CFD stimulation of gluconic acid production in a stirred gas-liquid fermenter

Designing large-scale stirred bioreactors with performance closely matching the one achieved in lab-scale fermenters presents continuous challenge. In this contribution, dynamic modelling of the aerobic biocatalytic conversion process in viscous batch stirred tank reactor is developed. Its operation is illustrated by simulation of the interaction of fluid flow, mass transfer and reaction relevant to gluconic acid production by a strictly aerophilic Aspergiluc niger based on a “twofluid” model. As a result of this simulation, the velocity fields, the local substrate, dissolved oxygen, product and biomass concentration profiles were obtained. Constant bubble size and global gas-liquid mass transfer were assumed. The algorithm employed could be used for fast evaluation procedures regarding predictions and feedback control of aerobic bioreactor performance

CFD modelling of two-phase stirred bioreaction systems by segregated solution of the Euler–Euler model

An advanced study of a bioreactor system involving a Navier–Stokes based model has been accomplished. The model allows a more realistic impeller induced flow image to be combined with the Monod bioreaction kinetics reported previously. The time-course of gluconic acid production by Aspergillus niger strain is simulated at kinetic conditions proposed in the literature. The simulation is based on (1) a stepwise solution strategy resolving first the fluid flow field, further imposing oxygen mass transfer and bioreaction with subsequent analysis of flow interactions, and (2) a segregated solution of the model replacing the multiple iterations per grid cell with single iterations. The numerical results are compared with experimental data for the bioreaction dynamics and show satisfactory agreement. The model is used for assessment of the viscosity effect upon the bioreactor performance. A 10-fold viscosity rise results in 2-fold decrease of KLa and 25% decrease of the specific gluconic acid production rate. The model allows better understanding of the mechanism of the important bioprocess

Application of CFD in gas-liquid bioreactor analysis

Ce travail, dans sa progression méthodologique, vise la validation et la mise en oeuvre de la contribution que peut apporter la dynamique des fluides, théorique et surtout numérique, aux procédés de fermentation en cuve agitée. Son apport dans d’autres domaines où coexistent écoulements et transformations de matières ne cessent de susciter de plus en plus d’intérêt. La description fine de l’évolution du contenu d’un réacteur propose en fin de compte le scénario à venir lors de l’exploitation industrielle de l’opération étudiée. Ce mémoire présente donc une approche de ce type pour l’activité dans un réacteur lors d’une fermentation. Le mélange multiphasique en écoulement avec ses échanges interphasiques et particulièrement ici l’aspect réactif de celui-ci font l’objet d’une intégration progressive conduisant à un modèle de «fermentation numérique». Une analyse statistique du volume de données recueillies lors du déroulement d’une telle opération, permet d’en évaluer plus d’une caractéristique, et d’en tirer des informations utiles tant pour son élaboration lors de l’étude du procédé lui même que pour l’accompagnement de l’exploitation productive de celui-ci. L’étude et la compréhension des interactions et des cinétiques de transfert en milieu hétérogène permettront de maîtriser aussi le comportement des molécules aux interfaces et d’en tirer profit pour la mise au point de bio-séparations des produits obtenus. La souplesse de l’outil informatique initie la compétition de cette méthode d’évaluation par simulation d’un procédé, avec la réalité elle-même du procédé pratiqué jusqu’à présent à travers le modèle de laboratoire ou le modèle-pilote largement plus coûteux sur plus d’un plan. Les méthodes numériques adaptées à ce type de problèmes se sont bien développées ces dernières décennies et le matériel supportant le calcul lui-même ne cesse de se mettre à la portée des modestes moyens d’acquisition. La réaction biologique, à l’instar de la réaction chimique aura donc la possibilité de tirer quelques profits de ce moyen d’étude non intrusif et sans dommages économiques ou même écologiques.This work, in its methodological progression, aims at validating and implementing the fluid dynamics contribution, both theoretical and numerical, to the fermentation processes in agitated vessels. Indeed, its contribution in other engineering fields, where material flows and transformations coexist, could arouse additional deep interest. The detailed description of the evolution of the reactor contents in the final analysis proposes the pattern that is realized during the industrial exploitation of the studied operation. The thesis thus presents an approach to a reactor performance during fermentation. Combining multiphase flow with its, inter-phase mass transfer kinetics and particularly with the reactive aspect of the latter is the subject of progressive integration leading to a model of "numerical fermentation". A statistical analysis over the bulk data collected in the course of such an operation allow to evaluate more than one characteristic, and to draw much useful information not only for the study in the stage of development of the process but also for the support of its productive exploitation. The flexibility of the data-processing tool thus developed initiates competition between this evaluation method for process simulation and the reality itself as far as such processes practised so far through laboratory models or pilot models are largely more expensive at more than one plane. The numerical methods adapted to such type of problems developed well in the last decade and the material that supports the calculation itself do not exclude employment of some modest means of acquisition. Not unlike chemical reaction engineering, biological reaction engineering would thus have the possibility to benefit of this nonintrusive technique of study excluding any economic or even ecological damage. ----------------------

THE CFD APPROACH FOR SHEAR ANALYSIS OF MIXING REACTOR: VERIFICATION AND EXAMPLES OF USE

The paper presents experimental evidence for the potentials of CFD methodology in revealing external flow and inner flow shear deformation rates in stirred tanks. Two basic issues are considered: could CFD produce valid solutions for shear rates in mixing vessels, and could practical shear rate differences relevant to specific impeller designs be reproduced by CFD. In a first part, the shear rate distribution in the flow fields of two basic impellers comprising flat and fluid-foil blades have been simulated and compared with measurement data obtained by electro-diffusion. Based on these and other reference data, coincidence of measured and simulation shear rates has been found. In a second part, a CFD shear deformation analysis procedure has been introduced and validated and shear rate functions relevant to two applications in viscous flow have been generated. The procedure is illustrated by practical examples showing its versatility for prompt characterisation of impeller shear deformation performance. Straight forward impeller selection by using CFD is implied