On-line monitoring and control of supersaturation and other massecuite parameters in vacuum pans: A control engineering approach

It is generally acknowledged that supersaturation is the most important parameter in sugar crystallization. It has a key role in determining product quality and yield, cost of production, profitability and survival of the manufacturer. Besides supersaturation the other important parameters are: crystal content, mother liquor purity (or purity drop) and massecuite solids content (“brix”). Unfortunately enough, only massecuite solids content can be directly measured by the popular microwave probes. The paper reviews common practice to control crystallization in vacuum pans. Most of them rely on the use of a single probe as the main instrument and on a kind of trial and error method of control. This is due to the fact that there is no single instrument being able to provide on-line data on supersaturation. Claims to the contrary are plainly false, because supersaturation is a function of several variables. The paper presents new solutions and devices (quite a few in use already) for the on-line monitoring of supersaturation based on the data which are needed for its exact calculation. These data can be used not only to implement automatic seeding of the vacuum pans based on supersaturation, but also for the advanced control of the complete strike. On-line monitoring of crystal content, mother liquor purity and other massecuite parameters is also possible.