US3393802A - Aerating assembly for froth flotation cells - Google Patents

Description

July 23, 1968 LOGUE ET AL 3,393,802

AERATING ASSEMBLY FOR FROTH FLOTATION CELLS Original Filed Feb. 5, 1964 2 Sheets-Sheet 1 A fh C DINVENTOIf/S r W aman, r: Leland H. Logue ATTORNEYS July 23, 1968 LOGUE ET AL 3,393,802

AERATING ASSEMBLY FOR FROTH FLOTATION CELLS 5, 1964 2 Sheets-Sheet 2 Arthur C. Damon, Jr: 1 1g- BY Leland H. Logue ATTORNEYS United States Patent 3,393,802 AERATING ASSEMBLY FOR FROTH FLOTATION CELLS Leland H. Logue, Denver, and Arthur C. Daman, Jr., Englewood, Colo., assignors to Denver Equipment Company, Denver, Colo., a corporation of Colorado Continuation of application Ser. No. 342,068, Feb. 3, 1964. This application Dec. 14, 1966, Ser. No. 601,804 Claims. (Cl. 209169) ABSTRACT OF THE DISCLOSURE Froth flotation machine of the hog-trough type having mechanical aerator and agitator assemblies recirculating pulp from upper portion of contained pulp body as sole pulp feed to enclosed impellers and flooding impeller intake above elevation of gas input thereto.

This application is a continuation of applicants application Ser. No. 342,068, now abandoned, filed Feb. 3, 1964 for Aerating Assembly for Froth Flotation Cells.

This invention relates to an aerating assembly for froth flotation cells and is an improvement of the aerating mechanism shown in Logue Patent No. 2,928,543, dated Mar. 15, 1960, assigned to the assignee of this application.

Froth flotation practices have undergone substantial changes in recent years, including the treatment of much coarser particles than could be effectively concentrated by earlier treatment methods. As an example, potash ores are now treated commercially in a size range of minus 6 plus 14 mesh. In order to obtain an effective flotation of the coarser particles in such a pulp, a large volume of aerating gas is introduced under pressure and is distributed through the pulp body in the cell to elevate the conditioned particles to the surface.

Where the gas is delivered into a covered impeller for mixing with pulp and discharge across the periphery of the impeller, the release of the gas within the impeller enclosure develops a back pressure condition which allows gas to escape through openings in the cover producing erratic and inefficient aeration. Such erratic aeration usually requires an undue amount of operator regulation and materially reduces flotation efficiency.

It is an object of our invention to provide a simple, durable and efficient aerator assembly for froth flotation cells which distributes large volumes of aerating gas in a uniform manner through the pulp circulated by the assembly.

Another object of this invention is to provide a simple, economical and eflicient aerating assembly which is capable of selective control of the aerating action of a flotation cell with a minimum of operator control.

A further object of our invention is to provide a novel aerating assembly for flotation cells which has provision for offsetting back pressures in discharging large volumes of aerating gas into the flow of pulp being circulated by said assembly.

Other objects reside in novel details of construction and novel combinations and arrangements of parts, all of which will be set forth in the following description.

One advantage of the arrangement of our aerating assembly is that it may be installed in existing flotation cells as a replacement for other aerating units, and also may be incorporated in new equipment designed to utilize such an aerator. One of the innovations of the present invention is the provision for recirculation of pulp from an upper level in the cell into and through the impeller enclosure which thereby establishes a displacement effect which moves previously settled solids into suspension with at least a part of the material so elevated being entrained in the recirculating flow and directed into the impeller where it is subjected to additional aeration. As a consequence, the particles adequately conditioned for flotation which are recirculated in this manner are elevated through the pulp in the impeller discharge and are carried to the surface as concentrate.

Another innovation is the utilization of a restrictive intake for the impeller enclosure establishing a gravitational pulp flow creating a hydrostatic seal over the impeller so that the aerating gas discharged onto the impeller is prevented from developing a back pressure escape and is discharged across the periphery of the impeller in a uniform manner effecting substantially uniform distribution throughout the pulp body.

This control permits gas introduction under relatively high pressure, i.e., pressure in excess of normal for this type of impeller enclosure. However, it should be understood that such high pressure must be less than the hydrostatic pressure at the intake opening in order to direct the gas flow into converging relation to the pulp being subjected to the mixing action of the impeller.

