GB2379175A

GB2379175A - Screening panel with debris elevator

Info

Publication number: GB2379175A
Application number: GB0120900A
Authority: GB
Inventors: Stephen Niel Hawes; Nigel Raymond Rogers
Original assignee: Ovivo UK Ltd
Current assignee: Ovivo UK Ltd
Priority date: 2001-08-29
Filing date: 2001-08-29
Publication date: 2003-03-05
Anticipated expiration: 2021-08-29
Also published as: GB2407782A; GB2379175B; GB2407782B; GB0120900D0; GB0500197D0

Abstract

A screening panel 1, which forms a component of a travelling band screen (Fig 5) for removing solid material from a flowing liquid in waste treatment plants, is moulded from a plastics material, is provided with a plurality of holes and incorporates a projecting lifting means, debris elevator 2, for lifting up the solid material. The plastics may be polypropylene and the holes may be tapered. The panels are joined together by inserting a ladder bar (21, Fig 2) into bearing eyes 4,5 to form a continuous endless belt mounted for movement around a closed path. Drive is transmitted to the belt via a sprocket (65, Fig 6) which engages the ladder bars.

Description

A Band Screen Assembly The present invention relates to a type of screening apparatus known as a travelling band screen, which is used to remove unwanted solid material from liquids flowing in channels.

A travelling band screen is a continuous travelling belt of screening panels which is installed vertically in, and above, a flow of water to be cleaned. The band screen can be arranged to rotate in a plane either parallel or perpendicular to the water flow. As the screen rotates, the panels may be designed to lift debris out of the flow of water. To do this, the panels may be arranged with buckets on their trailing edge, which lift up the debris on the screening side of the band screen. The water is allowed to pass through apertures in the panel. The apertures can vary in size depending on the level of screening that is required.

There are several problems with conventional band screens. A first is that the panels are difficult to clean effectively. Work has been done to improve the effectiveness of cleaning. For example in the Applicant's International Patent Application No PCT/GB91/00833, the panels are designed so that when they need to be cleaned, they form a continuous flat surface that can be cleaned effectively.

A second problem with conventional band screens is that when the panel is lifting heavy debris out of the water flow, the panels can be liable to deform, especially if

the panel is in the form of a mesh. It is therefore necessary to provide auxiliary mesh supports to prevent or reduce this deformation.

In addition, since the panels do not form a continuous belt at the point of screening, seals must be provided between the panels, and between the channel boundaries and band screen to prevent debris passing through the band screen unintentionally.

In conventional band screen assemblies the panels rotate by means of a chain which transmits the required band power. In total, there are therefore several components which need to be manufactured including the chain assembly, the panel, the auxiliary mesh supports, and the seals between panels. This adds significantly to the cost of manufacture. The large number of individual components means that the assembly is liable to running problems and it also means that it is difficult to exchange parts between different band screen assemblies since many components are not interchangeable.

It is an object of the present invention substantially to overcome or mitigate the above-mentioned problems of conventional band screen assemblies.

According to the invention, there is provided a screening panel for use in water and waste treatment plants for removing solid material from a flowing liquid by means of a plurality of screening panels, the screening panel being moulded from a plastics material, being provided with a plurality of holes and incorporating a

projecting lifting means for lifting solid material from the flowing liquid, the lifting means being incorporated into the moulding.

In an embodiment of the invention, the projecting lifting means is a projecting ledge angled at an acute angle to the vertical on the screening side of the screening panels when the screening panel is in the region of the flowing liquid to be screened. Preferably the projecting ledge is positioned at the bottom of the screening panel so that the debris being lifted is located on the projecting ledge between the projecting ledge and the screening panel to which it is connected.

However, the projecting ledge could be positioned at the top of the screening panel or at any position between the top and bottom of the screening panel.

Preferably the screening panel also includes strengthening means for strengthening the lifting means. Preferably the strengthening means is incorporated into the moulding. The strengthening means preferably comprises one or more stiffening webs.

Preferably the screening panel also includes connecting means for connecting the screening panel to at least one other screening panel.

Preferably the connecting means are such that when a plurality of screening panels are connected, they form a continuous screen. This means that no sealing is required between panels because no significant water flow can pass between the panels.

In an embodiment of the invention the connecting means are apertures for insertion of a linking piece.

In the embodiment described below, the linking piece is a substantially rigid rod which extends across the entire width of the linked screening panels.

In an embodiment of the invention the plastics material from which the panel is moulded is a thermoplastic material, for example, polypropylene.

