Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SPECIFIC~TION
This invention is in the field of classification
methods and apparatus wherein dispersed particles are
permitted to settle into a relatively wide basin to form
contiguous areas of particles having different sizes,
specific gravities, size distributions, compositions, or
other characteristic differences and such particles are
selectively removed by application of a reduced pressure
to particular areas of the basin floor in sequence.
Generally, classifiers for separating solid particles
into fractions from a dispersion of such solids in liquid
fall into three basic categories (1) non-mechanical,
(2) mechanical, and (3) hydraulic. The first two classes
are similar and differ only in the means for removing the
coarse material or sand as it is called. In hydraulic
settlers, the character of the separation is different
because of the hindered settling induced by the presence
of the water.
All wet classifiers depend on the difference in
settling rate between coarse and fine or heavy and light
particles confined within the settling enclosure. Rates
can be controlled to some extent by miId agitation, pro-
viding for hindered settling, and the use of power inputs
as in centrifuging types of settlers.
The most common types of non-mechanical classifiers
are the cone and liquid cyclone types. In the typical
cone classifier, the feed is directed to the center of a
cone-shaped vessel and the sand is removed from the apex
of the cone. A suitable overflow system is provided for
removing the overflow product.
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Liquid cyclones usually consist of a top cylindrical
section and a lower conical section terminating in an apex
opening. The unit operates under pressure induced by a
static hydraulic head or by means of a pump forcing feed
into the cylindrical portion tangentially, thus producing
centrifuging action and vortexing. The cover has a down-
wardly extending pipe to cut the vortex and remove the
overflow product. Coarse solids travel down the sides of
the steeply sided cone section and are removed in a par-
tially dewatered form at the apex.
One of the more common mechanical classifiers is the
drag classifier consisting of a single endless belt or
chain suspension with cross flights running in an inclined
trough. The sand is removed at one end of the conveyor
run, and the overflow product at the other.
Rake and spiral classifiers have also been used ex-
tensively. As evident from their names, they involve the
use of mechanical devices which are installed in sloping
bottom tanks. The feed is introduced intermediate the
ends of the rake or spiral, with the sand being removed at
the upper end and the overflow product being removed from-
the opposite end.
Separation of fine material from suspension is some-
times carried out with bowl classifiers. Generally, this
consists of a shallow bowl with a revolving plow which is
superimposed over a rake or screw dewatering section: The
feed enters i~t the center of the bowl and the fine solids
overflow at the periphery. Coarse solids collected on the
bowl bottom are raked to the center for discharge into the
dewatering compartment.
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Where large flow volumes are encountered, the bowl
disiltor is often used. In this type of classifier, rota-
ting blades are provided in the bowl which plow outward
and discharge settled coarse material at the periphery
where it drops into a drainage compartment. This type of
classifier has been extensively used for the recovery and
drainage of very fine material overflowing coarser washing
units in glass sand, concrete sand, coal, and limestone
processing plants.
Another type of mechanical classifier is the hydro-
separator which is a thickener-type machine which receives
more flow than can be clarified in the area provided. The
overflow contains fine solids and the greater the feed rate
per unit of area, the coarser the solids in the overflow.
This type of clarifier is frequently used for primary
dewatering of phosphate rock and silica sand products
following wet screening.
A solid bowl centrifuge, another type of mechanical
classifier, uses power instead of gravity to develop high
centrifugal forces. The machine consists of two rotating
elements, the outer being asOlid conically-shaped bowl and
the inner comprising a helical screw conveyor revolving at
a speed slightly lower than that of the bowl. The raw
feed slurry is delivered through a stationary feed pipe to
the conveyor where by means of centrifugal force it is
transferred to the revolving bowl. A circumferential
classifying pool is formed and contained at the larger
diameter of the cone shell. Oversized material is dis-
charged at ports located closer to the axis of rotation
than the ports for the overflow. Centrifugal force de-
posits the oversized particles against the bowl wall from
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which they are conveyed by the helix. The overflow frac-
j~ tions flow around the helix to the liquid discharge ports.
< The size of separation is controlled by the feed rate and
- the degree of centrifugal force.
Countercurrent classifiers consist of an inclined,
slowly rotating cylindrical drum with continuous spiral
flights attached to the interior of the shell forming
helical troughs. The direction of rotation is such that
the material in the troughs is impelled toward the higher
end. The lower end of the shell is closed except for a
central overflow opening. Attached to the upper end is
a sand-dewatering elevator which rotates with the shell.
