CA1181874A - Apparatus and method for froth flotation separation of the components of a slurry - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An improved method and apparatus for froth flotation separation of the components of a slurry, having particular utility for the beneficiation of coal by the flotation separation of coal particles from impurities associated therewith such as ash and sulfur. In this arrangement, a primary spray nozzle is positioned above a flotation tank having a water bath therein, and sprays an input slurry through an aeration zone into the surface of the water. The spraying operation creates a froth on the water surface in which a substantial quantity of parti-culate matter is floating, while other components of the slurry sink into the water bath. A skimming arrangement skims the froth from the water surface as a cleaned or beneficiated prod-uct. Moreover, a recycing operation is provided wherein parti-culate materials which do not float after being sprayed through the primary spray nozzle are recycled to a further recycle spray nozzle to provide a second opportunity for recovery of the recycled particles.

Description

This applica-tion is a divisional of App1ica-tion Serial No. 395,233, filed January 29, 1982.
The present inverltion relates generally to a method and apparatus for flotation separation of the components of a slurry and more particularly pertains to an improved method and apparatus for beneiciating coal 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 co~bined 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 i~perative 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 hhen large concentrations of particulate matter are being processed.

~' 1 Generally, these techniques are inefficient in providing sufficient contact area between the particulate rnatter 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 an~ carry impurities, such as ash in the froth slurry, and aceordingly the resultant beneficiated partieulate produet ean have more impurities therein than neeessary.
Methods have been suggested and are being explored in the benefieiation of coal, i.e., the cleaning of eoal of impurities sueh as ash and sulfur, either prior to burning the coal or after its combustion. In one recently developed teehnique for benefieiation, termed hereinehemieal surfaee treating, raw eoal is pulverized to a fine mesh size and is then ehemically treated. Aecording to this technique the treated coal is then separated from ash and sulfur, and a beneficiated or cleaned coal produet is reeovered therefrom.
In further detail, in the heretofore mentioned ehemiealsurEaee treating proeess coal is first cleaned of roek and the like, and is then pulverized to a fine size of about 48 to 300 mesh. The extended surfaees of the ground eoal partieles are then rendered hydrophobie and oleophilie by a polymerization reaetion. The sulfur and mineral ash impurities present in the eoal remain hydro-philie and are separated from the treated eoal produet in a water washing step. This step utilizes oil and water separation teehni~ues, and the eoaliparticleci made 3 hydrophobie~ can float in recovery on a water phase whieh eontains hydrophilie impurities.

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1 In accordance wi-th the teachings 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 separated. In this arrangement, at least one primary spray nozzle is positioned above a flota~ion tank h~ving 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 froth on the surface of the liquid in which a quantity of the particulate matter is floating, such that the ~roth containing the particulate matter 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 provlde a second opportunity for recovery. In a further embodi-ment,the recycle spray nozzle(s) is positioned in proximity 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-in~ from the sprays of the respective nozzles.

n acco:rdance with further details of -the present invention, the spray nozzle(s) utilized 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 uni~ue efficiency is provided by more effective cleaning of particulate matter 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 ano-ther 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 Lhe 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 1 the verticle in t~e direction in which the skimmer arrange-ment operates to direct the flow of froth in that direction along the water surface. Settling impurities are removed from ,he flotation tank by a circulating arrangement opera-ting near the bottom of the collection tank which xemovesboth water and settling impuritiesr While the froth flotation system of the present invention is described in detail herein in the context of a coal beneficiating operation, it is apparent that the teachings herein have direct applicability to other appli-cations of froth flotation separation technology. For instance, the froth flotation separation techni~ues 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 arrangement for froth flotation separation may be more readily understood 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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~6--1 ~igure 3 is a partially sectional elevational view of one type of spray no~zle which can be utilized in the embodiments of Figures 1, 2 and 4; and Figure ~ illustrates an elevational view of a more detailed embodiment of a flotati~n tan]c 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 of many types of particulate matter. U.~. Patent No. 4,30~,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 beneficiating 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 flotati~n 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 12. In alternative embodiments, two or more nozzles can be usecl to spray slurry and/or any other desired ingredients into the tank.
3o 1 I~he strearn of treated coal i5 pumped under pres-sure through a manifold to the sprav no7zle 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-wetting and releasing ash from the interstices between the coal flocs and breaking up the coal flocs so that exposed ash surfaces introduced into the water are separated from 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 sprayiIIg the slurry through an aeration zone 19 such that air i5 sorbed in the sprayed slurry. The combined effects on the treated coal cause the flocculated coal to decrease in apparent density and to float as a froth 17 on the surface of the water ba-th.
The hydrophilic ash remains in the bulk water phase, and tends to settle downwardly in tank 12 under the influence o~ 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 illustrated 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 generation princiPle in which the slurry is sprayed through an aeration zone such that substantial quantities of air a esorbed by the sprayed fine droplets of the slurry.
Accordingly,air is introduced into the slurrv in a unique 1 manner to generate the resultant froth. The advantages of this manner of froth generation make the teachings herein particularly 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 nozzle 16 -can be removed from the water sur-face by,e.g., a s}ci~ming arrangement 28 in which an endless conveyor belt 30 carries a plurality o 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 .ank. 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 hottom of the tank operates in a direction 40 flowing from an influent s-tream ~2 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.

