EPA-600/2-76-094
September 1976
RAPID METHOD FOR DETERMINING
NO EMISSIONS IN FLUE GASES
X
by
H. M. Barnes, Jr., and M. C. Caldwell
Emissions Measurement and Characterization Division
Environmental Sciences Research Laboratory
Research Triangle Park, North Carolina 27711
U. S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
-------
DISCLAIMER
This report has been reviewed by the Environmental Sciences
Research Laboratory, U. S. Environmental Protection Agency, and approved
for publication. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
-------
ABSTRACT
This report discusses the NO compliance procedure (Method 7) for
/\
stationary sources and the attempts to improve the procedure and decrease
analytical time. When the procedure is rigorously followed, Method 7 was
found to be precise and to give reproducible results. To decrease the
time necessary to oxidize NO to NO,,, Method 7 was modified by adding an
ozone lamp. Good agreement (±12% or less) was found between nitrate
measurements using Method 7 and measurements using modified Method 7.
Future work incorporating an ozone lamp into an integrated sampling
apparatus is discussed.
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CONTENTS
Abstract 11 i
Figures vi
Tables vii
Acknowledgments viii
I Introduction 1
II Conclusions 4
III Recommendations 6
IV Experimental Design and Procedure 7
V Experimental Results 11
Laboratory Studies 11
Field Studies 22
VI References 49
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FIGURES
Number Page
1 Method 7 Calibration Curve 8
2 Sampling Train, Flask Value, and Flask 9
3 Ultraviolet 2-Liter Sampling Flask 10
4 Effect of Sample Line Purging on Sample 13
Recovery in Method 7 Standard Procedure
5 Sampling Manifold Diagram 14
6 Laboratory Data Summary 31
7 Stationary Source Simulator Facility 33
Sampling Arrangement
8 Mehtod 7 Evaluation of Stationary Source 34
Simulator Facility
9 Sampling Site Configuration for Carolina 38
Power and Light Cape Fear Station Unit 9
10 Integrated Data Plot of Method 7, Modified 42
Method 7, and DuPont
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TABLES
Number Page
1 Effect of Purging Samples 12
2 Manifold Study of Random Variability 13
3 Irradiation of Gas Phase for Modified 16
Method 7
4 Effects of Ultraviolet Irradiation Time 17
5 Oxygen Effects at Various Concentrations 19
6 Method 7 Cylinder Calibration 20
7 Laboratory Test Data Summary 23
8 Chronological TECO, GFC, and Method 7 Data 35
9 Summary of Method 7 NO Data from Stationary 36
X
Source Simulator Facility Test
10 Cape Fear Power Plant Test Data 37
11 Chronological Summary of Duke Power Data 40
12 Summary of Field Test Data from Duke Power 44
Company--Riverbend Station
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Acknowledgments
The authors gratefully acknowledge the cooperation and assistance
of Dr. James A. Jahnke, EPA, and Mr. Michael Moran, Northrop Services,
Inc., in conducting the Source Simulator Facility experiments discussed
in this report.
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SECTION I
INTRODUCTION
Wet chemical methods for the determination of nitrogen oxides (NO )
/\
in gaseous mixtures are generally variations of either the phenoldisulfonic
1 2
acid procedure or the Saltzman procedure.
The phenoldisulfonic acid (PDS) method, although not as sensitive
as the Saltzman procedure, is sufficiently accurate for determining NO
/\
levels emitted by combustion sources and nitric acid manufacturing
plants (50 to 2000 ppm). In 1971, the Environmental Protection Agency
therefore, promulgated the PDS method (called EPA Method 7) as the
compliance test analytical technique to be used in determining NO
X
emissions levels from fossil-fuel-fired steam generators and from nitric
3
acid plants.
Various workers, including Chamot et al. in their original publica-
tion, have addressed the sources of error and shortcomings of the PDS
4
method. Beatty, for example, addressed problems of sample bottle
contaminations, preparation of the PDS reagent, instability of the
absorbing solution (hydrogen peroxide and sulfuric acid) as a function
of time, and requirements for spectrophotometric readings. He concluded
that the chief sources of error in the analytical method were improper
preparation of the PDS reagent, long-term stability of the hydrogen
peroxide absorbing solution, and the general use of inferior grade
chemicals in the preparation of reagents - all of which result in vari-
able "blank" readings and high sample standard deviations.
5
Di Martini, utilizing the fast oxidation of nitric oxide by ozone,
developed a semi-continuous analyzer for NO measurements in the 0-10 ppm
range. Using the more rapid gas-phase reaction NO + 03 -> N02 + On
rather than the 2NO + 02 -» 2N02 reaction as in the PDS method, and then
reading the nitrate ion concentration via a specific ion electrode (SIE)
technique, he was able to reduce analysis time to one hour. Although he
did not attempt analysis at higher concentrations, there is no apparent
reason why the technique would not be applied to emissions from fossil-
fuel-fired steam generators. Driscoll et al., using molecular oxygen as
the NO oxidizing agent and the nitrate SIE technique for determining
species concentration, obtained results similar to those of Di Martini.
1
-------
Driscoll also applied tne tetiuiiqi-c. to the analysis of NO emissions in
both oil- and gas-fired combustion effluents with satisfactory results
when compared with the PDS method.
7 8
Both Singh et al. and Harman and Neti utilized the fast oxidation
reaction between NO and CL in designing instruments for the continuous
analysis of NO in exhaust gases. The Singh method is based on the rapid
conversion of NO to NO- through ozonation and the subsequent determina-
tion of the NO concentration using a continuously flowing optical
photometer. The problems encountered in this system included a less
than 1:1 conversion efficiency of NO to NO- for a constant ozone concen-
tration with variable nitric oxide concentration and a lack of sensitivity
to flow parameter fluctuations by the detector. The Harman and Neit
instrument effects conversion of NO to N0? in a similar manner to the
Singh instrument and determines NO- via a continuous Saltzman method.
