Note: Descriptions are shown in the official language in which they were submitted.
CA 02271958 1999-07-22
K
CENTRIFUGAL SEPARATOR WITH INJECTION OF FLUiDIZING LIQUID
BETWEEN NON-FLUIDIZED RECESSES
This invention relates to a centrifugal separator of the type having a
plurality of axially spaced annular recesses on a peripheral wall of a
rotatable bowl.
BAC1COROUND OF THE INVENTION
In U.S. Patents 4,608,040, 4,776,833, 5,222,933 and 5,338,284 the
present applicant discloses a number of different arrangements of centrifugal
separator of the type including a rotatable bowl having a peripheral wall of
generally
frusto-conical shape on which is provided a plurality of axially spaced,
annular
recesses. The particulate material containing fractions of different specific
gravity to
be separated is fed in slurry form through a feed duct to a position at or
adjacent a
base of the bowl so that the feed materials pass over the peripheral wall with
heavier
particulate materials collecting in the annular recesses while lighter
particulate
materials escape from the bowl through the open mouth. In the above patents,
all of
the annular recesses are fluidized by the injection of fluidizing water
through holes in
the peripheral wall at the respective recesses thus acting to fluidize the
collecting
material within the recesses.
A further arrangement is disclosed in U.S. Patent 5,586,965, issued
December 24th, 1996 of the present inventor in which the number of recesses is
reduced and a frusto-conical lead-in section of the bowl is provided which is
free
from fluidized recesses so that the feed material is deposited onto the lead-
in section
and flows over that lead-in section prior to reaching the first annular
recess.
Fluidized recesses have the potential disadvantage that it is necessary
for the supply of the additional water for providing the fluidizing action
within the
recesses. In some cases where water is in short supply it is desirable to
provide a
reduction in the quantity of fluidizing water necessary for running the
machine.
CA 02271958 1999-07-22
2
Fluidized recesses also have the disadvantage that they should be
relatively deep and wide with a consequential large volume so that the total
volume
of material in the concentrate is relatively large and only some of this is
the required
heavier material. Thus the ratio of heavier in the collected concentrate is
relatively
low in many cases requiring a further concentration step before the heavier
material
is in sufficient concentration for direct use, for example smelting.
It is one object of the present invention to provide an improved
centrifugal separator of the above general type in which the quantity of
fluidizing
water can be reduced and the richness of the concentrate can be increased.
It is a further object of the present invention to provide a bowl which
can be used in an existing apparatus as a replacement part to provide an
improved
separation.
According to a first aspect of the invention, therefore, there is provided
an apparatus for separating intermixed particulate materials of different
specific
gravity in a slurry comprising:
a centrifuge bowl having a base and a peripheral wall surrounding an
axis passing through the base and generally upstanding from the base to an
open
mouth;
means mounting the bowl for rotation about the axis;
a feed duet for feeding the intem~ixed particulate materials in the sluny
into the bowl so that during rotation of the bowl the intermixed particulate
materials
flow over the peripheral wall for collection of heavier particulate materials
on the
peripheral wall and for discharge of the lighter particulate materials in the
sluny from
the open mouth;
CA 02271958 1999-07-22
3
a launder for collecting the lighter particulate materials in the slurry
discharged from the open mouth;
a plurality of annular non-fluidized recesses on the peripheral wall at
axially spaced positions over which the materials pass so that the heavier
particulate
materials collect in the recesses, each non-fluidized recess being defined by
a
surface portion of the peripheral wall between two axially spaced land
portions of the
peripheral wall which surface portion of the peripheral wall is substantially
imperforate such that fluidizing liquid is prevented from entering into the
recess by
passing through the surface portion of the peripheral wall;
and, between the surface portion of at least one non-fluidized recess
and the next, an annular fluidizing area of the peripheral wall which contains
a
plurality of angularly spaced fluidizing openings for adding fluidizing liquid
to the
materials as they pass over the recesses.
Preferably between each non-fluidized recess and the next is provided
a respective one of a plurality of annular fluidizing areas.
