A review on catalytic methane combustion at low temperatures:Catalysts, mechanisms, reaction conditions and reactor designs

International audienceNatural gas (with methane as its main component) provides an attractive energy source because of its large abundance and its high heat of combustion per mole of carbon dioxide generated. However, the emissions released from the conventional flame combustion (essentially NO x) have harmful impacts on the environment and the human health. Within the scope of rational and clean use of fossil energies, the catalytic combustion of natural gas appears as one of the most promising alternatives to flammable combustion. The presence of catalysts enables complete oxidation of methane at much lower temperatures (typically 500 � C), so that the formation of pollutants can be largely avoided. This work presents a literature review on the catalytic methane combustion. Various aspects are discussed including the catalyst types, the reaction mechanisms and kinetic characteristics, effects of various influencing operational factors and different reactor types proposed and tested. This paper may serve as an essential reference that contributes to the development of well-designed reactors, equipped with appropriate catalysts, and under well-handled operating conditions to realize the favorable (kinetic) performance, for their future applications and propagation in different industrial sectors

Preparation of Pt/γ-Al2O3 catalyst coating in microreactors for catalytic methane combustion

International audience• γ-Al 2 O 3 washcoated on FeCrAlloy substrates exhibited excellent adhesion. • γ-Al 2 O 3 particle size and pH are important factors affecting the slurry stability. • Polyvinyl alcohol as the binder effectively enhanced the washcoat adhesion. • Pt/γ-Al 2 O 3 coated in microreactors catalyzed methane combustion efficiently. • Temperature and oxygen-to-methane ratio greatly affected the methane conversion

Catalytic methane combustion in plate-type microreactors with different channel configurations:An experimental study

International audienceThis paper presents an experimental study on the catalytic methane combustion (CMC) in platetype microreactors with wall-coated Pt/γ-Al2O3 catalyst. Firstly, the influence of different operational conditions and coating properties on the CMC in the straight parallel-channel microreactor has been investigated. A specific catalyst loading of 57.6 g m-2 was found to yield the highest methane conversion over 3.5 wt% Pt/γ-Al2O3. A higher or lower loading tended to decrease the methane conversion due to either the limited internal diffusion through the thicker coating layer or insufficient active sites in the thinner coating layer. Then, the above microreactor was compared with other five different geometries, including cavity, double serpentine microchannels, obstacled microchannels, meshed circuit and vascular network. The double serpentine microchannel geometry presented the highest methane conversion (especially at

Experimental investigation on puffing and micro-explosion occurrence of water in rapeseed oil emulsions droplets : effect of the surfactant concentration

[EN] In this paper, the assessment of puffing and micro-explosion occurrence in emulsion drops with different water percentage is studied. The emulsified fuels are formulated using micro channel emulsifier, rapeseed oil and diesel fuel as continuous phase, as well as water and Sorbitan Sesquioleate as surfactant. The formulated dispersed systems are covered under different experimental factors such as water ratio and surfactant percentage. The puffing occurrence is reported in all emulsified fuels tested (i.e. with and without surfactant). A sudden puffing and highest number of occurrence is noted when the water amount increases in all emulsified fuels. The micro-explosion phenomenon is only noted in emulsified fuel formulated without surfactant.The authors wish to express their acknowledgement to the Centre National de la Recherche Scientifique (CNRSFrance) and Flemish Interuniversity Council’s (VLIR) University Development Cooperation, funding a South Initiatives Program entitled “Emulsified systems for biofuels. Assessment of their performance in diesel engines”, because of their support to this research.Melo-Espinosa, EA.; Bellettre, J.; Tarlet, D.; Piloto-Rodriguez, R.; Verhelst, S. (2017). Experimental investigation on puffing and micro-explosion occurrence of water in rapeseed oil emulsions droplets. Effect of the surfactant concentration. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 822-829. https://doi.org/10.4995/ILASS2017.2017.4594OCS82282

Emulsification en continu avec un microsystème en vue de l'encapsulation d'antioxydants