Prior to the determination of NO by the Saltzman technique, these
/\
workers incorporated an argentic oxide scrubber to remove excess ozone
and other possible interferants.
The PDS method has three disadvantages: (1) an exceptionally long
oxidation time is required for analysis, (2) a laborious (2-4 hours)
evaporation step is needed and (3) the fact that the samples are taken
in an evacuated flask for a 15- to 20- second time interval can require
numerous determinations to account for possible source fluctuations.
q
Margolis and Driscoll addressed the reaction kinetics problem and
concluded that oxidation of NO to the water soluble nitrate species
using molecular ozygen suffered from several problems. For moderate
source level concentrations (400-500 ppm), the calculated oxidation time
for 97 percent of the NO was about 28 hours. Because the reaction time
2
was dependent on (Pno)» for lower NO concentrations (below 100 ppm),
calculations showed that oxidation would require as long at 50 hours to
achieve 97 percent completion. They concluded that by increasing P ~ or
by using an oxidant that is more reactive than molecular oxygen, the
analysis time could be significantly reduced. The former principle has
been used by DuPont in its Model 460 NO analyzer. With this device,
X
the NO is converted to NO by oxygen at high pressures, and the oxidation
A
time is reduce to about 10 minutes.
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Coulehan and Lang modified the PDS procedure in an effort to
reduce analysis time. Their technique involves minimizing sample volume
and absorbing solution volume and performing the PDS nitration step in
50 percent H^SO, rather than fuming H2S04 as called for in Method 7.
The analysis time was substantially reduced, and excellent agreement
between the original and modified procedures was obtained.
This report discusses attempts to reduce the time of analysis for
the EPA Method 7 (POS) procedure, modifications to the procedure, and
the need for future work based on the results reported here.
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SECTION II
CONCLUSIONS
Based on initial experiments reported here, the following conclusions may be
made:
1. Method 7 appears to be a precise and repeatable laboratory procedure
when the written directions are carefully and scrupulously followed.
Typical standard deviations of ±5 percent of the mean value are attain-
able when analyzing cylinders of NO in N,,. Predictions of precision in
actual field applications are more problematic, however, because of
existing spatial and temporal macro and micro fluctuations in sources.
2. The precision of both Method 7 and the Modified Method 7 described here
is operator dependent. After suitable training and practice, experienced
personnel should be able to achieve 95 to 97 percent reproducibiV'.ty on
successive determinations from the same NO cylinder of source.
3. The use of ozone generation is a practical technique for obviating the
necessity for a lengthy oxidation step for converting NO to determinable
nitrate. In general, agreement between Method 7 and Modified Method 7
analyses for a cylinder of NO in N^ was within ±12 percent at the least,
and better in most cases.
4. Observations that additional 02 affected the procedure are unresolved at
this time. One operator concluded that it was necessary to add 02 to
the sampling flask to achieve reaction completion with a reasonable time
(30 minutes or less). In another case, a different operator concluded
that 02 addition was detrimental to the completion of the NO+O^NO^
reaction. Calculations of Op additions necessary to generate sufficient
0~ to convert stack level NO concentrations (200-600 ppm) show that 0?
concentrations in the excess air of the combustion process are more than
ample. Typically, there is 4-6 percent excess air or about 1-1.5 percent
02 available. The disagreement between the operators appears to reflect
variations in the procedure used and should be resolved by adhering
strictly to the specific procedure.
-------
The absolute accuracy of Method 7 appears to be in question. In
analyzing four NO-in-N^ cylinders purchased from various suppliers;
labelled cylinder concentrations were 10-20 percent higher than
determined either by Method 7 or the modified method. In the case
of low-concentration cylinders (below 100 ppm), analyses were as
much as 50 percent low.
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SECTION III
RECOMMENDATIONS
The accuracy of Method 7 should be established, especially with
respect to relatively low concentration cylinders and to cylinder
concentrations at or near the emission standard for the particular
source. This is important because of the pending promulgation of
performance specifications for S09 and NOV continuous monitors.
c. X
These specifications require instrumental calibration against
cylinders that have been standardized using the respective refer-
ence methods.
A substitute for the grab sampling technique for NO used in EPA
X
Method 7 should be developed to reduce the large number of samples
needed to achieve an ac:eptable mean value and confidence inte/val
in the present technique. Development of an integrated sampling
technique that uses the Modified Mehtod 7 procedure is presently
being investigated by EPA. The technique employs a 6-liter sampling
flask with connections for a thermometer, a pressure gauge, an
ultraviolet irradiation lamp, a sampling line, an absorbing solution
drain outlet, and a vacuum pump. A critical orifice is interfaced
through the sampling line to vary the sampling period from 2 to 30
minutes. Although initial studies with the system have been
limited to analyzing NO-in-N^ cylinders, the results have been
encouraging. After further laboratory studies, the system will be
tested at a coal-fired power plant and a nitric acid plant.
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SECTION IV
EXPERIMENTAL DESIGN AND PROCEDURE
METHOD 7
In the Method 7 procedure, a grab sample is collected in a 2-liter flask
evacuated a 75-mm pressure and containing a weak sulfuric acid-hydrogen
peroxide solution. The principal species present in the sample is NO.
Because of its low solubility in water, the NO is converted to the more
soluble nitric acid via the following reactions:
> HN03 (analyzed for nitrate)
NO
+
N02
°2
(slow)
N02
N2°3
N2°5
aqueous acidic
H2°2
Oxidation is effected by allowing the sample to stand overnight in the
sampling flask. After removal of the absorbing solution containing the
nitrate sample, the solution is neutralized to fix the nitrate as the
ammonium salt. This step is followed by evaporation to dryness on a
steam bath and reaction with the l-phenol-2,4, disulfonic acid to effect
nitration of the benzene ring. The resulting yellow solution produced
by neutralization of the nitrate-PDS solution is determined by spectro-
photometric analysis at 410 nanometers (nm). A calibration curve
(Figure 1) is prepared using potassium nitrate as a primary standard and
plotting NOp in micrograms (yg) versus the spectrophotometrically
determined absorbance. The slope of the absorbance versus the yg N0~
straight line has been found to be 0.0015 using a B&L Spectronic 20
instrument at 410 nm. The most suitable concentration range for the
analysis is 0 to 400 yg N0~. More highly concentrated solutions are
diluted to bring them within the known linear portion of the plot.
