Design of Hybrid Drying- Dedusting Unit Processor for Rough Rice Processing

摘要

Advanced drying technology enables drying of rough rice and dedusting of rice husks to bencarried out simultaneously in the same unit processor. This paper reports the efficiency of dedustingnof rice husks in a two-stage inclined cross flow fluidized bed dryer and the drying kineticsnof rough rice in a batch fluidized bed dryer as well as the conceptual design of a hybrid dryingn– dedusting unit processor. Experimental works had been carried out using rough rice (a GroupnD particle according to Geldart classification of powders) in a 2.5 m height two-stage inclinednfluidized bed column of cross sectional area of 0.61m x 0.15m and a 3 m high batch fluidized bedndryer. The objectives of the study was to investigate the separation efficiency of dedusting of ricenhusks in the two-stage cross flow fluidized bed dryer and to study the drying kinetics of roughnrice drying in the batch fluidized bed dryer. The experimental results showed that the dedustingnseparation efficiency at low superficial gas velocity gave unsatisfactory separation of merely 40%nof rice husks. At higher superficial gas velocity, separation efficiency of rice husks as high as 93%nwas achieved. In addition, higher distributor inclination angle gave slightly improved separationnefficiency. The drying kinetics showed that the residence time that is required to reduce the moisturencontent of rough rice to 18% (intermediate storage moisture content for second stage drying)nis 3 minutes whereas the residence time that is required to reduce the moisture content to 13%n(desirable final moisture content) is approximately 10 minutes regardless of the effect of kernelncracking. It was also found that higher drying temperatures gave higher drying rate. A conceptualndesign has been developed based on the results obtained in the studies. In order to maximize thenheat utilization and to carry out two processes viz. dedusting and drying in one unit processor, itnis suggested that drying – dedusting can be carried out in a multistage mode where drying is takennplace at each stage while dedusting is taking place at the upper stage. This concept can be appliednto a packed bed or a fluidized bed unit processor.