Note: Descriptions are shown in the official language in which they were submitted.
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SEPARATION DEVICE
BACKGROUND OF THE INVENTION
[0001] This invention relates to the physical separation of solids, using
gravity separation
devices such as a spiral separator or a shaker table.
[0002] A spiral separator consists of an open trough that is twisted helically
downward
about a vertical central axis. Slurry which is fed to the top of the trough,
then flows
downwardly in a spiral path, determined by the shape of the trough.
Centrifugal and
frictional forces acting on the moving slurry create distinct bands or streams
of the slurry,
with each band containing a respective category of separated solids. A nominal
interface
zone is formed at the junction of each pair of adjacent streams. Each stream
exits from the
spiral separator through a respective port. A stream is usually marshalled
towards its
respective port with the aid of a suitable splitter such as a flap-type
splitter, e.g. a mouth
organ splitter, located at an end of the trough, or through the aid of an
auxiliary splitter,
several of which may be located on the surface of the spiral at regular
intervals.
[0003] Similarly, a shaker table is used to separate solids contained in a
slurry. A
combined effect of mechanical reciprocating motion of the table and a thin
water layer on a
sloping surface of the table results in the creation of distinct regions and
interface zones,
formed between the regions, across the surface. The separated solids are
contained in
respective distinct streams, which flow over an edge of the surface and which
are collected
in respective troughs located at the edge. The streams are often marshaled to
respective
target troughs by means of suitable splitters located at the edge.
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[0004] The operation of the spiral separator is susceptible to fluctuating
feed quality and
solid content in the feed slurry and other process variables which may result
in changes in
the positions of the interface zones. A need therefore exists for the splitter
to be adjustable
to address changes in the feed conditions.
[0005] An incorrect splitter position relative to the position of a target
stream results in
mineral losses. The position of the splitter should be adjustable to reduce
this loss.
[0006] Traditionally the position of the splitter is manually adjusted. This
requires regular
monitoring and attention via an operator. This is a difficult and repetitive
task and is often
neglected. The splitter may be in a difficult-to-access location and an
appropriate manual
adjustment of the splitter might be challenging due to the harsh conditions in
which the
spiral separator operates.
[0007] Automated actuators have been developed to facilitate an adjustment of
a splitter's
position. This approach makes use of an optical sensor which, by detecting the
position of
a stream on the spiral or shaker table surface, controls an actuator which
mechanically
shifts the splitter from one position to another in response to a signal from
the sensor. A
high force is required to move the actuator, and frequent movement causes the
splitter to
become worn due to frictional contact with the surface, thereby increasing
cost and
complexity.
[0008] An object of the present invention is to address, at least to some
extent, the
aforementioned situation.
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SUMMARY OF THE INVENTION
[0009] The invention provides an apparatus for separating particulate material
in a slurry
which is caused to move to an exit location in at least first and second
distinct bands with
an interface zone between the first and second bands, the first band generally
containing a
first category of particles and the second band generally containing a second
category of
particles, the apparatus at least a first port and a second port at the exit
location, and a
mechanism for directing at least one jet of pressurized fluid onto or into the
slurry upstream
of the exit location to influence the position of the interface zone relative
to the first port and
the second port.
[0010] The apparatus may include at least one splitter at the exit location,
configured to
split the first band from the second band.
[0011] The jet of pressurized fluid may influence the position of the
interface relative to the
splitter.
[0012] The apparatus finds particular application for use in a system in which
the slurry is
caused to move to the exit location along an arcuate path generally under
gravity action.
Thus the apparatus may be employed with benefit in a spiral separator or an
equivalent
device. In a spiral separator the particles tend to separate from one another,
due at least
to the effects of centrifugal forces and friction, into first and second
generally parallel
bands. The first band may contain generally heavier particles and the second
band may
contain generally lighter particles.
[0013] Alternatively, the apparatus may be employed with a shaker table which
causes
particles contained in the slurry to separate under the combined effect of a
mechanical
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reciprocating motion and gravity action. The particles tend to separate from
one another
into, at least, first and second bands extending radially from a feed trough
which feeds the
slurry onto a surface of the table. The first band may contain generally
heavier particles
and the second band may contain generally lighter particles.
[0014] The pressurized fluid may be pressurised air, pressurised water,
pressurised slurry
or any other suitable gas or liquid under pressure.
[0015] The apparatus may include a first adjustment device to alter the
direction in which
the jet impinges on the slurry surface.
[0016] The apparatus may include a second adjustment device to alter the shape
of the jet
which impinges on the slurry surface.
[0017] The apparatus may include a controller for altering or regulating the
flow rate of the
fluid in the jet and its pressure. The type of fluid may also be varied
according to
requirement.