Preferably the holes are formed during the moulding process. Alternatively the holes can be formed after the moulding process, for example by drilling. In an embodiment of the invention, the holes are tapered. The holes can be tapered such that the cross-sectional area of the hole is larger on the screening side of the panel, or such that the cross-sectional area of the hole is smaller on the screening side of the panel. It is preferable however that the cross-sectional area of the hole is smaller on the screening side of the panel so that any debris which passes through the hole can pass easily through to the other side and does not form a blockage. Preferably, the holes are circular in cross section.

According to the invention, there is also provided a band screen assembly comprising a continuous endless belt that includes a succession of screening panels together forming a band screen and that is mounted for movement around a closed path, the screen including projections at the edges of the screen for

transmitting the required drive to the screen as it moves around the closed path, the drive being transmitted from one part of the screen to another via the connections of screening panels.

In an embodiment of the invention the band screen moves around the closed path with the band screen aligned with the general direction of the water flow.

Preferably, the water flows into the centre of the closed path on the upstream side of the band screen assembly and then passes through the band screen to the outside of the closed path on the downstream side of the band screen assembly.

However, it is possible for the band screen to be arranged such that the water flows to the outside of the closed path on the upstream side of the band screen assembly and then passes through the band screen to the centre of the closed path on the downstream side of the band screen assembly.

Alternatively, it is possible for the band screen to be arranged such that it moves around the closed path with the band screen perpendicular to the general direction of the water flow.

Preferably the band screen assembly also includes a guide for guiding the projections around the closed path. Preferably the guide includes at least one guiding surface for guiding the projections around the closed path and an end surface for defining the extreme edge of the band screen. In an embodiment of the invention the at least one guiding surface and the end surface are incorporated into one moulding. As described below, the guide may be in the form of a channel

with a guiding surface on either side of the channel and an end surface at one end of the channel. By including the guiding surfaces and the end surface into one moulding, the number of components required is reduced.

Preferably, the projections are located in the region where two adjacent screening panels join. Preferably the projections are located on linking pieces which link adjacent screening panels together. In an example described below, the linking pieces are substantially rigid rods which extend across the entire width of the linked screening panels.

Preferably guide rollers are mounted on the ends of the linking pieces. With such an arrangement the band screen can rotate smoothly around the closed path with the rollers contained within the guide. The rollers may roll along the guiding surface (s).

Preferably the band screen assembly also includes sealing pieces for inhibiting water flow between the screening panels and the guide. Preferably the sealing pieces are located between the screening panels and the guide. In an example described below each sealing piece is identical and when several sealing pieces are linked they form a continuous seal face. The sealing pieces can simply be reversed from one side of the band screen to the other.

In an embodiment of the invention, the band screen is held together only by the lateral constraint of the guide. In an example described below, the screening

panels, sealing fins and rollers all fit onto the linking pieces. The pieces are held onto the linking pieces only because of the lateral constraint of the guide.

By way of example, an embodiment of the invention will now be described with reference to the accompanying drawings, of which Figure 1 is a perspective view of an individual panel ; Figure 2 is a perspective view of four panels, linked ; Figure 3 is a rear view of a continuous screen of panels; Figure 4 is a perspective view of a seal fin; Figure 5 is a longitudinal sectional view of the band screen assembly installed in a channel ; Figure 6 is an enlarged view of the top part of the band screen assembly; Figure 7 is a view of the sprocket and gear unit along the line VII in Figure 6; and Figure 8 is a view of one edge of the band screen along the line VIII in Figure 5.

Figure 1 shows a moulded panel 1 according to the present invention. The panel is moulded in one piece from plastics material. The panel includes a debris elevator 2 and a screening section 3. The angle between the debris elevator 2 and the screening section 3 is an acute angle 8. At each side of the panel stiffening web 6 is provided which strengthens the debris elevator and prevents deformation when heavy debris is being lifted out of the water flow. The stiffening web 6 is incorporated into the moulding. The moulded panel incorporates bearing eyes 4 at the top of the panel and bearing eyes 5 at the bottom of the panel. This allows

individual panels to be linked together as described below with reference to Figures 2 and 3. The dimension marked a on Figure 1 is referred to as the pitch of the panel. The dimension marked b is referred to as the width of the panel. In a particular embodiment of the invention the pitch of the panel a is 200 mm, the width of the panel b is 150 mm and the angle 0 between the debris elevator 2 and the screening section 3 is 75 .

