US3369663A - Process and apparatus for the application of centrifugal force - Google Patents

Description

1968 J. J. SERRELL 69,663

PROCESS AND APPARATUS FOR THE APPLICATION OF CENTRIFUGAL FORCE Filed April 6, 1967 2 Sheets-Sheet l INVENTOR.

ATTORNEYS.

Feb. 20, 1968 J. J. SERRELL PROCESS AND APPARATUS FOR THE APPLICATION OF. CENTRIFUGAL FORCE 2 Sheets-Sheet 2 I Filed April 6, 1967 United States Patent 3,369,663 PROCESS AND APPARATUS FOR THE APPLICA- TION 0F CENTRIFUGAL FORCE John J. Serrell, Coopertown Road, Havel-ford, Pa. 19041 Continuation-impart of application Ser. No. 464,293,

June 16, 1965. This application Apr. 6, 1967, Ser. No. 633,352

14 Claims. (Cl. 210-78) ABSTRACT OF THE DISCLOSURE Process and apparatus for centrifugally separating material into two phases by means of a continuous belt which is driven through a predetermined path, one portion of which is an unconstrained gyre or helix unsupported along its width and length through its path of travel. The material to be separated is fed onto the inner curved surface of the belt at the point where the belt enters the unsupported gyre or helix and is removed from the belt at a point where the belts curvature reverses upon leaving the gyre or helical path.

This application is a continuation-in-part of my application Serial Number 464,293, filed June 16, 1965 now abandoned.

Background of the invention A wide variety of centrifugal machines using the principle of screening, have been develoepd for the separation of solids but, insofar as I am aware, all suffer from one or more major shortcomings.

One basic type consists of a rotating perforate basket which is loaded with slurry when the basket is at rest or moving slowly, accelerated to perform the separation of the mother liquid, then slowed or stopped to permit removal of the deliquefied solids. This is wasteful of time and power. The solids bed must be of appreciable thickness to permit economic quantities of solids to be treated each cycle. Construction must therefore be thick walled and expensive to withstand the stresses induced in the basket wall. If failure should occur, the release of great kinetic energy in a short time is dangerous.

In such a basket centrifuge, the thick solids layer forms a multiplicity of tiny interstices, requiring the liquid to drain relatively slowly through long and narrow passageways. Many of these are frequently small enough so that surface tension will retain liquid and drainage will not be complete. When the nature of the solids or mother liquor makes the use of a purifying rinse desirable, the rinse liquid must also find its way through these narrow passageways, with the additional difficulty that it will preferentially and inefficiently seek out the larger passages, shunning the smaller ones that may still be filled with impure liquid, which phenomenon is commonly known as channeling. If, additionally, the solids bed is flexible under the centrifugal loading of the thick layer, the interstices become even smaller at their exit ends and final residual moisture contents become even greater.

Considerable ingenuity has gone into efforts to mitigate the effect of the difiiculties described with the basket centrifuge, by automating the machine so as to cause the basket to rotate continuously in a controlled cycle, in which a predetermined charge is fed, and an attempt is made to level the charge mechanically to avoid unbalance. In such a machine, time is provided for drainage as best it can occur through the long passageways, and, after a predetermined rinse is added, time must again be provided for drainage. The solids are finally discharged by introducing a stationary knife to cut them out of the rotating basket.

Some of the problems encountered by such machines are glazing of the solids surface by the action of the discharge knife, screen blinding because of incomplete removal of the solids, danger of disastrous contact between the knife and the basket if more complete removal is attempted, and high wear rates on the knife and leveler. Further, if the solids are crystals, the knife will fracture them and if they are flexible or amorphous, satisfactory discharge may be impossible.

In other machines, the layer of solids is caused to move with respect to the screen. Some of these machines push the solids layer axially by complex mechanical or hydraulic mechanisms until they pass over the end of the basket. Others vibrate the solids axially along cylindrical or conical baskets. Others cause the solids layer to move over the basket by a multiplicity of differentially rotating vanes or scrolls, generally causing screen areas to be incompletely covered and therefore inefficiently used as Well as allowing passage of rinse liquid through such areas. Additionally, such machines are characterized by solids impact and breakage at discharge, particularly when the solids are crystals, grinding of the solids against each other and screen abrasion under the high centrifugal loadings. When the solids are flexible or amorphous, screen blinding is also common.

