MHD Stability of Aluminium Cells—Cathode Design Effects

An estimate of MHD stabilityMHD stability is an important criterion when attempting to increase the aluminium reduction cellAluminium reduction cell efficiency. The MHD stabilityMHD stability is achieved by optimizing the magnetic fieldMagnetic field and the electric current distributionCurrent distribution in the liquid metal. The magnetic fieldMagnetic field distribution is mostly determined by the external busbar network and the magnetized steel parts, while the electric current in the liquid metal is affected by the design elements of anodeAnode and cathodeCathode block collector bar construction details. Theoretical studies of MHD stabilityMHD stability often rely on a simplified uniform current distributionCurrent distribution over the cathodeCathode bottom. ModellingModelling of commercial cellsCell requires a detailed 3D representation of the cellCell cathodeCathode, coupled to the liquid metal. The software MHD-VALDIS permits to account for current distributionCurrent distribution in the liquid metal and the cathodeCathode including variable material properties, contact resistancesContact resistance, temperature dependent collector conductivity, carbon block length and ledgeLedge profile along cellCell perimeter. The software permits to compute full electric current and magnetic fieldMagnetic field 3D distribution change in time associated with the velocities and metal/electrolyte interface wave development leading to damping or growth in an unstable cellCell. To quantify the instability the damping rate is determined using a new technique based on the consecutive wave peak heights comparisonComparison. Examples of application to a commercial Trimet cellCell are presented.