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.