Développement d'un nouveau thermo-transformateur à absorption-démixtion (optimisation conjointe du cycle et du mélange de travail)

Ce travail porte sur l étude d un nouveau type de thermo-transformateur à absorption-démixtion (TTAD) utilisant un mélange présentant une lacune de miscibilité à basse température. Dans ce cycle, l opération de séparation, est effectuée par décantation gravitaire par simple refroidissement du mélange. La séparation est ainsi énergétiquement gratuite et permet d atteindre des rendements thermiques plus élevés que ceux des pompes à chaleur à absorption classiques dans lesquelles la séparation s effectue par distillation.Afin de trouver des mélanges de travail pour atteindre un saut thermique de 50C, un outil de simulation numérique a été développé pour évaluer les performances des TTAD en fonction des conditions opératoires (rapport d alimentation et nombre d étages de la colonne de rectification inverse) et des caractéristiques des composés du mélange de travail (Cp, Lv, paramètres caractéristiques des équilibres liquide-liquide et liquide-vapeur). L optimisation des conditions opératoires a ainsi permis d obtenir un saut thermique maximal de 12,4C pour le mélange n-heptane / DMF pris comme référence. En faisant varier les propriétés des composés autour de celles de ce mélange de référence, un saut maximum de 32C a été calculé pour un mélange fictif. L étude de 17 mélanges réels a permis atteindre 21C de saut thermique. Une liste d autres mélanges à étudier a été établie. A l aide d une unité pilote d une puissance de 4kW, des mesures expérimentales des performances du cycle modifié de TTAD pour le mélange n-heptane / DMF ont été réalisées et démontré la faisabilité de ce cycle même si le saut thermique de 11C atteint au maximum est inférieur à celui calculé par simulationThis work is a study of a new type of Absorption-Demixing Heat Transformer (ADHT), using a mixture exhibiting a miscibility gap at low temperature. In this cycle, the separation step is performed by settling obtained after cooling the mixture. The separation is then energetically free and enables to reach thermal yields higher than those obtained for classical absorption heat transformers where separation is done by distillation.In order to find suitable working mixtures to reach temperature lift of 50C, a numerical simulation tool was developed to calculate ADHT performances. This tool enabled to calculate thermal yield and thermal lift for different values of operating parameters (molar feed ratio, number of stages of rectification column) and different properties of working mixtures (Cp, Lv, parameters characterizing liquid-liquid and liquid-vapour equilibria). The best operating conditions allowed reaching a 12,4C thermal lift for the n-heptane / DMF mixture takes as a reference mixture. By varying the mixture properties around the values of the reference mixture properties, a maximal thermal lift of 32C was reached for an imaginary mixture. 17 real mixtures were also studied and enabled to reach a 21C temperature lift. A list of other working mixtures that should be suitable was established. A 4 kW ADHT pilot unit was designed and built. The technical feasibility of this cycle was then experimentally demonstrated with this unit. A maximum temperature lift of 11C was measured with the n-heptane / DMF mixture that is lower than the values calculated by simulationNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

Enhancement of the knowledge on the ultrasonic reactor by interdisciplinary approach

International audienceOur work is a step to a better understanding of high frequency ultrasonic reactors behaviour. Using finite elements calculations, it was demonstrated that localization of chemical and physical effects can be well correlated with mechanical behaviour of ultrasound emitter. This complementary approach enables us to propose a full interpretation of the sonochemical reactor behaviour. A major reason of scientific interest on ultrasound is the well-known enhancement of chemical or physical phenomena. This is so important that “Enhancement” is probably the most used word in the title of related publications. To fully understand experimental results, present work demonstrates that ultrasound needs also to significantly enhance a very difficult knowledge transfer operation that might be named interdisciplinary co-working. Hence, ultrasound is now used and studied in many different fields of science such as acoustic, chemistry, medical imaging, disease treatment (lithotripsy), non-destructive testing... Each one has his own vocabulary, approach, and method to describe the phenomenon. In this work four different methodologies were involved to study of the same effect but using a chemical, chemical engineering, physical and mechanical approach respectively. All these viewpoints were then brought together in order to explain new original results

Comparative life cycle assessment of eight alternatives for hydrogen production from renewable and fossil feedstock

International audienceThe objective of this study is to conduct a comparative life cycle assessment of eight hydrogen production scenarios. The analysis enables a comparison of the sustainability performance of H-2 production alternatives, as well as the identification of the key elements of each option. The scenarios investigated are based on (1) fossil CH4 reforming processes, namely steam reforming, partial oxidation and auto-thermal reforming; (2) biological CH4 reforming, i.e., steam CH4 reforming, partial oxidation and auto-thermal reforming; and (3) bioethanol-to-hydrogen systems, namely steam reforming and auto-thermal reforming. The assessment is carried out with the SimaPro 7.1 program. Both CML baseline 2000 and Eco-indicator 99 are used as life cycle impact assessment methods. The results indicate that the biomethane reforming systems have the lowest impact of all of the systems. The fossil CH4 reforming scenarios produce the highest emissions of global warming gas and have the greatest contribution to the abiotic depletion potential impact. Although wheat-derived bioethanol is considered to be a biofuel, bioethanol-to-hydrogen production systems have a higher impact than fossil CH4 on acidification, eutrophication, ozone layer depletion and toxicological impacts. This research provides regulators and policy makers with a basis upon which to guide further research and development in the H-2 sector

