Technologies plasmas appliquées aux traitements thermiques des déchets nucléaires.

Cette étude décrit plusieurs procédés chimiques à hautes températures développés au Commissariat à l’Energie Atomique et aux Energies Alternatives pour assurer le traitement de déchets issus de l’exploitation de la filière nucléaire. Ces procédés utilisent des technologies différentes de plasmas thermiques atmosphériques pour incinérer des familles de déchets organiques de formes et de compositions chimiques très variées. Dans chaque cas, un plasma d’oxygène à haute puissance est établi à partir d’une torche à plasma d’induction ou à partir d’une ou plusieurs torches à plasma d’arc électrique soufflé ou transféré garantissant une parfaite combustion de la fraction organique du déchet à traiter par le procédé

Production d hydrogène par cycles thermochimiques de dissociation de l eau couplés à une source d énergie solaire

This doctorate deals with a method for large scale production of hydrogen considered as the future energy vector replacing oil and gas in the transportation sector. Thermochemical cycles represent a promising pathway for the water-splitting into hydrogen and oxygen at medium temperature (500-2000C). The use of solar concentrated energy as heat supply allows the development of a sustainable and environmentally friendly process.After a first selection based on criteria, a list of 30 promising cycles was established. These cycles were analysed on an exergy point of view. Sulphates cycles and most of chlorine cycles were eliminated after thermodynamic study of reactions. The experimental study focused mainly on metal oxide cycles. The high temperature reduction (solar furnaces) and hydrolysis reactions were studied for non volatile and volatile oxide cycles. Reduced iron oxides (Fe3O4 and FeO) produced significant quantities of hydrogen in two or three steps.SnO2 and ZnO reduction was done and optimised to reduce the recombination of products, which was not the case for indium and gallium. Hydrogen production was better for SnO than for Sn, and it was rapid with indium.A process analysis was developed accounting for experimental results, which led to cycle energy efficiencies ranging from 26% to 42% after optimisation. A production of 250 kg.h-1 of H2 could be achieved with a solar tower like PS10 (55 MWth). The hydrogen production cost was estimated between 7.25 dollards/kg and 16 dollards/kg depending on the cycle and on the economic assumptions considered.Une méthode de production massive d hydrogène envisagé comme vecteur énergétique du futur se substituant au pétrole et au gaz dans les transports est étudié. Les cycles thermochimiques constituent une voie intéressante permettant une dissociation de l eau en hydrogène et oxygène à moyenne température (500-2000C). Avec l emploi d énergie solaire concentrée, le procédé est durable et respectueux de l environnement.A l issue d une analyse multicritères, une liste de 30 cycles a été établie. Ces cycles ont fait l objet d une analyse exergétique et d une étude thermodynamique détaillée qui ont conduit à l éviction des cycles sulfates et des cycles chlorures. L étude expérimentale s est focalisée sur des cycles oxydes . Les réactions de réduction à haute température (four solaire) et d hydrolyse ont été étudiées pour des cycles à oxydes non volatils et volatils . Les oxydes de fer réduits (Fe3O4 et FeO) ont permis une production significative d hydrogène en deux ou trois étapes. D autre part, la réduction de SnO2 et de ZnO a pu être effectuée et optimisée en limitant la recombinaison des produits, contrairement aux oxydes d indium et de gallium. Enfin, l étape de production d hydrogène est meilleure pour SnO que pour Sn et elle s avère très rapide pour l indium.L analyse procédé réalisée à l aide des résultats expérimentaux conduit après optimisation à des rendements de cycle thermochimique variant de 26% à 42%. Une production de 250 kg.h-1 d hydrogène est possible avec une tour solaire semblable à PS10 (55 MWth). Le coût de production de l hydrogène est alors compris entre 7,25 dollards/kg et 16 dollards/kg en fonction du cycle et des hypothèses économiques considérées.PERPIGNAN-BU Sciences (661362101) / SudocSudocFranceF

Analysis of solar chemical processes for hydrogen production from water splitting thermochemical cycles

International audienceThis paper presents a process analysis of ZnO/Zn, Fe3O4/FeO and Fe2O3/Fe3O4 thermochemical cycles as potential high efficiency, large scale and environmentally attractive routes to produce hydrogen by concentrated solar energy. Mass and energy balances allowed estimation of the efficiency of solar thermal energy to hydrogen conversion for current process data, accounting for chemical conversion limitations. Then, the process was optimized by taking into account possible improvements in chemical conversion and heat recoveries. Coupling of the thermochemical process with a solar tower plant providing concentrated solar energy was considered to scale up the system. An economic assessment gave a hydrogen production cost of 7.98$kg 1 and 14.75$ kg 1 of H2 for, respectively a 55 MWth and 11 MWth solar tower plant operating 40 years

An experimental analysis of PEMFC stack assembly using strain gage sensors

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Numerical study of the hydrodynamics in a two-phase induction melter for nuclear waste treatment under various operating parameters

International audienceThis article presents the numerical modeling of an in-can melter containing a metallic and a glass phase. Low-frequency electromagnetic induction is used to melt and stir the metal, and the latter heats and drags the glass phase. A careful choice of operating parameters is required to prevent the solidification of the glass, and to increase the performances of the process. Numerical modeling helps in avoiding experimental trial and error method and in studying the effect of the operating parameters on the hydrodynamics. The main difficulty for the numerical modeling comes from the deformation of the interfaces, produced by the magnetic pressure. First, a theoretical estimation of this phenomenon is performed and compared with numerical and experimental results. Then, numerical results are presented for different power inputs, AC frequencies, and quantities of glass. One of the phenomena obtained numerically is air entrainment at the triple point, creating bubbles in the glass

