EPA-650/2-75-022
February 1975
Environmental Protection Technology Series
^^^M^A^^iMM^^
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EPA-650/2-75-022
ANDERSEN
FILTER SUBSTRATE
WEIGHT LOSS
by
W.B. Smith, K.M. Gushing, andG.E. Lacey
Southern Research Institute
2000 Ninth Avenue South
Birmingham, Alabama 35205
Contract No. 68-02-0273
ROAP No. 21ADM-011
Program Element No. 1AB012
EPA Project Officer: D. Bruce Harris
Control Systems Laboratory
National Environmental Research Center
Research Triangle Park, N. C. 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
WASHINGTON, D. C. 20460
February 1975
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EPA REVIEW NOTICE
This report has been reviewed by the National Environmental Research
Center - Research Triangle Park, Office of Research and Development,
EPA, and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environ-
mental Protection Agency, have been grouped into series. These broad
categories were established to facilitate further development and applica-
tion of environmental technology. Elimination of traditional grouping was
consciously planned to foster technology transfer and maximum interface
in related fields. These 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
9. MISCELLANEOUS
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.
This document is available to the public for sale through the National
Technical Information Service, Springfield, Virginia 22161.
11
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CONTENTS
Andersen Filter Substrate Weight Loss Study 1
Weighing-Balance Errors and Moisture
Absorption Errors 2
Handling Losses 6
Running Losses 9
Miscellaneous 14
Conclusions 21
iii
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TABLES
No.
1 Steel Ferrule and Washer Weight Changes
Upon Desiccation 3
2 Andersen Substrate Cumulative Weight Changes
Due to Desiccation 5
3 Cumulative Changes in Weight Due to Desic-
cation of Andersen Substrates by Individ-
ual Set 7
4 Moisture Absorption by 3 Andersen Back-up
Filters 8
5 Desiccation and Handling Weight Change of
"Clean" Andersen Substrates 10
6 Desiccation and Handling Weight Change of
"Normal" Andersen Substrates 11
7 Desiccation and Handling Weight Change of
"Clean" Andersen Substrates by Set 12
8 Desiccation and Handling Weight Changes of
"Normal" Andersen Substrates by Set 13
9 Desiccation and Sampling Weight Change of
Andersen Substrates After Sampling Filtered
Air at 0. 5 acfm for 6 Hours at 24°C 15
10 Desiccation and Sampling Weight Change of
Andersen Substrates After Sampling Filtered
Air at 0. 5 acfm for 6 Hours at 120°C 16
11 Desiccation and Sampling Weight Changes of
Andersen Substrates by Set After Sampling
Filtered Air at 0. 5 acfm for 6 Hours at 24°C 17
iv
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Tables (Continued)
No.
12 Desiccation and Sampling Weight Changes of
Andersen Substrates by Set After Sampling
Filtered Air at 0.5 acfm for 6 Hours at 120°C 18
13 Weight Changes of Andersen Substrate After
Sampling Filtered Effluent from a Wet
Precipitator at an Aluminum Reduction
Plant. 125°F Gas Temperature 19
14 Typical Average Amounts of Collection for
an Andersen Impactor 20
15 Cumulative Weight Change of Teflon Filter
Substrate After Desiccation and Baking 22
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ANDERSEN FILTER SUBSTRATE WEIGHT LOSS STUDY
This study was undertaken to determine if weight losses from
the fiber filter substrates of the Andersen Impactor were
significant and to what extent they might affect field test measure-
ments. A procedure was set up to check for errors in the mechanics
of the weighing, moisture absorption by the substrates, errors
due to handling, and errors resulting from running an impactor.
These will be explained in detail later.
The filter substrates for the Andersen Impactors, with the
exception of the back-up filters, were baked for approximately
18 hrs in an oven at a temperature of 240°C. The back-up
filters were baked for about 6 hrs at the same temperature.
The substrates were from normal Andersen substrate stock.
The back-up filters were cut from glass fiber filter stock.
Mine Safety Appliance No. CT-75428.
