| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 96 === A fixed-bed air-blown stratified downdraft biomass gasifier was built in this study. The gasifier was coupled to a Stirling engine via a burner to construct a combined heat and power system. An air-sealed hopper was used for fuel storage and feeding, rather than an electric feeding system, to reduce the energy consumption. A water-cooled gamma-type Stirling engine filled with air as working fluid was built in this study. A burner was designed to combine the gasifier with Stirling engine, and preheating the intake air with flue gas exhausted from the burner can improve the system efficiency. The main purpose of this study is to investigate the influences of operation parameters including the height of air inlet, height of fuel ignition, airflow rate, air-fuel ratio, and the fuel feeding rate, on the producer gas heating value, the temperature of gas inside the burner, and the torque and power of Stirling engine. Tests have been performed by using wooden cubes (10×10×10 and 15×15×15 mm) of Red Lauan and White Lauan as gasification feedstock.
Experimental results of the gasifier indicate that reducing the height of grate to increase the length of gasification zone is required for prolonging the retention time of fuel in gasification region. Ignition of fuel at the height of air intake can shorten the time required for start-up and consequently reduce the consumption of fuel and energy during the start-up period. An optimum mean producer gas HHV of 5081 kJ/Nm3 was obtained as the gasifier was operated with small-sized fuels (10×10×10 mm ) at an airflow rate of 14 Nm3/h. Test results of the combined heat and power system indicate that the Stirling engine can run smoothly and be continuously driven by the combustion heat of the syngas produced by the gasifier. A maximum engine speed of 463 rpm and a maximum shaft power of 3.12 W were reached in the tests performed.
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