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International audience; Screw reactors are largely used devices in the industry. Very few studies focus on the powder hydrodynamics in screw reactors. The overflow point, a filling degree value when the powder passes over the shaft, was determined for different conditions and a dimensionless model was fitted to predict this parameter. The residence time distribution (RTD) has been measured with a pulse injection of salty powder. The influence of operating conditions and geometry parameters on the RTD has been studied. It appeared that the Hausner ratio, the pitch length and the filling degree mostly influence the RTD shape. Two models for the RTD have been compared: the compartment model was the most accurate and has one parameter of adjustment. A dimensionless model was developed and fitted with 51 experimental RTD results, predicting the RTD shape. The dimensionless model predicts with good accuracy other experimental data from the literature.

International audience

International audience; The impromptu closure of schools and universities and the strict lockdown decided by the French State in March 2020 forced us to find -urgently and without preparation- alternative solutions to conventional face-to-face teaching. Due to their experimental nature, the transposition of labs on pilot plants was particularly challenging. Despite this inherent difficulty, we succeeded in implementing a remote educational device within a few weeks, designed as a viable alternative to conventional food engineering labs for Master level students. Four engineering labs (corresponding to four unit operations widely found in the food industry) were transposed: appertization of cans; concentration in a falling film evaporator; frontal filtration in a plate filter; and spray drying. In the remote labs, hands-on experiments were replaced with various types of virtual tours of the equipment, a detailed description and illustration of its operation, and analysis of real data (previously collected). Evaluation was done via individual quizzes (counting for a small part of the mark, because their aim was above all formative), individual and collective written reports and an individual online oral exam. The teaching team comprised six lecturers, one pedagogical engineer and the person in charge of the technology platform, who also had long experience in distance learning. This experiment took place in the second half of May 2020, with approximately thirty first-year Master students. The effectiveness of the implemented system was evaluated through direct observation and discussions, marks obtained by the students and an anonymous survey. This teaching experiment presents certain flaws induced by the very peculiar conditions of its conception (short time frame, no direct access to the pilot plants). While an “all-digital” approach is not our ultimate aim for these lab sessions, where handling and testing are inherent to the learning process of the student, the educational resources deployed here can be seen as a great incentive to further develop hybrid teaching approaches in food engineering. Moreover, the educational resources and practices implemented in these exceptional circumstances are an opportunity to develop new teaching methods in the future. The present paper reports on this teaching experiment during lockdown due to the COVID-19 pandemic and tries to draw exciting lessons for the future and pitfalls to avoid.

Le Génie de la Réaction Chimique (GRC) est une branche du génie des procédés qui traite des méthodes de mise en œuvre rationnelle des transformations de la matière et des appareils dans lesquels sont conduites les réactions : les réacteurs. » Le plan de ce cours est le suivant : Un chapitre préliminaire fournit quelques rappels utiles de mathématiques et méthodes numériques.Le premier chapitre fait le point sur les notions de base du Génie de la Réaction Chimique, avec la classification des réactions et des réacteurs, quelques éléments de technologie, les définitions des grandeurs caractérisant une réaction chimique (coefficients stœchiométriques, taux de conversion et avancement) et le rappel des éléments de base de thermodynamique et de cinétique chimique (vitesse de réaction, lois usuelles, liens avec la thermodynamique).Le deuxième chapitre est consacré aux réacteurs idéaux isothermes. Les bilans de matière seront explicités dans plusieurs cas classiques : réacteur agité discontinu, réacteurs continus parfaitement agité ou à écoulement piston ; avant de détailler le comportement de ces réacteurs idéaux lorsqu'ils sont le siège d'une seule ou de plusieurs réactions, et d'aborder le problème de l'optimisation de la conversion ou du rendement.Le troisième chapitre traite de l'étude de l'écoulement dans les réacteurs réels grâce aux mesures de Distribution des Temps de Séjour (DTS) : après la description de la méthode et de la fonction de distribution associée, le diagnostic des écoulements et leur modélisation seront étudiés.Le quatrième et dernier chapitre s'intéresse aux effets thermiques dans les réacteurs : l'écriture des bilans d'énergie sera détaillée, puis la Progression Optimale de Température (POT) et le problème de l'emballement thermique seront abordés.

