Note: Descriptions are shown in the official language in which they were submitted.
S;636
BACKC.`ROUND OF TflE IMVENTION
Field of the Invention-
.... ... ..... __ :
The present invention broadly pertains to the
separation of mineral ~ubstances. More particularly, the present
inven~ion pertains ~o the e~fective recovery of resins from
resin-bearing coal through the application of centrifugal forcer
Background of the Invention:
Efficient and effective recovery or separation of one
solid mineral substance from another has long presented
problems. ~his is particularly true in the recovery of resins
from resin-bearing coal. Certain coal deposits, such as those of
the Wasatch Plateau and Book Cliffs fields of Utah, contain a
substantial ~uantity o~ natural fossil resins which, in a
pu~ified condition, has utility in adhesives, coatings, printing
inks, synthetic rubber compositions, traffic marking compounds,
water proofing agents and the like. However, the resin, as it
occurs in nature, is intimately admixed with the coal and the
problem of separatin~ it from the coal economically and on a
commercial scale has presented serious difficulties to ~he art.
In its natural state, the resin occurs in small lumps,
lenticular masses and in fracture planes of various thicknesses
within the coal seamsO Numerous investigators have demonstrated
~he fossil resins are considerably more friable than the coal
with which they are admixed. When the coal is removed in the
course of customary mining procedures, the majority Qf the
recoverable resin is released by the fracture o~ the coal along
the resin planes and by the tumbling action of the coal handling
~2~ ~
63~
machinery which dislodges resinous particles adhering to the coal
particles. A large portion of the recoverable resin is thereby
liberated from the coal in the course of ordinary handling so
that additional crushing of mine--run coal is not normally
required to enhance resin recovery~ Certain investigators,
however, have cited the necessity for crushing coal to specified
screen sizes for optimal resin recovery when employing certain
recovery techniques. The added crushing step detracts from the
economy of such techniques.
It is known in the art that r~sins may be separated
from coal by means of froth flotation, air-lift flotation,
float/sink separations employing inorganic salt solutions, and
the like. None of these procedures, however, is capable of
producing a high-purity resin concentrateO As well~ most of the
prior art processes ~or separating resin from coal are
economically infeasible because they fail to satisfactorily
resolve three basic problems, namely 1) since these resins are
more dense than water, they cannot be effectively separate~ in
~uiescent water due to the lower specific gravity of water, 2) a
high-purity resin concentrate cannot be efectively separated
rom the coal in agitated or upward flowing classi~ying systems,
however slight the agitation, due to the contamination of the
resin concentrate by appreciable quantities of coal fines and
slimes~ and 33 float/sink separatiQns usin~ aqueous solutions of
inorsanic salts are impractical because of the large volumes of
salt solutions to be handled~ the product and co-product
contamination, the salt losses incurred, and the not
inconsiderable environmental pollution problems associated with
the waste solution disposal~
In U.S. Patent No. lp773,9979 issued to Green, there is
disclosed the separation of resin by a froth flotation process
using one of several flotation agents to help separate the resins
from the coal~ While variations on this method are ln commercial
application today~ the resin concentrate product so obtained is
relatively impure, sel~om, if ever9 exceeding 50 weight percent
resin, and with up to 40~ by wei~ht or more sorbed moisture. The
re~in concentrate obtained by such flotation procedure is so
lmpure that it must be further refined as by solvent extraction,
and the drying and ~olvent refining of such an impure resin
concentrate is both tedious and economically di~advantageous.
In U.S~ Patent No. 2,378,152~ issued to Nagelvoort, it
is disclosed that wetted coal can be ~eparated from unwetted
resins using either upwardly flowing suspensions or air
agitation. However, the resin concentrate of the disclosed
invention is also relatively impure, cont~ining only about 60
resin, and re~uires still further refining.
U.S. Patent No~ 2,409,216, issued to Lee, discloses an
improvement on the reining of resin using a basic froth
10tation process by heating the froth flotation concentrate to
t}le order of 250 to 300C in order to melt the concentrate,
following which a solvent refilling process may be employed.
