Modélisation de la cinétique de biodégradation de phénol par granules aérobies

This work describes a model of the biodegradation of phenol carried out by aerobic granules. These granules were obtained by culturing an activated sludge supernatant in a sequencing batch reactor fed with a synthetic waste water and subsequently, by acclimation to phenol (100 mg/L). The kinetics of phenol biodegradation by the aerobic granules was investigated over a wide range of initial phenol concentrations (40–1112 mg/L) in shake‐flask cultures. A Haldane‐type model was adjusted to the experimental results, which depicts successfully the phenol biodegradation profiles in the entire range of initial concentrations studied by using only one set of parameters. It is our view that the proposed model could contribute to the knowledge about the ability of aerobic granular systems to biodegrade toxic, inhibitory compounds such as phenol.     

Méthodologie d'étude et de modélisation de la déphosphatation d'effluents aqueux

Due to phosphorus impact on water pollution, a P‐recovery process by calcium phosphate precipitation was developed. The reactor process is a fluidized bed in which phosphate precipitates continuously and coats sand grains. The pilot unit can treat synthetic wastewater flow rates ([P] = 50 mg/l) of about 0.1 m3/h. A two‐stage methodology is proposed to understand the physicochemical phenomena. Fluidized bed precipitation modeling involves thermodynamical concepts taking into account the various calcium phosphates that can precipitate vs. operating conditions (PH, [P], [Ca], T). Coating modeling is performed by a first‐order kinetics reaction between fines and sand grains, combined with a network of ideal reactors representing system hydrodynamics.     

Modélisation de la cinétique morphologique en corrosion générale et en corrosion localisée

Two theoretical methods have been proposed to investigate the evolution of the interface shape. The first one enables to relate the various types of overall morphological evolution (roughness levelling and increase) and the driving force intensities to the nature of the physical chemistry occurring at the interface and its neighbourhood. The second one deals with the quantitative characterization of local morphological evolutions, in particular in stress corrosion. It allows the determination of crack initiation and propagation kinetics from morphological information gathered with samples     

Modélisation de nanofiltration/osmose inverse en tenant compte du facteur de séparations minimale et maximale

Based on theorical analysis of existing models and on experimental observations, a model that allows us to connect the permeate flux tothe intrinsic separation factor takingaccount of the termsof the minimal and maximalseparation factors, was established. The experiments covering a large range of permeate flux (from several 10^?9 μL/m 2.s) to several 10.³ mL/(m 2.s)) permit us todetermine the values of maximal seaparation and minimal separation, as well as the solute transport parameterr for the solutions of sodiumchloride and sodium sulfate.     

Modèles Hydrodynamiques pour la Séparation des Courants dans un Décanteur Pilote

Despite of its general use in industry, particle sedimentation is still a not well understood unit operation. Hydrodynamics is complex in essence, mainly because the possible volumes are depending on the operating conditions, which in turn has consequences on the stability of the equipment in unsteady state conditions.     

Modélisation de l'efficacité de filtration d'un échangeur cyclone

This work is a modelling of the Aireco® filtration system. This heat exchanger, with particle catching capabilities, is made of a cyclonic body which contains refrigerated coils. The water vapour contained in the gas to be treated condensed on the coils surface. Our modelling considers two main capture surfaces: the entry zone in which particles are collected by inertial impaction and the cyclonic body in which particles diffused by centrifugal force is the main phenomena. We found that these considerations explain our experimental results with an accuracy more than 90%, when the Aireco® is on a normal point of working.     

Modélisation numérique du transfert de matière dans un écoulement annulaire faiblement tourbillonnaire non-entretenu

Mass transfer and hydrodynamics in a laminar swirling flow induced by a tangential inlet in a cylindrical annulus was investigated. The simplified version of the momentum and convection-diffusion equations using the boundary layer theory, was resolved by an implicit finite difference method. Although the proposed method cannot be applied to vortex flows and recirculating phenomena, the present work identified a relevant problem about the validity of the boundary layer theory for the mass transfer determination at high Schmidt numbers.     

Dépôt chimique CVD de silicium dopé in situ au phosphore. Partie 2: Analyse théorique et modélisation

The behaviour modelling of a CVD reactor is useful to better understand the involved complex mechanisms and determine the conditions required for the fabrication of depositions according to industrial standards. This approach was applied to the deposition of polycrystalline silicon doped in situ with phosphor. A model was developed to represent the deposition process which predicts correctly the excess of deposition thickness caused by silylene. The control of the deposition operation is mainly governed by the feed phosphine concentration and the inlet geometry where silylene is formed.     

L'électrolyseur dans l'optique de la dynamique des procédés

This article written for the non-specialists reviews the various methods for modeling electrolyzer behavior. Deterministic and stochastic models are discussed and the adaptation of process dynamic to electrolysers is emphasized.     

Décantation assistée par ultrasons des eaux résiduaires

The impact of ultrasound on settling in water treatment has been studied. The effects already measured of ultrasound on the settling properties of various effluents have been identified and these effects have been observed in a static and a dynamic study. Sonification conditions suitable for optimizing such a process have been determined. The results show the primary role that stationary wave systems have in the settling of effluents (flocculated or not, synthesized or real). With flocculated effluents, a true impact on settling can be observed.     

