AU720508B2

AU720508B2 - Froth separation apparatus

Info

Publication number: AU720508B2
Application number: AU19930/97A
Authority: AU
Inventors: David Taylor
Original assignee: Supaflo Technologies Pty Ltd
Current assignee: Outotec Pty Ltd
Priority date: 1996-05-01
Filing date: 1997-04-30
Publication date: 2000-06-01
Anticipated expiration: 2017-04-30
Also published as: AU1993097A

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT o

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ORIGINAL

Name of Applicant: Actual Inventor: SUPAFLO TECHNOLOGIES PTY LTD A.C.N. 003 491 165 David TAYLOR Address of Service: Invention Title: SHELSTON WATERS 60 MARGARET STREET SYDNEY NSW 2000 "FROTH SEPARATION APPARATUS" Details of Associated Provisional Application No. PN 9609 dated 1st May, 1996 The following statement is a full description of this invention, including the best method of performing it known to us:- -2- The present invention relates to a method and apparatus for de-aerating liquids, or separating entrained air or froth from liquids or pulps.

The invention has been developed primarily for use with thickeners, clarifiers, or concentrators and will be described hereinafter with reference to this application. It will be appreciated, however, that the invention is not limited to this particular field of use.

Thickeners, clarifiers and concentrators are typically used for separating solids from liquids and are often found in the mining, mineral processing, food processing, sugar refining, water treatment, sewage treatment, and other such industries.

S• These devices typically comprise a tank in which solids are deposited from io: suspension or solution and settle toward the bottom as pulp or sludge to be drawn off from ooo,• below and recovered. A dilute liquor of lower relative density is thereby displaced toward the top of the tank, for removal via an overflow launder. The liquid to be thickened is initially fed through a feedline into a feedwell disposed within the main tank. The purpose of the feedwell is to ensure relatively uniform distribution and to prevent turbulence from 15 the incoming feed liquid from disturbing the settling process taking place within the oooo surrounding tank.

In cases where the feed liquid comprises flotation concentrate, it is normally at least partially aerated. The air bubbles, if allowed to pass from the feedwell into the main tank, tend to produce a considerable amount of relatively stable froth on the surface of both the feedwell and the thickener. This froth can contain a significant proportion of entrained solids and thereby tends to reduce the separation efficiency of the thickener. In addition, air bubbles can become trapped in the sludge, resulting in slower settling rates and lower underflow densities, both of which reduce separation efficiency further still.

It is an object of the present invention to overcome or substantially ameliorate this problem in the prior art.

Accordingly, in a first aspect of the present invention there is provided an apparatus for separating froth from liquid, said apparatus comprising a feed conduit to carry partially aerated feed liquid, and separation means to receive and separate said feed liquid into a first component consisting substantially of froth or gas and a second component consisting substantially of de-aerated liquid or sludge, said separation means including a centrifugal separator adapted to induce a rotational flow of the feed liquid in a separation chamber whereby the froth or gas component emerges as an overflow stream from the separator and the liquid or sludge component emerges as an underflow stream.

Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of o "including, but not limited to".

ooo2 q S 15 A bank of separators connected in series, parallel or a combination of both, may optionally be used to achieve the desired level of separation. In one preferred embodiment, the centrifugal separator is a cyclone separator.

9 The apparatus preferably further includes an array of liquid spray jets positioned to •ego break down any froth following separation into a third component consisting substantially o: 20 of liquid, which optionally may be added to the second liquid or sludge component •ooe downstream of the separator or recycled upstream thereof into the feed liquid.

In a second aspect, the invention consists in a method for separating froth from liquid, said method comprising the steps of conveying a partially aerated feed liquid to i separation means, and separating said feed liquid into a first component consisting substantially of froth or gas and a second component consisting substantially of de-aerated liquid or sludge, wherein said separation step is performed by means of centrifugal separator adapted to induce a rotational flow of the feed liquid in a separation chamber whereby the froth or gas component emerges as an overflow stream from the separator and the liquid or sludge component emerges as an underflow stream.

