The axial segregation behavior of a binary mixture made of spherical and non-spherical particles is studied experimentally and numerically using Discrete Element Methods (DEM). Two different shape approximations are used for modeling cylindrical particles: the equivalent sphere and the multisphere approximation. The coefficients required by DEM are calibrated partly by separate experiments, partly by geometrical considerations. The main objective is to dispose of a simple procedure to characterize the friction coefficients and to evaluate the main changes imposed by shape in an axial segregated rotating tumbler. The simulations match with the experimental observations in the multisphere case, the transient behavior is caught with accuracy with both approximations.

A horizontal rotating tumbler provided with internal baffles and containing a mixture of two types of particles is investigated by discrete element method (DEM) simulations. The main objective of this study is to characterize the dynamics of a rotary kiln containing spherical steel balls and wood particles, investigating the effect of internal baffles and wood chip particle shape on segregation. The results show that the presence of baffles imposes a cyclic behavior to the solid bed and that the magnitude of this cyclic behavior depends on the solid holdup. The wood particle shape effects are analyzed considering two different approaches: a spherical approximation and a multisphere approximation. The differences between these two approaches are mitigated at relatively high velocity. This type of simulation can also serve for baffle sizing.

LORVER project: production chain of biomass for industrial purposes from former sites and materials. . Contaminated Site Management in Europe (CSME) & Sustainable Approaches to Remediation of Contaminated Land in Europe (SARCLE)

The aim of the present work is to simulate the segregation and interaction between the two kinds of particles involved. The simulation is made using the Discrete Elements Method (Ref 1) implemented in the Open Software LIGGGHTS (Ref 2). The wood chips are represented using either a multisphere approximation or a single sphere model. In both approximations, the model particles have the same volume and the same dynamic properties as the wood chips. The following differences differences between the two approximations are observed: - The transient behaviour of mixing is slower with the single sphere approximation than with the multisphere one. Differences are specially notable at low rotation speed. - The multisphere approximations shows that the orientation of the wood chips is approximately anisotropic except near the walls or the baffles - At given values of the number of steel balls and wood chips and of the rotating speed, the average porosity of the bed is smaller with the multisphere approximation than with the single sphere one. With both approximations, the final (stationary) value of the segregation index is independent of the rotating speed (in the range investigated); however, the values of this final segregation index is slightly larger with the single sphere model. This kind of simulations can be extended to the investigation of heat transfer between the two kinds of particles and to the fragmentation of the wood particles.

This poster gives an overview of current research developed at CNRS Nancy (France) on the thermochemical conversion of lignocellulosic biomass. The main studied processes are pyrolysis and gasification to produce electricity, biofuels intermediates or value-added chemicals such as aromatics. A multiscale approach is developed ranging from molecular to process scales. The studies at molecular and mesoscopic levels give insight into the mechanisms of biomass pyrolysis and are used to design reactors. Conversely, the detailed mass and energy balances of processes point out process units with low energy efficiency and/or high environmental impact and stress the improvement of reactors and the need of more fundamental knowledge. The methodology will be highlighted by examples at: 1. the molecular scale: advanced NMR studies are used for understanding primary pyrolysis of biomass. Tar are analysed by photo-ionisation mass spectrometry and tar cracking kinetics are studied. 2. the mesoscopic and particle scales: the mechanism of biomass pyrolysis are studied by in-situ rheology and H NMR. Heat and mass transfers inside biomass particles are studied by specific devices with an imposed heat flux density (W/m2) [1]. 3. the reactor scale: Fluidised bed or cyclone are designed and home built in the lab. Advanced reactor models are developed and handled hydrodynamic, transfers and chemical kinetics. 4. the process scale: Bioenergy chains are modelled under Aspen Plus [2] to provide advanced life cycle inventory: from forest growth to end products. [1] JAAP 103, 255-260, 2013. [2] Energy & Fuels 27 (12), 7398-7412, 2013.

