Solids slugging phenomena in fluidized bed reactors are not well understood, primarily due to difficulties associated with such phenomena. Furthermore, knowledge of dispersion and mass transfer coefficients is essential in designing fluidized bed reactors. These coefficients vary by several orders of magnitude. In this study, solids slugging phenomena, and dispersion and mass transfer coefficients were measured and computed for three Geldart groups, in three fluidized beds, using computational fluid dynamics (CFD) codes.
The solids slugging phenomena were examined in a symmetric Illinois Institute of Technology (IIT) riser for 1100 µm particles, at high velocity-high solids fluxes, using gamma ray densitometers. The measurements and computation using 2-D kinetic theory based IIT CFD code confirmed elimination of undesirable core-annular regime.
The solids slugging for 1100 µm particles was not present for extremely low solids fluxes. Particle image velocimetry (PIV) technique was used to measure laminar and turbulent properties for solids, including dispersion coefficients, non-invasively near the wall. This study was the first known measurement of solids dispersion coefficients in axial and radial directions using PIV techniques. The measured and computed total granular temperatures, and solids and gas dispersion coefficients, agreed with the literature.
PIV system was also used to measure laminar and turbulent properties for 750 µm high density polyethylene particles, non-invasively in the Department of Energy National Energy Technology Laboratory riser. Total granular temperatures agreed with the literature. However, solids dispersion coefficients were lower than the radially averaged literature values.
The PIV experiments were also performed non-invasively in free board region of the IIT 2-D circulating fluidized bed of 75 µm fluid catalytic cracking (FCC) particles. Solids dispersion coefficients were lower than the literature due to low particle velocities in free board. However, total granular temperatures were close to the literature.
Mass transfer coefficients and Sherwood numbers for catalyzed FCC particles were measured and computed in a 2-D bubbling fluidized bed, considering ozone decomposition. The measured and computed Sherwood numbers, using 3-D and 2-D CFD simulations with FLUENT, were of the order of 10−6−10 −2. The low Sherwood numbers were in agreement with the literature data for small particles, at low Reynolds numbers. CFD simulations showed that it is possible to compute conversions in fluidized bed reactors without using the conventional model with empirical mass transfer coefficients. This study showed the capabilities of the kinetic theory based CFD codes to successfully compute gas and solids dispersion coefficients in fluidized bed reactors.
|School:||Illinois Institute of Technology|
|School Location:||United States -- Illinois|
|Source:||DAI-B 73/08(E), Dissertation Abstracts International|
|Subjects:||Chemical engineering, Petroleum engineering|
|Keywords:||Dispersion coefficients, Fluidized beds, Granular flows, Mass transfer, Slugging|
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