Effect of Four Different Operational Methods for Drying Parboiled Paddy in BAU-STR Dryer

The study was conducted with a view to develop a suitable method for drying parboiled paddy in BAU-STR dryer. The experiment was conducted at Moti auto rice mill, Shyamganj bazar, Purbadhala, Netrokona, Bangladesh. The dryer was evaluated with 4 treatments using variety BRRI dhan28. Each Treatment had four steps of drying. Treatment 1 (T1) was comprised with first sun drying until moisture content reached 25% (wb) and then drying in BAU-STR dryer with high temperature (45±2.65°C). Treatment 2 (T2) was encompassed with first low temperature (35±2.15°C) drying until moisture content reached 25% (wb) and then drying in BAU-STR dryer with high temperature (45±2.65°C). Treatment 3 (T3) was contained with first only air flow until moisture content reached 25% (wb) and then drying in BAU-STR dryer with high temperature (45±2.65°C). Treatment 4 (T4) was comprised with first high temperature drying until moisture content reached 14% (wb) in inner part of grain and ambient air flow until the moisture gradient remain same in inner and outer grain. Each of the drying treatment had 2 hr ambient air flow when inner grain moisture reached 18% (wb). The total drying time were (7.5 hr sundry + 5.5 hr in dryer), 7 hr, 9 hr and 9 hr for T1, T2, T3 and T4, respectively. Parboiled paddy was dried from average initial moisture content 31.9% (wb) to final moisture content 15.1% (wb). The variation of moisture between inner and outer grain was 6%, 8.5%, 8.6% and 3% in T1, T2, T3 and T4, respectively. The drying rate was found 1.1%MC/hr, 2.0%MC/hr, 1.6%MC/hr and 1.9%MC/hr for T1, T2, T3 and T4, respectively. The efficiency of the dryer was found 53.2%, 62.9%, 62.7% and 66.9% for T1, T2, T3 and T4, respectively. The head rice yield was 45.27%, 43.38%, 45.76% and 52.47% for T1, T2, T3 and T4, respectively. All four solutions have higher running costs than the conventional sun drying method. In each treatment, the benefit cost ratio (BCR) was less than one (1.0). Although the head rice output was below the required level, the milling recovery of rice dried in a BAU-STR dryer was adequate.