Influence of Rotary Dryer on Paddy (Hashemi Var.) Drying and Rice Milling Quality

Long time processing, high energy consumption and non-uniformity in layers moisture are common problems in paddy drying using conventional batch type dryer, leading to increase the chance of kernel breaking during milling process. In this research, drying time, grains moisture content change and energy consumption of a newly rotary dryer were compared with that of a conventional batch type dryer for paddy (Hashemi variety) drying. Besides, quality parameters as hulling milling ratio, head rice yield and white rice breaking percent were studied in paddy dried using both dryers. All Experiments were done triplicate and data analyzed using T- student method in 5% probability. Results showed that newly rotary dryer caused uniformity in drying processes and cleaning of dried paddy; but, in conventional batch type dryer, because of environmental warm air around it, drying time and energy consumption were about 9 and 8.9 percent, respectively, less than what were calculated in newly rotary dryer. Specific energy consumption for paddy moisture evaporation was 13.5 MJ/kgH2O and it was about 11 percent less than that in rotary dryer. The difference of paddy moisture contents and temperatures in top and lower part of layers of batch type dryer were 2 percent and 6 °C respectively.  Milling ratio increased 3.8 percent when rotary dryer was used. Rotary dryer did not have significant effect on paddy hulling. The main effect of using rotary dryer occurred on head rice yield and it was increased about 7.5 percent, comparing with batch dryer. Using rotary dryer caused 7.8 percent decrease in broken kernels, comparing with conventional batch type dryer.