Group Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Title: 11.5.4 - Classifying the Fluidization and Segregation Behavior of Binary Mixtures using Particle Size and Density Ratios
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 Material Information
Title: 11.5.4 - Classifying the Fluidization and Segregation Behavior of Binary Mixtures using Particle Size and Density Ratios Particle-Laden Flows
Series Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Physical Description: Conference Papers
Creator: Rao, A.
Curtis, J.S.
Hancock, B.C.
Wassgren, C.
Publisher: International Conference on Multiphase Flow (ICMF)
Publication Date: June 4, 2010
 Subjects
Subject: fluidization
segregation
mixing
binary mixture
 Notes
Abstract: Experimental investigations show that fluidized binary mixtures exhibit varied pressure drop profiles and segregation patterns, depending on the level of disparity due to size and/or density differences. In this study, different mixture types are mapped on a graph of density ratio versus size ratio. It is found that the ratio of the minimum fluidization velocities of individual components can be used to categorize these mixtures. Classifying the binary mixtures in this manner gives a qualitative understanding of how the different mixtures behave upon fluidization.
General Note: The International Conference on Multiphase Flow (ICMF) first was held in Tsukuba, Japan in 1991 and the second ICMF took place in Kyoto, Japan in 1995. During this conference, it was decided to establish an International Governing Board which oversees the major aspects of the conference and makes decisions about future conference locations. Due to the great importance of the field, it was furthermore decided to hold the conference every three years successively in Asia including Australia, Europe including Africa, Russia and the Near East and America. Hence, ICMF 1998 was held in Lyon, France, ICMF 2001 in New Orleans, USA, ICMF 2004 in Yokohama, Japan, and ICMF 2007 in Leipzig, Germany. ICMF-2010 is devoted to all aspects of Multiphase Flow. Researchers from all over the world gathered in order to introduce their recent advances in the field and thereby promote the exchange of new ideas, results and techniques. The conference is a key event in Multiphase Flow and supports the advancement of science in this very important field. The major research topics relevant for the conference are as follows: Bio-Fluid Dynamics; Boiling; Bubbly Flows; Cavitation; Colloidal and Suspension Dynamics; Collision, Agglomeration and Breakup; Computational Techniques for Multiphase Flows; Droplet Flows; Environmental and Geophysical Flows; Experimental Methods for Multiphase Flows; Fluidized and Circulating Fluidized Beds; Fluid Structure Interactions; Granular Media; Industrial Applications; Instabilities; Interfacial Flows; Micro and Nano-Scale Multiphase Flows; Microgravity in Two-Phase Flow; Multiphase Flows with Heat and Mass Transfer; Non-Newtonian Multiphase Flows; Particle-Laden Flows; Particle, Bubble and Drop Dynamics; Reactive Multiphase Flows
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Volume ID: VID00290
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Resource Identifier: 1154-Rao-ICMF2010.pdf

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Classifying the Fluidization and Segregation Behavior of Binary Mixtures using Particle
Size and Density Ratios

Akhil Rao a, Jennifer S. Curtis a, Bruno C. Hancock b, Carl Wassgren c



a Chemical Engineering Department, University of Florida, Building No.723, Room 216, Gainesville, FL 32611, USA,
akhilraotiufl.edu

b Pfizer Global Research and Development, Groton, CT 06340, USA

School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907, USA



Keywords: Fluidization, Segregation, Mixing, Binary mixture.


Abstract
Experimental investigations show that fluidized binary mixtures exhibit varied pressure drop profiles and
segregation patterns, depending on the level of disparity due to size and/or density differences. In this study, different mixture
types are mapped on a graph of density ratio versus size ratio. It is found that the ratio of the minimum fluidization velocities
of individual components can be used to categorize these mixtures. Classifying the binary mixtures in this manner gives a
qualitative understanding of how the different mixtures behave upon fluidization.


Introduction

Fluidized beds are popular in industry. For
example, drying of pharmaceutical powders (Muzzio et. al.,
2002) and catalytic cracking of petroleum and coal
combustion for generating electricity (Kunii and
Levenspiel, 1991) are commonly performed in fluidized
beds. Fluidization operations are based on contact
between a fluid stream and a mixture of solid materials,
which varies for each process. A common, observable
phenomenon associated with multi-solid beds is that they
may segregate when subjected to fluidization. Segregation
is primarily due to particle size and/or density differences.

