US3348767A

US3348767A - Centrifugal separator

Info

Publication number: US3348767A
Application number: US449159A
Authority: US
Inventors: Francis X Ferney
Original assignee: Bird Machine Co Inc
Current assignee: Bird Machine Co Inc
Priority date: 1965-04-19
Filing date: 1965-04-19
Publication date: 1967-10-24
Anticipated expiration: 1984-10-24
Also published as: DE1532683A1; CH469511A; NL6605011A; GB1065340A

Description

F. X. FERNEY Oct. 24, 1967 CENTRIFUGAL SEPARATOR 2 Sheets-Sheet 1 Filed April 19, 1965 Oct. 24, 1967 F. x. FERNEY CENTRIFUGAL SEPARATOR 2 Sheets-Sheet 2 Filed April 19, 1965 United States Patent 3,348,767 CENTRIFUGAL SEPARATOR Francis X. Ferney, Walpole, Mass., assignor to Bird Machine Company, South Walpole, Mass., a corporation of Massachusetts Filed Apr. 19, 1965, Ser. No. 449,159 7 Claims. (Cl. 2337) This invention relates to a centrifugal separator for separating solid particles from liquid slurry and pertains more specifically to such a separator having a helical conveyor in combination with an imperforate frustoconical bowl or combination cylindrical and conical bowl for initial separation of solids from the liquid by drainage and a screen bowl for final separation or drainage.

Centrifugal separators having screen bowls which combine imperforate sections with perforate sections and having conveyors for moving the solids axially of the bowl have been previously proposed but they have been unsatisfactory in that the screens have had a tendency to become rapidly blinded by the finer portion of the solid particles, leading to the retention of an excessively large proportion of liquid in the solids discharge as well as to the necessity for frequent interruption of operation in order to clear the screens.

One object of the present invention is to provide a centrifugal separator for slurries in which the initial drainage of liquid from solid particles takes place in an imperforate conical portion of the bowl and the final drainage takes place in a screen portion of the bowl.

Another object is to provide a centrifugal separator of the type described in which the level of the liquid pool within the bowl is controlled to maintain its margin on the imperforate conical surface of the bowl spaced from the inlet into the screen bowl portion by a substantial distance along the axis of the bowl to promote initial drainage of the bulk of the slurry liquid from the solid particles, relying on the screen bowl portion only for drainage of the remaining liquid from the solid particles.

Still another object is to provide a centrifugal separator of high eflectiveness.

Other and further objects will be apparent from the drawing and from the description which follows:

In the drawing FIG. 1 is a view in side elevation partly broken away and in section showing one embodiment of the present invention;

FIG. 2 is a view in section taken along line 22 of FIG. 1;

FIG. 3 is a view in vertical section partly broken away showing another embodiment of the invention; and

FIG. 4 is a view in vertical section partly broken away showing still another embodiment of the invention.

The embodiment shown in FIG. 1 of the drawing comprises a base carrying at one end a bracket arm 12 supporting a fixed feed pipe 14 through the inlet end 16 of which is introduced the slurry which is to be separated into its solid and liquid components. The centrifuge bowl indicated generally by the numeral 18 is mounted for rotation about a central axis. It is supported at its right hand or inlet end as shown in FIG. 1 'by means of a flange 20 secured to trunnion 22 rotatably supported in pillow block 23 bolted to frame 10. A drive sheave 24 is secured to the free end of trunnion 22 and, when connected to any suitable source of power (not shown) serves to rotate bowl 18 at the desired rate of speed. The left hand end of bowl 18 as seen in FIG. 1, is similarly supported by means of flange 26 which in turn is secured to trunnion 28 mounted for rotation in pillow block 30 bolted to base 10.

Mounted concentrically within bowl 18 is conveyor 32 having helical flights 34 secured to a hollow cylindrical core 36. Core 36 is mounted at its right hand end on a flange 38 secured to a hollow shaft 40 mounted for rotation concentrically within trunnion 22 by means of bearings 42, 44. Inlet pipe 14 extends through the center of hollow shaft 40 into the interior of hollow core 36 which is provided with

apertures

54, 54 to permit the feed slurry to pass from feed pipe 14 into the interior of bowl 18. A pipe 15 for wash water extends concentrically through the center of feed pipe 14 and is mounted for sliding movement lengthwise to bring the outlet 17 at its inner end into registration with any one of the several chambers within hollow core 36 formed by annular bafllcs 1'9, 19. The Wash water may thus be directed to pass through any one or more of

nozzles

21, 21 in the wall of core 36. The left hand end of the hollow core 36 of conveyor 32 is secured to flange 46 which in turn is fixed to shaft 48 mounted for rotation concentrically within trunnion 28 by means of bearings 50.

