US2195739A

US2195739A - Method of clarification

Info

Publication number: US2195739A
Application number: US110737A
Authority: US
Inventors: Rolston William Airth
Original assignee: Individual
Current assignee: Individual
Priority date: 1936-11-13
Filing date: 1936-11-13
Publication date: 1940-04-02
Anticipated expiration: 1957-04-02

Description

April 2, 1940- w. A. ROLSTON ,HETHOD OF CLARIFICATIQN 2 Sheets-Sheet 2 Filed Nov. 13, 1936 Mum/w 4 0157 ATTORNEY INVENTOR Patented Apr. 2 1940 UNITED STATES PATENT OFFICE METHOD OF CLARIFICATION William Airth Rolston, Baton Rouge, La.

Application November 13, 1936, Serial No. 110,737 3 Claims. (01. 127-57) The general object of the present invention is to provide an improved method of continuous clarification of a liquid, such as sugar cane juice,

having a sugar content to be separated from the liquid, following its clarification.

In the practice of the present invention, I make use of a clarifying or sedimentation tank comprising a plurality of relatively shallow superposed sedimentation compartments or chambers each receiving liquid to be treated and separately delivering clarified liquid, and a liquid and solids mixture, the latter in the sugar juice clarification art, being commonly called mud. Clarification or sedimentation tanks of the general type mentioned, have long been used for the separation of solid matter from a liquid vehicle, in the treatment of sewage and finely divided ores, in the clarification of sugar juice, and for some other more or less analogous purposes.

The present invention is characterized however, by the novel and advantageous manner in which the steps of supplying the liquid to be treated, the withdrawal of the clarified liquid, and the discharge of mud from the superposed clarifying compartments are carried out and properly related to take proper care of special sugar juice clarification conditions, and particularly the relatively small differences between the densities of the liquid clarified, of the clarified liquid, and of the mud, and' the capacity of sugar for inversion, all to the ultimate end of the satisfactory clarification of a greater volume of sugar cane juice, or other sugar containing liquid, in a sedimentation tank of given bulk,

than is possible with clarification methods heretofore used and proposed. Satisfactory clarification of sugar juice requires not only adequate clarity of the clarified liquid but the production of mud which contains a relatively large solids content, and practically all attempts to obtain improved clarification results are directed either to increased clarity or increased mud concentration or to both of those results.

In the preferred mode of carrying out the.

the mud collecting on the bottom wall of the compartment is slowly moved. The aligned boots depending from the difierent compartment top walls, define, and surround different longitudinal sections of, a central vertical mud well or 5 passage, receiving the mud discharged through the different annular mud outlets. The mud well opens at its lower end into the upper portion of the lowermost compartment of the tank, which is preferably of somewhat greater vertical extent 10 than each of the upper compartments, and which is employed not only for the clarifying purpose served by each of the upper compartments, but also for the thickening or concentration, prior to its final delivery from the tank, of all of the 15 mud settled out of the liquid in the tank. The described arrangement of the mud well and its inlets facilitates and contributes to a result of prime importance; namely, the avoidance of any remixing of mud discharged from a clarifying 20 compartment in the liquid entering that or other clarifying compartments other than such remixing in the lowermost compartment as is incidental to the mud thickening purpose of the latter. 25

In accordance with the present invention, the liquid clarified in each compartment is supplied thereto through a supply connection individual" to the compartment, and opening into the latter in its top central portion. The different supply 30 connections receive liquid by gravity feed from a common supply reservoir at a level above the uppermost clarifying compartment. Each of the clarifying compartments delivers clarified liquid through an individual outlet opening to the com- 35 partment at its top and adjacent its periphery, at a rate which is regulated, as by the vertical adjustment ofa sleeve extension of an uprising portion of a discharge conduit leading from said outlet, to vary the height of the overflow or dis- 40 charge level for the corresponding compartment.