Analyse de cycle de vie exergétique de systèmes de production d'hydrogène

Considéré comme vecteur énergétique du futur, l'hydrogène semble être la solution miracle pour sortir de la crise énergétique et environnementale actuelle. Ceci peut être vrai à condition de résoudre tous les problèmes inhérents à son cycle de vie (production, distribution, stockage et utilisation). Face aux nombreux impacts environnementaux générés au cours de la production d hydrogène, la complexité de leur évaluation et les éventuelles interactions entre eux, le recours à des méthodes d évaluation environnementale semble nécessaire. Ainsi, l Analyse de Cycle de Vie Exergétique (ACVE) a été choisie comme l outil le plus intéressant pour l étude des scénarios de production d hydrogène. Elle va, d une part, comparer des systèmes de production d hydrogène dans le but de déterminer lequel est le plus éco-efficace et, d autre part, localiser leurs possibilités d amélioration environnementale. Huit scénarios de production d hydrogène ont été étudiés par cette approche ACVE. Ces scénarios se basent essentiellement sur des techniques de reformage du méthane fossile, du biométhane et du bioéthanol. Les résultats obtenus montrent que les scénarios de production d hydrogène à partir du méthane fossile, technique mûre et largement utilisée, sont les plus gros consommateurs de ressources abiotiques et les plus émetteurs de gaz à effet de serre (GES). Par contre, le recours au biométhane comme source d hydrogène peut présenter, dans certaines configurations, une bonne solution. Le profil environnemental d une filière hydrogène ex-biométhane peut encore être rendu plus attrayant par amélioration du système de digestion anaérobie avec un système de reformage sur site. Le recours au bioéthanol produit à partir du blé comme source d hydrogène présente des effets néfastes sur l environnement. En effet, ces procédés sont caractérisés par de grands pouvoirs d eutrophisation et d acidification en plus de leurs émissions importantes des gaz effet de serre (GES). Toutefois, le bioéthanol peut constituer une source durable et renouvelable pour la production d hydrogène si sa production ne nuit pas à l environnementConsidered as the future energy carrier, hydrogen appears to be the miracle solution to overcome the current energy crisis and environmental problems. This can be possible only by solving all the problems associated with its life cycle (production, distribution, storage and final use).Due to the large number of environmental impacts generated during hydrogen production, the complexity of their evaluation and the possible interactions among them the use of environmental assessment methods is necessary. The Exergetic Life Cycle Assessment (ELCA) approach was chosen as the most useful tool for hydrogen production scenarios investigation. It compares hydrogen production systems in order to identify which one is more eco-efficient and recognizes their opportunities for environmental improvement. Eight scenarios for hydrogen production were studied by the ELCA approach. These scenarios are essentially based on reforming techniques of fossil methane, biomethane and bioethanol. The results show that the hydrogen produced by fossil methane scenarios, a mature and widely used technique, are the largest consumers of abiotic resources and emitters of greenhouse gases (GHG). The use of biomethane as hydrogen source presents an interesting solution. The environmental profile of a hydrogen ex-bio-methane can be made even more attractive solution by improving anaerobic digestion system with on-site reforming process. The use of bio-ethanol produced from wheat as a hydrogen source has large environmental impacts. In fact, these processes are characterized by large eutrophication and acidification potentials in addition to their emissions of large amount of greenhouse gases (GHG). However, bio-ethanol can be a sustainable and renewable source for hydrogen production on condition that it is produced by environmentally friendly mannersNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

EasyMED: an innovative plate Multi-Effect evaporator for seawater desalination

The EasyMED programme, supported by the European Union within the 5 th Research Framework Programme, aims to contribute to the technological development of an improved cost and energy efficient plate Multi-Effect Distillation (MED) desalination process. The major objective is to provide the world desalination market with a construction friendly and easy maintenance technology. The proposed innovative thermal process will also contribute to the diversification of MED processes recognised as a promising technology for the world market. The EasyMED process is composed of an association of simple “human-size ” elementary cells. The plates, frames and grids constituting each cell are easy to construct and transport. The cells can be combined in parallel and series to form evaporators with variable capacity. Further, the innovative design enhances the thermal efficiency of the process. First results obtained on a laboratory unit are promising with a good heat transfer coefficient, thermal efficiency and production of high quality distillate water

A comparative study on energetic and exergetic assessment of hydrogen production from bioethanol via steam reforming, partial oxidation and auto-thermal reforming processes

International audienceThree known types of ethanol reforming processes, ethanol steam reforming (ESR), partial oxidation (PDX) and auto-thermal reforming (ATR), are investigated. Favorable operating conditions are identified for each reaction system to maximize the production of hydrogen from bioethanol. Each process consists of three sections: the main reactor (ESR, PDX or AIR), the CO clean-up section comprised of the water gas shift reactor and preferential CO oxidation reactor and finally, the purification section. The performances of these processes are evaluated through mass, energy and exergy analyses. The material balances show that the total amount of ethanol required to generate 1 mol of hydrogen is 0.23 mol for the ATR, 0.24 mol for the PDX and 0.25 mol for the ESR. The ATR reforming process is shown to have the highest energetic efficiency, i.e., the lowest amount of energy is consumed to produce the same amount of hydrogen from ethanol. Moreover, the AIR process has the best exergetic performance, as it presents the highest ratio of exergy recovered in the hydrogen stream to the total exergy supplied to the system. For all three of the systems, the exergy destruction occurs mainly in the reformer due to the high irreversibility of the reaction

SOLMED: heat transfer characterization

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