The essential features of the invention may be incorporated in a variety of structural embodiments and typical embodiments have been illustrated in the accompanying drawings. The practice of our invention will be described with reference to said drawings. In the drawings, in the several views of which like parts bear similar reference numerals,

FIG. 1 is a vertical section of one embodiment of an aerating assembly according to our invention illustrated as installed in a flotation cell;

FIG. 2 is a fragmentary vertical section of another embodiment of aerating assembly illustrated in relation to the bottom portion of a flotation cell in which it is installed;

FIG. 3 is a vertical section of a third embodiment of aerating assembly utilizing features of our invention; and

FIG. 4 is a vertical section of still another embodiment utilizing features of our invention and shown as installed in a froth flotation cell.

Referring first to FIG. 1, the flotation cell is shown as having a flat bottom 10, an upright rear wall 11 and a forward upright wall having an upper inclined portion 12 terminating in a froth overflow lip 12x. While omitted in the illustration, it will be understood that superstructure will be mounted at the top of the cell in the usual manner for support of drive components, control members and the like. A plate or beam 13 is shown in FIG. 1 as representing superstructure or corresponding supporting members. A shaft 14 is journaled for rotation in a bearing assenmbly 15 or beam 13 and extends downwardly to a point adjacent but spaced from cell bottom 10.

A dished impeller 16 is secured on the lower end of shaft 14 and has upstanding blades 16x in radial arrangement. A hollow column 17 is supported in a depending position from beam 13 and in enclosing relation to shaft 14. A cover member 18 is secured on the lower end of column 17, and has a central opening 18a and an imperforate top portion 18b extending outwardly therefrom. The column 17 has one or a plurality of upper openings 19 functioning as a pulp inlet providing a recirculating flow of pulp onto impeller 16.

A conduit 20 depends from beam 13 in encompassing relation to shaft 14 and has a sealed upper end secured on the beam and an open lower end 20x disposed in close proximity to the top of impeller 16 and at a lower elevation than the top of :a flanged portion 18x defining the central opening 18a. The cover member shown in FIG. 1 preferably has a series of depending vanes 18:: in radial arrangement which form a partial enclosure through which aerated pulp passes during discharge from the impeller. The flanged portion 18x is quite thick and in association with the lower end portion x of conduit 20 defines a restricted or restrictive passage through which the pulp discharges onto the impeller 16. A valve-controlled conduit 21 delivers large volumes of aerating gas into conduit 20 for discharge through its lower end 20x.

The released gas flows onto the dished surface of impeller 16 onto which pulp is delivered from the interior of column 17. The impeller is rotated at high speed and the confining relation of the cover and the proximity of the blades to the cover produce an intense beating and mixing action as the aerated pulp is directed to the periphery by the centrifugal action of the impeller. In such action, back pressures develop which may cause the gas flow to seek escape up column 17. The restriction of the passage through central opening 18a delays the gravitational flow of pulp from the column intake and maintains a liquid fill in the lower portion of the column which functions as a hydrostatic seal to prevent gas escape into column 17.

It will be apparent that the aerating assembly of FIG. 1 will deliver selected volumes of aerating gas through inlet 21 and conduit 20 onto impeller 16. While the impeller is rotating at high speed, pulp circulating in the cell is entrained through openings 19 in a larger volume than it can discharge through the restricted passage in opening 18a and stands to a considerable distance above said opening. This gives an effective head equivalent to the full depth of pulp in the cell.

As a consequence, all of the gas flow passing onto impeller 16 through end 20x is subjected to the beating and mixing action imparted by blades 16x and is discharged in fine bubble formation distributed through the pulp impelled across the periphery of the impeller by its centrifugal action. The tendency to develop a back pressure condition in such discharge is overcome by the depth of the liquid column descending through opening 18a, and the only escape for the gas input is with the discharge flow passing from the periphery of the impeller.

The elimination of back pressure release permits the operator to set the valve of inlet 21 to supply any required volume of gas and the operation thereafter requires no additional operator control until a new aerating requirement is determined. The mixing of pulp and gas etfects a substantially uniform dstribution of aerating gas in fine bubble formation throughout the circulating pulp body in the cell.

The aerated pulp discharge which distributes the gas in fine bubble formation is a part of the recirculating displacement effect that prevents solids stratification in the pulp body and fluidizes and elevates previously settled solids which otherwise would remain inert and develop a sanding up effect on the cell bottom. This action permits selective withdrawal of pulp from an upper portion of the circulating body for return through the impeller intake. In such environment and with proper aeration, the coarse sizes of the pulp, when properly conditioned, float readily and an eflicient flotation concentration is obtained, even with ore ground in a relatively coarse size range.

