US2685369A - Coagulation of finely divided suspended solids - Google Patents

Description

Aug. 3, 1954 J.E. cRos'lsLEY coAGULATIoN oF FINELY DIVIDED SUSPENDED soLIDs Filed June 27, 1951.

`2 Sheets-Sheet 1,

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Aug. 3,.v l` 954 COAGULATION Filed lJune 27, 1951 /27v 95 /lz 92 /la J..E. cRossLEY OF' FINELY DIVIDED SUSPENDED SQLIDS 2 Sheets-Sheet 2 FIGA..

INVENTOR.

JAMES E. CROSSLEY avia ATTORNEY.

Patented Aug. 3, 1954 CAGULATION OF FIN ELY DIVIDED SUSPENDED SOLIDS James E. Crossley, Collinsville, Ill., assignor to Allied Chemical t Dye Corporation, New York, N. Y., a corporation of New York Application June 27, 1951, Serial No. v233,757

3 Claims. 1

This invention is directed to improved method l"and means for separation and recovery of liquids from finely divided material suspended therein. More particularly, it is concerned with `such separation procedures in which a flocculat- .ing agent is employed to assist the removal of finely divided insoluble material from suspensions in liquid or solutions.

In separating suspended material and recovery of clear solutions from e. g. slurries or muds, it has been the practice tostore the liquid suspension in large vats to permit settling, whereupon clear liquor is withdrawn by decantation. The solid particles are frequently in such a fine 4,state of subdivision that use of prolonged periods ofsettling prior to decantation and consequent large volume of settling-decantation vessels are required. It will be appreciated that from the standpoint of keeping plant investment. at a minimum, affording maximum output of product from a given installation and providing flexibility of operation, the long settling time and resulting large volume of tanks are serious disadvantages. Various methods, such as diluting the f slurry with greater amounts of' water in order to increase the diierence in density between solution and mud particles and thereby effect an increase in rate of mud settling, have been proposed. However, when it is desired to recover the solution components in concentrated form, resorting to dilution of the mud with water causes a decrease in economy of operation by reason of increased steam costs in evaporating vsaid water in subsequent operating steps` One object of the present invention is to develop improved method and means for separating iinely divided and slow-separating suspended foreign material from liquid containing` the same, particularly such method and means for separating digest mud from mixtures with aluminum sulfate liquors obtained in the sulfuric acid-clay digestion method for manufacturing alum.

The invention and the manner in which the objects stated above are accomplished may be understood by considering the drawings in which like reference numbers designate equivalent iparts on the various figures.

Figure l represents an elevation View of one type of machine of the present invention with part of the machine broken away and shown in section. Figures 2 and 3 are vertical and horifzontal sections, respectively, of the central element ofthe rotor of the Figure l machine, illustrating certain variations of the invention. Figluref4 is'an elevation viewof another'type of machine built according to the present invention with certain portions thereof broken-away and shown in section. Figure 5 is a vertical section taken at plane 5-5 of Figure 4.

The invention will first be described in connection with Figure 1, which represents one embodiment. The stationary housing of the machineis indicated generally at IEB .and is securely mounted on supporting brackets not shown. Spider Il supports bearing i2, within which turns shaft l5 driven by belt and pulley lli. Shaft i5 extends through stationary collar Il and is attached at the bottom end to head piece 2li. Head piece 20 has Aa radially disposed apron or skirt 2l having ribs 22 which interlock with ribs 25 on basket or bowl 26, thereby transmitting motion from shaft l5 to basket 2E. Lock ring 2l is provided to permit-dismantling of the centrifugeibasket 26 when desired. Sleeve 3l which surrounds shaft I5 and the upper part of head 2E is supported onskirt 2i and spaced therefrom byknobs 40. Sleeve 3l supports, in turn, conical .discs 46 which are spaced from each other by knobs or detents i8. The weight of basket 26 and its contents arecarried by skirt 2l and shaft l5. The outermost periphery of basket 25 is provided with multiple spaced nozzles 42, communicating with discharge manifold 5i, leading in turn to recirculating line i2-t via ports 53 in the manifold. The rotor, or rotating portion of the centrifuge machine Comprises shaft'l, head 2B, basket or bowl 2t, sleeve 3l and discs 46.

