Modelling and Simulation of Acid Gas Condensation in an Industrial Chimney

International audienceCoal power stations as well as waste incinerators produce humid acid gases which may condense in industrial chimneys. These condensates can cause corrosion of chimney internal cladding which is made of stainless steel, nickel base alloys or non metallic materials. In the aim of polluting emission reduction and material optimal choice, it is necessary to determine and characterize all the phenomena which occur throughout the chimney and more especially condensation and dissolution of acid gases (in this particular case, sulfur dioxide SO2)

Modelling and simulation of condensation phenomena of acid gases in an industrial chimney

National audienceCoal power stations as well as waste incinerators produce humid acid gases which condensate in industrial chimneys. These condensates may cause corrosion of the internal cladding made of stainless steels, nickel base alloys or non metallic materials. In the aim of polluting emission reduction and material optimal choice, it is necessary to determine all the phenomena which occur throughout the chimney such as condensation and dissolution of acid gases (in this particular case, sulphur dioxide SO2). The production of energy from fossil fuels (coal, petroleum, natural gas, etc.) brings about the emission of gas containing sulphur compounds (SO2, SO3) as well as chlorine and fluorine compounds. To avoid this atmospheric pollution and its harmful effects (acid rains, impact on the health) due to hydrochloric, sulphuric and hydrofluoric acids produced in the presence of air, it is necessary to steam these flue gases. Nevertheless, a considerable quantity of residual acid gases remains in the gas discharge which also contains large amounts of water vapour. Thus, condensation may occur and by the way an acid attack of the internal cladding of the chimney. This results in high costs of maintenance and a reduction of their structural stability. The knowledge of the phenomena of heat and mass transfer during the condensation of these acid gases in chimney is essential for their conception and materials choice

Suivi en-ligne des procédés de cristallisation en solution en milieux pur et impur par émission acoustique

National audienceMany mechanical and physical processes are associated with the generation of acoustic waves produced by the rapid release of energy from localized sources within a material. Acquiring and processing these waves allows non-destructive control of phenomena such as the extension of cracks in a structure under stress, plastic deformation, phase transitions, etc. Few works were devoted in past to acoustic emission (AE) during crystallization processes. Moreover, most available studies are purely descriptive and do not provide results enabling to quantitatively monitor basic crystallization phenomena (i.e., nucleation, growth, agglomeration, etc.) New results dealing with the monitoring of batch solution crystallization operations are presented here. The acquired acoustic signals are interpreted thanks to the joint monitoring of the continuous phase (Measurement of the solute concentration thanks to ATR FTIR spectroscopy) and of the dispersed phase, thanks to the video in situ acquisition of images of crystals in suspension. It is shown that acoustic emission sensors "perceive" the development of the crystallization process and, in particular, that an early detection of the nucleation of crystals is allowed. Analysing the parameters of acoustic waves is shown to allow separate monitoring of basic crystallization phenomena which remain to be identified. As far as online monitoring of industrial crystallization processes is concerned, the measurements thus obtained open promising perspectives.De nombreux processus mécaniques et physiques s'accompagnent de la génération d'ondes acoustiques dues à une libération rapide et localisée d'énergie au sein des matériaux. L'acquisition et le traitement de ces ondes permet un contrôle non-destructif de nombreux phénomènes tels que la fissuration sous contrainte, la déformation élastique, le changement de phase, etc. Peu de travaux ont été consacrés par le passé à l'émission acoustique (EA) pendant les procédés de cristallisation et l'essentiel des travaux disponibles, purement descriptif, ne fournit pas de résultats susceptibles de permettre une évaluation quantitative indirecte des processus élémentaires de la cristallisation (i.e., nucléation, croissance, agglomération, etc.). On présente ici des résultats nouveaux obtenus pendant le suivi de cristallisations discontinues en solution. Les signaux acoustiques recueillis sont interprétés grâce à la mesure, en parallèle, de la phase continue (mesure de concentration par spectroscopie ATR FTIR) et de la phase dispersée, par acquisition d'images de la suspension à l'aide d'une sonde vidéo in situ. On montre que les capteurs d'émission acoustique "perçoivent" le déroulement de la cristallisation et, en particulier, qu'elle permet une détection extrêmement précoce de la nucléation des cristaux. Une analyse des composantes des signaux acoustiques montre également que l'EA permet de suivre séparément plusieurs processus élémentaires de la cristallisation qui restent à identifier clairement. Les mesures ainsi obtenues ouvrent des perspectives prometteuses quant au suivi en-ligne des opérations de cristallisation industrielle

