CFD simulation of dissolution process of alumina in an aluminum reduction cell with two-particle phase population balance model

The dissolution process of alumina in a three-dimensional 300 kA aluminum reduction cell was modeled and simulated employing our custom code. A two-particle phase population balance model (TPPBM) was proposed by dividing solid phase into two groups consisting of small and large size alumina particles separately. A CFD-TPPBM coupled model was developed to describe the liquid-solid flow and dissolution process based on dissolution reaction kinetics mechanism. The effects of alumina effective diffusion coefficient, bath superheat, alumina preheating temperature and alumina feeding positions were studied numerically. The results show that the transport characteristics of alumina are controlled to great extent by the bubble driven forces in some local areas, while the electromagnetic forces can help alumina transported from the feeding positions to the whole cell. An increase of alumina effective diffusion coefficient can effectively benefit the dissolution process of the small alumina particles. It is advantageous to improve the dissolution process of the large alumina particles using higher bath superheat or alumina preheating temperature. The point feeding zone is preferable located at inter-anode gaps. The small alumina particles are dissolved quickly and completely in about 10 s after the feeding while the large alumina particles are dissolved much slowly.