I need to select pressure sensors for a laboratory system where I fluidize particles from 1 to 10 mm in diameter and 1 to 2 g / cm3 in density. The fluidised bed is narrow and shallow. What are the expected drops of pressure across the distributor?
Dear Stanisław Anweiler,
In fluidization process, many factors that can be determine the amount of pressure drop across gas distributor depending on the hydrodynamics behaviour in the fluidized bed as following:
1) The number of holes in the gas distributor and their diameter (Free Area of Flow).
2) The amount of particles in the bed (Weight).
3) Um (minimum fluidization velocity).
4) The diameter of the column or bed.
5) The ratio of liquid height to the bed diameter H/D ratio (Aspect Ratio).
6) Liquid viscosity.
All these parameter are interacted and can determine the pressure drop across the gas distributor.
Best wishes
You may refer to: S. B. Reddy Karri, T. Knowlton, "Gas distributor and plenum design in fluidized beds", Ch. 6 in: Wen-Ching Yang (Ed.), "Handbook of Fluidization and Fluid-Particle Systems", 2nd ed., Marcel Dekker Inc. / Taylor & Francis, 2003.
Fluidization quality is closely related to particle intrinsic properties. The difference between fluidized bed and spouted bed lies in the dynamic behaviours of the solid particles. In a fluidized bed, air is passed through a multiorifice distributor/plate to fluidize the particles. Fluidized bed is divided mainly in two regions; bubble phase and emulsion phase as shown in Figure .
a comparative study on hydrodynamic behaviours such as minimum fluidization velocity and/spouting velocity pressure drop bed expansion ratio bed fluctuation ratio , and fluidization index for both the fluidized and spouted bed using fine particles. The experimentally observed results are analyzed and processed with the system parameters on the basis of dimensionless analysis.
The hydrodynamic behaviours of the fluidized bed or spouted bed have been studied in terms of bed pressure drop, bed expansion/fluctuation ratios and fluidization index using fine particles. The pressure drop profiles for different conditions are obtained from which the minimum fluidization/spouting velocities for fine particles are determined. A sample plot of pressure drop profile for both the processes is shown in attached Figure . It is observed that the bed pressure drop increases gradually with increase in velocity up to certain limit after which it remains constant for fluidization process. In spouting process, initially the bed pressure drop increases gradually with increase in minimum gas velocity up to certain limit. After that it increases abruptly due to bubbling and slugging, the bed is observed to fluctuate vigorously which is seen from the plot of pressure drop. Then the bed pressure drop decreases up to certain point after which it remains constant indicating stable fluidization. The peak part of the pressure drop profile due to sudden rise and fall in pressure drop values indicates the spout formation and breaking of spout respectively. From the attached Figure it is also observed that the bed pressure drop () of fine particle is about 6.5 kPa and 3.3 kPa for fluidization and spouting process, respectively. Minimum fluidization velocity (and spouting velocities are found to be 0.04 m/s and 8 m/s for fine particles, respectively, which is being validated . The fine particles are observed to have higher bed pressure drop in fluidization process than spouting process. The reason may be due to multiple orifices of small apertures used in fluidization instead of single large orifice. Again calming section in fluidized bed restricts the flow of air. That is why fluidization process needs more fluid for fluidizing fine particles than spouting process.
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