Design, development and evaluation of a continuous-flow mixing grain dryer

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A low-cost, 250kg to 1-tonne capacity continuous-flow mixing grain dryer (LSU type) was designed and developed. The dryer consists of three main parts: 1) the drying chamber made of inverted V-shaped ducts, to which the plenum inlet is connected; 2) the blower, with a 750 W (1 hp) electric motor and centrifugal fan which provides the drying air; 3) 1 kW electric heater, 4) discharge rollers powered by a 3kW electric gear-motor with a 37.5:1 reduction gearbox. Trials conducted between April and June, 2011 showed that paddy rice, at initial moisture content (MC) of 19.7%- 26.6% dried to 11.8%- 13.5% respectively. Sun drying was also carried out as control. The drying period for the mechanical drying ranged from 4.8-5.7h and that for sun drying was 5h. The moisture reduction rate ranged form 1.16-2.41%/h for the mechanical drying and 2.18% for sun drying. Milling recovery and head rice yield from mechanical drying were better than for sun drying. The heat efficiencies of drying the four consignments ranged from 36.40%-62.70%. Although power consumption was not measured, the operating cost would reduce if a biomass (rice husk) burner is used instead of electrical energy.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the award of the Degree of Master of Science in Agricultural Machinery Engineering, 2011