MODIFIED METHOD 7
The modified procedure deviates from the promulgated Method 7 procedures
as follows:
1. Method 7 employs'a 2-liter, round bottom flask protected
against implosion or breakage as shown in Figure 2. Modified
-------
100 200 300 400 500 600 700 800 900 1000 1100 1200
NOX CONCENTRATION,^
Figure 1. Method 7 calibration curve.
8
-------
o
C
to
oT
"co
C
'co
L_
<-J
O)
C
"a.
E
CO
CO
CN
O)
i_
3
O)
u_
-------
Method 7 requires a 2-liter flask protected against implosion
or breakage. The sampling flask for Modified Method 7 is
shown in Figure 3.
2. Method 7 calls for a 5-minute shaking time after taking the
sample and then allowing the flask to sit for a minimum of 16
hours. In the Modified Method 7, the sample is magnetically
stirred and simultaneously irradiated using an ultraviolet
lamp.
THREE-WAY VALVE
ULTRA-
VIOLET
LAMP
POWER
SUPPLY
25-ml ABSORBING SOLUTION
Figure 3. Ultraviolet 2-liter sampling flask.
10
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SECTION V
EXPERIMENTAL RESULTS
LABORATORY STUDIES
After observing variability in Method 7 and Modified Method 7 analytical
values, efforts were made to improve accuracy and assess repeatability
over a range of NO concentrations. The effect of various procedural
X
inconsistancies was investigated, and the subsequent application of any
procedural amendment was evaluated. The utilization of a precise
analytical procedure for both Method 7 and for the more rapid Modified
Method 7 is critical.
Sample Line Purging with Sample Gas
Long sampling line configurations have been found to affect accuracy and
repeatability of the NO analysis using either method. This effect can
/\
be understood in terms of the "dead space" or volume of the sample lines
in relation to the volume of the flask (approximately 2 liters). The
longer the sample lines, the more marked the effect on the measurement
accuracy. The results, in fact, can be as much as 10-15 percent low.
For this reason, live purging with the sample gas whether it be from a
cylinder or a stack must be done before the sample gas is drawn into the
flask.
The data in Table 1 reflect the errors resulting from incomplete sample
line purging in laboratory studies in which a 2-liter flask was utilized.
The magnitude of the error depended on flask volume, sample line volume,
and source pressure relative to atmospheric. Although the sample lines
were evacuated to 3 inches of mercury (absolute) as was the sampling
flask. Depending on conditions and equipment, field errors could be
equal to or greater than those mentioned in this report. The procedures
3
followed here were identical to those in the Federal Register except as
noted in the table. A complete data summary of the laboratory studies
in tabular form may be found at the end of this section.
11
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Table 1. EFFECT OF PURGING SAMPLES
Labeled
cylinder
concentration,
ppm N0v
A
510
60
Purged
1 ine,
ppm NO
428
23
Standard
deviation
ppm NOX
5
3
Number
, of
samples
6
4
Unpurged
line,
ppm N0x
356
28
Standard
deviation
ppm N0x
13
3
Number
of
samples
4
6
The 16.9 percent error caused by unpurged sample lines in Method 7 for
the 510 ppm cylinder gas is illustrated in Figure 4. Method 7 data
accumulated from the 60-ppm gas cylinder indicated a slight increase in
reported NO ; this increase may not be significant due to the standard
X
deviations of the various measurements.
Random Variability Resulting from Human Error
After refining the analytical procedure to some degree, the fluctuations
observed in reported NO caused by equipment varicMlity (flask volume),
A
incomplete transfers of absorbing solutions during analysis, and other
factors of nominal concern were tested for their contributions to the
standard deviation. To observe such effects, it was necessary to eliminate
fluctuations in sampling and analytical procedures. To ensure that the
samples were drawn as representatively as possible, a manifold was
designed to evacuate and monitor pressure as well as to allocate sample gas
equally to all samples (Figure 5). In addition, samples drawn through the
manifold were analyzed concurrently to minimize error.
The data presented in Table 2 reflect any variation resulting from human
error, random equipment failure, or both.
12
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Table 2. MANIFOLD STUDY OF RANDOM VARIABILITY
Labeled
cyl i
nder
concentra-
tion
a M7
b P..
,ppm N0x
510
500
500
500
500
575
575
= Method
miiTr}4-T\*^i -
Actual
concentra-
tion, ppm NO
428
455
455
455
455
untyped
untyped
7; MM7 = Modi
iif/^v-*^*"!/^ /~\-F r\r\v*
a
Procedure
M7
M7
M7 '
MM7
MM7
MM7
MM7
fied Method
/> /->r-» + <- -|- :i r»/-J a v*
Average
concentra-
tion, ppm NO
X
427.9
456.96
466.53
387.5
357.05
466.2
481.6
7.
A Aa\i n a + -i r\n
Standard
deviation
ppm, NOX
5.36
4.20
15.03
29.1
31.45
8.2
12.5
*3 "7 r\ o v» r< o n t*
Percent
standard ,
deviation
1.2
0.9
3.2
8.8
7.5
1.7
2.6
r\-P v^cino v^i'f^A
Sample
Number
1-3
4-6
7-9
17-18
14-15
1-2
3-4
NO values (all cylinder concentrations).
X
510-ppm CYLINDER
1-3
4-7
IU
oo
7-8
1-6
7.9
356.1
±12.9
60-ppm CYLINDER
(23.1
±3.0
LEGEND
YA SAMPLE LINE PURGED
Ja WITH SAMPLE GAS
SAMPLE LINE NOT
PURGED WITH SAMPLE GAS
100
200 300
NOX CONCENTRATION,ppm
400
500
Figure 4. Effect of sample-line purging on sample recovery in the M7 standard procedure.