According to the present invention, feed material containing liquid and solid material to be separated, preferably after preliminary settling or classification to remove the largest of the insoluble particles (primarily to reduce attrition on metallic parts) and toprevent plugging nozales ft2, is introduced through pipe 35i and enters the annular space 3l between stationary collars l1 and 32. It will be understood that up until the time the feed material reaches approximately the point 35 at the outlet of annular passage 3l, lthe liquid is still flowing in a ksaid zone having .an Aappreciable radial comp'oneht of-directio'n and in A`which the liquid is nrst subjected to'rapid'rotation and resultant shearing. The liquid feed passes underneath the bottom edge of sleeve 3l (supported on head 2li by multiple knobs lill) and enters separating zone ci of enlarged radial dimension. The present invention provides for supplying ilocculating agent to the feed slurry at such a point in the systemL that the material within separating zone ii is subjected to fiocculation and the effect of enhanced separation of solid particles from liquid produced by reason of the presence of said agents. High centrifugal force in separating zone el produced by the high rotational speed of basket 2GB, coupled with the enhanced ooculating effect of the agent produce the advantageous separation of lines from liquid accord ing to the present invention whereby solid material is induced to pass through multiple nozzles d2 while substantially clear solution or liquid passes through passageways 155 between inclined discs 5. Discs i6 assist clarification of the liquor by providing surface on which the solid particles can settle and inducing by friction outward movement of particles of insolubles that come into contact with the discs. he liquid, under the hydrostatic head of the feed introduced at 3E, passes upwardly through the annular discharge passage between sleeve 3i and basket 2E and over discharge lip il at the top of the basket and into discharge conduit 5cl Part of the underflow discharged through nozzles i2 and entering manifold 5| and recirculating pipe 52 is normally discharged through valve and pipe 55 and part is normally recirculated via pipe 5S and port 5l in the bottom of basket 2@ as indicated by the flow arrows. The recirculated liquid passes through apertures between skirt 2| and bowl 26 into separating zone 4| as shown. Wash liquid may be introduced through valve and piping et if needed.

A particular feature of the discovery of the present invention is that by introducing ilocculat ing agent into the feed stream in such a manner and at such a point in the stream as to effect dispersion of the iiocculating agent through the liquid downstream from the point at which said feed is first subjected to shear, remarkably iniproved separation of solid from liquid is realized. Pursuant to this feature of the discovery inlet pipe ci, communicating with the annular' passage between rotating shaft i5 and stationary collar Il, is provided. Through this pipe the flow of fiocculating agent, supplied from vessel 62 controlled by valve 65 and metered at S5, is supplied. This stream of flocculating agent is added to the main flow of feed material from pipe 3D at the point at which said feed flow is first subjected to the shearing action aforesaid. Since an appreciable interval of time is required to effect dissemination of the occulating agent through the feed material, it is apparent that dispersion of the flocculating agent through the liquid is effected downstream from the point at which the feed is rst subjected to shear. The stream of liquid, now comprising feed plus ilocculating agent, passes downwardly through inlet zone 35, under the bottom of sleeve 3l and into separating zone 4| where enhanced eifect of the ocoulating agent in separating solid from liquid is utilized as described above. Broadly considered, the invention comprises adding flocculating agent at any point between 35 (where the feed is first subjected to shear) and the discharge of separating zone 4|, preferably suihciently adjacent to the point of rst shear to permit adequate centrifuging of the feed to effect dispersion of the flocculating agent in zone 36 and separation of solid in zone 4| before discharge of liquid and solid from separating zone 4|. A particular embodiment of the invention comprises adding fiocoulating agent prior to the point at which the stream enters separating zone fil, i. e. be tween points 35 and de which dene the radially directed inlet zone.

Modifications of the invention are illustrated in Figures 2 and 3 which provide for introduction of iiocculating agent through axially disposed passageway El in shaft I5 and subsequent flow of the agent through multiple radial passages lil in head 25. The feed material is first subiected to shear above the outlet of passage lil and hence the fiocculating agent and feed are mixed in inlet zone SiS after the point at which the feed is first subjected to shear.