U.S. Patent No. 2~506,300~ i~sued to ~lepetko et alr
~eeks to circumvent the unsatisfactory per~ormance of froth
flotation and other prior art processes ~or preparing fo~sil
resin concentrates by employing a continuous ~olven~ leaching and
extractiorl processO llowever, becau~e of the large quan~ities of
coal fine~ which must be handled and the neces~ity for
desolventizirlg and drying the coal firles and slimes~ ~his process
3g~ -'
is economically di~advantageous and has never achieved successful
commercial implementation.
ln UOS. Patent No. 2,506~301, issued ~o ~lepetko et al~
ther is disclosed a flotation process not employing flotation
~gents or ~etting agen~s and u~ing air-lifk flotation in place oE
mechanical agitation. Thi~ process tend~ to minimize ~rushin~
and at~rition of the friable resin par~icles presen~ in
mechani~ally agita~ed flotation proce~ses. ~he process
demonstrates an improved recovery of larger sized resin
particles, i.e., 28 x 100 mesh, over that in conventional
mechanical systems, but still provides an impure flotation
product which admit~edly requires still fur~her refining, e.g.S
by solvent refining.
In u.S~ Patent Mo. 2,591,830t issued to Klepetko et al,
again it is sought to circumvent the unsatisfactory performance
o froth flotation and prior art processes and the economic
infeasibility of direct solvent refining processes by preparing
resin concentrates using a basic ~edimentation technique combined
with a frothing agent which assis~s the collection of resin
part.icles at ~he surface of ~he ~edimen~ation ~ank~ While the
method is simpler than the froth flotation process, ~he quality
c: f resin concentration is not significantly improvedO The
concentrate may contain a somewhat higher percentage of non~resin
contaminants than a concentrate~ e.g~, produced in a ~pecially
built flotation plant, but it i~ stated that he concentrate is
readily amena~le to reining by 601vent extraction~
In U~5. Patent No. 3~637,639t issued to Z~nni21 et a~,
still another process is described for the con~inuou~ solvent
extraction of re~in from coal. This proces~ employs ~pecial
;3~
extraction and recovery equipment and accomplishes the primary
segregation of coal fines from solutions of the resin dissolved
in suitable organic solvents by means of liquid cyclonic separa-
tors in a classical two phase (solid coal/resin solution) separ-
ation. However, the process is laborious, equipment intensive
and relatively quite expensive to operate.
Accordingly, it is an object of the present invention
to provide an improved method for separating or xecovering one
solid mineral substance from another solid mineral substance,
and in one aspect, an improved method ~or recovering a xesin
concentrate from resin-bearing coal.
In this form, the present invention provides a method
for recovering a high-purity resin concentrate from resin-
bearing coal, which resin concentrate may be suitable for use
without any further refining~
Yet another object o.f the present invention is to pro-
vid~ a most eE~icient and economically feasible method for sepa-
rating resins from resin-bearing coal.
These and other objects, as well as the scope, nature
~ and utilization of the invention, will be apparent to those
~ki:lled in the art from the following descr.iption, the accom-
panying drawings, and the appended claims.
--6--
3~;
SIJMMARY OF THE INVENTION
In accordance with the foregoing objectives, there is
provided a process for separating an admixture of
solid mineral substances, which process comprises mixing the
admixture of solid mineral substances with a non-solvent liquid
in order to form a slurry, and then subjecting the slurry to
cen~rif~gal force in the presence of a gas. By "non-solvent
liquid" is meant a liquid which is not a solvent for either
mineral substance. For example, in the separation of resins fro~
coal material, the non-solvent liquid with which the slurry is
formed does not act as a solvent for either the resins or coal
material. Thereby the separation which occurs upon the
application of the centrifugal force is not the classical two
phase separation of solid mineral/mineral solution, but is a
separation between the solid mineral substances, e.g., solid
coal/solid resin particles in a four phase system (solid coal,
solid resin, water and air~.
