Group Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Title: 16.3.2 - Filtration of Fly Ash Using a Moving Granular Bed Filter
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Permanent Link: http://ufdc.ufl.edu/UF00102023/00398
 Material Information
Title: 16.3.2 - Filtration of Fly Ash Using a Moving Granular Bed Filter Granular Media
Series Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Physical Description: Conference Papers
Creator: Chen, Y.S.
Chyou, Y.P.
Hsiau, S.S.
Lai, S.C.
Lee, H.Y.
Hsu, C.J.
Publisher: International Conference on Multiphase Flow (ICMF)
Publication Date: June 4, 2010
 Subjects
Subject: fly ashes
moving granular bed filter
filtration superficial velocity
mass flow rate
cross-flow
 Notes
Abstract: The goal of this study was to evaluate the performance of a moving granular bed filter designed for cold test to filter coal particulates. A series of experiments were carried out at room temperature to demonstrate the collection efficiency of this method of filtration technology (i.e., the moving granular bed filter) at different filtration superficial velocities and mass flow rates of filter granules but with a fixed inlet concentration of fly ash. The dynamic characteristics of the filter system were evaluated by measuring variations in the outlet concentration and size distribution of fly ashes. The collection mechanisms of the filter granules in the moving granular bed filter were also studied. Experimental results showed that the collection efficiency could be enhanced by using the filtration superficial velocity of 30 cm/sec and mass flow rate of 450 g/min. The results of this study indicate that this type of method could be useful for application in different cross-flow filter systems for gas clean-up. Moreover, the focus in the current study is essentially the development of a moving granular bed filter that could be applied in a high-temperature environment. The results are expected to serve as the basis for future research.
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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Bibliographic ID: UF00102023
Volume ID: VID00398
Source Institution: University of Florida
Holding Location: University of Florida
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Resource Identifier: 1632-Chen-ICMF2010.pdf

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Paper No 7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


Filtration of Fly Ash Using a Moving Granular Bed Filter


Y.S. Chen*, YP. Chyou*, S.S. Hsiaut, S.C. Lait, H.Y Leet, and C.J. Hsut


Institute of Nuclear Energy Research, Atomic Energy Council,

Longtan Township, Taoyuan County, Taiwan 32546, R.O.C.
t Department of Mechanical Engineering, National Central University,

Jhongli City, Taoyuan County,Taiwan 32001, R.O.C.
chenvs@iiner.gov.tw, vpchvou@iner.gov.tw, sshsiau@icc.ncu.edu.tw, 973403027@icc.ncu.edu.tw, hsuan-viAictci.com.tw,
943403033, Tcc ncu edu tw


Keywords: fly ashes; moving granular bed filter; filtration superficial velocity; mass flow rate; cross-flow


Abstract
The goal of this study was to evaluate the performance of a moving granular bed filter designed for cold test to filter coal
particulates. A series of experiments were carried out at room temperature to demonstrate the collection efficiency of this
method of filtration technology (i.e., the moving granular bed filter) at different filtration superficial velocities and mass flow
rates of filter granules but with a fixed inlet concentration of fly ash. The dynamic characteristics of the filter system were
evaluated by measuring variations in the outlet concentration and size distribution of fly ashes. The collection mechanisms of
the filter granules in the moving granular bed filter were also studied. Experimental results showed that the collection
efficiency could be enhanced by using the filtration superficial velocity of 30 cm/sec and mass flow rate of 450 g/min. The
results of this study indicate that this type of method could be useful for application in different cross-flow filter systems for
gas clean-up. Moreover, the focus in the current study is essentially the development of a moving granular bed filter that
could be applied in a high-temperature environment. The results are expected to serve as the basis for future research.


