GB2039769A - Apparatus for separating suspended solid particles from a liquid - Google Patents

Abstract

Apparatus for separating suspended solid particles from a liquid comprises a settling tank in which at least one inclined moving band filter 1 is placed. The or each filter includes at least one vacuum chamber 9 over which passes a movable screen fabric band from which the solid is subsequently scraped at 12. An outflow chamber 4 having a perforated fixed bottom 3 is arranged quid above the or each filter with the bottom parallel to the filter, and clear liquid leaves via the perforations. Chamber 4 may enclose parallel baffles (Fig. 5 not shown). <IMAGE>

Description

SPECIFICATION Apparatus for separating suspended solid particles from a liquid The present invention relates to apparatus for separating suspended solid particles from a liquid.

One known form of such apparatus comprises an open basin with at least one sloping filter unit, with means for introducing the suspension and for withdrawal of clear liquid from the basin, so that the upper end of the filter unit lies above the surface in the basin. The filter unit comprises at least one suction box which is open towards the top surface of the filter unit, a screen fabric is movable upwardly over this top surface of the suction box, and a member is provided at the upper end of the filter unit for removal of sediment that has been formed on the screen fabric.

An example of such an apparatus is shown in U.S. Patent 4,096,062. In this apparatus, a plurality of sloping filter units have been disposed one after the other in a basin, at least partly over each other, so that in combination with the side walls of the basin they constitute a plurality of flow passages for the suspension. The filter units extend from a point above the bottom of the basin to a point above the surface of the suspension and they comprise a frame of which more than twothirds of the upper and lower surface consist of a screen fabric.Means are provided to displace said screen fabric upwardly along the upper and downwardly along the lower surface of the filter unit to pass over at least two suction boxes having separate draining exits, said suction boxes opening towards the upper and lower surface of the filter unit to withdraw liquid from the suspension through the screen fabric. The filter units are in addition provided with means for taking off the sediment of solid particles from the screen fabric above the surface of the suspension.

In this apparatus the flow rate of the liquid is controlled in the flow passages to have such a height that the flow is turbulent but at the same time low enough to cause sedimentation of the matter suspended in the liquid to take place. Thus a clear layer is created having a substantially reduced content of suspended matter in the upper part of the liquid flow, more than half of the liquid introduced in the flow passage being filtered off through the upper sieve surface of the flow passage, while less than half of the liquid introduced in the flow passage is drawn through the sediment that is formed on the lower sieve surface in the flow passage.

According to the present invention we provide apparatus for separating suspended solid particles from a liquid, such apparatus comprising a basin, means for feeding a suspension to be separated into said basin, at least one inclined filter unit arranged in said basin, the or each filter unit including at least one suction box, opening towards its upper surface, a screen fabric movable upwardly over the upper surface of the suction box and means at the upper end of the filter unit for removing the sediment which has been formed on the fabric, an outflow chamber being provided above the or each filter unit, the lower surface of the outflow chamber being arranged substantially parallel to the upwardly movable screen fabric and having perforations therein and means for removing clear liquid from said outflow chamber.

It has thus been found altogether unexpectedly, that the apparatus of the prior art can be substantially simplified without reducing its capacity. This implies that the same separation capacity is achievable with a considerably more simple, and therefore less expensive apparatus than heretofore.

A considerable simplification of the apparatus according to U.S. Patent 4,096,062 can thus be gained in that one substitutes for the topmost filter unit an outflow chamber having a perforated fixed bottom. It should be noted that apparatus of this kind is equally efficient as the said prior art apparatus, while it commands a considerably lower price.

In a specially preferred embodiment of the present invention, a plurality of filter units are arranged radially in a conically upwardly divergent basin, around a central feed means therein and which is encircled by an annular collecting passage communicating with the outflow chamber, for collecting clear liquid, said chamber having an exit passage for the removal of the collected clear liquid.

Similarly, as in the apparatus according to U.S.

Patent 4,096,062, it is also in the present apparatus possible to dispose a plurality of filter units partly overlapping, the or each upper filter unit also forming an outflow chamber with a perforated bottom opening towards the lower filter unit for removal of clear liquid from the flow passages between the filter units.

