AU728638B2 - A thickener or clarifier - Google Patents

Description

,S P/00/011 Regulation 3.2

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD

PATENT

Name of Applicant: Address of Applicant: Actual Inventor: Address for Service: a a @9 ROBERT HUME PANNELL as trustee of Barchester Investment Trust 8 ELGEE ROAD BELLEVUE WA 6056 ROBERT HUME PANNELL Griffith Hack Co.

256 Adelaide Terrace (6 Floor) PERTH WA 6000 0 00 Standard Complete Specification for the invention entitled: A THICKENER OR CLARIFIER Details of Associated Provisional Applications: Australian provisional patent application No. P02275 filed on 12 September 1996.

The following is a full description of this invention, including the best method of performing it known to me:- 2 A THICKENER OR CLARIFIER The present invention relates generally to a thickener or clarifier and relates particularly, though not exclusively, to a relatively high rate thickener.

Australian patent No. 667938 describes and illustrates various thickeners relying on gravity settling of solids in a slurry contained within a vessel. The slurry flows via a feed conduit to a feed cylinder or well which is located within an upper free settling region of the vessel. Any flocculant or coagulant agents added to the slurry are allowed to freely disperse through the slurry in the feed cylinder or well. The flocculated slurry then passes into the free settling region, in one embodiment via several flocculating cylinders. A clarified or carrier liquid fraction moves upwardly through the vessel and is removed as a clarified liquid overflow, and a solids fraction under gravity settling moves downwardly through the vessel into a :lower compaction region. A thickened sludge can then be removed as an underflow from the base of the vessel.

20 The essence of the invention disclosed in Australian patent No. 667938 appears to reside in the inclusion of one or more inclined pathways defined by a series of angle-shaped members or inverted cones being arranged one upon the other. The inclined pathways are disposed within the lower S. 25 compaction region and allow clarified liquid within the %.00 thickened sludge to flow upwardly through the compaction region and into the upper free settling region thereby supposedly increasing the solids density of the underflow.

0: In one thickener described in Australian patent No. 667938, a conduit is connected between an uppermost cone of the series of inverted cones and the feed well so that some of the clarified liquid within the compaction region is recycled to the feed well. The recycled clarified liquid 0 (W -3contains "seed flocs" which then combine with the feed slurry in the feed well.

Although the thickener of Australian patent No: 667938 is an improvement on conventional gravity sedimentation devices it suffers from at least the following drawbacks: the inclined pathways are not particularly efficient in effectively increasing the solids density of the thickened sludge underflow; and (ii) the thickener is relatively ineffective in dispersing the flocculant agent through the feed slurry.

An intention of the present invention is to provide a thickener or clarifier which is effective in producing a relatively high density solids underflow.

According to one aspect of the present invention there is provided a thickener or clarifier comprising: a settling vessel being configured to permit gravity settling of solid particles from a feed slurry, said vessel having an upper gravity settling region from o: which a clarified liquid overflow can be removed and a 20 lower compaction region from which a relatively high S* density solids underflow can be removed; a feed well disposed within said upper region of the settling vessel, said well being in liquid communication with the settling vessel via a feed well outlet; a feed line operatively communicating with the feed well, the feed line being designed to deliver a flow of the feed slurry to the feed well via a feed line outlet; .0 0and oe a riser tube having a lower end operatively cooperating with one or more inclined surfaces at least a portion of said surfaces being located within the lower compaction region of the settling vessel, an upper end of the riser tube being positioned adjacent to the feed line 4 outlet or connected to the feed line whereby, in use, the flow of the feed slurry through the feed line produces a low pressure zone at the upper end of the riser tube thereby creating a venturi effect and thus promoting a flow of recycled clarified liquid from the lower compaction region of the settling vessel to the feed well, via said one or more inclined surfaces and the riser tube, so as to produce a relatively high density solids underflow.

Typically, the feed well includes a mixer chamber being designed to effectively disperse a flocculant or coagulant agent through the feed slurry.

Preferably, the riser tube is connected to the feed line which includes a nozzle and a throat immediately upstream and downstream, respectively, of the upper end of the riser tube so as to increase the venturi effect for promoting the flow of recycled clarified liquid to the feed well.

According to another aspect of the present invention there ::is provided a thickener or clarifier comprising: a settling vessel being configured to permit 20 gravity setting of solid particles from a feed slurry, said vessel having an upper gravity settling region from which a clarified liquid overflow can be removed and a lower S"compaction region from which a relatively high density solids underflow can be removed; 25 a feed well disposed within said upper region of the settling vessel, said well including a mixer chamber being designed to effectively disperse a flocculant or coagulant agent through the feed slurry, and being in liquid communication with the settling vessel via a feed well outlet; a feed line operatively communicating with the feed well, the feed line being designed to deliver a flow of the feed slurry to the feed well via a feed line outlet; and a riser tube having a lower end operatively cooperating with one or more inclined surfaces at least a portion of said surfaces being located within the lower compaction region of the settling vessel, an upper end of the riser tube being positioned within the feed well or connected to the feed line whereby, in use, the flow of the feed slurry to the feed well effectively mixes with the flocculant and/or coagulant agent in the mixer chamber prior to gravity settling of solid particles within the settling vessel wherein a recycled clarified liquid is forced from a lower compaction region of the settling vessel to flow to the feed well via said one or more inclined surfaces and the riser tube to combine with the feed slurry so as to produce a relatively high density solids underflow.

