Improved heat transfer modeling of the top of aluminum electrolysis cells

A thermal-electric model is developed using finite elements and thoroughly validated against thermal measurements performed in industrial aluminum electrolysis cells (AEC). Knowledge about the geometries of anode cover material (ACM) and anode crust is improved by measuring their profiles in industrial cells. Moreover, the shape of the cavity formed by the melting of the anode crust is predicted with the numerical model, using a radiosity module combined to an iterative method. The thermal conductivity and the emissivity of both ACM and anode crust are also evaluated based on experimental measurements. The thermal-electric model accurately predicts the measurements obtained from heat flux sensors and thermocouples installed on industrial anodes. Modeling results show that increasing the ACM thickness reduces the top heat losses and increases the heat dissipation from the side, while the bottom losses remain constant. With thicker top insulation, the side ledge shrinks and the anode crust melts. The impact of a film of sludge under the liquid aluminum is quantified with the model. Accordingly, the sludge increases the cathode voltage drop (CVD), enlarges the cavity, reduces the side ledge thickness and amplifies the side heat dissipation. The thermal-electric modeling provides insights to improve the design and operation of AEC in order to reach higher efficiency.