Hydrodynamic Characteristics
at Layer Inversion
Point
in Three-phase
Fluidized
Beds
with Binary Solids

Jun Young Kim^a, John R. Grace^b,
Norman Epstein^b,
Dong Hyun Lee^a

^a School of Chemical Engineering,
Sungkyunkwan University, 2066 Seobu-ro, Jangan, Suwon 440-746, Republic of
Korea.

^bDepartment
of Chemical & Biological Engineering,
University of British Columbia, 2360 East Mall Vancouver, Canada, V6T 1Z3.

 (^*Corresponding Author?s
E-mail: dhlee@skku.edu)

Keywords: Three phase fluidization, Binary
solids, Layer inversion, Pressure gradient variation, Bed expansion and contraction

ABSTRACT

Layer
inversion of binary solids can
occur in liquid-fluidized beds when the density ratio
and the size ratio of the binary components are on opposite sides of unity. The components
eventually switch
their relative positions in the bed as the liquid velocity is increased. The phenomenon was first
reported by Hancock (1936).
More than 20 layer inversion models of liquid-solid fluidized beds have been evaluated by Escudié et al. (2006),
but layer inversion of
gas-liquid-solid fluidized
beds has received only limited attention (Fan et al., 1985; Chun et
al., 2011; Rim et al., 2013,
2014). Rim et al.
(2013, 2014)
recently proposed a layer inversion model for three-phase fluidized beds based on the gas perturbed
liquid model of Zhang et al. (1995), written as

 However, the
study of Rim et al. (2013, 2014) was limited to only one
volume ratio of one binary, and was based on
the liquid holdup formula
of Han et al. (1990) for three-phase fluidization of mono-component solids. In the
present study, hydrodynamic characteristics at the layer inversion point is studied for
a gas-liquid-solid fluidized bed with binary solids differing in size, density and volume ratio.

Liquid holdup at layer inversion point was measured in a 0.210 m
inner diameter semi-cylindrical, 1.8 m tall acrylic fluidization column for various volumetric ratios of
binary solid mixture, polymer beads (PB)/glass beads (GB).
Properties of the experimental solids are provided in Table 1. Gas and liquid distributors were
positioned at the bottom of the test section, introducing both flows evenly. Tap water
and ambient air were used as
the fluidizing media of liquid and gas, respectively.
The pressure gradient variation method of Vivacqua et al. (2012) was used in these experiments to
find the inversion
point through the minimum difference of pressure gradient between the bottom and top zones. The bottom layer pressure gradient is always larger
than that of the top layer, but they approach equality at inversion points.

Fig.
1 shows the actual pressure drop measurements for a three-phase fluidized bed
of PB/GB binary. Both axial pressure drops (bottom and top zones) are proportional
to the bulk densities in these regions. Several experiments at other gas
velocities and with other volumetric fractions, from PB:GB=0.67:0.33 to
0.33:0.67, was carried out in three-phase fluidization. In addition, hydrodynamic
characteristics at layer inversion point with five combinations of PB:GB will be
proposed.

Fig.1. Pressure drops encompassing layer
inversion at U_g = 6.1 mm/s for PB:GB=0.33:0.67.

References

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