EPA-600/2-76-168b
June 1976
Environmental Protection Technology Series
EPA FABRIC FILTRATION STUDIES:
2. Performance of Non-woven
Polyester Filter Bags
Resi 'ark, Nortl:
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five 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 five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconornic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution. This
work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policy of the Agency, 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 Informa-
tion Service, Springfield. Virginia 22161.
-------
EPA-600/2-76-168b
June 1976
EPA FABRIC FILTRATION STUDIES:
2. PERFORMANCE OF
NON-WOVEN POLYESTER FILTER BAGS
by
G. H. Ramsey, R. P. Donovan (Research Triangle
Institute), B.E. Daniel, and J.H. Turner
*
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry .
Research Triangle Park, NC 27711
Program Element: EHE624
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
-------
PREFACE
This report is the second in a series of reports, entitled EPA
Fabric Filtration Studies, which summarize the results of EPA laboratory
testing of new baghouse fabric materials and present the conclusions of
specialized research studies in fabric filtration. These tests have
been carried out over the past four years by the Industrial Environmental
Research Laboratory, Research Triangle Park, North Carolina, and previously
by predecessor agencies. The purpose of these investigations was to
evaluate the potential of various new fabrics as baghouse filters and
to obtain data for use by the fabric filtration community. The testing
consisted of simulating a baghouse operation in a carefully controlled
laboratory setting that allowed measurement and comparison of bag performance
and endurance. The simulation discussed in this paper covered only a
very narrow range of operating conditions:
1) Redispersed, classified flyash {mass median diameter
between 5 and 6 ym) entrained in air was the only dust
used.
2) All filtering was done at room temperature.
3) Humidity was varied from about 30 to 70 percent.
4) The air to cloth ratio was held at 4 to 1.
5) The dust loading was held in the vicinity of
3 grains/ft3 (6.9 g/m3).*
6) The test cycle consisted of a constant 20 minute
feed, 1 minute delay, 2 minute shake cleaning, and
1 minute delay, regardless of the pressure drop
across the bag.
Extreme caution should be used in extrapolating the results reported
here to the substantially different conditions that occur in all field
applications. The usefulness of the present results is primarily as an
initial screen of candidate fabrics for baghouse applications.
*EPA policy is to use SI units only or to list both the common British
unit and its metric equivalent. For convenience and clarity, non-metric
units are used in this report. Readers more familiar with metric terms
may use the factors in the appendix to convert to that system.
iii
-------
The projected £_PA^dDrJc Filtration Studies series will contain:
1) Performance or Non-Woven Nylon Filter Bags.
2) Performance o~ 'ion-Woven Polyester Filter Bags (this report).
3) Performance of Expanded PTFE Laminate Filter Bags.
4) Aging Effects.
5) Bag Cleaning Technology.
6} Analysis of Particle Size Efficiency.
-------
TABLE OF CONTENTS
Page
Preface iii
List of Figures vi
List of Tables vi
List of Abbreviations and Symbols vii
Acknowledgments viii
SECTION I 1
SECTION II 3
SECTION III 7
SECTION IV 11
References 27
Appendix—Conversion Factors 28
-------
LIST OF FIGURES
Page
1 Apparatus used for testing spunbonded polyester bags. ..... 8
2 Mass collection efficiency of spunbonded bags (weight in
oz/yd2) 12
: O • " ' : '
3 Outlet concentration of spunbonded bags (weight in oz/yd ). . . 13
4 Specific cake resistance of flyash on spunbonded bags (weight
in oz/yd2) "14
5 Reemay fabric photomicrograph (Sample 3, 108X) 15
2
6 Effective drag of spunbonded bags (weight in oz/yd ) 16
7 Outlet concentration and efficiency versus number of shakes
for the 6 oz/yd2 spunbonded polyester bag 18
8 Specific cake resistance and pressure drops during endurance
testing of the 6 oz/yd2 spunbonded polyester bag 19
9 Effective and terminal drags during endurance testing of the
6 oz/yd2 spunbonded polyester bag 20
2
10 Outlet concentration versus relative humidity for the 3 oz/yd
acrylic coated polyester bag 23
11 Specific cake resistance, effective and terminal drags as a
function of relative humidity (3 oz/yd2 acrylic coated
polyester bag) 24
12 Size analysis of outlet dust (Sample 7) 26
LIST OF TABLES
Page
Properties of Reemay Spunbonded Polyester Fabrics 4
Performance of Spunbonded Polyester Filter Bag With Number
of Shakes 21
vi
-------
LIST OF ABBREVIATIONS AND SYMBOLS
A = filtration area of fabric, sq ft
CQ = mass outlet concentration, grains/1000 cu ft
E = mass collection efficiency, percent
F = fallout fraction (dust which goes directly to baghouse
hopper without contacting bag)
K2 = true value of specific cake resistance, (in. H20/fpm)/(lb/sq ft)
K£ = measured value of specific cake resistance, (in. H20/fpm)/(lb/sq ft)
AP£ = pressure drop across bag at time zero of filtration cycle (in. hLO)
APT = pressure drop across bag at end of filtration cycle (in. H20)
Q = flow rate through filter, cfm
qs = flow rate through sampling system, cfm
R = average dust feed rate, grams/min
SE = effective drag, in. H20/fpm
ST = terminal drag, in. HLO/fpm
T = filtration time, min
V = filtration rate, fpm (air/cloth ratio)
W = mass of dust collected in sampling system, grams
-------
ACKNOWLEDGMENTS
E.I. DuPont de Nemours and Co., Wilmington, Del. donated all the
spunbonded polyester bags used in this study. They manufactured the
fabric and assumed all costs of sewing and preparing the bags to fit the
EPA test facility. In addition, Messrs. Paul Langston and Harry Sandstedt
of DuPont's Textile Fiber Department provided advice and encouragement
throughout the evaluation.
