US2246559A - Aerating apparatus - Google Patents

Description

June 24, 1941. A. J. WEINIG 2,246,559

AERATING APPARATUS 7 Filed June 22, 1939 4 Sheets-Sheet l 9 INVENTOR. Fig.2. 4/? T'lfl/f? J wsnwe June 24, 1941. W NIG 2,246,559

AERATING APPARATUS Filed June 22, 1939 4 Sheets-Sheet 3 Figs.

INVENTOR. M11101? J WE/lV/G June 24, 1941. J wgm 2,246,559

AERATING APPARATUS Filed June 22, 1959 4 Sheets-Sheet 4 19/1 lune; INVENTOR. A/Pnw/RJ WEI/W6 ATTORN S.

Patented June .24, 1941 UNITED STATES PATENT OFFICE nam'rnfi fiifmarus Arthur I. Welnig, Golden, Colo. Applicatlzn (GEE-2:32:0- 280,595

This invention relates toaerating apparatus employed in the treatment of solids in liquid suspension and is particularly adapted for use in various froth flotation treatments in which aeration is an essential. v 1 F The present application is a continuation-inpart of my application, Serial No. 119,510, filed I January 7, 1937, for Method of and apparatus for flotation agitation;

which latter application stands abandoned as of August 7, 1939.

In the well-known froth flotation process, it is essential that the finely-divided particles of ore or other solid matter are subjected to the action of certain reagents. Thereafter, by bringing cer taln constituents of the solids and liquid mixture comprising the pulp into intimate contact with air or other gas dispersed and distributed throughout the liquid body, certain ofthe constituent solids form attachments to the bubbles of gas and are elevated thereby to the surface where they collect in a froth. This frothmay be removed separately from other constituents of the pulp remaining in non-floated condition below the froth bed.

While the selection and collection of the floated constituents are determined by the re-' agent action, the mechanical action of the process, namely, the production of gas bubbles and the contact of the gas with coated solids to promote the elevation thereof, is a function of the gas distribution which is essential to any such process.-

In such a treatment, the solids in liquid suspension are more or less uniformly distributed through and held in suspension in the liquid mass, and the efl'lciency of the operation, to a large extent, is determined by the amount of surface contact between solids and gas produced in the operation.

Due to the manner in which the materials ar introduced into the treatment, as well as the nahigh velocityIto induce a mixing of pulp. as and reagent in an agitation zone and thereafter moving the mixed material into a separation zone having a relatively quiescent action in which the flotation separation is completed. Generally such machines employ alower agitation zone with a separation zone above suitably separated by grids, baflles or other suitable devices.

In this way, agitation is restrained so that the effects thereof are confined largely to the agitation zone and the mineral particles attached to the gas bubbles in rising'to the froth are more or less unimpeded in the separation zone.

Despite this general condition, there is sufficient swirl within the liquid body of the separation zone to induce a mingling between particles in suspension and those particles that are being elevated by attachment to the gas rising to the surface. Further, there is in any given volume of pulp within the agitation zone a certain percentage of heavier particles thrown upwardly by the mechanical agitation, which is descending by gravity to the agitation zone.

face in an ascending action in the same zone or ture of the attachments aforesaid, excessive aethe liquid is gentle or at least within velocity limits which do not produce excessive turbulence.

\ While froth-flotation operations may be performed with a variety of machines, present practice shows a decided preference for machines of the -mechanical agitation type in most treatments. Such machines employ rotary impellers operating within the liquid body at relatively region in which another portion is descending by gravity. Obviously, under such conditions the falling particles will destroy the attachment of the gas bubbles contacted within the liquid body and by so doing, release the previously attached mineral which thereupon falls untilsuch time as it is again entrapped by contact with rising gas bubbles or is elevated in suspension by the velocity of the agitation.

Recognizing both the beneficial and deleterious effects of such operating methods, the present invention has been designed to satisfy the requirements in a treatment in which mechanical agitation is utilized to induce a sufllcient dispersion of gas to satisfy the elevating requirements in a controlled movement in which the disruption of elevating attachments has largely been eliminated.