According to a second aspect of the invention there is provided an
apparatus for separating intermixed particulate materials of different
specific gravity
in a slurry comprising:
a centrifuge bowl having a base and a peripheral wall surrounding an
axis passing through the base and generally upstanding from the base to an
open
mouth;
means mounting the bowl for rotation about the axis;
a feed duct for feeding the intermixed particulate materials in the slurry
into the bowl so that during rotation of the bowl the intermixed particulate
materials
flow over the peripheral wall for collection of heavier particulate materials
on the
CA 02271958 1999-07-22
4
peripheral wall and for discharge of the lighter particulate materials in the
slurry from
the open mouth;
a launder for collecting the lighter particulate materials in the slurry
discharged from the open mouth;
a plurality of annular non-fluidized recesses on the peripheral wall at
axially spaced positions over which the materials pass so that the heavier
particulate
materials collect in the recesses, each non-fluidized recess being defin~l by
a
surface portion of the peripheral wall between two axially spaced land
portions of the
peripheral wall which surface portion is substantially imperforate;
and at least one annular fluidizing recess axially spaced from each of
the non-fluidizing recesses, the or each fluidizing recess having a plurality
of
angularly spaced fluidizing openings for injection of fluidizing liquid
through the
peripheral wall for adding fluidizing liquid to the materials therein.
Preferably between at least one of the non-fluidizing recesses and a
next adjacent one is provided at least one of the fluidizing recesses for
adding
fluidizing liquid to the materials passing over said at least one and said
next non-
fluidizing recesses.
Preferably the non-fluidized recesses each have a depth less than that
of the fluidized recesses.
Preferably the fluidized recesses and the non-fluidized recesses are
arranged substantially alternately.
Preferably the recess closest to the open mouth is a fluidized recess.
Preferably one or more recesses closest to the base are non-fluidized
recesses.
Preferably above the plurality of the non-fluidized recesses closest to
the base is provided a plurality of fluidized recesses closest to the mouth.
CA 02271958 1999-07-22
According to a third aspect of the invention there is provided an
apparatus for separating intermixed particulate materials of different
specific gravity
in a slung comprising:
a centrifuge bowl having a base and a peripheral wall surrounding an
5 axis passing through the base and generally upstanding from the base to an
open
mouth;
means mounting the bowl for rotation about the axis;
a feed duct for feeding the intermixed particulate materials in the slung
into the bowl so that during rotation of the bowl the intermixed particulate
materials
flow over the peripheral wall for collection of heavier particulate materials
on the
peripheral wall and for discharge of the lighter particulate materials in the
slurry from
the open mouth;
a launder for collecting the lighter particulate materials in the slurry
discharged from the open mouth;
a plurality of annular non-fluidized recesses on the peripheral wall at
axially spaced positions over which the materials pass so that the heavier
particulate
materials collect in the recesses, each non-fluidized recess being defined by
a
surface portion of the peripheral wall between two axially spaced land
portions of the
peripheral wall which surface portion is substantially imperforate;
and, between at least one non-fluidized recess and the next, an
annular land area of the peripheral wall which is raised inwardly toward the
axis from
surface portions of the adjacent recesses and which carries a plurality of
angularly
spaced fluidizing openings for adding fluidizing liquid to the materials as
they pass
over the recesses.
Preferably between each non-fluidized recess and the next is provided
a respective one of a plurality of land areas, each of which is raised
inwardly toward
CA 02271958 1999-07-22
6
the axis from the adjacent recesses and which carries a plurality of angulariy
spaced
fluidizing openings for fluidizing the materials as they pass over the
recesses.
Preferably there is provided at least one annular fluidizing recess
axially spaced from the non-fluidizing recesses and arranged adjacent the
mouth of
the bowl for receiving the material after passing over the non-fluidized
recesses, the
or each fluidizing recess having a plurality of angularly spaced fluidizing
openings for
injection of fluidizing liquid through the peripheral wall for fluidizing the
materials
therein.
Preferably at least one of the fluidized recesses includes a first side
wall adjacent the mouth, a second side wall adjacent the base and an annular
base
interconnecting the side walls so as to define a volume therebetween and
wherein
the recess contains fixed elements therein which reduce the volume of the
recess so
as to reduce the quantity of separated materials contained therein.
