SIMULATION OF BIOMASS GASIFICATION IN A FLUIDIZED BED REACTOR USING CFD

Abstract

Biomass gasification in bubbling fluidized beds (BFB) 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 BFB 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 BFB 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 BFB biomass gasifier were studied in this thesis work systematically using, computational fluid dynamics (CFD) software FLUENT. This study highlights the model development for hydrodynamic study and the effect of particle size to the solid fluidization in fluidized bed gasifier using Eulerian-Eulerian multiphase model coupled with kinetic granular theory in CFD software, Ansys Fluent v6.3. The result obtained. has been compared with literature data and proven that the model is capable of accurately model the hydrodynamic of fluidized bed gasifier. Different particle size will give different hydrodynamic flow in the gasifier and particle size in range of 250-300 .tm is observed to give the best solid fluidization behavior in the gasifier. In the second part of study was performed in order to model mechanics in the riser of a bubbling fluidized bed (BFB). the effect of using different inter phase drag function on model predication were evaluated and compared the results showed that the drag model of Gidaspow and Syamlal and O'Brien overestimated the drag force for particle and predicted a greater bed expansion in comparison to the EMMS drag model. In the last part presented a gasification model and results which have been run to a statistically steady state. The results compare some main components and temperature at the outlet of the reactor with experimental data from a lab scale fluidized bed reactor