US3397792A - Apparatus for the application of centrifugal force - Google Patents

Description

1968 J. J. SERRELL 3,397,792

APPARATUS FOR THE APPLICATION OF CENTRIFUGAL FORCE Filed March 4, 1966 2 Sheets-Sheet 1 ni -gm 23 FIG. I.

I f/ll/l/l/l/l/ [ll/ll/l/ll/I/J/ I I f l O I z U101: I 1 x a? l l 2| l/lll/l/l/ll/l/l/j/ /////1 FIG. 2. INVENTOR JOHN J. SERRELL 1968 J. J. SERRELL 3,397,792

APPARATUS FOR THE APPLICATION OF CENTRIFUGAL FORCE Filed March 4, 1966 2 Sheets-Sheet 2 b v G RESIDUAL MOISTURE C .I I I0 I00 BED COMPOSITION IN NUMBERS OF PARTICLE LAYERS F l G. 5.

RESIDUAL MOISTURE GENTRIFUGAL FORGE F l G. 6.

INVENTOR JOHN J. SERRELL United States Patent APPARATUS FOR THE APPLICATION OF CENTRIFUGAL FORCE John J. Sen-ell, Coopertown Road, Haverford, Pa. 19041 Continuation-impart of application Ser. No. 464,293,

June 16, 1965. This application Mar. 4, 1966, Ser. No. 531,819

5 Claims. (Cl. 210--370) ABSTRACT OF THE DISCLOSURE Apparatus for centrifuging material. The apparatu includes an endless belt which is supported by and driven through a path defined by a separating pulley in engagement with the outside surface of the endless belt and at least two additional pulleys in engagement with the inside surface of the belt which maintain the belt in engagement with the separating pulley, such that the material to be separated can be fed onto the outside of the belt for passage around the separating pulley and then discharged away from the confines of the belt as the belts curvature changes as it passes one of the additional pulleys.

The method includes feeding material to be treated to the centrifuge such that the material may be spread thereon in a mono-particulate layer.

BACKGROUND OF INVENTION This application is a continuation-in-part of my parent application Ser. No. 464,293 filed June 16, 1965, and now abandoned, for Process and Apparatus for the Application of Centrifugal Force.

In my aforesaid parent application I described, in some detail, the problems arising with centrifugal machines of the type heretofore proposed and how, in accordance with the invention of that application, many of the problems of the prior art were overcome. I also explained in my parent application how one may treat materials by centrifugal force with such materials in very thin layers and some of the advantages thereof. In the present application I have directed the claims to that subject matter and also to further refinements thereof.

The subject of the present invention concerns centrifugal treatment of material deposited on a portion of an endless belt which is caused to move in an arcuate path. In the aforesaid application, the arcuate portion was freefloating and the time available for the continuous application of centrifugal force was not limited to less than one complete revolution. In the present application, it is shown how the combination of newly discovered techniques can be advantageously applied to those cases where the drainage rates are very high and thus make possible the use of a simpler machine with a constrained portion of the belt comprising less than one complete revolution, if the machine is also constructed in accordance with the present invention. It should be understood, of course, that these new techniques may also be advantageously applied to other equipment, including the free-floating type apparatus of my parent application.

