Analysis of Control Structures for Reaction/Separation/Recycle Processes with Second-Order Reactions

This work analyzes the effect of the process design on control structure for a system with a reactor, two distillation columns, and two recycle streams. The reaction A + B → C occurs in a reactor, and since component C is assumed to be the intermediate boiler, the two distillation columns recycle components A and B back to the reactor. A previous paper presented two workable control structures for this process. One fixed the flow rates of the two recycle streams and brought in makeup fresh feeds of components A and B on level control. The other control structure fixed the reactor effluent flow rate, controlled the composition of one reactant in the reactor by manipulating one fresh feed, and brought in the other fresh feed on reactor level control. These two structures have the undesirable feature of not being able to set directly the production rate and, in the second structure, requiring a reactor composition measurement, which can be difficult due to the hostile environment and can require expensive in...