CFD-PBM modelling of tailings flocculation in a lab-scale gravity thickener

Numerical simulation of a mechanical flocculation process with multi-chambers in series

A mechanical flocculation system with multi-chambers in series is commonly used as the advanced phosphorus removal technology for wastewater treatment. This work aims to numerically investigate the inner states and overall performance of industrial-scale mechanical flocculators in series. This is based on our previously developed computational fluid dynamics (CFD) flocculation model which is extended to consider the key chemical reactions of phosphorus removal. The effects of the number of flocculation chambers, locations, and sizes of the flocculation chamber connection as well as operational combinations of impeller speeds are investigated. With a decreasing number of flocculation chambers, the main vortexes and chemical reactions are weakened, while the small flocs form. Both the phosphorus removal efficiency η and the average floc size d_p reduce as the number of flocculation chambers decreases. The connection location of flocculation chambers directly determines the turbulent flow, thus influencing the key performance indicators. However, the phosphorus removal efficiency η and average particle size d_p are little affected by the size of the flocculation chamber connection. As the impeller speeds in series gradually increase, the gradient of floc size distribution in each chamber is enlarged and the chemical reaction is enhanced over the working volume.

Modelling of Red-Mud Particle-Solid Distribution in the Feeder Cup of a Thickener Using the Combined CFD-DPM Approach

The paper evaluates the behavior of a red-mud solid fraction in a thickener feeder cup, aiming to identify the main characteristics of particle distribution in the flocculation zone and to determine the dependencies affecting the further process taking place in the particle-free sedimentation zone in the thickener-thickening unit. This work used mathematical and numerical modeling to study the influence of such parameters as the flow rate of the feed pulp in the thickener, the flow rate of the flocculant, the density of pulp at the inlet to the unit, and the viscosity and temperature of the pulp on the particle-size distribution from under the feeder cup. The results and dependencies obtained are intended to be used as nominal values in the red-mud thickening process performed on a lab-scale unit.

Multiphase Flow Characteristics in the Classification Process of a Novel Wide Neck Thickener: Experiment and Simulation

A novel thickening equipment known as a wide neck thickener (WNT) was designed to solve the problem of depending only on gravity settlement of the thickener. The computational fluid dynamics method with the Reynolds stress and the volume of fluid models and the particle image velocimetry experimental method were both applied to investigate the pressure and velocity variation and turbulent characteristics of the WNT under different parameter settings. The results indicate that experiments and simulations are consistent. Under four parameter settings, the axial and tangential velocities decrease to the minimum and then increase from the wall to the center. Under different feed velocity, cone angle, and spigot diameter settings, turbulent kinetic energy k and intensity I decrease from the cylinder to the cone and from the wall to the center; the max k and I correspond to the area near the inlet followed by the cylinder, and k and I in the cone are the smallest. When the classification overflow outlet (COO) diameter is 200 mm, k and I increase rapidly, the max k and I are transferred from near the inlet to near the cylinder wall at the COO, and the k and I near the wall decrease significantly.