It has previously been proposed to construct a centrifugal machine by causing a belt to move over a portion of a separating pulley, or portions of more than one separating pulley with straight sections of the belt between the pulleys. Those machines in which the inside surface of the belt engages the separating pulley and in which the belt moves in the plane of the separating pulley, passing thereabout for less than a full revolution, such as the OBrien and Funk Patent 3,089,596, inherently must discharge the solids within the confines of the machine. This configuraice tion makes impossible the prevention of readmixture of the separated liquid which is present at high Velocity throughout the housing. Such machines also do not admit of the benefits to be gained by a collimated discharge of the solids for an appreciable unhindered distance, as outlined in my patent application. Machines employing a plurality of separating pulleys and therefore causing the belt to pass out of the plane of one separating pulley, such as the Walker Patent 1,767,905, could in theory be constructed so as to conduct the discharging solids away from this readmixture. Such machines are, however, cumbersome and not practical. The solids do not pass smoothly from one pulley to the next through the straight sections of the belt that are required. They come off the belt to an intolerable extent at these locations because of the influence of gravity, the necessary twist of the belt that gives rise to inertial forces, the vibration of the belt and air resistance. Machines of this type are therefore not successful. Machines of the OBrien type could be improved by mounting the discharge pulley at an angle with respect to the plane of the separating pulley. This would permit the discharging solids to have a clear path and make it possible to construct baffies designed to minimize readmixture of the discharging liquid. Such proposals would require operation with a twisted belt and would provide other problems that would make them inferior to the construction that is the subject of the present invention.

SUMMARY AND OBJECTS OF INVENTION It is an object of the present invention to provide a simple, rugged centrifugal machine, operating with an untwisted belt at high speed, in a configuration wherein the center-line of the belt is maintained in a single plane throughout its path of travel and such that will discharge the solids in a clear and unhindered path, without readmixture of the separated liquid.

It is another object of the present invention to provide a centrifuge which discharges the separated material from the centrifugal force-producing element which centrifuge includes a separating pulley, at least two additional pulleys and an endless centrifuge belt which forms a closed loop and defines an inside and outside surface of the belt. The belt is supported in its path of travel by means of the separating pulley and additional pulleys with the outside surface of the belt in engagement with the separating pulley while the inside surface of the belt is in engagement with the additional pulleys and the centrifuge further includes a chamber defined by the separating pulley and the belt together with means for driving the endless belt through its path of travel at a speed which develops a centrifugal separating force of substantial magnitude. It is another object to provide newly discovered techniques for those machines which can successfully employ a thin layer in order to achieve high production rates with minimum residual moisture.

Another object of the invention is to provide apparatus for the continuous centrifugal separation of solids from liquids whereby minimum residual moisture content in the separated solids is realized by destroying the effect of capillarity in the separating operation.

A further object of the invention is the provision of apparatus for the centrifugal separation of materials, whereby the particle size degradation inherent in conventional centrifugal apparatus operation is avoided and a reduced minimum final residual moisture content in the separated solids is achieved.

Still a further object of the invention is the provision of apparatus for the continuous centrifugal treatment of materials, wherein classification or separation of slimes or fines may be combined with the centrifugal drying operation and accomplished concurrently therewith,

rather than requiring classification processing prior to drying, as heretofore done, this invention thus achieving more rapid complete processing with lesser equipment requirements and overall greatly improved efficiencies in operation.

For further objects of the invention and for more details in respect to the theory underlying this invention, reference is to be had to the following description and the accompanying drawings in which:

FIG. 1 is a side elevation view of a preferred embodiment of a centrifuge with which my methods may be practiced;

FIG. 2 is a plan view in section, taken on the line 2-2 of FIG. 1 to illustrate the pulley arrangement, to which is added a schematic representation of the slurry feed to the machine;

FIG. 3 is a sectional view taken on the line 3-3 of FIG. 2 to show the belt and the separating pulley;

FIG. 4 is an enlarged fragmentary sectional view of the belt which is particularly adaptable for use with the apparatus of this invention.

FIG. 5 is a graph useful in illustrating the advantages of feeding less than one complete layer of solids;

FIG. 6 is a graph useful in illustrating the advantages of eliminating particle size degradation during centrifugation.

DESCRIPTION OF INVENTION Referring now to the drawings, there has been illustrated in FIGS. 1 and 2 a centrifuge comprising a housing 10-within which there is disposed an outside separating pulley 11, an inside discharge pulley 12, an inside feed pulley 13, or pulley after which feed is to be added and two idler pulleys 14.

