Superheated steam drying characteristic and moisture diffusivity of distillers’ wet grains and condensed distillers’ solubles Original Research Article

Samples of distillers’ spent grains were prepared by blending different proportions of distillers’ wet grains (DWG) with condensed distillers’ solubles (CDS). Such samples when dried with superheated steam (SS) at 110, 130 and 160 °C showed typical behaviour of drying in the falling rate period. The overall moisture diffusivity (Dm) increased with a decrease in moisture content under all drying conditions. An increase in moisture diffusivity with respect to the SS temperature was also observed. For all drying conditions, the values of average diffusivities (Dm)avg non-corrected for shrinkage ranged from 0.52 × 10−9 to 3.08 × 10−9 m2/s. For distillers’ spent grains of different ratios of DWG to CDS, the decrease in SS temperature from 160 to 110 °C caused a decrease in (Dm)avg by 69–82%. Increasing the amount of CDS added to the DWG from 0% to 100% caused an increase in (Dm)avg by 14–35% for the temperature range tested in this study. The values of (Dm)avg corrected for shrinkage ranged from 0.17 × 10−9 to 0.86 × 10−9 m2/s for all drying conditions studied. The decrease in SS temperature from 160 to 110 °C caused a decrease in (Dm)avg by 70–74%. Not much differences were observed for the same drying temperatures and different ratios of DWG to CDS. The differences between the values of average overall moisture diffusivity (Dm)avg corrected and non-corrected for shrinkage were significant, nearly one order of magnitude.