Measurement of crystal size spread through the high grade pan stage for an Indonesian and an Australian factory

Growth rate dispersion (GRD) has long been observed in industrial sugar vacuum pan operation and is a principal cause in broadening crystal size distributions. This is the phenomenon where seeds with an initially narrow size distribution spread their size distribution because each sugar crystal grows at a different rate. These rate differences are maintained as crystals grow towards shipment size. There is a special case of GRD termed common history (CH) crystals, where the crystal size is proportional to its relative growth rate. As CH crystals grow, the shape of the size distribution on a log size scale is unchanged. Also dimensionless measures of spread, such as the coefficient of variation (CV), are constant. The CV of material in the high grade pan stage in Gunung Madu Plantation sugar factory, Indonesia, which produces plantation white sugar, has been measured. The seed materials were prepared in high grade graining, without washing, using the dissolved intermediate products (B sugar and C sugar). A similar measurement also has been carried out at the Broadwater sugar mill that adopts the classical three massecuite boiling formula, in which C sugar is prepared into magma and serves as footing material for A and B strikes. Shipment sugar is made from the mixture of A sugar and B sugar. The results showed that high grade sugars behave as common history crystals. Within the accuracy of sampling and sizing, the crystal size distributions as the crystals grow appeared to be of identical shape on a log size basis, demonstrating the size distribution reflects the growth rate distribution. This occurred in graining as well as in growth pans. Furthermore, the coefficient of variation values remained constant throughout the boiling process. [This article is also published, with summaries in Spanish and German, in International Sugar Journal (2007) 109 (1308), pp. 727...738]