GB2293985A - Floatable screen - Google Patents

Abstract

A floating screen device (1) for screening floating debris in a stream of liquid flowing in a conduit comprises a screen (6) adapted to float at the surface of the liquid, and retaining means (15, 16) operable between the screen and the conduit to secure the screen against the liquid flow. As a result, the screen removes debris floating in the liquid but does not impede the flow of liquid under the screen. <IMAGE>

Description

FLOATABLE SCREEN This invention relates to sewage treatment, and more particularly to an apparatus for removing floating debris from storm water, thereby improving the quality of the effluent discharged without treatment into water courses during storm conditions.

In a conventional combined sewage system flows of up to 6 DWF (six times dry weather flow) can be passed on to the sewage treatment works wherein the organic and inorganic load may then be reduced to acceptable levels prior to discharge to a water course. However, within a combined system 'vents' or by-pass systems are incorporated in water conduits, such as culverts, to prevent works overload and thus flooding. These systems are known as Combined Storm Overflows (CSO's).

When CSO's operate, storm water combined with crude sewage is discharged from the sewage system and directly into a water course. Such discharge inevitably contains visible pollutants such as plastics, sanitary ware, rags etc. which are not readily bio-degradable and which impact on the receiving water course, bathing beach, harbour etc.

Ideally all discharges should be screened to remove the visible debris. However, the extreme flows commonly experienced during storm conditions present practical difficulties, with conventional systems blinding (i.e. blocking) rapidly. Such binding presents an impediment to the flow, causing the storm water to back up and threatens potentially serious flooding.

The present invention seeks to overcome the above problems by providing a floating screen which offers only a limited resistance to the flow of water whilst retaining most of the non-bio-degradable material which, being buoyant, remains close to the surface. The invention therefore provides for a screening system that rises and falls with the level of storm water in a discharge culvert. As the screen rises, a free passage is created under the screen which allows the relatively clean lower water to discharge unscreened and with unimpeded flow.

According to the invention, there is provided a floating screen device for screening floating debris in a stream of liquid flowing in a conduit, comprising a screen adapted to float at the surface of the liquid, and retaining means operable between the screen and the conduit to secure the screen against the liquid flow, whereby the screen removes debris floating in the liquid but does not impede the flow of liquid under the screen.

In one embodiment the screen floats freely in the conduit, and is located by lateral channels in the conduit which secure the screen against the liquid flow.

In another embodiment, the screen is pivoted to an arm which is in turn pivoted to a fixed point in the conduit. This both provides for the retaining of the screen against the liquid flow, and permits the screen to rise and fall with changing levels of liquid. The screen may have a buoyancy aid attached to it, to assist floating.

The apparatus according to the invention needs to be capable of withstanding extreme forces, such as those typically experienced in drainage systems during storm conditions. For this reason, a high strength material is preferred, for example, stainless steel.

The arm, when present, will generally possess a counter-balance close to the pivot point with the conduit. This will facilitate flotation of the screen and permit size reduction of the buoyancy aid which will in turn minimise resistance of the device to the liquid flow. The arm may be in the form of a four-bar chain or similar device with lower pairs either turning or sliding.

The operating weight of the counter-balance should be easily varied and for this reason a simple filler substance is preferably employed, for example, water.

In a preferred embodiment, the screen member is a wave-form screen and thus presents a large open area to the flow of liquid. Alternatively, other suitable screens include agitated sack fillers and rake bar screens.

Reference is now made to the accompanying drawings, in which: Figure 1 is a diagrammatic side view of a floatable screen device according to a preferred embodiment of the invention, with the screen in the lower most position; Figure 2 is a plan view of the device shown in Figure 1; Figure 3 is an end view of the device shown in Figure 1; and Figure 4 is an end view corresponding to Figure 3, but with the screen in a raised position.

The drawings show a floating screen device 1 arranged in a culvert having lower and upper walls 2 and 3 respectively, and side walls 4, 5. The screen itself is a wave-form screen 6 which, in plan view, is of sinusoidal shape so as to present a large surface area to the flow of water in the culvert, indicated by arrow 7. The screen 6 is of perforated stainless steel. It is supported in a framework having an upper member 8 and side members 9, 10 which are generally open, to allow access of the water to the screen.

Attached to the upper member 8 and on the upper part of the front and rear faces of the screen are buoyancy tanks 11, 12. The buoyancy tanks are generally open at their lower ends, and air is entrapped in the buoyancy tanks by water in the culvert. The dimensions of the buoyancy tanks in relation to the screen are such that the screen device as a whole is adapted to float in the water in the culvert, with the top of the screen at or near the surface of the water.

On the side walls 4, 5 of the culvert, four vertical flanges 13, 14, 15, 16 are arranged. These may, for example, be of U-shaped section whereby the central web provides a surface for attachment bolts to secure the flanges to the walls 4, 5 of the culvert. Respective pairs of flanges 13, 14 and 15, 16 define therebetween vertical channels in the side walls of the culvert for locating the screen device. A small clearance is provided between the screen device and the flanges to permit the screen device to float freely in water in the culvert. However, the flanges act as stop members and thus ensure that the screen itself remains generally vertical, i.e. transverse to flow of water in the culvert, and the screen is secured in the culvert against the flow of water.

In dry weather, the level of water in the culvert is quite low, and the screen will adopt the lower most position as shown in Figures 1 and 3. In storm conditions, the level of water flowing in the culvert is much higher. The screen will then float at a raised position, for example, as shown in Figure 4. The screen will then still act as an effective filter for debris at or near the surface of the water. However, the relatively clean water beneath the surface will be able to flow unimpeded under the screen.

Variations on the device specifically described above are possible whilst still embodying the principles of the invention. For example, the wave-form screen can be of sinusoidal shape when viewed from the side. The buoyancy tanks can be sealed, rather than open at their lower ends.

Claims (5)

CLAIMS:

1. A floating screen device for screening floating debris in a stream of liquid flowing in a conduit, comprising a screen adapted to float at the surface of the liquid, and retaining means operable between the screen and the conduit to secure the screen against the liquid flow, whereby the screen removes debris floating in the liquid but does not impede the flow of liquid under the screen.

2. A floating screen device according to claim 1, in which the screen is adapted to float freely in the conduit, and is located by lateral channels in the conduit which secure the screen against the liquid flow.

3. A floating screen device according to claim 1, in which the screen is pivoted to an arm which is in turn pivoted to a fixed point in the conduit, providing for the retaining of the screen against the liquid flow, and permitting the screen to rise and fall with changing levels of liquid.

4. A floating screen device according to any of claims 1 to 3, in which the screen has a buoyancy aid attached to it, to assist floating.

5. A floating screen device substantially as hereinbefore described with reference to and as shown in the accompanying drawings.