An original gas-liquid contacting system is proposed, consisting of a pump, an orifice, a vertical tube coaxial to the orifice and an impinging plate. The pump generates a downward vertical liquid jet through the orifice situated above the gas-liquid dispersion level. The two phase jet is directed towards an impinging plate near the bottom of the tank and dispersed in the volume of the liquid. Liquid is withdrawn below the impinging plate and recycled. This reactor may be used for gas-liquid reactions (ie hydrogenations) and also to mix liquids, to disperse particles, to oxygenate waste water etc.... Performances and design rules of this equipment are proposed. Then, the results are compared to performances of bubble columns, stirred tanks, and other academic and industrial jet systems. It is shown that, at a given energy dissipation, this system yields much higher mass transfer densities than a classical stirred tank provided with a Rushton turbine. Finally some suggestions about mass transfer mechanisms and efficiency of dissipated power are given.

Energy production from renewable feedstocks that Would simultaneously solve ecological problems related to waste disposals Would be very attractive. The present work is aimed at showing that atmospheric pressure thermal cracking of waste cooking oil in the presence of steam would be a potential option, particularly when the operating conditions direct the process either toward steam cracking or toward steam reforming in order to produce specific target bioenergy vectors: hydrogen, synthesis gas, or gaseous fuel. A commercial crude waste cooking oil (VEG) was selected as feed material. Using a bench-scale continuous flow tubular stainless steel reactor, experiments were conducted to study the Final product distribution as a function of temperature, residence time of the feed material, extent of dilution, addition of a cracking initiator, and addition of a surface catalytic effect inhibitor. Several operating conditions of the VEG thermal cracking in the presence of steam were identified to meet the above-mentioned objectives. Particularly, when operating steam reforming at 800 degrees C with a very low steam-to-carbon ratio (less than 1), VEG was totally converted into synthesis gas in a hydrogen-to-carbon monoxide molar ratio close to 2 (favorable for low-temperature Fischer-Tropsch catalysis), with additional hydrogen and light-hydrocarbon (methane, ethylene, propylene) production reaching 40 and 27 mol %,respectively, Further investigations (conducted with the same equipment) confirmed the occurrence of strong reactor wall effects that led to the formation of coke deposits with catalytic activity during the VEG steam cracking and steam reforming.

Two wire mesh tomography devices and a liquid collector were used to study the influence of the gas flow rate on liquid distribution when fluids distribution on top of the reactor is ensured by a perforated plate. In opposition to most of the studies realized by other authors, conditions in which the gas has a negative impact in liquid distribution were evidenced. Indeed, the obtained results show that the influence of gas flow rate depends on the quality of the initial distribution, as the gas forces the liquid to "respect" the distribution imposed at the top of the reactor. Finally, a comparison between the two measuring techniques shows the limitations of the liquid collector and the improper conclusions to which its use could lead.

Two sets of wire mesh tomography sensors have been developed for the study of liquid maldistribution in trickle bed reactors. The technique, based on the one used by Prasser et al. [H.M. Prasser, A. Böttger, J. Zschau, A new electrode-mesh tomograph for gas–liquid flows, Flow Meas. Instrum. 9 (1998) 111–119] in bubble columns, uses two horizontal planes of wires placed at fixed bed depths to measure the presence of a conductive liquid between them. Being only slightly invasive, the conceived wire mesh tomography device allows estimation of liquid concentration over a cross-sectional area of the column with a spatial resolution of 313 pixels. Examples of wire mesh tomography measurements inside a trickle bed reactor using different liquid distributors are presented here. Results are satisfying and wire mesh tomography appears to be a promising technique for the study of liquid maldistribution in trickle beds of non-porous particles.

