US2724549A - Centrifugal separator and method of operating the same - Google Patents

Description

Nov. 22, 1955 c. J. BROWN 2,724,549

CENTRIFUGAL SEPARATOR AND METHOD OF OPERATING THE SAME Filed April 9, 1951 2 Sheets-Sheet l INVENTOR. 56 CLARENCE J Bean N 2,724,549 Patented Nov. 22, 1955 CEN'IRIFUGAL SEPARATOR AND METHOD OF OPERATING THE SAME Clarence J. Brown, Burlingame, Calif. Application April 9, 1951, SerialNo. 220,008 16 Claims. (Cl. 233-2) My invention relates to centrifugal separators for assisting in settling out particles from a liquid medium and is particularly concerned with a centrifugal separator of a continuously or substantially continuously operating type particularly onehaving a return underfiow of some of the discharged material. My invention also relates to a method of operating centrifugal separators having a return underflow in order to improve the operating characteristics thereof and particularly to achieve better separation.

It is an object of my invention to improve the separation of solids from and the clarification of liquids carrying solids in suspension.

Another object of the invention is to increase the density of solids discharged from the underflow return circuit, particularly where the solid components of the feed consist of or include particles of normally slow settling characteristics.

A further object of the invention is in general to im prove the separating operation of centrifugal separators, particularly those having an underflow return.

A still further object of the invention is to devise a method of operating centrifugal separators in an im proved fashion to increase the yield of separated materials.

, A still further object of the invention is to provide a centrifugal separator generally compatible with separators now commercially available, yet which is eltective to produce enhanced results.

Other objects of the invention, together with the fore going, are attained in the embodiment of the invention described in the accompanying description and illustrated in the accompanying drawings, in which- Figure 1 is a diagrammatic section on a generally vertical plane through a diameter of a centrifugal separator constructed in accordance with my invention and having diagrammatically illustrated some of the associated fluid circuits. t

Figure 2 is a. fragmentary diagrammatic view similar to Figure 1 but showing a modified form of rotor for a centrifugal separator of the general type illustrated in Figure 1.

Figure 3 is a view comparable to Figure 2 but showing a further modified form of rotor.

Figure 4 is another view similar to Figure 2 and showing a still further modified form of rotor.

Figure 5 is a view like Figure 2 but showing an additionally modified formof rotor.

While the centrifugal separator of my invention can be embodied in a number of different ways and is susceptible to various different modes of operation, it is practically embodied in a form substantially as illustrated in Figure 1. It is assumed in this environment that the separator is designed to operate on a liquid medium carrying solids of various sizes, shapes, densities and other characteristics more or less in suspension and that such solids are to be removed insofar as possible from the liquid in order to afford a dense, substantially concentrated discharge of solids with some liquid as distinguished and separated from a relatively light, substantially clear, liquid.

For this purpose, .i provide a housing 6 preferably symmetrical about a central,vertical axis 7. The housing 6 is of a generally double conoidal configuration or is any other convenient figure of revolution having appropriate modifications to serve as a suitable enclosing and supporting structure. At its upper end, the housing 6 is extended to provide a bearing mounting 8 resting upon a feed chamber 9. A feed conduit 11 extending from a source of material to be separated; for example, a tank (not shown) containing the liquid and solid mixture, merges with the feed chamber 9. This leads into afeed tube 12 stationarily mounted in the housing 6 and depending past anoverflow chamber 13 into portion of the housing 6.

Theoverflow chamber 13 extends from acentral opening 16 to an overflow conduit 17 leading to any suitable point of discharge of the finally separated and clarified liquor. The housing 6 is approximately symmetrical about a horizontal plane H and in its lowermost portion is provided with a coaxially disposedunderflow opening 18. Substantially midway between theunderflow opening 18 and the overflow opening 16, the housing 6 is formed to provide avolute passageway 19 leading to adischarge opening 21.