Acoustic on-line monitoring of solution crystallization process in pure and impure media

International audienceWe show that acoustic emission (AE) is a very attractive non intrusive technique for monitoring crystallization processes. AE has been successfully applied in many fields of material sciences and it was also used in the pharmaceutical industry for monitoring various chemical engineering processes including fluidized bed granulation, fluidized bed coating, powder compaction, etc. However, few studies deal with the use of AE to monitoring crystallization processes. The objective of this work is to evaluate the potential for using acoustic emission to monitor polythermal batch crystallization in the absence and presence of impurities. The basic concept behind AE monitoring of crystallization processes is that the phase transitions occurring during crystallization in solution induce physicochemical changes in the suspension. Such changes release energy and therefore generate acoustic elastic waves propagating in the liquid medium. Furthermore, as crystal particles are generated, the elastic properties of the dispersed phase also change. The latter changes affect the acoustic emission caused by the particle collision impacts and inter-particles and/or particles-wall frictions. The elasticity of crystals and their kinetic energy are also affected by many other properties such as size, shape, hardness, density, uniformity of composition which obviously depend on the presence of impurities during the process. We report preliminary batch solution cooling experiments obtained with the model system Ammonium Oxalate/water (AO) in the presence of Nickel Sulfate as impurity. The experiments are monitored using AE, ATR FTIR measurement of supersaturation and CSD analysis performed thanks to in situ image acquisition. Complex but promising information is obtained thanks to AE monitoring

Controlled precipitation of an inorganic compound in solution using a polymeric matrix

National audiencePrecipitation of strontium molybdate was performed from aqueous solutions of sodium molybdate and strontium chloride in presence of hydroxypropylmethylcellulose. Three experiments were conducted: without cellulose, with dissolved cellulose and with a tablet containing cellulose and strontium chloride powder. The first one results in agglomerates of bipyramidal crystals, the second one in smaller monosized bipyramidal crystals and the last one in a mixture of bipyramidal, spherical, ellipsoidal particles and their agglomerates. Explanations based on the effect of solution viscosity are proposed

Influence of temperature on the compaction of an organic powder and the mechanical strength of tablets.

International audienceThe purpose of this work consists in following the dependence of physical properties on the temperature during the compaction of an organic component. A special thermo-regulated die has been developed to realize uniaxial compression at different constant temperatures. This study has shown that a temperature change modifies the microstructures and the mechanical behaviour of the tablets. The measurement of the tablet porosity during the compression cycle allows us to conclude that temperature influences mainly the phenomena occurring during the isobaric stage of the compression cycle and not the ones during the pressure increase. On the other hand, during the pressure increase, the acoustical activity of the powder is reduced when temperature increases. The tensile strength of tablets realized at different temperatures was also studied and shows a maximum around 60°C that can be explained by the SEM analysis of the microstructure of the tablets

Fragmentation de grains de sable. Suivi par émission acoustique et bilans de population.

