Characteristics of Gas -Solid Fluidization in Tapered Beds
Advancing the chemical engineering fundamentals
Particulate Systems (T2-3P)
Keywords: tapered bed,fluidization,critical fluidization velocity,peak pressure drop
Gas solid fluidization has a wide range of industrial applications like catalytic reactions, combustion, gasification, granulation, drying etc. In a number of these applications, the feed is not of uniform size and also there could be reduction in size due to attrition and during operation. These lead to entrainment and also limitation of operating velocity. The various problems associated with fluidization operation in cylindrical beds, could be overcome adopting tapered beds because of the decrease of superficial velocity with the height of the vessel.
The fluidization characteristics are different from those of cylindrical beds and depend strongly on particle size and apex angle of the vessel. In the present work, various aspects of the fluidization phenomenon have been experimentally studied in detail with respect to the effects of particle size, angle of the tapered bed employing a wide range of parameters like particle size (270-3600µm), and density (0.86 to 4.0 g/cc), apex angles of tapered vessels (50 to 300) and static bed height (0.08 to 0.55 m).The materials used include particles of sand of different sizes, mustard, urea, magnetite and hematite.
In vessels with apex angle less than 10 degrees, there is no circulation of particles and also it is not possible to maintain stable partial fluidized bed region irrespective of particle size. However, in the case of particles greater than 450µm there is formation of slugs in the bed. For vessels with apex angle greater than 10 degrees, the circulation of particles and bubble formation along the walls are the main features of the fluidization phenomena. Accordingly, the variations in phenomena taking place as a function of apex angle and particle size are brought out clearly.
Correlations have been developed for all hydrodynamic characteristics . Correlations for some of the characteristics like minimum velocity for full fluidization, maximum velocity for defluidization and hysterisis are proposed for the first time in the literature to the best of the knowledge of the authors. Results predicted by the present correlations are also validated with additional experimental data. The correlations for fluctuation ratio, peak pressure drop and critical fluidization velocity are compared with the results predicted by the correlations available in literature. The trends of all hydrodynamic characteristics with particle characteristics, apex angle and static bed height are discussed.
Presented Monday 17, 13:30 to 15:00, in session Particulate Systems (T2-3P).