[0018] In one form of the invention use is made of a plurality of nozzles,
each of which
emits a respective fluid jet onto or into the slurry. Each nozzle could be
separately
controlled to vary any of the aforementioned parameters. The plurality of
nozzles could be
in an array which extends at least across a part of the width of the first and
second bands,
or in an array which extends generally in the slurry flow direction, i.e.
towards the exit
location.
[0019] In a first embodiment of the invention the apparatus includes a spiral
separator
which includes a spiral chute which defines a slurry passage, an inlet for
feeding slurry to
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the slurry passage, an outlet from the slurry passage, and an off-take
assembly located at
the outlet, wherein the off-take assembly includes at least one splitter and
at least one
nozzle used to direct a fluid jet into the slurry passage at a location which
is upstream from
the splitter.
5 [0020] At least one auxiliary splitter and at least one nozzle which is
used to direct a fluid
jet into the slurry passage at a location that is upstream from the splitter
may be located in
the slurry passage. Preferably a plurality of auxiliary splitters, each of
which is associated
with at least one respective nozzle, are located, at displaced intervals, in
the slurry
passage.
[0021] The nozzle may be movable relative to the splitter thereby to adjust
the position at
which the fluid jet (in use) impinges on slurry in the slurry passage.
[0022] The splitter may divide the outlet into ports.
[0023] The off-take assembly may include a plurality of splitters with
adjacent splitters
defining a respective port between them.
[0024] The apparatus may include a plurality of nozzles, each of which is used
to direct a
jet of fluid into the slurry stream at a respective position in the slurry
passage.
[0025] In a second embodiment of the invention the apparatus includes a shaker
table
which includes a deck, mounted in a tilted position on a supporting frame,
which defines a
surface, a feed for introducing slurry onto the surface located at a feed side
of the deck, the
surface including a plurality of elongate raised formations, a mechanism for
allowing the
deck to reciprocally slide along an axis parallel to the raised formations to
separate the
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slurry into at least a first band and a second band, a collection structure at
a discharge
edge of the deck to collect at least the first and the second band which flows
from the
edge, and at least one nozzle to direct a fluid jet onto the surface at a
location which is
upstream from the discharge edge.
[0026] The shaker table may include an adjustment device for adjusting a
degree of tilt of
the deck.
[0027] The shaker table may include at least one splitter, which includes a
first side and a
second side, located e.g. at an adjacent edge of the deck. The splitter may be
associated
with the nozzle in such a manner that the fluid jet may be used to direct the
first band, at
least partially, to the first side of the splitter and the second band, at
least partially, to the
second side of the splitter.
[0028] The apparatus may include a plurality of splitters, each associated
with a respective
nozzle. The splitters may be located at spaced intervals along the edge of the
deck.
[0029] In each embodiment the apparatus may include a control system which
controls the
emission of the fluid jet which is emitted by a nozzle, in respect of at least
one of the
following: the direction of the fluid jet, the time at which the fluid jet is
emitted, the duration
of a period for which the fluid jet is emitted, the durations of intervals
between the
emissions of successive fluid jets, the angle of the fluid jet, i.e. its
orientation relative to the
slurry in the slurry passage, the strength of the fluid jet, i.e. the pressure
and the flow rate
of the fluid in the jet, and the size or shape of the fluid jet.
[0030] The control system may operate in response to at least one sensor. The
sensor
may be visually (optically) based and may be used to detect an event or
condition in
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response to which a fluid jet, of defined characteristics, is directed onto a
particular location
of a slurry stream in the slurry passage. In addition, or alternatively, a
sensor may be used
to verify that the fluid jet had been correctly emitted.
[0031] The sensor may be responsive to colour contrasts between discrete
adjacent slurry
streams or to differences in the intensity of light reflected from a surface
of each stream.
Alternatively, the sensor may be responsive to any other characteristic or
characteristic of
the material fed to or collected by the spiral or shaker table (as the case
may be). Thus the
characteristic need not be linked to a particular band but rather to a
collection port. For
example if the grade is too low the nozzle would exercise an adjusting effect
to ensure that
less low grade material is collected in a particular collection point
(irrespective of the band).
[0032] The invention also extends to a method of using a spiral separator of
the
aforementioned kind wherein a feed slurry which is passed through the inlet
into the slurry
passage moves along the slurry passage towards the outlet under gravity action
and
wherein, due at least to centrifugal forces, the slurry is caused to separate
into at least two
adjacent streams wherein each stream contains particles generally of a
particular density,
the method including the step of using a fluid jet to adjust the position of
an interface zone
between adjacent streams relative to the splitter at the outlet.
[0033] The position of an interface zone between adjacent streams may be
determined
optically due to contrasts in light reflections from the respective streams.
