>>EPA
United States Industrial Environmental Research EPA-600/7-79-112
Environmental Protection Laboratory May 1979
Agency Research Triangle Park NC 27711
Extended Tests of Saffil
Alumina Filter Media
Interagency
Energy/Environment
R&D Program Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
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The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
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This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
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essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
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EPA-600/7-79-112
May 1979
Extended Tests of Saffil
Alumina Filter Media
by
M. A. Shackleton
Acurex Corporation
485 Clyde Avenue
Mountain View, California 94042
Contract No. 68-02-2611
Task No. 20
Program Element No. EHE624A
EPA Project Officer: Dennis C. Drehmel
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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DISCLAIMER
This report has been reviewed by Industrial Research Laboratory,
U.S. Environmental Protection Agency, and approved for publication.
Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
m
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FORWARD
New methods of using coal in energy processes are being developed.
These methods include pressurized fluidized bed combustion (PFBC) and
gasification combined cycle (GCC) processes. These new technologies
require development of hot gas cleaning devices to remove particulates
from the process stream. This particulate control is required to protect
equipment downstream of the combustor in the process as well as for
protection of the environment. The economics of the process can be
improved if a single device or system can accomplish both objectives. The
Particulate Technology Branch of the Industrial Research Laboratory has
taken a lead in development of hot gas cleaning systems through their
support of investigative work in this area.
The work reported here is part of the EPA effort to support
development of hot gas cleaning devices. This effort has involved an
investigation at Acurex Corporation of ceramic fibers with respect to
application in high temperature and pressure filtration.
TV
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PREFACE
Previous work carried out under EPA Contract 68-02-2169 and
reported in EPA-600/7-78-194 examined the performance of a number of
commercially available ceramic fiber materials with respect to their
suitability for high temperature and pressure filtration. This earlier
work demonstrated that filtration with ceramic fibers was feasible.
SAFFIL alumina was identified as one of the most promising of the
materials currently available for application in construction of HTHP
filters.
This report presents the results of an effort to perform 200-hour
endurance tests of filters constructed of SAFFIL alumina. Three such
tests were completed, covering a range of filter media face velocity from
2.5 to 9 cm/sec. Tests were performed at nominally 815°C and 10 atm
pressure using fly ash obtained from the EPA/Exxon Miniplant. This work
was done in preparation of filter tests on a slipstream of gas from the
EPA/Exxon Miniplant. Slipstream tests were conducted under EPA
68-02-2611, Task 25 and will be presented in a separate report.
T M
SAFFIL is a registered trademark of Imperial Chemical Industries,
Limited for inorganic fibers.
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ABSTRACT
This research effort was performed with the objective of developing
filter media performance data under simulated PFBC conditions for one
ceramic filter media candidate. The media selected consisted of a low
solidity fiber bed constructed using SAFFIL alumina ceramic fibers.
Dust feeding tests were performed at a nominal temperature of
800°C and 10 atm pressure using reintrained fly ash which had been
collected at the EPA/Exxon Miniplant. Tests were performed at three
filter media face velocities: 2.5, 4.8, and 9.0 cm/sec. Each test was
performed for a duration of 200 hours.
Pressure drop and collection efficiency were determined as a
function of time and as a function of filter face velocity. Off-line
cleaning by reverse pulse was shown to be effective in maintaining low
pressure drop — <1.25 KPa after a cleaning cycle. Collection efficiency
was high (>99.9 percent) and was maintained over the 200 hour test.
Collection efficiency was also shown to be substantially independent of
face velocity over the range tested. Outlet concentration was less than
the most stringent requirements proposed for turbine applications
(generally
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CONTENTS
Page
Forward iii
Preface iv
Abstract v
List of Figures vii
Acknowledgements viii
Section
1 INTRODUCTION 1
2 SUMMARY AND CONCLUSIONS 3
3 RECOMMENDATIONS 4
4 TEST SETUP 5
5 TEST RESULTS
5.1 Background 10
5.2 High Temperature/Pressure Filtration Tests ... 11
References 20
vii
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FIGURES
Number Page
1 Simplified Test Schematic 6
2 Test Chamber Cross Section 7
3 Dust Feeder Schematic Cross Section 9
4 Cumulative Dust Fed 13
5 Total Dust Collected Downstream 14
6 Overall Collection Efficiency 15
7 Average Outlet Concentration 16
8 Outlet Concentration as a Function of Face Velocity ... 18
9 Collection Efficiency as a Function of Face Velocity. . . 19
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ACKNOWLEDGMENTS
Much of the data for this report was collected by Mr. Chris Chancy of
Acurex. Mr. Robert Fulton of Acurex provided engineering support for the
tests.
