Countercurrent multistage fluidized bed reactor for immobilized biocatalysts: III. Hydrodynamic aspects
In Parts I and II of this series we described the modelling, design, and operation of a multistage fluidized bed reactor (MFBR) for immobilized biocatalysts. This article deals with those aspects of the MFBR which are different from single‐stage fluidized beds which are operated in batch mode with respect to the solids. The semicontinuous transport of the particles requires perfect mixing of the particles in the reactor compartments, because particles are mainly transported from the bottom of these compartments. A large spread in the physical properties of the biocatalyst particles, especially of both size and density, may cause the particles to segregate into layers with different diameter and/or density. This affects the efficient use of the biocatalyst. The properties of the particles are dependent on the immobilization method. The suitability of different methods for possible future application in the MFBR is therefore compared. Because of segregation, successful use of a biofilm catalyst with a nonuniform thickness of the biofilm is doubtful. Experiments in a small scale reactor (± 0.1 m diameter) demonstrated that perfect particle mixing is possible using commercially available biocatalyst particles of uniform density. Co‐immobilization of the biocatalyst with glass powder in a gel is a simple and effective method of increasing gel density. High density particles allow high liquid flow rates, and thus an improved external mass transfer can be achieved.
Hydrodynamic studies of an advanced fluidized-bed bioreactor for direct coal liquefaction
Advanced bioreactors can play an important role in coal utilization and conversion. To obtain the high throughput and low inventory required for large-scale bioprocessing of coal, a new family of bioreactors is being developed. The reactors on which this study is focused are continuous columnar bioreactors, which can be operated as three-phase systems. In particular, this study is oriented toward fluidized-bed systems for direct biological interactions with fine (30–150 μm) coal particles. Illinois no. 6 bituminous coal was ball-milled and then suspended in a 0.1% aqueous solution of the surfactant (Tween 80 (polyoxyethlene), which was used to reduce particle aggregation. Experimental fluidized-bed studies were then performed, using size-screened coal fractions. Studies were performed to quantify the extent of particle segregation and to quantify particle mixing effects within the reactor. To do so, pressure drop vs time data has been recorded as a function of axial position along the bed height. To better understand this experimental data, predictive mathematical models based on fundamental principles of mass and momentum transfer have been developed. Comparisons of model predictions with experimental data are presented.
Transfert de matière par diffusion en fluidisation liquide
Resume Les auteurs proposent une methode permettant de determiner les influences respectives des variations du degre de vide et du nombre de Reynolds sur le transfert de matiere par diffusion, a partir de donnees relatives aux couches fluidisees uniquement. Ils obtiennent ainsi une relation semi-empirique qui represente les resultats experimentaux avec un ecart moyen de 4,5 pour cent. Les auteurs etablissent egalement que la dilution des particules actives par des particules inertes modifie l'intensite du transfert de matiere meme si les proprietes geometriques et physiques des deux produits sont tres voisines.