US2956414A - Apparatus for concentration of solutions by selective freezing of solvent - Google Patents

Description

Oct. 18, 1960 F. STEINBACHER EIAL 2,956,

APPARATUS FOR CONCENTRATION OF SOLUTIONS BY SELECTIVE FREEZING OF SOLVENT I Filed Oct. 23, 1956 2 Sheets-Sheet 1 III/In III/L Friedrich skinbacl'xcr cmoL Caaas JC/meidcr Jchmer /R INVENTORS 77/5? ATTORNEYS Oct. 18, 1960 F. STEINBACHER ETAL APPARATUS FOR CONCENTRATION OF SOLUTIONS Filed Oct. 23, 1956 BY SELECTIVE FREEZING OF SOLVENT 2 Sheets-Sheet 2 r edrich fieifllxcher Md W der 1mtrbck INVENTORS BY mom u MMXIYm dok THE/R ATTORNEYS Patented Oct. 18, 1960 APPARATUS FOR CONCENTRATION OF SOLU- TIONS BY SELECTIVE FREEZING OF SOLVENT Friedrich 'Steinbacher, Munich, Germany, and Carlos Schneider Schmerbeck, Gandia Camino de Daimuz 1, Gandia, near Valencia, Spain; said Steinbacher assignor to said Schmerheck Filed Oct. 23, 1956, Ser. No. 617,767

Claims priority, application Germany Oct. 27, '1955 7 Claims. (Cl. 6258) The present invention relates to a novel process and apparatus for concentrating solutions. More particularly, it relates to an apparatus and continuous process for the concentration of solutions by selectively freezing a portion of the solvent, and separating the solvent crystals from the solute particles which are dissolved in the residual solvent.

In previous procedures for eifecting concentration by freezing of the solvent, it has been found that the solvent solidifies in a laminar form and the crystals are of small size. As a result of the large ratio between the surface and volume of the solvent crystals the loss of solute clinging to the surface of the crystal is considerable and inefficient concentration results. In addition, the small particle size complicates the separation of the solid and liquid phases.

It is accordingly an object of the present invention to provide a process and apparatus for selectively freezing the solvent of a solution in such manner that the solvent crystals are of large size and non-laminar form.

It is a further object of the invention to provide an apparatus in which solvent crystals can be selectively frozen out of a solution in a form which permits ready separation from the residual concentrated solution.

These and other objects and advantages are realized in accordance with the present invention wherein the solution is caused to move spirally in a path extending approximately perpendicularly to the axis of a stirring device. As the solvent is selectively frozen, the crystals thereof tend to rise while the more concentrated residual solution drops through gravity. The spiral motion of the solution also causes the solvent crystals to move along a similar path and, instead of the conventional laminar form, the crystals are more compact and have a smaller ratio of surface to volume. The crystals are continuously Iii-directed toward the cooling surface so thaat additional frozen solvent molecules resulting from continued cooling of the solution add on to the already formed crystals rather than forming new nuclei. Consequently, the solvent crystals become large in size and separation is thereby facilitated.

By making the cooling zone an annular chamber the mixing of solvent crystals of difierent sizes is avoided; rather the size of the crystals increases progressively from bottom to top of the chamber. Consequently, the impermeability to the solution which would result from mixing of diiferent size crystals is avoided and the concentrated solution can readily be drawn oif continuously. Similarly, the solvent crystals can be discharged continuously without appreciable quantities of solute or solution entrained therewith.

By adding the fresh solution near the top, withdrawing concentrated solution from the bottom, and discharging solvent crystals at the top, there will be a continuous countercurrent percolation effect which will serve to increase the amount of solvent which is frozen and will also ensure that larger crystals are formed.

A suitable apparatus for performing the indicated process comprises a vessel with walls defining an annular freezing space, either one or both walls being cooled. A stirring device is arranged within the freezing space and carries stripping members which prevent the solidified solvent from adhering to the cooled Wall. In addition, guiding members are provided which impart to the solution a spiral motion within the freezing space and which redirect solvent crystals toward the cooled surface for continued growth. These guiding members may be carried either by the vessel or by the stirrer and the desired efiect may be achieved either through rotation of the vessel or the stirrer while the other member is stationary. The solvent crystals upon leaving the freezing space may be directed into a percolation column wherein they are washed by fresh solution, which solution is then passed into the freezing chamber.

A suitable apparatus will now be described with reference to the accompanping drawings, wherein:

Fig. l is a vertical sectional view, partly broken away, of an apparatus embodying the invention;

Fig. 2 is a top plan view of a portion of the structure shown in Fig. 1, with the cover removed;

Fig. 3 is a portion of an elevation showing the stirrer arms and guiding members carried thereby;

Fig. 4 is a diagrammatic development showing the sequential arrangement of the guiding members on the stirrer arms; and

Fig. 5 is a perspective view showing a portion of one of the guiding members.