It is an object of the present invention to produce a finer distribution or dispersion of gas throughout the body of solids in liquid suspension through the medium of mechanical agitation in an action in which the rate of rotation of mechanical agitators has been reduced to decrease the horsepower requirements of the operation.

vAnother object of the invention is the provi-. sion of a novel apparatus for mixing gas with pulp and/or reagent under the influence of mechanical agitation to induce a high degree of surface contact between gas and solids of the pulp while reducing turbulence in the body of material under treatment subject to the influence of mechanical agitation.

A further object of the invention is to. combine with the mixing action of the type described a combined pumping and sweeping action on solid; settling from the treatment for their recirculation through the mixing stages of the operation.

A still further object of the invention is the provision of novel aerating apparatus adapted to control the movement of materials through a zone of agitation in such a way that excessive wear is eliminated while mixing is promoted.

A still further object of the invention is the provision of aerating apparatus in which the extent and degree of aeration is variable and under regulation.

Other objects reside in novel combinations and arrangements of parts, all of which will appear more fully in the course of the following description.

Another condition of considerable consequence in the development of the present invention, has been the influence of altitude upon the flotation operation. Frequently, the mills in which the ores are treated are located at elevations between 9,000 and 12,000 feet and at such high altitudes the rarefied air does not afford a satisfactory supply for machines employing the suction action of impellers for entrainment of atmospheric air as the aerating medium.

The present invention satisfies the requirements of such an operation by employing gas under pressure (usually compressed air) as the medium for aeration of the pulp. Further, by defining the effective upper and lower limits of the gas pressure and providing means for regulating the pressure of the gas delivered to the machine, a highly eflicient operation is attained which is not influenced by the variable factors of altitude and air density.

In order to produce the desired mixing, two streams of material are moved in parallel and preferably in superposed relation to a point of discharge in which the streams are brought together in converging relation and immediately thereafter or simultaneously therewith are ejected into the more or less static body of the pulp in which the flotation separation occurs.

Preferably, the parallel travel occurs within a rotary impeller in which provision is made for suitable division and separation of the two streams during at least a part of their movement under the centrifugal influence of the impeller. To this end, a central opening is provided into the uppermost chamber into which a mixture of pulp, and recirculated and partially aerated pulp are brought together.

At the point of pulp introduction into the impeller, a nozzle connected with a suitable source of gas supply delivers the gas under pressure into this uppermost chamber and preferably in a direction corresponding to the movement of pulp through the chamber.

The lowermost chamber draws in pulp not yet subjected to the aerating influences of the flotation cell, which may be supplied either through a pulp inlet entering the bottom of the cell beneath the impeller or from that portion of the pulp in the cell which is below the impeller and consequently contains little or no undissolved air.

Such an arrangement results. in the uppermost compartment running in an overloaded contrance and the presence of large amounts of gas in the liquid body within the compartment at any given moment. The lower compartment, due to the absence of any substantial quantity of air and because the material is drawn in by the pumping action of the impeller, is always in an underloaded condition. The materials of the two streams even when moving in parallel but passing beyond the physical division of the partitioning member of the impeller will be brought into converging relation because of a partial vacuum condition developed through the underloaded condition of the lower compartment which is immediately satisfied by the excess pressure on the material in the upper stream induced by the overloaded condition.

As a consequence of such action, large amounts of air are entrained in the streams of material at the point of convergence and due to the thorough and intimate intermixture of air, solids and/or reagent within the liquid body, the pulp so treated on moving beyond the sphere of action or the impeller will assume an elevating movement adjacent the sides of the cell in which the gas in it finely-diffused condition will rise to the surface, carrying with it the minerals attached or attaching thereto during its ascension.

The central opening to the impeller draws in liquid and solids from the zone of the liquid body immediately above the same and because of the demands of the upper mixing compartment for material, there is a pronounced downward movement through the central zone of the cell into the impeller.

