US3194492A - Pressurized centrifuge - Google Patents

Description

July 13, 1965 R. A. KoFFlNKl-z ETAL 3,194,492

PRES SURI ZED CENTRIFUGE 2 Sheets--Sheetl l Filed June 28, 1962 July 13, 1965 R. A. KOFFINKE l-:TAL 3,194,492

PRESSURI ZED CENTRIFUGE Filed June 28, 1962 2 Sheets-Sheet 2 jj j United States Patent O 3,194,492 llllSSURlZED CENTREFUGE Richard A. Kofnke, 638 Comm-on St., Walpole, Mass., and Horace l?. Cools, 33 Leonard St., Foxboro, Mass. Filed .lune 28, 1962, Ser. No. 205,937 6 Claims. (Cl. 233-7) This invention relates to centrifugal separators for separating solids from liquids to produce dry solids or to clarify liquid, and more particularly to the provision of pressurized separator constructions capable of separating solid particles of sizes ranging from 1A; inch long and larger down to the micron ran-ge continuously for an extended period.

Many processes for producing pharmaceuticals, food products, synthetic resins, metals, etc., are greatly improved and some absolutely require conducting a solidsliquid .separation under high pressure, by which We mean pressures above psi. gauge, ranging upwardly of 75 and 150 p.s.i. gauge. Such high pressures prevent certain materials dissolved in liquids from precipitating to contaminate the soli-ds and also enable heating of the liquid to obtain the low slurry vi'scosities needed for centrifugal separation.

It is very desirable that any centrifugal separator construction be universal, suitable without major alteration, for a Wide range of these processes and that it be capable Iof operation over an extended period without repairs on the order of 10,000 hours and more. Otherwise, the costs of construction 4and maintaining such machines is greatly increased.

A completely satisfactory pressurized separator has not been produced because of the unique sealing and leakage problems that occur at the point where the separator driving shaft passes between the yatmosphere and the pressurized casing. Solid particles are always dispersed in the pressurized processing iluids within the casing and any outward leakage would cause these particles to deposit in the .seals and cause ythem to wear out quickly. Furtheromore, processing gases are often explosive, noxious or very expensive, and their loss to the atmosphere cannot be tolerated. On the other hand, leakage of sealing liquids into the casing from a buffer seal chamber cannot. be tolerated where the liquids are incompatable L with the process, and in many instances such liquids that are compatible are also noxious, volatile, or expensive, which makes the use of liquid as a sealant unsatisfactory for a universal pressurized separator.

Small quantities of dry inert gas such as nitrogen, or argon can be tolerated by almost all processes, but resort to such gas as a sealing fluid in a seal chamber has appeared to raise more problems than it solves. Gas is extremely difficult to seal against excessive leakage into the process and to the atmosphere, and it has lbeeny considered prohibitively expensive to provide a seal construction which has universal application and can last the thou-sands of hours required in continuously operating separators. Labyrinth and other clearance seals are out of the question because of excessive leakage. In contact seals for dry gas (by which we mean seals which maintain low friction contact between a member carried by a shaft and a stationary member fixed or sealed to the casing for primary sealing), if the relatively moving parts are pressed too tightly together, since there is no liquid lubrication,

a the seal will be destroyed within a few hundred hours but if held `too lightly, the part-s will allow unduly large quantities `of gas to pass into the separat-or casing, which wastes the expensive gas, and sometimes can disruptthe process or require special equipment to remove. For contact seals, the primary sealing surfaces must therefore ice be subjected to a critical light loading which appeared impractical for the long life requirements of numerous processes in which centrifugal separators are employed. Furthermore, the ordinary face contact seals for gas are extremely expensive to manufacture.

In `addition to the foregoing problems which apply to any pressurized centrifuge, there have been further unsolved problem-s with regard to the solid walled bowl, internal conveyer type centrifuges which ,are especially preferred where it is` necessary to continuously produce virtually dry solids. One of these problems is that such centrifuges require two horizontal, concentric high-speed trunnions opera-ting at different speeds, the vouter one carrying the bowl, and the inner one carrying a screw conveyer. Here the sealing problem is not merely to seal the outside of the bowl trunnion to the casing, but also to insure that the process gas and solids do not escape between the trunni-ons. Also, with such centrifuges, :any seal that is employed should be of small size as the length and' mass of the moving elements not -only contribute to the expense of the machine but also limit the speed at which it can operate.