After all substrates and filters had been baked, they were
allowed to cool to ambient temperature in room air. They then
were left sitting out for 4 days at room temperature and humidity
while their foil holders were cut. After being folded and
placed in the foil holders, the substrates, including
foil holder, were weighed. The process of placing the substrates
in the foils and then weighing them took 2 days, making a
total of 6 days elapsed time from the baking procedure. All
substrates were then placed in desiccators.
The balance used in the study was a Cahn Model G-2 Electro-
balance. The total weight of the substrates and foils was
greater than 200 mg but this scale was used with counter-
weights (tare weights) for improved accuracy. To keep
moisture at a minimum, the weighing chamber was loaded with
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a small pan containing Drierite, anhydrous CaSO,,. This is
our normal procedure in weighing Andersen substrates.
The average weights for the Andersen glass fiber substrates and
back-up filters were also measured so that the weight losses
could be evaluated relative to this total weight. Due to the
design of the Andersen Impactor, the filter substrates alter-
nate in pattern from stage 1 to stage 8; stage filters being
alike for stages 1, 3, 5, and 1, but different for stages 2, 4,
6, and 8. To obtain an average weight, 50 substrate filters
of the odd type (1, 3, 5, 7), 50 of the even type (2, 4, 6, 8),
and 50 back-up filters were baked at 240°C for 6 hours, desiccated
for 18 hours, and then weighed on a Mettler Gram-atic balance.
The average weights are:
Odd Filter Stage Substrates (1, 3, 5, 7) 189.54 mg average,
Even Filter Stage Substrates (2, 4, 6, 8) 178.92 mg average, &
Back-up Filter 215.04 mg average.
Weighing-Balance Errors and Moisture Absorption Errors
Three sets of the substrates, Nos. 13N, 15N, and 16N, were
used to check the possibility of errors being made just in
the process of weighing the substrates. Also, this was a
check on the reproducibility of the balance in weighing an
object. In addition to sets 13N, 15N, and 16N, two
stainless steel ferrules and one flat washer were included
in the weighing as standards, since these should neither
lose nor gain significant mass due to absorption. They
were cleaned in benzene to remove any grease and kept in
clean containers in a desiccator throughout the test. Tweezers
were always used in handling the ferrules, the washer, and
the foil-wrapped substrates.
The results of the ferrule and washer weighings are given in
Table 1. Approximately one weighing of each was made each
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Table 1. Steel Ferrule and Washer Weight Changes
Upon Desiccation
A
B
C
Initial
Weight,
mg
494.12
422.50
413.80
Cumulative
6
+ .02
.00
.00
24
.00
.02
.02
30
+ .02
.00
.02
48
.00
.00
.00
Hours
54
+ .02
.00
.02
of Desiccation
72
.02
.02
+ .02
78
.00
.02
.02
96
.00
+ .02
+ .02
120
+ .02
.02
.02
144
+ .02
.00
+ .02
Weight change in mg as compared to initial weight after indicated
number of hours of desiccation.
A & B are stainless steel Swagelok ferrules; C is a zinc-plated
steel washer.
All weight changes are negative unless otherwise noted.
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day during the study. (All weights in all tables are negative
except those preceded by a + sign). The two ferrules were
made of 316 stainless steel and are listed as "A" and "B"
in the table. The washer was made of zinc-plated steel and is
listed as "C". The true weight of A, B, and C can be derived
since the tare weight used with the Cahn balance was weighed
also. Its weight was 366.7 mg, as weighed on a Mettler
Gram-atic balance.
True weight = [Cahn reading x 200 + 366.?]
mg
The "Cahn reading" is the reading taken from the mass dial
as a fraction of full scale, which is unity; 200 is the range
multiplier; and 366.7 is the tare weight correction. Using
a mass reading of 0.4321 as an example:
[0.4321 x 200 + 366.7] mg = 453.1 mg
True weights were not generally calculated because weight
losses could be monitored by differences of direct readings
on the Cahn.
