CT U A '-'•"'• E'wiror!rT1<'n'al Protection Agency Industrial tnvironmental Research
fc™ • •» Office of Re.se;irjh iind Development Laboratory
Research Triangle Park. North Carolina 27711 Mdy 1977
EPA RESEARCH IN FABRIC
FILTRATION: ANNUAL REPORT
ON IERL-RTP INHOUSE PROGRAM
Interagency
Energy-Environment
Research and Development
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 seven series. These seven broad categories
were established to facilitate further development and application of environmental
technology. Elimination of traditional grouping was consciously planned to foster
technology transfer and a maximum interface in related fields. The seven 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)
7. Interagency Energy-Environment Research and Development
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 systems. The goal of the
Program is to assure the rapid development of domestic energy supplies in an environ-
mentally-compatible manner by providing the necessary environmental data and
control technology. Investigations include analyses of the transport of energy-related
pollutants and their health and ecological effects; assessments of, and development
of, control technologies for energy systems; and integrated assessments of a wide
range of energy-related environmental issues.
REVIEW NOTICE
This report has been reviewed by the participating Federal Agencies, and approved
for publication. Approval does not signify that the contents necessarily reflect the
views and policies of the Government, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Information
Service, Springfield, Virginia 22161.
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EPA-600/7-77-042
May 1977
EPA RESEARCH IN FABRIC FILTRATION:
ANNUAL REPORT ON IERL-RTP
INHOUSE PROGRAM
by
James H. Turner
Environmental Protection Agency
Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, N.C. 27711
Program Element No. EHE624
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, D.C. 20460
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PREFACE
A key mission of the Environmental Protection Agency is to support
the development of technology needed to monitor and control environ-
mental pollutants. This report reviews the EPA in-house research pro-
gram in fabric filtration that was initiated by the Division of Control
Systems/EPA, Cincinnati, Ohio, and continued by the Industrial Environ-
mental Research Laboratory/EPA and its predecessor divisions at Research
Triangle Park (RTP), N.C. The report is the first annual report on
fabric filtration to originate at RTP; it describes projects undertaken
in the preceding 5 years. The work was performed by what is now the
Particulate Technology Branch (PATB) under James H. Abbott, Chief. PATB
is responsible for advancing technology in the area of fine particulate
collection control devices, and is in lERL/RTP's Utilities and Industrial
Power Division (UIPD) under Everett L. Plyler, Director.
The present staff involved in the in-house program consists of
R. L. Ogan and Dr. J. H. Turner.
British units primarily are used throughout this report in order to
preserve the constants, scales and plots in which the original work was
performed. The Appendix lists conversion factors for computing the
metric equivalents of all British units used in the report.
m
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CONTENTS
Preface iii
Figures v
Section
1 Introduction 1
2 Conclusions 4
3 Program Description 6
3.1 Shake-Cleaned Baghouse 6
3.1.1 Description of the Shake-Cleaned
Apparatus 6
3.1.2 Experimental Programs (Shake-cleaned
Baghouse7 9
3.1.2.1 Fabric Filter Performance
Evaluation '9
3.1.2.2 Phenomena Research .... 14
3.2 Pulse-Jet Baghouse 16
3.2.1 Description of the Pulse-jet
Baghouse 16
3.2.2 Experimental Programs (Pulse-jet
Baghouse) ! ! .. '. .. . . . . . . 18
3.2.2.1 Fabric Evaluation .... 13
3.2.2.2 Specific Research .... 19
3.3 High Temperature Baghouse 21
3.4 The Versatile Fabric Filter Test Unit ... 23
4 Future Work 26
4.1 Evaluation of High Temperature Fabrics . . 26
4.2 Fabric Filtration Research 27
4.2.1 Dust Penetration Studies 28
4.2.2 Cleaning Characteristics of Jet
Pulses 28
4.2.3 Electrostatic Interactions 29
5 References 30
Appendix 32
IV
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FIGURES
Number Page
1 Test apparatus 7
2 Mechanisms for particle removal by a filter .... 12
3 Section through felted filter media showing
distribution of dust 12
4 Schematic of Mikro-Pulsaire collector 17
5 Laboratory baghouse for high temperature tests ... 22
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SECTION 1
INTRODUCTION
During the last 5 years baghouses have gained at least limited'
industrial acceptance as particulate control devices for coal-fired
emission sources, especially because of their efficiency in removing
fine particulates (0.01 ym to 3.0 pm effective diameter). This growing
interest in fabric filtration places new importance on EPA fabric
filtration research and on the in-house experimental program in parti-
cular. More questions about baghouse performance, costs and suitability
for specific applications, particularly coal-fired boilers, are being
asked by potential users, more requests for guidance are being received
and, as baghouses continue to grow in field use, more demands for
answers and information are anticipated. Already part of the in-house
program is in direct response to such inquiries; the primary part, of
course, is in support of the development of basic understanding of
fabric filtration and of the development of an optimum or near optimum
technology for carrying it out.
The EPA in-house fabric filtration laboratory is a unique facility
made up of equipment chosen to be the smallest elements compatible with
adequate simulation of baghouse field operation. A commonplace failing
of much fabric filtration research and development is that experimental
studies carried out on clean, flat fabric samples often bear little
relation to the actual fabric filter operation in a baghouse in the
field. The EPA in-house facility represents an attempt to create a
facility capable of meaningful simulation.
Fabric filtration as a technique for controlling emissions is
already a multi-million dollar industry, ranking behind electrostatic
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precipitators (ESPs) in annual dollar volume but well ahead of wet
scrubbers. Two factors augur well for accelerated growth of fabric
filtration at the expense of ESPs:
1) Increasingly tougher particulate emission laws which are just
beginning to include a fine particulate emission standard
(ESPs generally must be made larger 1n order to meet fine
particulate standards; baghouses generally do not require any
modification).
2) The added cost and size of ESPs designed to control emissions
from low sulfur coal.
Both of these factors have led td a growing interest in fabric
filtration as an alternative or, more and more now, a preferred particu-
late control device for both industrial and utility-owned coal-fired
boilers. This trend is in its infancy but, if fabric filters capture
even a fraction of the projected market, the impact of this new area of
use upon the baghouse industry will be major. Power generation and, to
a lesser extent, other combustion sources, such as incinerators, possess
the potential of increasing the investment in fabric filter installations
by an order of magnitude over the next 10 to 20 years [Ref. 1].
