D Newton

Fine particle effects in a fluidized-bed reactor

Abstract Recent experimental work has shown that when the concentration of fine particles (45 μm) in a fluidized bed is increased the gas flow pattern within the bed is altered, more gas being caused to flow through the emulsion phase and less through the bubble phase. In the case of a catalytic reaction system this effect should result in an increase in conversion for a given throughput of reactant and the work described here was carried out to test this hypothesis. Experimental results are presented for the catalytic oxidative dehydrogenation of butene-1 in fluidized beds of catalyst containing 0, 16 and 27% fines and it is shown that conversion does in fact increase with increasing fines content. The system can be modelled on the basis of emulsion-phase gas flows that are in excess of the minimum fluidization flow, agreement between model predictions and experimental results being quite satisfactory.

High temperature effects on the dense phase properties of gas fluidized beds

Abstract This paper reports some of the results obtained from an extensive experimental campaign aimed to study the influence of temperature on the fluidization behaviour of solid materials. The fluidization behaviour of a wide range of materials was investigated from ambient conditions up to 650°C. The aim of this work was to highlight the conditions under which the role of the hydrodynamic forces (HDFs) or interparticle forces (IPFs) were dominant, in order to make predictable the fluidization behaviour at elevated temperatures. To this end, the fluidization behaviour of three fresh FCC catalysts was studied. An E-cat FCC catalyst, which contained process residuals, was examined without performing pre-treatments prior to fluidization tests. Furthermore, a highly porous silica catalyst was doped with increasing amount of potassium acetate (KOAc), 1.7, 7 and 10 wt.%, and a sample of glass ballotini was doped with 0.1 wt.% of KOAc. This was done in the attempt of modifying their surface characteristics, thus triggering changes in their fluidization behaviour with increasing temperature. The measured pressure drop across the bed and deaeration tests was used to highlight changes in the fluidization behaviour as a function of temperature. The standardized collapse time (SCT) was obtained from the collapse profiles and was used to distinguish between systems of powders dominated by HDFs and IPFs. Results obtained from analytical techniques such as thermomechanical analysis (TMA), Gas Chromatography Mass Spectrometry analysis (GCMS) and scanning electron microscope (SEM) are also discussed, these techniques were used to investigate physical changes in the particles with increasing temperature.

A generalization of the Foscolo and Gibilaro particle-bed model to predict the fluid bed stability of some fresh FCC catalysts at elevated temperatures

Abstract The fluid-bed stability of three fresh FCC catalysts has been investigated both experimentally and theoretically as a function of increasing temperature. Values of the voidage at minimum bubbling conditions were obtained from 20°C up to 650°C, and compared with predictions given by the Foscolo and Gibilaro particle bed model. The formulation of the drag force proposed by Foscolo and Gibilaro has been generalized in order to correctly describe the homogeneous expansion of the three FCC catalysts. Consequently, the procedure followed to obtain the Foscolo and Gibilaro stability criterion has been re-examined, and a generalized expression of their criterion is proposed. Predictions obtained from the generalized particle-bed model were found in agreement with experimental data. This paper discusses also the effect of the drag and buoyancy force in predicting correct trends for e mb . To this end, results obtained using the Jean and Fan model are reported. The physical origin of the stability of these catalysts is also discussed, and the role of the hydrodynamic forces and interparticle forces is examined.