Preferably the elements comprise a plurality of inwardly projecting
axially space annular rings contained within the recess with fluid injection
openings
between each ring and the next.
Preferably at least some of the non-fluidized recesses include a
surface portion which is parallel to the axis.
Preferably on a side of each non-fluidized recess adjacent the mouth
the adjacent land portion defrnes a shoulder lying substantially in a radial
plane of
the axis.
Preferably below the non-fluidized recesses closest to the base of the
bowl is provided a frusto-conical wall portion having a wall angle for
directing the
materials across the recesses and wherein the feed duct is arranged to feed
the
materials so that they pass onto the frusto-conical portion.
CA 02271958 1999-07-22
7
Preferably each fluid injection opening includes a fluid injection duct
formed through the wall of the bowl and having a second duct portion at the
interior
of the bowl which is of larger diameter than a first duct portion supplying
the second
duct portion so as to reduce the velocity of the liquid as it passes to the
bowl.
Preferably the peripheral wall increases in diameter from the base to
the open mouth such that each recess closer to the open mouth has a diameter
greater than one closer to the base and such that an uppermost recess has a
largest
diameter and wherein there is provided an annular restricting member provided
on
the bowl at or adjacent the open mouth and extending from the peripheral wall
to an
inner edge of the restricting member spaced inwardly toward the axis for
causing the
lighter material and the slung to escape from the open mouth at a position
spaced
inwardly toward the axis relative to the uppermost recess.
Preferably the annular restricting member comprises an imperforate
ring.
Preferably the inner edge lies on an imaginary cylinder which
intersects with the peripheral wall at a position thereon at or below a
fluidized recess
which is the second from the open mouth.
In accordance with a further aspect of the invention there is provided a
centrifuge bowl for use in an existing apparatus for separating intermixed
particulate
materials of different specific gravity in a slurry comprising:
a base and a peripheral wall surrounding an axis passing through the
base and generally upstanding from the base to an open mouth;
a plurality of annular non-fluidized recesses on the peripheral wall at
axially spaced positions, each non-fluidized recess being defined by a surface
portion of the peripheral wall between two axially spaced land portions of the
CA 02271958 1999-10-O1
peripheral wall which surface portion is substantially imperforate so as to be
substantially non-fluidized;
and at least one annular fluidizing recess axially spaced from each of
the non-fluidizing recesses, the or each fluidizing recess having therein a
plurality of
angularly spaced fluidizing openings for injection of fluidizing liquid
through the
peripheral wall;
wherein the non-fluidized recesses each have a depth less than that of
the at least one fluidized recess.
BRIEF DESCRIPTION OF THE DRAWINGS
One embodiment of the invention will now be described in conjunction
with the accompanying drawings in which:
Figure 1 is vertical cross-sectional view through a first embodiment of
centrifugal separator according to the present invention.
Figure 2 is a cross-sectional view through a part of the bowl only of
figure 1 on an enlarged scale.
Figures 3, 4 and 5 are cross-sectional views through the bowl only of
respectively a second, third and fourth embodiment of an apparatus according
to the
present invention, the remainder of the apparatus being the same as that shown
in
figure 1.
DETAILED DESCRIPTION
The general arrangement of the centrifugal separator shown in Figure
1 is taken from the above U.S. patent 5,222,933 of the present inventor and
therefore will described only briefly in regard to the points of importance.
The
disclosure of the above patents of the present inventor should be referred to
for
further details which may be necessary for a full understanding.
CA 02271958 1999-07-22
9
The apparatus therefore comprising a bowl generally indicated at 10
having a base generally indicated at 11 and a peripheral wall 12 standing
upwardly
from the base to an open mouth 13. The bowl can rotate around an axis 15 on a
support shaft 16.
