US2981413A - Process for separating solids in liquid suspension - Google Patents

Description

April 25, 1961 E. B. FITCH 2,981,413

PROCESS FOR SEPARATING SOLIDS IN LIQUID SUSPENSION Filed NOV. 30, 1953 2 Sheets-Sheet l 23 FINE SOL/D5 27 FRAOGQGON 34 3 F551? r? wwoosrmflmu/o-m SUSPENSION $11-59 UNDER T'j/ Z 50 PRESSURE tyrfia-yfi) .sPF/vr uoum-our fowl P2 25 I3 24 37 3 29 004/755 souos [-761 FRACTION- 23 FINE $01. los

F ,8 27 RACTIO/V FEED SUSPENSION UNDER PRESSURE J r I (O-l-U) /7 25 cams/5 SOL/0S 5/ FRACTION u 35 V i E FINE soups 34 23 FRACTION P 0 2 FEED susPE/vsmg 29 24 UNDER PRESSUE INVENTOR aonnss sauos ELL/0T B. F/TCH, FRAZTION BYMLMM X ATTOR Y 2,981,413 PROCESS FOR SEPARATING SOLIDS IN LIQUID SUSPENSION 30, 1953 E. B. FITCH April 25 2 Sheets-Sheet 2 Filed Nov.

INVENTOR 1. 4/07 5. F/I'CA/ BY AI VORTEX ATTORNEY United States Patent PROCESS FOR SEPARATING SOLIDS IN LIQUID SUSPENSION Elliot B. Fitch, Westport, Conn, assignor to Dorr-Oliver Incorporated, a corporation of Delaware Filed Nov. 30, 1953, Ser. No. 395,017

7 Claims. (Cl. 209-211) This invention relates to hydrocyclones. More particularly, it relates to improvements on hydrocyclones whereby large capacity hydrocyclones are adapted for abnormally fine, hydraulic classifications.

As a hydraulic separating device the hydrocyclone is well known, being disclosed, for example, in the USA. patent to Samson et al., No. 2,377,534. Such an apparatus essentially comprises a hollow casing adapted to contain and confine under hydrostatic head a freely-whirling body of liquid unobstructed in its interior, and having a longitudinal axis of radial symmetry, which axis is referred to herein as the axis of revolution. Longitudinally, the inside periphery of the casing is required to be a smooth, stationary surface of revolution, the radius of which in any plane perpendicular to the axis of revolution is maximally limited to the radius at the infeed end region of the casing and preferably, commencing at a point on the axis of revolution, gradually-decreases to a minimum at the end opposite the infeed end of the casing.

The infeed end region of the casing is characterized by means for the forceful introduction of feed suspension into the interior of the casing generally tangentially to the surface of revolution. Such means usually comprise at least one inlet port formed by the tangential disposition of a conduit to the surface of revolution. Coaxially aligned with the axis of revolution and through the infeed end of the casing there is disposed a tubular exit, referred to as the overflow outlet, adapted for the continuous withdrawal of liquid as overflow from about the axis of revolution. At the opposite end of the casing and'preferably coaxially aligned with the axis of revolution there is another exit referred to as the underflow outlet, disposed through the casing and adapted for the continuous withdrawal of liquid as underflow.

The preferred form of hydrocyclone, which, to simplify matters, will be that referred to hereinafter, comprises a hollow casing having a cylindrical portion which at one end merges smoothly and without obstruction into the wide end of a truncated cone or tapering portion, and which is closed at the opposite end, the infeed end of the hydrocyclone. At the smaller end of the tapering portion there is located the underflow outlet while oppositely, through the closed end of the cylindrical portion, there is located the overflow outlet. This overflow outlet frequently comprises a tubular conduit, called a vortex finder, which extends coaxially into the interior of the cylindrical portion for an axial distance preferably slightly beyond the zone adjacent the end of the casing, into which the feed is introduced. The tangential feed introduction means usually comprises at least one conduit tangentially disposed to the cylindrical section and terminating at the surface of revolution to form an inlet port opening into the infeed zone adjacent the end closure member.

Under operative conditions a liquid suspension of particulate solids to be classified is forcibly and continuously introduced from the feed conduit through the inlet port tangentially into the chamber. The suspension swirls about the axis of revolution in the chamber forming a freely 2 whirling body of liquid, the energy for whirling being supplied by the hydrostatic head of the introduced feed suspension, whereby a free vortex is formed. The swirling action imparts angular velocities to the liquid and solids whereby centrifugal settling forces are developed throughout the body which tend to keep the liquid and solids at the radially symmetrical periphery of said body.

