Patent Publication Number: US-3880593-A

Title: Crystallization apparatus

Description:
United States Patent 1191 Windal 1451 Apr. 29, 1975 1 1 CRYSTALLIZATION APPARATUS [75] Inventor: Georges Windal, Roubaix. France [73] Assignee: Five Lille-Cail, Paris. France 122] Filed: Mar. 29. 1973 [211 App]. No.: 345,993  
 [30] Foreign Application Priority Data Mar. 29. 1972 France 72.10951 [52] US. Cl 23/273 R [51] Int. Cl BOld 9/00 [58] Field of Search 23/273 R. 295; 62/58; 159/45. 27 B; 202/173, 174  
 [561 References Cited UNITED STATES PATENTS 1340.653 5/1920 Gibson 202/173 1.799.478 4/1931 Pecblcs 23/273 R 2,658,029 11/1953 Uztcrmann 4. 202/173 2993.844 7/1961 Nilan 202/173 3.266.871 8/1966 Mizoguchi et a1.. 23/273 R 3.424.221 1/1969 Luce r 23/273 R 3.627.582 12/1971 Dambrinc et a1. 23/273 R 3,687.636 8/1972 Damhrinc ct al. 23/273 R 3,715,191 2/1973 Rushton 23/273 R 3.725.127 4/1973 Rclali ct a1 23/273 R Primary E.\&#39;uminer-Norman Yudkoff Asxislun! Examiner-D. Sanders Attorney Agent. or Firm-Kurt Kelman [57] ABSTRACT A crystallization apparatus with a closed cylindrical tank has radial dividing walls in the lower tank portion to define therebetween a plurality of compartments ranging from a first compartment upstream to an output compartment downstream. All the walls, except the one between the output compartment and the first compartment upstream thereof, have ports permitting communication between the compartments for continuous flow therethrough ofa solution whose solute is to be crystallized by evaporation. A feeding means for feeding an undersaturated solution of the solute into successive compartments is arranged in the upper portion of the tank for rotation about the vertical tank axis to sweep over the successive compartments. and shutters are provided for controlling the amount of the undersaturated solution fed to each of the compartments.  
 7 Claims, 5 Drawing Figures CRYSTALLIZATION APPARATUS The present invention relates to improvements in apparatus for crystallization of the solute of a solution by evaporating the solvent of the solution in a continuous operation. More particularly, it relates to such apparatus which has a closed cylindrical tank having a vertical axis andradially extending dividing walls in the lower portion of the tank defining therebetween a plurality of heated compartments ranging from a first compartment upstream to an output compartment downstream. All the walls, except the wall between the output compartment and the first compartment upstream thereof, have port means permitting communication between the compartments.  
  In apparatus of this type, it has been proposed to introduce into a first compartment a concentrated solution of a solute to be crystallized, together with seed crystals, and to cause this mixture to pass downstream through all of the successive compartments in the tank, which extend radially about the vertical axis thereof. As the mixture passes through the heated compartments, the solvent is evaporated and the final crystallized product is removed from the output compartment, the crystallization of the dissolved solute causing the progressive increase in the size of the seed crystals. An undersaturated solution of the solute is introduced into each compartment and the feed rate thereof is so controlled that the saturation of the solution in each compartment is maintained at a value corresponding to the optimum speed of crystallization, taking into account the rate of evaporation in the heated compartments.  
  It is the primary object of this invention to improve a crystallization apparatus of this general type which not only permits the ready control of the feed rate of the solution to the compartments but also assures effective washing of the tank and dividing walls defining each compartment with the undersaturated solution fed thereto.  
  The above and other objects are accomplished in accordance with the invention with a feeding means for feeding an undersaturated solution of the solute into successive ones of the compartments, which feeding means is arranged in the upper portion of the tank for rotation about the vertical tank axis to sweep over the successive compartments, and means for controlling the amount of the undersaturated solution fed by the feeding means into each of the successive compartments.  
  The above and other objects, advantages and features of the present invention will become more apparent from the following detailed description of two now preferred embodiments, taken in conjunction with the accompanying drawing wherein FIG. 1 is a vertical axial section of one embodiment of the crystallization tank of this invention;  
  FIG. 2 is a horizontal cross section of the tank of FIG.  
  FIG. 3 is a schematic developed view of the successive compartments of the tank of FIG. 1;  
  FIGS. 4 and 5 show another embodiment ofa tank in the same manner as FIGS. 1 and 2, respectively.  
  Referring now to the drawing and first to FIGS. 1 to 3, there is shown a cylindrical tank having a vertical axis. The respective ends of the tank are closed by conical end walls 12, 14. The lower portion of the tank adjacent closure wall 14 is divided into eight compartments 0 to 7 by vertical, radial walls 15 extending from end wall 14 up about two thirds of the height of the tank. Dividing walls 15 are fixed, on the one hand, to wall 11 of the tank and, on the other hand, to central post 16 extending along the tank axis. The successive evaporating compartments 0 to 7 are defined between the tank closure wall 14, the tank side wall 11 and respective pairs of adjacent dividing walls 15.  