1 Figure 3 is a partially 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 couplin~ 66 is provided to attach the nozzle to a primary or recycle manifold supplying the nozzle with slurry under pressure. The slurry encounters a frustoconical venturi section 68 which accelerates the flo~ veloci~y thereoL 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 deqrees, although other angles which provide the herein contem-plated results are included within the scope of this invention.
Spray nozzle 64 ~ay be a hollow jet nozzle as is commercially available from Sprayin~ Systems Co., Wheator., Illinois. Of course, it is contemplated herein that other types of nozzles, which function to provide the desired resl~lts as hereinbefore described, may also be used. The nozzles are preferably constructed o~
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 p.res-sure in the range of 5 to 40 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 o-f the nozzle relative to the liquid surface level), as shown in Figure 4 such that it functions to direct the flow of froth in a direction towaxds the skimmer arrangement 28. However, the angle of incidence ~ ~oes not appear to be critical, and the vertical positioning shown in Figure l may be preferred to create a condition most conducive to ayitation and froth generation at the water surface. It appears to be signif-icant that the agitation created by the nozzle sprays definea zone of turbulence extending a limited distance beneath the water surface level. Too much turbulence may actually reduce the amount of frothing produced at the water sur-face. Among other means, the depth of the turbulence zone may be adjusted by 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 aaita-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 utiliæina 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 spraved through a spray nozzle 16, designated a primary spray nozzle in context with this 3 embodiment, are recycled to a further recycle spray nozzle l~
to provide the coal particles a second opportunity for --ll--1 recovery. In this arrangement a collector trough 20, preferably in the form of an open hemispherical pipe, is positioned in t~nk 12 beneath the primary spray noz-zle(s) 1~ for collecting 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 pressuré to the recycle spray nozzle(s). At least one recycle spray nozzle 18, which may be the same type of nozzle as primary spray nozzle 16, is provided above the tan]c for respraying into the surface of the water bath the materials collected by the trough such tha-t coal particles collected therein are recycled and a portion of the recycled coal ~loats 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 2~
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,~urther stages of recycling may be provided by adding additional troughs and recycle noæ~les 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 recycling operation, the materials 3 which sink from the recycle spray tend to settle do~n-wardly in tank 12 under the influence of gravity, and are withdrawn in an ash-water stream 26 from the base of the vessel.

1 Figure 4 illustrates an eleva-tional view of a more detailed illustration of another emhodiment oE a flotation arrangement 46 pursuant to the teachings herein.
Tank 12 may be a conventional froth flotation tank com-mercially available from KO~-LINE-Sanderson Engineering Col, Peapack, N.J. modified as set forth below. The base of the tank can oe supported in a conventional manner by channel and flanged structural 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 sensiny 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 ~rom 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 skimmex plates are ~arried 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 surface, and each plate depends downwardly from the conveyor chains appxoximately 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 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 7~
~1 3--1 pump 22, not shown in Figure 2, which in ~urn suppli.es recycle manifold 58 with a slurry at a preferred feed pressure.
While several embodiments and variations of a method and apparatus for froth flotation separation of the components of a slurry have been described in detai.l herein, it should be apparent that the teachings and disclosure of the present patent will suggest many other embodiments and variations to those skilled in this art.

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Claims

WE CLAIM:

1. Apparatus for froth flotation separation of the components of a slurry having particulate matter therein which is to be separated, said apparatus comprising:
a. a flotation tank including means for withdraw-ing a floating fraction and means for withdrawing a tailings fraction;
b. means for feeding slurry comprising at least one primary spray nozzle adapted to cause a diverging spray, said spray nozzle positioned above said flotation tank and further adapted to spray under pressure input slurry of part-iculate matter so that said particulate matter is dispersed through an aeration zone of increasing cross sectional area into a liquid surface in the tank to create a froth on the surface;
c. a collector means positioned in said tank below said feed means for collecting sinking materials; and d. at least one recycle spray nozzle positioned above said tank for spraying said collected sinking materials through an aeration zone into the liquid surface.

2. Apparatus for froth flotation separation of the components of a slurry as claimed in claim 1, wherein said means for withdrawing said floating fraction includes a skimmer means, adapted to operate along the top of said tank, for skimming froth from the liquid surface of the tank.

3. Apparatus for froth flotation separation of the components of a slurry as claimed in claim 2, wherein said skimmer means includes a plurality of spaced skimmer plates depending from a conveyor arranged along the top of said tank, and an upwardly inclined surface extends from the top of said flotation tank to a collection tank arranged at one side of the flotation tank, whereby the skimmer plates skim the froth from the liquid surface up said inclined surface and into said collection tank.

