GB2287200A

GB2287200A - Improved Screening Panels

Info

Publication number: GB2287200A
Application number: GB9504413A
Authority: GB
Inventors: Arthur Hanson
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-03-05
Filing date: 1995-03-06
Publication date: 1995-09-13
Also published as: GB9504413D0

Abstract

This invention relates to the provision of a panel for use in the screening of solid material from a slurry. Said panel includes a plurality of slots which are arranged in sets and each of said sets is angularly displaced and/or offset from adjacent sets to allow the liquid to be screened more efficiently and to encourage the liquid to be screened substantially in one direction. <IMAGE>

Description

Improved Screening Panels The present invention relates to the field of screening of any liquid/solid mixture herein referred to as slurries by causing the slurry to pass onto a screening panel or a plurality of said panels. The screening panels are provided with a plurality of apertures formed, therein said apertures of a dimension to allow the liquid and fine particles of the slurry to pass therethrough but preventing the solids carried in the slurry from passing through the screen.

Conventionally the screens are manufactured from either of a plurality of wedge wires held at spaced distances apart by support bars or by winding said wedge wires around the support bars to form a screen drum. Alternatively it is possible to produce screening panels from wire mesh material or from panels of plastics or steel material provided with a plurality of perforations moulded or stamped therein.

This invention is specifically directed toward improving the effect of the perforated type of screening panel which has been in use for a considerable period of time in various industries which require to separate solids from liquids such as food processing, sewage treatment, waste processing.

With the advent of plastics material several screens are manufactured in plastic and two typical screens are detailed in GB Patent No. 1521255 and International Patent Application No. WO 9117808. The screen described in the British Patent discusses the problems of conventional plastics perforated screens which include the gathering of the screened solids material around the perforations to block the same and a further problem when the fibres double over a "hairpin" around the apertures. To overcome this problem it is stated that the depth of each perforation must be greater than or equal to the perforation's greatest width.

The International application discloses the feature ofthe perforations being formed in the plastics material as the material is being moulded to form the screening panel. It is claimed that by forming the screen in this way the screening efficiency is improved due to the removal of sharp surfaces around the peripheries to snag the fibres and solids in the slurry. The International application also discloses the possibility of tapering the perforations outwardly from the face upon which the slurry impacts thus allowing the improved flow of the liquid and fine particles therethrough and mimicking the effect produced when using a screening wire formed from wedge wires.

However, neither of the prior art screening panels address the problem of the solids which are carried in the slurry being transported across the surface of the screening panel and the possibility of the solids escaping through the apertures as they are carried by the flow of the slurry. In the conventional screening panels it is possible for the slurry to pass along a relatively continuous path and as it does so for the same to gather speed. This speed can be sufficient to cause solids, which normally would not pass through the apertures, to do so due to the effect of the speed of the slurry in which they are carried squeezing the solids through the apertures.

The aim of the present invention is to provide a screening plate with perforations in the form of slotted apertures formed therein, the perforations positioned such that the path of the flow of the slurry is interrupted by the perforations thereby breaking and reducing the speed of flow of the slurry across the screen panel and allowing the liquid to pass in substantially one direction and the solids in another.

The present invention provides apparatus for screening and separating solids and liquid material in a slurry said apparatus including at least one screening panel which passes through, or onto which is applied, the slurry, said panel incorporating a plurality of slotted apertures therein, and wherein said slotted apertures are arranged in sets with their longitudinal axes in parallel with either of a first plane or a second plane which is angularly displaced to the first plane and said panel is arranged in the apparatus with respect to the introduction of the slurry in a manner to cause the separated liquid to pass substantially in a first direction which allows the same to be further separated from the solids.

Typically the first direction is substantially in the direction of a first plane of the sets of slotted aperture and the second direction is substantially in the direction of the second plane of slotted apertures.

In a preferred embodiment the screening panel is formed with sets of slotted apertures formed therein such that each set, apart from those around the periphery of the panel, has six sets adjacent thereto, four of said sets angularly displaced thereto and the remaining two offset. Typically the two offset sets are parallel to the first set and the four angularly displaced sets are arranged perpendicularly to the first set. Preferably each set comprises three parallel slots of substantially equal length.

The embodiment of the screening panel can also be described as having successive diagonal lines of sets passing therealong with alternate lines of vertically and horizontally arranged sets characterised in that each repeated line of horizontally displaced sets is offset with respect to the last and each repeated line of vertically displaced sets is offset with respect to the last.