Typically, the mixer chamber is defined by a mixer box to which the feed line is connected, the mixer box having an opening so as to allow the slurry from the mixer chamber to flow to the mixer well. More typically, the mixer box 20 includes a series of mixer baffle plates being located within the mixer chamber thereby turbulating the flow of the slurry through the mixer chamber so as to effectively disperse the flocculant or coagulant agent through the feed slurry.

Alternatively, the mixer chamber is defined by a generally cylindrical or conical frustum shaped member positioned immediately downstream of the feed line outlet.

Advantageously, the cylindrical or conical frustum shaped 3 member includes one or more vanes formed on an internal 30 surface thereof, said vanes being configured to induce a turbulent flow of the slurry to the feed well.

Typically, the feed line outlet is tapered so that the velocity of the slurry flowing through said outlet is increased thereby enhancing the venturi effect which acts 6to promote the flow of recycled clarified liquid from the lower compaction region of the settling vessel to the feed well. More typically, the feed line upstream of its outlet includes a series of feed line baffle plates formed internally so as to increase the turbulence of the slurry flowing through said feed line.

Typically, the thickener or clarifier includes one or more polymer injection lines connected to the feed line and/or operatively communicating with the mixer chamber so as to provide a predetermined dose of flocculant or coagulant agent to the feed slurry. Alternatively, the thickener or clarifier includes a polymer injection line connected to the riser pipe whereby a dose of flocculant or coagulant can be added to the recycled clarified liquid.

Typically, the thickener or clarifier further includes a valve located within a wall of the feed well, the valve being designed to allow a portion of the clarified liquid overflow from the upper gravity settling region of the S. settling vessel to return to the feed well so as to control 20 the solids density of the slurry within the feed well.

More typically, the valve includes an overflow weir or opening formed within the wall of the feed well. In one embodiment, the valve also includes a downstream and an upstream flap covering the overflow weir or opening and being connected to an inner and an outer surface, respectively, of the feed well, the upstream flap being adjustable so as to provide a predetermined flow of the clarified liquid to the feed well and the downstream flap 3 acting as a non-return valve to prevent slurry flowing from 30 the feed well into the upper gravity settling region of the settling vessel.

Typically, the thickener or clarifier also comprises a slurry tube coupled to the feed well outlet, a flocculation cylinder being located about the slurry tube whereby a 7 relatively concentrated slurry fraction passes downwardly into the upper gravity settling region and a clarified liquid fraction passes upwardly into the upper gravity settling region to be withdrawn as the clarified liquid overflow.

Typically, said one or more inclined surfaces are defined by an inverted cone being at least partly located within the lower compaction region of the settling vessel. More typically, said inverted cone is one of a plurality of inverted cones located one upon the other about the riser tube, an apex opening of the lowermost cone being connected to the lower end of the riser tube and the riser tube between adjacent cones including one or more apertures so that the recycled clarified liquid being forced from the lower compaction region of the settling vessel can enter the riser tube from underneath the plurality of cones via the lower end of the tube and said one or more apertures.

Alternatively, an apex opening of each one of said eoeplurality of cones is connected to one riser tube of a 20 plurality of said tubes, respectively, whereby said tubes are arranged concentric with each other. In another embodiment, said one or more inclined surfaces are defined by a series of inverted cones spaced about the lower region of the settling vessel, an apex opening of each of said cones being connected to a riser tube which is connected to *.one of several of said feed well outlets, respectively.

Typically, the thickener or clarifier further includes a rake mechanism having a shaft with one or more rakes extending generally radially therefrom, said rakes being arranged within the lower compaction region of the settling vessel so that rotation of the shaft effects movement of the rakes thereby shearing solids within said compaction region of said vessel and thus driving clarified liquid upwardly into the upper gravity settling region of the 8 settling vessel or onto said one or more inclined surfaces.

More typically, the shaft passes through the riser tube and is adapted to be driven via a motor located above the thickener or clarifier. In one embodiment, the rake mechanism also includes a scroll or archimedean screw mounted on the shaft so as to promote the flow of clarified liquid onto said one or more inclined surfaces for recycle to the feed well.

Typically, each of said one or more rakes includes an elongate member having opposing concave convex surfaces facing downward and upward, respectively, whereby a substantially solids fraction of the slurry moving down the vessel passes across said convex surface and a liquor fraction of the slurry within the compaction region can be exhausted up the concave surface toward the upper gravity setting region. In one embodiment, the elongate member is an elongate angle-shaped member. Alternatively, the rake mechanism is constructed in the form of a conventional "flighted" rake.

