US3570754A

US3570754A - Centrifuge apparatus

Info

Publication number: US3570754A
Application number: US745945A
Authority: US
Inventors: William J Kirkpatrick
Original assignee: Pennwalt Corp
Current assignee: Pennwalt Corp
Priority date: 1966-11-10
Filing date: 1968-07-18
Publication date: 1971-03-16
Anticipated expiration: 1988-03-16
Also published as: GB1183858A; DE1632311A1; US3407999A

Abstract

Heavy phase liquid, centrifugally separated from light phase liquid and accumulated on the peripheral wall of a centrifuge bowl, is removed by a skimmer actuated by a heavy phase level detector. The latter includes structure defining an inwardly facing annular pocket mounted for rotation with the bowl and provided with a passageway leading outwardly from the pocket to a position outward of an overflow lip for the light phase liquid, also means for supplying control liquid to the pocket and a sensor which responds to accumulations of heavy phase liquid obstructing the outer end of the passageway.

Description

0 United States Patent [1113,570,754

[72] Inventor William J. Kirkpatrick [56] ReferencesCited Sprmgfield, Del UNITED STATES PATENTS [211 P "5945 981,681 1/1911 Peck 233/9 22 Filed July 18,1968

1,002,471 9/1911 Thelitz 237/12 [453 tamed 3167 509 1/1965 s:' k 233/20 [73] Assignee Pennwalt Corporation emac Philadel m H 3,261,546 7/1966 Gruver 305/35 P 3,301,476 1/1967 Hemfort 233/20 Continuation-impart of application Ser. No. 593,338, Nov. 10, 1966, now Patent No. 3,407,999, dated Oct. 29, 1968.

[54] CENTRIFUGE APPARATUS 9 Claims, 3 Drawing Figs.

521 us. 0...... 233/20 [511 .05m. .1 24! 11/00 [50] Field ofSearch 233/19, 20,

Primary Examiner-Robert W. Jenkins Attorney-Edward A. Sager Elluem PATENTEUHARISIQYI 3570.754

sum 1 or 2 INVENTOR. WILUAM J. KIRKPATRICK BY 6M4.

ATTORNEY.

PATENTED MARI 6197i I saw 2 or 2 iii! l Fig. 2

INVENTOR. WILLIAM J. KIRKPATRICK BY a ATTORNEY.

CENTRHFFUGE APPARATUS This application is a continuation-in-part of application Ser.

No. 593,338, filed Nov. 10, 1966, now US. Pat. No. 3,407,999, granted Oct. 29, 1968.

This invention relates to centrifuges. More specifically this invention relates to a solid bowl centrifuge operated on a cyclical-sludge-discharge basis and having automatic means for detecting the extent of sludge buildup and for removing the sludge from the bowl.

in the solid bowl cyclical-sludge-discharge centrifuges of the prior art, feed has been delivered into the bowl preferably at one end and the clear effluent has discharged over a lip at the other end. Sludge has built up a cake against the bowl wall. After a set period of time based on experience and approximating the time required for sludge to build up to the maximum level before it appears in the effluent, the feed has been shut off by a timer. The timer has actuated the sludge removal equipment. in most cases this has been simply a skimmer, the discharge of which is initially led to the clarified liquid discharge. As the skimmer reaches the sludge cake an operator, seeing the sludge in the skimmer discharge, has diverted it to waste. when the sludge has been removed from the bowl to the extent practicable the skimmer has returned to its inward rest position. Feed to the bowl is resumed.

The manual or semiautomatic processes of the prior art as described above have had severe disadvantages. Obviously sludge buildup rates vary even with the same slurry feed rate. The timed actuation as described takes no account of this. As a result process time may be lost in too frequent unloadings or, worse, the unloadings on occasion will not be frequent enough and sludge will appear in the clarified liquid. A further complaint has been that it was entirely possible and often happened that the operator would not detect early traces of sludge in the skimmer discharge. For this reason the effluent would become contaminated with an objectionable amount of sludge. Besides this, of course, there has been objection to the need. for an operator at all. He has been required full time to oversee the operation of the centrifuge and has had to be attentive. This complaint has become more and more significant with increasing labor costs.