None of the steps of my improved process, insofar as they have been previously described, is novel per se, but in accordance with my invention, those steps are combined or related in a novel manner, so that theamount of liquid received and treated in each clarifying compartment is made wholly dependent on the regulation of the effective flow capacity of the clarified liquid outlet of the compartment, as by adjustment of the above mentioned adjustablesleeve, while at the same time, 'mud is prevented from accumulating on the bottom wall of each upper compartment in amount great enough to objectionably reduce the effective clarification volume of the compartment notwithstanding that the vertical depth of the latter may be relatively small, as is desirable, or great enough to result in an objectionable tendency to sugar inversion. Furthermore, with my mode of carrying out the mud discharge and clarified juice withdrawal steps, I obtain the maximum separation of the juice and mud outlets, and the minimum risk of contamination of the clarified juice by movement of the mud into and through the mud outlet. Any solids moved into admixture with the liquid supplied, as a result of mud disturbances of the mud incidental to its movement into the mud outlet, has maximum opportunity to settle out of the liquid as the latter moves from the central feed inlet to the peripheral clarified liquid outlet. With the feed supply connection opening to each clarifying compartment adjacent the top of the latter, there is practically no possibility of the feed supply connection becoming clogged, or choked to any significant extent.

To the attainment of the desired control of the amounts of liquid clarified in the different clarifying compartments, I arrange the liquid supply connections thereto, so that while definitely individual to the different compartments respectively served by them, they have ample flow capacity to make their discharge pressures independent of velocity head and dependent upon the distances between their respective discharge levels and the level of the liquid in the common supply reservoir.

With supply connections of ample fiow capacity and the feed rate controlled as described, there is, and can be no significant tendency to backfiow into any of the upper compartments from the mud well, Moreover, the described mud outlets from the compartments, may be arranged to neutralize some backfiow tendency, by requiring backfiow into any upper compartment to be in an upward direction and opposed to the normal downfiow movement through the outlet of the mud. The latter, though of a density but little greater than that of the liquid being clarified, does have a certain backfiow preventing capacity due to its increased density, and provides a certain mud seal action against backfiow through the mud outlet.

While various methods of clarifying sugar juice in a sedimentation tank comprising superposed clarifying compartments have been proposed, the only such method which is now, or has been in practical use to any significant extent, is one in which a central passage or well serves the double purpose of a mud discharge well and a feed well. The present invention permits of the use of a greater number of superposed clarifying compartments than are practically usable with the prior method. Furthermore, with the present invention, the effective clarifying capacitypof the different superposed compartments may beequal and each at least as great as the clarifying capacity of the top compartment, of the same dimensions and volumetric capacity, of a clarifier operated in accordance with the prior method, whereas with the latter method, the effective clarifying capacity of a lower compartment is less than that of the top compartment. Thus for example, a clarifier having five superposed compartments, and operated in accordance with the prior method, has practically no greater capacity than a clarifier having only four compartments, but otherwise similar to the five compartment clarifier. I

I believe that the demonstrated advantage obtainable with my invention finds its explanation in the fact that when the central well or passage is used both as a feed well and as a mud receiving well, the lower compartments receive juice from the'common feed and discharge well which carries with it mud separated from the liquid clarified at higher levels, so that in the lower compartment, for example, of a five compartment clarifier, when operating at the rate corresponding to the normal full load capacity of the uppermost compartment, the solids content of the entering liquid is too high to permit proper clarification, and in such case, the liquid discharged through the clarified liquid outlet from the lower compartment may have at least as great a solid content as does the liquid passing to the clarifier for clarification therein. In consequence, it has been customary in the operation of clarifiers including a central passage serving both as a mud well and as a feed well, to regulate the clarified juice outlets from different superposed compartments so that substantially less clarified juice is withdrawn from a lower compartment than from a top compartment having the same dimensions.

In moving the mud accumulating on the bottom wall of each clarifying compartment to the compartment mud outlet, I may follow the customary practice heretofore employed, of providing a rotating vertical shaft centrally disposed in the clarifier with arms and scrapers attached thereto which plow or turn over the mud and move it towards the central mud outlet, the mud accumulating on the compartment bottom wall adjacent the periphery being thus moved toward the mud outlet by a plurality of separate movements, each effected by a different revolution of the scraper shaft.

In the mode of carrying out the present invention which I now consider preferable, however, I move the mud collecting on the bottom wall of each upper compartment to the compartment mud outletby means of a single scraping arm carried by the scraper shaft and suitably curved to enable the arm to move the mud continuously, by a sort of sliding movement alon the compartment bottom wall, from the periphery of the compartment to its central mud outlet. This mode of mud removal permits of a low scraper shaftv turning velocity, which may be only from a third to a fifth of the velocity required with the heretofore customary plowing, step by step, mud removing action.

