Frédéric Augier

Validation of a novel open-source work-flow for the simulation of packed-bed reactors

Abstract The simulation of flow and transport in packed-bed (catalytic and non-catalytic) reactors is of paramount importance in the chemical industry. Different tools have been developed in the last decades for generating particle packings, such as the Discrete Element Method (DEM), whereas Computational Fluid Dynamics (CFD) is generally employed for simulating fluid flow and scalar dispersion. This work-flow presents the main drawbacks of being computationally expensive, as most packing generation algorithms deal with non-convex objects, such as trilobes, with cumbersome strategies, and of making use of in-house or commercial codes, that are either difficult to access or costly. In this paper a novel open-source and easily accessible work-flow based on Blender , a rigid-body simulation tool developed for computer graphics applications, and OpenFOAM a very well-known CFD code, is presented. The approach, which presents the main advantage of being computationally fast, is validated by comparison with experimental data for global bulk porosity, particle orientation, local porosity and velocity distributions, and pressure drop. To our knowledge this is the very first application of Blender for the simulation of packed-bed reactors.

Advanced digital image analysis method dedicated to the characterization of the morphology of filamentous fungus

Filamentous fungi have a complex morphology that induces fermentation process development issues, as a consequence of viscosity increase and diffusion limitations. In order to better understand the relationship between viscosity changes and fungus morphology during fermentations of Trichoderma reesei, an accurate image analysis method has been developed to provide quantitative and representative data for morphological analysis. This method consisted of a new algorithm called FACE that allowed sharp images to be created at all positions, segmentation of fungus, and morphological analysis using skeleton and topological approaches. It was applied and validated by characterizing samples of an industrial strain of Trichoderma reesei that had or had not been exposed to an extreme shear stress. This method allowed many morphological characteristics to be identified, among which nine relevant criteria were extracted, regarding the impact of shear stress on the fungus and on the viscosity of the fermentation medium.

Effect of liquid viscosity on mixing times in bubble columns

Mixing is a key parameter in bioreactors studies as it can intensify mass and heat transfer and can affect biological reactions. In the present work, mixing times are investigated in a 42 L vessel with water and various polyethylene glycol and carboxymethyl cellulose solutions. To improve the physical description of dispersion induced by bubbles, the first step of our study was to characterize dispersion of tracers inside bubbly flows at various gas volume fractions for different liquid viscosities. A colorimetric technique is used in order to record mixing times corresponding to 95 or 80% of homogeneity. Bubble size is also measured at the same time by image processing. It clearly appears that the liquid viscosity impacts the mixing time value, the bubble size and the tracer propagation.

Modelling of a Simulated Moving Bed in case of non-ideal hydrodynamics

Abstract The one-dimensional hydrodynamic model proposed by Gomes et al. (2015) is coupled with adsorption and validated by comparing the concentration profiles of the one-dimensional model with those given by the CFD model of one adsorption column including obstacles as distribution network and beams. This one-dimensional model is capable of predicting the CFD results for different mass transfer rates, while the traditional dispersed plug flow (DPF) model is relevant for slow mass transfer rates only. The model proposed by Gomes et al. (2015) is capable of reproducing the adsorber Residence Time Distribution (RTD) while dissociating the selective zones from the non-selective ones. It is based on the CFD techniques developed by Liu and Tilton (2010) and Liu (2012) that transport the moments of the fluid age distribution and consequently calculate the degree of mixing (Danckwerts, 1958; Zwietering, 1959). Then, this new model is integrated in a cyclic solver in order to perform Simulated Moving Bed (SMB) studies. The new model provides a detailed hydrodynamic description, which appears to be mandatory especially when mass transfer exchanges are fast, without undergoing the prohibitive simulation times of CFD models.

Recovery of succinic acid in fermentation broth via reactive LL extraction: effect of chemical kinetics and solvent choice

In this paper, a study of kinetics effects on the reactive liquid-liquid extraction column is proposed. In a first part, design parameters of reactive liquid-liquid extraction column are derived from a method proposed by Mizzi (2016). In a second part, using a kinetic model, the performances of the column are studied with different configuration and design parameters. This study allows a comparison of the performances of the column in terms of conversion rate, recovery rate and purity. For the chosen examples, the kinetic limitation is very strong. So the unit operations of reactive liquid-liquid extraction with a high retention capacity will be privileged: a cascade of decanter mixers. In conclusion, this article shows that the choice of solvent and the parameters of the column as the solvent flowrate, the number of theoretical stage, liquid hold up or kinetics of the reaction have an important influence on the performances of the column and sometimes on the feasibility of the separation.