Modelling the formation and dissolution behavior of alumina agglomerate in the cryolite

Abstract

The presence of alumina agglomerates seriously affects the current efficiency of the aluminum electrolysis process. Clarify the dynamic dissolution process of agglomerates is essential to improve the current efficiency of aluminum electrolysis. A mathematical model is proposed to describe the different phenomena from the formation until complete dissolution of agglomerates. Considering permeation and solidification processes of cryolite, a semi-analytical mathematical model is developed to formulate the formation, melting and dissolution processes of agglomerates, and the time duration for each stage is deduced. Porosity and heat mass transfer of agglomerates are explored based on the packing theory and mechanism of heat mass transfer in wet porous media. Dimensionless approach is applied to investigate the main factors affecting the dissolution stages and porosity of agglomerates. The results show that the superheat has a great influence on the formation and melting stage, the diameter of agglomerates can reach 14.93 mm for 200 particles agglomerated. The density decreases with the increase of agglomerated particle number, which varies in the range of 2.27–2.28 g/cm3. The average dissolution rate of agglomerates is about 1.83×10−5−2.95×10−5 kg/s within the range of alumina concentration in this study.