Energy efficiency of paddy dehydration process using pneumatic dryer with spiral-pipe drying column

Abstract

Pneumatic dryer is one of the energy efficient dryers for removing surface moisture of particulate materials including freshly-harvested paddy. However, energy efficiency of dryer can still be improved. In this study, a spiral-pipe drying column was applied to the drying system instead of a conventional drying column (smooth pipe) in order to enhance the turbulence of hot air used as the drying medium. The effects of various operating parameters, i.e., inlet air temperature, air velocity and paddy feed flow rate, on the final moisture content of paddy and specific energy consumption (SEC) of the dryer were then studied. Comparison was also made with the smooth-pipe drying column results. It was found that the developed pneumatic dryer could reduce the moisture content of paddy by 4.4 to 10.3% (d.b.) within a very short period of time (less than 5 s) and the minimum moisture content of dried paddy was found to be 17.7% (d.b.). In addition, SEC of the developed dryer was lower than that of the conventional dryer at all drying conditions. In this study, the lowest value of SEC was found to be 1.78

MJ/kgwater when spiral-pipe drying column was applied at drying temperature of 100 oC, air velocity of 30 m/s and paddy feed flow rate of 150 kgdry solid/h.