Key factors influencing this trend are costs (both initial and
operating), performance (particulate removal efficiency, especially of
fine particulates) and high temperature compatibility. Most existing
baghouses operate at low temperature (<200°F). For coal-fired boiler
emissions (or combustion sources in general) the baghouse will have to
operate at higher temperatures. The highest temperature for continuous
baghouse operation at present is in the 500-550°F range. Because this
temperature range is often restrictive, the development of baghouses and
filter fabrics capable of higher temperature operation 1s one general
goal of fabric filter research. The in-house program at EPA has in-
cluded evaluation of candidate high temperature fabrics and measurement
of their endurance under high temperature operation.
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Measurement of fabric performance and identification of those
fabric/dust properties that influence performance and cost of per-
formance provide the background for the development of optimum fabrics
and operating conditions, a second general goal of the in-house research.
For baghouses to become the preferred control technology for combustion
sources, they must not only be able to control emissions as well as or
better than the competitive methods (baghouses are generally now granted
this edge), but must do so at a price competitive with the alternative
methods. Cost competitiveness is not always conceded to baghouses.
Development of fabrics and technology for baghouse operation at lower
drags and longer life continues as a specific goal of the EPA in-house
research.
The in-house research also has the beneficial side effect of pro-
viding EPA with first hand information and experience with which to
guide the contract/grant program. Knowing the problems because of
personal experience provides invaluable insight for making the decisions
required to direct and assess the work of others. Consequently, the in-
house program serves to keep EPA abreast of the state-of-the-art as well
as being an independent research facility making original contributions
to the fabric filtration community.
The facilities used in carrying out the in-house program are
described in this report along with a preview of more versatile fabric
filtration test apparatus now under construction. The report also
reviews specific research activities associated with the various ex-
perimental stations and outlines future plans and directions of the in-
house program.
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SECTION 2
CONCLUSIONS
The EPA in-house research program in fabric filtration consists of
two independent, concurrent activities: the evaluation of candidate
fabrics and the investigation of basic phenomena. Both activities will
continue using existing test facilities and new, more versatile equip-
ment scheduled to be put in service during 1977.
Accomplishments of the fabric evaluation program include:
1) The demonstration of superior filtration performance by
spunbonded fabrics when compared to similar weights of woven
fabrics of the same fiber. The laboratory evaluation justi-
fies field evaluation of this type fabric.
2) The confirmation of the unique filtering action of one of the
classes of PTFE laminate fabrics. The fabric evaluated fil-
tered flyash very efficiently and showed promise of being
especially effective for the filtration of respirable particu-
lates (0.01 ym to 3 ym).
3) The identification of polyester as a suitable candidate fabric
for filtering cotton dust.
4) The measurement of the performance of uncalendared needled
felt fabrics in the pulse-jet unit and the measurement of the
endurance of variously coated fibrous glass fabrics in the
high temperature baghouse.
Specific research topics investigated included:
1) Filtration Modeling
2) Particulate Penetration
3) Fabric Aging Effects
4) Particle Size Effects
5) High Temperature Effects
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Individual reports (in print, in press, or in preparation) describe
the details of each of the fabric evaluations and each of the research
topics.
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SECTION 3
PROGRAM DESCRIPTION
3.1 SHAKE-CLEANED BAGHOUSE
The busiest apparatus used in the in-house research program has
been the shake-cleaned baghouse. As many as three single-compartment
baghouses, operated as shake-cleaned baghouses, have been on line at one
time. These units were essentially identical in design and were used
interchangeably in certain studies. Their design and operation are
discussed in this section first (3.1.1), followed by a resume of the
work performed (3.1.2).
3.1.1 Description of the Shake-Cleaned Apparatus
The typical shake-cleaned baghouse used in the EPA in-house
research consists of a single-bag compartment with dimensions as shown
in Figure 1. A cylindrically sewn test filter bag 1s suspended vertically
between two mounting nipples: the top attachment is the entry port for
the dirty test dust; and the bottom attachment is the exit port to the
dust collection hopper. In operation the dust-laden air from the dust
feeder enters the inside of the bag at the top. The bag traps and
removes the dust from the air which passes through the fabric bag walls.
This cleaned air exits the baghouse compartment through a line leading
to a blower. The removed dust remains on the inside surface of the bag
until the air flow is stopped and the bag is shaken by the mechanical
linkage attached to the shaker. The contact between the shaker mechanism
and the bag is near the bottom of the bag. The shaking action dislodges
the dust from the inside surface of the bag, causing the dust to fall
into the collection hopper. After the bag is cleaned, the dirty air
flow is turned on again and the filtering 1s resumed until the next
cleaning period.
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96 In.
HUMIDITY CONTROL
CHAM3ER
MECHANICAL
SHAKER
DISPERSION
VENTURI
OPTICAL
PARTICLE
ANALYZER
VARIABLE SPEED DUST
FEEDER ( FLYASM)
MILLIPORE
FILTER SAMPLING
TRAIN
VALVE
ROTARY BLOWER
COLLECTION HOPPER
Figure 1. Test apparatus.
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Air flow through the apparatus is by an induced draft, Roots type
blower located in the outlet line. The primary air flow is determined
from the pressure drop across a flow venturi 1n the outlet line. Also
located in the outlet line are taps for measuring the mass concentration
in the outlet (the Millipore filter sampling train) and the particle
number concentration by an optical counter. Both the samples are taken
isokinetically. The optical counter must sample at a fixed flow rate as
well so that isokinetic conditions are achieved by selecting the dimen-
sions of the sampling nozzle to match the sampling flow rate to the
primary flow rate.
The compartment itself is fabricated of 10 gauge steel. One side
panel of the compartment is attached with quick-release fasteners that
allow complete removal of the side. This panel serves as an access port
for bag loading and unloading and for inner compartment maintenance. It
is made of transparent plastic, allowing visual inspection and observation
of the baghouse during operation.
Nominally, the bags are 5-1/2 inches in diameter and 6'feet long.