Dr. Dennis Drehmel was the EPA project officer and deserves special
thanks for his continuing interest and support which was required to see the
work through to a successful result.
Tx
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SECTION 1
INTRODUCTION
The need for hot gas cleanup associated with the development of
advanced coal utilization technology, including pressurized fluidized bed
combustion (PFBC) and gasification combined cycle plants, has been
apparent for several years. Current trends in PFBC technology development
indicate there is a continuing hope that turbines can be adequately
protected with particle removal from staged inertial separation devices.
Military experience does not support this hope. Helicoper turbine engines
have been fitted with small, high efficiency 2.5-cm diameter cyclone tube
banks to extend service life to a moderately acceptable level, where dust
loading is intermittent. The U.S. Army XM-1 Main Battle Tank is turbine
powered and employs a barrier filter system with a cyclone tube bank
precleaner. This system is capable of providing engine intake air as
clean as that required of heavy duty diesel engines. In the world's most
severe dust conditions (Yuma Proving Ground, Yuma, Arizona), dust loadings
at the rear deck of a tracked vehicle are about 17 g/Nm3. Dust loadings
in excess of this are encountered in the exhaust of the PFBC.
E. F. Sverdrup of the Westinghouse Research and Development Center
analytically determined the tolerance of large turbines to particulate
loading (Reference 1). Sverdrup's calculations indicate that cleaning of
turbine expansion gas to a level of 4.6 mg/Nm3 (0.002 grains/SCF) ~
with all particles larger than 6 ym removed — is currently the best
estimated level of cleanliness needed for turbines. This analysis
resulted in a maximum blade erosion of 0.10 inch in 10,000 hours of
operation. This level of cleanliness is approximately 80 times less than
the exit loading expected from three cyclones in series. Filtration tests
at Acurex have shown removal efficiencies resulting in a particulate exit
loading considerably lower than that specified by Westinghouse.
Nearly every type of particulate removal device has been proposed
for HTHP application, including acoustic agglomerators, molten salt
scrubbers, varieties of cyclones, granular beds, HTHP electrostatic
precipitators and ceramic filters. Professor E. Weber from the University
of Essen has published a review paper entitled "Problems of Gas
Purification Occurring in the Use of New Technologies for Power
Generation" (Reference 2). In this paper, he concludes that gravity and
momentum force separators will not adequately remove particles from HTHP
gas streams and will, therefore, be used only as precleaners. He also
states that the required degree of cleaning can be achieved using fabric
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filters, and points out that fibrous materials are available which can
withstand the temperatures expected in PFBC applications.
Granular bed filters have been considered the best available option
for HTHP particulate control. However, tests at the Exxon Miniplant have
shown that many problems remain to be solved before achieving high
efficiency and long life in these devices (Reference 3).
Many of the particle removal devices proposed for HTHP applications
operate primarily through the mechanism of inertial impaction. These
devices include all forms of cyclones, scrubbers and granular beds.
Because gas viscosity increases with rising temperatures, performance of
all inertial devices can be predicted to be worse at HTHP conditions than
at room ambient conditions. Barrier filtration, on the other hand, is
unique in that a theoretical basis exists to predict improved performance
at high temperature and pressure conditions. This improvement results
from using fine (3 ym) diameter ceramic fibers to construct the filter.
Conventional filter media usually employ fibers of 10 to 20 ym in
diameter. The fine diameter fibers increase the filter efficiency enough
to overcome the adverse effects of increased temperature.
In August 1976, Acurex began an EPA-sponsored program to
demonstrate the feasibility of employing available ceramic fibers in high
temperature and pressure filtration. Under this 2-year contract the
theory of barrier filtration was examined and a wide spectrum of ceramic
papers, cloth and blanket felts were tested for filtration performance at
room ambient conditions. A high temperature and pressure filter test rig
was built. Promising media from room ambient tests were subjected to
accelerated cleaning tests at HTHP conditions for 50,000 cleaning pulses.
