The operating conditions in the Hall Heroult process used for aluminium production have become more critical in recent years due to the trend to optimise current efficiency and minimise the energy consumption per kilogram of aluminium produced. The tightening of operating parameters makes it more difficult for current control systems employing global control practices to prevent an increase in the frequency of abnormal conditions occurring. Therefore, the development of control systems with fault diagnosis capabilities becomes more important. It is desirable for such development to be based on dynamical mathematical models so that the root causes of anomalies can be determined and more targeted control action can be made.

This paper presents the development of a mathematical model that can predict regional dynamic behaviours of the aluminium reduction process by calculating spatial thermal variations and anode current distribution in an operating cell. The dynamic model employs mass and heat balances and can determine cell voltage, individual anode current and localised values including alumina concentration, bath temperature and ledge thickness. The mathematical model is intended to be employed in a fault detection system that can be used to patch existing controllers. Such a modified control system is aimed to have the capability of providing early indications of impending abnormal conditions on a localised level.