A feed duct 17 carries feed materials 18 in the form of a mixture of
heavier and lighter particulate materials in a water slurry through the open
mouth to
a position adjacent to the base so the feed materials can be deposited onto a
horizontal guide plate 11A at the base 11 and can move therefrom onto the
peripheral wall 12 for separation of the heavier materials into a plurality of
recesses
19 on the peripheral wall while the lighter materials in the sluny pass over
the
peripheral wall to the open mouth for discharge. The recesses are annular and
are
axially spaced. The peripheral wall is frusto-conical so that the diameter of
the
recesses increases from a first recess at the base to a last recess at the
open
mouth. Material exiting from the open mouth is collected by a launder 2Q for
discharge.
Around the bowl 10 is provided a jacket 21 having a peripheral wall 22
and a base 23 both of which are connected to the respective elements of the
bowl
so as to form a compartment 21A fed with fluidizing water from a central duct
24 of
the shaft 16 through connecting ducts (not shown). The compartment 21A
therefore
receives fluidizing water under pressure which is communicated through
openings
in the peripheral wall 12 into the recesses for adding fluidizing water into
the
material collecting in the recesses.
The separation and collection process is a batch process so that the
heavier material is collected in the recesses for subsequent wash down and
25 collection. The collected materials when washed down to the base pass
through a
CA 02271958 1999-07-22
discharge opening 26 into a second collection system 27 for collecting the
concentrate.
The feed duct 17 comprises a cylindrical tube carried on a cover 28 of
the launder 20. Thus the tube forming the feed duct is in fixed position and
remains
5 stationary as the bowl rotates around the axis 15.
The apparatus described above is substantially as shown in the prior
patent and is modified in accordance with the present invention by the shape
and
arrangement of the bowl and particularly the recesses and peripheral wall
thereof as
described in detail hereinafter.
10 In the arrangement shown in Figures 1 and 2 a first series 30 of the
recesses 19 as indicated at 30A to 30 F provides recesses which are of the
conventional nature previously described particularly in U.S. Patents
4,776,833 and
4,608,040 of the present inventor.
A second series 40 of recesses indicated at 40A to 40D provides
recesses which are modified relative to the previously described recess
arrangement
so that the recesses are significantly reduced in depth and are free from
connection
to the chamber 21 A.
It will be noted in Figure 1 that the recesses 30 and the recesses 40
are arranged alternately so that the uppermost one of the recesses is of the
fluidized
type indicated at 30A, the second of the recesses is of the shallower, non-
fluidized
type indicated at 40A et cetera through to the lowermost two recesses 30E and
30F
which are both of the fluidized type.
It will be appreciated that the size of the bowl can be varied in
accordance with requirements so that the number of recesses is determined in
effect
by the height of the bowl and a diameter of the recesses is determined by the
diameter of the bowl.
CA 02271958 1999-07-22
11
Also the bowl type is not limited to one which include the central
opening 26 and another known type includes an opening offset to one side (not
shown) which allows the discharge of the material after collection.
In addition the attachment of the bowl to the surrounding jacket is
again not shown but it will be appreciated that the outside flange 50 mounted
at the
outer periphery of the upper part 51 of the bowl allows the bowl to be
attached to the
jacket 21 to define the injection water receptacle 21 A for passage of
injection water
through the openings 25 into the recesses 30.
As described in the previous patents, the bowl is formed from a
suitable elastomeric material which is molded to define the recesses 30 and
40. The
elastomeric material can be supported by a metal shell as shown in Figure 1 or
can
be unsupported.
The recesses 30 are molded into the resilient material so as to define a
generally V shape of the recess with side walls 31 and 32 converging
oufinrardly to a
flat outer base 33. The side walls define innermost edges 34 and 35
respectively.
The uppermost portion 51 of the bowl defines a flat inner surface 36 between
the
innermost edge 34 of the upper side wall 31 and the mouth of the bowl. The
openings 25 communicate with the base 33 substantially at a mid point across
the
base with the openings being spaced around the base. The base is narrower than
the width between the edges 34 and 35. The recesses have a depth between the
inner edges 34 and the base 33 which is generally greater than the width of
the
recess at the mouth of the recess. The openings 25 are arranged at an angle to
the
radius of the axis so as to tend to direct the injected angularly around the
recess.