Introduction

Coal-fired power plants release large amounts of
pollutants, such as particulates, SOx and NOx, into the
atmosphere. Air quality can be safeguarded only by
effectively reducing the emission of these types of
pollutants. Pressurized fluidized-bed combustion (PFBC)
and integrated gasification combined-cycle (IGCC) are
methods that have been applied in advanced coal-fired
power generation plants since the 1970's. In PFBC and
IGCC systems, fly ashes must be removed after the
gasification process but before the high-temperature
syngas enters the gas turbine. Due to the need to protect
the turbine blades and control fly ash emissions, it is
important to incorporate methods for high temperature gas
cleanup for the optimization of PFBC and IGCC systems.
Recent analyses suggest that granular bed filter is one of
the most promising approaches of hot gas cleanup for
advanced coal conversion technologies (Brown et al.,
2003). However, there were very few studies concerning
the cold test of granular bed filter, especially using
louvered wall with flow corrective elements.
Cyclones, fabric filters, electrostatic precipitators, and
wet scrubbers are conventionally employed to control the
emission of fly ashes in gas streams with relatively low
temperature conditions (Clift et al. 1991; Kamiya et al.
2001). An alternative technology, the granular bed filter,
has been in use for collecting micron and submicron-sized
fly ashes from syngas for many years. The granular bed
filter method is a fluid-solid process commonly applied to


remove fine fly ashes from the gas flows. The granular bed
filter is based on the principle that the suspended fly ashes
could be removed by the passage of flue gas (or syngas)
through filter granules. As the suspensions flow through
the filter granules, various forces acting on the fine fly
ashes cause them to be deposited on the surface of the
filter granules (Jung & Tien 1991). Unlike the
conventional filtration technologies, the granular bed filter
method has great potential to be developed for hot gas
filtration, because it employs low-cost refractory filter
granules and can work in a very high temperature
environment. Moreover, the fly ash matters are attached to
the filter granules moving in the filter which could be
cleaned and regenerated for continuous operation purpose.
In recent studies related to granular bed filter technology,
the focus has been on the mode of the bed movement
which allows the regeneration of the filter granules (Chou
et al., 2003, 2007a, 2007b; Everaert et al., 2003; Hsiau et
al. 2000, 2004, 2008; Sarra et al., 2005; Smid et al., 2005,
2006; Zhao et al., 2008).
The depth and the surface filtration mechanisms are
two main factors affecting filtration in moving granular
bed filters. The formation of a filter cake at the free surface
of the filter media is the key mechanism to achieve
high-efficiency filter performance. The fly ashes are
removed when the flue gas pass through the filter in which
the filter granules move at a very slow speed. The
mechanisms by which fly ashes are collected by the filter
granules include interception, inertial impaction, diffusion,
gravitational settling, and electrostatic attraction. The






