US3228594A - Centrifugal separator - Google Patents

Description

1966 c. L. AMERO CENTRIFUGAL SEPARATOR Filed Feb. 5. 1965 United States Patent 3,228,594 CENTRIFUGAL SEPARATOR Clifford L. Amero, 17 Woodland Road, East Walpole, Mass.

Filed Feb. 5, 1965, Ser. No. 433,537 4 Claims. (Cl. 233-7) This is a continuation-in-part of application Serial No. 154,752 filed Nov. 24, 1961 and now abandoned. This invention relates to apparatus for effecting separation of solids from liquids by centrifugal action and more particularly to such apparatus wherein the solids-liquid slurry may be subjected to chemical action while simultaneously undergoing centrifugal separation, the chemical being such as to assist the centrifugal force in producing separation of the solids.

With many slurries difficulty is experienced in obtaining satisfactory centrifugal separations of solids from liquids, particularly where it is necessary or desirable to remove very fine particles dispersed or in collodial suspension in the liquid phase or phases of the slurry. For many such dispersions or suspensions there exist chemicals which will aid separation of such solids under normal gravitational settling conditions, such as flocculants or coagulants or, in case the liquid is or includes an emulsion, in particular one stabilized by the presence of solids, individual chemicals or combinations of various chemicals known as demulsifying agents which, through their specifics actions, promote removal of the particles and destruction of the emulsion. All such chemicals are hereinafter referred to as flocculants.

In the past, efforts have been made to improve centrifugal separation by adding such flocculents to the slurry preliminary to feeding it to the centrifuge. However satisfactory results have not been obtained in that increased solids recoveries have been so disappointingly low as to be uneconomical for most purposes. In consequence, it has been assumed that flocculants act with very low efiiciency under the conditions involved in centrifugal separation.

The object of this invention is to provide a centrifuge having novel combination of structure for bringing flocculants together with the slurry and causing the same to act effectively to cause separation from the liquid of solids particles which are not separable therefrom by practical centrifugal force levels alone, providing substantial and economical yields of such particles from the centrifuging operation.

The centrifuge according to this invention is of the socalled solid bowl type in which slurry is continuously fed into the rotating bowl and the clarified liquor or effluent thereof continuously overflows therefrom. Means are provided to form a shallow pool of slurry within the bowl, of small depth compared to the bowl diameter, so that the differential in centrifugal force between the outer and inner faces of the pool is small and the pool is subjected throughout its depth to substantially the maximum centrifugal force of the rotating bowl. This means that the agglomerates formed by chemical action are separated by centrifugal force substantially as rapidly as they form and consequently before they flow with the liquid to any substantial extent. This is an important attribute, because I have found that chemically-induced agglomerates tend to redisperse under flow conditions, particularly if subjected to violent agitation, and once this occurs the degraded agglomerates do not reform readily or substantially without additional chemical treatment.

Preferably, the centrifuge is also equipped with means for continuously removing the separated solids from the bowl, this means taking the form of a conveyor coaxial with the bowl having helical blade or blades disposed in 'ating as a thin top layer on the bowl pool.

Patented Jan. 11, 1966 the pool and extending into the solids bed. By rotating the conveyor in the same direction as the bowl but at a small differential, a slow relative rotation of the bowl and conveyor is obtained, so that the solids may be continuously advanced to and discharged from one end of the bowl. Due to its slow relative rotation the conveyor does not agitate the slurry pool to cause turbulent flow, which would be adverse to effective chemical agglomeration. In addition to maintaining substantially constant liquidsolids conditions in the pool, the conveyor also acts to cause the liquid to flow in a spiral path about the bowl axis. For purposes of the present invention, this is desirable since it sub-divides the pool into one or more (depending upon the number of blades in the conveyor) relatively narrow streams which facilitates certain applications of the chemical as hereinafter described and, in addition, prevents any axial short-circuiting of flow which might tend to decrease the dwell of some of the liquid in the bowl.

In accordance with the invention, means are provided for feeding two different flocculants to the slurry at two different locations spaced apart from each other. In many cases the first flocculant added produces by itself very little flocculation or agglomeration, but instead it may condition the slurry so that it can be effectively acted upon by the second addition. In other cases the flocculant may be formed by the interaction of the two separate chemicals with each other in the presence of the slurry, as in the case, for example, with the use of lime and alum, in which case simultaneous addition of both chemicals at the same location produces poor results. In such cases, one of the chemicals must be added to the slurry sufliciently in advance of the other so that it becomes uniformly distributed in the slurry before the addition of the other.

