Factors Affecting PFC Emissions from Commercial Aluminum Reduction Cells

Abstract

The US Environmental Protection Agency (EPA) and the US Aluminum Association sponsored measurements of two perfluorocarbon (PFC) gases: tetrafluoromethane and hexafluoroethane. The measurements at six primary aluminum production facilities provided data on emissions of these compounds during normal aluminum smelting operations. The measurements were made using process mass spectrometry, a technique capable of monitoring the rate of emissions with a time resolution of seconds. The PFC concentration measurements were combined with smelting process data collected during the measurements to provide new insights into the relationships between the process variables and PFC emissions. Detailed data were obtained at several locations relating overall cell voltage and PFC emission rates. The profiles of PFC emissions and voltage at a time resolution of seconds provide valuable insight into how emissions vary with voltage. The data on emission rates from commercial cells as a function of cell voltage were compared with similar data developed on bench scale experiments. Other analyses included a comparison of emission rates among different cell technologies and anode effect (AE) kill strategies. Estimated PFC emissions for different definitions of AE were compared with total measured PFC emissions. Finally, the emission rate as a function of AE duration was examined.