Figure 2 shows in perspective four panels 1 which are linked together. Because the panels form a continuous screen no sealing is required between panels. The panels are identical and a screen of the desired width can be made up from several panels adjacent to one another. The total width of the screen is referred to as B. The bearing eyes 4 and 5 are located such that two panels can be linked together by a ladder bar 21. The ladder bar 21 passes through the top bearing eye 4 of one panel followed by the bottom bearing eye 5 of the above panel and so on, so that the panels are linked. The ladder bar 21 is circular in cross section and the length of ladder bar used depends on the required total width B of the screen. On each end of the ladder bar 21 is a simple tubular roller 22, which may be moulded or machined from stock plastic bar. The ladder bars effectively take the place of a chain and no separate chain assembly is required.

Figure 3 shows a continuous screen of panels. In this example five panels are linked adjacent to one another so that the total width B of the screen is five times the width of one panel b. The bearing eyes 4 and 5 are positioned on each panel so that the top bearing eye 4 of one panel fits snugly with the bottom bearing eye 5

of the panel immediately above. This means that there is no gap between the panels or between the bearing eyes so that the panels form a continuous screen and no sealing is required between panels. The ladder bar 21 passes through the bearing eyes and the rollers 22 on each end of the ladder bars 21 travel along a nylon guide (not shown in Figure 3) as will be described below with reference to Figure 8. At the end of each row of panels, between the screen and the rollers 22 of each ladder bar 21 is located a seal fin 32. The seal fin is described in more detail below with reference to Figure 4. The seal fin 32 receives the screen on one side and abuts the nylon guide (not shown) for the rollers 22 on the other side, thereby removing any gap between the guide and the screen. This prevents water bypassing the screen. Each panel is constructed with a plurality of apertures 31.

The size of the apertures 31 depends on the level of screening that is required.

The apertures 31 are formed by moulding and are such that the diameter of the holes is smaller on the screening side of the panel. This ensures that if a solid body in the water flow enters a hole from the screening side, the object can pass through the hole completely and does not remain in the hole causing a blockage.

Figure 4 shows a seal fin 32 in more detail. The seal fin 32 is moulded with three parts. The first part on the outside of the seal fin is formed with a first projection 41 containing an aperture 42. The second part at the centre of the seal fin is formed with a second projection 43 containing an aperture 44. The first projection 41 is a third the width of the entire seal fin 32 and is positioned towards the outside of the seal fin 32. The second projection 42 is also a third the width of the entire seal fin 32 and is positioned at the centre of the seal fin. The third part on the inside of the

seal fin is formed with a slot 46 in the central portion 45 of the seal fin 32, which receives the screening section 3 of a panel 1. Adjacent ladder bars 21 pass through the apertures 42 and 44. When the screen of panels is assembled, the first aperture 41 of the first seal fin abuts the second aperture 42 of the second seal fin and a ladder bar 21 passes through the adjacent apertures 42 and 44 in the two seal fins. The seal fins form a continuous seal face which removes any gap between the screen and the nylon guide for the rollers 22. It will be appreciated that only one form of seal fin is required since the seal fins can simply be reversed from one side of the band screen to the other.

Figure 5 shows a longitudinal sectional view of the band screen assembly installed in a channel. The water flow is perpendicular to this cross section. In this embodiment, the water passes into area 51 on the upstream side of the band screen assembly, passes through the band screen and passes into area 52 on the downstream side of the band screen assembly. The water is prevented from flowing directly into area 52 without passing through the band screen by seals (not shown) at the edge and bottom of the band screen assembly and at the downstream end of area 51. The screening side 53 of the band screen is on the inside of the rotation path 54. The band screen rotates around the path 54 in the direction shown by the arrows. The top part of the band screen 57 is canted over to one side to allow more effective cleaning. The water level is indicated at 55, so that the bottom part of the screen 56 is in the flow of water and the top part of the screen 57 is above the flow of water. The debris settles on the debris elevators 2 at the bottom part of the screen 56, is lifted out of the water flow as the band

screen rotates and is removed from the debris elevators 2 at the top part of the screen, as will be described below with reference to Figures 6 and 7.

The top part 57 of the band screen assembly is shown in more detail in Figures 6 and 7. The direction of rotation is shown by the arrows. The top part of the band screen is contained between side plates (not shown). The bottom edge of each side plate is indicated at 61. Each panel 1 moves upwards in region 62 along the rotation path 54. As the rotation path 54 curves inwards, the debris elevator 2 on each panel 1 becomes angled towards the inside of the rotation path 54 and the debris on each of the debris elevators 2 falls into the debris discharge hopper 63.

The debris discharge hopper may be constructed from a piece of sheet metal and is formed in the shape of a trough. The debris discharge hopper 63 is welded at each end to one of the side plates. The debris discharge hopper includes a projection 64, which prevents any debris that falls off the debris elevator 2 overshooting the debris discharge hopper 63 and falling back into the water flow.