viii
-------
SECTION I
CONCLUSIONS
Laboratory comparisons of various spunbonded polyester bags used to
filter redispersed flyash at room temperature show that:
1) Based only on measurements of efficiency, drag, and specific
cake resistance, the 6 oz/yd nominal weight crimped polyester
fiber offers the best overall performance/cost tradeoff; this bag
performed slightly better than the spunbonded nylon bags pre-
viously tested,(11 substantially better than the lighter weight
crimped polyester fibers tested, and somewhat better than the
straight fiber polyester bags tested (neglecting the endurance
data).
n
2) In the endurance tests, the 3 oz/yd acrylic coated bag with-
stood 3.5 million shakes and the 6 oz/yd^ crimped filter bag, 22
million shakes, both significantly less than the woven polyester
bag which withstood about 54 million shakes.
3) For both the crimped and the straight fiber spunbonded poly-
esters, increasing the fabric weight increased the filtration
efficiency.
p
4) For comparable fabric weights (3 oz/yd spunbonded polyster vs.
3.9 oz/yd^ woven polyester) the spunbonded polyester fabrics
have higher efficiencies, lower outlet concentrations, lower
specific cake resistances, and much lower effective drags than
the woven polyesters.
o
5) For comparable fabric weights (the 2.2 oz/yd straight fabric
versus the 2.4 oz/yd^ crimped fiber), bags made from straight
polyester fibers showed higher efficiencies and drags, and lower
outlet concentrations and specific cake resistances than bags
made from crimped polyester fibers.
6) No significant performance differences existed between the
acrylic coated and the uncoated spunbonded polyester bags
tested.
Other general conclusions of these experiments are the following:
1) The smallest sized particles measured (0.3 to 0.5 pm optical
diameter) are less effectively filtered than the larger sized
particles.
-------
2) As is true for typical woven ancl felted fabrics, the filter
efficiency is generally 'lowest immediately following a cleaning
cycle and highest at the end of the filtration cycle.
3) Following cleaning, high humidity (70 percent) reduces the time
required for the bag to reestablish high filtration efficiency.
4) Filtration efficiency is higher at high humidity (70 percent)
than at low humidity (30 percent), while specific cake resist-
ance has only a small humidity dependence and both effective
drag and terminal drag increase slightly over this humidity
range.
The best performing spunbonded polyester bags significantly out-
performed the woven polyester bags; they displayed higher efficiencies,
and lower cake resistances and effective drags. Their initial costs are
lower but they may have to be replaced more often.
2
The 6 oz/yd crimped fiber bag was clearly the all around superior
2
performer, based on both performance and endurance tests. The 3 oz/yd
bag performed nearly as well but proved much less rugged in the endurance
tests.
These conclusions are based on room temperature filtering of redis-
persed flyash. No conclusions regarding operation at -higher temperature,
in corrosive environments, with different dusts or other typical field
conditions are explicitly stated.
-------
SECTION II
INTRODUCTION
Non-woven fabrics are receiving increased attention as filtering
mediums. One type of non-woven fabric, referred to as "spunbonded," is
made by forming webs of continuous filaments which are then bonded into an
integral fabric structure. This type of fabric can be produced from any
polymer; commercial materials include polyamides, polyesters, and olefins.
This report summarizes tests carried out with bags made of spunbonded
polyester fibers manufactured by DuPont under the tradename of "Reemay."
