US3471010A - Automatically controlled floatation apparatus and method - Google Patents

Description

H. H. PICK ET AL 3,471,010

AUTOMATICALLY CONTROLLED FLOATATION APPARATUS AND METHOD Oct. 7, 1969 Filed Nov. 21, 1966 INVENTORS:

L IV T 5 m w i S m WM 8 C R N 0 R T WC M T P A (A .w M H 8 S NWA AA w HR R K C W United States Patent 3,471,010 AUTOMATICALLY CONTROLLED FLOATATION APPARATUS AND METHOD Hans H. Pick and Ralph W. Crosser, Jr., Salt Lake City,

Utah, assignors to Kennecott Copper Corporation, New

York, N.Y., a corporation of New York Filed Nov. 21, 1966, Ser. No. 600,684 Int. Cl. B03b 13/04 US. Cl. 209-1 9 Claims ABSTRACT OF THE DISCLOSURE with such a flotation cell, an electrical capacitance probe arranged above the froth overflow lip of the cell.

The invention This invention relates to .method and apparatus for carrying out flotation procedures in the separation of particles of various materials, such as minerals of different types, by processes of froth flotation, wherein an aqueous pulp of the material particles to be separated is subjected to aeration in a flotation machine to produce a froth overflow carrying certain of the particles and a tailings discharge carrying the other particles.

Flotation machines are normally made up of a series of individual cells, with the feed material flowing from cell to cell. Froth rises in and overflows from each cell to a launder for segregated discharge, while the ailings from one cell flow into the next cell in line as the feed for that cell. It is important that the liquid level in each cell be controlled to maintain optimum conditions for separation of the material particles concerned. This is normally accomplished by means of gates between the individual cells regulating tailings discharge from one cell to a succeeding cell or from the last cell in line, the gates being individually manipulated toetfect the desired liquid level control. I

In some instances, instead of gates other types of tailings discharge devices are employed, for example, plug valves. Also, in some instances, flotation machines are not divided into cells, in which event a single tailing discharge controls the liquid level along the entire length of the machine.

Liquid levels in flotation machines have been automatically controlled heretofore by devices that sense the varying hydrostatic heads of the liquid pulp in the respective cells and that effect opening or closing of respective gates by feeding signals into motorized power systems for operating such gates.

In accordance with the present invention, however, the quantity of froth overflowing from a flotation cell is sensed continuously, and the tailings discharge gate for such cell is raised or lowered to a greater or lesser extent, or whatever other type of tailings discharge device may be used in the particular instance is appropriately manipulated, in accordance with variations in such quantity.

. Continuous sensing of the quantity of froth overflow can be effectively accomplished in various ways, which represent specific aspects of the present invention.

Thus, the froth passing over a small portion of the total length of the overflow lip of a flotation cell may be continuously conducted into a sensing device, comprismg a relatively small sampling vessel having gravity discharge opening such that a body of material, reflecting fluctuations in inflow to such vessel, is maintained in the vessel. A standard type of air bubbler tube detects changes in hydrostatic head of such body of material, which consists of froth repulped in the vessel by a continuous spray of water. By keeping the supply of spray Water consistent, the level of the body of repulped froth fluctuates in accordance with fluctuations in the level of froth overflow from the flotation cell, and such changes in level are continuously sensed by the air bubbler tube and used to control a suitable motivating device, such as an electric motor, for the tailings discharge device by means of suitable circuitry which may be of well known type.

Again, a sensing device in the form of a plate-type capacitance proximity probe may be employed, together with standard electrical control circuitry for the actuating motor. The detector plate of the probe is mounted above and in spaced relationship with the froth overflow lip of the flotation cell and extends lengthwise with such lip. It senses variations in froth overflow level by reason of corresponding changes in spacing of the surface of the overflowing froth from the detector plate.

Other suitable types of sensing arrangements may, of course, be used in place of those specifically indicated above, but such specifically indicated arrangements are presently believed to be the best modes of carrying out the invention and are, consequently, illustrated and described in detail.

In the drawing:

FIG. 1 is a schematic perspective view of a typical single cell flotation machine, with which is combined a sampling vessel and air-bubbler tube 'type of froth overflow level sensing arrangement;

FIG. 2, a schematic view showing the sampling vessel and a fragment of the froth overflow lip of the flotation machine in vertical central section, with parts of a standard wiring diagram connecting sensing components of such sampling vessel with actuating mechanism for raising and lowering the tailings discharge gate of the flotation machine, which mechanism and gate are shown inelevation.

