AU704644B2

AU704644B2 - Liquid/solids separator

Info

Publication number: AU704644B2
Application number: AU51517/96A
Authority: AU
Inventors: Keith Edwin Frank Brown; Walters Francois Du Toit
Original assignee: ULTRASEP Ltd Pty
Current assignee: ULTRASEP Pty Ltd
Priority date: 1995-03-22
Filing date: 1996-03-22
Publication date: 1999-04-29
Anticipated expiration: 2016-03-22
Also published as: WO1996029135A1; AU5151796A; CA2214538A1; MX9707129A; EP0814886A1; NZ304348A; BR9607887A

Description

WO 96/29135 PCT/GB96/00688 LIOUID/SOLIDS SEPARATOR BACKGROUND TO THE INVENTION This invention relates to a clarifier/thickener or separator of the type adapted to be used to separate suspended solids from a liquid.

Clarifiers/thickeners of the above kind are used in many different applications and have particular relevance in the clarification of water, and thickening of slimes produced in mining and mineral processing operations.

However, it is to be understood that the invention is not limited to use in any particular application.

Generally liquid and suspended solids are fed into the inlet of the separator at relatively low density. Within the separator, a large portion of the solids is separated out of the liquid and a clear liquid is then discharged. usually at the top of the separator, and the solids wl-ch usually settle under the influence of gravity are withdrawn from the separator at the lower end thereof. The clarified liquid is frequently referred to as "overflow" The high density solids, in the form of a sludge, is frequently drawn out of the bottom outlet from the separator This sludge material is frequent'l termed "underflow".

In operation, the largest of the solid particles generally will separate under gravity to the lower region of the separator. The smaller particies. known as colloidal solids. will generally not settle within an acceptable time frame.

Clarifiersthickeners therefore rely on the addition of a coaculant or SUBSTITUTE SHEET (RULE 26) WO 96/29135 PCT/GB96/00688 2flocculant which provides an effective bridging mechanism between small particles. This bridging mechanism results in larger particles being formed which will then settle under the influence of gravity.

In order to join together the particles need to "collide" with each other, and for this reason energy must be applied to the liquid. Energy is generally provided by causing the liquid to flow through the separator. With the correct energy input particles will remain together after collision.

Prior art clarifiers/thickeners have often suffered from one or more disadvantages. Generally what is required is that the separator will operate to an acceptable degree of efficiency, be relatively automatic and maintenance free, and will require acceptable levels of flocculant.

SUMMARY OF THE INVENTION According to a first aspect of the ivention, a separator is provided for separating solids and liquids from a feed material containing a mix of solids and liquids, the separator comprising: a tank having a top, generally vertical side walls, and a convergently tapered bottom; a clarified liquid outlet at or near the top of the tank; a sludge outlet from the tapered bottom of the tank; and a generally vertically aligned feed conduit located within the tank near the top thereof.

the feed conduit including a feed section and a discharge section, the feed section being adapted to receive feed material and the discharge section being adapted to discharge feed material into the tank below the top thereof, the discharge section being of wider diameter than the feed section; a zone for upwardly flowing liquid between the side walls of the tank and the feed conduit, wherein at least part of the zone increases in cross-sectional area so that the velocity of liquid flowing upwardly within the zone will decrease; and a recycle conduit within the feed conduit.

This discharge section preferably tapers divergently in a downward direction.

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Preferably, the recycle conduit includes a downwardly diverging section.

Preferably, the downwardly diverging section of the recycle conduit is conical.

Preferably, the downwardly diverging section of the recycle conduit nests within the discharge section of the feed conduit.

Preferably, the recycle conduit includes a right circular cylindrical section located above the downwardly diverging section.

The separator may include a downwardly depending skirt extending from the lower edge of the discharge section of the feed conduit, between which downwardly depending skirt and the side walls of the tank a lower section of the zone for upwardly flowing liquid is defined.

@04 0 9 V. I IM1 1 1 The separator may include a supply conduit for feeding the feed material into the feed conduit below the upper end of the feed conduit.

