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International audience; The aim of the present work is to simulate the segregation and interaction between the two kinds of particles involved. Thesimulation 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 therange 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 thefragmentation of the wood particles.

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)

International audience; The thermochemical conversion of lignocellulosic biomass is still difficult to understand and model, whereas there is anindustrial need for process simulation in order to conceive new plants. Accurate models are needed to predict productcomposition, that are often complex. In this communication, biomass gasification modeling in bubbling fluidized bed is presented. This model has been developed on the basis of literature data, but also through the studies of bed segregation and tar gas-phase conversion, two phenomena that are not yet well understood. Bed segregation has been characterized in a cold fluidized bed with olivine sand and different wood particles (Ref 1). Tar gas-phase conversion has been modeled with detailed radical kinetic model under Chemkin Pro® and the results have been treated to get a lumped kinetic model. Finally, the whole gasifier model has been solved numerically through the combination of two softwares: Matlab® and Aspen Plus®. The simulated gas composition profiles are compared with experimental data obtained thanks to a new fluidized bed pilot. It will be also shown how this type of reactor model can be used under Aspen Plus® to simulate a whole gasification process. This type of process simulation allows to build accurate mass & energy balances (Ref 2), that could be used in technicoeconomic and/or LCA studies (Ref 3).

International audience; Lignocellulosic biomass (wood, straw, energy crops) may be converted efficiently into electricity through syngas production and combustion in a gas engine. One of the best reactor to gasify biomass at the 1-10 MW scale is the air-blown autothermal fluidized bed, but this technology is still suffering from two main technical problems: the tar content of the syngas that may cause fouling and the risk of bed agglomeration / defluidization. To understand these phenomena and find technical solutions, it is important to conduct accurate observations on a gasifier pilot. In this communication, we report the technical features of a new 5 kg/h air-blown fluidised bed pilot plant. Experiments have been achieved with dry pellets of the perennial crop Miscanthus x Giganteus at low equivalence ratio (0.2 to 0.4), high bed temperature (800 to 900°C) and high gas velocity (5 to 10 Umf). Gas composition at the exit of the bed is given in terms of N2, H2, CO, CO2, CH4, C2 & C3 hydrocarbons, BTX and GC-FID-MS measurable tar compounds. These results are compared with similar studies (Michel et al., 2008; Xue et al, 2014). Gas composition profiles along the fluidized bed height are also detailed, as well as final bed composition profiles. Each 50mm-thick layer of the bed contains various proportion of olivine, char and agglomerates of olivine and ashes. A specific sampling device has been used to collect 10 g of bed at specific position every 15 minutes under hot operating conditions in order to follow the agglomerates build-up in real-time.

International audience; The Chemical Looping Combustion (CLC) is an oxy-combustion carbon dioxide capture process using an oxygen carrier(NiO/NiAl2O4 in this study). The combustion is realized in two steps : The first one is the combustion of methane with nickeloxide (called reduction step), the second one is the regeneration (reoxydation) of the reduced nickel with air (oxidation step).The CLC process is based on this cycle of oxidation/reduction of the oxygen carrier. In order to have a better understanding of the phenomena occurring during the two steps and a better design of the oxygen carriers, the determination of the reaction kinetics during each step of the process is needed. For this purpose, some experiments and a model of a continuous perfectly auto-stirred tank reactor (CASTR) have been done and kinetic laws have been developed. In order to validate those kinetic laws, experiments in a fixed bed reactor and its modelling are also performed. The comparison of the predicted and the experimental results confirm the validity of the developed model.Details about the kinetic laws proposedThe reactions observed in both reduction and oxidation steps of the process have been studied. The Grainy Pellet Model, using the Shrinking Core Model for reactions occurring inside the grains, were used to represent the gas-solid reactions. For example, the rate of combustion r1 of methane with nickel oxide is given by the flowing equation (1). This equation depends on the internal diffusion of gas species in a grain (De,int), the grain properties (external radius Rg and interfacial radius between Ni and NiO in a grain rg) and the tablet porosity εt.The catalytic gas-gas reactions are described by typical Langmuir-Hinshelwood laws. For example, the rate of cracking ofmethane catalysed by reduced nickel is described by equation (2). With Kj the adsorption constant of gaseous component jand Pj its partial pressure.A deactivation law, due to deposited carbon at the surface of the grains, is also taken into account. The kinetic laws weredeveloped in a CASTR and will be validated in a fixed bed reactor.ConclusionExperiments have illustrated the influences of operating conditions on the efficiency of the CLC process (quantity of deposited carbon, conversion of methane, …) and very good agreements are obtained between experimental and simulated results, for CASTR and fixed bed reactors. The details of kinetics and adsorption parameters used in this study will be given

