US3228593A - Centrifugal separator - Google Patents

Description

Jan. 11, 1966 K. E. TOPPING CENTRIFUGAL SEPARATOR 2 Sheets-Sheet 1 Original Filed Jan. 11. 1961 Jam 1965 K. E. TOIPPING GENTRIFUGAL SEPARATOR 2 Sheets-Sheet 2 Original Filed Jan. 11, 1961 Unite States fiatetit G 3,228,593 I CENTRIFUGAL SEPARATQR Kenneth E. Topping, Foxboro, Mass, aasignor to Bird Machine (Iornpany, South Walpole, Mass, a corporation of Massachusetts Continuation of application Ser. No. 82,044, Jan. 11, 1961.

This application Dec. 3, 1964, Ser. No. 418,582 2 Claims. (Cl. 233-7) This application is a continuation of application Ser. No. 82,044, filed January 11, 1961, now abandoned.

This invention relates to centrifugal separators, and more particularly to such separators of the continuous solid bowl type wherein a helical conveyor, rotated at a differential speed from that of the bowl, progressively moves solids concentrated adjacent the bowl wall by centrifugal force toward the discharge end of the bowl, usually smaller than the entrance end.

With centrifugal separators of the type concerned, difficulties of choking have been encountered with'certain material such as coal fines'due to bridging of solids between the conveyor and the bowl, locking the two against relative motion, thus causing strain and even breakage in the operating gearing, and requiring dismantling and cleaning of the machine before it can again be placed in effective operation. In Milliken et al. Patent No. 2,600,372, issued June 10, 1952, there is disclosed a solution to this problem according to which the inner bowl surface is provided with raised strips which act to anchor a bed of solids to thevinner surface of the bowl. This arrangement, in combination with a smooth surfaced conveyor, was found to operate satisfactorily and without choking on coal fines and other materials with which a choking problem had theretofore been encountered.

In machines according to the aforesaid patent wherein the inner surface of the bowl is of ordinary iron or steel construction, the bed of solid particles initially formed between'the strips tends to remain intact and to provide the working surface of the bowl over which the subsequently centrifuged solids are'worked by the conveyor to the discharge end of the bowl. Prior to the present invention it was found that the operation of such machines upon soft, non-abrasive solids could be improved by forrning the bowl and strips of stainless steel with the surfaces thereof exposed within the bowl polished to a very smooth state. With this arrangement the solids bed was forced by the conveyor to slip on the polished surface toward and out of the discharge end along with the solids above the bed, the bed being constantly replenished by incoming centrifuged solids, and continuing to prevent clogging by means of the bowl strips in the same manner as the stationary bed. Machines so modified have been operated successfully on non-abrasive materials such as polyvinylchloride and other similar resins to provide increased capacity, greater separation efliciency and a better product than is obtained with the permanent bed machine.

The present invention resulted from efforts to obtain similar improvement with centrifuges operating on slurries of hard, abrasive solids. Due to the different character of the solids, it did not follow that by smoothing the bowl surface the sliding bed action which had produced improved results with soft-solid slurries" would be obtainable with hard, abrasive solids. Even if such action could be obtained, its utilization in processing. abrasive particle slurries appeared impractical because of the problem of bowl wear. Continued rubbing contac't of such particles with a surface even as hard as stainless steel produces rapid wear. In the centrifugingof; coal fine slurries, for example, in apparatus according'to the above patents, it has been found that the conveyor is worn by the abrasive solids at such a rate as to require repair or renewal after the processing of the order of one hundred thousand tons of the coal or, at the usual operatingrate of fifty tons per hour, about two thousandhoursof operation. from wear by the bed of solids permanently anchored thereto, but if this were transformedinto a sliding bed on a polished stainless steel bowl the wear rate on'the bowl would be high. Such wear would be expected either to prevent the sliding action, due toroughening of the bowl, or towear out the bowl at an uneconomically rapid rate.

As a possible means of overcoming the wear problem, it was conceived that the requisite hard smooth inner bowl surface and strips might be provided as a relatively thin, smooth stainless steel liner within the bowl'and removably attached thereto. If such a liner would'function to produce the sliding bed action it could be replaced when worn at afraction of the cost of replacing a bowl, and consequently might make the operation economical.