In a preferred embodiment of the present invention,
resins are effectively separated from resin-containing coal
~ In~t~ial by mixing the resin-containlng coal material with a non
solvent liquid, preferably waterr to form a slurry. The
preferred solids content of the slurry is from about 1 weight
percent to about 50 weight percent solids, more preferablv from
about 2 weight percent to about 20 weight percent solids, and
most preferably from about 3 to about 15 weight percent~ The
slurry is then passed to a separation zone wherein its resin
particle content is separated from the coal materials by
centrifugal force, preferably that obtained via cyclonic
separators such as classifying liquid cyclones. Such separation
is possible since in the presence of a ~as such as air the resin
particles collect at the water/air interface and are removed to
the overflow orifi~e of the cyclone. If classifying cyclones are
utilized in th~ separation process, they are preferably operated
at a pressure of from about 4 ~o about 60 p.s.i. and more
preerably at a pressure from about 5 to about 40 p.s.i.
The separated resin parti.cles can then be dewatered in
a ~uitable dewatering zone. This zone may comprise screens~
~ieves, and the like. It is preferred hat this dewatering zone
comprises sieves or screens having openings between from about 35
and about 150 microns in size (between about 400 to about 100
mesh).
If decired~ the separated coal materials can similarly
be dewatered, with both the dewatered resin concentrate and the
dewatered coal materials being removed from the process.
It has been ~ound that resin concentrates containing in
excess o 75 percent by weight, typically in excess of 95 weight
percent and not atypically in excess of 99.5 weight percent, can
be prepared with the process o the pre~sent invention without
resorting to expensive and time consuming solvent extraction and
refining techniques which are required with prior art processes.
BRIEF DESCRIPTION OF THE DRAWIN~:
. . . _.
Figure 1 schematically depicts an apparatus set-up in
one embodiment of the present invention wherein a single
centrifugal separating zone is employed.
~8--
Figure 2 schematically depicts a set-up in one
embodiment of ~he present invention wherein two centrifugal
separating zones are employed.
Figure 3 schematically depicts a set-up in accordance
with one embodiment of the present invention wherein a first
~entrifugal separating zone feeds directly to a second
centrifugal separating zone.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The basic problem with all prior art processes for the
physical separation and recovery of, for example, resins from
coal, is that it has not been possible heretofore to prepare a
quality mineral concentrater e.g., con~aining greater than about
65% resin, and in particular one of sufficient purity so as to be
usable and salable without subsequent refining. This i.t;
especially true in th~ recovery of resin~ from resin bearing
coal, wherein chemical (iOe., solvent1 refining of resinous
coals, with or without~prior resin concentration, has always
hereto:Eore been required and has been so expensive as to result
in a product of limited economic import.
It has now been discovered, however, that the
disadvantages of all ~ystems previously proposed for separating
mineral substances such as resins from coal can be overcome if
the, e~g., resins are ~eparated from the coal by use of a large
multiple of the earth's gravitational forceJ such as is present
in a centrifugal field, in a non-solvent liquid medium, e~g. ~ an
aqueous mediun), in which a su.itable gas such as air is induced or
admixed. By the proper employment of cen~rifugal force on such
a four phase system (solid coal, solid resinl water and air), a
very high purity resin concentrate con-taining in excess of 99~5
weight percent resin is readily pxepared without the use of
additives, flotation agents or chemicals.
More specifically, in the separation of resins f.rom
coal material, it has been discovered that ~he resin particles
may be separated with amazing effectiveness from the coal with
which they are admixed by treating a slurry of resin--bearing
coal in a non-solvent liquid, such as water, in a centrifugal
zone employing a large multiple of the earth's gravitational
force such as that obtained in a liquid cyclonic separator,
more commonly referred to as a cyclone, liquid cyclone, hydrau-
lic cyclone or classifying cyclone. Such separation is ef~
fected concomi.tantly in the presence of a gas such as air,
either as in the air core of a classifying cyclone or as air
induced in-to the inlet along with the slurry feed.
This discovery and the invention resultin~ therefrom
.i.s especially surprising slnce it preferably employs cyclon.ic
separators, typ.ically classi:Eying cyclones~ to separate two
sol.icl mineral substances both o:E which possess specific gravi
tie~ greater than the liquid media in which they are suspended.