The substrate sets 13N, 15N, and 16N were the control group
of substrates. They were weighed periodically while the other
tests were being conducted. They served as a check on desic-
cation losses, balance calibration, and zero shift. These
sets remained wrapped in their foil covers throughout the
tests to avoid any loss of the filter material. The results
of weighing these sets are shown in Table 2. The amount of
desiccation prior to each weighing is indicated in the table.
The table is structured as it is because Andersen substrates
are of two types, varying between even and odd impactor plates,
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Table 2. Andersen Substrate Cumulative Weight Changes Due to
Desiccation (Sets 13N, 15N, 16N)
Desiccation Period
Odd Numbered
Stage Substrates:
Average
a
No. of Filters
Even Numbered
Stage Substrates:
Average
o
No. of Filters
Back-Up Filters:
Average
a
No. of Filters
Initial 6 hrs
0.12 mg
0 . 0 3 mg
12
0 . 12 mg
0.04
12
0.05 mg
(0.01 mg)
3
24 hrs
0.15
0.03
12
0.15
0.03
12
0.09
(0.03)
3
48 hrs
0.14
0.02
12
0.14
0.02
12
0.09
(0.02)
3
72 hrs
0.14
0.03
12
0.14
0.02
12
0.09
(0.01)
3
96 hrs
0.15
0.02
12
0.15
0.03
12
0.07
(0.02)
3
120 hrs
0.15
0.02
12
0.16
0.02
12
0.10
(0.03)
3
Cumulative weight change as compared to initial weight after indicated number of hours
of desiccation.
All weight changes are negative unless otherwise noted.
Parentheses indicate loss of accuracy due to insufficient data.
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The substrates are cut to fit the impactor plate without
obstructing the jets. Any difference in surface area of
the filter might cause a different evaporation amount. The
back-up filter is also separated from the even and odd substrates.
Table 3 gives the raw data for each set of substrates by stage.
Table 4 indicates the moisture pickup of substrates which had
been baked and desiccated as previously described. Three back-up
filters were used, and instead of Drierite, a container of water
was placed in the balance weighing chamber to give maximum
humidity. Before the test, the balance was zeroed and calibrated.
Handling Losses
Handling losses in this case mean losses occurring in the
process of loading and unloading an impactor. The substrates
were taken from the foil covers and loaded into an impactor
just as if it were about to be run; but immediately after
assembling it, the impactor was unloaded and the substrates
placed in the foil covers.
Six sets of substrates were used. Three sets (ION, UN, 12N)
were treated entirely as typical substrates for a normal run.
The other three were cleaned. Each filter substrate was care-
fully checked for loose fiber pieces, which were removed,
and then each filter was blown off with dustless freon. These
were designated as the "clean" substrates (7N, 8N, 9N).
All six sets were desiccated for 48 hrs, weighed, loaded into
impactors, unloaded, and then placed in the desiccator for 48
additional hours.
During the unloading process, the jet plates were brushed down
to remove any bits of fiber which remained on them. Any
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Table 3. Cumulative Changes in Weight Due to Desiccation
of Andersen Substrates by Individual Set
Cumulative Desiccation Period
Set 13N
1
2
3
4
5
6
7
8
F
Set 15N
1
2
3
4
5
6
7
8
F
Set 16N
1
2
3
4
5
6
7
8
F
6 hrs
0.10 mg
0.04
0.10
0.08
0.10
0.10
0.08
0.10
0.06
0.16
0.14
0.10
0.14
0.16
0.14
0.16
0.14
0.06
0.14
0.16
0.12
0.16
0.14
0.10
0.10
0.08
0.04
24 hrs
0.15 mg
0.12
0.12
0.16
0.16
0.16
0.12
0.12
0.08
0.16
0.16
0.12
0.14
0.16
0.12
0.16
0.14
0.06
0.20
0.20
0.18
0.18
0.20
0.10
0.14
0.18
0.12
48 hrs
0.12 mg
0.10
0.12
0.14
0.18
0.16
0.14
0.12
0.10
0.14
0.14
0.12
0.14
0.18
0.12
0.14
0.16
0.06
0.14
0.18
0.16
0.16
0.18
0.12
0.12
0.12
0.10
72 hrs
0.10 mg
0.12
0.14
0.14
0.18
0.16
0.14
0.12
0.08
0.14
0.16
0.10
0.12
0.16
0.12
0.14
0.14
0.08
0.14
0.18
0.14
0.16
0.18
0.10
0.12
0.12
0.10
96 hrs
0.12 mg
0.10
0.12
0.16
0.18
0.18
0.12
0.10
0.10
0.16
0.18
0.12
0.14
0.16
0.12
0.12
0.16
0.06
0.16
0.18
0.18
0.18
0.16
0.12
0.16
0.16
0.06
120 hrs
0.14 mg
0.14
0.14
0.16
0.20
0.18
0.14
0.14
0.12
0.16
0.18
0.12
0.14
0.18
0.14
0.16
0.16
0.06
0.16
0.20
0.16
0.16
0.12
0.12
0.14
0.14
0.12
All weight changes are negative unless otherwise noted.
