AU2008202705B2

AU2008202705B2 - Dilution apparatus for a thickener

Info

Publication number: AU2008202705B2
Application number: AU2008202705A
Authority: AU
Inventors: Jeffrey Victor Belke; David John Buchanon TAYLOR
Original assignee: Outotec Oyj
Current assignee: Metso Finland Oy
Priority date: 2002-05-07
Filing date: 2008-06-19
Publication date: 2010-03-11
Anticipated expiration: 2023-04-30
Also published as: AU2007100006B4; AU2008100050A4; AU2008202705A1; AU2007100006A5; AU2008202705B8; AU2008100050B4

Description

AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL Name of Applicant/s: Outotec Oyj Actual Inventor/s: David John Buchanon Taylor and Jeffrey Victor Belke Address for Service is: SHELSTON IP 60 Margaret Street Telephone No: (02) 9777 1111 SYDNEY NSW 2000 Facsimile No. (02) 9241 4666 CCN: 3710000352 Attorney Code: SW Invention Title: DILUTION APPARATUS FOR A THICKENER Details of Original Application No. 2003227110 dated 30 Apr 2003 The following statement is a full description of this invention, including the best method of performing it known to me/us: File: 35114AUP04 -2 TITLE: DILUTION APPARATUS FOR A THICKENER This application is a divisional application of Australian Patent Application No. 2003227110, whose entire contents are hereby incorporated by reference. FIELD OF THE INVENTION 5 The present invention relates to separation devices for liquid suspensions and pulps and in particular to recycling of overflow liquor in thickeners. It has been developed primarily for use in separating mineral pulp from a liquid suspension and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of use. 10 BACKGROUND OF THE INVENTION The following discussion of the prior art is intended to present the invention in an appropriate technical context and allow its significance to be properly appreciated. Unless clearly indicated to the contrary, however, reference to any prior art in this specification should not be construed as an admission that such art is widely known or 15 forms part of common general knowledge in the field. Thickeners are known as a means of separating suspended pulps. They are commonly used in the field of mineral processing and extraction, as well as in other industries. Known thickeners typically include a thickening tank and a feedwell. The 20 feedwell includes a chamber having an inlet for receiving feed slurry and an outlet in fluid communication with the tank. In use, flocculation takes place in the tank, whereby pulp of higher relative density tends to settle towards the bottom of the tank, forming a bed of thickened pulp, and dilute liquor of lower relative density is thereby displaced towards the top of the tank. 25 The feedwell is configured to reduce the turbulence of the incoming feed slurry, to allow flocculants to be mixed into the liquid, and to allow sufficient residence time for reaction between flocculants and reagents, before the treated liquid is discharged into the -3 thickening tank. The configuration of the feedwell is typically also intended to promote uniform distribution of slurry flowing from its outlet into the thickening tank. Feed slurry concentration affects the rate of floc formation, and the dosage rate of flocculant required to achieve optimum separation. It also affects thickener performance 5 in terms of overflow clarity and underflow density versus flocculant consumption. Accordingly, the feed slurry entering the feedwell frequently requires dilution in order to achieve an optimum result. Existing technologies achieve feed slurry dilution by several methods. Some methods involve pumping supernatant or new liquid into the feed stream. Relatively 10 newer methods, however, use liquid from within the thickening tank to dilute the feed stream. These newer methods typically employ mechanisms of differential density or momentum transfer to move the liquid from the thickening tank into the feed stream. All of these existing methods have disadvantages. Those utilising pumps require considerable pipework and electrical power to transfer the diluting liquid. Conversely, 15 the internal systems, which use differential density or momentum transfer mechanisms, are relatively simpler and require little to no electrical power, but lack means to precisely control dilution under all operating conditions. It is an object of the invention to overcome or substantially ameliorate one or more of the deficiencies of the prior art, or at least to provide a useful alternative. 