Multi-Pass Sorption Drying of Paddy Using Rice Husk Adsorbent: Experiments and Simulation

Abstract

A single-stage sorption drying of paddy with rice husk adsorbent cannot reduce its moisture content to a safe level since the relative humidity of air inside the mixing tank is very high. To obtain a safe moisture content, multi-pass sorption drying was used and the effect of operating parameters—i.e., rice husk density, rice husk initial moisture content, and volumetric mixing ratio of paddy to rice husk—on the drying time and paddy quality were investigated for two paddy varieties, Suphanburi 1 and Khao Dawk Mali 105. A mathematical model associated with the transfers of heat and mass between the grain and adsorbent was also formulated to explore the sensitivity of the operating parameters to the drying time. Both the experiment and the simulation showed that the drying time was shorter by using a lower initial moisture content of rice husk, a higher rice husk bulk density, and a higher volumetric mixing ratio, the last factor being less important. For quality assessment, the color of white rice for both paddy varieties changed insignificantly under the influence of all the operating parameters, but the head rice quality was rather sensitive to the operating conditions especially for the Khao Dawk Mali 105, which had a 6–10% lower in head rice yield compared to that of the reference samples.