Recycling of the Flue Gas from Aluminium Electrolysis Cells

Recycling of the flue gas from aluminium reduction cells is a possible method for increasing the CO2 concentration, thereby enabling CO2 capture. The present paper represents a preliminary study concerning some of the consequences in the electrolysis cells. The energy balance in a hypothetic 400 kA cell was estimated, and it turned out that the heat flow into the superstructure could be kept constant by decreasing the thickness of the anode cover material even with a very hot gas. Recycling gives a higher amount of collectible heat from the cells, mainly because of higher temperature in the gas entering the cell. It will be advantageous to apply catalytic burning of CO to CO2, which represents considerable extra heat. Increased sulfuric acid dewpoint may represent a challenge. It is also necessary to address the amount of hydrogen fluoride that re-evolves from the secondary alumina at high superstructure temperature.