US2643960A - Centrifuging massecuite - Google Patents

Description

June 30, 1953 s, HOYT 2,643,960

CENTRIFUGING MAssEcUITE- Original Filed Dec. 14, 1948 5 Sheets-Sheet l IIZ fit;

v INVENTOR By 5/mes 7THo5 f ATTORNEY June 30, 1953. s, T. HOYT 2,643,960

.. CENTRIFUGING MASSECUITE Original Filed Dec. 14, 1948 5 Sheds-SheetZ \NVENTOR 5/nves 7. Hos f ATTORNEY June so, 1953 s. T. HOYT 1 3 6 CENTRIFUGING MASSECUITE Original Filed Dec. 14, 1948 5 She'et's-Shet 3 FlEi E INVENTOR BY 5/mes Thogf ATTORN EY June 30, 1953 s. 'r. HQYT CENTRIFUGING MASSECUITE 5 Sheets-Sheet 4 Original Filed Dec.

n E F INVENTOR 5l'rnes7fHayf AT TO FINE June 30, 1953 s. 'r. HOYT CENTRIFUGING MASSECUITE Original Filed Dec. 14, 1948 5 Sheets-Sheet 5 .INVENTOR 5 mes 71 Ho ATTO RN EY Patented June 30, 1953 STA'i'Ed HQE CENTRIFUGING MASSECUITE Original application December 14, 1948, Serial No. 65,093. Divided and this application May 25, 1951, Serial No. 228,252

4 Claims.

This invention relates to the treatment of a liquid containing a granular solid to the end that the two be separated; more particularly, the present invention relates to the treatment of sugar massecuites or magmas and is intended to solve certain problems that have long been a source of trouble and expense.

As one of the steps in the recovery of sugar crystals from the associated mother liquor, it is usual to centrifuge the mixture to the end that the sugar crystals are collected and separated as completely as possible from the mother liquor, or molasses. The present invention makes it possible to effect the separation of crystals from mother liquor continuously rather than intermittently as at present, more rapidly, and in some cases more nearly completely than is now economically possible.

In processing low grade massecuites, a limiting factor is the viscosity of the mother liquor, the molasses. The two principal factors afiecting viscosity of a massecuite are its composition and its temperature. A reduction in the water content increases the amount of sugar present in crystal form by reducing the" amount which can be held in solution, but also increases the viscosity. A reduction in temperature has a similar effect. For proper centrifuging, massecuite must flow readily enough to permit it to build up quickly in an even ring around the inside of the centrifugal basket and to permit proper separation of mother liquor and sugar crystals.

Sugar solutions in general, and low grade massecuites in particular, can, under certain conditions, become supersaturated. It is common practice to permit low grade massecuites to cool, after coming from the vacuum pan, thus encouraging crystal growth. Under such conditions there is usually a considerable degree of supersaturation. Before purging in the centrifugal, it is customary to dilute the massecuite by adding Water or to heat it, to approximate the point of saturation in order to reduce the viscosity as much as possible and so make it easier to handle in the centrifugal; If, at any point, the dilution or the heating goes beyond the point of saturation, sugar crystals in that zone will be redissolved, hence cannot be recovered in the centrifugal. The greater the sub-saturation, and the longer the time the sub-saturated mother liquor is in contact with sugar crystals, the greater the amount of redissolution.

I have found that it is possible to heat such a molasses in the presence of the'sugar crystals and thereafter to purge in acentriiugal and to recover the sugar crystals substantially without loss due to redissolution, providing the heating is practically instantaneous and, provided further, that immediately upon the massecuite attaining such a high temperature, it is subjected to the action of centrifugal force whereby the mother liquor and sugar crystals are separated in a very short period of time, c. g. of the order of one minute and preferably even less. I have found that the massecuite can be heated practically instantaneously by passing it in a continuous stream to the centrifuge, heating the stream immediately prior to its introduction into the centrifuge; the desired instantaneous heating I attain by passing the stream of massecuite over electrodes upon which a suitable current is impressed; the massecuite acts as a conductor between the electrodes and, due to its resistance, is heated practically instantaneously whereby its viscosity is reduced suitably as to below 600 pcises at the temperature of the massecuite. Thereafter, and with as little loss of time as is possible and within five seconds or less, the massecuite is subjected to centrifugal force whereby the sugar crystals are separated from the mother liquor before these have time to pass into solution in the mother liquor. Because of the very short time during which the heated molasses is in contact with the sugar crystals, it is possible to heat it to a materially higher temperature than present practice will permit without substantial loss by redissolution of crystal.

The invention is also concerned with the provision of a novel form of centrifuge particularly characterized by its simplicity of construction, its rugged nature, and its eifecti-veness in separating a solid from a liquid, as sugar crystals from the mother liquor in which they are carried,

It is a general and broad object of the present invention to provide a process enabling sugar crystals to be separated from their mother liquor.