A final class of screening centrifuge comprises an endless foraminous belt constrained in an arcuate path, such as the passage of a belt around a pulley with the slurry to be treated being fed to the inside of the belt. Such machines have never been satisfactory due to a number of reasons, the more important ones being the failure of the machine to treat the material through an arc of substantially less than a complete revolution, the

Y mechanical complexity introduced by necessary constraints, discharge of the solids within the mechanism and sealing difficulties between the pulley and the belt.

Conventional sedimentation centrifuges require that the sedimentation generally take place through long distances both radially and axially with much of the liquid in regions of less than the maximum centrifugal force available. It is well known that the power input to such centrifuges must generally be twice the kinetic energy of the discharging liquid, plus an amount of energy approximately equal to that kinetic energy required to be absorbed in internal passage through the machine and in turbulence despite the desire for quiesence in the sedimentation region.

Brief summary of invention My invention eliminates the undesirable features hereinbefore enumerated. It only requires a power input substantially equivalent to the energy loss in the discharging materials plus windage and friction. In the continuous screening centrifuge, it accomplishes rapid drainage, efficient rinsing, low residual moisture and discharges the solids without the necessity for high energy impact. In the sedimentation centrifuge, it affords short sedimentation paths, and treats all of the liquid at the maximum centrifugal force generated. It is mechanically simple, yet provides an effective length of time under centrifugal force.

In accordance with the present invention, considering first the separation of solids from liquids, a portion or linear segment of an endless foraminous belt, unsupported in its entirety along its length and width, is caused to move in an arcuate path at a high linear velocity. The mixture to be separated is fed to the inside surface of the belt at a rate to produce a thin film immediately after the point at which the belt passes into its unsupported configuration. Equilibrium with respect to surface tension is rapidly attained due to the short drainage path and, if desired, the thin layer of solids may be rinsed by directing Washing 3 liquid upon the solids layer. As the belt passes out of the gyre, its curvature is reversed about a guide pulley with consequent reversal of the direction of centrifugal force to effect discharge of the solids accumulation.

The invention is also applicable to clarification or separation by sedimentation. By using an impervious belt providing a gyre as already mentioned, the centrifugal force effects separation as the liquid moves outwardly. By constructing the belt with grooves along its edges, liquid of lesser density will overflow the edges of the belt and liquids or solids of greater density will be trapped to be discharged when the direction of curvature of the gyre is reversed. Although only one of the phases is completely purified at a time, the other may be recycled for further treatment.

The general objects of the invention will become apparent from the foregoing brief description, and these and other objects relating to details of construction and operation will become apparent from the following description read in conjunction with the accompanying drawings in which:

FIG. 1 is an elevation of a preferred form of the apparatus;

FIG. 2 is a section taken on the plane indicated at 22 in FIG. 1;

FIG. 3 is a fragmentary section taken on the plane indicated at 3-3 in FIG. 1;

FIG. 4 is a section taken on the plane indicated at 4-4 in FIG. 2 with certain parts omitted;

FIG. 5 is a section taken on the plane indicated at 5-5 in FIG. 4; and

FIG. 6 is a fragmentary sectional view illustrating the arrangement which may be used for liquid-from-liquid separation or separation by sedimentation of solids.

For purposes of brevity and to bring out the principles of the invention, the following description will deal in full with fundamentals from which mere mechanical details will be obvious to those skilled in the art.

Referring first to the embodiment of the invention concerned with removal .of solids from liquids, the apparatus comprises as its principal element an endless foraminous belt 12, of a type later described, having a section or linear segment forming a gyre 14 positioned within casing 16 and comprising a free-floating turn unsupported in its entirety along its length and width which gyre may involve a partial or a full turn or a plurality of turns, said gyre, as shown, taking more or less the shape of a. helix.