It is required that the hydrostatic head, and thus the velocity, under which the mixture of particles and liquid is introduced into the body be at least great enough't o cause centrifugal settling forces of such magnitude to be developed throughout the body that the force of gravity has no substantial effect on separation. Thus, it has been observed that hydrocyclones can be operated in any position, with the axis of revolution aligned with the horizontal, or with the vertical, without substantially affecting the classification.

Because the tangential introduction of the feed mixture is continuous, because of the required hydrostatic head of the feed to the body, and because the underflow outlet is adapted for continuous withdrawal of liquid, the liquid and particles at the periphery of the body tend to flow in a spiral-like stream towards the underflow outlet. This stream is sometimes referred to for purposes of explanation as an outer vortex because of its vortex-like character. Because the overflow outlet is adapted for continuous' withdrawal of liquid from the infeed end of the body, and because of the required hydrostatic head of the feed to the body, there will be a continuous flow of liquid from the so-called outer vortex to that outlet. Because of the order of magnitude of centrifugal forces developed in the body, and because the interior of the body is unobstructed, such a flow manifests itself in the form of a stream flowing inside the outer vortex in a helical or" spiral-like path about the axis of revolution towards he overflow outlet with the radius of said spiral gradually increasing from a minimum to that of the overflow outlet and with said stream receiving liquidthroughout its axial length in the body. This stream is sometimes referred to for purposes of explanation as an inner vortex because of its vortex-like characteristics. Incidentally, an air core coaxially located along the axis of revolution and within the inner vortex will inevitably appear under these conditions whenever the underflow outlet is open to the atmosphere. This flow of liquid from the outer vortex to the inner vortex and in the inner vortex to the overflow outlet tends to drag particles along with it so that in the body there are liquid drag forces acting on the individual particles in opposition to their centrifugal settling forces. It is important to note that these liquid drag forces are created somewhat independently of the centrifugal settling forces. Particles having developed centrifugal settling forces insuflicient to overcome said drag forces become entrained in the liquid reporting to the inner vortex whereas particles having developed centrifugal settling forces in excess of said drag forces tend to remain in the outer vortex. When dealing with solids of substantially the same specific gravity and shape, the coarser solids generally develop sufficient centrifugal settling forces while the finer solids generally develop insufflcient settling forces. Consequently, in hydrocyclonic classification (separation on the basis of particle size) the coarser particles are withdrawn in the underflow to give a coarse solids fraction and the finer particles are with drawn in the overflow to give a fine solids fraction. As a matter of definition, the size of the largest particles found in the overflow in a significant quantity will be referred to herein as the size of separation. A coarse separation, therefore, refers to a fairly large size of separation while a fine separation refers to a comparatively small size of separation. Fineness of separation refers to the quantity of any given particle size in the overflow.

Heretofore it was considered that the size of separation in a hydrocyclone is for the most part a function of the major diameter, the internal diameter at the infeed end. In other words, it was necessary heretofore to utilize hydrocyclones having large major diameters when it was desired to make a coarse separation and to utilize hydrocyclones having relatively small major diameters to make a fine separation, particularly in the micron ranges. The disadvantage of this is that hydrocyclones of smaller major diameters have a lesser capacity in terms of volumes of suspension treated per hour than hydrocyclones of larger major diameters. It is one object of this invention, therefore, to improve hydrocyclones of larger major diameters for the purpose of enabling the size of separation therein to be decreased to a range heretofore unobtainable in such hydrocyclones but obtainable in hydrocyclones of smaller major diameters.

A mathematical analysis of hydrocyclone performance leads one to believe that the inner vortex controls the size of the particles separated by hydrocyclones, at least from relatively non-viscous feed materials. If centrifugal forces can be increased to magnitudes beyond those now developed by solids in the inner vortex of large major diameter hydrocyclones without simultaneously decreasing the time taken by solids in traversing the inner vortex, then it would seem possible that finer separations could be made.

At present two methods are employed to increase the swirl or spin of the inner vortex, and hence the centrifugal forces developed therein.

The first method involves decreasing the radius of the inner vortex in any plane perpendicular to the axis of revolution through which the inner vortex passes by decreasing the radius of the overflow outlet. To the extent that viscosity effects may be neglected, momentum is conserved in a vortex so that the tangential velocity of any particle in suspension is inversely proportional to its radius of revolution; i.e. V l/r where V is the tangential velocity and r is the radius of revolution of any particle in suspension. With a given velocity the centrifugal force developed by a particle is also inversely proportional to the radius of that particle from the axis of revolution; in other words,

where f is the centrifugal force. Therefore, the centrifugal force acting on a particle in the vortex is inversely proportional to the cube of the radius of that particle from the axis of revolution; i.e. f l/r Therefore, if the radius of revolution of a particle in any plane perpendicular to the axis of revolution is decreased, the centrifugal force tending to make that particle settle towards the radial periphery of the body becomes rapidly greater.

