying drawings wherein; Figure 1 shows an end view of the rotary screen assembly, from the rear end, Figure 2 shows an end view of the rotary screen assembly from the front end, Figure 3 shows a side view of a typical rotary screen assembly, Figure 4 shows a side view of a rotary drum wall of the invention, Figure 5 shows a plan of a rolled out drum wall illustrating the herringbone pattern, Figure 6 illustrates a perspective view of the joint between segments from the outside of the drum; and Figure 7 illustrates a cross sectional view through A-A of Figure 6.

Referring firstly to Figure 1 there is shown a rotary screen 2 of the invention. The rotary screen comprises a drum 4 mounted on support wheels 6 for rotation about a central axis 8 and a support frame 10 for the said screen assembly. A series of spray nozzles 14 are provided to spray liquid onto the drum hence preventing solids from sticking to the said drum walls and preventing efficient separation of material.

Referring now to Figure 2 there is shown a view of the said screen from the front end along with the discharge chute 16 which serves to allow the screened solids material to be discharged from the drum. The rotary drum 4, has a hollow centre 12 into which is introduced a slurry of material which is required to be separated. Also provided are a series of lifting staves 18 provided between adjacent flanges 20 of the segments 22 of the drum wall. The staves serve to lift the unwanted solids and fibres to discharge the same into the chute 16. It is necessary to remove the screenings and unwanted debris from the outlet end of the discharge chute to avoid debris returning into the incoming flow of liquid. A discharge elevator 39, by means of a rotating screw, transports the unwanted debris away from the rotating screen.

Figure 3 shows a side view of the said rotary screen 2 wherein there is shown in greater detail the joining of segments 22 to form the rotary drum 4. Each of said segments 22 is at least partially formed of wedge wire 24 which, in this embodiment, is mounted at an angular displacement to the length of the said segments. Typically the said wedge wire is at an angle of more than 0 degrees and less than 90 degrees to the side of the segment 22. The wedge wires 24 has not been shown in complete detail due to the intricacy of the wire however representative areas are shown to illustrate the herringbone effect which is produced. This herringbone effect is produced by joining said segments 22 such that the angle of wires of each adjacent segment differ such that the angle of wire in one segment is at a negative angle to the angle of the wire in the other segment as shown.

Figure 3 also illustrates the provision of the flanges 20 on the edges of the segments 22. Each segment includes the flanges 20, wedge wires 24, stiffener flats 38 and support members 26. None of these parts protrude inwardly of the interior wall of the drum and therefore the interior wall of the drum is formed solely by the interior faces of the wedge wires and is only interrupted by any lifting staves 18 which may be provided.

Figure 4 illustrates the rotary drum assembly 4 and further illustrates the method of bolting the segments 22 together.

The segments 22 are provided on each length 30 with bolting flanges 20. Said bolting flanges 20 are provided with holes which match with those on the flange of the adjacent segment and hence joining of the said segments is performed by passing bolts through the said holes and tightening the flanges together. Commonly the space between the said plates will be sealed to prevent any leakage through these joints and in one embodiment there will be placed and bolted between pairs of adjacent flanges 20 lifting staves 18.

Figure 5 illustrates a "rolled out" plan of the segments which when joined at ends 34 will form a rotary drum wall of the invention. Typically each of said segments will be shaped such that when joined a circular rotary drum is formed and each of said segments is again shown to be provided with a series of supporting bars 26 and stiffener flats 38 which run perpendicularly to the flanges 20. The supporting bars 26 are in this embodiment provided to run perpendicularly across the wedge wires 24. Again the herringbone effect produced by the angular displacement of the wedge wires is shown.

Referring finally to Figure 6, there is shown a perspective view of the construction of the join of the segments 20 wherein there is shown two segments 40 and 42 with wedge wire areas represented by 24. There is provided a frame 43 formed of the flanges 20 and side supports 46 surrounding the wedge wire and to which said wedge wire is welded. Each of the flanges 20 is provided with matching holes 44 through which bolts can be passed to secure the flanges and hence the segments together. Also provided between the flanges 20 is a lifting stave 18 bolted in place in conjunction with the said flanges. Also provided as part of the frames are side flanges 46, which are provided with bolt holes such that when the drum is constructed and all the segments joined, additional modules can be bolted thereon.Typically said modules could be inlet apparatus bolted to the front of the drum and/or outlet apparatus or the drum drive assembly.

