Industrial Verification of Two Rotor Fluxing in Large Crucibles

摘要

Crucible fluxing is a well known method to reduce the alkaline metal content in potroom metal in an Aluminium smelter. By doing this the need to perform melt treatment inside the casthouse furnace will normally be eliminated. This approach has also made it possible with one-furnace-practice inside the casthouse, casting is done from the same furnace as the potroom metal is poured into. Other benefits are also documented by crucible fluxing as increased lifetime of the furnace lining and reduced metal loss. Hycast has been supplying crucible fluxing (RAM) to the Aluminium business for three decades. In this solution the active medium is Aluminium Fluoride (AlF_3) which is added together with Argon to ensure mixing (RAM). Recently Hycast has developed a solution for crucible fluxing in large crucibles with a closed lid used for crane tapping. This paper is about the different technical solutions and the measured performance during industrial operation. The main challenge when designing the new RAM was the closed lids on the crucibles. A small hatch in the lid gives access for the rotors into the crucible. The AlF_3 addition rate, rotor speed, and the effect of one versus two rotors are investigated. Halftimes of Sodium (Na) for the two-rotor version is ~ 0.3 min/mt. For the one-rotor version the half time of Sodium is ~0.5 min/mt. The temperature loss was lower than expected and the rotor torque higher than expected for the two-rotor RAM stations.