Computational modelling of superheated steam drying of compacted distillers' spent grain coated with solubles

摘要

Superheated steam (SS) could be a more effective medium than hot air for drying slurry-like materials such as distillers spent grain. As large scale drying of spent grain slurry has many challenges related to handling and transportation, a multilayered/coated product drying approach, where wet material is dried over a relatively dry core, could provide a potential solution for effective drying. The present study focuses on 3D modelling of SS drying of compacted distillers' spent grain coated with solubles. The drying experiments were conducted with cylindrical spent grain pellets with 25% moisture content coated with a thin layer of solubles (79 +/- 2% moisture) at different SS temperatures (120, 150, 180 degrees C) and velocities (0.5, 1.0, 1.5 m/s). The effective moisture diffusivity and the thermo-physical properties of wet distillers' grain pellets with or without solubles (0, 10, 30%, 100% w/w) were determined by experimentation. A coupling model was developed by combining the Reynolds-Average Navier-Stokes and energy equations for the SS flow and the diffusion models for the coated pellet using computational fluid dynamics approach. The prediction model showed appreciable accuracy with maximum percentage error values for moisture and temperature curves of coated pellet as 9.1 and 8.0%, respectively. Sensitivity analysis for the SS operating conditions showed that the effect of SS temperatures is more prominent than that of SS velocities on drying time. Such models, capable of predicting heat and mass transfer phenomena of SS drying of multilayered products, can provide valuable information for the design or optimization of industrial-scale SS drying units. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.