[0034] The invention further extends to a sensor for use in apparatus employed
to
separate particulate material in a slurry on the basis at least of particle
size and particle
density wherein, at least due to the effects of centrifugal forces and
friction, the slurry is
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separated into at least two adjacent bands and wherein the sensor optically
detects the
position of an interface zone between the adjacent first and second bands of
slurry by
sensing a contrast in colour or reflected light of a surface of the slurry in
the first band
relative to the colour or reflected light of a surface of the slurry in the
second band.
[0035] In this specification "streams" and "bands" are used interchangeably.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] The invention is further described by way of examples with reference to
the
accompanying drawings in which :
Figure 1 shows a spiral separator according to the invention,
Figure 2 depicts components at an outlet from the spiral separator, and
Figures 3 and 4 depict aspects of a shaker table according to the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0037] Figure 1 shows a spiral separator 10 according to one embodiment of the
invention.
[0038] The spiral separator 10 includes a spiral chute 12 of conventional
form, which
defines a slurry passage 14, an inlet 16 to the chute and an outlet 18 from
the chute. A
feeding mechanism 20 is used to direct slurry into the inlet 14. An off-take
assembly 22 is
located at the outlet 18.
[0039] The off-take assembly 22 includes at least one splitter 24. The
splitter is in the
form of a blade which is positioned in the passage 14 at the outlet 18. The
off-take
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assembly 22 additionally includes nozzles 26 and 28, on opposing sides of the
splitter 24
and upstream from the splitter. The nozzles are separately connected to a
source 30 of a
pressurised fluid. Control valves 32 and 34 are positioned in the connections
between the
nozzles 26 and 28 and the fluid source 30, respectively. The valves are
connected to a
controller 36 which controls operation of the valves.
[0040] Auxiliary splitters 38 and 40 (notionally shown), which could be in the
form of sliding
splitters (non-limiting), are located at displaced locations in the passage
14. Nozzles 42
and 44 are located upstream from the splitters 38 and 40, respectively. The
nozzles are
separately connected to the source 30 of the pressurised fluid. Control valves
46 and 48,
which are controlled by the controller 36, are used to control the flow of
fluid from the
source 30 to the nozzles 42 and 44.
[0041] An optical sensor 50 is positioned above the slurry passage 14 close to
the outlet
18. Optical sensors 52 and 54 are positioned above the slurry close to the
positions of the
auxiliary splitters 38 and 40. Signals produced by the sensors 50, 52 and 54
are directed to
the controller 36.
[0042] Figure 2 is a simplified plan view of the off-take assembly 22 and of
the slurry
passage 14 at the outlet 18. The optical sensor 50 (shown in dotted outline)
extends
across a width 56 of the slurry passage 14. The nozzles 26 and 28 are mounted
to
respective swivel joints 26A and 28A which allow the orientations of the
nozzles to be
adjusted in an angular sense, vertically relative to a surface of the spiral
chute 12 and
laterally as is indicated by means of double-headed arrows 26B and 28B
respectively.
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[0043] The invention is described herein with reference to the use of the
spiral separator
under conditions in which slurry 57 fed into the inlet 16 from the feeding
mechanism 20 has
a composition in which the slurry is divided due to the action of the spiral
separator, in
accordance with principles which are well established, into adjacent first and
second bands
5 or streams 58 and 60 respectively of the slurry, with an interface zone 62
between the
bands. As is known in the art the bands result due to the effects of
centrifugal forces and
friction as the slurry flows downwardly along the spiral path determined by
the spiral chute.
Each band generally contains a respective category of particles with each
category being
characterized by particles in a particular range of particle sizes and in a
particular range of
10 particle densities. As the bands generally contain different types of
particles, the bands
usually take on respective colours associated with the types of particles
included in each
band. Fluctuating feed quality and changes in the solid content in the feed
slurry can affect
the colours of the bands and the widths of the bands and hence the position of
the
interface zone 62 between the bands.
[0044] The "interface zone" is a phrase used to define and refer to the
junction between
adjacent bands of slurry. The zone is not necessarily distinct nor precisely
determinable.
Also, the zone may lie on a straight, wavy, or curved or other path.
[0045] The invention is described with reference to the use of a spiral
separator which
produces two bands. This is illustrative only and non-limiting. The principles
of the
invention can be used with equal effect under conditions in which three or
even more
bands of slurry are formed in a spiral separator.
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[0046] The fluid source 30 typically contains water under pressure. This is
exemplary only
and is non-limiting. Compressed air could be provided by the source. Another
possibility is
to make use of a slurry under pressure with the slurry being of the same
composition as
the feed slurry. Ideally the nature of the material in the source should be
such that the
.. addition thereof in a limited quantity to the feed slurry does not
materially alter the nature of
the feed slurry. This aspect can be addressed to some extent by ensuring, as
well, that
material from the source 30 is added to the feed slurry as close as possible
to the splitter
24.