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Table 4. Moisture Absorption by 3 Andersen
Back-Up Filters
Elapsed Time (min) Cumulative Weight Changes, mg
0
5
10
15
20
25
30
#1
+ .10
+ .10
+ .12
+ .12
+ .12
+ .12
#2
+ .08
+ .08
+ .12
+ .12
+ .12
+ .12
#3
+ .08
+ .08
+ .14
+ .14
+ .14
+ .14
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loose fiber was placed with the substrate nearest it. Sets
9N and UN which were loaded into Andersen No.507 showed signs
of the substrates being partially cut through by the metal
o-rings. These two sets were the only ones with noticeable
pieces of fiber left on the jet stages, which were brushed
onto corresponding substrates.
Table 5 gives average losses of the cleaned-up substrates.
Table 6 gives the same for the normal substrates. Tables
7 and 8 give individual stage losses for all six sets.
Running Losses
Six sets were used for determination of weight change while
sampling filtered air. They were treated as normal substrates
in loading them into the foil covers. No special cleaning of
the filters was done. All sets were desiccated for 48 hours.
Three of the sets (4Nf 5N, 6N) were loaded into impactors
after desiccation and the impactors were run at 0.5 acfm
for 6 hrs at room temperature, 24° C. A Gelman 47-mm filter
holder and filter were attached to the inlet of the impactors
to insure that clean air was sampled.
The other three sets (IN, 2N, 3N) were set up in the same
way and run at 0.5 acfm for 6 hrs in an oven at 120°C.
When these sets of substrates were unloaded, the same brushing
technique as described above was used. The substrates from the
impactors run at room temperature were similar to those that
had just been loaded and unloaded. The Andersen No. 507
impactor showed slight gasket cuts on several of the substrates,
Andersens No. 229 and 231 had no cut substrates, but were
crimped as required for a good seal.
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Table 5. Desiccation and Handling Weight Change of
"Clean" Andersen Substrates (7N, 8N, 9N)
Desiccation Weight Change
Odd numbered substrates
Even numbered substrates
Back-up filters
Average g Number in Average
0.02 mg 0.06 mg 12
0.10 0.04 12
+0.01 (0.05) 3
Handling Weight Change
Odd numbered substrates
Even numbered substrates
Back-up filters
0.06 mg
0.09
0.04
0.04 mg
0.04
(0.06)
12
12
3
Handling Weight Change
by Stage
Stage
1 0.03 mg
2 0.08
3 0.05
4 0.09
5 0.09
6 0.11
7 0.07
8 0.08
F 0.04
(0.04) mg
(0.02)
(0.02)
(0.03)
(0.05)
(0.01)
(0.03)
(0.05)
(0.06)
3
3
3
3
3
3
3
3
3
Numbers in parentheses indicate insufficient data for accurate a.
All weight changes are negative unless otherwise noted.
