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

ABSTRACT*

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 °C or 60 °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 °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 °C. However, it achieved its maximum of 64.6% during the drying in fluidized with dehumidification, and under 40 °C. The maximum rice whiteness of 41.8 was attained for fluidized with no dehumidification, and at 60 °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.

Highlights

• A fluidized bed drying system was modified to allow utilizing natural or dehumidified air as drying agents.

• The fluidized bed dryer removed more moisture from rough rice as compared with a fixed bed dryer.

• Dehumidification of the drying air had a positive effect on moisture removal.

• No clear trend was observed when rough rice was dried in a fixed bed or a fluidized bed as measured by head rice yield.

Keywords:

• Dehumidification
• fixed bed
• fluidized bed
• rice drying
• rice quality
• silica gel

Acknowledgments

The authors want to thank the Department of Biological & Agricultural Engineering, University of Arkansas, Fayetteville, AR and Division of Agriculture, University of Arkansas Systems, Little Rock, AR for the financial support. The authors are also appreciative of all the staff of the Department of Biological & Agricultural Engineering, Division of Agriculture, and Department of Food Science, University of Arkansas, Fayetteville, AR, for their continuous support. Additionally, they want to acknowledge Deacon Technologies, LLC, Prairie Grove, AR for allowing them to use their moisture probes.