20 Typically, the settling vessel consists of a cylindrical portion formed continuous with a large diameter end of a conical frustum portion. Typically, the upper gravity settling region and the lower compaction regions are located generally within the cylindrical portion and the conical frustum portion, respectively.

*According to yet another aspect of the present invention there is provided a method for thickening or clarifying a slurry, said method comprising the steps of: providing a thickener or clarifier including a settling vessel, a feed well having a feed well outlet disposed within an upper gravity settling region of the settling vessel, a feed line having a feed line outlet operatively communicating with the feed well, and a riser tube having a lower end operatively cooperating with one or 9 more inclined surfaces located within a lower compaction region of the settling vessel, an upper end of the riser tube being positioned adjacent to the feed line outlet or connected to the feed line and providing a flow of a feed slurry to the feed well via the feed line and the feed line outlet, said flow through the feed line producing a low pressure zone at the upper end of the riser tube thereby creating a venturi effect and thus promoting a flow of recycled clarified liquid from the lower compaction region of the settling vessel to the feed well, via said one or more inclined surfaces and the riser tube, so as to produce a relatively high density solids underflow.

In order to achieve a better understanding of the nature of the present invention several preferred embodiments of a thickener or clarifier will now be described in some detail, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a side sectional view of a thickener 20 or clarifier; Figure 2 is a detailed side sectional view of a "venturi arrangement" taken from the thickener or clarifier of Figure 1; Figure 3 is a detailed plan and side sectional 25 view of a mixer chamber together with an alternative "venturi arrangement"; S Figure 4 is a detailed plan and side sectional view of another mixer chamber and venturi arrangement together with polymer injection lines; Figure 5 is a detailed side sectional view of a further example of a "venturi arrangement"; Figure 6 is a plan sectional view of another mixer chamber and "venturi arrangement"; Figure 7 is a side sectional view of another thickener or clarifier; Figure 8 is a detailed side sectional view of another "venturi arrangement" without a mixer chamber; Figure 9 is a detailed sectional view of a further variation on the "venturi arrangement" shown in Figure 8; Figure 10 is a side sectional view of a further thickener or clarifier; Figure 11 is a detailed side sectional view of another type of "venturi arrangement", the thickener or clarifier also including a rake mechanism; Figure 12 is a side sectional view of yet another thickener or clarifier incorporating a further rake mechanism; Figure 13 is a detailed side sectional view of another rake mechanism incorporated within the thickener or clarifier of Figure 12; Figure 14 is a detailed side sectional view of yet another rake mechanism incorporated in the thickener or clarifier of Figure 12; Figure 15 is a detailed side view of a typical rake mechanism; and Figure 16 is a plan and detailed side sectional view of yet another mixer chamber together with polymer injection lines.

As shown in Figure 1 there is a thickener or clarifier comprising a settling vessel 12, a feed well 14, a feed *--line 16, a riser tube 18 together with one or more inclined surfaces 20, and a flocculation cylinder 22.

settling vessel 12 consists of a cylindrical-shaped 30 portion 24 formed continuous with a large diameter end of a conical frustum portion 26. The feed well 14 is located within an upper gravity settling region 28 of the vessel 12 and includes a cylindrical-shaped perimeter wall 30 having a circular-shaped base 32. The feed line 16 passes through -11both the cylindrical-shaped portion 24 of the vessel 12 and perimeter wall 30 of the feed well 14.

The feed well 14 includes a mixer chamber shown generally as 34. The mixer chamber 34 is defined by a mixer box 36 having a pair of opposing side walls 38 interconnected by a base The side walls 38 and base 40 are connected to the perimeter wall 30 of the feed well 14 around an outlet 42 of the feed line 16. The mixer box 36 has an open side facing the outlet 42 of the feed line 16. The base 40 of the mixer box 36 is slightly tilted upward in a direction away from the perimeter wall 30 of the feed well 14.

As shown in Figure 2, the mixer chamber 34 also includes a generally conical-shaped member 44 positioned about and immediately downstream of the feed line outlet 42. The conical member 44 includes several vanes 46 formed on an internal surface thereof. The vanes 46 are configured to induce a turbulent flow of slurry passing through the mixer chamber 34. Turbulence is useful for mixing and/or dispersing flocculant or coagulant through the feed slurry, as well as shearing and/or stripping gas particles off solid particles of slurry.

*o As illustrated in Figures 1 and 2, an upper end 48 of the riser tube 18 is located immediately adjacent an annular gap defined between the feed line outlet 42 and the conical member 44. Furthermore, the feed line outlet 42 is tapered so that :the velocity of slurry flowing through the feed line 16 is oooo g: 30 increased as it enters the conical member 44. It will be appreciated that the flow of slurry from the feed line outlet 42 produces a low pressure zone 50 adjacent the upper end 48 of the riser tube 18. The annular space 50 generally defines this low pressure zone. In operation, the low pressure zone 35 50 acts to draw recycled clarified liquid from the riser tube 18 so as to promote the flow of recycled clarified liquid from the settling vessel 12. That is, the configuration of the feed line outlet 42, the upper end of the riser tube 18 and the conical member 44 together form a "venturi arrangement" 12which promotes the flow of recycled clarified liquid through the riser tube 18.

