Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SOLIDS SEPARATOR
The invention relates to a separator for particulate solids, for classifying
particles
according to size. The separator may be used for minerals such as coal or
metallic ores,
waste material such as hardcore, ash or soil, process feedstocks, foodstuffs
such as in the
form of granules, and other materials whether wet or dry.
The present invention seeks to provide a simple and efficient means of
separating
particulate materials and to dispense with a sizing bed, with consequent
reduction in costs
and liability to failure.
Conventional sizing apparatus, for example as disclosed in GB 4.4.8838 or
GB l087921. includes screens composed of interlocking arrays of eccentric
rotating
discs. Such apparatus contains many moving parts and is complex, expensive and
liable
to breakage, particularly when using coarse minerals.
According to the present invention a particle separator includes:
a rotor comprising a plurality of small discs mounted for coaxial rotation, a
1 S multiplicity of large discs having a greater radial dimension than the
small discs and
being mounted for rotation coaxially with the small discs, the small discs
being located
between the large discs via a spacer disc;
a feed adapted to provide a flow of particulate material impinging said rotor;
and
a collector having means (such as a doctor with creneis or slots to
accommodate
the large discs, the merlons or edge of the doctor being arranged to co-
operate with edges
of the small discs) to collect material having a dimension allowing passage
between the
large discs but preventing passage between the small discs.
The edge of the doctor may abut the edges of the relevant discs or may be
spaced
from them, centrifugal force serving to propel a stream material outwardly
from the
centre of the rotor towards the collector. The collector may be positioned to
catch
correctly sized material taking into account the action of gravity on the
outwardly moving
stream.
A single rotor is preferred, although a succession of two or more apparatus in
accordance with the invention may be used to make successive separations from
a flow
of material. The rotor may be perturbed e.g. vibrated radially.
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The feed of unseparated material is preferably directed towards the rotor,
more
preferably towards the axis thereof, that is choke or partial choke feed. A
tangential
flow is not preferred for efficient separation. A free flow of unseparated
material, that
is under gravity, is preferred.
The large and small discs may be disposed alternately upon the rotor.
Alternatively the discs may be arranged in any convenient sequence to suit the
size
analysis of the particulate material, for example each large disc may be
separated by two
or more small discs. The rotor may have an axle upon which the discs are
mounted.
Alternatively an axle may carry a drum upon which the discs are mounted, the
drum
having a diameter substantially larger than that of an axle, for example up to
I m. The
large discs may themselves have different diameters according to their axial
location on
the rotor, preferably being largest at the middle of the rotor axis and
progressively
smaller towards the ends.
More than two sizes of discs may be employed.
Intermediate discs having a dimension between that of the large and small
discs
may be disposed between the latter upon the rotor. A plurality of collectors
may have
doctors arranged to collect material from the edges of each of the
intermediate discs.
A cleansing collector may be provided to clean the rotor during each
revolution.
The tines of the cleansing collector preferably pass between a11 of the discs
to remove any
particles lodged between them. Preferably, the circumferential locations of
axially
successive tines differ. The cleansing collector may be located at any
convenient position
between the first collector and feed during rotation of the rotor.
The discs are preferably circular. In a preferred embodiment of the invention,
the large discs are provided with a segment removed to form a peripheral
notch. This
prevents oversize pieces of material from becoming stationary upon the rotor
by engaging
such pieces and impelling them forwards. Alternatively, those discs, or all
the discs,
may have a non-circular periphery, e.g. polygonal or scalloped-edged.
In a first embodiment of the invention all of the discs are arranged to rotate
at the
same speed and may be secured on a common axis.
In a second preferred embodiment of the invention selected discs or disc
segments
may rotate at a different speed or may be stationary. This has the advantage
of reducing
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adhesion of material between the rotors. To prevent particles from being
thrown out
of the separator centrifugally or by bouncing outwardly when landing on a
rotor disc, the
separator according to the invention may have restraint means which, over part
of the
periphery, inhibit particles from leaving the separator radially of the discs.
Separators according to the invention can be made small enough to be conveyed
' more easily to temporary sites than is the case with conventional shaking-
screen
separators .
The invention will now be described by way of example with reference to the
accompanying drawings, in which:
Figure 1 is a schematic elevation of apparatus in accordance with the
invention,
Figure 2 shows a rotor in plan view for the apparatus in Figure 1,
Figure 3 shows a variant of the Figure 2 rotor in plan view,
Figure 4 shows an alternative rotor in plan view, with associated feed and
collector arrangements,
Figures 5 and 6 show alternative patterns of disc which may be used in the
rotors,
Figure 7 is a schematic end elevation in cross-section of apparatus using a
rotor
similar (but not identical) to that of Figure 4,
Figure 8 is a plan view and Figure 9 an end elevation of a further alternative
rotor. and
Figure 10 shows an alternative embodiment of the invention having an
adjustable
collector.