  Means for controlling access to the compartments is constituted in the illustrated embodiments by shutters 18 which are movably mounted on the upper parts of dividing walls 15 whereby moving of the shutters controls access to the respective compartments and thus the amount of the undersaturated solution fed into each of the successive compartments. The illustrated shutters are triangular and are pivotal about horizontal axes 20 defined by the upper edges of the dividing walls, to which they are hinged for pivotal movement in a manner best shown in FIG. 3.  
  The illustrated shutters have the configuration of isosceles triangles. Each triangular shutter has an apex close to the vertical tank axis, the angle at the apex being smaller than, or equal to, half of the smallest angle formed between the dividing wall whereon it is mounted and the two dividing walls immediately adjacent thereto. In this manner, neighboring shutters will not interfere with each other during their pivoting movements.  
  Control means which may be manipulated from outside the tank (not shown) permit the shutters to be pivoted into desired angular positions and to be held in such positions to determine the access to the compartments from above, in the manner illustrated clearly in FIG. 3.  
  In the embodiment shown in FIGS. 1 to 3, the volume of successively arranged compartments 1 to 7 increases regularly in an downstream direction. These compartments serve for the crystallization of the undersaturated solution fed thereto while compartment 0 serves for the concentration of the solution. Output compartment 7 has an outlet conduit 24 through which the crystallized product is removed.  
  All the dividing walls 15, except the wall between output compartment 7 and compartment 0 immediately upstream thereof, have ports 28 therein permitting communication between the compartments so as to permit the solution to flow therethrough from compartment 0 to compartment 7 whence the product is removed, there being no communication between compartments 7 and 0.  
  The heating means for the evaporating compartments shown in FIGS. 1 and 2 is steam radiator 30 mounted centrally in the bottom of the tank andbeing of circular shape to define an annular space 31 between the periphery of the radiator and the side wall 11 of the tank. A steam inlet 29 passes through tank closure wall 14 to supply steam to the radiator for heating the compartments. The radiator may have any desired form and may include, for instance, heat exchange tubes or radially or circularly arranged plates.  
  It would also be possible, of course, to arrange separate radiator or like heating means in each compartment, such heating means being the same or different in each compartment. For instance, the heat exchange elements of the heating means in compartment 0 and the first, of the first few, compartments may be more closely spaced because the undersaturated solution circulating therethrough is less concentrated and relatively fluid.  
  Undersaturated solution is fed into successive evaporating compartments by feeding means 32 arranged in the upper portion of tank for rotation about the vertical tank axis to sweep over the successive compartments during its rotation. The feeding means is a sprinkling pipe 32 mounted on the inlet pipe 13 supplying an undersaturated solution of the solute to be crystallized to the tank. A turning joint 17 mounts the pipe 32 on pipe 13to permit rotation of pipe 32, a suitable motor means (not shown) being provided for turning pipe 32 at a constant speed selected for efficient operation. Suitable means &#34;may be provided to regulate the speed of the motor whereby the rate of feeding solution to the successive compartments may be changed.  
  &#39;Sprinkling pipe 32 has a plurality of jet openings or nozzles 19 arranged to discharge the solution against the respective dividing walls and the tank side wall 11 so that the solution will run down the walls in a thin film and wash the walls with solution.  
  While the sprinkling pipe may extend horizontally or in any suitable direction, it has been illustrated to be inclined to the horizontal at substantially the same angle of inclination as an adjacent side of the triangular shutters 18 As shown&#39;in FIG. 1, the lower portion of tank 10 is surrounded by jacket 33 through which a heating fluid may be circulated so as to provide good heat insulation for the evaporating compartments in the tank.  
  The crystallization tank hereinabove described operates as follows:  
  As the sprinkling pipe 32 is rotated and sweeps over successive compartments 0 to 7, undersaturated solution of the solute to be crystallized is fed into the successive compartments periodically, i.e. once into each compartment during one revolution of the pipe 32. The solution is concentrated in compartment 0, the heat in this compartment being so regulated that sufficient solvent is evaporated therein to produce a super-saturated solution. This concentrated solution enters compartment 1 wherein seed crystals or a magma are introduced. This mixture then flows through the successive compartments, evaporation taking place in each one of them, until the final product is removed from output compartment 7 by outlet pipe 24.  
  The amount of solution supplied by pipe 32 to each compartment must be regulated to compensate for the volume of solvent evaporated so that the degree of desired supersaturation of the solution is maintained during the flow of the solution through the tank compartments. This regulation is&#39;effected by means of pivotal shutters 18 whose inclination may be so adjusted that the inlet section giving access to the compartments may be varied, as shown in FIG. 3. Since the amount of solution flowing into each compartment as the pipe 32 passes thereover depends on the size of this access opening, the shutters permit any desired variation of the distribution of the solution over the eight compartments of the total amount of solution discharged from pipe 32 during one revolution.  
