United States
Environmental Protection
Agency
Atmospheric Research and
Exposure Assessment Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-92/208 March 1993
EPA Project Summary
Volatile Organic Sampling
Train— Soot Interference Report
Gary D. Hinshaw, Frank W. Wilshire, and Larry D. Johnson
Boiler performance studies spon-
sored by the U.S. Environmental Pro-
tection Agency (EPA) have shown that
industrial boilers co-firing hazardous
waste are capable of achieving destruc-
tion and removal efficiencies (DREs) of
99.99 % for Resource Conservation and
Recovery Act (RCRA) Appendix VIII
compounds designated as principal or-
ganic hazardous constituents. Evalua-
tion of boiler DREs for volatile organic
compounds (VOCs) is accomplished in
part by sampling those compounds as
described in EPA Method 0030, the
Volatile Organic Sampling Train (VOST).
A hysteresis effect, resulting from soot
deposits on boiler surfaces, has been
observed in previous studies and is
the subject of several related reports.
Sorption behavior of organic com-
pounds on deposits of soot in boilers,
as demonstrated by these hysteresis
studies, has led to concern that similar
sorption effects from soot captured by
the paniculate filter of the VOST might
cause a low bias in measurement re-
sults. It seemed prudent, then, to de-
termine if such an effect is measurable,
to investigate the magnitude of any ob-
served effect on VOST sampling, and,
as appropriate, to also determine
whether the effect is greater for higher
boiling point VOCs as expected.
This study examined the effects of
soot deposits within the sampling ap-
paratus upon levels of VOCs recov-
ered. Specifically, collection efficiency
was evaluated by comparing VOC lev-
els collected in a control VOST, when a
soot-free paniculate filter (i.e., glass
wool plug) was used In the sampling
probe, to VOC levels recovered while
using a soot-laden paniculate filter in
the VOST probe. Samples were col-
lected at routine VOST sampling rates
and analyzed by gas chromatography
and mass spectrometry (GC/MS) as de-
scribed in EPA Methods 0030, 5040,
and 8240. Because of time and cost
considerations, the soot was generated
only from No. 2 fuel oil, as opposed to
that produced from hazardous waste.
Soot deposition on the filters varied
from 4 to 70 mg.
Volatile organic compounds evalu-
ated were selected to span the range
of boiling points covered by VOST
methodology. Emphasis was directed
to substances in the upper range of
VOC boiling points (i.e., 120 to 130 °C),
because sorption phenomena often cor-
relate with boiling points, and thus the
higher boiling point compounds were
deemed more likely to be seriously af-
fected.
The data collected were subjected to
descriptive and pattern recognition
techniques (i.e., percent difference and
rotated principal component analysis).
Results of these statistical analyses in-
dicated that at least two of the higher
boiling point VOCs appear to be nega-
tively biased by the presence of soot
on the glass wool filter. However, it is
not likely that these findings would have
a major impact on previously collected
hazardous waste incinerator data, since
the VOST-Soot effect was determined
at moderately high soot loadings, which
are atypical of properly operating haz-
Printed on Recycled Paper
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ardous waste Incinerators. Also, a level
of sooting where the effect ceases to
cause significant deterioration of the
data was not established In this study.
Consequently, the data gathered In this
study was not totally conclusive In de-
termining whether soot may Impact
ORE determinations from boilers using
the VOST methodology.
This Project Summary was devel-
oped by EPA's Atmospheric Research
and Exposure Assessment Laboratory,
Research Triangle Park, NC, to an-
nounce key findings of the research
project that Is fully documented In a
separate report of the same title (see
Project Report ordering Information at
back).
