Computational fluid dynamics modelling of hydrodynamics, mixing and oxygen transfer in industrial bioreactors with Newtonian broths

Gisela Nadal-Rey,Dale D Mcclure,John M Kavanagh,Benny Cassells,Sjef Cornelissen,David F Fletcher,Krist V Gernaey

doi:10.1016/j.bej.2021.108265

Abstract

Industrial aerobic fermentation processes are performed in large-scale bioreactors (> 20 m3). Understanding the local values of the velocity field, the eddy dissipation rate and the gas volume fraction is of interest, as these parameters affect mixing and mass transfer and hence fermentation process performance and profitability. Despite the industrial and academic importance of these flow variables in large-scale bioreactors, there is scarce literature addressing it. This article provides a numerical comparison using Computational Fluid Dynamics (CFD) of different industrially relevant reactor types (bubble columns and stirred tanks with different impeller configurations) operated within a realistic range of industrial conditions (40 – 90 m3, 0.3 – 6 kW m-3, 0.5 – 1 vvm). Local flow variables and mixing times are evaluated for all cases studied. The collection of these data allows the prediction of the typical values of mixing time (10 – 206 s) and oxygen transfer rate (1 – 8 kg m-3 h-1) in industrial bioreactors, and serves as basis for the comparison between different reactor types.

Highlights

Industrial-scale fermentation processes are widely used to produce a diverse range of compounds with applications in the food, chemical and pharmaceutical industries [1]
The flow pattern and magnitude were similar with different volumes, differences in mixing time and oxygen transfer values were observed
The aims of this work were to use Computational Fluid Dynamics (CFD) modelling to quantify the performance of different large-scale bioreactor designs resembling typical industrial operational conditions, as despite its industrial sig nificance relatively little information about this is available in the open literature

Summary

Introduction

Industrial-scale fermentation processes are widely used to produce a diverse range of compounds with applications in the food, chemical and pharmaceutical industries [1]. Most industrial-scale aerobic bioreactors are typically either bubble columns or stirred tanks [1]. Bubble columns are simpler; air is introduced through a sparger at the base of the column and this provides both mixing and a source of oxygen. In addition to the sparger, stirred tanks have an agitator which provides mixing. Agitators are typically classified based on whether they pump the liquid axially or radially. Rushton turbines are a commonly used radial flow impeller design, while a range of axial flow impellers exist [3]. The internal structure of stirred tanks is more complex than bubble columns, as it is typically necessary to include baffles to prevent vortex formation [3]

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