13
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STREAM FLOW
PROBE
L
FILLED WITH
GLASS WOOL
(TO CYLINDER
IN LAB WORK)
VACUUM
PUMP TO
27 in. Hgabs.
MANOMETER
Figure 5. Sampling manifold diagram.
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From these data, one may assume that, with all conditions held constant
within experimental groups, a standard deviation of ^3.7 percent is attain-
able. Any standard deviation significantly greater than 3.7 percent is
considered to be the result of experimental design problems or equipment
failure.
Irradiation Study of Modified Method 7
The ZNO+CL+ZNCL reaction in the recovery step of Method 7 is slow and
determines the rate at which the sample is evaluated. Reduction of the
16-hour waiting period to approximately 15 minutes can be effected,
however, by expediting the oxidation of NO to NCL. Rapid generation of
57
ozone, which rapidly oxidizes nitric oxide, ' is accomplished in the
Modified Method 7 procedure by using an in-flask ultraviolet photo-
chemical lamp.
The time of ultraviolet irradiation in Modified Method 7 seems critical
to its repeatability. Because the duration of ultraviolet irradiation
determines the relative concentration of 03 generated within a sample
flask, the consistent application of ultraviolet irradiation among
flasks is necessary to ensure that equivalent concentrations of 0^ are
available for oxidation. In an EPA laboratory study, the ultraviolet
irradiation period necessary to effect a 90 percent conversion (based on
Method 7 data) was reported to be 15 minutes (See Table 3). During-
extensive testing of Modified Method 7 in January 1975, some variability
observed in the NO response level was attributed to the inconsistent
A
irradiation periods administered in previous tests.
15
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Table 3. IRRADIATION OF GAS PHASE FOR MODIFIED METHOD 7
"
Labeled
cylinder
Evaluation concentrar
criteria tion, ppm
0 uv
5 sitr
10 stir
30 stir
15 stir
5 uv
5 stir
5 stir
10 uv
10 stir
10 stir
15 uv
15 stir
15 stir
15 stir
15 stir
15 stir
30 uv
30 stir
30 stir
30 stir
30 stir
30 stir
30 stir
560
560
560
560
560
560
560
560
560
560
560
280
280d
280
280
560
560
560
560
Reported
Op concentra-
added tion, ppm
yes 107
yes 25
yes 42
no 67
Average ppm = 60
yes 456
yes 457
Average ppm = 456
yes 502
yes 523
Average ppm =512
yes 622
no 129
no 134
yes 245
yes 283
Average ppm =
yes 258
yes 267
no 183
no 146
no 174
yes 578
Average ppm =
Flask
volume,
ml .
2080
2120
2078
2078
.2 ± 26.8 for
2025
2062
.5 ± 0.5 for
2025
2062
.5 ± 10.5 for
2025
2066
2062
2025
2062d
622.0 for 02
2062
2025
2078
2025
2062
2062
578 for 02
yg NOX
300
72
120
185
°2
1220
1290
°2
1270
1404
°2
"700
357
375
648
444
690
712
540
400
500
1650
Initial Final
pressure, pressure,
in. Hg in. Hg
3.0
2.0
2.2
3.0
2.4
2.3
2.2
2.1
2.1
3.0
3.0
2.3
2.2
2.2
2.2
2.0
2.2
2.1
2.0
29.4
29.4
28.6
29.6
31 .2
28.6
31.7
30.4
29.3
29.4
29.4
29.6
17.5
29.5
29.7
28.5
29.3
28.5
28.6
Indicates time (in minutes) of irradiation using the photochemical lamp and
the time (in minutes) of stirring the absorbing solution.
The manufacturer's values as determined by a chemiluminescence analyzer.
°Indicates whether cylinder oxygen was added to flask before sampling.
Tlask half filled.
16
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The high standard deviation observed in early Modified Method 7 tests
is believed to be caused by the Oo concentration differential between
flasks and/or the heat output of the operating ultraviolet lamp that
would allow a faster and more complete reaction for those samples that
were irradiated longer.
In attempts to increase the recovery of NO through the adoption of
A
Modified Method 7, longer ultraviolet irradiation periods were evaluated.
A comparison of samples drawn from a 500 ppm cylinder (actually 455 ppm)
utilizing the manifold is shown in Table 4. The net gain in recovery of
NO through increasing the ultraviolet irradiation period from 15 to 30
X
minutes was 3 to 10 percent.
The increase in sample recovery discovered during 30 minutes of irradia-
tion would warrant the use of the longer period for future Modified
Method 7 work.
Table 4. EFFECTS OF ULTRAVIOLET IRRADIATION TIME
Irradiation
time,
minutes
15
30
15
30
Labeled
cyl inder
concentration,
ppm NO
500
500
575
575
Concentrations
recovered,
ppm N0x
357.2
398.9
%
466.2
481.6
%
Standard
deviation,
ppm
±33.01
±27.06
recovery increase=10.5
± 8.2
±12.5
recovery increase=3.2
Oxygen Study
The effect of adding pure oxygen (Op) to the Modified Method 7 sampling
flask before sampling was investigated. Method 7 samples were not tested
for any effect with added oxygen because there is sufficient Op present
at the 3 in. Hg pressure used in sampling.
Four Modified Method 7 samples were takenboth with and without Q^ addition--
to determine whether the percentage of NO recovery would increase with extra
A
0? available. The samples with added 02 were taken in the following manner:
17
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(1) the absorbing solution was added to the 2-liter flask, (2) the flask
was evacuated to +75 mm Hg pressure, (3) cylinder 09 was then introduced
to the flask until atmospheric pressure was attained, (4) the flask was
reevacuated to +75 mm Hg pressure and was then ready for use.