Introduction
EPA-sponsored studies of boiler perfor-
mance under both normal and transient
conditions have shown that the boilers
can achieve a destruction and removal
efficiency (ORE) of at least 99.99% for
Resource Conservation and Recovery Act
(RCRA) Appendix VIII compounds
(40CFR261) that are principal organic
hazardous constituents (POHCs). How-
ever, the ORE measurements made dur-
ing some of the earlier EPA studies could
have been affected by the presence of
deposits of unburned, carbonaceous ma-
terial (i.e., soot) either (1) on cold boiler
surfaces or (2) within the organic sam-
pling system. The first concern deals with
a phenomenon referred to as hysteresis.
The second concern, however, is the pri-
mary focus of this project. Specifically, the
quality of data on volatile organic concen-
trations in boiler stack gases may be im-
pacted by the presence of soot if the soot
Is trapped on the glass wool plug (i.e.,
particulate filter) typically used in the probe
of a volatile organic sampling train (VOST)
and if the soot functions as an active
sorbent. If sufficient effect is present, the
current VOST sampling technique may not
be appropriate for certain boiler applica-
tions.
Experimental Procedure
The primary objective of this project was
to determine if combustion-generated soot
will sorb a sufficient quantity of volatile
organic compounds (VOCs) to cause an
erroneously low measurement of VOCs
by the VOST method. The type of soot,
that is, its source and conditions of forma-
tion, may affect its propensity to sorb
VOCs. Thus, soot generated by actual
mixtures of hazardous waste and fuel may
differ from soot generated by hydrocarbon
fuels alone in its effect upon VOST mea-
surements. However, for the initial "range-
finding" experiments described herein, soot
was generated in only one way, by No. 2
fuel oil combustion only, without any haz-
ardous waste constituents present (i.e.,
no RCRA Appendix VIII compounds).
These experiments followed a two-step
format. In the first step, the soot deposi-
tion step, the soot was collected upon the
glass wool plug of a VOST system probe
by withdrawing soot-laden gas through the
probe of the experimental VOST system
at a flow rate of 0.5 L/min. (The mass of
soot deposited was controlled by adjust-
ing the deposition time, ranging from 6 to
9 min for Experiments 14-16 and from 10
to 18 min for Experiments 17-19.) During
the second step, which was sampling,
gjass wool doped with soot_was used in
the experimental probes, but a clean glass
wool filter was used in the control probe.
(The control probe was positioned in the
VOST adapter after the soot deposition
step.)
A mixture of target VOCs was intro-
duced downstream of the flame zone fol-
lowing soot deposition, and the test VOST
and a control VOST were operated con-
currently. The target VOCs are shown in
Table 1. The VOCs in Table 1 were se-
lected by EPA personnel to span the range
of boiling points covered by the VOST
method and also to concentrate on the
upper range of boiling points (approxi-
mately 120 to 130 °C) associated with the
VOST method. All compounds except oc-
tane are Appendix VIII compounds that
could be used as POHCs for DRE deter-
mination.
Sampling procedures followed EPA
Method 0030, sample preparation proce-
dures followed Method 5040 (thermal de-
sorption), and analysis procedures
incorporating gas chromatography/mass
spectrometry (GC/MS) followed Method
8240. In 'the next phase' of the' experi-
ment, a well-mixed, diluted VOC mixture
was injected directly into the VOST probes,
instead of being injected into the middle
of the quartz flow tube of the soot genera-
tor, as was the case during Phase 2.
Table 1. Volatile Organic Compounds Injected
During Phase 2 Testing
Compound Name
Chloroform
Carbon tetrachloride
Toluene
Tetrachloroethene
Octane
Chlorobenzene
1, 1, 1,2-Tetrachloroethane
Boiling Point fC)
61
77
111
121
126
131
131
A mixing chamber was designed and
installed to improve the mixing of the VOC
mixture (from the diluent bag) with air. A
VOC mixture was introduced at the inlet
of the mixing chamber, and air was intro-
duced at the outlet of the chamber at
near-sonic velocity. The entire chamber
and the inlet and outlet lines were electri-
cally heated. The combined mixture, di-
luted with air and well mixed, then entered
the VOST adapter through a small tube
that passed through a port. The gases
then passed into a large stationary sec-
tion of glass tubing (electrically heated),
into which the VOST probes were inserted.