All that is required, however, is a bag that can be clamped to the
nipple or an adapter at each end of the compartment. The test bags are
typically installed under slight tension so that no droop or slack is
apparent.
The induction system consists of a temperature- and humidity-
controlled chamber, housing a screw-type dust feeder of variable pitch.
The dust is gravity fed into the inlet line and subsequently through a
dispersion venturi. Dust feed rate is determined by weighing the dust
discharge from the feeder over a known time interval.
Humidity is measured by wet and dry bulb thermometers. It can be
sampled both in the feed line and the baghouse outlet as well as in the
room ambient air.
Although not shown in Figure 1, a differential pressure cell con-
tinually monitors the pressure drop across the test bag during the
system operation. This pressure drop (plus that across the flow venturi),
the system humidity and temperature, the dust feed rate, and the mass
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and particle number analysis of the outlet constitute the primary measure-
ments recorded during (or after) a run.
3.1.2 Experimental Programs (Shake-cleaned Baghouse)
One purpose of the in-house program is to identify and publicize
fabrics that appear useful or advantageous in the control of fine
particulates--especially for powerplant applications. Procedures and
conclusions of this type of investigation are reported in Section
3.1.2.1.
Fundamental phenomena associated with fabric filtration have also
been studied as part of the in-house research. An ambitious modeling of
the fabric filtration process was concluded. New topics have been added
and are reported in Section 3.1.2.2.
3.1.2.1 Fabric Filter Performance Evaluation — A class of potentially
useful filter fabrics evaluated by the EPA in-house facility is that
called "spunbonded." These fabrics are non-woven fabrics deriving their
strength and stability from bonds between touching fibers rather than a
weave. These spunbonded joints are created by a heat treatment, by
incorporating a lower melting copolyester, by physical softening and
hardening using an appropriate solvent, or by some combination of these
methods. Their chief virtue is low cost, since they are made by simply
forming webs of continuous filaments and then bonding. Commercial
spunbonded fabrics have been made from materials such as polyamides,
polyesters, and olefins and marketed under various tradenames. This
phase of the in-house research evaluated two representative fabrics:
Cerex, a spunbonded nylon manufactured by Monsanto, and Reemay, a spun-
bonded polyester manufactured by DuPont.
Two categories of properties were used in the evaluations: per-
formance and endurance. The performance parameters measured or calculated
from the measured data were [Refs. 2,3]:
1) Collection Efficiency
2) Outlet Concentration
3) Effective and Terminal Drags
4) Specific Cake Resistance.
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In general the preferred baghouse operation 1s one which maximizes
parameter 1 and minimizes parameters 2 to 4. Parameters 3 and 4 measure
the energy required to operate the baghouse. They are, respectively,
the pressure drop across the bag per unit air flow through the bag and
the rate of increase of this quantity. Hence they can be used to cal-
culate the fan rating required for system operation and the frequency of
bag cleaning.
Endurance was determined by counting the total number of shakes a
bag could tolerate before showing irreversible degradation in performance.
Typically endurance would be measured in an accelerated test cycle
whereby the number of shake-clean oscillations per unit operating time
was greatly increased over what it would be in an actual installation.
Conversely the dust quantity passing through the bag would be less than
realistic. Such departures from reality, however, made it possible to
gather comparative bag life data in a practical calendar time period.
i
The results of the spunbonded tests have been published in References
2 and 3. When filtering redispersed flyash at room temperature, these
tests show that the spunbonded fabrics display higher efficiencies and
lower outlet concentrations than do woven fabrics of the same composition
and weight. In addition the drags and specific cake resistances of the
spunbonded fabrics are as low as or lower than those of the woven fabrics.
Bag endurance appears to be not as great, however, for the spunbonded
bags.
Based on these evaluations, spunbonded fabric filters warrant field
testing. They cost less than woven fabrics and cost less to operate, but
perform somewhat better—at least when filtering powerplant flyash at
room temperature. Lower drags and specific cake resistances also mean
that a bag does not have to be cleaned as often so even though the
spunbonded bags do not tolerate as many total shakes as their woven
counterparts, their superior flow interactions with flyash mean that
they will not have to be shake-cleaned as often over a given period of
operation. Just how these factors translate into bag life in an actual
installation is not clear. Nor is it clear as to how to extrapolate the
10
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endurance measurements made on this shake-cleaned test apparatus to the
commonly used reverse-air or pulse-jet cleaned units. Relative fabric
performance (collection efficiency, drags, etc.) would be expected to
hold in these other installations but endurance could change significantly.
The in-house EPA evaluation suggests that the spunbonded fabrics could
provide an optimum cost-effective fabric for certain applications and
further evaluation in field applications is warranted.
A third fabric evaluated in the shake-cleaned baghouse was an
expanded polytetrafluorethylene (PTFE) laminate. The specific fabric
tested consisted of a PTFE film supported on a woven Nomex scrim—the
Gore Tex/Nomex fabric.
The test sequences were similar to those run on the spunbonded
fabrics; both performance and endurance were measured. Reference 4
summarizes the results of this evaluation. Among the conclusions of the
study was the hypothesis that the PTFE laminate fabric depends on
sieving as the primary filtration mechanism when the dust is flyash (or
any similarly sized dust, most likely).
This conclusion means that this dust/fabric interaction varies
significantly from what is regarded as the "classical" particle capture
mechanisms by fiber and fabric filters. These classical mechanisms are
summarized in Figure 2.
1) Gravity — Large particles (>5 ym diameter) simply settle out
of the gas stream. This action occurs independently of the
fiber or fabric filter and depends upon gas stream velocity as
well as particle mass.
2) Direct Interception -- The particle, in streamline flow,
collides with the fiber.
3) Inertia! Impaction — The particle deviates from the gas
streamlines because of inertial forces and strikes the fiber.
4) Diffusion -- The particle, being of the same magnitude in size
as the molecules of the gas flow, moves in Brownian motion and
has a finite probability of colliding with the fiber along its
random path.
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Inertial
Particles impaction
Diffusion
Electrostatic
attraction
\ f ^^~~ I
*»* Flow streamlines \
\
i i
Interception
Gravity
Figure 2. Mechanisms for particle removal by a filter [Ref. 5].
Scrim
Felled rmda ipprox. 3 mm.
