US2743864A

US2743864A - Centrifuge with inclined conveyor blade and vanes for rapid collection of fine particles from suspensions

Info

Publication number: US2743864A
Application number: US414435A
Authority: US
Inventors: Sanford C Lyons
Original assignee: Bird Machine Co Inc
Current assignee: Bird Machine Co Inc
Priority date: 1954-03-05
Filing date: 1954-03-05
Publication date: 1956-05-01
Anticipated expiration: 1973-05-01

Description

May 1, 1956 s. c. LYONS 2,743,864

CENTRIFUGE WITH INCLINED CONVEYOR BLADE AND VANES FOR RAPID COLLECTION OF FINE PARTICLES FROM SUSPENSIONS Filed March 5, 1954 2 Sheets-Sheet l 10 41' jfl 1 w h w w J; W

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s. c. LYONS 2,743,864 CENTRIFUGE WITH INCLINED CONVEYOR BLADE AND VANES FOR RAPID COLLECTION OF FINE PARTICLES FROM SUSPENSIONS Filed March 5. 1954 2 Sheets-g 2 United States Patent CENTRIFUGE wrm INCLINED CONVEYOR I, BLADE VANES non RAPID councg lgg or FINE PARTICLES FROM SUSPEN- Sanford C. Lyons, Beuuin'gton, Vt., a'ssignor to Bird Machine South Walpole, Mass., a corporation of Massachusetts Application March 5, 1954,- Serial No. 414,435

6 Claims. (Cl. 233-7 This invention relates to a centrifuge of solid bowl type equipped with improved means for rapidly and effici'ently collecting from a fluid suspension and effectively discharging the fine particles which have sedimentation rates which are too low for economical recovery. For certain industrial uses, it is desirable to recover from a suspension of clay particles a substantial portion of the fines having equivalent spherical diameters of 1 micron or less. Single particles within this range have such low sedimentation rates that their recovery in an ordinary centrifuge requires the expenditure of too much time and power to be economical. By greatly shortening the free sedimentation paths of the individual particles and taking advantage of the fact that such particles when collected into a concentrated slurry are more rapidly acted on by centrifugal forces than are single particles of the same size, an, elhcie'nt recovery of a large percentage of such particles from an aqueous suspension thereof can be had, provided that the slurry can reach the wall of the bowl and be discharged therefrom without encountering such turbulenceof the watery vehicle as to result in excessive resuspen'sio'n of the particles. Auxiliary vanes for this purpose are described and illustrated in my- Patent No. 2,625,320, granted January 13, 1953. According to the present invention, an improved arrangement of vanes is provided for a mo're eflicient collection of the fine particles into streams of slurry and for a more effective avoidance of exposure to turbulence and consequent resuspension of particles as the slurry streams are delivered to the wall of the bowl and discharged.

Many centrifuges of the solid bowl type are provided with a helicoidal blade within the shell of the centrifuge bowl to scrape the inner wall and to advance the solids which are collected against the wall to the forward end ofthe bowl where they are discharged through suitable apertures in the forward end wall. These conveyor blades have heretofore usually been transversely radial; that is, the shape of such a. blade is generated by a segment of a radiusfromthe axis of thecentrifuge'as such radius simultaneously revolves around the axis and advances along the axis. Furthermore, some conveyor blades have been made with a transverse outward and forward inclination such-that the peripheral edge is the leading edge. Accordingto thepresent invention the conveyor blade is provided with a surface which is transversely inclined outward and rearward, the peripheral or scraping edge being the trailing edge. The angle of such inclination with respect to radii from the .axis is preferably to 30 or so. The function of the conveyor blade is to push the solids whichcollect by centrifugal sedimentation on the Wall of the centrifuge bowl longitudinally along the wall until they are discharged at an end of the bowl. Since the blade is helical, it is necessary that the solids slip along'its forward facesince if they stick to it, they simply re'volve with the blade without advancing toward the end of theboWI, thus defeating the purpose of the blade. By inclining-the blade transversely so thatthe scraping edge trails excellent results are had in the propulsion of the "ice ' concentrated solids to the discharge ports. It is believed that the reason for this is that in the mass of collected solid particles which are being pushed by the blade there is residual water'which is forced radially inward as it is displaced by the continued outward migration of the solid particles. Some of the displaced water is intercepted by the forward face of the blade and forms a lubricating film thereon which prevents the "solids from stickin'g. Furthermore, the centrifugal force which acts'on the particles adjacent to the forward face'of the" blade tends to move the particles away from the blade.