The belt 12 enters the casing 16 between guide pulleys 18 and 20, and takes the form of gyre 14 in casing 16, and leaves casing 16 between guide pulleys 22 and 24. The belt then passes over spaced guide pulleys 26 and 28, returning to ulleys 18 and 20 to complete the circuit. Guide pulley 22 desirably engages only the edges of the belt to avoid crushing .of material thereon.

The orientation of the pulleys need not be specifically described since it is in accordance with belt feed practices well-known in the art.

Any suitable means may be provided for driving the belt 12 to maintain the gyre 14; for instance, pulley 18 may be driven by a motor 19. A drag may be provided on pulley 24 by a braking device to maintain the belt 12 taut about pulleys 26 and 28, thus maintaining constant that portion of the endless belt available for the formation of the gyre.

The mixture containing the suspended solids preferably can be fed on the belt at any point subsequent to the initiation .of the gyre, for example by a feedpipe 30 passing through casing 16 and having its outlet 32 positioned to deposit the mixture upon the interior of the belt 12, preferably more or less tangentially and at a delivery velocity approximately equal to the linear speed of the belt.

T he liquid discharged through the belt in the gyre 14 is collected in casing 16 and flows off therefrom through outlet 34. The solids are removed from the belt 12 by inertia as the belt passes out of the gyre and reverses its direction at 36 in passing over the pulley 24. The solids are directed into hopper 38.

In the centrifugal separation of solids from liquids by screening, it is frequently desirable to wash or rinse the solids after their initial separation from the major part of the liquid, water being a commonly used liquid when the original suspension is aqueous. To accomplish this, the washing or rinsing liquid may be introduced through a pipe 40 passing through the casing 16 and having an outlet 42 positioned to deposit the rinse liquid upon the solids on the belt 12. It may be desirable to introduce the liquid at a speed somewhat different from the belt to provide a relative flow as the liquid is brought to belt speed, which flow will produce disturbance of the solid material and hence facilitate completing washing. If it is desired to collect rinse liquid separate from the liquid of the original mixture, which is usually the case, an annular baffle, shown at 44, attached to the inner wall of casing 16 and having an inner opening sufficient to clear gyre 14 when in operation, may be provided.

The gyre provided as described is free-running and stable in the sense that it will not depart to any great extent from a mean shape, though vibratory motions may take place. This may be understood by making comparison initially with a static gyre. If a uniform metal band is bent flexibly into a helical shape, the helical form will be stable. A small disturbing force may cause distortion of the helical shape temporarily, but when the force is removed, the helical shape will be regained. This results from the fact that the bending moment throughout the length of the band is constant at equilibrium. If the helical shape is disturbed, unequal bending moments are produced and tend to return the shape to that of the helix when the disturbing force is removed. Under the influence of gravity, the equilibrium position is one that shows some sag from a geometrical helix, the amount of sag depending primarily upon the length of span, the belt section modulus, the helix diameter and angle.

In the free-running gyre, there is substantially a uniform tension induced in the belt by the centrifugal force to which it is subjected. The tension is constant in mag nitude, but changing in direction, giving rise to force components at right angles that have an effect similar to those of the bending moments in the static case. Equilibrium, without the presence of an external disturbing force, requires these to be uniform. This requires the rate of curvature to be constant and produces a geometrical helix. The higher the belt speed, the higher the centrifugal force, and the higher the force components or stiffening that results. If the gyre has a certain stiffness when stationary and, hence, a certain sag, this sag will be less when the gyro is rotating, comparable to that of a stationary gyre having a static stiffness of the rotating gyre plus the induced stiffness due to the centrifugal force.

Thus, in a particular design of gyre, one or more longitudinal bars may be required to aid the gyre in maintaining a helical configuration while stationary and during start-up until operating speed has been reached at which time the belt will be free from the bars.