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Table 6. Desiccation and Handling Weight Change of
"Normal" Andersen Substrates (ION, UN, 12N)
Desiccation Weight Change
Odd numbered substrates
Even numbered substrates
Back-up filters
Average
0.02
0.00
0.08
0.04
0.03
(0.07)
Number in Average
12
12
3
Handling Weight Change
Odd numbered substrates
Even numbered substrates
Back-up filters
0.06
0.04
+0.01
0.06
0.04
(0.08)
12
12
3
Handling Weight Change
by Stage
Stage
1 0.10
2 0.07
3 0.08
4 0.05
5 0.01
6 0.01
7 0.03
8 0.03
F +0.01
(0.05)
(0.05)
(0.02)
(0.07)
(0.02)
(0.02)
(0.08)
(0.02)
(0.08)
3
3
3
3
3
3
3
3
3
Numbers in parentheses indicate insufficient data for accurate a.
All weight changes are negative unless otherwise noted.
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Table 7. Desiccation and Handling Weight Change of
"Clean" Andersen Substrates by Set
Weight Change Weight Change After
During Desiccation Impactor Loading
Set 7N
Andersen 229
1 0.12 mg 0.00 mg
2 0.18 0.06
3 0.02 0.04
4 0.16 0.01
5 0.02 0.08
6 0.08 0.12
7 0.02 0.04
8 0.14 0.04
F 0.04 +0.02
Set 8N
Andersen 231
1 0.06 0.08
2 0.10 0.10
3 0.04 0.04
4 0.12 0.12
5 0.00 0.14
6 0.06 0.12
7 0.06 0.06
8 0.06 0.06
F +0.02 0.04
Set 9N
Andersen 507
1 +0.04 0.02
2 0.06 0.08
3 0.00 0.08
4 0.06 0.14
5 +0.02 0.04
6 0.10 0.10
7 +0.10 0.10
8 0.04 0.14
F +0.06 0.10
All weight changes are negative unless other noted.
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Table 8. Desiccation and Handling Weight Changes of
"Normal" Andersen Substrates by Set
Weight Change Weight Change After
During Desiccation Irapactor Loading
Set ION
Andersen 229
1 0.00 mg 0.12 mg
2 +0.04 0.12
3 0.02 0.10
4 0.00 0.12
5 +0.02 0.04
6 +0.06 0.04
7 +0.06 0.12
8 +0.02 0.06
F 0.00 0.08
Set UN
Andersen 507
1 0.04 mg 0.14 mg
2 +0.02 0.04
3 0.00 0.08
4 0.00 0.04
5 0.04 0.00
6 0.02 0.00
7 0.00 0.02
8 0.04 0.02
F 0.10 +0.06
Set 12N
Andersen 231
1 0.10 mg 0.04 mg
2 0.02 0.04
3 0.04 0.06
4 0.02 +0.02
5 0.02 0.00
6 0.02 0.00
7 0.02 +0.04
8 0.00 0.02
F 0.14 +0.04
All weight changes are negative unless otherwise noted.
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The substrates run at 120°C showed more cutting. Again,
Andersen No. 507 had substrates which were cut by the seals
but slightly more severely. There were more pieces of
fiber on the jet stage than previously. Substrates from
Andersens No. 229 and 231 this time showed slight cuts in
some of the stages. This may have been due to heating the
impactor, or possibly to overtightening of the impactors,
although an attempt was made to tighten them equally each
time.
After sampling filtered air for 6 hrs, each set was unloaded,
brushed, foiled, and desiccated for 48 hours before weighing.
The results are shown in Tables 9-12.
Miscellaneous
In Table 13, the results of two blank sets of substrates
loaded normally and run under stack sampling conditions at
an aluminum reduction plant with a Gelman filter in front
of the impactor, are given. The stack temperature was 125°F
and the running times are listed in the table. Also shown
is the average of a blank set run at a hot side precipitator
on a coal-fired boiler.
For comparison and to gauge the significance of impactor
weight losses, Table 14 includes some averages of typical
Andersen Impactor stage net weight changes, including
possible filter weight loss, observed in sampling several
types of industrial particulate sources.
