Patent Application
20110067568
The present invention relates to deaerating liquids and in particular to an apparatus and method for deaerating or separating entrained air or froth from liquid suspensions or pulps. It has been developed primarily for use in thickeners, clarifiers, or concentrators 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.
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 forms part of common general knowledge in the field.
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.
These devices typically comprise a tank in which solids are deposited from suspension or solution and settle toward the bottom as pulp or sludge to be drawn off from 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 feed pipe or feed line into a feedwell disposed within the main tank. The purpose of the feedwell is to ensure relatively uniform distribution and to prevent turbulence from the incoming feed liquid from disturbing the settling process taking place within the surrounding tank.
In cases where the feed liquid comprises entrained air, such as 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, and contaminates the dilute liquor. 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. A further problem is that the froth leaves solid particulates in the overflow and these particulates eventually deposit in storage tanks or dams, which consequently must be frequently cleaned to remove accumulated sedimentation and contaminants. The particulates also contaminate the process water for the plant, as the dilute liquor is generally recycled for this use. This increases plant costs in the additional maintenance of the storage tanks or dams, and the removal of solid particulates from the process water.
One solution for this problem has been to provide a deaeration unit for separating froth from the feed liquid before it is fed into the separation device. This deaeration unit has a cyclonic separator, which generates a centrifugal vortex that separates partially aerated liquid into a froth or gas component and a deaerated liquid or sludge component. The froth or gas component is removed from the deaeration unit as an overflow stream while the deaerated liquid or sludge component leaves as an underflow stream that is subsequently fed into the separation device.
Whilst this solution has proved effective in reducing the amount of froth that is generated in the separation device, it has several limitations. First, the partially aerated feed liquid has to be pumped into the unit at high pressure, around 100 kPa, to generate a sufficiently powerful vortex to separate froth from the feed liquid. This means that a pumping system and its associated plumbing is required to be installed and maintained in the plant. Second, the maximum capacity of this deaeration unit is around 80 m3/hr. This places an upper limit on the throughput of feed slurry that can be processed by a single deaeration unit. For example, to process 400 m3, which is a typical amount of feed slurry, five such deaeration units are required.
It has also been found that to increase the capacity of these deaeration units would require a higher flow velocity to generate the vortex, meaning that higher pressure must be generated from the pumping system, rendering such upscaling uneconomical. In addition, using a pump system in the deaeration unit conflicts with many types of separation devices, such as thickeners and clarifiers, which prefer using a gravity feed for the incoming slurry to save on costs in installing and maintaining a pumping system.
It is an object of the invention to overcome or ameliorate one or more of the deficiencies of the prior art, or at least to provide a useful alternative.
According to a first aspect of the invention, there is provided an apparatus for deaerating a feed liquid comprising a liquid suspension or pulp, the apparatus comprising a feed conduit to convey the feed liquid into a separator, the separator comprising a mechanical agitator for inducing a rotational flow of the feed liquid in a separation chamber such that the rotational flow generates a centrifugal vortex to separate the feed liquid into a first component consisting essentially of froth or gas and a second component consisting essentially of deaerated liquid or sludge, the separator further comprising a device for controlling the location of the vortex in the separation chamber.
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 “including, but not limited to”.
Preferably, the vortex locating device controls a start point of the vortex. Preferably, the position of the vortex locating device is adjustable.
Preferably, the vortex locating device has a shape such that its transverse cross-section complements the cross-sectional shape of the separation chamber. Preferably, the vortex locating device is substantially circular. In one preferred form, the vortex locating device is a substantially horizontal circular disc.
Preferably, the mechanical agitator comprises a rotor mounted to a drive shaft and a drive mechanism for rotating the drive shaft so that the rotor induces the rotational flow in the separation chamber.
Preferably, the vortex locating device axially displaces a start point of the vortex from the rotor. Preferably, the vortex locating device is provided adjacent or on the drive shaft. Preferably, the vortex locating device extends substantially perpendicular to the drive shaft. Preferably, the vortex locating device has a diameter equal to or less than diameter of the rotor.
Preferably, the rotation of the rotor defines a shape that substantially complements the cross-sectional shape of the separation chamber.
Preferably, the rotor comprises a plurality of rotor blades. Preferably, the rotor blades are equidistant to each other. Preferably, the rotor blades extend substantially horizontally and vertically in the separation chamber. In one preferred form, the rotor blades define at least one V-shape or U-shape in the vertical plane. In another preferred form, the rotor blades define at least an X-shape in the horizontal plane.
Preferably, the separation chamber is substantially frusto-concial in shape. Alternatively, the separation chamber is substantially cylindrical in shape. In another preferred form, the separation chamber is partly cylindrical and partly conical in shape.
Preferably, the feed conduit is configured to permit a gravity feed of the feed liquid.
