Anti-Infectives, Process Development, Sandoz GmbH, Novartis Technical Operations, Kundl, Austria.
Institute for Process and Particle Engineering, Graz University of Technology, Graz, Austria.
Biotechnol Bioeng. 2021 Aug;118(8):3058-3068. doi: 10.1002/bit.27815. Epub 2021 Jun 6.
Multiple impeller reactors are widely used due to their advanced gas utilization and an increased volumetric mass transfer coefficient. However, with the application of Rushton impellers, gas dispersion efficiency varies between the bottom and the upper impeller levels. The present study analyzes the individual flow regime, power input, and gas hold-up in each compartment of a reactor equipped with four Rushton impellers. The results indicate that the pre-dispersion of the air introduced by the bottom impeller (up to 80%) plays a key role in a better gas retention efficiency of the upper impellers (>300%) and leads to a shift of the cavity and flooding lines in the flow map (Fr- vs Fl-Number) of the upper impellers. A novel analysis of the bubble flow in the dispersed state via a two-phase LES-based CFD model reveals that a more homogenous distribution of air bubbles in the upper compartments leads to high compartment gas hold-up values, but fewer bubbles in the vicinity of the impellers. The measured and simulated data of this study indicate that the upper impellers' efficiency mostly depends on the flow regime of and the pre-dispersion by the bottom impeller rather than on the upper impellers' flow regimes. These results contribute to the understanding of essential mixing processes and scaling of aerated bioreactors.
多叶轮反应器由于其先进的气体利用和增加的体积传质系数而被广泛应用。然而，在使用 Rushton 叶轮时，气液分散效率在底部和上部叶轮之间存在差异。本研究分析了装有四个 Rushton 叶轮的反应器中每个隔室的单独流型、功率输入和气体持液量。结果表明，底部叶轮引入的空气的预分散（高达 80%）对上部叶轮（>300%）的更好的气体保留效率起着关键作用，并导致流型图（Fr-与 Fl-数）中上部叶轮的空腔和淹没线的转移。通过基于两相 LES 的 CFD 模型对分散状态下的气泡流进行的新分析表明，在较高的隔室中，空气泡更均匀的分布导致了更高的隔室气体持液量，但在叶轮附近的气泡数量较少。本研究的测量和模拟数据表明，上部叶轮的效率主要取决于底部叶轮的流型和预分散，而不是上部叶轮的流型。这些结果有助于理解充气生物反应器的基本混合过程和放大。