Paper No


efficiency of each type of mechanism (except for
interception) is mainly related to the gas velocity and the
operation temperature. According to Zevenhoven et al.
(1992), inertial impaction is the predominant mechanism.
Nevertheless, diffusion also plays an important role in
capturing submicron-sized particulates, and electrostatic
enhancement can be used to increase the filtration
efficiency. In the filtration cold-test of this study, the fly
ashes follow the curvilinear path of gas motion and tend to
move along the gas streamlines until depositing on the
filter granules. The collection mechanisms considered
include inertial impaction and diffusion.
The collection efficiency of a moving granular bed filter
is a function of the bed depth, granular size, superficial gas
velocity at the inlet face, mass flow rate of the filter
granules, and the properties of the gas and fly ashes (Saxena
et al., 1985). Filtration superficial velocity is defined as the
actual volumetric flow rates through the filter divided by the
cross-sectional area of the filtration zone. In the studies on
fixed beds of glass fibers, Moresco & Cooper (1981)
developed a correlation form for penetration showing that
high Stokes number and high filtration superficial velocity
caused the increase of collection efficiency. Tsubaki & Tien
(1988) found that as filtration superficial velocity increased,
the collection efficiency also increased. Peukert & Loffler
(1991) found that the lower filtration superficial velocity
could improve the collection efficiency due to gravity
mechanism and decrease the pressure drop.
Kalinowski & Leith (1981) and Otani et al. (1988)
found that the collection efficiency decreased as mass flow
rate of the filter granules increased. Zevenhoven et al. (1992)
found that decreasing the mass flow rate of filter granules in
their counter-flow moving bed filter could increase the
collection efficiency. Saxena et al. (1985) studied the effect
of mass flow rate of the filter granules on both collection
efficiency and pressure drop and found little effect in both
cases. As for the granule size, Peukert & Loffler (1991)
found that using finer filter granules improved the collection
efficiency.
From above statements, we found that the bed depth,
granular size, filtration superficial velocity, and mass flow
rate of the filter granules have influences on the collection
efficiency of a filter system. Consequently, here we use the
moving granular bed filter to perform a series of cold tests.
In cold tests, the collection efficiency and the pressure drop
of the fly ashes and gases were measured and analyzed. The
mass flow rates of the filter granules, the filtration
superficial velocities, the concentration of the fly ashes and
the material and sizes of the filter granules are important
I factors.
Moreover, we should mention that we used the
louver-walled apparatus with a series of flow corrective
elements which are very helpful for diminishing the
stagnant zones (Hsiau et al., 2004; Smid et al., 2006) This
design equipped with flow corrective elements could solve
the plugging problems caused by the stagnant zones of filter
granules. Besides, our study essentially helps the
development of a moving granular bed filter that could be
applied to the removal of fly ashes in IGCC and PFBC
systems. The current results are very important to establish
the database of operation parameters in the moving bed
filter system.


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

Nomenclature

C Concentration of fly ash (ppmw)

Greek letters
I7 Collection efficiency (o%)

Subsripts
in Inlet of the granular bed filter
out Outlet of the granular bed filter

Materials and Apparatus

The fly ashes used in the study were collected from a
coal-fired power plant in Taipei, Taiwan. A particulate size
analysis system (Model: Mastersizer 2000) was utilized to
analyze the original size distribution of fly ashes, which
was plotted in Fig. 1. The sizes of the fly ashes ranged
from 0.24 to 363.08 upm, close to Gaussian distribution,
and the mass median aerodynamic diameter of fly ashes
was 22.12 pm. Silica sands, with particle size ranging from
2 to 4 mm, were used as the filter granules.


10 10o 10'
Particulate size (Pm)


102 103


Figure 1: Size distribution of the raw fly ashes.

Cold tests were performed in a moving granular bed
filter, as schematically illustrated in Fig. 2. This granular
bed filter design is modified from the quasi-2D design by
Hsiau et al. (2" 11). Filter granules flowed downward
through the system via a channel with louvers and flow
corrective elements. The flow corrective elements were
used to diminish the stagnant zones of filter granules along
the louvers. The mass flow rate of the filter granules was
controlled by a rotary valve underneath the granular bed.
Gas flowed horizontally from a dirty gas plenum through
the vertically flowing filter granules, which intercepted the
fly ashes, until finally exiting into a clean gas plenum. Fig.
3 shows the cold-test apparatus for our moving granular
bed filter. The filter bed had the following dimensions:
1070 mm high; 380 mm wide; and 500 mm deep. The gas
flow brought fly ashes at a concentration controlled by an
air fan and a screw feeder. The filtration superficial
velocity was controlled at the inlet of the granular bed
filter by the motorized air fan and measured by a Pitot tube.
The screw feeder for pushing the fly ashes into the gas
stream was comprised of an outer tube, a driving motor
and a screw threaded rod marked with a scale. Louvered
blades at the inlet of the filter system helped to improve


S- -

4 - -

3 -

2 -


11






Paper No


the performance of the ventilators (Sharples & Chilengwe
2006). Pitot tubes were utilized to measure the pressure
drop between the inlet and outlet of the granular bed filter.
A sampling probe was installed at the outlet of the granular
bed filter to measure the concentration of fly ash remaining
after passing through the filter system.