International audience; Using a synthetic method, the phase behavior of the CO2 (1) + cyclooctane (2) binary system was for the first time experimentally studied between 292.95 K and 373.55 K. In this temperature range, the bubble- and dew-point pressures, ranging from 13.2 to 183.4 bar were measured for carbon dioxide mole fractions between 0.1014 and 0.9701. A total of 96 experimental data points were acquired. The experimental data were obtained using a high-pressure cell by visual observation of phase transitions. These measurements made it possible to conclude that the studied binary system probably exhibits a type V phase behavior in the classification scheme of Van Konynenburg and Scott. In particular, the experimental temperature of the suspected lower critical end point (LCEP) was found to be 303 K. Despite the complexity of the phase behavior, the experimental data could be accurately correlated with the Peng-Robinson equation of state combined with sophisticated mixing rules that either involve temperature-dependent binary interaction parameters (kij(T)) or that embed the residual part of the Wilson activity coefficient model.

International audience; A series of experiments were carried out on an indirectly heated pilot scale rotary kiln. These experiments aimed at recording, while the solids flow, the temperature profiles of the freeboard gas, the solid particle bulk and the wall, as well as the power supplied for heating, over a range of operating conditions. Based on these data, the experimental wall-to-solid heat transfer coefficient was determined through an energy balance. The effects of operating conditions, namely rotational speed, filling degree, lifter shape and controlled temperature, on the heat transfer coefficient are discussed. A model based on dimensional analysis is proposed to calculate the wall-to-solid heat transfer coefficient for low to medium heating temperatures (100-500°C). The experimental and calculated results are in good agreement. The experimental results are also compared to the predictions of some existing models. While the predictions are within a reasonable order of magnitude with regard to the experimental results, these models fail to represent actual variations with operating conditions satisfactorily

International audience; Over the years, rotary kilns have become an inescapable benchmark in several industrial sectors. This is because they offer special possibilities regarding a wide range of materials which can be continuously processed with little or no operating labor, especially when they are automatically controlled. The wider the scope of applications, the greater the variety of kiln designs and sizes.Rotary kilns are widely used for the drying or cooling of solid particles, for instance in the food processing industry when dealing with wet or dry granular materials, for the calcination of limestone, petroleum coke, or production of cement. Other applications include: regeneration of spent catalyst, hazardous waste reclamation, defluorination and reduction of uranyl difluoride and so on. Industrial rotary kilns are usually equipped with internal fixtures such as lifters, baffles, constrictions or exit dams.The complex hydrodynamic behavior of the granular materials within rotary kilns has led to extensive research over the years. Most of these publications report on the influence of operating parameters (rotational speed, kiln slope, mass flow rate or exit dam height) on the residence time distribution (RTD) and axial dispersion of solid particles. However, few of these studies analyze the effect of the presence of lifters, their number or shape.We therefore decided to conduct a systematic experimental investigation of RTD, kiln holdup and axial dispersion coefficient for the continuous flow of granular materials in rotary kilns equipped with lifters.To do so, we used two different pilot scale rotary kilns. One is about twice the size of the other.We investigated both the influence of operating parameters (rotational speed, kiln slope, mass flow rate) and of the presence of internal devices (grid, different shapes and number of lifters, different height of exit dam) on a large range of size and shape of particles (two different sands, rice and beech chips).The large set of experimental data obtained, allowed us to build a model based on dimensional analysis, which is useful for industrial applications.

International audience; Up-scaling tracer experiments were carried out in a pilot-scale rotary kiln twice as big as the kiln used in the first two Parts of this study. Internal fixtures such as grid, or lifter structure arranged in 3 and 6 rows of single throughout lifters were used. The effects of these removable fixtures and other usual operating conditions, namely, mass flow rate of granular biomass materials, rotational speed and slope of the kiln on the residence time distribution (RTD), the mean and variance of residence time (MRT and VRT), the hold-up (HU), the Peclet number (Pe) and corresponding axial dispersion coefficient (D), were investigated. Scaling-up rules were derived for the MRT, HU volume fraction and D from the results of a comprehensive experimental work. Good agreement was found between the experimental data and the calculated values. The wide size distribution of the beech chips used in the present study allows analysis of particle segregation, which may further increase understanding of the flow characteristics of granular materials, notably within flighted rotary kilns. The results show that while significantly increasing the dispersion, ipso facto, enhancing the mixing, the lifters limit the extent of particle segregation.