There has thus been a need for a completely automatic sludge dumping cycle in a solid bowl centrifuge. Many attempts have been made in the past to provide such arrangement. Some detectors of sludge in the effluent have been based on the optical opacity of the discharging effluent and have employed electric eye means or equivalent. These have been fallible because the area in which such machines are disposed is often not clean and the lenses of such detectors have become clouded giving false indications of opacity. Other sludge detecting means have worked on the basis of the density of the discharging effluent. Because the density will go up as the effluent becomes a suspension of sludge solids, this means could theoretically be used to detect sludge solids in the effluent. However, the density sensing means have been extremely critical of adjustment because of the small difference in density between clear effluent and slightly clouded effluent. This has not been a satisfactory solution.

Under the present invention there is provided an extremely simple and virtually foolproof means for detecting the sludge level in a solid bowl centrifuge and for actuating the sludge discharge mechanism. The present arrangement provides for the actuation of the sludge discharge cycle when and as necessary but before sludge is actually present in the effluent, thereby avoiding any escape of solids into the clarified liquid. This is in contrast to the optical opacity and density means which indeed did not even commence to function until the cf fluent became clouded with sludge.

Qther objects of the invention will be clear from a reading of the following specification including the drawings in which:

llG. ii is a sectional view of a centrifuge embodying the invention and showing in schematic form some of the controls thereof;

H6. 2 is an enlarged fragmentary sectional view showing the control liquid ring of a centrifuge embodying the invention; and

FIG. 3 is similar to FIG. 2 being an enlarged fragmentary sectional view of the control ring but also showing a sludge level detector nozzle partially in section.

Briefly, the invention involves an automatic sludge discharge arrangement for a solid bowl cyclically unloading centrifuge. The dumping cycle is actuated upon the buildup of sludge in the bowl to a certain level and thereafter the feed is discontinued, the dumping of the sludge is automatically efficiently accomplished, and the feed is resumed.

Referring more specifically to the drawings, an arrangement embodying the invention is indicated in FIG. l and the apparatus is generally designated 10. it comprises a base 12 having a plurality of upstanding standards 14, only one of which is shown. Suspension means 16 attached to the standards hang the centrifuge bowl housing 18. At the lower end of the housing is a bearing 20. The centrifuge bowl 22 is mounted on a shaft which passes through the bearing and mounts on its lower end a pulley 24. The pulley is driven by belt means from the motor 26.

The bowl 22 presents an imperforate bottom wall 28 and peripheral wall 30. The upper end wall is likewise imperforate and provides a discharge lip 32. More or less radial vanes 34 are provided in the bowl. These extend upward from the bottom of the bowl to within a short distance from the top to provide clearance for the skimmer discharge as will be understood.

Feed slurry is introduced to the bowl through the feed tube 38 stationarily mounted over the bowl. The tube is provided with solenoid operated valve 39. A feed receiving cup 40 is mounted on the top of the bowl hub and rotates with the bowl. From the cup 40 a plurality of feed conduits 42 extend longitudinally of the bowl down to the bowl bottom. The ends to the conduits have openings and pass the feed slurry into the bowl with little turbulence.

Connected to the lower end of the centrifuge bowl housing 18 is the effluent outlet conduit 44. This leads the conduit to an effluent tank 46 from which the product effluent is drawn.

For removing the sludge in the cyclical operation the centrifuge is provided with a skimming device 50. This includes a tube substantially J-shape which presents an open mouth 52 facing the direction of rotation of the bowl. The skimmer is mounted on the housing in a plurality of bosses 54 in which the skimmer device is longitudinally movable. As in the past the basic operation of the skimmer is similar to other skimmers. As the skimmer is moved outward, that is deeper into the bowl, a combination of the velocity of the liquid passing into the stationary skimmer and the centrifugal pressure head of the liquid in which the skimmer is submerged causes the liquid to be pumped" into and through the skimmer device.

