CA1137030A - Compound hydrocyclone and method operable on coal slurries - Google Patents

Abstract

Abstract of the Disclosure A method, apparatus and system making use of the "heavy-medium" technique to effect efficient separation between desired and undesired solid components of a sized mineral (e.g., raw coal). It is characterized by use of two centrifugal separating operations performed in a single compound cyclonic device. The first stage of the device receives a feed comprising the sized mineral together with heavy-medium slurry. The second stage of the device receives heavier separated underflow solids from the first stage and a separately introduced feed of heavy-medium slurry. The overflow from the first stage of the device contains the lighter mineral. In a complete method and system, heavy-medium supplied to the separating operation is recovered for re-use.

Description

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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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~37~3() 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 ~L~l3~7~3!3~

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 .~
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 ~L3703~

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 g _ .

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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:
, ~ 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 , 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 : - 10 -37~3~

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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Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for removing undesired solid components 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 with a tangential inlet feed pipe and also a centrally disposed vortex finder for the dis-charge of a centrifugally separated overflow and an apex opening for discharge of centrifugally separated heavier material, the second stage having a head portion connected to the apex open ing of the first stage and having a tangential feed pipe and also having an apex opening, the method comprising forming a feed containing the sized mineral together with a heavy-medium slurry, the heavy-medium slurry comprising finely divided solid particles in water and having a specific gravity corresponding approximately to the specific gravity of separation between the desired and the undesired solid components of the sized mineral and having a particle size less than that of the desired solid mineral components, supplying 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 vortex finder of the first stage as an overflow, and the heavier cen-trifugally separated components and the balance of the heavy-medium slurry are discharged 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 pipe of the second cyclone stage, said last named feed material consisting substantially entirely of an additional quantity of said heavy-medium slurry, centrifugal forces in the second stage chamber serving to cause light solid components contained in the under-flow from the first stage to be separated from heavier solid components and returned to the first stage through the apex opening of the first stage for discharge with the overflow from the first stage, the heavier solid components centrifugally separated from the light solid components in the second stage being discharged as an underflow through the apex opening of the second stage, together with some of the heavy-medium solids, and separating the desired solid components of sized mineral out of the overflow from the first stage.

2. A method as in claim 1 in which heavy-medium solid particles removed from material discharged in the underflow from the second stage and as discharged in the overflow from the first stage, are reused in the method.

3. A method as in claim 1 in which the sized mineral is sized coal, the undesired components being refuse which is separated from the coal.

4. A method as in claim 1 in which the heavy-medium is magnetite slurry.