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Coanda’s leader, Clara Gomez recently presented a study on the Modeling of Fluid Fine Tailings (FFT) Withdrawals from Tailings Ponds at the 21st
International Hydrotransport Association Conference in Edmonton in May.

Tailings ponds contain a deep layer of fluid fine tailings (FFT), a non-Newtonian mixture below a layer of almost clear water. When FFT is withdrawn through a vertical pipe, such as from a barge with a submersible pump, the depth to which the mixture can be removed is limited by coning at the interface between the water and the FFT. The extent of this coning phenomenon depends greatly on the FFT properties, specifically the yield stress and apparent viscosity, known to vary as a function of depth (i.e. density changes due to stratification), applied shear rate, and time. Since the properties that govern this behaviour are not well defined, the withdrawal process is not well understood. Without being able to take the appropriate corrective actions to mitigate coning during suction, it is practically impossible to ensure a steady supply at a constant volumetric rate and density for the treatment processes that follow.

The study, a collaboration between Coanda and Syncrude, aimed to develop a model for single point FFT withdrawal from a pond, to predict the conning flow behaviour expected as a function of the varying rheology. We developed the model in stages of progressive complexity. First, simple experiments in a fish tank using transparent analog materials investigated the impact of process variables (such as withdrawal flow rate, suction geometry, and fluid rheology) on cone formation and breakthrough time.

Analytical and computational fluid dynamic (CFD) solutions for these simplified tests cases were obtained and validated against experimental data sets providing confidence in the ability of the models to predict the static coning formation over time. CFD simulations were then conducted at pond scale and the methodology was further refined to account for the variable rheological properties of FFT as a function of the expected pond density stratification.