Both trunnion 28 and shaft 48 are connected to differential gear unit 52 arranged so that when bowl 18 together with trunnion 28 is driven at the usual speed of several hundred r.p.m., shaft 48 together with conveyor 32 will be driven in the same direction as the bowl at a speed which differs from that of the bowl by only 10 to 40 r.p.m. This arrangement, which is conventional in solid or imperforate bowl centrifuges, causes theconveyor to advance any layer of solid particles deposited upon the inner surface of the bowl from the inlet end of the bowl toward the left hand or solids discharge end as seen in FIG. 1.

A casing 56 is mounted around the outside of bowl 18 and is provided with a solid discharge opening 58 and a liquid discharge opening 60. Annular baflles 62, 64, 66 fixed to the inside of casing 56 mate with corresponding baflles 62, 64', 66' secured to the outer face of bowl 18 and serve to maintain the solid discharge separate from the liquid discharge. Additional baflles 67 are provided inside the casing 56 to segregate the liquid (wash liquid or mother liquor) discharge from various parts of the screen portion. Baflies 67 are interrupted in one portion of their pe riphery, and a gutter 69 is slidably mounted in the interrupted portion to collect the discharge from any desired number of the compartments formed by baflles 67 and to provide any desired division of the discharge between

outlets

71 and 73 in casing 56. If desired, provision may be made for recirculating the liquid issuing from one or both

outlets

71 and 73 through pipe 15.

Bowl 18 includes a portion 68 having an imperforate truncated conical inner surface tapering in diameter from right to left as seen in FIG. 1 and connecting at its smaller end with the inlet end of cylindrical screen portion '70. The screen portion 70, the wall of which is provided with one or more perforate screens adapted to pass liquids but to retain the particulate solid materials separated from the feed slurry, extends from its inlet end through which the solid material is introduced by means of conveyor 32 to its opposite solids discharge end where it is provided with solids discharge apertures 72, 72. Conveyor 32 extends through both conical portion 68 and screen por tion 70 and is preferably continuous although a conventional conveyor having interrupted flights may also be used. Conventional double or triple helical conveyors may also be used, each extending through both conical portion 68 and screen portion 70.

A liquid overflow port 74 is provided in flange 20, arranged so that as the liquid slurry is introduced into bowl 18 it is formed into a pool by centrifugal force against the imperforate inner surface. The surface of the pool intercepts the conical surface of the bowl portion at a Zone A, the location of which is determined by the position of the overflow port 74. In order to minimize blinding or plugging of the screen portion 70, it has been found that zone A must be spaced from the smaller end of the conical portion 68, where it connects with the inlet end of the screen portion 70, by a distance, measured along the axis of the device, which is equal to at least 15 percent of the inner diameter of the bowl 18 measured at the larger end of the conical portion 68. Such spacing provides for adequate initial drainage of the liquid from the solid particles by the action of the helical conveyor urging the bed of solid material forwardly out of the liquid pool. Preferably the diameter at the smaller end of the conical portion 68 is from 65 to 95 percent of the diameter at the larger end for best results.

The size of the apertures in the screen portion 70 of the bowl may be varied depending upon the nature and particle size of the solids which are separated from the liquid feed slurry, generally being controlled so that a minimum of fine particles is permitted to pass through the screen. If desired, a plurality of spray nozzles 76, 76 connected to a suitable header or manifold 78 may be mounted on one part of casing 56 radially outwardly of screen portion 70; by supplying water or steam to the manifold when desired the nozzles may be used to clean the screen portion 70.

In operation of the device the bowl 18 and conveyor 32 are driven from sheave 24 at appropriate differential speeds while the liquid slurry is introduced through inlet opening 16 and flows through inlet pipe 14 thence through apertures 54 in core member 36 to form a liquid pool by centrifugal force against the inner surface of the imperforate conical portion 68 of bowl 18. As the level of liquid within the pool rises above the margin of liquid outlet 74 the liquid overflows into casing 56 thence through liquid discharge opening 60 in the bottom of the casing. The solid particles in the slurry, being of greater density than the liquid, form a layer directly against the inner surface of bowl 18 and are urged along it by flights 34 of conveyor 32 from right to left as seen in FIG. 1. As the layer of solid particles emerges from the liquid pool and is further advanced along the conical inner surface of the bowl toward the inlet end of screen portion 70, liquid continues to drain from it by centrifugal force and to flow back toward the liquid pool. This initial drainage of a large proportion of the liquid from the solid particles changes the flow characteristics of the mass of solid particles so that as it continues to be advanced.

by conveyor 32 across the screen portion 70 of thebowl, tendency of the apertures in the screen to become plugged or blinded by the solid particles is minimized, and additional and greater drainage of the liquid from the solid particles is achieved. Wash liquid or vapor (e.g. water'or steam) may be introduced through pipe 15 to wash and/ or dry the solid particles passing across screen portion 70. The mass of solid particles having been effectively washed and separated from the liquid portion is discharged through apertures 72, 72 into casing 56 from which it passes downwardly through solids discharge outlet 58. The liquid portion or portions is discharged through

outlets

60, 71 and 73.