The rotating gyre is a system of many degrees of freedom, giving rise to critical speeds. Critical speeds are familiar to the centrifugal designer because most cen trifugal machinery operates above one or more such speeds. It is usual to pass through the critical speed ranges either by rapid acceleration and deceleration, or by providing constraints to limit the pertubations to a tolerable level, or by the provision of damping, or by a combination of these means.

I A dynamic analysis of the gyre of the present invention, experimentally confirmed by example, shows that there are wide ranges of stable and satisfactory operation. One such gyre consisting of a two-turn helix, with a 14" helix diameter and 36" span, with a 6" wide perforated belt made of .100" thickness material having a modulus of elasticity of 150,000 p.s.i., shows a critical operation at about 80-100 ft./sec. and stable operation in the range of 120200 ft./sec. Although the helix will be in a state of substantial collapse when sationary, at operating speed, the equilbrium maximum sag under gravity at the center is about A At this point, reference may also be made to the nature of the belt. With an arrangement such as the generally helical gyre illustrated, it will be evident that the belt could not, if freed from all guides, assume a cylindrical configuration, i.e., it will necessarily involve a twist about its center line. In practice, of course, the ends of the belt will be secured together to provide the proper configuration. It may be noted that if instead of complete twists, half twists are provided, the liquid will pass through the belt alternately in one direction and then the reverse direction during succeeding cycles of passage of the belt. The configuration here referred to is the mathematical Moebius surface.

While reference has been made to the provision of at least a single complete turn in the gyre, it 'will be obvious that, under circumstances of very rapid removal of liquid from suspended solids and absent washing, there may be provided less than a complete turn.

The foraminous belt may be of numerous types depending upon both the physical and chemical nature of the material being handled.

With a perforated belt it can be seen that the holes tend to close on the inside of the gyre and open at the exit of the belt from the gyre, the opening during the reversal from the gyre serving to release more effectively any accumulated solid material which might tend to plug a hole. Whenever this effect is inadequate to keep the screen clear, backflushing can conviently be done by adding a rinse directed against the inside of the belt just before it passes over pulley 26.

A configuration of the belt 12 useful for screening purposes is shown particularly in FIG. 3, the belt being liquid pervious, and provided on its face, that is on the surface upon which the mixture to be separated is deposited, with laterally spaced longitudinally extending endless ribs or dams 56 attached to the belt in any desired manner. As shown, ribs 56 are V-shaped in cross-section but may be of any other suitable cross-sectional configuration. To accommodate ribs 56, pulleys over which the ribs pass are provided with corresponding clearance grooves 60. The other pulleys may have flat cylindrical surfaces as shown, although other configurations are not precluded.

The mixture to be separated is deposited on the face of belt 54 between ribs 56, such as in a manner above described. The solids are contained between the ribs 56 until discharged at 36.

While one form the free-floating gyre may take is referred to above as more or less the shape of a helix, one of the outstanding features of the invention is versatility in this respect resulting from the free-floating gyre concept. By reason of this concept, the gyre automatically adjusts itself to wide variation in loading conditions, with whatever attendant changes in shape take place from a true helical form and accommodates itself to stable rotation without being concerned with maintaining a given geometric axis coincident with an axis of inertia to mimimize bearing loads or accommodate unbalance. Included therein is loading and change in load as separation proceeds along the gyre.

Also, the free-floating concept permits other departures from a true helical form made possible, for example, by adjustment of entrance and/or outlet pulleys to tip the face of the belt relative to the axis of rotation, that is, from a condition of parallelism thereto.

With the more complete description, now available, it is easier to understand some of the advantages with respect to a conventional centrifuge of similar diameter and centrifugal force. Because of the small amount of material under treatment at any one time, the belt stresses are low and failure would involve only a relatively small amount of kinetic energy. Protective housings consequently need not be massive. Operation under a pressure atmosphere can also be readily conducted.

The conventional centrifuge discharges the solids at high linear velocity in clumps into a rotating air stream where they are centrifuged into the large collective housing and impacted. The machine of the invention discharges a thin layer in a narrow arc so that there is good dispersion. Rapid deceleration results and the discharge path can readily be of any desired length.