Preferably the length of the slots in either of the horizontally or vertically disposed sets will be greater than the length of slots in the perpendicular sets.

Typically the offset distance between sets on the repeated lines is equal to the width of one of the said slots. The width of the slots will depend on the type of slurry being screened. Preferably each slot is provided with walls which taper outwardly away from the face of the panel upon which the slurry impacts. The angle of taper is in one embodiment 2.3 degrees from the vertical.

A further aspect of the invention provides a screening panel for slurry material, the panel incorporating a plurality of slots to allow the passage of liquid and smaller particulate material therethrough characterised in that the slots are arranged in sets and each set comprises a plurality of parallel slots and is angularly displaced and/or offset from each set adjacent thereto.

Typically the slurry to be screened is any of; sewage effluent, digested sludges, tankered sludges, food slurries, industrial effluent or any mixture where it is desired to separate the solids held in the mixture from the liquid and smaller particles. The size and dimensioning of the slots of the screening panels is dependent on the particular application to which they are to be put.

In one embodiment the screening panel is provided in a fixed position onto which the slurry is passed. Alternatively the panels can be fitted to a moving belt or band screen where the panels are designed to travel around an endless path which passes into and out of the slurry.

In a further embodiment one, or a plurality of panels are joined at their edges joined to form a drum screen of a type mounted for rotation about its longitudinal axis such that the drum passes through the slurry medium or, alternatively the slurry is introduced onto the panels of the drum as the same rotates.

In whichever form the screening panel is used it is preferred that the panel be formed from a plastics material and particularly from a material known as Ultra High Molecular Weight Polyethylene or UHHWP. When the panel is formed from plastics material the slotted apertures can be punched therein or machined.

Alternatively the panel can be formed from a plurality of wires which are joined together and angularly disposed to create the slotted aperture arrangement disclosed herein.

A specific embodiment of the invention is now described with reference to the accompanying drawings wherein; Figure 1 illustrates a screening panel of the invention; Figure 2 illustrates part of the panel of Figure 1 in greater detail; and Figure 3 illustrates a cross sectional view through line AA of one of the sets of slots.

Referring firstly to Figure 1 there is shown a screening panel 2 of the invention. The panel is formed with a supporting and jointing frame 4 around its periphery. The majority of the panel is formed from UHMWP and said material has formed therein, typically by machining of the same, a plurality of perforations in the form of slots 6.

Figure 2 illustrates a detailed section of the panel 2 and in particular illustrates a layout of the slotted apertures 6 in the panel 2. In this embodiment the slots 6 are arranged in sets 8 each having three slots. Each set 8 includes three slots 6 of equal length and the sets can be split into two groupings, a first grouping 9A with sets which are disposed horizontally in parallel with the X-axis plane and a second grouping 9B which are disposed vertically and parallel with the Y-axis plane. Thus the travel path of the elements of the slurry is dictated by the positioning of the slots in the screen and the flow of the slurry liquid travelling over the screen will be along the horizontal slots, hence the X-axis, and the screenings and solids travel on the Y-axis. In this embodiment the slots in the grouping 9A are shorter in length than the slots in the grouping 9B. However the screen would be equally effective if the lengths of slots was reversed between groupings, as if the slots were all of the same length.

The sets 6 of the slots in each grouping 9A, 9B, are offset in relation to each adjacent set. For example set 6A in grouping 9A is horizontally and vertically offset in relation to adjacent set 6B which is in turn offset in relation to set 6C and so forth to give a step effect. This offset displacement is repeated in the adjacent sets of slots in grouping 9B. By providing the sets in this offset arrangement the overall pattern obtained is of a series of diagonal lines 10 of sets 6 with the sets 6 in one line lOA arranged perpendicularly to the sets 6 in the adjacent lines lOB.

Referring now to Figure 3 there is shown a cross sectional elevation of a set 6 of slots 3. It is clearly shown that the side walls 12 of each slot are tapered wherein the angle is approximately 2.3 degrees off the vertical plane. The slots are tapered such that the narrower opening 14 faces the flow of the slurry as indicated by arrow 16. By providing tapered slots 14 in this form the exit of the separated liquids and finer particulate material is encouraged and the opportunity for the slots to clog up greatly reduced.

