Hierarchical Sub-Optimal Control of Batch Distillation with Slop Recycling

Abstract

Slop recycle increases the production capacity of batch distillation. It avoids exhaustion of the mixture or decreases the difficulty of separation. A hierarchical control approach is proposed. At scheduling level predictions of the required component production times and the ratio between product and slop cut quantities are made. These predictions are based on the degree of difficulty of separation and the mean feed quality and quantity. At conditioning level sub-optimal operation under constant quality control is applied. The production capacity approximates the capacity under dynamic optimal control, and is up to 20% higher than under piecewise constant reflux control.