On the bearinghousing 8 and suspended therefrom is thecentral drive shaft 26 of acentrifugal rotor 27. The drive shaft at its upper end carries a pair ofpulleys 28 the central engaged bybelts 29 extending from any suitable source of rotary drive such as a motor (not shown). Theshaft 26 extends through the feed chamber 9 and through the stationaryinlet feed tube 12 and at its lower end flares into thebase 31 of the rotor. Thebase 31 is spread and curved upwardly partially to define afeed cavity 32 and is connected byimpelling vanes 33 to a.rotatable feed pipe 34 in effect telescoping over thefeed tube 12 and forming a substantial continuation thereof. Therotor base 31 is extended byimpeller blades 36 merging with a lowerconical shell 37 extending upwardly and outwardly. Thebase 31 is similarly extended by an innerconical shell 38 that, with theshell 37 defines a duct 39. In addition to theimpellers 36,supplemental impellers 41 connect the inner and lower shells.

Above the horizontal plane of symmetry, the upper portion of the rotor is contoured to provide an upperconical shell 42 converging inwardly to terminate in anoverflow weir 43 or opening.

Disposed between theinner shell 38 and theupper shell 42 within the rotor and extending upwardly from than the overflow opening 43. The outer peripheries of theconical bands 44 likewise terminate in what in effect is a circular cylindrical envelope surface 47. The conical bands are disposed between and help define thefeed cavity 32 as an inner chamber, as distinguished from theremaining volume 48 constituting an outer chamber within the hollow rotor.

In the starting or initial operation of this structure and following out the general method of my invention, ther pulleys 28 are appropriately driven to spin therotor 27 at a relatively high speed. A liquid material containing solids to be substantially separated from it is caused to flow substantially continuously through the feed conduit 11 into the feed chamber 9 from whence the material flows downwardly through thestationary feed tube 12 and into the revolvingfeed pipe 34. In thefeed pipe 34 the material encounters the rotatingimpelling vanes 33 that bring it up to the speed of the rotor itself. The material is discharged largely by centrifugal force from the lower end of thefeed pipe 34 by theimpellers 33. The material continues to flow by centrifugal force out between the lower ones of the nestedconical bands 44 and begins to occupy thechamber 48. As this chamber fills, some of the material flows out ofnozzles 52 disposed at appropriate intervals around the periphery of the rotor and discharging in such a direction that the reaction assists in turning the rotor. The discharged fluid issued from the nozzles travels through thescroll passageway 19 and through the discharge opening 21 into aconduit 53. The material continues to flow through the conduit and past a regulating device 54 to anoutlet 56 from which the material is released from the system.

Preferably, some of the efilux is diverted from theconduit 53 above the regulator 54 into anunderflow return conduit 57 extending to theunderflow inlet opening 18. At that point, theconduit 57 is provided with anorifice plate 58 so that a jet of returning material is reintroduced into the housing and impinges upon a target plate 59 on the lower part of therotor base 31. The material so impinging, being diverted laterally, is engaged by the revolvingimpellers 36 and 41 and so is moved by centrifugal force again outwardly into thechamber 48 adjacent thenozzles 52. The rate of material supply is enough greater than the initial rate of material discharged so that thechamber 48 and the interstices between the conical bands fill with fluid. When suflicient material has entered, there is built up over the diaphragm 46 a continuous, annular layer '51 of liquid and solids, established at a predetermined thickness of sufficiently small inner radius to cause discharge at the upper end over theupper overflow opening 43. The liquid so discharged is collected in thechamber 13 and flows from the separating system through the overflow conduit 17.

After the starting operation, adjustments for protracted operation are made. The quantity of feed entering through the conduit 11, the quantity of material leaving the structure through theoutlet 56 and the quantity of re circulated material travelling through theconduit 57 are such that a film or layer, or annulus of liquid, losing its solids as it ascends, is established within thediaphragm 46 which therefore defines an interface between axially stationary and axially moving material. The body of material within thechamber 48 prevents radial outflow of the liquid component'but receives the-settled out radially travelling solid particles. There is an upward, axial flow of material over the inside rims of the nested conical bands between which pass the'solid fractions of "material being treated.