The second method employed to increase the angular velocity of the inner vortex involves increasing the entrance velocity of the suspension of pulp entering the hydrocyclone chamber. The entrance velocity can be increased by decreasing the area of the inlet port, and/or by increasing the rate of introduction of feed suspension, which can be done by increasing the pressure.

The variables of overflow outlet diameter, inlet port area, and feed pressure are related to the size of separation in a complex manner, but it will sufilce to state that, at a given feed pressure, finer separations can be made by decreasing the areas of the feed inlet port and of the overflow outlet. As these areas are decreased, however, a limit is reached beyond which a further decrease is no longer accompanied by a significant change in the fineness of separation. In fact, beyond this limit the size of separation may actually start increasing again.

One reason for this limit is believed to reside in the fact that at about this point friction becomes so large within the body that energy s pplied by the feed input otherwise intended for increasing the angular velocities of the inner vortex is consumed without the desired increase in angular velocities. So it is another object of this invention to minimize this loss of energy due to friction which otherwise would occur in going beyond said limitation on entrance velocities and areas in order that greater centrifugal forces can be developed within the inner vortex whereby the size of separation maybe decreased down to what has heretofore been considered impossible in large capacity hydrocyclones.

Another contributing reason for this limit is that increasing the entrance velocity by increasing the rate of introduction of feed suspension results in a corresponding increase in the rate of withdrawal of overflow through the overflow outlet. The effect of this is not only to decrease the amount of time taken by particles to traverse the inner vortex but also to substantially increase the strength of the drag forces at about the same rate as the increase in centrifugal forces so that the size and separation does not decrease to that desired in the micron range. Under such conditions, not only is there insufficient time for coarser particles entrained in the inner vortex having developed higher centrifugal forces to settle out of the inner vortex, but there are also developed higher drag forces on those particles tending to keep them within the inner vortex and upon coarser particles in the outer vortex, which having developed insufiicient centrifugal settling forces, tend to move into the inner vortex. Another object of this invention, therefore, is to improve large capacity hydrocyclones whereby finer separations may be made therein by increasing the rate of introduction of feed suspension without a resultant increase in the rate of withdrawal of overflow.

These objects and others which may appear as this specification proceeds are attained by this invention which utilizes what might be termed a booster effect which is somewhat analagous to the principle of a paddle wheel. In summary, this invention essentially comprises abnormally boosting the angular velocities of the inner vortex by incrementally augmenting the tangential rate of introduction of liquid into the infeed end region of the hydrocyclone, and maintaining the rate of withdrawal of overflow substantially the same by separately bleeding-off liquid, in addition to the withdrawal of overflow and underfiow, at a rate substantially equal to the increment in the rate of tangential introduction of liquid, while controlling the fineness of separation by regulating the amount of said increment. In other words, ths invention involves the continuous tangential introduction of a quantity of booster liquid of high energy content into the infeed end of the hydrocyclone for the sole purpose of transmitting energy to the whirling body of liquid within the hydrocyclone, and then the continuous bleeding-off of .a substantially equivalent quantity of liquid to minimize an increase in the rate of withdrawal of overflow. With the increased angular velocities developed thereby within the inner vortex coarser particles are given a greater chance to develop maximum centrifugel forces without having to face an increase of the same order of the drag forces. Consequently, coarser particles in the inner vortex have a greater tendency to settle to the outer part of the inner vortex-like stream, and from this stream to the outer vortex. The finer particles, being incapable of developing centrifugal settling forces of greater magnitude than the drag forces, tend to remain within the inner vortex, and indeed within the inner part of the inner vortex.

The rate of tangential introduction of liquid into the infeed end region of the hydrocyclone is increased by introducing additional or augmenting liquid tangentially in the same direction as the main feed, through one or more inlets separate from the main inlet, or through the main inlet. The source of the additional liquid can be the feed itself since the requirement of increasing the rate of introduction of liquid into the infeed end region of the hydrocyclone is met by providing a greater supply of feed to the pump or other source of hydrostatic head and by increasing the hydrostatic head of the feed to the hydrocyclone. However, another source of the additional liquid may be, and preferably is, the additionally withdrawn. or bled-off liquid that in quantity corresponds substantially to the quantity of the booster liquid added to the feed.

