US3887456A - Classifier with rifflers and variable throat - Google Patents

Abstract

In a classifier for separating particle fractions of different densities from a liquid-borne stream, means are provided to gently open a bed of heavier particles and release lighter particles entrapped adjacent the chamber wall by the heavier particles, thereby permitting the lighter particles to be displaced and move centrally for more complete separation. An adjustable throat between the lower end of the overflow pipe and the underflow outlet is provided by a telescoping external support for the overflow pipe above the cover plate.

Description

United States Patent Loughner 1 June 3, 1975 [54] CLASSIFIE W RIFFLERS AND 3,389,793 3132: lgeleman 583%}: 3,399,770 a omon VARIABLE THROAT 3,620,370 11/1971 Swayze 209/144 Inventor: Ja s Loughner, Rt. No. 1, Box R26,72O 11/1969 Visman 209/211 456, Litton Heights, Scott Depot, 25560 Primary Examiner-Frank W. Lutter [22] Filed: Oct. 1, 1973 Assistant Examiner-Ralph J. Hill pp No: 402,193 Attorney, Agent, or Firm-Wood, Herron & Evans 52 us. or 209/211; 209/506 [57] ABSTRACT [51] Int. Cl. B041: 5/103 In a classifier for separating particle fractions of differl Field fl 209/2 1. 1 ent densities from a liquid-borne stream, means are 210/512 5/ provided to gently open a bed of heavier particles and release lighter particles entrapped adjacent the cham- [56] References Cited ber wall by the heavier particles, thereby permitting UNITED STATES PATENTS the lighter particles to be displaced and move cen- 624 684 5H8 Richards 209/58 trally for more complete separation. An adjustable 6311:1109 8/1899 Aberg....::III:21:12:: 209/211 throat between the lower end Ofthe Overflow P p and 1,149,463 8/1915 Pardee 209/211 x the underflow Outlet is Pwvided y a telescoping 1,832,256 11/1931 Stebbins................ 209/144 ternal support for the overflow pipe above the cover 2,102,525 12/1937 Freeman 209/211 plate. 2,743,815 5/1956 Goodwin 209/211 2,976,994 3/1961 Rodman et al. 209/211 5 Claims, 2 Drawing Figures wr f .f/ g I, F

a L .54 J0 4; 35 &J7 J9 s I 1. 4 /'J5 9 x 135 Z 11 2 Q a g 2 5 5 s 2 1 g /M -vfl 55 l 1 l 2/ s i 1 1 li a a 11 LEI CLASSIFIER WITH RIFFLERS AND VARIABLE THROAT This invention relates to apparatus for separating heavier or lighter fractions from a liquid-borne stream which carries a mixture of particles of different densities. Devices of this general type are commonly known as classifiers and are useful, by way of example, for separating and recovering coal (lighter) particles from an admixed rock (heavy) fraction in a water-borne stream.

The invention is particularly directed to classifiers of the centrifugal vortex type, in which the feed stream is directed tangentially into an annular chamber so that as it swirls around the chamber centrifugal force tends to cause the heavier particles to move along the wall of the chamber while the lighter fraction circulates inwardly of the heavier particles, closer to the center of the chamber. A lighter fraction is taken off upwardly through an overflow pipe that projects axially into the chamber, while the heavier fraction is withdrawn downwardly through an underflow orifice at the bottom of the chamber. To the extent that the heavier particles are incompletely or imperfectly separated from the light, or vice versa, process economics are adversely affected, and it is generally desirable to obtain as clean a separation as possible, consistently with the practicalities involved.

It is my belief that imperfect separation is caused, at least in part, from entrapment" of lighter particles by an overlying circulating layer of heavier particles. More specifically, it is theorized that, as centrifugal force acts on the mixed density particles as they swirl around the chamber and causes the heavier fraction to gravitate closer to the wall than the lighter particles, some light particles are occluded between the heavier particles and the chamber sidewall. These lighter particles if not thus entrapped would tend to be displaced inwardly toward the axis, but they are hindered from doing so by the heavier particles which overlie them and which tend to hold them against the outside wall.