The extent of spacing, both in terms of time and of distance, between the two separate additions, may vary considerably depending upon the precise nature of the slurry as well as upon the identity or nature of the chemicals added.

For best results, the second addition must be made to the pool within the bowl between adjacent turns of the conveyor blade. Liquids-solids slurries are fractionated under centrifugal force so that the pool is actually formed of two or more layers of liquid-solids suspensions of different properties and consistencies, only one of which may contain the suspended solids fraction which needs chemical agglomeration to be extractable by centrifugal force. Chemical addition to the pool within the ma chine, therefore, desirably selectively treats only those sollds requiring chemical agglomeration for settling. Some slurries contain an emulsion in which fine particles are suspended, this emulsion being lighter than the remaining liquid-solids mixture of the slurry, and fraction- In such cases, it is advantageous to add the demulsifying agent to the slurry in the pool and direct it to or into the particular layer which the agent is designed specifically to treat.

Another important factor as regards the point or points of the second chemical addition is that the dwell time of the liquid component to which it is added in the bowl pool, after such addition, be sullicient to permit the chemical substantially to exhaust its treating power on the materials on which it is intended to act and to give the treated fractions the maximum dwell possible under centrifugal force. To this end, I prefer to feed the slurry into the bowl adjacent the end opposite the liquid discharge end so that the liquid component must flow for substantially the full length of the bowl before it is discharged, thereby providing a maximum dwell of liquid in the bowl. The second addition of chemical to the slurry is preferably made to the pool as close as possible to the slurry feed point, so that a substantial dwell time of chemically treated slurry in the bowl is available.

The point at which the first addition of flocculant to the slurry must occur is spaced from the second addition, as pointed out above, by an extent which depends upon the nature of the slurry and of the flocculant.. Where the flocculants are of such a type that a short time delay only is neededbetween the first addition and the second, the first addition to the slurry may occur at a different point in the bowl pool, spaced from the first. If a somewhat longer time delay is required, the first addition to the. slurry may be made at or near its entrance into the feed compartment. Where a still longer time delay between the first and second additions and/ or a more thorough dispersion or intermingling of the first addition into the slurry is desired before the second addition is made, the first addition may be made to the feed slurry during or in. advance of its entrance into the centrifuge, as for example in the feed tank.

The machine of the invention includes separate feed lines connected or connectable to different discharge locations so that selectively the same chemical may be applied to the slurry at several points or different chemicals or concentrations of a. chemical may be fed to the slurry at different points. Further, at least some of the discharge means are desirably adjustable so that their points of chemical discharge. to the slurry may be individually varied.

The foregoing and other features and advantages of the invention will be more fully described with reference to the accompanying drawing, showing only preferred embodiments, wherein:

FIG. 1 is a view partially in vertical longitudinal section, partially in side elevation, in part broken away, of a centrifugal separator and certain auxiliary equipment according to the invention,.and

FIG. 2 is a fragmentary vertical longitudinal section view of a modification of the embodiment of FIG. 1.

Referring to FIG. 1, the centrifugal separator has a casing. Which houses the rotatingbowl and conveyor assembly of the machine. The bowl 12 has fixed to its opposite ends hollow shafts 14 and 16 extending rotatably through the opposite ends'of. casing 10 and supported in suitable bearing mounts (not shown) outside each end of the casing. Shaft 14 constitutes the drive shaft for the. assembly and has fixed to its outer end a belt drive sheave .18 by which the assembly may be rotated from a suitable power source (not. shown). Shaft 16 is connected at its outer end to a reduction gear unit 20 through which, in well known manner, the rotation of shaft 16 causes'rotation in the same direction at a slight speed differential of a shaft 22 rotatably journaled within shaft 16 and coaxial therewith. Shaft 22 is fixed to the corresponding end of conveyor24, the opposite end of which has a hollow shaft 26 rotatably journaled within bowl drive shaft 14. 7

As shown, conveyor 24 is formed of a cylindrical hollow casing 28 to the opposite ends of which the shafts 22 and 26 are secured and to the periphery of which is secured one or more (one being shown) conveyor blade 30, projecting therefrom to adjacent the inner surface of the bowl. Blade 30 is so directed and pitched as to convey the solids deposited on the inner surface of the bowl to the solids discharge end, which is the right-hand, end of the embodiment illustrated in FIG. 1.