Such bled-off liquid will ordinarily contain in suspension a mixture of coarse and fine particles. While the liquid may be discharged to waste or to other treatment, at least part, and preferably all can be recirculated to augment the rate of liquid input to the hydrocyclone as well as to utilize the residual energy content of the bled- Off liquid. In other words, at least a part and preferably all of this liquid after having its energy content increased as by a pump can then be introduced tangentially into the infeed end of the hydrocyclone. In case it is desired to recirculate all of the bled-off liquid, by controlling the rate of recirculation of the bled-off fraction, and thus the rate of bleed-off of liquidfrom the hydrocyclone, an eflicient method for controlling the decrease of the size of separation may be effected without having to increase the flow rate in the feed supply system preceding the improved hydrocyclone of this invention.

As to the bleeding off of liquid, the only requirement is that liquid be bled off from outside of the inner part of the inner vortex. ,For maximum energy transfer, however, it is preferred that the bled-off liquid be withdrawn from the whirling body of liquid in the same tangential direction as the direction of rotation in the region of withdrawal. While it is believed that the bledoif liquid can be withdrawn in more than one stream, it appears that normally only one stream is suflicient. In

a preferred embodiment of this invention a liquid is bled off in an annulus surrounding the overflow outlet but separated therefrom so that the overflow emerges from the inner part of the inner vortex while the bled-off liquid emerges from the outer part of the inner vortex.

Apparatus-wise, the conventionalhydrocyclone can be adapted for the increased rate of tangential introduction of liquid into the infeed end region of the hydrocyclone by one or more inlets formed respectively by the tangential disposition of a condut or conduits to the infeed end portion of the casing and in the same tangential direction as that of the main feed conduit or conduits. On the other hand, the invention is operable where only the main infeed conduit or conduits are utilized. To withdraw or bleed off liquid in addition to the withdrawal of overflow and underflow one or more auxiliary discharge outlets may be disposed about the casing, the only requirement being that they do not function to withdraw liquid from the inner part of the inner vortex. Preferably each one of the outlets that are so provided is formed by a conduit arranged to withdraw liquid in the same tangential direction as that of the rotating liquid in the region of withdrawal. Accordingly, in the aforementioned preferred embodiment of the invention the overflow outlet comprises an inner tubular conduit coaxially aligned with the axis of revolution but extending concentrically through a coaxially aligned outer tubular conduit of greater diameter disposed through the infeed end of the hydrocyclone casing, the annulus thus formed between the vortex finder and the larger tubular conduit being an auxiliary discharge outlet. The inner tubular conduit may actually comprise the conventional vortex finder in which case the adjacent auxiliary discharge outlet may comprise a tubular conduit extending into the interior of the hydrocyclone, although preferably not to the same distance to the inlet of the vortex finder. In either case, the auxiliary discharge outlet may communicate with a cylindrically shaped discharge chamber provided with a discharge conduit preferably tangentially disposed to the cylindrical wall to withdraw liquid from the chamber in the same tangential direction as the rotational direction of the liquid therein whereby loss of energy to turbulence, etc., is minimized. in either case, the tubular ,conduit comprising the overflow outlet may lead to a superimposed chamber with a tangential discharge type conduit, or it may lead to other conventional overflow discharge means.

Before proceding to a description it should be understood that inasmuch as this invention may be embodied in several forms Without departing from the spirit or essential characteristics thereof, the present embodiments are therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within the metes and bounds of the claims, or of forms that are their functional as well as conjointly cooperative equivalents are therefore intended to be embraced by those claims.

Turning now to the drawings:

Figures 1, 2 and 3 are diagrammatical illustrations of different embodiments of this invention;

Figure 4 is a perspective, partially cutaway view of a preferred embodiment of this invention.

In the drawings, basic hydrocyclone 12 comprises a hollow casing having a cylindrical section 13 of large diameter merging smoothly and without obstruction into a truncated cone section or tapering section 14 whereby a smooth, stationary surface of revolution 37 is provided. Means for forcibly introducing feed suspension tangentially into cylindrical section 13 are provided which comprise at least one conduit 17 tangentially disposed to the cylindrical section 13 to form feed inlet 18. Conduit 17 is connected to a source of hydrostatic head, not shown in the Figures 1, 2 and 3 but shown in Figure 4 as a pump 116 supplied by conduit 115. Hydrocyclone 12 is essentially provided with means for continuously withdrawing underflow at the small end of the truncated or tapering section 14, said means comprising an underflow or apex outlet 32 which, in Figures 1, 2 and 3 communicates with conduit 20, but which, in Figure 4, is open to the atmosphere, with a, surge chamber 119, to which discharge conduit 120 is attached, disposed in relation to outlet 32 to receive discharge therefrom. Hydrocyclone 12 also essentially comprises means for continuously withdrawing overflow from the infeed end region in cylindrical section 13. Such means comprise a withdrawal conduit 21 having an inlet 28 and an outlet 27, outlet 27 in Figures 1, 2 and 3 communicating with .a discharge conduit 23 while, in Figure 4, the outlet is located in fines receiving chamber 122 to which discharge conduit 123 is connected.

