The production rate of a given crystallizer is defined, in part, by the residence time provided by the crystallizer vessel. Typically, this parameter is based on small-scale tests, which exaggerate the effects of secondary nucleation. Scale-up of crystallization equipment should allow for lower secondary nucleation, and this may, on occasion, allow for lower residence time than that used in pilot testing. In scale-up, the attrition rate decreases with the square of the vessel size increase, at constant specific energy input, and crystal-crystal contact is more dependent on crystal size, than crystal number. To determine the results of increasing production (lowering the crystal residence time), one needs to consider specific characteristics of the crystal shape, hardness, brittleness, sources of attrition, stresses on the crystal structure, supersaturation, and type of equipment in use. A reduction in residence time is not necessarily going to bring about poorer crystal quality.
展开▼