The recesses 40 have a base 41 and side walls 42 and 43, the side
walls each having an innermost edge 44 and 45 respectively. The side waH 42
between the base surface 41 of the recess and the edge 44 forms a shoulder
lying in
CA 02271958 1999-07-22
12
a radial plane of the axis 15 and thus acts to help in trapping the materials
as they
flow over the bowl wall. A wall or land portion between the inner edge 35 and
the
inner edge 44 is straight and parallel to the axis of the bowl so as to form
an annular
band. The inner edges 34, 35 and 45 etc. lie generally on a frusto conical
surface
including the upper most edge of the bowl at the top of the wall 36 and this
forms
generally the inner surface of the bowl from which the recesses are recessed
outwardly of the axis of the bowl.
The side walls 42 and 43 are parallel and lie in radial planes of the
axis. The base 41 is at right angles to the side walls. The depth of the
recess 40 as
defined by the distance from the inner edges 44 and 45 to the base 41 is very
much
less than the depth of the recess 30. The recess 40, and its defining surfaces
41, 42
and 43, is not in any way connected with the outside surface of the bowl so
that
there is no communication of fluidizing liquid to the interior of the recess
40.
The material flowing over the periphery of the bowl thus generally
passes over the inner surface of the bowl defined by the edges of the recesses
and
provides a separation action at the interface befinreen the material in the
recesses
and the material passing over the peripheral surface.
It will be noted that the width from the innermost edge 35 of the lower
side waN 32 to the innermost edge 34 of the side wall 31 of the next adjacent
recess
is greater than the width of the recesses between the edges 34 and 35. This
width
is necessarily greater than the width of the recess itself since the recess 40
is
substantially the same width as the recess 30 and there is provided the wall
portions
between those recesses as previously described.
The depth of the recess 40 is just sufficient to atlow collection of some
material in the recess so that the surface between the innermost edge 45 and
the
innermost edge 35 is defined in effect by the collected materials lying on the
conical
CA 02271958 1999-07-22
13
surface which acts as the separation surface for the materials flowing over
the
conical surface of the bowl. As the depth of the recesses 40 is very much less
than
that of the recesses 30, the volume of material contained therein is very much
reduced. The majority of heavier material collected at the recess is collected
at the
separation surface with material outside of that being formed by the initial
material
fed into the bowl at start up. As the volume is thus reduced, the ratio or
richness of
heavier material to start up material in the non-fluidized shallower recesses
40 is
very much increased.
In essence the present arrangement using the shallower recesses 40
in replacement for some of the recesses 30 of the conventional system allows
the
system to use approximately 40% less water for fluidizing. This reduction in
fluidizing water has a significant improvement in the operation of the machine
and
overcomes some problems in the processing of the slurry.
The arrangement of the present invention allows the material to be
fluidized in every second recess between the non-fluidized recesses, that is
the
alternate recesses 30 and this fluidization in the alternate recesses allows
the
material to pass from one fluidizing recess over the non-fluidized recess to
the next
fluidizing recess without allowing the material to dry (squeeze the water out)
in a
short space between the fluidizing recesses.
At the same time each shallow recess 40 will allow some material to be
retained on the face of each recess area and this now sets up a textured
surface
defined by the inside surface of the collected material where fine gold
particles
(heavier materials) will have the ability to be trapped in the natural
interstices
created between the particles.
The reduction in depth of the recesses 40 will also create a smaller
amount of concentrate to be treated in secondary treatment. In addition, if
the same
CA 02271958 1999-07-22
14
total amount of materials to be collected is contained within the smaller
amount of
concentrate then the concentrate is increased in grade providing a further
bonus.
The modification does not decrease the ability of the bowl to handle
large volumes of throughput. Other proposals for reducing the number of
fluidized
recesses sometimes provides the problem that the material can dry on the wall
of
the bowl and as soon as the material dries it tends to collect in a stationary
mass
thus interfering with the proper operation of the bowl. The replacement of the
fluidizing recesses at the alternate positions by the non-fluidized recesses
40 allows
the material to properly flow through the bowl without the drying effect of
the material
on the bowl causing loading or imbalance.
