US3398888A - Centrifuge with improved discharge assembly - Google Patents

Description

27, 1958 M. M. KOENECKE ETAL $398,838

CENTRIFUGE WITH IMPROVED DISCHARGE ASSEMBLY 4 Sheets-Sheet 1 Filed Aug. 18, 1966 CENTRIFUGE WITH IMPROVED DISCHARGE ASSEMBLY FIG. 3

Aug. 27, 1968 M. M. KOENECKE ETAL 3,398,888

D DISCHARGE ASSEMBLY CENTRIFUGE WITH IMPROVE 4 Sheets-Sheet 3 Filed Aug. 18, 1966 Aug. 27, 1968 KOENECKE ETAL 3,398,888

CENTRIFUGE WITH IMPROVED DISCHARGE ASSEMBLY 4 Sheets-Sheet 4 Filed Aug. 18, 1966 FIG. 7

United States Patent 0 ABSTRACT OF THE DISCLOSURE A centrifuge having a bowl rotatably mounted in a housing. A plurality of expansionable and contractable panels are mounted on the interior of the housing opl posite the solids discharge end. Pulsating air pressure is supplied to the panels to break up and discharge solid cake material which normally would stick to the housing.

This invention relates to a centrifuge for separation of solids from liquid suspensions. More particularly the present invention relates to a centrifuge equipped with an improved assembly for the discharge of solids.

Commercial centrifuges have been in use for some time which embody a rotating bowl and screw conveyer to separate a solid phase from a liquid suspension by means of centrifugal force. These centrifuges are commercially used where the solid particles have a higher density than does the liquid phase. Considerable difficulty has been encountered in operation of the foregoing type centrifuges when used with solids having a tendency to adhere to each other and to the discharge surfaces of the centrifuge. Specifically a severe problem has been encountered in separating solid thermoplastic particles from suspensions. A particularly acute problem has been encountered in separating polyvinyl chloride particles made by the suspension process from the suspension liquid. In one commercial centrifuge installation it was found that it was necessary to shut down the centrifuge for manual cleaning after operating periods as short as two hours.

One prior art method has attempted to prevent the solid material from sticking to the area around the solids discharge end of the centrifuge by providing a single band of vulcanized rubber around the area (see US. Patent 2,324,933). In this centrifuge it was necessary to adhesively attach the edges of the single elastic strip to the housing to permit air pressure to be applied to the space between the centrifuge and the elastic band. The seal frequently leaked causing severe maintenance problems with this device. Further, the rubber strip was severely worn in certain localized areas in a very short time which necessitated changing the entire rubber strip. The centrifuge of the present invention overcomes the objectionable features of the foregoing prior art centrifuge.

An object of the present invention is to provide a centrifuge having an improved assembly for the discharge of the solid phase.

Another object of the present invention is to provide a centrifuge which can operate at sustained intervals without the necessity of shutting down for cleaning.

An additional object of the present invention is to provide a centrifuge having means for periodically cleaning the surfaces in the solids discharge area.

A further object of the present invention is the provision of a centrifuge having means to permit ready replacement of localized surface areas which are subject to wear from abrasive solid particles.

3,398,888 Patented Aug. 27, 1968 The foregoing, and other aims, objects and advantages of invention as may appear hereinafter are realized in a centrifuge having a housing and a bowl rotatably mounted in the housing. The bowl is provided with means for discharging solids at one end thereof. A screw conveyer is rotatably mounted inside the bowl. A plurality of expansionable members are provided within the housing in the solids discharge end of the centrifuge to break up the cake which normally forms at this end of the centrifuge.

In the drawings:

FIG. 1 is an elevational view of the centrifuge of the present invention having portions thereof broken away to show the internal structure;

FIG. 2 is a cross sectional view taken along the line 22 of FIGURE 1;

FIG. 3 is a longitudinal sectional view taken along line 3-3 of FIGURE 1;

FIG. 4 is an exploded view in perspective of the solids collection assembly utilized in the centrifuge of the present invention.

FIG. 5 is an elevational perspective view of one embodiment of the expansionable members utilized in present invention;

FIG. 6 is an elevational perspective view of a second embodiment of the expansionable members utilized in the present invention; and

FIG. 7 is a schematic diagram of the air supply system for the expansionable members.

