US3080109A

US3080109A - Centrifuge machine

Info

Publication number: US3080109A
Application number: US773788A
Authority: US
Inventors: Ralph H Halbach
Original assignee: Dorr Oliver Inc
Current assignee: Dorr Oliver Inc
Priority date: 1958-11-13
Filing date: 1958-11-13
Publication date: 1963-03-05
Anticipated expiration: 1980-03-05

Description

March 5, 1963 R. H. HALBACH CENTRIFUGE MACHINE 5 Sheets-Sheet 1 Filed Nov. 13, 1958 a 6 w 2 M w 6 3 .fl 2 z w my 3. V v w w), 1 j

ATTORNEY March 5, 1963 R. H. HALBACH 0,10

CENTRIFUGE MACHINE Filed Nov. 15, 1958 s Sheets-Sheet 2 &\\\\\\\\\\\\\ Pole/2 WT $20M avg-M ATTORNEY March 5, 1963 R. H. HALBACH I 10 CENTRIFUGE MACHINE Filed Nov. 13, 1958 a Sheets-Sheet s w Au: 0

M Q Q Q 8& N 53, w 2% & Q Q 8 [L N Q 2% g Q R- E a 3 5 Q Q) Q 3 a g R g a 3 a a a Q INVENTOR;

RJM CZQL United States Patent Filed Nov. 13, 1958, Ser. No. 773,788 7 Claims. (Cl. 233-28) This invention relates to continuous centrifugal devices, generally of the rotary bowl disc type. More particularly, this invention relates to means for utilizing the kinetic energy of the discharging clarified effluent to effect savings in the power required to drive such centrifuges.

Continuous rotary bowl disc type centrifuges have long been utilized as an effective tool to obtain a separation of lighter fractions from heavier fractions contalned III a given feed material. Commonly, these separations are made between liquids and solids but may, in some nstances, be a separation between two immiscible liquids of differing densities. In machines of this general type, feed material containing the two fractions to be separated is introduced into a rotor through a conduit coaxially disposed with relation to the rotor shaft. Due to the centrifugal forces developed through rotation of the rotor, the heavier constituents of the feed material are thrown toward the outer diameter of the rotor bowl and the lighter constituents are accordingly displaced inwardly. The separated heavier fraction is discharged from the periphery of the rotor through a plurality of nozzles while the lighter fraction overflows an annular lip of the centrifuge located at a point closer to the axis of rotation than the discharge point of the heavier material. By such means a slurry material may be fed to the centrifuge and two products recovered: a clarified overflow and a denser underflow comprised of solids.

The kinetic energy of the discharging overflow and underflow is quite high in centrifugal machines. This results from the fact that at the moment of discharge the material is traveling at substantially the same high velocity as the rotor. An energy gradient of the material within the rotor bowl exists between the axis of rotation and the outermost point of the rotor bowl. In theory, the kinetic energy of a particle located at the center of rotation of the rotor will be zero and the same particle will reach a maximum kinetic energy at the outer periphery of the rotor. In this latter case the kinetic energy will be a function of the velocity of the rotor at that outermost point. Ideally, then, if both the overflow and underflow fractions could be discharged at the center of rotation, no power would be required to drive such a centrifuge except to account for necessary losses due to friction and heat. This ideal means of discharge is impossible as, by necessity, the underflow material must be discharged at a point remote from the axis of rotation if the benefits of centrifugal forces are to be utilized. Also, for practical considerations, it is not possible to discharge overflow material at the center of rotation as, by necessity, provision must be made for the rotor shaft, feed passages and other mechanical devices which impose physical limitations on the location of the overflow discharge.

It is well known in the prior art that a substantial reduction in the power requirements for driving centrifuges may be achieved by utilizing nozzles that discharge backwardly with respect to the rotation of the rotor. These underflow nozzles work on a jet reaction principle whereby the discharging underflow is caused to deliver a thrust which acts in the direction of rotation and enables substantial reduction in the horsepower required to drive the centrifuge.

Ralph H.

Oliver Incorporated,

"ice

There are no teachings in the prior art, however, which disclose any method whereby some of the kinetic energy of the discharging overflow fraction can be utilized. Possibly such devices have never been attempted as it was thought that the energy which could be recovered from the overflow material was negligible in comparison to the energy that can be recovered at the point of underflow. This, as noted above, is due to the fact that the overflow material is discharged much closer to the axis of rotation than the underflow material. Another factor which undoubtedly has prevented people from developing means for so recovering power from the clarified overflow is that the physical embodiment and disposition of the overflow lip are such that mechanical adaptations to position jets there present a most diflicult and so far unsolved engineering problem.

