US EPA

6945197 

Journal Article 

Enhancing Gravity Thickener Feedwell Design and Operation for Optimal Flocculation through the Application of Computational Fluid Dynamics 

Fawell, PD; Nguyen, T; Solnordal, CB; Stephens, DW; , 

2019 

1 

Mineral Processing and Extractive Metallurgy Review
ISSN: 0882-7508 

TAYLOR & FRANCIS INC 

PHILADELPHIA 

10.1080/08827508.2019.1678156 

WOS:000492103300001 

As the expectations for more consistent and higher density thickened and paste tailings in the minerals industry increase, so do the demands on flocculation performance within gravity thickeners. Low solids feed suspensions are delivered at a high velocity to center feedwells, which not only serve to dissipate the feed's momentum and evenly distribute the solids, but are also the primary means by which polymer flocculant solutions are distributed across the fine particle to form fast settling (but fragile) aggregates. Computational fluid dynamics (CFD) is a powerful tool for optimizing the design and performance of unit operations used to achieve particle aggregation and sedimentation. Early CFD feedwell modeling gave predictions on the solids and fluid flows, which were useful for identifying discharge asymmetry and short-circuiting currents, but did not give major insights into aggregation states. Incorporating a population balance (PB) model of aggregate growth and breakage made it possible to capture the critical impacts of shear, residence time and solids concentration that characterize polymer-bridging flocculation, in particular the potential for prolonged higher shear conditions to give excessive breakage. This created a unique capability for understanding the complex balance between the hydrodynamic and physical chemistry requirements for flocculation, enabling systematic CFD studies of different design and operation elements. Some of the main conclusions on feedwell design optimization are outlined. Potential future applications of CFD outputs in feed-forward thickener control are also discussed.