US3799431A

US3799431A - Centrifuge apparatus

Info

Publication number: US3799431A
Application number: US00324287A
Authority: US
Inventors: A Lavanchy; J Caldwell
Original assignee: Pennwalt Corp
Current assignee: Alfa Laval AB
Priority date: 1973-01-17
Filing date: 1973-01-17
Publication date: 1974-03-26
Anticipated expiration: 1991-03-26
Also published as: FR2213810B3; CA986484A; JPS5237627B2; DE2401524A1; JPS507159A; GB1432921A; FR2213810A1

Abstract

A top-driven centrifuge having an internal disk stack and peripheral nozzles is provided with a housing completely surrounding the centrifuge bowl for collecting centrifugally separated heavy phase material, e.g. sludge, discharged from the nozzles, whereby the heavy phase material flows downwardly along the inner surface of the housing to a sump in the bottom thereof. Heavy phase material is collected in an annular well disposed about a vertical feed pipe. The feed pipe delivers fresh feed to the bowl through one inlet at the bottom of the bowl. An impeller carried by the bowl and rotated therewith extends into the annular well and contacts the heavy phase material in order to propell heavy phase material into a separate inlet at the bottom of bowl for material being recycled through the bowl. This invention relates to centrifuge apparatus, especially topdriven solid bowl centrifuges having an internal disk stack, with provision for peripheral nozzles and means for recycling sludge or other heavy phase material to a bottom inlet of the bowl after discharge from the nozzles, while fresh feed is delivered to a separate inlet at the bottom of the bowl.

Description

United States Patent [191 Lavanchy et al.

[ Mar. 26, 1974 CENTRIFUGE APPARATUS [75] Inventors: Andre G. Lavanchy, Devon; John W. Caldwell, Glenside, both of Pa.

[73] Assignee: Pennwalt Corporation, Philadelphia,

[22] Filed: Jan. 17, 1973 [21] Appl. No.1 324,287

Primary ExaminerGeorge H. Krizmanich Attorney, Agent, or Firm-Edward A. Sager [57] ABSTRACT A top-driven centrifuge having an internal disk stack and peripheral nozzles is provided with a housing completely surrounding the centrifuge bowl for collecting centrifugally separated heavy phase material. e.g. sludge. discharged from the nozzles. whereby the heavy phase material flows downwardly along the inner surface of the housing to a sump in the bottom thereof. Heavy phase material is collected in an annular well disposed about a vertical feed pipe. The feed pipe delivers fresh feed to the bowl through one inlet at the bottom of the bowl. An impeller carried by the bowl and rotated therewith extends into the annular well and contacts the heavy phase material in order to propell heavy phase material into a separate inlet at the bottom of bowl for material being recycled through the bowl.

This invention relates to centrifuge apparatus,

especially top-driven solid bowl centrifuges having an 12 Claims, 2 Drawing Figures CENTRIFUGE APPARATUS BACKGROUND OF THE INVENTION It is'well known to provide centrifuges of the type set forth wherein concentric pipes are provided for separately introducing fresh feed and recycled heavy phase material across an air gap into respective inlets for feed and recycled material at the bottom of the bowl. In this regard reference is made to US. Pat. No. 3,073,516. One of the problems associated with centrifuges of this type is the effectiveness of the means provided for pumping and conducting recycled heavy phase material from the peripheral nozzles to a recycle inlet at the bottom of the bowl. Heretofore, it has been common practice to provide an annular trough about the nozzles for collecting heavy phase material, and a pipe which leads from the trough and loops about the housing to the bottom of the housing and then upwardly through the housing and about the feed pipe to the bottom of the bowl. In these prior arrangements, the kinetic energy of the discharging heavy phase material propels it through the loop pipe, but an external pump is usually provided in the loop pipe in order to help in propelling recycled material back tothe 'bowl. It has been found, however, that with heavy phase material of relatively high viscosity the arrangement just described is not entirely satisfactory from the standpoint of dependability, efficiency, and overall appearance of the centrifuge.

