CONTROLLABILITY AND OPERABILITY OF AZEOTROPIC HETEROGENEOUS DISTILLATION SYSTEMS

Controllability, observability and flexibility are relevant operationa l indexes for the identification of a complete and effective control s tructure for a chemical plant. In this work, we present and discuss th e application of such a structural analysis to an azeotropic heterogen eous system, which is a very sensitive plant. No new theoretical aspec ts have been introduced, but the main feature of this paper is the ext ension of linear procedures to a strongly non-ideal systems. All the r esults have been carried out on the basis of a rigorous dynamic model, which allows to identify and verify the operational points of differe nt control schemes. Two operating designs have also been compared, sho wing that an ''upper tie line'' (UTL) design, close to the heterogeneo us boundary, is generally more flexible than a ''lower tie line'' (LTL ) design, close to the ternary azeotrope. Moreover, the results here r eported show how a suitable feedforward control structure allows to in crease the operability of the analyzed design configurations with a ge neral improvement of the corresponding operational flexibility.