  Systems are known for modifying the total amount of undersaturated solution fed to the crystallization tank as a function of the amount of steam consumed by the radiators for the evaporating compartments, as a function of the concentration of the fed solution, or as a function of the solution characteristics sensed in one of the compartments or at the output. Such known systems may be used to control the feed rate through pipe 32. Alternatively, the amount or pressu re of steam supplied to the radiator may be regulated in a &#39;manner which is also known per se.  
  As shown in FIG. 2, an inlet 38 to output ment 7 may be connected by feed conduit 37 to the inlet pipe 13 to permit a complementary supply of un-&#39; dersaturated solution to be fed into compartment 7. Control valve 39 in conduit 37 is regulatedautomatically in a known manner to maintain the flow rate of the complementary supply as a function of thedensity,  
 viscosity or other selected characteristic of the product leaving compartment 7. If desired, the inlet 38 may lead to a bank of sprinklers placed in compartment 7 along one of its walls above the level of the solution in the compartment.  
  If found desirable, complementary amounts of solution may also be supplied to other selected compartments.  
  The solution projected from feed pipe 32 against the compartment walls forms a liquid film running down the walls and dissolving the crystals which have been deposited thereon. The speed of rotation of the pipe is so selected as to assure efficient washing of the walls by the solution.  
  The vapor produced in the tank is evacuated therefrom through flue 34 connected to a vacuum pump; As in known crystallization apparatus of this type, the steam pressure for the radiators and the vacuum in the tank may be controlled in any desired manner.  
  If the solution is concentrated in a separate apparatus, as in some crystallization systems, compartment 0 would be eliminated from the tank and the concentrated solution mixed with seed crystals or magma would be introduced into the first evaporating compartment.  
  FIGS. 4 and 5 show an apparatus differing from the embodiment of FIGS. 1-3 in details of construction. In this embodiment, the radially extending dividing walls 15&#39; are equidistantly spaced and six evaporating compartments of equal volume are defined therebetween.  
  The centrally positioned circular heater is replaced by an annular radiator consisting of interdigitating long heat exchange plates 40 alternating with short heat exchange plates 42 affixed to the wall of the tank 10&#39; and radially extending towards the center post 16 thereof, leaving an annular space 31 between the radiator and the center post. The plates are hollow to receive steam from steam chests 44 and are stacked vertically around the center post, a separate steam chest being provided for the radiator plates of each compartment may be independently regulated.  
  Obviously, the heat exchange elements may also be circular hollow plates arranged concentrically, or they may be tubular radiators of known construction.  
  It will be understood by those skilled in the art that the structure and disposition of the heating means for the evaporating compartments may be changed at will.  
  The apparatus is useful for crystallizing any solute of a solution by evaporating the solvent thereof andhas been used successfully for the production of crystals of sugar from sugar-containing juices. I  
 . Whatis claimed is:  
  l; A crystallization apparatus for crystallizing the solute of a solution by evaporating the solvent of the solution in a continuous operation, comprising compart l. a closed cylindrical tank having a vertical axis, the  
 tank having an upper and a lower portion,  
 2. radially extending dividing walls in the lower portion of the tank defining therebetween a plurality of compartments ranging from a first compartment upstream to an output compartment downstream, a. all the walls, except the wall between the output compartment and the first compartment upstream thereof, having port means therein permitting communication between the compartments,  
 3. a feeding means for feeding an undersaturated solution of the solute into successive ones of the compartments,  
 a. the feeding means being arranged in the upper portion of the tank for rotation about the vertical axis to sweep over the successive compartments, and  
 4. means for controlling the amount of the undersaturated solution fed by the feeding means into each of the successive compartments.  
  2. The crystallization apparatus of claim 1, wherein the solution feed controlling means comprises shutters movably mounted on the upper parts of the dividing walls whereby moving of the shutters controls access to the respective compartments.  
  3. The crystallization apparatus of claim 2, wherein the shutters are pivotally mounted on the upper edges of the dividing walls.  
  4. The crystallization apparatus of claim 3, wherein each shutter has the configuration of a triangle having an apex close to the vertical tank axis, the angle at the apex not exceeding half the angle formed between two adjacent dividing walls.  
  5. The crystallization apparatus of claim 4, wherein the feeding means is inclined to the horizontal, having substantially the same inclination as an adjacent side of the triangular shutters.  
  6. The crystallization apparatus of claim 1, wherein the feeding means comprises a plurality of solution feeding nozzles, the nozzles being arranged to sprinkle the solution against the respective dividing walls and the tank.  
  7. The crystallization apparatus of claim 1, further comprising a supplemental liquid feed conduit leading to the output compartment for feeding a supplemental amount of the solution to the output compartment, and an adjustable valve mounted in the feed conduit for controlling the supplement solution amount fed to the output compartment.