流體化床操作對稻殼熱裂解反應的熱傳特性與產物分布的影響

Abstract

本研究以稻殼為生質物原料、氧化鋁為床質，在流體化床反應器進行熱裂解操作。在氮氣入口速度為0.42 m/s、壓力為1.5 atm，加熱爐溫度為670°C情況下，改變進料速率(F)為5 g/min、10 g/min或15 g/min，與床高/床徑比(H/D ratio)為1、0.75或0.5。分析F與H/D ratio對於產物產率、組成、高熱值與反應床溫度的影響，並以能量守恆進一步分析總體反應熱與流體化床內總熱傳係數。 生質油產率與熱值隨著F提升而上升；在F=15 g/min與H/D ratio=1時，具有最高生質油產率41%。當F降低，裂解氣體滯留時間下降而增加二次裂解，總體反應熱上升；在F = 5 g/min與H/D ratio=1時，具有最高總體反應放熱3.39 MJ/kg。H/D ratio對生質油產率與熱值、總體反應熱影響比起F小。 F與H/D ratio影響流體化床總熱傳係數，最終藉由反應器溫度變化影響產物產率與組成。生質物進料前，流體化床溫度與總熱傳係數隨H/D ratio增加而上升；生質物進料後，稻殼與焦炭造成總熱傳係數下降。當F=5 g/min、H/D ratio=0.75時，生質物進料後總熱傳係數下降最少，為進料前的75%；當F=15 g/min、H/D ratio=0.5時，生質物進料後總熱傳係數下降最多，為進料前的34%。

Rice husks are pyrolyzed in a fluidized bed reactor using alumina as the bed material. At the nitrogen velocity of 0.42 m/s and pressure of 1.5 atm, and the oven temperature of 670°C, we evaluate the effects of the biomass feeding rate, F, and the bed height/diameter ratio, H/D, on the pyrolysis performances. We monitor the product yield, composition and high heating value, and the reactor temperature variation at For5 g/min, 10 g/min, or 15 g/min with H/D ratio of 1, 0.75, or 0.5. The heat of reaction and the bed overall heat transfer coefficient are also analyzed based on the energy balance equations.The yield and high heating value of bio-oil increase with the F increasing. When F=15 g/min and H/D ratio=1, the bio-oil yield is the highest 41%. When F decreases, the retention time of pyrolyzed gas increases, which increases the possibility of the secondary pyrolysis reaction, and hence the overall exothermic heat of reaction increases. When F=5 g/min and H/D ratio=1, the overall exothermic heat of reaction is the highest 3.9 MJ/kg. Comparing to F, H/D ratio has less influence on the product yield, high heating value and the reaction heat. F and H/D ratio affect the reactor temperature through the bed overall heat transfer coefficient, thereby affecting the distribution and composition of products. Before the biomass feeding, the fluidized bed temperature and the bed overall heat transfer coefficient increase with the increasing of H/D ratio. After the biomass feeding, the bed overall heat transfer coefficient decreases due to the presence of rice husk and char with poor heat conductivity. When F=5 g/min and H/D ratio=0.75, the bed overall heat transfer coefficient decreases the least as 25% decreasing after the biomass feeding. When F=15 g/min and H/D ratio=0.5, the bed overall heat transfer coefficient decreases the most as 66% decreasing after the biomass feeding.