In an alternative embodiment of the present invention the outflow chamber is a lamella sedimentator having a plurality of parallel sloped lamellae for further separation of solid particles from the clear liquid and returning said solid particles to the suspension in the basin prior to withdrawing the clarified clear liquid from the lamella sedimentator and means for removing the clear liquid from the lamella sedimentator. Lamella sedimentators of this kind are well-known to a man skilled in the art and have been described among others in Swedish Application publication 7610792-9. Finnish Patent 52279 and U.K.

Patent 1463380, hereby incorporated by reference.

The flow passages between the outflow chamber and the filter unit thereinunder are preferably closed in the lateral direction by side walls.

In order that the present invention will be more fully understood, the following description is #given, merely by way of example, with reference to the accompanying drawings, in which:~ Figure 1 illustrates, in cross-section, the elevational view of one embodiment of apparatus according to the invention; Figure 2 is a similar view of a second, preferred embodiment of the invention; Figure 3 is a plan view of the apparatus of Figure 2; Figure 4 is a section taken along line A-A in Figure 3; and Figure 5 illustrates, in cross-section, the elevational view of an alternative embodiment of the invention.

In Figure 1 , the reference numeral 2 indicates a basin, into which that suspension from which solid suspended particles are to be separated is conducted through a launder 7 and which constitutes an inlet chamber for the inflow to the basin 2. Requisite flocculation agents are added into the launder 7 before the suspension runs over the rim of the launder 7 into the basin 2 at a point which may be provided with flow-guiding baffles 15 and with a mixer 8.

The bottom of the basin 2 is inclined, and at a height over its bottom there is a filter unit 1 arranged parallel to it and so disposed that one end of the filter unit is located under the liquid surface, while the opposite end lies above the free liquid surface in the basin 2. The suspension to be purified flows slowly through the basin 2. Above the filter unit 1, there is an outflow chamber 4 provided with a bottom hole 3. In the embodiment illustrated, with only one filter unit in the basin 2, the outflow chamber 4 extends over the whole breadth of the basin 2. The chamber 4 has been so shaped that the same passage geometry is obtained as in a column with two or several filter units 1.

The filter unit 1 is of the same type as has been disclosed in the U.S. Patent No. 4096062, with the exception that no suction box opens towards the lower surface of the filter unit if only one filter unit is used. In contrast, the filter unit has a frame carrying two rolls 11, disposed each at its own end of the filter unit. The roll 11 located at that end of the unit which is above the liquid surface in the basin 2 is rotated by a drive mechanism, which may be an electric motor. The roll 11 lying under the liquid in the basin 2 is a driveless return roll.

Over these rolls 11 runs an endless screen fabric 13, made for instance from a plastic or metal wire.

This screen fabric 13 is carried around by the rolls 11 so that the upper part moves obliquely upward along the upper surface of the filter unit 1 and the lower part moves obliquely downward along the lower surface of the filter unit 1 when the latter is in position in the basin 2. The screen fabric 13 has a breadth such that it extends across the entire filter unit 1.

In the frame of the unit, under the screen fabric 13, at least one suction box 9 has been formed.

Liquid may flow to the suction box 9 by a plurality of apertures through the screen fabric 13 from the flow passage between the perforated bottom 3 of the passage 4 and the filter unit. Another suction box 10 may be provided at the other end on the filter unit 1, which is above the suspension surface. Where several units are provided in the basin, partly overlapping, the filter units also have a suction box which opens towards the lower surface of the unit so that liquid is enabled to flow through the screen fabric and through a plurality of apertures covered by the screen fabric, from the flow passage located under the unit in question.

The filter units may alternatively have a flowthrough passage with perforated bottom and opening towards the lower surface of the unit, which in such a case is not covered by the screen fabric, so that clear liquid is allowed to run by itself from the flow passage between the units and the side walls.

That part of the filter unit 1 which is located above the free liquid surface has been provided with a means to remove sludge from the screen fabric, such as a doctor blade 12.

The through-flow rate and velocity are determined by a manually controlled valve 5 at the exit end of the outflow chamber container 4. The liquid level in the basin is monitored by a level indicator 6, which controls the output of the infeed device.

In a multiple row embodiment, i.e., with two or more filter units side by side and partly overlapping any one of the units in the top row may be replaced with an outflow chamber.

