Continuous microwave drying of sweet sorghum bagasse biomass

Sweet sorghum (Sorghum bicolor (L.)) biomass has been touted as an important bioenergy crop that can be converted into various biofuels. In order to minimize storage losses, and to optimize the processing parameters during biochemical or thermochemical conversion, the sorghum bagasse obtained after pressing the sugar-containing juice may need to be dried to specific moisture levels. In this study, the performance of a continuous microwave drying system using a traveling wave applicator was investigated with respect to moisture reduction, power consumption, and overall efficiency. The parameters investigated were microwave power level (0, 200, 600, and 1000 W) and ambient drying temperature (25 °C and 55 °C). A control test was performed using hot air alone (25 °C and 55 °C) during sample drying. The initial moisture contents were obtained through conventional hot air oven drying at 130 °C. The drying rate of microwave drying was compared to conventional oven drying and the control. It was determined that even though the highest drying rates were obtained at the highest power setting (1000 W), when accounting for the power consumed by the drying system, including fans, motors, and ambient air heater, the highest efficiency was obtained at a comparatively low power setting (200 W) and using just ambient temperature (25 °C). The drying rate for microwave drying was significantly higher than conventional drying. The results of this study can be used to design continuous microwave drying systems that can be more efficient and with higher throughputs than conventional air-blown systems.