The thickener or clarifier 10 depicted in Figure 1 also includes a flocculation cylinder 22 which is well known in the art. A slurry tube 52 having a conical-shaped upper portion connects to a feed well outlet 54 formed in the base 32 of the feed well 14. The flocculation cylinder 22 is located about the slurry tube 52 whereby a relatively concentrated slurry fraction can pass downwardly into the upper gravity settling region 28 and a clarified liquid fraction can pass upwardly to be withdrawn as a clarified liquid overflow.

In this embodiment, the thickener or clarifier 10 includes the single riser tube 18 which passes through the base 32 of the feed well 14 and is formed so that the upper end 48 is located adjacent the feed line outlet 42 as herein before described. A lower end 56 of the riser tube 18 is located within a lower compaction region 58 of the settling vessel 12. The lower compaction region 58 is generally S 20 defined within the conical frustum section 26 of the vessel S12. However, it will be appreciated that the gravity settling region 28 and compaction region 58 and the general interface therebetween may vary depending upon the nature of the feed slurry and operating conditions.

25 The inclined surfaces 20 described earlier are defined by three inverted cones 60A, 60B, 60C located one upon the other within the compaction region 58. An apex opening of the lowermost cone 60C is connected to the lower end 56 of S the riser tube 18. The intermediate and uppermost cones 60B, 60C are connected to the risertube 18 one above the other. The riser tube 18 between adjacent cones 60A to includes one or more apertures (not shown) which allow recycle clarified liquid being forced from the lower compaction region 58 to enter the riser tube 18.

13 Figure 3 illustrates another embodiment of the "venturi arrangement" described above. Like numerals are used to designate corresponding components of the thickener or clarifier 10 described above. In this example, the upper end 48 of the riser tube 18 is located immediately beneath the feed line outlet 42 so as to produce the low pressure zone and suction of recycled clarified liquid from the riser tube 18 as effected by the venturi effect.

Furthermore, the feed line 16 includes a series of feed line baffle plates 62 formed internally. The baffle plates 62 act so as to produce a turbulent flow of the slurry through the feed line 16. The mixer chamber 34 is defined by a single side wall 64 and base 66 connected to the perimeter wall 30 of the feed well 14.

Figure 4 illustrates another variation on the "venturi arrangement" together with a series of polymer injection lines 68A, 68B, 68C. In this embodiment, the upper end 48 of the riser tube 18 is located immediately downstream and generally in line with the feed line outlet 42. A low 20 pressure zone is thus formed about the periphery of the upper end 48 of the riser tube 18 so as to promote the flow of recycled clarified liquid through the riser tube 18.

The inclined surfaces 20 in the compaction region 58 are defined by one or more elongate angle-shaped members 70B. The angle-shaped members 70A, 70B converge to a region located beneath the lower end 56 of the riser tube 18. Thus, any clarified liquid moving upwardly on a concave surface of the angle-shaped members will enter the lower end 56 of the riser tube 18. One of the polymer 30 injection lines 68A is connected directly to the feed line 16 whereas the other two injection lines 68B, 68C discharge into the mixer chamber 34.

Figure 5 shows a detailed view of a "venturi arrangement" of the type depicted in Figure 2 but without the mixer box 14- 36. In this embodiment, the conical member 44 and vanes 46 alone define the mixer chamber 34. Figure 5 also shows in some detail a valve shown generally as 72 located within the perimeter wall 30 of the feed well 14. The valve 72 is designed to allow a portion of clarified liquid overflow from the upper gravity settling region 28 to return to the feed well 14 so as to control the solids density of the slurry within the feed well 14.

The valve 72 includes an overflow weir or opening 74 formed within the perimeter wall 30, and an upstream and downstream flap 76, 78 respectively covering the overflow weir or opening 74 on opposing sides of the perimeter wall In this example, the upstream flap 76 is adjustable via adjustment rod or cable 80 so as to provide a predetermined flow of the clarified liquid to the feed well 14, and the downstream flap 78 is merely constructed of a resiliently flexible material so as to act as a non-return valve to prevent slurry flowing from the feed well 14 into *f the upper gravity settling region 28. The thickener or 20 clarifier 10 of also includes an overflow launder 82 formed about an upper perimeter of the settling vessel 12. The overflow launder 82 is designed to remove clarified liquid from the gravity settling region 28.

Figure 6 illustrates a further embodiment of a "venturi arrangement" wherein the mixer chamber 34 is located centrally within the feed well 14. The mixer chamber 34 is generally box-shaped having three interconnected perimeter walls 84A, 84B, 84C and a base 86 with one side of the box being open to allow the slurry to pass into the 30 body of the feed well 14. The feed line baffle plates 62 of this embodiment are depicted by the hatched lines contained within the feed line 16.

