Beyond the dip stick: Level measurements in aluminum electrolysis

Abstract

Overview AluminumHow would you… …describe the overall signifi cance of this paper? The manual dip stick method is still the prevailing procedure for measuring the electrolyte and molten aluminum levels in an aluminum electrolysis cell. This paper describes existing methods and novel measurement techniques for estimating these crucial parameters to optimize the cell operation. Possible alternative solutions involve both hardware measuring devices and inferential methods.…describe this work to a materials science and engineering professional with no experience in your technical specialty?The aluminum electrolysis cell has different interfaces involving cryolite crust, molten cryolite, and the molten aluminum. In addition the interfaces between the anode and the molten cryolite and the molten aluminum and the cathode also restrict the actual volume available for the cell. Having reliable and accurate information on these interfaces is important in optimizing the performance of the electrolysis cell. The paper provides an overview and gives some suggestions for implementing new measurement strategies. Broadly, these methods can be classifi ed into two categories: methods based on innovative physical equipment with the necessary sensors and transducers, and inferential methods which exploit existing measurement data. The fi r st 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.

Characterization of Individual Anode Current Signals in Aluminum Reduction Cells

“…The resulting change in anode current will lead to only a small variation in overall cell voltage except when a significant number of anodes simultaneously have a very low alumina concentration adjacent to their interface. The local conditions can become more imbalanced when an anode is replaced in the cell near a point feeder because the decrease in superheat that results can retard alumina dissolution, especially in cells with lower bath volume per anode and fewer feeders per kiloampere. ,, …”

“…The local conditions can become more imbalanced when an anode is replaced in the cell near a point feeder because the decrease in superheat that results can retard alumina dissolution, especially in cells with lower bath volume per anode and fewer feeders per kiloampere. 14,15,35 Some examples of situations frequently cited as causing imbalanced anode current distribution within a reduction cell are depicted in Figure 2. These can arise through inaccuracies and spatial effects associated with work practices and include anode replacement (anode (b)), freeze disturbing mixing (anode (a) from a distant feeder and anode (c) adjacent to a feeder), an anode being set too high (anode (d)), or a low set anode (anode (e)).…”

Online Anode Current Signal in Aluminum Reduction Cells: Measurements and Prospects

“…Due to the process nature, it is difficult to directly obtain these parameters online, as few immersed sensors can withstand the corrosion of the very aggressive liquid metal and bath. Although many have tried some new approaches such as automatic bath-depth sensors 7 and bath temperature sensors, 8 it is evident that such sophisticated online measurements or costly consumable sensors will be difficult to justify if the improvement of the process performance is insufficient. Thus, to measure sidewall temperatures, cathode (collector bar) temperatures and anode current 9-11 are supposed to be the most promising ways to optimize the cell control.…”