US3407999A - Sludge discharge means for a centrifuge - Google Patents

Description

Oct. 29, 1968 Filed Nov. 10, 1966 94 EffuenT Waste W. J.. KIRKPATRICK SLUDGE DISCHARGE MEANS FOR A CENTRIFUGE 2 Sheets-Sheet l INVENTOR. WILLIAM J. KIRKPATRICK ATTORNEY.

Oct. 29, 1968 .w. J. KIRKPATRICK SLUDGE DISCHARGE MEANS FOR A CENTRIFUGE 2 Sheets-Sheet 2 INVENTOR. WILLIAM J. KIRKPATRICK Filed Nov. 10, 1966 1 ATTORNEY.

United States Patent 3,407,999 SLUDGE DISCHARGE MEANS FOR A CENTRIFUGE William J. Kirkpatrick, Springfield, Pa., assignor to Pennsalt Chemicals Corporation, Philadelphia, Pa., a corporation of Pennsylvania Filed Nov. 10, 1966, Ser. No. 593,338 8 Claims. (Cl. 233-19) ABSTRACT OF THE DISCLOSURE Solids separated from clarified liquid and accumulated on the peripheral wall of a solid bowl centrifuge are removed by a skimmer actuated in response to sensing action of a solids level detector. The latter includes structure defining an inwardly facing annular pocket rotatably mounted with the bowl and provided with a passageway leading outwardly from the pocket to a position outward of an efiluent overflow lip, and further provided with means for supplying control liquid to the pocket and means for sensing an accumulation of control liquid in the pocket when solids build up to a level which obstructs the opening at the outer end of the passageway.

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 build-up and for removing the sludge from the bowl.

In the solid bowl cyclicalsludge-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 semi-automatic processes of the prior art as described above have had severe disadvantages. Obviously sludge build-up 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 eflluent would become contaminated with an objectionable amount of sludge. Besides this, of course, there has been objection to the need of 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 efiluent have been based on the optical opacity of the discharging etlluent 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 3,407,999 Patented Oct. 29, 1968 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 efiluent. Because the density will go up as the efiluent becomes a suspension of sludge solids, this means could theoretically be used to detect sludge solids in the efiluent. 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 fool-proof 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 efiluent became clouded with sludge.

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

FIGURE 1 is a sectional view of a centrifuge embodying the invention and showing in schematic form some of the controls thereof;

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

FIGURE 3 is similar to FIGURE 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 efliciency accomplished, and the feed is resumed.

Referring more specifically to the drawings, an arrangement embodying the invention is indicated in FIGURE 1 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 turbulencc.

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

For removing the sludge in the cyclical operation the centrifuge is provided with a skimming device 50. This includes a tube of 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 4 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 FIGURE 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 FIGURE 3 the ring is formed about its circumference with equi-spaced 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 of the 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 nozzle 64 will determine the level to which sludge build up is permitted before the sludge unloading cycle commences.

Referring once more to FIGURE 1 the eflluent 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, /2 gallon per minute, may run continuously or may be shut oif 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 shut off purposes the control liquid line 70 may be provided with a solenoidoperated 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 of FIG. 1.

Referring once more to FIGURE 1, between bosses 54 the skimming device is provided with a trip which may take the form of any kind of 2. 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 solenoid-operated 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 efiluent flows over the lip 32 and is thrown outward and passes down the inside wall of the housing 30 and moves out through the efiluent discharge conduit 44 to the effluent tank 46. The sludge of the feed slurry gradually builds up against the wall 22 of the bowl.

Referring now to FIGURE 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- URE 2, when the liquid is built up in the ring to the extent where the capacitance of the probe 82 is sutficient- 1y 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 FIGURE 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 limited 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 build-upor 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 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 valve 39 and optionally 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 build up.

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 efiluent for actuation. The present device is simple and virtually fool-proof. 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 sludge-dumping 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 effiuent 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 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 claim:

1. A centrifugal comprising a rotatably mounted, centrifuge bowl having an inwardly extending clarified effluent lip at one end, means for feeding a slurry to the bowl so that the clarified liquid flows over the lip and the solids build up against the peripheral wall of the bowl, skimmer means for discharging built-up solids, means for detecting the level of solids build-up 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 to the pocket, and means to sense the build-up of control liquid in the pocket whereby when the solids reach a level and obstruct the opening the control liquid builds up in the pocket and the means senses the control liquid build-up and actuates the skimmer means for discharging the built-up solids from the bowl.

2. A centrifuge as described in claim 1 wherein the sensing means is electric and is dependent on the change in capacitance within the pocket.

3. A centrifuge as described in claim 1 wherein the passage from the pocket has a greater diameter than the opening.

4. A centrifuge as described in claim 1 wherein the centrifuge is provided with a plurality of radial vanes and the pocket is mounted on the vanes with the floor of the pocket being disposed at the radial level of the discharge lip of the centrifuge.

5. A centrifuge as described in claim 1 wherein the sensing means discontinue the flow of feed during the solids removal.

6. A centrifuge as described in claim 1 wherein the sensing means discontinues the flow of control liquid during the solids removal.

7. A centrifuge comprising an imperforate centrifuge bowl having a vertical axis and an inward clarified effluent lip at its upper end, means for rotating the bowl, means for feeding a slurry to the bowl so that clarified liquid flows over the lip and sludge builds up against the. peripheral wall of the bowl, movable skimmer means for discharging sludge from the bowl, means for detecting the level of sludge build-up comprising an inwardly facing annular pocket mounted to rotate with the bowl and disposed concentric about the axis, the pocket having an outward nozzle with a restricted opening at its outer end outward of the lip, means to supply a control liquid to the pocket, and electric means to sense the build up of control liquid in the pocket whereby when the sludge builds up and obstructs the opening at the end of the nozzle, the control liquid builds up in the pocket and the electric means senses the build up and actuates the means for discharging the built-up sludge from the bowl.

8. A centrifuge as described in claim 7 wherein the electric sensing means is dependent on the change in capacitance within the pocket.

References Cited UNITED STATES PATENTS 981,681 1/1911 Peck 23322 XR 1,002,471 9/1911 Thelitz. 3,167,509 1/ 1965 Steinacker 233-20 3,261,546 7/1966 Gruver 233-20 HENRY T. KLINKSIEK, Primary Examiner.

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