The apparatus shown in Figures 1 and 2 comprises a conveyor 8 arranged to
deposit particulate material, such as coal, after a drop of 1 metre upon a
spreader or
collector plate 1, at a rate of 50 tonnelhour for a typical mined coal feed.
The spreader
1 is arranged to distribute material evenly across the surface of a 1-m-radius
curved feed
chute 2. which is arranged, as best seen in Figure 10, by reason of its lower
(trailing)
edge conforming fairly closely to a rotor 3 and pointing towards the axis
thereof, to give
a "choke" or "partial choke" feed 2a to the rotor 3. Returning to Figure 1,
the spreader
plate 1 is provided with an end pivot and adjustable portion is to control the
flow to the
rotor. The spreader 1 and chute 2 may co-operate to emulate a hopper chute (or
a hopper
chute may indeed be provided). A curtain of heavy chains or a resiliently
sprung board
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(not shown] may hang from the lower end of the spreader plate 1/la, to allow
oversized
particles to travel clockwise out of the feed area but to encourage normal
particles to
enter the rotor. The chute 2 need not be curved. It may be mounted at 50 to 70
to the
horizontal and offset from being strictly radial to the rotor, i.e. its lower
edge terminates
S at the height of the axis of the rotor or not much above it. The rotor, as
shown in Figure
2, comprises an axle 6 carrying a multiplicity of circular discs. Alternate
discs 3c have
a radius of 200 mm. some 50 mm larger than smaller discs 3b disposed between
them.
In other versions, consecutive larger discs 3c have two, three or four smaller
discs 3b
between them. The discs are separated axially by spacers 3a some 10 mm thick
in the
axial direction and of radius around 90 mm. The spacers 3a may be mounted
coaxially
or eccentrically.
Figure 3 shows an alternative rotor. Here, consecutive larger discs 3c have
three
smaller discs 3b between them. The larger discs 3c are themselves graduated in
size,
from 500 mm at each end of the rotor 3 to 1 m at the centre. This arrangement
counterbalances the tendency of any typical conveyor 8 to deliver more
material along
the centre line of the belt than at the edges, which could overload the "Fig
2" rotor at the
centre notwithstanding spare capacity at its ends. The "Fig 3" rotor, by
virtue of the
graduated discs 3c, will tend to redistribute excess material delivered at the
centre,
towards the ends.
The feed 2 is adjustable to give a wide range of feed angles at its lower edge
into
the rotor, from 30-75 to the horizontal, preferably (as stated) SO-70, to suit
the feed
material size analysis, moisture content and specification (properties such as
hardness,
density and shape).
In use of the apparatus, material having a dimension less than the separation
between the small and large rotors can pass between them and fall into a chute
9. Large
particles of material which cannot pass between the large discs 3c are
deflected from the
periphery of the rotor into a second chute 10. Material having a dimension
such that it
may pass between the large discs 3c but not between the small discs 3b is
collected by
a slotted collector 4 which approaches to just short of the edges of the small
discs and
wherein the slots are to accommodate the large discs. This intermediate sized
material
may be collected in the chute 10 with the larger material or may have its own
collection
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chute (not shown).
A cleanser has tines 5 arranged to pass between all of the discs up to just
clearing
the surface of the spacers 3a. The tines may be located downstream of the
collector 4
at any position upstream of the chute 2. In this example, alternate tines 5
are at the
"6 o'clock" position and the others at the "9 o'clock" position. Staggering
their
circumferential positions in this way nunirnises the risk of a seizure; when
an oversized
particle jammed between adjacent discs 3 hits a tine 5, the discs can flex to
release the
particle.
A heavy upright plate pivoted at its top edge forms a barrier 7 which serves
to
prevent material entering the apparatus from overshooting into the collector
10.