These solid bowl continuous centrifuges in :small sizes, e.g. 10 gallons per minute rating or less, are preferably -of the overhung type in which the bowl and conveyer extend as a `cantilever intol the casing, supported' from only one end. In such constructions casing gas pressure will impose a substantial axial thrust upon the horizontal trunnion, which had been thought to dictate a complete redesign of prior machines to ena-ble high pressure operation, to incorporate main thrust bearings, which would add greatly to the expense of such centrifuges.

The principal object of the present invention is to surmount or avoid all of these problems.

The invention provides a means for adapting centrifugal separators of the various b-asic designs so that they can be employed over a wide range of processes andl pressures, employing a gas sealing system which has llong seal wear life, is inexpensive to repair and has the required low leakage-into the process and to the atmosphere. In particular, the invention enables loading of the seal to the exact desired amount with controlled fine adjustment to properly seat the seal, independent of the actual pressure of the process.

Another aspect of the invention is an extremely economical means in solid bowl separatorstfor sealing between the conveyer and bowl trunnions to prevent leakage and passage of solids between them, thus making it possible to use the solid bowl centrifuge design in high pressure processes with the resulting advantages of dryer solids and greater emciency in many instances.

Yet another aspect of the invention is a means for eliminating the thrust effects of casing pressure upon horizontal overhung solid bowl centrifuges, thus permitting the use of high speed radial ball main bearings and avoiding the necessity of re-designing such centrifuges for pressure operation.

Yet another aspect of the invention-is the combination of features which permits the use of small, circumferential Contact primary gas seals at the point where `seal-sare most likely to fail, thus making their renewal extremely less expensive than wouldv bev the case if the seals were of the face Contact design.

We have realized that the. controlling consideration for producing a successful high pressure, universal centrifuge lies in the variable nature ofthe pressures which can occur in separator casings. The seal chamber has a seal at the casing which should be designed for a low pressure drop, i.e., 5-15 p.s'.i., and if the pressure ydifferential across this seal is allowed to exceed the `design pressure by much, the seal life is drastically effected and excessive leakage P9 La occurs. Not only do diflerent processes require difleent pressure-s, but for any process over an extended period of operation, pressures may not be kept constant but may vary as much as from 1/2 to 2 times design pressure. The sealing chamber on the shaft at the point it extends from the casing must contain butler gas at a higher pressure than the casing to prevent solids from entering the seal.

Vle have -solved this problem by regulating the -bul'er gas pressure by the casing pressure, producing a constant pressure drop across the seal regardless of 'the actual value of the casing pres-sure. Then the seal can be designed so that the gas forces act in a predictable manner and the Yloading resulting from the dierential gas pressure can be minimized, which maximizes seal life.

-By making the pressure regulator adjustable, we have provided for slight adjustments in the field to initially properly seat the seals and accommodate the different kinds of buffer gas that may be employed, since certain gases are more diicult to seal than others.

A further and very important aspect of the invention is our discovery that by so regulating the buffer ga-s pressure, We are able to use a seal having a circumferential yarea primary seal surface. This type of seal is presently mass produced for use in jet engines, for a useful life of on the order of 500 hours in sealing oil bearings, and is therefore inexpensive. lts durability is extremely subject to pressure drop. Despite its advantages of very low cost and small size relative to the `so-called face seals, it has never found use in centrifugal separators. We have found, however, that the foregoing regulation of buffer gas pressure enables its successful use.

This sealing system has particular' merit in combination with the solid bowl separator, with a second gas sealing chamber provided between the two shafts and with this chamber communicating with the outer one, so that the pressure in both is regulated by the casing pres are.

Also, we have found that by the use of casing pressureregulated uid pressure applied to the outer end of the bowl trunnion, we can totally compensate for the thru-st applied by the casing pressure whatever its value may be, so that only high speed radial ball bearings need be employed as the main bowl trunnion bearings, enabling the use of the simple existinfr separator designs.

We have also provide a particularly efficient control system for fluid balancing and sealing whether liquid or gas as well as a particularly eihcient combination of buler gas system and seal design for small centrifugal separators.