Fitted around this configuration of pulleys in the manner shown is an endless foraminous belt 15, which may be tensioned by having one of the pulleys 14 spring loaded to move outwardly. It is to be observed that the endless belt 15 forms a closed planar loop. The surface of the belt on the inside of the closed loop will be referred to as the inside surface of the belt, and the opposite surface will be referred to as the outside surface. As best shown in FIGS. 1 and 2, the several pulleys 11, .12, 13 and 14 are all disposed so as to maintain the belt untwisted and with its center line in a single plane throughout its path of travel. Accordingly, the belt itself forms a closed planar loop, meaning it is not twisted and its center line is in a single plane.

As will now be explained, by the described arrangement, the material to be centrifuged will be introduced onto the outside surface of the belt and subjected to centrifugal force during its passage on the belt around a part of the periphery of the separating pulley 11. The solid material will then be discharged from the outside surface of the belt through an opening 10a as shown by the arrow 29. Although any one of the pulleys may serve as the driving element, FIG. 1 shows a motor 16 that drives pulley 11 through a belt drive 17, to cause belt 15 to be driven in the direction of the arrow 18 at a speed which develops a centrifugal force of substantial magnitude as the belt passes about the pulleys.

As shown in FIG. 3, the pulley 11 is provided with a peripheral recess 11a, forming an annular chamber between the outside surface of the belt 15 and pulley 11, within which the material under centrifugal force will be held, although this chamber might just as readily be formed by having protruding ridges on the belt in contact with a fiat or crowned pulley.

Material to be subjected to centrifugal force is supplied through pipe 20 by motor-driven pump 21, past valve 22, into inlet pipe 23 and through nozzle or feed spreader 24, located in substantially tangential relationship to pulley 11 near the region where belt 15 is driven through the arcuate path in which the centrifugal force is to be developed. The rate of feed of the material may be controlled by valve 22 or by a speed adjustment of the motor connected to pump 21. The speed of rotation of pulley 11 may be adjusted by changing the speed of drive motor 16 or the pulley ratio of belt drive 17, as required by materials of different kinds and the magnitude of the centrifugal force to be developed.

With the machine operating at conventional speeds, it will be understood that the velocity of the feed stream can be adjusted by varying the flow through inlet pipe 23 or the opening of nozzle 24, so that the material will move at the speed of the belt 15 into the arcuate portion Within which there is developed centrifugal force. As indicated, the belt 15 is foraminous and liquid moving outwardly under centrifugal force through the belt will strike baffie 25 and be deflected downwards and out of the plane of rotation of pulley 11, and into a collecting chamber 26 and thence discharged through outlet 27. Baflle 25 is formed in the manner as shown at 28, in order to prevent the carry-around of discharging liquid into the region of the discharge pulley 12. After the material has been treated within the arcuate path and the liquid drained away as described, the solids are discharged tangentially from the outside surface of the belt in a direction shown by arrow 29 as the inside surface of the belt passes over separating pulley 12 to cause the belt 15 to move away from the inertial path of the solids, and the solids pass out of housing 10 through opening 10a.

In this manner, the material being centrifuged is discharged outwardly of the closed loop and free of the belt inasmuch as the material is, in efiect, disposed on the outside surface of the belt in passage of the separating pulley rather than on the inside surface thereof as in the case of uniplaner centrifuges heretofore known.

In my aforesaid parent application, it was shown that it was easily possible to adjust the rate of feed with respect to the speed of the belt, so that less than one complete layer of particles would be present on the belt while the material Was being subjected to centrifugal force. This method of operation is so important and so beneficial, that it is desirable to show exactly how to obtain this condition and the manner in which it permits more efficient operation than is possible with centrifuges that are now available.