6 pagesDevenue très courante dans le domaine du contrôle non destructif, l'étude des ondes acoustiques est beaucoup moins utilisée pour suivre l'évolution de certains phénomènes. Pourtant elle peut se révéler utile, notamment pour caractériser les phénomènes intervenant lors de la compression des poudres. L'analyse de l'émission acoustique (E.A.) au cours de la compression de plusieurs poudres pharmaceutiques telles que l'aspirine, l'amidon, le saccharose et le kétoprofène a permis de mieux cerner les phénomènes qui se produisent pendant la formation du comprimé [1,2]. Les ondes acoustiques émises par la poudre dépendent des phénomènes se produisant pendant la compression, tels que le réarrangement granulaire, la fragmentation et la déformation plastique des grains. Serris [1,2] a également remarqué que l'intensité de l'émission acoustique est fonction de la poudre. L'émission d'ondes acoustiques peut alors être considérée comme une caractéristique intrinsèque d'une poudre

Zirconia matrix composite dispersed with stainless steel particles: Processing and oxidation behavior

International audienceMaterials with non uniform properties are being developed to optimize several functions of industrial components in severe atmospheres at high temperature. These composites called M(p)-CMC(s): "ceramic matrix composites dispersed with metal particles" are candidates for high-temperature structure materials as functionally graded materials (FGMs) such as intermediate components between electrolyte and interconnecting components in SOFC. Preparation of a model composite M(p)-CMC(s) is described. Powder metallurgy process is used to obtain a dense composite (98% of the theoretical density) based on yttrium stabilized zirconia for the ceramic part and on 304L stainless steel for the metallic part. The characteristics of this material as well as its behavior under oxidation at high temperature are reported

Etude de l'influence de la température sur la compressibilité et la résistance à la rupture de matériaux granulaires

9 pagesLes poudres sont couramment utilisées sous forme de comprimés. Le comportement de ces poudres est sensible à différents paramètres tels que la température et l'humidité. La plupart des études de comportement ont porté sur l'influence des paramètres contrôlant la compression mais très rarement sur l'influence des paramètres extérieurs. Aussi avons nous choisi d'étudier l'influence de la température au cours du cycle de compression sur la compressibilité et sur les caractéristiques finales des comprimés obtenus à partir d'un composé organique fixé. Des expériences ont été réalisées avec une presse uniaxiale LLOYDS. Un système de chauffage et de régulation en température a été adapté sur des matrices de compression uniaxiale. Un suivi de la porosité et des émissions acoustiques en cours de compression a été réalisé. Les relations de ces caractéristiques avec les mesures de la résistance à la rupture et l'évolution des microstructures des comprimés obtenus sont discutées

Couplage analyse thermogravimétrique et émission acoustique pour l'étude de la corrosion haute température

National audienceAfin d'améliorer les connaissances du comportement à haute température des matériaux, le couplage de plusieurs techniques d'analyse physique in situ est une voie prometteuse. Dans ce but, des thermobalances ont été équipées d'un appareil spécifi que de mesure des signaux acoustiques émis par les échantillons dont la variation de masse est continûment mesurée sous diverses atmosphères représentatives de conditions industrielles. Les corrosions de surface à haute température sont à l'origine d'émission d'ondes acoustiques générées lors de la croissance ou de la fi ssuration de couches formées. Des mesures simultanées in situ des variations de masse et des signaux acoustiques apportent donc des informations sur ces mécanismes de corrosion haute température. L'application de cette méthodologie aux mécanismes d'oxydation, réduction ou attaque par les atmosphères carbonées (cokage) est présentée dans ce document. Une perspective de ces études est de pouvoir établir des référentiels pour une éventuelle utilisation de l'émission acoustique pour l'étude de la corrosion des équipements fonctionnant à haute température. // In order to improve the knowledge on the high temperature behaviour of materials, the coupling of in situ physical analysis is a promising way. For this purpose, thermobalances have been equipped with specific devices to measure the acoustic signals emitted by samples for which the mass variation is continuously recorded under simulated industrial atmospheres. The high temperature corrosion of materials surfaces generates acoustic emission signals associated to the growth or the cracking of the formed layers. In situ simultaneous measurements of the mass variation and the acoustic signals give information on the high temperature corrosion mechanisms involved. In this document, this methodology has been applied to the study of oxidation, reduction or attacks under carbon-rich atmosphere (coke deposition). These studies could lead to reference data for a possible application of acoustic emission for the corrosion monitoring of high temperature equipments