Also investigated was the possibility of using Teflon filter
membranes as substrates. The type of Teflon filter used was
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Table 9. Desiccation and Sampling Weight Change of
Andersen Substrates (4N, 5N, 6N) after Sampling
Filtered Air at 0.5 acfm for 6 hours at 24°C
Weight Change During
Desiccation Average a
Odd numbered substrates 0.16 mg 0.05
Even numbered substrates 0.14 0.03
Back-up filters 0.17 (0.03)
Number in Average
12
12
3
Weight Changes Due
to Sampling
Substrates 1-4 average 0.06 mg 0.03
Substrates 5-8 average 0.07 0.03
Odd numbered substrates 0.07 0.03
Even numbered substrates 0.06 0.02
Back-up filters +0.03 (0.03)
12
12
12
12
3
Sampling Weight Change
by Stage
Stage
1
2
3
4
5
6
7
8
F
0.08 mg
0.06
0.05
0.05
0.06
0.06
0.07
0.07
+0.03
(0.02)
(0.02)
(0.05)
(0.03)
(0.02)
(0.02)
(0.03)
(0.03)
(0.03)
3
3
3
3
3
3
3
3
3
All weight changes are negative unless otherwise noted.
Parentheses indicate loss of accuracy due to insufficient data.
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Table 10. Desiccation and Sampling Weight Change of
Andersen Substrates (IN, 2N, 3N) after Sampling
Filtered Air at 0.5 acfm for 6 Hours at 120°C
Weight Change During
Desiccation Average a
Odd numbered substrates 0.14 mg 0.04
Even numbered substrates 0.15 0.05
Back-up filters 0.15 (0.06)
Number in Average
12
12
3
Weight Change Due
to Sampling
Substrates 1-4 average 0.15
Substrates 5-8 0.17
Odd numbered substrates 0.17
Even numbered substrates 0.15
Back-up filters +0.03
0.04
0.04
0.04
0.04
(0.08)
12
12
12
12
3
Sampling Weight Change
by Stage
Stage
1 0.15
2 0.11
3 0.17
4 0.13
5 0.14
6 0.17
7 0.19
8 0.19
F +0.03
(0.01)
(0.02)
(0.04)
(0.02)
(0.00)
(0.02)
(0.06)
(0.01)
(0.08)
3
3
3
3
3
3
3
3
3
All weight changes are negative unless otherwise noted.
Parentheses indicate loss of accuracy due to insufficient data.
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Table 11. Desiccation and Sampling Weight Changes of
Andersen Substrates by Set after Sampling
Filtered Air at 0.5 acfm for 6 Hours at 24°C
Weight Change During Weight Change Due
Desiccation to Sampling
Set 4N
Andersen 229
1 0.20 rag 0.08 mg
2 0.12 0.04
3 0.16 0.08
4 0.16 0.06
5 0.08 0.08
6 0.08 0.08
7 0.04 0.12
8 0.12 0.08
F 0.14 0.00
Set 5N
Andersen 231
1 0.22 mg 0.06 mg
2 0.12 0.08
3 0.18 0.00
4 0.16 0.02
5 0.18 0.06
6 0.12 0.06
7 0.18 0.08
8 0.18 0.10
F 0.20 +0.04
Set 6N
Andersen 507
1 0.20 mg 0.10 mg
2 0.18 0.06
3 0.18 0.08
4 0.16 0.08
5 0.12 0.04
6 0.12 0.04
7 0.18 0.10
8 0.14 0.04
F 0.18 +0.06
All weight changes are negative unless otherwise noted.
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Table 12. Desiccation and Sampling Weight Changes of
Andersen Substrates by Set after Sampling
Filtered Air at 0.5 acfm for 6 Hours at 120 C
Weight Change During
Desiccation
Weight Change Due
to Sampling
Set IN
Andersen 229
1
2
3
4
5
6
7
8
F
0.14 mg
0.12
0.12
0.18
0.16
0.16
0.14
0.14
0.10
0.16 mg
0.10
0.16
0.10
0.14
0.14
0.24
0.18
+ 0.06
Set 2N
Andersen 231
1
2
3
4
5
6
7
8
F
0.10 mg
0.10
0.06
0.12
0.16
0.10
0.08
0.10
0.12
0.14 mg
0.14
0.14
14
14
0.18
0.12
0.18
+ 0.10
0.
