US2582317A - Tank reactor - Google Patents

Description

Jan. 15, 1952 J DONOHUE 2,582,317

TANK REACTOR I v Filed April 22, 1946 1 5 Sheets-Sheet l I I I -zqb L 1 18 -55 J5 52 as 58 25 INVENTOB W/W/m J. 00/70/7419 Jan. 15, 1952 w, D N 2,582,317

TANK REACTOR Filed April 22, 1946 5 Sheets-Sheet 2 INVENTOR .W/W//WJ 00/70/2149 ATTORNEYS Jan. 15, 1952 w. J. DONOHUE 2,582,317

TANK REACTOR Filed April 22, 1946 5 Sheets-Sheet 5 15, 1952 w. J. DONOHUE 2,582,317

TANK REACTOR Filed April 22, 1946 5 Sheets-Sheet 4 INVENTOR 65 w/mwm/w 1; BY l m, M 972/6 0 ATTORNEYS w. J. DONOHUE 2,5823] 7 TANK REACTOR Jan. 15, 1952 Filed April 22, 1946 5 Sheets-Sheet 5 INVENTOR ATTORNEYS Patentecl Jan. 15, 1952 "I UNITED STATES PATENT OFFICE TANK REACTOR William J. Donohue, Aspinwall, Pa.

Application April 22, 1946, Serial No. 663,971

6 Claims.

1 The invention relates to conducting continuous reactions between a liquid and another material such as a solid or immiscible different p liquid or gas, by the general method of alternately mixing the materials into a suspension and separating them in stages. The principal objects of the invention are to improve the efliciency of such method so as to avoid short circuiting in the mixing steps and thereby provide more perfect control of the mixing time, and to provide apparatus in which these improvements may be 'achieved. More specifically, my apparatus and method insure in the mixing step co-current travel of the liquid and suspended particles. throughout long spiral paths, of controllable length and with controllable velocities. This is effected by the novel manner in which the materials are progressed from stageto stage, and particularly by certain improvements in apparatus adapted to efiect such treatment. The appara tus may be used with little or no variation for liquid-liquid treatment such as solvent de-waxing of oils or acid treatment of mineral oils, for

liquid-gas treatment such as absorption, and for liquid-solid treatment such as leaching, extraction, or liquid causticizing. While my method and apparatus may beused for carrying out various processes, they are specially suited for the causticizing of a solution of a metal salt, such as sodium carbonate by treatment with calcium hydroxide to produce a solution of sodium hydroxide and a precipitate of calcium carbonate. In this application, the liquid and solid entering into the reaction flow through the apparatus in the same direction at all times. In other instances, countercurrent flow from stage to stage may be provided.

In my co-pending application Serial No. 620,898, filed October 8, 1945, now Patent No.

2,539,732, I show and describe apparatus similar,

and in some respects identical, to the apparatus of the present application; but the invention of that application not claimed here relates rather broadly to the manner of progressing the solids and liquids being treated, the structure whereby the compartments are isolated and sealed from one another during shutdown, and other improvements not claimed herein.

In a preferred embodiment, my apparatus comprises a reaction vessel, such as a tank, having a plurality of vertically spaced floors therein. Alternate floors have outlets for descending material at the periphery and at the center, respectively. The spaces above the floors having peripheral outlets serve as agitation compartments and the spaces above the other floors constitute retention or settling compartments wherein the reaction products and the solid material being treated are separated from the unreacted treating liquid. The agitation compartments are provided with tangential nozzles adapted to cause a gentle agitation of the materials contained therein. A liquid (or in some cases a gas) is introduced through the nozzles, causing the materials to rotate about the axis of the tank. Solids (or other material immiscible with the fluid introduced through the nozzles) enter at the center, and travel with the liquid through a long spiral path to the peripheral outlet into the adjacent settling compartment. All the compartments may have rotary means for sweeping solids settling on the floors towards the outlets. When the apparatus is to be used for causticizing sodium carbonate solution or so-called "green liquor by reaction with lime, I provide means at the top of the tank for slaking the lime, CaO, by the Water of the entering solution to produce calcium hydroxide which reacts directly with the sodium carbonate.