A sliding section of slightly larger tubing
(also electrically heated) was used to help
contain the gases and prevent contamina-
tion by residual organic material in the
combustion system.' A nominal flow of 6 L/
min (dry, standard basis) was used, of
which only 1 L/min was withdrawn by the
two VOST systems during the sampling
step of each experiment.
As in Phase 2, only one type of soot
was tested during Phase 3; that is, only
soot generated from No. 2 fuel oil was
used. To deposit soot on the filter, the
soot-laden gas was withdrawn through the
probe of the experimental VOST system
at a flow rate of 0.5 L/min; the mass of
soot deposited was controlled by adjust-
ing the deposition time (ranging from 6 to
9 min for Experiments 14 to 16 [filter
type B] and from 10 to 18 min for Experi-
ments 17 to 19 [filter type A]). The deposi-
tion time was limited by the ability of the
sampling pump to accommodate the pres-
sure drop across the filter. Baseline ex-
periments, in which no soot was generated,
were run for comparison to experiments
involving soot generation. The soot mass
deposited on the glass wool plugs ranged
from 3.5 to 70 mg.
Results andJ)is.cusslon^_,,..
Analytical and Quality Control
Results
All VOST samples were analyzed within
2 weeks after collection. Percent differ-
ences between the control and experi-
mental VOST samples were calculated to
determine if any bias between the two
VOST systems existed.
Quality assurance/quality control (QA/
QC) results for Phase 3 were generally
very good. A performance audit (PA)
sample was prepared by the Midwest Re-
search Institute (MRI) Quality Assurance
Department and submitted for analysis.
The PA sample was analyzed by GC/MS
with the same instrumental parameters
planned for use with the VOST samples.
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Four of the eight target compounds were
identified and quantified in the PA sample,
and the remaining four were not found.
Results were then reported to the project
QA Coordinator prior to analysis of actual
project samples. All target compounds
present in the PA sample were correctly
identified and were quantified with recov-
eries of 100% to 108%, based upon the
actual concentrations.
The percent differences for the injected
VOCs were less than 10% (with one ex-
ception) in the baseline experiments. This
suggests that the VOC mixture was more
homogeneous in the vicinity of the VOST
probes. The high reproducibility shown by
the two VOSTs allows more confidence in
assessing any soot effects observed.
The percent differences for both octane
and chlorobenzerie Indicated a clear re-
duction with soot on the filter. In addition,
a positive bias was observed in the case
of benzene, which was monitored as a
residual product of incomplete combus-
tion (PIC).
Statistical Analysis
The concentration data generated in this
phase of the program were subjected to
rotated principal component analysis
(RPCA). In brief, RPCA reduces the di-
mensionality of the data set by creating
composite variables that are linear func-
tions of the original variables. This reduc-
tion in dimension is based upon the
observed correlations between the origi-
nal variables. The correlation coefficients
obtained by this technique are shown in
Table 2.
The RPCA results indicate that the mea-
sured variability in concentration among
the eight variables in the experiments can
be compactly expressed in terms of three
composite variables:
• Variable 1 is principally a weighted
• function of the compounds toluene,
octane, tetrachloroethene, and chlo-
robenzene; 1,1,1,2-tetrachloroethane
also figures into this composite, al-
though it is apparent that its
intercorrelations with other high boil-
ing point compounds are not as strong
as those exhibited between toluene,
octane, tetrachloroethene, and chlo-
robenzene.
• Variable 2 is dominated by benzene,
although some contribution from
1,1,1,2-tetrachloroethane also is indi-
cated.
• Variable 3 is a weighted function of
chloroform and carbon tetrachloride.
RPCA analyses indicated a tendency
for low boiling point compounds to be-
have differently from compounds with rela-
tively high boiling points. Differences in
standard scores between the control and
experimental trains are far more pro-
nounced for the high boiling point com-
posite variable than for the low boiling
point variable.