Since the settlement of the solid particles, as distinguished from the liquid, is radially outward, the particles tend to collect within thechamber 48. The heavier particles tend to agglomerate or congregate in the outward portion of the rotor but some of the particles which are lighter, tend to form an intermediate layer outside the conical bandsbut within theturbulent chamber 48 in a position to block or impede other particles tending to travel towardthenozzl'es 52. Solid particles passing outwardly between thebands 44 by centrifugal force tend to lodge'on the inner or under faces of the conical bands to build up and substantially restrict the space between the bands. Since all of these factors tend to interfere with optimum clarification of the overflow liquid or with optimumrecovery of solids from theoutlet 56, I provide a means for overcoming these deficiencies.

In the underflow return conduit 57 I provide a relativelylarge chamber 61; large, that is, with respect to the volumetric capacity of the rotor. Thechamber 61 is provided with avalve 62 having an operating stem 63 and is arranged normally to be closed with the valve seated on therim 64 of thechamber 61. The valve is, as shown in Figure l, of substantial size relative to the volume of the chamber. When the valve is opened, its discharge capacity is very great and it permits the entire contents of thechamber 61 quickly to discharge. Thechamber 61 is sometimes referred to as a dump chamber. It is of sufficient capacity so that any further entering material coming from theconduit 53 does not flow into the underflow return opening 18 but rather is bypassed through therim 64 into ahopper 66 leading to apipe 67 and out of the separating system.

In the normal operation of the device, the outflow from the system through theoutlet 56, the amount of the flow through theconduit 57 and the amount of feed are such that a given quantity of overflow passes in an annular layer or stream upwardly over thediaphragm 46 to maintain a stable interface. But because of the formation of a blocking intermediate layer of particles within thechamber 48, because of the aggregation of particles on the conical bands, and for other reasons, thevalve 62 is periodically opened suddenly. It is held open long enough for thechamber 61 to be evacuated, for the flow through the opening in theorifice plate 58 to be completely interrupted, and correspondingly, for the liquid level to recede outwardly and to occupy a new position in therotor chamber 48.

During this time, the denser materials which have been accumulating near the nozzles are rather quickly discharged from the system, particles from the intermediate zone and the finer particles adjacent thediaphragm 46 are suddenly removed outwardly into a zone previously occupied by denser material. Denser material discharges from the rotor periphery through the nozzles and leaves a much less dense material in the rotor periphery. Also, particles which have deposited on the under and inner faces of the conical bands are flushed or swept off for ultimate discharge through thenozzles 52. As soon as this abrupt change in operating conditions has taken place, thevalve 62 is again closed, permitting the underflow again to travel into the rotor and reestablishing the annular upflow over the diaphragm orinterface 46 and finally over theweir 43.

The adjustment of the various flows is such that the duration of opening of thevalve 62 is very brief, perhaps of the order of, say, 5 per cent, of the total operating time of the device. The recovery, despite this brief interruption, is in most instances greater than normal because the operating characteristics of the centrifugal separator for the remaining part of the time are considerably improved.

The valve stem 63 is operated periodically in any suitable fashion, preferably by an automatic apparatus that causes it to function intermittently. The fiow through thenozzle 58 and the overflow from the conduit 17 are interrupted in part or entirely when thevalve 62 is open but feed through the inlet conduit 11 is continuous. The annular upfiowing stream operates uniformly for most of the operating time of the centrifuge but periodically recedes suddenly in response to the opening of thevalve 62 to a much greater radius and is then restored to its former characteristics when the valve 62is closed.

