Note: Descriptions are shown in the official language in which they were submitted.
3525 (A9 - 22, 63g)
3 5 '13 (A9 2 ~, 6 3 ~ )
APPARPTUS Al~D METHOD FOR FLOTATI ON
SEPARATION UTILI ZING A SPRAY NOZ Zl,E
The present invention relates generally to
a method and apparatus for flotation separatlon of the
components of a sluxry and more partlcularly pertains
to an improved method and apparatus for beneficiating
co~l by flotation separation of a froth utilizing a
spray nozzle such that ground coal particles may be
separated from impurities associated therewith such
as ash and sulfur.
Coal is an extremely valuable natural resource
in the United States,as well as the remainder of the
world,because of its relative abundance. It has been
estimated that the United States alone has more energy
available in the form of coal than in the combined natural
resources of petroleum, natural gas, oil shale, and tar
sands. Recent energy shortages, together with the avail-
ability of abundant coal reserves and the continuing
uncertainties regarding the availability of crude oil,
have made it imperative that methods for converting coal
into a more useful energy source be developed.
Known prior art processes for froth flotation
separation of a slurry of particulate matter are based
on constructions wherein air is introduced into the
liquid slurry of the particulate matter as, e.g. through
a porous cell bottom or a hollow impeller shaft, thereby
producing a surface froth. These prior art methods are
relatively inefficient approaches especially when large
concentrations of particulate matter are being processed.
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1 Generally, these techniques are inefEicient in providing
sufficient contact area be-tween the particulate matter
and frothing air. AS a result large amounts of energy
can be expended in frothing. In addition, froth flotation
techniques which permit bubbles to rise in the slurry can
tend to trap and carry impurities, such as ash in the
froth slurry, and accordingly ~he resultant beneficiated
particu]ate product can have more impurities therein than
necessary.
Methods have been suggested and are being explored
in the beneficiation of coal, i.e., the cleaning of coal of
impurities such as ash and sulfur, either prior to burning
the coal or after its combustion. In one recently developed
technique for beneficiation, termed hereinchemical surface
treating, raw coal is pulverized to a fine mesh size and
is then chemically treated. According to this technique
the treated coal is then separated from ash and sulfur,
and a beneficiated or cleaned coal product is recovered
therefrom.
In further detail, in the heretofore mentioned
chemicalsurface treating process coal is first cleaned of
rock and the like, and is then pulverized to a fine size
of about 48 to 300 mesh. The extended surfaces of the
ground coal particles are then rendered hydrophobic and
oleophilic by a polymerization reaction. The sulfur and
mineral ash impurities present in the coal remain hydro-
philic and are separated from the treated coal product
in a water washing step. This step utilizes oil and
water separation techniques, and the coalparticles made
3 hydrophobic can float in recovery on a water phase which
contains hydrophilic impurities.
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In accordance with -the teachin~s herein, the
present invention provides an improved method and appara-
tus for froth flotation separation of the components of
a slurry having particulate matter therein which is -to be
separa-ted. In this arrangement, at leas-t one primary
spray nozzle is positioned above a flo-tation tank having
a liquia bath therein, and sprays an input slurry con-
taining particulate matter through an aeration zone into
the surface of the liquid. The spraying operation creates
a Eroth on the surface of the liquid in which a quantity
of the particula-te matter is floating, such that -the
- froth containing the particulate mat-ter can be removed
from -the water surface as a separated product. Other
components of the slurry and a minor quantity of particu-
later matter sink in the liquid bath.
Thus, in one embodiment of the present invention,a collector trough is positioned in the tank below the
primary spray nozzle(s) for collecting the sinking
materials. The collected materials are then recycled to
at least one recycle spray nozzle positioned above the
tank which resprays them through an aeration zone into
the liquid surface. Therefore,in this embodiment, the
present invention operates in an efficient manner by
providing a recycling operation wherein particles which
do not float after being sprayed through a primary spray
nozzle are recycled to a further spray nozzle to prov1de
a second opportunity for recovery. In a further embodi-
ment,the recycle spray nozzle(s) is positioned in pro~imity
to the primary spray nozzle(s), and a vertical baffle
3 plate is positioned in the tank between the primary and
recycle nozzles to provide separation for materials sink-
ing from the sprays of the respective nozzles.