Conclusions
The presence of soot on the glass wool
particulate filter within a VOST probe ap-
pears to have the potential to bias the
amount of certain VOCs collected in the
VOST traps, in particular, octane and chlo-
robenzene. The extent of the bias does
generally correlate with the amount of soot
on the filter. There is some evidence that
the higher boiling point compounds are
more likely to be biased by the presence
of soot, but other chemical or physical
properties may also be involved. The
cause of the negative bias is not known
for certain; it could be at least partially
based upon pressure differences in the
test VOST console as compared to a con-
trol VOST (due to a soot-based pressure
drop in the probe), in addition to a poten-
tial sorption of the VOC upon the soot.
Loss of VOCs due to soot on the appara-
tus surfaces was carefully controlled, which
thus clarified the effect of soot in the par-
ticulate filter. Also, a high degree of sam-
pling reproducibility was achieved in the
experiments, and this strengthened the
above conclusions.
In addition to a negative bias (i.e., loss
of VOCs known to be present in the gas
phase), a positive bias (i.e., desorption of
VOCs from the soot into the gas phase)
may be indicated so that compounds that
may not always be present in the sampled
gases may show up in the VOST analy-
sis. A positive bias was observed for ben-
zene, which was presumably formed as a
PIC during soot generation and tempo-
rarily trapped in the soot. (Alternatively,
the soot may have partially decomposed,
emitting benzene as a by-product.)
If the presence of soot in the filter of the
VOST probe does affect the VOCs with
boiling points above 120° C, as this study
indicates, it is highly unlikely that the ef-
fect would have a major impact on previ-
ous hazardous waste incinerator data. This
study examined moderately heavy soot
loadings, which are not typical of properly
operating hazardous waste incinerators.
Also, only two VOCs (octane and chlo-
robenzene) showed a significant effect
from the soot loadings. Both of these VOCs
have boiling points above 120° C, indicat-
ing that only VOCs with boiling points
above that level would be affected.
Since more than one POHC is chosen
for ORE determinations and four nines
(99.99%) must be achieved for all POHCs,
it is not likely that the VOST-Soot effect
on this one POHC (chlorobenzene) would
have any impact on permitting decisions.
However, this study does indicate that cau-
tion should be exercised in future VOST
sampling when potentially sooty conditions
are present or are expected in incinerator
emissions.
Table 2. Pearson Correlation Coefficients Between Test Compounds for Phase 3
CHCI3
CCI4
CSHSCH3
CaH10
CCI2CCI2
C6HSCI
CCI3CHpl
W.
CHCI3
1.000
0.775
0.001
0.001
0.250
0.055
0.518
0.239
CCI4
1.000
0.001
0.090
0.056
0.131
0.142
-0.031
CACW3
1.000
0.817
0.865
0.874
0.535
-0.164
CMo
1.000
0.557
0.969
0.268
-0.401
CC/2CC/2 CeHsCI CCI3CH.pl CgHg
1.000
0.669 1.000
0.852 0.360 1.000
0.053 -0.266 0.206 1.000
•U.S. Government Printing Office: 1993 — 750-071/60217
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The information in this document has
been funded wholly or in part by the U.S.
EPA under Contract No. 68-02-4463 to
Midwest Research Institute, Kansas City,
MO. It has been subjected to Agency re-
view and approved for publication. Men-
tion of trade names or commercial products
does not constitute endorsement or rec-
ommendation for use.
GaryD. Hinshawis with Midwest Research Institutef Kansas-CityfMO 64110^
EPA authors, Frank W. Wilshire (also the EPA Project Officer, see below) and
Larry D. Johnson, are with the Atmospheric Research and Exposure Assess-
ment Laboratory, Research Triangle Park, NC 27711.
The complete report, entitled "Volatile Organic Sampling Train—Soot Interference
Report,' (Order No. PB93-144145; Cost: $19.50; subject to change) will be
available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
Atmospheric Research and Exposure Assessment Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
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