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Advisor(s)
Abstract(s)
This paper presents a comparative scaling analysis of two different sized pilot-scale fluidized bed reactors
operating with biomass substrates. A multiphase Eulerian-Eulerian 2-D mathematical model was
implemented, coupled with in-house user-defined functions (UDF) built to enhance hydrodynamics and
heat transfer phenomena. The model validation was attained by comparison to experimental data
gathered from both reactors. A grid refinement study was carried out for both geometries to achieve an
appropriate computational domain. Hydrodynamics was deeply studied for both reactors concerning the
scale-up effect. Mixing and segregation phenomena, solid particle distribution and biomass velocity were
matters of great concern. Results showed that UDF implementation successfully minimized deviations
and increased the model’s predictability. The largest deviations measured between experimental and
numerical results for syngas composition were of about 20%. Solids mixing and segregation was found to
be directly affected by the particles size, density, and superficial gas velocity, with the larger reactor
revealing improved mixing ability. Improved mixing occurred for smaller particles size ratio (dbiomass
¼ 3 mm), smaller particles density ratio (rbiomass ¼ 950 kg/m3), and higher dimensionless superficial
gas velocities (U0=Umf¼3.5). The larger unit showed an increase in near-wall velocity, lateral dispersion,
and bubble size. As for the smaller reactor, higher velocities were obtained at the center region due to a
more pronounced wall boundary layer. Similarities were found between the two reactors regarding the
bubble distribution, dimensionless average bed pressure drop and biomass velocity vector profiles when
dimensionless parameters were employed.
Description
Keywords
Hydrodynamics Scale-up Pilot-scale bubbling fluidized bed gasifier Biomass gasification Mixing and segregation index ANSYS FLUENT