Reemay bags are made of polyester filaments containing a small amount of a
lower melting point copolyester to effect bonding. Typical physical
properties of Reemay spunbonded polyester are given in Table 1. Both the
manufacturer's nominal values and the values measured by the Fabric Research
Laboratory (FRL) on fabric samples furnished by EPA are listed in Table 1.
The measured and nominal sample weights agree reasonably well and correlate
well with other fabric properties. Thickness, on the other hand, varies
widely and does not correlate with weight or other properties. It appears
to be a marginally meaningful value as measured on these samples.
Fabric filtration is a proven method for the removal of parti oilates
from gas streams. The performance of a bag is often measured by its
efficiency, E, of dust removal or by the concentration of dust in the
effluent, C , (the outlet concentration). The experiments to be reported
here were carried out at constant dust feed rates and dust loadings so
that the outlet concentration is the preferred parameter of comparison
because of its direct dependence on VL, T, and q (see the List of Ab-
breviations and Symbols for all definitions of terms):
(WD)(Q)
E = 100 !1 u
-------
Table 1. PROPERTIES OF REEMAY SPUNBONDED POLYESTER FABRICS'
^-^ Sample No.
Characteristic ^^x^^
Weight (oz/yd2)
Thickness (mil)
Grab Tensile (Ibs)
Machine Direction
Cross Direction
Grab Elongation (%)
Machine Direction
Cross Direction
Tongue Tear (Ibs)
Machine Direction
Cross Direction
Mullen Burst (psi)
Frazier Permeability
(ft3/min)/ft2
Straight Fiber
1.27
10.7
35.4
50.3
25.0
48.5
3.10.
2.71
51
(measured
525
1 2
2.19 (2.2)b
18.9 (12.0)
35.2 (58.3)
45.0 (47.0)
45.2 (43)
57.2 (49)
2.67 (3.91)
1.96 (3.99)
3
3.04 (3.0)
13.9 (16.2)
89.6 (89.9)
53.0 (75.9)
72.2 (52)
61.6 (681
3.53 (6.44)
2.53 (6.27)
4
(acrylic
(coated)
2.95
16.0
69.8
39.4
54.7
41.1
2.70
2.80
72 (65) 111 (99) 97
at 0.5 in. fLO pressure differential)
307 (288) 175 (246) 253
Crimped Fiber
5
(1.9)
(13.4)
(30.4)
(28.3)
(3.34)
(3.40)
(28)
(392)
6
2.49 (2.4)
15.9 (17.5)
54.7 (47)
73.5 (41)
44.3 (69)
90.5 W)
4.83 (5.5)
3.93 (670)
59 (40)
312 (298)
5
14
123
97
112
114
12
12
107
160
7
.96 (6.0)
.8 (34.7)
(83)
(T08)
.16 (14.1)
.30 (15.7)
11051
(94)
affeasurements made by FRL, An Albany International Company, Rt. 128 at Rt. 1, Dedham, Mass. 02026.
ASTM test methods used.
^Numbers in parentheses are the nominal values published by the manufacturer (DuPont).
-------
05.43 ) (Hp) (IOOQ)
(T) (q^
In addition to the obvious requirement of high efficiency, other
important properties which are indicators of performance are pressure
drop through the bag, endurance, and cake buildup.
Pressure drop through a bag filter is an important cost
consideration, since the pressure drop is a measure of the energy
consumption of the system. This parameter is measured by the filter
effective drag,
SE = AP£/V; (3)
and the terminal drag,
ST = APT/V. (4)
During the filter cycle, pressure drop increases as the dust cake
builds up and the efficiency of the bag improves. However, the increase
in pressure drop implies an increase in the energy consumption of the
system. The most important parameter of the cake buildup is the specific
cake resistance, K2 or 10,, which is the rate of increase of drag with
cloth loading during the filter cycle, and can be a useful design
parameter. The value of 1C reflects how fast the bag recovers after a
cleaning cycle and is believed to be a function of both fabric and dust
characteristics. For more information consult the Handbook of Fabric
(2\
Filter Technology.v '
Fabric endurance is important for cost estimation. The bag life,
together with the initial bag cost and bag installation costs, determines
one portion of the baghouse operating costs. The primary factors which
influence bag life are the filtering environment (gas stream, temperature,
and chemistry), the bag cleaning technique, and the abrasiveness of the
dust. More information concerning endurance can be found in Fabric
Filter Cleaning Studies.
-------
The final factor considered in this report is the effect of humidity
upon bag performance. Humidity affects the collection efficiency by
altering both fabric and dust characteristics. Various types of woven
fabrics have been shown to respond differently to humidity changes, but
the humidity effects on spunbonded fabrics have not yet been studied in
great detail.