A further object of the present invention is to provide the novel apparatus for heating a mother liquor substantially instantaneously so that solids therein do not have an opportunity to pass into solution prior to a separation operation to remove theso-lids from the heated liquid. This disclosure contemplates that the mother liquor shall be a-fairly good conductor of electric current, as is the case with ordinary sugar massecuites. By the proper choice of voltage and frequency of the current used for heating, the desired heating effect can be obtained, even with non-conducting liquids. In such case, the electrodes would have to be suitably disposed, and theheating would be by the dielectric rather than "-2 by the resistance method. In the claims, the term electrically heatingis used to include dielectric as well as resistance heating.

The invention includes other objects and features of advantage, some of which, together with the foregoing, will appear hereinafter wherein the present preferred manner of practicing the process of this invention and the present preferred embodiment of the centrifuge of this. invention are disclosed.

Referring to the drawings accompanying and forming a part hereof, Figure 1 is a side elevation with portions of the apparatus broken away to illustrate certain constructions.

Figure 2 is a section taken along the line 2I--2 in Figure 1.

Figure 3 is a fragmentary view illustrating a portion of the drive mechanism utilized.

Figure 4 is a plan view of the apparatus.

Figure 5 is a section taken along the line 5--5 of Figure 2.

Figure 6 is a section taken along the line 6-3 of Figure 2.

Figure '7 is a section taken along the line 'I-'I of Figure 6.

Figure 8 is a fragmentary view which is partly schematic to illustrate the construction of the electrodes and the supply of power.

Referring to the drawings, the apparatus includes a suitable base structure 6 on which is mounted the outer casing structure 9 which supports the horizontal frame members 8 which form the principal supports for bearing I2, motor reducer I33, and frame I, which carries the main drive motor BI.

A hollow shaft II is mounted vertically of the casing structure, being supported for rotation adjacent its lower end by a bearing structure, generally indicated by the numeral I2, secured by studs I3 upon one of the horizontal frame mem bers 8. At its upper end, the hollow shaft II is supported by bearings I4 which is in turn secured upon inlet casing I6.

Bearing I2 includes a roller bearing 2i having its inner race mounted directly upon the hollow shaft II; the bearing 2| is resiliently supported by rubber ring 22 provided between the outer race of the roller bearing and casing 23, the latter being directly secured by studs I3 to the horizontal member 8. An annulus 24,. the lower edge of which projects downward within the top portion of casing 23, and which may be pulled downward against the rubber ring 22 by means of bolts 26, serves to constrain the bearing assembly ZI, on which the rubber ring 22 is firmly mounted, against any undue movement in any direction, while permitting the small amount of oscillation of shaft II which is necessary in a machine of this character. By adjusting the pressure of the annulus 24 on rubber ring 22, the damping effect of the rubber mounting may be regulated as required to give best performance of the machine.

.Mounted for rotation with the hollow shaft I I are a plurality of circular carrier plates 3i positioned at different elevations along the shaft and surrounded by screen 38. Disposed symmetrically about the longitudinal axis of the hollow shaft I I are a plurality of centrifuge cells or baskets 32, each in the form of an open ended cylinder.

In the form of device shown in the drawing, three cells are employed, but more or less than this number can be utilized so long as they are symmetrically disposed about the horizontal shaft I I. Each cell is mounted for rotation in a roller bearing 33 in each carrier plate 3|. Within each cell are provided two fixed scrolls 34 wound in a suitable direction to provide a shelf or support along which material can move downwardly when the cells are rotated. Between the scrolls 34 and the inner wall of each basket 32 are provided a plurality of strip members I4I which extend parallel to the axis of the basket and which are provided in a spaced but over-lapping relation to one another. Each strip includes a plurality of flat lugs I42 thereon fitting into circular holes 38 in the wall of the basket to retain the strip in place; the holes for supporting adjacent strips are staggered along the basket wall (Figure 2). Lugs I42 are at an angle to the strips (Figure 6) so that the latter extend away from the direction of rotation of the basket, that is, the strips extend counter-clockwise and the baskets rotate in a clockwise direction as viewed from the top of the cell. Each strip includes a plurality of projections I43 each of which projects downwardly from the outer edge of each strip to space. the strip from that strip next adjacent and which it overlies as is shown in Figure 6. The opening between the strip is controlled by the amount of off-set in each projection and is of such size that solids such as the sugar crystals do not pass through and yet the mother liquor can pass through freely. The scraping effect, due to the rotation, tends to prevent any build-up of a mass of crystals over an opening, and the direction of overlap of the strips, in relation to the direction of rotation, tends to prevent the crystals from moving toward the openings between strips, while liquid pressure, which is transmitted equally in all directions, causes the mother liquor or the molasses to flow outward between any pair of strips which is covered, and then out through the apertures 36 in the wall of each cell and thence into the space between adjacent carrier plates 3|, and finally outwardly through apertures 31 in the wall of screen 3%. Liquid ejected from the screen 38 co]- lects on casing S and is taken off by annular trough 39 through openings 4! in casing 9 and into trough 42. The strips I II are retained in place by the spring-like action of the scrolls 34.