T~u~ the separation so effected is obtained, not by the appar-
ent density or gravity of the minerals, but by means of frac-
tionating mineral particles with unwetted, hydrophobic surfaces
from a second mineral with wetted, hydrophilic surfaces with
which it is admixed~
The extraordinary efEectiveness in preparing
by physical means resin concentrates of such high
purity as has been heretofore achieved only by ~olvent
-10-
~ 95636
or chemical refining appears to result from the unexpected and
unpredictable effect of air, or some other suitable gas, within
the core of the cyclone which adheres to the hydrophobic,
unwetted surface of the resin particles, thus overcoming the
normal tendency for the resin particles to be separated and
rejected along with the coal particles from the underflow orifice
(apex) of the cyclone into the unaerflow stream of the
separator. This occurs irrespective of the fact that the resin
p;~rticles possess a specific gravity greater than that of the
water rnedium.
The effect of the gas within the core of the cyclone ~o
counteract the gravitational field within the cycl~ne is
significant to this embodiment of the inventionA Using a cyclone
whose diameter is two inches and operating at a pressure of 30
pounds per square inch, resinous particles as large as two mm in
c3iame~tr?r (ca. 10 mesh) can be easily separated from coal fines as
small as about 37 microns (min~ls 400 mesh). Cyclone theory would
indicate that resin particles (whose specific gr-~-ity ranges from
1.04 to about 1.10~ larger than about 40 to 60 rnicrons should be
~a r~ecte~ out th~.? underflow orifice (apex) of s~lch a classifying
c~clon~ ar)d into the underflow stream.
Tl~e surprising effect of a gas such as air in the
prc?s~nce of a large centrifugal field on the hydrophobic or
unwetted resin surface is demonstrated by the effect of wetting
agents on the recovery efficiency of the process of the present
invention. For example, unwetted resin particles two mm or more
in diameter are easily separated from the coal with which they
are admixed using the process of the present invention. However9
when the resin particles are well ~etted, as with an aqueous
3~
solution containing 20 to 100 ppm tannic acid, it becomes very
difficult to separate resin particles larger than about 100 to
150 microns in diameter (170 to 100 mesh). while the relative
purity of the resin concentrate prepared using certain forms of
the process of the invention in the presence of an adequate con-
centration of wetting agent may not diminish significantly be-
cause the more dense coal particles continue to be rejected out
the apex of the cyclone into the under:Elow stream, the efficien-
cy of the resin recovery diminishes dramatically due to the lar-
ger resin particles being rejected out the apex of the cyclonealong with the coal particles into the underflow stream.
If the process of the present invention is attempted
without utilizing air or some other suitable gas in the core of
the cyclone, as by closing the apex of the cyclone with a rub-
ber flap valve so as to prevent the induction of air up into
the core of the cyclone, the cyclone suEfers a "syphon effect"
such that coal particles sma].ler than about 100 to 300 micxons
(100 to 50 mesh) are separated along with the resin particles
out the vortex finder and into the overflow stream of the cy~
20 clone, and a ve.ry impure resin concentrate results
Any means for inducing centrifugal force to the ex-
tent .necessary to separate the resin particles from the coal
particles can be suitably employed. Generally, however, a clas-
sifying cyclone whose diameter is less than about sixteen
inches and whose included angle is less than about 45 degrees,
and preferably less than 20 degrees, may be suitably employed,
depending, of course, upon the operating pressure, which can
vary, e.g., from about 4 to abou~ 120 p.s.i.
-12-
In one embodiment of the present invention, smaller
cyclones, e.g., haYing a diame~er o less ban about 6 inches,
and operating at the higher pressures have been found most
advantageou~ in rejecting the smaller coal particles out the apex
and thu~ resulting in recovery oiE a purer resin concentrate with
fewer coal slimes in the cyclone over:Elow (vortex) stream. In
practice, it has beerl discovered that li~uid cyclones smaller
than six inches in diameter and opera~ g at pressures grea~er
than about six to eight pounds per square inch may readily yield
a resin concentrate satisfactory for commercial use and sale.
The particular magnitude of centri~ugal force required
in a cyclonic ~eparator to effect ~he desired separation of resin
and coal particles is generally difficult to be quantified other
than in t4rms of cyclone diameter as mentioned ab~ve. However,
the force in the conical section of ~ typical cyclone near the
apex is requently quoted as being from several hundred to
several thvusand times ~he force of the earth' 5 gravitational
~ield, depending UpOIl the operating pressure of the cyclone.