Figures 7 to 10 illustrate various constructions of the "venturi arrangement" where the riser tube(s) 18 are ,'S's 15 connected directly to the feed line 16. In these examples, the low pressure zone which creates the venturi effect and suction of recycled clarified liquid from the compaction region 58, is located generally at the upper end 48 of the riser tube(s) 18 at a region where the slurry in the feed line 16 flows across the connection of the riser tube(s) 18. In all of the embodiments illustrated in Figures 7 to the thickener or clarifier 10 does not incorporate a mixer chamber. Rather, the thickeners shown in Figures 8 and 9 include the turbulating baffles 62 downstream and upstream, respectively, of the riser tube 18 in connection to the feed line 16. Figures 7 and 10 illustrate two (2) sets of inverted cones 20A, 20B each set being connected to a riser tube 18A, 18B respectively. The inverted cones 20A, 20B are arranged within different areas of the settling vessel 12 so as to optimise the recovery of recycled clarified liquid largely from the compaction region 58 in order to increase the underflow solids density.

20 Figure 10 depicts a further variation on the "venturi arrangements" described. In this embodiment, a nozzle 88 and a throat 90 is formed within the feed line 16 immediately upstream and downstream, respectively, of the connection of the upper end 48 of the riser tube 18A, 18B 25 to the feed line 16. Thus, a low pressure zone is created between the nozzle 88 and throat 90 so as to increase the s.flow of recycled clarified liquid from the compaction region 58 to the feed well 14 via the riser tube 18A or 18B.

30 Figure 11 illustrates another thickener or clarifier 10, in this example including a rake mechanism 92. The rake mechanism 92 has a shaft 94 with a pair of arms 96 extending radially therefrom. The arms 96 each include one or more blades 98 connected to a bottom portion thereof, the blades 98 designed to force the high density solids 16underflow to the point of discharge (not shown). Although not depicted, the rake mechanism92 also includes a drive assembly together with a motor located above the thickener or clarifier The thickener or clarifier of Figure 11 includes yet another variation on the "venturi arrangement" where, in this embodiment, the feed line outlet 42 is enclosed by a recycle nozzle 100 connected to the upper end 48 of the riser tube 18. In a similar manner to the "venturi arrangement" illustrated in Figure 2, a low pressure zone is formed about an annulus space defined between the recycle nozzle 100 and the feed line outlet 42. Thus, clarified liquid is drawn from the compaction region 58 via the riser tube 18 and discharged into the mixer chamber 34 together with the feed slurry. Polymer injection lines 102A, 102B are connected directly to the recycle nozzle 100 and riser tube 18, respectively.

0*° S....Figures 12 and 13 show a variation on the thickener or

S

clarifier 10 of Figure 11. In these embodiments, the shaft 20 94 of the rake mechanism 92 passes longitudinally through the riser tube 18. As shown in Figure 12, the shaft 94 passes through the riser tube 18 within the feed well 14.

Figures 12 to 14 include various constructions of the rake .mechanism 92. All rake mechanisms 92 include a pair of divergent picket rakes 104A, 104B being configured so as to S*o. effect sharing of solids within the compaction region 58 0 adjacent the conical portion 26 of the settling vessel 12.

The rake mechanism 92 of Figure 13 includes an additional pair of picket rakes 106A, 106B mounted to the shaft 94 underneath the inverted cones 60A, 60B, 60C. Thus, shearing of solids in the compaction region 58 underneath the cones 60A, 60B, 60C exhausts recycled clarified liquid directly into the riser tube 18. Figure 14 shows a variation on the further pair of divergent picket rakes 17 106A, 106B wherein a scroll or archimedean screw 108 is mounted on the shaft 94. This also facilitates dewatering into the inverted cones 60A, 60B, 60C and the feed well 14 via the riser tube 18.

Figure 15 illustrates a particular rake design which assists shearing of solids in the compaction region 58 and thus dewatering to produce high density solids in the underflow. In this example, the picket rates are constructed of an elongate angle-shaped member 110 connected to the shaft 94 via a pair of coupling arms 112A, 112B. Opposing concave and convex surfaces of the elongate member 110 face downward and upward, respectively, so that mass material moving down the vessel 12 passes across the picket rake 110 (as shown by the solid arrow) and clarified liquid forced from the compaction region 58 exhausts up the concave section of the picket rake 110 (as shown by the broken arrow).

000 Figure 16 illustrates another aspect of the present invention wherein a polymer agent is effectively dispersed ¢ee S 20 through the feed slurry within a mixer chamber. Although not illustrated in Figure 16, the remainder of the thickener or clarifier 210 is similar in construction to the thickener or clarifier 10 described above. Like components of the thickener or clarifier 210 illustrated in Figure 16 have been prefixed with the numeral For example, the riser tube of the thickener or clarifier 210 has been denoted to 218.