Means for driving the skimmer device are indicated schematically at 56. These means may comprise a pair of pneumatic piston-cylinder assemblies which drive the skimmer alternately forward and back respectively. The drive means 56 is carefully arranged so that at one extreme of travel the skimmer is disposed with its mouth inward out of the liquid in the centrifuge bowl and inward of the lip 32. At the other end of its travel the skimmer mouth 52 has an extreme of roughly one-quarter inch from the peripheral wall of the shell so that it can remove sludge from virtually the peripheral wall of the bowl. Limit switches or valves assure the ends of travel and reversing valves or switches effect reversal of the drive means.

Attention is now directed to an essential portion of the invention. Mounted at the upper end along the inner edges of the vanes 34 is the control liquid ring 60. The ring is, of course, annular and is channel-shaped in cross section as shown in FIG. 2. The ring may be welded or otherwise attached to the top of the upper end of the vanes and is very preferably arranged so that the floor" of the channel section is at the same radial level as the effluent discharge lip 32; of the centrifuge. As shown in H6. 3 the ring is formed about its circurnference with equispaced threaded openings in its floor or web and into each opening is threadedly received a sludge level sensing nozzle 64. At its outer end the nozzle is formed with a restricted orifice plate 66, the orifice of which is a substantial reduction compared to the inside diameter ofthe nozzle 64. This avoids clogging of the nozzle from inside but at the same time assures proper obstruction of the opening in plate 66 by sludge as the sludge builds up inward. The position of the outer end of the nonle 64 will determine the level to which sludge buildup is permitted before the sludge unloading cycle commences.

Referring once more to FIG. 1 the effluent tank 46 has connected to it a control liquid line 70 which includes a pumping means 72. The discharge line from the pumping means is led to the top of the centrifuge housing and overhangs into the centrifuge bowl and directs its discharge into the ring 60. It is mounted securely and carefully spaced to avoid any kind of interference with the rotating parts of the centrifuge including the ring 60. Depending on the economics of the process and other factors this control liquid line which discharges control liquid at a very low rate, for instance, one-half gallon per minute, may run continuously or may be shut off with the feed. The size of the orifice in the plate 64 is such as to pass liquid out of the ring 60 at least as fast as the liquid is supplied thereto prior to any blocking of the orifice as described below. For shutoff purposes the control liquid line 70 may be provided with a solenoid-operated valve 74.

Electrical means are provided to sense the level of control liquid in the ring 60. In a preferred version these electrical means comprise a capacitance-actuated liquid detector 80 which has a depending probe 82 with its lower end disposed in the pocket or opening of the ring 60. The detector 80 is rigidly mounted and its probe 82 is carefully spaced to avoid interference with the ring 60.

A very suitable capacitance-actuated sensing means as illustrated at 80 in the drawings is sold under the trade name Level-Tek Model 303 and is available from Robertshaw Controls Company. This device has been found suitably sensitive to control the operation under the present invention. The device has a range of sensitivities in which it may be manually adjusted. It is actuated by small changes in capacitance as a function of level or product changes at the detecting probe 82.

As shown schematically the control liquid sensing means 80 is electrically connected to the feed valve 39 and to the skimmer drive means 56. It is also optionally connected to the control liquid line valve 74, as with electrical conductor or line 75 ofFIG. 1.

Referring once more to FIG. 1, between bosses 54 the skimming device is provided with a trip which may take the form of any kind of a lug or protuberance 90 rigidly or adjustably mounted on the skimming device. Schematically shown and positioned preferably on the housing is a limit switch 92 which is actuated by the lug in either direction of travel of the skimming device. The limit switch 92 is connected as shown to a solenoid-operated diversional valve 94 and it is arranged so that when the limit switch 92 is tripped in one direction as when the skimmer is driven outward toward the bowl wall, the solenoid-operated diversional valve 94 is thrown to the waste position. On return of the skimmer when the lug 90 engages the limit switch 92 the solenoidoperated diversional valve 94 is operated in the reverse direction to divert the flow from the skimmer to the effluent.

The operation of the device described herein commences with the bowl rotating with and feed being delivered to the bowl through the open valve 39 in feed tube 38. Control liquid is also being delivered through the line 70 to the ring 60 and passes out through the open sludge-level sensing nozzle 64. The clear effluent flows over the lip 32 and is thrown outward and passes down the inside wall of the housing 30 and moves out through the effluent discharge conduit 44 to the effluent tank 4 6. The sludge of the feed slurry gradually builds up against the wall 22 of the bowl.

