Significance of Particle Size Distribution on the Disintegration of Compacted Spent Grain during Drying in Superheated Steam

摘要

Drying of distiller's spent grain in conventional hot-air dryers is difficult because of the sticky and slurry nature of spent grain. Also, drying of spent grain is done at high temperature creating a high potential for dryers catching fire. One method to address this problem is to compact the wet spent grain and dry wet compacts in a superheated steam (SS) dryer although, the SS technology also brings some new technical challenges. Crumbling and disintegrating of biomass compacts while they are being dried in SS is a prevalent problem observed during the initial stage of SS drying. In the current study, this problem unique to the SS drying process was analyzed by changing the particle size distribution (PSD) of the distiller's spent grain compacts.Samples of 3 different particle size distributions (d(0.9)= 1283.6 pm, d(0.9)= 1069.3, d(0.9)= 812.8 urn) were prepared by grinding and their physical characteristics tested. The volumetric change and stress relaxation characteristics, in terms of asymptotic modulus (EA) for a 40% deformation, of the compacts while being dried in SS at a temperature of 150°C and a velocity of 0.9 m/s were analyzed for each PSD. The study showed that decreasing the particle size of the compact significantly reduces therelaxation of the compact during SS drying. The asymptotic modulus of the compact increased from 0.009 to 0.035 MPa when the PSD of the compact decreased from 1283.6 to 812.8 pm, during the warm-up period of SS drying.