0*0* The thickener or clarifier 210 includes polymer injection lines 268 connected directly onto the feed line 216 or entering the mixer chamber 234. In this example, the mixer chamber 234 includes a pair of opposing side walls 238 and a base 240 connected to the perimeter wall 230 of the feed well 214. A series of baffle plates 300 are connected in a staggered arrangement to the base 240 of the mixer chamber 18 234. The upper end 248 of the riser tube 218 connects to the base 240 of the mixer chamber 234 at a location downstream of the baffle plates 300. The baffle plates 300 act so as to intimately mix the slurry and flocculant or coagulant agents prior to combining with the recycled clarified liquid from the riser tube 218.

Furthermore, effective dilution of the feed slurry using clarified liquid via the overflow weir or opening 274 in the feed well 214 can be achieved prior to combining with the recycled clarified liquid. Advantageously, the baffles 300 are arranged so that a vortex is created in the proximity of the upper end 248 of the riser tube 218 so as not to disturb any seed flocs contained within the recycled clarified liquid.

In order to facilitate a further understanding of the present invention operation of the various thickeners or clarifiers 10 or 210 described above will now be explained.

A feed slurry is delivered to the thickener or clarifier or 210 via the feed line 216. The slurry may be practically any process stream which includes a suspension •of solids within a carrier liquid. For example, the feed o oslurry may be a nickel concentrate stream from an autoclave leach unit.

o° The feed slurry enters the feed well 14 from the feed line outlet 42. For the thickeners or clarifiers 10 illustrated e in Figures 1 to 6, the feed slurry is delivered to a mixer chamber 34 before entering the body of the feed well 14.

The mixer chamber 44 provides intimate mixing of the slurry and any flocculant or coagulant agents. The flocculated slurry then passes from the base of the feed well 14 into one or more of the flocculation cylinders 22. The flocculation cylinders 22 act in a conventional manner S.s whereby a concentrated slurry fraction passes downwardly 19 into the gravity settling region 28 and a clarified liquid fraction passes upwardly into the upper gravity settling region 28 to be withdrawn as the clarified liquid overflow.

Hindered and free settling of solids within the slurry contained in the settling vessel 12 occurs in a conventional manner. Similarly, compaction of a solids fraction of the slurry occurs in the lower compaction region 58 of the settling vessel 12.

The inverted cones 60A, 60B, 60C located in the conical frustum portion 26 of the settling vessel 12 promotes dewatering of the solids concentrate within the compaction region 58. Clarified liquid contained within the compaction region 58 is forced up a lower surface of the inverted cones 60A, 60B, 60C into the riser tube 18. This dewatering mechanism using inverted cones or the like is known in the art, for example reference is made to Volume 2 of "Mineral Processing" by Gustave Tarjan and in particular Figure 7.22 of this publication.

Recycled clarified liquid forced up the riser tube 18 is discharged into the feed well 14 at an upper end 48 of the tube 18. The essence of the invention resides in locating *the upper end 48 of the riser tube 18 adjacent the feed *line outlet 42 so as to create a low pressure zone at the upper end 48 of the tube 18. This low pressure zone 25 creates a venturi effect and promotes the flow of recycled o clarified liquid from the lower compaction region 58 via the inverted cones 60A to 60C and riser tube 18.

Accordingly, a relatively high density solids overflow is achieved. The recycled clarified liquid may also contain seed flocs which are combined with the incoming feed slurry to provide effective gravity sedimentation settling.

As best illustrated in Figure 5, a portion of the clarified liquid overflow can be returned to the feed well 14 so as to control the solids density of the slurry passing through to control the solids density of the slurry passing through said well 14. Adjustment of the cable or rod 80 regulates the flow of clarified liquid through the valve 72 which is located within the perimeter wall 30 of the feed well 14.

The clarified liquid overflow and high density solids underflow are removed from the thickener or clarifier 10 in a conventional manner. That is, the clarified liquor overflow enters the launder 82 located about the perimeter of the settling vessel 12 and can thereafter be pumped from the launder 82. The relatively high density solids underflow can be continuously or intermittently removed from the base of the conical frustum portion 26 of the settling vessel 12 via a pump or other means.

Now that several preferred embodiments of the present invention have been described in some detail it will be apparent to those skilled in the art that the thickener or clarifier has at least the following advantages over the admitted prior art.

1. The thickener or clarifier produces a relatively high density solids underflow wherein the various "venturi arrangements" maximise extraction of clarified liquid from the compaction region; 2. The thickener or clarifier is relatively "effective in dispersing polymer agents through the feed slurry to provide efficient flocculation of solids within 25 the feed slurry; :°ooo o 3. The thickener or clarifier can be designed so *.that it is suitable for a range of feed slurries having various solids density; and 4. The thickener or clarifier optimises the effect of flocculant or coagulant agents whereby seeding flocs are effectively recycled to combine with incoming feed slurry.

