STUDY OF HYDRODYNAMICS AND MIXING CHARACTERISTICS IN COCURRENT BUBBLE COLUMN.

摘要

Bubble columns have many important industrial applications, however their scale-up and design is difficult because of the complexity of the flow pattern characteristics. The aim of these experiments is to study the hydrodynamic and backmixing characteristics in a multiphase bubble column, and point out the usefulness of these characteristics in designing bubble column reactors for industrially important reactions which include coal liquefaction, Fischer-Tropsch synthesis and fermentation. The experiments are carred out in a .154 m (6") diameter, 3.35 m (11') tall, cocurrent continuous bubble column. The hydrodynamic characteristics are studied by measuring phase holdups using a hydrostatic head technique coupled with a gravimetric analysis. The backmixing characteristics are studied by measuring an axial dispersion coefficient using a dispersion model. A steady state method is employed using heat as a tracer for measuring the dispersion coefficient.; The effects of wide range of physical parameters such as gas and liquid velocities, surface tension, electrolyte solutions, solids size, density and concentration, are studied. Gas velocity is varied from .02 m/s to .25 m/s, while the liquid or slurry velocity is varied from .03 m/s to .1 m/s. Surface tension is varied from 40 to 73 dynes/cm, using dilute alcohol and surfactant solutions. Two different solids having densities of 1006 kg/m('3) (polystyrene beads) and 2300 kg/m('3) (oil shale particles) are utilized, having size range of 40 to 300 (mu)m. The solids concentration was varied from 5 to 15 wt%.; The data obtained can be divided into three main categories. Firstly, data for dilute alcohol solutions, that fairly simulate the behavior of liquid phase media in bioreactors, while the data in the presence of solids are helpful in designing coal liquefaction and Fischer-Tropsch synthesis reactors. The data collected in the presence of electrolyte solutions highlights the effect of non-coalescing media on hydrodynamic and backmixing characteristics. All the data are qualitatively and sometimes quantitatively explained using the available hydrodynamic and mixing models, and are compared with literature correlations. New empirical correlations for gas holdup and axial dispersion coefficients, for dilute alcohol and electrolyte solutions are developed to fill the void in the literature.