This invention is predicated in part upon the concept of jigging" or gently agitating the particles as they swirl over the wall of the chamber, that is, causing them to move inwardly, then outwardly again, along an undulating path. In accordance with this aspect of the invention, jigging means are provided to lightly disrupt the otherwise generally circular paths of movement of the particles around the chamber sidewall, and impart a wavy or sinuous motion which causes the heavier particles to tumble slightly or at least move relatively apart so that the entrapped lighter particles are provided an escape path to move away from the wall and inwardly of the heavier particles. The jigging means are referred to as rifflers herein, and comprise rounded semicircular projections, such as half-round bars, which are mounted at spaced positions within the chamber. These rifflers present gradually inclined leading and trailing surfaces to the liquid-borne stream as it moves across them, and gently agitates or jigs the particles adjacent the wall moving over them, but without creating such great turbulence as to remix the separated particles and thereby hinder the classification. The proper jigging action is manifested by release of entrapped particles and a better separation than would otherwise be obtained.

It is critical to the invention that both the leading and the trailing surface of the rifflers must not be angular nor present a steep or sharp angle to the stream; that is, both surfaces must be gradually angulated, as opposed to a right-angular or steep face. This avoids the formation of a dead space directly in front of, or be hind, the riffler, and the creation of turbulence which would counteract the separation otherwise taking place. Surprisingly, l have found that small half-round bars, having a height not more than about one-third the diameter of the largest particles being treated, work very effectively for this purpose.

The rifflers are mounted to the cylindrical wall of the chamber, between the inlet and the outlet. They are angulated with respect to the direction of fluid flow, so that particles move over, rather than parallel to, the rifflers. Below the cylindrical part of the chamber, the wall leads to a bowl portion wherein the wall curves downwardly and inwardly toward a central opening or cone. It is important that this bowl curve gradually from a steeply inclined upper region, to an almost horizontal central region. It is desirable that this bowl have a spherical curvature, with a generally constant radius of curvature, at least approximately equal to the width of the annular space between the overflow pipe and the chamber cylindrical wall. This prevents accumulation or hang-up of solids that might otherwise retard flow to the overflow outlet.

Another aspect of the invention involves the provision of a variable throat for a classifier. In accordance with this aspect, means are provided whereby the throat, i.e., the vertical spacing between the lower end of the overflow tube and the cone at the bottom of the chamber, can readily be adjusted or varied from the outside while the classifier is in use. In practice, the nature of the *cut" between the heavier and the lighter fractions, i.e., the division between the densities of lighter particles that come off through the overflow pipe and the density of heavier particles which are taken off downwardly through the cone, depends upon the spacing between the two opposed outlets. The greater the spacing, the lower the mean density of the particles taken off through the overflow pipe.

In the past, the overflow pipe has commonly been fixed with respect to the body so that it was difficult to make any adjustment or change in the throat spacing, at least without disassembling the classifier or removing the top closure. In accordance with this invention, a vertically adjustable overflow pipe is provided so that the throat dimension can be changed as may be desirable for different cuts or for different feed streams.

More specifically, an opening is provided in the body top cover and a circular sleeve is mounted axially to the cover around this opening. The overflow pipe telescopes or is slidable axially within this sleeve, in the upward or downward direction with respect to the outlet. A gasket is provided around the overflow pipe to seal it while maintaining shiftability of the overflow pipe. The overflow pipe has a diameter which substantially corresponds to the diameter of the cone at the point where the latter joins the curved bowl. A flange is mounted to the overflow pipe above the top cover, through which pass fixed upstanding threaded rods, and nuts on these rods support the flange and, hence, the pipe. The position of the overflow pipe with respect to the outlet can be adjusted by shifting the nuts as appropriate to shift the lower end of the pipe upwardly or downwardly within the chamber. Lock nuts secure the pipe in the desired vertical position.

By these throat adjusting means it is readily possible to change the cut even while the classifier is in use. This enables the device to be set or adjusted as may be desired in response to an analysis of the fractions which are being taken. or to change in input.

Both aspects of the invention can best be further described by reference to the accompanying drawings in which.

FIG. 1 is a vertical axial section of a preferred form of classifier in accordance with the invention, and

HG. 2 is a horizontal section taken on line 22 of FIG. 1, and shows the jigging affect of the rifflers on the circulating fluid stream.

