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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/2785

Title: CFD Modeling and Simulation on Hydrodynamics of CFB Biomass Gasifier using FLUENT
Authors: Beniyam, Kebede
Advisors: Dr.-Ing. Zebene Kiflie
Copyright: Jul-2011
Date Added: 8-May-2012
Abstract: Abstract Biomass gasification in Circulating fluidized beds (CFB) is one of the most promising conversion processes in meeting future ecologically compatible and sustainable energy demand, based on a combination of flexibility, efficiency, and environmental acceptability. Widespread industrial use of CFB technology in coal and biomass combustion and gasification depends on improved control of the fluidization process that demands a better understanding of fluidized bed hydrodynamics. However, its application to CFB systems is limited due to the high computational requirements for understanding complex fluid flow behavior. The effect of different operating parameters on the hydrodynamic behavior of a two-phase gas-solid CFB biomass gasifier were studied in this thesis work systematically using computational fluid dynamics (CFD) software FLUENT. Both 2-D and 3-D computational fluid dynamics (CFD) model based on Eulerian-Eulerian approach coupled with granular kinetic theory is developed to simulate the hydrodynamics and flow structures of the CFB under different operating conditions. A parametric analysis is performed to comprehensively investigate the influences of particle properties (Bagasse, sand and its sizes), operating parameters (gas velocity and solid circulation rate) and gasifier geometries (inlet structure/position). The dynamic characteristics obtained from CFD simulation have been compare ed with the some similar conditions experimental data obtained from open literatures and in general a good agreement has been observed. Eulerian-Eulerian granular multiphase flow model approach is capable of predicting the core-annulus structure in CFB. The lower region of the CFB riser is denser than the upper-dilute region. Back-mixing behavior or accumulation of particles near the wall has been perfectly exist in the CFB. Increasing solids flux slows down the flow development, but increasing superficial gas velocity makes the flow development faster. Superficial gas velocity has a strong influence on the axial solids velocity. The volume fraction of big particles is lower in the upper. This hydrodynamics model provides the powerful theoretical basis for next steps on CFB designs. This study proposes that the operating parameters (solid circulation rate and gas velocity) and solid inlet geometry may be the critical consideration in order to reduce non-uniform distribution of gas and solid in CFB gasifier.
URI: http://hdl.handle.net/123456789/2785
Appears in:Thesis - Chemical Engineering

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