Solar, Biomass and Hybrid Dryers - BioEnergy Discussion Lists

cylinder. This housing has been provided to enhance the heat transfer from the hotair to the sensing element in the thermostat. The thermostat is fixed on the centralheat exchanger pipe near the entrance of flue gas from the gasifier stove. Thetemperature of drying air inside of the dryer can be set to a particular value byadjusting the height of the thermostat expander rod above the heat exchanger pipe.When the average temperature inside the dryer rises above the desired level, thethermostatic element will extend and push the short arm of a lever; the long arm ofthe lever pulls a vertical rod to close the butterfly valve at the stove’s inlet so thatflow of primary air to the gasifier stove will be reduced.When the airflow to the reaction chamber is reduced, the amount of producer gasgenerated for combustion is also reduced, so that the temperature in the dryingchamber drops. When the temperature drops to a set level, the thermostat will moveback to the normal position and the butterfly valve will be opened.The mechanism of the control system of the thermostat is illustrated in Figure 2.18. Aphotograph of the thermostat, fixed inside the drying chamber, is presented inFigure 2.19.GasifierstoveThermostatDryingchamberPrimary air inletFigure 2.18: Thermostat working principleUsing the temperature controller, the inside temperature of air inside the dryingchamber can be maintained in the range of 55-65°C.17