Changes in Moisture Desorption Rate of Shelled Corn Layers in a Low-Temperature Deep-Bed Drying Column

Abstract

To optimize grain drying processes, high-moisture shelled corn was dried in a device using a combination of three temperatures (45, 55 and 65 °C) and hot-air velocities (0.7, 1.1 and 1.3 m·s^-1). The grain moisture and temperature, and the relative humidity (RH) of interstitial airflow were determined intelligently in grain layers of 7.5 to 32.5 cm with 5.0 cm intervals. The change in RH of interstitial airflow in grain layers of 7.5-27.5 cm with drying time all revealed the shape of a hyperbolic line and took turns to lag. These RH lines shortened with an increased drying temperature from 45 to 65 °C and hot-air velocity from 0.7 to 1.3 m·s^-1. The temperature lines were raised and shortened with an increase in drying temperature and hot-air velocity. A modified moisture diffusion exponential equation was developed to analyze the moisture desorption rate of corn kernels. For the average sorption rate curve from grain layers of 2.5-32.5 cm at 1.3 m·s^-1 of hot air, the transition points from adsorption to desorption occurred at 2.4 h, 2.7 h, and 3.0 h with drying temperatures of 65 and 45 °C, respectively, and represented the earliest and largest initial desorption rates among the three hot-air velocities. The moisture desorption rate of samples increased with increasing drying temperature. Compared with the average value of grain layers, at the same hot-air velocity, the kernel effective diffusivity (D_eff) values dried at 55 °C were correspondingly higher than those dried at 45 and 65 °C. At the same drying temperature, the kernel D_eff values tended to increase with an increase in hot-air velocity, whereas the activation energy decreased. These results suggested that an increase in drying temperature and hot-air velocity may considerably shorten adsorption time and increase desorption rates of shelled corn in deep bed drying.