I'c iB well lcnown that the separation efficiency of
~la~siylng c~clone~ decreases with particle sizeO It is an
embodiment o the present inventiont however~ that a cyclone of
~uficient size, wi~h appropriate orifice ratios and under
~uficien'c operatirlg parame~cers, be empls~yed to reject coal
particles smaller than about 50 micron~ ~nd preferabl57 smaller
than 25 microns. In a pre~E~rred embodiment of the present
invention, cyelones being from about two to s~ur inches in
diameter and being operaîed at about 20 to 30 pounds per sql~are
inch are employed wil:hout the use of any reagent~ 7 c:hemicals or
flotation aids or agents.
In recent years a second type of cyclonic separator,
commonly referred to as a gravimetric cyclone, water-only
cyclone, or hydrocyclone, has been employed for mineral
dressing and coal preparation in which a truncated cyclone body
usually with a large included angle near the apex (greater than
90 degrees) is employed to separate minerals according to their
specific gravity Such hydrocyclones typically employ a vortex
finder of adjustable length positioned relatively deeply within
the body of the hydrocyclone to skim off or separate out the
less dense particles from the bed of minerals as the bed moves
across the conical portion of the hydrocyclone toward the apex.
When employed in the process of the present invention, the
typical hydrocyclone is less effective than a classifying
cyclone of the same diameter because the long vortex finder
accepts sufficient quantities of lower gravity coal particles
to yield a less than pure resin concentrate in the overflow of
th~ cyclone. If, as is evident to those skilled in the art,
the vortex finder of a hydrocyclone is shortened to the point
that it effectively rejects the coal particles, such
hy~roc~cLone then tend~s to operate in the manner of a
c.La~ifylng cyclone. The ut.ilization o:E a hydrocyclone whose
~ort~x 1nder has been shortened sufficiently to act in the
manner o~ a classifying cyclone and yield a high-purity resin
concentrate is specifically an embodiment of the present
invention.
Using certain forms of the present invention allows
one to prepare resin concentrates of suc.h high purity that they
may be used directly for tackifying and resinous applications
without the need for additional, expensive refining, such as
solvent refining as has heretofore been the case. Depending
upon the concentration of slurry fed to the cyclonic separator,
-14-
the size and operating parameters of the cyclonic separator and
the method of dewatering the resin concentrate after separa-
tion, the process of the present invention can be utilized to
prepare resin concentrates of purity far in excess of that here-
tofore attainable by prior art processes i.eO, from 55 to 60
weight percent resin on a dry basis, and typically in excess of
95 weight percent resin and not atypically in excess of 99.5
weight percent resin. Such concentrates are significantly more
pure in resin content than products by any other concentration
process with which the art is familiar.
The present invention also allows for the separation
of resin without the costly use of reagents, chemicals or flota-
tion aids or agents, the cost of which can greatly detract from
the economic attractiveness of a method.
Another significant advantage of some embodiments of
the present invention is the ability to process coal and to re-
cover resin particles without concern as to particle size.
Since the fractured resin particles found in most mine run coal
are individually small, (almost all being less than 18 mesh),
it may be advantageous in some instances to prescreen the coal
and to recover and process coal fines smaller than about 1 to 6
millimeters in size (i.e., from about 28 mesh t.o about 1/4
inch) by the process of this invention. Such pre screening re-
duces the quantity of coal to be processed and also increases
the concentration of the resin particles in the more easily
handled coal fines~
The present invention may be more fully understood by
reference to -the accompanying drawings illustrating various
embodiments of the same.
Figure 1 illustrates one embodiment of this invention
wherein resin bearing coal, preferably screened to exclude
particles larger than about 1 to 6 mm in diameter, and which,
if desired, can have been subjected -to an initial separation,
is introduced through line 11 into mixing zone 13 where it is
mixed, by any of numerous means including pumps, mechanically
agitated reactors, eductox-equlpped hoppers, and the like, with
a non-solvent liquid, in this case water, introduced through
line 12. The resulting mixed slurry, preferably containing
from about 1 percent to 50 percent solids by weight, more
preferably from about 2 to 20 weight percent, and most
preferably from about 3 to about 15 weight percent solids. is
removed through line 14 to separating zone 15. This zone 15
can contain one or more cyclonic separators~ i.e., classifying
cyclones, preferably operatlng at a pressure of between about 4
and about 60 p.s.i. Each cyclone is of a size suitable to
separate the resin and coal without undue contamination of coal
fines in the resin-containing cyclone overflow. Separators
operating at relatively low pressure, typical].y between about
~0 eight and thirt.y p.s.i, are usually most advantageous in
m.i.nl.mizing cyclone wear without impairi.ng t.he effectiveness of
~he resin/coal separation.