It has been discovered that the available energy which may be recovered from the discharging overflow is unexpectedly quite considerable and, in fact, may account for as much as 10 to 20% of the power required to drive the centrifuge. It has further been discovered that simple and effective apparatus for recovering available power from this discharging overflow can be constructed in a practical and inexpensive manner without necessitating extensive modification of existing centrifuges of the rotary bowl disc type.

It is therefore an object of this invention to provide means whereby a portion of the kinetic energy of the clarified eflluent discharging from continuous rotary bowl centrifuges can be utilized. A corollary object of this invention is to provide means whereby the horsepower consumption of continuous rotary bowl disc type centrifuges can be effectively reduced.

A further object of this invention is to provide means whereby foaming or excessive aeration of the clarified effluent discharging from continuous rotary bowl centrifuges is materially reduced.

Quite briefly, the objects of this invention are achieved by the use of an annular ring which is positioned adjacent the overflow lip of continuous rotary bowl centrifugal machines. This annular ring is provided with closed channel sections which enforce a change in direction of the clarified efliuent liquid. By these means the velocity of the efliuent relative to the rotor housing is substantially reduced thereby enabling a reduction in the loss of krnetic energy from the system. Utilization of this device also tends to minimize foaming of the clarified .eflluent as such eflluent is channeled to discharge substantially as a solid stream. This is in distinction to the continuous thin curtain of liquid which is discharged over the conventional overflow lip, which, due to aspiration, may cause considerable foaming in the clarified overflow efliuent.

In the drawings:

FIG. 1 is a view in side elevation, partially cut away, showing the apparatus of this invention positioned within a rotor bowl, disc type centrifuge including additional reaction nozzle means.

FIG. 2 is a view in plan, partially cut away, of a preferred embodiment of the apparatus of this invention.

FIG. 3 is a view in section taken through line 33 of FIG. 2.

FIG. 4 is a detail view taken on line 4-4 of FIG. 2, showing an arrangement of the inlet openings of the additlonal reaction nozzle means.

FIG. 5 is a graph in which horsepower requirements versus feeding rates are plotted.

Referring to FIG. 1, there is generally illustrated a centrifuge having a housing 11, a rotor 12, a stationary feed passage 13 comprising concentric tubular members 13a and 13b, an overflow passage 14 and an underflow discharge passage '16. The interior of the rotor and more particularly the rotor bowl contains a series of stacked discs 17. These discs surround a feedwell structure 17a extending from a hub portion 17b and constituting therewith feed duct means'l7c extending radially to provide a feed connection between said feedwell structure and the interior or separating chamber of the rotor bowl. In operation feed material containing material to be separated enters via conduit 18 and passes through feed passage 13 into the interior of the rotor bowl section 19. The shaft 21 connected to the hub portion 17b is driven by a motor, not shown and the rotor is caused to spin at high velocities. The denser fraction of material in the feed is thrown toward the periphery in the separating chamber of the rotor bowl as at 22 while the lighter constituents of the feed are displaced upwardly and inwardly through the discs 17 to discharge via passage 14. Underflow material is discharged via nozzles 23 .into a volute section 24; conduit 26 conducts the underflow material from the volute section. While not illustrated herein, underflow material may be recycled from conduit 26 to the lower part of the rotor 28 Whereby such material is recycled via return tubes 27 to a point near the underfiow nozzles. Overflow material is discharged from annular ring 29 which contains a plurality of closed channel sections or passageways 38. These closed channel sections direct the overflow material backwardly with respect to the rotation of the rotor and into volute section 31 as a substantially solid stream. Conduit 32 communicates with volute 31 and leads the clarified efiluent from the centrifuge.

With specific reference to FIG. 2, details of the preferred embodiment of this invention are shown. Annular ring 29 is provided with holes 33 in order that the ring may be securely bolted onto the normal overflow lip 34 of the centrifuge. A plurality of passageways 38 are provided which force the clarified efliuent of change direction and discharge backwardly with respect to the rotation of the rotor bowl. This material discharges as at opening 36 of passageway 38. As can be seen, an overhang 37 is provided on ring 29 to provide a reservoir for the accumulation or" liquid in the event that the discharge passages 38 are temporarily unable to discharge the established quantity of clarified eflluent. Additionally, if the reservoir becomes entirely filled, liquid can discharge over lip 41 into the discharge volute. Thus, under conditions of overload, clarified eflluent will be discharged over the overflow lip 41 insuring adequate discharge and preventing an unbalance of operating con ditions within the rotor.