International audience; The aim of this work is to study a pre-treatment process of olive mill wastewaters based on ozonation. The efficiency of the process depends on the removal of pollutants and on ozone mass transfer performance. In order to choose an appropriate gas/liquid contactor, the rate constants of three phenolic compounds (gallic acid, p-hydroxybenzoic acid and p-coumaric acid) were determined by using competition kinetic model. These constants, obtained at pH 5, were found to be high (from 3.8 × 104 L/mol s to 2.9 × 105 L/mol s), inducing a diffusion controlled regime (Ha > 3). Thus, to obtain an efficient ozonation process, gas/liquid contactor should be adapted to this regime. An ejector was chosen as gas/liquid contactor. In a first time, treatment of synthetic effluent containing the three phenolic compounds was performed to evaluate efficiency of the process. Experimental conditions were chosen to obtain a diffusion controlled regime (Ha > 3). It appeared that this gas/liquid contactor permits obtaining complete and fast removal of pollutants with a very efficient ozone mass transfer (up to 90% during removal of phenolic compounds). So, this process was used to perform the ozonation treatment of olive mill wastewaters from Sfax (Tunisia). It was proved to be very efficient: up to 80% of phenolic compounds were removed and ozone mass transfer reached 95% during this oxidation.

Mass transfer of ozone in aqueous phase is a major aspect of ozonation and advanced oxidation processes. The aim of this study is to compare the performances of an ejector with those of a more traditional gas/liquid contactor: a bubble column. The hydrodynamic study showed that the volumetric mass transfer coefficient of the ejector (KLa = 7.2 × 10−2 to 1.35 × 10−1 s−1) was greater than that of the bubble column's (KLa = 1.5 × 10−2 to 2.8 × 10−2 s−1). Very important differences in the values of the residence time and gas retention rate were also observed. A study of phenol degradation was performed. Due to its specifications the ejector is very efficient when the kinetics of reaction is fast (diffusion-controlled regime). In both semi-batch and open circuits, the phenol was quickly eliminated and the ozone transfer was very high (up to 98%). It is to be noted that these results were obtained for a processing time of approximately 1 s.

International audience; Rotary kilns are gas-solid reactors commonly used in industry to achieve a wide range of material processing operations: mixing, heating or cooling, reacting of coarse, free-flowing or cohesive solids. Therefore rotary kilns are used for applications such as reduction of oxide ore, pyrolysis of biomass or hazardous waste, calcining of petroleum coke, conversion of uranium fluoride for the manufacture of nuclear fuel, and so on. When operated at atmospheric pressure, these units consist of a cylindrical shell that can be inclined, into which the solids burden is fed continuously at one end and discharged at the other. Most of them are equipped with lifting flights or lifters, and/or exit dam at the kiln outlet end. They can be classified into two main heating modes; they can be either directly heated or indirectly heated, depending on the heating source position with respect to the kiln’s tube wall. They usually require very little labor to operate in comparison with other industrial reactors.Though operational cost of these units is usually high, their design and intended operating conditions are often conservative due to the lack of fundamental understanding notably upon the solids flow behavior and the heat transfer mechanisms. Heat transfer in rotary kilns is very complex and may involve the exchange of energy via all the fundamental physical transfer mechanisms that are, conduction, convection, and radiation. There have been quite a few studies dealing with this subject in the literature. Although many researchers studied the main phenomena occurring in the kiln, the heat transfer between the wall and solid particles, or the (free) convection of non forced gas are not yet well understood. The present study investigates the convective gas-to-wall heat transfer coefficient, in the case of a non-forced air flow, and the wall-to-solids heat transfer coefficient. These coefficients were first experimentally determined, and then correlated based on a dimensional analysis, so to be used in a global model for rotary kilns.A series of experiments were carried out on a pilot scale rotary kiln at atmospheric pressure, whether or not equipped with lifters and fitted with a dam at the outlet end. The experimental apparatus, 1.95m in length and 0.01m in (internal) diameter, can be externally heated in two independent consecutive zones by electrical resistance up to 1000°C. Regarding the thermal metrology, thermocouples are positioned at five and four cross-sections, respectively in and outside along the kiln tube. Hence, after turning on the heating system, axial temperature profiles of gas, wall and solids were measured until steady state is achieved. Both coefficients were determined from the temperature profiles measurements data for low and medium wall temperature set point comprises between 100 and 500°C. In particular for the wall-to-solids heat transfer coefficient, the bulk materials used was quartz sand (average size about half a millimeter) with a narrow distributed size fraction; No solids were fed into the kiln when studying the air convection inside the kiln. Two shapes of lifters were compared to determine the influence of lifters presence and their geometry on the heat transfer: straight (one-section) lifters and rectangular (two-section) lifters (RL). The kiln operating conditions examined also include: the rotational speed (2-12 rpm), the mass flow rate (0.8-2.5 kg/h) and the exit dam height at the kiln outlet end (23.5-33.5 mm). An experimental matrix of about eighty experiments was achieved.For the determination of the experimental value, the lumped system analysis and a heat balance accounting for the measured power supplied for the heating are used. Results showed that the wall-to-gas convective heat transfer coefficient is significantly lower that what can be expected for natural convection. Though only small variations were observed, still some trends could be observed in presence of lifters, and when varying the rotational speed. The wall-to-solids heat transfer coefficient was notably lower in presence of lifters. It was also found to increase with the temperature set at the wall and the filling degree, which is imposed by the operating conditions set. Dimensional correlations were developed to describe these two heat transfer mechanisms from the experimental results.