The separator overflow is removed through line 16 to
~e.~3~n ~ew~tering zone 17 which can comprise screens, sieves,
~ilters, centrifuges or the like, wherein the resins are
dewatered. The dewatered resin concentrate is then removed
through line 18 for suhsequent drying and use. The water
stream 19 may be recycled through line 12 to mixing zone 13 if
desired.
The separator underflow, containing virtually all. the
coal particles, is removed from zone 15 through line 20 -to an
-16-
'.~
3~
adjacent coal dewatering zone which can also comprise screens 9
sieves,centrifuges, filters t or the like. In that zone the
coal is dewatered and the dewatered coal is removed for
subsequent use or disposalO The water stream from the coal
dewatering together with that from the de~atered resin, line
19~ may be recycled through line 12 to mixing zone 13.
In order to prevent a build up of undesirable coal
fines and slimes in the water circuit, which, among other
things, may increase the apparent specific gravity or viscosity
of the water media in separating zone 15 to an undesirably high
value, it may be desirable to insert in lines 19 and/or 12 a
system to facilitate bleeding the slimes and undesirable coal
fines to a settling pond or other disposal means, as will be
obvious to those skilled in the art of handling wash waters
from coal preparation and washing plants.
In order to improve the purity of the resin
concentrate prior to dewatering in zone 17, it may be desirable
-to insert a second separating zone, comprising one or more
cyclonic separators, such as classifying cyclones, between
zones 15 and 17 as illustrated in a second embocliment of the
present invention shown in Figtlre 2. In Figure 2 the resin
containing overflow from the first separation zone 15 is
removed throu~h li.ne 16 to an intermediate sump 21 from which
i~ ma~ be removed, as by pumping, through line 22 to the second
separating zone 23. This zone 23 can contain one or more
cyclonic separators operating at a pressure of between 4 and 60
p~s.i. If re~uired, water may be introduced into the
intermediate sump 21 by means of line 25, but generally little
or no additional water is required by the introduction
of a second separating zone 23 into the process of
-17-
3~
the present invention. Preferably, the cyclonic separator~ in
such secondary separating ~on 23 are smaller in diameter than
the cyclones employed in zone 15 in order to effectively reject
the finer coal particles. The çyclone overflow i~ removed
through line 24 to resin dewatering zone 17, which comprises
screens, sieves, filters, centrifuges and the like, and wherein
~he resins are dewatered. The under10w stream 26 from the
second separating zone 23, containiny additional ine coal
particles, may be combined wikh the underflow stream in line 20
from the first separating zone 15 for subsequent coal dewatering
and disposal.
The use of a second ~eparatinq zone cannot only improve
the purity of the resin concentrate~ but may also reduce the
volume of liquid fed to resin dewatering zone 17.
Figure 3 illustrates another embodimen~ of the presen~
invention in which a secondary separation zone 31 is employed i.n
the process. The second separating æone 31 is in~erted between
first separating zone 32 and resin dewatering zone 33, but
without the use of an intermediate sump zone as in zone 21 of
Figure 2~ In the depicted embodiment of Figure 3, resin bearing
coal, preferably screened to exclude particles larger than about
1 to 6 mm in di~meterd i~ introduced through line 34 into mixing
~one 35 where it is mixed~ by any of numerous ~eans including
pumps, mechanically agitated reactors~ eductor equipped hoppersJ
and the like, with water ~eing introduced through line 360 The
resulting mixed slurry, containing. from about 1 percent to 50
percent solids by weight, more preferably from 2 percent to 20
percent by weight, and most preferably from about 3 to 15 weight
percent is removed throu~h line 37 to the first ~eparating zone
~ -18
3~
3Z. This zone 32 contains one or more cyclonic separators,
(i>e., classifying cyclone) operating at a pressure of between
about 8 to 120 p.s.i., preferably between about 10 and 80 p.s.i.,
and typically about 60 p.s.i.