Under operative conditions a liquid suspension of particulate solids to be classified is continuously and forcibly introduced at a rate (0+U) through conduit 17 and inlet 18 tangentially into the interior of hydrocyclone 12 whereby .a free whirling body of liquid 36 is formed wherein centrifugal forces are developed. The hydrostatic head of the feed suspension is required to be suflicient to cause centrifugal forces to be developed of magnitude whereat the force of gravity has substantially no effect on the separation anywhere within body 36. Because apex outlet 32 is adapted for continuous withdrawal of underflow at a rate U, liquid and solids on entering body 36 tend to take a spiral-like path along the surface of revolution 37 towards the outlet 32 to thereby form outer vortex 10. Because withdrawal conduit 21 is adapted for continuous withdrawal of overflow at a rate 0 from the infeed end region of hydrocyclone 12 a portion of the liquid from the outer vortex 10 will report to inlet 28 of the withdrawal conduit 21 whereby a swirling stream or inner vortex 11 is formed in body 36. When the outlet 32 is opened to the atmosphere as in Figure 4, a centrally disposed air core 26 will be observed to lie within inner vortex 11.

Thus, two component forces act on each particle within body 36, the centrifugal force developed by each particle because of its angular velocity, which tends to move these particles towards the surface of revolution 37 and the generally oppositely directed drag force of liquid reporting to inlet 28, which tends to drag each particle towards that inlet. Particles having developed centrifugal forces in excess of these liquid drag forces, which generally are the coarser solids, tend to remain in the outer vortex 1t) and be withdrawn through outlet 32 in the under-flow whereby a coarse solids fraction is obtained at a rate U. Particles having developed centrifugal forces insufficient to overcome said liquid drag forces, which are generally the finer solids, tend to move from the outer vortex 10 into inner vortex 11 and be withdrawn through conduit 21 in the overflow, whereby a fines solids fraction is obtained at a rate 0.

To decrease the size of separation to .a value heretofore unobtainable in hydrocyclone 12, the angular velocities of the inner vortex 11 are abnormally boosted by incrementally augmenting the rate of tangential introduction of liquid into cylindrical section 13 and by bleeding off liquid from hydrocyclone 12, in addition to, and separate from, the withdrawal of overflow and underflow, at a rate substantially equal to the increment in the rate of liquid introduction. The fineness of separation is controlled by adjusting the increment of rate of tangential introduction of liquid into the body according to the fineness of separation desired.

In Figure 1 the rate of tangential introduction of liquid into cylindrical section 13 is incrementally augmented by introducing a booster liquid which has had its hydrostatic head increased to P by pump 31 into hydrocyclone 12 through outlet 35 of conduit 33 which is tangentially disposed to the cylindrical section 13 in the same direction as the rotation of the body 36. The increment Q in the rate of tangential introduction of liquid is controlled by means of valve 34 on conduit 33 according to the fineness of separation desired. In addition to the withdrawal of fine solids fraction at a rate and the withdrawal of coarse solids fraction at a rate U, liquid at a lower hydrostatic head P is separately bled oif through outlet 29 into conduit 24 leading to valve 30 and conduit 25. The rate Q of bleed-off of liquid is controlled by valve 30 so that Q is equal to Q Because the liquid is bled oif at a lower hydrostatic head P than the head P at which the booster liquid is introduced, this bled-off liquid may be termed spent liquid since it has transmitted energyto the whirling body of liquid and thus caused acceleration of the inner vortex to thereby increase the centrifugal forces in relation to the liquid drag forces and thus decrease the size of separation.

In Figure 2 the rate of tangential introduction of liquid into cylindrical section 13 is incremented by introducing booster liquid at a hydrostatic head P into the cylindrical section 13 from the tangentially disposed outlet 35 of conduit 33 while controlling its rate of introduction Q by adjustment of valve 34 according to the fineness of separation desired. In addition to the withdrawal of fine solids fraction at a rate 0 and the withdrawal of coarse solids fraction at a rate U, liquid having transmitted energy to body 36 and therefore having a hydrostatic head P is separately bled ofi? through outlet 29 into conduit 24 and recirculated therefrom through conduit 25 into pump 31 wherein the head is raised to P The liquid with its energy content thus boosted flows through conduit 33 into cylindrical section 13 as booster liquid. Valve 34 also functions in this embodiment to control the rate of bleed-off of "spent liquid.

