Process optimization of paddy drying in cross-flow aerated drying cum storage bin

Abstract

A cross-flow aerated drying cum storage bin was developed and the drying conditions for paddy was optimised. The drying cum storage bin consisted of a cylindrical outer drum with two inner basins having perorated walls made of galvanised iron to hold paddy, and a central perforated vertical duct. A blower (1.5 kW) connected at the base supplies air to the heating chamber (with 1 kW heater coil) and moves vertically through the central duct. The hot air passes horizontally through the grain bulk taking the moisture and moves towards the perforated walls of the bin and exit through the space between the drum and the basins. Drying experiments were conducted with bed thickness of 15 cm to study the drying characteristics of paddy and evaluate the performance of the dryer. Paddy was dried from 18 to 12% (wb) moisture content with the independent parameters selected being drying air temperature (35, 40 and 45 °C) and airflow rate (15, 21 and 27 m3 /h). The drying time varied 1.5 to 4.75 hours over the entire experimental conditions. The analysis of drying rates for both top and bottom bins showed minimum variation indicating uniform drying throughout the depth of the bin. The estimated optimum conditions of drying were 45°C temperature and 27 m3 /h airflow rate. The predicted values of responses at optimised conditions were 1.51 hours of drying time, 6.05x10-7 m2 /s of effective moisture diffusivity, 0.078 W/m2 K of heat transfer coefficient, and 8.23x105 kJ/kg of specific energy consumption. Further, exergy analysis indicated that exergy loss increased with increase in drying air temperature and airflow rate.