Control of counter-current washing operation in alumina production; classical and optimal solutions

Abstract

Entrapped caustic liquor in the red mud residue, a by-product of the Bayer Process used to produce alumina from bauxite ores, is recovered in a series of counter-current, multi-stage washer trains using the process diluting liquor. This paper addresses the problem of automatically stabilizing red mud levels within the tanks of a washer train, thus improving the washing efficiency and removing one of the factors contributing to the difficulties encountered in the control of the operation of the train. The development of a classical feedforward-feedback control strategy is first outlined, followed by the theoretical development and numerical implementation of optimal control theory.A comparison between classical and optimal control strategies, in the handling of typical disturbances, has shown an improvement in performance, over classical control strategy, achievable via the successful implementation of optimal control strategy.