Tradeoff between design and control

The optimal trajectory can be computed directly from Eq.(8) and this facilitates the investigation of chemical reactions with different kinetics parameters and vapour liquid equilibrium. More importantly, the trajectories obtained provided insight to possible tradeoffs between design and control for different bimolecular reactions. 

Before heaving this section, we would like to look at an important design parameter reactant distribution iyAlyn)- The reactant distribution in some cases represents an important tradeoff between design and control as shown in the case 2 Reyes and Luyben [10] where we have a bimolecular reaction with high activation energy. The optimal TAC corresponds to an almost equally distributed reactant distribution, but the operability consideration lead to a biased reactant distribution (e.g., one of the reactant is in excess). Let us consider the case where the reactant A is in excess. The sensitivity in the production rate variation for changes in yn can be expressed as ... 

The economical optimum number of reactive trays is seven in this system. However, the results demonstrate fliat this column has poor dynamics performance. Adding more reactive trays increases capital cost, but can it improve dynamic controllability We now demonstrate that it can indeed make control better. This is a good example of the ever present tradeoff between design and control that occurs in chemical processes. 

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