Computational fluid dynamic modelling of a pilot-scale bioreactor
Kemian tekniikan korkeakoulu | Master's thesis
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Process Systems Engineering
Master's Programme in Chemical Technology
AbstractThe master's thesis focuses on the investigation of mixing time of a fermentation process using lactic acid bacteria (LAB). Due to the microorganism growth, acid is produced in the process and base is added frequently into the bioreactor for pH control. In this case, gradients of substrate, product and pH might exist in the system. The gradients can result in negative effect on the microorganism growth and process productivity. Thus, it is important to investigate the mixing performance of the bioreactor. Computational fluid dynamic (CFD) modelling is applied in this thesis to predict fluid flow behavior and mixing time of the pilot-scale bioreactor. The lactic acid bacteria (LAB) fermentation is anaerobic and a one phase CFD model is built based on the pilot-scale bioreactor geometry. The model mesh elements, mesh quality and type and ANSYS CFX settings were studied to get an accurate and reliable CFD model. Pilot-scale mixing experiments were carried out in order to validate the CFD model. Six pH sensors were mounted on a rack measuring pH at different locations in the bioreactor. Base was added from the top and bottom of the bioreactor at 200rpm and 100rpm impeller speed. pH dynamic data with 1s sampling interval were collected. CFD simulations were performed at the same conditions as in the pilot experiments. The concentration of tracer at each time step and the calculated mixing time were compared with the pilot experiments for validation. In the final part of the project, the CFD model is combined a with LAB kinetic model to predict the kinetics of LAB growth and substrate consumption in the bioreactor. The combined CFD and kinetic model was compared at 200rpm, 100rpm and without the fluid flow fields.
Thesis advisorSpann, Robert
computational fluid dynamics, lactic acid bacteria fermentation, mixing time, pH gradient, pilot-scale bioreactor