Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

In the Saguenay region, Alcan operates two coke calcination rotary kilns to supply with calcined coke its prebaked anode and Soderberg paste smelters. The annual production is approximately 220 000 t of calcined coke. For the last few years, the unwanted emissions of under calcined coke dust (UCCD) emitted from the kilns along with the hot gas reaches approximately 16 000 t per year. A maximum of 6 000 t of UCCD are recycled in fabrication processes. In the search of new possibilities to recycle and sell the remaining 10 000 t the possibility of using this UCCD as a heating source in other processes has emerged, particularly for the calcination of alumina trihydrate. A feasibility study on the combustion as well as a plant trial showed the benefits of burning this UCCD in two 60 t/h capacity calcination units. In fact, appreciable savings in natural gas or oil, as well as increased energetic efficiency (gain of 6%) were observed in the calcination units. Furthermore, the impact on quality of the metallurgical alumina is negligible. These results can be explained partly by the use of a solid combustible which presents longer combustion time compared to natural gas. The combustion zones are therefore extended, favoring the heat transfer to the solid during calcination.