Tlma of travel 0.2-0.5
Figure 3. Section through felted filter media showing distribution
of dust [Ref. 5].
12
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5) Electrostatic Attraction -- Frictional charging of the fabric
or particles creates electrostatic forces between the fiber
and the particle which, depending on the species involved, can
be the largest forces on the dust particle--at least in the
vicinity of the fiber.
These mechanisms are generally accepted as describing the inter-
action between dust-laden air and a clean fabric filter. As the dust
layer accumulates on the filter, however, the primary interaction then
becomes one between the particles trapped in the dust cake and those in
the gas stream (Figure 3). Only then does particle capture by sieving
(particle capture because the openings in the fabric or dust cake are
smaller than the dust particle) become an additional important cap-ture
mechanism.
For the PTFE laminate filtering flyash, sieving dominated from the
beginning, making its behavior quite different from that usually observed.
Although the filtration efficiency of this fabric exceeded that of
all others tested, flyash is probably not the optimum dust for evaluating
Gore Tex/Nomex. The high fine-fiber content of this fabric suggests
that it would be especially effective for filtering submicron dusts.
This important property was not experimentally checked, however.
Other newly developed fabrics featuring special coatings, structure,
or composition have also been briefly evaluated to determine baghouse
potential. In general the most promising of these fabrics are those
described in the published reports [Refs. 2,3,4]. The function of pre-
liminary screening of new fabrics will continue as the search continues
for better performing, less costly fabric filters.
Questions involving the suitability of fabric filtration for a
specific application also have been addressed. For example, in response
to a request from the USDA's Southern Regional Research Center, New
Orleans, a brief evaluation of cotton dust filtering in the shake-
cleaned baghouse was carried out. This investigation showed that the
cotton dust/polyester fabric interaction allowed high efficiency filtration
at relatively lower operating energy. The fabric released the dust
easily during cleaning and gave no evidence of blinding. Testing was
13
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far too brief to permit any conclusions regarding bag life and endurance
but the application looks very attractive and could well lead to im-
proved dust control at costs comparable to those for existing control
methods. Assessing the suitability of specific dusts to control by
fabric filtration will continue as part of the in-house program.
3.1.2.2 Phenomena Research — Concurrent with or sandwiched between the
fabric evaluation activities of the various shake-cleaned baghouses have
been basic investigations of the dust/fabric interaction. A major
activity of the in-house program was an attempt to model the performance
of a filter fabric in terms of its structure. The significant, inde-
pendent variables in the model included dust properties in addition to
the various structural properties of the fabric. While the goal of
establishing a quantitative, mathematical model was not achieved, the
program did lead to important qualitative insights into the dust/fabric
interaction [Ref. 6].
Highlights of this work included the experimental confirmation of
the bridging phenomenon [Ref. 7], and of a critical pore size for bridging
which is on the order of 10 times the mass mean particle diameter of the
dust. The presence of fabric pores with dimensions exceeding this
critical value leads to excessive dust seepage through the fabric. The
concept of bridging arises from the commonly observed growth of particle
chains as a result of particle capture by the fibers of the fabric
filter [Ref. 7]. What this observation says is that, while the first
particle deposited on a clean fiber may adhere at a random position on
the fiber, the second, third and all subsequently deposited particles
prefer to adhere to that previously deposited particle rather than to
another site on the clean fiber. Consequently, the initial growth of
dust cake is in the form of long, thin chains or filaments of deposited
particles. These growths extend outward from the surface of the initial
deposition site into the gas flow until the aerodynamic forces break
them apart or until they reach some adjacent point of support, such as
another fiber or another growing particle chain. Once a particle chain
14
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establishes a stable anchor at its growing end, it has bridged^ a void
and itself becomes a semi-permanent surface capable of particle capture
in directions normal to its axis of growth. The critical pore size for
bridging is about 10 particle diameters. When the average spacing
between nearest neighbor fibers exceeds this distance, bridging becomes
a low probability event and the filter continues to pass considerable
dust along straight-through trajectories. If the average pore size is
less than 10 particle diameters, significant bridging occurs and the
filter rapidly blocks off most straight-through paths. The collection
efficiency becomes very high. Unfortunately, the pressure drop across
the filter also increases so that eventually some of the dust cake must
be removed. The art of cleaning consists of removing enough of the dust
to reduce the filter pressure drop, but not enough to eliminate all
bridging particle chains. Generally a compromise can be easily established
whereby both the pressure drops and the collection efficiencies cycle
between acceptable limits.
The experimental program in support of this investigation examined
over 100 fabrics of various sizes, construction, and composition using
three different dust sources. Most data were collected using the
shake-cleaned baghouses, but supplemental data were also gathered from
measurements made with a small bench-scale filter system [Ref. 6]. This
initial broad basic investigation has served as the foundation from
which much later work has followed--in both the shake-cleaned baghouses
and the pulse-jet baghouse to be discussed in Section 3.2.
One such investigation, carried out exclusively in the shake-
cleaned baghouse, has been a study of bag aging effects. Performance
parameters of woven polyester bags filtering flyash were measured over
an extended period of time, simulating field use. An accelerated shake
cycle was needed in order to complete a full life cycle in the laboratory
test. A partial cycle was also carried out under operation more typical
of field use. These data were used to identify and illustrate three
stages of bag life: (1) break-in, (2) steady-state, and (3) wearout.
Outlet concentration, for example, traces out the familiar bathtub curve
with time; that is, it decreases initially during the break-in period,
remains relatively constant during the steady-state, and rises rapidly
15
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during wearout. The time dependence of collection efficiency and drag
exhibits the inverse of the bathtub curve. Factors affecting the
transitions from one portion of the curve to the next include both the
dust loading and the cleaning parameters—the more dust remaining on or
in the fabric, the higher its collection efficiency but also its drag.
The details of where the dust resides in the fabric and how it "works"
its way through are less well understood than the straight-through/
single-capture models (Figure 2) applicable to single fibers [Ref. 8].
Reference 9 summarizes the initial experimental work and conclusions on
this broad subject.
3.2 PULSE-JET BAGHOUSE
The pulse-jet baghouse used in the EPA in-house work is a commer-
cially available Mikro-Pulsaire Dust Collector purchased from the Mikro-
Pul Division of the United States Fiber Corporation. It has been used
on several studies and evaluations and is continually being modified and
improved. Plans for its use are growing.
