Solar, Biomass and Hybrid Dryers - BioEnergy Discussion Lists

Package 2: Solar-Biomass Hybrid Cabinet DryerSmall-scale drying based on electricity, coal, LPG and other fossil fuels is normallyexpensive. Moreover, combustion of fossil fuels emits greenhouse and other gases.Solar drying is an attractive option to solve some of these problems. However, aninherent problem of solar drying is that it depends entirely on the weather and is notpossible to use during night-time.Biomass is locally available in rural areas of developing countries and is often thecheapest source of energy. In addition, biomass fuels can provide an uninterruptedsupply of thermal energy needed for continuous operation of dryers. Hybrid dryingpowered by biomass and solar energy is a potentially important option for smallscaleoperations since it combines the advantages of drying systems operated bysolar energy alone and those operated by biomass alone. During sunny weather, thedryer is operated in the solar mode which reduces the need for biomass fuels andassociated costs. Use of biomass fuels, however, enables a continuous day and nightoperation even during cloudy or rainy weather.A hybrid cabinet dryer with an automatic temperature control mechanism has beendeveloped at AIT for drying agricultural products. The hybrid pairs a domesticgasifier stove (DGS), developed at AIT, and a flat plate solar air heater to supply hotair for drying products inside a cabinet. The technical specifications of the dryer arepresented in Table 2.1.Table 2.1: Technical specifications of solar-biomass hybrid cabinet dryerSI. No. Parameter Specifications1. Solar Collector type Flat plate air-heating solar collector2. Solar Collector size 2m x 2m3. Drying chamber dimensions 2m (length) x 2m (breadth) x 1.95m (height)4. Drying chamber construction Bricks and mortar5. No. of trays 16 nos.6. Total tray area 14 m 27.No. of doors for loading/unloading4 nos., two at each side8. Stove type Natural convection cross-flow gasifier stove9. Gasifier stove capacity 4.5 kW (thermal)10. Fuel for gasifier stove Wood chips, wood twigs, briquette pieces11. Heat exchanger type Pipe heat exchanger12. Airflow inside the drying chamber Natural convection, with chimneys13. Temperature controller Thermostat-based, mechanical lever control5