4. The apparatus as defined in claim 1, wherein said at least one recycle spray nozzle is adapted to cause a diverging spray.

5. Apparatus for froth flotation separation of the components of a slurry as claimed in claim 1, wherein said means for withdrawing a tailings fraction includes circulating means, operating near the bottom of said tank, for removing liquid and settling materials therefrom.

5. Apparatus for froth flotation separation of the components of a slurry as claimed in claim 1, wherein said at least one primary and recycle nozzles are inclined from a ver-tical to assist in directing the flow of froth over the liquid surface.

7. Apparatus for froth flotation separation of the components of a slurry as claimed in claim 1, wherein said at least one recycle spray nozzle is positioned in proximity to said at least one primary spray nozzle, and a vertical baffle plate is positioned in said tank between said primary and re-cycle spray nozzles to provide separation for materials sinking from the sprays of the primary and recycle spray nozzles.

8. Apparatus for froth flotation separation of the components of a slurry as claimed in claim 1, further in-cluding an additional collector means positioned in said tank below said at least one recycle spray nozzle for collecting the sinking materials from its spray, and a further recycle spray nozzle positioned above said tank for spraying through an aeration zone into the liquid surface the materials collected by said additional collector means, whereby several stages of recycling are provided.

9. Apparatus for froth flotation separation of the components of a slurry as claimed in claim 1 , 3 or 8, further including means for supplying a slurry of coal particles and impurities associated therewith to said at least one primary spray nozzle, whereby the apparatus is utilized for the bene-ficiation of coal.

10. A method for froth flotation separation of the components of a slurry having particulate matter therein which is to be separated, said method comprising the steps of:
a. spraying under pressure an input slurry of par-ticulate matter through a means for feeding slurry, said means for feeding slurry comprising a primary spray nozzle adapted to cause a diverging spray so that said particulate matter is dis-persed through an aeration zone into a liquid surface to create a froth on the surface having a substantial quantity of parti-culate matter floating therein, while other components of the slurry and a minor quantity of particulate matter sink in the liquid, whereby the froth can be removed from the liquid sur-face;
b. collecting said sinking materials from the spray of the primary spray nozzle in a collector means positioned be-low said feed means;
c. utilizing a recycle spray nozzle to respray through an aeration zone into the liquid surface said collected sinking materials, whereby particulate matter therein is recycled and a portion of the recycled materials floats as a froth on the liquid surface;
d. withdrawing said froth formed in steps a and c;
and e. withdrawing a tailings fraction.

11. A method for froth flotation separation of the components of a slurry as claimed in claim 10, further includ-ing the step of skimming the froth from the liquid surface.

12. A method for froth flotation separation of the components of a slurry as claimed in claim 11, wherein said skimming step is accomplished utilizing a plurality of spaced skimmer plates depending from a conveyor arranged along the liquid surface.

13. A method for froth flotation separation of the components of a slurry as claimed in claim 10, wherein said step of utilizing a recycle spray nozzle is carried out in proximity to said step of utilizing a primary spray nozzle, and further including the step of providing a vertical baffle plate in the liquid between the positions at which the steps of utilzing a recycle spray nozzle and utilizing a primary spray nozzle are performed, to provide separation for the sinking materials from both steps.

14. A method for froth separation of the components of a slurry as claimed in claim 10, further including the steps of collecting the sinking materials from the spray of the re-cycle spray nozzle, and utilizing a further recycle spray nozzle to respray the collected materials through an aeration zone into the liquid surface whereby several stages of recycl-ing are provided.

15. A method for froth separation of the components of a slurry as claimed in claim 10, 11 or 14, further includ-ing the step supplying a slurry of cold particles and impurities associated therewith to said primary spray nozzle, whereby the method is utilized for the beneficiation of coal.

16. The method of claim 10, wherein said recycle spray nozzle is adapted to cause a diverging spray.

17. An apparatus for froth flotation separation of the components of a slurry having particulate matter therein which is to be separated, said apparatus comprising:
a. a flotation tank including means for withdrawing a floating fraction and means for withdrawing a tailings frac-tion;
b. means for feeding slurry comprising at least one primary spray nozzle for spraying an input slurry under pressure through an aeration zone, said primary spray nozzle positioned above said flotation tank and being adapted to spray a bulk of said input slurry as fine droplets through an aeration zone, which fine droplets are projected through said aeration zone and into the surface of a liquid in said flotation tank to form a froth phase on the surface of said liquid;
c. a collector means positioned in said tank below said feed means for collecting sinking materials; and d. at least one recycle spray nozzle positioned above said tank for spraying said collected sinking materials through an aeration zone into the liquid surface.

18. The apparatus for froth flotation separation of the components of a slurry as defined in claim 17, wherein said means for withdrawing a floating fraction comprises a skimmer means adapted to operate along the top of said tank for skimming froth from the liquid surface of the tank.

19. The apparatus for froth flotation separation of the components of a slurry as defined in claim 17, wherein said at least one recycle spray nozzle is adapted to spray said collected materials as fine droplets through said aeration zone.