Biomass steam gasification in fluidized bed of inert or catalytic particles: Comparison between experimental results and thermodynamic equilibrium predictions

In order to improve the understanding of biomass gasification in a bed fluidized by steam, the thermochemical equilibrium of the reactive system was studied. The equilibrium results were compared to LGC experimental results, obtained by the gasification of oak and fir in a laboratory-scale fluidized bed of different catalysts: sand, alumina, and alumina impregnated with nickel. The research was completed by a study of the influence on the equilibrium of additional parameters such as the quantity of steam, the pressure or the kind of biomass. Those results of simulation may be used for evaluating the limits of actual reactors.The following conclusion may be drawn from all the results: The thermodynamic equilibrium state calculated is far away from the experimental results obtained on sand particles. The steam to biomass ratio, between 0.4 and 1 kgsteam/kgdry biomass, has a strong influence on the gas mixture composition. The temperature increase and the use of catalyst allow producing a gas mixture with a high content of hydrogen and carbon monoxide. The H2:CO ratio may reach values greater than 3. The use of catalyst allows the system to get closer from the equilibrium, especially for the nickel based catalyst

Hydrodynamic and solid residence time distribution in a circulating fluidized bed: experimental and 3D computational study

Vertical profiles of local pressure, horizontal profiles of net vertical solid mass flux, and residence time distributions (RTD) of the solid phase are experimentally assessed in the riser of a small scale cold Circulating Fluidized Bed of 9 m high having a square cross section of 1111 cm. Air (density 1.2 kg/m3, dynamic viscosity 1.8×10-5 Pa.s) and typical FCC particles (density 1400 kg/m3, mean diameter 70 mm) are used. The superficial gas velocity is kept constant at 7 m/s while the solid mass flux ranges from 46 to 133 kg/m2/s. The axial dispersion of the solid phase is found to decrease when increasing the solid mass flux. Simultaneously, 3D transient CFD simulations are performed to conclude on the usability of the eulerian-eulerian approach for the prediction of the solid phase mixing in the riser. The numerical investigation of the solid mixing is deferred until later since the near-wall region where the solid phase downflow and mixing are predominant is not well predicted in spite of well-predicted vertical profiles of pressure

Phénomènes de transferts en lits fluidisés : de l'échelle locale à l'échelle du procédé. Approches expérimentale, théorique et numérique pour le développement des procédés de conversion thermochimique de la biomasse

Ce mémoire d'Habilitation à Diriger des Recherches présente la synthèse de mes activités de recherche, d'encadrement et d'enseignement. Il couvre une période qui a commencé en 1998 et qui s'étend jusqu'en septembre 2009, durant laquelle j'ai été accueilli par les équipes du LUMEN du LEMTA, UMR 7563 ; du groupe Ecoulement Et Combustion de l'IMFT, UMR 5502 ; du département Réaction-Mélange-Séparation du LGC, UMR 5503 ; du laboratoire de Génie des Procédés de Poly-Montréal, Canada ; du département Génie Chimique de la Division Procédé de l'IFP-Lyon. Mes activités de recherche se focalisent sur l'étude des transferts en écoulements gaz-particules réactifs, appliquée au développement des procédés à lits fluidisés gaz-particules. Les outils mis en œuvre sont expérimentaux, théoriques et numériques, à la fois suivant les approches classiques du Génie des Procédés et de la Mécanique des Fluides : pilotes représentatifs de conditions industrielles, techniques expérimentales associées, modélisation corrélative monodirectionnelle, et modélisation locale. Ce mémoire est organisé en trois parties. La première retrace ma trajectoire professionnelle et liste mes activités et les valorisations scientifiques et industrielles qui en ont découlé. La deuxième présente les temps forts de mes activités de recherche, leurs contextes, leurs objectifs et les principaux résultats obtenus. La troisième est consacrée à mes perspectives de recherche, qui concernent le développement des procédés des nouvelles technologies de l'énergie dédiés à la conversion thermochimique de la biomasse en réacteur gaz-particules

Etude expérimentale et numérique d'un séparateur gaz-solide en sortie du riser d'un pilote froid de FCC

