US2185279A - Centrifugal separator - Google Patents

Description

2, E4@ G. J. sTREzYNsKi CENTRIFUGAI.; SEPARATOR Filed sept. 24, 1938 v 3 Sheets-Sheet l Jan. 2, w40. v G. J, sTREzYNsIKl v Y 2,185,279

'CENTRIFUGAL SEPARATOR Filed Sept. 24, 1938 3 Sheets- Sheet 2 .Kan fg 20` f 'I 20 /0 Y /8 fi* Y IS. .(23 5"? .f2 /2 22 n) 22 2g 40 2/ 33 2/ 30 27 V3/ 14,/ 5.4* l Lp 29 l 26 y 32 2l 27 L,/' Z5 l (gr/j /M/Wrdf? Wm/ c?. 'Zcyzzdc M Y 5y i Jan. 2, i946.A G. J. sTREzYNsKl CENTRIFUGAL SEPAIKATORl Filed sept. 24. 1958 5 Sheets-Sheet 5 Flay.

` at right angles to their longitudinal axes.

atented Jan. 2, 1.94@

GEMV

oENrnmUGAL .sEPAA'roa George J. Strezynski, Poughkeepsie, N.- Y., as-

signor to The De Laval Separator Company, New York, N. Y., a corporation of New Jersey Application September 24, 1938, Seriali No. 231,459

1s claims. (ci. 23e-17) Centrifugal extractors, whether of small diameter and high speed or of large diameter and slow speed, must compete with gravity settling tanks.

Gravity settling tanks have no size limitations, whereas any increase in size of centrifugal extractors involves so great an increase in stresses that the speed must be reduced resulting in reduced efficiency.

In practically all commercial centrifugalI extractors it is found that the stresses in the wall of the rotating cylinder. are caused more by the weight of the walls than by the load due to the contained liquor. The self stress due to the weight of the wall is generally about 60% of the' total stress.

It'has been generally accepted that the strongest type of construction for a centrifugal bowl is substantially a cylinder rotating around its own axis; the main body of the cylinder being of monolithic structure, that is, made in one piece.

Long study and investigation causedme to seriously question the correctness of this principle. My work involved a comparison of cylinders rotat ing around their longitudinal axes with cylinders of the same dimensions rotating'around an axis ses of the forces and dimensions of cylinders of the latter type indicated a large variation in performance depending on the relation between the longitudinal and transverse axes of the cylinder.

In the forepart of this description it will be convenient to refer to certain of the accompanying drawings, and therefore all ofthem will be rst briey described.

Fig. 1 is a diagram of a cylinder rotatableabout its longitudinalv axis. Figs. 2 and 3 are diagrams, in vertical and plan cross-section respectively, of a cylinder of the same dimensions as in Fig. l but rota/table'on its short (transverse) axis. Fig. 4 is an end view of Figs. 2 and 3. Fig. 5 is a View, similar to Fig. 2 or 3, but of a cylinder of shorter length and greater width. Figs. 16 and 7 are diagrams illustrating the principle of my invention. Fig. 8 is a transverse sectional vlew of a centrifugal bowl taken through the center thereof perpendicular to its axis of rotation. Fig. 9 is a side view of the bowl of Fig. 3. Fig. l is a sectional view ofthe bowl ,of Fig. 8 taken on the line {I0-llt of Fig. 8.

Figs. l, 2 and 3 are diagrams of two cylinders of equal dimensions, the cylinder i in Fig. l rotating about its longitudinal axis and the cylinder 2 of Figs. 2 and 3 (Fig. 2 being a side View and Fig. 3 a plan) rotating about its transverse aris. In Fig. l, the thickness of the cylinder wall must be Analyuniform. In Figs. 2 and 3 there is no such requirement because the load in the direction X decreases, and it is therefore advisable to reduce the thickness of the wall from the center toward the periphery.

The total stress in Fig. 1 at 15,000 R.. P. M. is:

enfui-a.) l 2f s=(dia.)2 (rev.)2(1.oa+

S=37,50041bs. In Figs. 2 and 3, the following table gives stresses in direction Xat 7000 R. P. M.

