Cell Voltage Noise in Aluminium Smelting

Abstract

Aluminium reduction process is a nonlinear, time varying electrochemical process, in which alumina (Al2O3) dissolved in cryolite (Na3AlF6) is electrolysed to produce molten aluminium. In industrial practice the term noise refers to unsteady voltage signal in the reduction cell or random and/or uncontrolled fluctuations in the cell voltage; it can be used to identify problems in the cell operation. The main objectives of the reduction process is to achieve as high a current efficiency as possible with minimum energy consumption. Noises of certain frequencies are generally considered unfavorable to cell current efficiency and energy consumption. Therefore, noise control is an important issue in commercial cell automatic control system. The present paper analyses noise from different sources during cell operation and their possible causes with help of Fast Fourier Transformation techniques in terms of frequency and amplitudes of the fluctuations. An advanced data acquisition system was used for collecting the data required for the noise studies. The characterization of the three types of noise generated is discussed. Real-time algorithms have been implemented to allow on-line estimation of the noise sources and intensities.