In addition, ceramic blanket materials were shown to offer the greatest
promise for further development into high temperature filter application.
During extended duration tests of 200 hours over a range of filter media
face velocity (air-to-cloth ratio), SAFFIL alumina was judged to be the
best commercially available material for filter application.
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SECTION 2
SUMMARY AND CONCLUSIONS
Three filter elements were successfully tested for 200 hours each
in a high temperature and pressure environment (800°C, 10 atm) while
filtering injected fly ash. The tests were performed at filter face
velocity up to 9 cm/sec. When tested under laboratory conditions, the low
solidity ceramic fiber media achieved high collection efficiency
(>99.9 percent), and was cleanable, maintaining a steady level of pressure
drop (<2.5 kPa). It operated even in high dust loading conditions, and
survived the 200-hour tests without apparent mechanical degradation.
This test series strongly supports the conclusion that available
ceramic fibers can be successfully developed into filter media for high
temperature and pressure application.
High efficiency fine particle collection results from the use of
small fiber diameter (3 urn nominal) in the design of the filter media.
The media's ability to withstand cleaning stresses results from both fine
fiber diameter and low solidity. The individual fibers are not held
tightly together, and because of their low mass do not exert large forces
on each other. Filter cleaning is enhanced through the use of fine fibers
and off-line cleaning. The high collection efficiency of the fine fibers
results in collection of particles near the surface of the media.
Off-line cleaning eliminates reintrainment of dust to the filter element
being cleaned and to neighboring elements in the filter module taken
off-line. This feature also allows the filtration cycle to be
accomplished at high velocity because it is reintrainment which limits
air-to-cloth ratio in currently available pulse filter systems. The
ceramic components are not inherently expensive. High
temperature/pressure filters will cost more than standard filters, but
primarily because of the pressure vessels, insulation requirements and the
use of corrosion resistent alloys. These factors are present in all the
components of a PFBC system. Compared to the costs of these components,
the filter media cost is expected to be acceptable.
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SECTION 3
RECOMMENDATIONS
Testing of ceramic filters to date has been aimed at showing that
these materials can be used for filtration purposes. This objective has
been accomplished and it now seems clear that a practical high temperature
filter can be developed. Protecting gas turbines from the products of
coal combustion in a PFBC is a difficult task and Acurex recommends that
work on filtration using ceramic fiber media be resumed as quickly as
possible. Component development, performance optimization, and
verification of long term durability all need to be addressed for HTHP
applications.
Since ceramic filters are capable of suspending a dust cake having
a large surface area across the gas stream, this dust cake may be doped
with chemicals upstream of the filter. These chemicals have the potential
to react with gaseous constituents in the stream and to capture or modify
them. Thus, the high temperature filter has the potential of "dry
scrubbing" undesireable components from the gas stream, and this
capability should be fully investigated as well.
Furthermore, a high temperature filter in atmospheric pressure
applications offers the potential of obtaining the particle collection
benefits of filtration over a wider temperature range than is presently
available. For example, heat recovery and subsequent energy savings may
be enhanced with a high temperature filter. The size of such a device
could be reduced because the need for dilution air will not be as great.
This capability, coupled with operation at high filter face velocity and
heat recovery, could offer fine particle control at a lower total cost
than is presently possible in other applications. There are also many
process applications where a high temperature filter could offer savings
in energy, efficiency or product recovery.
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SECTION 4
TEST SETUP
This section describes the test procedure used in performing the
200-hour dust feeding durability test. An earlier report
(EPA-600/7-78-194) describes the filter media test rig.
Figure 1 shows a simplified schematic of the test setup, and
Figure 2 provides a cross section of the filter test chamber. The actual
piping is more complicated than shown because the test rig can also
operate in a reverse flow mode. However, the essential flow paths are as
shown. Primary air flow at 10 atm pressure is provided by a large
compressor. This air is preheated by being forced through a preheater
section and injected into the bottom of the test chamber. A second
compressor provides high pressure air for pulse cleaning and for feeding
dust into the test chamber. Cleaning pulses are introduced through a
fast-acting solenoid valve located above the test chamber. After passing
through the test filter, the cleaned gas flows through a heat exchanger
section to be cooled prior to the removal of any particles which have
penetrated the test filter. These penetrating particles are collected in
the absolute filter. A solenoid operated valve located downstream of this
point is used to stop forward flow of the primary gas for the cleaning
cycle. A critical orifice is used to regulate the flowrate of gas for the
test.
