Study On The Control Of Alumina Concentration For Large-scale Industrial Aluminium Reduction Cells

With the technology development of large-scale and energy-saving industrial aluminum reduction cells,the average amount of liquid electrolyte per thousand amperes in a cell decreases with the increase of cell current,which results in higher feeding rate of alumina.So,it is necessary to increase the alumina dissolution rate because of higher alumina consumption in the electrolyte.The narrow control band of alumina are very important for high current efficiency of aluminum electrolysis.Alumina dissolution in the electrolyte mainly depends on its physicochemical properties.Sandy alumina with moderate particle size,good fluidity,low content of?-Al2O3 and impurity has better dispersion and solubility in electrolyte.The variation range of alumina concentration depends on the automation level of cell.Too Higher and too lower alumina concentration break the energy balance and stability of the cell,resulting in a reduction in current efficiency.In this paper,the physical and chemical properties of the alumina used in three aluminum smelters were measured firstly,and the dissolution behaviors of alumina with different properties were studied by high temperature transparent cell.The primary alumina changes to the secondary alumina after transferring through the ultra-dense phase transmission system and gas treatment center.The physical chemical analysis shows that the ultrafine particle content,bulk density,angle of rest and sulfide impurity content of alumina become higher after transferring and absorption processes.However,phase composition does not change significantly.Alumina dissolution experiments show that the floating time of an imported alumina in bath is much longer than that of a domestic alumina,due to the higher average particle size and better flow ability.Longer floating time is very helpful to alumina dissolution in the industrial cell,the specific reasons worth further exploration.Strontium tracer method was used to determine the total amount of liquid electrolytes and flow rate of bath in the center channel in a 400kA pot and a 500kA pot,respectively.The results show that the total amount of liquid electrolyte in the 400kA pot was about 7.615t and the average bath flow rate in the center channel was 0.60m/min;the total amount of liquid electrolyte in the 500kA cell was about 8.297 tons,and the average bath flow rate in the center channel was 0.84m/min.Based on the above studies,this paper studied the relationship between the actual alumina concentration evolution and the auto-feeding mode of alumina in a 400kA pot and 500kA pot,respectively.The study found that the bath superheat at about 10? is benefit for the concentration of alumina within the target band and uniform distribution of alumina concentration in the whole cell.When the bath superheat is lower than 5?,the alumina concentration control of the electrolytic cell will be out of control.The above work is a preliminary study on the alumina concentration control of the high amperage aluminum reduction cell.The results have certain reference significance for the alumina control for high amperage aluminum reduction cell.