The invention is illustrated by the preferred embodiment of a small solid-walled bowl, concentric trunnion, overhang type pressurized centrifuge.

ln the drawings:

FIG. 1 is a partially sectional and partially diagrammatic side view of the separator;

FIG. 2 is a side sectionalview, on a larger scale, of the seal construction employed by the machine of FIG. 1;

FG. 3 is a partially broken away perspective view, on a still further magnified scale of the circumferential seal- 4ing member incorporated in the seal construction 0f FG. 2.

Referring to PIG. l, the centrifuge comprises a stationary housing l2, two concentric, horizontal axis rotating elements: a solid wall bowl i4 and a hollow hub-screw conveyor lo with blade tips 17 shaped to lit closely to the contour of the solid bowl. High pressure process gas and feed slurry are introduced within the conveyor hub through stationary pipe 18 and passes under the action of centrifugal force through the holes Ztl into the space between the conveyor and the bowl. he slurry is forced against the bowl, and the solids settle next to the wall. The liquid flows outwardly at oneend over a Weir 22 and the conveyor lo, Vwhich is -caused to rotate at a speed slightly dierent than that of the bowl by the differential gear unit 24, causes the solids to move up the inclined portion atascos The bowl and conveyor are overhung in that they are each supported from only one end,'the bowl ld being supported by bowl trnnnion 3d and the conveyer supported by conveyer trunnion 32 mounted concentrically within the bowl trunnion. Two spaced-apart main bearing pedestals 34 and 36 are provided, each supporting a high speed radial ball bearing 38, 39, respectively, which support the bowl trunnion. The housing for the planetary gear unit Z4 islixed to the bowl shaft between thevhigh speed bearings. The conveyor trunnionl which turns slowly with respect to the bowl trunnion 3i? is supported relative to the bowl trunnion by a pair of thrust bearings all and a bushing l5.

A flat drive belt 42 drives the ybowl trunnion 30 and the afxed gear unit 2d, and a planetary gear ratio Ycontrol shaft 4d controls the differential in speed between the bowl trunnion 3)- and the conveyor trunnion 32 that is produced by the gear unit.

r t the point where the trunnions 3% and 32 extend out of the casing l2, a sealing chamber 46 is provided, surrounding the bowl trunnion Si?. A second sealing chainber 48 is provided between'the bowl trunnion and the conveyer trunnion 32, and passages 5G com .iunicate between 14 ofthe bowl to a level 26 spaced radially inwardly from f the weir 22, at which point the bowl ends and the solids by centrifugal force are discharged through outlet 2S.

the two seal clnrnibers.y A casing pressure conduit 5?, is connected to the interior ofcasing l2, and extends to control a pressure relay device Se. The inlet conduit 55 of this relay is adapted to be connected to a source 5S of iuid, here an inert gas, at a steady pressure substantially above the casing pressure, and the outlet from the relay comprises a referencepressureV conduit adapted to actuate the regulators to be described. The relay Sais controlled by the casing pressure and reduces the fluid pressure fror conduit Se to equal the casing pressure in line S2, so that reference conduit d@ contains fluid that can be less noxious and expensive than the casi g gas, but at the same pressure. The reference press' re conduit d@ branches and connects to two pressure regulators o2. and 64. The regulator o?. is connected to inlet conduit o5, which is adapted to be connected to a source of sealing gas at a steady pressure substantially in excess of the casing pressure. This Yregulator discharges through conduit o to seal char lber do. Regulator 62; is controlled by the reference pressure -in conduit o@ to produce in conduit @E5 a pressure greater by a small, steadytincrement over that of the casing pressure, regardless ofwhat the casing pessure is or how it fluctuates. The regulator o2 has handleo? which enables the adjustment of the reduction ratio-of the regulator over a range of super-casing pressures to enable changing the loading of the seal chamber to adjust the Contact of ealing surfaces, and to control leakage.