The classifier has a main body portion generally at which may be formed of cylindrical pipe. The body 10 has an annular or cylindrical inside surface 11 which defines an internal chamber 12. An inlet pipe 14 is mounted to body 10 in such manner that it opens generally tangentially through wall 11 to the chamber 12 (see FIG. 2). through an inlet opening 15 which is generally adjacent the top of the chamber 12.

At the lower end of the body 10 an annular flange 16 is secured, to which a flat bottom plate 17 is mounted, as by bolts 18. Bottom plate 17 supports an annular casting or bowl 20 which has an inner surface 19 that curves from an almost vertical upper region 21 adjacent the inside wall 11 of body 10, downward and inwardly to an almost horizontal surface region 22 where it joins a central conical opening or cone 23 along a circular line 24. The bowl or casting 20 may be formed of Niehard or other hard metal or ceramic material. Cone 23 leads to an underflow orifice 25 which is mounted below bottom plate 17. This orifice 25 has a generally conical shape and a smaller apex angle than cone 23, and leads to a take-off means or a receiver for the heavier fraction which may be conventional in form.

A top plate or cover 26 is mounted across the top of the body 10 and secured to a pheripheral flange 27 as by bolts 28. A central opening 30 is formed in cover 26 and a cylindrical sleeve 31 is fastened as by welding around the opening. Preferably sleeve 31 projects into chamber 12 below cover 26, but it may extend above the cover. This sleeve 31 is aligned axially with respect to chamber 12, and functions as a sliding mount for an overflow tube or pipe 35. The diameter of the overflow pipe substantially conforms to the diameter of the conical surface 23 at the line 24 where the latter surface joins the bowl surface 22 as indicated by dashed lines in FIG. 1. Overflow tube 35 is sized so that it is slidable vertically within the sleeve 31 and a gasket or seal 36 is provided around the outside surface of the tube 35, above cover 26, to prevent fluid leakage. The gasket 36 is received and held within a V-shaped annular recess 37 that is defined jointly by two superimposed apertured plates 38 and 39 mounted on cover 26 around the opening 30 therein.

Screw adjusting means support the pipe 35 above the cover for changing the vertical position of the pipe. In preferred embodiment, threaded openings as at 41 are provided through the plates 26, 38 and 39 at a number of angular positions thereon, and threaded rods or bolts 44 are secured in these openings 41 and locked therein by nuts 45. The rods 44 project upwardly generally parallel to the axis of tube 35, and upwardly pass freely through openings 47 formed in a flange plate 49 secured to tube 35. Nuts 50 threaded on the respective rods 44 below flange plate 49 support the weight of pipe 35 and position it vertically with respect to the underflow orifice. Nuts 51 on the threaded rods 44 above the flange 49 prevent undesired relative movement of the flange plate 49 and pipe 35 in the vertical direction. it will be apparent that by releasing the nuts and 51 on each of the respective threaded rods 44, the throat dimension or vertical spacing (designated by X in FIG. 1) between the lower end 55 of overflow pipe 35 and cone 23 can be changed. The weight of pipe 35 is usually sufficient that as the nuts 50 are adjusted down wardly on the respective rods 44, the pipe will slide downward by gravity, toward the cone. In this respect the openings 47 in the plate 49 through which the rods pass. and the internal dimension of sleeve 31, should be sufficiently large that the overflow pipe 35 can slide without jamming as the nuts are incrementally threaded upwardly or downwardly on the respective rods. Such adjustability permits varying the throat dimension to change the nature of the cut which is taken. Overhead, a flexible connection (not shown) leads from pipe 35 to means for further processing of the light fraction. which may be conventional.

Rifflers are provided for gently disturbing the nearly laminar flow of materials over the inside wall 11 of the body 10. The rifflers 60 may comprise vertically oriented lengths of half-round rod, welded to the inside wall 11 and extending at least part of the distance between the inlet opening 15 and the upper bowl surface 21. With respect to the general direction of incoming fluid indicated by the arrow 59 in FIG. 2, each riffler 60 presents a gradually inclined leading surface 61 and trailing surface 62. That is to say, neither surface is abruptly or perpendicularly angulated with respect to the direction of flow. This is important to avoid turbulence which might remix the particles otherwise separated, and to achieve a stabilized separation.

