Implementation of Optimal Operation for Heat Integrated Distillation Columns

A multi-effect distillation where the condenser of a high pressure column is integrated with the reboiler of a low pressure column has been studied. The method of selfoptimizing control has been used to provide a systematic procedure for the selection of controlled variables, based on steady-state economics. The system has 10 degrees of freedom at steady state. The heat integrated distillation system was optimized to Ž nd the nominal operating point. It was found that the constraints on the product composition, area in the combined reboiler=condenser, the purity constraint in the low pressure column and the pressure in the low pressure column are active constraints. For the remaining unconstrained variable it was found that a temperature in the low-pressure column has good self-optimizing properties. The study also shows how there can be multiplicities in the objective function for certain variables in the system.