Author's School

School of Engineering & Applied Science

Author's Department/Program

Energy, Environmental and Chemical Engineering

Language

English (en)

Date of Award

January 2010

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Milorad Dudukovic

Abstract

Bubble columns and slurry bubble columns, as multiphase reactors, are favored for a wide range of applications in the chemical, biochemical, petrochemical and metallurgical industries. They are considered the reactor of choice for the Fischer Tropsch synthesis, among other applications, offering an alternative energy source and providing clean liquid fuels as compared to other reactors. Most of the industrial applications of bubble column reactors require the utilization of heat exchanging tubes, the effect of which on the reactor's performance is not fully understood. This study proposes detailed investigations of selected local hydrodynamics in bubble columns with and without internal heat exchanging tubes. The main focus of this dissertation is to enhance the understanding of the phenomena associated with the local gas holdup and the bubble dynamics: specific interfacial area, frequency, velocity, and chord length) and their radial profiles via detailed experimentations by means of the four-point optical fiber probe as a measuring technique. In addition, the liquid phase mixing is investigated. The effects of the presence of cooling tubes, which are commonly used in industrial applications of bubble columns, are thoroughly investigated in columns of different diameters to assess the effect of scale. Based on the insights gained from the above, one of the main limitations in bubble columns, scale up, is to be tackled in this study. A new approach, yet simple, for designing the reactor in order to reduce the scale-up risk is developed making use of the necessary heat exchanging vertical internals in controlling the effect of scale through reactor compartmentalization leading to an optimized, yet efficient, design of large scale bubble columns. The main findings of this work can be summarized as follows: The impact of vertical internals on bubble dynamics and liquid phase mixing is assessed: Increase in gas holdup, interfacial area. Decrease in bubble size due to higher break-up rates. Enhancement in the large scale recirculation cells. Increase in the liquid phase mixing. The new scaling methodology was proposed and proven viable.

Comments

Permanent URL: http://dx.doi.org/10.7936/K7ZK5DQ2

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