The segregation tendency of a powder mixture
influences the overall process efficiency and, hence,
segregation via fluidization is one of the key areas of
fluidization research. Much experimental data exists in the
literature concerning fluidized bed segregation, yet the
current understanding of the mechanisms controlling
multi-solid fluidization segregation is very poor, even for
two component particle mixtures. In fact, for a simple
binary mixture fluidized by a gas, there are a variety of
pressure drop profiles that have been observed and the
different pressure drop profiles lead to different
segregation patterns. For example, Formisani et al. (2008)
presented several binary mixtures having large density
and/or size ratios that fluidize at two different velocity
points, while Joseph et al. (2007) has reported mixtures
which fluidize at a single velocity point, just like a mono-
component powder. Marzocchella et al. (2000) studied an
extremely disparate mixture that mixes well at low
velocities, just beyond the point of fluidization, but
segregates at larger velocities. Complicating matters
further, the phenomenon of layer inversion has also been
observed in fluidized mixtures containing smaller, denser


particles and coarser, less dense particles (Rasul et al.,
1999).

The present study is the first attempt to catagorize
the various gas fluidized binary mixture types reported by
various authors. In addition, the classification uses the
U
minimum fluidization velocity ratio, U the
U
mmflotsa
p_ d
density ratio, p, and size ratio, d are
p df
used to distinguish between these mixture types, the
observed pressure drop profiles, and segregation patterns.



Experimental Facility




Particles and their preparation

Experiments were performed with glass (Mo Sci
Corporation), polystyrene (Norstone, Inc.), and steel
particles (Ervin Industries) with mean diameters ranging
from 83 pm to 550 pm and sizes following a log normal
distribution. All of the particles are in the Geldart B class.
The particles were carefully sieved, dried in an oven for
twelve hours and subject to an antistatic bar in order to
eliminate accumulated electrostatic charge. The particles
were stored in a desiccator so that cohesive forces due to
moisture and static effects were minimized.

Error! Reference source not found, summarizes
the experimental materials and their properties. The








notation used to represent the particle type has a letter
indicating material type (G for glass, P for polystyrene,
and S for steel) followed by the mean particle size in
microns. The error in the measurement of the minimum
fluidization velocities of all the particles was less than
10%.

Table 2 presents the studied mixtures and their
properties (composition, size ratio, density ratio,
Archimedes number ratio, and the ratio of the minimum
fluidization velocities). The notation followed for the
particle mixtures is in two parts. The first part describes
the jetsam percentage composition (by mass), material type
(glass, polystyrene and steel), and particle size. The second
part of the notation describes all of the same properties, but
for the flotsam.


Table 1: Experimental material and properties present
study

Diameter Density Umin
Material (pm) (kg/m3) Sphericity m) Notation
(im) (kg/m') S (cm/s)
75-89 2500 0.9 1.5 G083
104-125 2500 0.9 1.9 G116
125-152 2500 0.9 2.7 G138
152-178 2500 0.9 3.6 G165
178-211 2500 0.9 4.6 G195
Glass 211-251 2500 0.9 6 G231
251-297 2500 0.9 8 G275
297-354 2500 0.9 11 G328
354-422 2500 0.9 13 G385
422-500 2500 0.9 19 G460
500-600 2500 0.9 25 G550
251-297 1250 0.9 4 P275
Polystyrene
297-354 1250 0.9 7 P328
Steel 297-354 7800 0.85 46 S328


