Paddy drying using adsorption technique: Experiments and simulation

Quality of agricultural product can be degraded easily by heat. Heatless drying using an adsorption method may be a possible alternative to grain drying. The experiments of paddy drying using rice husk adsorbent were performed with single and multi-stages. In single stage, where high-moisture paddy were intimately mixed with rice husk in closed containers, high water concentration in the air within the container limits the moisture transfer rate and the resulting moisture content of the sample could not be decreased to the safe level for storage in spite of using low initial moisture content of the adsorbent or increasing the volumetric mixing ratio. However, the moisture content of paddy was reduced to the desire level as the multi-stage, where the adsorbent was physically separated in each stage and then replaced with the new one. The mathematical description of desorption-adsorption processes for a single kernel associated with the mass balance equation on the humidity ratio of the air surrounding the particles was formulated. The predictions of relative humidity and moisture contents of paddy and rice husk were shown to be in agreement with the experiments. The quality parameters, i.e., head-rice yield and rice whiteness obtained from multi-stage drying, were similar to those obtained by shade drying.