Numerical simulation of flow hydrodynamics of struvite pellets in a liquid-solid fluidized bed

Area of Science:

• Environmental Engineering
• Chemical Engineering
• Fluid Dynamics

Background:

• Phosphorus recovery as struvite offers dual benefits for eutrophication control and resource conservation.
• Struvite product usability is primarily determined by particle size, which is heavily influenced by hydrodynamics.
• Understanding fluidization behavior is crucial for optimizing struvite recovery processes.

Purpose of the Study:

• To simulate the flow behavior of struvite pellets in a liquid-solid fluidized bed reactor (FBR).
• To evaluate the impact of various operational conditions, particle characteristics, and reactor shapes on fluidization.
• To validate a computational model for predicting struvite fluidization dynamics.

Main Methods:

• Utilized an Eulerian-Eulerian two-fluid model coupled with the kinetic theory of granular flow.
• Conducted a parametric study on mesh size, time step, discretization, turbulence, and drag models.
• Evaluated operational parameters like liquid velocity, particle size, and reactor dimensions.

Main Results:

• A mesh resolution of 16x240, 0.001s time step, and first-order scheme accurately simulated fluidization.
• The Syamlal-O'Brien drag model best matched experimental data for struvite holdup.
• Liquid velocity and particle size significantly affected solid holdups and velocities; reactor diameter influenced solid velocity.

Conclusions:

• The developed model accurately predicts struvite fluidization, aiding in process control and operation.
• Model parameters provide a foundation for future struvite crystallization simulations.
• Optimized fluidization enhances the efficiency and usability of recovered struvite.