Consider the case of drainage through a relatively thick layer, or packed bed, as is required with the conventional centrifuge, in order to be able to obtain economic rates of throughput. When the mixture is first subjected to centrifugal force, the solids subside against the perforate bowl wall, leaving a layer of supernatant liquor. This layer drains through the solids, taking an appreciable time to do so, but the layer generally does not go all the way down to the perforate wall supporting the solids. It stops at a height called the capillary height, by others, and shown by them to be a function of the surface tension, size of the particles, density of the liquid, and the applied centrifugal force. Below this capillary level, the moisture content will be quite high. Above it, the lower moisture content will be composed of the moisture adhering to the surface of the particles and that held at the junctures of two or more particles. If the capillary level is low, as it is for most instances of commercial interest, the average moisture content will be approximately that for the upper layers. This condition is shown at a in FIG. 5. If the solids layer height in the centrifuge is decreased, the average moisture content becomes influenced by the greater proportion that is flooded under the capillary layer until, at total heights equal to or less than the capillary height, the average moisture content is that shown at b. If, however, the solids loading is still further decreased below that necessary for about one complete layer, the particles become laterally separated on the belt. The capillarity is thus destroyed and the average moisture content is sharply decreased. Because, on the average, the particles are not in contact with each other, the residual moismre is limited to that which can be held on the surface of each particle and at its interface with the supporting septum. This moisture is less than that for the thick layer, as shown at c.

It is desirable to determine the projected area of the particles, in order to be sure that less than a complete layer is fed. This can be done by a microscopic analysis, or generally to the accuracy required, by a sieve analysis. If the latter procedure is used, allowance should be made for the shape factor, in that irregular particles tend to go through the screen in accordance with one of their smaller sections, but lie on a plane in accordance with one of their larger and more stable dimensions. In this fashion, a particular crystal distribution was determined to have a projected area of about 3 square feet per pound. This material was fed in an aqueous slurry at the rate of three pounds of solids per second, to a machine built according to the present invention, having a belt with an effective width of 3 inches, travelling at a speed of 80 feet per second. Each 9 square feet of projected area of solids was thusly distributed over 20 square feet of belt, with the result that the residual moisture content was below that of a thick layer of the same material determined at the same centrifugal force, in the relationship of c to a on the graph at FIG. 5. The use of less than a complete layer thusly permitted a residual moisture content of the discharged solids below that which could be achieved at equilibirum with a thick layer subjected to the same centrifugal force.

The foregoing discussion emphasizes thin layer processing because the belt centrifuge is so 'much better than the conventional centrifuge when this is done. For smaller particle sizes, economical rates of throughput on the belt centrifuge may require more than one layer. If the drainage rate is high enough to cause complete drainage in the time available, performance may still be better than that of the conventional centrifuge because of the lack of increase in surface area, as described in more detail below.

Centrifuges of the general type of that of the present invention also have another important advantage. This has to do with the fact that it is possible to treat materials under centrifugal force without the particle size degradation that is inherent in the conventional centrifuge. In this respect, we are dealing not with the fracture that occurs on impact when the solids are flung out of the zone of centrifugal treatment, but with degradation that occurs prior to this time.

To describe this, it should be noted that others have observed the equilibrium moisture content of a quiescent packed bed under centrifugal force to be an inverse function of the square root of the applied centrifugal force. This is represented by curve d in FIG. 6, a straight line with a slope of minus one-half when the logarithm of the residual moisture content is plotted against the logarithm of the applied centrifugal force. Others have also observed that the residual moisture content is a function of surface area. In other words, if the material that performed under centrifugal force as curve d in FIG. 6, is further ground or crushed to reduce the particle size and thus increase the surface area in a similar size distribution, the equilibruim residual moisture will be increased proportionately, as shown in curve 2. The final moisture content under a given level of centrifugal force is increased from g to h.

As was pointed out in the parent application, approximately half of the power supplied by the motor of the conventional continuous centrifuge is frictionally absorbed by the liquids and solids within the centrifuge rotor. The solid particles are thus impacted by any accelerating means in the rotor and are ground over each other while they are tightly packed under centrifugal force. This degradation increases the surface area in the presence of moisture and thus shifts the equilibrium to a higher residual moisture content.