The data presented in Table 5 indicate that at higher NO concentrations
X
(around 500 ppm) the addition of 02 to the Modified Method 7 sample
flasks had an adverse effect on the NO recovery as compared with those
A
samples without Op. This result is difficult to explain because there
is a conflict in various sets of data (See Tables 3 and 5). Nevertheless,
in tests using a cylinder with a labeled concentration of 510 ppm NO in
N?, the data indicate a net decrease of recovered NO when the flask is
^- A
purged with 02 prior to evacuation for sampling. Three samples drawn
with no 02 additior averaged 372.7±20.3 ppm (Table 5). Four flasks
purged with 02 prior to the sampling evacuation averaged 250.9±23.2 ppm.
The effect of 02 was significant, and the net result was a decrease in
recovery of 121.8±23.2 ppm NO . The observed difference was puzzling
A
because previous experience with 02 in Modified Method 7 suggested that
any effect should have been either nominal or favor a more complete
recovery of NO . An identical procedure was utilized for a cylinder
A
containing 575 ppm NO in N2- Unlike the samples from the 510 ppm cylinder.
however, the ultraviolet period was set for exactly fifteen minutes,
utilizing a sampling manifold, two samples were simultaneously drawn and
purged with 09 to assure that variables would be minimized. The NO
L. X
level was calculated to be 466.2±8.2 ppm. The control group--one with
no 02 purgingwas sampled exactly as those to which 02 had been added.
The reported NO value for no 09 addition was 481.6±12.5 ppm NO . Here
X £ X
again, a reduction in NO recovery was noted when the 09 was added.
X L-
Although the diminution was not as pronounced in this study as it was in
the 510 ppm study, the net recovery of NO through 02 addition was
decreased by 15.4±12.5 ppm.
A study of the effect of 09 addition on low NO concentration sources
c. X
was investigated on a cylinder labeled 60 ppm (actual concentrations by
Method 7 was 28.3 ppm). At this low concentration, the expectation
that observable trends would be difficult to detect was confirmed (See
18
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Table 5. OXYGEN EFFECTS AT VARIOUS CONCENTRATIONS
Labeled cylinder
concentration, NO concentration,
ppm Variable ppm
510 02 addition 250.9±23.2
510 No addition 372.7±20.3
575 02 addition 466.2±8.2
575 No addition 481.6±12.5
60 02 addition 31.9±3.8
60 No addition 28.7±3.3
19
-------
Table 5). The Modified Method 7 flask samples that had no 02 addition
averaged 28.7±3.3 ppm NO over three trials; whereas, the 09-treated
A L
samples registered 31.9±3.8 ppm NO over four samples. At this low
X
concentration, the inverse relationship previously reported between 0~
and recovered NO was not observed if one considers the standard devia-
X
tion range.
Method 7 Evaluation and Cylinder Typing
In order to evaluate the Modified Method, Method 7 samples were taken at
various cylinder concentrations and were subsequently used for comparison
with Modified Method 7 data.
The Method 7 procedure included: purging the sample line with the
sample gas prior to final evacuation, pipetting the 25 milliliters of
absorbing solution into the flask, agitating the solution via magnetic
stirrer to maximize gas-liquid contact, and waiting the required 16
hours after sampling. The sample was analyzed as prescribed in the
3
Federal Register. The data in Table 6 relates the NO concentrations to
the nominal cylinder values.
Table 6
METHOD 7 NO CYLINDER CALIBRATION
/\
Labeled
cyl inder
concentration,
ppm
51 Oa
500
60
Method 7
average,
ppm
427.9
454.9
28.3
Standard
deviation,
ppm
5.36
10.48
2.9
Number of
samples
in calculation
3
9
6
Old, low-pressure cylinder that may have degenerated over time was used.
The magnitude of standard deviations in all cases is consistently low. In
percent, ages the standard deviations for the 510, 500, and 60 ppm cylinders
are 1.25, 2.30, and 10.25 percent, respectively.
Data accumulated on the "500 ppm" cylinder should be considered most sig-
nificant because the largest number of samples were drawn from it.
20
-------
Based on the low standard deviations listed in Table 6 and the repeat-
ability observed over the sampling period, Method 7 may be considered a
repeatable and dependable means of determining NO when precautions are
A
taken to avoid obvious sources of error (spillage, leakage into evacuated
flask, faulty sampling lines, etc.) and when experimental procedure is
followed rigorously.
Evaluation of Modified Method 7 Compared with Method 7
The possible utility of Modified Method 7 as a rapid analysis technique
was determined by comparing Modified Method 7 values for NO with those
A
values determined by Method 7 (reported in the previous section and in
the field section).
The accuracy of values reported depends upon the consistency of technique
utilized and the ability of the experimenter to minimize human error.
Unfortunately, many of the samples analyzed by Modified Method 7 were
inadvertently subject to inconsistencies from several sources including
human error and leaking equipment. The greatest source of error, however,
was undoubtedly the ultraviolet irradiation period because, until the
final stages of experimentation, an irradiation period of 15 minutes or
lower was assumed to ensure a consistent degree of NO-N02 conversion.
During subsequent investigation of the effect of the longer irradiation
periods, a 15-minute irradiation of samples drawn from the 500 ppm
cylinder (454.9 ppm based on Method 7 evaluation) effected a 78.4 percent
NO recovery (compared with Method 7 data). The 30-minute irradiation
A
period produced a 10.5 percent greater recovery of NO than the 15-
A
minute period (41.7 ppm increase). Total recovery of NO using the
A
longer irradiation period was 87.7 percent of the Method 7 calibration
of the 500 ppm cylinder (454.9 ppm). It may be assumed that the high
standard deviations observed in Modified Method 7 (relative to those of
Method 7 were partially caused by inconsistent application of ultra-
violet irradiation.
Regardless of any potential error or design malfunction, the Modified
Method 7 samples compare favorably with their Method 7 counterparts.
