| Rapid dissolution of alumina after feeding to aluminum cells is important so that sludge formation, leading to changes in the current profile of the cell, can be minimized. Alumina agglomerates formed during the feeding process can lead to sludge formation.;Agglomerates retrieved from an industrial cell were 1 to 5 cm in diameter, 1 to 2 cm thick, and with a density of 2400 kg/m;A new technique for immersing uncompacted powder in cylindrical form into liquids was developed. Cylindrical alumina agglomerates 1.5 cm diameter, 5 cm in height, were formed in the laboratory using this technique. Increasing electrolyte stirring and super heat, in the range of smelter operating conditions, decreased the 30 s frozen layer thickness by up to 2 mm. Little change in the frozen layer thickness was observed by increasing the agglomerate diameter to 2.6 cm.;Cylindrical agglomerates 6.5 cm in diameter were immersed in a 91 kA industrial cell. Evolution of volatiles causes transition alumina agglomerates to reach the bath temperature 1.5 times more rapidly than ;Cylindrical mathematical models based on both infinite and finite cylinder geometry were used to calculate the temperature profile and frozen layer thickness of the agglomerates. Both models produced similar results and compared well with experimental data. Agglomerate formation and disintegration involves convection, conduction, freezing, melting, and dissolution.;A spherical model was used to simulate the response of alumina agglomerates to sudden immersion in electrolyte. The agglomerate density, 2400 kg/m;Overall, agglomerate formation and disintegration is a stepwise process in which a frozen shell forms and melts back while bath infiltration leading to density increase and dissolution, occurs. |
