IE44015B1 - Apparatus for separating floating matter from a liquid - Google Patents

Abstract

1491324 Removing floating matter PATERSON CANDY INTERNATIONAL Ltd 25 May 1976 [28 July 1975] 31403/75 Heading B1D Floating matter is discharged from flotation tank 2 over pivoted weir 5 into box 4, the weir 5 being biassed towards its vertical position by counterweight 8. The weir may comprise a flat and a curved portion, one edge of the flat portion being pivoted. Liquid spraying pipes may be positioned along opposite sides of the tank 2 to aid the flow of matter to weir 5.

Description

The present invention relates to apparatus for separating a floating matter from a liquid.

In processes such as floatation where suspended solids material is removed as a scum from a liquid it is necessary, either continuously, or intermittently, to remove the scum from the surface.· The same situation holds true in the separation of oil and water.

In most applications the throughput may not necessarily remain constant. Thus, for example, the water in a floatation unit will usually be withdrawn at a low level, passing under a ring or skirt to be decanted over a weir and hence the precise level of liquid in the tank will vary with the flow rate. The simplest method of removing the scum is to decant it, but it is necessary to provide a weir whose depth below the scum surface is controlled, otherwise an excessive quantity of the subnatant water will be lost with the scum, or in the case of oil and water separations, water may be drawn out with the oil.

An object of the present invention therefore is to provide a simple arrangement whereby a surface scum or liquid layer may be .drawn off over a weir which adjusts its level automatically to maintain a general constant differential below the surface level in the tank as decanted matter is withdrawn therefrom.

The invention provides apparatus for separating floating matter from a liquid comprising a first tank for containing the liquid a second tank and a weir over which the floating matter is to be decanted from the first tank into the second tank, wherein the weir 4401s is pivotably mounted and biassed towards an upright position by means of a counterweight so that in use as decanted floating matter is withdrawn from the second tank the weir pivots and a differential between the level of liquid in the first tank and in the second tank is maintained.

Preferably, the counterweight extends downwardly into the first tank. Preferably, the weir is a flat plate pivoted about its lower edge.

Alternatively, the weir may comprise a substantially flat plate 10 pivoted along one edge and a curved portion extending upwardly from the opposite edge of the flat plate and centered about the pivot.

Preferably, the first tank is provided with distribution pipes along opposite side walls thereof for spraying the side walls thereof so as to separate the floating matter from the side walls.

Preferably, the distribution pipes are adapted to spray the side walls in a direction towards the weir thereby encouraging flow of the floating matter towards the weir. j. The invention will now be described with reference to the ./-,, accompanying drawings, wherein: Figure 1 is a sectional view of part of a first embodiment according to the invention, Figure 2 is a sectional view of part of a second embodiment X accordingto the invention, Figure 3 is a sectional view of the embodiment of Figure 1 provided with distribution pipes, and Figure 4 is a sectional view of a third embodiment according to the invention. 3. 4401S .. Ia the, drawings, a separation tank 1, contains liquid 2 having a scum layer 3» A weir tank or box 4 is mounted on the side of the tank 1 and is separated from the tank 1 by a hinged or pivoted weir plate 5· The weir box 4 is provided with an outlet 6 having a discharge valve 7. In figure Ί, the weir plate 5 is counterbalanced hy a weight 8» so that when the discharge valve 7 is closed the water level in the weir box 4 will rise, as a result of finite leakage round ths sides of the weir plate 5, to the same level as ia the tank 1. In l this situation the weir plate 5 will normally be in the vertical position.

When the discharge valve 7 is opened, the level in the weir box 4 will fall causing a differential in head between the tank 1 and the weir box 4. This pushes the weir plate 5 over as shown ia Figure 1 so that restoring torque provided by the counterweight δ matches the tipping torque provided by the differential head acting on the plate 5. The plate 5 will continue to tip as the level in the box 4 falls until a thin film of liquid commences to flow over the top of the plate. As soon as the flow over the top of the plate 5 equals the flow passing out through the discharge valve 7j the level in the box 4 ceases to fall and steady state conditions are established.