BRIEF SUMMARY OF THE INVENTION According to the present invention, the annular trough, theexternal loop pipe, and the external pump are eliminated, and substituted therefor is a housing which completely surrounds the centrifuge for collecting the heavy phase material discharged from the nozzles and for conducting the heavy phase material to the bottom of the housing where a sump is defined- Formed about a vertical feed pipe is a tubular riser which extends upwardly from the sump and defines with the feed pipe an annular well for recycled heavy phase material. In order to propel the heavy phase material from the well into the recycle inlet of the centrifuge bowl a vane impeller is provided which is connected to the rotating centrifuge bowl for rotation therewith. The impeller extends downwardly into the well and contacts the heavy phase material. This arrangement causes rapid rotation bf the recycled material in the well and its consequent outward projection from the rim of the riser into the recycle inlet of the bowl.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view ofa centrifuge embodying the invention.

FIG. 2 is a view, partly in elevation and partly in vertical section, with portions broken away, of a centrifuge embodying the invention.

Referring to the drawings, in FIG. 1 is shown centrifuge apparatus having a solid bowl 12 which rotates in a stationary housing 14. The bowl 12 is rotatably suspended by a vertical driving shaft 16. The shaft 16 is connected to the bowl 12 by a trunco-conical hub 18 for unitary rotation. Atlhough not shown, a motor, belt and pulley system may be employed in a well known manner to drive the shaft 16.

The bowl 12 comprises upper and lower

truncoconical portions

20 and 22 respectively, the large ends of which are arranged in mutually adjacent relationship and connected to an intermediate portion 24 of cylindrical shape. The narrow end at the top of the upper bowl portion 20 defines an annular discharge passage 26 for the overflow of centrifugally clarified liquid, which outlet leads to a compartment 28 wherein the clarified liquid is collected and thereafter discharged from a discharge outlet 30.

Disposed within the bowl l2, and mounted on the shaft 16, is a stack of vertically spaced, conical separator discs 32. As is well known in the art, the discs 32 promote the separation of heavy and light phase materials within the bowl, the heavy phase material sedimenting outwardly toward the intermediate bowl portion 24, and the light phase liquid material moving inwardly toward the shaft 16 and thence upwardly toward the discharge passage 26. A plurality of nozzles 34 are spaced along the periphery of the bowl 12, preferably at the intermediate portion 24, each nozzle having an orifice to provide a restricted passageway through the bowl wall for the discharge of a high concentration of solids in liquid suspension, e.g. sludge, as heavy phase material. Such discharge from the nozzles 34 may be referred to hereinafter as heavy phase material or recycle material.

Disposed about the lower bowl portion 22 is a stationary wind screen 36 which, to a large degree, confines the windage developed by the lower portion of the rotating bowl 12 to the annular region between the bowl 12 and the screen 36. This provision minimizes turbulence in the zone between the screen 36 and the housing 14.

Extending upwardly through the housing 14 is a feed pipe 38, the axis of which is substantially aligned with the vertical rotation axis of the shaft 16 and the bowl 12. The upper end of the feed pipe 38 is in vertically spaced relationship with a downwardly converging conical nut 40. Alternatively, the nut 40 may be of conventional shape with a separate part of conical configuration connected thereto. A plurality of passageways 42, formed in the hub 18 in an annular array, provide an inlet for feed which jets from the feed pipe 38, across the air gap, and into contact with the nut 40 from whence it is deflected radially outwardly through the passageways 42 into the interior of the bowl 12.

Located below and outwardly of the passageways 42 is one or more inlet openings 44 for recycled material. The openings 44 connect with passages 46 leading from the inlet openings 44 to a zone within the bowl 12 dis- .posed immediately inward of the intermediate bowl portion 24 and the nozzles 34. The passages 46 may be defined by a frusto-conical baffle 48, as illustrated, or by an annular array of tubes which are not shown but are nevertheless familiar to those skilled in the art.

Still referring to FIG. 1, feed comprising solids in liquid suspension is delivered to the feed pipe 38 and introduced to the interior of the bowl 12 in the manner described above. Once inside the bowl 12 the feed is subjected to centrifugal action within the separating zone defined by the space outwardly of the shaft 16 and inwardly of the bowl 12. The centrifugal action, augmented by the action of the discs 32, promotes the clarification of the liquid contained in the feed mixture, and thereafter the clarified liquid is discharged in the manner described above. Furthermore, concentrated solids sediment outwardly toward the nozzles 34 and, with some of the liquid, is discharged as heavy phase material through the orifices of the nozzles 34 out of the bowl 12.