20 DISCLOSURE OF THE INVENTION According to a first aspect, the invention provides a dilution apparatus for a thickener of the type having a thickening tank and a feedwell disposed upstream of the tank to receive feed liquid, said dilution apparatus including: a receiving vessel adapted for at least partial submersion within the thickening 25 tank to receive supernatant dilution liquid therefrom; and a submersible pump including an impeller adapted for at least partial submersion within the dilution liquid in the receiving vessel; -4 the pump being adapted to transfer the dilution liquid from the thickening tank through the receiving vessel to the feed liquid for dilution thereof, before transfer of the feed liquid from the feedwell into the thickening tank. Preferably, the receiving vessel is connected for fluid communication with the 5 feedwell. Preferably, the apparatus further includes control means to regulate the flow rate of the dilution liquid in response to one or more selected system parameters. The flow rate is preferably varied by adjusting the pump speed. In the preferred embodiment, the feedwell is disposed substantially within the 10 thickening tank, the dilution apparatus is positioned substantially within the tank, and all plumbing and pipe work for the dilution apparatus is substantially contained within an outer perimeter of the tank. Preferably also, the dilution apparatus is positioned closely adjacent the feedwell so as to minimise intermediate plumbing and pipe work within the tank. 15 The pump is preferably an axial flow pump. Preferably, the receiving vessel is generally cup shaped and is submerged in the supernatant dilution liquid. Preferably, the impeller is mounted on a rotatable shaft. The shaft is preferably driven by a motor and gearbox. Preferably also, the impeller and shaft are housed in a generally vertically oriented 20 elongate chamber extending upwardly from below the impeller. The chamber is preferably cylindrical in shape, and includes an outlet port for directing pumped fluid into the feedwell. Preferably, the impeller is located substantially within the receiving vessel. In a preferred embodiment, the receiving vessel forms part of the pump. 25 Preferably, the impeller transfers the dilution liquid into the feed liquid. Preferably, the dilution liquid is injected into the feed liquid upstream of the feedwell. Preferably, the dilution liquid is injected into a feed inlet upstream of the feedwell. Preferably, the dilution liquid is injected into a feed conduit upstream of the -5 feedwell. In one preferred embodiment, the dilution liquid is injected into a feed pipe upstream of the feedwell. In an alternative embodiment, however, the dilution liquid is injected directly into the feedwell. Preferably, the dilution apparatus is attached to a mounting hub of the feedwell. In 5 one preferred form, the dilution apparatus is bolted to the mounting hub. Alternatively, the dilution apparatus is attached to a side of the feedwell. In one preferred form, the dilution apparatus is bolted to the side of the feedwell. Preferably, a relatively small head difference is maintained between a liquid surface in the feedwell and a liquid surface in the thickening tank. 10 According to a second aspect, the invention provides a thickener including: a thickening tank; a feedwell located upstream of said tank to receive feed liquid; and a dilution apparatus as previously defined; the impeller being at least partially submerged within the dilution liquid, the pump 15 being adapted to transfer the dilution liquid from the thickening tank through the receiving vessel to the feed liquid for dilution thereof, before transfer of the feed liquid from the feedwell to the tank. Preferably, the thickener further includes control means to regulate the flow rate of the dilution liquid in response to one or more selected system parameters. 20 According to a third aspect, the invention provides a method of diluting feed liquid in a thickener having a thickening tank and a feedwell located upstream of said tank to receive feed liquid, said method including the steps of; providing a dilution apparatus having a receiving vessel and a submerible pump, the receiving vessel adapted for at least partial submersion within the thickening tank to 25 receive supernatant dilution liquid therefrom; providing the submersible pump with an impeller; submerging the impeller at least partially within the dilution liquid in the receiving vessel; and actuating the pump so as to transfer the dilution liquid from the thickening tank 30 through the receiving vessel to the feed liquid for dilution thereof, before transferring the feed liquid from the feedwell to the tank.