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1 In accordance with further de-tails of the
present invention, the spray nozzle(s) utllized herein
is preferably a hollow jet cone nozzle defining an approxi-
mately 30 spray pattern. Further, the slurry is preferably
supplied to the nozzle in a pressure range of from 5 to
40 psi,and more prefereably in the range of from 15 to
20 psi. Also, the present invention has particular
utility to a coal beneficiation operation for froth
flotation separation of a slurry of coal particles and
associated impurities.
The present invention operates in a manner which
is more efficient than prior art arrangements because of
the unique manner of froth generation in which the slurry
is sprayed through an aeration zone. Moreover, further
unique efficiency is provided by more effective cleaning
of particulate ~atter such as coal and higher product
recoveries by providing that those particles which do
not initially float are resprayed into the water surface
to promote and provide a high probability of secondary
recovery of the product from waste materials.
In accordance with further details of another
embodiment of the present invention, a skimmer arrange-
ment having a plurality of spaced skimmer plates depend-
ing from a conveyor is arranged along the top of the tank
to skim the resultant froth therefrom. An upwardly
inclined surface extends from the water surface in the
tank to a collection tank arranged at one side of the
flotation tank, and the skimmer plates skim the froth
from the water surface up the inclined surface and into
the collection tank. Moreover, in one embodiment the
primary and recycle spray nozzles are inclined from
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1 the verticle in the clirection in which the skimmer arrange-
ment operates to direc-t the flow of froth in that direction
along the water surEace. Settling impurities are removed
from the flotation tank by a circulating arrangement opera-
ting near the bottom of the collection tank which removesboth water and settling impurities.
While the froth flotation system of the present
invention is described in detail herein in the context of
a coal benefici2ting operation, it is apparent that the
teachings herein have direct applicability to otner appli-
cations of froth flotation separation technology. For
instance, the froth flotation separation techniques dis-
closed herein can be utilized in conjunction with particu-
late matter such as carbonaceous particles, noncarbonaceous
particles, or mixture of both, mine tailings, oil shale,
residuals, waste particulates, mineral dressings, graphite,
mineral ores, fines, etc.
The foregoing advantages of the present
invention for an arrangem~nt for froth flotation
separation may be more readily unders-tood by one skilled
in the art with reference being had to the following
detailed description of several preferred embodiments
thereof, taken in conjunction with the accompanying draw-
ings wherein like elements are designated by identical
reference numerals throughout the several drawings, and
in which:
Figure 1 is an elevational view of a schematic
exemplary embodiment of a flotation arrangement constructed
pursuant to the teachings of the present invention;
Figure 2 illustrates an elevational view of another
flotation tank utilizing the invention herein;
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1 Figure 3 is a partially sectional elevational
view of one type of spray nozzle wh.ich can be utilized in
the embodiments of Figures 1, 2 and 4; and
Figure 4 illustrates an elevational view of a
more detailed embodiment of a flotation tank constructed
pursuant to the teachings herein.
The apparatus and method of the present inven-
tion is adapted to the separation of a wide variety of
solid-fluid streams by the creation of a solids contain-
ing froth phase, and is suitable for the separation ofmany types of particulate matter. U.~. Patent No. 4,304,573
may be referred to for further details on the chemical
processes which are particularly useful in conjunction
with the subject invention.
The present invention is described herein with
reference to a coal beneficiatlng operation as disclosed, for
example, in detail in the aforementioned U.~. patent. Thus,
referring to the drawings herein in greater detail, Fig. 1
illustrates a first embodiment 10 of the ~resent invention
having a flotation tank 12 filled with water to level 14.
In operation,a slurry of finely ground coal particles,
associated impurities, and if desired additional additives,
such as monomeric chemical initiators, chemical catalysts
and fluid hydrocarbons is sprayed through at least one
primary spray nozzle 16 positioned at a spaced aPart dis-
tance above the water level in tank 1. In alternative
embodiments, two or more nozzles can be used to spray
slurry and/or any other desired inaredients into the tank.
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1 ~'he stream of treated coal is pum~ed under pres-
sure -througha m~nifold to the sprav no7.zle 16 wherein the
resultant shearing forces spray the coal flocculent slurry
as fine droplets such -that they are forcefully jetting into
the mass of a continuous water bath in tank 12 to form a
froth 17. High shearing forces are created in nozzle 16,
and the dispersed particles forcefully enter the surface
of the water and break up the coal-oil-water flocs thereby
water-wet-ting and releasing ash from the interstices hetween
the coal flocs and breaking up the coal flocs so that
exposed ash surfaces introduced into the wa-ter are separated
fro~. the floating coal particles and sink into the water
bath. The surfaces of the finely divided coal particles
now contain air sorbed in the atomized particles, much
of which is entrapped by spraying the slurry through an
aeration zone 19 such that air is sorbed in the sprayed
slurry. The combined effects on the treated coal cause
the flocculated ~oal to decrease in apparent density and
to float as a froth 17 on the sl-rface of the water bath.