It is important to note that in Figures 1 and 2 conduit 33 connected to inlet 35 is preferably tangentially disposed to cylindrical section 13 in the direction that will cause liquid flowing therethrough to be tangentially introduced into hydrocyclone 12 in the same direction as the direction of rotation of the body of liquid in the region of introduction. In such a manner, a maximum transfer of energy is obtained with a minimum of loss of energy through turbulence and friction. In any event,

in the embodiments of these figures, conduit 33 must never be tangentially disposed in the opposite direction to the direction of the rotation of the liquid since this would tend to slow down the whirling action in the body.

In Figure 3 the rate (0+U) of tangential introduction of liquid into cylindrical section 13 is increased by introducing additional liquid at a rate Q through outlet 35 of conduit 33 in which valve 34 is located into feed conduit 17. Liquid is separately bled off from the body 36 through outlet 29 into conduit 24 and is passed therefrom through conduit 25 into pump 31 wherein its energy is boosted to give a hydrostatic head P The rate Q of bleed-01f and thus the rate of booster liquid introduction into conduit 17 is controlled by valve 34 according to the fineness of separation desired.

In Figure 4 the rate (0+U) of tangential introduction of liquid into the infeed end region of hydrocyclone 12 is incrementally augmented by increasing the rate of introduction of feed to a rate (O-i-U-i-Q). Liquid is bled off at a rate Q from the body 36 through annular channel 129 formed between outer tubular conduit 124 and inner tubular conduit 21, and from the annular channel through discharge conduit 125. In this embodiment it willbe observed that annular channel 129 surrounds the inner tubular conduit 21 whereby inlet 28 of said conduit 21 functions to withdraw the inner portion of inner vortex 11 whereas the conduit 124 functions to remove the outer portion of inner vortex 11. Thus, with this embodiment, even finer separations are obtainable because of the segregation of particles within the inner vortex; i.e. coarser solids tend to move to the outer portion of the inner vortex as the liquid stream comprising that vortex spiralingly flows towards the infeed end of the hydrocyclone whereas the finer particles tend to re main within the inner portion of the inner vortex 11.

Although in Figure 4 valves are not shown, it will be realized by those skilled in the art that the rate of introduction of liquid can be controlled not only by a valve, but also by adjustment of the pump speed of pump 116, and that the rate of bleed-ofl? through conduit 125 may be controlled not only by a valve but also by using a pipe diameter of conduit 125 that will provide a rate of bleedoif substantially equivalent to the increment in the rate of tangential introduction of liquid. Means well known to the art such as hydrostatic pressure gauges, flow meters, and the like are not shown although it is to be understood such devices are of great help in carrying out the teachings of this invention.

In all of the described embodiments it is preferred that the bleed-oft" liquid be withdrawn in a manner to reduce losses of energy due to turbulence and friction to a minimum. This is accomplished by locating conduits 24 and 124 to hydrocyclone 12 in a manner that inlets 29 and 129 function to withdraw spent liquid from the body in the same direction of rotation as that of the body in the region of withdrawal.

This application is a continuation in part of my application for Process and Apparatus for Separating Solids in Liquid Suspension, bearing Serial No. 220,505, filed April 11, 1951, but abandoned as of January 21, 1954.

I claim:

