Three-dimensional CFD modelling of superheated steam drying of a single distillers’ spent grain pellet

Abstract

The classic method of modelling drying processes using the transfer coefficients can be replaced by a method of solving Reynolds-Averaged Navier-Stokes equations applicable to the drying medium. This specifically applies to superheated steam (SS) as the drying medium, where the mass transfer coefficient cannot be defined by heat transfer analogy. In this study, the heat and mass transfer phenomena of SS drying of distillers’ spent grain (DSG) pellets were numerically studied using a commercial Computational Fluid Dynamics (CFD) package by combining the drying models related to the moist cylinder with the model describing the external flow of SS. A three-dimensional (3D) model of the DSG pellet and the drying chamber was created. The governing differential equations for mass and energy balance of the pellet and steam-flow around it were solved using the finite volume method and SIMPLEC algorithm within the CFD package (ANSYS CFX). The validation of the numerical model with experimental observations showed a good agreement with a mean relative percentage error less than or equal to 10%. The obtained mathematical model could serve as a basic tool for optimization and design of large-scale SS dryers for DSG.