The embodiment of our invention shown in FIG. 2 functions similarly to the assembly shown in FIG. 1, but eliminates the column enclosing the conduit through which the gas is introduced onto the impeller and has means for varying the size of the restricted passage. While details of the cell structure are not shown in FIG. 2, they are essentially the same as in FIG. 1 and comprise a bottom 10, an upright rear wall 11 and a forward wall 12. A shaft 14 carries the impeller 16 disposed in close proximity to cell bottom 10. An air conduit 20 delivers aerating gas onto impeller 16 in the manner previously described.

The cover 28 in this form is generally similar to cover 18 and has a flanged portion 28x defining a central opening 28a, and the remaining top surface 28b is imperforate. Connectors 27 secured on conduit 20 are attached to the top portion 23b. Threaded rods 26 actuated from the top of the cell extend through blocks 25 on conduit 20 and carry at their lower ends an annular wedge-shaped portion 26x which is raised and lowered by the operator to selectively vary the effective size of the restricted passage through which circulating pulp descends onto the impeller.

This arrangement also provides a hydrostatic seal which effectively prevents back pressure leakage and regulates the volume of pulp recirculated from the cell onto the impeller. Some adjustment of the position of the wedgeshaped member 262: in opening 28a may be required in conjunction with the changed setting of the valve regulating gas input to column 20, but once the desired aeration eifect is attained, the unit will operate for long periods without operator control.

The aerator unit shown in FIG. 3 functions in the same manner as the FIG. 1 embodiment but differs therefrom in structural arrangement. The same type of cell is shown having bottom 10, upright rear wall 11, and a forward wall 12 terminating in an overflow lip 12x at its top. A shaft 14 is supported for rotation in a bearing assembly 15 on the beam or superstructure 13 and an impeller 16 is secured at the lower end of the shaft for rotation therewith. The shaft is enclosed by a conduit 20 having an open lower end 20x and a valve-controlled inlet 21 delivers aerating gas into conduit 20' for discharge onto impeller 16.

A tubular member 30, open at both ends seats on and is secured to a cover member 31 overhanging the impeller 16. The member 30 may be supported in any suitable manner. As shown, a spider 39 secured on conduit 20 is connected at points of contact with member 30 to provide such support. Cover member 31 has a central opening 31a bordered by an upstanding flange 31x and its top surface 31b is imperforate to confine material moving from opening 31a toward the periphery of the impeller.

In the embodiment shown in FIG. 3, pulp in the cell is recirculated through the opening in the top of member 30 and descends into the restricted passage 31a between flange 31x and conduit end portion 20x thereby maintaining a hydrostatic seal over the impeller. Gas descending through conduit 20 onto impeller 16 under pressure seeks its escape in the space between the dished surface of impeller 16 and the undersurface of cover 31. In such flow, it converges and is mixed with pulp entering from passage 31a and is subjected to an intense beating and mixing action by the impeller blades before it discharges across the periphery of the impeller and passes beyond the depending surfaces of cover 31. Back pressure gas release from impeller 16 is prevented by the liquid column above opening 31a, and the entire gas input is discharged in a uniform manner.

The form of aerator unit shown in FIG. 4 is quite similar to the embodiment shown in FIG. 2 but omits the adjustment arrangement in the passage through which pulp descends onto the impeller 16. As shown, the cell has a bottom 10, upright rear wall 11 and forward wall 12 terminating in an overflow lip 12x. The shaft 14 on which the impeller 16 is disposed adjacent bottom 10 is supported in a bearing assembly 15 on beam 13, and is enclosed by a conduit 20 having a valve-controlled gas inlet 21.

The aerating components of this unit include a cover 28, as previously described, supported from column 20 by a plurality of connectors 37, and the impeller 16 is secured on the lower end of shaft 14 with the tops of its blades disposed in closely spaced relation to the undersurface of cover 28. Circulating pulp of the cell is drawn into the impeller enclosure through the restricted opening 28a and functions as a hydraulic seal to prevent escape of gas if back pressures develop.

Consequently, the pressure discharge of gas from the open end 20x of column 20 is confined within the impeller enclosure and the gas is subjected to the beating and mixing action of the blades in its progressive movement to the point of discharge at the periphery of the impeller.