FIG. 3, a fragmentary vertical section taken on the line 33 of FIG. 2 and drawn to a larger scale;

i FIG. 4, a similar view taken on the line 4--4 of FIG.

; and

FIG. 5, a view similar to that of FIG. 2 but showing a different form of the apparatus of the invention, wherein a plate-type capacitance probe is utilized to sense changes in the level of froth overflowing the froth-overflow lip of the machine.

Referring to the drawing:

In the embodiment of FIGS. l-4, the single cell flotation machine illustrated schematically is typical of standard installations. It comprises an elongate tank 10' into which flotation pulp is fed through a usual feed box 11.

As is common, a plurality of impellers (not shown) are mounted for rotation at the lower ends of respective ir'npeller shafts 12 powered by respective electric motors 13. Mineral-laden froth rises to the surface of the body of pulp in tank 10 and discharges into lounder 14 over an elongate froth overflow lip 15. As usual, the tailings pass into tailings-box 16 through submerged outlet openings (not shown) and discharge over tailings gate 17, either into a next succeeding cell (not shown) at a lower level,

for repeated flotation treatment, or directly to Waste if mined capacity, which in this instance, is a valved, gravity discharge Opening 18a, is fed with a continuously flowing sample of the over-flowing froth by means of a sampling launder 19. The vessel 18 is advantageously of inverted frusto-conical formation, converging to a bottom opening, 18a, and such opening is advantageously valved by means of a plug 20 at the end of a stem 21 that is movable upwardly and downwardly in a supporting arm 22. Thus, the size of discharge opening 18a can be predetermined as desired for any given operation of the machine, and a body of material can be established and continuously maintained in the vessel 18 to reflect variations in quantity of froth inflow from time to time.

Provision is made for re-pulping the froth samples as they pass through sampling vessel 18. In the illustrated instance, a spray ring 23 is positioned over the interior of the sampling vessel, being supplied with water through pipe 24 under the control of a valve, as indicated.

In order to automatically control the raising and lowering of tailings gate 17 in accordance with fluctuating froth overflow levels from the flotation tank 10, a bubble tube 25, supplied with low-pressure air from valved air supply lines 26, is positioned to dip below the normal liquid level in sampling vessel 18 and to detect changes in hydrostatic head of the body of re-pulped froth maintained in such vessel.

Pressure differentials are used in well known manner to control an electrical switch 27 of standard type, which regulates the supply of electricity through circuit 28 to a reversible motor 29 that is adapted to raise or lower tailings gate 17, depending upon the direction of operation of such motor on any given activation thereof. The particular direction of operation, either forward or reverse, will, of course, depend upon whether the hydrostatic pressure in vessel 18 is either lowered or raised to trip switch 27.

As here illustrated, the mechanism by which motor 29 either raises or lowers tailings gate 17 comprises a lever 30, fulcrumed at one end by a pivot mounting 31 positioned on top frame member 32a of tailings gate frame 32, and an eccentric drive connecting the output shaft 29a of the motor to the free end of the lever.

The usual handwheel mechanism for normally raising or lowering the gate is modified by rotatably mounting the hub, 33a, of such handwheel, 33, in a bearing mount 34 that is swiveled by stub pins 34a in lever 30. A split ring 35, FIG. 3, fits into a circumferential groove 36 of handwheel hub 33a and holds the handwheel in place as it is turned to screw the threaded stern 17a of gate 17 either upwardly or downwardly, such split ring being bolted to bearing mount 34, and the swivel mounting of pins 34a being sufiiciently loose to accommodate the small amount of arcuate movement occurring as lever 30 is raised and lowered.

As illustrated, the eccentric drive between motor 29 and lever 30 comprises a disk 37, FIG. 4, secured to motor shaft 29a and provided with a crank pin 37a, which is connected to the free end of lever 30 by means of a connecting rod 38. v

A different type of sensing arrangement is shown in FIG. 5, where an electrical capacitance proximity probe 40 is employed to directly detect changes in level of froth 41 overflowing lip 15. The changes in froth level produce corresponding changes incapacitance by reason of increase or decrease of the dielectric space or air gap 42 between an elongate detector plate 40!: and the superficial surface of the overflowing froth 41. Such detector plate should, for best results, extend along substantiallythe entire length of a portion of overflow lip 15 that is s11b, ject to the action of an impeller unit represented by a shaft 12 and motor 13. In the particular cell illustrated, this is approximately one-quarter the length of lip 15, and the detector plate advantageously extends symmetrically at opposite sides of such shaft 12 and motor 13 and parallel with the superficial surface of the overflowing froth,

as indicated in FIG, 5, to provide a control for the en: tire cell. It is obvious that the mineral content in the froth will play a part in the electrical output of the sensing device as well as changes in the froth levels.

