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微生物多糖黄原胶高粘度发酵的搅拌系统特性研究
Study on Characteristics of Mixing System in High Viscosity Fermentation of Microbial Polysaccharides Xanthan Gum
【作者】 李艳;
【导师】 詹晓北;
【作者基本信息】 江南大学 , 生物化工, 2008, 硕士
【摘要】 以高粘度为特征的微生物多糖是近年来利用现代工业生物技术开发的新型产品,在食品、石油、医药等工业中具有广阔应用前景。虽然我国已成为黄原胶的第三大生产国,但高品质和高性能微生物多糖的生产仍基本上被国外著名生产企业所垄断,主要原因是我国在高粘度发酵技术方面存在着差距:常规搅拌桨的传质和混合效率不能满足高粘度发酵的需要,气体分散效果不理想,生产过程的能耗占成本的比重较大。因此,迫切需要建立自主创新的支撑技术和装备来克服高粘度发酵过程中存在的关键问题。本课题选取并制作了不同直径的新型径流式和轴流式搅拌桨——翼型轴流桨以及抛物线圆盘桨进行组合,以微生物多糖黄原胶为研究介质,对研究生物反应器中的关键设备——新型高效搅拌桨组合进行系统的搅拌系统特性的研究。研究结果如下:首先,研究了微生物多糖黄原胶的流变特性,其流变模型满足幂律流体模型,表现出良好的剪切稀释性,为典型假塑性流体。同时,对与其表观粘度相关的稠度系数k、流动特性指数n以及剪切速率进行了系统研究,得出了在搅拌系统下求解微生物多糖表观粘度的方法,在微生物多糖与搅拌系统特性之间建立了相关性。其次,在水和黄原胶溶液中,对四种搅拌桨组合的搅拌性能进行了研究,比较了各搅拌桨组合的传氧、气体分散和功率消耗性能。结果表明:在非牛顿流体中,抛物线圆盘桨+翼型轴流桨+翼型轴流桨耗能最少(Np≈1.7);在输入相同功率下传氧性能和气体分散性能明显好于其他三组桨,相对于小直径平直叶圆盘桨+小直径平直叶圆盘桨+小直径平直叶圆盘桨,体积传氧系数和气含率分别提高了45%、35%。因此,在微生物多糖高粘度假塑性流体中,BTD-A315-A315组合桨较有优势。最后,对BTD-A315-A315组合桨,实验系统研究分析了影响高粘度非牛顿流体中传氧效果的四个因素,并以单位体积总功率消耗下的体积传氧系数(kLa/(P/V))为考察指标,进行方差分析,研究比较了各因素的影响程度。结果表明:黄源胶溶液浓度>搅拌转速>搅拌桨直径>通气量。并对其结果进行关联拟和,旨在为其工业放大奠定基础。
【Abstract】 The microbial polysaccharides characterized by high viscosity are new products using modern industrial biotechnology in recent years. They have broad application in the food, oil, medicine and other industries. Although China has become the third largest country producing Xanthan gum, the production of high quality and performance microbial polysaccharides has still basically been monopolized by the well-known foreign enterprises. The main reason is that in high viscosity fermentation technology, there is a gap between China and foreign countries: the mass transfer and mixing efficiency of conventional impeller can not meet the needs of high-viscosity fermentation, gas dispersed is not effective, and the energy consumption is huge. Therefore, there is an urgent need to establish the independent innovation technology and equipment to overcome the key issues happened in the high-viscosity fermentation process.Four impeller combinations of new radial flow type impeller and axial flow type impeller, namely Rushton Turbine, Asymmetric Blade Impeller and A315 have been tested in a laboratory bioreactor. The liquid phase physical-chemical properties have been varied using Xanthan gum solutions in different concentration and water. There are some results which are as followed:First of all, the rheological properties of microbiology polysaccharides Xanthan gum have been studied, and the result showed that it was typical pseudoplastic fluid having good performance of the shear diluted. Meanwhile, the flow-behavior index n, fluid-consistency index k and shear stress, which associated with the apparent viscosity, have been tested to get the microbial polysaccharides apparent viscosity in the mixing system.Secondly, an experimental investigation was performed of four impeller combinations in water and Xanthan gum solution, the characteristics of oxygen transfer, fractional gas hold-up and power dissipation were studied. It has been observed that the impeller combination of MBTD-MA315-MA315 used the lowest power (Np≈1.7) and gave highest values of gas-liquid mass transfer coefficient and fractional gas hold-up, which were 45% and 35% higher than the impeller combination of DT-DT-DT, in the non-Newtonian fluid. Therefore, the impeller combination of BTD-A315-A315 has high effective in the non-Newtonian fluid.The last but not least, reached and analysis four factors which impact the oxygen transfer effect in non-Newtonian fluid and carried on the variance analysis to compare the impact of various factors using volumetric oxygen mass transfer coefficient per volumetric power. Correlations have been developed for the prediction of the mass transfer coefficient for the above media. It offers the gist to magnify the impeller combination.
【Key words】 New impeller combination; Non-Newtonian fluid; Mass transfer coefficient; Mixing; Xanthan gum;