The separator may include a solids concentration apparatus.

Preferably, the solids concentration apparatus consists of truncated cones.

The separator may include a launder into which clarified liquid can flow.

Preferably, the level of the launder and the upper end of the feed conduit are adjustable relative to one another.

According to a second aspect of the invention, a method is provided for separating a solids/liquids mixed feed material in a separation tank which has generally vertical side walls and a feed conduit including a downwardly diverging discharge o o g .0 0 0 S 0 90 0 0 *0

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i\ I I i IP section centrally located within the tank and spaced away from the walls of the tank thereby defining an annular throat between the tank and the discharge section, the method including the steps of: introducing the feed material into the tank through the feed conduit; adding a flocculent to the feed material either before or after it has entered the tank: allowing the feed material to pass through the discharge section whilst the velocity of the feed material decreases; allowing heavier solid particles to settle under the influence of gravity towards the bottom of the tank; 9**9a o 9* 9 o o 9..

6 I I M I I 1111" allowing lighter solid particles to pass upwardly through the annular throat to a zone which increases in cross-sectional area so that the velocity of liquid flowing upwardly within the zone will decrease; selecting and monitoring the flow of feed material into the tank so that a bed of solid particles forms within the tank above the throat in the zone which increases in cross-sectional area; and withdrawing clarified liquid from the top of the tank above the bed, and sludge from the bottom of the tank.

The method may include the step of diverting a percentage of the clarified liquid into the feed conduit to mix with the feed material.

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N I IM I 11" 1 -e g_ The method may include the step of varying the percentage of clarified liquid introduced into the feed conduit so as to vary the specific gravity of material passing into the feed conduit and thereby optimise the separation characteristics of the separator.

An embodiment of the invention is described below by way of example with reference to the accompanying drawings. The drawings, however, are merely illustrative of how the invention might be put into effect so that the specific form and arrangement of the various features shown is not to be understood as limiting on the invention.

6 *S a a e S S S o ,i S.' N 1 1111 1 1 I WO 96/29135 PCT/GB96/00688 -9 BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a cross-sectional side view through a typical clarifier/thickener according to the invention; and Figure 2 shows a plan view of the clarifier/thickener shown in Figure 1.

DFTAILED DESCRIPTION OF AN EMBODIMENT As shown in the drawings, a separator 10 for separating solids from liquids in a feed material includes a generally vertically extending tank 12 having vertical side walls 14, a substantially open top 16 and a downwardly tapering or cone shaped bottom 18. The tank 12 shown in the drawings is circular in cross-section, but the tank may be square or rectangular in cross-section and would operate in substantially the same manner as is described below.

The tank 12 has a clarified liquid outlet 20 located near the top 16, and a sludge outlet 22 through which sludge which has collected in the tapered bottom will be discharged.

A feed conduit 24 is located within the tank 12 near the upper end thereof.

The feed conduit is generally vertically aligned and includes a feed section 26 and a discharge section 28 which is located below the feed section 26.

The feed section 26 is preferably of cylindrical form. The discharge section 28 is of larger diameter from the feed section 26 and is preferably of downwardly diverging form as shown. The cross-sectional shape of the discharge section should match that of the tank so that the lower edge 30 of WO 96/29135 WO 96/9 135PCT/G1196/00688 jo the discharge section is equally spaced from thc walls 14 of the tank around the entire lower periphery of the discharge section 28.

Feed rmaterial is supplied to the feed conduit 24 through a feed pipe 32 which passes through the side wall 14 of the tank and extends into the feed conduit 24. The discharge end 34 of the feed pipe 32 may be downwardly directed as shown in the drawings to direct incoming feed material downwardly. The feed pipe has a flocculant supply pipe 36 connected thereto by means of which flocculat is added to the feed material as it travels in the feed pipe 32.

The discharge section 28 is, as mentioned above, preferably conically shaped. The half-cone angle of the discharge section may be between about and 45' and is preferably about 300. The axes of the feed section and the discharge section are preferably coincident with the axis 38 of the tank.