The affect of the rifflers is indicated somewhat schematically near the upper right riffler in FIG. 2. Some light density particles (shown as small particles) 63 are entrapped against the wall 11 by denser particles 64 (shown as larger particles), and are thereby prevented from being displaced inwardly of the heavier particles toward the centrifugally separated light particles 65. The rifflers open the bed of heavy particles, as indicated by arrow 66, separating the heavier particles from one another or otherwise permitting the entrapped light particles to be displaced inwardly, as at 67. As previously indicated, the heavy fraction moves to the underflow orifice, and is not remixed substantially with lights as they continue to circulate and move toward the overflow pipe.

In this latter regard. I have found it desirable that the rifflers be quite small in relation to the size of the largest particles in the mixture being processed. The height or radial dimension )1 (see FIG. 1) of the rifflers should not exceed about one-third the diameter of the largest particles (indicated at 68 in FIG. 2, exaggerated in size) for efficient release of entrapped particles consistent with minimization of separation loss by remixing. In one specific embodiment of the invention, by way of example, the chamber inside diameter was 18 inches, the o.d. of pipe 35 was 8 inches, annular width w was 5 inches, riffler dimension h was one-fourth inch, or 5% of annular chamber width w. for treating a mixture of particles 1 inch and smaller in size. The vertical dimension of the rifflers was 5 inches. The axial length of chamber wall 11, above bowl 20, was equal to the inside chamber diameter, i.e., l8 inches. The diameter of the circular join line at 24 was 9 inches. The pipe was adjustable vertically 4% inches from a minimal throat dimension x of 2 /2 inches to a maximum of 7 inches. Bowl surface 19 was approximately spherical, having a radius of curvature r equal to the dimension between join line 24 and the cylindrical wall 11, i.e., 5% inches. This classifier was used to separate residual coal from a so-called gob or refuse pile. The input feed contained 35% coal (65% rock) by weight; 30% of the input coal was removed, for an approximate 86% separation efficiency, at an input rate of 46 tons per hour.

Having described the invention, what is claimed is:

l. A classifier for separating heavier and lighter fractions in a liquid-borne stream of mixed particles of different densities, said classifier comprising,

a hollow cylindrical body having a wall defining an annular internal chamber,

a bowl at a lower end of said chamber, said bowl curving downwardly and inwardly from the wall of said body to a conical central opening,

an inlet pipe leading to a substantially tangential inlet opening through said wall into said chamber adjacent an upper end of the chamber,

a top cover for said chamber,

an overflow pipe projecting downwardly through said cover and axially into said chamber toward said conical opening, said overflow pipe having an open lower end positioned above said conical opening and below said inlet opening,

and a plurality of rifflers mounted to said wall at angularly spaced positions around said chamber below said inlet opening and above said bowl,

each said rifi'ler being a projection on said wall extending into said chamber and having a generally semicircular cross-sectional shape with gradually inclined leading and trailing surfaces thereon,

each riffler extending angularly with respect to the direction of fluid flow over said wall between said inlet opening and said central opening,

the dimension of said rifflers in the direction across the radius of said chamber being no greater than about one-third the diameter of the largest particles to be separated, said rifflers in use of said classifier jigging liquid-borne material passing over them and thereby releasing lighter particles entrapped by heavier particles so that such lighter particles move inwardly with respect to the heavier particles while said heavier particles continue to move over said wall.

2. The classifier of claim 1 wherein said rifflers comprise half-round bars welded to said wall around said chamber.

3. The classification of claim 2 wherein three such bars are mounted at equi-angularly spaced positions around said chamber.

4. The classifier of claim 1 wherein said bowl has a spherical curvature and has a radius of curvature approximately equal to the radial dimension between said wall and said central conical opening.