International audience; Rotary kilns are gas-solid reactors commonly used in industry to achieve a wide array of material processing operations. Rotary kilns are used for applications such as reduction of oxide ore, pyrolysis of hazardous waste, calcining of petroleum coke, conversion of uranium fluoride into uranium dioxide for the manufacture of nuclear fuel, and so on. When operated at atmospheric pressure, they consist of a cylindrical shell that can be inclined, into which the solid charge is fed continuously at one end and discharged at the other. They can be equipped with lifting flights or lifters, and/or dam(s) at the kiln end(s). They are classified into two main heating modes: either directly heated or indirectly heated, depending on the heating source location with respect to the solid material. They usually require very little labor to operate.Heat transfer in rotary kilns is very complex and may involve the exchange of energy via all the fundamental physical transfer mechanisms that are, conduction, convection, and radiation. There has been a significant amount of studies dealing with this subject in the literature. Although many researchers studied the main phenomena occurring in the kiln, the heat transfer between the wall and particles is not yet well understood. Therefore, this study aimed at determining the wall-to-solids heat transfer coefficient. The effects of various operational parameters such as the filling degree, the rotational speed, lifters profile as well as the temperature set point at the outer wall on the mentioned heat transfer coefficient are also analyzed in this study.A series of experiments were carried out on a pilot scale rotary kiln at atmospheric pressure, whether or not equipped with lifters and fitted with dam at the outlet end. The experimental rotary kiln is externally heated by electrical resistance and equipped with thermocouples positioned at five cross-sections, in and outside along the kiln tube. These experiments aimed at recording the heating up of the wall, gas and solid particles after turning on the heating system until temperatures are stabilized; the afore-mentioned coefficient was determined from the temperature profiles measurements data for low and medium wall temperature set point. The bulk materials used was quartz sand (average size 0.55 mm) with a narrow distributed size fraction. Furthermore, two shapes of lifters were compared to determine the influence of lifter and their geometry: straight lifters (SL) and rectangular lifters (RL). The other operational parameters mentioned were also varied so that a matrix of about 60 experiments (without including repeatability tests) was achieved. The solids temperature fluctuations after the start of the heating system can be considered as response of a first-order system, therefore characterized by a time constant. Results show that the time constant decrease with the temperature set point at the outer wall and the filling degree, but increase in presence of lifters. However for the two types of lifters used, the time constant remains of the same order of magnitude. Calculation of the heat transfer coefficient has been done from the overall heat balance ODE, its analytical solution and the time constant. The third method of calculation give results an order of magnitude greater than the first two but follow similar tendency. The heat transfer coefficient from wall to solids seems to decrease in presence of lifters and increase with the filling degree. The heat transfer coefficient also increases with the temperature set point at the outer wall as well as the rotational speed (for a constant filling degree).