A throat 40 is defined between the lower edge 30 of the discharge section 28 and the side walls 14. As mentioned above, the throat 40 is prefer-ably of constant width around the entire periphery of the discharge section. The width of the throat may be between 5% and 15% of the total width of the tank 12. In the preferred arrangement the width of the throat 40 is about of the diameter of the tank 12.

A recycle conduit 42 is located within the tank- co-axially with the feed conduit 24. The recycle conduit includes an upper cylindrical section 44, and a lower trunicated conical section 46. The conical section 46 is downwardly diverging as shown and is ne-sted Within the discharge section 28. An annular gap 48 is thus defined between the discharge section 28 and I_ I _I WO 96/29135 PCT/GB96/00688 11 the conical section 46.

Located below the recycle conduit 42 is a solids concentration apparatus The solids concentration apparatus comprises a plurality of downwardly converging truncated codes 52. The cones 52 lead one into the other and serve to direct solids settling within the tank 12 towards the sludge outlet 22.

The cones 52 are suspended from the recycle conduit 42 by a plurality of suspense rods 54.

The clarified liquid outlet 20 is supplied with clarified liqwud from the separator via a launder 56. The launder is of annular shape and is supported in position from a gantry 58 located at the top of the tank 12. The launder receives liquid which has been clarified in the tank 12. The liquid flows into the launder over a weir which is defined by both the radially inner edge and the radially outer edge 62 of the launder 56. The weir is defined by a series of V-shaped notches.

In the embodiment shown in the drawings the elevation of the launder 56, relative to the tank, is variable. The upper end 64 of the feed conduit also serves as a weir for clarified liquid. As shown the upper end 64 of the feed conduit is also provided with a senes of V-shaped notches. By varying the elevation of the launder 56 relative to the upper end 64 of the feed conduit the relative percentages of clarified liquid which flows into the launder and into the feed conduit can be varied. This feature is discussed in more detail below.

In use, feed material which contains a mix of solids and liquids will be introduced through the feed pipe 32. A controlled volume of flocculant will 1 WO 96/29135 PCT/GB96/00688 12 be added to the feed material via the flocculant supply pipe 36. The feed material, as it enters the feed conduit 24, will move downwardly towards the discharge section 28. As the feed material enters the discharge section and moves radially outwards through the gap 48 its flow velocity will slow and, in so doing, the heavier and larger solid particles in the flow will begin to settle towards the lower regions of the tank. The flocculant will assist particles to join together.

Lighter and smaller solid particles will tend to move around the lower edge of the discharge section 28. The liquid and similar particles will then move upwardly through the throat 40 into a settling bed or "floc bed", indicated by the shaded area 66 located above the throat 40. It will be noted that the floc bed 66 is upwardly diverging and therefore as the liquids and smaller solids flow upwardly there will be a tendency for the flow velocity to decrease. Thus, at the underside of the floc bed 66 the relatively rapidly upwardly moving solid particles will tend to collide with the underside of the floc bed 66. Solid particles will collide with each other thereby increasing the collective size of the particles. As the solid particles increase in size they will tend to begin settling downwardly, back through the throat, towards the bottom of the tank. The floc bed 66 thus acts somewhat like a sieve to trap upwardly flowing solid particles. Liquid will pass up through the floc bed towards the launder but even small solids will be trapped in the floc bed.

The floc bed 66 will form naturally as a consequence of the upwardly diverging configuration of the flow path above the discharge section 28.

Thus, the cone-shaped form of the discharge section serves firstly to slow the velocity of flow to allow larger particles to settle, and then secondly, as after

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WO 96/29135 PCT/GB96/00688 13 flow has passed through the throat, to again slow the flow velocity above the throat to allow the floc bed 66 to form.

It is important that the density of the feed material is optimised for proper efficiency of the settler. For this reason it is preferred that at least s'me of the clarified liquid which is available for disc'arge from the settler is fed back into the feed conduit 24 for mixing with fresh feed material. For this reason the relative elevations of the launder 56 and the upper end of the feed conduit should be adjustable. This can be achieved by either raising or lowering the launder, or by raising or lowering the feed conduit. In the embodiment shown the elevation of the launder 56 is adju-table and for this reason a flexible connecting pipe 67 is fitted between the launder 56 1 the clarified liquid outlet 20.. The V-shaped notches which define the respc /e weirs ensure relatively precise control of flow into the feed conduit and launder. Dilution of the fed material results in less flocculant consumption and higher settling rates.