La modélisation de la turbulence dans une enceinte avec ouvertures et sources chaudes localisées

The air circulation inside an enclosure with multiple openings and local heat sources was studied by means of a mathematical model. After a number of comparisons to studies in an experimental apparatus, it was concluded that a turbulence model should be introduced in order to improve the mathematical simulation. Two turbulence models, one based on the algebraic and the other on the differential (K-?-G) model of the turbulent viscosity, were investigated. The differential model provided only small improvements in the results and increased the running costs substantially when compared to the algebraic model. Hence the utilisation of the differential model was not justified in these simulations. The combined effect of the forced convection through the enclosure and the natural convection from the heat sources was simulated in an attempt to study the air circulation and the air temperature inside the building of an aluminum reduction plant.     

Une nouvelle technologie d'appareils de dépôt chimique en phase vapeur. Partie 2 : Modélisation du dépôt de silicium pur à partir de silane et de silicium dopé in situ au phosphore

A better understanding of Chemical Vapour Deposition (CVD) process can be obtained by modelling the phenomena involved in CVD reactors. The established model is then a useful tool for industrial equipment design and for the optimization of operating conditions. The research for optimal operating conditions is done by a more rational and efficient way using a model. The specific case of the polycristalline silicon deposition from silane in a new technology of LPCVD reactor is used to illustrate the approach. Hypotheses and methods necessary for the development of the model are presented and discussed first, then results are described and compared to experimental data. Finally, the more complex case of in situ phophorus doped polysilicon is discussed.     

Modéalisation de la copolyméarisation éathylégne α-oléafine par catalyse ziegler—natta

A copolymerization model of ethylene and a α-olefin describing the monomer uptake and the quality of the polymer produced, namely M_n, M_w, M_z, the distribution of molecular weight, short branching index and double bonds, is presented. This model assumes the existence of several types of active sites (2 or 3) and do not involve any limiting diffusion. It is applied to ethylene and butene-1 bulk copolymerization at high pressure and high temperature. Parameters are identified with CSTR experiments.     

Etude de l'oxydation du pentachlorophénol dans différentes géométries de réacteurs à ultrasons de haute fréquence

The determination of the key geometric parameters used for high-frequency sonoreactor modeling has been studied. The methodology allowing the characterization of the different reactors built in our laboratory has been defined. The methods are: calorimetry, determination of the residence time distributions, the observation of the chemiluminescence of luminol and the degradations of a prototype molecule: pentachlorophenol. After characterization of the studied reactors, it seems that volumetric power, with equivalent emitting system, is the major parameter of the reactor's performance.     

Etude numérique et paramétrique de la combustion de particules d'aluminium

Several numerical models have been investigated to study the reactivity of aluminium particles coming from the combustion of solid propellants in spatial launchers. The Law model has been rapidly selected as it yields a continuous model from an aluminium drop to an oxide drop. The model also gives the residue size at the end of the combustion process. This could explain the scaling observed in the rocket engines. In order to study the coupling between the flow and the combustion, the combusion of aluminium drops has been widely analyzed with 0D computation. The main mechanisms of the combustion process have been identified.     

Simulation bidimensionnelle de phénomènes de convection naturelle et forcée en formulation primitive

The air circulation, and the temperature and pressure profiles were simulated in two dimensions using a hybrid finite difference method which combines the MAC method and the stream function/vorticity approach. Three different flow problems were solved: (i) forced convection in a closed cavity; (ii) natural convection in a closed cavity; and (iii) forced and natural convection in a cavity with localised openings and hot sources. The results for the first two problems were compared to the literature and the results for the third problem were compared to data obtained from an experimental apparatus.     

Dispositif de déposition de couches de suspensions de céramiques appliqué à la stéréolithographie

A system to coat uniform layers of ceramic suspensions has been developed for rapid prototyping applications. The metering system is made of a gas injection nozzle which height, angle of attack and pressure can be adjusted. The coated layer homogeneity and the process reproducibility have been studied. The effect of each parameter on the coated layer thickness has been characterized using a design of experiments approach and a reliable mathematical model is proposed to optimze the coating system.     

Simulation de la distillation catalytique par un nouveau modèle de transfert – Application à la production d'acétate de méthyle

A catalytic distillation model, based on Maxwel‐Stefan Equations, is presented. In this model, the effective diffusion in porous catalyst is taken into account. Since this model is developed in a commercial environment (ProSim Plus process simulator), particular attention is paid to the solution strategy: robustness and adaptability are of particular importance for the user. The influence of catalyst characteristic, column design, mixture non – ideality and liquid/vapour interface are discussed. We conclude that an optimum design exists. Reflux ratio and catalyst location are key‐parameters.     

Modélisation d'un four de calcination du coke de pétrole: II. Simulation du procédé

A one-dimensional steady-state mathematical model has been developed to simulate the process of calcination of petroleum coke in a rotary kiln. A simulation is made to reproduce the operating conditions prevailing during a normal working day, in order to validate the model, and to study the effects of the main process control variables. It has been found that of the energy provided by combustion, 59.5 % comes from hydrogen, 14.6 % from the carbon of the coke bed, 13.8 % from coke dust, 11.3 % from methane and 0.8 % from tar. A comparison with existing models is made to identify eventual similarities between the various kilns under study. It appears that maximum coke temperature occurs at 45 to 55 % of kiln length, while volatile matters evolution takes place between 5 and 60 % of kiln length, measured from feed end.