In the causticizing of green liquor, the desired end product is usually the sodium hydroxide solution and an important factor in quality thereof is its clarity or freedom from suspended solids, such as minute particles of calcium carbonate. At the same time, it is desirable to use as small an excess of lime as possible over the amount theoretically required for reaction with all the sodium carbonate solution. A certain amount of excess lime is necessary, of course, to cause the reaction to proceed to a conclusion within a reasonable time. Agitation of the reacting materials tends to expedite the reaction but also leads to fragmentation of the precipitating particles which causes the liquid product to be cloudy rather than clear by reason of the presence of small suspended particles. The fineness of the calcium hydroxide delivered to the reaction chamber is also a factor in the size of the particles of the solid reaction product. The clarity of the product is also afiected by the amount of lime which remains unconsumed after reaction has been completed. In accordance with my invention, I utilize liquid jets for obtaining a gentle agitation sufficient to bring all portions of the reacting materials into contact with each other and at the same time avoiding such violent agitation as would prevent the growth of large crystals of precipitate which will settle rapidly in the liquid reaction product. The liquid re- --partments I], I8, I 9 and 23.

of. ".tral holes therein affording outlets from the action product should have as high a concentration as possible. This depends upon the completeness to which the reaction is carried out.

While the invention assists in obtaining calcium carbonate particles of relatively large size, the size may, of course be controlled by Varying the above-mentioned factors to include fine material in case this is desired. It is recognized that in some paper plants recovery of a fine carbonate to be used as filler ispreferred to coarse carbonate to be reburnt to produce the causticizing lime; and the invention is adapted to produce such crystals as well as large ones.

For a complete understanding of the invention, reference is made to the drawings illustrating a preferred embodiment and a' modification, both of which are described in detail herebelow. In the drawings,

Figure 1 is a central vertical section through a reaction apparatus according to my invention;

Figure2 isa plan view of the apparatus with the top-removed;

Figure 3 is a horizontal section taken along theplane of line III-III of Figure 1;

Figure 4 is a diagrammatic view showing the apparatus in central vertical section with most of .the mechanical details omitted to illustrate the flow of material therethrough;

Figure 5 is a horizontal section taken along the-planeof line V-V of .Figure 4, with parts omitted;

Figure 6 is an elevation of a modified form of apparatus;

Figure '7 is a central vertical sectiontherethrough;

Figure 8 is a horizontal section taken along the plane of line VIII-VIII of Figure 7;

"Figure 9 is a horizontal section taken along the planeof line IXIX of Figure 7;

"Figure 10' is a portion of Figure '7 toenlarged 'scale illustrating a detail; and

Figure 11 is a View showing alternative construction of 'a part of the apparatus.

Referring now in detail'tothe drawings and,

for the present, to Figures 1 through 4, theapparatus of my invention comprises a cylindrical tank l3. including a side wall II, .a top l2 and a bottom l3. Vertically spaced floors l4, l5 and lfitogether with the bottom I3 define a-plurality of alternate agitation and retention com- The' floors M and I6 terminate short of the wall I! affording peripheral outletsfrom the compartments-H and I9. These floors may be supported on brackets orbeams (not shown) secured-to 'the-* side wall ll of the tank If! and extending inwardly there- The floor i5'and the bottom 3 have cencompartments ISandsZlQ. The outlet'from the compartment '|,8 includes a neck 2| depending from thefloor l5 and radial baffles orswirlstop- ,pers 22 extending inwardly therefrom.

-A conical neck 23 extends downwardlyvfrom the opening i-nithe bottom I3 and has a dis- :chfillgc. pipe .24 connected thereto.

The apparatus is provided with -a vertical shaft 25'journaled centrally thereof on a thrust .32 provided With plows 33 spaced along the .length thereof.

The plows are-simply plates secured to the arms in such angular relation as to cause radial movement of solid material on the compartment floors toward the outlets, the lower edges of the plates being spaced a short distance above the floors.

Tangentially directed nozzles 34 are mounted in the agitation compartments l1 and l9 by any convenient means and are adapted, when connected to a source of treating liquid under suitable pressure; to cause circular movement of the material. in the compartments. A trough 35 in the retention compartment |8 permits a portion of the treating liquid to be withdrawn for recirculation to the agitation compartment l9. In the retention compartment 20 I provide a similar outlet trough 36 which is used for starting the apparatus as will be subsequently explained. Normally liquid in compartment 20 is not .drawn on" through trough 36, valve 36a (see Figure 4) ordinarily being closed; but the suspension of calcium carbonate in causticizedeliquid is continuously, drawn off throughpipe 24.