Since one of the functions of the nest ofconical bands 44 is to reduce turbulence of the zone of liquid adjacent the incoming material which flows upwardly, parallel to the axis, various different mechanical constructions are possible for the same end; For example, as shown in Figure 2, the structure otherwise is substantially identical with that previously described but in place of theconical bands 44, I preferably introduce a circularcylindrical trommel 71. This comprises a metallic cylinder of appropriate diameter perforated at frequent intervals to provideapertures 72 which serveas checks to or dampentially. the same but in place of the conical bands 44 I utilize a woven or reticulated screen 74 (or a plurality of concentric similar, screens) contoured to define a substantially circular cylindrical member affording an escape for the radially outwardtravel of solids. but also defining a diaphragm surface withinythe rotor to isolate the turbulent liquid in thechamber 48 from the non-turbulent, upwardly fiowing, inner annulus of liquid.

In Figire 4 there is illustrated a further modification in which the nested devices rather than being cones are annular,flat discs 76 of suitable interior and exterior radii to serve as means for channeling the radially outwardly travelling solids and for affording a suitable interior diaphragm so as'to reduce the disturbance of the axial flow of liquid a minimum amount.

In Figure 5, comparably, there is shown in full lines a somewhat similar device in whichthe conical bands are replaced by substantiallyradial blades 77 extending outwardly to any desired distance from the center in the manner of impellers. Although these permit the solid materials to pass radially outward therebetween in diverging paths, they also define an interior diaphragm andact, furthermore, since they are radially disposed, more or less as impellers. The advantage of the impeller arrangement is that the material between the blades is brought up to the angular velocity of the rotor at the instant radius. Settling particles agglomerate: on the leading face of the blades readily sloughing off in agglomerate masses, thereby increasingthe density of the What is claimed is: i

1. The method of operating a centrifugal separator having a return underflow which comprises establishing an upwardly flowing annular stream of material within 6 ing the inside diameter of said annular whirling body .by interrupting completely all underflow to said body.

5. The method of operating a centrifugal separator which comprises continuously establishing an annular whirling body of material with a hollow center, establishing a flow of material through said hollow center, withdrawingmaterial from said body, releasing some of said withdrawn material, returning the unreleased withdrawn a continuously rotating annular body of material supsaid body through said hollow center, and periodically increasing the inside diameter of said whirling body by periodically interrupting completely all underflow to said body.

.3. The method of operating a centrifugal separator having a rotor with a circular cylindrical envelope surface which comprises establishing an upward flow of material over the inside of said envelope surface, continuously maintaining an annular whirling body of material around the outside of said envelope surface, maintaining an underflow of material from said body and back to said body, and periodically increasing the inside diameter of said annular whirling body by interrupting completely all underflow to said body.

4. The method of operating a centrifugal separator having a. rotor with an envelope surface which comprises establishing a flow of material over the inside of said envelope surface, continuously maintaining an annular whirling body of material around the outsideof said envelope surface, maintaining an underflow of material from said body and back to said body, continually bleeding material from said underflow, and periodically increasmaterial to said body as underflow, and periodically increasing the inside diameter of said hollow body by periodically interrupting completely all underflow to said body.

6. The method of operating a centrifugal separator which comprises continuously establishing an annular whirling body of material with a hollow center concentric with an axis, establishing a flow of material into said hollow center and establishing a flow of some of said material axially along the hollow center of said body, withdrawing some of said material from the periphery of said body, releasing some of said withdrawn material, returning the unreleased Withdrawn material to said body outside of said hollow centeras underflow and periodically increasing the inside diameterof said hollow body by periodically interrupting completely all underflow to said body.

7. A centrifugal separator for separating heavier and lighter fractions of feed material comprising a housing, a rotor mounted for rotation in said housing about a central axis, means on said rotor including solid wall portions with spaces therebetween defining a circular cylindrical envelope surface concentric with said axis and constituting the outer wall of an inner chamber, means for conducting material containing heavier and lighter fractions into said inner chamber to a location on the interior of, said envelope surface whereby the heavier fraction during separation passes through said spaces in said outer Wall in a radially outward direction to the outer portion of said rotor, a recirculating impeller on said rotor, a conduit for conducting material from the periphery of said rotor to said recirculating impeller, a dump chamber in said conduit of substantial volume relative to the volume of said rotor, a valve in said dump.

chamber for quickly releasing material from said chamber, and a pipe for releasing material from said conduit.