In fact, if the centrifugal force is increased to 1' in FIG. 6 in an attempt to obtain a lower residual moisture, and overcome this effect the crystal degradation within the centrifuge will be increased and the residual moisture content will not be decreased to the extent predicted by the equilibrium curve. With particularly friable materials, it is even sometimes necessary to reduce the speed of the conventional centrifuge below that for which it is designed in order to obtain minimum residual moisture.

To be sure, the conventional centrifuge, by stirring the crystal bed vigorously during the acceleration process, and sometimes by the use of conveying arms or vibration, can reduce the proportion of capillary moisture and even cause a reduction in the moisture held between adjacent particles in comparison to that held under equiiibruim quiescent conditions, but this benefical effect is generally negligible compared to the deleterious effect of the increase in surface area.

As the crystals are discharged from the conventional centrifuge, they are impacted and further broken. This is undesirable and cannot be controlled to the extent permitted with my centrifuge, as more fully discussed in my parent application, but this action does not, of course, affect residual moisture content because this increase of surface area has occurred where there is no longer additional moisture to be carried out of the machine.

With friable materials such as coal, the increase in surface area within the conventional centrifuge rotor may be such as to double the feed surface area, with the result that the residual moisture content is very much higher than that for equilibrium of the original feed material.

With the apparatus and method of my invention, however, it is possible to accomplish the centrifugal treatment without any appreciable increase in surface area. The slurry is accelerated by a pump and the nozzle to the speed of the belt with negligible degradation and there is no requirement for fracture as this stream transits from straight-line flow into the arcuate path.

In actual operation, at production rates on a friable material, it proved possible to collect the solids from my centrifuge, after centrifugal drying, at a particle size distribution and surface area substantially identical with that present in the feed stream. As would be expected by the previous explanation, it would then be anticipated to be possible to obtain a residual moisture content below curve d in FIG. 6, and this is just what has been observed, as represented by point j.

The use of the thin layer, or less than a complete layer, with my type of centrifuge makes possible another type of process operation that is highly advantageous under many circumstances.

It is sometimes desired to discharge the liquid efiluent as free as possible from admixed fine particles from the feed stream feed particle size distribution. With this type of operation, the thick layer operation has a seeming advantage because it can trap some of the fine particles whereas, in the operation of the very thin layer, the fines must be trapped by using a belt with very fine pores. This is not as much of a disadvantage as might first appear because the increase in surface area with the conventional centrifuge thick layer, as has been described previously, has resulted from the preferential increase in the fine particles in the distribution. Many of these increased numbers of fines will not be trapped by the thick layer and thus the two types of operation will tend towards equality in fines loss in the effluent.

The ability to discharge fines when desired, however, can be used to great advantage on many other applications Where a loss of fines can be tolerated, or is an advantage. In treating coal slurries, for instance, the slurry is frequently treated to rid it of slirnes or fines prior to centrifugal drying. One of the reasons for this is that the fines may be undesirable in the end product. Another is the very poor conventional centrifugal drying when these fines are present in its feed. This reason for the classification step is an example, on a large scale, of the surface area effect with respect to equilibrium residual moisture content that has been described previously in detail.

With my centrifuge it is possible to select the size of the openings through the belt so that the fines pass to the effiuent with a high degree of efficiency. The fine particles have only a short and unhindered distance on the belt to travel before they are free to discharge through one of the holes of selected size. This eliminated a step in the processing by combining the classification and drying into one. The surface area of the particles remaining on the belt is thusly decreased and the residual moisture content of the solids discharge is decreased,

My parent application discussed types of foraminous belts which can be used, with no intent of being limited to any particular material or construction, but it has been observed that there is one type of belt that requires special care for best operation. When the belt consists of a flat surface pierced with holes, there is a substantial area for which the last of the moisture will drain slowly because the component of centrifugal force causing lateral flow toward the hole approaches zero as the quantity of liquid on the belt becomes very small. Because the time [for the last drainage to take place can be an appreciable amount of the time available for treatment, it is beneficial to slope the surface of the belt toward the holes as shown in FIG. 4 to an exaggerated degree for purposes of clarity, in order to facilitate rapid discharge of the last traces of liquid on the surface of the belt.