Modified Method 7 samples from the 510 ppm cylinder averaged 372.7+20.3
ppm NO ; those obtained by Method 7 averaged 427.9±5.36 ppm. The
X
21
-------
correlation between the two methods was 87.1 percent for that cylinder.
The correlation between samples from the 500 ppm cylinder tested by the
two methods was 87.7 percent.
A peculiar phenomenon was observed in Modified Method 7 data for the low
concentration cylinder (60 ppm). Values obtained through use of Modified
Method 7 averaged 31.9±3.8 ppm NO over four samples; whereas, the
/\
Method 7 average, which generally is higher than Modified Method 7 data,
was 28.3±2.9 ppm NO over six samples. The greater recovery by Modified
X
Method 7 is not deemed significant, however. The equivalent recovery
reported by Modified Method 7 at this concentration may reflect stoichio-
metric considerations involved with 03 generation and the resultant
higher temperatures found in the Modified Method 7 flasks. Nitrogen
oxides recovery for the 60 ppm cylinder using the modified method was
12.7 percent higher than that of Method 7.
The laboratory te^t data are summarized in Figure 6 and Table 7.
FIELD STUDIES
Field studies of Method 7 and Modified Method 7 were undertaken at three
stationary sources of nitrogen oxides emissions to determine the relative
efficiency of each method. In-stack, continuous source level monitors
were employed to establish baseline data at two of the three sampling
sites. Initial evaluation was begun at Carolina Power and Light Company's
Moncure, N. C., facility; a subsequent assessment was completed at Duke
Power Company's Mt. Holly, N. C., facility. Both sources are coal-fired
steam generating stations. EPA's Stationary Source Simulator Facility
served as the third site.
Stationary Source Simulator Facility Tests
Simulated stack conditions were achieved at the Stationary Source
Simulator Facility (SSSF) at the Environmental Research Center, Researcn
Triangle Park, N. C. Nitrogen oxides levels were monitored concurrently
by two in-stack instruments and Method 7.
A TECO chemiluminescence NO analyzer was utilized as the primary con-
X
tinuous monitoring standard; the use of the Philco-Ford Gas Correlation
instrument was limited to monitoring NO levels in the simulator. The
TECO instrument, which had been spanned for NO by a previously calibrated
/\
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fl+Vl
|
100
200
300
400
500
NOX CONCENTRATION,ppm
Figure 6. Laboratory data summary.
31
-------
cylinder gas, delivered an instantaneous digital display of NO concentration
X
in parts per million. Figure 7 illustrates the arrangement of the sampling
apparatus at the SSSF.
The inlet rate of NO gas introduction was periodically varied, and as the
gas recirculated through the source simulator, the total content of NO in
X
the system increased. Because of the rather lengthy residence time of the
NO inlet gas in the simulator (2 hours or more) and because of the presence
of 09 in the simulator, partial conversion of NO to N09 and N 0 occurred.
L. C. X J
A plot of NO and NO values is shown in Figure 8. The plot contains data
A
from both the TECO NO analyzer and the Phil co-Ford Gas Filter Correlation
X
instrument, which was undergoing preliminary testing at this site. The NO
A
values for the Method 7 samples compare favorably (^98 percent correlation)
with NO values measured by the TECO analyzer as well as with the GFC instru-
X
ment (^40-60 percent correlation), which operated in the NO mode. The
margin of difference between the TECO curve and the GFC curve represents
the continuous oxidation of NO to N02 in the circulating system. The GFC
curve indicates the amount of NO introduced in addition to the measurable
content of NO retention in the simulation return loop.
Correlation among the three Method 7 data sets and the GFC NO and TECO NO
X
data curves is depicted in as a chronological listing of experimental
values in Table 8. A summary of Method 7 data may be found in Table 9.
The Simualted Source Testing Facility allowed the precise control and
monitoring of NO concentrations as well as permitting the use of a wide
range of NO sample concentrations. The utilization of these capabilities
X
corroborated the assumption that the Method 7 procedure is reliable at a
range of NO concentrations, that the repeatability between samples at
A
static concentration is excellent (95 percent agreement), and that error
caused by equipment failure and/or human error is minimal (<5 percent)
under simulated field conditions.
Cape Fear Power Plant
The source used in the first field test of the modified method was the
Cape Fear Station of the Carolina Power and Light Company, which is a
360-MW, coal-fired generating station. The testing was performed on the
plant's Unit 9, which was an output of 120 MW. The duct that was used
as the sampling site was 4 feet deep and approximately 2 feet wide; the
sampling ports were spaced about 5 feet apart.
32
-------
METHOD 7
SAMPLING
TRAIN
GFC
OPTICS
TECO
NO-NOX
MONITOR
L_
UNIFORM
TUNNEL
FLOW
5ft
RETRO
T
TO
RETURN
LOOP
Figure 7. Stationary source simulator facility sampling arrangement.
-------
800
o
H
o
u
700
600
500
400
300
200
100
NO AND NOX DETERMINATIONS, 2/13/75
METHOD?
TECONO
ATECONOx
PHILCO-FORDGFCNO
10
20
50
30 40
TIME, minutes
Figure 8. Method 7 evaluation at SSSF.
60
70
80
-------
Table 8. CHRONOLOGICAL TECO, GFC, AND METHOD 7 DATA
Time,
minutes
5.8
8.4
11.6
16.0
18.0
19.0
19.4
26.0
29.0
30.0
31.0
38.2
49.0
54.8
65.0
69.0
71.0
74.5
Time,
minutes
16.0-19.0
29.0-31.0
65.0-71.0
Method 7 NO
ppm added
Yes
Yes
Yes
No
284 No
333 No
Yes
Yes
561 No
537 No
585 No
Yes
Yes
No
345 No
301 No
248 No
No
Method 7
average
N0x, ppm
310±10
561±16
298±34
GFC-NO,
ppm
110
148
160
180
218
224
230
282
290
292
286
330
340
282
128
180
74
60
TECO NO ,
ppm
331± 12
543± 45
283±145
TECO NO ,
ppm
158
218
273
313
334
346
362
418
522
542
566
692
783
655
346
260
244
192
Percent
agreement
94
97
95
35
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The rotary fan used to force-feed the stack was located downstream of the
sampling site resulting in a negative sampling pressure of 10 inches of
water. The plant layout and the sampling sites are shown in Figure 9.