8. A centrifugal separator for separating heavier and with spaces therebetween defining a circular cylindrical envelope surface concentric with said axis and constituting the outer wall of an inner chamber, means for conducting material having heavier and lighter fractions into said inner chamber to a location on the lower interior of said envelope surface whereby the heavier fraction during separation passes through said spaces in said outer wall in a radially outward direction to the outer portion of said rotor, means for releasing material from the outer portion of said rotor into the outer part of said housing, a conduit for returning material from the outer part of said housing back to the central part of said rotor, means on said rotor for impelling returned material from said central part of the rotor to flow to the outer portion of said rotor in a path in part separate from the path of said heavier fraction passing through said outer wall to the outer portion of said rotor, and a valve in said conduit for releasing material therefrom.

9. A centrifugal separator comprising a housing symmetrical about a vertical axis, a rotor mounted for rotation in said housing about said axis, means on said rotor including a number of spaced barriers concentric with said axis, the inner portions of said barriers defining an envelope surface for dividing said rotor into an inner chamber and an outer chamber, means for introducing material including heavier and lighter fractions into said rotor within the lower portion of said inner chamber.

wh reby .the f'sheavier fraction ;during separation wpasses throughthe envelope ssurface-in a radiallyoutward=direction do 3116 iperiphery of said rrotor, means in said housinggforrreceiving said :heavier .fraction from "the; periphery of {said roto'rpmeans ifor conducting .said .heavier fraction from saidzreceiving .me'ansbackzto saidouter chamber of Said totor,::means .forsreleasing said heavier fraction from said tQQnducting :means, .and means for .releasing --said lighter ;frae.tion from the .upper portion .of said inner Chamber.

@;-;1,0.;;A';centrifugal separator comprising a housing, a rotor mounted for rotation in said housing about a vertical-zaxishmeam :0n.=said rotordividing saidrotor into a radially inner chamber and a radially .outer chamber, said ,dividing means including spaced apart barriers cons iinrqd'ztogether constituting a substantially cylindrical envelope surface concentric :with said axis and establishin'gjhe outer :wallv of said-inner chamber, means for introducirrgmaterialrhaving heavier and lighter fractions into the lower :portion of said inner chamber, means for releasingtmaterial having a larger proportion of said light fraction from-the-upperportion of said inner chamber, means fordischarging material having a smaller proportion of said ,lightfraction from the periphery of said rotor into said housing, and means for returning part only of said material having ,a smaller proportion of said light fractionfrom :said housing to said outer chamber.

L1. centrifugal separator comprising a housing, a rotor mountedfforarotationin said housing about a vertical axis, ;a-circular cylindrical :wall concentrically disposed on ,said rotor ,div'iding said rotor into a radially inner eharnberand a radially outercharnber, said -wall having openings accommodating movement .of material substantiallyputwardly from said inner chamber to said outer chamber, means for introducing material having heavier andljghter fractions intosaid inner chamber adjacent the lower portion thereof, means on said rotor for spinning said ,materialwith said rotor, means for releasing material having .a larger proportion .of said light fraction from the upper end ,of said inner chamber. and means for releasing material having a smaller proportion of saiddightfraction from said outer chamber at the periphervpfsaidrotor.