Referring now more particularly to the drawing, in Fig. 1, there is shown a cooling apparatus 1 comprising a cylindrical vessel 2 having an outer wall 3 with a circular bottom 4, and an inner wall 5 with a circular bottom 6. The top of the annular space defined between the outer wall 3 and the inner wall 5 is covered by an annular cover 7 which may be formed of two portions. Both cylindrical walls 3 and 5 are provided with cooling jackets 8 for containing a cooling agent introduced through conduits 9 and drawn off through conduits 10. The cooling agent may be brine which is caused to traverse a helical path 11 as shown at the left in Fig. 1, or it may be a volatile refrigerant which cools by direct evaporation in the channels 12 welded to the cooling jackets as shown at the right in Fig. 1.

At the bottom of the annular freezing space there is provided a collector drain 13 terminating in a spout 14 for removal of the concentrated solution and for emptying of the space when necessary. Within the an nular space there is arranged a stirrer consisting of a supporting member 16 which may be provided with a displacement body 17 for reducing the capacity of the vessel, and with six arms 19 extending vertically from supporting member 16 at equal angular intervals thereabout. The arms 19 carry stripping members 18 staggered in vertical direction with a slight overlap so that they sweep the walls 3 and 5 along their entire height. Between adjacent arms 19 there are supported guiding members 20 (Figs. 2 and 3) which are formed of twisted sheet metal so as to impart to the solution in the freezing space a spiral movement. Guiding members 21 are; also carried between adjacent arms 19 and are provided with deflected blade portions (Fig. 5) which re-direct the solvent crystals toward the cooled walls of the vessel.

In Fig. 4 an illustration is given of the sequential arrangement of the guiding members 20 and 21. The efiectiveness of these members is due to the difference in speed between the stirrer and the solution as a result of the inertia of the latter.

In freezing devices with an inner cooling surface, in-- wardly directed guiding surfaces 22 may be arranged on the stirrer in addition to stripping members 18, the guid ing surfaces 22 approaching closely but being out of contact with the inner wall 5. As shown in Fig. 1, above the cooling jackets 8 the vessel 2 is provided with a solvent crystal discharge arrangement consisting of a ring 23 car- ,riediby the upper ends of arms 19 (Fig. 4).-and having radially directedcross pieces 24 defining cells which conltain the solvent crystals, such as ice. From the ring 23 the crystals pam on to a screwed portion 25 carried by the cover ,7 and move -along to be discharged from the vessel. F The supporting member 16 carrying the stirrer arms 19 is connected to a hollow shaft 26 disposed about the preferably stationary axle 27 of the vessel 2. Rotation of the stirrer 19 is effected by rotatable drive member 28 which is connected with the shaft 26. Fresh solution may be introduced into the annularfreezing space through conduit 29 or conduit 30 from a percolating column connected in series with the cooling vessel.

, In place of helical and deflected strips 20 and 21, the guiding members may be formed as small stationary or movable propellers, as suitably shaped guiding blades or as impact baflies changing the direction of movement of the solution. In an alternative arrangement, the stirrer may be driven from above. The stirrer arms may be provided in pairs so as to form U-shaped stirrups and the guiding members may be attached to the bottom of the annular freezing space and may project upwardly between the U-shaped stirrer arms. In place of rotating the stirrer, the cooling vessel may be rotated while the stirrer is.stationary and the same results will be achieved.

If desired, cooling agent may be provided only to one of the cooling jackets so that only one of the walls of the annular freezing space is cooled, preferably the inner one. In a further embodiment, a freezing device provided with inner and outer cooling jackets can be provided with a pair of spaced stirrers rotating in opposite directions, and a stationary support for the additional guiding members may be positioned between the stirrers. In this arrangement, the screw portion 25 may be carried by the stationary support rather than by the cover 7. The upward passage of the solvent crystals may be assisted by additional guiding blades in the shape of whole or subdivided helical members provided with concentrically arranged slots for treating clear pulp-free solutions.

In place of having the cooling vessel axle 27 extending vertically, however, the vessel may be turned on its side so that the axle extends horizontally, in which case the advance of the solvent crystals will be achieved solely by the guiding blades without taking advantage of the buoyancy of these crystals. 7

In Fig. -1 there is also shown a percolating column which can be serially connected with the cooling vessel 2. The column comprises a cylindrical tubular member 31 with a shaft 32 rotated by drive member 33. The tube 31 is closed off at its top by a cover 34 through which the shaft 32 passes and the bottom 35 is connected by the conduit 30 with the annular freezing space of the vessel 2. If the solution to be concentrated is to be admitted to the vessel solely through the percolating column, the conduit 29 may be wholly closed off or both conduits 29 and 30 may be used for introduction of solution.