Turning now to Figure 3 there is shown an alternative bowl
construction for use in the apparatus of Figure 1. The bowl is of the
construction
substantially as previously described including a plurality of fluidized
recesses 51
through 56 and a plurality of non-fluidized recesses 61 through 68. Each of
the
fluidized recesses has an opening 57 allowing injection of fluid into the
recesses for
fluidizing the materials as previously described.
In this embodiment the arrangement is modifred in that the bottom
three recesses are all of the non-fluidized type. The top recess is of the
fluidized
type. In between these recesses, the remaining recesses alternate between
fluidized and non-fluidized types.
The bottom three recesses are arranged so that the lowermost recess
is slightly deeper than the second recess 62 and the third recess 63. Thus in
one
example the lowermost recess 61 is 1/2 in depth, the second recess 62 is 1/4
inch in
depth and the remaining recess is of 1/8 inch in depth.
The bowl of Figure 3 is further modified by the addition of a restricting
member 70 in the form of annular imperforate ring attached to the open mouth
of the
CA 02271958 1999-07-22
bowl by bolts 71 which clamp an outer part of the ring to the bowl beyond the
open
mouth with an inner part of the ring projecting inwardly from the mouth to an
inner
edge 73 of the ring which is spaced inwardly from the peripheral wall at the
uppermost recess. It will be noted that each of the recesses is of course
defined by
5 inwardly projecting ribs and the ribs project inwardly to a height which is
substantially
equal throughout each of the recesses so that as the peripheral wall increases
in
diameter so the diameter of each recess increases.
The inner edge 73 is circular in plan thus lying on an imaginary cylinder
74 surrounding the axis 15 of the bowl. The cylinder 74 intersects the
peripheral
10 wall at the rib 76 which is at one of the recesses spaced downwardly from
the
uppermost recess and in the embodiment shown is the lower rib of the fifth
recess
from the top which is recess 54. The imaginary cylinder is thus spaced
inwardly
from the fluidized recesses 54, 55 and 56.
In operation, the bowl of Figure 3 allows a significant reduction in the
15 quantity of water while preventing or significantly reducing escape of
water outwardly
from the bowl through the injection openings 57 which could otherwise carry
fine
gold or heavier particles through into the jacket where they are lost.
The provision of the non-fluidized recesses significantly reduces the
number of fluidized recesses relative to a conventional bowl in which all of
the
recesses are fluidized so that the amount of fluid necessary to maintain the
fluidized
recesses fluidized is significantly reduced.
The recesses at the base of the bowl are all non-fluidized recesses.
These recesses are aggressively impacted by the entering materials so there is
a
significant tendency for those recesses to be scoured or washed. The provision
of
the shallower non-fluidized recesses at this point sign~cantly reduces the
escape of
water and particles in these recesses.
CA 02271958 1999-07-22
16
The shallow recesses do not themselves contain a significant volume
of the start up materials. However the shallow recesses do collect some
particulate
materials and thus define a layer of the particulate materials on the inside
surface of
the bowl. Additional particulate materials flowing over the surface of the
bowl impact
upon the particles already in place thus acting as a frictional surface to
slow those
particles closest to the wall which are the heavier particles and allow them
to enter
into the next fluidized recess. While the number of fluidized or collecting
recesses is
therefore reduced, the overall collection efficiency is not significantly
reduced and
may be enhanced due to the effect of the intervening strips or bands of
particulate
material which improve the separation when the material reaches the collecting
or
fluidized recess.
The restricting member which is ring 70 at the open mouth closes the
material to take up a path indicated at the dash line 80 in which the material
is thus
spaced inwardly from the recesses above the recess 66. In this way material
collects in the zone outwardly of the line of material 80. Additional
collection occurs
in this zone due to the fluidization in the recesses 54, 55 and 56. This ring
70 if used
with a conventional bowl in which all of the recesses are of the fluidized
type can
also have an improving effect in that the ring can also reduce escape of water
and
small particles in the lower recesses of this type of bowl.
As the bowl is frusto-conical, there tends to be a higher injection
pressure at the upper recesses than at the lower recesses. Thus in a
conventional
bowl the significant in diameter between the lowermost recess and the
uppermost
recess causes a significant increase in injection pressure at the uppermost
recess.