Wash water introduced at the upper end drains from the
lifting flights above the normal water level and progres-
ses countercurrent to the sand toward the overflow.
There are several types of hydraulic classifiers
which have been extensively used. The "Jet Sizer" is a
multi-compartment device having a series of pockets
arranged in series for flow through the device with
parallel pockets to take care of the high tonnage frac-
tions in a range of sizes. Each compartment is served
with low pressure hydraulic water. Hydraulic classifica-
tion generally insures the highest separating efficiency
' obtainable by wet classification means. The amount of
water is controlled so that in each succeeding compartment
the coarsest particles are maintained in a hindered
settling condition and the finer fractions pass along for
similar treatment.
; While these types of machines have been extensively
used in various applications, they are quite elaborate
mechanically and require substantial initial cost and
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upkeep. Since many involve rotating members of closely
fitting parts, maintenance is also a substantial expense.
The present invention involves a method of classi~
fying which makes use of the thickening device described
and claimed in Werner U.S. Patent No. 3,672,512, issued
June 27, 1972. Basically, the method of the present inven-
tion involves injecting a liquid dispersion containing
solid particles of different settling characteristics later-
ally into a settling basin with a sufficient velocity to
; 10 cause particles of differing settling characteristics to
settle in adjoining lateral zones of the basin. A reduced
pressure is applied separately and in sequence to particles
settled in each of the various zones to withdraw the same
separately from the basin, and a supernatant liquid effluent
is withdrawn from another portion of the basin. The process
of the present invention is particularly applicable to the
separation of impurities from a coal fraction, and the
recovery of usable coal from an influent which was hereto-
fore considered to be a waste material.
The attached sheets of drawings illustrate systems
which can be used in accordance with the present invention.
Figure 1 is a view partly in elevation and partly in
cross section illustrating one system for carrying out the
: method of the present invention;
Figure 2 is a rather schematic plan view of a control
system which can be used in conjunction with the apparatus
shown in Figure l; and
Figure 3 is a rather schematic representation of an-
other system which can be used for the purposes of the
present invention.
In Figure 1, reference numeral 10 indicates generally
a settling basin provided with a feed inlet pipe 11 having
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a plurality of orifices 12 which feed a suspension of
solid particles in water into the basin 10. A pair of
floating baffles 13 and a rigidly supported baffle 14 are
used to maintain the flow distribution through the basin
10. The baffles are shown for illustration only as it
will be understood that the use of such baffles is option-
al and that they can take different forms. For example,
the baffles may have apertures therein which permit flow
through the baffles rather than under them. In this type
of arrangement, the entire face of the baffle covers the
entire cross section of the basin and all the liquid flow-
ing through the length of the basin must pass through the
apertures of the baffle. With such an arrangement, a
better flow distribution is maintained throughout the en-
tire cross-sectional flow area.
The dispersion of solid particles in the aqueous
medium is injected into the basin through the feed pipe
11 with sufficient velocity so that the particles more or
less separate out into two or more fractions in settling
to the floor of the basin 10. In the form of the inven-
tion illustrated in the drawings,, three fractions are
definable, the fractions having different settling charac-
teristics due to differences in specific gravity, or
particle size or particle shape, or particle size distri-
bution or other physical differences which give rise to
differences in settling properties. The fraction nearest
the inlet end accumulates over a distance identified at A
in Figure 1 whichj for example, comprises a relatively
heavy material. In the case of a coal mine waste, this
might include refuse, pyrites, sand, and the like. The
intermediate or middling fraction is collected along an
area identified at B and includes the desirable coal
t
fraction to be recovered. A very lightweight fraction
identified at letter C contains very finely divided,
lightweight material such as clays. As indicated in
Figure 1, there may be some overlap between the areas A
through C but in general such commingling between the
fractions is not harmful.
The various fractions are selectively removed using
the type of apparatus shown and described in the afore-
mentioned U.S. Patent No. 3,672,512. Specifically, there
are provided three banks of pipes 15, 16 and 17 extending
substantiaîly across the width of the basin 10. At spaced
intervals along these pipes there are suction nozzles 15a,
16a and 17a, respectively, facing the floor of the basin
10. The suction nozzles in the pipes 15 are controlled by
means of valves 18, those in the pipes 16 are controlled
by valves 19, while those in the pipes 17 are controlled
by valves 20. The valves 18 through 20 can be mechanically
operated, electrically operated, or hydraulically operated.