The nozzlesfor introducing fluid tangentially may be aplurality of small. nozzles 34 as inFigures 4 and 5 or a single larger, nozzle'34aas in Figurelll, in which fluid from a relatively large pipe is deflected by. means of a vplateformed as a segment of a circle. Any means adapted to impart to the liquid a relatively large tangential velocity may be used. The spiral path results as the combined effect of the relatively low radial velocity and relatively high tangential velocity. The outward flow ,of solids may'be accelerated somewhat by centrifugal force; and at any rate thesolids are not required to flow counter to this force.

The peripheral outlets from compartmentsil'! and I9 are segmental passages between the tank wall and depending skirt |4a or upstanding rim |6a. The passages are separated by vertical baffies or'swirl stoppers |4biand [6b, which arrest the rotary motion of the materials and permit the suspension to flow out substantially radially into the compartmentbelow. An outlet'38 for solid rejects leads downwardly, from .the floor It through the side wall of the tank'and is provided with an upwardly directed nozzle 39.

When the apparatus is'to be used for causticizing. green liquor, I preferably provide a lime slaking compartment 40 in thenpper part of the tank. To this end, arevolving circular*tray4| having-a peripheral flangeor wal1'42 is mounted 'on radial arms 43 extending-from the shaft 25. A lime inlet pipe 44 extends'through the top l2. Stationary plows 45a and 4512 are mounted on radial beams 46 extendingacross'the top |2 asshown in Figure 2. Inlet nozzles 4! extend through the top |2 for spraying green liquor'on the lime delivered'to the tray 4| throughzthe pipe 44. The tray 4| hasa centralopening 4m providing an outletfor materials into'the compartment below.

The operation of the apparatus described above may best be explained by reference to'FigureA which illustrates certain auxiliaries, such as a chain and bucket elevator 48 and pumps 49 and 50. vLime is delivered by the elevator 48 to the pipe 44 and discharged onto the tray. Green liquorisdeliveredby the pump 5D,.through a pipe line 5| to thenozzles 41. Thellevelofliquidin the tankvmay .be maintained adjacent the upper edge of the flange 42 of the tray 4|, as indicated by the chain line 52 ortslightly belowthe-tray M as indicated by the chain line 53. As-thetray i .4| revolveswith'the shaft 25, the lime thereon is moved radially by the plows 45 and is subjected to hydration by the water content of the green liquor. The plows 45a move the lime radially inwardly and the plows 45b outwardly, so as to turn the lime over and work it back and forth as the liquid is applied. The pitch of plows 45a, however, is somewhat greater than that of plows 45b, so that the inward displacement is greater than the outward displacement, and the material is gradually progressed from the circumference of the tray to the central outlet M a. This effect may, of course, be achieved by any equivalent means, such as providing plows 45a of greater width than 45b or in a greater number, instead of at steeper pitch. The heat evolved is confined in the tank Ill and absorbed by the liquor therein. A vent stack 54 has a spray nozzle 55 therein to which a supply pipe 56 is connected. The pipe 56 branches from the pipe 51 supplied by the pump 50. The spray produced by the nozzle 55 collects lime dust resulting from the slaking operation and returns it to the tray 4| as well as most of the heat in the vapor passing to the vent.

When the lime has been moved radially of the tray 4| to the central outlet, it has been converted for the most part tocalcium hydroxide and descends with the excess green liquor into the agitation compartment H. The nozzles 34 therein supplied with additional green liquor through pipe 51 cause a spiral circulation of the calcium hydroxide and green liquor together as a suspension'fiowing towards the circumference.

The circulation maintains suiiicient velocity to hold the lime particles in suspension for reaction with the liquid, and provides a long spiral path through the-compartment by which short-circuiting is avoided, detention time is controlled, and the causticizing reaction caused to proceed in the desired manner. Heavy reject material such as sand and large lumps which may settle out on the floor I4 are swept toward the periphery thereof by the plows 33. In the retention compartment l8, the suspension is separated into solid and liquid portions by permitting the solid particles to settle through the reacting liquid. Partially causticized liquid is drawn off from this compartment through trough 35 by pump 49 and recirculated through the nozzles 34 in compartment l9.