Such reduction in the velocity of movement of the mud moving apparatus, particularly adjacent the periphery of the clarifier, and the continuous sliding movement of the mud in lieu of the prior step by step mud movement effected by progressive plowing action, facilitates clarification, and increases the clarifying capacity of a relatively shallow clarifying compartment, and particularly because it facilitates the maintenance of the condition in which the concentration of the mud, in excess of that directly due to the mud content of the liquid clarified and to the mud moving downward in the course of the settling process, is confined to a zone or layer which extends upward from the bottom wall of the compartment, for a distance which is a relatively small fraction only, of the total vertical depth of a desirably shallow compartment.

The supply of the liquid to each compartment and the withdrawal of the clarified liquid from the latter, at its top, and respectively adjacent the center and periphery of the latter, also contribute to the maintenance of the above mentioned desirable mud concentration condition. In respect to the movement both of the mud and of the liquid in each upper clarifying compartment, my method takes advantage of the principle, well known to those skilled in the sugar juice clarification art, that agitation or disturbance movement of settled mud in contact with the liquid clarified, or in process of clarification, should be as small in extent, and should be effected as slowly as conditions will permit,

For the attainment of the major advantages of the present invention, the lowermost compartment may be similar in its arrangements and operation to the upper compartments. As previously indicated, my invention in the form which I prefer, comprises a special thickening or concentration treatment of the mud in the lowertween the bafiie and the bottom wall of the tank,

works the mud inwardly from the periphery of the bafile to the bottom mud outlet. Preferably the baffle is of considerable radial extent, so that the mud is spread out by it over the major portion of the horizontal cross section of the tank.

This spreading out of the mud over the battle,

and its return movement to the central mud outlet beneath the baflie, contribute to a desirably high degree of mud concentration, considerably greater than is practically obtainable in thecase of mud discharged from a sedimentation tank used in the practice of the above mentioned prior method.

As those skilled in the art will understand, the increased thickening or concentration mud is a practically important and desirable result. The use of the lower compartment of the tank for the described thickening action has'no direct effect on the clarifying action of the upper compartments, but tends of itself, to a reduced clarification effectiveness of that compartment, which may be substantially neutralized, by making the vertical depth of that compartment suitably greater than vertical depth of each upper compartment. The described use of the spreading baffle also effectively prevents mud from moving from the mud well to the central mud outlet of the lower compartment, without being subjected to the secondary thickening process, as a result of what is customarily known as a channelling action, whereby flow paths of relatively low resistance leading directly to the bottom mud outlet, are formed in the general mud mass spread out over the bottom wall of the compartment.

While not necessary to the attainment of major advantages of the present invention, I may obtain special advantages by locating the feed supply reservoir directly above the top clarifying compartment, so that scum may be swept out of the top of the reservoir by a scraper arm or arms carried by the previously mentioned scraper shaft. In such case, the supply connections for the top clarifying compartment may be formed wall for the top clarifying compartment. This not only tends to compactness of the clarifying apparatus and its simplification, particularly in respect to the connections for passing liquid from the reservoir to the clarifying compartments, but also contributes to the thermal economy of the sugar juice clarification apparatus in which the juice in the reservoir is hot limed juice, the temperature of which is ordinarily slightly in excess of 212, and in which it is desirable to prevent the juice from cooling appreciably during the clarification operation. When directly above the top clarifying apparatus, the reservoir provides the most effective sort of heat insulation for the top wall of the top compartment, particularly when the reservoir is large enough to cover the entire top wall of the top compartment. The large reservoir volume obtained with the reservoir of suitable depth and of the same horizontal extent as the clarifying compartments, though not required for the use of the reservoir as a feed distributor to the clarifying compartments, has a special advantage in the case of certain modern cane juices, in that it provides a space in which the entering liquid is retained for a short period under conditions tending to the suitable initial formation of fioc, contributing directly and importantly to the speed and effectiveness of the subsequent clarification action proper. It is not necessary to make special provisions for the removal of mud settling on the bottom wall of the reservoir under the conditions prevailing in that reservoir, since because of the relatively short period required for the passage of liquid through the reservoir, and the character or condition of the liquid at the time, no significant mud settling action occurs in the reservoir.