4 From the solvent crystal discharge outlet of vessel 2, the solvent crystals pass through conduit 36 into member 31. A screw conveyor 37 carried on shaft 32 is arranged opposite conduit 36 and serves to move the crystals upwardly, supplementing the natural buoyancy effect. The crystals then pass into a mixing zone 38 in which mixing flaps 39 and 40 are alternately arranged on the shaft 32 screw so as not to interfere with rotation of the screw. The vertically extending cells defined by separators 46 will be filled with the solvent crystals, e.g., ice, and the crystals then proceed into an emptying device 49 attached to the hollow portion 43 of shaft 42 from which they are discharged through exit pipe 50. The percolating effect can be achieved Within the freezing vessel itself by combination of the structures shown in Fig. 1 into a unitary apparatus. To this end the vessel 1 would be elongated in the direction of advance of the ice, preferably with gradual reduction of the diameter. The conveying screw may be arranged either rotatably in the stationary jacket for the frozen solvent or it can be maintained stationary within the rotating jacket similar to element 23. 1 7

Various changes and modifications may be made without departing from the spirit and scope of the present invention and it is intended that such obvious changes and modifications be considered Within the purview of the annexed claims.

We claim:

1. An apparatus for concentrating solutions by cooling to solidify selectively a portion of the solvent and leave a more concentrated solution, comprising a vessel having a pair of walls defining an annular freezing space, means for cooling at least one wall of said vessel, a stirring member within said freezing space, means for producing relative movement between said vessel and said stirrer thereby to elfect movement of solution within said freezing space, stripper means carried by said stirrer and contacting the cooled wall of said vessel so as to prevent solvent crystals from adhering to said wall, bladed guiding means including a plurality of blades disposed in and extending transversely of said annular freezing space so as to re-direct solvent crystals toward said cooled wall, thereby causing said crystals to grow as opposed to forming many new small crystals, and helical guiding means within said annular freezing space, said helical guiding means supported by said stirrer and imparting a helical motion to the moving solution.

2. An apparatus as defined in claim 1, wherein said cooling means acts on the inner wall of said vessel.

3. An apparatus as defined in claim 1, wherein said cooling means acts on both walls of said vessel.

4. An apparatus as defined in claim 1, wherein said vessel is stationary and said means for producing relative movement acts on said stirrer.

5. An apparatus as defined in claim 1, including outlet means provided in said vessel adjacent the bottom thereof for withdrawing concentrated solution from the bottom of said annular freezing space, a percolating column, a large conduit connecting said column with the top of said freezing space, a small conduit connecting said column with said freezing space below the points of connection of said large conduit, a solvent crystal outlet adjacent the top of said column, and means for introducing fresh solution into said column intermediate its connection with said large conduit and said solvent crysand the member 31. Fresh solution is introduced either tal outlet.

6. An apparatus for concentrating solutions by cooling to solidify selectively a portion of the solvent and leave a more concentrated solution, comprising a vessel having a wall defining a freezing space, means for cooling said wall of said vessel, a stirring member having a longitudinal axis and being disposed within said freezing space, means for producing relative movement between said vessel and said stirring member thereby to effect movement of solution in said freezing space, stripper means carried by said stirring member and contacting the cooled wall of said vessel so 'as to prevent solvent crystals from adhering to said wall, bladed guiding means disposed within said annular freezing space and extending in-superposed annular zones concentric with said axis so as to re-direct solvent crystals toward said cooled wall, thereby causing said crystals to grow as opposed to forming many new small crystals, and helical guiding means supported by said stirrer and disposed within said superposed annular freezing space and extending in annular zones concentric with said axis whereby upon producing relative movement between said vessel and said stirring member said helical guiding means imparts to the solution a. helical motion Within said freezing space.

7. Apparatus as defined in claim 6 including outlet means provided in said vessel adjacent the bottom thereof for continuously withdrawing concentrated solution from said annular freezing space, a solvent crystal outlet adjacent the top of said annular freezing space, and inlet means adjacent the top of said annular freezing space for introducing fresh solution into said annular freezing space.

References Cited in the file of this patent UNITED STATES PATENTS 761,387 Monti May 31, 1904 2,119,182 Schuftan May 31, 1938 2,227,887 Koropchak Jan. 7, 1941 2,240,463 Schlumbohm Apr. 29, 1941 2,503,395 Leboeuf Apr. 11, 1950 2,552,524 Cunningham May 15, 1951 2,579,421 Egan Dec. 18, 1951 2,657,549 Wenzelberger Nov. 3, 1953 2,657,555 Wenzelberger Nov. 3, 1953

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