The method preferably comprises the further step of breaking down any froth component by means of liquid spray jets into a third component consisting substantially of liquid.

Optionally, the method comprises the further step of recombining the third liquid component with the second liquid component downstream of the separator or with the feed liquid upstream thereof. Alternatively, the overflow and underflow from the centrifugal separator may be directed to separate downstream process units.

In the preferred embodiment of both aspects, the invention is used for removal of flotation froth and air from the feed to a thickener. The thickener preferably comprises a 15 tank in which a dispersed solid component tends to settle from solution or suspension °*.toward a lower region of the tank to be drawn off from below whilst a relatively dilute liquor is thereby displaced toward an upper region of the tank for separation via an overflow launder.

A preferred embodiment of the invention will now be described, by way of example S 20 only, with reference to the accompanying drawing, which is a schematic flow diagram S.showing the invention as used in conjunction with a thickener.

Referring to the drawing, the invention provides an apparatus 1 for separating liquid from froth. The apparatus comprises a sump 2 adapted to receive feed liquid from an RAupstream process, and a feed conduit 3 extending from the sump to a separation station 4.

$upstream process, and a feed conduit 3 extending from the sump to a separation station 4.

A pump 5 and valve assembly 6 are disposed within the feed conduit 3 to regulate the flow of liquid. Alternatively, the separation station 4 may simply receive feed by gravity flow from the upstream process.

The separator takes the form of a centrifugal separation apparatus which has been found, unexpectedly, to be particularly efficient in separating froth from partially aerated pulps by "shearing" the air bubbles from the solid particles. Whilst a single separator is illustrated, it will be appreciated that a plurality of separators connected in series, parallel or a combination of both, may also be used depending upon the throughput, the degree of separation required, and other variables. In one preferred form of the invention, a cyclone type centrifugal separator is used.

Within the centrifugal separator 4, the feed liquid is split between the overflow line and the underflow line 11. The split between these lines 10 and 11 can be controlled as "appropriate by varying several operating parameters of the centrifugal separator including the diameter of the separator, the separator length, the angle of the separator barrel, the size q 15 of the inlet underflow and internal nozzles, the feed pressure and the feed density. In •testing it has been found, somewhat surprisingly, that with a partially aerated feed liquid, see*and appropriately tuned operating parameters, a relatively small overflow stream can be *oo• oo. produced which contains the vast majority of the froth, leaving a proportionately large volume of de-aerated underflow liquid having a density similar to that of the feed liquid.

ooe• ooo 20 In the preferred embodiment of the invention, the underflow line 11 feeds the de- ••oo "aerated liquid from the centrifugal separator to a thickener. This obviates the problem of accumulation of excess froth in the thickener and the associated feedwell, which in prior art devices significantly reduces the efficiency of the thickening process. The froth stream from the centrifugal separator overflow line 10 is fed to a launder 15 and broken down with -6fine water spray jets 16. This produces a third component consisting of liquid from the spray jets mixed with the liquid from the collapsed froth, which may be combined with the underflow liquid downstream of the centrifugal separator and thence fed to the thickener, or else recycled to the feed liquid upstream of the centrifugal separator.

It has also been found, again quite unexpectedly, that by appropriately controlling various process parameters of the separator, including flow rate, viscosity, density, dilution ratio, rotational speed, chamber shape, and the like, the froth can be substantially collapsed within the separator such that the overflow stream consists substantially of gas, in which case the supplementary spray jets 16 are not required.

Of course, it will be appreciated that the centrifugal separator arrangement need not necessarily be applied only to thickeners, since the principle of de-aeration performed by the centrifugal separators may be used in numerous other applications. There is also no specific requirement to recombine the overflow from the centrifugal separator with the o. o• underflow or with the feed material. The separated streams may simply be directed to discrete downstream process units as required. There is also no need for pumps if sufficient pressure head is otherwise available.