-6 Preferably, the method includes the further step of controlling the flow rate of the dilution liquid in response to one or more selected system parameters. Preferably, the method also includes the step of maintaining a relatively small head difference between a liquid surface in the feedwell and a liquid surface in the thickening 5 tank. Preferably, the method includes the further step of injecting the dilution liquid into the feed liquid. Preferably, the dilution liquid is injected into the feed liquid upstream of the feedwell. Preferably, the dilution liquid is injected into a feed inlet upstream of the feedwell. Preferably, the dilution liquid is injected into a feed conduit upstream of the 10 feedwell. Preferably, the dilution liquid is injected into a feed pipe upstream of the feedwell. Alternatively, the dilution liquid is injected directly into the feedwell. Preferably, the method further includes the step of attaching the dilution apparatus to a mounting hub of the feedwell. In one preferred form, the method further includes the step of bolting the dilution apparatus to the mounting hub. Alternatively, the method 15 further includes the step of attaching the dilution apparatus to a side of the feedwell. In one preferred form, the method further includes the step of bolting the dilution apparatus to the side of the feedwell. In the preferred embodiment, the method includes the steps of positioning the feedwell substantially within the thickening tank, positioning the dilution apparatus 20 substantially within the tank, and containing the plumbing and pipe work for the dilution apparatus substantially within the outer perimeter of the tank. Preferably also, the dilution apparatus is positioned closely adjacent the feedwell so as to minimise the intermediate plumbing and pipe work within the tank. BRIEF DESCRIPTION OF THE DRAWINGS 25 A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a sectional side elevation of one embodiment of a dilution apparatus according to the invention; -7 Figure 2 is a plan view of a thickener feedwell incorporating the dilution apparatus; Figure 3 is a partial plan view of the dilution apparatus and feedwell of Figure 2 in a thickening tank; 5 Figure 4 is a cross-sectional view of the dilution apparatus, feedwell and thickening tank of Figure 2; Figure 5 is a partial plan view of another embodiment of a dilution apparatus according to the invention attached to a feedwell in a thickening tank; Figure 6 is a cross-sectional view of the dilution apparatus, feedwell and 10 thickening tank of Figure 5. PREFERRED EMBODIMENTS OF THE INVENTION A preferred application of the invention is in the field of mineral processing, separation and extraction, whereby finely ground ore is suspended as pulp in a suitable liquid medium, such as water, at a consistency which permits flow, and settlement in 15 quiescent conditions. Referring to the drawings, the dilution apparatus I includes an axial flow pump I a for accurately injecting supernatant liquid 2 from adjacent the liquid surface 3 of a thickening tank (not shown) to dilute liquid in a feedwell 4. The pump dilution apparatus I also includes a cup shaped receiving vessel 5 submerged in the supernatant 20 liquid to receive the supernatant dilution liquid 2. The pump la includes a submerged impeller 6 adapted for at least partial submersion within the dilution liquid 2, and is thereby adapted to transfer the dilution liquid 2 from the thickening tank through the receiving vessel 5 to the feed liquid for dilution thereof, before transfer of the feed liquid from the feedwell 4 to the thickening 25 tank. The impeller 6 is mounted on a rotatable shaft 7 for drawing liquid through the vessel 5 and injecting it into the feedwell 4. The shaft 7 is driven by a motor and associated gearbox (not shown). The pump is responsive to system parameters for adjusting the flow rate of the supernatant liquid. In the illustrated embodiment, the flow rate is adjusted by varying the pump speed. However, in other embodiments, the flow 30 rate is adjusted using control valves or other means.

- 8 The impeller 6 and shaft 7 are housed in a vertical cylindrical chamber 8 extending upwards from below the impeller. The chamber extends above the surface 3 of the supernatant liquid, thereby overcoming the requirement for a seal at its apex and allowing for access and removal of the impeller 6. The chamber also includes an outlet 5 port 9 located above the impeller 6 for directing pumped fluid into a feed pipe 10 of the feedwell 4. It will be appreciated that one or more additional outlet ports can be provided, submerged or otherwise, to direct pumped fluid into the feed pipe 10. In use, the motor is activated to drive the shaft 7 and the impeller 6. The rotation of the impeller draws supernatant liquid from the thickening tank into and through the 10 vessel 5 and up through the chamber 8. This increases the pressure head between the liquid level in the thickening tank and the outlet port 9 and forces the liquid through the outlet and into the feed pipe 10 for dilution of the feed liquid. It will be appreciated by those skilled in the art that the feed pipe in this context may take a variety of forms, and in particular, may be open or closed and comprise any suitable profile. 15 In an alternative embodiment, the vessel 5 includes an additional aperture at its base to provide an additional path for liquid to be drawn. The dilution apparatus also includes a mounting flange 11 to permit its bolting onto a mounting hub 12 of the feedwell. Figures 3 and 4 illustrate partial plan and cross sectional views, respectively, of the dilution apparatus I of Figure 2 in a thickening tank 20 13, where corresponding features have been given the same reference numerals. In other embodiments, the apparatus 1 is bolted onto the side of the feedwell itself to allow supernatant liquid to be injected directly into the feedwell. For example, in the embodiment shown in Figures 5 and 6, where corresponding features have been given the same reference numerals, the dilution apparatus I is attached to the side of the 25 feedwell 4 in a thickening tank 13. In the preferred embodiment described above, the pump Ia is an axial flow pump. However, it will be appreciated that alternative pump types can also be used to inject the supernatant liquid 2 into the feedwell 4. Piston pumps and vacuum pumps are examples of some alternatives pump types that could be used.

