Effects of electrolysis process parameters on alumina dissolution and their optimization

The Box–Behnken design and desirability approach were used to investigate and optimize the process parameters for aluminum reduction cells related to alumina dissolution. The bath temperature, alumina content, current and alumina temperature were chosen as the design parameters. The content of cumulative dissolved alumina(CCDA) and the relative deviation from the target content(RDTC) were adopted as the responses. The interactive influence results show that increasing the bath temperature and alumina temperature, as well as decreasing the alumina content, can increase CCDA. Increasing the bath temperature and lowering the current are beneficial for obtaining a more uniform alumina distribution. The optimal operating parameters were determined to be as follows: bath temperature of 958.8 ℃, alumina content of 2.679 wt.%, current of 300 kA and alumina temperature of 200 ℃.

Simulation of alumina dissolution and temperature response under different feeding quantities in aluminum reduction cell

In the feeding process of aluminum electrolytic, feeding quantity of alumina affects eventually dissolved quantity at the end of a feeding cycle. Based on the OpenFOAM platform, dissolution model coupled with heat and mass transfer was established. Applying the Rosin-Rammler function, alumina particle size distribution under different feeding quantities was obtained. The temperature response of electrolyte after feeding was included and calculated, and the dissolution processes of alumina with different feeding quantities (0.6, 0.8, 1.0, 1.2, 1.4, 1.6 kg) after feeding were simulated in 300 kA aluminum reduction cell. The results show that with the increase of feeding quantity, accumulated mass fraction of dissolved alumina decreases, and the time required for the rapid dissolution stage extends. When the feeding quantity is 0.6 kg and 1.2 kg, it takes the shortest time for the electrolyte temperature dropping before rebounding back. With the increase of feeding quantity, the dissolution rate in the rapid dissolution stage increases at first and then decreases gradually. The most suitable feeding quantity is 1.2 kg. The fitting equation of alumina dissolution curve under different feeding quantities is obtained, which can be used to evaluate the alumina dissolution and guide the feeding quantity and feeding cycle.

Improved CFD modeling of full dissolution of alumina particles in aluminum electrolysis cells considering agglomerate formation

The full alumina dissolution process in aluminum electrolysis cells was investigated using an improved computational fluid dynamics(CFD)model based on the previous researches by consideration of agglomerate formation.The results show that the total mass of alumina agglomerate and its maximum size are mainly dependent on the feeding amount and increase with increasing it.Higher superheat can effectively inhibit the agglomerate formation and thus promote the full alumina dissolution behavior.The full alumina dissolution process mainly includes a fast stage and a slow stage,with an average dissolution rate of 17.24 kg/min and 1.53 kg/min,respectively.About 50%(mass percentage)of the total alumina particles,almost all of which are the well-dispersed alumina fine grains,dissolve within the fast dissolution stage of about 10 s.The maximum values of the average dissolution rate and final percentage of the cumulative dissolved alumina mass are obtained with a feeding amount of 1.8 kg for a superheat of 12℃.The formation of the alumina agglomerates and slow dissolution characteristics play a dominant role in the full dissolution of alumina particles.