INVESTIGATION ON APPROPRIATE TWO STAGE DRYING TECHNIQUES FOR QUALITY PADDY SEEDS

Abstract

An attempt was made to investigate appropriate two-stage drying techniques for quality rice seeds. In this research two options of two-stage drying were conducted for three varieties (BR-11, BRRI dhan-51and Guti swarna). The first option was employed by fluidized bed drying and tempering followed by sun-drying method and the second option was carried out by fluidized bed drying and tempering followed by further fluidized bed drying. In both options, the first stage drying in fluidized bed dryer was carried out using three temperatures (50°C, 55°C and 60°C) at a constant bed thickness of 15 cm. After the first stage of drying, all samples were immediately tempered for 45 min at grain temperature. All tempered samples were further dried in the second stage by sun-drying (29.67±.58°C) in the first option and in the same fluidized bed dryer using three temperature (35°C, 40°C, and 45°C) second option. Drying performance in terms of drying time and quality of seeds in terms of germination percentage was evaluated. Drying results showed that drying required 6.67 to 6.82 hours in the first option and only 2.32 to 5.32 hours in the second option of two-stage drying for reducing moisture content 24.71±.5% to 12.1±0.1% wb. On the other hand total drying time for single stage sun drying (complete sun drying method) required 9.25 hours. In evaluation drying time, it was found that drying time was 26.27-74.92% shorter than the single-stage sun drying. In comparison of germination percentage of seeds dried between first option and sun drying method, it revealed that higher germination percentage (96% of BR-11, 95.33% of BRRI dhan-51 and 96.33% of Guti swarna) was obtained than the sun drying method (94% of BR-11, 94.33% of BRRI dhan-51 and 96.33% of Guti swarna) while dried at 50°C in the first stage followed by sundry at 30±2°C in second stage except in case of Guti swarna). On the other hand comparison of germination percentage of seeds dried between second option and sun drying method, it revealed that higher germination percentage (96% of BR-11, 97.33% of BRRI dhan-51 and 96 of Guti swarna) was obtained than sun drying method while dried in the fluidized bed dryer at 50°C in the first stage followed by 35°C in the second stage except in case of variety Guti swarna. A clear effect of fluidized bed drying air temperature on the germination percentage was found. For the case of first option, optimum drying air temperature for rice seeds was 50°C in fluidized bed dryer first stage drying followed by sun drying as second stage. For second option drying air temperature of 50°C in the first stage and 35°C in the second stage in the fluidized bed dryer. The overall investigation showed that the proposed two-stage drying technique does not only facilitated faster removal of moisture content but also yielded higher germination percentage. Therefore drying at optimum air temperature (first option: first stage 50°C and second stage sun drying, second option: first stage 50°C and second stage 35°C in FBD) for both options of two-stage drying in the fluidized dryer can be applied for rice seed drying in Bangladesh.