Such a linerwas initially tried in the bowl of a centrifugeoperating on abrasive potash'slurries of finer'particle' size range than coal fines. In previous operation on th e same slurries the bowl had strips and ordinary unsrnooth inner bowl surface producing the bed-anchoring effect describedin the patent mentioned above. When'first'started, the smooth-surfaced liner and strips produced animproved operation characteristics of the sliding bed' effect that had been previously obtained with soft solid slurries. But' the effect was temporary and after a very short period of operation the machine lost all improvement and reverted to its former capacity, efficiency and product quality, it being obvious that the machine Wasoperating' with an anchored bed as before. Continued operation produced no change or improvement anddid not appreciably wear the liner as it would have done with sliding bed action. I

Despite this failure, it was decided to try another liner, this time in a centrifuge that had been operatingon coal fines with a solids bed permanently anchored in the stripped bowl. capacity, efficiency and product was obtained and maintained. The previous normal production rate of'50 tons per hour was raisedto 67 tons per hour while the conveying loads measured at the gear unit dropped from 430 pounds to only 300 pounds and the product degradation was substantially reduced due apparently to reduced shear. After this greatly improved operation had been maintained substantially unchanged for 600 hours, the

been installed in other machines operating on coal fines with the same improved results. These tests clearly indi- In that apparatus, the bowl was protected This time a remarkable improvement'in cate that the improved operation can be maintained even beyond the previous 100,000-ton limit for conveyor renewal because of the reduced wear on the conveyor and because the apparent wear rate on the liner was not great enough to call for liner replacement at that tonnage. In any event, the improvement was so substantial as to make use of the liner advantageous even if the liner lifewere substantially less than 100,000 tons processing.

Although this has not as yet been definitely proved, it is believed that the initial failure on potash was due to a lack of proper strip height and conveyor clearance in relation to slurry particle size range. In the potash machine, the height of the strips was inch and the clearance of the conveyor from the strips was inch and from the'liner surface, inch. Since the maximum particle size (greatest diameteryof the potash slurry was less than inch, the bed formed between the strips was more than six times the maximum particle size and the clearance of the conveyor over that was greater than the maximum particle size. In the initial liner. tested on coal fines the strip height was- /2 inch but this was only twice the maximum particle size of M4 inch. The clearance of the conveyor from the strips was /s inch or only one-half the maximum particle size. Apparently, the clearances in the potash machine were just at the maximum limit at which the conveyor was able to slide the solids bed, so that after only slight wear the limit was exceeded and the action was lost. r

In accordance wit-h the foregoing, the object of this invention is to provide a centrifuge of the type concerned having the above and other novel features of construction, which enable it to process slurries of abrasive particles without choking more efliciently and at less cost j FIG. 1 is a view partially in side elevation and partially in longitudinal vertical cross section of one form of the apparatus;

FIG. 2 is a partial side elevation and partial vertical cross section view of the bowl of the apparatus of FIG. 1;

FIG. 3 is a front (right hand) end view of the bowl of FIG. 2;

FIGS. 4 and 5 are fragmentary detail section views on the lines 4-4 and 5'5 respectively of FIG. 2;

FIG. 6 is a fragmentaryasection view of a bowl embodying a modified construction.

Referring now to the drawings, and first to FIG. 1, the machine as shown has a pair of supporting standards 10 and 12 upon which are fixedly mounted bearing collars,

14 and 16 respectively. Within the bearing collar 16 is rotatably journaled the drive sleeve 18 of the centrifuge bowl designated generally at 20, the sleeve 18 being fast at one end to a flange bolted to the bowl to form one end wall 22 thereof. A belt drive sheave 24 driven from a motor (not shown) is fixedly connectedto the outer end of drive sleeve '18.

Fixed to the opposite, or left hand, end wall 26 of the bowl, is a driven sleeve 28 'rotatably journaled within bearing sleeve 14, and operably connected at its outer end to a reduction gear unit 30 mounted within -a casing 32 fixed to the collar 14. A stub shaft 34 driven through the reduction gear unit has fixedly attached thereto the convv veyo r drive shaft 36 which isrotatably journaled within the driven sleeve 28.

The conveyor comprises a hollow casing 38 ,forrned of one large and one small diameter cylinderjoinedtogether, on the outer surface of which is supported the a feed pipe 52 which extends loosely through the sleeve 46 and end wall 44 of the casing 38 so that the conveyor and bowl are rotatable with respect to the pipe. A wall 54 fixed to the casing 38 is opposite the inner end of the feed pipe and acts to define a feed chamber into which the incoming slurry is discharged through pipe opening 55 and from which it is discharged into the bowl through outlets 56.

