LIQUID/SOLIDS SEPARATOR

Abstract: A separator for separating solids and liquids from a feed material containing a mix of solids and liquids, the separator includes a tank having a top, generally vertical side walls, and a convergently tapered bottom. A clarified liquid outlet is provided at or near the top of the tank and a sludge outlet is provided from the tapered bottom of the tank. A generally vertically aligned feed conduit is located within the tank near the top thereof, the feed conduit including a feed section and a discharge section. The feed section is adapted to receive feed material and the discharge section is adapted to discharge feed material into the tank below the top thereof. The discharge section preferably tapers outwardly in a downward direction.

Description: LIQUID/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discharged, usually at the top of the separator, and the solids which usually settle under the influence of gravity are withdrawn from the separator at the lower end thereof.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 frequently termed "underflow". In operation, the largest of the solid particles generally will separate under gravity to the lower region of the separator. The smaller particles, known as colloidal solids, will generally not settle within an acceptable time frame. Clarifiers/thickeners therefore rely on the addition of a coagulant or flocculant 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 ree, and will require acceptable levels of flocculant. SUMMARY OF THE INVENTION According to a first aspect of the invention, 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. The discharge section preferably tapers divergently in a downward direction. The feed conduit may be centrally located and vertically aligned within the tank. Preferably the feed section is cylindrical, and the discharge section is of inverted cone shape, and the axis of the feed section and the discharge section are coincident with each other and with the vertical axis of the tank. The discharge section may terminate in a lower edge which is substantially equidistantly spaced away from the vertical side walls of the tank around the entire periphery of the tank, thereby defining an annular throat between said lower edge and the vertical side walls. The width of the throat may be between 5% and 15% of the diameter of the tank. Preferably, the width of the throat is approximately 10% of the diameter of the tank. The upper surface of the cone shaped discharge section may define, together with the vertical side walls of the tank, an upwardly diverging settling bed. The half cone angle of the discharge section may be between 20" and 45°. Preferably, the half cone angle of the discharge section is approximately 30°. The separator may include a recycle conduit which extends upwardly within the tank from a region below the discharge section to the top or near the top of the tank. The recycle conduit may be located within the feed conduit, preferably coaxially therewith. The recycle conduit may comprise an upper right-circular cylindrical section, and a lower, downwardly diverging, conical section. The discharge section may comprise a downwardly diverging conical section, with the lower conical section of the recycle conduit nesting within the discharge section. The cone angles of the discharge section and the lower conical section are preferably substantially the same. The separator may further include a plurality of downwardly converging truncated cones suspended, one below the other, within the tank, the lowermost truncated cone leading towards the tapered bottom of the tank. Preferably, the separator has three truncated cones. The truncated cones are preferably suspended from and lie below the feed conduit. The separator may include a launder at or near the top of the tank into which clarified liquid will flow in use. The feed conduit may have an open upper end into which clarified liquid may flow in use. Preferably, the levels of the launder and the upper end of the feed conduit can be adjusted relative to each other to thereby provide means for selectively varying the relative percentages of clarified liquid which flow into the feed conduit and the launder respectively. The launder may be of annular shape and surround, but be spaced from, the upper end of the feed conduit. The launder preferably incorporates a weir over which the clarified liquid will flow into the launder, the weir comprising a plurality of V-shaped notches. The V-shaped notches are preferably evenly spaced around the launder. The launder may be adjustable relative to the open upper end of the feed conduit The level of the open end of the feed conduit may also be adjustable relative to the launder. The open upper end of the feed conduit may include a weir over which clarified liquid will flow into the feed conduit, the weir comprising a plurality of V-shaped notches spaced around the upper end of the feed conduit. The feed material may be fed into the feed conduit through a lateral supply conduit which joins into the feed conduit below the upper end of the feed conduit The lateral supply conduit may have an auxiliary conduit feeding into it, the auxiliary conduit being used to introduce flocculent into the feed material in use. According to a second aspect of the invention, there is provided a feed conduit for a liquids/solids separator, said feed conduit comprising a cylindrical feed section, and a downwardly diverging discharge section which is fixed to and coaxially aligned with the feed section, the feed conduit being adapted to be mounted with its axis generally vertical within a liquids/solids separator. The feed section may be right circular cylindrical, and the discharge section conical. The feed conduit may further include a recycle conduit which extends through and is coaxially aligned with the feed section and the discharge section. The recycle conduit may have an upper, right circular cylindrical section, and a lower, downwardly diverging, conical section. According to a third aspect of the invention, there is provided a solids concentration apparatus for use within a liquids/solids separator, said solids concentration apparatus comprising a plurality of aligned, truncated, right angled cones, adapted to be mounted one below the other within a liquids/solids separator, each cone being oriented so as to be downwardly convergent. The cone-angles of all of the truncated cones are preferably substantially the same. According to a fourth aspect of the invention there is provided a method of 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 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 discbarge section, the method including the steps of: introducing the feed material into the tank through the feed conduit; adding a flocculant to the feed material either before or after it has entered the tank; allowing the feed material to pass through the discharge section; 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 throat; 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, 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. 