Dust feeding is accomplished by using a rotary table dust feeder
mounted in a pressure vessel (see Figure 3). The dust feeder pressure
vessel is maintained at a pressure greater than the test system pressure
(about 1250 kPa). The exit tube for the dust feeder, located above the
table groove, is passed through the preheater and connected to the test
chamber. The dust injection tube is located so that dust is impacted
against a heavy metal plate below the test filter element. This is done
in an effort to redisperse the injected dust because excessive dust feeder
pressures are required to pass the dust through a shock. Consequently,
redispersion of the test dust was perhaps not as good as it could have
been in an atmospheric pressure test.
Fly ash collected from the second stage cyclone (Run 67) at the
EPA/Exxon Miniplant was used for all tests except those noted in the test
descripti9ns in Section 5. This dust has an average particle size
distribution of DSQ = 19 pm, which is coarser than as-generated dust.
Using redispersed fly ash instead of as-generated fly ash results in
somewhat lower than expected operating pressure drop.
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OCor.mressur
D=Dryer
R=Regulator
S=Sulenoid operatea valve
1700 KPa
Exhaust
t
Small S
tank f—|
/ nn
Primary flow
1000 KPa
Induction
l>reheater
•
~ T ""*""" T ""
1
i»AAj-«j»j' > > \
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Pulse In
Plenum
Venturl
Chamber heater
A1r outlet
Test media
Dust feeder
inlet
(U4"-tube)
0.635 cm
A1r Inlet
(3/4-Inch tube)
1,905 cm
Figure 2. Test chamber cross section.
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Nominal pressure = 1250 KPa
CO
Dust
hopper
Dry
compressed
air In
Table rotated with gear-motor
Oust pick-up
•Dust transported to
test chamber
Figure 3. Dust feeder schematic cross section.
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SECTION 5
TEST RESULTS
Section 5.1 presents a short review of theory and earlier test
results. High temperature and pressure dust feeding test results are
presented in Section 5.2.
5.1 BACKGROUND
Filtration Theory Review
The theory of barrier filtration has been presented in many
sources. The method used in this program was based on work by Torgeson,
Whitby and linoya for single fibers and fiber beds (Reference 4). The key
finding of the analysis was that low solidity fine fiber beds —
(y = 0.02), the ratio of filter volume occupied by fibers — could be
expected to provide high filtration efficiency for fine particles; that
is, even when loosely packed, fine (3 ym) diameter ceramic fibers should
provide high efficiency filtration performance. Results of this analysis
showed that low solidity fine fiber ceramic filters with basis weight
=500 g/m? theoretically capture 0.5 ym particles at 90 percent
efficiency (Reference 5). The analysis also indicated that filters could
perhaps be designed to operate at a filter face velocity of up to
15 cm/sec and still maintain high efficiency.
Room Ambient Filter Media Tests
A large number of ceramic fiber filter media candidates were
subjected to a series of filtration tests at room ambient conditions.
These tests also included some examples of conventional filter media for
comparision purposes. These tests included:
• Dioctylphtalate (OOP) smoke penetration as a function of
airflow velocity
0 Determination of maximum pore size (in micrometers)
• Measurement of permeability
• Flat-sheet dust loading using AC fine test dust (a standard
0 to 80 urn classified Arizona road dust). Overall collection
efficiency and dust loading required to develop 3.7 kPa
(15 inches HgO) pressure drop were determined from this test
which was operated at 10 cm/sec (20 ft/min) air-to-cloth ratio.
