Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Background of the Invention
This invention relates generally to wet cyclone(i.e., hydrocyclone) separating methods, apparatus
and systems making use of heavy-medium or dense-medium
techniques. While the invention is applicable to a ~
to a variety of minerals, it is particularly valuable
for the cleaning of raw coal.
The so-c~alled heavy-medium or dense-medium
technique making use of hydrau1ic separating devices ~;
has been well-known in connection with the cleaning of
minerals, particularly coal (see article in the Journal
of the Institute of ~'uel, December 1945, Volume XIX, ' .
' .~o. 105, entitled "The Vse of Centrifugal Force for Clean-
ing Fine Coal in ~eavy L1quids and SUspenslons w1th
Special Reference~to the Cyclone~Washeri'). Br1efly as ~;
i app1ied to the use~of hy~drocyclones, à heavy-medium slurry
, is added to the sized mineral, w~ereby the desired lighter
mineral solids are~discharge~ through the vortex finder
of the hydrocyclone as~an overflow, and the heavier cen-
trifugally separated minera~l solids are discharged through
the apex orifice as underflow.~ The heavy-medium slurry
concentration is adjusted~so that lts specific gravity
is suitable for the separation o~ the desired mineral and
the waste sol1ds (e.g., refuse) which are being separated
from the raw mineral. In a complete system such as is
applicable to the cleaning of~raw coal, the heavy medium
lS recovered from the underflow and overflow materials for
~;~ re-use. The method used for separating the heavy-medium
~- solids varies depending upon its properties, and may,
- 30 for example, employ screening, flotation or magnetic
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separation when the solids respond to magnetic force.
Assuming that screening is used in such recovery opera-
tions, the particle size of the heavy-medium solids is sub-
stantially finer than the particle size of the sized
mineral. A publication by the United State5 Department of
Interior, Bureau of Mines, identified as RI 7673 Bureau
of Mines Report of Investigations 1972, "Performance Charac-
teristics of Coal-~ashing Equipment: Dense-Medium Cyclones",
describes methods and systems using hydrocyclones and
lQ magnetite to provide the dense~medium that is recovered
for re-use by magnetic separators. In general, it has been
found that use of such heavy-medium techniques can effect
realti~ely precise separations of heavier and lighter
materials, such as the cleaning of a desired mineral ;~
(e.g., coal) from the undesired refuse.
While the heavy-medium technique gives rela-
tively efficient separation, it is recognized that some
desired solids may not be recovered by use of cyclones
as described in the above Bureau of Mines Report, because
the cyclone separating operation is not sufficiently
precise. In large scale operations, such as required
for the cleaning of coal, small percentage losses are
of economic importance.
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Objects of the Invention and Summary
In general, it is an object of the present
invention to improve upon the efficiency of heavy-medium
techniques as applied to separating operations using
hydrocyclones.
Another object is to provide apparatus especi-
elly edapted to carrying out the method of the invent~On,
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the apparatus being characterized as a single cyclone unit of two stages~
the firs~ st.age having its conical portion and its. Qp0X opening disposed
within the head portion of the second chamber.
Another ohject of the invention is to provide a system making
use of the method and appara-tus, the system being particularly applicable
to the washing of coal, with recovery and re~use of the heavy-medium
en~ployed. ~ .
~ccording to one aspect of the present invention, there is ~
provided a method for remov mg undesired solid comyonents from desired ~ -
solid components of sized mineral,~ the method making use of a two-stage ~:
cyclone~ the first stage of the cyclone~having a head portion provided w:ith
a tangential inlet feed pipe and also-a centrally disposed vortex finder :~ `
for the discharge of a centrifugally separated ov0rflow and an apex opening
for discharge of centrifugally separated heavier materlaI, the second :~
- stage having a head portion connected to the apex op0ning of ~he first
-~ stage and having a taneentlal feed pipe and also~havm g an~apex opening,
th0 method comprising forming a feed containing the sized mineral together
~ with a heavy-medium slurry, the heavy-medlum slurry comprlslng finely
:~ dividad solid particles in water and having a specific gravity corresponding
approximately to the speclfic gravity of separation between the deslred
and the undesired solid components~of the sized mineral and havi.ng a
particle size less than that of the desired solid mineral components, supply- ~
ing the feed under pressure to the feed pipe of the first stage whereby .