- The solid particles settling on the floor l are moved toward the central outlet thereof by the plows and are again mixed with and suspended in reacting liquid in compartment I 9 in the above described manner; the sand, heavy rejects, and any impurities mixed therewith settle on floor l E and are swept toward the rejects outlet 38 by the plows. The reaction products, sodium hydroxide solution with calcium carbonate particles sus-' pended therein, flow through the circumferential passages to the final retention compartment 20. The nozzle 39 in the outlet 38 may be connected to the outlet of pump 49 to deliver recirculated reacting liquid against the outflow of rejects, thus flushing them of fine particles, further to reduce the amount of lime discharged unused.

Liquid outlet 36 is provided in compartment for starting up only. At this time the tank is filled with a solution containing sodium carbonate, and lime alone is fed for a time to the slaking tray. Valve 36ais then opened and the liquid from compartment 20 drawn 01f by pump 50 to the nozzles 41; and the apparatus thus operated for several hours until desired operating equilibrium is reached. Valve 36a is then closed, and the pump 50 thereafter used to provide supply of green liquor instead of merely recirculating liquid within the apparatus.

The agitation produced in the compartments I! and 18 by the nozzles 34 is sufficient to accelerate reaction between the hydroxide and the green liquor but not sufficient to break up the calcium carbonate particles resulting from crystal growth as a result of the reaction between the solid and liquid. As a result, in later settling and washing operations the carbonate particles settle rapidly leaving a sodium hydroxide solution of a high degree of clarity. The agitation produced by the nozzles is suflicient to hold the largest carbonate particles in suspension in the compartments I! and i9, but not great enough to cause fragmentation of the carbonated crystals. The heavy hydroxide particles and impurities are not in suspension but sink promptly to the floors of the compartments and are pushed therealong toward the outlets. This is aided by the swirling action of the contents of the agitation compartments resulting from the tangential adjustment of the nozzles.

During the travel of the solid and liquid through the agitation compartment, the heaviest carbonate particles are held in motion close to the floor while the lighter carbonate particles and still lighter unreacted hydroxide particles are successively higher in the compartment. This stratification is desirable because it keeps the unreacted hydroxide in constant contact with the least causticized liquor. It is also helpful in holding down the amount of excess lime that must be supplied. A relatively small proportion of the entering liquor is sufiicient to produce the desired swirl in the agitation compartments. The balance of the green liquor flows gently out into the compartment from that above.

It will be noted that the materials spill over 1 rim Eta from the chamber [9 at a level well above the floor It, thus only material actually in suspension in liquid is allowed to pass into the compartment 20. The rapidly settling unused hydroxide particles and impurities collect on the floor l6 and are swept therefrom into the outlet 38. The agitation of the liquid in compartment [9 should be sufiicient to maintain the carbonate particles suspended but not enough to stir up the solid rejects, i. e., impure lime lumps,-

contact is prevented by the long spiral path which the reacting materials follow in passing through the agitating compartments. Short circuiting is further avoided by recirculating the lightest or least causticized liquor from the retention compartments to the agitation compartments where unreacted hydroxide is available. An extended period of time is available for reaction between the solid and liquid as they pass through the several compartments and this reduces the amount of excess lime required. Before any material is rejected from the ssytem, it is well worked over and all possible good lime is utilized. The scrapers that serve to clean the various compartment floors, do not touch the floor. Consequently, there is a half inch or so' of-clearance.

between the floor and the scraper which will fill with sand and other small reject material. This rough surface actsto scrape and scour the heavier and larger lime lumps that are moved across it, and by the time the lump is discharged from the secondary agitation compartment, there is little, if any, recoverable lime value remaining.

There are no fast moving mechanical parts in this apparatus that come in contact with abrasive solids. In consequence there is a minimum of abrasive wear with its always attendant replacement. Because all agitation is developed through the medium of pumped liquor, the use of quickly worn-out, mechanical agitation equipment is totally avoided. Furthermore, all liquor used to secure agitation is clear liquor and contains no abrasive solids. This helps keep pumps from wearing out.

