US2451144A - Froth level controlling device - Google Patents

Description

Oct. 12, 1948. w. M. AUBREY 2,451,144

FROTH LEVEL CONTROLLING DEVICE Filed Feb. 17, 1945 2 Sheets-Sheet 1 ATTORNEY Oct. 12, 1948. w. MQAUBREY 2,451,144

mom LEVEL 'coumonmne nsvxcn Filed Feb. 17. 1945 2 Sheets-Sheet 2 ATTORNEY Patented Oct. 12, 1948 morn LEVEL CONTROLLING DEVICE William Maynard Aubrey, Stamford, Conn, as-

signor to The Yale & Towne Manufacturing Company, Stamford, Conn., a corporation of Connecticut 1 Application February 17, 1945, Serial No. 578,513

Claims. 1

This invention relates to a device for maintaining a constant froth-level. More particularly, it relates to an improved means whereby froth may be continuously removed at a constant rate from a vessel containing a froth producing mechanism.

Various industrial operations, particularly in separating solids from liquids and solids from solids, make use of froth flotation principles. In such processes, liquid containing the solids to be separated therefrom, or an aqueous pulp of the solids to be separated from each other, is subjected to aeration and agitation in the presence of frothproducing and/or collecting agents. This results in the formation of a supernatant layer of froth in which is concentrated the desired solids fraction. The froth layer is ordinarily skimmed into a separate chamber in which the froth is allowed to collapse, the solids being subsequently separated therefrom, if so desired. The underlying layer is decanted in some way, usually a part being continuously withdrawn.

Removal of the froth layer is usually accomplished by a mechanical skimmer 'or crowder adapted to remove any froth which stands higher than a fixed level, usually the overflow lip of the chamber in which the froth is generated. As a result, the amount of froth removed will vary as the tendency of the liquids treated varies in ability to produce froth. If large masses of thick heavy froth are produced, the skimmer removes a much larger amount than when a thin light froth is being produced. This in turn directly affects the efflciency of the overall operation.

In the past, various attempts have been made to devise mechanical or electrical controls which will overcome this difficulty. Such devices usually operate to control the volume of liquid in the froth-producing apparatus. Since the real problem, however, is not one of maintaining any particular amount of liquid in the vessel, but rather one of maintaining a constant rate of froth removal, such a device, while useful, does not serve as a complete solution to the problem.

It is, therefore, the principal object of the present invention to provide control device so actu ated that the actual height of froth above a fixed level is directly controlled and therefore a constant amount of froth is continuously removed. It is also an object of the invention to provide such a means which is readily constructed, simple in operation, requires little care and is substantially automatic in action.

While the device of the present invention is intended to be applicable to all types of froth flotation operations, a demonstration of the invention with respect to all such operations would require excessive discussion. Recently, the clarification by froth flotation of various lubricating coolants used in machining operations has come into industrial importance. Since all the typical difficulties are encountered in this clarification, it will be used as illustrative of the invention, although the latter is not necessarily so limited.

In general, the problem is solved by using the amount of froth actually removed to actuate a device which in turn controls the height to which the froth is allowed to accumulate. This is usually done by taking advantage of the fact that when froth is allowed to collapse liquid is formed. The flow of this liquid is used to activate a control which in turn regulates the amount of the liquid entering or leaving the vessel containing the froth-producing means. However, in some cases the froth itself, rather than the liquid therefrom, is used as the motivating factor.

The invention will be more fully illustrated in conjunction with the accompanying drawings, in which:

Figure 1 is a projection of a simplified form of apparatus showing the interrelation of the various elements and the flow of materials therethrough;

Figure 2 is an elevation, in section, showinga second modification and using an electrical circuit to connect the elements;

Figure 3 is an elevation, in section, showing a further arrangement of the elements, and

Figures 4, 5 and 6 show various additional modifications of a part of the activating mechanism,

In Figure 1, liquid to be treated flows into the apparatus through conduit l into head box 2 which serves simply as a storage means so that a relatively constant flow into the remainder of the apparatus can be maintained more readily. Since the fluid to be treated sometimes contains relatively large particles which quickly settle on standing, the head box is usually provided with a cleanout 3. The opening therein is closed by means of cover 4 held in place by clamps 5 and 6. The latter form no part of the present invention, and obviously may be replaced with other equivalent but conventional means.

