Sugar Crystallization Case Study

Abstract— This paper presents a technical review of Multivariable Control Strategy to control industrial Sugar Crystallization process. This paper addresses the issue of modeling and control of multivariable chemical process systems. The sugar crystallization process in sugar factory is the last and a most crucial as well as critical process. As a case study this process has been used to illustrate the modeling and control of multivariable linear and nonlinear systems.
Index Terms— Sugar Processing, MIMO process model, Process dynamics, Dynamical decoupling control, Manipulation variable, Control Variable, Prediction.
Introduction
The Crystallization Process is a chemical process frequently used in various chemical industries like sugar, salt,

2. Various saturation and super saturation zones

First zone is called Intermediate zone in which existing crystals can grow but no new crystals can be formed.
Second zone termed as in Metastable zone which new crystals can be formed only in presence of the existing crystals.
Third zone called labile zone in which existing crystals grow and new crystals can be formed even in the absence of existing crystals.
Sugar Crystallization Process in Vacuum Pan

After juice extraction from sugar cane we get raw sugar juice which is sent for clarification process to get pure sugar juice. After clarification the pure juice is sent to evaporation process. The juice evaporation process is required to concentrate the juice before crystallization is done to obtain the syrup which acts as an input to sugar crystallization stage. Then the syrup sent to vacuum pans is of 55°-65° Bx. The entire process of crystallization on pan is conducted in three or four stages, the mother liquor from the final stage being discarded as final molasses. The feed material of the pans at second and later stages of boiling is of about 70° Bx. Mixture of sugar crystals in syrup is called massecuite. For recovering maximum sugar in crystalline form high concentration of the massecuite under vacuum is essential consistent with the requirements of discharging the mass from the pans. The brixes of first grade massecuite i.e. 'A' strikes from which white sugar is produced are 92°-94° Bx while the final massecuite,

The sugar boilers or the vacuum Pans (fig. 3) require syrup capable of dissolving the further crystals, so that they may dissolve false grain which may get formed at the beginning of the charge, a condition which is indispensable for good result in vacuum