At the outer end 3d ofthe bowl shaft, a balancing chamber ed is defined, adapted to .contain a balancing fluid to exert inward pressure upon the end surfaces 7d, 72 and 7dof the bowl trunnion. ln this embodiment the total area of these end surfaces equals the sunrof the crosssectional areas of therbowl and conveyer trunnions where they extend out of the pressurized casing, kat 7o, The seeond branch of the reference pressure conduit is connected lto regulator ed. The regulator has an'inlet conduit "f3 adapted to be connected to a source of fluid Sii at a steady Vpressure substantially in excess of the casing pressure. `The regulator ed is adapted todischarge through conduit S2 to the balancing charnber 63.. The regulator 6d is controlled by the reference pressureof'conduit dll to produce in conduit S3 a pressure exactly the same as the reference and casing pressures'. Regulator 64' is preferably not adjustable Vto insure that the balancing 4effect cannot be disturbed. t i f i Referring now to FlGS. 2 and 3, the sealing chamber Viev/bieb surrounds the bowl trunnion 34) is defined on the trunnion side, by a hard cylindrical sleeve 33 which is Vsecured to the bowlk trunnion. v A low pressure differential,

circumferential primary seal is effected between this sleeve andsealing ring assembly at point The ring also makes-a secondaryy seal at with a wall 9d, Vthe mating surfaces of face seal being` maintained in contact by spring 92. The wall 90 on oneV sideV is exposed to the casing pressure, and on the other side defines one end of the seal chamber. The opposite end of the seal chamber is defined by a hard annular ring- 94 sealed and secured to bowl trunnion 3f), and carbon sealing ring 96 forming a face seal 98 with ring 9d. Sealing ring 96 is supported by a resiliently expansible bellows 19t) which is xed at its opposite end to extension 162 of wall gli. The expansible bellows defines with the other surfaces a chamber which extends from the low pressure differential seal having primary sealing at 86 and secondaryV sealing at 88 to the high pressure differential primary seal 98. The sealing gas supply conduit 66 is connected with this chamber and maintains the pressure therein at a slight constant pressure differential above the casing pressure.

Referring to PEG. 3, the low pressure differential seal ring assembly 815 comprises three segmented carbon rings, seal ring d, back-up ring 1% and cover ring lill). Seal ring 10d has a cylindrical sealing darn 36' at the. portion of its cylindrical surface closest to the casing. This dam has an axial length of .02() inch. Buffer pressure slots 106 extend axially from this darn across the entire remaining surface of ring lud, and bach-up ring i081. The cover ring llt) is mounted on the outer periphery of the seal ring, and has the same axial length. A garter spring 112 having an accurately defined loadingy effect presses cover ring and seal ring down upon the sleeve 33, causing the seal dam 36' to engage the sleeve 33 to form primary seal S6 with the exactly proper force. Garter spring 114 holds the back-up ring against the sleeve 33. The curved surfaces of both seal ring ftd-t and back-up ring 168 engage the sleeve to position the seal, and to spread the loading effects of the springs, but the slots 1% cause the total pressure drop to occur across dam S6. Ina known manner the narrowness of the dam S6 limits the effective forces caused by the pressure differential. Most importantly, the regulator 62 insures that the pressure differential ofthe circumferential primary seal is kept at a substantially constant minimum, to enable the seal to run continously for the required thousands of hours without Wearing out.

The sealing ring assembly S4 forms the secondary -seal at 88 by means of a second dam SS formed in the plane face of seal ring fli4l, against wall 90. Pads 116 position the remaining portions of the seal ring and cover ring relative to wall 9u while allowing the seal pressure to extend to dam SSLthereby insuring that the pressure differential occurs over only a short length of seal.

Referring back to FIG. 2, the high-pressure-differential sealing ring 96 has a dam lfd positioned in the middle of the face of the ring and passages lll) and 122 in conjunction with grooves lfl and l22 insure that the total pressure drop occurs across this dam. This seal is designed for high pressure differential operation, so that a change in the casing pressure, and a corresponding change in the pressure in the seal chamber results in a much smaller percentage change in loading on this seal than in the low pressure differential seal, hence less drastic an effect on wear.

Referring again to FIG. 1, the second seal chamber defined between the conveyer trunnion 32 and the bowl trunnion 3l) is formed by an O-ring E4 at the casing end of the chamber, and a contact seal l26 at the other end. An inexpensive pair of angular contact ball bearings 40 under the low relative speed conditions between them can transfer thrust from the conveyer trunnion to the bowl trunnion.

While a very important advantage of the present invention is the fact that centrifugal separators can now successfully employ low-pressure-differential gas seals immediately adjacent the casings, where they are most likely to fail, and particularly ones having circumferential primary contact, with the attendant great advantages of low-cost, small size, and ease of replacement, the invention also offers certain advantages where the sealing fluid is a liquid.

d It should be understood that various of the specific details of the inventionv may be made within its spirit and scope.

