| Summary: | 博士 === 國立臺灣大學 === 機械工程學研究所 === 105 === The aim of this study is to investigate the use of waste heat that is recovered from a multifuel biomass (Japanese cedar and rice husk) gasifier. In the gasification process, the low heating value of the biomass can be transferred to a high heating value for combustible gaseous fuel, which is a form that is widely used in industry and power plants. Conventionally, some cleaning processes must be conducted under higher operating temperatures than the low temperatures typically used to burn biomass. Thus, a catalytic reactor was designed before installing the scrubber in the downdraft gasifier system to effectively utilize the waste heat. The experimental results show that the temperature of the gasifier outlet is approximately 250-400℃; dolomite is used for tar removal in the catalytic reactor. To further improve the use of waste heat, a thermoelectric generator is added to recover waste heat. The thermoelectric generator system is manufactured using a Bi2Te3-based material and is composed of eight thermoelectric modules on the surface of the catalytic reactor. The measured surface temperature of the catalytic reactor is 100-250℃, which is the correct temperature for using Bi2Te3 as a thermoelectric generator. The results of this study show that the maximum hydrogen concentration is approximately 17.82vol% from pure Japanese cedar gasification and approximately 15.89vol% from pure rice husk gasification. The optimal operation of the gasification performance was found when the fuel is pure Japanese cedar at Φ = 0.4, and the obtained cold gas efficiency (CGE) at these conditions is approximately 63.59%. However, the optimal available biogas condition was found when 50% Japanese cedar and rice husk are mixed at Φ = 0.2, with a biogas high heating value (HHV) of approximately 5.75 MJ/m3. The performance of the thermoelectric generation system (TEG) that is used for waste heat recovery shows that the maximum power output of the thermoelectric generator system is 5.8 W and that the thermoelectric generator power density is approximately 180.6 W/m2. In this study, the total efficiency of a multifuel gasifier with a waste heat recovery system from thermoelectric generation modules was also investigated. The maximum exergetic efficiencies for 100% and 75% Japanese cedar are 55.46% and 54.49%, respectively. As the rice husk ratio increased, the maximum exergetic efficiency decreased to 44.2%~46.7%.
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