. An opening 7 is provided in one side of the head box. Through it, fluid to be treated can be drawn to the remainder of the apparatus. This opening is somewhat above the bottom in order to prevent the possibility of its being closed by any settled solids. Fluid from the head box flows out through opening 1 and into the remainder of the apparatus through a conduit 8 having a, quick-opening valve 9 located therein. This valve is, asshown, a slid assures valve for simplicity of illustration but may be re-= placed by any conventional equivalent.

Fluid passing through conduit c is brought up under rotor it and stator ii of a conventional froth flotation unit, generically designated ii. In Figure 1, this is indicated as a Fagergren-type flotation machine. This machine, which is well known, was found generally preferable for the purposes of this invention, but may be replaced with other equivalent agitating and aerating means if so desired. As shown in Figure 1, the rotor unit is enclosed in a semicylindrical tank it having a vertical air inlet shield IE enclosing a space down which air is drawn by the action of the rotor. The rotor is also driven by means of a shaft is extending down through this space, the shaft being turned by motor I? or some equivalent motivating means.

Fluid entering chamber it from conduit 8 is agitated and aerated by the operation of rotor i0, and thrown out through stator ll into main chamber ii of the froth-producing unit. In this chamber, the air in the liquid expands and rises to the surface, forming froth layer it. Due to the inherent nature of the fluid being treated, or to the addition thereto of a suitable frothing agent and/or collector, this froth layer contains the desired collected solids.

All froth standing at a height above overflow lip 20 of the chamber i8 is forced down over apron 21' into settling tank 22 by means of a skimmer 23 which is motivated by some conventional means, as for example gear 24 and chain 25. The latter in turn is motivated by some conventional means which is not shown since it is not part of the invention. This skimming device may be at one end of the chamber as in Figure l or may be at both ends or either or both sides. Where two Skimmers are used, the frothing mechanism is preferably located in the center of the chamber.

The froth after entering chamber 22 collapms. This releases fluid which collects until a sumcient amount is obtained to flow under battle 2% over bafie ill and into a second chamber 2@. The openlag between these bafies is located sufiiciently above the bottom of tank 22 so that solids released by the collapsing froth are retained therein and may be removed as desired, the present invention not being concerned therewith. Thus, liquid in chambers 22 and 28 will stand at the same level, but the liquid in chamber as will be free from the solids which were carried out of chamber 68 along wlth'the froth. When the liquid level in chamber 28 exceeds the height of overflow lip 29, it flows over into launder 39 and is thereby carried away. When two or more shimmers are used, chambers 22 and 28 are duplicated and the launders arranged to deliver the flow to a common point.

Whether these steps of the fluid treating process are carried out in the exact apparatus described or in one in which some of the elements are replaced by other mechanical equivalents forms no part of the present invention. It is set forth to illustrate the application of the invention. However done, several factors will be the same. First, the skimmer or crowder will always remove all the froth standing above a certain height. Second, the froth volume, or the volume of liquid freed therefrom, represents a flow of material which is a function of the amount of froth actually removed. The present invention depends for its mode of operation on the use of the flow of this froth and/or liquid to activate a means adapted to hold constant the amount of froth removed by the er.

One means of accomplishing this result isalso shown in Figure l.

The means shown in this modification comprises the use of a receptacle 3i interposed in the path of liquid flowing out of launder 30. This receptacle is mounted on the side of tank 22 by means of arms 32 and 3t, ly connected to each other by a spacebar to or the like. These arms are pivoted at one end from lugs 35 and 36 on the side of the tank, the receptacle being suspended from the opposite ends, as for example, by means of the arms 37 and 38. Receptacle 3|, then, is so mounted that it can vertically swing through an arc having a, fixed radius. Liquid flowing in launder 30 is carried to a point above receptacle 3! and there discharged. The discharge end of this launder is so located that all the discharged liquid can fall directly into receptacle 3! if the latter is swung to the proper position in its vertical arc.

Receptacle 3| is pierced in some manner, for example by restricted weir opening 39 shown in the side thereof in Figure 1. Liquid flowing into the receptacle causes the latter to fill to some level, determined by the size of this opening, since when once filled to a certain level the amount of liquid entering the receptacle and the amount passing out through the opening becomes equal.

