GB2370999A

GB2370999A - A screening device with a rotating cleaning member

Info

Publication number: GB2370999A
Application number: GB0100754A
Authority: GB
Inventors: Gareth David Thomas
Original assignee: Mono Pumps Ltd
Current assignee: NOV Process and Flow Technologies UK Ltd
Priority date: 2001-01-11
Filing date: 2001-01-11
Publication date: 2002-07-17
Also published as: GB0100754D0

Abstract

A screening device comprises a part-cylindrical chamber, horizontally disposed with an inlet in a first side and a screened outlet in a lower portion of a second side, and a rotatable cleaning member 3 disposed within the chamber for sweeping the screened outlet 14. The cleaning member 3 may comprise a plurality of radially mounted blades (4, Fig 1) that extend for substantially the whole length of, and parallel to, the axis of the chamber, and may be provided with sealing strips 8 or brushes. The bottom of the inlet may be disposed higher than the bottom of the outlet to provide a head of water sufficient to rotate the cleaning member. Alternatively, both inlet and outlet may be at the same height and if required an additional power source e.g. electric motor may be provided to rotate the cleaning member. The chamber may be formed in sections comprising of a deflector plate 7 to ensure a sufficient head of water, a shield plate 6 to prevent large items of debris form being ejected at outlet, and a screen panel 2. The screen panel may be replaceable and may comprise a fixed grid which supports a replaceable mesh. Preferably each section extends approximately one quarter of a circle with an open final quarter that forms an inlet. The screening device may be used in municipal wastewater channels or riverbanks to prevent debris from reaching overflow channels(12, Figs 3 and 4).

Description

SCREENING DEVICE

The present invention relates to screening devices, principally but not exclusively for use in screening overflow in municipal wastewater channels or riverbanks and water abstraction from, e. g. , rivers.

Channels taking municipal wastewater, e. g. to water filtration or treatment plants, often need to be provided with overflow channels to cope with higher than normal flow volumes, e. g. in the event of a storm. Waste water will generally include both floating and suspended debris, particularly in the event of a storm, and it is desirable to keep this debris out of the overflow channel to prevent the overflow channel being blocked and because the overflow channel may well bypass the water filtration and treatment plant. A simple grid or mesh may be provided between the wastewater channel and overflow channel, but this will quickly become blocked with debris. To prevent blockages, it is known to provide a part cylindrical static screen, lying with its axis parallel to the surface of the water, which is kept clean by a rotating helical brush. In installations where power cannot be provided, or for economy, the helical brush may be driven by a water wheel which is driven by the flow of water into the overflow. To provide sufficient power to drive the helical brushes, the waterwheel is generally positioned in parallel with the screen and thus provides a route whereby debris may enter the overflow channel. There is therefore a need for an improved screening device suitable for use in, e. g. municipal wastewater channels to prevent debris reaching overflow channels.

According to the present invention there is provided a screening device comprising a horizontally disposed, generally cylindrical chamber, said chamber having an inlet in a first side and a screened outlet in a lower portion of a second side; and a rotatable cleaning member disposed within said chamber so as to sweep said screened outlet.

Preferably, the flow of water through the device drives the rotating brush to sweep the screened outlet and keep it free of debris, preventing blockages. In high flow situations, the inlet and outlet can be at the same height but if such an arrangement does not result in sufficient flow to drive the rotating cleaning member, the bottom of the inlet can be located higher than the bottom of outlet to provide a head of water. The

debris which does not pass through the screened outlet is swept around the inside of the chamber by the rotatable cleaning device and returned via the inlet. Where the inlet and outlet are at the same level, the retention of debns in the device when it is not operating is minimised.

The rotatable cleaning member preferably comprises a plurality of radial blades extending parallel to the axis of said chamber for substantially all the length of said chamber. In this arrangement, the radial blades provide the greatest area on which the pressure of the water flow can act to drive the rotating brush to rotate. The ends of the radial blades may be directed backwards relative to the direction of rotation of the rotatable brush in use and may be provided with a flexible sealing strip or brushes to make a seal to the wall of the chamber.

The invention will be further described below with reference to an exemplary embodiment and the accompanying drawings in which: Figure 1 is a sectional end view of the screen according to an embodiment of the invention ; Figure 2 is a view similar to Figure 1 showing the operation of the screen according to the embodiment of the invention; Figure 3 is a cross-section through a municipal wastewater channel with a screen according to the invention installed; and Figure 4 is a view similar to Figure 3 but with the wastewater channel in an overflow condition.

In the various drawings, like parts are indicated by like reference numerals.