Bowl 12 may have various shapes but as shown has a cylindrical. section and a frusto-conical section, the latter section being located at, and diminishing in diameter toward, the solids discharge end. Conveyor blade 30 is dimensioned to conform to the bowl shape and so as normally to provide a substantially uniform clearance from the inner surface of the bowl. A ring 32 projects radially from the outer surface of the bowl adjacent the solids discharge end and to, this ringis secured the annular base of a spider 34 which is'fixedly connected to the drive shaft 14. A ring 36 projecting inwardly from casing 10 and closely clearing the base of spider 34 forms with the adjacent end wall of casing 10 a solids discharge compartment 38 into which the solids are progressively dis charged by the action of the conveyor, through the adjacent open end of the bowl and between the arms of spider 34. Impeller blades 49 mounted on a portion of conveyor hub 28 projecting beyond the solids discharge end of the bowl, and having their inner edges close to this bowl end, facilitate solids discharge into compartment 38. Solids are continuously discharged from compart ment 38 through an outlet (not shown) in the base thereof.

At the opposite end of the bowl, an outwardly pro jecting annulus 42 has secured thereto an end closure plate 44'which is provided with'apertures in the form of slots 45. Weirs 46 are adjustably mounted on plate 44 so that they may be adjusted toward and away from the bowl axis to form adjustable dams over which the efiluent must flow in escaping from the bowl through slots 45, and thus defining the depth of the pool maintained in the bowl.

Within the hollow casing 28 of the conveyor, a transverse wall 48 adjacent the solids discharge end of the bowl defines one end of a slurry feed compartment, the opposite end of which is closed by a flange on shaft 26 and 'a cooperating inwardly projecting ring on the conveyor casing to which it is attached. A stationary slurry feed pipe 50 extends axiallythrough the hollow core of conveyor shaft 26, said shaft being rotatable about pipe 50. Pipe 50 is provided adjacent its inner end with an outlet opening 52 into the feed compartment and at its other end is connected by T connection 54 and. pipe 56 with a suitably regulated source of constant slurry flow (not shown). The slurry discharged into the feed compartment receives there its initial acceleration toward the ultimate rotaryspeed of the bowl, to which the slurry is discharged from the feed compartment through outlet 7 openings 58in the wall of casing 28.

A first chemical feed pipe 60 extends through slurry feed pipe 50 and has its inner end turned downwardly to discharge into the core of the slurry stream. passing into the feed compartment through the outlet 52. Pipe 68 is connected to a first chemical supply tank 62 through a flow regulator 64 and a flow control valve 66. A second chemical feed pipe 68 also extends through the slurry feed pipe 50 and has its inner discharge end extending through the closed end wall of feed pipe 50 and also through wall 48 into a compartment in casing 28 of conveyor 24 formed between wall 48 and a second transverse wall 70 in casing 28. Pipe 68 is connected .to a second chemical supply tank 71 through flow regulator 72 and flow control valve 74 .and intermediate piping.

Nozzles 76, 78 are arranged to discharge chemical from between the walls 70 and 48 to the bowl pool. Preferably, they are adjustable in length, for example, being exteriorly threaded and received through threaded bushings in the casing 28 so that they may be selectively positioned with their outlet ends located beneath the inner surface of the bowl pool (indicated by the dotted line P in FIG. 1), as in the case of nozzle 76, or they may have their outlet end located above the pool surface, as in the case of nozzle 78. It will be appreciated that wall 48 rotates around stationary feed pipe 68. As shown, clearance is provided between the wall and the pipe for this purpose as there is little likelihood of leakage between the slurry and chemical feed compartments, but, if desired, Wall 48may be connected to pipe 68 through a rotary seal.

The arrangement shown permits feeding of flocculant to the slurry both as it enters the slurry feed compartment and after it has entered the bowl pool. More or less than the two nozzles 76, 78 shown may be provided for discharging flocculant from the flocculant feed compartment, and they all may be adjusted to discharge the chemical below or above the inner surface P of the pool. Flocculants that are different either in nature or in concentration may be supplied through the two pipes.

Flocculant supplied through the pipe 60 is thoroughly intermixed with the slurry by the agitation produced as the slurry is accelerated toward the rotational speed of the bowl in the slurry feed compartment and discharged through the openings 58 to the bowl pool. The agitation involved in this acceleration is completed before the chemical has time to act on the slurry and therefore does not interfere with its operation. After the chemically treated slurry enters the bowl pool it remains in a relatively quiescent condition, flowing smoothly in the helical course provided between conveyor blades 30 toward the left hand end of the bowl as shown in FIG. 1, where it is discharged over dams 46 into an effluent discharge compartment 80 formed between the end wall of machine casing and the end of the rotating bowl and conveyor assembly. The efiiuent is continuously withdrawn from the bottom of compartment 80 through a suitable outlet (not shown). Thus, the chemical applied through pipe 60 acts on the slurry throughout its period of dwell in the pool and while it is in a relatively quiescent state, as is ideal for its effective action. It will be noted that the slurry feed is located at the maximum practical distance from the liquid discharge end of the bowl. This is desirable since it forces the slurry liquid to travel the full length of the bowl before discharging as efiluent, and also insures that all of the slurry liquid will flow past any point of chemical addition to the pool.