The crest of liquid passing over the top of the weir plate 5 in the tilted position depends solely upon the rate at which the liquid is flowing out from the box 4, i.e. that determined by the setting of the discharge valve 7. The angle of 4, tip of the plate will vary according to the water level in the tank 1.

With a simple plain plate as shown in Figure 1, a situation can arise where at low water levels a tipped tilting plate may assume bistable conditions where with the plate in an upright position the water on the upstream side is only acting over a small portion of the total height and the tilting moment is insufficient to cause operation. This situation can be overcome by designing the simple plate with sufficient depth in relation to the range of variation of the tank water level so that this situation does not occur.

In the embodiment shown in Figure 2, the flat weir plate 5 of Figure 1 has been replaced by a quadrant-shaped weir plate 10 which comprises ideally a flat portion 11, which in the rest position is horizontal. The flat portion 11 is provided at one edge and at the opposite edge is connected to a curved portion 13 centering on the pivot 12. The turning moment of the liquid in the tank 1, acts therefore, on the flat portion 11, which is submerged at all times along its entire length,' whereas the curved portion 13 merely acts as a water barrier.

Ia most applications a simple hinged, weir with a small clearance against the end walls, will meet the requirements satisfactorily* There is no reason however why a flexible membrance should not be fitted at the ends of the plate to give a perfect seal in applications such as the decanting of oil and other lower density fluids.

In the embodiment shown in Figures 3, the θ tank 1 has been provided with distribution pipes 14 extending along opposite sides of the tank 1. The pipes have apertures 15 along their length so that a thin film of water is sprayed onto the sides of the tank 1. This thin film of water prevents adhesion of the scum to the walls. In long thin tanks this adhesion frequently interferes with the smooth discharge of the scum over the tilting weir 5· As a further refinement the jets of water emerging from the distribution pipes 14 may be angled in a direction pointing towards the weir box-4 to provide -a net forward movement, thereby encouraging the flow of the scum blanket towards the'weir box 4.

As can be seen from the embodiment of Figure 4, the weir box 4 is placed at the opposite end of the floatation chamber from that 6, 4401S at which the air bubbles or air/water emulsion enters the tank 1 through inlet 16, so that the net flow entering the tank passes across the surface thereby encouraging the scum to move towards the weir box 4.

As in Figures 1 to 3 the scum 3 leaves the weir box 4 via the outlet 6 and discharge valve 7. Clarified water spills over a weir 17 into a collecting tank 18 and is lead away by a conduit 19.

The advantage of the embodiment of Figure 4 is that no special arrangements are required where more than one floatation unit is mounted in parallel for the flow to be uniformly distributed. The water decanting weir in such an arrangement provides flow balancing and the scum decanting weir operates automatically without any controls other than operating the discharge valve 7.

Claims (8)

1. Apparatus for separating floating matter from a liquid comprising a first tank for containing the liquid, a second tank and a weir over which the floating matter is to be decanted from the first tank into the second tank, wherein the weir is pivotably mounted and biassed towards an upright position by means of a counterweight so that in use^as decanted floating matter is withdrawn from the second tank the weir pivots and a differential between the level of liquid in the first tank and in the second tank is maintained.

2. Apparatus as claimed in claim 1, wherein the counterweight extends down wardly into the first tank.

3. Apparatus as claimed in claim I or 2, wherein the weir is a flat plate pivoted about its lower edge.

4. Apparatus as claimed in claim 1 or 2, wherein the weir comprises a substantially flat plate pivoted along one edge and a curved portion extending upwardly from the opposite edge of the flat plate and centred about the pivot.

5. Apparatus as claimed in any one of the preceding claims, wherein the first tank is provided with distribution pipes along opposite side walls thereof for spraying the side walls so as to separate the floating matter from the side walls.

6. Apparatus as claimed in claim 5, wherein the distribution pipes are adapted to spray the side walls in a direction towards the weir thereby encouraging flow of the floating matter towards the weir.

7. Apparatus for separating floating matter from a liquid substantially

8. as herein described with reference to any one of the embodiments shown in the accompanying drawings.