The drift flux concept has been used to describe and analyse some hydrodynamic parameters such as the flow regimes and the retention phases in three-phase fluidised and fixed bed reactors. The effects of the gas, liquid and solid properties and the characteristics of the apparatus (distributor quality) on the hydrodynamics have been studied. Two hydrodynamic data banks as well as experimental results have been used to study the influence of the coalescence inhibiting behaviour of liquids and to determine flow regime transitions and phase retentions. In heterogeneous regime, the ratio of the drift flux density to the superficial gas velocity tends to a limit, approximately independent on the liquid velocity in both fixed and fluidised beds. Two correlations of the drift flux have been developed by this analysis; the first of which is valid in the three-phase fluidised beds and the other in the three-phase fixed beds.

The cyclic variation of the mean residence time of the liquid phase is investigated in a trickle-bed reactor operated with a liquid feed rate modulated in a periodic square wave pattern. Experiments made using a salt tracer method are compared to a residence time model, based on the concept of continuity shock waves. The model predicts accurately the mean residence times and their cyclic variation in case of a non-zero base liquid flow rate. A particular application of the model is the adjustment of the feed cycle parameters in order to obtain a constant residence time of the liquid, no matter the moment at which it enters the bed. This particular cycle duration depends, among others, on the feed rates, but also on the bed length.

Deux systemes de tomographie a fils ont ete utilises pour etudier la maldistribution du liquide dans un reacteur a lit fixe arrose en ecoulement a co-courant descendant de gaz et de liquide (RCLFA). La technique, qui se base sur celle utilisee par Prasser et coll. (1998) dans les colonnes a bulles, utilise deux faisceaux de fils horizontaux places a une profondeur donnee pour detecter la presence d'un liquide conducteur entre eux. En occupant seulement 6,5% de la surface passante du reacteur, le systeme de tomographie a fils permet l'estimation de la retention liquide sur un plan transversal de la colonne avec une resolution spatiale de 313 pixels. Cet article presente quelques exemples de mesures faites avec ce systeme a l'interieur d'un lit fixe en utilisant differents types de distributeurs. Les resultats sont satisfaisants et font de la tomographie a fils une technique prometteuse pour l'etude de la maldistribution du liquide dans un lit fixe de particules non poreuses.

Bubble columns have been the object of much attention these last 20 years; it has become a kind of benchmarking reactor for both advanced measuring techniques and for CFD. However, the classical approaches are still of interest, and improving these reactors is still a field of research. In the present article, first some reminders on classical approaches of bubble columns and airlift reactors are presented with recent applications, then the different aspects of CFD as applied to bubble columns are presented, then highlights on some features specific to non-Newtonian fluids are given, finally some attempts to improve bubble columns are presented.

This article offers an overview of the instrumentation techniques developed for multiphase flow analysis either in gas/liquid or in gas/liquid/solid reactors. To characterise properly such reactors, experimental data have to be acquired at different space scale or time frequency. The existing multiphase flow metering techniques described give information concerning reactor hydrodynamics such as pressure, phases holdups, phases velocities, flow regime, size and shape of dispersed inclusions, axial diffusion coefficients. The measuring techniques are presented in two groups: the non-intrusive techniques that deliver global, cross-section-averaged or local data, and the intrusive probes that are dedicated to local measurements. Eventually some examples of multiphase instrumentation development are reported (trickle-bed and slurry bubble column at semi-industrial scale) in the refinery or petrochemical area.

A new diagnosis method for regime identification in bubble columns and airlift reactors based on a theoretical analysis of the auto-correlation function (ACF) of wall pressure fluctuations is proposed. It yields quantitative information, such as a characteristic time and a characteristic frequency of the two-phase flow, which are closely related to the flow structure in the prevailing regime. This method is shown to be simple, low-cost, reliable and efficient and has been applied successfully to a bubble column and an external loop airlift reactor. Experimental data on both reactors are shown to be in good agreement with theoretically predicted values. The order of magnitude of the characteristic time can be used for regime identification. Combined with an analysis of the cross-correlation function (CCF) of two signals recorded simultaneously, the method is also able to yield an estimate of the axial dimension of the flow structures. This analysis is, therefore, promising for regime identification and flow structure characterisation in industrial equipment.