GB2229773A - Apparatus and method for providing a controlled flow of foam - Google Patents

Abstract

A device for controlling the flow of foam for use in separating mineral particles from ore wherein an expandable container (9) receives foam at the rapid flow rate of a foam generator until the expandable container is substantially full of foam and then to dispense the foam at a lower flow rate by applying a pressurized gas to gradually push the foam out of the container. The container may be defined by a bellows or a cylinder (10) variable in volume by a piston (12). In operation foam supplied by a generator (8) flows into the container (9) through an opened solenoid valve (32). As the container fills with foam, gas previously admitted to a chamber (11) is discharged through a solenoid valve (36) until the container is filled, at which time a switch (40) is actuated. The switch causes the valves (32, 36) to close and a valve (34) to open so that pressurised gas from a source (22) collapses the container and expels the foam through a nozzle (50). <IMAGE>

Description

DEVICE FOR CONTROLLING THE FLOW OF FOAM Background of the Invention The present invention pertains to a device for controlling the production and flow of foam at low flow rates and is especially useful in connection with a froth flotation apparatus for separating minerals.

Small bubble foam generators are known, as described in my U.S. Patents No. 3,811,660 and 4,400,220, which are hereby incorporated by reference. These generators produce foam with small bubble size at fairly high rates, which is useful for many applications, such as the use of foam for dust suppression. However, there are some applications in which my small bubble foam is needed at low flow rates.

In accordance with my U.S. Patent No. 3,811,660, it is necessary to cause the air, water, and surfactant mixture to be subject to "substantial agitation" to produce small bubble foam. This process is performed by causing the mixture to flow at or above a minimum velocity through a pipe, hose or foamer (a unit having "tortuous passages"), or through a foamer as shown in my U.S. Patent No. 4,207,202 which is hereby incorporated by reference.

Many applications for "small bubble" foam require very small flow rates of the foam. These rates may be less than 1/16 gallon per minute. The problem of producing very small flow rates of small bubble foam is two-fold. One is the requirement for metering such small quantities or air, water, and surfactant on a continuous basis, and the second is the requirement for providing "substantial agitation" through some foaming device.

A particular application in which small bubble foam is needed at low flow rates is called froth flotation. Froth flotation, or benefication as it is sometimes called, is a concentration process for separating fine valuable minerals from their gangue impurities. It is known particularly in the coal industry for separating out impurities from the coal. To effect benefication, mineral-bearing ores are ground in water to form a mixture of mineral particles and non-mineral gangue particles. The resulting mixture (water, ore, mineral particles, and gangue particles) is conditioned with various chemicals including froth-producing compounds and agitated in flotation machines which introduce and disperse air in the form of bubbles throughout the pulp to liberate the mineral particles from the gangue particles.The bubbles collect at the surface of the pulp as a froth in which the valuable mineral particles are entrapped. The separated minerals are then either skimmed off or overflow with the froth to concentrate tanks, from which the minerals are then extracted for further processing.

There are many different flotation machines, but all require the formation of some type of air bubbles in the pulp.

The size of the air pockets (bubbles) in the pulp is determined by many factors including the air pressure, hole size, agitation of the pulp, etc. In one type of machine, compressed air is introduced under or into the pulp by perforated pipes or by expelling the air through multihole plates or fine mesh screens.

It is desirable to have the air pockets as small as possible to more efficiently separate the valuable fine mineral particles from the non-mineral gangue particles. However, present commercial equipment cannot produce air pockets much less than 1/64 inch diameter (0.015"); rather, they normally produce much larger bubbles between 1/32 and 1/4 inch diameter.

I have found in my actual measurement that the small bubble foam produced by equipment constructed according to my U.S. patents Nos. 3,811,660 and 4,400,220 has bubbles from 50 to 200 micron diameter (.05 to .2mm or .002 - .008 inches) when first ejected from the foam generator. These bubbles exist in a matrix consisting of water and surfactant in the form of highly stressed films surrounding small pockets of air. When this foam-is introduced into a tank containing a pulp consisting of ground ore containing fine mineral and non-mineral (gangue) particles, the water film of the mass of bubbles disperses into the water of the pulp, leaving each bubble as a pocket of air surrounded by water. This results in a mass of air pockets which forms a froth which is very effective in entrapping the mineral particles.Thus, by using my small bubble foam, the efficiency of the flotation machines is greatly improved.

The density (weight per unit volume) of the water into which the very small air pockets are introduced varies with the number of air pockets per unit volume of water.