Depth filtration
Granular midium

Surface filtration
(Cake)


\ Gas


Louver-
Insert


Figure 2:
filter.


Granular medium + Dust particulate

Schematic diagram of the moving granular bed


- Granular edlum upply d ce




s Samplmgprobe
Gas


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

velocities were 20, 25, 28, 30, 32, and 35 cm/sec,
respectively.
The test procedure could be divided into two stages,
i.e. the fixed-bed mode and the moving-bed mode. Prior to
testing, the filter granules in the filter bed were circulated
for one hour to allow the bulk density distribution to reach
a steady state. The movement of the bed was then stopped
and the fixed-bed mode was started. An air fan and a screw
feeder were used to mix the air and the fly ashes, which
entered the filter bed through the inlet feed pipe. The
pressure drop was measured simultaneously by Pitot tubes
mounted near the inlet and outlet. In the fixed-bed mode,
more and more fly ashes became trapped by the filter
granules, causing the pressure drop in the filter system to
increase (depth filtration). The decrease in the overall
porosity of the filter granules (in the fixed-bed mode) led
to the filter granules having a more compact structure,
which thus increased the collection efficiency. After the
depth filtration process, filter cakes built up along the free
surfaces of the filter granules at the inlet of the filter
system (surface filtration), with relatively few fly ashes.
Choi et al. (2i" 1 reported that the decrease in overall cake
porosity and the increase in pressure drop became
relatively slower with increasing filtration time after the
achievement stage of cake formation.
When the pressure drop increasing speed became
slower, the device was switched from the fixed-bed mode
to the moving-bed mode. In the moving-bed mode, the
mass flow rate of the filter granules was controlled by a
rotary valve. The outlet concentration of fly ash was
simultaneously measured by a sampling probe. The
collection efficiency q could be calculated from the
concentrations of fly ash at the inlet and outlet of filter
system as shown in the following equation:


7 =1-C"
C"


Figure 3: Schematic diagram of the current experimental
moving granular bed filter apparatus.

Experimental Procedure

Prior to the cold test experiments, silica sands were
placed in the granular bed. The mass flow rate of filter
granules was measured by weighting the discharged filter
granules in a bucket and the discharge time. In industrial
applications, the dirty silica sands from the granular bed
filter must be regenerated and circulated back to the filter.
However, to simplify the experimental set-up, we did not
reuse the silica sands at present. Instead, employing the
filter granules supply device, fresh and clean silica sands
were continuously fed from the upper hopper so that the
same amount of filter granules was maintained in the bed.
The walls of bed were cleaned carefully before each
experiment in order to reduce the wall friction effect on the
granular flows. The experimental conditions were listed in
Table 1. The mass flow rates of filter granules were
controlled to be 300, 350, 450, 550, and 600 g/min,
respectively. In addition, the flow of fly ashes was
regulated by a screw feeder to maintain a constant rate
throughout the tests. In this study, the concentration of fly
ash was fixed at 7500 ppmw. The filtration superficial


where C,, and C.,, were the concentrations of fly ash at the
inlet and outlet of the granular bed filter, respectively.

Results and Discussion

Figs. 4 and 5 show the variation of the pressure drop
and collection efficiency with time for different filtration
superficial velocities but at a fixed mass flow rate of filter
granules, 450 g/min. In the fixed-bed filter mode, the
pressure drop increased continually as more and more fly
ashes became trapped by the filter granules. Moreover, as
implied by Darcy's Law resistance equation, the pressure
drop and the filtration superficial velocity are linearly
dependent when the gas viscosity and the filtration
resistance are fixed. In this study, the pressure drop also
increased as the filtration superficial velocity increased, as
shown in Fig. 4. When the pressure drop increasing speed
became slower, the granular bed was switched to the
moving-bed mode. Moving bed granular filters obtain the
regenerated filtration media inside the filters by
continuously replacing dirty granules with clean ones.
Moreover, when the granular bed filter was transferred
from the fixed-bed mode to the moving-bed mode, there
was a sharp reduction in the pressure drop. This lessening
of the pressure drop was more significant if the filtration


Gas + Dust particulate
\\


Granular mediumhoper /
.Movggr mularbed filr


Dust partulateh






Paper No


superficial velocity was higher, because this caused the
flue gas to have higher kinetic energy, which in turn made
it easier to pass through the filter system to the outlet pipe.

