CA1181873A

CA1181873A - Apparatus and method for flotation separation utilizing a spray nozzle

Info

Publication number: CA1181873A
Application number: CA000395233A
Authority: CA
Inventors: James Duttera; Raymond P. Jefferis, Iii; David Matteson; Alexander Szentlaszloi; Phillip E. Mcgarry; David E. Herman
Original assignee: Gulf and Western Manufacturing Co
Current assignee: Gulf and Western Manufacturing Co
Priority date: 1981-01-29
Filing date: 1982-01-29
Publication date: 1985-01-29
Also published as: AU546684B2; EP0057445A2; DE3276901D1; EP0057445B1; AU7985382A; EP0057445A3

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 spray nozzle is positioned above a flo-tation 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 particulate 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 product. Moreover, a recycling operation is provided wherein particulate 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

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.

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.

;3 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 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;

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.
3o _7_ 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 7~

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 7~

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.

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 L~

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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Claims

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

1. Apparatus for froth flotation separation of the components of a slurry having particulate matter therein, said apparatus comprising:
a. a flotation tank;
b. at least one spray nozzle adapted to cause a diverging spray, said spray nozzle positioned above said flot-ation tank and further adapted to spray under pressure an input slurry containing said particulate matter so that said parti-culate matter is dispersed through an aeration zone of increas-ing cross sectional area into the surface of a liquid in said tank to create a froth phase on the surface in which a quantity of the particulate matter is floating; and c. means for controlling the agitation created by said at least one spray nozzle to provide a zone of turbulence extending a limited distance beneath the surface of a liquid in said tank.

2. Apparatus for froth flotation separation of the components of a slurry as claimed in claim 1, wherein said at least one spray nozzle is positioned at a spaced apart distance from said surface of a liquid in said tank.

3. Apparatus for froth flotation separation of the components of a slurry as claimed in claim 1, wherein said at least one spray nozzle includes a hollow jet nozzle spraying a hollow cone pattern into the liquid surface of the tank.

4. Apparatus for froth flotation separation of the components of a slurry as claimed in claim 3, said hollow jet nozzle including about a 30° hollow cone spray nozzle.

5. Apparatus for froth flotation separation of the components of a slurry as claimed in claim 1, including means for supplying said at least one spray nozzle with slurry under pressure in a range of from 5 to 40 psi.

6. Apparatus for froth flotation separation of the components of a slurry as claimed in claim 5, said means supply-ing said at least one spray nozzle with slurry under pressure in a pressure range of from 15 to 20 psi.

7. Apparatus for froth flotation separation of the components of a slurry as claimed in claim 1, including means for supplying said spray nozzle with a slurry of coal particles, associated impurities, and surface treating chemicals for the coal particles and means for skimming froth accumulated on said surface of a liquid in said tank, whereby the apparatus is utilized for the beneficiation of coal.

8. A method for froth flotation separation of the components of a slurry having particulate matter therein, said method comprising the steps of:
a. spraying under pressure an input slurry having particulate matter therein through at least one spray nozzle adapted to cause a diverging spray so that said particulate matter is dispersed through an aeration zone into a liquid surface to create a froth on the surface in which an quantity of the particulate matter is floating;
b. controlling the agitation created by said at least one spray nozzle to provide a zone of turbulence extend-ing a limited distance beneath said liquid surface; and c. removing the froth from the liquid surface.

9. A method for froth flotation separation of the components of a slurry as claimed in claim 8, said step of spraying including the step of spray-ing through at least one hollow jet nozzle to produce a hollow cone spray pattern.

10. A method for froth flotation separation of the components of a slurry as claimed in claim 9, said step of spraying including the step of spraying through at least one hollow cone spray nozzle to produce a 30° hollow cone spray pattern.

11. A method for froth flotation separation of the components of a slurry as claimed in claim 8, further includ-ing the step of supplying slurry to the spray nozzle with a pressure in the range of from 5 to 40 psi.

12. A method for froth flotation separation of the components of a slurry as claimed in claim 11, said step of supplying slurry including supplying slurry with a pressure in the range of from 15 to 20 psi.

13. A method for froth flotation separation of the components of a slurry as claimed in claim 8, further compris-ing the step of supplying the spray nozzle with a slurry of coal particles, associated impurities, and surface treating chemicals for the coal particles, whereby the process is utilized for the beneficiation of coal.

14. An apparatus for froth flotation separation of the components of a slurry having particulate matter therein, said apparatus comprising:
a. a flotation tank;
b. at least one spray nozzle for spraying an input slurry under pressure through an aeration zone, said at least one spray nozzle being adapted to spray a bulk of said slurry as fine droplets through said 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 on the sur-face of said liquid in which a quantity of said particulate matter floats; and c. means for controlling the agitation created by said at least one spray nozzle to provide a zone of turbulence extending a limited distance beneath the surface of a liquid in said tank.

15. An apparatus as defined in claim 14, wherein said at least one spray nozzle has a diverging outlet section.

16. An apparatus as defined in claim 14, wherein said at least one spray nozzle includes a hollow jet nozzle, spraying a hollow cone pattern into a liquid surface of the tank.

17. An apparatus as defined in claim 14, wherein said at least one spray nozzle has a frustoconical venturi section.

18. An apparatus as defined in claim 14, further comprising means for supplying said at least one spray nozzle with slurry under pressure in a pressure range of from 5 to 40 psi.

19. A method for froth flotation separation of the components of a slurry having particulate matter therein, said method comprising the steps of:
a. introducing an input slurry under pressure through at least one spray nozzle for spraying said input slurry through an aeration zone so that a bulk of said input slurry is divided into fine droplets, 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 in which a quantity of the particulate matter floats;
b. controlling the agitation created by said at least one spray nozzle to provide a zone of turbulence extend-ing a limited distance beneath the surface of said liquid sur-face; and c. removing the froth from the liquid surface.

20. A method as defined in claim 19 wherein said input slurry sprayed in step (a) is divided into atomized par-ticles which sorb air in said aeration zone thereby decreasing the apparent density of said atomized particles.

21. A method as defined in claim 19 wherein said at least one spray nozzle has a frustoconical venturi section.

22. A method as defined in claim 19 further compris-ing the step of spraying said input slurry through at least one hollow cone spray nozzle to produce a 30 degree hollow cone spray pattern.

23. A method as defined in claim 19 wherein said in-put slurry is supplied in a pressure range of from 5 to 40 psi.

24. A method as defined in claim 19 further com-prising the step of supplying said at least one spray nozzle with an input slurry comprising a slurry of coal particles, whereby the method is utilized for the beneficiation of coal.

25. A method as defined in claim 19 further compris-ing the step of supplying said at least one spray nozzle with a slurry of coal particles, associated impurities and surface treating chemicals for the coal particles, whereby the process is utilized for the beneficiation of coal.