Therefore, it is necessary to accurately control the amount of air in the form of small air pockets introduced into the flotation machines.

Summary of the Invention The present invention provides a device for supplying small bubble foam at low flow rates and a method for enhancing the benefication of minerals using small bubble foam.

The device includes an expandable container, foam supply means in flow communication with the inside of the expandable container and operable in response to the expansion and contraction of the expandable container, and gas supply means in flow communication with the outside of the expandable container and operable in response to expansion and contraction of the expandable container. The operation of this device is such as to permit the foam generator to operate at its normal output rate for short intervals, filling up the expandable container, and then to discharge the foam from the expandable container at a lower flow rate, consistent with the needs of the process.

When the device is used for the benefication of minerals, the output from the expandable container is put into the bottom of the tank to form the froth for entrapping the mineral particles.

Brief Description of the Drawings A better understanding of the present invention will be had upon reference to the following description, in conjunction with the accompanying drawings, wherein: Figure 1 is a schematic representation of a preferred embodiment of the present invention for controlling the flow rate of foam; Figure 2 is a schematic representation of a second embodiment of the invention using a different type of expandable container; Figure 3 is an enlarged sectional view of the expandable container of Figure 2; and Figure 4 is a schematic representation of a third embodiment of the invention using a different type of switching mechanism.

Detailed Description of the Invention The apparatus 6 shown in Figure 1 includes a foam generator 8 as described in my U.S. patents 3,811,660; 4,400,220; or 4,207,202 to operate at a normal discharge rate for only short periods of time. The foam generator 8 is in controlled fluid communication with an expandable container 9 by means of a foam inlet line 16 and a common foam conduit 20.

The expandable container 9 is the lower chamber of the cylinder 10, which is divided into a lower chamber 9 and an upper chamber 11 by the piston 12.

The lower chamber 9 is also in fluid communication with the foam outlet line 18 through the common foam conduit 20. The foam outlet 18 may include a nozzle 50 as shown to provide some back pressure on the line 18, or the length of the line 18 may itself provide enough back pressure to overcome any inertial and frictional forces in the piston and cylinder. If the foam outlet line 18 is placed at the bottom of a tank for the benefication of minerals, no nozzle is used, because the head of the fluid in the tank provides sufficient back pressure.

A source of pressurized fluid, preferably pressurized air 22 is in controlled fluid communication with the upper chamber 11 of the cylinder 10 through an air inlet line 24 and common air conduit 30. A fluid (air) regulator 25 can be positioned in the air inlet line 24. The setting of the air regulator 25 may be used as a means to control the discharge rate of the foam into a froth flotation or other process. The upper chamber 11 is also in controlled fluid communication with, for example, the ambient environment through the common air conduit 30 and the air discharge line 26. The air inlet line 24 and air exhaust line 26 join with the common air conduit 30 which opens into the upper chamber 11.

A first solenoid valve 32 is located in the foam inlet line 16 to control the flow of foam therethrough from the foam generator 8 to the lower chamber 9 of the cylinder 10. A second solenoid valve 34 is located in the air inlet line 24 to control the flow of air therethrough from the air source 22 to the upper chamber 11. A third solenoid valve 36 is located in the air discharge line 26 to control the flow of air being exhausted therethrough from the upper chamber 11. The first, second, and third solenoid valves are each operatively connected to an electrical relay 38. The functioning of the relay 38 is in turn controlled by a two position switch 40.

The two position switch 40 is operated between its two positions by a control rod 42 affixed to the piston 12 and extending through a sealed opening in the top end of the cylinder 10 adjacent to the two position switch 40. Two adjustable switch operators 44 and 46 are attached to the control rod 42 outside of the housing 12 and project from the rod 42 in spaced-apart relationship. The arms 44, 46 move with the rod 42 as the piston 12 moves up and down. This process is controlled by the movement back and forth of the piston 12 (corresponding to the expansion and contraction of the expandable container 9) which moves the control rod 42 with the two adjustable switch operators 4 and 46 in the longitudinal direction of the control rod 42 back and forth past the two way switch 40.

