Solar, Biomass and Hybrid Dryers - BioEnergy Discussion Lists

Chapter 2PACKAGES DEVELOPED AT RECAST, NEPALSolar dryers of various capacities and designs are being used in Nepal for dryingvarious agricultural, horticultural and medicinal products. The most popular dryersare box dryers, cabinet dryers, and tunnel dryers. These are being used forhousehold and small-scale commercial drying. Except for tunnel dryers and largecabinet dryers, most dryers are based on natural convection.Based on research carried out within the RETs in Asia programme, the ResearchCentre for Applied Science and Technology (RECAST) improved existing dryerdesigns with the following objectives: (i) to improve the thermalperformance/efficiency, (ii) to reduce the capital cost, (iii) to reduce weatherdependency, and (iv) to enhance the ease of operation and maintenance. Thefollowing solar dryer packages were developed: improved solar box dryer, cabinetdryer, tunnel dryer and solar/biomass hybrid cabinet dryer. The details of eachpackage are presented in the following sections.Package 4: Improved Solar Box DryerRECAST redesigned the classical solar box dryer to minimize heat losses and tofacilitate easy handling. The improved box dryer consists of an insulated dryingchamber and a chimney attached at the top. Window glass is used a glazing at thetop of the box. The dryer, shown in Figure 4.1, has three trays on which the productsto be dried are loaded. The products are spread in thin layers on the drying trays forbetter contact of drying air with the product. The trays are designed as drawers thatcan be pulled out individually for loading and unloading.Figure 4.1: Improved Box Dryer24