Table 2: Experimental mixtures and their properties
Type Mixtures Size Ratio Density Ratio Ar no. ratio Umin Ratio
Jetsam Flotsam
1 50G550-50G083 Glass Glass 6.6 1 291 16.7
2 50G462-50G083 Glass Glass 5.6 1 172 12.7
3 50G550-50G116 Glass Glass 4.7 1 107 13.2
4 50G385-50G083 Glass Glass 4.6 1 99.8 8.7
5 50G462-50G116 Glass Glass 4.0 1 63.2 10.0
Size 6 50G328-50G083 Glass Glass 4.0 1 61.7 7.3
Segregation 7 50G275-50G083 Glass Glass 3.3 1 36.4 5.3
8 50G231-50G083 Glass Glass 2.8 1 21.6 4.0
9 50G195-50G083 Glass Glass 2.3 1 13.0 3.1
10 50G165-50G083 Glass Glass 2.0 1 7.86 2.4
11 50G138-50G083 Glass Glass 1.7 1 4.60 1.8
12 50G116-50G083 Glass Glass 1.4 1 2.73 1.3
Density 13 135328-87P328 Steel Polystyrene 1 7.40 7.40 6.6
Segregation 14 755328-25G328 Steel Glass 1 3.10 3.10 4.2
Size and
density against 15 70G116-30P275 Glass Polystyrene 0.42 2.30 0.170 0.5
each other


Experimental setup

A fluidization segregation unit (Jenike and
Johanson, Fluidization Material Sparing Segregation
Tester, was used in the experiments. The tester has a
column diameter of 1.6 cm and a height of 9.5 cm. There is
a sliding disc assembly at the base of the column which can
be used to divide the bed into multiple horizontal sections.
Each of these sections may be transferred to a sampling
container, one at a time, via a carousel arrangement. Details
concerning the operation of the tester are given in Hedden
et al. (2006) and ASTMD-6941 (2003).

A schematic of the experimental set up is shown in
Fig. 1. A sintered metal plate with an average pore diameter
of 40 pm was used as a gas distributor for the columns. The
air enters the column from the bottom, with its flow rate
controlled by a mass flow controller. The pressure drop
across the entire setup was measured using a pressure
transducer. The instantaneous pressure drop and velocity
data were recorded on a computer.


Prior to running an experiment, air was passed
through the empty column to get a background pressure
drop due to the column, diffuser, and the filter sections. In
order to obtain the pressure drop profile for a segregated
state, the material expected to be the jetsam was first
weighed and a very small amount of antistatic powder
(Larostat HTS 905 S, BASF Corporation, approximately
2 mg) was mixed with the particles and loaded into the
column from the top. Next, the material expected to be the
flotsam was weighed and antistatic powder was mixed into
it and loaded into the column. The height, H, to which the
column was filled was recorded. The fixed bed height, H,
was approximately 4 cm for all experiments. The velocity
was slowly increased at a rate of 0.0833 cm/s2 to a velocity
much greater than that required to completely fluidize the
mixture. The velocity was then decreased to zero at the
same rate.


Experimental procedure







Next, the weight fraction of the jetsam for each
axial section of the column, x,, is determined. The
segregation index, si,, for the ih axial section of the column
is defined as,


1-X


for sections in which x, > xf and,


X -
s i =


Figure 1: Schematic of the experiment: (A) air
inlet, (B) mass flow controller, (C) computer, (D) column
diameter, (E) air in, (F) pressure signal, (G) diffuser, (H)
bed height, (I) air out, (J) air filter, (K) sliding disc
assembly, (L) slice

For the pressure drop profile measurements from a
mixed state, fresh amounts of the jetsam and flotsam, along
with the antistatic powder (approximately 5 mg), were
completely mixed either manually for disparate mixtures
(mixtures with 2-point fluidization), or for similar mixtures
(mixtures with 1-point fluidization) complete mixing was
obtained by maintaining the mixture at high air velocities
(three times the complete fluidization velocity) for thirty
minutes.
In order to obtain the segregation profiles for the
mixture at different velocities, the mixture was first
completely mixed by following the same procedure used in
the pressure drop profile measurements from a mixed state.
The fluidized bed was then maintained at the intended
velocity for thirty minutes. At the end of the thirty minutes,
the velocity was suddenly set to zero, and the bed collapsed
to a fixed bed state. Next, the bed was sectioned axially by
using the sampling disc assembly at the base of the column.
Each section was collected in a sampling container via the
carousel arrangement and its composition was analyzed.
The composition for mixtures with different sizes was
obtained by sieving, while mixtures involving steel and
glass or polystyrene were separated using magnets.
Mixtures of glass and polystyrene were chosen such that
they could be easily separated by sieves.

Segregation index

Multiple definitions of an axial mixing index or
segregation index for binary mixtures have been proposed
(Nienow et al., 1978; Joseph et al., 2007). The segregation
index usually varies between zero and one, with zero
indicating no segregation or uniform mixing and one
indicating a completely segregated mixture.