International audience; Experiments on the residence time distribution (RTD) and axial dispersion for the continuous flow of sand and broken rice, through a pilot scale rotary kiln at room temperature and equipped with lifters, are reported. Factors such as the rotational speed, the kiln slope, the materials flow rate and the exit dam height have been studied. Furthermore, two profiles of lifters were used: straight lifters (SL) and rectangular lifters (RL). Thus, under varying conditions the RTDs were obtained by the typical stimulus response test using a tracer and the corresponding axial dispersion coefficients were determined. The validity of the axial dispersion model was assessed in this study, and the model was found to match well with the experimental data. A large number of experiments was conducted, so that, a correlation could be developed to predict the axial dispersion coefficient of the solid particles within the kiln. Comparisons with reported models are also discussed. The second part of this study will be concerned with the experimental kiln hold-up and the mean residence time (MRT) of solid particles.

International audience; Experiments were carried out on a pilot scale rotary kiln equipped with lifters at room temperature to investigate the effects of the kiln slope, rotational speed, mass flow rate of materials, and exit dam height on the hold-up and the mean residence time (MRT). The MRT was determined from the residence time distribution measurements as detailed in Part I of this work. Two granular solids having different properties were used: sand and broken rice. Furthermore, two shapes of lifters were compared to determine the influence of lifter geometry: straight lifters (SL) and rectangular lifters (RL). A new model to predict the MRT was established by means of a dimensional analysis. The correlation not only gave good agreement with the experimental data from the present study, but also demonstrated good predictive performances when applied to published experimental data of other kilns; the model is applicable for inclined kilns that process materials in cascading (tumbling) motion, whether or not equipped with lifters or fitted with dams at the outlet end.

International audience; The axial and transverse solid distribution of a cohesive powder in flighted rotary kilns was calculated from an original method based on the lifter discharge law previously determined, geometrical calculations and supplementary measurements (in particular the fall velocity of the powder at high temperature). At a given axial position, the quantity of powder falling through the gas, the total quantity of flighted powder as well as the quantity remaining in the bulk are thus calculated; the axial bed depth profile is obtained from the Saeman-Kramers-Afacan model.

International audience; Rotary kilns are widely used in several branches of the chemical industry. In order to control the temperature of the solid and the gas flowing through the kiln, it is important to understand the heat exchange phenomena that occur. The design and construction of a novel experimental device to study heat exchange in rotary kilns is described. The device, which comprises a rotary kiln equipped with an external electrical heating system, enables the study of the influence of various parameters such as the solid flow rate, the kiln inclination angle, the rotational speed, or the presence of lifters on heat exchange and in particular on the heat exchange coefficient between the solid and the wall. Preliminary experimental results concerning the influence of the solid flow rate and the rotational speed on the solid-to-wall heat exchange coefficient are presented.

International audience; Gravity-induced mixing of two fluids in long vertical tubes is studied experimentally as a function of the density contrast characterized by the Atwood number At (10−5 to 0.2), the fluid viscosity ν (1 to 16×10−6 m2 s−1) and the tube diameter d (2 to 44 mm). At low density contrasts, a stable counterflow is observed over a large fraction of the tube and its region of existence increases at high viscosities and small tube diameters. For larger density contrasts, the flow is either convective or turbulent and the mean concentration profile math(x,t) follows a diffusive spreading law characterized by a diffusivity D. An unexpected increase of D and of the characteristic velocity Vf of random fluid motions is observed when ν increases. This results from the coarser mixing in more viscous fluids which increases local density contrasts and buoyancy forces. Dimensionless plots of the diffusion coefficient D/ν as a function of the Reynolds number of the flow indicate a transition between two different diffusive regimes. Scaling arguments are put forward to account for the dependence of Vf and of the characteristic diffusion length in the convective-diffusive regime.