In the lower position of the rod 42 corresponding to the lowermost position of the piston 12 which occurs when the foam is expelled and the lower chamber 9 is contracted, the switch operator 44 has opened the two position switch 40, deenergizing the relay 38. In this condition the first solenoid valve 32 in the input foam line 16 and the third solenoid valve 36 in the air discharge line 26 are both energized to an open position and the second solenoid valve or air supply valve 34 is de-energized to a closed position. This allows the foam generator 8 to operate at its normal discharge rate to fill the lower chamber 9 with foam through the foam inlet line 16 and common conduit 20. As the lower chamber 9 fills with foam, the piston 12 moves upward, and the air in the upper chamber 11 is expelled through the air discharge line 26 past the open third solenoid valve 36 to atmosphere.

As the lower chamber 9 is filled with foam, the piston is thereby pushed upward, expanding the expandable container 9. When the piston 12 reaches its upper position, the switch operator 46 on the control rod 42 shifts the two position switch 40 to the closed position to energize the relay 38; the first and third solenoid valves 32 and 36 (which were energized) are de-energized to closed positions, and the second solenoid valve 34 in the air inlet line 24 is energized to an open position. Closing the foam inlet valve 32 causes the foam generator 8 to stop operating, since it is set up to shut off when its output sees a high back pressure.The opening of the air inlet valve 34 allows pressurized air to enter the upper chamber 11 (the outside of the expandable container 9) through the air inlet line 24 and common air conduit 30, and the pressure of the air in the upper chamber 11 (the outside of the expandable container 9) acts on the piston 12, pushing it downward and forcing the foam out of the lower chamber 9 through the common conduit 20 and foam outlet line 18, thus completing the cycle and returning the expandable container 9 to its contracted position.When the expandable container 9 reaches its contracted position, the switch operator 44 shifts the switch 40 to the open position, opening the foam supply valve 32, which causes the foam generator 8 to start up again, opening the air exhaust valve 36, permitting the air in the upper chamber 11 to exhaust to atmosphere, and closing the air inlet valve 34, stopping the pressurized air from entering the upper chamber 11, so that the cycle is repeated.

The amount of foam to achieve optimal benefication varies according to many factors, including the type of mineral being separated, the specific gravity of the pulp, the density of the gangue, etc., such that the amount of foam required will usually be left to the empirical judgment of the operator to obtain the desired results.

The second embodiment of the invention, which is shown in Figure 2, works in the same way as the first embodiment, except that the expandable container 109 is a bellows rather than a piston-cylinder arrangement, and the air pressure is introduced into the bellows chamber 114 surrounding the bellows 109 rather than into the upper chamber 11 of the cylinder. The bellows 109 is constructed as shown in Figure 3, with internal ribs 148 and external ribs 150 supporting the flexible material of the bellows 109 so that it expands and contracts in a vertical manner and maintains its diameter in both its expanded and contracted positions. The bellows 109 is situated within a sealed bellows housing 115.

Otherwise, the functioning of the second embodiment is the same as the first. Beginning with the collapsed bellows 109, the switch operator 144 opens the switch 140, deenergizing the relay 138. This causes the input foam valve 132 and the air discharge valve 136 to open and the air supply valve 134 to close. Opening the input foam valve 132 causes the foam generator 108 to operate at its normal discharge rate to quickly fill the interior of the bellows 109 with foam. As the bellows 109 fills with foam, the control rod 142 moves upward, and air in the bellows chamber 114 is expelled through the common air line 130 and the air discharge line 126, past the valve 136 to atmosphere.When the bellows 109 fills with foam, the switch operator 146 shifts the switch 140 to the closed position to energize the relay 138; the foam input valve 132 and air exhaust valve 136 are closed, and the air input valve 134 is opened. Closing the foam input valve 132 causes the foam generator to shut down. Opening the air input valve allows pressurized air to enter the bellows chamber 114 surrounding the bellows 109, and the air pressure in the bellows chamber 114 acts on the outside of the bellows 109 to gradually collapse the bellows 109, pushing it downward and gradually forcing the foam out of the bellows 109 through the conduit 120 and foam outlet line 118, thus completing the cycle and returning the expandable container 109 to its contracted position.

The third embodiment, shown in Figure 4, is very similar to the second embodiment except that the switching mechanism 240 uses air rather than electricity to open and close the valves 232, 234, and 236. The switch 240 is a twoposition, four-way control valve. On the input side of the control valve 240 is the control air input line 250, which constantly receives pressurized air from the pressurized air source 222. On the output side of the control valve 240 are two control air output lines 251, 256 and a vent 258. The control air output line 251 splits into two lines 252, 254, which lead to the foam supply valve 232 and the air exhaust valve 236, respectively. The control air output line 256 leads to the air supply valve 234. The valves 232, 234, and 236 are now air-controlled valves instead of solenoid valves. The valves 232, 234 and 236 are normally closed but are caused to open when air pressure is exerted on them from their respective control lines 252, 256, and 254.