The embodimen shown in Figure 3 in which two or more
cyclonic separators are connected in series without an
intermediate sump and pump requires that the pressure in the line
37 at the inlet to the first separating zone 32 be sufficient so
that the pressure in the overflow stream 38 from the first
~eparating zone is adequate to operate also the second separating
zone 31 and effect a good resin/coal separation. For the
purposes of the illustration of this embodiment, it shall be
assumed that the classifying cyclones comprising the first
separating zone 32 and those comprising the second separating
zone 31 are of the same size and configuration such that the
pressure drop between the inlet and overflow orifice (vortex) of
each separating zone is approximately equal. However, it can be
readily seen that the size and conf iguration o the cyclones
e~ployed in zones 32 and 31 re~pectively should be chosen to
optlmize the process and to prepare a resin concentrate of
optimal purity irrespective of the pressure drop across each
separating zone.
The overflow from the first separation zone 32 is
removed through line 38, at a pressure between abou~ 4 and 60
p.s.i.0 preferably between about 5 and 40 p.s,i~, typically abou~
30 p.s.i., and introduced directly into a second separating zone
31. This zone contains one or more cyclonic separators, iOe.,
classifying cyclones. The re~in containing overflow from zone 31
is removed through line 39, typically at or near atmospheric
-19-
`- $~ 3~
pressure, to resin dewatering zone 33 comprisin~ screens, sieves,
filters~ centrifuges or ~he like, wherein the resins are
dewatered and rem~ved through line 40. The water stream 41
together with that from the dewatered coal may be re~ycled
through line ~6 to mixing zone 35.
The embodiment of the invention shown in Figure 3 in
which two cyclonic separtors are connected in series without the
use of an intermediate sump is particularly advantageous with
respect to the force acting to reject the coal fines in the first
separating zone 32. The pressure drop between the inlet and the
underflow oriice ~apex) of zone 32 is approximately double that
of zone 15 in the embodiment shown in Figure 1, iOe., between
about 8 and 120 p.s. i., preferably between about 10 and 80
p.s.i., and typically about 60 p.s.i. As compared with the
embodiment shown in Figure 1, this pressure drop increases,
typically doubles, the force acting in the conical section of the
first separating zone and greatly enhances the rejection of finer
coal particles out the apex of the first separati~g zone 32 and
into the underflow stream 42.
~ t the same time the pressure drop between the inlet
and overflow orifice (vortex) of the first separating xone 32
remains approximately the same as in the embodiment of Figure 1
without a second separating zone, i~e., between about 4 and 60
p.s.i., preferably between about 5 and 40 p.s.i. ~ typically about
30 p. s O i. This provides for gs:)od resin separation and recovery
in zone 32 as well as providing sufficient pressure, i.e.,
between about 4 and 60 poS~io ~ preferably between about 5 and 40
p~s-i., and typically about 30 p-S-io ~ to operate the second
separating zone 31 in a conventional manner.
-20~
3~
It is a special featur~ of certain forms of the pro-
cess of the present invention that the cyclonic separation of
resin Erom coal is enhanced when the cyclone underflow orifice
(apex) is relatively large and unrestricted. In this event the
apex discharges in a spray configuration and air is concomitant-
ly induced to flow upward through the underflow orifice exiting
through the overflow ori~ice (vortex). The air, so induced~
aids in the air-lift of the resin par~icles to the air/water
interface in the conical portion of the cyclonic separator, and
thence into the overflow stream. Depending upon cyclone design
and configuration, it may be desirable, and is contemplated in
one embodiment of this invention, to bleed air, or some other
suitable gas which iB relati~ely inert in the existing environ-
ment, into the inlet side or into the apex of the cyclone in
order to assist resin particles, particularly the larger ones,
to move to the air/water interface, and thence to enter the
overflow stream. This aforedescribed a.ir admixing decreases
the apparent density or effective density of the resin parti-
cles and adds to separation efficiency.
~() Conversely, a string- or rope-discharge o:E coal parti~
cle~ from the underf].ow orifice of a cyclonic sepa.rator serves
to inhi.bit the preparation of a high pur.ity resin concentrate
in paet because suf~icient air cannot be induced into the core
of the cyclonic separatorO Under such conditionsp and especial-
ly in the case of a heavy rope discharge, a significant portion
of the large resin particles would be rejected out the under-
flow orifice (apex) of the cyclone along with the coal parti-
cles .