5. A classifier for separating heavier and lighter fractions in a liquid-borne stream of mixed particles of different densities, said classifier comprising,

a hollow cylindrical body having a wall defining an annular internal chamber,

a bowl at a lower end of said chamber, said bowl curving downwardly and inwardly from the wall of said body to a conical opening,

an inlet pipe leading to a substantially tangential inlet opening through said wall into said chamber adjacent an upper end of the chamber,

a top cover for said chamber,

a central opening in said cover,

a sleeve secured to said cover around said central opening,

an overflow pipe slidable within said sleeve and projecting downwardly through said central opening and axially into said chamber toward said conical opening, said overflow pipe having an open lower end positioned above said conical opening and below said inlet opening,

means providing a slidable seal around said overflow screw adjusting means supporting said pipe above said cover for changing the vertical position of said pipe with respect to said conical opening,

and a plurality of rifflers mounted to said wall at angularly spaced positions around said chamber below said inlet opening and above said bowl,

each said riffler being a projection on said wall extending into said chamber and having a generally semicircular cross-sectional shape with gradually inclined leading and trailing surfaces thereon,

the dimension of said rifflers in the direction across the radius of said chamber being no greater than about one-third the diameter of the largest particles to be separated, said rifflers in use of said classifier jigging liquid-borne material passing over them and thereby releasing lighter particles entrapped by heavier particles so that such lighter particles move inwardly with respect to the heavier particles while said heavier particles continue to move over said wall.

Claims (5)

1. A classifier for separating heavier and lighter fractions in a liquid-borne stream of mixed particles of different densities, said classifier comprising, a hollow cylindrical body having a wall defining an annular internal chamber, a bowl at a lower end of said chamber, said bowl curving downwardly and inwardly from the wall of said body to a conical central opening, an inlet pipe leading to a substantially tangential inlet opening through said wall into said chamber adjacent an upper end of the chamber, a top cover for said chamber, an overflow pipe projecting downwardly through said cover and axially into said chamber toward said conical opening, said overflow pipe having an open lower end positioned above said conical opening and below said inlet opening, and a plurality of rifflers mounted to said wall at angularly spaced positions around said chamber below said inlet opening and above said bowl, each said riffler being a projection on said wall extending into said chamber and having a generally semicircular cross-sectional shape with gradually inclined leading and trailing surfaces thereon, each riffler extending angularly with respect to the direction of fluid flow over said wall between said inlet opening and said central opening, the dimension of said rifflers in the direction across the radius of said chamber being no greater than about one-third the diameter of the largest particles to be separated, said rifflers in use of said classifier jigging liquid-borne material passing over them and thereby releasing lighter particles entrapped by heavier particles so that such lighter particles move inwardly with respect to the heavier particles while said heavier particles continue to move over said wall.

1. A classifier for separating heavier and lighter fractions in a liquid-borne stream of mixed particles of different densities, said classifier comprising, a hollow cylindrical body having a wall defining an annular internal chamber, a bowl at a lower end of said chamber, said bowl curving downwardly and inwardly from the wall of said body to a conical central opening, an inlet pipe leading to a substantially tangential inlet opening through said wall into said chamber adjacent an upper end of the chamber, a top cover for said chamber, an overflow pipe projecting downwardly through said cover and axially into said chamber toward said conical opening, said overflow pipe having an open lower end positioned above said conical opening and below said inlet opening, and a plurality of rifflers mounted to said wall at angularly spaced positions around said chamber below said inlet opening and above said bowl, each said riffler being a projection on said wall extending into said chamber and having a generally semicircular crosssectional shape with gradually inclined leading and trailing surfaces thereon, each riffler extending angularly with respect to the direction of fluid flow over said wall between said inlet opening and said central opening, the dimension of said rifflers in the direction across the radius of said chamber being no greater than about one-third the diameter of the largest particles to be separated, said rifflers in use of said classifier jigging liquid-borne material passing over them and thereby releasing lighter particles entrapped by heavier particles so that such lighter particles move inwardly with respect to the heavier particles while said heavier particles continue to move over said wall.

2. The classifier of claim 1 wherein said rifflers comprise half-round bars welded to said wall around said chamber.

3. The classification of claim 2 wherein three such bars are mounted at equi-angularly spaced positions around said chamber.

4. The classifier of claim 1 wherein said bowl has a spherical curvature and has a radius of curvature approximately equal to the radial dimension between said wall and said central conical opening.

Images