A series of closely spaced auxiliary vanes are "mounted in the spaces between 'convolu'tions of the conveyor blade, these vanes being transversely inclined so that their transverse elements make angles of 45 to 60 orso with radii from the axis. Each of these auxiliary vanes "extends as far across the spaces between blade convolutions as its location will permit, the edges of the vanes which are the more remote from the axis being close to but spaced from the rear surface of the conveyor blade. The fine particles in the liquid suspension which fills the narrow spaces between the auxiliary vanes have short paths of sedimentation before they encounter one of the auxiliary vanes. The particles'reaching the vanes collect thereon into thin streams of slurry or concentrations of particles, the specific gravity of such concentrations being considerably greater than that of the residual suspension so that the subsidence rate of the collected particles is greatly increased. Each slurry stream travels across the inward face of an auxiliary vane and then across the small clearance between the discharge edge of the vane and the adjacent surface. The streams from the several vanes collect into larger streams on the inclined rear surface of the blade and flow on said surface to the outer edge of the blade which touches or nearly touches the wall of the centrifuge bowl. Since each stream of slurry from the vanes traverses only a narrow gap in passing to the rear face of the conveyor blade, the slurry is for'the most of its course to the bowl wall in contact with a solid surface. This minimizes 'resuspension 'of the particles in the effiuent liquid which flows over the slurry streams on its way to the effluent outlet at the near end of the centrifuge. The slurry which reaches the wall of the bowl is pushed by the next convolution of the conveyor blade, together with any larger particles which may have'collected against the wall, toward the front end of the centrifuge where the solids are discharged through suitable apertures. Resuspension of the collec'ted'particles which are being advanced by the conveyor blade is minimized by one or more baffles mounted in the spac'e'betwe'en theoutermost auxiliary vane and the bowl wall to check the flow of effluent liquid in this relatively open space as hereinafter described. Unless turbulence in the effluent stream is kept at a minimum, there is a'tendenc'y on the part of many of the particles in the slurry streams and the collected solids at the bowl wall to become resuspended in the liquid, thus reducing the output of the fine particles and diminishing the efliciency of operation of the machine.

For a more complete understanding of the invention, reference may be had' to the following descriptionthereof and to the drawing, of which- Figure 1 is a side elevation of a centrifuge embodying the invention, portions being broken away to show in section;

Figure 2 is a fragmentary sectional view on a larger scale of the centrifuge shown in Figure 1, on a vertical plane containing the axis.

Figure 3 is a section on the .line 3.- 3 of Figure 2; a

Figure 4 is a section on the line 4-4 of Figure 2;

Figure 5 is a fragmentary sectionalview similar to Figure 2 but at another point on the conveyor blade;

Figure 6 is a section on the line 6-6 of Figure 5;

Figure 7 is a section similar to Figure 6 but of a moditied form of baffle;

Figure 8 is a section on the line 8-8 of Figure 1;

Figure 9 is a perspective view of a unit of sedimentation vanes;

Figure 10 is a fragmentary sectional view on an enlarged scale of a modified securing means for the sedimentation vanes;

Figure 11 is a section on the line 1111 of Figure 10; and

Figure 12 is a fragmentary sectional view of another modified structure.

The centrifuge illustrated on the drawing is of the type comprising a cylindrical bowl 10 mounted in suitable bearings 12 and 14 to rotate about its axis which is horizontal. A helical conveyor blade 16 is mounted on a cylindrical hub 18 which is within and coaxial with the bowl 10, and touches or nearly touches the inner surface of the bowl wall.

According to the invention the blade is transversely inclined, sloping outward and rearward so that its outer or peripheral edge 17 trails, and its forward surface makes an acute angle (e. g. 60 or so) with the wall of the centrifuge when viewed in section as shown in Figures l, 2 and 10. The hub 18 is supported by a shaft 20 for rotation about its axis independently of the bowl. At the front end of the centrifuge (to the right in Figure 1) the shaft 20 is rotatably fitted within a hollow shaft 22 which rotates in the bearing 14. Fixed on the

shafts

20 and 22, respectively, are gear wheels 24 and 26 which are mechanically connected by means, not shown, by which the bowl 10 and the blade 16 are both rotated rapidly but at slightly different speeds, so that there is a slow relative rotation of these members which causes the blade to sweep slowly along the inner wall of the bowl so as to push the solid matter deposited on the wall by centrifugal action longitudinally along the wall to be discharged through suitable openings 28 in the front end of the bowl. At the same time there is a constant helical flow of solids-depleted fluid toward the rear end 30 of the bowl for discharge through suitable openings 31 which extend further radially from the axis of the centrifuge than do the openings 28.

