Production rate changes in a ternary two-recycle process

Recent studies of a ternary process with the reaction A + B --> C and two recycle streams have revealed some interesting dynamic problems in transitioning fi om one production rate to another, even though the new production rate is attainable from a steady-state point of view. If the process has been designed with a small reactor volume, which means large recycle flow rates, the process sometimes shuts itself down when the production rate is increased. The control structure used has fixed reflux. now rates on both columns. The basic problem is a buildup of impurity (component C) in one or both of the recycle streams. This can be prevented by modifying the control structure to use reflux-to-feed ratios for processes with intermediate reactor holdups or to use dual composition control on both columns for processes with low reactor holdups.