It should be understood that the present disclosure in illustrating preferred embodiments of my invention has been made only by way of example and that numerous changes in the details of construction and method and the combination and arrangement of elements thereof may be resorted to without departing from the spirit and the scope of the invention, and that the invention includes all modifications and equivalents which come within the scope of the appended claims.

What is claimed is:

1. A centrifuge comprising as the force producing element thereof an endless belt formed into a closed loop, the surface of said belt facing inwardly of said loop being the inside sunface and the opposite surface being the outside surface thereof, a separating pulley for said belt located without said closed loop, a portion of which is in engagement with the outside surface of said belt for establishing an elongated arcuate path for development therein of centrifugal force, a feed pulley and a discharge pulley each located within said closed loop, a portion of which is in engagement with the inside sunface of said belt and in spaced relation with the separating pulley and with each other and in positions for maintaining the belt in said arcuate path and against the outer surface of the separating pulley, said separating pulley and said belt forming between them a peripherally recessed space for the passage of material to be subjected to centrifugal force, means for supplying material to said belt in the direction of movement into said arcuate path, means for driving said endless belt through said arcuate path at a speed which develops a centrifugal .force of substantial magnitude, and 0 with said separating pulley in the region in which said belt is withdrawn from the surface thereof for discharge therethrough of the material which has traversed said arcuate path.

2. The centrifuge of claim 1 further including at least one additional pulley for establishing a return path, said additional pulley being located in spaced relation from said separating pulley on the opposite side thereof from said feed pulley and said discharge pulley.

3. The centrifuge of claim 1 in which all of the pulleys are so disposed as to maintain the belt untwisted with its center line in a single plane throughout its path of travel.

4. A centrifuge comprising an endless belt formed into a closed planar loop, the surface of said belt facing inwardly of said loop being the inside surface and the opposite surface being the outside surface thereof, a separating pulley located outside said closed loop for establishing an elongated arcuate path for development therein of centrifugal force, said belt being threaded over said separating pulley with said outside surface engaging a portion of said separating pulley, at least two additional pulleys disposed inside said closed loop for maintaining the belt in engagement with said separating pulley, means for moving said endless belt through said arcuate path at a speed which develops a centrifugal force of substantial magnitude, and said separating pulley and said belt being so constructed to define a peripherally recessed chamber therebetween, whereby the material to be centrifuged may be fed onto the outside surface of the belt as it enters the arcuate path, centrifuged within the chamber in its passage of said arcuate path and then discharged from the outside surface of the belt after its passage through the arcuate path.

5. A centrifuge providing for discharge, free of the centrifugal force producing element, comprising a separating pulley, at least two additional pulleys and an endless centrifuge belt forming a closed loop defining an inside and outside surface of said belt, said belt being supported in its path of travel by said separating pulley and said additional pulleys with its outside surface in engagement with said separating pulley and its inside surface in engagement with said additional pulleys, means for driving said endless belt through its path of travel at a speed which develops a centrifugal separating force of substantial magnitude, and said separating pulley and said belt being of such configuration to define a peripherally recessed chamber therebetween for passage of the material to be centrifuged.

References Cited UNITED STATES PATENTS 1,280,469 10/1918 Hiller 210-370 X 3,089,596 5/ 1963 OBrien et al 210369 FOREIGN PATENTS 532,968 9/1931 Germany.

REUBEN FRIEDMAN, Primary Examiner.

I. DECESARE, Assistant Examiner.

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