Les techniques de dépoussiérage les plus efficaces et largement utilisées pour séparer des particules ultrafines d’un fluide porteur sont les médias fibreux. Le principal problème est le colmatage du filtre qui induit une augmentation de la perte de charge dans le temps et nécessite donc un nettoyage régulier des médias (ou son remplacement). La séparation des particules ultrafines par voie liquide au moyen d’une colonne à bulles a été envisagée. L’influence des différentes conditions opératoires telles que la hauteur du liquide de piégeage, le débit de filtration, la taille des bulles et la présence d’un garnissage, sur la collecte des particules a été étudiée. Malgré des rendements de collecte inférieurs à ceux des filtres à fibres, les résultats expérimentaux montrent que les colonnes à bulles présentent des performances d’autant plus importantes que le niveau du liquide est élevé et que les orifices de bullage sont petits. Par ailleurs, si l’étude de l’influence de la vitesse de gaz à l’orifice sur l’efficacité de collecte des nanoparticules ne montre pas une tendance bien définie, la présence d’un garnissage dans le liquide de collecte permet d’augmenter significativement le temps de séjour des bulles dans la colonne et donc l’efficacité de collecte / The most effective and widely used dust separation techniques to separate ultrafine particles of a carrier fluid are fibrous media. The main problem is the clogging of the filter that induces a pressure drop increase over time and thus requires a regular cleaning of the media (or its replacement). In this context, the idea is to test bubble columns, which operate at a constant pressure drop, as an alternative to fibrous filters. This study proposes to investigate the influence of different operating conditions such as the liquid level, the air flow rate, the bubble size and the presence of beads, on the collection of ultrafine particles. Despite collection efficiencies lower than those of fibrous filters, experimental results show that bubble columns present high collection efficiency when the liquid level is high and bubbling orifices have low diameters. Besides, if gas velocity does not show an important influence on the collection e_ciency, the presence of beads in the liquid increases the residence time of the bubbles in the column and thus the collection efficiency

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Computational fluid dynamics (CFD) modeling was used to predict the hydrodynamics of a column reactor. Bubble columns have applications across many engineering disciplines and improved modeling techniques help to increase the accuracy of numerical predictions. An Eulerian-Eulerian multi-fluid model was used to simulate fluidization and to capture the complex physics associated therewith. The commercial code ANSYS Fluent was used to study two-dimensional gas-liquid bubble columns. A comprehensive parameter study, including a detailed investigation of grid resolution was performed. Specific attention was paid to the bubble diameter, as it was shown to be related to cell size have significant effects on the characteristics of the flow. The parameters used to compare the two-dimensional (2D) cases to experimental results of Rampure, et. al. were then applied to a three-dimensional (3D) geometry. It was demonstrated that the increase in accuracy from 2D to 3D is negligible compared to the increase in CPU required to simulate the entire 3D domain. Additionally, the reaction chamber of a microbial fuel cell (MFC) was modeled and a preliminary parameter study investigating inlet velocity, temperature, and acetate concentration was conducted. MFCs are used in wastewater treatment and have the potential to treat water while simultaneously harvesting electricity. The spiral spacer and chemical reactions were modeled in a 3D geometry, and it was determined that inlet velocity was the most influential parameter that was simulated. There were also significant differences between the 2D and 3D geometries used to predict the MFC hydrodynamics. / Master of Science