As a result of such forces, the mixing action of the present invention sets up a .pronounced circulatory movement in which solids not entrapped in the air bubbles, .but elevated by the agitating action, are drawn into the central portion of the cell before they assume a gravitational descent, while the mineralized particles which have formed attachments with the gas rise without impedance through the ascending column of the circulatory movement.

From the foregoing, it will be apparent that the present invention may be applied generally to machines of the mechanical agitation type and when so applied, is productive of a distinctive type of operating procedure that attains highly beneficial results.

While many structural arrangements may be employed to perform the operations of the present process, certain structural embodiments have proved highly effective in attaining the desired objects.

In order to afford a better understanding of the invention, reference will now be made to the accompanying drawings, in the several views of which like parts have been designated similarly and in which: a

Figure l is a side elevation of a typical flotation cell of the sub-aeration type to which the present invention has been applied;

Figure 2 is an enlarged sectional view of the impeller construction illustrated in Figure 1;

Figure 3 is a side elevation of another typical sub-aeration cell to which a modified form of the invention has been applied;

dition due to the hydrostatic head above the en- Figure 4 is an enlarged sectional view of the impeller construction illustrated in Figure 3;

Figure 5 is an enlarged sectional view of a modified type of impeller construction;

Figure 6 is a side elevation of another subaeration cell with another modification of the imor other receptacle (not illustrated).

The tailings discharge of the cell comprises an outlet l6 controlled by a float-actuated valve 11 determining the liquid level in the cell. A rotary shaft l8 driven in any suitable manner extends from a point above the tank 8 into the lower portion of the same and carries at its lower end a rotary impeller l9.

Gas under pressure is carried in a header 20 supported on the tank and connected with one or more conduits 2| which extend downwardly into the cell and terminate in nozzles 22 discharging through a central opening 19a into the upper portion of the impeller i9. Control of gas discharge is provided through the medium of valves 23.

In certain treatments, it will be desirable to introduce reagents directly into the cell and utilize the agitation and aeration of the treatment as a means of attaining the proper mixing of re-- Usually, such reagents v'll be of the water soluble type, such as xanthates,

agent and solids.

cresylic acid and pine oil, and are often so introduced in the treatment of copper, lead and zinc ores.

To this end, a reagent feeder is incorporated in the cell structure and comprises a funnel 24 at the upper end of a conduit 25 extending into the opening I9a of the impeller and discharging adjacent one of the gas discharge nozzles 22.

The form of the impeller illustrated in Figures 1 and 2 has top and bottom plates lab and I90 respectively, separated by a dividing member or partition l9d carried on a hub member He mounted on the shaft 18 to form superposed chambers A and B. In this form of impeller the bottom plate 190 has a central opening lBg to admit matter from inlet l4 into chamber B.

The dividing member [9d of this form of impeller is of a diameter equal to that of the top and bottom plates i9b and He and the chambers A and B have separate peripheral openings for the discharge of material into a mixing zone exterlorly of the impeller. Vanes, I971, preferably in radial arrangement, extend to the periphery from a point adjacent the center of the impeller and connect the top and bottom plates with the dividing member.

By the action of the vanes in compartments A and B, the two currents are forcibly ejected beyond the periphery of the agitator, with the current ejected from compartment B taking an outward trend, while the stream discharged from compartment A takes a downward trajectory ow- I ing to the partial vacuumcreated in the lower compartment B as previously explained.

The provision for impinging the streams beyond the periphery of the impeller and delivering relatively large quantities of air into the pulp body bordering the impeller, causes a 1*gh degree of intermingling of the ejected mi are with the pulp bodyin the cell and the action further serves to diminish frictional resistance to such an extent that th impellers may be operated at a speed of approximately one-third less than the requirements of present practice without impairing the quality of aeration and, in fact, improving the same.