-------
SECTION III
EXPERIMENTAL METHODS
The tests on the spunbonded polyester bags were conducted in an
experimental, single compartment baghouse as shown schematically in Figure
1. The area of each bag was 8.5 sq ft and the air to cloth ratio was held
fixed at 4/1. The test dust used for the evaluation was powerplant flyash
which was classified to remove over-sized particles. The size distribu-
tion, as determined by Coulter Counter analysis, showed that 10 percent
was less than 3.5 ym, 90 percent was less than 20 urn, and the mass median
diameter was between 5 and 6 pm.
Inlet air was fed to the system from the top to the inside of the
bag, passed through the bag, through a sampling area, and out of the
system. The dust loading, temperature, humidity, and quantity of air were
controlled. Pressure drop across the baghouse and the flow rate were
measured continuously with a differential pressure cell and a venturi.
Humidity and dust loading were checked periodically. Humidity was mea-
sured with wet bulb/dry bulb thermometers and the dust feed was measured
by periodically sampling the output of the feeder. The grain loading of
the outlet air stream was determined by sampling the stream isokinetically
and collecting the dust on a 0.45 um Millipore filter. The weight gain
acquired by the filter element during the sampling period became the Wp
term in equations 1 and 2.
The first set of tests was designed to evaluate bag performance as a
function of fabric weight. For each sample, tests began with a 24 hour
operating period as a "break in" cycle. Standard operating conditions
were 20 minutes of filtration, 1 minute delay, 2 minutes of shake clean-
ing, and 1 minute delay for each filtration cycle. Shake action applied
to the bottom of the bag consisted of periodic displacements at a fre-
quency of 240 cycles per minute and an amplitude of 0.81 inches. Mea-
surements began after 24 hours.
-------
HUMIDITY
CONTROL CHAMBER
96 in.
^FILTER
CHAMBER
MECHANICAL
SHAKER
DISPERSION
VENTURI
VARIABLE SPEED
DUST FEEDER (FLYASH)
MILLIPORE FILTER
SAMPLING TRAIN
ROTARY BLOWER
Figure 1. Apparatus used for testing spunbonded polyester bags.
8
-------
Three types of Reemay bags were tested at a constant humidity of 40
percent:
1) Three straight fiber bags of nominal weights, 1.35,
2.2, and 3.0 oz/yd? (Samples 1, 2, and 3, Table 1).
2) Three crimped fiber bags of the following nominal
weights: 1.9, 2.4, and 6.0 oz/yd2 (Samples 5, 6,
and 7).
2
3) A 3.0 oz/yd acrylic coated straight fiber bag
(Sample 4).
The acrylic coat is a fiber variation designed to increase abrasion
resistance.
2
Humidity tests were conducted on two of the bags--the 6 oz/yd
2
crimped fiber bag (Sample 7) and the 3 oz/yd acrylic coated bag (Sample
4). To establish equilibrium prior to testing, these bags were operated
for 96 hours before taking any humidity-dependent data. Following this
equilibrium period, the relative humidity was varied in a random fashion
between 30 and 70 percent. After each humidity change, the bag was oper-
ated for 48 hours before recording new data. The standard operating cycle
was used for these tests.
2
Endurance tests were also run on Sample 7 (6 oz/yd ) and Sample 4 (3
2
oz/yd ). For this test, the filtration cycle was changed to consist of 2
minute feed, 1 minute delay, 15 minute shake cleaning, and 1 minute delay.
The bags were operated until failure occurred, failure being defined by a
tear or large hole in the bag as detected by a high outlet concentration.
No attempts were made to seal pin holes or thin spots during the run.
For comparison, a 3/1 twill woven bag made from continuous filament
polyester was also tested for endurance. The weight of this woven poly-
2
ester bag was 3.9 oz/yd .
For certain of the tests, mostly the humidity tests, the outlet dust
was classified according to size with a Climet Counter. This counter
measures the concentration of particulates in the following size ranges:
-------
1)
2)
3)
4)
5)
6)
0.
0.
1
2
4
3 - 0.5 ym.
5 - 1 ym.
2 ym.
- 4 urn.
- 8 ym.
>8 ym.
This measurement is in real time and allows the size distribution
to be determined at various times during the 20 minute filtering cycle.
Typically the size distribution was determined at the beginning of the
filtration cycle and every 2 minutes thereafter throughout the 20 minutes.
The Climet data provided a comparison of populations in different
optical size ranges as a function of time rather than an absolute deter-
mination of outlet concentration. The Climet data were not used to mea-
sure any performance parameter but only to furnish additional qualitative
insight into the dust/fabric interaction. (The Millipore filter sample
furnished the measures of total dust, WD, from which filtration efficiency
was calculated.)