0.
Set 3N
Andersen 507
1
2
3
4
5
6
7
8
F
0.16 mg
0.20
0.16
0.20
0.18
0.22
0.22
0.20
0.22
0.20 mg
0.10
0.22
0.14
0.14
0.18
0.22
2.20
0.06
All weight changes are negative unless otherwise noted.
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Table 13. Weight Changes of Andersen Substrate after
Sampling Filtered Effluent from a Wet
Precipitator at an Aluminum Reduction Plant.
125°F Gas Temperature
Stage
1
2
3
4
5
6
7
8
average
Sampling Time
240 mm. 103 min.
+0.06 mg
0.04
0.02
+0.08
0.12
0.08
0.12
+0.02 mg
0.04
+0.04
04
16
0.10
0.10
0.
0.
0.04 mg
All weight changes are negative unless otherwise noted.
Average weight change of Andersen substrates after sampling
filtered effluent from a hot side precipitator on a coal
fired boiler.
Temperature = 635 F
Sampling Time = 90 min. Average = 0.02 mg
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-20-
Table 14. Typical Average Amounts of Collection for an
Andersen Impactor
Stage
Site and Amount in mg
A
1
2
3
4
5
6
7
8
F
1
0
0
0
0
1
1
2
22
.13
.78
.84
.80
.95
.25
.84
.72
.40
B
0
0
0
0
0
0
1
1
4
.37
.27
.30
.28
.32
.29
.10
.68
.51
C
1.70
1.29
1.08
1.17
2.12
4.96
5.06
2.64
5.53
D
15.
6.
11.
7.
8.
5.
2.
0.
3.
79
94
62
23
73
56
99
66
85
E
0.
0.
0.
0.
0.
0.
1.
1.
3.
59
39
35
34
25
48
08
00
91
F
6.74
2.45
2.08
1.63
2.52
5.30
4.99
2.52
3.01
G
9.70
6.97
8.23
8.93
12.62
14.48
8.61
4.39
8.56
Sampling
Time (min). 431 921 210
Stack Temp.
(°C) 121
38 371 140 255
41 335 166 66 152 167
A. Wet scrubber at submerged arc ferro-alloy furnace.
B. Wet precipitator on aluminum reduction pot lines.
C. Hot side precipitator on coal fired boiler.
D. Precipitator on coal fired boiler.
E. Wet scrubber on open hearth furnace.
F. Pilot scale precipitator on coal fired boiler.
G, Precipitator on coal fired boiler.
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Chemware filter membranes made of Zitex, which is a fibrous,
porous form of pure TFE-Teflon/Halon. They are produced by
Chemplast, Incorporated. A 75-mmf extra fine filter was
used. It was desiccated without being wrapped with anything
and weighed at various intervals. Then, it was baked for 6 hrs
at 205°C and weighed again, desiccated for 24 hrs, and weighed
one final time. The baking appeared to cause no damage to
the filter. Results are given in Table 15.
CONCLUSIONS
Several conclusions can be drawn from this study of Andersen
filter substrates:
1. From Table 1 it can be seen that the Cahn Model G-2
Electrobalance used in this study as well as our normal
laboratory and field test work is quite stable in
day-to-day operation. Repetitive weighings of metal
objects agreed within 0.02 mg over a six day period.
This degree of uncertainty represents a very small
percentage of normal stage weights (e.g., Table 14).
2. Tables 2 and 3 indicate that the substrates lose about
.10-.20 mg of absorbed moisture when desiccated for 24
hours at room temperature. Although further desiccation
does not remove additional moisture, losses do occur
when clean air is pulled through the impactors. These
losses are approximately .05-.10 mg for six hours
testing at 0.5 acfm at room temperature (24 C), and
.10-.20 mg at elevated temperatures (120°C). These
results are summarized in Tables 9, 10, 11, and 12.
Although a definitive reason for this has not been
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-22-
Table 15. Cumulative Weight Change of Teflon
Filter Substrate after Desiccation and
Baking
Original weight - 509.08 mg
Hours of Desiccation
24 -0.04 mg
48 -0.04
72 -0.04
96 -0.02
After baking 6 hrs
at 205°C -0.26
After 24 hrs desiccation -0.22
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-23-
established, one possibility is that the moving air
dries the substrates more than normal desiccation.