A suspension of solid particles may be introduced into the hub 18 through a supply pipe 32 entering the bowl axially through an end thereof. The shaft 20 may be made hollow for that purpose. The suspension flows outward from the hub through one or more holes 34 which are between convolutions of the blade 16 and which discharge the suspension into the space between the hub and the shell. A scoop or deflector 36 (Figure 8) is welded to the hub 18 and the adjacent convolutions of the blade 16 about each hole 34 to guide the stream of suspension therefrom to the narrow spaces between the auxiliary vanes hereinafter described. In these spaces the suspension flows helically between the convolutions of the blade 16 toward the rear end of the bowl. As it flows, the particles therein are acted on by centrifugal force, the larger particles being moved outward more rapidly than the fine particles toward the wall of the bowl.

Auxiliary vanes 40 which preferably are closely spaced apart, are mounted in the spaces between the convolutions of the blade 16 and preferably extend forward a substantial distance from the rear end of the bowl, that is, nearly to the holes 34. For convenience in assembling, these auxiliary vanes may be made in sections, and assembled in units as shown in Figure 9. The units are secured by welding or otherwise between convolutions of the conveyor blade 16. When so mounted, the several units together constitute a series of nested helical ribbons which extend transversely across the space between successive convolutions of the blade 16 except for

small clearances

46 and 48 at the edges of the vanes. The vanes 40 are transversely inclined outward and forward, making an angle of about 30 or with lines parallel to the axis.

On the rear faces of those convolutions of the conveyor blade 16 which have vanes 40 adjacent to them, transverse strips 50 of metal are welded or otherwise secured. The thickness of these strips determines the width of clearance between the edges of the vanes 40 which abut them and the rear face of the blade 16, and also form shallow channels on the rear face of the blade in which the streams of slurry from the vanes are partially protected from the current of the liquid which flows in helical paths in the spaces between the convolutions of the blade 16. The strips 59 preferably do not extend radially but are inclined to the radii from the axis, as are also the channels between the strips. The inclination is such that the streams of slurry in the channels which flow outward toward the shell wall flow in a direction which has a com ponent in the direction of the movement of the bowl wall relative to the blade, thus avoiding an abrupt change in the circumferential component of the motion of the slurry streams when they pass from the rear face of the blade 16 to the bowl wall.

For convenience in constructing and assembling the vanes 40 in the centrifuge, the individual vanes may be made in sections 52 of convenient length (Figure 9). To a face of each section 52 are welded spacer buttons 54, and a hole is made in each section to receive a tie-rod 56 which is riveted at one end to a small plate 58 (Figure 2) and is drilled and tapped at the other end to receive a screw 60. When a set of sections 52 have been threaded on a rod 56, a screw 60 is inserted through a bracket piece 62 and into the threaded end of the rod. This results in a loosely assembled unit such as is illustrated in Figure 9. To mount these units on the rotor of the centrifuge, a metal strip 64 is welded to the forward face of the blade 16 and is uniformly spaced inward from the edge 17. The assembled units of vanes are then inserted successively in the space between the convolutions of the blade 16. T he screw 60 of each unit is set up tight to grip the strip 64 between the bracket piece 62 and the outermost vane section. The unit is adjusted so that the forward edges of the vane sections bear on some of the strips 50 on the rear face of the blade 16. The bracket piece 62 may then be spot-welded to the strip 64. A second strip 66 is laid in the angle between the forward edge of the outermost vane section and the spacer strips 50 abutted by the vanes and is welded to the strips 50. If desired, the strip 66 may be locally notched where it meets the strips 50 to receive weld metal 68 for a secure bond (Figures 2, 3 and 4).

When the centrifuge is in operation, the fine particles in the suspension tend to collect on the vanes 40 and to form thin streams of slurry which flow to the forward edges of the vanes and then enter the shallow channels between the strips 50 on the rear face of the blade 16. The slurry which collects in these channels from the vanes flows outward to the bowl wall 10 and is then pushed forward by the next convolution of the blade. As the slurry flows across the face of the vanes and along the channels on the blade, it is washed by solids-depleted liquid which is flowing helically toward the efiluent discharge ports at the rear end of the centrifuge. Since the vanes are spaced close together, the drag of fluid friction on the vanes tends to cause too much of the liquid to flow in the larger triangular space defined by the outermost vane, the next convolution of the blade and the bowl wall. Excessive current here would tend to scour the slurry which has accumulated against the bowl wall and to cause excessive resuspension of the finer particles. To prevent this, one or more baffles may be mounted in this space to block or reduce the fiow therein. For example, a battle plate 70 may be hinged to the blade as shown at 72 in Figures 5 and 6, the outer edge of this blade being sufiiciently spaced from the bowl wall to clear the normal thickness of collected solids on the wall. If a lump or layer of sediment of exceptional thickness is encountered, the hinge enables the bafile to yield and pass over it without plowing it up and carrying it around in such a way as to interfere with its longitudinal advancing movement toward the forward end of the bowl.

