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 (within 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/kg water when spiral-pipe
drying column was applied at drying temperature of 100 °C, air velocity of 30 m/s and
paddy feed flow rate of 150 kgdry solid /h. In terms of quality, the head rice yield and whiteness of the dried paddy in the case of spiral-pipe drying column was lower than
those of in the case of smooth-pipe drying column.