A peripheral notch, or serrated circular arc, or scalloping, cut from the edge
of
some or each of the large discs 3a as shown in Figure 5 serves to prevent
large pieces
of material becoming seated upon the rotor. The impulse given to a large piece
by the
notch or other shaping of the edge of the rotor causes the piece to be
impelled through
the barrier 7 into the collector 10. Thus, Figure 5 illustrates a disc wherein
two
peripheral segments are removed or the disc edges curve or are serrated to
eject large
particles from the rotor. The angular extent 2 of the notch may be determined
by the size
and shape of material. For example pieces of slate may require use of
comparatively
large notches or serrations. It is preferred that all of the material to be
separated can
pass between the largest discs, only exceptionally large pieces requiring use
of the
notches. The elliptical disc shown in the lower part of the figure may be used
alternatively to achieve the same function. A further alternative disc shape
is regular
polygonal (e.g. 24 sides) or scalloped; this gives extra agitation to
particles before they
drop into an inter-disc slot, thus) especially in the case of damp "sticky"
feed, assisting
the accuracy of classification. The degree of agitation-enhancement is
directly related
to the radial height of the scallops. The greater the agitation, especially
around the '' 12
o'clock" position, the more the separation action is improved; particularly,
finer
particles are less likely to ride on coarse particles and report erroneously
to the "coarse''
discharge. Scalloped discs also help prevent wet feedstock from forming a
static
immobile bed 2a. Preferably, and especially preferably where hopper chute feed
is
employed at 1 / 1 a/2 or chains are present, a11 the discs 3 are scalloped,
with the largest
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discs (3c, 3d or 3e as the case may be) having larger, deeper, more
exaggerated
scalloping than the smaller discs. Figure 6 shows an elliptical disc which
could be used)
with long axes either aligned or offset.
Referring to Figures 1, 7 and 10, material (under "free flow") enters the
rotor
assembly as a "choke" or "partial choke" feed (i. e, this could be at 30A5
degrees firom
the horizontal for example depending on disc aperture, material analysis and
moisture).
A change of direction is required as material is "conveyed" round the disc
periphery.
At this point acceleration of a11 panicles occurs in the new direction of
rotation causing:-
(i) Primary separation of particles upon impingement with the rotor and
dependent
on the degree of free flow feed conditions and "open area" presented;
(ii) Secondary separation as material changes direction and is accelerated/re-
adjusted
by the smaller disc tip (circumference) and larger disc sides;
(iii) Tertiary separation of previously adhered fine particles to
larger/coarse material.
This is caused through contacr/rubbing between "oversize" particles and the
disc
sides/edges upon acceleration and material re-adjustment on the "peripheral
conveyor".
All undersized material from (i), (ii) or (iii) is caused to be released
between the small
discs into the chute 9. Options of larger material are dependent on the
position of the
collector 4. In such cases the peripheral velocity of the discs could be
greater than the
flow of material onto the rotor (in that direction).
Figure 4 illustrates an alternative rotor having discs 3c, 3d with radii
intermediate
between those of the small discs 3b and large discs 3e. Material having a
dimension
greater than the separation between the outer discs 3e is excluded from the
rotor.
Material having a smaller dimension can enter the rotor.
Particles smaller than the separation between discs 3d and 3e but greater than
that
between discs 3c and 3d may be removed by a collector abutting the edge of the
discs 3c.
Smaller material which is able to pass between the plates 3c and 3d can
similarly be
collected by tines of a collector abutting the edges of the discs 3b. Fine
material can pass
unimpeded through the rotor. To exploit this separation, a collector 4, or as
shown in
Figures 4 and 7, a multiplicity of circumferentially spaced collectors 4 (4w,
4x, 4y, 4z),
may be employed. Collector 4w, for the coarsest fraction, acts as a doctor and
stands
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just clear of the largest discs 3e. Collector 4x, for die next-to-coarsest
fraction, likewise
acts as a doctor as it projects radially inwardly as far as the next largest
discs 3d, with
crenels in the form of slots or cut-outs to allow the discs 3e to rotate.
Collector 4y, for
the next-finer fraction, projects event further radiaIly inwardly, namely up
to the smaller
discs 3c, and has cut-outs to clear the discs 3e and 3d. Finally, collector
4z, for the
' next-to-finest fraction) has interdigitations projecting radially inwardly
to the smallest
discs 3b, with slots or cut-outs to clear the discs 3c, 3d and 3e. The very
finest fraction
of particles passes into the gaps between the discs 3b and the adjacent discs
and can drop
out of the separator via the rear side of the collector 4z. (The separator
shown in Figure
7 omits discs 3e and the corresponding collector 4w.)
The variety of sizes of disc 3 helps the preseparation of the particles as
they fail
into the separator and reduces the likelihood of ftne particles reporting
falsely to the
coarse fraction.
