สำนักราชบัณฑิตยสภา

The Journal of the Royal Institute of Thailand Vol. 27 No. 1 Jan.-Mar. 2002 °“√ÕÕ°·∫∫ ∑¥ Õ∫ ·≈–À“·π«∑“ß∑’Ë ‡À¡“–∑’Ë ÿ ¥ ”À√— ∫ °“√Õ∫·Àâ ߢ⠓«‡ª≈◊ Õ° ‚¥¬‡∑§π‘ §°“√∑”‰À≈∫π∞“π —Ë π ˜Ú Abstract Design, Testing and Optimization of Vibro-fluidized Bed Paddy Drying Somchart Soponronnarit*, Somboon Wetchacama ✝ , Suwat Trutassanawin ✝ , Wuttikon Jariyatontivait # *Fellow, the Academy of Science, the Royal Institute, Thailand, ✝ School of Energy and Materials, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand, # Former master students. The objectives of this research were to design, construct and test a prototype of a vibro-fluid- ized bed paddy dryer with a capacity of 2.5-5.0 tons/h, and to develop a mathematical model that determines optimum operating parameters. Experimental conditions were: air flow rate, 1.7 m 3 /sec; bed velocity, 1.4 m/sec and average drying air temperature, 125-140˚C. Residence time of paddy was approximately one minute; fraction of air recycled, 0.85 and bed height, 11.5 cm. With a feed rate of 4,821 kg/h, the moisture content of paddy was reduced from 28 to 23 per cent dry bed (d.b.). Vibra- tion intensity was 1 (frequency 7.3 Hz and amplitude 5 mm). Electrical power consumption and average diesel oil consumption were 9,646 W and 17.6 L/h, respectively. Specific primary energy consumption (SPEC) was 6.15 MJ/kg of water evaporated. Electrical power of the blower motor and vibrator motor was 55 per cent as compared with the electrical power of the blower motor used in fluidized bed drying without vibration. For operation 12 hours/day and 90 days/year, the cost of paddy drying was 1.50 baht/kg of water evaporated, of which 0.50 baht was fixed cost and 1.00 baht was operating cost (US$ 1 = 40 baht). Comparison between the experimental and simulated results showed that the mathematical model could predict with fairly accuracy. For fluidized bed paddy drying with a capacity of 5 tons/h, initial moisture of paddy of 30 per cent d.b. and drying air velocity was 2.3 m/sec, the optimum operating parameters were: drying air temperature, 149˚C; fraction of air recycled, 0.93 and bed height, 11.9 cm. SPEC and final moisture content were 5.74 MJ/kg of water evaporated and 24.9 per cent d.b., respectively. For vibro-fluidized bed paddy drying with the same capacity and initial moisture content and drying air velocity of 1.5 m/sec, the optimum operating parameters were: drying air temperature, 143˚C; fraction of air recycled, 0.83; bed height, 9.9 cm; frequency, 5 Hz and vibration intensity, 2.5. SPEC and final moisture content were 5.36 MJ/kg of water evaporated and 26.0 per cent d.b., respectively. Paddy drying with vibro-fluidization tech- nique consumed 7 per cent less primary energy compared with fluidized bed drying without vibra- tion. Total electrical power and average diesel oil consumption of vibro-fluidized bed drying were 5.9 kW and 21.1 L/h, respectively. Total electrical power consumption was 30.1 per cent as compared with total electrical power consumption used in fluidized bed drying without vibration. Key words : vibro-fluidized bed, paddy drying, fluidization