Magnetohydrodynamic Analysis of Load Shifting in Hall-Héroult Cells

Abstract

The research project SynErgie aims to adapt large scale industrial processes to a volatile supply of renewable energy which is expected for the future. The aluminum electrolysis process is one of the biggest consumers of electric energy in Germany. The aim is to vary its nominal process power by ± 25%. This numerical study focuses on the magnetohydrodynamic (MHD) behavior of the electrolysis cells of Trimet Aluminum SE in Essen. To capture the MHD driven flow and electrodynamics inside the electrolysis cells a computational fluid dynamics (CFD) model is developed in the OpenFOAM® framework. This accounts for the influence of neighboring electrolysis cells, the magnetization of ferromagnetic materials, a static ledge profile and the dynamic changes of anode shape caused by the carbon consumption. The simulation predictions show the heave of the aluminum cryolite interface for different line currents. To analyze the behavior of flexible process operation, shifts of the line currents are studied in detail. After shifting the line current, the interface heave changes directly whereas the shape of the anode bottom reacts with a delay in time. This leads to a locally uneven anode cathode distance (ACD) followed by a disturbed current distribution inside the electrolysis cell after shifting the line current. The anodic current distribution is quantified by the model, which can help process operators to identify whether increased anode currents are caused by the line current shift or potential abnormalities like spikes. Graphical Abstract