The height of the drop from the conveyor 8 to the feed chute 2 (e.g. '/z m for
dry
feed, 1 m for damp feed), the abrasive action of the curtain of chains (not
shown) and
the abrasive action of the straps 12 all further help to reduce false
reporting, by detaching
small particles which are riding on larger ones . The separation is further
improved
by vibrating the axle 6, preferably vertically. at a high amplitude with low
frequency (e. g. by cam action) if organised mechanically, or at a small
amplitude with
high frequency if organised electrically) thus e.g. 10 mm/S0 Hz or 1 mm/S00
Hz. This
will afford a circumferentiai jigging action.
Figure 8 shows a plan view and Figure 9 an elevation of an alternative
arrangement for separating fine material from larger pieces. The larger and
smaller discs
20 and 21 are formed as a unitary construction so as to present a series of
grooves into
which fine matter may pass. Coarse material may be removed from the surface of
the
rotor by a collector 22 (the disc 20121 being enclosed by larger carrying
discs 30).
Figure 10 illustrates a modification of the invention having a collector
movable
about a pivot 14 to adjust the radius of the ends of the tines between a first
position
adjacent the edge of the rotor and a second position adjacent smaller discs
3b. This
allows the size of material collected to be adjusted as required. The speed of
the rotor
may also be adjusted for example between 75 and 300 rpm to further control the
degree
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of separation, a slower speed increasing the proportion of particles
classified as "fme" ,
all other things (such as feedstock size distribution, feed rate, moisture
content and chute
angles/positions) being equal. Such adjustability is not readily achieved with
previously
known separation apparatus. In addition the collector may be moved radially
around the
rotor. This allows the position of the ends of the tines to be adjusted to
compensate for
the effect of gravity on the stream of material propelled from the rotor.
In alternative embodiments of the invention the spacing between some or a11 of
the discs may be adjustable to regulate the sizes of particles separated.
Figures 7 and 10 show that the feed chute 2 need not be especially curved and
can
terminate either around the "10" or "11 o'clock" positions or even as low as
the "9
o'clock" position, provided a bed of finer particles has already formed, in
other words
there is choke feed, shown as 2a, in which circumstances material to be
classified can be
conveyed uphill on such bed by the clockwise rotating rotor 3, even if wet (in
which case
scalloped discs are more reliable). Figure 7 also shows that the discharge
ducts) 4 may
have its (their) upper (leading) edge level with, or lower than, the "3
o'clock" position,
the discharge ducts - when there are more than one - preferably having their
upper edges
at the same height.
The cleanser tines 5 may be located at the "8 o'clock" position (to be clear
of the
chute 2), or at 5 or 6 o'clock, or, as shown, alternately, and serve not only
to remove
jammed particles but also to scrape the spacers 3a clean of adherent fine
particles. An
advantage of locating alternate tines at different positions is that when a
tine engages a
jammed particle, the discs can flex relatively unhindered to release the
particle.
Figure 7 shows a variation of the pivoted barrier 7 of Figure 1. A heavy plate
7a as wide as the rotor 3 hangs from a pivot 11 above and parallel to the
rotor 3, before
top dead centre. Hanging from the lower edge of the plate 7a is a heavy
curtain 12 of
leather, rubber or other slightly flexible and not too slippery material. The
curtain 12
is deeply fringed, and may be considered as a set of laterally abutting
straps. More
effectively still, the curtain 12 may consist of numerous closely spaced heavy
chains
welded to the bottom of the plate 7a, as shown schematically. The curtain
rests draped
generally on the " 12 to 3 0' clock" quadrant of the rotor 3 , and acts to
restrain particles
which bounce outwardly and would otherwise report falsely to the "coarse"
collector 4x.
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Indeed the curtain, by its weight, even tends to push particles radially
inwardly, further
reducing the incidence of undersized particles reporting to the coarser
fractions. This
action is enhanced in the case of scalloped discs 3d, which both drive
particles clockwise
against the friction of the curtain 12 and cause the curtain to ripple and
bounce, giving
S a more dynamic impact of the curtain on the particles. These are all
beneficial results
of the effect of the curtain in lengthening the residence time of particles in
the separator,
thus lengthening their opportunity to undergo correct classification, without
reducing the
throughput of the separator. Friction between the particles and the curtain
also helps to
dislodge fine particles which are adhering to coarse particles, further
improving the
quality of the classification.
The curtain 12 may be alternative, or additional, to the chains hanging from I
/ 1 a
of Figure 1. The breadth of the chain links or straps and the spacing of the
chains are
optimised for the material. The chain links or straps may be small enough to
go between
discs 3c (Fig. 7) or larger, such that they ride on top of those discs, as
drawn.
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