Beyond the dip stick: Level measurements in aluminum electrolysis

Abstract

The “old fashioned” and imprecise approach of using a dip stick is still employed to measure the crucial level information in electrolysis baths in the aluminum industry. The dip stick method is based on manually immersing a metal rod into the cell and observing the marks left by the molten bath components to estimate the metal/electrolyte interface and the bath level. However, methods to improve height estimation have been developed in recent years, although none has yet been introduced as part of the routine measurement procedure in the aluminum manufacturing industries. An attempt is made here to give an overview of the promising methods for measuring or estimating the different levels of the bath constituents in an electrolysis cell. Broadly, these methods can be classified into two categories: methods based on innovative physical equipment with the necessary sensors and transducers, and inferential methods which exploit existing measurement data. The first category encompasses many physical and chemical disciplines, whereas the second relies on inferential methods employing approaches sometimes called soft computing or soft sensors. Both approaches are presented and discussed in this paper.