A stationary outer casing 58 of the centrifuge is fixedly connected at each end to the supports 10 and 12 by means of end walls 60 and 62 through which the sleeves 18 and 28 are rotatably journaled. An annular baffle 64 adjacent the left hand end of casing 58 cooperates with an annular lug 66 on the bowl to form a solids discharge chamber, into which the solids progressed to the smaller end of the bowl are discharged through ports 70 and from which they are removed through a connecting flue 72. An annular flange 74 within the opposite end of casing 58 cooperates with the end wall 22 of the bowl to form a liquid receiving chamber'76 from which the liquid component is withdrawn through pipe connections (not shown). The liquid is discharged into chamber 76 through openings in end wall 22 over anadjustable rim or dam 78.

In operation of the machine as sofar described, the bowl is driven through drive sheave 24 and sleeve 18 in one direction at a predetermined rate sufficient to provide the requisite centrifugal force, and the conveyor is driven therefrom through sleeve 28, the reduction gear unit and shaft 36 in the same direction but at a different rate to produce the required differential motion between the bowl and the conveyor. The solids from the incoming slurry whichtend to separate from the liquid toward the bowl due to centrifugal force are conveyed to the left by the conveyor and into the solids receiving chamber 68, while the liquid component overflows the dam 7 8 into the compartment 76.

As so far described, the machine is substantially the same as disclosed in the aforesaid Patent No. 2,600,372. Turning now to the improvements which the present invention provides in the bowl and its relation to the conveyor, it will be seen that the bowl as shown in FIGS. l-S has a cylindrical front section followed by two successive frusto-conical sections of diiferent cone angle, with the smaller angle cone forming the discharge end. This particular shape is notessential for purposes of the present invention, although it is preferred that the discharge end he of smaller diameter than the entrance end of the bowl. The front bowl section may also be frustoconical or the entire bowl may be of a single frustoconical section,as in the FIG. 5 embodiment of the aforesaidpatent.

Asshown in FIGS. 1-5, the bowl has an outer wall 80 of suitable metal such as cast iron or steel, conveniently formed in three sections joined together end to end by welding. Wall 80 is provided at four equally spaced intervals about its axis with four rows of bolt holes for receiving the shanks of bolts 82. Seated against the inner face of wall 80'is a liner 84 of relatively thin, hard wearing and smooth surfaced material, desirably of stainless steel and preferably of cold rolled stainless steel, as this material, particularly that formed with what is known in the trade as a No. 2-B finish, has a polished finish formed in the cold rolling which is exceedingly smooth and excellent for. purposes of the present invention. As in the:

case of the outer bowl wall 80, the liner may be conveniently formed in separate sections joined end to end by butt welding as shown in FIGS. 4 and 5, the weld preferably having the convex form shown at 86 in FIG. 4* to protect against wear.

. four rows of bolt holes to align with the bolt holes in the external. wall 80 and also to receive the shanks of bolts 82.

Upon the inner surface of 1 the liner are mounted by means of the bolts 82 four sets-of strips 88 overlying Liner 84 is also provided With-- the bolt holes in the outer wall and lining and being provided with countersunk, bolt holes 90 for receiving the inner ends of bolts 82. These strips are also of hard wearing, smooth surfaced material, preferably the same as that of the lining. As shown, the strips are formed of three separate sections, each conforming in length to one of the three bowl sections of difierent shape, although they may be formed of one piece bent to conform to the bowl contour.

In the construction shown, the strips may be removed from the liner and the bowl by partially withdrawing the bolts 82. By further withdrawing the bolts 82 the liner may be removed from the bowl through its larger end. This arrangement is preferred since it permits the strips to be removed and replaced independently of the liner in the event they wear faster than the liner, though this feature is not essential and the strips may be permanently attached to, or formed integral with, the liner. However, it is essential that the liner be removable, and this is preferably accomplished by bolting in the manner shown, which may be aided in security of fastening by readilyruptured tack welds of liner to outer wall at one or both ends.

Conveyor blade 40, also formed of hard wearing, smooth surfaced material, is contoured to the bowl so that it has a uniform clearance above the strips and the inner surface of the liner. As above indicated, these clearances are important since, if they are too great, satisfactory sliding-bed action, which provides improved operation according to the invention, may not be obtained. In general, it is preferable that the clearance of the conveyor above the strips be as small as consistent with manufacturing tolerances, and may be of the order of to 4; inch. Greater clearances may be provided, particularly where the machine is for processing slurries containing a substantial proportion of relatively large particles, such as coal fines, but it is desirable that this clearance be less than, or at least not substantially exceed, the maximum particle size if that is possible.