By the provision of the slaking compartment 40 and the revolving tray 5!, it is possible to use quicklime, CaO, as it comes from the kiln. Lime slaking for causticizing has heretofore generally been done in separate apparatus, and the product. pumped to the causticizer. It has always been necessary to include with the slaker some provision for removing foreign materials and large lumps because a purified lime is too expensive. In the apparatus, economy in the consumption of lime is obtained by Working over the solid material while it is in contact with the liquor: being treated, and removing rejects after causticizing instead of before causticizing. This prevents the impurities from passing through as adulterants to the calcium carbonate sludge, yetpermits all usable values to be reclaimed from lumpy materials such as lime. The tray 4| provides a steady feed of slaked lime and the heat evolved in thisoperation is conserved as well as the lime dust usually given off. As to its more general utility, the revolving tray may be suitable for feeding and preliminary treatment in a bulk state as compared to a suspended state, any solid substance subsequently to be reacted with liquid in suspension. Other examples might be included, such as dosing various mineral substances with acid or alkali prior to subsequent treatment, the preliminary mixing of caustic with rubber to be devulcanized, or any instance where the solids mass is required to be fed, treated with liquid and worked over continuously.

My apparatus and method thus provide a combination of agitation and redistribution of the solid and liquid constituents as they progress through several compartments in series. The agitation is effected by jet means whereby the liquid tobe treated isintroduced at an optimum level in a stratified, swirling cylinder of liquid and solids insuspension, the swirling being effected by the tangential setting of the jets with respect to the vertical axis of the apparatus. The optimum. level is that at which the suspension is rich in calcium hydroxide, the denser calcium carbonate being principally below this level. Redistribution is efiected by drawingoif the Weakest portion of the partially reacted liquor in a quiet intermediate compartment, and introducing it again through jets in a lower compartment at a similar optimum level richest in unreacted hydroxide. It is essentially merely a repetition of the first contacting step, with a separation of liquid and solid constituent between steps. The rate of circulating liquid handled in the redistributing steps, however, is subject to control, andmay be equal to, less than, or even greater than the netdownward flow of liquid through the apparatus. In causticizing, this rate would ordinarily beless than the net liquid flow, being a suitable portion thereof, e. g., most of t'heliquor below a nominal per cent of causticity, there being some liquor equal to or exceeding this causticity produced in the first-stage of th-eap paratus. In this case, the remainder of the liquid flows with the solids downwardly through the central opening'from the retention compartmentto the secondary agitation compartment. Ifthe liquid is pumped to the jets at the same rate'asthe net downward flow, nothing but solids settling through quiet liquid passes through this central opening. net flow rate, there is an upward flowof liquids through the central opening countercurrent to the downward flow of the solids, in which case the upward liquid velocity may not exceed such value as will carry the solids also upward; and

prevent their discharge into the secondary agitation compartment. It should be noted here that, if desired, vertical bafiles or swirl stoppersmay be provided in this opening.

In the causticizing apparatus described above. the reacting solid and liquid traverse the apparatus in the same direction. The invention is also applicable to apparatus in which countercur-- rent flow of the solid and liquid occurs. Figures 6 through 10 illustrate such an apparatus whichis generallyv similar to that already described. The apparatus there shown comprises a tank 60' having a side Wall 6 I, a top 52 and a frusto-conical bottom 53. partments by vertically spaced floors 64 through 15. numbered floors terminate short of the wall 6| affording peripheral outlets for descendin material. Floor 66 and the subsequent even numbered floors have central outlets similar to those from the floor 15 of the causticizer of Figures 1 through 5. The floors define a mixing compart ment T6 at the top of the tank, settling compartments T! and I8 therebelow and additional mixing and settling compartments 19 through 88, the mixing compartments being those with odd numbers.

A vertical shaft 89 disposed centrally of thetank is supported on a thrust bearing 90 and is journaled in guide bearings 9i and 92. The bearing 99 is suspended in a structural frame 93 on top of the tank. The shaft is driven by a motor 94 through reduction gearing 95 and a coupling- 96.

on the several floors toward the outlets.

The apparatus of Figures fi'through 1 0 is well delivered by a screw conveyor M2 to a press for removal of the solvent absorbed thereby. The liquor from the press is returned to the tank through an inlet I03 to the mixing compartment 8?. I

As in the case of the causticizer of Figures 1 through 5, agitation of the solvent and material to be extracted is produced by nozzles discharging the liquid tangentially into the mixing If the pumping rate exceeds the The tank is divided into com-- The floors 64, $5 and the remaining odd Radial arms. 9'! on the shaft are provided with plows 98 for radially moving solids settling compartments. Liquid is also withdrawn from the settling compartments and recirculated through the prior stage mixing compartment or compartments thereabove.