National audienceRESUME Cette étude porte sur une problématique qui intéresse le secteur des compléments alimentaires et celui de la santé. Des chercheurs ont récemment développé un protocole [1] permettant une extraction et une « encapsulation » par émulsification d'antioxydants naturels (astaxanthine,  carotènes ou lycopènes), pour la plupart issus de microalgues, basées sur l'emploi de molécules plus respectueuses de l'environnement et peu couteuses. Ce protocole est à ce stade réalisé manuellement, en réacteur batch et met en jeu des petits volumes. Il serait intéressant de le transposer vers un procédé fonctionnant en continu permettant de traiter des volumes plus importants, de manière plus reproductible et en limitant le contact de la phase lipidique avec l'oxygène. L'idée proposée ici est de mettre en oeuvre un micromélangeur [2] développé par les laboratoires GEPEA et LTeN afin d'étudier son potentiel vis-à-vis de ce type d'application. Ce type de micromélangeur (Figure 1), basé sur un mélange intime des fluides dans un volume très réduit (< 1mL) et avec un temps de séjour très faible (de l'ordre de la milliseconde), peut être une solution intéressante au regard des contraintes liées à cette application. Les débits maximaux atteints par ce dispositif sont de l'ordre de 600 mL/min ce qui est compatible avec une production à pteite ou moyenne échelle. D'autre part, s'agissant de la perspective de l' « usine du futur », la mise en oeuvre de systèmes intensifiés s'inscrit dans une dynamique de développement de procédés miniaturisés et globalement plus économes en énergie. Cette étude se concentre dans un premier temps sur des tests de formulation et d'émusification à l'échelle paillasse avec un système fonctionnant en batch, de type rotor-stator, en faisant varier divers paramètres tels que la vitesse et le temps de rotation du rotor, les proportions des deux phases et la composition de celles-ci. Cette première phase de l'étude permet d'affiner le choix de formulations d'émulsions de type huile dans eau offrant une bonne stabilité. Des essais sont ensuite menés avec le micromélangeur sur les formulations les plus intéressantes vis-à-vis de l'application visée. Les émulsions ainsi obtenues avec les deux systèmes sont alors comparées en termes de distribution granulométrique et de stabilité au cours du temps. Dans un dernier temps, l'étude s'intéresse à l'incorporation de  carotènes dans la formulation avec en particulier l'évaluation de l'efficacité de rétention des  carotènes dans la phase lipidique et l'étude de la stabilité chimique des émulsions obtenues. MOTS-CLES DU THEME Procédés émergents, Microprocédés, Microfluidique. MOTS-CLES LIBRES Emulsion, Fractionnement, procédé continu, antioxydan

Formulation and combustion of emulsified fuel: The changes in emission of carbonaceous residue

International audienceBurning dense, viscous combustibles such as heavy fuel-oil as a water-in-oil emulsified combustible enables to decrease the emission of solid carbonaceous residue, in comparison with raw, non-emulsified combustible. This is due to the phenomenon of micro-explosion, meaning the rapid (<0.1 ms) vaporization of the water droplets inside the emulsion, breaking up the initial emulsion droplet into numerous and faster 'daughter-droplets'. The present work is based on a small-scale furnace (300 kW max.) feed with heavy fuel-oil mixed with 10-20% of gasoil, with and without emulsion of water. The emulsification of combustible enables to record a reproducible lowering in emission of carbonaceous residue from the combustion of emulsified fuel, in comparison with raw fuel. This is added to a variation in granulometry of carbonaceous residue, hereby considered as an indicator of second atomization. Copyright (C) 2009 John Wiley & Sons, Ltd

The balance between surface and kinetic energies within an optimal micro-explosion

Micro-explosion is caused by the sudden vaporization of water drops inside water-in-oil emulsion. Past studies have shown an optimal diameter for dispersed water. This optimal micro-explosion produces the largest number of secondary droplets, i.e. the largest interfacial area among the resulting spray. Such an increase in the interfacial area within the spray causes a better and less polluting combustion process. By using an infra-red camera, the present experiments can measure the size and planar velocity of secondary droplets issued from an optimal and also a non-optimal emulsion. The distributions of kinetic energy and surface energy among the spray are then calculated and discussed. Among the secondary droplets, it results that the optimal micro-explosion favors surface energy over kinetic energy. (C) 2016 Elsevier Masson SAS. All rights reserved

Dimensional modeling of biomass pyrolysis based on a nodal approach

19th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems (ECOS 2006), Aghia Pelagia, GREECE, JUL 12-14, 2006International audienceThe purpose of the present research is to develop a numerical model for the biomass gasification processes suitable for the dimensioning of industrial installation. The end use of the producer gas being often internal combustion engines systems, the model concentrates on the quantitative and qualitative aspects of the process, with a particular interest in the problem of tar formation and destruction. This study focuses on the first two steps of the process: drying and pyrolysis. The pyrolysis model presented in this paper consists in a coupling between a heat transfer model based on a nodal approach and a chemical model for the thermal decomposition of the pyrolysed material. Drying is considered as a sub process included in pyrolysis. The shown results are in good agreement with experimental data