L'étape de séparation des gaz de réaction et des particules de catalyseur à la sortie de la zone réactionnelle est l'un des points critiques du procédé de craquage catalytique en lit transporté gaz-solide (Fluid Catalytic Cracking). L'objectif de cette étude est d'utiliser à terme la simulation numérique pour représenter le fonctionnement et contribuer au développement de séparateurs gaz-solide dans ce contexte industriel. L'approche retenue, la modélisation à deux fluides, est ainsi validée sur une expérimentation élémentaire gaz-solide à effet centrifuge. Ce travail est divisé en deux grandes parties. La première partie est consacrée à la conception et à l'exploitation expérimentale d'un pilote froid de FCC. Nous avons examiné les effets de la charge en solide et des pressions de sorties sur l'hydrodynamique de l'écoulement dans le riser et dans le séparateur. A l'issue de cette étude expérimentale, nous avons conclu sur l'influence notable de ces paramètres concernant la densification de la zone basse du riser, l'apparition de recirculation de solide contre les parois, la formation d'aggrégats éphémères, la diminution du micro-mélange, et les efficacités de séparation des deux phases. La deuxième partie concerne l'étude numérique de la veine d'essais. Le modèle tridimensionnel instationnaire reproduit correctement le comportement hydrodynamique du riser et du séparateur mais tend à sous-estimer la densification de la zone basse, les recirculations de solide contre les parois, et l'efficacité de séparation gazeuse. A l'issue de cette étude numérique, nous avons souligné l'influence dans le riser de la modélisation des interactions fluide-particules en zones pariétales et du couplage avec les élements externes de la veine d'essais, et l'influence, dans le séparateur, de la modélisation de la turbulence du fluid

Gas and solid behaviours during defluidisation of Geldart-A particles

Bed collapsing experiments were carried out in a cold-air transparent column 192 mm in diameter and 2 m high. Typical Fluid Catalytic Cracking (FCC) catalyst with a mean particle size of 76 μm and a density of 1400 kg/m3 was used. Both single and double-drainage protocols were tested. The local pressure drop and bed surface collapse height were acquired throughout the bed settling.Typical results were found regarding dense phase voidage of a fluidised bed and the bed surface collapse velocity. In addition, bubble fraction was calculated based on the collapse curve.Experimental results showed that windbox effect is significantly reduced compared to previous works since the volume of air within the windbox was reduced. The comparison of single/double-drainage protocols revealed a new period in the defluidisation of Geldart-A particles concerning gas compressibility. Through the temporal analysis of local pressure drop, the progress of the solid sedimentation front from bottom to top was determined, analysed and modelled

Multiscale Study of Reactive Dense Fluidized Bed for FCC Regenerator

This study deals with reactive gas particle flows like the coke combustion during the regeneration of FCC particles. In this kind of reactive flow, the global reaction rate is usually bad predicted. In a first approximation, the chemical scheme can be the reason because of the limitation of its modeling. It is usually based on macroscopic experimental results. The link between these macroscopic measurements and a local kinetics of the heterogeneous reaction occuring at the gas-particle interface is not confirmed. Results of kinetics coming from experimental measurements are used and we try to highlight the problems that appear when the same kinetics are used at different scales. In common industrial computations, coarse meshes are used to solve continuity equations. Averaged or filtered Navier-Stokes and species continuity equations have to be solved in which additional correlation terms appear because of non-linear terms in the original equations, including reaction rate correlation. Therefore a multiscale analysis is performed in order to improve the modeling of this terms. This paper, shows that the eulerian formulation of kinetics has to be improved due to the impact of the particle volume fraction on the reaction rate and the necessity to develop a subgrid model for the reaction rate due to the natural clustering that appears in gas-particle flows and non-linear additional terms appearing in filtered equations

Changes on wood powder morphology and flowability due to thermal pretreatment,

National audienceTorrefaction is a thermal pretreatment of lignocellulosic biomass before gasification. This mild form of pyrolysis, carried out at temperatures between 200 and 300 °C, changes the physical and chemical properties of the material. In particular, it improves the feedstocks homogenisation, enhances the aeration ability and makes the grinding easier. Our project deals with the study of the effects of the combined torrefaction and grinding processes on (i) the major particle behaviour: grindability, surface state, particle size, shape distribution (ii) and the major powder behaviour: bulk density, compressibility, aerability. In this article, the studied parameter is the torrefaction temperature. The characterisation of the particles and powders is performed using the following techniques: optical microscopy, Flodex® methodology and powder rheometry. The rheological behaviours of spruce torrefied at different temperatures then ground in the same apparatus (a knife mill with a sieving grid of 500 µm) are compared. It is shown that spruce torrefied at 240 °C (S240) has similar rheological properties compared to natural spruce (NS) after being ground, while the one torrefied at 300 °C exhibits a different rheological behaviour. The results are correlated to reproduce the coupled effect of the torrefaction and grinding conditions on the powder rheological behaviour

Influence of torrefaction treatment on wood powder properties

International audienceTorrefaction is a thermal pretreatment of lignocellulosic biomass before gazification. This mild form of pyrolysis, carried out at temperatures between 200 and 300 °C, changes the physical and chemical properties of the material. In particular, it improves the feedstocks homogenization, enhances the fluidization ability and makes the grinding easier. Our project deals with the study of the effects of the combined torrefaction and grinding processes on (i) the main particle behavior: anhydrous weight loss (AWL), grindability, particle size distribution (ii) and the main powder behavior: bulk densities, flowability and compressibility. The studied parameters are (i) the species of the biomass (spruce and beech) (ii) the torrefaction temperature (iii) and the sieving grid size of the used knife mill (0.12 and 0.5 mm). The characterization of the particles and powders is performed using the following techniques: optical microscope and powder rheometer. The rheological behaviours of spruce torrefied at different temperatures and ground at different grid sizes are compared. It is shown that spruce torrefied at 240 °C and ground at 0.5 mm (S240/0.5) has rheological properties not as good as S240/0.12 and S300/0.5 that seem to have similar characteristics. Finally, further experiments are necessary to obtain a better morphological and rheological particle characterization