400
350 / ', -R- 20 cm/se
350- 7
L--
300 -

CL 250 v^p o e
S200 ^ i &





50
A? 150-A ^AAAA AAAAAAAAAA




0 100 200 300 400
Time (min)

Figure 4: Variation of the pressure drop with filtration
time for different filtration superficial velocities, at a fixed
mass flow rate of filter granules, 450 g/min.


150 200 250 300
Time (min)


350 400


Figure 5: Variation of the collection efficiency with
filtration time for different filtration superficial velocities,
at a fixed mass flow rate of filter granules, 450 g/min.

To understand the mechanisms of the moving
granular bed filter in removing fly ashes through the
relationship between filtration superficial velocity and
collection efficiency, the collection mechanisms of filter
system, inertial impaction and diffusion, were considered.
From Fig. 5, when the filtration superficial velocity was
between 20 and 30 cm/sec, the higher filtration superficial
velocity caused a higher fly ash inertia and diffusion.
Consequently, the better collection efficiency promoted by
the higher filtration superficial velocity could be attributed
to the effects of inertial impaction and diffusion. On the
other hand, in the granular bed using a lower filtration
superficial velocity, because of the lower kinetic energy of
gas with the fly ashes, part of fly ashes did not pass
through the filter cake to the filter granules, causing the fly
ash packing on the inlet of filter system. Hence, in this
work, although the test showed that using a lower filtration
superficial velocity led to a lower concentration of fly ash
in the outlet of the filter system, the fly ashes were still not
fully removed by the filter granules. Moreover, because the


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

width of filter bed was fixed, the effect of higher filtration
superficial velocity caused the fly ashes relatively easily to
pass through the filter bed. Therefore, when the filtration
superficial velocity exceeded 30 cm/sec, the effects of
inertial impaction and diffusion decreased; hence, the
collection efficiency reduced. Consequently, the
experimental results showed that the optimal collection
efficiency was achieved when the filtration superficial
velocity was 30 cm/sec. This result was similar to that
reported by Gutfinger & Tardos (1979), i.e. the best
performance of collection dust at a filtration superficial
velocity of 30 cm/sec.
Figs. 6 and 7 show the variation in the pressure drop
and collection efficiency with filtration time under
different mass flow rates of filter granules, but using a
fixed filtration superficial velocity of 30 cm/sec. In the
fixed-bed mode, because the filtration superficial velocity
was the same, the variations in the pressure drop with
filtration time were almost the same (Fig. 6). During the
moving-bed process, the variation in the mass flow
affected the pressure drop performance. From Fig. 7, as the
filtration time increased, the amount of fly ashes
accumulated in the filter bed increased, and hence so did
the collection efficiency. This phenomenon held true for
different mass flow rates. Because of the higher effects of
inertial impaction and diffusion, the higher mass flow rate
led to more fly ashes being attached to the filter granules
which left the moving granular bed filter later. Thus, a
higher mass flow rate of filter granules (between 300 and
450 g/min) led to the better fly ash capture efficiency. With
a lower mass flow rate, it was relatively easier for the fly
ashes to pass through the filter cake and the filter granules,
to reach the outlet pipe, causing the decrease of collection
efficiency. Besides, in this work, the lower performances
of collection mechanisms of inertial impaction and
diffusion caused the lower collection efficiency.
When the mass flow rate exceeded 450 g/min, the
collection efficiency decreased as well. According to
Ghadiri et al. (1993), a reduction in the collection
efficiency would occur if fewer fly ashes were retained in
the filter system. Since the overall porosity of filter
granules was higher with a higher mass flow rate in this
regime, which subdued the effects of inertial impaction
and diffusion, it was relatively easy for the flue gas to pass
through the filter granules to the outlet of the filter system.
Thus, we found the outlet concentration of fly ash to be
higher if the mass flow was too high. In addition, at given
fixed inlet concentration of fly ash and filtration superficial
velocity, lower collection efficiency occurred if the fly
ashes were not trapped by the higher mass flow rate
leading to incomplete area of filter cake coverage. We
found that the best filtration performance of the current
granular bed existed when the mass flow rate of 450 g/min
was used.
The results also suggested that the variation in the
pressure drop also had a significant influence on the
collection efficiency. Fig. 8, extracting data from Figs. 6
and 7, shows the variation of the collection efficiency with
pressure drop for different mass flow rates of filter
granules but at a fixed superficial filtration velocity of 30
cm/sec. Fig. 8 demonstrates that the collection efficiency
was enhanced by increasing pressure drop in each
individual test series, for all flow rates. For a flow rate