International audience; Social Context Lignocellulosic biomass is a promising renewable resource that presents an alternative to fossil fuels and therefore leads us to achieve desirable environmental outcomes. That is why, in 2010, ADEME financed the GAYA project in France, which is coordinated by GDF-Suez with the goal of setting up a decentralized industrial facility for biomass gasification and methanation. Objectives The objective of this work is to contribute directly to the GAYA project database by studying the pyrolysis behavior of a wide range of biomass under the conditions of an industrial gasifier. More specifically, the aim is to determine the influence of the biomass nature on char yield. This variable will take an important role in the double-gasifier functioning and dimensioning. In order to accomplish this purpose, an experimental apparatus was designed to reproduce fluidized bed gasifier heating conditions: the Image Furnace. This setup was used to study the fast pyrolysis of 54 biomasses at a maximum temperature of 850ºC and specifically determine the yield of char, which is an important parameter for GAYA project's dual fluidized bed technology.

International audience; The process of Chemical Looping Combustion necessitates the use of two reactors. In the first one, called “fuelreactor”, the reaction of combustion of methane with an oxygen carrier takes place (reduction step of the oxygencarrier), then, the oxygen carrier is re-oxidised with air in the second reactor called “oxidation reactor” (oxidation step). Diminution of the oxygen carrier performances after some cycles of reduction and oxidation are observed. The main objective of this study is to understand the phenomena leading to a decrease of the process performances. For this purpose, some experiments and modelling of fixed bed reactor have been performed to determine the relation between oxygen carrier structure changes (variation of porosity, chemical composition, structural organisation,…) and process performances decrease (variation of methane conversion and oxygen carrier regeneration rate, …). In order to qualify the variation of physical properties of the oxygen carrier material, analysis like X-ray diffraction, BET surface measurements and scanning electron microscopy (SEM) observations, are done to bring out the variation of structure of oxygen carrier particles. The model of the used fixed bed is modified to take into account all the phenomena observed. Several points will be presented concerning the degradation of the oxygen carrier particles:- even in case of fixed bed reactor (avoiding high friction between particles), the shape of the oxygen carrier grains mayvaries after several cycles of oxidation/reduction of the material. BET analysis will be done to quantify the impact of thosemodifications on the reacting surface of each grain,- X-ray diffraction analyses will show the evolution of the proportion of NiO, Ni and NiAl2O4 in the oxygen carrier grains. Theanalysis of the X-ray signals should indicate that there are some structural modifications of the oxygen carrier.- after the reoxidation of the oxygen carrier, the grains are stuck to each other and form aggregates, measurements will bedone to determine if these aggregates impact the diffusion of gas species through the grains,- a complete analysis of the impact of experimental conditions on the structure of the oxygen carrier will be presented,- carbon deposition has a strong impact on the performances of the oxygen carrier.ConclusionThe modification of the oxygen carrier structure and composition has an impact on its performances in the CLC process(variation of methane conversion, …). A model was developed to represent one cycle of oxidation/reduction of the oxygen carrier in a previous study. The description of the modifications of the material will be used to extend the validity of this model to several cycles. The impact of different experimental conditions on the process performances is also studied.