Only a limited number of bags were used in the test program. In
general, one bag of each sample type was used for gathering performance
data which could be completed in about 2 days. For the two bags tested
for humidity dependence (Samples 4 and 7), a second fresh bag was used in
each humidity test series. Because of their superior performance, these
same two sample types were also those chosen for endurance tests. The
initial plan was to use the same bag on which the humidity series had been
run for the endurance tests. This plan was carried out for Sample 7 but,
because of an early failure on the Sample 4 bag, the endurance tests for
that type bag were completed (and essentially entirely carried out) on the
bag that had been used previously to measure the performance parameters.
Conceivably, some bias could have been introduced into the results because
of this difference in bag conditioning.
10
-------
SECTION IV
RESULTS
PERFORMANCE
The effect of fabric weight on the efficiency and outlet concen-
tration is shown in Figures 2 and 3. Comparisons are made with 3.9
oz/sq yd woven polyester fabric and with spunbonded nylons as tested and
(1 4)
reported previously. ' ' Both the coated and uncoated straight fiber
o
3 oz/yd spunbonded polyester bags exhibited a lower outlet concentration
o
(higher efficiency) than the 3.9 oz/yd woven polyester bag. An in-
crease in fabric weight resulted in a higher efficiency for both the
crimped and straight spunbonded fibers.
Fabric weight versus specific cake resistance is shown in Figure 4.
The specific cake resistance for the spunbonded nylons increased with
fabric weight^ ' but this pattern was not observed with the spunbonded
2
polyester bags: the single bag made from crimped 6 oz/yd polyester
consistently operated at lower Ki values than bags made from 1.9 or 2.4
2 2
oz/yd crimped fibers. The 3 oz/yd bag had a specific cake resistance
2
of about 70 percent of the 3.9 oz/yd woven polyester. The low weight,
crimped spunbonded polyester fibers had significantly higher specific
cake resistances than comparably low weight spunbonded nylons, but the
2
6 oz/yd spunbonded polyester bag had a specific cake resistance about
2
40 percent lower than both the 5.9 oz/yd spunbonded nylon and the 3.9
2
oz/yd woven polyester reference bag.
The spunbonded polyester bags contain trilobal cross-sectional yarn
as shown in -Figure 5 while the woven polyester and the spunbonded nylon
bags are made of yarn with round cross-sections. The crimped fiber and
the trilobal cross-sectional yarn probably influences the manner in
which dust builds up on the filter as has been found by Miller, Lamb and
/5\
Costanza.v '
The effective drag of the spunbonded polyester increased with
fabric weight as shown in Figure 6. The woven polyester had an effective
2
drag about three times as high as that of the 3 oz/yd spunbonded poly-
ester bags and slightly less than three times as high as that of the 6
2
oz/yd spunbonded polyester bags. The effective drag of the spunbonded
polyester bags was generally lower that of the spunbonded nylon bags.
11
-------
100
95
o
z
—• UJ
PO _
u.
u.
Ui
90
85
1.35
22
STRAIGHT FIBER
3.0
COATED
1.9
24
60
CRIMPED FIBER
SPUNBONDED
POLYESTER
3.9
WOVEN
POLYESTER
1.5 29 42 5.9
SPUNBONDED NYLON
Figure 2. Mass collection efficiency of spunbonded bags (weight in oz/yd ).
-------
300
u
O
O
O
200
I-
UJ
O
U
UJ
O
100
HH BH
JBSBL
1.35
22
3.0
STRAIGHT FIBER
3.0
COATED
1.9
2.4
6.0
CRIMPED FIBER
SPUNBONDED POLYESTER
3.9
WOVEN
POLYESTER
1.5 2.9 4.2 5.9
SPUNBONDED NYLON
p
Figure 3. Outlet concentration of spunbonded bags (weight in oz/yd ).
-------
10
E
CL
8
-CM
LU
(O
V)
UJ
o:
UJ
CJ
o
u.
o
UJ
Q.
tf)
1.35 Z2 _ 3.0 30
STRAIGHT FIBER COATED
24
CRIMPED FIBER
6.0
3.9
WOVEN
POLYESTER
1.5 2.9 4.2 5.9
SPUNBONDED NYLON
SPUNBONDED POLYESTER
•t
Figure 4. Specific cake resistance of flyash on spunbonded bags (weight in oz/yd ).