Although the invention has been described with reference to specific examples, it o. :will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

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Claims

1. An apparatus for separating froth from liquid, said apparatus comprising a feed conduit to carry partially aerated feed liquid, and separation means to receive and separate said feed liquid into a first component consisting substantially of froth or gas and a second component consisting substantially of de-aerated liquid or sludge, said separation means including a centrifugal separator adapted to induce a rotational flow of the feed liquid in a separation chamber whereby the froth or gas component emerges as an overflow stream from the separator and the liquid or sludge component emerges as an underflow stream.

2. An apparatus according to claim 1, wherein the centrifugal separator is a cyclone type separator.

3. An apparatus according to claim 1 or claim 2, including a bank of centrifugal separators connected in series or parallel and configured to achieve a predetermined degree of separation. rce. S

4. An apparatus according to any one of claims 1 to 3, further including an array of one or more liquid spray jets positioned to break down the froth component following eec. •separation into a third component consisting substantially of liquid. C

5. An apparatus according to claim 4, wherein said third liquid component is added to C• the second liquid or sludge component downstream of the separator. &to€

6. An apparatus according to claim 4, wherein said third liquid component is recycled o. 20 upstream of the separator and into the feed liquid. •oo oo°

7. An apparatus according to any one of claims 1 to 6, wherein the separator is configured, and the process parameters are controlled, such that the froth component is substantially collapsed within the separator whereby the overflow stream consists n substantially of gas. -8-

8. An apparatus according any one of the preceding claims, adapted for removal of flotation froth and air from a feedstream for a thickener, said thickener comprising a tank in which a dispersed solid component tends to settle from solution or suspension toward a lower region of the tank to be drawn off from below whilst a relatively dilute liquor is displaced toward an upper region of the tank for separation via an overflow launder.

9. A method for separating froth from liquid, said method comprising the steps of conveying a partially aerated feed liquid to separation means, and separating said feed liquid into a first component consisting substantially of froth or gas and a second component consisting substantially of de-aerated liquid or sludge, wherein said separation step is performed by means of centrifugal separator adapted to induce a rotational flow of the feed liquid in a separation chamber whereby the froth or gas component emerges as an overflow stream from the separator and the liquid or sludge component emerges as an underflow stream.

A method according to claim 9, wherein the separation step is performed by means of 15 a cyclone type separator.

11. A method according to claim 9 or claim 10, wherein the separation step is performed by a bank of centrifugal separators connected in series or parallel and configured to achieve a predetermined degree of separation.

12. A method according to any one of claims 9 to 11, including the further step of breaking down any froth component following separation, by means of an array of one or more liquid spray jets, into a third component consisting substantially of liquid.

13. A method according to claim 12, including the further step of adding said third liquid component to the second liquid or sludge component downstream of the separation RA process. I It -9-

14. A method according to claim 12, including the further step of recycling said third liquid component upstream of the separation process and into the feed liquid.

A method according to any one of claims 9 to 14, including a further step of controlling parameters of the separation process such that the froth component is substantially collapsed within the separator, whereby the overflow stream consists substantially of gas.

16. A method according to any one of claims 9 to 15, wherein the method is adapted for removal of flotation froth and air from a feedstream for a thickener comprising a tank in which a dispersed solid component tends to settle from solution or suspension toward a lower region of the tank to be drawn off from below whilst a relatively dilute liquor is displaced toward an upper region of the tank for separation via an overflow launder.

17. An apparatus for separating froth from liquid, said apparatus being substantially as hereinbefore described with reference to the accompanying drawing.

18. A method for separating froth from liquid, said method being substantially as •I 15 hereinbefore described with reference to the accompanying drawing. DATED this 10th Day of April, 2000 SUPAFLO TECHNOLOGIES PTY LTD .e Attorney: STUART M. SMITH ••go Fellow Institute of Patent Attorneys of Australia 20 of SHELSTON WATERS o oo•• o•