The exhaustion of C massecuites in cooling crystallisers is usually limited
by the high viscosity of the massecuites. Process conditions are chosen to ensure
that viscosities are held at manageable levels. In this paper correlations for sucrose solubility and the viscosities of massecuite and molasses have been applied to predict the limit to sugar recovery expected for different operating procedures and to investigate ways by which further recovery can be achieved.
Introduction
The extent of massecuite exhaustion which can be achieved in the crystalliser station depends on a number of factors including:
• Those variables which affect the growth velocity, e.g. pan discharge conditions,
cooling rate, shear rate;
• The holding time in the crystallisers;
• The maximum level of massecuite viscosity which can be adequately
managed through the station.
Invariably, factories encounter viscosity limitations because pan discharge
conditions are selected to maximise the crystal deposition rate in the crystallisers,
viz. high dry substance, high crystal content. As well, more rapid cooling
of the massecuite increases the supersaturation driving force. All these
factors produce an increase in the massecuite viscosity.
This paper investigates the manner in which the high viscosity of the
massecuite encountered in the cooling crystallisers imposes restrictions on the
extent of massecuite exhaustion.