In order to define a segregation index, the feed
composition of the jetsam by weight, xy, is first obtained.
Then the final jetsam composition in the mixture, x,, is
obtained. The two weight fractions are defined in order to
account for the material losses (losses in the present work
are approximately 5% by weight of the feed composition).


for sections in which x, < xf. Finally, the overall segregation
index, SI, is computed as,


[SI [ mass of section
SI= si of the en
mass of the entire bed


Since SI is a function of velocity, segregation profiles were
obtained at various velocities and the corresponding
segregation indices were calculated for each profile.

It was observed that the reproducibility of the
experiments increased as the disparity between the two
components decreased, especially for size segregated
mixtures. Hence, it was only necessary to conduct three
replicate experiments for two of mixtures with the greatest
disparity (mixture numbers 1 and 2 in Table 3). Only a
single set of experiments was carried out for the other
mixtures. The error in the value of SI was found to be
between 5 and 10%.

Results and Discussion

Table 3 provides a detailed summary of the
mixture parameters reported in the literature, as well as the
results from the experiments performed in the present
study, as outlined in Table 2. The mixtures are arranged in
descending order with respect to the jetsam to flotsam
minimum fluidization velocity ratio. This velocity ratio,
Ur, is a good measure of particle mixture disparity as
discussed later in this section.

Throughout the published literature, as well as in
this study, a wide variety of segregation behavior associated
with different types of mixtures has been observed. Here,
an attempt is made to qualitatively categorize these various
mixtures based on the density ratio, size ratio, and the ratio
of minimum fluidization velocities of the individual
components.

Although all of the published studies provide
information on segregation profiles, not all include pressure
drop information. Hence, in some cases, categorizing the
mixtures involves hypothesizing some aspects of the
mixture behavior based on other reported behavior for those
and similar mixtures. By analyzing the pressure drop, flow,
and segregation behavior of the various mixtures, seven
different mixture types can be identified (and are listed in








Table 3). In general, for binary mixture types A-D, both
the particle size and density ratios are equal to or greater
than one (dr > 1 and pr > 1). This is not true for mixture
types E-G, which have one of the ratios less than one with
the other greater than one.

Type A Mixtures: Very large particle size ratio (d, > 4.5;
Ur> 8).


- Fluidization
Defluidization



A vsD


V.I iv


Figure 2: Typical pressure drop profiles and segregation
index behavior for a Type A mixture 50G385-50G083. (a)
Pressure drop profile, initially segregated state. (b) Pressure
drop profile, initially mixed state. (c) Segregation index.

Type A mixtures fluidize at two distinct points
when fluidized from a completely segregated state (Fig.
2a). As the gas velocity increases, the entire segregated bed
remains in a fixed state and the pressure drop linearly
increases. Eventually, the flotsam becomes fluidized (point
A in Fig. 2a is the first point of fluidization), but the jetsam
remains in a fixed bed state. At this point, the pressure drop
curve follows a linear profile (as the velocity increases), but
with a different slope. This change in slope is due to the
partial fluidization of the bed. It is important to note that the
velocity required to fluidize the flotsam is slightly greater
than the minimum fluidization velocity of the flotsam
alone. As the velocity is further increased, a point is
reached at which both the jetsam and flotsam are fluidized
(point B in Fig. 2a, which is the second point of
fluidization). The pressure drop across the entire bed
remains constant for larger velocities. The velocity required
to fluidize both the jetsam and flotsam is slightly larger
than the minimum fluidization velocity of the jetsam alone.

As the gas velocity is reduced, the bed height
decreases and the jetsam settle at the bottom of the column
(point C in Fig. 2a is the first point of defluidization). The
velocity at which point C occurs is generally smaller than
both the velocity at point B and the minimum fluidization
velocity of the jetsam. Upon further reduction of the gas
velocity, the entire bed eventually settles (point D in Fig. 2a
is the second point of defluidization). The velocity at this


point is greater than the minimum fluidization velocity of
the flotsam. Points A and D occur at similar velocities.

When Type A mixtures are fluidized from an
initial uniformly-mixed state, there are multiple peaks
observed in the pressure drop profile (oval E in Fig. 2b
highlights this peaked behavior). These peaks are a
characteristic feature of mixtures with large particle size
disparity.