The provision of a screening panel with the configuration of slots shown greatly improves the screening efficiency over conventional screening means as the material being filtered from, for example when the screening panel is incorporated in a drum, as a moving rotational screen, will never be able to follow a continuous path because of the staggered pattern of the slots. Thus the travel path of the slurry will be interrupted thus minimising the chance of solids escaping through the slot and at the same time the offset of the perpendicular slots is used to provide an increase in the capture rate of the filtering process. Additionally the arrangement of the perpendicular slots in the manner described increases the evacuation rate of the filtered effluent liquid, by encouraging flow of the liquid in one direction.

When the screening panel is to be used individually or in conjunction with a plurality of panels to form a drum screen the panels will be formed into a cylinder or arcuate shape.

However the improved effect of the offset, in this case axial and radial, of the sets of slots will remain.

Claims

1. Apparatus for screening and separating solids and liquid material in a slurry said apparatus including at least one screening panel which passes through, or onto which is applied, the slurry, said panel incorporating a plurality of slotted apertures therein, and wherein said slotted apertures are arranged in sets with their longitudinal axes in parallel with either of a first plane or a second plane which is angularly displaced to the first plane and said panel is arranged in the apparatus with respect to the introduction of the slurry in a manner to cause the separated liquid to pass substantially in a first direction which allows the same to be further separated from the solids.

2. Apparatus according to Claim 1 wherein the screening panel is formed with sets of slotted apertures formed therein and, at least each set removed from the periphery of the panel, has six sets of slots adjacent thereto, four of said sets angularly displaced thereto and the remaining two parallel but offset.

3. Apparatus according to Claim 2 wherein the two offset sets of slotted apertures are parallel to the first set and four angularly displaced sets of slotted apertures are arranged perpendicularly to the first set.

4. Apparatus according to any of the preceding claims wherein each set comprises three parallel slotted apertures of substantially equal length.

5. Apparatus according to Claim 1 wherein at least one screen panel is provided with sets of parallel slotted apertures, said sets arranged in successive diagonal lines across said screening panel surface with alternate lines of vertically and horizontally arranged sets and characterised in that each repeated line of set of horizontally displaced slots is offset with respect to the last and each repeated line of set of vertically displaced slots is offset with respect to the last.

6. Apparatus according to Claim 5 wherein the length of the slotted apertures in the sets disposed in a first plane is greater than the length of the slotted apertures in the sets in the second plane.

7. Apparatus according to any of the preceding claims wherein the offset distance between adjacent sets in the same direction is substantially equal to the width of the slotted apertures.

8. Apparatus according to Claim 7 wherein the width of the slotted apertures is dependent on the type of slurry to be screened.

9. Apparatus according to any of the preceding claims wherein at least some of the slotted apertures have tapered walls.

10. Apparatus according to Claim 9 wherein the taper on the walls of each slotted aperture is such that the walls taper outwardly away from the face of the panel on which the slurry impacts.

11. Apparatus according to Claim 9 or 10 wherein the angle of taper is 2.30 from the vertical.

12. A screening panel for use in screening solids from liquids in a slurry said panel incorporating a plurality of slotted apertures to allow the passage of liquid and smaller particulate material therethrough and characterised in that the slots are arranged in sets and each set comprises a plurality of parallel slots and is angularly disposed and/or offset from each set adjacent thereto.

13. Apparatus according to any of the preceding claims wherein the slurry to be screened is any of or any combination of, sewage, effluent, digestive sludges, tanker sludges, food slurries, industrial effluent or any mixture where it is desired to separate solid matter held in the mixture from the liquid and smaller particles.

14. Apparatus according to any of the preceding claims wherein the screening panel is provided in a fixed position and onto which the slurry is applied.

15. Apparatus according to any of the preceding claims 1 to 13 wherein a plurality of panels are fitted to a moving belt or band screen wherein the panels are provided for movement into and out of the slurry.

16. Apparatus according to any of Claims 1 to 13 wherein a plurality of panels are joined edge to edge to form a drum screen mounted for rotation about its longitudinal axis.

17. Apparatus according to any preceding claim wherein the panels are curved.

18. Apparatus according to any preceding claim wherein the screening panels are formed from a plastics material.

19. Apparatus according to claim 18 wherein the apertures are punched into the plastics material.

20. Apparatus according to Claim 18 wherein the plastics material is ultra high molecular weight polyethylene or UHMWP.

21. Apparatus as herein described with reference to the accompanying drawings.