In order to preserve the horepower reduction thus attained, the air should be introduced as near the center of the impeller as possible and due to the balance required in the impeller when operating at high speeds, the inlet opening must be concentric with the shaft. Such an arrangement permits reduction in the size of the impelling vanes for ejection of the matter delivered to the chambers A and B for the size of the vanes must be increased proportionately to the distance from the center at which the material is introduced.

Theoretically, the upper-compartment should be narrower than the lower, but obstructions such as wood chips, etc., entering with the feed make it impractical to so reduce the passage in the standard sizes. However, in larger sizes such an arrangement would be preferable.

On the other hand, if the lower chamber is narrower, much of the aerating efiect is destroyed with increased turbulence and boiling in the cell which lowers recovery.

The arrangement of the air pipes and reagent feed of Figure 1 is also advantageous in the operation. The air pipesare so designed that a cleaning rod may be inserted through the top at the normally-closed opening 26 and from such position will penetrate through the discharge nozzle 22 when the opening i in the angular position indicated in Figure 2. This feature is of particular value in starting the machine following shut-downs and the like, which sometimes occur, causing the solids to settle out of suspension and fill the lower portion of the flotation cell.

The location of the pipes 2| and 25 with reference to the inlet opening 19a serves to prevent any vortex action in the material entering the inlet by restraining the swirl above the same at the same time that the discharging gas fills the void, which otherwise would be present below the opening.

Hlving thus described the structural arrangement, reference will now be made to the operating procedure within the cell. Pulp from. a suitable source of supply, such as a classifier, conditioner or preceding cell in a series enters through inlet it into the agitating compartment I! while tailings of the treatment discharge from the cell through outlet it at a rate determined by the float-actuated valve mechanism II.

This discharge control determines the liquid level in the cell, which usually is maintained in close proximity to the elevation of overflow l5. On entering chamber l2, the pulp it drawn into compartment B of impeller l9 by its suction influence, and upon being subjected to the centrifugal influence and the action of the vanes Hi is moved in a lengthwise direction through the compartment and discharge into the pulp body in the cell. At the same time, a portion of the previously aerated pulp recirculates through opening Ha into the upper compartment A of the impeller and there impinges upon the streams of air discharged through nozzles 22 and by the action of the vanes l9h and the centrifugal influence, moves in substantially parallel relation to the pulp stream in chamber B.

- The underloaded condition of compartmentB creates a condition of partial vacuum which at the peripheral termination of dividing member IM permits the overloaded condition of compartment A to satisfy the requirement of the material passing out of chamber B. As a result, there is a pronounced downward trajectory of the material discharging from chamber A into impinging relation with the discharge from chamber B. This impingement causes the high degree of intermixture and gas dispersion previously described.

In cells in which pulp enters through a bottom opening and i then subjected to the pumping action of the impeller, it is preferred practice to locate the impeller in close proximity to the inlet opening to prevent dissipation or losses of the suction influence.

Due to the shape of the cell and the movement of the discharging liquid under the influence of the impeller, coupled with the buoyant condition of the mass, the solids in suspension and the mineral entrapped by the air in the flotation action are caused to rise in a column moving substantially parallel with the upright walls of the cell. A the ascension progresses, that portion of the solids content which is not being elevated by the flotation reaction is drawn toward the center of the cell and when the gravitational eiIect overcomes the suspension tendencies on such particles, they descend in the central zone of the cell to return for further treatment through the inlet opening Isa.

In this manner, a pronounced and well-defined circulatory movement is set up in the cell, as indicated by the directional arrows in Figure l, in which the elevated and descending columns of material are definitely eparated, eliminating impedance of the elevated material of the flotation reaction and puncturing of the mineralladen bubbles, as would otherwise occur.

Whenever it is necessary to introduce reagent to a given cell, such reagent may be placed in funnel 24 and delivered through conduit 25 into the mixing zone of chamber A. Due to the proximity of the point of introduction of the reagent to the gas discharge into such chamber, the gas will assist in carrying the reagent into solution and the mixing action will be effective in bringing such solution into repeated and intimate contact with solids passing through the mixing zone.