Bubbly flows can be found in many applications in chemical, biological and power engineering. Reliable simulation tools of such flows that allow the design of new processes and optimization of existing one are therefore highly desirable. CFD-simulations applying the multi-fluid approach are very promising to provide such a design tool for complete facilities. In the multi-fluid approach, however, closure models have to be formulated to model the interaction between the continuous and dispersed phase. Due to the complex nature of bubbly flows, different phenomena have to be taken into account and for every phenomenon different closure models exist. Therefore, reliable predictions of unknown bubbly flows are not yet possible with the multi-fluid approach. A strategy to overcome this problem is to define a baseline model in which the closure models including the model constants are fixed so that the limitations of the modeling can be evaluated by validating it on different experiments. Afterwards, the shortcomings are identified so that the baseline model can be stepwise improved without losing the validity for the already validated cases. This development of a baseline model is done in the present work by validating the baseline model developed at the Helmholtz-Zentrum Dresden-Rossendorf mainly basing on experimental data for bubbly pipe flows to bubble columns, bubble plumes and airlift reactors that are relevant in chemical and biological engineering applications. In the present work, a large variety of such setups is used for validation. The buoyancy driven bubbly flows showed thereby a transient behavior on the scale of the facility. Since such large scales are characterized by the geometry of the facility, turbulence models cannot describe them. Therefore, the transient simulation of bubbly flows with two equation models based on the unsteady Reynolds-averaged Navier–Stokes equations is investigated. In combination with the before mentioned baseline model these transient simulations can reproduce many experimental setups without fitting any model. Nevertheless, shortcomings are identified that need to be further investigated to improve the baseline model. For a validation of models, experiments that describe as far as possible all relevant phenomena of bubbly flows are needed. Since such data are rare in the literature, CFD-grade experiments in an airlift reactor were conducted in the present work. Concepts to measure the bubble size distribution and liquid velocities are developed for this purpose. In particular, the liquid velocity measurements are difficult; a sampling bias that was not yet described in the literature is identified. To overcome this error, a hold processor is developed. The closure models are usually formulated based on single bubble experiments in simplified conditions. In particular, the lift force was not yet measured in low Morton number systems under turbulent conditions. A new experimental method is developed in the present work to determine the lift force coefficient in such flow conditions without the aid of moving parts so that the lift force can be measured in any chemical system easily.

O objetivo deste trabalho foi estudar a produção do antitumoral retamicina por células imobilizadas de Streptomyces olindensis ICB20 em biorreatores. A imobilização das células foi conseguida após uma etapa inicial de cultivo em erlenmeyers (reativação e pré-imobilização) e posterior envolvimento em gel, utilizando-se alginato de cálcio 3%; as esferas produzidas tinham diâmetro médio de 3,0 ± 0,2 mm. Foram utilizados neste trabalho os biorreatores tipo cesta (2,4 L de volume útil) e coluna de bolhas (1,6 L de volume útil), efetuando-se cultivos em batelada simples, bateladas repetidas e contínuos, visando-se uma comparação dos diferentes sistemas empregados. Também foram realizados alguns cultivos com células livres, a fim de efetuar uma comparação com os sistemas com células imobilizadas nos diferentes biorreatores. Os ensaios consistiram em empregar diferentes condições de agitação (300 e 500 rpm) e aeração (0,4 e 1 vvm) para o biorreator cesta em sistema com células imobilizadas, assim como diferentes vazões de aeração no biorreator coluna de bolhas (1, 2 e 3 vvm). Os cultivos em bateladas repetidas e contínuos foram operados a partir das melhores condições obtidas nos cultivos descontínuos. Foram aplicadas nos sistemas contínuos com células imobilizadas, as vazões específicas de alimentação de 0,05 e 0,2 h -1 no biorreator cesta e vazões de 0,015 a 0,05 h -1 no biorreator coluna de bolhas. A comparação entre os sistemas com células livres e imobilizadas mostrou que as limitações difusionais afetaram significativamente as cinéticas dos ensaios com células imobilizadas, considerando-se apenas uma batelada. A operação do biorreator cesta em sistema de bateladas repetidas apresentou os maiores valores de produção da retamicina (em torno de 1,5 a 1,7 UA), porém sua operação foi possível por apenas três bateladas. O sistema contínuo operado com vazão específica de alimentação de 0,03 h-1, com células imobilizadas no biorreator coluna de bolhas, mostrou ser o mais adequado dentre todos os ensaios realizados com células imobilizadas, apresentando