Comparison of the Paddy Drying Process and Milling Quality between Re-circulating and Conventional Batch Type Dryers

Introduction High energy consumption and non-uniformity drying in conventional batch type dryer are the common problems in paddy dying industry. Non-uniformity drying causes to kernel breaking chance in the milling process. Using new dryers with better performance can solve the drying problem and energy saving. In this research, the operation of a re-circulating batch dryer was compared with a fixed bed batch dryer (conventional dryer) for paddy drying. Materials and Methods This research was done in a paddy milling factory in Ferydonkenar and deputy of Rice Research Institute of Iran, in Amol, Mazandaran province. Both re-circulating dryer and conventional batch type dryer were made by Khazar Electric Company in Amol- Iran and they had 5 tonnes capacity. In the re-circulating dryer, ambient air was warmed in the furnace and blown to drying zone inside of grain bin. Natural Gas (NG) was used for air warming in dryers. Warm air absorbed paddy moisture and pushed away from the dryer. Drying temperature ranges for re-circulating dryer and conventional dryer was 48-50 °C and 38-52°C, respectively. The paddy variety was one of the Iranian rice varieties as Tarom and initial moisture content of grains was 21% (w.b), it was decreased using drying to 8-9% (w.b) for milling process. Paddy moisture content was measured each 60-120 min by SUNCUE TD-6 portable moisture tester-Taiwan. Energy consumption calculated by fuel and electrical energy summation in each experiment. Natural Gas and electrical power consumption were measured by Gas and electric counters respectively. Drying time, paddy moisture change trend and energy consumption were investigated for paddy drying in each dryers. Also, milling ratio, breaking percent, whitening degree, and elongation rate after cooking were studied after the milling process for rice dried using national standard methods and deputy of Rice Research Institute facilities in Amol. Experimental samples were 150 g and husker (SATAKE THU35B), a whitener (SATAKE TMU05) and KETT C-100 were used for husking, whitening and whiteness degree, respectively. All Experiments were done with three replication and data analyzed using T- student method in 5% probability. Results and Discussion Results showed that re-circulating dryer caused to reduce 54.12 percent in drying time and energy saving in paddy drying in compare with conventional paddy dryers. The trend of moisture content changes was longer and over-drying occurred in lower layers in co