Referring now to the drawings, particularly to FIG- UREE l and 2 thereof, the centrifuge includes a housing, designated generally by the numeral 10, and a base 11 which provides support for the rotatable bowl 12 positioned within the housing. A hollow, rotatable screw conveyer 13 is provided within the bowl 12 and is suspended independently of the bowl by means of a rearward solid shaft 14 and forward hollow shaft 15. Shaft 15 is supported by bearing assembly 16 which is received in the recess 17 provided in the forward end of the interior of bowl 12. Bowl 12 is rotatably supported at its forward end by means of hollow shaft 18 which is suported in bearing block assembly 19 which rests on a portion of the base 11. The rear end of the bowl 12 is supported by hollow shaft 24) which is in turn supported by bearing block assembly 21 resting on base 11. The rearward shaft 14 of the screw conveyer is supported by means of a bearing assembly (not shown) within the drive gear assembly 22.

Axial feed tube 23 is mounted on support bracket 24 and projects through the hollow forward shaft 15 to the hollow interior of the screw conveyor 13. Slurry flows from the opening 25 provided in the end of feed tube 23 through ports 26 provided in the wall of hollow screw conveyor 13. Pulley 27 is connected to hollow shaft 18 and rotates the bowl 12 in a counter-clockwise direction through V- belts and a drive motor (not shown). Screw conveyor 13 is rotated 'by means of drive shaft 14 through drive gear assembly 22 by means of a motor (not shown). The screw conveyor 13 and the rotating bowl 12 are rotated on their longitudinal axis in a clockwise direction as viewed from the end of the centrifuge equipped with pulley 27. Hollow screw conveyor 13 rotates in the same direction but at a lower r.p.m. than does the bowl 12 thereby moving sedimented solids by means of the flight screw 28 affixed to the outer surface of the screw conveyor 13. The centrifugal force imparted to the slurry separates the slurry into solid and liquid phases. Solids are sedi-rnented against the interior surface of the bowl 12 and propelled by flight screw 28 to the beach area 29 of the bowl 12 and then out through solids discharge ports 30 provided in one end of centrifuge bowl 12. The clarified liquid flows through ports 31 provided in the rearward end of the bowl 12. The discharged liquid then flows through liquid discharge pipe 32 to a drain or stor age vessel.

g The solids discharge end of the centrifuge is provided with a collector area defined by the forward end wall 33 of the housing 10 together with a bafiie plate 34 surrounding the bowl 12 and attached to the interior wall of housing 10.

Within the collector area a solid discharge assembly designated generally by the number 35, is provided. As can be seenrnore clearly than FIGURES 2, 3 and 4, the solid discharge assembly 35 includes a plurality of interconnected support panels 36 which form an inverted U- shaped structure within the solids collector area. The forward wall member 37 is attached to to one side of the interconnected support panels 36 by means of bolts 38 and nuts 39;. A rearward wall member number 40 is attached to the opposite edges of interconnected support panels 36 by bolts 38 and nuts 39. Two rows of expansionable panels, designated generally by number 41, are attached to support panels 36 by means of bolts 42 as shown in FIG. 4.

As can be seen more clearly in FIGURE. 3, the expansionable panels 41 have an elastic covering 43. An air space 44 is provided within each panel 41. A nipple 45 connects the air space 44 to a source of compressed air conveyed to each of the panels by means of tubing 46. The elastic covering 43 may be of any suitable mate-rial possessing the ability to expand and contract under the influence of compressed air. Among the suitable materials from which the elastic covering 43 may be fabri cated are the synthetic rubbers. A preferred material for elastic covering 43 is sheet polyurethane. This material has been found eminently suitable in that it is highly resistant to the abrasive action of hard solid particles. If desired the elastic covering 43 may be fabricated from thin, flexible panels of stainless steel or other suitable metal.

Referring now to FIGURE it can be seen that the expansionable panels 41 may be individual side-by-side mounted panels. An alternate embodiment is shown in FIGURE 6 wherein a series of single expansionable panels 41a may be utilized with each individual panel covering the width of the surface of the support panel 36.