Figure 2 shows the test equipment arrangement used at the sampling site.
The probe was a 3/8-inch diameter stainless steel tube filled with glass
wool to collect particulates. Teflon tubing was used for all connectors.
The sampling flasks used were of two types: (1) the standard 2-liter
o
sampling flask as shown in the Federal Register and (2) a 2-liter, 2-neck,
round bottom flask with no protective plastic foam outer coating (Figure 3).
The latter type was used in the photochemical irradiation lamp studies. The
flask pressures were monitored using a U-tube, mercury-filled manometer after
evacuation had been accomplished with an oil-filled vacuum pump.
The test results of the field program at the Cape Fear plant are presented
in Table 10.
Table 10. CAPE FEAR POWER PLANT TEST DATA
Series
number
V
VI
VII
VIII
Sample
number
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
Type
UV lamp
Method 7
Method 7
Method 7
UV lamp
Method 7
Method 7
Method 7
UV lamp
Method 7
Method 7
Method 7
UV lamp
Method 7
Method 7
Method 7
NO,
ppm
449
569
479
587
409
427
513
Sampl
393
401
358
370
275
480
471
396
(554)a
(470)a
e lost
(376)a
(449)a
or UV method: 429 ppm; standard deviation 85 ppm
or Method 7: 466 ppm; standard deviation 85 ppm
in parentheses is average using Method 7.
37
-------
FROM PRECIPITATOR
FRONTAL VIEW
OF DUCT
5ft ' 5ft ' 5ft ' 5ft ' 7ft.
27ft
Figure 9. Sampling site configuration for CP&L Cape Fear Station Unit 9.
38
-------
As can be seen from the data, the agreement between the Method 7 mean and
the modified procedure values was relatively good (about 8 percent differ-
ence). The standard deviation of both the Method 7 and the modified
Method 7 was rather poor (17-19 percent). This disagreement is probably
caused by temporal and spatial stratification within the duct being sampled.
Discussions with other EPA personnel who had worked at the site reinforced
these assumptions. Velocity, temperature, and oxygen profiles of the duct
showed spatial variations and temporal differences over a period of a week.
Because of these difficulties, the comparative evaluation of the two methods
was continued at the Duke Power Company station, which from previous experi-
ence appears to be a more suitable site.
River Bend Steam Generating Station
Duke Power Company's River Bend Station is a coal-fired steam generating
station with an output capacity of 800 MW. During the test period, how-
ever, the plant was operated at approximately 75 percent of output capacity.
Evaluation of Method 7 and modified Method 7 was performed on a boiler that
produced a maximum output of 125 MW. The circular, vertical stack of the
unit facilitated the horizontal placement of probes. Sampling ports were
spaced concentrically about the 3-meter stack diameter. There were no
internal obstructions for at least five stack diameters downstream, and
except for microfluctuations resulting from subcapacity output, uniform
flow characteristics were observed in the effluent.
The internal stack pressure was positive (about 3 inches of water) relative
to atmospheric pressure and the internal stack temperature was about-135°C.
Test equipment and sampling procedure used were identical with that of the
Cape Fear Study,
Data obtained during experimentation are listed chronologically and sum-
marized in Table II. An integrated chronological data plot is shown
in Figure 10.
A DuPont NO analyzer was utilized to establish a continuously monitored
A
data base for the work at River Bend. Unfortunately, because of unscheduled
maintenance, the analyzer was inoperative during a majority of the experi-
mentation. During the latter stages of work, however, the data generated
from the DuPont are representative of the fluctuations in source NO level--
/\
if not also representative of the concentration of NO present. Both
/\
39
-------
TABLE 11. CHRONOLOGICAL SUMMARY OF DUKE POWER DATA
Sampling
method and
sample number
Method 7
1-3
4-6
13-15
18-20
23-25
28-30
33-35
38-40
43-45
46-48
Modified
Method 7
(without 02)
7-10
51-52
53-54
55-56
Modified
Method 7
(with 02)
11-12
16-17
21-22
26-27
31-32
36-37
41-42
49-50
Average,
ppm
280.9 ± 2.2
260.8 ±14.7
307.6 ±10.5
318.0 ±12.2
284.4 ±22.1
318.9 ± 2.9
278.8 ± 9.3
234.8 ±20.0
204.5 ±45.2
259.7 ±12.8
260.4 ±16.8
284.3 ±34.9
223.7 ± 0.3
178.9 ±10.3
291.3 ± 1.0
288.2 ±61.3
273.2 ±42.0
290.2 ±79.9
212.0 ± 7.6
143.1 ±19.4
181.9 ±47.1
256.1 ±10.0
DuPont
condition
and
correlation
Inoperative
Inoperative
Inoperative
Inoperative
Inoperative
Inoperative
86.8
97.9
83.1
77.1
Inoperative
82.6
79.8
92.2
Inoperative
Inoperative
Inoperative
Inoperative
94.6
68.7
91.4
81.2
Number
of matrix
samples
3
3
3
3
2
3
3
3
3
3
3
2
2
2
2
2
2
2
2
2
2
2
DuPont inoperative; no comparison possible.
40
-------
Method 7 and DuPont samples drawn simultaneously indicate observable source
fluctuation with approximately 90 percent correlation. The DuPont analyzer
has a response time lag of about 10 minutes because of the need to pressurize
the NO sample with 02 for conversion of NO->N02- The time lag should be
noted during critical evaluation of the graphic representation of accumulated
data (Figure 10).
Modified Method 7 samples 7-10 and 51-56, which were taken with no 02 addi-
tion, show no effect under the conditions encountered at the River Bend
Station. The rate of the reaction 2NO+02+2N02 is dependent on [NO]2 and [0,,].