As best seen in Figure 2, the valves in each bank are
under control of timers 21, 22 and 23, respectively. The
timers also energize a control 24 which, in turn, actuates
and deactuates a series of motors 25, 26 and 27 which, in
turn, drive underflow pumps 28, 29 and 30, respectively.
It will be understood that all of the valves, for example,
valves 18 in bank 15 can be energized simultaneously or
they can be energized in sequence in a given bank to pick
up the particulate matter lying on the floor of ~he basin
10 through the suction valves 15a, for example.
In the case of a coal mine residue, the fraction de-
livered by the pump 30 can be sent to a vacuum filter or
to a centrifuge. The desired intermediate fraction pumped
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through the pump 29 is collected in a collect~r 31. The
very light fraction pumped by the pump 28 can be delivered
to a suitable filter or a dewatering cone. The superna-
tant effluent in the settling basin 10 is withdrawn
through an effluent conduit 32.
Referring to Figure 3, there is shown a settling
basin 40 having a feed inlet pipe 41 feeding a suspension
of particles into the basin 40. A pair of floating baffles
42 and a stationary baffle 43 maintain a suitable flow
distribution in the basin 40.
Extending along ~he floor of the basin 40 is a series
of pipes 44 through 55, respectively, each pipe being
provided with a series of suction nozzles 44a through 55a,
respectively, facing the floor of the settling basin 40.
The actuation of said suction nozzles is under the control
of valves 44b through 55b, respectively. The valves 44b
through 55b may be operated in any suitable fashion indi-
vidually from a controller 56 which delivers (control
signals to the individual) valves through a control line
57.
A single underflow pump 58 discharges slurries of
various consistencies from the settling basin 40. The
discharge of the pump 58 is directed through a monitoring
device 59 which senses specific gravity of the slurry,
specific gravity of the suspended solids, particle size,
particle size distribution, or composition of the suspen-
ded solids, depending on what the basis for classification
is to be. The discharge through the monitoring device is
selectively passed ~hrough one of a plurality of discharge
valves 60 to 62, depending on which of the valves is
rendered open by the controller 56 which actuates the -
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valves through a control line 63.
In operation, as the monitoring device 59 checks the
slurry being delivered by the pump 58, it sends a signal
- - via a control line 64 to the controller 56. Assuming
that the monitoring device is checking the specific
gravity of the slurry, the signal will cause the control-
ler 56 to selectively energize selected ones of the valves
44b to 55b. For example, if the product is to be separ-
ated into three fractions of varying specific gravity of
slurry, controller 56 will open the valves closest to the
inlet feed end of the basin and will simultaneously open
discharge valve 62 so that the heaviest slurries are dis-
charged through that valve. Now, when the slurry specific
gravity drops below a predetermined value, that condition
is signalled to the controller 56 by monitoring device 59
and the controller 56 responds by closing some or all of
the valves in the basin that were previously open and
opening others in the area of the basin floor where less
dense slurries are known to exist. At the same time, con-
troller 56 closes discharge valve 62 and opens discharge
valve 61 to direct the middling fraction of a different
area for recovery.
When the specific gravity of the discharged slurry
drops even further and is below another predetermined
- value, the monitoring device 59 relays this information to
controller 56, operating still others of the valves in the
basin 40, closing discharge valve 61 and opening discharge
valve 60 to deliver this lightest fraction to still another
point of recovery or disposal.
From the foregoing it will be understood that the
present invention provides a method of classifying solid
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particles carried in a liquid dispersion in a discrete
fraction by causing the particles of different settling
characteristics to settle in adjoining lateral zones of
the basin whereupon a reduced pressure is applied separ-
ately and in sequence to the particles settled in each of
the vacuum zones to withdraw the same separately from
the basin.
It should be evident that various modifications can
be made to the described embodiments. For example, the
respective valves 18 in the bank 15 can be operated in
unison or they can be operated sequentially. As a rule,
however, the timers 21 through 23 will be operated in
sequence so that each fraction is individually removed
from the settling basin before the next fraction is
picked up.
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