No abstract

In computational fluid dynamics modelling of gas-solid two phase flow, drag force is one of the dominant mechanisms for interphase momentum transfer. Despite the profusion of drag models, none of the available drag functions gives accurate results in their own original form. In this work the drag correlations of Syamlal and O'Brien (Syamlal and O'Brien, Int. J. Multiphase Flow. 1988; 14(4) Hill et al. (Hill et al., J. Fluid Mech. 2001; 448:243-278) are reviewed using a multi-fluid model of FLUENT V6.3.26 (FLUENT, 2007. Fluent 6.3 User's Guide, 23.5 Eulerian Model, Fluent, Inc.) software with the resulting hydrodynamics parameters being compared with experimental data. The main contribution of this work is to propose an easy to implement and efficient method for adjustment of Di Felice drag law which is more efficient compared to the one proposed by Syamlal-O'Brien. The new method adopted in this work showed a quantitative improvement compared to the adjusted drag model of Syamlal-O'Brien. Prediction of bed expansion and pressure drop showed excellent agreement with results of experiments conducted in a Plexiglas fluidized bed. A mesh size sensitivity analysis with varied interval spacing showed that mesh interval spacing with 18 times the particle diameter and using higher order discretization methods produces acceptable results.Dans la modélisation par la dynamique des fluides par ordinateur de l'écoulement diphasique gaz-solide, la force de traînée est l'un des mécanismes dominants dans le transfert de quantité de mouvement interphase. Malgré la profusion des modéles de traînée, aucune des fonctions de traînée disponibles ne donnent de résultats précis dans leur forme originale. (FLUENT, 2007. Fluent 6.3 User's Guide, 23.5 Eulerian Model, Fluent, Inc.), les paramétres hydrodynamiques résultantsétant comparés aux données expérimentales. La principale contribution de ce travail est de proposer une méthode efficace et facileá mettre en oeuvre pour l'ajustement de la loi de traînée de Di Felice qui est plus efficace comparativementá celle proposée par Syamlal-O'Brien. La nouvelle méthode adoptée dans ce travail montre une amélioration quantitative par rapport au modéle de traînée ajusté de Syamlal-O'Brien. La prédiction de l'expansion de lit et de la perte de charge montre un excellent accord avec les résultats des expériences menées dans un lit fluidisé en plexiglass. Une analyse de sensibilité de la taille des mailles avec des mailles de taille variable variés montre qu'une taille de mailleégaleá 18 fois le diamétre des particules et l'utilisation de méthodes de discrétisation d'ordre supérieur donnent des résultats acceptables.

The present paper is aimed at investigating the co-gasification of biomass with coal and oil sand fluid coke. Chars were obtained from individual fuels and blends with different blend ratios of coal, oil sand coke, and biomass in a drop tube furnace at different temperatures. The chars were then gasified in a thermogravimetric analyzer (TGA) under CO 2 atmosphere to determine their reactivity. Results showed that the effect of the blending ratio of biomass to other fuels on the reactivity of the co-pyrolyzed chars is more pronounced on chars prepared at low temperatures and the effect becomes less significant as the pyrolysis temperature increases. The increased reactivity at a higher biomass blending ratio is due to the presence of synergetic effects originating from the interaction of the two fuels. Scanning electron microscopy images showed differences in shapes and particle size distribution of char particles from biomass and coal/coke. These also showed the agglomeration of coal and coke chars with biomass char particles at high temperatures. The agglomeration may be the reason for the non-additive behavior of the blends. The chars were also analyzed for the particle size distribution using a laser diffraction Mastersizer instrument and surface area with the Brunauer-Emmett-Teller (BET) technique. BET analysis showed an increase in the surface area with an increasing temperature from 700 to 1400°C for biomass and coal, but the trend for coke was inversely related to the temperature.

Co-gasification of oil sand fluid coke with sub-bituminous coal was performed in an entrained-flow gasifier. The underlying objective of this work was to assess the combined effects of the operating variables (i.e., temperature and oxygen and steam concentrations) and coal/coke blending ratio in an entrained-flow gasification process, where the focus was to quantify the relationships between the response variables and vital operating factors. With a view to the shortcomings of the classical "onefactor-at-a-time" method in identification of the effect of experimental factors and their interactions, a statistical design of the experiment based on response surface methodology (RSM) was used. The response variables used in this work were H 2 , CO, H 2 /CO ratio, gasification efficiency, and carbon conversion. Experiments were conducted over a temperature range of 1000À1400°C, using steam and oxygen to carbon weight ratios of 0.9À4.3 and 0À0.4, respectively, equivalent to 15À50 vol % steam and 0À3 vol % oxygen in N 2 carrier gas. All of the response variables were successfully fitted to either a two-factor interaction or quadratic model. Using RSM, the effects of individual operating factors and their interactions were categorically determined, which were not otherwise possible by the classical design of experiment methodology. Using the resultant response variable correlations, H 2 production was optimized as a function of the temperature, steam and oxygen concentration, and different blending ratios. The full potentiality of Canadian oil sand coke for entrained-flow gasification was successfully investigated via RSM. The results of this work, however, are only applicable to entrained-flow gasification systems.

In the computational fluid dynamics modeling of gas-solid two phase flow, drag force is one of the dominant mechanisms for interphase momentum transfer. Despite the profusion of drag models, an extensive comparison is missing from the literature. In this work the drag correlations of Syamlal-O'Brien, Gidaspow, Wen-Yu, Arastoopour, Gibilaro, Di Felice, Zhang-Reese and Koch et al. are reviewed using a multifluid model of FLUENT software with the resulting hydrodynamics parameters being compared with experimental data. Also adjustment of drag models based on minimum fluidization was studied. A new method adopted to adjust the drag function of Di Felice showed a quantitative improvement compared to the adjusted drag model of Syamlal-O'Brien. Prediction of bed expansion and pressure drop showed excellent agreement with results of experiments conducted in a Plexiglas fluidized bed. A mesh size sensitivity analysis with varied interval spacing showed that mesh interval spacing with 18 times the particle diameter and using higher order discretization methods produces acceptable results.