It will be apparent from the foregoing description of the several embodiments shown in the drawings that the opening in the cover through which recirculating pulp descends onto the impeller is restricted sufliciently to imsure maintenance of a substantial head of liquid over the opening and under hydrostatic pressure to effectively prevent any gas release through said opening under whatever back pressures may develop in the impeller enclosure.

This control feature permits introduction of large volumes of gas under pressure which gas is effectively dispersed through the circulating pulp and provides an intense aeration which after discharge from the impeller raises the coarser sizes of conditioned particles to the surface where they are collected and discharged as concentrate.

Another feature common to the several structural embodiments described hereinbefore is that the pulp-conducting means by which recirculated pulp from the cell is directed through the cover opening or passage has an intake capacity exceeding the discharge capacity of the cover opening. This condition is due to the size or shape of the flow-directing surfaces and the 'volume of pulp available at the top of the opening which is maintained under substantial hydrostatic pressure. Consequently, the restriction of the passage in its various forms provides an effective seal against any back pressure tendency and forces the discharged gas to seek its escape across the periphery of the impeller.

In the forms shown in FIGS. 2 and 4, the upstanding flange bordering the central opening of the cover functions as the pulp conducting means, and is shaped to provide a greater intake capacity at its top than the discharge capacity of the lower portion of the opening. If desired, the flanged portion may be extended upwardly to a higher level to return pulp from an upper portion of the pulp body to the intake flow. In the other forms in which a hollow member conducts recirculating pulp to the cover opening, the intake capacity of such member exceeds its discharge capacity and produces a corresponding effect.

In all the forms described, the tendency of solids in the pulp to stratify within the pulp body is effectively offset by the recirculating action which returns a sufficient quantity of dilute pulp containing solids in finer sizes in the flow delivered onto the impeller to displace and fluidize settled solids on the bottom of the cell beyond the impeller. This displacement eflect maintains solids in all sizes in suspension, thereby permitting the flotation action to function continuously under optimum conditions.

We claim:

1. In a froth flotation cell having a froth overflow in its upper portion and an aerating assembly for circulating and aerating pulp in the lower portion of the cell, said assembly including 'a vertical rotary shaft, an impeller mounted on the lower end of the shaft for conjoint rotation therewith, a stationary cover member secured in closely spaced overhanging relation to the impeller and having a central intake opening, a stationary hollow conduit encompassing and spaced from said shaft and having a bottom discharge outlet at the central intake opening of the cover member, said conduit being sealed against admission of pulp throughout its length and having an inlet for aerating gas, means for delivering an aerating gas under pressure through the conduit inlet for discharge onto the impeller, said conduit being of lesser diameter than the cover intake opening and defining with the sides of said opening a restricted passage through which pulp descends onto the impeller, pulp-recirculating means exteriorly of the hollow conduit having a discharge passage into the restricted passage and having a submerged pulp intake passage in an upper portion of the cell, and the sides of the cover intake opening extending to a plane above the discharge outlet of the hollow conduit so as to confine pulp descending through the restricted passage in gas sealing relation, and means for varying the effective volume of said restricted passage inclusive of varying means supported in spaced relationship between said impeller and said cover member, said varying means being vertically adjustable.

2. In a froth flotation cell having a froth overflow in its upper portion and an aerating assembly for circulating and aerating pulp in the lower portion of the cell, said assembly including a vertical rotary shaft, an impeller mounted on the lower end of the shaft for conjoint rotation therewith, a stationary cover member secured in closely spaced overhanging relation to the impeller and having a central intake opening, a stationary hollow conduit encompassing and spaced from said shaft and having a bottom discharge outlet at the central intake opening of the cover member, said conduit being sealed against admission of pulp throughout its length and having an inlet for aerating gas, means for delivering an aerating gas under pressure through the conduit inlet for discharge onto the impeller, said conduit being of lesser diameter than the cover intake opening and defining with the sides of said opening a restricted passage through which pulp descends onto the impeller, pulp-recirculating means including a hollow imperforate column member in sealed connection at its lower end with the cover member and extending upwardly into the pulp body a substantial distance above the cover member in concentric relation with said hollow conduit, said column member 'hav ing a submerged pulp intake opening at the upper portion of the pulp body providing the sole pulp intake for the cell and enclosing the intake opening of the cover member at its lower end to provide a discharge passage into said restricted passage, and the sides of the cover intake opening extending to a plane above the discharge outlet of the hollow conduit so as to confine pulp descending through the restricted passage in gas sealing relation.