A further embodiment of the invention provides for removing threaded plugs 12, inserting similar plugs in passageway l and provide for iiow of occulating agent only through radial passageways '12. The latter arrangement also contemplates introducing the flocculating agent within inlet zone 35 after the feed is first subjected to shear and before the feed enters separating zone l.

Figure 4 represents a different, i. e. horizontal type centrifugal machine constructed according to the present invention. Pulley 85, driven by belts and motor not shown, is connected via flange BS to cylindrical sleeve 8'.' rotating on bearing 9B within pillow block Si. Sleeve 8'! is connected to centrifugal basket indicated generally at 92, housed in stationary casing 93, said basket come prising cylindrical section 95 and end wall sections 96 and 91, all of which are adapted to rotate at high speed about their horizontal axes. Vtfall section @l is connected to sleeve Hit which engages a gear unit not shown on the drawing. The motion of pulley S5 and bowl or basket $52 is transmitted through said gear unit to internal shaft lGi (separated from shaft I by packing |82), trunnion |135 and conveyor hub it. At its opposite end, hub Hifi is connected to internal sleeve lill', which rides on bearings |I|- and is separated from shaft 8'1' by packing Hi. Hub |68 is provided with helical conveyor blades H2 which, by reason of the slight relative rotation between bowl 32 and hub it, adapted to move material within the bowl to the end of the machine represented by the left end of the Figure fr drawing.

Feed slurry (preferably after preliminary settling or classification to remove the largest particles of solid) enters the machine through pipe i i5 and passes through the annular space between inner wash pipe |16 and pipe il?. The feed emerges from said annular space and en ters inlet zone H8 formed between the outlet of pipe il and separating zone l2?. The feed first falls into pool i2@ on the inside of hub |86 and between partitions |2| and |22, said pool being in the form of a cylinder by reason of centrifugal force. Feed liquid overflows from pool 52D into multiple overflow pipes |25 and enters separating zone |27 internally of bowl 92. Pipes 52d, which facilitate rotational flow of liquid thereby minimizing disturbance of the liquid as it enters pool E32 in separating zone |21 may be short as shown in Figure 4, or may extend into pool |32. Due to high centrifugal force, the denser solid particles of the mud tend to concentrate on the inner surface of cylinder 95 and are pushed to the left forming bed |28 which is discharged over a Weir 30 into the underflow connecting manifold 3| in stationary casing 93. Underiow is forced from manifold |3| by means of plow |33 attached to end Wall 91 and discharged from manifold I3! through a port not shown, near the bottom of the casing.

'Ihe overnovv from bowl S2 builds up in pool |32 in separating zone l2? and the clear liquid near the axis of bowl 92 overflows through discharge ports |35 into overflow collecting manifold |31 in casing S3. rThe overiiow is likewise withdrawn from the casing through a port near the bottom of the casing which is not shown in the drawing.

In the manner indicated above, the present invention provides for supplying an agent having iiocculating properties in separating zone l2? land subjecting the feed while in said zone to the combined action of said agent and centrifugal force thereby markedly to increase the effectiveness of the centrifugal force in separating the materials of different densities, i. e. the less dense liquid and the relatively more dense dispersed solid. The liquid flowing through the Vannular space between pipes I8 and Ill is non- -rotating as distinguished from rotational iovv,

i. e. the flow of a body of rapidly rotating liquid in a centrifuge machine. The stream is'rst subjected to the shearing action as it enters pool 42d, Accordingly, the invention broadly comprises adding iiocculating agent in the region from pool |29, to discharge ports |36 preferably in inlet zone H8.

A particular embodiment of the invention com.- prises supplying an additional partition |38 to the right of partition i212 forming a zone M0. containing flocculating agent in pool Idl which overiiows through multiple radially disposed distributing pipes m2 into separating zone l2?. Pipes m2 which may be short as shown or may extend into pool |32 facilitate rotational flow of flocculating agent entering pool i3d, thereby minimizing disturbance of the liquid. Flocculating agent is supplied to Zone i2? through feed pipe lil@ which communicates with annular passage |41 between external pipe its and pipe l l1, said. annular passage discharging into pool fil. A flow of flocculating agent from pipe ifii is established from storage vessel E50 Via flow control valve |5| and meter |52. According to the latter embodiment of the invention, fiocculating agent and feed are first mixed substantially at the end of inlet Zone lid, i. e. after the feed is first subjected to shear so as to permit dispersion of agent through the feed after iirst shearing the feed liquid.

