Investigation of rough rice drying in fixed and fluidized bed dryers utilizing dehumidified air as a drying agent

The high initial moisture content of freshly harvested rice accompanied by high relative humidity ambient air as well as no external heating source utilized for on-farm in-bin drying increase the risk of rice deterioration. Air dehumidification could be among the best management practices for rice drying in the high relative humidity environment. The current study aimed to explore the possibility of using silica gel to dehumidify the humid ambient air for drying rice in a fixed bed and fluidized bed. A dehumidification unit was added to the previously developed lab-scale fluidized bed dryer before the blower inlet to help dehumidify the moist inlet air. The effects of bed conditions, i.e., fixed or fluidized, dehumidification environment, i.e., with and without dehumidification, and air temperature; i.e., 40 degrees C or 60 degrees C on the dryer performance, were investigated. The fluidized bed dryer removed more moisture from rough rice as compared with a fixed bed dryer. Explicitly, under the conditions of a fluidized bed, no dehumidification and at 60 degrees C, the moisture removed was 1.5% moisture points more than under the same conditions for fixed bed. Dehumidifying the humid air removed between 0.2% and 1.6% moisture points from rough rice more than the environment of no dehumidification. Moisture content profile showed that about 87% to 90% of the moisture was removed during the first 30 minutes of the drying process. The maximum head rice yield achieved 66.7% during the drying in a fixed bed and with no dehumidification at 40 degrees C. However, it achieved its maximum of 64.6% during the drying in fluidized with dehumidification, and under 40 degrees C. The maximum rice whiteness of 41.8 was attained for fluidized with no dehumidification, and at 60 degrees C. The dryer energy consumption decreased with the use of air dehumidification techniques. Through this study, ambient air dehumidification using desiccant showed the noticeable potential to be used for on-farm in-bin ambient air drying, particularly during humid conditions.

Automated summary

The study found that air dehumidification using silica gel can effectively reduce the risk of rice deterioration in high humidity environments, with the fluidized bed dryer performing better than the fixed bed, removing around 1.5% more moisture. During the rice drying process, about 87% to 90% of the moisture was removed within the first 30 minutes.