Table A Weight Radius Force Btl-ess Pounds Inches i Pounds Pounds Cylinder 43. 6 116, 000 25, 000 Ends 2. 75 15. 0 28, 600 4, 100 Liquor 9. 30 10.0 64, 500 9, 200

Total 38, 200

The bursting stress in Figs. 2 and 3 is quite negligible. It may be seen on the plan view (Fig. 3) that as we proceed toward the end from A to D the bursting force becomes more and more parallel with the axis and therefore the bursting component becomes smaller and smaller. It is largest at point A, but at point A there is no liquid at all to superimpose its stress on metal stress. The liquid line is indicated by the dot and dash line. Also, as may be seen from the end view, Fig.- 4," only a very small part of the metal is at full radius :fromA axis Y-Y. In fact these bursting' stresses are so low at this reduced speed of '1000 R. P. M. and at this small radiusthat the investigation disclosed the advisability of extending this analysis toa somewhat shorter cylinder but of greater diameter, as diagrammed in Fig. 5.i

Table B gives the forces for a cylinder 3`dimensioned as in Fig. 5 at 6000 R. P. M.

, Referring to Fig. 5, it4 may be seen that the tensile stresses along the axis X'are considerably Alower at a speed of 6000 R. P. M. but the bursting Table c fj Av. rad. in

(R.P.M )2 imm-,smh 'mgl wt. Pfgrlg l, 000- 000 llx'g; of hquor columns r 1 225 1 s Poms'id 5o 31 zo Figs. 2 and 3 49 10.0 9. 3 4556 5 36 8.0 21.0 6050 It may be readily seen that there is a most favorable diameter and length at whicha cylinder can be rotated at the right angle to its axis and give the maximum clarifying eifect and at the same time provide very much larger volume for storage of any material to be'removed from the liquor being claried. A

-Actual tests made over a period ofone year substantiated the above gures and allowed me to use a speed of rotation about twice as high as used in a `cylinder of the same maximum peripheral diameter. That is a cylinder of 12 inch diameter and 48 inches from end to end wasspun at 2400 R. P. M., whereas a centrifugal basket of 48 inches and 6 inches deep and 20 inches wide at the periphery is usually spun at 800 R5. P. M. and in extreme cases at 1200 R. P. M.

' The investigation of stresses in the end plates reveals that they are quite low if these ends are made'semi-spherical or conical. For reasons explained later, theconical ends were found to be best.

Further work along these lines revealed that if two or more such cylinders are superimposed on each other so as to form a cross or star formation, the stresses in the individual cylinders are not exceeded, but on the contrary the bursting stress near the center is reduced. That is, it can be readily seen in Fig. 6 that the tendency of force f to bulge outward the wall w' of one of the cylinders l is counteracted by the reinforcing action` of wall w2 and wall w4. In the case of three cylinders 5, as diagrammed in Fig. '7, this reinforcing eifect is of such magnitude Athat a speed of '7000 R. P. M. is quite practical.

In practice the optimum conditions were found to be three such cylinders built into a monolithic star with some modification of the central portion to facilitate the casting or forging of the complete unit. Now if the values in Figs. 1 and 'l are tabulated the following results are obtained:

From Table D the clarifying effect is almost eightfold and the storage volume sevenfold as great as in the cylinder rotating around its own axis.

Though analysis of the bursting stresses reveals that for best effect the length of the cylinder should be about 3 to 4 times its diameter and while the ends should be cylindrical or conical, the central portion is subjected to dilerent types of forces and may be of square or rectangular construction. In fact, rectangular construction is preferable when two or more such cylinders. are superimposed. The rectangular sides of three such oblong ,vessels form a hexagonal center portion which is well adapted for commercial construction and allows an ample central chamber for feeding the liquor and accommodating auxiliary means for such operation. This is shown in Fig. 7. The optimum condition is gained when the ends are cylindrical, oval or conical for about 25% of the length of the longitudinal vessel from each end and the central 50% is rectangular or square. The central portion does not perform any clarifying function but it functions only as a distributor of the liquor. A distributor whose hollow diameter equals or exceeds the transverse dimension of the clarify ing vessel is one of the novel features 'of my invention.

Actual commercial tests revealed further advantages. Figs. 8, 9 and 10 illustrate a commercial bowl embodying the principle of Fig. 7. Its

extreme diameter across the tips of the cones is 4 8 inches and the diameter or the short dimen' sion of each vessel varies from l2 inches near the end to about 16 inches at the center. The central portion of each vessel is rectangular andmerges into a cylinder which in turn ends in individual cones.

Each cone is iltted with a removable tip containing a small orifice. The orice can be opened or closed at will by a needle valve operable by mechanism in the central chamber and connected, through small openings in the central hexagonal chamber, to the said needle valve.

If a horizontal' section is taken at any depth through one of the vessels comprising the unit in Fig. 8, the section will be oblong with walls fully streamlined without any violent breaks in the continuity of the stress flow.

-cylinders at right. angles to each other and 48 inches from tip to tip of each cylinder. The

figures are given. in Table E.

