Reduction of perfluorinated carbon compound emissions from primary aluminum production

Abstract

Two perfluorinated carbon compounds (PFCs), tetrafluoromethane and hexafluoroethane are produced periodically as by-products in primary aluminium production. Emissions of these compounds have received considerable attention over the current decade because their strong infrared absorbing power and relatively long atmospheric lifetimes result in high GWPs. World-wide primary aluminium production has been identified as the major anthropogenic source of these emissions. Early efforts have been quite successful in making substantial reductions in PFC emissions per unit of aluminium produced through implementation of new computer control systems, control of raw materials and careful attention to work practices. Primary aluminium producers are concerned about recent initiatives to establish 1995 as an alternative baseline year for PFC emissions reductions because it would discount the major PFC emissions reductions attained during the period from 1990 to 1995. Alcoa achieved approximately 70% reduction in aluminium specific PFC emission rate during that period for U.S. operations. At that same time world-wide international reductions, as documented by the International Primary Aluminium Institute, were also quite substantial. This paper reviews the processes in which PFC compounds are produced during aluminium production and discusses best methods for actual measurement of these compounds. Results of measurements made during primary aluminium production are reviewed and comparisons are made of the efficacy of methods of predicting PFC emissions. The logic of retaining 1990 as the base year for PFC emissions for the aluminium industry is reiterated.