In the event that insufficient water is supplied, there is a tendency for
water and fine
particles to escape from the recesses at the base so as to feed the increase
in water
being injected in the upper recesses. Any such particles entering into the
jacket are
CA 02271958 1999-07-22
17
of course lost from collection. Conventionally the jacket includes ejection
openings
which allow any particulates entering the jacket to escape so that the jacket
does not
become clogged. Such particulates enter into the slurry with the escaping
material
and thus are lost.
In the present invention, therefore, the provision of the three recesses
at the base which are non-fluidized reduced the differential in pressure since
the
differential is now obtained by comparing the pressure at recess 51 with the
preset
pressure at recess 56. Yet further the addition of the restriction member 70
tends to
decrease the excess pressure at the recess 56 so that it is substantially
equal to the
excess pressure at the recess 54. The differential therefore in pressure is
obtained
by comparing the pressure at recess 51 with that of recess 53 and this
differential is
significantly reduced since the difference in diameter is significantly
reduced. This
bowl therefiore has a reduced tendency for fluid and fine particles to escape
from the
recess 51.
In a situation therefore where there is insufficient water supply
available to provide the required amount of fluidizing water for the bowl the
provision
of the reduced number of fluidizing recesses and the addition of the
restriction
member allows the bowl to operate without significantly reducing the
collection of the
concentrate.
Turning now to Figure 4 there is shown a further modified bowl
arrangement utilizing the principles described hereinbefore.
In this arrangement the bowl has a peripheral wall formed of three
sections including a first section 80, a second section 81 and a third section
82.
In the first section 80 the bowl is smooth, imperforate and frusto
conical at an angle to the axis which is common to the remainder of the bowl
wall
and is at a shallow angle generally less than 15°.
CA 02271958 1999-07-22
18
In the second section of the bowl there is provided a plurality of
shallow non-fluidized recesses 83. In the embodiment shown there are four such
recesses extending from an upper end 85 of the frusto-conical portion 80 and
terminating at an upper most land portion 86 at which the bowl portion 82
commences.
The bowl portion 82 comprises a plurality of fluidized recesses 87 and
in the embodiment shown there are two such recesses. Each of the recesses is
divided from the next by a land portion 86A identical to the land portion 86.
The land
portions 86A and 86 lie on a common cone which is at the same angle as the
frusto-
conical portion 80. The land portions are raised slightly inwardly of a cone
containing the frusto conical portion 80.
Each of the recesses 83 comprises a shoulder 88 lying in a radial
plane of the axis and intersecting with the land on the upper side of the
recess. A
second surface 89 of the recess lies in a cylindrical surface surrounding the
axis and
parallel to the axis. A third portion 90 of the recess is a frusto conical
surface which
is inclined inwardly from a lower edge of the surface 89 to intersect with the
land on
the lower side of the recess. Thus there is no shoulder corresponding to the
shoulder 88 adjacent the lower land.
Each land portion 86A has a series of o~nings 91 at angularly spac~i
positions around the land portion. The openings connect with duct portions 92
communicating from the opening to a second opening 93 on the outside surface
of
the bowl so that water from the receptacle 21 A can pass through the duct 92
and the
opening 91 to communicate additional fluidizing water into the materials as
they
pass over the wall of the bowl and as they pass from each recess to the next.
Thus
additional fluidizing water is added to the materials as they flow across the
bowl wall
to ensure that the materials do not dry on the wall and in the non fluidized
recesses.
CA 02271958 1999-07-22
19
Each non fluidized recess as defined by the shoulder 88 and the surfaces 89
and 90
is imperforate so that no water enters the recess through the bowl wall at
this
location within the recess. Each duct 92 includes two duct portions first of
which
connects with the outside opening 93 and the second of which connects with the
inside opening 91. The first duct portion is narrower than the second duct
portion so
as to control the amount of liquid which passes from the receptacle 21A into
the
duct. The second duct portion is wider or of greater diameter so as to reduce
the
velocity of the liquid flowing through the duct 92 while of course the flow
rate
remains unchanged and controlled by the first narrower duct portion. In this
way the
jetting effect of the liquid entering through the land portion is reduced so
as to avoid
impacting and disturbing the particulate materials as they flow over the land
portion.