Table E an Pfvgg' Gassm- 1121110 machinein solids oi solids galsJhr. (percent) Standard mach 2, 700 0. 4 & 0 New mach 4,500 1.5 21.0

While it is believed that the essential structural features of the invention will be clear from the foregoing description, it may be advisable to more particularly describe the construction shown in Figs. 8, 9 and 10 illustrating in detail a preferred y vembodiment of my invention.

agissait The bowl is preferably made in two parts-an upper half and lower half-which-are welded together along the line :r to form an integral unit which then comprises a central hub I and. radiating therefrom six peripheral separating chambers ll, i2, I3, Ul, l and I6 (see Figs. 8 and spaced uniformly,.that is, 60 apart, around the peripheryof the hub. Each pair of diametrically opposite chambers (e. g., H- and i3) together with the webs or tension members E@ aligning with their side walls and connecting -them with the hub IIJ constitute, in principle, a

single cylinder such as is diagrammed in Fig. 5. The three cylinders comprising the entire bowl may be said to overlap at their central portions to form a central chamber 23, common to all cylinders, and small chambers 2| triangularr in horizontal section and positioned outside the central chamber and between adjacent separating.

chambers. That is, one side of one of these cylinders comprises the side of one peripheral separating chamber, a tension member in the form of a web 2t, a short arcuate section of the hub wall, another web 2D and the side of a diametrically opposite separating chamber, all these elements being located'in substantial alignment and integral one with another and thus imparting to the whole structure maximum strength. The sides `of adjacent cylindersintersect at the points I8 and the inner end of a web constituting an inward prolongation of one of the side walls of one peripheral chamber is integral, not only with the hub lil, but also with the inner end of a web 20 constituting an inward prolongation of one of the side walls of another peripheral chamber spaced 120 from the first mentioned chamber. l The webs 2d are not solid but are arranged toform an opening i9 though which the lighter (liquid) constituent separated in the adjacent peripheral separating chamber ows into the chamber 2l and from which it escapes through a discharge passage i2.

The mixture to be separated is admitted to the central hollow hub 23 through a stationary axial channel 2d and one or more stationary radial distributing'nozzles 25.

It will be observed, by reference more particularly to Fig. 9, that 4the central parts of the cylinders, including the inner ends of the peripheral separating chambers, are rectangular in crosssection and that the rectangular walls at the inner end of eachseparatlng chamber merge into a cylinder and thence into a cone which terminates in (substantially) a point. Thus each separating chamber, except at its inner end, is approximately circular in cross-section. By approximately circular Imean to include a true circle, as when the inner part of the chamber is square (as in the drawing) and also an oval, which would belthe shape if the inner part of the chamber were oblong. Variations in this respect are contemplated. Indeed, the peripheral chambers, especially the middle and outer end portions thereof, mayv have various shapes; the

ing chambers. to prevent the 'entrance to the separating chambe extracted flows from the central chamber through 'these holes into the peripheral separat- The holes are sumciently small bers of any large particles. Tubes t0 are also fixed in the same openings and convey the mixture to the chamber preferably radially beyond a point midway between said opening and the extremity of the cone. h

In the separating chambers the solids are separated from the lighter liquid constituent and are discharged through oriiices 28 in the point of the cone. Preferably each cone is tted with a two-inch removable tip 29A containing an orice 2B about V5 of an inch in diameter.

A'I'he orifice 28 may be opened and closed by means of a radiallyl movable needle valve 30, which extends slidably through a central orifice in the disc 26, its inner endextending loosely through the short end of a bell-crank lever 3l, lock nuts being threaded on the inner end of the valve rod. The long arm of the bell-crank engages a circumferential groove in a spool 32 suspended from a rod 33 extending'along the axis of rotation of the bowl upward (within the bowl spindle if the bowl is driven from above) to a point outside the bowl convenient for manual operation. It will also be understood that the rod 33 may be operated automatically to open and close the valve 30 at timed intervals. Mechanism for so doing is known in the art and is therefore not described. l

Preferably the bowl is suspended from a spindle (34) The means for suspending and driving the spindle are not shown, as they form no part of the invention.

While the bowl is more particularly intended for use in the extraction of solids from liquids it N ferent types of centrifugal separation is within the skill of centrifugal separator designers.

In the construction shown, the mixture to be separated is fed through a stationary channel 39 into the axial channel 24 and distributing nozzles 25 hereinbefore mentioned. The purified liquid discharges from the outlets 2,2 through the top of the bowl into a stationary channel 36. The solids are discharged into a stationary receptacle 3l, whence they are conveyed away through a channel 38.