The interior surface of forward wall member 37 is covered with a coating 47 of a material which provides a non-stick surface which resists build-up of solid materials. Rearward wall member nu-mbef 40 has a similar coating 47 provided on its interior wall as can be seen in FIG- URE 1. One material which has been found suitable for the non-stick coating 47 is polytetrafluoroethylene (Teflon) which may be applied in the form of an ladhesively attached sheet, or may be sintered onto the walls by means of conventional sintering techniques. If desired the forward and rearward Wall members may be covered with a plurality of expansionable panels 41 in place of the non-sticking coating 47.

Referring now to FIGURES 3 and 7 compressed air is applied to the air space 44 within each expansionable panel by means of interconnecting tubing 46. High pressure compressed air is supplied through pipe 48 to filter 49, then to a pressure regulator 50, and then to an electrical pressure sequence controller, designated generally by the number 51. Air from the sequence controller 51 is carried by pipe number 52 through exhaust valve number 53. Relief valve number 54 is connected to the exhaust valve 53 and to the sequence controller by a separate line. Tubing 46 conducts the low pressure air to each expansionable panel carried by the support panels 36 through a network of interconnected tubing runs as shown in FIGURE 7.

As seen in FIGURES 1 through 4 the solid material is discharged through ports 39 in the direction of the arrows where thesolid material then strikes the solids discharge assembly which surrounds the solids discharge end of the centrifuge. The major quantity of solids are thrown against the series of expansionable panels 41 where a gradual build-up of densely packed partcles occurs. After an interval of time determined by the setting of sequence controller 51 air pressure is supplied to each of the panels 41 to expand the elastic covering which results in breaking off the accumulated solid layer from surface of each of the panels 41. The sequence controller then vents the air through exhaust valve 53. The panels 41 are alternately expanded and contracted on a fixed schedule when the centrifuge is operating. A pulsating time of /2 to 1 second has been found satisfactory for discharging polyvinyl chloride particles. This broken caked material then drops into the solid collection system through the opening 55 in the bottom of the centrifuge. Relatively small quantities of solid materials are thrown against the forward wall 37 and rearward wall 40. The non-stick coating 47 on each of these walls prevents any substantial quantity of the solid material from adhering to the end walls of the discharge assembly. If desired one or more additional low pressure air supply lines 46 can be run from the sequence controller and connected to alternate panels. These additional supply lines are connected to a separate timer which is set to provide a pulsation cycle that is opposite to that on which the primary supply operates. This system is sometimes more effective in breaking up the caked material than is the simultaneous pulse system described hereinbefore.

The discharge assembly used in the centrifuge of the present invention is a decided improvement over a vibrating solids discharge ring which had been used with some centrifuges heretofore. As mentioned hereinbefore, sometimes a single band of elastic material, usually vulcanized rubber, has been used to attempt to break up the cake of solid particles in the solids discharge area of the centrifuge. Problems were encountered in that bonding of the elastic strip was difficult to secure and also the short life of the rubber strip required frequent shutdown of the centrifuge for replacement. Furthermore, the strip was subject to the high abrasion in localized areas and it would fail before a. reasonable life expectancy was achieved. The present centrifuge by utilizing a plurality of individual expansionable panels permits the replacement of those panels which are subjected to erosive forces without the necessity of renewing the entire surface that is exposed to the abrasive solids. Continuous openating periods as long as about fourteen days to about twentyeight days have been achieved using the present lCfil'ltIlfuge for separating polyvinyl chloride from a water suspension. Heretofore the maximum operating time for a centrifuge without the pulsating panels in PVC service was about two hours.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Other modifications will be apparent to those skilled in the art. Therefore the present invention is to be limited only by the scope of the appended claims.

We claim:

1. A centrifuge comprising: a housing; a bowl rotatably mounted in said housing, said bowl having means for dis- 4. The centrifuge of claim 3 wherein said last mentioned means includes compressed air.

5. The centrifuge of claim 4 including means for simultaneous-ly expanding alternate panels and contracting intermediate panels.

6. The centrifuge of claim 1 wherein said housing is provided with a coating of material to render the surface non-sticking in the area adjacent said plurality of expansionable members.

References Cited UNITED STATES PATENTS McGlaughlin.

Jones.

Abbott 233-46 XR Borig 233-22 Meryman et al. 233-27 HENRY T. KLINKSIEK, Primary Examiner.

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