This explanation is consistent with the larger losses
which occur when clean, hot air is drawn through the
impactors.
3. Table 4 confirms the reabsorption of water vapor by
previously desiccated substrates upon exposure to a
humid atmosphere. Within % hour, the weight lost
during a desiccation period of 24 hours is regained
(^.10-.20 mg). For this reason, the substrates and
stage catches from impactor tests should be desiccated
for at least 24 hours before weighing, and the weighing
should be done immediately upon removing each substrate
from the desiccator.
4. Tables 5, 6, 7, and 8 indicate that if careful
attention is maintained in weighing, loading, and
unloading substrates, then the handling losses are
not significantly better if the substrates are
"cleaned" before use. Poor handling and impactor
cleaning techniques would, of course, tend to magnify
these errors.
5. The field test data shown in Tables 13 and 14 indicate
that weight losses which may occur during impactor
measurements can amount to more than 50% of the particu-
late catch for any given stage, but more often are less
than 20%. The errors are most significant when
sampling sources with extremely low grain loadings
under circumstances that do not permit extended sampling
times.
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-24-
The data tabulated in Table 15 shows that the weight
losses as indicated in Tables 9 and 10 can be either
significant or insignificant depending on the amount
of particulate collected per stage. Partial compen-
sation for this weight loss could be obtained by
adding approximately 0.1 mg per stage.
Although the weight losses were progressively higher
for impactor loading and unloading, sampling clean
cool air, and sampling clean warm air respectively,
it was not proven whether the losses were due to
drying, to loss of filter material, or both. One
can generalize all the results, including field tests,
as indicating that with prebaking, 24 hour desiccation,
careful weighing and loading, careful unloading and
impactor cleaning, post test desiccation for 24
hours, and careful final weighing, the weight
losses can be minimized, and will probably be
less than .20 mg per stage. This may or may not
seriously degrade the accuracy of the particle size
measurements, depending upon the amount of material
collected. It would be desirable to collect 2-3 mg
of material on every substrate/ but this could result
in excessively long sampling times at some locations,
or overloading of other stages for some particle
size distributions.
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-25-
TECHNICAL REPORT DATA
(Plane read Inunctions on the reverse before completing)
1. REPORT NO.
EPA-650/2-75-022
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Andersen Filter Substrate Weight Loss
5 REPORT DATE
February 1975
6. PERFORMING ORGANIZATION CODE
7 AUTHOR(S)
Wallace B. Smith, Kenneth M. Gushing,
and George E. Lacey
8 PERFORMING ORGANIZATION REPORT NO,
SORI-EAS-74-392
9. PERFORMING ORG '\NIZATION NAME AND ADDRESS
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, Alabama 35205
10 PROGRAM ELEMENT NO.
1AB012; ROAP 21ADM-011
11. CONTRACT/GRANT NO.
68-02-0273
12 SPONSORING AGENCY NAME AND ADDRESS
EPA, Off ice of Research and Development
NERC-RTP, Control Systems Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Special; 10-12/74
14 SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16 ABSTRACT
The report gives results of an investigation, under laboratory conditions, to
determine the extent and cause of weight losses first noticed in field situations
on Andersen impactor fiberglass substrates. The investigation results indicated
that, if performed carefully throughout, sample acquisition should result in a
weight loss of no more than 0. 20 mg per stage. Such a loss is not of major
consequence when more than 2-3 mg is collected on a stage: however, it could
represent a serious error at less than 2-3 mg. Incomplete drying and careless
handling were found to be the major sources of weight loss.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Air Filters
Weight Measurement
Particle Size
Substrates
Sampling
Glass Fibers
Air Pollution Control
Stationary Sources
Andersen Impactor
Weight Loss
13B
13K
14B
11D
HE, 11B
8 DISTRIBUTION STATEMENT
Unlimited
19 SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
30
20 SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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