One form of apparatus adapted for use in the practice of my improved method is illustrated in the accompanying drawings, of which:

Fig. 1 is a plan view of the clarifying tank structure and associated apparatus,

Fig. 2 is an elevation in section on the broken line 2-2 of Fig. 1,

Fig. 3 is a vertical elevation on a plane parallel to that indicated by the line 3-3 of Fig. 1.

Fig. 4 is an enlarged sectional elevation taken similarly to Fig. 2 of a portion of the apparatus therein shown.

Fig. 5 is a view taken similarly to Fig. 4 illustrating a modified construction, and

Fig. 6 is a partial sectional plan on the line 66 of Fig. 2.

The tank structure shown in the drawings comprises a cylindrical shell I, a dished bottom wall 2, a top wall 3, and a superposed set of dished partition walls or trays 4, separating the tank interior into a lower thickening and clarifying compartment 5, a lower clarifying compartment 6, intermediate clarifying compartments I, a top clarifying compartment 8, and a liquid supply reservoir 9 above the top clarifying compartment 8. The said dished walls have their concave sides uppermost. As shown, there are three intermediate clarifying compartments 1. The reservoir chamber 9 receives the liquid to be clarified through a feed pipe III, which is norof cane sugar juice, the feed pipe I leads from the juice liming and heating apparatus customarily employed, and delivering the limed juice at a temperature which ordinarily is slightly in excess of 212 F.

The reservoir 9 supplies liquid to the

different compartments

5, 6, l, and 8, through separate connections. As shown, the supply connections for the

compartments

5, 6, and l comprise two diametrically opposed vertical conduits [2, each formed by welding the edges of a trough-shaped body of sheet metal to the outer surface of the tank shell. Each conduit 12 extends from the top of the tank structure downward to a level below the peripheral edge of the lowermost partition 4 and is closed at its lower end. Each conduit i2 receives liquid from the reservoir 8, through a corresponding branch l3, shown as extending through the top clarifying compartment 8 and connected at its inlet end to the top partition wall l, which is formed with an aperture through which the conduit branch is communicates with the reservoir 9. Each conduit 52 is provided with downwardly inclined branches it, one for eachof the compartments 5, ii, and 76, extending into the corresponding compartment and opening thereto in the upper central portion of the compartment. As shown, each supply conduit it extends through and is mechanically supported at its inner end by a cylindrical flange member l5 secured to and depending from the partition wall 3- above it, and forming the outer wall of an annular feed distributing channel it open at its lower side to the compartment to which it pertains. The inner wall of the chanel it, for the compartment 5 is formed by a cylindrical flange ll depending from the partition l directly above the compartment and surrounding a central aperture in the latter. The inner walls of the feed channel it for the compartments 6 and i are formed by conical flange members it carried by and depending from and surrounding central apertures in the partition walls 6, forming the top walls of the last mentioned compartment.

The top clarifying compartment 8 may receive liquid from the reservoir 9 through branches from the conduits 02 similar to those serving the lower compartments, but conveniently and as shown, the compartment 8 is supplied with liquid through a port or ports extending through the wall 4 between the compartment 8 and reservoir 9. As shown there are a plurality of such ports I9 arranged in a circular series surrounding the tank axis and opening into an annular feed channel 16, having its outer wall formed by a cylindrical flange l5 and its inner wall formed by the lower end portion of a sleeve or tubular member 20 secured to, and extending through the upper wall 4, and extending upwardly above the scum level in the reservoir 9.

As will be apparent from what has previously been said herein, the present invention is not concerned with the illustrated and described details of construction and arrangement of the liquid supply connections to the difierent clarifying compartments. It is essential for the purpose of the present invention however, that the liquid supply connection for each clarifying compartment should deliver liquid thereto in the upper central portion of the compartment, and should have a flow capacity great. enough so that with the maximum flow velocity therethrough, the velocity head will be negligible, and without significant effect on the liquid discharge pressure, which is thus due to the hydrostatic head of the liquid and hence is proportional to the vertical distance between the discharge level and the liquid level in the reservoir 9.