2
D v


0 0

0
<>


f m
[ O5c/e






Paper No


higher than 450 g/min, the increase of mass flow rate
caused the decrease of maximum pressure drop which
resulted in the decrease of the maximum collection
efficiency, due to the effect of the higher overall porosity
of filter granules. It was found that for mass flow rates
between 300 and 450 g/min, the collection efficiency was
greater than 99 %. This was the result of the corresponding
pressure drop in the filter system. In IGCC applications,
the enhancement of the pressure drop tends to cause higher
energy loss, and therefore leads to reduction in work output
from the gas turbine. Consequently, although the filter
system had better collection efficiency when the pressure
drop was higher, this caused higher energy loss, which
would reduce the practical application of the filter system.


200
Time (min)


Figure 6: Variation of the pressure drop with filtration time for
different mass flow rates, with a fixed filtration superficial
velocity of 30 cm/sec.


v v





0


D
A 0
v o
0
00

0
430 g/m3 n
S 450 g/mln
600 g/mln
100 200 300 400
Time (min)


Figure 7: Variation of the collection efficiency with
filtration time for different mass flow rates, with a fixed
filtration superficial velocity of 30 cm/sec.

Figs. 9 (a)-(c) depicts the size distribution of fly ashes
collected from the outlet of the filter bed under various
mass flow rates of 300, 450, and 600 g/min with the fixed
filtration superficial velocity of 30 cm/sec. The size
distribution of these fly ashes had similar characteristics
close to a Gaussian distribution. When the lower mass flow
rate of 300 g/min was employed, there were more
larger-sized fly ashes in comparison with the original size
distribution. It is possible that these larger fly ashes were


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

formed due to the agglomeration of smaller-sized fly ashes
during the collection process (Figs. 9 (a)) which could be
demonstrated by comparing the larger distributions of fly
ashes with the original-sized fly ashes from the inlet to the
filter system (Fig. 1). The size distribution of fly ashes
obtained at a higher mass flow rate of 600 g/min (Fig. 9(c))
was similar to that shown in Fig. 1, indicating that in this
case, the filter system did not achieve satisfactory
collection efficiency. When the mass flow rate was 450
g/min, the mass median aerodynamic diameter of fly ashes
at the outlet (4.13 pm) was smaller than that at the inlet
(22.12 pm), meaning that more larger-sized fly ashes were
removed (i.e., removal effectiveness had increased).


V


V
v0


0
O A



o V
A 0
Sso 450 g/mm
o 00 9/-
200 2
Pressure drop (Pa)


Figure 8: Pressure drop versus collection efficiency using
different mass flow rates.


4-
2 -1 1


1
10' 10, 10 10, 1C
Particulate size (pm)
(a)







S-- ---....-. .- -_--
4





2


101 10, 10
Particulate size (pm)
(b)


10' 10,






Paper No


Particulate size (pm)


Figure 9: Size distribution of the fly ash exiting the
moving granular bed filter bed for mass flow rates of: (a)
300; (b) 450; and (c) 600 g/min.