3. In a froth flotation cell having a froth overflow in its upper portion and an aerating assembly for circulating and aerating pulp in the lower portion of the cell, said assembly including a vertical rotary shaft, an impeller mounted on the lower end of the shaft for conjoint rotation therewith, a stationary cover member secured in closely spaced overhanging relation to the impeller and having a central intake opening, a stationary hollow conduit encompassing and spaced from said shaft and having a bottom discharge outlet at the central intake opening of the cover member, said conduit being sealed against admission of pulp throughout its length and having an inlet for aerating gas, means for delivering an aerating gas under pressure through the conduit inlet for discharge onto the impeller, said conduit being of lesser diameter than the cover intake opening and defining with the sides of said opening a restricted passage through which pulp descends onto the impeller, a hollow imperforate column member in sealed connection at its lower end with the cover member and extending upwardly into the pulp body a substantial distance above the cover member, said column member having a submerged pulp intake opening at the upper portion of the pulp body providing the sole pulp intake for the cell and enclosing the intake opening of the cover member at its lower end to provide a discharge passage into said restricted passage, and the sides of the cover intake opening extending to a plane above the discharge outlet of the hollow conduit so as to confine recirculating pulp descending into and through the restricted passage in gas sealing relation.

4. In a froth flotation machine having a froth overflow in its upper portion and an aerating assembly for circulating and aerating pulp in the lower portion of the machine, said assembly including a vertical rotary shaft, an impeller mounted at the lower end of the shaft for conjoint rotation therewith, a stationary cover member secured in closely spaced overhanging relation to the impeller and having a central intake opening, a stationary hollow conduit encompassing and spaced from said shaft and having a bottom discharge outlet at the central intake opening of the cover member, said conduit being sealed against admission of pulp throughout its length and having an inlet for aerating gas, means for delivering an aerating gas through the conduit inlet for discharge onto the impeller, said conduit being of lesser diameter than the cover intake opening and defining wtih the sides of said opening a restricted passage through which pulp descends onto the impeller, pulp recirculating means exteriorly of the hollow conduit, inclusive of an upstanding portion having an upper pulp intake opening at an elevation above the bottom outlet of the conduit, said pulp intake opening being submerged in the pulp body directly above the impeller and providing the sole pulp intake for the impeller, and the intake capacity of the intake opening of said pulp recirculating means being greater than the discharge capacity of said restricted passage thereby establishing a continuous flooding effect over the intake opening of the cover member and above the bottom discharge outlet of the gas supply conduit for delivering mixed flows of gas and recirculated pulp directly downward into the impeller enclosure.

5. In a froth flotation machine having a froth overflow in its upper portion and an aerating assembly for circulating and aerating pulp in the lower portion of the machine, said assembly including a vertical rotary shaft, an impeller mounted at the lower end of the shaft for conjoint rotation therewith, a stationary cover member secured in closely spaced overhanging relation to the impeller and having a central intake opening, a hollow conduit encompassing and spaced from said shaft and having a bottom discharge outlet at the central intake opening of the cover member, said conduit being sealed against admission of pulp throughout its length and having an inlet for aerating gas, means for delivering an aerating gas through the conduit inlet for discharge onto the impeller, said conduit being of lesser diameter than the cover intake opening and defining with the sides of said opening a restricted passage through which pulp descends onto the impeller, said cover member having an associated upstanding portion adjoining its central intake opening inclusive of an upper portion intake opening at an elevation above the bottom of the outlet of the conduit, and the intake capacity of the intake opening of said pulp recirculating means being greater than the discharge capacity of said restricted passage thereby establishing a continuous flooding effect over the intake opening of the cover member and above the bottom discharge outlet of the gas supply conduit for delivering mixed flows of gas and recirculated pulp directly downward into the impeller enclosure.

