Abstract:
Over the last decade CFBC (Circulating Fluidized Bed Combustion) technology has demonstrated its ability and reliability to burn a wide range of biomass fuels in large industrial utility steam generators while meeting stringent emission requirements. Coal is the predominant fuel used in these facilities. The driving force for introduction of CFBC has been the need for control of S02 and NOX emission. However, much still remains to be done to understand the CFB hydrodynamics due to the complexity of gas solid flow behaviour. Many factors including the inlet and exit configuration, particle size and distribution, velocity distribution of the gas are the important factors that determine flow behavior which in turn controls the S02 and NOx emissions. CFD (Computational Fluid Dynamics) in multiphase flow has now become an accepted and useful tool in modeling of gas-solids flow systems. Simulation was done using FLUENT 5.3, a CFD package by Fluent Inc. Sand particles and air were used as the solid and gas phases, respectively. A 2D flow was simulated for using the ASM (Algebraic Slip Mixture) model. The simulation was done using the geometrical configuration of a CFB test rig at the UTM (Universiti Teknologi Malaysia). The CFB riser column is 265 mm (width) 72 mm (depth), cross-section (rectangle), and 2.6 m height. The riser is made up of interchangeable Plexiglas columns. The results discuss the variation of velocity contours along the riser column and the effect of riser exit geometry on bed hydrodynamics in the upper region of a CFB riser column. The velocity contours along the riser height is influenced by the exit geometry. The velocity magnitude increases towards the riser exit, which in turn increases the turbulence intensity. The effect of riser inlet geometry on slip velocity is significant for about 600 mm length in the lower region of the riser column.
Page(s):
141-148
DOI:
DOI not available
Published:
Journal: Mehran University Research Journal of Engineering and Technology, Volume: 24, Issue: 2, Year: 2005