The growth rate spread of sugar seed crystals

To achieve a narrow product crystal size distribution is a great challenge and of great practical importance in sugar crystallisation. A major cause of the spread of the product crystal size distribution from batch pans is the spread of growth rates associated with the growing sugar crystals. This is termed growth rate dispersion (GRD). When nuclei seed are prepared, they exhibit a wide spread of growth rates. This spread will be maintained as the crystals grow, giving a resultant spread of crystal sizes (e.g. as measured by the CV). If there is a narrow GRD range of the initial seeds, then perhaps a narrower sized product could result. The spread of growth rates exhibited by seed crystals formed in different ways (e.g. milling, ultrasound, ethanol precipitation) and under different conditions (supersaturation, temperature, agitation) was investigated. Seeds prepared by alcoholic precipitation had a lower growth spread than commercial milled seeds, which were both less than seeds prepared by ultrasound.