Batch Drying of Wheat in a Multiple Porous Draft Tube Spouted Bed

Abstract

Various devices are used for solids drying. Spouted beds are most suitable for drying coarse granular solids like agricultural grains. Conventional single spout beds suffer from few inherent limitations. The use of multiple fluid inlets and draft tubes in a spouted bed will help in overcoming the limitation of maximum spoutable bed depth so that large scale drying operations are possible. In an operation like solids drying use of porous draft tubes in a multiple spouted bed helps in the lateral transport of hot air from spout to annulus region, thereby providing better contact between solid and fluid phases in annular region as well. As a result higher mean transfer rates of heat and mass in the entire bed may be achieved. In this work a multiple spouted bed with porous draft tubes has been used to carry out wheat drying studies. Batch experiments are conducted using grains having initial moisture contents of 20 and 25 % on dry basis: inlet air temperatures of 40, 50 and 60 °C, air flow rate of 36 m3/h are maintained. Fluid inlet diameters of 8, 15 and 21 mm are used in the study. Moisture content versus time plots are prepared for all runs; from these plots batch drying times needed to achieve a final moisture content of 10 % from given initial moisture content are obtained. The results indicate that the drying occurs under falling rate period under all conditions used. The drying rate is found to increase with increase in initial moisture content and air temperature. The batch drying times is found to be lower for the case of multiple spouted beds with porous draft tubes. The batch drying time is found to be decreasing as the fluid inlet size decreases.