As shown by the flow lines in FIG. 1, the heavy phase material travels outwardly into contact with the inner surface of the housing 14 and thereafter settles downwardly along the inner surface of the lower portion of the housing 14 into a region at the base of the housing 14 defining a sump 49. At least some of the heavy phase material in the sump 49 may be delivered to the inlet openings 44 for recycle material, while the remainder thereof is discharged from the housing 14 through a solids discharge outlet 50.

Although not shown in the drawings, suitable controls and valves may be provided to divert a selective portion of heavy phase material for recycle through the passages 46, while the remainder is discharged via the outlet 50. For example, see US. Pat. No. 3,073,516, referred to earlier herein.

Referring now to FIG. 2, like reference numerals are employed to designate parts corresponding to parts already identified and described with reference to FIG. 1. These descriptions will not be repeated for the sake of brevity. It will be noted that the discharge outlet 50 for heavy phase material not being recycled is in the form of a horizontal pipe connected to the spherical housing 14 at the base thereof. Shown in detail is the feed pipe 38 with a reduced upper end portion terminating in an orifice 52.

Further provided is a feed cone 54 for partitioning the feed and recycle streams jetting across an air gap in order to guide them respectively to the passageways 42 and the passages 46. Carried on the feed cone 54 is an annular array of spaced, radially disposed accelerator vanes 56. Similarly, an annular array of spaced, radially disposed accelerator vanes 58 are carried on a bottom plate 60. It is the function of the accelerator vanes 56 and 58 to bring the deflected streams of feed and recycle material, respectively, up to the speed of the rotating bowl 12 before entering the interior of the bowl 12.

As shown in FIG. 2, the housing 14 may be made in two, upper and lower, parts which are suitably joined together along a horizontal flange 62. The lower part of the housing is preferably of hemispherical shape, with adequate spacing from the wind screen 36 to provide a large annular zone 64 for the free flow of a discharged heavy phase material from the nozzles 34 to the sump 49.

The sump 49 is provided with a tubular riser 66 extending vertically upward, in concentric relationship with the feed pipe 38. At the upper end of the riser 66 is a circular rim which defines, with the exterior of the feed pipe 38, an annular well 68 for heavy phase material being recycled. ln other words, the upper end of the riser 66 has an upwardly facing open end of annular configuration. The riser 66 is supported on the base of the housing 14 by plate structure 70 which has large apertures 72 formed therein to provide flow passages between the sump 49 and the annular zone 64. Supported atop the riser 66 and plate structure 70 is a circular member 74 which carries not only the wind screen 36, but also an annular bumper 76. It is the function of the stationary bumper 76 to engage the downwardly extending circular flange 78 on the bottom plate 60 and limit excessive deflection of the bowl as during transient vibrations when the bowl 12 is accelerating to normal operating speed.

Connected to the lower end of the accelerator vane 58 is an integral vane extension 80 which extends from above the rim of the riser 66 to below the rim of the riser into the well for contact with heavy phase material therein. The vane extension provides an impeller, since it rotates with the bowl 12; and, by contact with the heavy phase material in the well 68, causes such material to rotate very rapidly. The rapidly swirling heavy phase material develops a parabolic surface, then overflows and is projected outwardly over the rim of the riser 66 into the inlet openings 44 of the passages 46.

The present invention has many advantages over prior centrifuges of the type set forth. The elimination of an external trough and loop pipe for recycle material not only avoids pressure drop losses in the pipe, but also improves the appearance of the centrifuge and simplifies its construction. The elimination of an external pump in the loop pipe reduces the cost of the centrifuge installation, and the internal arrangement of the present invention is no less reliable. A further advantage is that the nozzle orifices may now be directed opposite to the direction of bowl rotation in such manner that heavy phase material may be discharged with little or no velocity relative to the stationary housing, and therefore with less abrasive action, whereas prior centrifuges required high velocity discharge in order that kinetic energy of discharge might be converted to energy for pumping the recycle material through the loop pipe and across the air gap.

It is to be noted that the rim of the riser 66 is radially disposed between the vane 80 and the bumper 76.

The invention is not limited to two phase separation since it is applicable, for example, to known three phase separation centrifuges wherein two separated liquid phases are separately discharged from respective overflow passages.