International audience; The influence of the density contrast (characterized by the Atwood number At) on gravity-induced mixing between two miscible fluids in a long vertical tube has been studied experimentally. Cross-section averaged fluid concentration profiles along the tube are measured optically: for large enough At values, they display a self-similar dependence in a broad range of times and distances and verify a diffusion law with an effective diffusivity 105 times higher than for molecular diffusion. At lower At values, this diffusive domain is limited by a sharp front moving at a velocity increasing with At. Below a threshold At value the diffusive behavior disappears.

International audience; Rotary kilns are gas-solid reactors commonly used in industry to achieve a wide array of material processing operations. Rotary kilns are used for applications such as reduction of oxide ore, pyrolysis of hazardous waste, calcining of petroleum coke, conversion of uranium fluoride into uranium dioxide for the manufacture of nuclear fuel, and so on. When operated at atmospheric pressure, they consist of a cylindrical shell that can be inclined, into which the solid charge is fed continuously at one end and discharged at the other. They can be equipped with lifting flights or lifters, and/or an exit dam at the kiln outlet end. They usually require very little labor to operate.Though the operational cost of these units is usually high, their design is often conservative due to the lack of fundamental physical understanding of both solid flow and heat transfer. The objective of this presentation is to provide a new model to predict the mean residence time, axial dispersion coefficient and hold-up of fine to coarse solid particles within the rotary kiln based on a dimensional analysis. Flow of material through a rotary kiln depends on many factors: length and diameter of the kiln, design and number of lifters distributed around the circumference, rotational speed and slope of the kiln, exit dam height at the kiln outlet end, flow rate and physical properties of the material.Experiments were carried out on two pilot-scale rotary kilns at room temperature, whether equipped or not with different kinds of lifters or fitted with a dam at the outlet end. These experiments aimed at determining the effects of most of the factors listed above on the Residence Time Distribution of solid particles. The tracer impulse-response technique was used to establish residence time distribution curves. Four granular solids having different properties were used: fine and medium sand, broken rice and beech chips. The other operational parameters were also varied, maintaining the cascading (tumbling) motion.We have already presented* the results on the smaller kiln with two types of particles. In the present study, we will show that the correlation established with these earlier results had a good predictive ability over the larger kiln with coarser particles. New results with fine particles will also be presented. These new experiments will be used for the consolidation and validation of the previous model.* Alex Stéphane Bongo Njeng, Stéphane Vitu, Marc Clausse, Jean-Louis Dirion and Marie Debacq « Modeling of Mean Residence Time of Solid Particles in Rotary Kilns » 14AIChE annual meeting, Atlanta, November 2014 [paper 374307]

International audience; Rotary kilns are gas‐solid reactors used to achieve a wide range of materials processing. They are used in operations such as mixing, heating, cooling, or reacting of coarse, free‐flowing or cohesive solids in the chemical, cement, pharmaceutical, nuclear, food, or waste process industries for example. They mainly consist of a cylindrical shell usually inclined, into which the solid charge is fed continuously at one end and discharged at the other. They can be fitted with lifters, and/or dam(s) at the kiln end(s). They are classified into two main heating modes: either direct heated or indirect heated, depending on the heating source location with respect to the solids. They are convenient reactors with intensive heat and mass transfer, capable of handling large amount of materials. Heat transfer in rotary kilns is very complex and may involve the exchange of energy via all the fundamental physical transfer mechanisms, i.e., conduction, convection, and radiation. In particular, despite several studies on this field, the heat transfer between the wall and the particles is not yet fully understood, especially for flighted rotary kilns. Therefore, this study aimed at experimentally investigating the wall‐to‐solids heat transfer coefficient (whtc). An indirect heated, continuously fed pilot scale rotary kiln, that could be equipped with lifters (one‐section or two‐section) and fitted with a dam at the outlet end was used. For the longitudinal evaluation of inner (bulk bed, freeboard) and external (wall) temperatures, the equipment includes thermocouples positioned in‐and outside along the kiln tube at five sections. The solid material used was quartz sand with a narrow distributed size fraction around 0.5 mm. The whtc was determined from the heating of the bulk bed using the measure of heat supply for low and medium temperatures (100°C, 300°C and 500°C). The effects of operational parameters such as the filling degree, the rotational speed, the lifter profile and the temperature set at the wall on the heat transfer coefficient were analyzed in this study. Certain strategies and some assumptions were made on few parameters; a sensitivity analysis examines their effects on the whtc. The wall‐to‐solids heat transfer coefficient was lower in presence of lifters, and lowest for the two‐section lifters compared with the case without lifters. The whtc was also found to increase with the filling degree and the temperature set at the wall. The whtc was also influenced by the rotational speed when keeping a constant filling degree.