The bafiles may, if preferred, be welded as at 76 to the blade 16. Instead of transverse baflies, additional sedimentation vanes may be mounted in this triangular space, as illustrated in Figure 12 and hereinafter described.

Figure illustrates a different mode of mounting the sedimentation vanes 40 between some of the convolutions of the conveyor blade 16. Two series of bolts 80 and 82 (one of each series being shown in Figure 10) are inserted through the vanes 40 and spacers 84 between the vanes. Threaded end portions of the bolts are screwed into tapped holes in bosses 86 which are welded or otherwise secured to the hub 18. To protect the slurry streams on the rear face of the blade 16 channels 88 may be cut in the rear face. As indicated in Figure 11, the channels may be arcuate so that as the streams of slurry approach the shell wall, the circumferential component of their flow in the direction of the relative movement of the bowl wall will increase.

Figure 12 illustrates a modified structure which can be mounted in centrifuges having the usual form of conveyor blade 90 which is transversely radial. An auxiliary blade 92 may be welded to the rear face of the blade 90 to provide a transversely inclined surface 94 to receive the slurry streams from the forward edges of sedimentation vanes 96, which edges are close to the surface 94. If desired, a supplementary blade 98 may be welded to the outermost sedimentation vane or otherwise secured so as to be transversely parallel to the blade 92 as shown. This permits the employment of a few additional vanes 100 which are narrower than the vanes 96 and which have discharge edges 102 near to the rear face of the blade 98. The vanes may be secured in any suitable manner such as by

bolts

104 and 106 extending through holes in the vanes and through spacer elements 108 between the vanes into bosses 110 which are mounted on the tubular hub 18.

I claim:

1. In a centrifuge comprising a bowl rotatable about its axis, said bowl having end openings spaced inward from the circumference to maintain a pool of a liquid suspension in the bowl during the operation thereof, a helicoidal conveyor blade rotatably mounted within the bowl with its peripheral edge adjacent to the wall of the bowl, at least one of the turns of said blade being transversely inclined with said peripheral edge trailing, and means for driving said bowl and blade at slightly different speeds of rotation.

2. In a centrifuge comprising a bowl rotatable about its axis, said bowl having end openings spaced inward from the circumference to maintain a pool of liquid suspension in the bowl during operation thereof, a helicoidal conveyor blade rotatably mounted within the bowl with its peripheral edge adjacent to the wall of the bowl,

said blade having a rear surface transversely inclined outward and rearward with respect to radii from the axis of the bowl, and a series of closely spaced helicoidal auxiliary vanes mounted in the spaces between some of the convolutions of said blade, said vanes being transversely inclined with their peripheral edges adjacent to but spaced from a surface of said blade, and means for rotating said bowl and blade continuously at slightly different speeds.

3. Apparatus as in claim 2, said blade having shallow channels on its rear face extending outward substantially to the peripheral edge of the blade.

4. Apparatus as in claim 2, said blade consisting of a helical strip the front and rear faces of which are transversely inclined outward and rearward, whereby the peripheral edge of the blade trails.

5. Apparatus as in claim 4, the outermost vane defining with the convolution of the blade next to the rear and the bowl wall a triangular space, and at least one baffle carried by said blade and extending substantially across said space to impede flow of fluid therein toward the effluent ports.

6. In a centrifuge comprising a bowl rotatable about its axis, said bowl having end heads with ports therein for the discharge of solids at the forward end and the outflow of liquid at the rear end, a hollow hub within said bowl, a helical blade mounted on said hub and rotatable therewith relatively to the bowl, said blade having its peripheral edge closely adjacent to the bowl wall, at least one of the convolutions of the blade being transversely inclined with the peripheral edge trailing, a series of nested closely-spaced helical vanes mounted in the spaces between convolutions of said blade and extending forward from the rear end of the bowl a substantial distance toward the front end, a hole through the wall of said hub at a point adjacent to the forward end of said series of vanes, and a guiding member at said hole arranged to deflect fluid issuing from said hole into the spaces between said vanes.

References Cited in the file of this patent UNITED STATES PATENTS 832,191 Holzer Oct. 2, 1906 2,625,320 Lyons Jan. 13, 1953 2,670,131 Ried Feb. 23, 1954