Low Voltage PFC Measurements and Potential Alternative to Reduce Them at Alcoa Smelters

Perfluorocarbon (PFC) gases evolve from aluminum electrolysis pots almost continuously. They are not only emitted during anode effects (above 8 V) but also during pot instability periods where pot voltage is below 8 V. The so called "low voltage anode effects" (LVAE) can be emitted during anode changes, pot feeding underfeed cycles or pot tapping periods [1-7]. Procedures are shown how to measure and reduce LVAE. Fourier Transform Infrared (FTIR) method is reviewed to measure the very low emissions as well as together with gas bags used to measure total PFC emissions. Thus, equipment selection, measurements parameters and Quality Assurance/Quality Control (QA/QC) controls should be reinforced to comply with possible regulation change to measure total emissions. Results from feeding optimizations will be shown from three smelters with reduction on LV-PFC emissions.