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. 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. DETAILED 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 widiin 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 the discharge section is equally spaced from the walls 14 of the tank around the entire lower periphery of the discharge section 28. Feed material 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 flocculant 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 20° and 45° and is preferably about 30°. 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 preferably 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 10% 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 truncated conical section 46. The conical section 46 is downwardly diverging as shown and is nested within the discharge section 28. An annular gap 48 is thus defined between the discharge section 28 and the conical section 46. Located below the recycle conduit 42 is a solids concentration apparatus 50. 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 liquid 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 60 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 series 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 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 30 of the discharge section 28. The liquid and similar particles will then move upwardly through the throat 40 into a settling bed or "floe bed", indicated by the shaded area 66 located above the throat 40. It will be noted that the floe 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 floe bed 66 the relatively rapidly upwardly moving solid particles will tend to collide with the underside of the Hoc 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 floe bed 66 thus acts somewhat like a sieve to trap upwardly flowing solid panicles. Liquid will pass up through the floe bed towards the launder but even small solids will be trapped in the floe bed. The floe 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 flow has passed through the throat, to again slow the flow velocity above the throat to allow the floe 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 some of the clarified liquid which is available for discharge 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 adjustable and for this reason a flexible connecting pipe 67 is fitted between the launder 56 and the clarified liquid outlet 20. The V-shaped notches which define the respective 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 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 large 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 used. As previously mentioned, the separator does not need to be circular in cross-section. 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/solids 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-section of the clarifier/thickener upward of the annular throat 40 quickly stabilises the depth of the floe bed and also increases the efficiency of the floe bed since the upward velocity imparted on the floe particles rapidly decreases. This will lead to more collisions between particles and larger floes will quickly occur thus allowing the larger floe particles to fall under gravity through the throat 40 thereby constantly depleting the floe bed of solids. The discharge from the consolidation cone is essentially above the underflow discharge. The bulk of the high 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. 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 self- cleaning and it is envisaged that it wil] have a low flocculant consumption due to the larger particles tending to settle under gravity so they will not be carried up into the floe bed. The floe 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 lowering the top of the floe bed but would possibly improve the efficiency of the floe bed.

Claims: CLAIMS 1. A separator for separating solids and hquids 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. 2. A separator according to claim 1 wherein the discharge section tapers divergently in a downward direction. 3. A separator according to claim 1 or claim 2 wherein the feed conduit is centrally located and vertically aligned within the tank. 4. A separator according to claim 3 wherein the feed section is cylindrical, and the discharge section is of inverted cone shape, and the axis of the feed section and the discharge section are coincident with each other and with the vertical axis of the tank. 5. A separator according to claim 4 wherein the discharge section terminates in a lower edge which is substantially equidistantly spaced away from the vertical side walls of the tank around the entire periphery of the tank, thereby defining an annular throat between said lower edge and the vertical side walls. 6. A separator according to claim 6 wherein the width of the throat is between 5% and 15% of the diameter of the tank. 7. A separator according to claim 6 wherein the width of the throat is approximately 10% of the diameter of the tank. 8. A separator according to any one of claims 5 to 7 wherein the upper surface of the cone shaped discharge section defines, together with the vertical side walls of the tank, an upwardly diverging settling bed. 9. A separator according to any one of claims 4 to 8 wherein the half cone angle of the discharge section is between 20° and 45°. 