Visualisation of constrained predictive control of a liquid-liquid extractor

The extraction of aqueous oxalic acid into a mixture of tributyl phospate a nd dodecane in a pulsed column exhibited strong coupling between the two in puts, solvent feed-rate and pulsation frequency, and the two outputs, raffi nate pH and bottom conductivity (an indication of flooding). A visualisatio n technique in which both the outputs and inputs and their constraints were represented on a phase plane proved useful to explain circuitous reponses and settling points that did not agree with setpoints. The visualisation is proposed as a useful real-time diagnostic tool which condenses the availab le information and creates easily recognisable patterns as a basis for tuni ng or problem identification. (C) 2001 Elsevier Science Ltd. All rights res erved.