Particularly where the flocculant is lighter than the slurry and tends to concentrate at the inner surface of the pool, or where a light liquid phase tends to fractionate to the inner surface of the pool, it may be desirable to provide means for insuring a thorough mixing of flocculants with the slurry in the pool. To this end, there may be provided one or more (one shown) annular bafiie 82 attached to and surrounding conveyor casing 28 between turns of blade 30, the baffle extending in a plane substantially normal to the bowl axis below the surface of the liquid. In order to reach the effluent discharge end of the pool, the slurry liquid must pass from one side to the other of the bafiie and therefore must pass under it, with a tendency for the top layer of the pool to mix with underlying portions.

In certain cases it may be desirable to supply chemical from one of the supply tanks only to both feed pipes 60 and 68, or to switch either or both tanks from one feed pipe to the other. To this end, cross-connecting pipes 84, 86 may be provided connected at one end to control valves 66 or 74 and at the other end to the other pipe 60 or 68. In such case, valves 66 and 74 are adapted to switch all or part of the flow to pipe 84 or 86 and thereby to the other feed pipe 60 or 68.

FIG. 2 is a fragmentary view of apparatus similar to that of FIG. 1 but illustrating a modification, parts which are the same in the two figures being designated by primes of their reference numerals in FIG. 1. In the FIG. 2 modification, a third chemical feed pipe 90 is provided extending through slurry feed pipe 50' and may have its outer end connected to a third source of chemical (not shown) which may be similar to the source tanks and connections shown in FIG. 1. A third wall 92 within the conveyor casing 28' and inclined to the axis thereof forms two chemical receiving compartments between wall 92 and walls 48 and 70 respectively. Feed pipes 90 and 68' extend through wall 48 (which is rotatable with respect thereto), pipe 90 terminating in an outlet between walls 48 and 92. Pipe 68 extends through wall 92 (which is also rotatable with respect thereto), with its outlet located between walls 70' and 92. The nozzle or nozzles 7 6' discharge into the pool the chemical fed from pipe 68 and the nozzle or nozzles 78' discharge to the pool the chemical fed from pipe 90. Pipe 60 is available to discharge chemical into the slurry entering the slurry feed compartment, as in FIG. 1 embodiment. Wall 92 is inclined to the bowl axis to provide in each chemical feed compartment a maximum of conveyor casing wall space between helical turns of blade 30' in which nozzles may be inserted if more than one in each compartment is desired.

The arrangement of FIG. 2 make it possible to feed two different flocculants to the bowl pool separately and simultaneously at different points in the direction of liquid flow. By employing both pipes 68 and there is provided a minimal separation between the two additions, different adjustments of the two nozzles 76', 78 making it possible to feed two chemicals to the slurry pool at different distances from the bowl axis. Thus, as shown, the nozzle or nozzles 76 may discharge below the pool surface and the nozzle or nozzles 78 at or above the pool surface. In the case of slurries which tend to fractionate in the pool into layers of distinct solids-liquids compositions for which different chemical treatments are desirable, this arrangement permits such layers to be separately treated with the desired chemicals.

While there will be in general at least two feed pipes discharging separately to the slurry and connectable to two different chemical sources, it will be appreciated that three or more may be used simultaneously, depending on the nature of the slurry to be treated. Multiple feed pipes may, of course, be arranged coaxially rather than side by side as shown.

It should be understood that in the foregoing description of the invention, I have used the term fiocculant, as referring to any fluid which has, or which contains any material which has, when mixed with a liquid-solids slurry, a beneficial effect onseparation by centrifugal force of at least a portion of the solids content from the slurry. Such treating agents may act by flocculating, coagulating or sequestering the individual solid particles into agglomerates which are more subject to separation by centrifugal force. They may also act by breaking an emulsion or complex in which the particles are bound, or in other ways. They may or may not be beneficial to separation of solids from the particular slurry concerned under ordinary gravitational settling conditions.