The hydrophilic ash remains in the bulk water ~hase, and
tends to settle downwardly in tank 12 under the influence
of gravity. Tank 12 in Figs. 1, 2 and 4 may be a conven-
tional froth flotation tank commercially available from
KOM-LINE-Sanderson Engineering Co., Peapack, N.Y. modified
as set forth below. The flotation tank can also include
somewhat standard equipment which is not illustra-ted in
the drawings such as a liquid level sensor and control
system and a temperature sensing and control system.
The present invention operates on a froth
~eneration principle in which the slurry is sprayed through
an aeration zone such that substantial quantities of ai.
aresorbed by the sprayed fine droplets of the slurry.
Accordin~ly,air is introduced into the slurrv in a unique
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1 manner to generate the resultant froth. The advantages
of this manner of froth generation make the teachings
herein particularl~ applicable to froth flotation separa-
tion of slurries which have a substantial proportion
of particulate matter therein.
The coal particles in the floating froth 17
created by nozz]e 16 can be removed from the water sur-
face by,e.g., a skimming arrangement 28 in which an endless
conveyor belt 30 carries a plurali-ty of spaced skimmer
plates 32 depending therefrom. The skimmer plates are
pivotally attached to the conveyor belt -to pivot in two
directions relative to the belt, and the bottom run of
the belt is positioned above and parallel to the water
surface in the tank. The plates 32 skim the resultant
froth on the water surface in afirst direction 34 toward
a surface 36, preferably upwardly inclined, extending
from the water surface to a collection tank 38 arranged
at one side of the flotation tank, such that the skimmer
plates 32 skim the froth from the water surface up the
surface 36 and into the collection tank 38.
In the arrangement of the disclosed embodiment,
the waste disposal at the bottom of the tank operates in
a direction 40 flowing from an influent stream 42 to the
effluent stream 26, while the skimmer arrangement at the
top of the tank operates in direction 34, counter to that
ofthe waste disposal arrangement. Although the illustrated
embodiment shows a counterflow arrangement, alternative
embodiments are contemplated within the scope of the pre-
sent invention having, e.g., cross and concurrent flows
therein.
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1 Figure 3 is a par-tially sectional view of one
type of commercially available spray nozzle 64 which may
be used in conjunction with the systems shown in igures
1, 2 and 4. A recessed threaded coupling 66 is provided
to a-ttach the nozzle to a primary or recycle manifold
supplying the nozzle with slurry under pressure. The
slurry éncounters a frustoconical venturi section 6~
which accelerates the flow velocity thereof according to
the well known venturi effect. The slurry then flows
through the nozzle aperture having a nominal diameter 70,
which in combination with a diverging section 72 defines
a hollow cone spray pattern 74 having an encompassing spray
angle 76. In one preferred embodiment of the present
invention, angle 76 is approximately thirty dearees,
although other angles which provide the herein contem-
plated results are included within the scope of this
invention.
Spray nozzle 64 may be a hollow jet nozzle as
is commercially available from Spraying Systems Co.,
Wheaton, Illinois. Of course, it is contemplated herein
tha-t other types of nozzles, which function to provide
the desired results as hereinbefore described, may also
be used. The nozzles are preferably constructed of
stainless steel, ceramic or other suitable hard metal
to avoid erosion by the various particles in the slurry
being pumped therethrough. The nozzles are preferably
supplied with slurry in the supply manifolds at a pres-
sure in the range of 5 to dO psi, and more preferably
in a pressure range of 15 to 20 psi.
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l Each nozzle 16 may be -tilted at an angle ~ with
respect to a vertical, ~i.e., the position of the nozzle
relative to the liquid surface level), as shown in Figure ~,
such that it functions to direct the flow of froth in a
direction -towards the skimmer arrangement 28. However, the
angle of incidence ~ does not appear to be critical, and
the vertical positioning shown in Figure l may be preferred
to create a condition most conducive to agitation and froth
generation at the water surface. It appears to be signif-
icant that the agi-tation created by the nozzle sprays define
a zone o-E turbulence extending a limited dis-tance beneath
the water surface level. Too much turbulence may actually
reduce the amount of frothing produced at the water sur-
faceO Among other means, the depth of the turbulence
zone may be adjusted hy varying the supply pressure of
the slurry in the supply manifolds and also the distance
of the nozzles above the water surface. In one operative
embodiment, a zone of turbulence extending two to four
inches beneath the water surface producesvery good agita-
tion and froth generation, although the distance is depen-
dent on many variables such as the tank size, the medium
in the tank, etc. and accordingly may vary considerably in
other embodiments.