The clearance of the conveyor from the inner surface of the liner is a function of the thickness or height of the strips 88. Here also the most desirable clearance will depend to some extent on the nature of the slurry being processed. With large particle slurries such as coal fines, a strip thickness of /2 inch plus a conveyor clearance from strips of /s inch has been found satisfactory, although somewhat greater or lesser strip thicknesses and clearances may be used. With smaller particle slurries the strip thickness, as well as the total clearance from the conveyor to the liner, may desirably be less. Desirably, the strips correspond in thickness to from about one to four times the largest particle size present in significant quantity in the slurry being processed, making the desired clearance from the liner about two to five times such particle size.

The strips are desirably relatively narrow, about 1 inch width being suitable in bowls of 36 to 54-inch or larger diameters. The use of four strips, or set of strips, spaced at equal radial intervals is not essential. However, it has been found that the use of a greater or lesser number of strips tends to interfere undesirably with the sliding action of the conveyor on the solids bed formed between each pair of strips.

Due to the decrease in diameter of the bowl toward the exit end, the strips are closer together at that end than at the front end. This also has some tendency to interfere with the sliding bed action. Where such diameter difference is very substantial, it may be desirable to make the strips wider toward the front end and narrower toward the discharge end to reduce this difference in spacing.

In the embodiment so far described, the strips and liner are provided throughout the length of the conveyor. This is desirable but not essential. Most of the work of the conveyor is accomplished toward the exit end of 6. the bowl, so that the strips and liner may be omitted at the front end, for example from the cylindrical section in FIG. 2. The liner and strips should, however, extend from adjacent the discharge end for a substantial part of the conveyor length.

FIG. 6 illustrates a modification in which the liner and strips are confined in length to the effective working length of the conveyor, this figure also illustrating modifications in strip and bowl design. In FIG. 6 the outer wall 96 of the bowl is made in two sections, a front cylindrical section and a rearward frusto-conical section. The cylindrical section is preferably made somewhat thicker than the other with the two sections joined so that the thicker cylindrical section projects inwardly of the other. The liner 98 is coextensive in length only with the frusto-conical section which is opposite the effective working length of the conveyor. The inner end of the liner abuts the inwardly projecting end of the thicker cylindrical portion and is substantially flush with the surface thereof.

The strips 100 of the FIG. 6 embodiment are also modified and instead of being rectangular and arranged parallel to the bowl axis, they are formed as sections of a helix and the bolt holes 102 therein, as well 'as the matching holes in the liner and outer wall are arranged in a corresponding helix. This helix or spiral desirably has a pitch which approximates the angle to the bowl axis at which the conveyor tends to move the solids, which may be of the order of 30. This arrangement somewhat reduces the friction of the sliding bed on the sides of the strips, tending to reduce both strip wear and the conveyor load as compared with the previously described embodiment.

Visual observation has shown that with the bowl and conveyor properly constructed and interrelated in accordance with the invention as above described, the abrasive solids form into beds between the strips, and these beds are continually slid to and out of the exit end of the bowl by the conveyor. It is this action which is believed responsible for the greatly improved results obtained as above described. When the strips or liner become sufficiently worn to warrant it, either or both may be readily replaced with the construction shown and at insubstantial cost considering the improved operation obtained.

It will be appreciated that there have been particularly shown and described herein only preferred embodiments of the invention and that changes in the form and detail thereof may be made within the spirit and scope of the invention.

What is claimed is:

1. In a centrifuge for separating solid, abrasive particles from liquid which includes a rotatable bowl adapted to receive the fluid-solids mixture, a solids discharge chamber adjacent one end of the bowl, a liquid discharge outlet, a rotatable, helical conveyor coaxially mounted within the bowl, and means for rotating the bowl and conveyor at difierential speeds so that the solids are concentrated against the bowl by centrifugal force and are progressed to the discharge chamber by the conveyor, the improvement which comprises the combination with the bowl of a liner mounted within the bowl and forming a continuous inner working surface thereof surrounding its axis, said liner having at lea-st a portion thereof diminishing in diameter between its ends with the smaller end contiguous to said solids discharge chamber, said liner being of hard wearing, smooth surfaced material at least substantially as hard wearing and smooth surfaced as cold rolled stainless steel and being provided on its inner surface with a plurality of radially spaced, generally parallel raised strips extending longitudinally of the bowl axis substantially the full length of said liner portion, said strips being of such low number and relatively narrow width as to expose the major portion of the inner surface of the liner between them, the clearance 7 of the conveyor from the liner being of the order of two to five times the diameter of the largest particles present in significant quantity in the mixture to be processed,