In the modification shown in Figure 1, the weight of liquid in the receptacle forces it down through the fixed arc determined by the length of arms 32 and 33. As it does so, it tends to pass out of the stream of liquid flowing from launder 30. This is shown by the position of receptacle 3| in Figure 1. If no restricting force is present, the receptacle will pass entirely out of the stream. This tendency to swing is used as the motivating force in operating the control mechanism of the present invention.

The restricting force, 1. e., the control-motivating force, is obtained in the apparatus shown in Figure 1 by means of a vertically-ascending wire or cord 5i which is passed over a pulley t2 rigidly .counterweights, are set to counterbalance the weight of receptacle 3! and its mounting mechanism, which is thereby eliminated as a factor. The opposite end of wire 4! is attached tolever arm 53 of quick-opening valve 9-. Movement of the lever to is restricted by means of a spring which is usually a part of the valve, but for purposes of illustration is shown at 5%.

Liquid flowing out of opening 39 as well as that not caught in receptacle 3| falls into a small chamber 8b. This liquid is comparatively free from solids. In ore-dressing, it could be directly reused in pulping more ore. However, in the case of clarifying coolants it is. not sufiiciently clean to be directly reused and instead is returned to the head box. This may be done by any desired means, as for example as illustrated in Figure l, a submerged pump driven by motor 61, controlled in turn by a float-switch arrangement 62, which returzns the liquid through conduit 65 into head box Clarified coolant suitable for recirculation to the grinding circuit is withdrawn from chamber I 8 through an opening 66 located in the side of the chamber, but somewhat above'the bottom of chamber l8. Opening 66 is baflled by a closed partition 61, open only at the top, which extends from the bottom of chamber I8 to a height just below the bottom of foam layer l9. In this way, clarified coolant flows through opening 68, conduit 68, valve 59 and conduit 10 and into chamber II, which serves simply as a storage means. From chamber clarified liquid may be drawn by any desired means such as a submerged pump through conduit 12, the pump being motivated by motor 13 and controlled by float switch H. Obviously, the pump may be replaced by any other convenient equivalent means.

From the foregoing description, the operation of the control mechanism is quite apparent, The receptacle will swing through a fixed arc to receive more or less liquid depending upon its position along the arc. At any position, the amount of liquid leaving will become equal to that entering, but the weight of liquid in the receptacle will vary in accordance with the volume passing therethrough. The weight of this volume exerts a pull on the wire 4|, which in turn exerts a pull on the lever arm 53 and controls the extent to which the valve 9 is opened.

If too great a volume of froth is carried over into settling tank 22, a correspondingly increased amount of liquid overflows into launder 30, causes a depression of receptacle 3| which in turn pulls the lever arm 53, thereby partially closing valve 9 and decreasing the amount of liquid entering the froth-producing mechanism. The-liquid level in the latter then falls and in so doing the height of froth above the overflow lip is also lowered. When this is done, the amount'of froth removed by the skimmer decreases and brings the system back into equilibrium.

Conversely, if too little material is being overflowed, a smaller amount of liquid enters the receptacle and less weight is held therein. Receptacle 3| is therefore lifted along its are by the action of the spring and/or counterweights. As a result, valve 9 is opened, more liquid enters chamber l8, the height to which the froth reaches is raised and the apparatus again comes into equilibrium.

Several features of the apparatus as shown in Figure 1 should be noted. First, receptacle 3| is suspended in such a manner that it swings vertically through a fixed arc. A definite advantage exists therein due to the fact that in cutting more or less of the stream a quicker response is obtained. A similar arrangement in which a receptacle corresponding to 3| is mounted for vertical movement only and is so located as to receive the entire discharge from launder would provide a usable actuating mechanism. However, its response, due to the fact that it receives all the flow, would be considerably more sluggish.

Second, the mechanism using a mechanical connection such as wire 4| between the activating mechanism and the control valve will never remain for an extended time in a stationary position. Once receptacle 3| has either raised or lowered in response to a change in flow through launder 3B, the foam level will be quickly brought to the proper height. But receptacle 3| will then move into the neutral position which would be held if ideal conditions were constantly maintained. But this movement into the neutral position also causes a further change in the-valve setting which will presently require a further compensation. This occurs repeatedly. As a result, an average froth level approximating that Figure 2 may control the flow either into or out of chamber la, the valve 9 in Figure 1 being replaced by any conventional motor-driven valve. One such valve is shown in Figure 2 in which motor 16 drives a worm TI and gear 18. Gear 18 being screw-threaded through its central hole and fixed against horizontal displacement, reciprocates threaded shaft 19 as motor 15 turns forward or in reverse and shaft 19 in turn opensor closes valve 15.

