| Summary: | 博士 === 國立臺灣大學 === 機械工程學研究所 === 99 === A novel fast pyrolysis reactor for converting biomass into bio-oil has been developed in this study. A reaction chamber equipped with a single tapered screw extruder was designed for simultaneous feeding and pyrolyzing the biomass. The screw extruder is chain-driven by a motor with adjustable rotation speed. In the system development, the aim is to have the capability and simplicity to achieve high production rate, so that it can be easily scaled up with low cost. Moreover, the screw extruder was made of a special type of cast iron having excellent heat resistance and low thermal expansion coefficient, so distortion or warp and hence interference of the screw extruder can be prevented during the operation.
The effect of pyrolysis temperature (ranging from 460~560oC) on bio-oil yield was investigated for cedar, camphor and jatropha trees. The experimental results, indicate that the highest bio-oil yields of 42.9 wt% can be obtained for cedar tree with 18.73 MJ/kg HHV at 520oC. For camphor and jatropha trees, the highest bio-oil yields respectively reach 49.6 wt% with 19.14 MJ/kg HHV at 500oC and 41.6 wt% with 31.41 MJ/kg HHV at 560 oC.
The effects of process parameters of camphor tree biomass grain size (ranging from 0.425 to 3.35mm), rotational speed (ranging from 20 to 60rpm) and the pyrolysis temperature (ranging from 400 to 550 oC) on the yield of bio-oil were investigated in this study by using a fast pyrolysis reactor with a single tapered screw extruder. This study gives the optimal pyrolysis temperatures and rotational speeds for different grain sizes to achieve peak bio-oil yield. The results indicate that higher feed rates are required for larger grain sizes to achieve peak bio-oil yields.
Taguchi experimental design method and the SPSS (Statistical Package for Social Sciences) multiple regression analysis software were employed to analyze the effects of key process parameters for camphor. The results showed that the optimal pyrolysis temperature depends on the grain size and rotation speed. (1) At fixed 20rpm feed rare, the pyrolysis temperature was varied from 400 to 550oC for different grain sizes to attain the optimal pyrolysis temperatures. For the grain size of 0.425~0.6mm and 0.6~0.85mm, the peak bio-oil yields were obtained at 470oC respectively with 60.4wt% and 58.2wt%. In addition, at 500oC the peak bio-oil yields reached 50.2wt%, 57.6wt%, 52.5wt%, 53.0wt%, 50.8wt% respectively for the grain sizes of <0.425mm, 0.85~1.18mm, 1.18~1.70mm, 1.70~2.50 mm and 2.50~3.35mm. (2) At constant temperature of 500oC, the rotation feed rate was varied from 20 to 60 rpm for different grain sizes. Based upon the experimental results was then conducted to evaluate the effect of rotational speed, ranging from 20rpm to 60rpm, on the yield of bio-oil for different biomass grain sizes.
The results show that different optimal pyrolysis temperatures and rotational speeds are required for different grain sizes to achieve peak liquid yield. In addition, when larger grain sizes were used, higher feed rates were required to achieve peak bio-oil yield, implying that a significant increase in productivity is resulted. This implies that the productivity of bio-oil can be significantly increased in the current system. For the case of 2.5~3.35mm grain size, which corresponds to an optimal rotational speed of 40rpm, the production rate was estimated to be around 4kg/h.
From the experiments, we can see the production yield and high heating value of the bio-oil were influenced by the process parameters (grain size, pyrolysis temperature, and biomass feed rate). The S/N ratios were obtained using Taguchi’s methodology. Here, the intended objective is to obtain higher product yields. Hence, the larger the better type S/N ratio was used to transform the yields of the bio-oil.
Therefore, the SPSS multiple regression analysis was performed to obtain the regression formulae that correlate the production yield (Y, dependent variable) with the process parameters (pyrolysis temperature, X1：450oC, 470oC and 500oC , feed rate, X2：20rpm, 40rpm and 60rpm, and grain size, X3：0.425mm, 1.70mm and 3.35mm). The regression formula model is as follows: Y = a + b1X1 + b2X2 + b3X3 + e, where a is the interception, b1, b2, and b3 are the regression factors, and e is the random error. The obtained formula is:
Ycamphor = 1409.04+0.00672X12–0.0519X22–6.253X32 + 0.0071X1X2–0.133X1X3+ 0.157X2X3–6.221X1+ 87.99X3
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