Control of bath temperature

Abstract

A constant bath temperature close to the liquidus temperature is needed for high current efficiency and long pot life. In daily pot operation the bath composition, the pot voltage and the metal height are used to control the bath temperature. At the TMS Annual Meetings of 1992 and 93 [1,2] a model was presented to control the AlF 3 concentration of the electrolyte. This model has been extended to control also the bath temperature. Conventional regression methods were used to determine a set of parameters, which describe the temperature behavior of the pot. Special account was taken of the time lag between actions on the pots and the reaction of the system. The paper shows, how the temperature model controls production pots, and it presents the corresponding operation results. A Graphic Pot Information System displays the predictions of the model which are compared visually with measured data. By changing pot parameters, such as the pot voltage on the screen, the reaction of the pots is studied interactively.