Effect of Particle Size Distribution on Local Voidage in a Bench-Scale Conical Fluidized Bed Dryer

Abstract

The effect of particle size distribution (PSD) on local voidage has been investigated in a conical fluidized bed containing dried placebo pharmaceutical granule. For each of the five PSDs examined, the static bed height was varied between 0.12 and 0.17 m and the superficial gas velocity was varied between 0.05 and 0.75 m/s. The local voidage was measured using a twin-plane electrical capacitance tomography (ECT) system. A wide PSD containing 12 wt% solids with a 1273 diameter of 2 mm or larger resulted in two different types of gas flow: an annular gas flow up to a gas velocity of 0.50 m/s and a centrally concentrated gas flow above 0.50 m/s. The mixtures containing less coarse material exhibited a centrally concentrated gas flow surrounded by a dense phase at the walls of the bed over the entire range of gas velocities and bed heights examined. Consideration of previous work by other researchers suggests that the behavior of the wide PSD mixture is due to segregation at the lower velocities. The local voidage was sensitive to small changes in static bed height. For the wide PSD mixture at a fixed gas velocity, the gas tended to spread more uniformly over the bed crosssection as static bed height increased. The opposite was true of the other mixtures, i.e., the gas flow became more centralized with increasing bed height.

PEPT visualisation of particle motion in a tapered fluidised bed coater

“…It should be pointed out that the taper angle of the conical fluidised bed used in the work of Tanfara et al (2002) (±20°) was well above that of the equipment used in this research (8.1°). For the Glatt GPCG-1 fluidised bed operating under drying conditions, Chaplin et al (2004) reported a more uniform fluidisation over the whole cross-section of the bed.…”

“…For a bench-scale conical fluidised bed dryer, Tanfara et al (2002) identified a centralised lean core flow and a denser annular region, with flow patterns similar to those in a spouted bed (Mathur and Epstein, 1974). It should be pointed out that the taper angle of the conical fluidised bed used in the work of Tanfara et al (2002) (±20°) was well above that of the equipment used in this research (8.1°).…”

Emulsion phase expansion of Geldart a particles in bubbling fluidized bed methanation reactors: A CFD–DEM study

“…The bed aspect ratio has a significant influence on solid mixing [51,52] and gas dispersion [53] in a bubbling fluidized bed, indicating the interaction between of the two phases changing with the amount of bed materials. Hence the interphase mass transfer rate may also change accordingly.…”

Effect of slip boundary conditions on the simulation of microparticle velocity fields in a conical fluidized bed

“…Fluidized and spouted beds are extensively used for various industrial applications in pharmaceuticals, 1,2 drying, 3,4 food processing, 5 combustion, 6,7 pyrolysis, and catalytic polymerization. 8,9 A conical fluidized bed has the characteristics of both fluidized and spouted beds, being, therefore, suitable for handling agglomerating or sticky powders.…”

“…Bed volume also expands gradually by increasing airflow velocity until large heavy agglomerates start to move and a transition regime from the channeling regime to full fluidization regime is reached in the bed. 2,3,31,55,56,59 However, large agglomerates of the particle phase are observed in certain cases at the bottom of the conical bed. It should be noted that the fluidization of fine particles and/or large agglomerates is delayed and even completely stopped due to the presence of interparticle cohesive forces and/or weight.…”