A further embodiment comprises omitting partition so that riocculating agent from annular space ifi'i enters pool '12B directly, thereby effecting dispersion of occulating agent through the feed liquid after the point at which the feed is rst subjected to shear, i. e. pool |20. The mixture thereafter fl ws through pipes |25 (preferably elongated to reach pool |32) into the pool. If desired, pool ld and distribution pipes i2 also may be dispensed with and feed and flocculating agent permitted to fall directly into pool |32 in separating zone i2?. It will further be noted that, in accordance with the principles stated above, introducing iiocculating agent into pool i2@ or directly into pool E32 provides for addition of agent in the region from the point at Which the feed is first subjected'to shear (pool or pool |32, as the case maybe) to overow pipe |35 at the discharge end ofseparating zone 'As exemplifying the size of machinesuitable for the purpose of the present invention, in the Figure 1 apparatus, the inside diameter of the .basket 26 may be 9 inches. The distance from port 51 to discharge lip el' may be 9% inches. The outside diameter of apron 2| may be 6% inches. The approximate length of inlet Zone 3E, i. e. between points 5 and i0 may be 5 inches. Separating zone d! may have capacity of 2 gallons. Discs 46 may be 28 in number, disposed at 45 from the horizontal and l-Z- inches long in section. With respect to the Figure 4 apparatus, cylinder 95 may 18 inches in diameter and the distance between end walls iii and Si' may be 28 inches. Separating .Gone i2? ymay have capacity of 5 gallons. The Figure l apparatus may suitably operate at about ddd@ to 9000 r. p. m., thereby producing centrifugal force of 5460 to 19,003 times gravity; and the ie e apparatus operated at 2000 to 2500 r. p. m. thereby producing a force equal to 1000 to i500 times gravity. The principle of this invention applies when operating u ithany elevated degree of centrifugal force, but lower forces generally require longer retention time in the separating zone, as described below. Hence it is preferred to operate with centrifugal force not less than about 100) times gravity. The use 0f this invention is not limited to machines of the above dimensions since such dimensions vary in accordance with type and size of equipment.

The foregoing method and apparatus have general application where it is desired to separate nnely divided insoluble material from liquid containing the Specific instances for using the present invention include recovery of sulfuric acid from sludge obtained via scrubbing impure sulfuric acid synthesis gases; removal of gypsum from phosphoric acid in the manufacture thereof by treatment of phosphate rock with sulfuric acid; removal of solids from mixtures resulting from the treatment of aluminous materials with acids and allralis; and recovery of oxide of titanium from ilmenite ore.

The flocculating agent employed in each instance may depend largely on the particular foreign materiai to be removed and the particular solution to be clarified. Suitable flocculating agents which be mentioned include prosein (a protein material derived from soya bean) gluesuliide (equal parts of animal glue and sodium sulfide) and animal glue alone. In each case the flocculating agent is first dispersed in a suitable solvent such as water to facilitate distribution thereof through the material to be treated.

It has been found that the method and apparatus outlined above may be advantageously applied to separation of aqueous aluninum sulfate solutions from insolubles in the manufacture of aluminum sulfate by the sulfuric acid-clay digestion process. In the commercial process for maxing aluminum sulfate from clay or other aluminous material, the starting material, either in the raw state or after calcination to remove water and render the clay more susceptible to subsequent attack by sulfuric acid, is digested with strong sulfuric acid to convert the combined aluminous materials in the clay to aluminum sulfate. rThe product of digestion is diluted with water or Weak aluminum sulfate soiution to dissolve out sought-for aluminum sulfate. The slurry so formed is introduced into large settling tanks to permit undissolved and insoluble portions of the clay (referred to as digest mud) tosettle until'theheight of the-mud level drops to about or less of the total column of diluted reaction mixture. Clear supernatent liquor is Withdrawn through stand pipes and concentrated in steamheated evaporators to alum, cake strength. The mud may be reslurried in Water and subjected to resettling to recover' aluminum sulfate present in mud liquor. The solid particles of the digest mud are generally in such a fine state of subdivision that use of prolonged periods of settling prior to decantation, e. g. up to 24 hours or more in some cases and consequent large volumes of settling-decantation vessels are necessitated. .ficcording to the present invention, more eifectivc and efficient recovery of clear aluminum sulfate solution from aluminum sulfate slurries may be realized Without incurring the disadvantages of increased steam costs for evaporation or excessive investment in unduly large settling tanks which were inherent in previously proposed method and means (i. e. dilution of slurry to increase density differences and thereby speed settling) for improving recovery of aluminum sulfate.

