Converting Waste Agricultural Biomass into a Resource - UNEP

The dryer end is fitted with a wire net of appropriate size to prevent insects
and flies from entering the drying chamber. Trays to hold the products to be
dried are made from aluminum frames and stainless steel wire mesh.
A biomass stove-heat exchanger assembly is placed at the inlet of the tunnel
dryer to improve the reliability of the dryer and the quality of the dried product.
The heat exchanger is of cross-flow type with flue gas from the stove passing
through the tubes and the ambient air flowing over the tubes before entering
the dryer. Five fans, each of 14 W capacity, are used to force ambient air into
the dryer, through the bank of heat exchanger tubes. The ‘tubes’ of the heat
exchanger are connected to a biomass stove at one end and a chimney at the
other. Noting that the maximum permissible temperature for fruits and
vegetable drying is about 60°C, the design temperature at the outlet of the
heat exchanger should not be less than this value. Eight galvanised iron (GI)
pipes with outer diameter 50 mm and inner diameter 44 mm are used to
provide the required heat transfer area of the heat exchanger; the tubes are
arranged in a staggered manner, as shown in Figure 3.2. The tube bank is
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