Finally stiffener flats 38 and supporting bars 26 are provided on the external surface of the segments . The stiffener flats 38 are fitted by welding same to the frame 43 and wedge wires 24 and the supporting bars 26 are provided by welding the same to the wedge wires to strengthen the wedge wires and to maintain the gap between the said wires.

Typically the base of said wedge shaped wires will face inwardly of the drum.

Figure 7 illustrates a cross section through line A-A of Figure 7 wherein it can be clearly seen that the interior 50 of the drum is formed wholly by the interior faces 51 of the plurality of wedge wires 24. The ends of the wedge wire are welded to the flanges 20 on the side 52 thereof and at a point 53 such that the faces 54 of the flanges which are to face inwardly of the drum wall and the interior faces 51 of the wedge wires are substantially flush. The support bars 26 and stiffener flats (not shown) both lie on the external face of the wedge wires and are welded to the same to provide support therefor without breaking the interior wall surface.

Although the wedge wires 24 and support bars 26 are shown in an angled embodiment in Figure 7 it should be noted that the segments can also be provided with wedge wires which run perpendicularly to, and support bars 26 which run parallel with the flanges 20 of the segments 22.

In the embodiment where perforated plate is used flanges 20 and side plates 46 are again used to define each segment with perforated plate sections mounted between the flanges and side plates and attached to the flanges and side plates in a similar manner and in a similar relationship as with the wedge wires as discussed above.

The rotary screen 2 of the invention operates by serving to separate the liquid from the solids of the material to be sorted. The solids cannot pass through the wedge wire drum wall while the liquids are allowed to pass through and are collected at a point remote from the said rotary screen. The solids are lifted within the said rotary drum by the lifting staves 18 and carried in a circular motion until they are positioned in such a way that they are removed by gravity from the lifting staves and drop into the discharge flume.

The provision of a herringbone effect in the wedge wire of each of the segments, allows for the breakage of solids into smaller particles as the angling of the wedge wire to the introduction of the said material acts to cut into and break up the solids in the material. The fact that the drum wall is formed by a series of segments allows the easy replacement and removal of one or several of the said segments without the need to remove all of the said drum wall as is currently the case with known drums. The need to remove at least one of said segments can be due to damage occurring to one of said segments from the solids held within the drum or by the requirement to alter the width between the said wedge wire due to the processing of different forms of material.This ability to change the segments as required without the need to totally dismantle the rotary screen improves the adaptability of the rotary screen tremendously and therefore reduces costs to the user and allows the device to be efficiently working for a greater length of time without interruption and greatly reduces the downtime incurred when changes are required.

Importantly the provision of support bars and stiffener flats for the wedge wires, and if required for the perforated plate, in each segment act to maintain the integrity of the drum walls and by placing the same on the external surface of the segments it is ensured that the interior face of the drum is formed wholly of the internal faces of the wedge wire and the lifting staves. Thus there are no interior support members or bars on the interior wall surface and therefore the problem of solids and other debris wrapping around the interior support members is avoided.

The support wheels provided both above and below the axis of rotation of the cylinder which runs longitudinally of the said drum allows greater dynamic stability for the drum wall during rotation of the same. Typically at present only upper wheels are provided to support the said drum wall however the provision in this invention of lower support wheels allows a greater uniformity of rotation and hence acts to reduce damage to the drum should any of the upper support wheels fail by preventing the drum from falling from its central axis of rotation.

It is the advantages as so described, both individually and as a whole which we believe serve to distinguish the rotary screen of this application from rotary screens which are already known.

Claims

1. A rotary screen for the separation of materials in a slurry, said screen including a drum mounted to be rotatably driven about its longitudinal axis wherein the wall of said drum is formed from a series of segments, each of said segments formed at least partially from a plurality of wires of wedge shaped cross section, known as wedge wires, said segments, when joined to adjacent ones, forming the wall of said drum and wherein intermediate the edges of at least one of said segments there is provided a plurality of support members passing over and attached to said wedge wires to provide support therefor.

2. A rotary screen as in claim 1 wherein the support members on the segments which form the drum are provided on and attached to the face of the wedge wires which are external to the interior of the drum.