In conclusion, it may be stated that the radical improvement in performance hereinbefore explained in detail, as applicable to the embodiment oi my inventionshown in the drawings, is due mainly to four factors: Y

(l) Higher speed at the point of maximum diameter is possible than in any other commercial machine of corresponding size.

(2) Complete absence of slippage prevents remixing and breaking up of occulated' masses. In all commercial machines the main body of the liquor is contained lin the central cylinder andA as the liquid at each point of the diameter is rotating at a different lineal speed while it travels inward and outward, there is tremendous slippage between the different layers of liquid. This results in continuous breaking up of the chemical flocs to be precipitated. In a bowl embodying my invention substantially allthe liquid is contained in limited radiating vessels and no slippage is possible. The liquor is brought into each vessel by a tube of ample cross-section and extends to comparatively near the tip of the vessel so that the incoming liquid does not disturb the separated liquid. The introduction of the liquid and solids directly in line with the tip of the vessel allows the precipitation of the solids at a point fr om which their removal is easiest.

(3) The heavy-phase, solid or liquid. isconcentrated in a very small vportion of the vessel but at the maximum force available, and its prompt removal by suitable means, like an automatic or timed valve, leaves most of the vessel available for clarification of the light phase. -(4) The high speed attained at the tips of these vessels, combined with the great depth of the liquid column above the tips of the vessels, provides hydrostatic forces never reached before in a commercial machine. The pressure is 1300#/sq. in. in the bowl illustrated in Fig. 8, whereas in heretofore known commercial machines the pressure does not exceed 800#/sq. in. This high hydrostatic pressure allows exuding of semi-solids much drier or more viscous than hitherto.

In considering theseadvantages and improvements the size of the 2i'nachine must be kept in mind. Several factors are involved, namely, speed, volume, diameter and depth. If we compare two bowls, one of vwhich has twice the dimensions of the other one, the larger diameter bowl will have at the same rotation twice the lineal speed at the periphery, but it will have four times as high self-stresses, eight times as much volume. When force, time and settling distance are taken into consideration, such bowl should have eight times the clarifying eiect, but due to the fact that the annulus of the larger cylinder has an area only four times as large as in the smaller bowl the velocity toward the center which determines the slippage is not the same but is twice as great and therefore the e'ect of slippage is not the same. For that reason there is no analogy between commercial machines and laboratory apparatus. The conditions of stresses, design and clarification are radically different. It will be understood that my invention is intended more particularly for embodiment in commercial machines. In using that term in the foregoing description I mean to be understood as referring to machines whose clarifying e'ect is determined by no smaller product of volume and revolutions than 100,000 cc.sec.

This application is a continuation in part` of an application filed November 18, 1937, Serial No. 175,177.

What I claim and desire to Patent is: A

1. A centrifugal separator bowl comprising a central hub and peripheral separating chambers spaced sixty degrees apart, webs rigid with and constituting inward extensions of the side walls of the chambers, each web of a chamber being connected and rigidvwith the hub and with a web extending from the side wall of a chamber spaced therefrom, the two webs extending from the adjacent side walls of each two adjacent separating chambers forming between them and the hub a lighter separated liquid outflow space communicating with the inner portions of both said adjacent chambers.

2. A centrifugal separator bowl comprising a plurality oiA cylinders, each cylinderv extending protect by Letters equal distances on opposite sides of the bowls axis, the longitudinal axis of each cylinder being perpendicular to and intersecting the bowls axis, each cylinder intersecting the other cylinder or cylinders and thereby forming two opposite peripheral separating chambers rigidly 'connected together and a central space surrounding the bowls axis common to the cylinders, the cylinders'bing substantially rectangular at their intersectin'g central portions and at the inner ends of the separating chambers, the outer portion of each separating chamber being circular in cross- Section.

3.A A continuous centrifugal separator bowl comprising a central hollow chamber and a plurality of pairs of peripheral chambers, the chambers of each pair being arranged diametrically opposite each other, each side wall of a periph'- eral chamber being insubstantial alignment with one of the side walls of the other chamber of the pair and tension members, constituting inward extensions of said two side walls, the inner ends of which are connected together, said tension members, as well as said two side walls, being all in substantial alignment and rigid each with the others.

