Measurement-based Optimization of a Batch Distillation Column

Dominique Bonvin, Bala Srinivasan, Carsten Weltz


istillation is utilized in industry to separate liquid mixtures containing components with different volatilities. Batch distillation offers a high flexibility and low investment costs, especially for small product quantities. The type and the amount of products can be changed instantaneously according to marked conditions.

The objective of batch distillation operations is to maximize product quantity at final time while satisfying terminal constraints on product purity. When temperature sensitive mixtures are distilled, additional path constraints have to be considered. In general, the reflux ratio is the main input variable, besides the reboiler heat-duty, the condenser cooling-duty and the column pressure.
Optimal operation for a binary mixture consists of three intervals: 1) A full reflux phase in order to heat up the column and increase composition in the condenser, 2) A distillate withdrawal phase where distillate is accumulated in a product tank, and 3) A zero reflux phase in order to empty the condenser which still contains product at high purity.

The implementation of the reflux ratio policy without feedback results in infeasible and non-optimal operation in the presence of uncertainties (for example inaccurate vapor-liquid equilibrium data). In order to ensure the required product purity at final time, conservative operation strategies have to be implemented, which diminish performance. The objective of this project is to examine the use of online and/or batch-end measurements to reduce conservatism. Experiments are carried out on a laboratory scale batch-distillation column in collaboration with the CIC group at the University of Applied Sciences of Fribourg (EIF).
Keywords : ;


related publications related research projects related students projects