6. In a froth flotation cell having a froth overflow in its upper portion and an aerating assembly for circulating and aerating pulp in the lower portion of the cell, said assembly including a vertical rotary shaft, an impeller mounted at the lower end of the shaft for conjoint rotation therewith, a stationary cover member secured in closely spaced overhanging relation to the impeller and having a central intake opening, a stationary hollow conduit encompassing and spaced from said shaft and having a bottom discharge outlet at the central intake opening of the cover member, said conduit being sealed against admission of pulp throughout its length and having an inlet for aerating gas, means for delivering an aerating gas through the conduit inlet for discharge onto the impeller, said condit being of lesser diameter than the cover intake opening and defining with the sides of said opening a restricted passage through which pulp descends onto the impeller, pulp-recirculating means exteriorly of the ho]- low conduit including a hollow imperforate column member in sealed connection at its lower end with the cover member and extending upwardly into the pulp body a substantial distance above the cover member, said column member having an upper pulp intake opening at an elevation above the bottom of the outlet of the conduit, said pulp intake opening being submerged in an upper portion of the pulp body directly above the impeller and providing the sole pulp intake for the impeller, and the intake capacity of the intake opening of said pulp recirculating means being greater than the discharge capacity of said restricted passage thereby establishing a continuous flooding effect over the intake opening of the cover member and above the bottom discharge outlet of the gas supply conduit for delivering mixed flows of gas and recirculated pulp directly downward into the impeller enclosure.

7. A cell as defined in claim 6, in which the means for delivering aerating gas through the conduit inlet is an opening to atmosphere above the pulp level in the-cell.

8. In a froth flotation cell having a froth overflow in its upper portion and an aerating assembly for circulating and aerating pulp in the lower portion of the cell, said assembly including a vertical rotary shaft, an impeller mounted on the lower end of the shaft for conjoint rotation therewith, a stationary cover member secured in closely spaced overhanging relation to the impeller and having a central intake opening, a stationary hollow conduit encompassing and spaced from said shaft and having a bottom discharge outlet within the central intake opening of the cover member and below the top of said intake opening, said conduit being sealed against admission of pulp throughout its length and having an inlet for aerating gas, means for delivering an aerating gas under pressure through the conduit inlet for discharge onto the impeller, said conduit being of lesser diameter than the cover intake opening and defining with the sides of said opening a restricted passage through which pulp descends onto the impeller, pulp-recirculating means inclusive of a tubular member in sealed connection at its lower end with the cover member and extending upwardly into the pulp body a substantial distance above the cover member, said tubular member having an upper pulp intake opening at an elevation above the bottom outlet of the conduit, said pulp intake opening being submerged in the upper portion of the pulp body directly above the impeller and providing the sole pulp intake for the impeller, the tubular body between the intake opening and the sealed connection being imperforate and enclosing the restricted passage, and the intake capacity of the intake opening of said pulp recirculating means being greater than the discharge capacity of said restricted passage thereby establishing a continuous flooding effect over the intake opening of the cover member and above the bottom discharge outlet of the gas supply conduit for delivering rnixed flows of gas and recirculated pulp directly downward into the impeller enclosure.

9. A cell as defined in claim 8, in which the hollow conduit, the tubular member and the central intake opening are in concentric arrangement.

10. In a froth flotation cell having a froth overflow in its upper portion and an aerating assembly for circulating and aerating pulp in the lower portion of the cell, said assembly including a vertical rotary shaft, an impeller mounted on the lower end of the shaft for conjoint rotation therewith, a stationary cover member secured in closely spaced overhanging relation to the impeller and having a central intake opening, a stationary hollow conduit encompassing and spaced from said shaft and having a bottom discharge outlet at the central intake opening of the cover member, said conduit being sealed against admission of pulp throughout its length and having an inlet for aerating gas, means for delivering an aerating gas under pressure through the conduit inlet for discharge onto the impeller, said conduit being of lesser diameter than the cover intake opening and defining with the sides of said opening a restricted passage through which pulp descends onto the impeller, pulp-recirculating means exteriorly of the hollow conduit including a hollow irnperforate column member in sealed connection at its lower end with the cover member and extending upwardly into the pulp body a substantial distance above the cover member, said column member having a submerged pulp intake opening at the upper portion of the pulp body providing the sole pulp intake for the cell and enclosing the intake opening of the cover member at its lower end to provide a discharge passage into said restricted passage, and the intake capacity of the intake opening of said pulp recirculating means being greater than the discharge capacity of said restricted passage thereby establishing a continuous flooding effect over the intake opening of the cover member and above the bottom discharge outlet of the gas supply conduit for delivering mixed flows of gas and recirculated pulp directly downward into the impeller enclosure.

References Cited UNITED STATES PATENTS HARRY B. THORNTON, Primary Examiner.

10 ROBERT HALPER, Assistant Examiner.

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