Above the debris discharge hopper 63 and on the outside of the band screen is positioned a wash water jet pipe 68 which extends along the width B of the band screen for cleaning the band screen. The curvature of the rotation path 54 towards the top part of the band screen allows the wash water jet pipe 68 to be angled more directly over the debris discharge hopper 63.

In use, once the panel has passed the debris discharge hopper 63 and the wash water jet pipe 68, it then moves towards the sprocket 65. Each ladder bar 21 fits into a notch 66 on the sprocket 65. It will be appreciated that each panel is

substantially rigid and therefore as the screen rotates around the sprocket 65 the panels do not move in a continuous circular path. Instead they move in a polygonal path with the ladder bars 21 at the edge of the screen fitting into the notches 66 on the sprocket 65. The sprocket 65 is driven by a gear unit 67 via a head shaft 69. That drive is transmitted from sprocket 65 to the ladder bars 21 that are at that time in engagement with it and is then transmitted to the screening panels via the ladder bar connecting between the panels.

Figure 8 shows the edge of a part of the band screen in more detail. The panels shown are linked by the ladder bar 21 and the tubular roller 22 on the end of the ladder bar 21 fits into the nylon guide 81. The nylon guide 81 is attached to and protrudes from the side frame 82. The nylon guide 81 is formed in a U-shape. The nylon guide includes a side thrust wearing surface 83 and roller surfaces 84 and 85. It can be seen in Figure 8 that, without the seal fins 32 there would be a gap between the nylon guide 81 and the panel 1 which would allow water to pass to the downstream side of the band screen assembly without being screened. The seal fins 32 seal this gap since they extend outwards further than the panels 1 and they create a continuous seal face. The screen is constructed with all slip-on parts.

The panels 1, ladder bars 21, seal fins 32 and tubular rollers 22 all hold together because they are contained within the nylon guide 81 and the side frames 82. The nylon guide 81 and side frames 82 therefore extend around the complete path of the band screen. In this embodiment, a wave spring 86 is also included to push the panels together and to push the seal fins 32 towards the nylon guide'81. This could equally be replaced by a resilient foam disc or similar.

Claims

CLAIMS :

1. A screening panel for use in water and waste treatment plants for removing solid material from a flowing liquid by means of a plurality of screening panels, the screening panel being moulded from a plastics material, being provided with a plurality of holes and incorporating a projecting lifting means for lifting solid material from the flowing liquid, the lifting means being incorporated into the moulding.

2. A screening panel according to claim 1 in which the projecting lifting means is a projecting ledge angled at an acute angle to the vertical on the screening side of the screening panels when the screening panel is in the region of the flowing liquid to be screened.

3. A screening panel according to claim 1 or 2, also including strengthening means for strengthening the lifting means.

4. A screening panel according to claim 3 in which the strengthening means is incorporated into the moulding.

5. A screening panel according to any one of the preceding claims, also including connecting means for connecting the screening panel to at least one other screening panel.

6. A screening panel according to claim 5, in which the connecting means are such that when a plurality of screening panels are connected, they form a continuous screen.

7. A screening panel according to claim 5 or 6 in which the connecting means are apertures for insertion of a linking piece.

8. A screening panel according to claim 7 in which the linking piece is a substantially rigid rod which extends across the entire width of the linked screening panels.

9. A screening panel according to any one of the preceding claims in which the plastics material is a thermoplastic material.

10. A screening panel according to any one of the preceding claims in which the holes are formed during the moulding process.

11. A screening panel according to any one of the preceding claims, in which the holes are tapered.

12. A screening panel according to any one of the preceding claims in which the holes are circular in cross section.

13. A band screen including a plurality of screening panels, each panel being according to any one of the preceding claims.

14. A band screen assembly comprising a continuous endless belt that includes a succession of screening panels together forming a band screen and that is mounted for movement around a closed path, the screen including projections at the edges of the screen for transmitting the required drive to the screen as it moves around the closed path, the drive being transmitted from one part of the screen to another via the connections of screening panels.

15. A band screen assembly according to claim 14 also including a guide for guiding the projections around the closed path.

16. A band screen assembly according to claims 14 or 15 in which the projections are located in the region where two adjacent screening panels join.

17. A band screen assembly according to claim 16 in which the projections are located on linking pieces which link adjacent screening panels together.

18. A band screen assembly according to claim 17 in which the linking pieces are substantially rigid rods which extend across the entire width of the linked screening panels.

19. A band screen assembly according to claims 17 or 18 in which the guide rollers are mounted on the ends of the linking pieces.

20. A band screen assembly according to any one of claims 14 to 19 also including sealing pieces for inhibiting water flow between the screening panels and the guide the sealing pieces being located between the screening panels and the guide.