【作者】 俞路；

【导师】 白凤武；

【作者基本信息】 大连理工大学 ， 生物化工， 2011， 博士

【摘要】 能源和环境对于各个国家来说,都是一个重要的课题。随着现代化程度的提高,社会对于能源的需求越来越大,然而现在广泛使用的石油、煤和天然气等都是不可再生的一次性能源,随着消耗量的不断增大面临着供应不足甚至有枯竭的危险,能源供应面临严峻的挑战。因此,世界各国都在积极开发潜力巨大的、对环境友好的新型可再生能源。生物质能源作为一种可再生、存量巨大的能源得到高度重视。其中燃料乙醇因具有清洁环保、可再生的优点而被广泛应用。利用酵母细胞自絮凝形成颗粒作为固定化方法的自固定化细胞技术,已经在燃料乙醇生产中得到实际应用并取得了良好经济收益。然而由于缺乏理论指导,装置的设计、放大、操作仍依靠工程经验。本论文以絮凝酵母SPSC01悬浮液为研究对象,对其在悬浮床生物反应器内的流变特征和流体动力学行为进行研究,旨在为过程设备设计和生产运行提供理论指导。首先,利用旋转粘度计对絮凝酵母悬浮液流变行为进行了测定,考察了各因素的影响。研究结果表明：絮凝酵母悬浮液呈非牛顿性流体特征,其流变特性符合幂律指数模型,模型参数受菌体浓度影响。絮凝酵母细胞生物量是影响其流变特性的主要因素。利用激光聚焦反射式颗粒测量系统在线检测絮凝酵母颗粒的弦长频率分布,发现絮凝酵母颗粒聚集状态是影响其流变特性的重要因素。在此基础上,对自絮凝酵母连续发酵乙醇过程中发酵液流变行为进行了四批次时程跟踪检测。实验结果表明：发酵液的表观粘度和稠度系数与细胞生长有一定相关性；用流动特性指数表征非牛顿型流体的显著程度有如下规律：在发酵初期生物量浓度较低时,体系流变特性受发酵液影响呈牛顿型流体特性,随着絮凝酵母细胞的大量生长,体系流变特性开始由细胞浓度决定,颗粒间的相互作用令流动特性指数向非牛顿型流体转变。整个发酵过程中,细胞代谢产物的逐渐分泌对体系流变特性的影响可忽略,研究结果对预测生物反应器的传热传质性能具有重要意义。最后,利用空气-发酵液两相流体系为研究对象,对气升式生物反应器内的液相循环速度和气含率进行了实验研究。并将欧拉连续介质模型应用于空气-发酵液两相流体系,构建了基于Mixture两相流模型和湍流封闭模型(RNGk-ε)的连续-分散相三维瞬态计算流体力学(CFD)模型,并将模拟结果与实验值进行了对比和验证,结果表明该模拟结果与实验数据吻合较好,验证了模型的准确性。在上述模型验证的基础上,对气升式内环流生物反应器内气、液两相流场进行了瞬态三维模型预测,这些结果将有助于建立自絮凝颗粒酵母在反应器中均匀悬浮的流体力学条件。更多还原

【Abstract】 Yeast flocs developed by the self-flocculation of yeast cells are significantly different from free yeast cells. Not only is their size much larger, but their configuration is not uniform. Moreover, they are susceptible to shearing force. These characteristics present a challenge for developing a suitable bioreactor for their immobilization and efficient ethanol production. The objectives of this project are to investigate the rheological property of the yeast flocs slurry, one of the prerequisites for bioreactor design and operation, and the hydrodynamics of the suspended-bed bioreactor (SBB) for the suspension of the yeast flocs.The rheological property of the simulation system with yeast flocs suspended in water was first studied, which exhibited the non-Newtonian fluid behavior and fitted with the power law index model. The model parameters were correlated with the concentration of the yeast flocs. Moreover, the size distribution of the yeast flocs was measured in situ using the focused beam reflectance measurement system, and it was found that the degree of the flocculation of the yeast flocs characterized by their average chord length was the major factor affecting the rheological behavior of the yeast flocs slurry.Furthermore, the rheological property of the real ethanol fermentation system with yeast flocs was investigated under batch fermentation conditions. The experimental results demonstrated that the growth of yeast flocs affected the apparent viscosity and consistency coefficient of the yeast flocs slurry. At the initial stage of the fermentation when the concentration of yeast flocs was low, the rheological property of the yeast flocs slurry exhibited the Newtonian fluid behavior, due to the contribution of the low viscosity fermentation broth. With the massive growth of the yeast flocs, the rheological property was shifted to the non-Newtonian fluid behavior due to the contribution of the yeast flocs.Finally, the hydrodynamics of the SBB was explored using air-fermentation broth biphase fluid as a model system, and the overall circulation velocity was predicted. Based on the 3-D two-phase fluid model and RNGk-εturbulence model, a 3-D computational fluid dynamics (CFD) model was established for the continue-discontinue phase and validated by the experimental data. The gas-liquid fluidic field within the SBB was further simulated using the 3-D CFD model, which will facilitate the identification of the hydrodynamic conditions for the suspension of the yeast flocs within the bioreactor as well as preventing the breaKage of the yeast flocs by the shearing force.更多还原