Type A mixtures are not only characterized by 2-
point fluidization, but also by a minimum observed in the
segregation index profile (Fig. 2c). As the velocity
increases beyond the complete fluidization velocity (points
C and F in Figs. 2a and 2b, respectively), the bed begins to
mix and the SI decreases. However, as the gas velocity
increases further, the bed expansion due to the flotsam is
greater than that for the jetsam and the bed begins to
segregate with a corresponding increase in SI. Thus, for
Type A mixtures, there exists an optimum velocity at which
the SI is minimized.

Type B Mixtures: Significant level of disparity in particle
size and density (pr> 3 or 4.5 > dr> 3.3; 4.2 < Ur< 8)


Fluidization
Defluidization
B
rr
L D C




Y- acyMcY


S Fluidization
S--Defluidizaion

v a c- i *c ,
""9,)


Veloclly lncm



Figure 3: Typical pressure drop profiles and segregation
index behavior for a Type B mixture 75S328-25G328. (a)
Pressure drop profile, initially segregated state. (b) Pressure
drop profile, initially mixed state. (c) Segregation index.

The pressure drop profiles for Type B mixtures are
similar to those observed for Type A, where fluidization
from a segregated state exhibits 2-point fluidization
behavior, and fluidization from an initially mixed state
exhibits peaked behavior (points A-D and E-G in Figs. 3a
and 3b, respectively, have the same definitions as the
corresponding points in Figs. 2a and 2b). The key
difference between a Type A and Type B mixture is the
behavior of the segregation index. For Type B mixtures, the
segregation index decreases as the gas velocity increases
(Fig. 3c) rather than exhibiting a minimum. For Type B
mixtures, the mixing quality improves as the gas velocity
increases, although complete mixing is difficult to achieve








and can be attained only at very large fluidization
velocities.

Type C Mixtures: Intermediate level of disparity (2 < pr <
3 or 2 < dr< 3.3; 2.5 < Ur< 4.2)


velocities (Fig. 5c). Furthermore, they do not exhibit
segregation even at low velocities which are slightly above
the complete fluidization velocity.


/ A Fluidization
Defluidization




Vtlodlylncn t


"A

-Fluidanon
Deflwd.zat



fb ,' ic
. .


SDefludizalou n




Velotmy cI CM


I"'
N

k "-* "
--,




VelocitymInscf
CI_


Figure 4: Typical pressure drop profiles and segregation
index behavior for a Type C mixture 50G195-50G083. (a)
Pressure drop profile, initially segregated state. (b) Pressure
drop profile, initially mixed state. (c) Segregation index.

When Type C mixtures are fluidized from an
initially segregated state, they exhibit 2-point fluidization
(points A and B in Fig. 4a are the first and second points of
fluidization, respectively). However, when these mixtures
are fluidized from a mixed state, they may either
demonstrate single peak behavior (oval D in Figs. 4b) or
single point fluidization behavior. Single peak behavior is
generally observed in either small diameter columns (Kunii
and Levenspiel, 1969) or when the data acquisition system
is sufficiently fast. It is this latter effect that is observed in
the present study. When the mixtures were fluidized
rapidly, fewer data points were obtained since the data
acquisition rate remained the same and some of the key
features (such as the peaks) of the pressure drop profiles
were lost. Thus, it was necessary to fluidize the material
slowly (the rate of velocity increase was 0.0833 cm .li. The
mixtures that have a single point or a single peak in their
pressure drop profile show similar patterns.

The segregation index profile (Fig. 4c) shows that
at low velocities the segregation index is large, but at higher
velocities (approximately twice the complete fluidization
velocity), the mixture mixes completely.

Type D Mixtures: Minimal disparity in particle size and
density (1
These mixtures behave like single component
particle beds and fluidize at a single point from both the

initially segregated or well mixed state (Figs. 5a
and 5b). Type D mixtures also tend to mix easily at low


Figure 5: Typical pressure drop profiles and segregation
index behavior for a Type D mixture 50G165-50G083. (a)
Pressure drop profile, initially segregated state. (b) Pressure
drop profile, initially mixed state. (c) Segregation index.