By means of the apparatus of the present invention, I have found it possible to treat slurries of various types with appropriate such flocculants to produce substantial increases in solids recovery which are not obtainable by adding the same agent or agents, even in greater quantity, to the slurry in the feed tank preliminary to feeding it to the centrifuge. Slurries so successfully treated have included simple water-solids mixtures such as aqueous suspensions of fine clay particles and more complex slurries such as digested sewage sludge and oil-water emulsions from refinery waste containing suspended fine solid particles.

The diameter of the bowl and the speed at which it is rotated may vary widely, depending upon the nature of the slurry, the capacity needed and the amount of centrifugal force required. In general, in order to insure maximum separation they should be such as to produce high centrifugal force on the pool, of the order of up to 3,000 X gravity or more.

It should be appreciated that I have described and illustrated on'ly preferred embodiments of the invention and that various changes may be made in details thereof without departing from the spirit and scope of the invention.

I claim:

1. Apparatus for separating solid particles from liquid which includes a rotatable solid bowl adapted to receive a stream of the fluid-solids slurry to be separated, said bowl having end outlets for discharging the liquid and solid fraction separately therefrom, said liquid fraction outlet being positioned to maintain an annular pool of slurry within the bowl of a depth which is a small fraction of the bowl diameter, said pool extending substantially the full length of the bowl, a conveyor rotatably, co-' axially mounted within the bowl and having a blade ex tending helical'ly of the bowl axis and projecting into said pool, means connected to the bowl and conveyor for rotating the same at a small differential speed in the same direction such as to maintainv said pool under high centrifugal force, so that solids of said slurry are concentrated against the bowl and are progressed to said solids discharge outlet by said conveyor blade, and flocculant feed means associated with said slurry supply means for adding fiocculant to said slurry, including two supply tanks each containing a different flocculant, and separate feed lines to feed flocculant from each tank to said slurry before the slurry has been subjected to substantial centrifugal action in said bowl, at least one of said feed lines extending into said bowl to discharge flocculant to said slurry pool between adjacent turns of said conveyor blade, and the other of said feed lines having its inlet positioned to discharge flocculant to said slurry in advance of said said one feed line.

2. Apparatus as claimed in claim 1 wherein one of said flocculant feed lines includes nozzle means extending into said pool for discharging the flocculant below the pool surface.

3, Apparatus as claimed in claim 1 wherein said floc- 8;: culant feed lines each include a compartment in said conveyor, each compartment separated from the other, and nozzle means for discharging fiocculant from each of said two compartments, one of said nozzle means having its outlet disposed above, and the other having its outlet disposed below, the surface of said slurry pool.

4. Apparatus as claimed in claim 1 in which said slurry supply means includes a compartment within said conveyor through which the slurry stream is fed and in which the slurry is initially accelerated to a rotary speed approching that of the bowl, and one of said flocculant feed lines discharges into said slurry stream as it reaches said compartment.

References Cited by the Examiner UNITED STATES PATENTS 2,308,559 1/1943 Winkler 2337 X 2,685,369 8/1954 Crossley 233-14 X 2,867,582 1/1959 Shuman et al. 3,096,282 7/1963 Trotter 233--7 M. CARY NELSON, Primary Examiner. H. KLINKSIEK, Assistant Examiner.

Claims (1)

1. APPARATUS FOR SEPARATING SOLID PARTICLES FROM LIQUID WHICH INCLUDES A ROTATABLE SOLID BOWL ADAPTED TO RECEIVE A STREAM OF THE FLUID-SOLIDS SLURRY TO BE SEPARATED, SAID BOWL HAVING END OUTLETS FOR DISCHARGING THE LIQUID AND SOLID FRACTION SEPARATELY THEREFROM, SAID LIQUID FRACTION OUTLET BEING POSITIONED TO MAINTAIN AN ANNULAR POOL OF SLURRY WITHIN THE BOWL OF A DEPTH WHICH IS A SMALL FRACTION OF THE BOWL DIAMETER, SAID POOL EXTENDING SUBSTANTIALLY THE FULL LENGTH OF THE BOWL, A CONVEYOR ROTATABLY, COAXIALLY MOUNTED WITHIN THE BOWL AND HAVING A BLADE EXTENDING HELICALLY OF THE BOWL AXIS AND PROJECTING INTO SAID POOL, MEANS CONNECTED TO THE BOWL AND CONVEYOR FOR ROTATING THE SAME AT A SMALL DIFFERENTIAL SPEED IN THE SAME DIRECTION SUCH AS TO MAINTAIN SAID POOL UNDER HIGH CENTRIFUGAL FORCE, SO THAT SOLIDS OF SAID SLURRY ARE CONCEN-

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