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These data revealed which of the available ceramic media candidates
would most likely provide good filtration performance. The data is
provided in detail in EPA-600/7-78-194 and has also been reported
previously (Reference 6). A summary of findings from these tests is given
below:
• Several of the ceramic paper and felt materials are capable of
removing fine particles at high efficiency without excessive
filter weights
• The ceramic paper and felt materials had filtration
characteristics and performed similarly to paper and felt
commercial filter media in a series of filter media tests
• The ceramic woven materials in general were characterized by
large pores and poor collection efficiency in the dust loading
tests, but the parameter range exhibited by the various
materials indicates that an acceptable woven ceramic filter
media could probably be fabricated. Such filter media would,
however, have the same limitations as currently available woven
filters — that is, acceptable performance would only occur at
low air-to-cloth ratios
• "Blanket" ceramic fiber materials (felts) consisting of small
diameter fibers (3.0 ym) appear to be the most promising
materials for high temperature and pressure tests because they
combine good filtration performance and relatively high strength
High Temperature/Pressure Mechanical Durability Tests
Two major questions concerning the suitability of ceramic fibers
for HTHP filtration needed to be answered:
1. How durable are ceramic fiber structures when subjected to
environmental conditions associated with filtration
applications?
2. How well do ceramic fibers perform as filters in HTHP
environment?
Concerning the first of these questions, three ceramic filter media
configurations survived a test during which the filter elements were
subjected to 50,000 cleaning pulses. These tests were set up to simulate
approximately a year's operation of mechanical cleaning loads on the media
at high temperature and pressure, and showed that the low solidity fine
fiber bed filters were undamaged by pulse cleaning loads. They also
showed that the fly ash dust cake was deposited essentially on the surface
of the low solidity fine fiber bed media. Details of these tests were
also reported earlier and in EPA-600/7-78-194.
5.2 HIGH TEMPERATURE/PRESSURE FILTRATION TESTS
Filter performance tests were intended to simulate actual filter
operation at high temperatures and pressure for a period of 200 hours.
10
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The filter media configuration selected as being most promising consisted
of an approximately 1-cm-th ;ck layer of SAFTIL alumina mat insulation
material. This ceramic material was contained between two layers of knit
304 stainless steel screen. The stainless steel screen was suitable for
these relatively short tests, but would probably not survive long term
exposure to the PFBC environment. However, we have fabricated similar
filter elements, substituting the stainless steel screen with a ceramic
screen made using a leno weave. The ceramic screen and media filter
elements have not yet been tested, but we are confident they will be
satisfactory.
Three 200-hour tests were attempted and completed. The tests were
performed at a media face velocity of 2.5 cm/sec (5 ft/min), 9 cm/sec
(18 ft/min) and 4.8 cm/sec (9.5 ft/miri), and were performed in that order.
The first 200-hour test was performed at a nominal air-to-cloth
ratio of 5 to 1 (2.54 cm/sec). Pulse duration was 150 msec. Pulse
interval was one cleaning cycle every 10 minutes. Pulse pressure was
1100 kPa. Cleaning was performed "off-line" with a 4-second bleed down
followed by reverse flow for 2 seconds; the pulse superimposed followed by
a 2-second settling period prior to continuing the filtration cycle. We
now feel that the reverse flow portion of the cleaning cycle is
unnecessary and that off-line pulse cleaning will be sufficient.
Exxon Miniplant fly ash was used as the test dust. A fine dust,
DSQ = 4 um, was used for the first 75 hours. When this dust was no
longer available, a coarse sample, 050 = 19 urn, was used for the
remainder of the test.
Cumulative dust fed, total dust collected downstream, and overall
collection efficiency by mass are plotted as function of time on
Figures 4, 5, and 6. The inlet concentration for this test was high,
having an overall average of 14.4 g/Nm3. Shortly after the fine dust
was substituted with the coarse, overall efficiency was reduced and the
rate of penetration in weight per unit time was increased. At about
120 hours and again at 150 hours into the test, the rate of dust feeding
was reduced. The rate of penetration seemed to follow this. These
occurrences were consistent with leakage through a defect mechanism in the
media. Visual examination of the inside surface of media after the test
revealed it to be basically clean with some localized staining. Overall
collection efficiency remained high throughout the test, never falling
below 99.964 percent.
Outlet concentration as a function of time is shown on Figure 7.
These results are lower on a mass basis than turbine requirements as
reported by Sverdrup in EPA 600/9-78-004. The outlet concentrations for
this first test were based on a flow of 0.566 Mm3 per minute during the
200 hours that dust was being fed. They do not include the additional
flow occurring during warmup and cooldown when the dust feeder was off.
Because of various test rig difficulties, this first run was interrupted
many times. Pressure drop was maintained at <0.75 kPa (3 inches H?0)
throughout the test.
