Hydrodynamics and Mass Transfer in Bubble and Three-phase Fluidized Columns with and Without Baffles PDF Download
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Author: Alain B. P. Catros
Publisher:
ISBN:
Category : Fluidization
Languages : en
Pages : 1110
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Author: Alain B. P. Catros
Publisher:
ISBN:
Category : Fluidization
Languages : en
Pages : 1110
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Author: Subrata Kumar Majumder
Publisher: CRC Press
ISBN: 1351249843
Category : Science
Languages : en
Pages : 168
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Book Description
Slurry bubble column reactors are intensively used as a multiphase reactor in the chemical, biochemical, and petrochemical industries for carrying out reactions and mass transfer operations in which a gas, made up of one or several reactive components, comes into contact or reacts with a liquid. This volume describes the hydrodynamics of three-phase gas-liquid-solid flow in a downflow slurry bubble column. The efficiency of the downflow gas interacting system is characterized by the self-entrainment of secondary gas. The book covers the gas entrainment phenomena, gas holdup characteristics, pressure drop, gasliquid mixing characteristics, bubble size distribution, interfacial phenomena, and the mass transfer phenomena in the downflow slurry system. This volume will be useful in chemical and biochemical industries and in industrial research and development sectors, as well as in advanced education courses in this area. The book will be helpful for further understanding the multiphase behavior in gas interacting multiphase systems for research and development. The hydrodynamic and mass transfer characteristics discussed will be useful in the design and installation of the modified slurry bubble column in industry for specific applications.
Author: Onkar N. Manjrekar
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 101
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Bubble columns and slurry bubble columns are multiphase reactors used for a wide range of applications in the biochemical, chemical, petrochemical, and metallurgical industries. In spite of their widespread usage, the scale-up of bubble columns remains an ongoing challenge. Various scale-up approaches, based on concepts ranging from ideal mixing to complex 3-D multiphase CFD models, have been used for assessing the effect of column size and gas and liquid flow rates on column hydrodynamics and reactor performance. Among these approaches, phenomenological models based on either single-class or multi-class bubbles that were validated on cold flow systems have been successful in predicting the residence time distributions of gas and liquid in pilot-scale bubble columns (Chen et al., 2004) (Gupta, 2002). However, such models are not entirely predictive, since they are validated using columns having the same size as hot operating units. To provide better predictive capability, we need prior knowledge of local hold-up, transport coefficients, and bubble dynamics. This dissertation provides an improved understanding of the key design parameters (gas hold-up, volumetric mass transfer coefficients, gas-liquid interfacial area, and their spatial distribution) for predictive scale-up of bubble columns. In this work, a 4-point optical probe is used to estimate local gas hold-up and bubble dynamics (specific interfacial area, frequency, bubble velocity, and bubble chord-lengths) and their radial profiles in a cold-flow slurry bubble column and a bubble column photo-bioreactor. Along with local bubble dynamics, the effect of superficial gas velocity on volumetric mass transport coefficients in several sizes of bubble columns, with and without internals, and in slurry bubble columns and photo-bioreactors are studied. Key findings: In the bubbly flow regime, bubble dynamics in photo-bioreactors with suspended algae were dominated by the physicochemical properties of the liquid, as distinguished from the churn-turbulent flow regime in the slurry bubble columns, where bubble dynamics were mainly affected by turbulent intensities. In the bubbly-flow regime, volumetric mass transfer coefficients increased with an increase in superficial gas velocity. However, in the churn-turbulent flow regime, they approached a constant value with an increase in the superficial gas velocity. A new methodology was proposed to identify the flow regime from optical probe signals based on the support vector machine algorithm, which can uniquely classify flow regimes for various systems on a single flow regime map. A new model for the liquid phase mixing, that with a proper choice of the mass transfer coefficients enables a good match of the predicted and measured tracer response is described. This model provides a better prediction of volumetric mass transfer coefficients than the currently used well mixed model for the liquid phase (CSTR). The dissertation improves the fundamental understanding of the connection between bubble dynamics and mass transfer. Using the 4-point optical probe as a tool, it demonstrates a connection between bubble dynamics and volumetric mass transfer coefficients. Present work addresses the need of industries to have a method that can be used as an online process control tool to identify flow regime, this method has been tested at cold flow conditions and needs to be implemented at hot flow conditions. The parameters (radial distributions of gas hold-up, bubble velocities, and volumetric mass transfer coefficient) that are evaluated in the present work can be used to validate phenomenological models and CFD results at cold flow conditions, which can later be combined with process chemistry to accomplish scale-up (Chen et al., 2004). The open literature on multiphase reactors is mainly limited to cold flow condition, and techniques such as the optical probe need to be extended to hot flow conditions. The optical probe described here can withstand high temperature and pressure, but for hot flow conditions it requires a better binding agent to hold the probe tips together, one that will not dissolve in industrial solvents.
Author: Wai Man R. Lau
Publisher:
ISBN:
Category : Fluidization
Languages : en
Pages :
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Abstract: Slurry bubble columns and gas-solid fluidized bed reactors are some of the most commonly used industrial processes. Considerable interests have been recognized in the field of physical, chemical, petrochemical, electrochemical, and biochemical operations (Fan, 1989). In these reactor systems, large axial dispersion of phases and high flow patterns can be achieved by the excellent macromixing characteristics. It also provides excellent heat and mass transfer without the aid of external mechanisms and relatively easy operation. Despite the advantages of operations, the transport behavior in these systems is very complex and a comprehensive knowledge of the hydrodynamics, heat and mass transfer and mixing are required for successful application of these systems. Some aspects of the fundamental characteristics of evaporative liquid jets in gas-liquid-solid flows are studied and some pertinent literature is reviewed. It is found that the injection of an evaporative liquid jet decreases the minimum fluidization velocity at a high pressure due to the additional gas flow generated from liquid evaporation. Fluidizing gas velocities have no significant effect on the jet penetration length in a dense phase fluidized bed while it reduces the radial dispersed distance of the evaporative liquid. The tomographic images of liquid nitrogen injection in a dense phase fluidized bed indicate a distribution of reduced bubble sizes compared to a dry bed. The hydrodynamics, gas-liquid mass transfer properties and liquid entrainment phenomena in a high pressure and high temperature bubble column is investigated. Effects of pressure on hydrodynamics and mass transfer properties are mainly through the change in gas and liquid physical properties, which in turn changes the bubble dynamics that govern the transport phenomena. Experimental results show that liquid velocities have a direct influence on kl while other factors have a dominant effect on the interfacial area over kl. Liquid entrainment in bubble columns is controlled by the droplet formation during bubble bursting at interface. Effect of pressure on liquid entrainment is to due to the higher drag force exerted on the liquid droplet with higher gas density and the formation of smaller droplet by the smaller bubbles at high pressure.
Author: Vinodkumar R. Dhanuka
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Manuel Alvarez-Cuenca
Publisher:
ISBN:
Category : Bubbles
Languages : en
Pages : 1194
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Houman Shirzadi
Publisher:
ISBN: 9783844009460
Category :
Languages : en
Pages : 104
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Author:
Publisher:
ISBN:
Category : Dissertation abstracts
Languages : en
Pages : 696
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Author: Anand Prakash
Publisher:
ISBN:
Category : Fluidization
Languages : en
Pages : 590
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