Efficiency of pot tightness in reduced pot draft conditions based on multi-length scale CFD simulations

Reduction of pot draft in aluminum smelting cells is a promising approach for energy saving and waste heat recovery. The control of fugitive emissions (hazardous by-product gases escaping from cells to potroom) is investigated in a smelting cell with the reduced pot draft, down to half of the current level based on CFD simulations. Physical models with different length scales are created in order to directly resolve the very narrow escaping gaps on the pot shell in the physical model with smallest scale. A systematic analysis of the pot tightness is presented by considering various factors in the simulations, e.g., pot draft and hood placement. The results have shown that current pot structure, even within ideal operating conditions, fails to maintain 100% hooding efficiency under a 50% reduced pot draft. Two design modifications are proposed to enhance the pot tightness. An efficient sealing is observed when covering the lower half of the gaps between hoods. An estimation of the leaking hydrogen fluoride is made under different scenarios in order to quantitatively verify the modifications.