3. Support members as in claim 2 wherein the members are attached to the wedge wires perpendicularly to the direction of said wedge wires.

4. Support members as in claim 3 wherein said members are attached to the wedge wires by welding each of said members to at least a majority of said wires in the segment.

5. A rotary screen as in claim 1 wherein the drum is formed from a series of segments connected together and wherein each of said segments is provided with a flange along each of the longitudinal edges and said flanges are provided with means for the connection of the flanges of adjacent segments together.

6. Segments as in claim 5 wherein said segment flanges are provided with a series of apertures to match with apertures on an adjacent segment flange and to allow the passing through of bolts to connect the flanges and segments together.

7. Segments as in claims 5 or 6 wherein the segments which form the wall of the drum are shaped such that when the same are joined together a cylindrical drum is formed with a wall of substantially circular cross section.

8. A rotary screen as in claim 1 where the segments which form the drum are formed substantially from wire with wedge shaped cross section and, along longitudinal edges of the segments, flanges are provided, and wherein at each said edge of each segment the ends of the wedge wires abut with and are joined to a side face of the flange such that the face of the flange which faces the interior of the drum is substantially flush with the inwardly facing faces of the wedge wires.

10. Segments as in claim 9 wherein the ends of the wire are joined to the side of the flange by welding.

11. A rotary screen as in claim 1 wherein there is provided in the drum at regular intervals lifting staves, at least a portion of which protrude inwardly into the drum from the drum wall for the movement of the slurry and separated solids round the drum wall.

12. Lifting staves as in Claim 11 wherein the staves are supported in the drum by mounting portions of the same between flanges provided on the longitudinal edges of adjacent segments.

13. Lifting staves as in claim 12 wherein said staves are provided with connecting means similar to those provided on the flanges to allow the staves to be supported by the connection means for the flanges.

14. A rotary screen as in claim 1 wherein the wedge shaped wires provided in each of the segments are provided at an angle relative to the side edges of the segment of more than 0 degrees and less than 90 degrees.

15. Segments as in claim 14 wherein adjacent segments are joined together in such a manner that the relative angle of the wedge shaped wires in one segment is the negative angle of the wedge shaped wires in the other segment to form a "herringbone" effect around the wall of the drum.

16. Segments as in claim 14 wherein each segment includes a quantity of wedge shaped wires lying at an angle to the side edges of the segment and a further quantity of wedge shaped wires lying at the negative angle to the first quantity.

17. A rotary screen as in any of the preceding claims wherein there is provided on each segment a plurality of stiffener flats and wherein said flats are provided in connection with the external faces of the wedge shaped wires and to run perpendicularly to the longitudinal edges of the said segments.

18. A rotary screen for the separation of materials from a slurry, said screen comprising a drum mounted for rotation about a longitudinal axis and the wall of the said drum is formed from a plurality of segments, each segment formed substantially of perforated plate and wherein there is provided a connecting means along each longitudinal edge of the segment to allow the same to be joined together to form ~ho v.rnl 1 ozFI ho 19 A rotary screen as in claim 18 wherein the longitudinal edges of the perforated plate which forms each segment abut with and are joined to a side of the connecting means such that the face of the connecting means which faces inwardly of the drum is substantially flush with the interior face of the perforated plate.

20. A rotary screen as in claim 18 wherein there is provided a series of lifting staves around the drum and said staves are mounted between adjacent connecting means such that a portion of said stave protrudes inwardly from the drum wall.

21. A rotary screen as in any of claims 18 -20 wherein the connecting means are flanges which are welded to the abutting longitudinal edge of the perforated plate to form the segment.

22. A rotary screen as in any of the preceding claims wherein the drum is provided with a plurality of support wheels by which the said drum is rotatably mounted and wherein at least one of said wheels is mounted below the axis of rotation of said drum.

23. A rotary screen as in claim 22 wherein the series of wheels are provided in a configuration to ensure that should one of the wheels mounted above the axis of rotation of the drum fail the drum is prevented from falling by the support wheels mounted below the axis of rotation.

24. A rotary screen as in any of the preceding claims wherein the screen comprises a drum, a slurry supply inlet means and a solid waste deposits outlet means, and wherein said inlet and outlet means are separately removable and replaceable modules.

25. A rotary screen as hereinbefore referred to in the accompanying drawings.