Evaluation of the Dispersion Coefficient and Residence Time Distribution in Packed Bed Using Computational Fluid Dynamics

Packed beds are widely used in the chemical and petroleum industries. The processes often involve a single fluid or mixture of fluids that pass through a packed bed for processing or purifying the fluids.  The fluid flow distribution inside the packed bed plays an important role affecting the process efficiency, yield and sometimes the lifetime of the particles. Flow in the packed bed is greatly affected by the design of the vessel, internals and bed loading.  The dispersion coefficient and Residence Time Distribution (RTD) are two important parameters that are widely used to quantify the flow characteristics in packed bed. The measurement of the two parameters in large-scale industrial units is expensive, time consuming and sometimes not feasible. As an alternative, Computational Fluid Dynamics (CFD) can be used to calculate the RTD and dispersion coefficient.

This paper presents a few different methods on how to calculate the dispersion coefficient and RTD using CFD. The results will be compared to experimental data reported in literature. The issues and potentials of this technique are then discussed, along with several examples from the UOP technologies.