Direct adaptive control of a pulsed liquid‐liquid extraction column

Abstract

AbstractThis paper describes an application of a direct adaptive control scheme to a pulsed liquid‐liquid extraction column. Liquid—liquid extraction has been increasingly used in several industries as a separation technique. It performs a high degree of purification and is not heavy on energy. In spite of the flow and physical properties of solvent (the extractor) and solute (the liquid mixture) fluctuations, the control objective is to maintain the column at the flooding point. The pulser frequency and the conductivity measured under the distributor at the bottom of the column have been selected as control variables. A simplified linear discrete model of the complex dynamics of the process was assumed. The control algorithm is derived using the pole placement method as the underlying design procedure and is based on estimation of both model and controller parameters. This estimation procedure is bilinear in these parameters and is obtained from input and output prediction error models. A least‐square criterion minimization is adopted to solve this identification problem. In this approach no assumptions are made on the stabilizability of the identified model nor on the persistence of excitation. The column was interfaced by a PDP‐11 microcomputer. Attention was paid to practical problem implementation of the algorithm for permanent plant operation. Experimental results demonstrate that this algorithm accomplishes satisfactory and robust control of this highly sensitive plant.