Referring now to FIG. 3 the sludge builds up to the outer end of the sludge-level detecting nozzle 64 and eventually covers the orifice in the plate 66. This blocks the further escape of control liquid from the ring 60 and liquid builds up within the ring. Referring to FIG. 2, when the liquid is built up in the ring to the extent where the capacitance of the probe 82 is sufficiently influenced thereby, the detector (FIG. 1) is actuated. The actuation of detector 80 electrically closes the solenoid-operated feed valve 39 and actuates the skimmer drive means 56 to drive the skimmer to the rightward as shown in FIG. 1 causing the mouth 52 of the skimmer to engage the liquid in the bowl. This liquid is pumped" out by the action of the skimmer and is sent to the clarified liquid discharge. When the skimmer drive means 56 moves the skimmer 50 far enough to the right however the lug engages the switch limit 92 which actuates the solenoid-operated diversional valve 94 to divert the outflow from the skimmer to waste. The position of the limit switch 92 is set such that this will be just before the mouth of the skimmer 52 reaches the level of sludge buildupor approximately the level of the outer end of the nozzle 64- 'so that all sludge is diverted to waste with none moving out to the clarified liquid discharge.

The skimmer drive means 56 drives the skimmer on to its outer limit of travel. As already indicated the proper limit is when the mouth 52 of the skimmer reaches a point about onequarter inch from the inner face of wall 22 of the bowl. The skimmer drive means 56 then reverses the travel of the skimmer. When the position of the skimmer is such on its leftward travel (FIG. 1) that the lug or trip 90 engages the limit switch 92, the switch 92 will cause the solenoid-operated diversional valve 94 to divert the flow from the skimmer back to the effluent. By this time, however, no material is passing through the skimmer and the skimmer discharge flow is reset so to speak for its next cycle of operation. When the skimmer reaches its leftward position inward of lip 32, the skimmer drive means 56 reverses itself, ready for the cycle of operation, and stops.

The valves 39 and optionally control liquid line valve 74 then open until the cycle is triggered once more by the electric control liquid detector 80.

It will be apparent that once the sludge has been removed from the bowl by the skimmer 50, centrifugal force throws any adhering sludge away from the opening of the orifice plate 66 at the outer end of the nozzle 64. The nozzle is thereby unobstructed and control liquid flows therethrough and does not accumulate in the ring until subsequent sludge buildup.

It will be clear from the above description that the centrifuge embodying the invention is completely automatic in operation and operates on a sludge level sensing basis rather than on a time basis. The time basis is fallible since the amount of solids in a given feed slurry may vary from time to time. Also it is clear that the present invention provides positive automatic means for precluding the passage of sludge into the clarified liquid effluent and does not rely on the presence of sludge in the effluent for actuation. The present device is simple and virtually foolproof. Once it is set into initial operation it requires no personal attention of an operator.

Obviously variations of the invention are possible. For instance the preferred control liquid detector means may be replaced by a pair of simple electric probes which may be shorted by the liquid in the ring 60 to actuate the sludgedumping cycle. The version shown in the drawings and described herein, however, is the preferred arrangement. The electrical and fluid flow arrangements may be varied as well. For instance it has been discussed that the valve 74 is optional and skimmer drive means 56 may come from a wide range of motor means. They may even be electric.

The apparatus shown has been put to effective use in the clarification of electrolyte from an electrochemical machining operation. It can be used in the clarification of fruit juices and in the purification of sodium alginate, an extract from cooked seaweed. Limitless other uses are envisioned.

In the case described the effluent has been the valued discharge and the sludge has been simply waste. It should be understood, however, that the invention is applicable to processes where the solid phase is of value and accordingly it is discharged to an appropriate container. Hence sludge as used herein includes any solids.