Whatfis claimed is:

1. In a centrifugal separator comprising a pressure casing,

a solid-walled bowl within said casing,

a rotatably mounted bowl trunnion extending out of said casing, said trunnion being hollow and in driving relation with said bowl,

4a conveyer within said bowl,

a rotatably mounted conveyer trunnion extending concentrically within said bowl trunnion, in driving relation With said conveyer,

meansoutside said casing fory driving said trunnions at high but different speeds, said speeds being sufficient te produce high separating forces in said bowl,

means for introducing into said casing and said bowl a slurry to be separated and a gas to maintain superatmospheric pressure in said casing,

a first fluid sealing chamber surrounding said bowl trunnion at the point where it extends out of said casing,

and means for supplying said fluid chamber with seal fluid at a pressure higher than the pressure within said casing,

the improvement comprising,

a low-pressure-differential fluid contact seal sealing between said bowl trunnion and said casing against leakage from said fluid sealing chamber into said casing,

a high-pressure-differential fluid contact seal sealing between a Wall of said fluid sealing chamber and said bowl trunnion against leakage from said charnber to the atmosphere,

pressure regulating means for regulating the seal fluid pressure in said first fluid sealing chamber,

control means for controlling said pressure regulating means, said control means connected and arranged in an exposed relation to said casing pressure, said control means connected to said regulating means and adapted to operate said regula-ting means in response to said casing pressure, said pressure regulating meansV and said control means constructed and arranged to maintain the fluid seal pressure in said first fluid sealing chamber at a constant positive pressure differential above said casing pressure,

a second fluid sealing chamber defined between said trunnions,

and means connected with said second fluid sealing chamber forsupplying said chamber with seal fluid at a pressure higher than that within said casing.

2. The centrifugal separator of claim l wherein said means for supplying said second chamber with seal fluid at a pressure higher than that Within said casing cornprise at least one fluid passage extending from said second fluid sealing chamber through said bowl trunnion to said first fluid sealing chamber, whereby the pressure in the two chambers can be maintained the same.

3. The centrifugal separator of claim 1 wherein said pressure regulating means comprise a pressure regulator, a first conduit communicating between said pressure regulator and said means for supplying sealing fluid to said first fluid sealing chamber, and a second conduit communicating between said pressure regulator and said fluid sealing chamber, and said control means includes third conduit means communicating with said pressure regulator and exposed to said casing pressure.

4. A centrifugal separator comprising,

a pressure casing,

a solid-walled bowl Within said casing,

a rotatably mounted bowl trunnion extending from one end of said bowl through said casing to the exterior of said casing, the other end of said bowl terminating within said casing, said trunnion being in driving relation with said bowl,

means for driving said trunnion at a high speed to produce high separating forces in said bowl,

means for introducing into said casing and said bowl a slurry to be separated and a gas to maintain superatmospheric pressure in said casing, said pressure thereby producing an axial thrust against said bowl trunnion relative to said casing,

sealing means sealing between said bowl trunnion and said casing,

`a balancing chamber enclosing a surace of said trunnion,'said surface extending at an angle to the axis of rotation of said trunnion in a manner to provide an effective piston area to receive an axial force, said surface directed away from said bowl,

means for introducing pressurized fluid into said balancing chamber to act upon said surface, the force of said pressurized fluid thereupon acting to oppose said axial thrust against said trunnion.

pressure regulating means for regulating the pressure in said balancing chamber,

control means for controlling said pressure regulating means, said control means connected and arranged in an exposed relation to said casing pressure, said control means connected to said regulating means and adapted to operate saidregulating means in response to said casing pressure, said pressure regulating means and said control means constructed and arranged to maintain the tluid pressure in said balancing chamber at a level effective to balance said axial thrust against said trunnion.

5, The centrifugal separator of claim 4 wherein said bowl trunnion is hollow and said separator further comprises a conveyor within said bowi,

a rotatably mounted conveyor trunnion extending from one end of said conveyor through said hollow bowl trunnion to the exterior of said casing, the other end of said conveyor terminating within said casing, said casing pressure thereby producing an axial thrust against said conveyor trunnion relative to said casing,

means for driving said conveyor trunnion at a high speed slightly different from that of said bowl trunnion,

and thrust bearing means located between said trunnions and adapted to transfer to said bowl trunnion said axial thrust produced by said casing pressure on said conveyer trunnion.