1. In the continuous process of hydraulically classifying solids into a coarse solids fraction and a fine solids fraction, which comprises the steps of establishing and maintaining a confined, longitudinally radially symmertical body of liquid unobstructed in its interior and bounded by a smooth, stationary surface of revolution, the radius of which in any plane perpendicular to the axis of radial symmetry is maximally limited to the radius at the infeed end of the body, said surface being formed by a casing having a coaxially aligned tubular outlet for the withdrawal of liquid as overflow from the infeed end of the body and an outlet at the opposite end of the casing for the withdrawal of liquid from the body as underflow; tangentially and forcibly introducing, into the infeed end of the body, liquid and particulate solids to be classified as feed at a velocity sufficient to rapidly rotate the body on said axis and to cause solids throughout the body to develop centrifugal settling forces of magnitude sulficiently great to settle toward the surface of revolution substantially unaffected by the force of gravity; withdrawing underflow through the underflow outlet whereby liquid and coarse solids spiralingly flow without interruption adjacent the surface of revolution in an outer vortex-like stream from the infeed end of the body to said opposite end of the body and out said underflow outlet as a coarse solids fraction; continuously withdrawing overflow whereby fine solids are dragged in opposition to their centrifugal settling forces from throughout said outer stream toward said axis and in an inner vortex-like stream spiralingly flowing without interruption about said axis from the opposite end of the body into the region of withdrawal of overflow and out said overflow outlet as a fine solids fraction; the improvement for increasing the fineness of said fine solids fraction which comprises increasing the angular velocities of said inner vortex-like stream by incrementally augmenting the rate of tangential and forcible introduction of liquid into the infeed end of the body and by separately bleeding off liquid from outside of the inner portion of the inner vortex-like stream of the body at a rate substantially equivalent to the increment in the rate of tangential introduction of liquid into the infeed end of the body; and increasing the velocity of at least a portion of said bled-01f liquid; forcibly and tangentially reintroducing it into the infeed end of the body in the same tangential direction as the introduction of the feed to increase the rate of tangential introduction of liquid into the infeed end of the body; and controlling the fineness of separation by regulating the rate at which liquid is bled-off.

2. In the continuous process of hydraulically classifying solids into a coarse solids fraction and a fine solids I fraction, which comprises the steps of establishing and maintaining a confined, longitudinally radially symmetrical body of liquid unobstructed in its interior and bounded by a smooth, stationary surface of revolution, the radius of which in any plane perpendicular to the axis of radial symmetry is maximally limited to the radius at the infeed end of the body, said surface being formed by a casing having a coaxially aligned tubular outlet for the withdrawal of liquid as overflow from the infeed end of the body and an outlet at the opposite end of the casing for the withdrawal of liquid from the body as underflow; tangentially and forcibly introducing, into the infeed end of the body, liquid and particulate solids to be classified as feed at a velocity sufiicient to rapidly rotate the body on said axis and to cause solids throughout the bed to develop centrifugal settling forces of magnitude sufficiently great to settle toward the surface of revolution substantially unaffected by the force of gravity; withdrawing underflow through the underflow outlet whereby liquid and coarse solids spiralingly flow without interruption adjacent the surface of revolution in an outer vortex-like stream from the infeed end of the body to said opposite end of the body and out said underflow outlet as a coarse solids fraction; continuously withdrawing overflow whereby fine solids are dragged in opposition to their centrifugal settling forces from throughout said outer stream toward said axis and in an inner-vortex like stream spiralingly flowing without interruption about said axis from the opposite end of the body into the region of withdrawal of overflow and out said overflow outlet as a fine solids fraction; the improvement for increasing the fineness of said fine solids fraction which comprises increasing the angular velocities of said inner vortex-like stream by incrementally augmentingthe rate of tangential and forcible introduction of liquid into the infeed end of the body and by separately bleeding oif liquid from the outside of the inner portion of the inner vortex-like stream of the body at a rate substantially equivalent to the increment in the rate of tangential introduction of liquid into the infeed end of the body; and increasing the velocity of at least a portion of the bled-off liquid; introducing it into the in coming feed stream whereby the rate of introduction of liquid to the infeed end of the body is increased; and controlling the fineness of separation by regulating the rate of introduction of bled-01f liquid into said feed stream.

3. In the continuous process of hydraulic classification of solids into a fine solids fraction and a coarse solids fraction, which comprises the steps of establishing and maintaining a confined, longitudinally radially symmetrical, body of liquid unobstructed in its interior and bounded by a smooth, stationary surface of revolution, the radius of which in any plane perpendicular to the axis of radial symmetry is maximally limited to the radius at the infeed end of the body, said surface being formed by a casing having a coaxially aligned tubular outlet for the withdrawal of liquid as overflow from the infeed end of the body and an outlet at the opposite end for the withdrawal of liquid as underflow; tangentially and forcibly introducing continuously into the infeed end of the body liquid and particulate solids to be classified as feed at a velocity suflicient to rapidly rotate the body on said axis and to cause solids throughout the body to develop centrifugal settling forces of magnitude sufficiently great to settle solids towards the surface of revolution substantially unaffected by the force of gravity; continuously Withdrawing underflow through the underflow outlet whereby liquid and coarse solids spiralingly flow without interruption adjacent the surface of revolution in an outer vortex-like stream from the infeed end of the body to said opposite end of the body and out said underflow outlet as a coarse solids fraction; continuously withdrawing overflow at a significant rate whereby fine solids are dragged in opposition to their centrifugal settling forces from throughout the outer stream towards said axis and in an inner vortex-like stream spiralingly flowing without interruption about said axis from the opposite end of the body into the region of withdrawal of overflow and out said overflow outlet as a fine solids fraction; the improvement for increasing the fineness of said fine solids fraction which comprises con tinuously withdrawing in an annulus the inner portion of the inner vortex-like stream in the overflow While separately and continuously withdrawing the outer portion of the inner vortex-like stream whereby the overflow comprises fine solids substantially free from coarser solids; controlling the rate of withdrawal of overflow to be substantially equal to said significant rate by regulating the rate of withdrawal of said outer portion of the inner vortex-like stream; increasing the velocity of said withdrawn outer portion of the inner vortex-like stream and forcibly and tangentially reintroducing said increased velocity portion into the infeed end of the body to incrementally augment the rate of introduction of liquid into the infeed end of the body; and controlling the fineness of separation by regulating the rate of reintroduction.

