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1. Fixed bed batch dryers usually have rectangular
bins with plenum chamber underneath or circular bins with central duct.
2. The most common fixed bed dryers are flat bed dryers which have a very simple design. Grains are laid out on a perforated screen, and dried by forcing air from below.
3. The air fan that provides the drying air is usually a simple axial flow fan, powered by a diesel engine or by an electric motor.
4. A kerosene burner or a biomass stove provides drying heat. The capacity of the dryer varies from one to ten tons.
5. Generally the drying floor is flat although dryers with reclining sections or vibrating sections exist as well. The height of the layer is usually 40 cm. The most common smaller dryers have a capacity of one to three tons per day with drying times of six to twelve hours.
6. For drying of paddy in tropical areas, an air temperature of 40-45ºC is normally used with a heater capable of raising the air temperature 10-15º C above ambient.
7. An air velocity 0.15-0.25 m/s is required and typical fan power requirements are 1.5-2.5 kW /ton of paddy. The efficiency of these dryers as well as the head rice recovery is improved by stirring the grain during drying. Other fixed bed dryers have a cylindrical duct made out of porous materials with a central duct for drying air delivery.