US 2673724 A
Description (OCR text may contain errors)
March 30, 1954 J. 'r. POTTS I 2,673,724
IMPELLER FOR FLOTATION MACHINES Filed July 14, 1951 & l 24 F/(;. 2.
Patented Mar. 30, 1954 IMPELLER FOR FLOTATION MACHINES John T. Potts, Salt Lake City, Utah, assignor to The Galigher Company, Salt Lake City, Utah, a corporation of Utah Application July 14, 1951, Serial No. 236,712
This invention relates to the art of froth flotation as extensively utilized in the separation of certain particles from an intimate mixture of same with other particles in an aqueous pulp, and is concerned particularly with aeration impellers as employed in flotation machines.
Flotation machines of subaeration type employ agitation impellers in connection with the introduction of air into a body of pulp. The construction and operating characteristics of such impellers are largely responsible for the overall performance of a flotation cell.
Many different varieties of impellers have been developed in the past, with varying degrees of satisfaction in the performance of and in the recoveries obtained by the flotation cells of which they constitute a part.
In the flotation cells manufactured by The Galigher Company of Salt Lake City, Utah, under the proprietary name Agitair, a modified form of the impeller disclosed by Lionel E. Booth in his United States Patent No. 2,085,947, issued July 6, 1937, for Aerating Machine, has long been used with generally good results.
I have now found, however, that considerably improved results are obtained if an impeller of this type is provided with a number of relatively small openings through its otherwise imperforate top.
Improved results are particularly noticeable in the almost complete elimination of boiling of the pulp at the sides and in the corners of the cell, thereby considerably enhancing the aerating action of the machine and stabilizing the froth to an extent heretofore impossible. Furthermore, the aerating action is evened out by the elimination of sudden surges of air going into the pulp when there is a change in valve setting during operation of the machine or when some other factor suddenly causes increased delivery of air from the forced supply of same. Additionally, any tendency for air to be trapped within the impeller and force pulp backwardly through the air supply passages is eliminated.
The impeller disclosed by the aforesaid Booth patent is of hollowopen-bottom, conical formation, and is fixed to the lower end of a rotatably mounted drive shaft. The shaft rises centrally from the imperforate top of the impeller. Air under pressure is introduced to the hollow interior of the impeller, either by way of a supply pipe projecting upwardly through the open impeller bottom, or by way of the drive shaft when hollow. The air so introduced is disseminated in the pulp by a plurality of spaced teeth or fingers, which depend from the lower rim f the cone to form, in effect, a denture.
As modified for more recent models of the above-mentioned Agitair machine, the impeller has an imperforate, fiat disk top, rather than one of conical formation.
My present invention is applicable to both the conically formed impellers and to those with flat disc tops. In both forms, I have found that the provision of a number of relatively small openings through the otherwise imperforate top, in accordance with the invention, establishes localized, upward currents of air or air and pulp in the flotation cell, which exert a highly beneficial action on the dynamic body of pulp above the impeller in stabilizing and quieting the activity thereof. Specifically, it is believed that these localized, upward currents break up the centrifugal flow of pulp across and outwardly'of the top of the impeller.
As is well known in flotation practice, it is most desirable that a relatively quiescent bubble column be established in the flotation cell, and that the superficial layer of froth be substantially undisturbed by activity of the underlying pulp. Aeration impellers conforming to this invention by reason of the provision of a plurality of relatively small openings through the otherwise closed tops of same have been found to accomplish these desired result in flotation practice to much greater extent than the original imperforate form of impellers utilized in the presently standard Agitair machine.
Accordingly, a principal object of the present invention is to provide an aeration impeller for flotation machines which will contribute materially to eflicient operation and the achievement of high recoveries, particularly by coupling effective pulp aeration with stabilization of the body of pulp.
As stated hereinbefore, the outstanding feature of the invention is the provision for limited discharge of air upwardly into the surrounding body of pulp from and through the top of a lateral discharge type of aerating impeller, coincidental with normal lateral discharge from such impeller.
While I prefer to embody my invention in standard Agitair impellers, as an improved form thereof, it will be apparent to those skilled in the art that the invention can be utilized in connection with other generally similar types of impellers.
Further objects and features of the invention will become apparent from the following detailed description of the preferred embodiments there of illustrated in the accompanying drawing.