Type E Mixtures: Smaller, denser component as jetsam (pr
> 2 and dr< 1)

Type E mixtures contain smaller, denser particles
and coarser, less dense particles such that the size
difference opposes the density difference. Generally, the
smaller, denser component behaves as jetsam when the
density ratio is large. The pressure drop profile may show
multiple peaks or a single peak depending upon the
disparity level based on U, (Joseph et al., 2007 and
Formisani et al., 2008). Additionally, the segregation index
decreases as the velocity increases.

Type F Mixtures: Mixtures exhibiting layer inversion (1 <
Pr< 1.5, 0.3
Mixtures with smaller, denser particles and
coarser, less dense particles having a low density ratio and a
low to intermediate size ratio may exhibit the phenomenon
of layer inversion. At lower velocities, the smaller, denser
component behaves as jetsam. However, at higher
velocities, the coarser, lighter component behaves as
jetsam. For these mixtures, pressure drop data and
segregation index are not readily available in the literature
and were not examined here.


5 1 IS 2
VIlocfylncmil
(CI








Table 3: Details of mixtures and their properties published work and present study


Ur Mixtures Size Ratio Density Ratio Ar#Ratio Ur _
Srno. Regime J/F Mixtures Jetsam Flotsam J/F J/F J/F J/F Reference


1 A 16.67
2 A 13.16
3 A 12.94
4 A 12.67
5 B 11.61
6 A 10.00
7 A 8.67
8 A 7.98
9 B 7.50
10 B 7.33
11 B 6.57
12 B 6.00
13 B 5.33
14 B 5.30
15 G 5.00
16 B 4.57
17 B 4.35
18 B 4.18
19 C 4.00
20 C 3.56
21 C 3.33
22 C 3.11
23 C 3.07
24 C 3.00
25 C 2.53
26 C 2.50
27 D 2.40
28 D 2.11
29 D 1.93
30 D 1.86
31 D 1.80
32 D 1.73
33 D 1.67
34 E 1.39
35 E 1.35
36 D 1.33
37 D 1.27
38 D 1.25
39 E 0.96
40 E 0.69
41 E 0.67
42 F 0.52
43 E 0.45
44 E
45 E
46 E
47 F


50G550-50G083 Glass Glass
50G550-50G116 Glass Glass
50G500-505i125 Glass Silica Sand
50G462-50G083 Glass Glass
105324-90G165 Steel Glass
50G462-50G116 Glass Glass
50G385-50G083 Glass Glass
50G612-50G154 Glass Glass
10G550-90G165 Glass Glass
50G328-50G083 Glass Glass
135328-87P328 Steel Polystyrene
50G499-50G172 Glass Glass
50G275-50G083 Glass Glass
105273-90G231 Steel Glass
50MS624-50G154 Mol Sieves Glass
10Cp461-90Q273 Copper Powder Quartz
10S390-90S138 Steel Steel
755328-25G328 Steel Glass
50G231-50G083 Glass Glass
50G565-50G285 Glass Glass
55G5490-45G1590 Glass Glass
25G231-75G116 Glass Glass
506195-506083 Glass Glass
50G499-50G271 Glass Glass
505439-50G428 Steel Glass
55G4260-45G2300 Glass Glass
506165-506083 Glass Glass
50G565-50G365 Glass Glass
75G231-25P231 Glass Polystyrene
46P328-54P231 Polystyrene Polystyrene
506138-506083 Glass Glass
SS500-PP500 Silica sand Polypropylene
50G3750-50PE3750 Glass Polyethylene
505439-50MS800 Steel Mol Sieves
50G593-50MS624 Glass Mol Sieves
50G3750-50A3750 Glass Alumina
50G116-50G083 Glass Glass
50A3750-50PE3750 Alumina Polyethylene
10B273-90G461 Bronze Glass
805G375-2055125 Silica Sand Silica Gel
50B235-50G565 Bronze Glass
FCC-Pumice FCC Pumice
70G116-30P275 Glass Polystyrene
FCC-Bagasse FCC Bagasse
Bagasse-P2000 Bagasse Polystyrene
PVC-Bagasse PVC Bagasse
Cenolyte-Bagasse Cenolyte Bagasse