The invention is also applicable to apparatus for centrifuging feed primarily comprising two liquids of different specific gravity in order to effect separation thereof into two light and heavy phase components. In such case the control liquid fed to the control ring 60, as through line 70, may be the light phase liquid from the tank 46. When the heavy phase liquid builds up to the level ofthe outer. end of nozzle 64 and covers the opening in the orifice plate 66, control liquid will not enter the 1 basket 22 but will build up in the ring 60 for detection as aforesaid by the probe 82 of the detector 80. Thus, the

skimming device 50 is actuated for removal of light and heavy phase liquids in the same manner as for a light phase liquid and heavy phase solid.

For correct operation the control liquid has a lower specific 4 gravity than the heavy phase liquid or material.

, For example, in the case of jet fuel water having a specific gravity of 1.0 and kerosene having a specific gravity of approximately 0.81 can be so separated. And in like manner, it is possible to separate water having a specific gravity of 1.0 from gasoline having a specific gravity of approximately 0.73.

If rust, dirt orother solids contaminate the mixture these have a higher specific gravity than the water in the examples given and therefore will be sedimented against the bowl wall as a third, outer layer. Removal of such sedimented solids can be accomplished with the skimmer 50 or with a knife. In case a skimmer is employed, such sedimented solids can be passed to waste along with the water or other heavy phase liquid.

It can be seen, therefore, that the invention is applicable to liquid-liquid separations as well as liquid-solid separations.

The present invention may thus be embodied in other specific forms without departing from the spirit or central attributes thereof and, accordingly, reference should be made to the appended claims rather than the foregoing specification as indicating the scope of the invention. I

I claim: 1. A centrifuge including a rotatably mounted, centrifuge bowl having an inwardly extending liquid overflow lip at at least one end, means for feeding to the bowl a mixture of at least two materials wherein one material has a higher specific gravity than the other material and said one material builds up against the peripheral wall of the bowl, means for discharging accumulations of said one material, and means for detecting the level of accumulation of said one material, said detecting means comprising structure defining an inwardly facing annular pocket mounted to rotate with the bowl, a passageway leading outwardly from the pocket. and tenninating with an opening thereof in the bowl outward of the pocket and lip, means to supply a control liquid lower in specific gravity than said one material to the pocket, 'and sensing means to sense the buildup of control liquid in the pocket whereby when said one material reaches a level and obstructs said opening the control liquid builds up in the pocket and the sensing means senses the control liquid buildup and actuates said means for discharging accumulation of said one material from the bowl.

2. A centrifuge according to claim] wherein said control liquid is the same as said other material.

3. A centrifuge according to claim 1 wherein said one material and said other material are liquids.

4. A centrifuge according to claim 3 wherein said control liquid is the same as said other material.

5. A centrifuge according to claim 3 wherein the sensing means is electric and is dependent on the change in capacitance within the pocket.

6. A centrifuge according to claim 3 wherein the passage from the pocket has a greater diameter than the opening.

7. A centrifuge according to claim 3 wherein said pocket is disposed at the radial level of said lip.

8. A centrifuge according to claim 3 wherein the sensing means discontinue the flow of feedduring removal of an accumulation of said one material from the bowl.

9. A centrifuge as described in claim 3 wherein the sensing means discontinues the flow of control liquid during removal of an accumulation of said one material from the bowl.

Claims

1. A centrifuge including a rotatably mounted, centrifuge bowl having an inwardly extending liquid overflow lip at at least one end, means for feeding to the bowl a mixture of at least two materials wherein one material has a higher specific gravity than the other material and said one material builds up against the peripheral wall of the bowl, means for discharging accumulations of said one material, and means for detecting the level of accumulation of said one material, said detecting means comprising structure defining an inwardly facing annular pocket mounted to rotate with the bowl, a passageway leading outwardly from the pocket and terminating with an opening thereof in the bowl outward of the pocket and lip, means to supply a control liquid lower in specific gravity than said one material to the pocket, and sensing means to sense the buildup of control liquid in the pocket whereby when said one material reaches a level and obstructs said opening the control liquid builds up in the pocket and the sensing means senses the control liquid buildup and actuates said means for discharging accumulation of said one material from the bowl.

2. A centrifuge according to claim 1 wherein said control liquid is the same as said other material.

8. A centrifuge according to claim 3 wherein the sensing means discontinue the flow of feed during removal of an accumulation of said one material from the bowl.