The detector plate 40a should extend over a representative area of the overflowing stream of froth. The usual downwardly-sloping apron 15a of the overflow lip of the flotation cell provides an effective detection surface for the overflowing froth. It is preferable that the width of detector plate 40a be commensurate therewith, as illustrated. Both the capacitance probe 40 and the electrical control circuit therefor (merely indicated at 43), may be of standard type, such as provided by the commercial level measuring and indicating system manufactured and sold by Aeronautical and Instrument Division, Robertshaw Controls Company, Anaheim, Calif, as detailed in its Bulletin 30 under the trade designation Level-Tel Model 305, which advantageously includes a visual display unit 44 to indicate how the system is operatingand to house various circuit components, which need not be detailed here.

We claim:

1. Automatically controlled flotation apparatus, including in combination:

a flotation cell, comprising a tank having an elongate froth overflow lip, pulp feed, and variable tailings discharge means;

power means for varying said tailings discharge means;

means for continuously sensing variations in the quantity of froth overflowing said lip of the flotation cell; and

control circuitry between the sensing means and the power means for translating sensed changes in froth quantity into related changes in power applied to said power means, whereby the tailings discharge will be varied in accordance with variations in froth quantity. i

p 2. Apparatus as recited in claim 1, wherein the means for sensing variations in the quantity of froth overflowing the lip of the flotation cell comprises:

a froth sampling vessel having continuously operating discharge means of predetermined capacity for material flowing into said vessel;

a sampling launder leading from a localized area along said lip of the flotation cell into said sampling vessel;

means for continuously mixing a re-pulping liquid with samples of froth in said sampling vessel;

an air-bubbler tube in said sampling vessel, with its discharge end disposed below the normal level of'repulped froth therein and below the lowest point of variation of said level;

means for supplying air under pressure to said bubbler tube; and

wherein the control circuitry between the sensing means and the power means includes electrical switch means responsive to changes in pressure of the air being supplied said bubbler tube.

3. Apparatus as recited in claim 2, wherein the sampling vessel is of inverted frusto-conical formation, with the discharge means being a valved opening at the downwardly-directed, convergent bottom of said vessel.

4. Apparatus as recited in claim 2 wherein the means for continuously mixing a re-pulping liquidwith samples of froth in the sampling vessel comprises a spray nozzledirected inwardly of said vessel, and means for'supplying water under pressure to said spray nozzle.

5. Apparatus as recited in claim 1, wherein the means for sensing variations in the quantity of froth overflowing the lip of the flotation cell comprisesz' an electrical capacitance probe having an elongate detector plate spaced above said lip of the flotation cell and extending along the length thereof.

6. Apparatus as recited in claim 5,'wherein'the detector plate has a width substantially equal to the width of the apron portion of the overflow lip.

7. A method of automatically controlling the operation of a flotation machine, comprising continuously sensing the quantity of froth overflow during operation of the machine to produce signals indicative of variations in said quantity; and utilizing said signals to control the quantity of tailings discharged from the machine so as to keep the pulp level in the machine substantially constant. 8. A method as' recited in claim 7, wherein the quantity of froth overflow is sensed by continuously repulpin'g a portion of the normal froth overflow from the machine, and by sensing variations in pressure of air discharged below the fluctuating surface of the repulped portion of said froth overflow.

of froth overflow is sensed on the basis of variations in electrical capacitance brought about by variations in froth discharge across the froth overflow lip of the machine.

References Cited UNITED STATES PATENTS 1,708,075 4/ 1929 Allen.

2,931,502 4/1960 Schoeld 209-164 3,255,882 6/1966 McCarty -.1 209-1 3,282,217 11/1966 Slover l37392 X HARRY B. THORNTON, Primary Examiner R. HALPER, Assistant Examiner US. Cl. X.R.

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