-9 It will be appreciated that the illustrated apparatus provides an efficient and accurately controllable means for diluting the feed slurry in a thickener. As the head difference between the liquid surface in the feedwell 4 and the liquid surface 3 in the thickening tank are maintained at a similar level, the axial pump Ia requires only a small 5 pressure head to drive the diluting supernatant liquid. The proximity of the apparatus to the feedwell reduces the amount of piping required and also reduces power consumption. Also, the apparatus does not require a wear resistant impeller as it pumps relatively clean liquid. The apparatus also allows flocculants to be introduced either upstream or downstream of the impeller to achieve dispersion and dilution of flocculants 10 prior to contact with solid particles in the stream. In this embodiment, flocculant is added through apertures 13 in the feed pipe 10. In all these respects, the invention represents a practical and commercially significant improvement over the prior art. Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in 15 many other forms.

Claims

2. A dilution apparatus according to claim 1, wherein the receiving vessel is connected for fluid communication with the feedwell.
3. A dilution apparatus according claim 1 or claim 2, further including control 15 means to regulate a flow rate of the dilution liquid in response to one or more selected system parameters.
4. A dilution apparatus according to claim 3, wherein the flow rate is varied by adjusting the pump speed.
5. A dilution apparatus according to any one of the preceding claims, wherein the 20 feedwell is disposed substantially within the thickening tank, the dilution apparatus is positioned substantially within the tank, and all plumbing and pipe work for the dilution apparatus is substantially contained within an outer perimeter of the tank.
6. A dilution apparatus according to claim 5, wherein the dilution apparatus is positioned closely adjacent the feedwell so as to minimise intermediate plumbing and 25 pipe work within the tank.
7. A dilution apparatus according to any one of the preceding claims, wherein the pump is an axial flow pump.
8. A dilution apparatus according to any one of the preceding claims, wherein the receiving vessel is generally cup shaped and is submerged in the supernatant dilution liquid.
9. A dilution apparatus according to claim 8, wherein the impeller is mounted on a 5 rotatable shaft.
10. A dilution apparatus according to claim 9, wherein the shaft is driven by a motor and gearbox. I1. A dilution apparatus according to claim 9 or claim 10, wherein the impeller and shaft are housed in a generally vertically oriented elongate chamber extending upwardly 10 from below the impeller.
12. A dilution apparatus according to claim 11, wherein the chamber is generally cylindrical in shape, and includes an outlet port for directing pumped fluid into the feedwell.
13. A dilution apparatus according to any one of the preceding claims, wherein the 15 impeller is substantially located within the receiving vessel.
14. A dilution apparatus according to any one of claims 1 to 12, wherein the receiving vessel forms part of the pump.
15. A dilution apparatus according to any one of the preceding claims, wherein the impeller transfers the dilution liquid into the feed liquid. 20 16. A dilution apparatus according to any one of the preceding claims, wherein the dilution liquid is injected into the feed liquid upstream of the feedwell.
17. A dilution apparatus according to any one of the preceding claims, wherein the dilution liquid is injected into a feed inlet upstream of the feedwell.
18. A dilution apparatus according to any one of claims I to 16, wherein the 25 dilution liquid is injected into a feed pipe upstream of the feedwell.
19. A dilution apparatus according to any one of claims I to 16, wherein the dilution liquid is injected into a feed conduit upstream of the feedwell. - 12
20. The dilution apparatus according to any one of the preceding claims, wherein the dilution apparatus is attached, preferably bolted, to a mounting hub of the feedwell.
21. The dilution apparatus according to any one of claims 1 to 19, wherein the dilution apparatus is attached, preferably bolted, to a side of the feedwell. 5 22. A dilution apparatus according to any one of claims I to 15, wherein the dilution liquid is injected directly into the feedwell.