Clarified liquid is withdrawn from the upper peripheral portion of the difierent clarifying compartments through outlet or drawoff connections individual to the different compartments, and each shown as comprising a horizontally disposed arc-shaped pipe 2 l, within the compartment and extending about the axis of the compartment for a considerable distance, as shown for approximately 270, and provided with a plurality of distributed inlets 22 at its upper side. Each pipe 24 is connected by a conduit portion 23 extending through the wall of the tank to a corresponding external stand-pipe 2d. Each of the standpipes 26 has its upper end extending through the bottom wall of a clarified juice receiver or overflow box, 25,and within the box is in telescopic engagement with a sleeve or tubular extension 26. The vertical adjustment of each extension 28 determines the overflow level of the corresponding standpipe, and, hence, the gravitational flow capacity of the clarified juice outlet from the particular clarifying compartment to which the extension and the associated standpipe 2t pertains. Advantageously, the different sleeve members to may be vertically adjusted similarly and simultaneously, to vary the general rate of clarification without varying the relative rates of clarification in the different compartments, while each sleeve 26 may also be adjusted independently of the others, to vary the rate of clariflcation in the particular clarifying compartment to which it pertains, without varying the rates of clarification in the other compartments. As shown, the described adjustments are effected by connecting each sleeve 26 to a common cross head 27, by means of a threaded supporting stem 28, for the sleeve which passes through the cross head and is supported by a hand wheel 29, and threaded on the stem 28, resting on the cross head so the stem and sleeve may be vertically adjusted. relative to the cross head by rotation of the hand wheel. The cross head is formed 'with vertical rack bar end portions 30, through which the cross head may be bodily adjusted vertically by the rotation of a shaft 3|, mounted on the box 25 and carrying a spur gear 32 in engagement with each rack bar portion 30. Clarifled juice overflowing from the standpipes into the box 25 passes from the latter to the sugar house for concentration or to other receiving apparatus through a delivery pipe 33, connected to the bottom wall of the box 25. As shown each standpipe 24 is provided with a depending valved drain pipe 34.

As will be apparent from what has previously been said, the present invention is not concerned with the details of construction and arrangement of the clear juice outlet connections for the different clarifying compartments, but for the purpose of the present invention, it is essential that means should be provided for independently regulating the gravitational outflow capacity of each clarified juice outlet connection, since that capacity controls the rate at which liquid to be clarified, enters the corresponding compartment through its feed or supply connection,

The mud accumulating on the bottom wall of each of the clarifying compartments 6, I, and 8 is moved out of the compartment as hereinafter described, through a corresponding mud outlet into a central mud well which is surrounded and is defined in part by the various conical baifles or flanges l8 previously mentioned and by conical extensions 35, of the conical parts l2. Each of the conical extensions 35 is supported by arms 36 from a rotatable vertical scraper or mud removal shaft 31 coaxially disposed in the tank and mud well and extending downwardly from the latter, nearly to the bottom of the compartment 5 and extending upwardly above the top wall 3 of the tank into engagement with shaft rotating mechanism hereinafter described. As shown, the larger upper end of each conical part 35 is in an abutting relation with the smaller lower. end of the conical flange l8 for which it forms an extension. An external sealing ring 38 is shown as overlapping the abutting ends of each part I 8 and associated part 35, and carried by the part l8.

Each flange l8 and its extension 35 collectively 4 form what may be called a discharge boot, for

mud accumulating on the partition wall 4 from which the boot depends. With each of those boots extending downwardly to a level below the immediately subjacent wall 4, as shown, the adjacent boots overlap so that the two boots respectively depending from the top and bottom walls 4 for each intermediate compartment provide an annular mud outlet from that compartment, leading downwardly into the mud well collectively surrounded, and defined in part, by said boots. In the construction shown, the lowermost portion of the mud well proper is surrounded and defined by the cylindrical flange I! which in conjunction with the adjacent conical part 35 forms a downwardly leading annular mud outlet from the compartment 5.

' The shaft 31 supports a tubular depending extension 35 of the sleeve 20, associated with the latter as each of the parts 35 is associated with a corresponding conical part l8. The part 35' might be conical, and extended into the subjacent mud discharge boot, but as shown, the part 35 is cylindrical, and its lower end terminates at a level above that at the top of the subjacent boot. The mud outlet from the top clarifying compartment 9, while annular, is thus not definitely downwardly directed as are the subjacent mud outlets in which each discharge boot extends into the upper end of the immediately subjacent discharge boot. The difference in form between the mud outlet provisions for the compartment 8 and for the subjacent compartment illustrated, is of significance only as illustrating that the precise form of those provisions is not essential. However, the extension of each discharge boot from an upper clarifying compartment into the discharge boot for the subjacent compartment is a preferred arrangement in the case of each boot discharging mud into the mud well at a level below that at which the mud well receives mud'from a clarifying compartment or compartments above. As shown. the diameters of the conical parts l8 and 35, and thereby the diameter of the mud well which they assist in defining, increases progressively from the top to the bottom of the clarifying apparatus.

