| Summary: | 碩士 === 中原大學 === 化學工程研究所 === 102 === Rice is one of the important crops in Asia, and rice straw is a major byproduct from rice cultivation. The global rice straw production is approximately 720 million tonnes per year. Finding an effective way to deal with rice straw is urgent. Fluidized bed technology is an effective combustion method of biomass products, but agglomeration and defluidization are a persistent issue during rice straw combustion. The experiments are conducted in bench scale vortexing fluidized bed combustor (VFBC) using silica sand as bed material and rice straw as fuel. The effects of bed temperature, secondary gas flow rate and superficial gas velocity on the defluidization time, alkali concentration within the bed, the compositions and morphology of particles, fly ash, pollutant emissions, and combustion efficiency are investigated.
The results reveal that the defluidization accelerates with bed temperature. This is due to melting increases with temperature, which increases viscous force among particles. Particles agglomerate which causes defluidization. Defluidization accelerates and the amount of bottom ash increases with secondary gas flow rate. The amount of bottom ash reaches the critical point for agglomeration in a short time. Defluidization decelerates with superficial gas velocity, due to the uniform bed temperature at high superficial gas velocity, which reduces the melting phenomena and the hot spot forming probability in the bed. The bed can be divided into three sections which are upper-bubbling zone, lower-bubbling zone and grid zone. The potassium concentration in lower-bubbling zone and grid zone do not change significantly with operating parameters. In upper-bubbling zone, bed temperature has a strong influence on potassium concentration.
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