EP1279745B1 - Process for batchwise preparation of big sugar crystals - Google Patents

Abstract

To produce large sugar crystals of ≥ 5 mm and preferably ≥ 8 mm, in batches, the crystals are developed by vapor crystallizing in a crystallizing vessel. A relative movement is generated between the developing crystals and the over-saturated sugar solution, to give the crystals a floating movement. To produce large sugar crystals of at least 5 mm and preferably at least 8 mm, in batches, they are developed by vapor crystallizing in a crystallizing vessel. A relative movement is generated between the developing crystals and the over-saturated sugar solution, to give the crystals a floating movement. The relative movement is developed by a rising flow of the sugar solution, without any mechanical action, controlled by the water content recovered from evaporation. The heating is controlled to maintain the over-saturation of the sugar solution at a constant level. The assembly also has a heated sieve base, and a separation system for newly-formed fine grains in a collection vessel which calms the flow.

Description

The present invention is a process for the batch production of large sugar crystals with crystal sizes over 5 mm, preferably over 8 mm by evaporation crystallization in a crystallization vessel, wherein between the growing sugar crystals and the supersaturated sugar solution, a relative movement is produced, which suspended the growing sugar crystals holds using a device as defined in the claims for carrying out this method. Large sugar crystals over 5 mm, produced by special crystallization processes from concentrated, pure sugar solutions, are also called candy sugar.

In special applications of sugar, it is important that the sugar slowly dissolves and only slowly sets a high concentration or the sweet taste. For this purpose, sugar candy with crystal sizes over 5 mm, preferably even over 8 mm is still used.

The production processes for sugar crystals with crystal sizes over 5 mm, preferably over 8 mm, developed from the crystallization of threads, which, introduced into supersaturated sugar solutions, allow a slow and uniform growth of the sugar crystals. However, the threads remain in the sugar crystals, which is perceived by consumers as disturbing. For Kandis without threads, therefore, various manufacturing processes have been developed and used for about 100 years; see. AT 35 841 ,

Crystallization of sugar from supersaturated solutions produces, depending on the process conditions, more or less fine-grained products and, under certain other conditions, solid agglomerates of crystals of various sizes, which are mechanically coarsely granular. These products have the irregular shape of regrind and not the regular monklin sphenoidal form of sugar crystals, which is a sign of quality and purity to the consumer.

From the patent literature of the years 1896 to 1910 a number of more or less complicated and complicated processes for the production of candy are known, ie coarsely crystalline sugar. A summary of this patent literature can be found in the journal of the Association of the German sugar industry 62, (1912) pages 1212 to 1228 , Later added is still the German Patent 239906 , which describes a bottom training for crystallization vessels. In this case, the supersaturated sugar solution is conveyed from top to bottom by a mechanical stirrer at the bottom of the crystallization vessel and introduced into the mixture of sugar solution and crystals in such a way that the sugar crystals are stirred up continuously and the friction on the vessel walls is reduced. This method is still used in principle today for the production of sugar crystals without threads, but it succeeds hereby only extremely difficult to produce crystal sizes over 5 mm.

As the specific surface area of crystals (area / crystal mass) decreases with increasing crystal diameter, the difficulty of controlling crystallization increases with crystal size. The removal of water from the solution, by which the supersaturation is generated as a driving force of crystallization, should not be greater than the possible crystallization rate at the given crystal surface. The existing procedures do not maintain equilibrium. This results in unwanted crystal nuclei, which reduce the yield of large crystals and reduce their quality.

Furthermore, the method according to Wulf and Bock is known, in which a longer, shallow tray with seed crystals is kept in rocking motion. However, the yield is only 18 to 20% of the amount of sugar introduced; see. Technology of Sugar, M. & H. Schaper Hannover, 1968, pages 491 and 492 ,

From the DD 294 731 For example, a process for the production of stringent candy is known in which a continuously supersaturated hot sucrose solution circulated outside the crystallization vessel is recirculated is, are added during the crystallization process at constant temperature seed crystals in cocurrent or countercurrent. The sucrose crystals growing in the recycled sucrose solution are separated by sieving after reaching the desired crystal size. This method also leads to a relatively strong mechanical stress on the sugar crystals and thus not or only with very low yields to the desired large sugar crystals.

Also, the method according to DE-B-1172200 leads only to crystal conglomerates and not to the desired large crystals.

The object of the invention is therefore to provide a process for producing large sugar crystals having crystal sizes of more than 5 mm, preferably more than 8 mm, in which a relative movement is produced by evaporation crystallization in a crystallization vessel between the growing sugar crystals and the supersaturated sugar solution which keeps the growing sugar crystals in suspension, however, further measures are taken to control the crystallization process so as to minimize nucleation disturbances so that the incorporated sugar crystals surely reach the size otherwise achievable only in poor yields.