The recesses in the bowl portion 82 are of the fluidized type. Each
recess is defined between the respective land portions 86 and includes side
walls 94
and 95 which converge to a base 96 of the recess. The recess is modified
relative
to the recesses previously described in that the recess includes a plurality
of annular
dbs or rings 97 which project inwardly from the base to an innermost edge 98
which
lies outside of an imaginary conical Fine containing the lands 86. Thus the
ribs or
rings 97 reduce the volume of the recess 87 between the side walls and
inwardly of
the base. Between each ring and between the rings and the sidewalk are
provided
fluid injection ducts 99 of the type previously described. The ducts are
inclined to
the radius of the bowl as previously described so as to tend to inject the
material
around the recess. The recesses 87 are therefore deeper than the recesses 83
and
provide a bed of generally fluidized material which thus acts more effectively
to trap
heavier materials and also to trap larger particles. In the event that heavier
materials and larger particles therefore roll over the shallow recesses 83,
these
particles are collected in the fluidized recesses and are therefore maintained
in the
CA 02271958 1999-07-22
bowl and prevent from escaping with the slurry. The lands 86 are not fluidized
and
contain no openings.
In an alternative embodiment (not shown), only alternate ones of the
lands 86A are fluidized so as to further reduce the quantity of additional
fluidizing
5 water. However the amount of fluidizing water is maintained sufficient so as
to
ensure that the materials are fluidized in a movement across the wall. The
number
of non fluidized recesses and the number of fluidized recesses can of course
vary
and may be increased in larger size bowls.
The reduction in volume of the fluidized recesses in conjunction with
10 the shallow depth and rich concentrate of the non fluidized recesses
ensures that
their coNective concentrate is of very high ratio and in some cases will allow
smelting
of the concentrate directly without further concentration.
Turning now to Figure 5 there is shown a further alternative
construction of bowl. This is modified relative to the construction of Figure
4 in that it
15 includes a first bowl portion 80A similar to the bowl portion 80 and the
second bowl
portion 81A similar to the bowl portion 81 but does not include a bowl portion
82 and
thus does not contain any fluidized recesses. Thus the bowl consists solely of
the
frusto-conical portion 80A and the recesses 83A of the portion 81 A.
The bowl portion 81A includes lands 86B of the same instruction as
20 the lands 86A. However the recesses are of a modified shape in that they
include a
shoulder 88A and a portion 90A but between those portions there is provided
two
further shoulders 88B and 88C and two inclined portions 89A and 89B thus
forming
a zig-zag shape with additional shoulders for engaging the materials as they
flow
over the bowl wall.
Alternative shapes of the non fluidized recess can be used. In another
example (not shown) the recesses are of the same shape as shown in Figure 2
with
CA 02271958 1999-07-22
21
the lands between the non fluidized recesses being fluidized with openings
identical
to the openings 91 of the embodiment of Figure 4. In each embodiment, the
shallow, non fluidized recesses defne a surface portion which is recessed from
the
adjacent lands so as to provide an area in which the particles can collect for
separation of the heavier particles from the lighter particles and slurry as
previously
described.
As shown in Figure 4, the recesses 83 are wholly imperforate from the
land 91 to the next land 91, that is, the shoulder 88 and the surfaces 89 and
90 are
wholly imperforate so that no fluidizing liquid enters the recess at all
through these
surfaces. Thus the whore of the fluidizing liquid is injected through the land
portions
91. The land portions lie on imaginary surfaces which are cylindrical or at a
slight
cone angle matching the cone angle of the bowl. It is also possible in an
alternative
arrangement (not shown) that the injection openings be provided on a surface
which
is at an angle inclined upwardly and outwardly relative to the land surface
and
immediately in advance of the main surfaces of the recess. In this way the
recess
itself is not fluidized but fluidizing liquid is added to the materials as
they pass over
the peripheral wall and particularly over the recesses.