In the case of the River Bend Station [02] = 6 percent, a rather large
excess with respect to the 150-250 ppm NO typically was encountered.
Because excess 02 already exists in the stack sample, the introduction of
additional 02 would not be expected to have an appreciable effect. In
future work, an evaluation of plant operating conditions should be made in
order to anticipate the need for 02 addition.
Figure 10 illustrates the correlation between Method 7 and modified
Mehtod 7. The agreement ranges from 55 percent in samples 36 and 37 to
95 percent in samples 43-45. Overall correlation was computed by averaging
all deviations of modified Method 7 from the reference method data plot.
A complete data summary from River Bend Steam Station is found in Table 12.
41
-------
<»>-
-OOCr-OOO
OUTLIER,
NOT INCLUDED
IN AVERAGE
11 12 13 15 17 1820
14 16 19
2122 2325 262830
24 27 29
3:00p.m. 4:00 5:00 9:00 a.m. 10:00 11:00 12:00 1:00 2:00 3:00
TIME
Figure 10. Integrated M7, MM7, and duPont data.
4:00
42
-------
500
400
z
o
o
o
200
100
1/29/75
143.1
1 III
212.0 278.8 234.8
LEGEND
o»M7
204,5
III
181.9 259.7
256.1
A A MM7 WITH OXYGEN
O MMM7 WITHOUT OXYGEN
O+DUPONT
SOLID POINTS INDICATE
AVERAGE (MATRIX VALUES)
3132
33
QC
36 3840
37 39
A O
,1, 43 ^
41 44 47
42 45 48
49
50
1/30/75
III
284.3 223.7 178.9
' V
\k
51 53 55
52 54 56
\
8:00 a.m. 9:00 10:00 11:00 12:00 1:00 2:00 3:00 4:00 7:00 a.m. 8:00 9:00 10:00 11:00
TIME
Figure 10 (continued). Integrated M7, MM7, and duPont data.
43
-------
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SECTION VI
REFERENCES
1. Chamot, E. M., D. S. Pratt, and H. W. Redfield. Study on the
Phenolsulfonic Acid Method for the Determination of Nitrates in
Water. Jour. Am. Chem. Soc. 33:366-381, 1911.
2. Saltzman, B. E. Anal. Chem. 26_: 1949-1955, 1954.
3. Title 40-Protection of Environment. Standards of Performance for
New Stationary Sources. Federal Register 36 (247):24876-24895,
December 23, 1971.
4. Beatty, R. L., L. B. Berger, and H. H. Schrenk. The Determination
of the Oxides of Nitrogen by the Phenoldisulfonic Acid Method. U. S.
Dept. of Interior - Bureau of Mines R. I. 3687. 1943. 17 p.
5. Di Martini, R. Determination of Nigrogen Dioxide and Nitric Oxide
in the Parts Per Million Range in Flowing Gaseous Mixtures by Means
of the Nitrate-Specific-Ion Electrode. Anal. Chem. 42J9):1102-1105,
1970.
6. Driscoll, J. N., A. W. Berger, J. H. Becker, J. T. Funkhouser, and
J. R. Valentine. Determination of Oxides of Nitrogen in Combustion
Effluents with a Nitrate Ion Selective Electrode. JAPCA 22_(2): 119-122,
1972.
7. Singh, T., R. F. Sawyer, E. S. Starkman, and L. S. Caretto. Rapid
Continuous Determination of Nitric Oxide Concentration in Exhaust
Gases. JAPCA 18(2):102-105, 1968.
8. Harman, J. N., and R. M. Neti. Nitric Oxide Analysis. United
States Patent No. 3,652,227. March 28, 1972. 6 p.
9. Margolis, G., and J. N. Driscoll. Critical Evaluation of Rate-
Controlling Processes in Manual Determination of Nitrogen Oxides
in Flue Gases. Environ. Sci. and Tech. 6_(8):727-731, 1972.
10. Conlehan, B. A., and H. W. Lang. Rapid Determination of Nitrogen
Oxides with Use of Phenoldisulfonic Acid. Environ. Sci. and Tech.
j>(2):163-164, 1971.
49
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TECHNICAL REPORT DATA
se read Iiiotnictwis on the revert-' before completing)
1 REPORT NO.
EPA- 600/2-76-094
3 RECIPIENT'S ACCESSIOI^NO.
4 TITLE AND SUBTITLE
RAPID METHOD FOR DETERMINING
NO EMISSIONS IN FLUE GASES
x
b. REPORT DATE
September 1976
6 PERFORMING ORGANIZATION CODE
7 AL-THOR(S)
H. M. Barnes and M. C. Caldwell
9 PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Sciences Research Laboratory
Office of Research and Development
U. S. Environmental Protection Agency
Research Triangle Park, N. C. 27711
S. PERFORMING ORGANIZATION REPORT NO
10. PROGRAM .ILEMENT NO.
1AA010
TTTCONTRACTYGRANT NO7~
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Sciences Research Laboratory
Office of Research and Development
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
In-house 9/74-5/75
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report discusses the NC compliance procedure (Method 7) for stationary
A
sources and the attempts to improve the procedure and decrease analytical time.
When the procedure is rigorously followed, Method 7 was found to be precise and to
give reproducible results. To decrease the time necessary to oxidize NO to N02,
Method 7 was modified by adding an ozone lamp. Good agreement (±12% or less) was
found between nitrate measurements using Method 7 and measurements using modified
Method 7. Future work incorporating an ozone lamp into an integrated sampling
apparatus is discussed.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
*Air pollution
*Nitrogen oxides
Nitrogen oxide
Nitrogen dioxide
Flue gases
*Chemical analysis
improvement
*0xidizers
Ozone
13B
07B
21B
07D
11G
13 DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. S
'his Report)
21 NO OF PAGES
20 SECURITY CLASS (This page)
UNCLASSIFIED
22 PRICE
EPA Form 2220-1 (9-73)
50
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