Each cell is rotated with respect to the hollow shaft I I and also rotates with the shaft. This is accomplished by providing a gear 46 about the upper end of each cell 32, each gear being engaged with a gear 41 upon the end of a shaft 48, the latter being mounted in bearings 49 and 5| for rotation in the hollow shaft II. The hollow shaft II is cut away at 52 (Figure 5) at the elevation of and opposite to each gear 46 so that these can be driven by gear 61 during the rotation of the cells with the hollow shaft II.

Shaft 48 is driven with respect to hollow shaft I I to rotate the cells in the carrier plates 3! dur ing their rotation about the hollow shaft II by the following mechanism: Mounted on the frame structure is a prime mover such as the electric motor 6! having a shaft 62 upon which are mounted a first V-belt pulley 83 and a second V-belt pulley M. A V-belt pulley 66 is mounted on hollow shaft II opposite V-belt pulley 63 and a plurality of belts 67 are trained about these to provide driving means between the motor GI and the hollow shaft I I.

A V-belt pulley 6B is provided opposite V-belt pulley 64 and a plurality of V-belts 69 are trained between these two; however, V-belt pulley 68 is mounted by bearing II upon the hollow shaft for rotation with respect to such shaft (Figure 3). The lower end of the V-belt pulley 68 includes a flange I2, the latter being secured by studs I3 to a housing or casing structure generally indicated at I4 and including a plate 16 which serves to support the housing generally indicated at '14 and which includes gear'case TI and cover BI; the housing rotates about the shaft II with pulley 68. Projecting downward from .the bottom of casing I4 and integral with it, is the smaller cylindrical portion 86, in whichis mounted hearing 82. mount and adjust bearing 82, and a closure to prevent escape of lubricant from the casing 14.

Mounted for rotation in bearings 86 and-81 provided respectively in annular member 14 and plate 76 are shafts 88, each having affixed thereto a first set of gears 89 and a second set of gears SI. The first .set of gears 89 are in mesh with a gear 92 formed upon an end of the hollow shaft II, while the second set of gears 9I are in mesh with the gear 93 provided upon the end of the solid shaft 48. The ratio of gears 89, 9I, 92 and 93 is such that, in conjunction with gears 46 and 41 and with pulleys and belts 646869 and 63-666'I, each cell is caused to rotate with respect to the plate carriers 3I in which it is mounted. Thus, a useful combination of speeds is: motor speed and pulleys, Nos. 64, Hand 68, 1750 R. P. M.; shaft II, pulley 66, rotating assembly 3|, 38, etc., 1275-R. P. M.; shaft 48, gears 93 and 41, 54 R. P. M.; gears 46 and cells 32, R. P. M., with respect to plates 3| within which they rotate. The effect of such independent rotation of the cells is to distribute liquid fed thereto uniformly over the cell wall and to move the solids through the cell.

Mother liquor containing crystals is fed into the inlet casing I 6 and thence down through tubes IIlI into the casing structure I92 suitably mounted on shaft I I and the uppermost of plates SI, and forming a part of the rotating assembly. Magma from the casing I02 is discharged by pipes I83 into each cell. In accordance with this invention, means are provided for heating the mother liquor substantially instantaneously. Each feed pipe IUI (Figure 2) is made of electrically non-conducting material and carries annular electrodes III! and III disposed with their inner annular faces flush with the inner surface or face of the feed pipe as is shown in Figures 2 and 8. A suitable electric potential is impressed on the electrodes to heat liquid flowing through the tube or feed pipe I9 I. Electrodes I I, near the middle of the tubes, are electrically hot, i. e.. connected to a controllable source of electric potential, while electrodes IIO, near the ends of the tubes, are electrically grounded, thus limiting the zone of passage of electric current through the massecuite substantially to the space within the feed pipes and eliminating the effect of stray currents, electrolysis, etc., which might otherwise cause damage to parts of the device. In most cases, alternating current of commercially available frequency will be suitable and. preferable.

In operation, the potential applied across electrodes I I6 and II I is regulated to secure the desired temperature increase in the massecuite or other fluid; such regulation is necessary because the initial viscosity of the massecuite will affect its ease of heating as will its composition and, as either or both vary so is it desirable to increase or decrease the applied potential. With one massecuite fed at an initial temperature of 100 F., current was applied at the rate of 65.8 kw. to a stream fed at the rate of 250 pounds per minute; the massecuite was heated to 150 F.