It has been found that in the case of aluminum sulfate recovery, animal glue is a particularly eiiective locculating agent, said glue being used according to the method and means described generally and in detail above. Hence, one specific embodiment comprises supplying means for and utilizing glue as iiocculating agent in recovery of aluminum sulfate from slurries according to the invention described above. For example a rapidly rotating body of liquid is maintained in a centrifuge machine and a non-rotating stream of slurry7 to be centrifuged is added to the rotating body thereby to create a zone of shear between the feed of non-rotating slurry and the rotating liquid. Centrifuged clear liquid is withdrawn from the rotating body. An aqueous glue solution is introduced to the rotating body of liquid substantially in the region but after the point at which the slurry feed stream is first subjected to shear upon introduction into the rotating body of liquid undergoing centrifuging.

The ilocculating agent, e. g. glue used in amount sufdcient to effect the degree of removal of insolubles desired. Excessive amounts of glue do not appreciably increase the emciency of clariiication. A suitable concentration range of glue in the aluminum sulfate solution affording usual enicient operation without undue Waste of glue is 0.50 to 1.12 grams of dry glue per gallon of solution to be clarified.

A further signiiicant variable is the concentration of glue in the glue solution to be added to the slurry. In concentrations below about 0.1 lb. of dry glue per gallon of Water appreciable decrease in effectiveness of the fioccuiating agent may be noted and hence concentration is preierably maintained not less than about 0.1 lb. of dry glue per gallon of water. To facilitate dispersicn oi the locculating agent into and through the process material and efficient utilization of glue, concentration of glue in the solution is preferably maintained not greater than about 0.2 lb. per gallon of Water although higher concentration may be used ii desired. By maintaining glue solution concentration in the range approximately 0.1 to 0.2 lb. per gallon of water, adding such solution at the rate of about 30 cc. or more per gallon of aluminum sulfate slurry to be clarified, according to the technique outlined above, effective clarification of the aluminum sulfate digest mud may be obtained.

The slurry being treated is retained in the centrifuge machine under the influence of flocculating agent and centrifugal force for time sumcient to effect the degree oi clariiication desired. As previously indicated, the effect of centrifugal force producing separation of insolubles is aided by the presence of discs in the separating zone, and hence the retention time required for eective clarification Will be determined by the presence of the discs as Well as the centrifugal force. lThe retention time, of course, Will be controlled by the rate of flow of feed material and influenced by the volume of the centrifuge bowl or .it will be understood that generally, large volume machines will accommodate larger ilow rates While still affording the required retention time and, conversely, small volume machines will normally accommodate only smaller oW rates. Using a machine of the type described in Figure l, having dimensions and operating according to the procedure described above, retention time of the order of 0.56 to 0.25 minute (corresponding with rates of now of feed of 3 to 8 G. P. M., respectively) may be found to produce suitable olariiication. Operating with the type of machine described in Figure i. having dimensions indicated above and operating according to previously described procedure, retention times in the range approximately 5 to i minutes (corresponding with feed rates ci 1 to 5 G. P. M., respectively) niay be suitable. For any given installation and set of conditions, retention time and rate of flow of feed may best be determined by making test runs and noting results.

Requirements oi product quality may vary, but in manufacture of high grade alum, it is preferred to reduce content of insoluble in the claried solution to below about 0.1% (corresponding with about .25% based on the nal 17.2% 1.12633 solid product). Eiilciency of clarification may be measured by the volume ratio of overflow having acceptable clarity to underflow (containing the majority of the insolubles). In the interest of high capacity and eificient operation, and to reaiize advantages of the invention, conditions are preferably maintained so as to produce volume ratio of overiiow (having not more than about 0.1% insolubles) to underflow not less than about 3.

rShe apparatus and procedure of this invention were found to be eifective in clarifying aluminum sulfate solutions of substantially any AMSOQS strength, e. g. in the range 1 B. to 40 B. Within the limits oi operativeness of the iiocculating agent, the procedure may be carried out at any temperature, i. e. temperatures as lov.l as '70 F. and as high as 200 F. have been found to be suitable in clarifying aluminum sulfate digest muds with glue as flocculating agent.