The organization of this section is as before, the equipment'being
described first (3.2.1), followed-by a brief review of the experimental
highlights to date (3.2.2).
3.2.1 Description of the Pulse-jet Baghouse
The pulse-jet apparatus used for all EPA in-house work is a
commercially available, nine-bag Mikro-Pul baghouse (Figure 4), consisting
of three rows of three bags each. The cross section of the housing is
square (34 inches on a side); it is 103 inches long. The dust-laden air
enters at the bottom of the compartment and is drawn through the bags,
into the clean air plenum, and out to the analytic line. Bag cleaning
is by directing a short (- 0.1 sec) pulse of high pressure air through
the venturi nozzle located in the top, open end of each bag. The venturi
shapes the air pulse and aspirates additional air flow from the plenum
to create a shock wave that travels the length of bag and back. This
action snap-cleans the bag by dislodging the accumulated dust cake from
its outside surface. The agglomerated dust cake drops into the collection
bin below.
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Induced flow
To Exhauster
Dust LaJen Air
A Filter bag
B Tube sheet
C Blow pipe
D Air supply pipe
E Solenoid valve
F Diaphragm valve
G Blow pipe orifice
H Remote timer
J Clean air outlet
K Plenum chamber
L Collar
M Venturi nozzle
N Wire cage
0 Housing
P Rotary valve air lock
Q Hopper
R Diffuser
S Dirty air inlet
T Manometer
Material Discharge
Figure 4. Schematic of Mikro-Pulsaire collector.
(reproduced with permission of the Mikro-
Pul Corporation, Summit, N. J.)
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The source of the air pulse is a compressor which charges the air
pipes placed in rows above each set of three bags. Each pipe has a
diaphragm valve and three orifices, one positioned directly opposite the
exit opening of each bag. When actuated by a timer-controlled solenoid
pilot valve, the diaphragm valve passes an air pulse into the air pipe,
out each of the three orifices, and into the venturi beneath each orifice.
The diaphragm valves are sequenced so that only one row of the three
bags is cleaned at a time. Consequently, the flow of air through the
baghouse continues uninterrupted even during cleaning.
The dirty-gas induction system and the outlet gas analytic chain
are the same as used with the shake-cleaned system previously described
(Section 3.1.1).
In fact installing the pulse-jet unit consisted simply of removing
the baghouse compartment from one of the shake-cleaned systems, replacing
it with the pulse-jet compartment, and hooking up the appropriate inlet
and outlet lines already in place. Dust feed and temperature-humidity
control are by an Acrison screw- type feeder and an Inreco Humidity and
Temperature Control Unit, respectively. As with the shake-cleaned
system, outlet analysis employs both a Millipore sampling filter assembly
and a Climet optical counter. Air flow is measured by the pressure drop
across a flow venturi in the outlet line and is maintained at the de-
sired flow rate by a flow controller. Pressure drop across the bags is
continuously recorded.
3.2.2 Experimental Programs (Pulse-jet Baghouse)
The pulse-jet baghouse has also served two purposes—the evalua-
tion of candidate fabric filters and the investigation of basic filtration
phenomena. This section is divided into two subsections, one on each
aspect.
3.2.2.1 Fabric Evaluation — Although various bags have been tested in
the pulse-jet baghouse, the primary evaluation has been of a class of
needled, uncalendared felt fabrics prepared under an EPA grant by the
Schools of Engineering and Textiles at North Carolina State University
(NCSU) [Ref. 'lO]. These felts were evaluated in support of a study of
the relationship between fabric structures and filtration performance.
18
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Variations in needling technique (depth and spacing, dimensions), fabric
structure, weight, and density were correlated with filtration per-
formance both in the EPA pulse-jet baghouse as well as in a filtration
apparatus at NCSU. From the comparative measurements of the NCSU-
prepared felts with those already commercially available, it could be
seen that under most normal operating conditions the NCSU fabrics were
superior [Ref. 10]. At high dust loading and at high air-to-cloth
ratios, however, cleaning difficulties were severer with the NCSU
fabrics than with the commercial fabrics [Ref. 10].
Other fabrics have also been evaluated in the EPA pulse-jet unit.
These evaluations have been brief and were generally terminated early
because of obvious fabric deficiencies. Among these brief evaluations
was a high pile fabric which showed promise because of its low pressure
drops. Unfortunately this fabric proved to have poor collection
efficiency from the beginning. With service, the efficiency degraded
further as though the fabric pores were stretching to pass large
quantities of dust.
3.2.2.2 Specific Research — The key experiment performed in the pulse-
jet baghouse was a comparison of the penetration of two types of test
dusts—rock dust and Detroit Edison flyash—through two types of felt
bags, Dacron and Nomex. This research actually responded to requests
for information and assistance from members of the asphalt industry as
well as from non-R&D segments of EPA, but provided valuable, supple-
menting information on the effect of changing dusts. The rock dust used
for experimentation was finer than the flyash; its mass median diameter
(DCQ) was on the order of 2.5 urn as compared with a DcQ for flyash of
4.0 Mm or greater. Both types of fabric filter bags showed consistently
higher pressure drops, higher values of specific cake resistance, and
more dust penetration when filtering the rock dust than when filtering
the flyash. For both fabrics, the collection efficiency increased with
increasing inlet loading more significantly for rock dust than for
19
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flyash. The type of dust is clearly of first order importance in
determining filtration behavior. While both fabrics could efficiently
remove rock dust from the air flow, it was more costly and more difficult
to remove than flyash.
This investigation also looked for fabric blinding or the suggestion
of blinding when filtering these dusts. No concrete evidence of blinding
was observed using either fabric with either dust. The maximum dust
•3
loading employed, however, was on the order of 12-13 grains/ft so that
the occurrence of blinding in a field installation (operating at, say,
3
100 grains/ft of inlet dust) could not be ruled out.