While the theory of operation of the present invention may not be fully understood and applicant does not wish to be bound by the following explanation, it is believed that the great effectiveness of the device of the present invention in separating liquid from solid particles and the reduction of the tendency for the screen portion to become blinded or plugged during operation are the result of the initial drainage of a large portion of the liquid away from the mass of solid particles while the latter are still retained within the imperforate portion of the bowl. The fact that there is less liquid present when the mass of solid particles reaches the screen portion means that there is less tendency for the liquid to float or convey the smaller particles to or through the screen, consequently less loss of solids with the liquid and less tendency for the screen portion to become plugged.

In another embodiment of the invention as shown in FIG. 2 of the drawing the bowl 80 consists of an imperforate conical portion 82 which merges with a conical screen portion 84 of matching taper. In this embodiment the entire bowl is conical in configuration and possesses no cylindrical portion at all. However, for satisfactory operation it is essential that the liquid overflow outlet be arranged so that the margin of the liquid pool at zone A where it terminates on the inner surface of imperforatc conical portion 82 be spaced from the inlet of screen portion 84 by a distance, measured along the axis of the centrifugal separator, equal to atleast 15 percent of the inside diameter of the conical portion 82 at its larger end. As in the embodiment shown in FIG. 1, the inner diameter at the smaller end of the imperforate conical portion 82 should be for best results, from 65 to 95 percent of the inner diameter at the larger end.

In the embodiment shown in FIG. 3 of the drawing bowl consists of an imperforate conical portion 92 connected at its smaller end with a screen portion 94 which is conically divergent outwardly towards the solid discharge end. In this embodiment conveyor 96 terminates at the inlet to screen portion 94, the divergence of the screen portion together with centrifugal force being sufficient to convey the layer of solids along the length of the screen portion 94 without the help of a conveyor. However, it may be desirable to extend the conveyor into the screen portion in some cases. The operation of this embodiment is otherwise the same as that of the embodiments of FIGS. 1 and 2, and the minimum spacing between the margin of the liquid pool and the inlet of screen portion 94 is also the same.

Although specific embodiments of the invention have been described herein, it is not intended to limit the invention solely thereto, but to include all of the obvious variations and modifications within the spirit and scope of the appended claims.

What is claimed is:

1. In a centrifugal separator for separating solid particles from the liquid portion of a slurry comprising a rotatable bowl including an imperforate truncated conical inner surface connected at its smaller end with the inlet end of a portion extending coaxially therefrom having at least one screen in its wall and having a solids discharge end opposite said inlet end, said portion having a diameter at its outlet end no less than its diameter at its inlet end, a helical conveyor coaxially mounted for rotation within said bowl, means for introducing said slurry into said'bowl in advance of the inlet end of said screen portion by a distance, measured along the axis, equal to at least 15% of the diameter of the larger end of said conical surface, and means for rotating the bowl and the conveyor in the same sense at slightly different speeds to cause the solids in said slurry to deposit on the inner surface of the bowl and to advance the solids deposit in one direction along said conical surface toward the discharge end of said screen portion, the improvement which comprises means for removing the liquid portion of said slurry to maintain the depth of liquid within said bowl at such a level that the surface of the liquid intersects the conical surface at a distance from the inlet end of said screen portion, measured along the axis, equal to at least 15% of the diameter of the larger end of said conical surface.

2. A centrifugal separator as claimed in claim 1 in which the diameter of the smaller end of said conical surface is from 65 to 95% of the diameter of the larger end.