4. A centrifugal' separator bowl comprising a plurality of pairs of peripheral separating chambers, the inner portion of each peripheral chamber being rectangular in cross-section and its' 5. A centrifugal separator bowl comprising a central hollow chamber and three pairs of peripheral chambers, the chambers of each pair being arranged diametrically opposite each other, all the chambers being equally spaced apart around the central chamber, each side,

wall of a peripheral chamber being in substantial alignment with one of the side Walls of the other chamber of the pair and tension members rigid with the side walls of said chambers and constituting inward extensions thereof, the in-I ner ends of opposite tension members being rigid with and connected together by an arcuate section of the central chamber.

6. A centrifugal separator bowl as defined in claim 5 in which the inner end of.each tension.

member merges and is rigid with the inner end of a tension member that constitutes a side wall extension of a peripheral chamber spaced 120 therefrom.

*7. A centrifuga separator Abowl as dennen m.

claim 5 in which the inner end portion of each peripheral chamber is substantially rectangular in cross-section, so that opposite periphcentral chamber and sixfperipheral separating.

chambers spaced sixty degrees apart, tensionmembers rigid withthe side walls of said chambers and constituting inward extensions thereof, the inner ends of opposite tension members bei118 rigid with vand connected together by an,

arcuate section of the central chamber, the inner end of each tension member merging and rigid with the inner end of a tension member that constitutes a side wall extension of a peripheral chamber spaced therefrom.

10. A centrifugal separator bowl comprising a a central chamber and six peripheral separating chambers spaced sixty degrees apart, tension members rigid with the side walls of said chambers and constituting inward extensions thereof, the inner ends of each tension member being secured to the central chamber and merging and rigid with the inner end of a tension member that constitutes a side wall extension of a chamber spaced 120 therefrom 11. A centrifugal separator bowl comprising a central hollow hub and a plurality of peripheral separating chambers radiating therefrom and rigid therewith, and outlet chambers for lighter separated liquid corresponding in number to the peripheral separating chambers, each outlet chamber being arranged outside said hub and between and communicating with two adjacent peripheral separating chambers and each peripheral separating chamber Acommunicating with two adjacent outlet chambers.

l2. A centrifugal separator bowl comprising a central hollow hub and a plurality of pairs of peripheral separating chambers, the chambers of each pair being arranged diametrically opposite each other, opposite side walls of the inner end of each peripheral chamber extending in one direction parallel to the axis of the bowl, said side walls intersecting the side walls of two adjacent peripheral chambers and extending substantially tangentally to and rigid with the wall of the hollow hub, arcuate diametrically opposite sections of which connect and align with the opposing side walls of the two separating chambers.

13. A centrifugal separator bowl comprising a central hollow chamber of substantially cylindrical shape and a plurality of pairs of peripheral chambers, the chambers of each pair being arranged diametrically opposite each other, each peripheral chamber being rectangular in crosssection at its inner end with two opposite sides at that end extending parallel to the axis of the bowl and two opposite sides extending at right angles to the axis of the bowl, the width of the inner end of each peripheral chamber, measured between the side walls extending parallel to the axis of the bowl, being substantially equal to the diameter of the central chamber, said side walls of each peripheral chamber being substantially tangential to the cylindrical wall of the central chamber, the adjacent side walls of adjacent chambers intersecting along a line parallel to the axis of the bowl and outside and spaced from the central chamber.

14. A centrifugal separator bowl comprising threerigidly connected cylinders, all the cylinders extending equal distances on opposite sides of the bowls axis, the longitudinal axis of Ieach cylinder being perpendicular to and intersecting -the bowl's axis, opposite peripheral portions of each cylinder enclosing separating chambers, the three cylinders intersecting to form a central chamber and six relatively small chambers, ar-

ranged alternately with the six separating chambers, outside the central chamber, means to feed into the central chamber the mixture to be separated, there being openings between the central chamber and the separating chambers for passage from the former to the latter of the mixture to be separated and openings between each of said small chambers and the inner portions of two adjacent separating chambers for the passage from the latter to such small chambers of separated lighter constituent.

15. A centrifugal separator bowl comprising three rigidly connected cylinders, all the cylinders extending equal distances on opposite sides of the bowls' axis, the longitudinal axis of each cylinder being perpendicular to and intersecting the bowls axis; the three cylinders overlapping at their central portions andV together forming a central hollow hub and, outside the hub six light constituent outlet chambers approximately triangular in cross-section, the non-overlapping outer ends of the cylinders forming six peripheral separating chambers, two walls of each of the triangular chambers being cut away to atford an opening for the escape from two adjacent separating chambers of separated light liquid, and means to feed the mixture to be separated to the central hollow hub, there being openings between the central hollow hub and the six separating chambers for passage from the former to the latter of the mixture to be separated.

GEORGE J. STREZYNSKI.

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