Multi-physical field coupling numerical investigation of alumina dissolution

Abstract

• A solution module for alumina dissolution was established coupling heat and mass transfer. • A multi-physics field coupling process including flow field, temperature field and concentration field was modeled and simulated. • Particle shrinkage and thermal response in bath during dissolution were considered in this study. • The critical diameter which can identify the dominant mechanism between heat and mass transfer was proposed and investigated. • Optimal feeding quantity of alumina for 300 kA aluminum electrolytic cell was obtained. Alumina dissolution, which is controlled by both heat and mass transfer mechanisms, is a key process in the aluminum electrolytic cell. A solution module for alumina dissolution coupling heat and mass transfer was established using the open source platform OpenFOAM, including particle shrinking, bubble driven flow and thermal response associated with dissolution. The dissolution process was modeled, and the critical diameter which can identify whether the dominant mechanism for dissolution is heat or mass transfer was proposed and computed. The calculated results show that the critical diameter of alumina dissolution is about 520 µm. Alumina particles with diameter less than 520 µm are controlled by the mass transfer mechanism, while particles with diameter larger than 520 µm are controlled by the heat transfer mechanism. Optimal feeding quantity was calculated by simulating and comparing different feeding quantities in a 300 kA aluminum electrolytic cell. The optimal feeding quantity is 1.2 kg based on the analysis of concentration fluctuation in the space-time domain and average dissolution rate. The models and methods can provide guidance for the design of feeding strategy for large aluminum electrolytic cells.