Étude dynamique et effet du changement d'échelle pour plusieurs systèmes particulaires en mélangeur Turbula® : application à un mélange destiné à la fabrication de plaques composites

L'optimisation d'une opération de mélange de poudre repose essentiellement sur un travail expérimental à l'échelle du laboratoire qui doit pouvoir être transposer aux mélangeurs de plus grandes tailles. Définir des lois d'extrapolation et améliorer notre connaissance de la dynamique du mélange est donc nécessaire. Dans ces travaux, la dynamique de mélange au sein des mélangeurs Turbula® a été étudiée en s'appuyant sur l'analyse des cinétiques de mélange et des fonctions d'autocorrélation pour plusieurs systèmes particulaires. Selon les vitesses de rotation de l'axe moteur, 3 régimes d'écoulement ont été définis et les principaux mécanismes de mélange et de ségrégation apparaissant pour chacun de ces régimes ont été identifiés en lien avec les propriétés d'écoulement des produits. Dans un deuxième temps, les qualités de mélange obtenues dans différentes tailles de mélangeurs ont été comparées sur la base du principe des similitudes afin de mettre en évidence les facteurs ayant une influence lors du passage d'une taille de mélangeur à une autre. Enfin dans le cadre d'une application industrielle, une méthodologie s'appuyant sur l'intensité de ségrégation et l'autocorrélation spatiale, a été développée pour identifier des défauts d'homogénéité au sein de plaques bipolaires composites. ABSTRACT : The optimization of a powder mixing step typically involves an experimental work at lab scale in order to be transposed to larger mixers. Defining scale-up laws and improving our knowledge of the mixing dynamics remains some of the mains industrial issues of this century. In this work, the mixing dynamics of several particulate systems has been studied in Turbula mixers thanks to the analysis of mixing kinetics and autocorrelation functions. According to the engine speed, three flow regimes have been defined. The corresponding main mixing and segregation mechanisms at play for each of these regimes have been identified in relation with the flow properties of the products. In a second phase, the qualities of the mixtures obtained in the different mixer sizes have been compared on the basis of the principle of similarities in order to shed light the factors which influencing scale-up. Finally, as part of an industrial application, a methodology has been developed using the concept of intensity of segregation and the spatial autocorrelation tools to identify heterogeneities in bipolar plates made of composite materials

Unravelling the consequences of ultra-fine milling on physical and chemical characteristics of flax fibres

In recent years, lignocellulosic biomass has been increasingly used in various applications, often replacing petro-sourced materials. While for many of these applications the plant materials require coarse milling, some new applications for green chemistry, bio-energy and bio-packaging necessitate comminution to obtain very finely calibrated particles (below 200 m in size). This milling step is not inconsequential for lignocellulosic materials and can influence the physical (size, shape) and chemical characteristics (cellulose crystallinity, composition) of the powder. However, these different effects are still poorly understood. In this work, we study and elucidate the impact of intense and ultra-fine milling on the physico-chemical properties of plant fibres. Flax was chosen for this study because of its well-described hierarchical structure and biochemical composition in literature, making it a model material. Our main results evidence a strong impact of 0 to 23hrs ball milling on flax fibre morphology, especially on fibre aspect ratio falling from 20 to 5 but also on cell wall ultrastructure and composition. Cellulose content and crystallinity significantly decrease with milling time, leading to higher water sorption and lower thermal stability.The authors also thank the French national research Network ‘GDR 3710 INRA/ CNRS SYMBIOSE – Synthons et matériaux biosourcés’, for its financial suppor

Dry fractionation of plant material powders using an electrostatic corona separator: a model study

In a dry bioreffinery scheme, the separation of plant materials into fractions of interest compound is a crucial step. In recent years, electrostatic separation of agri-resources has sparked a growing interest for its potential but optimization efforts remain to be done especially in case of fine powders. The present work is an experimental investigation of factors, which influence the separation process of plant biomass powders in a custom built corona electrostatic separator with view to optimization. Three particle size classes of cork, semolina and wood powders have been characterized in term of charge decay curves and their behavior on the device have been studied. Separation tests of a blend constituted of 1g of wood powder and 1g of semolina have also been conducted with very promising results. Please click Additional Files below to see the full abstract

Au cœur de la raffinerie sèche du végétal : description mécanistique des procédés et conception de poudres fonctionnalisées pour la chimie, l’énergie et les matériaux

Au coeur de la raffinerie sèche du végétal : description mécanistique des procédés et conception de poudres fonctionnalisées pour la chimie, l'énergie et les matériaux

Dynamic study and impact of scale-up for different particulate system in Turbula mixer : application to a mixture use for composite plate manufacturing

