After the automation of crystallization in sugar factories

In the sugar industry the crystallization process is carried out by evaporation. Removing water from the solution ensures the stability and growth of sugar crystals.

For this, the concentration of sucrose in the solution must be maintained at a point where the transformation of liquid sugar to a solid state (crystals) is feasible.

This concentration point is called the supersaturation index. In such a way that if the index is very low (less than 1.0) the crystals dissolve and if it is very high (greater than 1.3) the formation of spontaneous crystals occurs, which damage the quality of the final sugar.

Traditionally, the sugar crystallization process has operated with manual operation, which means that each tacho operator uses their own criteria to crystallize. Therefore, the final results vary from one operator to another in terms of processing time, exhaustion, crystal size, coefficient of variation (of size) and steam energy consumption.

The implementation of automatic control strategies for the crystallization process is not easy because a tacho has multiple variables to manipulate, such as pressure, temperature, level and ˚Brix.

Impurities affect crystallization and, currently, there is no direct measurement of supersaturation, the growth rate or crystal shape is not known online.

Recognizing all these factors, Cenicaña works on some automatic control proposals that guarantee supersaturation to benefit sugar production and favor its quality (color, size and coefficient of variation), with less processing time.

By reducing the time, energy benefits are obtained, since the cans are one of the main consumers of steam in the sugar factory with approximately 40% of the total consumption.

What has been done?

The research project 'Exploration of advanced control techniques for the improvement and stability of the evapo-crystallization process' reviewed modeling proposals, monitoring of variables and control strategies that contribute to improving the stability of variables in the face of operational disturbances and changes.

In this sense, the feasibility of automating the crystallization of sugar was evaluated using a mathematical simulation model in all temples (A, B and C) for batch-type cans. The results of comparison of real values ​​and simulation in all cases gave errors of less than 4%.

A traditional versus modern control strategy was also designed, validated and compared in simulation. Traditional strategies seek to satisfy specific ˚Brix values ​​depending on the process and cooked dough, while a modern control strategy needs a mathematical model to calculate supersaturation.

In the simulation, it was found that a traditional ˚Brix - level control strategy was not able to maintain a stable value of supersaturation that guaranteed a higher crystallization rate and sugar quality. For its part, the modern strategy for supersaturation - level obtained a lower honey purity by 1%, which is equivalent to higher sugar production. With the proposed strategy it is possible to obtain the expected quality, production and energy benefits.

The results of this research will begin to be implemented in a pilot plant in order to validate the simulation results.