12. .A centrifugal separator comprising a housing, a notor mounted for rotation in said housing about'a verti alaaxis, a circular cylindrical wall concentrically dispcsedion said rotor dividing said rotor into a radially innerchambertand a radially outer chamber, said wall having openings accommodating movement of material Substantially outwardly from said inner chamber to said outer .chamber, means for introducing material having heavier :and lighter fractions into said inner chamber adjacent 111,6:1OW6! portion thereof, means on said rotor for spinning said material with said rotor, means for releasing'materialhaving :a larger proportion of said light fractionifrom the-uppertend .of said inner chamber, means for releasingtmaterial having a smaller proportion of said light fiactionxfrom said outer chamber at the periphery of said rotor, means for conducting released material having a Smaller proportion of said light fractions back to said outer chamber of said rotor, a dump chamber in said mnductingmeans of substantial volume relative to the volume ofisaid rotor, land-a valve in said dump chamber of substantial size relative to the volume of said dump chamber vforlquickly releasing material from said dump chamber.

13. A centrifugal separator comprising a housing substantially symmetrical about a central axis and having upper and lower axial openings and an annular scroll passagewaypositioned substantially midway between said axialopenings, a rotor mounted for rotation in said housing about said axis, a circular cylindrical Wall on said rotor concentric with said axis dividing said rotor into inner and outer chambers, said wall having openings therein for accommodating movement of material out- .8 wardly, 311183.118 {for :conducting ffeed material through said upper opening into the ::lower portion of said inner cham- 'her,.1an overflow aweir coaxially disposed on 'said rotor adjacent said upper :opening and having a diameter less than itheediameter of saidrwall, means for releasing material from said outer chamber into said scroll passageway, .a conduit :for -conducting material from said scroll passageway'through said Blower opening into said outer chamber, :a dump chamber in said conduit large relative to the volumeof said 'rotor,.and a valve for quickly releasing material from said dump chamber.

:14. A centrifugal separator comprising a rotor having a peripheraldischarge, means for mounting said rotor for rotation about a vertical axis, a circular cylindrical =-wall on 'saicl'rotortconcentric with said :axis and dividing said rotor into :an inner chamber-and an outer chamber, said wall having openings for accommodating movementof material outwardly from said inner chamber to said outer chamber, a feed tube .on said mounting means and extending downwardly into said rotor from the upper end thereof to a pointof discharge adjacent the lower portion of said inner chamber, and means-on saidrotoradjae'ent the lower portion of said inner chamber fc-rspinningtead material discharged by said :tubeintosaid rotor.

15. A centrifugal separator comprising -a housing having avertical axis and having an upper overflow opening, a peripheral discharge opening, and a lower underfiow opening; a hollow rotor disposed in said housing and mounted to revolveabout saidaxis; means on said rotor constituting a perforate member and dividing said rotor into ,aninner feed cavity and an'outer settling chamber, said perforate mernber constituting the outer defining Wall of said feed cavity; a feed vtube on said housing extending through said overflow opening into said feed cavity and annually spaced from said perforate member; nozzles on said/rotor establishing communication between said settling chamber and said discharge opening; a duct in said rotor establishing communication between said underflow opening and said settling chamber; means for revolving said rotor; a conduit for conducting material from said discharge opening to said underfiow opening; means for continuously releasing material from sa-idconduit; and ,a dump chamber of large volume relative to the volume of said rotor for intermittently releasing materia-l from said conduit whereby conductive material to said underflowis interrupted.

16. A centrifugal separator comprising a housing having a vertical axis and having an upper overflow opening, a peripheral discharge opening, and a lower underflow opening; a hollow rotor disposed in said housing and mounted to revolve about said axis; means on said rotor constituting .a perforate member and dividing said rotor intoaninner feed cavity and an outer settling chamber, said perforate member constituting the outer defining wall- ReferencesCitcd in the file of this patent UNITED STATES PATENTS 1,846,076 Andersson Feb. 23, .1932 1,847,751 Coe Mar. v1, .1932 1,923,454 Peltzer et a1. Aug. 22, 1933 2,013,668 Peltzeretalh Sept. 10., .1935 2,323,077 .Peltzer N June 29,, 1943 2,559,453 vMerrill etal. July 3. .1951v 2,616,620 Zimmerman Nov. 4, 1952

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