Study of tray and pulsed fluidized bed drying of brewer’s spent grain

Abstract

The major residue from beer production is the brewer’s spent grain (BSG). At present, BSG is mainly used as feed for cattle. Spent grains have been considered as a potential source of protein and energy for human nutrition. For such use, BSG must be dried to reduce its mass and increase its shelf life. In this study, the drying kinetics of BSG were investigated in a tray dryer and in a pulsed fluidized bed (PFB) dryer. Five different combinations of temperature and air velocity (70 °C and 1.0 m/s, 70 °C and 1.7 m/s, 80 °C and 1.35 m/s, 90 °C and 1.0 m/s, 90 °C and 1.35 m/s) were investigated for the tray dryer and four for the PFB at 900 rpm (70 °C and 0.52 m/s, 70 °C and 0.72 m/s, 90 °C and 0.52 m/s, 90 °C and 0.72 m/s). Six thin-layer drying models were fitted to the experimental data obtained for the tray dryer: Lewis, Page, Modified Page, Midilli et al., Verma et al. and Henderson-Pabis. Both temperature and air flow influenced drying rate. A moisture ratio reduction of 90% was four times faster at 90 °C and 1.7 m/s than at 70 °C and 1.0 m/s in the tray dryer. The drying models, except Lewis, showed good fit. Drying in the PFB was considerably faster compared to the tray dryer. A moisture reduction of 90% was twice as fast at 90 °C and 0.72 m/s (PFB) than at 90 °C and 1.70 m/s (tray dryer).