Cover 8I provides a means of access to 6 Depending on'the initial viscosity. the initial-temperature, and the composition of. the massecuite. the potential can'be, suitably applied and regulated "to raise the, temperature of the massecuite substantially instantaneously and its viscosity reduced to less than 600 poises.

Solids discharged by each cellcollect in the circular well I2I supported from annular trough 39-and are moved along the circular we1lI2I to the discharge outlet I22 by scrapers I23. These are'rotated about the hollow shaft II by arms I26 which depend from annular ring I26. The ring includesan annular channel I21 carried upon a plurality of bearings I28. A ring gear I29 is mounted :in the channel and is driven by :a gear I3I, the latter being supported upon a shaft I32 which is driven by a motor-reducer I33 by means of sprocket I34, chain I35, and sprocket I36 on the shaft I32.

To maintain the upper end of the casing structure 9 in alignment with the feed or inlet casing I6 and with the bearing I4 supporting the upper end of hollow shaft I I, a trough I4Ia is provided upon casing 9. A pneumatic rubber tire and tube, generally indicated at MM, and such as are employed upon an automobile, are mounted upon the exterior of easing I6 with the periphery of the tire in engagement with the trough I4 Ia; in this manner, a flexible and yet relatively strong connection is provided between the two. The disposition of the tire in its mounting and the air pressure are advantageously such as to cause the weight of the rotating parts to be carried approximately half by bearing I4 at the top of the shaft II and half by bearing 2|, near the bottom of the same shaft.

From the foregoing, I believe it will be apparent that I have provided a relatively novel and simple centrifuge particularly useful in the treatment of various massecuites, magmas and the like, as well as a simple, rugged centrifuge particularly adapted to the separation of various liquids from solids carried therein.

This is a division of application Serial No.

- 65,093, filed December 14, 1948, now Patent Number 2,626,055.

Iclaim:

1. A' process for separating sugar crystals from mother liquor wherein said mother liquor contains sugar crystals and is supersaturated with sugar, comprising electrically heating the mother liquor substantially instantaneously to a temperature of about F., to produce a mother liquor containin sugar crystals and having a dissolved sugar content substantially 'below saturation, and immediately introducing a stream of the heated mother liquor into a zone wherein epicyclic centrifugal force is applied to the stream to effect a substantially complete separation of the liquid and solid phases, such separation being completed within one minute of said heating.

2. A process for separating sugar crystals from low grade massecuite wherein said massecuite contains sugar crystals and is supersaturated with sugar, comprising electrically heating the massecuite substantially instantaneously to a temperature of about 150 F. to produce a massecuite containing sugar crystals and having a dissolved sugar content substantially below saturation, and immediately introducing a stream of the heated massecuite into a zone wherein epicyclic centrifugal force is applied to the stream to effect a substantially complete separation of the liquid and solid phases, such separation being completed within one minute of said heating.

"3. The process of claim 2 wherein the' massecuit'e when heated'to a temperature of 150 F. has a viscosity not greater than 600 poises.

4} A process for separating sugar crystals from mother liquor wherein said mother liquor contains sugar crystals supersaturated with sugar, comprising electrically heating the mother liquor substantially "instantaneously to a temperature of about: 150 F. to produce a mother liquor containin sugar; crystals and having a dissolved sugar content substantially below saturation, and immediately continuously subjecting a stream of the mixture of sugar crystals and heated mother liquor to centrifugal force of sufficient magnitude to separate the mother liquor from the crystals, in a centrifugal zone having apertures of such size as to permit ejection of the mother liquor but with retention of the crystals, the separation of the crystals from the mother liquor being completed within one minute of said heating,

Claims (1)

1. 4. A PROCESS FOR SEPARATING SUGAR CRYSTALS FROM MOTHER LIQUOR WHEREIN SAID MOTHER LIQUOR CONTAINS SUGAR CRYSTALS SUPERSATURATED WITH SUGAR, COMPRISING ELECTRICALLY HEATING THE MOTHER LIQUOR SUBSTANTIALLY INSTANTANEOUSLY TO A TEMPERATURE OF ABOUT 150* F. TO PRODUCE A MOTHER LIQUOR CONTAINING SUGAR CRYSTALS AND HAVING A DISSOLVED SUGAR CONTENT SUBSTANTIALLY BELOW SATURATION, AND IMMEDIATELY CONTINUOUSLY SUBJECTING A STREAM OF THE MIXTURE OF SUGAR CRYSTALS AND HEATED MOTHER LIQUOR TO CENTRIFUGAL FORCE OF SUFFICIENT MAGNITUDE TO SEPARATE THE MOTHER LIQUOR FROM THE CRYSTALS, IN A CENTRIFUGAL ZONE HAVING APERTURES OF SUCH SIZE AS TO PERMIT EJECTION OF THE MOTHER LIQUOR

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