In the drawing:
Fig. 1 represents a vertical section taken through a standard Agitair flotation machine altered only by the provision of an impeller which conforms to the teachings of this invention, the impeller being illustrated in elevation;
Fig. 2, a considerably enlarged perspective view of the impeller assembly of Fig. 1, looking downwardly upon the perforate top of the impeller proper;
Fig. 3, a bottom plan view of the impeller of Fig. 2, drawn to a somewhat larger scale;
Fig. 4, a vertical section taken on the line 4-4 of Fig. 3, upper portions of the assembly being broken out; and
Fig. 5, a top perspective view of a conical type Agitair impeller conforming to the present invention.
Referring to the drawing: the single cell flotation machine illustrated in Fig. 1 is typical of subaeration flotation machines produced by The Galigher Company under the proprietary name Agitair.
Pursuant to present practice, the impeller of such machine may be of what is known as flat disk type, as shown in Figs. 1 to 4, or it may be of what is known as conical type, as shown in Fig. 5. The present invention may be embodied in either type, as can be readily seen from the illustrations.
As illustrated, the impeller proper comprisesin either instance-a plurality of closely spaced fingers depending from the outer periphery of a generally circular top member, which is adapted for fastening, at its center, to a rotatable shaft. As ordinarily constructed for incorporation in an Agitair machine, the top member, whether of disk or hollow conical formation, is imperforate, so as to discharge only laterally into the surrounding body of pulp. In accordance with the present invention, however, a plurality of relatively small openings or perforations are distributed throughout the top member of the impeller, providing for limited upward discharge in addition to the normal lateral discharge.
Considering, first, the flat disk type of impeller shown in Figs. 1 through 4, the impeller proper comprises a top member I of flat disk formation, from the outer periphery of which depend a plurality of closely spaced fingers ll. Between the fingers II are defined slot-like openings l2.
through which air under pressure is discharged laterally of the impeller during operation of the machine.
The impeller proper is rigidly fastened to the lower end of a hollow shaft [3, which is rotatably mounted in a bearing assembly I l. The latter provides for the introduction of air under pressure to the hollow shaft I 3, see the passage i5, Fig. 4, from piping l6, Fig. l, which is connected with any suitable source of pressure air, usually a blower (not shown). For this purpose, the center of the top member it of the impeller proper is provided with a receiving opening through which the lower end of shaft :3 extends, and a retaining nut I1 is screwed onto the end of the shaft.
In the machine as a whole, the bearing assembly I4 is supported by structural members 18, which bridge the open top of a tank-like container 19 for pulp. The impeller shaft l3 and impeller proper, thus, depend deeply into the container [9, and, during operation of the machine, are surrounded by a body of pulp 20 and a superimposed column of froth 2 l, somewhat as indicated. A set of peeler blades 22, customary against the abrasive action of the pulps operated upon. Accordingly, the impeller proper is here illustrated as comprising a rigid metal core 26, which is formed as a casting, fabricated from steel, or otherwise constructed, and a protective covering 21, which is ordinarily resilient rubber applied to the core by the use of a vulcanizing mold, but which may be any other abrasive-resistant material suitably applied.
In accordance with the present invention, a plurality of holes or perforations 28 are provided through the top member I0 of the impeller proper in preferably a symmetrical arrangement which comprehends the entire area of such top member. As illustrated, see Fig. 3, there are inner and outer circles of openings 28 concentric with the shaft I 3 and with the circumferential periphery of the top member Hi. There are the same number of openings 28 in each of these circles, the spacing of individual openings in the outer circle being twice as great as in the inner circle.
This particuiar arrangement of openings has been found to produce very satisfactory results in the #36 Agitair machine, which has a volume of twenty-two cubic feet per cell. In such instance, best results are obtained when the respective openings 28 are from to inch in diameter, depending upon operating conditions. It should be noted that the particular arrangement, spacing, and size of the openings will vary somewhat in accordance with the size and type of machine and with the operating conditions in particular instances of use, though the teachings hereof with respect to the reasons for and the action of these openings must be taken into account in the making of any such variations.
The hollow conical impeller of Fig. 5 is mounted in the flotation machine of Fig. 1 similarly to the mounting of the flat disk impeller described above. It comprises a hollow conical top member 30, having an open bottom and depending fingers 3!. A plurality of openings or perforations 32 are provided through the top member at in similar fashion to the holes 28 of the previously described embodiment.