The clarification procedure of the invention has been described chiefly as being carried out continuously, but batchwise operation is not thereby excluded. For example, a batch of feed material may be introduced to the centrifuge basket, a proportionate amount of ilocculating agent added thereto, the mixture centrifuged, sediment removed from the basket and the clariiied solution subsequently recovered.

Although this invention is not limited to any speciiic theory, I believe that the occulating agent in some fashion probably causes agglomeraticn or flocculation of the finely divided and slow settling particles into relatively larger, more rapidly settling agglomeraties or ilocls, thereby facilitating separation of insolubles from the body of the solution. When the feed stream passes t rough the zone of shear upon entering the rotating'basket oi the centrifuge, any such flocks or agglomerates previously formed are somewhat disintegrated, thereby diminishing the previous beneiicial result of flock formation. Hence, according to a particular embodiment of the invention, by adding rlocculating agent in the region from the point where the feed stream is first subjected to shear to the separating zone, the docks or agglomerates after once being formed are not subjected to further shearing or other violent agitation which might result in breaking up of the agglomerates. Hence, the effect of flock formation .in improving settling characteristics is preserved until the suspension reaches the separating zone wherein insolubles and solution are separated from each other.

The following example illustrates practice of the present invention carried out with apparatus described in Figure l., the parts and percentages being weight.

Erw/cple The sulfate. slurry chosen for test was produced by .l lurc acidtreatment of calcined clay. Frio-r to centriuging, the slurry was permitted to settle for a shorJ time to remove the largest particiesvof insolubles. This slurry, hav' 3.8% solids, aluminum sulfate content eq .aient to 8.48% AlzOe. and speciic gravity of 37.10 at 60 F., was introduced at the rate of 5.1i G. P. M. through feed pipe 3e of the Figure 1 apparatus. rihe feed temperature was 190 F. (34.6 B). rThe machine speed (no load) was 6,5m R. P. lvl. Nogales i2 were .052 inch in diameter. in aqueous glue solution containing 1.5 at glue on a dry basis was introduced through pipe Si at the rate of 30 cc. per minute per gallon aluminum sulfate slurry (corresponding with 0.001 lb. per minute of dry glue per gallon aluminum sulfate slurry). No wash Water was introduced through pipe and valve Underow was withdrawn from pipe and valve at the rate oi 1.3 G. P. M. and overiiow through pipe t at the rate of 4.1 G. P. M. With these conditions the overflow contained 0.06% solids (which corresponded with 0.3% solids based on the 17.2% A1203 aluminum sulfate produced after evaporation of the solution) and was 35.5 B. at 60 F. The underiiow contained 17.3% solids and was 37.8 Be. at 60 F. The percentage of feed solution recovered in the overflow was 80% and the recovery oi solids in the underflow was 99%.

The foregoing example illustrates single pass operation. If desired, the underiiow, containing substantially all of the solids and a certain amount of the aluminum sulfate present in the orieinal feed, may be reslurried with additional water, then treated again in a separate centrifuge machine with additional occulating agent to eiect recovery of residual amounts of aluminum sulfate. By such treatment of digest muds in a series of centrifuging operations, any desired proportion, e. g. preferably $38 to 99%, of the original aluminum sulfate may be recovered as clear aluminum sulfate solution.