10. A separator according to claim 9 wherein the half cone angle of the discharge section is approximately 30°. 11. A separator according to any preceding claim which includes a recycle conduit which extends upwardly within the tank from a region below the discharge section to the top or near the top of the tank. 12. A separator according to claim 11 wherein the recycle conduit is located within the feed conduit. 13. A separator according to claim 12 wherein the recycle conduit is coaxially located within the feed conduit 14. A separator according to any one of claims 11 to 13 wherein the recycle conduit comprises an upper right-circular cylindrical section, and a lower, downwardly diverging, conical section. 15. A separator according to claim 14 wherein the discharge section comprises a downwardly diverging conical section, and the lower conical section of the recycle conduit nests within the discharge section. 16. A separator according to claim 15 wherein the cone angles of the discharge section and the lower conical section are substantially the same. 17. A separator according to any preceding claim which further includes a plurality of downwardly converging truncated cones suspended, one below the other, within the tank, the lowermost truncated cone leading towards the tapered bottom of the tank. 18. A separator according to claim 17 which has three truncated cones. 19. A separator according to either claim 17 or 18 wherein the truncated cones are suspended from and lie below the feed conduit 20. A separator according to any preceding claim which includes a launder at or near the top of the tank into which clarified liquid will flow in use. 21. A separator according to claim 20 wherein the feed conduit has an open upper end into which clarified liquid may flow in use. 22. A separator according to claim 1 wherein the levels of the launder and the upper end of the feed conduit can be adjusted relative to each other to thereby provide means for selectively varying the relative percentages of clarified liquid which flow into the feed conduit and the launder respectively. 23. A separator according to claim 22 wherein the launder is of annular shape and surrounds, but is spaced from, the upper end of the feed conduit. 24. A separator according to any one of claims 20 to 23 wherein the launder incorporates a weir over which the clarified liquid will flow into the launder, the weir comprising a plurality of V-shaped notches. 25. A separator according to claim 24 wherein the V-shaped notches are evenly spaced around the launder. 26. A separator according to claim 22 wherein the level of the launder is adjustable relative to the open upper end of the feed conduit. 27. A separator according to claim 22 wherein the level of the open end of the feed conduit is adjustable relative to the launder. 28. A separator according to any one αf claims 21 to 23 wherein the open upper end of the feed conduit includes a weir over which clarified liquid will flow into the feed conduit, the weir comprising a plurality of V-shaped notches spaced around the upper end of the feed conduit. 29. A separator according to any preceding claim wherein the feed material is fed into the feed conduit through a lateral supply conduit which joins into the feed conduit below the upper end of the feed conduit. 30. A separator according to claim 29 wherein the lateral supply conduit has an auxiliary conduit feeding into it, the auxiliary conduit being used to introduce fLocculent into the feed material in use. 31. A feed conduit for a liquids/solids separator, said feed conduit comprising a cylindrical feed section, and a downwardly diverging discharge section which is fixed to and coaxially aligned with the feed section, the feed conduit being adapted to be mounted with its axis generally vertical within a liquids/solids separator. 32. A feed conduit according to claim 31 wherein the feed section is right circular cylindrical, and the discharge section is conical. 33. A feed conduit according to claim 31 or claim 32 which further includes a recycle conduit which extends through and is coaxially aligned with the feed section and the discharge section. 34. A feed conduit according to claim 33 wherein the recycle conduit has an upper, right circular cylindrical section, and a lower, downwardly diverging, conical section. 35. Solids concentration apparatus for use within a liquids/solids separator, said solids concentration apparatus comprising a plurality of aligned, truncated, right angled cones, adapted to be mounted one below the other within a liquids/solids separator, each cone being oriented so as to be downwardly convergent 36. Solids concentration apparatus according to claim 35 wherein the cone-angles of all of the truncated cones are substantially the same. 37. A method of 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 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 flocculant to the feed material either before or after it has entered the tank; allowing the feed material to pass through the discharge section; 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 throat; 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; and withdrawing clarified liquid from the top of the tank above the bed, and sludge from the bottom of the tank. 38. A method according to claim 37 which includes the step of diverting a percentage of the clarified liquid into the feed conduit to mix with the feed material. 39. A method according to claim 38 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. 40. A separator substantially as hereinbefore described with reference to the drawings. 41. A feed conduit substantially as hereinbefore described with reference to the drawings. 42. A separation apparatus substantially as hereinbefore described with reference to the drawings. 43. A method of separating a solids/liquids mix substantially as hereinbefore described with reference to the drawings.

Inventors: BROWN KEITH EDWIN FRANK, DU TOIT WALTERS FRANCOIS, BROWN, KEITH, EDWIN, FRANK, DU TOIT, WALTERS, FRANCOIS
Applicants: BROWN KEITH EDWIN FRANK, TOIT WALTERS FRANCOIS DU, BROWN, KEITH, EDWIN, FRANK, DU TOIT, WALTERS, FRANCOIS
Application year: 1996
Main classification: B01D21
IPC codes: B01D21