lighter mineral solids:with some heavy-medium slurry are discharged through
~;: the vor~ex finder of the first stage as an overflowj and the heavier
centrifugally separated components and the balanc0 o~ the heavy-medium :
slurry are dischargsd as an underflow through the first stage apex opening, :
delivering the underflow from the first stage into the head portion of the
second cyclone stage, and separately delivering feed material to the feed ::
plpe of the second cyclone stage~ said last named feed mat0rial consisting
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substantially entirely of an additional quantity of said heavy-medium
slurry, centrifugal foroes in the second stage chamber serving to cause
light solid componen~s contained in the underflow from the first stage to
be separated from heavier solid components and returned to the first stage
through the apex opening of the flrst stage for discharge with the overflow
from the first stage, the heavier solid components centrifugally separated
from the ligh~ solid components in the second stage being discharged as an
underflow through tT~e apex opening of the second stage, together with
some of the heavy-medium solîds, and separating the desired solid
components of sized mineral out of the overflow from the first stage.
Additional objects and features of the invention will appear from
the following description in which the preferred embodiment has been set
forth in detail in conjlmction with the accompanying drawing.
Brief Description of the Drawing
Figure 1 is a side elevational view, partIy in section,
illustrating apparatus m corporating the present invention.
Figure 2 is a flow diagram illustrating the apparatus of Figure 1
incorporated in a system for the cleaning of si~ed coal.
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Figure 3 is a flow diagram illustxating the
apparatus of Figure 1 in a different system for the clean-
ing of sized coal.
Descri~tion of the Preferred Embodiment
S The apparatus shown in Figure 1 consists of
two cyclone stages 10 and 11 which are disposed on a
common central axis and form two separating chambers.
The body of the first cyclone stage has a head portion
12 in tangential communication with the inflow pipe 13.
The body portion 14 is conical and terminates with the
underflow apex opening 16. The second stage 11 likewise
has a head portion 17 which is in tangential communica-
tion with the inflow pipe 18. Its conical portion 19
likewise terminates with ~he apex opening 20. As is
` 15 apparent in Figure 1, the apex opening 16 and adjacent
~' conical portioD of the first stage are disposed withln
the head~portion 17 of the second stage. The first cyclone
,
stage has a vortex finder 22 disposed axially and which com-
municates wi~h the outflow pipe 23. In operations such
as the cleaning of coal, it is desirable to mount the
apparatus in an inclined position such as shown in Figure
1. The design and operation of the compound cyclone
are such tha~ it can be described as having a low Ep
characteristic (i.e., low error probability).
~5 The present method, making use of the above
described apparatus, is as follows. A feed containing
mineral solids together with heavy-medium slurry is
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introduced through pipe 13 into the separating chamber
of the first cyclone stage 10. The specific gravity of the
heavy-medium slurry corresponds approximately to the specific
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gravity of separation, and the particle si~e is sub- ;~
stantially finer than that of the coal solids (e.g.,
minus 325 mesh). Assuming proper flowrate of feed, swirl-
ing motion is imparted to the material within the cyclone
chamber wheraby centrifugal forces effect a separation
between heavier and lighter components. The lighter
material reports to the vortex finder 22 and discharges
through the overflow pipe 23, while the heavier centri~
fugally separated material is discharged through the apex
opening 16 into the separatlng chamber of the second stage
; 11. Additional heavy-medium slurry of the same specific gra-
vity is introduced into the head portion of the cyclone 11
through the inlet pipe 18, again with sufficient velocity
to effect swirling motion within the separating chamber
of the cyclone ll. Centrifugal forces acting upon the
material in the cyclone stage ll cause separation of
residual llghter solids (e.g., coal)from heavier sollds
~e.g., refuse) of the relatively concentrated material
~i received from the first stage. The lighter components
and part of the heavy-medium slurry are returned back
; through the apex opening 16 and report to the vortex
finder 22. The heavier solids separated in cyclone 11
are transported by the balance of the heavy-medium slurry
and are discharged through the apex opening 20.