Rheological and morphological characterization of torrefied wood biomass

International audienceBiomass flowability is a major issue in the processes dedicated to the thermochemical conversion of biomass based on technologies such as downward-moving bed reactor, dense fluidized bed reactor and entrained flow gasifier. Torrefaction is an example of process influencing powder mechanical property: researchers [1] recently proved torrefaction changes the physical and chemical properties of the material. In particular, it improves the feedstocks homogenization and makes the grinding easier. In the field of this biomass pretreatment for biofuel production, IFP Energies nouvelles and Ecole des Mines de Saint-Etienne study the effects of the combined torrefaction and grinding processes. An experimental protocol then was developed to observe (i) the major particle behavior: anhydrous weight loss (AWL), grindability, particle size and shape, surface state, (ii) and the major powder behavior: bulk density, flowability, compressibility, aerability. One parameter is studied there, the torrefaction temperature. To perform the particles and powders characterization, several techniques were used: optical microscopy, scanning electron microscopy, Flodex® methodology and powder rheometer. Samples of spruce are first torrefied at different temperatures (S240, S300) then ground with a sieving grid of 0.5 mm. From 200 to 300°C, the AWL increases from 1 to 26%. The rheological study of the biomass powders shows that flowability is significantly improved in the only case of a high torrefaction (S300). Compressibility and aerability are also increased with the level of torrefaction temperature. These results are correlated to particles morphological characterization: the powder rheological behavior is only influenced by a characteristic size parameter, such as Sauter mean diameter

Synthesis and Fluidization of Wood Powders Application to biofuel production

7th World Congress on Particle Technology: New Paradigm of Particle Science and Technology - Procedia Engineering Volume 102 - Editeur: Elsevier Procedia - ISBN: 978-1-5108-0304-6International audienceSynthesizing fuels from biomass sounds a promising path to reduce the overall green house gases emissions and replace the oil-based fuels. Among the main conversion routes, i.e. biological and thermochemical, the latter presents the advantage of being in the continuation of traditional process engineering, thus more inclined to be rapidly industrialized. Here, we investigate two key points of the process consisting in the transformation of solid wood into suitably sized particles, their transport and injection into an entrained flow gasifier and the Fischer-Tropsch conversion of the resulting syngas in liquid fuel. Because of the very large elasticity of ligno-cellulosic materials, the size reduction by grinding requires too much energy to be economically competitive. In order to increase the wood fragility, and thus decrease the energy consumption, the biomass is preliminarily torrefied (i.e. heated up to 300°C under inert atmosphere). In this section, we present new results correlating the required specific energy, the size of the grid holes used in the knife-mill, the torrefaction intensity and the resulting particle size. For two types of wood (beech for hard wood and spruce for softwood), it is evidenced that the grinding energy decreases exponentially when the particle size increases. Both the prefactor and the characteristic length linearly decrease when the torrefaction becomes more severe. The anisotropic microstructure of ligno-cellulosic materials is the cause of the elongated particles morphology. The poor flowability associated with this particle shape makes the pneumatic transport and injection problematic, which is clearly an obstacle to the industrialization of the process. Indeed, to avoid jamming, larger flow rates of inert gas must be used to convey the particles, with an increasing cost of gas separation at later stages. Here, we present new experimental results showing how flowability is modified by the particles size and shape, which in turn depend on the wood species and the torrefaction intensity. Due to its complex nature, the flowability is characterized in three configurations. The jammed-unjammed threshold is evaluated by shear tests performed on a packed bed. The dense quasistatic flowability is evaluated using a powder rheometer that measures the energy required by a rotating blade to circulate through the bed. The fluidization ability is evaluated at two different scales: in the powder rheometer in presence of an upwards air flow and in a standard fluidization column. Results show that the flowability of torrefied wood particles is very poor and very dependent on the wood species (hardwood or softwood). Due to particles interlocking, the bed is highly porous. This is evidenced by the pressure drop which is about 4 times smaller than expected by the Wu & Yen correlation for compact particles of same size. Also, this interlocking is the cause of an apparent cohesivity, which manifests itself by a channeling tendency and a minimum fluidization velocity about 5 to 10 times larger than expected by the Wu & Yen correlation. The significant difference between spruce and beech flowability is attributed to the particles morphology