As previously noted, use of this overflow discharge ring is advantageous not only in reducing the power consumption of the centrifuge, but also it is extremely useful in preventing the formation of foam and froth which normally attends the discharge of certain liquids. By confining the discharge of the clarified effiuent to comparatively solid streams, aspiration and aeration of this efiluent can be greatly reduced. In the design of the annular ring it is essential that a sufficient clearance or passageway or recess 42 be provided to enable the backwardly discharging effluent to escape from the ring. Ideally, all of the available energy of the eflluent could be recovered if it were discharged at zero velocity or, in other words, discharged backwardly at the same velocity at which the discharge lip of the rotor is traveling forward. If this condition prevails, however, the effluent will have zero velocity with respect to the housing and fall straight downward. In this instance, the effluent would not get out of the way of the rotating ring and thus would be impinged against the trailing edge of recess 42. This, of course, would destroy much of the power saving made possible by use of this invention. Accordingly, the discharging velocity of the efiluent and the shape of recess 42 must cooperate to enable the effluent to discharge from opening 36 in such a manner that the effluent clears the an- 4 nular ring and is not impinged against the trailing edge 42a of recess 42.

A detailed view of the cross section of the discharge ring 29 is shown in FIG. 3. Also FIG. 4 shows a preferred shape given to the entrance to channel section 38.

As previously mentioned, the object of the annular ring is to enforce a change in direction in the discharging eflluent. Unlike a jetting action which is obtained by means of the nozzles 23 used for discharging the heavier underflow, the passageways of the annular ring depend not upon a jet action but rather upon an enforced change in the direction of the fluid. For example, when operating a machine discharging at 200 gallons per minute while rotating the centrifuge at about 3000 rpm, one standard design of 30 inch rotor will provide a velocity at the point of discharge of the clarified efiiuent of approximately 185 feet per second. (This being, of course, the velocity of the overflow lip.) If an annular ring as herein shown is installed utilizing 10 backwardly di rected channel sections, the speed of the discharging liquid relative to the moving rotor can be changed from zero to approximately feet per second. Alternatively, as stated with respect to a point fixed in space, the discharging clarified effluent from an overflow lip will be flung from the lip of the rotor tangentially at a velocity of approximately 185 feet per second in the direction of rotation and by utilizing the backwardly discharging channel sections, the efliuent will be discharged tangentially at a velocity of only about feet per second ft./sec.-85 ft./sec.) in the direction of rotation. Such utilization of the kinetic energy of the effluent will effect a considerable reduction of the overall power requirements for operating the centrifuge.

The graph of FIG. 5 is illustrative of the power savings made possible by the discharge ring. As can be observed, power requirements for driving centrifuges are plotted along the ordinant in horsepower and the feed rates to the centrifuge are plotted along the abscissa in gallons per minute. The upper curve is a plot of test data obtained using the normal overflow lip while the lower curve is a plot of test data obtained using the discharge ring herein disclosed. In each case, this data was obtained when the centrifuge was operated at 3000 r.p.m. Inspection of these curves dramatically illustrates the power savings made possible through the use of the dis charge ring. For example, at a feed rate of 200 g.p.m., about 100 HP. is required to drive a standard centrifuge while only about 83 HP. is required to drive the same centrifuge with the herein described discharge ring installed, representing a savings of 17% in overall power consumption.

I claim:

1. In a centrifugal machine for separating a liquidsolids suspension into a heavy slurry fraction discharging as underflow from the discharge nozzles of the rotor bowl and a light fraction discharging as overflow from the bowl, and having means for feeding the suspension into the 'bowl, and means for continuously recirculating underfiow rnaterial into the bowl at a controlled rate; a rotor structure which comprises a rotor bowl having a first trunco-conical section provided with an overflow neck portion at the constricted end, a second trunco-conical section, an intermediate section interconnecting the wide ends of said trunco-conical sections and provided with discharge nozzles spaced from one another along the periphery thereof for discharging said underfiow and providing substantial recovery of power input required for the rotation of the bowl, and a hub portion closing the narrow end of said second trunco-conical section and defining with said trunco-conical sections an annular separating chamber, a. rotor shaft extending from said hub portion centrally through the area defined by said overflow neck, and an auxiliary power recovery arrangement comprising an annular energy recovery means located on the end of said neck portion concentrically therewith and having an inner cylindrical face defining the area of the overflow, and formed at the outer periphery with outwardly facing recesses spaced from one another along said periphery, each of which recesses is defined by a substantially radial face located substantially in a plane containing the rotor axis and by an associated face extending substantially at right angles from said radial face and substantially parallel to the rotor axis, said annular means further having overflow reaction discharge passageways communicating with respective recesses and extending in a plane transversal of the rotor axis and curved rearwardly with respect to the direction of rotation of the bowl and in said transverse plane defined in plan view by an inner wall shaped as a sharply bent curve and by an outer Wall spaced horizontally from said inner wall and shaped as a shallow curve converging towards said sharply bent curve, an elongated inlet opening located in said inner cylindrical face and extending in the peripheral direction thereof, an outlet opening in said radial face, said outlet opening in said radial face being significantly smaller than said inlet opening, said inner and said outer walls connecting said inlet opening with said outlet opening, whereby the flow cross-sections of each passageway diminish gradually and smoothly from said elongated inlet opening located in said inner cylindrical face to said significantly smaller outlet opening in said radial face, each passageway comprising a straight discharge end portion directed substantially at right angles to said radial face and having said outlet opening thereof spaced from said associated face at a mnimum radial distance from said cylindrical inner face, whereby the overflowing liquid discharges in a direction normal to said radial face at a velocity great enough to avoid impingement upon said associated face, thereby providing recovery of a substantial portion of the energy expended for maintaining said recirculation of underflow, in addition to the power being recovered through the reaction nozzles discharging the underflow.

2. The machine according to claim 1, wherein there is provided a longitudinal feedwell structure extending from the hub portion concentric with the shaft and having feed duct means extending radially therefrom to provide a feed connection between said feedwell structure and said separating chamber, and wherein said means for feeding the suspension comprise a first stationary tubular member surrounding said shaft in spaced relationship therewith, and a second stationary tubular member surrounding said first member in concentrically spaced relationship therewith to constitute therewith an annular stationary feed inlet passage extending into the interior of said feedwell structure.

3. The machine according to claim 1, wherein said inlet opening of the passageways is oval, and said straight discharge end portion of the passageways is of tubular configuration.

4. The arrangement according to claim 1, wherein said overflow neck of the bowl has a terminal face and said annular power recovery means is a ring member fastened to said terminal face.

5. The machine according to claim 1, wherein said overflow neck of the bowl has a terminal face and said annular power recovery means is a ring member fastened to said terminal face, with fastening bolt members extending through said ring member in the space between respective reaction passageways, securing said ring member to said neck.

6. The machine according to claim 5, wherein said bolt members are located in the respective areas extending between said inner cylindrical face of the ring member and said sharply bent curve of the respective above defined passageways.

7. The machine according to claim 4, wherein said inner cylindrical face of the ring member provides the effective overflow diameter, and wherein said ring member has a transverse annular shelf portion located at the outer end thereof and extending inwardly from said inner cylindrical face to provide an annular inwardly overhanging dam against spillage of overflow liquid overflowing through said passageways.

References Cited in the file of this patent UNITED STATES PATENTS 1,032,285 Jahn July 9, 1912 1,256,810 Leitch et al. Feb. 19, 1918 1,290,983 Hall Jan. 14, 1919 1,718,081 Ruda June 18, 1929 2,169,300 Svensson Aug. 15, 1939 2,625,321 Glasson Jan. 13, 1953 2,695,748 Millard Nov. 30, 1954 2,747,793 Caddell May 29, 1956