An interesting sidelight of this work came about by continuously
recording the output of the optical detector. The trace reveals pulses
of penetrating particles corresponding to the time periods of the bag
cleaning pulse, confirming the results of other investigations that the
bulk of the particles that penetrate the fabrics do so during or imme-
diately after the cleaning pulse. This conclusion 1s particularly
striking for the flyash particles larger than 1 ym. At 0.3 and 0.5 ym
the penetration of flyash is more uniform. Rock dust, on the other
hand, shows strong pulse-related penetration over all size ranges,
although the peaks become broad for the submicron dust populations.
Recovery of high efficiency of filtration following a cleaning pulse
takes a significant fraction of the filtration period when filtering.
submicron rock dust.
While both the Dacron and Nomex fabric filters displayed high
collection efficiencies (99+%) under all test conditions, both bags
filtered the flyash more efficiently than the rock dust (99.9+% for
flyash vs. 99.9% for the rock dust). The major differences were in the
much higher pressure drops (5-7 in. H20 for rock dust vs. 1-3 in. H20
for flyash) and specific cake resistances (>20 in. H20/fpm/lb/ft2 for
rock dust vs. 2 to 5 in. H20/fpm/lb/ft2 for flyash) characteristic of
rock dust filtration. Type-of-fabric differences were smaller than the
type-of-dust differences. The experimental results served to emphasize
once again the importance of the dust Itself in selecting optimum operating
conditions. One cannot blithely assume that what works well for one dust
20
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will work equally well for another. In the absence of adequate under-
standing, as is true for the present state-of-the-art, some experimental
trial and error seems necessary before making major commitments to any
particular mode or range of operation.
This uncertainty that characterizes fabric filtration restricts the
rate at which the method will be accepted. An urgent goal of the EPA
in-house program in fabric filtration (and the outside contractor/grantee
program as well) continues to be better understanding of the process
whereby field results can be better predicted and designed for, reducing
costly full scale corrections and surprises and the preliminary trial
and error procedures now needed to avoid them.
3.3 HIGH TEMPERATURE BAGHOUSE
The high temperature baghouse was built in order to investigate
fabric endurance at high temperature. At the time of its construction
few, if any, experimental baghouses had a high temperature capability.
The role of this apparatus, now dismantled, was to evaluate fabric
endurance at the high temperatures more closely corresponding to field
conditions. The hope was that this apparatus, because it allowed more
realistic testing than could be found with standard fabric tests, would
provide a better measure of fabric life in the field. The results, when
compared with field tests, were anomalous and the decision was made to
design a more versatile unit before doing further testing of high tempera-
ture fabrics.
The unit had a four-bag capacity and operated on a dust batch basis
(Figure 5). A given quantity of dust in a heated air flow would be
filtered by the fabric. The filtration period was 75 sees after which
the fabric was shake-cleaned for 35 sees. During cleaning, the dust
dropped to the bottom of the bag into the dust pot. The dust pot con-
tained a blow pipe system through which the hot air of the next filtra-
tion cycle entered and redispersed the dust. The dust became reentrained
and recaptured by the fabric filter. Except for pressure drops across
the bag, no measurements of filtration efficiency or other filter per-
formance parameters were made. The evaluation was of endurance only so
the apparatus simply cycled the dust on and off the fabric in a high
temperature gas flow. Coulter counter analysis of the dust did show
21
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ro
(S3
Ball Bushing
Support
Frame
Ball
Bushing
Shaker
Arm
['l1et*~{(~)]""*~
CD
Blower
Thermocouples
i
\
To Shaker Assembly
en
*T3
CO
i.
01
4J
-Rotameter
•Flow Control Valve
-Solenoid Valves
-Heater
Figure 5. Laboratory baghouse for high temperature tests.
-------
that the mass median diameter increased slightly with time of operation,
presumably because more of the finer particles penetrated the fabric and
were lost from the recycled dust supply.
The fabrics evaluated were made mostly of fibrous glass coated with
one type of surface finish or another in an effort to improve bag life.
One series of tests was run, however, to test the cleaning recommenda-
tions generated from contract work done by 6CA Corporation [Ref. 11].
The recommendations were for higher cleaning frequency and generally
greater amplitude than normally used. The purpose of the high tem-
perature baghouse testing was to ensure that commercial fabrics could be
cleaned at the recommended conditions and at their maximum recommended
service temperature without severe degradation of the fabric.
Among the fabrics tested were woven cotton (operated at 180°F) and
woven polyester (operated at 275°F). These woven fabrics withstood over
2 million shakes at high temperature without failure. The tests showed
that high temperature operation did not alter the cleaning recommendations
in any major way [Ref. 12].
The one felted wool fabric tested (also at 180°F) failed when
subjected to a period of shake-testing but a relatively early failure
was expected. Felts are not ordinarily used in shake-cleaned units and
cannot withstand the stresses imparted by shaker mechanisms.
3.4 THE VERSATILE FABRIC FILTER TEST UNIT
New apparatus is now being built for continuing the high tempera-
ture testing. This equipment will also be capable of simulating operation
in acidic environments and at various dust loadings and humidities,
opening up new areas of research (such as reagent injection filtration,
whereby selected gases are removed by the filter after being adsorbed by
an appropriate injected sorbent reagent). Bag cleaning will be by any
of the three common methods: mechanical-shake, reverse-air, or pulse-
jet. With the completion of this facility in 1977, the in-house test
program will for the first time have a reverse-air cleaning capability.
Table 1 summarizes the range of operating variables being built into
this equipment. Each of the four bags is mounted .in a separate
23
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TABLE 1. OPERATING RANGE OF THE VERSATILE FABRIC FILTER TEST UNIT
Variable
Range
Temperature
Bag face velocity
Humidity
Number of bags
Bag size
Cleaning methods
Reactive fluids
Grain loading
70°F to 1500°F
1 to 12 ft/min
Dew point of 32°F to saturation.
Above 212°F, up to 20 percent
by volume.
35.5" overall length; 2.5" cuffs;
5" inside diameter; variable L/D
Mechanical shake
Frequency: 0 to 20 cps
Duration: 0 to 60 min
Amplitude: 0 to 1 in
Reverse flow
Duration: 0 to 15 min
Repetition rate: variable
Reverse pulse
Repetition rate: variable
S0?: 100 ppm to 10 percent
SQ~: 5 to 500 ppm
Cror HC1: 100 to 1000 ppm
HF: 5 to 100 ppm
0.05 to 15 grains/ft3
24
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isolated compartment that is fitted with a changeable lid corresponding
to the chosen cleaning technique. While each compartment is fed from a
common input gas line, it will be possible to simultaneously test
different fabrics and to shut off one or more compartments off while
continuing to run on the others.