The two-stage operation described above provides
relatively precise separation between lighter and heavier
solids, compared to separation which can be obtained in
a conven~ional single stage heavy-medium cyclone. This is ~ -
attributed in part to the mixing/dilution action which takes
place within the cyclone stage 11, which frees light solids
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trap~ed with the heavier solids discharging through
the apex opening 16 of the first stage~ This enables the
light solids to be displaced toward the axis of the cyclone
and to be carried bac]c into the first-stage section for
discharge in the overflow. The heavy fraction in the second
stage is thickened in the conical portion 19, thus pro-
viding a thickened underflow slurry. As is customary in the
operationofhydrocyclones used for heavy-medium separations,
the apex o~ening -0 of the second stage must be sized to
control the volume being discharged as underflow.
The flow ~diagram~of Figure 2 illustrates a
system making use of the ap~aratus and method described
above for the cleaning of coal. Raw coal is supplied
to the wetting step 26, where it is mixed with water,
and this material is then subjected to de-sliming 27 by
screening. The resultlng~material lS supplled to the two~
stage hydrocyclone apparatus together wit~l the heavy-
; medium slurry by a suitable pump 28, or by a head tank
capable of supplying the material at a suitable pressure.
As indicated by line 29, a heavy medium slurry is mixedwith the de-slimed coal. Pump 31 serves to introduce a
heavy-medium slurry o~ the same speciflc gravity into
the second stage 11. The underflow from the second
stage 11 is shown being subjected to separa~ing operation
32 whicn serves to effect separation between the heavy-
medium and refuse. The refuse may be subjected to
further washing 33 to effect some further recovery
of heavy-medium. This may be thickened in step 34.
The overflow from the first stage 10 contains
a substantial amount of dense-medium which is recovered
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for re-use. Thus it is shown being delivered to screening
and draining 36, and the coal solids to further washing
37. Hea~7-medium recovered in operation 36 is shown being
delivered to the heavy-medium slurry sump 38 which also
receives heavy-medium from the thickening step 34.
Pump 39 delivers the heavy-medium slurry from sum~ 38
to the density control means 40 from which the slurry, at
a controlled density, is supplied to pump 28 by way of
line 29 and to pump 31 which delivers the heavy-medium
slurry to the second stage 11.
It will be evident that the various treatment
steps illustrated in Figure 2 for separating the heavy-
medium from the overflow and underflow discharged from
the two-stage hydrocyclone may vary depending upon various
factors, such as~the type of mineral feed, the capacity
of the over-all system, and the properties of the heavy- -
medium employed.
Figure 3 shows a s~7stem ma~ing use of so-called
Zero cleaning heavy-medium technique, in which slimes
are not removed as in step 22 of Figure 2. Thus in
this system the feed slurry is pre~?ared by directly mix~
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ing the raw coal with the heavy~medium slurry. Also it
is assumed in Figure 3 that the feed slurry is being ;
supplied at a sufficient gravity head to avoid use of
a pump. The overflow from the combination cyclone
(10 and 11) is shown being delivered to the drain
and rinse screen 51 where heavy-medium slurry
(in this instance magnetite slurry) is removed and sent to
the heavS7-medium slurry sump 52. The cleaned coal recovered
from screen 51 is a coarse fraction as indicated. Slurry
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removed in rinsing contains magnetite which is removed ~`
in the magnetic separators 53 and routed to the sump 52.
As indicated, the. removal of magnetite by separa~ors 53
provides the fine clean coal fraction. The underflow from
cyclone stage 11 is routed to the drain and rinse screen
54. Heavy-medium thereby removed ~rom the und~rflow is
sent to the sump 52, and slurry from rlnsing is routed
t.o the magnetic separators and the heavy-medium thereby
recovered is sent~to the sump 52. The drain and rinse
screen operations 54 produce coarse refuse as indicated
;~ and separating operation 56 produces the indicated fine
refuse. As in Pigure 1 heavy medium-slurry i9 delivered
from sump 52 by pump 39 to the gravity control means 40,
and from thence it is delivered to the two stages 10
and 11 of the combination cycle. ~
An example~of the invention is as follows:
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~ Example 1.
