Design and Control of a Complete Heterogeneous Azeotropic Distillation Column System

In this work, design and control of an industrial-scale complete heterogeneous azeotropic distillation column system of isopropyl alcohol (IPA) + water (H₂O) with cyclohexane (CyH) as an entrainer is investigated. There are two feasible approaches to design the complete flowsheet for the separation of IPA and H₂O. One approach is to use a total of three columns and another simpler design is to use only two columns. From total annual cost (TAC) analysis, optimum design of the two-column approach has been established and it is much more economical than the three-column approach. The suitable control strategy of this complete heterogeneous azeotropic distillation column system has also been studied extensively in this paper. From process analysis and dynamic simulation, the developed overall control strategy is rather unconventional which seems to contradict several common control heuristics. The proposed control strategy requires two temperature-control loops in the first column and one temperature-control loop in the second column. This overall control strategy is tested with both feed composition and flow rate disturbances. The product purity specifications of the IPA and wastewater streams can all be met despite various disturbance changes.