DE3819789A1 - COOLING CRYSTALIZATION METHOD FOR PRODUCING SUGAR - Google Patents

Abstract

Sugar is manufactured by crystallisation by cooling, in several stages. Each of these stages envisages, in cascade formation, a concentration of the sugar solution, preferably in a vacuum, at a temperature of about 80 DEG C, and then crystallisation obtained by cooling the solution slowly down to about 35 DEG C. Crystallisation is preceded by the addition of microcrystals and followed by the removal of the crystals which have formed during the process. <IMAGE>

Description

The invention relates to a cooling crystallization process for the production of commercial grade sugar.

As is well known, discoloration is undesirable with sugar, and one therefore tries to discolour already in the crystallization phase to avoid exercises. Recent studies have shown that both color inclusions and inclusions of ash in the Sugar crystals are the more pronounced the more drastic they are Crystallization conditions are, in particular with regard

• Temperature,
• Oversaturation and
• viscosity

of the considered sugar solutions.

As a result, it is practically impossible to get one out rich white sugar by means of a usual crystallization procedure. Some professionals already have that  Application of a cooling crystallization process for the Crystallization of sugar solutions proposed (De Vries, Accinelli) is a viable solution for industrial purposes.

The object of the invention is to remedy this to create by demonstrating a crystallization process that is suitable for industrial use.

According to the invention, this object is achieved by a cooling kri Installation procedure, in several, in a row successive stages takes place, each stage a vacuum concentration and then a cooling crisis stallization includes. In the initial phase of the cooling crystals sation of saturated syrup is provided. At the At the end of crystallization, the crystals which have separated out become secreted.

Two or three stages of this type lead to the last con centering step to a low purity syrup, the crystallized in the traditional way by evaporation must be settled. The sugar obtained in this way can be restored dissolved and added to the starting mass.

Embodiments of the invention are outlined in the claims. In the description below referring to the drawing Exercise is the invention based on exemplary embodiments in individual explained.

Show it:

A schematically simplified representation of an experimental arrangement by means of which the process on a laboratory scale is feasible Fig. 1;

Fig. 2 is a flowchart to illustrate the operational flow in one embodiment of the method and

Examples approximately Fig. 3 and 4 of Fig. 2 similar flow charts illustrating two further exporting.

The simple apparatus shown in FIG. 1 was used for experimental operation on a laboratory scale.

The following symbols are used in the description below:

BRIX = dry matter content of the solution; Qz = purity quotient corresponding to the ratio of the sugar substance contained in the solution to the total dry matter (sugar and "non" sugar) X 100; CS = saturation coefficient of the contaminated solution in relation to the pure solution; BETA = supersaturation coefficient; CV = coefficient of variability; MA = middle opening.

A first series of experiments was carried out with a subset of a factory-made standard syrup with BRIX = 72 and Qz = 91, which was initially concentrated to BRIX = 81 and kept in a storage flask A at a temperature of 80 ° C.

Assuming a CS of 1.05, the syrup is saturated under these conditions.

Part of the same factory standard syrup was concentrated in flask B until BRIX = 84 was reached at a temperature of 80 ° C. At a CS of 1.05 the syrup has a supersaturation coefficient BETA = 1.23 under these conditions. A small amount of seed solution, as is normally used in factory sugar production (one or two drops), was then added to the crystallization flask B.

After crystal formation was found, slow cooling was started, with syrup being simultaneously slowly fed from piston A to piston B by means of a suction device. The ratio between the amount of the base initially charged into the flask B and the syrup supplied was 1: 9. The feed was stopped after about 40 minutes and the cooling was progressively carried out over a period of 4 hours. At the end of this crystallization, the pulp was centrifuged using a basket-type laboratory centrifuge and the sugar was washed thoroughly to completely remove the layer of adhering syrups. The syrup obtained had a BRIX of 74, confirming the theoretically possible yield, as discussed below.

At the same time, samples of sugar were obtained by centrifugation Factory made filler mass from the same standard dard syrup had been obtained in exactly the same way washed like the samples of the sugar obtained by cooling.

The comparison between the properties of medium samples of both Types of sugar are listed in Table 1. The sub Differences between the two types of sugar are visual Observation recognizable, both what the coloring as also affects the grain size.

The outflowing syrup obtained in this first crystallization with BRIX = 74 at 35 ° C and Qz = 86 still contains a remarkable amount of potentially crystallizable sucrose.

