Fluidized Bed Drying Characteristics of Soybeans

Abstract

The present study investigated the influence of air temperature and velocity on the drying kinetics and specific energy consumption during fluidized bed drying of soybean at 80, 100, 120 and 140ºC and airflow rates of 1.8, 3.1 and 4.5 m s-1. Six mathematical models for describing the fluidized bed drying behavior were investigated. The value of the drying rate coefficient (k) increased with increasing air temperature and velocity and thus reduced the drying time. Although the Midilli model showed the best fit, the Page’s model was selected, since it had almost a similar performance but the model is simpler with two parameters instead of four. The drying of soybean seeds took place in the falling rate period and was controlled by moisture diffusion. A third order polynomial relationship was found to correlate the effective moisture diffusivity with moisture content. Effective diffusivity increased with decreasing moisture content and increasing temperature and air velocity. It varied from 4.595×10−11 to 3.325×10−10 m2 s-1 over the temperature and velocity ranges. Values of the activation energy for moisture diffusion were determined as 35.33, 32.85 and 30.73 kJ mol-1 for air velocities of 1.8, 3.1 and 4.5 m/s, respectively. It was found that decrease in energy of activation caused an increase in drying rate. The minimum and the maximum specific energy requirements for drying of soybean seeds were determined as 26.90 and 111.05 kWh kg-1 for 140ºC with 1.8 m s-1 and 80ºC with 4.5 m s-1 air velocity, respectively. Keywords: Drying rate, Mathematical modeling, Moisture diffusivity, Energy consumption.