I claim:

l. A two zone continuous method for separating iinely divided suspended solid material from liquid containing the same which comprises in a first dispersing zone rotating a body of said liquid containing finely divided suspended solid material without substantial turbulence about an axis in a dispersing zone disposed near said axis at a linear velocity suiicient to eect dispersion of addediiocculating agent to the rotating body` of liquid in thedispersing Zone without effectingl substantial separation of suspended material from the liquid in said dispersing zone, continuously introducing a non-rotating stream of. liquid containing finely divided suspended material to the dispersing Zone through conduit means located near said axis thereby to create a Zone of shear between said feed of non-rotating liquid and said rotating liquid in said dispersing Zone, continuously introducing through axially disposed conduit means a flocculating agent to said rotating body of liquid in the dispersing zone after the point atA which said feed liquid is first subjected to shear, continuously flowing the liquid containing iinely divided suspended solid material and dispersed occulating agent from the rst rotating body of liquid in the dispersing zone Without subjecting said liquid to shearing and violent agitation which would result in breaking up of iocs to a second separating zone containing a body of liquid rotating about the axis at a higher linear velocity than the rotating body of liquid in the rst dispersing zone and with suiiicient velocity to eiiect separation or" neiy divided suspended solid material from the liquid by centrifugal iorce, continuously removing said seprated solid materialirom the secondzone, and continuously discharging clarified liquid from the second zone.

2. A two zone co tinuous method for recovery of aluminum sulfate solution from liquid containing the same and insoluble mate 1iai produced in the suliuric acid-clay digestion process for manufacture of aluminum sulfate, which comprises in a rst dispel-sing zone rotating a body of aluminum sulfate solution containing insoluble material without substantial turbulence about an axis in a disp-ersing zone disposed near said axis at a linear velocity sucient to eiect dispersion of added flocculating agent to the roeating body of liquid in the dispersing zone without effecting substantial separation or" suspended material from the liquid in said dispersing zone, continuously introducing a non-rotating stream oi' aluminum sulfate liquid containing insoluble material to the dispersing zone through conduit means located near said axis thereby to create a zone oi` shear between said feed or" non-rotating liquid and said rotating liquid in said dispensing zone, continuously introducing through axially disposed conduit means a occulating agent to said rotating body of liquid in the dispensing zone after the point at which said feed liquid is nrst subjected to shear, continuously iiowing the aluminum sulfate liquid containing insoluble material and dispersed iiocoulating agent from the rotating body of liquid in the rst dispersing zone without subjecting said liquid to shearing and violent agitation which would resuit in breaking up of ocs to a second separating zone containing a body of aluminum sulfate liquid rotating about the axis at a higher linear velocity than the rotating body of liquid in the first dispersing zone and with sufficient velocity to eiiect separation of suspended material from the liquid by centrifugal force, continuously removing said separated solid material from the second zone, and continuously discharging clarified aluminum sulfate liquid from said secondzone.

3. A two Zone continuous method for recovery oi aluminum sulfate solution from liquid containing the same and insoluble material produced in the sulfuric acid-clay digestion process 11 for manufacture of aluminum sulfate, which comprises in a rst dispersing zone rotating a body of aluminum sulfate solution containing insoluble material without substantial turbulence about an axis in a dispersing zone disposed near said axis at a linear velocity sufiicient to eiect dispersion of added flocculating agent to the rotating body of liquid in the dispersing zone without eiecting substantial separation of suspended material from the liquid in said dispersing zone,

continuously introducing a non-rotating stream of aluminum sulfate liquid containing insoluble material to the dispersing zone through conduit means located near said axis thereby to create a zone of shear between said feed of non-rotating liquid and said rotating liquid in` said dispersing zone, continuously introducing through axially disposed conduit means a flocculating agent comprising an aqueous glue solution of concentration in the range of 0.1 to 0.2 lb. dry glue per gallon of water and in amount corresponding with 0.50 to 1.12 grams of dry glue per gallon of aluminum sulfate liquid feed to said rotating body of liquid in the dispersing zone after the point at which said feed liquid is rst subjected to shear, continuously flowing the aluminum sulfate liquid containing insoluble material and dispersed iiocoulating agent from the rotating body of liq- References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,356,665 Sturgeon Oct. 26, 1920 1,525,016 Weir Feb. 2, 1925 1,546,871 Thompson July 21, 1925 1,604,427 Spicer Oct. 26, 1926 2,111,788 Klchma Mar. 22, 1938 2,128,393 Allen Aug. 30, 1938 2,138,463 Ayres Nov. 29, 1938 2,190,596 Dorr Feb. 13, 1940 2,245,587 Hughes July 17, 1941 2,312,545 Haug Mar. 2, 1943 2,553,936 Patrick May 22, 1951

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