DIGESTER DESIGN USING CFD

摘要

In the Bayer process, dissolution of gibbsite and kaolinite occur in the digester train. Understanding the hydrodynamics of the digester is key to improving the extent of dissolution, and thus the extraction of alumina and re-precipitation of silica. Deviation from ideal plug flow results in a miscalculation of the slurry retention time. The outcome may be a loss of undigested alumina to the red mud with a consequent reduction in extraction efficiency. To address this issue, the hydrodynamics of a digester train were modeled using computational fluid dynamics (CFD). The impact of column aspect ratio and inlet configuration on the slurry residence time distribution (RTD) was investigated. The RTD was used to estimate reaction extents and evaluate the effect of design parameters on performance. The modeling approach allows the inclusion of the digestion chemistry to directly evaluate the yield. Results show that the choice of slurry inlet configuration significantly impacts performance.