23. A dilution apparatus according to any one of the preceding claims, wherein a relatively small head difference is maintained between a liquid surface in the feedwell and a liquid surface in the thickening tank. 10 24. A thickener including: a thickening tank; a feedwell located upstream of said tank to receive feed liquid; and a dilution apparatus as defined in any one of the preceding claims; the impeller being at least partially submerged within the dilution liquid, the 15 pump being adapted to transfer the dilution liquid from the thickening tank through the receiving vessel to the feed liquid for dilution thereof, before transfer of the feed liquid from the feedwell to the tank.
25. A method of diluting feed liquid in a thickener having a thickening tank and a feedwell located upstream of said tank to receive feed liquid, said method including the 20 steps of; providing a dilution apparatus having a receiving vessel and a submersible pump, the receiving vessel adapted for at least partial submersion within the thickening tank to receive supernatant dilution liquid therefrom; providing the submersible pump with an impeller; 25 submerging the impeller at least partially within the dilution liquid in the receiving vessel; and actuating the pump so as to transfer the dilution liquid from the thickening tank through the receiving vessel to the feed liquid for dilution thereof, before transferring the feed liquid from the feedwell to the tank. 30 26. A method according to claim 25, including the further step of controlling the flow rate of the dilution liquid in response to one or more selected system parameters. - 13 27. A method according to claim 25 or claim 26, wherein the pump is an axial flow type pump.
28. A method according to any one of claims 25 to 27, wherein the receiving vessel is generally cup shaped and is submerged in the dilution liquid. 5 29. A method according to any one of claims 25 to 28, including the further step of injecting the dilution liquid into the feed liquid.
30. A method according to any one of claims 25 to 29, including the further step of injecting the dilution liquid into the feed liquid upstream of the feedwell.
31. A method according to any one of claims 25 to 30, including the further step of 10 injecting the dilution liquid into a feed inlet upstream of the feedwell.
32. A method according to any one of claims 25 to 30, wherein the dilution liquid is injected into a feed pipe of the feedwell.
33. A method according to any one of claims 25 to 30, including the further step of injecting the dilution liquid into a feed conduit upstream of the feedwell 15 34. A method according to any one of claims 25 to 33, further including the step of attaching, preferably bolting, the dilution apparatus to a mounting hub of the feedwell.
35. A method according to any one of claims 25 to 33, further including the step of attaching, preferably bolting, the dilution apparatus to a side of the feedwell.
36. A method according to any one of claims 25 to 29, wherein the dilution liquid is 20 injected directly into the feedwell.
37. A method according to any one of claims 25 to 36, including the further step of maintaining a relatively small head difference between a liquid surface in the feedwell and a liquid surface in the thickening tank.
38. A method according to any one of claims 25 to 37, including the further steps of 25 positioning the feedwell within the thickening tank, positioning the dilution apparatus within the tank, and containing all plumbing and pipe work for the dilution apparatus within an outer perimeter of the tank. - 14
39. A method according to claim 38, including the further step of positioning the dilution apparatus adjacent the feedwell and thereby minimising intermediate plumbing and pipe work within the tank.
40. A method according to claim 38 or claim 39, wherein the feedwell is positioned 5 substantially centrally within the tank.
41. A dilution apparatus for a thickener of the type having a thickening tank and a feedwell disposed upstream of the tank to receive feed liquid, substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples. 1o 42. A thickener, substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.
43. A method of diluting feed liquid in a thickener having a thickening tank and a feedwell located upstream of said tank to receive feed liquid, substantially as herein is described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.