Individual Pot Sampling for Low-Voltage PFC Emissions Characterization and Reduction

Abstract

PFC emissions from aluminum smelting are characterized by two mechanisms, high-voltage generation (HV-PFCs) and low-voltage generation (LV-PFCs). HV-PFCs are emissions produced when a cell is undergoing an anode effect, typically >8 V. Modern cell technology has enabled pre-bake smelters to achieve low anode effect rates and durations, thereby lowering their HV-PFC emissions. LV-PFCs are the emissions produced when the cell voltage is below 8 V. Lacking a clear process signal to act upon, LV-PFCs can be difficult to treat. To tackle this issue, Alcoa has conducted sampling on individual electrolysis cells, during which continuous process and emissions data, as well as periodic bath samples, were collected. In the sampled cells, a variety of conditions were observed where LV-PFCs were generated. Understanding what was occurring at the cell level allowed for the identification of opportunities for process improvement, both for the reduction of LV-PFC emissions and cell performance.