4. In the process according to claim 3, adding said increased velocity portion to the incoming feed whereby the rate of introduction of liquid into the infeed end of the body is incrementally increased.

5. In the continuous process of hydraulic classification of solids into a fine solids fraction and a coarse solids fraction, which comprises the steps of establishing and maintaining a confined, longitudinally radially symmetrical body of liquid unobstructed in its interior and bounded by a smooth, stationary surface of revolution, the radius of which in any place perpendicular to the axis of radial symmetry is maximally limited to the radius at the infeed end of the body, said surface being formed by a casing having a coaxially aligned tubular outlet for the withdrawal of liquid as overflow from the infeed end of the body and an outlet at the opposite end for the withdrawal of liquid as underflow; tangentially and forcibly introducing continuously, into the infeed end of the body, liquid and particulate solids to be classified as feed'at a velocity sufficient to rapidly rotate the body on said axis and to cause solids throughout the body to develop centrifugal settling forces of magnitude sufliciently great to settle solids towards the surface of revolution substantially unaffected by the force of gravity; continuously withdrawing underflow through said underflow outlet whereby liquid and coarse solids spiralingly flow without interruption adjacent the surfaces of revolution in an outer vortex-like stream from the infeed end of the body to said opposite end of the body and out said underflow outlet as a coarse solids fraction; continuously withdrawing overflow whereby fine solids are dragged in opposition to their centrifugal settling forces from throughout the outer stream towards said axis and in an inner vortex-like stream spiralingly flowing without interruption about said axis from the opposite end of the body into the region of withdrawal of overflow and out said overflow outlet as a fine solids fraction; the improvement for controlling the fineness of separation which comprises continuously withdrawing in an annulus the inner portion of the inner vortex-like stream as said overflow while separately and continuously withdrawing the outer portion of the inner vortex-like stream whereby said overflow comprises fine solids substantially free from coarser solids; controlling the rate of withdrawal of overflow to give a predetermined fineness of separation by regulating the rate of withdrawal of one of said portions of the inner vortex-like stream; and increasing the velocity of at least a part of one of the withdrawn portions of the inner vortex-like stream and forcibly and tangentially introducing it to the infeed end of the body to incrementally augment the rate of introduction of liquid into the infeed end of the body.

6. In the process according to claim 5, adding said increased velocity portion to the incoming feed whereby said increased velocity portion is introduced into the in- 3 feed end of the body.

7. Method of operating .a hydrocyclone classifier having a body of liquid rapidly rotating within a casing which is provided with axial overflow and underflow outlets at opposite ends of said casing, and in which a liquid suspension is continually tangentially and forcibly fed to said body at one end of said casing at a velocity sufficient to rapidly rotate the body to cause solids therein to develop centrifugal settling forces of a magnitude sumciently great to substantially render the settling force of gravity ineffective, continually discharging a coarse solids fraction of said suspension from said underflow and a fine solids fraction of said suspension from said overflow outlets; characterized by the steps comprising continually and simultaneously forcibly introducing a volume of booster liquid tangentially to the infeed end of said body and in the direction of rotation thereof, and continually discharging from outside the inner portion of said body a volume of liquid equal to said booster volume.

References Cited in the file of this patent UNITED STATES PATENTS 762,867 Allen June 21, 1904 2,098,608 Berges Nov. 9, 1937 2,360,355 McBride Oct. 17, 1944 2,498,832 Watson Feb. 28, 1950 2,724,503 Fontein Nov. 22, 1955 2,756,878 Herkenhofi July 31, 1956 FOREIGN PATENTS 340,027 Great Britain Dec. 19, 1930 OTHER REFERENCES Canadian Mining Journal, volume 71, Number 6, June 1950, The Dorrclone System, pages 68-69.

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