R. Sean Sanders

Flocculation kinetics and aggregate structure of kaolinite mixtures in laminar tube flow.

Flocculation is commonly used in various solid-liquid separation processes in chemical and mineral industries to separate desired products or to treat waste streams. This paper presents an experimental technique to study flocculation processes in laminar tube flow. This approach allows for more realistic estimation of the shear rate to which an aggregate is exposed, as compared to more complicated shear fields (e.g. stirred tanks). A direct sampling method is used to minimize the effect of sampling on the aggregate structure. A combination of aggregate settling velocity and image analysis was used to quantify the structure of the aggregate. Aggregate size, density, and fractal dimension were found to be the most important aggregate structural parameters. The two methods used to determine aggregate fractal dimension were in good agreement. The effects of advective flow through an aggregates porous structure and transition-regime drag coefficient on the evaluation of aggregate density were considered. The technique was applied to investigate the flocculation kinetics and the evolution of the aggregate structure of kaolin particles with an anionic flocculant under conditions similar to those of oil sands fine tailings. Aggregates were formed using a well controlled two-stage aggregation process. Detailed statistical analysis was performed to investigate the establishment of dynamic equilibrium condition in terms of aggregate size and density evolution. An equilibrium steady state condition was obtained within 90 s of the start of flocculation; after which no further change in aggregate structure was observed. Although longer flocculation times inside the shear field could conceivably cause aggregate structure conformation, statistical analysis indicated that this did not occur for the studied conditions. The results show that the technique and experimental conditions employed here produce aggregates having a well-defined, reproducible structure.

CFD Methodology to Determine the Hydrodynamic Roughness of a Surface with Application to Viscous Oil Coatings

AbstractWater-lubricated pipe flow technology is an economic alternative for the long-distance transportation of viscous oils, such as heavy oil and bitumen. In the industrial-scale application of ...

Governing Friction Loss Mechanisms and the Importance of Off-Line Characterization Tests in the Pipeline Transport of Dense Coarse-Particle Slurries

For more than 20 years, the Saskatchewan Research Council’s PipeFlow model has been used by companies across the globe to predict pressure losses and minimum operating velocities (‘deposition velocities’) for the pipeline transport of heterogeneous (settling) slurries. The success of this semi-mechanistic, phenomenological model comes from the fact that the friction loss contributions of the dispersed, coarse particle phase are accounted for in a physically meaningful way. The focus of this study is on the need to make accurate off-line slurry characterization measurements to obtain accurate predictions of slurry flow behavior. The results of a number of slurry pipeline tests conducted under controlled conditions are presented. These results clearly demonstrate that, in addition to accurate measurements of particle size distribution and density, proper characterization of the following parameters is also critical: carrier fluid viscosity, settled bed coarse particle concentration, particle drag coefficient / particle terminal settling velocity, and the coefficient of friction between the particles and the pipe wall.© 2013 ASME

Numerical Study of Liquid-Liquid Vertical Dispersed Flows

Numerical simulations of liquid-liquid dispersed flow in a vertical pipe (38mm) have been carried out using the two-fluid approach implemented in a commercial CFD code, ANSYS CFX. A dispersion of oil in water (where water is the continuous phase) was studied. Both fluids were considered as turbulent flows. The k-e model was used for the continuous phase, with the eddy viscosity of the dispersed phase estimated from that of the continuous phase. A comparison of the present numerical results with previous experimental and numerical results in terms of volume fraction, mean velocity and turbulent kinetic energy is discussed. In general, good agreement between the simulation results and experimental measurements was observed.Copyright

Modelling Concentrated Slurry Pipeline Flows

A numerical investigation of two-phase solid-liquid (slurry) flow in horizontal pipes has been carried out. Simulations of concentrated slurry flows in pipes 0.0515 m and 0.15 m in diameter were performed using the two-fluid approach implemented in the commercial CFD code, ANSYS CFX. Mixtures of monosized and bimodal particle sizes were tested. Several test cases were investigated to predict particle velocity- and concentration-distributions and frictional pressure gradients. The effects of turbulence model selection, dispersed phase wall boundary conditions, and interphase force terms on model performance were evaluated. The selection of turbulence model had a significant impact on the dispersed phase velocity and concentration distributions. Comparison of simulations with benchmark experimental data shows clearly that for the relatively small particle sizes (∼100 microns), poor solids concentration profile predictions are obtained if the turbulent dispersion force is not included. In general, very good agreement between numerical and experimental results was observed.© 2012 ASME