In the operation of both the flat disk and hollow conical types of impellers, air under pressure is forced down through the hollow shaft to the underside of the top member of the impeller for discharge, in major degree, laterally through the slot-like openings between the fingers. In both, a limited proportion of such air discharges upwardly through the several openings provided in the top member, and establishes localized, upwardly-directed flows which cut across the normal centrifugal flow of pulp in the vicinity of the top of the impeller and break up such centrifugal flow. Thus, strong impingement of pulp streams against the sides and corners of the container I9 is prevented, and consequent boiling of the pulp at these locations eliminated; Furthermore, the usual tendency for the pulp to form a vortex around the impeller shaft is greatly reduced, thereby largely eliminating sucking of froth back into the body of pulp.
It should be noted, also, that the openings 28 and 32 in the respective impellers shown serve to bleed off air which may otherwise have a tendency to become trapped within the impeller, and that any sudden surges of air from the pressure supply will be evened out.
The net operating result is that much greater quiescence of froth is obtained than has been possible heretofore, froth flow is even, improved aeration is had, and greater recoveries are achieved with fewer mechanical and other diniculties. Furthermore, any tendency toward the formation of a heavy flocculated froth at the center of the cell appears to have been eliminated.
From the above and as is apparent from the drawing, the collective discharge capacity of the relatively small openings 28, or 32, is considerably less than the collective discharge capacity of the major discharge ports [2.
Whereas this invention is here illustrated and described with respect to particular preferred forms thereof, it should be understood that various changes may be made therein and various other forms constructed on the basis of the teachings hereof, by those skilled in the art, without departing from the scope of the claims which follow.
1. In combination with a flotation cell of subaeration type, an impeller having a closed top of circular formation, a substantially entirely open bottom, and side-delivery ports defined by a plurality of closely spaced fingers which depend from and about the rim of said closed top; a plurality of openings distributed throughout said closed top of the impeller, said openings having relatively low discharge capacity as compared to said side delivery ports and being fewer in number, whereby major discharge capacity is disposed sidewardly of said impeller; means mounting the impeller for rotation; and means for supplying air under pressure beneath said closed top of the impeller.
2. An impeller for subaeration flotation machines, comprising a closed top member of circular formation, a plurality of closely spaced fingers depending from the rim of said top member in mutually spaced relationship to define a plurality of side-discharge ports; and a plurality of openings distributed throughout the said closed top member, the bottom of said impeller being substantially entirely open, and said openings having relatively low discharge capacity as compared to said side delivery ports and being 6 fewer in number, whereby major discharge capacity is disposed sidewardly of said impeller.
3. An impeller for subaeration flotation machines, comprising a substantially fiat disk; a plurality of closely spaced fingers depending from the outer periphery of said disk to define a plurality of side-discharge ports; and a plurality of openings passing through and distributed substantially throughout said flat disk, the bottom of said impeller being substantially entirely open, and said openings having relatively low discharge capacity as compared to said side delivery ports and being fewer in number, whereby major discharge capacity is disposed sidewardly of said impeller.
4. An impeller for subaeration flotation machines, comprising a hollow, substantially conical body, having its bottom substantially entirely open; a plurality of fingers depending in closely spaced. relationship from the bottom rim of said body to define a plurality of side-delivery ports; and a plurality of openings passing through and distributed substantially throughout said body, said openings having relatively low discharge capacity as compared to said side delivery ports and being fewer in number, whereby major discharge capacity is disposed sidewardly of said impeller.
5. The combination recited in claim 3, wherein the said openings passing through the flat disk are arranged in a plurality of circles concentric with the circumference of the disk and spaced progressively inwardly thereof, the openings in any given circle being substantially equally spaced, and there being the same number of openings in each circle, whereby no two openings are aligned radially of said impeller.
6. The combination recited in claim 4, wherein the said openings passing through the conical body are arranged in a plurality of circles concentric with the circumstance of the base of said body and spaced progressively inwardly of said body, the openings in any given circle being substantially equally spaced, and there being the same number of openings in each circle, whereby no two openlngs are aligned radially of said impeller.
JOHN T. POTTS.
References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,242,445 Ittner Oct. 9, 1917 1,350,605 Greenawalt Aug. 24, 1920 1,374,446 Greenawalt Apr. 12, 1921 1,374,499 Greenawalt Apr. 12, 1921 2,05 ,065 Booth Sept. 22, 1936