The electrical circuit is quite simple. A reversing mercury switch 8|] is mounted on arm 8| which is pivotedjrom lug 82, switch 80 being connected to motor 16 by the leads 83 and 84 and current being brought to the circuit through leads B5 and 8B. A time switch 81 is interposed on lead 85 and periodically makes contact for short time intervals only, thus keeping motor 16 from running away. As in Figure 1, a wire 4| or other flexible means is used to connect the arm to a counicer-balancing, system. As the receptacle rises and falls in' response to the amount of material flowing in launder 30, contact is made by the mercury switch. When time switch 81 is also closed, motor 16 is energized and causes an adjustment of the opening of valve 15. Once the adjustment is made and the material flow comes into equilibrium the receptacle naturally returns to a neutral position, but since the circuit is then open, no further movement of the valve occurs until flow conditions require further compensation. The adjustments are therefore relatively stable as compared with those obtained using a mechanical connection as in the arrangement of Figure 1.

- Several other modifications of the apparatus will also be noted in Figure 2. It will be seen that the froth-settling tank 22 has been eliminated and the material flowing in launder 30 instead of being settled liquid is the foam or froth itself. This arrangement has a particular advantage in small installations which take care of the coolant supply for one, or only a few, material-modifying machines such as individual lathes or grinders. The response is not as delicate as when the foam is allowed to settle and the liquid flow is used as the motivating agent." However, on small installations where only a small amount of fluid is handled, a direct use of the froth eliminates the expense incurred for additional apparatus.

Because the foam itself, rather than the liquid, is used, the receptacle shown in Figure 2 is of a, modified form. The foam naturally carries the solid contaminants which, if given the opportunity, will gradually accumulate in the receptacle and alter its weight. Therefore, the square sectioned receptacle 3| of Figure 1 has been replaced by a cylindrical receiver 88 having a conical lower section 89 with a funnel-like opening 93 in the bottom. This shape insures the eventual passage from receptacle 80 of all material which enters therein. The foam may be collected in a tank 9| which may be simply a storage means or may be comparable. in functio t0 e th r tank 22 or tank 90 of Figure 1 depending upon the size' of the installation. 7

In Figure 1 the arrangement of elements is shown as controlling the amount of fluid fed to the tank containing the agitating and aerating means. However, as noted above, the actual foam level may be controlled not only by adjusting the feed 'rate as in Figure 1 but also by controlling the amount of fluid decanted from chamber I8.- There is a definite advantage in controlling the rate of removal rather than feed in that itdirec'tly controls the total volume of liquid in chamber I9 and thereby induces a quicker adjustment of the froth level. One such arrangement is diagrammatically illustrated in Figure 3. The operation of the device of Figure 3 is readily apparent from an inspection of its arrangement. Material to be treated overflows head box 2, down over splashboard 92 into a passage 99 having an opening 941 located therein immediately below rotor I of a conventional Fagergren-type flotation machine similar to that of Figure 1. As in Figure 1, rotor I0 is driven by a shaft I9 extending up through an air shaft I5. The normal action of the rotor creates a vortex of liquid as shown at 95, but to prevent any splashing, guards 96 are provided. The fluid, after agitation and aeration, is thrown out through stator II into chamber I8 in which the fine bubbles of air entrapped in the liquid expand and rise, forming froth layer I9 which contains the desired, collected solids. This froth layer is skimmed off over the sides of the chamber I8 into a settling tank corresponding to chamber 22 in the usual way..

A novel feature in the apparatus of Figure 3 lies in controlling the effluent from chamber I9 by replacing baiile 61 and conduit 68 of Figure 1 by a tion since this port may be located at will almost anywhere in the chamber 99. Fluid flows out sired. In this way, the control operates only on a by-pass instead of the whole flow and a quickeracting control may be obtained.

In Figure 1 receptacle 9| is shown as a square box open at the top and having a restricted weir opening in one side thereof. That the mechanism is not necessarily limited to such a structure is shown in Figure 2. Several other modifications thereof are shown in Figures 4, 5 and 6.