The centrifuge 10 is provided with at least a sufficient number of equally spaced nozzles 34 to remove heavy phase material and prevent any accumulation of such material within the bowl 12 which would enter the disc stack 32. It is preferred that there be as many equally spaced vanes 58 as there are nozzles 34. However, vane extensions 80 may be provided on less than all of the vanes 58. A suitable number of equally spaced vanes 56 are also provided.

What is claimed is:

1. A centrifuge having a top-driven rotor bowl, a disc stack within said bowl, annular overflow means at the top of said bowl for discharging centrifugally clarified liquid from said bowl, said bowl including a hub in the bottom portion thereof and a driving shaft connected to said hub and extending upwardly through said overflow means, a first passageway for feed extending through said hub for conducting feed into said bowl for centrifugal separation therein during rotation of said bowl about the rotational axis of said shaft, with first inlet means for said first passageway annularly disposed about said axis, first accelerator means rotatable with said bowl and including at least one vane disposed at said first inlet means for accelerating feed directed thereto, nozzles peripherally arranged on said bowl about said axis for discharging heavy phase material from said bowl, a second passageway for conducting recycled heavy phase material to said bowl from a bottom portion of said bowl to the interior of said bowl adjacent said nozzles, with second inlet means for said second passageway annularly disposed about said axis, said second inlet means being in vertically spaced relationship with said first inlet means, second accelerator means rotable with said bowl and including at least one vane disposed at said second inlet means for accelerating recycled heavy phase material directed thereto, a stationary housing surrounding said bowl, a feed pipe extending upwardly through said housing toward the bottom portion of said bowl, means for directing feed from said feed pipe toward said first inlet means, and that improvement comprising: a sump at the bottom of said housing in communication with said nozzles through the annular space between said bowl and said housing, a tubular riser for said sump extending upwardly therefrom and about said feed pipe, said riser at its upper end having an upwardly facing open end of annular configuration defined by its peripheral rim and said feed pipe to provide a well for heavy phase material being recycled to said bowl, and an impeller for directing heavy phase material from said well to said second inlet means, said impeller comprising at least one vane connected to said bowl for rotation therewith and extending downwardly from above the level of said rim to below the level of said rim and into contact with the heavy phase material in said well to cause rotation of the heavy phase material in the upper end of said riser and consequent outward projection of the heavy phase material into the second inlet means.

2. A centrifuge according to claim 1 wherein said hub is of upwardly tapering, trunco-conical shape.

3. A centrifuge according to claim 1 wherein the intermediate portion.

5. A centrifuge according to claim 1 wherein the second inlet means is vertically spaced below said first inlet means.

6. A centrifuge according to claim 1 wherein said housing includes a lower portion of hemispherical configuration, there being open communication from said sump to the space between said housing and said nozzles for the free flow of heavy phase material from said nozzles to said sump.

7. A centrifuge according to claim 1 wherein said vane of said impeller is connected to said second accelerator means for rotation therewith.

8. A centrifuge according to claim 1 wherein said first and second inlet means includes a trunco-conical member for partitioning the feed and heavy phase material from one another in the spaces between the feed pipe and the first passageway and the well and the second passageway.

9. A centrifuge according to claim 1 wherein the means for directing feed from the feed pipe to the first inlet is a downwardly tapering member at the bottom end of said shaft radially adjacent said first inlet means.

10. A centrifuge according to claim 1 further including an annular bumper in radially spaced relation to bottom portions of said bowl, with said rim being disposed between said bumper and said vane of the impeller.

11. A centrifuge according to claim 1 further including a stationary wind screen formed about said bowl and defining with said housing an annular zone for the flow of heavy phase material from said nozzles to said sump.

12. A centrifuge according to claim 1 in which said housing is provided with a discharge outlet through which a portion of the heavy phase material is removed from the housing.

Claims

3. A centrifuge according to claim 1 wherein the bowl includes upper and lower portions, each being of trunco-conical shape, with the large ends of said bowl portions being disposed in mutually adjacent relationship.

4. A centrifuge according to claim 3 further including a cylindrical bowl portion intermediate the upper and lower portions of said bowl and connected to the large ends thereof, with said nozzles being arranged on said intermediate portion.