Preferably, the first component leaves the separator as an overflow stream. Preferably, the separation chamber comprises an upper outlet for the first component. In one preferred form, the upper outlet is located centrally about the drive shaft. Preferably, the second component leaves the separator as an underflow stream. Preferably, the separation chamber comprises a lower outlet for the second component. The overflow and underflow may be directed to separate downstream process units. More preferably, the underflow stream is directed as a feed stream into a separation device. The separation device is preferably a thickener.
According to a second aspect, the invention provides a method for deaerating a feed liquid comprising a liquid suspension or pulp, the method comprising the steps of conveying the feed liquid into a separation chamber, mechanically agitating the feed liquid to induce a rotational flow, such that the rotational flow generates a centrifugal vortex to separate the feed liquid into a first component consisting essentially of froth or gas and a second component consisting essentially of deaerated liquid or sludge, and controlling the location of the vortex in the separation chamber with a vortex locating device.
Preferably, the vortex locating step comprises controlling a start point of the vortex. Preferably, the vortex locating step comprises adjusting the position of the vortex locating device.
Preferably, the method further comprises the step of forming the vortex locating device such that its transverse cross-section complements the cross-sectional shape of the separation chamber. Preferably, the vortex locating device is substantially circular in shape or is a substantially horizontal circular disc.
Preferably, the mechanical agitating step comprises rotating a rotor about a drive shaft to induce the rotational flow of the feed liquid.
Preferably, the vortex locating step comprises axially displacing a start point of the vortex from the rotor. Preferably, the vortex locating step comprises locating a vortex start point adjacent or on the drive shaft.
Preferably, the method further comprises the step of forming the rotor such that rotation of the rotor defines a shape that substantially complements the shape of the separation chamber.
Preferably, the feeding step comprises feeding the feed liquid under gravity into the separation chamber.
Preferably, the method further comprises the steps of removing the first component as an overflow stream and removing the second component as an underflow stream. Preferably, the method further comprises the step of directing the overflow and underflow streams to separate downstream process units.
Preferably, the method further comprises the step of directing the underflow stream into a separation device. Preferably, the separation device is a thickener
In the preferred embodiments of both aspects, the invention is used for removal of froth and air from a feed slurry before it is fed into a thickener. The thickener preferably comprises 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 thereby displaced toward an upper region of the tank for separation via an overflow launder.
Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
A preferred application of the invention is in the fields 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 quiescent conditions. The pulp is settled from the suspension by a combination of gravity with chemical and/or mechanical processes. The pulp gradually clumps together to form aggregates of larger pulp particles as it descends from the feedwell towards the bottom of the tank. This is typically enhanced by the addition of flocculating agents, also known as flocculants, which bind the settling solid or pulp particles together. These larger and denser pulp aggregates settle more rapidly than the individual particles by virtue of their overall size and density relative to the surrounding liquid, gradually forming a compacted arrangement within a pulp bed at the bottom of the tank.
Referring to
The feed inlet 2 receives the feed liquid 3 by a gravity flow from an upstream process, and may be provided with a valve assembly (not shown) to regulate the flow of the feed liquid. In other embodiments, the feed liquid is pumped through the feed inlet 2 into the apparatus 1. It will also be appreciated by one skilled in the art that instead of a feed inlet, the feed conduit may comprise a feed line, channel (open or closed) or trough upstream of the apparatus 1.
The froth component 7 leaves the separator 4 as an overflow stream through an upper outlet 9 centrally located at the top of the separation chamber 6 while the deaerated component 8 leaves the separator as an underflow stream through a lower outlet 10. The overflow and underflow streams from the separator 4 may be directed to separate downstream process units (not shown).
The mechanical agitator 5 comprises a rotor 11 mounted to a drive shaft 12 and a drive mechanism 13 for rotating the drive shaft (as shown by arrow 14). The rotor 11 induces rotational flow of the feed liquid 3 in the separation chamber 6 to create a centrifugal vortex 15 that separates the feed liquid into the froth component 7 and the deaerated liquid or sludge component 8. The rotor 11 comprises four rotor blades 16 equidistantly spaced to define an X-shape when viewed in the horizontal plane.
A device 17 for controlling the location of the vortex 15 in the separation chamber 6 is provided on the drive shaft 12 in the form of a substantially horizontal disc. The disc 17 locates the vortex 15 so that its start point 18 begins adjacent or on the upper surface 19 of the disc, as best shown in
It will be appreciated that the vortex locating device 17 need only maintain a sufficient distance between the rotor 11 and the start point 18 of the vortex 15 to ensure that the vortex does not extend past the rotor. Thus, the vortex locating device 17 can be positioned axially lower on the drive shaft 12 so that the vortex 15 is not confined in the upper section of the separation chamber 6 but extends further down and occupy more volume of the separation chamber.