Conclusions


100 -"n D


99 -
,

98 -


S97


96 -
I , , , I I ,
20 25 30 35
Filtration superficial velocity (cm/sec)
Figure 10: Variation of the collection efficiency with
filtration superficial velocities, with a fixed mass flow rate
of 450 g/min.


100 0


99 -


S98 -
05

S97 -


96I I I I
300 400 500 600
Mass flow rate (g/min)
Figure 11: Variation of the collection efficiency with mass
flow rates, with a fixed filtration superficial velocity of 30
cm/sec.

Cold tests of the filtration of fly ashes using the
moving granular bed technology were performed in this
study. The filter bed incorporated the designs of louvered
walls with flow corrective elements to diminishing the


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

stagnant zones of filter granules, in order to solve the
plugging problem. The filtration superficial velocity and
the mass flow rate of the filter granules affected the
removal efficiency of fly ashes. Fly ash collection became
difficult when the filtration superficial velocity was either
too high or too low, and/or the mass flow rate of the filter
granules was too high or too low. Either of these
conditions could lead to poor collection efficiency. The
results demonstrated that the efficiency of the moving
granular bed filter was good. By employing the current
filter facility and related tested conditions, the filter had the
ability to filter out 99.95 % of the fly ashes when the
filtration superficial velocity was 30 cm/sec and the mass
flow rate of filter granules was 450 g/min (Figs. 10 and 11).
Because the width of filter bed was fixed (380 mm), the
better collection efficiency obtained by the filtration
superficial velocity of 30 cm/sec could be attributed to the
effect of inertial impaction and diffusion. Besides, in this
work, the smaller-sized distribution of fly ashes could be
achieved in the outlet of filter system.
The cold test results provide industries the important
design information for building a prototype of moving
granular bed filter for the hot tests. With the research of
this study, we wish that the design rules for the
commercialized moving granular bed filter can be
developed. Moreover, the current results could have
important contribution to the development of a
high-temperature gas cleanup system for PFBC or IGCC.

Acknowledgements

The financial support from the National Science
Council of TAIWAN ROC, under the code numbers NSC
98-3114-Y-042A-005 and NSC 98-3114-E-008-004, is
acknowledged.

References

Brown, R.C. & Shi, H. & Colver, G. & Soo, S.C. Similitude
study of a moving bed granular filter, Powder Technology,
Vol. 138, 201-210 (2003)
Choi, J.H. & Ha, S.J. & Jang, H.J. Compression properties
of dust cake of fine fly ashes from a fluidized bed coal
combustor on a ceramic filter, Powder Technology, Vol. 140,
106-115 211"'4)
Chou, C.S. & Lo, W.F. & Smid, J. & Kuo, J.T & Hsiau, S.S.
The Flow patterns and stresses on the wall in a symmetric
louvered-wall moving granular filter bed, Powder
Technology, Vol. 131, 166-184 (2003)
Chou, C.S. & Chen, S.H. Moving granular filter bed of
quartz sand with louvered-walls and flow-corrective inserts,
Powder Technology, Vol. 172, 41-49 (' i 1 T'
Chou, C.S. & Lee, A.F. & Yeh, C.H. Gas-solid flow in a
two-dimensional cross-flow moving granular filter bed with
a symmetric boundary, Particle & particle systems
characterization, Vol. 24, 210-222 (2007b)
Clift, R. & Ghadiri, M. & Hoffman, A.C. A critique of two
models for cyclone performance, AIChE Journal, Vol. 37,
285-259 (1991)
Everaert, K. & Baeyens, J. & Creemers, C. Adsorption of
dioxins and furans from flue gases in an entrained flow or
fixed/moving bed reactor, Journal of chemical technology
and biotechnology, Vol. 78, 213-219 (2003)