. In Figure 4 a square receptacle Ii I is shown in which the restrictedweir opening 31 of Figure l Figure 2 is shown in Figure 6 in which a conical I funnel H5 is shown having a lower cylindrical section I I9. Adjustment of the opening in section H6 is obtained by setting therein a smaller funnel. II1. Such a variable opening is seldom required but in some installations which operate at different times on widely different total fluid flows their use is helpful. They are not particularly useful in arrangements such as that of Figure 2 in which the contaminant-bearing froth passes directly therethrough since solid particles tend to accumulate behind the edge of the insert and alter the effective tare weight of the receptacle;

I claim:

1. In combination, a chamber; aerating and agitating means therein; means adapted to continuously feed frothable fluid into said agitating and aerating means, whereby a supernatantfrothlayer is formed in said chamber; -means adapted tocontinuously remove fluid from the underlying layer; means to remove substantially all the froth standing above a fixed overflow level and a froth level control comprising a movable receptacle, said receptacle being open at the top to permit unrestricted entry of fluid material thereinto and having at least one restricted discharge through port I02, conduit I03, valve I04, conduit I05 and port I06 into a storage chamber.

corresponding to chamber I0 of Figure 1. From chamber I0 the liquid may be removed by pump I 01 through conduit I2 to any desired point as in Figure l. Valve I04 is shown as a quick? opening valve, corresponding to valve 9 of Figure 1, actuated by a pull-wire 4| which corresponds to pull-wire M in Figure 1 and is motivated by a similar mechanism to that shown in Figure 1. It will be noted in Figure'3 that by the height of wall I00 an overflow arrangement for chamber 99 is provided; This prevents flooding if the 1 level in chamber I9 rises too high. .In such a case, if liquid in chamber 99 rises .to a sufllcient height it will flow over the adjustable lip IOI of wall I00 into a chamber I09 formed by wall I00,

a .port IIO located therein communicating directly with storage chamber I0 to discharge any the fluid therein, said counterbalance means .be ing adapted to position said receptacle on said of fluid material in said receptacle; pivoted lever support means for said receptacle, said support means being adapted to permit motion of the receptacle in a vertical-plane along a fixed path only; means to conduct at least a portion of fluent material removed from said froth layer into said receptacle; means to control the volume of fluid in said underlying layer; means to communicate motion of said movable receptacle along said fixed path, resultant from variation in the weight of fluidretained in said receptacle, to said fluid volume controlling means; and counterbalance means to overcome the weightof said re ceptacle and the weight of at least a portion of fixed path at that level determinedby the weight the extensions of the side walls of chambers I9 and 99 and an end wall I09. Chamber I08 has fluid flowing into chamber I09. Perhaps the best.v

operation-of this arrangement is to adjust the. height of overflow lip IOI while valve I04 is in mid-position so that the froth level is as deof the fluid retained therein.

2. A combination according to claim l'in which:

said receptacle is open at the'top, whereby ad-' mission'of fluid is unrestricted, and has at least one opening of limited size. whereby discharge,

of fluid-therefrom is restricted; said mean'slfor conducting fluent material-terminates in an elevated discharge opening, whereby discharged masaid receptacle is open at the top, whereby admission of fluid is unrestricted and has at least one opening of limited size, whereby discharge of fluid therefrom is restricted; said means for conducting fluent material terminates in an elevated discharge opening, whereby discharged material falls vertically; said positioning means constitutes an elongated member pivoted at one end; said receptacle is mounted on said member; said pivot is so fixed that movement of said receptacle can only follow a fixed arc and said arc is so located that said receptacle in moving therethrough passes into and through at least a portion of said vertically-falling discharge.

4. A combination according to claim 1 having an external conduit means so located as to remove at least a portion of the fluid from said underlying layer and a quick acting valve in said conduit adapted to control the flow of fluid therethrough.

5. A combination according to claim 1 including a, settling chamber; means adapted to cont 10 duct the froth removed from said supernatant layer into said settling chamber; means for withdrawing fluid, regenerated by collapse of the froth in said chamber, from said chamber; and means for conducting at least a part of said regenerated fiuid into said movable receptacle.

WILLIAM MAYNARD AUBREY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 729,349 Hutchinson May 26, 1903 1,315,662 Gouchenour Sept. 9, 1919 1,530,836 Kuzilik Mar. 24, 1933 1,908,691 Coe May 16, 1933 FOREIGN PATENTS Number Country Date 7,586 Great Britain 1903

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