US3506486A - Continuous crystallization - Google Patents

Description

N. GANIARIS CONTINUOUS CRYSTALLIZAIION A ril 14, 1970 2 Sheets-Sheet 1 Filed Jan. 2, 1968 Ap 1970 N. GANlARlS 3,506,486

CONTINUOUS CRYSTALLI ZATION Filed Jan. 2, 1968 2 Sheets-Sheet 2 United States Patent O 3,506,486 CONTINUOUS CRYSTALLIZATION Neophytos Gauiaris, Riverdale, N.Y., assignor to Struthers Scientific and International Corporation, a corporation of Delaware 'Filed Jan. 2, 1968, Ser. No. 695,083 Claims priority, application Great Britain, Dec. 30, 1966,

58,299/66 Int. Cl. C13f 1/02 US. Cl. 127-58 4 Claims ABSTRACT OF THE DISCLOSURE Dextrose is continuously crystallized from a massecuite in a crystal slurry which is continuously recycled between a hold-up tank and a tubular crystallizer and which has a mother liquor from a crystal separating centrifuge recycled to the crystallizer to control the percentage of crystals in the crystllization zone.

BACKGROUND OF THE INVENTION Dextrose is conventionally crystallized from a massecuite in batch crystallizers which require 70 to 100 hours to grow crystals to the desired size of about 200 microns. This invention crystallizes dextrose (monohydrate or anhydrous) in a continuous process which is less costly, produces crystals with a desired average size distribution of at least 150 to 250 microns, and reduces residence time in the continuous crystallizer to less than 24 hours.

SUMMARY OF THE INVENTION crystals in the slurry and thus promote crystal growth in the crystallizer and the hold-up tank.

BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is a schematic drawing showing apparatus used in the process of this invention; and

FIGURE 2 is a phase diagram for dextrose and water.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGURE 1, massecuite at 140 to 160 F. with a concentration of about 80 percent dextrose flows from reed pipe into feed tank 11. By means of pipes 12 and 13 and pump 14, feed is introduced into the crystallizer 15.

Crystallizer 15 is of the tubular type having a central tube 16 to contain the feed and an outer cooling jacket 17 into which cooling water enters through pipe 18 and from which the cooling water exits through pipe 19. Disposed Within central tube 16 is a shaft 20 which is oscillated by a motor drive 21. Agitator blades 22 are mounted on shaft 21 to extend with a slight clearance from the walls of tube 19. The blades 22 are oscillated to sweep past a given point on the walls of tube 19 at a rate of 20 to 45 cycles per minute. This agitation ensures a high heat transfer rate from the viscous feed to the walls of tube 16.

Feed with crystals forming therein flows from crystallizer 15 through pipe 24 into hold-up tank 25 which 3,506,486 Patented Apr. 14, 1970 is equipped with an agitator 26 driven by motor 27 to maintain crystals within the feed in suspension as a slurry. Pipe 28, pump 29, and pipe 30 recycle crystal slurry from hold-up tank 25 back into feed entering crystallizer. Efiluent crystal slurry flows from tank 25 through pipe 31 to centrifuge 32. Crystal water enters centrifuge 32 through pipe 33; crystals are removed as a product through pipe 34; and, mother liquor flows from centrifuge 32 through pipe 35.

The agitator 26 maintains crystals in tank 25 in suspension Where crystals continue to grow in the cooled slurry. The volume of hold-up tank 25 is related to the residence time required to grow crystals of a desired average size of 200 to 300 microns. In the process of this invention, the residence time is less than 24 hours and the volume of the crystallizer 15 should be less than /6 the total volume required for such residence time. Thus, the hold-up tank should have a capacity at least five times that of the crystallizer 15.

Centrifuge 32 is preferrably a high speed centrifuge having a perforated basket with a screw type crystal advancing apparatus turning 5 to 15 rpm. faster than the basket. If desired, other equivlent types of centrifuges or separation apparatus may be used;

Mother liquor from centrifuge 32 passes through pipe 35 to the mother liquor tank 36. Pump 37 recycles mother liquor through pipes 38 and 39 to feed tank 11. The recycle of mother liquor into the feed tank 11 adds mother liquor to the feed. Since substantially all the dextrose has been crystallized from the recycled mother liquor, it will reduce the percentage of crystals by Weight in the slurry which enters the crystallizer 15 through pipe 30. This. renders the slurry in crystallizer 15 less viscous to impove heat transfer and crystal growth in the slurry. For best results, the slurry entering crystallizer 15 should contain 25 to 45 pecent crystals by weight. This percentage is controlled by the amount of mother liquor recycled from tank 36. Efiluent mother liquor flows from tank 36 through pipe 40 and may be further processed and sold as a syrup.

As an example of this invention, a system with a residence time of 12 hours was operated for one Week on a continuous basis. The feed composition was 74 percent dextrose with 6 percent impurities in the form of higher sugars and 20 percent water. The slurry recycle rate was eight times the feed rate and the mother liquor recycle rate Was 25 percent of the feed rate. The feed entered at a temperature of to F. and was crystallized at 115 F. for the production of dextrose monohydrate crystals. Crystals of approximately 200 microns in size were continuously produced.

As may be seen from FIGURE 2, a change in crystallization temperatures will produce monohydrate dextrose crystals if desired. It is to be pointed out that crystal growth takes place both in the crystallizer 15 and in the hold-up tank 25. To grow crystals of the desired size, the recirculation rate of the slurry should be between 4 and 15 times the feed rate from tank 11.

What is claimed is:

1. A process for the continuous crystallization of a dextrose from a massecuite comprising the steps of:

(a) passing a feed of a massecuite through a crystallizer into an agitated hold-up tank to form a dextrose crystal slurry,

(b) recirculating the slurry from the agitated hold-up tank through the crystallizer at a rate of at least four times the feed rate to continue the growth of dextrose crystals therein,

(0) withdrawing some of the slurry from the hold-up tank to a crystal separating device separating dextrose crystals from mother liquor, and

3 4 (d) recycling at least some of the mother liquor into References Cited the feed to reduce the percentage by weight of dex- UNITED STATES PATENTS trose crystals entering the crystallizer.

2. The process according to claim 1 wherein mother 1,652,393 12/1927 cP1a[ 1d liquor is recrycled reducing the percentage by weight of r 1,722,761 7/ 1929 Newlilrk 127-60 X dextrose crystals entering the crystallizer to between 0 1,750,939 3/1930 Nwk1rk 127-60 X 25 and 45 percent. 2,091,900 8/ 1937 Wldmer 127-15 3. The process according to claim 2 wherein residence 2651566 9/1953 Warner et 23 273 X time in said process is less than 24 hours and dextrose 3257665 6/1966 Idaszak "f" 127 60X crystals separated from mother liquor have an average MORRIS O.WOLK, Primary Examiner size of 200 microns.

4. The process according to claim 3 wherein the feed CONLIN Asslstant Exammer is passed through a tubular crystallizer containing an US. Cl. X.R.

agitator oscillating between to cycles per minute. 127-15,

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