The form of the cell to which the invention has been applied as illustsated in Figure 3, is one in which the feed to the machine either from an outside source or a preceding cell, enters the cell at an elevation above its bottom.

In order to provide a feed for compartment B of impeller ii) of this form, which is substantially free of gas, the impeller is spaced at a distance from the cell bottom to insure a portion of the liquid body acted on by the suction influence of the impeller being free of gas previously ejected through the peripheral openings of the impeller.

In this form, gas is introduced into compartment A through conduits 22 in the manner previously described, and recirculating pulp which has been at least partially aerated by the previous action of the impeller, returns through the opening i 90. and mixes with the gas before its ejection from chamber A. The impeller exerts a pumping action at the central opening lag to draw settled solids along the bottom and to elevate solids and liquid into the chamber B.

As a consequence, the material under treatment in this form of cell is substantially identical with that previously described and except in the respects noted, the operation performed in the cell of Figure 3 is identical with that performed in the cell of Figure 1.

The form of impeller illustrated in Figure 5 employs the same mixing principle as the impeller of Figure 2, for example, but the dividing member lid in this form of construction terminates at a substantial distance from the periphery of the impeller.

Again, in this form, the chamber A is operated in an overloaded condition, while the chamber B is operated in an underloaded condition,

Due to the pressure differential between the materials of the respective chambers, the stream of pulp ejecting from the passage defined in chamber A assumes a downward trajectory and impinges on the material travelling through chamber B, adjoining but inside the periphery of the impeller. As a consequence, a substantial portion of the material thrown out by the impeller is premixed and thoroughly aerated before it entersthe substantially static body of pulp beyond the impeller.

As in the other forms of impeller previously described, pulp is drawn in through the central bottom opening of chamber B and the vanes |9h assist in the impelling movement of the pulp through the chambers. Sweeping blades lam are shown on the bottom of the'impeller and move settled solids on the tank bottom back into suspension in the liquid body.

In Figures 6 and 7, a form of construction is illustrated in which the impeller housing is of conical form. As clearly illustrated in Figure 7, the impeller contains the usual dividing member it which terminates short of the periphery of the impeller to .provide a mixing zone adjoining but within the periphery of the impeller.

While the impeller illustrated has a sharp inclination to its conical surface, it will be obvious to those skilled in the art that any desired degree of inclination may be used, and if desired, the conical cover portion need not extend in encompasslng relation to the dividing member in constructions in which only a slight pitch is employed.

In such an impeller, the vanes in the chamber B are an essential, particularly if the bottom plate is omitted, as illustrated. The provision of the vanes lBh in this form of construction insures adequate pumping action to draw substantial quantities of pulp into and through chamber B and as in the other types of impellers, the second stream of pulp, moving through compartment A assumes a downward trajectory, induced in part by the pressure differential of the streams and also by the crowding action of the inclined surface to impinge upon and mix with the pulp stream of compartment B as in the other forms of the invention.

The construction of Figure 7 necessitates a convergence of the streams within the impeller enclosure and the ejection of the mixture at the lower edge of the cone.

The foregoing description illustrates a condition of general application to all the forms illustrated herein, namely, that under favorable conditions the bottom plate may be omitted without destroying the function and identity of the chamber B and the pulp in which the impeller is immersed will enter centrally of the lower compartment and be discharged at its periphery by the action of the pumping vanes.

Thus, it is apparent that th mixing function of the present construction may be embodied in a variety of forms to satisfy difierent operating and manufacturing requirements and in all such forms the horsepower savings previously described will be effected and a highly eflicient mixing action will be attained.

Further, with respect to the flexibility of the 4 present construction, it will be noted that the dividing member defining the compartments A and B may be of a lesser diameter or the same diameter as the upper or lower plates of the impeller. Also, the length of the impelling vanes within the impeller may be varied and while a shortened vane is preferable from the standpoint of horsepower requirements, under some circumstances as when the bottom plate is omitted,

it may be preferable to have longer vanes in the lower compartment at least.

