This study examines the effects of the design variables of a continuous crystallization process on the production rate of the large crystals and ease of control. The ease of control for a given design of a crystallizer is evaluated using indices which indicate the relative strength of the control action and physical feedback effects. It is shown that an increase in the volume of the external heater or the cross sectional area of the annular settling zone enlarges the area of operating condition, where the crystallizer can be easily controlled. However, an increase in either one of these design variables decreases the feasible area or the production rate of large crystals. It is shown that by properly adjusting both the design variables it is possible to increase the production rate of large crystals without narrowing the area of the feasible operating conditions. (C) 2000 Elsevier Science Ltd. All rights reserved.