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Micro-scale study of the first stage of cake formation for the microfiltration of model particle and yeast suspensions : In-situ and real-time experimental approach

Valencia Navarro, Alberto Jorge. Micro-scale study of the first stage of cake formation for the microfiltration of model particle and yeast suspensions : In-situ and real-time experimental approach. PhD, Dynamique des fluides, Institut National Polytechnique de Toulouse, 2020

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Abstract

Filtration is a widely used industrial process, which nature and purpose result in fouling and hence reduction of its efficiency with associated economic losses. This project aims to better understand the fouling through the microscale monitoring and analysis of the filtration process. For that, a new dead-end microfiltration apparatus is constructed and coupled with an imaging system to provide direct observation (DO) from the side. Particle deposition is characterized in-situ and in real time for four different suspensions: a cultivated yeast (Saccharomyces Cerevisiae) suspension and three suspensions of model particles in the same size range as the yeast cells (spherical particles, non-spherical particles and polydispersed particles in both size and shape). Model membranes are used to achieve fluid-particle separation, and different membrane geometries were created for studying the pore configuration effect on particle deposition and cake structure. Image processing is used to measure the observed cake height and to evaluate the concentration and particle velocity. This information is combined with the continuous pressure measurement and the qualitative description of the acquired images to provide a complete analysis of the microfiltration process. A mass balance is performed to estimate the porosity and the Kozeny coefficient (KK) along with complementary analysis using Darcy equation and the Carman-Kozeny formula. The system is validated for model conditions using the suspensions of spherical particles. The filtration performance for the different membrane geometries is similar. However, the initial cake structure is conditioned by the membrane geometry. This has an influence on pore blocking and further cake growth, which impacts on the pressure drop across the cake. Numerical simulations were used to investigate the initial behavior (pore blocking and hydraulic resistance) when the cake is forming and show good agreement with the experimental data. Monodispersed particle suspensions show a very similar behavior in terms of porosity and permeability regardless of the different particle shapes. However, for a higher specific surface KK coefficient decreases. For monodispersed particle suspensions, KK behaves linearly with the porosity. In the case of the cake formed by the polydispersed particles, an exponential evolution for KK coefficient is observed, which resembles more the yeast cake behavior. Additionally, when analyzing the porosity evolution of the four suspensions, the cake of polydispersed particles shows an intermediate behavior between the monodispersed cases and the yeast cells. This confirms the influence of polydispersity and explains partly the yeast cake behavior, the high specific resistance and low permeability. Yeast cake behavior is explained by the combined effect of cell polydispersity and the compressibility of the cake. Yeast cakes were the only to exhibit a compressible behavior, which was confirmed by a volume expansion after transmembrane pressure was removed. The analysis of this expansion results in a porosity after relaxation close to the estimate for polydispersed particles ~0.26. It remains to explain the nature of this compressibility. The experimental protocol is an accurate approach for the study of the filtration cake formation for different suspensions. The DO resolution was improved (~ 0.6 µm) allowing better imaging of particles in the microfiltration size range. Combining the velocity information with the pressure measurements makes it possible to characterize filtration processes where both pressure and flowrate are variables

Item Type:PhD Thesis
Uncontrolled Keywords:
Institution:Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
Laboratory name:
Research Director:
Schmitz, Philippe and Lafforgue, Christine
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Deposited On:03 Sep 2020 13:25

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