Origins of the Gain in Hydrophobicity of Polystyrene Linked to the Addition of Tailored Fluorinated Oligo-Polystyrene Additives

International audienceThis work aims at understanding the effect of random perfluorinated polystyrene (PS) copolymers added in a PS matrix to enhance its hydrophobic properties. Three synthetized random fluorinated copolymers, named POISE-a (Polymer prOcessing Interface StabilizEr), with various amounts of chemically bonded fluorine were blended with a commercial PS matrix by a solvent-cast process. Their effects on the static wettability properties of PS were studied with water. It was noticed that the static contact angle increases with the additive content according to a sigmoidal law, from 95 to 116°, depending on the type of POISE-a. To decorrelate the chemical and physical effects on the wetting properties, analyses of the morphology of the polymer blends were undertaken using optical microscopy and laser confocal microscopy measurements. These analyses allowed us to show that the increase of the contact angles of the PS/POISE-a blends was mainly due to the chemical heterogeneities of the surface of the films, and in particular with the formation of crystalline fluorine-rich nodules. A singular hydrophobic behavior was evidenced for PS/POISE-a blends containing 20 mol % of the fluorinated comonomer and has been related to their specific structures, showing an interdigitation of the fluorinated chains at a nanoscale leading to nodules more homogeneously distributed in the PS matrix at a microscale

In-can incineration and vitrification process: glass formulation and glass melt/liquid metal interactions

International audienceThe PIVIC project was dedicated for the management of solid technological waste, mainly made up of metals, organic matter (plastics), and silica-based fibber bags. The project aims at developing a sequential single process that thermally treat this technological waste and then condition in metallic containers the resulting Intermediate-Level Long-Lived radioactive waste. During the high temperature conditioning step (≈ 1400°C), the liquid metal phase strongly interacts with the molten glass: redox reactions, crystallization and dissolution mechanisms occur which has an impact on both glass melt viscosity, glass composition and final microstructure. The process environment is highly reducing. Furthermore, due to the coexistence of both metal and glass liquid phases, aluminum from the metal phase can be oxidized, leading to an increase of glass alumina content. Lastly, in the configuration where the waste is introduced in silica-based fibber bags, the silica content of the glass phase will increase, which has to be taken into account when evaluating candidates for glass formulation. It is important to remember that silica, alumina and alkaline contents play a key role on the glass melt viscosity.In order to reach good process reliability and to master the final conditioning material, such reactions have to be controlled along with a good knowledge of both phases behavior and glass melt viscosity. Furthermore actinides surrogates localization is also required. This poster presents the impact of metal-glass composition, temperature and actinides surrogates on the viscosity of glass melt and on final conditioning matrix

Catalytic Pyrolysis of High-Density Polyethylene: Decomposition Efficiency and Kinetics

Organic waste is generally characterized by high volume-to-weight ratios, requiring implementation of waste minimization processes. In the present study, the decomposition of high-density polyethylene (HDPE), was studied under thermal and catalytic pyrolysis conditions on two experimental systems. Firstly, pyrolytic conditions for HDPE decomposition were optimized in a laboratory-scale batch reactor. In order to maximize gas yields and minimize secondary waste, the effects of aluminosilicate catalysts, catalyst loading, and reaction temperature on decomposition efficiency were examined. Secondly, kinetics and reaction temperatures were studied on a large capacity thermobalance, especially adjusted to perform experiments under pyrolytic conditions at a larger scale (up to 20 g). The addition of catalysts was shown to enhance polymer decomposition, demonstrated by higher gas conversions. Condensable yields could be further minimized by increasing the catalyst to polymer ratio from 0.1 to 0.2. The most prominent reduction in pyrolysis temperature was obtained over ZSM-5 catalysts with low Si/Al ratios; however, this impact was accompanied by a slower reaction rate. Of the zeolites tested, the ZSM-5 catalyst with a Si/Al of 25 was found to be the most efficient catalyst for waste minimization and organic destruction, leading to high gas conversions (~90 wt%.) and a 30-fold reduction in solid waste mass

Catalytic Pyrolysis of High-Density Polyethylene: Decomposition Efficiency and Kinetics

Organic waste is generally characterized by high volume-to-weight ratios, requiring implementation of waste minimization processes. In the present study, the decomposition of high-density polyethylene (HDPE), was studied under thermal and catalytic pyrolysis conditions on two experimental systems. Firstly, pyrolytic conditions for HDPE decomposition were optimized in a laboratory-scale batch reactor. In order to maximize gas yields and minimize secondary waste, the effects of aluminosilicate catalysts, catalyst loading, and reaction temperature on decomposition efficiency were examined. Secondly, kinetics and reaction temperatures were studied on a large capacity thermobalance, especially adjusted to perform experiments under pyrolytic conditions at a larger scale (up to 20 g). The addition of catalysts was shown to enhance polymer decomposition, demonstrated by higher gas conversions. Condensable yields could be further minimized by increasing the catalyst to polymer ratio from 0.1 to 0.2. The most prominent reduction in pyrolysis temperature was obtained over ZSM-5 catalysts with low Si/Al ratios; however, this impact was accompanied by a slower reaction rate. Of the zeolites tested, the ZSM-5 catalyst with a Si/Al of 25 was found to be the most efficient catalyst for waste minimization and organic destruction, leading to high gas conversions (~90 wt%.) and a 30-fold reduction in solid waste mass