Design considerations for selecting the number of point feeders in modern reduction cells

Abstract

Point feeding systems are now installed in most modern reduction cells in preference to bar breakers. The main reason for this choice is that point feeders allow improved alumina dissolution. However complete alumina dissolution is not an explicit design criterion for selecting the size of the alumina dump or the number of feeders required. In this paper, three performance criteria for determining the number of point feeders required in a cell are investigated. These are: acceptable alumina dissolution, satisfactory mixing to avoid concentration gradients and a satisfactory rate of alumina concentration increase after anode effect. Using a combination of laboratory data and measurements from industrial cells, it is shown that the alumina dissolution requirement is likely to be the most difficult to satisfy. Complete alumina dissolution upon addition is unlikely to be achieved with the point feeder designs installed in most modern cells.