said clearance of the conveyor from said strips not substantially exceeding said diameter, whereby to enable the conveyor to continuously push said beds over the smooth surface of the liner and from the exit end thereof and to maintain sai-d action despite substantial wear produced thereby on said liner and strips, and means removably attaching the liner to the bowl to permit removal and replacement thereof when required by wear.

2. A combination according to claim 1 wherein said 8 strips are of theorder of four 'in number andof one inch in width.

References Cited by the Examiner UNITED STATES PATENTS 1,064,184 6/1913 Wels 233 7 2,600,372 6/1952 Milliken 61 al. 233*? 3,096,282 7/1963 Trotter 233 '7 10 M. 'CARY'NELSOVN, Primary Examiner.

H. K'LINKSIEK, Assistant Examiner.

Claims (1)

1. IN A CENTRIFUGE FOR SEPARATING SOLID, ABRASIVE PARTICLES FROM LIQUID WHICH INCLUDES A ROTATABLE BOWL ADAPTED TO RECEIVE THE FLUID-SOLIDS MIXTURE, A SOLIDS DISCHARGE CHAMBER ADJACENT ONE END OF THE BOWL, A LIQUID DISCHARGE OUTLET, A ROTATABLE, HELICAL CONVEYOR COAXIALLY MOUNTED WITHIN THE BOWL, AND MEANS FOR ROTATING THE BOWL AND CONVEYOR AT DIFFERENTIAL SPEEDS SO THAT THE SOLIDS ARE CONCENTRATED AGAINST THE BOWL BY CENTRIFUGAL FORCE AND ARE PROGRESSED TO THE DISCHARGE CHAMBER BY THE CONVEYOR, THE IMPROVEMENT WHICH COMPRISES THE COMBINATION WITH THE BOWL OF A LINER MOUNTED WITHIN THE BOWL AND FORMING A CONTINUOUS INNER WORKING SURFACE THEREOF SURROUNDING ITS AXIS, SAID LINER HAVING AT LEAST A PORTION THEREOF DIMINISHING IN DIAMETER BETWEEN ITS ENDS WITH THE SMALLER END CONTIGUOUS TO SAID SOLIDS DISCHARGE CHAMBER, SAID LINER BEING OF HARD WEARING, SMOOTH SURFACED MATERIAL AT LEAST SUBSTANTIALLY AS HARD WEARING AND SMOOTH SURFACED AS COLD ROLLED STAINLESS STEEL AND BEING PROVIDED ON ITS INNER SURFACE WITH A PLURALITY OF RADIALLY SPACED, GENERALLY PARALLEL RAISED STRIPS EXTENDING LONGITUDINALLY OF THE BOWL AXIS SUBSTANTIALLY THE FULL LENGTH OF SAID LINER PORTION, SAID STRIPS BEING OF SUCH LOW NUMBER AND RELATIVELY NARROW WIDTH AS TO EXPOSE THE MAJOR PORTION OF THE INNER SURFACE OF THE LINER BETWEEN THEM, THE CLEARANCE OF THE CONVEYOR FROM THE LINER BEING OF THE ORDER OF TWO TO FIVE TIMES THE DIAMETER OF THE LARGEST PARTICLES PRESENT IN SIGNIFICANT QUANTITY IN THE MIXTURE TO BE PROCESSED, SAID CLEARANCE OF THE CONVEYOR FROM SAID STRIPS NOT SUBSTANTIALLY EXCEEDING SAID DIAMETER, WHEREBY TO ENABLE THE CONVEYOR TO CONTINUOUSLY PUSH SAID BEDS OVER THE SMOOTH SURFACE OF THE LINER AND FROM THE EXIT END THEREOF AND TO MAINTAIN SAID ACTION DESPITE SUBSTANTIAL WEAR PRODUCED THEREBY ON SAID LINER AND STRIPS, AND MEANS REMOVABLY ATTACHING THE LINER TO THE BOWL TO PERMIT REMOVAL AND REPLACEMENT THEREOF WHEN REQUIRED BY WEAR.

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