Industrial Aluminium Production: the Hall-Heroult Process Modelling

Aluminium is produced according with the Hall-Heroult process. At the cathode, AlxFy species are reduced and lead to liquid aluminium. At the consumable carbon anode, AlxOzFy species are oxidized to lead to carbon dioxide bubbles evolving and not O2 bubbles because of the carbon anode consumption. During this complex electrolyte two- phase electrolysis, it is difficult to model the current distribution and to optimize the process. The flow is the result of the magneto-hydrodynamic phenomena induced by the strong imposed currents and of the bubbles evolving. The reactivity and species concentration distribution are difficult to model: the molten salt chemistry is few developped compared with the aqueous chemistry. The mass, heat and charge transport are also stongly difficult to model, because of the created bubbles which imply transfer properties disturbance. Bubbles are motion sources for the electrolysis cell flow, hydrodynamic properties are strongly coupled with species transport and electrical performances. Bubbles presence modifies these global and local properties: the electrolysis cell and the current density distribution are modified. The goal of this proposition is to present the electrochemical engineering modelling of the Hall-Heroult two-phase electrolysis properties in the inter electrode interval. The numerical simulations are performed from both the chemistry and two-phase hydrodynamic point of views. Chemical calculations are first performed to describe dissolved gas species and bubble nucleation and growth. In a second step, a simple Euler-Lagrange two-phase model is presented to calculate hydrodynamic properties in