The instrumentation built into the bag housing includes the measure-
ment of the mechanical tension under which the bag is mounted. Tension
can be adjusted at operating temperature to eliminate uncontrolled
changes because of differing thermal coefficients of expansion between
any given bag and the housing. In addition to the standard monitors for
temperature, pressure, and humidity, a provision for measuring electrostatic
charge on the bag surface is also included. This measurement is by an
electrostatic probe on which the electrostatic charge induces a voltage.
A 30-channel data logger keeps a running record of the many dependent
and independent variables.
The availability of this test equipment will open up new horizons
for the in-house program. Research previously beyond the scope of the
in-house facility will become possible.
25
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SECTION 4
FUTURE WORK
Over the near term the in-house program will continue evaluations
of specific fabrics and investigations of the basic mechanisms of fabric
filtration. A highlight of the coming year is the acquisition of a
versatile, high temperature test facility (Section 3.4). This new
equipment will not only replace an older unit used for high temperature
tests, but will also add new test capability such as reverse-air cleaning,
electrostatic charge measurements (by an induced voltage), and measure-
ment of bag tension. Thus the in-house program, while pursuing the same
dual goals as in the past, will have greatly enhanced capability for
both evaluation and investigation. This section discusses several tasks
of the immediate future.
4.1 EVALUATION OF HIGH TEMPERATURE FABRICS
One limitation to fabric filter applications and/or techniques is
that imposed by the temperature stability of the fabrics. Present
commercial fabrics—at least those in widespread use--cannot operate
continuously at a temperature in excess of 500-550°F, and only the most
temperature-tolerant of the commercially available fabrics (fibrous
glass) can operate at this temperature. Most fabrics have far lower
temperature limitations.
A potentially significant payoff awaits the developer of a fabric
capable of operating at much higher temperatures. For example, particu-
late removal from the fuel gas used to fire a COGAS* turbine must be
*COGAS, Combined GAs and Steam power system.
26
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very efficient—much better than is required for ambient air standards.
Failure to meet this requirement would jeopardize the proposed scheme
of coal gasification/power generation. Fabric filtration can meet the
particulate removal requirements, but present fabrics introduce the need
for a fuel gas cooling step between the gasifier and the C06AS power
system, severely penalizing the overall efficiency of the coal-to-power
conversion. Having a high temperature fabric that could eliminate the
need for fuel gas cooling would be highly desirable, perhaps necessary.
The availability of high temperature fabrics in general enhances
the range of interactions and reactions that can be carried out—high
temperature fabrics imply more process versatility. For example, the
adsorption of S02 by a nahcolite-seeded gas is more efficient at high
temperature. Removal of SO? in a dry scrubbing process such as nah-
colite adsorption would, of course, greatly enhance the value of fabric
filtration to operators of coal-fired boilers.
Because of their value, then, high temperature fabrics are con-
tinually being developed. A key part of the near-term fabric evaluation
at EPA will be performance measurements on candidate high temperature
fabrics such as woven stainless steel, glass-asbestos, and those woven
from alumina-boria-silica fibers. The initial tests will be at room
temperature and, with the availablity of the versatile fabric filter
test unit, high temperature testing is also planned.
Other fabrics will continue to be tested with appropriate dusts as
the need for evaluation arises. New fabrics developed to possess superior
properties of some sort—acid resistance, abrasion resistance, etc.—or
lower costs are expected to remain part of the fabric evaluation program
throughout the foreseeable future. All the existing experimental
baghouses will participate in this function from time to time as will
the new versatile baghouse.
4.2 FABRIC FILTRATION RESEARCH
The fabric filtration industry operates largely in the empirical
mode. New installations are designed on what has worked in similar,
previous installations. A new dust to filter typically means small
27
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scale testing to confirm a workable set of operating parameters on which
to base a full scale design. This empirical procedure is required be-
cause not enough of the significant parameters of the dust/fabric capture
and release processes are understood. The EPA in-house program continually
undertakes research that will lead to a better understanding of the
science underlying fabric filtration. This section lists three ex-
periments now either underway or 1n the formative stages. These three
and others will be part of the in-house basic research work for the
coming year.
4.2.1 Dust Penetration Studies
All the mechanisms of dust penetra'tion through a fabric filter
are not yet understood. The delayed component of dust penetration—that
which does not pass straight through without collision or temporary
capture—makes up a complex sequence of interactions which depend on
many variables, many of which have not yet been identified. The ongoing
in-house work is investigating the properties of the delayed component
of dust penetration for various dust/fabric systems. This work will
continue with the goal of developing models by which the magnitude and
behavior of this component can be predicted.
4.2.2 Cleaning Characteristics of Jet Pulses
The cleaning efficiency of a jet pulse used in a pulse-jet bag-
house depends on the properties of the jet pulse in addition to the bag
properties and the dust/fabric interactions. Among the major independent
variables of any specific pulse jet are the pressure and duration of the
initiating air. If the shaping venturi and the plenum are assumed
fixed, as well as the orifice dimensions and position of the blow pipe,
then pulsing pressure, duration, and frequency are the primary controls
over the pulse-jet cleaning. Work is now underway to correlate these
independent variables with bag cleaning efficiency and also dust pene-
tration. Triggering circuits, now incorporated Into the pulse-jet
baghouse, allow correlation between bursts of penetrating particles
(detected optically in the outlet) and the independent variables used to
form the cleaning pulse. Improved understanding could lead to more
efficient cleaning at lower costs in energy, making a more desirable
baghouse operation.
28
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4.2.3 Electrostatic Interactions
Electrostatic interactions can dominate the dust/fabric inter-
action under certain conditions, as has been dramatically demonstrated
on numerous occasions. Unfortunately such demonstrations have not yet
led to adequate understanding of the role of electrostatic forces in
fabric filtration or to useable models for predicting the magnitude or
importance of electrostatic forces in a given dust/fabric system. Now
being developed at the in-house facility is a technique for measuring
electrostatic charge buildup on a bag during pulse-jet operation. The
technique consists of measuring the voltage on the electrically isolated
cage during operation and requires only the addition of a wire lead to
the cage on which to measure the voltage (or alternatively the charge).