The mixing compartments I6, I9, BI, 83, 85 and'8'l are provided with jet agitation means I04 which enter through the partitions forming the floors of the above-mentioned compartments, the piping thereto being disposed in the compartment immediately therebelow. As shown in Figures 9 and 10, the agitation means 104 comprises nozzles I08 directed upwardly from a manifold Il-through the floor of mixing compartment. The ends of the nozzles are flush with the floor level and are so formed, as shown in Figure 10, that they discharge in a generally horizontal direction tangentially of the tank and with a slight upward deflection. It will be apparent that this causes a spiral movement of the material in the mixing compartment-s, providing sufficient agitation to cause the meal to be suspended in the solvent and providing a long path through which solvent and meal particles travel co-currently at each mixing stage. The suspension flows downward continuously through the circumferential passages and radially into the separating or settling compartments, bafiles 65b arresting the rotary motion established in the mixing compartments.

Compartments 11, I8, 80, 82, 84, 86 and 88 are the settling compartments, and each is provided with collecting trough I located near the center, from which separated liquid is withdrawn, and scrapers for moving th solids inwardly towards the solids outlets. The two uppermost settling compartments (1! and 18) are operated in parallel to effect final clarification of the extract or miscella, the liquid outlets I05 therein being connected through pipes IN and H6 to the overflow box II'I. These thus provide large combined floor area for settling and low liquid velocity, thereby producing miscella of good clarity substantially free of suspended solids. Coarser particles descend directly through the circumferential passages to compartment 18, bypassing compartment 11. Such fines as flow with the liquid into compartment 11, settle out on the floor thereof and are plowed radially outwards over the edge of the floor to mingle with and become entrained by the coarse material "and pass into compartment I8, where the plows move all the settled solids towards the central outlet. Bafiles 22 in the throat of this outlet arrest any vortex which might otherwise progress upwardly from mixing compartment I9, and insure the minimum of disturbance in the settling compartment I8. Separation in the other settling compartments need not be so thorough, as it is primarily to provide countercurrent flow from stage to stage, and single compartments at each stage are generally sufficient. The progress of the extracting liquid will probably be made clearer by describing the apparatus here beginning at the bottom, where the solvent is introduced, and proceeding upwardly through the machine.

The inlet I00 is connected. to the manifold I01 in the compartment 88. The inlet I03 may also be connected to the same manifold. The fresh solvent is thus introduced in the lowest mixing compartment 81. partment 88 is withdrawn through trough I05 therein and a radial pipe I08 by a pump I09 and delivered through a pipe IIO to the manifold I01 in compartment 86 and thence through the floor into compartment 85. The pump I09 is driven Liquid in the settling com- .the side of the tank. Pumps II2 through II5 similarly withdraw liquid from the settling compartments 86, 84, 82 and and deliver it to the manifolds in compartments 84, 82, 80 and H for discharge in the form of tangential jets into compartments 83, 8!, 79 and 16. The trough I05 in compartments I? and I8 are connected by pipes NH and H6 to an overflow box Hi, from which the miscella is removed from the apparatus.

It will be apparent from the foregoing that the mix-settle type of countercurrent extraction apparatus of Figures 6 through 10 is adapted to receive the material to be extracted at the top thereof and introducing the extracting solvent at the bottom. By a process of successively agitating the solvent with the material to be extracted in the several compartments, with opportunity for settling between successive agitations and recirculation of the solvent between stages, the solvent becomes progressively more concentrated with the soluble content of the material being extracted and is eventually taken off through the outlets WI and H6 or more if necessary. At the same time, the material being extracted descends progressively through the several stages of mixing and settling and is finally discharged by the screw conveyor I02 to the press. By this countercurrent operation, the fresh solvent is brought into contact with the solid material having the least remaining soluble content while the more concentrated solvent in the upper portion of the tank has contact with the solid material having the maximum soluble content. It will be understood that the tank is normally filled with material to a level adjacent the top 62 and that the concentration of the soluble content of the material being extracted increases progressively from the bottom of the tank to the top. The apparatus in the form illustrated in Figures 6 through 10 is characterized by advantages similar to those of the causticizer in Figures 1 through 5 which have already been enumerated. The extractor utilizes jets of solvent formed by tangentially directed nozzles to effect the desired gentle agitation of the solid and solvent. The liquid and solid move slowly through the apparatus from stage to stage in opposite directions, the liquid being circulated upwardly'by pumps and the solid settling by gravity, while the action is co-current in each treating stage. Only a slight pressure differential exists between successive stages and the flow of liquid is thus relatively slow and free from excessive turbulence.

