ON THE ALF3 AND TEMPERATURE CONTROL OF AN ALUMINUM ELECTROLYSIS CELL

In this paper we propose a control strategy for excess AlF3 and bath t emperature of a prebake aluminum electrolysis cell based on analyzes o f measured data and studies of a simple dynamic model. Model validatio n indicates that there are dynamics that the model does not capture, a nd hence, we use real data of excess AlF3 and bath temperature to esti mate AlF3 and energy disturbances respectively. The estimation results show that the energy disturbance is the dominating disturbance. Hence , the proposed control strategy is based on an almost constant AlF3 in put close to average consumption and energy manipulations to compensat e for the disturbances. This requires the possibility for the resistan ce reference to be reduced without decreasing the current efficiency. Compared to present control strategies, this introduces an additional degree of freedom in the controller. The control strategy may imply a significant economic potential through increased and stabilized curren t efficiency, reduced and stabilized energy consumption, reduced consu mption of expensive additives and prolongation of cell life.