The conical parts 35' and 35 carried by and rotating with mud removal shaft 31, form hubs. so to speak, for the mud scraper means in each of the different clarifying compartments employed to move the mud accumulating on the bottom wall of the. compartment to its mud outlet. While, as previously stated, the scraper provisions may take different forms, I now consider preferable a single mud scraper for each compartment, in the form of a bar 40, bent into spiral form, extending as shown in Fig. 6 to the periphery of the clarifying compartment, whereby with the shaft direction of rotation indicated by the arrow in Fig. 6, each particle of mud engaged by the plate is continuously advanced toward the mud outlet. The mud is thus advanced by a sort of sliding motion along the bottom wall of the corresponding compartment with a minimum disturbance of the mud, and minimum resultant tendency to effect up movement and remixing of the mud. with the liquid in the upper portion of the compartment. Each scraper arm 40 is stiffened, and given driving support, by the use of a plurality of arms 4| carried by the corresponding part 35 or 35', and extending therefrom at different angles into engagement with the arm 40 at different points along the length of the latter.

The lower thickening and clarifying compartment 5 is formed with a central mud outlet 42 in its bottom wall connected to a mud discharge conduit 43, through which the mud may be passed to a filter, or returned to the bagasse in the milling circuit, or otherwise disposed of, as conditions of operation make desirable. While means are necessarily provided for moving mud accumulating on the bottom wall of the compartment 5 to the outet 42, and are preferably adapted to subject the mud in the compartment 5 to a special concentration action, that means may take various forms as has been previously stated. The special form of the means which I now consider preferable, and have illustrated, comprises a horizontally-disposed baflle 44, coaxial with the tank structure and of substantial radial extent, by which the mud received from the mud well,

and much of the mud settling out of the liquid clarified in the compartment 5, is spread out over a major portion of the horizontal cross section of the compartment 5, before passing to the relatively shallow space between the baflie and the bottom wall 2 of the tank structure. As shown, the shaft 31 extends through the baffle 44, which is supported by arms 45 depending from the partition 4 forming the top wall of the compartment 5. Preferably, the baffle 44 is' slightly dished, with its convex side uppermost.

A scraper arm 41 carried by the shaft 3! is provided to work mud accumulating on the baffie away from the shaft to the edge of the baflle beneath the baffle. The shaft carries a scraper arm 48 which may be formed similarly to the previously described arms 40, and serves to move the mud collecting on the portion of the bottom wall beyond the periphery of the baffle, and dropping off the peripheral edge of the bafiie, to the outlet 42. As shown, the latter is conical, and the shaft 31 carries a scraper element 49 extending into the outlet 42 and tending to prevent any tendency of the mud to cake in, and clog that outlet.

Since the compartment 5 receives'all of the mud settled out of the liquid in the clarifying tank and that'mud is subjected to a concentration action in the compartment 5 which would interfere with the proper clarification action therein, if the lower compartments were as shallow as is' desirable in the case of the upper clarifying compartments, I make the compartment 5 of appreciably greater vertical depth than any of the upper clarifying compartments.

Even with theconsiderable concentration of the mud affected with the special concentrating provisions described, the mud passing from the outlet 42 into the discharge conduit 43 is sumciently fluid to permit of the discharge movement of the mud through the conduit by gravitational flow, if the conduit is not too long and has its discharge end suitably below the level of the liquid in the reservoir 9. In many cases, and as shown, it is desirable however, to provide a mud pump for moving the mud through and away from the outlet 42. In accordance with common practice in the sugar juice clarification process, I employ a duplex mud pump mechanism 59, having two pumping chambers, one connected to one, and the other to the second of the two branches 43 of an uprising portion of the mud conduit it.

