CFD Simulation Of Gas-Liquid Two-Phase Flow In Large Scale Fermentation Reactor With Side-Entry Impellers

The fermentation reaction plays an important role in the production of fuel ethanol. However, the current design of fermentation reactor mainly depend on past engineering experience. Because of the limit of many factors, this design method could not offer the best project. Computational Fluid Dynamics (CFD) is used to assist industrial design, and it can overcome deficiency of experience design methods. Moreover, it will contribute to technological innovation and theoretical development. Carbon dioxide is released during the fermentation process. Bubbles are generated in the fermentation system with different sizes. The distributions of these bubbles not only decide local composition and local flow patterns, but also affect the power input. The effects of bubbles are significant when the fermentation reactor is large. Thus, it is necessary to describe the bubbles generation and distribution in the mixing system.The CFD method was used to describe the mixing performance of the fermentation reactor which is equipped with side-entry impellers. The non-Newtonian viscosity was considered, and the introduction of gas was defined by heterogeneous reaction. The mono-size bubbles model and Population Balance Model (PBM) were used to describe bubbles in the bio-reactor. The PBM can include the birth and death of bubbles due to aggregation and breakage, which is found to be more suitable for describing the fermentation system.The results showed that the mixing effect was obvious by relays of side-entry impellers, but the liquid velocity is quite low in the centre of the tank bottom. Preventing the deposition of solid particles in the centre of the tank bottom is the key issues, which is needed to be considered in the design of fermentation reactor. The flow field at the upper tank was changed by production and escape of different size bubbles. These findings could provide useful guidance for the design of bio-reactor. The established model was used to analyze the flow field of the bio-reactor. Moreover, the PBM was used for different bio-reactors. The optimum installation of impellers was obtained by comparison of flow rate and turbulent value.