291
107
63
172
19.10
63.18
99.80
62.76
37.04
61.71
7.43
24.42
36.37
4.16
0.03
16.10
22.57
3.12
21.56
7.79
41.16
7.90
12.97
6.24
3.31
6.35
7.86
3.71
2.33
2.86
4.60
2.89
2.39
0.86
1.46
1.57
2.73
1.52
0.6012
0.1605
0.2508
0.3114
0.1747
0.0946
0.0025
0.0633
0.0460


16.67
13.16
12.94
12.67
11.61
10.00
8.67
7.98
7.50
7.33
6.57
6.00
5.33
5.30
5.00
4.57
4.35
4.18
4.00
3.56
3.33
3.11
3.07
3.00
2.53
2.50
2.40
2.11
1.93
1.86
1.80
1.73
1.67
1.39
1.35
1.33
1.27
1.25
0.96
0.69
0.67
0.52
0.45


Present Study
Present Study
Marzocchella et al.2000
Present Study
Nienowetal.1987
Present Study
Present Study
Formisani etal. 2008
Nienow etal. 1978/87
Present Study
Present Study
Formisani etal. 2001
Present Study
Nienow etal. 1978
Formisani etal. 2008
Nienow et al. 1978
Nienowetal.1987
Present Study
Present Study
Hoffmann etal. 1993
Huilin etal. 2003
Joseph etal. 2007
Present Study
Formisani et al. 2001/08
Formisani etal. 2008
Huilin etal. 2003
Present Study
Hoffmann etal. 1993
Joseph etal. 2007
Joseph etal. 2007
Present Study
Olivieri etal. 2004
Ochoa etal. 1989
Formisani etal. 2008
Formisani etal. 2008
Ochoa etal. 1989
Present Study
Ochoa etal. 1989
Nienow etal. 1978
Olivieri et. al 2004
Hoffmann etal. 1993
Rasul etal. 1999
Joseph etal. 2007
Rasul etal. 1999
Rasul etal. 1999
Rasul etal. 1999
Rasul etal. 1999










Type G Mixtures: Coarser, lighter component as jetsam (1

For mixtures with smaller, denser particles and
coarser, less dense particles having a low density ratio and a
large size ratio, the coarser, less dense components behave
as jetsam. As an example, mixture number 15 from Table 4
exhibits this kind of behavior. When mixture number 15
was fluidized from an initially segregated state, it had two
points of fluidization, and when it was fluidized from an
initially mixed state, it showed multiple peaks. The
segregation index of mixture number 15 reduced as the
operating velocity was increased.

Classification Diagram


Figure 6: The mixture type diagram. Type A: Very large
particle size ratio. Type B: Significant level of disparity in
particle size and density. Type C: Intermediate level of
disparity. Type D: Minimal disparity in particle size and
density. Type E: Smaller, denser component as jetsam.
Type F: Mixtures exhibiting layer inversion. Type G:
Coarser, lighter component as jetsam.

Figure 6 summarizes all of the data presented in
Table 3 in a more concise manner. A log-log plot is used to
due to the significant amount of available data for mixtures
of smaller, denser particles and coarser, less dense particles
(pr > 1 and 0.1 < d < 1). In addition, there have been many
experiments performed for purely size segregating mixtures
or density segregating mixtures. Hence, there are many
data points along the x-axis and y-axis.

The various mixture types can be classified via a
plot of particle density ratio (y-axis) versus particle size
ratio (x-axis). The boundary lines give an approximate
range of the particle properties associated with each
mixture type. The segregation index minimum
phenomenon is not present for mixtures with large density
difference (Pr = 7.4). Since most practical cases involve
density ratios less than this value, the boundary line for
Type A mixtures is drawn as a straight line parallel to the y-
axis.


If Ur > 8, then the disparity level is extremely
high (mixtures 1 to 8 in Table 3) and if 4.2 < Ur < 8, then
there is a high level of disparity (mixtures 9 18 in Table
3). Further, mixtures having Ur between 2.5 and 4.2 have
intermediate disparity level (mixtures 19 to 26 in Table 3).
And finally, if Urvaries from 1 to 2.5, there is a low level of
disparity (mixtures 27 43 in Table 3).


