Effect of batch dryer with agitator and moisture controller on drying paddy and milling factor

Non-uniformity of dried paddy using conventional batch type dryer is one of the important factors on rice breakage and losses in milling operations in Iran. For optimizing drying process, a laboratory batch type paddy dryer with agitator and automatic moisture controller was designed and fabricated. The performance of the dryer was evaluated after fabrication. 

The experimental variables were dryer type in two levels (batch dryer with agitator and batch dryer without agitator) and paddy variety in four levels (Hashemi, Gohar, Tarom and Shirodi). The time of drying, drying rate, milling yield, head rice yield, track percentage and whiteness, was conducted in factorial layout based on completely randomized design with three replications. 

The results obtained revealed that the drying time from initial paddy moisture content (average of 14.2 %) to final moisture content (about 8.5 %) lasted about 14.2 h and 43.1 h in batch dryer with and without agitator, respectively. The average drying rate in batch dryer without agitator for all varieties was 0.135%.h-1 and that of the batch dryer with agitator was 0.412%.h-1. There was a significant effect of dryer type on milling recovery and head rice yield (P<0.01) of different variety (P<0.05). The highest milling recovery and head rice yield was determined in Hashemi (69.16 and 87.66 %, respectively) and the lowest corresponding values were registered in Shirodi (62.16 and 57.83 %, respectively). The head rice yield in batch dryer without and with agitator was found to be 67.91 % and 73.16 %, respectively. There was non-significant difference between percentages of track in two types of dryers. The rice whiteness of Hashemi variety dried with batch dryer with agitator (50.46 %) was significantly (P<0.01) higher than the rice whiteness in batch dryer without agitator (46.10 %), however there was non-significant difference between the means of rice whiteness in the other paddy varieties in the two tested dryers.Fabrication and installation of dryer with agitator and automatic moisture controller has benefit of saving time of drying to one third and increasing head rice yield to 5% compare with traditional paddy dryer