As shown, the mud pumping apparatus 5E3 is located adjacent the top of the tank, so that it may be operated by the same motor 51] employed to rotate the shaft m. The motor M is mounted on a bridge structure 52 above, and supported by the tank, and carrying the gearing through which the motor rotates the shaft 3i. That gearing, as shown, comprises a worm gear 53 secured to the upper end of the shaft il'l, and a worm in mesh therewith, and carried by a shaft 5 mounted on the bridge 52, and rotated by the motor 5!! so as to give the shaft 31 its continuous slow rotative movement. fhe speed of rotation of that shaft may vary with conditions, but by way of example, I note, that the shaft speed may be such as to give a complete rotation to the shaft in 15 minutes, or so, which results in a relatively very slow linear velocity of the tips of the scraper bars 3G and 41d, even in a large capacity tank which may have a diameter as reat as 28 or 30 feet.

The shaft 3? is provided with suitable bearings which as shown, include an upper bearing 55 carried by the top wall 3 of the tank structure, and a lower bearing carried by the flange member i'i supported by the lower partition wall 3. An arm 5'8 carried by the shaft 3? above the scum level in the reservoir 9 supports a depending hinge connected scum removal blade 58 having its lower edge below the top of the scum removal trough ii, and serving to sweep scum collecting on the liquid in the reservoir into the open top of the scum removal trough.

In the modification shown in Fig. 5, the shaft carried boot extensions 35 are replaced in efiect by integral elongations of the boot members l8. and the scraper are carried by spider elements 59, each including a hub portion 60 secured directly to the shaft 31, and including inclined arms extending upwardly through the mud outlet for the compartment containing the scraper supported and rotated by those arms.

Since the clarifying action in each of the different compartments 6, l7, and 8, is practically independent of the clarifying action in any other of the clarifying compartments, all of these clarifying compartments are of similar effectiveness regardless of their number. It is thus practical to provide a sin le clarifying unit operated in accordance with the present invention with a considerably greater number of superposed clarifying compartments, than it has been practically possible to employ heretofore in sugar juice clarification apparatus including superposed clarifying compartments. The invention thus permits of the effective use of a clarifying unit of greater capacity than has been heretofore practically possible, and permits a given volume of juice to be clarified in a clarifying unit of substantially smaller bulk than has been heretofore required.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In the clarification of a sugar containing liquid prior to the separation of sugar-therefrom in a clarifier comprising a plurality of shallow superposed clarifier compartments, a central mud well extending downward from the top compartment through the subjacent compartments, and separate clear juice outlets for the gravitational outflow of clear juice from the outer upper portions of the different compartments, the method which consists in passing said liquid into the central upper portion of each of said compartments without prior contact with the mud well contents to replace liquid moving from said portion as liquid passes out of the compartment through its clear juice outlet, and with the liquid so passing into the compartment under a static pressure which is substantially independent of the rate at which the liquid is passed into the compartment and is substantially equal to the static pressure of the liquid replaced, whereby the relative amounts of clarified liquid withdrawn from the different compartments may be varied without creating a significant tendency to flow between any of said compartments and the mud well, and which consists in regulating the gravitational outlet capacities of said outlets and thereby regulating the amounts of liquid passing into the different compartments to insure suitable liquid clarificationin each compartment, and which consists in moving mud accumulating on the bottom wall of each compartment into the mud well as required to prevent the formation of mud layer on each compartment bottom wall of a thickness greater than a small fraction of the vertical depth of the compartment, whereby interference with the accumulation of clarified liquid in the upper portion of each compartment and with the concentration of solids in the lower portion thereof by fluid movements toward the corresponding mud and clear juice outlets, is minimized.

2. A method as specified in claim 1, further characterized by removing the mud from each clarifying compartment by a slow continuous movement toward the outlet.

3. A method as specified in claim 1, further characterized by passing the mud received in the mud well downward into a clarifying and thickening compartment beneath the lowermost of the clarifying compartments specified in claim 1, and supplying liquid to, and withdrawing clear liquid from said clarifying and thickening compartment as it is supplied and withdrawn, respectively, from each of the said clarifying compartments above it, and in first spreading the mud received from the mud well out over a large portion of the horizontal area of said clarifying and thickening compartment, and then moving the mud to a central mud outlet in the bottom wall of the last mentioned compartment to thereby concentrate the mud discharged from, and to avoid channeling of the mud adjacent the last mentioned outlet.

WILLIAM A. ROLS'ION.