-------
Figure 5. Reemay fabric photomicrograph (Sample 3-
-------
0.7
0.6
0.5
. 0.4
O.3
UJ
UJ
0.2
0.1
1.35 2.2 _ 3.0
STRAIGHT FIBER"
3.0 1.9 2.4 _ 60
COATED CRIMPED FIBER
ffi
SPUNBONDED POLYESTER
3.9
WOVEN
POLYESTER
1.5 2.9 4.2_ 5.9
SPUNBONDED NYLON
•j
Figure 6. Effective drag of spunbonded bags (weight in oz/yd ).
-------
ENDURANCE
The endurance testing was interrupted periodically in order to
measure bag performance. For these measurements, the cycle was changed
from the endurance cycle (2 minute filtration, 1 minute delay, 15 minute
shake) to the standard operating cycle (20 minute filtration, 1 minute
delay, 2 minute shake). As usual, the average of three cycles was used
to measure the performance.
2
6 oz/yd Spunbonded Fabric (Sample 7)
2
The first signs of fabric deterioration for the 6 oz/yd bag
occurred after 12.5 million shakes when a small tear about 1/2 inch long
and numerous weak spots were discovered (outlet concentration of 14
o
grains/1000 ft ). After 20 million more shakes, the outlet concentration
3
was approximately 34 grains/1000 ft . The bag was inspected again and
rotated 180 degrees during remounting so as to place the tear directly
above the baghouse outlet. This reorientation of the tear caused the
3
outlet concentration to increase immediately to 88 grains/1000 ft .
The bag was considered to have failed after 22 million shakes and the
test was concluded. Various bag performance parameters versus number of
shakes are plotted in Figures 7-9. Although the bag was declared a
failure after 22 million shakes, the failure was not catastrophic and
the bag remained functional even after 32 million shakes.
3 oz/yd Spunbonded (Sample 4)
The outlet concentration and efficiency versus number of shakes for
2
the 3 oz/yd acrylic coated spunbonded bag are shown in Table 2. A bag
was installed initially which failed after 370,000 shakes. Failure was
due to a 3 inch tear located at the bottom of the bag where the cuff was
sewn.
An identical bag was installed with approximately 370,000 shakes
from a previous run. The second bag performed satisfactorily for 3.5
million shakes at which time the outlet concentration rose to over
3
46 grains/1000 ft . Visual inspection revealed a number of breaks in
the bag over the entire length. The bag was considered failed at this
point.
17
-------
-.100
- 10
8
10
12
14 16 18 20
SHAKES x I06
22 24 26 28 30 32 34 36
Figure 7. Outlet concentration and efficiency versus number of
shakes for the 6 oz/yd2 spunbonded polyester bag.
-------
26 28 30 32 34
SHAKES x 10
6
Figure 8.
Specific cake resistance and pressure drops during endurance
testing of the 6 oz/yd2 spunbonded polyester bag.
-------
ro
o
1.2
I.I
1.0
.9
O 7
-'
co
2
.6
.5
.3
.2
Sample 7
O EFFECTIVE DRAG
O FINAL RESIDUAL DRAG
8
Figure 9.
10 12
14
16
18
20 22 24 26 28 30 32
SHAKES x I06
Effective and terminal drags during endurance testing
of the 6 oz/yd^ spunbonded polyester bag.
-------
Table 2. PERFORMANCE OF SPUNBONDED POLYESTER*1 FILTER BAG
WITH NUMBER OF SHAKES
^^^-^ Number of ,-
\4hakes x 10°
Charac- ^"^x.
teristic ^^^^
Efficiency (%)
Outlet Concentration.,
(CQ), grains/1000 ft3
Specific Resistance (K?)
(in.H20/fpm)/(lb/sq ft)
Effective Drag (Sc)
in.H20/fpm b
Terminal Drag (ST)
in.H20/fpm
Terminal Pressure Drop
(APT), in.H20
0.845
99.54
13.91
3.88
0.16
0.29
1.18
1.10
99.24
22.95
4.35
0.15
0.30
1.21
1.34
99.43
17.66
4.47
0.16
0.32
*.• • •
1.27
2.10
99.56
13.25
4.26
0.16
0.31
1.24
2.88
99.49
15.33
4.59
0.19
0.34
1.38
3.56
98.46
46.42
4.23
0.20
0.35
1.38
Fabric weight = 3 oz/sq yd
plotted in
(endurance data for the 6 oz/yd bag is
Figures 7-9).
Both of these spunbonded polyester bags failed significantly sooner
than woven polyester bags. In a similar endurance test a bag made of
woven polyester (with properties plotted in Figures 2» 3, 5, and 6)
showed signs of wear after 18 million shakes, but was not considered
failed until about 54 million shakes.