The screen shown in Figure 1 comprises a framework 1 which supports a generally cylindrical chamber formed by a deflector plate 7, screen panel 2 and shield plate 6. The deflector plate 7, screen panel 2 and shield plate 6 each, in section, extend around approximately a quarter of a circle with the fourth quarter being left open. In use, the chamber is disposed with its axis generally horizontal so that the open quarter is

in an upper part of the side receiving the liquid flow and the screen panel in the lower portion of the other side and opening into the channel for screened liquid. In this arrangement, liquid, usually water, can flow in the open quarter and out of the screen panel 2. The open quarter then forms an inlet and the screen panel forms a screened outlet. The screen panel 2 may take any suitable form to pass only debris of a certain

minimum size. The screen panel 2 may be replaceable and may comprise a fixed grid which supports a replaceable mesh with smaller holes.

To prevent the screen panel 2 becoming clogged with debris that is too large to pass through it, a cleaning drum 3 is provided. This comprises a plurality of blades 4 mounted radially. The cleaning drum 3 is rotatably mounted by bearing assembly 5 concentrically within the cylindrical chamber formed by deflector plate 7, screen panel 2 and shield plate 6. The blades 4 act as a water wheel so that the cleaning drum 3 is driven to rotate by the flow of water from the inlet to and out of screen panel 2. End portions of the blades 4 may be angled backwards relative to the direction of rotation in use of the device and are provided with sealing strips 8 or brushes to provide a seal to the walls of the chamber and also effect the cleaning of the screen panel 2.

The deflector plate 7 is provided in this embodiment to ensure a good head of water to provide sufficient power to drive the cleaning drum 3. However, the screen may retain solid debris when the cleaning drum stops rotating and so the deflector plate 7 is preferably omitted in applications where a sufficient head of water to drive the cleaning drum can be expected.

The use of the apparatus is shown in Figure 2. The liquid on the inlet side of the device contains large debris items 13 and small debris items 14. Both large and small debris items 13,14 will flow into and around the screen as indicated by arrows.

The smaller debns items 14 may pass through the screen panel 2 but larger debris items 13 are prevented from doing so. These are then picked up and swept around by rotation of the cleaning drum. The shield plate 6 prevents the larger debris items 13 from being ejected at the outlet side of the screen and they are instead ejected through the inlet, back into the main liquid flow.

Figures 3 and 4 show the screening device of the invention used in a municipal wastewater channel. The wastewater channel comprises a main channel 9 and an overflow channel 12 separated by a wall on top of which the screen device 11 is mounted. In the situation shown in Figure 3, the water level 10 in the main channel 9 is relatively low and the screening device is not employed. However, when the water level 10 in the main channel 9 rises, e. g. because of a storm, the screen 11 becomes operative.

In this situation the water level 10 is above the level of the inlet to the screen 11 allowing water to flow into and through the screen 11 to the overflow channel 12.

Small debris items 14 may pass through the screening device 11 but larger items 13 are returned to the main flow preventing blockage of the overflow channel 12. It has also been found that the splashing which occurs upon rotation of the cleaning drum 3 in the screening device 11 tends to discourage floating debris from entering the screening device 11 thereby increasing its effectiveness.

The screening device 11 is preferably arranged so as to be self-operating, driven by the flow of water through it. However, in case this flow does not provide sufficient motive power, an additional, e. g. electric, motor can be provided to drive the cleaning drum 3. Appropriate sensors e. g. float switches, may also be provided to automatically turn on the motor if the waste water level rises to the appropriate level.

Whilst we have described above a preferred embodiment of the present invention it will be appreciated that modifications may be made by the person skilled in the art. The above description is not intended to be limitative to the invention which is defined by the appending claims. In particular, the screening device of the present invention may be constructed at any size, diameter and length, appropriate to the use to which it is to be put.

Claims

1. A screening device comprising a generally cylindrical, horizontally disposed chamber having an inlet in a first side and a screened outlet in a lower portion of a second side ; and a rotatable cleaning member disposed within said chamber and arranged to sweep said screened outlet.

2. A screening device according to claim 1 wherein said cleaning member comprises a plurality of radial blades extending generally parallel to the axis of said chamber and for substantially the whole length thereof.

3. A screening device according to claim 2 wherein each of said radial blades is provided with a flexible web at its outer most end to form a seal with the wall of said chamber.

4 A screening device according to any one of claims 1 to 3 wherein said cleaning member is adapted to be rotatable under the pressure of the flow of liquid from said inlet to said screen outlet without additional motive power.

5. A screening device according to any one of claims 1 to 3 further comprising a motor for driving said rotating cleaning member to rotate.

6. A screening device according to any one of the preceding claims wherein the lower edge of said inlet is higher than the lower edge of said screened outlet.

7. A screening device constructed and arranged to operate substantially as herembefore described with reference to the accompanying drawings.