11
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100
S» 80
Q
60
40
20
0
Exxon mini pi ant fly ash
air-to-cloth ratio:
© 2.5 cm/sec
4.8 cm/sec
9.0 cm/sec
50
100 150
Time - hours
i
200
Figure 4. Cumulative dust fed.
12
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Exxon miniplant fly ash
air-to-cloth ratio:
©2.5 cm/sec
^4.8 cm/sec
B 9.0 cm/sec
\
Figure 5. Total dust collected downstream.
13
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Exxon mi nip!ant fly ash
air-to-cloth ratio:
0 2.5 cm/sec
^ 4.8 cm/sec
GJ 9.0 cm/sec
(4
Ws
CD
O
O)
O.
O
c
0)
•r-
u
0)
•I- CO
O (O
O) E
O
100
99.99
99.98
99.97
99.96-
_L
50 ' 100 150
Time -- hours
200
Figure 6. Overall collection efficiency.
14
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Exxon mini pi ant fly ash
air-to-cloth ratio
0 2.5 cm/sec
4.8 cm/sec
9.0 cm/sec
ft
61-
50
100 150 200
Time — hours
Figure 7. Average outlet concentration.
15
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Subsequent test results showed lower outlet concentrations and led
us to believe that the test filter used in the first test had a leak.
The second 200-hour test attempted to achieve the highest
air-to-cloth ratio possible using the present test rig configuration.
This test was performed at a filter media face velocity (air-to-cloth
ratio) of 9 cm/sec (18 ft/min). Because of compressor limitations it was
only possible to maintain a system pressure of 500 kPa. Earlier tests
were performed at system pressures of 930 kPa. Cleaning pulse pressure
was set at 860 kPa to compensate for the reduced system pressure.
Cleaning cycle pulse duration and pulse interval were the same as in the
previous test at 2.5 cm/sec with both tests using offline cleaning.
As before, fly ash from the Exxon Miniplant was used as the test
dust. This dust had a 050 = 19 ym. Cumulative dust fed, total dust
collected downstream and overall collection efficiency are plotted as a
function of time on Figures 4, 5, and 6. Outlet concentration as a
function of time is shown in Figure 7. Overall collection efficiency for
200 hours was 99.992 percent. The filter, which has only 0.146 m2
(1.5 ft2) of filter media area, removed 43,772 g (96.5 Ib) of dust from
16,887 Mm3 of air. Average inlet concentration was 2.59 g/Nm3 and
average outlet concentration for 200 hours was 0.2 mg/Nm3. Thus, on a
mass basis the outlet concentration is cleaner than projected turbine
requirements. Pressure drop varied from about 0.5 kPa to 2.25 kPa (2 to 9
in H£0) over the 10-minute cycle between cleaning events.
The third 200-hour test was performed at an intermediate
air-to-cloth ratio of 4.8 cm/sec (9.5 ft/min). For this test, as for the
higher velocity test, compressor limitations required that system pressure
be set at 660 kPa. Cleaning pulse pressure was 1100 kPa. Other aspects
of the cleaning cycle were the same as in the previous tests. The same
dust was used (050 = 19 ym). Cumulative dust fed, total dust collected
downstream, and overall collection efficiency by mass are plotted as a
function of time on Figures 4, 5, and 6. Outlet concentration as a
function of time is plotted on Figure 7. Cleaned down pressure drop was
maintained at less than 1.25 kPa (5 inches H20) throughout the test.
Outlet concentration as a function of face velocity (air-to-cloth
ratio) is plotted on Figure 8 for three time periods of 50, 100 and
200 hours. If we assume the filter used in the first test at 2.5 cm/sec
developed a leak and extrapolate expected performance (dotted lines), it
is apparent that outlet concentration is reduced as a function of time at
all velocities. This result is similar to what one would expect from a
test using conventional filter media in a room ambient dust feeding test.
Overall particle collection efficiency is plotted as a function of
face velocity (air-to-cloth ratio) on Figure 9 for three time periods of
50, 100 and 200 hours. Again, if the two discrepant data points are
ignored, collection efficiency is substantially independent of face
velocity in the range tested. This is consistent with a hypothesis which
holds that filter penetration occurs primarily during cleaning. The
filter was cleaned at zero forward flow in all three tests (off-line).