21 Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. For example, the overflow weir or valve may also include biasing means such as a spring forcing the downstream flap into a closed position. The thickener or clarifier may also employ a rake mechanism within the feed well, the rake mechanism acting so as to force diffusion of feed material from the well periphery into the settling vessel. In this embodiment, the thickener or clarifier would not include the floc cylinders described herein. Although the rake mechanism described has a pair of rakes it will be appreciated that depending on the size and capacity of the thickener or clarifier the rake mechanism may include any number of rakes or rake arms. The thickener or clarifier may comprise practically any number of columns of nested cones, each column of cones feeding back to the feed well via the riser tube. In the various embodiments where rakes are included it may be preferable to install suction tubes on the rake arms oriented behind the flights of said arms.

The suction tubes feed into a bushed manifold that draws recycled clarified liquid or liquor into the feed well via the riser tube. In this embodiment, as the rakes move through the thickening underflow recycled clarified liquid or liquor is exhausted behind the rakes and the suction tubes will draw the clarified liquid or liquor out as it is released behind the rake.

All such variations and modifications are to be considered within the scope of the present invention, the nature of which is to be determined from the foregoing description.

Claims (20)

1. 2. A thickener or clarifier as defined in claim 1 wherein the feed well includes a mixer chamber being designed to effectively disperse a flocculant or coagulant agent through the feed slurry. 23
2. 3. A thickener or clarifier as defined in either of claims 1 or 2 wherein the riser tube is connected to the feed line which includes a nozzle and a throat immediately upstream and downstream, respectively, of the upper end of the riser tube so as to increase the venturi effect for promoting the flow of recycled clarified liquid to the feed well.
3. 4. A thickener or clarifier comprising: a settling vessel being configured to permit gravity setting of solid particles from a feed slurry, said vessel having an upper gravity settling region from which a clarified liquid overflow can be removed and a lower compaction region from which a relatively high density solids underflow can be removed; a feed well disposed within said upper region of the settling vessel, said well including a mixer chamber being designed to effectively disperse a flocculant or coagulant agent through the feed slurry, and being in liquid communication with the settling vessel via a feed well outlet; a feed line operatively communicating with the feed well, the feed line being designed to deliver a flow "of the feed slurry to the feed well via a feed line outlet; 0 and o a riser tube. having a lower end operatively cooperating with one or more inclined surfaces at least a portion of said surfaces being located within the lower compaction region of the settling vessel, an upper end of the riser tube being positioned within the feed well or connected to the feed line whereby, in use, the flow of the feed slurry to the feed well effectively mixes with the flocculant or coagulant agent in the mixer chamber prior to gravity settling of solid particles within the settling vessel wherein a recycled clarified liquid is forced from a 35 lower compaction region of the settling vessel to flow to the feed well via said one or more inclined surfaces and -24- the riser tube to combine with the feed slurry so as to produce a relatively high density solids underflow. A thickener or clarifier as defined in claim 4 wherein the mixer chamber is defined by a mixer box to which the feed line is connected, the mixer box having an opening so as to allow the slurry from the mixer chamber to flow to the mixer well.
4. 6. A thickener or clarifier as defined in claim wherein the mixer box includes a series of mixer baffle plates being located within the mixer chamber thereby turbulating the flow of the slurry through the mixer chamber so as to effectively disperse the flocculant or coagulant agent through the feed slurry.
5. 7. A thickener or clarifier as defined in claim 4 wherein the mixer chamber is defined by a generally cylindrical or conical frustum shaped member positioned 20 immediately downstream of the feed line outlet. oooo
6. 8. A thickener or clarifier is defined in claim 7, 0go• wherein the cylindrical or conical frustum shaped member includes one or more vanes formed an internal surface e 25 thereof, said vanes being configured to induce a turbulent eeo: flow of the slurry to the feed well.
7. 9. A thickener or clarifier as defined in any one of the preceding claims wherein the feed line outlet is tapered so that the velocity of the slurry flowing through said outlet is increased thereby enhancing the venturi effect which acts to promote the flow of recycled clarified liquid Sfrom the lower compaction region of the settling vessel to the feed well. A thickener or clarifier as defined in claim 9 wherein the feed line upstream of its outlet includes a series of feed line baffle plates formed internally so as to increase the turbulence of the slurry flowing through said feed line.
8. 11. A thickener or clarifier as defined in any one of the preceding claims further comprising one or more polymer injection lines connected to the feed line or operatively communicating with the mixer chamber so as to provide a predetermined dose of flocculant or coagulant agent to the feed slurry.
9. 12. A thickener or clarifier as defined in any one of claims 1 to 10 wherein the thickener or clarifier includes a polymer injection line connected to the riser pipe whereby a dose of flocculant can be added to the recycled clarified 20 liquid. oooo