estabilidade na produção, em torno de 0,8 UA, durante 96 horas de alimentação (cerca de três tempos de residência). / The purpose of this study was to investigate the production of the antitumor antibiotic retamycin by immobilized cells of Streptomyces. olindensis ICB20 in bioreactors. Cells were immobilized by entrapment in Ca-alginate gel (3%) after being grown in Erlenmeyers (reactivation and pre-immobilization cultures). The average diameter of the Ca-alginate beads was 3.0 ± 0.2 mm. Aiming to compare different cell systems, immobilized cell cultures were carried out in a 2.4L working volume basket-type stirred tank reactor (BSTR) and a 1.6 L working volume bubble column reactor (BCR) in batch, repeated-batch and continuous modes. Free cell suspension cultures were also performed and the results obtained compared to those in immobilized cell systems. Different agitation rates (300 and 500 rpm) and air flow rates (0.4 and 1.0 v.v.m.) were employed in the BSTR immobilized cell experiments.The BCR cultures were conducted at 1.0, 2.0 and 3.0 v.v.m. The optimal operating conditions for the batch mode were used in the repeated-batch and continuous cultures. Immobilized cells were grown in continuous mode at feed dilution rates of 0.05 and 0.2 h-1 in the BSTR and at 0.015 and 0.05 h-1 in the BCR. The comparative evaluation of the batch cultures with free and immobilized cells showed that diffusion limitations had affected the kinetics of cell growth and retamycin production in the immobilized cell systems. The highest average values of retamycin content (from 1.5 to 1.7 AU) were achieved in repeated batch cultures conducted in the basket-type reactor (BSTR) in spite of a limited number of batches (3 batches). Of all the systems, the continuous cell immobilized culture carried out in the BCR at a dilution rate of 0.03 h-1 proved to be the most adequate for retamycin production as retamycin levels remained stable (around 0.8 AU) over 96 hours (about 3 residence times).

L(+)-Lactic acid is a commonly occurring organic acid, which is valuable due to its wide use in food and food-related industries, and its potential for the production of biodegradable and biocompatible polylactate polymers. The aim of this study was to optimize and scale-up a biotechnological process of L(+)-lactic acid production by suspended cells of R. arrhizus DAR 36017 with waste potato starch as the substrate. Commonly used inorganic and organic nitrogen sources, including ammonium sulphate, ammonium nitrate, urea, yeast extract and peptone, were assessed in conjunction with various ratios of carbon to nitrogen (C:N). Fermentation media with a low C:N ratio enhanced the production of lactic acid, biomass and ethanol, while a high C:N ratio led to production of more fumaric acid as a by-product. The use of organic nitrogen sources (yeast extract, peptone and urea) resulted in a significant reduction of lactic acid yields by 15% - 34% with a decrease of C:N from 168 to 28. The use of inorganic nitrogen sources (ammonium nitrate and ammonium sulphate) led to a high lactic acid yield of 84% - 91% at a C:N below 168. Therefore, ammonium nitrate and ammonium sulphate were considered to be better nitrogen sources for lactic acid production. Small pellets are the favoured morphological form for many fermentation processes by filamentous fungi. However, to control filamentous Rhizopus sp in the pellet form in a submerged fermentation system is difficult due to its filamentous characteristics. An acidadapted preculture technique was developed to induce the formation of the pellet form in bioreactors. Using the acid-adapted precultures, the fungal biomass can be controlled in small dispersed pellets as a dominant morphological form. With these small pellets, a lactic acid yield of 86-89%, corresponding to a concentration of 86-89g/L, was obtained in a laboratory scale process using a stirred tank reactor (STR) and a bubble column reactor (BCR). A batch bioprocess for lactic acid production was successfully scaled-up from shake flasks to laboratory scale bioreactors. Results from a simulated scale-up process revealed that the concentration and productivity of lactic acid decreased with the increase of the scale-up steps because of increased pellet size. This suggested that a one-step scale-up process using the acid-adapted preculture may be feasible in an industrial-scale bioreactor system. A comprehensive investigation of the impact of cultivation parameters on the morphology of R. arrhizus and lactic acid production was carried out in the BCR. The results showed that the fungal morphology was significantly influenced