[0047] In use of the spiral separator the optical sensor 50 monitors the
intensities of light
reflections from the band 58, from the interface zone 62, and from the band
60. The
position of the sensor 50 is fixed relative to the spiral chute and the
signals which are
produced by the sensor 50 are thus in some way physically related to or
dependent on the
width of each band and the width of the interface zone. This information is
fed to the
controller 36. An objective is to ensure that, as far as is possible, the
splitter 24 is
positioned to intercept the downwardly flowing slurry at the interface zone 62
so that only
material in the band 58 is directed by the splitter to a first exit path 58A
and so that only
material from the band 60 is directed by the splitter 24 to a second exit path
60A. The
splitter position is however not adjustable.
[0048] If the optical sensor 50 detects that the interface zone 62 is moving
laterally across
.. the width 56, ie laterally away from the splitter then this is an
indication that efficient
splitting of the slurry stream cannot be effected by the splitter 24. The
controller 36 detects
in which direction the slurry stream is to be moved so that the interface zone
62 is correctly
positioned relative to the splitter 24. The controller 36 opens the respective
control valve
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32 or 34, to an appropriate extent, so that a controlled jet of fluid from the
source 30 is
directed by the corresponding nozzle 26, 28 onto the surface of the slurry
upstream of the
splitter 24. The orientation of each nozzle relative to the slurry surface is
adjusted
manually or automatically according to requirement. The intention is to ensure
that at least
.. one jet of fluid with an appropriate flow rate is directed onto the slurry
surface, upstream of
the splitter 24, to influence the movement of the slurry relative to the
splitter and, in the
process, to ensure that the interface zone 62 is brought into alignment with
the splitter.
When this state is achieved effective and efficient splitting of the bands 58
and 60 takes
place.
[0049] The nozzles 42 and 44 can be used to exert a "splitting" action on the
bands 58 and
60 in the passage 14, upstream of the splitter 24, as shown in Figure 2B. The
band 60 is
directed towards the splitter 38 or 40 (as the case may be) and is taken off
the chute 12, as
a band 60B, while the band 58 continues down the passage 14, as a band 58B.
The
optical sensor 52 or 54, in each case detects the position of the interface
zone 62. In
.. response to a signal from the respective sensor 52 or 54, the controller 36
opens the
corresponding valve 46 or 48 so that the associated nozzle directs a fluid jet
onto the slurry
surface to move the interface zone relative to the position of the respective
auxiliary splitter
38 or 40.
[0050] The control technique is implemented continuously. It may well be that
the colour
contrast between the bands 58A and 60A, due to differing mineral contents in
the bands, is
of a transient or short-lived nature. In this event the corrective action of
the fluid jet is
terminated when the sensor 50 detects that a fluid jet is exerting an over-
correcting action.
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[0051] Figure 2 schematically illustrates the use of two nozzles 26, 28, one
above each
respective band of slurry which is formed by the separating action of the
spiral separator. It
is possible to make use of more than two nozzles. For example, an array of
nozzles could
be positioned stretching across the width 56 of the slurry passage 14. In a
variation an
array of nozzles is used extending generally in the direction of flow of the
slurry in the
passage. The displacement force exerted by the nozzles on the slurry
flow is
accumulative, over the region of the length of the array. The slurry is
continuously
contacted by the jets of the fluid. Other nozzle configurations are of course
possible.
[0052] The invention has been described with reference to the use of an
optical sensor 50
to detect mineral bands in a spiral separator. This is exemplary and non-
limiting.
[0053] The principles of the invention can also be used in respect of a
separator such as a
shaker table which does not work on a spirally induced centrifugal process.
Figures 3 and
4 show a shaker or riffle table 100, which includes a deck 102 mounted in a
tilted position
on a supporting frame 104, and a feed trough 106 for introducing slurry 108
onto a tilted
surface 110 of the deck 102 at a feed side of the deck. A plurality of
elongate raised
formations, provided by bars or ridges 112, are formed on the surface 110.
These
formations extend transversely from the feed side to the opposed discharge
edge.
[0054] A shaker mechanism 114 causes reciprocating movement of the deck 102
along
an axis which is parallel to the longitudinal dimensions of the formations
112. The
mechanism 114 repeatedly produces a slow forward stroke, followed by a rapid
return
strike, which can cause the slurry 108 to form adjacent bands 116, 118, 120
and 122 of
material with respective interface zones 124, 126 and 128 formed between
adjacent bands.
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The interface zones move, relative to respective splitters 132, 134 and 136,
according to
the composition of each band. Suitable troughs, not shown, are used to collect
these bands
which flow over the discharge edge. In a manner which is similar to what has
been
described in connection with Figures 1 and 2, and through the use of similar
equipment,
the interface zones can be moved by judicious use of respective nozzles 142,
144, 146 and
148 in response to sensors (not shown) which detect the position of each
interface zone
relative to the associated splitter.
