Drying of Sludge in a Pneumatic Dryer Using Computational Fluid Dynamics

Abstract

A control volume–based technique implemented in FLUENT computational fluid dynamics (CFD) package was applied along with the kinetic theory of granular flow (KTGF) to simulate the flow pattern and heat and mass transfer processes for wet PVC and sludge material in a large-scale pneumatic dryer. User-defined subroutines were added to extend FLUENT capability to account for mixture properties and to simulate the drying rate for surface moisture evaporation. The convective heat and mass transfer coefficients were modeled using published correlations for Nusselt and Sherwood numbers. Initially, the model was validated against experimental data in the open literature for polyvinyl chloride (PVC) particles. Sensitivity analysis was conducted to determine the effect of gas-phase velocity and temperature on the final product outcome. In addition, mixture inlet conditions such as the particle moisture content and gas turbulent intensity were examined. The model showed high sensitivity to the turbulent conditions at the mixture inlet for the gas phase; high turbulent intensities were needed to disperse the particulate phase in the dryer reasonably well. The numerical model demonstrated the successful implementation of a commercial CFD code with user-defined heat and mass transfer models for complex multiphase flows.

Keywords:

• CFD modeling
• Heat and mass transfer
• Pneumatic dryer
• Sludge drying
• Two-fluid model