The outflow from the chamber is then expediently taken care of by the frame construction supporting the filter units, the supporting horizontal braces of this construction being shaped to constitute a chamber.

Figures 2 and 3 illustrate a specially preferred embodiment of the present invention, wherein filter units 1 and the outflow chambers 4 have been arranged in pairs radially in the basin 2 around a common infeed member 18. Here too, the filter units 1 and chambers 4 constitute obliquely upwardly directed flow passages confined by side walls 17 and through which the suspension to be purified will flow. The major part of the suspended material is removed by the screen fabric 13, while the clear liquid in the topmost layer in the liquid flow runs off under own pressure through the perforated bottoms 3 and in the chambers 4. The embodiment illustrated is very compact and it provides a good degree of space utilization in spaces and basins already existing and taken out of use.

The central infeed member 18 is additionally encircled by an angular collecting passage 16 communicating with the outflow chambers 4 by valve-controlled apertures 5 in their side wall, for collecting that clear liquid which has run into the chambers 4, as has been shown in Figure 4. The collected clear liquid runs out from the collecting passage through the exit 14.

It is obvious that a plurality of filter units may be arranged partly overlapping in the basin, in which connection the fiow-through passages have been suitably built into the units, so that in the units there is a flow-through passage with perforated bottom and constituting part of the lower surface of the unit and which is not covered by the wire.

Figure 5 illustrates an alternative embodiment in which the outflow chamber is constituted by a lamella sedimentator 20 of common type. This kind of a lamella sedimentator consists of obliquely placed lamellae 21. The clear solution flows in between the lamellae 21 from the flow passage between the bottom 3 of the lamella sedimentator and the unit 1. In the spaces between the lamellae 21 further sludge is separated from the clear solution, which sludge goes down to the flow passage between the bottom 3 of the lamella sedimentator 20 and the unit 1 and ends up on the screen fabric 13. The pure clear solution, again, is removed in a manner known per se at the upper portion of the lamella sedimentator 20 and collected and removed through outlet opening 14. The construction and utilization of lamella sedimentators of this kind belong to the normal skill in the art and have therefore not been closer described in this connection.

Claims (7)

1. Apparatus for separating suspended solid particles from a liquid, such apparatus comprising a basin, means for feeding a suspension to be separated into said basin, at least one inclined filter unit arranged in said basin, the or each filter unit including at least one suction box, opening towards its upper surface, a screen fabric movable upwardly over the upper surface of the suction box and means at the upper end of the filter unit for removing the sediment which has been formed on the fabric, an outflow chamber being provided above the or each filter unit, the lower surface of the outflow chamber being arranged substantially parallel to the upwardly movable screen fabric and having perforations therein and means for removing clear liquid from said outflow chamber.

2. Apparatus according to claim 1, wherein a plurality of filter units are arranged radially in a conically upwardly divergent basin, around a central feed means therein and which is encircled by an annular collecting passage communicating with the outflow chamber, for collecting clear liquid, said chamber having an exit passage for the removal of the collected clear liquid.

3. Apparatus according to claim 1 or 2, wherein a plurality of filter units have been disposed at least partly overlapping, the or each upper filter unit also forming an outflow chamber with a perforated bottom opening towards the lower filter unit for removal of clear liquid from the flow passages between the filter units.

4. Apparatus according to claim 1 or 2, wherein the outflow chamber is a lamella sedimentator having a plurality of parallel sloped lamellae for further separation of solid particles from the clear liquid and returning said solid particles to the suspension in the basin prior to withdrawing the clarified clear liquid from the lamella sedimentator and means for removing the clear liquid from the lamella sedimentator.

5. Apparatus for separating suspended solid particles from a liquid, such apparatus being constructed and arranged substantially as hereinbefore described with reference to and as illustrated in Figure 1 of the accompanying drawings.

6. Apparatus for separating suspended solid particles from a liquid, such apparatus being constructed and arranged substantially as hereinbefore described with reference to and as illustrated in Figures 2, 3 and 4 of the accompanying drawings.

7. Apparatus for separating suspended solid particles from a liquid, such apparatus being constructed and arranged substantially as hereinbefore described with reference to and as illustrated in Figure 5 of the accompanying drawings.