Another crystallization can be achieved by this outflowing syrup at high temperature (e.g. 80 ° C) saturates by doing a quick evaporation leads, and that the cooling crystallization be as above wrote repeatedly. To do this on a laboratory scale too mixes of standard syrup and factory Made green syrup used to the conditions to reproduce for this second cooling crystallization.

Using the same equipment as shown in Fig. 1 and preparing the matrix in exactly the same manner as in the first crystallization, the second cooling crystallization was carried out, whereby an outflowing syrup with BRIX = 76 and Qz of about 80 was obtained which was practically saturated at a temperature of 35 ° C. In order to obtain an effluent syrup as a by-product which is sufficiently exhausted to be processed further by cooking in a traditional manner, it was necessary to carry out a further crystallization by repeating the process described above, ie the effluent syrup again Rapid evaporation concentrated at 80 ° C to saturation and cooling crystallization was carried out again. In this case again, in order to obtain a sufficient amount of mass for crystallization, it was necessary to prepare a mixture of factory-made syrup and molasses. The third crystallization was also carried out using a base mass which had been prepared in the same way, whereby, as in the two preceding cases, the ratio of 1: 9 between the base mass and the syrup supplied was maintained and the third stage of the cooling kri Installation was carried out so that an outflowing syrup with a BRIX of about 78.5 and Qz of about 73 was obtained. It can be seen that such an outflowing syrup can be finally exhausted using a conventional cooking method for obtaining lees.

The analytical properties of the three types of sugar produced are shown in Table 2 together. These properties are in the sugar obtained in the second stage and in the sugar obtained in the third stage, what the coloring and the ash content of the sugar, less favorable than the sugar from the first crystallization stage. This stems from the fact that the syrup supplied in both cases Mixtures of factory made syrups are used had to be done before a high temperature cooking process was subjected. However, if from cooling crystallization pro would be available originating syrup would be both the color and the ash content, especially at the crystals obtained from the third crystallization stage, much less. In fact, the cooling Crystallization described the increase in discoloration during the three levels extremely limited since the syrups do not last very long remain at high temperatures, as is the case with the traditional one Cooking is the case.

Examination of the CV values of the three sugars, especially in comparison with the CV of factory-made cane sugar, Table 1, shows a uniformity in the size of the crystals obtained. It is also noteworthy that the crystals obtained by cooling have a special luster because they have not been subjected to any particular thermal shock.

On the basis of the laboratory tests described above, a crystallization process shown in FIG. 2 with three cooling crystallization stages was set up. The values given for the BRIX, Qz and the crystal yield come from theoretical calculations which are based on the changes in the solubility at different temperatures and the saturation coefficients of the syrup at different purities. When examining the values for BRIX and Qz of the various syrups, it can be seen that the crystallization yields obtained in the laboratory test open up the possibility of optimally exhausting the various syrups. It is noteworthy that the crystallization yield varies between 37 and 38% in the three stages, which leads to the fact that the material mass is very liquid, which facilitates centrifuging and washing.

The total crystal yield is approximately 73% of the initial sucrose with the following distribution of the percentages to the individual levels: 45.6 for the first level, 32.2 for the second stage and 22.1 at the third stage. In this first rough scheme is neither a use of that sugar considered by crystallization of the after product is obtained, still use of the syrup refining after washing centrifugation of the crystals.  

In the diagram of FIG. 3, refining of the raw sugar of the by-product, its redissolution and the addition and addition to the standard syrup as well as the redissolution of 8% of the crystals during the washing centrifugation are considered. It can be seen that a different amount of sugar has to be crystallized in the individual stages and therefore a different distribution of the temperatures is required for the cooling processes.

In the diagram of FIG. 4, sugar of the by-product is added to the last stage of the cooling crystallization after it has been refined, the dissolution of 8% of the crystals during centrifuging washing being taken into account in each case. In this case, too, as can be seen, different amounts of sugar have to crystallize in the individual stages, so that the temperature distribution for the cooling processes must be selected accordingly in order to achieve the best possible degree of exhaustion.