The wire cage, being in intimate contact with the bag at many discrete
points, is assumed to acquire charge from the fabric. This charge corres-
ponds to an average electrostatic charge buildup on the fabric. The
method does not depend totally on induced voltage; it allows actual
charge transfer between the fabric and the wire cage. It has the merits
of being simple to implement and of introducing only minimal disturbances
into the standard equipment found in the field. This latter feature
promises observations in the laboratory that correspond closely to what
is observed in actual installations.
29
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SECTION 5
REFERENCES
1. Hudson, S. R. "The Filter Fabric Market Report" (as quoted in
The Fabric Filter Newsletter, Vol.1, No.12, October 10, 1976, The
Mcllvaine Company, 2970 Maria Ave., Northbrook, 111. 60062).
2. Turner, J. H., "EPA Fabric Filtration Studies: 1. Performance of
Non-Woven Nylon Filter Bags," EPA-600/2-76-168a (In press).
3. Ramsey, G. H., R. P. Donovan, B. E. Daniel, and J. H. Turner, "EPA
Fabric Filtration Studies: 2. Performance of Non-Woven Polyester
Filter Bags," EPA-600/2-76-168b, June 1976, (NTIS No. PB 258025/AS),
EPA Industrial Environmental Research Laboratory, Research Triangle
Park, N. C. 27711.
4. Donovan, R. P., B. E. Daniel, and J. H. Turner, "EPA Fabric Filtration
Studies: 3. Performance of Filter Bags Made from Expanded PTFE
Laminate," EPA-600/2-76-168c, December 1976, (NTIS No. PB 263132/AS),
EPA Industrial Environmental Research Laboratory, Research Triangle
Park, N. C. 27711.
5. Bergman, L. "New Fabrics and Their Potential Application," J. Air
Poll. Cont. Assn. 24_, No.12, Dec. 1974, pp. 1187-1192.
6. Draemel, D. C., "Relationship Between Fabric .Structure and Filtration
Performance in Dust Filtration" EPA-R2-73-288, July 1973, (NTIS No.
PB 222237), EPA Control Systems Laboratory, Research Triangle Park,
N. C. 27711.
7. Billings, C. E. and J. Wilder, "Handbook of Fabric Filter Technology,
Vol.1, Fabric Filter Systems Study" EPA No. APTD 0690, December
1970, (NTIS No. PB 200 648), GCA Technology Division, Bedford,
Mass. 01730.
8. Leith, D., S. N. Rudnick, and M. W. First, "High-Velocity, High-
Efficiency Aerosol Filtration," EPA-600/2-76-020, January 1976,
(NTIS No. PB 249457/AS), Harvard School of Public Health, 665
Huntington Avenue, Boston, Mass. 02115.
9. Donovan, R. P., B. E. Daniel, and J. H. Turner, "EPA Fabric Filtration
Studies: 4. Bag Aging Effects" (In press).
30
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10. Mohamed, M. and E. Afify, "Efficient Use of Fibrous Structures in
Filtration," EPA-600/2-76-204, July 1976, (NTIS No. PB 257147/AS),
North Carolina State University, Schools of Engineering and Textiles,
Raleigh, N. C. 27607.
11. Dennis, R. and J. Wilder, "Fabric Filter Cleaning Studies," EPA-
650/2-75-009, January 1975, (NTIS No. PB 240372/AS),GCA Technology
Division, Bedford, Mass 01730.
12. Daniel, B. E., J. H. Turner, and R. P. Donovan, "EPA Fabric Filtration
Studies: 5. Bag Cleaning Technology (High Temperature Tests)" (In
press).
31
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APPENDIX
CONVERSION FACTORS
To Convert from:
3
grains/foot
foot
inch
grain
inch of water (60°F)
foot/min (fpm)
in. H:
Multiply by:
Ib(m)/ft2
°F
kg/m
meter
meter
kilogram
f
newton/meter*
meter/sec
newton-sec
meter-kg
°K
2.29
3.05
2.54
6.48
2.49
5.08
104
10
10
10
10
10
10
-1
-2
-5
,+2
-3
c '
= f (°F + 459.67)
32
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-77-042
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
EPA Research in Fabric Filtration: Annual Report
on IERL-RTP Tnhouse Program
5. REPORT DATE
May 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
James H. Turner
8. PERFORMING ORGANIZATION REPORT NO,
9. PERFORMING ORGANIZATION NAME AND ADDRESS
(Same as Block 12.)
10. PROGRAM ELEMENT NO.
EHE624
11. CONTRACT/GRANT NO.
NA (IERL-RTP Inhouse)
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
Annual: 4/72-9/76 .
14. SPONSORING AGENCY CODE
EPA/600/13
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The report summarizes EPA's inhouse research program in fabric
filtration, involving investigations into the basic mechanisms of dust/fabric inter-
action in order to develop improved understanding of the process. Evaluation of new
fabrics in laboratory tests that can be extrapolated to field applications is a second
major goal of the inhouse research. Among the fabrics evaluated were a spun-
bonded nylon (Cerex), a spunbonded polyester (Reemay), and expanded polytetra-
fluorethylene (PTFE) laminate (Gore Tex/Nomex), and various specially developed
fabrics, including uncalendared needled felts and coated fibrous glasses. These
fabrics all performed well or exhibited some desirable property. Other fabrics,
less attractive for particulate control, were tested less completely. Development of
a mathematical model capable of predicting fabric filtration performance was attemp-
ted. The complexities of this task led to breaking the overall process into simpler
subdivisions for study, including: particle penetration mechanisms, temperature
and age effects, bag cleaning techniques, and electrostatic effects.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b,IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Dust Control
Fabrics
Nylon Fibers
Polyester Fibers
Felts
Glass Fibers
Mathematical Models
Electrostatics
Cleaning
Air Pollution Control
Stationary Sources
Particulate
Fabric Filters
Baghouses
Polytetrafluorethylene
13B
11E
11B
12A
20C
13H
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
38
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
33
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