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Ghadiri, M. & Seville, J.P.K. & Clift, R. Fluidized-bed
filtration of gases at high-temperatures, Chemical
engineering research & design, Vol. 71, 371-381 (1993)
Gutfinger, C. & Tardos GI. Theoretical and experimental
investigation on granular bed dust filters, Atmospheric
Environment, Vol. 13, 853-867 (1979)
Hsiau, S.S. & Smid, J. & Tsai, H.H. & Kuo, J.T. & Chou,
C.S. Flow patterns and velocity fields of granules in dorfan
impingo filters for gas cleanup, Chemical engineering
science, Vol. 55, 4481-4494 (2000)
Hsiau, S.S. & Smid, J. & Tsai, F.H. & Kuo, J.T & Chou,
C.S. Placement of flow corrective elements in a moving
granular bed with louvered walls, Chemical engineering and
processing, Vol. 43, 1037-1045 (2"114)
Hsiau, S.S. & Smid, J. & Tsai, S.A. & Tzeng, C.C. & Yu, Y.J.
Flow of filter granules in moving beds with louvers and
sublouvers, Chemical engineering and processing, Vol. 47,
2084-2097 (2008)
Jung, Y. & Tien, C. New correlations for predicting the
effect of deposition on collection efficiency and pressure
drop in granular filtration, Journal of aerosol science, Vol.
22, 187-200 (1991)
Kamiya, H. & Deguchi, K. & Gotou, J. & Horio, M.
Increasing phenomena of pressure drop during dust removal
using a rigid ceramic filter at high temperatures, Powder
Technology, Vol. 118, 160-165 (2001)
Moresco, L.L. & Cooper, J.L. Symp. on Industrial Aerosol
Technology, AIChE 91 tNational Mtg., Detroit, MI (1981).
Otani, Y & Emi, H. & Kanaoka, C. & Uchijima, I. &
Nishino, H. Removal of mercury vapor from air with
sulfur-impregnated adsorbents, Environmental science &
technology, Vol. 22, 708-711 (1988)
Peukert, W. & Loffler, F. Influence of temperature on
particle separation in granular bed filters, Powder
Technology, Vol. 68, 263-270 (1991)
Sarra, A. & Miller, A.L. & Shadle, L.J. Experimentally
measured shear stress in the standpipe of a circulating
fluidized bed, AIChE Journal, Vol. 51, 1131-1143 (2005)
Saxena, S.C. & Henry, R.F. & Podolski, W.F. Particulate
removal from high temperature, high-pressure combustion
gases, Progress in energy and combustion science, Vol. 11,
193-251 (1985).
Sharpies, S. & Chilengwe, N. Performance of ventilator
components for natural ventilation applications, Building
and environment, Vol. 41, 1821-1830 (2006)
Smid, J. & Hsiau, S.S. & Peng, C.Y & Lee, H.T. Moving
bed filters for hot gas cleanup, Filtration & separation, Vol.
42, 34-37 (2005)
Smid, J. & Hsiau, S.S. & Kuo, J.T. & Chou, C.S. & Peng,
C.Y & Lee, H.T. Granular moving-bed apparatus, US Patent
7,132,088 B2, 2006.
Smid, J. & Hsiau, S.S. & Peng, C.Y & Lee, H.T. Hot gas
cleanup: Pilot testing of moving bed filters, Filtration &
separation, Vol. 43, 21-24 (2006)
Tsubaki, J. & Tien, C. Gas filtration in granular moving
beds an experimental study, The Canadian journal of
chemical engineering, Vol. 66, 271-275 (1988)
Zevenhoven, C.A.P & Scarlett, B. & Andries, J. The
Filtration of PFBC combustion gas in a granular bed filter,
Filtration & separation, Vol. 29, 239-244 (1992).
Zhao, J. & Huang, J. & Wu, J. & Fang, Y & Wang, Y
Modeling and optimization of the moving granular bed for
combined hot gas desulfurization and dust removal, Powder


Technology, Vol. 180, 2-8 (2008)


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