The toggle 249 on the control valve 240 is shown in the downward position which has caused the control valve to move to the foam filling position, permitting pressurized air to flow from the control line 250 into the output line 251 to the control lines 252 and 254 to the foam supply valve 232 and the air exhaust valve 236, causing those valves to open. At the same time, the control valve 240 puts the control line 256 in fluid communication with the control exhaust 258, relieving pressure in that control line and causing the air supply valve 234 to close.

With the valves in these positions, the foam generator 208 operates to produce foam, which flows through the foam inlet line 216 and fills the expandable container 209.

Air in the bellows chamber 214, which is inside the bellows housing 215 and outside the bellows 209, exhausts through the air exhaust line 230, through the air exhaust valve 236, to atmosphere.

As the expandable container fills, the control rod 242 attached to the movable end of the bellows 209 moves upward. When the expandable container 209 has filled up enough, the lower switch operator 246 will contact the toggle 249, moving it to its upper position. This causes the control valve 240 to move to the foam emptying position in which the control line 251 is connected to the control exhaust 258 and the control line 256 is connected to the pressurized air control line 250. When the control line 251 is exhausted, the foam inlet valve 232 and the air exhaust valve 236 are closed.

When the control line 256 is pressurized, it causes the air input valve 234 to open, introducing pressurized air from the air source 222, through the line 224, into the bellows chamber 214. The pressurized air in the bellows chamber 214 acts on the outside of the bellows, squeezing out foam through the foam lines 220 and 218.

When the foam has been squeezed out of the bellows 209, the upper switch operator 244 moves downward, contacting the toggle 249 and shifting it downward, putting the control valve 240 back into the fill position, so the cycle repeats.

The foregoing detailed description is given primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom, for modification will become obvious to those skilled in the art upon reading this disclosure and may be made without departing from the spirit of the invention and scope of the appended claims.

Claims (25)

What is claimed is:

1. An apparatus for providing foam at a controlled, slow rate, comprising: an expandable container; a foam generator in controlled fluid communication with the inside of said expandable container; a pressurized gas source in controlled fluid communication with the outside of said expandable container; and control means triggered by the expansion and contraction of said expandable container such that expansion of said container to a certain point closes fluid communication with said foam generator and opens fluid communication with said pressurized gas source, causing said container to contract and expel foam; and contraction of said container to a certain point closes fluid communication with-said pressurized gas source and opens fluid communication with said foam generator, causing said container to fill with foam and expand.

2. An apparatus for controlling the flow rate of foam, comprising: a piston; a cylinder which surrounds said piston and defines an upper chamber at one end of the piston and a lower chamber at the other end of the piston; foam supply means in flow communication with the lower chamber and operable in response to the movement of said piston; and gas supply means in flow communication with said upper chamber and operable in response to the movement of said piston.

3. The apparatus of Claim 2 wherein movement of said piston to its lower position actuates means to introduce foam into said lower chamber from said foam supply means, and movement of said piston to its upper position actuates means to introduce pressurized gas

4. The apparatus of Claim 3 wherein said means to introduce foam into said lower chamber and said means to introduce pressurized gas into said upper chamber include a plurality of valves actuated in response to a switch means which is actuated in response to the movement of said piston.

5. The apparatus of Claim 4 wherein said switch means includes: an elongated rod attached to said piston; a pair of switch operators ounted onto and spaced at preselected positions along said elongated rod; a two-position switch operable in response to the movement of said switch operators; and a relay activated in response to said two-position switch and adapted to activate said plurality of valves.

6. The apparatus of Claim 5 wherein said foam supply means is constructed so as to provide small bubble foam having an average bubble size less than 0.015 inches in diameter.

7. The apparatus of Claim 5 wherein said foam supply means is constructed so as to provide small bubble foam having a bubble size from 0.002 to 0.008 inches in diameter.

8. An apparatus for controlling the flow rate of foam, comprising: a bellows chamber; a bellows inside said bellows chamber; a foam supply means in controlled fluid communication with the inside of said bellows; an air supply means in controlled fluid communication with the outside of said bellows; and means for making said foam supply means and said air supply means function in response to the expansion and contraction of said bellows.