L'optimisation d'une opération de mélange de poudre repose essentiellement sur un travail expérimental à l'échelle du laboratoire qui doit pouvoir être transposer aux mélangeurs de plus grandes tailles. Définir des lois d'extrapolation et améliorer notre connaissance de la dynamique du mélange est donc nécessaire. Dans ces travaux, la dynamique de mélange au sein des mélangeurs Turbula® a été étudiée en s'appuyant sur l'analyse des cinétiques de mélange et des fonctions d'autocorrélation pour plusieurs systèmes particulaires. Selon les vitesses de rotation de l'axe moteur, 3 régimes d'écoulement ont été définis et les principaux mécanismes de mélange et de ségrégation apparaissant pour chacun de ces régimes ont été identifiés en lien avec les propriétés d'écoulement des produits. Dans un deuxième temps, les qualités de mélange obtenues dans différentes tailles de mélangeurs ont été comparées sur la base du principe des similitudes afin de mettre en évidence les facteurs ayant une influence lors du passage d'une taille de mélangeur à une autre. Enfin dans le cadre d'une application industrielle, une méthodologie s'appuyant sur l'intensité de ségrégation et l'autocorrélation spatiale, a été développée pour identifier des défauts d'homogénéité au sein de plaques bipolaires compositesThe optimization of a powder mixing step typically involves an experimental work at lab scale in order to be transposed to larger mixers. Defining scale-up laws and improving our knowledge of the mixing dynamics remains some of the mains industrial issues of this century. In this work, the mixing dynamics of several particulate systems has been studied in Turbula mixers thanks to the analysis of mixing kinetics and autocorrelation functions. According to the engine speed, three flow regimes have been defined. The corresponding main mixing and segregation mechanisms at play for each of these regimes have been identified in relation with the flow properties of the products. In a second phase, the qualities of the mixtures obtained in the different mixer sizes have been compared on the basis of the principle of similarities in order to shed light the factors which influencing scale-up. Finally, as part of an industrial application, a methodology has been developed using the concept of intensity of segregation and the spatial autocorrelation tools to identify heterogeneities in bipolar plates made of composite material

Effect of Mechanical Stress from the Grinding Device on the Biomass Powder Properties and Energy Consumption

The use of biomass as a source of energy has increased in recent years. Whatever the application, the potential of the raw materials, such as cereal or wood by-products (CBP/WBP), needs to be enhanced by grinding processes to ensure the best conversion into energy vectors. However, the energy consumption by the grinding step could vary significantly according to the mechanical properties of the biomass, the process parameters and the targeted size. In this work, we study the influence of the mechanical stress generated by the grinder on the properties of the ground powder (size distribution, particle shape), and on the required energy. The materials were ground in a laboratory ball mill in impact and attrition modes with the same input of energy. Results showed that grinding kinetics were faster with impact than attrition, initial particle sizes being reduced by 98% in 10 and 40 minutes, respectively. An agglomeration index was defined as the ratio between specific surface areas determined with and without ultrasonic treatment. Powder obtained by impact displayed an agglomeration index of 0.5 (CBP) and 0.4 (WBP) after 60 minutes of grinding whereas in attrition this index was lower around 0.4 and 0.2 after 200 minutes of grinding. Moreover, in terms of energy, impact mode seemed to be more energy efficient than attrition

Scale-up in Turbula (R) mixers based on the principle of similarities

International audienceMany processes from a wide range of industries use powders as raw materials. In most of them, mixing of dry particles is a critical step. However, the complexity of granular materials leads to difficulties in predicting behavior of powders inside a blender. Cost and amount of raw materials needed to achieve these studies imply that such work is often performed at the laboratory scale. The main challenge then lies in the extrapolation of results from lab to pilot or industrial scale with minimum testing in order to optimize costs. Defining reliable scale-up laws for powder mixers remains one of the main industrial issues. The work presented here concerns the scaling-up of Turbula (R) mixers that are commonly used both in industry and research. Mixtures obtained in different mixer sizes have been compared on the basis of kinematic and dynamic similarities and discussed according to the different flow regimes involved. The dynamic similarities appear to lead to mixture qualities at different scales closer to each other than those obtained on the basis of kinematic similarities probably because of similar flow regimes. However, some other parameters must be taken into consideration, such as the free surface of powder related to the filling ratio

Influence of biomass dry fractionation on the processability and quality of 3D printable biomaterials from rice husk

Influence of biomass dry fractionation on the processability and quality of 3D printable biomaterials from rice husk . Exploring Lignocellulosic Biomass - ELB 201

Innovation et tradition : le point de vue des PME françaises de la filière blé dur

International audienceThis work investigates the potential of innovations from recent research to boost the competitiveness of French SMEs in the durum wheat sector. Results reveal the importance for SME to innovate without losing the traditional image of their products. High ratings for training suggest the need for concrete actions such as tailored training courses, an online portal, a traditional food-oriented magazine, and a joint technology demonstration platform.Ce travail vise à évaluer le potentiel des innovations issues de la recherche pour relancer la croissance des PME françaises de la filière blé dur. Les résultats mettent en évidence le double enjeu des PME de ce secteur pour rester compétitif : parvenir à innover en préservant le caractère traditionnel de leurs produits et leur savoir-faire. Ils montrent également l’importance d’actions concrètes telles des formations, des journaux spécialisés ou des plateformes technologiques de démonstration