In one operation utilizina the present invention
as shown in Fig. 2, a recycling technique is employed to
further improve the efficency relative to prior art arrange-
ments. In the recycling technique, coal particleswhich
do no float after being sprayed through a spray nozzle 16,
designated a primary spray nozzle in context with this
3 embodiment, are recycled to a further recycle spray nozzle 18
to provide the coal particles a second opportunity for
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1 recovery. In this arrangemen-t a collector trough 20,
preferably in the ~orm of an open hemispherical pipe,
is positioned in tank 12 beneath the primary spray noz-
zle(s) 16 for collectlng the sinking materials. A pump
22 is coupled to trough 20 and functions to draw settling
materials into the trough from which it is pumped under
pressure to -the recycle spray nozzle(s). At least one
recycle spray nozzle 18, ~hich may be the same type of
nozzle as primary spray nozzle 16, is provided above the
tank ~or respraying into the surface of the water bath
the materials collected by the trough such that coal
particles collected therein are recycled and a portion
of the recycled coal floats as a froth on the water
surface an additional time and is recovered. The recycled
spray nozzle(s) 1~ is positioned in proximity to the pri-
mary spray nozzle(s) 16, and a vertical baffle plate 2a
is positioned in the tank 12 between primary and recycle
nozzles to provide separation for materials sinking from
the sprays of the respective nozzles. In alternative
embodiments,Further stages of recycling may be provided
by adding additional troughs and recycle noæzles in the
tank.
This arrangement results in an efficient opera-
tion, providing more effective cleaning of the coal and
higher product recoveries by providing that coal particles
which do not initially float have a high probability of
being resprayed onto the water surface to promote secondary
recovery of the product from waste materials.
After the rec~cling operation, the materials
3 which sink from the recycle spray tend to settle down-
wardly in tank 12 under the influence of gravity, and
are withdrawn in an ash-water stream 26 from the base of
the vessel.
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l Figure 4 illustrates an elevational view of a
more detailed illustration of another embodiment of a
flotation arrangement 46 pursuant -to the teachings herein.
Tank 12 may be a conventional froth flotation tank com-
mercially availahle from KOM-LINE-Sanderson Engineering
Col, Peapack, N.J. modified as set forth below. The base
of the tank can be supported in a conventional manner by
channel and flanged structura] members, as illustrated.
The flotation tank can also include somewhat standard
equipment which is not illustrated in the drawings such
as a liquid level sensor and control system and a tempera-
ture sensing and control system.
The conveyor system in this embodiment includes
a drive roller 48 at one end, driven by a chain or equiva-
lent linkage from a skimmer drive 50 mounted on the tank.The other end of the conveyor is defined by an idler
roller 52 which in combination with a second idler roller
54 defines a horizontal run for the conveyor along the top
of the flotation tan];. The conveyor belt in this design
is defined by two strands of two inch, double pitch chain
with each strand having ninety-six pitches. Twelve
skimmer plates are carried by the two chains, with each
plate being eight pitches apart on the two conveyor chains.
The bottom run of the conveyor arrangement is positioned
approximately ten inches above the water surEace, and
each plate depends downwardly from the conveyor chains
approximately ten inches to the water surface. The
skimmer plates carry the coal bearing froth up an
inclined surface 36 to a chute 37 through which the froth
3 is directed to a collection tank.
Trough 20 is in the form of an open hemispherical
pipe positioned below the area at which the spray from the
primary spray nozzle 16 impinges on the water, and is coupled
by lengths of vertical and horizontal conduits 60 and 62 to
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1 pump 22, not shown in Figure 2, which in turn supplies
recycle manifold 58 with a slurry at a preferred feed
pressure.
While several en~odiments and variations of
a method and apparatus for froth flotation separation of
the components of a slurry have been described in detail
herein, i-t should be apparent that the teachings and
disclosure of the present patent will suggest many other
embodi.ments and variations to those skilled in this art.
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