As solid particles settle they will pass towards the tapered bottom 18. The lower part of the tank is referred to as the consolidation zone. The cones 52 serve to de-water solid material passing downwardly into the consolidation zone so that material drawn out of the sludge outlet 22 is sludge-like in nature.

As solid material deposits on the upper surface of the cones 52 it will begin to slide down the inner surfaces of those cones through the respective throats of the cones until it deposits as sludge in the cone shaped bottom 18.

Liquid, depicted by arrows 68, will move in an upward direction and will move upward into the cone shaped lower section of the recycle conduit. It WO 96/29135 PCT/GB96/00688 14 is envisaged that the liquid 68 will be moving upwardly at a relatively low upward flow rate so as not to carry with it many solid particles moving downward in this consolidation zone.

One distinct advantage of the configuration of the cones 52 is that the cones serve to guide solid particles moving down in this consolidation zone towards the centre of the cone shaped bottom 18. It will be noted that a solid particle build up as indicated at numeral 70 occurs below the lower most cone 52. The advantage of this is that discharge which takes place through the outlet 22 will tend to draw sludge from this central region and thus the problem of open sludge free passages (known as "rat holes") being formed in the sludge will, to a lar-e extent, be eliminated. Instead, discharge which does take place through the outlet 22 will tend to consolidate the solid sludge material and this sludge material will generally be guided towards the centre of the bottom 18 thereby plugging any such "rat holes" that may tend to occur.

It is envisaged that a separator of the type described will have a number of advantages. The separator will, it is envisaged, remove suspended solids over a wide range of flow rates and solids levels. It will also remove particles of varying densities and provide a relatively clear overflow.

Controllable underflow densities over a wide range of densities is also possible. The separator can also be used to achieve classification of solid particles by monitoring the feed flow rate, flocculant addition levels and optimising or adjusting the annular opening to suit the required classification.

Clearly there may be multiple inlets and a separator shown in the drawings a relatively simple example of the manner in which the invention may be WO 96/29135 PCT/GB96/00688 15 used. As previously mentioned, the separator does not need to be circular in cross-secuon. A square or rectangular separator may be used. Thus, where the term "cone" is used in this specification it is not intended to only refer to circular cones. The term should be taken to include within its scope pyramid or other shaped cones.

There are many advantages to be obtained by using a clarifier/thickener of the type described herein. Firstly, dilution of the feed may be automatically controlled over a full range of operational conditions and could be changed to cope with changes in feed flow rates and feed material liquid/solds ratios.

The change in area of the annular passage leads to a very high rate of mixing due to the change in feed velocities. This is particularly advantageous when multiple units are employed in counter current decantation (washing) when high mixing efficiencies are required. The change in cross-secdon of the clarifier/thickener upward of the annular throat quickly stabilises the depth of the floc bed and also increases the efficiency of the floc bed since the upward velocity imparted on the floc particles rapidly decreases. This will lead to more zollisions between particles and larger flocs will quickly occur thus allowing the larger floc particles to fall under gravity through the throat 40 thereby constantly depleting the floc bed of solids.

The discharge from the consolidation cone is essentially above the underflow discharge. The bulk of the hign density sludge is thus allowed to build from the centre outwards thereby ensuring minimising the effect of "rat holes" and blockages or compaction which often results from "rat holes" forming.

WO 96/29135 PCT/GB96/00688 16 It is envisaged that corrosion/erosion rates will be low due to the slow movement of solids in a downward direction. It will also be appreciated that there are no moving parts of the apparatus. The apparatus will be selfcleaning and it is envisaged that it will have a low flocculant consumption due to the larger particles tending to settle under gravity so they will not be carried up into the floc bed. The floc bed above the annular throat 40 is self-balancing.

