Design, development and testing of a vibro-fluidized bed paddy dryer

Abstract

A laboratory model vibro-fluidized bed dryer of 50 kg capacity was fabricated for drying paddy. The dryer was tested to compare the performance of drying paddy in static as well as vibratory bed. Mixing index of grain was studied with mixing time during vibration of drying bed. Paddy was conditioned to initial moisture content of 32% (w.b.) and drying experiments were conducted for 20 kg paddy with 10 cm bed thickness at 40 °C in both static and vibratory mode of operation. Drying was continued for a total period of 3 h and samples were drawn at regular intervals of 30 minutes for moisture content measurement. The drying curves, dryer performance parameters and milling quality were determined to compare the static and vibratory bed drying. The mixing index was observed to be more than 0.99 after 30 min of operation and there was no significant difference of coloured grain proportions with mixing time indicating that proper mixing occurred within 30 min of operation of the dryer. It took 120 and 180 min to dry paddy from an initial average moisture content of 48 to 14% (d.b.) when the dryer was operated in vibratory and static mode, respectively. It was observed that both drying time and vibration had significant effect (p<0.05) on moisture content of sample during drying. The drying rate was found to be more in vibratory bed than static bed and drying took place under falling rate period in both the modes of operation. The specific energy consumption were 1.0 and 0.79 kWh/kg water whereas, drying efficiency were 69.8 and 87.8% for static and vibratory mode of drying, respectively. Head rice yield of paddy dried in vibratory mode was 1.3% more than dried in static mode due to uniform drying. From the above study, it was concluded that vibro-fluidised bed dryer could be used for drying paddy efficiently at farm level with less drying time, lower energy consumption and higher head rice yield.