A thorough review of the three diagrams shows that, depending on the solution type selected, it is possible to achieve the planned degree of exhaustion based on a suitable choice of the distribution of the temperatures in the three crystallization stages. Table 3 shows various possibilities, including the case that a smaller amount (5%) of sugar is dissolved during centrifugation, the Qz value of the thick juice is 90 instead of 91, and the hypothetical case that the crystallization in four stages instead of three. Appropriate calculations were carried out for the evaluation of the entire cooling crystallization process from the standpoint of energy consumption and with regard to the plant technology, the example according to FIG. 3 being compared both with the conventional refining technology and with white sugar free-cooking methods. The data obtained, shown in Table 4, show that the energy balance in the cooling crystallization process is far more favorable than in the conventional refining process (the energy consumption is less than half). A comparison with a white sugar free cooking process shows that the consumption values are comparable. However, it should be noted that in the latter case the quality of the sugar produced is far lower. With regard to the evaporation area, it should be noted that the total evaporator area in the cooling crystallization process is considerably smaller (approximately the fourth part) than in the conventional process. Finally, the volume of the crystallization containers required in the cooling crystallization is larger than in the conventional crystallization (about 1.5 times).

The advantages of the invention can be derived from the above values summarize in some essential aspects as follows:

• - Starting from thick juice can directly crystalline sugar in Trade grade can be obtained.
• - None of the three crystallization stages provided the crystallization time exceeds four hours.
• - The temperature jump during cooling is between 80 and 35 ° C, and it is possible to make suitable modifications depending of the system used.
• - The sugar produced is easily centrifuged and washable due to the fluidity of the mother liquid. In addition to the good analytical properties, it has a beautiful, characteristic gloss and good MA and CV values.
• - The color increase of the individual syrups is over the whole Crystallization phase less than with conventional processes.

Table 1

Comparison of the properties of in the first stage sugar obtained by cooling with factory-made provided sugar (first product).  

Table 2

Analytical properties of the three types of sugar that in laboratory operation in the three cooling crystallization levels can be obtained.  

Table 3

Different ways of performing the cooling crystallization.  

Table 4

Comparison between cooling crystallization, refining and White sugar free cooking process. Production volume 1000 t / day.  

• - Compared to the traditional crystallization, the Energy comparison in favor of the cooling crystallization ver driving out.
• - The total evaporator surface is significantly reduced.
• - The additional volume required for crystallization men is very low.

Limit the foregoing description and drawings referring only to the specification of characteristics for the example wise embodiment of the invention are essential. So much for the features in the description and in the drawing disclosed and are not mentioned in the claims serve if necessary, they also determine the object the invention.

Claims (8)

1. Cooling crystallization process for the production of commercial grade sugar, characterized by the following sequence of process steps.

• a) that a starting mass in the form of a standard syrup with a dry matter content (BRIX) between 65 and 75 and a purity ratio (Qz) between 85 and 95 is concentrated to saturation at a given temperature between 75 and 100 ° C within the shortest possible time by vacuum heating;
• b) that crystallization nuclei are added to the concentrated solution obtained in step a);
• c) that the cores added in step b) are increased by increasing cooling and
• d) that the crystals formed during the previous cooling are separated by centrifugation.

2. The method according to claim 1, characterized in that that the syrup masses, the cooling crystals one after the other should be subjected to saturation at pre given temperature can be concentrated by vacuum-quick evaporator are used so that the syrup masses during the shortest possible time at a high temperature level remain in order to prevent the coloring taking place at high temperatures to keep the intake as low as possible.   3. The method according to claim 1 or 2, characterized net that the four steps a) to d) went through more than once be followed, following steps using the at advance mother solutions obtained. 4. The method according to any one of claims 1 to 3, characterized characterized in that with the addition of crystallization nuclei Cores are used that are contained in a basic mass. 5. The method according to any one of claims 1 to 3, characterized characterized in that with the addition of crystallization nuclei these are added in the form of powdered sugar sludge. 6. The method according to any one of claims 1 to 5, characterized characterized in that the phase of increasing cooling approximately for four hours with a temperature gradient of approximately 10 ° C per hour and is stopped when the tempe temperature of the supersaturated solution is about 30 to 40 ° C. 7. The method according to claim 4 and one of the others in advance outgoing claims, characterized in that the ratio between the base mass and that in the crystallization phase solution between 1 to 8 and 1 to 12 and preferably between 1 to 9 and 1 to 11 lying. 8. The method according to any one of claims 1 to 7, characterized characterized in that at the last crystallization phase obtained low purity solution a traditional crystal tion process with molasses is subjected, the Any sugar obtained after refining is dissolved and the starting standard syrup or an intermediate the cooling crystallization is added.