Claims

1. IN A CENTRIFUGAL MACHINE FOR SEPARATING A LIQUIDSOLIDS SUSPENSION INTO A HEAVY SLURRY FRACTION DISCHARGING AS UNDERFLOW FROM THE DISCHARGE NOZZLES OF THE ROTOR BOWL AND A LIGHT FRACTION DISCHARGING AS OVERFLOW FROM THE BOWL, AND HAVING MEANS FOR FEEDING THE SUSPENSION INTO THE BOWL, AND MEANS FOR CONTINUOUSLY RECIRCULATING UNDERFLOW MATERIAL INTO THE BOWL AT A CONTROLLED RATE; A ROTOR STRUCTURE WHICH COMPRISES A ROTOR BOWL HAVING A FIRST TRUNCO-CONICAL SECTION PROVIDED WITH AN OVERFLOW NECK PORTION AT THE CONSTRICTED END, A SECOND TRUNCO-CONICAL SECTION, AN INTERMEDIATE SECTION INTERCONNECTING THE WIDE ENDS OF SAID TRUNCO-CONICAL SECTIONS AND PROVIDED WITH DISCHARGE NOZZLES SPACED FROM ONE ANOTHER ALONG THE PERIPHERY THEREOF FOR DISCHARGING SAID UNDERFLOW AND PROVIDING SUBSTANTIAL RECOVERY OF POWER INPUT REQUIRED FOR THE ROTATION OF THE BOWL, AND A HUB PORTION CLOSING THE NARROW END OF SAID SECOND TRUNCO-CONICAL SECTION AND DEFINING WITH SAID TRUNCO-CONICAL SECTIONS AN ANNULAR SEPARATING CHAMBER, A ROTOR SHAFT EXTENDING FROM SAID HUB PORTION CENTRALLY THROUGH THE AREA DEFINED BY SAID OVERFLOW NECK, AND AN AUXILIARY POWER RECOVERY ARRANGEMENT COMPRISING AN ANNULAR ENERGY RECOVERY MEANS LOCATED ON THE END OF SAID NECK PORTION CONCENTRICALLY THEREWITH AND HAVING AN INNER CYLINDRICAL FACE DEFINING THE AREA OF THE OVERFLOW, AND FORMED AT THE OUTER PERIPHERY WITH OUTWARDLY FACING RECESSES SPACED FROM ONE ANOTHER ALONG SAID PERIPHERY, EACH OF WHICH RECESSES IS DEFINED BY A SUBSTANTIALLY RADIAL FACE LOCATED SUBSTANTIALLY IN A PLANE CONTAINING THE ROTOR AXIS AND BY AN ASSOCIATED FACE EXTENDING SUBSTANTIALLY AT RIGHT ANGLES FROM SAID RADIAL FACE AND SUBSTANTIALLY PARALLEL TO THE ROTOR AXIS, SAID ANNULAR MEANS FURTHER HAVING OVERFLOW REACTION DISCHARGE PASSAGEWAYS COMMUNICATING WITH RESPECTIVE RECESSES AND EXTENDING IN A PLANE TRANSVERSAL OF THE ROTOR AXIS AND CURVED REARWARDLY WITH RESPECT TO THE DIRECTION OF ROTATION OF THE BOWL AND IN SAID TRANSVERSE PLANE DEFINED IN PLAN VIEW BY AN INNER WALL SHAPED AS A SHARPLY BENT CURVE AND BY AN OUTER WALL SPACED HORIZONTALLY FROM SAID INNER WALL AND SHAPED AS A SHALLOW CURVE CONVERGING TOWARDS SAID SHARPLY BENT CURVE, AN ELONGATED INLET OPENING LOCATED IN SAID INNER CYLINDRICAL FACE AND EXTENDING IN THE PERIPHERAL DIRECTION THEREOF, AN OUTLET OPENING IN SAID RADIAL FACE, SAID OUTLET OPENING IN SAID RADIAL FACE BEING SIGNIFICANTLY SMALLER THAN SAID INLET OPENING, SAID INNER AND SAID OUTER WALLS CONNECTING SAID INLET OPENING WITH SAID OUTLET OPENING, WHEREBY THE FLOW CROSS-SECTIONS OF EACH PASSAGEWAY DIMINISH GRADUALLY AND SMOOTHLY FROM SAID ELONGATED INLET OPENING LOCATED IN SAID INNER CYLINDRICAL FACE TO SAID SIGNIFICANTLY SMALLER OUTLET OPENING IN SAID RADIAL FACE, EACH PASSAGEWAY COMPRISING A STRAIGHT DISCHARGE END PORTION DIRECTED SUBSTANTIALLY AT RIGHT ANGLES TO SAID RADIAL FACE AND HAVING SAID OUTLET OPENING THEREOF SPACED FROM SAID ASSOCIATED FACE AT A MINIMUM RADIAL DISTANCE FROM SAID CYLINDRICAL INNER FACE, WHEREBY THE OVERFLOWING LIQUID DISCHARGES IN A DIRECTION NORMAL TO SAID RADIAL FACE AT A VELOCITY GREAT ENOUGH TO AVOID IMPINGEMENT UPON SAID ASSOCIATED FACE, THEREBY PROVIDING RECOVERY OF A SUBSTANTIAL PORTION OF THE ENERGY EXPENDED FOR MAINTAINING SAID RECIRCULATION OF UNDERFLOW, IN ADDITION TO THE POWER BEING RECOVERED THROUGH THE REACTION NOZZLES DISCHARGING THE UNDERFLOW.