Conclusions

This paper presents a new classification scheme
for the minimum fluidization velocity ratio, pressure drop
profiles, and segregation behavior of binary fluidized
mixtures. Seven mixture types are proposed. This
classification scheme is based on the particle size and
density ratio of the two components and incorporates new
data as well as previously published data exhibiting a wide
range of fluidization behavior. Additional experimentation
will be necessary to further refine the boundaries for the
seven mixture types.

In addition, based the ratio of minimum
fluidization velocities of the individual components the
level of disparity can be identified. The knowledge of the
mixture type and level of disparity in advance is a
significant aid when one can select the size or density ratio
in order to mitigate fluidization segregation and improve
process efficiency. Further, identifying the jetsam and the
flotsam in case of mixtures with a difference in size and
density opposing each other may also help explain
deviations from regular behavioral patterns due to layer
inversion.



Acknowledgements

Jim Prescott and colleagues at Jenike & Johanson
are thanked for their support of this research and for
providing the segregation testing equipment. Dr. C. Hrenya
at the University of Colorado (Boulder) is also thanked for
sharing data.


References

ASTMD-6941. Standard practice for measuring fluidization
segregation tendencies of powders. (2003)

Formisani, B., De Cristofaro, G., & Girimonte, R. A
fundamental approach to the phenomenology of fluidization
of size segregating binary mixtures of solids. Chemical
Engineering Science Vol. 56, 109-119 (2001).

Formisani, B., Girimonte, R., & Longo, T. The fluidization
process of binary mixtures of solids: Development of the
approach based on the fluidization velocity interval.
Powder Technology, Vol. 185, 97-108 (2008).

Garcia, F., Romero, A., Villar, J., & Bello, A. A study of
segregation in a gas solid fluidized bed: Particles of


7 -
6 E
5 -
. 4


S ............... \ A
...........

G F D\ .

10 ize10ati 10'
Size Ratio







different density. Powder Technology Vol. 58, 169-174
(1989).

Hedden D, Brone D, Clement S, McCall M, Olsofsy A,
Patel P, Prescott J, Hancock B. Development of an
improved fluidization segregation tester for use with
pharmaceutical powders. Pharmaceutical Technology,
Vol. 30, 54-64 (2006).

Hoffmann, A., Janssen, L., & Prins, J. Particle segregation
in fluidised binary mixtures. Chemical Engineering Science
, Vol. 48, 1583-1592 (1993).

Huilin, L., Yurong, D., Gidaspow, D., Lidan, Y., & Yukun,
Q. Size segregation of binary mixture of solid in bubbling
fluidized bed. Powder Technology, Vol. 134, 86-97 (2003).

Joseph, G., Leboreiro, J., Hrenya, C., & Stevens, A.
Experimental segregation profiles in bubbling gas fluidized
bed. AIChE Journal, Vol. 53, 2804-2813 (2007).

Kunii, D., & Levenspiel, O. Fluidization Engineering (2nd
Edition). Newton: Butterworth Heinemann. (1991).

Marzocchella, A., Salatino, P., Di Pastena, V., & Lirer, L.
Transient fluidization and segregation of binary mixtures of
particles. AIChE Journal, Vol. 46, 2175-2182 (2000).


Muzzio, F., Shinbort, T., & Glasser, B. Powder Technology
in pharmaceutical industry; the need to catch up fast.
Powder Technology, Vol. 124, 1-7 (2002).

Nienow, A., Naimer, N., & Chiba, T. Studies of
segregation/mixing in fluidised beds of different size
particles. Chem. Eng. Comm. Vol. 62, 53-66 (1987).

Nienow, A., Rowe, P., & Cheung, L. A quantitative
analysis of the mixing of two segregation powders of
different densities in a gas fluidized bed. Powder
Technology, Vol. 20, 89-97 (1978).

Olivieri, G., Marzocchella, A., & Salatino, P. Segregation
of fluidized binar mixtures of granular solids. AIChE
Journal, Vol. 50, 3095-3106 (2 r14).

Rasul M, Rudolph V, Carsky M. Segregation potential in
binary gas fluidized beds. Powder Technology, Vol. 103,
175-181 (1999).

Rowe, P., Nienow, A., & Agbim, A. The mechanism by
which particles segregate in gas fluidised beds binary
systems of near spherical particles. Trans. Inst. Chem. Eng.
SVol. 50, 310-333 (1972).




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