9. The apparatus recited in Claim 8, further comprising: a foam supply valve between said foam supply means and said bellows; an air supply valve between said air supply means and said bellows chamber; and valve control means actuated by the movement of said bellows such that, when said bellows moves into its contracted position, said valve control means closes said air supply valve and opens said foam supply valve, and, when said bellows moves into its extended position, said valve control means opens said air supply valve and closes said foam supply valve.

10. The apparatus recited in Claim 9, wherein said air supply valve and said foam supply valve are solenoid valves, and said valve control means includes a switch means actuated in response to the expansion and contraction of said bellows.

11. The apparatus recited in Claim 10, wherein said switch means comprises: an elongated rod attached to a movable end of said bellows; a pair of switch operators mounted onto and spaced at preselected positions along said elongated rod; a two-position switch operable in response to the movement of said switch operators; and a relay activated by said switch, said relay in turn adapted to activate said solenoid valves.

12. The apparatus recited in Claim 11, wherein said foam supply means is constructed so as to provide small bubble foam having an average bubble size less than 0.015 inches in diameter.

13. The apparatus recited in Claim 11, wherein said foam supply means is constructed so as to provide small bubble foam having a bubble size between 0.002 and 0.008 inches in diameter.

14. A method for controlling the flow rate of foam, comprising the steps of: introducing foam into the inside of an expandable container so as to cause the container to expand; stopping the introduction of said foam into said expandable container at a preselected point in the expansion of said container; and applying pressurized gas to the outside of said expandable container so as to collapse the container and push said foam out of the container.

15. A method for controlling the flow rate of foam comprising the steps of: introducing foam into the lower cylinder chamber of a piston-cylinder arrangement; interrupting the introduction of said foam into said lower chamber at a preselected point in the movement of the piston; and introducing pressurized gas into the upper cylinder chamber of the piston-cylinder arrangement to move the piston in the direction of the lower chamber, thereby forcing said foam out of said lower chamber.

16. The method of Claim 15, further comprising performing the step of interrupting the introduction of foam into said lower chamber and the step of introducing gas into said upper chamber substantially simultaneously.

17. The method of Claim 16 wherein said foam is small bubble foam comprising bubbles having an average diameter less than 0.015 inches.

18. The method of Claim 16 wherein said foam is small bubble foam having bubble size diameters between 0.002 and 0.008 inches.

19. A method for separating mineral particles from mineral-bearing ore, comprising the steps of: grinding said ore into fine particles comprising a mixture of mineral particles and non-mineral gangue particles; combining said mixture of particles with water and chemicals to form a pulp of desired specific gravity; producing a quantity of small bubble foam from a mixture of air, water and surfactant through a foamer having tortuous passages therein, each of said small bubbles comprising a highly stressed film surrounding an air pocket; introducing a controlled quantity of said small bubble foam into an expandable container for containing said foam, expanding said expandable container as it fills with foam; interrupting said introduction of said small bubble foam into said expandable container after said container has expanded to a certain point; and applying a pressurized gas to the outside of said expandable container, thereby causing said expandable container to collapse and forcing said controlled quantity of foam out of said expandable container and introducing said foam below the surface of said pulp; whereby the surface film of each of said small bubbles disperses into said pulp, leaving a multitude of air pockets which interact with said pulp to entrap said mineral particles of said pulp and separate said mineral particles from said gangue particles.

20. A method for separating mineral particles from mineral-bearing ore, as recited in Claim 19, wherein said expandable container is a bellows.

21. A method for separating mineral particles from mineral-bearing ore, as recited in Claim 20, wherein said expandable container is the lower cylinder chamber of a piston-cylinder arrangement.

22. The method of Claim 21 wherein said small bubble foam comprises foam having an average bubble size less than 0.015 inches in diameter.

23. The method of Claim 21 wherein said small bubble foam comprises foam having a diameter in the range of 0.002 to 0.008 inches.

24. An apparatus for providing foam as recited Claim 1, where said control means comprises: a two-position control valve which is mounted such that movement of said expandable container causes said control valve to shift between a filling position and an emptying position; a foam inlet valve in fluid communication with said control valve; a pressurized gas inlet valve in fluid communication with said control valve; and an air exhaust valve in fluid communication with said control valve.

25. An apparatus for providing foam as recited in Claim 24, wherein said control means further comprises: an elongated rod mounted so as to move with the expansion and contraction of said expandable container; a pair of switch operators mounted on said elongated rod so as to contact said two-position control valve to switch said two-position control valve to its filling position and to its emptying position at the lower and upper limits of movement of said rod, respectively.