Analysis of Introducing Slotted Anodes in Smelter Operations
A smelter introduced slotted anodes to enhance performance but faced issues like increased dusting and a drop in current efficiency (CE). The root cause was identified as the increase in surface area due to the slots, leading to more CO2 burn and dusting. While the slots could offer benefits, the negative impact on CE suggests the need to address dusting before considering slot introduction.
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Presentation Transcript
ICPMA - Group VII 1stof June, 2017
The task A smelter introduced slotted anodes to improve performance Green anodes were formed with two transversal slots Dusting was already a problem CE 92.5 %, net anode consumption 430kg/t Al Initial experience with slots good lower bubble voltage drop raised amperage 3 months after implementation: increased dusting, CE drop of 1% Reasons for the problems? 2
Anode geometry Figure not to scale, all measures in mm 3
Some initial reflections Why would you want slots? Reduced voltage drop due to bubbles Turbulence in center channel Less disturbance of metal pad Longitudinal slots would be preferable Lead the gas to the center channel Equipment limitations during forming could dictate orientation The green anodes are formed with slots - machining slots after baking is more usual Avoid cleaning after baking Potentially lower scrap rate Avoid inhomogeneities Choice may be related to investment cost The slots amount to 15.4kg of carbon assuming consumption of 30kg/day, this corresponds to roughly half a day of anode life 4
Root cause of the problem Mechanisms for dusting: air burn, CO2 burn Hypothesis: slots increase the surface area, with a corresponding increase in CO2 burn and dusting Original contribution of CO2 burn to net anode consumption: 35kg/t Al Surface area without slots: 4m2 Additional surface area effectively open to CO2 burn due to slots: 0.72m2 18% increase, amounts to 6kg/t Al net anode consumption, which could explain the dusting The positive effects of introducing slots could outweigh the increased net anode consumption However, the significant loss in CE probably means that the introduction of slots would not make financial sense for this plant Dusting problem should be solved first, then slots may be introduced 5