10. 13. A thickener or clarifier as defined in any one of the preceding claims further comprising a valve located within a wall of the feed well, the valve being designed to 25 allow a portion of the clarified liquid overflow from the •go@ :o upper gravity settling region of the settling vessel to •return to the feed well so as to control the solids density •of the slurry within the feed well. 0 30 14. A thickener or clarifier as defined in claim 13 wherein the valve includes an overflow weir or opening formed within the wall of the feed well. -26- A thickener or clarifier as defined in claim 14 wherein the valve also includes a downstream and an upstream flap covering the overflow weir or opening and being connected to an inner and an outer surface, respectively, of the feed well, the upstream flap being adjustable so as to provide a predetermined flow of the clarified liquid to the feed well and the downstream flap acting as a non-return valve to prevent slurry flowing from the feed well into the upper gravity settling region of the settling vessel.
11. 16. A thickener or clarifier as defined in any one of the preceding claims further comprising a slurry tube coupled to the feed well outlet, a flocculation cylinder being located about the slurry tube whereby a relatively concentrated slurry fraction passes downwardly into the upper gravity settling region and a clarified liquid fraction passes upwardly into the upper gravity settling region to be withdrawn as the clarified liquid overflow. 6 0.° o. 20 17. A thickener or clarifier as defined in any one of o the preceding claims wherein said one or more inclined surfaces are defined by an inverted cone being at least 0 .partly located within the lower compaction region of the settling vessel. eo o 0 18. A thickener or clarifier as defined in claim 17 eeo wherein said inverted cone is one of a plurality of inverted cones located one upon the other about the riser tube, an apex opening of the lowermost cone being connected to the lower end of the riser tube and the riser tube between adjacent cones including one or more apertures so that the recycled clarified liquid being forced from the lower compaction region of the settling vessel can enter the riser -27- tube from underneath the plurality of cones via the lower end of the tube and said one or more apertures.
12. 19. A thickener or clarifier as defined in claim 18 wherein an apex opening of each one of said plurality of cones is connected to one riser tube of a plurality of said tubes, respectively, whereby said tubes are arranged concentric with each other.
13. 20. A thickener or clarifier as defined in any one of claims 1 to 17 wherein said one or more inclined surfaces are defined by a series of inverted cones spaced about the lower region of the settling vessel, an apex opening of each of said cones being connected to a riser tube which is connected to one of several of said feed well outlets, respectively.
14. 21. A thickener or clarifier as defined in any one of the preceding claims further comprising a rake mechanism having a shaft with one or more rakes extending generally radially therefrom, said rakes being arranged within the lower compaction region of the settling vessel so that rotation of the shaft effects movement of the rakes thereby shearing solids within said compaction region of said vessel 25 and thus driving clarified liquid upwardly into the upper *o*gravity settling region of the settling vessel or onto said •one or more inclined surfaces.
15. 22. A thickener or clarifier as defined in claim 21 wherein the shaft passes through the riser tube and is adapted to be driven via a motor located above the thickener or clarifier. -28-
16. 23. A thickener or clarifier as defined in either of claims 21 or 22 wherein the rake mechanism also includes a scroll or archimedean screw mounted on the shaft so as to promote the flow of clarified liquid onto said one or more inclined surfaces for recycle to the feed well.
17. 24. A thickener or clarifier as defined in any one of claims 21, 22 or 23 wherein each of said one or more rakes includes an elongate member having opposing concave convex surfaces facing downward and upward, respectively, whereby a substantially solids fraction of the slurry moving down the vessel passes across said convex surface and a liquor fraction of the slurry within the compaction region can be exhausted up the concave surface toward the upper gravity setting region. A thickener or a clarifier as defined in claim 24, wherein the elongate member is an elongate angle-shaped member. o 26. A thickener or clarifier as defined in any one of g :the preceding claims wherein the settling vessel consists of a cylindrical portion formed continuous with a large diameter end of a conical frustum portion. :oo.27. A method for thickening or clarifying a slurry, said method comprising the steps of: providing a thickener or clarifier including a S.settling vessel, a feed well having a feed well outlet 30 disposed within an upper gravity settling region of the settling vessel, a feed line having a feed line outlet operatively communicating with the feed well, and a riser Stube having a lower end operatively cooperating with one or -29- more inclined surfaces located within a lower compaction region of the settling vessel, an upper end of the riser tube being positioned adjacent to the feed line outlet or connected to the feed line and providing a flow of a feed slurry to the feed well via the feed line and the feed line outlet, said flow through the feed line producing a low pressure zone at the upper end of the riser tube thereby creating a venturi effect and thus promoting a flow of recycled clarified liquid from the lower compaction region of the settling vessel to the feed well, via said one or more inclined surfaces and the riser tube, so as to produce a relatively high density solids underflow.
18. 28. A thickener or clarifier, substantially as herein described with reference to and as illustrated in the accompanying drawings.
19. 29. A method for thickening or clarifying a slurry 20 substantially as herein before described with reference to and as illustrated in the accompanying drawings. Dated this 1 3 t h day of November
20. 2000. ROBERT HUME PANNELL as trustee of Barchester Investment Trust oo": By His Patent Attorneys: GRIFFITH HACK Fellows Institute of S