After centrifugal drying, many materials, require further heat drying. For the conventional processing operations, the solids must be collected from the centrifuge and then dispersed into the heating chamber or spray drier. For the gyre, this dispersal is already ideally available and properly directed and all that is necessary is to counterflow warm gas through housing 38 axially extended, or to permit housing 38 to abut the drying chamber more conventionally arranged. For many materials, particularly those that compress or mat, further treatment may require redispesrion in liquid, vapor or gas treatment, or the like. With conventional centrifuges, this requires a complete intervening process of redispersal after collection. With the gyre, the intervening process is eliminated.

Heretofore, reference has been made to accumulation of the solid material in the form of discrete particles. If the solid material is fibrous, as, for example, if a paper stock is fed to the gyre, felting may be produced, and in such case, as the belt passes out of the gyre the resulting felted sheet may be stripped 01f as a continuous web to pass to drying apparatus or other further processing.

A belt suitable for sedimentation is illustrated at 48 in FIG. 6. Belt 48 is provided with laterally spaced endless annular grooves 50, that is, grooves that extend throughout the length of the belt. The mixture to be separated is fed onto the middle of the belt 48 through feed plate 52. The mixture spreads outwardly toward the edges of belt 48, whereupon the heavier phase deposits in grooves 50, and the lighter phase overflows the edges of belt 48 to be collected in casing 16. As belt 48 passes around pulley 24, the heavier phase is deposited in hopper 38.

In addition to separation, the invention also lends itself to the production of sheets by the utilization of an impervious belt to which material may be fed with the production of a solid film or sheet on the belt. For example, a molten material, such as a metal or a liquefied plastic, may be fed onto the belt with temperatures such that, during the passage through the extent of the gyre, solidification into a film or sheet will result, with peeling off of the film or sheet as the gyre terminates. Cooling fluid may be sprayed on the belt or molten material. In similar fashion, a material in a volatile solvent may be sprayed or flowed upon the belt under conditions to provide rapid evaporation leaving the solute as a sheet or film. For example, the gyre may be located in a vessel under high vacuum, with heating of the belt to provide for the rapid evaporation. In the case of sheeting, the impervious belt would desirably be provided with edge dams as in the case of the screening belts previously described.

While the device has been described in preferred form, it is not limited to the exact structures illustrated, as various changes and modifications may be made without departing from the scope of the appended claims.

What is claimed is:

1. A centrifugal separator comprising:

a belt,

means for moving said belt,

means for maintaining a portion of said belt in the form of a free-floating gyre unsupported along its length and Width,

means for feeding a mixture of phases onto said belt for centrifugal separation Within said gyre,

means for removing said phases in separated condition from said belt, and

said belt being impervious to liquid and provided with means for holding the heavier of said phases on said belt during discharge of the lighter of said phases from said belt.

2. The method of separating material into two phases which comprises:

driving at high speed through at least substantially one revolution of an arcuate path, a linear segment of an endless linear element, said segment being upsupported in its entirety along its length and width in its passage through said arcuate path for the development in said path of centrifugal forces upon said element, supplying said material to said element as it enters into said arcuate path for centrifugal separation of said phases, and removing said phases from said linear elements.

3. The method of separating a mixture of liquid and solid materials into two phases by transport of the same through a helical-like path on a foraminous belt, one portion of which is unsupported along its length and width, and the remaining portion of the belt being supported by driving and idler pulleys which comprises:

driving the unsupported portion of said foraminous belt at high speed through a helical-like path of length at least about one turn,

developing tensional forces lengthwise of said supported portion of said belt during said driving of said unsupported portion of said belt through said helical-like path,

continuously supplying said mixture of said materials to said belt for flow of the liquid phase through the belt by the applied centrifugal force as said mixture is carried through said helical-like path, and removing the remaining solid phase from the belt.