The number of shakes to failure measured here does not directly
correspond to bag life in field use, since most shaker baghouses in the
field operate on a pressure-drop-controlled cycle; that is, the filtra-
tion cycle continues until the pressure drop across the bag reaches a
predetermined maximum value, following which the shake cleaning cycle
commences and continues until the pressure drop falls to a predetermined
low value. Because of the Blower drags and lower specific cake resis-
tances associated with the spunbonded polyester bags, a given number of
21
-------
shakes in the fixed cycle test reported here implies a longer field life
for the spunbonded bags than the same number of shakes would for the
woven polyester bags.
HUMIDITY
The effect of relative humidity on the outlet concentration of the
2
3 oz/yd acrylic coated bag is given in Figure 10. Outlet concentration
decreases with increasing humidity but the data show large scatter and
2
poor reproducibility. Similar testing of the 6 oz/yd bag produced the
same general trend but with even greater scatter. The outlet concentra-
2 3
tion of the 6 oz/yd bag was 3 grains/1000 ft for all filtering done
at 70 percent relative humidity. At 40 percent relative humidity, the
3
outlet concentration varied between 2.5 and 11 grains/1000 ft .
Cake resistance was insensitive to relative humidity, while the
effective drag and terminal drag both reflected a small dependence on
humidity, being lower at the lower values of relative humidity. Since
the effective drag increases with time, plots of Sr and ST versus relative
humidity (Figure 11) depend on the order in which the data are taken.
All data in Figure 11 were taken with a single acrylic coated bag (Sample
No. 4) over a 3 week period. The number next to each of the data
points refers to the order in which that specific point occurred in the
sequence of test runs. Time alone causes an increase in both the drags,
SE and ST (compare points 1, 2, and 3; 4 and 5; 7, 8, and 9). The
humidity dependence is superimposed upon this time dependence of the
drags.
2
The Sample 7 bag (6 oz/yd ) showed similar behavior.
For both these spunbonded polyester bags, then, the effect of humidity
upon performance is not very large when filtering redispersed flyash.
SIZE DISTRIBUTION
The size distribution of dust at the bag outlet was determined
every 2 minutes during the humidity tests. The analysis showed that
immediately after cleaning—at the beginning of the next filtration
cycle—the concentration of the larger sized particles was greatest and
decreased rapidly with time. The smallest sized fraction (0.3 to 0.5 urn),
however, increased in concentration initially, peaked anywhere from 4 to
22
-------
ro
(A)
IO
li.
O
o
O
o:
o
V ^
LU
o
UJ
o
10
9
8
7
6
5
4
3
2
I
20
Figure 10.
30
40
50
60
70
80
RELATIVE HUMIDITY (%)
Outlet concentration versus relative humidity for the
3 oz/yd2 acrylic coated polyester bag.
-------
5
s
E
D. CM
9vi £> 4
.c
-
O
10
O
ii
O4
05
O
13
CM
3 -
O
3
o?
0.5
M
X
d
H-
tf)
04
u'n
0,3
S
4
A
13
9 8
0.3-
D
13
1
O
x*1 0.2
UJ
CO
O.I
CD G
Q 9 8
7
no
03 09
data points 6
® and 12 not
available
I till)
2.0 30 40 50 60 70 8(
RELATIVE HUMIDITY (%)
Figure 11. Specific cake resistance, effective and terminal drags as
a function of relative humidity (3 oz/yd? acrylic coated
polyester bag).
24
-------
10 minutes after the filtration cycle began, and then decreased (Figure
12).
In nearly all the samples evaluated, the 0.3 - 0.5 ym sized particu-
lates were the dominant size at the end of the 20 minute filtration
cycle but never at the beginning. At the start of the filtration cycle
either the 0.5 to 1 ym group or the 1 to 2 urn group was the largest.
The concentrations of these two groups both fell more rapidly than that
of the smallest group so that by the end of the filtration cycle, the
smallest sized particles dominated. Fall-off was according to size
range, the largest sized particles falling off in concentration most
rapidly. As is shown in Figure 12, humidity affects the time dependence
of the size distribution of particles in the outlet. The concentration
curves measured at 59 percent relative humidity decay more rapidly than
those measured at 28 percent.
Cake resistance (K^), and the effective (S£) and terminal (Sj)
drags were higher at 59 percent than at 28 percent relative humidity but
some of this increase was probably a time effect (the 28 percent humidity
data were taken several weeks before the 59 percent data), as illustrated
in Figure 11 for bag Sample 4. The humidity dependence of K^, S£, and
ST is probably small.
25
-------
• 2-4
+ 1-2
O 0.5-1.0
D 0.3 - 0.5
6 8 10 12 14
FILTRATION TIME (min)
16
REL. HUM. 28%
16
m
REL. HUM. 59%
18
20
2468 10 12 14
FILTRATION TIME (min)
Figure 12. Size analysis of outlet dust (Sample 7)
18 20
26
-------
REFERENCES
Turner, J. H., "Performance of Non-Woven Nylon Filter Bags" (in
press).