3. A centrifugal separator as claimed in claim 2 in at least one screen in its wall and having a solids dis-- charge end opposite said inlet end, a helical conveyor coaxially mounted for rotation Within said bowl, means for introducing said slurry into said bowl in advance of the inlet end of said screen portion by a distance measured along the axis equal to at least 15% of the diameter of the larger end of said conical surface, and means for rotating the bowl and the conveyor in the same sense at slightly different speeds to cause the solids in said slurry to deposit on the inner surface of the bowl and to advance the solids deposit along said conical surface in one direction toward the discharge end of said screen portion, the improvement which comprises means for removing the liquid portion of said slurry to maintain the depth of liquid within said bowl at such a level that the surface of the liquid intersects the conical surface at a distance from the inlet end of said screen portion, measured along the axis, equal to at least 15% of the diameter of the larger end of said conical surface, and the diameter of the smaller end of said conical surface is from 65 to 95% of the diameter of the larger end.

6. The separator of claim 5 wherein said screen portion is arranged to discharge liquid into a stationary casing for said rotatable bowl.

7. In a centrifugal separator for separating solid particles from the liquid portion of a slurry comprising a rotatable bowl including an imperforate .truncated conical inner surface connected at its smaller end with the inlet end of a portion extending coaxially therefrom having at least one screen in its wall and having a solids discharge end opposite said inlet end, said portion having a diameter at its outlet end no less than its diameter at its inlet end, a helical conveyor coaxially mounted for rotation within said bowl, means for introducing said slurry into said bowl in advance of the inlet end of said screen portion by a distance measured along the axis equal to at least 15 of the diameter of the larger end of said conical surface, and means for rotating the bowl and the conveyor in the same sense at slightly diflFerent speeds to cause the solids in said slurry to deposit on the inner surface of the bowl and to advance the solids deposit in one direction along said conical surface toward the discharge end of said screen portion, the improvement which comprises means mounted radially outwardly of said screen portion for applying cleaning fluid thereto, and means for removing the liquid portion of said slurry to maintain the depth of liquid within said bowl at such a level that the surface of the liquid intersects the conical surface at a distance from the inlet end of said screen portion, measured along the axis, equal to at least 15% of the diameter of the larger end of said conical surface.

References Cited UNITED STATES PATENTS 535,306 3/1895 Stewart 233-7 X 695,754 3/1902 Moore 210-211 1,146,445 7/1915 Phillips 210211 2,283,457 5/1942 Pecker 210-374 2,685,369 8/1954 Crossley 233-14 X FOREIGN PATENTS 963,409 5/ 1957 Germany.

1,026,692 3/ 1958 Germany.

M. CARY NELSON, Primary Examiner. H. T. KLINKSIEK, Examiner,

Claims

1. IN A CENTRIFUGAL SEPARATOR FOR SEPARATING SOLID PARTICLES FROM THE LIQUID PORTION OF A SLURRY COMPRISING A ROTATABLE BOWL INCLUDING AN IMPERFORATE TRUNCATED CONICAL INNER SURFACE CONNECTED AT ITS SMALLER END WITH THE INLET END OF A PORTION EXTENDING COAXIALLY THEREFROM HAVING AT LEAST ONE SCREEN IN ITS WALL AND HAVING A SOLIDS DISCHARGE END OPPOSITE SAID INLET END, SAID PORTION HAVING A DIAMETER AT ITS OUTLET END NO LESS THAN ITS DIAMETER AT ITS INLET END, A HELICAL CONVEYOR COAXIALLY MOUNTED FOR ROTATION WITHIN SAID BOWL, MEANS FOR INTRODUCING SAID SLURRY INTO SAID BOWL IN ADVANCE OF THE INLET END OF SAID SCREEN PORTION BY A DISTANCE, MESURED ALONG THE AXIS, EQUAL TO AT LEAST 15% OF THE DIAMETER OF THE LARGER END OF SAID CONICAL SURFACE, AND MEANS FOR ROTATING THE BOWL AND THE CONVEYOR IN THE SAME SENSE AT SLIGHTLY DIFFERENT SPEEDS TO CAUSE THE SOLIDS IN SAID SLURRY TO DEPOSIT ON THE INNER SURFACE OF THE BOWL AND TO ADVANCE THE SOLIDS DEPOSIT IN ONE DIRECTION ALONG SAID CONICAL SURFACE TOWARD THE DISCHARGE END OF SAID SCREEN PORTION, THE IMPROVEMENT WHICH COMPRISES MEANS FOR REMOVING THE LIQUID PORTION OF SAID SLURRY TO MAINTAIN THE DEPTH OF LIQUID WITHIN SAID BOWL AT SUCH A LEVEL THAT THE SURFACE OF THE LIQUID INTERSECTS THE CONICAL SURFACE AT A DISTANCE FROM THE INLET END OF SAID SCREEN PORTION, MEASURED ALONG THE AXIS, EQUAL TO AT LEAST 15% OF THE DIAMETER OF THE LARGER END OF SAID CONICAL SURFACE.