1. a) einem senkrecht stehenden Kristallisationsbehälter mit
2. b) einer unteren Zuführung für die übersättigte Zuckerlösung,
3. c) einem beheizbaren Siebboden,
4. d) einem Überlauf in ein Auffanggefäß mit größerem Durchmesser als der Kristallisationsbehälter, welcher Einbauten zur Strömungsberuhigung aufweist,
5. e) einer Rückführleitung mit Pumpe für die Zuckerlösung vom Auffanggefäß zur unteren Zuführung des Kristallisationsbehälters,
6. f) einer Abführung im oberen Teil des Auffanggefäßes für Wasserdampf
7. g) einer Zuführöffnung im oberen Teil des Auffanggefäßes für Impfkristalle
8. h) eine Entleerungsöffnung oberhalb des Siebbodens für die fertigen Zuckerkristalle
9. i) Mess- und Steuerungseinrichtungen für Temperatur, Wärmezufuhr und Fließgeschwindigkeit der Zuckerlösung.

The object is now achieved in that the relative movement is produced without mechanically moving parts in the crystallization vessel by an upward stream of sugar solution, which holds the growing sugar crystals in suspension, whereby the amount of water discharged by evaporation from the system is controlled by the heat input into the Sugar solution and the heat supply is controlled so that the supersaturation of the sugar solution is maintained using a device consisting of

1. a) a vertical crystallization vessel with
2. b) a lower feed for the supersaturated sugar solution,
3. c) a heated sieve tray,
4. d) an overflow into a collecting vessel with a larger diameter than the crystallization vessel, which has internals for flow calming,
5. e) a return line with pump for the sugar solution from the collecting vessel to the lower feed of the crystallization tank,
6. f) a discharge in the upper part of the collecting vessel for water vapor
7. g) a feed opening in the upper part of the collecting vessel for seed crystals
8. h) an emptying opening above the sieve bottom for the finished sugar crystals
9. i) measuring and control devices for temperature, heat input and flow rate of the sugar solution.

The crystallization vessel according to the invention has an overflow at the upper end into a collecting vessel with a larger diameter than the crystallization vessel, which already leads to a slowing down of the flow velocity. Through installations for flow calming, this leads to a sedimentation of newly formed fine grain, which can collect at the bottom of the collecting vessel and thus can no longer disturb the crystal growth of the large sugar crystals.

By measuring the temperature, the heat input and the flow rate of the sugar solution, it is possible to control the entire system in such a short time undisturbed large sugar crystals with crystal sizes over 5 mm and well over 8 mm may arise, so that crystal sizes available be made, which otherwise could only be achieved in poor yields.

Preferably, it is ensured that newly formed fine grain is separated in the sugar solution and thus can not interfere with the further growth of the large sugar crystals.

As the surface of the growing sugar crystals becomes increasingly larger, so does the amount of sugar removed from the solution. This is preferably used to increase the rate of production by increasing the rate of upward flow of the sugar solution as the size of the growing sugar crystals increases.

In order to maintain the supersaturation in the solution as a driving force for the crystallization, water must be removed from the solution. In the process according to the invention, this is preferably done by evaporation under reduced pressure. The amount of heat consumed by the evaporation is supplied by appropriate heat in the sugar solution, with a small part is also available through the released heat of crystallization available. The process according to the invention is capable of producing large sugar crystals with high yields, with crystal sizes of up to 25 mm.

Claims (4)

1. A process for the discontinuous preparation of large sugar crystals with crystal sizes of above 5 mm, preferably above 8 mm, by evaporation crystallization in a crystallization tank, wherein a relative motion is created between the growing sugar crystals and the supersaturated sugar solution, keeping the growing sugar crystals floating, characterized in that said relative motion is created without mechanically moving parts in the crystallization tank, by an upward stream of the sugar solution, wherein the amount of water removed from the system by evaporation is controlled by the heat supply into the sugar solution, and the heat supply is controlled to maintain the supersaturation of the sugar solution using a device consisting of:

   a) a vertically oriented crystallization tank comprising

   b) a lower inlet for the supersaturated sugar solution,

   c) a heatable perforated base,

   d) a level drain leading into a collector vessel having a larger diameter than that of the crystallization tank and having built-in structures for calming the flow,

   e) a return line with a pump for the sugar solution leading from the collector vessel to the lower inlet of the crystallization tank;

   f) an exhaust for water vapor in the upper part of the collector vessel,

   g) an inlet for seed crystals in the upper part of the collector vessel,

   h) a discharge opening above the perforated base for the finished sugar crystals,

   i) measuring and controlling means for temperature, heat supply and flow rate of the sugar solution.
2. The process according to claim 1, characterized in that newly formed fine grains are separated from the stream of said supersaturated sugar solution.
3. The process according to claim 1 or 2, characterized in that the velocity of the upward stream of the sugar solution is increased as the size of the growing sugar crystals increases.
4. The process according to any of claims 1 to 3, characterized in that the evaporation of the water is effected under reduced pressure.