4. Apparatus for separating a mixture of liquid and solid materials into its liquid and solid phases comprising:

a foraminous endless belt, a linear segment of which is in the form of a helix within which helix said segment is unsupported in its entirely along its length and width for establishment of an arcuate path of at least substantially one revolution for traverse thereof by said belt,

means for feeding the materials to be separated onto said belt,

means for driving said belt at high speed through said arcuate path for removal of liquid by flow through said belt under the influence of centrifugal force on said liquid thereby separating said material into its said liquid and solid phases, and

means for removing the separated materials from said belts.

5. Apparatus for separating materials into two phases by application thereto of centrifugal force which comprises:

an endless belt, a linear segment of which is constrained and the remaining linear segment of which is unconstrained, said remaining unconstrained linear segment of said belt forming a generally helical configuration within which said remaining linear segment is in its entirety unsupported along its length and width to establish an arcuate path of at least substantially one revolution for traverse thereof by said belt,

means disposed at the junctures between said constrained and said unconstrained segments of said belt for driving the same at high speed through said arcuate path and for maintaining said constrained segment of said belt under tension,

means for supplying said material to said belt for separation of the same into said two phases by the centrifugal force applied thereto during traverse of said arcuate path, and

means for removing said two phases from said belt.

6. Apparatus for separating material into two phases by application thereto of centrifugal force which comprises:

an endless belt, a linear segment of which is constrained under tension and the remaining linear segment of which is unconstrained and unsupported in its entirety along its length and width, said unconstrained segment-of said belt being of generally helical configuration to establish an arcuate path of at least substantially one revolution for traverse thereof by said belt,

driving means disposed at one of the junctures between said constrained and said unconstrained portions of said belt for driving the same through said helical path,

means at the other of said junctures for developing said tension on said constrained portion of said belt, means for supplying said material to said belt for separation into said two phases by the centrifugal force applied thereto during traverse of said arcuate path, and means for removing said two phases from said belt.

7. A centrifugal separator comprising:

a belt,

means for moving said belt,

means for maintaining a linear segment of said belt in the form of a free-floating gyre the entire segment within said gyre being unsupported along its length and width, means for feeding a mixture of phases onto said belt for centrifugal separation within said gyre, and means for removing said phases in separated condition from said belt.

8. The centrifugal separator of claim 7 wherein said belt is pervious to liquid.

9. The centrifugal separator of claim 8 wherein said belt is provided with laterally spaced ridges,

10. The centrifugal separator of claim 7 having means for distributing said mixture of phases across the width of said belt.

11. Apparatus comprising:

a belt,

means for moving said belt,

means for maintaining a linear segment of said belt in the form of a free-floating gyre, the entirety of said segment within said gyre being unsupported along its length and width,

means for feeding a material upon the interior of the belt in its passage as said gyre, and

means for removing the material from the belt.

12. A centrifugal separator comprising:

an endless foraminous belt.

means for moving said belt,

means for maintaining a linear segment of said belt in the formof a free-floating substantially helical gyre, the entire segment of said belt forming said gyre being unsupported along its length and width and having a plurality of turns,

means for feeding a mixture of phases onto said belt for centrifugal separation within said gyre, and means for removing the retained phase from said belt.

13. A centrifugal separator comprising:

an endless foraminous twisted belt,

means for moving said belt,

means for maintaining a linear segment of said belt in the form of a free-floating substantially helical gyre which gyre is unsupported in its entirety along its length and width and has a plurality of turns, means for feeding a mixture of phases onto said belt for centrifugal separation within said gyre, and means for removing the retained phase from said belt.

14. A centrifugal separato i comprising: Referen c s Cited an igrigminous twisted belt in the form of a UNITED STATES PATENTS means f moving said belt, 736,596 8/ 1903 Grondahl 210401 X means for maintaining a linear segment of said belt 5 1346,1655 2/1932 Webb in the form of a free-floating substantially helical gyre which gyre is unsupported in its entirety along SAMIH ZAHARNA Pnmm'y Exammer' its length and width and has a plurality of turns, REUBEN FRIEDMAN Emmi-"en means for feeding a mixture of phases onto said belt for centrifugal separation Within said gyre, and 10 I. L. DE CESARE, Assistant Examiner.

means for removing the retained phase from said belt.

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