6. The centrifugal separator of claim 5 wherein said sealing means comprise 5^, Y trunnion at the point where it extends out of said casing, Y

means for supplying said iiuid sealing chamber with seal iluid at a pressurefhigher tiran the pressure within said casing,

a low-pressure-diterential fluid contact seal sealing between said bowl trunnion and said casing against leakage from said fiuid sealing chamber into said casing,

a high-pressure-dierential luid contact seal sealing between a wall of said duid sealing chamber and said bowl trunnion against leakage from said chamber to the atmosphere,

second pressure regulating meansV for regulating the seal uid pressure in said iirst iiuid sealing chamber, second control means for controliing said second pressure regulating means, said control means connectedand arranged in an exposed relation to said casing pressure, said control means connected to said regulating means and adapted to operate Ysaid regulating means in response to `said casing pressure, said second pressure regulating means and said second control means constructed and arranged to maintain the seal fluid pressure in said iirst huid seaiing chamber at a constant positive pressure diierential above said casing pressure, said separator further comprising a second fluid sealing chamber deiined lbetween said trunnions, and means connected with said second uid sealing chainber for supplying said chambery with seal fluid at a pressure higher than that within said casing.

seerences Cited by the Examiner UNITED STATES PATENTS 750,668 ,l/04 Liedbeck.l Y 849,115 4/07 France Y 277-3 1,634,246 6/27 Jones et al 233-13 2,095,587 6/35 Lorig 277-88 2,175,868 10/39 Bentley 277-3 2,496,471 2/50 Hornbostel Y 2,536,793 l/Sl Andersson et al. 233-l 2,710,205 6/55 Brkich 277-3 2,835,514 5/58 McGahan 227---3 2,903,970 9/59- Elovi'tz et a1. 227-3 X 2,917,228 12/59 Lewis et al. 233-1 2,956,824 10/60 Kuehler et al 277-32 X 3,051,497 8/62 Wigg et al. 277-3 3,069,173 12/62 Best 277-3 3,088,744 5/63 Ezekielet al. 277-3 HARRY B. THORNTON, Primary Examiner..

ROBERT F. BURNETT, Examiner.

Claims (1)

1. IN A CENTRIFUGAL SEPARATOR COMPRISING A PRESSURE CASING, A SOLID-WALLED BOWL WITHIN SAID CASING, A ROTATABLY MOUNTED BOWL TRUNNION EXTENDING OUT OF SAID CASING, SAID TRUNNION BEING HOLLOW AND IN DRIVING RELATION WITH SAID BOWL, A CONVEYER WITHIN SAID BOWL, A ROTATABLY MOUNTED CONVEYER TRUNNION EXTENDING CONCENTRICALLY WITHIN SAID BOWL TRUNNION, IN DRIVING RELATION WITH SAID CONVEYER, MEANS OUTSIDE SAID CASING FOR DRIVING SAID TRUNNIONS AT HIGH BUT DIFFERENT SPEEDS, SAID SPEEDS BEING SUFFICIENT TO PRODUCE HIGH SEPARATING FORCES IN SAID BOWL, MEANS FOR INTRODUCING INTO SAID CASING AND SAID BOL A SLURRY TO BE SEPARATED AND A GAS TO MAINTAIN SUPERATMOSPHERIC PRESSURE IN SAID CASING, A FIRST FLUID SEALING CHAMBER SURROUNDING SAID BOWL TRUNNION AT THE POINT WHERE IT EXTENDS OUT OF SAID CASING, AND MEANS FOR SUPPLYING SAID FLUID CHAMBER WITH SEAL FLUID AT A PRESSURE HIGHER THAN THE PRESSURE WITHIN SAID CASING, THE IMPROEMENT COMPRISING, A LOW-PRESSURE DIFFERENTIAL FLUID CONTACT SEALING BETWEEN SAID BOWL TRUNNION AND SAID CASING AGAINST LEAKAGE FROM SAID FLUID SEALING CHAMBER INTO SAID CASING,

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