Billings, C. E., Wilder, J., Handbook of Fabric Filter Technology,
Vol. I, Fabric Filter Systems Study, EPA publication APTD 0690,
NTIS No. PB-200 648, 2-1 to 2-219 (December 1970).
Dennis, R. and Wilder, J., "Fabric Filter Cleaning Studies,1' EPA-650/2-
75-009, NTIS No. PB-240 372/AS (January 1975).
Durham, J. F. and Harrington, R. E., "Influence of Relative Humidity
on Filtration Resistance and Efficiency of Fabric Dust Filters,"
Filtration and Separation 8. July/August 1971, pp. 389-393.
Miller, B.C., Lamb, E. R., and Costanza, P., "Influence of Fiber
Characteristics on Particulate Filtration," EPA 650/2-75-002, NTIS
No. PB-239 997/AS (January 1975).
27
-------
APPENDIX
To Convert From:
foot
foot2
foot3
foot/min (fpm)
grain
grains/1000 ft3
inch
inch2
inch3
inch of water (60°F)
Ib (force)
Ib (mass)
lb/foot2
Ib/1nch2 (psi)
mil
oz/yd2
yard2
yard3
Conversion Factors
To:
meter
meter2
meter3
meter/sec
kilogram
g/m3
meter
meter2
meter3
newton/meter2
newton
kilogram
newton/meter^
newton/meter2
meter
kg/m2
meter
meter2
meter3
Multiply By:
3,05
9.29
2,
5,
6,
2,
2,
6,
1,
2,
4,
4,
6,
2.
3,
9,
83
08
48
29
54
45
64
49
49
54
4.79
89
54
39
14
10-1
10-2
10-2
10-3
10-5
io-3
io-2
10-4
TO'*
io-2
8.36
7.65
x 10-1
x 10-1
x ID'3
x 10-5
x TO'2
x 10-
x IO-1
x 10-1
28
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO. ,
EPA-600/2-76-168b
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
EPA Fabric Filtration Studies: 2. Performance of
Non-woven Polyester Filter Bags
5. REPORT DATE
June 1976
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S) G R Ramsey, R. P. Donovan (Research Tri-
angle Institute), B.E.Daniel, and J. H.Turner
8. PERFORMING ORGANIZATION REPORT NO. (
IERL-RTP-155
9. PERFORMING OP3ANIZATION NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, North Carolina 27711
10. PROGRAM ELEMENT NO.
EHE624
11. CONTRACT/GRANT NO.
NA--In-house Report
12. SPONSORING AGENCY NAME AND ADDRESS
(NA—In-house Report)
13. TYPE OF REPORT AND PERIOD COVERED
Iri-house Final: 6/74-8/75
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES JERL-RTP project officer for this in-house report is J.H. Turner J
Mail Drop 61, 919/549-8411, Ext 2925. ^
16. ABSTRACT The report gives results of an evaluation of fabric filter bags made of non-
woven, spunbonded polyester in a laboratory simulation of a baghouse operating at
room temperature. Using only redispersed power plant flyash, the collection effi--
ciency, specific cake resistance, and pressure drops (effective and terminal drags)
were measured for seven bags each of which was made from one of seven different
spunbonded polyester fabrics. The two best-performing bags were further evaluated
in humidity and endurance tests. Overall, the bag made from crimped polyester fiber
of 6 oz/sq yd (0.20 kg/sq m) nominal weight provided the best performance/operating
cost tradeoff. It significantly outperformed a woven polyester bag (included in the
tests as a reference) but lasted less than half as long in the endurance tests. Classi-
fication of the outlet dust according to size during the humidity tests showed that:
filtration efficiency is higher at 70 than at 30 % relative humidity; although filtration
efficiency is always lowest immediately after a cleaning cycle, high relative humidity
(70 %) reduces the time required to re-establish operation at high filtration efficiency;
and the smallest particles measured (0.3 to 0. 5 micrometer optical diameter) are
less efficiently filtered than larger particles.
17.
KEY WORDS AND DOCUMENT ANALYSIS
a,
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Air Pollution
Dust
Filtration
Dust Filters
Fabrics
Nonwoven Fabrics
Polyester Fibers
Fly Ash
Air Pollution Control
Stationary Sources
Particulate
Fabric Filters
Baghouses
Collection Efficiency
13B
11G
11D
13K
HE
21B
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
§F F
7
20. SECURITY CLASS (Thispage/
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
29
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