Two stage drying of high moisture paddy for the humid tropics

Combination of high temperature and ambient air in-storage drying of high moisture paddy was evaluated in terms of milling quality and energy consumption. Four drying air temperature 50, 60, 70 and 80 deg C using high airflow rate of 18 cubic m/min/square m were used in the first-stage high temperature drying of paddy for two level of initial moisture content of 24 and 28 % wet basis (w.b.). The high moisture paddy was quickly dried up to about 19-20 % w.b. in the first-stage. This stage was followed by ambient-air in-storage drying up to the safe storage moisture content of 13-14 % w.b.. Milling tests showed that using drying temperature of 50 and 60 deg C in the first stage and drying up to 19-20 % w.b., the head yield was found better than conventional batch drying. As drying air temperature increased, the head yield was found to be decreased. In second-stage of ambient air drying, the same head yield was also reflected. There was no significant difference in the milling quality in the different layers of ambient air dried paddy. Energy analysis showed that as the drying air temperature increased, energy consumption in MJ/kg of water removed also increased for both level of initial moisture content of 24 and 28 % w.b.. Energy consumptions in high temperature drying of 24 % initial moisture content up to 20 % w.b. at 50, 60, 70 and 80 deg C were found 3.80, 4.07, 4.32 and 4.94 MJ/kg of water removed respectively. These values were found 3.41, 3.54, 3.69 and 3.90 MJ/kg of water removed respectively for drying of 28 % up to 20 % w.b.. Energy consumption in combination of high temperature and ambient air drying was found less by using 50 and 60 deg C drying air temperature in the first-stage than the conventional heated air batch drying. High moisture paddy can be stored temporarily using low air flow rate without deterioration in the milling quality. High moisture paddy can be stored for one day only without aeration. If high moisture paddy is aerated with high airflow rate ambient air, energy consumption was quite high. Hence, energy consumption point of view aeration of high moisture paddy with high airflow rate is not economical.