The impellers may be composed of separate parts suitably fastened together or may be inito discharge gas into the pulp stream entering therethrough in the direction of its movement.

2. In aerating apparatus, a rotary hollow body having in its top an opening around its axis of rotation for admission of pulp, a dividing memher in the body defining upper and lower chambers therein, there being an inlet opening in the body for admission of pulp to the lower chamber, vanes in both chambers for impellent action on the pulp admitted through the respective openings, and means for introducing gas under pressure into the pulp as it enters the impeller through the upper opening.

tially formed as an integral unit and the simplicity of the present design makes possible the adaptation of the impeller in a variety of ma-.

that changes in any one form may be incorporated in accordance with the disclosures of the other forms.

i'he setting of the lmpeller'in the tank likewise is subject to variation. Where the feed enters the cell from underneath, it is preferable to have the impeller operating in close proximity to the feed inlet to exert the strongest possible suction influence thereon, but where conditions require, the spacing of the impeller from the inlet may be varied if necessary.

Similarly, in machines in which the feed enters the tank other than through a bottom opening, it is preferable to have the impeller operating at a distance from the bottom in order to provide a portion of the pulp body adjacent the bottom which is substantially free from gas. However, any means of providing a liquid body free from gas other than the s acing of the impeller, will satisfy the needs of the present invention and is with n contemplation thereof.

The introduction of the reagent has only been shown in connect on with the impeller form of Figures 1 and 2, but it will be understood that the funnel 24 and associated conduit 25 may be incorporated in all of the embodiments of t e invention where reagent feed direct to the cell is an. essential operating requirement.

What I claim and desire to secure by Letters Patent is: r

1. Apparatus of the charact r de cribed, comprising a tank for solids in liquid su pensi n.

open to the atmosphere, a rotary im e ler in the lower portion of the tank divided into u per and the delivery of gas from the source into the impeller and provided with a nozzle extending 3. In aerating apparatus, a rotary conical body having in its top an opening around its axis of rotation for admission of pulp, a dividing member in the body defining upper and lower chambers therein, there being an inlet opening in the body for admission of pulp to the lower chamber, vanes in both chambers for impellent action on the pulp admitted through the respective openings, and means for introducing gas under pressure into pulp entering through the upper opening.

4. Froth flotation apparatus, comprising a tank having a feed inlet and a discharge outlet determining a liquid level therein and divided into a lower agitation compartment and an upper separation compartment, a rotary impeller in the lower portion of the agitation compartment at a distance from the bottom thereof and comprising upper and lower chambers, separately open adjacent the periphery of the element for the separate discharge of two currents of pulp into a mixing zone adjoining said periphery, both chambers having openings to admit pulp centrally thereof, and conduit means extending from above the liquid level and terminating at the central opening in the upper chamber of the impeller for the delivery of gas under pressure thereto.

5. Froth flotation apparatus, comprising a tank having a bottom feed inlet and a discharge outlet determining a liquid level therein and divided into a lower agitation compartment and an upper separation compartment, a rotary impeller in the lower portion of the agitation compartment in close proximity to the bottom thereof, and comprising upper and lower chambers, separately open adjacent the periphery of the element for the separate discharge of two currents of pulp into a mixing zone adjoining said periphery, both chambers having central openings to admit pulp thereto, conduit means extending from above the liquid level and terminating at the upper central opening for introducing gas under pressure into'pulp entering therethrough, and vanes in the lower chamber to accelerate outward movement of vpulp through the peripheral opening thereof.

6. In flotation apparatus, a.' cell open to the atmosphere having a feed inlet and a discharge outlet determining a liquid level therein, a rotary impeller within the body of pulp having upper through the upper central opening in a position and lower chambers and having a central intake opening in each of said chambers, and mean; for

introducing gas above atmospheric pressure into the uppermost of said intake openings to induce with the hydrostatic pressure of the pulp, an overloaded condition in the upper chamber while the -lower'chamber is maintained in an underloaded condition by the absence of gas at its intake opening.

- ARTHUR J. wanna.

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