16
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50 hours
100 hours
200 hours
Filter fice velocity cm/sec
(a1r-to-cloth ratio)
Figure 8. Outlet concentration as a function of face velocity.
17
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50 hours
O100 hours
^200 hours
c
OJ
o
0)
o.
o
c
QJ
(U
C
o^
•I- (/)
-t-> V)
U ID
100
99.99
99.98
99.97
99.96
468
Filter face velocity cm/sec
(air-to-cloth ratio)
10
Figure 9. Collection efficiency as a function of face velocity.
18
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REFERENCES
1. Sverdrup, E. F., 0. H. Archer, and M. Menguturk. "The Tolerance of
Large Gas Turbines to 'Rocks,' 'Dusts,' and Chemical Corrodants."
EPA-600/9-78-004, CONF-770970, March 1978, pp. 14-32.
2. Weber, E. "Problems of Gas Purification Occurring in the Use of New
Technologies for Power Generation." EPA-600/9-78-004, CONF-770970,
March 1978, pp. 249-277.
3. Hoke, R. C., and M. W. Gregory. "Evaluation of a Granular Bed Filter
for Particulate Control in Fluidized Bed Combustion."
EPA-600/9-78-004, CONF-770970, March 1978, pp. 111-131.
4. Calvert, S., "Wet Scrubber Systems Study, Vol. I," EPA-R2-72-118a,
NTIS-PB213016.
5. Shackleton, M., and J. Kennedy, "Ceramic Fabric Filtration at High
Temperatures and Pressures," EPA-600/9-78-004, CONF-770970,
March 1978, pp. 193-234.
6. Orehmel, D.C., and M. Shackleton, "High-Temperature Filtration,
Proceedings of Third Symposium on Fabric Filters for Particle
Collection," Tucson, Arizona, EPA sponsored, December 1977.
19
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-79-112
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Extended Tests of Saffil Alumina Filter Media
5. REPORT DATE
May 1979
6. PERFORMING ORGANIZATION CODE
7. AUTHOH(S)
8. PERFORMING ORGANIZATION REPORT NO.
M.A. Shackleton
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Acurex Corporation
485 Clyde Avenue
Mountain View, California 94042
10. PROGRAM ELEMENT NO.
E HE 62 4 A
11. CONTRACT/GRANT NO.
68-02-2611, Task 20
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Task Final; 2/78 - 2/79
14. SPONSORING AGENCY CODE
EPA/600/13
15.SUPPLEMENTARY NOTES IERL-RTP project officer is Dennis C. Drehmel, Mail Drop 61
919/541-2925. P '
16. ABSTRACT
The report gives results of research aimed at developing filter media
performance data under simulated pressurized fluidized-bed combustion conditions
for one ceramic filter media candidate. A low-solidity fiber bed, using Saffil alu-
mina ceramic filters was selected. Dust feeding was tested at a nominal 800 C and
10 atm pressure, using reentrained fly ash which had been collected at the EPA/Ex-
xon Miniplant. Tests were performed at three filter media face velocities: 2.5, 4. 8,
and 9.0 cm/sec. Each test was 200 hours long. Pressure drop and collection effi-
ciency were determined as functions of time and filter face velocity. Off-line clean-
ing by reverse pulse was effective in maintaining low pressure drop (<1.25 kPa)
after a cleaning cycle. Collection efficiency was high O99. 9 percent) and was main-
tained over the 200 hour test. Collection efficiency was also substantially indepen-
dent of face velocity over the range tested. Outlet concentration was less than the
most stringent requirements proposed for turbine applications (generally <1 mg/cu
Nm). Outlet concentration showed a trend toward lower values at higher filtration
velocity. Mechanical durability was indicated in that none of the test filters appeared
to have been damaged by the 200-hour tests with cleaning at 10-minute intervals.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
Pollution Dust
Filtration Fly Ash
Combustion Gas Turbines
Fluidized Bed Processors
Aluminum Oxide
Ceramic Fibers
Pollution Control
Stationary Sources
Saffil Fibers
Particulate
13B
07D
21B
07A
07B
11G
13G
8. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
20. SECURITY CLASS (Thispage)
Unclassified
21. NO. OF PAGES
27
22. PRICE
EPA Form 2220-1 (9-73)
20
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