International audience; Rotary kilns are gas-solid reactors commonly used in industry to achieve a wide array of material processing operations. Rotary kilns are used for applications such as reduction of oxide ore, pyrolysis of hazardous waste, calcining of petroleum coke, conversion of uranium fluoride into uranium dioxide for the manufacture of nuclear fuel, and so on. When operated at atmospheric pressure, they consist of a cylindrical shell that can be inclined, into which the solid charge is fed continuously at one end and discharged at the other. They can be equipped with lifting flights or lifters, and/or exit dam at the kiln outlet end. They usually require very little labor to operate.Though operational cost of these units is usually high, their design is often conservative due to the lack of fundamental physical understanding of both solids flow and heat transfer. The objective of this presentation is to provide a new model to predict the residence time of solid particles within the rotary kiln based on a dimensional analysis. This model can be used for process control as well as for design purposes. Progress of material through a rotary kiln is affected by a number of factors, namely: length and diameter of the kiln, design and number of lifters distributed around the circumference, rotational speed, and slope of the kiln, exit dam height at the kiln outlet end, flow rate and physical properties of the material.Experiments were carried out on a pilot scale rotary kiln at room temperature, whether or not equipped with lifters or fitted with dam at the outlet end. These experiments aimed at determining the effects of most of the factors listed above on the mean residence time of solid particles; the mean residence time was determined from residence time distribution measurements data. The tracer impulse-response technique was used to establish residence time distribution curves. Two granular solids having different properties were used: sand and broken rice. Furthermore, two shapes of lifters were compared to determine the influence of lifter geometry: straight lifters (SL) and rectangular lifters (RL). The other operational parameters were also varied so that a matrix of 69 experiments (without including repeatability tests) was achieved. These experiments were used for the consolidation and validation of the presented model.The model not only gave good agreement with the experimental data from the present study, but also demonstrated good predictive performances when applied to published experimental data of other kilns, having different design, materials, and order of magnitude of the operating parameters. The excellent predictive capacity of the model compared to other semi-empirical models shows its capacity to handle a wide range of conditions and operating variables. The model is applicable for inclined kilns that process materials in cascading (tumbling) motion, whether or not equipped with lifters or fitted with dams at the outlet end.

International audience; Le concept d'opération unitaire a permis de rassembler par grandes catégories les innombrables équipements utilisés par les industries de procédés. Ces opérations unitaires sont nombreuses et il ne s'agit pas d'en donner ici une présentation exhaustive. Ce chapitre en balaie donc quelques-unes, choisies parce que particulièrement emblématiques ou bien représentatives de tel ou tel type d'opération. Ainsi sont successivement présentés : la distillation, la plus importante opération de séparation et aussi certainement la plus mature scientifiquement ; quelques opérations de séparation mécanique fluide/solide, très répandues industriellement mais encore aujourd'hui relativement empiriques ; l'agitation, comme symbole de l'importance de l'hydrodynamique (c'est-à-dire l'étude des mouvements des fluides) en génie des procédés ; les échangeurs thermiques, principaux représentants des opérations de transferts (thermiques non couplés) ; et enfin les réacteurs, qui sont au cœur des procédés et responsables de la transformation de la matière à l'échelle des molécules elles-mêmes.

International audience; Le génie des procédés, bien qu'omniprésent tout autour de nous, est pour ainsi dire inconnu du grand public. Le début de ce chapitre s'attache donc à donner quelques définitions et repères historiques à propos de cette jeune science appliquée. Les fondamentaux du génie des procédés sont ensuite présentés : en commençant par la thermodynamique, puis les transferts et enfin la cinétique chimique et la catalyse. La dernière partie du chapitre présente la démarche « système-bilans-performance » pour la conception des procédés par le biais de deux exemples simples. Un encadré présente le tout premier niveau de calcul sur les procédés, à savoir les bilans de matière.