-21-
A further advantage of ce.rtain forms of the present
invention is tha~ the mixing zone in which the resin-bearing
coal is slurried in water, and also any coal dewatering zones
may be located at points far removed fxom the separation zones
15, 23, 31 and/or 32. This is true since the coal slurry is
readily pumpable and may be easily moved by pipeline. Trans-
:Eerring the coal in slurry form is much easier, less e~pensive,
and far less cumbersome than utilizing conveyors and other
.Yolids handling equipment to move dry coal solids. Thus an
~0 ~dditional advantage of the present invention is that the
process permits the resin to be easily separated from the coal
at a location distant from the coal source and does not depend
upon resin recovery at a coal washing or preparation plant as
in tradit.ional flotation processing.
In a preferred embodiment o the presen~ inventiont
~he resin dewa~ering zo.ne compxises a s.ieve bend, a horizontal
or inclined screen or sieve, or the like. These may be either
stat:ic, vibrating or rotary, such that the slurry of resin COII--
c~ntrate introduced to the :resin dewatering æone is dewatered
~ by flowing the slu.rry of resin concentrate over the sieve or
sc~en of such mesh size or slot open:ing that the undesirable
~Ln~ coal~ and slimes are allowed to pass through the sieve or
screen, thus enhancing the purity of the resin concentrate so
produced.
When the resin slurry is dewatered over sieves or
screens which are inclined, it is preferred that they be inclined
at an angle between 5 and 75 degrees to the horizontal, and most
preferably between about 10 and 55 degrees to the horizontal~ At
such an incline, the very fine resin particles generally tend to
r.ide up and over the sieve or screen openings and are thus
-22-
~ ~ 9~G;36;
ag~lomera~ed into the mass of ~he resins on the ~urface. The
quantitativP recovery of the re~in concentrate is thus enhanced
without affecting the purity of said concentrate~
The following examples are given as specific
illustrations of the invention. It should be understood,
however, that the specific de~ails et forth in the examples are
merely illustrative and in nowise limitative. All parts and
percentages in the examples and the remainder of the
~peci~ication are by weight unless otherwise specified~
EXAMPLE I
Utilizing the embodiment shown in Figure 1, 2904 pounds
of resin bearing coal fines containing 10.4 weight percent resin
are mixed with 20.0 gallons of water to yield a slurry suspension
of 15~0 weight percent solids. The slurry is pumped at 30 pos~i~
through a two inch classifying cyclone whose underflow orifice
(apex) has been enlarged to permit a spray di~charge whose
included angle i5 ahou~ 125 d~grees. The cyclone overflow is
recovered and dewatered throu~h a 270 mesh sieve. The resulting
resin concentrate is dried and analyzed, and found to contain
98.3 weight percent resin. The yield i5 84 percent of theory~
EX~MPLE II
Utilizing a variation of the embodimerlt shown in Figure
2, 43.8 pounds of resin-bearing coal cont2ining 6.3 weight
percent resin are mixed with 100,0 gallons of water to yield a
slurry suspension of 5~0 weight percent. The slurry is pumped,
at 30 p~s~io ~ through a two-inch classifying cyclone whose
underflow orifice gives a spray discharge whose included angle is
--~3-
3~
about 100 degrees. The cyclone overflow i5 reco~ered and
dewatered ~hrough a 200 mesh sieveO The resulting resin
concentrate is dried and analyzed, and found to contain 99.5
weight percent resin.
While the present invention has been described in
detail in terms of separating resins rom resin-bearing coal, the
present invention can find applicability in the separation of any
suitable mixture of solid mineral substances, e.g., an admixture
o mineral particles where one particle is largely unwettable by
a non-solvent liquid and where the other mineral particle is
wettable by the same non-solvent liquid.
Thus, although the invention has been described with
regard to pre~erred embodiments, it is to be understood that
variations and modifications may be resorted to as will be
apparent to those skilled in the art. Such variations and
modifications are to be considered within the preview and the
scope of the claims appended hereto.
-24-