Although adjusting the rpm (revolutions per minute) of the rotor 11 could also control the vortex, it will be appreciated that the disc 17 provides a more convenient and efficient means for controlling the location of the vortex 15.
In operation, the feed inlet 2 feeds aerated slurry 3 into the separation chamber 6, preferably tangentially. The drive mechanism 13 and the drive shaft 12 rotate the rotor 11 so as to induce a rotational flow of the slurry 3 that develops into a centrifugal vortex 15 initiating from the vortex locating disc 17. The vortex 15 separates the feed slurry 3 into the froth component 7 and the deaerated liquid or sludge component 8. Due to its lighter density, the froth 7 migrates upwardly in the separation chamber 6 and is removed through the upper outlet 9 as an overflow stream. The deaerated liquid or sludge 8, due to its heavier density, migrates downwardly towards the bottom 20 of the separation chamber 6 and is removed through the lower outlet 10 as an underflow stream.
The centrifugal-type separator 4 is particularly efficient in separating froth from partially aerated pulps by centrifugal forces and/or “shearing” to remove the air bubbles from the solid particles. The proportion of deaeration of the feed liquid can be controlled as appropriate by varying several operating parameters of the centrifugal separator 4, including the diameter of the separator, the separator length, the angle of the separator barrel, the size of the feed conduit, the feed density, throughput of feed liquid into the separator and the speed of rotation of the rotor. With a partially aerated feed liquid, and appropriately tuned operating parameters, a relatively small overflow stream can be produced with the apparatus 1 which contains the vast majority of the froth, leaving a proportionately large volume of deaerated underflow liquid having a density similar to that of the feed liquid.
A deaeration apparatus 21 according to a second embodiment of the invention is illustrated in
Referring
The second embodiment of the invention works in substantially the same manner as is described in relation to the first embodiment of
A third embodiment of the invention is illustrated in
A fourth embodiment of the invention is illustrated in
A fifth embodiment of the invention is illustrated in
Referring to
In the preferred embodiments of the invention, the underflow stream from the lower outlet 10 feeds the deaerated liquid or sludge from the centrifugal separator 4, 22, 41, 51 and 61 to a thickener (not shown). 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 overflow stream from the upper outlet 9 is fed to a launder (not shown), where is can be broken down with fine water spray jets (not shown). This produces a third component consisting essentially 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.
Whilst a single separator is illustrated in the preferred embodiments, 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. However, it is preferred that the separator is upscaled in capacity to meet the required throughput of feed liquid that needs to be processed.
Of course, the centrifugal separator arrangement need not necessarily be applied only to thickeners, since the principle of deaeration 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 underflow or with the feed material. The separated streams may simply be directed to discrete downstream process units as required.
In other embodiments, the position of the vortex locating device is adjustable upwardly or downwardly on the drive shaft. This additionally provides more control of the location of the vortex within the separation chamber and allows the amount of deaeration to be controlled within the apparatus, in conjunction with other operational parameters. Other embodiments use vortex locating devices of differing shapes, such as square, rectangular, triangular or other polygonal shapes. While the preferred embodiments of the invention have been described using vortex locating devices having a diameter equal to or less than the diameter of the rotor, vortex locating devices having diameters greater than the rotor diameter can also be used.
One skilled in the art will appreciate that the rotor configuration can be varied according to the shape of the separation chamber and is not limited to the configurations illustrated in the described embodiments.
It will also be appreciated by one skilled in the art that the invention provides a useful apparatus for mechanically deaerating liquids, especially liquid suspensions or pulps, thus reducing or substantially eliminating the harmful effects of froth in the subsequent separation processes conducted downstream of the deaeration apparatus.
Moreover, the illustrated deaeration apparatuses according to embodiments of the invention avoid the operational restrictions and additional expense involved with the installation and maintenance of the cyclonic-type centrifugal separators in the prior art. Consequently, the invention permits the deaeration apparatus to be scaled up to increase its capacity without requiring significant power to generate the centrifugal force required in cyclonic separators. For example, where five cyclonic centrifugal separator units would have been required to process 400 m3 of feed slurry, only a single deaeration apparatus according to the invention needs to be installed. In addition, the invention permits a simple means of feeding of the feed liquid or slurry by gravity, rendering it compatible with the majority of separation devices and facilitating retrofitting to existing plants and avoiding the use of pumps. Consequently, maintenance and installation costs for the deaeration apparatus are significantly less than the associated installation and maintenance cost for a comparable cyclonic separator unit. The increased capacity of the deaeration apparatus of the invention, coupled with its lower installation and maintenance costs, results in improved production efficiency in separation devices employing such apparatuses. 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 many other forms.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008902417 | May 2008 | AU | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/AU09/00585 | 5/8/2009 | WO | 00 | 11/15/2010 |
