Energy consumption and rice milling quality upon drying paddy with a newly-designed horizontal rotary dryer

Abstract

Paddy drying is an energy-intensive process which affects final product quality. Energy consumption and rice milling quality upon drying paddy with an industrial horizontal rotary dryer (IHRD) developed in northern Iran were investigated and compared with those of the conventional industrial batch-type bed dryer (IBBD) at five paddy final moisture levels (8.0, 9.0, 10.0, 11.0, and 12.0%, w.b.). The results indicated that the IHRD consumed specific electrical energy between 5.5 and 17.41 MJ kg−1 water evaporated compared to 2.64–7.48 MJ kg-1 water evaporated in IBBD and specific thermal energy between 11.5 and 36.44 MJ kg−1 water evaporated in IHRD compared to 7.78–22.09 MJ kg−1 water evaporated in IBBD with a decrease in paddy final moisture content in the range of 12.0%–8.0% (w.b.). Thermal energy use efficiency was estimated to be as 38.8% and 26.3% for IBBD and IHRD, respectively, at moisture drop range of 14.5%–12%, w. b. Major milling quality attributes of the final product of paddy dried with IHRD were significantly superior to those of IBBD. It was concluded that the drying time of IHRD can be cut down about 26% without any significant changes in final milled rice quality; resulting to reduce the IBBD's total specific energy use around 10.43 MJ kg−1 water evaporated. Completely discharging the drying air and kick turning the drying drum of IHRD with a suitable time interval were proposed as a subject of investigation to improve the energy efficiency of the tested dryer.