The Baie-Comeau Smelter has both a prebake anode plant and a Söderberg plant. Söderberg anodes, a mixture of tar pitch and coke, bake during the electrolysis process rather than in a dedicated oven, as at the other plants. This results in polycyclic aromatic hydrocarbons (PAH) emissions. In the Söderberg potrooms, approximately 85% of emissions are captured at the source to be treated by dry scrubbers. The remainder is emitted through the roof vents.
There are currently no standards for PAH emissions. However, Alcoa made a voluntary commitment to the Ministère du Développement durable, de l’Environnement et des Parcs to meet a target of 0.25 kg PAH/t Al for 2011. The increase in emissions recorded in 2010 was due to the variability in the hybrid pitch sourced to make the anodes. Emissions decreased in 2011 following improvements in the quality of the anodes and in pot operating procedures.