The foregoing illustrations have described applications where the suspension on separating causes settling of solids or immiscible liquids to the bottom of the various compartments. If the suspended solid or fluid particles are lighter than the liquid, the separation takes place in the reverse or upward direction. It is within the scope of the present invention to operate in either manner, and where desirable to enter solids at the bottom and solvent at the top and to provide scrapers cleaning the roofs of the various compartments instead of cleaning the floors as shown and described in the specific examples.

Although I have illustrated and described but two preferred embodiments of the invention, it will be recognized that changes in the details of the construction disclosed may be made without departing from the spirit of the invention or the scope of the appended claims.

I claim:

1. Causticizing apparatus comprising a cylindrical tank having a plurality of vertically spaced floors, alternate floors having peripheral and central outlets, respectively, and defining agitation compartments above the floors with peripheral outlets and retention compartments above the floors with central outlets, rotary means for sweeping solids settling on said floors toward the outlets, tangentially directed nozzles in said agitation compartments, and means for supplying treating liquid to said nozzles, a floor above the uppermost agitation compartment providing a slaking compartment, the lowermost agitation compartment having an upwardly extending flange at the edge of its peripheral outlet and a second outlet leading from the floor of the compartment adjacent the flange out through the tank whereby solid rejects may be removed from the tank by the rotary means in the compartment.

2. The apparatus defined by claim 1 in which said rejects removing means has a nozzle in said outlet discharging liquid opposite to the flow of rejects through the outlet.

3. Causticizing apparatus comprising a cylindrical tank having a plurality of fixed vertically spaced floors, alternate floors having peripheral and central outlets, respectively, and defining agitation compartments above the floors with peripheral outlets and retention compartments above the floors with central outlets, rotary means for sweeping solids settling on said floors toward the outlets, tangentially directed nozzles in said agitation compartments, and conduits for supplying treating liquid to said nozzles from the upper portions of the settling compartments, a fioor above the upper agitation compartment providing a slaking compartment, a shaft extending through said floors, said sweeping means and said slaking compartment floor being mounted on said shaft, stationary sweeping means cooperating with said last-mentioned floor, and means for removing reacted mixture from the lowermost agitating compartment, said agitating compartment also having an upwardly extending flange at the edge of its peripheral outlet and a second outlet leading from the floor of the compartment adjacent the fiange out through the tank whereby solid rejects may be removed from the tank by the rotary means in the compartment.

4. Apparatus for continuously treating solids with liquids comprising a cylindrical tank having a plurality of fixed vertically spaced floors, alternate floors having peripheral and central outlets, respectively, and defining agitation-compartments above the floors with peripheral outlets and retention compartments above the floors with central outlets, tangentially directed nozzles in said agitation compartments, means for sup plying treating liquid to said nozzles and flanges extending downwardly at the edges of said outlets whereby the amount of motion of materials in the agitation compartments which is transferred to the settling compartments is reduced.

5. Apparatus as defined in claim 4 in which said nozzles discharge through the floors of the agitation compartments from below and terminate substantially flush with said floors.

6. Apparatus for continuously treating solids with liquids comprising a cylindrical tank having a plurality of fixed vertically spaced floors, alternate floors having peripheral and central outlets, respectively, and defining agitation compartments above the floors with peripheral outlets and retention compartments above the floors with central outlets, tangentially directed nozzles in said agitation compartments, means forsupplying treating liquid to said nozzles, and downwardly extending flanges at the edges of the outlets of the agitating and settling compartments and radial flanges extending inwardly from the flanges around the central outlets whereby the amount of motion of materials in the agitation compartments which is transferred to the settling compartments is reduced.

WILLIAM J. DONOHUE.

REFERENCES CITED The following references are of record'in the file of'this patent:

UNITED STATES PATENTS Number Name Date 1,220,995 Schafier Mar. 27, 1917 1,231,707 Christensen July 3, 1917 1,308,184 McAfee July 1, 1919 1,678,787 Remick July 31,1928 1,691,511 Bates Nov. 13, 1928 1,810,125 Brooks et al June 16, 1931 1,815,646 Bates etal July 21, 1931 1,978,536 Jeavons et al Oct. 30,-1934 2,007,799 Gloersen July 9,1935

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