It should be noted that the form of the throat 40 can be varied. For example, a downwardly depending skirt could be attached to the lower edge of the discharge section 28. Such a skirt will than define an annular cylindrically shaped throat which will have the effect of lowrcmg the top of the floc bed but would possibly improve the efficiency of the floc bed.

Claims

1. A separator for separating solids and liquids from a feed material containing a mix of solids and liquids, the separator comprising: a tank having a top, generally vertical side walls, and a convergently tapered bottom; a clarified liquid outlet at or near the top of the tank; a sludge outlet from the tapered bottom of the tank; and a generally vertically aligned feed conduit located within the tank near the top thereof; the feed conduit including a feed section and a discharge section, the feed section being adapted to receive feed material and the discharge section being adapted to discharge fe,-d material into the tank below the top thereof, the discharge section being of wider diameter than the feed section; a zone for upwardly flowing liquid between the side walls of the tank and the feed conduit, wherein at least part of the zone increases in cross-sectional area so that the velocity of liquid flowing upwardly within the zone will decrease; and a recycle conduit within the feed conduit.

2. The separator of claim 1 wherein the discharge section of the feed conduit tapers divergently in a downward direction.

3. The separator of claim 1 or claim 2 wherein the recycle conduit includes a downwardly diverging section.

4. The separator of claim 3 wherein the downwardly diverging section of the recycle conduit is conical. The separator of claim 3 or claim 4 wherein the downwardly diverging section of the recycle conduit nests within the discharge section of the feed conduit.

6. The separator of any of claims 3 to 5 wherein the recycle conduit includes a right circular cylindrical section located above the downwardly diverging section. 30 The separator of any of the above claims including a downwardly depending skirt extending from the lower edge of the disLharge section of the feed conduit, between which downwardly depending skirt and the side walls of the tank a lower section of the zone for upwardly flowing liquid is defined.

8. The separator of any of the above claims including a supply conduit for feeding the feed material into the feed conduit below the upper end of the feed conduit. *V V V V. V V V

9. The separator of any of the above claims including a solids concentration apparatus. -18- The separator of claim 9 wherein the solids concentration apparatus consists of truncated cones.

11. The separator of any of the above claims including a launder into which clarified liquid can flow.

12. The separator of claim 11 wherein the level of the launder and the upper end of the feed conduit are adjustable relative to one another.

13. A separator substantially as herein described and illustrated with reference to the accompanying drawings.

14. A method of separating a solids/liquids mixed feed material in a io separation tank which has generally vertical side walls and a feed conduit including a downwardly diverging discharge section centrally located within the tank and spaced away from the walls of the tank thereby defining an annular throat between the tank and the discharge section, the method including the steps of: 5 introducing the feed material into the tank through the feed conduit; adding a flocculent to the feed material either before or after it has entered the tank; allowing the feed material to pass through the discharge section whilst the velocity of the feed material decreases; allowing heavier solid particles to settle under the influence of gravity towards the bottom of the tank; allowing lighter solid particles to pass upwardly through the annular throat to a zone which increases in cross-sectional area so that the velocity of liquid flowing upwardly within the zone will decrease; selecting and monitoring the flow of feed material into the tank so that a bed of S 25 solid particles forms within the tank above the throat in the zone which increases in cross-sectional area; and withdrawing clarified liquid from the top of the tank above the bed, and sludge from the bottom of the tank.

15. A method according to claim 14 which includes the step of diverting a e g. 30 percentage of the clarified liquid into the feed conduit to mix with the feed material.

16. A method according to claim 15 which includes the step of varying the percentage of clarified liquid introduced into the feed conduit so as to vary the specific gravity of material passing into the feed conduit and thereby optimise the separation characteristics of the separator. A IN LI1H[l bo2'27 1CW u~ r I 19

17. A method of separating a solids~ liquids mnix substantially as hereinbefore described with reference to the drawings. Dated 25 February, 1999 Ultrasep (Proprietary) Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON *a .00. [11 1.1111.1 102 '7 I