by carbon sources, pH, starch concentrations, sparger designs and aeration rates. The favoured morphology for lactic acid production was freely dispersed small pellets, which could be retained as a dominant morphology under operation conditions at pH 5.0 – 6.0, starch concentrations of 60 – 120 g/L and aeration rates of 0.2 – 0.8 vvm, using a sintered stainless steel disc sparger. The optimal cultivation conditions at pH 6.0 and aeration rate of 0.4 vvm resulted in the formation of the freely dispersed small pellets and production of 103.8 g/L lactic acid, with a yield of 87%, from 120 g/L liquefied potato starch in 48 h. This study shows a technically feasible and economically promising process for the production of lactic acid from waste potato starch. The use of waste potato starch instead of pure glucose or starch as substrate can significantly reduce the production cost, making this technology environmentally and economically attractive. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1339122 / Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2008

Ce travail est une investigation expérimentale de l’hydrodynamique, du transfert massique et du mélange induit par un panache de bulles dans des milieux de différentes viscosités. Dans l’industrie on est souvent confronté à des problèmes de transfert et de mélange d’une phase liquide et d’une phase gazeuse afin de provoquer des réactions chimiques ou biochimiques. La plupart du temps on utilise des colonnes à bulles, simple à mettre en œuvre, pour ce type de procédé. Mais il existe d’autres situations adaptées aux très grands volumes comme par exemple les bassins d’aération de traitement des eaux ou les méthaniseurs. Dans ce cas de figure, la répartition des injecteurs de gaz doit être adaptée aux dimensions du bassin et contribuer au mélange du liquide. Ceci est autant plus vrai pour le bioréacteur de méthanisation où l’état du liquide change en continu pendant la fermentation. Cependant, il y a un manque d'informations concernant l'hydrodynamique induit par l'injection de gaz en milieu visqueux. Afin de mieux comprendre l'écoulement, le transfert massique et finalement le mélange dans ces situations, il a été décidé d’étudier le cas d'un panache de bulles, généré par un seul injecteur dans des liquides de différentes viscosités. Pour cela des expériences ont été effectuées dans deux types de colonne à bulles avec injection centrale. Un grand nombre de méthodes métrologiques tel que la PIV, l’ombroscopie, différents capteurs etc. ont été utilisés. Une attention particulière a été donnée aux fluctuations à différentes échelles induit par le mouvement oscillatoire du panache de bulles. / This work is an experimental investigation on hydrodynamics, mass transfer and mixing induced by a bubble plume. In chemical engineering, people are often confronted to mixing problems of liquid and gas to create chemical or biochemical reactions. Most of the time, bubble column of big height compared to its diameter are used for such kind or processes.But there are also situations using large scale reactors like tanks for methanization or wastewater treatment. In such configurations, spargers must be adapted to reactor dimensions and fluid properties. This particularly important for methanization reactors since fluid properties are changing continuously during the fermentation. In order to understand hydrodynamics, mass transfer and mixing it is easier to study one single bubble swarm, or so called bubble plume, first.Different experiments were figured out in two different columns types. First one is a pseudo two dimensional column (6cm * 35 cm * 130cm ) allowing the application of optical metrological methods. Hence, the gas phase was studied via shadowgraphy and the liquid phase via PIV. Plus, light intensity measurements after dye injection were done. Besides, pressure sensors and oxygen probes were used.In this way, one could study the oscillating behavior, the corresponding characteristic frequency, mass transfer and mixing time scales. In order to analyze fluid properties, a copolymer called Breox was used. Plus, two different spargers generating different bubble shapes and sizes were applied to estimate their impact. Additional experiments in a cylindrical bubble column were performed at the HDZR in Germany. The same fluids and the same spargers were used to compare results from both geometries. Due to the difficulty to apply optical methods, a Wire-Mesh system recently developed at the HZDR was used to follow the bubble plume movement. Finally, first CFD simulations showing encouraging results are presented at the end of the manuscript.