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`The feed material is assumed to be 100 tons of
. raw, sized coal (e.~., Pocahontas No. 3 bed coal),
the pieces of which range in siz~ from 3/4 inch to 28
mesh. The physical characteristics of this material
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and ~he results obtained by processing according t~ the
present method are shown in the following table.
S.G. Fraction Wt. % Rec'y 1st Prod. 1st Ref. 2d Prod.
- or tons ~Tons) ~Tons) (Tons)
1.30 F 18.0~98717.766 0.234 0.231
1.35 38.6 .98738.09~30.5Q2 0.495
1.40 18.1 .94917.1770.923 0.876
1.~5 5.1 .3871.9743.126 1.210
1.50 1.9 .113.2151.685 0~190
1.60 1.~ .037.0591.541 0.091
1.70 .9 .006.Q050.895 0.005
1.80 .6' .000.0000.600 0.000
1.80S +15.2 .000~.000+15.20Q 0.000
L ~ s 75.294- 24.706 3.098
Raw Coal
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In the calculation above, "lst Prod"
shows the recovery o~ clean coal to product as would
be achieved by the first stage of the LoW Ep Cyclone,
this being the same recovery that would be anticipated
5. from a conventional heavy-medium cyclone. "2nd Prod"
shows the additional recovery attributable to re~
dilution and displacement of coal (light mineral) from the
first refuse product as achieved in the 2nd stage of
the compound cyclone. The calculation is based on
100 tons of raw coal in the cyclone feed, and the
weight recovery produced by the first stage separation
may be 75.294 tons, and as a result of further treatment
afforded by the second stage separationl an additional
recovery of 3.098 tons for a total recovery of 78.392
tons for the complete method can be obtained. This
; represents an increased recovery of 4.1~ over that
;~ of a conventional single-stage hydrocyclone.
In preparing the slurry for feeding to the
cyclone, approximately 400 tons of magnetite slurry may be
added to 100 tons of raw coal after the coal has been de- !1
slimed for removal of solids finer than 28 mesh. The magne- ~`
tite slurry may have a specific gravity of 1.34 and a particle
size of from 85 to 99% minus 325 mesh. Approximately 100 tons of
magnetite slurry of the same specific gravity may be supplied
to the second-stage cyclone. The diameters of the first
and second stage chambers may be 26" and 15" respectively,
and the included angle of the conical sectionc about 20. ~ -
The fol~o~ingtable serves to illustrate the amount
of ash removed from the first stage separation, and by the
~econdstage separation according to the present method.
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Clean CoalT
Ash96 _1st Prod. Tons ~sh 2d~rod. Ton~ Ash
(Tons) (Tons)
1.30 F2.017.766 0.355 0.231 0.005
1.35 4.838.098 1.829 0~495 0.024
1.40 9.517.177 1.632 0.~76 0.083
1.45 13.21.97~ 0.261 1.210 0.160
1.50 1~.9 .~15 0.041 0.190 0.036
1.60 25.1 .059 0.015 0.091 0.023
1.70 36.3 .005 0.002 0.005 0.002
1.~0 ~5.8 .000 0.000 0.000 0.000 `-
1.80 s86.9 ~ .000 + 0.000 + OOOOO + 0.000
Totals 75.2g4 4.135 3.098 0.333
As illustrated in the above table, for the
1.30 specific gravity fraction/ c~ne-stage operation is~
98.7~6 efficient, while the two-stage operation according
to the present method is 99.983~6 efficient. As indicated,
simllar increases in efficiency can be obtained for each
of the gravity fractions.
The fourth collLmn of the above table designated
"Tons Ash" has reference to the ash in the corresponding
1st Product. Likewise the sixth column desiynated "Tons
Ash" has reference to the ash in the corresponding 2nd Prrduct.
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